Screening Criteria

Since it is virtually impossible to observe molecular-level events directly, how can we know whether a given reaction is elementary The answer is that we never can know with absolute certainty. However, we can make some reasonable judgments based on rules of simplicity. 

Above all, a single-step, molecular-level event must he simple. It must involve a small number of molecules, preferably only one or two, and it must involve the breaking and/or forming of a relatively small number of bonds, preferably only one or two. If too many molecules and/or too many bonds are involved, then the reaction probably will occur as a series of simpler elementary reactions, rather than as a single, molecular-level event. 

Elementary reactions cannot involve fractional molecules. We may choose to write a balanced stoichiometric equation so that it contains fractional molecules, e.g., 

at the molecular level, there is no such thing as half of a N2 molecule or half of a H2 molecule. Therefore, the above reaction, which describes the stoichiometry of the commercial synthesis of ammonia, cannot he elementary as written. 

Is it reasonable to suppose that the reaction now is elementary as written To answer this question, the mles of simplicity must he applied. The reaction as written requires a four-body collision, where one molecule of N2 and three of H2 colhde simultaneously. This is extremely unlikely. Moreover, in order for the reaction to he elementary as written, one N-N bond and three H-H bonds would have to he broken and six N-H bonds would have to he formed, simultaneously, in a single, molecular-level event This also is radtemely unlitely. Both criteria, the molecularity of the event, i.e., the number of molecules colliding, and the number of bonds being broken and formed, lead to the conclusion diat the reaction, as written, is not elementary. 

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With unlimited resources, the investor would take on all projects which meet the screening criteria. Project ranking is necessary to optimise the business when the investor s resources are limited and there are two or more projects to choose between. 

Potential vibration problems of this type should be considered early in the design stage of the flare header system. The following screening criteria have been developed to assist the designer in recognizing services with potential vibration problems requiring further detail evaluation ... 

A distinction must be made regarding the length of service of the pressure reducing systems. Fatigue failure of any mechanical system depends on time, i.e., the number of cycles to failure. Therefore, the treatment required for a continuous service may not be justified for a short term service. A System in short term service is defined as one which operates a total of 12 hours or less during the life of the plant. Pressure relief valves typically meet this limit. Systems in short term service exceeding the screening criteria indicated above should be evaluated. 

Taber J.J., Martin F.D., et al. EOR screening criteria revisited-Partl introduction to screening criteria and enhanced recovery field projects. 1997 SPEReservoir Engineering 12(3) 189-198. 

KovscekA.R. Screening criteria for C02 storage in oil reservoirs. 2002 Petroleum Science Technologies 20(7/8) 841-866. 

In addition to desulfurization activity, several other parameters are important in selecting the right biocatalyst for a commercial BDS application. These include solvent tolerance, substrate specificity, complete conversion to a desulfurized product (as opposed to initial consumption/removal of a sulfur substrate), catalyst stability, biosurfactant production, cell growth rate (for biocatalyst production), impact of final desulfurized oil product on separation, biocatalyst separation from oil phase (for recycle), and finally, ability to regenerate the biocatalyst. Very few studies have addressed these issues and their impact on a process in detail [155,160], even though these seem to be very important from a commercialization point of view. While parameters such as activity in solvent or oil phase and substrate specificity have been studied for biocatalysts, these have not been used as screening criteria for identifying better biocatalysts. 

We have found that one excellent way to make the translation tangible is to establish what we call screening criteria. Working with a... 

In all our studies, we were concerned about possible bad trips as well as the more remote likelihood of uncovering a latent psychosis. When testing LSD, we took special pains to ensure a favorable set and setting and selected only volunteers who met the most stringent screening criteria for psychological stability. Nevertheless, some form of hostile behavior surfaced in 20% of subjects given doses above 2.0 mcg/kg (i.e., about 150 meg). Most lower dose LSD tests, however, turned out to be relatively calm and uneventful. 

Another thing I was interested in was the incapacitating dose of atropine itself historically the natural mother of all belladonnoids. We did not have sufficient data on atropine to make precise comparisons with the synthetic belladonnoids. We tiierefore put on the schedule several volunteers who met all the screening criteria. 

Flexural strength and flexural modulus are being used as the screening criteria for a new ADA specification 27 which adopts the new ISO standards. The minimum flexural strength required will be 50 MPa. In addition, the criterion makes it mandatory that the flexural strength must exceed a value, N, based on the flexural modulus, where N = (flexural modulus 0.0025) + 40. This stipulation will require higher flexural moduli from the stiffer composites like the conventional, small particle and hybrid systems. 

Screening criteria are developed from job analyses. Job analyses are systematic reviews of the requirements of a job (Donnelly, Gibson, and Ivancevich, 1995). Job analyses attempt to identify some of the following aspects of a job ... 

Screening criteria for Usually loose Usually specific and strict dependent... 

Waste Control Limit Screening Criteria for Off-site Management of Chemical Agent Disposal Facility Secondary Waste, 39... 

The objectives of this test pattern is to analytically resolve these problems into three manageable segments. The first task will be to define the viscoelastic kinetic properties of a material as a function of various reaction temperatures. These properties (viscosity, viscous modulus, elastic modulus, tan delta) define the rate of change in the polymers overall reaction "character" as it will relate to article flow consolidation, phase separation particle distribution, bond line thickness and gas-liquid transport mechanics. These are the properties primarily responsible for consistent production behavior and structural properties. This test is also utilized as a quality assurance technique for incoming materials. The reaction rates are an excellent screening criteria to ensure the polymer system is "behaviorally" identical to its predecessor. The second objective is to allow modeling for effects of process variables. This will allow the material to undergo environmental... 

Another increasingly important strategy for the pharmaceutical industry is assessing whether a new product s therapeutic category is on the MCO s radar screen . Criteria for inclusion of a product s therapeutic category on an MCO s radar screen include the following ... 

Sevilla O, Wagner N, Anderson W et al. Sensitivity of a set of myocardial infarction screening criteria in patients with anatomically documented single and multiple infarcts. Am J Cardiol 1990 66 792-5. 

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