1,804 research outputs found
Multi-band D-TRILEX approach to materials with strong electronic correlations
We present the multi-band dual triply irreducible local expansion (D-TRILEX) approach to interacting electronic systems and discuss its numerical implementation. This method is designed for a self-consistent description of multi-orbital systems that can also have several atoms in the unit cell. The current implementation of the D-TRILEX approach is able to account for the frequency- and channel-dependent long-ranged electronic interactions. We show that our method is accurate when applied to small multi-band systems such as the Hubbard-Kanamori dimer. Calculations for the extended Hubbard, the two-orbital Hubbard-Kanamori, and the bilayer Hubbard models are also discussed
Energy dependence of pion double charge exchange
The energy dependence of forward angle pion double charge exchange is calculated in the energy range of 0–250 MeV. The most striking feature is a peak around 40 MeV which is in excellent agreement with the data when distorted waves obtained from a realistic optical model are used. Two possible short-range corrections to the reaction mechanism are addressed
Outgassing of icy bodies in the solar system - I. The sublimation of hexagonal water ice through dust layers
Our knowledge about the physical processes determining the activity of comets
were mainly influenced by several extremely successful space missions, the
predictions of theoretical models and the results of laboratory experiments.
However, novel computer models should not be treated in isolation but should be
based on experimental results. Therefore, a new experimental setup was
constructed to investigate the temperature dependent sublimation properties of
hexagonal water ice and the gas diffusion through a dry dust layer covering the
ice surface. We show that this experimental setup is capable to reproduce known
gas production rates of pure hexagonal water ice. The reduction of the gas
production rate due to an additional dust layer on top of the ice surface was
measured and compared to the results of another experimental setup in which the
gas diffusion through dust layers at room temperature was investigated. We
found that the relative permeability of the dust layer is inversely
proportional to its thickness, which is also predicted by theoretical models.
However, the measured absolute weakening of the gas flow was smaller than
predicted by models. This lack of correspondence between model and experiment
may be caused by an ill-determination of the boundary condition in the
theoretical models, which further demonstrates the necessity of laboratory
investigations. Furthermore, the impedance of the dust layer to the ice
evaporation was found to be similar to the impedance at room temperature, which
means that the temperature profile of the dust layer is not influencing the
reduction of the gas production. Finally, we present the results of an extended
investigation of the sublimation coefficient, which is an important factor for
the description of the sublimation rate of water ice and, thus, an important
value for thermophysical modeling of icy bodies in the solar system.Comment: Submitted to Icaru
Formation and evolution of dwarf galaxies in the CDM Universe
We first review the results of the tidal stirring model for the
transformation of gas-rich dwarf irregulars into dwarf spheroidals, which turns
rotationally supported stellar systems into pressure supported ones. We
emphasize the importance of the combined effect of ram pressure stripping and
heating from the cosmic ultraviolet background in removing the gas and
converting the object into a gas poor system as dSphs. We discuss how the
timing of infall of dwarfs into the primary halo determines the final
mass-to-light ratio and star formation history. Secondly we review the results
of recent cosmological simulations of the formation of gas-rich dwarfs. These
simulations are finally capable to produce a realistic object with no bulge, an
exponential profile and a slowly rising rotation curve. The result owes to the
inclusion of an inhomogeneous ISM and a star formation scheme based on regions
having the typical density of molecular cloud complexes. Supernovae-driven
winds become more effective in such mode, driving low angular momentum baryons
outside the virial radius at high redshift and turning the dark matter cusp
into a core. Finally we show the first tidal stirring experiments adopting
dwarfs formed in cosmological simulations as initial conditions. The latter are
gas dominated and have have turbulent thick gaseous and stellar disks disks
that cannot develop strong bars, yet they are efficiently heated into spheroids
by tidal shocks.Comment: 14 pages, 4 Figures, o appear in the proceedings of the CRAL
conference, Lyon, June 2010, "A Universe of Dwarf Galaxies", eds. Philippe
Prugniel & Mina Koleva; EDP Sciences in the European Astronomical Society
Publications Series. (invited talk
Different extraction methods of biologically active components from propolis: a preliminary study
Abstract Background Propolis is widely used in apitherapy, preparations, and food and beverage additives. Various extraction techniques were applied in the extraction of the biologically active constituents of poplar type propolis in order to compare their efficiency. The methods employed were: traditional maceration extraction, ultrasound extraction (UE), and microwave assisted extraction (MAE). Results The total amounts of extracted phenolics and flavonoids were determined, and the effectiveness of the methods compared. MAE was very rapid but led to the extraction of a large amount of non-phenolic and non-flavonoid material. UE gave the highest percentage of extracted phenolics. Conclusion Compared to the maceration extraction, MAE and UE methods provided high extraction yield, requiring short timeframes and less labour. UE was shown to be the most efficient method based on yield, extraction time and selectivity.</p
Death receptor 5 signaling promotes hepatocyte lipoapoptosis.
