10 skills found
uvhw / Bitcoin FoundationBitcoin: A Peer-to-Peer Electronic Cash System Satoshi Nakamoto satoshin@gmx.com www.bitcoin.org Abstract. A purely peer-to-peer version of electronic cash would allow online payments to be sent directly from one party to another without going through a financial institution. Digital signatures provide part of the solution, but the main benefits are lost if a trusted third party is still required to prevent double-spending. We propose a solution to the double-spending problem using a peer-to-peer network. The network timestamps transactions by hashing them into an ongoing chain of hash-based proof-of-work, forming a record that cannot be changed without redoing the proof-of-work. The longest chain not only serves as proof of the sequence of events witnessed, but proof that it came from the largest pool of CPU power. As long as a majority of CPU power is controlled by nodes that are not cooperating to attack the network, they'll generate the longest chain and outpace attackers. The network itself requires minimal structure. Messages are broadcast on a best effort basis, and nodes can leave and rejoin the network at will, accepting the longest proof-of-work chain as proof of what happened while they were gone. 1. Introduction Commerce on the Internet has come to rely almost exclusively on financial institutions serving as trusted third parties to process electronic payments. While the system works well enough for most transactions, it still suffers from the inherent weaknesses of the trust based model. Completely non-reversible transactions are not really possible, since financial institutions cannot avoid mediating disputes. The cost of mediation increases transaction costs, limiting the minimum practical transaction size and cutting off the possibility for small casual transactions, and there is a broader cost in the loss of ability to make non-reversible payments for non- reversible services. With the possibility of reversal, the need for trust spreads. Merchants must be wary of their customers, hassling them for more information than they would otherwise need. A certain percentage of fraud is accepted as unavoidable. These costs and payment uncertainties can be avoided in person by using physical currency, but no mechanism exists to make payments over a communications channel without a trusted party. What is needed is an electronic payment system based on cryptographic proof instead of trust, allowing any two willing parties to transact directly with each other without the need for a trusted third party. Transactions that are computationally impractical to reverse would protect sellers from fraud, and routine escrow mechanisms could easily be implemented to protect buyers. In this paper, we propose a solution to the double-spending problem using a peer-to-peer distributed timestamp server to generate computational proof of the chronological order of transactions. The system is secure as long as honest nodes collectively control more CPU power than any cooperating group of attacker nodes. 1 2. Transactions We define an electronic coin as a chain of digital signatures. Each owner transfers the coin to the next by digitally signing a hash of the previous transaction and the public key of the next owner and adding these to the end of the coin. A payee can verify the signatures to verify the chain of ownership. Transaction Hash Transaction Hash Transaction Hash Owner 1's Public Key Owner 2's Public Key Owner 3's Public Key Owner 0's Signature Owner 1's Signature The problem of course is the payee can't verify that one of the owners did not double-spend the coin. A common solution is to introduce a trusted central authority, or mint, that checks every transaction for double spending. After each transaction, the coin must be returned to the mint to issue a new coin, and only coins issued directly from the mint are trusted not to be double-spent. The problem with this solution is that the fate of the entire money system depends on the company running the mint, with every transaction having to go through them, just like a bank. We need a way for the payee to know that the previous owners did not sign any earlier transactions. For our purposes, the earliest transaction is the one that counts, so we don't care about later attempts to double-spend. The only way to confirm the absence of a transaction is to be aware of all transactions. In the mint based model, the mint was aware of all transactions and decided which arrived first. To accomplish this without a trusted party, transactions must be publicly announced [1], and we need a system for participants to agree on a single history of the order in which they were received. The payee needs proof that at the time of each transaction, the majority of nodes agreed it was the first received. 3. Timestamp Server The solution we propose begins with a timestamp server. A timestamp server works by taking a hash of a block of items to be timestamped and widely publishing the hash, such as in a newspaper or Usenet post [2-5]. The timestamp proves that the data must have existed at the time, obviously, in order to get into the hash. Each timestamp includes the previous timestamp in its hash, forming a chain, with each additional timestamp reinforcing the ones before it. Hash Hash Owner 2's Signature Owner 1's Private Key Owner 2's Private Key Owner 3's Private Key Block Item Item ... 