| Gear |
| | Mon Jul 21, 2008 13:58 |
| A gear is a wheel with teeth around its circumference, the purpose of the teeth being to mesh with similar teeth on another mechanical device possibly another gear wheel so that force can be transmitted between the two strategies in a direction tangential to their surfaces. A non-toothed wheel can transmit some tangential force but will slip if the force is large; teeth put off slippage and permit the transmission of large forces.
A gear can mesh with any device having teeth friendly with the gear's teeth. Such devices include racks and other non-rotating policy; however, the most common condition is for a gear to be in mesh with another gear. In this case revolution of one of the gears necessarily causes the other gear to rotate. In this way, rotational motion can be transferred from one position to another. While gears are sometimes used simply for this reason to transmit rotation to another shaft perhaps their most significant feature is that, if the gears are of asymmetrical sizes, a mechanical advantage is also achieved, so that the rotational speed, and torque, of the second gear are dissimilar from that of the first. In this way, gears provide a means of increasing or decreasing a turning speed, or a torque.
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| Sports |
| | Tue Jul 8, 2008 8:31 |
| Sport is an action to make possible is governed by a set of rules or customs and regularly engaged in competitively. Used by itself, sports usually refer to activities where the physical capabilities of the member are the sole or primary determiner of the outcome, but the term is also used to encompass activities such as mind sports and motor sports where psychological acuity or equipment quality are main factors. Sports are used as hobby for the player and the viewer. It has also proved by experiments that daily exercise would improve mental strength and power to study. Sports have been ever more organized and maintenance pace from the time of the Ancient Olympics up to the present century. Industrialization has brought enhanced leisure time to the citizens of developed and developing countries, leading to more time for people to be present at and follow spectator sports, greater contribution in athletic activities, and increased accessibility. These trends sustained with the beginning of mass media and global statement. |
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| Weather |
| | Wed Jun 18, 2008 8:56 |
| Weather most frequently results from temperature differences from one planet to another. On large scales, temperatures differences arise mainly as areas closer to Earth's equator get more energy per unit area from the Sun than do regions nearer to Earth's poles. On local scales, temperature differences can arise because different surfaces have opposed physical characteristics such as reflectivity, roughness, or moisture content. Surface temperature differences in roll cause pressure differences. A hot surface heats the air over it and the air expands, lowering the air pressure. The resulting parallel pressure rise accelerates the air from high to low pressure, creating wind, and Earth's rotation then causes curvature of the pour via the Coriolis Effect. The strong temperature contrast among polar and tropical air gives rise to the jet flow. Most weather systems in the mid-latitudes are caused by instabilities of the jet stream flow. Weather systems in the tropics are caused by different processes, such as monsoons shower systems. |
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| Weather and climate |
| | Thu May 29, 2008 15:20 |
The atmosphere of the Earth serves as a key factor in sustaining the planetary ecosystem. The thin layer of gases that envelops the Earth is held in place by the planet's gravity. Dry air consists of 78% nitrogen, 21% oxygen, 1% argon and other inert gases, carbon dioxide, etc.; but air also contains a variable amount of water vapor. The atmospheric pressure declines steadily with altitude, and has a scale height of about 8 kilometers at the Earth's surface: the height at which the atmospheric pressure has declined. The ozone layer of the Earth's atmosphere plays an important role in depleting the amount of ultraviolet (UV) radiation that reaches the surface. As DNA is readily damaged by UV light, this serves to protect life at the surface. The atmosphere also retains heat during the night, thereby reducing the daily temperature extremes.
