283 research outputs found
Limit for thermal transport reduction in Si nanowires with nanoengineered corrugations
Non-equilibrium molecular dynamics simulations reveal that the thermal conductance of Si nanowires with periodic corrugations is lower than that of smooth wires with cross-sections equivalent to the constricted portions. This reduction in conductance is up to 30% and tends to plateau with increasing corrugation height. Spatially resolved temperature and heat current maps provide a microscopic understanding of this effect; we find that 80% of the heat current is carried through the constricted area even for high-amplitude corrugations. More importantly, we show that temperature gradient inversion and heat current vortices at the ridge peaks establish fundamental limits on maximum conductance reduction. (C) 2013 AIP Publishing LLC
METAL CONTAMINATION AND FOOD WEB CHANGES ALTER EXPOSURE TO UPPER TROPHIC LEVELS IN UPPER BLACKFOOT RIVER BASIN STREAMS, MONTANA
Reduced invertebrate abundance and diversity are common responses to metals contamination in mining-impacted streams. The resulting changes in community composition may have implications for metals accumulation and transfer through the food web. We investigated how changes in invertebrate community composition (abundance, species richness, and food web complexity) influence metals bioaccumulation and exposure risk to upper trophic levels along a contamination gradient in the upper Blackfoot River Basin, Montana. Invertebrate species richness exhibited the strongest decline with increasing sediment metals concentrations, driven by the loss of metals-sensitive taxa. These changes in invertebrate community composition resulted in a decline in the proportion of invertebrates in the scraper functional feeding group, likely influencing dietary metals exposure to the invertebrate community. Additionally, invertebrates with a strong propensity-to-drift increased with sediment contamination, potentially facilitating metals transfer to fish and higher trophic levels through predation. Using invertebrate exposure values (invertebrate abundance x metals concentrations), we found that moderately contaminated sites in our study area produced both the highest invertebrate exposure values and the highest fish tissue metals concentrations. Considering both changes in invertebrate community composition and metal concentrations is an important step towards understanding and evaluating potential toxic effects to upper trophic levels in mining-impacted streams.
Note that there are several datasets associated with this article
Dataset for the article: Metal contamination and food web changes alter exposure to upper trophic levels in upper Blackfoot River basin streams, Montana
Reduced invertebrate abundance and diversity are common responses to heavy metals contamination in mining-impacted streams. The resulting changes in community composition may have implications for metals accumulation and transfer through the food web. We investigated how changes in invertebrate community composition (abundance, species richness, and food web complexity) influence metals bioaccumulation and exposure risk to upper trophic levels along a contamination gradient in the upper Blackfoot River basin, Montana. Invertebrate species richness exhibited the strongest decline with increasing sediment metals concentrations, driven by the loss of metals-sensitive taxa. These changes in invertebrate community composition resulted in a decline in the proportion of invertebrates in the scraper functional feeding group, likely influencing dietary metals exposure to the invertebrate community. Additionally, invertebrates with a strong propensity-to-drift increased with sediment contamination, potentially facilitating metals transfer to fish and higher trophic levels through predation. By using invertebrate exposure values (invertebrate abundance x metals concentrations), we found that moderately contaminated sites in our study area produced both the highest invertebrate exposure values and the highest metals concentrations in fish tissues. Our results indicate that considering both changes in invertebrate community composition and metal concentrations is an important step towards understanding and evaluating potential toxic effects to upper trophic levels in mining-impacted streams.
Geographic location: Upper Blackfoot River, Montana and tributaries in the vicinity of the Upper Blackfoot Mining Complex
Associated data and attachments (files available below): Water quality [Water_quality.csv] Fine sediment metals [Fine_sediment_metals.csv] Invertebrate community composition [Invertebrate_community_composition.csv] Invertebrate metals concentrations [Invertebrate_metals.csv] Fish tissue metals [Fish_metals.csv] Fish population estimate [Fish_population.csv] Site descriptions [Site_descriptions.csv] Site map [Site_map.pdf] (see Download button above
QuickCough: An instrumentational proximal airway clearance technique (ACT) for select patients with Neuromuscular Disease (NMD)
Patients with neuromuscular disease (NMD) requiring tracheostomy and mechanical ventilation secondary to respiratory failure encounter increased difficulty in removing pulmonary secretions from the airways. To combat issues associated with current treatment modalities for insufficient cough efficacy (cost, poor mobility, discomfort, lack of evidence), we have developed an instrumentational proximal airway clearance technique (ACT) which augments a manual proximal ACT developed by a client with NMD. QuickCough is a 3D-printed PLA attachment to the tracheostomy apparatus which has demonstrated its ability to facilitate pressure changes necessary to increase patient’s peak cough flow (PCF) by providing a stronger exsufflation for the patient. QuickCough meets client needs by providing a machine-washable, inexpensive method of facilitating secretion expulsion without the use of bulky equipment in-transit. This novel instrumentational augmentation of a manual ACT was designed using the engineering design process discussed in The University of Akron’s biomedical engineering design course 4800:470. Future work ought to focus on development of an automated procedure to allow application of QuickCough in cases of global paralysis or insufficient home-care
A perspective on the pathway to a scalable quantum internet using rare-earth ions
The ultimate realization of a global quantum internet will require advances
in scalable technologies capable of generating, storing, and manipulating
quantum information. The essential devices that will perform these tasks in a
quantum network are quantum repeaters, which will enable the long-range
distribution of entanglement between distant network nodes. In this
perspective, we provide an overview of the primary functions of a quantum
repeater and discuss progress that has been made toward the development of
repeaters with rare-earth ion doped materials while noting challenges that are
being faced as the technologies mature. We give particular attention to erbium,
which is well suited for networking applications. Finally, we provide a
discussion of near-term benchmarks that can further guide rare-earth ion
platforms for impact in near-term quantum networks
Professional Organizations and Healthcare Industry Support: Ethical Conflict?