2 Block Item Item ... Verify Verify Sign Sign 4. Proof-of-Work To implement a distributed timestamp server on a peer-to-peer basis, we will need to use a proof- of-work system similar to Adam Back's Hashcash [6], rather than newspaper or Usenet posts. The proof-of-work involves scanning for a value that when hashed, such as with SHA-256, the hash begins with a number of zero bits. The average work required is exponential in the number of zero bits required and can be verified by executing a single hash. For our timestamp network, we implement the proof-of-work by incrementing a nonce in the block until a value is found that gives the block's hash the required zero bits. Once the CPU effort has been expended to make it satisfy the proof-of-work, the block cannot be changed without redoing the work. As later blocks are chained after it, the work to change the block would include redoing all the blocks after it. The proof-of-work also solves the problem of determining representation in majority decision making. If the majority were based on one-IP-address-one-vote, it could be subverted by anyone able to allocate many IPs. Proof-of-work is essentially one-CPU-one-vote. The majority decision is represented by the longest chain, which has the greatest proof-of-work effort invested in it. If a majority of CPU power is controlled by honest nodes, the honest chain will grow the fastest and outpace any competing chains. To modify a past block, an attacker would have to redo the proof-of-work of the block and all blocks after it and then catch up with and surpass the work of the honest nodes. We will show later that the probability of a slower attacker catching up diminishes exponentially as subsequent blocks are added. To compensate for increasing hardware speed and varying interest in running nodes over time, the proof-of-work difficulty is determined by a moving average targeting an average number of blocks per hour. If they're generated too fast, the difficulty increases. 5. Network The steps to run the network are as follows: 1) New transactions are broadcast to all nodes. 2) Each node collects new transactions into a block. 3) Each node works on finding a difficult proof-of-work for its block. 4) When a node finds a proof-of-work, it broadcasts the block to all nodes. 5) Nodes accept the block only if all transactions in it are valid and not already spent. 6) Nodes express their acceptance of the block by working on creating the next block in the chain, using the hash of the accepted block as the previous hash. Nodes always consider the longest chain to be the correct one and will keep working on extending it. If two nodes broadcast different versions of the next block simultaneously, some nodes may receive one or the other first. In that case, they work on the first one they received, but save the other branch in case it becomes longer. The tie will be broken when the next proof- of-work is found and one branch becomes longer; the nodes that were working on the other branch will then switch to the longer one. 3 Block Nonce Tx Tx ... Block Nonce Tx Tx ... Prev Hash Prev Hash New transaction broadcasts do not necessarily need to reach all nodes. As long as they reach many nodes, they will get into a block before long. Block broadcasts are also tolerant of dropped messages. If a node does not receive a block, it will request it when it receives the next block and realizes it missed one. 6. Incentive By convention, the first transaction in a block is a special transaction that starts a new coin owned by the creator of the block. This adds an incentive for nodes to support the network, and provides a way to initially distribute coins into circulation, since there is no central authority to issue them. The steady addition of a constant of amount of new coins is analogous to gold miners expending resources to add gold to circulation. In our case, it is CPU time and electricity that is expended. The incentive can also be funded with transaction fees. If the output value of a transaction is less than its input value, the difference is a transaction fee that is added to the incentive value of the block containing the transaction. Once a predetermined number of coins have entered circulation, the incentive can transition entirely to transaction fees and be completely inflation free. The incentive may help encourage nodes to stay honest. If a greedy attacker is able to assemble more CPU power than all the honest nodes, he would have to choose between using it to defraud people by stealing back his payments, or using it to generate new coins. He ought to find it more profitable to play by the rules, such rules that favour him with more new coins than everyone else combined, than to undermine the system and the validity of his own wealth. 7. Reclaiming Disk Space Once the latest transaction in a coin is buried under enough blocks, the spent transactions before it can be discarded to save disk space. To facilitate this without breaking the block's hash, transactions are hashed in a Merkle Tree [7][2][5], with only the root included in the block's hash. Old blocks can then be compacted by stubbing off branches of the tree. The interior hashes do not need to be stored. Block Hash0 Hash1 Hash2 Hash3 Tx0 Tx1 Tx2 Tx3 Block Header (Block Hash) Prev Hash Nonce Root Hash Hash01 Hash23 Block Block Header (Block Hash) Prev Hash Nonce Root Hash Hash01 Hash23 Hash2 Hash3 Tx3 Transactions Hashed in a Merkle Tree After Pruning Tx0-2 from the Block A block header with no transactions would be about 80 bytes. If we suppose blocks are generated every 10 minutes, 80 bytes * 6 * 24 * 365 = 4.2MB per year. With computer systems typically selling with 2GB of RAM as of 2008, and Moore's Law predicting current growth of 1.2GB per year, storage should not be a problem even if the block headers must be kept in memory. 