Does the scatterometer see wind speed or friction velocity?

Studies of radar backscatter from the sea surface are referred either to the wind speed, U, or friction velocity, u(sub *). Bragg scattering theory suggests that these variations in backscatter are directly related to the height of the capillary-gravity waves modulated by the larger waves in tilt and by straining of the short wave field. The question then arises as to what characteristic of the wind field is most probably correlated with the wave number spectrum of the capillary-gravity waves. The justification for selecting U as the appropriate meteorological parameter to be associated with backscatter from L-band to Ku-band are reviewed. Both theoretical reasons and experimental evidence are used to demonstrate that the dominant parameter is U/C(lambda) where U is the wind speed at a height of about lambda/2 for waves having a phase speed of C(lambda)

Preliminary design of a Primary Loop Pump Assembly (PLPA), using electromagnetic pumps

A preliminary design study of flight-type dc conduction-permanent magnetic, ac helical induction, and ac linear induction pumps for circulating 883 K (1130 F) NaK at 9.1 kg/sec (20 lb/sec) is described. Various electromagnetic pump geometrics are evaluated against hydraulic performance, and the effects of multiple windings and numbers of pumps per assembly on overall reliability were determined. The methods used in the electrical-hydraulic, stress, and thermal analysis are discussed, and the high temperature electrical materials selected for the application are listed

Scaling of Inertial Delays in Terrestrial Mammals

As part of its response to a perturbation, an animal often needs to reposition its body. Inertia acts to oppose the corrective motion, delaying the completion of the movement—we refer to this elapsed time as inertial delay. As animal size increases, muscle moment arms also increase, but muscles are proportionally weaker, and limb inertia is proportionally larger. Consequently, the scaling of inertial delays is complex. Our intent is to determine how quickly different sized animals can produce corrective movements when their muscles act at their force capacity, relative to the time within which those movements need to be performed. Here, we quantify inertial delay using two biomechanical models representing common scenarios in animal locomotion: a distributed mass pendulum approximating swing limb repositioning (swing task), and an inverted pendulum approximating whole body posture recovery (posture task). We parameterized the anatomical, muscular, and inertial properties of these models using literature scaling relationships, then determined inertial delay for each task across a large range of movement magnitudes and the full range of terrestrial mammal sizes. We found that inertial delays scaled with an average of M0.28 in the swing task and M0.35 in the posture task across movement magnitudes—larger animals require more absolute time to perform the same movement as small animals. The time available to complete a movement also increases with animal size, but less steeply. Consequently, inertial delays comprise a greater fraction of swing duration and other characteristic movement times in larger animals. We also compared inertial delays to the other component delays within the stimulus-response pathway. As movement magnitude increased, inertial delays exceeded these sensorimotor delays, and this occurred for smaller movements in larger animals. Inertial delays appear to be a challenge for motor control, particularly for bigger movements in larger animals

Using Asymmetry to Your Advantage: Learning to Acquire and Accept External Assistance During Prolonged Split-belt Walking

People can learn to exploit external assistance during walking to reduce energetic cost. For example, walking on a split-belt treadmill affords the opportunity for people to redistribute the mechanical work performed by the legs to gain assistance from the difference in belts’ speed and reduce energetic cost. Though we know what people should do to acquire this assistance, this strategy is not observed during typical adaptation studies. We hypothesized that extending the time allotted for adaptation would result in participants adopting asymmetric step lengths to increase the assistance they can acquire from the treadmill. Here, participants walked on a split-belt treadmill for 45 min while we measured spatiotemporal gait variables, metabolic cost, and mechanical work. We show that when people are given sufficient time to adapt, they naturally learn to step further forward on the fast belt, acquire positive mechanical work from the treadmill, and reduce the positive work performed by the legs. We also show that spatiotemporal adaptation and energy optimization operate over different timescales: people continue to reduce energetic cost even after spatiotemporal changes have plateaued. Our findings support the idea that walking with symmetric step lengths, which is traditionally thought of as the endpoint of adaptation, is only a point in the process by which people learn to take advantage of the assistance provided by the treadmill. These results provide further evidence that reducing energetic cost is central in shaping adaptive locomotion, but this process occurs over more extended timescales than those used in typical studies

"Body-In-The-Loop": Optimizing Device Parameters Using Measures of Instantaneous Energetic Cost

