Meteorological factors in Earth-satellite propagation

Using the COMSTAR D/4 28.56 GHz beacon as a source, a differential gain experiment was performed by connecting a 5-meter paraboloidal antenna and a 0.6-meter paraboloidal antenna alternately to the same receiver. Substantial differential gain changes were observed during some, but not all, rain events. A site-diversity experiment was implemented which consists of two 28.56 GHz radiometers separated by 9 km. The look-angle corresponds to that of the D/4 beacon, and data were obtained with one radiometer during several weeks of concurrent beacon operation to verify the system calibration. A theoretical study of the effect of scattering from a nonuniform rain distribution along the path is under way to aid in interpreting the results of this experiment. An improved empirical site diversity-gain model was derived from data in the literature relating to 34 diversity experiments. Work on the experiment control and data acquisition system is continuing with a view toward future experiments

Fast Differentially Private Matrix Factorization

Differentially private collaborative filtering is a challenging task, both in terms of accuracy and speed. We present a simple algorithm that is provably differentially private, while offering good performance, using a novel connection of differential privacy to Bayesian posterior sampling via Stochastic Gradient Langevin Dynamics. Due to its simplicity the algorithm lends itself to efficient implementation. By careful systems design and by exploiting the power law behavior of the data to maximize CPU cache bandwidth we are able to generate 1024 dimensional models at a rate of 8.5 million recommendations per second on a single PC

Prediction of Fatigue Life in 7075-T6 Aluminum from Neural Network Analysis of Acoustic Emission Data

Through the use of an acoustic emission (AE) data acquisition system, a Kohonen self-organizing map, and a back-propagation neural network, AE data from 7075-T6 aluminum specimens were used to classify failure mechanisms and predict the number of fatigue cycles to failure. AE waveforms were captured from 40 notched tensile specimens during the low-cycle fatiguing process. A Kohonen self-organizing map and initial data filters were used to classify the data into two distinct failure mechanisms, plane strain and plane stress fracture, plus a third less prevalent mechanism. These results were employed to construct a back-propagation neural network to predict the number of cycles to failure from the first 250 cycles of AE data. Due to a scarcity of AE data, optimal prediction results were not obtained on all 40 specimens. However, a smaller set of 18 specimens, 9 for training and 9 for testing, produced a worst case prediction error of-13.9%

AutoCPA: Automatic Continuous Profiling and Analysis

Poor data locality is a performance bottleneck in modern applications. The hierarchy of caches exiting in computer processors reduces data access latency from the main memory. However, inefficient cache utilization results in data cache miss overhead. Applications usually make frequent accesses to far away data that neglects the locality in the memory hierarchy. One approach to boost applications’ performance is to reorder structure fields in a manner that efficiently utilizes the cache. To do so, extensive program-wide information is needed to gain insight about the access frequencies and access patterns of data. This thesis introduces AutoCPA, which exploits hardware performance monitoring counters to find optimization opportunities in target applications, and provides insightful guidance for structure reordering. This system is a low-overhead and easy-to-use toolchain that uses a sampling-based approach to collect and analyze memory traces. Moreover, it generates a prioritized set of reordering that can improve cache utilization and locality. The recommendations for the optimal structure layout provided by this tool are obtained from multiple cache analysis algorithms implemented in AutoCPA. Performance results obtained by running AutoCPA on two widely-used applications, Redis and Memcached, illustrate the benefit of the implementation. These results confirm the general performance improvement of applications, with up to 10% instruction per cycle increase in Redis operations and 7.1% cache miss reduction in Memcached

Implementation of recursive algorithms for delay-time estimation using the fast Walsh transform

Use of the fast Walsh transform to resolve noisy signals into Walsh function series to digitally implement maximum-likelihood parameter estimators for real-time use is investigated. Realization of estimators which seek a null in the derivative of the log-likelihood function, instead of direct maximization, results in feedback algorithms which yield considerable savings in computation time and storage. Performance of these feedback delay-estimation algorithms is characterized in terms of mean-squared error (MSE) and response to a delay step by Monte Carlo simulation. The effect of changing the number of points in the transform on the MSE is also investigated. Hard limiting of the estimator input signal is simulated to represent the limited range of an analog-to-digital converter. Initial time estimates indicate that it is indeed feasible to use the algorithms presented to perform delay estimation in real time. The relative merits of implementing estimators with dedicated hardware, software, and/or firmware is also discussed --Abstract, page ii

Universal computer test stand (recommended computer test requirements)

Techniques are considered which would be used to characterize areospace computers with the space shuttle application as end usage. The system level digital problems which have been encountered and documented are surveyed. From the large cross section of tests, an optimum set is recommended that has a high probability of discovering documented system level digital problems within laboratory environments. Defined is a baseline hardware, software system which is required as a laboratory tool to test aerospace computers. Hardware and software baselines and additions necessary to interface the UTE to aerospace computers for test purposes are outlined

Telecommunications media for the delivery of educational programming

The technical characteristics of various telecommunications media are examined for incorporation into educational networks. FM radio, AM radio, and VHF and UHF television are considered along with computer-aided instruction. The application of iteration networks to library systems, and microform technology are discussed. The basic principles of the communications theory are outlined, and the operation of the PLATO 4 random access system is described