4 8. Simplified Payment Verification It is possible to verify payments without running a full network node. A user only needs to keep a copy of the block headers of the longest proof-of-work chain, which he can get by querying network nodes until he's convinced he has the longest chain, and obtain the Merkle branch linking the transaction to the block it's timestamped in. He can't check the transaction for himself, but by linking it to a place in the chain, he can see that a network node has accepted it, and blocks added after it further confirm the network has accepted it. Longest Proof-of-Work Chain Block Header Block Header Block Header Prev Hash Nonce Prev Hash Nonce Prev Hash Nonce Merkle Root Merkle Root Merkle Root Hash01 Hash23 Merkle Branch for Tx3 Hash2 Hash3 Tx3 As such, the verification is reliable as long as honest nodes control the network, but is more vulnerable if the network is overpowered by an attacker. While network nodes can verify transactions for themselves, the simplified method can be fooled by an attacker's fabricated transactions for as long as the attacker can continue to overpower the network. One strategy to protect against this would be to accept alerts from network nodes when they detect an invalid block, prompting the user's software to download the full block and alerted transactions to confirm the inconsistency. Businesses that receive frequent payments will probably still want to run their own nodes for more independent security and quicker verification. 9. Combining and Splitting Value Although it would be possible to handle coins individually, it would be unwieldy to make a separate transaction for every cent in a transfer. To allow value to be split and combined, transactions contain multiple inputs and outputs. Normally there will be either a single input from a larger previous transaction or multiple inputs combining smaller amounts, and at most two outputs: one for the payment, and one returning the change, if any, back to the sender. It should be noted that fan-out, where a transaction depends on several transactions, and those transactions depend on many more, is not a problem here. There is never the need to extract a complete standalone copy of a transaction's history. 5 Transaction In Out In ... ... 10. Privacy The traditional banking model achieves a level of privacy by limiting access to information to the parties involved and the trusted third party. The necessity to announce all transactions publicly precludes this method, but privacy can still be maintained by breaking the flow of information in another place: by keeping public keys anonymous. The public can see that someone is sending an amount to someone else, but without information linking the transaction to anyone. This is similar to the level of information released by stock exchanges, where the time and size of individual trades, the "tape", is made public, but without telling who the parties were. Traditional Privacy Model Identities Transactions New Privacy Model Identities Transactions As an additional firewall, a new key pair should be used for each transaction to keep them from being linked to a common owner. Some linking is still unavoidable with multi-input transactions, which necessarily reveal that their inputs were owned by the same owner. The risk is that if the owner of a key is revealed, linking could reveal other transactions that belonged to the same owner. 11. Calculations We consider the scenario of an attacker trying to generate an alternate chain faster than the honest chain. Even if this is accomplished, it does not throw the system open to arbitrary changes, such as creating value out of thin air or taking money that never belonged to the attacker. Nodes are not going to accept an invalid transaction as payment, and honest nodes will never accept a block containing them. An attacker can only try to change one of his own transactions to take back money he recently spent. The race between the honest chain and an attacker chain can be characterized as a Binomial Random Walk. The success event is the honest chain being extended by one block, increasing its lead by +1, and the failure event is the attacker's chain being extended by one block, reducing the gap by -1. The probability of an attacker catching up from a given deficit is analogous to a Gambler's Ruin problem. Suppose a gambler with unlimited credit starts at a deficit and plays potentially an infinite number of trials to try to reach breakeven. We can calculate the probability he ever reaches breakeven, or that an attacker ever catches up with the honest chain, as follows [8]: p = probability an honest node finds the next block q = probability the attacker finds the next block qz = probability the attacker will ever catch up from z blocks behind Trusted Third Party q ={ 1 if p≤q} z q/pz if pq 6 Counterparty Public Public Given our assumption that p > q, the probability drops exponentially as the number of blocks the attacker has to catch up with increases. With the odds against him, if he doesn't make a lucky lunge forward early on, his chances become vanishingly small as he falls further behind. We