Physically-based Mathematical Model Research Articles

New Physically-Based Mathematical Model and Experiments for a Recently Invented Solar Pot

The studied solar pot is a recent invention, which is made for environmentally friendly cooking or heating (by utilizing solar energy) of foods and liquids. Its structure is similar to a double pipe heat exchanger, it has an outer mantle and an inner cooking tank. The goals of the paper are proposing a new physically-based mathematical model describing the solar pot and carrying out computer experiments with it, assembling an experimental system of the pot connected with a solar collector and performing measurements on it. Based on the results, the solar pot can successfully be used for cooking or sterilizing foods or liquids during the studied time period, in Hungary. In particular, based on measured data, the temperature level needed for heat treatment (75 °C) can be maintained in the cooking tank for several hours (~5 h, on the average) in a typical day in May.

Modeling sand slides by a mechanics-based degenerate parabolic equation

Avalanching plays a crucial role in granular materials dynamics, in particular in the evolution of the shape of the leeward side of sand dunes. This paper presents a physically-based mathematical model capable of reproducing the kinematic evolution of the surface of sand piles and to obtain eventually the stationary configurations, in the presence of external sources as well. Simulation results with different boundary conditions and geometries are reported in order to show the high flexibility of the model. The model is also validated by means of comparison with the experimental results of different authors.

Influence of Thermal Stress and Kinetic Bias Stress on the Electrical Performance of Mixed Oxide Thin Film Transistors

This study discusses thermally activated defects in the channel layer of indium zinc oxide (IZO) thin film transistors (TFTs) under electrical and thermal stress resembling practical stress scenarios. Operating temperatures of 20, 50, and 80 {degree sign}C have been chosen to establish a relation between temperature and failure mechanism. With increasing stress period, acceptor- and donor-like traps contribute towards degrading drain current and subthreshold swing. Low temperature long hour anneal for 12, 24, 36, 48 and 60 hr at 150 {degree sign}C are performed on the TFTs post fabrication to cure the defects formed during fabrication. Structures treated for 48 hr demonstrate high stability under extended kinetic stresses, maintaining a high transistor Ion/Ioff ratio of ~ 108. A physically-based mathematical model discusses the reduction in the density of acceptor-like trap states by 50 % for TFTs treated for 12 hrs, and to insignificant numbers for TFTs treated for 48 hr.

Simulation of erosion-deposition processes at basin scale by a physically-based mathematical model

The development and application of the physically-based and spatially-distributed mathematical model CTSS8-SED is presented. The model simulates hydrologic-hydraulic processes produced by storm events and related soil erosion and sediment transport processes at basin scale in lowland areas. The model simulates (i) storm runoff, (ii) soil detachment by raindrop impact and overland flow (gross sediment yield), (iii) sediment transport by overland flow and associated erosion-deposition processes and (iv) sediment transport by stream flow and riverbed erosion-deposition processes. A quasi two-dimensional representation of water flow and sediment transport routing is made by means of interconnected cells approach. The model is applied to simulate two flooding events in the Ludueña Creek basin (Santa Fe, Argentina) occurred in April 1994 and March 2007 due to extraordinary rainfalls.

Desenvolvimento e calibração de guias de onda para TDR

A medição da umidade do solo é crucial para a pesquisa e o manejo de irrigação. Entre os métodos mais recentes de determinação da umidade está o da reflectometria no domínio do tempo (TDR) que se baseia na correlação entre a capacidade dielétrica do solo e a sua umidade. A obtenção do perfil de umidade do solo requer a utilização de um grande número de guias de onda, cujo custo ainda é elevado. Por outro lado, as curvas de calibração relacionando umidade com a capacidade dielétrica do solo foram desenvolvidas para outros meios porosos, solos desestruturados e solos de países com clima temperado. O objetivo deste trabalho foi construir uma guia de onda com materiais facilmente encontrados no mercado nacional e calibrá-la para solos tropicais. As curvas de calibração para o Neossolo quartzarênico e Latossolo Vermelho são distintas e diferentes dos modelos apresentados na literatura. A modificação de um modelo matemático, fisicamente embasado, permitiu a geração de curvas de calibração com ajuste adequado, porém independentes para cada tipo de solo.

