758 research outputs found
Many-Body Mobility Edge in a Mean-Field Quantum Spin Glass
The quantum random energy model provides a mean-field description of the equilibrium spin glass transition. We show that it further exhibits a many-body localization–delocalization (MBLD) transition when viewed as a closed quantum system. The mean-field structure of the model allows an analytically tractable description of the MBLD transition using the forward-scattering approximation and replica techniques. The predictions are in good agreement with the numerics. The MBLD transition lies at energy density significantly above the equilibrium spin glass transition, indicating that the closed system dynamics freezes well outside of the traditional glass phase. We also observe that the structure of the eigenstates at the MBLD critical point changes continuously with the energy density, raising the possibility of a family of critical theories for the MBLD transition
Clustering of Nonergodic Eigenstates in Quantum Spin Glasses
The two primary categories for eigenstate phases of matter at a finite temperature are many-body localization (MBL) and the eigenstate thermalization hypothesis (ETH). We show that, in the paradigmatic quantum
p
-spin models of the spin-glass theory, eigenstates violate the ETH yet are not MBL either. A mobility edge, which we locate using the forward-scattering approximation and replica techniques, separates the nonergodic phase at a small transverse field from an ergodic phase at a large transverse field. The nonergodic phase is also bounded from above in temperature, by a transition in configuration-space statistics reminiscent of the clustering transition in the spin-glass theory. We show that the nonergodic eigenstates are organized in clusters which exhibit distinct magnetization patterns, as characterized by an eigenstate variant of the Edwards-Anderson order parameter
Many-body localization beyond eigenstates in all dimensions
Isolated quantum systems with quenched randomness exhibit many-body localization (MBL), wherein they do not reach local thermal equilibrium even when highly excited above their ground states. It is widely believed that individual eigenstates capture this breakdown of thermalization at finite size. We show that this belief is false in general and that a MBL system can exhibit the eigenstate properties of a thermalizing system. We propose that localized approximately conserved operators
(
l
∗
-bits
)
underlie localization in such systems. In dimensions
d
>
1
, we further argue that the existing MBL phenomenology is unstable to boundary effects and gives way to
l
∗
-bits
. Physical consequences of
l
∗
-bits
include the possibility of an eigenstate phase transition within the MBL phase unrelated to the dynamical transition in
d
=
1
and thermal eigenstates at all parameters in
d
>
1
. Near-term experiments in ultracold atomic systems and numerics can probe the dynamics generated by boundary layers and emergence of
l
∗
-bits
The many-body localized phase of the quantum random energy model
The random energy model (REM) provides a solvable mean-field description of the equilibrium spin-glass transition. Its quantum sibling (the QREM), obtained by adding a transverse field to the REM, has similar properties and shows a spin-glass phase for sufficiently small transverse field and temperature. In a recent work, some of us have shown that the QREM further exhibits a many-body localization-delocalization (MBLD) transition when viewed as a closed quantum system, evolving according to the quantum dynamics. This phase encloses the familiar equilibrium spin-glass phase. In this paper, we study in detail the MBLD transition within the forward-scattering approximation and replica techniques. The predictions for the transition line are in good agreement with the exact diagonalization numerics. We also observe that the structure of the eigenstates at the MBLD critical point changes continuously with the energy density, raising the possibility of a family of critical theories for the MBLD transition
Many-body mobility edge due to symmetry-constrained dynamics and strong interactions
We provide numerical evidence combined with an analytical understanding of the many-body mobility edge for
the strongly anisotropic spin-1/2 XXZ model in a random magnetic field. The system dynamics can be understood
in terms of symmetry-constrained excitations about parent states with ferromagnetic and antiferromagnetic short
range order. These two regimes yield vastly different dynamics producing an observable, tunable many-body
mobility edge. We compute a set of diagnostic quantities that verify the presence of the mobility edge and discuss
how weakly correlated disorder can tune the mobility edge further
Health care professionals' views towards self-management and self-management education for people with type 2 diabetes
Objectives Significant problems with patients engaging
with diabetes self-management education (DSME) exist.
