The one-body density matrix in Helium droplets

The growth of the Bose condensate in Helium droplets is studied through variational Monte Carlo calculations of the one-body density matrix. Both the off-diagonal and the =0 component of the one-body density matrix show unmistakable finite range ordering within the core of the droplet.     

A conserving approximation evaluation of superfluid density within the pair theory of superfluids

The evaluation of the superfluid density, defined by the weak field response of the system, within the pairing theory of pure superfluids of Fermi or Bose statistics is considered. The need for evaluating this within what Baym and Kadanoff term a conserving approximation is emphasized. A formalism for generating manifestly conserving response kernels by analytic continuation at finite temperatures is developed and applied to the problem in question. At zero temperatures this is equivalent to the work of Nambu and others. The superfluid density is obtained in terms of the solution of a linear integral equation, the kernel and inhomogeneous term of which depends on the self-consistent equilibrium solution to the pair model. It is shown in general that this superfluid density tends to the full density at the absolute zero and vanishes above the critical temperature. Finally, some numerical work on the Bose superfluid is presented which is an extension of the calculations of Evans and Imry in the sense that a pseudopotential that more closely parameterizes the dispersion spectrum in He II is employed and that the superfluid density is evaluated as a function of temperature.     

Kinetic theory of anisotropic Fermi superfluids

A kinetic theory of anisotropic Fermi superfluids is presented. The kinetic equation for the quasiparticle matrix distribution function is derived from the microscopic theory, supplemented by definitions of the relevant densities and currents. The static spin susceptibility, the normal fluid density, and the specific heat are calculated from the static limit of the kinetic equation. Special attention is given to the collision integral, which is presented explicitly in terms of normal Fermi liquid quantities. The energy dependence of the collision integral makes necessary the introduction of two other distribution function matrices, for which kinetic equations are also derived.     

Open matrix very low density explosive formulations

In this paper, we have established the feasibility of preparing open-cell matrix explosive charges by two entirely different techniques, one based on a     

Spectral density matrix description of polarization mode dispersion

We introduce a power spectral density matrix formalism that incorporates both the pulse shape and the field polarization and can therefore easily describe averages over random fluctuations of the local birefringence vector. We demonstrate that quantities such as the differential time delay, power diffusion, and decoherence effects can be obtained directly from the equations of motion for the power density matrix. This approach can be applied to pulses with arbitrary frequency-dependent polarization and intensity distributions and in particular makes possible the minimization of the eye-opening penalty through the proper choice of the initial pulse profile.     

Advantage and limitation of density matrix renormalization group method

Density matrix renormalization group method introduced recently by White proves to be highly successful for interacting one and quasi-one dimensional systems. We compare this new method with the conventional numerical renormalization group. We discuss the common goal and different strategies used in both methods. The limitations of the new method as well as the ways to overcome them are explored.     

Effects of phase fluctuation on a mixture of rotating superfluids

It is shown that if the root-mean-square of the gradient of the phase fluctuation of either of the components exceeds the corresponding inverse of the coherence length or if the chemical potential exceeds ₁ ⁰ or ₂ ⁰ , where is the volume integrals of the interaction function between the components, and ₁ ⁰ , ₂ ⁰ are the densities of the two components, the mixture of two rotating superfluids has an instability.     

Preparation of an arbitrary density matrix of a harmonic oscillator

Abstract

We propose a deterministic method to generate an arbitrary (pure or mixed) density matrix of a harmonic oscillator. The general density matrices are achieved by manipulating quantum entanglement between the oscillator and an auxiliary oscillator. We discuss how our preparation scheme can be realized by cavity quantum electrodynamics interactions so that a general density matrix of a single-mode electromagnetic field can be created.     

