Modeling Security Policy and the Effect for End-Users

Many "good practices" in computer security are based on assumptions and local evidence that do not generalize. There are few quantifiable methods of establishing or refuting the validity of these practices from a user perspective. We propose a formal model of security policies that allows us to evaluate the claimed benefits to the user of the system quantitatively. We illustrate the use of the model by looking at a security policy we all live with daily: The Password Policy

Analog and Mixed Signal Verification

More and more electronic systems have components that are not purely digital. Verification of such systems is a much less developed discipline than the digital equivalents and the application of formal (mathematically complete) techniques is a nascent area. In this paper, we will discuss the nature of analog circuit design and describe the way verification is done in practice today. We will describe some “formal” approaches coming from the analog design community. We will describe some of the approaches to formal verification that have been presented in recent literature. Finally, we will mention some areas where there are opportunities for future work

NPLOT: an Interactive Plotting Program for NASTRAN Finite Element Models

The NPLOT (NASTRAN Plot) is an interactive computer graphics program for plotting undeformed and deformed NASTRAN finite element models. Developed at NASA's Goddard Space Flight Center, the program provides flexible element selection and grid point, ASET and SPC degree of freedom labelling. It is easy to use and provides a combination menu and command driven user interface. NPLOT also provides very fast hidden line and haloed line algorithms. The hidden line algorithm in NPLOT proved to be both very accurate and several times faster than other existing hidden line algorithms. A fast spatial bucket sort and horizon edge computation are used to achieve this high level of performance. The hidden line and the haloed line algorithms are the primary features that make NPLOT different from other plotting programs

The Distribution of Fitness Effects of Spontaneous Mutations in Vibrio fischeri

Mutations are the ultimate source of the biological diversity on which natural selection acts, but the vast majority of these mutations are harmful. As such, mutations lead to disease states like cancer, extinction of small populations, and can drive pathogen evolution. Unfortunately, because mutations are rare and past studies have been subject to detection biases, very little is known about the distribution of fitness effects from naturally occurring mutations. In this study, we used mutation accumulation and full genome sequencing to capture naturally occurring mutations before they were exposed to the sieve of natural selection in Vibrio fischeri. We then measured the effects of these mutations on the fitness of the individuals harboring these mutations. We hypothesized that most mutations would be deleterious, and that deletions and insertions would be more detrimental to fitness than base substitutions, particularly in coding regions. Additionally, we expected to show that mutations on primary chromosomes, which are more highly expressed and evolutionarily conserved, would have more harmful effects than mutations on accessory secondary chromosomes. Using a subset of eleven mutation accumulation isolates, each harboring between two and nine mutations, we show that the majority of mutations have minor deleterious effects, with a subset of those errors resulting in more drastic fitness declines. However, extending this study to more genotypes will be required to examine the relationship between particular mutation types and fitness. Ultimately, an enhanced understanding of the relationship between genotype and fitness will broaden our understanding of the distribution of mutational effects and elucidate the susceptibility of different genome regions to deleterious variation