Waterloo Research

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Probabilistic Optimal Power Flow in Electricity Markets Based on a Two-Point Estimate Method
(Institute of Electrical and Electronics Engineers (IEEE), 2006-11-30) Verbic, Gregor; Canizares, Claudio A.
This paper presents an application of a two-point estimate method (2PEM) to account for uncertainties in the optimal power flow (OPF) problem in the context of competitive electricity markets. These uncertainties can be seen as a by-product of the economic pressure that forces market participants to behave in an “unpredictable” manner; hence, probability distributions of locational marginal prices are calculated as a result. Instead of using computationally demanding methods, the proposed approach needs2nruns of the deterministic OPF fornuncertain variables to get the result in terms of the first three moments of the corresponding probability density functions. Another advantage of the 2PEM is that it does not require derivatives of the nonlinear function used in the computation of the probability distributions. The proposed method is tested on a simple three-bus test system and on a more realistic 129-bus test system. Results are compared against more accurate results obtained from MCS. The proposed method demonstrates a high level of accuracy for mean values when compared to the MCS; for standard deviations, the results are better in those cases when the number of uncertain variables is relatively low or when their dispersion is not large.
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.
Energy Storage in Microgrids: Compensating for Generation and Demand Fluctuations While Providing Ancillary Services
(Institute of Electrical and Electronics Engineers (IEEE), 2017-08-16) Farrokhabadi, Mostafa; Solanki, Bharatkumar V.; Canizares, Claudio A.; Bhattacharya, Kankar; Koenig, Sebastian; Sauter, Patrick S.; Leibfried, Thomas; Hohmann, Soren
Driven by global environmental emission issues, energy access in remote communities, and tighter requirements for system resilience and reliability, electricity production is shifting from a centralized paradigm to a decentralized one. In this context, renewable energy sources (RESs) have proliferated over the past decade, exhibiting a steadily increasing trend. Thus, today, a large number of wind turbines and photovoltaic (PV) panels are connected to medium- (1-69 kV) and low-voltage (=1 kV) grids, with traditional integrated bulk power systems becoming decentralized in the presence of active distribution networks, where the flow of power is bidirectional between generators and "prosumers." In particular, with decreasing RES s costs, these technologies are becoming attractive solutions to bring energy to remote communities and/or replace expensive fossil-fuel-based generators. However, RES s such as wind and solar are intermittent sources of energy, difficult to predict, and prone to large output fluctuations-therefore, significantly affecting system voltage and frequency.
Impact of 100‐MW‐scale PV plants with synchronous power controllers on power system stability in northern Chile
(Institution of Engineering and Technology (IET), 2017-08-11) Remon, Daniel; Cañizares, Claudio A.; Rodriguez, Pedro
The impact that renewable energy sources interfaced by power electronics have on power systems becomes more important as their share in the generation mix increases, thus requiring detailed analyses that take into account their dynamics and controllers. In this study, the impact of photovoltaic (PV) power plants on the power system of northern Chile is analysed. The studied plants employ a controller that allows power converters to interact with the grid like virtual synchronous generators, and their model includes the dynamics of the plant and converter controllers, as well as the dc and PV system. The presented analysis, which comprises modal analysis and time-domain simulations of large disturbances, evaluates the impact of these plants with respect to PV plants based on a conventional converter controller. Tests and validations of the proposed models and controllers are carried out for an actual PV plant connected to the power system of northern Chile, and for a higher PV penetration case. The results show the ability of PV plants formed by virtually synchronous power converters to limit frequency excursions induced by large power imbalances, and to mitigate power oscillations of the synchronous machines in the system.
