29 research outputs found
Mass-loss rates for transiting exoplanets
Exoplanets at small orbital distances from their host stars are submitted to
intense levels of energetic radiations, X-rays and extreme ultraviolet (EUV).
Depending on the masses and densities of the planets and on the atmospheric
heating efficiencies, the stellar energetic inputs can lead to atmospheric mass
loss. These evaporation processes are observable in the ultraviolet during
planetary transits. The aim of the present work is to quantify the mass-loss
rates (dm/dt), heating efficiencies (eta), and lifetimes for the whole sample
of transiting exoplanets, now including hot jupiters, hot neptunes, and hot
super-earths. The mass-loss rates and lifetimes are estimated from an "energy
diagram" for exoplanets, which compares the planet gravitational potential
energy to the stellar X/EUV energy deposited in the atmosphere. We estimate the
mass-loss rates of all detected transiting planets to be within 10^6 to 10^13
g/s for various conservative assumptions. High heating efficiencies would imply
that hot exoplanets such the gas giants WASP-12b and WASP-17b could be
completely evaporated within 1 Gyr. We further show that the heating efficiency
can be constrained when dm/dt is inferred from observations and the stellar
X/EUV luminosity is known. This leads us to suggest that eta ~ 100% in the
atmosphere of the hot jupiter HD209458b, while it could be lower for HD189733b.
Simultaneous observations of transits in the ultraviolet and X-rays are
necessary to further constrain the exospheric properties of exoplanets.Comment: 10 pages, 5 figures, 2 tables. Accepted for publication in Astronomy
& Astrophysic
Galactic Effects on Habitability
The galactic environment has been suspected to influence planetary
habitability in many ways. Very metal-poor regions of the Galaxy, or those
largely devoid of atoms more massive than H and He, are thought to be unable to
form habitable planets. Moreover, if such planets do form, the young system is
subjected to close stellar passages while it resides in its stellar birth
cluster. Various potential hazards remain after clusters disperse. For
instance, central galactic regions may present risks to habitability via nearby
supernovae, gamma ray bursts (GRBs), and frequent comet showers. In addition,
planets residing within very wide binary star systems are affected by the
Galaxy, as local gravitational perturbations from the Galaxy can increase the
binary's eccentricity until it destabilizes the planets it hosts. Here we
review the most recent work on the main galactic influences over planetary
habitability. Although there must be some metallicity limit below which rocky
planets cannot form, recent exoplanet surveys show that they form around stars
with a very large range of metallicities. Once formed, the probability of star
clusters destabilizing planetary systems only becomes high for rare, extremely
long-lived clusters. Regarding threats to habitability from supernovae, GRBs,
and comet showers, many recent studies suggest that their hazards are more
limited than originally thought. Finally, denser regions of the Galaxy enhance
the threat that very wide binary companions pose to planetary habitability, but
the probability that a very wide binary star disrupts habitability will always
be substantially below 100% for any environment. While some Milky Way regions
must be more hospitable to habitable planets than others, it is difficult to
state that habitable planets are confined to any well-defined region of the
Galaxy or that any other particular region of the Galaxy is uninhabitable.Comment: Invited review chapter, accepted for publication in the "Handbook of
Exoplanets"; 19 pages; 2 figure
The Diversity of Planetary Systems Architectures: Contrasting Theory with Observations
We develop a semi-analytical model for computing planetary system formation
with the aim of explaining the observed diversity of planetary systems
architectures and relate this primordial diversity with the initial properties
of the disc where they were born. We adopt different initial conditions based
on recent results in protoplanetary discs observations, to generate a variety
of planetary systems and analyze them statistically. We explore the relevance
of the mass and size of the disc, its metallicity, the mass of the central star
and the time-scale of gaseous disc dissipation, in defining the architecture of
the planetary system. We also test different values of some key parameters of
our model, to find out which factors best reproduce the diverse sample of
observed planetary systems. According to this, we predict which systems are the
most common in the solar neighbourhood. Our results show that planetary systems
with only terrestrial planets are the most common, being the only planetary
systems formed when considering low metallicity discs and which also represent
the best environment for the developing of rocky, potentially habitable
planets. We also found that planetary systems like our own are not rare in the
solar neighbourhood, being its formation favoured in massive discs where there
is not a large accumulation of solids in the inner region of the disc.
