A one-parameter family of interpolating kernels for Smoothed Particle Hydrodynamics studies

A set of interpolating functions of the type f(v)={(sin[v pi/2])/(v pi/2)}^n is analyzed in the context of the smoothed-particle hydrodynamics (SPH) technique. The behaviour of these kernels for several values of the parameter n has been studied either analytically as well as numerically in connection with several tests carried out in two dimensions. The main advantage of this kernel relies in its flexibility because for n=3 it is similar to the standard widely used cubic-spline, whereas for n>3 the interpolating function becomes more centrally condensed, being well suited to track discontinuities such as shock fronts and thermal waves.Comment: 36 pages, 12 figures (low-resolution), published in J.C.

Evolución tectónica y sedimentaria durante el Priaboniense superior-Mioceno inferior, en el frente de cabalgamiento de las Sierras Marginales occidentales

Four systems tracts have been distinguished in the uppermost Eocene-lower Miocene continental deposits of the northern margin of the Ebro basin. 1) The Satinar systems tract 5pper Pnabonian-Stampian) consists of an alluvial system (Salinar Fm) located in the north, that passes to playa-lake evapontes (lower Barbastro Fm) towards the foreland. The alluvial sediments are represented only by distal fan and alluvial plain facies which are in the footwall of the Sierras Marginales thrust. The top of the Salinar systems tract is inarked by lacustrine limestones that represerit the alluvial fan retre,at and a change to less saline conditions. 2) The Peralta systems tract (upperPriaboniiin?-Stampian) consists of srnall alluvial fans attached to the Sierras Marginales (Peralta Fm) that pass to playa-lake evaporites towards ;he foreland (upper Barbastro Fm). The alluvial facies are represented by calcareous conglomerates, that grade in a few kilometers to thin-bedded sandstones and mudstones. Evaporitic facies are represented by nodular and larninated gypsum. The top of the Peralta systems tract is also marked by an extensive body of lacustrine carbonates that represent a new alluvial fan retreat. 3) The Peraltilla systems tract (Stampian-Chattian) consists of small alluvial fans (Calasanz Fm), that show i;imilar characteristics to those of the Peralta I'rn but they interfinger distally with a large fluvial systern sourced in the axial Pyrenees (Peraltilla Fm). This fluvial fan consists of red overbank deposits with paleosoils, and channelized bodies, which are mostly conglomeratic in the Azanuy syncline and become sandy towards the southern limb of Barbastro anticline. This granulometric change is accompanied by a change in channel type, from typical braided to sinuouir or straight. The Salinar and Peralta systerns are contemporaneous with the emplacernent of the Sierras Marginales thrust sheet. The clastic sedirnents accumulated in a flexura1 trough that widens while the thrust propagates. As a consecuence, the saline lake facies expand towards the foreland. During the Peralta systerns tract a blind detachment located in the base of the Barbastro evaporitic formation propagated and started to fold the foreland. The Peraltilla systems tract is contemporaneous with the end of displacement of the Sierras Marginales thrust sheet and the rnain growth of the Peralta detachment anticline. However, these tectonic events were accompanied by a significant forelandward shift of the basin depocenter and a more homogeneous subsidence. 4) The Sarinena systems tract (Chattian-Aquitanian) is very similar to the Peraltilla one but it shows a marked southwards shift of the proximal facies. It consists of srnall fans of local provenance (Baells Fm) that interfinger distally with alarge fluvial fan (Sarinena Fm). The sedimentation of the Sariñenasystems tract is contemporaneous with the continued southward propagation of the detachment through the foreland evaporites, that creates new detachment folds (Barbastro and Altarriba anticlines, Azanuy syncline). An episode of out-of sequence thrusting generates small thrust-top basins on the Sierras Marginales, filled by the Baells conglomerates. The Sariñena systems tract accumulated in a wide foreland trough, with a strongly subsiding located in the Azanuy syncline

Explosion models for thermonuclear supernovae resulting from different ignition conditions

We have explored in three dimensions the fate of a massive white dwarf as a function of different initial locations of carbon ignition, with the aid of a SPH code. The calculated models cover a variety of possibilities ranging from the simultaneous ignition of the central volume of the star to the off-center ignition in multiple scattered spots. In the former case, there are discussed the possibility of a transition to a detonation when the mean density of the nuclear flame decreases below 2x10**7 g cm**-3, and its consequences. In the last case, the dependence of the results on the number of initial igniting spots and the chance of some of these models to evolve to the pulsating delayed detonation scenario are also outlined.Comment: 5 pages, 1 figure, proceedings of IAU Colloquium 192, 'Supernovae (10 years of SN1993J)', 22-26 April 2003, Valencia, Spai

