1,226 research outputs found
The Future is Now: the Formation of Single Low Mass White Dwarfs in the Solar Neighborhood
Low mass helium-core white dwarfs (M < 0.45 Msun) can be produced from
interacting binary systems, and traditionally all of them have been attributed
to this channel. However, a low mass white dwarf could also result from a
single star that experiences severe mass loss on the first ascent giant branch.
A large population of low mass He-core white dwarfs has been discovered in the
old metal-rich cluster NGC 6791. There is therefore a mechanism in clusters to
produce low mass white dwarfs without requiring binary star interactions, and
we search for evidence of a similar population in field white dwarfs. We argue
that there is a significant field population (of order half of the detected
systems) that arises from old metal rich stars which truncate their evolution
prior to the helium flash from severe mass loss. There is a consistent absence
of evidence for nearby companions in a large fraction of low mass white dwarfs.
The number of old metal-rich field dwarfs is also comparable with the
apparently single low mass white dwarf population, and our revised estimate for
the space density of low mass white dwarfs produced from binary interactions is
also compatible with theoretical expectations. This indicates that this channel
of stellar evolution, hitherto thought hypothetical only, has been in operation
in our own Galaxy for many billions of years. One strong implication of our
model is that single low mass white dwarfs should be good targets for planet
searches because they are likely to arise from metal-rich progenitors. We also
discuss other observational tests and implications, including the potential
impact on SN Ia rates and the frequency of planetary nebulae.Comment: ApJ published versio
In Vitro Assay and Characterization of the Farnesylation-Dependent Prelamin a Endoprotease
The 72-kDa nuclear lamina protein lamin A is synthesized as a 74-kDa farnesylated precursor. Conversion of this precursor to mature lamin A appears to be mediated by a specific endoprotease. Prior studies of overexpressed wild-type and mutant lamin A proteins in cultured cells have indicated that the precursor possesses the typical carboxyl-terminal S- farnesylated, cysteine methyl ester and that farnesylation is required for endoproteolysis to occur. In this report, we describe the synthesis of an S- farnesyl, cysteinyl methyl ester peptide corresponding to the carboxyl- terminal 18 amino acid residues of human prelamin A. This peptide acts as a substrate for the prelamin A endoprotease in vitro, with cleavage of the synthetic peptide at the expected site between Tyr657 and Leu658. Endoproteolytic cleavage requires the S-prenylated cysteine methyl ester and, in agreement with transfection studies, is more active with the farnesylated than geranylgeranylated cysteinyl substrate. N-Acetyl farnesyl methyl cysteine is shown to be a noncompetitive inhibitor of the enzyme. Taken together, these observations suggest that there is a specific farnesyl binding site on the enzyme which is not at the active site
Spectral modeling of gaseous metal disks around DAZ white dwarfs
We report on our attempt for the first non-LTE modeling of gaseous metal
disks around single DAZ white dwarfs recently discovered by Gaensicke et al.
and thought to originate from a disrupted asteroid. We assume a Keplerian
rotating viscous disk ring composed of calcium and hydrogen and compute the
detailed vertical structure and emergent spectrum. We find that the observed
infrared CaII emission triplet can be modeled with a hydrogen-deficient gas
ring located at R=1.2 R_sun, inside of the tidal disruption radius, with Teff
about 6000 K and a low surface mass density of about 0.3 g/cm**2. A disk having
this density and reaching from the central white dwarf out to R=1.2 R_sun would
have a total mass of 7 10**21 g, corresponding to an asteroid with about 160 km
diameter.Comment: Proceedings, 16th European White Dwarf Workshop, Barcelona, 200
Manifestations of Top Compositeness at Colliders
We explore the possibility that the right-handed top quark is composite,
identifying possible signatures of compositeness and how they might manifest
themselves at the LHC and Tevatron. We perform a complete analysis of the
dimension six modifications of the top coupling to gluons and find that
cancellations among operators in the t\bar{t} rate allow for very low
compositeness scales, but this can be drastically improved by looking at
kinematic distributions. Turning to the LHC, we examine four top production
from a dimension six four-top operator and estimate the LHC with 100 {\rm
fb}^{-1} collected luminosity to be sensitive to compositeness scales as high
as 5 TeV.Comment: 8 pages, 6 figures, updated figure 6, updated references, final
version published in JHE
Decreased mitochondrial DNA content drives OXPHOS dysregulation in chromophobe renal cell carcinoma
