837 research outputs found
A Quarter-Century of Observations of Comet 10P/Tempel 2 at Lowell Observatory: Continued Spin-Down, Coma Morphology, Production Rates, and Numerical Modeling
We report on photometry and imaging of Comet 10P/Tempel 2 obtained at Lowell
Observatory from 1983 through 2011. We measured a nucleus rotation period of
8.950 +/- 0.002 hr from 2010 September to 2011 January. This rotation period is
longer than the period we previously measured in 1999, which was itself longer
than the period measured in 1988. A nearly linear jet was observed which varied
little during a rotation cycle in both R and CN images acquired during the 1999
and 2010 apparitions. We measured the projected direction of this jet
throughout the two apparitions and, under the assumption that the source region
of the jet was near the comet's pole, determined a rotational pole direction of
RA/Dec = 151deg/+59deg from CN measurements and RA/Dec = 173deg/+57deg from
dust measurements (we estimate a circular uncertainty of 3deg for CN and 4deg
for dust). Different combinations of effects likely bias both gas and dust
solutions and we elected to average these solutions for a final pole of RA/Dec
= 162 +/- 11deg/+58 +/- 1deg. Photoelectric photometry was acquired in 1983,
1988, 1999/2000, and 2010/2011. The activity exhibited a steep turn-on ~3
months prior to perihelion (the exact timing of which varies) and a relatively
smooth decline after perihelion. The activity during the 1999 and 2010
apparitions was similar; limited data in 1983 and 1988 were systematically
higher and the difference cannot be explained entirely by the smaller
perihelion distance. We measured a "typical" composition, in agreement with
previous investigators. Monte Carlo numerical modeling with our pole solution
best replicated the observed coma morphology for a source region located near a
comet latitude of +80deg and having a radius of ~10deg. Our model reproduced
the seasonal changes in activity, suggesting that the majority of Tempel 2's
activity originates from a small active region located near the pole.Comment: Accepted by AJ; 29 pages of text (preprint style), 8 tables, 7
figure
MCMC implementation of the optimal Bayesian classifier for non-Gaussian models: model-based RNA-Seq classification
BACKGROUND: Sequencing datasets consist of a finite number of reads which map to specific regions of a reference genome. Most effort in modeling these datasets focuses on the detection of univariate differentially expressed genes. However, for classification, we must consider multiple genes and their interactions. RESULTS: Thus, we introduce a hierarchical multivariate Poisson model (MP) and the associated optimal Bayesian classifier (OBC) for classifying samples using sequencing data. Lacking closed-form solutions, we employ a Monte Carlo Markov Chain (MCMC) approach to perform classification. We demonstrate superior or equivalent classification performance compared to typical classifiers for two synthetic datasets and over a range of classification problem difficulties. We also introduce the Bayesian minimum mean squared error (MMSE) conditional error estimator and demonstrate its computation over the feature space. In addition, we demonstrate superior or leading class performance over an RNA-Seq dataset containing two lung cancer tumor types from The Cancer Genome Atlas (TCGA). CONCLUSIONS: Through model-based, optimal Bayesian classification, we demonstrate superior classification performance for both synthetic and real RNA-Seq datasets. A tutorial video and Python source code is available under an open source license at http://bit.ly/1gimnss. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12859-014-0401-3) contains supplementary material, which is available to authorized users
The Design and Validation of the Quantum Mechanics Conceptual Survey
The Quantum Mechanics Conceptual Survey (QMCS) is a 12-question survey of
students' conceptual understanding of quantum mechanics. It is intended to be
used to measure the relative effectiveness of different instructional methods
in modern physics courses. In this paper we describe the design and validation
of the survey, a process that included observations of students, a review of
previous literature and textbooks and syllabi, faculty and student interviews,
and statistical analysis. We also discuss issues in the development of specific
questions, which may be useful both for instructors who wish to use the QMCS in
their classes and for researchers who wish to conduct further research of
student understanding of quantum mechanics. The QMCS has been most thoroughly
tested in, and is most appropriate for assessment of (as a posttest only),
sophomore-level modern physics courses. We also describe testing with students
in junior quantum courses and graduate quantum courses, from which we conclude
that the QMCS may be appropriate for assessing junior quantum courses, but is
not appropriate for assessing graduate courses. One surprising result of our
faculty interviews is a lack of faculty consensus on what topics should be
taught in modern physics, which has made designing a test that is valued by a
majority of physics faculty more difficult than expected.Comment: Submitted to Physical Review Special Topics: Physics Education
Researc
Global silicate weathering flux over-estimated because of sediment-water cation exchange
Rivers carry the dissolved and solid products of silicate mineral
weathering, a process that removes CO2 from the atmosphere and
provides a key negative climate feedback over geological timescales.
Here we show that in some river systems, a reactive exchange pool
on river suspended particulate matter, bonded weakly to mineral
surfaces, increases the mobile cation flux by 50%. The chemistry
of both river waters and the exchange pool demonstrate exchange
equilibrium, confirmed by Sr isotopes. Global silicate weathering
fluxes are calculated based on riverine dissolved sodium (Na+) from
silicate minerals. The large exchange pool supplies Na+ of non-
silicate origin to the dissolved load, especially in catchments with
widespread marine sediments, or where rocks have equilibrated with
saline basement fluids. We quantify this by comparing the riverine
sediment exchange pool and river water chemistry. In some basins,
cation exchange could account for the majority of sodium in the
river water, significantly reducing estimates of silicate weathering.
