1,803 research outputs found
Multi-Fluid Simulation of the Magnetic Field Evolution in Neutron Stars
Using a numerical simulation, we study the effects of ambipolar diffusion and
ohmic diffusion on the magnetic field evolution in the interior of an isolated
neutron star. We are interested in the behavior of the magnetic field on a long
time scale, over which all Alfven and sound waves have been damped. We model
the stellar interior as an electrically neutral plasma composed of neutrons,
protons and electrons, which can interact with each other through collisions
and electromagnetic forces. Weak interactions convert neutrons and charged
particles into each other, erasing chemical imbalances. As a first step, we
assume that the magnetic field points in one fixed Cartesian direction but can
vary along an orthogonal direction. We start with a uniform-density background
threaded by a homogeneous magnetic field and study the evolution of a magnetic
perturbation as well as the density fluctuations it induces in the particles.
We show that the system evolves through different quasi-equilibrium states and
estimate the characteristic time scales on which these quasi-equilibria occur.Comment: It will be published in AIP Proceedings of the Conference '40 Years
of Pulsars: Milisecond Pulsars, Magnetars and More' held at University of
McGill, Montreal, Canada, August 2007. Contributed Talk at Conference '40
Years of Pulsars: Milisecond Pulsars, Magnetars and More
Late cenozoic identation/escape tectonics in the eastern Betic Cordilleras and its consequences on the Iberian foreland
The structuration of the southeastern quarter of the Iberian Peninsula (eastern Betics and Iberian foreland), since Messinian time, was the result of a series of complex deformational events, as related to a major NNE-SSW sinistral shear zone disrupting the southeasternmost part of the Betic cordilleras (Trans-Alborán-Palomares shear zone; TAPSZ). Deformation along this shear zone was characterized by two differentiated and sequential scenarios: 1) periods of stress-build-up associated to momentary slip-obstruction along the TAPSZ, involving NW-directed indentation of the southeastern Iberian domain, and 2) periods of stress-release resulting from the lateral escape of wedge-shaped blocks, thus allowing full-scale strike-slip displacements along the TAPSZ. These events imposed compressional stress fields on the Iberian foreland, with a series of consequences such as alkaline volcanism in Calatrava and Cofrentes, protorift zones, changes in previous structural trends, localized uplift/doming processes, and changes in the sedimentary records of sorne basins.La estructuración del cuadrante SE de la Península Ibérica (Béticas orientales y antepaís Ibérico), desde el Messiniense hasta la actualidad, ha sido el resultado de una serie compleja de eventos deformativos, relacionados con la actividad de una megazona de cizalla NNE-SSO en el SE de las Cordilleras Béticas (zona de cizalla Trans-Alborán-Palomares; TAPSZ). La deformación a lo largo de esta zona de cizalla se caracteriza por dos escenarios secuenciales diferentes: 1) períodos de concentración de esfuerzos, asociados con un frenado momentáneo del movimiento a lo largo de la TAPSZ, y con procesos de identación dirigidos hacia el NO, y 2) períodos de disipación de esfuerzos, que serían el resultado del escape lateral de bloques en forma de cuña, y del movimiento transcurrente renovado a lo largo de la TAPSZ. Estos eventos han generado campos de esfuerzos en el antepaís Ibérico, con una serie de consecuencias tales como el vulcanismo alcalino de Calatrava y Cofrentes, zonas de protorift, modificaciones de directrices estructurales previas, levantamientos/abombamientos localizados, y cambios en el régimen sedimentario de algunas cuencas
Synchrotron radiation photoionization mass spectrometry of laser ablated species
The present paper describes an experimental apparatus suitable to create and study free clusters by combining laser ablation and synchrotron radiation. First tests on sulfur samples, S, showed the production, through laser ablation, of neutral Sn clusters (n = 1–8). These clusters were ionized using synchrotron radiation at photon energies from 160 eV to 175 eV, across the S 2p core edge. The feasibility of such combined ablation–synchrotron radiation experiments is demonstrated, opening new possibilities on the investigation of free clusters and radical
Least action description of dynamic pairing correlations in the fission of Curium and Californium isotopes based on the Gogny energy density functional
The impact of dynamic pairing correlations and their interplay with Coulomb
antipairing effects on the systematic of the spontaneous fission half-lives for
the nuclei Cm and Cf is analyzed, using a hierarchy of
approximations based on the parametrization D1M of the Gogny energy density
functional (EDF). First, the constrained Hartree-Fock-Bogoliubov (HFB)
approximation is used to compute deformed mean-field configurations, zero-point
quantum corrections and collective inertias either by using the Slater
approximation to Coulomb exchange and neglecting Coulomb antipairing or by
fully considering the exchange and pairing channels of the Coulomb interaction.
