Leland Stanford Junior University is a private research university in Stanford, California. Stanford is known for its academic strength, proximity to Silicon Valley, ranking as one of the world's top universities; the university was founded in 1885 by Leland and Jane Stanford in memory of their only child, Leland Stanford Jr. who had died of typhoid fever at age 15 the previous year. Stanford was a U. S. Senator and former Governor of California who made his fortune as a railroad tycoon; the school admitted its first students on October 1, 1891, as a coeducational and non-denominational institution. Stanford University struggled financially after the death of Leland Stanford in 1893 and again after much of the campus was damaged by the 1906 San Francisco earthquake. Following World War II, Provost Frederick Terman supported faculty and graduates' entrepreneurialism to build self-sufficient local industry in what would be known as Silicon Valley; the university is one of the top fundraising institutions in the country, becoming the first school to raise more than a billion dollars in a year.
The university is organized around three traditional schools consisting of 40 academic departments at the undergraduate and graduate level and four professional schools that focus on graduate programs in Law, Medicine and Business. Stanford's undergraduate program is the most selective in the United States by acceptance rate. Students compete in 36 varsity sports, the university is one of two private institutions in the Division I FBS Pac-12 Conference, it has gained the most for a university. Stanford athletes have won 512 individual championships, Stanford has won the NACDA Directors' Cup for 24 consecutive years, beginning in 1994–1995. In addition, Stanford students and alumni have won 270 Olympic medals including 139 gold medals; as of October 2018, 83 Nobel laureates, 27 Turing Award laureates, 8 Fields Medalists have been affiliated with Stanford as students, faculty or staff. In addition, Stanford University is noted for its entrepreneurship and is one of the most successful universities in attracting funding for start-ups.
Stanford alumni have founded a large number of companies, which combined produce more than $2.7 trillion in annual revenue and have created 5.4 million jobs as of 2011 equivalent to the 10th largest economy in the world. Stanford is the alma mater of 30 living billionaires and 17 astronauts, is one of the leading producers of members of the United States Congress. Stanford University was founded in 1885 by Leland and Jane Stanford, dedicated to Leland Stanford Jr, their only child; the institution opened in 1891 on Stanford's previous Palo Alto farm. Despite being impacted by earthquakes in both 1906 and 1989, the campus was rebuilt each time. In 1919, The Hoover Institution on War and Peace was started by Herbert Hoover to preserve artifacts related to World War I; the Stanford Medical Center, completed in 1959, is a teaching hospital with over 800 beds. The SLAC National Accelerator Laboratory, established in 1962, performs research in particle physics. Jane and Leland Stanford modeled their university after the great eastern universities, most Cornell University and Harvard University.
Stanford opened being called the "Cornell of the West" in 1891 due to faculty being former Cornell affiliates including its first president, David Starr Jordan. Both Cornell and Stanford were among the first to have higher education be accessible and open to women as well as to men. Cornell is credited as one of the first American universities to adopt this radical departure from traditional education, Stanford became an early adopter as well. Most of Stanford University is on one of the largest in the United States, it is located on the San Francisco Peninsula, in the northwest part of the Santa Clara Valley 37 miles southeast of San Francisco and 20 miles northwest of San Jose. In 2008, 60% of this land remained undeveloped. Stanford's main campus includes a census-designated place within unincorporated Santa Clara County, although some of the university land is within the city limits of Palo Alto; the campus includes much land in unincorporated San Mateo County, as well as in the city limits of Menlo Park and Portola Valley.
