763 research outputs found
Competition between Antiferromagnetism and Superconductivity in High Cuprates
Using variational cluster perturbation theory we study the competition
between d-wave superconductivity (dSC) and antiferromagnetism (AF) in the the
t-t'-t''-U Hubbard model. Large scale computer calculations reproduce the
overall ground state phase diagram of the high-temperature superconductors as
well as the one-particle excitation spectra for both hole- and electron-doping.
We identify clear signatures of the Mott gap as well as of AF and of dSC that
should be observable in photoemission experiments.Comment: 4 pages, 4 figure
ASSESSING IMPACTS OF ENVIRONMENTAL CHANGE ON ABORIGINAL PEOPLE: AN ECONOMIC EXAMINATION OF SUBSISTENCE RESOURCE USE AND VALUE
The report describes the research design, data collection and preliminary analysis of an economic assessment of non-timber resource use by Aboriginal People in Northwest Saskatchewan. The project is designed to develop methods of valuing resource use by Aboriginal People so that these values can be incorporated into forest resource management decisions and to evaluate the impact of forest management actions on the economic well-being of Aboriginal People living in the region. Data on non-timber resource use are collected and spatially explicit economic models are developed in order to construct estimates of behavioral change and value associated with changes in the environment and landscape (through forestry, access, or other landscape changes).Environmental Economics and Policy, Resource /Energy Economics and Policy,
Optimal Wavelength Selection for Optical Spectroscopy of Hemoglobin and Water within a Simulated Light-Scattering Tissue
An algorithm that selects optimal wavelengths for spectral fitting of diffuse light reflectance spectra using a nonnegative least squares method is presented. Oxyhemoglobin, deoxyhemoglobin, and water are considered representative absorbers, but the approach is not constrained or limited by absorber selection provided native basis spectra are available. The method removes wavelengths iteratively from a scattering-modulated absorption matrix by maximizing the product of its singular values and offers considerable improvements over previously published wavelength selection schemes. Resulting wavelength selections are valid for a broad range of optical properties and yield lower RMS errors than other wavelength combinations. The method is easily modified and broadly applicable to tissue optical spectroscopy. Adaptation of the algorithm to select optimal light-emitting diodes for fitting blood is described
On-sky observations with an achromatic hybrid phase knife coronagraph in the visible
CONTEXT: The four-quadrant phase mask stellar coronagraph, introduced by D.
Rouan et al., is capable of achieving very high dynamical range imaging and was
studied in the context of the direct detection of extra-solar planets.
Achromatic four-quadrant phase mask is currently being developed for broadband
IR applications. AIMS: We report on laboratory and on-sky tests of a prototype
coronagraph in the visible. This prototype, the achromatic hybrid phase knife
coronagraph, was derived from the four-quadrant phase mask principle. METHODS:
The instrumental setup implementing the coronagraph itself was designed to
record the pre- and post-coronagraphic images simultaneously so that an
efficient real-time image selection procedure can be performed. We describe the
coronagraph and the associated tools that enable robust and repeatable
observations. We present an algorithm of image selection that has been tested
against the real on-sky data of the binary star HD80081 (* 38 Lyn). RESULTS
Although the observing conditions were poor, the efficiency of the proposed
method is proven. From this experiment, we derive procedures that can apply to
future focal instruments associating adaptive optics and coronagraphy,
targeting high dynamic range imaging in astronomy, such as detecting
extra-solar planets
Discovery of a 66 mas Ultracool Binary with Laser Guide Star Adaptive Optics
We present the discovery of 2MASS J21321145+1341584AB as a closely separated
(0.066") very low-mass field dwarf binary resolved in the near-infrared by the
Keck II Telescope using laser guide star adaptive optics. Physical association
is deduced from the angular proximity of the components and constraints on
their common proper motion. We have obtained a near-infrared spectrum of the
binary and find that it is best described by an L5+/-0.5 primary and an
L7.5+/-0.5 secondary. Model-dependent masses predict that the two components
straddle the hydrogen burning limit threshold with the primary likely stellar
and the secondary likely substellar. The properties of this sytem - close
projected separation (1.8+/-0.3 AU) and near unity mass ratio - are consistent
with previous results for very low-mass field binaries. The relatively short
estimated orbital period of this system (~7-12 yr) makes it a good target for
dynamical mass measurements. Interestingly, the system's angular separation is
the tightest yet for any very low-mass binary published from a ground-based
telescope and is the tightest binary discovered with laser guide star adaptive
optics to date.Comment: 10 pages, 3 figures; accepted for publication to A
Disrupting prefrontal cortex prevents performance gains from sensory-motor training
Humans show large and reliable performance impairments when required to make more than one simple decision simultaneously. Such multitasking costs are thought to largely reflect capacity limits in response selection (Welford, 1952; Pashler, 1984, 1994), the information processing stage at which sensory input is mapped to a motor response. Neuroimaging has implicated the left posterior lateral prefrontal cortex (pLPFC) as a key neural substrate of response selection (Dux et al., 2006, 2009; Ivanoff et al., 2009). For example, activity in left pLPFC tracks improvements in response selection efficiency typically observed following training (Dux et al., 2009). To date, however, there has been no causal evidence that pLPFC contributes directly to sensory-motor training effects, or the operations through which training occurs. Moreover, the left hemisphere lateralization of this operation remains controversial (Jiang and Kanwisher, 2003; Sigman and Dehaene, 2008; Verbruggen et al., 2010). We used anodal (excitatory), cathodal (inhibitory), and sham transcranial direct current stimulation (tDCS) to left and right pLPFC and measured participants' performance on high and low response selection load tasks after different amounts of training. Both anodal and cathodal stimulation of the left pLPFC disrupted training effects for the high load condition relative to sham. No disruption was found for the low load and right pLPFC stimulation conditions. The findings implicate the left pLPFC in both response selection and training effects. They also suggest that training improves response selection efficiency by fine-tuning activity in pLPFC relating to sensory-motor translations
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