Electrocaloric response of a ferroelectric capacitor to a periodic electric field

The electrocaloric response of a ferroelectric capacitor to a periodic electric field has been analyzed in terms of the nonstationary heat conduction equation. A linear physical model is considered for an electrocaloric element in which one end (x = 0) is thermally insulated and a constant temperature T ₀ is maintained at the boundary x = l. The effect of a periodic electric field on the capacitor gives rise to temperature oscillations about a decreasing average value that reaches saturation. A relatively simple analytic expression is derived for the temperature distribution along the electrocaloric element and the heat flux density under stationary conditions. The calculations are carried out using the results obtained from measurements performed for a PMN-PT relaxor ferroelectric in the temperature range of the phase transition. A temperature gradient and a heat flux of ～150 W/cm² are observed in an electric field of 2.4 V/μm at a frequency of 10 Hz.     

A free convective boundary layer in a conducting fluid in the presence of a transverse magnetic field

The properties of free convection in a conducting fluid in laminar regime near a hot solid vertical w all in the presence of a transverse magnetic field are theoretically analyzed. The existence of two regimes of heat transfer from the wall to the fluid are established. In the first regime, at small heights x?x* where the magnetic field effect can be disregarded, heat transfer is described by the well-known results for a free convective boundary layer in a nonconducting fluid with the Nusselt number Nu_x∝x^3/4. In the second regime, at x? x* where the magnetic field plays a crucial role, the dependence of heat transfer on the height and field strength is \(Nu_x \propto {{\sqrt x } \mathord{\left/ {\vphantom {{\sqrt x } B}} \right. \kern-\nulldelimiterspace} B}\). The location of the boundary between these regimes strongly depends on the magnetic field, x*∝ B^?4.     

Long Time,Large Scale Limit of the Wigner Transform for a System of Linear Oscillators in One Dimension

We consider the long time, large scale behavior of the Wigner transform W _? (t,x,k) of the wave function corresponding to a discrete wave equation on a 1-d integer lattice, with a weak multiplicative noise. This model has been introduced in Basile et al. in Phys. Rev. Lett. 96 (2006) to describe a system of interacting linear oscillators with a weak noise that conserves locally the kinetic energy and the momentum. The kinetic limit for the Wigner transform has been shown in Basile et al. in Arch. Rat. Mech. 195(1):171–203 (2009). In the present paper we prove that in the unpinned case there exists γ ₀>0 such that for any γ∈(0,γ ₀] the weak limit of W _? (t/? ^3/2γ ,x/? ^γ ,k), as ??1, satisfies a one dimensional fractional heat equation \(\partial_{t} W(t,x)=-\hat{c}(-\partial_{x}^{2})^{3/4}W(t,x)\) with \(\hat{c}>0\). In the pinned case an analogous result can be claimed for W _? (t/? ^2γ ,x/? ^γ ,k) but the limit satisfies then the usual heat equation.     

MHD mixed convection flow and heat transfer in a porous medium

The effects of a steady two-dimensional laminar MHD mixed convection flow and heat transfer against a heated vertical semi-infinite permeable surface in a porous medium are discussed. The coupled nonlinear partial differential equations describing the conservation of mass, momentum, and energy are solved by a perturbation technique. The results are presented to illustrate the influence of Hartmann number (M), Prandtl number (Pr), permeability parameter (K _p ), suction/blowing parameter (f _w ), heat generation/absorption coefficient (?), and mixed convection or buoyancy parameter (γ). The effects of different parameters on the velocity and temperature as well as the skin friction and wall heat transfer are discussed with the help of figures.     

Isomeric ratios of (γ,p) and (γ,α) reactions on <Superscript>117<Emphasis Type="Italic">m,g</Emphasis></Superscript>In

The isomeric ratios of the (γ,p) and (γ,α) reactions on ^117m,g In have been measured. The ratios Y _m /Y _g was found to be 1.18(9) and 0.23(9), respectively, at a boundary energy of 22 MeV. The statistical character of the reactions under such conditions is shown.     

