405 research outputs found
Secondary peak on asymmetric magnetization loop of type-II superconductors
Asymmetric magnetization loops with a second peak effect were parameterized
by the extended critical state model. The magnetic field distribution in a
sample is considered. Expression is suggested for a peak of the critical
current density and corresponding depression on field dependence of the depth
of surface layer with equilibrium magnetization. These functions determine the
width and the asymmetry of a magnetization loop. Asymmetry of the secondary
peak height on magnetization branches for increasing and decreasing field is
reproduced on the computed magnetization curves.Comment: 6 pages, 2 figures, Equation 6 is modified to be f=0 at B=
Rapid analysis of pyrethroid insecticides in aquaculture seawater samples via membrane-assisted solvent extraction coupled with gas chromatography-electron capture detection
A simple, efficient, and environmentally friendly membrane-assisted solvent extraction (MASE) method for the extraction and preconcentration of six pyrethroid insecticides from aquaculture seawater samples followed by gas chromatography-electron capture detection (GC-ECD) was successfully proposed. The operating conditions for MASE, such as the extraction solvent, solvent volume, NaCl concentration, stirring rate, extraction time, and temperature, were optimized. Compared to conventional Florisil-solid phase extraction (SPE), higher extraction recoveries (85.9% to 105.9%) of three spiked levels of the six pyrethroid pesticides in aquaculture seawater were obtained using MASE, and the RSD values were lower than 7.9%. The limits of detection (LOD, signal-to-noise ratio (S/N)=3) and quantification (LOQ, S/N = 10) were in the range of 0.037–0.166 and 0.12–0.55 µg L-1, respectively. The results demonstrate the excellent applicability of the MASE method in analyzing the six pyrethroid pesticides in aqueous samples. The proposed method exhibited a high potential for routine monitoring analysis of pyrethroid insecticides in seawater samples
Inter- and Intragranular Effects in Superconducting Compacted Platinum Powders
Compacted platinum powders exhibit a sharp onset of diamagnetic screening at
mK in zero magnetic field in all samples investigated. This
sharp onset is interpreted in terms of the intragranular transition into the
superconducting state. At lower temperatures, the magnetic ac susceptibility
strongly depends on the ac field amplitude and reflects the small intergranular
critical current density . This critical current density shows a strong
dependence on the packing fraction f of the granular samples. Surprisingly,
increases significantly with decreasing f ( A/cm for f = 0.67 and A/cm for f
= 0.50). The temperature dependence of shows strong positive curvature
over a wide temperature range for both samples. The phase diagrams of inter-
and intragranular superconductivity for different samples indicate that the
granular structure might play the key role for an understanding of the origin
of superconductivity in the platinum compacts.Comment: 11 pages including 9 figures. To appear in Phys. Rev. B in Nov. 0
Magnetic enhancement of CoZnFeO spinel oxide by mechanical milling
We report the magnetic properties of mechanically milled
CoZnFeO spinel oxide. After 24 hours milling of the
bulk sample, the XRD spectra show nanostructure with average particle size
20 nm. The as milled sample shows an enhancement in magnetization and
ordering temperature compared to the bulk sample. If the as milled sample is
annealed at different temperatures for the same duration, recrystallization
process occurs and approaches to the bulk structure on increasing the annealing
temperatures. The magnetization of the annealed samples first increases and
then decreases. At higher annealing temperature ( 1000C) the system
shows two coexisting magnetic phases {\it i.e.}, spin glass state and
ferrimagnetic state, similar to the as prepared bulk sample. The room
temperature M\"{o}ssbauer spectra of the as milled sample, annealed at
300C for different durations (upto 575 hours), suggest that the observed
change in magnetic behaviour is strongly related with cations redistribution
between tetrahedral (A) and octahedral (O) sites in the spinel structure. Apart
from the cation redistribution, we suggest that the enhancement of
magnetization and ordering temperature is related with the reduction of B site
spin canting and increase of strain induced anisotropic energy during
mechanical milling.Comment: 14 pages LaTeX, 10 ps figure
Studies of Prototype CsI(Tl) Crystal Scintillators for Low-Energy Neutrino Experiments
Crystal scintillators provide potential merits for the pursuit of low-energy
low-background experiments. A CsI(Tl) scintillating crystal detector is being
constructed to study low-energy neutrino physics at a nuclear reactor, while
projects are underway to adopt this technique for dark matter searches. The
choice of the geometrical parameters of the crystal modules, as well as the
optimization of the read-out scheme, are the results of an R&D program.
Crystals with 40 cm in length were developed. The detector requirements and the
achieved performance of the prototypes are presented. Future prospects for this
technique are discussed.Comment: 32 pages, 14 figure
Contribution of biomimetic collagen-ligand interaction to intrafibrillar mineralization
Contemporary models of intrafibrillar mineralization mechanisms are established using collagen fibrils as templates without considering the contribution from collagen-bound apatite nucleation inhibitors. However, collagen matrices destined for mineralization in vertebrates contain bound matrix proteins for intrafibrillar mineralization. Negatively charged, high\u2013molecular weight polycarboxylic acid is cross-linked to reconstituted collagen to create a model for examining the contribution of collagen-ligand interaction to intrafibrillar mineralization. Cryogenic electron microscopy and molecular dynamics simulation show that, after cross-linking to collagen, the bound polyelectrolyte caches prenucleation cluster singlets into chain-like aggregates along the fibrillar surface to increase the pool of mineralization precursors available for intrafibrillar mineralization. Higher-quality mineralized scaffolds with better biomechanical properties are achieved compared with mineralization of unmodified scaffolds in polyelectrolyte-stabilized mineralization solution. Collagen-ligand interaction provides insights on the genesis of heterogeneously mineralized tissues and the potential causes of ectopic calcification in nonmineralized body tissues
A CsI(Tl) Scintillating Crystal Detector for the Studies of Low Energy Neutrino Interactions
Scintillating crystal detector may offer some potential advantages in the
low-energy, low-background experiments. A 500 kg CsI(Tl) detector to be placed
near the core of Nuclear Power Station II in Taiwan is being constructed for
the studies of electron-neutrino scatterings and other keV-MeV range neutrino
interactions. The motivations of this detector approach, the physics to be
addressed, the basic experimental design, and the characteristic performance of
prototype modules are described. The expected background channels and their
experimental handles are discussed.Comment: 34 pages, 11 figures, submitted to Nucl. Instrum. Method
Partial wave analysis of J/\psi \to \gamma \phi \phi
Using events collected in the BESII detector, the
radiative decay is
studied. The invariant mass distribution exhibits a near-threshold
enhancement that peaks around 2.24 GeV/.
A partial wave analysis shows that the structure is dominated by a
state () with a mass of
GeV/ and a width of GeV/. The
product branching fraction is: .Comment: 11 pages, 4 figures. corrected proof for journa
Measurements of the observed cross sections for exclusive light hadrons containing at , 3.650 and 3.6648 GeV
By analyzing the data sets of 17.3, 6.5 and 1.0 pb taken,
respectively, at , 3.650 and 3.6648 GeV with the BES-II
detector at the BEPC collider, we measure the observed cross sections for
, , ,
and at the three energy
points. Based on these cross sections we set the upper limits on the observed
cross sections and the branching fractions for decay into these
final states at 90% C.L..Comment: 7 pages, 2 figure
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