216 research outputs found
Using a coherent hydrophone array for observing sperm whale range, classification, and shallow-water dive profiles
Sperm whales in the New England continental shelf and slope were passively localized, in both range and bearing, and classified using a single low-frequency (<2500 Hz), densely sampled, towed horizontal coherent hydrophone array system. Whale bearings were estimated using time-domain beamforming that provided high coherent array gain in sperm whale click signal-to-noise ratio. Whale ranges from the receiver array center were estimated using the moving array triangulation technique from a sequence of whale bearing measurements. Multiple concurrently vocalizing sperm whales, in the far-field of the horizontal receiver array, were distinguished and classified based on their horizontal spatial locations and the inter-pulse intervals of their vocalized click signals. The dive profile was estimated for a sperm whale in the shallow waters of the Gulf of Maine with 160 m water-column depth located close to the array's near-field where depth estimation was feasible by employing time difference of arrival of the direct and multiply reflected click signals received on the horizontal array. By accounting for transmission loss modeled using an ocean waveguide-acoustic propagation model, the sperm whale detection range was found to exceed 60 km in low to moderate sea state conditions after coherent array processing.National Science Foundation (U.S.)United States. Office of Naval Researc
Role of Interfaces in the Proximity Effect in Anisotropic Superconductors
We report measurements of the critical temperature of YBCO-Co doped YBCO
Superconductor-Normal bilayer films. Depending on the morphology of the S-N
interface, the coupling between S and N layers can be turned on to depress the
critical temperature of S by tens of degrees, or turned down so the layers
appear almost totally decoupled. This novel effect can be explained by the
mechanism of quasiparticle transmission into an anisotropic superconductor.Comment: 13 pages, 3 figure
Andreev bound states in high- superconducting junctions
The formation of bound states at surfaces of materials with an energy gap in
the bulk electron spectrum is a well known physical phenomenon. At
superconductor surfaces, quasiparticles with energies inside the
superconducting gap may be trapped in bound states in quantum wells,
formed by total reflection against the vacuum and total Andreev reflection
against the superconductor. Since an electron reflects as a hole and sends a
Cooper pair into the superconductor, the surface states give rise to resonant
transport of quasiparticle and Cooper pair currents, and may be observed in
tunneling spectra. In superconducting junctions, these surface states may
hybridize and form bound Andreev states, trapped between the superconducting
electrodes. In d-wave superconductors, the order parameter changes sign under
rotation and, as a consequence, Andreev reflection may lead to the
formation of zero energy quasiparticle bound states, midgap states (MGS). The
formation of MGS is a robust feature of d-wave superconductivity and provides a
unified framework for many important effects which will be reviewed: large
Josephson current, low-temperature anomaly of the critical Josephson current,
-junction behavior, junction crossover with temperature,
zero-bias conductance peaks, paramagnetic currents, time reversal symmetry
breaking, spontaneous interface currents, and resonance features in subgap
currents. Taken together these effects, when observed in experiments, provide
proof for d-wave superconductivity in the cuprates.Comment: 52 pages, 20 figures. Review article under consideration for
publication in Superconductor Science and Technolog
Half-Metallic Ferrimagnetism in Mn_2VAl
We show that Mn_2VAl is a compound for which the generalized gradient
approximation (GGA) to the exchange-correlation functional in density
functional theory makes a qualitative change in predicted behavior compared to
the usual local density approximation (LDA). Application of GGA leads to
prediction of Mn_2VAl being a half-metallic ferrimagnet, with the minority
channel being the conducting one. The electronic and magnetic structure is
analyzed and contrasted with the isostructural enhanced semimetal Fe_2VAl.Comment: 5 pages, Latex, 6 postscript figures. Description and figures of the
(minority) Fermi surfaces have been adde
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University of Minnesota aquifer thermal energy storage (ATES) project report on the third long-term cycle
The University of Minnesota aquifer thermal energy storage (ATES) system has been operated as a field test facility (FTF) since 1982. The objectives were to design, construct, and operate the facility to study the feasibility of high-temperature ATES in a confined aquifer. Four short-term and two long-term cycles were previously conducted, which provided a greatly increased understanding of the efficiency and geochemical effects of high-temperature aquifer thermal energy storage. The third long-term cycle (LT3) was conducted to operate the ATES system in conjunction with a real heating load and to further study the geochemical impact that heated water storage had on the aquifer. For LT3, the source and storage wells were modified so that only the most permeable portion, the Ironton-Galesville part, of the Franconia-Ironton-Galesville aquifer was used for storage. This was expected to improve storage efficiency by reducing the surface area of the heated volume and simplify analysis of water chemistry results by reducing the number of aquifer-related variables which need to be considered. During LT3, a total volume of 63.2 {times} 10{sup 3} m {sup 3} of water was injected at a rate of 54.95 m{sup 3}/hr into the storage well at a mean temperature of 104.7{degrees}C. Tie-in to the reheat system of the nearby Animal Sciences Veterinary Medicine (ASVM) building was completed after injection was completed. Approximately 66 percent (4.13 GWh) of the energy added to the aquifer was recovered. Approximately 15 percent (0.64 GWh) of the usable (10 building. Operations during heat recovery with the ASVM building`s reheat system were trouble-free. Integration into more of the ASVM (or other) building`s mechanical systems would have resulted in significantly increasing the proportion of energy used during heat recovery
Enhancement and suppression effects resulting from information structuring in sentences
Information structuring through the use of cleft sentences increases the processing efficiency of references to elements within the scope of focus. Furthermore, there is evidence that putting certain types of emphasis on individual words not only enhances their subsequent processing, but also protects these words from becoming suppressed in the wake of subsequent information, suggesting mechanisms of enhancement and suppression. In Experiment 1, we showed that clefted constructions facilitate the integration of subsequent sentences that make reference to elements within the scope of focus, and that they decrease the efficiency with reference to elements outside of the scope of focus. In Experiment 2, using an auditory text-change-detection paradigm, we showed that focus has similar effects on the strength of memory representations. These results add to the evidence for enhancement and suppression as mechanisms of sentence processing and clarify that the effects occur within sentences having a marked focus structure
Checking the list: Can a model of Down syndrome help us explore the intellectual accessibility of Heritage sites?