now consider how long the recipient of a new transaction needs to wait before being sufficiently certain the sender can't change the transaction. We assume the sender is an attacker who wants to make the recipient believe he paid him for a while, then switch it to pay back to himself after some time has passed. The receiver will be alerted when that happens, but the sender hopes it will be too late. The receiver generates a new key pair and gives the public key to the sender shortly before signing. This prevents the sender from preparing a chain of blocks ahead of time by working on it continuously until he is lucky enough to get far enough ahead, then executing the transaction at that moment. Once the transaction is sent, the dishonest sender starts working in secret on a parallel chain containing an alternate version of his transaction. The recipient waits until the transaction has been added to a block and z blocks have been linked after it. He doesn't know the exact amount of progress the attacker has made, but assuming the honest blocks took the average expected time per block, the attacker's potential progress will be a Poisson distribution with expected value: = z qp To get the probability the attacker could still catch up now, we multiply the Poisson density for each amount of progress he could have made by the probability he could catch up from that point: ∞ ke−{q/pz−k ifk≤z} ∑k=0 k!⋅ 1 ifkz Rearranging to avoid summing the infinite tail of the distribution... z ke− z−k 1−∑k=0 k! 1−q/p Converting to C code... #include <math.h> double AttackerSuccessProbability(double q, int z) { double p = 1.0 - q; double lambda = z * (q / p); double sum = 1.0; int i, k; for (k = 0; k <= z; k++) { double poisson = exp(-lambda); for (i = 1; i <= k; i++) poisson *= lambda / i; sum -= poisson * (1 - pow(q / p, z - k)); } return sum; } 7 Running some results, we can see the probability drop off exponentially with z. q=0.1 z=0 P=1.0000000 z=1 P=0.2045873 z=2 P=0.0509779 z=3 P=0.0131722 z=4 P=0.0034552 z=5 P=0.0009137 z=6 P=0.0002428 z=7 P=0.0000647 z=8 P=0.0000173 z=9 P=0.0000046 z=10 P=0.0000012 q=0.3 z=0 P=1.0000000 z=5 P=0.1773523 z=10 P=0.0416605 z=15 P=0.0101008 z=20 P=0.0024804 z=25 P=0.0006132 z=30 P=0.0001522 z=35 P=0.0000379 z=40 P=0.0000095 z=45 P=0.0000024 z=50 P=0.0000006 Solving for P less than 0.1%... P < 0.001 q=0.10 z=5 q=0.15 z=8 q=0.20 z=11 q=0.25 z=15 q=0.30 z=24 q=0.35 z=41 q=0.40 z=89 q=0.45 z=340 12. Conclusion We have proposed a system for electronic transactions without relying on trust. We started with the usual framework of coins made from digital signatures, which provides strong control of ownership, but is incomplete without a way to prevent double-spending. To solve this, we proposed a peer-to-peer network using proof-of-work to record a public history of transactions that quickly becomes computationally impractical for an attacker to change if honest nodes control a majority of CPU power. The network is robust in its unstructured simplicity. Nodes work all at once with little coordination. They do not need to be identified, since messages are not routed to any particular place and only need to be delivered on a best effort basis. Nodes can leave and rejoin the network at will, accepting the proof-of-work chain as proof of what happened while they were gone. They vote with their CPU power, expressing their acceptance of valid blocks by working on extending them and rejecting invalid blocks by refusing to work on them. Any needed rules and incentives can be enforced with this consensus mechanism. 8 References [1] W. Dai, "b-money," http://www.weidai.com/bmoney.txt, 1998. [2] H. Massias, X.S. Avila, and J.-J. Quisquater, "Design of a secure timestamping service with minimal trust requirements," In 20th Symposium on Information Theory in the Benelux, May 1999. [3] S. Haber, W.S. Stornetta, "How to time-stamp a digital document," In Journal of Cryptology, vol 3, no 2, pages 99-111, 1991. [4] D. Bayer, S. Haber, W.S. Stornetta, "Improving the efficiency and reliability of digital time-stamping," In Sequences II: Methods in Communication, Security and Computer Science, pages 329-334, 1993. [5] S. Haber, W.S. Stornetta, "Secure names for bit-strings," In Proceedings of the 4th ACM Conference on Computer and Communications Security, pages 28-35, April 1997. [6] A. Back, "Hashcash - a denial of service counter-measure," http://www.hashcash.org/papers/hashcash.pdf, 2002. [7] R.C. Merkle, "Protocols for public key cryptosystems," In Proc. 1980 Symposium on Security and Privacy, IEEE Computer Society, pages 122-133, April 1980. [8] W. Feller, "An introduction to probability theory and its applications," 1957. 9
aldanjav / Saddle DetectorA novel similarity-covariant feature detector that extracts points whose neighborhoods, when treated as a 3D intensity surface, have a saddle-like intensity profile. The saddle condition is verified efficiently by intensity comparisons on two concentric rings that must have exactly two dark-to-bright and two bright-to-dark transitions satisfying certain geometric constraints. Saddle is a fast approximation of Hessian detector as ORB detector is for Harris detector. Experiments show that the Saddle features are general, evenly spread and appearing in high density in a range of images. The Saddle detector is among the fastest proposed. In comparison with detector with similar speed, the Saddle features show superior matching performance on number of challenging datasets.
