1,339 research outputs found
Separation-dependent localization in a two-impurity spin-boson model
Using a variational approach we investigate the delocalized to localized
crossover in the ground state of an Ohmic two-impurity spin-boson model,
describing two otherwise non-interacting spins coupled to a common bosonic
environment. We show that a competition between an environment-induced Ising
spin interaction and externally applied fields leads to variations in the
system-bath coupling strength, , at which the delocalized-localized
crossover occurs. Specifically, the crossover regime lies between
and depending upon the spin separation and the
strength of the transverse tunneling field. This is in contrast to the
analogous single spin case, for which the crossover occurs (in the scaling
limit) at fixed . We also discuss links between the
two-impurity spin-boson model and a dissipative two-spin transverse Ising
model, showing that the latter possesses the same qualitative features as the
Ising strength is varied. Finally, we show that signatures of the crossover may
be observed in single impurity observables, as well as in the behaviour of the
system-environment entanglement.Comment: 12 pages, 9 figures. Published version. Expanded discussion of the
distance dependence between the impurities, and added a related figur
Photon statistics from a resonantly driven quantum dot
Photon correlations in the emission of a resonantly driven quantum dot are
investigated, accounting for the influence of the solid-state phonon
environment. An analytical expression is derived for the second-order
fluorescence intensity correlation function, from which regimes of correlated
and uncorrelated photon emission are predicted as the driving field is varied.
Experiments to investigate this effect would provide valuable insight into
quantum dot carrier-phonon dynamics and are feasible with current technology.Comment: 5 pages, 3 figures, published versio
Matter collineations of Spacetime Homogeneous G\"odel-type Metrics
The spacetime homogeneous G\"odel-type spacetimes which have four classes of
metrics are studied according to their matter collineations. The obtained
results are compared with Killing vectors and Ricci collineations. It is found
that these spacetimes have infinite number of matter collineations in
degenerate case, i.e. det, and do not admit proper matter
collineations in non-degenerate case, i.e. det. The degenerate
case has the new constraints on the parameters and which characterize
the causality features of the G\"odel-type spacetimes.Comment: 12 pages, LaTex, no figures, Class. Quantum.Grav.20 (2003) 216
Attitude towards diabetes and social and family support among type 2 diabetes patients attending a tertiary-care hospital in Bangladesh: a cross-sectional study
Background: Bangladesh has been suffering from an epidemiological transition from infectious and maternal diseases to non-communicable lifestyle-related diseases like diabetes, cardiovascular diseases, cancers etc. The burden of diabetes has been increasing rapidly due to high incidence as well as poor glycemic control leading to various macro and micro-vascular complications. In this study, we aim to assess the attitude towards diabetes and social and family support among the Bangladeshi type 2 diabetic mellitus (T2DM) patients. Methods: This was a cross-sectional study among 144 patients with T2DM at the medicine outpatient department of Dhaka Medical College Hospital (DMCH) in Dhaka, Bangladesh between 1 July and 31 July 2014. Data collection was done by interviewing patients using structured questionnaire. Understanding diabetes, education/advice received, attitude towards diabetes, family and friend support were measured by validated scales adapted from diabetes care profile. Results: This study includes a total of 144 patients (101 males and 43 females) with type 2 diabetes aged between 20 and 84 years. 87 % of the patients had inadequate blood glucose control (fasting blood sugar >7.2 mmol/L or >130 mg/dl). Statistically significant differences were observed in the mean scores of various attitude scales (i.e. positive, negative, care ability and self-care adherence scale) among patients with adequate and inadequate blood glucose control (p < 0.05). Statistically significant positive correlations were found between these three categories of social and family support. Self-satisfaction with diabetic care was significantly associated with adequate blood glucose control (p = 0.05). Conclusions: Positive attitude towards diabetes management and support from friends and family were associated with adequate diabetes management. Appropriate public health interventions should be designed to educate and motivate the family members to offer greater support to the diabetes patients
