1,056 research outputs found
Implementation of an anisotropic damage material model for non-proportional loading
Anisotropic damage for non-proportional loading is incorporated in an implicit finite element code under the framework of continuum damage models, using two different methodologies. Simple simulations are carried out to check the performance of the models. The advantages and drawbacks of both methodologies are discussed briefly
Magnetic frustration in a stoichiometric spin-chain compound, CaCoIrO
The temperature dependent ac and dc magnetization and heat capacity data of
CaCoIrO, a spin-chain compound crystallizing in a KCdCl-derived
rhombohedral structure, show the features due to magnetic ordering of a
frustrated-type below about 30 K, however without exhibiting the signatures of
the so-called "partially disordered antiferromagnetic structure" encountered in
the isostructural compounds, CaCoO and CaCoRhO. This class
of compounds thus provides a variety for probing the consequences of magnetic
frustration due to topological reasons in stoichiometric spin-chain materials,
presumably arising from subtle differences in the interchain and intrachain
magnetic coupling strengths. This compound presents additional interesting
situations in the sense that, ac susceptibility exhibits a large frequency
dependence in the vicinity of 30 K uncharacteristic of conventional
spin-glasses, with this frustrated magnetic state being robust to the
application of external magnetic fields.Comment: Physical Review (Rapid Communications), in pres
^{17}O and ^{51}V NMR for the zigzag spin-1 chain compound CaV2O4
V NMR studies on CaV2O4 single crystals and O NMR studies on
O-enriched powder samples are reported. The temperature dependences of
the O NMR line width and nuclear spin-lattice relaxation rate give
strong evidence for a long-range antiferromagnetic transition at Tn = 78 K in
the powder. Magnetic susceptibility measurements show that Tn = 69 K in the
crystals. A zero-field V NMR signal was observed at low temperatures (f
237 MHz at 4.2 K) in the crystals. The field swept spectra with the
field in different directions suggest the presence of two antiferromagnetic
substructures. Each substructure is collinear, with the easy axes of the two
substructures separated by an angle of 19(1) degree, and with their average
direction pointing approximately along the b-axis of the crystal structure. The
two spin substructures contain equal number of spins. The temperature
dependence of the ordered moment, measured up to 45 K, shows the presence of an
energy gap Eg in the antiferromagnetic spin wave excitation spectrum.
Antiferromagnetic spin wave theory suggests that Eg lies between 64 and 98 K.Comment: 11 pages, 14 figures. v2: 2 new figures; version published in Phys.
Rev.
Hot Die Forming - Flat (HDF-F<sup>Al</sup>):An innovative hot forming technology for extreme lightweight in aluminum sheet alloys
Aluminum is an ideal material for light transport applications. Despite the obvious advantages in weight ratio and corrosion resistance, high strength aluminum alloys have limited formability compared to traditional steels at room temperature conditions. A solution is to combine mechanical loading with thermal component i.e. deformation at elevated temperature. Currently super plastic forming and Quick Plastic Forming (QPF) is used to enhance the formability of Aluminum alloys. However, the cycle time for super plastic forming as well as for QPF is too high for mass production. An innovative and novel forming method called Hot Die Forming (HDF) has been developed to achieve high strains in high strength aluminum alloys (maximum 700 [MPa]) by heating them to Solution Heat Temperature (SHT), while keeping the cycle time suitable for large scale production. To study the feasibility and optimize the process parameters, a digital platform has been developed for simulations of HDF process. The simulation process has been automated, the user can provide tool geometries and input parameters to check the feasibility of HDF process or to optimize the parameters and die shape
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Sensitivity analysis of time-step in modeling river and aquifer interaction
Center for Water and the Environmen
Stage-dependent effects of retinoic acid on regenerating urodele limbs
Following amputation through the distal zeugopodium, regenerating limbs of larvalAmbystoma mexicanum and pre and post-metamorphic Pleurodeles waltlii were treated with 150 μg of retinoic acid (RA) per gram of body weight, at the dedifferentiation, early bud, medium bud, late bud or early redifferentiation stages of regeneration. The effect of RA on regenerate morphogenesis differed as a function of the stage at which it was administered. When given during dedifferentiation or at early bud stages, RA evoked proximodistal duplications of stump segments in the regenerates. The maximum duplication index (DI) in Abystoma was achieved when RA was injected at 4 days post-amputation, which corresponds to the stage of dedifferentiation; and inPleurodeles at 10 days post-amputation, which corresponds to a stage midway between early bud and medium bud. When RA was administered at later stages, the DI declined progressively to zero or nearly zero by the stage of early redifferentiation in both species. The decline in DI was due to a decreased frequency of duplication, not to a decrease in the magnitude of duplication in individual regenerates. At the same time, there was an increase in hypomorphism and aberrant morphogenesis of both duplicating and non-duplicating regenerates. These results indicate that regenerative cells are differentially sensitive to RA in a stage-dependent way
Toxicity evaluation of e-juice and its soluble aerosols generated by electronic cigarettes using recombinant bioluminescent bacteria responsive to specific cellular damages
Electronic-cigarettes (e-cigarette) are widely used as an alternative to traditional cigarettes but their safety is not well established. Herein, we demonstrate and validate an analytical method to discriminate the deleterious effects of e-cigarette refills (e-juice) and soluble e-juice aerosol (SEA) by employing stress-specific bioluminescent recombinant bacterial cells (RBCs) as whole-cell biosensors. These RBCs carry luxCDABE-operon tightly controlled by promoters that specifically induced to DNA damage (recA), superoxide radicals (sodA), heavy metals (copA) and membrane damage (oprF). The responses of the RBCs following exposure to various concentrations of e-juice/SEA was recorded in real-time that showed dose-dependent stress specific-responses against both the e-juice and vaporized e-juice aerosols produced by the e-cigarette. We also established that high doses of e-juice (4-folds diluted) lead to cell death by repressing the cellular machinery responsible for repairing DNA-damage, superoxide toxicity, ion homeostasis and membrane damage. SEA also caused the cellular damages but the cells showed enhanced bioluminescence expression without significant growth inhibition, indicating that the cells activated their global defense system to repair these damages. DNA fragmentation assay also revealed the disintegration of total cellular DNA at sub-toxic doses of e-juice. Despite their state of matter, the e-juice and its aerosols induce cytotoxicity and alter normal cellular functions, respectively that raises concerns on use of e-cigarettes as alternative to traditional cigarette. The ability of RBCs in detecting both harmful effects and toxicity mechanisms provided a fundamental understanding of biological response to e-juice and aerosols.open
Crystallography, magnetic susceptibility, heat capacity, and electrical resistivity of heavy fermion LiVO single crystals grown using a self-flux technique
Magnetically pure spinel compound is a rare -electron
heavy fermion. Measurements on single crystals are needed to clarify the
mechanism for the heavy fermion behavior in the pure material. In addition, it
is known that small concentrations ( mol%) of magnetic defects in the
structure strongly affect the properties, and measurements on single crystals
containing magnetic defects would help to understand the latter behaviors.
Herein, we report flux growth of and preliminary measurements
to help resolve these questions. The magnetic susceptibility of some as-grown
crystals show a Curie-like upturn at low temperatures, showing the presence of
magnetic defects within the spinel structure. The magnetic defects could be
removed in some of the crystals by annealing them at 700 C\@. A very
high specific heat coefficient = 450 mJ/(mol K\@) was obtained
at a temperature of 1.8 K for a crystal containing a magnetic defect
concentration = 0.5 mol%. A crystal with = 0.01 mol% showed a residual resistivity ratio of 50.Comment: 6 pages, 7 figures, Title modifie
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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