Analytic Solutions to the Constraint Equation for a Force-Free Magnetosphere around a Kerr Black Hole

The Blandford-Znajek constraint equation for a stationary, axisymmetric black-hole force-free magnetosphere is cast in a 3+1 absolute space and time formulation, following Komissarov (2004). We derive an analytic solution for fields and currents to the constraint equation in the far-field limit that satisfies the Znajek condition at the event horizon. This solution generalizes the Blandford-Znajek monopole solution for a slowly rotating black hole to black holes with arbitrary angular momentum. Energy and angular momentum extraction through this solution occurs mostly along the equatorial plane. We also present a nonphysical, reverse jet-like solution.Comment: 6 pages, accepted for publication in Ap

Evolution of Sonar Survey Systems for Sea Floor Studies

Approximately 71% of our planet is covered with oceans. It is also known that oceans are the last frontiers for the mankind’s survival and therefore it becomes pertinent that they are studied in great details. It has been found that the exploration of the oceans can be done more precisely using acoustics as one of the methods, as the acoustic waves can propagate over large distances and also using a broad spectrum of frequencies various issues of the ocean studies can be addressed more effectively than many of the other methods, both in terms resolution (using high frequency components) of measuring parameters and over large ranges (using low to very low frequency components). Currently with the technological advancement and improved computing algorithms, we have state of art systems for ocean exploration, which can provide information about the sea floor, sub-surface including ocean floor classification. These could be projected in 2-D and 3-D visualization to a great accuracy. Also available are acoustical methods wherein one can obtain an extremely important information about water column properties (both in terms of bioinformation and physical properties), and has great importance as this water column is the medium for transmission of all kind of energies(acoustic for short, medium and long ranges and some time light source for exploration over a very short distance) that are used for exploration on the oceans. It will therefore be interesting to understand the progress of underwater acoustics from its very primitive stage, where acoustic transmission through water medium was used for first time to the present day highly complex but very advanced acoustic sea-floor surveying systems. It will also be interesting to know, with a very old maritime history of using seas for transportation, as to what were the methods used by early time seafarers to understand depths of the oceans they were sailing. It has taken almost a century in developing an acoustic system to arrive at the present day advancement. An attempt has been made to present a perspective of evolution and advancement in underwater acoustics and related electronic, material and computational advancement, starting from the early attempts to the modern day acoustic equipments

Quasiparticle spectra from a non-empirical optimally-tuned range-separated hybrid density functional

We present a method for obtaining outer valence quasiparticle excitation energies from a DFT-based calculation, with accuracy that is comparable to that of many-body perturbation theory within the GW approximation. The approach uses a range-separated hybrid density functional, with asymptotically exact and short-range fractional Fock exchange. The functional contains two parameters - the range separation and the short-range Fock fraction. Both are determined non-empirically, per system, based on satisfaction of exact physical constraints for the ionization potential and many-electron self-interaction, respectively. The accuracy of the method is demonstrated on four important benchmark organic molecules: perylene, pentacene, 3,4,9,10-perylene-tetracarboxylic-dianydride (PTCDA) and 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA). We envision that for finite systems the approach could provide an inexpensive alternative to GW, opening the door to the study of presently out of reach large-scale systems

Possible large-N fixed-points and naturalness for O(N) scalar fields

We try to use scale-invariance and the large-N limit to find a non-trivial 4d O(N) scalar field model with controlled UV behavior and naturally light scalar excitations. The principle is to fix interactions by requiring the effective action for space-time dependent background fields to be finite and scale-invariant when regulators are removed. We find a line of non-trivial UV fixed-points in the large-N limit, parameterized by a dimensionless coupling. They reduce to classical la phi^4 theory when hbar -> 0. For hbar non-zero, neither action nor measure is scale-invariant, but the effective action is. Scale invariance makes it natural to set a mass deformation to zero. The model has phases where O(N) invariance is unbroken or spontaneously broken. Masses of the lightest excitations above the unbroken vacuum are found. We derive a non-linear equation for oscillations about the broken vacuum. The interaction potential is shown to have a locality property at large-N. In 3d, our construction reduces to the line of large-N fixed-points in |phi|^6 theory.Comment: 23 page