Nonalcoholic steatohepatitis is characterized by hepatic steatosis, elevated levels of circulating free fatty acids (FFA), endoplasmic reticulum (ER) stress, and hepatocyte lipoapoptosis. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) death receptor 5 (DR5) is significantly elevated in patients with nonalcoholic steatohepatitis, and steatotic hepatocytes demonstrate increased sensitivity to TRAIL-mediated cell death. Nonetheless, a role for TRAIL and/or DR5 in mediating lipoapoptotic pathways is unexplored. Here, we examined the contribution of DR5 death signaling to lipoapoptosis by free fatty acids. The toxic saturated free fatty acid palmitate induces an increase in DR5 mRNA and protein expression in Huh-7 human hepatoma cells leading to DR5 localization into lipid rafts, cell surface receptor clustering with subsequent recruitment of the initiator caspase-8, and ultimately cellular demise. Lipoapoptosis by palmitate was not inhibited by a soluble human recombinant DR5-Fc chimera protein suggesting that DR5 cytotoxic signaling is ligand-independent. Hepatocytes from murine TRAIL receptor knock-out mice (DR(-/-)) displayed reduced palmitate-mediated lipotoxicity. Likewise, knockdown of DR5 or caspase-8 expression by shRNA technology attenuated palmitate-induced Bax activation and apoptosis in Huh-7 cells, without altering induction of ER stress markers. Similar observations were verified in other cell models. Finally, knockdown of CHOP, an ER stress-mediated transcription factor, reduced DR5 up-regulation and DR5-mediated caspase-8 activation upon palmitate treatment. Collectively, these results suggest that ER stress-induced CHOP activation by palmitate transcriptionally up-regulates DR5, likely resulting in ligand-independent cytotoxic signaling by this death receptor
Gravitational Quenching by Clumpy Accretion in Cool Core Clusters: Convective Dynamical Response to Overheating
Many galaxy clusters pose a "cooling-flow problem", where the observed X-ray
emission from their cores is not accompanied by enough cold gas or star
formation. A continuous energy source is required to balance the cooling rate
over the whole core volume. We address the feasibility of a gravitational
heating mechanism, utilizing the gravitational energy released by the gas that
streams into the potential well of the cluster dark-matter halo. We focus here
on a specific form of gravitational heating in which the energy is transferred
to the medium thorough the drag exerted on inflowing gas clumps. Using
spheri-symmetric hydro simulations with a subgrid representation of these
clumps, we confirm our earlier estimates that in haloes >=10^13 solar masses
the gravitational heating is more efficient than the cooling everywhere. The
worry was that this could overheat the core and generate an instability that
might push it away from equilibrium. However, we find that the overheating does
not change the global halo properties, and that convection can stabilize the
cluster by carrying energy away from the overheated core. In a typical rich
cluster of 10^{14-15}solar masses, with ~5% of the accreted baryons in gas
clumps of ~10^8 solar masses, we derive upper and lower limits for the
temperature and entropy profiles and show that they are consistent with those
observed in cool-core clusters. We predict the density and mass of cold gas and
the level of turbulence driven by the clump accretion. We conclude that
gravitational heating is a feasible mechanism for preventing cooling flows in
clusters.Comment: 16 pages, 7 figures, accepted by MNRA
Gravitational Quenching in Massive Galaxies and Clusters by Clumpy Accretion
We consider a simple gravitational-heating mechanism for the long-term
quenching of cooling flows and star formation in massive dark-matter haloes
hosting ellipticals and clusters. The virial shock heating in haloes >10^12 Mo
triggers quenching in 10^12-13 Mo haloes (Birnboim, Dekel & Neistein 2007). We
show that the long-term quenching in haloes >Mmin~7x10^12 Mo could be due to
the gravitational energy of cosmological accretion delivered to the inner-halo
hot gas by cold flows via ram-pressure drag and local shocks. Mmin is obtained
by comparing the gravitational power of infall into the potential well with the
overall radiative cooling rate. The heating wins if the gas inner density cusp
is not steeper than r^-0.5 and if the masses in the cold and hot phases are
comparable. The effect is stronger at higher redshifts, making the maintenance
easier also at later times. Clumps >10^5 Mo penetrate to the inner halo with
sufficient kinetic energy before they disintegrate, but they have to be <10^8
Mo for the drag to do enough work in a Hubble time. Pressure confined ~10^4K
