614 research outputs found
The approach to typicality in many-body quantum systems
The recent discovery that for large Hilbert spaces, almost all (that is,
typical) Hamiltonians have eigenstates that place small subsystems in thermal
equilibrium, has shed much light on the origins of irreversibility and
thermalization. Here we give numerical evidence that many-body lattice systems
generically approach typicality as the number of subsystems is increased, and
thus provide further support for the eigenstate thermalization hypothesis. Our
results indicate that the deviation of many-body systems from typicality
decreases exponentially with the number of systems. Further, by averaging over
a number of randomly-selected nearest-neighbor interactions, we obtain a
power-law for the atypicality as a function of the Hilbert space dimension,
distinct from the power-law possessed by random Hamiltonians.Comment: 6 pages, 2 png figures, revtex
Planet Hunters. V. A Confirmed Jupiter-Size Planet in the Habitable Zone and 42 Planet Candidates from the Kepler Archive Data
We report the latest Planet Hunter results, including PH2 b, a Jupiter-size
(R_PL = 10.12 \pm 0.56 R_E) planet orbiting in the habitable zone of a
solar-type star. PH2 b was elevated from candidate status when a series of
false positive tests yielded a 99.9% confidence level that transit events
detected around the star KIC 12735740 had a planetary origin. Planet Hunter
volunteers have also discovered 42 new planet candidates in the Kepler public
archive data, of which 33 have at least three transits recorded. Most of these
transit candidates have orbital periods longer than 100 days and 20 are
potentially located in the habitable zones of their host stars. Nine candidates
were detected with only two transit events and the prospective periods are
longer than 400 days. The photometric models suggest that these objects have
radii that range between Neptune to Jupiter. These detections nearly double the
number of gas giant planet candidates orbiting at habitable zone distances. We
conducted spectroscopic observations for nine of the brighter targets to
improve the stellar parameters and we obtained adaptive optics imaging for four
of the stars to search for blended background or foreground stars that could
confuse our photometric modeling. We present an iterative analysis method to
derive the stellar and planet properties and uncertainties by combining the
available spectroscopic parameters, stellar evolution models, and transiting
light curve parameters, weighted by the measurement errors. Planet Hunters is a
citizen science project that crowd-sources the assessment of NASA Kepler light
curves. The discovery of these 43 planet candidates demonstrates the success of
citizen scientists at identifying planet candidates, even in longer period
orbits with only two or three transit events.Comment: 35 pages, 11 figures, 6 tables, accepted and published on ApJ ApJ,
776, 1
Heterotopic Ossification Causing Radiculopathy after Lumbar Total Disc Arthroplasty
To date, no reports have presented radiculopathy secondary to heterotopic ossification following lumbar total disc arthroplasty. The authors present a previously unpublished complication of lumbar total disk arthroplasty (TDA) secondary to heterotopic ossification (HO) in the spinal canal, and they propose a modification to the McAfee classification of HO. The patient had undergone an L5/S1 lumbar TDA two years prior due to discogenic back pain. His preoperative back pain was significantly relieved, but he developed new, atraumatic onset radiculopathy. Radiographs and a computed tomography myelogram revealed an implant malposition posteriorly with heterotopic bone formation in the canal, causing an impingement of the traversing nerve root. Revision surgery was performed with implant extraction, L5/S1 anterior lumbar interbody fusion, supplemental posterior decompression, and pedicle screw fixation. The patient tolerated the procedure well, with complete resolution of the radicular leg pain. At a two-year follow up, the patient had a solid fusion without subsidence or recurrence of heterotopic bone. This case represents a novel pattern of heterotopic ossification, and it describes a previously unreported cause for implant failure in lumbar disc replacement surgery-reinforcing the importance of proper intraoperative component positioning. We propose a modification to the existing McAfee classification of HO after TDA with the addition of Class V and VI HO
A ‘movement for improvement’?: a qualitative study of the adoption of social movement strategies in the implementation of a quality improvement campaign
Given the difficulties of implementing ‘top-down’ quality improvements, health service leaders have turned to methods that empower clinicians to co-produce ‘bottom-up’ improvements. This has involved the adoption of strategies and activities associated with social movements, with clinicians encouraged to participate in collective action towards the shared goal of improvement. This paper examines the adoption of social movement methods by hospital managers as a strategy for implementing a quality improvement ‘campaign’. Our case study suggests that, despite the claim of empowering clinicians to develop ‘bottom-up’ improvements, the use of social movement methods is narrowly concerned with engaging clinicians in a pre-determined programme of ‘top-down’ change. It finds a prominent role for ‘hybrid’ clinical leaders and other staff representatives in the mobilisation of the campaign, especially for enrolling clinicians in change activities. The work of these ‘hybrids’ suggests some degree of creative mediation between clinical and managerial interests, but more often alignment with the aspirations of management. The study raises questions about the translation of social movements theories as a strategy for managing change and re-inventing professionalism
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The Prevalence and Clinical Implications of Comorbid Back Pain in Shoulder Instability: A Multicenter Orthopaedic Outcomes Network (MOON) Shoulder Instability Cohort Study.
