Property Variables

The mechanical properties and the failure mechanisms of transition-metal carbides are reviewed in detail by Toth.t l Generally, large spreads in the reported values found in the literature are common. This is particularly true in older reports which were mostly performed on sintered materials. More recently, testing has been switched to single crystals or polycrystalline materials obtained from the melt or by thin-film deposition. These are believed to yield more accurate and consistent information. Yet, any test must be carefully characterized in order to be meaningful. The following factors influence mechanical testing.l H  

Transition metal carbides are often processed by sintering with a metal binder such as cobalt and nickel. The mechanical properties of such composites are often quite different from those of single crystal or polycrystalline materials. ) This often adds to the confusion when quoting property values (see Ch. 17). 

The mechanical properties of Group IV carbides are summarized in Table 4.6. The values are average values reported in the recent litera- 

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Timber is derived from a great number of botanical species, and has a wide range of properties. Variability also occurs within a single species and in order to achieve acceptable levels of uniformity, selection by grading is necessary. The timber trade differentiates between softwoods and hardwoods, and the latter are again separated into temperate and tropical types. Hardwoods are derived from broad-leaved and mainly deciduous trees, which are anatomically more complex and differ in chemical composition... 

A quick estimate of the overall column efficiency can be obtained from the correlation given by O Connell (1946), which is shown in Figure 11.13. The overall column efficiency is correlated with the product of the relative volatility of the light key component (relative to the heavy key) and the molar average viscosity of the feed, estimated at the average column temperature. The correlation was based mainly on data obtained with hydrocarbon systems, but includes some values for chlorinated solvents and water-alcohol mixtures. It has been found to give reliable estimates of the overall column efficiency for hydrocarbon systems and can be used to make an approximate estimate of the efficiency for other systems. The method takes no account of the plate design parameters and includes only two physical property variables. 

Continuous distribution functions Some experiments, such as liquid chromatography or mass spectrometry, allow for the determination of continuous or quasi-continuous distribution functions, which are readily obtained by a transition from the discrete property variable X to the continuous variable X and the replacement of the discrete statistical weights g, by the continuous probability density g(X). For simplicity, we assume g(X) as being normalized J ° g(X)dX = 1. Averages and moments of a quantity Y(X) are defined by analogy to the discrete case as... 

It is also apparent that the composite pad properties of interest are affected by a large number of process and structural variables. Interaction effects make analysis of property variability particularly difficult. As a consequence,... 

No single polymer can match all of the above criteria. This has led companies to develop application-specific polymers and/or series of polymers that may have the structure property variability to encompass all potential applications. As listed in Table 3, several properties of the polymer have a direct effect on its degradation kinetics and consequently on the drug release profile. Hence novel polymers that... 

Physical Property Variables. These variables are concerned with the physical properties of materials with the exception of those properties which are related to chemical composition and direct mass and weight. Variables included are density and specific gravity, humidity, moisture content, viscosity, consistency, and structural characteristics, such as hardness, ductility, and lattice structure. 

We should remember that an ordered set of data can be written in the form of a matrix, which in most instances contains the values of measured or known properties (variables, features) listed in columns. The rows of the matrix are then associated with the objects (e.g. samples at different locations or times) under study. 

The pressure profile thus depends on a number of variables geometrical (Ho, Hi, and L), operational (q, Vo), and physical property variables, and the viscosity fi. The maximum pressure that can be attained is = 1 (z = L) at closed discharge condition (q = 0)... 

The removal of residual volatile components from polymers is an operation of some importance in the plastics industry. A generalized, although somewhat idealized, model for continuous, wiped-film devolatilization of viscous polymer melts is presented which relates devolatilization capability to important geometry, < perating, and fluid property variables. The applicability and limitations of the model are analyzed experimentally. The data support many aspects of the theory, but also reveal certain deficiencies in the model which should be considered in designing for maximum efficiency. 

An intensive property (variable, parameter) is one whose value is not additive and does not vary with the quantity of material in the subsystem. For example, temperature, pressure, density (mass per volume), and so on, do not change if the system is sliced in half or if the halves are put together. 

The directional spectral absorptivity is a property (variable of state) of the absorbing gas. Its direction dependence manifests itself in the dependence on the beam length s, through which the radiation passes in the gas. 

Since the property variables are discontinuous across the interface, one may expect either excessive numerical diffusion or problems with oscillations around the jump if no special treatment is used at the front. To avoid these problems local smoothing of the variables across the discontinuous interface is introduced. This is accomplished by use of the smoothed indicator function calculating the fluid properties at each point on the fixed grid by ... 

