1,497 research outputs found
Comentarios a la ponencia "Igualdades, desigualdades y derechos", presentada por Mirta Lobato
Teniendo en cuenta -como advierte Mirta Lobato a los comentaristas- que cuando habla de desigualdades en su ponencia se refiere a que "el trabajo es el eje articulador de estas reflexiones", y sin dejar de reconocer la importancia que cabe a los otros temas y sujetos sobre los que tan bien desarrolla su exposición, quiero centrarme en un grupo que estoy estudiando desde hace unos años, como es el de los inmigrantes limítrofes a la Argentina de fin de siglo XX e inicios del XXI. Para ello, voy a analizar brevemente -como así lo exigen las reglas del comentario- a estos sujetos sociales, a quienes, como también ella afirma, ya los habríamos de encontrar censalmente a inicios del siglo pasado, aunque su visibilidad fuera menor porque aún no habían arribado a Buenos Aires; es decir, al escenario donde "las cosas suceden".Fil: Benencia, Roberto Rodolfo. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Shock compression and isentropic release of granite
New equation of state data for a weathered granite shocked to about 125 GPa are reported and combined with the Westerly granite data of McQueen, Marsh & Fritz (1967). The shock velocity (U_s)-particle velocity (U_p) relations can be fitted with two linear regressions: U_s= 4.40 + 0.6U_p for a range of U_p up to about 2 km s^(-1) and U_s= 2.66 + 1.49U_p for a range of about 2 to 5 km s^(-1). The third-order Birch-Murnaghan equation of state parameters are K_(os) = 51-57 GPa and K'_(os) = 1.4-1.8 for the low-pressure regime and K_(os) = 251 ± 30 GPa and an assumed K'_(os) = 4 for the high-pressure regime. Compressive waveforms in dry and water-saturated granite were measured at 10-15 GPa using the VISAR technique. The measured wave profiles were successfully modelled using a Maxwellian stress-relaxation material model. Water-saturated granite is characterized by a ~25 per cent lower yield strength and a ~75 per cent longer material relaxation time than dry granite
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Distribution of early life Pacific halibut and comparison with Greenland halibut in the eastern Bering Sea
Information about spatial distribution patterns during early life stages of fish is key to understanding dispersal trajectories and connectivity from spawning to nursery areas, as well as adult population dynamics. More than 30 years of historical field data were analyzed in order to describe the horizontal and vertical distributions of Pacific halibut early life stages (larvae to juveniles) in the eastern Bering Sea and to compare the distributions between Pacific halibut and Greenland halibut. Our results indicate that spawning for both species likely occurred in Bering and Pribilof canyons, along the slope between the two canyons, and on the eastern side of the Aleutian Islands during winter, but Pacific halibut spawning was protracted until early spring. Larvae of both species rose to shallower depths in the water column as they developed, but Pacific halibut larvae had an abrupt movement toward shallower depths. Geographically, larvae for both species either advected northwestward along the Bering Sea Slope or crossed onto the shelves from the slope regions, but the timing in Pacific halibut larval progression onto the shelf and along the slope was earlier than for Greenland halibut larvae. Pacific halibut juveniles (≤ 90 mm total length (TL)) were mostly found in the inner shelf between Bristol Bay and Nunivak Island, along the Alaskan Peninsula, and in the vicinity of the Pribilof Islands. The range of Greenland halibut juvenile (≤ 90 mm TL) distribution was expanded to south of the Pribilof Islands in the middle shelf and to the inner shelf. Although the two species share some attributes (i.e., spawning location) during early life stages, there were species-specific differences associated with spatial distribution (vertically and horizontally), timing differences in larval progression onto the shelves, pelagic larval duration, and juvenile nursery areas.Keywords: Early life history, Settlement, Distribution, Greenland halibut, Pacific halibut, Eastern Bering Se
Thermal Equation of State of Tantalum
We have investigated the thermal equation of state of tantalum from first
principles using the Linearized Augmented Plane Wave (LAPW) and pseudopotential
methods for pressures up to 300 GPa and temperatures up to 10000 K. The
equation of state at zero temperature was computed using LAPW. For finite
temperatures, mixed basis pseudopotential computations were performed for 54
atom supercells. The vibrational contributions were obtained by computing the
partition function using the particle in a cell model, and the the finite
temperature electronic free energy was obtained from the LAPW band structures.
We discuss the behavior of thermal equation of state parameters such as the
Gr\"uneisen parameter , , the thermal expansivity , the
Anderson-Gr\"uneisen parameter as functions of pressure and
temperature. The calculated Hugoniot shows excellent agreement with shock-wave
experiments. An electronic topological transition was found at approximately
200 GPa
A Study of the Antiferromagnetic Phase in the Hubbard Model by means of the Composite Operator Method
We have investigated the antiferromagnetic phase of the 2D, the 3D and the
extended Hubbard models on a bipartite cubic lattice by means of the Composite
Operator Method within a two-pole approximation. This approach yields a fully
self-consistent treatment of the antiferromagnetic state that respects the
symmetry properties of both the model and the algebra. The complete phase
diagram, as regards the antiferromagnetic and the paramagnetic phases, has been
drawn. We firstly reported, within a pole approximation, three kinds of
transitions at half-filling: Mott-Hubbard, Mott-Heisenberg and Heisenberg. We
have also found a metal-insulator transition, driven by doping, within the
antiferromagnetic phase. This latter is restricted to a very small region near
half filling and has, in contrast to what has been found by similar approaches,
a finite critical Coulomb interaction as lower bound at half filling. Finally,
it is worth noting that our antiferromagnetic gap has two independent
components: one due to the antiferromagnetic correlations and another coming
from the Mott-Hubbard mechanism.Comment: 20 pages, 37 figures, RevTeX, submitted to Phys. Rev.
