10,508 research outputs found
Model-based sensor fusion and filtering for localization of a semi-autonomous robotic vehicle
Direct observation of charge order in triangular metallic AgNiO2 by single-crystal resonant X-ray scattering
We report resonant X-ray scattering measurements on the orbitally-degenerate
triangular metallic antiferromagnet 2H-AgNiO2 to probe the spontaneous
transition to a triple-cell superstructure at temperatures below 365 K. We
observe a strong resonant enhancement of the supercell reflections through the
Ni K-edge. The empirically extracted K-edge shift between the
crystallographically-distinct Ni sites of 2.5(3) eV is much larger than the
value expected from the shift in final states, and implies a core-level shift
of ~1 eV, thus providing direct evidence for the onset of spontaneous honeycomb
charge order in the triangular Ni layers. We also provide band-structure
calculations that explain quantitatively the observed edge shifts in terms of
changes in the Ni electronic energy levels due to charge order and
hybridization with the surrounding oxygens.Comment: 5 pages, 4 figure
Neel order, quantum spin liquids and quantum criticality in two dimensions
This paper is concerned with the possibility of a direct second order
transition out of a collinear Neel phase to a paramagnetic spin liquid in two
dimensional quantum antiferromagnets. Contrary to conventional wisdom, we show
that such second order quantum transitions can potentially occur to certain
spin liquid states popular in theories of the cuprates. We provide a theory of
this transition and study its universal properties in an expansion.
The existence of such a transition has a number of interesting implications for
spin liquid based approaches to the underdoped cuprates. In particular it
considerably clarifies existing ideas for incorporating antiferromagnetic long
range order into such a spin liquid based approach.Comment: 18 pages, 17 figure
Dynamics of earthquake nucleation process represented by the Burridge-Knopoff model
Dynamics of earthquake nucleation process is studied on the basis of the
one-dimensional Burridge-Knopoff (BK) model obeying the rate- and
state-dependent friction (RSF) law. We investigate the properties of the model
at each stage of the nucleation process, including the quasi-static initial
phase, the unstable acceleration phase and the high-speed rupture phase or a
mainshock. Two kinds of nucleation lengths L_sc and L_c are identified and
investigated. The nucleation length L_sc and the initial phase exist only for a
weak frictional instability regime, while the nucleation length L_c and the
acceleration phase exist for both weak and strong instability regimes. Both
L_sc and L_c are found to be determined by the model parameters, the frictional
weakening parameter and the elastic stiffness parameter, hardly dependent on
the size of an ensuing mainshock. The sliding velocity is extremely slow in the
initial phase up to L_sc, of order the pulling speed of the plate, while it
reaches a detectable level at a certain stage of the acceleration phase. The
continuum limits of the results are discussed. The continuum limit of the BK
model lies in the weak frictional instability regime so that a mature
homogeneous fault under the RSF law always accompanies the quasi-static
nucleation process. Duration times of each stage of the nucleation process are
examined. The relation to the elastic continuum model and implications to real
seismicity are discussed.Comment: Title changed. Changes mainly in abstract and in section 1. To appear
in European Physical Journal
Model Independent Extraction of Without Heavy Quark Symmetry
A new method to extract is proposed based on a sum--rule for
semileptonic decays of the meson. The method relies on much weaker
assumptions than previous approaches which are based on heavy--quark symmetry.
This sum--rule only relies on the assumption that the virtual
pair content of the meson can be neglected. The extraction of the CKM
matrix element also requires that the sum--rule saturates in the kinematically
accessible region.Comment: 10 pages revtex3 manuscript. No figures, U. of MD PP #94--086. With
our apologies, some innocuous errors corrected and some references added that
had been brought to our attentio
A Novel UV Photon Detector with Resistive Electrodes
In this study we present first results from a new detector of UV photons: a
thick gaseous electron multiplier (GEM) with resistive electrodes, combined
with CsI or CsTe/CsI photocathodes. The hole type structure considerably
suppresses the photon and ion feedback, whereas the resistive electrodes
protect the detector and the readout electronics from damage by any eventual
discharges. This device reaches higher gains than a previously developed
photosensitive RPC and could be used not only for the imaging of UV sources,
flames or Cherenkov light, for example, but also for the detection of X-rays
and charged particles.Comment: Presented at the International Workshop on Resistive Plate Chambers,
Korea, October 200
Fourfold oscillations and anomalous magnetic irreversibility of magnetoresistance in the non-metallic regime of Pr1.85Ce0.15CuO4
Using magnetoresistance measurements as a function of applied magnetic field
and its direction of application, we present sharp angular-dependent
magnetoresistance oscillations for the electron-doped cuprates in their
low-temperature non-metallic regime. The presence of irreversibility in the
magnetoresistance measurements and the related strong anisotropy of the field
dependence for different in-plane magnetic field orientations indicate that
magnetic domains play an important role for the determination of electronic
properties. These domains are likely related to the stripe phase reported
previously in hole-doped cuprates.Comment: 11 pages, 5 figure
Eigenstate Structure in Graphs and Disordered Lattices
We study wave function structure for quantum graphs in the chaotic and
disordered regime, using measures such as the wave function intensity
distribution and the inverse participation ratio. The result is much less
ergodicity than expected from random matrix theory, even though the spectral
statistics are in agreement with random matrix predictions. Instead, analytical
calculations based on short-time semiclassical behavior correctly describe the
eigenstate structure.Comment: 4 pages, including 2 figure
The mean energy, strength and width of triple giant dipole resonances
We investigate the mean energy, strength and width of the triple giant dipole
resonance using sum rules.Comment: 12 page
Big Bluestem and Indiangrass from Remnant Prairies: Plant Biomass and Adaptation
Big bluestem (Andropogon gerardii Vitman) and indiangrass (Sorghastrum nutans L.) were collected from remnant Midwestern prairies and evaluated as individual prairie accessions in replicated space-transplanted nurseries near Mead, NE, Ames, IA, and West Lafayette, IN. The objective was to determine the extent of differences among the accessions for plant biomass (g plant−1) and biomass quality, the extent of strain x location interactions, and the relationship between geographical locations of collection sites and evaluation locations for plant biomass production. Plant biomass has been used previously as a measure of plant adaptation and fitness. Big bluestem and indiangrass accessions differed significantly (P \u3c 0.05) for plant biomass at all locations. Strain mean squares for plant biomass were 10´ greater than strain x location effects for big bluestem and were not significant for indiangrass, indicating a general lack of specific adaptation across the Midwest. Accessions were identified that had high plant biomass at all three locations. These accessions should have value in breeding programs and for use in revegetation. Regression analyses were used to test the effect of north-to-south, east-to-west, and direct distances between the collection sites and the evaluation locations on plant biomass. The most important distance effects were the north-to-south effects, which were significant for plant biomass for big bluestem at all locations and for indiangrass at West Lafayette. Moving northern big bluestem accessions south resulted in reduced plant biomass, with the opposite effect when southern accessions were moved north. Results support the regional adaptation of the best accessions and cultivars for these grasses
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