299 research outputs found
Random Mass Dirac Fermions in Doped Spin-Peierls and Spin-Ladder systems: One-Particle Properties and Boundary Effects
Quasi-one-dimensional spin-Peierls and spin-ladder systems are characterized
by a gap in the spin-excitation spectrum, which can be modeled at low energies
by that of Dirac fermions with a mass. In the presence of disorder these
systems can still be described by a Dirac fermion model, but with a random
mass. Some peculiar properties, like the Dyson singularity in the density of
states, are well known and attributed to creation of low-energy states due to
the disorder. We take one step further and study single-particle correlations
by means of Berezinskii's diagram technique. We find that, at low energy
, the single-particle Green function decays in real space like
. It follows that at these energies the
correlations in the disordered system are strong -- even stronger than in the
pure system without the gap. Additionally, we study the effects of boundaries
on the local density of states. We find that the latter is logarithmically (in
the energy) enhanced close to the boundary. This enhancement decays into the
bulk as and the density of states saturates to its bulk value on
the scale . This scale is different from
the Thouless localization length . We
also discuss some implications of these results for the spin systems and their
relation to the investigations based on real-space renormalization group
approach.Comment: 26 pages, LaTex, 9 PS figures include
"i was able to eat what i am supposed to eat" - Patient reflections on a medically-tailored meal intervention: A qualitative analysis
Background: Medically-tailored meal programs that provide home-delivered medically-appropriate food are an emerging intervention when type 2 diabetes co-occurs with food insecurity (limited or uncertain access to nutritious food owing to cost). We sought to understand the experiences of medically-tailored meal program participants. Methods: We conducted semi-structured interviews with participants in a randomized trial of medically-tailored meals (NCT02426138) until reaching content saturation. Participants were adults (age > 20 years) with type 2 diabetes in eastern Massachusetts, and the interviews were conducted from April to July 2017. Interviews were transcribed verbatim and coded by two independent reviewers. We determined emergent themes using content analysis. Results: Twenty individuals were interviewed. Their mean age was 58 (SD: 13) years, 60.0% were women, 20.0% were non-Hispanic black, and 15.0% were Hispanic. Key themes were 1) satisfaction and experience with medically-tailored meals 2) food preferences and cultural appropriateness, 3) diabetes management and awareness, and 4) suggestions for improvement and co-interventions. Within these themes, participants were generally satisfied with medically-tailored meals and emphasized the importance of receiving culturally appropriate food. Participants reported several positive effects of medically-tailored meals, including improved quality of life and ability to manage diabetes, and stress reduction. Participants suggested combining medically-tailored meals with diabetes self-management education or lifestyle interventions. Conclusions: Individuals with diabetes and food insecurity expressed satisfaction with the medically-tailored meal program, and reported that participation reduced stress and the burden of diabetes management. Suggestions to help ensure the success of medically-tailored meal programs included a strong emphasis on culturally acceptability and accommodating taste preferences for provided foods, and combining medically-tailored meals with diabetes education or lifestyle intervention. Trial registration: ClinicalTrials.gov NCT02426138
Medically Tailored Meal Delivery for Diabetes Patients with Food Insecurity: a Randomized Cross-over Trial
Background: Food insecurity, defined as inconsistent food access owing to cost, leads to poor health. Objective: To test whether a medically tailored meal delivery program improved dietary quality in individuals with type 2 diabetes and food insecurity. Design: Randomized cross-over clinical trial. Participants: Forty-four adults with diabetes, hemoglobin A1c > 8.0%, and food insecurity (defined as at least one positive item on the two-item “Hunger Vital Sign”). Intervention: In the Community Servings: Food as Medicine for Diabetes cross-over clinical trial (NCT02426138), conducted from June 2015 to July 2017, we randomly assigned the order of “on-meals” (home delivery of 10 meals/week for 12 weeks delivered by Community Servings, a non-profit organization) and “off-meals” (12 weeks usual care and a Choose MyPlate healthy eating brochure) periods. Main Measures: The primary outcome was Healthy Eating Index 2010 score (HEI), assessed by three 24-h food recalls in both periods. Higher HEI score (range 0–100; clinically significant difference 5) represents better dietary quality. Secondary outcomes included food insecurity and self-reported hypoglycemia. Key Results: Mean “on-meal” HEI score was 71.3 (SD 7.5) while mean “off-meal” HEI score was 39.9 (SD 7.8) (difference 31.4 points, p < 0.0001). Participants experienced improvements in almost all sub-categories of HEI score, with increased consumption of vegetables, fruits, and whole grains and decreased solid fats, alcohol, and added sugar consumption. Participants also reported lower food insecurity (42% “on-meal” vs. 62% “off-meal,” p = 0.047), less hypoglycemia (47% “on-meal” vs. 64% “off-meal,” p = 0.03), and fewer days where mental health interfered with quality of life (5.65 vs. 9.59 days out of 30, p = 0.03). Conclusions: For food-insecure individuals with diabetes, medically tailored meals improved dietary quality and food insecurity and reduced hypoglycemia. Longer-term studies should evaluate effects on diabetes control (e.g., hemoglobin A1c) and patient-reported outcomes (e.g., well-being)
