Waterloo Research

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Now showing 1 - 20 of 2766

Unexpected high digestion rate of cooked starch by the Ct-Maltase-Glucoamylase small intenstine mucosal a-Glucosidase subunit
(Public Library of Science (PLOS), 2012) Lin, Amy Hui-Mei; Nichols, Buford L.; Quezada-Calvillo, Roberto; Avery, Stephen E.; Sim, Lyann; Rose, David R.; Naim, Hassam Y.; Hamaker, Bruce R.
For starch digestion to glucose, two luminal a-amylases and four gut mucosal a-glucosidase subunits are employed. The aim of this research was to investigate, for the first time, direct digestion capability of individual mucosal a-glucosidases on cooked (gelatinized) starch. Gelatinized normal maize starch was digested with N- and C-terminal subunits of recombinant mammalian maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI) of varying amounts and digestion periods. Without the aid of a-amylase, Ct-MGAM demonstrated an unexpected rapid and high digestion degree near 80%, while other subunits showed 20 to 30% digestion. These findings suggest that Ct-MGAM assists a-amylase in digesting starch molecules and potentially may compensate for developmental or pathological amylase deficiencies.
Rapid determination of myosin heavy chain expression in rat, mouse, and human skeletal muscle using multicolor immunofluorescence analysis
(Public Library of Science (PLOS), 2012) Bloemberg, Darin; Quadrilatero, Joe
Skeletal muscle is a heterogeneous tissue comprised of fibers with different morphological, function, and metabolic properties. Different muscles contain varying proportions of fiber types; therefore, accurate identification is important. A number of histochemical methods are used to determine muscle fiber type; however, these techniques have several disadvantages. Immunofluorescence analysis is a sensitive method that allows for simultaneous evaluation of multiple MHC isoforms on a large number of fibers on a single cross-section, and offers a more precise means of identifying fiber types. In this investigation we characterized pure and hybrid fiber type distribution in 10 rat and 10 mouse skeletal muscles, as well as human vastus lateralis (VL) using multicolor immunofluorescence analysis. In addition, we determined fiber type-specific cross-sectional area (CSA), succinate dehydrogenase (SDH) activity, and a-glycerophosphate dehydrogenase (GPD) activity. Using this procedure we were able to easily identify pure and hybrid fiber populations in rat, mouse, and human muscle. Hybrid fibers were identified in all species and made up a significant portion of the total population in some rat and mouse muscles. For example, rat mixed gastrocnemius (MG) contained 12.2% hybrid fibers whereas mouse white tibialis anterior (WTA) contained 12.1% hybrid fibers. Collectively, we outline a simple and time-efficient method for determining MHC expression in skeletal muscle of multiple species. In addition, we provide a useful resource of the pure and hybrid fiber type distribution, fiber CSA, and relative fiber type-specific SDH and GPD activity in a number of rat and mouse muscles.
A biomechanical analysis of ventral furrow formation in the Drosophila melanogaster embryo
(Public Library of Science (PLOS), 2012) Conte, Vito; Ulrich, Florian; Baum, Buzz; Munoz, Jose; Veldhuis, Jim; Brodland, Wayne; Miodownik, Mark
The article provides a biomechanical analysis of ventral furrow formation in the Drosophila melanogaster embryo. Ventral furrow formation is the first large-scale morphogenetic movement in the fly embryo. It involves deformation of a uniform cellular monolayer formed following cellularisation, and has therefore long been used as a simple system in which to explore the role of mechanics in force generation. Here we use a quantitative framework to carry out a systematic perturbation analysis to determine the role of each of the active forces observed. The analysis confirms that ventral furrow invagination arises from a combination of apical constriction and apical-basal shortening forces in the mesoderm, together with a combination of ectodermal forces. We show that the mesodermal forces are crucial for invagination: the loss of apical constriction leads to a loss of the furrow, while the mesodermal radial shortening forces are the primary cause of the internalisation of the future mesoderm as the furrow rises. Ectodermal forces play a minor but significant role in furrow formation: without ectodermal forces the furrow is slower to form, does not close properly and has an aberrant morphology. Nevertheless, despite changes in the active mesodermal and ectodermal forces lead to changes in the timing and extent of furrow, invagination is eventually achieved in most cases, implying that the system is robust to perturbation and therefore over-determined.
