521 research outputs found
Eclipsing binary and white dwarf features associated with K2 target EPIC251248385
White dwarfs, remnants of Sun-like stars which have completed their evolution, are one of the most common types of stars in space. Despite this, very few white dwarfs have been observed in transiting or eclipsing systems, and only two planetary systems around white dwarfs are currently known, thus motivating a search for white dwarfs with transits or eclipses as seen by the Kepler telescope. A systematic search of K2 white dwarf targets revealed one candidate with regular eclipses, but additional research was necessary to confirm the transits and white dwarf signal were coming from the same astrophysical source. The software package PyKe was utilized to adjust the light curve aperture, and perform principal component analysis which revealed that the transits were originating from a single pixel. Generating a new lightcurve from this pixel revealed the absolute transit depth, which was unconstrained previously. Ten additional images taken with the 2m LCOGT telescope revealed that a potential target star in the single Kepler pixel was actually a cluster of three stars, but no clear transits were seen from any of the potential target stars in the followup images. Additionally, analysis of transit depths in the single pixel light curve and additional investigation of nearby bright sources supported the hypothesis that the transits were more likely to be coming from the white dwarf rather than the two other sources. However, the transit duration and shape appear atypical for white dwarf systems. Thus, despite determining the potential sources and relative sizes for the potential eclipsing white dwarf candidate, or whether the eclipses come from the white dwarf target cannot be confirmed without additional data.https://iopscience.iop.org/article/10.3847/2515-5172/ab5861Published versio
Artrodese Tibio-talo-calcaneana com Placa de Compressão lateral
OBJECTIVE: The objective of this study was to evaluate the short-term clinical and radiographic results from a TTC fusion procedure using a lateral locking plate specifically designed for this purpose. METHODS: All the fourteen patients were evaluated using a variety of methods, including a visual analogue scale (VAS), the AOFAS hindfoot score and a subjective satisfaction scale. The average follow-up was 10 months. RESULTS: The average AOFAS score improved from 41 points preoperatively to 63 points postoperatively. The VAS pain score decreased from 7 to 3 points. Four patients reported excellent results, eight good, one fair and one poor. CONCLUSION: Our study provides support for using a specially designed plate for TTC fusion in hindfoot salvage surgery.OBJETIVO: O propósito deste estudo é avaliar os resultados clínicos e radiológicos a curto prazo do procedimento de fusão tíbio-talo-calcaneana (TTC) com o uso de uma placa lateral bloqueada especificamente concebida para este fim. MÉTODOS: Todos os 14 pacientes foram avaliados usando uma variedade de métodos, incluindo a escala analógico visual da dor (EAV), escore da AOFAS para o retropé e escala subjetiva de satisfação. O acompanhamento médio foi de 10 meses. RESULTADOS: O escore AOFAS médio melhorou de 41 pontos no período pré-operatório para 63 pontos no período pós-operatório. O escore da dor (EAV) caiu de 7 para 3 pontos. Quatro pacientes foram classificados como excelentes resultados, oito bons, um moderado e um ruim. CONCLUSÃO: Nosso estudo dá suporte ao uso da placa especialmente desenhada para a fusão tibio-talo-calcaneana (TTC) nas cirurgias de salvamento do retropé.Universidade Federal de São Paulo (UNIFESP), Escola Paulista de Medicina (EPM)UNIFESP, EPMSciEL
Machine-directed gravitational-wave counterpart discovery
Joint observations in electromagnetic and gravitational waves shed light on
the physics of objects and surrounding environments with extreme gravity that
are otherwise unreachable via siloed observations in each messenger. However,
such detections remain challenging due to the rapid and faint nature of
counterparts. Protocols for discovery and inference still rely on human experts
manually inspecting survey alert streams and intuiting optimal usage of limited
follow-up resources. Strategizing an optimal follow-up program requires
adaptive sequential decision-making given evolving light curve data that (i)
maximizes a global objective despite incomplete information and (ii) is robust
to stochasticity introduced by detectors/observing conditions. Reinforcement
learning (RL) approaches allow agents to implicitly learn the physics/detector
dynamics and the behavior policy that maximize a designated objective through
experience.
