Papers by Keyword: Empirical Model

Abstract: In this work, an empirical model of structural and material composition of low-ohmic nickel silicide contact formation on n-type 4H-SiC by laser annealing as well as by RTA is presented. For this purpose, systematic studies with different annealing parameters were performed. The development of the empirical model is based on results from characterization of the nickel silicide by FIB-SEM, TEM, XRD analysis as well as electrical characteristics received from 4-point-measurements.

Abstract: The elastic modulus (E_c) of concrete is usually calculated from the compressive strength (f_c) in the design of concrete structures using standard models found in the various design codes. Most of these models were fundamentally developed for concrete made with natural coarse aggregate (NCA). Concrete containing coarse recycled concrete aggregate (CRCA) is known to have inferior mechanical properties to concrete made with NCA. Accordingly, the E_c-f_c relationship of CRCA concrete differs from that of NCA concrete. Hence, a number of researchers have endeavoured to develop predictive models for concrete made with CRCAs using different software programs. In an attempt to contribute to this subject, the present study seeks to propose a new model for predicting the E_c of CRCA concrete using an empirical approach. Data obtained from the literature was used to develop the model. Validations of the model using independent data sources gave realistic predictions. The new model can be used for practical E_c prediction, design, and analysis of sustainable concrete structures made with CRCAs.

Abstract: The present work had the objective of studying the osmotic dehydration process of cassava cubes (Manihot esculentaCrantz.) in ternary solutions containing water, sucrose, and sodium chloride. The osmotic dehydration process was studied by using a 2⁴ factorial planning with central points at different conditions of temperature (19-63°C), solute concentration (23-67% w/w), operating time (70-190 min.) and NaCl concentration (0-20% w/w). The process optimization was verified through the performance ratio of minimum solids gain, in conjunction with the maximum moisture loss and reduction of water activity of the material. From the analysis, the optimum condition for osmotic dehydration of cassava cubes was temperature52°C, concentration of the osmotic solution 56%solute,10% NaCl concentration,160 minutes of immersion time and 180 rpm . The study of osmotic dehydration kinetics in the optimized condition showed that the moisture loss reached equilibrium in 180 minutes and the solids gain in 30 minutes. The model of Azuara and contributors was fitted to experimental data of moisture lost and total solids gain, in the optimal condition and good agreement were obtained. From this comparison, the average effective diffusivity coefficients of moisture (1.99x10^-8m2/s) and total solids (2.77x10^-8m2/s) were estimated.

Abstract: In the literature, several correlation models have been developed to predict solar radiation on horizontal surfaces. In this paper, the daily solar radiation data and sunshine duration data measured during the period of 2006-2010, were used to calculate the monthly mean values of daily total solar radiation using five modified Angstrom–Prescott model and three day of the year based empirical models of Oran city (35°42 N and 00°36 W) in Algeria. Furthermore, those modified models are compared with three existing models. In order to evaluate the accuracy of the models, the statistical testing error such as R², RMSE, rRMSE, MAPE and MBE are used. According to statistical test results and from the sunshine duration models, the polynomial model (#4) showed the best estimation results with a coefficient of determination R²=0.991, rRMSE=4.129%, and MAPE=3.635%. Furthermore, the accurate model from the day of the year models is the model (7), with R²=0.987, rRMSE=4.067%, and MAPE=3.5194%. Moreover, this paper finds that the best accuracy model to estimate the monthly mean daily solar radiation on horizontal surfaces in Oran city is the sine and cosine wave trigonometric model (#7).

