Proteins need fold to perform their biological function. Thus, understanding how proteins fold could be the key to understanding life. In the first study, the stability and structure of several !-hairpin peptide variants derived from the C-terminus of the B1 domain of protein G (PGB1) were investigated by a number of experimental and computational techniques. Our analysis shows that the structure and stability of this hairpin can be greatly affected by one or a few simple mutations. For example, removing an unfavorable charge near the N-terminus of the peptide (Glu42 to Gln or Thr) or optimization of the N-terminal charge-charge interactions (Gly41 to Lys) both stabilize the peptide, even in water. Furthermore, a simple replacement of a charged residue in the turn (Asp47 to Ala) changes the !-turn conformation. Our results indicate that the structure and stability of this !?hairpin peptide can be modulated in numerous ways and thus contributes towards a more complete understanding of this important model !-hairpin as well as to the folding and stability of larger peptides and proteins. The second study revealed that PGB1 and its variants can form amyloid fibrils in vitro under certain conditions and these fibrils resemble those from other proteins that have been implicated in diseases. To gain a further understanding of molecular mechanism of PGB1 amyloid formation, we designed a set of variants with mutations that change the local secondary structure propensity in PGB1, but have similar global conformational stability. The kinetics of amyloid formation of all these variants have been studied and compared. Our results show that different locations of even a single mutation can have a dramatic effect on PGB1 amyloid formation, which is in sharp contrast with a previous report. Our results also suggest that the "-helix in PGB1 plays an important role in the amyloid formation process of PGB1. In the final study, we investigate the forces that contribute to protein stability in a very general manner. Based on what we have learned about the major forces that contribute to the stability of globular proteins, protein stability should increase as the size of the protein increases. This is not observed: the conformational stability of globular proteins is independent of protein size. In an effort to understand why large proteins are not more stable than small proteins, twenty single-domain globular proteins ranging in size from 35 to 470 residues have been analyzed. Our study shows that nature buries more charged groups and more non-hydrogen-bonded polar groups to destabilize large proteins.

Phytochemical composition, antioxidant activity, pigment stability, bioactive properties, and in-vitro absorption of polyphenolics in acai fruit (Euterpe oleracea Mart.) were investigated. Detailed characterization of phenolic compounds present in acai fruit, acai fruit pulp, and a polyphenolic-enriched acai oil were conducted by HPLCESI- MSn analyses and their stability and influence on antioxidant capacity determined. Anthocyanins were predominant in acai fruits, which also contained several flavone and flavonol glycosides, flavanol derivatives, and phenolic acids. In-vitro absorption and antiproliferative effects of phytochemical extracts from acai pulp and acai oil were determined as a function of chemical composition. Polyphenolic mixtures from both acai pulp and acai oil extracts significantly inhibited HT-29 colon cancer cell proliferation, also inducing the generation of reactive oxygen species. In-vitro intestinal absorption using Caco-2 cell models demonstrated that phenolic acids and monomeric flavanol derivatives are readily transported through cell monolayers in-vitro. The influence of polyphenolic cofactors on the stability of anthocyanins in acai fruit under varying conditions of temperature and pH was evaluated. Significant time, temperature, and pH-dependent anthocyanin losses were observed in all models, yet the presence of phenolic acids, procyanidins, and flavone-C-glycosides had a positive influence on anthocyanin stability. External addition of flavone-C-glycosides significantly enhanced visual color, increased anthocyanin stability during exposures to high pH or storage temperatures, and had comparable effects to those of a commercial anthocyanin enhancer. Anthocyanin polymerization reactions occurring during storage of acai fruit juice models were investigated and potential mechanisms and reaction products identified. Polymeric anthocyanin fractions contained several anthocyanin-flavanol adducts based on cyanidin or pelargonidin aglycones and their presence was related to increased anthocyanin sulfite bleaching resistance and to the appearance of large, unresolved peaks in HPLC chromatograms. A reaction mechanism involving the nucleophilic addition of anthocyanins in their hydrated form to flavanol carbocations resulting from cleavage of interflavanic bonds was proposed for the formation of flavanol-anthocyanin adducts in acai fruit juices. Antiproliferative activity and in-vitro absorption of monomeric and polymeric anthocyanin fractions were also evaluated. Both fractions inhibited HT-29 colon cancer cell growth in a similar, concentration-dependent manner, yet in-vitro absorption trials using Caco-2 intestinal cell monolayers indicated the presence of anthocyanin polymers may influence anthocyanin absorption in acai fruit products.

