斯坦福大学

What is the best compromise in a situation where different people value different things? The most common method for answering this question is to look at all the options, add up the utility per person associated with each, and pick the option with the largest sum. This approach seems like the obvious, theory-neutral solution, though, in fact, it relies on substantive utilitarian commitments. A second, quite common approach, involves integrating egalitarian concerns, and picking an option that trades off maximizing utility with equalizing outcomes. But there is an important, though often-ignored, third approach as well: a contractualist approach, which models what rational actors would agree to. In this paper, we test the proposals of these three competing preference aggregation algorithms in social decision-making contexts that are systematically sampled across a wide range. While the dominant approach to value aggregation up to now has been utilitarian, we find that participants strongly prefer the aggregations recommended by the contractualist algorithm, which also dominates the egalitarian approach across a range of parameterizations. Finally, we compare the judgments of large language models (LLMs) to those of our (human) participants, finding important misalignment between model and human preferences.

Implant-associated infection remains one of the leading causes of failure in orthopaedics, imposing substantial clinical and economic burdens despite advances in surgical techniques and antibiotic therapy. Conventional infection management strategies, including systemic antibiotics, local drug delivery, surface coatings, and physical surface modifications, primarily provide short-term protection. These approaches fail to deliver sustained antibacterial performance over the long service life expected for load-bearing implants. This review critically evaluates existing antibacterial strategies, highlighting their mechanisms, advantages, and translational limitations. Particular emphasis is placed on the fundamental shortcomings of surface-based approaches and external stimulus-responsive systems in long-term clinical scenarios. Building on these insights, the emerging paradigm of bulk antibacterial alloy design for infection-resistant implants is discussed. Copper, silver, and zinc are widely accepted antibacterial elements; however, they cannot be used as standalone bulk materials because they do not independently meet the mechanical, corrosion, and biocompatibility requirements of metallic implants. Among them, silver is limited by elution-driven activity and cytotoxicity concerns, zinc exhibits relatively weaker antibacterial efficacy, while copper offers a favorable balance of antibacterial performance, alloyability, and structural compatibility. Copper-, silver-, and zinc-containing alloy systems are systematically examined with respect to antibacterial efficacy, cytocompatibility, corrosion behavior, and mechanical integrity. Copper-added alloys, which offer broad-spectrum antibacterial activity through contact killing and controlled ion release while preserving structural performance when appropriately alloyed, are extensively discussed. Finally, future directions are outlined, including biodegradable antibacterial metals, multi-functional alloy design, and data-driven alloy optimisation strategies, providing a roadmap toward clinically viable, long-term infection-resistant implant materials.

Flammable liquids leaking on hot surfaces are an ignition hazard for fires in aircraft, vehicles, and heavy machinery. Engineering analysis to assess fire risk in these devices must account for the flammability properties of fuels and other liquids. The autoignition temperature (AIT) is most often used for this purpose. AIT is determined following a standard procedure, such as ASTM E659, but it is well-established that the minimum ignition temperature in practical industrial configurations is often significantly higher than the AIT. In this work, we introduce a canonical experimental apparatus that addresses this issue. This proposed apparatus enables the characterization of the probabilistic hot surface ignition behavior of flammable liquids in configurations featuring thermal stratification and reduced residence times compared to ASTM E659. The apparatus is highly flexible, enabling testing with various surface materials, droplet diameters, impact velocities, and repetition rates. The introduction of automated optical diagnostics enables rapid testing of multiple fuels. The main focus of the present work is to demonstrate the repeatability of the measurements conducted in this apparatus: In repeated experiments with n-hexane, we find that the standard deviation of the hot surface ignition temperature is 3.8K. A thorough analysis of the experimental uncertainties is also conducted. We demonstrate the capabilities of the apparatus by examining fuel effects on the ignition behavior of eight fuels: n-hexane, a conventionally-derived Jet A fuel, and six synthetic aviation turbine fuels (SATFs). We find that the 50% ignition probability temperature of the most ignitable and least ignitable of our six SATFs differs by 70K, which motivates future efforts to better account for fuel effects in ignition risk analysis as new SATFs are entering the aviation fuel market.

Research shows that maintenance of Spanish, the heritage or home language of 75% of U.S. Latine children and adolescents, is associated with their positive psychosocial development and academic achievement. Furthermore, a solid foundation in oral language skills in early childhood contributes to their literacy and overall academic success. Use of Spanish in the home by parents/caregivers has been studied in relation to Latine children’s Spanish oral language skills, yet relatively little is known about the cultural factors that shape these skills in early childhood. Using observation based measures of language production in the interactions of 166 Mexican-origin young mothers (Mage = 19.98; SD = 1.00) with their children, this study examined mothers’ Mexican cultural involvement when their children were three years of age, their cultural socialization practices and Spanish language use with their children at child age 4, and the direct and indirect associations of these cultural factors with children’s language production in Spanish at child age 5. Results showed that mothers’ Mexican cultural involvement positively predicted their young children’s Spanish oral language production at age 5, even after controlling for mothers’ use of Spanish in mother-child interactions and efforts to socialize their young children to the Mexican culture. Mothers’ use of Spanish and their cultural socialization efforts differentially mediated the association between their Mexican cultural involvement and their young children’s Spanish language skills. Findings highlight the critical role of Mexican-origin mothers’ cultural assets for their children’s bilingual development in early childhood.

Supercritical CO2 (scCO(2)) plays a crucial role as a solvent in separation processes, advanced power cycles, and materials processing. Nonetheless, the atomistic comprehension of how the dense scCO(2) matrix influences the fundamental reaction of carbon monoxide (CO) is still insufficiently explored. Experimental studies and molecular dynamics (MD) simulations frequently fail to detect the highly reactive, transient intermediates, such as atomic oxygen (O), that drive these reactions. To address this issue, we have developed a novel ReaxFF reactive force field for the CO2/CO/O system. The force field parameters were calibrated using density functional theory and second-order M & oslash;ller-Plesset calculations to model CO2 crystal properties, intermolecular interactions, bond dissociation curves, and reaction energy barriers. The force field reproduces the cohesive energy of the CO2 crystal, the pressure characteristics of bulk scCO(2), the equation-of-state behavior over a wide pressure-density range, the pressure dependence of the C-O bond length under compression, and the structural properties of liquid and scCO(2), as documented by experiments, ab-initio MD, and prominent non-reactive models. The force field was subsequently applied to study the CO + O -> CO2 reaction. In a dilute environment, the reaction is inefficient as the newly formed CO2 rapidly dissociates due to excess kinetic and potential energy acquired from the exothermic reaction. Conversely, in a dense scCO(2) environment, the surrounding matrix acts as an efficient third body, stabilizing the emerging CO2 product via molecular collisions. Statistical analysis confirms an average excess energy dissipation of 133.9 +/- 3.6 kcal/mol over 112.4 +/- 17.9 ps. Kinetic energy decomposition reveals that similar to 92% of the excess kinetic energy is stored in internal (rotational and vibrational) degrees of freedom. This ReaxFF force field establishes a mechanistic foundation for third-body stabilization in dense reactive environments.