When too much is not enough: Obsessive-compulsive disorder as a pathology of stopping, rather than starting
(Public Library of Science (PLOS), 2012) Hinds, Andrea L.; Woody, Erik Z.; Ameringen, Michael Van; Schmidt, Louis A.; Szechtman, Henry
Background In obsessive-compulsive disorder (OCD), individuals feel compelled to repeatedly perform security-related behaviors, even though these behaviours seem excessive and unwarranted to them. The present research investigated two alternative ways of explaining such behavior: (1) a dysfunction of activation - a starting problem - in which the level of excitation in response to stimuli suggesting potential danger is abnormally strong; versus (2) a dysfunction of termination - a stopping problem - in which the satiety-like process for shutting down security-related thoughts and actions is abnormally weak. Method In two experiments, 70 patients with OCD (57 with washing compulsions, 13 with checking compulsions) and 72 controls were exposed to contamination cues - immersing a hand in wet diapers - and later allowed to wash their hands, first limited to 30 s and then for as long as desired. The intensity of activation of security motivation was measured objectively by change in respiratory sinus arrythmia. Subjective ratings (e.g., contamination) and behavioral measures (e.g., duration of hand washing) were also collected. Results Compared to controls, OCD patients with washing compulsions did not differ significantly in their levels of initial activation to the threat of contamination; however, they were significantly less able to reduce this activation by engaging in the corrective behavior of hand-washing. Further, the deactivating effect of hand-washing in OCD patients with checking compulsions was similar to that for controls, indicating that the dysfunction of termination in OCD is specific to the patient's symptom profile. Conclusions These results are the first to show that OCD is characterized by a reduced ability of security-related behavior to terminate motivation evoked by potential danger, rather than a heightened initial sensitivity to potential threat. They lend support to the security-motivation theory of OCD (Szechtman & Woody, 2004) and have important implications both for research into the biological mechanisms underlying OCD and for the development of new treatment approaches.
Deriving mechanisms responsible for the lack of correlation between hypoxia and acidity in solid tumors
(Public Library of Science (PLOS), 2011) Molavian, Hamid R.; Kohandel, Mohammad; Milosevic, Michael; Sivaloganathan, Sivabel
Hypoxia and acidity are two main microenvironmental factors intimately associated with solid tumors and play critical roles in tumor growth and metastasis. The experimental results of Helmlinger and colleagues (Nature Medicine 3, 177, 1997) provide evidence of a lack of correlation between these factors on the micrometer scale in vivo and further show that the distribution of pH and pO2 are heterogeneous. Here, using computational simulations, grounded in these experimental results, we show that the lack of correlation between pH and pO2 and the heterogeneity in their shapes are related to the heterogeneous concentration of buffers and oxygen in the blood vessels, further amplified by the network of blood vessels and the cell metabolism. We also demonstrate that, although the judicious administration of anti-angiogenesis agents (normalization process) in tumors may lead to recovery of the correlation between hypoxia and acidity, it may not normalize the pH throughout the whole tumor. However, an increase in the buffering capacity inside the blood vessels does appear to increase the extracellular pH throughout the whole tumor. Based on these results, we propose that the application of anti-angiogenic agents and at the same time increasing the buffering capacity of the tumor extracellular environment may be the most efficient way of normalizing the tumor microenvironment. As a by-product of our simulation we show that the recently observed lack of correlation between glucose consumption and hypoxia in cells which rely on respiration is related to the inhomogeneous consumption of glucose to oxygen concentration. We also demonstrate that this lack of correlation in cells which rely on glycolysis could be related to the heterogeneous concentration of oxygen inside the blood vessels.
