Search results for "Polar"
showing 10 items of 3817 documents
Photoproduction of η and η′ mesons with EtaMAID
2016
The unitary isobar model EtaMAID has been updated with an extended list of nucleon resonances, fitted to recent and new data for differential cross sections and polarization observables. The nonresonant background is described by Regge trajectories of ω,ρ and a 1 , b 1 mesons and in addition Regge cuts, where vector and axial vector mesons are exchanged together with Pomeron and f 2 mesons.
Effects of Higher-Order Scattering in a Molecular Atmosphere
1964
The effects of higher-order scattering on intensity, degree of polarization, and direction of the plane of polarization in a molecular atmosphere have been calculated.Inclusion of higher-order scattering changes these parameters strongly. Particularly, consideration of higher-order scattering is essential in the blue wavelength range (large optical thickness). The influence increases with decreasing zenith distance of the sun. The earth albedo augments the effect, except for direction of the polarization, which is independent of higher-order scattering.
The Elliptical Polarization of Light Scattered by a Volume of Atmospheric Air
2010
The scattering of linearly polarized light by aerosol particles produces partly polarized light whose ellipticity is theoretically and experimentally investigated for the specific case of a continental atmospheric aerosol in a volume of air. With the Mie theory and under the assumption of various aerosol size-distribution models, the ellipticity has been computed as a function of the scattering angle for various wavelengths. The computations have been based upon complex indices of refraction: M = 1.5-0.0i, M = 1.5-0.0li, M = 1.5-0.li, M = 1.44-0.0i, M = 1.4-0.0i, M = 1.33-0.0i. The comparison between computed and measured values for the wavelengths of lambda = 0.45 micro to lambda = 0.65 mi…
Absolute instability in backward wave four-wave mixing: spatial effects
2010
The spatial distribution of new beams generated above the threshold of absolute instability of two counterpropagating incoherent light waves is studied and compared with the results of calculation.
Design and development of a microscopic model for polarization
2009
As research shows that the knowledge and use of models and modelling by teachers is limited, particularly for predicting phenomena, we developed and applied a sequence of three representations of a simulated model focusing on polarization and specifically showing the behaviour of an atom, and forces exerted on a dipole and an insulator, when a charged particle is placed anywhere near them. The sequence was tested with beginning student teachers. They worked with specially developed worksheets in which the simulated model was treated, before carrying out hands-on experiments embedded in a model-based instructional unit which aimed to help the student teachers understand polarization and beco…
New Information on Nuclear Structure in the Cd-In-Sn Region from Laser Spectroscopy and the Question of Core Polarization Contribution to Nuclear Rad…
1986
Nuclear spin, moments and isotope shifts of charge radii have been measured by laser spectroscopy for about 70 nuclear states in the range 48 ≦ Z ≦ 50, 54 ≦ N ≦ 78. 1/2--states in heavy In-isotopes cross the Schmidt line, indicating complex nuclear structure. Magnetic as well as spectroscopic quadrupole moments of most of the odd odd In-isotopes can be reproduced satisfactorily by coupling the respective experimental moments of odd even and even odd neighbouring nuclei. The isotope shift of all three elements exhibits a parabolic shape, which is superimposed to the almost linear droplet model expectation. The shape can be fitted quantitatively to Talmis core polarization model. The curvatur…
Action potentials induce biomagnetic fields in Venus flytrap plants
2020
Upon stimulation, plants elicit electrical signals that can travel within a cellular network analogous to the animal nervous system. It is well-known that in the human brain, voltage changes in certain regions result from concerted electrical activity which, in the form of action potentials (APs), travels within nerve-cell arrays. Electrophysiological techniques like electroencephalography, magnetoencephalography, and magnetic resonance imaging are used to record this activity and to diagnose disorders. In the plant kingdom, two types of electrical signals are observed: all-or-nothing APs of similar amplitudes to those seen in humans and animals, and slow-wave potentials of smaller amplitud…
Laser driven structured quantum rings
2015
In this work we study harmonic emission from structured quantum rings (SQRs). In SQRs, electrons trapped in two-dimensional structures are further confined by an external potential composed of N scattering centers arranged on a circle. We build a suitable one-dimensional model Hamiltonian describing this class of systems and analytically solve the associated Schödinger equation. We find that the solution can be expressed in terms of Mathieu functions and focus on the specific case of N = 6. By exactly solving the time-dependent Schödinger equation, we then show how the harmonic response to linearly polarized lasers strongly depends on the ring physical parameters. The results illustrate how…
Electrons on a spherical surface: Physical properties and hollow spherical clusters
2012
We discuss the physical properties of a noninteracting electron gas constrained to a spherical surface. In particular we consider its chemical potentials, its ionization potential, and its electric static polarizability. All these properties are discussed analytically as functions of the number $N$ of electrons. The trends obtained with increasing $N$ are compared with those of the corresponding properties experimentally measured or theoretically evaluated for quasispherical hollow atomic and molecular clusters. Most of the properties investigated display similar trends, characterized by a prominence of shell effects. This leads to the definition of a scale-invariant distribution of magic n…
Stopping a slow-light soliton: an exact solution
2005
We investigate propagation of a slow-light soliton in Λ-type media such as atomic vapours and Bose–Einstein condensates. We show that the group velocity of the soliton monotonically decreases with the intensity of the controlling laser field, which decays exponentially after the laser is switched off. The shock wave of the vanishing controlling field overtakes the slow soliton and stops it, while the optical information is recorded in the medium in the form of spatially localized polarization. In the strongly nonlinear regime we find an explicit exact solution describing the whole process.