Brócoli envasado en polietileno de baja densidad y policloruro de vinilo

p.191-198La atmósfera modificada con películas plásticas y el control de la temperatura son tecnologías recomendadas para mantener la calidad y extender la vida de almacenamiento de hortalizas. Larespiración natural en brócoli envasado es suficiente para lograr niveles de dióxido de carbono (C 02) y de oxígeno (0 2) en el interior del envase que permitan alargar la vida del producto. Se realizaron tres ensayos a 0ºC, 8ºC y 12ºC en un diseño en parcela dividida con arreglo factorial. Se utilizaron dos películas plásticas: policloruro de vinilo y polietileno de baja densidad, y 4 diseños de paquete: 50, 100, 150 y 200 gramos de brócoli. Se midió la concentración de C 00 y 0 2 del interior de cada envase durante 7 días. Los cambios en la calidad se evaluaron por la pérdida de peso, el color y contenidos de ácido málico y de sólidos solubles durante el período analizado. La selección de la película óptima para el envasado de brócoli depende de la temperatura de almacenamiento y del peso del producto. A 0ºC, con PBD se logra una atmósfera adecuada con muy poca pérdida de peso y cambios químicos. A 8ºC, dado que no hay una variación importante de la calidad, la selección deberá realizarse por la concentración interna del gas lograda en el equilibrio y por la pérdida de peso durante el almacenamiento; así, es conveniente optar por PBD con una masa inferior a 100 gramos para obtener concentraciones óptimas de C 0 2 y de O, y por PVC cuando la masa es superior a 150 gramos para mantener baja la pérdida de peso. A 12ºC ninguna de las dos películas fueron buenas para el envasado de brócoli, porque generan la excesiva perdida de color y de peso (PVC) o la presencia de olores desagradables (PBD)

BMSSM Implications for Cosmology

The addition of non-renormalizable terms involving the Higgs fields to the MSSM (BMSSM) ameliorates the little hierarchy problem of the MSSM. We analyze in detail the two main cosmological issues affected by the BMSSM: dark matter and baryogenesis. The regions for which the relic abundance of the LSP is consistent with WMAP and collider constraints are identified, showing that the bulk region and other previously excluded regions are now permitted. Requiring vacuum stability limits the allowed regions. Based on a two-loop finite temperature effective potential analysis, we show that the electroweak phase transition can be sufficiently first order in regions that for the MSSM are incompatible with the LEP Higgs mass bound, including parameter values of \tan\beta \lsim 5, m_{\tilde{t}_{1}} > m_t, m_Q << TeV.Comment: 28 pages, 4 figures. References adde

Coupling Spatial And Time Scales In The Hydrological Modelling Of Mediterranean Regions: WiMMed

Mediterranean catchments usually exhibit strong gradients of both weather variables at different time scales and soil uses, which add complexity to their hydrological modelling, especially in mountainous areas. WiMMed (Water integrated Management model for Mediterranean regions) model was designed to include such variability of scales in an operational suite capable of connecting GIS-based representations of the catchment (soil characteristics and uses, vegetation cover and snow dynamics) with advanced algorithms for simulating the energy and water balance on a physical basis. Widely used throughout the South of Spain, WiMMed efficiently represents the spatial patterns of precipitation, temperature, solar radiation, and evapotranspiration on an hourly basis, the daily evolution of the vegetation cover fraction, and the observed soil use changes over the study period, by means of specific interpolation algorithms and the inclusion of data derived from remote sensing. These high resolution data input to the physical equations of the energy and water balance performed on three series control volumes: canopy, snowpack, and soil, allow for the distributed characterization of water dynamics. Rainfall excess and infiltration and groundwater fluxes are routed towards selected control points along the fluvial network, where the corresponding baseflow, subsurface flow and direct runoff hydrographs that can be routed downstream by means of hydraulic or hydrological equations. WiMMed’s physical basis together with its high resolution multiscale scheme provides managers with an advanced support tool for flood/drought studies, natural regime restitution, short to long term water resource planning, evaluation of changes of soil use, etcetera. This work shows WiMMed capabilities from its use in selected watersheds throughout Andalusia (Spain) performed on the available free-distributed users’ interface designed for technicians and turnkey applications, some of which have been selected as examples

Effect of the CB1 cannabinoid agonist WIN 55212-2 on the acquisition and reinstatement of MDMA-induced conditioned place preference in mice

