Résultats pour "radiatives"

Sun - astronomy.

A The Sun’s Place in the Milky Way The Milky Way Galaxy contains about 400 billion stars. All of these stars, and the gas and dust between them, are rotating about a galactic center. Stars that arefarther away from the center move at slower speeds and take longer to go around it. The Sun is located in the outer part of the galaxy, at a distance of 2.6 × 10 17 km (1.6 × 10 17 mi) from the center. The Sun, which is moving around the center at a velocity of 220 km/s (140 mi/s), takes 250 million y...

Grand oral du bac : Médecine LES CANCERS

Les cancers céreuses, et ainsi de suite. La descendance d'une cellule cancéreuse est appelée clone. À la différence des cellules normales, les cel lules du clone se divisent non seulement sans ordre mais aussi à une fréquence plus élevée. Cette rapidité reste relative: il faut en effet près de 1 milliard de cellules cancéreuses pour que le clone devienne une petite tumeur de 1 cm de diamètre ... , ce qui peut prendre plusieurs années, voire des...

Atom - chemistry.

Atoms have several properties that help distinguish one type of atom from another and determine how atoms change under certain conditions. A Atomic Number Each element has a unique number of protons in its atoms. This number is called the atomic number (abbreviated Z). Because atoms are normally electrically neutral,the atomic number also specifies how many electrons an atom will have. The number of electrons, in turn, determines many of the chemical and physical properties ofthe atom. The ligh...

Atom I INTRODUCTION Water Molecule A water molecule consists of an oxygen atom and two hydrogen atoms, which are attached at an angle of 105°.

spontaneously break apart and change, or decay, into other atoms. Unlike electrons, which are fundamental particles, protons and neutrons are made up of other, smaller particles called quarks. Physicists know of six different quarks.Neutrons and protons are made up of up quarks and down quarks —two of the six different kinds of quarks. The fanciful names of quarks have nothing to do with their properties; the names are simply labels to distinguish one quark from another. Quarks are unique amo...

Astrophysics - astronomy.

Radar.

gathers the weak returning radar signals and converts them into an electric current. Because a radar antenna may both transmit and receive signals, the duplexerdetermines whether the antenna is connected to the receiver or the transmitter. The receiver determines whether the signal should be reported and often does furtheranalysis before sending the results to the display. The display conveys the results to the human operator through a visual display or an audible signal. B1 The Antenna The rec...

Cancer (medicine).

unable to repair the DNA damage, p53 instructs the cell to undergo programmed cell death, or apoptosis , putting a stop to runaway cell division before it starts. Programmed cell death is a normal part of cell life and is tightly controlled by many genes, primarily p53. In a cancerous cell, one or more mutations prevent these genes from doing their jobs. When mutated, p53 allows a cell to continue to divide, even with damaged DNA.This can lead to additional mutations in proto-oncogenes or tumor...

Physics I INTRODUCTION Physics, major science, dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces.

Starting about 1665, at the age of 23, Newton enunciated the principles of mechanics, formulated the law of universal gravitation, separated white light into colors,proposed a theory for the propagation of light, and invented differential and integral calculus. Newton's contributions covered an enormous range of naturalphenomena: He was thus able to show that not only Kepler's laws of planetary motion but also Galileo's discoveries of falling bodies follow a combination of his ownsecond law of m...

Color I INTRODUCTION Color © Microsoft Corporation.

The colors that absorb light of the additive primary colors are called subtractive primary colors. They are magenta (purplish-pink), which absorbs green; yellow, whichabsorbs blue; and cyan (light greenish-blue), which absorbs red. Thus, if a green light is thrown on a magenta pigment, the eye will perceive black. These subtractiveprimary colors are also called the pigment primaries. They can be mixed together in varying amounts to match almost any hue. If all three are mixed in about equalamoun...

SYSTÈME SOLAIREGÉNÉRALITÉSOn entend par « Système solaire » une famille de corps célestes formée par l'étoileSoleil et par une multitude de corps distribués autour d'elle.

2 auraient échappé jusqu'ici à nos observations. La génération actuelle d'instruments astronomiques n'est pas en mesure d'identifier des corps de dimensions planétaires aux confins du domaine gravitationnel du Soleil. Les astronomes pensent que, s'il y avait une autre planète au-delà des orbites de Neptune et de Pluton, celle-ci pourrait être découverte grâce aux perturbations induites par sa force d'attraction. Vers la fin des années 80, analysant les trajectoires des sondes interplanét...

Pioneer (spacecraft) - astronomy.

The Pioneer Venus spacecraft contributed a tremendous amount of new information about Venus. Venus showed an enormous difference between night (-170°C, or -274°F) and day (40°C, or 104°F) temperatures in the highest regions of the atmosphere (the thermosphere during the day and the cryosphere at night) at altitudesbetween 130 and 200 km (between 81 and 120 mi). Below the clouds was a region of constantly high temperature and pressure and almost no wind. The Pioneer Venuscraft found the clouds ar...

nuage1PRÉSENTATIONnuage, masse de petites gouttelettes d'eau ou de minuscules cristaux de glace en suspension dans l'atmosphère et sans contact avec le sol.

