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1. Non-stochastic Budgeted Online Pricing with Semi-Bandit Feedback

   https://doi.org/10.1609/aaai.v39i18.34089  

   Liu, Xiang; Chan, Hau; Li, Minming; Wu, Weiwei; Tran-Thanh, Long (April 2025, Proceedings of the AAAI Conference on Artificial Intelligence)

   We consider a general non-stochastic online pricing bandit setting in a procurement scenario where a buyer with a budget wants to procure items from a fixed set of sellers to maximize the buyer's reward by dynamically offering purchasing prices to the sellers, where the sellers' costs and values at each time period can change arbitrarily and the sellers determine whether to accept the offered prices to sell the items. This setting models online pricing scenarios of procuring resources or services in multi-agent systems. We first consider the offline setting when sellers' costs and values are known in advance and investigate the best fixed-price policy in hindsight. We show that it has a tight approximation guarantee with respect to the offline optimal solutions. In the general online setting, we propose an online pricing policy, Granularity-based Pricing (GAP), which exploits underlying side-information from the feedback graph when the budget is given as the input. We show that GAP achieves an upper bound of O(n{v_{max}}{c_{min}}sqrt{B/c_{min}}ln B) on the alpha-regret where n, v_{max}, c_{min}, and B are the number, the maximum value, the minimum cost of sellers, and the budget, respectively. We then extend it to the unknown budget case by developing a variant of GAP, namely Doubling-GAP, and show its alpha-regret is at most O(n{v_{max}}{c_{min}}sqrt{B/c_{min}}ln2 B). We also provide an alpha-regret lower bound Omega(v_{max}sqrt{Bn/c_{min}}) of any online policy that is tight up to sub-linear terms. We conduct simulation experiments to show that the proposed policy outperforms the baseline algorithms. 

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2. The effectiveness of selection in a species affects the direction of amino acid frequency evolution

   https://doi.org/10.1101/2023.02.01.526552  

   McShea, Hanon; Wheeler, Andrew L; Goodman, Peter; Weibel, Catherine; Wehbi, Sawsan; James, Jennifer E; Huttley, Gavin; Masel, Joanna (February 2023, bioRxiv)

   Nearly neutral theory predicts that species with higher effective population size (N_e) are better at purging slightly deleterious mutations. We compare evolution in high N_e vs. low-N_e vertebrates to reveal subtle selective preferences among amino acids. We take three complementary approaches. First, we fit non-stationary substitution models using maximum likelihood, comparing the high-N_e clade of rodents and lagomorphs to its low-N_e sister clade of primates and colugos. Second, we compared evolutionary outcomes across a wider range of vertebrates, via correlations between amino acid frequencies and N_e. Third, we dissected which amino acids substitutions occurred in human, chimpanzee, mouse, and rat, as scored by parsimony – this also enabled comparison to a historical paper. All methods agree on amino acid preference under more effective selection. Preferred amino acids are less costly to synthesize and use GC-rich codons, which are hard to maintain under AT-biased mutation. These factors explain 85% of the variance in amino acid preferences. Parsimony-induced bias in the historical study produces an apparent reduction in structural disorder, perhaps driven by slightly deleterious substitutions in rapidly evolving regions. Within highly exchangeable pairs of amino acids, arginine is strongly preferred over lysine, aspartate over glutamate, and valine over isoleucine, consistent with more effective selection preferring a marginally larger free energy of folding. Two of these preferences (K→R and I→V), but not a third (E→D) match differences between thermophiles and mesophilic relatives. These results reveal the biophysical consequences of mutation-selection-drift balance, and demonstrate the utility of nearly neutral theory for understanding protein evolution. 

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3. Convex polytopes in restricted point sets in R^d

   https://doi.org/10.19086/aic.2025.1  

   Bukh, Boris; Zichao, Dong (January 2025, Advances in Combinatorics)

   For a finite point set P⊂R^d, denote by diam(P) the ratio of the largest to the smallest distances between pairs of points in P. Let c_{d,α}(n) be the largest integer c such that any n-point set P⊂R^d in general position, satisfying diam(P)<αn^{1/d}, contains an c-point convex independent subset. We determine the asymptotics of c_{d,α}(n) as n→∞ by showing the existence of positive constants β=β(d,α) and γ=γ(d) such that βn^{(d−1)/(d+1)}≤c_{d,α}(n)≤γn^{(d−1)/(d+1)} for α≥2. 

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4. Revisiting the Dependence of Poisson’s Ratio on Liquid Fragility and Atomic Packing Density in Oxide Glasses

   https://doi.org/10.3390/ma12152439  

   Østergaard, Martin B.; Hansen, Søren R.; Januchta, Kacper; To, Theany; Rzoska, Sylwester J.; Bockowski, Michal; Bauchy, Mathieu; Smedskjaer, Morten M. (August 2019, Materials)

   Poisson’s ratio (ν) defines a material’s propensity to laterally expand upon compression, or laterally shrink upon tension for non-auxetic materials. This fundamental metric has traditionally, in some fields, been assumed to be a material-independent constant, but it is clear that it varies with composition across glasses, ceramics, metals, and polymers. The intrinsically elastic metric has also been suggested to control a range of properties, even beyond the linear-elastic regime. Notably, metallic glasses show a striking brittle-to-ductile (BTD) transition for ν-values above ~0.32. The BTD transition has also been suggested to be valid for oxide glasses, but, unfortunately, direct prediction of Poisson’s ratio from chemical composition remains challenging. With the long-term goal to discover such high-ν oxide glasses, we here revisit whether previously proposed relationships between Poisson’s ratio and liquid fragility (m) and atomic packing density (Cg) hold for oxide glasses, since this would enable m and Cg to be used as surrogates for ν. To do so, we have performed an extensive literature review and synthesized new oxide glasses within the zinc borate and aluminoborate families that are found to exhibit high Poisson’s ratio values up to ~0.34. We are not able to unequivocally confirm the universality of the Novikov-Sokolov correlation between ν and m and that between ν and Cg for oxide glass-formers, nor for the organic, ionic, chalcogenide, halogenide, or metallic glasses. Despite significant scatter, we do, however, observe an overall increase in ν with increasing m and Cg, but it is clear that additional structural details besides m or Cg are needed to predict and understand the composition dependence of Poisson’s ratio. Finally, we also infer from literature data that, in addition to high ν, high Young’s modulus is also needed to obtain glasses with high fracture toughness. 

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5. Polymer Glasses

   https://doi.org/10.1002/9783527815562.mme0064  

   Connie B. Roth (March 2022, Macromolecular Engineering: From Precise Synthesis to Macroscopic Materials and Applications)

   Matyjaszewski, Krzysztof; Gnanou, Yves; Hadjichristidis, Nikos; Muthukumar, Murugappan (Ed.)

   Polymers exist in the glass state for a wide range of applications. The slow and limited crystallizability of polymers means that solid polymer materials are either wholly or in part glassy, giving them great importance. The glass is a nonequilibrium amorphous state that occurs because the cooperative molecular dynamics become kinetically trapped on cooling as the available thermal energy for molecular motion decreases. This article aims to provide the reader with a molecular picture of what this packing frustration that causes glass formation means for polymers. Experimental considerations for accurately measuring the glass transition temperature 𝑇𝑔 given this nonequilibrium nature will be discussed. Basic concepts underpinning theoretical efforts to model the glass transition will be summarized to provide the reader with a lexicon and paradigm for understanding different approaches used in the field to capture the main characteristics of glasses. Current research areas of interest in polymer glasses will be briefly outlined. Hopefully, this article will provide the beginning investigator a starting point for their own studies. 

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