1,828 research outputs found
Effect of aromatic hydrocarbon addition on in situ powder-in-tube processed MgB2 tapes
We fabricated in situ powder-in-tube processed MgB2/Fe tapes using aromatic
hydrocarbon of benzene, naphthalene, and thiophene as additives, and
investigated the superconducting properties. We found that these aromatic
hydrocarbons were very effective for increasing the Jc values. The Jc values of
20mol% benzene-added tapes reached 130A/mm2 at 4.2K and 10T. This value was
almost comparable to that of 10mol% SiC-added tapes and about four times higher
than that of tapes with no additions. Microstructure analyses suggest that this
Jc enhancement is due to both the substitution of carbon for boron in MgB2 and
the smaller MgB2 grain size.Comment: 6 pages, 4 figure
Preserving Transportation Corridors for the Future: Another Look at Railroad Deeds in Washington State
This Comment will analyze the recent approach the Washington court has incorporated in settling trail development disputes across the State. In particular, the Comment will examine the court\u27s use of common law deed interpretation principles in upholding property rights while preserving valuable public transportation corridors. Furthermore, the Comment will show how the Washington court\u27s recent approach in interpreting railroad deeds has made recreational trail construction more appropriately a legislative matter, rather than a legal one. Section I of the Comment will begin with an historical overview of railroads in the United States, background on the public Rails-to-Trails movement, and an explanation of the underlying public policy and enabling federal law. Section II will then examine the leading federal case on railbanking. Section III will look at how Washington courts have addressed the railroad corridor preservation issue, particularly the Washington Supreme Court\u27s reasoning pertaining to deed interpretation in Brown v. State. Section IV will address how the court has handled rail corridor quiet title actions subsequent to Brown. Finally, Section V will conclude with observations for future trail construction within Washington State
Transport properties of diluted magnetic semiconductors: Dynamical mean field theory and Boltzmann theory
The transport properties of diluted magnetic semiconductors (DMS) are
calculated using dynamical mean field theory (DMFT) and Boltzmann transport
theory. Within DMFT we study the density of states and the dc-resistivity,
which are strongly parameter dependent such as temperature, doping, density of
the carriers, and the strength of the carrier-local impurity spin exchange
coupling. Characteristic qualitative features are found distinguishing weak,
intermediate, and strong carrier-spin coupling and allowing quantitative
determination of important parameters defining the underlying ferromagnetic
mechanism. We find that spin-disorder scattering, formation of bound state, and
the population of the minority spin band are all operational in DMFT in
different parameter range. We also develop a complementary Boltzmann transport
theory for scattering by screened ionized impurities. The difference in the
screening properties between paramagnetic () and ferromagnetic ()
states gives rise to the temperature dependence (increase or decrease) of
resistivity, depending on the carrier density, as the system goes from the
paramagnetic phase to the ferromagnetic phase. The metallic behavior below
for optimally doped DMS samples can be explained in the Boltzmann theory
by temperature dependent screening and thermal change of carrier spin
polarization.Comment: 15 pages, 15 figure
Femtosecond Demagnetization and Hot Hole Relaxation in Ferromagnetic GaMnAs
We have studied ultrafast photoinduced demagnetization in GaMnAs via
two-color time-resolved magneto-optical Kerr spectroscopy. Below-bandgap
midinfrared pump pulses strongly excite the valence band, while near-infrared
probe pulses reveal sub-picosecond demagnetization that is followed by an
ultrafast (1 ps) partial recovery of the Kerr signal. Through comparison
with InMnAs, we attribute the signal recovery to an ultrafast energy relaxation
of holes. We propose that the dynamical polarization of holes through -
scattering is the source of the observed probe signal. These results support
the physical picture of femtosecond demagnetization proposed earlier for
InMnAs, identifying the critical roles of both energy and spin relaxation of
hot holes.Comment: 7 pages, 6 figure
Randomly Diluted e_g Orbital-Ordered Systems
