1,134 research outputs found
Formación de líneas espectrales fuera de equilibrio termodinámico en la atmósfera solar
Es sabido que para obtener perfiles de líneas fuera de equilibrio termodinámico, es necesario resolver en forma auto-consistente las ecuaciones de equilibrio estadístico y de transporte radiativo en la atmósfera. El programa que se presenta resuelve este problema en forma iterativa en base al método de Skumanich y Domenico. Las variables de entrada son el modelo, [Tₑ(h), nₑ(h), Mₐ.(h)] y la radiación incidente externa. Además de los perfiles de línea, se obtiene información complementaria sobre transformación de energía, opacldades, etc.Asociación Argentina de Astronomí
Constraints on the SZ Power Spectrum on Degree Angular Scales in WMAP Data
The Sunyaev-Zel'dovich (SZ) effect has a distinct spectral signature that
allows its separation from fluctuations in the cosmic microwave background
(CMB) and foregrounds. Using CMB anisotropies measured in Wilkinson Microwave
Anisotropy Probe's five-year maps, we constrain the SZ fluctuations at large,
degree angular scales corresponding to multipoles in the range from 10 to 400.
We provide upper bounds on SZ fluctuations at multipoles greater than 50, and
find evidence for a hemispherically asymmetric signal at ten degrees angular
scales. The amplitude of the detected signal cannot be easily explained with
the allowed number density and temperature of electrons in the Galactic halo.
We have failed to explain the excess signal as a residual from known Galactic
foregrounds or instrumental uncertainties such as 1/f-noise.Comment: 14 pages, 3 figures, 2 tables. Simple typos fixe
Anti-inflammatory effects of hepatocyte growth factor: induction of interleukin-1 receptor antagonist
Hepatocyte growth factor (HGF) prevents liver failure in various animal models including endotoxin-induced acute liver failure. We were interested to find out whether human HGF exerts anti-inflammatory effects by modulation of cytokine synthesis. Therefore, human HepG2 cells were cultured with increasing concentrations of HGF. HGF dose-dependently upregulated the production of interleukin-1 receptor antagonist (IL-1Ra). Incubation of HepG2 cells with interleukin-1beta (IL-1beta) caused an increase in IL-1Ra levels, while interleukin-6 (IL-6) had no effect on IL-1Ra synthesis. Co-stimulation of HepG2 cells with HGF + IL-1beta resulted in a synergistic effect on IL-1Ra mRNA and protein expression. Stimulation of freshly isolated mouse hepatocytes from male C57 BL/6 mice with HGF increased IL-1Ra mRNA and protein synthesis dose-dependently. A co-stimulation with HGF and IL-1beta had a synergistic effect on IL-1Ra mRNA expression but only a partially additive effect on IL-1Ra protein synthesis. HGF-induced IL-1Ra production was significantly decreased by the mitogen-activated protein kinase (MAPK) inhibitor PD98059. Accordingly, HGF stimulation specifically increased MAPK-dependent signalling pathway (p42/44). In contrast, in preactivated PBMC mRNA expression and protein synthesis of IL-1Ra, interleukin-10 (IL-10) and tumor necrosis factor-alpha (TNF-alpha) were unaffected after stimulation with HGF. In conclusion, our data suggest that HGF exerts anti-inflammatory effects by modulating the signal transduction cascade leading to increased expression of IL-1Ra, which might explain the protective and regenerative properties of this cytokine in animal models of liver failure
Derivation of fluid dynamics from kinetic theory with the 14--moment approximation
We review the traditional derivation of the fluid-dynamical equations from
kinetic theory according to Israel and Stewart. We show that their procedure to
close the fluid-dynamical equations of motion is not unique. Their approach
contains two approximations, the first being the so-called 14-moment
approximation to truncate the single-particle distribution function. The second
consists in the choice of equations of motion for the dissipative currents.
Israel and Stewart used the second moment of the Boltzmann equation, but this
is not the only possible choice. In fact, there are infinitely many moments of
the Boltzmann equation which can serve as equations of motion for the
dissipative currents. All resulting equations of motion have the same form, but
the transport coefficients are different in each case.Comment: 15 pages, 3 figures, typos fixed and discussions added; EPJA: Topical
issue on "Relativistic Hydro- and Thermodynamics
Constraint methods for determining pathways and free energy of activated processes
Activated processes from chemical reactions up to conformational transitions
of large biomolecules are hampered by barriers which are overcome only by the
input of some free energy of activation. Hence, the characteristic and
rate-determining barrier regions are not sufficiently sampled by usual
simulation techniques. Constraints on a reaction coordinate r have turned out
to be a suitable means to explore difficult pathways without changing potential
function, energy or temperature. For a dense sequence of values of r, the
corresponding sequence of simulations provides a pathway for the process. As
only one coordinate among thousands is fixed during each simulation, the
pathway essentially reflects the system's internal dynamics. From mean forces
the free energy profile can be calculated to obtain reaction rates and insight
in the reaction mechanism. In the last decade, theoretical tools and computing
capacity have been developed to a degree where simulations give impressive
qualitative insight in the processes at quantitative agreement with
experiments. Here, we give an introduction to reaction pathways and
coordinates, and develop the theory of free energy as the potential of mean
force. We clarify the connection between mean force and constraint force which
is the central quantity evaluated, and discuss the mass metric tensor
correction. Well-behaved coordinates without tensor correction are considered.
