3,505 research outputs found
Positive effective Q12 electrostrictive coefficient in perovskites
It is demonstrated that for classical perovskites such as BaTiO3, SrTiO3 and
PbTiO3 electrostrictive strain induced by an electric field may not obey
traditionally considered "extension along the field, contraction perpendicular
to it" behavior if a sample is cut obliquely to the cubic crystallographic
directions
A Typology of Corrupt Transactions in Developing Countries
Summary Economic theory has attempted to identify the conditions under which corruption has particularly harmful effects. This article evaluates these theories and argues that the classifications offered are misleading. Very successful interventionist states have suffered from corruption just as much as very unsuccessful ones. Policy responses to corruption require an understanding of the effects of corruption and the determinants of these effects. The fact which appears to have a strong effect in determining the harmfulness of corruption is the balance of power between the state and its clients. An alternative classification of the effects of corruption is suggested on this basis
Packet utilisation definitions for the ESA XMM mission
XMM, ESA's X-Ray Multi-Mirror satellite, due for launch at the end of 1999 will be the first ESA scientific spacecraft to implement the ESA packet telecommand and telemetry standards and will be the first ESOC-controlled science mission to take advantage of the new flight control system infrastructure development (based on object-oriented design and distributed-system architecture) due for deployment in 1995. The implementation of the packet standards is well defined at packet transport level. However, the standard relevant to the application level (the ESA Packet Utilization Standard) covers a wide range of on-board 'services' applicable in varying degrees to the needs of XMM. In defining which parts of the ESA PUS to implement, the XMM project first considered the mission objectives and the derived operations concept and went on to identify a minimum set of packet definitions compatible with these aspects. This paper sets the scene as above and then describes the services needed for XMM and the telecommand and telemetry packet types necessary to support each service
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 âhardâ aspects of its foreign policy, but also within the desire to project its cultural reach through âsofterâ 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
Electromagnetic wave scattering by a superconductor
The interaction between radiation and superconductors is explored in this
paper. In particular, the calculation of a plane standing wave scattered by an
infinite cylindrical superconductor is performed by solving the Helmholtz
equation in cylindrical coordinates. Numerical results computed up to
of Bessel functions are presented for different wavelengths
showing the appearance of a diffraction pattern.Comment: 3 pages, 3 figure
Optimal configuration of microstructure in ferroelectric materials by stochastic optimization
An optimization procedure determining the ideal configuration at the
microstructural level of ferroelectric (FE) materials is applied to maximize
piezoelectricity. Piezoelectricity in ceramic FEs differ significantly from
that of single crystals because of the presence of crystallites (grains)
possessing crystallographic axes aligned imperfectly. The piezoelectric
properties of a polycrystalline (ceramic) FE is inextricably related to the
grain orientation distribution (texture). The set of combination of variables,
known as solution space, which dictates the texture of a ceramic is unlimited
and hence the choice of the optimal solution which maximizes the
piezoelectricity is complicated. Thus a stochastic global optimization combined
with homogenization is employed for the identification of the optimal granular
configuration of the FE ceramic microstructure with optimum piezoelectric
properties. The macroscopic equilibrium piezoelectric properties of
polycrystalline FE is calculated using mathematical homogenization at each
iteration step. The configuration of grains characterised by its orientations
at each iteration is generated using a randomly selected set of orientation
distribution parameters. Apparent enhancement of piezoelectric coefficient
is observed in an optimally oriented BaTiO single crystal. A
configuration of crystallites, simultaneously constraining the orientation
distribution of the c-axis (polar axis) while incorporating ab-plane
randomness, which would multiply the overall piezoelectricity in ceramic
BaTiO is also identified. The orientation distribution of the c-axes is
found to be a narrow Gaussian distribution centred around . The
piezoelectric coefficient in such a ceramic is found to be nearly three times
as that of the single crystal.Comment: 11 pages, 7 figure
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
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
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