acguidoum / Sim.DiffProcAn R package for symbolic and numerical computations on scalar and multivariate systems of stochastic differential equations (SDEs). It provides users with a wide range of tools to simulate, estimate, analyze, and visualize the dynamics of these systems in both forms Itô and Stratonovich <doi:10.18637/jss.v096.i02>.
concorde-speed / ConcordeDate of Concorde In January of the year 1976 after 29 years of the first to penetrate to the speed of sound military aircraft jet - Two Concord took off together at the same time, one from London and one from Paris, the first airline service ultrasound for travelers. The aircraft Almottaghtan has looked towards the west as if they were Tgaraan - even Tsabakan - the sun. Where they arrived as if they did not Taathrca, in terms of time, in a new event launches air transport stage supersonic passenger wealthy people who do not allow them to narrow their time to stay in the air for long periods. How the project began and evolved, and how the outcome of the remaining Concorde lounges to museums ... This is what Santapah in the following lines: The emergence of the Concorde The deal "supersonic" between England and France was signed in 1962, for the design and construction of the first civilian supersonic plane manufactured by Airbus for them. After long years of arduous efforts and research strenuous, in addition to more than 5,000 hours in the air tunnels, proved to be a form of equity Almstrq with the body long cylinder for aircraft relatively large passengers, it is the best form executable command and control speeds ultrasound. The first two aircraft of this type making and Tjeribhma in 1969, and since then about 20 aircraft of this model, called the "Concord" was produced (the only civilian aircraft that exceed the speed of sound speed), and who serve in the British Airways and Air France in income 1976, the rate of seven aircraft of the British lines and five lines in French. The first fly line is the London - Singapore via Bahrain. In 1976 received Bahrain Airport very important event, which is to start regular flights between Bahrain and London, the fastest of the British Airways sound Concorde, the airport first and the only one who was receiving this type of aircraft in the Middle East, given that the Concorde need to Airports women with special specifications, so they need to take-off and landing runways longer than the regular airports runways, and the noise from the power of their engines leads to smash windows of buildings ordinary airports, and the speed has a crush Madarjha. What Concorde is distinct from other aircraft?Characterized by Concorde slim form in the form of a triangle (delta). And fly faster and higher than other aircraft altitudes, using the "upward vortex" method to accomplish extraordinary mission. For example, while the "Boeing 747" aircraft speed, better known as "jumbo" around 900 km / h (about 84.0 Mach) at an altitude of 35 thousand feet, the Concorde fly quickly 2172 km / h (Mach 2) at an altitude of 60 thousand Foot. It is known that Almaj is the real rate of speed compared to the speed of sound, and is equivalent to an average of 1225 kilometers per hour, so that the speed of sound changes with temperature change, which moves rapidly 1190 km / h at sea level, but it drops to 1060 km / h at an altitude of 36,000 feet above the ground, where the air temperature drops. Because the Place de la Concorde to fly faster than the speed of sound, they differ from the rest of the aircraft on several characteristics. First, in terms of the flow of the fuselage, where you need to own dynamic shape to face severe air resistance at these high speeds, and it is achieved by taking the body form of a high pin tapered, triangular wings tilted back, my head and a tail, and an introduction brushes can be moved to the bottom of takeoffs and landings to be able to see the pilot of the corridor, to the top during flight to improve the flow of the fuselage. Amounting to 83 feet and 8 inches tall plane wings in the company "Oarossbesiak" has produced and supplied surfaces work together Kdvh depth, also works differentially Kjnahat. There is no tip installed inside the concavity of the wing, but no spire parties descend and spin at the same time. The second difference is related engines, where the Concorde's engines proved directly in the wings to avoid the use of any parts of the conductive would crash at high speeds, and the engine fitted with a special friendly hotel to exploit the resulting exhaust for initial combustion cycle combustion again mixing with more new fuel to increase efficient engines and power, where this process provides the engine in the final stage of heating fuel for the production of the required additional power for takeoff and the transition from one phase to the heating of supersonic flight, allowing aircraft takeoff speed of 360 km / h. The useful load carried by the Concorde's less than a third of what was done other than in the weight of the jets under the sound, so it was no reduction in the efficiency of the engine, it is actually the difference between profit and loss. Every Concorde has supplied four-engine aircraft, "Snecma Olympus DS 593," the momentum of 17259 kg. The company "Rolls Royce" design engines, which provided all Dagtin separate engine in order to fuel economy. Each engine and also provided additional Aq. Engine reverse payment system is also equipped. On the other hand, the Concorde is distinct from other aircraft fuel tanks and the presence of more and larger, with four engines burn