524 research outputs found
Preprint arXiv: 2201.05529 Submitted on 14 Jan 2022
We study the thermalization of individual spins of a short XYZ Heisenberg chain with strongly coupled thermal leads by checking the consistency of two-time correlations with the fluctuation-dissipation theorem. To compute these correlations we develop and apply a general numerical method for chains of quantum systems, where each system may couple strongly to a structured environment. The method combines the process tensor formalism for general (possibly non-Markovian) open quantum systems with time evolving block decimation for 1D chains. It systematically reduces the numerical complexity originating from system-environment correlations before integrating them into the full many-body problem, making a wide range of applications numerically feasible. Our results show the complete thermalization of the chain when coupled to a single bath, and reveal distinct effective temperatures in low, mid, and high frequency regimes when placed between a hot and a cold bath
Haemodialysis activates phospholipase A2 enzyme
Background Clinical and experimental evidence suggest that haemodialysis (HD) procedure is an inflammatory process. For the production of proinflammatory lipid mediators in many inflammatory reactions, the release of arachidonic acid by phospholipase A2 (PLA2 enzyme is a prerequisite. Therefore, the purpose of the present investigation was to establish whether the activity of PLA2 increases during HD and whether the increase depends on the type of dialyser used. Methods We performed dialysis in eight chronic HD patients. Blood samples entering and leaving the dialyser were obtained before and at 15, 60, 120 and 180 min after the dialysis was started, on one occasion using a cuprophane and on another occasion a cellulose triacetate dialyser. PLA2 activity was assessed in crude plasma and in plasma extract. Results PLA2 activity in plasma extract exhibited similar biochemical properties to that of inflammatory human synovial fluid PLA2 enzyme which is of group II PLA2. PLA2 activity in crude plasma represents a type of PLA2 other than the synovial type. In HD patients, baseline PLA2 activities in crude plasma and plasma extract were significantly increased when compared to normal subjects. An increase in PLA2 activity was observed in crude plasma with a peak appearing at 15 min when the patients were dialysed with cuprophane and cellulose triacetate membranes. This increase was observed in both arterial and venous blood samples and was more pronounced when the patients were dialysed with cuprophane than with cellulose triacetate membranes. When PLA2 was assessed in plasma extract, the activity increased only with cuprophane but not with cellulose triacetate membranes. Conclusions PLA2 activity in plasma is increased in HD patients and increases during the dialysis procedure to a greater extent with a less biocompatible membrane. Continuous activation of PLA2 might be relevant for long-term deleterious consequences of H
Effect of Central Mass Concentration on the Formation of Nuclear Spirals in Barred Galaxies
We have performed smoothed particle hydrodynamics (SPH) simulations to study
the response of the central kiloparsec region of a gaseous disk to the
imposition of nonaxisymmetric bar potentials. The model galaxies are composed
of the three axisymmetric components (halo, disk, and bulge) and a
non-axisymmetric bar. These components are assumed to be invariant in time in
the frame corotating with the bar. The potential of spherical -models
of Dehnen is adopted for the bulge component whose density varies as
near the center and at larger radiiand hence, possesses
a central density core for and cusps for . Since the
central mass concentration of the model galaxies increases with the cusp
parameter , we have examined here the effect of the central mass
concentration by varying the cusp parameter on the mechanism
responsible for the formation of the symmetric two-armed nuclear spirals in
barred galaxies. Our simulations show that the symmetric two-armed nuclear
spirals are formed by hydrodynamic spiral shocks driven by the gravitational
torque of the bar for the models with and 0.5. On the other hand,
the symmetric two-armed nuclear spirals in the models with and 1.5
are explained by gas density waves. Thus, we conclude that the mechanism
responsible for the formation of the symmetric two-armed nuclear spirals in
barred galaxies changes from the hydrodynamic shocks to the gas density waves
when the central mass concentration increases from to 1.5.Comment: 29 pages, 5 figures (Color Figures 3-5), Accepted for Publication in
Astrophysical Journal (ApJ
The Pattern Speed of the Galactic Bar
Most late-type stars in the solar neighborhood have velocities similar to the
local standard of rest (LSR), but there is a clearly separated secondary
component corresponding to a slower rotation and a mean outward motion.
