• Volume 80, Issue 6

June 2013,   pages  917-1097

• New travelling wave solutions for nonlinear stochastic evolution equations

The nonlinear stochastic evolution equations have a wide range of applications in physics, chemistry, biology, economics and finance from various points of view. In this paper, the $(G'/G)$-expansion method is implemented for obtaining new travelling wave solutions of the nonlinear (2 + 1)-dimensional stochastic Broer–Kaup equation and stochastic coupled Korteweg–de Vries (KdV) equation. The study highlights the significant features of the method employed and its capability of handling nonlinear stochastic problems.

• Single-peak solitary wave solutions for the variant Boussinesq equations

This paper presents all possible smooth, cusped solitary wave solutions for the variant Boussinesq equations under the inhomogeneous boundary condition. The parametric conditions for the existence of smooth, cusped solitary wave solutions are given using the phase portrait analytical technique. Asymptotic analysis and numerical simulations are provided for smooth, cusped solitary wave solutions of the variant Boussinesq equations.

• The Kepler problem in the Snyder space

In this paper the Kepler problem in the non-commutative Snyder scenario was studied. The deformations were characterized in the Poisson bracket algebra under a mimic procedure from quantum standard formulations by taking into account a general recipe to build the noncommutative phase space coordinates (in the sense of Poisson brackets). An expression for the deformed potential was obtained, and then the consequences in the precession of the orbit of Mercury were calculated. The result could be used for finding an estimated value for the non-commutative deformation parameter.

• Microscopic study of positive-parity yrast bands of 224−234Th isotopes

The positive-parity bands in 224−234Th are studied using the projected shell model (PSM) approach. The energy levels, deformation systematics, $B(E2)$ transition probabilities and nuclear 𝑔-factors are calculated and compared with the experimental data. The calculation reproduces the observed positive-parity yrast bands and $B(E2)$ transition probabilities. Measurement of $B(E2)$ transition probabilities for higher spins and 𝑔-factors would be a stringent test for our predictions. The results of theoretical calculations indicate that the deformation systematics in 224−234Th isotopes depend on the occupation of low 𝑘 components of high j orbits in the valence space and the deformation producing tendency of the neutron–proton interaction operating between spin orbit partner (SOP) orbits, the $[(2g_{9/2}_{\pi}) - (2g_{7/2})_{\nu}]$ and $[(1i_{13/2})_{\pi} - (1i_{11/2})_{\nu}]$ SOP orbits in the present context. In addition, the deformation systematics also depend on the polarization of $(1h_{11/2})_{\pi}$ orbit. The low-lying states of yrast spectra are found to arise from 0-quasiparticle (qp) intrinsic states whereas the high-spin states turn out to possess composite structure.

• Three-dimensional simulation studies of 10 MeV, 352.2 MHz drift tube Linac

It is proposed to build a drift tube Linac (DTL) at Raja Ramanna Centre for Advanced Technology, Indore, India, that will form a part of the future Spallation Neutron Source. This DTL will accelerate 30 mA H-ion beam from 3 MeV to 10 MeV. The DTL is designed to operate at 352.2 MHz with a maximum duty cycle of $3$%. The DTL tank will consist of three sections, each about 1.2 m in length having 60 cells. The DTL has a ramped accelerating field, which is ramped in the first section of DTL from 1.8 to 2.2 MV/m and remains constant over the rest of the length of DTL. The field in DTL will be stabilized using post-couplers. The three-dimensional (3D) design of the DTL is done using CST microwave studio (CST MWS) incorporating the various nonaxisymmetric components such as tuners, post-couplers and vacuum ports. The frequency shifts due to these components have been evaluated. This paper presents the details of the studies and analysis of 3D simulations of post-couplers, tuners and vacuum ports.

