kuliahku

life

2008-06-16T00:51:00.000-07:00

Life is a condition that distinguishes organisms from non-living objects, such as non-life, and dead organisms, being manifested by growth through metabolism and reproduction. Some living things can communicate and many can adapt to their environment through changes originating internally. A physical characteristic of life is that it feeds on negative entropy.[1][2] In more detail, according to physicists such as John Bernal, Erwin Schrödinger, Eugene Wigner, and John Avery, life is a member of the class of phenomena which are open or continuous systems able to decrease their internal entropy at the expense of substances or free energy taken in from the environment and subsequently rejected in a degraded form (see: entropy and life).[3][4]

A diverse array of living organisms can be found in the biosphere on Earth. Properties common to these organisms—plants, animals, fungi, protists, archaea and bacteria—are a carbon- and water-based cellular form with complex organization and heritable genetic information. They undergo metabolism, possess a capacity to grow, respond to stimuli, reproduce and, through natural selection, adapt to their environment in successive generations.

An entity with the above properties is considered to be a living organism, that is an organism that is alive hence can be called a life form. However, not every definition of life considers all of these properties to be essential. For example, the capacity for descent with modification is often taken as the only essential property of life. This definition notably includes viruses, which do not qualify under narrower definitions as they are acellular and do not metabolize.

Definitions

There is no universal definition of life; there are a variety of definitions proposed by different scientists. To define life in unequivocal terms is still a challenge for scientists.[5][6]

Conventional definition: Often scientists say that life is a characteristic of organisms that exhibit the following phenomena:

1. Homeostasis: Regulation of the internal environment to maintain a constant state; for example, sweating to reduce temperature.
2. Organization: Being composed of one or more cells, which are the basic units of life.
3. Metabolism: Consumption of energy by converting nonliving material into cellular components (anabolism) and decomposing organic matter (catabolism). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.
4. Growth: Maintenance of a higher rate of synthesis than catalysis. A growing organism increases in size in all of its parts, rather than simply accumulating matter. The particular species begins to multiply and expand as the evolution continues to flourish.
5. Adaptation: The ability to change over a period of time in response to the environment. This ability is fundamental to the process of evolution and is determined by the organism's heredity as well as the composition of metabolized substances, and external factors present.
6. Response to stimuli: A response can take many forms, from the contraction of a unicellular organism when touched to complex reactions involving all the senses of higher animals. A response is often expressed by motion, for example, the leaves of a plant turning toward the sun or an animal chasing its prey.
7. Reproduction: The ability to produce new organisms. Reproduction can be the division of one cell to form two new cells. Usually the term is applied to the production of a new individual (either asexually, from a single parent organism, or sexually, from at least two differing parent organisms), although strictly speaking it also describes the production of new cells in the process of growth.

Plant life.
Plant life.
Herds of zebra and impala gathering on the Masai Mara plain
Herds of zebra and impala gathering on the Masai Mara plain
Marine life around a coral reef.
Marine life around a coral reef.

However, others cite several limitations of this definition.[citation needed] Thus, many members of several species do not reproduce, possibly because they belong to specialized sterile castes (such as ant workers), these are still considered forms of life. One could say that the property of life is inherited; hence, sterile or hybrid organisms such as mules, ligers, and eunuchs are alive although they are not capable of self-reproduction. However, (a) The species as a whole does reproduce, (b) There are no cases of species where 100% of the individuals reproduce, and (c) specialized non-reproducing individuals of the species may still partially propagate their DNA or other master pattern through mechanisms such as kin selection.

Viruses and aberrant prion proteins are often considered replicators rather than forms of life, a distinction warranted because they cannot reproduce without very specialized substrates such as host cells or proteins, respectively. Also, the Rickettsia and Chlamydia are examples of bacteria that cannot independently fulfill many vital biochemical processes, and depend on entry, growth, and replication within the cytoplasm of eukaryotic host cells. However, most forms of life rely on foods produced by other species, or at least the specific chemistry of Earth's environment.

The systemic definition of life is that living things are self-organizing and autopoietic (self-producing). These objects are not to be confused with dissipative structures (e.g. fire).

Variations of this definition include Stuart Kauffman's definition of life as an autonomous agent or a multi-agent system capable of reproducing itself or themselves, and of completing at least one thermodynamic work cycle.

