17 research outputs found
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
Equalizing resolution in smoothed-particle hydrodynamics calculations using self-adaptive sinc kernels
The smoothed-particle hydrodynamics (SPH) technique is a numerical method for
solving gas-dynamical problems. It has been applied to simulate the evolution
of a wide variety of astrophysical systems. The method has a second-order
accuracy, with a resolution that is usually much higher in the compressed
regions than in the diluted zones of the fluid. In this work, we propose and
check a scheme to balance and equalize the resolution of SPH between high- and
low-density regions. This method relies on the versatility of a family of
interpolators called Sinc kernels, which allows increasing the interpolation
quality by varying only a single parameter (the exponent of the Sinc function).
The scheme is checked and validated through a number of numerical tests, from
standard one-dimensional Riemann problems in shock tubes, to multidimensional
simulations of explosions, hydrodynamic instabilities and the collapse of a
sun-like polytrope. The analysis of the hydrodynamical simulations suggests
that the scheme devised to equalizing accuracy improves the treatment of the
post-shock regions and, in general, of the rarefacted zones of fluids while
causing no harm to the growth of hydrodynamic instabilities. The method is
robust and easy to implement with a low computational overload. It conserves
mass, energy, and momentum and reduces to the standard SPH scheme in regions of
the fluid that have smooth density gradients.Comment: 29 pages, 18 figures, accepted by A&
Ultrafast resonant interatomic coulombic decay induced by quantum fluid dynamics
Interatomic processes play a crucial role in weakly bound complexes exposed to ionizing radiation; therefore, gaining a thorough understanding of their efficiency is of fundamental importance. Here, we directly measure the timescale of interatomic Coulombic decay (ICD) in resonantly excited helium nanodroplets using a high-resolution, tunable, extreme ultraviolet free-electron laser. Over an extensive range of droplet sizes and laser intensities, we discover the decay to be surprisingly fast, with decay times as short as 400 fs, nearly independent of the density of the excited states. Using a combination of time- dependent density functional theory and ab initio quantum chemistry calculations, we elucidate the mechanisms of this ultrafast decay process, where pairs of excited helium atoms in one droplet strongly attract each other and form merging void bubbles, which drastically accelerates ICD
Platinum-group elements, S, Se and Cu in highly depleted abyssal peridotites from the Mid-Atlantic Ocean Ridge (ODP Hole 1274A): Influence of hydrothermal and magmatic processes
Highly depleted harzburgites and dunites were recovered from ODP Hole 1274A, near the intersection between the Mid-Atlantic Ocean Ridge and the 15°20′N Fracture Zone. In addition to high degrees of partial melting, these peridotites underwent multiple episodes of melt-rock reaction and intense serpentinization and seawater alteration close to the seafloor. Low concentrations of Se, Cu and platinum-group elements (PGE) in harzburgites drilled at around 35-85 m below seafloor are consistent with the consumption of mantle sulfides after high degrees (>15-20 %) of partial melting and redistribution of chalcophile and siderophile elements into PGE-rich residual microphases. Higher concentrations of Cu, Se, Ru, Rh and Pd in harzburgites from the uppermost and lowest cores testify to late reaction with a sulfide melt. Dunites were formed by percolation of silica- and sulfur-undersaturated melts into low-Se harzburgites. Platinum-group and chalcophile elements were not mobilized during dunite formation and mostly preserve the signature of precursor harzburgites, except for higher Ru and lower Pt contents caused by precipitation and removal of platinum-group minerals. During serpentinization at low temperature (<250 °C) and reducing conditions, mantle sulfides experienced desulfurization to S-poor sulfides (mainly heazlewoodite) and awaruite. Contrary to Se and Cu, sulfur does not record the magmatic evolution of peridotites but was mostly added in hydrothermal sulfides and sulfate from seawater. Platinum-group elements were unaffected by post-magmatic low-temperature processes, except Pt and Pd that may have been slightly remobilized during oxidative seawater alteration
Lactante con hiperexcitabilidad. Hipocalcemia sintomática tras el período neonatal
The presence of symptomatic hypocalcemia is an emergency that requires immediate ion correction. In addition to hypopa-rathyroidism,Vitamine D and rickets deficiency always has to be ruled as a causative mechanism, because although it is unco-mmon in developed countries, it has been an increase in our environment due to migration and other factors. A case ofsymptomatic hypocalcemia in 3 months infant is presented.La presencia de hipocalcemia sintomática constituye una urgencia que requiere corrección iónica inmediata.Ademásdel hipoparatiroidismo,siempre se debe descartar el déficit de vitamina D y el raquitismo carencial como mecanismoetiológico, ya que aunque es infrecuente en países desarrollados, se ha producido un aumento en nuestro medio enlos últimos años debido a los fenómenos migratorios, entre otros factores. Presentamos un caso de hipocalcemiasintomática en un lactante de 3 meses
Equalizing resolution in smoothed-particle hydrodynamics calculations using self-adaptive sinc kernels
Targeting Epidermal Growth Factor Receptors in Recurrent Glioblastoma Via a Novel Epithelial Growth Factor Receptor-Conjugated Nanocell Doxorubicin Delivery System
Interatomic processes play a crucial role in weakly bound complexes exposed to ionizing radiation; therefore, gaining a thorough understanding of their efficiency is of fundamental importance. Here, we directly measure the timescale of interatomic Coulombic decay (ICD) in resonantly excited helium nanodroplets using a high-resolution, tunable, extreme ultraviolet free-electron laser. Over an extensive range of droplet sizes and laser intensities, we discover the decay to be surprisingly fast, with decay times as short as 400 fs, nearly independent of the density of the excited states. Using a combination of time-dependent density functional theory and ab initio quantum chemistry calculations, we elucidate the mechanisms of this ultrafast decay process, where pairs of excited helium atoms in one droplet strongly attract each other and form merging void bubbles, which drastically accelerates ICD.ISSN:2160-330