Diffusion limited aggregation, resetting and large deviations of Brownian motion

Models of fractal growth commonly consider particles diffusing in a medium and that stick irreversibly to the forming aggregate when making contact for the first time. As shown by the well-known diffusion limited aggregation (DLA) model and its generalisations, the fractal dimension is sensitive to the nature of the stochastic motion of the particles. Here, we study the structures formed by finite-lived Brownian particles, i.e., particles constrained to find the aggregate within a prescribed time, and which are removed otherwise. This motion can be modelled by diffusion with stochastic resetting, a class of processes which has been widely studied in recent years. In the short lifetime limit, a very small fraction of the particles manage to reach the aggregate. Hence, growth is controlled by atypical Brownian trajectories, that move nearly in straight line according to a large deviation principle. In $d$ dimensions, the resulting fractal dimension of the aggregate decreases from the DLA value and tends to 1, instead of increasing to $d$ as expected from ballistic aggregation. In the zero lifetime limit one recovers the non-trivial model of "aggregation by the tips" proposed long ago by R. Jullien [J. Phys. A: Math. Gen. 19, 2129 (1986)].Comment: 13 pages, 5 figure

Static circularly symmetric perfect fluid solutions with an exterior BTZ metric

In this work we study static perfect fluid stars in 2+1 dimensions with an exterior BTZ spacetime. We found the general expression for the metric coefficients as a function of the density and pressure of the fluid. We found the conditions to have regularity at the origin throughout the analysis of a set of linearly independent invariants. We also obtain an exact solution of the Einstein equations, with the corresponding equation of state $p=p(\rho)$, which is regular at the origin.Comment: 10 pages, 1 figure, revtex 4. This paper is in honor of Alberto Garcia's sixtieth birthday. Accepted by Gen. Rel. Gra

Ultrasound treatments of tef [Eragrostis tef (Zucc.) Trotter] flour rupture starch α-(1,4) bonds and fragment amylose with modification of gelatinization properties

Producción CientíficaTef is a nutritionally-rich ancient grain gaining increasing interest in gluten-free market. Molecular and structural properties in the main biopolymers of two Spanish ecotypes of tef flour physically modified by ultrasound (US) treatments under different temperatures (20, 40, 45, 50 and 55 °C) were studied. Modifications achieved were dependent on tef ecotype, where white tef presented higher susceptibility. Size-exclusion chromatography indicated higher proportion of intermediate amylose chains (degree of polymerization 300–1600) across the whole amylose chain-length distribution and a higher amylose/amylopectin ratio, that increased up to 23% and 19% in treated samples of white and brown tef respectively. US increased the starch short-range order crystallinity and promoted the formation of random coil protein structure and the disappearance of β-sheet, as confirmed from FTIR spectroscopy. XRD and 1H NMR revealed a higher fragmentation of α-(1,4) than α-(1,6) bonds due ultrasonication. The gelatinization temperature range and ΔHgel decreased after ultrasonication up to 6 °C and 13%, an effect that was reinforced or counteracted, respectively, by the treatment temperature, indicating that annealing modulates the impact of sonication on flour gelatinization properties. Tef starch structural properties were found to be significantly modified by US treatments, where temperature was a determining variable influencing the degree of modification achieved.Ministerio de Ciencia e Innovación (PID2019-110809RB-I00/AEI/10.1303/501100011033)Junta de Castilla y León and FEDER (VA195P20

Future challenges in cephalopod research

We thank Anto´nio M. de Frias Martins, past President of the Unitas Malacologica and Peter Marko, President of the American Malacological Society for organizing the 2013 World Congress of Malacology, and the Cephalopod International Advisory Committee for endorsing a symposium held in honour of Malcolm R. Clarke. In particular, we would like to thank the many professional staff from the University of the Azores for their hospitality, organization, troubleshooting and warm welcome to the Azores. We also thank Malcolm Clarke’s widow, Dorothy, his daughter Zoe¨, Jose´ N. Gomes-Pereira and numerous colleagues and friends of Malcolm’s from around the world for joining us at Ponta Delgada. We are grateful to Lyndsey Claro (Princeton University Press) for granting copyright permissions.Peer reviewedPublisher PD

FECUNDIDAD DE «CHIOCHÍO» Psectrogaster rutiloides (PISCES: CURIMATIDAE) EN UCAYALI, PERÚ.

