2,798 research outputs found
Ring-apodized vortex coronagraphs for obscured telescopes. I. Transmissive ring apodizers
The vortex coronagraph (VC) is a new generation small inner working angle
(IWA) coronagraph currently offered on various 8-meter class ground-based
telescopes. On these observing platforms, the current level of performance is
not limited by the intrinsic properties of actual vortex devices, but by
wavefront control residuals and incoherent background (e.g. thermal emission of
the sky) or the light diffracted by the imprint of the secondary mirror and
support structures on the telescope pupil. In the particular case of unfriendly
apertures (mainly large central obscuration) when very high contrast is needed
(e.g. direct imaging of older exoplanets with extremely large telescopes or
space- based coronagraphs), a simple VC, as most coronagraphs, can not deliver
its nominal performance because of the contamination due to the diffraction
from the obscured part of the pupil. Here we propose a novel yet simple concept
that circumvents this problem. We combine a vortex phase mask in the image
plane of a high-contrast instrument with a single pupil-based amplitude ring
apodizer, tailor designed to exploit the unique convolution properties of the
VC at the Lyot-stop plane. We show that such a ring-apodized vortex coronagraph
(RAVC) restores the perfect attenuation property of the VC regardless of the
size of the central obscuration, and for any (even) topological charge of the
vortex. More importantly the RAVC maintains the IWA and conserves a fairly high
throughput, which are signature properties of the VC.Comment: 10 pages, 6 figure
Stellar Double Coronagraph: a multistage coronagraphic platform at Palomar observatory
We present a new instrument, the "Stellar Double Coronagraph" (SDC), a
flexible coronagraphic platform. Designed for Palomar Observatory's 200" Hale
telescope, its two focal and pupil planes allow for a number of different
observing configurations, including multiple vortex coronagraphs in series for
improved contrast at small angles. We describe the motivation, design,
observing modes, wavefront control approaches, data reduction pipeline, and
early science results. We also discuss future directions for the instrument.Comment: 25 pages, 12 figures. Correspondence welcome. The published work is
open access and differs trivially from the version posted here. The published
version may be found at
http://iopscience.iop.org/article/10.1088/1538-3873/128/965/075003/met
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Decidual cell regulation of trophoblast is altered in pregnancies at risk of pre-eclampsia
Successful implantation and placentation are dependent on the interaction between decidual stromal cells (DSC) and extravillous trophoblast (EVT) cells. The extent of trophoblast invasion relies on communication between the placenta and maternal decidua. The cyclical process of decidualisation induces a transformation of endometrial fibroblasts to secretory DSC; these secreted products have many functions including the control of trophoblast invasion. Inadequate trophoblast invasion and remodelling of the uterine vessels (the spiral arteries) are associated with pregnancy disorders such as pre-eclampsia. Uterine artery Doppler resistance index (RI) in the first trimester of pregnancy can be used as a proxy measure of remodelling. DSC were isolated from pregnancies with normal (normal RI) or impaired (high RI) spiral artery remodelling. Following isolation, DSC were re-decidualised using cAMP and MPA and secretion of the decidualisation markers IGFBP-1 and prolactin assessed. We examined the impact of DSC secreted factors on trophoblast cell function, using the EVT cell line SGHPL-4. We demonstrated that DSC exposed to decidual factors were able to re-decidualise in vitro and that the chemoattraction of trophoblasts by DSC is impaired in pregnancies with high RI. This study provides new insights into the role that DSC play in regulating EVT functions during the first trimester of pregnancy. This is the first study to demonstrate that DSC from pregnancies with impaired vascular remodelling in the first trimester secrete factors that inhibit the directional movement of trophoblast cells. This finding may be important in understanding aberrant trophoblast invasion in pregnancies where vascular remodelling is impaired
The Under-Reporting of Transfers in Household Surveys: Its Nature and Consequences
High rates of understatement are found for many government transfer programs and in many datasets. This understatement has major implications for our understanding of economic well-being and the effects of transfer programs. We provide estimates of the extent of under-reporting for ten transfer programs in five major nationally representative surveys by comparing reported weighted totals for these programs with totals obtained from government agencies. We also examine imputation procedures and rates. We find increasing under-reporting and imputation over time and sharp differences across programs and surveys. We explore reasons for under-reporting and how under-reporting biases existing studies and suggest corrections.
