508 research outputs found
Incommensurability in the magnetic excitations of the bilinear-biquadratic spin-1 chain
We study the magnetic excitation spectrum of the S=1 quantum Heisenberg spin
chain with Hamiltonian : H = sum_i cos(theta) S_i S_i+1 + sin(theta) (S_i
S_i+1)^2. We focus on the range -pi/4 < theta < +pi/4 where the spin chain is
in the gapped Haldane phase. The excitation spectrum and static structure
factor is studied using direct Lanczos diagonalization of small systems and
density-matrix renormalization group techniques combined with the single-mode
approximation. The magnon dispersion has a minimum at q=pi until a critical
value theta_c = 0.38 is reached at which the curvature (velocity) vanishes.
Beyond this point, which is distinct from the VBS point and the Lifshitz point,
the minimum lies at an incommensurate value that goes smoothly to 2pi/3 when
theta approaches pi/4, the Lai-Sutherland point. The mode remains isolated from
the other states: there is no evidence of spinon deconfinement before the point
theta =+pi/4. These findings explain recent observation of the magnetization
curve M approx (H -H_c)^1/4 for theta =theta_c.Comment: 14 pages, 8 encapsulated figures, REVTeX 3.
Low temperature spin diffusion in the one-dimensional quantum nonlinear -model
An effective, low temperature, classical model for spin transport in the
one-dimensional, gapped, quantum non-linear -model is developed.
Its correlators are obtained by a mapping to a model solved earlier by Jepsen.
We obtain universal functions for the ballistic-to-diffusive crossover and the
value of the spin diffusion constant, and these are claimed to be exact at low
temperatures. Implications for experiments on one-dimensional insulators with a
spin gap are noted.Comment: 4 pages including 3 eps-figures, Revte
Physical activity and health related quality of life
Copyright @ 2012 Anokye et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.This article has been made available through the Brunel Open Access Publishing Fund.BACKGROUND: Research on the relationship between Health Related Quality of Life (HRQoL) and physical activity (PA), to date, have rarely investigated how this relationship differ across objective and subjective measures of PA. The aim of this paper is to explore the relationship between HRQoL and PA, and examine how this relationship differs across objective and subjective measures of PA, within the context of a large representative national survey from England. METHODS: Using a sample of 5,537 adults (40â60âyears) from a representative national survey in England (Health Survey for England 2008), Tobit regressions with upper censoring was employed to model the association between HRQoL and objective, and subjective measures of PA controlling for potential confounders. We tested the robustness of this relationship across specific types of PA. HRQoL was assessed using the summary measure of health state utility value derived from the EuroQol-5 Dimensions (EQ-5D) whilst PA was assessed via subjective measure (questionnaire) and objective measure (accelerometer- actigraph model GT1M). The actigraph was worn (at the waist) for 7âdays (during waking hours) by a randomly selected sub-sample of the HSE 2008 respondents (4,507 adults â 16 plus years), with a valid day constituting 10 hours. Analysis was conducted in 2010. RESULTS: Findings suggest that higher levels of PA are associated with better HRQoL (regression coefficient: 0.026 to 0.072). This relationship is consistent across different measures and types of PA although differences in the magnitude of HRQoL benefit associated with objective and subjective (regression coefficient: 0.047) measures of PA are noticeable, with the former measure being associated with a relatively better HRQoL (regression coefficient: 0.072). CONCLUSION: Higher levels of PA are associated with better HRQoL. Using an objective measure of PA compared with subjective shows a relatively better HRQoL.This project was funded by the NIHR Health Technology Assessment programme (project number 08/72/01)
Nonlinear atom optics and bright gap soliton generation in finite optical lattices
We theoretically investigate the transmission dynamics of coherent matter
wave pulses across finite optical lattices in both the linear and the nonlinear
regimes. The shape and the intensity of the transmitted pulse are found to
strongly depend on the parameters of the incident pulse, in particular its
velocity and density: a clear physical picture for the main features observed
in the numerical simulations is given in terms of the atomic band dispersion in
the periodic potential of the optical lattice. Signatures of nonlinear effects
due the atom-atom interaction are discussed in detail, such as atom optical
limiting and atom optical bistability. For positive scattering lengths, matter
waves propagating close to the top of the valence band are shown to be subject
to modulational instability. A new scheme for the experimental generation of
narrow bright gap solitons from a wide Bose-Einstein condensate is proposed:
the modulational instability is seeded in a controlled way starting from the
strongly modulated density profile of a standing matter wave and the solitonic
nature of the generated pulses is checked from their shape and their
collisional properties
Lipocalin 2 is protective against E. coli pneumonia