Ground state and dynamics of the biased dissipative two-state system: Beyond variational polaron theory
We propose a ground-state ansatz for the Ohmic spin-boson model that improves
upon the variational treatment of Silbey and Harris for biased systems in the
scaling limit. In particular, it correctly captures the smooth crossover
behaviour expected for the ground-state magnetisation when moving between the
delocalised and localised regimes of the model, a feature that the variational
treatment is unable to properly reproduce, while it also provides a lower
ground-state energy estimate in the crossover region. We further demonstrate
the validity of our intuitive ground-state by showing that it leads to
predictions in excellent agreement with those derived from a non-perturbative
Bethe-ansatz technique. Finally, recasting our ansatz in the form of a
generalised polaron transformation, we are able to explore the dissipative
two-state dynamics beyond weak system-environment coupling within an efficient
time-local master equation formalism.Comment: 12 pages, 5 figures, comments welcome. Published version, including
revised dynamics section and new discussion on the Toulouse poin
Study of ZÎł events and limits on anomalous ZZÎł and Zγγ couplings in ppÌ collisions at s=1.96TeV
We present a measurement of the ZÎł production cross section and limits on anomalous ZZÎł and Zγγ couplings for form-factor scales of Î=750 and 1000 GeV. The measurement is based on 138 (152) candidates in the eeÎł (ÎŒÎŒÎł) final state using 320(290)pb-1 of ppÌ collisions at s=1.96TeV. The 95% C.L. limits on real and imaginary parts of individual anomalous couplings are |h10,30Z|<0.23, |h20,40Z|<0.020, |h10,30Îł|<0.23, and |h20,40Îł|<0.019 for Î=1000GeV. © 2005 The American Physical Society
Human surfactant protein D alters oxidative stress and HMGA1 expression to induce p53 apoptotic pathway in eosinophil leukemic cell line
This article is made available through the Brunel Open Access Publishing Fund. Copyright: © 2013 Mahajan et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Surfactant protein D (SP-D), an innate immune molecule, has an indispensable role in host defense and regulation of
inflammation. Immune related functions regulated by SP-D include agglutination of pathogens, phagocytosis,
oxidative burst, antigen presentation, T lymphocyte proliferation, cytokine secretion, induction of apoptosis and
clearance of apoptotic cells. The present study unravels a novel ability of SP-D to reduce the viability of leukemic
cells (eosinophilic leukemic cell line, AML14.3D10; acute myeloid leukemia cell line, THP-1; acute lymphoid leukemia
cell lines, Jurkat, Raji; and human breast epithelial cell line, MCF-7), and explains the underlying mechanisms. SP-D
and a recombinant fragment of human SP-D (rhSP-D) induced G2/M phase cell cycle arrest, and dose and timedependent
apoptosis in the AML14.3D10 eosinophilic leukemia cell line. Levels of various apoptotic markers viz.
activated p53, cleaved caspase-9 and PARP, along with G2/M checkpoints (p21 and Tyr15 phosphorylation of cdc2)
showed significant increase in these cells. We further attempted to elucidate the underlying mechanisms of rhSP-D
induced apoptosis using proteomic analysis. This approach identified large scale molecular changes initiated by SPD
in a human cell for the first time. Among others, the proteomics analysis highlighted a decreased expression of
survival related proteins such as HMGA1, overexpression of proteins to protect the cells from oxidative burst, while a
drastic decrease in mitochondrial antioxidant defense system. rhSP-D mediated enhanced oxidative burst in
AML14.3D10 cells was confirmed, while antioxidant, N-acetyl-L-cysteine, abrogated the rhSP-D induced apoptosis.
