11,021 research outputs found
Strongly correlated fermions on a kagome lattice
We study a model of strongly correlated spinless fermions on a kagome lattice
at 1/3 filling, with interactions described by an extended Hubbard Hamiltonian.
An effective Hamiltonian in the desired strong correlation regime is derived,
from which the spectral functions are calculated by means of exact
diagonalization techniques. We present our numerical results with a view to
discussion of possible signatures of confinement/deconfinement of fractional
charges.Comment: 10 pages, 10 figure
Systematic Errors in the Estimation of Black Hole Masses by Reverberation Mapping
The mass of the central black hole in many active galactic nuclei has been
estimated on the basis of the assumption that the dynamics of the broad
emission line gas are dominated by the gravity of the black hole. The most
commonly-employed method is to estimate a characteristic size-scale from
reverberation mapping experiments and combine it with a characteristic velocity
taken from the line profiles; the inferred mass is then estimated by . We critically discuss the evidence supporting the assumption of
gravitational dynamics and find that the arguments are still inconclusive. We
then explore the range of possible systematic error if the assumption of
gravitational dynamics is granted. Inclination relative to a flattened system
may cause a systematic underestimate of the central mass by a factor , where is the aspect ratio of the flattening. The coupled
effects of a broad radial emissivity distribution, an unknown angular radiation
pattern of line emission, and sub-optimal sampling in the reverberation
experiment can cause additional systematic errors as large as a factor of 3 or
more in either direction.Comment: 19 pages, 4 figures, AASLaTeX, accepted by Ap
Unsolicited written narratives as a methodological genre in terminal illness: challenges and limitations
Stories about illness have proven invaluable in helping health professionals understand illness experiences. Such narratives have traditionally been solicited by researchers through interviews and the collection of personal writings, including diaries. These approaches are, however, researcher driven; the impetus for the creation of the story comes from the researcher and not the narrator. In recent years there has been exponential growth in illness narratives created by individuals, of their own volition, and made available for others to read in print or as Internet accounts. We sought to determine whether it was possible to identify such material for use as research data to explore the subject of living with the terminal illness amyotrophic lateral sclerosis/motor neuron disease—the contention being that these accounts are narrator driven and therefore focus on issues of greatest importance to the affected person. We encountered and sought to overcome a number of methodological and ethical challenges, which is our focus here
Finite energy/action solutions of Yang-Mills equations on Schwarzschild and deSitter backgrounds for dimension
Physically relevant gauge and gravitational theories can be seen as special
members of hierarchies of more elaborate systems. The Yang-Mills (YM) system is
the first member of a hierarchy of Lagrangians which we will index by ,
and the Einstein-Hilbert (EH) system of general relativity is the first member
of another hierarchy which we index by . In this paper, we study the
classical equations of the YM hierarchy considered in the
background of special geometries (Schwarzschild, deSitter,anti-deSitter) of the
EH hierarchy. Solutions are obtained in various dimensions and lead
to several examples of non-self-dual YM fields. When self-dual
solutions exist in addition. Their action is equal to the Chern-Pontryagin
charge and can be compared with that of the non-self-dual solutions.Comment: LaTeX, 25 pages, 2 figures, new title, minor change
Near-field interaction between domain walls in adjacent Permalloy nanowires
The magnetostatic interaction between two oppositely charged transverse
domain walls (DWs)in adjacent Permalloy nanowires is experimentally
demonstrated. The dependence of the pinning strength on wire separation is
investigated for distances between 13 and 125 nm, and depinning fields up to 93
Oe are measured. The results can be described fully by considering the
interaction between the full complex distribution of magnetic charge within
rigid, isolated DWs. This suggests the DW internal structure is not appreciably
disturbed by the pinning potential, and that they remain rigid although the
pinning strength is significant. This work demonstrates the possibility of
non-contact DW trapping without DW perturbation and full continuous flexibility
of the pinning potential type and strength. The consequence of the interaction
on DW based data storage schemes is evaluated.Comment: 4 pages, 4 figures, 1 page supplimentary material (supporting.ps
Quantum Non-demolition Measurements on Qubits
We discuss the characterization and properties of quantum non-demolition
(QND) measurements on qubit systems. We introduce figures of merit which can be
applied to systems of any Hilbert space dimension thus providing universal
criteria for characterizing QND measurements. We discuss the controlled-NOT
gate and an optical implementation as examples of QND devices for qubits. We
also discuss the QND measurement of weak values
Effectiveness of aerobic exercise for adults living with HIV: systematic review and meta-analysis using the Cochrane Collaboration protocol
Background: People with HIV are living longer with the health-related consequences of HIV, multi-morbidity, and
aging. Exercise is a key strategy that may improve or sustain health for people living with HIV. Our aim was to
examine the safety and effectiveness of aerobic exercise interventions on immunological, virological,
cardiorespiratory, strength, weight, body composition, and psychological outcomes in adults living with HIV.
