Time period, determination

Chain transfer occurs frequently during the polymerization of vinyl chloride. The ratio of propagation events to chain transfer events in a given time period determines the average molecular weight of the final polymer. This finding can be summarized by the empirical formula ... 

Figure4.2 The number of documents using we at least once (relative to the number using the) over three time periods, determined using the ACS Journals Search. (Note J. Phys. Chem. includes]. Phys. Chem. A and B after 1996.)...

Current Efficiency. Current efficiency for caustic production in diaphragm and membrane cells can be estimated from collection of a known amount of caustic over a period of time and from a knowledge of the number of coulombs of electricity passed during that time period. An alternative method involves analysis of the gases evolved during electrolysis and determining the anolyte composition. Material balance considerations (7) show the expression for the caustic efficiency for membrane cells to be... 

The Du Pont HaskeU Laboratory for Toxicology and Industrial Medicine has conducted a study to determine the acute inhalation toxicity of fumes evolved from Tefzel fluoropolymers when heated at elevated temperatures. Rats were exposed to decomposition products of Tefzel for 4 h at various temperatures. The approximate lethal temperature (ALT) for Tefzel resins was deterrnined to be 335—350°C. AH rats survived exposure to pyrolysis products from Tefzel heated to 300°C for this time period. At the ALT level, death was from pulmonary edema carbon monoxide poisoning was probably a contributing factor. Hydrolyzable fluoride was present in the pyrolysis products, with concentration dependent on temperature. 

Degradable plastic is a plastic designed to undergo a significant change in its chemical stmcture under specific environmental conditions, resulting in a loss of some properties that may vary as measured by standard test methods appropriate to the plastic and the appHcation in a particular period of time that determines its classification. 

Subchronic Studies. Although short-term repeated exposure studies provide valuable information about toxicity over this time span, they may not be relevant for assessment of ha2ard over a longer time period. For example, the minimum and no-effects levels determined by short-term exposure may be significantly lower if exposure to the test material is extended over several months. Also, certain toxic effects may have a latency which does not allow their expression or detection over a short-term repeated-exposure period for example, kidney dysfunction or disturbances of the blood-forming tissues may not become apparent until subchronic exposure studies are undertaken. 

A sequence of tests has been devised to evaluate antioxidants for use in automotive crankcase lubricants. The Indiana Stirring Oxidation Test (ISOT) JISK2514 is an example of a laboratory screening test. The oil is stirred at 165.5°C in the presence of air. Copper and iron strips are used as metal catalysts. The development of sludge, viscosity, and acidity are deterrnined periodically. Failure time is determined when the development of acidity requires... 

The question of stiffness then depends on the solution at the current time. Consequently nonhuear problems can be stiff during one time period and not stiff during another. While the chemical engineer may not actually calculate the eigenvalues, it is useful to know that they determine the stabihty and accuracy of the numerical scheme and the step size used. 

Average airport visibilities over the eastern half of the United States have been determined over a period of approximately 25 years (1948-1974) (6). Although seasonal variations occur, the long-term trend has been decreased visual air quality over the time period. 

The most important evaluation of an ANG storage systems performance is the measurement of the amount of usable gas which can be delivered from the system. This is frequently defined as the volume of gas obtained from the storage vessel when the pressure is reduced from the storage pressure of 3.5 MPa (35 bar) to one bar, usually at 298 K. This parameter is referred to as the delivered V/V and is easy to determine directly and free from ambiguity. Moreover, it is independent of the ratio of gas adsorbed to that which remains in the gaseous state. To determine the delivered V/V an adsorbent filled vessel of at least several hundred cubic centimeters is pressurized at 3.5 MPa and allowed to cool under that pressure to 298 K. The gas is then released over a time period sufficient to allow the bed temperature to return to 298 K. A blank, where the vessel is filled with a volume of non-porous material, such as copper shot. 

