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What is a high CD4/CD8 ratio?

Measurements in CD4 and CD8 counts are considered low if they fall below 200 cells per cubic millimeter, though some doctors will begin preventive measures when counts fall below 350. In general, CD4 and CD8 counts decrease as the HIV disease progresses. It is possible to have a change in these counts even though the patient's health status has not changed.

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What are the four biogeochemical cycles?

The water, or hydrologic, cycle, primarily involves the evaporation of moisture from the ocean and its return to lakes, oceans, waterways and groundwater sources in the form of rain. The carbon and phosphorous cycles primarily involve the flow of nutrients and biological wastes to and from plant, animal and microbiological life. The nitrogen cycle is more complex, as nitrogen is fixated by lightning, ultraviolet radiation and bacteria in some processes and returned to Earth's atmosphere in other processes.

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What is a hydride shift?

Hydride shifts are common in reactions involving alcohol and hydrogen halides, including HBr, HCl and HI. Because of its instability and fast reactivity rate, HF is not normally used. Hydride shifts occur when alkenes undergo hydration. Hydride shifts normally occur at low temperatures, but the reaction may be sped up by heating the solution of the cation. Other types of carbocation rearrangements occur, including alkyl and aryl shifts.

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How do you cross reference a cr2032 battery?

Using a basic watch battery cross reference chart shows that the generic CR2032 is compatible with a number of batteries from major manufacturers. Duracell calls this battery the DL2032, Rayovac calls it the CR2032-1W, Kodak produces this battery as the KCR2032 and Energizer calls it the ECR2032. Despite the different names, all of these batteries are totally compatible and work in any device that uses CR2032 batteries.\nWhile some battery manufacturers use unique model numbers for watch batteries, most companies use the generic name. For instance, Panasonic, Toshiba and Maxell all use the gen..

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What are the general characteristics of bacteria?

Bacteria can thrive in hot and cold environments. Psychrophiles are bacteria that prefer colder environments, while thermophiles thrive in hot environments. Extreme thermophiles can live around extremely hot hydrothermal vents on the ocean floor.\nBacteria that live in an organism's digestive system can help break down tough food material for easier digestion. These types of bacteria also serve an essential role as waste decomposers.

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What is a petrified rock?

Petrification typically takes millions of years. Normally, trees decompose, but when a tree lands in a swamp or is otherwise covered up, decomposition is halted. The cells within the tree are hollowed out, and mineral-rich water seeps in. As the water evaporates, the minerals are left behind, creating a copy of what was there. It is possible to see growth rings in well-preserved samples.

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Why do some men have no chest hair?

With a deficiency in a male sex hormone, a man may not have the capability of growing hair in particular areas. Male sex hormones are responsible for the regulation of hair growth and other developmental processes. The most significant androgen is testosterone. Testosterone plays a role in bodily functions such as muscle development, prostate function and hair growth, explains the Better Health Channel. A deficiency in this hormone impedes these bodily functions, leading to many symptoms including hair loss.\nThe technical term for a testosterone deficiency is hypogonadism, notes Vertical Heal..

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What are some interesting facts about salt marshes?

The decay of the plant matter in peat absorbs oxygen, so the peat itself often has extremely low oxygen levels. The bacteria that absorb the oxygen as they break down the plant matter release gases with sulfur in them, often causing salt marshes to smell like rotten eggs. Salt marshes are rich with both plant and animal life, and they serve as an important buffer against erosion on coastlines. They also play an important role in delivering nutrients to coastal waters.\nSalt marshes usually form where rivers flow into marine estuaries or other areas that are protected from waves and other power..

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What factors affect soil fertility?

Decomposition of plant and animal wastes releases nutrients and minerals into soil, and microorganisms aid the decomposition process. Texture and structure influence soil's ability to retain nutrients, minerals and other components essential for fertility. Sandy loam, a combination of sand, silt and clay, offers the best balance of drainage and nutrient retention for most gardens. In addition, soil structure determines drainage rates, aeration and the ease with which plant roots move through the soil. Gardeners prefer soil that readily crumbles. Removing the components that support fertil..

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What are the types of acceleration?

Acceleration can be also categorized depending on whether the motion of the object is linear or angular. For objects with a linear motion, acceleration can be divided into two types: average and instantaneous. For objects with angular motion, it can be divided into three types: centripetal, tangential and angular acceleration. Since acceleration depends on velocity, which has both magnitude and direction, the acceleration of an object can change depending on a change of magnitude, a change in direction or change in both direction and magnitude.

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