The role of healthcare professionals (HCPs) has been
highlighted, with a lack of enthusiasm, inadequate
information provision and poor promotion of available
programmes all cited as affecting patients’ decisions to
attend. However, little is known about HCPs’ views towards
DSME. This study investigates the views of HCPs towards
self-management generally and self-management in the
context of DSME more specifically.
Design A qualitative study using semi-structured
interviews to investigate HCPs views of type 2 diabetes
self-management and DSME. Data were analysed
thematically and emergent themes were mapped on to the
constructs of Normalisation Process Theory (NPT).
Setting Two boroughs in London, UK.
Participants Sampling was purposive to recruit a diverse
range of professional roles including GPs, practice nurses,
diabetes specialist nurses, healthcare assistants (HCAs),
receptionists and commissioners of care.
Results Interviews were conducted with 22 participants.
The NPT analysis demonstrated that while a selfmanagement approach to diabetes care was viewed by
HCPs as necessary and, in principle, valuable, the reality is
much more complex. HCPs expressed ambivalence about
pushing certain patients into self-managing, preferring
to retain responsibility. There was a lack of awareness
among HCPs about the content of DSME and benefits to
patients. Commitment to and engagement with DSME was
tempered by concerns about suitability for some patients.
There was little evidence of communication between
providers of group-based DSME and HCPs or of HCPs
engaging in work to follow-up non-attenders.
Conclusions HCPs have concerns about the
appropriateness of DSME for all patients and discussed
challenges to engaging with and performing the tasks
required to embed the approach within practice. DSME, as
a means of supporting self-management, was considered
important in theory, but there was little evidence of HCPs
seeing their role as extending beyond providing referrals
Estimation of health effects of prenatal methylmercury exposure using structural equation models
BACKGROUND: Observational studies in epidemiology always involve concerns regarding validity, especially measurement error, confounding, missing data, and other problems that may affect the study outcomes. Widely used standard statistical techniques, such as multiple regression analysis, may to some extent adjust for these shortcomings. However, structural equations may incorporate most of these considerations, thereby providing overall adjusted estimations of associations. This approach was used in a large epidemiological data set from a prospective study of developmental methyl-mercury toxicity. RESULTS: Structural equation models were developed for assessment of the association between biomarkers of prenatal mercury exposure and neuropsychological test scores in 7 year old children. Eleven neurobehavioral outcomes were grouped into motor function and verbally mediated function. Adjustment for local dependence and item bias was necessary for a satisfactory fit of the model, but had little impact on the estimated mercury effects. The mercury effect on the two latent neurobehavioral functions was similar to the strongest effects seen for individual test scores of motor function and verbal skills. Adjustment for contaminant exposure to poly chlorinated biphenyls (PCBs) changed the estimates only marginally, but the mercury effect could be reduced to non-significance by assuming a large measurement error for the PCB biomarker. CONCLUSIONS: The structural equation analysis allows correction for measurement error in exposure variables, incorporation of multiple outcomes and incomplete cases. This approach therefore deserves to be applied more frequently in the analysis of complex epidemiological data sets
Antimicrobial and antioxidant activity of kaempferol rhamnoside derivatives from Bryophyllum pinnatum