<p>Abstract</p> <p>Background</p> <p>Lipocalin 2 is a bacteriostatic protein that binds the siderophore enterobactin, an iron-chelating molecule produced by <it>Escherichia coli </it>(<it>E. coli</it>) that is required for bacterial growth. Infection of the lungs by <it>E. coli </it>is rare despite a frequent exposure to this commensal bacterium. Lipocalin 2 is an effector molecule of the innate immune system and could therefore play a role in hindering growth of <it>E. coli </it>in the lungs.</p> <p>Methods</p> <p>Lipocalin 2 knock-out and wild type mice were infected with two strains of <it>E. coli</it>. The lungs were removed 48 hours post-infection and examined for lipocalin 2 and MMP9 (a myeloid marker protein) by immunohistochemical staining and western blotting. Bacterial numbers were assessed in the lungs of the mice at 2 and 5 days after infection and mortality of the mice was monitored over a five-day period. The effect of administering ferrichrome (an iron source that cannot be bound by lipocalin 2) along with E.coli was also examined.</p> <p>Results</p> <p>Intratracheal installation of <it>E. coli </it>in mice resulted in strong induction of lipocalin 2 expression in bronchial epithelium and alveolar type II pneumocytes. Migration of myeloid cells to the site of infection also contributed to an increased lipocalin 2 level in the lungs. Significant higher bacterial numbers were observed in the lungs of lipocalin 2 knock-out mice on days 2 and 5 after infection with <it>E. coli </it>(p < 0.05). In addition, a higher number of <it>E. coli </it>was found in the spleen of surviving lipocalin 2 knock-out mice on day 5 post-infection than in the corresponding wild-type mice (p < 0.05). The protective effect against <it>E. coli </it>infection in wild type mice could be counteracted by the siderophore ferrichrome, indicating that the protective effect of lipocalin 2 depends on its ability to sequester iron.</p> <p>Conclusions</p> <p>Lipocalin 2 is important for protection of airways against infection by <it>E. coli</it>.</p
Studies on changes of estimated breeding values of U.S. Holstein bulls for final score from the first to second crop of daughters
The purpose of this study was to find ways of reducing changes of sire predicted transmitting ability for typeâs final scores (PTATs) from the first to second crop of daughters. The PTATs were estimated from two datasets: D01 (scores recorded up to 2001) and D05 (scores recorded up to 2005). The PTAT changes were calculated as the difference between the evaluations based on D01 and D05. The PTATs were adjusted to a common genetic base of all evaluated cows born in 1995. The single-trait (ST) animal model included the fixed effects of the herdâyearâseasonâclassifier, age by year group at classification, stage of lactation at classification, registry status of animals, and additive genetic and permanent environment random effects. Unknown parent groups (UPGs) were defined based on every other birth year starting from 1972. Modifications to the ST model included the usage of a single record per cow, separate UPGs for first and second crop daughters, separate UPGs for sires and dams, and deepened pedigrees for dams with missing phenotypic records. Also, the multiple-trait (MT) model treated records of registered and grade cows as correlated traits. The mean PTAT change, for all of the sires, was close to zero in all of the models analyzed. The estimated mean PTAT change for 145 sires with 40 to 100 first crop and â„200 second crop daughters was â0.33, â0.20, â0.13, â0.28, and â0.12 with ST, only first records, only last records, updated pedigrees, and allowing separate parent groups (PGs) for sires and dams after updating the pedigrees, respectively. The percentages of sires showing PTAT decline were reduced from 74.5 (with ST) to 57.3 by using only the last records of cows, and to 56.4 by allowing separate UPGs for sires and dams after updating the pedigrees. Though updating of the pedigrees alone was not effective, separate UPGs for sires together with additional pedigree was helpful in reducing the bias
Impact of the use of cryobank samples in a selected cattle breed: a simulation study
<p>Abstract</p> <p>Background</p> <p>High selection pressure on domestic cattle has led to an undesirable increase in inbreeding, as well as to the deterioration of some functional traits which are indirectly selected. Semen stored in a cryobank may be a useful way to redirect selection or limit the loss of genetic diversity in a selected breed. The purpose of this study was to analyse the efficiency of current cryobank sampling methods, by investigating the benefits of using cryopreserved semen in a selection scheme several generations after the semen was collected.</p> <p>Methods</p> <p>The theoretical impact of using cryopreserved semen in a selection scheme of a dairy cattle breed was investigated by simulating various scenarios involving two negatively correlated traits and a change in genetic variability of the breed.</p> <p>Results</p> <p>Our results indicate that using cryopreserved semen to redirect selection will have an impact on negatively selected traits only if it is combined with major changes in selection objectives or practices. If the purpose is to increase genetic diversity in the breed, it can be a viable option.</p> <p>Conclusions</p> <p>Using cryopreserved semen to redirect selection or to improve genetic diversity should be carried out with caution, by considering the pros and cons of prospective changes in genetic diversity and the value of the selected traits. However, the use of genomic information should lead to more interesting perspectives to choose which animals to store in a cryobank and to increase the value of cryobank collections for selected breeds.</p
Spin dynamics and transport in gapped one-dimensional Heisenberg antiferromagnets at nonzero temperatures
We present the theory of nonzero temperature () spin dynamics and
transport in one-dimensional Heisenberg antiferromagnets with an energy gap
. For , we develop a semiclassical picture of thermally
excited particles. Multiple inelastic collisions between the particles are