Measuring Black Hole Spin using X-ray Reflection Spectroscopy
I review the current status of X-ray reflection (a.k.a. broad iron line)
based black hole spin measurements. This is a powerful technique that allows us
to measure robust black hole spins across the mass range, from the stellar-mass
black holes in X-ray binaries to the supermassive black holes in active
galactic nuclei. After describing the basic assumptions of this approach, I lay
out the detailed methodology focusing on "best practices" that have been found
necessary to obtain robust results. Reflecting my own biases, this review is
slanted towards a discussion of supermassive black hole (SMBH) spin in active
galactic nuclei (AGN). Pulling together all of the available XMM-Newton and
Suzaku results from the literature that satisfy objective quality control
criteria, it is clear that a large fraction of SMBHs are rapidly-spinning,
although there are tentative hints of a more slowly spinning population at high
(M>5*10^7Msun) and low (M<2*10^6Msun) mass. I also engage in a brief review of
the spins of stellar-mass black holes in X-ray binaries. In general,
reflection-based and continuum-fitting based spin measures are in agreement,
although there remain two objects (GROJ1655-40 and 4U1543-475) for which that
is not true. I end this review by discussing the exciting frontier of
relativistic reverberation, particularly the discovery of broad iron line
reverberation in XMM-Newton data for the Seyfert galaxies NGC4151, NGC7314 and
MCG-5-23-16. As well as confirming the basic paradigm of relativistic disk
reflection, this detection of reverberation demonstrates that future large-area
X-ray observatories such as LOFT will make tremendous progress in studies of
strong gravity using relativistic reverberation in AGN.Comment: 19 pages. To appear in proceedings of the ISSI-Bern workshop on "The
Physics of Accretion onto Black Holes" (8-12 Oct 2012). Revised version adds
a missing source to Table 1 and Fig.6 (IRAS13224-3809) and corrects the
referencing of the discovery of soft lags in 1H0707-495 (which were in fact
first reported in Fabian et al. 2009
Selberg Supertrace Formula for Super Riemann Surfaces III: Bordered Super Riemann Surfaces
This paper is the third in a sequel to develop a super-analogue of the
classical Selberg trace formula, the Selberg supertrace formula. It deals with
bordered super Riemann surfaces. The theory of bordered super Riemann surfaces
is outlined, and the corresponding Selberg supertrace formula is developed. The
analytic properties of the Selberg super zeta-functions on bordered super
Riemann surfaces are discussed, and super-determinants of Dirac-Laplace
operators on bordered super Riemann surfaces are calculated in terms of Selberg
super zeta-functions.Comment: 43 pages, amste
Measurement of the Charged Multiplicities in b, c and Light Quark Events from Z0 Decays
Average charged multiplicities have been measured separately in , and
light quark () events from decays measured in the SLD experiment.
Impact parameters of charged tracks were used to select enriched samples of
and light quark events, and reconstructed charmed mesons were used to select
quark events. We measured the charged multiplicities:
,
, from
which we derived the differences between the total average charged
multiplicities of or quark events and light quark events: and . We compared
these measurements with those at lower center-of-mass energies and with
perturbative QCD predictions. These combined results are in agreement with the
QCD expectations and disfavor the hypothesis of flavor-independent
fragmentation.Comment: 19 pages LaTex, 4 EPS figures, to appear in Physics Letters
Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results
The chromosphere is a thin layer of the solar atmosphere that bridges the
relatively cool photosphere and the intensely heated transition region and
corona. Compressible and incompressible waves propagating through the
chromosphere can supply significant amounts of energy to the interface region
and corona. In recent years an abundance of high-resolution observations from
state-of-the-art facilities have provided new and exciting ways of
disentangling the characteristics of oscillatory phenomena propagating through
the dynamic chromosphere. Coupled with rapid advancements in
magnetohydrodynamic wave theory, we are now in an ideal position to thoroughly
investigate the role waves play in supplying energy to sustain chromospheric
and coronal heating. Here, we review the recent progress made in
characterising, categorising and interpreting oscillations manifesting in the
solar chromosphere, with an impetus placed on their intrinsic energetics.Comment: 48 pages, 25 figures, accepted into Space Science Review
Pion condensation in a dense neutrino gas
We argue that using an equilibrated gas of neutrinos it is possible to probe
the phase diagram of QCD for finite isospin and small baryon chemical
potentials. We discuss this region of the phase diagram in detail and
demonstrate that for large enough neutrino densities a Bose-Einstein condensate
of positively charged pions arises. Moreover, we show that for nonzero neutrino
density the degeneracy in the lifetimes and masses of the charged pions is
lifted.Comment: 10 pages, 7 figures. Modifications to Section II, IIIc, and I
Produção de almeirão em função de níveis de fertirrigação nitrogenada e disposição de mangueiras gotejadoras nos canteiros
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