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FAQs
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Did Raghuram Rajan know about the demonetization scheme of Narendra Modi?
The following persons only were aware of the plan.1. PM Narendra Modi2. Finance Minister Arun Jaitley3. RBI Ex-Governor Raghuram Rajan4. RBI Governor Urijit Patel5. Secretary of Economic Affairs Shaktikanta Das6. Secretary of Investments & Currency Dr. Saurabh Garg7. and a few others in finance ministry.Because the plan was finalized six months back and Mr. Rajan left office on 4th September 2016 only. So such a decision can’t be carried out without the approval of RBI Governor.The detailed execution went something like this.Before Six Months- Plan was finalized and execution for the D-Day started.June - Banks were directed to dispense more 100 rupee note by RBI.Before three Months- Design of new 500 & 2000 rupee note was finalized and went for printing at Mysuru Mint press.PS: Only the design of the plate was finalized. The printing didn't start that time as Mr. Rajan denied continuing for next term and new governor was declared.The printing facility at Bharatiya Reserve Bank Note Mudran Private Ltd. (BRBNMPL) in Mysuru under Reserve Bank of India was set up with the De La Rue Giori, now KBA Giori, Switzerland.20 August - Mr. Urjit Patel was declared as new governor.4 September - Mr. Urjit Patel joined office as new governor and gave a green signal to Modi for demonetization after a thorough discussion. He sent his signature sample in English and Hindi to be added to newly designed 2000 currency plate.5–6 September - Signature was added to the plate and new dye was made. Printing of currency started.27 October - The central bank put out a warning about fake currencies on its website. It asked banks to put entire banking areas under CCTV surveillance and ensure that cash receipts in the denominations of Rs 100 and above are not put into re-circulation without the notes being machine-processed for authenticity.The CCTV surveillance is now being used to monitor and record all the money exchanges that are taking place at banks.2 November - Banks were directed again to dispense more Rs 100 notes through ATMs within the next fortnight.7 November - The Heads of currency management divisions in all banks received a confidential communication from the Reserve Bank of India (RBI) to be present at the headquarters.8 November Morning- They were given charge of a double-locked currency chest, which they were told contained currency notes of the new denomination: Rs.2,000.Though it also had the RS 500 new notes, but it wasn’t disclosed.8 November 7 PM- All MDs of banks were called for a meeting at RBI and were kept waited till 8PM. At PMO, all cabinet ministers were called for a meeting, but no one was allowed to carry mobile.Privacy was of top most priority. Even leak of the news by a few minutes could have caused disaster.8 November 8 PM- Disclosure of demonetization by PM on National TV.The entire nation came to know about it at the exact same time.A master stroke that left the nation spellbound !But the question to ponder is - Did Mr. Rajan leave the office, because he wasn’t in full support of the plan ?Here is what he had to say on demonetization in 2014: Ref“I am not quite sure if what you meant is demonetise the old notes and introduce new notes instead. In the past demonetization has been thought off as a way of getting black money out of circulation. Because people then have to come and say "how do I have this ten crores in cash sitting in my safe" and they have to explain where they got the money from. It is often cited as a solution. Unfortunately, my sense is the clever find ways around it.They find ways to divide up their hoard in to many smaller pieces. You do find that people who haven't thought of a way to convert black to white, throw it into the Hundi in some temples. I think there are ways around demonetization. It is not that easy to flush out the black money. Of course, a fair amount may be in the form of gold, therefore even harder to catch. I would focus more on the incentives to generate and retain black money. A lot of the incentives are on taxes.My sense is the current tax rate in this country is for the most part reasonable. We have a reasonable tax regime, for example, the maximum tax rate on high-incomes is 33%, in the US it is already 39% plus State taxes, etc., it takes it to near 50. We are actually lower than many industrial countries. Given that, there is no reason why everybody who should pay taxes is not paying taxes. I would focus more on tracking data and better tax administration to get at where money is not being declared. I think it is very hard in this modern economy to hide your money that easily.”Source - LivemintHuffingtonpostBusiness StandardEdit1: The new 2000 currency note was initially printed at Mysuru Mint. Thank you User-12623941048551877892 for pointing this out. ReferenceEdit2: Those who are cursing the government for demand supply mismatch of notes should read below possible reasons.a) Had Mr. Rajan had continued as governor, the scenario could have been different. More 2000 notes could have been printed due to availability of time.b) Only one printing press (Mysuru) was used to print the new notes initially. So it limited the printing capability and increased the distribution duration to all banks across the country.c) Only availability of 100 rupee notes decreased ATM's capability in terms of value.d) Change in dimensions of the currency note increased ATM up-gradation time both in terms of software and hardware.e) The no of ATMs for withdrawal got reduced as CDMs couldn't be used for withdrawal. Otherwise people would get same old currency deposited by some other person.Details on SPMCILThank you everyone for the Upvotes. This is not so a customary ‘thank you’ note, but it means a lot to me in keep going. This was my 2nd answer on Quora and 1st answer to receive 1000+ Upvotes that too within two days. :)PS: I’m politically neutral and don’t have any strong support for any of the political parties. But whenever I come across some exceptional steps by them( may be by BJP or Congress or AAP), I criticize or appreciate. The scenario is not ideal always and as per a report 61% of all projects fail to succeed (delivered on time, on budget, and with required features and functions) 43% are challenged (late, over budget, and/or with fewer than the required features and functions) 18% fail (either cancelled prior to completion or delivered and never used). So let’s appreciate this man for the huge step taken.
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Did Greeks originate from north Africa?
No. I understand that this question is related to E-V13, found in the Balkan. E-V13 isn't a quantifier of Greek genetics, it is one of many Greek founding lineages.Haplogroup E1b1b may have arrived in Europe by two routes: through the Middle East/Levant and directly from North Africa.The oldest E-M78 in Africa has been found at Taforalt Morocco. The Max Planck Institute for Evolutionary Anthropology in Leipzig, have sequenced DNA from individuals from Morocco dating to approximately 15,000 years ago, as published in Science. This is the oldest nuclear DNA from Africa ever successfully analyzed.The Y-DNA of 4 males waa found in E1b1b1a1-M78. This haplogroup occurs most frequently in present-day North East African populations The closely related E1b1b1b (M-123) haplogroup has been reported for Epipaleo- lithic Natufians and Pre-Pottery Neolithic Levantines (“Levant_N”). Unsupervised genetic clustering also suggests a connection of Taforalt to the Near East.What we are learning now is that certainly NW Africa's was genetically/demographically connected to NE Africa and to West Asia even at the very beginning of the local Upper Paleolithic, demolishing quite apparently all the theories that linked it to European Upper Paleolithic (from which it got its "Ibero-Maurusian" name).Also this quote from the authors in the press release:“The Iberomaurusians lived before the Natufians, but they were not their direct ancestors: The Natufians lack DNA from Africa, Krause says. This suggests that both groups inherited their shared DNA from a larger population that lived in North Africa or the Middle East more than 15,000 years ago, the team reports today in Science”The population exhumed from the archaeological site of Taforalt in Morocco is a valuable source of information toward a better knowledge of the settlement of Northern Africa region and provides a revolutionary way to specify the origin of Ibero-Maurusian populations.I wouldnt consider these Taforalt samples as thé ancestors of modern E-M78 subclades carriers (V22, V12, V65) What we see by contrasting the map of inferred patterns or E1b1b-M81(the berber marker and dominant in north west Africa) expansion and this ancient Y-DNA data from Taforalt is that the main E-M78 expansion most likely was already done, considering its age( formed 19800 ybp, TMRCA 13400 ybp) that it could represent an expansion from older times, much as I2 seems to have expanded in Europe. This would allow for V65 ("from west Egypt to Morocco" per one decription of its geography) to have expanded from NW Africa, not necessarily from Taforalt though but somewhow related to it.According to the authors "Several lines of evidence suggest that E-M78 sub-haplogroups have been involved in trans-Mediterranean migrations (in)directly from Africa. E-M78 and E-V65 haplogroups are common in northern Africa, where they originated, while other clades(like E-V13) are observed almost exclusively in Mediterranean Europe, as opposed to central and eastern Europe and the Horn of Africa among somali males (E-V32)The oldest to date sample of E-V13 we have is from Later Neolithic Hungary (1 in Sopot culture and 1 in Lengyel, c. 4500 BC and the earliest known prehistoric sample, the couple from Epi-Cardial Spain (c. 5000 BC).E-V13 has also been found in a skeleton of Avelanner Cave in Catalonia dating from 5000BC (cardial culture)So we know for sure that E1b1b was present in southern Europe at least since the Early Neolithic. Nonetheless, the possibility of other migrations of E1b1b to southern Europe during the Mesolithic or Late Palaeolithic cannot be ruled out.Research shows that the ancestors of modern Greeks were( indeed )the Minoans and Mycenaeans, already inhabiting the Greek peninsula for the past 5000 years, since 3000bc.Minoan Boxing Boys, restored fresco from Thera (modern-day Santorini), c.1600 BC. Currently located at the National Archaeological Museum in Athens, Greece.The Fisherman fresco is from the 16th century BCE from the Akrotiri site in GreeceTheir ancestors moved into Greece during the neolithic and bronze age from Anatolia and before that from the Caucasus..Mycenaean Fresco wall painting of an elborately dressed women in a procession from the Tiryns, Greece 14th, 13th Century BC Cat No 5883 Athens Archaeological MuseumScientists have obtained and analyzed the genome of ancient Mycenaean people and found they are strongly related to modern Greeks. Around three-quarters of the Mycenaeans' and Minoans' ancestry originated in Anatolia, present-day Turkey. The remaining quarter can be traced back to the Caucasus, near modern-day Iran.The Minoan Civilization and its counterpart on the Greek Mainland, the Mycenaean Civilization, were Europe’s first literate societies and the cultural ancestors of later Classical Greece. However, the question of the origins of the Minoans and their relationship to the Mycenaeans has long puzzled researchers.The Mycenaeans, with their roots in mainland Greece, seem to have adopted much of the Minoan technology and culture, but it is not clear how they were related. “We wanted to determine if the people who made up the Minoan and Mycenaean populations were actually genetically distinct or not. How were they related to each other? Who were their ancestors? And how are modern Greeks related to them?” says Johannes Krause, director at the Max Planck Institute for the Science of Human History and one of the corresponding authors of the study.A paper from 2017 in Nature suggests that, rather than being recently arrived, advanced outsiders, the Minoans had deep roots in the Aegean. The primary ancestors of both the Minoans and Mycenaeans were populations from Neolithic Western Anatolia and Greece and the two groups were very closely related to each other, and to modern Greeks.