A numerical study of field-aided diffusion

A numerical method for determining the effect of the internal electric field on the diffusion of impurity ions in semiconductors is described. The model of the diffusion process is defined by the flux equations, the continuity equations and Gauss' law. Due to the complexity of this model, there is no known analytical solution. However, the system of nonlinear equations is solved numerically using an iteration technique.Diffusion profiles are presented for boron diffusing in silicon at 1100°C for various values of surface concentration C₀. These profiles are compared to the complementary error function which is the correct solution neglecting the internal electric field. The impurity profiles are also compared to those obtained by solving an approximate diffusion equation derived by using the concept of a concentration dependent “effective” diffusion coefficient.It is shown that the influence of the electric field on the motion of the impurities is a strong function of the surface concentration. For high values of C₀, the impurity profile becomes exponential. The accuracy of the solutions obtained by solving the approximate diffusion equation depends on both the value of C₀ and the diffusion time.     

The Internet revolution in law: teaching in new ways

The Internet is revolutionizing the law, legal institutions, and the roles of lawyers and law schools. Legislatures and courts all over the world are discovering how a $3,000 Internet-connected computer can be a remarkably cheap printing press for legal publishing, through which to instantly communicate new statutes, court decisions and administrative regulations. Law schools have an important role to play in connection with this revolution. They should support electronic publishing and virtual library initiatives by public institutions. They must continue to generate intellectual and human capital in the form of scholarship and well-educated graduates, accounting for new and substantive legal issues that the Internet presents. Finally, it is increasingly clear that the Internet provides a new set of educational tools for distance learning that more schools must begin to understand and use to improve teaching quality. Distance learning extends to all uses of computer, telecommunications, and digital networking technologies that permit education to occur outside a conventional classroom. Thus defined, it includes preparation of video taped lectures, preprogrammed computer-assisted legal instruction (CALI) exercises, and use of the Web to deliver these and other materials. The paper focuses on distance learning in law.     

Population-based analysis of the effect of the Northridge Earthquake on cardiac death in Los Angeles County, California

OBJECTIVES: We sought to determine whether a natural disaster affected total cardiovascular mortality and coronary mortality in an entire population. BACKGROUND: The effect of the January 17, 1994 Northridge Earthquake (NEQ) on all deaths and causes of deaths within the entire population of Los Angeles County is unknown. The purposes of our study were to analyze all deaths in this entire population before, during and after the NEQ and to determine whether the NEQ temporally and spatially altered death due to cardiovascular disease. METHODS: We analyzed all death certificate data (n = 19,617) from Los Angeles County during January of 1992, 1993 (control periods) and 1994, using International Classification of Diseases, 9th Revision codes for ischemic heart disease (IHD) and atherosclerotic cardiovascular disease (ASCVD), as well as other causes of death. RESULTS: There was an average of 73 deaths per day due to IHD and ASCVD during January 1 to 16, 1994; this increased to 125 on the day of the NEQ, and then decreased to 57 deaths per day from January 18 to 31 (p < 0.00001, before NEQ vs. day of NEQ; after NEQ vs. day of NEQ; and before NEQ vs. after NEQ). The NEQ was associated with an increase in deaths due to myocardial infarction and trauma but not cardiomyopathy, hypertensive heart disease, valvular heart disease, cerebrovascular disease or noncardiovascular causes. Based on plots of daily deaths due to IHD and ASCVD, the decrease in deaths during the 14 days after the NEQ (-144) overcompensated for the increase on the day of the NEQ (+55). Geographic analysis revealed a redistribution of deaths due to IHD and ASCVD toward the epicenter on the day of the NEQ. CONCLUSIONS: When an entire population simultaneously experiences a major environmental stress, there is an increase in death due to coronary artery disease (but not other cardiac causes), followed by a decrease that overcompensates for the excess of death. The overcompensation may represent a residual population that is more resistant to stress or a possible preconditioning effect of the stress, or both. This study supports the concept that cardiovascular events within an entire population can be triggered by a shared stress.