Homogeneous material

Often in stress analysis we may be required to make simplified assumptions, and as a result, uneertainties or loss of aeeuraey are introdueed (Bury, 1975). The aeeuraey of ealeulation deereases as the eomplexity inereases from the simple ease, but ultimately the eomponent part will still break at its weakest seetion. Theoretieal failure formulae are devised under assumptions of ideal material homogeneity and isotropie behaviour. Homogeneous means that the materials properties are uniform throughout isotropie means that the material properties are independent of orientation or direetion. Only in the simplest of eases ean they furnish us with the eomplete solution of the stress distribution problem. In the majority of eases, engineers have to use approximate solutions and any of the real situations that arise are so eomplieated that they eannot be fully represented by a single mathematieal model (Gordon, 1991). 

For most of the methods mentioned above the method uncertainty - important for the expression of material homogeneity, better inhomogeneity - is influenced by different analytical steps such as digestion, and/or extraction, derivatization, separation etc., that are often required to achieve the final result. This consequently increases the method uncertainty. 

Becker DA (1993) Unique quality assurance aspects of INAA for reference material homogeneity and certification. Fresenius J Anal Chem 345 298-301. 

CO2 [67]. Early work examining the free-radical telomerization of TFE in supercritical C02 took advantage of the high solubility of the low molecular weight perfluoroalkyl iodides products to prepare these materials homogeneously [77]. In these reactions, we utilized perfluorobutyl iodide as the telogen... 

Homogeneity. The degree to which a property or substance is randomly distributed throughout a material. Homogeneity depends on the size of the units under consideration. Thus a mixture of two minerals may be inhomogeneous at the molecular or atomic level but homogeneous at the particulate level. 

The ultrasound-assisted extraction of freeze-dried plant-based materials normally takes 2 hr. If the extract is evaporated to dryness, a total of 3 hr is necessary. As an additional sample preparation step, 2 to 4 days should be allotted for freeze-drying fresh plant materials, depending on the quantity of the material. Homogenizer-assisted extraction of fresh fruit takes <4 hr. 

Direct comparison with certified reference materials Homogeneity testing results A primary method of chemical measurement Consensus value from expert laboratories Consensus of participants... 

For tabletted materials, homogenization is more problematic since if the tablet was homogenized, it would also be destroyed. For this reason, a sample is taken from the tablet and gently scraped from the dose form, away from any ballistic features which are likely to be of use in subsequent examinations. The powder is then thoroughly homogenized prior to testing. 

Alloy means a metallic material, homogeneous on a macroscopic scale, consisting of two or more elements so combined that they cannot be readily separated by mechanical means. Alloys are considered to be mixtures for the purpose of classification under the GHS ... 

Is the density/porosity convenient for the final use What is the optimum processing temperature Is the material homogeneous What are the differences between the skin and the bulk Where are the second phases located ... 

If, in the first instance, the plasma membrane is considered to be a strip of lipoidal material, homogeneous in nature and with a defined thickness, one must assume that only lipid-soluble agents will pass across this barrier. As most dmgs are weak electrolytes it is to be expected that the unionised form (U) of either acids or bases, the lipid-soluble species, will diffuse across the membrane, while the ionised forms (1) will be rejected. This is the basis of the pH-partition hypothesis in which the pH dependence of drug absorption and solute transport across membranes is considered. The equations of Chapters 3 and 5 are relevant here. 

Material homogeneous and well established to be used for the calibration of an... 

Note that the molar concentration values are relevant to decision levels where accurate measurement is crucial for medical decision. The category of synthetic-type reference material sera needs to be certified by means of primary methods. According to international regulations [6], the methods of certification of the clinical reference materials followed several steps regarding the preparation of the material, homogeneity testing, performance of interlaboratory analyses, assignment of the certified value and uncertainty. 

In all cases the laboratory or the group of laboratories which test the method benefit from the high quality of the material (homogeneity, stability, representativeness as described in Chapter 4 on production of CRMs) but also may benefit from the uncertainty of the certified value. Such a test should be done for all standardised methods before they are accepted and published. 

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