The results of measured soil property variables for both core locations appear in Figures 1, 2 and 3. Portions of the profiles were not sampled and appear as breaks in the figure columns. 

The influences of sample size and material quality (or property variability) are illustrated in Table 5.3. The property is identified with plane strain fracture toughness (i.e., X( ) = Kjc( ) = 50ksi Vim, with a = 2.5 or 5.0 ksi Vim to reflect two different levels of variability, or manufacturing control). The results show marginal improvements with increasing number of tests to characterize variability in the property data, and substantial improvement in variabihty with quality control. It is recognized that the values shown at the lower numbers of test samples (say, n = 5) are inappropriate, but they do convey the need for a quantitative basis for design and reliability analyses. 

Here the subscript cp refers to the constant property variable, and all temperatures in Eq. 

One of the most important bulk property variables of polymers is the glass transition temperature 7g, which must be well below the use temperature to allow the interdiffusion and entanglement of polymer chains when the particles get in contact, once the aqueous phase has been evaporated. Thus, the monomer(s) used have to be selected such that the desired is obtained. Useful tables showing Tg and other physical and chemical properties of homopolymers are available in the literature [66-68]. The well-known Fox equation [69] can be used to estimate the Tg of a copolymer as a function of monomer composition and TgS of the component monomers. It is important to take into account that polar polymers tend to hydroplasticize, reducing the in the film formation process [70]. Several commercial latexes are terpolymers that contain two of the monomers present in major amounts to grossly obtain the basic desired properties, with the third monomer present in a minor amount for fine tuning of a special property [71-73]. 

Likewise, in continuous polymerizations, the end-use and polymer properties variables may be measured very infrequently, and most often, off-line. In addition, the laboratory analysis time adds a large delay to the measurement Under these circumstances, the measurements are substantially uncorrelated in time, and again, statistical process control may be an appropriate approach to control of polymer quality or end-use properties. If the samples are sufficiently infrequent that the process settles between samples, conventional SPC can be applied. This amounts to manual steady-state ccxitrol with the need for control identified by statistical techniques. If the system does not "settle between samples, more specialized techniques of analysis are available [63]. Good reviews of the applicability of SPC to chemical processes are given by MacGregor [64,65]. 

Figures Ic and Id show no advantage for boron-aluminum over boron-epoxy. There are some cryogenic applications, however, where a high electrical conductivity and a strong, stiff structure are required, e.g., in eddy-current shields in rotating superconducting machinery. The high thermal conductivity of boron-aluminum limits its cryogenic applications. The excellent properties and low property variability observed with boron-epoxy were also observed for boron-6061 aluminum at 4 K [ ].

On the drying gas stream interface, one can specify pressure, one of the three temperature parameters (either dry-bulb temperature, wet-bulb temperature, or dew-point temperature), and one of the two humidity parameters (either absolute humidity or relative humidity) then all the other thermal physical property variables are automatically calculated by Simprosys and displayed on the interface. Whenever one of the flow rate parameters (either mass flow rate wet basis, mass flow rate dry basis, or volume flow rate) is specified and the state of the moist air is determined, the other flow rates are automatically calculated and displayed on the gas stream s interface. 

The structural variability of these materials leads to the appearance of new chemical and physical properties - variable magnetism [1, 2], efficient catalysis, adsorption and high ion-exchange capacity [3]. The use of such nanocomposites promises to improve the mechanical and thermal stability of polymers in which composites have been dispersed [4], and also opens up the possibility for a creation of new optoelectronic devices (stochastic lasers, LEDs, sensors [5-7]), including a variety of diagnostic purposes [8]. Layered materials have potential application in pharmacology and medical science [9],... 

Extensive property (variable) Property (variable) of a system that is proportional to mass. 

The effect of ground loads on pipes can be described by equations that involve the primary geometric and material property variables. Various analytical approaches have been adopted and there has been some disagreement between different national codes. The analyses are usually based on techniques first described by Spangler to calculate deflection of highway culverts. In the UK equations devised by the Transport and Road Research Laboratory (TRRL) [4] have been used. The German and Scandinavian codes have become widely used in Europe but in future it is likely that computer-interpreted... 

The control of the PLA hydrolytic degradation is necessary for medical applications and for the plastics industry. The mechanism of abiotic-hydrolytic degradation as well as the rate of degradation reaction for PLA-based materials seems to be affected by a wide variety of compositional and property variables, as reported in this chapter. Consequently, knowing and understanding all parameters could bring the possibility to control in a certain vray... 

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