1,173 research outputs found
Characterizing HMX/AP Cocrystal Propellant Through Planar Laser Induced Fluorescence
Energetic cocrystals, or energetic materials that consist of two or more components that form a unique crystalline structure with unique properties, are currently being investigated as a possible method for decreasing the sensitivity of high energy density explosives for use in powerful solid composite propellants. Fuels more powerful than those in current use have not been practical because of their increased safety hazard due to higher sensitivity to being ignited. This has been one of the barriers that has prevented solid composite propellants from seeing significant improvements in performance. This study is an attempt to characterize a cocrystal of HMX and ammonium perchlorate (AP) of 2:3 molar mass ratio. The cocrystal was compared to the equivalent physical mix and baseline propellants of HMX and AP. Planar laser induced fluorescence (PLIF) was performed to measure hydroxyl (OH) concentrations in the propellantsâ flames. It appeared that the flame structure of the cocrystal was very similar to that of HMX, as well as the distribution of OH concentrations around the flame. The results were inconclusive, and it is believed that the cocrystalâs constituents were not sufficiently bonded at the molecular level; thus, the cocrystal was instead more a mixture of smaller individual crystals of HMX and AP. Future research could include cocrystals created by varying methods, and perform cyano (CN) PLIF to characterize these cocrystals, which may display a better defined region of interest in the flame that can be more closely studied and answer more questions
High resolution clustering of Salmonella enterica serovar Montevideo strains using a next-generation sequencing approach
<p>Abstract</p> <p>Background</p> <p>Next-Generation Sequencing (NGS) is increasingly being used as a molecular epidemiologic tool for discerning ancestry and traceback of the most complicated, difficult to resolve bacterial pathogens. Making a linkage between possible food sources and clinical isolates requires distinguishing the suspected pathogen from an environmental background and placing the variation observed into the wider context of variation occurring within a serovar and among other closely related foodborne pathogens. Equally important is the need to validate these high resolution molecular tools for use in molecular epidemiologic traceback. Such efforts include the examination of strain cluster stability as well as the cumulative genetic effects of sub-culturing on these clusters. Numerous isolates of <it>S</it>. Montevideo were shot-gun sequenced including diverse lineage representatives as well as numerous replicate clones to determine how much variability is due to bias, sequencing error, and or the culturing of isolates. All new draft genomes were compared to 34 <it>S</it>. Montevideo isolates previously published during an NGS-based molecular epidemiological case study.</p> <p>Results</p> <p>Intraserovar lineages of <it>S</it>. Montevideo differ by thousands of SNPs, that are only slightly less than the number of SNPs observed between <it>S</it>. Montevideo and other distinct serovars. Much less variability was discovered within an individual <it>S</it>. Montevideo clade implicated in a recent foodborne outbreak as well as among individual NGS replicates. These findings were similar to previous reports documenting homopolymeric and deletion error rates with the Roche 454 GS Titanium technology. In no case, however, did variability associated with sequencing methods or sample preparations create inconsistencies with our current phylogenetic results or the subsequent molecular epidemiological evidence gleaned from these data.</p> <p>Conclusions</p> <p>Implementation of a validated pipeline for NGS data acquisition and analysis provides highly reproducible results that are stable and predictable for molecular epidemiological applications. When draft genomes are collected at 15Ă-20Ă coverage and passed through a quality filter as part of a data analysis pipeline, including sub-passaged replicates defined by a few SNPs, they can be accurately placed in a phylogenetic context. This reproducibility applies to all levels within and between serovars of <it>Salmonella </it>suggesting that investigators using these methods can have confidence in their conclusions.</p
Half-Metallic Graphene Nanoribbons
Electrical current can be completely spin polarized in a class of materials
known as half-metals, as a result of the coexistence of metallic nature for
electrons with one spin orientation and insulating for electrons with the
other. Such asymmetric electronic states for the different spins have been
predicted for some ferromagnetic metals - for example, the Heusler compounds-
and were first observed in a manganese perovskite. In view of the potential for
use of this property in realizing spin-based electronics, substantial efforts
have been made to search for half-metallic materials. However, organic
materials have hardly been investigated in this context even though
carbon-based nanostructures hold significant promise for future electronic
device. Here we predict half-metallicity in nanometre-scale graphene ribbons by
using first-principles calculations. We show that this phenomenon is realizable
if in-plane homogeneous electric fields are applied across the zigzag-shaped
edges of the graphene nanoribbons, and that their magnetic property can be
controlled by the external electric fields. The results are not only of
scientific interests in the interplay between electric fields and electronic
spin degree of freedom in solids but may also open a new path to explore
spintronics at nanometre scale, based on graphene
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Model Documentation for the MiniCAM
The MiniCAM, short for the Mini-Climate Assessment Model, is an integrated assessment model of moderate complexity focused on energy and agriculture sectors. The model produces emissions of greenhouse gases (carbon dioxide, methane and nitrous oxide) and other radiatively important substances such as sulfur dioxide. Through incorporation of the simple climate model MAGICC, the consequences of these emissions for climate change and sea-level rise can be examined. The MiniCAM is designed to be fast and flexible
Fermion correlators in non-abelian holographic superconductors
We consider fermion correlators in non-abelian holographic superconductors.
The spectral function of the fermions exhibits several interesting features
such as support in displaced Dirac cones and an asymmetric distribution of
normal modes. These features are compared to similar ones observed in angle
resolved photoemission experiments on high T_c superconductors. Along the way
we elucidate some properties of p-wave superconductors in AdS_4 and discuss the
construction of SO(4) superconductors.Comment: 49 pages, 11 figure
Experimentally Engineering the Edge Termination of Graphene Nanoribbons
The edges of graphene nanoribbons (GNRs) have attracted much interest due to
their potentially strong influence on GNR electronic and magnetic properties.