To demonstrate the utility of such an approach for the kilonova follow-up
problem, we train a toy RL agent for the goal of maximizing follow-up
photometry for the true kilonova among several contaminant transient light
curves. In a simulated environment where the agent learns online, it achieves
3x higher accuracy compared to a random strategy. However, it is surpassed by
human agents by up to a factor of 2. This is likely because our hypothesis
function (Q that is linear in state-action features) is an insufficient
representation of the optimal behavior policy. More complex agents could
perform at par or surpass human experts. Agents like these could pave the way
for machine-directed software infrastructure to efficiently respond to next
generation detectors, for conducting science inference and optimally planning
expensive follow-up observations, scalably and with demonstrable performance
guarantees.Comment: Submitted to the Astrophysical Journal; Comments welcome
Constraints on the neutron star equation of state from AT2017gfo using radiative transfer simulations
The detection of the binary neutron star GW170817 together with the
observation of electromagnetic counterparts across the entire spectrum
inaugurated a new era of multi-messenger astronomy. In this study we
incorporate wavelength-dependent opacities and emissivities calculated from
atomic-structure data enabling us to model both the measured lightcurves and
spectra of the electromagnetic transient AT2017gfo. Best-fits of the
observational data are obtained by Gaussian Process Regression, which allows us
to present posterior samples for the kilonova and source properties connected
to GW170817. Incorporating constraints obtained from the gravitational wave
signal obtained by the LIGO-Virgo Scientific Collaboration, we present a
upper bound on the mass ratio and a lower bound on the tidal
deformability of , which rules out sufficiently
soft equations of state. Our analysis is a path-finder for more realistic
kilonova models and shows how the combination of gravitational wave and
electromagnetic measurements allow for stringent constraints on the source
parameters and the supranuclear equation of state
A luminosity distribution for kilonovae based on short gamma-ray burst afterglows
The combined detection of a gravitational-wave signal, kilonova, and short
gamma-ray burst (sGRB) from GW170817 marked a scientific breakthrough in the
field of multi-messenger astronomy. But even before GW170817, there have been a
number of sGRBs with possible associated kilonova detections. In this work, we
re-examine these "historical" sGRB afterglows with a combination of
state-of-the-art afterglow and kilonova models. This allows us to include
optical/near-infrared synchrotron emission produced by the sGRB as well as
ultraviolet/optical/near-infrared emission powered by the radioactive decay of
-process elements (i.e., the kilonova). Fitting the lightcurves, we derive
the velocity and the mass distribution as well as the composition of the
ejected material. The posteriors on kilonova parameters obtained from the fit
were turned into distributions for the peak magnitude of the kilonova emission
in different bands and the time at which this peak occurs. From the sGRB with
an associated kilonova, we found that the peak magnitude in H bands falls in
the range [-16.2, -13.1] ( of confidence) and occurs within after the sGRB prompt emission. In g band instead we obtain a peak
magnitude in range [-16.8, -12.3] occurring within the first after
the sGRB prompt. From the luminosity distributions of GW170817/AT2017gfo,
kilonova candidates GRB130603B, GRB050709 and GRB060614 (with the possible
inclusion of GRB150101B) and the upper limits from all the other sGRBs not
associated with any kilonova detection we obtain for the first time a kilonova
luminosity function in different bands.Comment: Published in MNRAS, 24 pages, 14 figure
Somatic PIK3R1 variation as a cause of vascular malformations and overgrowth
PURPOSE: Somatic activating variants in the PI3K-AKT pathway cause vascular malformations with and without overgrowth. We previously reported an individual with capillary and lymphatic malformation harboring a pathogenic somatic variant in PIK3R1, which encodes three PI3K complex regulatory subunits. Here, we investigate PIK3R1 in a large cohort with vascular anomalies and identify an additional 16 individuals with somatic mosaic variants in PIK3R1.
METHODS: Affected tissue from individuals with vascular lesions and overgrowth recruited from a multisite collaborative network was studied. Next-generation sequencing targeting coding regions of cell-signaling and cancer-associated genes was performed followed by assessment of variant pathogenicity.