Evolución tectónica y sedimentaria durante el Priaboniense superior-Mioceno inferior, en el frente de cabalgamiento de las Sierras Marginales occidentales

Four systems tracts have been distinguished in the uppermost Eocene-lower Miocene continental deposits of the northern margin of the Ebro basin. 1) The Satinar systems tract 5pper Pnabonian-Stampian) consists of an alluvial system (Salinar Fm) located in the north, that passes to playa-lake evapontes (lower Barbastro Fm) towards the foreland. The alluvial sediments are represented only by distal fan and alluvial plain facies which are in the footwall of the Sierras Marginales thrust. The top of the Salinar systems tract is inarked by lacustrine limestones that represerit the alluvial fan retre,at and a change to less saline conditions. 2) The Peralta systems tract (upperPriaboniiin?-Stampian) consists of srnall alluvial fans attached to the Sierras Marginales (Peralta Fm) that pass to playa-lake evaporites towards ;he foreland (upper Barbastro Fm). The alluvial facies are represented by calcareous conglomerates, that grade in a few kilometers to thin-bedded sandstones and mudstones. Evaporitic facies are represented by nodular and larninated gypsum. The top of the Peralta systems tract is also marked by an extensive body of lacustrine carbonates that represent a new alluvial fan retreat. 3) The Peraltilla systems tract (Stampian-Chattian) consists of small alluvial fans (Calasanz Fm), that show i;imilar characteristics to those of the Peralta I'rn but they interfinger distally with a large fluvial systern sourced in the axial Pyrenees (Peraltilla Fm). This fluvial fan consists of red overbank deposits with paleosoils, and channelized bodies, which are mostly conglomeratic in the Azanuy syncline and become sandy towards the southern limb of Barbastro anticline. This granulometric change is accompanied by a change in channel type, from typical braided to sinuouir or straight. The Salinar and Peralta systerns are contemporaneous with the emplacernent of the Sierras Marginales thrust sheet. The clastic sedirnents accumulated in a flexura1 trough that widens while the thrust propagates. As a consecuence, the saline lake facies expand towards the foreland. During the Peralta systerns tract a blind detachment located in the base of the Barbastro evaporitic formation propagated and started to fold the foreland. The Peraltilla systems tract is contemporaneous with the end of displacement of the Sierras Marginales thrust sheet and the rnain growth of the Peralta detachment anticline. However, these tectonic events were accompanied by a significant forelandward shift of the basin depocenter and a more homogeneous subsidence. 4) The Sarinena systems tract (Chattian-Aquitanian) is very similar to the Peraltilla one but it shows a marked southwards shift of the proximal facies. It consists of srnall fans of local provenance (Baells Fm) that interfinger distally with alarge fluvial fan (Sarinena Fm). The sedimentation of the Sariñenasystems tract is contemporaneous with the continued southward propagation of the detachment through the foreland evaporites, that creates new detachment folds (Barbastro and Altarriba anticlines, Azanuy syncline). An episode of out-of sequence thrusting generates small thrust-top basins on the Sierras Marginales, filled by the Baells conglomerates. The Sariñena systems tract accumulated in a wide foreland trough, with a strongly subsiding located in the Azanuy syncline

Detailed Spectral Modeling of a 3-D Pulsating Reverse Detonation Model: Too Much Nickel

We calculate detailed NLTE synthetic spectra of a Pulsating Reverse Detonation (PRD) model, a novel explosion mechanism for Type Ia supernovae. While the hydro models are calculated in 3-D, the spectra use an angle averaged hydro model and thus some of the 3-D details are lost, but the overall average should be a good representation of the average observed spectra. We study the model at 3 epochs: maximum light, seven days prior to maximum light, and 5 days after maximum light. At maximum the defining Si II feature is prominent, but there is also a prominent C II feature, not usually observed in normal SNe Ia near maximum. We compare to the early spectrum of SN 2006D which did show a prominent C II feature, but the fit to the observations is not compelling. Finally we compare to the post-maximum UV+optical spectrum of SN 1992A. With the broad spectral coverage it is clear that the iron-peak elements on the outside of the model push too much flux to the red and thus the particular PRD realizations studied would be intrinsically far redder than observed SNe Ia. We briefly discuss variations that could improve future PRD models.Comment: 15 pages, 4 figures, submitted to Ap

