Toxic level hypergolic vapor detection sensor development

Development of an electrochemical sensor technology capable of PPB level hypergolic vapor sensing is reported. A portable instrument capable of meeting the design goals is described

Evaluation of present thermal barrier coatings for potential service in electric utility gas turbines

The resistance of present-day thermal barrier coatings to combustion gases found in electric utility turbines was assessed. The plasma sprayed coatings, both duplex and graded types, were primarily zirconia-based, although a calcium silicate was also evaluated. Both atmospheric burner rig tests and high pressure tests (135 psig) showed that several present-day thermal barrier coatings have a high potential for service in gas turbines burning the relatively clean GT No. 2 fuel. However, coating improvements are needed for use in turbines burning lower grade fuel such as residual oil. The duplex ZrO2.8Y2O3/NiCrA1Y coating was ranked highest and selected for near-term field testing, with Ca2SiO4/NiCrA1Y ranked second. Graded coatings show potential for corrosive turbine operating conditions and warrant further development. The coating degradation mechanisms for each coating system subjected to the various environmental conditions are also described

A novel phase focusing mechanism in multipactor discharge

In spite of the mutual repulsion among the space charges, a new phase‐focusing mechanism is discovered whereby the leading edge of the multipactor discharge in an rf circuit grows at the expense of the trailing edge. This effect arises from the different impact energies, and hence different secondary electron yields, experienced by different portions of the discharge. This phase focusing mechanism may shape the steady‐state multipactor discharge in the form of a very tight bunch of electrons. © 1996 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69854/2/PHPAEN-3-5-1481-1.pd

Electron emission: From the Fowler–Nordheim relation to the Child–Langmuir law

Universal voltage‐current characteristics are presented for a planar diode, showing the general transition from the Fowler–Nordheim relation to the Child–Langmuir law. These curves are normalized to the intrinsic scales that are constructed from the Fowler–Nordheim coefficients A, B. They provide an immediate assessment of the importance of the space charge effects, once the gap voltage, gap spacing, and the Fowler–Nordheim coefficients are specified. An example in the parameter regime of vacuum microelectronics is presented.  Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69957/2/PHPAEN-1-6-2082-1.pd

Small-Signal Frequency Response Theory for piecewise-constant two-switched-network dc-to-dc converter systems

Small-Signal Frequency Response Theory is a theory for calculating the output spectrum of ideal dc-to-dc converter systems, i.e. systems with system coefficients piecewise constant in time, for a given spectrum of the signal injected into the control-input, in the small-signal limit. This theory, unlike other methods, can be applied to both resonant and PWM converters, and gives analytic results in closed form for ideal converters. This paper discusses the special case of ideal two-switched-network converter systems in PWM, programmed, and bang-bang operation. For the examples under study, theoretical prediction and experimental results are found to differ by at most 2dB in amplitude and 10 degrees in phase at most frequencies up to three times the switching frequency. Examples are given in this paper for which the theory gives the correct prediction, while other methods fail

Thin film contact resistance with dissimilar materials

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98706/1/JApplPhys_109_124910.pd

Getting active with active video games: A quasi-experimental study

Given the cultural emphasis on academic achievement and environmental constraints to physical activity (PA), active video games (AVGs) may be used to decrease sedentary behavior and increase PA of Hong Kong children. This study explored the potential of a school-based AVG intervention on sedentary time, PA, body composition, and psychosocial factors among children. Eighty-seven children (intervention n = 30) were recruited from one primary school. Classes in Grades 4–6 were allocated to either the intervention group or the control group in a 2:1 ratio. The eight-week intervention involved children playing AVGs in an after-school class twice a week. Participants in the control group continued with their usual activities. Outcome included the change of participants in sedentary time, PA, percentage body fat, body mass index (BMI), and psychosocial variables (enjoyment, self-efficacy and social support), from baseline to eight weeks. No significant group differences were observed in sedentary time (−33.9 min/day, 95% CI −70.8 to 4.8; p = 0.07). The intervention group significantly increased total PA (53.7 counts/min, 95% CI 8.6 to 104.2; p = 0.04) compared with those in the control condition. No differences were found in body composition and psychosocial variables. However, significant treatment effects were found on BMI z score among boys (−0.1, 95% CI −0.2 to 0; p = 0.04). An eight-week school-based AVG intervention delivered during after-school hours was effective in increasing activity levels among Hong Kong children. The treatment effects of AVGs on sedentary behavior and body composition need to be further demonstrated in a more robust study, especially in boys

Steady state multipactor and dependence on material properties

The interaction of multipactor discharge and an rf circuit is analyzed with the use of a simple model, in which the multipactor electrons are in the form of a single sheet that is released from the surface with a monoenergetic velocity. An explicit formula is derived for the saturation level of multipactor current in steady state. This formula is given in terms of the secondary electron yield properties of the multipactoring surfaces and the level of the external rf drive. It is valid when the quality factor QQ of the rf circuit is higher than 10, in which case the space charge effects do not contribute significantly to the saturation level. When it occurs, the steady state multipactor may consume tens of percents of the external rf power that is needed to sustain the gap voltage. Numerical computations determine the accessibility to steady state from the transient buildup. In particular, they suggest various conditions for the multipactor to exhibit in a burst mode or in a steady state mode. The dynamic linkage of the rf circuit and material properties allows the construction of the susceptibility diagram for various materials, within the limitations imposed by the present model. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70121/2/PHPAEN-4-3-863-1.pd

Cognitive bias modification training in adolescents: persistence of training effects

Negative biases in the interpretation of social information are associated with anxious symptoms in adolescents. Previous studies have attempted to modify interpretive biases to alleviate anxious mood responses but the longevity of such training effects has not been established. A cognitive bias modification of interpretations (CBM-I) paradigm was administered to sixty-nine 15–17 year-olds. Participants were either trained to interpret ambiguous social situations positively, or received control training that contained no emotional content. Participants showed significantly weaker endorsement of negative interpretations of novel ambiguous information following positive training than following control. Positive CBM-I training effects on interpretation did not differ between a group tested immediately following training and one tested 24 h later. Results provided no evidence of differential changes in state anxiety as a direct result of CBM-I training. The persistence of training effects of suppressing negative biases for ambiguous social information is encouraging for future work that might use bias-training methods in adolescents as buffers against negative emotional responses