Investigating Dielectric and Metamaterial Effects in a Terahertz Traveling-Wave Tube Amplifier

Adding material enhancements to a terahertz traveling-wave tube amplifier is investigated. Isotropic dielectrics, negative-index metamaterials, and anisotropic crystals are simulated, and plans to increase the efficiency of the device are discussed. Early results indicate that adding dielectric to the curved sections of the serpentine-shaped slow-wave circuit produce optimal changes in the cold-test characteristics of the device and a minimal drop in operating frequency. Additional results suggest that materials with simultaneously small relative permittivities and electrical conductivities are best suited for increasing the efficiency of the device. More research is required on the subject, and recommendations are given to determine the direction

Socioeconomic indicators of heat-related health risk supplemented with remotely sensed data

<p>Abstract</p> <p>Background</p> <p>Extreme heat events are the number one cause of weather-related fatalities in the United States. The current system of alert for extreme heat events does not take into account intra-urban spatial variation in risk. The purpose of this study is to evaluate a potential method to improve spatial delineation of risk from extreme heat events in urban environments by integrating sociodemographic risk factors with estimates of land surface temperature derived from thermal remote sensing data.</p> <p>Results</p> <p>Comparison of logistic regression models indicates that supplementing known sociodemographic risk factors with remote sensing estimates of land surface temperature improves the delineation of intra-urban variations in risk from extreme heat events.</p> <p>Conclusion</p> <p>Thermal remote sensing data can be utilized to improve understanding of intra-urban variations in risk from extreme heat. The refinement of current risk assessment systems could increase the likelihood of survival during extreme heat events and assist emergency personnel in the delivery of vital resources during such disasters.</p

Investigating Holey Metamaterial Effects in Terahertz Traveling-Wave Tube Amplifier

Applying subwavelength holes to a novel traveling-wave tube amplifier is investigated. Plans to increase the on-axis impedance are discussed as well as optimization schemes to achieve this goal. Results suggest that an array of holes alone cannot significantly change the on-axis electric field in the vicinity of the electron beam. However, models of a beam tunnel with corrugated walls show promise in maximizing the amplifier s on-axis impedance. Additional work is required on the subject, and suggestions are made to determine research directions

Using COMSOL Multiphysics Software to Model Anisotropic Dielectric and Metamaterial Effects in Folded-Waveguide Traveling-Wave Tube Slow-Wave Circuits

The electromagnetic effects of conventional dielectrics, anisotropic dielectrics, and metamaterials were modeled in a terahertz-frequency folded-waveguide slow-wave circuit. Results of attempts to utilize these materials to increase efficiency are presented

Method of modeling the socio-spatial dynamics of extreme urban heat events

A method of coupling surface urban heat island measures with socio-economic indicators of vulnerability to create improved spatially specific models to assist public health professionals in predicting extreme heat events mortality in urban environments. The method includes utilizing landsat TM imagery for the measuring of the urban heat island intensity levels and a spatial analysis of the variables in question

Considerations for Improving the Capacity and Performance of AeroMACS

The Aeronautical Mobile Airport Communications System (AeroMACS) has progressed from concept through prototype development, testing, and standards development and is now poised for the first operational deployments at nine US airports by the Federal Aviation Administration. These initial deployments will support fixed applications. Mobile applications providing connectivity to and from aircraft and ground-based vehicles on the airport surface will occur at some point in the future. Given that many fixed applications are possible for AeroMACS, it is necessary to now consider whether the existing capacity of AeroMACS will be reached even before the mobile applications are ready to be added, since AeroMACS is constrained by both available bandwidth and transmit power limitations. This paper describes some concepts that may be applied to improve the future capacity of AeroMACS, with a particular emphasis on gains that can be derived from the addition of IEEE 802.16j multihop relays to the AeroMACS standard, where a significant analysis effort has been undertaken

Bayes linear kinematics in the analysis of failure rates and failure time distributions

