1,958 research outputs found
An experiment on the shifts of reflected C-lines
An experiment is described that tests theoretical predictions on how C-lines
incident obliquely on a surface behave on reflection. C-lines in a polarised
wave are the analogues of the optical vortices carried by a complex scalar
wave, which is the usual model for describing light and other electromagnetic
waves. The centre of a laser beam that carries a (degenerate) C-line is shifted
on reflection by the well-known Goos-H\"anchen and Imbert-Fedorov effects, but
the C-line itself splits into two, both of which are shifted longitudinally and
laterally; their shifts are different from that of the beam centre. To maximise
the effect to be measured, internal reflection in a glass prism close to the
critical angle was used. In a simple situation like this two recently published
independent theories of C-line reflection overlap and it is shown that their
predictions are identical. The measured differences in the lateral shifts of
the two reflected C-lines are compared with theoretical expectations over a
range of incidence angles.Comment: 9 pages, 2 figure
Polarization of tightly focused laser beams
The polarization properties of monochromatic light beams are studied. In
contrast to the idealization of an electromagnetic plane wave, finite beams
which are everywhere linearly polarized in the same direction do not exist.
Neither do beams which are everywhere circularly polarized in a fixed plane. It
is also shown that transversely finite beams cannot be purely transverse in
both their electric and magnetic vectors, and that their electromagnetic energy
travels at less than c. The electric and magnetic fields in an electromagnetic
beam have different polarization properties in general, but there exists a
class of steady beams in which the electric and magnetic polarizations are the
same (and in which energy density and energy flux are independent of time).
Examples are given of exactly and approximately linearly polarized beams, and
of approximately circularly polarized beams.Comment: 9 pages, 6 figure
The modalities of Iranian soft power: from cultural diplomacy to soft war
Through exploring Iran's public diplomacy at the international level, this article demonstrates how the Islamic Republic's motives should not only be contextualised within the oft-sensationalised, material or ‘hard’ aspects of its foreign policy, but also within the desire to project its cultural reach through ‘softer’ means. Iran's utilisation of culturally defined foreign policy objectives and actions demonstrates its understanding of soft power's potentialities. This article explores the ways in which Iran's public diplomacy is used to promote its soft power and craft its, at times, shifting image on the world stage
Abrupt grain boundary melting in ice
The effect of impurities on the grain boundary melting of ice is investigated
through an extension of Derjaguin-Landau-Verwey-Overbeek theory, in which we
include retarded potential effects in a calculation of the full frequency
dependent van der Waals and Coulombic interactions within a grain boundary. At
high dopant concentrations the classical solutal effect dominates the melting
behavior. However, depending on the amount of impurity and the surface charge
density, as temperature decreases, the attractive tail of the dispersion force
interaction begins to compete effectively with the repulsive screened Coulomb
interaction. This leads to a film-thickness/temperature curve that changes
depending on the relative strengths of these interactions and exhibits a
decrease in the film thickness with increasing impurity level. More striking is
the fact that at very large film thicknesses, the repulsive Coulomb interaction
can be effectively screened leading to an abrupt reduction to zero film
thickness.Comment: 8 pages, 1 figur
A Low Temperature Nonlinear Optical Rotational Anisotropy Spectrometer for the Determination of Crystallographic and Electronic Symmetries
Nonlinear optical generation from a crystalline material can reveal the
symmetries of both its lattice structure and underlying ordered electronic
phases and can therefore be exploited as a complementary technique to
diffraction based scattering probes. Although this technique has been
successfully used to study the lattice and magnetic structures of systems such
as semiconductor surfaces, multiferroic crystals, magnetic thin films and
multilayers, challenging technical requirements have prevented its application
to the plethora of complex electronic phases found in strongly correlated
electron systems. These requirements include an ability to probe small bulk
single crystals at the micron length scale, a need for sensitivity to the
entire nonlinear optical susceptibility tensor, oblique light incidence
reflection geometry and incident light frequency tunability among others. These
measurements are further complicated by the need for extreme sample
environments such as ultra low temperatures, high magnetic fields or high
pressures. In this review we present a novel experimental construction using a
rotating light scattering plane that meets all the aforementioned requirements.
