314 research outputs found
Fast ion transport in quasisymmetric equilibria in the presence of a resonant Alfv\'{e}nic perturbation
Significant progress has been made in designing magnetic fields that provide
excellent confinement of the guiding enter trajectories of alpha particles
using quasisymmetry (QS). Given the reduction in this transport channel, we
assess the impact of resonant Alfv\'{e}n eigenmodes (AEs) on the guiding center
motion. The AE amplitudes are chosen to be consistent with experimental
measurements and large-scale simulations. We evaluate the drift resonance
condition, phase-space island width, and island overlap criterion for
quasisymmetric configurations. Kinetic Poincar\'{e} plots elucidate features of
the transport, including stiff transport above a critical perturbation
amplitude. Our analysis highlights key departures from the AE-driven transport
in tokamaks, such as the avoidance of phase-space island overlap in
quasihelical configurations and the enhanced transport due to wide phase-space
islands in low magnetic shear configurations. In configurations that are closer
to QS, with QS deviations , the transport is
primarily driven by the AE, while configurations that are further from QS,
, experience significant transport due to the
QS-breaking fields in addition to the AE
Oscillation Effects On Neutrinos From The Early Phase Of a Nearby Supernova
Neutrinos emitted during stellar core collapse leading to a supernova are
primarily of the electron neutrino type at source which may undergo oscillation
between flavor eigenstates during propagation to an earth-bound detector.
Although the number of neutrinos emitted during the pre-bounce collapse phase
is much smaller than that emitted in the post-bounce phase (in which all
flavors of neutrinos are emitted), a nearby supernova event may nevertheless
register a substantial number of detections from the pre-bounce phase at
SuperKamiokande (SK) and the Sudbury Neutrino Observatory (SNO). The
calorimetric measurement of the supernova neutrino fluence from this stage via
the charge current and neutral current detection channels in SNO and the
corresponding distortion of detected spectrum in SK over the no-oscillation
spectrum, can probe information about neutrino mass difference and mixing which
are illustrated here in terms of two- and three-flavor oscillation models
Production of pulsed atomic oxygen beams via laser vaporization methods
Energetic pulsed atomic oxygen beams were generated by laser-driven evaporation of cryogenically frozen ozone/oxygen films and thin films of indium-tin oxide (ITO). Mass and energy characterization of beams from the ozone/oxygen films were carried out by mass spectrometry. The peak flux, found to occur at 10 eV, is estimated from this data to be 3 x 10(20) m(-2) s(-1). Analysis of the time-of-flight data indicates a number of processes contribute to the formation of the atomic oxygen beam. The absence of metastable states such as the 2p(3) 3s(1) (5S) level of atomic oxygen blown off from ITO films is supported by the failure to observe emission at 777.3 nm from the 2p(3) 3p(1) (5P sub J) levels. Reactive scattering experiments with polymer film targets for atomic oxygen bombardment are planned using a universal crossed molecular beam apparatus
Properties of a mixed-valent iron compound with the kagomélattice
An organically templated iron sulfate of the formula [HN(CH2)6NH][FeIIIFe2IIF6(SO4)2]·[H3O] possessing the kagomé lattice has been prepared and characterized by single-crystal crystallography and other techniques. This mixed-valent iron compound shows complex magnetic properties including spin-glass behavior and magnetic hysteresis. The low-temperature specific heat data show deviation from the T2 behavior found in two-dimensional frustrated systems. Simple calculations have been carried out to understand the properties of this kagomé compound
SU(6), Triquark states, and the pentaquark
The purported observation of a state with strangeness S = +1 led
to its quark model interpretation in terms of a pentaquark combination
involving a triquark-diquark structure -- the Karliner-Lipkin model. In this
work, the proper colour-spin symmetry properties for the triquark
are elucidated by calculating the SU(6) unitary scalar factors and Racah
coefficients. Using these results, the colour-spin hyperfine interactions,
including flavour symmetry breaking therein, become straight-forward to
incorporate and the pentaquark masses are readily obtained. We examine the
effect on the pentaquark mass of (a) deviations from the flavour symmetric
limit and (b) different strengths of the doublet and triplet hyperfine
interactions. Reference values of these parameters yield a mass
prediction of 1601 MeV but it can comfortably accommodate 1540 MeV for
alternate choices. In the same framework, other pentaquark states (S=--2)
and (with charm C=--1) are expected at 1783 MeV and 2757 MeV,
respectively.Comment: 17 pages, 1 figure. accepted for publication in Phys. Rev.
