1,600 research outputs found
Commensurate-Incommensurate Magnetic Phase Transition in Magnetoelectric Single Crystal LiNiPO
Neutron scattering studies of single-crystal LiNiPO reveal a spontaneous
first-order commensurate-incommensurate magnetic phase transition. Short- and
long-range incommensurate phases are intermediate between the high temperature
paramagnetic and the low temperature antiferromagnetic phases. The modulated
structure has a predominant antiferromagnetic component, giving rise to
satellite peaks in the vicinity of the fundamental antiferromagnetic Bragg
reflection, and a ferromagnetic component giving rise to peaks at small
momentum-transfers around the origin at . The wavelength of the
modulated magnetic structure varies continuously with temperature. It is argued
that the incommensurate short- and long-range phases are due to
spin-dimensionality crossover from a continuous to the discrete Ising state.
These observations explain the anomalous first-order transition seen in the
magnetoelectric effect of this system
Surface and bulk polaritons in a linear magnetoelectric multiferroic with canted spins: Transverse Electric polarisation
Some magnetoelectric multiferroics have a canted spin structure that can be
described by a Dzyaloshinkii-Moriya coupling. We calculate properties and
features expected for surface and bulk magnon polaritons in such media with a
linear magnetoelectric interaction for the case of transverse electric
polarisation. The dielectric polarisation and magnetisation of weak
ferromagnetism are constrained to lie in the plane parallel to the surface. We
examine a geometry with the polarisation oriented in the film plane and present
numerical results for the transverse electric polarisation. Particular
attention is given to non-reciprocal surface modes, which exist in frequency
between two bulk bands, and show how these modes can be modified by external
magnetic field. Results for attenuated total reflection are presented, and
discussed in relation to nonreciprocity. Example results are calculated for the
canted antiferromagnet BaMnF4.Comment: 14 pages, 6 figure
Subclinical Shed of Infectious Varicella zoster Virus in Astronauts
Aerosol borne varicella zoster virus (VZV) enters the nasopharynx and replicates in tonsillar T-cells, resulting in viremia and varicella (chickenpox). Virus then becomes latent in cranial nerve, dorsal root and autonomic nervous system ganglia along the entire neuraxis (1). Decades later, as cell-mediated immunity to VZV declines (4), latent VZV can reactivate to produce zoster (shingles). Infectious VZV is present in patients with varicella or zoster, but shed of infectious virus in the absence of disease has not been shown. We previously detected VZV DNA in saliva of astronauts during and shortly after spaceflight, suggesting stress induced subclinical virus reactivation (3). We show here that VZV DNA as well as infectious virus in present in astronaut saliva. VZV DNA was detected in saliva during and after a 13-day spaceflight in 2 of 3 astronauts (Fig. panel A). Ten days before liftoff, there was a rise in serum anti-VZV antibody in subjects 1 and 2, consistent with virus reactivation. In subject 3, VZV DNA was not detected in saliva, and there was no rise in anti-VZV antibody titer. Subject 3 may have been protected from virus reactivation by having zoster <10 years ago, which provides a boost in cell-medicated immunity to VZV (2). No VZV DNA was detected in astronaut saliva months before spaceflight, or in saliva of 10 age/sex-matched healthy control subjects sampled on alternate days for 3 weeks (88 saliva samples). Saliva taken 2-6 days after landing from all 3 subjects was cultured on human fetal lung cells (Fig. panel B). Infectious VZV was recovered from saliva of subjects 1 and 2 on the second day after landing. Virus specificity was confirmed by antibody staining and DNA analysis which showed it to be VZV of European descent, common in the US (5). Further, both antibody staining and DNA PCR demonstrated that no HSV-1 was detected in any infected culture. This is the first report of infectious VZV shedding in the absence of clinical disease. Spaceflight presents a uniquely stressful environment which includes physical isolation and confinement, anxiety, sleep deprivation, as well as exposure to increased radiation and microgravity. It is interesting that in our study, VZV and not HSV-1 reactivation was detected, since stress-induced HSV-1 reactivation has been reported (6). Future studies are needed to determine the specific inducer of VZV reactivation
Integrated Clinical Training for Space Flight Using a High-Fidelity Patient Simulator in a Simulated Microgravity Environment
This viewgraph presentation reviews the use of telemedicine in a simulated microgravity environment using a patient simulator. For decades, telemedicine techniques have been used in terrestrial environments by many cohorts with varied clinical experience. The success of these techniques has been recently expanded to include microgravity environments aboard the International Space Station (ISS). In order to investigate how an astronaut crew medical officer will execute medical tasks in a microgravity environment, while being remotely guided by a flight surgeon, the Medical Operation Support Team (MOST) used the simulated microgravity environment provided aboard DC-9 aircraft teams of crew medical officers, and remote flight surgeons performed several tasks on a patient simulator
The Abundance of New Kind of Dark Matter Structures
A new kind of dark matter structures, ultracompact minihalos (UCMHs) was
proposed recently. They would be formed during the radiation dominated epoch if
the large density perturbations are existent. Moreover, if the dark matter is
