31 research outputs found
Spin-dynamics simulations of the triangular antiferromagnetic XY model
Using Monte Carlo and spin-dynamics methods, we have investigated the dynamic
behavior of the classical, antiferromagnetic XY model on a triangular lattice
with linear sizes . The temporal evolutions of spin configurations
were obtained by solving numerically the coupled equations of motion for each
spin using fourth-order Suzuki-Trotter decompositions of exponential operators.
From space- and time-displaced spin-spin correlation functions and their
space-time Fourier transforms we obtained the dynamic structure factor for momentum and frequency . Below
(Kosterlitz-Thouless transition), both the in-plane () and the
out-of-plane () components of exhibit very strong
and sharp spin-wave peaks. Well above , and
apparently display a central peak, and spin-wave signatures are still seen in
. In addition, we also observed an almost dispersionless domain-wall
peak at high below (Ising transition), where long-range order
appears in the staggered chirality. Above , the domain-wall peak
disappears for all . The lineshape of these peaks is captured reasonably
well by a Lorentzian form. Using a dynamic finite-size scaling theory, we
determined the dynamic critical exponent = 1.002(3). We found that our
results demonstrate the consistency of the dynamic finite-size scaling theory
for the characteristic frequeny and the dynamic structure factor
itself.Comment: 8 pages, RevTex, 10 figures, submitted to PR
CDMS, Supersymmetry and Extra Dimensions
The CDMS experiment aims to directly detect massive, cold dark matter
particles originating from the Milky Way halo. Charge and lattice excitations
are detected after a particle scatters in a Ge or Si crystal kept at ~30 mK,
allowing to separate nuclear recoils from the dominating electromagnetic
background. The operation of 12 detectors in the Soudan mine for 75 live days
in 2004 delivered no evidence for a signal, yielding stringent limits on dark
matter candidates from supersymmetry and universal extra dimensions. Thirty Ge
and Si detectors are presently installed in the Soudan cryostat, and operating
at base temperature. The run scheduled to start in 2006 is expected to yield a
one order of magnitude increase in dark matter sensitivity.Comment: To be published in the proceedings of the 7th UCLA symposium on
sources and detection of dark matter and dark energy in the universe, Marina
del Rey, Feb 22-24, 200
Observing the First Stars and Black Holes
The high sensitivity of JWST will open a new window on the end of the
cosmological dark ages. Small stellar clusters, with a stellar mass of several
10^6 M_sun, and low-mass black holes (BHs), with a mass of several 10^5 M_sun
should be directly detectable out to redshift z=10, and individual supernovae
(SNe) and gamma ray burst (GRB) afterglows are bright enough to be visible
beyond this redshift. Dense primordial gas, in the process of collapsing from
large scales to form protogalaxies, may also be possible to image through
diffuse recombination line emission, possibly even before stars or BHs are
formed. In this article, I discuss the key physical processes that are expected
to have determined the sizes of the first star-clusters and black holes, and
the prospect of studying these objects by direct detections with JWST and with
other instruments. The direct light emitted by the very first stellar clusters
and intermediate-mass black holes at z>10 will likely fall below JWST's
detection threshold. However, JWST could reveal a decline at the faint-end of
the high-redshift luminosity function, and thereby shed light on radiative and
other feedback effects that operate at these early epochs. JWST will also have
the sensitivity to detect individual SNe from beyond z=10. In a dedicated
survey lasting for several weeks, thousands of SNe could be detected at z>6,
with a redshift distribution extending to the formation of the very first stars
at z>15. Using these SNe as tracers may be the only method to map out the
earliest stages of the cosmic star-formation history. Finally, we point out
that studying the earliest objects at high redshift will also offer a new
window on the primordial power spectrum, on 100 times smaller scales than
probed by current large-scale structure data.Comment: Invited contribution to "Astrophysics in the Next Decade: JWST and
Concurrent Facilities", Astrophysics & Space Science Library, Eds. H.
