Contribution to the theory of single-mode laser modulation II. Conduction modulation

The problem of conduction modulation of laser radiation is considered. It is shown that acoustic wave interacting with photon field in active medium causes a periodic modulation of the number of quanta in the single-mode gas laser. The problem of modulation is solved quantum mechanically and it is shown that dielectric and conduction modulation give similar results.     

Soft modes in semiconducting SrTiO3: II. The ferroelectric mode

The frequency, temperature and wavevector dependence of the ferroelectric soft mode in semiconducting SrTiO₃ was investigated by temperature derivative Raman spectroscopy and by inelastic neutron scattering. A tremendous shift in mode frequency with free electron and oxygen vacancy concentration, respectively, was observed.     

Effect of bias field on the dielectric properties of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single crystals with different orientations

Microdomain-macrodomain transformations and phase transitions in 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ single crystals were investigated by studying their relative permittivity under various dc bias at constant heating and cooling rates. The orientation dependence of the bias field effect was revealed by examining the temperature dependence of relative permittivity as a function of crystal orientation (the 111, 011 and 001 directions) and dc bias field. The crystals have a microdomain rhombohedral ferroelectric state in the ferroelectric phase under zero dc bias. External bias field could modulate the domain state and induce a macrodomain state in the crystals. Also, it is proposed that the dc bias applied along the 001 or 011 direction could induce a tetragonal ferroelectric phase or an orthorhombic ferroelectric phase, respectively, in an intermediate temperature range. PACS 77.80.-e; 77.22.-d; 81.40.-z     

Einstein-Fokker-Planck Equation for a Collapsing Perfect Fluid Star in a Thermal Noise Bath: Static Thermal Black Hole as the Equilibrium Solution

This paper considers sphericalOppenheimer-Snyder gravitational collapse of dust orperfect fluid stars immersed within aspacetime containing a thermal bath of (Gaussian) whitenoise at a temperature T, obeying the autocorrelations of thefluctation-dissipation theorem. Candidates for theresulting non-linear Einstein-Langevin (EL) stochasticdifferential field equations are developed. A collapsing fluid or dust star coupled to the stochastic,external thermal bath of fluctuations is theninterpreted as an example of a non-linear, noisy system,somewhat analogous to a non-linear Brownian motion in a viscous, thermal bath at temperature T. AnEinstein-Fokker-Planck (EFP) hydrodynamical continuityequation, describing the collapse as a probability flowwith respect to the exterior standard time t_s outside the collapsing body, is developed. Thethermal equilibrium or stationary solution can bederived in the infinite standard time relaxation limit.This limit (t_s ) only exists for a static, external observer within thenoise bath viewing the collapsing sphere such that R 1 (the event horizon) with unit probability ast_s . The stationary or thermalequilibrium solution of the efp equations therefore seemsto correspond to a static black hole in a Hartle-Hawkingstate at the Hawking temperature t_H. The OSmodel first predicted event horizons and singularities. It is interesting that through a simplestochastic extension of the model, one can conclude thatthe final collapsed, static, equilibrium state of thebody must be a thermal black hole at the Hawkingtemperature.     

Entropy of the Quantum Electromagnetic Field in Static, Spherically Symmetric Dilaton Black Holes

The quantum correction to the entropy of four-dimensional nonextreme static,spherically symmetric dilaton black holes arising from electromagnetic fields isinvestigated by 't Hooft's brick wall model. The Garfinkle-Horowitz-Strominger,Gibbons-Maeda, and Garfinkle-Horne dilaton black holes areconsidered. It is shown that the one-loop quantum correction arising from theelectromagnetic fields is exactly twice that due to a massless scalar field. Theresult agrees with that of the Schwarzschild and Reissner-Nordström blackholes.     

Dependence of the TDPAC spectra on teh orientation of the principal axis system of the electric field gradient

Analytical expressions are derived, which give the frequency amplitudes of a time differential perturbed angular correlation pattern, as a function of the orientation angles of the principal axis system of the electric field gradient tensor. We show, that allowed - TDPAC experiments are anisotropic only if the main axis of the electric field gradient forms a unique angle with the crystal symmetry axis or if the multiple crystallographically equivalent directions in a cubic crystal are unequally populated.     

Phase uniqueness and correlation length in diluted-field Ising models

The diluted-field Ising model, a random nonnegative field ferromagnetic model, is shown to have a unique Gibbs measure with probability I when the field mean is positive. Our methods involve comparisons with ordinary uniform field Ising models. They yield as a corollary a way of obtaining spontaneous magnetization through the application of a vanishing random magnetic field. The correlation lengths of this model defined as (lim _n-(1/n) log ₀; _n)^-1, wheren is the site on the first coordinate axis at distancen from the origin and ₀; _n is the origin ton two-point truncated correlation function, is non-random. We derive an upper bound for it in terms of the correlation length of an ordinary nonrandom model with uniform field related to the field distribution of the diluted model.     

