Publications

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The peridynamic theory of continuum mechanics allows damage, fracture, and long-range forces to be treated as natural components of the deformation of a material. In this paper, the peridynamic approach is applied to small thickness two- and one-dimensional structures. For membranes, a constitutive model is described appropriate for rubbery sheets that can form cracks. This model is used to perform numerical simulations of the stretching and dynamic tearing of membranes. A similar approach is applied to one-dimensional string like structures that undergrow stretching, bending, and failure. Long-range forces similar to van der Waals interactions at the nanoscale influence the equilibrium configurations of these structures, how they deform, and possibly self-assembly.

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A laser hazard analysis to determine the Extended Ocular Hazard Distances associated with a possible intrabeam aided viewing of the Sandia Remote Sensing System (SRSS) airborne AURA laser (Big Sky Laser Technology) was performed based on the 2000 version of the American National Standard Institute's (ANSI) Standard Z136.1, for the Safe Use of Lasers and the 2000 version of the ANSI Standard Z136.6, for the Safe Use of Lasers Outdoors. The AURA lidar system is installed in the instrument pod of a Proteus airframe and is used to perform laser interaction experiments and tests at various national test sites. The targets are located at various distances (ranges) from the airborne platform. Nominal Ocular Hazard Distance (NOHD) and maximum ''eye-safe'' dwell times for various operational altitudes associated with unaided intrabeam exposure of ground personnel were determined and presented in a previous SAND report. Although the target areas are controlled and the use of viewing aids are prohibited there is the possibility of the unauthorized use of viewing aids such as binoculars. This aided viewing hazard analysis is supplemental to the previous SAND report for the laser hazard analysis of the airborne AURA.

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We present all-atom molecular dynamics simulations of biologically realistic transmembrane potential gradients across a DMPC bilayer. These simulations are the first to model this gradient in all-atom detail, with the field generated solely by explicit ion dynamics. Unlike traditional bilayer simulations that have one bilayer per unit cell, we simulate a 170 mV potential gradient by using a unit cell consisting of three salt-water baths separated by two bilayers, with full three-dimensional periodicity. The study shows that current computational resources are powerful enough to generate a truly electrified interface, as we show the predicted effect of the field on the overall charge distribution. Additionally, starting from Poisson's equation, we show a new derivation of the double integral equation for calculating the potential profile in systems with this type of periodicity.

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Sandia National Laboratories (SNL) has developed a number of security risk assessment methodologies (RAMs) for various infrastructures including dams, water systems, electrical transmission, chemical facilities and communities. All of these RAMs consider potential malevolent attacks from different threats, possible undesired events and consequences and determine potential adversary success. They focus on the assessment of these infrastructures to help identify security weaknesses and develop measures to help mitigate the consequences from possible adversary attacks. This paper will focus on RAM-C, the security risk assessment methodology for communities. There are many reasons for a community to conduct a security risk assessment. They include: providing a way to identify vulnerabilities, helping a community to be better prepared in the event of an adversary attack, providing justification for resources to address identified vulnerabilities and planning for future projects. RAM-C provides a systematic, risk-based approach useable by public safety and emergency planners to determine relative risk and provides useful information in making security risk decisions. RAM-C consists of a number of steps starting with a screening step which selects facilities based on a documented process; characterization of the community and facilities; determination of severity of consequences for identified undesired events; determination of the community protection goals and defining the threat; defining existing baseline safeguard measures; analyzing protection system effectiveness against identified scenarios, determining a relative risk and finally deciding if that risk is too high. If the risk is too high then possible countermeasures and mitigation measures are considered. RAM-C has been used by a number of communities within the United States. From these assessments there have been many results. Some communities have been surprised by the vulnerabilities that have been identified; have identified the need to test procedures and responses to many different situations; have identified the need to have redundancy in certain systems and have identified who within their community are valuable resources. The RAM-C process is a systematic way to assess vulnerabilities and make decisions based on risk. It has provided valuable information to community planners.

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