Proposed definitions of life include:

1. Living things are systems that tend to respond to changes in their environment, and inside themselves, in such a way as to promote their own continuation.[7]
2. Life (a living individual) is defined as a network of inferior negative feedbacks (regulatory mechanisms) subordinated to a superior positive feedback (potential of expansion, reproduction)[8]
3. Life is a characteristic of self-organizing, self-recycling systems consisting of populations of replicators that are capable of mutation, around most of which homeostatic, metabolizing organisms evolve.
4. Type of organization of matter producing various interacting forms of variable complexity, whose main property is to replicate almost perfectly by using matter and energy available in their environment to which they may adapt. In this definition "almost perfectly" relates to mutations happening during replication of organisms that may have adaptive benefits.
5. Life is a potentially self-perpetuating open system of linked organic reactions, catalyzed simultaneously and almost isothermally by complex chemicals (enzymes) that are themselves produced by the open system.

copy from http://en.wikipedia.org/wiki/Life

Oil shale

2008-05-28T22:36:00.001-07:00

Oil shale is a fine-grained sedimentary rock containing significant amounts of kerogen (a solid mixture of organic chemical compounds), from which liquid hydrocarbons can be extracted. The name oil shale has been described as a promotional misnomer, since the rock is not necessarily a shale and its kerogen is not crude oil; it requires more processing than crude oil, which affects its economic viability as a crude oil substitute.[1][2] Deposits of oil shale are located around the world, including major deposits in the United States. Global deposits are estimated as equivalent to 2.8 trillion to 3.3 trillion barrels (450×109 to 520×109 m3) of recoverable oil.[2][3][4][5]
The chemical process of pyrolysis can convert the kerogen in oil shale into synthetic crude oil. When oil shale is heated to a sufficiently high temperature a vapor is driven off which can be distilled (retorted) to yield a petroleum-like shale oil—a form of non-conventional oil—and combustible shale gas (shale gas can also refer to gas occurring naturally in shales). Oil shale can also be burnt directly as a low-grade fuel for power generation and heating purposes and can be used as a raw material in the chemical and construction materials industries.[6][2]
Oil shale has gained attention as an energy resource as the price of conventional sources of petroleum has risen and as a way for some areas to secure independence from external suppliers of energy.[7][8] The oil shale industry is well-established in Estonia, China, and Brazil, and the United States is taking steps in that direction. At the same time oil shale mining and processing involves a number of environmental issues, such as land use, waste disposal, water use and waste water management, and air pollution.[9][10] The industry has foundered in Australia due to opposition on these grounds.
Geolog
Oil shale consists of organic-rich sedimentary rock: it belongs to the group of sapropel fuels.[11] It is differentiated from bitumen-impregnated rocks (tar sands and petroleum reservoir rocks), humic coals and carbonaceous shale. While tar sands have been created by biodegradation of oil, the kerogen in oil shales has not yet been naturally transformed into petroleum by heat and pressure.[2][12][13] Coal contains a higher percentage of organic matter than oil shale. In commercial grades of oil shale the ratio of organic matter to mineral matter is about 0.75:5 to 1.5:5. At the same time, the organic matter in oil shale has an atomic ratio of hydrogen to carbon approximately the same as for crude oil and four to five times higher than for coals.[2][11]
Oil shale does not have a definite geological definition nor a specific chemical formula. Oil shales vary considerably in their mineral content, chemical composition, age, type of kerogen, and depositional history.[14] The organic components of oil shale derive from a variety of organisms, such as the remains of algae, spores, pollen, plant cuticles and corky fragments of herbaceous and woody plants, and cellular debris from other aquatic and land plants.[2][15] Some deposits contain significant fossils; Germany's Messel Pit is a Unesco World Heritage Site. The mineral matter in oil shale includes various fine-grained silicates and carbonates.[11][6]
Geologists can classify oil shales on the basis of their composition as carbonate-rich shales, siliceous shales, or cannel shales.[16] Another classification, assigning kerogen types, is based on the hydrogen, carbon, and oxygen content of oil shales' original organic matter. This classification is known as the van Krevelen diagram.[14] The most used classification of oil shales was developed between 1987 and 1991 by Adrian C. Hutton of the University of Wollongong, adapting petrographic terms from coal terminology. According to this classification, oil shales are designated as terrestrial, lacustrine (lake-bottom-deposited), or marine (ocean bottom-deposited), based on the environment where the initial biomass was deposited. [6][17] Hutton's classification scheme has proven useful in estimating the yield and composition of the extracted oil.[2]
From : http://en.wikipedia.org/wiki/Oil_shale

plato

2008-05-27T01:26:00.000-07:00

Plato (Greek: Πλάτων, Plátōn, "wide, broad-browed"^[1]) (428/427 BC^[a] – 348/347 BC), was a Classical Greek philosopher, who together with his teacher, Socrates, and his student, Aristotle, helped to lay the philosophical foundations of Western culture.^[2] Plato was also a mathematician, writer of philosophical dialogues, and founder of the Academy in Athens, the first institution of higher learning in the western world. Plato was originally a student of Socrates, and was as much influenced by his thinking as by what he saw as his teacher's unjust death.

