10,101 research outputs found
Concept to standardize space vehicle piggyback experiment modules
Study investigates the use of spent launch vehicle stages and modules to support earth orbital operations and functions after successful completion of the primary mission. Emphasis is placed primarily on determination of those uses that afford the greatest utility with minimum possibility of degradation to the primary mission
Spin Hall effect and Weak Antilocalization in Graphene/Transition Metal Dichalcogenide Heterostructures
We report on a theoretical study of the spin Hall Effect (SHE) and weak
antilocal-ization (WAL) in graphene/transition metal dichalcogenide (TMDC)
heterostructures, computed through efficient real-space quantum transport
methods, and using realistic tight-binding models parametrized from ab initio
calculations. The graphene/WS 2 system is found to maximize spin proximity
effects compared to graphene on MoS 2 , WSe 2 , or MoSe 2 , with a crucial role
played by disorder, given the disappearance of SHE signals in the presence of
strong intervalley scattering. Notably, we found that stronger WAL effects are
concomitant with weaker charge-to-spin conversion efficiency. For further
experimental studies of graphene/TMDC heterostructures, our findings provide
guidelines for reaching the upper limit of spin current formation and for fully
harvesting the potential of two-dimensional materials for spintronic
applications.Comment: This document is the unedited Author's version of a Submitted Work
that was subsequently accepted for publication in Nano Letters,
copyright\c{opyright}American Chemical Society after peer review. To access
the final edited and published work see
http://pubs.acs.org/articlesonrequest/AOR-c2pZ8WnmG7pcF4MIivj
Spin transport in graphene/transition metal dichalcogenide heterostructures
Since its discovery, graphene has been a promising material for spintronics:
its low spin-orbit coupling, negligible hyperfine interaction, and high
electron mobility are obvious advantages for transporting spin information over
long distances. However, such outstanding transport properties also limit the
capability to engineer active spintronics, where strong spin-orbit coupling is
crucial for creating and manipulating spin currents. To this end, transition
metal dichalcogenides, which have larger spin-orbit coupling and good interface
matching, appear to be highly complementary materials for enhancing the
spin-dependent features of graphene while maintaining its superior charge
transport properties. In this review, we present the theoretical framework and
the experiments performed to detect and characterize the spin-orbit coupling
and spin currents in graphene/transition metal dichalcogenide heterostructures.
Specifically, we will concentrate on recent measurements of Hanle precession,
weak antilocalization and the spin Hall effect, and provide a comprehensive
theoretical description of the interconnection between these phenomena.Comment: 21 pages, 11 figures. This document is the unedited Author's version
of a Submitted Work that was subsequently accepted for publication in Nano
Letters, copyright\c{opyright}American Chemical Society after peer review. To
access the final edited and published work see
http://pubs.rsc.org/en/Content/ArticleLanding/2018/CS/C7CS00864
Results of phase change paint thermal mapping test OH46 using the 0.006-scale model 90-0 in the NASA LaRC variable density tunnel
Results of a test conducted in the NASA LaRC Mach 8 variable density tunnel to obtain thermal contours on a 0.006 scale model of the configuration 140B Space Shuttle Orbiter are presented using the phase change paint technique. The model was tested at 25 deg, 30 deg, and 35 deg angle of attack at unit Reynolds numbers ranging from 1.0 through 8.0 million per foot. The model was tested with and without a ventral fin mounted on its bottom centerline. Elevon deflections of 0 deg and 10 deg and bodyflap deflections of 0 and 13.75 deg were investigated
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Innovative Selective Laser Sintering Rapid Manufacturing using Nanotechnology
The objective of this research is to develop an improved nylon 11 (polyamide 11) polymer
with enhanced flame retardancy, thermal, and mechanical properties for selective laser sintering
(SLS) rapid manufacturing (RM). A nanophase was introduced into nylon 11 via twin screw
extrusion to provide improved material properties of the polymer blends. Atofina (now known
as Arkema) RILSAN® nylon 11 injection molding polymer pellets was used with three types of
nanoparticles: chemically modified montmorillonite (MMT) organoclays, nanosilica, and carbon
nanofibers (CNF) to create nylon 11 nanocomposites. Wide angle X-ray diffraction (WAXD)
and transmission electron microscopy (TEM) were used to determine the degree of dispersion.
Fifteen nylon 11 nanocomposites and control nylon 11 were fabricated by injection molding.
