Synthesis,characterization and third-order nonlinear optical properties of polydiacetylene nanostructures,silver nanoparticles and polydiacetylene–silver nanocomposites

We have synthesized, characterized and studied the third-order nonlinear optical properties of two different nanostructures of polydiacetylene (PDA), PDA nanocrystals and PDA nanovesicles, along with silver nanoparticles-decorated PDA nanovesicles. The second molecular hyperpolarizability γ(?ω; ω, ?ω, ω) of the samples has been investigated by antiresonant ring interferometric nonlinear spectroscopic (ARINS) technique using femtosecond mode-locked Ti:sapphire laser in the spectral range of 720–820 nm. The observed spectral dispersion of γ has been explained in the framework of three-essential states model and a correlation between the electronic structure and optical nonlinearity of the samples has been established. The energy of two-photon state, transition dipole moments and linewidth of the transitions have been estimated. We have observed that the nonlinear optical properties of PDA nanocrystals and nanovesicles are different because of the influence of chain coupling effects facilitated by the chain packing geometry of the monomers. On the other hand, our investigation reveals that the spectral dispersion characteristic of γ for silver nanoparticles-coated PDA nanovesicles is qualitatively similar to that observed for the uncoated PDA nanovesicles but bears no resemblance to that observed in silver nanoparticles. The presence of silver nanoparticles increases the γ values of the coated nanovesicles slightly as compared to that of the uncoated nanovesicles, suggesting a definite but weak coupling between the free electrons of the metal nanoparticles and π electrons of the polymer in the composite system. Our comparative studies show that the arrangement of polymer chains in polydiacetylene nanocrystals is more favourable for higher nonlinearity.     

Quillen bundle and geometric prequantization of non-abelian vortices on a Riemann surface

In this paper we prequantize the moduli space of non-abelian vortices. We explicitly calculate the symplectic form arising from L ² metric and we construct a prequantum line bundle whose curvature is proportional to this symplectic form. The prequantum line bundle turns out to be Quillen’s determinant line bundle with a modified Quillen metric. Next, as in the case of abelian vortices, we construct line bundles over the moduli space whose curvatures form a family of symplectic forms which are parametrized by Ψ₀, a section of a certain bundle. The equivalence of these prequantum bundles are discussed.     

The information paradox: Conflicts and resolutions

Many relativists have been long convinced that black hole evaporation leads to information loss or remnants. String theorists have however not been too worried about the issue, largely due to a belief that the Hawking argument for information loss is flawed in its details. A recently derived inequality shows that the Hawking argument for black holes with horizon can in fact be made rigorous. What happens instead is that in string theory, black hole microstates have no horizons. Thus the evolution of radiation quanta with E??kT is modified by order unity at the horizon, and we resolve the information paradox.     

Experimental study of yttrium barium copper oxide superconducting tape’s critical current under twisting moment

Critical current (I _c) characteristics of 2G YBCO superconducting tape under the influence of twisting moment was experimentally investigated at varying current ramp rates in the self-field. Under a uniform twist, the degradation in the current-carrying capacity of YBCO tape up to 30% was observed at 77 K. The degradation is largely attributed to the shear stress and torsional shear strain resulting from the twisting. The superconductor to resistive transition index, n, is also found to behave in an identical manner with increase in the twisting. Finite element analysis (FEA) of the tape in the experimental configuration with twisting moment being applied on to it has been carried out in COMSOL. The torsional strain calculated analytically as per the experimental configuration matches closely with that of FEA results, which shows that the critical current degradation is a function of strain.     