“It is remarkable how persistent the ancestry of the first European farmers is in Greece and other parts of southern Europe, but this does not mean that the populations there were completely isolated. There were at least two additional migrations in the Aegean before the time of the Minoans and Mycenaeans and some additional admixture later. The Greeks have always been a ‘work in progress’ in which layers of migration through the ages added to, but did not erase the genetic heritage of the Bronze Age populations,” stated Iosif Lazaridis of Harvard Medical School, lead author of the study.Genetic origins of the Minoans and Mycenaeans“Minoans, Mycenaeans, and modern Greeks also had some ancestry related to the ancient people of the Caucasus, Armenia, and Iran. This finding suggests that some migration occurred in the Aegean and southwestern Anatolia from the further east after the time of the earliest farmers," according to lead author Iosif LazaridisA European population in Minoan Bronze Age CreteMinoan were genetically very similar to modern-day Europeans but distinct from Egyptian or Libyan populations.EV-13 marker is neolithic and came into Greece and the Balkans before the arrival of the Dorians and Myceneans. When the Greek speaking Dorian and Mycenean proto-Greeks arrived in Greece around 1500 BC they mixed with the indigenous E-V13 neolithic peoples and the percentage of neolithic E-V13 marker became reduced in the population. The Dorians and Myceneans who brought the Greek language into Greece were not E-V13 carriers.The proto-Greeks (Myceneans / Dorians) who brought the Greek language into Greece were R1a carriers. They mixed with the neolithic peoples / Pelasgians of Greece who were E-V13 carriers.Neolithic farmers spread all around Europe,they didn't just sit in one placePericic et al. (2005) give a 7.3 kya estimate for the expansion of E-M78α (almost perfectly equivalent to E-V13) for Southeastern European populations north of Greece. Due to their use of the 3.6x slower mutation rate, this figure needs to be converted to equivalent years. The Nea Nikomedeia time depth was estimated as 9.2kya by King et al. Therefore, the equivalent age for the Pericic et al. (2005) expansion is (7.3/9.2) * 149 generations or 118 generations (1,540-950BC). They note that STR variance is higher in Greece, Macedonia, and Apulia, all areas with well-known historical Greek connections.Tracing Past Human Male Movements in Northern/Eastern Africa and Western Eurasia: New Clues from Y-Chromosomal Haplogroups E-M78 and J-M12Cruciani et al. (2007) propose that E-V13 arrived in Europe from West Asia and underwent an expansion in Europe at 4-4.7 kya. This age is calculated using effective mutation rates that are 2.4 or 2.8 slower than the germline rate, which seems to suggest a Late Bronze Age or even later expansion with a rate closer to the germline one.The signature North African marker E-M78, dominant in Egypt with its subclade E-V22 descends from Eurasian Adam CT-M168 E-M78 is a Non_African genetic marker. (Hodgson et al 2014)E-M78 has a near eastern neolithic origin"Both the King et al. E-V13 data, as well as the diverse, mostly European Haplozone E-V13 agree in placing the expansion of this haplogroup squarely in the Aegean Bronze Age.Haplogroup E1b1b has been associated with the earliest development of Neolithic lifestyle and the advent of agriculture, which is so far believed to have arisen in the Fertile Crescent, but could have developed earlier in parts of North/North East Africa. Agriculture spread from the Near East to Europe, at first mostly ovicaprid and cattle herders. E1b1b men (accompanied by G2a, J and T men) appear to have been associated at least with the diffusion of Neolithic painted pottery from the Levant to the Balkans (Thessalian Neolithic), and with the Cardium Pottery culture (5000-1500 BCE) in the Western Mediterranean. The only concrete evidence for this at the moment is the presence of this E-V13 subclade, commonest in the southern Balkans today, at a 7000-year old Neolithic site in north-east Spain, which was tested by Lacan et al (2011).E-v13 marker is considered a Greek marker because it follows the foot-print of ancient Greek colonisation - wherever ancient Greeks colonised the ev-13 marker went with them. R1a is also proto Greek and was carried by the proto-Greeks (Dorians and Myceneans) into Greece when they migrated there. Modern Greek DNA is the most similar to Southern Italian DNA which makes sense since Southern Italy was heavily populated by “Greek” colonists from 900 BC.On genetic test Sicilians are very similar to Peloponnese Greeks, Greek islanders & South ItaliansDifferential Greek and northern African migrations to Sicily are supported by genetic evidence from the Y chromosomeCornelia Di Gaetano et al.AbstractThe presence or absence of genetic heterogeneity in Sicily has long been debated. Through the analysis of the variation of Y-chromosome lineages, using the combination of haplogroups and short tandem repeats from several areas of Sicily, we show that traces of genetic flows occurred in the island, due to ancient Greek colonization and to northern African contributions, are still visible on the basis of the distribution of some lineages. The genetic contribution of Greek chromosomes to the Sicilian gene pool is estimated to be about 37% whereas the contribution of North African populations is estimated to be around 6%.In particular, the presence of a modal haplotype coming from the southern Balkan Peninsula and of its one-step derivates associated to E3b1a2-V13, supports a common genetic heritage between Sicilians and Greeks. The estimate of Time to Most Recent Common Ancestor is about 2380 years before present, which broadly agrees with the archaeological traces of the Greek classic era. The Eastern and Western part of Sicily appear to be signNowly different by the chi2-analysis, although the extent of such differentiation is not very high according to an analysis of molecular variance. The presence of a high number of different haplogroups in the island makes its gene diversity to signNow about 0.9. The general heterogeneous composition of haplogroups in our Sicilian data is similar to the patterns observed in other major islands of the Mediterranean, reflecting the complex histories of settlements in Sicily.Differential Greek and northern African migrations to Sicily are supported by genetic evidence from the Y chromosomeSouthern Italians/Sicilians are partially Greek (Magna Graecia).An additional piece of evidence is Y-chromosome distribution in Calabria, a Southern Italian region with well-known Greek connections. According to Semino et al. (2004) [Am. J. Hum. Genet. 74:1023–1034, 2004], the Calabrian sample has an E-M78 frequency of 16.3%, whereas "Calabria 2" representing the "Albanian community of the Cosenza province" has only 5.9%. This is consistent with the idea that E-V13 in modern Albanians is to a great degree due to Greek founders (Epirotes or ancient colonists).Albanians also coalesce to Roman/Late Antique times, consistent with the idea that their high frequency of haplogroup E-V13 (which signNowes very high numbers in e.g. Kosovars) is not associated with high diversity. Founder effects in that time frame are the reason for the high frequency of E-V13 in them.Albanians are a mix of Bronze Age invaders of Yamnaya culture and Neolithic residents of Balkans.Cruciani 2007 also mentions some oddballs for the Greek maritime theory:- Slovaks: 8.33% E-V13- Hungarians: 9.43% E-V13No mention of Serbs but the Republic of Macedonia has as much E-V13 as mainland Greece (17%), while Albanians double that figure (32%).Slavomacedonians from the former Yugoslav Republic of Macedonia coalesce well into AD times, at around the time of the first Slavic arrivals in the Balkans. This suggests that E-V13 in them is the result of local founders at around that time who adopted the Slavic language. However, Pericic et al. (2005) report high (but unspecified) diversity of E-M78α in "Macedonia", so it is possible that a larger number of earlier inhabitants were absorbed.Finally the highest concentrations of E-V13 west of Sicily are among Atlantic Iberians (Portuguese, Asturians), where historical Greek colonization was zero. This confirms again some older flow of Neolithic or maybe Chalcolithic age. There are other significative ammounts of this clades in most unlikely places like Denmark (3%), Germany (4%). All that can only be explained with Neolithic founder effects or something of the like. Ukranians (strong in E-V13) may have affected Northern Europe genetically... but at a time when the Greek ethnicity did not yet exist as such.Conclusion. Based on these results Minoans and Mycenaeans were genetically highly similar but not identical and that modern Greeks descend from these populations. The Minoans and Mycenaeans descended mainly from early Neolithic farmers, likely migrating thousands of years prior to the Bronze Age from Anatolia, in what is today modern Turkey.“Minoans, Mycenaeans, and modern Greeks also had some ancestry related to the ancient people of the Caucasus, Armenia, and Iran. This finding suggests that some migration occurred in the Aegean and southwestern Anatolia from further east after the time of the earliest farmers,” said Lazaridis.While both Minoans and Mycenaeans had both “first farmer” and “eastern” genetic origins, Mycenaeans traced an additional minor component of their ancestry to ancient inhabitants of Eastern Europe and northern Eurasia. This type of so-called Ancient North Eurasian ancestry is one of the three ancestral populations of present-day Europeans, and is also found in modern Greeks. There was genetic continuity in the Aegean from the time of the first farmers to present-day Greece, but not in isolation. The peoples of the Greek mainland had some admixture with Ancient North Eurasians and peoples of the Eastern European steppe both before and after the time of the Minoans and Mycenaeans, which may provide the missing link between Greek speakers and their linguistic relatives elsewhere in Europe and Asia.
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What are the variants of the Boeing 747?