• Searching for universal behaviour in superheated droplet detector with effective recoil nuclei

Energy calibration of superheated droplet detector is discussed in terms of the effective recoil nucleus threshold energy and the reduced superheat. This provides a universal energy calibration curve valid for different liquids used in this type of detector. Two widely used liquids, R114 and C4F10, one for neutron detection and the other for weakly interacting massive particles (WIMPs) dark matter search experiment, have been compared. Liquid having recoil nuclei with larger values of linear energy transfer (LET) provides better neutron-𝛾 discrimination. Gamma (𝛾) response of C4F10 has also been studied and the results are discussed. Behaviour of nucleation parameter with the effective recoil nucleus threshold energy and the reduced superheat have been explored.

• High harmonic generation in H$_{2}^{+}$ and HD+ by intense femtosecond laser pulses: A wave packet approach with nonadiabatic interaction in HD+

We have theoretically investigated the high harmonic generation (HHG) spectra of H$_{2}^{+}$ and HD+ using a time-dependent wave packet approach for the nuclear motion with pulsed lasers of peak intensities $(I_{0})$ of $3.5 \times 10^{14}$ and $4.5 \times 10^{14}$ W/cm2, wavelengths ($\lambda_{L}$) of 800 and 1064 nm, and pulse durations (𝑇) of 40 and 50 fs, for initial vibrational levels $\nu_{0} = 0$ and 1. We have argued that for these conditions the harmonic generation due to the transitions in the electronic continuum by tunnelling or multiphoton ionization will not be important. Thus, the characteristic features of HHG spectra in our model arise only due to the nuclear motions on the two lowest field-coupled electronic states between which both interelectronic and intraelectronic (due to intrinsic dipole moments, for HD+) radiative transitions can take place. For HD+, the effect of nonadiabatic (NA) interaction between the two lowest Born–Oppenheimer (BO) electronic states has been taken into account and comparison has been made with the HHG spectra of HD+ obtained in the BO approximation. Even harmonics and a second plateau in the HHG spectra of HD+ with the NA interaction and hyper-Raman lines in the spectra of both H$_{2}^{+}$ and HD+ for $\nu_{0} = 1$ have been observed for higher value of $I_{0}$ or $\lambda_{L}$. Our calculations indicate reasonable efficiencies of harmonic generation even without involving the electronic continuum.

• Temperature profile evolution in quenching high-$T_{c}$ superconducting composite tape

Irreversible normal zones leading to quench is an important aspect of high-temperature superconductors (HTS) in all practical applications. As a consequence of quench, transport current gets diverted to the matrix stabilizer material of the high-$T_{c}$ composite and causes Joule heating till the original conditions are restored. The nature of growth of the resistive zone in the superconductor greatly influences the temperature evolution of the quenched zone. In this investigation, a complete mathematical analysis of the temperature profile evolution following a quench in a HTS has been carried out. Such prediction in temperature profile would aid the design of HTS tape-based practical applications in limiting the thermal stress-induced damages in off-normal scenarios.

• Solitary heat waves in nonlinear lattices with squared on-site potential

A model Hamiltonian is proposed for heat conduction in a nonlinear lattice with squared on-site potential using the second quantized operators and averaging the same using a suitable wave function, equations are derived in discrete form for the field amplitude and the properties of heat transfer are examined theoretically. Numerical analysis shows that the propagation of heat is in the form of solitons. Furthermore, a systemized version of tanh method is carried out to extract solutions for the resulting nonlinear equations in the continuum case and the effect of inhomogeneity is studied for different temperatures.

• Nonlinear propagation of dust-acoustic solitary waves in a dusty plasma with arbitrarily charged dust and trapped electrons

A theoretical investigation of dust-acoustic solitary waves in three-component unmagnetized dusty plasma consisting of trapped electrons, Maxwellian ions, and arbitrarily charged cold mobile dust was done. It has been found that, owing to the departure from the Maxwellian electron distribution to a vortex-like one, the dynamics of small but finite amplitude dust-acoustic (DA) waves is governed by a nonlinear equation of modified Korteweg–de Vries (mKdV) type (instead of KdV). The reductive perturbation method was employed to study the basic features (amplitude, width, speed, etc.) of DA solitary waves which are significantly modified by the presence of trapped electrons. The implications of our results in space and laboratory plasmas are briefly discussed.

