1,087 research outputs found
Microwave dielectric spectrum of rocks
A combination of several measurement techniques was used to investigate the dielectric properties of 80 rock samples in the microwave region. The real part of the dielectric constant, epsilon', was measured in 0.1 GHz steps from 0.5 to 18 GHz, and the imaginary part, epsilon'', was measured at five frequencies extending between 1.6 and 16 GHz. In addition to the dielectric measurements, the bulk density was measured for all the samples and the bulk chemical composition was determined for 56 of the samples. The study shows that epsilon' is frequency-dependent over the 0.5 to 18 GHz range for all rock samples, and that the bulk density rho accounts for about 50 percent of the observed variance of epsilon'. For individual rock types (by genesis), about 90 percent of the observed variance may be explained by the combination of density and the fractional contents of SiO2, Fe2O3, MgO, and TiO2. For the loss factor epsilon'', it was not possible to establish statistically significant relationships between it and the measured properties of the rock samples (density and chemical composition)
The DLV System for Knowledge Representation and Reasoning
This paper presents the DLV system, which is widely considered the
state-of-the-art implementation of disjunctive logic programming, and addresses
several aspects. As for problem solving, we provide a formal definition of its
kernel language, function-free disjunctive logic programs (also known as
disjunctive datalog), extended by weak constraints, which are a powerful tool
to express optimization problems. We then illustrate the usage of DLV as a tool
for knowledge representation and reasoning, describing a new declarative
programming methodology which allows one to encode complex problems (up to
-complete problems) in a declarative fashion. On the foundational
side, we provide a detailed analysis of the computational complexity of the
language of DLV, and by deriving new complexity results we chart a complete
picture of the complexity of this language and important fragments thereof.
Furthermore, we illustrate the general architecture of the DLV system which
has been influenced by these results. As for applications, we overview
application front-ends which have been developed on top of DLV to solve
specific knowledge representation tasks, and we briefly describe the main
international projects investigating the potential of the system for industrial
exploitation. Finally, we report about thorough experimentation and
benchmarking, which has been carried out to assess the efficiency of the
system. The experimental results confirm the solidity of DLV and highlight its
potential for emerging application areas like knowledge management and
information integration.Comment: 56 pages, 9 figures, 6 table
Measured g factors and the tidal-wave description of transitional nuclei near A = 100
The transient-field technique has been used in both conventional kinematics
and inverse kinematics to measure the g factors of the 2+ states in the stable
even isotopes of Ru, Pd and Cd. The statistical precision of the g(2+) values
has been significantly improved, allowing a critical comparison with the
tidal-wave version of the cranking model recently proposed for transitional
nuclei in this region.Comment: Accepted for publication in Physical Review C, April 201
New Measurements of the Motion of the Zodiacal Dust
Using the Wisconsin H-Alpha Mapper (WHAM), we have measured at high spectral
resolution and high signal-to-noise the profile of the scattered solar Mg I
5184 absorption line in the zodiacal light. The observations were carried out
toward 49 directions that sampled the ecliptic equator from solar elongations
of 48\dg (evening sky) to 334\dg (morning sky) plus observations near +47\dg
and +90\dg ecliptic latitude. The spectra show a clear prograde kinematic
signature that is inconsistent with dust confined to the ecliptic plane and in
circular orbits influenced only by the sun's gravity. In particular, the
broadened widths of the profiles, together with large amplitude variations in
the centroid velocity with elongation angle, indicate that a significant
population of dust is on eccentric orbits. In addition, the wide, flat-bottomed
line profile toward the ecliptic pole indicates a broad distribution of orbital
inclinations extending up to about 30\dg - 40\dg with respect to the ecliptic
plane. The absence of pronounced asymmetries in the shape of the profiles
limits the retrograde population to less than 10% of the prograde population
and also places constraints on the scattering phase function of the particles.