Presence of Jahn-Teller distortions in a novel six-coordinate Ag(II) complex: temperature dependent EPR,optical and magnetic susceptibility measurements

Single-crystal variable temperature EPR, optical and polycrystalline magnetic susceptibility studies have been made on a novel six-coordinate Ag(II) complex. Temperature dependent EPR studies on pure single crystals of this compound reveal that dynamic Jahn-Teller distortion operates above 230 K, between 230 K and 120K static Jahn-Teller distortion sets in and below 110 K there is evidence of exchange interaction. Crystal g values were obtained by least-squares fitting with the data obtained from the orientation dependent EPR spectra of the undiluted single crystal of this complex at 300 K and 77 K. From an optical study the Jahn-Teller stabilization energy is found to be ～2250cm^?1. Comparison of Abs_max values for other silver(II) compounds enables us to conclude that the formal geometry of this complex is a tetragonally distorted octahedral. Infrared spectra of this complex were also recorded over a wide range of temperature. Magnetic susceptibility measurements over a wide range of temperature on the powder sample of this compound reveal that the complex is antiferromagnetically coupled in the temperature range 5–40 K with 2J = 0.906cm^?1, and above 40K it is ferromagnetically coupled with 2J = +7.4cm^?1. The effective magnetic moment (μ_eff) of this complex has been compared with that of a series of other silver(II) complexes available in the literature. Finally, the spectral and magnetic data of this complex have been compared with those of a corresponding isostructural and isomorphous copper(II) complex.     

An analytical study on the Rayleigh wave generation in a stratified structure

In this paper, an analytical method is used to investigate the Rayleigh wave generation in a stratified structure and the wave generation in a dry sandy layer constrained between the couple stress and inhomogeneous orthotropic half-spaces. This study is devoted to analyzing the impact of various effective parameters associated with the media on the phase velocities of the wave. The displacement components for each medium are derived by implementing the separable variable method. The frequency eq...     

B s data at Tevatron and possible new physics

The new physics (NP) is parametrized with four model-independent quantities: the magnitudes and phases of the dispersive part M ₁₂ and the absorptive part ??₁₂ of the NP contribution to the effective Hamiltonian. We constrain these parameters using the four observables ??M _s, ????_s, the mixing phase $\beta_\mathrm{s}^{J/\psi\phi}$ and $A^b_{\rm sl}$ . This formalism is extended to include charge-parity-time reversal (CPT) violation, and it is shown that CPT violation by itself, or even in the presence of CPT-conserving NP without an absorptive part, helps only marginally in the simultaneous resolution of these anomalies.     

The effect of nuclear structure in the emission of reaction products in heavy-ion reactions

Study of intermediate mass fragments (IMFs) and light charged particles (LCPs) emission has been carried out for a few reactions involving α-cluster and non- α-cluster systems to see how the emission processes are affected by nuclear clustering. Li, Be, B and α-particles have been studied from α-clustered system ¹⁶O + ¹²C for 117, 125, 145 and 160 MeV bombarding energies respectively. The enhanced yields of near-entrance channel fragment B and large quadrupole deformation of the produced composite ²⁸Si^? extracted from LCP spectra indicate the survival of orbiting-like process in ¹⁶O + ¹²C system at these energies. The same IMFs emitted from the α-cluster system ¹²C (77 MeV) + ²⁸Si and nearby non- α cluster ¹¹B (64 MeV) + ²⁸Si and ¹²C (73 MeV) + ²⁷Al (all having the same excitation energy of ～67 MeV) have also been studied. The fully energy damped (fusion–fission) and the partially energy damped (deep inelastic) components of the fragment energy spectra have been extracted. It has been found that the yields of the fully energy damped fragments for all the above reactions are in conformity with the respective statistical model predictions. The time-scales of various deep inelastic fragment emissions have been extracted from the angular distribution data. The angular momentum dissipation in deep inelastic collisions has been estimated from the data and it has been found to be close to the corresponding sticking limit value.     

High harmonic generation in \textbf{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 $\textrm{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 ×10¹⁴ and 4.5 ×10¹⁴ W/cm², wavelengths (λ_L) of 800 and 1064 nm, and pulse durations (T) of 40 and 50 fs, for initial vibrational levels v 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 $\textrm{H}_2^+ $ and HD^?+? for v ₀?=?1 have been observed for higher value of I ₀ or λ_L. Our calculations indicate reasonable efficiencies of harmonic generation even without involving the electronic continuum.