In Situ Measurements of Electron-Beam-Induced Surface Voltage of Highly Resistive Materials

This study presents the development, calibration, characterization, and use of new instrumentation for in situ measurements of electron-beam-induced surface voltage. The instrument capabilities allow for measurements of a full range of insulating materials that are of concern to NASA spacecraft charging experts. These measurements are made using moveable capacitive sensor electrodes that can be swept across the sample using an in vacu stepper motor. Testing has shown a voltage range of more than ±30 kV with a low-voltage resolution of 0.2 V. The movable sensors allow for a radial measurement of surface voltage with spatial resolution as low as 1.5 mm. The instrumentation has response time of ~7 s from the time the beam is shut off until the probe is in position to take data and uses computer automation to stabilize the system and acquire data over the period of several days or longer. Three types of measurements have been made on two prototypical polymeric spacecraft materials, Low-density Polyethylene (LDPE) and polyimide (KaptonTM HN), to illustrate the research capabilities of the new system. Surface voltage measurements were made periodically during the charging process using a pulsed electron beam and subsequently as the surface voltage discharged to a grounded substrate; these were used to obtain information about the material’s electron yields and bulk resistivity. The spatial profile of the voltage across the sample surface was also measured by sweeping the electrode across the surface. Subsequent measurements monitored the time evolution of the magnitude and spatial charge distribution as charge dispersed radially across the sample surface. The results of these measurements are present and compared to literature values validating the instrument’s effectiveness

Folate intakes of vegetarian and non vegetarian adolescent females

Background: Folate is a water soluble B vitamin found naturally among food sources such as dark green vegetables, legumes, beans and offal such as liver. The synthetic form of folic acid is found in fortified food sources and supplements. Nationally and worldwide, folate is a nutrient of concern, as many populations consume intakes below the estimated average requirement. Thus, mandatory fortification of the food supply is common practice for many countries. New Zealand’s policy allows the voluntary fortification. It is unknown whether New Zealand adolescent females are achieving their recommended needs, particularly as dietary patterns change, such as increased consumption of plant-based diets. Objective: The objective of the present study was to evaluate the dietary intake of folate, and major food group contributors among a sample of adolescent vegetarian and non-vegetarian females in New Zealand. Design: This is a cross-sectional study designed as part of the larger Survey of Nutrition Dietary Assessment and Lifestyle (SuN DiAL) project. Healthy females between 15 to 18 years old were recruited in two phases from 13 high schools, and through targeted recruitment. Participant data were collected via two 24-hour diet recalls, anthropometric measurements, as well as, online sociodemographic and dietary questionnaires. Usual energy and folate intakes (total, natural food folate and folic acid), and the prevalence of folate inadequacy were assessed. Food consumption was categorised into 33 food groups and major contributors to folate intake were calculated. Results: Two-hundred and eighty-two participants enrolled in the study, with 250 participants completing one 24 hour recall; of those, 213 (85%) completed a second recall. The majority of participants identified as non-vegetarian, with 31 (12%) identifying as vegetarian. The average age of participants was 16.8 years; however, vegetarian participants were slightly older (17.1 years). Over three-quarters of participants were New Zealand European and Other, with approximately 16% of participants classified as Māori and a small proportion of Pacific and Asian participants. Dietary results showed median total intake of folate (IQR) was 306 (232.3, 409.5) µg dietary folate equivalents (DFEs)/day, with an estimated folic acid intake of 33 (0.0, 90.0) µg/day. Over half of all participants consumed folate intakes below the EAR. However, the usual folate intakes among vegetarians were higher, and prevalence of inadequacy was substantially lower than non-vegetarians (32 vs 61%, respectively), despite lower energy intakes among vegetarians. Moreover, folic acid intakes were higher among vegetarians. The major folate contributors for vegetarians were vegetables and bread, as for non-vegetarians the result was reversed. A slightly higher percentage of vegetarian participants were consuming food items from both food groups (87.1 and 83.9% for vegetables and bread, respectively). Conclusion: Results show that adolescent females, in general, continue to have a high prevalence of inadequate folate intakes although vegetarians had a lower risk of inadequacy compared to non-vegetarians. These findings are a concern as achieving optimal folate intakes are important for reproductive age women. Mandatory fortification has shown to be an effective intervention among this target group globally. More research is required to better understand the impact of increased voluntary fortification or a mandatory policy on the folate intakes of both New Zealand reproductive women and other population lifecycle groups

