N-Type Field-Effect Transistors Using Multiple Mg-Doped ZnO Nanorods

Nanorod field-effect transistors (FETs) that use multiple Mg-doped ZnO nanorods and a SiO₂ gate insulator were fabricated and characterized. The use of multiple nanorods provides higher on-currents without significant degradation in threshold voltage shift and subthreshold slopes. It has been observed that the on-currents of the multiple ZnO nanorod FETs increase approximately linearly with the number of nanorods, with on-currents of ~1 muA per nanorod and little change in off-current (~4times10^-12). The subthreshold slopes and on-off ratios typically improve as the number of nanorods within the device channel is increased, reflecting good uniformity of properties from nanorod to nanorod. It is expected that Mg dopants contribute to high n-type semiconductor characteristics during ZnO nanorod growth. For comparison, nonintentionally doped ZnO nanorod FETs are fabricated, and show low conductivity to compare with Mg-doped ZnO nanorods. In addition, temperature-dependent current-voltage characteristics of single ZnO nanorod FETs indicate that the activation energy of the drain current is very low (0.05-0.16 eV) at gate voltages both above and below threshold     

Lidar-based mapping of flood control levees in South Louisiana

Flood protection in south Louisiana is largely dependent on earthen levees, and in the aftermath of Hurricane Katrina the state’s levee system has received intense scrutiny. Accurate elevation data along the levees are critical to local levee district managers responsible for monitoring and maintaining the extensive system of non-federal levees in coastal Louisiana. In 2012, high resolution airborne lidar data were acquired over levees in Lafourche Parish, Louisiana, and a mobile terrestrial lidar survey was conducted for selected levee segments using a terrestrial lidar scanner mounted on a truck. The mobile terrestrial lidar data were collected to test the feasibility of using this relatively new technology to map flood control levees and to compare the accuracy of the terrestrial and airborne lidar. Metrics assessing levee geometry derived from the two lidar surveys are also presented as an efficient, comprehensive method to quantify levee height and stability. The vertical root mean square error values of the terrestrial lidar and airborne lidar digital-derived digital terrain models were 0.038 m and 0.055 m, respectively. The comparison of levee metrics derived from the airborne and terrestrial lidar-based digital terrain models showed that both types of lidar yielded similar results, indicating that either or both surveying techniques could be used to monitor geomorphic change over time. Because airborne lidar is costly, many parts of the USA and other countries have never been mapped with airborne lidar, and repeat surveys are often not available for change detection studies. Terrestrial lidar provides a practical option for conducting repeat surveys of levees and other terrain features that cover a relatively small area, such as eroding cliffs or stream banks, and dunes.     

Variations in the Usability of Independent Web-Based Personal Health Records

ABSTRACT

Previous research on personal health records (PHRs) has focused on applications that are “tethered” to a specific electronic health record (EHR). However, there is a gap in research on the usability of unaffiliated, independent PHRs, as well as research on college-aged PHR users. Therefore, we performed a comparative usability study with 18 college-aged participants on three popular, freely available, independent PHRs. Participants completed the same six tasks in three different PHRs. Dependent variables included task time, mouse movement, mouse clicks, keystrokes, errors, and user satisfaction ratings based on the Computer System Usability Questionnaire (CSUQ). Analysis of variance (ANOVA) was used to determine the significance in the difference of the means for each dependent variable. Results showed statistically significant differences in CSUQ survey categories, errors, and keystrokes. Results supported one of the three PHRs (“System A”) as having better usability than its tested counterparts; participants scored best in System A of all categories of the CSUQ, and used System A with less mouse movement, commission errors, and keystrokes than the other PHRs.     

