Noise and distortion limit the channel capacity and degrade the system performance in AM-VSB SCM CATV Distribution Networks. The use of star couplers and fiber amplifiers is an approach to overcome these problems and meet the increasing demand for large capacity and high quality. The capacity and performance analyses of three different network configurations are compared based on the results of computer modeling. In practice, the best configuration depends on the optical amplifiers and the pump lasers used in the system as well as the requirement on the number of channels and the number of subscribers. It is found that in a two-stage star network the largest improvement in the capacity and performance may be achieved when the optical amplifiers between the stages are individually pumped. For example, a capacity of 200 channels and 572 output nodes may be obtained. There is an optimal length of the erbium-doped fiber amplifier (EDFA) and there is also an optimal position where the EDFA is located between the two star couplers. The modeling is based on an extensive analysis of noise and distortion in the system. A discrepancy in the power behavior of laser relative intensity noise (RIN) is pointed out. A previous analysis on reflection-induced noise is extended to include the effect of quadruply-reflected light and optical amplifiers. Since chirp-dispersion distortion and gain tilt distortion are found to be negligible, clipping distortion is the main limitation on the system capacity. Optical amplifier noise provides an additional limitation to the system. Because the gain and amplified spontaneous noise depend on the input signal power and pump power, the gain and spontaneous emission factor are modeled for the comparison of the different systems. / Master of Science

Being held accountable for one's views in an ambiguous situation has been found to increase cognitive processing and reduce possible biases often pervasive in performance appraisals (Tetlock, 1983a). The present study examined the effects of making raters more accountable for their performance ratings through expectations of a supervisory review. Two types of accountability were manipulated. Interpersonal accountability induced subjects to believe that they would receive feedback based on their justifications of their ratings. Reward accountability subjects expected that they would receive a reward based on the quality of their ratings compared to true performance scores. Half of the subjects were also told that the supervisor gave the ratee a negative performance rating. 191 female subjects rated an interviewer's performance after receiving accountability and view manipulations. Results indicated that subjects who received accountability manipulations in conjunction with the view gave more unfavorable ratings and were less accurate on Cronbach's (1955) elevation component of accuracy than no accountability and/or no view groups. Accountable subjects who did not receive the view were expected to increase cognitive processing. These hypotheses pertaining to increases in cognitive complexity and dimensional accuracy were not supported. Although unexpected, interpersonal accountability in conjunction with reward accountability prevented a decrement in processing when given the view. A biased versus unbiased vigilant processing hypothesis was proposed to explain these results. Possible limitations are also proposed as well as implications for future research. / Master of Science

Metal matrix composites have two important interfacial problems between the matrix and the reinforcement which can reduce its desirable mechanical properties. Chemical differences between the matrix and the reinforcement can lead to reactions and deterioration of the reinforcement. Secondly, structural differences between the matrix and the reinforcement lead to bonding conditions which are far from ideal. By using a reinforcement which has a similar chemistry and local atomic structure to that of the matrix, these critical problems can be reduced. A crystalline matrix reinforced with an amorphous form of the matrix is a possible solution to the problem. Composites of amorphous Fe-W alloy particles reinforcing an Fe matrix were produced using mechanical alloying. Bulk samples were produced and their properties were studied. After analyzing the results, the amorphous alloys were determined to be effective strengtheners. However, porosity in the composites led to a reduction of the strengthening imparted by the reinforcement. / Master of Science

With multimedia communication growing in popularity, it has become important to develop techniques that will allow a multimedia application to access multimedia files from local as well as remote sites. This thesis describes the methodology used in the design of the Network Multimedia File System (NMFS) protocol. The protocol provides “transparent access to shared files across networks” much like Sun’s Network File System (NFS) protocol. However, NMFS differs from NFS in that it provides a connection-oriented service that allows the user to specify quality of service (QOS) parameters and reserve resources to achieve the desired QOS. NMFS is an application layer protocol and is intended to work with existing multimedia applications, unaltered, on multiple platforms. NMFS will provide real-time delivery of multimedia data over networks both designed and not designed to carry multimedia traffic. A unique feature of this protocol is that it uses an anticipated delivery schedule (ADS) to guide prefetch of portions of files that are likely to be requested in the future. This prefetched data is stored in a local buffer which reduces the need to transfer the data over the variable latency network when the application actually requests it. Thus NMFS provides most unaltered application programs with almost constant latency accesses over a network with variable latency. / Master of Science