The academic central campus is adjacent to Palo Alto, bounded by El Camino Real, Stanford Avenue, Junipero Serra Boulevard, Sand Hill Road. The United States Postal Service has assigned it two ZIP Codes: 94305 for campus mail and 94309 for P. O. box mail. It lies within area code 650. Stanford operates or intends to operate in various locations outside of its central campus. On the founding grant: Jasper Ridge Biological Preserve is a 1,200-acre natural reserve south of the central campus owned by the university and used by wildlife biologists for research. SLAC National Accelerator Laboratory is a facility west of the central campus operated by the university for the Department of Energy, it contains the longest linear particle accelerator in the world, 2 miles on 426 acres of land. Golf course and a seasonal lake: The university has its own golf course and a seasonal lake, both home to the vulnerable California tiger salamander; as of 2012 Lake Laguni
Vida Whitmore Vida L. W. Hudson, was an American musical theatre actress and major benefactor of Columbia University. Vida L. Whitmore was from Petersburg, one of seven siblings born to Emmet Archer Whitmore and Martha Merrill Whitmore. Whitmore went to London in 1903 with the show Dolly Varden. On Broadway she appeared in the Girl, Miss Dolly Dollars, Up and Down Broadway, and The Balkan Princess. She co-founded Whitmore & Lyden Dressmaking Company, incorporated in New York in 1907; the company employed twenty dressmakers in its first year of operation. Vida Whitmore married twice, she married Mandeville de Marigny Hall in 1908. He was still married to his first wife at the time, was soon arrested for passing bad checks and other crimes. Hall pawned about $20,000 worth of Whitmore's jewelry; that marriage was annulled in 1912. She married Percy Kierstede Hudson, a stockbroker, after being named in his well-publicized 1928 divorce; the couple were living in Guatemala in 1959. She was widowed in 1962, she died in 1978, aged 95 years, in Palm Beach, Florida.
Together the Hudsons left twelve million dollars to Columbia University. There are several professorships at Columbia named for Vida L. W. Hudson. Vida Whitmore Hudson's gravesite in Georgia, on Find a Grave
In databases and transaction processing, two-phase locking is a concurrency control method that guarantees serializability. It is the name of the resulting set of database transaction schedules; the protocol utilizes locks, applied by a transaction to data, which may block other transactions from accessing the same data during the transaction's life. By the 2PL protocol, locks are applied and removed in two phases: Expanding phase: locks are acquired and no locks are released. Shrinking phase: locks are released and no locks are acquired. Two types of locks are utilized by the basic protocol: Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions. A lock is a system object associated with a shared resource such as a data item of an elementary type, a row in a database, or a page of memory. In a database, a lock on a database object may need to be acquired by a transaction before accessing the object.
Correct use of locks prevents undesired, incorrect or inconsistent operations on shared resources by other concurrent transactions. When a database object with an existing lock acquired by one transaction needs to be accessed by another transaction, the existing lock for the object and the type of the intended access are checked by the system. If the existing lock type does not allow this specific attempted concurrent access type, the transaction attempting access is blocked. In practice, a lock on an object does not directly block a transaction's operation upon the object, but rather blocks that transaction from acquiring another lock on the same object, needed to be held/owned by the transaction before performing this operation. Thus, with a locking mechanism, needed operation blocking is controlled by a proper lock blocking scheme, which indicates which lock type blocks which lock type. Two major types of locks are utilized: Write-lock is associated with a database object by a transaction before writing this object.
Read-lock is associated with a database object by a transaction before reading this object. The common interactions between these lock types are defined by blocking behavior as follows: An existing write-lock on a database object blocks an intended write upon the same object by another transaction by blocking a respective write-lock from being acquired by the other transaction; the second write-lock will be acquired and the requested write of the object will take place after the existing write-lock is released. A write-lock blocks an intended read by another transaction by blocking the respective read-lock. A read-lock blocks an intended write by another transaction by blocking the respective write-lock. A read-lock does not block an intended read by another transaction; the respective read-lock for the intended read is acquired after the intended read is requested, the intended read itself takes place. Several variations and refinements of these major lock types exist, with respective variations of blocking behavior.
