11,115 research outputs found
A Lattice Boltzmann method for simulations of liquid-vapor thermal flows
We present a novel lattice Boltzmann method that has a capability of
simulating thermodynamic multiphase flows. This approach is fully
thermodynamically consistent at the macroscopic level. Using this new method, a
liquid-vapor boiling process, including liquid-vapor formation and coalescence
together with a full coupling of temperature, is simulated for the first time.Comment: one gzipped tar file, 19 pages, 4 figure
The masses of hot subdwarfs
Masses are a fundamental parameter, but they are not well known for most hot
subdwarfs. In general, the mass of a hot subdwarf is derived with
asteroseismology or dynamical methods, for which it is often difficult to
obtain the necessary data from observations. We intend to find an approach to
deriving the masses of hot subdwarfs from observational data in the literature.
We presented full evolutionary calculations for hot subdwarfs in a wide mass
range (0.33 to 1.4 ) for a Population I metallicity of
=0.02, and obtained a relation between and , where , , and are the most probable
mass, effective temperature, and gravity. This relation is used to study the
masses of some observed hot subdwarfs. We proposed a method of determining the
masses of hot subdwarfs. Using this method, we studied the masses of hot
subdwarfs from the ESO supernova Ia progenitor survey and Hamburg quasar
survey. The study shows that most of subdwarf B stars have masses between 0.42
and 0.54 , whilst most sdO stars are in the range 0.40 0.55
. Comparing our study to the theoretical mass distributions of Han et
al. (2003), we found that sdO stars with mass less than 0.5
may evolve from sdB stars, whilst most high-mass( 0.5 ) sdO stars
result from mergers directly.Comment: 5 pages, 6 figures, accepted for publication in A&A Letter
Mechanisms for High-frequency QPOs in Neutron Star and Black Hole Binaries
We explain the millisecond variability detected by Rossi X-ray Timing
Explorer (RXTE) in the X-ray emission from a number of low mass X-ray binary
systems (Sco X-1, 4U1728-34, 4U1608-522, 4U1636-536, 4U0614+091, 4U1735-44,
4U1820-30, GX5-1 and etc) in terms of dynamics of the centrifugal barrier, a
hot boundary region surrounding a neutron star. We demonstrate that this region
may experience the relaxation oscillations, and that the displacements of a gas
element both in radial and vertical directions occur at the same main
frequency, of order of the local Keplerian frequency. We show the importance of
the effect of a splitting of the main frequency produced by the Coriolis force
in a rotating disk for the interpretation of a spacing between the QPO peaks.
We estimate a magnitude of the splitting effect and present a simple formula
for the whole spectrum of the split frequencies. It is interesting that the
first three lowest-order overtones fall in the range of 200-1200 Hz and match
the kHz-QPO frequencies observed by RXTE. Similar phenomena should also occur
in Black Hole (BH) systems, but, since the QPO frequency is inversely
proportional to the mass of a compact object, the frequency of the
centrifugal-barrier oscillations in the BH systems should be a factor of 5-10
lower than that for the NS systems. The X-ray spectrum formed in this region is
a result of upscattering of a soft radiation (from a disk and a NS surface) off
relatively hot electrons in the boundary layer. We also briefly discuss some
alternative QPO models, including a possibility of acoustic oscillations in the
boundary layer, the proper stellar rotation, and g-mode disk oscillations.Comment: The paper is coming out in the Astrophysical Journal in the 1st of
May issue of 199
Helium star donor channel for the progenitors of type Ia supernovae
Type Ia supernovae (SNe Ia) play an important role in astrophysics,
especially in the study of cosmic evolution. There are several progenitor
models for SNe Ia proposed in the past years. In this paper, we have carried
out a detailed study of the He star donor channel, in which a carbon-oxygen
white dwarf (CO WD) accretes material from a He main sequence star or a He
subgiant to increase its mass to the Chandrasekhar mass. Employing Eggleton's
stellar evolution code with an optically thick wind assumption, and adopting
the prescription of Kato & Hachisu (2004) for the mass accumulation efficiency
of the He-shell flashes onto the WDs, we performed binary evolution
calculations for about 2600 close WD binary systems. According to these
calculations, we mapped out the initial parameters for SNe Ia in the orbital
period--secondary mass () plane for various WD
masses from this channel. The study shows that the He star donor channel is
noteworthy for producing SNe Ia (i.e. in
the Galaxy), and that the progenitors from this channel may appear as supersoft
X-ray sources. Importantly, this channel can explain SNe Ia with short delay
times (\la 10^{8} yr), which is consistent with recent observational
implications of young populations of SN Ia progenitors.Comment: 9 pages, 8 figure, accepted by MNRA
Inter- and Intragranular Effects in Superconducting Compacted Platinum Powders
Compacted platinum powders exhibit a sharp onset of diamagnetic screening at
mK in zero magnetic field in all samples investigated. This
sharp onset is interpreted in terms of the intragranular transition into the
superconducting state. At lower temperatures, the magnetic ac susceptibility
strongly depends on the ac field amplitude and reflects the small intergranular
critical current density . This critical current density shows a strong
dependence on the packing fraction f of the granular samples. Surprisingly,
increases significantly with decreasing f ( A/cm for f = 0.67 and A/cm for f
= 0.50). The temperature dependence of shows strong positive curvature
over a wide temperature range for both samples. The phase diagrams of inter-
and intragranular superconductivity for different samples indicate that the
granular structure might play the key role for an understanding of the origin
of superconductivity in the platinum compacts.Comment: 11 pages including 9 figures. To appear in Phys. Rev. B in Nov. 0
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RORγ is a targetable master regulator of cholesterol biosynthesis in a cancer subtype.
