bluuebunny/crossref_metadata_2025 huggingface dataset:
Treatment of Streptococcus mutans bacteria by a plasma needle
Authors: Zhang Xianhui , Huang Jun , Liu Xiaodi , Peng Lei , Guo Lihong , Lv Guohua , Chen Wei , Feng Kecheng , Yang Si-ze
Published: March 2009

A dielectric barrier discharge plasma needle was realized at atmospheric pressure with a funnel-shaped nozzle. The preliminary characteristics of the plasma plume and its applications in the inactivation of Streptococcus mutans (S. mutans), the most important microorganism causing dental caries, were presented in this paper. The temperature of the plasma plume does not reach higher than 315 K when the power is below 28 W. Oxygen was injected downstream in the plasma afterglow region through the powered steel tube. Its effect was studied via optical-emission spectroscopy, both in air and in agar. Results show that addition of 26 SCCM O2 does not affect the plume length significantly (SCCM denotes cubic centimeter per minute at STP). The inactivation of S. mutans is primarily attributed to ultraviolet light emission, O, OH, and He radicals.
Hypothesis testing for Gaussian states on bosonic lattices
Authors: Mosonyi Milán
Published: March 2009

The asymptotic state discrimination problem with simple hypotheses is considered for a cubic lattice of bosons. A complete solution is provided for the problems of the Chernoff and the Hoeffding bounds and Stein’s lemma in the case when both hypotheses are Gaussian states with gauge- and translation-invariant quasifree parts.
Volume viscosity in fluids with multiple dissipative processes
Authors: Zuckerwar Allan J. , Ash Robert L.
Published: March 2009

The variational principle of Hamilton is applied to derive the volume viscosity coefficients of a reacting fluid with multiple dissipative processes. The procedure, as in the case of a single dissipative process, yields two dissipative terms in the Navier–Stokes equation: The first is the traditional volume viscosity term, proportional to the dilatational component of the velocity; the second term is proportional to the material time derivative of the pressure gradient. Each dissipative process is assumed to be independent of the others. In a fluid comprising a single constituent with multiple relaxation processes, the relaxation times of the multiple processes are additive in the respective volume viscosity terms. If the fluid comprises several relaxing constituents (each with a single relaxation process), the relaxation times are again additive but weighted by the mole fractions of the fluid constituents. A generalized equation of state is derived, for which two special cases are considered: The case of “low-entropy production,” where entropy variation is neglected, and that of “high entropy production,” where the progress variables of the internal molecular processes are neglected. Applications include acoustical wave propagation, Stokes flow around a sphere, and the structure and thickness of a normal shock. Finally, it is shown that the analysis presented here resolves several misconceptions concerning the volume viscosity of fluids.
Isochronal annealing study of low energy electron irradiated Al-doped p-type 6H silicon carbide with deep level transient spectroscopy
Authors: Luo J. M. , Zhong Z. Q. , Gong M. , Fung S. , Ling C. C.
Published: March 2009

Al doped p-type 6H silicon carbide was irradiated by low energy electrons to create primary defects. Two deep levels at EV+0.36 eV and EV+0.81 eV were created by this irradiation. Isochronal annealing study was carried out on the electron irradiated sample to investigate the annealing out of the two primary defects and the creation of thermal annealing-induced secondary defects. Four more deep hole traps (0.45, 0.56, 0.74, and 0.71 eV above the valence band) were formed during the whole annealing process up to a temperature of 1600 °C. All the electron irradiated deep level defects were annealed out after the 1600 °C annealing.
Some improvements of the activation-relaxation technique method for finding transition pathways on potential energy surfaces
Authors: Cancès E. , Legoll F. , Marinica M.-C. , Minoukadeh K. , Willaime F.
Published: March 2009

The activation-relaxation technique nouveau is an eigenvector following method for systematic search of saddle points and transition pathways on a given potential energy surface. We propose a variation in this method aiming at improving the efficiency of the local convergence close to the saddle point. The efficiency of the method is demonstrated in the case of point defects in body centered cubic iron. We also prove the convergence and robustness of a simplified version of this new algorithm.
Dynamics of counterions in dendrimer polyelectrolyte solutions
Authors: Karatasos K. , Krystallis M.
Published: March 2009

