Thermodynamics of the classical spin-ice model with nearest neighbour interactions using the Wang-Landau algorithm

In this article we study the classical nearest-neighbour spin-ice model (nnSI) by means of Monte Carlo simulations, using the Wang-Landau algorithm. The nnSI describes several of the salient features of the spin-ice materials. Despite its simplicity it exhibits a remarkably rich behaviour. The model has been studied using a variety of techniques, thus it serves as an ideal benchmark to test the capabilities of the Wang Landau algorithm in magnetically frustrated systems. We study in detail the residual entropy of the nnSI and, by introducing an applied magnetic field in two different crystallographic directions ([111] and [100],) we explore the physics of the kagome-ice phase, the transition to full polarisation, and the three dimensional Kasteleyn transition. In the latter case, we discuss how additional constraints can be added to the Hamiltonian, by taking into account a selective choice of states in the partition function and, then, show how this choice leads to the realization of the ideal Kasteleyn transition in the system.Comment: 9 pages, 9 figure

Crossing regions for supersonic cones

The original study of a conical body of circular cross section at zero angle of attack inside a supersonic flow was developed by Taylor & Maccoll 1933, see [1]. After this year a large amount of numerical and perturbation techniques were developed to approximate solutions and to deal with the problem.www.proceedings.blucher.com.br/evento/10wccmFil: Ferreyra, R. T. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Matemática; Argentina.Fil: Tamagno, J. P. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Aeronaútica; Argentina.Otras Ingenierías y Tecnología

Development of a narrowband multichannel active noise control system for enclosures

This paper presents the development of a multichannel active noise control system for enclosures. It is applied on reducing low frequency car engine noise, where passive noise control techniques are inefficient. This work focuses on system optimization for optimal results when implementing on a commercial digital signal processor

Flujo de partículas en un ambiente costero Antártico de aguas someras: un estudio con trampas de sedimento

Sediment trap arrays were deployed at Potter Cove, King George Island, Antarctica, between December 1991 and August 1992 and in the summer seasons of 1993-1994, and 1995. The sampling sites reached 30 m depth, and traps were placed during the different seasons at various distances from the sea bottom (0.1 to 25 m), some being buried in the sediments. Daily sedimentation rates of total particulate matter (TPM) and chlorophyll-a were estimated. Water column temperature and salinity as well as pigment and TPM concentration were also measured and related to traps´ results. Water column data evidenced processes in relation with phytoplankton dynamics, stormy events and particles containing fresh water runoff. Similar trends were observed in the traps located at 25 m, 1 m and sometimes even in those located to around 0.1 m from sea bottom, although traps buried in the sediments mainly reflected resuspension events. Chlorophyll a fluxes were higher in the bottom traps, but the sedimented organic fraction of the TPM (particulate organic matter, POM) was higher in the traps located remotely from the bottom, being significantly lower in the buried traps (i.e. POM represented 50% of TPM at 1 m and 9% POM in the buried trap on November 23 in 1993, although a great variability among sampling dates was also observed). The significance of these dynamics for the food availability for the macrozoobenthic organisms present in the area is discussed.Entre diciembre de 1991 y agosto de 1992 y durante las campañas de verano de 1993-1994 y 1995 se estudió la tasa de sedimentación de partículas en Caleta Potter, Isla King George - 25 de Mayo, Antártida, mediante el empleo de trampas de sedimento. La profundidad en los sitios de muestreo fue de 30 m. Las trampas fueron colocadas a distintas distancias del fondo (0,1 a 25 m), habiéndose enterrado algunas en los sedimentos. Se estimaron las tasas diarias de sedimentación para el total de material particulado y los pigmentos. Se midieron además la temperatura y la salinidad, así como la concentración de material particulado total y pigmentos en la columna de agua. Estos parámetros fueron relacionados con aquellos de las trampas de sedimento. Los resultados de la columna de agua reflejaron procesos relacionados con la dinámica del fitoplancton, eventos de tormentas y aportes terrígenos de agua dulce. Esto fue válido para las trampas colocadas a 25 m, 1 m y en ocasiones aún para aquellas colocadas a 0,1 m, si bien los datos obtenidos de las trampas enterradas en el sedimento se relacionan con episodios de resuspensión. Los flujos de clorofila a fueron mayores en las trampas más cercanas al fondo, pero la fracción orgánica del material particulado sedimentada fue significativamente menor en las trampas enterradas. Por ejemplo, el porcentaje de materia orgánica en las trampas del 23 de noviembre de 1993 fue de 50% a 1 m y del 9% en la trampa enterrada en los sedimentos, si bien pudo observarse una gran variabilidad entre fechas de muestreo. Se discute la importancia de esta dinámica para la nutrición de los organismos del macrozoobentos presentes en el área