Abstract Background Bryophyllum pinnatum (Lank.) Oken (Crassulaceae) is a perennial succulent herb widely used in traditional medicine to treat many ailments. Its wide range of uses in folk medicine justifies its being called "life plant" or "resurrection plant", prompting researchers' interest. We describe here the isolation and structure elucidation of antimicrobial and/or antioxidant components from the EtOAc extract of B. pinnatum. Results The methanol extract displayed both antimicrobial activities with minimum inhibitory concentration (MIC) values ranging from 32 to 512 μg/ml and antioxidant property with an IC50 value of 52.48 μg/ml. Its partition enhanced the antimicrobial activity in EtOAc extract (MIC = 16-128 μg/ml) and reduced it in hexane extract (MIC = 256-1024 μg/ml). In addition, this process reduced the antioxidant activity in EtOAc and hexane extracts with IC50 values of 78.11 and 90.04 μg/ml respectively. Fractionation of EtOAc extract gave seven kaempferol rhamnosides, including; kaempferitrin (1), kaempferol 3-O-α-L-(2-acetyl)rhamnopyranoside-7-O-α-L-rhamnopyranoside (2), kaempferol 3-O-α-L-(3-acetyl)rhamnopyranoside-7-O-α-L-rhamnopyranoside (3), kaempferol 3-O-α-L-(4-acetyl)rhamnopyranoside-7-O-α-L-rhamnopyranoside (4), kaempferol 3-O-α-D- glucopyranoside-7-O-α-L-rhamnopyranoside (5), afzelin (6) and α-rhamnoisorobin (7). All these compounds, except 6 were isolated from this plant for the first time. Compound 7 was the most active, with MIC values ranging from 1 to 2 μg/ml and its antioxidant activity (IC50 = 0.71 μg/ml) was higher than that of the reference drug (IC50 = 0.96 μg/ml). Conclusion These findings demonstrate that Bryophyllum pinnatum and some of its isolated compounds have interesting antimicrobial and antioxidant properties, and therefore confirming the traditional use of B. pinnatum in the treatment of infectious and free radical damages.</p
Immunomodulatory factors in cervicovaginal secretions from pregnant and non-pregnant women: A cross-sectional study
<p>Abstract</p> <p>Background</p> <p>Pregnant women are at an increased risk for HIV infection due to unknown biological causes. Given the strong effect of sex-hormones on the expression of immunomuodulatory factors, the central role of mucosal immunity in HIV pathogenesis and the lack of previous studies, we here tested for differences in immunomuodulatory factors in cervico-vaginal secretions between pregnant and non-pregnant women.</p> <p>Methods</p> <p>We compared concentrations of 39 immunomodulatory factors in cervicovaginal lavages (CVL) from 21 pregnant women to those of 24 non-pregnant healthy women from the US. We used Bonferroni correction to correct for multiple testing and linear regression modeling to adjust for possible confounding by plasma cytokine concentration, cervical ectopy, total protein concentration, and other possible confounders. Cervical ectopy was determined by planimetry. Concentration of immunomodulatory factors were measured by a multiplex assay, protein concentration by the Bradford Method.</p> <p>Results</p> <p>Twenty six (66%) of the 39 measured immunomodulatory factors were detectable in at least half of the CVL samples included in the study. Pregnant women had threefold lower CVL concentration of CCL22 (geometric mean: 29.6 pg/ml versus 89.7 pg/ml, p = 0.0011) than non-pregnant women. CVL CCL22 concentration additionally correlated negatively with gestational age (Spearman correlation coefficient [R<sub>S</sub>]: -0.49, p = 0.0006). These associations remained significant when corrected for multiple testing.</p> <p>CCL22 concentration in CVL was positively correlated with age and negatively correlated with time since last coitus and the size of cervical ectopy. However, none of these associations could explain the difference of CCL22 concentration between pregnant and non-pregnant women in this study, which remained significant in adjusted analysis.</p> <p>Conclusions</p> <p>In this study population, pregnancy is associated with reduced concentrations of CCL22 in cervicovaginal secretions. The role of CCL22 on HIV transmission should now be investigated in prospective studies.</p
Search for CP violation in D+→ϕπ+ and D+s→K0Sπ+ decays
A search for CP violation in D + → ϕπ + decays is performed using data collected in 2011 by the LHCb experiment corresponding to an integrated luminosity of 1.0 fb−1 at a centre of mass energy of 7 TeV. The CP -violating asymmetry is measured to be (−0.04 ± 0.14 ± 0.14)% for candidates with K − K + mass within 20 MeV/c 2 of the ϕ meson mass. A search for a CP -violating asymmetry that varies across the ϕ mass region of the D + → K − K + π + Dalitz plot is also performed, and no evidence for CP violation is found. In addition, the CP asymmetry in the D+s→K0Sπ+ decay is measured to be (0.61 ± 0.83 ± 0.14)%
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