A Model with Propagating Spinons beyond One Dimension

For the model of frustrated spin-1/2 Heisenberg magnet described in A. A. Nersesyan and A. M. Tsvelik, (Phys. Rev. B{\bf 67}, 024422 (2003)) we calculate correlation functions of staggered magnetization and dimerization. The model is formulated as a collection of antiferromagnetic chains weakly coupled by a frustrated exchange interaction. The calculation done for the case of four chains demonstrates that these functions do not vanish. Since the correlation functions in question factorize into a product of correlation functions of spinon creation and annihilation operators, this constitutes a proof that spinons in this model propagate in the direction perpendicular to the chains.Comment: revised version to appear in Phys. Rev B., 8 pages, a reference adde

On Load balancing in distributed systems with large time delays: Theory and experiment

In a distributed computing environment with a high communication cost, limiting the number of balancing instants results in a better performance than the case where load balancing is executed continuously. Therefore, finding the optimal number of balancing instants and optimizing the performance over the interbalancing time and over the load-balancing gain becomes an important problem. In this paper we discuss the performance of a previously reported, control-theoretic motivated single load-balancing strategy on a distributed physical system and the performance is compared to our simulation predictions. Based on the concept of regeneration, we also present a mathematical model for the distributed system with two nodes where a one-shot balancing is done. We obtain a system of four difference-differential equations characterizing the mean of the overall completion time. and compare its predictive capabilities via simulation to the physical system

Quantitative and Compositional Study of Monospecies Biofilms of Spoilage Microorganisms in the Meat Industry and Their Interaction in the Development of Multispecies Biofilms

Food spoilage is a serious problem in the food industry, since it leads to significant economic losses. One of its main causes is the cross-contamination of food products from industrial surfaces. Three spoilage bacterial species which are highly present in meat and the gastrointestinal tract of chickens were selected: Pseudomonas fragi, Leuconostoc gasicomitatum, and Lactobacillus reuteri. The dual aim was to determine their ability to form monospecies biofilms and to examine how they interact when they coexist together. To do so, mature monospecies biofilms were produced statically for seven days at a temperature of 30 ◦C. L. gasicomitatum was also used to investigate the behavior of P. fragi and L. reuteri in the formation of multispecies biofilms. The structure and composition of the monospecies biofilms were evaluated by direct epifluorescence microscopy, and the multispecies biofilms were evaluated by plate counting. Both L. gasicomitatum and L. reuteri were able to form biofilms, with counts of approximately 7 Log CFU/cm2 and a defined structure. However, P. fragi obtained counts to the order of 4 Log CFU/cm2 , which is significantly different from the previous species (P < 0.05), and it had no network of cell conglomerates. The content of the L. gasicomitatum and L. reuteri biofilm matrices were 70-80% protein, unlike P. fragi, which presented a higher polysaccharide content (P < 0.05). In the multispecies biofilms, the presence of P. fragi did not affect the growth of L. gasicomitatum, which remained at between 5.76 to 6.1 Log CFU/cm2 . However, L. reuteri was able to displace L. gasicomitatum growth after 24 h of coexisting in a mixed biofilm, presenting differences in counts of approximately 2 Log CFU/cm2 . The study of the biofilms constructed by food industry resident microbiota can help to understand the ecological relations that exist between species, characterize them, and propose strategies to eliminate them. The name of genes and species should be written in italic

Listeria monocytogenes Biofilms in the Food Industry : Is the Current Hygiene Program Sufficient to Combat the Persistence of the Pathogen?

Biofilms contain microbial cells which are protected by a self-produced matrix and they firmly attach themselves to many different food industry surfaces. Due to this protection, microorganisms within biofilms are much more difficult to eradicate and therefore to control than suspended cells. A bacterium that tends to produce these structures and persist in food processing plants is Listeria monocytogenes. To this effect, many attempts have been made to develop control strategies to be applied in the food industry, although there seems to be no clear direction on how to manage the risk the bacteria poses. There is no standardized protocol that is applied equally to all food sectors, so the strategies for the control of this pathogen depend on the type of surface, the nature of the product, the conditions of the food industry environment, and indeed the budget. The food industry performs different preventive and corrective measures on possible L. monocytogenes -contaminated surfaces. However, a critical evaluation of the sanitization methods applied must be performed to discern whether the treatment can be effective in the long-term. This review will focus on currently used strategies to eliminate biofilms and control their formation in processing facilities in different food sectors (i.e., dairy, meat, fish, chilled vegetables, and ready-to-eat products). The technologies employed for their control will be exemplified and discussed with the objective of understanding how L. monocytogenes can be improved through food safety management systems

