187 research outputs found
A tree code for planetesimal dynamics: Comparison with a hybrid direct code
We present a tree code for simulations of collisional systems dominated by a central mass. We describe the implementation of the code and the results of some test runs with which the performance of the code was tested. A comparison between the behaviour of the tree code and a direct hybrid integrator is also presented. The main result is that tree codes can be useful in numerical simulations of planetary accretion, especially during intermediate stages, where possible runaway accretion and dynamical friction lead to a population with a few large bodies in low-eccentricity and low-inclination orbits embedded in a large swarm of small planetesimals in rather excited orbits. Some strategies to improve the performance of the code are also discussed.Fil: Brunini, Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica la Plata; ArgentinaFil: Viturro, Hector Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica la Plata; Argentin
Parallelized tree–code for clusters of personal computers
We present a tree-code for integrating the equations of the motion of collisionless systems, which has been fully parallelized and adapted to run in several PC-based processors simultaneously, using the well-known PVM message passing library software. SPH algorithms, not yet included, may be easily incorporated to the code. The code is written in ANSI C; it can be freely downloaded from a public ftp site. Simulations of collisions of galaxies are presented, with which the performance of the code is tested.Fil: Viturro, Hector Ruben. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Carpintero, Daniel Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica la Plata; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentin
Acantholippia salsoloides : Phytochemical Composition and Biological Potential of a Thujonic Population
Acantholippia salsoloides (Verbenaceae) is an aromatic plant widespread in the Andean region. The infusion (leaves and flowers) is widely used as a digestive stimulant as well as for the treatment of various diseases in traditional medicine. A. salsoloides attributes its common name “rica-rica” to the fresh and sweet fragrance of the plant. In this work, 2 different polar extracts and the essential oil of a selected rica-rica population were studied. The phenolic composition was analyzed by high-performance liquid chromatography diode array detector; the essential oil profile was determined by gas-chromatography ion-trap mass spectrometry/flame ionization detection. For all extracts, the antibacterial potential was performed by in vitro assays; the antioxidant and α-glucosidase inhibition were determined in decoction and hydroethanolic extracts. The volatile profile allowed the identification of 26 volatile compounds, β-thujone (84%) being the major one in this rica-rica population. Eighteen phenolic compounds were identified; isoferulic acid (16%-18%) and cynaroside (45%-47%) were the larger ones. In a general way, the hydroethanolic extract was more active against Staphylococcus aureus and Micrococcus luteus (minimum inhibitory concentrations= 0.3- 1.3 mg/mL). Both polar extracts have strong antiradical activities although decoction extract proved to be more active against DPPH· (half-maximal inhibitory concentration [IC50] =36 µg/mL) and O2•− (IC50 =28 µg/mL) while hydroethanolic extract shows higher action over α-glucosidase (IC50 =217 µg/mL). The results suggest that A. salsoloides leaves and flowers may be an interesting source of natural antioxidants, antidiabetics, or antimicrobials, and could be used in dietary supplements, medicinal products and pharmaceutical formulations.Fil: Celaya, Liliana Soledad. Universidad Nacional de Jujuy. Centro Interdisciplinario de Investigaciones En Tecnologias y Desarrollo Social Para El Noa. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Saltajujuy. Centro Interdisciplinario de Investigaciones En Tecnologias y Desarrollo Social Para El Noa.; Argentina. Universidad Nacional de Misiones; ArgentinaFil: Viturro, Carmen Ines. Universidad Nacional de Jujuy. Centro Interdisciplinario de Investigaciones En Tecnologias y Desarrollo Social Para El Noa. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Saltajujuy. Centro Interdisciplinario de Investigaciones En Tecnologias y Desarrollo Social Para El Noa.; Argentina. Universidad Nacional de Jujuy; ArgentinaFil: Silva, Luís R.. Universidade da Beira Interior; Portuga
A tree code for planetesimal dynamics: Comparison with a hybrid direct code
We present a tree code for simulations of collisional systems dominated by a central mass. We describe the implementation of the code and the results of some test runs with which the performance of the code was tested. A comparison between the behaviour of the tree code and a direct hybrid integrator is also presented. The main result is that tree codes can be useful in numerical simulations of planetary accretion, especially during intermediate stages, where possible runaway accretion and dynamical friction lead to a population with a few large bodies in low-eccentricity and low-inclination orbits embedded in a large swarm of small planetesimals in rather excited orbits. Some strategies to improve the performance of the code are also discussed.Facultad de Ciencias Astronómicas y Geofísica