<p>Abstract</p> <p>Background</p> <p>Numerous reports indicate that MDMA users consume other psychoactive drugs, among which cannabis is one of the most common. The aim of the present study was to evaluate, using the conditioned place preference, the effect of the cannabinoid agonist WIN 55,212-2 on the rewarding effects of MDMA in mice.</p> <p>Methods</p> <p>In the first experiment adolescent mice were initially conditioned with 1.25, 2.5 or 5 mg/kg of MDMA or 0.1 or 0.5 mg/kg of WIN and subsequently with both drugs. Reinstatement of the extinguished preference by priming doses was performed in the groups that showed CPP. In the second experiment, animals were conditioned with 2.5 or 5 mg/kg of MDMA and, after extinction, reinstatement of the preference was induced by 0.5 or 0.1 mg/kg of WIN.</p> <p>Results</p> <p>A low dose of WIN 55212-2 (0.1 mg/kg) increased the rewarding effects of low doses of MDMA (1.25 mg/kg), although a decrease in the preference induced by MDMA (5 and 2.5 mg/kg) was observed when the dose of WIN 55212-2 was raised (0.5 mg/kg). The CB1 antagonist SR 141716 also increased the rewarding effects of the lowest MDMA dose and did not block the effects of WIN. Animals treated with the highest WIN dose plus a non-neurotoxic dose of MDMA exhibited decreases of striatal DA and serotonin in the cortex. On the other hand, WIN 55212-2-induced CPP was reinstated by priming injections of MDMA, although WIN did not reinstate the MDMA-induced CPP.</p> <p>Conclusions</p> <p>These results confirm that the cannabinoid system plays a role in the rewarding effects of MDMA and highlights the risks that sporadic drug use can pose in terms of relapse to dependence. Finally, the potential neuroprotective action of cannabinoids is not supported by our data; on the contrary, they are evidence of the potential neurotoxic effect of said drugs when administered with MDMA.</p

Flavour Matters in Leptogenesis

We give analytic approximations to the baryon asymmetry produced by thermal leptogenesis with hierarchical right-handed neutrinos. Our calculation includes flavour-dependent washout processes and CP violation in scattering, and neglects gauge interactions and finite temperature corrections. Our approximate formulae depend upon the three CP asymmetries in the individual lepton flavours as well as on three flavour-dependent efficiency factors. We show that the commonly used expressions for the lepton asymmetry, which depend on the total CP asymmetry and one single efficiency factor, may fail to reproduce the correct lepton asymmetry in a number of cases. We illustrate the importance of using the flavour-dependent formulae in the context of a two right-handed neutrino model.Comment: Additional typos corrected (in particular, the plots and captions now agree

Estrategias didácticas motivadoras en física para estudiantes de agronomía

The objective of this work was to compare traditional teaching strategies of lectures and activities in discussion groups through the analysis of performance in problem solving and in the laboratory practices of students who studied General and Biological Physics. Also, surveys were conducted among students and teachers. 42 % of the students who solved the problems rich in con-text and 10 % of those who solved the problems with the traditional modality, reached the level of achievement "very good", achieving more complete, reflective and rich productions in theoretical content. The work in discussion groups of the laboratory activities had advantages over the lecture class modality, since the students were more active and autonomous. We conclude that teaching strategies that let students have a leading role in their learning processes motivate them to achieve deeper and more lasting learning.El objetivo de este trabajo fue comparar estrategias de enseñanza tradicional de clases expositivas y actividades en grupos de discusión, a través del análisis del desempeño en la resolución de problemas y en las prácticas de laboratorio de estudiantes que cursaron Física general y biológica. También, se realizaron encuestas a los estudiantes y a los docentes. El 42 % de los estudian-tes que resolvieron los problemas ricos en contexto y el 10 % de los que resolvieron los problemas con la modalidad tradicional, alcanzaron el nivel de logro “muy bueno”, elaborando producciones más completas, reflexivas y ricas en contenido teórico. El trabajo en grupos de discusión de las actividades de laboratorio tuvo ventajas respecto a la modalidad de clase expositiva, ya que los estudiantes fueron más activos y autónomos. Concluimos que las estrategias de enseñanza que convierten a los estudiantes en protagonistas del proceso de aprendizaje, los motiva a lograr aprendizajes más profundos y duraderos. &nbsp

