Is samoquasine A indeed benzo[f]phthalazin-4(3H)-one? Unambiguous, straightforward synthesis of benzo[f]phthalazin-4(3H)-one and its regioisomer benzo[f]phthalazin-1(2H)-one

In search for the structural elucidation of samoquasine A, a natural product isolated from the seeds of Annona squamosa L., two benzo[f]phthalazinone isomers have been synthesized. The synthetic pathway followed to build up these skeletons is based on the combination of two Suzuki reactions on a pyridazinone precursor and a ring closure reaction via a condensation reaction. ¹H NMR data of the synthesized compound allowed to establish that the structure of the natural product samoquasine A is not benzo[f]phthalazin-4(3H)-one, as previously suggested.     

Initial characterization of the primary photochemistry of AppA, a blue-light-using flavin adenine dinucleotide-domain containing transcriptional antirepressor protein from Rhodobacter sphaeroides: a key role for reversible intramolecular proton transfer from the flavin adenine dinucleotide chromophore to a conserved tyrosine?

The flavin adenine dinucleotide (FAD)-containing photoreceptor protein AppA (in which the FAD is bound to a novel so-called BLUF domain) from the purple nonsulfur bacterium Rhodobacter sphaeroides was previously shown to be photoactive by the formation of a slightly redshifted long-lived intermediate that is thought to be the signaling state. In this study, we provide further characterization of the primary photochemistry of this photoreceptor protein using UV-Vis and Fourier-transform infrared spectroscopy, pH measurements and site-directed mutagenesis. Available evidence indicates that the FAD chromophore of AppA may be protonated in the receptor state, and that it becomes exposed to solvent in the signaling state. Furthermore, experimental data lead to the suggestion that intramolecular proton transfer (that may involve [anionic] Tyr-17) forms the basis for the stabilization of the signaling state.     

A Session Layer Concept for Overlay Networks

Current day mobility solutions are characterized by a number of essential restrictions that prevent them from being successful in an overlay network environment. This paper proposes 4 properties that mobility solutions must have to address these restrictions: application cooperation, higher layer mobility awareness, general applicability and protocol heterogeneity. Subsequently, a mobility solution that realizes all these properties is described. The solution introduces a session layer in the protocol stack that consists of two subsystems: the connection abstraction system and the address management system. Other mobility solutions found in the literature, session layer and others, typically only realize a subset of the four properties. Tom Mahieu holds a Bachelor's and Master's degree in computer sciences that he obtained at the Catholic University of Leuven. After obtaining his Master's degree in 1997, he was admitted into the Distrinet research group at the Department of Computer Science of the Catholic University of Leuven in Belgium as a research and teaching assistant, where he is current working on flexible component architectures for protocol stacks under the supervision of Prof. Pierre Verbaeten and Prof. Wouter Joosen. His Ph.D. dissertation deals with protocol stack support for applications that operate in dynamically changing network environments, such as mobile and wireless networks. Pierre Verbaeten is the head of the DistriNet research group. His main research interest is on system support and software engineering support for distributed systems. Under his supervision, DistriNet has grown to a group of 40 researchers (both Ph.D. students and postdocs) and 6 professors. He is responsible for teaching courses on computer architecture, computer networks and distributed systems. Wouter Joosen received a Ph.D. degree at the K.U. Leuven in 1996. His main research interests are in the areas of software architecture for distributed systems, aspect-oriented and component-based development, middleware, software security and embedded systems. Over the last 10 years, Wouter Joosen has been researching software development technologies (processes, architectures, notations and prototypes) that enable the construction and management of distributed applications that need support for a number of non-functional requirements, including security, real-time aspects, reliability and load balancing.     

Abrupt breakdown in dielectric/metal gate stacks: a potential reliability limitation?

In downscaled poly-Si gate MOSFET devices reliability margin is gained by progressive wearout. When the poly-Si gate is replaced with a metal gate, the slow wearout phase observed in ultrathin SiON and HfSiON dielectrics with poly-Si gate disappears, and with it, the reliability margin. We demonstrate for several combinations of dielectric and gate materials that the large abrupt current increase (/spl Delta/I) as compared to poly-Si is not likely due to process issues, but is an intrinsic property of the dielectric/metal gate stack. The occurrence of large /spl Delta/I is a potential limitation for the reliability of metal gate devices.     

C?H bonds with a Positive Dipole Gradient Can Form Blue‐Shifting Hydrogen Bonds: The Complex of Halothane with Methyl Fluoride

The complex of halothane (CF₃CBrClH) with ([D₃])methyl fluoride is investigated theoretically by means of ab initio calculations at the MP2/6‐311++G(d,p) level and experimentally by infrared spectroscopy of solutions in liquid krypton. The complexation energy is calculated to be ?12.5 kJ mol^?1. The dipole moment of halothane monomer as a function of the C? H stretching coordinate is calculated with different methodologies and the value of (?μ/?Q₁)₀ is found to be positive. In the spectra, formation of a 1:1 complex is observed. The standard complexation enthalpy is measured to be ?8.4(2) kJ mol^?1. The C? H stretching vibration of halothane shows a blueshift of +15.4 cm^?1 on complexation, and its infrared intensity ratio ε_complex/ε_monomer is found to be 1.39(7). The frequency shift is analyzed by a Morokuma analysis, and the infrared intensities are rationalized by using a model which includes the mechanical and electrical anharmonicity of the C? H stretching vibration.     

Searching for the dopant ion in Eu-activated BaMgAl10O17 phosphor with synchrotron diffraction

Searching for the multiple sites predicted in the literature for the europium activator in the BaMgAl₁₀O₁₇:Eu²⁺ phosphor, we undertook a detailed structural study using synchrotron powder diffraction. Three different positions were found for Eu²⁺ in the Beevers-Ross site, near the mid-oxygen position and in substitution for the interblocks Al-O-Al bridge. By favoring the migration of the activator ion, the resulting vacancies in the Beevers-Ross sites may be a major cause of the degradation of the phosphor.     

Forward and inverse modeling of near-well flow using discrete edge-based vector potentials

Homogeneous effective permeabilities in the near-well region are generally obtained using analytical solutions for transient flow. In contrast, this paper focuses on heterogeneous permeability obtained from steady flow solutions, although extensions to unsteady flow are introduced too. Exterior calculus and its discretized form have been used as a guide to derive the system of algebraic equations. Edge-based vector potentials describing 3-D steady and unsteady flow without mass balance error stabilize the solution. After a physics-oriented introduction, relatively simple analytic examples of forward and inverse discrete modeling demonstrate the applicability.