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The Limits of Longevity
No full textDo all animals age? Although aging seems to be a widespread phenomenon, some demographic studies have failed to find evidence of aging in certain species, including some highly regenerative species of planarians and Hydra that reproduce through asexual fission. However, all demographic studies have limits on observation times and sample sizes, so it is unknown if these failures were because of an actual absence of aging or these inherent study limitations. Some argue that these species must be ageless. Because of pressures that result from the lack of a clean division between the germ line and the soma in fissiparous organisms, agelessness becomes necessary as a prerequisite of this kind of reproductive strategy. Others argue that fundamental theories of the evolutionary biology of aging absolutely preclude agelessness. Even putting evolutionary arguments aside, some mathematical models of cellular competition and senescence argue that agelessness is impossible mechanistically in multicellular organisms. In this work, I address evolutionary and mechanistic arguments for and against agelessness. I develop mathematical models of the Disposable Soma Theory that incorporate facets of the arguments for agelessness in asexual fissioning organisms. I construct models of mutation accumulation and drift within an individual and explore how this genetic decay could manifest in the mortality rates. I use these models to understand if aging is inevitable generally and apply them to planarians and Hydra to seek to estimate the likelihood of aging more narrowly in those specific cases. Contrary to other work, I find that agelessness (defined as non-increasing mortality rates in a population) is indeed possible as the optimal evolutionary strategy for multicellular organisms. However, the evolution and mechanistic realization of agelessness requires conditions that are unlikely to be met in any existing species. In the case of planarians and Hydra, they likely do not face the right kind of evolutionary pressure to completely avoid aging. Even if they do face necessary evolutionary pressure, intraindividual genetic decay will almost certainly induce increasing mortality on the population with little recourse. Therefore, these species likely do age, although they could have median lifespans on the order of hundreds or perhaps even thousands of years, which would make detecting aging in any given population study quite difficult indeed.Ph.D
Adapting temporal preference to scarcity: A role for emotion?
No full textA critical optimization problem is how to distribute resource consumption over time. Humans tend to value immediate rewards over equivalent future rewards—a phenomenon called temporal discounting. Such imbalance can lead to poor health, education, and financial decisions. It is also a hurdle for implementing sustainability policies. A major research goal is to identify factors that influence temporal discounting, so that policymakers could develop interventions to correct for this imbalance. One such factor is available resources; scarcity may increase in temporal discounting. Another potential factor is emotion; negative emotions may lead to high temporal discounting. However, emotion and resources are not independent. For example, losing a large sum of money will lead to negative affect. Here, we take advantage of one of the largest global ‘income shocks’ in history, to tease apart the role of emotion and income on temporal discounting. We tested 1,145 individuals as the market was crashing in late March 2020 and unemployment rising and then retested 200 of those individuals as the market was recovering in June 2020. We found that income shock was strongly related to an increase in delay discounting using cross-sectional and longitudinal data. Importantly, this relationship was independent of the negative impact on affect. These findings suggest that, contrary to wide held assumptions, people directly adapt delay discounting to environmental constraints, without the need for input from the affective system. This independence may be adaptive, as affect is a noisy reflection of environmental constraints, which may lead to suboptimal choice
Problem-Independent Regrets on Expectation-Dependent Multi-Armed Bandits
No full textThe independence axiom (IA) proposed by Von Neumann and Morgenstern [50] is the cornerstone of the expected utility theory. However, some empirical experiments show that the IA is often violated in the real world. We propose a new kind of multi-armed bandit problem where the expectation of outcomes may influence the agent’s utility which we call expectation-dependent multi-armed bandits and rationalize the choice of agents in Machina’s paradox lacking the IA. We design provably efficient algorithms with low minimax regrets and show their consistency of time horizon T with corresponding regret lower bounds, revealing statistical optimality. Furthermore, as we first consider bandits whose corresponding utility depends on both reality and expectation, it provides a bridge between machine learning and economic behavior theory, shedding light on how to interpret some counterintuitive economic scenarios, like bounded rationality explored by Zhang et al. [54].S.M
