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41.
Enthalpies of solution of -D-fructose and sucrose in binary solvent mixtures of water and N,N-dimethylformamide (DMF) at 25°C over the whole mole fraction region are reported and compared to those of -D-glucose. Because in these solvent systems the mutarotation of -D-fructose is fast and accompanied by large enthalpy changes, the measured enthalpies of solution of this compound had to be corrected for this effect. The dependences of the enthalpies of solution on the composition of the solvent mixtures are considered to result from preferential hydrogen-bonding of the hydroxyl groups and hydrophobic hydration of the apolar parts of the surface of the solute molecule. Distinctions between the enthalpy of transfer curves are discussed in terms of conformational differences and additivity aspects in the solvation behavior of the compounds. The predominance of furanose forms of fructose in DMF and that of pyranose forms of the same solute in water are related to differences in solvation. 相似文献
42.
Balk S. Körner J. G. Pirjol D. Schilcher K. 《Zeitschrift fur Physik C Particles and Fields》1994,64(1):37-44
Starting from an operator product expansion in the heavy quark effective theory up to order 1/m
b
2
we calculate the inclusive semileptonic decays of unpolarized bottom hadrons including lepton mass effects. We calculate the differential decay spectra d/(dE
), and the total decay rate forB meson decays to final states containing a lepton.Supported by the Graduiertenkolleg Teilchenphysik, Universität Mainz 相似文献
43.
B. C. Erdoğan A. T. Seyhan Y. Ocak M. Tanoğlu D. Balköse S. Ülkü 《Journal of Thermal Analysis and Calorimetry》2008,94(3):743-747
The cure kinetics of epoxy resin and epoxy resin containing 10 mass% of natural zeolite were investigated using differential
scanning calorimetry (DSC). The conformity of the cure kinetic data of epoxy and epoxy-zeolite system was checked with the
auto-catalytic cure rate model. The results indicated that the hydroxyl group on the zeolite surface played a significant
role in the autocatalytic reaction mechanism. This group was able to form a new transition state between anhydride hardener
and epoxide group. The natural zeolite particles acted as catalyst for the epoxy system by promoting its curing rate. 相似文献
44.
45.
Sevdiye Atakul Savrık Devrim Balköse Semra Ülkü 《Journal of Thermal Analysis and Calorimetry》2011,104(2):605-612
Lubricating oil additives based on boron compounds are promising materials for lubrication due to their tribological advantages
such as antiwear efficiency, good film strength, and high temperature resistance. This article deals with the preparation
of zinc borate particles that are well dispersed and colloidally stabilized in mineral oil. This method starts with preparing
two inverse emulsions (water-in-oil) with sorbitan monostearate (Span 60) as a surfactant, light neutral oil as a continuous
phase, and the aqueous solutions of borax decahydrate (Na2B4O7·10H2O) and zinc nitrate (Zn(NO3)2·6H2O) as the dispersed phases. The produced particles were zinc borate crystals having both rod-like and spherical morphologies,
and the diameters of spherical particles were changing between 20 and 30 nm. FTIR spectra of the obtained particles showed
the characteristic peaks of trihedral borate (B(3)-O) and tetrahedral borate (B(4)-O) groups as well as the specific peaks
of the sorbitan monostearate. TG showed 30.42% and 22.08% mass loss at 600 °C for the samples prepared by inverse emulsion
and precipitation techniques, respectively. The endothermic peak at 50 °C is observed due to the melting of sorbitan monostearate
and the heat of melting is evaluated as −3.50 J/g. Tribological studies revealed that sorbitan monostearate not only outperformed
as a dispersing agent of inorganic particles, but also it proved to be an anti-wear agent. Zinc borate produced by precipitation
decreased the wear scar diameter from 1.402 to 0.639 mm and the friction coefficient from 0.099 to 0.064. The inverse emulsion
was effective in decreasing wear scar diameter and the friction coefficient by lowering them to 0.596 and 0.089 mm, respectively. 相似文献
46.
Holger Frauenrath Sven Balk Helmut Keul Hartwig Hcker 《Macromolecular rapid communications》2001,22(14):1147-1151
We report the first successful block copolymerization of ethylene and methyl methacrylate using a zirconocene‐based catalyst system. The catalyst is generated in situ from Me2C(Cp)(Ind)ZrMe2 and B(C6F5)3 in toluene. Block copolymerization is achieved via the sequential addition of the monomers, starting with ethylene. The composition of the block copolymer is shown to be dependent on the time allowed for ethylene polymerization. The solubility of the resulting polymers, NMR data and GPC measurements are discussed, and a polymerization mechanism is proposed. 相似文献
47.
48.
Thermal oxides were implanted with common dopants (As, P) and inert elements (Ar). After different post-implantation annealing treatments the hole trapping in the samples was characterized by means of avalanche injection. Hole capture is reduced by anneal in an oxidizing ambient, but less for As and P than for Ar samples. It is shown that defect centers are produced by chemical interaction between network formers and the damaged oxide structure and in addition by recoil damage. 相似文献
49.
Graham R. Fleming Scott H. Courtney Michael W. Balk 《Journal of statistical physics》1986,42(1-2):83-104
Photochemical isomerization in stilbene and diphenyl butadiene has been studied as a model for activated barrier crossing. Experiments have been carried out from isolated molecule conditions up to 3000 atm pressure in solution-phase samples. The qualitative features predicted by Kramers theory are observed. The system undergoes a transition from energy-controlled to diffusion-controlled behavior in the high-pressure gas phase. The influences of multidimensionality, intramolecular vibrational relaxation, and frequency dependent friction are discussed.Camille and Henry Dreyfus Teacher Scholar. 相似文献
50.
Ludwig Josef Balk 《Fresenius' Journal of Analytical Chemistry》1987,329(2-3):159-164
Summary Techniques of scanning acoustic microscopy generally rely on local variations of such solid state parameters influencing generation or propagation of acoustic waves. Depending on the manner of impressing acoustic waves into the sample various methods are distinguished. In conventional scanning acoustic microscopy ultrasound is generated by a lens-transducer arrangement outside the sample and focussed onto or below its surface. Changes in the propagation of this ultrasound wave, like absorption and reflexion or temporal propagation delays, enable analysis of the mechanical or elastic response. At very high frequencies and with additional time-resolving detection techniques applications of this technique to surface analysis become possible. Other scanning acoustic microscopes imply the generation of sound or ultrasound directly within the sample itself due to the impact of temporarily modulated particle or photon beams. These are presently laser, electron, or ion beams. With these methods the acoustic signal as detected by a transducer attached to the sample is on principle affected by propagation properties, too, but it is dominated by local changes of the generation process for the acoustic wave, mainly because the frequency ranges used presently are associated with very long acoustic wavelengths. Depending on the physical nature of the primary probe used many sound generation mechanisms are given resulting in a large amount of different applications. By adjusting the probe parameters in a suitable manner the sound generation process can be confined to the direct vicinity of the specimen surface, which makes this technique feasible for surface characterization. The principles of the various techniques are described, and their usability for surface analysis is discussed. 相似文献