Distributed Computing Architecture for Optimal Control of Distribution Feeders With Smart Loads
(Institute of Electrical and Electronics Engineers (IEEE), 2016-09-28) Mosaddegh, Abolfazl; Canizares, Claudio A.; Bhattacharya, Kankar; Fan, Hongbing
This paper presents a distributed computing architecture for solving a distribution optimal power flow (DOPF) model based on a smart grid communication middleware (SGCM) system. The system is modeled as an unbalanced three-phase distribution system, which includes different kind of loads and various components of distribution systems. In this paper, fixed loads are modeled as constant impedance, current and power loads, and neural network models of controllable smart loads are integrated into the DOPF model. A genetic algorithm is used to determine the optimal solutions for controllable devices, in particular load tap changers, switched capacitors, and smart loads in the context of an energy management system for practical feeders, accounting for the fact that smart loads consumption should not be significantly affected by network constraints. Since the number of control variables in a realistic distribution power system is large, solving the DOPF for real-time applications is computationally expensive. Hence, to reduce computational times, a decentralized system with parallel computing nodes based on an SGCM system is proposed. Using a “MapReduce” model, the SGCM system runs the DOPF model, communicates between master and worker computing nodes, and sends/receives data among different parts of parallel computing system. Compared to a centralized approach, the proposed architecture is shown to yield better optimal solutions in terms of reducing energy losses and/or energy drawn from the substation within adequate practical run-times for a realistic test feeder.
Semantic partitioning facilitates memory for object location through category-partition cueing.
(Taylor & Francis, 2024) Lu, Xinyi; Zhu, Mona J.H.; Risko, Evan F.
In our lived environments, objects are often semantically organized (e.g., cookware and cutlery are placed close together in the kitchen). Across four experiments, we examined how semantic partitions (that group same-category objects in space) influenced memory for object locations. Participants learned the locations of items in a semantically partitioned display (where each partition contained objects from a single category) as well as a purely visually partitioned display (where each partition contained a scrambled assortment of objects from different categories). Semantic partitions significantly improved location memory accuracy compared to the scrambled display. However, when the correct partition was cued (highlighted) to participants during recall, performance on the semantically partitioned display was similar to the scrambled display. These results suggest that semantic partitions largely benefit memory for location by enhancing the ability to use the given category as a cue for a visually partitioned area (e.g., toys—top left). Our results demonstrate that semantically structured spaces help location memory across partitions, but not items within a partition, providing new insights into the interaction between meaning and memory.
Semantic relatedness can impair memory for item locations
(Springer, 2024) Lu, Xinyi; Zhu, Mona J.; Risko, Evan F.
While memory for semantically related items is improved over unrelated items in many cases, relatedness can also lead to memory costs. Here we examined how the semantic relatedness of words within a display influenced memory for their locations. Participants learned the locations of words inside grid displays; the words in a given display were either from a single category or were from different assorted categories. When a display containing words from a single category was compared to a scrambled display containing words from multiple categories, location memory performance was rendered worse, while word recall performance was significantly improved. Our results suggest that semantically structured spaces can both help and harm memory within the context of a location memory task. We hypothesize that relatedness can improve memory performance by increasing the likelihood that matching candidates will be retrieved, yet might worsen performance that requires distinguishing between similar target representations.
Productions need not match study items to confer a production advantage, but it helps.
(Hogrefe, 2024) Kelly, Megan O.; Lu, Xinyi; Ensor, Tyler M.; MacLeod, Colin M.; Risko, Evan F.
The production effect is the finding that, relative to silent reading, producing information at study (e.g., reading aloud) leads to a benefit in memory. In most studies of this effect, individuals are presented with a set of unique items, and they produce a subset of these items (e.g., they are presented with the to-be-remembered target item TABLE and produce “table”) such that the production is both unique and representative of the target. Across two preregistered experiments, we examined the influence of a production that is unique but that does not match the target (e.g., producing “fence” to the target TABLE, producing “car” to the target TREE, and so on). This kind of production also yielded a significant effect—the mismatching production effect—although it was smaller than the standard production effect (i.e., when productions are both unique and representative of their targets) and was detectable only when targets with "standard" productions were included in the same study phase (i.e., when the type of production was manipulated within participant). We suggest that target-production matching is an important precursor to the production effect, and that the kind of production that brings about a benefit depends on the other productions that are present.
The prod eff: Partially producing items moderates the production effect.
(Springer, 2024) Kelly, Megan O.; Ensor, Tyler M.; MacLeod, Colin M.; Risko, Evan F.