Towards optimal energy efficiency: analysing generalized and tailored retrofitting decisions
No full textA building’s energy performance, in terms of thermal comfort, energy demand, cost and CO2 emissions, is considerably affected by its envelope. Enhancing energy efficiency through maintenance and retrofitting is essential to reduce consumption and emissions, thereby mitigating climate change. However, selecting the most cost-effective retrofitting solution remains challenging for decision-makers. Analysing real data across multiple scenarios provides valuable insights, supporting informed decision-making. This study discusses the impact of thermal retrofitting decisions on the energy efficiency of an existing single-family home, by analysing multiple scenarios concerning the implementation of measures on external walls, roof and windows. Both generalized and tailored approaches, particularly for external walls, are evaluated. Options include different insulation materials for the roof and façades—with the latter employing an external thermal insulation composite system (ETICS)—and various framing materials with double-glazing for window replacement. Various scenarios are discussed based on thermal simulations, implementation costs, and cost-benefit analysis. Additionally, multi-criteria (MCA) and sensitivity (SA) analyses are conducted to determine the optimal retrofitting solution. The most effective combined strategy applies ETICS with rock wool on the external walls, extruded polystyrene panels on the roof, and aluminium-framed windows with a thermal break, balancing energy efficiency, costs, durability, and sustainability. Although not part of the optimal solution, tailored retrofitting of façade F2 presents a viable alternative under cost constraints
Paratrouper: Exploratory Creation of Character Cast Visuals Using Generative AI
No full textJoanne Leong, David Ledo, Thomas Driscoll, Tovi Grossman, George Fitzmaurice, and Fraser Anderson. 2025. Paratrouper: Exploratory Creation of Character Cast Visuals Using Generative AI. In Proceedings of the 2025 CHI Conference on Human Factors in Computing Systems (CHI '25). Association for Computing Machinery, New York, NY, USA, Article 189, 1–20.Great characters are critical to the success of many forms of media, such as comics, games, and films. Designing visually compelling casts of characters requires significant skill and consideration, and there is a lack of specialized tools to support this endeavor. We investigate how AI-driven image-generation techniques can empower creatives to explore a variety of visual design possibilities for individual and groups of characters. Informed by interviews with character designers, Paratrouper is a multi-modal system that enables creating and experimenting with multiple permutations for character casts and visualizing them in various contexts as part of a holistic approach to design. We demonstrate how Paratrouper supports different aspects of the character design process, and share insights from its use by eight creators. Our work highlights the interplay between creative agency and serendipity, as well as the visual interrelationships among character aesthetics
The Future of Drug Delivery
No full textDrug delivery technologies have been proven to improve treatment outcomes in many ways, including enhancing therapeutic efficacy, reducing toxicity, increasing patient compliance, and enabling entirely new medical treatments. As the therapeutic landscape has evolved from small-molecule drugs to a new generation of therapeutics including proteins, peptides, monoclonal antibodies, nucleic acids, and even live cells, drug delivery technologies have also evolved to meet their unique delivery needs
Fueling Conflict: A Global Dataset of Energy Protests
No full textHow do popular grievances about (the lack of) access to energy lead to political violence and instability? I use a mixed-methods approach to answer this question, based on a qualitative case study in Sri Lanka and a quantitative framework for tracking energy protests worldwide. Specifically, through an analysis of the 2022 Aragalaya protest movement in Sri Lanka, I elaborate on how breakdowns in state capacity to provide energy to its citizens can trigger civilian unrest. Building on this case study, as well as insights from the empirical literature on the drivers of instability related to energy access, I then pilot a machine learning (ML) framework to identify energy-related protest events in the Armed Conflict Events Database (ACLED) based on context-specific keywords, which results in the creation of the first global dataset on energy protests. This novel source of evidence, in turn, will open new avenues