The Spatial Product of Arveson Systems is Intrinsic

We prove that the spatial product of two spatial Arveson systems is independent of the choice of the reference units. This also answers the same question for the minimal dilation the Powers sum of two spatial CP-semigroups: It is independent up to cocycle conjugacy

Graph Sparsifications using Neural Network Assisted Monte Carlo Tree Search

Graph neural networks have been successful for machine learning, as well as for combinatorial and graph problems such as the Subgraph Isomorphism Problem and the Traveling Salesman Problem. We describe an approach for computing graph sparsifiers by combining a graph neural network and Monte Carlo Tree Search. We first train a graph neural network that takes as input a partial solution and proposes a new node to be added as output. This neural network is then used in a Monte Carlo search to compute a sparsifier. The proposed method consistently outperforms several standard approximation algorithms on different types of graphs and often finds the optimal solution.Comment: arXiv admin note: substantial text overlap with arXiv:2305.0053

A Game-Theoretic Approach for Hierarchical Policy-Making

We present the design and analysis of a multi-level game-theoretic model of hierarchical policy-making, inspired by policy responses to the COVID-19 pandemic. Our model captures the potentially mismatched priorities among a hierarchy of policy-makers (e.g., federal, state, and local governments) with respect to two main cost components that have opposite dependence on the policy strength, such as post-intervention infection rates and the cost of policy implementation. Our model further includes a crucial third factor in decisions: a cost of non-compliance with the policy-maker immediately above in the hierarchy, such as non-compliance of state with federal policies. Our first contribution is a closed-form approximation of a recently published agent-based model to compute the number of infections for any implemented policy. Second, we present a novel equilibrium selection criterion that addresses common issues with equilibrium multiplicity in our setting. Third, we propose a hierarchical algorithm based on best response dynamics for computing an approximate equilibrium of the hierarchical policy-making game consistent with our solution concept. Finally, we present an empirical investigation of equilibrium policy strategies in this game in terms of the extent of free riding as well as fairness in the distribution of costs depending on game parameters such as the degree of centralization and disagreements about policy priorities among the agents

Tuning crystalline ordering by annealing and additives to study its effect on exciton diffusion in a polyalkylthiophene copolymer

M.C, M.T.S, A.R and I.D.W.S acknowledge support from the European Research Council (EXCITON grant 321305). I.D.W.S acknowledges Royal Society Wolfson Research Merit Award. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515The influence of various processing conditions on the singlet exciton diffusion is explored in films of a conjugated random copolymer poly-(3-hexylthiophene-co-3-dodecylthiophene) (P3HT-co-P3DDT) and correlated with the degree of crystallinity probed by grazing incidence X-ray scattering and with exciton bandwidth determined from absorption spectra. The exciton diffusion coefficient is deduced from exciton-exciton annihilation measurements and is found to increase by more than a factor of three when thin films are annealed using CS2 solvent vapour. A doubling of exciton diffusion coefficient is observed upon melt annealing at 200 °C and the corresponding films show about 50% enhancement in the degree of crystallinity. In contrast, films fabricated from polymer solutions containing a small amount of either solvent additive or nucleating agent show a decrease in exciton diffusion coefficient possibly due to formation of traps for excitons. Our results suggest that the enhancement of exciton diffusivity occurs because of increased crystallinity of alkyl-stacking and longer conjugation of aggregated chains which reduces the exciton bandwidth.Publisher PDFPeer reviewe

Long-term feeder-free culture of human pancreatic progenitors on fibronectin or matrix-free polymer potentiates β cell differentiation

With the aim of producing β cells for replacement therapies to treat diabetes, several protocols have been developed to differentiate human pluripotent stem cells to β cells via pancreatic progenitors. While in vivo pancreatic progenitors expand throughout development, the in vitro protocols have been designed to make these cells progress as fast as possible to β cells. Here, we report on a protocol enabling a long-term expansion of human pancreatic progenitors in a defined medium on fibronectin, in the absence of feeder layers. Moreover, through a screening of a polymer library we identify a polymer that can replace fibronectin. Our experiments, comparing expanded progenitors to directly differentiated progenitors, show that the expanded progenitors differentiate more efficiently into glucose-responsive β cells and produce fewer glucagon-expressing cells. The ability to expand progenitors under defined conditions and cryopreserve them will provide flexibility in research and therapeutic production

