351 research outputs found
First-order restoration of SU(Nf) x SU(Nf) chiral symmetry with large Nf and Electroweak phase transition
It has been argued by Pisarski and Wilczek that finite temperature
restoration of the chiral symmetry SU(Nf) x SU(Nf) is first-order for Nf >=3.
This type of chiral symmetry with a large Nf may appear in the Higgs sector if
one considers models such as walking technicolor theories. We examine the
first-order restoration of the chiral symmetry from the point of view of the
electroweak phase transition. The strength of the transition is estimated in
SU(2) x U(1) gauged linear sigma model by means of the finite temperature
effective potential at one-loop with the ring improvement. Even if the mass of
the neutral scalar boson corresponding to the Higgs boson is larger than 114
GeV, the first-order transition can be strong enough for the electroweak
baryogenesis, as long as the extra massive scalar bosons (required for the
linear realization) are kept heavier than the neutral scalar boson. Explicit
symmetry breaking terms reduce the strength of the first-order transition, but
the transition can remain strongly first-order even when the masses of pseudo
Nambu-Goldstone bosons become as large as the current lower bound of direct
search experiments.Comment: 18 pages, 18 figures, minor corrections, references adde
Using Short Half-life Nuclide 107Cd for Real-time Imaging and Analysis of Cadmium Dynamics in Cd-Hyperaccumulator Arabidopsis halleri ssp. gemmifera by PETIS System
Spin-polarized current amplification and spin injection in magnetic bipolar transistors
The magnetic bipolar transistor (MBT) is a bipolar junction transistor with
an equilibrium and nonequilibrium spin (magnetization) in the emitter, base, or
collector. The low-injection theory of spin-polarized transport through MBTs
and of a more general case of an array of magnetic {\it p-n} junctions is
developed and illustrated on several important cases. Two main physical
phenomena are discussed: electrical spin injection and spin control of current
amplification (magnetoamplification). It is shown that a source spin can be
injected from the emitter to the collector. If the base of an MBT has an
equilibrium magnetization, the spin can be injected from the base to the
collector by intrinsic spin injection. The resulting spin accumulation in the
collector is proportional to , where is the proton
charge, is the bias in the emitter-base junction, and is the
thermal energy. To control the electrical current through MBTs both the
equilibrium and the nonequilibrium spin can be employed. The equilibrium spin
controls the magnitude of the equilibrium electron and hole densities, thereby
controlling the currents. Increasing the equilibrium spin polarization of the
base (emitter) increases (decreases) the current amplification. If there is a
nonequilibrium spin in the emitter, and the base or the emitter has an
equilibrium spin, a spin-valve effect can lead to a giant magnetoamplification
effect, where the current amplifications for the parallel and antiparallel
orientations of the the equilibrium and nonequilibrium spins differ
significantly. The theory is elucidated using qualitative analyses and is
illustrated on an MBT example with generic materials parameters.Comment: 14 PRB-style pages, 10 figure
Theory of spin-polarized bipolar transport in magnetic p-n junctions
The interplay between spin and charge transport in electrically and
magnetically inhomogeneous semiconductor systems is investigated theoretically.
In particular, the theory of spin-polarized bipolar transport in magnetic p-n
junctions is formulated, generalizing the classic Shockley model. The theory
assumes that in the depletion layer the nonequilibrium chemical potentials of
spin up and spin down carriers are constant and carrier recombination and spin
relaxation are inhibited. Under the general conditions of an applied bias and
externally injected (source) spin, the model formulates analytically carrier
and spin transport in magnetic p-n junctions at low bias. The evaluation of the
carrier and spin densities at the depletion layer establishes the necessary
boundary conditions for solving the diffusive transport equations in the bulk
regions separately, thus greatly simplifying the problem. The carrier and spin
density and current profiles in the bulk regions are calculated and the I-V
characteristics of the junction are obtained. It is demonstrated that spin
injection through the depletion layer of a magnetic p-n junction is not
possible unless nonequilibrium spin accumulates in the bulk regions--either by
external spin injection or by the application of a large bias. Implications of
the theory for majority spin injection across the depletion layer, minority
spin pumping and spin amplification, giant magnetoresistance, spin-voltaic
effect, biasing electrode spin injection, and magnetic drift in the bulk
regions are discussed in details, and illustrated using the example of a GaAs
based magnetic p-n junction.Comment: 36 pages, 11 figures, 2 table
Novel multi-layer plastic-scintillator-based solid active proton target for inverse-kinematics experiments
We have constructed and tested a novel plastic-scintillator-based solid-state
active proton target for use in nuclear spectroscopic studies with nuclear
reactions induced by an ion beam in inverse kinematics. The active target
system, named Stack Structure Solid organic Scintillator Active Target (S4AT),
consists of five layers of plastic scintillators, each with a 1-mm thickness.