Disruption of an SP2/KLF6 repression complex by SHP is required for farnesoid X receptor-induced endothelial cell migration
The farnesoid X receptor (FXR) signaling pathway regulates bile acid and cholesterol homeostasis. Here, we demonstrate, using a variety of gain- and loss-of-function approaches, a role of FXR in the process of cell motility, which involves the small heterodimeric partner (SHP)-dependent up-regulation of matrix metalloproteinase-9. We use this observation to reveal a transcriptional regulatory mechanism involving the SP/KLF transcription factors, SP2 and KLF6. Small interference RNA-based silencing studies in combination with promoter, gel shift, and chromatin immunoprecipitation assays indicate that SP2 and KLF6 bind to the matrix metalloproteinase-9 promoter and together function to maintain this gene in a silenced state. However, upon activation of FXR, SHP interacts with SP2 and KLF6, disrupting the SP2/KLF6 repressor complex. Thus, together, these studies identify a mechanism for antagonizing Sp/KLF protein repression function via SHP, with this process regulating endothelial cell motility
Abatement of particulate-laden SO2 in tapered bubble column with internals
The performance of particulate-laden SO2 scrubbing in a modified tapered bubble column with internals is reported in this article. The presence of particles improved the particulate-laden SO2 removal efficiency to about 15% that was elucidated by the facilitated adsorptive mass transport. Experimentation revealed that nearly 100% removal efficiency of particulate-laden SO2 was achievable without any additives or pretreatment under certain operating condition of the scrubber. An empirical correlation was developed to predict the performance of the modified tapered scrubber. Experimental values fitted excellently well with the predicted values through the correlation (within ±5% deviation). The performance of the modified tapered bubble scrubber with column internals has been found to be better than a tapered bubble column without any internals
Outgassing Behavior and Heat Treatment Optimization of JSC-1A Lunar Regolith Simulant
As NASA Strives towards a Long Duration Presence on the Moon, It Has Become Increasingly Important to Learn How to Better Utilize Resources from the Lunar Surface for Everything from Habitats, Vehicle Infrastructure, and Chemical Extraction. to that End, a Variety of Lunar Simulants Have Been Sourced from Terrestrially Available Volcanic Minerals and Glass as Apollo Regolith is Unavailable for Experimentation Needing Large Masses. However, While Mineralogy and Chemical Composition Can Approach that of Lunar Material in These Simulants, There Are Still Distinct Non-Lunar Phases Such as Hydrates, Carbonates, Sulfates, and Clays that Can Cause Simulants to Behave Distinctly Non-Lunar in a Variety of Processing Conditions that Maybe Applied In-Situ to Lunar Material. Notably, Severe Glassy Bubbling Has Been Documented in a Variety of Vacuum Sintering Experiments on JSC-1A Lunar Mare Simulant Heated Via Microwaves. the Origins of This Outgassing Have Not Been Well Understood But Are Normally Attributed to the Decomposition of Non-Lunar Contaminates Intrinsic to Virtually All Terrestrially Sourced Simulants. as Such, a Series of Controlled Environmental Tests Were Performed to Ascertain the Origins of the High Temperature Outgassing and to Develop Heat Treatments that Can Drive JSC-1A Closer to Lunar Composition and Behavior. It Was Found that in JSC-1A at Elevated Temperatures Distinct Gas Evolutions of Water, Carbon Dioxide, and Sulfur Dioxide Occur in Both Inert Gas and Vacuum. Additionally, the Presence of Hydrogen during Heat Treatments Was Shown to Dramatically Change Gas Evolutions, Leading to Distinctly More Lunar-Like Composition and Behavior from JSC-1A Simulant
Universal behavior of highly-confined heat flow in semiconductor nanosystems: from nanomeshes to metalattices
Nanostructuring on length scales corresponding to phonon mean free paths
provides control over heat flow in semiconductors and makes it possible to
engineer their thermal properties. However, the influence of boundaries limits
the validity of bulk models, while first principles calculations are too
computationally expensive to model real devices. Here we use extreme
ultraviolet beams to study phonon transport dynamics in a 3D nanostructured
silicon metalattice with deep nanoscale feature size, and observe dramatically
reduced thermal conductivity relative to bulk. To explain this behavior, we
develop a predictive theory wherein thermal conduction separates into a
geometric permeability component and an intrinsic viscous contribution, arising
from a new and universal effect of nanoscale confinement on phonon flow. Using
both experiments and atomistic simulations, we show that our theory is valid
for a general set of highly-confined silicon nanosystems, from metalattices,
nanomeshes, porous nanowires to nanowire networks. This new analytical theory
of thermal conduction can be used to predict and engineer phonon transport in
boundary-dominated nanosystems, that are of great interest for next-generation
energy-efficient devices
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