Test conditions

Electric strength data are meaningful only if the test conditions are adequately defined for example, if d.c. loading is employed the rate of voltage increase should be specified, if pulsed voltages are used the rise time should be specified and if a.c. loading is adopted the frequency and waveform should be specified. 

When testing electric strength there is the risk of flash-over across the specimen surface between the electrodes. This is avoided by making the measurement with the specimen immersed in an insulating liquid, such as transformer oil, which displaces air from the ceramic surface. 

When a homogeneous specimen is subjected to a steadily increasing voltage under well-controlled laboratory conditions, a small current begins to flow which increases to a saturation value. As the voltage is further increased a stage is reached when the current suddenly rises steeply from the saturation value in a time as short as 10—8 s and breakdown occurs. The very short rise time suggests that the breakdown process is electronic in character. 

Intrinsic breakdown is explained as follows. When the field is applied the small number of electrons in thermal equilibrium in the conduction band gain kinetic energy. This energy may be sufficient to ionize constituent ions, thus increasing the number of electrons participating in the process. The result may be an electron avalanche and complete failure. Intrinsic breakdown strengths are typically of the order of 100 M V m 1. 

Inhibitor concentrations vary from a few parts per million in continuous injection applications, to several thousand parts per million in closed systems, to batch treatments of the neat or undiluted inhibitor. Concentrations used influence test conditions and often determine whether or not 

The relationship between additive concentration and corrosion rate raises the question of just what can be accomplished in reducing corrosion. Should complete stifling of corrosion be the goal If some small amount of corrosion is acceptable, is this then in the form of increased pitting, compared to the untreated system, thus making the situation worse than without the inhibitor This consideration is particularly important when working with anodic-type inhibitors such as chromate. 

Before undertaking a program of evaluating inhibitors for effectiveness in mitigating corrosion, one must review the overall problem and determine what is required of the inhibitor, that is, exactly what parameters are to be tested and what factors affect test results. These questions and their answers will help in obtaining meaningful data for selection of the most efficient inhibitor in the environment of interest. The first step is to select the critical environmental conditions of interest and to incorporate them in the test. 

If the corrosion problem is stress cracking, it is of little value to design a test that mainly involves general corrosion. Unfortunately, many tests consider only the overall loss of metal, a measure of uniform corrosion, and attempt to read into the data information that cannot be or is not measured. 

In designing a laboratory test, it is important to simulate physical field conditions and to select cor-rodent(s) important to the field conditions. Some important corrodents dissolved in aqueous systems are listed below (in some cases, combinations of these will be common)  

Dose Levels and Frequency of Exposure In chronic toxicity studies, it is desirable to have a dose-response relationship as well as a no-observed-toxic-effect level (NOEL). Therefore, at least three dose levels should be used in addition to the concurrent control group. The highest-dose level should elicit some signs of toxicity without causing excessive lethality. The low dose should produce signs of toxicity. For a diet mixture, the highest concentration should not exceed 5% with the exception of nutrients. 

Frequency of exposure is normally daily, but may vary according to the route chosen. If the chemical is administered in the drinking water or mixed in the diet, it should be continuously available. The frequency of administration may be adjusted according to the toxicokinetic profile of the test chemical. 

The effect of botanical products on the expression of drug-metabolizing enzymes or transport proteins can be examined in cell culture with established cell lines or primary human hepatocytes. The cells are incubated under 

Standard conditions and treated with the blank, positive, or negative controls and the botanical extracts. Vehicle use should be consistent in all cultures. Multiple time points should examine the immediate and prolonged effect of these treatments. After treatment, total RNA and/or microsomes are prepared from the harvested cells using standard methodologies. 

All assays should be performed under reduced or F40 gold fluorescence lighting to minimize the potential for photodecomposition or activation. Assays are run in triplicate to determine percent inhibition. The tests are repeated at least once with a freshly prepared sample. If there is greater than 15% coefflciency of variation, the samples are run at least one additional time. When the reaction mixture is incubated within the plate reader, readings are taken immediately and at set times throughout the prescribed incubation period as established by the microsome supplier. For assays incubated outside of the plate reader, reactions were stopped in accordance with the product test procedure. 

In studies where either intrinsic fluorescence or quenching is a confounding variable, the botanical product should be examined in an assay using a chromatographic separation step with a representative probe substance for the isozyme (29) being examined. 

The number of fresh varieties, dosage forms, and formulations in combination with the variability in botanical material make it impossible to evaluate all of these products in animal models or clinical trials. As a minimum, several products used by the patient community should be obtained and authenticated. The testing and selection criteria should include multiple-lot testing, cost, and product availability, and take into consideration how these products are used. Drug combinations are being examined 

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The radiation and temperature dependent mechanical properties of viscoelastic materials (modulus and loss) are of great interest throughout the plastics, polymer, and rubber from initial design to routine production. There are a number of laboratory research instruments are available to determine these properties. All these hardness tests conducted on polymeric materials involve the penetration of the sample under consideration by loaded spheres or other geometric shapes [1]. Most of these tests are to some extent arbitrary because the penetration of an indenter into viscoelastic material increases with time. For example, standard durometer test (the "Shore A") is widely used to measure the static "hardness" or resistance to indentation. However, it does not measure basic material properties, and its results depend on the specimen geometry (it is difficult to make available the identity of the initial position of the devices on cylinder or spherical surfaces while measuring) and test conditions, and some arbitrary time must be selected to compare different materials. 

