Wednesday, July 29, 2009

The United States Army is the branch of the United States armed forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military and is one of seven uniformed services. The modern Army has its roots in the Continental Army which was formed on 14 June 1775, before the establishment of the United States, to meet the demands of the American Revolutionary War. Congress created the United States Army on 14 June 1784 after the end of the war to replace the disbanded Continental Army. The Army considers itself to be descended from the Continental Army and thus dates its inception from the origins of that force.
The primary mission of the Army is to "provide necessary forces and capabilities ... in support of the National Security and Defense Strategies."Control and operation is administered by the Department of the Army, one of the three service departments of the Department of Defense. The civilian head is the Secretary of the Army and the highest ranking military officer in the department is the Chief of Staff, unless the Chairman of the Joint Chiefs of Staff or Vice Chairman of the Joint Chiefs of Staff are Army officers. The Regular Army reported a strength of 539,675 soldiers; the Army National Guard (ARNG) reported 360,351 and the United States Army Reserve (USAR) reported 197,024 putting the combined component strength total 1,097,050 soldiers (2008 Financial).

Origins
The Continental Army was created on 14 June 1775 by the Continental Congress as a unified army for the states to fight Great Britain, with George Washington appointed as its commander.The Army was initially led by men who had served in the British Army or colonial militias and who brought much of British military heritage with them. As the Revolutionary war progressed, French aid, resources, and military thinking influenced the new army, while Prussian assistance and instructors also had a strong influence.
George Washington made use of the Fabian strategy and used hit-and-run tactics, hitting where the enemy was weakest, to wear down the British forces and their Hessian mercenary allies. Washington led victories against the British at Trenton and Princeton, and then turned south. With a decisive victory at Yorktown, and the help of the French, the Spanish and the Dutch, the Continental Army prevailed against the British, and with the Treaty of Paris, the independence of the United States was acknowledged.
After the war, though, the Continental Army was quickly disbanded as part of the American distrust of standing armies, and irregular state militias became the new nation's sole ground army, with the exception of a regiment to guard the Western Frontier and one battery of artillery guarding West Point's arsenal. However, because of continuing conflict with Native Americans, it was soon realized that it was necessary to field a trained standing army. The first of these, the Legion of the United States, was established in 1791.
19th century
The War of 1812 (1812-1815), the second and last American war against the British, was less successful than the Revolution had been. An invasion of Canada failed, and U.S. troops were unable to stop the British from burning the new capital of Washington, D.C.. However, the Regular Army, under Generals Winfield Scott and Jacob Brown, proved they were professional and capable of defeating a British army in the Niagara campaign of 1814. Two weeks after a treaty was signed, though, Andrew Jackson defeated the British invasion of New Orleans. However this had little effect, as per the treaty both sides returned to the status quo.
Between 1815 and 1860, a spirit of Manifest Destiny struck the United States, and as settlers moved west the U.S. Army engaged in a long series of skirmishes and battles with Native Americans that the colonists uprooted. The U.S. Army also fought the short Mexican–American War, which was a victory for the United States and resulted in territory which became all or parts of the states of California, Nevada, Utah, Colorado, Arizona, Wyoming and New Mexico.
The Civil War (1861-1865) was the most costly war for the United States. After most states in the South seceded to form the Confederate States of America, CSA troops opened fire on the Union-held Fort Sumter in Charleston, South Carolina, starting the war. For the first two years Confederate forces solidly defeated the U.S. Army, but after the decisive battles of Gettysburg in the east and Vicksburg in the west, combined with superior industrial might and numbers, Union troops fought a brutal campaign through Confederate territory and the war ended with a Confederate surrender at Appomatox Courthouse in April 1865. Based on 1860 census figures, 8% of all white males aged 13 to 43 died in the war, including 6% in the North and an extraordinary 18% in the South.
Following the Civil War, the U.S. Army fought a long battle with Native Americans, who resisted U.S. expansion into the center of the continent. But by the 1890s the U.S. saw itself as a potential international player. U.S. victories in the Spanish-American War (1898) and the controversial and less well known Philippine-American War (1898-1913), as well as U.S. intervention in Latin America and the Boxer Rebellion, gained America more land.

