831 research outputs found
Synergistic Effects of High Particle Fluxes and Transient Heat Loading on Material Performance in a Fusion Environment
The work presented in this thesis focuses on the thermal and structural evolution of different materials when exposed to both high-flux ion irradiation and high intensity pulsed heat loading. Nuclear fusion devices create an intense radiation environment consisting of very energetic deuterium (D+) and helium (He+) ions. During operation, off-normal plasma events, such as edge-localized modes (ELMs), could cause intense heating of the plasma-facing component (PFC) surface, leading to melting and possible splashing into the fusion plasma. High-Z, refractory metals, such as tungsten (W), are therefore seen as favorable, due to their high melting point, high thermal conductivity, and low sputtering yield. However, potential splashing of the molten wall could contaminate the plasma and shut down the reactor. High-flux He+ wall loading could further exacerbate melting and splashing of the PFC surface, due to the growth of fiber form nanostructures, called fuzz, which possess a much lower mechanical and thermal strength than that of a pristine surface. Experiments performed throughout the dissertation attempt to qualify the effect of He+-induced surface structuring on the PFC thermal response during type-I ELMs. Elementary surface characterization revealed that He+ loading blurs clear melting and droplet emission thresholds observed on pristine surfaces during ELM-like heat loading, inducing thermal damage gradually through localized melting and conglomeration of fuzz tendrils. The reduced thermal conductivity of fuzz nanostructures led to increased levels of erosion due to fragmentation of molten material. Decreasing the imparted heat flux, at the sacrifice of higher frequencies, through ELM mitigation techniques showed the potential for an intermediate operating window that could heal fuzz nanostructures via annealing without the onset of splashing. Tests on transversally-oriented W microstructures (which will be used in ITER) revealed that radiation hardening along grain boundaries due to high-flux He+ loading may preferentially enhance brittle failure. Differences in penetration depth between experimental heat loading methods (millisecond laser vs. electron beam) affected heat deposition in and plasticity of the damaged surface. Simultaneous He+ particle loading and ELM-like heat loading inhibited fuzz formation due to repetitive shock-induced conglomeration. The addition of D+ ion irradiation appeared to further reduce evidence of early-stage fuzz formation, due to super-saturation of D in the near-surface layer. Significant structuring due to D+ particle loading may diminish the impact of ELM intensity on surface roughening and melting. Future studies need to expand upon the surface analysis presented throughout this dissertation and investigate the details of the subsurface to determine how intense thermal loading impacts gas trapping and migration. In addition, future PFC erosion research must utilize highly sensitive, in situ measurement techniques to obtain reliable information on material lifetime and performance
Vitamin D enzymes (CYP27A1, CYP27B1 and CYP24A1) and receptor expression in non-melanoma skin cancer
No abstract available for this paper
Resonantly enhanced second-harmonic generation using III-V semiconductor all-dielectric metasurfaces
Nonlinear optical phenomena in nanostructured materials have been challenging
our perceptions of nonlinear optical processes that have been explored since
the invention of lasers. For example, the ability to control optical field
confinement, enhancement, and scattering almost independently, allows nonlinear
frequency conversion efficiencies to be enhanced by many orders of magnitude
compared to bulk materials. Also, the subwavelength length scale renders phase
matching issues irrelevant. Compared with plasmonic nanostructures, dielectric
resonator metamaterials show great promise for enhanced nonlinear optical
processes due to their larger mode volumes. Here, we present, for the first
time, resonantly enhanced second-harmonic generation (SHG) using Gallium
Arsenide (GaAs) based dielectric metasurfaces. Using arrays of cylindrical
resonators we observe SHG enhancement factors as large as 104 relative to
unpatterned GaAs. At the magnetic dipole resonance we measure an absolute
nonlinear conversion efficiency of ~2X10^(-5) with ~3.4 GW/cm2 pump intensity.
