Development of overturning circulation in sloping waterbodies due to surface cooling

This work was supported by the Swiss National Science Foundation (project Buoyancy driven nearshore transport in lakes, HYPOlimnetic THErmal SIphonS, HYPOTHESIS, reference 175919) and by the Physics of Aquatic Systems Laboratory (APHYS), EPFL.Cooling the surface of freshwater bodies, whose temperatures are above the temperature of maximum density, can generate differential cooling between shallow and deep regions. When surface cooling occurs over a long enough period, the thermally induced cross-shore pressure gradient may drive an overturning circulation, a phenomenon called ‘thermal siphon’. However, the conditions under which this process begins are not yet fully characterised. Here, we examine the development of thermal siphons driven by a uniform loss of heat at the air–water interface in sloping, stratified basins. For a two-dimensional framework, we derive theoretical time and velocity scales associated with the transition from Rayleigh–Bénard type convection to a horizontal overturning circulation across the shallower sloping basin. This transition is characterised by a three-way horizontal momentum balance, in which the cross-shore pressure gradient balances the inertial terms before reaching a quasi-steady regime. We performed numerical and field experiments to test and show the robustness of the analytical scaling, describe the convective regimes and quantify the cross-shore transport induced by thermal siphons. Our results are relevant for understanding the nearshore fluid dynamics induced by nighttime or seasonal surface cooling in lakes and reservoirs.Swiss National Science Foundation (SNSF) European Commission 175919Physics of Aquatic Systems Laboratory (APHYS), EPF

Análisis de la gestión de seguridad de los protocolos WPA y WPA2 en el tráfico de datos de una red LAN con tecnología WiFi

Este documento pretende explicar paso a paso el sistema utilizado por los protocolos de seguridad de acceso e intercambio de datos WPA Y WPA2 utilizados por el sistema de comunicaciones WiFi. En primera instancia, debemos comprender el funcionamiento y régimen que lleva consigo una red LAN, tratando de enfocarnos en lo que es la tecnología WiFi. Hablaremos de los estándares que rigen la tecnología WiFi y su evolución lo cual nos permite tener una introducción al tema principal y que veremos reflejado en lo que llamamos el Capítulo 1. En el capítulo 2, llevamos a cabo la explicación del funcionamiento y gestión que realizan los protocolos WPA y WPA2, los cuales utilizan sistemas conocidos e implementados desde hace muchos años y aplicados a lenguaje de computadora como es la encriptación y la autenticación que serán las principales herramientas en la defensa de una red WiFi. El paso a seguir ahora, será, el de identificar los ataques que podemos tener en nuestra red casera o empresarial, puesto que desde la implementación de las redes inalámbricas se han generado una serie de ataques con enfoque malicioso,por lo que es indispensable el uso de sistemas de protección. También mostraremos la gestión y los pasos que debemos seguir para minimizar estos riesgos

Development of overturning circulation in sloping waterbodies due to surface cooling

Cooling the surface of freshwater bodies, whose temperatures are above the temperature of maximum density, can generate differential cooling between shallow and deep regions. When surface cooling occurs over a long enough period, the thermally induced cross-shore pressure gradient may drive an overturning circulation, a phenomenon called 'thermal siphon'. However, the conditions under which this process begins are not yet fully characterised. Here, we examine the development of thermal siphons driven by a uniform loss of heat at the air-water interface in sloping, stratified basins. For a two-dimensional framework, we derive theoretical time and velocity scales associated with the transition from Rayleigh-Benard type convection to a horizontal overturning circulation across the shallower sloping basin. This transition is characterised by a three-way horizontal momentum balance, in which the cross-shore pressure gradient balances the inertial terms before reaching a quasi-steady regime. We performed numerical and field experiments to test and show the robustness of the analytical scaling, describe the convective regimes and quantify the cross-shore transport induced by thermal siphons. Our results are relevant for understanding the nearshore fluid dynamics induced by nighttime or seasonal surface cooling in lakes and reservoirs