If a first lock blocks another lock, the two locks are called incompatible. Lock types blocking interactions are presented in the technical literature by a Lock compatibility table; the following is an example with the common, major lock types: X indicates incompatibility, i.e, a case when a lock of the first type on an object blocks a lock of the second type from being acquired on the same object. An object has a queue of waiting requested operations with respective locks; the first blocked lock for operation in the queue is acquired as soon as the existing blocking lock is removed from the object, its respective operation is executed. If a lock for operation in the queue is not blocked by any existing lock, it is acquired immediately. Comment: In some publications, the table entries are marked "compatible" or "incompatible", or "yes" or "no". According to the two-phase locking protocol, a transaction handles its locks in two distinct, consecutive phases during the transaction's execution: Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired. The two phase locking rule can be summarized as: never acquire a lock after a lock has been released; the serializability property is guaranteed for a schedule with transactions. Without explicit knowledge in a transaction on end of phase-1, it is safely determined only when a transaction has completed processing and requested commit. In this case, all the locks can be released at once; the difference between 2PL and C2PL is that C2PL's transactions obtain all the locks they need before the transactions begin. This is to ensure that a transaction that holds some locks will not block waiting for other locks. Conservative 2PL prevents deadlocks. To comply with the S2PL protocol, a transaction needs to comply with 2PL, release its write locks only after it has ended, i.e. being either committed or aborted. On the other hand, read locks are released during phase 2; this protocol is not appropriate
Travelling salesman problem
The travelling salesman problem asks the following question: "Given a list of cities and the distances between each pair of cities, what is the shortest possible route that visits each city and returns to the origin city?" It is an NP-hard problem in combinatorial optimization, important in operations research and theoretical computer science. The travelling purchaser problem and the vehicle routing problem are both generalizations of TSP. In the theory of computational complexity, the decision version of the TSP belongs to the class of NP-complete problems. Thus, it is possible that the worst-case running time for any algorithm for the TSP increases superpolynomially with the number of cities; the problem was first formulated in 1930 and is one of the most intensively studied problems in optimization. It is used as a benchmark for many optimization methods. Though the problem is computationally difficult, a large number of heuristics and exact algorithms are known, so that some instances with tens of thousands of cities can be solved and problems with millions of cities can be approximated within a small fraction of 1%.
The TSP has several applications in its purest formulation, such as planning and the manufacture of microchips. Modified, it appears as a sub-problem in many areas, such as DNA sequencing. In these applications, the concept city represents, for example, soldering points, or DNA fragments, the concept distance represents travelling times or cost, or a similarity measure between DNA fragments; the TSP appears in astronomy, as astronomers observing many sources will want to minimize the time spent moving the telescope between the sources. In many applications, additional constraints such as limited resources or time windows may be imposed; the origins of the travelling salesman problem are unclear. A handbook for travelling salesmen from 1832 mentions the problem and includes example tours through Germany and Switzerland, but contains no mathematical treatment; the travelling salesman problem was mathematically formulated in the 1800s by the Irish mathematician W. R. Hamilton and by the British mathematician Thomas Kirkman.
Hamilton’s Icosian Game was a recreational puzzle based on finding a Hamiltonian cycle. The general form of the TSP appears to have been first studied by mathematicians during the 1930s in Vienna and at Harvard, notably by Karl Menger, who defines the problem, considers the obvious brute-force algorithm, observes the non-optimality of the nearest neighbour heuristic: We denote by messenger problem the task to find, for finitely many points whose pairwise distances are known, the shortest route connecting the points. Of course, this problem is solvable by finitely many trials. Rules which would push the number of trials below the number of permutations of the given points, are not known; the rule that one first should go from the starting point to the closest point to the point closest to this, etc. in general does not yield the shortest route. It was first considered mathematically in the 1930s by Merrill M. Flood, looking to solve a school bus routing problem. Hassler Whitney at Princeton University introduced the name travelling salesman problem soon after.
In the 1950s and 1960s, the problem became popular in scientific circles in Europe and the USA after the RAND Corporation in Santa Monica offered prizes for steps in solving the problem. Notable contributions were made by George Dantzig, Delbert Ray Fulkerson and Selmer M. Johnson from the RAND Corporation, who expressed the problem as an integer linear program and developed the cutting plane method for its solution, they wrote what is considered the seminal paper on the subject in which with these new methods they solved an instance with 49 cities to optimality by constructing a tour and proving that no other tour could be shorter. Dantzig and Johnson, speculated that given a near optimal solution we may be able to find optimality or prove optimality by adding a small number of extra inequalities, they used this idea to solve their initial 49 city problem using a string model. They found. While this paper did not give an algorithmic approach to TSP problems, the ideas that lay within it were indispensable to creating exact solution methods for the TSP, though it would take 15 years to find an algorithmic approach in creating these cuts.
