Development of Synthetic Pathways for Carbon Nanohoops

A synthetic pathway was developed for the preparation of a precursor of a [6]cycloparaphenylene derivative, which represents the shortest repeating carbon nanohoop segment of an armchair (6,6) carbon nanotube. As a key intermediate of the synthetic sequence, trans,trans-1,4-di(4-bromophenyl)-1,3-butadiene was synthesized by using the Homer-Wadsworth-Emmons reaction between 4-bromocinnamaldehyde and diethyl 4-bromobenzylphosphonate reported in the literature. The use of BF3˙OEt2 as a Lewis acid for the Lewis acid-catalyzed Diels-Alder reaction between trans,trans-1 ,4- di(4-bromophenyl)-1,3-butadiene and 1,4-benzoquinone was successful in producing cis-5,8-di(4-bromophenyl)-5,8-dihydro-1 ,4-naphthalenediol. The Diels-Alder reaction ensures that the two 4-bromophenyl substituents are cis to each other in the sixmembered ring, which is of critical importance for the subsequent dimerization reaction. Methylation with dimethyl sulfate in the presence of potassium carbonate afforded the corresponding methylated hydroquinone. The nickel(O)-catalyzed homocoupling reactions produced the corresponding dimers as a mixture of diastereomers with the two 1,4-dimethoxyphenyl groups pointing either in the same direction or in the opposite directions. It is envisioned that aromatization of the dimers could then lead to the [6]cycloparaphenylene derivative

Reinforcement Learning Approaches to Improve Spatial Reuse in Wireless Local Area Networks

The ubiquitous deployment of IEEE 802.11 based Wireless Local Area Networks (WLANs) or WiFi networks has resulted in dense deployments of Access Points (APs) in an effort to provide wireless links with high data rates to users. This, however, causes APs and users/stations to experience a higher interference level. This is because of the limited spectrum in which WiFi networks operate, resulting in multiple APs operating on the same channel. This in turn affects the signal-tonoise-plus interference ratio (SINR) at APs and users, leading to low data rates that limit their quality of service (QoS). To improve QoS, interference management is critical. To this end, a key metric of interest is spatial reuse. A high spatial reuse means multiple transmissions are able to transmit concurrently, which leads to a high network capacity. One approach to optimize spatial reuse is by tuning the clear channel access (CCA) threshold employed by the carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) protocol. Specifically, the CCA threshold of a node determines whether it is allowed to transmit after sensing the channel. A node may increase its CCA threshold, causing it to transmit even when there are other ongoing transmissions. Another parameter to be tuned is transmit power. This helps a transmitting node lower its interference to neighboring cells, and thus allows nodes in these neighboring cells to transmit as well. Apart from that, channel bonding can be applied to improve transmission rate. In particular, by combining/aggregating multiple channels together, the resulting channel has a proportionally higher data rate than the case without channel bonding. However, the issue of spatial reuse remains the same whereby the focus is to maximize the number of concurrent transmissions across multiple channels

A Vision for Future Development in Historic District: Greenway Planning, Green Infrastructure Adaptation and Landscape Design in Historic Districts of US and China

This paper is trying to explore the future development for historic district. “Historic districts” talked in this paper are mostly part of modern cities and have valuable architectures and profuse cultural backgrounds. These historic districts now are legally protected by policies and also by the government, and most of those are involving supremely significant green spaces or greenway systems which can also date hundreds of years ago. However, some of them are still facing serious problem of losing the green patterns of the city and therefore become a scattered puzzle of urban open space system; and some others facing the problem of building facilities decomposed and keep distant to fulfill urban sustainable development. So whether, greenway planning can be adapted to the future development of these historic districts, and can green infrastructure adaptation make their functions to turn the communities green and sustainable? These are the research questions this paper will discuss. The two study sites that the paper will discuss are Back Bay historic district in Boston, Massachusetts in US and former Concession in Wuhan, China

Renormalization-group exponents for superconducting phases in two-leg ladders

In previous studies, we proposed a scaling ansatz for electron-electron interactions under renormalization group transformation. With the inclusion of phonon-mediated interactions, we show that the scaling ansatz, characterized by the divergent logarithmic length $l_d$ and a set of renormalization-group exponents, also works rather well. The superconducting phases in a doped two-leg ladder are studied and classified by these renormalization-group exponents as demonstration. Finally, non-trivial constraints among the exponents are derived and explained.Comment: 4 pages, 3 figures; minor revisions with references adde

Analysis of Operations Management Problems in Currency and Food Supply Chains

This dissertation is constituted of three essays addressing operational issues be- longing to two research domains including (i) Logistics and Supply Chain Management for Currency Supply Network and (ii) Facility Location and Capacity Optimization for Food Supply Chains. Minimum cost ow network model and mixed integer programming model (linear and nonlinear) are developed to analyze and optimize supply chains of banknotes, coins, and foods. Approaches developed are general and can easily be applied to other categories of supply chains under different settings around the world with appropriate modifications. The first domain comprises two essays with different scopes and objectives, in which two unique monetary supply chains with distinctive operations and governmental regulations are analyzed from both supply-side and demand-side perspectives. In the first essay, in order to improve the efficiency of the central bank's currency network in a large country, currency vaults are upgraded by expanding their capacities, and the sourcing of the updated currency network is optimized. This is the first study that analyzes a country's overall currency network's operations from the supply-side perspective. In the same domain, the second essay presents general models for analyzing the operational issues in the U.S. Coin Supply Chain. As the first study to view the U.S. Coin Supply Chain as a closed-loop/reverse supply chain, it investigates the supply chain from both supply-side and demand-side perspectives to increase efficiency and effectiveness in ordering, producing, packaging, distributing and managing inventory of coins. This essay provides efficient methods and guidelines for effectively managing the supply chain that can be implemented in practice. Belonging to the second domain, the third essay optimizes a food supply chain to assure food safety and provides suggestions to government agencies and private companies concerning where to locate new irradiation facilities with appropriate capacities strategically, how to source the demand of U.S. hubs from the supply of Mexican growing regions through irradiation facilities tactically, and how to efficiently transport fresh fruits imported from Mexico to the U.S. operationally