Collections of related Poisson or binomial counts arise, for example, from a number of different failures in similar machines or neighbouring time periods. A conventional Bayesian analysis requires a rather indirect prior specification and intensive numerical methods for posterior evaluations. An alternative approach using Bayes linear kinematics in which simple conjugate specifications for individual counts are linked through a Bayes linear belief structure is presented. Intensive numerical methods are not required. The use of transformations of the binomial and Poisson parameters is proposed. The approach is illustrated in two examples, one involving a Poisson count of failures, the other involving a binomial count in an analysis of failure times

Using the Framingham Risk Score to Evaluate Immigrant Effect on Cardiovascular Disease Risk in Mexican Americans

Background—This study uses the Framingham Risk Score (FRS) for 10-year cardiovascular disease (CVD) to evaluate differences between Mexican American immigrants and the U.S.-born population. Methods and Results—Data from the Cameron County Hispanic Cohort (N=1,559). Average total risk scores were generated by age group for each gender. Regression analysis was conducted adjusting for covariates and interaction effects. Both women and men in the CCHC sample who were long-term immigrant residents (mean FRS scores women 4.2 with p\u3c.001 vs. men 4.0 with p\u3c.001) or born in the U.S. (mean FRS scores women 4.6 with p\u3c.001 vs. men 3.3 with p\u3c.001) had significantly higher risk scores than immigrants who had only been in this country for less than 10 years. The interaction model indicates that differences between immigrant and native-born Mexican Americans are most greatly felt at lowest levels of socioeconomic status for men in the CCHC. Conclusions—This study suggests that in terms of immigrant advantage in CVD risk, on whom, where, and how the comparisons are being made have important implications for the degree of difference observed

Nonsteroidal Anti-Inflammatory Drugs Are an Important Cause of Acute Kidney Injury in Children

Objective To characterize nonsteroidal anti-inflammatory drug (NSAID)-associated acute kidney injury (AKI) in children. Study design We conducted a retrospective chart review of children diagnosed with AKI through the use of International Classification of Diseases, Ninth Revision diagnosis code 584.5 or 584.9 from January 1999 to June 2010. Medical records were reviewed to confirm the diagnosis of AKI and to quantify NSAID administration. Pediatric RIFLE criteria were used to codify AKI. Patients were not classified as having NSAID-associated AKI if they had a diagnosis explaining AKI or comorbid clinical conditions predisposing to AKI development. Results Patients (N = 1015) were identified through International Classification of Diseases, Ninth Revision screening. Twenty-one children had clinical, laboratory, and radiographic studies suggesting NSAID-associated acute tubular necrosis and 6 had findings suggesting NSAID-associated acute interstitial nephritis, representing 2.7% (27 of 1015) of the total cohort with AKI and 6.6% when excluding complex patients with multifactorial AKI. Children with NSAID-associated AKI had a median (range) age of 14.7 years (0.5-17.7 years); 4 patients (15%) were (75%) for whom dosing data were available received NSAIDs within recommended dosing limits. Patients (100% vs 0%, P \u3c .001), intensive care unit admission (75% vs 9%, P = .013), and a longer length of stay (median 10 vs 7 days, P = .037). Conclusions NSAID-associated AKI accounted for 2.7% of AKI in this pediatric population. AKI typically occurred after the administration of correctly dosed NSAIDs. Young children with NSAID-associated AKI may have increased disease severity

Interface stoichiometry control to improve device voltage and modify band alignment in ZnO/Cu_2O heterojunction solar cells

The interface stoichiometry of cuprous oxide (Cu_2O) was controlled by adjusting the O_2 and Zn partial pressures during ZnO sputter deposition and measured by high-resolution X-ray photoelectron spectroscopy of ultrathin (<3 nm) ZnO films on Cu_2O. Open-circuit voltage measurements for ZnO/Cu_2O heterojunctions under AM1.5 illumination were measured and it was found that a stoichiometric interface can achieve the voltage entitlement dictated by the band alignment, whereas the non-stoichiometric interface showed large open-circuit voltage deficits. These results highlight not only the need for stoichiometric interfaces in Cu_2O devices, but also a reproducible experimental method for achieving stoichiometric interfaces that could be applied to any potential heterojunction partner. Additionally, valence-band offset measurements indicated changing the interface stoichiometry shifted the band alignment between Cu_2O and ZnO, which accounts for the variation in previously reported band offset values