Static charged spheres with anisotropic pressure in general relativity

We report a generalization of our earlier formalism [Pramana, 54, 663 (1998)] to obtain exact solutions of Einstein-Maxwell’s equations for static spheres filled with a charged fluid having anisotropic pressure and of null conductivity. Defining new variables: w=(4π/3)(ρ+ε)r ², u=4πξr ², v _r=4πp _r r ², v _⊥=4πp _⊥ r ²[ρ, ξ(=−(1/2)F ₁₄ F ¹⁴), p _r, p _⊥ being respectively the energy densities of matter and electrostatic fields, radial and transverse fluid pressures whereas ε denotes the eigenvalue of the conformal Weyl tensor and interpreted as the energy density of the free gravitational field], we have recast Einstein’s field equations into a form easy to integrate. Since the system is underdetermined we make the following assumptions to solve the field equations (i) u=v _r=(a ²/2κ)r ⁿ⁺², v _⊥=k ₁ v _r, w=k ₂ v _r; a ², n(>0), k ₁, k ₂ being constants with κ=((k ₁+2)/3+k ₂) and (ii) w+u=(b ²/2)r ⁿ⁺², u=v _r, v _⊥−v _r=k, with b and k as constants. In both cases the field equations are integrated completely. The first solution is regular in the metric as well as physical variables for all values of n>0. Even though the second solution contains terms like k/r ² since Q(0)=0 it is argued that the pressure anisotropy, caused by the electric flux near the centre, can be made to vanish reducing it to the generalized Cooperstock-de la Cruz solution given in [14]. The interior solutions are shown to match with the exterior Reissner-Nordstrom solution over a fixed boundary. Dedicated to Prof. F A E Pirani.     

Timing compensation for an excimer laser solid-state pulsed powermodule (SSPPM)

For certain applications, it is critical to minimize variations in the (throughput) timing between trigger and the output pulse of a magnetic modulator. A circuit is described that maintains a relatively constant delay over a large operating voltage range (600-1150 V) and temperature range (25 °C-65 °C) range, The circuit operates by sampling the charging voltage and magnetic switch temperature just prior to the start switch trigger. Those parameters are then used to calculate the appropriate amount of delay to add into the low-level trigger chain to ensure that the delay stays constant over the voltage and temperature operating range. Although other approaches can be conceived and implemented, this particular design is relatively simple and inexpensive and meets the desired performance goals. Data presented show that the ideal correction function is nonlinear in nature and, as a result, simple linear approximations are limited in their ability to minimize the timing variations. Improvements to the original circuit use a multiple, piece-wise, linear approach in order to obtain better performance. The results are that an initial timing variation of almost 3 μs has been reduced to a total variation of less than 100 ns     

A short range many-body potential for modelling bcc metals

The problem considered is the fitting of a many-body interaction potential to bulk crystal data. A parameterisation of the potential is assumed which is based on physical considerations. The free parameters are determined by using global optimization to perform a least squares fit, to a large number of crystal properties. This has been achieved for body centered cubic (bcc) materials. The approach adopted here fits the bcc crystal structure, as the preferred minimum energy configuration for tungsten, and also fits the dimer energetics and the elastic properties of crystalline tungsten.     

Spins of levels in 194Pt

Selected cascades in the level scheme of the ¹⁹⁴Pt nucleus have been studied by the γ-γ directional correlation method and the spins of the 924, 1513, 1623, 1672 and 1798 keV levels determined to be 3, 2, 2, 2 and 1 respectively. The multipole mixing ratios of the 301, 594, 1184 and 1295 keV γ-transitions have been determined and a number of B(E2) ratios are compared with theory.     

Torsion-rotation far-infrared spectrum of O-18 methanol

High-resolution Fourier transform spectra have been recorded from 15–470 cm^–1 for the far-infrared trosion-rotation band of O-18 methanol in the vibrational ground state. So far, 57 subbands have been assigned in the 15–220 cm^–1 region for a wide range of rotational and torsional states, and their J-independent origins have been determined to an estimated accuracy of ±0.01 cm^–1. The observed origins were found to deviate in many cases by several tenths of a cm^–1 from the values calculated with the previous molecular parameters. Together with 4 known microwave origins, the new data have been fitted to a model torsion-rotation Hamiltonian in order to refine the set ofb-type molecular constants for the ground state. With the new parameter set, the experimental subband origins are reproduced with an rms error of ±0.02 cm^–1, representing a substantial improvement over the earlier situation. The spectroscopic results have also been of great assistance with our assignments of optically-pumped FIR laser emission in CH₃ ¹⁸OH, in providing FIR data for checking the identification of the IR-pump/FIR-laser transition systems through combination loop relations.     

Synthesis of novel imidazo[1,2-a]pyridines with potent activity against herpesviruses

[reaction: see text] Synthesis of a novel imidazopyridine with potent activity against herpes simplex viruses is presented. Several synthetic approaches that describe the introduction of a C-3 pyrimidine substituent on the imidazopyridine core via construction of the pyrimidine or Stille coupling are outlined. Methodology for efficient installation of C-8 amine substituents was developed. The outlined strategies provide a high-yielding, scalable route that is amenable to rapid analogue synthesis.