8,662 research outputs found
Spatial clustering of interacting bugs: Levy flights versus Gaussian jumps
A biological competition model where the individuals of the same species
perform a two-dimensional Markovian continuous-time random walk and undergo
reproduction and death is studied. The competition is introduced through the
assumption that the reproduction rate depends on the crowding in the
neighborhood. The spatial dynamics corresponds either to normal diffusion
characterized by Gaussian jumps or to superdiffusion characterized by L\'evy
flights. It is observed that in both cases periodic patterns occur for
appropriate parameters of the model, indicating that the general macroscopic
collective behavior of the system is more strongly influenced by the
competition for the resources than by the type of spatial dynamics. However,
some differences arise that are discussed.Comment: This version incorporates in the text the correction published as an
Erratum in Europhysics Letters (EPL) 95, 69902 (2011) [doi:
10.1209/0295-5075/95/69902
Ice morphology modification and solute recovery improvement by heating and annealing during block freeze-concentration of coffee extracts
Several treatments on ice blocks can be applied during block freeze-concentration to increase the solute recovery from the ice. In the present study, the changes in the ice block’s temperature and the application of annealing during the block freeze-concentration of aqueous coffee extracts were studied. The ice block was subjected to heating and annealing prior to the thawing stage. The effect of coolant temperature during ice block heating (T = -10 and -5 °C) and the application of annealing (+, -) on solute recovery and ice structure morphology was evaluated. The use of annealing during block freeze-concentration modified the ice crystal morphology and increased the solute recovery only when it is applied at the highest temperature. In general, the annealing process increased the size and circularity of the ice crystals, consequently improving the solute recovery. Thus, annealing can be used to increase the solute recovery during block freeze-concentration.Postprint (published version
Star formation history in the solar neighborhood: the link between stars and cosmology
Using a cosmological galactic evolutionary approach to model the Milky Way,
we calculate the star formation history (SFH) of the solar neighborhood. The
good agreement we obtain with the observational inferences suggests that our
physical model describes accurately the long term/large spatial trends of the
local and global Milky Way SFH. In this model, star formation is triggered by
disk gravitational instabilities and self-regulated by an energy balance in the
ISM. The drivers of the SFH are the cosmological gas infall rate and the gas
surface density determined by the primordial spin parameter. A LambdaCDM
cosmology was used throughout.Comment: 8 pages, uses kluwer.cls. Invited talk, to appear in "New Quests in
Stellar Astrophysics: The link between Stars and Cosmology", eds. M. Chavez,
A. Bressan, A. Buzzoni & D. Mayya, Kluwer Academic Publisher
Hot spot analysis in integrated circuit substrates by laser mirage effect
3 páginas, 2 figuras.This work shows an analytical and experimental technique for characterizing radial heat flow present in integrated circuits (ICs) when power is dissipated by integrated devices. The analytical model comes from the resolution of the Fermat equation for the trajectory of rays and supposing a spherical heat source dissipating a time-periodic power. An application example is presented; hence demonstrating how hot spots and heat transfer phenomena in the IC substrate can be characterized. The developed method may become a practical alternative to usual off-chip techniques for inspecting hot spots in ICs and to experimentally characterize heat flow in the semiconductor substrate.This work has been partially supported by the Consejo
Superior de Investigaciones CientĂficas (CSIC) (under contract
“Junta para la Ampliación de Estudios,” JAEDoc No.
E-08–2008–0637732) and the Spanish Ministry of Science
and Innovation (research programs THERMOS TEC2008-
05577, RUE CSD2009-00046, TERASYSTEMS TEC2008-
01856, and RamĂłn y Cajal RYC-2010-07434).Peer reviewe
A super-Earth orbiting the nearby M-dwarf GJ 536
We report the discovery of a super-Earth orbiting the star GJ 536 based on
the analysis of the radial-velocity time series from the HARPS and HARPS-N
spectrographs. GJ 536 b is a planet with a minimum mass M sin of 5.36 +-
0.69 Me with an orbital period of 8.7076 +- 0.0025 days at a distance of
0.066610(13) AU, and an orbit that is consistent with circular. The host star
is the moderately quiet M1 V star GJ 536, located at 10 pc from the Sun. We
find the presence of a second signal at 43 days that we relate to stellar
rotation after analysing the time series of Ca II H&K and H alpha spectroscopic
indicators and photometric data from the ASAS archive. We find no evidence
linking the short period signal to any activity proxy. We also tentatively
derived a stellar magnetic cycle of less than 3 years.Comment: 14 pages, 14 figures, 5 tables, Accepted in A&
Reduced-Order Thermal Behavioral Model Based on Diffusive Representation
14 páginas, 15 figuras, 2 tablas.-- et al.The virtual prototyping of power electronic converters requires electrothermal models with various abstraction levels and easy identification. Numerous methods for the construction of compact thermal models have been presented in this paper. Few of them propose state-space models, where the model order can be controlled according to the necessity of the virtual prototyping analyses. Moreover, the model reduction methods require the experience of the engineer and previous calibration. Diffusive representation (DR) is proposed here as an original and efficient method to build compact thermal models as state-space models. The model reduction is obtained through the model parameter identification and/or the time horizon of the measurement data provided for the identification. Instead of eigenvalue elimination, the method enables to specify adequately inside the model the frequency domain wished for the virtual analysis at hand. The proposed method is particularly dedicated to the system optimization phases. Experimental and simulation results are in good agreement. The advantages and limitations of the DR are discussed in comparison to published methods.Peer reviewe
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