• Vibrational properties of vacancy in bcc transition metals using embedded atom method potentials

The embedded atom method (EAM) potentials, with the universal form of the embedding function along with the Morse form of pair potential, have been employed to determine the potential parameters for three bcc transition metals: Fe, Mo, and W, by fitting to Cauchy pressure $(C_{12} − C_{44})/2$, shear constants $G_{v} = (C_{11} − C_{12} + 3C_{44})/5$ and $C_{44}$, cohesive energy and the vacancy formation energy. The obtained potential parameters are used to calculate the phonon dispersion spectra of these metals. Large discrepancies are found between the calculated results of phonon dispersion using the EAM and the experimental phonon dispersion results. Therefore, to overcome this inadequacy of the EAM model, we employ the modified embedded atom method (MEAM) in which a modified term along with the pair potential and embedding function is added in the total energy. The phonon dispersions calculated using potential parameters obtained from the MEAM show good agreement with experimental results compared to those obtained from the EAM. Using the calculated phonons, we evaluate the local density of states of the neighbours of vacancy using the Green’s function method. The local frequency spectrum of first neighbours of vacancy in Mo shows an increase at higher frequencies and a shift towards the lower frequencies whereas in Fe and W, the frequency spectrum shows a small decrease towards higher frequency and small shift towards lower frequency. For the second neighbours of vacancy in all the three metals, the local frequency spectrum is not much different from that of the host atom. The local density of states of the neighbours of the vacancy has been used to calculate the mean square displacements and the formation entropy of vacancy. The calculated mean square displacements of the first neighbours of vacancy are found to be higher than that of the host atom, whereas it is lower for the second neighbours. The calculated results of the formation entropy of the vacancy compared well with other available results.

• Finding confined water in the hexagonal phase of Bi0.05Eu0.05Y0.90P$O$_{4}·𝑥H2O and its impact for identifying the location of luminescence quencher

1H MAS NMR spectra of Bi0.05Eu0.05Y0.90PO4·𝑥H2O show chemical shift from −0.56 ppm at 300 K to −3.8 ppm at 215 K and another one at 5–6 ppm, which are related to the confined or interstitial water in the hexagonal structure and water molecules on the surface of the particles, respectively. Negative value of the chemical shift indicates that H of H2O is closer to metal ions (Y3+ or Eu3+), which is a source of luminescence quencher. H coupling and decoupling 31P MAS NMR spectra at 300 and 250 K show the same chemical shift (−0.4 ppm) indicating that there is no direct bond between P and H. It is concluded that the confined water is not frozen even at 215 K because of the less number of H-bonding.

• Durability of rewritable phase-change Ge$_{X}$Sb$_{Y}$ Te$_{1−X−Y}$ memory devices

The bond constraint theory (BCT) dealing with the rigidity caused by bond constraints and the long-range potential fluctuations (LRPF) arising from the defects and heterogeneities in the disordered semiconductors are important for understanding the atomic and electronic properties of amorphous semiconductors. Here, they are applied to the already commercialized Ge$_{X}$Sb$_{Y}$ Te$_{1−X−Y}$ (GST) chalcogenide glasses used in the rewritable phase change memory (PCM) devices. The main concern at present is to improve their ability to withstand a large number of phase change cycles, by choosing the right composition. The two considerations (BCT and LRPF) are briefly described and tested on the most commonly used Ge2Sb2Te5 and the nearby compositions. While these considerations provide significant insight into their atomic and electronic structures, the ansatz linking them with the durability of the PCM devices need to be justified by more work.

• Erratum to: Quadrupole moments of low-lying baryons with spin $-\dfrac{1}{2}^{+}$, spin$-\dfrac{3}{2}^{+}$, and spin$-\dfrac{3}{2}^{+} \rightarrow \dfrac{1}{2}^{+}$ transitions

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