Gravitating dyons and the Lue-Weinberg bifurcation

Gravitating t'Hooft-Polyakov magnetic monopoles can be constructed when coupling the Georgi-Glashow model to gravitation. For a given value of the Higgs boson mass, these gravitating solitons exist up to a critical value of the ratio of the vector meson mass to the Planck mass. The critical solution is characterized by a degenerate horizon of the metric. As pointed out recently by Lue and Weinberg, two types of critical solutions can occur, depending on the value of the Higgs boson mass. Here we investigate this transition for dyons and show that the Lue and Weinberg phenomenon is favorized by the presence of the electric-charge degree of freedom.Comment: RevTeX, 6 pages, 8 figure

A Barren Landscape?

We consider the generation of a non-perturbative superpotential in F-theory compactifications with flux. We derive a necessary condition for the generation of such a superpotential in F-theory. For models with a single volume modulus, we show that the volume modulus is never stabilized by either abelian instantons or gaugino condensation. We then comment on how our analysis extends to a larger class of compactifications. From our results, it appears that among large volume string compactifications, metastable de Sitter vacua (should any exist) are non-generic.Comment: 14 pages, comments adde

Locating the minimum : Approach to equilibrium in a disordered, symmetric zero range process

We consider the dynamics of the disordered, one-dimensional, symmetric zero range process in which a particle from an occupied site $k$ hops to its nearest neighbour with a quenched rate $w(k)$. These rates are chosen randomly from the probability distribution $f(w) \sim (w-c)^{n}$, where $c$ is the lower cutoff. For $n > 0$, this model is known to exhibit a phase transition in the steady state from a low density phase with a finite number of particles at each site to a high density aggregate phase in which the site with the lowest hopping rate supports an infinite number of particles. In the latter case, it is interesting to ask how the system locates the site with globally minimum rate. We use an argument based on local equilibrium, supported by Monte Carlo simulations, to describe the approach to the steady state. We find that at large enough time, the mass transport in the regions with a smooth density profile is described by a diffusion equation with site-dependent rates, while the isolated points where the mass distribution is singular act as the boundaries of these regions. Our argument implies that the relaxation time scales with the system size $L$ as $L^{z}$ with $z=2+1/(n+1)$ for $n > 1$ and suggests a different behaviour for $n < 1$.Comment: Revtex, 7 pages including 3 figures. Submitted to Pramana -- special issue on mesoscopic and disordered system

Driven Lattice Gases with Quenched Disorder: Exact Results and Different Macroscopic Regimes

We study the effect of quenched spatial disorder on the steady states of driven systems of interacting particles. Two sorts of models are studied: disordered drop-push processes and their generalizations, and the disordered asymmetric simple exclusion process. We write down the exact steady-state measure, and consequently a number of physical quantities explicitly, for the drop-push dynamics in any dimensions for arbitrary disorder. We find that three qualitatively different regimes of behaviour are possible in 1-$d$ disordered driven systems. In the Vanishing-Current regime, the steady-state current approaches zero in the thermodynamic limit. A system with a non-zero current can either be in the Homogeneous regime, chracterized by a single macroscopic density, or the Segregated-Density regime, with macroscopic regions of different densities. We comment on certain important constraints to be taken care of in any field theory of disordered systems.Comment: RevTex, 17pages, 18 figures included using psfig.st

Efficacy of once-weekly Isoniazid-Streptomycin in preventing relapse of pulmonary tuberculosis

Two controlled studies were undertaken to assess the efficacy of streptomycin 1 g. or 0.75 g. (by random allocation) plus isoniazid 15 mg./kg. body-weight once-weekly (the SHOW regimen) in the prevention of bacteriological relapse over a 4 year period, in patients with quiescent pulmonary tuberculosis at the end of one year of chemotherapy. In the first study which involved patients with residual cavitation at one year, bacteriological relapse requiring treatment occurred in 3 per cent of 87 patients given the SHOW regimen for 12 months as compared with 21 per cent of 94 patients on a placebo, a high proportion of the relapses in the latter occurred in the 2nd year and with sensitive organisms. In the second study on patients with no residual cavitation at one year, relapse requiring treatment occurred in 2 per cent of 98 patients given the SHOW regimen for 6 months as compared with 1 per cent of 90 patients given isoniazid approximately 4.5 mg./kg. daily for 12 months

