2,433 research outputs found
Re-examination of the Population, Stratigraphy, and Sequence of Mercurian Basins: Implications for Mercurys Early Impact History and Comparison with the Moon
Mercury has one of the best preserved impact records in the inner Solar System due to the absence of an atmosphere, but it has much higher rates of surface modification than on the Moon. The earliest geological mapping of the planet revealed a variety of important differences from the Moon, regarding the impact basin (D 300 km) and cratering record, as well as the extensive volcanic plains of Mercury [1-3]. It has been shown [3] that the bombardment history of the terrestrial planets is lunar-like and linked in terms of impactor population(s) and impact rates. Recent studies suggest that Mercury and the Moon had the same early impactor populations based on the similarity of their crater size-frequency distributions (CSFD), however the impact rates on Mercury are higher than on the Moon. Catalogued and characterized the basin population on Mercury using early optical data obtained by the MESSENGER spacecraft and found 46 certain and probable impact basins, as well as 41 tentative
Intestinal microbiota influences non-intestinal related autoimmune diseases
Indexación: Scopus.The human body is colonized by millions of microorganisms named microbiota that interact with our tissues in a cooperative and non-pathogenic manner. These microorganisms are present in the skin, gut, nasal, oral cavities, and genital tract. In fact, it has been described that the microbiota contributes to balancing the immune system to maintain host homeostasis. The gut is a vital organ where microbiota can influence and determine the function of cells of the immune system and contributes to preserve the wellbeing of the individual. Several articles have emphasized the connection between intestinal autoimmune diseases, such as Crohn's disease with dysbiosis or an imbalance in the microbiota composition in the gut. However, little is known about the role of the microbiota in autoimmune pathologies affecting other tissues than the intestine. This article focuses on what is known about the role that gut microbiota can play in the pathogenesis of non-intestinal autoimmune diseases, such as Grave's diseases, multiple sclerosis, type-1 diabetes, systemic lupus erythematosus, psoriasis, schizophrenia, and autism spectrum disorders. Furthermore, we discuss as to how metabolites derived from bacteria could be used as potential therapies for non-intestinal autoimmune diseases. © 2018 Opazo, Ortega-Rocha, Coronado-Arrázola, Bonifaz, Boudin, Neunlist, Bueno, Kalergis and Riedel.https://www.frontiersin.org/articles/10.3389/fmicb.2018.00432/ful
High and low molecular weight crossovers in the longest relaxation time dependence of linear cis-1,4 polyisoprene by dielectric relaxations
The dielectric relaxation of cis-1,4 Polyisoprene [PI] is sensitive not only to the local and segmental dynamics but also to the larger scale chain (end-to-end) fluctuations. We have performed a careful dielectric investigation on linear PI with various molecular weights in the range of 1 to 320 kg/mol. The broadband dielectric spectra of all samples were measured isothermally at the same temperature to avoid utilizing shift factors. For the low and medium molecular weight range, the comparisons were performed at 250 K to access both the segmental relaxation and normal mode peaks inside the available frequency window (1 mHz–10 MHz). In this way, we were able to observe simultaneously the effect of molecular mass on the segmental dynamics—related with the glass transition process—and on the end-to-end relaxation time of PI and thus decouple the direct effect of molecular weight on the normal mode from that due to the effect on the monomeric friction coefficient. The latter effect is significant for low molecular weight (M w < 33 kg/mol), i.e., in the range where the crossover from Rouse dynamics to entanglement limited flow occurs. Despite the conductivity contribution at low frequency, careful experiments allowed us to access to the normal mode signal for molecular weights as high as M w = 320 kg/mol, i.e., into the range of high molecular weights where the pure reptation behavior could be valid, at least for the description of the slowest chain modes. The comparison between the dielectric relaxations of PI samples with medium and high molecular weight was performed at 320 K. We found two crossovers in the molecular weight dependence of the longest relaxation time, the first around a molecular weight of 6.5 ± 0.5 kg/mol corresponding to the end of the Rouse regime and the second around 75 ± 10 kg/mol. Above this latter value, we find a power law compatible with exponent 3 as predicted by the De Gennes theory
Fractional ac Josephson effect in unconventional superconductors
For certain orientations of Josephson junctions between two p_x-wave or two
d-wave superconductors, the subgap Andreev bound states produce a 4pi-periodic
relation between the Josephson current I and the phase difference phi: I ~
sin(phi/2). Consequently, the ac Josephson current has the fractional frequency
eV/h, where V is the dc voltage. In the tunneling limit, the Josephson current
is proportional to the first power (not square) of the electron tunneling
amplitude. Thus, the Josephson current between unconventional superconductors
is carried by single electrons, rather than by Cooper pairs. The fractional ac
Josephson effect can be observed experimentally by measuring frequency spectrum
of microwave radiation from the junction.Comment: 8 pages, 3 figures, RevTEX 4; v2. - minor typos corrected in proof
Josephson current in unconventional superconductors through an Anderson impurity
Josephson current for a system consisting of an Anderson impurity weakly
coupled to two unconventional superconductors is studied and shown to be driven
by a surface zero energy (mid-gap) bound-state. The repulsive Coulomb
interaction in the dot can turn a junction into a 0-junction. This effect
is more pronounced in p-wave superconductors while in high-temperature
superconductors with symmetry it can exit for rather large
artificial centers at which tunneling occurs within a finite region.Comment: 4 pages 3.eps figure
Nonadiabatic effects in a generalized Jahn-Teller lattice model: heavy and light polarons, pairing and metal-insulator transition
The ground state polaron potential of 1D lattice of two-level molecules with
spinless electrons and two Einstein phonon modes with quantum phonon-assisted
transitions between the levels is found anharmonic in phonon displacements. The
potential shows a crossover from two nonequivalent broad minima to a single
narrow minimum corresponding to the level positions in the ground state.