RESULTS: The phenotypic and variant spectrum associated with somatic variation in PIK3R1 is reported herein. Variants occurred in the inter-SH2 or N-terminal SH2 domains of all three PIK3R1 protein products. Phenotypic features overlapped those of the PIK3CA-related overgrowth spectrum (PROS). These overlapping features included mixed vascular malformations, sandal toe gap deformity with macrodactyly, lymphatic malformations, venous ectasias, and overgrowth of soft tissue or bone.
CONCLUSION: Somatic PIK3R1 variants sharing attributes with cancer-associated variants cause complex vascular malformations and overgrowth. The PIK3R1-associated phenotypic spectrum overlaps with PROS. These data extend understanding of the diverse phenotypic spectrum attributable to genetic variation in the PI3K-AKT pathway
Maintaining Structural Stability of Poly(lactic acid): Effects of Multifunctional Epoxy based Reactive Oligomers
In order to reduce the effects of hydrolytic degradation and to maintain sufficient viscosity during processing of biomass based poly(l-lactic acid) (PLLA), various epoxy functional reactive oligomers have been characterized and incorporated into the degraded fragments as chain extenders. The molecular weight of PLLA increased with the increase in functionality of the reactive oligomers. No further increase in molecular weight was observed for oligomers with functionality of greater than five. Under our experimental conditions, no gelation was found even when the highest functionality reactive oligomers were used. This is attributed to the preferential reaction of the carboxylic acid versus the negligible reactivity of the hydroxyl groups, present at the two ends of the degraded PLLA chains, with the epoxy groups. The study provides a clear understanding of the degradation and chain extension reaction of poly(lactic acid) (PLA) with epoxy functional reactive oligomers. It is also shown that a higher functionality and concentration of the reactive oligomers is needed, to bring about a sufficient increase in the molecular weight and hence the hydrolytic stability in circumstances when PLA chains suffer significant degradation during processing
Identification of long-duration noise transients in LIGO and Virgo
The LIGO and Virgo detectors are sensitive to a variety of noise sources,
such as instrumental artifacts and environmental disturbances. The Stochastic
Transient Analysis Multi-detector Pipeline (STAMP) has been developed to search
for long-duration (t1s) gravitational-wave (GW) signals. This pipeline
can also be used to identify environmental noise transients. Here we present an
algorithm to determine when long-duration noise sources couple into the
interferometers, as well as identify what these noise sources are. We analyze
the cross-power between a GW strain channel and an environmental sensor, using
pattern recognition tools to identify statistically significant structure in
cross-power time-frequency maps. We identify interferometer noise from
airplanes, helicopters, thunderstorms and other sources. Examples from LIGO's
sixth science run, S6, and Virgo's third scientific run, VSR3, are presented.Comment: 10 pages, 7 figures, Gravitational-wave Physics & Astronomy Worksho
Standardizing kilonovae and their use as standard candles to measure the Hubble constant
The detection of GW170817 is revolutionizing many areas of astrophysics with the joint observation of gravitational waves and electromagnetic emissions. These multimessenger events provide a new approach to determine the Hubble constant, thus, they are a promising candidate for mitigating the tension between measurements of type-Ia supernovae via the local distance ladder and the cosmic microwave background. In addition to the "standard siren"provided by the gravitational-wave measurement, the kilonova itself has characteristics that allow one to improve existing measurements or to perform yet another, independent measurement of the Hubble constant without gravitational-wave information. Here, we employ standardization techniques borrowed from the type-Ia community and apply them to kilonovae, not using any information from the gravitational-wave signal. We use two versions of this technique, one derived from direct observables measured from the light curve, and the other based on inferred ejecta parameters, e.g., mass, velocity, and composition, for two different models. These lead to Hubble constant measurements of H0=109-35+49 km s-1 Mpc-1 for the measured analysis, and H0=85-17+22 km s-1 Mpc-1 and H0=79-15+23 km s-1 Mpc-1 for the inferred analyses. This measurement has error bars within ∼2 to the gravitational-wave measurements (H0=74-8+16 km s-1 Mpc-1), showing its promise as an independent constraint on H0
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