NIDIFICACIÓN DE LA LECHUCITA CANELA (AEGOLIUS HARRISII) EN MISIONES, ARGENTINA

Resumen ∙ Aunque el conocimiento de la distribución de la Lechucita Canela (Aegolius harrisii) se amplió notablemente en la última década, su biología permanece poco conocida. El conocimiento de la nidificación se basa en un solo nido confirmado, que no fue monitoreado, y una serie de observaciones de posibles nidos donde no fue comprobada la presencia de huevos o pichones. Entre diciembre de 2018 y enero de 2019, confirmamos y estudiamos un nido en una vieja cavidad excavada por una pareja de Carpintero Garganta Estriada (Dryocopus lineatus) a 9,6 m de altura en una grapia (Apuleia leiocarpa) muerta en selva Atlántica primaria del Parque Provincial Cruce Caballero, Misiones, Argentina. El nido contenía tres huevos blancos que eclosionaron en días alternos. Durante la incubación encontramos abundantes restos de escarabajos (Scarabaeidae: Coleoptera) debajo de la entrada del nido. Al nacer, los pichones tenían plumón natal gris oscuro muy ralo; a los 10 días empezaban a tener disco facial como el de los adultos; y a los 24 días se asemejaban a los adultos. Un adulto pasó todo el día dentro del nido desde la incubación hasta que el pichón mayor tenía 20–24 días de edad. Desde que nació el primer pichón hasta que voló el último los adultos trajeron por lo menos 32 roedores pequeños. Hubo un pico de aportes de alimentación justo después de la puesta del sol. Los tres pichones volaron exitosamente luego de 35–37 días, lo cual está en el límite superior del rango conocido para el Mochuelo Boreal (A. funereus) y el Mochuelo Cabezón (A. acadicus). No volvieron a utilizar la cavidad una vez que voló el último pichón. Aún es importante esclarecer el período de incubación, el rol de cada sexo en la reproducción y el rol de las cavidades (e.g., como dormidero) fuera del ciclo reproductivo. Abstract ∙ Nesting of the Buff-fronted Owl (Aegolius harrisii) in Misiones, Argentina Knowledge of the distribution of the Buff-fronted Owl (Aegolius harrisii) has increased notably in the last decade, but its biology remains poorly known. Knowledge of nesting is based on one confirmed nest, which was not monitored, and a series of observations of possible nests where the presence of eggs or nestlings was not confirmed. Between December 2018 and January 2019, we confirmed and studied a nest in an old cavity excavated by Lineated Woodpeckers (Dryocopus lineatus), 9.6 m above the ground in a dead garapa (Apuleia leiocarpa) tree, in primary Atlantic Forest at Parque Provincial Cruce Caballero, Misiones, Argentina. The nest contained three white eggs that hatched on alternate days. During incubation we found abundant beetle (Scarabaeidae: Coleoptera) remains below the nest entrance. On hatching, nestlings had sparse dark grey down; at 10 days old they began to have a facial disk like the adults; and by 24 days they looked similar to adults. One adult roosted in the nest all day from incubation until the oldest nestling reached 20–24 days of age. From when the first nestling hatched until the last nestling fledged, the adults brought at least 32 small rodents to the nest. There was a peak in prey delivery just after sunset. The three nestlings fledged successfully 35 to 37 days after hatching, which is at the high end of the range reported for Boreal (A. funereus) and Northern Saw-whet Owl (A. acadicus). They did not return to use the cavity once the last nestling had fledged. Further study is required to clarify the incubation period, the role of each sex in reproduction, and the role of cavities (e.g., for roosting) outside of the breeding cycle