Artificial Intelligence, the Environment and Resource Conflict: Emerging Challenges in Global Governance
(Balsillie School of International Affairs, 2025-06-27) Okoi, Obasesam
Artificial intelligence (AI) embodies a system's capacity to autonomously collect and interpret data from its environment, learn from that data, and apply these insights to inform decision making, problem solving and actions that traditionally require human intelligence. At the heart of this technological process are data centres - facilities where AI models are trained, deployed and maintained. As AI infrastructures expand rapidly across the globe, they bring into sharper focus the often-overlooked costs of digital innovation, particularly their entanglement with extractive economies and conflict dynamics.
Fast prediction of loadability margins using neural networks to approximate security boundaries of power systems
(Institution of Engineering and Technology (IET), 2007-05-10) Gu, Xuenping; Cañizares, Claudio A.
Determining loadability margins to various security limits is of great importance for the secure operation of a power system, especially in the current deregulated environment. Here, a novel approach is proposed for fast prediction of loadability margins of power systems based on neural networks. Static security boundaries, comprised of static voltage stability limits, oscillatory stability limits and other operating limits such as generator power output limits, are constructed by means of loading the power system until these security limits are reached from a base operating point along various loading directions. Back-propagation neural networks for different contingencies are trained to approximate the security boundaries. A search algorithm is then employed to predict the loadability margins from any stable operating points along arbitrary loading directions through an iterative technique based on the trained neural networks. The simulation results for the IEEE two-area benchmark system and the IEEE 50-machine test system demonstrate the effectiveness of the proposed method for on-line prediction of loadability margins.
Multiobjective optimal power flows to evaluate voltage security costs in power networks
(Institute of Electrical and Electronics Engineers (IEEE), 2003-05-31) Rosehart, William D.; Canizares, Claudio A.; Quintana, Victor H.
In this paper, new optimal power flow (OPF) techniques are proposed based on multiobjective methodologies to optimize active and reactive power dispatch while maximizing voltage security in power systems. The use of interior point methods together with goal programming and linearly combined objective functions as the basic optimization techniques are explained in detail. The effects of minimizing operating costs, minimizing reactive power generation, and/or maximizing loading margins are then compared in both a 57-bus system and a 118-bus system, which are based on IEEE test systems and modeled using standard power flow models. The results obtained using the proposed mixed OPFs are compared and analyzed to suggest possible ways of costing voltage security in power systems.
On the Parameter Estimation and Modeling of Aggregate Power System Loads
(Institute of Electrical and Electronics Engineers (IEEE), 2004-05-04) Knyazkin, Valery; Canizares, Claudio A.; Soder, Lennart H.
This paper addressed some theoretical and practical issues relevant to the problem of power system load modeling and identification. Two identification techniques are developed in the theoretical framework of stochastic system identification. The identification techniques presented in this paper belong to the family of output error models; both techniques are based on well-established equations describing load recovery mechanisms having a commonly recognized physical appeal. Numerical experiments with artificially created data were first performed on the proposed techniques and the estimates obtained proved to be asymptotically unbiased and achieved the corresponding Crame/spl acute/r-Rao lower bound. The proposed techniques were then tested using actual field measurements taken at a paper mill, and the corresponding results were used to validate a commonly used aggregate load model. The results reported in this paper indicate that the existing load models satisfactorily describe the actual behavior of the physical load and can be reliably estimated using the identification techniques presented herein.
New techniques to speed up voltage collapse computations using tangent vectors
(Institute of Electrical and Electronics Engineers (IEEE), 2002-08-06) de Souza, Antonio C.Z.; Canizares, Claudio A.; Quintana, Victor H.
This paper discusses various methods based on power network partitioning and voltage stability indices to accelerate the computation of voltage collapse points using continuation techniques. Partitioning methods derived from right eigenvector and tangent vector information are thoroughly studied, identifying limitations and probable application areas; a mixed partition-reduction technique is then proposed to reduce computational burden. Also, tangent vectors are used to define a clustering method for the identification at any operating condition of the critical area at the collapse point, and a new voltage stability index is defined based on the identification of this critical area. Finally, a predictor-corrector methodology based on this index and the continuation method is proposed for fast computations of voltage collapse points. All the different methods are compared based on the results obtained for the IEEE 300-bus test system, and a methodology is recommended based on its prospective computational savings.
