Authors:Xiao-Xi Zheng, Dan Wang, Li-Ming Tang, Ke-Qiu Chen Abstract: Modern Physics Letters B, Ahead of Print. Using the first-principles calculations, the holes-induced [math] magnetism associated with oxygen vacancy [math] in [math] and [math] has been investigated. To obtain holes, the divalent calcium and tetravalent IVB-group ions are replaced respectively by the monovalent alkali, IB-group and trivalent III-group ions. It is found that the [math] can enhance the magnetic moment of few acceptors-doped [math], whereas it enhances the magnetic moment in most acceptor-doped [math] except for La doping. Mainly, it is because the [math] gives rise to no gap-states in [math] but generates gap-states in [math]. Based on the similar effect of [math] on the band structure in [math] or in [math] (X = Ca, Sr, Ba), we suggest that there exists a similar effect of [math] on [math] magnetism in acceptor-doped alkaline titanium (zirconium) perovskites. Citation: Modern Physics Letters B PubDate: 2015-08-27T09:00:32Z DOI: 10.1142/S0217984915501377

Authors:Penghua Mu, Wei Pan, Shuiying Xiang, Nianqiang Li, Xinkai Liu, Xihua Zou Abstract: Modern Physics Letters B, Ahead of Print. High speed random number generation (RNG) utilizing a nonlinear optoelectronic oscillator (OEO) is explored experimentally. It has been found that by simply adjusting either the injected optical power or the gain of the modulator driver, low complexity dynamics such as square wave, and more complex dynamics including fully developed chaos can be experimentally achieved. More importantly, physical RNG based on high-speed-oscilloscope measurements and pseudo RNG based on post-processing are implemented in this paper. The generated bit sequences pass all the standard statistical random tests, indicating that fast physical and pseudo RNG could be achieved based on the same OEO entropy source. Our results could provide further insight into the implementation of RNG based on chaotic optical systems. Citation: Modern Physics Letters B PubDate: 2015-08-27T09:00:32Z DOI: 10.1142/S0217984915501420

Authors:Rana Arslan Afzal, Rahat Afrin, Umair Manzoor, Arshad Saleem Bhatti, Mohammad Islam, Muhammad T. Amin, Abdulrahman A. Alazba Abstract: Modern Physics Letters B, Ahead of Print. Multi-walled carbon nanotubes (CNTs) were grown via pyrolytic chemical vapor deposition technique and explored for their infrared sensing behavior. CNT synthesis was carried out over cobalt zinc ferrite [math] catalyst nanoparticles under different gas flow conditions to control outside diameter of the nanotubes. It was found that a progressive decrease in the carbon precursor gas (acetylene in this case) from 5:1 to 9:1 (v/v) causes reduction of average CNT diameter from 85 nm to 635 nm. Growth conditions involving higher temperatures yield nanotubes/nanofibers with outer diameter of [math][math]500 nm, presumably due to surface aggregation of nanoparticles or increased flux of carbonaceous species at the catalyst surface or both. Current–voltage characteristics of the nanotubes depending on the CNT diameter, revealed linear or nonlinear behavior. When incorporated as sensing layer, the sensitivity of [math][math]5.3 was noticed with response time of [math][math]4.1 s. It is believed that IR sensing characteristics of such CNT-based detectors can be further enhanced through post-synthesis purification and chemical functionalization treatments. Citation: Modern Physics Letters B PubDate: 2015-08-24T03:15:07Z DOI: 10.1142/S0217984915501316

Authors:Zun Cai, Zhen-Guo Wang, Ming-Bo Sun, Qing Li, Hong-Bo Wang Abstract: Modern Physics Letters B, Ahead of Print. In order to study the effect of ignition enhancement of partially covered cavity, ignition and flame propagation process of the partially covered cavity in a scramjet combustor are investigated numerically. Employing the cavity active injection, the characteristics of ignition and flame propagation of three cavity configurations are compared under inflow conditions of Ma = 2.1 with stagnation state [math] MPa, [math] K. It reveals that the cover plate of the cavity is detrimental to flame propagation but beneficial for ignition enhancement. The average static pressure and temperature of the partially covered cavity increases rapidly after ignition and the cover plate works in assembling the fuel in the corner recirculation zone. The covered region will become a fuel-rich region with high pressure and temperature, which acts as an intensified ignition source in the cavity. However, the application of cover plate in the cavity decreases the length-to-depth ratio of the cavity, restricts the flame propagation process and also decreases the thrust generated in the expansion section of the scramjet. Citation: Modern Physics Letters B PubDate: 2015-08-13T09:38:45Z DOI: 10.1142/S0217984915501328

Authors:Paul Bracken Abstract: Modern Physics Letters B, Ahead of Print. It is shown that the Kubo equation for the Hall conductance can be expressed as an integral which implies quantization of the Hall conductance. The integral can be interpreted as the first Chern class of a [math] principal fiber bundle on a two-dimensional torus. This accounts for the conductance given as an integer multiple of [math]. The formalism can be extended to deduce the fractional conductivity as well. Citation: Modern Physics Letters B PubDate: 2015-08-13T09:38:42Z DOI: 10.1142/S0217984915501353

