4,504 research outputs found
Surface composition and taxonomic classification of a group of near-Earth and Mars-crossing asteroids
In the past, constraining the surface composition of near-Earth asteroids
(NEAs) has been difficult due to the lack of high quality near-IR spectral data
(0.7-2.5 microns) that contain mineralogically diagnostic absorption bands.
Here we present visible (0.43-0.95 microns) and near-infrared (0.7-2.5 microns)
spectra of nine NEAs and five Mars-crossing asteroids (MCs). The studied NEAs
are: 4055 Magellan, 19764 (2000 NF5), 89830 (2002 CE), 138404 (2000 HA24),
143381 (2003 BC21), 159609 (2002 AQ3), 164121 (2003 YT1), 241662 (2000 KO44)
and 2007 ML13. The studied MCs are: 1656 Suomi, 2577 Litva, 5407 (1992 AX),
22449 Ottijeff and 47035 (1998 WS). The observations were conducted with the
NTT at La Silla, Chile, the 2.2 m telescope at Calar Alto, Spain, and the IRTF
on Mauna Kea, Hawai'i. The taxonomic classification (Bus system) of asteroids
showed that all observed MC asteroids belong to the S-complex, including the S,
Sr and Sl classes. Seven of the NEAs belong to the S-complex, including the S,
Sa, Sk and Sl classes, and two NEAs were classified as V-types. The
classification of the NEA 164121 (2003 YT1) as a V-type was made on the basis
of its near-infrared spectrum since no visible spectrum is available for this
asteroid. A mineralogical analysis was performed on six of the asteroids (those
for which near-IR spectra were obtained or previously available). We found that
three asteroids (241662 (2000 KO44), 19764 (2000 NF5), 138404 (2000 HA24)) have
mafic silicate compositions consistent with ordinary chondrites, while three
others (4055 Magellan, 164121 (2003 YT1), 5407 (1992 AX)) are
pyroxene-dominated basaltic achondrite assemblages. In the case of 5407 (1992
AX) we found that its basaltic surface composition contrasts its taxonomic
classification as a S-type.Comment: 23 pages, 10 figures, 3 tables, accepted for publication in Icaru
Composition of Near-Earth Asteroid (4179) Toutatis
Surface composition of near-Earth asteroid (4179) Toutatis is consistent with
an undifferentiated L-chondrite composition. This is inconsistent with early
observations that suggested high pyroxene iron content and a differentiated
body.Comment: 15 pages, 2 figures 1 table. Accepted for publication in Icaru
Phase Angle Effects on 3-micron Absorption Band on Ceres: Implications for Dawn Mission
Phase angle-induced spectral effects are important to characterize since they
affect spectral band parameters such as band depth and band center, and
therefore skew mineralogical interpretations of planetary bodies via
reflectance spectroscopy. Dwarf planet (1) Ceres is the next target of NASA's
Dawn mission, which is expected to arrive in March 2015. The visible and
near-infrared mapping spectrometer (VIR) onboard Dawn has the spatial and
spectral range to characterize the surface between 0.25-5.0 microns. Ceres has
an absorption feature at 3.0 microns due to hydroxyl- and/or water-bearing
minerals (e.g. Lebofsky et al. 1981, Rivkin et al. 2003). We analyzed phase
angle-induced spectral effects on the 3-micron absorption band on Ceres using
spectra measured with the long-wavelength cross-dispersed (LXD: 1.9-4.2
microns) mode of the SpeX spectrograph/imager at the NASA Infrared Telescope
Facility (IRTF). Ceres LXD spectra were measured at different phase angles
ranging from 0.7o to 22o. We found that the band center slightly increases from
3.06 microns at lower phase angles (0.7o and 6o) to 3.07 microns at higher
phase angles (11 o and 22o), the band depth decreases by ~20% from lower phase
angles to higher phase angles, and the band area decreases by ~25% from lower
phase angles to higher phase angles. Our results will have implications for
constraining the abundance of OH on the surface of Ceres from VIR spectral
data, which will be acquired by Dawn starting spring 2015.Comment: 12 pages, 1 figure, 2 table
Effect of the Inlet Gas Humidification on PEMFC Behavior and Current Density Distribution
Water management represents one of the main challenges in the
design and operation of PEMFCs. The influence of inlet gas
humidification on cell performance is analyzed using in-situ
diagnostic tools, such as cyclic voltammetry and segmented cell
current density measurements, supported by post-mortem ex-situ
investigations. Particular attention is paid to the effect of low
humidity conditions in both cathode and anode, under which the
cell is observed to suffer severe voltage decline. A simple onedimensional
water balance model is proposed to contribute to the
understanding of the various operation regimes observed in
PEMFCs under medium-to-low humidification conditions
MODELING THE EFFECT OF THE INLETGAS HUMIDIFICATION ON PEMFC BEHAVIOR AND CURRENT DENSITYDISTRIBUTION
Exploring Exogenic Sources for the Olivine on Asteroid (4) Vesta
The detection of olivine on Vesta is interesting because it may provide
critical insights into planetary differentiation early in our Solar System's
