EAM-SOA millimeter-wave frequency up-converter for radio-over-fiber applications

We present an optical scheme for photonic frequency up-conversion at the millimeter-wave bands based on Semiconductor Optical Amplifier. The proposed scheme modulates the bias current with the Intermediate Frequency in order to achieve frequency mixing of an incoming optical signal modulated with the Local Oscillator. Theory indicates that the proposed scheme supports data bandwidths in the tens of GHz for LO values above 10 GHz. This scheme allows for photonic integration of the considered optical devices. A laboratory demonstration of the scheme for up-conversion to the 40 GHz band, using narrow-band IF signals, showed relatively low thresholds for the optical input power and bias current level to achieve error free operation: − 14.5 dBm 100 mA for a 64-QAM signal. Spurious-Free Dynamic Range showed an acceptable performance, with a linearity about 52.5 dB·Hz^2/3 for an optical input power of − 6 dBm.     

Determination of the X-pinch-based X-ray source size

It is shown that an X-ray source 0.5–2 μm in size for the spectral region above 3 keV can be implemented based on a compact pulse generator with an impedance of 0.13Ω using an X-pinch made of four molybdenum wires. The technique for determining the source sizes and the results of the experimental determination of the X-pinch emitting region sizes are presented. The parameters of the X-pinch consisting of wires of different diameters are optimized for this generator to fabricate an X-ray source of minimum sizes.     

Acoustical characteristics of a multichannel transmission line

The properties of an acoustic system called by the author ”a multichannel transmission line” (MTL) are considered. Analytical expressions are derived for the following main acoustical characteristics of an MTL consisting of an arbitrary number N of single lines: the input impedance, the resonance frequencies, the reflection and transmission factors for an MTL-insulator, and the reflection factor for an MTL-absorber. For these quantities, numerical calculations are performed, and their frequency dependences are presented for different parameters of the constituent lines in the cases N=2 and 3. It is shown that the acoustical characteristics of MTL-insulators and MTL-absorbers have considerable advantages over the characteristics of similar systems designed on the basis of single lines.     

Analytical formulas for calculating photoelectric attenuation coefficients

Photoelectric absorption is an interaction in which an incoming gamma ray virtually transfers all of its energy to an atomic electron, usually the most tightly bound K-shell electron of an atom. This paper uses the Win XCOM computer code as a reference base. We found analytical photoelectric attenuation coefficients for researchers using the Monte Carlo simulation program for Z∈ [1; 100] and E∈[10 keV; 3 MeV]. We define a photoelectric effect operator and coefficient operators and a series for photoelectric absorption. We have calculated two polynomial coefficient operators for use with XCOM for photoelectric absorption. We determined 14 energies and atomic number limits for elements, and we find that they are accurate limits of photoelectric absorption for fitting with XCOM.     

Band crossing in Pb1−xSnxSe under hydrostatic pressure

Laser emission from Pb_1−xSn_x Se diodes for x = 0.115 at 78.5°K is observed under hydrostatic pressure up to 14.7kbar. Direct evidence for an inversion of valence and conduction bands is obtained from the pressure coefficient measured on the same diode over the whole experimental range. We discuss briefly the nature of the band structure after the cross over point and suggest an explanation for an abrupt increase of the threshold current for laser action in these diodes at small gaps.     

Vertex Operators Arising from the Homogeneous Realization for

We use the underlying Fock space for the homogeneous vertex operator representation of the affine Lie algebra to construct a family of vertex operators. As an application, an irreducible module for an extended affine Lie algebra of type A _{N −1} coordinatized by a quantum torus ℂ _q of 2 variables (or 3 variables) is obtained. Moreover, this module turns out to be a highest weight module which is an analog of the basic module for affine Lie algebras. Received: 16 August 1999 / Accepted: 18 January 2000     

The representation of thermodynamic properties at high pressures

It is sometimes advantageous to have an expression for the Gibbs energy, G_m(T,P), from which one can analytically derive an expression for the Heimholtz energy, F_m(T, V_m). Such an expression is suggested for solid substances and it is shown how expressions for other physical properties can be derived from it.     