Detailed simulations of the response of a stellar disk to a central bar show
that such a bi-modality is expected from outer-Lindblad resonant scattering.
When constraining the run of the rotation curve by the proper motion of Sgr A*
and the terminal gas velocities, the value observed for the rotation velocity
separating the two components results in a value of (53+/-3)km/s/kpc for the
pattern speed of the bar, only weakly dependent on the precise values for Ro
and bar angle phi.Comment: 5 pages LaTeX, 2 Figs, accepted for publication in ApJ Letter
Formation of Nuclear Spirals in Barred Galaxies
We have performed smoothed particle hydrodynamics (SPH) simulations for the
response of the gaseous disk to the imposed moderately strong non-axisymmetric
potentials. The model galaxies are composed of the three stellar components
(disk, bulge and bar) and two dark ones (supermassive black hole and halo)
whose gravitational potentials are assumed to be invariant in time in the frame
corotating with the bar. We found that the torques alone generated by the
moderately strong bar that gives the maximum of tangential-to-radial force
ratio as are not sufficient to drive the gas
particles close to the center due to the barrier imposed by the inner Lindblad
resonances (ILRs). In order to transport the gas particles towards the nucleus
( pc), a central supermassive black hole (SMBH) and high sound speed of
the gas are required to be present. The former is required to remove the inner
inner Lindblad resonance (IILR) that prevents gas inflow close to the nucleus,
while the latter provides favourable conditions for the gas particles to lose
their angular momentum and to spiral in. Our models that have no IILR show the
trailing nuclear spirals whose innermost parts reach close to the center in a
curling way when the gas sound speed is km s. They
resemble the symmetric two-armed nuclear spirals observed in the central
kiloparsec of spiral galaxies. We found that the symmetric two-armed nuclear
spirals are formed by the hydrodynamic spiral shocks caused by the
gravitational torque of the bar in the presence of a central SMBH that can
remove IILR when the sound speed of gas is high enough to drive a large amount
of gas inflow deep inside the ILR. However, the detailed morphology of nuclear
spirals depends on the sound speed of gas.Comment: 38 pages, 10 figures, accepted for publication in Ap
The properties of the Galactic bar implied by gas kinematics in the inner Milky Way
Longitude-velocity (l-V) diagrams of H I and CO gas in the inner Milky Way
have long been known to be inconsistent with circular motion in an axisymmetric
potential. Several lines of evidence suggest that the Galaxy is barred, and gas
flow in a barred potential could be consistent with the observed ``forbidden''
velocities and other features in the data. We compare the H I observations to
l-V diagrams synthesized from 2-D fluid dynamical simulations of gas flows in a
family of barred potentials. The gas flow pattern is very sensitive to the
parameters of the assumed potential, which allows us to discriminate among
models. We present a model that reproduces the outer contour of the H I l-V
diagram reasonably well; this model has a strong bar with a semimajor axis of
3.6 kpc, an axis ratio of approximately 3:1, an inner Lindblad resonance (ILR),
and a pattern speed of 42 km/s/kpc, and matches the data best when viewed from
34\deg to the bar major axis. The behavior of the models, combined with the
constraint that the shocks in the Milky Way bar should resemble those in
external barred galaxies, leads us to conclude that wide ranges of parameter
space are incompatible with the observations. In particular we suggest that the
bar must be fairly strong, must have an ILR, and cannot be too end-on, with the
bar major axis at 35\deg +/- 5\deg to the line of sight. The H I data exhibit
larger forbidden velocities over a wider longitude range than are seen in
molecular gas; this important difference is the reason our favored model
differs so significantly from other recently proposed models.Comment: 23 pages, 14 figures, 1 table, uses emulateapj and psfig, 640 kb.
