4,160 research outputs found
Geometric phase and o-mode blue shift in a chiral anisotropic medium inside a Fabry-P\'erot cavity
Anomalous spectral shift of transmission peaks is observed in a
Fabry--P\'erot cavity filled with a chiral anisotropic medium. The effective
refractive index value resides out of the interval between the ordinary and the
extraordinary refractive indices. The spectral shift is explained by
contribution of a geometric phase. The problem is solved analytically using the
approximate Jones matrix method, numerically using the accurate Berreman method
and geometrically using the generalized Mauguin--Poincar\'e rolling cone
method. The -mode blue shift is measured for a
4-methoxybenzylidene-4'--butylaniline twisted--nematic layer inside the
Fabry--P\'erot cavity. The twist is electrically induced due to the
homeoplanar--twisted configuration transition in an ionic-surfactant-doped
liquid crystal layer. Experimental evidence confirms the validity of the
theoretical model.Comment: the text is available both in English (Timofeev2015en.tex) and in
Russian (download: other formats - source - Timofeev2015ru.tex,
Timofeev2015rus.pdf
Coulomb corrections to bremsstrahlung in electric field of heavy atom at high energies
The differential and partially integrated cross sections are considered for
bremsstrahlung from high-energy electrons in atomic field with the exact
account of this field. The consideration exploits the quasiclassical electron
Green's function and wave functions in an external electric field. It is shown
that the Coulomb corrections to the differential cross section are very
susceptible to screening. Nevertheless, the Coulomb corrections to the cross
section summed up over the final-electron states are independent of screening
in the leading approximation over a small parameter ( is
a screening radius, is the electron mass, ). Bremsstrahlung from
an electron beam of the finite size on heavy nucleus is considered as well.
Again, the Coulomb corrections to the differential probability are very
susceptible to the beam shape, while those to the probability integrated over
momentum transfer are independent of it, apart from the trivial factor, which
is the electron-beam density at zero impact parameter. For the Coulomb
corrections to the bremsstrahlung spectrum, the next-to-leading terms with
respect to the parameters ( is the electron energy) and
are obtained.Comment: 13 pages, 4 figure
Symmetric achromatic low-beta collider interaction region design concept
We present a new symmetry-based concept for an achromatic low-beta collider
interaction region design. A specially-designed symmetric Chromaticity
Compensation Block (CCB) induces an angle spread in the passing beam such that
it cancels the chromatic kick of the final focusing quadrupoles. Two such CCBs
placed symmetrically around an interaction point allow simultaneous
compensation of the 1st-order chromaticities and chromatic beam smear at the IP
without inducing significant 2nd-order aberrations to the particle trajectory.
We first develop an analytic description of this approach and explicitly
formulate 2nd-order aberration compensation conditions at the interaction
point. The concept is next applied to develop an interaction region design for
the ion collider ring of an electron-ion collider. We numerically evaluate
performance of the design in terms of momentum acceptance and dynamic aperture.
The advantages of the new concept are illustrated by comparing it to the
conventional distributed-sextupole chromaticity compensation scheme.Comment: 12 pages, 17 figures, to be submitted to Phys. Rev. ST Accel. Beam
Dynamical Model of Coherent Pion Production in Neutrino-Nucleus Scattering
We study coherent pion production in neutrino-nucleus scattering in the
energy region relevant to neutrino oscillation experiments of current interest.
