This paper describes the development of a simulation model for heating of foods in microwave ovens and its uses to optimize food heating strategies. The solution of the coupled energy and mass microscopic balances considers the electromagnetic energy absorption as well as temperature-dependent thermal, transport, and dielectric properties. The microscopic balances are highly nonlinear coupled differential equations, which were solved using finite element software (Comsol Multiphysics). Maxwell equations were employed in order to describe the interaction between electromagnetic radiation and food. The mathematical model allowed the evaluation of the effect of product size and composition in the temperature profiles that developed inside the food that was radiated either on one or both sides. In order to improve the nonuniform temperature profiles that occurred within foods under continuous operation, different operation schemes were evaluated: intermittent cycles, joint action of microwaves with air impingement, and the effect of interference of electromagnetic waves.

The aim of the present study was to evaluate the effect of solar and microwave drying on raspberries (Rubus Idaeus) cv. Heritage. The efficiency of drying was evaluated in terms of weight reduction in function of the time. The quality properties evaluated were color, texture, antioxidant capacity and total polyphenols content. The results showed that solar drying and microwave drying allowed a good preservation of surface color in the final product. However, the solar drying achieved a desirable texture in dried raspberries compared to microwave drying. Neither solar drying nor microwave drying allowed a high retention of the antioxidant capacity. Nevertheless, both processes allow obtaining final stable fruits (low water activity) at any time of the year.

We aim to reach an analytic expression that describes the path of light rays through the Earth’s atmosphere in the particular situation in which an inferior mirage is occurring. To achieve our goal, we assume an exponential refractive index profile close to the ground, as suggested by empirical and theoretical studies on the state of air when an inferior mirage is taking place. We consider a parallel-plane atmosphere and assume that the laws of geometric optics apply. Since Fermat’s principle holds, we solve the Euler’s equation and, from the solution we obtain an analytic expression that describes the ray paths in a plane perpendicular to the ground. Given that we focus on the particular case of inferior mirages, we were able to find a very simple and easy-to-use expression to describe the ray paths, allowing us to extract additional valuable information with minimal computational effort. We take advantage of it to impose a limit to the thickness of the air layer next to the ground where appropriate conditions exist to bend the rays upwards, and produce an inferior mirage.

No abstract

We propose a model for the potential barrier for electrons crossing a metal surface, in which (1) we reproduce the effective potential of Lang and Kohn, in fact, better than any approximation in the existing literature and (2) we approach the classical image potential for large separation from the surface. Our potential does not diverge as the electron approaches the surface and goes over smoothly to the electron-electron interaction potential in the bulk. It reproduces the first peak in the e6'ective potential of Lang and Kohn, which is a Friedel oscillation. %'e achieve better agreement with the Lang-Kohn potential than Jennings, Jones, and Weinert in their barrier model. This makes our model useful in the analysis of low-energy electron-diFraction Gne-structure experiments. Our simple barrier model allows analytical solutions of the Schrodinger equation in the density-functional formalism.