Preparative history

A comparison of the dynamic mechanical properties of our HB at 35 Hz has been made to that of LDPE in Figures 14 A and B. The thermal and sample preparative history affects the mechanical properties of HB films to such an extent that in order to make a meaningful comparison one has to describe the exact history of the samples. Such a thermal history dependence has been examined for LDPE(54,57) and recently for HB.(12) Shown in Figures A and B are the mechanical spectra for HB-PQ, HB-Tol, and LDPE-PQ films. The compression molded films were prepared 1 to 2 days prior to the test. The solution cast film (from toluene), HB-Tol, was annealed at 80°C for 2-3 days and stored at room temperature for 1 week... 

In model systems for bilayers, one typically considers systems which are composed of one type of phospholipid. In these systems, vesicles very often are observed. The size of vesicles may depend on their preparation history, and can vary from approximately 50 nm (small unilamellar vesicles or SUVs) up to many pm (large unilamellar or LUV). Also one may find multilamellar vesicular structures with more, and often many more than, one bilayer separating the inside from the outside. Indeed, usually it is necessary to follow special recipes to obtain unilamellar vesicles. A systematic way to produce such vesicles is to expose the systems to a series of freeze-thaw cycles [20]. In this process, the vesicles are repeatedly broken into fragments when they are deeply frozen to liquid nitrogen temperatures, but reseal to closed vesicles upon thawing. This procedure helps the equilibration process and, because well-defined vesicles form, it is now believed that such vesicles represent (close to) equilibrium structures. If this is the case then we need to understand the physics of thermodynamically stable vesicles. 

Timing of occurrences Location of personnel Environmental conditions Positions of personnel and victims Anything moved/repositioned Emergency response activities Indicators of conditions Actions of other people Training and preparation Histories of similar incidents Information gaps Inconsistencies in data Management and staff involvement Possible causal areas... 

The precursor used to create the 3-APTHS solutions was 3-aminopropyl-triethoxysilane (3-APTES). Commercial 3-APTES obtained from Huls Petrarch Systems Inc. was twice vacuum-distilled. Individual ampules were filled with the distilled precursor and sealed for later use. Triply-distilled HPLC grade water was used to prepare the 3-APTHS solutions used for sample treatment. For isotopically labelled 3-APTHS studies, we used 99 atom % 15N labelled 3-APTES, and 97.8 atom % l80 labelled water. Both compounds were obtained from MSD Isotopes [12]. The substrates used were polished Si wafers 1.5 cm in diameter. The Cr was sputter-deposited to a thickness of 1000 A onto one half of the Si wafer so that both the Si and Cr surfaces had identical preparation histories up to and including the analysis for every sample prepared. 

To avoid complications by impurities, pure samples of artificial graphite are used whose preparation, history, analysis, and gas and surface oxide contents are accurately known. <... 

Nitrogen clathrate in j3-quinol was studied by Scott28) in spite of many experimental difficulties. Among the findings obtained in this study, we may mention the existence of a seven-line spectrum whose intensity depends upon the preparation, history and age of the sample a slow loss of nitrogen by the sample the fact that the line frequencies are independent of the factors which alter line intensities and that the structure may be due to a partial filling of the (3-quinol lattice holes. 

Clarke and co-workers studied the effect of chain configurational properties on the stress—strain behavior of glassy linear polymers. They examined the relationship between chain structure and strain hardening by employing controlled stress molecular dynamics on a polyethylenelike chain. Variation of the sample preparation history produces chemically identical materials with vastly different responses to applied stress. 

Somew hat similar results were obtained for saran char under near-isothermal conditions in oxygen. The sample temperature was increased at bOK/min to 435°C and then held there. The sample mass actually began to decrease prior to attaining isothermal conditions. This illustrates the difficulty of resolving the porosity development history under isothermal conditions where the burn-off behavior typically varies widely with the nature and preparation history of the sample. Nonisothermal temperature programs appear to be more efficient in this regard. 

The active centers proposed by Taylor (1) are believed to be lattice imperfections of the solid surface. The concentration and variety of the lattice imperfections will be governed both by the physical and chemical structures of the catalyst surface and by the preparative history of the surface concerned. 

The reduction of tungsten oxides by carbon or carbon-containing compoimds can be easily performed. Statements about the starting temperature for the reaction between WO3 and solid carbon (carbon blacks, graphite) vary in the current literature between 655 °C and 783 °C. Differences in WO3 and C properties (particle size of the powders, preparation history, crystallinity, etc.) as well as in atmospheres may be responsible for that. The temperature range coincides with the begirming of self-conductivity and sublimation of WO3. Carbon monoxide starts to react witii WO3 at 535 °C (reduction pressure 1 bar, PcoJPco equilibrium ratio 8.52) [3.45]. 

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