Our approach is based on a combined use of the Sato-Lee model of electroweak
pion production on a nucleon and the Delta-hole model of pion-nucleus
reactions. Thus we develop a model which describes pion-nucleus scattering and
electroweak coherent pion production in a unified manner. Numerical
calculations are carried out for the case of the 12C target. All the free
parameters in our model are fixed by fitting to both total and elastic
differential cross sections for pi-12C scattering. Then we demonstrate the
reliability of our approach by confronting our prediction for the coherent pion
photo-productions with data. Finally, we calculate total and differential cross
sections for neutrino-induced coherent pion production, and some of the results
are (will be) compared with the recent (forthcoming) data from K2K, SciBooNE
and MiniBooNE. We also study effect of the non-locality of the
Delta-propagation in the nucleus, and compare the elementary amplitudes used in
different microscopic calculations.Comment: 42 pages, 21 figure
Chiral Optical Tamm States at the Interface between a Cholesteric and an All-Dielectric Polarization-Preserving Anisotropic Mirror
The chiral optical Tamm state is a new localized state of light at the
interface between a polarization-preserving anisotropic mirror and an optically
chiral medium such as a cholesteric liquid crystal. In this study the
metal-free polarization-preserving mirror is used for efficient resonance
control. We stress the advantage of the all-dielectric structure in obtaining
high Q factor. The light is localized near the interface and the field
decreases exponentially with the distance from the interface. The penetration
of the field into the chiral medium is virtually blocked at wavelengths
corresponding to the photonic band gap and close to the pitch of the helix. The
polarization-preserving mirror has another photonic band gap as well. Our
analytics agrees well with precise calculations, enabling intelligent design
for laser and sensing applications.Comment: in Russia
Electron shielding of the nuclear magnetic moment in hydrogen-like atom
The correction to the wave function of the ground state in a hydrogen-like
atom due to an external homogenous magnetic field is found exactly in the
parameter . The projection of the correction to the wave
function of the state due to the external homogeneous magnetic field
is found for arbitrary . The projection of the correction to the
wave function of the state due to the nuclear magnetic moment is
also found for arbitrary . Using these results, we have calculated the
shielding of the nuclear magnetic moment by the electron.Comment: 15 page
Strength of Higher-Order Spin-Orbit Resonances
When polarized particles are accelerated in a synchrotron, the spin
precession can be periodically driven by Fourier components of the
electromagnetic fields through which the particles travel. This leads to
resonant perturbations when the spin-precession frequency is close to a linear
combination of the orbital frequencies. When such resonance conditions are
crossed, partial depolarization or spin flip can occur. The amount of
polarization that survives after resonance crossing is a function of the
resonance strength and the crossing speed. This function is commonly called the
Froissart-Stora formula. It is very useful for predicting the amount of
polarization after an acceleration cycle of a synchrotron or for computing the
required speed of the acceleration cycle to maintain a required amount of
polarization. However, the resonance strength could in general only be computed
for first-order resonances and for synchrotron sidebands. When Siberian Snakes
adjust the spin tune to be 1/2, as is required for high energy accelerators,
first-order resonances do not appear and higher-order resonances become
dominant. Here we will introduce the strength of a higher-order spin-orbit
resonance, and also present an efficient method of computing it. Several
tracking examples will show that the so computed resonance strength can indeed
be used in the Froissart-Stora formula. HERA-p is used for these examples which
demonstrate that our results are very relevant for existing accelerators.Comment: 10 pages, 6 figure
The versatile terahertz reflection and transmission spectrometer with the location of objects of researches in the horizontal plane
The experimental setup of versatile pulse terahertz reflection and transmission spectrometer and operation concept were described. Using this setup the temporary forms of THz signal reflected from and transmitted through the samples like amino acids, dental tissue and normal were obtained. The possibility of structural determination of powdered media was demonstrated using this method
Ecology of the Granular Spiny Frog <em>Quasipaa verrucospinosa</em> (Amphibia: Anura - Dicroglossidae) in Central Vietnam
We conducted a large-scale assessment at 35 primary forest sites and 42 secondary forest sites in Bach Ma National Park, central Vietnam, using the detection/non-detection data for each site over multiple visits, to quantify the site proportions that were occupied by granular spiny frogs (Quasipaa verrucospinosa). We additionally investigated the effect of site covariates (primary versus secondary forests) and sample covariates (temperature, humidity, and precipitation) to examine the environmental needs that may be incorporated for conserving rain forest amphibians in Vietnam. From the best model among all candidate models, We estimated a site occupancy probability of 0.632 that was higher than the naïve occupancy estimate of 0.403 and a 57% increase over the proportion of sites at which frogs were actually observed. The primary forest variable was an important determinant of site occupancy, whereas occupancy was not associated with the variable of secondary forest. In a combined AIC model weight, the detection model p (temperature, humidity, precipitation) included 90.9% of the total weight, providing clear evidence that environmental conditions were important sample covariates in modeling detection probabilities of granular spiny frogs. Our results substantiate the importance of incorporating occupancy and detection probabilities into studies of habitat relationships and suggest that the primary forest factor associated with environmental conditions influence the occupancy of granular spiny frogs
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