The objective of this project was to investigate two mechanisms that are commonly thought to be responsible for heavy metal resistance in aquatic invertebrates. Data were generated based on comparisons of growth and respiration experiments using instar III and IV Chironomus riparius under the influence of 0.0, 62.5, 125, 250, and 500 ppb zinc. Main comparisons were made between larvae that were cultured in clean water conditions and larvae from cultures that had been exposed to 10 ppb zinc for over a year and a half. Instar III larvae from clean water cultures showed significant reductions in growth and respiration rates when exposed to zinc concentrations of 62.5 ppb and greater; growth and respiration rates were significantly reduced in instar IV larvae at 125 and 62.5 ppb, respectively. Instar IV larvae from zinc cultures demonstrated increased tolerance to the metal while instar III larvae displayed no additional tolerance. To determine if the resistance was an acclimation or population adaptation phenomenon, additional growth and respiration experiments were conducted with F2 progeny of adults from zinc cultures that were reared in clean water. Results suggest that both acclimation and adaptation may be responsible for the increased tolerance to the metal. When growth and respiration data were converted to a caloric basis (calories respired per day and calories allocated as growth per day), non-tolerant individuals decreased the amount of energy assimilated per day and increased the proportion of energy respired vs. energy allocated to growth with increasing zinc concentration. Resistant individuals, as a result of changes in toxicological trends, demonstrated less dramatic versions of the previously described trends. / Master of Science

A new experimental method was developed to measure the hysteresis loss during a fatigue test from the load and stroke signals of a standard servo-hydraulic materials testing system. The method was used to characterize changes in properties and performance induced by long-term cyclic loading. Advantages of the load-stroke hysteresis loop include: (1) the fact that contact with the specimen is not required, (2) the fatigue test is not interrupted for data collection, (3) the measured quantity (the hysteresis loop area) is directly related to the (damage) events that alter material properties and life, and (4) a quantitative measure of damage extent and development is obtained. / Master of Science

Three experiments were conducted using crossbred weanling pigs (n=462) to determine the effect of yeast culture (YC) additions to starter diets containing dried whey or a fiber source on performance and nutrient digestibility. An 18% CP corn-soybean meal basal diet was used in all experiments. In Exp. I (n=192), YC (O or .75%) was used in diets with dried whey (0 or 15%) in two 5-wk trials (1 and 2). In Exp. II (n=174), YC (0 or .75%) was used in diets containing no added fiber, 8% soybean hulls (SH), or 8% peanut hulls (PH) in two 5-wk trials (3 and 4). Fifty-four of the pigs in Trial 4 were continued on test for three additional weeks in a grower phase. In Exp. II (n=96), YC (0 or .75%) was used in diets containing three levels of PH (0, 8, and 16%) in one 6-wk trial. In Exp. II, .05% chromic oxide was added to all six diets, and six grab samples were taken (twice daily every other day) during wk 4 and 6 for determination of the digestibility of DM, N, P, and fibrous components using the indirect method. Pigs in all experiments had ad libitum access to feed and water, and body weight and feed consumption were measured weekly. Results from all experiments showed that there was no overall effect of treatments on ADFI. In Exp. I, there was no significant overall effect of YC on ADG or G:F in either trial. In Trial 2 of Exp. I, whey depressed overall ADG (P < .10) and G:F (P < .005). In the nursery phases of Exp. I, there were no significant dietary treatment effects on ADG. Gain to feed ratios tended to be increased (P < .10) by YC additions, but only in diets which also contained fiber. In the grower phase of Trial 4 (Exp. II), fiber additions depressed ADG (P < .005), whereas YC additions improved ADG (P < .01), particularly in pigs fed diets which also contained SH (P < .05). In Exp. III, pigs fed diets containing YC and 8% PH had an overall ADG similar to controls, whereas pigs fed diets containing YC alone or both YC and 16% PH had a lower overall ADG than control pigs (P < .10). Overall G:F ratios were decreased by PH inclusion (P < .01) and by supplemental YC (P < .05). Apparent digestibilities were not influenced by the inclusion of YC. The addition of PH linearly decreased the digestibilities of DM (P < .001), N (P< .05), NDF (P < .001), and ADF (P < .05), and increased the absorption of P (P < .05). These results suggest that YC additions had no effect on ADG or ADFI, variable effects on G:F, and no effect on digestibilities of DM, N, NDF, or ADF, or the apparent absorption of P. Fiber additions, particularly PH at the 16% level, appear to depress ADG and G:F, and the digestibilities of DM, N, NDF, and ADF, but increase apparent absorption of phosphorus. / Master of Science

