2,972 research outputs found
A model of gravitation with global U(1)-symmetry
It is shown that an embedding of the general relativity space into a flat
space gives a model of gravitation with the global symmetry and the
discrete one. The last one may be transformed into the symmetry
of the unified model, and the demand of independence of and
transformations leads to the estimate where
is an analog of the Weinberg angle of the standard model.Comment: 7 page
West African equatorial ionospheric parameters climatology based on Ouagadougou ionosonde station data from June 1966 to February 1998
This study is the first which gives the climatology of West African equatorial ionosphere by using Ouagadougou station through three solar cycles. It has permitted to show the complete morphology of ionosphere parameters by analyzing yearly variation, solar cycle and geomagnetic activity, seasonal evolution and diurnal development. This work shows that almost all ionospheric parameters have 11-year solar cycle evolution. Seasonal variation shows that only <I>fo</I>F2 exhibits annual, winter and semiannual anomaly. <I>fo</I>F2 seasonal variation has permitted us to identify and characterize solar events effects on F2 layer in this area. In fact (1) during quiet geomagnetic condition <I>fo</I>F2 presents winter and semiannual anomalies asymmetric peaks in March/April and October. (2) The absence of winter anomaly and the presence of equinoctial peaks are the most visible effects of fluctuating activity in <I>fo</I>F2 seasonal time profiles. (3) Solar wind shock activity does not modify the profile of <I>fo</I>F2 but increases ionization. (4) The absence of asymmetry peaks, the location of the peaks in March and October and the increase of ionization characterize recurrent storm activity. F1 layers shows increasing trend from cycle 20 to cycle 21. Moreover, E layer parameters seasonal variations exhibit complex structure. It seems impossible to detect fluctuating activity effect in E layer parameters seasonal variations but shock activity and wind stream activity act to decrease E layer ionization. It can be seen from Es layer parameters seasonal variations that wind stream activity effect is fairly independent of solar cycle. E and Es layers critical frequencies and virtual heights diurnal variations let us see the effects of the greenhouse gases in these layers
Resonant two-magnon Raman scattering in antiferromagnetic insulators
We propose a theory of two-magnon {\it resonant\/} Raman scattering from
antiferromagnetic insulators, which contains information both on the magnetism
and the carrier properties in the lighly doped phases. We argue that the
conventional theory does not work in the resonant regime, in which the energy
of the incident photon is close to the gap between the conduction and valence
bands. We identify the diagram which gives the dominant contribution to Raman
intensity in this regime and show that it can explain the unusual features in
the two-magnon profile and in the two-magnon peak intensity dependence on the
incoming photon frequency.Comment: 11 pages (REVTeX) + 3 figures in a single postscript file are
appended in uuencoded format, preprint TCSUH-94:09
Investigation of the prevalence of antibodies against neurotropic polyomaviruses BK, JC and SV40 in sera from patients affected by multiple sclerosis.
Viral agents seem to be linked to multiple sclerosis (MS). This association is based on evidence of (1) early exposure to viruses and MS onset; (2) increased prevalence of MS disease in specific geographic regions; (3) likelihood of developing MS being more prevalent in high-risk areas; (4) altered immune responses to different viruses. In this study, sera from patients affected by MS and controls, represented by sera from patients with other neurologic diseases, both inflammatory and non-inflammatory, and from healthy donors, were investigated for the presence of antibodies against neurotropic polyomaviruses BKV, JCV and SV40 in their sera. Our study has indicated that the prevalence of BKV antibodies in sera from MS patients is higher than that detected in normal individuals, while levels of antibodies against BKV and JCV are lower in MS patients compared to those of normal subjects
How do edge states position themselves in a quantum Hall graphene pn junction?
Recent experiments have shown that electronic Mach-Zehnder interferometers of
unprecedented fidelities could be built using a graphene pn junction in the
quantum Hall regime. In these junctions, two different edge states
corresponding to two different valley configurations are spatially separated
and form the two arms of the interferometer. The observed separation, of
several tens of nanometers, has been found to be abnormally high and thus
associated to unrealistic values of the exchange interaction. In this work, we
show that, although the separation is due to exchange interaction, its actual
value is entirely governed by the sample geometry and independent of the value
of the exchange splitting. Our analysis follows the lines of the classical work
of Chklovski-Shklovskii- Glazman on electrostatically induced edge state
reconstruction and includes quantitative numerical calculations in the
experimental geometries.Comment: 4 pages, 4 figure
Does ohmic heating influence the flow field in thin-layer electrodeposition?
In thin-layer electrodeposition the dissipated electrical energy leads to a
substantial heating of the ion solution. We measured the resulting temperature
field by means of an infrared camera. The properties of the temperature field
correspond closely with the development of the concentration field. In
particular we find, that the thermal gradients at the electrodes act like a
weak additional driving force to the convection rolls driven by concentration
gradients.Comment: minor changes: correct estimation of concentration at the anode,
added Journal-re
Biharmonic pattern selection
A new model to describe fractal growth is discussed which includes effects
due to long-range coupling between displacements . The model is based on the
biharmonic equation in two-dimensional isotropic defect-free
media as follows from the Kuramoto-Sivashinsky equation for pattern formation
-or, alternatively, from the theory of elasticity. As a difference with
Laplacian and Poisson growth models, in the new model the Laplacian of is
neither zero nor proportional to . Its discretization allows to reproduce a
transition from dense to multibranched growth at a point in which the growth
velocity exhibits a minimum similarly to what occurs within Poisson growth in
planar geometry. Furthermore, in circular geometry the transition point is
estimated for the simplest case from the relation
such that the trajectories become stable at the growing surfaces in a
continuous limit. Hence, within the biharmonic growth model, this transition
depends only on the system size and occurs approximately at a distance far from a central seed particle. The influence of biharmonic patterns on
the growth probability for each lattice site is also analysed.Comment: To appear in Phys. Rev. E. Copies upon request to
[email protected]
Welfare regimes and social cohesion regimes: do they express the same values?
Welfare regime types are classified according to the role played by three main institutions, namely the market, the state and the family. They can be reinterpreted as systems of exchanges for providing resources based on the main principles of liberty, equality and solidarity. Depending on the different possible dialectical relations between these three principles, they lead to different social cohesion regimes. This paper is the first attempt to empirically test this hypothesis at a European level by elaborating a measure of social cohesion based on values and creating a typology of social cohesion regimes. In comparison to welfare regimes, it invites to go one step further by considering the articulation between the three main principles and proposes a more precise classification for countries. The results invite further research on the links between welfare and social cohesion regimes. The analysis is based on data from the 2008 European Values Study (EVS) in 43 countries using principal component analysis, multidimensional scaling and cluster analyses
Early stages of ramified growth in quasi-two-dimensional electrochemical deposition
I have measured the early stages of the growth of branched metal aggregates
formed by electrochemical deposition in very thin layers. The growth rate of
spatial Fourier modes is described qualitatively by the results of a linear
stability analysis [D.P. Barkey, R.H. Muller, and C.W. Tobias, J. Electrochem.
Soc. {\bf 136}, 2207 (1989)]. The maximum growth rate is proportional to
where is the current through the electrochemical cell,
the electrolyte concentration, and . Differences
between my results and the theoretical predictions suggest that
electroconvection in the electrolyte has a large influence on the instability
leading to ramified growth.Comment: REVTeX, four ps figure
- …