The polarization properties of the SHG reveal that both bulk and surface
nonlinearities play important roles in the observed nonlinear process
Mesoscale eddies release pelagic sharks from thermal constraints to foraging in the ocean twilight zone
Author Posting. © National Academy of Sciences, 2019. This article is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences 116 (35), (2019): 17187-17192, doi:10.1073/pnas.1903067116.Mesoscale eddies are critical components of the ocean’s “internal weather” system. Mixing and stirring by eddies exerts significant control on biogeochemical fluxes in the open ocean, and eddies may trap distinctive plankton communities that remain coherent for months and can be transported hundreds to thousands of kilometers. Debate regarding how and why predators use fronts and eddies, for example as a migratory cue, enhanced forage opportunities, or preferred thermal habitat, has been ongoing since the 1950s. The influence of eddies on the behavior of large pelagic fishes, however, remains largely unexplored. Here, we reconstruct movements of a pelagic predator, the blue shark (Prionace glauca), in the Gulf Stream region using electronic tags, earth-observing satellites, and data-assimilating ocean forecasting models. Based on >2,000 tracking days and nearly 500,000 high-resolution time series measurements collected by 15 instrumented individuals, we show that blue sharks seek out the interiors of anticyclonic eddies where they dive deep while foraging. Our observations counter the existing paradigm that anticyclonic eddies are unproductive ocean “deserts” and suggest anomalously warm temperatures in these features connect surface-oriented predators to the most abundant fish community on the planet in the mesopelagic. These results also shed light on the ecosystem services provided by mesopelagic prey. Careful consideration will be needed before biomass extraction from the ocean twilight zone to avoid interrupting a key link between planktonic production and top predators. Moreover, robust associations between targeted fish species and oceanographic features increase the prospects for effective dynamic ocean management.We thank D. McGillicuddy, G. Lawson, and G. Flierl for helpful discussions while developing this work and 2 anonymous reviewers whose feedback significantly improved the manuscript. We also thank C. Fischer and the OCEARCH team for their support of this research. This work was funded by awards to C.D.B. from the Martin Family Society of Fellows for Sustainability Fellowship at the Massachusetts Institute of Technology; the Grassle Fellowship and Ocean Venture Fund at the Woods Hole Oceanographic Institution; and the National Aeronatics and Space Administration (NASA) Earth and Space Science Fellowship. C.D.B. and P.G. acknowledge support from the NASA New Investigator Program Award 80NSSC18K0757, and P.G. acknowledges support from NSF Award OCE-1558809. This research is partially supported by funding to S.R.T. as part of the Audacious Project, a collaborative endeavor, housed at TED. We thank donors to the Woods Hole Oceanographic Institution (WHOI) ProjectWHOI crowdfunding campaign: The Secret Lives of Sharks. Computational support was provided by the Amazon Web Services Cloud Credits for Research program. Funding for the development of HYCOM has been provided by the National Ocean Partnership Program and the Office of Naval Research.2020-02-0
Spectrum of orientifold QCD in the strong coupling and hopping expansion approximation
We use the strong coupling and hopping parameter expansions to calculate the
pion and rho meson masses for lattice Yang-Mills gauge theories with fermions
in irreducible two-index representations, namely the adjoint, symmetric and
antisymmetric. The results are found to be consistent with orientifold planar
equivalence, and leading order 1/N corrections are calculated in the lattice
phase. An estimate of the critical bare mass, for which the pion is massless,
is obtained as a function of the bare coupling. A comparison to data from the
two-flavour SU(2) theory with adjoint fermions gives evidence for a bulk phase
transition at beta~2, separating a pure lattice phase from a phase smoothly
connected to the continuum.Comment: 16 page
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OPTIMIZATION OF COAL PARTICLE FLOW PATTERNS IN LOW NOX BURNERS
The proposed research is directed at evaluating the effect of flame aerodynamics on NO{sub x} emissions from coal fired burners in a systematic manner. This fundamental research includes both experimental and modeling efforts being performed at the University of Arizona in collaboration with Purdue University. The objective of this effort is to develop rational design tools for optimizing low NO{sub x} burners to the kinetic emissions limit (below 0.2 lb./MMBTU). Experimental studies include both cold and hot flow evaluations of the following parameters: flame holder geometry, secondary air swirl, primary and secondary inlet air velocity, coal concentration in the primary air and coal particle size distribution. Hot flow experiments will also evaluate the effect of wall temperature on burner performance. Cold flow studies will be conducted with surrogate particles as well as pulverized coal. The cold flow furnace will be similar in size and geometry to the hot-flow furnace but will be designed to use a laser Doppler velocimeter/phase Doppler particle size analyzer. The results of these studies will be used to predict particle trajectories in the hot-flow furnace as well as to estimate the effect of flame holder geometry on furnace flow field. The hot-flow experiments will be conducted in a novel near-flame down-flow pulverized coal furnace. The furnace will be equipped with externally heated walls. Both reactors will be sized to minimize wall effects on particle flow fields. The cold-flow results will be compared with Fluent computation fluid dynamics model predictions and correlated with the hot-flow results with the overall goal of providing insight for novel low NO{sub x} burner geometry's
A validation of the Oswestry Spinal Risk Index
Purpose
The purpose of this study was to validate the Oswestry Spinal Risk Index (OSRI) in an external population. The OSRI predicts survival in patients with metastatic spinal cord compression (MSCC).