Current accounts of the production effect suggest that production leads to the encoding of additional production-associated features and/or better feature encoding. Thus, if it is the act of production that leads to the storage and/or enhanced encoding of these features, then less of this act should reduce the resulting production effect. In two experiments, we provide a direct test of his idea by manipulating how much of a given item is produced within a single mode of production (typing). Results demonstrate that such partial production can yield a significant production effect that is smaller than the effect that emerges from producing the entire item. These results suggest that how much of an item is produced can moderate the size of the production effect and are considered in the context of recent modelling efforts.
Speeding lectures to make time for retrieval practice: Can we improve the efficiency of interpolated testing?
(American Psychology Association, 2024) Risko, Evan F.; Liu, Junwen; Bianchi, Laura
Testing is increasingly recognized as an important tool in learning. One form of testing often used in lectures, particularly recorded lectures, is interpolated testing wherein tests are interspersed throughout the lecture. Like testing in general, interpolated testing appears to benefit performance on content tests amongst other outcome variables (e.g., mind wandering). While beneficial, adding testing also increases instructional time. In the present investigation we examine one strategy to mitigate the costs of this increase in instructional time in the context of recorded lectures. Specifically, we examine the interaction between increasing the playback speed of a recorded lecture and adding interpolated tests. Results demonstrate that the conjoint effects of these two interventions is largely additive. That is, the benefit of testing was as robust in a normal speed lecture and a lecture that was sped up 1.5x.
On our susceptibility to external memory store manipulation: examining the influence of perceived reliability and expected access to an external store.
(Taylor & Francis, 2022) Pereira, April E.; Kelly, Megan O.; Lu, Xinyi; Risko, Evan F.
Offloading memory to external stores (e.g., a saved file) allows us to evade the limitations of our internal memory. One cost of this strategy is that the external memory store used may be accessible to others, and thus, manipulated. Here we examine how reducing the perceived reliability of an external memory store may impact participants’ susceptibility to its manipulation (i.e., endorsing manipulated information as authentic). Across two pre-registered experiments, participants were able to store to-be-remembered information in an external store and on two critical trials, we surreptitiously manipulated the information in that store. Results demonstrate that an explicit notification of a previous manipulation, a reduction in perceived reliability, can decrease susceptibility to manipulation of the external memory store.
The gist of it: offloading memory does not reduce the benefit of list categorisation.
(Taylor & Francis, 2022) Lu, Xinyi; Kelly, Megan O.; Risko, Evan F.
When we can offload to-be-remembered information to an external store, our ability to recall that information from internal memory can be diminished. However, previous research has suggested that associative memory processes may remain intact in the face of offloading behavior. In the present investigation, we examine how the opportunity to offload memory demands affects the learning of categorized word lists. Across six experiments, participants studied and wrote down word lists that were either strongly associated with a semantic theme (categorized) or word lists that consisted of the same set of words but shuffled across the categorized lists (shuffled). When participants expected to have access to their written lists during the recall test (i.e., a condition that would encourage offloading) but were not given access to it, we found the typical recall advantage for categorized lists. This effect was found to be the same size or larger compared to a condition where participants did not expect to have access to their written lists during the recall test (i.e., a condition that would not allow offloading). We propose that gist memory supported by semantic associations is not substantially reduced in offloading.
Study effort and the memory cost of external store availability.
(Elsevier, 2022) Kelly, Megan O.; Risko, Evan F.
Previous work demonstrates that individuals often recall less information if, at study, there is expectation that an external memory store will be available at test. One explanation for this effect is that when individuals can expect access to an external memory store, they forgo intentional, controlled efforts at encoding. The present work offers a novel test of this account by examining study effort, indexed by study time and self reported strategy use, as a function of instructed external store availability. In two preregistered experiments, participants studied lists of to-be- remembered items for a free recall test and were either instructed that they could use their study list to support them at test or that they could not. Critically, participants controlled their own study time, and no participant had their study list at test, regardless of instruction. Consistent with the effort at encoding account, external store availability influenced both study time and strategy use, and there was evidence that these effects mediated the influence of external store availability on recall performance. Interestingly, much of the memory cost remained when controlling for study effort, thus, suggesting that the cost is potentially multiply determined.
On the influence of evaluation context on judgments of effort.