Terrestrial weather occurs almost exclusively in the lower part of the atmosphere, and serves as a convective system for redistributing heat. Ocean currents are another important factor in determining climate, particularly the major underwater thermohaline circulation which distributes heat energy from the equatorial oceans to the Polar Regions. These currents help to moderate the differences in temperature between winter and summer in the temperate zones. Also, without the redistributions of heat energy by the ocean currents and atmosphere, the tropics would be much hotter, and the polar regions much colder. |
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| Historical perspective |
| | Thu May 29, 2008 15:18 |
Based on the available evidence, scientists have reconstructed detailed information about the planet's past. Earth is estimated to have formed approximately 4.55 billion years ago out of the solar nebula, along with the Sun and other planets. The moon formed relatively soon afterwards.
Initially molten, the outer layer of the planet cooled, resulting in the solid crust. Outgas sing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice delivered by comets, produced the oceans. The highly energetic chemistry is believed to have produced a self-replicating molecule around 4 billion years ago.
Continents formed, then broke up and re-formed as the surface of Earth reshaped itself over the course of hundreds of millions of years, occasionally combining to make a super continent. Roughly 750 million years ago, the earliest known super continent Rodinia, began to break apart. The continents later recombined to form Pannotia which broke apart about 540 million years ago, then finally Pangaea, which broke apart about 180 million years ago. |
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| Yoga |
| | Wed May 28, 2008 9:17 |
| Yoga is one of the six schools of Hindu philosophy, focusing on meditation as a trail to self-knowledge and freedom. Yoga is seen as a means to mutually physiological and spiritual mastery. Outside India, Yoga has become mainly related with the practice of asanas of Hatha Yoga, although it has influenced the whole dharmic religions family and other spiritual practices throughout the world. 5,000 year old carvings from the Indus Valley Civilization represent a figure that archaeologists think represents a yogi sitting in meditation posture. The sitting in a conventional cross-legged yoga pose with its hands resting on its knees. The explorer of the seal, archaeologist Sir John Marshall, named the figure Shiva Pashupati.
A seal from the Indus Valley Civilization, The first known written reference to yoga is in the Rig Veda, likely by the western scholars to be at least 3,500 years old. The Upanishads, Bhagavad-Gita, and the Yoga Sutras of Patanjali also converse the concepts and teachings of yoga. |
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| Pollution |
| | Mon May 19, 2008 5:44 |
| Pollution is the overture of contaminants into an surroundings, of whatsoever prearranged or decided upon proportions or enclose of reference; these contaminants grounds insecurity, confusion, destruction or uneasiness to the physical systems or living organisms therein. Pollution can get the structure of chemical substances, or power, such as sound, temperature, or light energy. Pollutants, the essentials of pollution, can be distant substances or energies, or naturally happening; while naturally happening, they are considered contaminants at what time they go over normal levels. Pollution is frequently classed as point basis or nonpoint source pollution. |
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| Birds |
| | Tue May 13, 2008 17:19 |
Many species of bird undertake long distance annual migrations, and many more perform shorter irregular movements. Birds are social and communicate using visual signals and through calls and song, and participate in social behaviors including cooperative hunting, cooperative breeding, flocking and mobbing of predators. Birds are primarily socially monogamous, with engagement in extra-pair copulations being common in some species-other species have polygamous or polyandrous breeding systems. Eggs are regularly laid in a nest and incubated and most birds have an extended period of parental care after hatching.
Birds are economically important to humans: many are important sources of food, acquired either through hunting or farming, and they provide other products. Some species, particularly songbirds and parrots, are popular as pets. Birds figure prominently in all aspects of human culture from religion to poetry and popular music. About 120-130 species have become extinct as a result of human activity since 1600, and hundreds more before this. Currently around 1,200 species of birds are threatened with extinction by human activities and efforts are underway to protect them |
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| Arts&Crafts |
| | Thu Feb 28, 2008 7:18 |
| The Arts and Crafts progress began mainly as a search for real and meaningful styles for the 19th century and as a response to the miscellaneous revival of famous styles of the Victorian era and to "inexpressive" machine-made manufacture aided by the Industrial Revolution. Considering the instrument to be the source cause of all repetitive and ordinary evils, some of the protagonists of this association turned completely away from the use of technology and towards handcraft, which tended to focus their productions in the hands of receptive but comfortable consumers. Yet, while the Arts and Crafts movement was in great part a effect to industrialization, if looked at on the entire, it was neither anti-modern. Some of the European factions thought that machines were in fact required, but they should only be used to reduce the tediousness of routine, repetitive tasks. At the same time, some Arts and Crafts leaders felt that things should also be reasonable. The difference between quality production and 'demo' design, and the effort to settle the two, subject design debate at the turn of the twentieth century.