Szydiik W Economic - technical test conditions presented hy CJD and RTG for welded joints. Materials of the 21 st. National Conference on Non-destroying methods, Szczyrk 1992, p. 127-132. 

Under testing conditions the fuel element to be tested is placed at the stand. Then it is moved into the control unit and gripped with a collet. First the density distribution of the vibro-compacted fuel along the total length of the fuel element is tested. Proceeding from the obtained data the section to be investigated in detail is chosen and a tomogramm of this section is obtained. 

Because of the diversity of the used equipment for the evaluation of parameters setting, we can ask about the testing conditions allowing a reproducibility of the results and the obtaining... 

This work allows the optimization of the testing conditions in order to minimize human error in the inteipretation and obtaining of an reproducible and clear anomaly spectrum. 

The autoignition temperature is the minimum temperature required for self-sustained combustion in the absence of an external ignition source. The value depends on specified test conditions. Tht flammable (explosive) limits specify the range of concentration of the vapor in air (in percent by volume) for which a flame can propagate. Below the lower flammable limit, the gas mixture is too lean to burn above the flammable limit, the mixture is too rich. Additional compounds can be found in National Fire Protection Association, National Fire Protection Handbook, 14th ed., 1991. 

Standard Test MethodforDeterminingFormaldehjdeEevels from Wood Products Under Defined Test Conditions Using aEarge Chamber ASTM E1333-90, American Society for Testing and Materials, Philadelphia, Pa., 1990. 

Design operating efficiencies of fans under test conditions are ia the range of 40—80%. Actual efficiency can be affected appreciably by the arrangement of inlet and outiet duct connections. 

Smoke, Flash, and Fire Points. These thermal properties may be determined under standard test conditions (57). The smoke poiat is defined as the temperature at which smoke begias to evolve continuously from the sample. Flash poiat is the temperature at which a flash is observed whea a test flame is appHed. The fire poiat is defiaed as the temperature at which the fire coatiaues to bum. These values are profouadly affected by minor coastitueats ia the oil, such as fatty acids, moao- and diglycerides, and residual solvents. These factors are of commercial importance where fats or oils are used at high temperatures such as ia lubricants or edible frying fats. 

Toxicity. The products of combustioa have beea studied for a number of plastic foams (257). As with other organics the primary products of combustion are most often carbon monoxide and carbon dioxide with smaller amounts of many other species depending on product composition and test conditions. 

The agar [9002-18-0] plate method consists of adding a known quantity of sample, usually 1.0 or 0.1 mL, depending on the concentration of bacteria, to a sterile petti plate and then mixing the sample with a sterile nutrient medium. After the agar medium solidifies, the petti plate is incubated at 32°C for 48 hours after which the bacterial colonies are counted and the number expressed ia terms of a 1 mL or 1 g sample. This procedure measures the number of viable organisms present and able to grow under test conditions, ie, 32°C. 

Tests using a constant stress (constant load) normally by direct tension have been described in ISO 6252 (262). This test takes the specimen to failure, or a minimum time without failure, and frequently has a flaw (drilled hole or notch) to act as a stress concentrator to target the area of failure. This type of testing, as well as the constant strain techniques, requires careful control of specimen preparation and test conditions to achieve consistent results (263,264). 

Piston Cylinder (Extrusion). Pressure-driven piston cylinder capillary viscometers, ie, extmsion rheometers (Fig. 25), are used primarily to measure the melt viscosity of polymers and other viscous materials (21,47,49,50). A reservoir is connected to a capillary tube, and molten polymer or another material is extmded through the capillary by means of a piston to which a constant force is appHed. Viscosity can be determined from the volumetric flow rate and the pressure drop along the capillary. The basic method and test conditions for a number of thermoplastics are described in ASTM D1238. Melt viscoelasticity can influence the results (160). 

Indicators can determine if uniform steam penetration has been achieved during a Bowie Dick-type test. Produced in the form of sheets (23 X 30 cm), chemical indicators are capable of uniform color change over their entire surface when exposed to pure saturated steam under test conditions. Nonuniform color development is an indication of failure of the test. U.S. and international stands for the performance and accuracy of chemical indicators have been pubHshed (13,14). 

Tire cords are characterized for their physical, adhesion, and fatigue properties for use in tires. These characterizations are conducted under normal and varying test conditions to predict their performance during tire operation. Various test methods used to characterize tire cords are described. 

Short-term repeated exposures involve consecutive daily exposures to the test chemical which are continued over a period of a few days to a few weeks but usually not more than 5% of the lifespan of the animal. These test conditions are sometimes referred to as subacute, but this is a misleading term which should be avoided in order to prevent confusion between single and repetitive exposure toxicity. 

If the experiment is conducted in stages, precautions must be taken to ensure that possible differences between the stages do not invaUdate the results. Appropriate procedures to compare the stages must be included, both in the test plan and in the statistical analysis. For example, some standard test conditions, known as controls, may be included in each stage of the experiment. 

An additional advantage of biU factorial and fractional factorial designs is that by providing a comprehensive scanning of the experimental region they can often identify, without any further analyses, one or two test conditions that are better than any others. The region around these conditions can then be explored further in subsequent experimentation. 

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