Dynamic modeling of fluid transmission lines of the DSN 70-meter antennas by using a lumped parameter model

Fluid transmission lines and fittings were found to significantly affect the dynamic and steady state operation of the engineering system in which they are incorporated. Therefore, a better understanding of the operation of a system can be obtained by including the performance of the transmission lines and fittings within the system model. The most accurate model of a transmission line or fitting is obtained by using a distributed parameter model. However, a distributed parameter model tends to be very complex. This complexity can be avoided without significant loss of model accuracy by using a lumped parameter model when the length of the fluid path through the transmission line or fitting is short. This article develops a lumped parameter model for short fluid transmission lines and fittings, describes the conditions under which the model is valid, and presents the model parameters associated with the servo hydraulic system of the Deep Space Network (DSN) 70-meter antennas

Dynamic modeling of the servovalves incorporated in the servo hydraulic system of the 70-meter DSN antennas

As the pointing accuracy and service life requirements of the DSN 70 meter antenna increase, it is necessary to gain a more complete understanding of the servo hydraulic system in order to improve system designs to meet the new requirements. A mathematical model is developed for the servovalve incorporated into the hydraulic system of the 70 meter antenna and uses experimental data to verify the validity of the model and to identify the model parameters

Reducing the net torque and flow ripple effects of multiple hydraulic piston motor drives

The torque and flow ripple effects which result when multiple hydraulic motors are used to drive a single motion of a mechanical device can significantly affect the way in which the device performs. This article presents a mathematical model describing the torque and flow ripple effects of a bent-axis hydraulic piston motor. The model is used to show how the ripple magnitude can be reduced when multiple motors are used to drive a motion. A discussion of the hydraulic servo system of the 70-m antennas located with the Deep Space Network is included to demonstrate the application of the concepts presented

Harmful Algal Blooms: Dominance in Lakes and Risk for Cyanotoxin Exposure in Food Crops

Climate change and human activities are promoting the dominance of a photosynthetic family of aquatic bacteria, cyanobacteria. Blooms of cyanobacteria are not only a visual nuisance but can produce a variety of cyanotoxins than can harm the liver, skin, and nervous system of animals and humans. We analyzed lakes in the contiguous United States and found that between 2007 and 2012, the number of lakes that produced measurable quantities of cyanotoxins increased from 33% to 45%. Nitrogen and phosphorus pollution were the main drivers of cyanobacteria blooms and toxin production between these years. Many of these lakes and reservoirs are used for crop irrigation and more frequent and toxic cyanobacteria blooms intensifies the risk of human and animal exposure to cyanotoxins through the consumption of toxic plants. We assessed how three cyanotoxins are distributed between soil, irrigation water, and lettuce plants to evaluate the exposure risk that cyanotoxins in food pose to human health. We found soil to sorb between 12 to 52% of two cyanotoxins from water, which could temporarily prevent the toxins from being taken up by plant roots and deposited into edible tissue. Also, we grew lettuce plants in a greenhouse and irrigated them with cyanotoxins. Cyanotoxins did not affect plant growth, however, we were unable to quantify the concentration of the toxins in the lettuce due to analytical limitations or that the plants were unable to sorb the toxins. Lastly, we analyzed the results from 14 published research studies on cyanotoxins in food irrigated with contaminated water. We found significant relationships between cyanotoxin concentrations in the irrigation water and those measured in plant tissues. Generally, the more cyanotoxins in the irrigation water the more cyanotoxins are measured in plants. The increase in cyanotoxin producing blooms needs to be mitigated to reduce associated health and economic risks. Management and policies should be implemented that not only mitigate the drivers of cyanobacteria and their toxins but also places limits on the acceptable concentrations in irrigation water

Connectionist Modelling of Category Learning

A shortcoming is identified with respect to the ability of exemplar-based connectionist models of category learning to offer accounts of learning about stimuli with variable dimensionality. Models which may simulate these tasks, such as the configural-cue network (Gluck & Bower, 1988b), appear to be unable to accurately simulate certain data well simulated by exemplar-based models such as ALCOVE (Kruschke, 1992). A task in which the advantage of ALCOVE is exemplified is the prediction of human learning rates on the six category structures tested by Shepard, Hovland, and Jenkins (1961). The ability of ALCOVE to simulate the observed order of difficulty depends on its incorporation of selective attention processes (Nosofsky, Gluck, Palmeri, McKinley, & Glauthier, 1994). This thesis focuses on developing configural-cue network models which incorporate these processes. Informed by an information-theoretic approach to modelling the implementation of selective attention using a configural-cue representation, five connectionist models are developed. Each is capable of predicting the order of difficulty reported by Shepard et al. (1961). Two models employ a modular structure, but analysis suggests that these may lack much of the functionality of the basic configural-cue network. The remaining three incorporate dimensional attention schemes. These models appear to offer superior generalisability in relation to the simulation of learning about variable dimensionality stimuli. This generalisability is examined by applying a variant of one of these dimensional attention models, to data collected by Kruschke (1996a) on the inverse base-rate effect and base-rate neglect. The model provides a qualitative fit to this data. The success of these configural-cue models on these two tasks, only successfully modelled previously using two distinct types of representation, indicates that the approach has some potential for further applications. Differences between the models applied, however, indicates that more sophisticated conceptions of the attention process may be required to allow further generalisability.

Interagency telemetry arraying for Voyager-Neptune encounter

The reception capability of the Deep Space Network (DSN) has been improved over the years by increasing both the size and number of antennas at each complex to meet spacecraft-support requirements. However, even more aperture was required for the final planetary encounters of the Voyager 2 spacecraft. This need was met by arraying one radio astronomy observatory with the DSN complex in the United States and another with the complex in Australia. Following a review of augmentation for the Uranus encounter, both the preparation at the National Radio Astronomy (NRAO) Very Large Array (VLA) and the Neptune encounter results for the Parkes-Canberra and VLA-Goldstone arrays are presented

Aspen mortality summit, December 18 and 19, 2006, Salt Lake City, Utah

The USDA Forest Service Rocky Mountain Research Station sponsored an aspen sum- mit meeting in Salt Lake City, Utah, on December 18 and19, 2006, to discuss the rapidly increasing mortality of aspen (Populus tremuloides) throughout the western United States. Selected scientists, university faculty, and managers from Federal, State, and non-profit agencies with experience working with aspen were invited. Participants were first asked to share information on recent aspen mortality. Subject matter working groups were then asked to determine factors associated with recent aspen mortality, recommend research needs, and organize those needs into testable questions and hypotheses. This report documents their findings, and will serve as a platform for Resource Managers to address the Sudden Aspen Decline issue