These results do not show the radial outflow or evening--morning velocity
amplitude asymmetry reported in some earlier investigations. The reduction of
the spectra included the discovery and removal of extremely faint, unidentified
terrestrial emission lines that contaminate and distort the underlying Mg I
profile. This atmospheric emission is too weak to have been seen in earlier,
lower signal-to-noise observations, but it probably affected the line centroid
measurements of previous investigations.Comment: 24 pages, 8 figures, 1 table, to appear in ApJ v612; figures appear
low-res only on scree
The First Detections of the Extragalactic Background Light at 3000, 5500, and 8000A (II): Measurement of Foreground Zodiacal Light
We present a measurement of the absolute surface brightness of the zodiacal
light (3900-5100A) toward a fixed extragalactic target at high ecliptic
latitude based on moderate resolution (~1.3A per pixel) spectrophotometry
obtained with the du Pont 2.5m telescope at Las Campanas Observatory in Chile.
This measurement and contemporaneous Hubble Space Telescope data from WFPC2 and
FOS comprise a coordinated program to measure the mean flux of the diffuse
extragalactic background light (EBL). The zodiacal light at optical wavelengths
results from scattering by interplanetary dust, so that the zodiacal light flux
toward any extragalactic target varies seasonally with the position of the
Earth. This measurement of zodiacal light is therefore relevant to the specific
observations (date and target field) under discussion. To obtain this result,
we have developed a technique that uses the strength of the zodiacal Fraunhofer
lines to identify the absolute flux of the zodiacal light in the
multiple-component night sky spectrum. Statistical uncertainties in the result
are 0.6% (1 sigma). However, the dominant source of uncertainty is systematic
errors, which we estimate to be 1.1% (1 sigma). We discuss the contributions
included in this estimate explicitly. The systematic errors in this result
contribute 25% in quadrature to the final error in our coordinated EBL
measurement, which is presented in the first paper of this series.Comment: Accepted for publication in ApJ, 22 pages using emulateapj.sty,
version with higher resolution figures available at
http://www.astro.lsa.umich.edu/~rab/publications.html or at
http://nedwww.ipac.caltech.edu/level5/Sep01/Bernstein2/frames.htm
Narrow-band Imaging for Detection of Neoplasia at Colonoscopy: a Meta-analysis of Data From Individual Patients in Randomized Controlled Trials
Background & Aims
Adenoma detection rate (ADR) is an important quality assurance measure for colonoscopy. Some studies suggest that narrow band imaging (NBI) may be more effective at detection of adenomas than white-light endoscopy (WLE) when bowel preparation is optimal. We conducted a meta-analysis of data from individual patients in randomized controlled trials that compared the efficacy of NBI to WLE in detection of adenomas.
Methods
We searched MEDLINE, EMBASE, and Cochrane library databases, through April 2017, for randomized controlled trials that assessed detection of colon polyps by high-definition WLE vs NBI and from which data on individual patients was available. The primary outcome measure was ADR adjusted for bowel preparation quality. Multilevel regression models were used with patients nested within trials, and trial included as a random effect.
Results
We collected data from 11 trials, comprising 4491 patients and 6636 polyps detected. Adenomas were detected in 952/2251 (42.3%) participants examined by WLE vs 1011/2239 (45.2%) participants examined by NBI (unadjusted odds ratio [OR] for detection of adenoma by WLE vs NBI, 1.14; 95% CI, 1.01–1.29; P=.04). NBI outperformed WLE only when bowel preparation was best: adequate preparation OR, 1.07 (95% CI, 0.92–1.24; P=.38) vs best preparation OR, 1.30 (95% CI, 1.04–1.62; P=.02). Second-generation bright NBI had a better ADR than WLE (second-generation NBI OR, 1.28; 95% CI, 1.05–1.56; P=.02), whereas first-generation NBI did not. NBI detected more non-adenomatous polyps than WLE (OR, 1.24; 95% CI, 1.06–1.44; P=.008) and flat polyps than WLE (OR, 1.24; 95% CI, 1.02–1.51; P=.03).
Conclusions
In a meta-analysis of data from individual patients in randomized controlled trials, we found NBI to have a higher ADR than WLE, and that this effect is greater when bowel preparation is optimal
Farmers’ market use is associated with fruit and vegetable consumption in diverse southern rural communities
Background
While farmers’ markets are a potential strategy to increase access to fruits and vegetables in rural areas, more information is needed regarding use of farmers’ markets among rural residents. Thus, this study’s purpose was to examine (1) socio-demographic characteristics of participants; (2) barriers and facilitators to farmers’ market shopping in southern rural communities; and (3) associations between farmers’ market use with fruit and vegetable consumption and body mass index (BMI).
