3,096 research outputs found
Hall Current Plasma Source Having a Center-Mounted or a Surface-Mounted Cathode
A miniature Hall current plasma source apparatus having magnetic shielding of the walls from ionized plasma, an integrated discharge channel and gas distributor, an instant-start hollow cathode mounted to the plasma source, and an externally mounted keeper, is described. The apparatus offers advantages over other Hall current plasma sources having similar power levels, including: lower mass, longer lifetime, lower part count including fewer power supplies, and the ability to be continuously adjustable to lower average power levels using pulsed operation and adjustment of the pulse duty cycle. The Hall current plasma source can provide propulsion for small spacecraft that either do not have sufficient power to accommodate a propulsion system or do not have available volume to incorporate the larger propulsion systems currently available. The present low-power Hall current plasma source can be used to provide energetic ions to assist the deposition of thin films in plasma processing applications
Spectroscopic distance, mass, and age estimations for APOGEE DR17
We derive distances and masses of stars from the Sloan Digital Sky Survey
(SDSS) Apache Point Observatory Galactic Evolution Experiment (APOGEE) Data
Release 17 (DR17) using simple neural networks. Training data for distances
comes from Gaia EDR3, supplemented by literature distances for star clusters.
For masses, the network is trained using asteroseismic masses for evolved stars
and isochrone masses for main sequence stars. The models are trained on
effective temperature, surface gravity, metallicity and carbon and nitrogen
abundances. We found that our distance predictions have median fractional
errors that range from at low log g and at higher
log g with a standard deviation of . The mass predictions have a
standard deviation of . Using the masses, we derive ages for evolved
stars based on the correspondence between mass and age for giant stars given by
isochrones. The results are compiled into a Value Added Catalog (VAC) called
DistMass that contains distances and masses for 733901 independent spectra,
plus ages for 396548 evolved stars.Comment: 23 pages, 18 figure
Directional Phytoscreening: Contaminant Gradients in Trees for Plume Delineation
Tree Sampling Methods Have Been Used in Phytoscreening Applications to Delineate Contaminated Soil and Groundwater, Augmenting Traditional Investigative Methods that Are Time-Consuming, Resource-Intensive, Invasive, and Costly. in the Past Decade, Contaminant Concentrations in Tree Tissues Have Been Shown to Reflect the Extent and Intensity of Subsurface Contamination. This Paper Investigates a New Phytoscreening Tool: Directional Tree Coring, a Concept Originating from Field Data that Indicated Azimuthal Concentrations in Tree Trunks Reflected the Concentration Gradients in the Groundwater Around the Tree.To Experimentally Test This Hypothesis, Large Diameter Trees Were Subjected to Subsurface Contaminant Concentration Gradients in a Greenhouse Study. These Trees Were Then Analyzed for Azimuthal Concentration Gradients in Aboveground Tree Tissues, Revealing Contaminant Centroids Located on the Side of the Tree Nearest the Most Contaminated Groundwater. Tree Coring at Three Field Sites Revealed Sufficiently Steep Contaminant Gradients in Trees Reflected Nearby Groundwater Contaminant Gradients. in Practice, Trees Possessing Steep Contaminant Gradients Are Indicators of Steep Subsurface Contaminant Gradients, Providing Compass-Like Information About the Contaminant Gradient, Pointing Investigators toward Higher Concentration Regions of the Plume. © 2013 American Chemical Society
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Pre-vaccination prevalence of anogenital and oral human papillomavirus in young HIV-infected men who have sex with men.
