5,370 research outputs found
Constrained Cost-Coupled Stochastic Games with Independent State Processes
We consider a non-cooperative constrained stochastic games with N players
with the following special structure. With each player there is an associated
controlled Markov chain. The transition probabilities of the i-th Markov chain
depend only on the state and actions of controller i. The information structure
that we consider is such that each player knows the state of its own MDP and
its own actions. It does not know the states of, and the actions taken by other
players. Finally, each player wishes to minimize a time-average cost function,
and has constraints over other time-avrage cost functions. Both the cost that
is minimized as well as those defining the constraints depend on the state and
actions of all players. We study in this paper the existence of a Nash
equilirium. Examples in power control in wireless communications are given.Comment: 7 pages, submitted in september 2006 to Operations Research Letter
Stress engineering at the nanometer scale: Two-component adlayer stripes
Spontaneously formed equilibrium nanopatterns with long-range order are
widely observed in a variety of systems, but their pronounced temperature
dependence remains an impediment to maintain such patterns away from the
temperature of formation. Here, we report on a highly ordered stress-induced
stripe pattern in a two-component, Pd-O, adsorbate monolayer on W(110),
produced at high temperature and identically preserved at lower temperatures.
The pattern shows a tunable period (down to 16 nm) and orientation, as
predicted by a continuum model theory along with the surface stress and its
anisotropy found in our DFT calculations. The control over thermal fluctuations
in the stripe formation process is based on the breaking/restoring of
ergodicity in a high-density lattice gas with long-range interactions upon
turning off/on particle exchange with a heat bath.Comment: 6 pages, 4 figure
Noise Correlations of Hard-core Bosons: Quantum Coherence and Symmetry Breaking
Noise correlations, such as those observable in the time of flight images of
a released cloud, are calculated for hard-core bosonic (HCB) atoms. We find
that the standard mapping of HCB systems onto spin-1/2 XY models fails in
application to computation of noise correlations due to the contribution of
multiply occupied virtual states in HCB systems. Such states do not exist in
spin models. An interesting manifestation of such states is the breaking of
particle-hole symmetry in HCB. We use noise correlations to explore quantum
coherence of strongly correlated bosons in the fermionized regime with and
without external parabolic confinement. Our analysis points to distinctive new
experimental signatures of the Mott phase.Comment: 17 pages, 6 figures. This is a detailed revised version of
quant-ph/0507153. It has been submitted to Journal of Physics B: the special
edition for the Cortona BEC worksho
Phase diagram of two-component bosons on an optical lattice
We present a theoretical analysis of the phase diagram of two--component
bosons on an optical lattice. A new formalism is developed which treats the
effective spin interactions in the Mott and superfluid phases on the same
footing. Using the new approach we chart the phase boundaries of the broken
spin symmetry states up to the Mott to superfluid transition and beyond. Near
the transition point, the magnitude of spin exchange can be very large, which
facilitates the experimental realization of spin-ordered states. We find that
spin and quantum fluctuations have a dramatic effect on the transition making
it first order in extended regions of the phase diagram. For Mott states with
even occupation we find that the competition between effective Heisenberg
exchange and spin-dependent on--site interaction leads to an additional phase
transition from a Mott insulator with no broken symmetries into a spin-ordered
insulator
SO(4) Theory of Competition between Triplet Superconductivity and Antiferromagnetism in Bechgaard Salts
Motivated by recent experiments with Bechgaard salts, we investigate the
competition between antiferromagnetism and triplet superconductivity in quasi
one-dimensional electron systems. We unify the two orders in an SO(4) symmetric
framework, and demonstrate the existence of such symmetry in one-dimensional
Luttinger liquids. SO(4) symmetry, which strongly constrains the phase diagram,
can explain coexistence regions between antiferromagnetic, superconducting, and
normal phases, as observed in (TMTSF)PF. We predict a sharp neutron
scattering resonance in superconducting samples.Comment: 5 pages, 3 figures; Added discussion of applicability of SO(4)
symmetry for strongly anisotropic Fermi liquids; Added reference
Biomarkers of cardiovascular risk across phenotypes of osteoarthritis
Abstract: Background: The objective of this study was to explore the associations between ultrasonographic and radiographic joint scores and levels of arterial CVD risk markers in patients with osteoarthritis (OA). Secondly, to compare the levels of arterial CVD risk markers between OA phenotypes and controls. Method: The “Musculoskeletal pain in Ullensaker” Study (MUST) invited residents of Ullensaker municipality with self-reported OA to a medical examination. OA was defined according to the American College of Rheumatology (ACR) criteria and phenotyped based on joint distribution. Joints of the hands, hips and knees were examined by ultrasonography and conventional radiography, and scored for osteosteophytes. Hands were also scored for inflammation by grey scale (GS) synovitis and power Doppler (PD) signal. Control populations were a cohort of inhabitants of Oslo (OCP), and for external validation, a UK community-based register (UKPC). Pulse pressure augmentation index (AIx) and pulse wave velocity (PWV) were measured using the Sphygmocor apparatus (Atcor®). Ankel-brachial index (ABI) was estimated in a subset of patients. In separate adjusted regression models we explored the associations between ultrasonography and radiograph joint scores and AIx, PWV and ABI. CVD risk markers were also compared between phenotypes of OA and controls in adjusted analyses. Results: Three hundred and sixty six persons with OA were included (mean age (range); 63.0 (42.0–75.0)), (females (%); 264 (72)). Of these, 155 (42.3%) had isolated hand OA, 111 (30.3%) had isolated lower limb OA and 100 (27.3%) had generalized OA. 108 persons were included in the OCP and 963 persons in the UKPC; (mean age (range); OCP: 57.2 (40.4–70.4), UKPC: 63.9 (40.0–75.0), females (%); OCP: 47 (43.5), UKPC: 543 (56.4%). Hand osteophytes were associated with AIx while GS and PD scores were not related to CVD risk markers. All OA phenotypes had higher levels of AIx compared to OCP in adjusted analyses. External validation against UKPC confirmed these findings. Conclusions: Hand osteophytes might be related to higher risk of CVD. People with OA had higher augmented central pressure compared to controls. Words 330
Safety of the Deferral of Coronary Revascularization on the Basis of Instantaneous Wave-Free Ratio and Fractional Flow Reserve Measurements in Stable Coronary Artery Disease and Acute Coronary Syndromes.