Studies on the potential fecundity of chiochío, Psectrogaster rutiloides, are scarce despite this is one of the main fish species for small scale commercial and subsistence fishing catch in the Ucayali basin (Peru). A total of 74 female specimens on maturity stage IV were collected in October and November 2009. Total length, body weight, and gonad weight were recorded, and fecundity was assessed through the number of oocytes by the gravimetric method. Body length and weight were 15.2 ± 1.9 cm and 68.5 ± 24.7 g respectively, and the weight of gonads was 12.5 ± 5.3 g. The estimate number of oocytes was 45 058 ± 20 770. The relative fecundity varied from 1194 to 6619 oocytes per cm of body length, from 302 to 1202 oocytes per gram of body weight, and from 2654 to 8739 oocytes per gram of gonad weight. The regression analysis showed that gonad weight is a suitable predictor of the fecundity in this species.Estudios sobre el potencial de fecundidad del chiochío, Psectrogaster rutiloides, son escasos pese a ser una de las principales especies en la pesca semicomercial y de subsistencia para consumo humano de la cuenca del Ucayali, Perú. Se colectaron 74 hembras en estadio de madurez IV en octubre y noviembre de 2009. Se midió la longitud total, se registró el peso corporal y el peso de las gónadas y se determinó el número de ovocitos por el método gravimétrico. La talla y peso corporal fue de 15.2 ± 1.9 cm y 68.5 ± 24.7 g, respectivamente, y el peso de las gónadas fue de 12.5 ± 5.3 g. El número estimado de ovocitos fue de 45 058 ± 20 770. La fecundidad relativa varió entre 1194 y 6619 ovocitos por cm de talla, entre 302 y 1202 ovocitos por gramo de peso corporal, y entre 2654 y 8739 ovocitos por gramo de gónadas. El análisis de regresión indica que el peso de las gónadas es un buen elemento para estimar la fecundidad en esta especie

North American megadroughts in the Common Era: reconstructions and simulations

During the Medieval Climate Anomaly (MCA), Western North America experienced episodes of intense aridity that persisted for multiple decades or longer. These megadroughts are well documented in many proxy records, but the causal mechanisms are poorly understood. General circulation models (GCMs) simulate megadroughts, but do not reproduce the temporal clustering of events during the MCA, suggesting they are not caused by the time history of volcanic or solar forcing. Instead, GCMs generate megadroughts through (1) internal atmospheric variability, (2) sea-surface temperatures, and (3) land surface and dust aerosol feedbacks. While no hypothesis has been definitively rejected, and no GCM has accurately reproduced all features (e.g., timing, duration, and extent) of any specific megadrought, their persistence suggests a role for processes that impart memory to the climate system (land surface and ocean dynamics). Over the 21st century, GCMs project an increase in the risk of megadrought occurrence through greenhouse gas forced reductions in precipitation and increases in evaporative demand. This drying is robust across models and multiple drought indicators, but major uncertainties still need to be resolved. These include the potential moderation of vegetation evaporative losses at higher atmospheric [CO₂], variations in land surface model complexity, and decadal to multidecadal modes of natural climate variability that could delay or advance onset of aridification over the the next several decades. Because future droughts will arise from both natural variability and greenhouse gas forced trends in hydroclimate, improving our understanding of the natural drivers of persistent multidecadal megadroughts should be a major research priority

Motion of charged particles on the Reissner-Nordstr\"om (Anti)-de Sitter black holes

In this work we address the study of movement of charged particles in the background of charged black holes with non-trivial asymptotic behavior. We compute the exact trajectories for massive-charged particles in term of elliptic Jacobi function. Finally we obtain a detailed description of orbits for Reissner-Nordstr\"om (Anti)-de Sitter black holes in terms of charge, mass and energy of the particles.Comment: 21 pages, 10 figure

The Absolute Magnitude of RRc Variables From Statistical Parallax

We present the first definitive measurement of the absolute magnitude of RR Lyrae c-type variable stars (RRc) determined purely from statistical parallax. We use a sample of 247 RRc selected from the All Sky Automated Survey (ASAS) for which high-quality light curves, photometry and proper motions are available. We obtain high-resolution echelle spectra for these objects to determine radial velocities and abundances as part of the Carnegie RR Lyrae Survey (CARRS). We find that M_(V,RRc) = 0.52 +/- 0.11 at a mean metallicity of [Fe/H] = -1.59. This is to be compared with previous estimates for RRab stars (M_(V,RRab) = 0.75 +/- 0.13 and the only direct measurement of an RRc absolute magnitude (RZ Cephei, M_(V, RRc) = 0.27 +/- 0.17). We find the bulk velocity of the halo to be (W_pi, W_theta, W_z) = (10.9,34.9,7.2) km/s in the radial, rotational and vertical directions with dispersions (sigma_(W_pi), sigma_(W_theta), sigma_(W_z)) = (154.7, 103.6, 93.8) km/s. For the disk, we find (W_pi, W_theta, W_z) = (8.5, 213.2, -22.1) km/s with dispersions (sigma_(W_pi), sigma_(W_theta), sigma_(W_z)) = (63.5, 49.6, 51.3) km/s. Finally, we suggest that UCAC2 proper motion errors may be overestimated by about 25%Comment: Submitted to ApJ. 11 pages including 6 figure

Alternativas de búsqueda directa en Metalib y SFX

La presentación se llevó a cabo durante las 5as. Jornadas de Expania (Grupo de usuarios de ExLibris en España) celebradas en la Universitat Pompeu Fabra (Barcelona, 19-20/06/2008)La presentación describe las alternativas a SFX y Metalib, que la Biblioteca de la Universidad de Navarra, ofrece a sus usuarios para la búsqueda de sus recursos electrónicos. En concreto, un formulario Web, una barra de herramientas, utilizando LibX, y un Gadget para iGoogle