Google and Wikipedia are your friends…I’m your friend too, so let me describe the different variants of the Boeing 747 for you on Quora:747–100First flight: February 9, 1969Number built: 168We start with the first generation 747. The prototype aircraft was named City of Everett, and it took off from the Boeing Field in Washington for its maiden flight.The inaugural commercial 747 flight took place on January 22, 1970. The plane serving the flight was Clipper Victor, the 11th Jumbo Jet built.On August 2, 1970, this plane was involved in the first ever hijacking of a 747. Pan Am Flight 299 was hijacked en-route to San Juan with 379 people aboard.The hijacker had a gun and explosives, and he demanded the captain to fly the plane to Cuba. The captain complied with his order.Having been notified of the hijacking, Cuban Prime Minister Fidel Castro visited Jose Marti Airport to witness the landing of a 747—a plane he had never seen before.Castro was intrigued by the unprecedented size of the Jumbo Jet. When the captain disembarked the plane with the terrorist, Castro bombarded the captain with questions about the jet’s capabilities, seemingly forgetting that he had just endured the sheer terror of a hijack.Unfortunately, Clipper Victor would later be involved in the worst aviation accident ever. On March 27, 1977, while operating as Pan Am Flight 1736, the plane was struck by KLM Flight 4805 on a runway, resulting in 583 fatalities.The second Boeing 747 ever built was turned into a noodle restaurant after retiring from service. However, the restaurant failed and the plane was scrapped.747–100SRFirst flight: August 31, 1973Number built: 7When Japanese airlines requested a high-capacity, domestic version of the 747, Boeing launched the 747–100 Short-Range. This variant has lower fuel capacity, and higher payload allowance. This is the first airliner to be configured to carry more than 500 passengers. Japan Airlines’ 747–100SR can carry up to 550 passengers.As the –100SR was designed to perform twice as many flight cycles as the –100, Boeing had to strengthen its airframe and landing gear.A –100SR was involved in the deadliest single-aircraft aviation accident, when Japan Airlines Flight 123 crashed in 1985, killing 520 people.▲ The aircraft involved in the tragedy.747–100BFirst flight: June 20, 1979Number built: 9This variant borrowed the stronger fuselage and landing gear design from the 747–100SR. Compared to the 747–100, it has a greater fuel capacity and longer range. Boeing also offered new engine options.In 1996, an Ilyushin Il-76TD struck a Boeing 747–100B flying at about 14,000 feet, resulting in the most fatal mid-air collision in history.747–100B SRFirst flight: November 3, 1978Number built: 20The difference between this model and the regular 747–100SR is an increased maximum take-off weight.747–100B SR SUDFirst flight: February 26, 1986Number built: 2This model has the same features as the 747–100B SR, but with a Stretched Upper Deck that is around 7 meters longer, providing a 10% increase in capacity and allowing for more seats. This new upper deck also came with a pair of full-size emergency exit doors for faster evacuation.▲ This image depicts an actual 747–100, not a –300.747–100SFThe 747–100 Special Freighter is a 747–100 converted to carry cargo. A main-deck side cargo door and cargo loading mechanisms were added. The main deck was strengthened to accommodate the increased weight of the payload.If you look closely at the image below, you’ll be able to see three exit doors that are sealed off, and the side cargo door behind the wing.747SPFirst flight: July 4, 1975Number built: 45The 747 Special Performance is truly unique and quirky. It is derived from the 747–100, and it’s about 14.7 meters shorter than a regular 747. It also has one less pair of exit doors on the main deck.It has a stubby fuselage, a huge vertical stabiliser, four turbofan engines and two passenger decks. It just looks ludicrous, and wonderful.The following was stated in Boeing’s 1984 edition of “747 Airplane Characteristics — Airport Planning”:[The 747SP] can fly higher, faster and farther than any other wide-body aircraft, and as a result serves well on long-distance air routes that do not require the size of the standard 747.The 747SP apparently had a top speed of approximately Mach 0.92 (630 mph/ 1013 kmh).One plane was involved in a near-disaster. In February 1985, China Airlines Flight 6 plummeted 30,000 feet in under 2 and a half minutes, before the pilots were able to regain control and level their jet out at 9,600 feet. The flight landed safely.▲ Damage sustained by the plane’s empennageThe plane was repaired, but its wings were permanently bent upwards by 5 cm.747–200BFirst flight: October 11, 1970Number built: 225The “second-generation” 747 entered service in February 1971, just a year after the original model. It has more powerful engines, higher maximum take-off weight and longer range.The 747-200B denotes the “basic” passenger version.▲ The KLM 747–200B that collided with Clipper Victor on the runway747–200FFirst flight: Early 1972Number built: 73This is the first freighter version of the 747 to be manufactured by Boeing.Boeing stated that this plane has “virtually” the same cargo space as the 747–100SF.747–200CFirst flight: Early 1973Number built: 13Equipped with a nose cargo door, the 747–200 Convertible is capable of being quickly converted from a passenger aircraft to a cargo aircraft, and vice versa. It can also carry a mix of cargo and passengers.▲ There are passenger windows on the nose cargo door.An El Al Boeing 747–200C carried a record-breaking 1,087 passengers on a single flight during Operation Solomon in 1991 (figure excludes babies board on the flight).747–200MFirst flight: Late 1974Number built: 78Also known as the –200B Combi, this plane is functionally similar to the –200C. It was built with a passenger cabin in the front half of the plane, and a cargo compartment in the back half.This model does not have a nose cargo door. Instead, a left-side main-deck cargo door was implemented near the rear of the aircraft. Unlike the –200C, this model cannot be converted into an all-cargo configuration.747 (SUD)While Boeing built the 747–100B SR SUD from scratch, they offered the Stretched Upper Deck as a retrofit to the 747–100B, 747–100SR, 747–200B and 747–200M variants.These images show the SUD modification process:All 747s that were upgraded with the extended upper deck were designated as “SUD” models. For example, the “747–200B SUD”.▲ Top: An original KLM 747–200B | Bottom: The same plane with the SUD upgrade747–300First flight: October 5, 1982Number built: 56The 747–300 is the third-generation passenger 747, and it came with the stretched upper deck as standard. To reiterate, the upper deck was stretched to be about 7 meters longer than older, non-retrofitted 747s, and it came with a pair of full-size exit doors.Boeing gave customers the option for updated engines, or the same engines from the 747–200 models.While older 747 variants had spiral staircases connecting the two passenger decks, the 747–300 featured a new staircase design which occupied less space in the cabin, providing room for more seats.▲ Left: Spiral staircase on a 747–200B | Right: Staircase on the 747–300747–300MFirst flight: Late 1982Number built: 21As with the 747–200M, the updated –300M can carry passengers and freight on the main deck. It is also referred to as the 747–300 Combi.747–300SRFirst flight: Late 1987Number built: 4This plane was once again introduced for Japanese airlines. It has a capacity of 584 passengers.747–300SFBoeing didn’t produce a freighter version of the 747–300, but they initiated a modification program in May 2000 to turn the passenger variants into cargo planes.747–400First flight: April 29, 1988Number built: 442The fourth-generation 747 introduced numerous structural and technological advancements, providing greater efficiency. It has more range, more fuel tanks, longer wings, and new wingtips that increase fuel efficiency by 4%.More importantly, this model came equipped with a glass cockpit consisting of multifunctional digital screens, which supersede many analog instruments. More computerised flight control systems were implemented, eliminating the need for a flight engineer and largely reducing the amount of knobs, dials and switches.Additionally, the model came with new powerplants choices and a refreshed passenger cabin. With 442 planes constructed, the 747–400 is the most popular 747 model.Unsurprisingly, the 1000th 747 produced is a 747–400.▲ This plane was delivered to Singapore Airlines in October 1993.747–400FFirst flight: Late 1993Number built: 126The freighter version of the 747–400.Since an extended upper deck is redundant and adds weight to the aircraft, every 747–400F retained the same upper deck dimensions as the 747–200F.747–400MFirst flight: Mid 1989Number built: 61Otherwise known as the 747–400 Combi, this aircraft can haul passengers and cargo on the main deck. Compared to older Combi aircraft, this model came with enhanced fire protection systems.The 747th 747 was a –400M. It was delivered to Lufthansa in September 1989.747–400DFirst flight: Early 1991Number built: 19For their high-capacity, short-range 747–400, Boeing decided to drop the “SR” label in favour of a new name, the 747–400 Domestic.Yet again, this variant was produced for the Japanese market. Because it’s tailored for short-haul flights, no winglets were installed on newly-manufactured 747–400D. Boeing later offered the winglets as a retrofit.This airplane has a maximum capacity of 660 passengers in a single-class configuration.747–400ERFirst flight: July 2002Number built: 6The 747–400 Extended Range was launched with an option of one or two additional fuel tanks in the forward cargo bay. Structural modifications allowed for a higher maximum takeoff weight.▲ Qantas is the sole operator of the –400ERThe Boeing Signature Interior, which debuted on the Boeing 777, was installed on every 747–400ER.The 747–400ER is expected to be retired by 2020.747-400ERFFirst flight: September 2002Number built: 40This model can fly 525 kilometres farther than the standard 747–400F. Like the -400ER, this plane has a more robust structure, enabling higher maximum takeoff weight allowance.747-400BCFFirst flight: October 5, 2005Every 747–400 Boeing Converted Freighter was once a passenger 747–400. Boeing appoints contractors like HAECO and SIAEC to perform the conversion work.Like the –400F, it has a side main-deck door situated behind the wings.747–8IFirst flight: March 20, 2011Number built: 47 as of September 2018Initially named the 747 Advanced, the 747–8 Intercontinental was launched in 2005.This model was developed with technologies and design derived from the 787. For the first time, Boeing lengthened the 747’s airframe. As a result, the 747–8I is the longest 747, and the longest commercial aircraft to date.It is powered by GEnX engines, the same ones found on the 787.The 747–8I features a redesigned wing and raked wingtips inspired by the 787. To reduce weight and improve efficiency, parts of the wings are constructed using carbon-fibre composites.It comes with updated flight deck systems and avionics, along with the Boeing Sky Interior. Its passenger windows are 16% larger than those on the 747–400, but unlike the 787, the windows don’t dim electrically.747–8FFirst flight: February 8, 2010Number built: 82 as of September 2018This freighter aircraft shares many attributes with the 747–8I, including its record fuselage length. However, the dimensions of the upper deck remain identical to original 747.The two 747–8 models are 5.6 meters longer than older 747 models, and 20.3 meters longer than the 747SP. They were stretched in different areas to suit their purposes:DreamlifterFirst flight: September 9, 2006Number converted: 4The 747–400 Large Cargo Freighter, better known as the Dreamlifter, is an oversized cargo transporter. This colossal aircraft has three times the cargo capacity of a –400F. It was exclusively designed and used by Boeing to carry parts of the 787 Dreamliner from suppliers around the world to the assembly plant.Like the –400BCF, this airplane model was converted from passenger 747–400s.