3,412 research outputs found
Biochemical characterisation, enteropathogenicity and antimicrobial resistance plasmids of clinical and environmental Aeromonas isolates
One hundred and eight strains of Aeromonas from clinical and environmental samples were speciated. Seven species were identified, the most prevalent of which was A. hydrophila. Experimental studies in an animal model with 36 representative strains of different species revealed that all strains could cause significant fluid accumulation in rabbit ileal loops. Of 107 strains showing single or multiple antimicrobial resistance, the highest incidence of resistance was shown for β-lactam antibiotics other than cefotaxime. Transferable resistance plasmids, encoding resistance to ampicillin, cephalexin, cefoxitin, erythromycin and furazolidone, either alone or in combination, were detected in 35 strains. A further proportion of strains could be cured of one or more resistance markers, including resistance to nalidixic acid, and this was accompanied by the loss of plasmid DNA. The plasmids ranged in size between 85.6 and >150 kb
High Scale Physics Connection to LHC Data
The existing data appears to provide hints of an underlying high scale
theory. These arise from the gauge coupling unification, from the smallness of
the neutrino masses, and via a non-vanishing muon anomaly. An overview of high
scale models is given with a view to possible tests at the Large Hadron
Collider. Specifically we discuss here some generic approaches to deciphering
their signatures. We also consider an out of the box possibility of a four
generation model where the fourth generation is a mirror generation rather than
a sequential generation. Such a scenario can lead to some remarkably distinct
signatures at the LHC.Comment: 23 pages, no figures. Based on invited lectures at the 46th Course at
the International School of Subnuclear Physics- Erice -Sicily: 29 August -7
September, 200
Nonminimal Supersymmetric Standard Model with Baryon and Lepton Number Violation
We carry out a comprehensive analysis of the nonminimal supersymmetric
standard model (NMSSM) with baryon and lepton number violation. We catalogue
the baryon and lepton number violating dimension four and five operators of the
model. We then study the renormalization group evolution and infrared stable
fixed points of the Yukawa couplings and the soft supersymmetry breaking
trilinear couplings of this model with baryon and lepton number (and R-parity)
violation involving the heaviest generations. We show analytically that in the
Yukawa sector of the NMSSM there is only one infrared stable fixed point. This
corresponds to a non-trivial fixed point for the top-, bottom-quark Yukawa
couplings and the violating coupling , and a trivial one
for all other couplings. All other possible fixed points are either unphysical
or unstable in the infrared region. We also carry out an analysis of the
renormalization group equations for the soft supersymmetry breaking trilinear
couplings, and determine the corresponding fixed points for these couplings. We
then study the quasi-fixed point behaviour, both of the third generation Yukawa
couplings and the baryon number violating coupling, and those of the soft
supersymmetry breaking trilinear couplings. From the analysis of the fixed
point behaviour, we obtain upper and lower bounds on the baryon number
violating coupling , as well as on the soft supersymmetry
breaking trilinear couplings. Our analysis shows that the infrared fixed point
behavior of NMSSM with baryon and lepton number violation is similar to that of
MSSM.Comment: 35 pages, Revtex, 6 eps fig
Spin correlations and exchange in square lattice frustrated ferromagnets
The J1-J2 model on a square lattice exhibits a rich variety of different
forms of magnetic order that depend sensitively on the ratio of exchange
constants J2/J1. We use bulk magnetometry and polarized neutron scattering to
determine J1 and J2 unambiguously for two materials in a new family of vanadium
phosphates, Pb2VO(PO4)2 and SrZnVO(PO4)2, and we find that they have
ferromagnetic J1. The ordered moment in the collinear antiferromagnetic ground
state is reduced, and the diffuse magnetic scattering is enhanced, as the
predicted bond-nematic region of the phase diagram is approached.Comment: 4 pages, 4 figure
Testing Supergravity Grand Unification at Future Accelerator and Underground Experiments
The full parameter space of supergravity grand unified theory with
type proton decay is analysed using renormalization
group induced electroweak symmetry breaking under the restrictions that the
universal scalar mass and gluino mass are TeV (no extreme fine
tuning) and the Higgs triplet mass obeys . Future proton
decay experiments at SuperKamiokande or ICARUS can reach a sensitivity for the
mode of yr allowing a number of
predictions concerning the SUSY mass spectrum. Thus either the decay mode will be seen at these experiments or a
chargino of mass GeV will exist and hence be observable
at LEP2. Further, if yr,
then either the light Higgs has mass GeV or GeV i.e. either the light Higgs or the light chargino (or both) would be
observable at LEP2. Thus, the combination of future accelerator and future
underground experiments allow for strong experimental tests of this theory.Comment: 7 figures available upon request, CTP-TAMU-32/93, NUB-TH-3066/93 and
SSCL-Preprint-44
Lyman alpha absorption lines from mini pancakes
[Abridged abstract:] Recent numerical simulations show that many \lyal
absorption lines of column densities \nha \la 10^{15} cm are produced
in transient, mini pancakes. Such pancakes are modeled here, approximating the
initial perturbation leading to the formation of the pancake as a single
sinusoidal wave. The density and temperature profiles of the gas in the pancake
are determined for , where is the collapse redshift. The
\lyal absorption line profiles for a line of sight through the pancake are
then calculated. The absorption lines in general have wings signifying bulk
motions in the gas. It is shown that the deviation from a single Voigt profile
is large for small H I column density lines, in which the effect of bulk
motions is large. For lines with \nha > 10^{13} cm, high temperature
tend to wash out the signatures of bulk motion. The analytical modeling of mini
pancakes associated with \lyal forest lines --- with 10^{13} \la \nha \la
10^{15} cm---gives the corresponding mass scales. It is shown here
that, for typical values of cosmological parameters, absorption lines with
\nha \sim 10^{14} cm correspond to structures with baryonic mass of
M with an overdensity of at .