20th century
The United States joined World War I (1914-1918) in 1917 on the side of Russia, Britain and France. U.S. troops were sent to the front and were involved in the push that finally broke through the German lines. With the armistice on 11 November 1918, the Army once again decreased its forces.
The U.S. joined World War II after the Japanese attack on Pearl Harbor on 7 December 1941. On the European front, U.S. Army troops formed a significant portion of the forces that captured North Africa and Sicily. On D-Day and in the subsequent liberation of Europe and defeat of Germany, millions of U.S. Army troops played a central role. In the Pacific, Army soldiers participated alongside U.S. Marines in the "island hopping" campaign that wrested the Pacific Islands from Japanese control. Following the Axis surrenders in May (Germany) and September (Japan) of 1945, Army troops were deployed to Japan and Germany to occupy the two defeated nations. Two years after World War II, the Army Air Forces separated from the Army to become the United States Air Force on 18 September 1947 after decades of attempting to separate. Also, in 1948 the Army was desegregated.
However, the end of World War II set the stage for the East-West confrontation known as the Cold War (late 1940s to late 1980s/early 1990s). With the outbreak of the Korean War, concerns over the defence of Western Europe rose. Two corps, V and VII, were reactivated under Seventh United States Army in 1950 and American strength in Europe rose from one division to four. Hundreds of thousands of U.S. troops remained stationed in West Germany, with others in Belgium, the Netherlands and the United Kingdom, until the 1990s in anticipation of a possible Soviet attack.
During the Cold War, American troops and their allies fought Communist forces in Korea and Vietnam (see Domino Theory). The Korean War began in 1950, when the Soviets walked out of a U. N. Security meeting, removing their possible veto. Under a United Nations umbrella, hundreds of thousands of U.S. troops fought to prevent the takeover of South Korea by North Korea, and later, to invade the northern nation. After repeated advances and retreats by both sides, and the Peoples' Republic of China 's entry into the war, a cease-fire returned the peninsula to the status quo in 1953.
The Vietnam War is often regarded as a low point in the Army's record due to the use of drafted personnel, the unpopularity of the war with the American public, and frustrating restrictions placed on the Army by US political leaders (i.e. no invading communist held North Vietnam). While American forces had been stationed in the Republic of Vietnam since 1959, in intelligence & advising/training roles, they did not deploy in large numbers until 1965, after the Gulf of Tonkin Incident. American forces effectively established and maintained control of the "traditional" battlefield, however they struggled to counter the guerrilla hit and run tactics of the communist Viet Cong and the North Vietnamese Army. On a tactical level, American soldiers (and the US military as a whole) never lost a sizable battle.[citation needed] For instance in the Tet Offensive in 1968, the US Army turned a large scale attack by communist forces into a massive defeat of the Viet Cong on the battlefield (though at the time the offensive sapped the political will of the American public) which permanently weakened the guerrilla force; thereafter, most large scale engagements were fought with the regular North Vietnamese Army. In 1973 domestic political opposition to the war finally forced a US withdrawal. In 1975, Vietnam was unified under a communist government.
The Total Force Policy was adopted by Chief of Staff of the Army General Creighton Abrams in the aftermath of the Vietnam War and involves treating the three components of the Army - the Regular Army, the Army National Guard and the Army Reserve as a single force. Believing that no US president should be able to take the United States (and more specifically the US Army) to war without the support of the American people, General Abrams intertwined the structure of the three components of the Army in such a way as to make extended operations impossible, without the involvement of both the Army National Guard and the Army Reserve.
The 1980s was mostly a decade of reorganization. The Army converted to an all-volunteer force with greater emphasis on training and technology. The Goldwater-Nichols Act of 1986 created Unified Combatant Commands bringing the Army together with the other four armed forces under unified, geographically organized command structures. The Army also played a role in the invasions of Grenada in 1983 (Operation Urgent Fury) and Panama in 1989 (Operation Just Cause).
By 1991 Germany was reunited and the Soviet Union was near collapse. The Cold War was, effectively, over. In 1990 Iraq invaded its smaller neighbor, Kuwait. In January 1991 Operation Desert Storm commenced, a U.S.-led coalition which deployed over 500,000 troops, the bulk of them from U.S. Army formations, to drive out Iraqi forces. The campaign ended in total victory for the Army, as Western coalition forces routed an Iraqi Army organized along Soviet lines in just one hundred hours.
After Desert Storm, the Army did not see major combat operations for the remainder of the 1990s. Army units did participate in a number of peacekeeping activities, such as the UN peacekeeping mission in Somalia in 1993, where the abortive Operation Gothic Serpent led to the deaths of eighteen American soldiers and the withdrawal of international forces. The Army also contributed troops to a NATO peacekeeping force in the former Yugoslavia in the middle of the decade.

