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1.
We have studied a strongly asymmetric Al single-electron transistor with R1 ? R2 and C1 ? C2, where R1, 2 and C1, 2 are the tunnel resistances and capacitances of the first and second junction respectively. Due to the asymmetry in its electric parameters leading to strong asymmetry of the nonlinear I–V curve at zero bias (V = 0), the transistor demonstrated a remarkable current response to an AC signal at the values of the gate charge Q0 close to (n + 1/2)e, where n is integer. A rather delicate regime of the transistor operation (V ? e/CΣ) being important for unperturbed measurements was examined. The measured curves are in good agreement with a model based on the orthodox theory of single electron tunneling. This specific zero bias regime of an asymmetric transistor opens new opportunities for a single-electron transistor as an ultrasensitive charge/field sensor.  相似文献   

2.
Using nuclear (proton) magnetic resonance relaxometry (NMRR) was studied oil disperse systems. Dependences of NMR–relaxation parameters—spin–lattice T1i, spin–spin T2i relaxation times, proton populations P1i and P2i, and petrophysical correlations were received for light and heavy oils. Experimental results are interpreted on the base of structure-dynamical ordering of oil molecules with structure unit formation.  相似文献   

3.
Within the model of delocalized atoms, it is shown that the parameter δTg, which enters the glasstransition equation qτg = δTg and characterizes the temperature interval in which the structure of a liquid is frozen, is determined by the fluctuation volume fraction \({f_g} = {\left( {{{\Delta {V_e}} \mathord{\left/ {\vphantom {{\Delta {V_e}} V}} \right. \kern-\nulldelimiterspace} V}} \right)_{T = {T_g}}}\) frozen at the glass-transition temperature Tg and the temperature Tg itself. The parameter δTg is estimated by data on fg and Tg. The results obtained are in agreement with the values of δTg calculated by the Williams–Landel–Ferry (WLF) equation, as well as with the product qτg—the left-hand side of the glass-transition equation (q is the cooling rate of the melt, and τg is the structural relaxation time at the glass-transition temperature). Glasses of the same class with fg ≈ const exhibit a linear correlation between δTg and Tg. It is established that the currently used methods of Bartenev and Nemilov for calculating δTg yield overestimated values, which is associated with the assumption, made during deriving the calculation formulas, that the activation energy of the glass-transition process is constant. A generalized Bartenev equation is derived for the dependence of the glass-transition temperature on the cooling rate of the melt with regard to the temperature dependence of the activation energy of the glasstransition process. A modified version of the kinetic glass-transition criterion is proposed. A conception is developed that the fluctuation volume fraction f = ΔVe/V can be interpreted as an internal structural parameter analogous to the parameter ξ in the Mandelstam–Leontovich theory, and a conjecture is put forward that the delocalization of an active atom—its critical displacement from the equilibrium position—can be considered as one of possible variants of excitation of a particle in the Vol’kenshtein–Ptitsyn theory. The experimental data used in the study refer to a constant cooling rate of q = 0.05 K/s (3 K/min).  相似文献   

4.
An analytical model has been developed to describe the influence of solute trapping during rapid alloy solidification on the components of the Gibbs free energy change at the phase interface with emphasis on the solute drag energy. For relatively low interface velocity V < V D , where V D is the characteristic diffusion velocity, all the components, namely mixing part, local nonequilibrium part, and solute drag, significantly depend on solute diffusion and partitioning. When VV D , the local nonequilibrium effects lead to a sharp transition to diffusionless solidification. The transition is accompanied by complete solute trapping and vanishing solute drag energy, i.e. partitionless and “dragless” solidification.  相似文献   

5.
The velocityv of the propagation of discharge along the anode of a self-quenchingG—M-counter is a function of total pressureP, pressure of the quenching gasP D, radius of the cathoder a and of the anoder i andV ü the difference between working- and starting-potential. For the mixtures argon-methylal, argon-alcohol and helium-alcohol isv=v 0·exp[k·(V ü/V e)1/2] withv 0 the velocity at the starting potentialV e v 0=(a+b·P D/PV n 1/2 ·exp [(c?d·PD/P·V n ?1/2 ] andV n=V e·(lnr a/r i)?1.k, a, b, c andd are characteristical constants of the filling gas.  相似文献   

6.
The structural stability and lattice dynamics of the high-pressure bcc phase of Zr at a constant temperature T = 500 K are studied for various volumes using molecular dynamics simulation with the Animalu pair pseudopotential. Dispersion curves of the vibrational spectrum calculated by the molecular dynamics method for various volumes are compared to the phonon spectrum obtained in the harmonic approximation. It is demonstrated that, as the volume decreases, all frequencies of the vibrational spectrum increase gradually and bcc zirconium remains strongly anharmonic along all high-symmetry directions of the Brillouin zone over the entire range of volumes studied. The strongly anharmonic N T1 phonon is significantly softened near the point of structural instability of bcc-Zr at T = 500 K and V = 0.87V 0. As the volume decreases to V = 0.73V 0 under pressure, the anharmonic corrections for this phonon decrease by almost an order of magnitude and the phonons near the H point of the Brillouin zone become anharmonic. The damping of the T 1 phonon mode along the [110] direction is calculated as a function of pressure.  相似文献   

