Effect of Hall current on MHD natural convection flow from vertical permeable flat plate with uniform surface heat flux

The effect of the Hall current on the magnetohydrodynamic (MHD) natural convection flow from a vertical permeable flat plate with a uniform heat flux is analyzed in the presence of a transverse magnetic field.It is assumed that the induced magnetic field is negligible compared with the imposed magnetic field.The boundary layer equations are reduced to a suitable form by employing the free variable formulation (FVF) and the stream function formulation (SFF).The parabolic equations obtained from FVF are numer...     

Ring and jet study on the azimuthal substructure of pions at CERN SPS energy

We have presented an investigation on the ring- and jet-like azimuthal angle substructures in the emission of secondary charged hadrons coming from ³²S–Ag/Br interactions at 200 A GeV/c. Nuclear photographic emulsion technique has been employed to collect the experimental data. The presence of such substructures, their average behaviour, their size, and their position of occurrence have been examined. The experimental results have also been compared with the results simulated by Monte-Carlo method. The analysis strongly indicates the presence of ring- and jet-like structures in the experimental distributions of particles beyond statistical noise. The experimental results are in good agreement with I M Dremin idea, that the phenomenon is similar to the emission of Cherenkov electromagnetic radiation.     

Investigation of exotic modes of spinning nuclei near 9 0 Zr

Recently, a digital data acquisition system with 96 channels has been set up for the Indian National Gamma Array (INGA) consisting of 24 Compton-suppressed clover detectors. The digital system provides higher throughput, better energy resolution and better stability for the multidetector Compton-suppressed clover array compared to the previous conventional system with analog shaping. A number of nuclear spectroscopic experiments have been carried out using the array. Selected results from this array will be presented which highlight different excitations of nuclei near-shell gaps.     

Quantum restoration of broken symmetry in one-dimensional loop space

For one-dimensional loop space, a nonlinear nonlocal transformation of fields is given to make the action of the self-interacting quantum field to the free one. A specific type of classically broken symmetry is restored in quantum theory. One-dimensional sine-Gordon system and sech interactions are treated as the explicit examples.     

A near-infrared zero-order achromatic retarder

Phase retarders normally show strong wavelength dependence. Achromatic retarders which exhibit nearly identical characteristics over a wide wavelength spectrum is used in polychromatic light. The present investigation deals with a technique to design and study the characteristics of an achromatic combination of birefringent plates in 800–2000 nm range. The retarder has been designed using calcite, crystalline quartz and ADP. The thicknesses of the plates are 19.38 μm, 446.14 μm and 12.57 μm respectively. The new arrangement of three birefringent plates proposed has the promise of producing a zero-order quarter wave achromatic combination with fairly good accuracy.     

Ionization of Rydberg atoms by the kicks of half-cycle pulses

We present a quantum mechanical model to study the ionization of quasione-dimensional Rydberg atoms interacting with half-cycle pulses (HCPs) and use it to demonstrate the inadequacy of semiclassical approaches to calculate ionization probabilities of such atoms subject to the impact of more than one HCP. For a single-kicked atom both models correctly reproduce the experimentally observed ‘s-curve’ as can be seen by plotting the ionization probability P as a function of momentum transfer q₁. We demonstrate that for a twice-kicked atom, the semiclassical model yields numbers for P which are not physically realizable. For fixed values of momentum transfers q₁ and q₂, in a twice-kicked atom, the ionization probability as a function of time delay between the kicks exhibits periodic decay and revival. The results of the semiclassical approach appear to agree with the quantum mechanical values at the times of revival of P, else these show considerable deviation. We attempt to provide a physical explanation for the limitation of the semiclassical approach.     

Effect of Hall current on MHD natural convection flow from vertical permeable fiat plate with uniform surface heat flux

The effect of the Hall current on the magnetohydrodynamic (MHD) natural convection flow from a vertical permeable flat plate with a uniform heat flux is analyzed in the presence of a transverse magnetic field.It is assumed that the induced magnetic field is negligible compared with the imposed magnetic field.The boundary layer equations are reduced to a suitable form by employing the free variable formulation (FVF) and the stream function formulation (SFF).The parabolic equations obtained from FVF are numerically integrated with the help of a straightforward finite difference method.Moreover,the nonsimilar system of equations obtained from SFF is solved by using a local nonsimilarity method,for the whole range of the local transpiration parameter ζ.Consideration is also given to the regions where the local transpiration parameter ζis small or large enough.However,in these particular regions,solutions are acquired with the aid of a regular perturbation method.The effects of the magnetic field M and the Hall parameter m on the local skin friction coefficient and the local Nusselt number coefficient are graphically shown for smaller values of the Prandtl number Pr (=0.005,0.01,0.05).Furthermore,the velocity and temperature profiles are also drawn from various values of the local transpiration parameterζ.     

Top polarization and exploration of \mathbf{\emph{t}} \boldsymbol{\bar t} forward–backward asymmetry?

The large forward?Cbackward asymmetry in top pair-production observed at the Tevatron has generated much excitement in recent times. Many different models have been proposed as possible explanations for this anomaly. We discuss how the measurement of the polarization of the top quark can be used to establish the role of new physics in generating the observed asymmetry and to characterize and discriminate among various models.     

An elementary approach to the meromorphic continuation of some classical Dirichlet series

Here we obtain the meromorphic continuation of some classical Dirichlet series by means of elementary and simple translation formulae for these series. We are also able to determine the poles and the residues by this method. The motivation to our work originates from an idea of Ramanujan which he used to derive the meromorphic continuation of the Riemann zeta function.     

High harmonic generation in H2 + and HD + by two-colour femtosecond laser pulses

We have theoretically investigated the high harmonic generation (HHG) spectra of H₂ ^?+? and HD^?+? using a time-dependent wave packet approach for the nuclear motion with combined two-colour (1ω _L –3ω _L ) pulsed lasers for ω _L corresponding to wavelengths 1064 nm and 800 nm. The 1ω _L and 3ω _L lasers have peak intensities of I ₁ ⁰?=?5.0×10¹³ W/cm² and I ₂ ⁰?=?2.0×10¹⁴ W/cm², respectively. We have taken the pulse duration of T = 50 fs for both the fields, and the molecular initial vibrational level v ₀?=?0. We have argued that for these combinations, the harmonic generation due to transitions in the electronic continuum by tunnelling or multiphoton ionization may be neglected and only the electronic transitions within the two lowest electronic states would be important. Thus, the characteristic features of HHG spectra in the two-colour field are determined, in our model, by the nuclear motions on the two lowest field-coupled electronic states between which interelectronic and intraelectronic (due to the intrinsic dipole moments in case of HD^?+?) radiative transitions can take place. We have studied the role of relative phase (φ) of the two fields on the HHG spectra of the molecular ions. In case of HD^?+?, the effect of nonadiabatic (NA) nonradiative interaction between the two lowest Born-Oppenheimer (BO) electronic states (1sσ _g , 2pσ _u ) has been taken into account. Our calculations give realistic HHG spectra which are reasonably efficient and extended for both H₂ ^?+? and HD^?+? in the mixed two-colour field without involving the electronic continuum. The use of two-colour (1ω _L –3ω _L ) field enables us to generate high harmonics beyond that achievable with a single 1ω _L or 3ω _L field of the corresponding intensity, frequency and pulse time.