Physical combinations

In the design of preceramic polymers, achievement of the desired elemental composition in the ceramic obtained from them (SiC and Si3N4 in the present cases) is a major problem. For instance, in the case of polymers aimed at the production of SiC on pyrolysis, it is more usual than not to obtain solid residues after pyrolysis which, in addition to SiC, contain an excess either of free carbon or free silicon. In order to get close to the desired elemental composition, two approaches have been found useful in our research (1) The use of two comonomers in the appropriate ratio in preparation of the polymer, and (2) the use of chemical or physical combinations of two different polymers in the appropriate ratio. 

A combination vaccine consists of two or more separate immunogens physically combined in a single preparation. A combination vaccine gives protection from more than one disease. 

Fig. 14.2 Nanobiocatalysis publications by subject area (1995-2009). Physics (combined) physics, apphed physics, condensed matter, Materials science (combined) materials science, multidisciplinary materials science, biomateiials, Biochemistry (combined) biochemistry molecular biology biochemical research methods, Medicine pharmacology (combined) pharmacology pharmacy engineering, biomedical medicine, research experimental chemistry, medicinal...

Polybrominated Diphenyl Ethers. PBDEs are used as additive flame retardants in thermoplastics. Additive flame retardants are physically combined with the polymer material being treated rather than chemically combined (as in reactive flame retardants). This means that there is a possibility that the flame retardant may diffuse out of the treated material to some extent. 

Radiopharmaceutical kit reactants, and inactive ingredients, which chemically or physically combine with active ingredients to facilitate drug transport, are considered as inactive ingredients for the purposes of the database. 

Pretazettine (395) has been the subject of numerous biological studies, and it has been shown to exhibit a number of interesting activities (96,97,101,178-187). For example, 395 was found to inhibit HeLa cell growth as well as protein synthesis in eukaryotic cells by interfering with the peptide bond formation step (97,101). Furthermore, pretazettine inhibited the purified RNA-dependent DNA polymerase (reverse transcriptase) from avian myeloblastosis virus, a typical C-type virus (178), in an unusual fashion since it physically combined with the polymerase enzyme itself rather than interacted with the nucleic acid template. Pretazettine also exhibited antiviral activity against the Rauscher leukemia virus in mouse embryo cell cultures by suppressing viral replication (179). 

All matter can be classified into two groups mixtures and pure substances. A mixture is a physical combination of two or more kinds of matter. For example, soil is a mixture of sand, clay, silt, and decomposed leaves and animal bodies. If you look at soil under a magnifying glass, you can see these different components. Figure 1.11 shows another way to see the components of soil. 

Which of these chemicals can you mix together without producing a chemical change In your notebook, record as many of these physical combinations as you can. 

Mixing and compounding are used synonymously to describe the action of physically combining a number of different materials into one. 

Two or more substances—elements, compounds, or both—can combine physically to produce a mixture. A mixture can be separated into its components by physical means. Mixtures are physical combinations of substances that have properties related to those of their components but that do not have definite compositions. They can be either heten eneons or homc eneons mixtures. In heterogeneous mixtures, two or more different types of matter can be seen to be present with the naked eye or a good optical microscope. Homogeneous mixtures, also called solutions, look alike throughout, even under a microscope. 

Matter includes every material thing in the universe. To be able to understand such a wide variety of items, we must classify matter. Matter is divided into pure substances and mixtures. Pure substances may be elements or compounds. Mixtures may be either heterogeneous or homogeneous. Elements are the fundamental building blocks of matter and cannot be broken down to simpler substances by chemical or physical means. Compounds are chemical combinations of elements they have their own sets of properties and have definite compositions. A physical combination of substances results in a mixture, whose components retain most of their properties. Mixtures do not have definite compositions. Homogeneous mixtures, called solutions, look alike throughout, but some parts of a heterogeneous mixture can be seen to be different from other parts. (Section 1.1)... 

Whereas a compound is made from the chemical combination of two or more substances, a mixture is made from two or more substances that are physically combined. You don t need a chemical reaction to make a mixture, nor do you need one to separate a mixture. If you had a handful of copper coins and a handful of silver coins, and you mixed them together in a purse, you would have a mixture. Notice that, unlike in the example of compounds, the substances that make up a mixture do not lose their individual properties. The copper coins don t stop being copper coins just because they are physically combined with silver ones. 

There are many different types of mixtures, but they all have these common characteristics They represent physical combinations of two or more substances. The individual substances in a mixture do not lose their original properties, and the substances in a mixture can be separated by physical means. Another characteristic that all mixtures share is that their composition is variable. By this I mean that the substances that are found in the mixture can be mixed in with varying proportions or concentrations. If you mixed in five silver coins and three copper coins, or four silver coins and seven copper coins, you still end up with a mixture of copper and silver coins. 

D. NaCl(aq)]—The (aq) indicates that the salt has been dissolved in water, making it a mixture of two or more substances physically combined. 

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