Flavour Issues in Leptogenesis

We study the impact of flavour in thermal leptogenesis, including the quantum oscillations of the asymmetries in lepton flavour space. In the Boltzmann equations we find different numerical factors and additional terms which can affect the results significantly. The upper bound on the CP asymmetry in a specific flavour is weaker than the bound on the sum. This suggests that -- when flavour dynamics is included -- there is no model-independent limit on the light neutrino mass scale,and that the lower bound on the reheat temperature is relaxed by a factor ~ (3 - 10).Comment: 19 pages, corrected equations for flavour oscillation

Stochastic Assessment Of Environmental Flows In Semiarid Environments

The regimen of environmental flows (EF) must be included as terms of environmental demand in the management of water resources. Even though there are numerous methods for the computation of EF, the criteria applied at different steps in the calculation process are quite subjective whereas the results are fixed values that must be meet by water planners. This study presents a friendly-user tool for the assessment of the probability of compliance of a certain EF scenario with the natural regimen in a semiarid area in southern Spain. 250 replications of a 25-yr period of different hydrological variables (rainfall, minimum and maximum flows, ...) were obtained at the study site from the combination of Monte Carlo technique and local hydrological relationships. Several assumptions are made such as the independence of annual rainfall from year to year and the variability of occurrence of the meteorological agents, mainly precipitation as the main source of uncertainty. Inputs to the tool are easily selected from a first menu and comprise measured rainfall data, EF values and the hydrological relationships for at least a 20-yr period. The outputs are the probabilities of compliance of the different components of the EF for the study period. From this, local optimization can be applied to establish EF components with a certain level of compliance in the study period. Different options for graphic output and analysis of results are included in terms of graphs and tables in several formats. This methodology turned out to be a useful tool for the implementation of an uncertainty analysis within the scope of environmental flows in water management and allowed the simulation of the impacts of several water resource development scenarios in the study site

Baryogenesis at Low Reheating Temperatures

We note that the maximum temperature during reheating can be much greater than the reheating temperature $T_r$ at which the Universe becomes radiation dominated. We show that the Standard Model anomalous $(B+L)$-violating processes can therefore be in thermal equilibrium for 1 GeV \simlt T_{r}\ll 100 GeV. Electroweak baryogenesis could work and the traditional upper bound on the Higgs mass coming from the requirement of the preservation of the baryon asymmetry may be relaxed. Alternatively, the baryon asymmetry may be reprocessed by sphaleron transitions either from a $(B-L)$ asymmetry generated by the Affleck-Dine mechanism or from a chiral asymmetry between $e_R$ and $e_L$ in a $B-L = 0$ Universe. Our findings are also relevant to the production of the baryon asymmetry in large extra dimension models.Comment: 4 pages, version to appear in PRL: references added, new titl

Weather Generator Tool For The Assessment Of Water Resource Planning In Mediterranean Watersheds

Water resource planning requires the forecasting of precipitation at different time scales that are dependent on the planning horizon for decision making. In Mediterranean areas, the uncertainty associated to precipitation occurrence and amount is very much linked to alternate sequences of highly variable dry and wet pluriannual cycles, and the torrential character of some of the rainfall events within the wet season. Moreover, most of the precipitation is associated to cyclonic fronts passing over the region, and their interaction with the regional and local topography. This work presents a Weather Generator (WG) tool to simulate annual sequences of rainfall events in Mediterranean watersheds based on Monte Carlo simulation and Bayesian techniques. Ground measurements of precipitations and synoptic maps are used to define cyclonic-front rainfall events in terms of duration and rainfall amount on a local (basin) basis. The resulting event series are statistically studied to develop empirical probability functions for every step in the Bayesian hierarchy ranging from annual precipitation and number of events to every event occurrence and its amount and duration, to build N equally-probable samples of V years of precipitation in a given watershed, each year consisting of M precipitation events of given duration/amount at the watershed scale, distributed within each year. The Weather Generator was applied to the Guadalfeo River Basin (Southern Spain), a 1360-km2 coastal mountainous watershed with altitudes ranging from 3200 to 0 m.a.s.l. . The synthetic samples of V years obtained through the WG tool are used in this work to assess the current variability of climate in this area, the uncertainty of water resource availability in a 30-yr time horizon, and the uncertainty of extreme flood events in the main course of the river. These application examples are representative of the potential uses of the tool