Zerfallsschemata, β-Matrixelemente und γ-Multipolordnungen für die Übergänge Co56→Fe56 und J131→Xe131

In the decay of Co⁵⁶ the following quantities have been measured:γ-ray intensities,β-γ directional correlation, andβ-(circularly polarizedγ) correlation. The directional correlation anisotropy was found to be, forβ energies above 300 keV,A ₂=0.5±0.4 per cent, corresponding to small or vanishing twice forbidden contributions to the allowed decay. The asymmetry parameterA of theβ-(circularly polarizedγ) correlation was measured to beA=?0.01±0.05 which implies a ratiox between Fermi and Gamow-Teller contributions to the decay ofx=?0.10±0.07, in agreement with the isospin selection rule. In the decay of J¹³¹ the following quantities have been measured: shape of the 606 keVβ-ray group,γ-ray intensities, conversion coefficients, andβ-(circularly polarizedγ) correlations. The measuredK/L ratio of the 364 keVγ-transition,K/L=6.0±0.2, is compatible with the conversion tables of Sliv and Band only. The multipolarities of theγ rays of 364, 637, and 723 keV were deduced. The 606 keVβ-364 keVγ cascade was used as a new calibration standard for analysers of circularly polarizedγ-rays.     

Asymmetry with respect to the magnetic field direction in the interaction between the quantum states of two coupled superconducting rings

The interaction between the quantum states of two circularly asymmetric superconducting aluminum rings forming figure eight, threaded by a magnetic flux and biased by an external sinusoidal ac current with zero dc component, has been investigated. Quantum oscillations in the dependence V _dc(B) of the rectified dc voltage on magnetic field for these structures have been measured at different external currents and temperatures close to critical. Fourier and wavelet analyses of the function V _dc(B) have revealed, along with the two fundamental ring frequencies, various combination frequencies; this fact is indicative of interaction in the structure. Deviation of the function V _dc(B) from oddness with respect to the magnetic field direction has been found for the first time.     

Der Zerfall des Co55,T 1/2=18h

Co⁵⁵ T ^1/2=18 h) was produced by bombarding iron-foiles with 9 MeV deuterons.γ-spectra from the decay of Co⁵⁵ have been investigated using a scintillation fast-slow-coincidence circuit and a Li-drifted Ge-counter. 18γ-transitions were observed having the following energies in keV and intensities per Co⁵⁵-decay:γ ₁=95 (0.006),γ ₂=413 (0.016),γ ₃=475 (0.12),γ ₄=645 (0.005),γ ₅=750 (0.002),γ ₆=810 (0.025),γ ₇=900 (0.024),γ ₈=940 (0.80),γ ₉=985 (0.009),γ ₁₀=1055 (0.005),γ ₁₁=1210 (0.01),γ ₁₂=1320 (0.065),γ ₁₃=1375 (0.042),γ ₁₄=1410 (0.13),γ ₁₅=1600 (0.001),γ ₁₆=1800 (0.0006),γ ₁₇=2160 (0.001),γ ₁₈=2310 (0.0042).     

Doppelkonversion

An excited nuclear state can decay by three different modes of double quantum emission, namely doubleγ-emission,γ-electron emission and double conversion electron emission. The emission of twoγ-quanta has been considered in an earlier paper¹. The purpose of the present work is to treat all three processes together in a systematic manner. It is shown that the connection between the transition rates forγ-electron emissionT _γc and doubleγ-quantum emissionT _γγ is more complicated than in the case of single quantum processes. However,T _γc can still be expressed in terms of the usual conversion coefficients. This is also true for the transition rate T_cc for the emission of twoK-shell electrons, although only approximately. For the emission of electrons from different atomic shells the formulas become rather complicated, because of interference effects. The electron andγ-quantum spectra in all of the three second order processes are discussed in detail for the decay of the isomeric level in Xe¹³¹.     

Kinetic Features of the Laser Ablation of Gamma-Irradiated Polyvinylidene Fluoride

We study the effect of γ-radiation from ⁶⁰Co on the rate of post-irradiation laser ablation of polyvinylidene fluoride (PVDF). The laser ablation of both the initial and γ-irradiated polymer occurs without an incubation period and does not require time to heat up the polymer target by the laser within the time scale of our measurements. The second feature of the laser ablation of PVDF is an extreme dependence of the ablation rate on the dose of γ-radiation over a wide range (10 kGy – 3.5 MGy) and the appearance of a minimum ablation rate of 0.1 mg/s at a dose 300 kGy. A gradual increase in the dose of γ-irradiation above 300 kGy is accompanied by a rise in the laser ablation rate. At γ-irradiation doses up to 2.3 MGy, the rate of the post-irradiated laser ablation of PVDF reaches 6.5 mg/s, which is equal to the laser ablation rate of non-irradiated PVDF.     

