Modern Physics Letters B

The stability of the time base of an oscilloscope has been analyzed by digitizing sinusoidal signals from precision sinusoidal voltage generators. Frequency domain analysis of the recorded data has been performed using the Fourier transform routine built into the recording device, after suitable windowing. Due to the stability of the frequency of the used signals, the expected frequency spectra would be Gaussian functions due to any uncorrelated noise born in all devices connecting the voltage signal generator to the memories of the oscilloscope. The experimental power spectra present instead a non-Gaussian shape, mainly in the points far from their mean values, showing raised "skirt", which a pure Gaussian function is clearly unable to fit. Among the many "deformed" Gaussian distribution functions, those named q-Gaussian and κ-Gaussian respectively, from the symbols used for the characterizing parameters, are instead in good agreement with all experimental power spectra. These results can be attributed mainly to correlated drifts in the time base of the oscilloscope.

The theory of mixed-order kinetics is well-established for the description of single thermoluminescence (TL) glow-peaks. The main advantage of mixed-order kinetics relative to the more widely used general-order kinetic theory is that the former is physically meaningful whereas the latter is entirely empirical. In the case of optically stimulated luminescence (OSL) either non-first-order or second-order kinetics are studied using the empirical general-order kinetics theory. In the present work, expressions for mixed-order kinetics are derived for OSL curves. A peak shape parameter for linear modulation OSL is developed and special mixed-order expressions are derived for use in the computerized OSL curve deconvolution analysis.

Detecting communities in weighted networks is becoming a challenging and interesting work. In this paper, a novel quantitative measure called weighted normalized modularity density is proposed and optimized to detect communities in weighted networks. Both theoretical certifications on simple schematic examples and numerical experiments on a suit of simulated networks and real-world networks show that the proposed quantitative measure not only improves the resolution limit in optimizing weighted modularity, but also avoids the emergence of negative communities in optimizing weighted modularity density.

A theoretical scheme of bidirectional quantum secure direct communication is proposed in the context of driven cavity QED. We first present an entanglement swapping scheme in cavities where two atoms without previous interaction can be entangled with a success probability of unity. Then, based on a novel property of entanglement swapping, we propose a bidirectional quantum secure direct communication protocol, in which two legitimate users can exchange their different secret messages simultaneously in a direct way. The probability of success in our scheme is 1.0. This scheme does not involve apparent (or direct) Bell-state measurements and is insensitive to the cavity decay and the thermal field.

A series of Ho:LiNbO₃ crystals with various concentration of Ho₂O₃ were grown by Czochralski technique. Transmittance spectrum, absorption spectrum and modified Judd–Ofelt approach have been used to investigate its spectroscopic properties. Ho concentrations in crystals were analyzed by an inductively-coupled plasma optical emission spectrometry (ICP-OE/MS). The results of the spectroscopic analysis of transition strengths for Ho ion in a series of Ho:LiNbO₃ crystals with various Ho content are reported. It is concluded that all the Ω_λ values of the Ho ion decrease with increasing Ho content. For Ho (4 mol%): LiNbO₃, the obtained intensity parameters and radiative lifetime of the ⁵I₅ level are: Ω₂=5.75×10^-20 cm², Ω₄=22.69×10^-20 cm², Ω₆=14.10×10^-20 cm², and τ=4.08 ms respectively. The results showed that the Ho₂O₃-codoped LiNbO₃ crystal increases the Ho ion radiative lifetimes, but has less influence on the fluorescence branching ratio.

The plane-wave pseudopotential method, based on density functional theory (DFT), has been used to calculate the electronic and optical properties of pure ZnO and N-doped ZnO. The results of density of states (DOS) indicate that the band gap of N-doped ZnO decreases due to the increase of p states in the valence band. Meanwhile, the results of the imaginary part of dielectric function ε₂(ω) reveal that the optical transition between O 2p states in the highest valence band and Zn 4s states in the lowest conduction band shifts to the low energy range due to N doping. The optical band gap of ZnO decreases from 3.2 to 2.2 eV after N doping.

The super extensions of g-cKdV and mKdV integrable systems are proposed. Two hierarchies of super-integrable nonlinear evolution equations are found. In addition, making use of the super-trace identity, we construct the super-Hamiltonian structures of zero-curvature equations associated with Lie superalgebras.

