1,526 research outputs found
The spin-1/2 XXZ Heisenberg chain, the quantum algebra U_q[sl(2)], and duality transformations for minimal models
The finite-size scaling spectra of the spin-1/2 XXZ Heisenberg chain with
toroidal boundary conditions and an even number of sites provide a projection
mechanism yielding the spectra of models with a central charge c<1 including
the unitary and non-unitary minimal series. Taking into account the
half-integer angular momentum sectors - which correspond to chains with an odd
number of sites - in many cases leads to new spinor operators appearing in the
projected systems. These new sectors in the XXZ chain correspond to a new type
of frustration lines in the projected minimal models. The corresponding new
boundary conditions in the Hamiltonian limit are investigated for the Ising
model and the 3-state Potts model and are shown to be related to duality
transformations which are an additional symmetry at their self-dual critical
point. By different ways of projecting systems we find models with the same
central charge sharing the same operator content and modular invariant
partition function which however differ in the distribution of operators into
sectors and hence in the physical meaning of the operators involved. Related to
the projection mechanism in the continuum there are remarkable symmetry
properties of the finite XXZ chain. The observed degeneracies in the energy and
momentum spectra are shown to be the consequence of intertwining relations
involving U_q[sl(2)] quantum algebra transformations.Comment: This is a preprint version (37 pages, LaTeX) of an article published
back in 1993. It has been made available here because there has been recent
interest in conformal twisted boundary conditions. The "duality-twisted"
boundary conditions discussed in this paper are particular examples of such
boundary conditions for quantum spin chains, so there might be some renewed
interest in these result
A sufficient criterion for integrability of stochastic many-body dynamics and quantum spin chains
We propose a dynamical matrix product ansatz describing the stochastic
dynamics of two species of particles with excluded-volume interaction and the
quantum mechanics of the associated quantum spin chains respectively. Analyzing
consistency of the time-dependent algebra which is obtained from the action of
the corresponding Markov generator, we obtain sufficient conditions on the
hopping rates for identifing the integrable models. From the dynamical algebra
we construct the quadratic algebra of Zamolodchikov type, associativity of
which is a Yang Baxter equation. The Bethe ansatz equations for the spectra are
obtained directly from the dynamical matrix product ansatz.Comment: 19 pages Late
Low molecular weight heparin versus unfractionated heparin for perioperative thromboprophylaxis in patients with cancer
Background
The choice of the appropriate perioperative thromboprophylaxis in patients with cancer depends on the relative benefits and harms of low molecular weight heparin (LMWH) and unfractionated heparin (UFH).
Objectives
To systematically review the evidence for the relative efficacy and safety of LMWH and UFH for perioperative thromboprophylaxis in patients with cancer.
Search strategy
A comprehensive search for trials of anticoagulation in cancer patients including a February 2010 electronic search of: the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE and ISI Web of Science.
Selection criteria
Randomized controlled trials (RCTs) that enrolled cancer patients undergoing a surgical intervention and compared the effects of LMWH to UFH on mortality, deep venous thrombosis (DVT), pulmonary embolism(PE), bleeding outcomes, and thrombocytopenia.
Data collection and analysis
Two review authors used a standardized form to independently extract in duplicate data on risk of bias, participants, interventions and outcomes of interest. Where possible, we conducted meta-analyses using the random-effects model.
Main results
Of 8187 identified citations, we included 16 RCTs with 11,847 patients in the meta-analyses, all using preoperative prophylactic anticoagulation. The overall quality of evidence was moderate. The meta-analysis did not conclusively rule out either a beneficial or harmful effect of LMWH compared to UFH for the following outcomes: mortality (RR = 0.90; 95% CI 0.73 to 1.10), symptomatic DVT (RR = 0.73; 95% CI 0.23 to 2.28), PE (RR = 0.59; 95% CI 0.25 to1.41), minor bleeding (RR = 0.88; 95% CI 0.47 to 1.66) and major bleeding (RR = 0.84; 95% CI 0.52 to 1.36). LMWH was associated with lower incidence of wound hematoma (RR = 0.60; 95% CI 0.43, 0.84) while UFH was associated with higher incidence of intra-operative transfusion (RR = 1.16; 95% CI 0.69,1.62).
Authors' conclusions
We found no difference between perioperative thromboprophylaxis with LMWH verus UFH in their effects on mortality and embolic outcomes in patients with cancer. Further trials are needed to more carefully evaluate the benefits and harms of different heparin thromboprophylaxis strategies in this population
Multiplicities of charged pions and unidentified charged hadrons from deep-inelastic scattering of muons off an isoscalar target
Multiplicities of charged pions and unidentified hadrons produced in
deep-inelastic scattering were measured in bins of the Bjorken scaling variable
, the relative virtual-photon energy and the relative hadron energy .
