Radiation effects on polymeric materials

It is important to study changes in properties of polymeres after irradiation with charged particles, with ultraviolet radiation, and with combinations of both. An apparatus for this purpose has been built at the NASA Langley Research Center. It consists of a chamber 9 inches in diameter and 9 inches high with a port for an electron gun, another port for a mass spectrometer, and a quartz window through which an ultraviolet lamp can be focused. The chamber, including the electron gun and the mass spectrometer, can be evacuated to a pressure of 10 to the 8th power torr. A sample placed in the chamber can be irradiated with electrons and ultraviolet radiation separately, sequentially, or simultaneously, while volatile products can be monitored during all irradiations with the mass spectrometer. The apparatus described above has been used to study three different polymer films: lexan; a polycarbonate; P1700, a polysulfone; and mylar, a polyethylene terephthalate. All three polymers had been studied extensively with both electrons and ultraviolet radiation separately, but not simultaneously. Also, volatile products had not been monitored during irradiation for the materials. A high electron dose rate of 530 Mrads/hr was used so that a sufficient concentration of volatile products would be formed to yield a reasonable mass spectrum

The effects of the space environment on two aramid materials

Two aramid fibers having closely related chemical structures were chosen for important roles in the first tether to be used to connect pairs of orbiting vehicles. The protective outer jackets of the tethers will consist of woven fibers of poly(m-phenylene isophthalamide), commercially available from du Pont as Nomex. A cylindrical sheath of woven Kevlar 29, whose principal constituent is poly(p-phenylene terephthalamide), will be the load-bearing component for the tethers. Orbiting tethers will be in a hostile environment in which short wavelength electromagnetic radiation and energetic charged particles degrade exposed organic materials. At lower orbiting altitudes atomic oxygen is an especially serious hazard. Studies on the effects of ultraviolet radiation and atomic oxygen on fibers and films of Kevlar and Nomex are in progress. In an experiment to simulate the effects of atomic oxygen in space, small tows of Kevlar and Nomex were mounted in a commercial ashing device filled with oxygen at low pressure. An RF discharge in the instrument dissociated the molecular oxygen producing a strongly oxidizing atmosphere containing O(3P)(sup 4). Erosion was measured in terms of mass loss. Kevlar films were exposed to UV radiation in an apparatus consisting of a small vacuum chamber, 23 cm in diameter, into which a mass spectrometer and a quartz window were incorporated. Samples were exposed under vacuum with a 1000 watt xenon-arc lamp. Volatile products could be monitored with the mass spectrometer during the exposures. Transmission infrared spectra were taken before and after exposure to monitor chemical changes in the films

The effects of the interaction of polymeric materials with the space environment

Polymeric materials in low earth orbit will be exposed to a harmful environment mainly due to atomic oxygen and ultraviolet radiation. In geosynchronous earth orbit, the major hazards to such materials are energetic charged particles and ultraviolet radiation. The progress of studies on the effects of these hazards on a polyetherimide, a polyimide, and an epoxy adhesive is presented

Space environmental effects on polymeric materials

Two of the major environmental hazards in the Geosynchronous Earth Orbit (GEO) are energetic charged particles and ultraviolet radiation. The charged particles, electrons and protons, range in energy from 0.1 to 4 MeV and each have a flux of 10 to the 8th sq cm/sec. Over a 30 year lifetime, materials in the GEO will have an absorbed dose from this radiation of 10 to the 10th rads. The ultraviolet radiation comes uninhibited from the sun with an irradiance of 1.4 kw/sq m. Radiation is known to initiate chain sission and crosslinking in polymeric materials, both of which affect their structural properties. The 30-year dose level from the combined radiation in the GEO exceeds the threshold for measurable damage in most polymer systems studied. Of further concern is possible synergistic effects from the simultaneous irradiation with charged particles and ultraviolet radiation. Most studies on radiation effects on polymeric materials use either electrons or ultraviolet radiation alone, or in a sequential combination

Remarks on the issue of time and complex numbers in canonical quantum gravity

We develop the idea that, as a result of the arbitrariness of the factor ordering in Wheeler-DeWitt equation, gauge phases can not, in general, being completely removed from the wave functional in quantum gravity. The latter may be conveniently described by means of a remnant complex term in WDW equation depending of the factor ordering. Taking this equation for granted we can obtain WKB complex solutions and, therefore, we should be able to derive a semiclassical time parameter for the Schroedinger equation corresponding to matter fields in a given classical curved space.Comment: Typewritten using RevTex, to appear in Phys. Rev.

