A flexible regression model for count data

Poisson regression is a popular tool for modeling count data and is applied in a vast array of applications from the social to the physical sciences and beyond. Real data, however, are often over- or under-dispersed and, thus, not conducive to Poisson regression. We propose a regression model based on the Conway--Maxwell-Poisson (COM-Poisson) distribution to address this problem. The COM-Poisson regression generalizes the well-known Poisson and logistic regression models, and is suitable for fitting count data with a wide range of dispersion levels. With a GLM approach that takes advantage of exponential family properties, we discuss model estimation, inference, diagnostics, and interpretation, and present a test for determining the need for a COM-Poisson regression over a standard Poisson regression. We compare the COM-Poisson to several alternatives and illustrate its advantages and usefulness using three data sets with varying dispersion.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS306 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Generalized dynamic engine simulation techniques for the digital computer

Recently advanced simulation techniques have been developed for the digital computer and used as the basis for development of a generalized dynamic engine simulation computer program, called DYNGEN. This computer program can analyze the steady state and dynamic performance of many kinds of aircraft gas turbine engines. Without changes to the basic program DYNGEN can analyze one- or two-spool turbofan engines. The user must supply appropriate component performance maps and design-point information. Examples are presented to illustrate the capabilities of DYNGEN in the steady state and dynamic modes of operation. The analytical techniques used in DYNGEN are briefly discussed, and its accuracy is compared with a comparable simulation using the hybrid computer. The impact of DYNGEN and similar all-digital programs on future engine simulation philosophy is also discussed

Feasibility study of alpha particle densitometers for measuring planetary atmospheric density Final report, Jul. 1968 - May 1969

Radioactive alpha particle density measuring system for atmospheric analyse

Army/NASA small turboshaft engine digital controls research program

The emphasis of a program to conduct digital controls research for small turboshaft engines is on engine test evaluation of advanced control logic using a flexible microprocessor based digital control system designed specifically for research on advanced control logic. Control software is stored in programmable memory. New control algorithms may be stored in a floppy disk and loaded directly into memory. This feature facilitates comparative evaluation of different advanced control modes. The central processor in the digital control is an Intel 8086 16 bit microprocessor. Control software is programmed in assembly language. Software checkout is accomplished prior to engine test by connecting the digital control to a real time hybrid computer simulation of the engine. The engine currently installed in the facility has a hydromechanical control modified to allow electrohydraulic fuel metering and VG actuation by the digital control. Simulation results are presented which show that the modern control reduces the transient rotor speed droop caused by unanticipated load changes such as cyclic pitch or wind gust transients

Control means for a gas turbine engine

A means is provided for developing a signal representative of the actual compressor casing temperature, a second signal representative of compressor inlet gas temperature, and a third signal representative of compressor speed. Another means is provided for receiving the gas temperature and compressor speed signals and developing a schedule output signal which is a representative of a reference casing temperature at which a predetermined compressor blade stabilized clearance is provided. A means is also provided for comparing the actual compressor casing temperature signal and the reference casing temperature signal and developing a clearance control system representative of the difference. The clearance control signal is coupled to a control valve which controls a flow of air to the compressor casing to control the clearance between the compressor blades and the compressor casing. The clearance control signal can be modified to accommodate transient characteristics. Other embodiments are disclosed

The application of tissue culture methods to the study of the vesicular diseases of animals