Callawayasaurus colombiensis (Welles) Carpenter 1999 el plesiosaurio de Villa de Leyva (Boyacá, Colombia). ¿Un nuevo espécimen?

En los depósitos del Cretácico (Aptiano) de Villa de Leyva se han reportado dos especies de plesiosaurios,&nbsp;un pliosaurio Kronosaurus boyacensis Hampe 1992, y un plesiosaurio Callawayasaurus colombiensis&nbsp;(Welles) Carpenter, 1999 (= Alzadasaurus colombiensis Welles, 1962). Se realiza la determinación de un&nbsp;espécimen de elasmosaurio encontrado por los pobladores de la zona rural de Villa de Leyva en 1999 con&nbsp;base en material fotográfico del mismo, siendo muy probable que corresponda a la especie Callawayasaurus&nbsp;colombiensis (Welles) Carpenter, 1999.In the deposits of the Cretaceous (Aptian) of Villa de Leyva two plesiosaurs species have been reported, a&nbsp;pliosaur Kronosaurus boyacensis Hampe 1992, and a plesiosaur Callawayasaurus colombiensis (Welles)&nbsp;Carpenter, 1999 (= Alzadasaurus colombiensis Welles, 1962). We carried out the determination of elasmosaur&nbsp;specimen found by the inhabitants of the rural area of Villa de Leyva in 1999, on the basis of photographic&nbsp;material of it. Probably it corresponds to the Callawayasaurus colombiensis specie (Welles) Carpenter,&nbsp;1999. &nbsp

Tardí­grados (Animalia: Tardigrada) de la Reserva El Diviso - Santander, Colombia

El Diviso es una reserva ubicada en la microcuenca del río Frío Alto y la subcuenca del mismo, entre los 1700-2100 metros de altura, con una temperatura promedio de 16°C, localizada a 22.5 Km de la ciudad de Bucaramanga a un costado de la vía que conduce a la ciudad de Cúcuta. Es propiedad de la Corporación Autónoma Regional para la Defensa de la Meseta de Bucaramanga CDMB. Su área total es de 85 hectáreas, de las cuales 69 corresponden a bosque natural, 15 a plantaciones de cipreses (Cupresus lusitanica) y pino pátula (Pinus patula), y una hectárea en la cual se localiza una casa y áreas para cultivo

Callawayasaurus colombiensis (Welles) Carpenter 1999 el plesiosaurio de Villa de Leyva (Boyacá, Colombia). ¿Un nuevo espécimen?

In the deposits of the Cretaceous (Aptian) of Villa de Leyva two plesiosaurs species have been reported, a&nbsp;pliosaur Kronosaurus boyacensis Hampe 1992, and a plesiosaur Callawayasaurus colombiensis (Welles)&nbsp;Carpenter, 1999 (= Alzadasaurus colombiensis Welles, 1962). We carried out the determination of elasmosaur&nbsp;specimen found by the inhabitants of the rural area of Villa de Leyva in 1999, on the basis of photographic&nbsp;material of it. Probably it corresponds to the Callawayasaurus colombiensis specie (Welles) Carpenter,&nbsp;1999. &nbsp;En los depósitos del Cretácico (Aptiano) de Villa de Leyva se han reportado dos especies de plesiosaurios,&nbsp;un pliosaurio Kronosaurus boyacensis Hampe 1992, y un plesiosaurio Callawayasaurus colombiensis&nbsp;(Welles) Carpenter, 1999 (= Alzadasaurus colombiensis Welles, 1962). Se realiza la determinación de un&nbsp;espécimen de elasmosaurio encontrado por los pobladores de la zona rural de Villa de Leyva en 1999 con&nbsp;base en material fotográfico del mismo, siendo muy probable que corresponda a la especie Callawayasaurus&nbsp;colombiensis (Welles) Carpenter, 1999

