- 行业: Printing & publishing
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McGraw Hill Financial, Inc. is an American publicly traded corporation headquartered in Rockefeller Center in New York City. Its primary areas of business are financial, publishing, and business services.
Forests play a key role in cleaning water. Precipitation is “filtered” through the tree canopy and filtered again through the organic matter on the forest floor. The water then seeps into the subsurface to replenish the ground water. Approximately 80% of the freshwater in the United States originates in the 650 million acres (265 million hectares) of forest that cover approximately one-third of the nation. These forested watersheds are the primary source of drinking water for nearly two out of three people in the United States. The United States’ national forests and grasslands, which cover nearly 192 million acres (78 million hectares), are the largest single source of freshwater in the country, and the headwaters of many large river basins originate in the national forests. Forests are thus an important source of freshwater; however, mining, forestry practices, and altered fire regimes have increasingly caused the contamination of these valuable water resources.
Industry:Science
Formerly, a group of reptiles that was recognized in rank-based classifications. Amniotes were once divided into subclasses, based on the patterns of temporal fenestrae (openings in the skull roof posterior to the openings for the eyes). Subclass Synapsida included taxa that exhibit a single pair of temporal fenestrae (synapsid condition). Subclass Diapsida included taxa that feature two pairs of temporal fenestrae (diapsid condition) and those that are descended from ancestors that had them. The absence of temporal fenestrae is known as the anapsid condition. Mesosaurids, pareiasaurids, and captorhinids are examples of fossil reptiles that lack temporal fenestrae, whereas turtles are the only living reptiles that lack them; these reptiles were placed together in the subclass Anapsida. Certain Paleozoic reptiles (for example, millerettids) that exhibited synapsid-like temporal fenestrae but clearly did not belong in Synapsida (or Diapsida) were placed in Anapsida.
Industry:Science
Chromosomes are physical carriers of genetic information that all organisms rely on as blueprints. The chromosome consists of deoxyribonucleic acid (DNA) and proteins. The DNA of the chromosome stores genetic information, with the content and the selective expression of which determining the diversity of all living organisms. Chromosomes come in different shapes. Prokaryotic organisms usually have simple circular chromosomes, whereas eukaryotic organisms such as plants and animals have developed highly organized linear chromosome structures. In eukaryotes, DNA and histone proteins are packaged into nucleosomes. Nucleosomes and the “linker” DNA (DNA between nucleosomes) are the basic units of the chromosome fiber called chromatin. The 10-nanometer chromatin is further compacted into other higher-order structures such as the metaphase chromosomes (that is, chromosomes in the metaphase stage of the cell cycle), which are visible under a light microscope after staining.
Industry:Science
In a cylinder, the piston displacement plus clearance volume, divided by the clearance volume. This is the nominal compression ratio determined by cylinder geometry alone. In practice, the actual compression ratio is appreciably less than the nominal value because the volumetric efficiency of an unsupercharged engine is less than 100%, partly because of late intake valve closing. In spark ignition engines the allowable compression ratio is limited by incipient knock at wide-open throttle. Knock in turn depends on the molecular structure of the fuel and on such engine features as the temperature of the combustible mixture prior to ignition, the geometry and size of the combustion space, and the ignition timing. For example, isooctane, benzene, and alcohol can be burned at much higher compression ratios than <i>n</i>-heptane. In compression ignition engines critical compression ratio is that necessary to ignite the fuel and depends on fuel and cylinder geometry.
Industry:Science
Each species of multicellular organisms has a set number of chromosomes that carry all genes required for development and living processes. However, some species in both the plant and animal kingdoms have extra chromosomes, called B chromosomes, which are dispensable. They only exist in some individuals of a species and often are variable in number. Variation in number of the normal chromosomes is highly detrimental, but B chromosomes seldom have any detrimental effects unless many copies are present. Thus, they are considered to be mostly inert, being neither required nor detrimental. They exist in populations because they have properties that foster their accumulation; normal chromosomes do not possess these properties. In some plant species, particularly corn, they have been used to make translocations with the normal chromosomes, which have proven to be useful for mutation mapping, chromosomal dosage studies, and recently production of engineered minichromosomes.
