Preliminary system design study for a digital fly-by-wire flight control system for an F-8C aircraft

The design of a fly-by-wire control system having a mission failure probability of less than one millionth failures per flight hour is examined. Emphasis was placed on developing actuator configurations that would improve the system performance, and consideration of the practical aspects of sensor/computer and computer/actuator interface implementation. Five basic configurations were defined as appropriate candidates for the F-8C research aircraft. Options on the basic configurations were included to cover variations in flight sensors, redundancy levels, data transmission techniques, processor input/output methods, and servo actuator arrangements. The study results can be applied to fly by wire systems for transport aircraft in general and the space shuttle

Design of FIR digital filters for pulse shaping and channel equalization using time-domain optimization

Three algorithms are developed for designing finite impulse response digital filters to be used for pulse shaping and channel equalization. The first is the Minimax algorithm which uses linear programming to design a frequency-sampling filter with a pulse shape that approximates the specification in a minimax sense. Design examples are included which accurately approximate a specified impulse response with a maximum error of 0.03 using only six resonators. The second algorithm is an extension of the Minimax algorithm to design preset equalizers for channels with known impulse responses. Both transversal and frequency-sampling equalizer structures are designed to produce a minimax approximation of a specified channel output waveform. Examples of these designs are compared as to the accuracy of the approximation, the resultant intersymbol interference (ISI), and the required transmitted energy. While the transversal designs are slightly more accurate, the frequency-sampling designs using six resonators have smaller ISI and energy values

Modeling methane emissions from US natural gas operations: national gathering station emission factor development and facility/regional-scale top-down to bottom-up reconciliations

2017 Summer.Includes bibliographical references.United States natural gas dry production increased by 47% between 2005 and 2015 due to the widespread use of horizontal drilling and hydraulic fracturing to extract gas from shale and other tight formations. Natural gas production and consumption is projected to continue to increase for the foreseeable future. In 2016, the natural gas supply chain delivered 29% of the energy used in the U.S., and natural gas surpassed coal as the leading electricity generating source for the first time in U.S. history. When combusted, natural gas produces less CO2 per unit energy released compared to coal or petroleum. However, uncombusted methane (the primary component of natural gas) has a global warming potential 30 times higher than CO2 on a 100 year time horizon (including oxidation to CO2, but excluding climate-carbon feedbacks). Therefore, the net greenhouse gas impacts resulting from displacement of coal and petroleum by natural gas depend on the emission rate of uncombusted natural gas. Short term climate benefits resulting from coal substitution, for example, are lost if the net rate of methane (CH4) emission from the natural gas supply chain exceeds 3—4% . Three studies were conducted to quantify CH4 emissions from the natural gas industry. In particular, these studies focused on quantifying emissions from the gathering and processing sector and reconciling emissions estimates developed using top-down (tracer flux and aircraft) vs. bottom-up (on-site component-level) measurement approaches. In the first study, facility-level CH4 emissions measurements were made at 114 natural gas gathering facilities and 16 processing plants in 13 U.S. states during a 20-week field campaign conducted from October 2013 through April 2014. Measurement results were combined with facility counts obtained from state air permit databases and national inventories in a Monte Carlo simulation to estimate CH4 emissions from U.S. natural gas gathering and processing operations. Annual CH4 emissions from normal operations at gathering facilities totaled 1699 Gg (95% CI=1539—1863 Gg), while normal operations at processing plants totaled 505 Gg (95% CI=459—548 Gg). CH4 emissions from abnormal operations at gathering facilities were estimated in a separate Monte Carlo simulation based on field observations and a sub-set of field measurements. These emissions totaled 169 Gg (+426%/-96%). In the second study, coordinated dual-tracer, aircraft-based, and direct component-level measurements were made at midstream natural gas gathering and boosting stations in the Fayetteville shale in Arkansas, USA. On-site component-level measurements were combined with engineering estimates to generate comprehensive facility-level CH4 emission rate estimates ("study on-site estimates (SOE)") comparable to tracer and aircraft measurements. Concurrent measurements at 14 normally-operating facilities showed a strong correlation between tracer and SOE, but indicated that tracer measurements estimated lower emissions (regression of tracer to SOE=0.91 (95% CI=0.83—0.99, R2=0.89). Tracer and SOE 95% confidence intervals overlapped at 11/14 facilities. Contemporaneous measurements at six facilities suggested that aircraft measurements estimated higher emissions than SOE. Aircraft and study on-site estimate 95% confidence intervals overlapped at 3/6 facilities. In the third study, a detailed spatiotemporal inventory model was developed and used to reconcile top down and bottom-up CH4 emission estimates from natural gas infrastructure and other sources in the Fayetteville shale on two consecutive days. On Thursday October 1, 2015 13:00—15:00 CDT top-down aircraft mass balance flights estimated 28.7 (20.1—37.3 Mg/h 95% CI) from the study area, while the bottom-up ground level area estimate predicted 23.9 (20.9—27.3 Mg/h 95% CI). On Friday October 2, 2015 14:30—16:30 CDT top-down estimated 36.7 (21.3—52.1 Mg/h 95% CI), while bottom-up estimated 21.1 (18.4—24.2 Mg/h 95% CI). Production and gathering activities were the largest contributors to modeled CH4 emissions. In contrast to prior studies, comparisons on two consecutive days indicated overlapping confidence intervals between top-down aircraft estimates and bottom-up inventory-driven estimates. Operator participation and extensive activity data proved critical in understanding emissions as observed by aircraft. In particular, the agreement obtained was possible only because bottom-up models included the variability in production maintenance activities, which showed substantially higher emissions during daytime hours when aircraft-based measurements were performed. Results indicated that that poor activity estimates (counts and timing) for large episodic events likely drives divergence in CH4 emission estimates from production basins, and that even more precise activity data would be required to improve agreement between these two approaches

