Perturbation analysis of communication networks with feedback control using stochastic hybrid models

Communication networks may be abstracted through Stochastic Fluid Models (SFM) with the node dynamics described by switched flow equations as various events take place, thus giving rise to hybrid automaton models with stochastic transitions. The inclusion of feedback mechanisms complicates these dynamics. In a tandem setting, a typical feedback mechanism is the control of a node processing rate as a threshold-based function of the downstream node’s buffer level. We consider the problem of controlling the threshold parameters so as to optimize performance metrics involving average workload and packet loss and show how Infinitesimal Perturbation Analysis (IPA) can be used to analyze congestion propagation through a network and develop gradient estimators of such metrics.     

Efficient synthesis of 8,11-dimethylene-bicyclo[5.3.1]undecan-2-one

We report here, an effective methodology for the preparation of 8,11-dimethylene-bicyclo[5.3.1]undecan-2-one. The key steps in these reactions were chloromethylation, cationic-alkyne cyclization and anionic fragmentation sequence.     

Organic Polymer Dots as Photocatalysts for Visible Light‐Driven Hydrogen Generation

For the first time, organic semiconducting polymer dots (Pdots) based on poly[(9,9′‐dioctylfluorenyl‐2,7‐diyl)‐co‐(1,4‐benzo‐{2,1′,3} thiadiazole)] (PFBT) and polystyrene grafting with carboxyl‐group‐functionalized ethylene oxide (PS‐PEG‐COOH) are introduced as a photocatalyst towards visible‐light‐driven hydrogen generation in a completely organic solvent‐free system. With these organic Pdots as the photocatalyst, an impressive initial rate constant of 8.3 mmol h^?1 g^?1 was obtained for visible‐light‐driven hydrogen production, which is 5‐orders of magnitude higher than that of pristine PFBT polymer under the same catalytic conditions. Detailed kinetics studies suggest that the productive electron transfer quench of the excited state of Pdots by an electron donor is about 40 %. More importantly, we also found that the Pdots can tolerate oxygen during catalysis, which is crucial for further application of this material for light‐driven water splitting.     

Self-assembly of Nafion molecules onto silica nanoparticles formed in situ through sol-gel process

Self-assembly of Nafion onto in situ formed silica nanoparticles in ethylene glycol–water mixture solvent has been investigated in this study. It was found that the formation of silica nanoparticles depends on the concentration of Nafion in dispersions. At relatively low concentration, 0.8% in weight in this case, the existing Nafion is not sufficient to prevent further growth of the initially formed silica nanoparticles, leading to large aggregates of silica particles. When the concentration of Nafion increased to 2% in weight, self-assembled Nafion layer on the surface stabilizes the initial formed silica nanoparticles and silica particles with average diameters of 4.2±0.5 nm were found to be uniformly distributed in the dispersion. With further increasing the concentration of Nafion, the number of Nafion aggregates increases and silica nanoparticles were mainly formed inside the entangled Nafion chains, resulting in an observation of clusters of silica nanoparticles.     

Dual‐Confined Sulfur Nanoparticles Encapsulated in Hollow TiO2 Spheres Wrapped with Graphene for Lithium–Sulfur Batteries

Lithium–sulfur (Li?S) batteries are attractive owing to their higher energy density and lower cost compared with the universally used lithium‐ion batteries (LIBs), but there are some problems that stop their practical use, such as low utilization and rapid capacity‐fading of the sulfur cathode, which is mainly caused by the shuttle effect, and the uncontrollable deposition of lithium sulfide species. Herein, we report the design and fabrication of dual‐confined sulfur nanoparticles that were encapsulated inside hollow TiO₂ spheres; the encapsulated nanoparticles were prepared by a facile hydrolysis process combined with acid etching, followed by “wrapping” with graphene (G?TiO₂@S). In this unique composite architecture, the hollow TiO₂ spheres acted as effective sulfur carriers by confining the polysulfides and buffering volume changes during the charge‐discharge processes by means of physical force from the hollow spheres and chemical binding between TiO₂ and the polysulfides. Moreover, the graphene‐wrapped skin provided an effective 3D conductive network to improve the electronic conductivity of the sulfur cathode and, at the same time, to further suppress the dissolution of the polysulfides. As results, the G?TiO₂@S hybrids exhibited a high and stable discharge capacity of up to 853.4 mA h g^?1 over 200 cycles at 0.5 C (1 C=1675 mA g^?1) and an excellent rate capability of 675 mA h g^?1 at a current rate of 2 C; thus, G?TiO₂@S holds great promise as a cathode material for Li?S batteries.     

Density functional theory investigation on the mechanism of the hepatitis delta virus ribozyme

Density functional theory methods have been used to investigate the hepatitis delta virus (HDV) ribozyme and its catalyzed phosphodiester cleavage. In particular, the effects of the environment's polarity and/or specific hydrogen-bond interactions on the proton affinity of the active site cytosine's N3 ring center have been considered. In addition, the basicities of possible hydrated Mg2+ ion species were also examined. The mechanism previously proposed for the HDV ribozyme in which the active site cytosine (C75) is protonated and thus acts as an acid while the Mg2+ species acts as the complementary base was then investigated. The possible role of tautomerization of C75 is also discussed.     

Acid-catalyzed regioselective sulfetherification of alkenols and stereoselective rearrangement of tetrahydrofuran to tetrahydropyran

An efficient acid-catalyzed sulfetherification of various unsaturated alcohols with sulfenamides to form tetrahydrofurans and tetrahydropyrans regioselectively is described. Mechanistic studies have shown that the tetrahydrofurans can stereoselectively rearrange to the corresponding tetrahydropyrans.     

An acid-catalyzed formal allylic C-H oxidation of aryl cycloalkenes with N-propylthiosuccinimide

A mild acid-catalyzed formal allylic C-H oxidation of aryl cycloalkenes with N-propylthiosuccinimide in the presence of various nucleophiles to generate allylic ethers, esters, and sulfonamides is described. A possible reaction mechanism has been proposed.     

微波消解-分光光度法快速测定农药废水中的总磷

利用微波消解技术对农药废水样品进行预处理,然后进行其中总磷的测定,消解时间从传统的高温高压消解30 min缩短到8 min.用微波消解-分光光度法和高压消解-分光光度法对两个农药废水样品进行了6次平行比对测定,测定结果经统计检验无显著性差异.微波消解法测定结果的相对标准偏差为0.483％～0.906％(n=6),加标回收率为95.5％～97.0％.该方法准确、快捷,适用于农药废水中总磷的快速测定.     

Enantioselective oxysulfenylation and oxyselenenylation of olefins catalyzed by chiral Brønsted acids

This paper describes Brønsted acid catalyzed enantioselective oxysulfenylation and oxyselenenylation of olefins. Enantiomerically enriched tetrahydrofurans are formed with up to 63% ee with dibenzoyl-d-tartaric acid and its derivatives as catalyst. Chiral β-carboxyl sulfides and selenides have also been obtained with up to 50% and 84% ee, respectively, via enantioselective desymmetrization of thiiranium and seleniranium ions in the presence of catalytic amounts of chiral binaphthol derived N-triflyl phosphoramide.