The value of \nha can change by a factor in the course of evolution
of the pancake in time. It is also shown that there is an upper limit to \nha
from a pancake due to the slow recombination rate and the importance of
collisional ionization at high temperatures. Mini pancakes do not give rise to
\lyal lines with \nha \ga 10^{14.5} cm, for \j21=1 and
.Comment: Latex with aaspp4.sty (25 pages), 6 figures, Accepted for publication
in The Astrophysical Journa
Single crystal growth and physical properties of the layered arsenide BaRh_2As_2
Single crystals of BaRh_2As_2 have been synthesized from a Pb flux. We
present the room temperature crystal structure, single crystal x-ray
diffraction measurements as a function of temperature T, anisotropic magnetic
susceptibility \chi versus T, electrical resistivity in the ab-plane \rho
versus T, Hall coefficient versus T and magnetic field H, and heat capacity C
versus T measurements on the crystals. The single crystal structure
determination confirms that BaRh_2As_2 forms in the tetragonal ThCr_2Si_2 type
structure (space group I4/mmm) with lattice parameters a = b = 4.0564(6)\AA and
c = 12.797(4) \AA. Band structure calculations show that BaRh_2As_2 should be
metallic with a small density of states at the Fermi energy N(E_ F) = 3.49
states/eV f.u. (where f.u. \equiv formula unit) for both spin directions.
\rho(T) data in the ab-plane confirm that the material is indeed metallic with
a residual resistivity \rho(2K) = 29 \mu \Omega cm, and with a residual
resistivity ratio \rho(310K)/\rho(2K) = 5.3. The observed \chi(T) is small
(\sim 10^{-5} cm^3/mol) and weakly anisotropic with \chi_{ab}/\chi_ c \approx
2. The C(T) data indicate a small density of states at the Fermi energy with
the low temperature Sommerfeld coefficient \gamma = 4.7(9) mJ/mol K^2. There
are no indications of superconductivity, spin density wave, or structural
transitions between 2K and 300K. We compare the calculated density of states
versus energy of BaRh_2As_2 with that of BaFe_2As_2.Comment: Accepted for publication in Phys. Rev.
Heating of Intracluster Gas by Jet Activities of AGN: Is the "Preheating" Scenario Realistic?
We investigate the non-gravitational heating of hot gas in clusters of
galaxies (intracluster medium; ICM) on the assumption that the gas is heated
well before cluster formation ('preheating'). We examine the jet activities of
radio galaxies as the sources of excess energy in ICM, and the deformation of
the cosmic microwave background (the Sunyaev-Zel'dovich effect) by hot
electrons produced at the jet terminal shocks. We show that the observed excess
entropy of ICM and {\sl COBE/FIRAS} upper limit for the Compton -parameter
are compatible with each other only when the heating by the jets occurred at
relatively small redshift (). Since this result contradicts the
assumption of 'preheating', it suggests that the heating occurred
simultaneously with or after cluster formation.Comment: 10 pages including 2 figures, accepted for publication in ApJ
The Role of Heating and Enrichment in Galaxy Formation
We show that the winds identified with high-redshift low-mass galaxies may
strongly affect the formation of stars in more massive galaxies that form
later. With 3D realizations of a simple linear growth model we track gas
shocking, metal enrichment, and cooling, together with dark halo formation. We
show that outflows typically strip baryonic material out of collapsing
intermediate mass halos, suppressing star formation. More massive halos can
trap the heated gas but collapse late, leading to a broad bimodal redshift
distribution, with a larger characteristic mass associated with the lower
redshift peak. This scenario accounts for the observed bell-shaped luminosity
function of early type galaxies, explains the small number of Milky Way
satellite galaxies relative to Cold Dark Matter models predictions, and
provides a possible explanation for the lack of metal poor G-dwarfs in the
solar neighborhood and the more general lack of low-metallicity stars in
massive galaxies relative to ``closed-box'' models of chemical enrichment.
Intergalactic medium heating from outflows should produce spectral distortions
in the cosmic microwave background that will be measurable with the next
generation of experiments.Comment: 19 pages, 12 figures, accepted to ApJ, models refined and minor
revisions mad
Constraints on the minimal supergravity model from the b->s+\gamma decay
The constraints on the minimal supergravity model from the b->s+\gamma decay
are studied. A large domain in the parameter space for the model satisfies the
CLEO bound, BR(b->s+\gamma)<5.4X10^{-4}. However, the allowed domain is
expected to diminish significantly with an improved bound on this decay. The
dependence of the b->s+\gamma branching ratio on various parameters is studied
in detail. It is found that, for A_t<0 and the top quark mass within the
vicinity of the center of the CDF value, m_t^{pole}=174\pm17 GeV, there exists
only a small allowed domain because the light stop is tachyonic for most of the
parameter space. A similar phenomenon exists for a lighter top and A_t negative
when the GUT coupling constant is slightly reduced. For A_t>0, however, the
branching ratio is much less sensitive to small changes in m_t, and \alpha_G.Comment: 12 pages, plain tex file, three figures avaliable upon request,
CTP-TAMU-03/94, NUB-TH.7316/94, and CERN-TH.3092/9
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