First Record of Freckled Madtom (Noturus nocturnus) in Iowa

This is the first record of freckled madtom in Iowa and is one of the northern most records. On 30 August 1984, five freckled madtoms were collected from the English River, Washington County. The specimens ranged from 46 to 95mm in total length and mean weight of 3.3g. Estimate of standing stock was 0.807 Kg/ha with a density of 44 fish/ha

Standing Stocks of Fish in Some Iowa Streams, with a Comparison of Channelized and Natural Stream Reaches in the Southern Iowa Drift Plain

Comparisons were made of fish populations inhabiting 11 channelized and natural stream reaches in the Southern Iowa Drift Plain and two drainage ditches in the Des Moines Lobe. Fish were sampled with rotenone, identified, enumerated, and weighed. Total densities of fish ranged from 483/ha at Cylinder Creek to 51,941/ha at Walnut Creek. Total standing stocks of fish ranged from 14 kg/ha at a channelized site on the Chariton River to 1,344 kg/ha at an unchannelized site on the same river. Number of fish species ranged from six sampled at Silver Creek to 16 sampled at Jack Creek. Channelized sites contained fewer fish and substantially lower standing stocks of fish than natural reaches; however the number of species sampled was often similar. The abundance of sport fish was significantly higher in the natural stream reaches, particularly channel catfish (lctalurus punctatus), flathead catfish (Pylodictis olivaris), bullhead (I. melas and natalis), and carp (Cyprinus carpio). The Index of Biotic Integrity average was higher at the natural stream reaches (x = 36) than channelized sites (x = 29. 7). The major differences in fish populations were due to habitat quality and diversity found in the natural sites as compared to the homogeneous habitat of channelized reaches. Iowa streams have insufficient protection from the inroads of man

Extraordinary Results In Ordinary Communities: Transforming Towns and Growing People

This Kettering Foundation Study reports on research conducted in a number of small rural communities struggling to deal with persistent problems that threaten their very existence. The report tells the stories of these places: Bakersville, North Carolina; Haven Acres (a neighborhood in Tupelo, Mississippi); Houston, Minnesota; and Colquitt, Georgia. And it tells the story of how citizens in these communities worked together -- one difficult step at a time -- to breathe new life into their struggling communities

Food Habits of Largemouth Bass (Micropterus salmoides) at Big Creek Lake

Food habits of largemouth bass (Micropterus salmoides) were studied at Big Creek Lake, from 1974-76, to determine the utilization of various prey species, temporal food habits, size at which bass became piscivorous, and size of fish-food items in relation to size of bass. Stomach contents from 259 bass were examined and 75 were empty. Entomostraca and insects were important food items of young bass but a transition stage was noted at about 125 mm TL when fish became the prominent food item. Crayfish were important food items early in the spring. Bass fed mostly on 0-age Centrarchids, and particularly bluegill and Notropis sp. Fish provided 29 to 86% of the biomass consumed and 2 to 70% by number. Larger bass (300+ mm) tended to utilize larger but fewer fish-food items while smaller bass (200-299 mm) consumed smaller fish more frequently

Characteristics of Channel Catfish Populations in Streams and Rivers of Iowa with Varying Habitats

From 1983 co 1985, more than 1,000 channel catfish (Icatalurus punctatus) were sampled with rotenone from 50 streams and rivers in Iowa to assess differences in population densities, standing stocks, viral statistics, age and growth, and habitat use Catfish densities ranged from 5 fish/ha in sites on the South Skunk and Upper Iowa Rivers to more than 4,400 fish/ha at a site on the Thompson Fork of the Grand River. Standing stocks ranged from a low of 0.1 kg/ha on a site on the South Skunk River to a high of 467 kg/ha on the East Fork of the Des Moines River. In general, catfish in rivers grew at a slower rate than lake populations (taking about four years to reach 305 mm), but total annual morality was relatively low compared to one published lake population, usually between 20 and 35% for fish age III and older. Larger catfish were usually found in streams of larger watersheds, but headwater streams were important nursery areas for fish less than age III. Mean standing stocks of channel catfish were similar between landforms (P\u3e0.05), but both relative weight (W,) of channel catfish and PSD was higher (