Methods
We analysed the data of 100 patients undergoing surgical intervention for MSCC at a tertiary spinal unit and recorded the primary tumour pathology and Karnofsky performance status to calculate the OSRI. Logistic regression models and survival plots were applied to the data in accordance with the original paper.
Results
Lower OSRI scores predicted longer survival. The OSRI score predicted survival accurately in 74% of cases (p = 0.004).
Conclusions
Our study has found that the OSRI is a significant predictor of survival at levels similar to those of the original authors and is a useful and simple tool in aiding complex decision making in patients presenting with MSC
Critical Review and Consensus Statement for Neural Monitoring in Otolaryngologic Head, Neck, and Endocrine Surgery
BACKGROUND: Enhancing patient outcomes in an array of surgical procedures in the head and neck requires the maintenance of complex regional functions through the protection of cranial nerve integrity. This review and consensus statement cover the scope of cranial nerve monitoring of all cranial nerves that are of practical importance in head, neck, and endocrine surgery except for cranial nerves VII and VIII within the temporal bone. Complete and applied understanding of neurophysiologic principles facilitates the surgeon\u27s ability to monitor the at-risk nerve.
METHODS: The American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) identified the need for a consensus statement on cranial nerve monitoring. An AAO-HNS task force was created through soliciting experts on the subject. Relevant domains were identified, including residency education, neurophysiology, application, and various techniques for monitoring pertinent cranial nerves. A document was generated to incorporate and consolidate these domains. The panel used a modified Delphi method for consensus generation.
RESULTS: Consensus was achieved in the domains of education needs and anesthesia considerations, as well as setup, troubleshooting, and documentation. Specific cranial nerve monitoring was evaluated and reached consensus for all cranial nerves in statement 4 with the exception of the spinal accessory nerve. Although the spinal accessory nerve\u27s value can never be marginalized, the task force did not feel that the existing literature was as robust to support a recommendation of routine monitoring of this nerve. In contrast, there is robust supporting literature cited and consensus for routine monitoring in certain procedures, such as thyroid surgery, to optimize patient outcomes.
CONCLUSIONS: The AAO-HNS Cranial Nerve Monitoring Task Force has provided a state-of-the-art review in neural monitoring in otolaryngologic head, neck, and endocrine surgery. The evidence-based review was complemented by consensus statements utilizing a modified Delphi method to prioritize key statements to enhance patient outcomes in an array of surgical procedures in the head and neck. A precise definition of what actually constitutes intraoperative nerve monitoring and its benefits have been provided
6.7 GHz methanol absorption toward the Seyfert 2 galaxy NGC 3079
The detection of the 6.7 GHz line of methanol (CH3OH) is reported for the
first time toward an object beyond the Magellanic Clouds. Using the Effelsberg
100 m telescope, two absorption features were identified toward the Seyfert 2
galaxy NGC 3079. Both components probably originated on lines-of-sight toward
the central region, presumably absorbing the radio continuum of the nuclear
sources A, B, and E of NGC 3079. One absorption feature, at the systemic
velocity, is narrow and may arise from gas not related to the nuclear
environment of the galaxy. The weaker blue-shifted component is wider and may
trace outflowing gas. Total A-type CH3OH column densities are estimated to be
between a few times 10^13 and a few times 10^15 cm^-2. Because of a highly
frequency-dependent continuum background, the overall similarity of HI, OH, and
CH3OH absorption profiles hints at molecular clouds that cover the entire area
occupied by the nuclear radio continuum sources ~ 4 pc.Comment: 4 pages, 1 figure, accepted for publication in A&A Letter
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