Here we report the ability to engineer the microscopic edge termination of high
quality GNRs via hydrogen plasma etching. Using a combination of
high-resolution scanning tunneling microscopy and first-principles
calculations, we have determined the exact atomic structure of plasma-etched
GNR edges and established the chemical nature of terminating functional groups
for zigzag, armchair and chiral edge orientations. We find that the edges of
hydrogen-plasma-etched GNRs are generally flat, free of structural
reconstructions and are terminated by hydrogen atoms with no rehybridization of
the outermost carbon edge atoms. Both zigzag and chiral edges show the presence
of edge states.Comment: 16+9 pages, 3+4 figure
Veliparib in Combination with Carboplatin and Etoposide in Patients with Treatment-Naive Extensive-Stage Small Cell Lung Cancer:A Phase 2 Randomized Study
Purpose: This study investigated the efficacy and safety of oral PARP inhibitor veliparib, plus carboplatin and etoposide in patients with treatment-naive, extensive-stage small cell lung cancer (ED-SCLC). Patients and Methods: Patients were randomized 1:1:1 to veliparib [240 mg twice daily (BID) for 14 days] plus chemotherapy followed by veliparib maintenance (400 mg BID; veliparib throughout), veliparib plus chemotherapy followed by placebo (veliparib combination only), or placebo plus chemotherapy followed by placebo (control). Patients received 4-6 cycles of combination therapy, then maintenance until unacceptable toxicity/progression. The primary endpoint was progression-free survival (PFS) with veliparib throughout versus control. Results: Overall (N = 181), PFS was improved with veliparib throughout versus control [hazard ratio (HR), 0.67; 80% confidence interval (CI), 0.50-0.88; P = 0.059]; median PFS was 5.8 and 5.6 months, respectively. There was a trend toward improved PFS with veliparib throughout versus control in SLFN11-positive patients (HR, 0.6; 80% CI, 0.36-0.97). Median overall survival (OS) was 10.1 versus 12.4 months in the veliparib throughout and control arms, respectively (HR, 1.43; 80% CI, 1.09-1.88). Grade 3/4 adverse events were experienced by 82%, 88%, and 68% of patients in the veliparib throughout, veliparib combination-only and control arms, most commonly hematologic. Conclusions: Veliparib plus platinum chemotherapy followed by veliparib maintenance demonstrated improved PFS as first-line treatment for ED-SCLC with an acceptable safety profile, but there was no corresponding benefit in OS. Further investigation is warranted to define the role of biomarkers in this setting
Spatially Resolving Spin-split Edge States of Chiral Graphene Nanoribbons
A central question in the field of graphene-related research is how graphene
behaves when it is patterned at the nanometer scale with different edge
geometries. Perhaps the most fundamental shape relevant to this question is the
graphene nanoribbon (GNR), a narrow strip of graphene that can have different
chirality depending on the angle at which it is cut. Such GNRs have been
predicted to exhibit a wide range of behaviour (depending on their chirality
and width) that includes tunable energy gaps and the presence of unique
one-dimensional (1D) edge states with unusual magnetic structure. Most GNRs
explored experimentally up to now have been characterized via electrical
conductivity, leaving the critical relationship between electronic structure
and local atomic geometry unclear (especially at edges). Here we present a
sub-nm-resolved scanning tunnelling microscopy (STM) and spectroscopy (STS)
study of GNRs that allows us to examine how GNR electronic structure depends on
the chirality of atomically well-defined GNR edges. The GNRs used here were
chemically synthesized via carbon nanotube (CNT) unzipping methods that allow
flexible variation of GNR width, length, chirality, and substrate. Our STS
measurements reveal the presence of 1D GNR edge states whose spatial
characteristics closely match theoretical expectations for GNR's of similar
width and chirality. We observe width-dependent splitting in the GNR edge state
energy bands, providing compelling evidence of their magnetic nature. These
results confirm the novel electronic behaviour predicted for GNRs with
atomically clean edges, and thus open the door to a whole new area of
applications exploiting the unique magnetoelectronic properties of chiral GNRs
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Climate Change Mitigation: An Analysis of Advanced Technology Scenarios
This report documents a scenario analysis that explores three advanced technology pathways toward climate stabilization using the MiniCAM model
Stratosphereâtroposphere coupling and annular mode variability in chemistryâclimate models
The internal variability and coupling between the stratosphere and troposphere in CCMValâ2 chemistryâclimate models are evaluated through analysis of the annular mode patterns of variability. Computation of the annular modes in long data sets with secular trends requires refinement of the standard definition of the annular mode, and a more robust procedure that allows for slowly varying trends is established and verified. The spatial and temporal structure of the modelsâ annular modes is then compared with that of reanalyses. As a whole, the models capture the key features of observed intraseasonal variability, including the sharp vertical gradients in structure between stratosphere and troposphere, the asymmetries in the seasonal cycle between the Northern and Southern hemispheres, and the coupling between the polar stratospheric vortices and tropospheric midlatitude jets. It is also found that the annular mode variability changes little in time throughout simulations of the 21st century. There are, however, both common biases and significant differences in performance in the models. In the troposphere, the annular mode in models is generally too persistent, particularly in the Southern Hemisphere summer, a bias similar to that found in CMIP3 coupled climate models. In the stratosphere, the periods of peak variance and coupling with the troposphere are delayed by about a month in both hemispheres. The relationship between increased variability of the stratosphere and increased persistence in the troposphere suggests that some tropospheric biases may be related to stratospheric biases and that a wellâsimulated stratosphere can improve simulation of tropospheric intraseasonal variability
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