2,200 research outputs found
Transits and Occultations of an Earth-Sized Planet in an 8.5-Hour Orbit
We report the discovery of an Earth-sized planet () in
an 8.5-hour orbit around a late G-type star (KIC 8435766, Kepler-78). The
object was identified in a search for short-period planets in the {\it Kepler}
database and confirmed to be a transiting planet (as opposed to an eclipsing
stellar system) through the absence of ellipsoidal light variations or
substantial radial-velocity variations. The unusually short orbital period and
the relative brightness of the host star ( = 11.5) enable robust
detections of the changing illumination of the visible hemisphere of the
planet, as well as the occultations of the planet by the star. We interpret
these signals as representing a combination of reflected and reprocessed light,
with the highest planet dayside temperature in the range of 2300 K to 3100 K.
Follow-up spectroscopy combined with finer sampling photometric observations
will further pin down the system parameters and may even yield the mass of the
planet.Comment: Accepted for publication, ApJ, 10 pages and 6 figure
No arbitrage and closure results for trading cones with transaction costs
In this paper, we consider trading with proportional transaction costs as in Schachermayerâs paper (Schachermayer in Math. Finance 14:19â48, 2004). We give a necessary and sufficient condition for , the cone of claims attainable from zero endowment, to be closed. Then we show how to define a revised set of trading prices in such a way that, firstly, the corresponding cone of claims attainable for zero endowment, , does obey the fundamental theorem of asset pricing and, secondly, if is arbitrage-free then it is the closure of . We then conclude by showing how to represent claims
From time-series to complex networks: Application to the cerebrovascular flow patterns in atrial fibrillation
A network-based approach is presented to investigate the cerebrovascular flow
patterns during atrial fibrillation (AF) with respect to normal sinus rhythm
(NSR). AF, the most common cardiac arrhythmia with faster and irregular
beating, has been recently and independently associated with the increased risk
of dementia. However, the underlying hemodynamic mechanisms relating the two
pathologies remain mainly undetermined so far; thus the contribution of
modeling and refined statistical tools is valuable. Pressure and flow rate
temporal series in NSR and AF are here evaluated along representative cerebral
sites (from carotid arteries to capillary brain circulation), exploiting
reliable artificially built signals recently obtained from an in silico
approach. The complex network analysis evidences, in a synthetic and original
way, a dramatic signal variation towards the distal/capillary cerebral regions
during AF, which has no counterpart in NSR conditions. At the large artery
level, networks obtained from both AF and NSR hemodynamic signals exhibit
elongated and chained features, which are typical of pseudo-periodic series.
These aspects are almost completely lost towards the microcirculation during
AF, where the networks are topologically more circular and present random-like
characteristics. As a consequence, all the physiological phenomena at
microcerebral level ruled by periodicity - such as regular perfusion, mean
pressure per beat, and average nutrient supply at cellular level - can be
strongly compromised, since the AF hemodynamic signals assume irregular
behaviour and random-like features. Through a powerful approach which is
complementary to the classical statistical tools, the present findings further
strengthen the potential link between AF hemodynamic and cognitive decline.Comment: 12 pages, 10 figure
Quasi-circular Orbits for Spinning Binary Black Holes
Using an effective potential method we examine binary black holes where the
individual holes carry spin. We trace out sequences of quasi-circular orbits
and locate the innermost stable circular orbit as a function of spin. At large
separations, the sequences of quasi-circular orbits match well with
post-Newtonian expansions, although a clear signature of the simplifying
assumption of conformal flatness is seen. The position of the ISCO is found to
be strongly dependent on the magnitude of the spin on each black hole. At close
separations of the holes, the effective potential method breaks down. In all
cases where an ISCO could be determined, we found that an apparent horizon
encompassing both holes forms for separations well inside the ISCO.
Nevertheless, we argue that the formation of a common horizon is still
associated with the breakdown of the effective potential method.Comment: 13 pages, 10 figures, submitted to PR
Global alterations to the choroid plexus blood-CSF barrier in amyotrophic lateral sclerosis
© 2020 The Author(s). The choroid plexus (CP) is a highly vascularized structure located in the ventricles that forms the blood-CSF barrier (BCSFB) and separates the blood from the cerebrospinal fluid (CSF). In addition to its role as a physical barrier, the CP functions in CSF secretion, transport of nutrients into the central nervous system (CNS) and a gated point of entry of circulating immune cells into the CNS. Aging and neurodegeneration have been reported to affect CP morphology and function and increase protein leakage from blood to the CSF. Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease associated with both upper and lower motor neuron loss, as well as altered proteomic and metabolomic signatures in the CSF. The role of the BCSFB and the CP in ALS is unknown. Here we describe a transcriptomic and ultrastructural analysis of BCSFB and CP alterations in human postmortem tissues from ALS and non-neurologic disease controls. ALS-CP exhibited widespread disruptions in tight junctional components of the CP epithelial layer and vascular integrity. In addition, we detected loss of pericytes around ALS blood vessels, accompanied by activation of platelet aggregation markers vWF and Fibrinogen, reminiscent of vascular injury. To investigate the immune component of ALS-CP, we conducted a comprehensive analysis of cytokines and chemokine panels in CP lysates and found a significant down-regulation of M-CSF and V-CAM1 in ALS, as well as up-regulation of VEGF-A protein. This phenotype was accompanied by an infiltration of MERTK positive macrophages into the parenchyma of the ALS-CP when compared to controls. Taken together, we demonstrate widespread structural and functional disruptions of the BCSFB in human ALS increasing our understanding of the disease pathology and identifying potential new targets for ALS therapeutic development
