Volume 66, Issue 2
February 2006, pages 313-478
pp 313-324 February 2006
A new algorithm for anisotropic solutions
We establish a new algorithm that generates a new solution to the Einstein field equations, with an anisotropic matter distribution, from a seed isotropic solution. The new solution is expressed in terms of integrals of an isotropic gravitational potential; and the integration can be completed exactly for particular isotropic seed metrics. A good feature of our approach is that the anisotropic solutions necessarily have an isotropic limit. We find two examples of anisotropic solutions which generalise the isothermal sphere and the Schwarzschild interior sphere. Both examples are expressed in closed form involving elementary functions only.
pp 325-344 February 2006
The trace identity and the planar Casimir effect
The familiar trace identity associated with the scale transformationx^{Μ}→ x′^{Μ} = e^{-λ}x^{Μ} on the Lagrangian density for a noninteracting massive real scalar field in 2 + 1 dimensions is shown to be violated on a single plate on which the Dirichlet boundary condition Φ(t, x^{1}, x^{2} = -a) = 0 is imposed. It is however respected in: (i) 1 + 1 dimensions in both free space and on a single plate on which the Dirichlet boundary condition Φ(t, x^{1} = -a) = 0 holds and (ii) in 2 + 1 dimensions in free space, i.e. the unconstrained configuration. On the plate where Φ(t, x^{1}, x^{2}= -a) = 0, the modified trace identity is shown to be anomalous with a numerical coefficient for the anomalous term equal to the canonical scale dimension, viz. 1/2. The technique of Bordaget al [Ann. Phys. (N.Y.),165, 162 (1985)] is used to incorporate the said boundary condition into the generating functional for the connected Green’s functions.
pp 345-360 February 2006
The energy—momentum tensor, the trace identity and the Casimir effect
The trace identity associated with the scale transformation x^{Μ} → x′^{Μ} = e^{-ρ}x^{Μ} on the Lagrangian density for the noninteracting electromagnetic field in the co-variant gauge is shown to be violated on a single plate on which the Dirichlet boundary conditionA^{Μ}(t, x^{1}, x^{2}, x^{3} = -a) = 0 is imposed. It is however respected in free space, i.e. in the absence of the plate. These results reinforce our assertions in an earlier paper where the same exercise was carried out using the Lagrangian density for the free, massive, real scalar field in 2 + 1 dimensions.
pp 361-375 February 2006
Discriminating neutrino mass models using type-II see-saw formula
N Nimai Singh Mahadev Patgiri Mrinal Kumar Das
An attempt has been made to discriminate theoretically the three possible patterns of neutrino mass models,viz., degenerate, inverted hierarchical and normal hierachical models, within the framework of Type-II see-saw formula. From detailed numerical analysis we are able to arrive at a conclusion that the inverted hierarchical model with the same CP phase (referred to as Type [IIA]), appears to be most favourable to survive in nature (and hence most stable), with the normal hierarchical model (Type [III]) and inverted hierarchical model with opposite CP phase (Type [IIB]), follow next. The degenerate models (Types [IA,IB,IC]) are found to be most unstable. The neutrino mass matrices which are obtained using the usual canonical see-saw formula (Type I), and which also give almost good predictions of neutrino masses and mixings consistent with the latest neutrino oscillation data, are re-examined in the presence of the left-handed Higgs triplet within the framework of non-canonical see-saw formula (Type II). We then estimate a parameter (the so-called discriminator) which may represent the minimum degree of suppression of the extra term arising from the presence of left-handed Higgs triplet, so as to restore the good predictions on neutrino masses and mixings already acquired in Type-I see-saw model. The neutrino mass model is said to be favourable and hence stable when its canonical see-saw term dominates over the non-canonical (perturbative) term, and this condition is used here as a criterion for discriminating neutrino mass models.
pp 377-387 February 2006
On diquark clustering in quark—gluon plasma
A K Sisodiya V S Bhasin R S Kaushal
The possibility that pairs of quarks will form diquark clusters in the regime above deconfinement transition for hadron matter at finite density is revisited. Here we present the results on the diquark-diquark (dq-dq) interaction in the framework of constituent quark model taking account of spin, isospin and color degrees of freedom in the spirit of generalized Pauli principle. By constructing the appropriate spin and color states of the dq-dq clusters we compute the expectation values of the interaction Hamiltonian involving pairwise quark—quark interaction. We find that the effective interaction between two diquark clusters is quite sensitive to different configurations characterized by color and spin states, obtained after the coupling of two diquark states. The value of the coupling parameter for a particular color—spin state, i.e., -3, 1 is compared to the one obtained earlier by Donoghue and Sateesh,Phys. Rev.D38, 360 (1988) based on the effective Φ^{4}-theory. This new value of λ derived for different color-spin dq-dq states, may lead to several important implications in the studies of diquark star and diquark gas.
pp 389-401 February 2006
Microscopic study of low-lying collective bands in^{77}Kr
The structure of the collective bands in^{77}Kr is investigated within our deformed shell model (DSM) based on Hartree-Fock states. The different levels are classified into collective bands on the basis of their B(E2) values. The calculatedK = 5/2^{+} ground band agrees reasonably well with the experiment. An attempt has been made to study the structure of the 3-quasiparticle band based on large J state in this nucleus. The calculated collective bands, the B(E2), and B(M1) values are compared with available experimental data. The nature of alignments in the low-lying bands is also analyzed.
