837 research outputs found
Star-graph expansions for bond-diluted Potts models
We derive high-temperature series expansions for the free energy and the
susceptibility of random-bond -state Potts models on hypercubic lattices
using a star-graph expansion technique. This method enables the exact
calculation of quenched disorder averages for arbitrary uncorrelated coupling
distributions. Moreover, we can keep the disorder strength as well as the
dimension as symbolic parameters. By applying several series analysis
techniques to the new series expansions, one can scan large regions of the
parameter space for any value of . For the bond-diluted 4-state
Potts model in three dimensions, which exhibits a rather strong first-order
phase transition in the undiluted case, we present results for the transition
temperature and the effective critical exponent as a function of
as obtained from the analysis of susceptibility series up to order 18. A
comparison with recent Monte Carlo data (Chatelain {\em et al.}, Phys. Rev.
E64, 036120(2001)) shows signals for the softening to a second-order transition
at finite disorder strength.Comment: 8 pages, 6 figure
Neutron matter with a model interaction
An infinite system of neutrons interacting by a model pair potential is
considered. We investigate a case when this potential is sufficiently strong
attractive, so that its scattering length tends to infinity. It appeared, that
if the structure of the potential is simple enough, including no finite
parameters, reliable evidences can be presented that such a system is
completely unstable at any finite density. The incompressibility as a function
of the density is negative, reaching zero value when the density tends to zero.
If the potential contains a sufficiently strong repulsive core then the system
possesses an equilibrium density. The main features of a theory describing such
systems are considered.Comment: 8 pages, LaTeX. In press, Eur. Phys. J.
Dimeric FcγR ectodomains detect pathogenic anti-platelet factor 4-heparin antibodies in heparin-induced thromobocytopenia
Background
Heparin‐induced thrombocytopenia (HIT) is a major and potentially fatal consequence of antibodies produced against platelet factor 4 (PF4)–heparin complexes following heparin exposure. Not all anti‐PF4–heparin antibodies are pathogenic, so overdiagnosis can occur, with resulting inappropriate use of alternative anticoagulation therapies that have associated risks of bleeding. However, definitive platelet functional assays are not widely available for routine analysis.
Objectives
To assess the utility of dimeric recombinant soluble FcγRIIa (rsFcγRIIa) ectodomains for detecting HIT antibodies.
Patients/Methods
Plasma from 27 suspected HIT patients were tested for pathogenic anti‐PF4–heparin antibodies by binding of a novel dimeric FcγRIIa ectodomain probe. Plasmas were also tested by the use of PF4–heparin IgG ELISA, the HemosIL AcuStar HIT IgG‐specific assay, and a serotonin release assay (SRA).
Results
The dimeric rsFcγRIIa test produced no false positives and excluded four samples that were positive by IgG ELISA. In this small patient cohort, the novel assay correctly assigned 93% of the suspected HIT patients, with two of the HIT patients being scored as false negatives. The improved discrimination of the novel assay over the IgG ELISA, which scored four false positives, supports the mechanistic interpretation that binding of dimeric rsFcγRIIa detects pairs of closely spaced IgG antibodies in PF4–heparin immune complexes.
Conclusions
This study found the cell‐free, function‐based dimeric rsFcγRIIa assay to be convenient, simple, and potentially predictive of HIT. The assay had improved specificity over the IgG ELISA, and correlated strongly with the AcuStar HIT IgG‐specific assay, warranting further evaluation of its potential to identify HIT in larger patient cohorts
Bayesian Nonparametric Inverse Reinforcement Learning
Inverse reinforcement learning (IRL) is the task of learning the reward function of a Markov Decision Process (MDP) given the transition function and a set of observed demonstrations in the form of state-action pairs. Current IRL algorithms attempt to find a single reward function which explains the entire observation set. In practice, this leads to a computationally-costly search over a large (typically infinite) space of complex reward functions. This paper proposes the notion that if the observations can be partitioned into smaller groups, a class of much simpler reward functions can be used to explain each group. The proposed method uses a Bayesian nonparametric mixture model to automatically partition the data and find a set of simple reward functions corresponding to each partition. The simple rewards are interpreted intuitively as subgoals, which can be used to predict actions or analyze which states are important to the demonstrator. Experimental results are given for simple examples showing comparable performance to other IRL algorithms in nominal situations. Moreover, the proposed method handles cyclic tasks (where the agent begins and ends in the same state) that would break existing algorithms without modification. Finally, the new algorithm has a fundamentally different structure than previous methods, making it more computationally efficient in a real-world learning scenario where the state space is large but the demonstration set is small
Equivalence of the Calogero-Sutherland Model to Free Harmonic Oscillators
A similarity transformation is constructed through which a system of
particles interacting with inverse-square two-body and harmonic potentials in
one dimension, can be mapped identically, to a set of free harmonic
oscillators. This equivalence provides a straightforward method to find the
complete set of eigenfunctions, the exact constants of motion and a linear
algebra associated with this model. It is also demonstrated that
a large class of models with long-range interactions, both in one and higher
dimensions can be made equivalent to decoupled oscillators.Comment: 9 pages, REVTeX, Completely revised, few new equations and references
are adde
A Study in Depth of f0(1370)
Claims have been made that f0(1370) does not exist. The five primary sets of
data requiring its existence are refitted. Major dispersive effects due to the
opening of the 4pi threshold are included for the first time; the sigma -> 4pi
amplitude plays a strong role. Crystal Barrel data on pbar-p -> 3pizero at rest
require f0(1370) signals of at least 32 and 33 standard deviations in 1S0 and
3P1 annihilation respectively. Furthermore, they agree within 5 MeV for mass
and width. Data on pbar-p -> eta-eta-pizero agree and require at least a 19
standard deviation contribution. This alone is sufficient to demonstrate the
existence of f0(1370). BES II data for J/Psi -> phi-pi-pi contain a visible
f0(1370) signal > 8 standard devations. In all cases, a resonant phase
variation is required. The possibility of a second pole in the sigma amplitude
due to the opening of the 4pi channel is excluded. Cern-Munich data for pi-pi
elastic scattering are fitted well with the inclusion of some mixing between
sigma, f0(1370) and f0(1500). The pi-pi widths for f2(1565), rho3(1690),
rho3(1990) and f4(2040) are determined.Comment: 25 pages, 22 figures. Typos corrected in Eqs 2 and 7. Introduction
rewritten. Conclusions unchange
The 3-D O(4) universality class and the phase transition in two-flavor QCD
We determine the critical equation of state of the three-dimensional O(4)
universality class. We first consider the small-field expansion of the
effective potential (Helmholtz free energy). Then, we apply a systematic
approximation scheme based on polynomial parametric representations that are
valid in the whole critical regime, satisfy the correct analytic properties
(Griffiths' analyticity), take into account the Goldstone singularities at the
coexistence curve, and match the small-field expansion of the effective
potential. From the approximate representations of the equation of state, we
obtain estimates of several universal amplitude ratios.