Trabajo decente desde los lineamientos de la OIT: aplicabilidad en el sector agrícola cebollero de Aquitania Boyacá

The concept of "decent work" is an essential element in the legal systems of democratic States and even more so of those that are part of the International Labour Organization (ILO). Likewise, the obligation of the Member States to guarantee labour rights in the context of decent work must be reflected in effective action to protect it even more in the agricultural sector. From this logic, the proposed objective leads to an analysis of "decent work from the guidelines of the ILO and its applicability in the agricultural sector of the municipality of Aquitaine-Boyacá". Research developed from a qualitative approach, which allowed interaction with the population sample. Likewise, it was necessary to choose 46 workers from the agricultural sector, in 5 companies marketing long onions, each with an average of 13 workers, in which a semi-structured interview was carried out, establishing categories and subcategories that allowed the information to be specified, in addition to the analysis and interpretation of both primary and secondary sources that were taken into account for this purpose. The result of this process has allowed us to infer that workers in the agricultural sector suffer from the protection of the State in labor matters, and even less from the guarantee that the convention with the ILO provides in order to achieve decent work. Therefore, it is important to rethink and restructure the normative methodology regarding its application in order to guarantee labor rights to this population.El concepto de “trabajo decente” es un elemento esencial en los ordenamientos jurídicos de los Estados democráticos y aún más de aquellos que hacen parte de la Organización Internacional del Trabajo (OIT). Así mismo, la obligación que contraen los Estados miembro respecto a la garantía de los derechos laborales desde el contexto del trabajo decente, debe verse reflejada en una acción efectiva de protección aún más en el sector agrícola. Desde esta lógica, el objetivo planteado conlleva a efectuar un análisis sobre “el trabajo decente desde los lineamientos de la OIT y su aplicabilidad en el sector agrícola cebollero del municipio de Aquitania-Boyacá”. Investigación desarrollada desde un enfoque cualitativo, el cual permitió interactuar con la muestra poblacional. Así mismo, fue necesario elegir 46 trabajadores del sector agrícola, en 5 empresas comercializadoras de cebolla larga, cada una con un promedio de 13 trabajadores, en las cuales se practicó una entrevista semi­estructurada, estableciendo categorías y subcategorías que permitieron concretar la información, además del análisis y la interpretación de las fuentes tanto primarias como secundarias que se tuvieron en cuenta para tal fin. El resultado de este proceso, ha permitido inferir que los trabajadores del sector agrícola adolecen de la protección del Estado en materia laboral y menos aún desde la garantía que otorga el convenio con la OIT en orden a la consecución de un trabajo decente. Por tanto es importante repensar y reestructurar la metodología normativa respecto a su aplicación con el fin de garantizar los derechos laborales a dicha población

Decent work from the ILO guidelines: applicability in the Aquitania Boyacá agricultural sector