Children’s Disclosure of School Bullying: The Relation Between Peer Victimization, Internalizing Symptoms, Negative Affect, and Gender

Children who are bullied by their peers are at risk for several negative developmental outcomes and are therefore advised to tell an adult when they are. However, victims of school bullying are often reluctant to disclose to adults that they are being bullied. Some bullied children also experience symptoms of anxiety or depression, which could further reduce their likelihood of telling an adult. In this study, I tested the degree to which children’s internalizing symptoms predicted their likelihood of telling adults about being bullied at school, and if this relation was exacerbated by children’s negative feelings associated with telling an adult. I also tested whether this relation was different for boys and girls. Data were drawn from a short-term, longitudinal study (N = 375, 52% female, M age = 9.33 years, SD = 1.07) that spanned a single academic year. Findings suggest that boys with internalizing symptoms are less likely to tell an adult when bullied, compared to peers. Findings also indicate that children with internalizing symptoms likely feel heightened negative emotions when telling a teacher about being bullied. Implications are discussed

Children’s Disclosure of School Bullying: The Relation Between Peer Victimization, Internalizing Symptoms, Negative Affect, and Gender

Children who are bullied by their peers are at risk for several negative developmental outcomes and are therefore advised to tell an adult when they are. However, victims of school bullying are often reluctant to disclose to adults that they are being bullied. Some bullied children also experience symptoms of anxiety or depression, which could further reduce their likelihood of telling an adult. In this study, I tested the degree to which children’s internalizing symptoms predicted their likelihood of telling adults about being bullied at school, and if this relation was exacerbated by children’s negative feelings associated with telling an adult. I also tested whether this relation was different for boys and girls. Data were drawn from a short-term, longitudinal study (N = 375, 52% female, M age = 9.33 years, SD = 1.07) that spanned a single academic year. Findings suggest that boys with internalizing symptoms are less likely to tell an adult when bullied, compared to peers. Findings also indicate that children with internalizing symptoms likely feel heightened negative emotions when telling a teacher about being bullied. Implications are discussed

Wetland mapping from digitized aerial photography

Computer assisted interpretation of small scale aerial imagery was found to be a cost effective and accurate method of mapping complex vegetation patterns if high resolution information is desired. This type of technique is suited for problems such as monitoring changes in species composition due to environmental factors and is a feasible method of monitoring and mapping large areas of wetlands. The technique has the added advantage of being in a computer compatible form which can be transformed into any georeference system of interest

The Coherence of Primordial Fluctuations Produced During Inflation

The behaviour of quantum metric perturbations produced during inflation is considered at the stage after the second Hubble radius crossing. It is shown that the classical correlation between amplitude and momentum of a perturbation mode, previously shown to emerge in the course of an effective quantum-to-classical transition, is maintained for a sufficiently long time, and we present the explicit form in which it takes place using the Wigner function. We further show with a simple diffraction experiment that quantum interference, non-expressible in terms of a classical stochastic description of the perturbations, is essentially suppressed. Rescattering of the perturbations leads to a comparatively slow decay of this correlation and to a complete stochastization of the system.Comment: LaTeX (7 pages

Tracking Pacific bluefin tuna (Thunnus thynnus orientalis) in the northeastern Pacific with an automated algorithm that estimates latitude by matching sea-surface-temperature data from satellites with temperature data from tags on fish

Data recovered from 11 popup satellite archival tags and 3 surgically implanted archival tags were used to analyze the movement patterns of juvenile northern bluefin tuna (Thunnus thynnus orientalis) in the eastern Pacific. The light sensors on archival and pop-up satellite transmitting archival tags (PSATs) provide data on the time of sunrise and sunset, allowing the calculation of an approximate geographic position of the animal. Light-based estimates of longitude are relatively robust but latitude estimates are prone to large degrees of error, particularly near the times of the equinoxes and when the tag is at low latitudes. Estimating latitude remains a problem for researchers using light-based geolocation algorithms and it has been suggested that sea surface temperature data from satellites may be a useful tool for refining latitude estimates. Tag data from bluefin tuna were subjected to a newly developed algorithm, called “PSAT Tracker,” which automatically matches sea surface temperature data from the tags with sea surface temperatures recorded by satellites. The results of this algorithm compared favorably to the estimates of latitude calculated with the lightbased algorithms and allowed for estimation of fish positions during times of the year when the lightbased algorithms failed. Three near one-year tracks produced by PSAT tracker showed that the fish range from the California−Oregon border to southern Baja California, Mexico, and that the majority of time is spent off the coast of central Baja Mexico. A seasonal movement pattern was evident; the fish spend winter and spring off central Baja California, and summer through fall is spent moving northward to Oregon and returning to Baja California