made up of weakly interacting massive particles, the UCMHs can have effect on
cosmological evolution because of the high density and dark matter annihilation
within them. In this paper, one new parameter is introduced to consider the
contributions of UCMHs due to the dark matter annihilation to the evolution of
cosmology, and we use the current and future CMB observations to obtain the
constraint on the new parameter and then the abundance of UCMHs. The final
results are applicable for a wider range of dark matter parametersComment: 4 pages, 1 tabl
Canopy nitrogen, carbon assimilation, and albedo in temperate and boreal forests: Functional relations and potential climate feedbacks
The availability of nitrogen represents a key constraint on carbon cycling in terrestrial ecosystems, and it is largely in this capacity that the role of N in the Earth\u27s climate system has been considered. Despite this, few studies have included continuous variation in plant N status as a driver of broad-scale carbon cycle analyses. This is partly because of uncertainties in how leaf-level physiological relationships scale to whole ecosystems and because methods for regional to continental detection of plant N concentrations have yet to be developed. Here, we show that ecosystem CO2 uptake capacity in temperate and boreal forests scales directly with whole-canopy N concentrations, mirroring a leaf-level trend that has been observed for woody plants worldwide. We further show that both CO2 uptake capacity and canopy N concentration are strongly and positively correlated with shortwave surface albedo. These results suggest that N plays an additional, and overlooked, role in the climate system via its influence on vegetation reflectivity and shortwave surface energy exchange. We also demonstrate that much of the spatial variation in canopy N can be detected by using broad-band satellite sensors, offering a means through which these findings can be applied toward improved application of coupled carbon cycle–climate models
No increase in radiation-induced chromosome aberration complexity detected by m-FISH after culture in the presence of 5’-bromodeoxyuridine
The thymidine analogue, 5’-bromodeoxyuridine (BrdU), is a known mutagen that is routinely introduced into culture media for subsequent Harlequin stain analysis and determination of cell cycle status. Previously, we examined the induction of chromosome aberrations in human peripheral blood lymphocytes (PBL) known to be in their 1st cell division following exposure to a low dose (0.5 Gy, average one -particle per cell) of high-LET α-particles. We found complex chromosome aberrations to be characteristic of exposure to high-LET radiation and suggested the features of complex exchange to reflect qualitatively the spatial deposition of this densely ionising radiation. To exclude the possibility that BrdU addition post-irradiation influenced the complexity of chromosomal damage observed by m-FISH, the effect of increasing BrdU concentration on aberration complexity was investigated. Comparisons between BrdU concentration (0, 10, and 40 M) and between sham- and α-particle irradiated PBL, were made both independently and in combination to enable discrimination between BrdU and high-LET radiation effects. Aberration type, size, complexity and completeness were assessed by m-FISH, and the relative progression through cell division was evaluated. We found no evidence of any qualitative difference in the complexity of damage as visualized by m-FISH but did observe an increase in the frequency of complex exchanges with increasing BrdU concentration indicative of altered cell cycle kinetics. The parameters measured here are consistent with findings from previous in vitro and in vivo work, indicating that each complex aberration visualised by m-FISH is characteristic of the structure of the high-LET α-particle track and the geometry of cell irradiated
Reactions at polymer interfaces: A Monte Carlo Simulation
Reactions at a strongly segregated interface of a symmetric binary polymer
blend are investigated via Monte Carlo simulations. End functionalized
homopolymers of different species interact at the interface instantaneously and
irreversibly to form diblock copolymers. The simulations, in the framework of
the bond fluctuation model, determine the time dependence of the copolymer
production in the initial and intermediate time regime for small reactant
concentration . The results are compared to
recent theories and simulation data of a simple reaction diffusion model. For
the reactant concentration accessible in the simulation, no linear growth of
the copolymer density is found in the initial regime, and a -law is
observed in the intermediate stage.Comment: to appear in Macromolecule
Sharpening the predictions of big-bang nucleosynthesis
Motivated by the recent measurement of the primeval abundance of deuterium,
we re-examine the nuclear inputs to big-bang nucleosynthesis (BBN). Using
Monte-Carlo realization of the nuclear cross-section data to directly estimate
the theoretical uncertainties for the yields of D, 3-He and 7-Li, we show that
previous estimates were a factor of 2 too large. We sharpen the BBN
determination of the baryon density based upon deuterium, rho_B = (3.6 +/- 0.4)
* 10^{-31} g/cm^3 (Omega_B h^2 = 0.019 +/- 0.0024), which leads to a predicted
4-He abundance, Y_P = 0.246 +/- 0.0014 and a stringent limit to the equivalent
number of light neutrino species: N_nu < 3.20 (all at 95% cl). The predicted
7-Li abundance, 7-Li/H = (3.5 + 1.1 - 0.9) * 10^{-10}, is higher than that
observed in pop II stars, (1.7 +/- 0.3) * 10^{-10} (both, 95% cl). We identify
key reactions and the energies where further work is needed.Comment: 5 pages, 4 figures (epsfig), REVTeX; submitted to Phys. Rev. Let
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