Slow solitary waves in multi-layered magnetic structures

The propagation of slow sausage surface waves in a multi-layered magnetic configuration is considered. The magnetic configuration consists of a central magnetic slab sandwiched between two identical magnetic slabs (with equilibrium quantities different from those in the central slab) which in turn are embedded between two identical semi-infinite regions. The dispersion equation is obtained in the linear approximation. The nonlinear governing equation describing waves with a characteristic wavelength along the central slab much larger than the slab thickness is derived. Solitary wave solutions to this equation are obtained in the case where these solutions deviate only slightly from the algebraic soliton of the Benjamin-Ono equation

Absence of spontaneous magnetic order at non-zero temperature in one- and two-dimensional Heisenberg and XY systems with long-range interactions

The Mermin-Wagner theorem is strengthened so as to rule out magnetic long-range order at T>0 in one- or two-dimensional Heisenberg and XY systems with long-range interactions decreasing as R^{-alpha} with a sufficiently large exponent alpha. For oscillatory interactions, ferromagnetic long-range order at T>0 is ruled out if alpha >= 1 (D=1) or alpha > 5/2 (D=2). For systems with monotonically decreasing interactions ferro- or antiferromagnetic long-range order at T>0 is ruled out if alpha >= 2D.Comment: RevTeX, 4 pages. Further (p)reprints available from http://www.mpi-halle.de/~theory ; v2: revised versio

Signal of Quark Deconfinement in the Timing Structure of Pulsar Spin-Down

The conversion of nuclear matter to quark matter in the core of a rotating neutron star alters its moment of inertia. Hence the epoch over which conversion takes place will be signaled in the spin-down "signal_prl.tex" 581 lines, 22203 characters characteristics of pulsars. We find that an observable called the braking index should be easily measurable during the transition epoch and can have a value far removed (by orders of magnitude) from the canonical value of three expected for magnetic dipole radiation, and may have either sign. The duration of the transition epoch is governed by the slow loss of angular momentum to radiation and is further prolonged by the reduction in the moment of inertia caused by the phase change which can even introduce an era of spin-up. We estimate that about one in a hundred pulsars may be passing through this phase. The phenomenon is analogous to ``bachbending'' observed in the moment of inertia of rotating nuclei observed in the 1970's, which also signaled a change in internal structure with changing spin.Comment: 5 pages, 4 figures, Revtex. (May 12, 1997, submitted to PRL

Charged Hydrogenic, Helium and Helium-Hydrogenic Molecular Chains in a Strong Magnetic Field

A non-relativistic classification of charged molecular hydrogenic, helium and mixed helium-hydrogenic chains with one or two electrons which can exist in a strong magnetic field $B \lesssim 10^{16}$G is given. It is shown that for both $1e-2e$ cases at the strongest studied magnetic fields the longest hydrogenic chain contains at most five protons indicating to the existence of the $\rm{H}_5^{4+}$ and $\rm{H}_5^{3+}$ ions, respectively. In the case of the helium chains the longest chains can exist at the strongest studied magnetic fields with three and four \al-particles for $1e-2e$ cases, respectively. For mixed helium-hydrogenic chains the number of heavy centers can reach five for highest magnetic fields studied. In general, for a fixed magnetic field two-electron chains are more bound than one-electron ones.Comment: 32 pages, 2 figures, 9 table

Effects of Steady Flow on Magnetoacoustic-Gravity Surface Waves: I. The Weak Field Case

Magnetoacoustic gravity (MAG) waves have been studied for some time. In this article, we investigate the effect that a shear flow at a tangential discontinuity embedded in a gravitationally stratified and magnetised plasma has on MAG surface waves. The dispersion relation found is algebraically analogous to the relation of the non-flow cases obtained by Miles and Roberts (Solar Phys.141, 205, 1992), except for the introduction of a Doppler-shifted frequency for the eigenvalue. This feature, however, introduces rather interesting physics, including the asymmetric presence of forward- and backward-propagating surface waves. We find that increasing the equilibrium flow speed leads to a shift in the permitted regions of propagation for surface waves. For most wave number combinations this leads to the fast mode being completely removed, as well as more limited phase speed regimes for slow-mode propagation. We also find that upon increasing the flow, the phase speeds of the backward propagating waves are increased. Eventually, at high enough flow speeds, the wave’s direction of propagation is reversed and is in the positive direction. However, the phase speed of the forward-propagating wave remains mainly the same. For strong enough flows we find that the Kelvin–Helmholtz instability can also occur when the forward- and backward-propagating modes couple

Lepton Jets in (Supersymmetric) Electroweak Processes

We consider some of the recent proposals in which weak-scale dark matter is accompanied by a GeV scale dark sector that could produce spectacular lepton-rich events at the LHC. Since much of the collider phenomenology is only weakly model dependent it is possible to arrive at generic predictions for the discovery potential of future experimental searches. We concentrate on the production of dark states through $Z^0$ bosons and electroweak-inos at the Tevatron or LHC, which are the cleanest channels for probing the dark sector. We properly take into account the effects of dark radiation and dark cascades on the formation of lepton jets. Finally, we present a concrete definition of a lepton jet and suggest several approaches for inclusive experimental searches.Comment: 23 pages, 13 figures, published version, added section 3.3 expanding on lepton jet's morpholog

