Molecular probes sound

Sound speed and sound absorption measurements in polymers are useful both as a probe of the molecular structure of polymers and as a source of engineering design properties. As a molecular probe, acoustic properties are related to such structural factors as the glass transition (qv), cross-link density, morphology (qv), and chemical composition. Thus, acoustic measurements can be used as a measure of any of these factors, or at least to monitor changes that may occur as a fimction of time, temperature, pressure, or some other variable. As a source of engineering properties, acoustic measurements are used for applications such as the absorption of unwanted sound and the construction of acoustically transparent windows. 

The identification of both short chain and long chain branches in polyethylene at concentrations of 1 per 10,000 carbon atoms has become feasible with the availability of improved probes and improved computer hardware/ software capabilities. Reviewed in this chapter are the methods and computations as well as the basic requirements for sound quantitative analyses namely, correct choice of solvent, a consideration of concentration effect on line widths and satisfying nuclear Overhauser effects and spin lattice relaxation time requirements. Finally, the NMR generated structural information is put to use in correlations with polyethylene physical properties and measurements of number average molecular weight. 

It is so often stated that water is a ubiquitous liquid on earth and a general solvent for many kinds of solutes that such statements sound as clichds. Nevertheless, they are correct and merit discussion. Other common statements are that the properties of water are unique among liquids and are difficult to understand No one really understands water. It s embarrassing to admit it, but the stuff that covers two-thirds of our planet is still a mystery. Worse, the more we look, the more the problems accumulate new techniques probing deeper into the molecular architecture of liquid water are throwing up more puzzles. (Ball 2008). Unfortunately, to date this situation keeps being rather true and should be accorded a more comprehensive treatment. 

The basic method of these SPMs (Birdi, 2003b Chen, 2008) was essentially to be able to move a tip over the substrate surface with a sensor (probe) with molecular sensitivity (nm) in both longitudinal and vertical directions (Figure 1.53). This may be compared with the act of sensing with a finger over a surface or more akin to the old-fashioned vinyl record player with a metallic needle (a probe for converting mechanical vibrations to music sound). 

The Philae lander carries ten scientific instruments panoramic, stereoscopic and descent camera a-p-x-ray spectrometer evolved gas analyser for elemental, molecular and isotopic composition infrared microscope comet acoustic surface and sounding experiment permittivity probe dust impact monitor multi-purpose sensor for surface and sub-surface science magnetometer plasma monitor comet nucleus sounding experiment drill and sample distribution system. 

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