A GaAs/AlGaAs multi-quantum well (MQW) structure has been grown by solid source molecular beam epitaxy (MBE) and fabricated to detectors. A spectral response curve of the detector with full width at half maximum (FWHM) = 3.78 μm and peak wavelength = 9.73 μm has been obtained at a bias of E = 3 × 10³Vcm^-1 at T = 77 K. We study the bandwidth of the GaAs/AlGaAs quantum well infrared photodetector (QWIP) by using effective mass approximation. It is found that the transmissivity of the electron through the potential barrier reaches its maximum value (T = 1) on the condition of resonance transmission in a multi-quantum well structure, if the energy state is defined as a conduction state when the transmissivity of electron through the potential barrier on which is bigger than 1/2, then, a series of separated conduction microbands were formed above the barriers which consist of conduction states. Under the influence of an external electric field, the conduction microbands stagger periodically among the quantum wells to form a Wannier–Stark ladder. When optical excitation occurs, electrons not only vertically transit from Fermi level EF in a quantum well to conduction microbands above the well, but also obliquely transit to the conduction microbands above the neighboring well, and the formed photocurrent peaks overlap together; consequently, the bandwidth of the photoresponsive spectrum is improved. The calculated bandwidth of the photocurrent spectrum agrees well with the measured one in our experiment.

We study the eigenenergies and the eigenfunctions of the ground and the first excited states of an electron, which is strongly coupled to the LO-phonon in a quantum dot with triangular bound potential by using the Pekar variational method. This system may be used as a two-level qubit. Our numerical results indicate that the decoherence rate will decrease with increasing the confinement length of the quantum dot (QD) and decrease with increasing electron-LO-phonon coupling constant. The influences of the polar angle on the decoherence rate are dominant when the coupling constant increases, while the effects of the polar angle on that are strong when the confinement length increases. Meanwhile, the decoherence rate varies periodically with respect to the polar angle.

Arc erosion of Cu-C composites was investigated in air. The eroded zones on the cathode surface were observed by a scanning electron microscope, and the cathode erosion rates were measured. It can be found that the main mass loss results from ejection of copper and oxidization of carbon during discharges. The degree of erosion increases with the copper content. Meanwhile, the arc erosion rate is larger for the Cu-C materials with higher copper content. A large number of bubble-like particles appear on the electrode surface. The formation of those particles is closely related to the melting and ejection of copper and material transfer between the electrodes.

CoLa_xFe_2-xO₄ (x = 0.00, 0.05 and 0.1) nanoparticles were prepared simply by a modified citrate precursor route. Effects of La-substituting level on the their magnetic properties were investigated on the basis of the structural analysis. The thermal evolution of the precursor, as well as the microstructure of as-prepared products were studied by means of a thermogravimetric analyzer (TGA), X-ray diffractometer (XRD) and Fourier transform infrared (FTIR) spectrometer. The magnetic properties of the as-prepared samples were measured using a vibrating sample magnetometer (VSM). It was found that the magnetic properties were dependent on many factors such as La-substituting level, particle size and microstructure. The observed saturation magnetization decreased with increasing La content, whereas coercivity exhibited reverse behavior.

A sol–gel route based on tatrate/acetate was used to synthesize RuSr₂(Gd_2-xCe_x)Cu₂O_10-δ (x = 0.5 to 0.7) cuprate superconductors. A sample, with x = 0.6, was heated to 1050°C in oxygen flow for 24 h, followed by cooling at a rate of 1°C/min until it reached 100°C. The sample showed a single Ru-1222 phase with tetragonal symmetry. The lattice parameters for the sample were a = b = 3.863 Å and c = 28.57 Å. The onset transition temperature was 59 K, and the zero-resistance temperature was 40 K.

A recent paper [I. Klebanov et al., Mod. Phys. Lett. B22 (2008) 3153] claims that the exact solution of the Percus–Yevick (PY) integral equation for a system of hard spheres plus a step potential is obtained. The aim of this paper is to show that Klebanov et al.'s result is incompatible with the PY equation since it violates two known cases: the low density limit and the hard sphere limit.