In order to meet the increasing demand for higher data rates, next generation wireless networks must incorporate additional functionalities to enhance network throughput. Multihop networks are considered as a promising alternative due to their ability to exploit spatial reuse and to extend coverage. Recently, industry has shown increased interest in multihop networks as they do not require additional infrastructure and have relatively low deployment costs. Many advances in physical and network layer techniques have been proposed in the recent past and they have been studied mostly in single-hop networks. Very few studies, if any, have tried to quantify the gains that these techniques could provide in multihop networks. We investigate the impact of simple network coding, advanced physical layer and cooperative techniques on the maximum achievable throughput of wireless multihop networks of practical size. We consider the following advanced physical layer techniques: successive interference cancellation, superposition coding, dirty-paper coding, and some of their combinations. We achieve this by formulating several cross-layer frameworks when these techniques are jointly optimized with routing and scheduling. We also formulate power allocation subproblems for the cases of continuous power control and superposition coding. We also provide numerous engineering insights by solving these problems to optimality.

The initial research of this thesis involves the evaluation of different strategies for developing diverse chemistries of highly stable coatings for the automated 96-blade (thin-film) solid phase microextraction (SPME) system. Thin-film geometry increases the volume of extractive phase, and consequently improves the sensitivity of the analysis. Sol-gel technology was used for the preparation of octadecyl (C18)-silica gel thin-film coating. The evaluation of the C18-silica gel SPME extractive phase resulted in stable physical and chemical characteristics and long-term reusability with a high degree of reproducibility. Biocompatible polyacrylonitrile (PAN) polymer was used for the preparation of particle-based extractive phases in order to improve the biocompatible characteristics of SPME coatings for the extraction from biological samples. Three different immobilization strategies were evaluated for developing highly stable coatings for the automated 96-blade SPME system. The spraying was found to be the optimal method in terms of stability and reusability for long-term use. The optimized C18-PAN coating demonstrated improved biocompatibility, stability, and reusability for the extraction of benzodiazepines from human plasma in comparison with those of C18-silica gel coating. To improve the biocompatible properties of the C18-PAN SPME coating for long-term direct analysis from whole blood, different modification strategies were studied and evaluated. The modification of the coating with an extra layer of biocompatible polyacrylonitrile resulted in significant improvement in the blood compatibility in long-term use. ‘Extracted blood spot’ (EBS) sampling was introduced as a novel approach to overcome the limitations of dried blood spot sampling. EBS includes the application of a biocompatible SPME coating for spot sampling of blood or other biofluids. The compatibility of EBS sampling with different analytical methods was demonstrated. The utilization of EBS as a fast sampling and sample preparation method resulted in a significant reduction of matrix effects through efficient sample clean-up. Modified polystyrene-divinylbenzene (PS-DVB)-PAN and phenylboronic acid (PBA)-PAN 96-blade SPME coatings were developed and evaluated for the extraction of analytes in a wide range of polarity. These coatings demonstrated efficient extraction recovery for both polar and non-polar groups of compounds, and presented chemical and mechanical stabilities and reproducible extraction efficiencies for more than 100 usages in biological sample.

Code-Division Multiple-Access (CDMA) is one of the leading digital wireless communication methods currently employed throughout the world. Third generation (3G) and future wireless CDMA systems are required to provide services to a large number of users where each user sends data burst only occasionally. The preferred approach is packet based CDMA so that many users share the same physical channel simultaneously. In CDMA, each user is assigned a pseudo-random (PN) code sequence. PN codephase synchronization between received signals and a locally generated replica by the receiver is one of the fundamental requirements for successful implementation of any CDMA technique. The customary approach is to start each CDMA packet with a synchronization preamble which consists of PN code without data modulation. Packets with preambles impose overheads for communications in CDMA systems especially for short packets such as mouse-clicks or ATM packets of a few hundred bits. Thus, it becomes desirable to perform PN codephase synchronization using the information-bearing signal without a preamble. This work uses a segmented matched filter (SMF) which is capable of acquiring PN codephase in the presence of data modulation. Hence the preamble can be eliminated, reducing the system overhead. Filter segmentation is also shown to increase the tolerance to Doppler shift and local carrier frequency offset. <p>Computer simulations in MATLAB® were carried out to determine various performance measures of the acquisition system. Substantial improvement in probability of correct codephase detection in the presence of multiple-access interference and data modulation is obtained by accumulating matched filter samples over several code cycles prior to making the codephase decision. Correct detection probabilities exceeding 99% are indicated from simulations with 25 co-users and 10 kHz carrier frequency offset or Doppler shift by accumulating five or more PN code cycles, using maximum selection detection criterion. Analysis and simulation also shows that cyclic accumulation can improve packet throughput by 50% and by as much as 100% under conditions of high offered traffic and Doppler shift for both fixed capacity and infinite capacity systems.