Recent glitches detected in the Crab pulsar

From 2000 to 2010, monitoring of radio emission from the Crab pulsar at Xinjiang Observatory detected a total of nine glitches. The occurrence of glitches appears to be a random process as described by previous researches. A persistent change in pulse frequency and pulse frequency derivative after each glitch was found. There is no obvious correlation between glitch sizes and the time since last glitch. For these glitches $\Delta\nu_{p}$ and $\Delta\dot{\nu}_{p}$ span two orders of magnitude. The pulsar suffered the largest frequency jump ever seen on MJD 53067.1. The size of the glitch is $\sim$ 6.8 $\times 10^{-6}$ Hz, $\sim$ 3.5 times that of the glitch occured in 1989 glitch, with a very large permanent changes in frequency and pulse frequency derivative and followed by a decay with time constant $\sim$ 21 days. The braking index presents significant changes. We attribute this variation to a varying particle wind strength which may be caused by glitch activities. We discuss the properties of detected glitches in Crab pulsar and compare them with glitches in the Vela pulsar.Comment: Accepted for publication in Astrophysics & Space Scienc

The HeH+HeH^+ molecular ion in a magnetic field

A detailed study of the low-lying electronic states {}^1\Si,{}^3\Si,{}^3\Pi,{}^3\De of the $\rm{HeH}^+$ molecular ion in parallel to a magnetic field configuration (when \al-particle and proton are situated on the same magnetic line) is carried out for $B=0-4.414\times 10^{13}$ G in the Born-Oppenheimer approximation. The variational method is employed using a physically adequate trial function. It is shown that the parallel configuration is stable with respect to small deviations for \Si-states. The quantum numbers of the ground state depend on the magnetic field strength. The ground state evolves from the spin-singlet {}^1\Si state for small magnetic fields $B\lesssim 0.5$ a.u. to the spin-triplet {}^3\Si unbound state for intermediate fields and to the spin-triplet strongly bound $^3\Pi$ state for $B \gtrsim 15$ a.u. When the $\rm{HeH}^+$ molecular ion exists, it is stable with respect to a dissociation.Comment: 13 pages, 5 figures, 4 table

Activation of AMP-Activated Protein Kinase by Interleukin-6 in Rat Skeletal Muscle: Association With Changes in cAMP, Energy State, and Endogenous Fuel Mobilization

OBJECTIVE: Interleukin-6 (IL-6) directly activates AMP-activated protein kinase (AMPK) in vivo and in vitro; however, the mechanism by which it does so is unknown. RESEARCH DESIGN AND METHODS: We examined this question in skeletal muscle using an incubated rat extensor digitorum longus (EDL) muscle preparation as a tool. RESULTS: AMPK activation by IL-6 coincided temporally with a nearly threefold increase in the AMP:ATP ratio in the EDL. The effects of IL-6 on both AMPK activity and energy state were inhibited by coincubation with propranolol, suggesting involvement of β-adrenergic signaling. In keeping with this notion, IL-6 concurrently induced a transient increase in cAMP, and its ability to activate AMPK was blocked by the adenyl cyclase inhibitor 2′5′-dideoxyadenosine. In addition, like other β-adrenergic stimuli, IL-6 increased glycogen breakdown and lipolysis in the EDL. Similar effects of IL-6 on AMPK, energy state, and cAMP content were observed in C2C12 myotubes and gastrocnemius muscle in vivo, indicating that they were not unique to the incubated EDL. CONCLUSIONS: These studies demonstrate that IL-6 activates AMPK in skeletal muscle by increasing the concentration of cAMP and, secondarily, the AMP:ATP ratio. They also suggest that substantial increases in IL-6 concentrations, such as those that can result from its synthesis by muscles during exercise, may play a role in the mobilization of fuel stores within skeletal muscle as an added means of restoring energy balance.United States Public Health Service (RO1DK19514, RO1DK067509); Ruth L. Kirschstein NRSA Postdoctoral Training Grant (HL-07224); Fonds de la Recherche en Santé du Québe

Radiation properties of extreme nulling pulsar J1502-5653

We report on radiation properties of extreme nulling pulsar J1502-5653, by analyzing the data acquired from the Parkes 64-m telescope at 1374 MHz. The radio emission from this pulsar exhibits sequences of several tens to several hundreds consecutive burst pulses, separated by null pulses, and the appearance of the emission seems quasi-periodic. The null fraction from the data is estimated to be 93.6%. No emission is detected in the integrated profile of all null pulses. Systematic modulations of pulse intensity and phase are found at the beginning of burst-pulse sequences just after null. The intensity usually rises to a maximum for the first few pulses, then declines exponentially afterwards, and becomes stable after few tens of pulse periods. The peak phase appears at later longitudes for the first pulse, then drifts to earlier longitudes rapidly, and then systematic drifting gradually vanishes while the intensity becomes stable. In this pulsar, the intensity variation and phase modulation of pulses are correlated in a short duration after the emission starts following a null. Observed properties of the pulsar are compared with other nulling pulsars published previously, and the possible explanation for phase modulation is discussed.Comment: 5 pages, 7 figures. Accepted by MNRA