The concept of "decent work" is an essential element in the legal systems of democratic States and even more so of those that are part of the International Labour Organization (ILO). Likewise, the obligation of the Member States to guarantee labour rights in the context of decent work must be reflected in effective action to protect it even more in the agricultural sector. From this logic, the proposed objective leads to an analysis of "decent work from the guidelines of the ILO and its applicability in the agricultural sector of the municipality of Aquitaine- Boyacá". Research developed from a qualitative approach, which allowed interaction with the population sample. Likewise, it was necessary to choose 46 workers from the agricultural sector, in 5 companies marketing long onions, each with an average of 13 workers, in which a semi-structured interview was carried out, establishing categories and subcategories that allowed the information to be specified, in addition to the analysis and interpretation of both primary and secondary sources that were taken into account for this purpose. The result of this process has allowed us to infer that workers in the agricultural sector suffer from the protection of the State in labor matters, and even less from the guarantee that the convention with the ILO provides in order to achieve decent work. Therefore, it is important to rethink and restructure the normative methodology regarding its application in order to guarantee labor rights to this population.El concepto de “trabajo decente” es un elemento esencial en los ordenamientos jurídicos de los Estados democráticos y aún más de aquellos que hacen parte de la Organización Internacional del Trabajo (OIT). Así mismo, la obligación que contraen los Estados miembro respecto a la garantía de los derechos laborales desde el contexto del trabajo decente, debe verse reflejada en una acción efectiva de protección aún más en el sector agrícola. Desde esta lógica, el objetivo planteado conlleva a efectuar un análisis sobre “el trabajo decente desde los lineamientos de la OIT y su aplicabilidad en el sector agrícola cebollero del municipio de Aquitania- Boyacá”. Investigación desarrollada desde un enfoque cualitativo, el cual permitió interactuar con la muestra poblacional. Así mismo, fue necesario elegir 46 trabaja- dores del sector agrícola, en 5 empresas comercializadoras de cebolla larga, cada una con un promedio de 13 trabajadores, en las cuales se practicó una entrevista semiestructurada, estableciendo categorías y subcategorías que permitieron concretar la información, además del análisis y la interpretación de las fuentes tanto primarias como secundarias que se tuvieron en cuenta para tal fin. El resultado de este proceso, ha permitido inferir que los trabajadores del sector agrícola adolecen de la protección del Estado en materia laboral y menos aún desde la garantía que otorga el convenio con la OIT en orden a la consecución de un trabajo decente. Por tanto es importante repensar y reestructurar la metodología normativa respecto a su aplicación con el fin de garantizar los derechos laborales a dicha población

Lake surface cooling drives littoral-pelagic exchange of dissolved gases

The extent of littoral influence on lake gas dynamics remains debated in the aquatic science community due to the lack of direct quantification of lateral gas transport. The prevalent assumption of diffusive horizontal transport in gas budgets fails to explain anomalies observed in pelagic gas concentrations. Here, we demonstrate through high-frequency measurements in a eutrophic lake that daily convective horizontal circulation generates littoral-pelagic advective gas fluxes one order of magnitude larger than typical horizontal fluxes used in gas budgets. These lateral fluxes are sufficient to redistribute gases at the basin-scale and generate concentration anomalies reported in other lakes. Our observations also contrast the hypothesis of pure, nocturnal littoral-to-pelagic exchange by showing that convective circulation transports gases such as oxygen and methane toward both the pelagic and littoral zones during the daytime. This study challenges the traditional pelagic-centered models of aquatic systems by showing that convective circulation represents a fundamental lateral transport mechanism to be integrated into gas budgets. Cooling-induced horizontal circulation redistributes gases daily between littoral and pelagic lake waters under calm conditions

Experimental study of the free evolution of the internal gravitational waves affect by Coriolis in a stratified flow

Abstract Laboratory experiments are presented to analyze the free evolution of large-scale internal gravitational waves in a stratified water body affected by Coriolis. This investigation was made in a rotating table, where a two-layer stratification was created into a circular basin, using a fresh water layer on top of a dyed salty water layer on the bottom. The control parameters used to characterize the experiments were the dimensionless Burger number, Wedderburn number and aspect ratio of the stratified water column. The free evolution of the internal waves field was measured by tracking the vertical displacements of the pycnocline using an optical method based on digital image analysis. Three sets of experiments were developed for capturing the internal gravity waves behavior as a function of the dimensionless numbers. The results show that the dynamics of the density interface is mainly modulated by the Kelvin-Poincaré interaction and the nonlinear response of solitary type waves, observed in the experiments for specific conditions. Finally, the results show that Earth rotation and nonlinear interactions are important aspects to understand the energy dissipation of internal gravitational basin scale waves