Advantages and disadvantages of using various computer tools in electrical engineering courses
(Institute of Electrical and Electronics Engineers (IEEE), 1997-08-31) Canizares, Claudio A.; Faur, Zeno T.
This paper discusses different computer tools used to help deliver, administer, and teach the material covered in two basic undergraduate courses in electrical engineering. The computer facilities, programs and tutorials developed are discussed; however, the paper concentrates more on analyzing the results of using these tools in the student learning process. The students' marks and the results of several student surveys, as well as the teaching staff's observations, are used to evaluate the usefulness of the different tools and determine their advantages and disadvantages. Some unexpected results regarding the actual students' use of these tools are also presented and thoroughly analyzed.
Kincolith, B.C.: Leadership Continuity in a Native Christian Village, 1867-1887
(Canadian Journal of Anthropology, 1982) Patterson II, E Palmer
Through an adaptive strategy which began with an invitation to Anglican missionaries and extended through accepting Christianity, serving on the village "missionary council," and holding elected office under the Indian Advancement Act, traditional chiefs of the Nishga Indians maintained the continuity of their leadership after the founding of the native Christian village of Kincolith, B.C.
A Decade of Change: Origins of the Nishga And Tsimshian Land Protests in the 1880s
(University of Toronto Press, 1983) Patterson II, E Palmer
The decade of the 1880s was one of ferment and change for the Nishga. Internal and external factors operated. The allotment of reserves, the coming of Indian administration, the changing role of the missionary, the conflict within the missionary community — all of these were felt and reacted to by the Nishga. Rivalries between Nishga and Tsimshian and among the Nishga contributed to the sharpened awareness of changes regarding the land. The threat to the land was keenly felt and became the public issue. It retained that position for the next one hundred years, with intermittent periods of greater or lesser intensity.
Comparing secondary voltage regulation and shunt compensation for improving voltage stability and transfer capability in the Italian power system
(Elsevier, 2004-10-01) Cañizares, Claudio A.; Cavallo, Claudio; Pozzi, Massimo; Corsi, Sandro
This paper concentrates on comparing the advantages and disadvantages, including costs, of using secondary voltage regulation (SVR) versus using shunt-connected controllers, in particular mechanical switched capacitors (MSC), static var compensators (SVC) and static synchronous compensators (STATCOM), to improve voltage stability (VS) and the external transfer capability (TC) of the Italian power network. Basic VS and TC concepts and tools, as well as the models of the various controllers, particularly SVR, used to obtain the results presented are described in detail. The model of the Italian system used and the assumptions made for these studies are also discussed. The paper demonstrates that SVR is an option that should be seriously considered in practice when trying to improve VS and TC of power systems.
A vector energy function approach for security analysis of AC/DC systems
(Institute of Electrical and Electronics Engineers (IEEE), 2002-08-06) DeMarco, Christopher L.; Canizares, Claudio A.
The authors examine dynamic behavior in system models that reflect reasonably detailed third-order high-voltage DC (HVDC) dynamics along with AC system models that include reactive flows, and frequency and voltage-dependent load models. A vector Lyapunov function approach is used to define a system-wide energy function that can be used for general security analysis. They describe the derivation of individual component Lyapunov functions for simplified models of HVDC links connected to infinitely strong AC systems, along with a standard AC only system Lyapunov function. A novel method of obtaining weighting coefficients to sum these components for the overall system energy function is proposed. Use of the new energy function for transient stability and security analysis was illustrated in a test system.
Application of a Stability-Constrained Optimal Power Flow to Tuning of Oscillation Controls in Competitive Electricity Markets
(Institute of Electrical and Electronics Engineers (IEEE), 2007-10-29) Kodsi, Sameh K. M.; Canizares, Claudio A.