Excited state spectroscopy and spin splitting in atomically thin quantum dots

Semiconducting transition metal dichalcogenides (TMDCs) are very promising materials for quantum dots and spin-qubit implementation. Reliable operation of spin qubits requires the knowledge of Land\'e g-factor, which can be measured by exploiting the discrete energy spectrum on a quantum dot. However, the quantum dots realized in TMDCs has yet to reach the required quality for reliable measurement of g-factor. Quantum dot sizes reported in TMDCs so far are not small enough to observe discrete energy levels on them. Here, we report on electron transport through discrete energy levels of quantum dot in a single layer MoS2. The quantum dot energy levels are separated by few (5-6) meV such that the ground state and the excited state transitions are clearly visible. This well resolved energy separation allows us to accurately measure the ground state g-factor of ~5 in MoS2 quantum dots. We observe a spin filling sequence in our quantum dot under perpendicular magnetic field. Such a system offers an excellent testbed to measure the key parameters for evaluation and implementation of spin-valley qubits in TMDCs, thus accelerating the development of quantum systems in two dimensional semiconducting TMDCs.Comment: 17 pages, 10 figure

Non-Supersymmetric Attractors and Entropy Function

We study the entropy of non-supersymmetric extremal black holes which exhibit attractor mechanism by making use of the entropy function. This method, being simple, can be used to calculate corrections to the entropy due to higher order corrections to the action. In particular we apply this method for five dimensional non-supersymmetric extremal black hole which carries two magnetic charges and find the R^2 corrections to the entropy. Using the behavior of the action evaluated for the extremal black hole near the horizon, we also present a simple expression for C-function corrected by higher order corrections.Comment: 15 pages, Latex file, v2: references and some additional comments added, minor corrections, some comments about 5D supersymmetric BH added. v3:minor corrections, few comments added, refs. adde

Diversity amongst human cortical pyramidal neurons revealed via their sag currents and frequency preferences

In the human neocortex coherent interlaminar theta oscillations are driven by deep cortical layers, suggesting neurons in these layers exhibit distinct electrophysiological properties. To characterize this potential distinctiveness, we use in vitro whole-cell recordings from cortical layers 2 and 3 (L2&3), layer 3c (L3c) and layer 5 (L5) of the human cortex. Across all layers we observe notable heterogeneity, indicating human cortical pyramidal neurons are an electrophysiologically diverse population. L5 pyramidal cells are the most excitable of these neurons and exhibit the most prominent sag current (abolished by blockade of the hyperpolarization activated cation current, Ih). While subthreshold resonance is more common in L3c and L5, we rarely observe this resonance at frequencies greater than 2 Hz. However, the frequency dependent gain of L5 neurons reveals they are most adept at tracking both delta and theta frequency inputs, a unique feature that may indirectly be important for the generation of cortical theta oscillations

Continuous engagement of a self-specific activation receptor induces NK cell tolerance

Natural killer (NK) cell tolerance mechanisms are incompletely understood. One possibility is that they possess self-specific activation receptors that result in hyporesponsiveness unless modulated by self–major histocompatability complex (MHC)–specific inhibitory receptors. As putative self-specific activation receptors have not been well characterized, we studied a transgenic C57BL/6 mouse that ubiquitously expresses m157 (m157-Tg), which is the murine cytomegalovirus (MCMV)–encoded ligand for the Ly49H NK cell activation receptor. The transgenic mice were more susceptible to MCMV infection and were unable to reject m157-Tg bone marrow, suggesting defects in Ly49H+ NK cells. There was a reversible hyporesponsiveness of Ly49H+ NK cells that extended to Ly49H-independent stimuli. Continuous Ly49H–m157 interaction was necessary for the functional defects. Interestingly, functional defects occurred when mature wild-type NK cells were adoptively transferred to m157-Tg mice, suggesting that mature NK cells may acquire hyporesponsiveness. Importantly, NK cell tolerance caused by Ly49H–m157 interaction was similar in NK cells regardless of expression of Ly49C, an inhibitory receptor specific for a self-MHC allele in C57BL/6 mice. Thus, engagement of self-specific activation receptors in vivo induces an NK cell tolerance effect that is not affected by self-MHC–specific inhibitory receptors