447 research outputs found
Solid-State Relays for Control
Solid-state relays (SSRs) »J offer improved reliability and performance over that of electro-mechanical relays (EMRs) in applications requiring large numbers of contact closures, interfacing to low power solid-state circuits, maximum speed and control of contact closure, and minimum production of radio-frequency interference. SSRs may not be used as a direct replacement for EMRs in many circuits, however, and a number of the important fac-tors required for satisfactory SSR application and performance are considered
Solvent Effects on Extractant Conformational Energetics in Liquid-Liquid Extraction: A Simulation Study of Molecular Solvents and Ionic Liquids
Extractant design in liquid-liquid extraction (LLE) is a research frontier of
metal ion separations that typically focuses on the direct extractant-metal
interactions. However, a more detailed understanding of energetic drivers of
separations beyond primary metal coordination is often lacking, including the
role of solvent in the extractant phase. In this work, we propose a new
mechanism for enhancing metal-complexant energetics with nanostructured
solvents. Using molecular dynamics simulations with umbrella sampling, we find
that the organic solvent can reshape the energetics of the extractant's
intramolecular conformational landscape. We calculate free energy profiles of
different conformations of a representative bidentate extractant,
n-octyl(phenyl)-N,N-diisobutyl carbamoyl methyl phosphinoxide (CMPO), in four
different solvents: dodecane, tributyl phosphate (TBP), and dry and wet ionic
liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
([EMIM][Tf_2N]). By promoting reorganization of the extractant molecule into
its binding conformation, our findings reveal how particular solvents can
ameliorate this unfavorable step of the metal separation process. In
particular, the charge alternating nanodomains formed in ILs substantially
reduce the free energy penalty associated with extractant reorganization.
Importantly, using alchemical free energy calculations, we find that this
stabilization persists even when we explicitly include the extracted cation.
These findings provide insight into the energic drivers of metal ion
separations and potentially suggest a new approach to designing effective
separations using a molecular-level understanding of solvent effects
Synthesis, Structure, and Ferromagnetism of a New Oxygen Defect Pyrochlore System Lu2V2O_{7-x} (x = 0.40-0.65)
A new fcc oxygen defect pyrochlore structure system Lu2V2O_{7-x} with x =
0.40 to 0.65 was synthesized from the known fcc ferromagnetic semiconductor
pyrochlore compound Lu2V2O7 which can be written as Lu2V2O6O' with two
inequivalent oxygen sites O and O'. Rietveld x-ray diffraction refinements
showed significant Lu-V antisite disorder for x >= 0.5. The lattice parameter
versus x (including x = 0) shows a distinct maximum at x ~ 0.4. We propose that
these observations can be explained if the oxygen defects are on the O'
sublattice of the structure. The magnetic susceptibility versus temperature
exhibits Curie-Weiss behavior above 150 K for all x, with a Curie constant C
that increases with x as expected in an ionic model. However, the magnetization
measurements also show that the (ferromagnetic) Weiss temperature theta and the
ferromagnetic ordering temperature T_C both strongly decrease with increasing x
instead of increasing as expected from C(x). The T_C decreases from 73 K for x
= 0 to 21 K for x = 0.65. Furthermore, the saturation moment at a field of 5.5
T at 5 K is nearly independent of x, with the value expected for a fixed spin
1/2 per V. The latter three observations suggest that Lu2V2O_{7-x} may contain
localized spin 1/2 vanadium moments in a metallic background that is induced by
oxygen defect doping, instead of being a semiconductor as suggested by the C(x)
dependence.Comment: 9 pages including 7 figures, 3 table
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Solution spectroelectrochemical cell for in situ X-ray absorption fine structure
A purpose-built spectroelectrochemical cell for in situ fluorescence XAFS (X-ray Absorption Fine Structure) measurements of bulk solution species during constant-potential electrolysis is described. The cell performance was demonstrated by the collection of europium L{sub 3}-edge XANES (X-ray Absorption Near Edge Structure) throughout the course of electrolysis of an aqueous solution of EuCl{sub 3}{center_dot}6H{sub 2}O in 1 M H{sub 2}SO{sub 4}. The europium L{sub 3}-edge resonances reported here for the Eu{sup III} and Eu{sup II} ions demonstrate that their 2p{sub 3/2} {yields} 5d electronic transition probabilities are not the same
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Synthesis and properties of lanthanide-exchanged Preyssler`s heteropolyanions
Na{sup +} in the Preyssler heteropolytungstate anion [NaP{sub 5}W{sub 30}O{sub 110}]{sup 14{minus}} can be exchanged for a trivalent lanthanide ion. The potential significance of this new class of lanthanide heteropolyanions relates to their applications in catalysis science. This view follows from the fact that Keggin heteropolyanions and their free acids are used as heterogeneous solid catalysts and homogeneous solution catalysts. The authors describe synthetic conditions that lead to the incorporation of Ce{sup 3+} and Pr{sup 3+} within the Preyssler anion, and the coprecipitation of Ce{sup 3+} and the Preyssler anion. Initial studies indicate that the latter, coprecipitated, material deserves study for bifunctional catalytic activity
Functional Electrical Stimulation following nerve injury in a Large Animal Model.