Nanofiber density determines endothelial cell behavior on hydrogel matrix

When cultured under static conditions, bacterial cellulose pellicles, by the nature of the polymer synthesis that involves molecular oxygen, are characterized by two distinct surface sides. The upper surface is denser in fibers (entangled) than the lower surface that shows greater surface porosity. Human umbilical vein endothelial cells (HUVECs) were used to exploit how the microarchitecture (i.e., surface porosity, fiber network structure, surface topology, and fiber density) of bacterial cellulose pellicle surfaces influence cell–biomaterial interaction and therefore cell behavior. Adhesion, cell ingrowth, proliferation, viability and cell death mechanisms were evaluated on the two pellicle surface sides. Cell behavior, including secondary necrosis, is influenced only by the microarchitecture of the surface, since the biomaterial is extremely pure (constituted of cellulose and water only). Cell–cellulose fiber interaction is the determinant signal in the cell–biomaterial responses, isolated from other frequently present interferences such as protein and other chemical traces usually present in cell culture matrices. Our results suggest that microarchitecture of hydrogel materials might determine the performance of biomedical products, such as bacterial cellulose tissue engineering constructs (BCTECs).     

Properties of combined phonon-high-energy boson mechanism

We consider the properties of a superconductor with a joint mechanism. One involves, otherwise unspecified, high-energy excitations and is modelled with a BCS pairing potential. The other is of low energy, presumably involving phonons. When the second contribution is significant, the resulting properties can differ greatly from BCS, and for most but not all properties, in a direction opposite to that expected for conventional strong coupling systems.     

Determination of photon statistics and density matrix from double homodyne detection measurements

Abstract

We consider double balanced homodyne detection schemes with and without (local oscillator) phase-randomized detection. We discuss the reconstruction of the photon statistics from phase-randomized measurements. We show how the Wigner function of a photon-number state can be synthesized from phase-randomized double homodyne measurements of two properly prepared field states. Moreover we propose a new procedure to determine the whole density matrix from the Q function. Finally we express the Q function in terms of normally ordered moments and discuss their reconstruction.     

Long-range order in the half-diagonal two-body density matrix of a Bose superfluid

Consequences of Bose-Einstein condensation on the long-range behavior of the two-body density matrix are investigated. An exact relationship between the chemical potential and the functionF ₁ (r) characterizing the long-range order of the half-diagonal density matrix is derived. The hydrodynamic(q 0) limit of the Fourier transformF ₁ (q) is discussed and shown to be determined by the pressure dependence of the density of particles in the condensate. Consequences on the residue of the particle-particle Green's function in the phonon branch are pointed out.     

Evolution of vortex rings after the collapse of ultrasound bubbles in superfluids

No Heading Collapse of ultrasound bubbles in superfluids leads to the nucleation of vortex rings. Using the Gross-Pilaevskii equation for a uniform condensate we elucidate the various stages of the vortex formation and establish conditions necessary for the vortex nucleation after collapse of an oblate moving bubble. In the case of a stationary spherically symmetrical bubble we calculate the vortex line length as a function of time after collapse.PACS numbers: 03.75.Lm, 05.45.–a, 67.40. Vs, 67.57.De     

Slave boson theories of correlated electron systems

Slave boson theories of various models of correlated fermions are critically reviewed and several new results are presented. In the example of the Andersen impurity model the limitations of slave boson mean field theory are discussed. Self-consistent conserving approximations are compared with results obtained from the numerical renormalization group. The gauge field theory of the t-J-model is considered in the quasistatic approximation. It is shown that weak localization effects can give valuable information on the existence of gauge fields. Applications of the slave-boson approach due to Kotliar and Ruckenstein to the Hubbard model are also discussed.     

Direct multi-level density matrix calculation of nonlinear optical rotation spectra in rubidium vapour

We propose a rapid solution algorithm for the calculation of the full density matrix evolution for a multi-level atom. The calculation principle is similar to the split-step algorithm widely used for modelling the nonlinear propagation in media with Kerr-type nonlinearity, optical fibres in particular. The spectrum of nonlinear Faraday rotation in the D₂ natural rubidium line is calculated and compared with the experiment. Good agreement is obtained.     

Shape of the power spectral density matrix components: Influence on fatigue damage

The damage estimation for a structure under random loading is a challenge in fatigue assessment, especially when the loading is multiaxial. The comparison of the effect of different spectra on fatigue damage is essential when the structure can be subjected to different types of loadings. Therefore, in the present paper, the expected fatigue damage produced on metallic structures by combined bending and torsion stationary proportional and nonproportional loading is evaluated varying the shape of spectra of the normal and shear stress tensor components.