72 research outputs found
Ferroelectricity in strained CaSrTiO from first principles
We present a density functional theory investigation of strained
CaSrTiO. We have determined the structure and polarization
for a number of arrangements of Ca and Sr in a 222 supercell.
The a and b lattice vectors are strained to match the lattice constants of the
rotated Si(001) face. To set the context for the CSTO study, we also include
simulations of the Si(001) constrained structures for CaTiO and SrTiO.
Our primary findings are that all CaSrTiO structures
examined except one are ferroelectric, exhibiting polarizations ranging from
0.08 C/m for the lowest energy configuration to about 0.26 C/m for the
higher energy configurations. We find that the configurations with larger
polarizations have lower c/a ratios. The net polarization of the cell is the
result of Ti-O ferroelectric displacements regulated by A-site cations.Comment: 13 pages, 4 figure
The chemistry of La on the Si(001) surface
This paper reports state-of-the-art electronic structure calculations of La
adsorption on the Si(001) surface. We predict La chains in the low coverage
limit, which condense in a stable phase at a coverage of 1/5 monolayer. At 1/3
monolayer we predict a chemically rather inert, stable phase. La changes its
oxidation state from La(3+) at lower coverages to La(2+) at coverages beyond
1/3 monolayer. In the latter oxidation state, one electron resides in a state
with a considerable contribution from La-d and f states.Comment: 10 pages, 13 figures, 3 table
Commissioning of NASA's 3rd Generation Tracking and Data Relay Satellites (TDRS KLM)
In the summer of 2017, the third and final spacecraft of the 3rd generation of the Tracking and Data Relay Satellites (TDRS) launched aboard an Atlas V rocket from Complex 41 on the Eastern Test Range. Finishing final testing and integration in the first quarter of 2018, the TDRS-M communication and navigation satellite completes a constellation that began service in the early 1980s. The 3rd generation of spacecraft, TDRS-K, L, and M, not only provided beneficial systems engineering lessons in handling anomalous Radio Frequency and Doppler interference as well as integrating new spacecraft into an aging ground support infrastructure, but also supplies NASA with a valuable test bed for new operational concepts and technologies useful in defining the future architecture of the NASA Space Network. This paper presents an overview of the TDRS-K, L, and M missions, including transfer orbit, Level 5 bus and payload testing, and finally NASA-led Level 6 testing, which includes active TDRS System (TDRSS) users. Highlights include relevant testing results, commissioning challenges, and lessons learned. The final discussion includes a brief overview of future NASA communication and navigation technologies and network architectures
Color Bimodality in M87 Globular Clusters
We present an analysis of a 50 orbit HST ACS observation of the M87 globular
cluster system. We use the extraordinary depth of this dataset to test whether
the colors and magnitudes show evidence for a mass-metallicity relation in
globular cluster populations. We find only a weak or absent relation between
the colors and magnitudes of the metal poor subpopulation of globular clusters.
The weakness or absence of a color-magnitude relation is established over a
wide range in luminosity from to , encompassing most of the
M87 globular clusters. The constancy of the colors of the metal-poor
subpopulation seen in our 50 orbit observation is in contrast to suggestions
from single orbit ACS data that the metal-poor globular clusters in M87 and
several other galaxies show a "blue tilt." The formal best fit for the
mass-metallicity relation for the metal-poor subpopulation in our much deeper
data is . Our analysis of these data also shows a
possible small "red tilt" in the metal-rich globular cluster subpopulation.
While either of these small tilts may be real, they may also illustrate the
limit to which mass-metallicity relations can be determined, even in such
extraordinarily deep data. We specifically test for a wide range of systematic
effects and find that while small tilts cannot be confirmed or rejected, the
data place a strong upper limit to any tilt of . This upper
limit is much smaller than some earlier claims from single orbit data, and
strongly limits self-enrichment within globular clusters. This mass-metallicity
relation for globular clusters is also shallower than the relation for
galaxies, suggesting that the formation mechanisms for these two types of
objects are different.Comment: 25 pages, 3 figures. Accepted for publication in the Astrophysical
Journa
Neoadjuvant chemoradiation compared to neoadjuvant radiation alone and surgery alone for Stage II and III soft tissue sarcoma of the extremities
<p>Abstract</p> <p>Background</p> <p>Neoadjuvant chemoradiation (NCR) prior to resection of extremity soft tissue sarcoma (STS) has been studied, but data are limited. We present outcomes with NCR using a variety of chemotherapy regimens compared to neoadjuvant radiation without chemotherapy (NR) and surgery alone (SA).</p> <p>Methods</p> <p>We conducted a retrospective chart review of 112 cases.</p> <p>Results</p> <p>Treatments included SA (36 patients), NCR (39 patients), and NR (37 patients). NCR did not improve the rate of margin-negative resections over SA or NR. Loco-regional relapse-free survival, distant metastases-free survival, and overall survival (OS) were not different among the treatment groups. Patients with relapsed disease (OR 11.6; p = 0.01), and tumor size greater than 5 cm (OR 9.4; p = 0.01) were more likely to have a loco-regional recurrence on logistic regression analysis. Significantly increased OS was found among NCR-treated patients with tumors greater than 5 cm compared to SA (3 year OS 69 vs. 40%; p = 0.03). Wound complication rates were higher after NCR compared to SA (50 vs. 11%; p = 0.003) but not compared to NR (p = 0.36). Wet desquamation was the most common adverse event of NCR.</p> <p>Conclusions</p> <p>NCR and NR are acceptable strategies for patients with STS. NCR is well-tolerated, but not clearly superior to NR.</p
The interface between silicon and a high-k oxide
The ability to follow Moore's Law has been the basis of the tremendous