▲ This 747–400 is one of the 4 aircraft to be modified into Dreamlifters.The first Dreamlifter rolled out of the hangar in August 2006, and it wasn’t particularly sightly. Then-president of Boeing Commercial Airplanes, Scott Carson, was reportedly heard apologising to the designer of the 747, Joe Sutter, by saying:[Sorry] for what we did to your plane.VC-25AFirst flight: May 16, 1987Number built: 2Commonly mistaken as the “Air Force One”, the VC-25A is a heavily modified version of the 747–200B. It’s only known as Air Force One when the POTUS is on board.In recent years, it has made many cameo appearances in tabloid newspapers.VC-25BFirst flight: July 8, 2016 (as a 747–8I)Number to be converted: 2The VC-25B will supplant the ageing VC-25A. It should be operational by 2024.To keep costs low, the US Air Force purchased two 747–8I airplanes that were originally built for a Russian airline which went bankrupt.▲ The two undelivered 747s destined to be VC-25Bs, stored in the Mojave desert747 SupertankerFirst flight: February 19, 2004Number converted: 3This is a Boeing 747 variant that was transformed into an aerial firefighting air tanker. It can carry up to 74,000 litres of fire retardant or water, and holds the record for the largest firefighting aircraft.Three Supertankers were built from a 747–100, –200C and –400BCF. However, only two entered service. This image below shows the 747–100 Supertanker:Presently, only the 747–400BCF Supertanker is in service.▲ This passenger plane was first converted into a freighter, then an air tanker.SOFIAFirst flight: April 26, 2007The Stratospheric Observatory for Infrared Astronomy is a heavily retrofitted 747SP. It has a telescope installed near the rear of the airframe, and flies at up to 45,000 feet during its missions.This 747SP was formerly owned by Pan Am, and subsequently United.▲ SOFIA, before make-up▲ SOFIA, after make-upBoeing YAL-1First flight: July 18, 2002This plane was once a 747–400F, before becoming the YAL-1 Airborne Laser. It has an infrared chemical laser mounted on its nose, which was intended to destroy tactical ballistic missiles.▲ This plane gives Rudolph a run for its moneyThe plane successfully destroyed two test missiles. However, it was expensive and not operationally feasible. Hence, it was scrapped in 2014.Boeing E-4First flight: June 13, 1973Number built: 4The E-4 is an airborne strategic command and control post. It is derived from the 747–200B. When in operation, the E-4 is identified as a “National Airborne Operations Center”.This plane is capable of aerial refuelling, and was designed to remain airborne for a week during an emergency.▲ This 747 variant has a hump on top of its hump, which houses an antenna.There are two versions of the model, the E-4A and E-4B. The US Air Force initially had three E-4A planes. In 1979, Boeing delivered a new E-4, with upgraded equipment, which was designated as the E-4B. Thereafter, the E-4A jets were refurbished to become E-4B models.Shuttle Carrier AircraftFirst flight with a space shuttle: February 18, 1977Number converted: 2The Shuttle Carrier Aircraft was designed to transport space shuttles from landing sites back to the launch complex. In 1974, an American Airlines 747–100 was acquired by NASA and turned into the SCA.During the maiden flight with an orbiter, Enterprise, the SCA signNowed a speed of 462 km/h (287 mph), and an altitude of 16,000 feet.In 1988, a 747–100SR was obtained from Japan Airlines and converted into a second SCA.▲ The SCA piggybacking Space Shuttle Enterprise▲ Space Shuttle Endeavour riding on the SCAAfter the conclusion of the space shuttle program, the Shuttle Carrier Aircraft carried the shuttles from the Kennedy Space Centre to various museums.Thereafter, the SCA were sourced for spare parts that could be reused on SOFIA. Both planes are now preserved at museums.▲ The 747–100 SCA on display at Space Center HoustonJumbohostelFirst night: January 15, 2009This 747–200B was transformed into a hostel.After some additional work, the engine nacelles were turned into small rooms.Let’s move on to some 747 variants that were conceptualised but never built.747 trijetPeriod of study: Late 1960s — Early 1970sBoeing engineers crafted a concept for a 747 trijet to compete with the DC-10 and L-1011, but they realised it was too costly to develop. Boeing engineers figured that making a three-engine version of the 747 would require a redesign of the wings and the vertical stabiliser, along with other hassles that made the concept uneconomical.So, Boeing scrapped the 747 trijet.747–500X/ –600X/ –700XAnnounced: September 2, 1996Boeing proposed three versions of the 747 with longer fuselages as potential competitors to the hypothetical A3XX plane, which would later become the A380.The concept models were to feature an improved wing design taken from the Boeing 777, more landing gear wheels and a new interior design.▲ 747–400 (Top) compared to the 500X and 600XThe 747–600X and –700X were planned to receive longer and wider fuselages, while retaining the existing wing dimensions and landing gear structures. Furthermore, Boeing stated that the –700X would potentially have a capacity of 650 passengers in a typical three-class configuration.The –500X and –600X were offered for sale at the 1996 Farnborough Airshow, but they didn’t receive any orders. Thereafter, Boeing axed these three models.Oh and one last variant…747–8 PSPImagined: October 18, 2018The Boeing 747–8 Photoshopped Special Performance is the chubbiest 747 ever.Thanks for viewing.// //If you’re interested to know how the worst aviation accident in history happened, and learn about other mid-air disasters, check out Isaac Low's answer to Have planes crashed into each other?Image sources1st — General Aviation News2nd — Aviation Safety Network3rd — The Pan Am Historical Foundation4th — Vecamspot5th — SOBIFY6th — Wikimedia Commons7th — National Geographic8th — Wikimedia Commons9th — Dennis HKG/Flickr10th — Wikimedia Commons11th — Wikimedia Commons12th — Wikimedia Commons13th — Airliners[.]net14th — Cargo Facts15th — NACOE16th — Airline Reporter17th — Top: Airport-Data[.]com | Bottom: Bureau of Aircraft Accidents Archives18th — Airlines Inform19th — Left: Sam Chui | Right: Airliners[.]net20th — Airplane-Pictures[.]net21st — Wikimedia Commons22nd — Rohan Patel/Flickr23rd — Wikimedia Commons24th — Air Charter25th — (Thumbnail of YouTube video by akino33 Aviation Video Channel)26th — Wikimedia Commons27th — Airliners[.]net28th — Airplane-Pictures[.]net29th — Wikimedia Commons30th — Wikimedia Commons31st — Wired32nd — Modern Airliners33rd — Wikimedia Commons34th — australianaviation[.]com[.]au35th — JetPhotos36th — indicator[.]gr37th — unilad[.]co[.]uk38th — Defense One39th — Planespotters[.]net40th — The Gazette41st — Wikimedia Commons42nd — Wikimedia Commons43rd — SOFIA Science Centre44th — Wikimedia Commons45th — Wikimedia Commons46th — Wikimedia Commons47th — NASA48th — Wikimedia Commons49th — Amusing Planet50th — Hostelworld[.]com51st — robertcatanescu[.]wordpress[.]com52nd — Simple Flying53rd — Boeing Images54th — Wikimedia Commons (photo edited by me)Note: Due to Quora’s policy, I cannot add the image URL sources in my answer. To view the image links, click here.
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What are some great tools to use for sales prospecting?
I think that we all agree that the days of manual prospecting are long gone. If you automate your prospecting efforts you can save a lot of time and money, and streamline your whole sales process. But, since there are lots of prospecting tools in the market, it can be hard to figure out which ones are good and which ones you should avoid.I’ll give you a couple of suggestions based on the tools I used.Email Hunter is a decent little program that can extract a list of every single one company email. All you need to enter is a company domain, and you will soon be able to email any person from a company. You can use either its dedicated Chrome plugin, or you can do your search by means of their browser version. This program can come in really handy if you want to find the email of a particular decision maker and get in touch with them directly.HeadsignNow is another interesting tool that offers more options than Email Hunter as it has some advanced search features. This means that you can search prospects based on various criteria such as name, company, title, or website. You can also expect to find your prospects’ social media handles and memorize your search logs.Autoklose isn’t your average prospecting tool, mainly because it offers much more. It’s actually a sales automation platform that can dramatically speed up your sales cycle, and prospecting is just one of the weapons in its arsenal. Apart from automating your prospecting efforts and saving you a tremendous amount of time, Autoklose will make your job and life easier by automating your email marketing efforts, amplifying your follow-ups, providing you with detailed campaign stats and metrics, and streamlining numerous dull, repetitive tasks that have to be done during the sales process.When it comes to prospecting, Autoklose allows you several powerful methods of filling your funnel with quality leads.Upload your own reliable contacts from .CSV files and Autoklose will import the information in the database so that you can make lists according to various parameters, and additionally segment them in order to create customized outsignNow campaigns and improve your open and click-through rates;Connect your Salesforce account and sync the data with Autoklose thus growing your internal database. What’s great about this platform is that it prevents you from sending the same email to the same person twice;Gain access to a huge B2B leads database and find prospects from virtually any industry. I was impressed with the abundance of prospects that I could actually contact. This database is managed by Autoklose’s reliable third-party providers, and it’s absolutely clean and packed with verified, complete, and updated contact information.It’s clear that Autoklose gives you a plenty of prospecting options, and the fact that you can search for your potential customers by using different parameters makes it in a way similar to HeadsignNow, but one of the main and most important differences is that Autoklose provides you with validated data which undergoes a meticulous 50-point data-scrub, meaning that every missing field is filled in, and every email, phone number, address, and job title is checked both manually and through the proprietary technology. To cut the long story short, Autoklose keeps you covered and gives your prospecting a big boost.
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How do I upgrade my passport application from normal to tatkal in India?