Baseline data of four insecticides with different modes of action for Anastrepha fraterculus and Ceratitis capitata (Diptera: Tephritidae)

La mosca de la fruta del Mediterráneo, Ceratitis capitata (Wiedemann), y la mosca sudamericana de los frutos, Anastrepha fraterculus (Wiedemann) son plagas de gran importancia económica en Argentina y el mundo. Una de las formas de control es el uso de insecticidas en pulverizaciones totales o en cebos. El uso reiterado de un determinado producto ejerce una fuerte presión de selección, pudiendo ocasionar la aparición de resistencia. El objetivo de este trabajo fue determinar el dato de nivel básico de cuatro insecticidas con diferentes mecanismos de acción mediante bioensayos en laboratorio. Los productos utilizados fueron formulaciones comerciales de ciantraniliprol, clorpirifos, lambdacialotrina y spinosad. La concentración letal media se estimó mediante un análisis de la curva dosis-respuesta. Para ciantraniliprol y clorpirifós los machos y las hembras de ambas especies fueron igualmente susceptibles. Para lambdacialotrina se detectaron diferencias entre las dos especies; la CL50 de A. fraterculus (0,058 y 0,074 para machos y hembras respectivamente) fue menor que la de C. capitata (0,523 y 0,624 para machos y hembras respectivamente). Para spinosad, los machos de A. fraterculus fueron igualmente susceptibles que los machos y las hembras de C. capitata. Estos resultados generan valores de referencia para Argentina y evidencian la necesidad de completar este tipo de estudios con evaluaciones de poblaciones naturales sobre las cuales se ejerce control químico así como con ensayos en campo y semi-campo. Asimismo muestran la necesidad de completar este tipo de estudios con evaluaciones de los niveles de ingesta en las distintas concentraciones.The Mediterranean fruit fly, Ceratitis capitata (Wiedemann), and the South American fruit fly, Anastrepha fraterculus (Wiedemann) are pests of major economic importance in Argentina and worldwide. One way to control them is the use of insecticide in sprays or baits. The repeated use of a particular product exerts a strong selection pressure and can lead to development of resistance. The aim of this study was to determine baseline data of four insecticides with different mechanisms of action through laboratory bioassays. The products used were commercial formulations of cyantraniliprole, chlorpyrifos, lambdacyalothrin and spinosad. The mean lethal concentration was estimated by a dose-response curve analysis. Cyantraniliprole and chlorpyrifos were equally susceptible for males and females of both species. For lambdacyalothrin differences between the two species were detected; LC50 of A. fraterculus (0.058 and 0.074 for males and females respectively) was lower than that of C. capitata (0.523 and 0.624 for males and females respectively). For spinosad, A. fraterculus males were equally susceptible than males and females of C. capitata. These results generate reference values for Argentina and demonstrate the need to complete these studies with field evaluations of natural populations on which chemical control is exercised as well as with field and semi-field trials. It also shows the need to complete these studies in which the intake at different concentrations is measured.Fil: Paez Jerez, P. G.. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia. Cátedra. Terapéutica Vegetal; ArgentinaFil: Carrizo, B. N.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Tucumán-Santiago del Estero. Estación Experimental Agropecuaria Famaillá; ArgentinaFil: Musse, R.. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia. Cátedra. Terapéutica Vegetal; ArgentinaFil: Varela, E.. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia. Cátedra. Terapéutica Vegetal; ArgentinaFil: Armiñana, A.. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia. Cátedra. Terapéutica Vegetal; ArgentinaFil: Milla, F.. Instituto Nacional de Tecnología Agropecuaria. Centro Nacional de Investigaciones Agropecuarias. Centro de Investigación de Ciencias Veterinarias y Agronómicas. Instituto de Genética; ArgentinaFil: Vera, Maria Teresa. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia. Cátedra. Terapéutica Vegetal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: de la Vega, M. H.. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia. Cátedra. Terapéutica Vegetal; Argentin