Molecular dynamics simulations were employed in models of peripherally charged dendrimers in solutions of explicit solvent and monovalent counterions in order to explore aspects of the dynamic behavior of counterions. The present study explores the effects of varying strength of electrostatic interactions for models of two dendrimer generations, in explicit solvent solutions below the dendrimer overlap concentration. Counterion diffusional motion as well as residence lifetimes of pairs formed by charged dendrimer beads and condensed counterions is monitored in the different electrostatic regimes. Spatiotemporal characteristics of self- and collective counterion motion are explored by means of space-time Van Hove correlation functions. A characteristic scaling law is found to describe the counterion diffusion coefficient as a function of Bjerrum length in the strong electrostatic regime, independent of the size of the dendrimer molecules at the examined volume fractions. The change noted in the diffusional motion of counterions in the range of strong Coulombic interactions is also reflected to their relevant residence times. Development of dynamic heterogeneities in counterion self-motion is observed during the gradual increase in the strength of electrostatic interactions, characterized by the emergence of distinct counterion populations in terms of their mobility. The time scale for the development of such a mobility contrast in the self-motion of the counterions can be correlated with that describing their collective motion as well. The latter increases with Bjerrum length but remains shorter compared to the time scale at which free diffusional motion sets in. Findings from the present study provide further insight on the mechanisms pertinent to ion migration in macroion dispersions and may serve as a basis for the interpretation of ionic motion in a broader range of polyelectrolyte systems.
Theoretical studies of angle-resolved ion yield spectra of core-to-valence transitions of acetylene
Authors: Kimberg Victor , Kosugi Nobuhiro , Gel’mukhanov Faris
Published: March 2009

Recent experimental results on angle-resolved photoion-yield spectroscopy (ARPIS) spectra near the core-to-valence excitation in acetylene show significant anisotropies in the spectral profile measured at 0° and 90° regarding to the polarization direction of x-ray photons. In the present work, a theoretical model is proposed to simulate the fine structure and anisotropy in ARPIS. This employs two-dimensional potential energy surfaces of the ground and core-excited states, as well as transition dipole moments, including symmetric and antisymmetric bending modes to account for Duschinsky effect. The ARPIS is simulated by evaluation of the ion flux, which is found as a projection of the excited state wave packet on a particular direction in the molecular frame. Numerical simulations explain qualitatively the angular dependence of the experimental spectra of the 1s→1πg∗ and 1s→3σu∗ transitions. The effects of the lifetime of the core-excited state, the direction of the ion flux, and the transition dipole moment are discussed.
State specific equation of motion coupled cluster method in general active space
Authors: Kong Liguo , Shamasundar K. R. , Demel Ondrej , Nooijen Marcel
Published: March 2009

The state specific equation of motion coupled cluster (SS-EOMCC) method is an internally contracted multireference approach, applicable to both ground and excited states. Attractive features of the method are as follows: (1) the SS-EOMCC wave function is qualitatively correct and rigorously spin adapted, (2) both orbitals and dynamical correlation are optimized for the target state, (3) nondynamical correlation and differential orbital relaxation effects are taken care of by a diagonalization of the transformed Hamiltonian in the multireference configuration-interaction singles space, (4) only one- and two-particle density matrices of a complete-active-space self-consistent-field reference state are needed to define equations for the cluster amplitudes, and (5) the method is invariant with respect to orbital rotations in core, active, and virtual subspaces. Prior applications focused on biradical-like systems, in which only one extra orbital is needed to construct the active space, and similarly, single bond breaking processes. In this paper, the applicability of the method is extended to systems of general active spaces. Studies on F2, H2O, CO, and N2 are carried out to gauge its accuracy. The convergence strategy is discussed in detail.
First principles study of Si-doped BC2N nanotubes
Authors: Rupp C. J. , Rossato J. , Baierle R. J.
Published: March 2009

