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121.
[reaction: see text] Pd[(-)-sparteine]Cl(2) catalyzes the formation of dialkyl acetals from styrene derivatives with Markovnikov regioselectivity. The substrate scope of this reaction has been investigated, and initial mechanistic studies indicate that the reaction proceeds through an enol ether intermediate and a Pd-hydride. 相似文献
122.
In a M/M/N+M queue, when there are many customers waiting, it may be preferable to reject a new arrival rather than risk that arrival
later abandoning without receiving service. On the other hand, rejecting new arrivals increases the percentage of time servers
are idle, which also may not be desirable. We address these trade-offs by considering an admission control problem for a M/M/N+M queue when there are costs associated with customer abandonment, server idleness, and turning away customers. First, we formulate
the relevant Markov decision process (MDP), show that the optimal policy is of threshold form, and provide a simple and efficient
iterative algorithm that does not presuppose a bounded state space to compute the minimum infinite horizon expected average
cost and associated threshold level. Under certain conditions we can guarantee that the algorithm provides an exact optimal
solution when it stops; otherwise, the algorithm stops when a provided bound on the optimality gap is reached. Next, we solve
the approximating diffusion control problem (DCP) that arises in the Halfin–Whitt many-server limit regime. This allows us
to establish that the parameter space has a sharp division. Specifically, there is an optimal solution with a finite threshold
level when the cost of an abandonment exceeds the cost of rejecting a customer; otherwise, there is an optimal solution that
exercises no control. This analysis also yields a convenient analytic expression for the infinite horizon expected average
cost as a function of the threshold level. Finally, we propose a policy for the original system that is based on the DCP solution,
and show that this policy is asymptotically optimal. Our extensive numerical study shows that the control that arises from
solving the DCP achieves a very similar cost to the control that arises from solving the MDP, even when the number of servers
is small. 相似文献
123.
Two related case studies of secondary mathematics teachers examine the roles and conditions helpful in initiating, directing, and/or supporting teachers' own professional development. Using multiple data sources from school‐based and professional settings, we applied analytic induction to identify patterns of similarities and differences in teachers' experiences and developmental trajectories. Findings revealed how the teachers served as brokers in their own development process and how attitude, attention, and awareness played important roles in teacher learning. As the teachers initiated learning processes, they demonstrated awareness of broader educational contexts that support learning by identifying external policies and priorities that aligned with teachers' attitudes. They then used these external priorities as boundary objects to broker for teachers' learning, including other teachers' learning. They attended to learning needs in directing a plan for learning activities, rather than using externally mandated goals for changing practice (e.g., an external focus on improving students' tests scores). These cases suggest that in structuring professional learning, opportunities to self‐identify learning needs should be part of the process, and external supports can become more powerful when teachers play a brokering role in relating these supports to their immediate contexts. Further implications for professional development processes are explored. 相似文献
124.
Amy F. Szczepański 《代数通讯》2013,41(11):4159-4169
A result of Artin, Small, and Zhang is used to show that a Noetherian algebra over a commutative, Noetherian Jacobson ring will be Jacobson if the algebra possesses a locally finite, Noetherian associated graded ring. This result is extended to show that if an algebra over a commutative Noetherian ring has a locally finite, Noetherian associated graded ring, then the intersection of the powers of the Jacobson radical is nilpotent. The proofs rely on a weak generalization of generic flatness and some observations about G-rings. 相似文献
125.
126.
