10,256 research outputs found
Collapse of Vacuum Bubbles in a Vacuum
Motivated by the discovery of a plenitude of metastable vacua in a string
landscape and the possibility of rapid tunneling between these vacua, we
revisit the dynamics of a false vacuum bubble in a background de Sitter
spacetime. We find that there exists a large parameter space that allows the
bubble to collapse into a black hole or to form a wormhole. This may have
interesting implications to inflationary physics.Comment: 8 pages including 6 figures, LaTex; references adde
High- superconductivity in undoped ThFeAsN
Unlike the widely studied ReFeAsO series, the newly discovered iron-based
superconductor ThFeAsN exhibits a remarkably high critical temperature of 30 K,
without chemical doping or external pressure. Here we investigate in detail its
magnetic and superconducting properties via muon-spin rotation/relaxation
(SR) and nuclear magnetic resonance (NMR) techniques and show that ThFeAsN
exhibits strong magnetic fluctuations, suppressed below 35 K, but no magnetic
order. This contrasts strongly with the ReFeAsO series, where stoichiometric
parent materials order antiferromagnetically and superconductivity appears only
upon doping. The ThFeAsN case indicates that Fermi-surface modifications due to
structural distortions and correlation effects are as important as doping in
inducing superconductivity. The direct competition between antiferromagnetism
and superconductivity, which in ThFeAsN (as in LiFeAs) occurs at already zero
doping, may indicate a significant deviation of the -wave superconducting
gap in this compound from the standard scenario.Comment: 6 pages, 5 figure
Room-temperature structural phase transition in the quasi-2D spin-1/2 Heisenberg antiferromagnet Cu(pz)(ClO)
Cu(pz)(ClO) (with pz denoting pyrazine CHN) is a
two-dimensional spin-1/2 square-lattice antiferromagnet with =
4.24 K. Due to a persisting focus on the low-temperature magnetic properties,
its room-temperature structural and physical properties caught no attention up
to now. Here we report a study of the structural features of
Cu(pz)(ClO) in the paramagnetic phase, up to 330 K. By employing
magnetization, specific heat, Cl nuclear magnetic resonance, and neutron
diffraction measurements, we provide evidence of a second-order phase
transition at = 294 K, not reported before. The absence of a
magnetic ordering across in the magnetization data, yet the
presence of a sizable anomaly in the specific heat, suggest a structural
order-to-disorder type transition. NMR and neutron-diffraction data corroborate
our conjecture, by revealing subtle angular distortions of the pyrazine rings
and of ClO counteranion tetrahedra, shown to adopt a configuration of
higher symmetry above the transition temperature.Comment: 10 pages, 12 figure
Isolation and characterization of a bacteriocin produced by an isolated Bacillus subtilis LFB112 that exhibits antimicrobial activity against domestic animal pathogens
The emergence of multidrug-resistant pathogens and the restriction on the use antibiotics as growth promoters in feed have drawn attention to the search for possible alternatives. Much interest has been focused on bacteriocins because they exhibit inhibitory activity against pathogens. In this study, an antibacterial substance produced by an isolated Bacillus subtilis strain LFB112 from Chinese herbs, was identified as bacteriocin. It was effective against both Gram-positive and Gram-negative bacteriainvolved in domestic animal diseases, including Escherichia coli, Salmonella pullorum, Pseudomonas aeruginosa, Pasteurella multocida, Clostridium perfringens, Micrococcus luteus, Streptococcus bovisand Staphylococcus aureus. Two multidrug-resistant clinical isolates and a phytopathogenic yeast strain were also inhibited. The antimicrobial substance was secreted at the middle of the exponential phase, whose activity was sensitive to proteinase K and pronase E but resistant to the proteolytic action of papain, trypsin and pepsin. The antimicrobial activity was relatively heat resistant and also active over a wide range of pH 3 - 10. Sodium dodecyl sulfate-polyacrylamide gel electrophoresisanalysis revealed that the active peptide had an apparent molecular weight of about 6.3 kDa. It exhibited a bactericidal activity against S. aureus IVDC C56005. Such characteristics indicate that this bacteriocin may be a potential candidate for alternative agents to control important pathogens in domestic animal diseases
An experimental study of the influence of elevated buoyancy levels on flame spread rate over thermally thin cellulosic materials
The role of buoyancy on the flame spread rate over paper and its effect on extinction was studied by changing the gravity level and pressure. It was found that the flame spread rate decreases as the buoyancy induced flow increases. A method for correlating flame spread data using dimensionless parameters is presented. The Damkohler number is shown to be the dependent variable
Heavy quark polarizations of in the general two Higgs doublet model
The polarizations of the heavy quark ( or ) in the process have been calculated in the general two Higgs doublet model.
The CP violating normal polarization of the top quark can reach 8%, and for the bottom quark, while it is zero in the standard model. The
longitudinal and transverse polarizations of the bottom quark can be
significantly different from those in SM and consequently could aslo be used as
the probe of the new physics.Comment: 12 pages, discussion on statistic significance added, version to
appear in PR
Dependence of quantum correlations of twin beams on pump finesse of optical parametric oscillator
The dependence of quantum correlation of twin beams on the pump finesse of an
optical parametric oscillator is studied with a semi-classical analysis. It is
found that the phase-sum correlation of the output signal and idler beams from
an optical parametric oscillator operating above threshold depends on the
finesse of the pump field when the spurious pump phase noise generated inside
the optical cavity and the excess noise of the input pump field are involved in
the Langevin equations. The theoretical calculations can explain the previously
experimental results, quantitatively.Comment: 27 pages, 8 figure
Ising-type Magnetic Anisotropy in CePdAs
We investigated the anisotropic magnetic properties of CePdAs by
magnetic, thermal and electrical transport studies. X-ray diffraction confirmed
the tetragonal ThCrSi-type structure and the high-quality of the single
crystals. Magnetisation and magnetic susceptibility data taken along the
different crystallographic directions evidence a huge crystalline electric
field (CEF) induced Ising-type magneto-crystalline anisotropy with a large
-axis moment and a small in-plane moment at low temperature. A detailed CEF
analysis based on the magnetic susceptibility data indicates an almost pure
CEF ground-state doublet with the dominantly
and the doublets at 290 K and 330
K, respectively. At low temperature, we observe a uniaxial antiferromagnetic
(AFM) transition at K with the crystallographic -direction being
the magnetic easy-axis. The magnetic entropy gain up to reaches almost
indicating localised -electron magnetism without significant
Kondo-type interactions. Below , the application of a magnetic field along
the -axis induces a metamagnetic transition from the AFM to a
field-polarised phase at T, exhibiting a text-book example
of a spin-flip transition as anticipated for an Ising-type AFM.Comment: 9 Pages, 8 figure
Ground State Energy of the One-Component Charged Bose Gas
The model considered here is the `jellium' model in which there is a uniform,
fixed background with charge density in a large volume and in
which particles of electric charge and mass move --- the
whole system being neutral. In 1961 Foldy used Bogolubov's 1947 method to
investigate the ground state energy of this system for bosonic particles in the
large limit. He found that the energy per particle is in this limit, where .
Here we prove that this formula is correct, thereby validating, for the first
time, at least one aspect of Bogolubov's pairing theory of the Bose gasComment: 38 pages latex. Typos corrected.Lemma 6.2 change
- …