Polarization Limits in K-Rb Spin-Exchange Mixtures

We present measurements of the optical absorption of K vapor at 795 nm due to the presence of high pressure He gas. The results set a limit on the polarization attainable in hybrid spin-exchange optical pumping of He-3

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

A child care center for the Boston Model Cities Program,

Massachusetts Institute of Technology. Dept. of Architecture. Thesis. 1969. B.Arch.Two unnumbered leaves inserted.Includes bibliographical notes.by Joseph H. Lancor and Young Hoon Kwak.B.Arch

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

Optical Magnetometer Array for Fetal Magnetocardiography

We describe an array of spin-exchange relaxation free optical magnetometers designed for detection of fetal magnetocardiography (fMCG) signals. The individual magnetometers are configured with a small volume with intense optical pumping, surrounded by a large pump-free region. Spin-polarized atoms that diffuse out of the optical pumping region precess in the ambient magnetic field and are detected by a probe laser. Four such magnetometers, at the corners of a 7 cm square, are configured for gradiometry by feeding back the output of one magnetometer to a field coil to null uniform magnetic field noise at frequencies up to 200 Hz. Using this array, we present the first measurements of fMCG signals using an atomic magnetometer

Risperidone Treatment of Autistic Disorder: Longer-Term Benefits and Blinded Discontinuation After 6 Months

Objective: Risperidone is effective for short-term treatment of aggression, temper outbursts, and self-injurious behavior in children with autism. Because these behaviors may be chronic, there is a need to establish the efficacy and safety of longer-term treatment with this agent. Method: The authors conducted a multisite, two-part study of risperidone in children ages 5 to 17 years with autism accompanied by severe tantrums, aggression, and/or self-injurious behavior who showed a positive response in an earlier 8-week trial. Part I consisted of 4-month open-label treatment with risperidone, starting at the established optimal dose; part II was an 8-week randomized, double-blind, placebo-substitution study of risperidone withdrawal. Primary outcome measures were the Aberrant Behavior Checklist irritability subscale and the Clinical Global Impression improvement scale. Results: Part I included 63 children. The mean risperidone dose was 1.96 mg/day at entry and remained stable over 16 weeks of open treatment. The change on the Aberrant Behavior Checklist irritability subscale was small and clinically insignificant. Reasons for discontinuation of part I included loss of efficacy (N=5) and adverse effects (N=1). The subjects gained an average of 5.1 kg. Part II included 32 patients. The relapse rates were 62.5% for gradual placebo substitution and 12.5% for continued risperidone; this difference was statistically significant. Conclusions: Risperidone showed persistent efficacy and good tolerability for intermediate-length treatment of children with autism characterized by tantrums, aggression, and/or self-injurious behavior. Discontinuation after 6 months was associated with a rapid return of disruptive and aggressive behavior in most subjects

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.