Fluidized bed spray granulation—A new model for the description of particle wetting and of temperature and concentration distribution

This article presents a physically-based mathematical model for the description of particle wetting and of temperature and concentration distribution in fluidized bed spray-granulation. The air humidity, air temperature, degree of wetness of the particles, liquid film temperature and particle temperature can all be calculated while taking into account the apparatus wall, the influence of the environment and of heating surfaces, which might be implemented in the fluidized bed. The effects which the unsteady start-up and shut-down procedures, as well as the alteration of process parameters, such as the mass flow rate of the liquid sprayed in with a jet and the liquid temperature as well as the fluidizing airflow rate and air temperature, have on the balance quantities, can be simulated. The bed mass and particle diameter growth in discontinuous granulation are taken into account and the two-dimensional calculation of the temperature and concentration distributions were carried out for the steady, continuous fluidized bed spray-granulation. The validation of the model was carried out at the Institute using a semi-industrial fluidized bed plant with a diameter of 0.4 m in the bed area. Dimensionless constants are proposed for the evaluation of the process.

Modeling enrichment of soluble pollutants in snow covers

Snowmelt runoff presents an enhanced threat of environmental damage. Soluble impurities which have accumulated in the snow during winter months are transported to the lower portion of the snow cover early in the melting season due to melt-freeze cycles. These contaminants are removed rapidly at very high concentrations within the first fractions of snowmelt runoff causing sudden bursts of enriched pollutants. This paper reports a physically-based mathematical model to simulate the enrichment process in a snow cover. The model is based on the liquid water flow, heat transport, and pollutant transport equations. These nonlinear partial differential equations are solved simultaneously using a six-point implicit finite difference scheme.

The Rational Formula Interpreted Using a Physically-Based Mathematical Model

A new interpretation is given for the rational formula in view of a mathematical model founded on the kinematic overland flow and Green and Ampt infiltration equations. The potential variability of the runoff coefficient with various rainfall and basin characteristics is demonstrated. However, using the concept of hydrologic similarity, it is possible to predict the runoff coefficient in terms of several physically-based non dimensional parameters for homogeneous planar, rectangular basins.

A physically-based model for the agrohydrologic processes

A physically-based mathematical model has been developed to simulate the four most important parts of the watershed continuum that are controlled by the properties of soils and plants and by meteorological factors. The model couples three-dimensional transient subsurface flow (varied saturation soil water flow), soil evaporation and plant transpiration, forest interception and one-dimensional unsteady overland flow. The nonsteady, saturated and unsaturated subsurface flow module uses a finite difference method to solve numerically the soil water flow equations. The evaporation-transpiration module which has dynamic properties, calculates the soil evaporation and plant transpiration separately. It takes into consideration, the influence of the vegetation, soil moisture status, vegetative cover intensity and depth of root zone. The overland flow module uses the single step Lax-Wendroff explicit technique to solve numerically the kinematic wave equation. The main aspects of the model and its potential capabilities have been studied and visualized for Nolsjön watershed in south Sweden during summer periods. The results indicated that this computational tool can provide valuable information for water development and management.

Simulation analysis of interatrial transposition of venous return (Mustard's operation).

Transposition of the great arteries is functionally corrected by Mustard's operation, an operation in which the atrial septum is removed and the resulting common atrial chamber repartitioned by a baffle to transpose venous return to the heart. To better understand the new physiology, a physically-based mathematical model of the infant circulation following Mustard's operation was developed and studied with the aid of computer simulation. The model reproduces certain clinical observations, including the tendency for mean pressure in both atria to be equal early postoperatively and for the pressure waveform to exhibit a steep y-descent in the systemic venous atrium. Simulation studies suggest that the mechanism for the former is transbaffle pressure coupling resulting from dynamic motion of the baffle; the mechanism for the latter is limitation of the extent of such baffle excursions. Dynamic volume of the two atria is found in the model to change according to the relative performance of the two ventricles, and stiffening the baffle leads to pressure waveforms characteristic of a small, noncompliant atrium. Mechanisms for venous "obstruction" and decompression were also studied. The baffle and its movements, however, have little effect upon cardiac output in the model, leaving unexplained the clinical observation of low output early postoperatively.