87 research outputs found
Current-driven Magnetization Reversal in a Ferromagnetic Semiconductor (Ga,Mn)As/GaAs/(Ga,Mn)As Tunnel Junction
Current-driven magnetization reversal in a ferromagnetic semiconductor based
(Ga,Mn)As/GaAs/(Ga,Mn)As magnetic tunnel junction is demonstrated at 30 K.
Magnetoresistance measurements combined with current pulse application on a
rectangular 1.5 x 0.3 um^2 device revealed that magnetization switching occurs
at low critical current densities of 1.1 - 2.2 x 10^5 A/cm^2 despite the
presence of spin-orbit interaction in the p-type semiconductor system. Possible
mechanisms responsible for the effect are discussed.Comment: 16 pages, 4 figure
Estimation of the spin polarization for Heusler-compound thin films by means of nonlocal spin-valve measurements: Comparison of CoFeSi and FeSi
We study room-temperature generation and detection of pure spin currents
using lateral spin-valve devices with Heusler-compound electrodes, CoFeSi
(CFS) or FeSi (FS). The magnitude of the nonlocal spin-valve (NLSV)
signals is seriously affected by the dispersion of the resistivity peculiarly
observed in the low-temperature grown Heusler compounds with ordered
structures. From the analysis based on the one-dimensional spin diffusion
model, we find that the spin polarization monotonically increases with
decreasing the resistivity, which depends on the structural ordering, for both
CFS and FS electrodes, and verify that CFS has relatively large spin
polarization compared with FS.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. B (Rapid
communication
Disentangling Cooper-pair formation above Tc from the pseudogap state in the cuprates
The discovery of the pseudogap in the cuprates created significant excitement
amongst physicists as it was believed to be a signature of pairing, in some
cases well above the room temperature. In this "pre-formed pairs" scenario, the
formation of pairs without quantum phase rigidity occurs below T*. These pairs
condense and develop phase coherence only below Tc. In contrast, several recent
experiments reported that the pseudogap and superconducting states are
characterized by two different energy scales, pointing to a scenario, where the
two compete. However a number of transport, magnetic, thermodynamic and
tunneling spectroscopy experiments consistently detect a signature of
phase-fluctuating superconductivity above leaving open the question of whether
the pseudogap is caused by pair formation or not. Here we report the discovery
of a spectroscopic signature of pair formation and demonstrate that in a region
of the phase diagram commonly referred to as the "pseudogap", two distinct
states coexist: one that persists to an intermediate temperature Tpair and a
second that extends up to T*. The first state is characterized by a doping
independent scaling behavior and is due to pairing above Tc, but significantly
below T*. The second state is the "proper" pseudogap - characterized by a
"checker board" pattern in STM images, the absence of pair formation, and is
likely linked to Mott physics of pristine CuO2 planes. Tpair has a universal
value around 130-150K even for materials with very different Tc, likely setting
limit on highest, attainable Tc in cuprates. The observed universal scaling
behavior with respect to Tpair indicates a breakdown of the classical picture
of phase fluctuations in the cuprates.Comment: 9 pages, 4 figure
Hard X-ray Detector (HXD) on Board Suzaku
The Hard X-ray Detector (HXD) on board Suzaku covers a wide energy range from
10 keV to 600 keV by combination of silicon PIN diodes and GSO scintillators.