a tremendous amount of kerosene has more than 25 thousand liters per flight hour. However, the fuel tanks lead a purpose whatever else, which is to maintain the equilibrium plane, where the center to raise the plane travels at high speeds for its center of gravity and then you move amounts of fuel between private additional tanks at the front of the plane and the rear to offset that effect, and returned those quantities at low speed in preparation for landing to bring the situation back to its origin. For example, a flight plan requires the distance between Paris and the French coast on the Atlantic equator at less than the speed of sound speed is determined to 0.93 Mach, to be at the height of about 9000 meters, after which the plane begins to jump quickly to reach the speed of take-off and altitude wanted, it performs speed between the two situations difference to a change in the dynamics of the plane to move from the airline less than the sound quickly to other higher speed of sound, and to overcome this situation, the transfer of fuel in an aircraft using a payment of reservoirs located in the introduction to the reservoirs in the system rear. During the transitional situation between the two modes of ex (between Mach 1 and Mach 1.6) increases air resistance sharply, and at this moment is to break the sound barrier. Once access to 1.7 Mach the captain to stop the internal combustion process, after more than a very plane speed of up to Mach 2, or 2200 km / h, more than twice the speed of sound, which represent the target aircraft speed, while the estimated target of 16000 and 18000 meters altitude. But when approaching landing, the fuel will move to the front of the plane, and the concomitant rise in the plane's nose, to land the plane in a scene it looks like a bird landing on the surface of the water. Finally remains the difference in the fuselage coating, where the Concorde is exposed at high speeds to a very large rise in body temperature as a result of increased friction of air molecules, so they coated special material properties and reflective stronger than those in the other aircraft, capable of dispersing such high temperatures . The fuselage itself is made from a special metal is characterized by a greater capacity to withstand the heat and stress resistance resulting from inflation fuselage resulting in turn from high temperature. The speed of the plane have been identified in the horizontal flight Mach 2.2, which is just before the thermal barrier (which is the speed at which if exceeded temperature increases dramatically), but it has identified the chronological age of the structure of 60,000 flight hours. And making the structure of the aluminum-alloy steel by thermal changes from -35 degrees to +120 degrees, as the flight above the speed limit of the plane requires that the structure is made with a mixture of steel and titanium, which means more weight. Fly the Concorde at the highest altitudes of 50,000 feet, where the air is equal to a tenth of what Tsawiyeh at sea density, and the temperature at that very low altitude, and despite all this work ultrasonic motors with high efficiency. According to reports of the pilots can handle the plane easily. The acceleration of the aircraft and transit speeds TransitionAnd what is characterized travel Balkounkord from other aircraft? Accommodate the Concorde for a hundred passengers and crew consists of a pilot and a flight engineer and his assistant in addition to the six hosts. When quitting, the passenger feels strongly pay back as a result of the launch aircraft from sleep to the speed of 362 km / h in just 30 seconds, which is called the Earth's gravitational force, and quickly reach the maximum height of the plane and penetrate the speed of the sound barrier. In all the flight times travelers can know the speed, through a private display panel installed in front of them, and are entitled to see the curve of the globe and Northern Lights because of the high altitude, which is flying the plane. Travelers can also watch the first layer colors of the atmosphere, where the height of the plane boundary between the first two Tbaktah. It takes Atlantic crossing Balkounkord three and a half hours only, while the that time about nine hours in the other underneath the aircraft sounds. And up the Concorde passengers who starts his journey from London at ten thirty in the morning to New York at nine thirty in the morning, before the date of its launch radios. This of course does not mean a retreat in time, but due to time differences and the short flight time! Over the last quarter-century, Concorde was the five weekly flights between Paris and New York in a record speed of less than 4 hours, at which time it cut the best of conventional aircraft, the same distance in 8 hours. He was landing at Kennedy Airport (according to US time) at eight in the morning, and exiting back to France at the eleventh hour before noon, where businessmen French used to negotiate with the Americans their customers at the airport Salons, without having to go to the business and financial district in Manhattan, and then return to Paris the same day. And to what the fate of the Concorde? I tried both the US and Soviet governments (former) develop similar Balkounkord aircraft, but those attempts ended in retreat, either because the magnitude of the required expenditures on the American side, or the occurrence of accidents due to human error on the Soviet side. Some of these Soviet aircraft had stayed (model "T U-144"), as amended to date, but used in air mail services, also