54,312 research outputs found
Enhanced Macroscopic Quantum Tunneling in BiSrCaCuO Intrinsic Josephson Junction Stacks
We have investigated macroscopic quantum tunneling in
BiSrCaCuO intrinsic Josephson junctions at millikelvin
temperatures using microwave irradiation. Measurements show that the escape
rate for uniformly switching stacks of N junctions is about times higher
than that of a single junction having the same plasma frequency. We argue that
this gigantic enhancement of macroscopic quantum tunneling rate in stacks is
boosted by current fluctuations which occur in the series array of junctions
loaded by the impedance of the environment.Comment: 4 pages and 5 figure
Bulk Superconductivity at 14 K in Single Crystals of Fe1+yTexSe1-x
Resistivity, magnetic susceptibility and heat capacity measurements are
reported for single crystals of Fe1+yTexSe1-x grown via a modified Bridgeman
method with 0 < y < 0.15, and x= 1, 0.9, 0.75, 0. 67, 0.55 and 0.5. Although
resistivity measurements show traces of superconductivity near 14 K for all x
except x=1, only crystals grown with compositions near x=0.5 exhibit bulk
superconductivity. The appearance of bulk superconductivity correlates with a
reduction in the magnitude of the magnetic susceptibility at room temperature
and smaller values of y, the concentration of Fe in the Fe(2) site.Comment: Submitted to Phys. Rev.
Thermodynamics of lattice QCD with 2 sextet quarks on N_t=8 lattices
We continue our lattice simulations of QCD with 2 flavours of colour-sextet
quarks as a model for conformal or walking technicolor. A 2-loop perturbative
calculation of the -function which describes the evolution of this
theory's running coupling constant predicts that it has a second zero at a
finite coupling. This non-trivial zero would be an infrared stable fixed point,
in which case the theory with massless quarks would be a conformal field
theory. However, if the interaction between quarks and antiquarks becomes
strong enough that a chiral condensate forms before this IR fixed point is
reached, the theory is QCD-like with spontaneously broken chiral symmetry and
confinement. However, the presence of the nearby IR fixed point means that
there is a range of couplings for which the running coupling evolves very
slowly, i.e. it 'walks'. We are simulating the lattice version of this theory
with staggered quarks at finite temperature studying the changes in couplings
at the deconfinement and chiral-symmetry restoring transitions as the temporal
extent () of the lattice, measured in lattice units, is increased. Our
earlier results on lattices with show both transitions move to weaker
couplings as increases consistent with walking behaviour. In this paper
we extend these calculations to . Although both transition again move to
weaker couplings the change in the coupling at the chiral transition from
to is appreciably smaller than that from to .
This indicates that at we are seeing strong coupling effects and that
we will need results from to determine if the chiral-transition
coupling approaches zero as , as needed for the theory
to walk.Comment: 21 pages Latex(Revtex4) source with 4 postscript figures. v2: added 1
reference. V3: version accepted for publication, section 3 restructured and
interpretation clarified. Section 4 future plans for zero temperature
simulations clarifie
Lifetime Difference and Endpoint effect in the Inclusive Bottom Hadron Decays
The lifetime differences of bottom hadrons are known to be properly explained
within the framework of heavy quark effective field theory(HQEFT) of QCD via
the inverse expansion of the dressed heavy quark mass. In general, the spectrum
around the endpoint region is not well behaved due to the invalidity of
expansion near the endpoint. The curve fitting method is adopted to treat the
endpoint behavior. It turns out that the endpoint effects are truly small and
the explanation on the lifetime differences in the HQEFT of QCD is then well
justified. The inclusion of the endpoint effects makes the prediction on the
lifetime differences and the extraction on the CKM matrix element
more reliable.Comment: 11 pages, Revtex, 10 figures, 6 tables, published versio
Phase structure of SU(3) gauge theory with two flavors of symmetric-representation fermions
We have performed numerical simulations of SU(3) gauge theory coupled to Nf=2
flavors of symmetric representation fermions. The fermions are discretized with
the tadpole-improved clover action. Our simulations are done on lattices of
length L=6, 8, and 12. In all simulation volumes we observe a crossover from a
strongly coupled confined phase to a weak coupling deconfined phase.
Degeneracies in screening masses, plus the behavior of the pseudoscalar decay
constant, indicate that the deconfined phase is also a phase in which chiral
symmetry is restored. The movement of the confinement transition as the volume
is changed is consistent with avoidance of the basin of attraction of an
infrared fixed point of the massless theory.Comment: 12 pages, 11 figure
Semi-Inclusive B\to K(K^*) X Decays with Initial Bound State Effects
The effects of initial quark bound state for the semi-inclusive decays
are studied using light cone expansion and heavy quark
effective theory methods. We find that the initial bound state effects on the
branching ratios and CP asymmetries are small. In the light cone expansion
approach, the CP-averaged branching ratios are increased by about 2% with
respect to the free -quark decay. For , the
CP-averaged branching ratios are sensitive to the phase and the CP
asymmetry can be as large as 7% (14%), whereas for the CP-averaged branching ratios are not sensitive to and
the CP asymmetries are small (). The CP-averaged branching ratios are
predicted to be in the ranges [] for and [] for , depending on the value of the CP violating phase . In
the heavy quark effective theory approach, we find that the branching ratios
are decreased by about 10% and the CP asymmetries are not affected. These
predictions can be tested in the near future.Comment: 29 pages, 12 ps figure
Attenuation of ischemic liver injury by prostaglandin E<inf>1</inf> analogue, misoprostol, and prostaglandin I<inf>2</inf> analogue, OP-41483
Background: Prostaglandin has been reported to have protective effects against liver injury. Use of this agent in clinical settings, however, is limited because of drugrelated side effects. This study investigated whether misoprostol, prostaglandin E1 analogue, and OP-41483, prostaglandin I2 analogue, which have fewer adverse effects with a longer half-life, attenuate ischemic liver damage. Study Design: Thirty beagle dogs underwent 2 hours of hepatic vascular exclusion using venovenous bypass. Misoprostol was administered intravenously for 30 minutes before ischemia and for 3 hours after reperfusion. OP-41483 was administered intraportally for 30 minutes before ischemia (2 μg/kg/min) and for 3 hours after reperfusion (0.5 μg/kg/min). Animals were divided into five groups: untreated control group (n = 10); high-dose misoprostol (total 100 μg/kg) group (MP-H, n = 5); middle-dose misoprostol (50 μg/kg) group (MP-M, n = 5); low-dose misoprostol (25 μg/kg) group (MP-L, n = 5); and OP-41483 group (OP, n = 5). Animal survival, hepatic tissue blood flow (HTBF), liver function, and histology were analyzed. Results: Two-week animal survival rates were 30% in control, 60% in MP-H, 100% in MP-M, 80% in MP-L, and 100% in OP. The treatments with prostaglandin analogues improved HTBF, and attenuated liver enzyme release, adenine nucleotrides degradation, and histologic abnormalities. In contrast to the MP-H animals that exhibited unstable cardiovascular systems, the MP- M, MP-L, and OP animals experienced only transient hypotension. Conclusions: These results indicate that misoprostol and OP-41483 prevent ischemic liver damage, although careful dose adjustment of misoprostol is required to obtain the best protection with minimal side effects
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