Background:Understanding predictors of pain is critical, as recent literature shows that comorbid back pain is an independent risk factor for worse functional and patient-reported outcomes (PROs) as well as increased opioid dependence after total joint arthroplasty. Purpose/Hypothesis:The purpose of this study was to evaluate whether comorbid back pain would be predictive of pain or self-reported instability symptoms at the time of stabilization surgery. We hypothesized that comorbid back pain will correlate with increased pain at the time of surgery as well as with worse scores on shoulder-related PRO measures. Study Design:Cross-sectional study; Level of evidence, 3. Methods:As part of the Multicenter Orthopaedic Outcomes Network (MOON) Shoulder Instability cohort, patients consented to participate in pre- and intraoperative data collection. Demographic characteristics, injury history, preoperative PRO scores, and radiologic and intraoperative findings were recorded for patients undergoing surgical shoulder stabilization. Patients were also asked, whether they had any back pain. Results:The study cohort consisted of 1001 patients (81% male; mean age, 24.1 years). Patients with comorbid back pain (158 patients; 15.8%) were significantly older (28.1 vs 23.4 years; P < .001) and were more likely to be female (25.3% vs 17.4%; P = .02) but did not differ in terms of either preoperative imaging or intraoperative findings. Patients with self-reported back pain had significantly worse preoperative pain and shoulder-related PRO scores (American Shoulder and Elbow Surgeons score, Western Ontario Shoulder Instability Index) (P < .001), more frequent depression (22.2% vs 8.3%; P < .001), poorer mental health status (worse scores for the RAND 36-Item Health Survey Mental Component Score, Iowa Quick Screen, and Personality Assessment Screener) (P < .01), and worse preoperative expectations (P < .01). Conclusion:Despite having similar physical findings, patients with comorbid back pain had more severe preoperative pain and self-reported symptoms of instability as well as more frequent depression and lower mental health scores. The combination of disproportionate shoulder pain, comorbid back pain and mental health conditions, and inferior preoperative expectations may affect not only the patient's preoperative state but also postoperative pain control and/or postoperative outcomes
Improved high-temperature expansion and critical equation of state of three-dimensional Ising-like systems
High-temperature series are computed for a generalized Ising model with
arbitrary potential. Two specific ``improved'' potentials (suppressing leading
scaling corrections) are selected by Monte Carlo computation. Critical
exponents are extracted from high-temperature series specialized to improved
potentials, achieving high accuracy; our best estimates are:
, , , ,
. By the same technique, the coefficients of the small-field
expansion for the effective potential (Helmholtz free energy) are computed.
These results are applied to the construction of parametric representations of
the critical equation of state. A systematic approximation scheme, based on a
global stationarity condition, is introduced (the lowest-order approximation
reproduces the linear parametric model). This scheme is used for an accurate
determination of universal ratios of amplitudes. A comparison with other
theoretical and experimental determinations of universal quantities is
presented.Comment: 65 pages, 1 figure, revtex. New Monte Carlo data by Hasenbusch
enabled us to improve the determination of the critical exponents and of the
equation of state. The discussion of several topics was improved and the
bibliography was update
Quantum teleportation on a photonic chip
Quantum teleportation is a fundamental concept in quantum physics which now
finds important applications at the heart of quantum technology including
quantum relays, quantum repeaters and linear optics quantum computing (LOQC).
Photonic implementations have largely focussed on achieving long distance
teleportation due to its suitability for decoherence-free communication.
Teleportation also plays a vital role in the scalability of photonic quantum
computing, for which large linear optical networks will likely require an
integrated architecture. Here we report the first demonstration of quantum
teleportation in which all key parts - entanglement preparation, Bell-state
analysis and quantum state tomography - are performed on a reconfigurable
integrated photonic chip. We also show that a novel element-wise
characterisation method is critical to mitigate component errors, a key
technique which will become increasingly important as integrated circuits reach
higher complexities necessary for quantum enhanced operation.Comment: Originally submitted version - refer to online journal for accepted
manuscript; Nature Photonics (2014
Coordinated optimization of visual cortical maps (II) Numerical studies
It is an attractive hypothesis that the spatial structure of visual cortical
architecture can be explained by the coordinated optimization of multiple
visual cortical maps representing orientation preference (OP), ocular dominance
(OD), spatial frequency, or direction preference. In part (I) of this study we
defined a class of analytically tractable coordinated optimization models and
solved representative examples in which a spatially complex organization of the
orientation preference map is induced by inter-map interactions. We found that
attractor solutions near symmetry breaking threshold predict a highly ordered
map layout and require a substantial OD bias for OP pinwheel stabilization.
Here we examine in numerical simulations whether such models exhibit
biologically more realistic spatially irregular solutions at a finite distance
from threshold and when transients towards attractor states are considered. We
also examine whether model behavior qualitatively changes when the spatial
periodicities of the two maps are detuned and when considering more than 2
feature dimensions. Our numerical results support the view that neither minimal
energy states nor intermediate transient states of our coordinated optimization
models successfully explain the spatially irregular architecture of the visual
cortex. We discuss several alternative scenarios and additional factors that
may improve the agreement between model solutions and biological observations.Comment: 55 pages, 11 figures. arXiv admin note: substantial text overlap with
arXiv:1102.335
Distinct Visual Working Memory Systems for View-Dependent and View-Invariant Representation
Background: How do people sustain a visual representation of the environment? Currently, many researchers argue that a single visual working memory system sustains non-spatial object information such as colors and shapes. However, previous studies tested visual working memory for two-dimensional objects only. In consequence, the nature of visual working memory for three-dimensional (3D) object representation remains unknown. Methodology/Principal Findings: Here, I show that when sustaining information about 3D objects, visual working memory clearly divides into two separate, specialized memory systems, rather than one system, as was previously thought. One memory system gradually accumulates sensory information, forming an increasingly precise view-dependent representation of the scene over the course of several seconds. A second memory system sustains view-invariant representations of 3D objects. The view-dependent memory system has a storage capacity of 3–4 representations and the view-invariant memory system has a storage capacity of 1–2 representations. These systems can operate independently from one another and do not compete for working memory storage resources. Conclusions/Significance: These results provide evidence that visual working memory sustains object information in two separate, specialized memory systems. One memory system sustains view-dependent representations of the scene, akin to the view-specific representations that guide place recognition during navigation in humans, rodents and insects. Th
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