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| Transportation |
| | Thu Dec 27, 2007 4:52 |
| Transportation is the movement of people and goods from one place to another. The term is derived from the portare ("to carry") and Latin trans ("across") . Industries which have the business of providing equipment, actual transport, transport of people or goods and services used in transport of goods or people make up a huge broad and important segment of most national economies, and are collectively referred to as transport industries. The field of transport has several aspects: loosely they can be divided into a triad of infrastructure, vehicles, and operations. Infrastructure includes the transport networks (roads, railways, airways, waterways, canals, pipelines, etc.) that are used, as well as the nodes or terminals (such as airports, railway stations, bus stations and seaports). The vehicles generally traverse on the networks, such as automobiles, bicycles, buses, trains, aircrafts.
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| Forest |
| | Fri Dec 14, 2007 5:32 |
| A forest is an area with a high bulk of trees. There are several definitions of a forest, based on a variety of criteria. These plant communities face large areas of the globe and function as animal habitats, and soil conservers, constituting one of the most important aspects of the Earth's biosphere. While frequently thought of as carbon dioxide sinks, grown-up forests are approximately carbon neutral with only troubled and young forests acting as carbon sinks. However mature forests do play a main role in the global carbon cycle as stable carbon pools, and authorization of forests leads to an increase of impressive carbon dioxide levels. Forests sometimes have many tree species within a small area or comparatively few species over large areas. Forests are frequently home to many animal and plant species, and biomass per unit area is high compared to other plants communities. Much of this biomass occurs below-ground in the origin systems and as partly decomposed plant accumulation. The woody element of a forest contains lignin, which is comparatively slow to decompose compared with other organic materials such as cellulose or carbohydrate.
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| Music |
| | Fri Nov 30, 2007 4:20 |
Music
Music is an art form consisting of sound and silence expressed through time. Elements of sound as used in music are pitch (including melody and harmony), rhythm (including tempo and meter), and sonic qualities of timbre, articulation, dynamics, and texture.
The creation, performance, significance and even the definition of music, varies according to culture and social context. Music ranges from strictly organized compositions and performances to improvisational or aleatoric forms. For purposes of discussion and exploration of the topic, music is divided into genres and sub-genres, although the dividing lines and relationships between music genres are often unclear and/or controversial. Within "the arts", music can be classified as a performing art, a fine art, or an auditory art form.
Music may also involve generative forms in time through the construction of patterns and combinations of natural stimuli, principally sound. Music may be used for artistic or aesthetic, communicative, entertainment, ceremonial or religious purposes and by many composers purely as an academic instrument for study.
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| Hardware |
| | Wed Nov 28, 2007 3:27 |
Hardware is a general term that refers to the physical artifacts of a technology. It may also mean the physical components of a computer system.
Hardware historically meant the metal parts and fittings that were used to make wooden products stronger, more functional, longer lasting and easier to fabricate or assemble. In modern usage it includes equipment such as keys, locks, hinges, latches, corners, handles, wire, chains, plumbing supplies, tools, utensils, cutlery and machine parts, especially when they are made of metal. In the United States, this type of hardware has been traditionally sold in hardware stores, a term also used to a lesser extent in the UK.
In the electronics and especially computer industries, computer hardware specifically means the physical or tangible parts of the equipment, such as circuit boards, keyboards, monitors etc., in contrast to non-physical software running on the computer or other device.