Natural products improve healthspan in aged mice and rats: a systematic review and meta-analysis
Over the last decades a decrease in mortality has paved the way for late onset pathologies such as cardiovascular, metabolic or neurodegenerative diseases. This evidence has led many researchers to shift their focus from researching ways to extend lifespan to finding ways to increase the number of years spent in good health; âhealthspanâ is indeed the emerging concept of such quest for ageing without chronic or disabling diseases and dysfunctions. Regular consumption of natural products might improve healthspan, although the mechanisms of action are still poorly understood. Since preclinical studies aimed to assess the efficacy and safety of these compounds are growing, we performed a systematic review and meta-analysis on the effects of natural products on healthspan in mouse and rat models of physiological ageing. Results indicate that natural compounds show robust effects improving stress resistance and cognitive abilities. These promising data call for further studies investigating the underlying mechanisms in more depth
Real-time measurement of the intracellular pH of yeast cells during glucose metabolism using ratiometric fluorescent nanosensors
Intracellular pH is a key parameter that influences many biochemical and metabolic pathways that can also be used as an indirect marker to monitor metabolic and intracellular processes. Herein, we utilise ratiometric fluorescent pH-sensitive nanosensors with an extended dynamic pH range to measure the intracellular pH of yeast (Saccharomyces cerevisiae) during glucose metabolism in real-time. Ratiometric fluorescent pH-sensitive nanosensors consisting of a polyacrylamide nanoparticle matrix covalently linked to two pH-sensitive fluorophores, Oregon green (OG) and 5(6)carboxyfluorescein (FAM), and a reference pH-insensitive fluorophore, 5(6)carboxytetramethylrhodamine (TAMRA), were synthesised. Nanosensors were functionalised with acrylamidopropyltrimethyl ammonium hydrochloride (ACTA) to confer a positive charge to the nanoparticle surfaces that facilitated nanosensor delivery to yeast cells, negating the need to use stress inducing techniques. The results showed that under glucose-starved conditions the intracellular pH of yeast population (n â 200) was 4.67 ± 0.15. Upon addition of D-(+)-glucose (10 mM), this pH value decreased to pH 3.86 ± 0.13 over a period of 10 minutes followed by a gradual rise to a maximal pH of 5.21 ± 0.26, 25 minutes after glucose addition. 45 minutes after the addition of glucose, the intracellular pH of yeast cells returned to that of the glucose starved conditions. This study advances our understanding of the interplay between glucose metabolism and pH regulation in yeast cells, and indicates that the intracellular pH homestasis in yeast is highly regulated and demonstrates the utility of nanosensors for real-time intracellular pH measurements
RXTE All-Sky Monitor Detection of the Orbital Period of Scorpius X-1
The orbital period of Scorpius X-1 has been accepted as 0.787313 d since its
discovery in archival optical photometric data by Gottlieb, Wright, & Liller
(1975). This period has been confirmed in both photometric and spectroscopic
optical observations, though to date only marginal evidence has been reported
for modulation of the X-ray intensity at that period. We have used data taken
with the RXTE All Sky Monitor to search for such a modulation. A major
difficulty in detecting the orbit in X-ray data is presented by the flaring
behavior of Sco X-1, which contributes white noise to Fourier transforms of the
intensity time series, and tends to obscure weak modulations. We present a new
technique for substantially reducing the effects of the flaring behavior while
retaining much of any periodic orbital modulation, provided only that the two
temporal behaviors exhibit different spectral signatures. Through such a
search, we have found evidence for orbital modulation at about the 1% level
with a period of 0.78893 d, equal within our accuracy to a period which differs
by 1 cycle per year from the accepted value. If we compare our results with the
period of the 1 year sideband cited by Gottlieb et al. we conclude that the
actual period may be 0.78901 d.Comment: AASTeX, 20 pages, 5 Postscript figure
Modeling and verifying a broad array of network properties
Motivated by widely observed examples in nature, society and software, where
groups of already related nodes arrive together and attach to an existing
network, we consider network growth via sequential attachment of linked node
groups, or graphlets. We analyze the simplest case, attachment of the three
node V-graphlet, where, with probability alpha, we attach a peripheral node of
the graphlet, and with probability (1-alpha), we attach the central node. Our
analytical results and simulations show that tuning alpha produces a wide range
in degree distribution and degree assortativity, achieving assortativity values
that capture a diverse set of many real-world systems. We introduce a
fifteen-dimensional attribute vector derived from seven well-known network
properties, which enables comprehensive comparison between any two networks.
Principal Component Analysis (PCA) of this attribute vector space shows a
significantly larger coverage potential of real-world network properties by a
simple extension of the above model when compared against a classic model of
network growth.Comment: To appear in Europhysics Letter
Finite-Size Scaling in the Energy-Entropy Plane for the 2D +- J Ising Spin Glass
For square lattices with the 2D Ising spin glass with
+1 and -1 bonds is found to have a strong correlation between the energy and
the entropy of its ground states. A fit to the data gives the result that each
additional broken bond in the ground state of a particular sample of random
bonds increases the ground state degeneracy by approximately a factor of 10/3.
For (where is the fraction of negative bonds), over this range of
, the characteristic entropy defined by the energy-entropy correlation
scales with size as . Anomalous scaling is not found for the
characteristic energy, which essentially scales as . When , a
crossover to scaling of the entropy is seen near . The results
found here suggest a natural mechanism for the unusual behavior of the low
temperature specific heat of this model, and illustrate the dangers of
extrapolating from small .Comment: 9 pages, two-column format; to appear in J. Statistical Physic
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