A stochastic processing network is a system that takes materials of various kinds as inputs, and uses processing resources to produce other materials as outputs. Such a network provides a powerful abstraction of a wide range of real world, complex systems, including semiconductor wafer fabrication facilities, networks of data switches, and large-scale call centers. Key performance measures of a stochastic processing network include throughput, cycle time, and holding cost. The network performance can dramatically be affected by the choice of operational policies. We propose a family of operational policies called maximum pressure policies. The maximum pressure policies are attractive in that their implementation uses minimal state information of the network. The deployment of a resource (server) is decided based on the queue lengths in its serviceable buffers and the queue lengths in their immediate downstream buffers. In particular, the decision does not use arrival rate information that is often difficult or impossible to estimate reliably. We prove that a maximum pressure policy can maximize throughput for a general class of stochastic processing networks. We also establish an asymptotic optimality of maximum pressure policies for stochastic processing networks with a unique bottleneck. The optimality is in terms of minimizing workload process. A key step in the proof of the asymptotic optimality is to show that the network processes under maximum pressure policies exhibit a state space collapse.

Performance evaluation continues to play an important role in network research. Two types of research efforts related to network performance evaluation are particularly noteworthy: (1) using performance evaluation to understand specific problems and to design better solutions, and (2) designing efficient performance evaluation methodologies. This thesis addresses several performance evaluation challenges, encompassing both categories of effort listed above, in building high-performance TCP-based network services in the context of overlay routing and peer-to-peer systems. With respect to the first type of research effort, this thesis addresses two issues related to the design of TCP-based network services: 1. Prediction of large transfer TCP throughput: Predicting the TCP throughput attainable on given paths is used for applications such as route selection in overlay routing. Based on a systematic measurement study, we evaluate the accuracy of two categories of TCP throughput prediction techniques. We then analyze the factors that affect the accuracy of each. 2. Congestion control and message loss in Gnutella peer-to-peer networks: We evaluate the congestion control mechanisms and message loss behavior in a real-world overlay network, the Gnutella system. The challenges for congestion control in such a network are analyzed, as are the design tradeoffs of alternative mechanisms. In order to study systems such as the above with details of the network, we build a scalable, extensible and portable packet-level simulator of peer-to-peer systems. The second part of the thesis, representing the second type of effort above, proposes two techniques to improve network simulation by exploiting the detailed knowledge of TCP: 1. Speed up network simulation by exploiting TCP steady-state predictability: We develop a technique that uses prediction to accurately summarize a series of packet events and, therefore, to save on processing cost while maintaining fidelity. Our technique integrates well with packet-level simulations and is more faithful in several respects than previous optimization techniques. 2. TCP workload generation under link load constraints: We develop an algorithm that generates traffic for a specific network configuration such that realistic and specific load conditions are obtained on user-specified links. At the same time, the algorithm minimizes the simulation memory requirement.

Biocatalysts offer advantages over their chemical counterparts in terms of their high enantioselectivity and the opportunity to develop more environmentally friendly processes. However, the widespread adoption of biocatalytic processes is hampered by the long development times for enzymes with novel and sufficient activity and adequate stability under operating conditions. Protein engineering, while extremely useful for modifying the properties of protein catalysts in select cases, still cannot be performed rapidly enough for many applications. In order for biocatalysts to become a competitive alternative to chemical catalysts, new tools to make the tailoring of biocatalysts by protein engineering methods speedier and more efficient are necessary. The aim of this work was to develop methods to aid in the faster production of novel biocatalysts. Protein engineering involves two steps: the generation of diversity and the screening or selection of variants with the desired properties. Both of these must be targeted to create a faster protein engineering process. In the case of the former, this work sought to clone and overexpress some template enzymes which would create smaller, more manageable libraries of mutants with a higher likelihood of function by the manipulation of a few focused amino acid residues. For the latter, this work developed and validated a Monte-Carlo simulation model of pooling to increase screening throughput and created a set of vectors to aid in high-throughput screening by eliminating unwanted mutants from the assay procedure entirely.

