2,983 research outputs found
Semi-relativistic charge-current density operator
The charge-current density and two-photon operators consistent with a
single-particle semi-relativistic Hamiltonian are derived within a suitable
functional derivative formalism which preserves gauge invariance. An
application to electron scattering is presented and results are compared with a
fully relativistic case and the non-relativistic cases corrected through fourth
order in M^{-1}.Comment: 20 pages, 3 postscript figures, typos correcte
Spin-polarization-induced structural selectivity in Pd and Pt () compounds
Spin-polarization is known to lead to important {\it magnetic} and {\it
optical} effects in open-shell atoms and elemental solids, but has rarely been
implicated in controlling {\it structural} selectivity in compounds and alloys.
Here we show that spin-polarized electronic structure calculations are crucial
for predicting the correct crystal structures for Pd and Pt
compounds. Spin-polarization leads to (i) stabilization of the structure
over the structure in PtCr, PdCr, and PdMn, (ii) to the
stabilization of the structure over the structure in PdCo
and to (iii) ordering (rather than phase-separation) in PtCo and PdCr.
The results are analyzed in terms of first-principles local spin density
calculations.Comment: 4 pages, REVTEX, 3 eps figures, to appear in PR
Economic impact and risk analysis of integrating sustainable aviation fuels into refineries
The growth of the aviation industry coupled with its dependence on energy dense, liquid fuels has brought sustainable aviation fuel (SAF) research to the forefront of the biofuels community. Petroleum refineries will need to decide how to satisfy the projected increase in jet fuel demand with either capital investments to debottleneck current operations or by integrating bio-blendstocks. This work seeks to compare jet production strategies on a risk-adjusted, economic performance basis using Monte-Carlo simulation and refinery optimization models. Additionally, incentive structures aiming to de-risk initial SAF production from the refinerâs perspective are explored. Results show that market sensitive incentives can reduce the financial risks associated with producing SAFs and deliver marginal abatement costs ranging between 136-182 $/Ton-CO2e
Specific heat of quasi-2D antiferromagnetic Heisenberg models with varying inter-planar couplings
We have used the stochastic series expansion (SSE) quantum Monte Carlo (QMC)
method to study the three-dimensional (3D) antiferromagnetic Heisenberg model
on cubic lattices with in-plane coupling J and varying inter-plane coupling
J_perp < J. The specific heat curves exhibit a 3D ordering peak as well as a
broad maximum arising from short-range 2D order. For J_perp << J, there is a
clear separation of the two peaks. In the simulations, the contributions to the
total specific heat from the ordering across and within the layers can be
separated, and this enables us to study in detail the 3D peak around T_c (which
otherwise typically is dominated by statistical noise). We find that the peak
height decreases with decreasing J_perp, becoming nearly linear below J_perp =
0.2J. The relevance of these results to the lack of observed specific heat
anomaly at the ordering transition of some quasi-2D antiferromagnets is
discussed.Comment: 7 pages, 8 figure
The detection of the imprint of filaments on cosmic microwave background lensing
Galaxy redshift surveys, such as 2dF, SDSS, 6df, GAMA and VIPERS, have shown
that the spatial distribution of matter forms a rich web, known as the cosmic
web. The majority of galaxy survey analyses measure the amplitude of galaxy
clustering as a function of scale, ignoring information beyond a small number
of summary statistics. Since the matter density field becomes highly
non-Gaussian as structure evolves under gravity, we expect other statistical
descriptions of the field to provide us with additional information. One way to
study the non-Gaussianity is to study filaments, which evolve non-linearly from
the initial density fluctuations produced in the primordial Universe. In our
study, we report the first detection of CMB (Cosmic Microwave Background)
lensing by filaments and we apply a null test to confirm our detection.
Furthermore, we propose a phenomenological model to interpret the detected
signal and we measure how filaments trace the matter distribution on large
scales through filament bias, which we measure to be around 1.5. Our study
provides a new scope to understand the environmental dependence of galaxy
formation. In the future, the joint analysis of lensing and Sunyaev-Zel'dovich
observations might reveal the properties of `missing baryons', the vast
majority of the gas which resides in the intergalactic medium and has so far
evaded most observations
Nucleon to Delta Weak Excitation Amplitudes in the Non-relativistic Quark Model
We investigate the nucleon to Delta(1232) vector and axial vector amplitudes
in the non-relativistic quark model of the Isgur-Karl variety. A particular
interest is to investigate the SU(6) symmetry breaking, due to color hyperfine
interaction. We compare the theoretical estimates to recent experimental
investigation of the Adler amplitudes by neutrino scattering.Comment: \documentstyle[aps]{revtex}, 21pages; 11 postscript figures. Accepted
for publication by Phys. Rev.