21st century
After the September 11 attacks, and as part of the Global War on Terror, U.S. and NATO combined arms (i.e. Army, Navy, Air Force, Marine, Special Operations) forces invaded Afghanistan in 2001, replacing the Taliban government.
The Army took part in the combined U.S. and allied invasion of Iraq in 2003. In the following years the mission changed from conflict between regular militaries to counterinsurgency, with large numbers of suicide attacks resulting in the deaths of more than 4,000 U.S. servicemen (as of March 2008) and injuries to thousands more.[7] The lack of stability in the theater of operations has led to longer deployments for Regular Army as well as Reserve and Guard troops.

Thursday, July 9, 2009

Google search is a web search engine owned by Google Inc. and is the most-used search engine on the Web . Google receives several hundred million queries each day through its various services. Google search was originally developed by Larry Page and Sergey Brin in 1997.
Beyond the original word-search capability, Google Search provides more than 22 special features, such as: synonyms; weather forecasts; time zones; stock quotes; maps; earthquake data; movie showtimes; airports; home listings; sports scores, etc. There are special features for numbers: prices; temperatures; money/unit conversions ("10.5 cm in inches"); calculations ( 3*4+sqrt(6)-pi/2 ); package tracking; patents; area codes; plus rudimentary language translation of displayed pages.
A Google search-results page is ordered by a priority rank called "PageRank" which is kept secret to avoid spammers from forcing their pages to the top. Google Search provides many options for customized search (see below: Search options), such as: exclusion ("-xx"), inclusion ("+xx"), alternatives ("xx OR yy"), and wildcard matching ("*").

The search engine

PageRank

Google's algorithm uses a patented system called PageRank to help rank web pages that match a given search string.The PageRank algorithm computes a recursive score for web pages, based on the weighted sum of the PageRanks of the pages linking to them. The PageRank derives from human-generated links, and is thought to correlate well with human concepts of importance. The exact percentage of the total of web pages that Google indexes is not known, as it is very hard to actually calculate. Previous keyword-based methods of ranking search results, used by many search engines that were once more popular than Google, would rank pages by how often the search terms occurred in the page, or how strongly associated the search terms were within each resulting page. In addition to PageRank, Google also uses other secret criteria for determining the ranking of pages on result lists, reported to be a number over 200.

Search results
Google not only indexes and caches web pages but also takes "snapshots" of other file types, which include PDF, Word documents, Excel spreadsheets, Flash SWF, plain text files, online videos such as YouTube and much more. Except in the case of text and SWF files, the cached version is a conversion to (X)HTML, allowing those without the corresponding viewer application to read the file.
Users can customize the search engine, by setting a default language, using the "SafeSearch" filtering technology and set the number of results shown on each page. Google has been criticized for placing long-term cookies on users' machines to store these preferences, a tactic which also enables them to track a user's search terms and retain the data for more than a year. For any query, up to the first 1000 results can be shown with a maximum of 100 displayed per page.

Non-indexable data
Despite its immense index, there is also a considerable amount of data available in online databases which are accessible by means of queries but not by links. This so-called invisible or deep Web is minimally covered by Google and other search engines. The deep Web contains library catalogs, official legislative documents of governments, phone books, and other content which is dynamically prepared to respond to a query.

Google optimization

Since Google is the most popular search engine, many webmasters have become eager to influence their website's Google rankings. An industry of consultants has arisen to help websites increase their rankings on Google and on other search engines. This field, called search engine optimization, attempts to discern patterns in search engine listings, and then develop a methodology for improving rankings to draw more searchers to their client's sites.
Search engine optimization encompasses both "on page" factors (like body copy, title elements, H1 heading elements and image alt attribute values) and Off Page Optimization factors (like anchor text and PageRank). The general idea is to affect Google's relevance algorithm by incorporating the keywords being targeted in various places "on page", in particular the title element and the body copy (note: the higher up in the page, presumably the better its keyword prominence and thus the ranking). Too many occurrences of the keyword, however, cause the page to look suspect to Google's spam checking algorithms.
Google has published guidelines for website owners who would like to raise their rankings when using legitimate optimization consultants.