Regarding the planetary systems that harbor hot and warm Jupiter planets, we
found that this systems are born in very massive, metal-rich discs. Also a fast
migration rate is required in order to form these systems. According to our
results, most of the hot and warm Jupiter systems are composed by only one
giant planet, which is also a tendency of the current observational data.Comment: MNRAS in pres
Three New Eclipsing White-dwarf - M-dwarf Binaries Discovered in a Search for Transiting Planets Around M-dwarfs
We present three new eclipsing white-dwarf / M-dwarf binary systems
discovered during a search for transiting planets around M-dwarfs. Unlike most
known eclipsing systems of this type, the optical and infrared emission is
dominated by the M-dwarf components, and the systems have optical colors and
discovery light curves consistent with being Jupiter-radius transiting planets
around early M-dwarfs. We detail the PTF/M-dwarf transiting planet survey, part
of the Palomar Transient Factory (PTF). We present a Graphics Processing Unit
(GPU)-based box-least-squares search for transits that runs approximately 8X
faster than similar algorithms implemented on general purpose systems. For the
discovered systems, we decompose low-resolution spectra of the systems into
white-dwarf and M-dwarf components, and use radial velocity measurements and
cooling models to estimate masses and radii for the white dwarfs. The systems
are compact, with periods between 0.35 and 0.45 days and semimajor axes of
approximately 2 solar radii (0.01 AU). We use the Robo-AO laser guide star
adaptive optics system to tentatively identify one of the objects as a triple
system. We also use high-cadence photometry to put an upper limit on the white
dwarf radius of 0.025 solar radii (95% confidence) in one of the systems. We
estimate that 0.08% (90% confidence) of M-dwarfs are in these short-period,
post-common-envelope white-dwarf / M-dwarf binaries where the optical light is
dominated by the M-dwarf. Similar eclipsing binary systems can have arbitrarily
small eclipse depths in red bands and generate plausible small-planet-transit
light curves. As such, these systems are a source of false positives for
M-dwarf transiting planet searches. We present several ways to rapidly
distinguish these binaries from transiting planet systems.Comment: 14 pages, 14 figures, submitted to Ap
Effects of Anacetrapib in Patients with Atherosclerotic Vascular Disease
BACKGROUND:
Patients with atherosclerotic vascular disease remain at high risk for cardiovascular events despite effective statin-based treatment of low-density lipoprotein (LDL) cholesterol levels. The inhibition of cholesteryl ester transfer protein (CETP) by anacetrapib reduces LDL cholesterol levels and increases high-density lipoprotein (HDL) cholesterol levels. However, trials of other CETP inhibitors have shown neutral or adverse effects on cardiovascular outcomes.
METHODS:
We conducted a randomized, double-blind, placebo-controlled trial involving 30,449 adults with atherosclerotic vascular disease who were receiving intensive atorvastatin therapy and who had a mean LDL cholesterol level of 61 mg per deciliter (1.58 mmol per liter), a mean non-HDL cholesterol level of 92 mg per deciliter (2.38 mmol per liter), and a mean HDL cholesterol level of 40 mg per deciliter (1.03 mmol per liter). The patients were assigned to receive either 100 mg of anacetrapib once daily (15,225 patients) or matching placebo (15,224 patients). The primary outcome was the first major coronary event, a composite of coronary death, myocardial infarction, or coronary revascularization.
RESULTS:
During the median follow-up period of 4.1 years, the primary outcome occurred in significantly fewer patients in the anacetrapib group than in the placebo group (1640 of 15,225 patients [10.8%] vs. 1803 of 15,224 patients [11.8%]; rate ratio, 0.91; 95% confidence interval, 0.85 to 0.97; P=0.004). The relative difference in risk was similar across multiple prespecified subgroups. At the trial midpoint, the mean level of HDL cholesterol was higher by 43 mg per deciliter (1.12 mmol per liter) in the anacetrapib group than in the placebo group (a relative difference of 104%), and the mean level of non-HDL cholesterol was lower by 17 mg per deciliter (0.44 mmol per liter), a relative difference of -18%. There were no significant between-group differences in the risk of death, cancer, or other serious adverse events.
CONCLUSIONS:
Among patients with atherosclerotic vascular disease who were receiving intensive statin therapy, the use of anacetrapib resulted in a lower incidence of major coronary events than the use of placebo. (Funded by Merck and others; Current Controlled Trials number, ISRCTN48678192 ; ClinicalTrials.gov number, NCT01252953 ; and EudraCT number, 2010-023467-18 .)
