Workshop to identify critical windows of exposure for children\u27s health: Neurobehavioral work group summary

Summarizes the deliberations of a work group charged with addressing specific questions relevant to risk estimation in developmental neurotoxicology. Importance of multiple factors addressing critical windows of exposure on neurological function; Role that compensatory mechanisms play in the manifestation of the effects of developmental exposures

Workshop to identify critical windows of exposure for children's health: neurobehavioral work group summary.

This paper summarizes the deliberations of a work group charged with addressing specific questions relevant to risk estimation in developmental neurotoxicology. We focused on eight questions. a) Does it make sense to think about discrete windows of vulnerability in the development of the nervous system? If it does, which time periods are of greatest importance? b) Are there cascades of developmental disorders in the nervous system? For example, are there critical points that determine the course of development that can lead to differences in vulnerabilities at later times? c) Can information on critical windows suggest the most susceptible subgroups of children (i.e., age groups, socioeconomic status, geographic areas, race, etc.)? d) What are the gaps in existing data for the nervous system or end points of exposure to it? e) What are the best ways to examine exposure-response relationships and estimate exposures in vulnerable life stages? f) What other exposures that affect development at certain ages may interact with exposures of concern? g) How well do laboratory animal data predict human response? h) How can all of this information be used to improve risk assessment and public health (risk management)? In addressing these questions, we provide a brief overview of brain development from conception through adolescence and emphasize vulnerability to toxic insult throughout this period. Methodological issues focus on major variables that influence exposure or its detection through disruptions of behavior, neuroanatomy, or neurochemical end points. Supportive evidence from studies of major neurotoxicants is provided

High-resolution zero-dispersion wavelength mapping in single-mode fiber

We present a new noninvasive technique for measuring the spatial variation of the zero-dispersion wavelength (λ0) in single-mode fibers. This technique uses low-power continuous-wave lasers and is simple to implement. When applying this technique to dispersion-shifted fibers, we can resolve subnanometer fluctuations in λ0 with a potential spatial resolution of better than 100 m. We also discuss and show the limits of this and other techniques that arise from polarization-mode dispersion in the fibers. © 1998 Optical Society of America

Variable Modulus Materials Based Upon F2MC Reinforced Shape Memory Polymers

The performance of a new variable modulus composite material based upon shape memory polymer (SMP) reinforced with fluidic flexible matrix composite (F2MC) tubes is investigated in this research. The new composite material is a unique combination of shape memory polymers acting as the matrix material with reinforcing embedded F2MC tubes. The recently developed F2MC tubes are small diameter tubes capable of potentially achieving more than three orders of magnitude change in effective stiffness through utilization of anisotropic flexible matrix composite (FMC) tubes, a high bulk modulus internal working fluid, and simple valve control. Similarly shape memory polymers can achieve more than three orders of magnitude change in stiffness through temperature regulation. To investigate the SMP-F2MC variable modulus composite material, an analytical model of the SMP-F2MC variable stiffness composite material is developed and design studies are performed. The results demonstrate that the new material system can achieve a wider range and greater selection of modulus values than the SMP or F2MC systems alone. Experimental results show good agreement with analysis