Industry:Science
Early Egyptians and Mesopotamians discovered that if barley grains were wetted, allowed to germinate, and subsequently dried, the barley would be sweeter and less perishable. When water was added, a mildly alcoholic beverage was produced through the action of naturally occurring yeast. The first recorded evidence of brewing was found in Egypt in 6000 <small>B.C.</small> From there, the technology passed to Greece, to Rome, and to the rest of the Roman Empire. By the thirteenth and fourteenth centuries, brewing was well established in the monasteries of northern Europe. Later in Europe and in early America, most households brewed their own beer. As towns and cities developed, home brewing was replaced by the small brewery, which eventually disappeared during Prohibition in the United States. Thereafter, the commercial brewing industry emerged. A good economy, improved technology, and better ingredients have allowed home brewing to flourish again as a leisure-time hobby.
Industry:Science
Continuous casting is a solidification method used to mass-produce long, semifinished shapes of constant cross section from basic metals. Using this method, over 800 million tons (730 million metric tons) of steel, 20 million tons (18 million metric tons) of aluminum, 1 million tons (900,000 metric tons) of copper, and other metal products (such as nickel) are processed annually worldwide. Cross sections can be rectangular (for later rolling into a plate or sheet), square for long products, circular for wire and seamless pipes, “dog-bone” shapes for I or H beams, thin strips, or rods. Continuous casting is distinguished from other solidification processes by its steady-state appearance. That is, the molten metal freezes against the mold walls and is withdrawn from the bottom of the mold at a rate which keeps the solid/liquid interface at a constant position with time, relative to an outside observer. The process works best when all of its aspects operate in this manner.
Industry:Science
Forensic biology is the scientific analysis of biological evidence to provide objective information on legal matters or those that pertain to criminal and civil law. Biological evidence such as bodily fluids or tissues that may be found at crime scenes can be analyzed through deoxyribonucleic acid (DNA) typing. Typing requires detection and screening of the biological evidence, such as blood, semen, or saliva, extracting the DNA from a specimen, amplifying specific regions of the DNA using the polymerase chain reaction (PCR), and typing the resulting PCR products to determine a DNA profile. The DNA profile from the evidence is then compared to known profiles from suspects, victims, or database samples to determine the significance of the result. Samples containing mixtures require additional interpretation to infer individual donor allele designations. Forensic biologists must also assess the statistical significance of their results, write reports, and testify in court.
Industry:Science
Any of a group of naturally occurring or synthetic organic compounds with a steroid ring structure, having a hydroxyl (–OH) group, usually attached to carbon-3. This hydroxyl group is often esterified with a fatty acid (for example, cholesterol ester). The hydrocarbon chain of the fatty-acid substituent varies in length, usually from 16 to 20 carbon atoms, and can be saturated (containing no double bonds) or unsaturated (containing one or more double bonds). Sterols commonly contain one or more double bonds in the ring structure and also a variety of substituents attached to the rings. Sterols and their fatty-acid esters are essentially water insoluble. For transport in an aqueous milieu (for example, the bloodstream of mammals), sterols and other lipids are bound to specific proteins, forming lipoprotein particles. These particles are classified based on their composition and density. One lipoprotein class is abnormally high in the blood of humans prone to heart attacks.
Industry:Science
As concern regarding environmental issues such as pollution and global climate change escalates and energy independence grows in importance, substantial international research continues to be focused on hydrogen as an alternative to fossil fuels. Hydrogen, which in pure form exists as molecular H<sub>2</sub>, is an attractive option for a variety of reasons. First, it occurs in vast amounts on Earth as a component of water (H<sub>2</sub>O) and other chemical compounds, and it is the most abundant element in the universe. Second, the combustion of H<sub>2</sub> with oxygen releases energy with only water vapor and heat as by-products; no carbon dioxide (CO<sub>2</sub>), a greenhouse gas, is produced. This aspect makes fuel cells operating with H<sub>2</sub> leading candidates to replace gasoline-powered internal combustion engines. Third, on a gravimetric basis (kilogram for kilogram), hydrogen in the form of H<sub>2</sub> contains about three times the energy of gasoline.
Industry:Science