Additional file 1 of Complement propagates visual system pathology following traumatic brain injury
Additional file 1. Inhibition of the complement system reduces microglia counts and partially attenuates morphological changes chronically in the dLGN ipsilateral to injury without affecting synapse or C3 internalization. A Representative microglial reconstructions with internalized VGLUT2 (green) and C3 (red), and microglial morphology (IBA1, magenta). Scale barâ=â10 ”m. B Microglia filament length to volume ratio in the ipsilateral dLGN. (C-D) Microglia count per 63âĂâhigh power field. Scale barâ=â15 ”m E Microglial internalization of VGLUT2 and (F) microglial internalization of C3 in the ipsilateral dLGN. B, C, E, F one-way ANOVA with Tukey correction for multiple comparisons. *pâ<â0.05, **pâ<â0.01, ***pâ<â0.001, ****pâ<â0.0001. Error barsâ=âmeanâ±âs.e.m
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Detection of aryl hydrocarbon receptor agonists in human samples
The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor with important functions in the immune response and cancer. AHR agonists are provided by the environment, the commensal flora and the metabolism. Considering AHR physiological functions, AHR agonists may have important effects on health and disease. Thus, the quantification of AHR agonists in biological samples is of scientific and clinical relevance. We compared different reporter systems for the detection of AHR agonists in serum samples of Multiple Sclerosis (MS) patients, and assessed the influence of transfection methods and cell lines in a reporter-based in vitro assay. While the use of stable or transient reporters did not influence the measurement of AHR agonistic activity, the species of the cell lines used in these reporter assays had important effects on the reporter readings. These observations suggest that cell-specific factors influence AHR activation and signaling. Thus, based on the reported species selectivity of AHR ligands and the cell species-of-origin effects that we describe in this manuscript, the use of human cell lines is encouraged for the analysis of AHR agonistic activity in human samples. These findings may be relevant for the analysis of AHR agonists in human samples in the context of inflammatory and neoplastic disorders
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Dynamic regulation of serum aryl hydrocarbon receptor agonists in MS
Objective: Several factors influence the clinical course of autoimmune inflammatory diseases such as MS and inflammatory bowel disease. Only recently, the complex interaction between the gut microbiome, dietary factors, and metabolism has started to be appreciated with regard to its potential to modulate acute and chronic inflammation. One of the molecular sensors that mediates the effects of these environmental signals on the immune response is the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor with key functions in immune cells. Methods: In this study, we analyzed the levels of AHR agonists in serum samples from patients with MS and healthy controls in a case-control study. Results: We detected a global decrease of circulating AHR agonists in relapsing-remitting MS patients as compared to controls. However, during acute CNS inflammation in clinically isolated syndrome or active MS, we measured increased AHR agonistic activity. Moreover, AHR ligand levels in patients with benign MS with relatively mild clinical impairment despite longstanding disease were unaltered as compared to healthy controls. Conclusions: Collectively, these data suggest that AHR agonists in serum are dynamically modulated during the course of MS. These findings may guide the development of biomarkers to monitor disease activity as well as the design of novel therapeutic interventions for MS
Mutational Analysis of Deinococcus radiodurans Bacteriophytochrome Reveals Key Amino Acids Necessary for the Photochromicity and Proton Exchange Cycle of Phytochromes*Sâ
The ability of phytochromes (Phy) to act as photointerconvertible light
switches in plants and microorganisms depends on key interactions between the
bilin chromophore and the apoprotein that promote bilin attachment and
photointerconversion between the spectrally distinct red light-absorbing Pr
conformer and far red light-absorbing Pfr conformer. Using structurally guided
site-directed mutagenesis combined with several spectroscopic methods, we
examined the roles of conserved amino acids within the bilin-binding domain of
Deinococcus radiodurans bacteriophytochrome with respect to
chromophore ligation and Pr/Pfr photoconversion. Incorporation of biliverdin
IXα (BV), its structure in the Pr state, and its ability to
photoisomerize to the first photocycle intermediate are insensitive to most
single mutations, implying that these properties are robust with respect to
small structural/electrostatic alterations in the binding pocket. In contrast,
photoconversion to Pfr is highly sensitive to the chromophore environment.
Many of the variants form spectrally bleached Meta-type intermediates in red
light that do not relax to Pfr. Particularly important are Asp-207 and
His-260, which are invariant within the Phy superfamily and participate in a
unique hydrogen bond matrix involving the A, B, and C pyrrole ring nitrogens
of BV and their associated pyrrole water. Resonance Raman spectroscopy
demonstrates that substitutions of these residues disrupt the Pr to Pfr
protonation cycle of BV with the chromophore locked in a deprotonated
Meta-Rc-like photoconversion intermediate after red light
irradiation. Collectively, the data show that a number of contacts contribute
to the unique photochromicity of Phy-type photoreceptors. These include
residues that fix the bilin in the pocket, coordinate the pyrrole water, and
possibly promote the proton exchange cycle during photoconversion