placed some of them in museums, while one of them devoted to project Russian joint US. And remained the Concorde, solo travel of passengers faster than the speed of sound even temporarily suspended service to make adjustments after the accident led to an explosion killed one of them and all of them were. In addition, the high run that made the ticket price between Paris, London and New York round-trip $ 10,000, which led to limited use of the rich and famous costs, as well as what caused the noise and pollution, suffered Concorde most suffered from weak passenger demand for flights, in Following the incident, which came under the air France one in Paris in July 2000 to a near Charles de Gaulle airport hotels, which led to the deaths of 109 people on board and four people on the ground. Consequently After some major attended by experts and investigators, scientists, lawyers, artists, religious leaders and industrialists from different generations, between believers technology and Muslims in terms of authority to the modern age and among those who believe that it is necessary to rein in scientific progress and the development of ethical and legal controls him, took the final decision to stop flights Place de la Concorde. In July of 2003, tens of thousands of lovers of the Concorde gathered along the road to Heathrow Airport in the fog of London, the capital, in a bid farewell final before this model withdraw aircraft from service, after it made its first commercial flight in 1976. This has three Concorde planes reviewing the air before landing at Heathrow Airport in a reference to the termination of commercial flights known aircraft at supersonic speed. And charged the British Airways Concorde plane carrying 100 special guest at the final flight, which launched from Kennedy Airport in New York towards London, penetrated the sound barrier for the last time. Upon entering British airspace acceded Two Concord British Airways, one coming from the city of Edinburgh in Scotland, and the other from the Bay of Biscay west of France. Lovers plane Odalla in July of 2003 in Paris, as well as a pool, in the last trip out between Paris and New York, after a 27-year-old was cut where the distance between the two cities in a matter of three hours and a half. Where he lined up more than 250 workers from the maintenance workers bodyguards honor of the plane at Charles de Gaulle airport, with thousands of French gathered on the edge of the airport to see the plane taking off, holding a banner reading "We love you, Concord." The French lines: that the plane Concorde belong to the humanitarian aviation heritage and must therefore provide an opportunity for more people to see it, and added that it would apply to all of the fleet of Air France Concorde aircraft, which will be displayed every aircraft in museums in France, Germany and the United States, such as the Museum aviation and aerospace in the suburb of "Le Bourget" Paris, the Museum of Aviation near the Scottish capital "Edinburgh". Parts of the plane crashed as sold at Christie's for souvenirs to those who died to travel out, varied between the nose of the plane and the door of cabin leadership and a seat pilot and antenna radar warning in which the two motors of the engines and parts of the dashboard to the instructions and cutlery dishwasher ceramic spoons and silver booklet, worth total amounted to 3.29 million euros, went in favor of a charitable institution of the air France is working in the field of care for the poor children. Last auction for the sale of pieces of a British Airways Concorde has also been established. The British and French companies have announced at the beginning of the month of April of the same year 2003, he stopped Concorde flights after the company "Airbus" that produced externa announced: What's next in the field of transport ultrasonic? American company, "Boeing" is currently working on the supersonic jet, is supposed to be placed in service during the coming years, while filling the attention of European rival, "Airbus" accomplish its flagship aircraft, "Airbus A380 (superjumbo) capable of carrying about 800 passengers, which had been achieved in 2007, while scientists tried to Japanese to develop a model of the plane was enable fly twice as fast as the Concorde, but their experience after the plane landed long model briefly after take-off from the site "Woomera" to launch rockets in the desert south of Australia, and it failed within the project included my company, "Mitsubishi heavy Industries" and "Nissan Motor." He held this paradigm of a length of 11 meters on a rocket, Plans for him to be separated from the booster rocket above the ground, and falling faster than twice the speed of sound, but it got out of control since it was launched. It was supposed to reach the aircraft remotely piloted altitude of 20 thousand meters, before Taud.aly ground faster than twice the speed of sound. The goal was to become a plane "NeXT 1" transport aircraft the fastest in the world to succeed Concorde, with the difference that it will be less noise and damaging to the environment and can accommodate up to 300 passengers: Thus crossed another Concorde SST recent trip mounted aboard a ship in the River Thames sailing from London to the Museum of Flight in Edinburgh, after he has made more than eight thousand flight during which 22 thousand and 768 hours and 56 cut-minute flight, the folded thereby separating mythic unique and important commercial aviation history, a supersonic flight, waiting for what the future holds for us of new inventions ?!
