Search results for "Heat"
showing 10 items of 2717 documents
The modelling of the cathode sheath of an electrical arc in vacuum
2003
This paper presents a simple model of the fragment in the cathode electrical arc root taking into account the physical phenomena occuring on the cathode surface and the sheath. The goal is the obtainment of characteristics values of the heat flux, the electrons, and atoms density in the sheath. Computation is carried out on a one-dimensional model with a coupling between the equation obtained in the sheath and an enthalpy model of the cathode to describe the temperature evolution. In the modelling, we introduce a friction zone above the sheath edge to characterize the heavy particle interactions. Numerical simulation shows that the ionic friction phenomenon deriving from ion–atom collision …
Strategies for Active Learning to Improve Student Learning and Attitudes Towards Physics
2021
Over the last several years, active learning methods and strategies have received considerable attention from the educational community and are commonly presented in the related literature as a credible solution to the reported lack of efficacy of more “traditional” educative approaches. Research has shown that a possible factor is the strongly contextualized nature of active learning that focuses on the interdependence of situation and cognition. In this paper, we report the results of a Symposium with different contributions in the field of research on active learning. We start with a system analysis of the mental processes involved in learning physics which explains how active learning i…
Thermodynamic properties of a liquid–vapor interface in a two-component system
2010
Abstract We report a complete set of thermodynamic properties of the interface layer between liquid and vapor two-component mixtures, using molecular dynamics. The mixtures consist of particles which have identical masses and diameters and interact with a long-range Lennard-Jones spline potential. The potential depths in dimensionless units for like interactions is 1 (for component 1) and 0.8 (for component 2). The surface excess entropy decreases when the temperature increases, so the surface has a negative excess heat capacity. This is a consequence of the fact that the surface tension decreases to zero at the critical point, proportional to ( T C , i − T ) 2 ν . The surface entropy decre…
Thermodynamic properties of N-octyl- and N-dodecylnicotinamide chlorides in water
1990
Densities, heat capacities and enthalpies of dilution at 25°C and osmotic coefficients at 37°C were measured for N-octyl- and N-dodecylnicotinamide chlorides in water over an extended concentration region. Partial molar volumes, heat capacities, relative enthalpies and nonideal free energies and entropies at 25°C were derived as a function of the surfactant concentration. For both surfactants, plots of volumes, enthalpies and free energies vs. concentration are regular whereas those of heat capacities and entropies present anomalies at about 0.8 and 0.1m for the octyl and dodecyl compounds, respectively. Changes in the slope of a plot of osmotic coefficients times molality vs. molality were…
An approximation to the diachronic analysis of mitigation and face in dialogues between mother and child in the nineteenth and twentieth centuries
2018
Este artículo aborda la evolución del uso de la atenuación en los diálogos madre-hijo y sus efectos en la imagen sociocultural en los siglos XIX y XX. Para ello, utilizando como corpus cuatro obras de teatro de este periodo, se analiza cualitativa y cuantitativamente el empleo de la atenuación como estrategia pragmática en los actos directivos realizados en la proyección de estas relaciones. Los resultados de este estudio apuntan a que se ha producido una evolución desde la jerarquía hacia una progresiva solidaridad. This paper aims to analyse the evolution of the use of mitigation in dialogues between mother and child and their effects on sociocultural face in the nineteenth and twentieth …
La transformación de DICAT: el potencial de la visualización digital de redes para el teatro clásico español
2021
This paper analyses and proposes the steps to transform Diccionario biográfico de actores del teatro clásico español DICAT in order to be federated on ASODAT system of databases. We intend to assess whether or not the visualization of nets may be a useful and operational tool to analysing the biographical and professional information established between actors and actress of early modern Spanish theater, and to show patterns of social relation. Este artículo analiza y propone los pasos para transformar el Diccionario biográfico de actores del teatro clásico español DICAT para que pueda ser federado en el sistema de bases de datos ASODAT. Se pretende evaluar si la visualización de redes pued…
Daily evapotranspiration assessment by means of residual surface energy balance modeling: A critical analysis under a wide range of water availability
2012
Summary An operational use of the actual evapotranspiration assessed by remote sensing approaches requires the integration of instantaneous fluxes to daily values. This is commonly achieved under the hypotheses of daytime self-preservation of evaporative fraction and negligible daily ground heat flux. The aim of this study is to evaluate the effect of these assumptions on estimate daily evapotranspiration over a full phenological cycle, including phases characterized by significant changes both in net radiation and vegetation cover. To assess the reliability of these hypotheses, the observations made by a flux tower, installed within a homogeneous field of cereal located in the valley part …
The impact of in-canopy wind profile formulations on heat flux estimation in an open orchard using the remote sensing-based two-source model
2010
Abstract. For open orchard and vineyard canopies containing significant fractions of exposed soil (>50%), typical of Mediterranean agricultural regions, the energy balance of the vegetation elements is strongly influenced by heat exchange with the bare soil/substrate. For these agricultural systems a "two-source" approach, where radiation and turbulent exchange between the soil and canopy elements are explicitly modelled, appears to be the only suitable methodology for reliably assessing energy fluxes. In strongly clumped canopies, the effective wind speed profile inside and below the canopy layer can strongly influence the partitioning of energy fluxes between the soil and vegetation co…
Effects of rainfall events on the evapotranspiration retrieved by an energy balance model
2009
An alternative way to map the actual evapotranspiration (ET) spatial distribution at daily scale is the application of residual surface energy balance models to satellite images that are characterised by high temporal frequency and moderate spatial resolution, like those acquired by the MODIS sensors on board of TERRA and AQUA platforms. Within this research the well-known SEBAL model has been applied on an area located in the southern part of Sicily (Imera Meridionale catchment) using four images acquired between the 27th of March and the 11th of April 2007. The catchment extends for about 2000 km2 and includes both mountains and hill areas: the first are located in the northern part (the …
Applications of a remote sensing-based two-source energy balance algorithm for mapping surface fluxes without in situ air temperature observations
2012
Abstract The two-source energy balance (TSEB) model uses remotely sensed maps of land–surface temperature (LST) along with local air temperature estimates at a nominal blending height to model heat and water fluxes across a landscape, partitioned between dual sources of canopy and soil. For operational implementation of TSEB, however, it is often difficult to obtain representative air temperature data that are compatible with the LST retrievals, which may themselves have residual errors due to atmospheric and emissivity corrections. To address this issue, two different strategies in applying the TSEB model without requiring local air temperature data were tested over a typical Mediterranean…