Spin polarized density functional theory is used to investigate the incorporation of substitutional Si atoms in the zigzag (5,0) and in the armchair (3,3) BC2N nanotubes (NTs). Our results show that the Si impurities in BC2N NTs have lower formation energy when compared to Si in carbon and boron nitride NTs. In neutral charge state, Si in the boron site (SiB) presents a spin split with two electronic levels within the NT band gap and it gives rise to a net spin magnetic moment net of 1μB. Si in the nitrogen site (SiN) introduces electronic levels near the top of the valence band that lead the system to exhibit acceptor properties, which suggest the formation of defect-induced type-p BC2N NTs. The defective levels for Si in the two nonequivalent carbon atom sites (SiCI and SiCII) are resonant with the valence and conduction bands, respectively. The calculations of formation energy in charge state show that for all the available values of the electronic chemical potential, SiCI and SiCII have lower formation energy in neutral charge state, while SiB and SiN present lower formation energy in neutral or single negative charge state depending on the position of the electronic chemical potential.
Dipolar truncation in magic-angle spinning NMR recoupling experiments
Authors: Bayro Marvin J. , Huber Matthias , Ramachandran Ramesh , Davenport Timothy C. , Meier Beat H. , Ernst Matthias , Griffin Robert G.
Published: March 2009

Quantitative solid-state NMR distance measurements in strongly coupled spin systems are often complicated due to the simultaneous presence of multiple noncommuting spin interactions. In the case of zeroth-order homonuclear dipolar recoupling experiments, the recoupled dipolar interaction between distant spins is attenuated by the presence of stronger couplings to nearby spins, an effect known as dipolar truncation. In this article, we quantitatively investigate the effect of dipolar truncation on the polarization-transfer efficiency of various homonuclear recoupling experiments with analytical theory, numerical simulations, and experiments. In particular, using selectively C13-labeled tripeptides, we compare the extent of dipolar truncation in model three-spin systems encountered in protein samples produced with uniform and alternating labeling. Our observations indicate that while the extent of dipolar truncation decreases in the absence of directly bonded nuclei, two-bond dipolar couplings can generate significant dipolar truncation of small, long-range couplings. Therefore, while alternating labeling alleviates the effects of dipolar truncation, and thus facilitates the application of recoupling experiments to large spin systems, it does not represent a complete solution to this outstanding problem.
Effect of trapped electrons on soliton propagation in a plasma having a density gradient
Authors: Aziz Farah , Stroth Ulrich
Published: March 2009

A Korteweg–deVries equation with an additional term due to the density gradient is obtained using reductive perturbation technique in an unmagnetized plasma having a density gradient, finite temperature ions, and two-temperature nonisothermal (trapped) electrons. This equation is solved to get the solitary wave solution using sine-cosine method. The phase velocity, soliton amplitude, and width are examined under the effect of electron and ion temperatures and their concentrations. The effect of ion (electron) temperature is found to be more significant in the presence of larger (smaller) number of trapped electrons in the plasma.
Magnetic properties of Fe∕MgO granular multilayers prepared by pulsed laser deposition
Authors: García-García A. , Vovk A. , Pardo J. A. , Štrichovanec P. , Magén C. , Snoeck E. , Algarabel P. A. , De Teresa J. M. , Morellón L. , Ibarra M. R.
Published: March 2009

Granular multilayers [Fe(tnm)∕MgO(3nm)]N with 0.4nm⩽t⩽1.5nm were prepared by sequential pulsed laser deposition. Transmission electron microscopy (TEM) images show that increasing t causes the growth of the sizes of Fe nanoparticles and broadening of the particle size distribution. For t>0.81nm, continuous Fe layers are formed. The evolution of the shapes and sizes of the particles is reflected in the magnetic properties of the investigated films. A crossover from superparamagnetic to ferromagnetic behavior upon formation of a continuous Fe layer is observed. The fit of zero field cooled and field cooled susceptibility measurements and magnetization curves using Curie–Weiss law and a weighted sum of Langevin functions, respectively, allows the estimation of the average granule size for the films with t<0.61nm. The results of the estimations correlate with the data obtained from TEM images. Reduction of saturation magnetization for Fe nanoparticles and an increase of the coercivity up to 1200Oe at low temperatures were found. It is attributed to the formation of Fe-core∕FeOx-shell structured nanocrystals. The oxide shell gives rise to a strong contribution of surface anisotropy. Isotropic tunneling magnetoresistance up to ∼3% at room temperature and in magnetic field up to 18kOe was found for the film with t=0.61nm. For higher t, an anisotropic magnetoresistance typical for continuous ferromagnetic films was observed.
A simple method for the analysis of neutron resonance capture spectra
Authors: Clarijs Martijn C. , Bom Victor R. , van Eijk Carel W. E.
Published: March 2009