Dynamic Opalescence upon Phase Transitions and in Inhomogeneous Systems

The temperature isofrequency dependences of Raman intensities are studied in a number of crystals (lithium tantalate, barium sodium niobate, barium titanate, and quartz) in the low-frequency range near the structural phase-transition points. In the case of ferroelectrics, poly- and single-domain single crystals are studied with a stationary electric field applied to the sample. A drastic increase in the intensity of the quasielastic (low-frequency) light scattering is found when approaching the phase-transition point. The studies are carried out for the 90° scattering geometry as well as at angles close to 180° (backscattering geometry). The anomalies of the quasielastic light scattering near the points of phase transition are observed in the latter case. The position of the maximum intensity of the isofrequency dependence on the temperature scale is found to be dependent on the frequency value = ₀ – (₀ and are the frequency of exciting radiation and the frequency to which the monochromator is tuned, respectively). A theory explaining satisfactorily the observed effect of dynamic opalescence near the phase-transition points in crystals is developed. The specific features of light scattering in an inhomogeneous medium as well as the dynamic properties of the model of such a medium in the form of periodically arranged microresonators are studied. Additional vibrational branches (superlattice vibrations) are shown to be formed in such a medium under certain conditions. These branches give rise to a central peak and strongly affect the characteristics of the structural phase transition depending on the microresonator dimensions. The observing conditions of the dynamic opalescence in inhomogeneous media by the isochronous spectroscopy technique upon pulsed laser excitation are analyzed.     

A new high frequency “relaxation window” for measuring molecular field fluctuations

We report a new Mössbauer relaxation window which allows the fluctuation rate of a molecular field acting on an impurity in a strongly correlated spin system to be obtained. For a molecular field of 1 T, the fluctuation rate can be measured up to 10 THz, which is three orders of magnitude higher than for the classical relaxation window. The calculated line shapes show that Ising-like fluctuations of the molecular field can be distinguished from other types of fluctuations (in-plane or in space). An application and some other possible uses of this new relaxation window are discussed.     

Maximal violation of Bell's inequalities is generic in quantum field theory

Under weak technical assumptions on a net of local von Neumann algebras {A(O)} in a Hilbert space , which are fulfilled by any net associated to a quantum field satisfying the standard axioms, it is shown that for every vector state in there exist observables localized in complementary wedge-shaped regions in Minkowski space-time that maximally violate Bell's inequalities in the state . If, in addition, the algebras corresponding to wedge-shaped regions are injective (which is known to be true in many examples), then the maximal violation occurs in any state on () given by a density matrix.     

An alternative approach to quantum phenomena

This paper outlines the qualitative foundations of a quasiclassical theory in which particles are pictured as spatially extended periodic excitations of a universal background field, interacting with each other via nonlinearity in the equations of motion for that field, and undergoing collapse to a much smaller volume if and when they are detected. The theory is based as far as possible directly on experiment, rather than on the existing quantum mechanical formalism, and it offers simple physical interpretations of such concepts as mass, 4-momentum, interaction, potentials, and quantization; it may lead directly to the standard equations of quantum theory, such as the multiparticle Schrödinger equation, without going through the conventional process of quantizing a classical theory. The theory also provides an alternative framework in which to discuss wave-particle duality and the quantum measurement problem; in particular, it is suggested that the unpredictability of quantum phenomena may arise from deterministic chaos in the behavior of the background field.     

Modified London model for the determination of λ and ζ in a high κ superconductor

We present a modified London model suggested by Brandt [1–3] which introduces a finite vortex core size appropriate for isotropic superconductors in which the average internal field is less than approximately (1/4)H _c2. TheSR lineshape resulting from this model possesses a distinctive shape due to the magnetic penetration depth and the vortex core diameter (approximately equal to twice the coherence length ). However, for a given lineshape, there is a large range of values of and which produce nearly the same lineshape. Lineshape smearing caused by disorder in the vortex lattice increases uncertainty in values for and . If well-determined values of either (T) or (T) are not available from another technique, both of them can be determined bySR measurements alone if runs in more than one applied field at the same temperature are fit with and as shared parameters. We also present our method of estimating the degree of disorder in the vortex lattice.     

Quadrupole interaction at111Cd nuclein in single-crystalline thallium

The quadrupole interaction of¹¹¹Cd nuclei in a single crystal of hexagonal thallium has been investigated for different geometries and sample temperatures employing the perturbed - angular correlation technique. The observed variation of the electric field gradient with temperature is attributed to local modes of thermal vibrations of the Cd impurities. An analytical relationship has been derived from lattice-dynamical models, expressing the temperature dependence in terms of impurity-host mass ratios and local force-constants.     