Methods: We conducted a systematic review using the Cochrane Collaboration protocol. We searched databases
up to April 2013. We included randomized controlled trials comparing aerobic exercise with no exercise or another
intervention performed at least three times per week for at least four weeks among adults living with HIV. Two
reviewers independently determined study eligibility. Data were extracted from studies that met inclusion criteria
using standardized forms. We assessed risk of bias using the Cochrane Collaboration’s tool for assessing risk of bias.
Outcomes were analyzed as continuous and meta-analyses conducted using random effects models with Review
Manager (RevMan) computer software.
Results: Twenty-four studies met inclusion criteria (n = 936 participants at study completion); the majority of
participants were men (73 %) and the majority were taking antiretroviral therapy (19/24 included studies). The
exercise intervention included aerobic exercise alone (11 studies) or a combination of aerobic and resistive exercise
(13 studies) ranging from 5 to 52 weeks. Fifty-eight meta-analyses were performed. Main results indicated
statistically significant improvements in selected outcomes of cardiorespiratory status (maximum oxygen
consumption, exercise time), strength (chest press, knee flexion), body composition (lean body mass, percent body
fat, leg muscle area), depression symptoms, and quality of life (SF-36 questionnaire) among exercisers compared
with non-exercisers. No significant differences in change in CD4 count and viral load were found.
Conclusions: Performing aerobic exercise or a combination of aerobic and resistive exercise at least three times per
week for at least five weeks is safe and can lead to improvements in cardiorespiratory fitness, strength, body
composition and quality of life for adults with HIV. Aerobic exercise is safe and beneficial for adults living with HIV
who are medically stable
Analysis of uncertainty in health care cost-effectiveness studies: an introduction to statistical issues and methods
Cost-effectiveness analysis is now an integral part of health technology assessment and addresses the question of whether a new treatment or other health care program offers good value for money. In this paper we introduce the basic framework for decision making with cost-effectiveness data and then review recent developments in statistical methods for analysis of uncertainty when cost-effectiveness estimates are based on observed data from a clinical trial. Although much research has focused on methods for calculating confidence intervals for cost-effectiveness ratios using bootstrapping or Fieller’s method, these calculations can be problematic with a ratio-based statistic where numerator and=or denominator can be zero. We advocate plotting the joint density of cost and effect differences, together with cumulative density plots known as cost-effectiveness acceptability curves (CEACs) to summarize the overall value-for-money of interventions. We also outline the net-benefit formulation of the cost-effectiveness problem and show that it has particular advantages over the standard incremental cost-effectiveness ratio formulation
Preparation of Knill-Laflamme-Milburn states using tunable controlled phase gate
A specific class of partially entangled states known as
Knill-Laflamme-Milburn states (or KLM states) has been proved to be useful in
relation to quantum information processing [Knill et al., Nature 409, 46
(2001)]. Although the usage of such states is widely investigated, considerably
less effort has been invested into experimentally accessible preparation
schemes. This paper discusses the possibility to employ a tunable controlled
phase gate to generate an arbitrary Knill-Laflamme-Milburn state. In the first
part, the idea of using the controlled phase gate is explained on the case of
two-qubit KLM states. Optimization of the proposed scheme is then discussed for
the framework of linear optics. Subsequent generalization of the scheme to
arbitrary n-qubit KLM state is derived in the second part of this paper.Comment: 5 pages, 4 figures, accepted in Journal of Physics
Domain size effects in Barkhausen noise
The possible existence of self-organized criticality in Barkhausen noise is
investigated theoretically through a single interface model, and experimentally
from measurements in amorphous magnetostrictive ribbon Metglas 2605TCA under
stress. Contrary to previous interpretations in the literature, both simulation
and experiment indicate that the presence of a cutoff in the avalanche size
distribution may be attributed to finite size effects.Comment: 5 pages, 3 figures, submitted so Physical Review
- …