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991.
Magnetic nanocomposite material composed of poly vinyl alcohol encapsulated Ni0.2Ca0.8Gd0.08Fe1.92O4 was synthesized by a two step chemical method including sol-gel combustion and solvent casting technique. The obtained samples were characterized by powder X-ray diffraction; transmission electron microscopy and Fourier transform infrared spectroscopy. The results of spectroanalysis pointed towards the existence of a considerably feasible interaction between the polymer chain and the ferrite particles. The dc magnetization measurements divulged that both pristine and the nanocomposite samples under applied magnetic field exhibit no hysteretic behavior at room temperature, symptomatic of the superparamagnetic behavior. The departure of field cooled and zero field cooled curves in the moment-versus-temperature plot further confirmed the room temperature superparamagnetic behavior. The extrapolation of the slope of the curves to M=0 imparted the average value of Curie temperature at ∼323 K (50 °C) for both the samples, suggestive of the efficacy of the material for finding application in self controlled hyperthermia. 相似文献
992.
The use of the far‐infrared spectral range presents a novel approach for analysis of the hydrogen bonding in proteins. Here it is presented for the analysis of Fe? S vibrations (500–200 cm?1) and of the intra‐ and intermolecular hydrogen bonding signature (300–50 cm?1) in the Rieske protein from Thermus thermophilus as a function of temperature and pH. Three pH values were adequately chosen in order to study all the possible protonation states of the coordinating histidines. The Fe? S vibrations showed pH‐dependent shifts in the FIR spectra in line with the change of protonation state of the histidines coordinating the [2Fe? 2S] cluster. Measurements of the low‐frequency signals between 300 and 30 K demonstrated the presence of a distinct overall hydrogen bonding network and a more rigid structure for a pH higher than 10. To further support the analysis, the redox‐dependent shifts of the secondary structure were investigated by means of an electrochemically induced FTIR difference spectroscopic approach in the mid infrared. The results confirmed a clear pH dependency and an influence of the immediate environment of the cluster on the secondary structure. The results support the hypothesis that structure‐mediated changes in the environment of iron? sulfur centers play a critical role in regulating enzymatic catalysis. The data point towards the role of the overall internal hydrogen bonding organization for the geometry and the electronic properties of the cluster. 相似文献
993.
Abstract An optical autoclave for phase studies on mixtures in the temperature range from 80 to 373 K and for pressures up to 200 MPa is described. The cell is fitted with sapphire windows and employs magnetic stirring. Measurements are performed according to the synthetical (e.g. by visual observation) or analytical method (e.g. by sampling and online gaschromatography). Results for the crystallization and fluid phase equilibria of the binary systems nitrogen + trifluoromethane and argon + trifluoromethane from 110 K to 230 K and up to 200 MPa are presented and discussed in comparison with other N2- and CHF3-systems. 相似文献
994.
Abstract We have compared the effect of hydrostatic pressure on the threshold current, Ith, and lasing energy, Elase, of 1.3 pm quantum-well devices based upon AlGaInAs and InGaAsP. Whilst we observe a very similar dependence of Elase on pressure for the two materials, we measure strikingly different variations of Ith. By applying pressure to 1.3 μm InGaAsP lasers, Ith typically decreases by ~ 10% over 1 GPa consistent with the reduction of Auger recombination, which forms ~ 50% of Ith at room temperature. However, for the 1.3 μm AlGaInAs-based lasers, we observe an increase in Ith by ~ 8% over the same pressure range. From these results we conclude that non-radiative recombination accounts for only ~ 20% of Ith in AlGaInAs-based devices. This is in good agreement with previous temperature dependence measurements and shows why AlGaInAs-based devices exhibit a reduced temperature sensitivity of Ith which is very important for telecommunications applications. 相似文献
995.
Martin Bohner 《Applied mathematics and computation》2010,216(10):2855-2976
In this work, we establish Weyl-Titchmarsh theory for symplectic difference systems. This paper extends classical Weyl-Titchmarsh theory and provides a foundation for studying spectral theory of symplectic difference systems. 相似文献
996.
Mehdi Ramezani Mehdi Dehghan Mohsen Razzaghi 《Numerical Methods for Partial Differential Equations》2008,24(1):1-8
In this work the combined finite difference and spectral methods have been proposed for the numerical solution of the one‐dimensional wave equation with an integral condition. The time variable is approximated using a finite difference scheme. But the spectral method is employed for discretizing the space variable. The main idea behind this approach is that we can get high‐order results. The new method is used for two test problems and the numerical results are obtained to support our theoretical expectations. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007 相似文献
997.
998.
The values of the gas-chromatographic indicator reflecting the capacity of analytes for self-association in pure liquids,
δT
b.p., were estimated for C1–C9 and C11
n-alkanols by capillary gas chromatography on a nonpolar stationary phase under isothermal conditions. The δT
b.p. values ofn-alkanols, found as the difference between the boiling points measured directly and those calculated from GC data, are correlated
with thermodynamic characteristics of the formation ofn-alkanol associates in pure liquids. Usingn-alkanols as analytes with insignificant temperature increments of the retention indices, it was shown that the δT
b.p. values can be determined under conditions used in gas chromatography with temperature programming. In this way a single chromatographic
run can be used to compare the capacities for self-association of analytes boiling over a wide temperature range. The C2–C9
n-alkanethiols, which are not associated in neat liquids, have negative δT
b.p. values. An interpretation of this finding is proposed.
Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 315–318 February, 2000. 相似文献
999.
J. J. Mareš 《Journal of Thermal Analysis and Calorimetry》2000,60(3):1081-1091
A brief outline of the history of development of the temperature concept in physics is given. Simultaneously, some persisting
imperfections in the conceptual basis of classical thermodynamics closely related to the first and the second law of thermodynamics
are discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
1000.
We present an improved immersed boundary method for simulating incompressible viscous flow around an arbitrarily moving body on a fixed computational grid. To achieve a large Courant–Friedrichs–Lewy number and to transfer quantities between Eulerian and Lagrangian domains effectively, we combined the feedback forcing scheme of the virtual boundary method with Peskin's regularized delta function approach. Stability analysis of the proposed method was carried out for various types of regularized delta functions. The stability regime of the 4‐point regularized delta function was much wider than that of the 2‐point delta function. An optimum regime of the feedback forcing is suggested on the basis of the analysis of stability limits and feedback forcing gains. The proposed method was implemented in a finite‐difference and fractional‐step context. The proposed method was tested on several flow problems, including the flow past a stationary cylinder, inline oscillation of a cylinder in a quiescent fluid, and transverse oscillation of a circular cylinder in a free‐stream. The findings were in excellent agreement with previous numerical and experimental results. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献