Authors:Ke-Zhi Zhang, Yan Chen, Yong-Lin He, Zheng-Lai Liu Abstract: Modern Physics Letters B, Ahead of Print. We consider a dynamical model for superfluid Fermi gas, trapped in the central well of an axially symmetric Bessel optical lattice potential. The equation includes nonlinear power-law form of the chemical potential [math], for [math]), which accounts for Fermi pressure. Reducing the equation to two-dimensional (2D) form, we obtain the basic steady state solutions of the system along the Bose–Einstein condensation (BEC) side to Bardeen–Cooper–Schrieffer (BCS) side by employing the energy balance condition, which are guided by the variational approximation. It is found that the strength [math] and the radial scale r of the Bessel optical lattice have an extreme effect on the characters of basic steady state solution. Analytically, we deduce the atomic density distribution, the average atom number and the average energy of basic steady state, where the atom distribution of the system presents on periodic change with r, and increases faster at unitarity than in the BEC limit. Furthermore, because of the Fermi pressure, the atomic density distribution at the unitarity is more extensive than that in the BEC limit. In particular, there exist very interesting changes, the average energy intends to collapse state with r, however it emerges as a stable state with varying L both in the BEC limit and at unitarity. Citation: Modern Physics Letters B PubDate: 2015-08-03T09:33:05Z DOI: 10.1142/S021798491550133X

Authors:Santao Qi, Chuan-Hui Zhang, Bao Chen, Jiang Shen Abstract: Modern Physics Letters B, Ahead of Print. In this study, we have investigated the structural, electronic, magnetic and elastic properties of the full-Heusler [math] alloy in the framework of density functional theory with generalized gradient approximation (GGA). The calculated results showed that [math] was stable in ferrimagnetic configuration and crystallized in the [math]-type structure. From the band structure and density of states calculation results, we concluded that [math] belongs to a kind of half-metallic compound with an indirect band gap of 0.37[math]eV. Immediately thereafter, we have analyzed the origin of half-metallic band gap. The total magnetic moment of [math] at the stable state is [math] per formula unit, obeying the Slater–Pauling rule [math]. In addition, various mechanical properties have been obtained and discussed based on the three principle elastic tensor elements [math] and [math] for the first time in the present work. We expect that our calculated results may trigger the application of [math] in future spintronics field. Citation: Modern Physics Letters B PubDate: 2015-08-03T09:33:04Z DOI: 10.1142/S0217984915501390

Authors:Jian He, Lamei Liao, Qingguo Zhang Abstract: Modern Physics Letters B, Ahead of Print. In this paper, using the collisions between ion and free electron, we analyze the conditions of electron collision equilibrium (ECE) for laser-induced plasma (LIP). Considering the collision excitation and de-excitation, we discuss the principle for temperature diagnostic for the three level ions for LIP. Taking the Ne[math]v ion spectral lines in infrared as an example, for the intensity ratio of the (3-2) transition to the (2-1) transition, we compare the temperature in local thermal equilibrium and electron collision equilibrium when the intensity ratio varies from 0 to 1.8, and we obtain some important conclusions. This discussion is useful in the LIP diagnostic under the conditions of electron collision equilibrium. Citation: Modern Physics Letters B PubDate: 2015-08-03T09:33:04Z DOI: 10.1142/S0217984915501389

Authors:Feng Li, Peng Xu, Xiaochong Sui, Fujian Zhou Abstract: Modern Physics Letters B, Ahead of Print. Sealing problems, subsequent cleaning processes and poor force transmission effect etc. series of problems which strongly restrict the development and application of traditional medium pressure-based sheet forming technology. To overcome these problems, the magnetorheological fluid (MRF) can be used as the alternative force transmission medium. In this study, the deep drawing process of a 304 stainless steel sheet using MRF was investigated. The die cavity was filled with MRF and electric current was used to quantitatively adjust the magnetic fields distribution, which then controls the deformation behavior of the forming sheet. As compared to the conventional deep drawing process, experimental results clearly show that significant improvement in the produced sample quality was obtained when using the MRF with the electric current of 2[math]A. These improvements include: the height of the boundary circle reduces by 20%, the wall thickness distribution is more uniform, the rebound ratio correspondingly reduces from 9.6% to 0.67%, and the degree of sticking mode and the size precision are significantly increased. The results of this study provide scientific guidance to solve the bottleneck in the traditional deep drawing forming technology. The potential applications of the MRF-based new deep drawing technology to improve the product quality were explored. Citation: Modern Physics Letters B PubDate: 2015-08-03T09:33:03Z DOI: 10.1142/S0217984915501419

