Discharge characteristics of dielectric materials examined in mono-, dual-, and spectral energy electron charging environments

The effects of midenergy electrons on the charge and discharge characteristics of spacecraft dielectric materials and the data base from which basic discharge models can be formulated is expanded. Thin dielectric materials were exposed to low, mid combined low and mid, and spectral energy electron environments. Three important results are presented: (1) it determined electron environments that lead to dielectric discharges at potentials less negative than -5 kV; (2) two types of discharges were identified that dominate the kinds of discharges seen; and (3) it is shown that, for the thin dielectric materials tested, the worst-case discharges observed in the various environments are similar

Dynamic Inversion and Backstepping Controller Robustness Analysis for a Reusable Launch Vehicle

The Air Force has been working towards developing technology for operationally responsive space (ORS), which is the ability to launch military assets into space without the long set up time currently required. Part of the solution to ORS is to develop a reusable booster vehicle capable of sending any vehicle into orbit, then descending back to the atmosphere and landing unpowered so that it may take another vehicle into orbit with a 48 hour turnaround time. Currently classical gain tuning techniques are used to design a controller for a specific mission, which may hinder the vehicle’s ability to perform multiple missions if gains have to be re-tuned. Advanced nonlinear control methods like dynamic inversion and backstepping may eliminate the need to use classical gain tuning techniques that may increase quick turnaround time, reliability, and performance. Both methods consider the dynamics of the vehicle allowing the controller to be applied to the whole flight envelope. However, they are model-based methods that require knowledge of plant aerodynamics. The objective was to develop a backstepping outer loop and dynamic inversion inner loop controller for a reusable launch vehicle configuration and evaluate its robustness characteristics by inserting aerodynamic uncertainties into the static and control surface aerodynamic data separately and together. Both dynamic inversion and backstepping were susceptible to control surface aerodynamic uncertainties more than static aerodynamics. The benefit of using dynamic inversion and backstepping was that it was formulated so that it decouples the system of equations as long as the dynamics were modeled accurately. The control variable became a bank of decoupled integrators. However, when uncertainties were introduced into the plant model, the controller was unable to accurately model the dynamics, which re-introduced axes coupling inherent in the plant. The coupling caused performance in one axis to degrade if another axis degraded

An assessment and application of turbulence models for hypersonic flows

The current approach to the Accurate Computation of Complex high-speed flows is to solve the Reynolds averaged Navier-Stokes equations using finite difference methods. An integral part of this approach consists of development and applications of mathematical turbulence models which are necessary in predicting the aerothermodynamic loads on the vehicle and the performance of the propulsion plant. Computations of several high speed turbulent flows using various turbulence models are described and the models are evaluated by comparing computations with the results of experimental measurements. The cases investigated include flows over insulated and cooled flat plates with Mach numbers ranging from 2 to 8 and wall temperature ratios ranging from 0.2 to 1.0. The turbulence models investigated include zero-equation, two-equation, and Reynolds-stress transport models

Integrating Students into Interdisciplinary Health and Health Disparities Research Teams

Major initiatives by the U.S. Department of Health and Human Services as well as the World Health Organization have produced a large and compelling body of evidence on how to reduce health disparities, which entails having a clear understanding of how social factors shape health and healthcare outcomes. Specifically, there is a need for healthcare professionals to understand social determinants of health (e.g., low socioeconomic status, lack of health insurance, and poor education) and how these lead to disparities in health for people of minority racial and ethnic groups. Little is known about how students are developed as health disparities researchers or how their research experiences impact their views about addressing social determinants of health as a career goal. The purpose of this paper is to describe how health and human sciences students were integrated into three minority HIV prevention and testing projects using the lifelong learning for health professionals (LLHP) principles and activities framework, which entails a focus on: (a) education, (b) community, and (c) organization in the planning, development, implementation, and evaluation of interdisciplinary research

How profitable are FX technical trading rules?

This paper provides a comprehensive empirical investigation of the profitability of foreign exchange technical trading rules over the 1996:10?2015:06 period for 22 currencies quoted in US dollars. It reports evidence of profitability across a universe of 113,148 rules that include traditional moving average rules and those constructed on the basis of technical indicators such as Bollinger bands and the relative strength index. The best trading rules achieve annualised returns of up to 30%. The Step-SPA test (Hsu, Hsu, & Kuan, 2010) results show a sharp fall in the total number of rules that are robust to data snooping bias. Virtually no traditional rule is significant in the 2006?2015 sub-sample, in line with the adaptive markets hypothesis. By contrast, rules based on new technical indicator such as Bollinger Band and relative strength index rules remain robustly profitable across all currencies over the more recent sub-sample

Exploring Child Welfare Workers\u27 Attitudes and Practice With Fathers

This cross-sectional study explored child welfare agency workers\u27 attitudes and practice regarding working with fathers whose children are at-risk for abuse and neglect. Agency workers completed a questionnaire about their attitudes towards working with fathers, their knowledge of barriers to fathers\u27 engagement, and their experiences with their own fathers. They also completed open-ended items about services and supports they felt would be most helpful to fathers. A content analysis of the data revealed critical themes for four areas that workers felt could be enhanced to effectively engage fathers: (a) use diligent efforts that ensure fathers are present to contribute, (b) provide equitable services, supports, and policies for fathers, (c) address father-specific needs, and (d) promote a positive worker-father relationship. The findings provide insight into ways that social workers can maximize fathers\u27 strengths and reduce their challenges

Host parasite communications—Messages from helminths for the immune system:Parasite communication and cell-cell interactions

Helminths are metazoan organisms many of which have evolved parasitic life styles dependent on sophisticated manipulation of the host environment. Most notably, they down-regulate host immune responses to ensure their own survival, by exporting a range of immuno-modulatory mediators that interact with host cells and tissues. While a number of secreted immunoregulatory parasite proteins have been defined, new work also points to the release of extracellular vesicles, or exosomes, that interact with and manipulate host gene expression. These recent results are discussed in the overall context of how helminths communicate effectively with the host organism

A method to quantitatively evaluate Hamaker constant using the jump-into-contact effect in Atomic Force microscopy

We find that the jump-into-contact of the cantilever in the atomic force microscope (AFM) is caused by an inherent instability in the motion of the AFM cantilever. The analysis is based on a simple model of the cantilever moving in a nonlinear force field. We show that the jump-into-contact distance can be used to find the interaction of the cantilever tip with the surface. In the specific context of the attractive van der Waals interaction, this method can be realized as a new method of measuring the Hamaker constant for materials. The Hamaker constant is determined from the deflection of the cantilever at the jump-into-contact using the force constant of the cantilever and the tip radius of curvature, all of which can be obtained by measurements. The results have been verified experimentally on a sample of cleaved mica, a sample of Si wafer with natural oxide and a silver film, using a number of cantilevers with different spring constants. We emphasize that the method described here is applicable only to surfaces that have van der Waals interaction as the tip-sample interaction. We also find that the tip to sample separation at the jump-into-contact is simply related to the cantilever deflection at this point, and this provides a method to exactly locate the surface.Comment: 11 pages, 4 figures, 1 tabl