Seasonality modulates wind-driven mixing pathways in a large lake

Turbulent mixing controls the vertical transfer of heat, gases and nutrients in stratified water bodies, shaping their response to environmental forcing. Nevertheless, due to technical limitations, the redistribution of wind-derived energy fuelling turbulence within stratified lakes has only been mapped over short (sub-annual) timescales. Here we present a year-round observational record of energy fluxes in the large Lake Geneva. Contrary to the standing view, we show that the benthic layers are the main locus for turbulent mixing only during winter. Instead, most turbulent mixing occurs in the water-column interior during the stratified summer season, when the co-occurrence of thermal stability and lighter winds weakens near-sediment currents. Since stratified conditions are becoming more prevalent –possibly reducing turbulent fluxes in deep benthic environments–, these results contribute to the ongoing efforts to anticipate the effects of climate change on freshwater quality and ecosystem services in large lakes

Effect of cutting and storage temperature on Packham’s Triumph pears (Pyrus communis L.)

For the minimally processed (MP) fruit, the cutting type and temperature are the main factors in order to maintain good quality and appearance. The objective of this work was to evaluate the effects of cutting type and storage on the metabolic activity, color, firmness, aroma profile and, organic acid and sugar content of MP pears (Pyrus communis L. cv. Packham’s Triumph). Whole fruits were washed, peeled and cut in wedges or dice. Then, the pieces were packaged in plastic containers and stored 8 days at 5 or 8 ºC. The cutting type and storage temperature had an important effect on the physiological parameters, color, firmness and organic acid and sugar content. However, the aroma volatile content was reduced independently of the cutting type and the storage temperature. Therefore, the pear cultivar Packham’s Triumph should be cut in wedges and stored 8 d at 5º C to maintain an optimum global quality.En los frutos mínimamente procesados en fresco (MPF) el tipo de corte y la temperatura son factores por considerar para mantener una calidad y apariencia adecuada. El objetivo de este trabajo fue evaluar los efectos del corte y la temperatura de conservación sobre la actividad metabólica, color, firmeza, perfil aromático y concentración de ácidos orgánicos y azúcares de peras (Pyrus communis L. cv. Packham’s Triumph). Los frutos enteros fueron lavados, pelados, cortados en cascos o cubos, envasados en tarrinas y posteriormente almacenados 8 d a 5 o 8 ºC. El tipo de corte y la temperatura tuvieron un efecto significativo sobre los parámetros fisiológicos, color, firmeza y en el contenido de ácidos orgánicos y azúcares.  Sin embargo, el contenido de compuestos aromáticos volátiles se redujo independientemente del tipo de corte y las temperaturas de conservación. Por tanto, esta variedad de peras Packham’s Triumph deben ser procesadas en cascos y deben almacenarse a 5º C para mantener una calidad general óptima durante 8 días

Hydrodynamics of a periodically wind‑forced small and narrow stratified basin: a large‑eddy simulation experiment

We report novel results of a numerical experiment designed for examining the basin-scale hydrodynamics that control the mass, momentum, and energy distribution in a daily wind-forced, small thermally-stratified basin. For this purpose, the 3-D Boussinesq equations of motion were numerically solved using large-eddy simulation (LES) in a simplified (trapezoidal) stratified basin to compute the flow driven by a periodic wind shear stress working at the free surface along the principal axis. The domain and flow parameters of the LES experiment were chosen based on the conditions observed during summer in Lake Alpnach, Switzerland. We examine the diurnal circulation once the flow becomes quasi-periodic. First, the LES results show good agreement with available observations of internal seiching, boundary layer currents, vertical distribution of kinetic energy dissipation and effective diffusivity. Second, we investigated the wind-driven baroclinic cross-shore exchange. Results reveal that a near-resonant regime, arising from the coupling of the periodic wind-forcing (T=24 h) and the V2H1 basin-scale internal seiche (TV2H1≈24 h), leads to an active cross-shore circulation that can fully renew near-bottom waters at diurnal scale. Finally, we estimated the bulk mixing efficiency, Γ, of relevant zones, finding high spatial variability both for the turbulence intensity and the rate of mixing (10−3≤Γ≤10−1). In particular, significant temporal variability along the slopes of the basin was controlled by the periodic along-slope currents resulting from the V2H1 internal seiche