4.3 Nuages de l’étage inférieur : strato-cumulus, stratus et nimbo-stratus Les nuages de l’étage inférieur, également formés par des gouttelettes d’eau, se situent à une altitude généralement inférieure à 1,5 km. Ce groupe comprend trois formesprincipales : les strato-cumulus, les stratus et les nimbo-stratus. - Les strato-cumulus sont de gros rouleaux de nuages, d’apparence molle et grise, qui couvrent souvent la totalité du ciel ; parce que la masse nuageuse n’esthabituellement pas très épa...

comète - astronomie.

4.3 Les queues des comètes Chaque comète porte une queue originale, qui dépend de la composition du noyau, de sa taille, etc. Mais de manière générale, les comètes possèdent au moins deuxqueues : une queue de poussières et une queue de plasma. 4.3. 1 La queue de poussières Les poussières éjectées du noyau forment une traînée lumineuse, appelée queue de poussières, qui prolonge la chevelure. Cette queue, dont la longueur peut atteindreplusieurs millions de kilomètres, est toujours dirigée à l’o...

unités de mesure1PRÉSENTATIONunités de mesure, grandeurs conventionnelles et abstraites, choisies pour représenter des grandeurs physiques mesurables, telles que la masse, le temps, la longueur.

En astronomie, on emploie quatre unités spécifiques : l'unité astronomique (149 597 870 km), l'année-lumière (9,461.10 12 km), le rayon équatorial terrestre (6 378,14 km) et le parsec, distance à laquelle une unité astronomique sous-tend un angle de 1'', soit environ 30 857.10 12 m. 4 UNITÉS DE MASSE Dans le système SI, l'unité fondamentale de masse est le kilogramme (kg), adopté en 1889 par la première Conférence générale des poids et mesures. Par définition, le kilogramme est la masse du...

océan (géographie) 1 PRÉSENTATION océan (géographie), vaste étendue d'eau salée qui occupe un bassin profond entre deux continents.

météorologique), entre 27 et 28 °C ; elles décroissent de part et d’autre en direction des pôles, mais il existe des anomalies liées aux courants marins. Autour del’Antarctique et au centre de l’océan Glacial Arctique, les eaux de surface ont une température inférieure à - 1 °C toute l’année, dès le 75 e parallèle ; la mer y est gelée en permanence ; la banquise (ou pack ) s’étend encore plus en hiver mais on observe actuellement sa fonte et une diminution de son extension que l’on attribue au...

Aerospace Medicine - astronomy.

medically as aeroembolism and popularly as the bends, leads to confusion, paralysis, or neurocirculatory collapse. The most characteristic symptoms of the bends arepain in the large joints resulting from pressure of the gas on tendons and nerves, together with spasm of the blood vessels. Preflight inhalation of pure oxygen toeliminate nitrogen from the system has proved valuable as a preventive measure. Rapid decompression, resulting from accidental failure at high altitudes of thepressure withi...

Uranus (planet) - astronomy.

V COMPOSITION AND STRUCTURE A Interior of Uranus Uranus contains mostly rock and water, with hydrogen and helium (and trace amounts of methane) in its dense atmosphere. Astronomers believe that Uranus, likeNeptune, formed from the same material—principally frozen water and rock—that composes most of the planet’s moons. As the planet grew, pressures andtemperatures in the planet’s interior increased, heating the planet’s frozen water into a hot liquid. Uranus probably has a relatively small roc...

Glacier.

covered. In spring the snow cover begins to melt in the lower reaches, exposing the ice surface. As temperatures increase, the melting moves up the glacier. Thesnowline is the highest position the melting reaches during the year. Firn is old granular snow. The firn limit may not exactly coincide with the annual snowline since insome years rapid melting leaves behind firn patches below the snowline. Some glaciers exhibit features called ice streams and icefalls. Ice streams are valley glaciers th...

Human Evolution.

Strepsirhines are the most primitive types of living primates. The last common ancestors of strepsirhines and other mammals—creatures similar to tree shrews andclassified as Plesiadapiformes—evolved at least 65 million years ago. The earliest primates evolved by about 55 million years ago, and fossil species similar to lemursevolved during the Eocene Epoch (about 55 million to 38 million years ago). Strepsirhines share all of the basic characteristics of primates, although their brains are notpa...

Human Evolution - biology.

classified as Plesiadapiformes—evolved at least 65 million years ago. The earliest primates evolved by about 55 million years ago, and fossil species similar to lemursevolved during the Eocene Epoch (about 55 million to 38 million years ago). Strepsirhines share all of the basic characteristics of primates, although their brains are notparticularly large or complex and they have a more elaborate and sensitive olfactory system (sense of smell) than do other primates. B Haplorhines B1 Tarsiers T...

120 résultats pour "radiatives"