Generalized variational approach implies prominent nonadiabatic effects:(i) In
the limit of the symmetric E-e Jahn- Teller situation they cause transition
between the regime of the predominantly one-level "heavy" polaron and a "light"
polaron oscillating between the levels due to phonon assistance with almost
vanishing polaron displacement. It implies enhancement of the electron transfer
due to decrease of the "heavy" polaron mass (undressing) at the point of the
transition. Pairing of "light" polarons due to exchange of virtual phonons
occurs. Continuous transition to new energy ground state close to the
transition from "heavy" polaron phase to "light" (bi)polaron phase occurs. In
the "heavy" phase, there occurs anomalous (anharmonic) enhancements of quantum
fluctuations of the phonon coordinate, momentum and their product as functions
of the effective coupling. (ii) Dependence of the polaron mass on the optical
phonon frequency appears.(iii) Rabi oscillations significantly enhance quantum
shift of the insulator-metal transition line to higher values of the critical
effective e-ph coupling supporting so the metallic phase. In the E-e JT case,
insulator-metal transition coincide with the transition between the "heavy" and
the "light" (bi)polaron phase at certain (strong) effective e-ph interaction.Comment: Paper in LaTex format (file jtseptx.tex) and 9 GIF-figures
(ppic_1.gif,...ppic_9.gif
The entropy of the QCD plasma
Self-consistent approximations in terms of fully dressed propagators provide
a simple expression for the entropy of an ultrarelativistic plasma, which
isolates the contribution of the elementary excitations as a leading
contribution. Further approximations, whose validity is checked on a soluble
model involving a scalar field, allow us to calculate the entropy of the QCD
plasma. We obtain an accurate description of lattice data for purely gluonic
QCD, down to temperatures of about twice the transition temperature.Comment: 12 pages, 3 figures, REVTEX (minor modifications
Current correlations and quantum localization in 2D disordered systems with broken time-reversal invariance
We study long-range correlations of equilibrium current densities in a
two-dimensional mesoscopic system with the time reversal invariance broken by a
random or homogeneous magnetic field. Our result is universal, i.e. it does not
depend on the type (random potential or random magnetic field) or correlation
length of disorder. This contradicts recent sigma-model calculations of
Taras-Semchuk and Efetov (TS&E) for the current correlation function, as well
as for the renormalization of the conductivity. We show explicitly that the new
term in the sigma-model derived by TS&E and claimed to lead to delocalization
does not exist. The error in the derivation of TS&E is traced to an incorrect
ultraviolet regularization procedure violating current conservation and gauge
invariance.Comment: 8 pages, 3 figure
Use of Nutritional Supplements in Youth with Medicated and Unmedicated Attention-Deficit/Hyperactivity Disorder
Objective: To find out whether use of nutritional supplements (NUS) differs between children and adolescents with attention-deficit/hyperactivity disorder (ADHD; medicated or unmedicated), compared with those without the disorder.
Methods: We used cross-sectional data from the population-based I.Family study conducted between 2013 and 2014 in eight European countries. Parents completed questionnaires and participated in interviews, for example, on health and medical history of their child. Data from 5067 children and adolescents aged 5-17 years were included. Exposures were medicated (with ADHD-approved medication) and unmedicated ADHD. The outcome was the use of NUS, measured by use of any or multiple different NUS. Multivariable logistic regression adjusted for sociodemographics and health determinants was used to find ADHD-depending differences.
Results: The study sample comprised 4490 children and adolescents without ADHD and 51 medicated and 76 unmedicated subjects with ADHD. Regarding the use of any NUS, no statistically significant differences were found between children and adolescents without ADHD (18%) and those with medicated (18%) or unmedicated ADHD (22%). However, discrepancies appear when considering multiple use of NUS, not reported for any medicated ADHD subject but remarkably often for unmedicated ADHD subjects (13%), resulting in an adjusted odds ratio of 2.6 (95% confidence interval, 1.2-5.6) when compared with those without ADHD (5%).
Conclusion: Children and adolescents who were not using medication for treating ADHD potentially took NUS as oral remedies. Given the potential for a delay of indicated treatments and for use of those NUS which have no proven effectiveness, pediatricians should actively explore whether NUS have been used to treat ADHD core symptoms, and families should be informed that the average effect size has to be considered small
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