The Synthesis of Some Naphtho[2,3-b]pyran-5,10-Quinones as Preliminary Models for Biological Evaluations

Naphtho[2,3-b]pyran-5,10-quinones related to the known antibiotic, erythrostominone 5, have been synthesized and demonstrate that biological activity is a function of the pyran ring as well as substituents at C-2 and C-4.     

Applying diamond like carbon layer on carbon/carbon composites and its effect on the deposition of hydroxyapatite coating

The biomedical application of carbon/carbon (C/C) composites is limited by lacking bioactivity and releasing carbon debris. Hydroxyapatite (HA) coating has been used to improve the bioactivity of C/C composites, but it cannot reduce the release of carbon debris effectively because of poor wear resistance property. In this work, a wear‐resistant layer of diamond like carbon (DLC) is applied on C/C composites, followed by an ultrasound‐assisted electrochemical deposition to prepare HA coatings. The microstructure, morphology and chemical composition of the DLC layer and the HA coating are characterised by scanning electron microscopy, X‐ray diffraction, energy dispersive spectroscopy (EDS), X‐ray photoelectron spectroscopy, Fourier transformed infrared spectroscopy and Raman spectrum. The bonding strength between the HA coating and the DLC layer modified C/C composites is examined by a tensile test. The results show that the DLC layer has a spherical morphology and provides a uniform surface for the deposition of the HA coating. The HA coating shows flaky morphology with a compact structure. The tensile strength of the HA coating on the DLC layer modified C/C composites is 6.24 ± 0.40 MPa, which is significantly higher than that of HA coating on unmodified C/C composites(3.04 ± 0.20 MPa). Copyright © 2013 John Wiley & Sons, Ltd.     

The first synthesis of the epoxide-containing macrolactone nucleus of oximidine I

A synthesis of the epoxydiene-containing macrolide nucleus of oximidine I is reported, starting from commercially available 3-butyn-1-ol. The key macrocyclisation step is achieved using Horner-Wadsworth-Emmons methodology in the presence of an epoxide.     

Monomer, clusters, liquid: an integrated spectroscopic study of methanol condensation

We have combined static pressure, spectroscopic temperature, Fourier transform infrared spectroscopy (FTIR), and small angle X-ray scattering (SAXS) measurements to develop a detailed picture of methanol condensing from a dilute vapor-carrier gas mixture under the highly supersaturated conditions present in a supersonic nozzle. In our experiments, methanol condensation can be divided into three stages as the gas mixture expands in the nozzle. In the first stage, as the temperature decreases rapidly, small methanol n-mers (clusters) form, increase in concentration, and evolve in size. In the second stage, the temperature decreases more slowly, and the n-mer concentrations continue to rise. Thermodynamic and FTIR experiments cannot, however, definitively establish if the average cluster size is constant or if it continues to increase. Finally, when the vapor becomes supersaturated enough, liquid droplets form via nucleation and growth, consuming more monomer and reducing the concentration of clusters. At the point where liquid first appears, cluster formation has already consumed up to 30% of the monomer. This is significantly more than is predicted by a model that describes the vapor phase as an equilibrium mixture of methanol monomer, dimer, and tetramer. An energy balance suggests that a significant fraction of the cluster population is larger than the tetramer, while preliminary SAXS measurements suggest that these clusters contain, on average, 6 monomers.     

Synthesis and stereochemical assignment of (+)-chamuvarinin

A stereocontrolled total synthesis of (+)-chamuvarinin, isolated from the root extract of Uvaria Chamae, utilizes a convergent modular strategy to construct the adjacently linked C15-C28 ether array, followed by a late-stage Julia-Kocienski olefination to append the butenolide motif. This constitutes the first total synthesis of (+)-chamuvarinin, defining the relative and absolute configuration of this unique annonaceous acetogenin.     

Imaging high-energy electrons propagating in a crystal

It has recently become possible to focus a beam of high-energy electrons to a spot smaller than an atom, with vast potential for the study of condensed matter. We devise an experiment that can image, with subangstrom resolution, the distribution of such an electron beam as it scatters within an atomic lattice. Our experiments reveal the acute sensitivity of the scattered electron distribution to 0.1 ? shifts of the impact point. Scattering due to plasmon excitations is also examined. Implications for the study of the atomic and electronic structure of condensed matter are discussed.     

Using Student Reasoning to Inform the Development of Conceptual Learning Goals: The Case of Quadratic Functions

Despite the proliferation of mathematics standards internationally and despite general agreement on the importance of teaching for conceptual understanding, conceptual learning goals for many K-12 mathematics topics have not been well-articulated. This article presents a coherent set of five conceptual learning goals for a complex mathematical domain, generated via a method of systematic empirical analysis of students' reasoning. Specifically, we compared the reasoning of pairs of students who performed differentially on the same task and inferred the pivotal intermediate conceptions that afforded one student deeper engagement with the task than another student. In turn, each pivotal intermediate conception framed an associated conceptual learning goal. While the empirical analysis of student reasoning is typically used to understand how students learn, we argue that such analysis should also play an important role in determining what concepts students should learn.     

On the Approximation of the SABR Model: A Probabilistic Approach

Abstract

In this article, we derive a probabilistic approximation for three different versions of the SABR model: Normal, Log-Normal and a displaced diffusion version for the general case. Specifically, we focus on capturing the terminal distribution of the underlying process (conditional on the terminal volatility) to arrive at the implied volatilities of the corresponding European options for all strikes and maturities. Our resulting method allows us to work with a variety of parameters that cover the long-dated options and highly stress market condition. This is a different feature from other current approaches that rely on the assumption of very small total volatility and usually fail for longer than 10 years maturity or large volatility of volatility (Volvol).