International Journal of Modern Physics B

Via the route of developing Dirac's symbolic method by virtue of the technique of integration within an ordered product (IWOP) of operators we derive various entangled state representations, squeezed states, and operator ordering formulae. We show how the entangled states can be applied to many aspects of quantum optics theory. The applications of the entangled states in the interdisciplinary study of quantum optics and Fourier optics are also introduced. All these discussions exhibit the power of Dirac's symbolic method with the aid of the IWOP technique.

We have studied the ohmic property of parallel coupled single-electron tunnel-junction arrays. When a current flows in one array ('driving' array), the Coulomb blockade state of the other array ('passive' array) is lifted, leading to an ohmic relationship between the tunneling current and the bias voltage. The driving current basically plays the role of a switch for the current in the passive array, as it can vary the ohmic conductance as well. Since the ohmic characteristic and the switching function are quite robust to the background or stray charges, the parallel coupled tunnel-junction system can be used as a variable resistor in logic circuits. As its specific application, we have proposed a Hopfield neural network with single-electron synapses.

In this paper we consider the problem of a polymer chain in random media with finite correlation. We show that the mean square end-to-end distance of a polymer chain can be obtained using the Feynman path integral developed by Feynman for treating the polaron problem and successfuly applied to the theory of heavily doped semiconductor. We show that for short-range correlation or the white Gaussian model we derive the results obtained by Edwards and Muthukumar using the replica method and for long-range correlation we obtain the result of Yohannes Shiferaw and Yadin Y. Goldschimidt.

The main idea of this paper is to generalize the model proposed by Edwards and Muthukumar for short-range correlation to finite correlation. Instead of using a replica method, we employ the Feynman path integral by modeling the polymer Hamiltonian as a model of non-local quadratic trial Hamiltonian. This non-local trial Hamiltonian is essential as it will reflect the translation invariant of the original Hamiltonian. The calculation is proceeded by considering the differences between the polymer propagator and the trial propagator as the first cumulant approximation. The variational principle is used to find the optimal values of the variational parameters and the mean square end-to-end distance is obtained. Several asymptotic limits are considered and a comparison between this approaches and replica approach will be discussed.

The conserving sum rules for the electron gas form a set of fundamental and powerful constraints on the description of electronic transport, at any length scale. We examine the particular role of the compressibility sum rule for open mesoscopic conductors, and show that the compressibility in such systems is absolutely invariant under nonequilibrium transport. The compressibility sum rule provides a stringent consistency check on models of mesoscopic conduction.

A prototype apparatus that uses two platinum wires for the simultaneous estimation of the thermal conductivity and specific heat capacity of liquids is described. The first wire is used both as a hot wire and a resistance thermometer, while the second one is used as a resistance thermometer. The aim of the work was to experimentally verify the advantages of employing a second wire to improve the reliability of the estimation of the properties. Three different liquids: water, propylene glycol, and a mixture of these are considered. An analytical solution with a changing heat flux is adopted. The thermal conductivity and the specific heat capacity are simultaneously estimated with a nonlinear regression (Maximum Likelihood) of the experimental data, using two-wire measurements or only hot-wire measurements. A comparison between these two approaches is reported and discussed.

Glasses of the xMnO·(100–x)[Bi₂O₃·CdO] system with 0<x≤50 mol%, were prepared and studied by means of EPR and magnetic susceptibility measurements. The EPR investigations indicated the compositional domains favorable to isolated manganese ions or to those magnetically clustered. The magnetic measurements evidenced the presence of both Mn²⁺ and Mn³⁺ ions, with their relative content depending on the MnO concentration. The prevalence of the dipolar and respectively the superexchange interactions between the manganese ions can be correlated with the relative content of the Mn²⁺ and Mn³⁺ species.

We investigate the vibrational energy eigenvalues and eigenfunctions of the neutral sodium atom trapped by the optical dipole potential due to a cavity mode. Our model is based on the optical confinement of a sodium atom between parallel plates with its dipole moment vector fixed in the axial direction of the cavity. The negative detuning situation and suitable parameters are taken in order to maintain a sufficiently deep central well of the optical dipole potential to allow many quasi harmonics trapped states of the atom.

Glasses of the xFe₂O₃·(100–x)[3B₂O₃·KF] system, with 0<x≤35 mol%, were investigated by means of EPR and magnetic susceptibility measurements. When increasing the iron content the EPR absorption spectra undergo modification reflecting structural changes of the glass matrix and also the distribution and valence states of iron ions. The magnetic measurement data pointed out the character of interaction involving iron ions as depending on concentration and the simultaneous presence of both Fe³⁺ and Fe²⁺ ionic species.

A transfer matrix formalism is employed to study the occurrence of the localized modes associated with an impurity cell embedded within a semi-infinite Heisenberg ferromagnetic superlattice with nearest-neighbor exchange interactions. The cell is at arbitrary distance from the deformed surface cell. We find that, in addition to bulk spin waves, there may arise localized modes associated both with the impurity cell and with the surface. Two situations were analyzed numerically: impurity is close to the surface and the impurity is practically in the bulk region. The modes influence each other when the impurity cell is near the surface, modifying spin wave energies.