Flight Experiments on the Effects of Contamination on Electron Emission of Materials

We report on a study of the effects of prolonged exposure to the space environment and of chargeenhanced contamination on the electron emission and resistivity of spacecraft materials. The State of Utah Space Environment & Contamination Study (SUSpECS) was deployed on the International Space Station (ISS) in March 2008 onboard the MISSE-6 payload during STS-123. The Materials International Space Station Experiment (MISSE-6) program is designed to characterize the performance of candidate new space materials over the course of its ~17 month exposure to the LEO environment, with a target return date of August 2009 on STS-127. Approximately 165 samples are mounted on three separate SUSpECS panels in the ram and wake sides on the ISS. They have been carefully chosen to provide needed information for different ongoing studies and a broad cross-section of prototypical materials used on the exteriors of spacecrafts. Design of the sample panels are detailed, including a three tiered configuration intended to provide variable atomic oxygen and ultraviolet radiation exposure. The methods used to simulate charge enhanced contamination by actively biasing samples to low positive and negative voltages are also described. A primary emphasis of SUSpECS is the study of modifications to the electron emission resulting from exposure to the space plasma environment and to environmental contamination. There is presently little available data related to the effects of sample deterioration and contamination on emission properties for materials actually flown in space. Electron emission and transport properties of materials are key in determining the amount of charge build-up and the time for the charge to dissipate, as well as the likelihood of deleterious spacecraft charging effects. Such materials properties are essential parameters in modeling spacecraft charging with engineering tools like NASCAP-2K code. SUSpECS studies will test the validity of our predictions from ground-based studies that very thin layers of contamination can lead to severe charging effects under certain circumstance. Electron-, ion-, and photon-induced electron emission yield curves, crossover energies and emission spectra, as well as resistivity and dielectric strength, have been tested for most SUSpECS samples in their pristine conditions before flight. These measurements will be compared with post-flight measurements. Additional pre- and post-flight characterization measurements include optical and electron microscopy, reflection spectroscopy, emissivity and Auger electron spectroscopy

The Effects of Lesions in the Dorsolateral Pons on the Coordination of Swallowing and Breathing in Awake Goats

The purpose of this retrospective study was to gain insight into the contribution of the dorsolateral pons to the coordination of swallowing and breathing in awake goats. In 4 goats, cannulas were chronically implanted bilaterally through the lateral (LPBN) and medial (MPBN) parabrachial nuclei just dorsal to the Kölliker–Fuse nucleus (KFN). After \u3e2 weeks recovery from this surgery, the goats were studied for 5½ h on a control day, and on separate days after receiving 1 and 10 μl injections of ibotenic acid (IA) separated by 1 week. The frequency of swallows did not change during the control and 1 μl IA studies, but after injection of 10 μl IA, there was a transient 65% increase in frequency of swallows (P \u3c 0.05). Under control conditions swallows occurred throughout the respiratory cycle, where late-E swallows accounted for 67.6% of swallows. The distribution of swallow occurrence throughout the respiratory cycle was unaffected by IA injections. Consistent with the concept that swallowing is dominant over breathing, we found that swallows increased inspiratory (TI) and expiratory (TE) time and decreased tidal volume (VT) of the breath of the swallow (n) and/or the subsequent (n + 1) breath. Injections of 10 μl IA attenuated the normal increases in TI and TE and further attenuated VT of the n breath. Additionally, E and I swallows reset respiratory rhythm, but injection of 1 or 10 μl IA progressively attenuated this resetting, suggesting a decreased dominance over respiratory motor output with increasing IA injections. Post mortem histological analysis revealed about 50% fewer (P \u3c 0.05) neurons remained in the KFN, LPBN, and MPBN in lesioned compared to control goats. We conclude that dorsolateral pontine nuclei have a modulatory role in a hypothesized holarchical neural network regulating swallowing and breathing particularly contributing to the normal dominance of swallowing over breathing in both rhythm and motor pattern generation

In Situ Surface Voltage Measurements of Dielectrics Under Electron Beam Irradiation

