1,202 research outputs found
Effects of Fe2O3 addition on the nitridation of silicon powder
The reaction of silicon powder and nitrogen was studied in the range of 1300-1400 C. When an addition of Fe2O3 was more than 0.8wt%, the reaction was linear and compared to samples with no Fe2O3, the reaction velocity increased 5 to 10 times. The reactions were mediated by the process of peeling and cracking in a thin layer of Si2N4 formed on the silicon particles or on the surface of the Fe-Si melts. As the addition of Fe2O3 increased, the reaction activation energy for highly pure samples decreased. Fe2O3 which exceeded the Si3N4 solubility limits was finally converted to d-Fe
Quasi-classical path integral approach to supersymmetric quantum mechanics
{}From Feynman's path integral, we derive quasi-classical quantization rules
in supersymmetric quantum mechanics (SUSY-QM). First, we derive a SUSY
counterpart of Gutzwiller's formula, from which we obtain the quantization rule
of Comtet, Bandrauk and Campbell when SUSY is good. When SUSY is broken, we
arrive at a new quantization formula, which is found as good as and even
sometime better than the WKB formula in evaluating energy spectra for certain
one-dimensional bound state problems. The wave functions in the stationary
phase approximation are also derived for SUSY and broken SUSY cases. Insofar as
a broken SUSY case is concerned, there are strong indications that the new
quasi-classical approximation formula always overestimates the energy
eigenvalues while WKB always underestimates.Comment: 13 pages + 5 figures, complete paper submitted as postscript file, to
appear in Phys. Rev.
An Effective Reduction of Critical Current for Current-Induced Magnetization Switching by a Ru Layer Insertion in an Exchange-Biased Spin-Valve
Recently it has been predicted that a spin-polarized electrical current
perpendicular-to-plane (CPP) directly flowing through a magnetic element can
induce magnetization switching through spin-momentum transfer. In this letter,
the first observation of current-induced magnetization switching (CIMS) in
exchange-biased spin-valves (ESPVs) at room temperature is reported. The ESPVs
show the CIMS behavior under a sweeping dc current with a very high critical
current density. It is demonstrated that a thin Ruthenium (Ru) layer inserted
between a free layer and a top electrode effectively reduces the critical
current densities for the CIMS. An "inverse" CIMS behavior is also observed
when the thickness of the free layer increases.Comment: 15 pages with figure
Possible observation of energy level quantization in an intrinsic Josephson junction
Energy level quantization (ELQ) is studied to clarify the macroscopic quantum
dynamics of the d-wave Josephson junction (JJ). The influences of the nodal
quasiparticles of d-wave superconductivity on the damping effect are
numerically evaluated on the basis of a phenomenological model. The
calculation, based on realistic parameters for a Bi2Sr2CaCu2O8+d (Bi2212)
intrinsic JJ, shows that the observation of ELQ is possible when the sweep rate
of the bias current exceeds 10 A/sec. High-sweep- rate measurements (121A/sec)
performed on a Bi2212 intrinsic JJ result in the appearance of multiple peaks
in the switching current distribution suggesting the realization of ELQ in the
d-wave JJ.Comment: 5 pages, 3 figure
Large Dispersive Shift of Cavity Resonance Induced by a Superconducting Flux Qubit in the Straddling Regime
We demonstrate enhancement of the dispersive frequency shift in a coplanar
waveguide resonator induced by a capacitively-coupled superconducting flux
qubit in the straddling regime. The magnitude of the observed shift, 80 MHz for
the qubit-resonator detuning of 5 GHz, is quantitatively explained by the
generalized Jaynes-Cummings model which takes into account the contribution of
the qubit higher energy levels. By applying the enhanced dispersive shift to
the qubit readout, we achieved 90% contrast of the Rabi oscillations which is
mainly limited by the energy relaxation of the qubit.Comment: 10 pages, 8 figure
Transport of FNPP1-derived radiocaesium from subtropical mode water in the western North Pacific Ocean to the Sea of Japan
This study investigated the spatio-temporal variations in activity
concentrations in the Sea of Japan (SOJ) of 137Cs and these transport
process from the North Pacific Ocean to the SOJ through the East China Sea
(ECS) during 2012–2016. The 137Cs activity concentrations in the SOJ
have been increasing since 2012–2013 and reached a maximum in 2015–2016 of
approximately 3.4 Bq m−3, more than twice the pre-Fukushima accident
137Cs activity concentration of  ∼ 1.5 Bq m−3. The
134Cs ∕ 137Cs activity ratios ranged from 0.36 to 0.51 in 2016.
After taking into account radioactive decay and ocean mixing, we concluded
that these 134Cs ∕ 137Cs activity ratios were evidence that the
Fukushima accident caused the increase in the 137Cs activity
concentrations. In the North Pacific south of Japan (NPSJ), the highest
137Cs activities in 2012–2013 were observed in water from a depth of
300 m, the potential water density anomaly (σθ) of which
corresponded to subtropical mode water (STMW). In the ECS, a clear increase
in the 137Cs activity concentration started at a depth of 140 m
(σθ =  25.2 kg m−3) in April 2013, propagated to the
surface layers at depths of roughly 0–50 m, reached a maximum in 2015 and
decreased in subsequent years. In the ECS, the Fukushima-derived radiocaesium
activity concentration in surface water reached a maximum in 2014–2015,
whereas the concentration in the SOJ reached a maximum in 2015–2016. The
propagation of Fukushima-derived radiocaesium in surface seawater from the
ECS into the SOJ therefore required approximately 1Â year. These temporal
changes in 137Cs activity concentrations and 134Cs ∕ 137Cs
activity ratios indicated that part of the 137Cs and 134Cs derived
from the Fukushima accident (FNPP1-derived 137Cs and134Cs) was
transported within several years to the ECS and then to the SOJ via STMW from
the NPSJ. The integrated amount of FNPP1-derived 137Cs that entered the
SOJ before 2016 was estimated to be 0.21±0.01 PBq, 5.0 % of the
estimated total amount of FNPP1-derived 137Cs in the STMW. The
integrated amount of FNPP1-derived 137Cs that returned to the North
Pacific Ocean through the Tsugaru Strait was estimated to be 0.09±0.01 Bq, 43 % of the total amount of FNPP1-derived 137Cs
transported to the SOJ and 2.1 % of the estimated total amount of
FNPP1-derived 137Cs in the STMW.</p
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