This paper demonstrates methods for the online optimization of assistive robotic devices such as powered prostheses, orthoses and exoskeletons. Our algorithms estimate the value of a physiological objective in real-time (with a body “in-the-loop”) and use this information to identify optimal device parameters. To handle sensor data that are noisy and dynamically delayed, we rely on a combination of dynamic estimation and response surface identification. We evaluated three algorithms (Steady-State Cost Mapping, Instantaneous Cost Mapping, and Instantaneous Cost Gradient Search) with eight healthy human subjects. Steady-State Cost Mapping is an established technique that fits a cubic polynomial to averages of steady-state measures at different parameter settings. The optimal parameter value is determined from the polynomial fit. Using a continuous sweep over a range of parameters and taking into account measurement dynamics, Instantaneous Cost Mapping identifies a cubic polynomial more quickly. Instantaneous Cost Gradient Search uses a similar technique to iteratively approach the optimal parameter value using estimates of the local gradient. To evaluate these methods in a simple and repeatable way, we prescribed step frequency via a metronome and optimized this frequency to minimize metabolic energetic cost. This use of step frequency allows a comparison of our results to established techniques and enables others to replicate our methods. Our results show that all three methods achieve similar accuracy in estimating optimal step frequency. For all methods, the average error between the predicted minima and the subjects’ preferred step frequencies was less than 1% with a standard deviation between 4% and 5%. Using Instantaneous Cost Mapping, we were able to reduce subject walking-time from over an hour to less than 10 minutes. While, for a single parameter, the Instantaneous Cost Gradient Search is not much faster than Steady-State Cost Mapping, the Instantaneous Cost Gradient Search extends favorably to multi-dimensional parameter spaces

Conflict and comedy. Insults, threats, and slapstick in the plays of Aristophanes

This thesis examines the form and function of insults, threats, and aggressive slapstick in the comedies of Aristophanes. It seeks to fill a gap in our understanding of Aristophanes’ dramatic technique by considering how conflict between characters serves as a vehicle for humour. I begin with a discussion of three different approaches to mimetic conflict. The first considers Aristotle’s ideas on pity, the second looks at Bakhtin’s theory of grotesque realism, the third compares slapstick and visual gags from early silent cinema. My own approach is based on an analysis of Aristophanic language and staging. The body of the thesis is divided into three chapters, one dedicated to each of the conflict elements under investigation (insults, threats, slapstick). Technical discussions are combined with broader analyses of how conflict is integrated into the narratives of Aristophanes’ plays and exploited for laughs. The chapter on insults includes a discussion of verbal abuse in situations of conflict, four case studies (Acharnians, Frogs, Peace, Clouds), and a glossary of Aristophanic insults. The chapter on threats looks at how these generate humour when they elicit unexpected reactions, or when characters make threats that are incommensurate with their situation. A formal analysis concludes the chapter, revealing differences between comic and tragic threat constructions. The chapter on slapstick considers Aristophanes’ parabatic comments regarding visual humour, the role of aggressive choruses, and instances of physical contact between individual characters. It transpires that lasting and significant harm is never the outcome of physical attacks in Aristophanes. Gratuitous slapstick is also generally avoided; attacks are, rather, integrated into the story or employed in conjunction with puns and other jokes

Health Information Technology in the United States: The Information Base for Progress

Health information technology (HIT) has the potential to advance health care quality by helping patients with acute and chronic conditions receive recommended care, diminishing disparities in treatment and reducing medical errors. Nevertheless, HIT dissemination has not occurred rapidly, due in part to the high costs of electronic health record (EHR) systems for providers of care—including the upfront capital investment, ongoing maintenance and short-term productivity loss. Also, many observers are concerned that, if HIT follows patterns observed with other new medical technologies, HIT and EHRs may diffuse in ways that systematically disadvantage vulnerable patient populations, thus increasing or maintaining existing disparities in access to and quality of care. These and other concerns have led to public and private efforts that aim to increase the pace of and reduce disparities in HIT diffusion by formulating national plans for dissemination, catalyzing the development of standards to encourage interoperability and promoting public-private partnerships to develop HIT infrastructures at the local and regional levels

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SUMMARY We isolated step-to-step transitions from other contributors to walking mechanics using a cyclical rocking task and then examined the contribution of individual joints to the total work required to redirect the velocity of the center of mass (COM). Nine participants were instructed to rock backward and forward in the sagittal plane, eliminating the need to swing the legs and progress forward. To systematically increase the required work, we increased step length from 60 to 100% of leg length, keeping rocking frequency constant. The individual limbs method quantified the COM work and the joint power method apportioned the COM work among its various sources. As predicted by a physics-based model, we found that work in rocking was performed mainly during the step-to-step transitions and increased strongly with step length. We also found that increases in the average COM work rate exacted a proportional metabolic cost. The similar patterns of COM work and COM work rate during rocking and walking support the use of rocking to isolate the mechanics of step-to-step transitions. We found that the ankle was the main joint contributing to the positive work required to redirect the COM velocity during forward rocking. At the longest length, it accounted for 88% of the work performed by the trailing leg joints. Interestingly, the summed contribution of ankle, knee and hip joint work accounted for only 39% of the front leg negative COM work during the forward transition, suggesting that most of the collision work is performed by passive tissue