OBJECTIVES:
The aim of this study was to investigate the clinical outcomes of patients deferred from coronary revascularization on the basis of instantaneous wave-free ratio (iFR) or fractional flow reserve (FFR) measurements in stable angina pectoris (SAP) and acute coronary syndromes (ACS).
BACKGROUND:
Assessment of coronary stenosis severity with pressure guidewires is recommended to determine the need for myocardial revascularization.
METHODS:
The safety of deferral of coronary revascularization in the pooled per-protocol population (n = 4,486) of the DEFINE-FLAIR (Functional Lesion Assessment of Intermediate Stenosis to Guide Revascularisation) and iFR-SWEDEHEART (Instantaneous Wave-Free Ratio Versus Fractional Flow Reserve in Patients With Stable Angina Pectoris or Acute Coronary Syndrome) randomized clinical trials was investigated. Patients were stratified according to revascularization decision making on the basis of iFR or FFR and to clinical presentation (SAP or ACS). The primary endpoint was major adverse cardiac events (MACE), defined as the composite of all-cause death, nonfatal myocardial infarction, or unplanned revascularization at 1 year.
RESULTS:
Coronary revascularization was deferred in 2,130 patients. Deferral was performed in 1,117 patients (50%) in the iFR group and 1,013 patients (45%) in the FFR group (p < 0.01). At 1 year, the MACE rate in the deferred population was similar between the iFR and FFR groups (4.12% vs. 4.05%; fully adjusted hazard ratio: 1.13; 95% confidence interval: 0.72 to 1.79; p = 0.60). A clinical presentation with ACS was associated with a higher MACE rate compared with SAP in deferred patients (5.91% vs. 3.64% in ACS and SAP, respectively; fully adjusted hazard ratio: 0.61 in favor of SAP; 95% confidence interval: 0.38 to 0.99; p = 0.04).
CONCLUSIONS:
Overall, deferral of revascularization is equally safe with both iFR and FFR, with a low MACE rate of about 4%. Lesions were more frequently deferred when iFR was used to assess physiological significance. In deferred patients presenting with ACS, the event rate was significantly increased compared with SAP at 1 year.info:eu-repo/semantics/publishedVersio
Survey of the quality of experimental design, statistical analysis and reporting of research using animals
For scientific, ethical and economic reasons, experiments involving animals should be appropriately designed, correctly analysed and transparently reported. This increases the scientific validity of the results, and maximises the knowledge gained from each experiment. A minimum amount of relevant information must be included in scientific publications to ensure that the methods and results of a study can be reviewed, analysed and repeated. Omitting essential information can raise scientific and ethical concerns. We report the findings of a systematic survey of reporting, experimental design and statistical analysis in published biomedical research using laboratory animals. Medline and EMBASE were searched for studies reporting research on live rats, mice and non-human primates carried out in UK and US publicly funded research establishments. Detailed information was collected from 271 publications, about the objective or hypothesis of the study, the number, sex, age and/or weight of animals used, and experimental and statistical methods. Only 59% of the studies stated the hypothesis or objective of the study and the number and characteristics of the animals used. Appropriate and efficient experimental design is a critical component of high-quality science. Most of the papers surveyed did not use randomisation (87%) or blinding (86%), to reduce bias in animal selection and outcome assessment. Only 70% of the publications that used statistical methods described their methods and presented the results with a measure of error or variability. This survey has identified a number of issues that need to be addressed in order to improve experimental design and reporting in publications describing research using animals. Scientific publication is a powerful and important source of information; the authors of scientific publications therefore have a responsibility to describe their methods and results comprehensively, accurately and transparently, and peer reviewers and journal editors share the responsibility to ensure that published studies fulfil these criteria
Superconductivity and antiferromagnetism in a hard-core boson spin-1 model in two dimensions
A model of hard-core bosons and spin-1 sites with single-ion anisotropy is
proposed to approximately describe hole pairs moving in a background of
singlets and triplets with the aim of exploring the relationship between
superconductivity and antiferromagnetism. The properties of this model at zero
temperature were investigated using quantum Monte Carlo techniques. The most
important feature found is the suppression of superconductivity, as long range
coherence of preformed pairs, due to the presence of both antiferromagnetism
and excitations. Indications of charge ordered and other phases are
also discussed.Comment: One figure, one reference, adde
Quantum magnetism and counterflow supersolidity of up-down bosonic dipoles
We study a gas of dipolar Bosons confined in a two-dimensional optical
lattice. Dipoles are considered to point freely in both up and down directions
perpendicular to the lattice plane. This results in a nearest neighbor
repulsive (attractive) interaction for aligned (anti-aligned) dipoles. We find
regions of parameters where the ground state of the system exhibits insulating
phases with ferromagnetic or anti-ferromagnetic ordering, as well as with
rational values of the average magnetization. Evidence for the existence of a
novel counterflow supersolid quantum phase is also presented.Comment: 8 pages, 6 figure
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