Homogeneous Uniform in composition

Hodgkin, Dorothy Crowfoot, 248 Homarus Americanus, 157 Homogeneous Uniform in composition, 2,4-5... 

Isotropic membranes are t5q)ically homogeneous/uniform in composition and structure. They are divided into three subgroups, namely micropo-rous, dense and electrically charged membranes. Isotropic microporous membranes have evenly distributed pores (Figure 9.10a). Their pore diameters range between 0.01-10 pm and operate by the sieving mechanism. The microporous membranes are mainly prepared by the phase inversion method albeit other methods can be used. Conversely, isotropic dense membranes do not have pores and as a result they tend to be thicker than... 

Another important consideration is the need for good precision. If clays from a single source are not uniform in composition, this approach is not appropriate there will be a large spread in the pottery composition and it will not be possible to distinguish this source from the others. If clays from one source are reasonably homogeneous one must not introduce an artificial spread by using a technique with poor precision. 

A homogeneous mixture is a combination of two (or more) pure substances that is uniform in composition and appearance throughout. Examples of homogeneous mixtures include rubbing alcohol (70% isopropyl alcohol and 30% water) and gasoline (a mixture of hydrocarbons). 

Homogeneous mixtures are uniform in composition and heterogeneous mbdures are not. 

Homogeneous mixtures, sometimes called solutions, are relatively uniform in composition every portion of the mixture is like every other portion. If you dissolve sugar in water and mbc it really well, your mbcture is basically the same no matter where you sample it. 

Mixtures that are uniform in composition are said to be homogeneous. 

Only rarely do we encounter substances in nature in the form of pure elements or compounds. Most of the time we encounter substances that have been mixed together. Usually a mixture is not uniform in composition and is referred to as being heterogeneous. If the mixture is uniform in composition, however, it is called a solution and is referred to as being homogeneous. This chapter is about both heterogeneous and homogeneous mixtures. 

Homogeneity of data. Homogeneous data will be uniform in structure and composition, usually possible to describe with a fixed number of parameters. Homogeneous data is encountered in simple NDT inspection, e.g. quality control in production. Inhomogeneous data will contain various combinations of indications from construction elements, defects and noise sources. An example of inhomogenous data are ultrasonic B-scan images as described in [Hopgood, 1993] or as encountered in the ultrasonic rail-inspection system described later in this paper. 

Although this article is limited to synthetic membranes, excluding all biological stmctures, the topic is stiU large enough to include a wide variety of membranes that differ in chemical and physical composition and in the way they operate. In essence, a membrane is a discrete, thin interface that moderates the permeation of chemical species in contact with it. This interface may be moleculady homogeneous, that is, completely uniform in... 

In a uniaxial tension test to determine the elastic modulus of the composite material, E, the stress and strain states will be assumed to be macroscopically uniform in consonance with the basic presumption that the composite material is macroscopically Isotropic and homogene-ous. However, on a microscopic scSeTBotFTfhe sfre and strain states will be nonuniform. In the uniaxial tension test,... 

The term "pliase" for a pure substance indicates a state of matter - that is, solid, liquid, or gas. For mi. tures, however, a more stringent connotation must be used, since a totally liquid or solid system may contain more dian one phase. A phase is characterized by uniformity or homogeneity die same composition and properties must c. ist tliroughout the pliase region. At most temperatures and pressures, a pure substance normally exists as a single phase. At certain temperatures mid pressures, two or perhaps even dmee phases can coe.xist in equilibrium. 

A critical issue in scaling up a process is the uniformity in deposition rate and material quality. In general, once the deposition rate is constant within 5% over the whole substrate area, the material properties also do not vary much. After fine-tuning the power and gas flow rates, operators still may face in homogeneity issues. These can be caused by local changes in temperature, RF voltage, and gas composition, due to various causes. As an example, it has been reported that improper attachment of the substrate to the grounded electrode results in a local decrease of the deposition rate [150, 151]. 

Some other points worth noting in connection with alloy film composition are The loss in weight from separate sources is a guide to mean composition but not an exact measure because the sources become themselves alloyed. It is often important to determine the composition of the actual specimen on which other characterizing measurements have been made. If there is confidence that the films are reasonably homogeneous, lattice constants determined by X-ray diffraction can be used to examine the uniformity of composition (69), but the change of lattice constant with composition may be inconveniently small. 

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