history. Ground-based and Hubble Space Telescope (HST) observations of asteroid
(4) Vesta have suggested the presence of olivine on the surface. These
observations were reinforced by the discovery of olivine-rich HED meteorites
from Vesta in recent years. However, analysis of data from NASA's Dawn
spacecraft has shown that this olivine-bearing unit is actually impact melt in
the ejecta of Oppia crater. The lack of widespread mantle olivine, exposed
during the formation of the 19 km deep Rheasilvia basin on Vesta's South Pole,
further complicated this picture. Ammannito et al., (2013a) reported the
discovery of local scale olivine-rich units in the form of excavated material
from the mantle using the Visible and InfraRed spectrometer (VIR) on Dawn. Here
we explore alternative sources for the olivine in the northern hemisphere of
Vesta by reanalyzing the data from the VIR instrument using laboratory spectral
measurements of meteorites. We suggest that these olivine exposures could be
explained by the delivery of olivine-rich exogenic material. Based on our
spectral band parameters analysis, the lack of correlation between the location
of these olivine-rich terrains and possible mantle-excavating events, and
supported by observations of HED meteorites, we propose that a probable source
for olivine seen in the northern hemisphere are remnants of impactors made of
olivine-rich meteorites. Best match suggests these units are HED material mixed
with either ordinary chondrites, or with some olivine-dominated meteorites such
as R-chondrites.Comment: 62 pages, 12 figures, 4 tables; Icarus, Available online 30 January
2015, ISSN 0019-1035, http://dx.doi.org/10.1016/j.icarus.2015.01.01
Lithologic Mapping of HED Terrains on Vesta using Dawn Framing Camera Color Data
The surface composition of Vesta, the most massive intact basaltic object in
the asteroid belt, is interesting because it provides us with an insight into
magmatic differentiation of planetesimals that eventually coalesced to form the
terrestrial planets. The distribution of lithologic and compositional units on
the surface of Vesta provides important constraints on its petrologic
evolution, impact history and its relationship with Vestoids and
howardite-eucrite-diogenite (HED) meteorites. Using color parameters (band tilt
and band curvature) originally developed for analyzing lunar data, we have
identified and mapped HED terrains on Vesta in Dawn Framing Camera (FC) color
data. The average color spectrum of Vesta is identical to that of howardite
regions, suggesting an extensive mixing of surface regolith due to impact
gardening over the course of solar system history. Our results confirm the
hemispherical dichotomy (east-west and north-south) in albedo/color/composition
that has been observed by earlier studies. The presence of diogenite-rich
material in the southern hemisphere suggests that it was excavated during the
formation of the Rheasilvia and Veneneia basins. Our lithologic mapping of HED
regions provides direct evidence for magmatic evolution of Vesta with diogenite
units in Rheasilvia forming the lower crust of a differentiated object.Comment: Accepted for Meteoritics and Planetary Science special issue for
Composition of Vesta/Dawn Missio
Biomarker and Histopathology Evaluation of Patients with Recurrent Glioblastoma Treated with Galunisertib, Lomustine, or the Combination of Galunisertib and Lomustine
Galunisertib, a Transforming growth factor-βRI (TGF-βRI) kinase inhibitor,
blocks TGF-β-mediated tumor growth in glioblastoma. In a three-arm study of
galunisertib (300 mg/day) monotherapy (intermittent dosing; each cycle =14
days on/14 days off), lomustine monotherapy, and galunisertib plus lomustine
therapy, baseline tumor tissue was evaluated to identify markers associated
with tumor stage (e.g., histopathology, Ki67, glial fibrillary acidic protein)
and TGF-β-related signaling (e.g., pSMAD2). Other pharmacodynamic assessments
included chemokine, cytokine, and T cell subsets alterations. 158 patients
were randomized to galunisertib plus lomustine (n = 79), galunisertib (n = 39)
and placebo+lomustine (n = 40). In 127 of these patients, tissue was adequate
for central pathology review and biomarker work. Isocitrate dehydrogenase
(IDH1) negative glioblastoma patients with baseline pSMAD2+ in cytoplasm had
median overall survival (OS) 9.5 months vs. 6.9 months for patients with no
tumor pSMAD2 expression (p = 0.4574). Eight patients were IDH1 R132H+ and had
a median OS of 10.4 months compared to 6.9 months for patients with negative
IDH1 R132H (p = 0.5452). IDH1 status was associated with numerically higher
plasma macrophage-derived chemokine (MDC/CCL22), higher whole blood FOXP3, and
reduced tumor CD3+ T cell counts. Compared to the baseline, treatment with
galunisertib monotherapy preserved CD4+ T cell counts, eosinophils,
lymphocytes, and the CD4/CD8 ratio. The T-regulatory cell compartment was
associated with better OS with MDC/CCL22 as a prominent prognostic marker.
