Circular Dichroism of RbHe and RbN2_2 Molecules

We present measurements of the circular dichroism of optically pumped Rb vapor near the D1 resonance line. Collisions with the buffer gases $^3$He and N$_2$ reduce the transparency of the vapor, even when fully polarized. We use two methods to measure this effect, show that the He results can be understood from RbHe potential curves, and show how this effect conspires with the spectral profile of the optical pumping light to increase the laser power demands for optical pumping of very optically thick samples

Effects of Nitrogen Quenching Gas on Spin-Exchange Optical Pumping of He-3

We consider the degree of conservation of nuclear spin polarization in the process of optical pumping under typical spin-exchange optical pumping conditions. Previous analyses have assumed that negligible nuclear spin precession occurs in the brief periods of time the alkali-metal atoms are in the excited state after absorbing photons and before undergoing quenching collisions with nitrogen molecules. We include excited-state hyperfine interactions, electronic spin relaxation in collisions with He and N_2, spontaneous emission, quenching collisions, and a simplified treatment of radiation trapping

Breakdown of Angular Momentum Selection Rules in High Pressure Optical Pumping Experiments

We present measurements, using two complementary methods, of the breakdown of atomic angular momentum selection rules in He-broadened Rb vapor. Atomic dark states are rendered weakly absorbing due to fine-structure mixing during Rb-He collisions. The effect substantially increases the photon demand for optical pumping of dense vapors

On use of personal information processing properties for dynamic network security applications

Heightened interest and increased accessibility to computer systems have presented new threats to computer security, particularly in the areas of unauthorized system access. To counter such threats, computer password systems are used due to ease of implementation and low cost. However, there is nothing to prohibit access to a system if an adversary has discovered a valid password. Passwords are therefore open to compromise without the knowledge of their disclosure. In addition, passwords are static identity verifiers implying the same person is assumed until log-off.^ There is very limited evidence of studies done with respect to techniques which aid in dynamically discriminating among users to ascertain whether the user at the terminal is actually the verified and authorized user at login time. A new authentication model is developed which is based on the variability in individual human-computer interactions, and implements a technique for formally modeling and analytically evaluating human-computer interactions. It employs dynamic, continuous, unobtrusive verification throughout a user\u27s login session. The model is used in conjunction with a system\u27s existing password mechanism and is composed of individual user models, based on users\u27 personal cognitive characteristics and usage patterns. Each user model is developed using probabilistic finite automata theory combined with time measures. This work also addresses informational issues regarding data accumulation, calibration, and model dimensionality.