Environmental factors contracts

Temperature and Humidity. Temperature is probably the easiest environmental factor to control. The main concern is that the temperature remains constant to prevent the thermal expansions and contractions that are particularly dangerous to composite objects. Another factor regarding temperature is the inverse relation to relative humidity under conditions of constant absolute humidity, such as exist in closed areas. High extremes in temperature are especially undesirable, as they increase reaction rates. Areas in which objects are exhibited and stored must be accessible thus a reasonable temperature setting is generally recommended to be about 21°C. 

Tension-type headache (TTH) is the most common primary headache disorder. It is often underrepresented in clinical practice, as many patients do not present for care.6 The term tension-type headache is used to describe all headache syndromes in which muscle contraction is the most significant factor in the pathogenesis of pain. The 1-year prevalence of TTH in the population ranges from 30% to 90%.6 It is more common in adult females. Environmental factors, as opposed to genetic predisposition, play a more central role in their development. Tension-type headaches can be further divided into episodic or chronic the mean frequency of attacks is 3 days per month in episodic disorders, and chronic TTH is defined as 15 or more attacks in a 1-month period.7 The estimated prevalence of chronic TTH is less than 5%.6 Some researchers believe that chronic TTHs represent a continuum of headache severity with migraine headache.8 When severe headaches are difficult to differentiate clinically, treatment should initially target TTH. 

Edgar, T, F. Humenick, M. J. Thompson, T. W. "Support Research on Chemical, Mechanical, and Environmental Factors in Underground Coal Gasification" Final Report to U.S. Department of Energy, Contract DE-AS20-81LC10713, 1984. 

Static factors may be accentuated by environmental factors. Patients who are stressed or in pain may experience an exacerbation of voiding difficulty. In these situations, increased a -adrenergic tone may precipitate excessive contraction of prostatic stromal tissue. When the stressful event resolves, voiding symptoms often disappear. ... 

Collagen fibrils seem ideally constructed to provide simple experimental models which may be used, by observation of swelling, contraction, and extension as functions of chemical or physical environments, to simulate the possible roles of protein fibrous systems in tissues or to learn how the environmental factors influence protein chain configuration in general. Pryor (181) has already offered suggestions of this sort in connection with problems of muscle contraction. 

Aspergillosis is the most common, often associated with an environmental factor (exposure to dusts). Spore inhalation is the main route by which As-pergillus infections are contracted. This fungus affects the lungs, the sinuses, and the peripheral and central nervous systems. The prognosis is usually poor, despite the availability of appropriate antimicrobial agents (amphotericin B, itraconazole, voriconazole). 

Epidemiologic, experimental, and in vitro mechanistic data indicate that lead exposure elevates blood pressure in susceptible individuals. In populations with environmental or occupational lead exposure, blood lead concentration is linked with increases in systolic and diastolic blood pressure. Studies of middle-aged and elderly men and women have identified relatively low levels of lead exposure sustained by the general population to be an independent risk factor for hypertension. In addition, epidemiologic studies suggest that low to moderate levels of lead exposure are risk factors for increased cardiovascular mortality. Lead can also elevate blood pressure in experimental animals. The pressor effect of lead may be mediated by an interaction with calcium mediated contraction of vascular smooth muscle, as well as generation of oxidative stress and an associated interference in nitric oxide signaling pathways. 

Many industrial processes require accurate environmental control. Examples include chemical reactions and processes that are affected by atmospheric conditions biochemical reactions quality, uniformity, and standardization of certain products factors such as rate of crystallization and size of crystals product moisture content or regain deliquescence, lumping, and caking of hygroscopic materials expansion and contraction of macliines and products physical, chemical, and biological cleanliness effects of static electricity odors and fumes conditions in storage and packaging quality of painted and lacquered finishes simulation of stratosphere or space conditions and productivity and comf ort of workers. Controlled atmospheric conditions are... 

With respect to contributions of other mobile sources to the atmospheric burden of trace metals, very few data are available. The National Aeronautics and Space Administration in 1974 published calculated annual average ambient concentrations at or near airports of 49 trace elements attributable to aircraft most values were less than numbers. Of interest, however, are the estimates for the environmentally important metals, titanium, vanadium, and cadmium these were given as 24 ng/m , 0.12 ng/m and < 14 ng/m , respectively (56). EflForts to characterize aircraft emissions and to develop emissions factors by means of dynamometer tests are under way. One such experiment is being performed at Pratt and Whitney under contract to the Environmental Protection Agency results from this study should be available in mid-1978 (57). 

In the polymer melt conformational rearrangements are associated with the motions of the macromolecule (reptation) curvilinearly along its contour in an environmental tube to which the molecule is confined. The tube can only be altered, topologically, by contractions and reelongations of the chain as its ends diffuse, eliminate and redefine, new tube sections. The time for the renewal of the entire tube, by this process, is proportional to the cube of the molecular weight. The rotation of the macromolecule in simple shear, as well, requires up and down motions along the tube. Hence, if the viscosity of the melt is governed by the same friction factor as in diffusion it should scale as... 

As the temperature decreases, the pipe gains strength. The pipe may be designed to hold rated pressure at 73.4°F with recognition of a greater safety factor at lower temperatures. Allowances for thermal expansion and contraction shonld be engineered into any installation based upon the fluid or environmental temperature. 

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