Dilution effects on the long-range ordered state of the doubly degenerate
orbital are investigated. Quenched impurities without the orbital degree
of freedom are introduced in the orbital model where the long-range order is
realized by the order-from-disorder mechanism. It is shown by the Monte-Carlo
simulation and the cluster-expansion method that a decrease in the orbital
ordering temperature by dilution is remarkable in comparison with that in the
randomly diluted spin models. Tiltings of orbitals around impurity cause this
unique dilution effects on the orbital systems. The present theory provides a
new view point for the recent experiments in KCuZnF.Comment: 4 pages, 4 figure
Spin dynamics of a one-dimensional spin-1/2 fully anisotropic Ising-like antiferromagnet in a transverse magnetic field
We consider the one-dimensional Ising-like fully anisotropic S=1/2 Heisenberg
antiferromagnetic Hamiltonian and study the dynamics of domain wall excitations
in the presence of transverse magnetic field . We obtain dynamical spin
correlation functions along the magnetic field and
perpendicular to it . It is shown that the line shapes of
and are purely symmetric at the
zone-boundary. It is observed in for that the
spectral weight moves toward low energy side with the increase of . This
model is applicable to study the spin dynamics of CsCoCl in the presence of
weak interchain interactions.Comment: 19 pages, LaTeX, 12 eps figure
Squamous cell carcinoma antigen suppresses radiation-induced cell death
Previous study has demonstrated that squamous cell carcinoma antigen (SCCA) 1 attenuates apoptosis induced by TNFα, NK cell or anticancer drug. In this study, we have examined the effect of SCCA2, which is highly homologous to SCCA1, but has different target specificity, against radiation-induced apoptosis, together with that of SCCA1. We demonstrated that cell death induced by radiation treatment was remarkably suppressed not only in SCCA1 cDNA-transfected cells, but also in SCCA2 cDNA-transfected cells. In these transfectants, caspase 3 activity and the expression of activated caspase 9 after radiation treatment were suppressed. Furthermore, the expression level of phosphorylated p38 mitogen-activated protein kinase (p38 MAPK) was suppressed compared to that of the control cells. The expression level of upstream stimulator of p38 MAPK, phosphorylated MKK3/MKK6, was also suppressed in the radiation-treated cells. Thus, both SCCA1 and SCCA2 may contribute to survival of the squamous cells from radiation-induced apoptosis by regulating p38 MAPK pathway. © 2001 Cancer Research Campaign http://www.bjcancer.co
Varietal differences in the texture of grape berries measured by penetration tests
Penetration tests were made on 8 mm thick flesh sections from grape berries of 22 cultivars of Vitis vinifera L. and 18 of Vitis labruscana Bailey. Deformation at the first major peak (DFP), maximum force (MF), force at the first major peak (FFP) and work to the first major peak (WFP) were recorded. High correlation coefficients were obtained between the rating of difficulty of breakdown on mastication in the sensory tests and DFP (r=0.86**), and the rating of flesh firmness in the sensory test and MF (r=0.84**). The mean value and variance of DFP and WFP were significantly higher in V. labruscana than in V. vinifera, whereas those of MF were nearly the same. DFP and MF were not correlated for V. vinifera cultivars, but were for V. labruscana cultivars (r=0.68**). These results indicate that the texture of V. labruscana had a wide variation in toughness whereas that of V. vinifera was brittle and did not have a wide variation in toughness; both groups had the same variation in firmness
Mechanism of carrier-induced ferromagnetism in magnetic semiconductors
Taking into account both random impurity distribution and thermal
fluctuations of localized spins, we have performed a model calculation for the
carrier (hole) state in GaMnAs by using the coherent potential
approximation (CPA). The result reveals that a {\it p}-hole in the band tail of
GaMnAs is not like a free carrier but is rather virtually bounded
to impurity sites. The carrier spin strongly couples to the localized {\it d}
spins on Mn ions. The hopping of the carrier among Mn sites causes the
ferromagnetic ordering of the localized spins through the double-exchange
mechanism. The Curie temperature obtained by using conventional parameters
agrees well with the experimental result.Comment: 7 pages, 4 figure
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