18,370 research outputs found
Coupling the solar surface and the corona: coronal rotation, Alfv\'en wave-driven polar plumes
The dynamical response of the solar corona to surface and sub-surface
perturbations depends on the chromospheric stratification, and specifically on
how efficiently these layers reflect or transmit incoming Alfv\'en waves. While
it would be desirable to include the chromospheric layers in the numerical
simulations used to study such phenomena, that is most often not feasible. We
defined and tested a simple approximation allowing the study of coronal
phenomena while taking into account a parametrised chromospheric reflectivity.
We addressed the problems of the transmission of the surface rotation to the
corona and that of the generation of polar plumes by Alfv\'en waves (Pinto et
al., 2010, 2011). We found that a high (yet partial) effective chromospheric
reflectivity is required to properly describe the angular momentum balance in
the corona and the way the surface differential rotation is transmitted
upwards. Alfv\'en wave-driven polar plumes maintain their properties for a wide
range of values for the reflectivity, but they become bursty (and eventually
disrupt) when the limit of total reflection is attained.Comment: Solar Wind 13: Proceedings of the Thirteenth International Solar Wind
Conferenc
Systemic inflammation and residual viraemia in HIV-positive adults on protease inhibitor monotherapy: a cross-sectional study.
Increased levels of markers of systemic inflammation have been associated with serious non-AIDS events even in patients on fully suppressive antiretroviral therapy. We explored residual viremia and systemic inflammation markers in patients effectively treated with ritonavir-boosted protease inhibitor monotherapy (PImono)
Large classical universes emerging from quantum cosmology
It is generally believed that one cannot obtain a large Universe from quantum
cosmological models without an inflationary phase in the classical expanding
era because the typical size of the Universe after leaving the quantum regime
should be around the Planck length, and the standard decelerated classical
expansion after that is not sufficient to enlarge the Universe in the time
available. For instance, in many quantum minisuperspace bouncing models studied
in the literature, solutions where the Universe leave the quantum regime in the
expanding phase with appropriate size have negligible probability amplitude
with respect to solutions leaving this regime around the Planck length. In this
paper, I present a general class of moving gaussian solutions of the
Wheeler-DeWitt equation where the velocity of the wave in minisuperspace along
the scale factor axis, which is the new large parameter introduced in order to
circumvent the abovementioned problem, induces a large acceleration around the
quantum bounce, forcing the Universe to leave the quantum regime sufficiently
big to increase afterwards to the present size, without needing any classical
inflationary phase in between, and with reasonable relative probability
amplitudes with respect to models leaving the quantum regime around the Planck
scale. Furthermore, linear perturbations around this background model are free
of any transplanckian problem.Comment: 8 pages, 1 figur
Ketogenic diet-induced weight loss is associated with an increase in vitamin d levels in obese adults
Vitamin D is an important micronutrient involved in several processes. Evidence has shown a strong association between hypovitaminosis D and cardio-metabolic diseases, including obesity. A ketogenic diet has proven to be very effective for weight loss, especially in reducing fat mass while preserving fat-free mass. The aim of this study was to investigate the effect of a ketogenic diet-induced weight loss on vitamin D status in a population of obese adults. We enrolled 56 obese outpatients, prescribed with either traditional standard hypocaloric Mediterranean diet (SHMD) or very low-calorie ketogenic diet (VLCKD). Serum 25(OH)D concentrations were measured by chemiluminescence. The mean value of serum 25-hydroxyvitamin D (25(OH)D) concentrations in the whole population at baseline was 17.8 +/- 5.6 ng/mL, without differences between groups. After 12 months of dietetic treatment, in VLCKD patients serum 25(OH)D concentrations increased from 18.4 +/- 5.9 to 29.3 +/- 6.8 ng/mL (p < 0.0001), vs 17.5 +/- 6.1 to 21.3 +/- 7.6 ng/mL (p = 0.067) in the SHMD group (for each kilogram of weight loss, 25(OH)D concentration increased 0.39 and 0.13 ng/mL in the VLCKD and in the SHMD groups, respectively). In the VLCKD group, the increase in serum 25(OH)D concentrations was