Hypoxic ventilatory responsiveness in Tibetan compared with Han residents of 3,658 m

Lifelong high-altitude residents of North and South America acquire blunted hypoxic ventilatory responses and exhibit decreased ventilation compared with acclimatized newcomers. The ventilatory characteristics of Himalayan high-altitude residents are of interest in the light of their reportedly lower hemoglobin levels and legendary exercise performance. Until recently, Sherpas have been the only Himalayan population available for study. To determine whether Tibetans exhibited levels of ventilation and hypoxic ventilatory drives that were as great as acclimatized newcomers, we compared 27 lifelong Tibetan residents of Lhasa, Tibet, China (3,658 m) with 30 acclimatized Han ("Chinese") newcomers matched for age, body size, and extent of exercise training. During room air breathing, minute ventilation was greater in the Tibetan than in the Han young men because of an increased respiratory frequency, but arterial O2 saturation and end-tidal PCO2 did not differ, indicating similar levels of effective alveolar ventilation. The Tibetan subjects had higher hypoxic ventilatory response shape parameter A values and hypercapnic ventilatory responsiveness than the Han subjects. Among the Han subjects, duration of high-altitude residence correlated with the degree of blunting of the hypoxic ventilatory drive. Paradoxically, hyperoxia (inspired O2 fraction 0.70) increased minute ventilation and decreased end-tidal PCO2 in the Tibetan but not in the Han men. We concluded that lifelong Tibetan residents of high altitude neither hypoventilated nor exhibited blunted hypoxic ventilatory responses compared with acclimatized Han newcomers, suggesting that the effects of lifelong high-altitude residence on ventilation and ventilatory response to hypoxia differ in Tibetan compared with other high-altitude populations.     

Compression pre-cracking to generate near threshold fatigue-crack-growth rates in two aluminum alloys

A test program was conducted to generate threshold and near-threshold data on two aluminum alloys: 2324-T39 and 7075-T7351, using compression pre-cracking constant-amplitude (CPCA) threshold testing procedures. Compact tension specimens were tested under stress ratios (R) of 0.1, 0.4, 0.7 or 0.8. Results were compared with either existing load-reduction data from the literature or with data that were generated using the load-reduction procedures. On the 2324 alloy, very little difference was observed between the load-reduction and CPCA test methods, although the CPCA test method consistently produced slightly lower thresholds or slightly faster crack-growth rates. But on the 2324 alloy, most of the load-reduction tests used extremely low initial ΔK values to grow the cracks under load reduction, which may explain the reason for the agreement. These low ΔK values were achieved by using compression pre-cracking to initiate a crack at the crack-starter notch. In contrast, the 7075 alloy showed very large differences between the CPCA and load-reduction results in the near-threshold and threshold regimes for R=0.1 and 0.4. Results under high R conditions (R=0.7) agreed very well between the two threshold test methods. An expression was also developed to generate fatigue-crack-growth-rate data using the CPCA threshold test method that would be unaffected by compressive yielding at the crack-starter notch and produce ‘steady-state’ constant-amplitude data in the near threshold regime.     

Anion structural effects on interaction of rare earth element ions with Dowex 50W X8 cation exchange resin

The effect of the anion in the original rare earth element(REE) solution on the reversible ion exchange of Ce nitrate and Ce sulfate with the Dowex 50 W X8 was investigated using attenuated total reflection infrared(ATR-IR) spectroscopy, continuous flow reactor studies coupled with inductively coupled plasma mass spectroscopy(ICP-MS), and density functional theory(DFT). The simulated IR spectrum at the DFT B3 LYP/6-31 G(d) level was compared to the experimental results to characterize the IR spectrum, molecular interactions, and bonding of the ion exchanged species. The continuous liquid flow reactor studies show a capacity of 0.72 mmol/g sorbent for the Ce nitrateand 0.96 mmol/g sorbent for the Ce sulfate with the Dowex 50 W X8. The flow reactor studies reveal the type of solute anion(SO_4~((2-)) or NO_3~((-))) associated with the REE during cation exchange significantly affects the sorption capacity of the Dowex 50 W X8 ion exchange resin. The calculated REE binding energy(BE) and the DFT optimized structures suggest that the differences in sorption capacity is the result of the formation of different types of partially ionexchanged Ce_2~((3+))2 SO_4~((2-)) and Ce~((3+)) 3 NO_3~((-)). These results suggest that the solute anion affects the equilibrium constants of the Dowex resin by the formation of a charged layer capable of retaining the counterion. Modifying the sulfonic acid site(H+) in the Dowex 50 W X8 with the NH_4~+ counterion does not affect the sorption capacity and retention times of the Ce nitrate and Ce sulfate species. These results suggest that the counterions and co-ions having a finite size, may limit access to the Dowex sulfonate active site where the type of REE cation as a nitrate or sulfate in solution may significantly modify the sorption capacity of the ion exchange resin. Similar results are obtained during sorption with nitrates and sulfates of Sm and Yb.     