malikfahad / Particle FilterParticle filters or Sequential Monte Carlo (SMC) methods are a set of genetic, Monte Carlo algorithms used to solve filtering problems arising in signal processing and Bayesian statistical inference. The filtering problem consists of estimating the internal states in dynamical systems when partial observations are made, and random perturbations are present in the sensors as well as in the dynamical system. The objective is to compute the posterior distributions of the states of some Markov process, given some noisy and partial observations. Particle filters implement the prediction-updating transitions of the filtering equation directly by using a genetic type mutation-selection particle algorithm. The samples from the distribution are represented by a set of particles; each particle has a likelihood weight assigned to it that represents the probability of that particle being sampled from the probability density function.
Sid-darthvader / Machine Learning For Thermoelectrics DiscoveryTransition metal oxides are attractive materials for high temperature thermoelectric applications due to their thermal stability, low cost bulk processing and natural abundance. Notwithstanding the high power factor, their high thermal conductivity is a roadblock in achieving higher efficiency. The search space for new thermoelectric oxides has been limited to the alloys of a few previously explored systems, such as ZnO, SrTiO3 and CaMnO3. The phenomenon of thermal conduction in crystalline alloys and its dependence on crystal properties is also poorly understood, which limits the ability to design new alloys. In this paper, we apply machine-learning models for discovering novel transition metal oxides with low lattice thermal conductivity (kL). A two-step process is proposed to address the problem of small datasets frequently encountered in materials informatics. First, a gradient boosted tree classifier is learnt to categorize unknown compounds into three categories of thermal conductivity: Low, Medium, and High. In the second step, we fit regression models on the targeted class (i.e. low kL) to estimate kL with an R2 value of 0.96. Gradient boosted tree model was also used to identify key material properties influencing classification of kL, namely lattice energy per atom, atom density, electronic energy band gap, mass density, and ratio of oxygen by transition metal atoms. Only fundamental materials properties describing the crystal symmetry, compound chemistry and interatomic bonding were used in the classification process, which can be readily used as selection parameters. The proposed two-step process addresses the problem of small datasets and improves the predictive accuracy.
Tarnvedra / Warehouse LayoutWeb Application development written in PHP/Laravel (in transition from (Origin - PHP/HTML5)) for efficient product selection, using web app for efficient placement of stock using layout planning and with volumetrics (calculations using Mass , Volume and Density)
ImInsulator / Implementation Of The Wang Landau AlgorithmThe Wang-Landau algorithm based on the Monte Carlo method is proposed by Fugao Wang and David Landau [1] to calculate density of the states(DOS) efficiently. This method constructs the DOS through non-Markov random transitions, traversing all possible states. After reviewing Wang-Landau algorithm, the analysis of the results through the implementation in Python for 2D Ising model is shown in this short report.
juliankappler / PySTFPPython module for (symbolic) evaluation of the short-time Fokker-Planck propagator to arbitrary accuracy
ragnarstroberg / NutbarNUshellx Transitions from Binary ARrays - a tool to calculate one and two-body transition densities from the results of the nuclear shell model code NuShellX