Chromophobe renal cell carcinoma (chRCC) and renal oncocytoma (RO) are closely related, rare kidney tumors. Mutations in complex I (CI)-encoding genes play an important role in dysfunction of the oxidative phosphorylation (OXPHOS) system in RO but are less frequently observed in chRCC. As such, the relevance of OXPHOS status and role of CI mutations in chRCC remain unknown. To address this issue, we performed proteome and metabolome profiling as well as mitochondrial whole-exome sequencing to detect mitochondrial alterations in chRCC tissue specimens. Multi-omic analysis revealed downregulation of electron transport chain (ETC) components in chRCC that differed from the expression profile in RO. A decrease in mitochondrial (mt)DNA content, rather than CI mutations, was the main cause for reduced OXPHOS in chRCC. There was a negative correlation between protein and transcript levels of nuclear DNA- but not mtDNA-encoded ETC complex subunits in chRCC. In addition, the reactive oxygen species scavenger glutathione (GSH) was upregulated in chRCC due to decreased expression of proteins involved in GSH degradation. These results demonstrate that distinct mechanisms of OXPHOS exist in chRCC and RO and that expression levels of ETC complex subunits can serve as a diagnostic marker for this rare malignancy
On the Solution of the Monge-Ampere Equation ZxxZyy - Z²xy= f (x, y) with Quadratic Right Side
For the Monge{Ampere equation ZxxZyy-Z²xy = b₂₀x²+b₁₁xy+b₀₂y²+b₀₀ we consider the question on the existence of a solution Z(x, y) in the class of polynomials such that Z = Z(x, y) is a graph of a convex surface. If Z is a polynomial of odd degree, then the solution does not exist. If Z is a polynomial of 4-th degree and 4b₂₀b₀₂ - b₁₁² > 0, then the solution also does not exist. If 4b₂₀b₀₂ - b₁₁² = 0, then we have solutions
Rectal catheterization for the diagnosis of iatrogenic descending colon injuries during co2 laparoscopy: an experimental study
The Spectral Energy Distributions of White Dwarfs in 47 Tucanae: The Distance to the Cluster
We present a new distance determination to the Galactic globular cluster 47
Tucanae by fitting the spectral energy distributions of its white dwarfs to
pure hydrogen atmosphere white dwarf models. Our photometric dataset is
obtained from a 121 orbit Hubble Space Telescope program using the Wide Field
Camera 3 UVIS/IR channels, capturing F390W, F606W, F110W, and F160W images.
These images cover more than 60 square arcmins and extend over a radial range
of 5-13.7 arcmin (6.5-17.9 pc) within the globular cluster. Using a likelihood
analysis, we obtain a best fitting unreddened distance modulus of (m -
M)o=13.36+/-0.02+/-0.06 corresponding to a distance of 4.70+/-0.04+/-0.13 kpc,
where the first error is random and the second is systematic. We also search
the white dwarf photometry for infrared excess in the F160W filter, indicative
of debris disks or low mass companions, and find no convincing cases within our
sample.Comment: Accepted to The Astronomical Journal, 13 Figures, 2 Tables. Figures 3
and 6 are figure sets, each composed of 59 subfigures (to appear in the
electronic journal). This is a Companion paper to the article ID:
submit/037561
Vectorlike Confinement at the LHC
We argue for the plausibility of a broad class of vectorlike confining gauge
theories at the TeV scale which interact with the Standard Model predominantly
via gauge interactions. These theories have a rich phenomenology at the LHC if
confinement occurs at the TeV scale, while ensuring negligible impact on
precision electroweak and flavor observables. Spin-1 bound states can be
resonantly produced via their mixing with Standard Model gauge bosons. The
resonances promptly decay to pseudo-Goldstone bosons, some of which promptly
decay to a pair of Standard Model gauge bosons, while others are charged and
stable on collider time scales. The diverse set of final states with little
background include multiple photons and leptons, missing energy, massive stable
charged particles and the possibility of highly displaced vertices in dilepton,
leptoquark or diquark decays. Among others, a novel experimental signature of
resonance reconstruction out of massive stable charged particles is
highlighted. Some of the long-lived states also constitute Dark Matter
candidates.Comment: 33 pages, 6 figures. v4: expanded discussion of Z_2 symmetry for
stability, one reference adde
Spectrophotometrically Identified stars in the PEARS-N and PEARS-S fields
Deep ACS slitless grism observations and identification of stellar sources
are presented within the Great Observatories Origins Deep Survey (GOODS) North
and South fields which were obtained in the Probing Evolution And Reionization
Spectroscopically (PEARS) program. It is demonstrated that even low resolution
spectra can be a very powerful means to identify stars in the field, especially
low mass stars with stellar types M0 and later. The PEARS fields lay within the
larger GOODS fields, and we used new, deeper images to further refine the
selection of stars in the PEARS field, down to a magnitude of mz = 25 using a
newly developed stellarity parameter. The total number of stars with reliable
spectroscopic and morphological identification was 95 and 108 in the north and
south fields respectively. The sample of spectroscopically identified stars
allows constraints to be set on the thickness of the Galactic thin disk as well
as contributions from a thick disk and a halo component. We derive a thin disk
scale height, as traced by the population of M4 to M9 dwarfs along two
independent lines of sight, of h_thin = 370 +60/-65 pc. When including the more
massive M0 to M4 dwarf population, we derive h_thin = 300 +/- 70pc. In both
cases, we observe that we must include a combination of thick and halo
components in our models in order to account for the observed numbers of faint
dwarfs. The required thick disk scale height is typically h_thick=1000 pc and
the acceptable relative stellar densities of the thin disk to thick disk and
the thin disk to halo components are in the range of 0.00025<f_halo<0.0005 and
0.05<f_thick<0.08 and are somewhat dependent on whether the more massive M0 to
M4 dwarfs are included in our sample
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