As well as cutting plane methods, Dantzig and Johnson used branch and bound algorithms for the first time. In the following decades, the problem was studied by many researchers from mathematics, computer science, chemistry and other sciences. In the 1960s however a new approach was created, that instead of seeking optimal solutions, one would produce a solution whose length is provably bounded by a multiple of the optimal length, in doing so create lower bounds for the problem. One method of doing this was to create a minimum spanning tree of the graph and double all its edges, which produces the bound that the length of an optimal tour is at most twice the weight of a minimum spanning tree. Christofides made a big advance in this approach of giving an approach for which we know the worst-case scenario. Christofides algorithm given in 1976, at worst is 1.5 times longer than the optimal solution. As the algorithm was so simple and quick, many hoped it would give way to a near optimal solution method.
This remains the method with the best worst-case sc
Athens is the capital and largest city of Greece. Athens dominates the Attica region and is one of the world's oldest cities, with its recorded history spanning over 3,400 years and its earliest human presence starting somewhere between the 11th and 7th millennium BC. Classical Athens was a powerful city-state that emerged in conjunction with the seagoing development of the port of Piraeus, a distinct city prior to its 5th century BC incorporation with Athens. A center for the arts and philosophy, home of Plato's Academy and Aristotle's Lyceum, it is referred to as the cradle of Western civilization and the birthplace of democracy because of its cultural and political impact on the European continent, in particular the Romans. In modern times, Athens is a large cosmopolitan metropolis and central to economic, industrial, maritime and cultural life in Greece. In 2012, Athens was ranked the world's 39th richest city by purchasing power and the 67th most expensive in a UBS study. Athens is a global one of the biggest economic centres in southeastern Europe.
It has a large financial sector, its port Piraeus is both the largest passenger port in Europe, the second largest in the world. While at the same time being the sixth busiest passenger port in Europe; the Municipality of Athens had a population of 664,046 within its administrative limits, a land area of 38.96 km2. The urban area of Athens extends beyond its administrative municipal city limits, with a population of 3,090,508 over an area of 412 km2. According to Eurostat in 2011, the functional urban area of Athens was the 9th most populous FUA in the European Union, with a population of 3.8 million people. Athens is the southernmost capital on the European mainland; the heritage of the classical era is still evident in the city, represented by ancient monuments and works of art, the most famous of all being the Parthenon, considered a key landmark of early Western civilization. The city retains Roman and Byzantine monuments, as well as a smaller number of Ottoman monuments. Athens is home to two UNESCO World Heritage Sites, the Acropolis of Athens and the medieval Daphni Monastery.
Landmarks of the modern era, dating back to the establishment of Athens as the capital of the independent Greek state in 1834, include the Hellenic Parliament and the so-called "architectural trilogy of Athens", consisting of the National Library of Greece, the National and Kapodistrian University of Athens and the Academy of Athens. Athens is home to several museums and cultural institutions, such as the National Archeological Museum, featuring the world's largest collection of ancient Greek antiquities, the Acropolis Museum, the Museum of Cycladic Art, the Benaki Museum and the Byzantine and Christian Museum. Athens was the host city of the first modern-day Olympic Games in 1896, 108 years it welcomed home the 2004 Summer Olympics, making it one of only a handful of cities to have hosted the Olympics more than once. In Ancient Greek, the name of the city was Ἀθῆναι a plural. In earlier Greek, such as Homeric Greek, the name had been current in the singular form though, as Ἀθήνη, it was rendered in the plural on, like those of Θῆβαι and Μυκῆναι.
