Characteristics of screens

The terminology involved in screen design and evaluation and the characteristics of a screen should be clearly stated and imderstood. The characteristics of screen performance are defined as follows  

Later we will contrast some of these characteristics with key elements of study design. 

These characteristics may be optimized for a particular use, if we also consider both the mathematics and the errors underlying them. 

A brief review of the basic relationships between error types and statistical power starts with considering each of five interacting factors [3-5] that serve to determine power and define competing error rates. 

the probability of our committing a type II error (a false negative) 

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Efficiency and capacity oppose each other, and in order to obtain maximum efficiency the capacity must be small. A large capacity is achievable only at the expense of a reduction in efficiency. In practice, a reasonable balance between capacity and effectiveness is struck. Although accurate correlations are not obtainable for judging or calculating these operating characteristics of screens, certain principles apply, and these can be used as guidelines in grasping the basic features of screen performance. 

An excellent introduction to the characteristics of screens is Redman s (1981) interesting approach, which identifies four characteristics of an assay. Redman assumes that a compound is either active or inactive and that the proportion of... 

Useful information about the characteristics of screening tests can be obtained by development of the characteristic operating curve (32). In this technique, a panel of test samples is produced by fortifying control matrix at several levels with the analyte of interest. The test is run on each sample witli 15-20 replicates at each concentration level. For rapid screening tests this should not represent an undue analytical burden. The results are plotted as the percentage of samples that are positive at each concentration level. 

Cady, E.C., 1977. Effect of transient liquid flow on retention characteristics of screen acquisition systems -final report. NASA-CR-135218. 

Tegart, J.R., Aydelott, J.C., 1978. Effect of vibration on retention characteristics of screen acquisition systems. In AIAA-78-1030, 14th Joint Propulsion Conference, Las Vegas, NV, July 25-27. 

The Pr EN 12668-1 concerns the verification of characteristics of ultrasonic flaw detector. It is mainly applicable to portable equipment incorporating Ascan visualisation on screen, and which bandwidth is comprised between 0,5 and 15 Mhz. The project describes three levels of verification ... 

With the reference block method the distance law of a model reflector is established experimentally prior to each ultrasonic test. The reference reflectors, mostly bore holes, are drilled into the reference block at different distances, e.g. ASME block. Prior to the test, the reference reflectors are scanned, and their maximised echo amplitudes are marked on the screen of the flaw detector. Finally all amplitude points are connected by a curve. This Distance Amplitude Curve (DAC) serves as the registration level and exactly shows the amplitude-over-distance behaviour" of the reference reflector for the probe in use. Also the individual characteristics of the material are automatically considered. However, this curve may only be applied for defect evaluation, in case the reference block and the test object are made of the same material and have undergone the same heat treatment. As with the DGS-Method, the value of any defect evaluation does not consider the shape and orientation of the defect. The reference block method is safe and easy to apply, and the operator need not to have a deep understanding about the theory of distance laws. 

Suspended Solids Removal. Depending on the concentration and characteristics of the suspended soflds, they can be removed by filtration, flotation, or sedimentation. Coarse soflds are removed by screening. Settleable suspended soflds are removed in a clarifier, which may be circular or rectangular. The efficiency of soflds removal is a function of the overflow rate (m /-d (gal/ft -d) as shown in Figure 5. 

Bosch and co-workers devised laboratory reactors to operate at high pressure and temperature in a recycle mode. These test reactors had the essential characteristics of potential industrial reactors and were used by Mittasch and co-workers to screen some 20,000 samples as candidate catalysts. The results led to the identification of an iron-containing mineral that is similar to today s industrial catalysts. The researchers recognized the need for porous catalytic materials and materials with more than one component, today identified as the support, the catalyticaHy active component, and the promoter. Today s technology for catalyst testing has become more efficient because much of the test equipment is automated, and the analysis of products and catalysts is much faster and more accurate. 

Characteristics of Size Classifiers (See Sec. 19 Screening on screening equipment and Wet Classification on wet classifiers.) Types of classifiers and commercially available equipment are de-... 

Coke The grinding characteristics of coke vary widely. Byproduct coke is hard and abrasive, while certain foundry and retort coke is extremely hard to grind. For certain purposes it may be necessary to produce a uniform granule with minimum fines. This is best accomplished in rod or bah mihs in closed circuit with screens. Hourly capacity of a 1.2- by 3-m (4- by 10-ft) rod mill with screens, operating on by-product-coke breeze, was 8.1 Mg (9 tons), 100 percent through No. 10 sieve, and 73 percent on No. 200 sieve power requirement, 30kW(40 hp). 

Biosensors ai e widely used to the detection of hazardous contaminants in foodstuffs, soil and fresh waters. Due to high sensitivity, simple design, low cost and real-time measurement mode biosensors ai e considered as an alternative to conventional analytical techniques, e.g. GC or HPLC. Although the sensitivity and selectivity of contaminant detection is mainly determined by a biological component, i.e. enzyme or antibodies, the biosensor performance can be efficiently controlled by the optimization of its assembly and working conditions. In this report, the prospects to the improvement of pesticide detection with cholinesterase sensors based on modified screen-printed electrodes are summarized. The following opportunities for the controlled improvement of analytical characteristics of anticholinesterase pesticides ai e discussed ... 

J.J. Lander, R. D. Weaver, A.J. Salkind, J.J. Kelley in Characteristics of Separators for Alkaline Silver Oxide Zinc Secondary Batteries. Screening Methods (Eds. J.E. Cooper, A. Fleischer), NASA Technical Report NAS 5-2860,1964. 

In addition to blood, certain types of specimens are submitted to the Pediatric laboratory which would not be commonly seen elsewhere. An example of this is sweat for analysis of chloride. The process of obtaining the sweat by iontophoresis usually falls to the personnel of the Laboratory of Neonatology (17). Stool for analysis of lipids and trypsin is more commonly submitted to the Laboratory of Neonatology than to the laboratory which services the adult population. The reason for this is that one is screening for certain intestinal diseases characteristic of infants and newborns which are rare in adults. Such conditions would be celiac disease, cystic fibrosis and others. 

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