1,618 research outputs found
El principio de reciprocidad y la globalización del derecho desde la perspectiva de la regla de oro.
Analysis of Bi Distribution in Epitaxial GaAsBi by aberration-corrected HAADF-STEM
The Bi content in GaAs/GaAs1 − xBix/GaAs heterostructures grown by molecular beam epitaxy at a substrate temperature
close to 340 °C is investigated by aberration-corrected high-angle annular dark-field techniques. The analysis at low
magnification of high-angle annular dark-field scanning transmission electron microscopy images, corroborated by EDX
analysis, revealed planar defect-free layers and a non-homogeneous Bi distribution at the interfaces and within the GaAsBi
layer. At high magnification, the qHAADF analysis confirmed the inhomogeneous distribution and Bi segregation at the
GaAsBi/GaAs interface at low Bi flux and distorted dumbbell shape in areas with higher Bi content. At higher Bi flux, the
size of the Bi gathering increases leading to roughly equiaxial Bi-rich particles faceted along zinc blende {111}
and uniformly dispersed around the matrix and interfaces. FFT analysis checks the coexistence of two phases in
some clusters: a rhombohedral pure Bi (rh-Bi) one surrounded by a zinc blende GaAs1 − xBix matrix. Clusters may
be affecting to the local lattice relaxation and leading to a partially relaxed GaAsBi/GaAs system, in good agreement
with XRD analysis
Present day challenges in understanding the geomagnetic hazard to national power grids
Power grids and pipeline networks at all latitudes are known to be at risk from the natural hazard of geomagnetically induced currents. At a recent workshop in South Africa, UK and South African scientists and engineers discussed the current understanding of this hazard, as it affects major power systems in Europe and Africa. They also summarised, to better inform the public and industry, what can be said with some certainty about the hazard and what research is yet required to develop useful tools for geomagnetic hazard mitigation
The origin of the high velocity circumstellar gas around SN 1998S
Modelling of high resolution Balmer line profiles in the early-time spectra
of SN 1998S shows that the inferred fast (roughly 400 km/s) circumstellar (CS)
gas on days 23 and 42 post-explosion is confined to a narrow, negative velocity
gradient shell just above the photosphere. This gas may be identified with a
slow (v < 40 km/s) progenitor wind accelerated at the ejecta-wind interface. In
this scenario, the photosphere coincides with a cool dense shell formed in the
reverse shock. Acceleration by radiation from the supernova or by a
shock-accelerated relativistic particle precursor are both possible
explanations for the observed fast CS gas. An alternative, equally plausible
scenario is that the fast CS gas is accelerated within shocked clouds engulfed
by the outer shock, as it propagates through the intercloud wind.Comment: 9 pages, 6 figures. MNRAS, accepted. Typos added, acknowledgments
correcte
Feasibility and dominance rules in the electromagnetism-like algorithm for constrained global optimization
This paper presents the use of a constraint-handling technique, known as feasibility and dominance rules, in a electromagnetismlike
(ELM) mechanism for solving constrained global optimization problems. Since the original ELM algorithm is specifically designed for solving bound constrained problems, only the inequality and equality constraints violation together with the objective function value are used to select
points and to progress towards feasibility and optimality. Numerical experiments are presented, including a comparison with other methods recently reported in the literature
Competing tunneling trajectories in a 2D potential with variable topology as a model for quantum bifurcations
We present a path - integral approach to treat a 2D model of a quantum
bifurcation. The model potential has two equivalent minima separated by one or
two saddle points, depending on the value of a continuous parameter. Tunneling
is therefore realized either along one trajectory or along two equivalent
paths. Zero point fluctuations smear out the sharp transition between these two
regimes and lead to a certain crossover behavior. When the two saddle points
are inequivalent one can also have a first order transition related to the fact
that one of the two trajectories becomes unstable. We illustrate these results
by numerical investigations. Even though a specific model is investigated here,
the approach is quite general and has potential applicability for various
systems in physics and chemistry exhibiting multi-stability and tunneling
phenomena.Comment: 11 pages, 8 eps figures, Revtex-
Effect of Antimony and Cerium on the Formation of Chunky Graphite during Solidification of Heavy-Section Castings of Near-Eutectic Spheroidal Graphite Irons
Thermal analysis is applied to the study of the formation of chunky graphite (CHG) in heavysection castings of spheroidal graphite cast irons. To that aim, near-eutectic melts prepared in one single cast house were poured into molds containing up to four large cubic blocks 30 cm in size. Four melts have been prepared and cast that had a cerium content varying in relation with the spheroidizing alloy used. Postinoculation or addition of antimony was achieved by fixing appropriate amounts of materials in the gating system of each block. Cooling curves recorded in the center of the blocks show that solidification proceeds in three steps: a short primary deposition of graphite followed by an initial and then a bulk eutectic reaction. Formation of CHG could be unambiguously associated with increased recalescence during the bulk eutectic reaction. While antimony strongly decreases the amount of CHG, it appears that the ratio of the contents in antimony and cerium should be higher than 0.8 in order to avoid this graphite degeneracy
The Relationship Between Plasma Flow Doppler Velocities and Magnetic Field Parameters During the Emergence of Active Regions at the Solar Photospheric Level
A statistical study has been carried out of the relationship between plasma
flow Doppler velocities and magnetic field parameters during the emergence of
active regions at the solar photospheric level with data acquired by the
Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory
(SOHO). We have investigated 224 emerging active regions with different spatial
scales and positions on the solar disc. The following relationships for the
first hours of the emergence of active regions have been analysed: i) of peak
negative Doppler velocities with the position of the emerging active regions on
the solar disc; ii) of peak plasma upflow and downflow Doppler velocities with
the magnetic flux growth rate and magnetic field strength for the active
regions emerging near the solar disc centre (the vertical component of plasma
flows); iii) of peak positive and negative Doppler velocities with the magnetic
flux growth rate and magnetic field strength for the active regions emerging
near the limb (the horizontal component of plasma flows); iv) of the magnetic
flux growth rate with the density of emerging magnetic flux; v) of the Doppler
velocities and magnetic field parameters for the first hours of the appearance
of active regions with the total unsigned magnetic flux at the maximum of their
development.Comment: 14 pages, 8 figures. The results of article were presented at the
ESPM-13 (12-16 September 2011, Rhodes, Greece, Abstract Book p. 102-103,
P.4.13,
http://astro.academyofathens.gr/espm13/documents/ESPM13_abstract_programme_book.pdf
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