159 research outputs found
Mechanism of Magnetic Flux Loss in Molecular Clouds
We investigate the detailed processes working in the drift of magnetic fields
in molecular clouds. To the frictional force, whereby the magnetic force is
transmitted to neutral molecules, ions contribute more than half only at cloud
densities , and charged grains contribute more
than 90% at . Thus grains play a decisive role
in the process of magnetic flux loss. Approximating the flux loss time by
a power law , where is the mean field strength in
the cloud, we find , characteristic to ambipolar diffusion,
only at . At higher densities,
decreases steeply with , and finally at , where magnetic fields
effectively decouple from the gas, is attained, reminiscent of
Ohmic dissipation, though flux loss occurs about 10 times faster than by Ohmic
dissipation. Ohmic dissipation is dominant only at . While ions and electrons drift in the direction of
magnetic force at all densities, grains of opposite charges drift in opposite
directions at high densities, where grains are major contributors to the
frictional force. Although magnetic flux loss occurs significantly faster than
by Ohmic dissipation even at very high densities as , the process going on at high densities is quite different from ambipolar
diffusion in which particles of opposite charges are supposed to drift as one
unit.Comment: 34 pages including 9 postscript figures, LaTex, accepted by
Astrophysical Journal (vol.573, No.1, July 1, 2002
Evolution of Molecular Abundance in Protoplanetary Disks
We investigate the evolution of molecular abundance in quiescent
protoplanetary disks which are presumed to be around weak-line T Tauri stars.
In the region of surface density less than g cm (distance from
the star AU in the minimum- mass solar nebula), cosmic rays are
barely attenuated even in the midplane of the disk and produce chemically
active ions such as He and H. Through reactions with these ions CO
and N are finally transformed into CO, NH, and HCN. In the region
where the temperature is low enough for these products to freeze onto grains,
considerable amount of carbon and nitrogen is locked up in the ice mantle and
is depleted from the gas phase in a time scale yr.
Oxidized (CO) ice and reduced (NH and hydrocarbon) ice naturally
coexist in this part of the disk. The molecular abundance both in the gas phase
and in ice mantle varies significantly with the distance from the central star.Comment: 7 pages latex file (using aas2pp4.sty), 3 figures (ps file), to
appear in the Astrophysical Journal Letter
Doping Dependence of Anisotropic Resistivities in Trilayered Superconductor Bi2Sr2Ca2Cu3O10+delta (Bi-2223)
The doping dependence of the themopower, in-plane resistivity rho_ab(T),
out-of-plane resistivity rho_c(T), and susceptibility has been systematically
measured for high-quality single crystal Bi2Sr2Ca2Cu3O10+delta. We found that
the transition temperature Tc and pseudogap formation temperature T_rho_c*,
below which rho_c shows a typical upturn, do not change from their optimum
values in the "overdoped" region, even though doping actually proceeds. This
suggests that, in overdoped region, the bulk is determined by the always
underdoped inner plane, which have a large superconducting gap, while the
carriers are mostly doped in the outer planes, which have a large phase
stiffness.Comment: 5 pages, 4 figures. to be published in PR
Tomography of a solar plage with the Tenerife Inversion Code
We apply the Tenerife Inversion Code (TIC) to the plage spectropolarimetric
observations obtained by the Chromospheric LAyer SpectroPolarimeter (CLASP2).
These unprecedented data consist of full Stokes profiles in the spectral region
around the Mg II h and k lines for a single slit position, with around two
thirds of the 200 arcsec slit crossing a plage region and the rest crossing an
enhanced network. A former analysis of these data had allowed us to infer the
longitudinal component of the magnetic field by applying the weak field
approximation (WFA) to the circular polarization profiles, and to assign the
inferred magnetic fields to different layers of the solar atmosphere based on
the results of previous theoretical radiative transfer investigations. In this
work, we apply the recently developed TIC to the same data. We obtain the
stratified model atmosphere that fits the intensity and circular polarization
profiles at each position along the spectrograph slit and we compare our
results for the longitudinal component of the magnetic field with the
previously obtained WFA results, highlighting the generally good agreement in
spite of the fact that the WFA is known to produce an underestimation when
applied to the outer lobes of the Mg II h and k circular polarization profiles.