A novel technique based on a stability-constrained Optimum Power Flow (OPF) algorithm that properly captures important rotor angle and voltage stability conditions is proposed and described. The application of this technique to the optimal tuning of both Power System Stabilizers (PSS) and thyristor controlled series compensators (TCSC) to damp power system oscillations within the context of competitive electricity markets is proposed and discussed as well. The proposed technique is tested on the IEEE 14-bus benchmark system and compared with a "standard" OPF algorithm. The results obtained demonstrate the advantages of the proposed technique over existent dispatching techniques from the point of view of power dispatch and system stability conditions, and especially locational marginal prices.
Equivalency of Continuation and Optimization Methods to Determine Saddle-Node and Limit-Induced Bifurcations in Power Systems
(Institute of Electrical and Electronics Engineers (IEEE), 2008-05-28) Avalos, Rafael J.; Canizares, Claudio A.; Milano, Federico; Conejo, Antonio J.
This paper presents a comprehensive and detailed study of an optimization-based approach to identify and analyze saddle-node bifurcations (SNBs) and limit-induced bifurcations (LIBs) of a power system model, which are known to be directly associated with voltage stability problems in these systems. Theoretical studies are presented, formally demonstrating that solution points obtained from an optimization model, which is based on complementarity constraints used to properly represent generators' voltage controls, correspond to either SNB or LIB points of this model. These studies are accomplished by proving that optimality conditions of these solution points yield the transversality conditions of the corresponding bifurcation points. A simple but realistic test system is used to numerically illustrate the theoretical discussions.
A Procurement Market Model for Reactive Power Services Considering System Security
(Institute of Electrical and Electronics Engineers (IEEE), 2008-01-21) El-Samahy, Ismael; Bhattacharya, Kankar; Canizares, Claudio; Anjos, Miguel F.; Pan, Jiuping
This paper proposes a two-level framework for the operation of a competitive market for reactive power ancillary services. It is argued that the first-level, i.e., reactive power procurement, be on a seasonal basis while the second-level, i.e., reactive power dispatch, be close to real-time operation. To this effect, a reactive power procurement market model is proposed here taking into consideration system security aspects. This procurement procedure is based on a two-step optimization model. First, the marginal benefits of reactive power supply from each provider with respect to system security are obtained by solving an optimal power flow (OPF) that maximizes system loadability subject to transmission security constraints imposed by voltage limits, thermal limits, and stability limits. Second, the selected set of generators is then determined by solving an OPF-based auction to maximize a societal advantage function comprising generators' offers and their corresponding marginal benefits with respect to system security, considering all transmission system constraints. The proposed procedure yields the selected set of generators and zonal price components, which would form the basis for seasonal contracts between the system operator and the selected reactive power service providers.
Point of collapse methods applied to AC/DC power systems
(Institute of Electrical and Electronics Engineers (IEEE), 2002-08-06) Canizares, Claudio A.; Alvarado, Fernando L.; DeMarco, Christopher L.; Dobson, I.an; Long, Willis F.
The authors describe an extension of the point of collapse method developed for studies of AC systems to the determination of saddle-node bifurcations in power systems including high voltage direct current (HVDC) transmission. Bus voltage profiles are illustrated for an AC/DC test system. They significantly differ from the profiles of pure AC systems for typical system models. In particular, voltage dependent current order limits are shown to affect the voltage profiles and the loadability margin of the system. It is also shown that Hopf bifurcations, which are possible in purely AC lossless systems with second-order generator models, become plausible when the dynamics for the HVDC system are included.
Point of collapse and continuation methods for large AC/DC systems
(Institute of Electrical and Electronics Engineers (IEEE), 2002-08-06) Canizares, Claudio A.; Alvarado, Fernando L.
The implementation of both point of collapse (PoC) methods and continuation methods for the computation of voltage collapse points (saddle-node bifurcations) in large AC/DC power systems is described. The performance of these methods is compared for real systems of up to 2158 buses. Computational details of the implementation of the PoC and continuation methods are detailed, and the unique problems encountered due to the presence of high-voltage direct-current (HVDC) transmission, area interchange power control, regulating transformers, and voltage and reactive power limits are discussed. The characteristics of a robust PoC power flow program are presented, and its application to detection and solution of voltage stability problems is demonstrated.

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