In a more colloquial sense, hardware can refer to major items of military equipment, such as tanks, aircraft or ships.
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| Science |
| | Sat Nov 24, 2007 2:29 |
Science refers to any systematic knowledge or practice. In a more restricted sense, science refers to a system of acquiring knowledge based on the scientific method, as well as to the organized body of knowledge gained through such research. This article focuses on the more restricted use of the word.
Fields of science are commonly classified along two major lines:
• Natural sciences, which study natural phenomena (including biological life), and
• Social sciences, which study human behavior and societies.
These groupings are empirical sciences, which mean the knowledge must be based on observable phenomena and capable of being experimented for its validity by other researchers working under the same conditions.
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| Communication |
| | Wed Nov 21, 2007 3:17 |
Communication is a process that allows organisms to exchange information by several methods. Communication requires that all parties understand a common language that is exchanged. There are auditory means, such as speaking or singing, and nonverbal, physical means, such as body language, sign language, paralanguage, touch, eye contact, or the use of writing.
Communication happens at many levels (even for one single action), in many different ways, and for most beings, as well as certain machines. Several, if not all, fields of study dedicate a portion of attention to communication, so when speaking about communication it is very important to be sure about what aspects of communication one is speaking about. Definitions of communication range widely, some recognizing that animals can communicate with each other as well as human beings, and some are more narrow, only including human beings within the parameters of human symbolic interaction.
Nonetheless, communication is usually described along a few major dimensions:
1. Content (what type of things are communicated)
2. Source (by whom)
3. Form (in which form)
4. Channel (through which medium)
5. Destination/Receiver (to whom)
6. Purpose/Pragmatic aspect (with what kind of results).
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| Business |
| | Sat Nov 17, 2007 6:35 |
In economics, a business is a legally-recognized organizational entity existing within an economically free country designed to sell goods and/or services to consumers, usually in an effort to generate profit.
In predominantly capitalist economies, where most businesses are privately owned, businesses are typically formed to earn profit and grow the personal wealth of their owners. The owners and operators of a business have as one of their main objectives the receipt or generation of a financial return in exchange for their work - that is, the expense of time and energy - and for their acceptance of risk-investing work and money without certainty of success. Notable exceptions to this rule include cooperative businesses and government institutions. This model of business functioning is opposed by socialists, who advocate either government, public, or worker ownership of most sizable businesses; and to a lesser extent by individuals advocating for a mixed economy of private and state-owned enterprises.
The etymology of "business" refers to the state of being busy in the context of the individual as well as the community or society. In other words, to be busy is to be doing commercially viable and profitable work. The term "business" has at least three usages, depending on the scope - the general usage (above), the singular usage to refer to a particular company or corporation, and the generalized usage to refer to a particular market sector, such as "the record business," "the computer business," or "the business community"-the community of suppliers of goods and services.
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| Mental health |
| | Wed Oct 31, 2007 5:16 |
Mental health is a concept that refers to a human individual's emotional and psychological well-being. Merriam-Webster defines mental health as "A state of emotional and psychological well-being in which an individual is able to use his or her cognitive and emotional capabilities, function in society, and meet the ordinary demands of everyday life."
According to the World Health Organization, there is no one "official" definition of mental health. Cultural differences, subjective assessments, and competing professional theories all affect how "mental health" is defined. In general, most experts agree that "mental health" and "mental illness" are not opposites. In other words, the absence of a recognized mental disorder is not necessarily an indicator of mental health.
One way to think about mental health is by looking at how effectively and successfully a person functions. Feeling capable and competent; being able to handle normal levels of stress, maintain satisfying relationships, and lead an independent life; and being able to "bounce back," or recover from difficult situations, are all signs of mental health.