PCL Nanopillars Versus Nanofibers: A Contrast in Progenitor Cell Morphology,Proliferation, and Fate Determination

The role of nanotopography on the long‐term response of progenitor cells is explored using polycaprolactone (PCL) nanopillar and nanofiber surfaces seeded with plastic‐adherent rat multipotent mesenchymal stromal cells (MSCs). After 4 weeks in culture under normal expansion media conditions, MSCs cultured on nanofibers exhibit better adherence, increased proliferation, and maintain increasingly dense fibroblast‐like morphologies. In contrast, MSCs seeded on nanopillar surfaces display lowered adherence, reduced proliferation, and adopt highly elongated cellular morphologies. Immunofluorescent staining of MSCs on PCL nanopillars reveals the presence of two bone marker proteins, osteopontin and osteocalcin, providing evidence for surface induced differentiation into osteoblast‐like cells. Unlike the nanopillar topography, MSCs cultured on nanofiber and smooth PCL surfaces did not appear to undergo osteogenesis. Observed differences in cellular response to the PCL nanotopographies offer strategies to direct progenitor cell populations solely based upon submicron surface modifications. This study provides a foundation for future work exploring variations in PCL nanopillar topography with the goal of optimizing adherence and osteogenic response of MSCs.     

Enhanced performance of counter flow SOFC with partial internal reformation

We study a counter-flow solid oxide fuel cell system and consider the challenges faced in minimizing thermal variations from the nominal operating conditions for a reasonable range of power tracking. Blower dynamics, reformer transport delays, spatial distribution of the heat generated and the resulting thermal response are among the issues considered. A novel approach, relying on partial internal reformation of the feedstock is proposed as a remedy to maintain a strong level of power tracking with minimal thermal stress to the fuel cell.     

Discharge-based QMRA for estimation of public health risks from exposure to stormwater-borne pathogens in recreational waters in the United States

This study is the first to report a quantitative microbial risk assessment (QMRA) on pathogens detected in stormwater discharges-of-concern, rather than relying on pathogen measurements in receiving waters. The pathogen concentrations include seven “Reference Pathogens” identified by the U.S. EPA: Cryptosporidium, Giardia, Salmonella, Norovirus, Rotavirus, Enterovirus, and Adenovirus. Data were collected from 12 sites representative of seven discharge types (including residential, commercial/industrial runoff, agricultural runoff, combined sewer overflows, and forested land), mainly during wet weather conditions during which times human health risks can be substantially elevated. The risks calculated herein therefore generally apply to short-term conditions (during and just after rainfall events) and so the results can be used by water managers to potentially inform the public, even for waters that comply with current criteria (based as they are on a 30-day mean risk). Using an example waterbody and mixed source, pathogen concentrations were used in QMRA models to generate risk profiles for primary and secondary water contact (or inhalation) by adults and children. A number of critical assumptions and considerations around the QMRA analysis are highlighted, particularly the harmonization of the pathogen concentrations measured in discharges during this project with those measured (using different methods) during the published dose–response clinical trials. Norovirus was the most dominant predicted health risk, though further research on its dose–response for illness (cf. infection) is needed. Even if the example mixed-source concentrations of pathogens had been reduced 30 times (by inactivation and mixing), the predicted swimming-associated illness rates – largely driven by Norovirus infections – can still be appreciable. Rotavirus generally induced the second-highest incidence of risk among the tested pathogens while risks for the other Reference Pathogens (Giardia, Cryptosporidium, Adenovirus, Enterovirus and Salmonella) were considerably lower. Secondary contact or inhalation resulted in considerable reductions in risk compared to primary contact. Measurements of Norovirus and careful incorporation of its concentrations into risk models (harmonization) should be a critical consideration for future QMRA efforts. The discharge-based QMRA approach presented herein is particularly relevant to cases where pathogens cannot be reliably detected in receiving waters with detection limits relevant to human health effects.