Get the documents which are required for application and while going for passport application on the appointment day, report at the regional passport office instead of going to the psk. Fresh application can be converted to Tatkaal, but only at RPO of your jurisdiction. Furnish the extra payment with the verification certificate and Annex E, as both of them are documents required for tatkaal, also a form stating that you want to change from normal to tatkaal. Make sure you get them done with all details correct and that would do with all the other documents of a normal passport application also.Documents that you need apart from the normal application set are-1. Annex e form filled and signed.2. 2 original verification certificate, issued and dully signed by a Govt Gazzeted office of a pay grade higher that 5400.3. 2 photo copies of id of the gazetted office.4. A form of mode change from normal to tatkaal.Rest the passport office staff will help you when you'd be present there on your appointment day.Edit. - There have been signNow changes in tatkaal service of passport. You may refer to the legit indian passpoet site to clear your concern regarding new set of rules.Edit 2- After the recent amendments in passport rules there has been an astounding change. Now for conversion of normal to tatkaal form, all you need to have is 2 valid address proofs and along with that 1 dob proof on the desired name. A hand written declaration will be necessary stating that applciant would like to change the mode of process and a signature of acceptance by app with the tatkaal fee i.e. 2000 Rs will suffice the purpose and get your mode of process changed. This is 100 percent correct information and this is the procedure which works. Good luck.
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Is it true that the United States military is the most powerful military in the world?
Very much true.The US military has massive power projection, more than any country in the history of man. The US has 11 (CATOBAR/STOBAR) Aircraft Carriers, while the next country has 1 which is, China, Russia, India, UK, and France. Also, the US Carriers are not just regular carriers, they are known as Super Carriers. Which is a term coined by the public to say that these carriers are so large that they exceed the definition of an Aircraft Carrier. Also, the US carriers were designed in the 70’s and countries are now just starting to make designs that could compete with the American Carriers. However, the US just redesigned the carrier and is coming out with the new Gerald R. Ford Class Carrier, which is supposed to be years possibly decades ahead of any other countries design. If you include Helicopter Carriers, and Amphibious Assault ships, that number jumps up to 20, soon to be 22. Then the next highest is tied between Japan and France with 4. My favorite part about the US having so many Aicraft Carriers is that if we divided them up between the major oceans, we could have 4 in each ocean… Crazy. The US carriers are also nuclear powered, they are the only carriers to be nuclear powered besides the French R91 Charles de Gaulle.Note the types of planes on the US Carriers. If you look at the USS Gerald R. Ford, it is fielding 5 different aircraft. 4 planes and 1 helicopter. We will look at the planes. Woden note, the USN has the 2nd largest Air Force in the world, right behind the USAF.First plane- McDonnell Douglas F/A-18 Hornet/Super Hornet: The plane is one of the most decorated planes, with thousands of successful missions, while requiring 3x less maintenance and failures than its counterparts. The plane has electronic warfare capabilities, air to air, and air to ground capabilities. Also, has spy and early warning capabilities. It was one of the first aircraft to heavily use multifunction displays, which at the switch of a button allow a pilot to perform either fighter or attack roles or both. The airframe is complex yet so simple, that a 4 man team can remove and install a new F404 engine in 40 minutes. Was also one of the very first 4th generation fighter on an aircraft carrier.Second plane- Northrop Grumman X-47B: This guy will be the very first and only Carrier based Drone. Northrop Grumman intends to develop the prototype X-47B into a battlefield-ready aircraft, the Unmanned Carrier-Launched Airborne Surveillance and Strike (UCLASS) system, which will enter service in the 2020s. So it’ll have strike options and surveillance capabilities.Third plane- Northrop Grumman E-2 Hawkeye: Many countries have AWAC systems or Airborne early warning and control. But only the United States have a Carrier based AWAC system. With the creation of this system, carriers that are hundreds of miles away from the nearest AWAC system, this plane gives the ability for a carrier strike group to potentially detect fifth-generation fighters like the Russian Sukhoi Su-57 and the Chinese Chengdu J-20 and Shenyang J-31 farther out. Also, gives the ability to guide fleet weapons, such as AIM-120 AMRAAM and SM-6 missiles, onto targets beyond a launch platform's detection range or capabilities.Fourth plane- Lockheed Martin F-35C Lightning II: This plane is the first and only carrier based 5th Generation Stealth fighter. The plane is meant as an air superiority fighter and a plane capable of ground support. It also has a very low, almost undetectable, cross section and radar signature. Besides radar stealth measures, the F-35 incorporates infrared signature and visual signature reduction measures. With the addition of a 5th generation stealth fighter, this gives the US military and Navy, the opportunity to do more damage and to have true air superiority over all other aircraft carrier based planes and land based planes. The US, in the event of a war, can now bring 5th gen fighters to the battle without the need of the Air Force against other 4th gen fighters, or possibly the few Chinese or Russian 5th gen fighters.Furthermore, the US have some of the best destroyers on the planet. With the highly acclaimed Arleigh-Burke Class Destroyer, and the brand new, low production Zumwalt Class Destroyer. The US has the most destroyers in the world with about double the next country, with another 4 undergoing sea trials and we are currently building 5 more and have awarded contracts for 5 more. By 2024 the US is expected to have 79 destroyers in service.Zumwalt Destroyer- The Zumwalt class warships are the largest destroyer ever built. The USS Zumwalt has unusual hull design optimized for wave piercing. There is a composite deckhouse. Angular shape minimizes its radar signature. The ship has hidden radar and sensors. The despite its size the USS Zumwalt has a radar signature of a fishing boat. Also it has reduced sound and infrared signature what makes this ship harder to detect. The ship is the First american surface warship to integrate electronic propulsion, it generates enough power to light up a small city. Sound levels of the Zumwalt are comparable with Los Angeles class submarines.Arleigh-Burke Destroyer- These guided missile destroyers entered service with the US Navy in 1991 were the first large US Navy vessel designed to incorporate stealth shaping techniques to reduce radar cross-section. Also these are one of the biggest destroyers in the world that incorporate highly advanced weaponry and systems. Hull profile of the Arleight Burke class signNowly improves seakeeping, permitting high speeds to be maintained in difficult sea states. The AN/SPY-1D phased array radar incorporates signNow advances in the detection capabilities of the AEGIS weapons system, particularly in its resistance to enemy electronic countermeasures. Missile are stored in vertical launch systems, that can also house smaller Evolved Sea Sparrow (ESSM) missiles, Tomahawk land attack cruise missiles, ASROC anti-submarine missiles. For point defense the ships are equipped with two Phalanx Close-In Weapon Systems (CIWS). Also there are 324 mm launchers for Mk.46 or Mk.50 torpedoes.Daily dose of freedom right here.Obviously, we can’t forget about the immaculate US submarine fleet. The US has some of the most advanced and quietest submarines. All of them use nuclear propulsion for extended range and stealth capabilities. The US has the…Ohio class (18 in commission) – 14 ballistic missile submarines (SSBNs), 4 guided missile submarines (SSGNs)- The U.S. Ohio-class submarines, of which 14 are Trident II SSBN, each capable of carrying 24 SLBMs. The first four which were all equipped with the older Trident I missiles have been converted to SSGN's each capable of carrying 154 Tomahawk guided missiles and have been further equipped to support Special OperationsSeawolf class (3 in commission) – attack submarines- The Seawolf class boats were intended to seek and destroy the latest Soviet ballistic missile submarines, such as the Typhoon class and attack submarines such as the Akula class. Seawolf class submarines are arguably the quietest submarines in the world ever constructed. It is exceptionally quiet even at high speeds. Most submarines need to keep their speed down to as little as 5 knots to avoid detection by passive sonar arrays, while the Seawolf class are credited with being able to cruise at 20 kots and still be impossible to locate. A Seawolf at 25 knots makes less noise than an older Los Angeles class submarine tied up alongside the pier. And these came out in 1989.Virginia class (11 in commission, 5 under construction, 2 on order) – fast attack submarines- The Virginia class submarines incorporate newly designed anechoic coating, isolated deck structures and new design of propulsor to achieve low acoustic signature. It is claimed that noise level of the Virginia is equal to that of the Seawolf class. The Virginia class submarines are fitted with 12 vertical launch system (VLS) tubes. These are used to launched Tomahawk land attack cruise missiles with a range of 1 700 km. Also there are four 533-mm torpedo tubes. These are used to fire a total of 26 Mk.48 heavyweight torpedoes and Sub-Harpoon anti-ship missiles. It is the first US submarine to employ a built-in Navy SEAL staging area allowing a team of 9 men to enter and leave the submarine.(Improved) Los Angeles class (34 in commission, 2 in reserve) – attack submarines- The Improved submarines are much quieter. It is described that improved Los Angeles class boats are 7 times quieter than the original Los Angeles class boats. The class features a very potent weapon array, including Mk.48 torpedoes, Sub-Harpoon anti-ship missiles and Tomahawk land attack cruise missiles. Tomahawk missiles can be launched from torpedo tubes of from dedicated vertical launching systems. These boats can operate under ice where the Russian ballistic missile submarines tend to hide.Surfacing of a US Submarine.Let’s move onto the air. While the USN has a quite capable Air Force. But that is dwarfed by the sheer magnitude and strength of the United States Air Force. The Air Force articulates its core missions as air and space superiority, global integrated ISR, rapid global mobility, global strike, and command and control. The USAF flys a multitude of different planes and helicopters. The USAF is the largest Air Force in the world, here is the list of what America flys. Most of these are at the cutting edge of innovation, with two of them being 5th generation stealth fighters. That’s really really good because no other country has an active 5th gen while the US has 2. The USAF also has the largest bomber, tanker, fighter, and transport fleets in the world. The USAF has so many staging areas around the world, that the US can have bombers or any other planes on station, anywhere around the world in a matter of hours.Attack: A-10, AC-130, MQ-1, MQ-9Bomber: B-1B, B-2, B-52HElectronic warfare: E-3, E-8, EC-130Fighter: F-15C, F-15E, F-16, F-22 (5th gen), F-35A (5th gen)Helicopter: HH-60, UH-1NReconnaissance: MC-12, RC-135, RQ-4, RQ-170, U-2, U-28Trainer: T-1, T-6, T-38, T-41, T-51, T-53, TG-16Transport: C-5, C-12, C-17, C-21, C-32, C-37, C-130, C-40, CV-22, VC-25Tanker: KC-10, KC-135Let’s look at the two of my favorite ones and the most technologically advanced planes in the world.F-22 RaptorThe F-22 Raptor air superiority fighter is almost invisible to radars. This aircraft carries a powerful array of weaponry. It is the most advanced and most expensive production fighter aircraft to date. Many of sensors and avionics of this plane remain classified. Engines of the raptor allow the aircraft to supercruise over long ranges, while thrust-vectoring nozzles, combined with a triplex fly-by-wire flight control system, make it exceptionally maneuverable. The highly integrated avionics systems also include a data-link, inertial navigation system with embedded GPS for high-accuracy navigation, and advanced electronic warfare, warning and countermeasures systems. Two central computers manage the automatic switching of the sensors between completely passive and wholly active operation, according to the tactical situation. Artificial intelligence algorithms fuse data from the sensors and present only relevant information to the pilot to