The rhSP-D mediated reduced viability was specific to the cancer cell lines and viability of human PBMCs from
healthy controls was not affected. The study suggests involvement of SP-D in hostâs immunosurveillance and
therapeutic potential of rhSP-D in the eosinophilic leukemia and cancers of other origins.Department of Biotechnology, Indi
Single-molecule experiments in biological physics: methods and applications
I review single-molecule experiments (SME) in biological physics. Recent
technological developments have provided the tools to design and build
scientific instruments of high enough sensitivity and precision to manipulate
and visualize individual molecules and measure microscopic forces. Using SME it
is possible to: manipulate molecules one at a time and measure distributions
describing molecular properties; characterize the kinetics of biomolecular
reactions and; detect molecular intermediates. SME provide the additional
information about thermodynamics and kinetics of biomolecular processes. This
complements information obtained in traditional bulk assays. In SME it is also
possible to measure small energies and detect large Brownian deviations in
biomolecular reactions, thereby offering new methods and systems to scrutinize
the basic foundations of statistical mechanics. This review is written at a
very introductory level emphasizing the importance of SME to scientists
interested in knowing the common playground of ideas and the interdisciplinary
topics accessible by these techniques. The review discusses SME from an
experimental perspective, first exposing the most common experimental
methodologies and later presenting various molecular systems where such
techniques have been applied. I briefly discuss experimental techniques such as
atomic-force microscopy (AFM), laser optical tweezers (LOT), magnetic tweezers
(MT), biomembrane force probe (BFP) and single-molecule fluorescence (SMF). I
then present several applications of SME to the study of nucleic acids (DNA,
RNA and DNA condensation), proteins (protein-protein interactions, protein
folding and molecular motors). Finally, I discuss applications of SME to the
study of the nonequilibrium thermodynamics of small systems and the
experimental verification of fluctuation theorems. I conclude with a discussion
of open questions and future perspectives.Comment: Latex, 60 pages, 12 figures, Topical Review for J. Phys. C (Cond.
Matt
Impact of age on outcome after colorectal cancer surgery in the elderly - a developing country perspective
<p>Abstract</p> <p>Background</p> <p>Colorectal cancer (CRC) is a major source of morbidity and mortality in the elderly population and surgery is often the only definitive management option. The suitability of surgical candidates based on age alone has traditionally been a source of controversy. Surgical resection may be considered detrimental in the elderly solely on the basis of advanced age. Based on recent evidence suggesting that age alone is not a predictor of outcomes, Western societies are increasingly performing definitive procedures on the elderly. Such evidence is not available from our region. We aimed to determine whether age has an independent effect on complications after surgery for colorectal cancer in our population.</p> <p>Methods</p> <p>A retrospective review of all patients who underwent surgery for pathologically confirmed colorectal cancer at Aga Khan University Hospital, Karachi between January 1999 and December 2008 was conducted. Using a cut-off of 70 years, patients were divided into two groups. Patient demographics, tumor characteristics and postoperative complications and 30-day mortality were compared. Multivariate logistic regression analysis was performed with clinically relevant variables to determine whether age had an independent and significant association with the outcome.</p> <p>Results</p> <p>A total of 271 files were reviewed, of which 56 belonged to elderly patients (â„ 70 years). The gender ratio was equal in both groups. Elderly patients had a significantly higher comorbidity status, Charlson score and American society of anesthesiologists (ASA) class (all p < 0.001). Upon multivariate analysis, factors associated with more complications were ASA status (95% CI = 1.30-6.25), preoperative perforation (95% CI = 1.94-48.0) and rectal tumors (95% CI = 1.21-5.34). Old age was significantly associated with systemic complications upon univariate analysis (p = 0.05), however, this association vanished upon multivariate analysis (p = 0.36).</p> <p>Conclusion</p> <p>Older patients have more co-morbid conditions and higher ASA scores, but increasing age itself is not independently associated with complications after surgery for CRC. Therefore patient selection should focus on the clinical status and ASA class of the patient rather than age.</p
Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events
The - oscillation frequency has been measured with a sample of
23 million \B\bar B pairs collected with the BABAR detector at the PEP-II
asymmetric B Factory at SLAC. In this sample, we select events in which both B
mesons decay semileptonically and use the charge of the leptons to identify the
flavor of each B meson. A simultaneous fit to the decay time difference
distributions for opposite- and same-sign dilepton events gives ps.Comment: 7 pages, 1 figure, submitted to Physical Review Letter
- âŠ