Low Energy Cathodoluminescence Spectroscopy of Semiconductor Interfaces
Low energy cathodoluminescence spectroscopy (CLS) is a powerful new technique for characterizing the electronic structure of buried semiconductor interfaces. This extension of a more conventional electron microscopy technique provides information on localized states, deep level defects, and band structure of new compounds at interfaces below the free solid surface. From the energy dependence of spectral features, one can distinguish interface versus bulk state emission and assess the relative spatial distribution of states below the free surface. Low energy CLS reveals process changes in the electronic structure of semiconductor interfaces due to metallization, laser annealing, and thermal desorption. Spectral features of metal-semiconductor interfaces uncovered by CLS also provide a new perspective on physical mechanisms of Schottky barrier formation
On the trapping of stars by a newborn stellar supercluster
Numerical experiments conducted by Fellhauer et al. (MNRAS, 372, 338, 2006)
suggest that a supercluster may capture up to about 40 per cent of its mass
from the galaxy where it belongs. Nevertheless, in those experiments the
cluster was created making appear its mass out of nothing, rather than from
mass already present in the galaxy. Here we use a thought experiment, plus a
few simple computations, to show that the difference between the dynamical
effects of these two scenarios (i.e., mass creation vs. mass concentration) is
actually very important. We also present the results of new numerical
experiments, simulating the formation of the cluster through mass
concentration, that show that trapping depends critically on the process of
cluster formation and that the amounts of gained mass are substantially smaller
than those obtained from mass creation.Comment: 6 pages, 3 figures. Submitted to MNRA
Tree-Particle-Mesh: an adaptive, efficient, and parallel code for collisionless cosmological simulation
An improved implementation of an N-body code for simulating collisionless
cosmological dynamics is presented. TPM (Tree-Particle-Mesh) combines the PM
method on large scales with a tree code to handle particle-particle
interactions at small separations. After the global PM forces are calculated,
spatially distinct regions above a given density contrast are located; the tree
code calculates the gravitational interactions inside these denser objects at
higher spatial and temporal resolution. The new implementation includes
individual particle time steps within trees, an improved treatment of tidal
forces on trees, new criteria for higher force resolution and choice of time
step, and parallel treatment of large trees. TPM is compared to P^3M and a tree
code (GADGET) and is found to give equivalent results in significantly less
time. The implementation is highly portable (requiring a Fortran compiler and
MPI) and efficient on parallel machines. The source code can be found at
http://astro.princeton.edu/~bode/TPM/Comment: 29 pages, includes 12 figures; to appear in ApJS. Source code at
http://astro.princeton.edu/~bode/TPM
Niveles hormonales y perfil lipídico en la edad puberal
Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Medicina. Fecha de lectura: 19-1-200
A tree code for planetesimal dynamics: Comparison with a hybrid direct code
We present a tree code for simulations of collisional systems dominated by a central mass. We describe the implementation of the code and the results of some test runs with which the performance of the code was tested. A comparison between the behaviour of the tree code and a direct hybrid integrator is also presented. The main result is that tree codes can be useful in numerical simulations of planetary accretion, especially during intermediate stages, where possible runaway accretion and dynamical friction lead to a population with a few large bodies in low-eccentricity and low-inclination orbits embedded in a large swarm of small planetesimals in rather excited orbits. Some strategies to improve the performance of the code are also discussed.Facultad de Ciencias Astronómicas y Geofísica
Looking for Self-Organized Critical Behavior in Avalanches of Slightly Cohesive Powders
We report results from a statistical analysis of avalanches of cohesive powders in a slowly rotated drum. Interparticle adhesion, which diminishes the effect of inertia and whose magnitude strongly fluctuates in a local scale, makes avalanches in slightly cohesive powders eligible for displaying self-organized criticality. However, the results show that avalanche sizes, time interval between avalanches, and maximum stable angle do not follow a power-law distribution. Otherwise, these parameters scale with powder cohesiveness
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