Plato's sophistication as a writer and thinker can be witnessed by reading his Socratic dialogues. Some of the dialogues, letters, and other works that are ascribed to him are considered spurious.^[3] Interestingly, although there is little question that Plato lectured at the Academy that he founded, the pedagogical function of his dialogues, if any, is not known with certainty. The dialogues have since Plato's time been used to teach a range of subjects, mostly including philosophy, logic, rhetoric, mathematics, and other subjects about which he wrote.

Biography

[edit] Early life

Main article: Early life of Plato

[edit] Birth and family

The exact birthdate of Plato is unknown. Based on ancient sources, most modern scholars estimate that he was born in Athens or Aegina^[b] between 429 and 423 BC^[a] His father was Ariston. According to a disputed tradition, reported by Diogenes Laertius, Ariston traced his descent from the king of Athens, Codrus, and the king of Messenia, Melanthus.^[4] Plato's mother was Perictione, whose family boasted of a relationship with the famous Athenian lawmaker and lyric poet Solon.^[5] Perictione was sister of Charmides and niece of Critias, both prominent figures of the Thirty Tyrants, the brief oligarchic regime, which followed on the collapse of Athens at the end of the Peloponnesian war (404-403 b.c.e.).^[6] Besides Plato himself, Ariston and Perictione had three other children; these were two sons, Adeimantus and Glaucon, and a daughter Potone, the mother of Speusippus (the nephew and successor of Plato as head of his philosophical Academy).^[6] According to the Republic, Adeimantus and Glaucon were older than Plato.^[7] Nevertheless, in his Memorabilia, Xenophon presents Glaucon as younger than Plato.^[8]

According to certain reports of ancient writers, Plato' s mother became pregnant through a virginal conception: Ariston tried to force his attentions on Perictione, but failed of his purpose; then the ancient Greek god Apollo appeared to him in a vision, and, as a result of it, Ariston left Perictione unmolested.^[9] Another legend related that, while he was sleeping as an infant, bees had settled on the lips of Plato; an augury of the sweetness of style in which he would discourse philosophy.^[10]

Ariston appears to have died in Plato's childhood, although the precise dating of his death is difficult.^[11] Perictione then married Pyrilampes, her mother's brother,^[12] who had served many times as an ambassador to the Persian court and was a friend of Pericles, the leader of the democratic faction in Athens.^[13] Pyrilampes had a son from a previous marriage, Demus, who was famous for his beauty.^[14] Perictione gave birth to Pyrilampes' second son, Antiphon, the half-brother of Plato, who appears in Parmenides.^[15]

In contrast to his reticence about himself, Plato used to introduce his distinguished relatives into his dialogues, or to mention them with some precision: Charmides has one named after him; Critias speaks in both Charmides and Protagoras; Adeimantus and Glaucon take prominent parts in the Republic.^[16] From these and other references one can reconstruct his family tree, and this suggests a considerable amount of family pride. According to Burnet, "the opening scene of the Charmides is a glorification of the whole [family] connection ... Plato's dialogues are not only a memorial to Socrates, but also the happier days of his own family".^[17]

[edit] Name

According to Diogenes Laertius, the philosopher was named Aristocles after his grandfather, but his wrestling coach, Ariston of Argos, dubbed him "Platon", meaning "broad" on account of his robust figure.^[18] According to the sources mentioned by Diogenes (all dating from the Alexandrian period), Plato derived his name from the breadth (platutês) of his eloquence, or else because he was very wide (platus) across the forehead.^[19] In the 21st century some scholars disputed Diogenes, and argued that the legend about his name being Aristocles originated in the Hellenistic age.^[c]

[edit] Education

Apuleius informs us that Speusippus praised Plato's quickness of mind and modesty as a boy, and the "first fruits of his youth infused with hard work and love of study".^[20] Plato must have been instructed in grammar, music, and gymnastics by the most distinguished teachers of his time.^[21] Dicaearchus went so far as to say that Plato wrestled at the Isthmian games.^[22] Plato had also attended courses of philosophy; before meeting Socrates, he first became acquainted with Cratylus (a disciple of Heraclitus, a prominent pre-Socratic Greek philosopher) and the Heraclitean doctrines.^[23]

^{from : http://en.wikipedia.org/wiki/Plato}