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Photometric Properties of Ceres from Telescopic Observations using Dawn Framing Camera Color Filters
The dwarf planet Ceres is likely differentiated similar to the terrestrial
planets but with a water/ice dominated mantle and an aqueously altered crust.
Detailed modeling of Ceres' phase function has never been performed to
understand its surface properties. The Dawn spacecraft began orbital science
operations at the dwarf planet in April 2015. We observed Ceres with flight
spares of the seven Dawn Framing Camera color filters mounted on ground-based
telescopes over the course of three years to model its phase function versus
wavelength. Our analysis shows that the modeled geometric albedos derived from
both the IAU HG model and the Hapke model are consistent with a flat and
featureless spectrum of Ceres, although the values are ~10% higher than
previous measurements. Our models also suggest a wavelength dependence of
Ceres' phase function. The IAU G-parameter and the Hapke single-particle phase
function parameter, g, are both consistent with decreasing (shallower) phase
slope with increasing wavelength. Such a wavelength dependence of phase
function is consistent with reddening of spectral slope with increasing phase
angle, or phase-reddening. This phase reddening is consistent with previous
spectra of Ceres obtained at various phase angles archived in the literature,
and consistent with the fact that the modeled geometric albedo spectrum of
Ceres is the bluest of all spectra because it represents the spectrum at 0
degree phase angle. Ground-based FC color filter lightcurve data are consistent
with HST albedo maps confirming that Ceres' lightcurve is dominated by albedo
and not shape. We detected a positive correlation between 1.1-micron absorption
band depth and geometric albedo suggesting brighter areas on Ceres have
absorption bands that are deeper.Comment: 40 pages, 9 figures, 5 tables. Accepted for publication in Icaru
Intramuscular Stimulation of Muscle Afferents Attains Prolonged Tremor Reduction in Essential Tremor Patients
This study proposes and clinically tests intramuscular electrical stimulation below motor threshold to achieve prolonged reduction of wrist flexion/extension tremor in Essential Tremor (ET) patients. The developed system consisted of an intramuscular thin-film electrode structure that included both stimulation and electromyography (EMG) recording electrodes, and a control algorithm for the timing of intramuscular stimulation based on EMG (closed-loop stimulation). Data were recorded from nine ET patients with wrist flexion/extension tremor recruited from the Gregorio Mara\uf1\uf3n Hospital (Madrid, Spain). Patients participated in two experimental sessions comprising: 1) sensory stimulation of wrist flexors/extensors via thin-film multichannel intramuscular electrodes; and 2) surface stimulation of the nerves innervating the same target muscles. For each session, four of these patients underwent random 60-s trials of two stimulation strategies for each target muscle: 1) selective and adaptive timely stimulation (SATS) - based on EMG of the antagonist muscle; and 2) continuous stimulation (CON) of target muscles. Two patients underwent SATS stimulation trials alone while the other three underwent CON stimulation trials alone in each session. Kinematics of wrist, elbow, and shoulder, together with clinical scales, were used to assess tremor before, right after, and 24 h after each session. Intramuscular SATS achieved, on average, 32% acute (during stimulation) tremor reduction on each trial, while continuous stimulation augmented tremorgenic activity. Furthermore, tremor reduction was significantly higher using intramuscular than surface stimulation. Prolonged reduction of tremor amplitude (24 h after the experiment) was observed in four patients. These results showed acute and prolonged (24 h) tremor reduction using a minimally invasive neurostimulation technology based on SATS of primary sensory afferents of wrist muscles. This strategy might open the possibility of an alternative therapeutic approach for ET patients
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