reduce workload while at the same time improving tactical awareness. The datalink allows tactical information to be shared with other F-22s. The tech is so special that other countries, not even NATO allies are given the chance to procure the plane.B-2 SpiritThe B-2A Spirit is the silver bullet of US policy, reserved for use against targets of the highest priority. The B-2's stealth characteristics enable the undetected penetration of sophisticated anti-aircraft defenses and to attack even heavily defended targets. This stealth comes from a combination of reduced acoustic, infrared, visual and radar signatures (multi-spectral camouflage) to evade the various detection systems that could be used to detect and be used to direct attacks against an aircraft. Composites are extensively used to provide a radar-absorbent honeycomb structure; the bomber has a minimal IR signature, does not contrail and uses its shielded APQ-181 radar only momentarily to identify a target just before attacking. The onboard DMS is capable of automatically assessing the detection capabilities of identified threats and indicated targets. The DMS will be upgraded by 2021 to detect radar emissions from air defenses to allow changes to the auto-router's mission planning information while in-flight so it can receive new data quickly to plan a route that minimizes exposure to dangers. Also, most of the B-2s are stationed in Missouri, and they are capable of bombing any target in the world despite being in the heart of America.Now for the US ARMYThe US army it self is massive in numbers, coming in at 1.01 million personnel, it self is one of the biggest standing armies in the world, and that's just one branch of the US military. Also, in the US military, it is the largest branch out of them all surpassing any other branch by almost 600,000 personnel. They provide the bulk of security for the US's foreign interests. The mission of the U.S. Army is to fight and win our Nation's wars, by providing prompt, sustained, land dominance, across the full range of military operations and the spectrum of conflict, in support of combatant commanders. Which is mainly air domination and land domination. They mainly engage is conventional warfare, and asymmetrical warfare. The US Army's main responsibilities is preserving the peace and security and providing for the defense of the United States, the Commonwealths and possessions and any areas occupied by the United States, Supporting the national policies, Implementing the national objectives, Overcoming any nations responsible for aggressive acts that imperil the peace and security of the United States. The US Army is also home to some of the most dangerous, prestigious and hardest working special forces teams in the world such as the frontline special force, the Rangers, we also have the green berets and the iconic 1st Special Forces Operational Detachment-Delta (Airborne) also known as Delta Force. The US army is thought to be one of the most battle tested and battle proven militaries in the world. With the mobility of the USAF an army QRF can be anywhere on earth in less than 24 hours. The US ARMY uses the M1A2 Abrams tank. One of the most badass, heaviest, fastest, and battle hardened tanks in the world.This tank has incredible technology and armor. Also it has seen combat. It is one of the most feared MBTs. The M1A2 offers signNow protection against all well-known anti-tank weapons. This main battle tank uses advanced armor, reinforced with depleted uranium layers. The M1A2 has signNow level of protection against all known anti-tank weapons. It can also employ counter-IED equipment. The tank is armed with the same 120-mm M256 smoothbore gun as its predecessor. Range of effective fire is in excess of 4 km. This main battle tank is powered by a Honeywell AGT1500 gas turbine engine, developing 1 500 hp. The tank is one of the fastest in the world, clocking in (with no governor) at 60 mph while being THE heaviest tank in the world. As of April of 2018, the US has no combat losses with the Abrams, the Abrams has only been lost due to friendly fire, never to enemy fire.I don’t think I need to explain the marines. Just know that they use the same tech as the Army (with some exceptions) but they are also the main invasion force for the US. And they are badass.The US military signNow is massive with the Aircraft carriers and the 700+ military bases around the world. The US is truly the most powerful military in the world. The fact that they can have a men anywhere in the world in less than 24 hours and being able to bomb any place on earth, just proves how powerful the US military is.
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What are some mind blowing facts about the Indian Air Force?
Indian Air Force is an interesting topic to read and know about with many jaw-dropping facts that are particularly unbeknownst to the general populace of one of the largest air forces in the world. Here I will discuss some 11 amazing facts about the Indian Air Force from past and the present which I hope , people would like to know about :A. When IAF inducted 140 Fighters in just 1.5 years !You read that right. After the 1965 Indo-Pak War , Indian Air Force was heavily modernizing its combat fleet and to stop the squadron numbers from diminishing. For this purpose , Sukhoi Su-7 was selected which was the first Sukhoi to serve in Indian Air Force. The procurement were done in a record time which were quite unprecedented as Indian Air Force went on to induct 140 Su-7 in just 1.5 Years which was almost 8 Fighters each month. No.26 Squadron first converted to Su-7 followed by No.101 Squadron and during the induction process , IAF raised some 6 Strike Squadrons which served with distinction during the 1971 Indo-Pak War.B. When an Indian Air Force Mig-25 shot the sun !A Lamborghini Huracan Avio posing in front of the MiG-25 Foxbat at Indian Air Force Museum at Palam AFSOn 24th October 1995 , an IAF Mig-25 ‘Garuda’ flown by Group Captain, Air Marshal Mukerji shot the sun during the total solar eclipse which might sound simple but was quite challenging as the pilots were required to be specialized in navigation and earth’s geometry. An upward looking camera was cued by the pilot towards the sun while another pilot flew the ‘Garuda’ in the exact direction as the earth rotated around the sun. They filmed the magnificent scene from the stratosphere for one and more minutes. Mig-25 was one of the legends of Indian Air Force which served as a Strategic Reconnaissance Aircraft and its presence was kept as a secret for many years as it flew many hostile High-Risk Sorties in enemy airspace clicking high defenition pictures of enemy installments on the ground.C. Indian Air Force ‘Mammoth Formation’ :The largest Indian Air Force Formation flew from Ambala Air Force Station on 1987–88 which was nicknamed the “Mammoth Formation”. These aircrafts consisted of Canberra Bomber Aircraft , Mig-25 “Garuda” , Mig-29 “Baaz” , Ajeet , Mirage 2000 , Mig-27 “Bahadur” , Hawker Hunter , Jaguar “Shamsher” , Mig-23MF and finally the good-old Mig-21.D. When an Indian Air Force Military Transport Aircraft flew without using propellers :Here is an Indian Air Force C-119G Flying Boxcar Military Transport Aircraft somewhere in 1960s. If you closely notice this particular photo , the propellers are idle and the engine has been put off. Now you must be wondering how is this particular aircraft flying.This has been made possible only by its Orpheus Jet pod which has been placed on top of its fuselage. The aircraft is flying solely due to the power supplied by the pod as it was utilized by IAF to shorten the takeoff distance thereby enabling the aircraft of Short Takeoff and Landing Capabilities. IAF also used the J34 turbojet engine for short take-off and IAF’s C-119 also holds the record for being the first aircraft to take-off from the Daulat Beg Oldi with an Orpheus Pod.E. How was Garud Commando Force established :In early stages , PARA SF and MARCOS Officers advised the top brass of Indian Air Force to establish a dedicated Commando Force modeled on the Commando Force of Royal Air Force Regiment. They also advised IAF Officers to procure few numbers of C-130J Strategic Airlifters which can be used to air drop the Commandos in Combat Search and Rescue Missions and also in high-threat missions. Garuds were established on same lines as RAF Regiments and were trained on similar lines as PARA SF and MARCOS though the top brass of Indian Air Force did not pay heed to the second recommendation and no additional C-130J were procured.F. Indian Air Force was the first Air Force to Operate Fighter Jets in Asia :Indian Air Force inducted de Havilland Vampires with the No.7 Squadron “Battle Axes” in 1949 making Indian Air Force the first Air Force in Asia to induct Fighter Jets in its inventory. Vampire served in almost all Fighter Squadrons of Indian Air Force for a span of over 3 decades as a Fighter-Bomber and Reconnaissance Aircraft.G. Indian Air Force was the first Air Force to induct an indigenous Fighter Jet in Asia (outside Soviet Union ) :HF-24 was the first indigenous Fighter Jet which was inducted by an Asian Air Force outside Soviet Union. Conceptualized for Air Staff Requirement (ASR) as a Multi-Role Fighter jet , HF-24 was never realized to its true potential as it was primarily used as a Fighter-Bomber for Ground Attacks. It was inducted by No.10 Daggers Squadron of Indian Air Force in April 1967 making Indian Air Force the first Asian Air Force outside Soviet Union to induct an indigenously made Fighter Jet.H. When an Indian Air Force Mig-21 almost shot down an Indian Helicopter in a Special Operation :During 1971 Indo-Pak War , an Indian Alouette 3 helicopter was flying for a Special Operation in a hostile zone where no supposed friendlies were to be spotted. The helicopter was spotted by an Indian Air Force Mig-21 who decided to engage the helicopter by firing its 57mm Rockets , considering it an enemy asset , which was quickly dodged off by the Alouette Pilot. Realizing his miscalculation , he decided to re-engage the helicopter but that attack was also dodged off by the helicopter pilot. This time the Mig-21 pilot did not wanted to take any risk and closely approached the Helicopter and finally noticed the Indian markings on it. He sighed in relief as he has almost shot down the friendlies.I. Ashok Chakra Roundel for Indian Air Force :After Independence in 1947 , Indian Air Force adopted new markings for its Fighter Aircrafts in June 1948 to distinguish itself from the Royal Indian Air Force Markings. The roundel adopted by Indian Air Force was a ‘Ashok Chakra’ on the Fuselage and the wings. Since these roundels were difficult to paint in correct dimensions , they were soon replaced by Saffron White Green Roundels . Nevertheless these Ashok Chakra Roundels saw service during the 1947–48 Kashmir War when IAF Aircrafts flew with these markings.J. Missiles on Overwing Pylons !Indian Air Force utilized the unusual provision on the SEPECAT Jaguar Aircrafts to mount Air-to-Air Missiles like Matra R.550 Magic on overwing pylons thus freeing the underwing pylons to carry other weapons like Bombs and Missiles. The advantage of this was a quick height gain for Air-to-Air Missiles when they are launched at enemy interceptors at higher altitude who might arrive in the scene to intercept the low flying Jaguar Strike Aircraft. It also helped in additional payload carrying capacity for the Jaguars and is truly an amazing capability with an IAF Fighter still in service after 3 decades.K. First Indian Air Force Fighter with an InfraRed Search and Track System :IRST is a system deployed on Aircrafts to detect and track potential hostiles by scanning their Infrared Signatures. Indian Air Force was one of the first Air Force to deploy an IRST System on it's frontline Fighter Aircraft. IAF's Mig-23MF was fitted with TP-23 IRST at its undernose with the legacy continued by Su-30MKIs and Mig-29UPG at present and by Rafales in future.L. ‘Eye in the Sky' for Indian Air Force :India has acquired 3 EL/W-2090 Airborne Early Warning and Control Radar System from Israel to serve as the ‘Eye in the Sky' for Indian Air Force mounted on A-50EI Platform . This Radar System was adjudged as the most advanced AEW&C by Federation of American Scientists in 1999 and 2008 Articles. It can detect a fighter sized target at a distance of 500 kilometres relying on its L-Band AESA radar. It can also carry out L-band radar, then adds electronic and communications intelligence gathering (ELINT and COMINT ).Hope my answer serves the purpose =)References :Sukhoi-7 BMK - A whale of a fighterhttps://www.livefistdefence.com/...This Stunning Old Photo Of An IAF ‘Mammoth Formation’ Just Showed UpEL/W-2090 - WikipediaStory behind missiles over the wings (25 Photos)https://www.secretprojects.co.uk...Indian Air Force Gallery :: De Havilland Vampire F3 and FB52 (Single Seaters) - Bharat RakshakRoundels (Independence and Chakra)HAL HF-24 Marut - Wikipedia
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What are the best features of Microsoft Office 365?