Optical surface <Emphasis Type="Italic">TM</Emphasis>-waves at the boundary of a nonlinear Kerr-type medium

Solutions for a nonlinear system of Maxwell’s equations and for a corresponding boundary problem describing the propagation of a surface TM-wave (p-polarization) along an interface with an optically nonlinear Kerr-type medium are presented. An analytical expression for the intensity of an integrated flux J₀ carried by such a wave along the interface between two media has been derived as a function of both the wave propagation constant ξ and the optical characteristics of the adjacent media. It is shown that flux intensities corresponding to the same values of the propagation constant ξ are much smaller for p-polarization than for s-polarization.     

Calculation of the probability of optical transitions in strong electric fields

An algorithm is proposed for calculating the spectrum of the cross section for photoionization of carriers on deep centers in electric fields on the basis of the form function of an optical transition.An experiment and calculations were performed for the complex V_Ga-S_As in GaAs. The proposed model is compared with theoretical works based on the single-coordinate approximation. It is concluded that the single-coordinate model is applicable for describing the field-dependence of the cross section for photoionization of an electron on a V_Ga-S_As center. Data on the influence of an external electric field on the change in the moments of the form function of the absorption band of the complex V_Ga-S_As in GaAs are obtained. It is concluded that an electric field influences the adiabatic potentials of the center investigated.     

Measurement of the electron mean free path using a bending effect

It has been observed experimentally that elastically bending a metal whisker increases its resistance. Such an increase in resistance depends on the metal, the temperature and the orientation of the whisker axis. This effect is observable below 6°K for Zn, 8°K for In, 20°K for Sn, and 300°K for Bi. It is suggested that the effect may be due to an enhancement of surface scattering due to the bending of the whisker. A calculation for such an effect for an “ideal metal” is presented along with data for Zn and Bi. This work has been supported by the Air Force Office of Scientific Research under grant number 68-1548.     

Interpretation of electronic spectra by configuration analysis: Absorption spectra of monosubstituted naphthalenes with an electron-accepting group

The electronic absorption spectra of four monosubstituted naphthalenes with an electron-accepting group, 1- and 2-naphthonitriles and 1- and 2-naphthaldehydes, have been investigated by means of configuration analysis with particular attention to the dependence of spectra on the position of substitution. The results of molecular orbital calculations based on the Pariser-Parr-Pople method were analyzed in terms of locally excited states and charge-transfer configurations. The characteristic changes in location of the L_b, L_a, and B_b bands caused by the substitution at 1- or 2-position are adequately explained by the analysis for monosubstituted naphthalenes with an electron-accepting group as well as for those with an electron-donating group. The results of the present configuration analysis for naphthalene derivatives with an electron-accepting group are compared with the results for those with an electron-donating group.     

Mass gap and universality for euclidean O(N) and CPN−1 models

From a suitably defined correlation function we evaluate the strong coupling expansion for the mass gap of an euclidean version of the O(N) models in 2D. Good agreement is found for N = 0, 1 and 2 with the known values of the critical temperature and for N ? 3 with the continuum mass gap as evaluated in an hamiltonian approach. Another test of universality based on the use of an asymmetric lattice also yields good results. An analogous discussion for the CP^N?1 models is performed.     

Simple recursive implementation of fast multipole method

In this paper we present an implementation of the well known “fast multipole” method (FMM) for the efficient calculation of dipole fields. The main advantage of the present implementation is simplicity—we believe that a major reason for the lack of use of FMMs is their complexity. One of the simplifications is the use of polynomials in the Cartesian coordinates rather than spherical harmonics. We have implemented it in the context of an arbitrary hierarchical system of cells—no periodic mesh is required, as it is for FFT (fast Fourier transform) methods. The implementation is in terms of recursive functions. Results are given for application to micromagnetic simulation. Complete source code is provided for an open-source implementation of this method, as well as an installer for the resulting program.     