The three-dimensional O(4) universality class is expected to describe the
finite-temperature chiral transition of quantum chromodynamics with two light
flavors. Within this picture, the O(4) critical equation of state relates the
reduced temperature, the quark masses, and the condensates around T_c in the
limit of vanishing quark masses.Comment: 19 pages, 5 fig
The position of graptolites within Lower Palaeozoic planktic ecosystems.
An integrated approach has been used to assess the palaeoecology of graptolites both as a discrete group and also as a part of the biota present within Ordovician and Silurian planktic realms. Study of the functional morphology of graptolites and comparisons with recent ecological analogues demonstrates that graptolites most probably filled a variety of niches as primary consumers, with modes of life related to the colony morphotype. Graptolite coloniality was extremely ordered, lacking any close morphological analogues in Recent faunas. To obtain maximum functional efficiency, graptolites would have needed varying degrees of coordinated automobility. A change in lifestyle related to ontogenetic changes was prevalent within many graptolite groups. Differing lifestyle was reflected by differing reproductive strategies, with synrhabdosomes most likely being a method for rapid asexual reproduction. Direct evidence in the form of graptolithophage 'coprolitic' bodies, as well as indirect evidence in the form of probable defensive adaptations, indicate that graptolites comprised a food item for a variety of predators. Graptolites were also hosts to a variety of parasitic organisms and provided an important nutrient source for scavenging organisms
Formation of a conceptual framework during the development of a patient-reported outcome measure for early gastrointestinal recovery: phase I of the PRO-diGi study
Aim
Patients admitted to hospital for abdominal surgery often experience gastrointestinal dysfunction. Many studies have reported outcomes following gastrointestinal dysfunction, yet there is no unified definition of recovery or a validated patient-reported outcome measure (PROM). The first stage of PROM development requires formation of a conceptual framework to identify key themes to patients. The aim of this study was to utilize semistructured interviews to identify core themes and concepts relevant to patients to facilitate development of a conceptual framework.
Method
Adult patients admitted to hospital for major gastrointestinal, urological or gynaecological surgery, in an emergency or elective setting, were eligible to participate. Patients treated nonoperatively for small bowel obstruction were also eligible. Interviews were conducted by telephone, audio-recorded, transcribed, coded and analysed using NVivo software by two researchers and reviewed by lay members of the steering group. Interviews continued until data saturation was reached. Ethical approval was gained prior to interviews (21/WA/0231).
Results
Twenty nine interviews were completed (17 men, median age 64 years) across three specialties (20 gastrointestinal, six gynaecological, three urological). Two overarching themes of ‘general recovery’ and ‘gastrointestinal symptoms’ were identified. General recovery included three themes: ‘life impact’, ‘mental impact’, including anxiety, and ‘physical impact’, including fatigue. Gastrointestinal symptoms included three themes: ‘abdominal symptoms’ such as pain, ‘diet and appetite’ and ‘expulsory function’, such as stool frequency. A total of 18 gastrointestinal symptoms were identified during patient recovery—many of which lasted several weeks following discharge.
Conclusion
This study reports a range of gastrointestinal and nongastrointestinal symptoms experienced by patients during early gastrointestinal recovery. Identified symptoms have been synthesized into a conceptual framework to enable development of a definitive PROM for early gastrointestinal recovery
A Unified Algebraic Approach to Few and Many-Body Correlated Systems
The present article is an extended version of the paper {\it Phys. Rev.} {\bf
B 59}, R2490 (1999), where, we have established the equivalence of the
Calogero-Sutherland model to decoupled oscillators. Here, we first employ the
same approach for finding the eigenstates of a large class of Hamiltonians,
dealing with correlated systems. A number of few and many-body interacting
models are studied and the relationship between their respective Hilbert
spaces, with that of oscillators, is found. This connection is then used to
obtain the spectrum generating algebras for these systems and make an algebraic
statement about correlated systems. The procedure to generate new solvable
interacting models is outlined. We then point out the inadequacies of the
present technique and make use of a novel method for solving linear
differential equations to diagonalize the Sutherland model and establish a
precise connection between this correlated system's wave functions, with those
of the free particles on a circle. In the process, we obtain a new expression
for the Jack polynomials. In two dimensions, we analyze the Hamiltonian having
Laughlin wave function as the ground-state and point out the natural emergence
of the underlying linear symmetry in this approach.Comment: 18 pages, Revtex format, To appear in Physical Review
- …