The application of tissue cultures in the study of vesicular diseases of animals has been illustrated by reference to pig kidney tissue cultures and the virus of foot-and-mouth disease.Investigation ^ras carried cut on the most suitable method of producing monolayer tissue cultures from pig kidneys by the trypsinisution technique and it was found possible to produce monolayers in suitable quality and quantity. The monolayers were used for titration of the virus of foot-and-mouth disease and study was made of the factors affecting the formation of plaques on the monolayers. It was found that the number, size and shape of the plaques formed were affected by the state of the cells, the nature of the overlay, the conditions of culture incubation arid the strain of virus used. By adherence to a standard techhique and by comparison of titrea obtained from assay of a standard virus on different sets of cultures it was possible to obtain accurate and useful results.Strains of the virus of foot-and-mouth disease, which had been passaged through mice and chick embryos did not multiply or cause eytopathogenic effect in calf and ox kidney monolayers to the same extent as strains passagsci in cattle or in kidney cultures and It was possible to correlate their behaviour with non-infactivity tests in cattle. All strains of the virus tested grew in pig kidney mono¬ layers and caused cytopathogenic effect but gave rise to plaques of varying size and shape. The plaques arising from the different strains were compared and it was found that the relative number of the different plaque sizes varied with the origin of the virus and that the plaque population changed on peerage in different cultures or animals.The adsorption and multiplication of the virus was followed in pig kidney cell euepensions and monolayers, It was found difficult to infect all the cells after 30 minutes absorption with a high input of virus. The latent period was found to be 2.5 - 3 hours for cell suspensions and monolayers and at the end of that time there was a rapid virus increase. The titra of the culture reached a peak of 10(6.7)-10(7.5) pfu/ml at 6 - 8 hours after which it remained constant for a period up to 18 hours and then fell gradually,Virus grown in pig kidney monolayers was inactivated by adsorption on aluminium hydroxide and treatment with 0,03 formalin. The vaccine thus produced protected guinea pigs agniast challenge with liomologous culture virus arid stimulated the production of neutralising antibody. Investigatione were made into the optimum time of virus harvest. It was found that vaccine made from virus harvested 24 - 42 hours after infection of the monolaye -B, when the cytopathogmic effect was complete, gave the best protection to guinea pigs on challenge- The siae of challenge dose which distinguished between different levels of protection,was found to be 104 guinea pig IX^q, and & tentative scheme for a potency teat was put forward baaed on the dilution of vaccine protecting 5* the guinea pigs from generalisation after challenge with 104ITjq of virus.Pig kidney monolayer tissue cultures were also used &3 a means of differential diagnosis of vesicular diseases and for the assay of neutralising antibody.These findings ware discussed in relation to diagnosis, identification and classification of outbreaks of foot-and-mouth disease in the field and to the selection of virus strains for preparation of attenuated and inactivated vaccines. The method of virus titration by the plaque technique was discussed with regard to vaccine production, fundamental virus research, plaque analysis of strains and genetic studies. The importance of virus growth studies and production of high tltre virus stocks was emphasised in relation to virus-cell interactions and in relation to provision of suitable material for biophysical, biochemical and biological investigations on the virus

Design, fabrication and calibration of alpha particle densitometers for measuring planetary atmospheric density

An alpha particle densitometer was developed for possible application to measurement of the atmospheric density-altitude profile on Martian entry. The device uses an Am-241 radioactive-foil source, which emits a distributed energy spectrum, located about 25 to 75 cm from a semiconductor detector. System response - defined as the number of alphas per second reaching the detector with energy above a fixed threshold - is given for Ar and CO2. The altitude profile of density measurement accuracy is given for a pure CO2 atmosphere with 5 mb surface pressure. The entire unit, including dc-dc converters, requires less than 350 milliwatts of power from +28 volts, weighs about 0.85 lb and occupies less than 15 cubic inches volume

Flight of a UV spectrophotometer aboard Galileo 2, the NASA Convair 990 aircraft

An ultraviolet interference-filter spectrophotometer (UVS) fabricated for aircraft-borne use on the DOT Climatic Impact Assessment Program (CIAP) has been successfully tested in a series of flights on the NASA Convair 990, Galileo II. UV flux data and the calculated total ozone above the flight path are reported for several of the flights. Good agreement is obtained with the total ozone as deducted by integration of an ozone sonde vertical profile obtained at Wallops Island, Virginia near the time of a CV-990 underpass. Possible advantages of use of the UVS in the NASA Global Atmospheric Sampling Program are discussed

Analysis of control concepts for gas and shaft-coupled V/STOL aircraft lift fan systems

For lift-fan powered V/STOL aircraft, two unconventional propulsion system types were proposed. The first type uses fans connected by hot gas ducting, and the second type uses fans connected by cross shafting. An analytical study identified the basic steady-state and dynamic characteristics for each type of system. For the gas-coupled system, the control concepts analyzed were variable-area fan turbines and throttling valves in the ducting. For the shaft-coupled system, the control concepts analyzed were variable-pitch fans and variable fan inlet guide vanes. All of these concepts are capable of meeting V/STOL aircraft control moment and transient response requirements when appropriate propulsion controls are used

Propulsion system mathematical model for a lift/cruise fan V/STOL aircraft

A propulsion system mathematical model is documented that allows calculation of internal engine parameters during transient operation. A non-realtime digital computer simulation of the model is presented. It is used to investigate thrust response and modulation requirements as well as the impact of duty cycle on engine life and design criteria. Comparison of simulation results with steady-state cycle deck calculations showed good agreement. The model was developed for a specific 3-fan subsonic V/STOL aircraft application, but it can be adapted for use with any similar lift/cruise V/STOL configuration