Authors:Shuying Zhong, Xueling Lei, Lang Zhou Abstract: Modern Physics Letters B, Ahead of Print. Atomic and electronic structures of monovacancy (V1), divacancy (V2) and ring hexavacancy (V6) in crystalline silicon are studied using first-principles calculations in periodic supercells. Our results show that the V6 defect is the most stable among V1, V2 and V6 defects, and the V2-RB structure is a little more stable than the V2-LP structure due to lower vacancy formation energy. Furthermore, it is found that both V1 and V2 undergo the Jahn–Teller (JT) distortion while V6 does not. As a result, V1 and V2 have deep levels in the gap which mainly come from the neighboring atoms to vacancy. V6 has tailing bands in the gap, and so has a more stable electronic structure than V1 and V2. In addition, the JT distortion also reflects in the band decomposed charge density and the difference charge density. Citation: Modern Physics Letters B PubDate: 2015-08-03T09:33:02Z DOI: 10.1142/S0217984915501365

Authors:Nansha Gao, Jiu Hui Wu, Li Jing Abstract: Modern Physics Letters B, Ahead of Print. In this paper, we study the band gaps (BGs) of the two-dimensional (2D) Sierpinski fractal phononic crystals (SFPGs) embedded in the homogenous matrix. The BGs structure, transmission spectra and displacement fields of eigenmodes of the proposed structures are calculated by using finite element method (FEM). Due to the simultaneous mechanisms of the Bragg scattering, the structure can exhibit low-frequency BGs, which can be effectively shifted by changing the inclusion rotation angle. The initial stress values can compress the BGs is proposed for the first time. Through the calculation, it is shown that, in the 2D solid–solid SFPG, the multi-frequency BGs exist. The whole BGs would incline to the low-frequency range with the increase of the fractal dimension. The SFPGs with different shape inclusions, can modulate the number, width and location of BGs. The study in this paper is relevant to the design of tuning BGs and isolators in the low-frequency range. Citation: Modern Physics Letters B PubDate: 2015-08-03T09:33:02Z DOI: 10.1142/S0217984915501341

Authors:Yunpeng Fan, Junhua Hou Abstract: Modern Physics Letters B, Ahead of Print. The electron–optical-phonon interaction between an electron and two branches of LO-phonon modes in a quasi-one-dimensional ternary mixed crystal (TMC) of polar semiconductors is studied. The new electron–phonon interaction Hamiltonian including the unit-cell volume variation in TMCs is obtained by using the modified random element isodisplacement model and Born–Huang method. The energies of polaron are numerically calculated for several systems of III–V compounds. A group of III-nitride mixed crystals is also taken into numerical calculation in our theory. It is verified theoretically that the obvious nonlinearity of the polaronic energy and effective mass with the composition is essential and the unit-cell volume effects cannot be neglected except the very weak e–p coupling. Citation: Modern Physics Letters B PubDate: 2015-07-29T01:01:41Z DOI: 10.1142/S0217984915501304

Authors:Yue-Feng Liu, Rui Guo, Hua Li Abstract: Modern Physics Letters B, Ahead of Print. Under investigation is the complex modified Korteweg–de Vries (KdV) equation, which has many physical significance in fluid mechanics, plasma physics and so on. Via the Darboux transformation (DT) method, some breather and localized solutions are presented on two backgrounds: the continuous wave background [math] and the constant background [math]. Some figures are plotted to illustrate the dynamical features of those solutions. Citation: Modern Physics Letters B PubDate: 2015-07-29T01:01:40Z DOI: 10.1142/S0217984915501298

Authors:Bobo Xu, Gaige Zheng, Yigen Wu Abstract: Modern Physics Letters B, Ahead of Print. Using finite difference time domain (FDTD) method, we numerically investigate one-dimensional photonic crystals (1D PCs) with [math] structure, where A and B stand for different dielectric materials, and C the graded-index (GRIN) material. The transmission properties of the multilayer structure have been studied, and the results show that a tunable narrow band-pass filter (BPF) can be obtained by changing gradient coefficients of the GRIN defect layer. For an increasing incident angle, although the transmittance becomes smaller, positions of the resonant peak remain the same, which can act as the angle-insensitive filter. Citation: Modern Physics Letters B PubDate: 2015-07-29T01:01:40Z DOI: 10.1142/S0217984915501286

Authors:R. Khordad Abstract: Modern Physics Letters B, Ahead of Print. In this paper, the specific heat, entropy and magnetic susceptibility of an asymmetric GaAs quantum dot (QD) are studied under the influence of temperature and a tilted external magnetic field. We first calculate the analytical wave functions and energy levels using a transformation to simplify the Hamiltonian of the system. Then, we obtain the analytical expressions for specific heat, entropy and magnetic susceptibility as the function of temperature, magnetic field and its direction for various anisotropy of the system. According to the results obtained from the present work, we find that (i) the specific heat and entropy are decreased when the magnetic field increases. (ii) When anisotropy is increased, the specific heat and entropy decrease. (iii) At large magnetic fields, the anisotropy has not important effect on specific heat and entropy. In briefly, the magnetic field, magnetic field direction and anisotropy play important roles in the specific heat, entropy and magnetic susceptibility of an asymmetric QD. Citation: Modern Physics Letters B PubDate: 2015-07-29T01:01:39Z DOI: 10.1142/S0217984915501274