Next, the properties of the {\it{least action}} and {\it{least energy}} fission
paths are compared. In the {\it{least action}} case, pairing is identified as
the relevant degree of freedom in order to minimize the action entering the
Wentzel-Kramers-Brillouin (WKB) approximation to the tunneling probability
through the fission barrier. Irrespective of the treatment of Coulomb exchange
and antipairing, it is shown that the {\it{least action}} path obtained taking
into account the pairing degree of freedom leads to stronger pairing
correlations that significantly reduce the spontaneous fission half-lives
improving thereby the comparison with the experiment by several orders
of magnitude. It is also shown that the Coulomb antipairing effect is, to a
large extent, washed out by the {\it{least action}} procedure and therefore the
values obtained by the two different treatments of the Coulomb
exchange and pairing are of similar quality.Comment: 13 pages, 8 figure
Disordered loops in the two-dimensional antiferromagnetic spin-fermion model
The spin-fermion model has long been used to describe the quantum-critical
behavior of 2d electron systems near an antiferromagnetic (AFM) instability.
Recently, the standard procedure to integrate out the fermions to obtain an
effective action for spin waves has been questioned in the clean case. We show
that in the presence of disorder, the single fermion loops display two
crossover scales: upon lowering the energy, the singularities of the clean
fermionic loops are first cut off, but below a second scale new singularities
arise that lead again to marginal scaling. In addition, impurity lines between
different fermion loops generate new relevant couplings which dominate at low
energies. We outline a non-linear sigma model formulation of the single-loop
problem, which allows to control the higher singularities and provides an
effective model in terms of low-energy diffusive as well as spin modes.Comment: 22 pages, 8 figure
Descripción de la sintomatología asociada a fusariosis y comparación con otras enfermedades en gulupa (Passiflora edulis Sims.) en la región del Sumapaz (Colombia)
Estudios encaminados a determinar la etiología de patologías relacionadas con fusariosis en el cultivo de gulupa en la región del Sumapaz (Colombia), indicaron la presencia de las enfermedades denominadas, marchitez por Fusarium y pudrición del cuello causadas por F. oxysporum y F. solani, respectivamente. El objetivo de la presente nota científica es describir la sintomatología asociada a las enfermedades mencionadas, haciendo una comparación con la sintomatología asociada a enfermedades causadas por bacterias y nematodos
Stellar Populations Found in the Central kpc of Four Luminous Compact Blue Galaxies at Intermediate Redshift
We investigate the star formation history of the central regions of four
Luminous Compact Blue Galaxies (LCBGs). LCBGs are blue (B-V<0.6), compact
(MU_B<21.5 mag arcsec^-2) galaxies with absolute magnitudes M_B brighter than
-17.5. The LCBGs analyzed here are located at 0.436<z<0.525. They are among the
most luminous (M_B < -20.5), blue (B-V < 0.4) and high surface brightness (MU_B
< 19.0 mag arcsec^-2) of this population. The observational data used were
obtained with the HST/STIS spectrograph, the HST/WF/PC-2 camera and the
HST/NICMOS first camera. We find evidence for multiple stellar populations. One
of them is identified as the ionizing population, and the other one corresponds
to the underlying stellar generation.
The estimated masses of the inferred populations are compatible with the
dynamical masses, which are typically 2--10x 10^9 M_sun. Our models also
indicate that the first episodes of star formation the presented LCBGs
underwent happened between 5 and 7 Gyr ago.
We compare the stellar populations found in LCBGs with the stellar
populations present in bright, local HII galaxies, nearby spheroidal systems
and Blue Compact Dwarf Galaxies. It turns out that the underlying stellar
populations of LCBGs are similar yet bluer to those of local HII galaxies. It
is also the case that the passive color evolution of the LCBGs could convert
them into local Spheroidal galaxies if no further episode of star formation
takes place. Our results help to impose constraints on evolutionary scenarios
for the population of LCBGs found commonly at intermediate redshifts.Comment: 35 pages, 10 Figures. Accepted for publication in AJ. Compile with
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