(American Psychology Association, 2022) Ashburner, Michelle; Risko, Evan F.
Cognitive effort is a central construct in our lives, yet our understanding of the processes underlying our judgments of effort are limited. Recent work has suggested that our judgments of effort are sensitive to the context in which they are made (i.e., the judgment context). Using a cognitive task and stimulus set that has produced a reliable dissociation between judgments of effort and cognitive demand (as measured by performance and other indirect measures of demand), we examined whether evaluation context might be able to eliminate this dissociation (i.e., bring judgments of effort more in line with measures of cognitive demand). To address this question, we conducted four experiments manipulating a number of aspects of the judgment context including, principally, a manipulation of joint vs. separate evaluation; whether the judgment was prospective, or retrospective; and whether prospective judgments were made with or without having experienced the cognitive task. Additionally, we collected objective demand measures and examined participants’ self-reported reasons for their judgments of effort across the joint and separate evaluation contexts. Results demonstrated that evaluation context has a marked effect on judgments of effort; however, no judgment context appeared to yield a pattern more similar to what is found using measures of cognitive demand. Moreover, the reasons individuals cited for their judgments varied across evaluation contexts. Implications of the present work for our understanding of judgments of effort are discussed.
Reducing retrieval time modulates the production effect: Empirical evidence and computational accounts.
(Elsevier, 2022) Kelly, Megan O.; Ensor, Tyler M.; Lu, Xinyi; MacLeod, Colin M.; Risko, Evan F.
Memory is reliably better for information read aloud relative to information read silently—the production effect. Three preregistered experiments examined whether the production effect arises from a more time-consuming retrieval process operating at test that benefits items that were produced at study. Participants studied items either aloud or silently and then completed a recognition test which required responding within a short deadline, under the assumption that a time-consuming retrieval process would be less able to operate when less time was available. Results generally supported this prediction. Even under speeded responding instructions, however, there was a robust production effect, suggesting that other, more rapid, processes also contribute to the production effect. Based on two extant verbal accounts, a computational model of the production effect using REM is introduced.
The role of graphics in video lectures
(Taylor & Francis, 2021) Bianchi, Laura J.; Risko, Evan F.
With the increase in online course use (Allen & Seaman, 2017), there is an increasing need to determine the most effective (i.e., the most conducive for learning) way to present lectures online (e.g., video lectures). Lecture graphics that are interesting but extraneous to the content (e.g., a celebrity), have been shown to impair comprehension of the material, likely resulting from an increase in cognitive load. In this study, the use of graphics on the slides of an online psychology lecture was manipulated to determine the extent to which images can improve (or impair) comprehension as well as the effect it may have on intentional and unintentional mindwandering. Across our two experiments, we demonstrate no differences across conditions (i.e., unnecessary graphics, relevant graphics, no graphics) in overall comprehension and limited differences in mind wandering behavior.
You can’t bullshit a bullshitter (or can you?): Bullshitting frequency predicts receptivity to various types of misleading information
(British Psychological Society, 2021) Littrell, Shane; Risko, Evan F.; Fugelsang, Jonathan A.
Research into both receptivity to falling for bullshit and the propensity to produce it have recently emerged as active, independent areas of inquiry into the spread of misleading information. However, it remains unclear whether those who frequently produce bullshit are inoculated from its influence. For example, both bullshit receptivity and bullshitting frequency are negatively related to cognitive ability and aspects of analytic thinking style, suggesting that those who frequently engage in bullshitting may be more likely to fall for bullshit. However, separate research suggests that individuals who frequently engage in deception are better at detecting it, thus leading to the possibility that frequent bullshitters may be less likely to fall for bullshit. Here we present three studies (N = 826) attempting to distinguish between these competing hypotheses, finding that frequency of persuasive bullshitting (i.e., bullshitting intended to impress or persuade others) positively predicts susceptibility to various types of misleading information and that this association is robust to individual differences in cognitive ability and analytic cognitive style.
