Radiation heating in selected NERVA engine components

The role of heating from nuclear radiation in design of the NERVA engine is treated. Some components are subjected to very high gamma heating rates in excess of 0.5 Btu/cubic inch/sec in steel in the primary nozzle or 0.25 Btu/cubic inch/sec in aluminum in the pressure vessel. These components must be cooled by a fraction of the liquid hydrogen propellant before it is passed through the core, heated, and expanded out the nozzle as a gas. Other components that are subjected to lower heating rates such as the thrust structure and the disk shield are designed so that they would not require liquid hydrogen cooling. Typical gamma and neutron heating rates, resulting temperatures, and their design consequences are discussed. Calculational techniques used in the nuclear and thermal analyses of the NERVA engine are briefly treated

Prevalence and Use of Fitness Tracking Devices within a College Community

Purpose: Wearable devices for tracking health and fitness related activities are thought to motivate individuals to participate in regular exercise. The purpose of this study was to examine the frequency of these wearable fitness tracking devices in a college setting. Methods: Students, faculty, administration, and staff of Linfield College were asked to complete a survey that examined the types of fitness tracking devices owned, frequency of use, and application of the device. Results: Of 217 participants surveyed (67 males, 150 females), 29.49% own a fitness tracker, with the most common types being a phone app (46.2% of faculty, staff, and administration) and a specific wearable wrist device (44.7% of students). Step count tracking was the most popularly used feature among all participants (86.8% of students and 96.2% of faculty, staff, and administration). 84% of all participants reported that the device encouraged their participation in physical activity. For those not owning a device (70.51% of participants), lack of interest was the most prevalent reason reported against purchasing a device, followed by expense. Conclusion: Our results suggest that a small percentage of individuals across a college community own fitness tracking devices, despite the fact that they are perceived to encourage physical activity

GaAs monolithic frequency doublers with series connected varactor diodes

GaAs monolithic frequency doublers using series connected varactor diodes have been fabricated for the first time. Output powers of 150 mW at 36.9 GHz with 24% efficiency and 300 mW at 24.8 GHz with 18% efficiency have been obtained. Peak efficiencies of 35% at output power levels near 100 mW have been achieved at both frequencies. Both K-band and Ka-band frequency doublers are derived from a lower power, single-diode design by series connection of two diodes and scaling to achieve different power and frequency specifications. Their fabrication was accomplished using the same process sequence

Derivation of Delay Equation Climate Models Using the Mori-Zwanzig Formalism

Models incorporating delay have been frequently used to understand climate variability phenomena, but often the delay is introduced through an ad-hoc physical reasoning, such as the propagation time of waves. In this paper, the Mori-Zwanzig formalism is introduced as a way to systematically derive delay models from systems of partial differential equations and hence provides a better justification for using these delay-type models. The Mori-Zwanzig technique gives a formal rewriting of the system using a projection onto a set of resolved variables, where the rewritten system contains a memory term. The computation of this memory term requires solving the orthogonal dynamics equation, which represents the unresolved dynamics. For nonlinear systems, it is often not possible to obtain an analytical solution to the orthogonal dynamics and an approximate solution needs to be found. Here, we demonstrate the Mori-Zwanzig technique for a two-strip model of the El Nino Southern Oscillation (ENSO) and explore methods to solve the orthogonal dynamics. The resulting nonlinear delay model contains an additional term compared to previously proposed ad-hoc conceptual models. This new term leads to a larger ENSO period, which is closer to that seen in observations.Comment: Submitted to Proceedings of the Royal Society A, 25 pages, 10 figure

Monadic Functional Reactive Programming

Functional Reactive Programming (FRP) is a way to program reactive systems in functional style, eliminating many of the problems that arise from imperative techniques. In this paper, we present an alternative FRP formulation that is based on the notion of a reactive computation: a monadic computation which may require the occurrence of external events to continue. A signal computation is a reactive computation that may also emit values. In contrast to signals in other FRP formulations, signal computations can end, leading to a monadic interface for sequencing signal phases. This interface has several advantages: routing is implicit, sequencing signal phases is easier and more intuitive than when using the switching combinators found in other FRP approaches, and dynamic lists require much less boilerplate code. In other FRP approaches, either the entire FRP expression is re-evaluated on each external stimulus, or impure techniques are used to prevent redundant re-computations. We show how Monadic FRP can be implemented straightforwardly in a purely functional way while preventing redundant re-computations

Interactive manipulation of microparticles in an octagonal sonotweezer

An ultrasonic device for micro-patterning and precision manipulation of micrometre-scale particles is demonstrated. The device is formed using eight piezoelectric transducers shaped into an octagonal cavity. By exciting combinations of transducers simultaneously, with a controlled phase delay between them, different acoustic landscapes can be created, patterning micro-particles into lines, squares, and more complex shapes. When operated with all eight transducers the device can, with appropriate phase control, manipulate the two dimensional acoustic pressure gradient; it thus has the ability to position and translate a single tweezing zone to different locations on a surface in a precise and programmable manner

Spinal Progenitor-Laden Bridges Support Earlier Axon Regeneration Following Spinal Cord Injury.

Impact statementSpinal cord injury (SCI) results in loss of tissue innervation below the injury. Spinal progenitors have a greater ability to repair the damage and can be injected into the injury, but their regenerative potential is hampered by their poor survival after transplantation. Biomaterials can create a cell delivery platform and generate a more hospitable microenvironment for the progenitors within the injury. In this work, polymeric bridges are used to deliver embryonic spinal progenitors to the injury, resulting in increased progenitor survival and subsequent regeneration and functional recovery, thus demonstrating the importance of combined therapeutic approaches for SCI

The choice agenda in the Australian supported housing context: a timely reflection

The last 30 years has seen significant developments in the Australian housing sector for people with disabilities. Despite much change in the sector, and advancements in disability services, the range of current supported housing options for younger Australian adults with a neurological disability remains vastly under-developed. This is despite a widely accepted and endorsed recognition that, as is the general population, people with all forms of disability have a right to housing of their choice. This paper presents a timely critique of the key actions made by the Australian disability and housing sectors and subsequently proposes a more informed approach to supported housing design and development: one that is based on a comprehensive understanding of consumer housing priorities and preferences, and is conducive to a person’s biopsychosocial health

Functional reactive programming, refactored

Functional Reactive Programming (FRP) has come to mean many things. Yet, scratch the surface of the multitude of realisations, and there is great commonality between them. This paper investigates this commonality, turning it into a mathematically coherent and practical FRP realisation that allows us to express the functionality of many existing FRP systems and beyond by providing a minimal FRP core parameterised on a monad. We give proofs for our theoretical claims and we have verified the practical side by benchmarking a set of existing, non-trivial Yampa applications running on top of our new system with very good results