Bulk Viscous Cosmological Models in Barber's Second Self Creation Theory

Barber's second self creation theory with bulk viscous fluid source for an LRS Bianchi type-I metric is considered by using deceleration parameter to be constant where the metric potentials are taken as function of $x$ and $t$. The coefficient of bulk viscosity is assumed to be a power function of the mass density. Some physical and geometrical features of the models are discussedComment: latex, 10 pages, submitted in Int. J. Mod. Phys.

Studying the Variation of the Fine Structure Constant Using Emission Line Multiplets

As an extension of the method by Bahcall et al. (2004) to investigate the time dependence of the fine structure constant, we describe an approach based on new observations of forbidden line multiplets from different ionic species. We obtain optical spectra of fine structure transitions in [Ne III], [Ne V], [O III], [OI], and [SII] multiplets from a sample of 14 Seyfert 1.5 galaxies in the low-z range 0.035 < z < 0.281. Each source and each multiplet is independently analyzed to ascertain possible errors. Averaging over our sample, we obtain a conservative value alpha^2(t)/\alpha^2(0) = 1.0030+-0.0014. However, our sample is limited in size and our fitting technique simplistic as we primarily intend to illustrate the scope and strengths of emission line studies of the time variation of the fine structure constant. The approach can be further extended and generalized to a "many-multiplet emission line method" analogous in principle to the corresponding method using absorption lines. With that aim, we note that the theoretical limits on emission line ratios of selected ions are precisely known, and provide well constrained selection criteria. We also discuss several other forbidden and allowed lines that may constitute the basis for a more rigorous study using high-resolution instruments on the next generation of 8 m class telescopes.Comment: 20 pages, 4 figures, sumbitted to A

Magnetic Order Beyond RKKY in the Classical Kondo Lattice

We study the Kondo lattice model of band electrons coupled to classical spins, in three dimensions, using a combination of variational calculation and Monte Carlo. We use the weak coupling `RKKY' window and the strong coupling regime as benchmarks, but focus on the physically relevant intermediate coupling regime. Even for modest electron-spin coupling the phase boundaries move away from the RKKY results, the non interacting Fermi surface no longer dictates magnetic order, and weak coupling `spiral' phases give way to collinear order. We use these results to revisit the classic problem of 4f magnetism and demonstrate how both electronic structure and coupling effects beyond RKKY control the magnetism in these materials.Comment: 6 pages, 4 figs. Improved figures, expanded captions. To appear in Europhys. Let

Sampling rare fluctuations of height in the Oslo ricepile model

We have studied large deviations of the height of the pile from its mean value in the Oslo ricepile model. We sampled these very rare events with probabilities of order $10^{-100}$ by Monte Carlo simulations using importance sampling. These simulations check our qualitative arguement [Phys. Rev. E, {\bf 73}, 021303, 2006] that in steady state of the Oslo ricepile model, the probability of large negative height fluctuations $\Delta h=-\alpha L$ about the mean varies as $\exp(-\kappa {\alpha}^4 L^3)$ as $L \to \infty$ with $\alpha$ held fixed, and $\kappa > 0$.Comment: 7 pages, 8 figure

Simulation of air breakdown mechanism using different electrodes

Rapid growth in power sector of nation has given the opportunity to power engineers to protect the power equipment for reliable operation during their operating life. It has been seen from the several studies conducted by power engineers that one of the main problem in high voltage power (HV) equipment is the degradation of insulation i.e., quality of insulation of power equipment. As the high voltage power equipments are mainly subjected with spark over voltage causes by the lighting strokes, switching action, a protective device is used for determine the safe clearance required for proper insulation level. The sphere gaps are commonly used for measurements of peak values of high voltages and have been adopted by IEC and IEEE as a calibration device. Generally, the standard sphere gaps are widely used for protective device in electrical power equipments. The sphere gaps are filled up with insulating medium such as liquid insulation (transformer oil), and gas insulation (SF6, N2, CO2, CCl2F2 etc.) in HV power equipments. Normally, air medium is widely used as an insulating medium in different electrical power equipments as its breakdown strength is 30kV/cm. Therefore electrical breakdown characteristic of small air gap under the different applied voltage has its great significance for the design consideration of various air insulated HV equipment. In addition, the effect of breakdown voltage on different insulation like lamiflex, leatheroid, plywood, craft paper, and polyester fiber has also been studied. To observe the effect on insulation due to breakdown mechanism, the insulation samples are collected both before and after breakdown voltage test and analysis has been done with the help of Scanning electron microscope (SEM). To simulate the air breakdown voltage with and without the insulation barrier has been studied experimentally in high voltage laboratory, a standard diameter of 25 cm spheres are used for measurement of air breakdown voltages and electric field of the high voltage equipments. The above experiment is conducted at the normal temperature and pressure. The simulation of such air breakdown voltage has been carried out in the COMSOL environment. Finally, the experimental result has been compared with theoretical, and simulation results.