The root of the word is not of Greek or Indo-European origin, is a remnant of the Pre-Greek substrate of Attica. In antiquity, it was debated whether Athens took its name from its patron goddess Athena or Athena took her name from the city. Modern scholars now agree that the goddess takes her name from the city, because the ending -ene is common in names of locations, but rare for personal names. During the medieval period, the name of the city was rendered once again in the singular as Ἀθήνα. However, after the establishment of the modern Greek state, due to the conservatism of the written language, Ἀθῆναι became again the official name of the city and remained so until the abandonment of Katharevousa in the 1970s, when Ἀθήνα, Athína, became the official name. According to the ancient Athenian founding myth, the goddess of wisdom, competed against Poseidon, the god of the seas, for patronage of the yet-unnamed city. According to the account given by Pseudo-Apollodorus, Poseidon struck the ground with his trident and a salt water spring welled up.
In an alternative version of the myth from Vergil's Georgics, Poseidon instead gave the Athenians the first horse. In both versions, Athena offered the Athenians the first domesticated olive tree. Cecrops declared Athena the patron goddess of Athens. Different etymologies, now rejected, were proposed during the 19th century. Christian Lobeck proposed as the root of the name the word ἄθος or ἄνθος meaning "flower", to denote Athens as the "flowering city". Ludwig von Döderlein proposed the stem of the verb θάω, stem θη- to denote Athens as having fertile soil. In classical literature, the city was sometimes referred to as the City of the Violet Crown, first documented in Pindar's ἰοστέφανοι Ἀθᾶναι, or as τὸ κλεινὸν ἄστυ. In medieval texts, variant names include Setines and Astines, all derivations involving false splitting of p
The United States of America known as the United States or America, is a country composed of 50 states, a federal district, five major self-governing territories, various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U. S. is the third most populous country. The capital is Washington, D. C. and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico; the State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean; the U. S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The diverse geography and wildlife of the United States make it one of the world's 17 megadiverse countries.
Paleo-Indians migrated from Siberia to the North American mainland at least 12,000 years ago. European colonization began in the 16th century; the United States emerged from the thirteen British colonies established along the East Coast. Numerous disputes between Great Britain and the colonies following the French and Indian War led to the American Revolution, which began in 1775, the subsequent Declaration of Independence in 1776; the war ended in 1783 with the United States becoming the first country to gain independence from a European power. The current constitution was adopted in 1788, with the first ten amendments, collectively named the Bill of Rights, being ratified in 1791 to guarantee many fundamental civil liberties; the United States embarked on a vigorous expansion across North America throughout the 19th century, acquiring new territories, displacing Native American tribes, admitting new states until it spanned the continent by 1848. During the second half of the 19th century, the Civil War led to the abolition of slavery.
By the end of the century, the United States had extended into the Pacific Ocean, its economy, driven in large part by the Industrial Revolution, began to soar. The Spanish–American War and World War I confirmed the country's status as a global military power; the United States emerged from World War II as a global superpower, the first country to develop nuclear weapons, the only country to use them in warfare, a permanent member of the United Nations Security Council. Sweeping civil rights legislation, notably the Civil Rights Act of 1964, the Voting Rights Act of 1965 and the Fair Housing Act of 1968, outlawed discrimination based on race or color. During the Cold War, the United States and the Soviet Union competed in the Space Race, culminating with the 1969 U. S. Moon landing; the end of the Cold War and the collapse of the Soviet Union in 1991 left the United States as the world's sole superpower. The United States is the world's oldest surviving federation, it is a representative democracy.
The United States is a founding member of the United Nations, World Bank, International Monetary Fund, Organization of American States, other international organizations. The United States is a developed country, with the world's largest economy by nominal GDP and second-largest economy by PPP, accounting for a quarter of global GDP; the U. S. economy is post-industrial, characterized by the dominance of services and knowledge-based activities, although the manufacturing sector remains the second-largest in the world. The United States is the world's largest importer and the second largest exporter of goods, by value. Although its population is only 4.3% of the world total, the U. S. holds 31% of the total wealth in the world, the largest share of global wealth concentrated in a single country. Despite wide income and wealth disparities, the United States continues to rank high in measures of socioeconomic performance, including average wage, human development, per capita GDP, worker productivity.
