Efectos del cambio clim��tico y usos del suelo sobre los recursos h��dricos de la cuenca del r��o Tordera (Barcelona, Espa��a)

Se presentan los efectos del cambio global en la cuenca del r��o Tordera (Espa��a) para el periodo 2000-2050, escenarios clim��ticos A2 (medio-alto) definidos por el Panel Intergubernamental del Cambio Clim��tico (IPCC, 200) y escenarios socioecon��micos (cambios previstos en la cuenca) denominados estable y tendencial. Los efectos sobre los recursos h��dricos se han analizado de forma conjunta superficial-subterr��nea mediante una metodol��gica de tipo acoplado. Para establecer los impactos futuros sobre los recursos h��dricos se ha seleccionado el Modelo de Circulaci��n Global ECHAM5 (Max Planck Institute). Los resultados obtenidos indican una disminuci��n de la precipitaci��n del 11.3% y un aumento de la temperatura de 1��C, respecto a los valores hist��ricos de la zona. De acuerdo a la proyecci��n futura (2050) sobre cambios en los recursos h��dricos, la escorrent��a superficial obtenida mediante simulaci��n con el c��digo HEC-HMS 3.4 experimenta una reducci��n del 31.8% respecto al valor hist��rico y la recarga natural, estimada mediante VISUAL-Balan, se reduce en un 11.7%. El balance en el acu��fero deltaico simulado mediante MODFLOW 2009.1 Pro muestra igualmente una disminuci��n de los par��metros del balance. Los cambios del uso del suelo previstos de acuerdo a la legislaci��n vigente (escenarios socioecon��micos) no conducen a la generaci��n de un impacto apreciable en los recursos h��dricos; seg��n los escenarios definidos la variaci��n de precipitaci��n y temperatura son los par��metros fundamentales del cambio previsto.

Identifying student and teacher difficulties in interpreting atomic spectra using a quantum model of emission and absorption of radiation

Our study sets out to identify the difficulties that high school students, teachers, and university students encounter when trying to explain atomic spectra. To do so, we identify the key concepts that any quantum model for the emission and absorption of electromagnetic radiation must include to account for the gas spectra and we then design two questionnaires, one for teachers and the other for students. By analyzing the responses, we conclude that (i) teachers lack a quantum model for the emission and absorption of electromagnetic radiation capable of explaining the spectra, (ii) teachers and students share the same difficulties, and (iii) these difficulties concern the model of the atom, the model of radiation, and the model of the interaction between them.

An alternative disjunctive optimization model for heat integration with variable temperatures

This paper presents an alternative model to deal with the problem of optimal energy consumption minimization of non-isothermal systems with variable inlet and outlet temperatures. The model is based on an implicit temperature ordering and the ���transshipment model��� proposed by Papoulias and Grossmann (1983). It is supplemented with a set of logical relationships related to the relative position of the inlet temperatures of process streams and the dynamic temperature intervals. In the extreme situation of fixed inlet and outlet temperatures, the model reduces to the ���transshipment model���. Several examples with fixed and variable temperatures are presented to illustrate the model's performance.

Mathematical programming model for heat exchanger design through optimization of partial objectives

Mathematical programming can be used for the optimal design of shell-and-tube heat exchangers (STHEs). This paper proposes a mixed integer non-linear programming (MINLP) model for the design of STHEs, following rigorously the standards of the Tubular Exchanger Manufacturers Association (TEMA). Bell���Delaware Method is used for the shell-side calculations. This approach produces a large and non-convex model that cannot be solved to global optimality with the current state of the art solvers. Notwithstanding, it is proposed to perform a sequential optimization approach of partial objective targets through the division of the problem into sets of related equations that are easier to solve. For each one of these problems a heuristic objective function is selected based on the physical behavior of the problem. The global optimal solution of the original problem cannot be ensured even in the case in which each of the sub-problems is solved to global optimality, but at least a very good solution is always guaranteed. Three cases extracted from the literature were studied. The results showed that in all cases the values obtained using the proposed MINLP model containing multiple objective functions improved the values presented in the literature.