2,515 research outputs found
Spin injection from EuS/Co multilayers into GaAs detected by polarized electroluminescence
We report on the successful spin injection from EuS/Co multilayers into (100) GaAs at low temperatures. The spin injection was verified by means of polarized electroluminescence (EL) emitted from AlGaAs/GaAs-based spin-light-emitting diodes in zero external magnetic field. Spin-polarized electrons were injected from prototype EuS/Co spin injector multilayers. The use of semiconducting and ferromagnetic EuS circumvents the impedance mismatch. The EL was measured in side emission with and without an external magnetic field. A circular polarization of 5% at 8 K and 0 T was observed. In view of the rather rough interface between the GaAs substrate and first EuS layer, improvement of the interface quality is expected to considerably enhance the injected electron spin polarization
Theory of radiation trapping by the accelerating solitons in optical fibers
We present a theory describing trapping of the normally dispersive radiation
by the Raman solitons in optical fibers. Frequency of the radiation component
is continuously blue shifting, while the soliton is red shifting. Underlying
physics of the trapping effect is in the existence of the inertial gravity-like
force acting on light in the accelerating frame of reference. We present
analytical calculations of the rate of the opposing frequency shifts of the
soliton and trapped radiation and find it to be greater than the rate of the
red shift of the bare Raman soliton. Our findings are essential for
understanding of the continuous shift of the high frequency edge of the
supercontinuum spectra generated in photonic crystal fibers towards higher
frequencies.Comment: Several misprints in text and formulas corrected. 10 pages, 9
figures, submitted to Phys. Rev.
Looking at a soliton through the prism of optical supercontinuum
A traditional view on solitons in optical fibers as robust particle-like
structures suited for informa- tion transmission has been significantly altered
and broadened over the past decade, when solitons have been found to play the
major role in generation of octave broad supercontinuum spectra in
photonic-crystal and other types of optical fibers. This remarkable spectral
broadening is achieved through complex processes of dispersive radiation being
scattered from, emitted and transformed by solitons. Thus solitons have emerged
as the major players in nonlinear frequency conversion in optical fibers.
Unexpected analogies of these processes have been found with dynamics of
ultracold atoms and ocean waves. This colloquium focuses on recent
understanding and new insights into physics of soliton-radiation interaction
and supercontinuum generation.Comment: http://rmp.aps.org/abstract/RMP/v82/i2/p1287_1 (some figures have
been deleted due to space limits imposed by archive
Identification of Selective Agonists and Antagonists to G Protein-Activated Inwardly Rectifying Potassium Channels: Candidate Medicines for Drug Dependence and Pain
G protein-activated inwardly rectifying K+ (GIRK) channels have been known to play a key role in the rewarding and analgesic effects of opioids. To identify potent agonists and antagonists to GIRK channels, we examined various compounds for their ability to activate or inhibit GIRK channels. A total of 503 possible compounds with low molecular weight were selected from a list of fluoxetine derivatives at Pfizer Japan Inc. We screened these compounds by a Xenopus oocyte expression system. GIRK1/2 and GIRK1/4 heteromeric channels were expressed on Xenopus laevis oocytes at Stage V or VI. A mouse IRK2 channel, which is another member of inwardly rectifying potassium channels with similarity to GIRK channels, was expressed on the oocytes to examine the selectivity of the identified compounds to GIRK channels. For electrophysiological analyses, a two-electrode voltage clamp method was used. Among the 503 compounds tested, one compound and three compounds were identified as the most effective agonist and antagonists, respectively. All of these compounds induced only negligible current responses in the oocytes expressing the IRK2 channel, suggesting that these compounds were selective to GIRK channels. These effective and GIRK-selective compounds may be useful possible therapeutics for drug dependence and pain
Cosmological test of gravity with polarizations of stochastic gravitational waves around 0.1-1 Hz
In general relativity, a gravitational wave has two polarization modes
(tensor mode), but it could have additional polarizations (scalar and vector
modes) in the early stage of the universe, where the general relativity may not
strictly hold and/or the effect of higher-dimensional gravity may become
significant. In this paper, we discuss how to detect extra-polarization modes
of stochastic gravitational wave background (GWB), and study the separability
of each polarization using future space-based detectors such as BBO and DECIGO.
We specifically consider two plausible setups of the spacecraft constellations
consisting of two and four clusters, and estimate the sensitivity to each
polarization mode of GWBs. We find that a separate detection of each
polarization mode is rather sensitive to the geometric configuration and
distance between clusters and that the clusters should be, in general,
separated by an appropriate distance. This seriously degrades the signal
sensitivity, however, for suitable conditions, space-based detector can
separately detect scalar, vector and tensor modes of GWBs with energy density
as low as ~10^-15.Comment: 16 pages, 11 figure
Direct Measurement of the Positive Acceleration of the Universe and Testing Inhomogeneous Models under Gravitational Wave Cosmology
One possibility for explaining the apparent accelerating expansion of the
universe is that we live in the center of a spherically inhomogeneous universe.
Although current observations cannot fully distinguish CDM and these
inhomogeneous models, direct measurement of the acceleration of the universe
can be a powerful tool in probing them. We have shown that, if CDM is
the correct model, DECIGO/BBO would be able to detect the positive redshift
drift (which is the time evolution of the source redshift ) in 3--5 year
gravitational wave (GW) observations from neutron-star binaries, which enables
us to rule out any Lema\^itre-Tolman-Bondi (LTB) void model with monotonically
increasing density profile. We may even be able to rule out any LTB model
unless we allow unrealistically steep density profile at . This test
can be performed with GW observations alone, without any reference to
electromagnetic observations, and is more powerful than the redshift drift
measurement using Lyman forest.Comment: 5 pages, 2 figure
On a q-analogue of the multiple gamma functions
A -analogue of the multiple gamma functions is introduced, and is shown to
satisfy the generalized Bohr-Morellup theorem. Furthermore we give some
expressions of these function.Comment: 8 pages, AMS-Late
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