Flammability properties (using a cone calorimeter with a radiant flux of 50 kW/m2
) and
mechanical properties such as tensile strength and modulus, flexural modulus, elongation at
break were determined for the nylon 11 nanocomposites and compared with the baseline nylon
11. Based on flammability and mechanical material performance, five polymers including four
nylon 11 nanocomposites and a control nylon 11 were cryogenically ground into fine powders
for SLS RM. SLS specimens were fabricated for flammability, mechanical, and thermal
properties characterization. Nylon 11-CNF nanocomposites exhibited the best overall properties
for this study.Mechanical Engineerin
A balloon-borne imaging gamma-ray telescope
A balloon-borne coded-aperture gamma-ray telescope for galactic and extragalactic astronomy observations is described. The instrument, called Gamma Ray Imaging Payload (GRIP), is designed for measurements in the energy range from 30 keV to 5 MeV with an angular resolution of 0.6 deg over a 20 deg field of view. Distinguishing characteristics of the telescope are a rotating hexagonal coded-aperture mask and a thick NaI scintillation camera. Rotating hexagonal coded-apertures and the development of thick scintillation cameras are discussed
The Progression of β-amyloid Deposition in the Frontal Cortex of the Aged Canine
Brains from 41 aged canines (≥10 years of age) were examined immunohistochemically to characterize the laminar distribution and age-related progression of β-amyloid (Aβ) in frontal cortex. We classified the Aβ patterns into four distinct types. Type I was characterized by small, faint deposits of Aβ in deep cortical layers. Type II consisted of diffuse deposits of Aβ mainly in layers V and VI. Type III had both dense plaques in superficial layers, and diffuse deposits in deep layers. Finally, Type IV had solely dense plaques throughout all layers of cortex. We compared the Aβ distribution pattern between the Old canines (10–15 years, n=22) and the Very Old canines (\u3e15 years, n=19). The Old group primarily had negative staining, or Type I and Type II patterns of amyloid deposition (73%). Conversely, the Very Old group had predominantly Types II, III and IV deposits (89.5%), a difference that was significant (Pβ deposition in canine frontal cortex is a progressive age-related process beginning with diffuse deposits in the deep cortical layers followed by the development of deposits in outer layers. In support of this hypothesis, the deeper layer diffuse plaques in the Very Old group of dogs also contain the largest proportion of β-amyloid with an isomerized aspartic acid residue at position 7, indicating that these deposits had been present for some time. We also observed fiber-like Aβ immunoreactivity within regions of diffuse Aβ deposits. These fibers appeared to be degenerating neurites, which were negative for hyperphosphorylated tau. Therefore, these fibers may represent a very early form of neuritic change that precede tau hyperphosphorylation or develop by an alternative pathway
Odds of Acute Kidney Injury in Patients Receiving Dipeptidyl Peptidase 4 Inhibitors: A National Cohort Study Within the Department of Veterans Affairs
Preclinical and clinical data of dipeptidyl peptidase 4 (DPP‐4) inhibitors have demonstrated discordant data regarding acute kidney injury (AKI). Therefore, we aimed to evaluate the association between DPP‐4 use and AKI. This cohort study utilized data from the Department of Veterans Affairs evaluating patients diagnosed with type 2 (T2) diabetes with a DPP‐4 inhibitor and compared with nondiabetic and diabetic patients. The primary end point is the development of AKI, and statistical analyses were performed to examine the association. DPP‐4 use is associated with a lower odds of AKI compared with diabetics (adjusted odds ratio (OR) = 0.39; 95% confidence interval (CI) = 0.32–0.48) and nondiabetics (OR = 0.64; 95% CI = 0.52–0.79). DPP‐4 use in patients with T2 diabetes mellitus is associated with lower odds of AKI within 120 days compared with nondiabetic and diabetic controls when adjusting for study covariates
Dissolution in a field
We study the dissolution of a solid by continuous injection of reactive
``acid'' particles at a single point, with the reactive particles undergoing
biased diffusion in the dissolved region. When acid encounters the substrate
material, both an acid particle and a unit of the material disappear. We find
that the lengths of the dissolved cavity parallel and perpendicular to the bias
grow as t^{2/(d+1)} and t^{1/(d+1)}, respectively, in d-dimensions, while the
number of reactive particles within the cavity grows as t^{2/(d+1)}. We also
obtain the exact density profile of the reactive particles and the relation
between this profile and the motion of the dissolution boundary. The extension
to variable acid strength is also discussed.Comment: 6 pages, 6 figures, 2-column format, for submission to PR
The Association Between Phosphodiesterase-5 Inhibitors and Colorectal Cancer in a National Cohort of Patients
INTRODUCTION: To examine the association between phosphodiesterase-5 (PDE-5) inhibitor use and incidence of colorectal cancer among patients with erectile dysfunction treated in the Veterans Affairs (VA) Healthcare System. METHODS: A retrospective cohort study using the Veterans Affairs Informatics and Computing Infrastructure was conducted, with data spanning January 2001-December 2016. Patients were followed up from index until (i) the first diagnosis of colorectal cancer, (ii) death, or (iii) the end of study period. Statistical analyses evaluated demographics and baseline characteristics between cohorts (PDE-5 exposed or not) and the effect of additional dosages of each specific PDE-5 inhibitor using adjusted multivariate Cox proportional hazards models. RESULTS: A total of 221,538 patients met the study inclusion criteria, 192,691 patients in the PDE-5 cohort and 29,227 patients in the never use PDE-5 cohort. The multivariate Cox proportional hazards model results revealed that the those who had any exposure to a PDE-5 inhibitor have an 18% lower hazard of colorectal cancer (adjusted hazard ratio [HR] = 0.816, 95% confidence interval [CI] = 0.754-0.882). For each additional 100-mg dosage of sildenafil and 10-mg dosage of tadalafil, the hazard of colorectal cancer is reduced by 2.4% (adjusted HR = 0.976, 95% CI = 0.973-0.979) and 1.7% (adjusted HR = 0.983, 95% CI = 0.972-0.996), respectively. DISCUSSION: PDE-5 inhibitor usage in patients with erectile dysfunction is associated with a lower hazard of colorectal cancer compared with patients not exposed to PDE-5 inhibitors
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