Solid phase extraction (SPE) has become a popular sample preparation method for the extraction of analytes from complex matrices. Solid phase extraction overcomes such disadvantages as large solvent usage and waste, large amounts of time spent in sample preparation and labor intensive methods with little hope of automation. In this report, SPEC®⋅ Microcolumns are evaluated for the extraction of Zantac® (ranitidine hydrochloride) from urine for high performance liquid chromatography (HPLC) analysis. SPEC®⋅Microcolumns are rigid disc structures with glass fiber impregnated with silica gel. These microcolumns look like packed-bed SPE cartridges but have the advantages of low void volumes and low bed mass that give clean extracts with the use of small amounts of solvents. An SPE method was developed and evaluated for the recovery of Zantac® from water and spiked urine. Percent recoveries and matrix interferences are reported. The limit of detection and analytical range tor the HPLC method of analysis with ultraviolet detection will be presented. / Master of Science

It is known that transform techniques do not represent an optimal way in which to code a signal in terms of theoretical rate distortion bounds. A signal may be coded more efficiently if side information is included with the signal during transmission. This side information can then be used to reconstruct the image at some later time. In this thesis, the type of transform coding used is Multiple Bases Representation (MBR). This coding scheme is known to perform better than transform coding that uses a single basis. The method of Projection Onto Convex Sets (POCS) is used to reconstruct an approximation to the MBR signal using the side information. Thus, any number of constraints may be used as long as they form closed and convex sets and the side information is a priori knowledge required to implement projections onto the defined closed and convex sets. Several closed and convex sets are examined including the MBR, positivity, sign, zero crossing, minimum increase, and minimum decrease constraints. Constraints that tend to limit energy are not as effective as constraints that introduce energy into the signal especially when the observed image is used as the initialization vector. When a different initialization vector is used, the POCS reconstruction performs considerably better. Two initialization vectors are proposed; the observed signal plus white noise and the observed signal plus a constant. The performance of POCS with initialization by the observed signal plus a constant is superior to that when using the observed signal only. One nonconvex constraint is considered. The Laplacian histogram constraint requires other convex constraints to help ensure convergence of the reconstruction algorithm, but produces good quality images. / Master of Science

Fatigue and electrical degradation including low voltage breakdown of ferroelectric lead zirconate titanate Pb(Zr_xTi₁)O₃ (i.e. PZT) thin films are the major limitations for commercial memory applications of these films. It is noted that the presence of oxygen vacancies and their entrapment at the electrode-ferroelectric interfaces are the sources of the degradation phenomena. Attempts were made in this study to solve these problems: 1) by minimizing oxygen vacancy entrapment at the interfaces by employing RuO₂ electrodes; 2) by lowering the oxygen vacancy concentration in PZT films using donor doping (e.g. La³⁺ at Pb²⁺ site and Nb⁵⁺ at Ti/Zr⁴⁺ site). For this study, PZT thin films were prepared by a sol-gel method and deposited on both Pt/Ti/SiO₂/Si and RuO₂/SiO₂/Si substrates. The microstructure and electrical properties, such as hysteresis properties, fatigue, leakage current, time-dependent dielectric breakdown (TDDB), and retention, were studied with regard to the Zr/Ti ratio, the excess lead, the annealing temperature, the electrode material, and the doping amount. Furthermore, the pyrochlore to perovskite phase transformation of PZT on RuO₂ electrodes was also investigated. It was shown that PZT films (Zr/Ti=50/50) with 10 at.% excess lead annealed at 650°C for 30 min possessed the best electrical properties for ferroelectric memory application. In confirmation with earlier theoretical and experimental results, no polarization loss was observed up to 10¹¹ switching cycles for the PZT films deposited on RuO₂ electrodes. However, the low Schottky barrier at the interfaces between RuO₂ and PZT films resulted in a higher leakage current at a high electric fields. Donor doping of PZT films decreased carrier concentrations in PZT films, and thus, decreased the leakage current to acceptable limits. In addition, it was also noted that the pyrochlore to perovskite phase transformation of PZT on RuO₂ was similar to that of PZT on Pt electrodes. It can be concluded that the combination of RuO₂ electrodes and donor doping produced PZT films with high fatigue endurance and low leakage currents which are suitable for memory applications. / Master of Science