Self-Complementary Structures and Their Application in Grid Amplifiers

An extension to Deschamps’s theorem for a class of 3-terminal bounded structures with one axis of symmetry is presented. For these structures, a simple relationship between the impedance matrix of the odd mode excitation of the original structure and the admittance matrix of the even mode excitation of its complement exists. Using this, a self-complementary grid amplifier is designed and the measured results are presented

Properties of periodic arrays of symmetric complementary structuresand their application to grid amplifiers

Deschamps' theorem for n-terminal complementary structures is reviewed. An extension to Deschamps' theorem for a class of three-terminal bounded structures with one axis of symmetry is presented. It is shown that, for these structures, a simple relationship between the impedances of the odd mode of the original structure and the admittances of the even mode of the complementary structure exists, and that these modes are orthogonal. Using this, a self-complementary grid amplifier is designed and the measured results are presented

Pulsed Film Cooling on a Turbine Blade Leading Edge

Unsteadiness in gas turbine film cooling jets may arise due to inherent unsteadiness of the flow through an engine or may be induced as a means of flow control. The traditional technique used to evaluate the performance of a steady film cooling scheme is demonstrated to be insufficient for use with unsteady film cooling and is modified to account for the cross coupling of the time dependent adiabatic effectiveness and heat transfer coefficient. The addition of a single term to the traditional steady form of the net heat flux reduction equation with time averaged quantities accounts for the unsteady effects. An experimental technique to account for the influence of the new term was devised and used to measure the influence of a pulsating jet on the net heat flux in the leading edge region of a turbine blade. High spatial resolution data was acquired in the near-hole region using infrared thermography coupled with experimental techniques that allowed application of the appropriate thermal boundary conditions immediately adjacent to the film cooling hole. The turbine blade leading edge was simulated by a half cylinder in cross flow with a blunt afterbody. The film cooling geometry consisted of a coolant hole located 21.5° from the leading edge, angled 20° to the surface and 90° from the streamwise direction. Investigated parameters include pulsation frequency, duty cycle, and waveform shape. Separate experiments were conducted in a water channel to provide visualization of the unsteady coolant propagation behavior. Further insight into the flow physics was obtained through computational simulations of the experimental apparatus. The computational results afforded time resolved flow field and net heat flux reduction data unobtainable with the experimental techniques. A technique to predict the performance of an unsteady film cooling scheme through knowledge of only the steady film cooling behavior was developed and demonstrated to be effective

Teaching ESL Students Adverb Position to Develop Rhetorical Emphasis

This paper highlights the importance of teaching ESL students adverb placement to increase rhetorical awareness. Instructors are encouraged to consider designing grammar lessons at early stages in ESL composition for adverbs that focus not only on prescriptive accuracy but also on those that create rhetorical emphasis. As previous researchers have indicated, placing adverbs in unique positions can add emphasis to particular words or phrases such as using an interrupting adverbial modifier or adverbial fronting. This paper provides a review of literature that promotes teaching adverb placement as rhetorical emphasis, which is significant in ESL composition because it can help ESL writers gain native competency, and foster in them rhetorical awareness

A 100-Element MODFET Grid Amplifier

A 100-element quasi-optical amplifier is presented. The active devices are custom-fabricated modulation-doped field-effect transistors (MODFETs). Common-mode oscillations were suppressed using resistors in the input gate leads. The grid has 9 dB of gain at 10.1 GHz. The 3-dB bandwidth is 1.2 GHz. We present a model for the gain of the grid versus frequency and compare measurement with theory

COMPARING MANAGEMENT SYSTEMS FOR BEEF CATTLE BACKGROUNDING: A MULTIDISCIPLINARY APPROACH

Livestock Production/Industries,

Aeolian removal of dust from radiator surfaces on Mars

Simulated radiator surfaces made of arc-textured Cu and Nb-1 percent-Zr and ion beam textured graphite and C-C composite were fabricated and their integrated spectral emittance characterized from 300 to 3000 K. A thin layer of aluminum oxide, basalt, or iron (III) oxide dust was then deposited on them, and they were subjected to low pressure winds in the Martian Surface Wind Tunnel. It was found that dust deposited on simulated radiator surfaces may or may not seriously lower their integrated spectral emittance, depending upon the characteristics of the dust. With Al2O3 there is no appreciable degradation of emittance on a dusted sample, with basaltic dust there is a 10 to 20 percent degradation, and with Fe2O3 a 20 to 40 percent degradation. It was also found that very high winds on dusted highly textured surfaces can result in their abrasion. Degradation in emittance due to abrasion was found to vary with radiator material. Arc-textured Cu and Nb-1 percent Zr was found to be more susceptible to emittance degradation than graphite or C-C composite. The most abrasion occurred at low angles, peaking at the 22.5 deg test samples