The aims of this study were to: 1) determine prevalence of anogenital and oral HPV, 2) determine concordance between HPV at anal, perianal, scrotal/penile, and oral sites; and 3) describe factors associated with anogenital HPV types targeted by the 9-valent vaccine. Data were collected from 2012 to 2015 among men who have sex with men 18-26 years of age enrolled in a vaccine trial (N = 145). Penile/scrotal, perianal, anal, and oral samples were tested for 61 HPV types. Logistic regression was used to identify factors associated with types in the 9-valent vaccine. Participants' mean age was 23.0 years, 55.2% were African-American, and 26.2% were Hispanic; 93% had anal, 40% penile, and 6% oral HPV. Among those with anogenital infection, 18% had HPV16. Concordance was low between anogenital and oral sites. Factors independently associated with a 9-valent vaccine-type HPV were: race (African-American vs. White, OR=2.67, 95% CI=1.11-6.42), current smoking (yes vs. no, OR=2.37, 95% CI=1.03-5.48), and number of recent receptive anal sex partners (2+ vs. 0, OR=3.47, 95% CI=1.16-10.4). Most MSM were not infected with HPV16 or HPV18, suggesting that they may still benefit from HPV vaccination, but anogenital HPV was very common, highlighting the importance of vaccinating men before sexual initiation. CLINICAL TRIAL NUMBER: NCT01209325
Characterizing large-scale quantum computers via cycle benchmarking
Quantum computers promise to solve certain problems more efficiently than
their digital counterparts. A major challenge towards practically useful
quantum computing is characterizing and reducing the various errors that
accumulate during an algorithm running on large-scale processors. Current
characterization techniques are unable to adequately account for the
exponentially large set of potential errors, including cross-talk and other
correlated noise sources. Here we develop cycle benchmarking, a rigorous and
practically scalable protocol for characterizing local and global errors across
multi-qubit quantum processors. We experimentally demonstrate its practicality
by quantifying such errors in non-entangling and entangling operations on an
ion-trap quantum computer with up to 10 qubits, with total process fidelities
for multi-qubit entangling gates ranging from 99.6(1)% for 2 qubits to 86(2)%
for 10 qubits. Furthermore, cycle benchmarking data validates that the error
rate per single-qubit gate and per two-qubit coupling does not increase with
increasing system size.Comment: The main text consists of 6 pages, 3 figures and 1 table. The
supplementary information consists of 6 pages, 2 figures and 3 table
Can muon-induced backgrounds explain the DAMA data?
We present an accurate simulation of the muon-induced background in the DAMA/LIBRA experiment. Muon sampling underground has been performed using the MUSIC/MUSUN codes and subsequent interactions in the rock around the DAMA/LIBRA detector cavern and the experimental setup including shielding, have been simulated with GEANT4.9.6. In total we simulate the equivalent of 20 years of muon data. We have calculated the total muon-induced neutron flux in the DAMA/LIBRA detector cavern as Φμn = 1.0 ×10-9 cm-2s-1, which is consistent with other simulations. After selecting events which satisfy the DAMA/LIBRA signal criteria, our simulation predicts 3.49 ×10-5 cpd/kg/keV which accounts for less than 0.3% of the DAMA/LIBRA modulation amplitude. We conclude from our work that muon-induced backgrounds are unable to contribute to the observed signal modulation
Design of the Subpopulations and Intermediate Outcome Measures in COPD (SPIROMICS) AIR Study.