Functionality

The Google search engine has many intuitive features making it more functional. This could have played a role in making it as popular as it is today. Google is one of the top ten most-visited websites today.Some of its features include a definition link for most searches including dictionary words, a list of how many results you got on your search, links to other searches (e.g. you misspelled something, it gives you a link to the search results had you typed in the correct search), and many more. It is unknown whether functionality, speed, or luck brought it its peak status.

Search syntax
Google's search engine normally accepts queries as a simple text, and breaks up the user's text into a sequence of search terms, which will usually be words that are to occur in the results, but may also be phrases, delimited by quotations marks ("), qualified terms, with a prefix such as "+", "-", or one of several advanced operators, such as "site:". The webpages of "Google Search Basics" describe each of these additional queries and options.
Google's Advanced Search web form gives several additional fields which may be used to qualify searches by such criteria as date of first retrieval. All advanced queries transform to regular queries, usually with additional qualified terms.

Query expansion
Google applies query expansion to the submitted search query, transforming it into the query that will actually be used to retrieve results. As with page ranking, the exact details of the algorithm Google uses are deliberately obscure, but certainly the following transformations are among those that occur:
Term reordering: in information retrieval this is a standard technique to reduce the work involved in retrieving results. This transformation is invisible to the user, since the results ordering uses the original query order to determine relevance.
Stemming is used to increase search quality by keeping small syntactic variants of search terms
There is a limited facility to fix possible misspellings in queries.

"I'm Feeling Lucky"
Google's homepage includes a button labeled "I'm Feeling Lucky". When a user clicks on the button the user will be taken directly to the first search result, bypassing the search engine results page. The thought is that, if a user is "feeling lucky", the search engine will return the perfect match the first time without having to page through the search results.
According to a study by Tom Chavez of "Rapt", this feature costs Google $110 million a year as 1% of all searches use this feature and bypass all advertising.



Rich Snippets
On 12 May 2009, Google announced that they would be parsing the hCard, hReview and hProduct microformats, and using them to populate search result pages with what they called "Rich Snippets".

Special features
Besides the main search-engine feature of searching for text, Google Search has more than 22 "special features" (activated by entering any of dozens of trigger words) when searching:
synonym search - A search can match words similar to those specified, by placing the tilde sign (~) immediately in front of a search term, such as: ~fast food.
weather - The weather humidity, temperature and forecast, for many cities, can be viewed by typing "weather" followed by the city and state, U.S. zip code, or city and country (such as: weather Lawrence, Kansas; weather Paris; weather Bremen, Germany).
stock quotes - The market data[6] for a specific company or fund can be viewed, by typing the ticker symbol (or include "stock"), such as: CSCO; MSFT; IBM stock; F stock (lists Ford Motor Co.); or AIVSX (fund). Results show inter-day changes, or 5-year graph, etc.
time zone - The current time in many cities (worldwide), can be viewed by typing "time" and the name of the city (such as: time Cairo; time Pratt, KS).
sports scores - The scores and schedules, for sports teams,can be displayed by typing the team name or league name into the search box.
calculator - Calculation results can be determined,as calculated live, by entering a formula in numbers or words, such as: 6*77 +pi +sqrt(e^3)/888 plus 0.45. The user is given the option to search for the formula, after calculation.
unit conversion - Measurements can be converted, by entering each phrase, such as: 10.5 cm in inches; or 90 km in miles
currency conversion - A money or currency converter can be selected, by typing the names or currency codes (listed by ISO 4217): 6789 Euro in USD; 150 GBP in USD; 5000 Yen in USD; 5000 Yuan in lira (the U.S. dollar can be USD or "US$" or "$", while Canadian is CAD, etc.).
dictionary lookup - A definition for a word or phrase can be found, by entering "define" plus the word(s) to lookup (such as: Define philosophy)
maps - Some related maps can be displayed, by typing in the name or U.S. ZIP code of a location and the word "map" (such as: New York map; Kansas map; or Paris map).
movie showtimes - Reviews or film showtimes can be listed for any movies playing nearby, by typing "movies" or the name of any current film into the search box. If a specific location was saved on a previous search, the top search result will display showtimes for nearby theaters for that movie.
public data - Trends for population (or unemployment rates) can be found for U.S. states & counties, by typing "population" or "unemployment rate" followed by a state or county name.
real estate and housing - Home listings in a given area can be displayed, using the trigger words "housing", "home", or "real estate" followed by the name of a city or U.S. zip code.
travel data/airports - The flight status for arriving or departing U.S. flights can be displayed,by typing in the name of the airline and the flight number into the search box (such as: american airlines 18). Delays at a specific airport can also be viewed (by typing the name of the city or three-letter airport code plus word "airport").
package tracking - Package mail can be tracked by typing the tracking number of a UPS, Fedex or USPS package directly into the search box. Results will include quick links to track the status of each shipment.
patent numbers - U.S. patents can be searched by entering the word "patent" followed by the patent number into the search box (such as: Patent 5123123).
area code - The geographical location (for any U.S. telephone area code) can be displayed by typing a 3-digit area code (such as: 650).
U.S. Government search - Searching of U.S. government websites can be performed from webpage: www.google.com/ig/usgov.