At a global scale, we demonstrate that silicate weathering fluxes
are over-estimated by 12-28%. This over-estimation is greatest in
regions of high erosion and high sediment loads where the negative
climate feedback has a maximum sensitivity to chemical weathering
reactions. In the context of other recent findings that reduce the
net CO2 consumption through chemical weathering, the magnitude
of the continental silicate weathering fluxes and its implications for
solid Earth CO2 degassing fluxes needs to be further investigated.NER
L-Edge Spectroscopy of Dilute, Radiation-Sensitive Systems Using a Transition-Edge-Sensor Array
We present X-ray absorption spectroscopy and resonant inelastic X-ray
scattering (RIXS) measurements on the iron L-edge of 0.5 mM aqueous
ferricyanide. These measurements demonstrate the ability of high-throughput
transition-edge-sensor (TES) spectrometers to access the rich soft X-ray
(100-2000eV) spectroscopy regime for dilute and radiation-sensitive samples.
Our low-concentration data are in agreement with high-concentration
measurements recorded by conventional grating-based spectrometers. These
results show that soft X-ray RIXS spectroscopy acquired by high-throughput TES
spectrometers can be used to study the local electronic structure of dilute
metal-centered complexes relevant to biology, chemistry and catalysis. In
particular, TES spectrometers have a unique ability to characterize frozen
solutions of radiation- and temperature-sensitive samples.Comment: 19 pages, 4 figure
Network analysis identifies proinflammatory plasma cell polarization for secretion of ISG15 in human autoimmunity
Plasma cells (PCs) as effectors of humoral immunity produce Igs to match pathogenic insult. Emerging data suggest more diverse roles exist for PCs as regulators of immune and inflammatory responses via secretion of factors other than Igs. The extent to which such responses are preprogrammed in B-lineage cells or can be induced in PCs by the microenvironment is unknown. In this study, we dissect the impact of IFNs on the regulatory networks of human PCs. We show that core PC programs are unaffected, whereas PCs respond to IFNs with distinctive transcriptional responses. The IFN-stimulated gene 15 (ISG15) system emerges as a major transcriptional output induced in a sustained fashion by IFN-α in PCs and linked both to intracellular conjugation and ISG15 secretion. This leads to the identification of ISG15-secreting plasmablasts/PCs in patients with active systemic lupus erythematosus. Thus, ISG15-secreting PCs represent a distinct proinflammatory PC subset providing an Ig-independent mechanism of PC action in human autoimmunity
Multimetallic Arrays: Bi-, Tri-, Tetra-, and Hexametallic Complexes Based on Gold(I) and Gold(III) and the Surface Functionalization of Gold Nanoparticles with Transition Metals
Low-frequency cortical activity is a neuromodulatory target that tracks recovery after stroke.
Recent work has highlighted the importance of transient low-frequency oscillatory (LFO; <4 Hz) activity in the healthy primary motor cortex during skilled upper-limb tasks. These brief bouts of oscillatory activity may establish the timing or sequencing of motor actions. Here, we show that LFOs track motor recovery post-stroke and can be a physiological target for neuromodulation. In rodents, we found that reach-related LFOs, as measured in both the local field potential and the related spiking activity, were diminished after stroke and that spontaneous recovery was closely correlated with their restoration in the perilesional cortex. Sensorimotor LFOs were also diminished in a human subject with chronic disability after stroke in contrast to two non-stroke subjects who demonstrated robust LFOs. Therapeutic delivery of electrical stimulation time-locked to the expected onset of LFOs was found to significantly improve skilled reaching in stroke animals. Together, our results suggest that restoration or modulation of cortical oscillatory dynamics is important for the recovery of upper-limb function and that they may serve as a novel target for clinical neuromodulation
IMPACT OF TRANSITIONING FROM SPECT TO PET ON MYOCARDIAL ISCHEMIA DETECTION: EXPERIENCE FROM A HIGH VOLUME “REAL WORLD” PRACTICE
The Landsat Data Continuity Mission Operational Land Imager (OLI) Sensor
The Landsat Data Continuity Mission (LDCM) is being developed by NASA and USGS and is currently planned for launch in January 2013 [1]. Once on-orbit and checked out, it will be operated by USGS and officially named Landsat-8. Two sensors will be on LDCM: the Operational Land Imager (OLI), which has been built and delivered by Ball Aerospace & Technology Corp (BATC) and the Thermal Infrared Sensor (TIRS)[2], currently being built and tested at Goddard Space Flight Center (GSFC) with a planned delivery of Winter 2012. The OLI covers the Visible, Near-IR (NIR) and Short-Wave Infrared (SWIR) parts of the spectrum; TIRS covers the Thermal Infrared (TIR). This paper discusses only the OLI instrument and its pre-launch characterization; a companion paper covers TIRS
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