Relationship between lightning flash rates and radar observations from Colorado and Australia

Summer 1999.Also issued as Jesse James Ryan's thesis (M.S.) -- Colorado State University, 1999.Includes bibliographical references.Relationships between lightning flash rates and radar observations were examined for two regions; northeastern Colorado and Darwin, Australia. Five case studies from Colorado were analyzed using observational data from: the CSU-CHILL multiparameter radar, the ONERA VHF lightning interferometer, a field change meter and the National Lightning Detection Network. Three case studies from tropical Australia were analyzed using data from: the C-POL BMRC/NCAR multiparameter radar, a field change meter and an Advanced Lightning Detection Finder network. For each case, parameters such as peak echo height (H), storm area (A), and storm volume (V) were computed using different radar reflectivity and temperature thresholds. Storm areas and volumes were computed above the altitude of various temperature thresholds. Cloud echo-top height (Ho) was defined as the peak height using the O dBZ reflectivity threshold. Correlations existed between H, A, and V, and the total lightning flash rate on a majority of the cases and were strongest when higher reflectivity and colder temperature thresholds were used. An increased correlation between H, A, and V, and total flash rate for high reflectivity (> 20 dBZ) thresholds was noted for storms which contained broad areas of stratiform precipitation. Since stronger correlations were found between total flash rate and the product of A and V (AV) than between the total flash rate and H5, this study suggests that significant error can be introduced by assuming that the horizontal scale of a thunderstorm charge generation is comparable to the vertical scale. In addition, we show that AV and H5 at high reflectivities (> 20 dBZ) are both better correlated to total flash rate than H/, a parameter commonly used as a predictor for lightning flash rates in modeling studies. The ratio of intracloud (IC) to cloud-to-ground (CG) lightning was also analyzed for each case. This ratio was subsequently compared to cold cloud thickness (CCTh), defined as the distance between cloud top and the environmental freezing level. The relationships between IC/CG ratio and CCTh were similar to prior research, except for storms with high (> 40) IC/CG ratios.Sponsored by the National Oceanic and Atmospheric Administration under grant NA76GP0370

Degradation of radiator performance on Mars due to dust

An artificial mineral of the approximate elemental composition of Martian soil was manufactured, crushed, and sorted into four different size ranges. Dust particles from three of these size ranges were applied to arc-textured Nb-1 percent Zr and Cu radiator surfaces to assess their effect on radiator performance. Particles larger than 75 microns did not have sufficient adhesive forces to adhere to the samples at angles greater than about 27 deg. Pre-deposited dust layers were largely removed by clear wind velocities greater than 40 m/s, or by dust-laden wind velocities as low as 25 m/s. Smaller dust grains were more difficult to remove. Abrasion was found to be significant only in high velocity winds (89 m/s or greater). Dust-laden winds were found to be more abrasive than clear wind. Initially dusted samples abraded less than initially clear samples in dust laden wind. Smaller dust particles of the simulant proved to be more abrasive than large. This probably indicates that the larger particles were in fact agglomerates

Clustering Revisited: A Spectral Analysis of Microseismic Events

Identifying individual subsurface faults in a larger fault system is important to characterize and understand the relationship between microseismicity and subsurface processes. This information can potentially help drive reservoir management and mitigate the risks of natural or induced seismicity. We have evaluated a method of statistically clustering power spectra from microseismic events associated with an enhanced oil recovery operation in southeast Utah. Specifically, we were able to provide a clear distinction within a set of events originally designated in the time domain as a single cluster and to identify evidence of en echelon faulting. Subtle time-domain differences between events were accentuated in the frequency domain. Power spectra based on the Fourier transform of the time-domain autocorrelation function were used, as this formulation results in statistically independent intensities and is supported by a full body of statistical theory upon which decision frameworks can be developed