9,210 research outputs found
Quantum Fluctuations and Excitations in Antiferromagnetic Quasicrystals
We study the effects of quantum fluctuations and the excitation spectrum for
the antiferromagnetic Heisenberg model on a two-dimensional quasicrystal, by
numerically solving linear spin-wave theory on finite approximants of the
octagonal tiling. Previous quantum Monte Carlo results for the distribution of
local staggered magnetic moments and the static spin structure factor are
reproduced well within this approximate scheme. Furthermore, the magnetic
excitation spectrum consists of magnon-like low-energy modes, as well as
dispersionless high-energy states of multifractal nature. The dynamical spin
structure factor, accessible to inelastic neutron scattering, exhibits
linear-soft modes at low energies, self-similar structures with bifurcations
emerging at intermediate energies, and flat bands in high-energy regions. We
find that the distribution of local staggered moments stemming from the
inhomogeneity of the quasiperiodic structure leads to a characteristic energy
spread in the local dynamical spin susceptibility, implying distinct nuclear
magnetic resonance spectra, specific for different local environments.Comment: RevTex, 12 pages with 15 figure
Empirical wind model for the middle and lower atmosphere. Part 1: Local time average
The HWM90 thermospheric wind model was revised in the lower thermosphere and extended into the mesosphere and lower atmosphere to provide a single analytic model for calculating zonal and meridional wind profiles representative of the climatological average for various geophysical conditions. Gradient winds from CIRA-86 plus rocket soundings, incoherent scatter radar, MF radar, and meteor radar provide the data base and are supplemented by previous data driven model summaries. Low-order spherical harmonics and Fourier series are used to describe the major variations throughout the atmosphere including latitude, annual, semiannual, and longitude (stationary wave 1). The model represents a smoothed compromise between the data sources. Although agreement between various data sources is generally good, some systematic differences are noted, particularly near the mesopause. Root mean square differences between data and model are on the order of 15 m/s in the mesosphere and 10 m/s in the stratosphere for zonal wind, and 10 m/s and 4 m/s, respectively, for meridional wind
Submillimeter wavelength molecular spectroscopy of the Orion molecular cloud
A submillimeter wavelength spectroscopic study of the Orion molecular cloud has been made in the J = 4-3 HCN, H13CN, HCO+, H13CO+, and J = 7-6 CS molecular transitions. Densities of up to a few times 106 cm-3 are found coupled with high inferred brightness temperatures, indicating kinetic temperatures of 120 K. Evidence for lower densities in the surrounding ambient molecular cloud is presented along with maps of HCN and HCO+ emission. The maps indicate different spatial distributions in the two lines. The abundances of HCN and HCO+ in the plateau source are found to be enhanced relative to those in the surrounding molecular cloud, and there is a suggestion that a number of small-angular-diameter clumps may be present. The present observations do not confirm the previously reported detection of CO+ in the interstellar medium
Exploring service providers’ perceptions of the barriers and enablers to recruitment of service users into social prescribing research
\ua9 2024 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.Objective: To explore the views of social prescribing service providers on the barriers and enablers to recruitment of service users in social prescribing research. Design: A qualitative study design, using semi-structured interviews with social prescribing service providers in the voluntary, community, faith, and social enterprise sector. Data were analysed using Thematic Framework Analysis. Results: Ten interviews were conducted with service providers from five different social prescribing services. Three analytical themes were created. (1) What are you talking about?, related to service provider experiences of attempting to engage service users in social prescribing research, specifically confusion about the term social prescribing. (2) You’ve got a friend in me, focused on the positive impact of quality relationships between service providers and service users on recruitment. (3) No, no, no. Not today, reflected the experiences of service providers who reported that service users will often experience fluctuations in their mental and physical health, limiting their capacity to engage with structured research activity. Conclusions: Key implications arising from this study is a need for more accessible and person-centred strategies for strengthening recruitment to, and participation in, social prescribing research. Increasing accessibility of research language (and information about participation), providing flexibility in recruitment methods, and conduct of research can also improve recruitment and retention. Service providers are vital for supporting engagement of service users in social prescribing research
EIT-MESHER – Segmented FEM Mesh Generation and Refinement
EIT-MESHER (https://github.com/EIT-team/Mesher) is C++ software, based on the CGAL library, which generates high quality Finite Element Model tetrahedral meshes from binary masks of 3D volume segmentations. Originally developed for biomedical applications in Electrical Impedance Tomography (EIT) to address the need for custom, non-linear refinement in certain areas (e.g. around electrodes), EIT-MESHER can also be used in other fields where custom FEM refinement is required, such as Diffuse Optical Tomography (DOT)
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Submillimetre CO observations of the Cepheus A outflow
The authors have carried out spectral mapping of the Cep A region in the J = 3-2 transition of CO. The high velocity wings symptomatic of outflowing gas are evident over a region ~6Ă—6 arc min in extent (~1.3Ă—1.3 pc). There appear to be 2 outflows, as found also for HCO+ by Loren et al. (1985). The CO J = 3-2 red wing intensity is enhanced relative both to lower transition CO data and to HCO+ J = 1-0, particularly to the south and east of Cep A, a result which suggests the presence of hot, optically thin gas in the flow. No such significant enhancement is seen, however, in the blue wing. The data are discussed in terms of a 2 component outflow in which the HCO+ emission originates mainly from dense clumps in the flow while a less dense (but >4Ă—104cm-3) interclump medium is responsible for most of the 12CO emission
Analytic, Group-Theoretic Density Profiles for Confined, Correlated N-Body Systems
Confined quantum systems involving identical interacting particles are to
be found in many areas of physics, including condensed matter, atomic and
chemical physics. A beyond-mean-field perturbation method that is applicable,
in principle, to weakly, intermediate, and strongly-interacting systems has
been set forth by the authors in a previous series of papers. Dimensional
perturbation theory was used, and in conjunction with group theory, an analytic
beyond-mean-field correlated wave function at lowest order for a system under
spherical confinement with a general two-body interaction was derived. In the
present paper, we use this analytic wave function to derive the corresponding
lowest-order, analytic density profile and apply it to the example of a
Bose-Einstein condensate.Comment: 15 pages, 2 figures, accepted by Physics Review A. This document was
submitted after responding to a reviewer's comment
Prospectus, November 6, 1970
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Intertwining Relations for the Deformed D1D5 CFT
The Higgs branch of the D1D5 system flows in the infrared to a
two-dimensional N=(4,4) SCFT. This system is believed to have an "orbifold
point" in its moduli space where the SCFT is a free sigma model with target
space the symmetric product of copies of four-tori; however, at the orbifold
point gravity is strongly coupled and to reach the supergravity point one needs
to turn on the four exactly marginal deformations corresponding to the blow-up
modes of the orbifold SCFT. Recently, technology has been developed for
studying these deformations and perturbing the D1D5 CFT off its orbifold point.
We present a new method for computing the general effect of a single
application of the deformation operators. The method takes the form of
intertwining relations that map operators in the untwisted sector before
application of the deformation operator to operators in the 2-twisted sector
after the application of the deformation operator. This method is
computationally more direct, and may be of theoretical interest. This line of
inquiry should ultimately have relevance for black hole physics.Comment: latex, 23 pages, 3 figure
Electronic collection of patient-reported outcomes following discharge after surgery:systematic review
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