Finally, we use the inverted model atmospheres to give a rough estimation of
the energy that could be carried by Alfv\`en waves propagating along the
chromosphere in the plage and network regions, showing that it is sufficient to
compensate the estimated energy losses in the chromosphere of solar active
regions.Comment: Accepted for publication in The Astrophysical Journa
Evidence for the Operation of the Hanle and Magneto-Optical Effects in the Scattering Polarization Signals Observed by CLASP2 Across the Mg II h and k Lines
Radiative transfer investigations of the solar Mg II h and k resonance lines
around 280~nm showed that, while their circular polarization (Stokes V) signals
arise from the Zeeman effect, the linear polarization profiles (Stokes Q and U)
are dominated by the scattering of anisotropic radiation and the Hanle and
magneto-optical (MO) effects. Using the unprecedented observations of the Mg II
and Mn I resonance lines obtained by the Chromospheric LAyer
Spectro-Polarimeter (CLASP2), here we investigate how the linear polarization
signals at different wavelengths (i.e., at the center, and at the near and far
wings of the k line) vary with the longitudinal component of the magnetic field
() at their approximate height of formation. The is estimated
from the V signals in the aforementioned spectral lines. Particular attention
is given to the following quantities that are expected to be influenced by the
presence of magnetic fields through the Hanle and MO effects: the sign of the U
signals, the total linear polarization amplitude () and its direction
() with respect to a reference direction. We find that at the center and
near wings of the line, the behavior of these quantities is significantly
different in the observed quiet and plage regions, and that both and
seem to depend on . These observational results are indicative of
the operation of the Hanle effectComment: 26 pages, 18 figures, accepted for publication in the Astrophysical
Journa
Studying Exotic Hadrons in Heavy Ion Collisions
We investigate the possibilities of using measurements in present and future
experiments on heavy ion collisions to answer some longstanding problems in
hadronic physics, namely identifying hadronic molecular states and exotic
hadrons with multiquark components. The yields of a selected set of exotic
hadron candidates in relativistic heavy ion collisions are discussed in the
coalescence model in comparison with the statistical model. We find that the
yield of a hadron is typically an order of magnitude smaller when it is a
compact multiquark state, compared to that of an excited hadronic state with
normal quark numbers. We also find that some loosely bound hadronic molecules
are formed more abundantly than the statistical model prediction by a factor of
two or more. Moreover, due to the significant numbers of charm and bottom
quarks produced at RHIC and even larger numbers expected at LHC, some of the
proposed heavy exotic hadrons could be produced with sufficient abundance for
detection, making it possible to study these new exotic hadrons in heavy ion
collisions.Comment: 18 pages, 2 figure
Optical Alignment of the High-Precision UV Spectro-Polarimeter (CLASP2)
No abstract availabl
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Memory-specific correlated neuronal activity in higher-order auditory regions of a parrot.
Funder: Kayamori Foundation for Informational Science AdvancementFunder: the Netherlands Organization for Scientific ResearchFunder: Multi-Career Path Support Model for Female Researchers project of Japan’s Women UniversityFunder: Japan Society for the Promotion of Science (JSPS) Grant-in-AidFunder: ALW Open Competition and GW Horizon ProgrammeMale budgerigars (Melopsittacus undulatus) are open-ended learners that can learn to produce new vocalisations as adults. We investigated neuronal activation in male budgerigars using the expression of the protein products of the immediate early genes zenk and c-fos in response to exposure to conspecific contact calls (CCs: that of the mate or an unfamiliar female) in three subregions (CMM, dNCM and vNCM) of the caudomedial pallium, a higher order auditory region. Significant positive correlations of Zenk expression were found between these subregions after exposure to mate CCs. In contrast, exposure to CCs of unfamiliar females produced no such correlations. These results suggest the presence of a CC-specific association among the subregions involved in auditory memory. The caudomedial pallium of the male budgerigar may have functional subdivisions that cooperate in the neuronal representation of auditory memory
Emergence of a Helical Flux Rope Under an Active Region Prominence
Continuous observations were obtained of active region 10953 with the Solar
Optical Telescope (SOT) on board the \emph{Hinode} satellite during 2007 April
28 to May 9. A prominence was located over the polarity inversion line (PIL) in
the south-east of the main sunspot. These observations provided us with a time
series of vector magnetic fields on the photosphere under the prominence. We
found four features: (1) The abutting opposite-polarity regions on the two
sides along the PIL first grew laterally in size and then narrowed. (2) These
abutting regions contained vertically-weak, but horizontally-strong magnetic
fields. (3) The orientations of the horizontal magnetic fields along the PIL on
the photosphere gradually changed with time from a normal-polarity
configuration to a inverse-polarity one. (4) The horizontal-magnetic field
region was blueshifted. These indicate that helical flux rope was emerging from
below the photosphere into the corona along the PIL under the pre-existing
prominence. We suggest that this supply of a helical magnetic flux into the
corona is associated with evolution and maintenance of active-region
prominences.Comment: 10 pages, 2 figures, accepted for publication in ApJ Letter
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