In this communication we shall focus on the three microscopic processes whose interplay determine the surface morphology of MBE growth: namely, surface diffusion, desorption and accretion and Schwoebel back diffusion. We gain insight into the dynamics of growth via one-loop perturbative techniques. This allows us to analyze our numerical data. We conclude that there is a crossover behavior from a roughening regime to a very long-time, large length scale smoothening regime.

The possibility to improve the quality of the selective excitation, at low radio-frequency power, in the strongly inhomogeneous magnetic fields of the NMR-MOUSE is explored. Important safe of RF power is obtained by replacing the standard Hahn echo pulse sequence by DANTE–DANTE echo pulse sequence. The quality of the response spectrum is analyzed in function of the parameters of DANTE pulse sequence. The development of low-power selective excitation in unilateral NMR is an important step towards low-power operation of the NMR-MOUSE to increase its mobility.

A quasiclassical theory for DC magnetotransport in a modulated quantum Hall system near filling factor ν=½ is presented. A weak one-dimensional electrostatic potential acts on the two-dimensional electron gas. Closed form analytic expressions are obtained for the resistivity ρ_⊥ corresponding to a current at right angles to the direction of the modulation lines as well as a smaller component ρ_‖ for a current along the direction of the modulation lines. It is shown that both resistivity components are affected by the presence of the modulation. Numerical results are presented for ρ_⊥ and ρ_‖ and show reasonable agreement with the results of recent experiments.

In a recent paper several species of octagonal patterns have been introduced with the help of a construction which allows us to derive them by means of inflation rules. Non-deterministic patterns can be generated by composition of the inflation rules. In this paper we show how a similar construction produces patterns with hexagonal symmetry. The non-deterministic rhombus–triangle tilings are obtained by local rearrangements of tiles which are included in the inflation rules. This property allows to compute the configurational entropy.

Equilibrium properties of Blume–Emery–Griffiths (BEG) model with the arbitrary bilinear (J), biquadratic (K) and crystal field interaction (D) are studied on a body centered cubic lattice by using the pair approximation of the cluster variation method, which is identical to the Bethe approximation. The thermal variation of the stable, metastable and unstable dipole and quadrupolar moment order parameters are found for various values of the two different coupling parameters J/K and D/K. The phase transitions of the stable, metastable and unstable branches of the order parameters are investigated extensively. The critical temperatures in the case of a second-order phase transition are obtained for different values of J/K and D/K by the Hessian determinant. The first-order phase transition temperature is determined by matching the values of the two branches of the free energy values. On the other hand, nonequilibrium behavior of the model is studied by using the path probability method with the pair distribution and the set of nonlinear differential equations, which is also called the dynamic or rate equations, is obtained. The solution of the dynamic equations is expressed by means of flow diagrams. The stable, metastable and unstable solutions are shown and the "overshooting" phenomenon is seen in the flow diagrams, explicitly. The role of the unstable points, as separators between the stable and the metastable points, is described and how a system freezes in a metastable state is also investigated, extensively. Moreover, the dynamic equations are also solved by using the Runge–Kutta method in order to study the relaxation of order parameters. In this investigation, the "flatness" property of metastable states and the "overshooting" phenomenon are seen explicitly.

2D and 3D lattice complexes with increased self-coordination numbers T_i (i=1–3), of nearest, second and third neighbors were derived for characteristic Wyckoff sets with zero or one parameters. Structure types of adsorbed atoms in 2D or elements A in 3D and A_xB_y compounds are approximated to the list of lattice complexes. Covalent bonding or electronic effects of atoms such as lone electron pairs or Jahn–Teller distortion give rise to deviations from lattice complexes.

The behavior of the compensation of a mixed spin-1 and spin-1/2 Heisenberg ferrimagnetic system on a square lattice is investigated theoretically by a two-time Green-function technique which takes into account the quantum nature of Heisenberg spins. The model includes the nearest and next-nearest neighbor interactions between spins, a crystal field and an external magnetic field. This model can be relevant for understanding the magnetic behavior of bimetallic molecular ferrimagnets that are currently being synthesized by several experimental groups. We study the spin-wave spectra of the ground state and investigate the effects of the next-nearest neighbor interactions, a crystal field and an external magnetic field on the compensation temperature. It is found that a compensation point appears and it is basically unchanged when the next-nearest-neighbor interaction between spin-1/2 is taken into account and exceeds a minimum value for other values in Hamiltonian fixed. The compensation temperature is influenced by the next-nearest-neighbor interaction between spin-1 and the external magnetic field and it is disappearing as these parameters exceed the trivial values.

Glasses of the xFe₂O₃·(100-x)[3B₂O₃·KF] system, with 0≤x≤35 mol%, were prepared and investigated by infrared (IR) and Raman spectroscopies in attempt to determine the local structure of glasses. The results shown that BO₃ and BO₄ are the main structural units of the glass system and the iron ions are located in the network as FeO₄ and FeO₆.