84 research outputs found
Quantum States of Neutrons in Magnetic Thin Films
We have studied experimentally and theoretically the interaction of polarized
neutrons with magnetic thin films and magnetic multilayers. In particular, we
have analyzed the behavior of the critical edges for total external reflection
in both cases. For a single film we have observed experimentally and
theoretically a simple behavior: the critical edges remain fixed and the
intensity varies according to the angle between the polarization axis and the
magnetization vector inside the film. For the multilayer case we find that the
critical edges for spin up and spin down polarized neutrons move towards each
other as a function of the angle between the magnetization vectors in adjacent
ferromagnetic films. Although the results for multilayers and single thick
layers appear to be different, in fact the same spinor method explains both
results. An interpretation of the critical edges behavior for the multilyers as
a superposition of ferromagnetic and antifferomagnetic states is given.Comment: 6 pages, 5 figure
Neutron resonances in planar waveguides
Results of experimental investigations of a neutron resonances width in
planar waveguides using the time-of-flight reflectometer REMUR of the IBR-2
pulsed reactor are reported and comparison with theoretical calculations is
presented. The intensity of the neutron microbeam emitted from the waveguide
edge was registered as a function of the neutron wavelength and the incident
beam angular divergence. The possible applications of this method for the
investigations of layered nanostructures are discussed
A proposal of a UCN experiment to check an earthquake waves model
Elastic waves with transverse polarization inside incidence plane can create
longitudinal surface wave (LSW) after reflection from a free surface. At a
critical incidence angle this LSW accumulates energy density, which can be
orders of magnitude higher than energy density of the incident transverse wave.
A specially arranged vessel for storage of ultracold neutrons (UCN) can be used
to verify this effect.Comment: 8 pages 3 figures added a paragraph on vibrations along surface at
critical angl
Coherent Schwinger Interaction from Darboux Transformation
The exactly solvable scalar-tensor potential of the four-component Dirac
equation has been obtained by the Darboux transformation method. The
constructed potential has been interpreted in terms of nucleon-nucleon and
Schwinger interactions of neutral particles with lattice sites during their
channeling Hamiltonians of a Schwinger type is obtained by means of the Darboux
transformation chain. The analitic structure of the Lyapunov function of
periodic continuation for each of the Hamiltonians of the family is considered.Comment: 12 pages, Latex, six figures; six sections, one figure adde
Rayleigh Imaging of Graphene and Graphene Layers
We investigate graphene and graphene layers on different substrates by
monochromatic and white-light confocal Rayleigh scattering microscopy. The
image contrast depends sensitively on the dielectric properties of the sample
as well as the substrate geometry and can be described quantitatively using the
complex refractive index of bulk graphite. For few layers (<6) the
monochromatic contrast increases linearly with thickness: the samples behave as
a superposition of single sheets which act as independent two dimensional
electron gases. Thus, Rayleigh imaging is a general, simple and quick tool to
identify graphene layers, that is readily combined with Raman scattering, which
provides structural identification.Comment: 8 pages, 9 figure
Electronic beam shifts in monolayer graphene superlattice
Electronic analogue of generalized Goos-H\"{a}nchen shifts is investigated in
the monolayer graphene superlattice with one-dimensional periodic potentials of
square barriers. It is found that the lateral shifts for the electron beam
transmitted through the monolayer graphene superlattice can be negative as well
as positive near the band edges of zero- gap, which are different from
those near the band edges of Bragg gap. These negative and positive beam shifts
have close relation to the Dirac point. When the condition () is satisfied, the beam shifts can be controlled from
negative to positive when the incident energy is above the Dirac point, and
vice versa. In addition, the beam shifts can be greatly enhanced by the defect
mode inside the zero- gap. These intriguing phenomena can be verified
in a relatively simple optical setup, and have potential applications in the
graphene-based electron wave devices.Comment: 5 pages, 4 figures, submitted on Oct. 15, 201
Amiloride Enhances Antigen Specific CTL by Faciliting HBV DNA Vaccine Entry into Cells
The induction of relatively weak immunity by DNA vaccines in humans can be largely attributed to the low efficiency of transduction of somatic cells. Although formulation with liposomes has been shown to enhance DNA transduction of cultured cells, little, if any, effect is observed on the transduction of somatic tissues and cells. To improve the rate of transduction, DNA vaccine delivery by gene gun and the recently developed electroporation techniques have been employed. We report here that to circumvent requirement for such equipment, amiloride, a drug that is prescribed for hypertension treatment, can accelerate plasmid entry into antigen presenting cells (APCs) both in vitro and in vivo. The combination induced APCs more dramatically in both maturation and cytokine secretion. Amiloride enhanced development of full CD8 cytolytic function including induction of high levels of antigen specific CTL and expression of IFN-γ+perforin+granzymeB+ in CD8+ T cells. Thus, amiloride is a facilitator for DNA transduction into host cells which in turn enhances the efficiency of the immune responses
The neutron and its role in cosmology and particle physics
Experiments with cold and ultracold neutrons have reached a level of
precision such that problems far beyond the scale of the present Standard Model
of particle physics become accessible to experimental investigation. Due to the
close links between particle physics and cosmology, these studies also permit a
deep look into the very first instances of our universe. First addressed in
this article, both in theory and experiment, is the problem of baryogenesis ...
The question how baryogenesis could have happened is open to experimental
tests, and it turns out that this problem can be curbed by the very stringent
limits on an electric dipole moment of the neutron, a quantity that also has
deep implications for particle physics. Then we discuss the recent spectacular
observation of neutron quantization in the earth's gravitational field and of
resonance transitions between such gravitational energy states. These
measurements, together with new evaluations of neutron scattering data, set new
constraints on deviations from Newton's gravitational law at the picometer
scale. Such deviations are predicted in modern theories with extra-dimensions
that propose unification of the Planck scale with the scale of the Standard
Model ... Another main topic is the weak-interaction parameters in various
fields of physics and astrophysics that must all be derived from measured
neutron decay data. Up to now, about 10 different neutron decay observables
have been measured, much more than needed in the electroweak Standard Model.
This allows various precise tests for new physics beyond the Standard Model,
competing with or surpassing similar tests at high-energy. The review ends with
a discussion of neutron and nuclear data required in the synthesis of the
elements during the "first three minutes" and later on in stellar
nucleosynthesis.Comment: 91 pages, 30 figures, accepted by Reviews of Modern Physic
The Krueger problem
We present a compact solution of the Schroedinger equation for one-dimensional neutron elastic and inelastic scattering from the combination of constant and radio-frequency (RF) magnetic fields, confined in a limited area of spac
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