High-temperature heat capacity,thermodynamic properties and debye temperature of CuGe2P3

The heat capacity at constant pressure of CuGe₂P₃ is measured in the temperature range from 180 to 550 K. Standard enthalpies and entropies relative to 298.15 K are calculated from the heat capacity data. The Debye temperature in the high-temperature limit is estimated to be about 710 K.     

Cross-gain modulation in closely spaced energy states quantum dash semiconductor optical amplifiers

A detailed small-signal analysis of cross-gain modulation is performed for closely spaced energy state quantum dash (QDsh) semiconductor optical amplifier (SOA). The analysis takes into account the carrier transition in all electron and hole states, the gain dispersion of the active layer, the effect of the energy detuning between the probe and pump signals and the effect of doping on the characteristics of cross-gain wavelength conversion. Our analysis reveals that broadband conversion efficiency can be obtained in QDsh SOA when the energy of the pump signal is at − 20 meV below the ground state. Also we find that large 3 dB bandwidth can be achieved when the energy of the pump and the probe signals is at + 30 meV. Our analysis shows that doping the dashes with P-type concentration can enhance the efficiency and the intrinsic 3 dB bandwidth of cross-gain wavelength conversion.     

Contrast ratio and hysteresis width of optical bistability in quantum-dot vertical-cavity semiconductor optical amplifiers integrated with MEMS membrane

The characteristics of optical bistability in quantum dot vertical cavity semiconductor optical amplifier integrated with MEMS membrane have been investigated, and a closed-form model is derived taking into account the effect of the quantum dot discrete states and the membrane deflection and reflectivity. We show that small membrane deflection significantly adjusts the resonant wavelength, the contrast ratios and the hysteresis width. The shape of the input–output characteristics of the device can be adjusted to display clockwise, butterfly and counterclockwise hysteresis loops depending on the membrane deflection and the initial wavelength detuning. Our analysis reveals that the contrast ratios of the upper and lower bistable levels are totally different. Also, it has been shown that the characteristics of the bistability are strong function of the active layer linewidth enhancement factor and the membrane reflectivity.     

Effect of static disorder in an electron Fabry-Perot interferometer with two quantum scattering centers

In a recent paper—F. Ciccarello et al., New J. Phys. 8, 214 (2006)—we have demonstrated that the electron transmission properties of a one-dimensional (1D) wire with two identical embedded spin-1/2 impurities can be significantly affected by entanglement between the spins of the scattering centers. Such an effect is of particular interest in the control of the transmission of quantum information in nanostructures and can be used as a detection scheme of maximally entangled states of two localized spins. In this letter, we relax the constraint that the two magnetic impurities are equal and investigate how the main results presented in the above paper are affected by a static disorder in the exchange coupling constants of the impurities. Good robustness against deviation from impurity symmetry is found for both the entanglement dependent transmission and the maximally entangled states generation scheme.     

Hidden-gauge model and radiative decays

We consider the radiative decay widths in a hidden-gauge model. For calculating the decay widths we use the anomalousVVP Lagrangian.g _VVP is a function off _P due to the symmetry breaking effects. It is shown thatf _P is consistent with that obtained by the one-loop calculation. A reasonable agreement with the experimental decay widths is achieved.     

A rigorous time domain analysis of gyrotrons

A self-consistent time domain analysis of gyrotrons is presented which allows studying multi-mode, multi-frequency operation. The electromagnetic field in the gyrotron cavity is expanded with respect to complete sets of eigenfunctions so that space charge effects are included in the analysis. Two improvements of the modal expansion inside gyrotron cavities are suggested which significantly increase the accuracy and the numerical efficiency of this method, namely, the removal of the non-uniform convergence of some field series at the coupling apertures and the estimation of the asymptotic values of some slowly converging series related to the modal analysis by a moderate number of cavity eigenfunctions. Discrete Fourier transform is used to obtain the time dependence of the electromagnetic field. The electron beam is described by a set of relativistic single particles. It is demonstrated that the strong numerical requirements of the suggested method can be overcome by using a vector computer. Two gyrotrons are investigated, namely, a low Q 35 GHz TE₀₁- and a 150 GHz TE₀₃-gyrotron. Both oscillation build-up and steady state operation are investigated including mode competition and window reflections. The simulations show that the assumption of a monofrequent steady state operation of gyrotrons, which is made by the commonly used frequency domain methods, is not always justified.     

Radio resource management for LTE-A relay-enhanced cells with spatial reuse and max–min fairness

One of the major issues in LTE-Advanced (LTE-A) systems is the poor capacity at the cell edge. This is mainly due to the interference experienced by the users as a result of the aggressive frequency reuse usually implemented. Relaying offers an attractive solution for this problem by offering better links than those with the eNodeB (eNB) for the terminals suffering from high path loss or high interference. However, adding relays complicates the resource allocation problem at the eNB and therefore the need for more efficient schemes arises. This is also aggravated by the reuse of resource blocks (RBs) by the relays to fully exploit the scarce spectrum, which, in turn, leads to intra-cell interference. In this paper, we study the joint power and resource allocation problem in LTE-A relay-enhanced cells that exploit spatial reuse. To guarantee fairness among users, a max–min fair optimization objective is used. This complex problem is solved using coordinate ascent and the difference of two convex functions (DC) programming techniques and the proposed scheme indeed converges to a local-optimum quickly. This is shown to be a satisfactory solution according to the simulation results that indicate an almost sevenfold increase in the 10th percentile capacity when compared to previously proposed solutions.     

A new video magnification technique using complex wavelets with Radon transform application

Magnifying micro-movements of natural videos that are undetectable by human eye has recently received considerable interests, due to its impact in numerous applications. In this paper, we use dual tree complex wavelet transform (DT-CWT), to analyze video frames in order to detect and magnify micro-movements to make them visible. We use DT-CWT, due to its excellent edge-preserving and nearly-shift invariant features. In order to detect any minor change in object’s spatial position, the paper proposes to modify the phases of the CWT coefficients decomposition of successive video frames. Furthermore, the paper applies Radon transform to track frame micro-movements without any temporal band-pass filtering. The paper starts by presenting a simple technique to design orthogonal filters that construct this CWT system. Next, it is shown that modifying the phase differences between the CWT coefficients of arbitrary frame and a reference one results in image spatial magnification. This in turn, makes these micro-movements seen and observable. Several simulation results are given, to show that the proposed technique competes very well to the existing micro-magnification approaches. In fact, as it manages to yield superior video quality in far less computation time.     

Validation and Correction for 208Tl Activity to Assay 232Th in Equilibrium with Its Daughters

Physics of Particles and Nuclei Letters - The natural radioactivity measurements and analysis of 232Th have been studied using γ-ray spectroscopy depending on its decay daughters in...