Evidence for ion acceleration by oscillations in the discharge plasma of ion engines

The hollow cathode discharge plasma in ion engines is highly non-uniform, geometrically complex, and confined by a magnetic field; elucidating the mechanisms responsible for producing ions with anomalously high energies observed in the downstream regions of hollow cathodes will contribute to understanding the behavior of complex plasmas. Ions with energies in excess of ten times greater than the energy associated with electrostatic acceleration from the largest steady-state potential difference in the plasma discharge of ion engines have been detected

Letters between W. J. Kerr and Mary E. Polk

Letters concerning a position at Utah Agricultural College

Letters between Mary E. Polk and W. J. Kerr

Letters concerning a position at Utah Agricultural College

Scanning optical pyrometer for measuring temperatures in hollow cathodes

Life-limiting processes in hollow cathodes are determined largely by the temperature of the electron emitter. To support cathode life assessment, a noncontact temperature measurement technique which employs a stepper motor-driven fiber optic probe was developed. The probe is driven inside the hollow cathode and collects light radiated by the hot interior surface of the emitter. Ratio pyrometry is used to determine the axial temperature profile. Thermocouples on the orifice plate provide measurements of the external temperature during cathode operation and are used to calibrate the pyrometer system in situ with a small oven enclosing the externally heated cathode. The diagnostic method and initial measurements of the temperature distribution in a hollow cathode are discussed

Socioeconomic factors in adolescents’ oral health: are they mediated by oral hygiene behaviors or preventive interventions?

Polk DE, Weyant RJ, Manz MC. Socioeconomic factors in adolescents’ oral health: are they mediated by oral hygiene behaviors or preventive interventions? Community Dent Oral Epidemiol 2010; 38: 1–9. © 2009 John Wiley & Sons A/STo determine whether there is a socioeconomic status (SES) disparity in caries experience (i.e., DMFT) in an adolescent sample from Pennsylvania and to determine whether differences in oral hygiene behaviors and preventive interventions account for this disparity.A cross-sectional clinical assessment was conducted on a representative sample of 9th grade and 11th grade students across Pennsylvania. These students also completed a brief questionnaire regarding their oral hygiene behaviors. From this group of students, a random subsample of 530 parents completed a questionnaire assessing SES, fluoride exposure, and recency of receipt of dental services. DMFT was examined at two thresholds of severity: simple prevalence (DMFT > 0) and severe caries (DMFT > 3).Using structural equation modeling, we found that lower SES was associated with higher prevalence of DMFT and higher prevalence of severe caries. Although lower SES was associated with lower rates of brushing, less use of sealants, and less recent receipt of dental services, these oral health behaviors and preventive interventions did not account for the disparities in DMFT defined by SES.There is an SES gradient in caries experience in adolescents in Pennsylvania. Disparities in caries experience, however, cannot be accounted for by SES-associated differences in brushing, flossing, sealant use, fluoride exposure, or recency of use of dental services. To facilitate the design of preventive interventions, future research should determine the pathways through which SES-associated disparities occur.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78657/1/j.1600-0528.2009.00499.x.pd

Is there an Appalachian disparity in dental caries in Pennsylvania schoolchildren?

ObjectivesTo determine whether there is an Appalachian disparity in caries prevalence or extent in children living in Pennsylvania.MethodsWe conducted a cross‐sectional clinical assessment of caries in a sample representing 1st, 3rd, 9th, and 11th grade students across Pennsylvania. We used logistic regression and zero‐inflated negative binomial regression controlling for age to examine the association of residence in an Appalachian county with caries prevalence and extent in the primary and permanent dentitions.ResultsCompared with children living outside Appalachia, more children living in Appalachia had a dft >0 (OR = 1.37, 95% CI = 1.07–1.76) and more had a DMFT >0 (OR = 1.32, 95% CI = 1.06–1.64). In addition, compared with children living outside Appalachia, children living in Appalachia had a greater primary but not permanent caries extent (IRR = 1.10, 95% CI = 1.01–1.19).ConclusionsWe found Appalachian disparities in caries prevalence in both the primary and permanent dentitions and an Appalachian disparity in caries extent in the primary dentition. None of the disparities was moderated by age. This suggests that the search for the mechanism or mechanisms for the Appalachian disparities should focus on differential exposures to risk factors occurring prior to and at the start of elementary school.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110608/1/cdoe12135.pd

Noninvasive Techniques for Intracranial Pressure Assessment: A Review from Aerospace Medicine Perspective

Microgravity-induced changes in fluid distribution and other physiological factors due to space flight have been implicated as the cause of increased intracranial pressure (ICP) in a number of space crewmembers. The modest levels of ICP elevation and absence of severe symptoms in this group do not warrant invasive diagnostic interventions. However, the long-term trends and residual or consequential changes secondary to the observed ICP elevation in this group are not yet known. Therefore, close attention is needed to evaluate the potential techniques of noninvasively assessing ICP, including those feasible for in-flight use. Of particular interest is continuity between ground and in-flight testing, whereby data from the same or different techniques allow reasonably dependable estimation of ICP trends and responses. Methods: A thorough review of current literature, analysis of NASA data, and interviews with subject matter experts were conducted to construct a presentation that reflects the state of the art for noninvasive ICP measurement and monitoring. Results: Multiple imaging and non-imaging modalities are available to assess ICP in terrestrial clinical and experimental environments. Imaging alternatives include magnetic resonance imaging (MRI) and high-resolution sonography. Non-imaging techniques include transcranial Doppler, certain audiological methods, and venous ophthalmodynamometry, among others. Special functional techniques have been proposed recently that allow the use of advanced MRI methods to calculate ICP in addition to the acquisition of high-resolution images. Our data include many of these applications, with several cases of correlation with lumbar puncture, the invasive "gold standard" measurement of ICP

Traditional Cardiovascular Risk Factors as Predictors of Cardiovascular Events in the U.S. Astronaut Corps

Risk prediction equations from the Framingham Heart Study are commonly used to predict the absolute risk of myocardial infarction (MI) and coronary heart disease (CHD) related death. Predicting CHD-related events in the U.S. astronaut corps presents a monumental challenge, both because astronauts tend to live healthier lifestyles and because of the unique cardiovascular stressors associated with being trained for and participating in space flight. Traditional risk factors may not hold enough predictive power to provide a useful indicator of CHD risk in this unique population. It is important to be able to identify individuals who are at higher risk for CHD-related events so that appropriate preventive care can be provided. This is of special importance when planning long duration missions since the ability to provide advanced cardiac care and perform medical evacuation is limited. The medical regimen of the astronauts follows a strict set of clinical practice guidelines in an effort to ensure the best care. The purpose of this study was to evaluate the utility of the Framingham risk score (FRS), low-density lipoprotein (LDL) and high-density lipoprotein levels, blood pressure, and resting pulse as predictors of CHD-related death and MI in the astronaut corps, using Cox regression. Of these factors, only two, LDL and pulse at selection, were predictive of CHD events (HR(95% CI)=1.12 (1.00-1.25) and HR(95% CI)=1.70 (1.05-2.75) for every 5-unit increase in LDL and pulse, respectively). Since traditional CHD risk factors may lack the specificity to predict such outcomes in astronauts, the development of a new predictive model, using additional measures such as electron-beam computed tomography and carotid intima-media thickness ultrasound, is planned for the future