pp 403-414 February 2006
Ionization and excitation of some atomic targets and metal oxides by electron impact
K N Joshipura B G Vaishnav C G Limbachiya
We have calculated total inelastic and total ionization cross-sections for collisions of electrons on atomic targets oxygen (O), aluminium (Al) and copper (Cu) and metal oxides AlO and Al_{2}O, at impact energies from near excitation threshold to 2000 eV. A complex (optical) energy-dependent interaction potential is used to derive total inelastic cross-sections resulting from ionization as well as excitation processes. The inelastic cross-sections are bifurcated into discrete and continuum contributions and total ionization cross-sections have been deduced therefrom. Our calculation also provides information, hitherto sparse, on the excitation processes in the atomic targets O, Al, Cu and metal oxides AlO, Al_{2}O. Adequate comparisons are made with other theoretical and experimental data.
pp 415-422 February 2006
Coulomb—Born—Oppenheimer approximation in Ps—H scattering
To improve the Coulomb-Born approximation (CBA) theory of ionization in positronium (Ps) and atom scattering, the effect of exchange is introduced. The nine-dimensional exchange amplitude for ionization of Ps in Ps—H scattering is reduced to a two-dimensional integral using the present Coulomb-Born-Oppenheimer approximation (CBOA). The methodology is extremely useful to evaluate ionization parameters for different target systems and for different types of ionization processes. It is then applied to evaluate the Ps-ionization cross-section and to estimate the effect of exchange on Psionization in Ps-H system. We establish the importance of exchange at lower energy region.
pp 423-433 February 2006
Van der Waals coefficients for alkali metal clusters and their size dependence
In this paper we employ the hydrodynamic formulation of time-dependent density functional theory to obtain the van der Waals coefficientsC_{6} andC_{8} of alkali metal clusters of various sizes including very large clusters. Such calculations become computationally very demanding in the orbital-based Kohn-Sham formalism, but are quite simple in the hydrodynamic approach. We show that for interactions between the clusters of the same sizes,C_{6} andC_{8} scale as the sixth and the eighth power of the cluster radius, respectively, and approach their classically predicted values for the large size clusters.
pp 435-446 February 2006
Speed of sound and densities of the ternary mixture 2-propanol + diethyl ether + n-hexane and also the binary mixtures 2-propanol + diethyl ether and 2-propanol + n-hexane have been measured at the entire composition range at 298.15 K. The excess isentropic compressibilities and the excess speed of the sound have been calculated from experimental densities and speed of sound. These excess properties of the binary mixtures were fitted to Redlich-Kister equation, while the Cibulka’s equation was used to fit the values related to the values to the ternary system. These excess properties have been used to discuss the presence of significant interactions between the component molecules in the binary mixtures and also the ternary mixtures.
Speed of sound of the binary mixtures and the ternary mixture have been compared with calculated values from free length theory (FLT), collision factor theory (CFT), Nomoto’s relation (NR), Van Deal’s ideal mixing relation (IMR) and Junjie’s relation (JR). The results are used to compare the relative merits of these theories and relations in terms of the root mean square deviation relative (RMSD_{r}).
pp 447-453 February 2006
Field-theoretic calculation of kinetic helicity flux
V Avinash Mahendra K Verma Amar V Chandra
In this paper we apply perturbative field-theoretic technique to helical turbulence. In the inertial range the kinetic helicity flux is found to be constant and forward. The universal constantK^{H} appearing in the spectrum of kinetic helicity was found to be 2.47.
pp 455-465 February 2006
Electron-confined LO-phonon scattering in GaAs-Al_{0.45}Ga_{0.55}As superlattice
We develop a theoretical model to the scattering time due to the electron-confined LO-phonon in GaAs-Al_{x}Ga_{1-x}As superlattice taking into account the sub-band parabolicity. Using the new analytic wave function of electron miniband conduction of superlattice and a reformulation slab model for the confined LO-phonon modes, an expression for the electron-confined LO-phonon scattering time is obtained. In solving numerically a partial differential equation for the phonon generation rate, our results show that forx = 0.45, the LO-phonon in superlattice changes from a bulk-like propagating mode to a confined mode. The dispersion of the relaxation time due to the emission of confined LO-phonons depends strongly on the total energy.
pp 467-472 February 2006
Thermal effects on parallel resonance energy of whistler mode wave
Devendra A Siingh Shubha Singh R P Singh
In this short communication, we have evaluated the effect of thermal velocity of the plasma particles on the energy of resonantly interacting energetic electrons with the propagating whistler mode waves as a function of wave frequency and L-value for the normal and disturbed magnetospheric conditions. During the disturbed conditions when the magnetosphere is depleted in electron density, the resonance energy of the electron enhances by an order of magnitude at higher latitudes, whereas the effect is small at low latitudes. An attempt is made to explain the enhanced wave activity observed during magnetic storm periods.
pp 473-478 February 2006
Optical phase-conjugation in erioglaucine dye-doped thin film
T Geethakrishnan P K Palanisamy
Optical phase-conjugation (OPC) has been demonstrated in erioglaucine (acid blue 9) dye-doped gelatin films via continuous-wave degenerate four-wave mixing (DFWM) using a low-power He-Ne laser at 633 nm. DFWM and holographic processes are found to contribute to the observed phase-conjugate signal. A maximum phase-conjugate beam reflectivity of about 0.24% has been observed in these dye-doped gelatin films.
Current Issue
Volume 93 | Issue 5
November 2019
Click here for Editorial Note on CAP Mode
© 2017-2019 Indian Academy of Sciences, Bengaluru.