Saturday, July 4, 2009

The term digital signal is used to refer to more than one concept. It can refer to discrete-time signals that have a discrete number of levels, for example a sampled and quantified analog signal, or to the continuous-time waveform signals in a digital system, representing a bit-stream. In the first case, a signal that is generated by means of a digital modulation method is considered as converted to an analog signal, while it is considered as a digital signal in the second case.

An analog signal is a datum that changes over time—say, the temperature at a given location; the depth of a certain point in a pond; or the amplitude of the voltage at some node in a circuit—that can be represented as a mathematical function, with time as the free variable (abscissa) and the signal itself as the dependent variable (ordinate). A discrete-time signal is a sampled version of an analog signal: the value of the datum is noted at fixed intervals (for example, every microsecond) rather than continuously.
If individual time values of the discrete-time signal, instead of being measured precisely (which would require an infinite number of digits), are approximated to a certain precision—which, therefore, only requires a specific number of digits—then the resultant data stream is termed a digital signal. The process of approximating the precise value within a fixed number of digits, or bits, is called quantization.
In conceptual summary, a digital signal is a quantized discrete-time signal; a discrete-time signal is a sampled analog signal.
In the Digital Revolution, the usage of digital signals has increased significantly. Many modern media devices, especially the ones that connect with computers use digital signals to represent signals that were traditionally represented as continuous-time signals; cell phones, music and video players, personal video recorders, and digital cameras are examples.
In most applications, digital signals are represented as binary numbers, so their precision of quantization is measured in bits. Suppose, for example, that we wish to measure a signal to two significant decimal digits. Since seven bits, or binary digits, can record 128 discrete values (viz., from 0 to 127), those seven bits are more than sufficient to express a range of one hundred values.

Waveforms in digital systems

In computer architecture and other digital systems, a waveform that switches between two voltage levels representing the two states of a Boolean value (0 and 1) is referred to as a digital signal, even though it is an analog voltage waveform, since it is interpreted in terms of only two levels.
The clock signal is a special digital signal that is used to synchronize digital circuits. The image shown can be considered the waveform of a clock signal. Logic changes are triggered either by the rising edge or the falling edge.
The given diagram is an example of the practical pulse and therefore we have introduced two new terms that are:
Rising edge: the transition from a low voltage (level 1 in the diagram) to a high voltage (level 2).
Falling edge: the transition from a high voltage to a low one.
Although in a highly simplified and idealised model of a digital circuit we may wish for these transitions to occur instantaneously, no real world circuit is purely resistive and therefore no circuit can instantly change voltage levels. This means that during a short, finite transition time the output may not properly reflect the input, and indeed may not correspond to either a logically high or low voltage.

Logic voltage levels

The two states of a wire are usually represented by some measurement of an electrical property: Voltage is the most common, but current is used in some logic families. A threshold is designed for each logic family. When below that threshold, the wire is "low," when above "high." Digital circuits establish a "no man's area" or "exclusion zone" that is wider than the tolerances of the components. The circuits avoid that area, in order to avoid indeterminate results.
It is usual to allow some tolerance in the voltage levels used; for example, 0 to 2 volts might represent logic 0, and 3 to 5 volts logic 1. A voltage of 2 to 3 volts would be invalid, and occur only in a fault condition or during a logic level transition. However, few logic circuits can detect such a condition and most devices will interpret the signal simply as high or low in an undefined or device-specific manner. Some logic devices incorporate schmitt trigger inputs whose behaviour is much better defined in the threshold region, and have increased resilience to small variations in the input voltage.
The levels represent the binary integers or logic levels of 0 and 1. In active-high logic, "low" represents binary 0 and "high" represents binary 1. Active-low logic uses the reverse representation.