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1.
The dielectric-resonator method was used to study the dielectric constant and loss of K1–xLixTaO3 crystals for lithium contents x=0.02, 0.05, and 0.1 in the frequency of 0.5 GHz (in the temperature interval from 4.2 to 300 K) the dielectric constant, the static nonlinearity, and the dynamic nonlinearity were studied, the dielectric properties of K1–xLixTaO3 are determined simultaneously by the relaxation of impurity ions and by the soft mode, but at helium temperatures the contribution of the soft mode to predominates. The addition of lithium leads to a reduction of at 4.2 K and to a lessening of the steepness of the (t) curve. KTaO3 crystals alloyed with lithium exhibited exceptionally low losses at helium temperatures (at 4.2 K in the range 12–14 GHz, tan =2 · 10–5 for x=0.1). With a rise in temperature the loss increased just as in the case of unalloyed KTaO3, but less steeply. Measurements of crystals with x=0.1 revealed considerable dispersion of the nonlinearity: the coefficient of static nonlinearity was an order of magnitude of magnitude higher than the coefficient of dynamic nonlinearity 1 dyn, which was determined according to the efficiency of generation of the second harmonic.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 3–7, January, 1988.  相似文献   

2.
The growth of ordered domains in lattice gas models, which occurs after the system is quenched from infinite temperature to a state below the critical temperatureT c, is studied by Monte Carlo simulation. For a square lattice with repulsion between nearest and next-nearest neighbors, which in equilibrium exhibits fourfold degenerate (2×1) superstructures, the time-dependent energy E(t), domain size L(t), and structure functionS(q, t) are obtained, both for Glauber dynamics (no conservation law) and the case with conserved density (Kawasaki dynamics). At late times the energy excess and halfwidth of the structure factor decrease proportional tot –x, whileL(t) t x, where the exponent x=1/2 for Glauber dynamics and x1/3 for Kawasaki dynamics. In addition, the structure factor satisfies a scaling lawS(k,t)=t 2xS(ktx). The smaller exponent for the conserved density case is traced back to the excess density contained in the walls between ordered domains which must be redistributed during growth. Quenches toT>T c, T=Tc (where we estimate dynamic critical exponents) andT=0 are also considered. In the latter case, the system becomes frozen in a glasslike domain pattern far from equilibrium when using Kawasaki dynamics. The generalization of our results to other lattices and structures also is briefly discussed.  相似文献   

3.
4.
We report on the development of antenna-coupled thin-film nanometer Ni-NiO-Ni diodes which are used to detect 10.6 m CO2-laser radiation. The Ni-NiO-Ni diodes have a minimum contact area of 0.056 m2. This is smaller than those of any previously fabricated thin-film Metal-metalOxide-Metal (MOM) diodes. By measuring the second derivative of the dc current-voltage characteristics I(V), we demonstrate that the nonlinearity of the dc I(V) characteristics of our Ni-NiO-Ni diodes is larger than that of the dc I(V) characteristics of thin-film MOM diodes fabricated before by other authors. It is comparable to the nonlinearity of the dc I(V) characteristics of point-contact MOM diodes. Furthermore, we show that the polarisation-dependent infrared response of the Ni-NiO-Ni diodes is due to antenna coupling and that the polarisation-independent response is mainly of thermal origin. Consequently, the heating of the Ni-NiO-Ni diodes is due to the absorption of the incident CO2-laser radiation in the SiO2, and dissipation of the laser-induced ac antenna currents in the antenna.  相似文献   

5.
Thermal reaction rates for the gas-phase reaction Mu+C2H6MuH+C2H5 have been measured bySR over the temperature range 510–730 K. The usual Arrhenius expression,k=Aexp(–E a /RT), fits the data well, giving parametersA=1.0×10–9 cm3 molecule–1 s–1 andE a =15.35 kcal/mol. The activation energyE a is 5.5 kcal/mol higher than for the H atom variant of this reaction, indicating a marked difference in reaction dynamics. Preliminary analysis indicates a still greater difference between Mu and H for the corresponding CH4 reaction.  相似文献   

6.
The spin dynamics of the muonium (Mu) atom diffusing quantum mechanically in solid nitrogen (s-14N2) has been studied using the technique of Mu spin relaxation. A strong relationship between longitudinal (T 1 –1 ) and transverse (T 2 –1 ) relaxation rates (familiar in NMR) has been experimentally demonstrated for the first time for muonium relaxation. At low temperatures the results are inconsistent with diffusion models using a single correlation time c; this is taken as evidence for the intrinsic inhomogeneity of the problem. The temperature dependence of theaverage Mu hop rate c –1 gives clear evidence that Mu quantum diffusion ins-N2 is governed by the two-phonon interaction.  相似文献   

7.
We study properties of the random configuration {s j (1)} j=1 N produced by the first step of the parallel dynamics in the Sherrington-Kirkpatrick model. We show that the law of large numbers holds for the sequence of overlaps between the initial (nonrandom) configuration {s j (0)} j=1 N and {s j (1)} j=1 N , and obtain the distribution of the fluctuations around the limiting value. As a by-product we derive the average number of the fixed points {s j (1)} j=1 N with a given value of the magnetization .  相似文献   

8.
The forward current-voltage (I–V) characteristics of Pd2Si/n-Si(100) Schottky barrier diodes are shown to follow the Thermionic Emission-Diffusion (TED) mechanism in the temperature range of 52-295 K. The evaluation of the experimentalI–V data reveals a decrease of the zero-bias barrier height ( b0) and an increase of the ideality factor () with decreasing temperature. Further, the changes in b0 and become quite significant below 148 K. It is demonstrated that the findings cannot be explained on the basis of tunneling, generation-recombination and/or image force lowering. Also, the concepts of flat band barrier height and T 0-effect fail to account for the temperature dependence of the barrier parameters. The 1n(I s /T 2) vs 1/T plot exhibits nonlinearity below 185 K with the linear portion corresponding to an activat ion energy of 0.64 eV, a value smaller than the zero-bias barrier height energy (0.735 eV) of Pd2Si/n-Si Schottky diodes. Similarly, the value of the effective Richardson constant A** turns out to be 1.17 × 104 A m–2 K–2 against the theoretical value of 1.12 × 106 A m–2 K–2. Finally, it is demonstrated that the observed trends result due to barrier height inhomogeneities prevailing at the interface which, in turn, cause extra current such that theI–V characteristics continue to remain consistent with the TED process even at low temperatures. The inhomogeneities are believed to have a Gaussian distribution with a mean barrier height of 0.80 V and a standard deviation of 0.05 V at zero-bias. Also, the effect of bias is shown to homogenize barrier heights at a slightly higher mean value.  相似文献   

9.
We have obtained the solution of the stationary problem for P-polarized nonlinear surface polaritons (NLSP) near the interface of two media, one of which is optically linear and the other having an optical nonlinearity with saturation and a dielectric function of the form: =xx=zz=0+a|E|2/(1+b|E|2), where E is the amplitude of the electric field. On this basis the NLSP energy and propagation properties, the polarization structure and the localization depth of the NLSP field as well as the physically allowed region in the parameter space have been investigated for the case in which the parameter 0 is positive, b is non-negative, and a and 1 are negative (1 is the dielectric function of the linear medium); 0>|1|.  相似文献   

10.
Two random aggregation models are used in demonstrating the properties of the random displacementsr i of the center of mass of aggregating particles. It is found that r i is a randomly decreasing sequence that scales with the cluster size (steps)s and i =1/s r i s 1/D , whereD is the fractal dimension. The center-of-mass random walk is a consistent representation of the dynamics of aggregation.  相似文献   

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