Neutron resonance capture analysis (NRCA) is a method used to determine the bulk composition of various kinds of objects and materials. It is based on analyzing direct capture resonance peaks. However, the analysis is complicated by scattering followed by capture effects in the object itself. These effects depend on the object’s shape and size. In this paper the new Delft elemental analysis program (DEAP) is presented which can automatically and quickly analyze multiple NRCA spectra in a practical and simple way, yielding the elemental bulk composition of an object, largely independent of its shape and size. The DEAP method is demonstrated with data obtained with a Roman bronze water tap excavated in Nijmegen (The Netherlands). DEAP will also be used in the framework of the Ancient Charm project as data analysis program for neutron resonance capture imaging (NRCI) experiments. NRCI provides three-dimensional visualization and quantification of the internal structure of archaeological objects by performing scanning measurements with narrowly collimated neutron beams on archaeological objects in computed tomography based experimental setups. The large amounts (hundreds to thousands) of spectra produced during a NRCI experiment can automatically and quickly be analyzed by DEAP.
Internal strains and crystal structure of the layers in AlGaN/GaN heterostructures grown on a sapphire substrate
Authors: Kladko V. P. , Kolomys A. F. , Slobodian M. V. , Strelchuk V. V. , Raycheva V. G. , Belyaev A. E. , Bukalov S. S. , Hardtdegen H. , Sydoruk V. A. , Klein N. , Vitusevich S. A.
Published: March 2009

In this paper, we investigate the structural properties of AlGaN/GaN heterostructures grown by metal organic chemical vapor deposition on sapphire substrates with different thicknesses using high-resolution x-ray diffraction and Raman scattering methods. We discuss the microscopic nature of spatial-inhomogeneous deformations and dislocation density in the structures. Microdeformations within mosaic blocks and the sizes of regions of coherent diffraction are determined. We reveal a gradient depth distribution of deformations in the mosaic structure of nitride layers, as well as at the interface regions of the sapphire substrate on the microscale level using confocal micro-Raman spectroscopy. We determine that an increase in substrate thickness leads to a reduction in dislocation density in the layers and an increase in the elastic deformations. The features of the block structure of nitrides layers are shown to have a significant influence on their elastic properties.
Enhanced performance of GaN-based light emitting diode with isoelectronic Al doping layer
Authors: Lee Jae-Hoon , Lee Jung-Hee
Published: March 2009

The effects of isoelectronic Al doping into epitaxial GaN films grown by metal organic chemical vapor deposition on sapphire substrates were investigated. It was found, based on the measured electron mobility and x-ray analysis, that there is a limiting point of the incorporation of Al into GaN in improving the crystal quality. The electron mobility of the undoped GaN film was 178 cm2/V s and the value greatly increased to 524 cm2/V s by doping a small amount of Al (up to 0.45% in concentration) into the GaN layer. A further increase in the Al concentration resulted in a degradation of the electron mobility, which decreased to 138 cm2/V s when the Al concentration was 0.82%. The output power of a side view light emitting diode (LED) with the Al-doped GaN layer was estimated to be 15.76 mW at a forward current of 20 mA, which improved by 19% compared to that of a conventional LED. These results show that a small amount of Al incorporation into a GaN layer improves the electrical and optical properties of the layer, which are attributed to the reduction of Ga vacancy and associated defects, such as dislocations.
Submonolayer quantum dot infrared photodetector
Authors: Ting David Z.-Y. , Bandara Sumith V. , Gunapala Sarath D. , Mumolo Jason M. , Keo Sam A. , Hill Cory J. , Liu John K. , Blazejewski Edward R. , Rafol Sir B. , Chang Yia-Chung
Published: March 2009

