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1. Time-Resolved Measurements of Photocarrier Dynamics in TiS ₃ Nanoribbons

   https://doi.org/10.1021/acsami.6b04092  

   Cui, Qiannan; Lipatov, Alexey; Wilt, Jamie Samantha; Bellus, Matthew Z.; Zeng, Xiao Cheng; Wu, Judy; Sinitskii, Alexander; Zhao, Hui (July 2016, ACS Applied Materials & Interfaces)
2. Set Cover in Sub-linear Time

   Indyk, Piotr; Mahabadi, Sepideh; Rubinfeld, Ronitt; Vakilian, Ali; Yodpinyanee, Anak (January 2018, Annual ACM-SIAM Symposium on Discrete Algorithms)

   We study the classic set cover problem from the perspective of sub-linear algorithms. Given access to a collection of m sets over n elements in the query model, we show that sub-linear algorithms derived from existing techniques have almost tight query complexities. On one hand, first we show an adaptation of the streaming algorithm presented in [17] to the sub-linear query model, that returns an α-approximate cover using Õ(m(n/k)^1/(α–1) + nk) queries to the input, where k denotes the value of a minimum set cover. We then complement this upper bound by proving that for lower values of k, the required number of queries is , even for estimating the optimal cover size. Moreover, we prove that even checking whether a given collection of sets covers all the elements would require Ω(nk) queries. These two lower bounds provide strong evidence that the upper bound is almost tight for certain values of the parameter k. On the other hand, we show that this bound is not optimal for larger values of the parameter k, as there exists a (1 + ε)-approximation algorithm with Õ(mn/kε^2) queries. We show that this bound is essentially tight for sufficiently small constant ε, by establishing a lower bound of query complexity. Our lower-bound results follow by carefully designing two distributions of instances that are hard to distinguish. In particular, our first lower bound involves a probabilistic construction of a certain set system with a minimum set cover of size αk, with the key property that a small number of “almost uniformly distributed” modifications can reduce the minimum set cover size down to k. Thus, these modifications are not detectable unless a large number of queries are asked. We believe that our probabilistic construction technique might find applications to lower bounds for other combinatorial optimization problems. 

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3. OnDistribution Dependent Sub-Logarithmic Query Time of Learned Indexing

   Zeighami, Speanta; Shahabi, Cyrus (July 2023, ICML 2023)
4. H ₂ O time histories in the H ₂ ‐NO ₂ system for validation of NOx hydrocarbon kinetics mechanisms

   https://doi.org/10.1002/kin.21286  

   Mulvihill, Clayton R.; Mathieu, Olivier; Petersen, Eric L. (May 2019, International Journal of Chemical Kinetics)

   Abstract The development and refinement of NOx chemical kinetic mechanisms have been instrumental in understanding and reducing NOx formation. However, relatively little work has been performed with NOx species as the oxidizer, and such experiments can provide unique insights into NOx kinetics. Furthermore, speciation data can often provide useful information that complements global measurements such as ignition delay times in facilitating mechanism refinement. To provide such speciation data in the H₂‐NO₂system, H₂O measurements were performed using a fixed‐wavelength, direct absorption laser diagnostic near 1.39 µm behind reflected shock waves in fuel‐lean, near‐stoichiometric, and fuel‐rich mixtures of H₂and NO₂highly diluted in argon. Experiments were performed between 917 and 1782 K near atmospheric pressure. The H₂O profiles obtained herein are markedly different from those using O₂as the oxidizer obtained in a previous study. The GRI 3.0 mechanism was found to greatly underestimate the H₂O formation, whereas two modern mechanisms were found to predict the H₂O formation quite accurately except at colder temperatures for fuel‐rich conditions. Explanations for the differences between these mechanisms are given and discussed, with the conclusion that older mechanisms such as GRI 3.0 should not be used to model hydrocarbon/NOx combustion chemistry as they are lacking several key reactions and species, namely NO₃and HONO. The discrepancy between models and data at lower temperatures could not be reconciled even when modifying two of the most‐sensitive reaction rates. To the best of the authors’ knowledge, this study presents the first shock‐tube speciation study in the H₂‐NO₂system. 

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5. MoS ₂ pixel arrays for real-time photoluminescence imaging of redox molecules

   https://doi.org/10.1126/sciadv.aat9476  

   Reynolds, M. F.; Guimarães, M. H.; Gao, H.; Kang, K.; Cortese, A. J.; Ralph, D. C.; Park, J.; McEuen, P. L. (November 2019, Science Advances)

   Measuring the behavior of redox-active molecules in space and time is crucial for understanding chemical and biological systems and for developing new technologies. Optical schemes are noninvasive and scalable, but usually have a slow response compared to electrical detection methods. Furthermore, many fluorescent molecules for redox detection degrade in brightness over long exposure times. Here, we show that the photoluminescence of “pixel” arrays of monolayer MoS 2 can image spatial and temporal changes in redox molecule concentration. Because of the strong dependence of MoS 2 photoluminescence on doping, changes in the local chemical potential substantially modulate the photoluminescence of MoS 2 , with a sensitivity of 0.9 mV / Hz on a 5 μm × 5 μm pixel, corresponding to better than parts-per-hundred changes in redox molecule concentration down to nanomolar concentrations at 100-ms frame rates. This provides a new strategy for visualizing chemical reactions and biomolecules with a two-dimensional material screen. 

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