7.
We study a one-dimensional quasiperiodic system described by the Aubry–André model in the small wave vector limit and demonstrate the existence of almost mobility edges and critical regions in the system. It is well known that the eigenstates of the Aubry–André model are either extended or localized depending on the strength of incommensurate potential V being less or bigger than a critical value V c , and thus no mobility edge exists. However, it was shown in a recent work that for the system with V < V c and the wave vector α of the incommensurate potential is small, there exist almost mobility edges at the energy E c±, which separate the robustly delocalized states from “almost localized” states. We find that, besides E c±, there exist additionally another energy edges E c′±, at which abrupt change of inverse participation ratio (IPR) occurs. By using the IPR and carrying out multifractal analyses, we identify the existence of critical regions among |E c±|?≤?|E|?≤?|E c′±| with the mobility edges E c± and E c′± separating the critical region from the extended and localized regions, respectively. We also study the system with V > V c , for which all eigenstates are localized states, but can be divided into extended, critical and localized states in their dual space by utilizing the self-duality property of the Aubry–André model.  相似文献   

8.
We study the asymptotic structure of the first K largest eigenvalues λ k,V and the corresponding eigenfunctions ψ(?;λ k,V ) of a finite-volume Anderson model (discrete Schrödinger operator) \(\mathcal{H}_{V}= \kappa \Delta_{V}+\xi(\cdot)\) on the multidimensional lattice torus V increasing to the whole of lattice ? ν , provided the distribution function F(?) of i.i.d. potential ξ(?) satisfies condition ?log(1?F(t))=o(t 3) and some additional regularity conditions as t→∞. For zV, denote by λ 0(z) the principal eigenvalue of the “single-peak” Hamiltonian κΔ V +ξ(z)δ z in l 2(V), and let \(\lambda^{0}_{k,V}\) be the kth largest value of the sample λ 0(?) in V. We first show that the eigenvalues λ k,V are asymptotically close to \(\lambda^{0}_{k,V}\). We then prove extremal type limit theorems (i.e., Poisson statistics) for the normalized eigenvalues (λ k,V ?B V )a V , where the normalizing constants a V >0 and B V are chosen the same as in the corresponding limit theorems for \(\lambda^{0}_{k,V}\). The eigenfunction ψ(?;λ k,V ) is shown to be asymptotically completely localized (as V↑?) at the sites z k,V V defined by \(\lambda^{0}(z_{k,V})=\lambda^{0}_{k,V}\). Proofs are based on the finite-rank (in particular, rank one) perturbation arguments for discrete Schrödinger operator when potential peaks are sparse.  相似文献   

9.
We propose a model of a Brownian motor that performs a useful work against a load force F in an asymmetric periodic potential V(x) = V(x + 2L) that undergoes random shifts by a half period L with a frequency γ. An arbitrarily shaped potential profile is repeated with an energy shift ΔV in both half-periods L, while the periodicity of the function V(x) is ensured by its jumps at x = 0 and x = L. The boundary condition at x = 0 for the distribution function of a Brownian particle allows us to introduce a high and narrow potential barrier V0 that blocks the reverse current and leads to high efficiency of the motor (the ratio of the useful work done against the load force F to the energy imparted to the particle through the potential shifts). Based on this model, we derived exact analytical expressions for the current J and the efficiency η. In the special case of piecewise-linear potentials, J and η were plotted against F and γ for various values of the parameters ΔV and V0. We discuss the influence of the potential shape and fluctuation frequency on the main characteristics of the motor.  相似文献   

10.
Ceramic solid solutions (Bi1 ? x La x )4V2O11 ? z (I), Bi4(V1 ? x Fe x )2O11 ? y (II), and (Bi1 ? x La x )4(V0.96Fe0.04)2O11 ? y (III) (x = 0–0.3, step Δx = 0.02) are prepared using solid-phase synthesis. The concentration and temperature ranges of stabilization of different polymorphic modifications, including the ranges of concentrations x corresponding to the stabilization of the ferroelectric phase, are established. It is revealed that an increase in the concentration x in the region of existence of the pseudoorthorhombic phase α of the solid solutions studied leads to a decrease in the transition temperature, smearing of the transition, and an increase in the width of the thermal hysteresis of the ferroelectric phase transition. The effect of compressing of the domain walls by oxygen vacancies was revealed in the samples from the region of existence of the ferroelectric α phase, and the effect of dielectric relaxation was detected in the samples from the region of existence of the orthorhombic phase β.  相似文献   

11.
12.
The unit cell parameters a, b, and c of [N(CH3)4]2ZnCl4 have been measured by x-ray diffraction in the temperature range 80–293 K. Temperature dependences of the thermal expansion coefficients αa, αb, and αc along the principal crystallographic axes and of the unit cell thermal expansion coefficient αV were determined. It is shown that the a=f(T), b=f(T), and c=f(T) curves exhibit anomalies in the form of jumps at phase transition temperatures T1=161 K and T2=181 K and that the phase transition occurring at T3=276 K manifests itself in the a=f(T) and b=f(T) curves as a break. A slight anisotropy in the coefficient of thermal expansion of the crystal was revealed. The phase transitions occurring at T1=161 K and T2=181 K in [N(CH3)4]2ZnCl4 were established to be first-order.  相似文献   