We discuss the theoretical background and practical implementation on the
example of the reaction coordinate of targeted molecular dynamics simulation.
Finally, we compare applications of constraint methods and other techniques
developed for the same purpose, and discuss the limits of the approach
Phi meson production in Au+Au and p+p collisions at sqrt (s)=200 GeV
We report the STAR measurement of Phi meson production in Au+Au and p+p
collisions at sqrt (s)=200 GeV. Using the event mixing technique, the Phi
spectra and yields are obtained at mid-rapidity for five centrality bins in
Au+Au collisions and for non-singly-diffractive p+p collisions. It is found
that the Phi transverse momentum distributions from Au+Au collisions are better
fitted with a single-exponential while the p+p spectrum is better described by
a double-exponential distribution. The measured nuclear modification factors
indicate that Phi production in central Au+Au collisions is suppressed relative
to peripheral collisions when scaled by the number of binary collisions. The
systematics of versus centrality and the constant Phi/K- ratio versus beam
species, centrality, and collision energy rule out kaon coalescence as the
dominant mechanism for Phi production.Comment: 6 pages, 3 figures, submitted to Phys. Rev. Let
Azimuthal anisotropy and correlations in p+p, d+Au and Au+Au collisions at 200 GeV
We present the first measurement of directed flow () at RHIC. is
found to be consistent with zero at pseudorapidities from -1.2 to 1.2,
then rises to the level of a couple of percent over the range . The latter observation is similar to data from NA49 if the SPS rapidities
are shifted by the difference in beam rapidity between RHIC and SPS.
Back-to-back jets emitted out-of-plane are found to be suppressed more if
compared to those emitted in-plane, which is consistent with {\it jet
quenching}. Using the scalar product method, we systematically compared
azimuthal correlations from p+p, d+Au and Au+Au collisions. Flow and non-flow
from these three different collision systems are discussed.Comment: Quark Matter 2004 proceeding, 4 pages, 3 figure
Azimuthal anisotropy: the higher harmonics
We report the first observations of the fourth harmonic (v_4) in the
azimuthal distribution of particles at RHIC. The measurement was done taking
advantage of the large elliptic flow generated at RHIC. The integrated v_4 is
about a factor of 10 smaller than v_2. For the sixth (v_6) and eighth (v_8)
harmonics upper limits on the magnitudes are reported.Comment: 4 pages, 6 figures, contribution to the Quark Matter 2004 proceeding
Plasma Wakefield Acceleration with a Modulated Proton Bunch
The plasma wakefield amplitudes which could be achieved via the modulation of
a long proton bunch are investigated. We find that in the limit of long bunches
compared to the plasma wavelength, the strength of the accelerating fields is
directly proportional to the number of particles in the drive bunch and
inversely proportional to the square of the transverse bunch size. The scaling
laws were tested and verified in detailed simulations using parameters of
existing proton accelerators, and large electric fields were achieved, reaching
1 GV/m for LHC bunches. Energy gains for test electrons beyond 6 TeV were found
in this case.Comment: 9 pages, 7 figure
The energy dependence of angular correlations inferred from mean- fluctuation scale dependence in heavy ion collisions at the SPS and RHIC
We present the first study of the energy dependence of angular
correlations inferred from event-wise mean transverse momentum
fluctuations in heavy ion collisions. We compare our large-acceptance
measurements at CM energies $\sqrt{s_{NN}} =$ 19.6, 62.4, 130 and 200 GeV to
SPS measurements at 12.3 and 17.3 GeV. $p_t$ angular correlation structure
suggests that the principal source of $p_t$ correlations and fluctuations is
minijets (minimum-bias parton fragments). We observe a dramatic increase in
correlations and fluctuations from SPS to RHIC energies, increasing linearly
with $\ln \sqrt{s_{NN}}$ from the onset of observable jet-related
fluctuations near 10 GeV.Comment: 10 pages, 4 figure
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