crucial, and are described by a two-particle S-matrix which has a
super-universal form at low momenta. This is established by computations on the
O(3) -model, and strong and weak coupling expansions (the latter using
a Majorana fermion representation) for the two-leg S=1/2 Heisenberg
antiferromagnetic ladder. As an aside, we note that the strong-coupling
calculation reveals a S=1, two particle bound state which leads to the presence
of a second peak in the T=0 inelastic neutron scattering (INS) cross-section
for a range of values of momentum transfer. We obtain exact, or numerically
exact, universal expressions for the thermal broadening of the quasi-particle
peak in the INS cross-section, for the magnetization transport, and for the
field dependence of the NMR relaxation rate of the effective
semiclassical model: these are expected to be asymptotically exact for the
quantum antiferromagnets. The results for are compared with the
experimental findings of Takigawa et al and the agreement is quite good. In the
regime we argue that a
complementary description in terms of semiclassical waves applies, and give
some exact results for the thermodynamics and dynamics.Comment: REVTEX, 53 pages and 23 postscript figures; added additional
reference and associated clarificatio
Which medical error to disclose to patients and by whom? Public preference and perceptions of norm and current practice
<p>Abstract</p> <p>Background</p> <p>Disclosure of near miss medical error (ME) and who should disclose ME to patients continue to be controversial. Further, available recommendations on disclosure of ME have emerged largely in Western culture; their suitability to Islamic/Arabic culture is not known.</p> <p>Methods</p> <p>We surveyed 902 individuals attending the outpatient's clinics of a tertiary care hospital in Saudi Arabia. Personal preference and perceptions of norm and current practice regarding which ME to be disclosed (5 options: don't disclose; disclose if associated with major, moderate, or minor harm; disclose near miss) and by whom (6 options: any employee, any physician, at-fault-physician, manager of at-fault-physician, medical director, or chief executive director) were explored.</p> <p>Results</p> <p>Mean (SD) age of respondents was 33.9 (10) year, 47% were males, 90% Saudis, 37% patients, 49% employed, and 61% with college or higher education. The percentage (95% confidence interval) of respondents who preferred to be informed of harmful ME, of near miss ME, or by at-fault physician were 60.0% (56.8 to 63.2), 35.5% (32.4 to 38.6), and 59.7% (56.5 to 63.0), respectively. Respectively, 68.2% (65.2 to 71.2) and 17.3% (14.7 to 19.8) believed that as currently practiced, harmful ME and near miss ME are disclosed, and 34.0% (30.7 to 37.4) that ME are disclosed by at-fault-physician. Distributions of perception of norm and preference were similar but significantly different from the distribution of perception of current practice (P < 0.001). In a forward stepwise regression analysis, older age, female gender, and being healthy predicted preference of disclosure of near miss ME, while younger age and male gender predicted preference of no-disclosure of ME. Female gender also predicted preferring disclosure by the at-fault-physician.</p> <p>Conclusions</p> <p>We conclude that: 1) there is a considerable diversity in preferences and perceptions of norm and current practice among respondents regarding which ME to be disclosed and by whom, 2) Distributions of preference and perception of norm were similar but significantly different from the distribution of perception of current practice, 3) most respondents preferred to be informed of ME and by at-fault physician, and 4) one third of respondents preferred to be informed of near-miss ME, with a higher percentage among females, older, and healthy individuals.</p
The Impact of Different Antibiotic Regimens on the Emergence of Antimicrobial-Resistant Bacteria
Backgroud: The emergence and ongoing spread of antimicrobial-resistant bacteria is a major public health threat. Infections caused by antimicrobial-resistant bacteria are associated with substantially higher rates of morbidity and mortality compared to infections caused by antimicrobial-susceptible bacteria. The emergence and spread of these bacteria is complex and requires incorporating numerous interrelated factors which clinical studies cannot adequately address. Methods/Principal Findings: A model is created which incorporates several key factors contributing to the emergence and spread of resistant bacteria including the effects of the immune system, acquisition of resistance genes and antimicrobial exposure. The model identifies key strategies which would limit the emergence of antimicrobial-resistant bacterial strains. Specifically, the simulations show that early initiation of antimicrobial therapy and combination therapy with two antibiotics prevents the emergence of resistant bacteria, whereas shorter courses of therapy and sequential administration of antibiotics promote the emergence of resistant strains. Conclusions/Significance: The principal findings suggest that (i) shorter lengths of antibiotic therapy and early interruption of antibiotic therapy provide an advantage for the resistant strains, (ii) combination therapy with two antibiotics prevents the emergence of resistance strains in contrast to sequential antibiotic therapy, and (iii) early initiation of antibiotics is among the most important factors preventing the emergence of resistant strains. These findings provide new insights into strategies aimed at optimizing the administration of antimicrobials for the treatment of infections and the prevention of the emergence of antimicrobial resistance
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