Euler's fluid equations: Optimal control vs optimization

An optimization method used in image-processing (metamorphosis) is found to imply Euler's equations for incompressible flow of an inviscid fluid, without requiring that the Lagrangian particle labels exactly follow the flow lines of the Eulerian velocity vector field. Thus, an optimal control problem and an optimization problem for incompressible ideal fluid flow both yield the same Euler fluid equations, although their Lagrangian parcel dynamics are different. This is a result of the gauge freedom in the definition of the fluid pressure for an incompressible flow, in combination with the symmetry of fluid dynamics under relabeling of their Lagrangian coordinates. Similar ideas are also illustrated for SO(N) rigid body motion.     

Vibrational relaxation of a molecule in strong interaction with a reservoir: Nonmonotonic temperature dependence

This theoretical study of the vibrational relaxation of a molecule in interaction with a reservoir uncovers a noteworthy temperature (T) dependence of the time evolution of the relaxation. Its rate increases with T in one interval but decreases in another. The feature arises not for a weak molecule-reservoir interaction but only for coupling strong enough to require polaronic dressing transformations. Our treatment, based on a recent generalization of the well-known Montroll–Shuler equation for relaxation and an explicit calculation of bath correlations from the microscopically specified Hamiltonian, could provide an alternative explanation of an “inverted” T-dependence of relaxation in an experimental report by Fayer and collaborators on W(CO)₆ dissolved in CHCl₃.     

Moment coupling in the interaction of atoms and their ions with a 3<Emphasis Type="Italic">d</Emphasis>-electron shell

The moment coupling of an interacting ion and an atom with a 3d-electron shell is analyzed for the ground state of identical atoms and ions where resonant charge exchange proceeds with transition of a 4s-electron. The interaction of the ion charge with the atom quadrupole moment is important for this system along with the exchange interactions and spin-orbit interactions inside an isolated atom and an ion. The quadrupole moment for 3d-atoms in the ground states is evaluated. The hierarchy of interactions in a molecular ion is analyzed depending on ion-atom distances and is compared with the standard Hund scheme. The resonant charge exchange proceeds effectively at separations corresponding to an intermediate case between cases “a” and “c” of the Hund coupling scheme.     

EXPERIMENTAL STUDY OF TURBULENT NATURAL CONVECTION IN A TALL AIR CAVITY

Abstract

This article describes an experimental study of turbulent natural convection in an air cavity with an aspect ratio of 28.6. The study provides data for the velocities and temperatures at a Rayleigh number based on cavity width of 0.83 × 10⁶, which is useful in validating computational and theoretical results. A laser Doppler anemometer was used for velocity measurements, while fine thermocouples were used for temperature measurements. Heal transfer rates and heat losses from the cell are evaluated. Further, the experimental data in the central portion of the tall cavity have been averaged to simulate an antisymmetric, Boussinesq, fully developed flow in an infinitely tall air cavity. Causes of asymmetry of the data, including radiation absorption, are also assessed.     

On the dynamics of a curved deflagration front

An equation describing evolution of a curved deflagration front of finite thickness is obtained for the case of an arbitrary equation of state of the “fuel”, an arbitrary type of energy release and an arbitrary type of thermal conduction. The equation is complemented by conservation laws for the mass flux and the momentum flux through the deflagration front of finite thickness. As an illustration of the method, the growth rates and the cutoff wavelengths for the linear stage of the flame instability are calculated for the case of a flame in an ideal gaseous fuel and for the case of a thermonuclear deflagration propagating in a strongly degenerate matter of white dwarfs. Zh. éksp. Teor. Fiz. 111, 514–527 (February 1997) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Cosmological solution in the scalar—tensor theory of gravity

We consider the problem of exact integration of the field equations in the scalar—tensor theory of gravity for the case in which matter is an ideal fluid and the metric for space is given in Robertson—Walker form. We obtain a solution (in quadratures) for an arbitrary equation of state and an arbitrary time-dependent density for matter. Tomsk State Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 124–127, January, 1997.     

Pták sum of a Boolean algebra with an effect algebra and its completeness

The aim of the present paper is to show that a bounded Boolean power of an effect algebra has all the analogous properties required for Pták's sum of a Boolean algebra and an orthomodular lattice and to prove a theorem about its completeness. We also give for elements of that Pták sum an important form for their expression.