Orbital images of high resolution and their role in the study of the matter state in lunar craters

Fil: Shpekin, M. I. Kazan Federal University; Rusia.Fil: Ferreyra, R. T. Universidad Nacional de Córdoba; Argentina.Fil: Mukhametshin, Ch. R. Kazan Federal University; Rusia.Fil: Semenov, A. A. Kazan Federal University; Rusia.Fil: Rysayev, T. F. Kazan Federal University; Rusia.The concept of high and super-high resolution came into use since the LRO mission. The images with a resolution of 10-20 meters on the lunar surface began to refer to the high resolution and images with a resolution of 1-2 meters - to the super-high. So images of the spacecrafts "Apollo-15, -16, -17" metric cameras are included in the group of high-resolution, and images of the same spacecrafts, obtained by panoramic cameras, are super-high resolution images. As for the unique «LRO» images, it is necessary to emphasize the experimental survey from low orbit, when the resolution reaches two feet on the lunar surface. This is not just a low-orbit, but it was a risky orbit, taking into account the elevation changes on the Moon, which is comparable to an orbital altitude of 25 km.http://ms2016.cosmos.ruFil: Shpekin, M. I. Kazan Federal University; Rusia.Fil: Ferreyra, R. T. Universidad Nacional de Córdoba; Argentina.Fil: Mukhametshin, Ch. R. Kazan Federal University; Rusia.Fil: Semenov, A. A. Kazan Federal University; Rusia.Fil: Rysayev, T. F. Kazan Federal University; Rusia.Astronomía (incluye Astrofísica y Ciencias del Espacio

One sided Star and Core orthogonality of matrices

We investigate two one-sided orthogonalities of matrices, the first of which is left (right) $*$-orthogonality for rectangular matrices and the other is left (right) core-orthogonality of index $1$ matrices. We obtain some basic results for these matrices, their canonical forms, and characterizations. Also, relations between left (right) orthogonal matrices and parallel sums are investigated. Finally under these one-sided orthogonalities we explore the conditions of additivity of the Moore-Penrose inverse and the core inverse

Concurrent ionic migration and electronic effects at the memristive TiOx/La1/3Ca2/3MnO3-x interface

The development of reliable redox-based resistive random-access memory devices requires understanding and disentangling concurrent effects present at memristive interfaces. We report on the fabrication and electrical characterization of TiOx/La1/3Ca2/3MnO3-x microstructured interfaces and on the modeling of their memristive behavior. We show that a careful tuning of the applied external electrical stimuli allows controlling the redox process between both layers, obtaining multilevel non-volatile resistance states. We simulate the oxygen vacancies dynamics at the interface between both oxides, and successfully reproduce the experimental electrical behavior after the inclusion of an electronic effect, related to the presence of an n-p diode at the interface. The formation of the diode is due to the n- and p-character of TiOx and La1/3Ca2/3MnO3-x, respectively. Our analysis indicates that oxygen vacancies migration between both layers is triggered after the diode is polarized either in forward mode or in reverse mode above breakdown. Electrical measurements at different temperatures suggest that the diode can be characterized as Zener-type. The advantages of our junctions for their implementation in RRAM devices are finally discussed.Fil: Roman Acevedo, Wilson Stibens. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Ferreyra, Cristian Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Sánchez, M.J.. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Acha, Carlos Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Gay, R.. Centro de Investigación Cooperativo nanoGUNE; EspañaFil: Rubi, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentin

Field-tuned order by disorder in frustrated Ising magnets with antiferromagnetic interactions

We demonstrate the appearance of thermal order by disorder in Ising pyrochlores with staggered antiferromagnetic order frustrated by an applied magnetic field. We use a mean-field cluster variational method, a low-temperature expansion, and Monte Carlo simulations to characterize the order-by-disorder transition. By direct evaluation of the density of states, we quantitatively show how a symmetry-broken state is selected by thermal excitations. We discuss the relevance of our results to experiments in 2D and 3D samples and evaluate how anomalous finite-size effects could be exploited to detect this phenomenon experimentally in two-dimensional artificial systems, or in antiferromagnetic all-in-all-out pyrochlores like Nd2Hf2O7 or Nd2Zr2O7, for the first time.Publisher PDFPeer reviewe