Thronson, A. Tielens, M. Stiavelli, Springer: Dordrecht (2008
TRY plant trait database â enhanced coverage and open access
Plant traitsâthe morphological, anatomical, physiological, biochemical and phenological characteristics of plantsâdetermine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of traitâbased plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traitsâalmost complete coverage for âplant growth formâ. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and traitâenvironmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives
Chemical reactivity and the structure of gels
The structures of sel-gel-derived networks are a product of a series of condensation reactions. In solution, the evolving structures are limited to species which are stable in the synthesis medium (alcohol/water). During consolidation metastable species form, which are temporarily stabilized by the high viscosity of the surrounding matrix. Chemical reactivity of gel-derived networks provides insight to their structure and vice versa
Effect of Non-Symmetrical Lateral Diffusion on Film Cooling Effectiveness from a Row of Shaped Holes
Acute coronary syndromes: cardiac rehabilitation programmes and quality of life
Aims. This paper reports a study examining the quality of life of clients following hospital admission with acute coronary syndrome in Hong Kong and their use of cardiac rehabilitation.\ud
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Background. Coronary heart disease is a major source of mortality and morbidity in Hong Kong. Western studies have suggested that participation in cardiac rehabilitation improves the quality of life of clients with coronary heart disease yet the use of cardiac rehabilitation has been reported to be low. Better understanding is needed of the psychosocial status of these clients in Hong Kong and their use of cardiac rehabilitation services.\ud
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Methods. A prospective, pretestpost-test study was carried out, with data collected over a period of 6 months with convenience sample of 182 participants. Baseline data were obtained within one week after hospital admission for individuals experiencing ACS. The second phase of data collection commenced at 6 months after hospital discharge. Total period of data collection took over 12 months between 2002 and 2003. The Chinese version of the SF-36 was used to assess quality of life, and demographic data and the extent to which clients participated in the cardiac rehabilitation programme were assessed.\ud
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Results. Only 25% of the participants attended at least one session of the cardiac rehabilitation programme. Significant improvement occurred in all clients' perceived quality of life 6 months following initial hospital admission. No significant group differences in perceived quality of life were found according to whether or not clients used the cardiac rehabilitation services.\ud
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Conclusion. Improvement in perceived health-related quality of life was evident over a 6-month period. Yet our findings suggested that participation in the cardiac rehabilitation programme did not have any apparent effects in subjects' perceived quality of life. Further studies using both generic and disease-specific health-related quality of life instruments, as well as the inclusion of control group, are recommended. Continual improvement in cardiac rehabilitation programmes, and consideration of alternative modes of delivery other than the traditional attendance at hospital outpatient services, are also recommended
Lipoxygenase activities during development of root and nodule of soybean Atividade de lipoxigenases durante o desenvolvimento da raiz e do nĂłdulo de plantas de soja
The objective of this work was to evaluate root and nodule soybean lipoxygenases in Doko cultivar and in a near isogenic line lacking seed lipoxygenases, inoculated and uninoculated with Bradyrhizobium elkanii. The lipoxygenase activities from roots collected at 3, 5, 9, 13, 18 and 28 days post-inoculation and from nodules collected at 13, 18 and 28 days post-inoculation were measured. The pH-activity profiles from root and nodules suggested that the lipoxygenases pool expressed in these organs from Doko cultivar and triple-null near isogenic lines are similar. The root lipoxygenase activity of Doko and triple-null lines, inoculated and uninoculated, reduced over time. The highest lipoxygenase activity observed at the beginning of root formation suggests the involvement of this enzyme in growth and development of this organ. However, for nodules an expressive increase of lipoxygenase activity was noticed 28 days post-inoculation. Root and nodule showed, at least, two mobility groups for lipoxygenases in immunoblottings, with approximately 94 and 97 kDa.<br>O objetivo deste trabalho foi avaliar lipoxigenases de raĂzes e nĂłdulos de plantas de soja da variedade Doko e da linhagem triplo nula derivada, desprovida das lipoxigenases da semente, com e sem inoculação de Bradyrhizobium elkanii. A atividade de lipoxigenase foi avaliada em raĂzes coletadas aos 3, 5, 9, 13, 18 e 28 dias apĂłs a inoculação e em nĂłdulos coletados aos 13, 18 e 28 dias apĂłs a inoculação. Os perfis de pH-atividade de raiz e nĂłdulo sugerem que o "pool" de lipoxigenases expresso nesses ĂłrgĂŁos nĂŁo difere nos dois genĂłtipos. A atividade de lipoxigenases nas raĂzes de Doko e Doko triplo nula, com e sem inoculação, declinou com o passar do tempo. A maior atividade de lipoxigenases no inĂcio de formação da raiz sugere o envolvimento desta enzima no crescimento e desenvolvimento deste ĂłrgĂŁo. Nos nĂłdulos houve um aumento acentuado na atividade de lipoxigenase aos 28 dias apĂłs a inoculação. Dois grupos de mobilidade com aproximadamente 94 e 97 kDa foram encontrados nos "immunoblottings" para lipoxigenases de raiz e de nĂłdulo