IntroductionPopulation-based epidemiological evidence suggests that exposure to ambient air pollutants increases hospitalisations and mortality from chronic obstructive pulmonary disease (COPD), but less is known about the impact of exposure to air pollutants on patient-reported outcomes, morbidity and progression of COPD.Methods and analysisThe Subpopulations and Intermediate Outcome Measures in COPD (SPIROMICS) Air Pollution Study (SPIROMICS AIR) was initiated in 2013 to investigate the relation between individual-level estimates of short-term and long-term air pollution exposures, day-to-day symptom variability and disease progression in individuals with COPD. SPIROMICS AIR builds on a multicentre study of smokers with COPD, supplementing it with state-of-the-art air pollution exposure assessments of fine particulate matter, oxides of nitrogen, ozone, sulfur dioxide and black carbon. In the parent study, approximately 3000 smokers with and without airflow obstruction are being followed for up to 3 years for the identification of intermediate biomarkers which predict disease progression. Subcohorts undergo daily symptom monitoring using comprehensive daily diaries. The air monitoring and modelling methods employed in SPIROMICS AIR will provide estimates of individual exposure that incorporate residence-specific infiltration characteristics and participant-specific time-activity patterns. The overarching study aim is to understand the health effects of short-term and long-term exposures to air pollution on COPD morbidity, including exacerbation risk, patient-reported outcomes and disease progression.Ethics and disseminationThe institutional review boards of all the participating institutions approved the study protocols. The results of the trial will be presented at national and international meetings and published in peer-reviewed journals
Fine-scale predictions of distributions of Chagas disease vectors in the state of Guanajuato, Mexico
One of the most daunting challenges for Chagas disease surveillance and control in
Mexico is the lack of community level data on vector distributions. Although many states now have
assembled representative domestic triatomine collections, only two triatomine specimens had been
collected and reported previously from the state of Guanajuato. Field personnel from the stateÕs
Secretarõ´a de Salud conducted health promotion activities in 43 of the 46 counties in the state and
received donations of a total of 2,522 triatomine specimens between 1998 and 2002. All specimens were
identiÞed, and live insects examined for Trypanosoma cruzi. In an effort to develop Þne-scale distributional
data for Guanajuato, collection localities were georeferenced and ecological niches were
modeled for each species by using evolutionary-computing approaches. Five species were collected:
Triatoma mexicana (Herrich-Schaeffer), Triatoma longipennis (Usinger), Triatoma pallidipennis
(Stål), Triatoma barberi (Usinger), and Triatoma dimidiata (Latreille) from 201 communities located
at elevations of 870Ð2,200 m. Based on collection success, T. mexicana had the broadest dispersion,
although niche mapping indicates that T. barberi represents the greatest risk for transmission of Chagas
disease in the state. T. dimidiata was represented in collections by a single adult collected from one
village outside the predicted area for all species. For humans, an estimated 3,755,380 individuals are
at risk for vector transmission in the state, with an incidence of 3,500 new cases per year; overall
seroprevalences of 2.6% indicate that 97,640 individuals are infected with T. cruzi at present, including
29,300 chronic cases
Integrated DNA and RNA Sequencing Reveals Drivers of Endocrine Resistance in Estrogen Receptor Positive Breast Cancer
PURPOSE: Endocrine therapy resistance (ETR) remains the greatest challenge in treating patients with hormone receptor–positive breast cancer. We set out to identify molecular mechanisms underlying ETR through in-depth genomic analysis of breast tumors. EXPERIMENTAL DESIGN: We collected pre-treatment and sequential on-treatment tumor samples from 35 patients with estrogen receptor–positive breast cancer treated with neoadjuvant then adjuvant endocrine therapy; 3 had intrinsic resistance, 19 acquired resistance, and 13 remained sensitive. Response was determined by changes in tumor volume neoadjuvantly and by monitoring for adjuvant recurrence. Twelve patients received two or more lines of endocrine therapy, with subsequent treatment lines being initiated at the time of development of resistance to the previous endocrine therapy. DNA whole-exome sequencing and RNA sequencing were performed on all samples, totalling 169 unique specimens. DNA mutations, copy-number alterations, and gene expression data were analyzed through unsupervised and supervised analyses to identify molecular features related to ETR. RESULTS: Mutations enriched in ETR included ESR1 and GATA3. The known ESR1 D538G variant conferring ETR was identified, as was a rarer E380Q variant that confers endocrine hypersensitivity. Resistant tumors which acquired resistance had distinct gene expression profiles compared with paired sensitive tumors, showing elevated pathways including ER, HER2, GATA3, AKT, RAS, and p63 signaling. Integrated analysis in individual patients highlighted the diversity of ETR mechanisms. CONCLUSIONS: The mechanisms underlying ETR are multiple and characterized by diverse changes in both somatic genetic and transcriptomic profiles; to overcome resistance will require an individualized approach utilizing genomic and genetic biomarkers and drugs tailored to each patient
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