Segmented polyurethaneureas (SPUU) are thermoplastic elastomers with excellent elastic properties, high abrasion resistance and tear strength, making them very useful in numerous industrial applications ranging from microelectronics (slurry pad) to biomedical (artificial heart vessels) applications. The elastic and mechanical properties of these materials are strongly influenced by their two phase morphology. The factors that influence phase separation include difference in polarity between the hard and soft phases, composition and temperature. In general good phase separation results in materials with superior mechanical and elastic properties. Due to the immense potential applications of SPUU elastomers, there is a need for materials with higher strength. However, higher strength is not desired at the detriment of elasticity. If fact, stronger materials with enhanced elasticity are desired. In this thesis, high-strength SPUU elastomers were synthesized by incorporating reactive Laponite particles with surface-active free amine. The synthesis of pure SPUU is very complex, and addition of a reactive silicate further increases the complexity. To remedy this challenge, combinatorial methods and high-throughput screening techniques were used to optimize the diamine concentration and cure temperature. It was determined that pure SPUU elastomers prepared at a diamine stoichiometry of 85 100 mole %, and cured at 90 95 oC produced materials with higher strength and elongation at break. SPUU nanocomposites were prepared by maintaining the overall diamine stoichiometry at 95 mole %, and cured at 90 oC. Uniaxial tensile strength was optimized at a particle weight fraction of 1 wt. %, with a nearly 200 % increase in tensile strength and a 40 % increase in elongation at break, compared to pristine SPUU.

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Abstract Background: Emergency department (ED) overcrowding has become a significant problem throughout the large medical centers, leading to possible threatened medical quality, causing raised stress levels among staff and patients in EDs, and most importantly, adversely affecting patient outcomes. Due to its complexity, a large concerted group effort will be needed to increase awareness, implement proposed solutions, and make a change. ED overcrowding is a multifaceted problem that will require a multifaceted solution. Methods: We set up the "Input-Throughput-Output" model provides a structure for examining the factors that affect ED access, quality and outcomes. Using this model, we clarify the issues of ED overcrowding into three stages, propose ways to obtain needed information in each stage, test the strategies and then evaluate their outcomes. We utilized the analytic hierarchy process (APH) method to measure the weights of the physician¡¦s stress and arrange more efficacious and flexible duties accordingly. Results: This is a prospective study investigating ED overcrowding at this medical center from January 2008 through December 2009. Hospitals developed and implemented a number of best practices revolved around patient flow initiatives, specifically looking to improve input, throughput, and output. Conclusion: This study suggests that a decrease in ED overcrowding can be achieved through ongoing collaboration of the indicators and the implementation of best practices via the Input-Throughput-Output model.

In this dissertation, we present performance prediction models for rate-based and window¡Vbased flow control mechanisms. For rate-based flow control, such as in ATM network, we derive two analytical models to predict the ACR rates for congestion-free and congestion networks, respectively. To coordinate the cooperative problems of TCP over ATM networks, we propose a new algorithm to monitor the states of ATM switches and adjust TCP congestion window size based on RM cells. For window-based flow control mechanisms, such as in TCP-Reno and TCP-SACK, we respectively present analytical models to systematically capture the characteristics of multiple consecutive packet losses in TCP windows. Through fast retransmission, the lost packets may or may not be recovered. Thus, we present upper bound analyses for slow start and congestion avoidance phases to study the effects of multiple packet losses on TCP performance. Above the proposed upper bounds, the lost packets may not be successfully recovered through fast retransmission. Finally, we develop a model to study the TCP performance in terms of throughput degradation resulted from multiple consecutive packet losses. The analytical results from the throughput degradation model are validated through OPNET simulation.