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| Electronic media |
| | Fri Oct 26, 2007 5:25 |
In the last century, a revolution in telecommunications has greatly altered communication by providing new media for long distance communication. The first transatlantic two-way radio broadcast occurred in 1906 and led to common communication via analogue and digital media:
• Analog telecommunications include traditional telephony, radio, and TV broadcasts.
• Digital telecommunications allow for computer-mediated communication, telegraphy, and computer networks.
Communications media impact more than the reach of messages. They impact content and customs; for example, Thomas Edison had to discover that hello was the least ambiguous greeting by voice over a distance; previous greetings such as hail tended to be garbled in the transmission. Similarly, the terseness of e-mail and chat rooms produced the need for the emoticon.
Modern communication media now allow for intense long-distance exchanges between larger numbers of people (many-to-many communication via e-mail, Internet forums). On the other hand, many traditional broadcast media and mass media favor one-to-many communication (television, cinema, radio, newspaper, magazines)
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| Wilderness |
| | Mon Oct 22, 2007 5:58 |
Wilderness is generally defined as a natural environment on Earth that has not been directly modified by human activity. Ecologists consider wilderness areas to be an integral part of the planet's self-sustaining natural ecosystem (the biosphere).
The word, "wilderness", derives from the notion of wildness; in other words that which is not controllable by humans. The word's etymology is from the Old English wildeornes, which in turn derives from wildeor meaning wild beast (wild + deor = beast, deer). From this point of view, it is the wildness of a place that makes it a wilderness. The mere presence or activity of people does not disqualify an area from being "wilderness." Many ecosystems that are, or have been, inhabited or influenced by activities of people may still be considered "wild." This way of looking at wilderness includes areas within which natural processes operate without very noticeable human interference.
Looked at through the lens of the visual arts, nature and wildness have been important subjects in various epochs of world history. An early tradition of landscape art occurred in the Tang Dynasty (618-907). The tradition of representing nature as it is became one of the aims of Chinese painting and was a significant influence in Asian art. Artists learned to depict mountains and rivers "from the perspective of nature as a whole and on the basis of their understanding of the laws of nature … as if seen through the eyes of a bird." In the 13th century, Shih Erh Chi listed "scenes lacking any places made inaccessible by nature," as one of the 12 things to avoid in painting.
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| Human interrelationship |
| | Tue Oct 16, 2007 5:53 |
Although humans currently comprise only about one-half of one percent of the total living biomass on Earth, the human effect on nature is disproportionately large. Because of the extent of human influence, the boundaries between what we regard as nature and "made environments" is not clear cut except at the extremes. Even at the extremes, the amount of natural environment that is free of discernible human influence is presently diminishing at an increasingly rapid pace, or, according to some, has already disappeared.
The development of technology by the human race has allowed the greater exploitation of natural resources and has helped to alleviate some of the risk from natural hazards. In spite of this progress, however, the fate of human civilization remains closely linked to changes in the environment. There exists a highly complex feedback-loop between the use of advanced technology and changes to the environment that are only slowly becoming understood. Manmade threats to the Earth's natural environment include pollution, deforestation, and disasters such as oil spills. Humans have contributed to the extinction of many plants and animals.
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| Microbes |
| | Wed Oct 10, 2007 6:29 |
The first form of life to develop on the Earth were microbes, and they remained the only form of life on the planet until about a billion years ago when multi-cellular organisms began to appear. Microorganisms are single-celled organisms that are generally smaller than the human eye can see. They include Bacteria, Fungi, Archaea and Protista.
These life forms are found in almost every location on the Earth where there is liquid water, including the interior of rocks within the planet. Their reproduction is both rapid and profuse. The combination of a high mutation rate and a horizontal gene transfer ability makes them highly adaptable, and able to survive in new environments, including outer space. They form an essential part of the planetary ecosystem. However some microorganisms are pathogenic and can post health risk to other organisms.