The static stability of a Tension Leg Platform (TLP) with an intact tendon system is principally provided by its tendons and hence quite different from those of a conventional ship or even a floating structure positioned by its mooring system. Because small deformations in tendons are capable of providing sufficient righting moment to a TLP, the contribution from the inclination of its hull is relatively insignificant, especially when its tendon system is intact. When the tendon system of a TLP is completely damaged, the static stability of a TLP behaves and is calculated in a similar manner as those of a conventional ship. In the case of a TLP with a partially damaged tendon system, the stability of a TLP may be provided by the deformation of its tendons and to a certain extent the inclination of its hull. Several hurricanes in recent years have raised concerns about the feasibility and the robustness of the TLP concept in the deep water Gulf of Mexico. To the best of our knowledge, existing publications on the research of static stability of TLPs are limited. This study investigates the static stability of different types of TLPs representing those deployed in the Gulf of Mexico, under three different scenarios. That is, a TLP with 1) an intact tendon system, 2) a partially damaged tendon system, and 3) a completely damaged tendon system. The four different types of TLP chosen for this study are 1) a conventional four-leg TLP, 2) three-leg mini TLP, 3) extended four-leg TLP and 4) mini four-leg TLP. To avoid buckling and yielding occurring in a tendon, we define that the maximum righting moment provided by an intact or partially damaged tendon system is reached when the tension in one or more tendons on the down tension leg becomes zero or when the tension in one or more tendons on the up tension leg starts to yield. This definition leads us to identify the most dangerous (or vulnerable) directions of met-ocean conditions to a TLP with an intact or partially damaged tendon system. Hence, our finding may also be used in the study on the pitch/roll dynamic stability of a TLP. The righting moments of each TLP in the three different scenarios are respectively computed and compared with related wind-induce static upsetting moment at certain velocities. By comparing their ratios, the static stability of a TLP and the redundancy of its tendon system may be revealed, which has important implication to the design of a TLP.

In this study, the effect of synthesis conditions and annealing process on the sensitivity and stability of gas sensors made of flame-synthesized Zn-doped γ-Fe2O3 particles was investigated. Zn-doped γ-Fe2O3 particles were synthesized by flame spray pyrolysis using either H2/Air or H2/O2 coflow diffusion flames. The particles were then annealed at 325~350˚C in a tube furnace under air atmosphere. Both as-synthesized and annealed particles were used as gas sensing materials to construct gas sensors. Transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller surface area measurement (BET), Williamson and Hall (WH) method were employed to characterize the particles. Gas sensors were fabricated by applying the as-synthesized and annealed particles on interdigitated electrodes. The response of the gas sensor to acetone vapor, H2 in dry synthetic air was measured before and after three days of aging. High-temperature flame (H2/O2) generated nanometer-sized particles; lower temperature flame (H2/Air) generated micrometer-sized particles. Fe2O3 particles doped with 15% Zn showed the highest sensitivity. The sensors made from as-synthesized particles showed a gas sensing sensitivity that was 20 times higher than the literature value. The sensors made of microparticles lost their sensing ability after three days of aging, but sensors made of nanoparticles did not show significant change after aging. Sensors made of annealed particles (either micro or nano) did not have significant gas sensing ability, but annealing process improved the stability of gas sensors. Analysis using the WH method showed that the microstrains decreased significantly in both H2/O2 and H2/Air flame particles after annealing. The results showed that sensors made of nanoparticles have higher gas sensing signal, and more resistant toward aging than sensors made of microparticles. In addition, annealing process affected on the stability favorably due to reduction of structural defects.

The purpose of thesis is to investigate the transient stability and operation feasibility of power islanding with different type of dispersed generation in distribution system. A substation of Taipower system is selected for case study to simulate the system transient stability. The mathematical models of dispersed generations including exciters, governors of gas turbine and pitch controller of wind-driven induction generator are used in the simulation program. To represent the load behavior more accurately, the load ratio of residence, commercial, industrial customer class and the composition of electric equipments in feeder, such as induction motors, air conditioners etc, have been identified through load survey study. The load models of end users are employed in simulation to solve the power consumption as function of bus voltage and system frequency. Besides, the dynamic model of induction motors is integrated to solve more accurate system power demand under transient condition. The simulation analysis of transient stability is executed for unbalance distribution system with dispersed generations of gas turbines and wind-driven turbines with three operations sceneries after the distribution system has been disconnected from Taipower system. Different load shedding schemes and output power control of dispersed generation are considered to maintain the stable operation of islanding power system. It is suggested that the system reliability of power system can be enhanced by the dispersed power generation with proper design of load shedding in the transient stability analysis.

