1,764 research outputs found
Doping dependence of charge-transfer excitations in La_{2-x}Sr_xCuO_4
We report a resonant inelastic x-ray scattering (RIXS) study of the doping
dependence of charge-transfer excitations in . The mome
ntum dependence of these charge excitations are studied over the whole
Brillouin zone in underdoped (x=0.05) and optimally doped (x=0.17) samples, and
compared with that of the undoped (x=0) sample. We observe a large change in
the RIXS spectra between the x=0 and x=0.17 sample, while the RIXS spectra of
the x=0.05 sample are similar to that of the x=0 sample. The most prominent
effect of doped-holes on the charge excitation spectra is the appearance of a
continuum of intensity, which exhibits a strong momentum-dependence below 2 eV.
For the x=0.17 sample, some of the spectral weight from the lowest-lying
charge-transfer excitation of the undoped compound is transferred to the
continuum intensity below the gap, in agreement with earlier optical studies.
However, the higher energy charge-transfer excitation carries significant
spectral weight even for the x=0.17 sample. The doping dependence of the
dispersion of this charge-transfer excitation is also discussed and compared
with recent theoretical calculations.Comment: 7 pages, 6 figures, to appear in Phys. Rev.
Resonant inelastic X-ray scattering study of overdoped LaSrCuO
Resonant inelastic x-ray scattering (RIXS) at the copper K absorption edge
has been performed for heavily overdoped samples of LaSrCuO
with and 0.30. We have observed the charge transfer and
molecular-orbital excitations which exhibit resonances at incident energies of
and 8.998 keV, respectively. From a comparison with previous
results on undoped and optimally-doped samples, we determine that the
charge-transfer excitation energy increases monotonically as doping increases.
In addition, the -dependences of the RIXS spectral weight and absorption
spectrum exhibit no clear peak at keV in contrast to results in
the underdoped samples. The low-energy ( eV) continuum excitation
intensity has been studied utilizing the high energy resolution of 0.13 eV
(FWHM). A comparison of the RIXS profiles at and
indicates that the continuum intensity exists even at in the
overdoped samples, whereas it has been reported only at and
for the sample. Furthermore, we also found an additional excitation on
top of the continuum intensity at the and positions.Comment: 7 pages, 7 figure
Spin-Orbit Coupling in Iridium-Based 5d Compounds Probed by X-ray Absorption Spectroscopy
We have performed x-ray absorption spectroscopy (XAS) measurements on a
series of Ir-based 5d transition metal compounds, including Ir, IrCl3, IrO2,
Na2IrO3, Sr2IrO4, and Y2Ir2O7. By comparing the intensity of the "white-line"
features observed at the Ir L2 and L3 absorption edges, it is possible to
extract valuable information about the strength of the spin-orbit coupling in
these systems. We observe remarkably large, non-statistical branching ratios in
all Ir compounds studied, with little or no dependence on chemical composition,
crystal structure, or electronic state. This result confirms the presence of
strong spin-orbit coupling effects in novel iridates such as Sr2IrO4, Na2IrO3,
and Y2Ir2O7, and suggests that even simple Ir-based compounds such as IrO2 and
IrCl3 may warrant further study. In contrast, XAS measurements on Re-based 5d
compounds, such as Re, ReO2, ReO3, and Ba2FeReO6, reveal statistical branching
ratios and negligible spin-orbit coupling effects.Comment: 9 pages, 4 figure
Double-Stranded RNA Binding Protein, Staufen, Is Required for the Initiation of RNAi in Coleopteran Insects
RNA interference (RNAi) is being used to develop methods to control pests and disease vectors. RNAi is robust and systemic in coleopteran insects but is quite variable in other insects. The determinants of efficient RNAi in coleopterans, as well as its potential mechanisms of resistance, are not known. RNAi screen identified a double-stranded RNA binding protein (StaufenC) as a major player in RNAi. StaufenC homologs have been identified in only coleopteran insects. Experiments in two coleopteran insects, Leptinotarsa decemlineata and Tribolium castaneum, showed the requirement of StaufenC for RNAi, especially for processing of double-stranded RNA (dsRNA) to small interfering RNA. RNAi-resistant cells were selected by exposing L. decemlineata, Lepd-SL1 cells to the inhibitor of apoptosis 1 dsRNA for multiple generations. The resistant cells showed lower levels of StaufenC expression compared with its expression in susceptible cells. These studies showed that coleopteran-specific StaufenC is required for RNAi and is a potential target for RNAi resistance. The data included in this article will help improve RNAi in noncoleopteran insects and manage RNAi resistance in coleopteran insects
