arXiv subjects

Thomas Larsen

Publications and source records attributed to Thomas Larsen.

5 recordsLinked to original sources

arXiv2024

Decoupling elasticity and electrical conductivity of carbon black gels filled with insulating non-Brownian grains

A unique bistable transition has been identified in granular/colloidal gel-composites, resulting from shear-induced phase separation of the gel phase into dense blobs. In energy applications, it is critical to understand how this transition influences electrical performance. Mixing conductive colloids with conductive inclusions, we find the conductivity and elasticity move in concert, both decreasing in the collapsed phase-separated state. Surprisingly, with insulating inclusions these properties can become decoupled, with the conductivity instead increasing despite the collapse of the gel structure.

cond-mat.soft↗

arXiv2024

Safety Cases: How to Justify the Safety of Advanced AI Systems

As AI systems become more advanced, companies and regulators will make difficult decisions about whether it is safe to train and deploy them. To prepare for these decisions, we investigate how developers could make a 'safety case,' which is a structured rationale that AI systems are unlikely to cause a catastrophe. We propose a framework for organizing a safety case and discuss four categories of arguments to justify safety: total inability to cause a catastrophe, sufficiently strong control measures, trustworthiness despite capability to cause harm, and -- if AI systems become much more powerful -- deference to credible AI advisors. We evaluate concrete examples of arguments in each category and outline how arguments could be combined to justify that AI systems are safe to deploy.

cs.CY↗

arXiv2023

Controlling the rheo-electric properties of graphite/carbon black suspensions by 'flow-switching'

The ability to manipulate rheological and electrical properties of colloidal carbon black gels makes them attractive in composites for energy applications such as batteries and fuel cells, where they conduct electricity and prevent sedimentation of `granular' active components. While it is commonly assumed that granular fillers have a simple additive effect on the composite properties, new phenomena can emerge unexpectedly, with some composites exhibiting a unique rheological bi-stability between solid-like and liquid-like states. Here we report such bi-stability in suspensions of non-Brownian graphite and colloidal carbon black in oil, a model system to mimic composite suspensions for energy applications. Steady shear below a critical stress elicits a transition to a persistent mechanically weak and poorly conducting state, which must be `rejuvenated' using high-stress shear to recover a stronger, high-conductivity state. Our findings highlight the highly tunable nature of binary granular/gel composite suspensions, and present new possibilities for optimizing mixing and processing conditions for Li-ion battery slurries.

cond-mat.soft↗

arXiv2022

Pressure-Independent Through-Plane Electrical Conductivity Measurements of Highly Filled Conductive Polymer Composites

Highly filled conductive polymer composites (CPCs) are widely used in applications such as bipolar plate materials for polymer electrolyte membrane fuel cells and redox flow batteries, electromagnetic interference shielding and sensors due to their useful electrical properties. A common method for determining through-plane electrical conductivities $\left(\sigma_{\rm tp} \right)$ of such highly filled CPCs applies a conductive carbon paper between electrodes and sample with application of external pressure to improve electrical contact. We show the pressure-dependence of the measured $\sigma_{\rm tp}$ can be eliminated by using a liquid metal such as the gallium-indium eutectic alloy (EGaIn) as contact material. Results indicate that EGaIn reduces contact resistances and cause three to five times larger $\sigma_{\rm tp}$ compared to measurements with carbon paper contacts and pressures up to 20 bar.

cond-mat.mtrl-sci↗

arXiv2020

The effect of temperature on basal metabolism of Mnemiopsis leidyi

To evaluate the influence of temperature on metabolic performance on the invasive ctenophore Mnemiopsis leidyi, we exposed fully acclimatized adults to conditions typical for the annual variability of the Western Baltic Sea region. We derived basal metabolic rates from oxygen consumption rates of adult M. leidyi specimens exposed to temperatures between 3.5°C to 20.5°C at a salinity of 22. We found a Q10 value of 3.67, which means that the carbon specific respiration rates are about 9 times greater at 20°C than 3°C. According to this rate, a small-sized individual 20 mm in oral-aboral length, would without feeding have enough nutrient reserves to survive 80 days at 3°C, but only 9 days at 20°C. Thus, prey availability during late summer is critical for M. leidyi population survival.

q-bio.PE↗