High resolution simulations of the head-on collision of white dwarfs

The direct impact of white dwarfs has been suggested as a plausible channel for type Ia supernovae. In spite of their (a priori) rareness, in highly populated globular clusters and in galactic centers, where the amount of white dwarfs is considerable, the rate of violent collisions between two of them might be non-negligible. Even more, there are indications that binary white dwarf systems orbited by a third stellar-mass body have an important chance to induce a clean head-on collision. Therefore, this scenario represents a source of contamination for the supernova light-curves sample that it is used as standard candles in cosmology, and it deserves further investigation. Some groups have conducted numerical simulations of this scenario, but their results show several differences. In this paper we address some of the possible sources of these differences, presenting the results of high resolution hydrodynamical simulations jointly with a detailed nuclear post-processing of the nuclear abundances, to check the viability of white dwarf collisions to produce significant amounts of 56Ni. To that purpose, we use a 2D-axial symmetric smoothed particle hydrodynamic code to obtain a resolution considerably higher than in previous studies. In this work, we also study how the initial mass and nuclear composition affect the results. The gravitational wave emission is also calculated, as this is a unique signature of this kind of events. All calculated models produce a significant amount of 56Ni, ranging from 0.1 Msun to 1.1 Msun, compatible not only with normal-Branch type Ia supernova but also with the subluminous and super-Chandrasekhar subset. Nevertheless, the distribution mass-function of white dwarfs favors collisions among 0.6-0.7 Msun objects, leading to subluminous events.Comment: 24 pages, 12 figures, accepted for publication in MNRA

Mixing Sinc kernels to improve interpolations in smoothed particle hydrodynamics without pairing instability

The smoothed particle hydrodynamics technique strongly relies on the proper choice of interpolating functions. In this work, we revisit and extend the main properties of a family of interpolators called $Sinc~kernels$ and compare them with those of the widely used family of Wendland kernels. We show that a linear combination of low and high-order Sinc kernels generates good quality interpolators, which are resistant to the pairing instability while keeping good sampling properties in a wide range of neighbor interpolating points, $60\le n_b\le 400$. We show that a particular case of this linear mix of Sincs produces a well-balanced and robust kernel, that improves previous results in the Gresho-Chan vortex experiment even when the number of neighbors is not large, while yielding a good convergence rate. Although such a mixing technique is ideally suited for Sinc kernels owing to their excellent flexibility, it can be easily applied to other interpolating families such as the B-splines and Wendland kernels.Comment: 13 pages, 14 figures, 4 tables, submitted to MNRA

Mobility-Dependence of the Critical Density in Two-Dimensional Systems: An Empirical Relation

For five different electron and hole systems in two dimensions (Si MOSFET's, p-GaAs, p-SiGe, n-GaAs and n-AlAs), the critical density, $n_c$ that marks the onset of strong localization is shown to be a single power-law function of the scattering rate $1/\tau$ deduced from the maximum mobility. The resulting curve defines the boundary separating a localized phase from a phase that exhibits metallic behavior. The critical density $n_c \to 0$ in the limit of infinite mobility.Comment: 2 pages, 1 figur

Integral smoothed particle hydrodynamics with an improved partition of unit and a better track of contact discontinuities

The correct evaluation of gradients is at the cornerstone of the smoothed particle hydrodynamics (SPH) technique. Using an integral approach to estimate gradients has proven to enhance accuracy substantially. Such approach retains the Lagrangian structure of SPH equations and is fully conservative. In this paper we study, among other things, the connection between the choice of the volume elements (VEs), which enters in the SPH summations, and the accuracy in the gradient estimation within the integral approach scheme (ISPH). A new kind of VEs are proposed which improve the partition of unit and are fully compatible with the Lagrangian formulation of SPH, including the grad-h corrections. Using analytic considerations, simple static toy models in 1D, and a few full 3D test cases, we show that any improvement in the partition of unit also leads to a better calculation of gradients when the integral approach is used jointly. Additionally, we propose a simple-to-implement variant of the ISPH scheme which is more adequate to handle sharp density contrasts.Comment: 29 pages, 17 figures, submitted to Journal of Computational Physic

Analysis of the temperature-dependent quantum point contact conductance in view of the metal-insulator transition in two dimensions

The temperature dependence of the conductance of a quantum point contact has been measured. The conductance as a function of the Fermi energy shows temperature-independent fixed points, located at roughly multiple integers of $e^{2}/h$. Around the first fixed point at e$^{2}$/h, the experimental data for different temperatures can been scaled onto a single curve. For pure thermal smearing of the conductance steps, a scaling parameter of one is expected. The measured scaling parameter, however, is significantly larger than 1. The deviations are interpreted as a signature of the potential landscape of the quantum point contact, and of the source-drain bias voltage. We relate our results phenomenologically to the metal-insulator transition in two dimensions.Comment: 5 pages, 3 figure