Here’s a breakdown of some awesome Features Office 3651. Work Smarter, EverywhereAfter buying Office 365, you also gain access to its accompanying mobile apps and browser apps. This allows you to access their cloud service from any up to date web browser on your desktop or mobile device. Even better yet, you don’t have to install Office software on your computer to do this.The mobile app allows you to access all of your Office 365 subscriptions and Office products right from your smartphone or tablet; this includes Word, Excel, Powerpoint, Onenote, and more. Cut the cord and stop working on your PC only — download the Microsoft Office 365 mobile app to stay productive, even while on the go.2. Enjoy 50 GB of StorageEach Office 365 user receives a whopping 50 GB of storage with Exchange Online; this can be used to save emails, calendar events, task lists, meeting notes, contact information, and email attachments.You can save some more space in your mailbox by utilizing the OneDrive cloud storage feature to share attachments.Your OneDrive storage is also synced to your device, enabling you to work offline on files. As soon as you reconnect to the web, the newest versions of your documents will be automatically uploaded to your cloud storage. The new versions of your documents will also be sent to any other connected device, including your phone or tablet — nifty!3. Edit Documents with Real-Time Co-AuthoringCollaborate online and see changes your team makes to shared documents within your Office apps as they happen with the real-time co-authoring feature in Word. Save your file to OneDrive cloud storage or SharePoint so your team can access the document and make any necessary edits or updates. You can also share it directly from Word by utilizing a handily integrated sidebar. As the publisher and access-giver, you can edit accessibility settings at any time.With the improved version control that was rolled out with Office 2016 co-authoring, you can see which changes to the document were made by which contributor and when the update was made. You can also easily revert back to a previous version of the file whenever you need to.4. Connect with Co-WorkersYou may not have known this, but Office apps include a Skype in-app integration. You can use this feature to instant message your teammates, share your screen during meetings and have audio or visual conversations — without even exiting the Office apps you’re working in. You can continue Skype conversations even after you close your office apps via your desktop or mobile version of Skype. The best part? Your team will receive unlimited Skype minutes.Source: Microsoft5. Send Links, Not FilesIt’s time to move away from email attachments. It’s never been easier to share documents for co-authoring!Simply upload your file to Office 365’s cloud storage. Then, write your email via Outlook or the Outlook web app. Rather than attaching your document to the email, you can insert a link to the file on your cloud. Outlook will automatically allow email recipients to edit the document you wish to share. You can always change permissions on any document at your convenience.6. Convert OneNote Items into Outlook Calendar EventsEasily configure OneNote items to tasks within your Outlook calendar. You can also assign tasks to colleagues, complete with follow-up reminders and concise due dates. You can also transfer meeting notes taken in OneNote via email to your teammates, and add important details (date, location, and attendees) to their respective meeting.7. Use Your Mouse as a Laser Pointer during PowerPoint PresentationsWith only a simple keyboard shortcut (Ctrl + P), your mouse can be used as a laser pointer during your PowerPoint presentations. You can also use the “presenter mode” commands while using this feature.The laser pointer tool has been a nifty trick within older versions of the office apps for years; however, it was only recently integrated for touch-screen devices. All you have to do is hold down on your device’s screen, and the laser pointer will appear.8. Create a Power Map Using ExcelTurn data into a 3-D interactive map with Power Map, one of the many Power BI-enhanced data visualization features that Excel has to offer. It comes with three different filters: List, Range, or Advanced. The Power Map will help you not only convey your data more effectively, but also support your claims by creating a tangible story from the numbers.
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What's an explanation of dark matter in details, with very high accuracy?
To fulfill your stated requirements would require (1) a post the length of a book, and (2) a deeper understanding than I personally have. However, given that Quora is not the right place to write a book anyway, I may know enough to take a reasonable crack at this. With that said, though, if you're an actual expert on one of these areas and catch something I've explained incorrectly, please let me know in the comments so that I can fix it!Yes, it's still quite long, but keep in mind that this is the short version.What is Dark Matter (DM)?Dark Matter is just matter that doesn't interact via the Electromagnetic (EM) or Strong Nuclear forces. No EM interactions means that it can't give off light, or absorb light, or reflect, refract, or scatter light in any way. This, naturally, makes it rather difficult to see (thus "dark" matter, although I suppose it's more "transparent" than "dark"). Our current best measurements indicate that something like 85% of the matter in our observable Universe (about a quarter of the total mass-energy content) is Dark Matter.Isn't Dark Matter weird/spooky?Not at all. Neutrinos, for example, satisfy the definition of Dark Matter, they just represent such a tiny fraction of the total DM in the Universe that people tend to neglect them when they ask, "what is Dark Matter made of?"There is nothing at all strange or unusual about certain particles not interacting in certain ways. Neutrons have no electric charge (although they do have EM properties, but that's neither here nor there), and electrons don't interact via the Strong Force, so why shouldn't there be particles that interact with neither, like the neutrinos? Saying that interacting with light is "normal" is purely human bias, because we rely so much on sight. Having lots of DM in the Universe is in no way "weird"; it just means that the Universe doesn't revolve around what humanity finds convenient!Why are we confident that DM exists?This is by no means a complete list, but it should give a sense of the kinds of evidence we have. Each of these would take at least a chapter of a book to explain properly, but hopefully this will give the general idea.Galactic rotation curves.When one object orbits another, the orbiting object has to be constantly accelerating towards the central object (or, more precisely, they both accelerate towards their combined center of mass). Without that acceleration, the orbiting body would just fly off. The faster the orbiting body is moving, the more acceleration is needed to keep it in its orbit. Since in this case the acceleration is due to gravity, this means that the central mass has to be bigger. For a circular orbit of a small object [math]m[/math] at distance [math]r[/math] and velocity [math]v[/math] around a large (and assumed stationary) object [math]M[/math], the acceleration requirement gives[math]\frac{v^2}{r} = \frac{GM}{r^2}[/math]which in turn gives us the relation[math]v = \sqrt{\frac{GM}{r}}[/math].(I'm doing this with Newtonian gravity for simplicity; to do it with full rigor would require General Relativity. In this situation, the Newtonian approximation is actually generally pretty good.)For a more complicated object than just two point particles, as long as there's enough symmetry, the gravitational version of Gauss's law says that the relevant [math]M[/math] is the total mass of everything in the galaxy that's at a distance less than [math]r[/math] from the center. [Edited to note: For this to be exactly right, the matter distribution would have to be spherically symmetric, which galaxies aren't. As a result, actual calculations are a bit more complicated than shown here.]This allows us to "weigh" different parts of the galaxy, by measuring the relationship between [math]r[/math] and [math]v[/math]. (We can measure the rotational velocities by comparing redshifts on the approaching and receding sides of the galaxy.) This image from Wiki shows the result of this measurement:The "expected from visible disk" line is determined by adding up the masses of all the parts of the galaxy that we can see. (How we measure that mass is a whole different discussion.)Gravitational Lensing.In General Relativity, whenever light passes through a gravitational field, that field bends its path slightly. This acts like a Gravitational lens, and can produce, for example, "Einstein Rings", like this image from Wiki:The "ring" is a distorted image of a single blue galaxy located behind the red galaxy at the center. Light from the blue galaxy goes out in all directions, but is bent by the red galaxy's gravity. This means that the light that starting out on a "direct path" to us never signNowes us, but light that was originally missing us by a specific amount (in any direction) gets bent back towards us, which makes it look like it's coming from a bunch of different directions, resulting in the ring image seen here.This is a highly dramatic example of gravitational lensing, but there are much more subtle effects that can still be useful. In Weak gravitational lensing, statistical analysis of distortions in the light we receive allows us to "map out" the gravitational field between us and distant galaxies. Often, this just shows more mass than we know how to account for, but that could be explained away by just assuming that our understanding of gravity is off. There's something else, however, that's a lot harder to explain away in that manner: the Bullet Cluster.(Image from A Matter of Fact on nasa.gov)What's going on here? Well, two galaxy clusters collided with each other, and this is the aftermath. The red coloring represents where the visible matter is, while the blue coloring represents where the dark matter is, as inferred by gravitational lensing. Why are they separated so much? Well, most of the luminous matter in a galaxy cluster is in the Intracluster medium, a hot, dense, plasma. When these plasmas collide with each other, a signNow amount of the matter slows down. However, since Dark Matter interacts only very weakly, the DM components of the two clusters were free to pass through each other unimpeded, resulting in a separation (as seen here). Not only is there "not enough" luminous matter... it's in the wrong place! A small number of scientists remain committed to finding ways to explain this without DM, and they have had partial success, but only by including as-of-yet-unmeasured things that are far stranger than DM (for example, a rank-3 tensor field, which, while possible, would be the first tensor field of such a high rank ever found).Effect on the Cosmic Microwave Background.For the first few hundred thousand years after the Big Bang, The Universe was hot enough that it was highly ionized, which made it more or less opaque to light; photons were pinballing around just like any other particle. However, once things cooled down enough, signNow amounts of the protons and electrons combined into neutral Hydrogen, which is (more or less) transparent to most of the light that was around at the time. This happened fairly quickly (in terms of cosmological time), and so it was as if all of the light pinballing around all over the Universe were suddenly released all at once, effectively capturing a