Benzothiazines in organic synthesis. Synthesis of fluorescent 7-amino-2,1-benzothiazines

Fluorescent 7-amino-2,1-benzothiazines were prepared in high yields using the palladium-catalyzed reaction of 4-amino-2-chlorobenzaldehydes with a sulfoximine or the reaction of 7-fluoro-2,1-benzothiazines with amines.     

The mystery of gold's chemical activity: local bonding, morphology and reactivity of atomic oxygen

Recently, gold has been intensely studied as a catalyst for key synthetic reactions. Gold is an attractive catalyst because, surprisingly, it is highly active and very selective for partial oxidation processes suggesting promise for energy-efficient "green" chemistry. The underlying origin of the high activity of Au is a controversial subject since metallic gold is commonly thought to be inert. Herein, we establish that one origin of the high activity for gold catalysis is the extremely reactive nature of atomic oxygen bound in 3-fold coordination sites on metallic gold. This is the predominant form of O at low concentrations on the surface, which is a strong indication that it is most relevant to catalytic conditions. Atomic oxygen bound to metallic Au in 3-fold sites has high activity for CO oxidation, oxidation of olefins, and oxidative transformations of alcohols and amines. Among the factors identified as important in Au-O interaction are the morphology of the surface, the local binding site of oxygen, and the degree of order of the oxygen overlayer. In this Perspective, we present an overview of both theory and experiments that identify the reactive forms of O and their associated charge density distributions and bond strengths. We also analyze and model the release of Au atoms induced by O binding to the surface. This rough surface also has the potential for O(2) dissociation, which is a critical step if Au is to be activated catalytically. We further show the strong parallels between product distributions and reactivity for O-covered Au at low pressure (ultrahigh vacuum) and for nanoporous Au catalysts operating at atmospheric pressure as evidence that atomic O is the active species under working catalytic conditions when metallic Au is present. We briefly discuss the possible contributions of oxidants that may contain intact O-O bonds and of the Au-metal oxide support interface in Au catalysis. Finally, the challenges and future directions for fully understanding the activity of gold are considered.     

Chromium chains as polydentate fluoride ligands for lanthanides

Hexametallic chromium(III) chains can act as fluoride donor ligands to lanthanide ions giving {(Cr(6))Ln(x)}(n) complexes; preliminary spectroscopic studies are reported.     

Exploring the Responses of Underrepresented Students in Science to an Elementary Classroom Outreach Program

This paper describes a subset of results from a large‐scale two‐year independent evaluation study conducted with the Scientists in School (SiS) outreach program and two large school boards in Ontario, Canada. Specifically, it explores the responses of elementary students (n= 811) from typically underrepresented groups in science (English language learners [ELL], girls, and students at low‐achieving schools) to the SiS outreach program. It explores responses related to enjoyment, interest, perceptions of role modeling, and future career choice in science. Compared to other students, findings suggest that girls and students from low‐achieving schools found the program more enjoyable and reported that it provided positive science role models. Students at schools with high ELL populations also reported higher levels of enjoyment and reported that the program helped get them excited about science.     

Some aspects of causal & neutral equations used in modelling

The problem that motivates the considerations here is the construction of mathematical models of natural phenomena that depend upon past states. The paper divides naturally into two parts: in the first, we expound the inter-connection between ordinary differential equations, delay-differential equations, neutral delay-differential equations and integral equations (with emphasis on certain linear cases). As we show, this leads to a natural hierarchy of model complexity when such equations are used in mathematical and computational modelling, and to the possibility of reformulating problems either to facilitate their numerical solution or to provide mathematical insight, or both. Volterra integral equations include as special cases the others we consider. In the second part, we develop some practical and theoretical consequences of results given in the first part. In particular, we consider various approaches to the definition of an adjoint, we establish (notably, in the context of sensitivity analysis for neutral delay-differential equations) rôles for well-defined adjoints and ‘quasi-adjoints’, and we explore relationships between sensitivity analysis, the variation of parameters formulae, the fundamental solution and adjoints.     

A simple strategy for varying the restart parameter in GMRES()

When solving a system of linear equations with the restarted GMRES method, a fixed restart parameter is typically chosen. We present numerical experiments that demonstrate the beneficial effects of changing the value of the restart parameter in each restart cycle on the total time to solution. We propose a simple strategy for varying the restart parameter and provide some heuristic explanations for its effectiveness based on analysis of the symmetric case.     

Modeling and device parameter design to improve reset time in binary-oxide memristors

A simulation-based analysis is conducted to study the set and reset times of TiO₂-based memristor device. This analysis uses nonlinear device model that captures the effects of large electric field inside memristor devices. Previous studies report strong asymmetry between reset and set times with reset time being several orders of magnitude higher than set time. The aim of this work was to investigate the effect of the device length and oxygen vacancies profile on the switching time. Our results show that a device model with a length of 10 nm and accurate parameters can result in more realistic device characteristics. Also, oxygen vacancies profile can be tuned to improve the reset time. MATLAB is used to simulate a 10-nm device, and the initial vacancy profile is chosen to look like inverted parabola. The results show reduced ratio between reset and set times from several orders of magnitude presented in the literature to not more than 1.5×. Thus, the proposed oxygen vacancies profile and quantitative results derived from it can be used to suggest a physical memristor device. In addition, the tuned parameters and model that matches actual device behavior can be factored in memristor fabrication.     

Nearest-neighbor-atom core-hole transfer in isolated molecules

A new phenomenon sensitive only to next-door-neighbor atoms in isolated molecules is demonstrated using angle-resolved photoemission of site-selective core electrons. Evidence for this interatomic core-to-core electron interaction is observable only by measuring nondipolar angular distributions of photoelectrons. In essence, the phenomenon acts as a very fine atomic-scale sensor of nearest-neighbor elemental identity.     

Bose-Einstein condensation in the relativistic ideal Bose gas

The Bose-Einstein condensation (BEC) critical temperature in a relativistic ideal Bose gas of identical bosons, with and without the antibosons expected to be pair-produced abundantly at sufficiently hot temperatures, is exactly calculated for all boson number densities, all boson point rest masses, and all temperatures. The Helmholtz free energy at the critical BEC temperature is lower with antibosons, thus implying that omitting antibosons always leads to the computation of a metastable state.