We demonstrate the efficacy of our scheme by making symmetry measurements on a
micron scale facet of a small bulk single crystal of SrIrO using
optical second and third harmonic generation.Comment: 8 pages, 5 figure
Elastic constants of beta-eucryptite: A density functional theory study
The five independent elastic constants of hexagonal -eucryptite have
been determined using density functional theory (DFT) total energy
calculations. The calculated values agree well, to within 15%, with the
experimental data. Using the calculated elastic constants, the linear
compressibility of -eucryptite parallel to the c-axis, , and
perpendicular to it, , have been evaluated. These values are in close
agreement to those obtained from experimentally known elastic constants, but
are in contradiction to the direct measurements based on a three-terminal
technique. The calculated compressibility parallel to the c-axis was found to
positive as opposed to the negative value obtained by direct measurements. We
have demonstrated that must be positive and discussed the implications
of a positive in the context of explaining the negative bulk thermal
expansion of -eucryptite.Comment: 3 eps figures, submitted for publicatio
Observations of the 8 December 1987 occultation of AG+40 deg 0783 by 324 Bamberga
The occultation of AG+40 deg 0783 by 324 Bamberga on 8 December 1987 was observed at 13 sites in the United States, Japan, and China. At four sites the event was observed photoelectrically; the other observations were visual. A least-squares fit of a circular limb profile to the data gives a diameter of 227.6 + or - 1.9 km. However, this solution is inconsistent with a negative visual observation near the northern edge of the ground track. The inconsistency cannot be removed by assuming an elliptical profile. The data suggest that Bamberga, despite its low-amplitude lightcurve, may depart significantly from a spherical or ellipsoidal shape. The asteroid also appears to be at least 10 percent smaller than indicated by infrared radiometry
Trends in the elastic response of binary early transition metal nitrides
Motivated by an increasing demand for coherent data that can be used for
selecting materials with properties tailored for specific application
requirements, we studied elastic response of nine binary early transition metal
nitrides (ScN, TiN, VN, YN, ZrN, NbN, LaN, HfN, and TaN) and AlN. In
particular, single crystal elastic constants, Young's modulus in different
crystallographic directions, polycrystalline values of shear and Young's
moduli, and the elastic anisotropy factor were calculated. Additionally, we
provide estimates of the third order elastic constants for the ten binary
nitrides.Comment: 10 pages, 7 figure
Precision Measurement of the 29Si, 33S, and 36Cl Binding Energies
The binding energies of 29Si, 33S, and 36Cl have been measured with a
relative uncertainty using a flat-crystal spectrometer.
The unique features of these measurements are 1) nearly perfect crystals whose
lattice spacing is known in meters, 2) a highly precise angle scale that is
derived from first principles, and 3) a gamma-ray measurement facility that is
coupled to a high flux reactor with near-core source capability. The binding
energy is obtained by measuring all gamma-rays in a cascade scheme connecting
the capture and ground states. The measurements require the extension of
precision flat-crystal diffraction techniques to the 5 to 6 MeV energy region,
a significant precision measurement challenge. The binding energies determined
from these gamma-ray measurements are consistent with recent highly accurate
atomic mass measurements within a relative uncertainty of .
The gamma-ray measurement uncertainties are the dominant contributors to the
uncertainty of this consistency test. The measured gamma-ray energies are in
agreement with earlier precision gamma-ray measurements.Comment: 13 pages, 4 figure
Local probing of ionic diffusion by electrochemical strain microscopy: spatial resolution and signal formation mechanisms
Electrochemical insertion-deintercalation reactions are typically associated
with significant change of molar volume of the host compound. This strong
coupling between ionic currents and strains underpins image formation
mechanisms in electrochemical strain microscopy (ESM), and allows exploring the
tip-induced electrochemical processes locally. Here we analyze the signal
formation mechanism in ESM, and develop the analytical description of operation
in frequency and time domains. The ESM spectroscopic modes are compared to
classical electrochemical methods including potentiostatic and galvanostatic
intermittent titration (PITT and GITT), and electrochemical impedance
spectroscopy (EIS). This analysis illustrates the feasibility of spatially
resolved studies of Li-ion dynamics on the sub-10 nanometer level using
electromechanical detection.Comment: 49 pages, 17 figures, 4 tables, 3 appendices, to be submitted to J.
Appl. Phys
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