Sample Size and Shape

Different factors contribute to the mechanical properties of plant tissue cell turgor, which is one of the most important ones, cell bonding force through middle lamella, cell wall resistance to compression or tensile forces, density of cell packaging, which defines the free spaces with gas or liquid, and some factors, also common to other products, such as sample size and shape, temperature, and strain rate (Vincent, 1994). Depending on the sample properties (mainly turgor and resistance of middle lamella), two failure modes have been described (Pitt, 1992) cell debonding and cell rupture. 

How do sample size and shape, gas pressure and atmosphere, and ignition of the sample affect the results ... 

Several factors influence TGA data. Sample size and shape affect the rate and efficiency of decomposition. Powdered versus solid bulk samples will have different decomposition profiles due to the differing surface areas from which exiting decomposition products can leave the sample and be registered as mass losses. Similarly, the packing of the sample in the pan must be even and reproducible from run to run. Loosely distributed particles will heat more evenly and evolve volatilized products more evenly than mounded or densely packed samples. This can be especially important when looking at determinations of residual solvents, moisture or diffusion controlled losses such as plasticizer in the samples. 

A basic assumption in DSC kinetics is that heat flow relative to the instrumental baseline is proportional to the reaction rate. In the case of temperature scanning experiments the heat capacity of the sample contributes to the heat flow (endothermic), and this is compensated by the use of an appropriate baseline under the exo- or endothermic peak produced by the reaction. It is also assumed that the temperature gradient through the sample and the sample-reference temperature difference are small. Careful control of the sample size and shape, and the operating conditions are necessary in order to justify these assumptions. 

In order to obtain reproducible results and characteristic pyrograms, one must define the optimal experimental parameters, which must then be strictly standardized, as the thermal degradation of a polymer is often sensitive to even minor changes in the pyrolysis conditions. Apart from the cell type, the determining experimental parameters are (1) the pyrolysis temperature and time, (2) the sample size and shape, (3) the nature and velocity of the carrier gas and (4) the chromatographic separation conditions. Let us now consider in greater detail the effect of the above factors on the yield of pyrolysis products and the specificity of pyrolysis. 

Drying methods and conditions, sample size, and shape have been shown to influence various physical characteristics including structure, density, porosity, shrinkage, and rehydration of dried potato products. These are important properties characterizing the texture and the quality of the dried potato product. 

The properties of information apply regardless of sample size and shape. Work and heat exchanges plus time are necessary for producing and processing the macroscopic information. To ascertain p—obtain information about it— the chemist must allow the cyclohexanone vapor to push down on the fluid of a barometer or vice versa. Alternatively, he or she can measure the electrical or thermal conductivity of the gas. Regardless of method, the chemist and apparatus must expend work in order to purchase information about the system. There are heat exchanges between the vapor and measuring devices if the material is not thermally equilibrated beforehand. Even with equilibration, there is friction internal to a barometer and heat dissipation in the... 

In general, chiral resolution by CE is very sensitive and is controlled by a number of parameters. The optimization factors may be categorized into two classes, the independent and dependent. The independent parameters, which are under the direct control of the operator, include the choice of buffer, the pH of the buffer, the ionic strength of the buffer, the type of chiral selector, the applied voltage, the temperature of the capillary, the dimensions of the capillary, the BGE additives and some other parameters. On the other hand, the dependent parameters, which are those that are directly affected by the independent parameters, and are not under the direct control of the operator, are the field strength (V m ), the EOF, the Joule heating, the BGE viscosity, the sample diffusion, the sample mobility, the sample charge, the sample size and shape, the interaction of the sample with the capillary and the BGE, the molar absorptivity and so on. Therefore,... 

The optimum relationship between sample size, detector size and measured energy range is now being paid more attention. The manufacturers now refer to the detector profile . Indeed, current ORTEC catalogues include the PROFILE series of GEM detectors to help buyers select the right detector for their anticipated sample size and shape. 

Methods suitable for hard viscoelastic solids in fiber form require some special attention because of the restrictions imposed by sample size and shape. In particular, the sample shape cannot be chosen to suit the experimenter s convenience often the only dimension which can be adjusted is the length. 

The production of a variety of smaller molecules from some larger original molecules has fostered the use of pyrolysis as a (destmctive) sample preparation technique. As a result, capillary GC, MS, and FTIR spectroscopy may be used routinely for analysis of synthetic polymers, composites and other complex industrial materials. In pyrolysis experiments sample size and shape, homogeneity and contamination are important issues. Generally, 10-50 /u.g of sample is desirable for direct PyGC, and about twice that for direct PyETIR. 

It shows pronounced thermal effects on heating and generally has a more ordered structure than other clay minerals. Figures I and 2 illustrate typical DTA data for kaolinite, halloysite, and montmorillonite. Kaolinite and halloysite lose their hydroxyls between 450 to 600°C. Variations within this range are attributed to differences in entrapped water vapor that is dependent on sample size and shape factors. The loss of hydroxyls from montmo-rillonites in the range of 450 to 650°C is t5q)ical for dioctahedral forms of these minerals. Dehydroxylation is more gradual for trioctahedral forms and can continue to temperatures up to 850°C. 

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