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| Microbes |
| | Wed Oct 10, 2007 6:22 |
The first form of life to develop on the Earth were microbes, and they remained the only form of life on the planet until about a billion years ago when multi-cellular organisms began to appear. Microorganisms are single-celled organisms that are generally smaller than the human eye can see. They include Bacteria, Fungi, Archaea and Protista.
These life forms are found in almost every location on the Earth where there is liquid water, including the interior of rocks within the planet. Their reproduction is both rapid and profuse. The combination of a high mutation rate and a horizontal gene transfer ability makes them highly adaptable, and able to survive in new environments, including outer space. They form an essential part of the planetary ecosystem. However some microorganisms are pathogenic and can post health risk to other organisms.
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| Evolution |
| | Thu Oct 4, 2007 7:29 |
Life, as we understand it, is currently only known to exist on the planet Earth. The origin of life is still a poorly understood process, but it is thought to have occurred about 3.9 to 3.5 billion years ago during the hadean or archean eons on a primordial earth that had a substantially different environment than is found at present. These life forms possessed the basic traits of self-replication and inheritable traits. Once life had appeared, the process of evolution by natural selection resulted in the formation of ever-more diverse life forms.
Species that were unable to adapt to the changing environment and competition from other life forms became extinct. However, the fossil record retains evidence of many of these older species. Current fossil and DNA evidence shows that all existing species can trace a continual ancestry back to the first primitive life forms.
The advent of photosynthesis in very basic forms of plant life worldwide allowed the sun's energy to be harvested to create conditions allowing for more complex life. The resultant oxygen accumulated in the atmosphere and gave rise to the ozone layer. The incorporation of smaller cells within larger ones resulted in the development of yet more complex cells called eukaryotes. Cells within colonies became increasingly specialized, resulting in true multicellular organisms. With the ozone layer absorbing harmful ultraviolet radiation, life colonized the surface of Earth.
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| Life |
| | Thu Sep 27, 2007 5:22 |
Properties common to terrestrial organisms (plants, animals, fungi, protists, archaea and bacteria) are that they are cellular, carbon-and-water-based with complex organization, having a metabolism, a capacity to grow, respond to stimuli, and reproduce. An entity with these properties is generally considered life. However, not every definition of life considers all of these properties to be essential. Human-made analogs of life may also be considered to be life.
The biosphere is the part of Earth's outer shell -including air, land, surface rocks and water - within which life occurs, and which biotic processes in turn alter or transform. From the broadest geophysiological point of view, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere (rocks), hydrosphere (water), and atmosphere (air). Currently the entire Earth contains over 75 billion tons (150 trillion pounds or about 6.8 x 1013 kilograms) of biomass (life), which lives within various environments within the biosphere.
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| Resistors |
| | Thu Sep 6, 2007 5:31 |
| Resistors A resistor is a block of fabric that limits the flow of current. The greater the resistance, the lower the current will be. Since conductors have an "electron soup" around the atoms, they behave like a wide pipe filled with water, and have low resistance to a flow of water. Insulators, on the other hand, work more like a tiny pipe, or a sponge-filled pipe. While they are absorbent and allow current to flow, a sponge that is denser and has less holes will have a higher resistance and a lesser flow of current, if the force pushing on the water is the similar. Resistance can vary from very small to very large. A superconductor has zero resistance, while something like the input to an op-amp can have a resistance near 1012 Ω, and even higher resistances are possible. For most materials, as hotness increases resistance tends to increase as well. Resistance converts electrical energy into heat. Resistors which dissipate large amounts of power are cooled so that they are not shattered, typically with finned heat sinks. Resistors have two leads to which the resistor can be connected to an electrical circuit. A symbol for a resistor used in electrical circuit diagrams is shown below. The two black dots indicate the points of contact for the resistor. The ratio of the voltage to current will always be positive, since a higher voltage on one side of a resistor is a positive voltage, and a current will flow from the positive side to the negative side, resulting in a positive current. If the voltage is reversed, the current is reversed, leading again to a positive resistance.
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