strongly associated with body mass index, waist circumference, and fatty mass variation. In a multiple regression analysis, fatty mass was the strongest independent predictor of serum 25(OH)D concentration, explaining 15.6%, 3.3%, and 9.4% of its variation in the whole population, in SHMD, and VLCKD groups, respectively. We also observed a greater reduction of inflammation (evaluated by high-sensitivity C reactive protein (hsCRP) values) and a greater improvement in glucose homeostasis, confirmed by a reduction of HOMA values, in the VLCKD versus the SHMD group. Taken together, all these data suggest that a dietetic regimen, which implies a great reduction of fat mass, can improve vitamin D status in the obese
Effects of zinc on microalgal biofilms in intertidal and subtidal habitats
Microalgal biofilms are sensitive to environmental conditions. Impacts of contaminants on assemblages of marine biofilm are often investigated in laboratories or in mesocosms. Such experiments are rarely representative of the effects of contaminants on biofilms under natural conditions. Studies in field situations, with enough power to detect impacts, are necessary to develop a better understanding of the effects of contaminants on ecological processes. Metals are a common contaminant of marine systems and can cause disturbances to assemblages. Using a new technique to experimentally deliver contaminants to microalgal assemblages, hypotheses were tested regarding the effects of zinc on microalgal biofilms growing on settlement panels in subtidal and intertidal habitats. PAM fluorometry was used to assess the amount and physiological state of biofilms on panels. Control panels deployed for 1 month in each habitat had significantly greater amounts of biofilm than those exposed to zinc. After deployment for 3 months, the results varied with location. The observed effects on the biofilm did not, however, cause significant changes in the macro-invertebrate assemblages that developed on the panels
On the quantumness of correlations in nuclear magnetic resonance
Nuclear Magnetic Resonance (NMR) was successfully employed to test several
protocols and ideas in Quantum Information Science. In most of these
implementations the existence of entanglement was ruled out. This fact
introduced concerns and questions about the quantum nature of such bench tests.
In this article we address some issues related to the non-classical aspects of
NMR systems. We discuss some experiments where the quantum aspects of this
system are supported by quantum correlations of separable states. Such
quantumness, beyond the entanglement-separability paradigm, is revealed via a
departure between the quantum and the classical versions of information theory.
In this scenario, the concept of quantum discord seems to play an important
role. We also present an experimental implementation of an analogous of the
single-photon Mach-Zehnder interferometer employing two nuclear spins to encode
the interferometric paths. This experiment illustrate how non-classical
correlations of separable states may be used to simulate quantum dynamics. The
results obtained are completely equivalent to the optical scenario, where
entanglement (between two field modes) may be present
A Search for Environmental Effects on Type Ia Supernovae
We use integrated colors and B and V absolute magnitudes of Type Ia supernova
(SN) host galaxies in order to search for environmental effects on the SN
optical properties. With the new sample of 44 SNe we confirm the conclusion by
Hamuy et al. (1996a) that bright events occur preferentially in young stellar
environments. We find also that the brightest SNe occur in the least luminous
galaxies, a possible indication that metal-poorer neighbourhoods produce the
more luminous events. The interpretation of these results is made difficult,
however, due to the fact that galaxies with younger stellar populations are
also lower in luminosity. In an attempt to remove this ambiguity we use models
for the line strengths in the absorption spectrum of five early-type galaxies,
in order to estimate metallicities and ages of the SN host galaxies. With the
addition of abundance estimates from nebular analysis of the emission spectra
of three spiral galaxies, we find possible further evidence that luminous SNe
are produced in metal-poor neighborhoods. Further spectroscopic observations of
the SN host galaxies will be necessary to test these results and assist in
disentangling the age/metallicity effects on Type Ia SNe.Comment: 14 pages, 5 figures, to appear in the September 2000 issue of The
Astronomical Journa
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