To determine the reaction point in the thickness direction, we exploit the
difference in the energy losses due to the beam particle and the charged
reaction product(s) in the scintillator material. S4AT offers the prospect of a
relatively thick target while maintaining a good energy resolution. By
considering the relative energy loss between different layers, the energy loss
due to unreacted beam particles can be eliminated. Such procedure, made
possible by the multi-layer structure, is essential to eliminate the effect of
unreacted accompanying beam particles, thus enabling its operation at a
moderate beam intensity of up to a few Mcps. We evaluated the performance of
S4AT by measuring the elastic proton-proton scattering using a 70-MeV proton
beam at Cyclotron and Radioisotope Center (CYRIC), Tohoku University.Comment: 32 pages, 14 figure
Cilostazol Inhibits Accumulation of Triglyceride in Aorta and Platelet Aggregation in Cholesterol-Fed Rabbits
Cilostazol is clinically used for the treatment of ischemic symptoms in patients with chronic peripheral arterial obstruction and for the secondary prevention of brain infarction. Recently, it has been reported that cilostazol has preventive effects on atherogenesis and decreased serum triglyceride in rodent models. There are, however, few reports on the evaluation of cilostazol using atherosclerotic rabbits, which have similar lipid metabolism to humans, and are used for investigating the lipid content in aorta and platelet aggregation under conditions of hyperlipidemia. Therefore, we evaluated the effect of cilostazol on the atherosclerosis and platelet aggregation in rabbits fed a normal diet or a cholesterol-containing diet supplemented with or without cilostazol. We evaluated the effects of cilostazol on the atherogenesis by measuring serum and aortic lipid content, and the lesion area after a 10-week treatment and the effect on platelet aggregation after 1- and 10-week treatment. From the lipid analyses, cilostazol significantly reduced the total cholesterol, triglyceride and phospholipids in serum, and moreover, the triglyceride content in the atherosclerotic aorta. Cilostazol significantly reduced the intimal atherosclerotic area. Platelet aggregation was enhanced in cholesterol-fed rabbits. Cilostazol significantly inhibited the platelet aggregation in rabbits fed both a normal diet and a high cholesterol diet. Cilostazol showed anti-atherosclerotic and anti-platelet effects in cholesterol-fed rabbits possibly due to the improvement of lipid metabolism and the attenuation of platelet activation. The results suggest that cilostazol is useful for prevention and treatment of atherothrombotic diseases with the lipid abnormalities
Spintronics: Fundamentals and applications
Spintronics, or spin electronics, involves the study of active control and
manipulation of spin degrees of freedom in solid-state systems. This article
reviews the current status of this subject, including both recent advances and
well-established results. The primary focus is on the basic physical principles
underlying the generation of carrier spin polarization, spin dynamics, and
spin-polarized transport in semiconductors and metals. Spin transport differs
from charge transport in that spin is a nonconserved quantity in solids due to
spin-orbit and hyperfine coupling. The authors discuss in detail spin
decoherence mechanisms in metals and semiconductors. Various theories of spin
injection and spin-polarized transport are applied to hybrid structures
relevant to spin-based devices and fundamental studies of materials properties.
Experimental work is reviewed with the emphasis on projected applications, in
which external electric and magnetic fields and illumination by light will be
used to control spin and charge dynamics to create new functionalities not
feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes
from the published versio
Spin-polarized Zener tunneling in (Ga,Mn)As
We investigate spin-polarized inter-band tunneling through measurement of
(Ga,Mn)As based Zener tunnel diode. By placing the diode under reverse bias,
electron spin polarization is transferred from the valence band of p-type
(Ga,Mn)As to the conduction band of an adjacent n-GaAs layer. The resulting
current is monitored by injection into a quantum well light emitting diode
whose electroluminescence polarization is found to track the magnetization of
the (Ga,Mn)As layer as a function of both temperature and magnetic field.Comment: 11 pages, 4 figures. Submitted, Physical Review B15 Rapid
Communication
Electron Spin Polarization in Resonant Interband Tunneling Devices
We study spin-dependent interband resonant tunneling in double-barrier
InAs/AlSb/ GaMnSb heterostructures. We demonstrate that these structures can be
used as spin filters utilizing spin-selective tunneling of electrons through
the light-hole resonant channel. High densities of the spin polarized electrons
injected into bulk InAs make spin resonant tunneling devices a viable
alternative for injecting spins into a semiconductor. Another striking feature
of the proposed devices is the possibility of inducing additional resonant
channels corresponding to the heavy holes. This can be implemented by
saturating the in-plane magnetization in the quantum well.Comment: 11 pages, 4 eps figure
Physics of leptoquarks in precision experiments and at particle colliders
We present a comprehensive review of physics effects generated by leptoquarks
(LQs), i.e., hypothetical particles that can turn quarks into leptons and vice
versa, of either scalar or vector nature. These considerations include
discussion of possible completions of the Standard Model that contain LQ
fields. The main focus of the review is on those LQ scenarios that are not
problematic with regard to proton stability. We accordingly concentrate on the
phenomenology of light leptoquarks that is relevant for precision experiments
and particle colliders. Important constraints on LQ interactions with matter
are derived from precision low-energy observables such as electric dipole
moments, (g-2) of charged leptons, atomic parity violation, neutral meson
mixing, Kaon, B, and D meson decays, etc. We provide a general analysis of
indirect constraints on the strength of LQ interactions with the quarks and
leptons to make statements that are as model independent as possible. We
address complementary constraints that originate from electroweak precision
measurements, top, and Higgs physics. The Higgs physics analysis we present
covers not only the most recent but also expected results from the Large Hadron
Collider (LHC). We finally discuss direct LQ searches. Current experimental
situation is summarized and self-consistency of assumptions that go into
existing accelerator-based searches is discussed. A progress in making
next-to-leading order predictions for both pair and single LQ productions at
colliders is also outlined.Comment: 136 pages, 22 figures, typographical errors fixed, the Physics
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