success of the semiconductor industry in the past decades. To date, the
greatest challenge for device scaling is the required replacement of silicon
dioxide-based gate oxides by high-k oxides in transistors. Around 2010 high-k
oxides are required to have an atomically defined interface with silicon
without any interfacial SiO2 layer. The first clean interface between silicon
and a high-K oxide has been demonstrated by McKee et al. Nevertheless, the
interfacial structure is still under debate. Here we report on first-principles
calculations of the formation of the interface between silicon and SrTiO3 and
its atomic structure. Based on insights into how the chemical environment
affects the interface, a way to engineer seemingly intangible electrical
properties to meet technological requirements is outlined. The interface
structure and its chemistry provide guidance for the selection process of other
high-k gate oxides and for controlling their growth. Our study also shows that
atomic control of the interfacial structure can dramatically improve the
electronic properties of the interface. The interface presented here serves as
a model for a variety of other interfaces between high-k oxides and silicon.Comment: 10 pages, 2 figures (one color
Economic and environmental assessment of seed and rhizome propagated Miscanthus in the UK
Growth in planted areas of Miscanthus for biomass in Europe has stagnated since 2010 due to technical challenges, economic barriers and environmental concerns. These limitations need to be overcome before biomass production from Miscanthus can expand to several million hectares. In this paper we consider the economic and environmental effects of introducing seed based hybrids as an alternative to clonal M. x giganteus (Mxg). The impact of seed based propagation and novel agronomy was compared with current Mxg cultivation and used in ten commercially relevant, field scale experiments planted between 2012 and 2014 in the UK, Germany and Ukraine. Economic and greenhouse gas (GHG) emissions costs were quantified for the following production chain: propagation, establishment, harvest, transportation, storage and fuel preparation (excluding soil carbon changes). The production and utilisation efficiency of seed and rhizome propagation were compared. Results show that new hybrid seed propagation significantly reduces establishment cost to below ?900 ha-1. Calculated GHG emission costs for the seeds established via plugs, though relatively small, was higher than rhizomes because fossil fuels were assumed to heat glasshouses for raising seedling plugs (5.3 and 1.5 kg CO2 eq. C Mg (dry matter (DM))-1), respectively. Plastic mulch film reduced establishment time, improving crop economics. The breakeven yield was calculated to be 6 Mg DM ha-1 y-1, which is about half average UK yield for Mxg; with newer seeded hybrids reaching 16 Mg DM ha-1 in second year UK trials. These combined improvements will significantly increase crop profitability. The trade-offs between costs of production for the preparation of different feedstock formats show that bales are the best option for direct firing with the lowest transport costs (?0.04 Mg -1 km-1) and easy on-farm storage. However if pelleted fuel is required then chip harvesting is more economic. We show how current seed based propagation methods can increase the rate at which Miscanthus can be scaled up; ~x100 those of current rhizome propagation. These rapid ramp rates for biomass production are required to deliver a scalable and economic Miscanthus biomass fuel whose GHG emissions are ~1/20th those of natural gas per unit of heatpublishersversionPeer reviewe
The SLUGGS Survey: Calcium Triplet-based Spectroscopic Metallicities for Over 900 Globular Clusters
Although the colour distribution of globular clusters in massive galaxies is
well known to be bimodal, the spectroscopic metallicity distribution has been
measured in only a few galaxies. After redefining the calcium triplet
index-metallicity relation, we use our relation to derive the metallicity of
903 globular clusters in 11 early-type galaxies. This is the largest sample of
spectroscopic globular cluster metallicities yet assembled. We compare these
metallicities with those derived from Lick indices finding good agreement. In 6
of the 8 galaxies with sufficient numbers of high quality spectra we find
bimodality in the spectroscopic metallicity distribution. Our results imply
that most massive early-type galaxies have bimodal metallicity, as well as
colour, distributions. This bimodality suggests that most massive galaxies
early-type galaxies experienced two periods of star formation.Comment: 23 pages, 13 figures. Accepted for publication in MNRAS. For more
information about the SLUGGS Survey please see http://sluggs.swin.edu.a
Breeding Strategies to Improve Miscanthus as a Sustainable Source of Biomass for Bioenergy and Biorenewable Products
Antibody agonists trigger immune receptor signaling through local exclusion of receptor-type protein tyrosine phosphatases
Antibodies can block immune receptor engagement or trigger the receptor machinery to initiate signaling. We hypothesized that antibody agonists trigger signaling by sterically excluding large receptor-type protein tyrosine phosphatases (RPTPs) such as CD45 from sites of receptor engagement. An agonist targeting the costimulatory receptor CD28 produced signals that depended on antibody immobilization and were sensitive to the sizes of the receptor, the RPTPs, and the antibody itself. Although both the agonist and a non-agonistic anti-CD28 antibody locally excluded CD45, the agonistic antibody was more effective. An anti–PD-1 antibody that bound membrane-proximally excluded CD45, triggered SHP2 phosphatase recruitment, and suppressed systemic lupus erythematosus and delayed-type hypersensitivity in experimental models. Paradoxically, nivolumab and pembrolizumab, anti–PD-1 blocking antibodies used clinically, also excluded CD45 and were agonistic in certain settings. Reducing these agonistic effects using antibody engineering improved PD-1 blockade. These findings establish a framework for developing new and improved therapies for autoimmunity and cancer
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