Nonrelativistic polarization operator of a photon in an external nonabelian field of magnetic type

The photon polarization operator is computed in the presence of a constant external chromomagnetic field in nonrelativistic approximation. The found branching points of the polarization operator are compared with the minimal energy necessary for creation of scalar colored particles. The absence of confinement for such quarks in the field under consideration is noted.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 23–26, October, 1990.     

Coherent raman spectroscopy of nitrogen molecules and clusters in supersonic jets

Coherent Stokes and anti-Stokes Raman scattering CSRS and CARS have been employed to study the spectroscopy of nitrogen molecules and clusters in the expansion of a supersonic jet. In the vibrational spectrum, at strong stagnation conditions, an intense redshifted peak is observed which can be assigned to the intramolecular vibrations in large N₂ clusters having adopted the -phase structure. Another weak feature is assigned to nitrogen clusters in the -phase. In the rotational region of the spectrum only monomer features have been observed. The failing to observe librational motions is consistent with the finding that the nitrogen clusters are predominantly in the orientationally unordered -phase. The low rotational temperature suggests supercooling of the -phase.     

Acoustomagnetoelectric current effects on mesoultrasound in anisotropic semiconductors

The acoustomagnetoelectric (AME) current effects on mesoultrasound in monopolar single-valley semiconductors with anisotropic scattering in arbitrary classical magnetic fields are computed analytically. The specimen is considered short-circuited along the q-wave vector of the ultrasound (US) wave. Two configurations are examined: 1) q is directed at an arbitrary angle 9 to the axis of highest order crystal symmetry C₆ (z axis), the y axis to the (q, C₆) plane, the magnetic field B lies in the (q, y) plane at an arbitrary angle to the vector q. Two transverse AME field components are calculated: along y and in the (q, C₆) plane. They express the Hall effects at mesoultrasound, the planar and normal, 2) q is directed along the y axis while B is in the (x, z) plane at an angle to the C₆(z) axis. The AME field component along B, the Grobner effect at mesoultrasound, is calculated. The dependence of the effects onB is studied and their estimate is given in weak and strong fields.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 57–61, July, 1989.     

The effect of microsegregation on the generation of dislocations in zinc single crystals

The applicability of Tiller's considerations on the production of dislocations is proved. The density of dislocations appearing during impurity microsegregation increases with increasing rate of growth as a consequence of the corresponding change in the effective distribution coefficient. The real value of C at the microsegregation boundaries is at least twice as great as the average value of the concentration of impurities in the crystal in question.

---

. , , . C , .

     

Correlation inequalities for the truncated two-point function of an Ising ferromagnet

We establish the following new correlation inequalities for the truncated twopoint function of an Ising ferromagnet in a positive external field: _j ; _l ^T _j ; _k ^T _k ; _l ^T , and _j ; _l ^T _{k K j} ; _k ^T _{k l} , whereK is any set of sites which separatesj froml. The inequalities are also valid for the pure phases with zero magnetic field at all temperatures. Above the critical temperature they reduce to known inequalities of Griffiths and Simon, respectively.NSERC Postgraduate Fellow, 1978–1981. Research supported in part by NSF Grant No. PHY-78-25390-A02.     

Derivation and solution of a low-friction Fokker-Planck equation for a bound Brownian particle

The low-friction region of an anharmonically bound Brownian particle is examined using systematic elimination procedures. We obtain an asymptotic expression for the spectrum of the Fokker-Planck operator. Asymptotic means both small anharmonicities and small friction constants compared to the oscillatory frequency . We conclude that Kramers' low-friction equation is generally valid only for 0<0.01 and has to be modified for 0.01 by including phase-dependent terms. From these the nonlinear part of the force field in connection with a finite temperature is shown to shorten the correlation time of the equilibrium velocity autocorrelation function and to renormalize the frequency of the corresponding spectral density.     

Mechanism Study for Thermal/Electric Field Poling of Fused Silica

On the basis of the experimental reports, the mechanism of the second-order susceptibility ⁽²⁾ for the thermal/electric field poling of fused silica is analyzed, and expressions for ⁽²⁾ are detailedly derived and numerically calculated for the first time. By comparison the theoretical value of ⁽²⁾ with the experiment results, we propose that the effective ⁽²⁾ is created via both the interaction of the intense electric field with the third-order susceptibility ⁽³⁾ and the dipole orientation. The theoretical results show that, in the differently applied voltage, the dipole orientation and ⁽³⁾ play different role in the formation of ⁽²⁾. This theory successfully explains some experiment results.