Maps into projective spaces

We compute the cohomology of the Picard bundle on the desingularization $\tilde{J}^d(Y)$ of the compactified Jacobian of an irreducible nodal curve Y. We use it to compute the cohomology classes of the Brill–Noether loci in $\tilde{J}^d(Y)$ . We show that the moduli space M of morphisms of a fixed degree from Y to a projective space has a smooth compactification. As another application of the cohomology of the Picard bundle, we compute a top intersection number for the moduli space M confirming the Vafa–Intriligator formulae in the nodal case.     

Spectral analysis of K-shell X-ray emission of magnesium plasma produced by ultrashort high-intensity laser pulse irradiation

Spectral analysis of K-shell X-ray emission of magnesium plasma, produced by laser pulses of 45 fs duration, focussed up to an intensity of ～10¹⁸ W cm^?2, is carried out. The plasma conditions prevalent during the emission of X-ray spectrum were identified by comparing the experimental spectra with the synthetic spectra generated using the spectroscopic code PrismSPECT. It is observed that He-like resonance line emission occurs from the plasma region having sub-critical density, whereas K-α emission arises from the bulk solid heated to a temperature of 10 eV by the impact of hot electrons. K-α line from Be-like ions was used to estimate the hot electron temperature. A power law fit to the electron temperature showed a scaling of I ^0.47 with laser intensity.     

Computational evaluation of Henry's constants and isosteric heats of sorption for Lennard-Jones sorbates in Na-Y zeolite

Henry's constants and isosteric heats of sorption at infinite dilution are calculated for Lennard-Jones sorbates, including the rare gases Ar, Kr and Xe, in Na-Y zeolite. Isosteric heats of sorption are calculated as a function of sorbate size by molecular dynamics (MD) as well as from the temperature dependence of Henry's constants. The MD approach samples the low potential energy regions which form part of the dynamically connected pore space. In contrast, the Henry's constants are evaluated from the infinite dilution limit of the Widom particle insertion method and therefore can, in principle, sample all available, low potential energy pore regions regardless of dynamical connectivity. We show that the difference in the results obtained by the two approaches depends significantly on sorbate size. For a certain range in the sorbate size parameter, the extent of consistency between the two approaches will be sensitive to both temperature and the MD run lengths, providing an interesting illustration of the distinction between available and dynamically connected pore volumes.     

Bond orientational order in atomic clusters

Bond orientational order parameters for the global minimum energy configurations of a number of Lennard-Jones and Morse clusters are calculated. The results demonstrate that the bond orientational order parameters, particularly the third-order invariants, provide a fairly discriminating set of symmetry markers for different cluster geometries. Since they are relatively easy to calculate from simulation data, they may be useful in studies of local order in a wide variety of contexts, including studies of melting, nucleation and the glass transition     

Electric field enhancement at multiple densities in laser-irradiated nanotube plasma

The electric field enhancement inside a nanotube irradiated by intense ultrashort laser pulse (?1?ps) is calculated. The hollowness of the nanotubes determines the field enhancement and the electron density at which such structures exhibit resonance. The electric field in a nanotube plasma is shown to be resonantly enhanced at multiple densities during the two phases of interaction: the ionization phase and the hydrodynamic expansion phase. It is further shown that by a proper choice of hollowness of the nanotubes, a continued occurrence of the resonance over a longer time can be achieved. These properties make nanotubes efficient absorbers of intense ultrashort laser pulses.     

Structure and melting of Morse solids

Isothermal-isobaric ensemble Monte Carlo simulations are used to study the melting of Morse solids. At a given pressure, the temperature at which the solid ceases to be metastable and also the fractional changes in density and potential energy increase with decreasing range of the Morse pair potential. The structural properties of the liquid and solid phases vary significantly with the range. The longer range, softer potentials are associated with increased densities and cohesive energies in both the solid and liquid phases. The extent of local disorder associated with lattice sites in the solid phase, as measured by the Lindemann and bond orientational order parameters, increases with increasing range of the pair potential.     

Linearly polarized intracavity passive Q-switched Yb-doped photonic crystal fibre laser

In this paper we report linearly polarized high average power passive Q-switched ytterbium-doped photonic crystal fibre laser with a Cr⁴⁺:YAG crystal as a saturable absorber. An average output power of 9.4 W with pulse duration of 64 ns and pulse repetition rate of 57.4 kHz with a slope efficiency of 52% was achieved. Measured polarization extinction ratio (PER) of the Q-switched laser output was 10.5 dB.