Data were obtained by the COMPASS Collaboration using a 160 GeV muon beam and
an isoscalar target (LiD). They cover the kinematic domain in the photon
virtuality > 1(GeV/c, , and . In addition, a leading-order pQCD analysis was performed using the
pion multiplicity results to extract quark fragmentation functions
Large Anomalous Hall effect in a silicon-based magnetic semiconductor
Magnetic semiconductors are attracting high interest because of their
potential use for spintronics, a new technology which merges electronics and
manipulation of conduction electron spins. (GaMn)As and (GaMn)N have recently
emerged as the most popular materials for this new technology. While Curie
temperatures are rising towards room temperature, these materials can only be
fabricated in thin film form, are heavily defective, and are not obviously
compatible with Si. We show here that it is productive to consider transition
metal monosilicides as potential alternatives. In particular, we report the
discovery that the bulk metallic magnets derived from doping the narrow gap
insulator FeSi with Co share the very high anomalous Hall conductance of
(GaMn)As, while displaying Curie temperatures as high as 53 K. Our work opens
up a new arena for spintronics, involving a bulk material based only on
transition metals and Si, and which we have proven to display a variety of
large magnetic field effects on easily measured electrical properties.Comment: 19 pages with 5 figure
Flux Modulations seen by the Muon Veto of the GERDA Experiment
The GERDA experiment at LNGS of INFN is equipped with an active muon veto.
The main part of the system is a water Cherenkov veto with 66~PMTs in the water
tank surrounding the GERDA cryostat. The muon flux recorded by this veto shows
a seasonal modulation. Two effects have been identified which are caused by
secondary muons from the CNGS neutrino beam (2.2 %) and a temperature
modulation of the atmosphere (1.4 %). A mean cosmic muon rate of /(sm) was found in good agreement with other experiments at
LNGS at a depth of 3500~meter water equivalent.Comment: 7 pages, 6 figure
Functional gastro-intestinal disorder algorithms focus on early recognition, parental reassurance and nutritional strategies
The Polarised Valence Quark Distribution from semi-inclusive DIS
The semi-inclusive difference asymmetry A^{h^{+}-h^{-}} for hadrons of
opposite charge has been measured by the COMPASS experiment at CERN. The data
were collected in the years 2002-2004 using a 160 GeV polarised muon beam
scattered off a large polarised ^6LiD target and cover the range 0.006 < x <
0.7 and 1 < Q^2 < 100 (GeV/c)^2. In leading order QCD (LO) the asymmetry
A_d^{h^{+}-h^{-}} measures the valence quark polarisation and provides an
evaluation of the first moment of Delta u_v + Delta d_v which is found to be
equal to 0.40 +- 0.07 (stat.) +- 0.05 (syst.) over the measured range of x at
Q^2 = 10 (GeV/c)^2. When combined with the first moment of g_1^d previously
measured on the same data, this result favours a non-symmetric polarisation of
light quarks Delta u-bar = - Delta d-bar at a confidence level of two standard
deviations, in contrast to the often assumed symmetric scenario Delta u-bar =
Delta d-bar = Delta s-bar = Delta s.Comment: 7 pages, 3 figures, COMPASS, revised: details added, author list
update
Gln-tRNAGln synthesis in a dynamic transamidosome from Helicobacter pylori, where GluRS2 hydrolyzes excess Glu-tRNAGln
In many bacteria and archaea, an ancestral pathway is used where asparagine and glutamine are formed from their acidic precursors while covalently linked to tRNAAsn and tRNAGln, respectively. Stable complexes formed by the enzymes of these indirect tRNA aminoacylation pathways are found in several thermophilic organisms, and are called transamidosomes. We describe here a transamidosome forming Gln-tRNAGln in Helicobacter pylori, an ε-proteobacterium pathogenic for humans; this transamidosome displays novel properties that may be characteristic of mesophilic organisms. This ternary complex containing the non-canonical GluRS2 specific for Glu-tRNAGln formation, the tRNA-dependent amidotransferase GatCAB and tRNAGln was characterized by dynamic light scattering. Moreover, we observed by interferometry a weak interaction between GluRS2 and GatCAB (KD = 40 ± 5 µM). The kinetics of Glu-tRNAGln and Gln-tRNAGln formation indicate that conformational shifts inside the transamidosome allow the tRNAGln acceptor stem to interact alternately with GluRS2 and GatCAB despite their common identity elements. The integrity of this dynamic transamidosome depends on a critical concentration of tRNAGln, above which it dissociates into separate GatCAB/tRNAGln and GluRS2/tRNAGln complexes. Ester bond protection assays show that both enzymes display a good affinity for tRNAGln regardless of its aminoacylation state, and support a mechanism where GluRS2 can hydrolyze excess Glu-tRNAGln, ensuring faithful decoding of Gln codons
Limit on the Radiative Neutrinoless Double Electron Capture of Ar from GERDA Phase I
Neutrinoless double electron capture is a process that, if detected, would
give evidence of lepton number violation and the Majorana nature of neutrinos.
A search for neutrinoless double electron capture of Ar has been
performed with germanium detectors installed in liquid argon using data from
Phase I of the GERmanium Detector Array (GERDA) experiment at the Gran Sasso
Laboratory of INFN, Italy. No signal was observed and an experimental lower
limit on the half-life of the radiative neutrinoless double electron capture of
Ar was established: 3.6 10 yr at 90 % C.I.Comment: 7 pages, 3 figure
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