There is currently a lack of provision for, and research into, the intellectual accessibility of heritage sites. This paper explores some possible ways forward. It examines recent research with people described as having Down syndrome and uses the syndrome's identified characteristics to create good practice guidelines. It assesses these guidelines against an audio tour written for people with learning difficulties. In conclusion, the paper suggests that drawing upon a generalised model of Down syndrome and these good practice guidelines will allow sites to identify some potential barriers and enablers to intellectual accessibility, but that fully to appreciate the effectiveness of their provision they must still institute site?specific research by people with learning difficulties
Tuning a Josephson junction through a quantum critical point
We tune the barrier of a Josephson junction through a zero-temperature
metal-insulator transition and study the thermodynamic behavior of the junction
in the proximity of the quantum-critical point. We examine a
short-coherence-length superconductor and a barrier (that is described by a
Falicov-Kimball model) using the local approximation and dynamical mean-field
theory. The inhomogeneous system is self-consistently solved by performing a
Fourier transformation in the planar momentum and exactly inverting the
remaining one-dimensional matrix with the renormalized perturbation expansion.
Our results show a delicate interplay between oscillations on the scale of the
Fermi wavelength and pair-field correlations on the scale of the coherence
length, variations in the current-phase relationship, and dramatic changes in
the characteristic voltage as a function of the barrier thickness or
correlation strength (which can lead to an ``intrinsic'' pinhole effect).Comment: 16 pages, 15 figures, ReVTe
Elevated plasma sclerostin is associated with high brain amyloid-b load in cognitively normal older adults
Osteoporosis and Alzheimer’s disease (AD) mainly affect older individuals, and the possibility of an underlying link contributing to their shared epidemiological features has rarely been investigated. In the current study, we investigated the association between levels of plasma sclerostin (SOST), a protein primarily produced by bone, and brain amyloid-beta (A ) load, a pathological hallmark of AD. The study enrolled participants meeting a set of screening inclusion and exclusion criteria and were stratified into A − (n = 65) and A + (n = 35) according to their brain A load assessed using A -PET (positron emission tomography) imaging. Plasma SOST levels, apolipoprotein E gene (APOE) genotype and several putative AD blood-biomarkers including A 40, A 42, A 42/A 40, neurofilament light (NFL), glial fibrillary acidic protein (GFAP), total tau (t-tau) and phosphorylated tau (p-tau181 and p-tau231) were detected and compared. It was found that plasma SOST levels were significantly higher in the A + group (71.49 ± 25.00 pmol/L) compared with the A − group (56.51 ± 22.14 pmol/L) (P \u3c 0.01). Moreover, Spearman’s correlation analysis showed that plasma SOST concentrations were positively correlated with brain A load (ρ = 0.321, P = 0.001). Importantly, plasma SOST combined with A 42/A 40 ratio significantly increased the area under the curve (AUC) when compared with using A 42/A 40 ratio alone (AUC = 0.768 vs 0.669, P = 0.027). In conclusion, plasma SOST levels are elevated in cognitively unimpaired older adults at high risk of AD and SOST could complement existing plasma biomarkers to assist in the detection of preclinical AD
Age-dependent white matter disruptions after military traumatic brain injury: Multivariate analysis results from ENIGMA brain injury
Mild Traumatic brain injury (mTBI) is a signature wound in military personnel, and repetitive mTBI has been linked to age-related neurogenerative disorders that affect white matter (WM) in the brain. However, findings of injury to specific WM tracts have been variable and inconsistent. This may be due to the heterogeneity of mechanisms, etiology, and comorbid disorders related to mTBI. Non-negative matrix factorization (NMF) is a data-driven approach that detects covarying patterns (components) within high-dimensional data. We applied NMF to diffusion imaging data from military Veterans with and without a self-reported TBI history. NMF identified 12 independent components derived from fractional anisotropy (FA) in a large dataset (n = 1,475) gathered through the ENIGMA (Enhancing Neuroimaging Genetics through Meta-Analysis) Military Brain Injury working group. Regressions were used to examine TBI- and mTBI-related associations in NMF-derived components while adjusting for age, sex, post-traumatic stress disorder, depression, and data acquisition site/scanner. We found significantly stronger age-dependent effects of lower FA in Veterans with TBI than Veterans without in four components (q \u3c 0.05), which are spatially unconstrained by traditionally defined WM tracts. One component, occupying the most peripheral location, exhibited significantly stronger age-dependent differences in Veterans with mTBI. We found NMF to be powerful and effective in detecting covarying patterns of FA associated with mTBI by applying standard parametric regression modeling. Our results highlight patterns of WM alteration that are differentially affected by TBI and mTBI in younger compared to older military Veterans
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