Tumor subtype-specific metabolic reprogrammers could serve as targets of therapeutic intervention. Here we show that triple-negative breast cancer (TNBC) exhibits a hyper-activated cholesterol-biosynthesis program that is strongly linked to nuclear receptor RORγ, compared to estrogen receptor-positive breast cancer. Genetic and pharmacological inhibition of RORγ reduces tumor cholesterol content and synthesis rate while preserving host cholesterol homeostasis. We demonstrate that RORγ functions as an essential activator of the entire cholesterol-biosynthesis program, dominating SREBP2 via its binding to cholesterol-biosynthesis genes and its facilitation of the recruitment of SREBP2. RORγ inhibition disrupts its association with SREBP2 and reduces chromatin acetylation at cholesterol-biosynthesis gene loci. RORγ antagonists cause tumor regression in patient-derived xenografts and immune-intact models. Their combination with cholesterol-lowering statins elicits superior anti-tumor synergy selectively in TNBC. Together, our study uncovers a master regulator of the cholesterol-biosynthesis program and an attractive target for TNBC
He star evolutionary channel to intermediate-mass binary pulsar PSR J1802-2124
The intermediate-mass binary pulsars (IMBPs) are characterized by relatively
long spin periods (10 - 200 ms) and massive (\ga 0.4 M_{\odot}) white dwarf
(WD) companions. Recently, precise mass measurements have been performed for
the pulsar and the WD in the IMBP PSR J1802-2124. Some observed properties,
such as the low mass of the pulsar, the high mass of the WD, the moderately
long spin period, and the tight orbit, imply that this system has undergone a
peculiar formation mechanism. In this work, we attempt to simulate the detailed
evolutionary history of PSR J1802-2124. We propose that a binary system
consisting of a neutron star (NS, of mass ) and an He star (of
mass ), and with an initial orbital period of 0.5 d, may have
been the progenitor of PSR J1802-2124. Once the He star overflows its Roche
lobe, He-rich material is transferred onto the NS at a relatively high rate of
, which is significantly higher
than the Eddington accretion rate. A large amount of the transferred material
is ejected from the vicinity of the NS by radiation pressure and results in the
birth of a mildly recycled pulsar. Our simulated results are consistent with
the observed parameters of PSR J1802-2124. Therefore, we argue that the NS + He
star evolutionary channel may be responsible for the formation of most IMBPs
with orbital periods \la 3 \rm d.Comment: 4 pages, 3 figures, Astronomy and Astrophysics in pres
ROR-γ drives androgen receptor expression and represents a therapeutic target in castration-resistant prostate cancer.
The androgen receptor (AR) is overexpressed and hyperactivated in human castration-resistant prostate cancer (CRPC). However, the determinants of AR overexpression in CRPC are poorly defined. Here we show that retinoic acid receptor-related orphan receptor γ (ROR-γ) is overexpressed and amplified in metastatic CRPC tumors, and that ROR-γ drives AR expression in the tumors. ROR-γ recruits nuclear receptor coactivator 1 and 3 (NCOA1 and NCOA3, also known as SRC-1 and SRC-3) to an AR-ROR response element (RORE) to stimulate AR gene transcription. ROR-γ antagonists suppress the expression of both AR and its variant AR-V7 in prostate cancer (PCa) cell lines and tumors. ROR-γ antagonists also markedly diminish genome-wide AR binding, H3K27ac abundance and expression of the AR target gene network. Finally, ROR-γ antagonists suppressed tumor growth in multiple AR-expressing, but not AR-negative, xenograft PCa models, and they effectively sensitized CRPC tumors to enzalutamide, without overt toxicity, in mice. Taken together, these results establish ROR-γ as a key player in CRPC by acting upstream of AR and as a potential therapeutic target for advanced PCa
WUDAPT: Facilitating advanced urban canopy modeling for weather, climate and air quality applications
Environmental issues and impacts to society will be exacerbated with increased population, diminishing resources and the prospects for extreme weather events and climate changes. Current community-based models available for weather, climate and air quaity applications are powerful state-of-science modeling systems, which, with careful considerations, can be employed to address the impact of these issues fo urban areas. Given the complex and high degree of spatial inhomogeneity of the underlying surface area we will review mesh size, appropriate multi-scale science and morphological descriptions and their data requirements including unique city specific gridded morphology and material composition for their forecasting and climate applications.
For this presentation, we discuss, describe and show examples from an ongoing but preliminary prototypic collaborative effort, whose design bases is to provide the experience and recommendations toward extending the scope of the National Urban Database and Access Portal Tools (NUDAPT) to worldwide coverage (WUDAPT). WUDAPT would thus provide requisite gridded data for urban applications of advanced forecast and climate models throughout the world. Strategically, the prototypic efforts will be designed to provide proven protocols for the facilitaton of the data gathering and processing based on available remote sensing and ground-based sampling. Tactically, we employ an iterative approach first obtaining coarse gridded Local Climate Zone (LCZ) classification derived from available Web-based products such as Google-Earth, and Landsat satellite magery. Further sub-class discretization of LCZs and the application of GeoWiki technology facilitates further refinements and ground truthing to yield the desired gridded building morphological distribution parameters and their material composition. Local experts would be encouraged to become involved to ensure factors unique to their area in the world would be incorporated. Finally, given that model applications may require data with different grid resolution we present an outline that employs the new and powerful Multiple Resolution Analyses scheme that can address this need within the scope of WUDAPT
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