A good deal of attention has been recently focused on the presumed advertising excesses of the healthcare industry in its promotion techniques to healthcare professionals, whether through offering gratuities such as gifts, honoraria, or travel support2-6 or through deception. Two basic concerns have been expressed: Does the acceptance of gratuities bias the recipient, tainting his or her responsibilities as the patient's agent? Does acceptance of the gratuity by the healthcare professional contribute to the high cost of healthcare products? The California Society of Hospital Pharmacists was recently asked by its members to formulate a policy for an appropriate relationship between the Society and the healthcare industry, addressing these concerns. In formulating its policy, it became clear that the Society depended on healthcare industry support, gathered through journal advertising, fees for booths at its various educational events, and grants for speaker
Photoluminescence spectra of point defects in semiconductors: validation of first principles calculations
Optically and magnetically active point defects in semiconductors are
interesting platforms for the development of solid-state quantum technologies.
Their optical properties are usually probed by measuring photoluminescence
spectra, which provide information on excitation energies and on the
interaction of electrons with lattice vibrations. We present a combined
computational and experimental study of photoluminescence spectra of defects in
diamond and SiC, aimed at assessing the validity of theoretical and numerical
approximations used in first principles calculations, including the use of the
Franck-Condon principle and the displaced harmonic oscillator approximation. We
focus on prototypical examples of solid-state qubits, the divacancy centers in
SiC and the nitrogen-vacancy in diamond, and we report computed
photoluminescence spectra as a function of temperature that are in very good
agreement with the measured ones. As expected we find that the use of hybrid
functionals leads to more accurate results than semilocal functionals.
Interestingly our calculations show that constrained density functional theory
(CDFT) and time-dependent hybrid DFT perform equally well in describing the
excited state potential energy surface of triplet states; our findings indicate
that CDFT, a relatively cheap computational approach, is sufficiently accurate
for the calculations of photoluminescence spectra of the defects studied here.
Finally, we find that only by correcting for finite-size effects and
extrapolating to the dilute limit, one can obtain a good agreement between
theory and experiment. Our results provide a detailed validation protocol of
first principles calculations of photoluminescence spectra, necessary both for
the interpretation of experiments and for robust predictions of the electronic
properties of point defects in semiconductors
Quasi-deterministic Localization of Er Emitters in Thin Film TiO through Submicron-scale Crystalline Phase Control
With their shielded 4f orbitals, rare-earth ions (REIs) offer optical and
electron spin transitions with good coherence properties even when embedded in
a host crystal matrix, highlighting their utility as promising quantum emitters
and memories for quantum information processing. Among REIs, trivalent erbium
(Er) uniquely has an optical transition in the telecom C-band, ideal for
transmission over optical fibers, and making it well-suited for applications in
quantum communication. The deployment of Er emitters into a thin film
TiO platform has been a promising step towards scalable integration;
however, like many solid-state systems, the deterministic spatial placement of
quantum emitters remains an open challenge. We investigate laser annealing as a
means to locally tune the optical resonance of Er emitters in TiO
thin films on Si. Using both nanoscale X-ray diffraction measurements and
cryogenic photoluminescence spectroscopy, we show that tightly focused
below-gap laser annealing can induce anatase to rutile phase transitions in a
nearly diffraction-limited area of the films and improve local crystallinity
through grain growth. As a percentage of the Er:TiO is converted to rutile,
the Er optical transition blueshifts by 13 nm. We explore the effects of
changing laser annealing time and show that the amount of optically active
Er:rutile increases linearly with laser power. We additionally demonstrate
local phase conversion on microfabricated Si structures, which holds
significance for quantum photonics.Comment: 7 pages, 4 figure
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