We describe the concept of the submonolayer quantum dot infrared photodetector (SML QDIP) and report experimental device results on long-wavelength infrared detection. An SML QDIP structure was fabricated into megapixel focal plane arrays, which produced clear infrared images up to 80 K. Detectors in the focal plane showed a responsivity peak at 7.8 μm and noise equivalent temperature difference of 33 mK at 70 K.
P
-type electrical, photoconductive, and anomalous ferromagnetic properties of Cu2O nanowires
Authors: Liao L. , Yan B. , Hao Y. F. , Xing G. Z. , Liu J. P. , Zhao B. C. , Shen Z. X. , Wu T. , Wang L. , Thong J. T. L. , Li C. M. , Huang W. , Yu T.
Published: March 2009

Cu 2 O nanowires are synthesized by reduction of CuO nanowires with hydrogen gas. Strong green photoluminescence dominated by band-edge emission is observed. Field effect transistors fabricated from individual Cu2O nanowires present high on-off ratio (>106) and high mobility (>95 cm2/V s). Furthermore, the device demonstrates a fast photoelectric response to blue illumination in air at room temperature. In addition, anomalous ferromagnetism appears in Cu2O nanowires, which may originate from the defects in Cu2O nanowires. This work shows the application potentials of the Cu2O nanowires, especially in an electrical and photonic device.
Nd-doped BiFeO3 ceramics with antipolar order
Authors: Karimi S. , Reaney I. M. , Levin I. , Sterianou I.
Published: March 2009

Bi 1 − x Nd x FeO 3  (0≤x≤0.2) ceramics have been investigated using x-ray diffraction (XRD) and electron diffraction (ED). XRD patterns for x≤0.1 were consistent with rhombohedral BiFeO3, whereas those for x=0.15 and x=0.2 exhibited peak splitting and superlattice reflections representative of orthorhombic, antiferroelectric PbZrO3. ED for the latter samples confirmed the presence of 14(hk0) superlattice reflections typical of a PbZrO3-like structure but additional superlattice reflections were observed at 14(00l) yielding a √2a,2√2a,4a (where a is the pseudocubic lattice parameter) unit cell. The transition from rhombohedral BiFeO3 to the PbZrO3-like structure implies a modification from polar to antipolar behavior.
Magnetocaloric effect in the La0.67Ca0.33Mn0.9Fe0.1O3 perovskite over a broad temperature range
Authors: Mukadam M. D. , Yusuf S. M.
Published: March 2009

We report the magnetocaloric effect in the La0.67Ca0.33Mn0.9Fe0.1O3 perovskite. A peak in the magnetic entropy change [ΔSM(H)] versus T curve, centered around 113 K, has been observed. −ΔSM(H) increases with an increasing applied magnetic field. The maximum value of −ΔSM(H) for ΔH=3 T field has been found to be 1.18 J kg−1 K−1 at 113 K with a relative cooling power of ∼87 J kg−1 and a quite broad operative temperature range 65–160 K. The hysteresis loss has been found to be very small. A large magnetocaloric effect with a relatively low material cost makes the studied perovskite attractive for magnetic refrigeration.
UV photovoltaic cells based on conjugated ZnO quantum dot/multiwalled carbon nanotube heterostructures
Authors: Li Fushan , Cho Sung Hwan , Son Dong Ick , Kim Tae Whan , Lee Sun-Kyun , Cho Yong-Hoon , Jin Sungho
Published: March 2009

In situ growth of ZnO quantum dots (QDs) on the surface of multiwalled carbon nanotubes (MWCNTs) was realized via a mild solution-process method, which resulted in an improvement in photoinduced charge separation and transport of carriers to the collecting electrode. The charge transfer efficiency was significantly increased by more than 90% due to the conjugation of ZnO QDs with MWCNTs, as confirmed by photoluminescence measurements. Ultraviolet photovoltaic cells based on the charge transfer at the ZnO QD-MWCNT heterostructures were fabricated, and their power conversion efficiency was measured to be above 1%.
Impacts of size and cross-sectional shape on surface lattice constant and electron effective mass of silicon nanowires
Authors: Yao Donglai , Zhang Gang , Lo Guo-Qiang , Li Baowen
Published: March 2009