for research on the conflict-energy nexus, particularly on the impact of market shocks on civilian unrest and instability in low- and middle-income countries – a topic for which current empirical work is limited. I show how the ML framework I develop here can be used to enable continuous monitoring of protest activity related to energy access, as well as how the framework can be extended to other forms of political violence, offering a promising tool for peace-building initiatives across contexts. Therefore, such a framework could inform key evidence to support policymakers, practitioners, and researchers in the design of strategic policies that facilitate the provision of energy while mitigating the risk of conflict and instability worldwide, particularly in "energy-poor" countries.S.M.S.M
Report to the President for year ended June 30, 2025, Dean, School of Engineering
No full textThis report contains the following sections: Administrative Initiatives, Personnel Information, Educational Activities, Strategic Initiatives, Entrepreneurship, Leadership, and Innovation Activities
Evaluating the Strategic Intent and Competitive Dynamics of China’s Satellite Communications Constellations
No full textThis thesis examines the strategic, technical, and economic feasibility of China’s two flagship low Earth orbit (LEO) satellite megaconstellation programs, Guowang and Qianfan, in the context of the rapidly evolving global satellite communication (Satcom) market. Against the backdrop of SpaceX’s Starlink dominance and intensifying geopolitical competition, China’s efforts represent not only a telecommunications infrastructure push but also a broader assertion of technological sovereignty and global influence. This study uses a scenario-based analysis that integrates system throughput analysis and financial forecasting. Three deployment scenarios (base, optimistic, and pessimistic) are analyzed, accounting for satellite production rates, launch capabilities, and regional adoption patterns, particularly across Belt and Road Initiative (BRI) markets. The study also evaluates "system-of-systems" integration with China’s military objectives, and spectrum coordination challenges. Key findings reveal that Guowang becomes marginally viable only in the optimistic scenario, assuming deployment of at least 9,000 satellites, reduced satellite unit costs (targeting ~76B. Resource allocation problem (RAP) modeling suggests that projected throughput may saturate early without major gateway expansion. Both constellations require China to scale reusable rockets and sustain a combined annual launch rate exceeding 1,000 satellites by the early 2030s. Neither constellation system meets China’s 2030 rural broadband targets under base-case conditions, over 40% of the 336M unconnected citizens remain underserved without terminal subsidies. Ultimately, China’s LEO Satcom strategy depends not on satellite count alone but on coordinated progress in launch economics, affordability, dual-use policy, and international partnerships.S.M
A multi-modal network equilibrium model considering captive travelers and mode correlation
No full textIn making daily commuting trips, a part of travelers, which are called captive travelers, rely on one transport mode due to a lack of access or affordability to other transport modes. To account for the effect of such captive travelers on network equilibrium performances, this paper proposes a multi-modal network equilibrium (MMNE) model that accounts for the captive travelers and the correlations between modes and between routes. First, a hybrid mode choice model is developed by integrating the dogit and nested logit (NL) models. The hybrid dogit–NL (DNL) model has smaller direct and cross elasticity than the NL model, it alleviates the property of irrelevant from independent alternatives and takes the dogit and NL modal splits as bounds. Second, the path-size logit (PSL) model is adopted for predicting travelers’ route choices with overlapping routes. The DNL–PSL MMNE model is formulated as a mathematical programming problem that admits an equivalent and unique solution. Then, a partial linearization algorithm with the Barzilai–Borwein (BB) step sizes is developed. The numerical results reveal that captive travelers lead to lower sensitivity toward transport policies and may cause higher network total travel time; while the perception of mode similarity may impair the overall attractiveness of modes with a high degree of similarity. The observations indicate that to promote green transportation, policy efforts should be made to make use of or adjust the captivity structure and produce diversified perceptions of and preferences for different green transport modes. The BB step sizes are suggested for low travel demand cases when solving the combined travel choice problems. Further, extensions of the DNL model with bundle captivities are discussed. The results of the paper help improve the network equilibrium prediction and support transport policymaking