Submitted to Ap
Detailed Analysis of Nearby Bulgelike Dwarf Stars III. Alpha and Heavy-element abundances
The present sample of nearby bulgelike dwarf stars has kinematics and
metallicities characteristic of a probable inner disk or bulge origin. Ages
derived by using isochrones give 10-11 Gyr for these stars and metallicities
are in the range -0.80< [Fe/H]< +0.40. We calculate stellar parameters from
spectroscopic data, and chemical abundances of Mg, Si, Ca, Ti, La, Ba, Y, Zr
and Eu are derived by using spectrum synthesis.
We found that [alpha-elements/Fe] show different patterns depending on the
element. Si, Ca and Ti-to-iron ratios decline smoothly for increasing
metallicities, and follow essentially the disk pattern. O and Mg, products of
massive supernovae, and also the r-process element Eu, are overabundant
relative to disk stars, showing a steeper decline for metallicities [Fe/H] >
-0.3 dex. [s-elements/Fe] roughly track the solar values with no apparent trend
with metallicity for [Fe/H] < 0, showing subsolar values for the metal rich
stars. Both kinematical and chemical properties of the bulgelike stars indicate
a distinct identity of this population when compared to disk stars.Comment: 21 pages, 9 figures, to appear in Ap
Kinematics of the Galactic Globular Cluster System: New Radial Velocities for Clusters in the Direction of the Inner Galaxy
HIRES on the Keck I telescope has been used to measure the first radial
velocities for stars belonging to eleven, heavily-reddened globular clusters in
the direction of the inner Galaxy. The question of kinematic substructuring
among the Galactic globular cluster system is investigated using an updated
catalog of globular cluster distances, metallicities and velocities. It is
found that the population of metal-rich globular clusters shows significant
rotation at all Galactocentric radii. For the metal-rich clusters within 4 kpc
of the Galactic center, the measured rotation velocity and line-of-sight
velocity dispersion are similar to those of bulge field stars. We investigate
claims that the metal-rich clusters are associated with the central Galactic
bar by comparing the kinematics of the innermost clusters to that of the atomic
hydrogen in the inner Galaxy. The longitude-velocity diagram of both metal-rich
and metal-poor clusters bears a remarkable similarity to that of the gas,
including the same non-circular motions which have traditionally been
interpreted as evidence for a Galactic bar, or, alternatively, a
non-axisymmetric bulge. However, uncertainties in the existing
three-dimensional Galactocentric positions for most of the clusters do not yet
allow an unambiguous discrimination between the competing scenarios of
membership in a rigidly rotating bar, or in a bulge which is an oblate
isotropic rotator. We conclude that the majority of metal-rich clusters within
the central 4 kpc of the Galaxy are probably associated with the bulge/bar, and
not the thick disk. (ABRIDGED)Comment: 18 pages, including 7 of 13 postscript figures. Figures 1-6 available
at http://astro.caltech.edu/~pc. Accepted for publication in the Astronomical
Journa
On the age heterogeneity of the Pleiades, Hyades and Sirius moving groups
We investigate the nature of the classical low-velocity structures in the
local velocity field, i.e. the Pleiades, Hyades and Sirius moving groups. After
using a wavelet transform to locate them in velocity space, we study their
relation with the open clusters kinematically associated with them. By directly
comparing the location of moving group stars in parallax space to the
isochrones of the embedded clusters, we check whether, within the observational
errors on the parallax, all moving group stars could originate from the
on-going evaporation of the associated cluster. We conclude that, in each
moving group, the fraction of stars making up the velocity-space overdensity
superimposed on the background is higher than the fraction of stars compatible
with the isochrone of the associated cluster. These observations thus favour a
dynamical (resonant) origin for the Pleiades, Hyades and Sirius moving groups.Comment: 8 pages, 8 figures, accepted for publication in A&
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