We investigate the surface lattice and electronic structure of [110] oriented hydrogen-passivated silicon nanowires (SiNWs) of different cross-sectional shapes by using the first-principles tight-binding method. Remarkable quantum confinement effects are observed on the surface lattice constant and the electron effective mass. Moreover, with the same cross-sectional area, the triangular-SiNW has more obvious size dependence than rectangular-SiNW. The significant size and cross-sectional shape effects are explained by the concept of surface-to-volume ratio. Our results demonstrate that due to the smaller electron effective mass, the rectangular-SiNW has obvious advantage over triangular-SiNW in application in higher on current in SiNW transistor.
Valence-differential spectroscopy of Co–Fe cyanide films
Authors: Moritomo Y. , Nakada F. , Kurihara Y.
Published: March 2009

Electrochromism is extensively investigated for practical application of display and memory devices. To develop the material, reliable information on the optical and electronic properties of the solid film is indispensable. Here, we propose valence-differential spectroscopy that can selectively extract the spectral components related to the oxidized/reduced metal site. We applied the spectroscopy to Co2+–Fe2+δ and Co2+δ–Fe2+ cyanide films with finely control of averaged valence (δ) of the transition metal by external electric pulses. The spectroscopy revealed transition energy E, width Γ, and oscillator strength f of the spectral components related to the transition metal.
Tunable ferromagnetic resonance in NiFe nanowires with strong magnetostatic interaction
Authors: Kou Xiaoming , Fan Xin , Zhu Hao , Xiao John Q.
Published: March 2009

Magnetic materials with tunable ferromagnetic resonant (FMR) frequencies are highly desirable in microwave devices. In this manuscript, we demonstrate that the natural FMR of Ni90Fe10 nanowire array can be tuned continuously from 8.2 to 11.7 GHz by choosing different remanent states. Theoretical model based on magnetostatic interaction among nanowires has been developed to explain the observed phenomena.
Strong coupling through optical positioning of a quantum dot in a photonic crystal cavity
Authors: Thon Susanna M. , Rakher Matthew T. , Kim Hyochul , Gudat Jan , Irvine William T. M. , Petroff Pierre M. , Bouwmeester Dirk
Published: March 2009

Single self-assembled InAs quantum dots embedded in GaAs photonic crystal defect cavities are a promising system for cavity quantum electrodynamics experiments and quantum information schemes. Achieving controllable coupling in these small mode volume devices is challenging due to the random nucleation locations of individual quantum dots. We have developed an all optical scheme for locating the position of single dots with sub-10 nm accuracy. Using this method, we are able to deterministically reach the strong coupling regime with a spatial positioning success rate of approximately 70%. This flexible method should be applicable to other microcavity architectures and emitter systems.
Direct to indirect band gap transition in ultrathin ZnO nanowires under uniaxial compression
Authors: Zhang Yang , Wen Yu-Hua , Zheng Jin-Cheng , Zhu Zi-Zhong
Published: March 2009

The direct to indirect band gap transition in ultrathin [0001] ZnO nanowires with the structural transformation from the regular wurtzite structure to a more close-packed hexagonal structure during uniaxial compression is studied by using the first-principles calculations. The results show that all ZnO nanowires exhibit direct band gap in wurtzite structure and indirect band gap in hexagonal structure. For the same wire the band gap in hexagonal structure is smaller than that in wurtzite structure. The origin of the band gap transition from direct to indirect one is discussed.
Silver Trees: Chemistry on a TEM Grid
Authors: Nadagouda Mallikarjuna N. , Varma Rajender S.
Published: March 2009