The Effect of Liquidity on the Spoofability of Financial Markets

We investigate the relationship between market liquidity and spoof- ing, a manipulative practice involving the submission of deceptive orders aimed at misleading other traders. Utilizing an agent-based market simulator, we model markets with varying levels of liquidity, adjusting the spread and intervals of a market maker’s orders to control liquidity. Within these simulated markets, we evaluate the effectiveness of two novel spoofing strategies against a benchmark approach. Our experiments show that in high-liquidity markets, spoofing is substantially less profitable and less detrimental to other traders compared to their low-liquidity counterparts. Additionally, we identify two distinct spoofing behavior regimes based on liq- uidity, each of which employ drastically different profit-making strategies. Finally, building on our quantitative findings, we iden- tify and expound upon the mechanisms through which liquidity mitigates market manipulation

Quantitative Proteomics of an Amphibian Pathogen, Batrachochytrium dendrobatidis, following Exposure to Thyroid Hormone

Batrachochytrium dendrobatidis (Bd), a chytrid fungus, has increasingly been implicated as a major factor in the worldwide decline of amphibian populations. The fungus causes chytridiomycosis in susceptible species leading to massive die-offs of adult amphibians. Although Bd infects the keratinized mouthparts of tadpoles and negatively affects foraging behavior, these infections are non-lethal. An important morphogen controlling amphibian metamorphosis is thyroid hormone (T3). Tadpoles may be infected with Bd and the fungus may be exposed to T3 during metamorphosis. We hypothesize that exposure of Bd to T3 may induce the expression of factors associated with host colonization and pathogenicity. We utilized a proteomics approach to better understand the dynamics of the Bd-T3 interaction. Using liquid chromatography-mass spectrometry (LC-MS), we generated a data set of a large number of cytoplasmic and membrane proteins following exposure of Bd to T3. From these data, we identified a total of 263 proteins whose expression was significantly changed following T3 exposure. We provide evidence for expression of an array of proteins that may play key roles in both genomic and non-genomic actions of T3 in Bd. Additionally, our proteomics study shows an increase in several proteins including proteases and a class of uncommon crinkler and crinkler-like effector proteins suggesting their importance in Bd pathogenicity as well as those involved in metabolism and energy transfer, protein fate, transport and stress responses. This approach provides insights into the mechanistic basis of the Bd-amphibian interaction following T3 exposure

Site-selective generation of lanthanoid binding sites on proteins using 4-fluoro-2,6-dicyanopyridine

The paramagnetism of a lanthanoid tag site-specifically installed on a protein provides a rich source of structural information accessible by nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy. Here we report a lanthanoid tag for selective reaction with cysteine or selenocysteine with formation of a (seleno)thioether bond and a short tether between the lanthanoid ion and the protein backbone. The tag is assembled on the protein in three steps, comprising (i) reaction with 4-fluoro-2,6-dicyanopyridine (FDCP); (ii) reaction of the cyano groups with α-cysteine, penicillamine or β-cysteine to complete the lanthanoid chelating moiety; and (iii) titration with a lanthanoid ion. FDCP reacts much faster with selenocysteine than cysteine, opening a route for selective tagging in the presence of solvent-exposed cysteine residues. Loaded with Tb3+ and Tm3+ ions, pseudocontact shifts were observed in protein NMR spectra, confirming that the tag delivers good immobilisation of the lanthanoid ion relative to the protein, which was also manifested in residual dipolar couplings. Completion of the tag with different 1,2-aminothiol compounds resulted in different magnetic susceptibility tensors. In addition, the tag proved suitable for measuring distance distributions in double electron–electron resonance experiments after titration with Gd3+ ions.This research has been supported by the Australian Research Council (grant no. FL170100019 and DP210100088), the Australian Research Council Centre of Excellence for Innovations in Peptide and Protein Science (grant no. CE200100012) and the European Regional Development Fund (ERDF; PostDoc grant no. 1.1.1.2/VIAA/2/18/381)