Scattering of long wavelengths into thin silicon photovoltaic films by plasmonic silver nanoparticles
Nanoparticles and nanostructures with plasmonic resonances are currently being employed to enhance the efficiency of solar cells. Ag stripe arrays have been shown theoretically to enhance the short-circuit current of thin silicon layers. Monolayers of Ag nanoparticles with diameter d < 300 nm have shown strong plasmonic resonances when coated in thin polymer layers with thicknesses < d. We study experimentally the diffuse vs. specular scattering from monolayer arrays of Ag nanoparticles (spheres and prisms with diameters in the range 50 â 300 nm) coated onto the front side of thin (100 nm < t < 500 nm) silicon films deposited on glass and flexible polymer substrates, the latter originating in a roll-to-roll manufacturing process. Ag nanoparticles are held in place and aggregation is prevented with a polymer overcoat. We observe interesting wavelength shifts between maxima in specular and diffuse scattering that depend on particle size and shape, indicating that the nanoparticles substantially modify the scattering into the thin silicon film.United States. Air Force (United States. Army. Natick Soldier Research Development and Engineering Center Contract FA8721-05-C-0002)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract W911NF-07-D0004
Exact spectra, spin susceptibilities and order parameter of the quantum Heisenberg antiferromagnet on the triangular lattice
Exact spectra of periodic samples are computed up to .
Evidence of an extensive set of low lying levels, lower than the softest
magnons, is exhibited.
These low lying quantum states are degenerated in the thermodynamic limit;
their symmetries and dynamics as well as their finite-size scaling are strong
arguments in favor of N\'eel order.
It is shown that the N\'eel order parameter agrees with first-order spin-wave
calculations. A simple explanation of the low energy dynamics is given as well
as the numerical determinations of the energies, order parameter and spin
susceptibilities of the studied samples. It is shown how suitable boundary
conditions, which do not frustrate N\'eel order, allow the study of samples
with spins.
A thorough study of these situations is done in parallel with the more
conventional case .Comment: 36 pages, REVTeX 3.0, 13 figures available upon request, LPTL
preprin
Adaptive RSK-EphA2-GPRC5A signaling switch triggers chemotherapy resistance in ovarian cancer
Metastatic cancers commonly activate adaptive chemotherapy resistance, attributed to both microenvironment-dependent phenotypic plasticity and genetic characteristics of cancer cells. However, the contribution of chemotherapy itself to the non-genetic resistance mechanisms was long neglected. Using high-grade serous ovarian cancer (HGSC) patient material and cell lines, we describe here an unexpectedly robust cisplatin and carboplatin chemotherapy-induced ERK1/2-RSK1/2-EphA2-GPRC5A signaling switch associated with cancer cell intrinsic and acquired chemoresistance. Mechanistically, pharmacological inhibition or knockdown of RSK1/2 prevented oncogenic EphA2-S897 phosphorylation and EphA2-GPRC5A co-regulation, thereby facilitating a signaling shift to the canonical tumor-suppressive tyrosine phosphorylation and consequent downregulation of EphA2. In combination with platinum, RSK inhibitors effectively sensitized even the most platinum-resistant EphA2(high), GPRC5A(high) cells to the therapy-induced apoptosis. In HGSC patient tumors, this orphan receptor GPRC5A was expressed exclusively in cancer cells and associated with chemotherapy resistance and poor survival. Our results reveal a kinase signaling pathway uniquely activated by platinum to elicit adaptive resistance. They further identify GPRC5A as a marker for abysmal HGSC outcome and putative vulnerability of the chemo-resistant cells to RSK1/2-EphA2-pS897 pathway inhibition.Peer reviewe
Responses to the 2017 â1 Million Gray Questionâ: ASTRO membershipâs opinions on the most important research question facing radiation oncology
At the American Society for Radiation Oncology's (ASTRO's) 2017 annual meeting in San Diego, CA, attendees were asked, âWhat is the most important research question that needs to be answered in the next 3 to 5 years?â This request was meant to start a dialogue, promote thoughtful discussion within our professional community, and help inform topics for ASTRO workshops and focus meetings. Nearly 100 people responded while in attendance at the meeting, with questions that ranged from âHow can we remove barriers so low- and middle-income countries can have radiation oncology facilities?â to âWhat is the exact role of radiation in stage IV disease in combination with immunotherapy or targeted agents to combat resistance development?â to âHow can personalized care be better integrated into the oncology and radiation oncology clinical space?
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