Sample low-temperature

For minerals and inorganic samples, low temperature is almost useless to improve structure solution and only marginally relevant to improve the refinement, unless dealing with host-guest materials like zeolites. In facts, for harder materials ambient temperature is already quite comparable and sometimes lower than the Debye temperature. Therefore, resolution is seldom a limitation for structure refinement of minerals at ambient temperature. On the contrary, for macromolecules and especially for proteins, the low temperature significantly increases the number of... 

ESR observations were conducted at 9.5 GHz, using a Varian E-line ESR spectrometer with variable temperature capabilities from 90K-300K. The g value was determined using a Varian pitch standard with a g-value of 2.00302 + 0.00005. The integrated intensity was also calibrated to a Varian pitch standard. The parameters g, AH u, AH-p and the radical density were determined for each sample. Saturation measurements were made on a selected subset of samples. Low temperature runs at 125 K were made for all inertinite samples, as well as for selected samples of the other maceral types. Little temperature variation in g value, linewidth, or lineshape, was seen in any sample. The integrated intensity varied approximately as 1/T, suggesting Boltzmann polarization of the spins at lower temperatures. 

Moreover, in the case of the low level of hydration h = 0.25 the evolution of the density of states as a function of the temperature is less pronounced than in the case of h = 0.5. This is in agreement with the structural study [43] at the lower hydration (h = 0A 75), which only detected small changes when the temperature is lowered from room temperature to 77 K, and with further structural studies of low-hydrated Vycor samples. Low temperatures do not significantly affect the overall structure of the protein and the bound water molecule, and no crystallization of water has been observed. This could reflect the fact that at room temperature the interfacial water behaves like a dense supercooled liquid. 

Fig. h.1-73 AlSb. Thermal conductivity vs. temperature for an n-typeand ap-type sample, low-temperature range [1.69, 70]... 

Rotomolded tanks were treated to irradiation levels of 120, 200 and 280 kilogray and the test results were compared against an un-irradiated control sample. Two test methods, environmental stress crack resistance (ESCR) and low temperature impact were used to determine differences between the samples. Low temperature impact testing was performed at -40 C. ESCR testing used both a 10% and 100% Igepal solution and the comparison used only the 280 kGy sample. This test was performed for a maximum of 1000 hours. The results of these tests are shown in figures 3 and 4. 

Figure C2.17.10. Optical absorjDtion spectra of nanocrystalline CdSe. The spectra of several different samples in the visible and near-UV are measured at low temperature, to minimize the effects of line broadening from lattice vibrations. In these samples, grown as described in [84], the lowest exciton state shifts dramatically to higher energy with decreasing particle size. Higher-lying exciton states are also visible in several of these spectra. For reference, the band gap of bulk CdSe is 1.85 eV.

A similar algorithm has been used to sample the equilibrium distribution [p,(r )] in the conformational optimization of a tetrapeptide[5] and atomic clusters at low temperature.[6] It was found that when g > 1 the search of conformational space was greatly enhanced over standard Metropolis Monte Carlo methods. In this form, the velocity distribution can be thought to be Maxwellian. 

Do we expect this model to be accurate for a dynamics dictated by Tsallis statistics A jump diffusion process that randomly samples the equilibrium canonical Tsallis distribution has been shown to lead to anomalous diffusion and Levy flights in the 5/3 < q < 3 regime. [3] Due to the delocalized nature of the equilibrium distributions, we might find that the microstates of our master equation are not well defined. Even at low temperatures, it may be difficult to identify distinct microstates of the system. The same delocalization can lead to large transition probabilities for states that are not adjacent ill configuration space. This would be a violation of the assumptions of the transition state theory - that once the system crosses the transition state from the reactant microstate it will be deactivated and equilibrated in the product state. Concerted transitions between spatially far-separated states may be common. This would lead to a highly connected master equation where each state is connected to a significant fraction of all other microstates of the system. [9, 10]... 

I still did not have suitable low-temperature instrumentation of my own to carry out the low-temperature NMR studies, but Martin Saunders at Yale did. Thus our samples now traveled the Massachusetts Turnpike from Boston to New Haven, where with Marty we were able to study solutions of the norbornyl cation at increasingly lower temperatures using his home-built variable-temperature NMR instrumentation housed in the basement of the old Yale chemistry building. We... 

Note 2. Traces of oxygen will induce polymerization of the cumulene. The NMR tube must therefore be filled with nitrogen before putting the sample in it. Low-temperature NMR gives the most representative results. 

A discussion of the adsorption of water on oxides would be incomplete without some reference to the irreversible effects which are often encountered when samples of oxide, hydroxide or oxide-hydroxide are exposed to the vapour. These effects ( low-temperature ageing ), which manifest themselves in changes in surface area, in pore structure and sometimes in the lattice structure itself, are complex and difficult to reproduce exactly. ... 

Some solids inlet systems are also suitable for liquids (solutions) if the sample is first evaporated at low temperatures to leave a residual solid analyte, which must then be vaporized at higher temperatures. 

Fig. 7. The effect of preparation on the pore size distribution (a), titanium dispersion (b), and the activity for epoxidation of cyclohexene (c) of titania—siUca containing 10 wt % titania and calcined in air at 673 K. Sample A, low-temperature aerogel Sample B, high-temperature aerogel Sample C, aerogel.

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