Nine bovine muscles (m. adductor, m. gluteobiceps, m. gluteus medius, m. longissimus lumborum, m. longissimus thoracis, m. psoas major, m. semimembranosus, m. supraspinatus and m. semitendinosus) were removed from beef carcasses (n = 18) to study the affects of muscle, grade, and display time on color stability. Carcasses represented two USDA quality grades (Choice and Select) equally. Muscles were cut into steaks at 10 d postmortem and displayed under retail conditions for 7 d. Percent fat had a muscle × grade interaction as muscle reacted differently based on grade. The m. gluteobiceps, m. gluteus medius, and m. semitendinosus from Choice carcasses tended to be higher in percent fat than those from Select carcasses. Percent metmyoglobin increased from d 1 to d 7. High color stable muscles (e.g., m. longissimus lumborum and m. longissimus thoracis) displayed the least percent metmyoglobin. Generally most muscles displayed high metmyoglobin reductase activity throughout retail display. Aerobic reducing ability for low color stability muscles were high on d 1 and decreased dramatically by d 7, whereas high color stability muscles (m. longissimus lumborum and m. longissimus thoracis) showed an increase in aerobic reducing ability before decreasing on d 7. Oxygen penetration depth was highest over the retail display in the two most color stable muscles (m. longissimus lumborum and m. longissimus thoracis). Myoglobin content decreased over time for all muscles despite differences in initial myoglobin concentration between muscles. TBARS values generally were a good indicator of discoloration and lean color. Color panel found that low color stability muscles decreased rapidly in lean color and increased in discoloration. Those muscles with poor color stability tended to have lower Hunter L* (lightness) and a* (redness). Muscle clearly had a major impact on overall color stability; however, grade showed only few differences, which conflicted with results from previous research. The USDA Select steaks tended to be higher in color stability than USDA Choice. Data indicated that differences in muscle types and grades play a major role in shelf-stability due to different oxidative potentials and reducing ability, and remain complicated factors in the quest to better understand color stability.

For any congestion control mechanisms, the most fundamental design objectives are stability and scalability. However, achieving both properties are very challenging in such a heterogeneous environment as the Internet. From the end-users' perspective, heterogeneity is due to the fact that different flows have different routing paths and therefore different communication delays, which can significantly affect stability of the entire system. In this work, we successfully address this problem by first proving a sufficient and necessary condition for a system to be stable under arbitrary delay. Utilizing this result, we design a series of practical congestion control protocols (MKC and JetMax) that achieve stability regardless of delay as well as many additional appealing properties. From the routers' perspective, the system is heterogeneous because the incoming traffic is a mixture of short- and long-lived, TCP and non-TCP flows. This imposes a severe challenge on traditional buffer sizing mechanisms, which are derived using the simplistic model of a single or multiple synchronized long-lived TCP flows. To overcome this problem, we take a control-theoretic approach and design a new intelligent buffer sizing scheme called Adaptive Buffer Sizing (ABS), which based on the current incoming traffic, dynamically sets the optimal buffer size under the target performance constraints. Our extensive simulation results demonstrate that ABS exhibits quick responses to changes of traffic load, scalability to a large number of incoming flows, and robustness to generic Internet traffic.

Due to the difficulty of reinforcement in power network and the interconnection of more distributed generators, fault current level has become a serious problem in transmission and distribution system operations. The utilization of fault current limiters (FCLs) in power system provides an effective way to suppress the fault currents. In this thesis the sensitivity of impedance matrix due to changes in the branch parameters is derived and used to choose the candidates for FCL installation in a complex power system. The proposed method also considers the effect on power system transient stability due to the installation of FCL. The Extended Equal Area Criterion (EEAC) is used to simplify the multi-machine transient stability problem to a simple equivalent modal and to simplify the transient stability evaluation. A fuzzy logic approach considering impedance of FCL, transient stability and voltage sag effects is used to choose good FCL installation locations in loop transmission systems.

Based on the Lyapunov stability theorem, a decentralized adaptive sliding mode control scheme is proposed in this thesis for a class of mismatched perturbed large-scale systems containing dead-zone input to solve regulation problems. The main idea is that some adaptive mechanisms are embedded both in the sliding surface and in the controllers, so that not only the mismatched perturbations are suppressed during the sliding mode, but also the information of upper bound of perturbations is not required. The sliding surface function is firstly designed through the usage of a pseudo controller which is capable of stabilizing the reduced-order systems. The second step is to design the controllers so that the trajectories of the controlled systems are able to reach sliding surface in a finite time. Once the controlled system enters the sliding mode, the asymptotical stability is guaranteed for each subsystem even the mismatched perturbations exist. A numerical example and a practical example are given to demonstrate the feasibility of the proposed design technique.

Based on the Lyapunov stability theorem, an adaptive sliding mode control scheme is proposed in this thesis for a class of systems with mismatched state-delayed perturbations to solve regulation problems. The main idea is that some adaptive mechanisms are embedded both in the sliding surfaces and in the controllers, so that not only the mismatched perturbations are suppressed during the sliding mode, but also the information of upper bound of perturbations is not required. The sliding surface functions are firstly designed through the usage of designed pseudo controllers, which is capable of stabilizing the reduced-order systems. The number of the sliding surface functions required by the proposed control scheme depends on the relationship between systems's dimension and number of inputs. The second step is to design the controllers so that the trajectories of the controlled system are able to reach sliding surface in a finite time. Once the controlled system enters the sliding mode, the asymptotical stability is guaranteed. Two numerical examples and one practical experiment are given for demonstrating the feasibility of the proposed control scheme.