An indicative limit value is a more common type of limit that reflects expert evaluation based on scientific data where it is possible to identify the highest level of exposure along with the corresponding reference time period for which one can have confidence that there will be no adverse effects on health. For any chemical agent for which an indicative occupational exposure limit value is established at the community level, member states shall establish a national occupational exposure limit value, taking into account the community limit value and determining its nature in accordance with national legislation and practice. 

Cleaning period The total elapsed time that a section of the baghouse is off-stream for cleaning. (This time increment determines the total availability of section fabric for filtration use.)... 

The gravimetric method depends on the sampling of flowing, particulate-laden gas from different positions across the exhaust gas duct and the determination of the mass of the particulate material. The sample is collected over a certain time period from each point. The volumetric gas flow is measured. The result is obtained by the following steps ... 

One could assume that this characteristic behavior of the mobility of the polymers is also reflected by the typical relaxation times r of the driven chains. Indeed, in Fig. 28 we show the relaxation time T2, determined from the condition g2( Z2) = - g/3 in dependence on the field B evidently, while for B < B t2 is nearly constant (or rises very slowly), for B > Be it grows dramatically. This result, as well as the characteristic variation of with B (cf. Figs. 27(a-c)), may be explained, at least phenomenologically, if the motion of a polymer chain through the host matrix is considered as consisting of (i) nearly free drift from one obstacle to another, and (ii) a period of trapping, r, of the molecule at the next obstacle. If the mean distance between obstacles is denoted by ( and the time needed by the chain to travel this distance is /, then - (/ t + /), whereby from Eq. (57) / = /Vq — k T/ DqBN). This gives a somewhat better approximation for the drift velocity... 

The response of humans to var> ing doses of radiation is a field tlmt has been widely studied. The obscr ed radiation effects can be categorized as stochastic or nonstochastic effects, depending upon tlie dose received and tlie time period over which such dose was received. Contrary to most biological effects, effects from radiation usually fall under tlie category of stochastic effects. The nonstochastic effects can be noted as having three qualities a minimum dose or tlucshold dose must be rcceii ed before the particular effect is obsen ed the magnitude of the effect increases as the size of the dose increases and a clear, casual relationship can be determined between the dose and the subsequent effects. 

Shorter chain dienes have an increased propensity to form stable five-, six-, and seven-membered rings. This thermodynamically controlled phenomenon is known as the Thorpe-Ingold effect.15 Since ADMET polymerization is performed over extended time periods under equilibrium conditions, it is ultimately thermodynamics rather than kinetics that determine the choice between a selected diene monomer undergoing either polycondensation or cyclization. 

Toxicity Test (Bioassay). Organisms representative of those to be protected are exposed to the test water under rigorously controlled conditions, usually in a laboratory environment. In this test the organisms, normally fish, are exposed for a standard time period in aquaria to various dilutions of waste or river water while some physiological parameter is carefully monitored to determine fish response. Behavior is also observed. 

In order to investigate the kinetics, heat of reaction and other aspects of the system, the RCl reaction calorimeter was employed. This system allows to perform the reaction in a 2 liters glass reactor, while controlling the reactor and jacket temperatures. Following the reaction, the heat released at any time period can be determined. The operation and application of this system has been discussed in numerous publications (refs. 5,6). 

How then are these ions/decompositions chosen Before considering this we must define, very carefully, the requirements of the analysis to be carried out. Is a single compound to be determined or are a number of compounds of interest If a single compound is involved, its mass spectrum and MS-MS spectra can be obtained and scrutinized for any appropriate ions or decompositions. If the requirement is to determine a number of analytes, their chromatographic properties need to be considered. If they are well separated, different ions/decompositions can be monitored for discrete time-periods as each compound elutes, thus obtaining the maximum sensitivity for each analyte. If the analytes are not well separated, this approach may not be possible and it may then be necessary to monitor a number of ions/decompositions for the complete duration of the analysis. If this is the case, the analyst should attempt to find the smallest number of ions/decompositions that give adequate performance for all of the analytes (remember the more ions/decompositions monitored, then the lower the overall sensitivity will be). 

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