clumps are stable against their own gravity and remain gaseous once below the
Bonnor-Ebert mass ~10^8 Mo. They are also immune to tidal disruption. Clumps in
the desired mass range could emerge by thermal instability in the outer halo if
the conductivity is not too high. Alternatively, such clumps may be embedded in
dark-matter subhaloes if the ionizing flux is ineffective, but they separate
from their subhaloes by ram pressure before entering the inner halo. Heating by
dynamical friction becomes dominant for massive satellites, which can
contribute up to one third of the total gravitational heating. We conclude that
gravitational heating by cosmological accretion is a viable alternative to AGN
feedback as a long-term quenching mechanism.Comment: 24 pages, 20 figures, some improvements, MNRAS accepted versio
Gravitational Quenching in Massive Galaxies and Clusters by Clumpy Accretion
We consider a simple gravitational-heating mechanism for the long-term
quenching of cooling flows and star formation in massive dark-matter haloes
hosting ellipticals and clusters. The virial shock heating in haloes >10^12 Mo
triggers quenching in 10^12-13 Mo haloes (Birnboim, Dekel & Neistein 2007). We
show that the long-term quenching in haloes >Mmin~7x10^12 Mo could be due to
the gravitational energy of cosmological accretion delivered to the inner-halo
hot gas by cold flows via ram-pressure drag and local shocks. Mmin is obtained
by comparing the gravitational power of infall into the potential well with the
overall radiative cooling rate. The heating wins if the gas inner density cusp
is not steeper than r^-0.5 and if the masses in the cold and hot phases are
comparable. The effect is stronger at higher redshifts, making the maintenance
easier also at later times. Clumps >10^5 Mo penetrate to the inner halo with
sufficient kinetic energy before they disintegrate, but they have to be <10^8
Mo for the drag to do enough work in a Hubble time. Pressure confined ~10^4K
clumps are stable against their own gravity and remain gaseous once below the
Bonnor-Ebert mass ~10^8 Mo. They are also immune to tidal disruption. Clumps in
the desired mass range could emerge by thermal instability in the outer halo if
the conductivity is not too high. Alternatively, such clumps may be embedded in
dark-matter subhaloes if the ionizing flux is ineffective, but they separate
from their subhaloes by ram pressure before entering the inner halo. Heating by
dynamical friction becomes dominant for massive satellites, which can
contribute up to one third of the total gravitational heating. We conclude that
gravitational heating by cosmological accretion is a viable alternative to AGN
feedback as a long-term quenching mechanism.Comment: 24 pages, 20 figures, some improvements, MNRAS accepted versio
Shallowed cusp slope of dark matter in disc galaxy formation through clump clusters
Cusp-core problem is a controversial problem on galactic dark matter haloes.
Cosmological N-body simulations has demonstrated that galactic dark matter
haloes have a cuspy density profile at the centre. However, baryonic physics
may affect the dark matter density profile. For example, it was suggested that
adiabatic contraction of baryonic gas makes the dark matter cusp steeper.
However, it is still an open question if the gas falls into the galactic centre
in smooth adiabatic manner. Recent numerical studies suggested that disc
galaxies might experience clumpy phase in their early stage of the disc
formation, which could also explain clump clusters and chain galaxies observed
in high redshift Universe. In this letter, using numerical simulations with an
isolated model, we study how the dark matter halo responds to these clumpy
nature of baryon component in disc galaxy formation through the clump cluster
phase. Our simulation demonstrates that such clumpy phase leads to a shallower
density profile of the dark matter halo in the central region while clumps fall
into the centre due to dynamical friction. This mechanism helps to make the
central dark matter density profile shallower in the galaxies whose virial mass
is as large as 5.0*10^11 solar masses. This phenomenon is caused by reaction to
dynamical friction of the stellar clumps against the dark matter halo. The halo
draws the clumps into the galactic centre, while kinematically heated by the
clumps. We additionally run a dark matter only simulation excluding baryonic
component and confirm that the resultant shallower density profile is not due
to numerical artifact in the simulation, such as two-body relaxation.Comment: 5 pages, 2 figures, accepted for publication in MNRAS Letter
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