We study exploration in stochastic multi-armed bandits when we have access to a divisible resource that can be allocated in varying amounts to arm pulls. We focus in particular on the allocation of distributed computing resources, where we may obtain results faster by allocating more resources per pull, but might have reduced throughput due to nonlinear scaling. For example, in simulation-based scientific studies, an expensive simulation can be sped up by running it on multiple cores. This speed-up however, is partly offset by the communication among cores, which results in lower throughput than if fewer cores were allocated per trial to run more trials in parallel. In this paper, we explore these trade-offs in two settings. First, in a fixed confidence setting, we need to find the best arm with a given target success probability as quickly as possible. We propose an algorithm which trades off between information accumulation and throughput and show that the time taken can be upper bounded by the solution of a dynamic program whose inputs are the gaps between the sub-optimal and optimal arms. We also prove a matching hardness result. Second, we present an algorithm for a fixed deadline setting, where we are given a time deadline and need to maximize the probability of finding the best arm. We corroborate our theoretical insights with simulation experiments that show that the algorithms consistently match or outperform baseline algorithms on a variety of problem instances.
We report the α-arylation of ketones with a range of aryl chlorides with enantioselectivities from 90 to 99% ee catalyzed by the combination of Ni(COD)(2) and (R)-BINAP and the coupling of ketones with a range of heteroaryl chlorides with enantioselectivities up to 99% ee catalyzed by Ni(COD)(2) and (R)-DIFLUORPHOS. The analogous reactions of bromoarenes occur with much lower enantioselectivities. Mechanistic studies showed that the difference in the rates of decomposition of the arylnickel(II) halide intermediates to {[(R)-BINAP]NiX}(2) likely accounts for the difference in the enantioselectivities of the reactions of bromoarenes and chloroarenes. This catalyst decomposition can be overcome by conducting the reactions with [(R)-BINAP]Ni(η(2)-NC-Ph) (4), which undergoes oxidative addition to haloarenes at room temperature.
The efficiency of photosynthetic electron transport depends on the coordinated interaction of photosystem II (PSII) and photosystem I (PSI) in the electron-transport chain. Each photosystem contains distinct pigment-protein complexes that harvest light from different regions of the visible spectrum. The light energy is utilized in an endergonic electron-transport reaction at each photosystem. Recent evidence has shown a large variability in the PSII/PSI stoichiometry in plants grown under different environmental irradiance conditions. Results in this work are consistent with the notion of a dynamic, rather than static, thylakoid membrane in which the stoichiometry of the two photosystems is adjusted and optimized in response to different light quality conditions. Direct evidence is provided that photosystem stoichiometry adjustments in chloroplasts are a compensation strategy designed to correct unbalanced absorption of light by the two photosystems. Such adjustments allow the plant to maintain a high quantum efficiency of photosynthesis under diverse light quality conditions and constitute acclimation that confers to plants a significant evolutionary advantage over that of a fixed photosystem stoichiometry in thylakoid membranes.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Canards are a new phenomenon in slow-fast systems. The canard phenomenon in three types of nonlinear systems is studied. The authors first study the behavior of the Hopf bifurcation for the following two-dimensional systems: (a) a slow-fast system with a cubic nonlinearity, (b) a system with a constrained curve, and (c) a slow-fast system with a piecewise linear nonlinearity. It is shown that systems (a) and (b) have canard cycles, but the other forgets them. The Hopf bifurcation scheme of the system (a) is continuous, but (b) and (c) are discontinuous. The same questions are considered for three-dimensional systems. The canard with a pseudosingular saddle point is studied, and its role in the system dynamics is explained. It is shown that the slow-fast system with a piecewise linear nonlinearity drops this kind of canard. By using this result, the existence of a chaotic attractor is shown.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
From alcohol to ether: Iridium-catalyzed allylations yield α chiral ether derivatives directly from aliphatic alcohols with a simple alkali metal base (see equation). These reactions form ethers from primary, secondary, and tertiary alkoxides with high enantioselectivity. By-products from isomerization were suppressed by the use of an alkyne additive.
Organizations have increasingly turned to alternative organizational forms such as joint ventures and internal corporate ventures to enhance innovation. The present study examines the use of a similar, newly-developing organizational form for purposes of innovation; namely, the internal corporate joint venture (ICJV), which has characteristics of both traditional joint ventures and internal corporate venturing. This study presents an industry-specific analysis of innovation across 53 ICJV's (hospital/physician group combinations), using qualitative and quantitative analyses to identify those factors most strongly associated with the degree of innovativeness in these new organizations. The empirical findings suggest three factors most significantly associated with innovation in the ICJV's in our sample: (1) age similarity among organizational members, (2) the sponsoring organization's orientation towards innovation, and (3) ICJV participation in integrative activities with the sponsoring organization. The study concludes by suggesting that greater attention be devoted to studying “nested innovation,” i.e., innovation within a new organizational form that is itself an administrative innovation.
The human heat rate is roughly 40 million beats per year. To prosthetic implants such as mechanical heart valves and endovascular stents, this means that they must endure almost 109 fatigue cycles during the patient’s lifetime. To prevent premature mechanical failures of such devices, which inevitably lead to patient fatalities, considerations of damage-tolerant design and life-prediction methodologies represent a preferred approach. In this presentation, a damage-tolerant approach to life prediction and “quality control” for both metallic and ceramic heart valve prostheses is presented, based on the notion that the useful life of the device is governed by the time for incipient defects in the material to propagate, by stress corrosion or more critically fatigue, to failure. Based on these analyses, the relative benefits of metallic (Co-Cr, Ti-6Al-4V) vs. ceramic (pyrolytic carbon) valves are discussed. Finally, analogous considerations are presented for endovascular stents, particularly those processed by laser cutting of the superelastic Ni-Ti alloy Nitinol. Again, the relative benefits of Nitinol vs. more traditional metallic implant materials (stainless steel, Co-Cr, titanium, titanium alloys) are discussed.
Chapter 1 presents an introduction to this title. It discusses the classification of psychological disorders (the DSM and ICD), the advantages of a transdiagnostic perspective (comorbidity, treatment development, response to treatment) and disadvantages. Processes for evaluating the transdiagnostic process perspective are also outlined (the cognitive behavioural processes, psychological disorders, quality of evidence, and research samples), and the aims of this title.