snapshot of the Universe at that moment in its evolution. Since this light was released everywhere in the Universe, we can point our radio telescopes in any direction we like, and there it is: the Cosmic microwave background (CMB). It's almost the same temperature in every direction, but there are small differences (generally around one part in [math]10^5[/math]), and we have measured these tiny variations with extraordinary accuracy: first via the COBE satellite, which was then replaced by the more advanced WMAP, which was then replaced by the more advanced Planck (spacecraft), which is currently in operation.These tiny variations can tell us a lot about the early universe. For example, statistical analyses of these variations show the distinct signature of pressure waves propagating through that early plasma, and the nature of these Baryon acoustic oscillations can tell us a lot about what kinds of things were around. Specifically, the protons and electrons would be dragged along by the (dominant) photons, becoming part of the wave, but Dark Matter wouldn't, and would only be indirectly affected by the resulting small changes in gravity. The presence and abundance of Dark Matter therefore affects how these waves impact the temperature variations in the CMB.The formation of large-scale structure.The standard story given in popular science explanations goes like this: the Universe started out hot and dense and more or less uniform, then it expanded and cooled and clumped into stars and galaxies. However, this story is incomplete, in a way that means that galaxies wouldn't exist without dark matter.At a surface level, the story makes sense; heck, I got almost half-way through a Ph.D. in Physics without noticing any problem with it! It sounds so plausible because of how gravity works: if matter is distributed more or less evenly, but some places are a tiny bit more dense than others, gravity will tend to make those overdensities bigger and bigger. Why? Well, even if a region is just a little denser than its neighbors, it's still going to win the gravitational tug-of-war and gradually accumulate more and more mass. Of course, once it has more mass, it wins the tug-of-war by even more, and so it's a run-away process that ends in big gravitationally-bound clumps.So, what's the problem? Well, consider the air in the room with you right now. Are there tiny density variations? Of course, since perfect uniformity is impossible. But, is it forming into exponentially denser clumps? Certainly not! The reason for this is that, under these kinds of conditions, when the density of a gas goes up, so does its pressure. That pressure makes the over-dense region expand outwards again, returning the density back to average!Now, of course, the scales and temperatures involved are totally different. A huge region of gas will have more gravitational attraction than a tiny pocket of denser air in your room, and gas in space has no need to be at room temperature, either. So, if the gas can cool down enough, that can reduce the pressure enough for gravity to win. But, the more it compresses, the more it heats up, because it's converting gravitational energy into thermal energy, and so the pressure goes up again. This means that forming a galaxy is a very gradual process, during which it has to constantly be getting rid of tremendous amounts of energy. If it were just a cloud of gas, without any outside interference, this process wouldn't be nearly fast enough, and we wouldn't have galaxies today.But, as you know, hot things give off heat much faster than cold things. So, if we want galaxies to form by the present day (or, indeed, before the expansion of space makes matter too dilute to form galaxies at all), something has to be forcing the gas to compress and become denser and hotter than it would be able to under its own gravity. Enter: Dark Matter. Because it interacts only weakly, Dark Matter doesn't have pressure like gas does. So, the argument about the run-away gravitational process actually works for Dark Matter. DM can't get rid of energy very easily, and so conservation of energy and angular momentum mean that it can only collapse to about 200 times the background density, but the resulting Dark matter halo provides enough of a gravity well to "seed" the formation of visible galaxies. So, it's not a coincidence that the galactic rotational curves showed large amounts of dark matter... the galaxies wouldn't have formed there without it!As a result of this DM "seeding" process, theoretical models and computer simulations of the formation of DM structures have been fairly successful in describing the statistical properties of how galaxies are distributed now, as well as how they were distributed earlier in the history of the Universe (which we can measure by looking at very distant galaxies).Okay, so that's why we think Dark Matter exists. But, the next obvious question is... well... what is it? What's it actually made of? What are its properties? Here, we have only very partial knowledge, and multiple different theories, any combination of which could be correct (or, perhaps, none of them). This leads us to:What do we know about the properties of Dark Matter?Again, this is in no way exhaustive, but it should give you a decent idea.It's "cold".This is why the current dominant model of cosmology is called the Lambda-CDM model: "Lambda" ([math]\Lambda[/math]) stands for the Cosmological constant, and "CDM" stands for "Cold Dark Matter".When an astrophysicist describes something as "cold", they generally mean that the associated thermal velocity is much less than the speed of light. By this standard, the air in Death Valley is "cold". But, then again, to cosmologists, galaxies are basically point-particles, so everything's a matter of scale and perspective!So, why does DM need to be "cold"? Well, remember that DM clumping together was integral to the formation of structures like galaxies. However, if DM were very hot (and therefore the particles were moving very fast), this would prevent it from clumping properly. I have explained it in very vague terms, but the effects are actually well-understood mathematically. In fact, it's similar to something that does happen, with photons: Diffusion damping (or "Silk damping"). However, in the case of Dark Matter, the result would be a signNow delay (or even outright prevention) of the formation of galaxies, to the extent that "warm" Dark Matter can be observationally ruled out.Incidentally, this is how we know that it's not all just neutrinos: given what we know about the early Universe, they would be far too hot!It interacts only very weakly.This is somewhat part of the definition of Dark Matter, but it's good to see observational confirmation. I know fewer of the details on this, but I do know that there are observational bounds in the "interaction cross-section" of Dark Matter, both in terms of its interactions with luminous matter and for its theorized self-annihilation processes (in which two DM particles could interact and annihilate each other). Also, as discussed before, the Bullet Cluster shows giant dark matter halos more or less just passing through each other, which suggests very weak interactions.So... given those properties,What might Dark Matter be made of?There are two leading theories (as far as I'm aware) that suggest the existence of specific types of new particles. Both are well-motivated theoretically (as in, we have good reasons for suspecting that particles with those particular properties might exist), but neither has been experimentally confirmed yet. Interestingly, the two predicted particles are totally different from one another, not slight variations on the same theme.At the end of the day, either of these theories could be right, or both (given the existence of neutrinos, there's no need for all the rest of the DM to be a single type of particle), or, of course, neither.So, what are the theories?Axions.I feel morally obliged to put this one first, even though the other one is more popular at the moment, because my university is heavily involved in the Axion Dark Matter Experiment (ADMX), and so of course I'm rooting for my colleagues!The existence of Axions has been theorized since the 1970s, but we only recently have the technology to even properly start to try to measure them in the lab. Axions are extremely tiny particles (unlike WIMPs, the other leading option), and so they would have to exist in truly huge quantities. Still, because they interact so weakly, it's hard to detect them, even with billions of them passing through your detector in a tiny fraction of a second. The linked wiki articles do a better job of explaining the theoretical motivation and experimental search than I could. It's really quite elegant, and would solve a lot of outstanding mysteries in particle physics (like the Strong CP Problem), but I can't do it justice.Weakly Interacting Massive Particles (WIMPs)(Wiki reference: Weakly interacting massive particles)To explain why WIMPs are theoretically attractive, I have to take a little detour into "relic abundance", i.e., how many particles of a given type were left over after the Universe cooled down and generally became a more stable place.In the early universe, everything was very dense, and many different kinds of particles were "tightly coupled" (i.e., they interacted with each other frequently). However, as the universe got larger and cooler, these interaction rates slowed down, more or less to a stop, a phenomenon known as "freezing out". The time at which something "freezes out" depends on a number of things, including its mass and how strongly it interacts with other things. This "freezing out" has a huge effect on the abundances of various particles in the Universe. For example, consider the process[math]n \Leftrightarrow p + e^- + \overline{\nu_e}[/math],in which a neutron can turn into a proton, electron, and electron anti-neutrino (or vice versa). If you go back far enough, this reaction will be in thermodynamic equilibrium, just like with any chemical reaction that can go either direction. However, once the neutrinos "freeze out", equilibrium can't be maintained anymore (although other processes, like beta decay, can still happen). The relative abundance of protons and neutrons at the moment of freeze-out is determined by two factors: the mass difference [math]\Delta m[/math] between the two particles, and the temperature of the Universe when freeze-out occurred. These factors combine to determine by how much the lighter particle is thermodynamically favored, with an exponential dependence:[math] \frac{N_n}{N_p} \propto e^{-\Delta m c^2 / k T}[/math]where [math]k[/math] is Boltzmann's constant.This clearly impacts the "relic abundance" of the particles involved (here, protons and neutrons). So, in general, the abundance of a given particle in the Universe today is signNowly influenced by the mass of that particle and how strongly it interacts (since that affects freeze-out time and thus freeze-out temperature). This brings us to the so-called "WIMP miracle": a particle that interacts predominantly via the Weak Nuclear Force, and that has a mass near the mass scale associated with Weak interactions ([math]\sim 100 \text{ GeV}/c^2[/math]), would have a relic abundance that would match the measured abundance of Dark Matter in the Universe. Given that such a particle was already speculated to exist (in the context of Supersymmetry), this was very theoretically attractive to a lot of people, although our inability to find it so far has damped some of their spirits.So, there you have it: my summary of Dark Matter. Hope it was worth the time it took to read! (Let alone write...)
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