The HXD is designed to achieve an extremely low in-orbit back ground based on a
combination of new techniques, including the concept of well-type active shield
counter. With an effective area of 142 cm^2 at 20 keV and 273 cm2 at 150 keV,
the background level at the sea level reached ~1x10^{-5} cts s^{-1} cm^{-2}
keV^{-1} at 30 keV for the PI N diodes, and ~2x10^{-5} cts s^{-1} cm^{-2}
keV^{-1} at 100 keV, and ~7x10^{-6} cts s^{-1} cm^{-2} keV^{-1} at 200 keV for
the phoswich counter. Tight active shielding of the HXD results in a large
array of guard counters surrounding the main detector parts. These
anti-coincidence counters, made of ~4 cm thick BGO crystals, have a large
effective area for sub-MeV to MeV gamma-rays. They work as an excellent
gamma-ray burst monitor with limited angular resolution (~5 degree). The
on-board signal-processing system and the data transmitted to the ground are
also described.Comment: 35 pages, 25 figures and 4 tables; acceted for Publication of the
Astronomical Society of Japa
Prospective study of daily low-dose nedaplatin and continuous 5-fluorouracil infusion combined with radiation for the treatment of esophageal squamous cell carcinoma
<p>Abstract</p> <p>Background</p> <p>Protracted low-dose concurrent chemotherapy combined with radiation has been proposed for enhanced treatment results for esophageal cancer. We evaluated the efficacy and the toxicity of a novel regimen of daily low-dose nedaplatin (cis-diammine-glycolatoplatinum) and continuous infusion of 5-fluorouracil (5-FU) with radiation in patients with esophageal squamous cell carcinoma.</p> <p>Methods</p> <p>Between January 2003 and June 2008, 33 patients with clinical stage I to IVB esophageal squamous cell carcinoma were enrolled. Nedaplatin (10 mg/body/day) was administered daily and 5-FU (500 mg/body/day) was administered continuously for 20 days. Fractionated radiotherapy for a total dose of 50.4-66 Gy was administered together with chemotherapy. Additional chemotherapy with nedaplatin and 5-FU was optionally performed for a maximum of 5 courses after chemoradiotherapy. The primary end-point of this study was to evaluate the tumor response, and the secondary end-points were to evaluate the toxicity and the overall survival.</p> <p>Results</p> <p>Twenty-two patients (72.7%) completed the regimen of chemoradiotherapy. Twenty patients (60.6%) achieved a complete response, 10 patients (30.3%) a partial response. One patient (3.0%) had a stable disease, and 2 (6.1%) a progressive disease. The overall response rate was 90.9% (95% confidence interval: 75.7%-98.1%). For grade 3-4 toxicity, leukopenia was observed in 75.8% of the cases, thrombocytopenia in 24.2%, anemia in 9.1%, and esophagitis in 36.4%, while late grade 3-4 cardiac toxicity occurred in 6.1%. Additional chemotherapy was performed for 26 patients (78.8%) and the median number of courses was 3 (range, 1-5). The 1-, 2- and 3-year survival rates were 83.9%, 76.0% and 58.8%, respectively. The 1- and 2-year survival rates were 94.7% and 88.4% in patients with T1-3 M0 disease, and 66.2% and 55.2% in patients with T4/M1 disease.</p> <p>Conclusion</p> <p>The treatment used in our study may yield a high complete response rate and better survival for each stage of esophageal squamous cell carcinoma.</p> <p>Trial registration</p> <p>ClinicalTrials.gov Identifier: NCT00197444</p
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First order phase transformations: scaling relations for grain self-correlation functions
At high pressure many alkali halides transform from the NaCl (B1) structure to the CsCl (B2) structure. We have recently studied this transformation in polycrystalline RbI, which transforms at a critical pressure, P/sub c/ = 3.5 kbar. By observing the time development of the neutron diffraction pattern after sudden increase of hydrostatic pressure from P<P/sub c/ to P>P/sub c/ we directly deduced X(t), the fraction of the sample converted from metastable to stable phase, as a function of time. We showed that X(t) taken at different P could be approximately scaled onto a universal growth curve by introducing an adjustable characteristic time tau(P) for each curve. The success of the Kolmogorov in fitting X(t) suggests that comparisons of model predictions with other experimental observables be made on the system. For example, by a trivial (in principle) extension of the neutron diffraction techniques described above, one might determine the broadening of the powder diffraction peaks due to finite grain size as a function of time throughout growth. This particle size broadening is related by Fourier transformation to the grain autocorrelation function, G/sub s/(r,t), which measures the ensemble average of the overlap of grains with themselves upon translation of the grain pattern by an amount r. We present some results of a study of the scaling properties of G/sub s/(r,t) for the Kolmogorov model for d=1 and d=2. Although the model is highly idealized, it is perhaps the simplest conceivable one which obeys correlation function scaling in early stages of growth and undergoes nontrivial saturation due to volume fraction effects in the late stages. 4 refs., 6 figs
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