INTRODUCTION: Controversy exists over the effects of functional electrical stimulation (FES) on reinnervation. We hypothesized that intramuscular FES would not delay reinnervation after recurrent laryngeal nerve (RLn) axonotmesis. METHODS: RLn cryo-injury and electrode implantation in ipsilateral posterior cricoarytenoid muscle (PCA) were performed in horses. PCA was stimulated for 20 weeks in eight animals; seven served as controls. Reinnervation was monitored through muscle response to hypercapnia, electrical stimulation and exercise. Ultimately, muscle fiber type proportions and minimum fiber diameters, and RLn axon number and degree of myelination were determined. RESULTS: Laryngeal function returned to normal in both groups within 22 weeks. FES improved muscle strength and geometry, and induced increased type I:II fiber proportion (p=0.038) in the stimulated PCA. FES showed no deleterious effects on reinnervation. DISCUSSION: Intramuscular electrical stimulation did not delay PCA reinnervation after axonotmesis. FES can represent a supportive treatment to promote laryngeal functional recovery after RLn injury. This article is protected by copyright. All rights reserved
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Nanoscale encapsulation: the structure of cations in hydrophobic microporous aluminosilicates
Hydrophobic microporous aluminosilicates, created by organic surface modification of inherently hydrophilic materials such as zeolites and clays, are currently being investigated as storage media for hazardous cations. Use of organic monolayers to modify the surface of an aluminosilicate after introducing an ion into the zeolite/clay reduces the interaction of water with the material. Resulting systems are about 20 times more resistant to leaching of stored ion. XAS spectra from the encapsulated ion demonstrate that byproducts from the organic modifier can complex with the stored cation. This complexation can result in a decreased affinity of the cation for the aluminosilicate matrix. Changing the organic modifier eliminates this problem. XAS spectra also indicate that the reactivity and speciation of the encapsulated ion may change upon application of the hydrophobic layer
Temperature-dependent spin gap and singlet ground state in BaCuSi2O6
Bulk magnetic measurements and inelastic neutron scattering were used to
investigate the spin-singlet ground state and magnetic gap excitations in
BaCuSi2O6, a quasi-2-dimensional antiferromagnet with a bilayer structure. The
results are well described by a model based on weakly interacting
antiferromagnetic dimers. A strongly temperature-dependent dispersion in the
gap modes was found. We suggest that the observed excitations are analogous to
magneto-excitons in light rare-earth compounds, but are an intrinsic property
of a simple Heisenberg Hamiltonian for the S=1/2 magnetic bilayer.Comment: 10 pages, 4 figures, REVTeX and PS for text, PS for figures direct
download: http://papillon.phy.bnl.gov/preprints/bacusio.htm
Radar and environment-based hail damage estimates using machine learning
Large hail events are typically infrequent, with significant time gaps between occurrences at specific locations. However, when these events do happen, they can cause rapid and substantial economic losses within a matter of minutes. Therefore, it is crucial to have the ability to accurately observe and understand hail phenomena to improve the mitigation of this impact. While in situ observations are accurate, they are limited in number for an individual storm. Weather radars, on the other hand, provide a larger observation footprint, but current radar-derived hail size estimates exhibit low accuracy due to horizontal advection of hailstones as they fall, the variability of hail size distributions (HSDs), complex scattering and attenuation, and mixed hydrometeor types. In this paper, we propose a new radar-derived hail product developed using a large dataset of hail damage insurance claims and radar observations. We use these datasets coupled with environmental information to calculate a hail damage estimate (HDE) using a deep neural network approach aiming to quantify hail impact, with a critical success index of 0.88 and a coefficient of determination against observed damage of 0.79. Furthermore, we compared HDE to a popular hail size product (MESH), allowing us to identify meteorological conditions that are associated with biases on MESH. Environments with relatively low specific humidity, high CAPE and CIN, low wind speeds aloft, and southerly winds at the ground are associated with a negative MESH bias, potentially due to differences in HSD, hail hardness, or mixed hydrometeors. In contrast, environments with low CAPE, high CIN, and relatively high specific humidity aloft are associated with a positive MESH bias.</p
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