Interference of ballistic electrons in an open quantum dot at high temperatures

The Aharonov-Bohm-type oscillations in the ballistic magnetoconductivity of an open quantum dot ～1 μm in size created in the GaAs/AlGaAs heterostructure by local anode oxidation have been studied. The measurements have been performed at temperatures of 4.2 and 1.5 K, which are high enough to expect a considerable suppression of the oscillations with period h/e (in magnetic flux units). The magnetoconductivity oscillations with a period less than the quantum h/e with respect to the magnetic field are observed at 1.5 K. The explanation is proposed on the basis of the interference of the electrons moving along the time-reversed paths inscribed into the quantum dot that have their initial and final points at one of the contacts, i.e., corresponding to a period of h/2e.     

Cross sections of the reactions16O(γ,x)13 N and16O (γ,x)11 C,and Yield of12C (γ, t) up to 55 MeV

Yield curves of the reactions¹⁶O (γ, x)¹¹C,¹⁶O (γ, x)¹³N and¹²C(γ, t) have been measured relative to¹²C(γ, n)¹¹C with bremsstrahlung. The cross section σ[¹⁶O(γ, x)¹¹C] has a shape similar to σ[¹⁶O(γ, t)] and shows a broad maximum near 38 MeV. Differences between σ[¹⁶O(γ, x)¹³ N] and σ[¹⁶O(γ, t)] point to a reaction mechanism via quadrupole absorption in¹⁶O. The yield of¹²C(γ, t) exceeds the¹⁶O(γ,t) yield by a factor of two.     

Energy spectra of secondary particles in γ families and their sensitivity to the spectrum of primary cosmic rays

Spectra of secondary particles (γ-rays) in γ-families detected in the X-ray chambers in the Pamirs (H = 600 g cm^?2) have been analyzed. These γ-ray spectra show a bend at the energy E* _γ ≈ (ΣE _γ )^min, where (ΣE _γ )^min is the lowest total energy of γ-rays in the families above which γ-families were selected. The bend is not related to the knee in the spectrum of primary particles; it is due to the use of the ΣE _γ selection criterion. The E _γ spectrum slope is sensitive to the spectrum of the primary cosmic rays in the region E _γ ≥ (ΣE _γ )^min.     

Transition form factors and light-cone distribution amplitudes of pseudoscalar mesons in the chiral quark model

It is shown that a chiral quark model of the Nambu-Jona-Lasinio type can be used to describe “soft”-momentum parts of the amplitudes with large momentum transfer. As a sample, the processes γ* → γ(π, η, η′), where one of the photons, γ*, has large spacelike virtuality, are investigated. The γ* → γ(π, η, η′) transition form factors are calculated for a wide region of the momentum transfer. The results are consistent with the calculations performed in the instanton-induced chiral quark model and agree with experimental data. The distribution amplitudes of pseudoscalar mesons are derived.     

Laminar free convection heat transfer between vertical isothermal plates

The paper represents results on numerical investigation of flow and heat transfer between two isothermal vertical plates under laminar natural convection. A system of complete Navier–Stokes equations is solved for a two-dimensional gas flow between the plates along with additional rectangular regions (connected to inlet and outlet sections), whose characteristic sizes are much greater than the spacing between the plates. The calculations were performed over very wide ranges of Rayleigh number Ra = 10 ÷ 10⁵ and a relative channel length AR = L/w = 1 ÷ 500. The influence of the input parameters on the gas-dynamic and thermal structure of thermogravitational convection, the local and mean heat transfer, and also the gas flow rate between the plates (convective draft. We determined sizes of the regions and regime parameters when the local heat flux on the walls tends to zero due to the gas temperature approach to the surface temperature. It is shown that the mean heat transfer decreases as the relative channel length AR grows, whereas the integral gas flow rate (convective draft) and Reynolds number in the channel Re = 2wUm/ν increase. The use of a modified Rayleigh number Ra* = Ra · (w/L) (Elenbaas number) leads to generalization of calculation data on mean heat transfer. These data are in good agreement with the correlations for heat transfer [1, 2] and gas flow rate [3]. The reasons of variation of the data in the range of low Rayleigh numbers are discussed in detail.     