Influence of human chorionic gonadotropin (hCG) on in vitro growth of Plasmodium falciparum
<p>Abstract</p> <p>Background</p> <p>During pregnancy, women are more susceptible to <it>Plasmodium falciparum </it>infections and frequently have a higher parasitaemia than non-pregnant women. Several mechanisms are responsible for their increased susceptibility, including down-modulation of immune responses that aid in parasite clearance and sequestration of infected erythrocytes in the placenta. Early in pregnancy, a third mechanism may contribute to higher parasitaemia, since it has been reported that addition of human chorionic gonadotropin (hCG) to <it>in vitro </it>cultures of the NF54-strain of <it>P. falciparum </it>results in increased parasite growth rates. The goal of this study was to further examine the effect of hCG on <it>P. falciparum </it>growth.</p> <p>Methods</p> <p>The NF54-3D7, FVO and 7G8 strains of <it>P. falciparum </it>were cultured <it>in vitro </it>with various physiological concentrations of hCG purchased from three sources. Infected erythrocytes were also co-cultured with a human cell line that naturally secretes hCG.</p> <p>Results</p> <p>Results from 14 experiments using different combinations of parasite strains and concentrations of hCG from different sources, as well as the co-culture studies, failed to provide convincing evidence that hCG enhances parasite growth <it>in vitro</it>.</p> <p>Conclusion</p> <p>Based on these data, it seems unlikely that hCG has a direct effect on the rate of parasite growth early in pregnancy.</p
Toward three-dimensional echocardiographic determination of regional myofiber structure
As a step toward the goal of relating changes in underlying myocardial structure to observed altered cardiac function in the hearts of individual patients, this study addresses the feasibility of creating echocardiography-derived maps of regional myocardial fiber structure for entire, intact, excised sheep hearts. Backscatter data were obtained from apical echocardiographic images acquired with a clinical ultrasonic imaging system and used to determine local fiber orientations in each of seven hearts. Systematic acquisition across the entire heart volume provided information sufficient to give a complete map for each heart. Results from the echocardiography-derived fiber maps compare favorably with corresponding results derived from diffusion tensor magnetic resonance imaging. The results of this study provide evidence of the feasibility of using echocardiographic methods to generate individualized whole heart fiber maps for patients
Observing Exoplanets with High-Dispersion Coronagraphy. II. Demonstration of an Active Single-Mode Fiber Injection Unit
High-dispersion coronagraphy (HDC) optimally combines high contrast imaging
techniques such as adaptive optics/wavefront control plus coronagraphy to high
spectral resolution spectroscopy. HDC is a critical pathway towards fully
characterizing exoplanet atmospheres across a broad range of masses from giant
gaseous planets down to Earth-like planets. In addition to determining the
molecular composition of exoplanet atmospheres, HDC also enables Doppler
mapping of atmosphere inhomogeneities (temperature, clouds, wind), as well as
precise measurements of exoplanet rotational velocities. Here, we demonstrate
an innovative concept for injecting the directly-imaged planet light into a
single-mode fiber, linking a high-contrast adaptively-corrected coronagraph to
a high-resolution spectrograph (diffraction-limited or not). Our laboratory
demonstration includes three key milestones: close-to-theoretical injection
efficiency, accurate pointing and tracking, on-fiber coherent modulation and
speckle nulling of spurious starlight signal coupling into the fiber. Using the
extreme modal selectivity of single-mode fibers, we also demonstrated speckle
suppression gains that outperform conventional image-based speckle nulling by
at least two orders of magnitude.Comment: 10 pages, 7 figures, accepted by Ap
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Predicting Persistent Opioid Use, Abuse, and Toxicity Among Cancer Survivors.
BackgroundAlthough opioids play a critical role in the management of cancer pain, the ongoing opioid epidemic has raised concerns regarding their persistent use and abuse. We lack data-driven tools in oncology to understand the risk of adverse opioid-related outcomes. This project seeks to identify clinical risk factors and create a risk score to help identify patients at risk of persistent opioid use and abuse.MethodsWithin a cohort of 106 732 military veteran cancer survivors diagnosed between 2000 and 2015, we determined rates of persistent posttreatment opioid use, diagnoses of opioid abuse or dependence, and admissions for opioid toxicity. A multivariable logistic regression model was used to identify patient, cancer, and treatment risk factors associated with adverse opioid-related outcomes. Predictive risk models were developed and validated using a least absolute shrinkage and selection operator regression technique.ResultsThe rate of persistent opioid use in cancer survivors was 8.3% (95% CI = 8.1% to 8.4%); the rate of opioid abuse or dependence was 2.9% (95% CI = 2.8% to 3.0%); and the rate of opioid-related admissions was 2.1% (95% CI = 2.0% to 2.2%). On multivariable analysis, several patient, demographic, and cancer and treatment factors were associated with risk of persistent opioid use. Predictive models showed a high level of discrimination when identifying individuals at risk of adverse opioid-related outcomes including persistent opioid use (area under the curve [AUC] = 0.85), future diagnoses of opioid abuse or dependence (AUC = 0.87), and admission for opioid abuse or toxicity (AUC = 0.78).ConclusionThis study demonstrates the potential to predict adverse opioid-related outcomes among cancer survivors. With further validation, personalized risk-stratification approaches could guide management when prescribing opioids in cancer patients
Evaluating LAANC Utilization & Compliance for Small Unmanned Aircraft Systems in Controlled Airspace
On July 23, 2019, the Federal Aviation Administration (FAA) expanded the Low Altitude Authorization and Notification Capability (LAANC)—the system that processes airspace approvals for sUAS operators in controlled airspace—to include recreational operations. Researchers sought to collect and evaluate 30 days of UAS operational activity in controlled airspace using UAS detection equipment. Detected UAS flight data was compared against UAS Facility Maps and LAANC approval data to assess UAS operator compliance and behavior patterns. Researchers documented 94 LAANC approvals and detected 271 UAS flights within the sample area during the sampling period. The research team noted that UAS detections exceeded LAANC authorizations by a rate of approximately four-to-one. Only 7.0% of detected UAS operations could be correlated to a LAANC authorization, possibly indicating significant rates of non-compliance. Additionally, researchers determined that 34.3% (n =93) of detected UAS operations exceeded maximum altitudes prescribed for their respective location. Forty-four percent (n =41) of UASFM altitude exceedances occurred above 500 feet AGL, posing potential risk to manned aviation operations in the National Airspace System. Researchers advocate for the implementation of additional measures to curtail non-compliance, including additional UAS operator training, deterrence, and enforcement measures. The research team intends to expand this study to additional airports via related research projects within the FAA’s ASSURE Program
Emissivity Results on High Temperature Coatings for Refractory Composite Materials
The directional emissivity of various refractory composite materials considered for application for reentry and hypersonic vehicles was investigated. The directional emissivity was measured at elevated temperatures of up to 3400 F using a directional spectral radiometric technique during arc-jet test runs. A laboratory-based relative total radiance method was also used to measure total normal emissivity of some of the refractory composite materials. The data from the two techniques are compared. The paper will also compare the historical database of Reinforced Carbon-Carbon emissivity measurements with emissivity values generated recently on the material using the two techniques described in the paper
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