13.
The magnetization M(H) in the superconducting state, dc magnetic susceptibility χ(T) in the normal state, and specific heat C(T) near the superconducting transition temperature T c have been measured for a series of fine-crystalline YBa2Cu3O y samples having nearly optimum values of y = 6.93 ± 0.3 and T c = (91.5 ± 0.5) K. The samples differ only in the degree of nanoscale structural inhomogeneity. The characteristic parameters of superconductors (the London penetration depth and the Ginzburg–Landau parameter) and the thermodynamic critical field H c are determined by the analysis of the magnetization curves M(H). It is found that the increase in the degree of nanoscale structural inhomogeneity leads to an increase in the characteristic parameters of superconductors and a decrease in H c(T) and the jump of the specific heat ΔC/T c. It is shown that the changes in the physical characteristics are caused by the suppression of the density of states near the Fermi level. The pseudogap is estimated by analyzing χ(T). It is found that the nanoscale structural inhomogeneity significantly enhances and probably even creates the pseudogap regime in the optimally doped high-T c superconductors.  相似文献   

14.
A square lattice of microcontacts with a period of 1 μm in a dense low-mobility two-dimensional electron gas is studied experimentally and numerically. At the variation of the gate voltage V g , the conductivity of the array varies by five orders of magnitude in the temperature range T from 1.4 to 77 K in good agreement with the formula σ(V g ) = (V g ?V g * (T))β with β = 4. The saturation of σ(T) at low temperatures is absent because of the electron–electron interaction. A random-lattice model with a phenomenological potential in microcontacts reproduces the dependence σ(T, V g ) and makes it possible to determine the fraction of microcontacts x(V g , T) with conductances higher than σ. It is found that the dependence x(V g ) is nonlinear and the critical exponent in the formula σ ∝ ? (x - 1/2) t in the range 1.3 < t(T, V g ) < β.  相似文献   

15.
The effect of pressure on the superconducting transition temperature T c of vanadium and V94Ti6, V85Ti15, V67Ti33, and V48Ti52 (at %) bcc alloys has been studied. It has been found that the T c(P) dependence of pure vanadium is close to linear in the pressure ranges 0–14 and 23–32 GPa, whereas dT c/dP decreases to zero with a pressure increase in the 14–23 GPa range. The T c(P) curves for all alloys are nonmonotonic and have two features in the respective pressure ranges of 3–11 and (a peak-shaped feature) 15–25 GPa.  相似文献   

16.
Using the microscopic theory formulated by de Gennes and extended by Takahashi and Tachiki, we calculate the transition temperatureT c and the pair functionF for the superlattices consisting of superconducting and ferromagnetic layers. Superconducting layers. (s) and ferromagnetic layers (f) are modeled byV s ≠0 andI m,s =0 andV f =0 andI m,f ≠0, whereV s .(V f ) is the BCS coupling constant andI m,s (I m,f ) is the molecular field fors (f) layers.  相似文献   

17.
Photoionization of the Xe atom and Xe@C60 molecule have been studied usingthe random phase approximation with exchange (RPAE) method. The Xe atom was described byrelaxed orbitals including overlap integrals. The C60 fullerene has beenrepresented by an attractive short range spherical well with potentialV(r), given byV(r) =  ?V 0 forr i  < r < r o ,otherwise V(r) = 0 wherer i andr o are respectively, the inner and outerradii of the spherical shell. The time independent Schrödinger equation was solved usingboth regular and irregular solutions and the continuous boundary conditions atr i andr o . The results demonstrate improvementto previous calculations for both the Xe atom and Xe@C60 molecule and comparevery well with the recent experimental data.  相似文献   

18.
For a two-dimensional Schrödinger operator H α V  = ?Δ ?αV with the radial potential V(x) = F(|x|), F(r) ≥ 0, we study the behavior of the number N ?(H α V ) of its negative eigenvalues, as the coupling parameter α tends to infinity. We obtain the necessary and sufficient conditions for the semi-classical growth N ?(H α V ) = O(α) and for the validity of the Weyl asymptotic law.  相似文献   

19.
The electro-optical coefficients r ij and half-wave voltage Vλ/2 of strontium-barium niobate crystals poled in the ferroelectric phase are shown to vary along the polar axis. The r ij (z) and Vλ/2(z) dependences indicate the presence of a residual domain density D(z) and clearly depend on the sign of the polarizing field, with r ij being minimum (D being maximum) near the negative electrode. This character of the D(z) distribution and, hence, the r ij (z) and Vλ/2(z) coordinate dependences can be explained by predominant domain nucleation near the negative electrode, which is revealed when the switching processes are studied using 90° (Rayleigh) light scattering from domain walls.  相似文献   

20.
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