10,707 research outputs found
Snake orbits and related magnetic edge states
We study the electron motion near magnetic field steps at which the strength
and/or sign of the magnetic field changes. The energy spectrum for such systems
is found and the electron states (bound and scattered) are compared with their
corresponding classical paths. Several classical properties as the velocity
parallel to the edge, the oscillation frequency perpendicular to the edge and
the extent of the states are compared with their quantum mechanical
counterpart. A class of magnetic edge states is found which do not have a
classical counterpart.Comment: 8 pages, 10 figure
Discovery of a 6.4 keV Emission Line in a Burst from SGR 1900+14
We present evidence of a 6.4 keV emission line during a burst from the soft
gamma-ray repeater SGR 1900+14. The Rossi X-ray Timing Explorer (RXTE)
monitored this source extensively during its outburst in the summer of 1998. A
strong burst observed on August 29, 1998 revealed a number of unique
properties. The burst exhibits a precursor and is followed by a long (~ 1000 s)
tail modulated at the 5.16 s stellar rotation period. The precursor has a
duration of 0.85 s and shows both significant spectral evolution as well as an
emission feature centered near 6.4 keV during the first 0.3 s of the event,
when the X-ray spectrum was hardest. The continuum during the burst is well fit
with an optically thin thermal bremsstrahlung (OTTB) spectrum with the
temperature ranging from about 40 to 10 keV. The line is strong, with an
equivalent width of 400 eV, and is consistent with Fe K-alpha fluorescence from
relatively cool material. If the rest-frame energy is indeed 6.4 keV, then the
lack of an observed redshift indicates that the source is at least 80 km above
the neutron star surface. We discuss the implications of the line detection in
the context of models for SGRs.Comment: AASTex preprint, 14 pages, 3 embedded figures. Accepted for
Publication in Astrophysical Journal Letter
Preparation of a geologic photo map and hydrologic study of the Yemen Arab Republic
There are no author-identified significant results in this report
Developing a Performance Criteria for Stone Columns to Improve Surface Pavement for Weak Subgrade Conditions
AbstractSoft, saturated, fine grained subgrade soils are distinguished by their low undrianed shear strength and high compressibility. Such soils cover most of the middle and southern parts of Iraq. The effect of using stone column, encased in geogrid and steel mesh to improve pavement's performance is experimentally investigated and evaluated. To compare the experimental and analytical outputs, three dimensions finite element throughout elastic and elasto-plastic models using ABAQUS ver.6.12.3 software are developed to simulate and analyze the relations between the cycling load and deformation of the suggested pavement modes. Based on the results and the limitation of this study it is concluded that, using encased stone columns, is more practical and suitable alternative to improve weak subgrade against permanent deformation as compared with the other simulated pavement modes. The results of ABAQUS program are very close to results of laboratory tests
An Approach in Evaluating of Flexible Pavement In Permanent Deformation OF Paved AND Unpaved Roads Over Sand Dunes Subgrade Under Repeated Loads
Thickness of flexible pavement play very important factor in cost of construction of road ,in this study effect of change thickness of pavement on rutting of road is investigated . Two approaches are adopted; the first is the laboratory tests through simulation of three layers of paved road and two layers for unpaved road, using a steel box with dimensions of 600mm length 500mm width and 400mm depth. Sand dunes are used as a subgrade layer to investigate its behavior by using it as a part of flexible pavement structure under repeated load at relative density 55.7%. The effect of change in thickness of asphalt layer in permanent deformation is also investigated, through using three models at three different thicknesses, starting from zero (unpaved), 50mm and 100 mm. The second approach is the development of a three-dimensional finite element model for flexible pavements using ABAQUS (6.12-3) to simulate the laboratory test The results indicate that increase in the thickness of flexible pavement to 50mm from zero (unpaved), increases the number of passes about 971.42%, while the increase of thickness from 50mm to 100 mm, increases the number of passes by 517.33%. The results of ABAQUS program are very close to results of laboratory tests. Keywords: Sand Dunes subgrade, Thickness of Flexible Pavement, ABAQUSÂ Â Model
Probing scalar-pseudoscalar mixing in the CP violating MSSM at high-energy colliders
We study the production processes , and
in the context of the CP violating MSSM. In a given
channel we show that the cross-section for all i (=1,2,3) can be above 0.1 fb
provided M_{H_{2,3}}\la 300 GeV. This should be detectable at a Next Linear
Collider and would provide evidence for scalar-pseudoscalar mixing.Comment: 17 pages, RevTex, 4 ps figures, figure 4 changed, minor modifications
to text, version to appear in PR
The Electric Dipole Moment and CP Violation in in SUGRA Models with Nonuniversal Gaugino Masses
The constraints of electric dipole moments (EDMs) of electron and neutron on
the parameter space in supergravity (SUGRA) models with nonuniversal gaugino
masses are analyzed. It is shown that with a light sparticle spectrum, the
sufficient cancellations in the calculation of EDMs can happen for all phases
being order of one in the small tan case and all phases but
() order of one in the large tan case. This is
in contrast to the case of mSUGRA in which in the parameter space where
cancellations among various SUSY contributions to EDMs happen
must be less than for small and for
large . Direct CP asymmetries and the T-odd polarization of lepton in
are investigated in the models. In the large tan case,
and for l= () can be enhanced by about a factor of
ten (ten) and ten (three) respectively compared to those of mSUGRA.Comment: 12 pages, latex, 4 figures, a few change
Neutralino Pair Production and 3-Body Decays at Linear Colliders as Probes of CP Violation in the Neutralino System
In the CP-invariant supersymmetric theories, the steep S-wave (slow P-wave)
rise of the cross section for any non-diagonal neutralino pair production in
annihilation, (), near threshold is accompanied by the slow P-wave (steep S-wave) decrease
of the fermion invariant mass distribution of the 3-body neutralino decay,
( or ), near the end
point. These selection rules, unique to the neutralino system due to its
Majorana nature, guarantee that the observation of simultaneous sharp S-wave
excitations of the production cross section near threshold and the lepton and
quark invariant mass distribution near the end point is a qualitative,
unambiguous evidence for CP violation in the neutralino system.Comment: 11 pages, 1 eps figure, a reference adde
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