Spins und γ-Multipolordnungen beim Zerfall Fe59→Co59

In the decay of Fe⁵⁹ the following quantities have been measured:γ-ray intensities, conversion coefficients andβ-(circularly polarizedγ) correlations. The conversion coefficients were found to be: for the 1.10 MeVγ-transition, α_tot.=(1.36±0.10)·10^?4 and for the 1.29 MeVγ-transition, α_tot.=(1.07±0.08)·10^?4. The asymmetry parameterA of the correlationβ(0.27 MeV)?γ(1.29 MeV) were measured to beA= ?0.17±0.10, and forβ(0.46 MeV)?γ(1.10 MeV),A=?0.13±0.04. From these data and publishedγ?γ angular correlation measurements the following spins of Co⁵⁹ levels could be deduced: 1.10 MeV,I=5/2^?; 1.29 MeV,I=5/2^?; and 1.43 MeV,I=3/2^?. The two strongβ-ray groups are pure Gamow-Teller transitions (ΔI=1). The multipolarities of all fiveγ-rays are given.     

Zener tunneling between Landau levels in a double quantum well at high filling factors

Differential resistance r _xx in a double GaAs quantum well with two occupied size-quantization subbands has been studied at a temperature of 4.2 K in magnetic fields B < 2 T. The oscillations of r _xx with a period in the inverse magnetic field determined by the value of a dc bias current I _dc have been discovered in the electron system under investigation at high filling factors in the presence of I _dc. The amplitude of magneto-intersubband oscillations has been shown to increase in the r _xx oscillation maxima, while the oscillation reversal has been observed in the minima. The discovered oscillations have been shown to be due to Zener tunneling of electrons between Landau levels tilted by a Hall electric field. The experimental data are qualitatively explained by the effect of intersubband transitions on the I _dc-dependent component of the electron distribution function.     

Dependence of the magnitude and direction of the persistent current on the magnetic flux in superconducting rings

The obtained periodic magnetic-field dependences I _c+(Φ/Φ₀) and I _c?(Φ/Φ₀) of the critical current measured in opposite directions on asymmetric superconducting aluminum rings has made it possible to explain previously observed quantum oscillations of dc voltage as a result of alternating current rectification. It was found that a higher rectification efficiency of both single rings and ring systems is caused by hysteresis of the current-voltage characteristics. The asymmetry of current-voltage characteristics providing the rectification effect is due to the relative shifts of the magnetic dependences I _c?(Φ/Φ₀) = I _c+(Φ/Φ₀ + Δ?) of the critical current measured in opposite directions. This shift means that the position of I _c+(Φ/Φ₀) and I _c?(Φ/Φ₀) minima does not correspond to n + 0.5 magnetic flux Φ quanta, which is in direct contradiction to measured Little-Parks resistance oscillations. Despite this contradiction, the amplitude I _{c, an}(Φ/Φ₀) = I _c+(Φ/Φ₀) ? I _c?(Φ/Φ₀) of critical current anisotropy oscillations and its variations with temperature correspond to the expected amplitude of persistent current oscillations and its variations with temperature.     

<Emphasis Type="Italic">SU</Emphasis>(2) Non-Abelian Photon

In this paper, we have proposed S U(2) non-Abelian electromagnetism gauge theory. In the theory, photon has self-interaction and interaction between them, which can explain photon entanglement phenomenon in quantum information. Otherwise, we find there are three kinds photons γ ⁺, γ ^? and γ ⁰, they have electric charge + e _γ , ? e _γ and 0, respectively, these prediction are accordance with some experiment results.     

Process <Emphasis Type="Italic">γ</Emphasis>*<Emphasis Type="Italic">γ</Emphasis> → <Emphasis Type="Italic">σ</Emphasis> at large virtuality of <Emphasis Type="Italic">γ</Emphasis>*

The process γ*γ → σ is investigated in the framework of the SU(2)×SU(2) chiral NJL model. The form factor of the process is derived for arbitrary virtuality of γ* in the Euclidean kinematic domain. The asymptotic behavior of this form factor resembles the asymptotic behavior of the γ*γ → π form factor.