Plasmaspheric effects on one way satellite timing signals

The effects of the ionospheric retardation of satellite-emitted timing signals was presented. The retardation at the navigation frequencies, which is proportional to the total ionospheric electron content (TEC), was determined by Faraday polarization measurements of VHF emissions of a geostationary satellite. The polarization data yielded TEC up to approximately 1200 km only, since the measurement technique is based on the Faraday effect which is weighted by the terrestrial magnetic field

Ionospheric effects on one-way timing signals

A proposed navigation concept requires that a user measure the time-delay that satellite-emitted signals experience in traversing the distance between satellite and user. Simultaneous measurement of the propagation time from four different satellites permits the user to determine his position and clock bias if satellite ephemerides and signal propagation velocity are known. A pulse propagating through the ionosphere is slowed down somewhat, giving an apparent range that is larger than the equivalent free space range. The difference between the apparent range and the true range, or the free space velocity and the true velocity, is the quantity of interest. This quantity is directly proportional to the total electron content along the path of the propagating signal. Thus, if the total electron content is known, or is measured, a perfect correction to ranging could be performed. Faraday polarization measurements are continuously being taken at Fort Monmouth, N. J., using beacon emissions of the ATS-3 (137.35 MHz) satellite. Day-to-day variability of the diurnal variation of total electron content values is present with differences of up to 50% or more not being uncommon. In addition, superposed on the overall diurnal variation are smaller scale variations of approximately 5 to 10% of the total content which are attributed to ionospheric density irregularities

The Role of the Neighborhood Fast Food Environment in Weight Status of Inner-City Children

In the past three decades prevalence of obesity has increased substantively in the US and has reached epidemic proportions both among adults and among children. Childhood obesity is of significant concern because it is associated with childhood morbidity, adverse social outcomes and may be associated with life-long implications. In recent years, there has been an increased interest in understanding the possible role of local food environment in shaping individual's behavior in ways that may encourage food consumption and affect weight status. This study examines whether fast food availability at the residential neighborhood may explain children's risk for obesity. Data from the Fragile Families and Child Wellbeing study, a population-based panel data of urban children and their families, were linked to locations of fast food outlets. Using both cross-sectional and longitudinal analytic techniques and numerous robustness checks, I find no discernible effect of exposure to fast food at the residential neighborhood on children's weight. Policies designed to reduce accessibility to fast food in children's residential neighborhood may not be effective in the effort to fight the childhood obesity epidemic

Terrestrial Nutrient and Sediment Fluxes to the Coastal Waters of West Maui, Hawai'i

Water-quality degradation is often linked to land use practices in adjacent and upstream areas. Such linkages are here explored for the Lahaina District of Maui, Hawai'i, where severe algae blooms in 1989 and 1991 prompted public concern and a subsequent search for the factors contributing to algal growth. Because we expected that elevated nutrient levels might play a role in the blooms, this study examined the nutrient and sediment budgets from terrestrial sources entering the coastal waters. Although our work did not show any definitive causal relationship between algal growth and terrestrial nutrient and sediment loading, it clearly established that the principal agricultural activities in the area of sugarcane and pineapple cultivation contribute elevated loads of nutrients and sediments to the coastal waters. Likewise, disposal of treated domestic sewage effluent into subsurface injection wells contributes substantial nutrient loads to the coastal waters. Conversely, golf courses appear to have negligible impacts on the nutrient and sediment loading of coastal waters in the area. Finally, although groundwater discharges substantially greater annual nutrient loads than streamflow, the groundwater discharge is fairly evenly distributed in time and is dispersed over nearly 25 km of shoreline. Streamflow, however, often discharges intensely for short periods of time at a few discrete locations, and thus may have substantial impact locally on coastal water quality

Crime and Circumstance: The Effects of Infant Health Shocks on Fathers’ Criminal Activity

Few studies in the economics literature have linked individuals’ criminal behavior to changes in their personal circumstances. Life shocks, such as natural or personal disasters, could reduce or sever a person’s connections to his/her family, job, or community. With fewer connections, crime may become a more attractive option. This study addresses the question of whether an exogenous shock in life circumstances affects criminal activity. Specifically, we estimate the effects of the birth of a child with a random and serious health problem (versus the birth of a healthy infant) on the likelihood that the child’s father becomes or remains involved in illegal activities. Controlling for the father’s pre-birth criminal activity, we find that the shock of having a child with a serious health problem increases both the father’s post-birth conviction and incarceration by 1 to 8 percentage points, depending on the measure of infant health used.