The United States is the foremost military power in the world, making up a third of global military spending, is a leading political and scientific force internationally. In 1507, the German cartographer Martin Waldseemüller produced a world map on which he named the lands of the Western Hemisphere America in honor of the Italian explorer and cartographer Amerigo Vespucci; the first documentary evidence of the phrase "United States of America" is from a letter dated January 2, 1776, written by Stephen Moylan, Esq. to George Washington's aide-de-camp and Muster-Master General of the Continental Army, Lt. Col. Joseph Reed. Moylan expressed his wish to go "with full and ample powers from the United States of America to Spain" to seek assistance in the revolutionary war effort; the first known publication of the phrase "United States of America" was in an anonymous essay in The Virginia Gazette newspaper in Williamsburg, Virginia, on April 6, 1776. The second draft of the Articles of Confederation, prepared by John Dickinson and completed by June 17, 1776, at the latest, declared "The name of this Confederation shall be the'United States of America'".
The final version of the Articles sent to the states for ratification in late 1777 contains the sentence "The Stile of this Confederacy shall be'The United States of America'". In June 1776, Thomas Jefferson wrote the phrase "UNITED STATES OF AMERICA" in all capitalized letters in the headline of his "original Rough draught" of the Declaration of Independence; this draft of the document did not surface unti
Message sequence chart
A message sequence chart is an interaction diagram from the SDL family standardized by the International Telecommunication Union. The purpose of recommending MSC is to provide a trace language for the specification and description of the communication behaviour of system components and their environment by means of message interchange. Since in MSCs the communication behaviour is presented in a intuitive and transparent manner in the graphical representation, the MSC language is easy to learn and interpret. In connection with other languages it can be used to support methodologies for system specification, simulation and documentation; the first version of the MSC standard was released in March 12, 1993. The 1996 version added references and inlining expressions concepts, introduced HMSC, which are the way of expressing a sequence of MSCs; the MSC 2000 version added object orientation, refined the use of data and time in diagrams, added the concept of remote method calls. Latest version has been published in February 2011.
The existing symbols are: MSC head and end: a vertical line with a box at the top, a box or a cross at the bottom. Instance creation: horizontal dashed arrow to the newly created instance. Message exchange: horizontal arrow. Control flow: horizontal arrow with the'call' prefix, dashed arrow for reply symbol and suspension symbols in between. Timers: start, time out. Time interval: relative and absolute with a dashed vertical arrow. Conditions: used to represent a state of the underlying state machine. Action: a box. In-line expressions: alternative composition, sequential composition, optional region, parallel composition, iteration. Reference: reference to another MSC. Data concept: The user can use any data concept, if binding is undefined the default data concept is the one from SDL as defined in Z.121 recommendation. Coregion: a double dashed instance line to describe unordered events. SDL-RT has introduced: a semaphore instance representation. A save symbol to save messages. UML 2.0 Sequence Diagram is inspired by the ITU-T MSC.
Still, for historical reasons, the default basic principles are quite different: LifelinesIn an MSC, the vertical lines are autonomous execution entities. They represent state machines executing in parallel; the state machines need not be on the same computer. In a Sequence Diagram, a vertical line is an object; the object can be passive. ArrowsIn an MSC an arrow is an asynchronous message sent from one entity to another one. Once the message is sent the sending entity resumes its execution. In a Sequence Diagram an arrow is understood as an operation call on a class, it is therefore synchronous and the calling entity hangs until the operation returns. It has been said that MSC has been considered as a candidate for the interaction diagrams in UML. However, proponents of MSC such as Ericsson think that MSC is better than UML 2.0 for modelling large or complex systems. David Harel suggested that MSC had shortcomings such as: MSC propose a weak partial ordering semantics that makes it impossible to capture some behavioral requirements, The relationship between the MSC requirements and the executable specification is not clear,and proposed Live Sequence Charts as an extension on the MSC standard.
PSC Property Sequence Chart, a way to describe properties in an MSC or a Sequence Diagram. SDL Specification and Description Language, an MSC related ITU-T language. Interaction diagrams in UML. ITU-T Recommendation Z.120 message sequence chart