Single Mode Theory for Impedance Eduction in Large-Scale Ducts with Grazing Flow
An impedance eduction theory for a rigid wall duct containing an acoustic liner with an unknown impedance and uniform grazing flow is presented. The unique features of the theory are: 1) non-planar waves propagate in the hard wall sections of the duct, 2) input data consist solely of complex acoustic pressures acquired on a wall adjacent to the liner, and 3) multiple higher-order modes may exist in the direction perpendicular to the liner and the opposite rigid wall. The approach is to first measure the axial propagation constant of a dominant higher-order mode in the liner sample section. This axial propagation constant is then used in conjunction with a closed-form solution to a reduced form of the convected Helmholtz equation and the wall impedance boundary condition to educe the liner impedance. The theory is validated on a conventional liner whose impedance spectrum is educed in two flow ducts with different cross sections. For the frequencies and Mach numbers of interest, no higher-order modes propagate in the hard wall sections of the smaller duct. A benchmark method is used to educe the impedance spectrum in this duct. A dominant higher-order vertical mode propagates in the larger duct for similar test conditions, and the current theory is applied to educe the impedance spectrum. Results show that when the theory is applied to data acquired in the larger duct with a dominant higher-order vertical mode, the same impedance spectra is educed as that obtained in the small duct where only the plane wave mode is present and the benchmark method is used. This result holds for each higher-order vertical mode that is considered
Improved description of Ar(p,d) transfer reactions
An improved description of single neutron stripping from Ar
beams at 33 MeV/nucleon by a hydrogen target is presented and the dependence on
the neutron-proton asymmetry of the spectroscopic factors is further
investigated. A finite range adiabatic model is used in the analysis and
compared to previous zero range and local energy approximations. Full
three-body Faddeev calculations are performed to estimate the error in the
reaction theory. In addition, errors from the optical potentials are also
evaluated. From our new spectroscopic factors extracted from transfer, it is
possible to corroborate the neutron-proton asymmetry dependence reported from
knockout measurements.Comment: 7 pages, 3 figure
Possibilities for pedagogy in Further Education: Harnessing the abundance of literacy
In this report, it is argued that the most salient factor in the contemporary communicative landscape is the sheer abundance and diversity of possibilities for literacy, and that the extent and nature of students' communicative resources is a central issue in education. The text outlines the conceptual underpinnings of the Literacies for Learning in Further Education project in a social view of literacy, and the associated research design, methodology and analytical framework. It elaborates on the notion of the abundance of literacies in students' everyday lives, and on the potential for harnessing these as resources for the enhancement of learning. It provides case studies of changes in practice that have been undertaken by further education staff in order to draw upon students' everyday literacy practices on Travel and Tourism and Multimedia courses. It ends with some of the broad implications for conceptualising learning that arise from researching through the lens of literacy practices
A Cure for HIV Infection: "Not in My Lifetime" or "Just Around the Corner"?
With the advent and stunning success of combination antiretroviral therapy (ART) to prolong and improve quality of life for persons with HIV infection, HIV research has been afforded the opportunity to pivot towards studies aimed at finding "a cure." The mere idea that cure of HIV might be possible has energized researchers and the community towards achieving this goal. Funding agencies, both governmental and private, have targeted HIV cure as a high priority; many in the field have responded to these initiatives and the cure research agenda is robust. In this "salon" two editors of Pathogens and Immunity, Michael Lederman and Daniel Douek ask whether curing HIV is a realistic, scalable objective. We start with an overview perspective and have asked a number of prominent HIV researchers to add to the discussion
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