Environment, Not Social or Governance, Oh My: Sustainability Priorities in Canadian University Sustainability Documents
(Emerald Insight, 2025-06-23) Dickson, Brandon
Design/methodology/approach Comparing sustainability policies with the overarching goals of the United Nations Sustainable Development Goals through the approach of narrative policy analysis, this research explores the priorities present and what patterns emerge in these priorities. Purpose Universities are significant in their sustainability action not just for the education that they provide, but how they operate as mini cities, with massive environmental footprints, meaning that, their sustainability direction matters. As a result, this research investigates the priorities present in university sustainability policy documents from 33 Canadian universities. Findings Findings include that across Canada, planet related sustainability priorities, particularly those focused on cities, climate action and consumption are the most present, while people and prosperity elements of sustainability often fall outside the scope of these policies. Some regional variation emerges in key areas such as energy and climate action, and size also sees a correlation to prioritization of specific areas of sustainability such as waste. Originality/value This research will be of interest to researchers in the emerging field of sustainability in higher education, practitioners and administrators in university sustainability and policy makers looking to understand sustainability prioritization shape the future of nuanced sustainability directions.
Revisiting the influence of offloading memory on free recall.
(2022) Kelly, M. O., & Risko, E. F.
Relying on external memory aids is a common memory strategy that has long allowed us to “remember” vast amounts of information more reliably than with our internal memory alone. However, recent work has provided evidence consistent with the idea that offloading memory demands encourages a reduced engagement in intentional or topdown memory strategies/efforts, leading to lower memory performance in general. Evidence for this view comes from results demonstrating a reduced primacy effect but intact recency and isolation effects when individuals could offload memory demands (but had to unexpectedly rely on their internal memory at test). In the present investigation, we attempt a replication of these critical results, given some inconsistencies in the findings between studies. In addition, we extend the examination of offloading’s impact on memory via examining individual differences in reliance on the external store (when available) and different strategies for the use of that store. Results of the replication are generally consistent with previous research. An individual differences analysis yielded results consistent with the notion that increased reliance on an external store can compromise internal/biological memory in the absence of that store. Finally, a verbal model of offloading memory demands within a framework of effort and study time allocation is presented. Together, the results both reinforce extant research and extend it in new directions.
Exploring and prioritizing content to include a medication self-management toolkit for persons with spinal cord injury/dysfunction concept mapping approach
(Public Library of Science (PLOS), 2024) Cadel, Lauren; El-Kotob, Rasha; Hitzig, Sander L.; McCarthy, Lisa M.; Hahn-Goldberg, Shoshana; Packer, Tanya L.; Ho, Chester H.; Patel, Tejal; Cimino, Stephanie R.; Lofters, Aisha K.; Guilcher, Sara J. T.
Background Adults with spinal cord injury/dysfunction (SCI/D) face challenges with medications they take to manage their secondary conditions (e.g., pain, urinary tract infections, autonomic dysreflexia). With many healthcare providers typically involved in care, there are additional challenges with care fragmentation and self-management. Prior research emphasized the desire for more support with medication self-management among this population. Objective To explore what content should be included in a medication self-management resource (i.e., toolkit) for adults with SCI/D, as well as considerations for delivery from the perspectives of adults with SCI/D, caregivers, healthcare providers, and representatives from community organization. Methods A concept mapping study was conducted. Participants took part in one or more of three activities: brainstorming; sorting and rating; and mapping. Participants generated ideas about the content to include in a medication self-management toolkit. Participants sorted the statements into conceptual piles and assigned a name to each. All statements were rated on a five-point Likert-type scale on importance and realistic to include in the toolkit. Participants decided on the final cluster map, rearranged statements, and assigned a name to each cluster to create visual representations of the data. Results Forty-four participants took part in this study. The final map contained eight clusters: 1) information-sharing and communication; 2) healthcare providers interactions and involvement; 3) peer and community connections; 4) supports and services for accessing prescription medications and medication information; 5) information on non-prescription medication and medication supplies; 6) safety and lifestyle considerations; 7) general medication information; and 8) practical information and strategies related to medication-taking. Safety and lifestyle considerations was rated as the most important and realistic to include in the toolkit. Conclusions Give the limited tools to help adults with SCI/D with managing their medications, there is great potential to better support this population across all areas of medication self-management.

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