Raman spectrum and lattice parameters of MgB2 as a function of pressure
We report Raman spectra and synchrotron x-ray diffraction measurements of
lattice parameters of polycrystalline MgB2 under hydrostatic pressure
conditions up to 15 GPa. An anomalously broadened Raman band at 620 cm-1 is
observed that exhibits a large linear pressure shift of its frequency. The
large mode damping and Gruneisen parameter indicate a highly anharmonic nature
of the mode, broadly consistent with theoretical predictions for the E2g
in-plane boron stretching mode. The results obtained may provide additional
constraints on the electron-phonon coupling in the system.Comment: 3 pages, 3 figure
Spin Liquid State around a Doped Hole in Insulating Cuprates
The numerically exact diagonalization study on small clusters of the t-J
model with the second- and third- neighbor hopping terms shows that a novel
spin liquid state is realized around a doped hole with momentum k=(pi,0) and
energy \sim 2J compared with that with (pi/2,pi/2) in insulating cuprates,
where the spin and charge degrees of freedom are approximately decoupled. Our
finding implies that the excitations in the insulating cuprates are mapped onto
the the d-wave resonating valence bond state.Comment: 4 pages, 4 EPS figures, to be published in J. Phys. Soc. Jpn. Vol.
69, No.1 January, 200
A polarized neutron-scattering study of the Cooper-pair moment in Sr2RuO4
We report a study of the magnetization density in the mixed state of the
unconventional superconductor S2RuO4. On entering the superconducting state we
find no change in the magnitude or distribution of the induced moment for a
magnetic field of 1 Tesla applied within the RuO2 planes. Our results are
consistent with a spin-triplet Cooper pairing with spins lying in the basal
plane. This is in contrast with similar experiments performed on conventional
and high-Tc superconductors.Comment: Submitted to Physical Review Letter
Randomised controlled trial of mammographic screening in women from age 40: predicted mortality based on surrogate outcome measures
A trial in the UK to study the effect on mortality from breast cancer of invitation for annual mammography from the age of 40–41, has randomised a total of 160 921 women in the ratio 1 : 2 to the intervention and control arms. All breast cancers diagnosed in the two arms have been identified, and the histology reviewed. This paper presents the results of an interim analysis using surrogate outcome measures to compare predicted breast cancer mortality in the two arms based on 1287 cases diagnosed to 31.12.1999. Due to earlier diagnosis, there is currently an 8% excess of invasive breast cancers in the intervention arm. The ratio of predicted deaths at 10 years in the intervention arm relative to the control arm, adjusted for this excess diagnosis, ranges from 0.89 (95% confidence interval (CI) 0.78–1.01) to 0.90 (95% CI 0.80–1.01). Screening from age 40 may result in a lower reduction in breast cancer mortality than that observed in other trials including women below age 50. This analysis based on surrogate outcome measures suggests that a reduction in breast cancer mortality may be observed in this trial. However, a number of assumptions have been necessary and firm conclusions must await the analysis of observed mortality from breast cancer
Resonant Raman Scattering in Antiferromagnets
Two-magnon Raman scattering provides important information about electronic
correlations in the insulating parent compounds of high- materials. Recent
experiments have shown a strong dependence of the Raman signal in
geometry on the frequency of the incoming photon. We present an analytical and
numerical study of the Raman intensity in the resonant regime. It has been
previously argued by one of us (A.Ch) and D. Frenkel that the most relevant
contribution to the Raman vertex at resonance is given by the triple resonance
diagram. We derive an expression for the Raman intensity in which we
simultaneously include the enhancement due to the triple resonance and a final
state interaction. We compute the two-magnon peak height (TMPH) as a function
of incident frequency and find two maxima at and . We argue that the
high-frequency maximum is cut only by a quasiparticle damping, while the
low-frequency maximum has a finite amplitude even in the absence of damping. We
also obtain an evolution of the Raman profile from an asymmetric form around
to a symmetric form around . We
further show that the TMPH depends on the fermionic quasiparticle damping, the
next-nearest neighbor hopping term and the corrections to the
interaction vertex between light and the fermionic current. We discuss our
results in the context of recent experiments by Blumberg et al. on
and and R\"{u}bhausen et al. on
and show that the triple resonance theory yields a qualitative
and to some extent also quantitative understanding of the experimental data.Comment: 19 pages, RevTeX, 16 figures embedded in the text, ps-file is also
available at http://lifshitz.physics.wisc.edu/www/morr/morr_homepage.htm
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