Abstract: This work is focused on the development of empirical model to predict the mechanical properties of welded Al-SiC metal matrix composites. Autogenous pulsed current-Tungsten inert gas (PC-TIG) welding was performed on 5mm thick Al-8%SiC composite plates. Regression equations were developed to predict the tensile strength, yield strength, percentage of elongation and bend strength of pulsed current TIG weld Al-SiC composite by varying weld parameters such as peak current, base current, pulse on time and pulse frequency. The effect of each pulsed current TIG welding parameters and interaction between two more parameters on the ultimate tensile strength, yield strength, percentage of elongation and bend strength were studied for clear understanding of PCTIG welding parameters. Improved mechanical properties viz. 136 MPa tensile strength, 117 MPa yield strength with 15% elongation were achieved using optimal PCTIG welding parameters. The predicted values were experimentally verified for consistency and validation. This study also resulted in understanding the significant factors which were responsible for improved weld strength of the chosen candidate material.

Abstract: Hard milling is considered to be a precise and efficient machining method for the die and mold manufacturing industry. The main criterion for evaluating the cutting processes of the parts designed for these applications is the quality of the machined surfaces. For this reason, the analysis of the factors that influence the surface roughness obtained in this processes is important for helping the process become more productive and competitive. The present paper presents some results and an empirical model for surface roughness when high speeds face milling of AISI W1 tool steel. The influence of cutting parameters and material hardness is investigated by using Taguchi design of experiments. The results obtained show that high speed face milling of hardened tool steel AISI W1 can be carried out in economical conditions(on plant milling machines) and can lead to satisfactory surface quality (Ra =0.2-0.36 μm).

Abstract: The laser beam drilling is generally included in the larger group of laser beam machining methods based on the material removal. The problem addressed in this paper referred to the laser beam drilling of test pieces made of Plexiglas. Some theoretical aspects were highlighted by analyzing the physical effects developed in Plexiglas by the laser beam action. Experimental research was developed in order to highlight the influence exerted by the duration of the CO₂ laser beam action on the Plexiglas in obtaining blind and through-holes. Empirical mathematical models and graphical representations allowed formulation of some remarks concerning the results of experimental research.

Abstract: Earthquake is common but one of the major natural disasters that cause heavy casualties in the world. In China, half of the deaths caused by natural disasters were brought by earthquakes since 1950. Undertaking effective relief operations when an earthquake strikes is important not only for life saving but also for the sustainable development of the affected area. Estimation of seismic mortality is an important part of relief operation. Based on the analysis of existing seismic mortality estimation models, the paper compares three empirical models of estimating the deaths caused by four earthquakes in China, discovers large errors in the models, and proposes that the models should be improved to meet the needs of emergency rescue. The paper also discusses factors that affect model precision and makes some suggestions on how to improve these empirical models.

Abstract: Vegetative filter strip (VFS) is be defined as areas of vegetation designed to remove sediment and other pollutants from surface runoff. Many factors affect the effectiveness of VFS. So the quantitative analysis on relation between effectiveness and influencing factors had been conducted based on the plot experiment data in this paper. Result reveals that the order in impact degree of its factors is: inflow rate factor > width factor > vegetation condition > pollutants concentration in inflow > initial soil water content factor, the relation equation of purification effect and VFS width is the form of logarithm, and the relation equation of concentration reduction rate and inflow rate is the form of power function. Furthermore, a simple empirical model had been developed to predict sediment trapping efficiency in allusion to Chinese northwest region, which can provide computational basis for design of VFS in northwest region and other similar areas.

Abstract: Empirical acoustic models were developed for dense-graded and open-graded asphalt concrete. Tire/pavement noise data were collected from in-service flexible pavements at different frequency bands for four consecutive years. These data were panel structured, and with a portion of observations missed arbitrarily. A Monte Carlo Markov Chain (MCMC) sampling and a multiple imputation (MI) algorithm were used to capture the unobserved heterogeneity and deal with missing observations by Bayesian simulations that are associated with the data. Models for the two mixes at different frequency bands were constructed. Major findings of the study include: first, tire/pavement noise increases with age at all frequency bands; second, tire/pavement noise level increases with air-void content of the surface mixes at medium and high frequencies but decreases at low frequencies; third, tire/pavement noise level increases with mean profile depth (MPD) at low and medium frequencies but decreases at high frequencies; and fourth, open-graded mix has low noise level compared to its dense-graded counterpart.