718 research outputs found
Probing the internal solar magnetic field through g-modes
The observation of g-mode candidates by the SoHO mission opens the
possibility of probing the internal structure of the solar radiative zone (RZ)
and the solar core more directly than possible via the use of the p-mode
helioseismology data. We study the effect of rotation and RZ magnetic fields on
g-mode frequencies. Using a self-consistent static MHD magnetic field model we
show that a 1% g-mode frequency shift with respect to the Solar Seismic Model
(SSeM) prediction, currently hinted in the GOLF data, can be obtained for
magnetic fields as low as 300 kG, for current measured modes of radial order
n=-20. On the other hand, we also argue that a similar shift for the case of
the low order g-mode candidate (l=2, n=-3) frequencies can not result from
rotation effects nor from central magnetic fields, unless these exceed 8 MG.Comment: 6 pages, 2 figures; final version to appear in MNRA
Coriolis force corrections to g-mode spectrum in 1D MHD model
The corrections to g-mode frequencies caused by the presence of a central
magnetic field and rotation of the Sun are calculated. The calculations are
carried out in the simple one dimensional magnetohydrodynamical model using the
approximations which allow one to find the purely analytical spectra of
magneto-gravity waves beyond the scope of the JWKB approximation and avoid in a
small background magnetic field the appearance of the cusp resonance which
locks a wave within the radiative zone. These analytic results are compared
with the satellite observations of the g-mode frequency shifts which are of the
order one per cent as given in the GOLF experiment at the SoHO board. The main
contribution turns out to be the magnetic frequency shift in the strong
magnetic field which obeys the used approximations. In particular, the fixed
magnetic field strength 700 KG results in the mentioned value of the frequency
shift for the g-mode of the radial order n=-10. The rotational shift due to the
Coriolis force appears to be small and does not exceed a fracton of per cent,
\alpha_\Omega < 0.003.Comment: RevTeX4, 9 pages, 4 eps figures; accepted for publication in
Astronomy Reports (Astronomicheskii Zhurnal
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Losses in superconducting multifilament composites under alternating changing fields
The first part of this report presents a brief review of the losses in superconducting composites in a changing external field. The losses are expressed for a single triangular shaped pulse and for a field varying exponentially with time. The losses are calculated as a function of two important time constants. The first is due to the coupling currents between the filaments, the second is due to the eddy currents induced in the matrix. In the second part of the report, the case of an oscillating sinusoidal field is considered. In particular, in a rapidly varying field, several layers of filaments can be saturated by returning currents. Complete expressions of the losses are provided together with simplified expressions which enable one to calculate the losses in most cases. In the third part, a comparison between several kinds of conductors shows that in some cases the losses are reduced by increasing the twist pitch of the conductor
Solar opacity, neutrino signals and helioseismology
In connection with the recent suggestion by Tsytovich et al. that opacity in
the solar core could be overestimated, we consider the following questions: i)
What would a 10\% opacity reduction imply for the solar neutrino puzzle? ii) Is
there any hope of solving the solar neutrino puzzle by changing opacity? iii)
Is a 10\% opacity reduction testable with helioseismological data?Comment: revtex file of 3 pages + 2 postscipt figures, in a uuencoded
compressed tarred file, send any offprint request to [email protected]
Standard Solar models in the Light of New Helioseismic Constraints II. Mixing Below the Convective Zone
In previous work, we have shown that recent updated standard solar models
cannot reproduce the radial profile of the sound speed at the base of the
convective zone (CZ) and fail to predict the Li7 depletion. In parallel,
helioseismology has shown that the transition from differential rotation in the
CZ to almost uniform rotation in the radiative solar interior occurs in a
shallow layer called the tachocline. This layer is presumably the seat of large
scale circulation and of turbulent motions. Here, we introduce a macroscopic
transport term in the structure equations, which is based on a hydrodynamical
description of the tachocline proposed by Spiegel and Zahn, and we calculate
the mixing induced within this layer. We discuss the influence of different
parameters that represent the tachocline thickness, the Brunt-Vaissala
frequency at the base of the CZ, and the time dependence of this mixing process
along the Sun's evolution. We show that the introduction of such a process
inhibits the microscopic diffusion by about 25%. Starting from models including
a pre-main sequence evolution, we obtain: a) a good agreement with the observed
photospheric chemical abundance of light elements such as He3, He4, Li7 and
Be9, b) a smooth composition gradient at the base of the CZ, and c) a
significant improvement of the sound speed square difference between the
seismic sun and the models in this transition region, when we allow the
phostospheric heavy element abundance to adjust, within the observational
incertitude, due to the action of this mixing process. The impact on neutrino
predictions is also discussed.Comment: 15 pages, 7 figures, to be published in ApJ (used emulateapj style
for latex2e). New email for A. S. Brun: [email protected]
Helioseismology, solar models and solar neutrinos
We review recent advances concerning helioseismology, solar models and solar
neutrinos. Particularly we shall address the following points: i) helioseismic
tests of recent SSMs; ii)the accuracy of the helioseismic determination of the
sound speed near the solar center; iii)predictions of neutrino fluxes based on
helioseismology, (almost) independent of SSMs; iv)helioseismic tests of exotic
solar models.Comment: 11 pages with 6 ps figures included, procsla style, based on the
talks presented at Neutrino Telescopes '99, Venice, February 1999, and at
Valencia '99, Valencia, May 1999, to appear in the proceeding
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Time-dependent metabolomic profiling of Ketamine drug action reveals hippocampal pathway alterations and biomarker candidates
Ketamine, an N-methyl-D-aspartate receptor (NMDAR) antagonist, has fast-acting antidepressant activities and is used for major depressive disorder (MDD) patients who show treatment resistance towards drugs of the selective serotonin reuptake inhibitor (SSRI) type. In order to better understand Ketamine's mode of action, a prerequisite for improved drug development efforts, a detailed understanding of the molecular events elicited by the drug is mandatory. In the present study we have carried out a time-dependent hippocampal metabolite profiling analysis of mice treated with Ketamine. After a single injection of Ketamine, our metabolomics data indicate time-dependent metabolite level alterations starting already after 2 h reflecting the fast antidepressant effect of the drug. In silico pathway analyses revealed that several hippocampal pathways including glycolysis/gluconeogenesis, pentose phosphate pathway and citrate cycle are affected, apparent by changes not only in metabolite levels but also connected metabolite level ratios. The results show that a single injection of Ketamine has an impact on the major energy metabolism pathways. Furthermore, seven of the identified metabolites qualify as biomarkers for the Ketamine drug response
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