New instrumentation has been developed for non- contact, in vacuo measurements of the electron beam-induced surface voltage as a function of time and position for non- conductive spacecraft materials in a simulated space environment. The novel compact system uses two movable capacitive sensor electrodes to measure surface charge distributions on samples, using a non-contact method that has little effect on charge dissipation from sample. Design details, calibration and characterization measurements of the system are presented, with \u3c1 V to \u3e30 kV surface voltage range, \u3c0.5 V voltage resolution, and \u3c1.5 mm spatial resolution. Used in conjunction with the capabilities of an existing ultrahigh vacuum electron emission test chamber, the new instrumentation facilitates measurements of charge accumulation, bulk resistivity, effects of charge depletion and accumulation on yield measurements, electron induced electrostatic breakdown potentials, radiation induced conductivity effects, and the radial dispersion of surface voltage. Three types of measurements of surface voltage for polyimide (Kapton HNTM) serve to illustrate the research capabilities of the new system: (i) accumulation using a pulsed electron beam, while periodically measuring the surface voltage; (ii) post charging, as deposited charge dissipated to a grounded substrate; and (iii). the evolution of spatial profile resulting from an incident Gaussian beam. Theoretical models for sample charging and discharge are outlined to predict the time, temperature, and electric field dependence of the sample’s net surface voltage

Objective determination of the extratropical transition of tropical cyclones in the Northern Hemisphere

Extratropical transition (ET) has eluded objective identification since the realisation of its existence in the 1970s. Recent advances in numerical, computational models have provided data of higher resolution than previously available. In conjunction with this, an objective characterisation of the structure of a storm has now become widely accepted in the literature. Here we present a method of combining these two advances to provide an objective method for defining ET. The approach involves applying K-means clustering to isolate different life-cycle stages of cyclones and then analysing the progression through these stages. This methodology is then tested by applying it to five recent years from the European Centre of Medium-Range Weather Forecasting operational analyses. It is found that this method is able to determine the general characteristics for ET in the Northern Hemisphere. Between 2008 and 2012, 54% (±7, 32 of 59) of Northern Hemisphere tropical storms are estimated to undergo ET. There is great variability across basins and time of year. To fully capture all the instances of ET is necessary to introduce and characterise multiple pathways through transition. Only one of the three transition types needed has been previously well-studied. A brief description of the alternate types of transitions is given, along with illustrative storms, to assist with further stud

Evolution of Spur-Length Diversity in Aquilegia Petals Is Achieved Solely Through Cell-Shape Anisotropy

The role of petal spurs and specialized pollinator interactions has been studied since Darwin. Aquilegia petal spurs exhibit striking size and shape diversity, correlated with specialized pollinators ranging from bees to hawkmoths in a textbook example of adaptive radiation. Despite the evolutionary significance of spur length, remarkably little is known about Aquilegia spur morphogenesis and its evolution. Using experimental measurements, both at tissue and cellular levels, combined with numerical modelling, we have investigated the relative roles of cell divisions and cell shape in determining the morphology of the Aquilegia petal spur. Contrary to decades-old hypotheses implicating a discrete meristematic zone as the driver of spur growth, we find that Aquilegia petal spurs develop via anisotropic cell expansion. Furthermore, changes in cell anisotropy account for 99 per cent of the spur-length variation in the genus, suggesting that the true evolutionary innovation underlying the rapid radiation of Aquilegia was the mechanism of tuning cell shape.Engineering and Applied SciencesOrganismic and Evolutionary Biolog

Evolution of Spur-Length Diversity in Aquilegia Petals is Achieved solely through Cell-Shape Anisotropy

The role of petal spurs and specialized pollinator interactions has been studied since Darwin. Aquilegia petal spurs exhibit striking size and shape diversity, correlated with specialized pollinators ranging from bees to hawkmoths in a textbook example of adaptive radiation. Despite the evolutionary significance of spur length, remarkably little is known about Aquilegia spur morphogenesis and its evolution. Using experimental measurements, both at tissue and cellular levels, combined with numerical modelling, we have investigated the relative roles of cell divisions and cell shape in determining the morphology of the Aquilegia petal spur. Contrary to decades-old hypotheses implicating a discrete meristematic zone as the driver of spur growth, we find that Aquilegia petal spurs develop via anisotropic cell expansion. Furthermore, changes in cell anisotropy account for 99 per cent of the spur-length variation in the genus, suggesting that the true evolutionary innovation underlying the rapid radiation of Aquilegia was the mechanism of tuning cell shape