Three‐Dimensional Block Copolymer Nanostructures by the Solvent‐Annealing‐Induced Wetting in Anodic Aluminum Oxide Templates

Block copolymers have been extensively studied over the last few decades because they can self‐assemble into well‐ordered nanoscale structures. The morphologies of block copolymers in confined geometries, however, are still not fully understood. In this work, the fabrication and morphologies of three‐dimensional polystyrene‐block‐polydimethylsiloxane (PS‐b‐PDMS) nanostructures confined in the nanopores of anodic aluminum oxide (AAO) templates are studied. It is discovered that the block copolymers can wet the nanopores using a novel solvent‐annealing‐induced nanowetting in templates (SAINT) method. The unique advantage of this method is that the problem of thermal degradation can be avoided. In addition, the morphologies of PS‐b‐PDMS nanostructures can be controlled by changing the wetting conditions. Different solvents are used as the annealing solvent, including toluene, hexane, and a co‐solvent of toluene and hexane. When the block copolymer wets the nanopores in toluene vapors, a perpendicular morphology is observed. When the block copolymer wets the nanopores in co‐solvent vapors (toluene/hexane = 3:2), unusual circular and helical morphologies are obtained. These three‐dimensional nanostructures can serve as naontemplates for refilling with other functional materials, such as Au, Ag, ZnO, and TiO₂.

     

Synthesis on large area and uniform nanosheet morphology of polycrystalline cobalt oxide Co3O4 obtained from oxidation of Co films in a pure oxygen atmosphere

Large area and uniform nanosheets Co₃O₄ have been fabricated by thermal annealing of cobalt thin film under the DC magnetron sputtering method. The synthesis is based on controlling the simple thermal oxidative formation of precursor Co films. The Co films were heated at 300, 400, and 500 °C for two hours in a pure oxygen atmosphere. At 300 °C, CoO and Co₃O₄ phases appear to survive together. An amount of pure polycrystalline Co₃O₄ nanosheets were observed at 400 °C. The structural and morphological properties of the nanosheets Co₃O₄ were characterized by means of transmission electron microscopy (TEM) and Raman spectroscopy.     

A general rhodium-catalyzed cross-coupling reaction of thiols with aryl iodides

The general procedure for the rhodium-catalyzed cross-coupling of thiols with aryl iodides is described. The catalytic system consists of 5 mol % of [RhCl(cod)]₂ and 10 mol % of PPh₃ as a ligand. A variety of aryl iodides reacted with thiols, giving aryl thioethers in good to excellent yields. It is important to note that the deactivated aryl iodides such as 4-iodoanisole is worked smoothly to provide the corresponding aryl thioethers in excellent yields. Functional groups such as free-amines, chloro, are all tolerated under the employed reaction conditions.     

Syntheses of (-)-pelletierine and (-)-homopipecolic acid

Enantiomeric syntheses of (-)-homopipecolic acid and (-)-pelletierine have been achieved by chiral resolution of tropanol followed by Baeyer-Villiger oxidation. The methodology provides a practical route for the synthesis of optically pure piperidines.     

Noncomputability,unpredictability, undecidability,and unsolvability in economic and finance theories

We outline, briefly, the role that issues of the nexus between noncomputability and unpredictability, on the one hand, and between undecidability and unsolvability, on the other hand, have played in Computable Economics (CE). The mathematical underpinnings of CE are provided by (classical) recursion theory, varieties of computable and constructive analysis and aspects of combinatorial optimization. The inspiration for this outline was provided by Professor Graça's thought‐provoking recent article. © 2012 Wiley Periodicals, Inc. Complexity, 2012     

Spin-resolved NEXAFS from resonant X-ray scattering (RXS): Application to MnO

Resonantly excited metal K core line spectra of NiO, MnO, CuO and other compounds have been investigated at the beamlines X21 (NSLS/BNL), BW1 and W1.1 (HASYLAB/DESY). A novel technique for quantitative resolution of NEXAFS spectra into spin-up and spin-down components has been developed. Since the method employs spin conservation and local spin references, it needs no circularly polarized radiation and no sample magnetization for taking both the RXS and NEXAFS spectra. Hence antiferromagnetic and paramagnetic materials can be investigated as well.By utilizing linear dichroism with angular-dependent measurements on single-crystal samples, additional resolution of NEXAFS spectra is possible with respect to the orbital symmetry. Application of the method to paramagnetic MnO, for the first time, provides new and unambiguous experimental results confirming modern (LSDA+U) calculations. Received: 29 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001     

A Uniform Approach to the Analysis of Trie Structures That Store Prefixing-Keys

Triesare data structures for storing sets where each element is represented by a key that can be viewed as a string of characters over a finite alphabet. These structures have been extensively studied and analyzed under several probability models. All of these models, however, preclude the occurrence of sets in which the key of one element is a prefix of that of another—such a key is called aprefixing-key. This paper presents an average case analysis of several trie varieties, which we generically calledprefixing-tries, for representing sets with “unrestricted” keys, that is, sets in which the key of one element may be a prefix of that of another. The underlying probability model, which we call theprefix model, _{h, n, m}assumes as equally likely alln-element sets whose keys are composed of at mosthcharacters from a fixed alphabet of sizem. For each of the trie varieties analyzed, we derive exact formulas for the expected space required to store such a set, and the average time required to retrieve an element given its key, as functions ofh,n, andm. Our approach to the analysis is of interest in its own right. It provides a unifying framework for computing the expectations of a wide class of random variables with respect to the prefix model. This class includes the cost functions of the trie varieties analyzed here.     

Lesions involving the fourth ventricle evaluated by CT and MR: A comparative study

A retrospective review of 21 patients with lesions involving the fourth ventricle was performed to determine the relative capability of computed tomography (CT) and MR for detection, characterization, localization, and diagnosis. Lesions involving the fourth ventricle included ependymoma (three), subependymoma (one), glioma (five), cysticercosis cyst (three), medulloblastoma (three), bleeding into the fourth ventricle (two), epidermoid cyst (two), “trapped” fourth ventricle (one), and lymphomatoid granuloma (one). Posterior fossa lesions that displaced but did not invade the fourth ventricle were excluded. Lesion detectability on CT was judged excellent in ten, good in 8, and fair or poor in 3. Detectability of lesions by MR was judged excellent in 16 and good in 5. There was complete agreement on lesion extension between CT and MR in 6 lesions, mild disagreement in 4, and moderate to significant disagreement in 11. Preoperatively, MR alone correctly diagnosed seven lesions, and CT alone correctly diagnosed three lesions. A review of the combined scans (after the correct diagnosis was given) showed both CT and MR were equal in the diagnosis of 14 lesions, MR better than CT in six, and CT better in one. There was complete agreement on both CT and MR with the surgical/pathologic findings in three lesions. Both studies proved disappointing in their ability to make the correct histologic diagnosis, probably because CT and MR characteristics may not always offer a definitive diagnosis and because of the wide spectrum of pathologic processes that may involve the fourth ventricle.     

The MT-MSXα(R) method: Applications to Li2, F2, and N2 molecules

The multiple scattering Xα(R) method with the scaling parameter α expressed as a function of the internuclear distance is applied to the Li₂, N₂, and F₂ molecules. Compared with the results obtained by the Xα method, the calculated Xα(R) equilibrium distances are smaller, the total energies are lower, and the dissociation energies are larger.