19,425 research outputs found
Atypical Thermonuclear Supernovae from Tidally Crushed White Dwarfs
Suggestive evidence has accumulated that intermediate mass black holes (IMBH)
exist in some globular clusters. As stars diffuse in the cluster, some will
inevitable wander sufficiently close to the hole that they suffer tidal
disruption. An attractive feature of the IMBH hypothesis is its potential to
disrupt not only solar-type stars but also compact white dwarf stars. Attention
is given to the fate of white dwarfs that approach the hole close enough to be
disrupted and compressed to such extent that explosive nuclear burning may be
triggered. Precise modeling of the dynamics of the encounter coupled with a
nuclear network allow for a realistic determination of the explosive energy
release, and it is argued that ignition is a natural outcome for white dwarfs
of all varieties passing well within the tidal radius. Although event rates are
estimated to be significantly less than the rate of normal Type Ia supernovae,
such encounters may be frequent enough in globular clusters harboring an IMBH
to warrant a search for this new class of supernova.Comment: 13 pages, 4 figures, ApJ, accepte
The symmetry of the spin Hamiltonian in herbertsmithite, a spin-1/2 kagom\'{e} lattice
We present magnetization measurements on oriented powder of
ZnCu(OH)Cl along and perpendicular to the orienting field. We
find a dramatic difference in the magnetization between the two directions. It
is biggest at low measurement fields or high temperatures. We show that the
difference at high temperatures must emerge from Ising-like exchange
anisotropy. This allows us to explain muon spin rotation data at in
terms of an exotic ferromagnetic ground state.Comment: 5 pages, 5 figure
High-precision laser spectroscopy of the CO A - X (2,0), (3,0) and (4,0) bands
High-precision two-photon Doppler-free frequency measurements have been
performed on the CO A - X fourth-positive system (2,0),
(3,0), and (4,0) bands. Absolute frequencies of forty-three transitions, for
rotational quantum numbers up to , have been determined at an accuracy
of cm, using advanced techniques of two-color 2+1'
resonance-enhanced multi-photon ionization, Sagnac interferometry,
frequency-chirp analysis on the laser pulses, and correction for AC-Stark
shifts. The accurate transition frequencies of the CO A - X
system are of relevance for comparison with astronomical data in the search for
possible drifts of fundamental constants in the early universe. The present
accuracies in laboratory wavelengths of may be considered exact for the purpose of such comparisons.Comment: 13 pages, 6 figures, The Journal of Chemical Physics (2015) accepte
Steroid-Induced Psychosis Presenting as Alice in Wonderland Syndrome
A 40 year old overweight male with a history of bronchial asthma, hypertension, and “schizophrenia” was admitted for intractable bronchial asthma. He did not have a history of drug or alcohol use.
Upon admission, he was treated with high doses of IV methyl prednisone, oral prednisone, and triamcinolone inhaler. He developed complex visual hallucinations which decreased following tapering of prednisone and discontinuation of the triamcinolone. EEG showed diffuse slowing suggesting a toxic metabolic state
Epitaxial Thin Films of the Giant-Dielectric-Constant Material CaCu_3Ti_4O_{12} Grown by Pulsed-laser Deposition
Pulsed-laser deposition has been used to grow epitaxial thin films of the
giant-dielectric-constant material CaCu_3Ti_4O_{12} on LaAlO_3 and SrTiO_3
substrates with or without various conducting buffer layers. The latter include
YBa_2Cu_3O_7, La_{1.85}Sr_{0.15}CuO_{4+\delta} and LaNiO_3. Above 100K - 150K
the thin films have a temperature independent dielectric constant as do single
crystals. The value of the dielectric constant is of the order of 1500 over a
wide temperature region, potentially making it a good candidate for many
applications. The frequency dependence of its dielectric properties below 100K
- 150K indicates an activated relaxation process.Comment: 11 pages, 4 figure
Recommended from our members
Plasma Membrane-Associated Restriction Factors and Their Counteraction by HIV-1 Accessory Proteins.
The plasma membrane is a site of conflict between host defenses and many viruses. One aspect of this conflict is the host's attempt to eliminate infected cells using innate and adaptive cell-mediated immune mechanisms that recognize features of the plasma membrane characteristic of viral infection. Another is the expression of plasma membrane-associated proteins, so-called restriction factors, which inhibit enveloped virions directly. HIV-1 encodes two countermeasures to these host defenses: The membrane-associated accessory proteins Vpu and Nef. In addition to inhibiting cell-mediated immune-surveillance, Vpu and Nef counteract membrane-associated restriction factors. These include BST-2, which traps newly formed virions at the plasma membrane unless counteracted by Vpu, and SERINC5, which decreases the infectivity of virions unless counteracted by Nef. Here we review key features of these two antiviral proteins, and we review Vpu and Nef, which deplete them from the plasma membrane by co-opting specific cellular proteins and pathways of membrane trafficking and protein-degradation. We also discuss other plasma membrane proteins modulated by HIV-1, particularly CD4, which, if not opposed in infected cells by Vpu and Nef, inhibits viral infectivity and increases the sensitivity of the viral envelope glycoprotein to host immunity
Continuity of Local Time: An applied perspective
Continuity of local time for Brownian motion ranks among the most notable
mathematical results in the theory of stochastic processes. This article
addresses its implications from the point of view of applications. In
particular an extension of previous results on an explicit role of continuity
of (natural) local time is obtained for applications to recent classes of
problems in physics, biology and finance involving discontinuities in a
dispersion coefficient. The main theorem and its corollary provide physical
principles that relate macro scale continuity of deterministic quantities to
micro scale continuity of the (stochastic) local time.Comment: To appear in: "The fascination of Probability, Statistics and Their
Applications. In honour of Ole E. Barndorff-Nielsen on his 80th birthday
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