Methods
Cross-sectional surveys were conducted with a purposive sample of farmers’ market customers and a representative sample of primary household food shoppers in eastern North Carolina (NC) and the Appalachian region of Kentucky (KY). Customers were interviewed using an intercept survey instrument at farmers’ markets. Representative samples of primary food shoppers were identified via random digit dial (RDD) cellular phone and landline methods in counties that had at least one farmers’ market. All questionnaires assessed socio-demographic characteristics, food shopping patterns, barriers to and facilitators of farmers’ market shopping, fruit and vegetable consumption and self-reported height and weight. The main outcome measures were fruit and vegetable consumption and BMI. Descriptive statistics were used to examine socio-demographic characteristics, food shopping patterns, and barriers and facilitators to farmers’ market shopping. Linear regression analyses were used to examine associations between farmers’ market use with fruit and vegetable consumption and BMI, controlling for age, race, education, and gender.
Results
Among farmers’ market customers, 44% and 55% (NC and KY customers, respectively) reported shopping at a farmers’ market at least weekly, compared to 16% and 18% of NC and KY RDD respondents. Frequently reported barriers to farmers’ market shopping were market days and hours, “only come when I need something�, extreme weather, and market location. Among the KY farmers’ market customers and NC and KY RDD respondents, fruit and vegetable consumption was positively associated with use of farmers’ markets. There were no associations between use of farmers’ markets and BMI.
Conclusions
Fruit and vegetable consumption was associated with farmers’ market shopping. Thus, farmers’ markets may be a viable method to increase population-level produce consumption
Reversible Keap1 inhibitors are preferential pharmacological tools to modulate cellular mitophagy
Mitophagy orchestrates the autophagic degradation of dysfunctional mitochondria preventing their pathological accumulation and contributing to cellular homeostasis. We previously identified a novel chemical tool (hereafter referred to as PMI), which drives mitochondria into autophagy without collapsing their membrane potential (ΔΨm). PMI is an inhibitor of the protein-protein interaction (PPI) between the transcription factor Nrf2 and its negative regulator, Keap1 and is able to up-regulate the expression of autophagy-associated proteins, including p62/SQSTM1. Here we show that PMI promotes mitochondrial respiration, leading to a superoxide-dependent activation of mitophagy. Structurally distinct Keap1-Nrf2 PPI inhibitors promote mitochondrial turnover, while covalent Keap1 modifiers, including sulforaphane (SFN) and dimethyl fumarate (DMF), are unable to induce a similar response. Additionally, we demonstrate that SFN reverses the effects of PMI in co-treated cells by reducing the accumulation of p62 in mitochondria and subsequently limiting their autophagic degradation. This study highlights the unique features of Keap1-Nrf2 PPI inhibitors as inducers of mitophagy and their potential as pharmacological agents for the treatment of pathological conditions characterized by impaired mitochondrial quality control
Magnetoluminescence
Pulsar Wind Nebulae, Blazars, Gamma Ray Bursts and Magnetars all contain
regions where the electromagnetic energy density greatly exceeds the plasma
energy density. These sources exhibit dramatic flaring activity where the
electromagnetic energy distributed over large volumes, appears to be converted
efficiently into high energy particles and gamma-rays. We call this general
process magnetoluminescence. Global requirements on the underlying, extreme
particle acceleration processes are described and the likely importance of
relativistic beaming in enhancing the observed radiation from a flare is
emphasized. Recent research on fluid descriptions of unstable electromagnetic
configurations are summarized and progress on the associated kinetic
simulations that are needed to account for the acceleration and radiation is
discussed. Future observational, simulation and experimental opportunities are
briefly summarized.Comment: To appear in "Jets and Winds in Pulsar Wind Nebulae, Gamma-ray Bursts
and Blazars: Physics of Extreme Energy Release" of the Space Science Reviews
serie
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