Gabrielle A. Leith Allison M. Rice Brandon J. Yarbrough Anna A. Berseneva Richard T. Ly Charles N. Buck III Dr. Denis Chusov Amy J. Brandt Prof. Dr. Donna A. Chen Benjamin W. Lamm Prof. Dr. Morgan Stefik Kenneth S. Stephenson Dr. Mark D. Smith Prof. Dr. Aaron K. Vannucci Dr. Perry J. Pellechia Prof. Dr. Sophya Garashchuk Prof. Dr. Natalia B. Shustova 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(15):6056-6062
The effect of donor (D)–acceptor (A) alignment on the materials electronic structure was probed for the first time using novel purely organic porous crystalline materials with covalently bound two- and three-dimensional acceptors. The first studies towards estimation of charge transfer rates as a function of acceptor stacking are in line with the experimentally observed drastic, eight-fold conductivity enhancement. The first evaluation of redox behavior of buckyball- or tetracyanoquinodimethane-integrated crystalline was conducted. In parallel with tailoring the D-A alignment responsible for “static” changes in materials properties, an external stimulus was applied for “dynamic” control of the electronic profiles. Overall, the presented D–A strategic design, with stimuli-controlled electronic behavior, redox activity, and modularity could be used as a blueprint for the development of electroactive and conductive multidimensional and multifunctional crystalline porous materials. 相似文献
127.
128.
Aspartate‐Based CXCR4 Chemokine Receptor Binding of Cross‐Bridged Tetraazamacrocyclic Copper(II) and Zinc(II) Complexes
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Randall D. Maples Amy N. Cain Dr. Benjamin P. Burke Dr. Jon D. Silversides Dr. Ryan E. Mewis Thomas D'huys Prof. Dominique Schols Prof. Douglas P. Linder Prof. Stephen J. Archibald Prof. Timothy J. Hubin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(36):12916-12930
The CXCR4 chemokine receptor is implicated in a number of diseases including HIV infection and cancer development and metastasis. Previous studies have demonstrated that configurationally restricted bis‐tetraazamacrocyclic metal complexes are high‐affinity CXCR4 antagonists. Here, we present the synthesis of Cu2+ and Zn2+ acetate complexes of six cross‐bridged tetraazamacrocycles to mimic their coordination interaction with the aspartate side chains known to bind them to CXCR4. X‐ray crystal structures for three new Cu2+ acetate complexes and two new Zn2+ acetate complexes demonstrate metal‐ion‐dependent differences in the mode of binding the acetate ligand concomitantly with the requisite cis‐V‐configured cross‐bridged tetraazamacrocyle. Concurrent density functional theory molecular modelling studies produced an energetic rationale for the unexpected [Zn(OAc)(H2O)]+ coordination motif present in all of the Zn2+ cross‐bridged tetraazamacrocycle crystal structures, which differs from the chelating acetate [Zn(OAc)]+ structures of known unbridged and side‐bridged tetraazamacrocyclic Zn2+‐containing CXCR4 antagonists. 相似文献
129.
130.
Stack the Bowls: Tailoring the Electronic Structure of Corannulene‐Integrated Crystalline Materials
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Allison M. Rice Ekaterina A. Dolgopolova Brandon J. Yarbrough Gabrielle A. Leith Corey R. Martin Kenneth S. Stephenson Rebecca A. Heugh Amy J. Brandt Prof. Dr. Donna A. Chen Dr. Stavros G. Karakalos Dr. Mark D. Smith Prof. Dr. Kelsey B. Hatzell Dr. Perry J. Pellechia Prof. Dr. Sophya Garashchuk Prof. Dr. Natalia B. Shustova 《Angewandte Chemie (International ed. in English)》2018,57(35):11310-11315
We report the first examples of purely organic donor–acceptor materials with integrated π‐bowls (πBs) that combine not only crystallinity and high surface areas but also exhibit tunable electronic properties, resulting in a four‐orders‐of‐magnitude conductivity enhancement in comparison with the parent framework. In addition to the first report of alkyne–azide cycloaddition utilized for corannulene immobilization in the solid state, we also probed the charge transfer rate within the Marcus theory as a function of mutual πB orientation for the first time, as well as shed light on the density of states near the Fermi edge. These studies could foreshadow new avenues for πB utilization for the development of optoelectronic devices or a route for highly efficient porous electrodes. 相似文献