A snapshot of Central Bank (two year) forecasting: a mixed picture

Central Banks normally adjust monetary policy so that inflation hits the Inflation Target (IT) within two years. Since a central bank must believe its policy stance is appropriate to achieve this goal, its inflation forecast at the two-year horizon should generally be close to target. We examine whether this has held for three main Central Banks, Bank of England, ECB and Fed. During the IT period, there have been two crisis periods, The Great Financial Crisis (GFC), and then Covid/Ukraine. We examine how the two-year forecasts differed depending on whether we were in a crisis, or more normal, period. Although over the whole IT period, up until 2022, both forecasts and outcomes were commendably close to target, we found that this was due to a sizeable forecast underestimate of the effects of policy and inherent resilience to revive inflation after each crisis hit, largely offset by an overestimate of the effect of monetary policy to restore inflation to target during more normal times. We attribute such latter overestimation to an unwarranted belief in forward looking, ‘well anchored’, expectations amongst households and firms, and to a failure to recognise the underlying disinflationary trends, especially in 2010-2019. We outline a novel means for assessing whether these latter trends were primarily demand driven, e.g. secular stagnation, or supply shocks, a labour supply surge. Finally, we examine how forecasts for the uncertainty of outcomes and relative risk (skew) to the central forecast have developed by examining the Bank of England’s fan chart, again at the two-year horizon

Crossover Behavior in Burst Avalanches of Fiber Bundles: Signature of Imminent Failure

Bundles of many fibers, with statistically distributed thresholds for breakdown of individual fibers and where the load carried by a bursting fiber is equally distributed among the surviving members, are considered. During the breakdown process, avalanches consisting of simultaneous rupture of several fibers occur, with a distribution D(Delta) of the magnitude Delta of such avalanches. We show that there is, for certain threshold distributions, a crossover behavior of D(Delta) between two power laws D(Delta) proportional to Delta^(-xi), with xi=3/2 or xi=5/2. The latter is known to be the generic behavior, and we give the condition for which the D(Delta) proportional to Delta^(-3/2) behavior is seen. This crossover is a signal of imminent catastrophic failure in the fiber bundle. We find the same crossover behavior in the fuse model.Comment: 4 pages, 4 figure

Two-dimensional Nanolithography Using Atom Interferometry

We propose a novel scheme for the lithography of arbitrary, two-dimensional nanostructures via matter-wave interference. The required quantum control is provided by a pi/2-pi-pi/2 atom interferometer with an integrated atom lens system. The lens system is developed such that it allows simultaneous control over atomic wave-packet spatial extent, trajectory, and phase signature. We demonstrate arbitrary pattern formations with two-dimensional 87Rb wavepackets through numerical simulations of the scheme in a practical parameter space. Prospects for experimental realizations of the lithography scheme are also discussed.Comment: 36 pages, 4 figure

A comprehensive set of UV and x-ray radiative transition rates for Fe XVI

Sodium-like Fe XVI is observed in collisionally ionized plasmas such as stellar coronae and coronal line regions of active galactic nuclei including black hole-accretion disc environments. Given its recombination edge from neon-like Fe XVII at ~25 Å, the Fe XVI bound-bound transitions lie in the soft x-ray and EUV (extreme ultraviolet) range. We present a comprehensive set of theoretical transition rates for radiative dipole allowed E1 transitions including fine structure for levels with nℓ(SLJ) ≤ 10, ℓ ≤ 9 using the relativistic Breit-Pauli R-matrix (BPRM) method. In addition, forbidden transitions of electric quadrupole (E2), electric octupole (E3), magnetic dipole (M1) and magnetic quadrupole (M2) type are presented for levels up to 5g(SLJ) from relativistic atomic structure calculations in the Breit-Pauli approximation using code SUPERSTRUCTURE. Some of the computed levels are autoionizing, and oscillator strengths among those are also provided. BPRM results have been benchmarked with the relativistic coupled cluster method and the atomic structure Dirac-Fock code GRASP. Levels computed with the electron collision BPRM codes in bound state mode were identified with a procedure based on the analysis of quantum defects and asymptotic wavefunctions. The total number of Fe XVI levels considered is 96, with 822 E1 transitions. Tabulated values are presented for the oscillator strengths f, line strengths S and Einstein radiative decay rates A. This extensive dataset should enable spectral modelings up to highly excited levels, including recombination-cascade matrices.This work was partially supported by the NASA Astronomy and Physics Research Program and the Astrophysical Theory Program. The computational work was carried out at the Ohio Supercomputer Center in Columbus, Ohio. CS acknowledges discussions with Professor B P Das, Professor D Mukherjee and Professor R K Chaudhuri