The copper–carbon substrate of a transmission electron microscopy (TEM) grid reacted with aqueous silver nitrate solution within minutes to yield spectacular tree-like silver dendrites, without using any added capping or reducing reagents. These results demonstrate a facile, aqueous, room-temperature synthesis of a range of noble metal nano- and meso-structures that have widespread technological potential in the design and development of next-generation fuel cells, catalysts, and antimicrobial coatings.
Microwave-Induced Synthesis of Aromatic Polyamides by the Phosphorylation Reaction
Authors: Carretero Paula , Sandin Ricardo , Mercier Regis , Lozano Angel E. , de la Campa Jose G. , de Abajo Javier
Published: March 2009

This paper reports an optimization of the Yamazaki–Higashi method of direct polyamidation from aromatic diacids and aromatic diamines. As a model reaction, the polycondensation between 4,4′-oxydianiline and isophthalic acid was studied in the presence of a phosphorylation agent and under microwave irradiation. This experimental study revealed that optimal results can be attained by using a great excess of pyridine as catalyst (pyridine-to-monomer ratio of 7), at moderate radiation intensity (200 W), and up to 25% (w/v) monomer concentration. Although the inherent viscosity achieved by microwave and by conventional heating was comparable, an exceptional reaction rate under microwave irradiation yielded a polyamide inherent viscosity of around 1 dL g–1 in only a few minutes.
Microwave-Assisted Ruthenium-Catalyzed Reactions
Authors: Nicks François , Borguet Yannick , Delfosse Sébastien , Bicchielli Dario , Delaude Lionel , Sauvage Xavier , Demonceau Albert
Published: March 2009

Since the first reports on the use of microwave irradiation to accelerate organic chemical transformations, a plethora of papers has been published in this field. In most examples, microwave heating has been shown to dramatically reduce reaction times, increase product yields, and enhance product purity by reducing unwanted side reactions compared with conventional heating methods. The present contribution aims at illustrating the advantages of this technology in homogeneous catalysis by ruthenium complexes and, when data are available, at comparing microwave-heated and conventionally heated experiments. Selected examples refer to olefin metathesis, isomerization reactions, 1,3-dipolar cycloadditions, atom transfer radical reactions, transfer hydrogenation reactions, and H/D exchange reactions.
Interconversion of Nitrenes, Carbenes, and Nitrile Ylides by Ring Expansion, Ring Opening, Ring Contraction, and Ring Closure: 3-Quinolylnitrene, 2-Quinoxalylcarbene, and 3-Quinolylcarbene
Authors: Kvaskoff David , Mitschke Ullrich , Addicott Chris , Finnerty Justin , Bednarek Pawel , Wentrup Curt
Published: March 2009

Photolysis of 3-azidoquinoline 6 in an Ar matrix generates 3-quinolylnitrene 7, which is characterized by its electron spin resonance (ESR), UV, and IR spectra in Ar matrices. Nitrene 7 undergoes ring opening to a nitrile ylide 19, also characterized by its UV and IR spectra. A subsequent 1,7-hydrogen shift in the ylide 19 affords 3-(2-isocyanophenyl)ketenimine 20. Matrix photolysis of 1,2,3-triazolo[1,5-c]quinoxaline 26 generates 4-diazomethylquinazoline 27, followed by 4-quinazolylcarbene 28, which is characterized by ESR and IR spectroscopy. Further photolysis of carbene 28 slowly generates ketenimine 20, thus suggesting that ylide 19 is formed initially. Flash vacuum thermolysis (FVT) of both 6 and 26 affords 3-cyanoindole 22 in high yield, thereby indicating that carbene 28 and nitrene 7 enter the same energy surface. Matrix photolysis of 3-quinolyldiazomethane 30 generates 3-quinolylcarbene 31, which on photolysis at >500 nm reacts with N2 to regenerate diazo compound 30. Photolysis of 30 in the presence of CO generates a ketene (34). 3-Quinolylcarbene 31 cyclizes on photolysis at >500 nm to 5-aza-2,3-benzobicyclo[4.1.0]hepta-2,4,7-triene 32. Both 31 and 32 are characterized by their IR and UV spectra. FVT of 30 yields a mixture of 2- and 3-cyanoindenes via a carbene–carbene–nitrene rearrangement 31 → 2-quinolylcarbene 39 → 1-naphthylnitrene 43. The reaction mechanisms are supported by density functional theory calculations of the energies and spectra of all relevant ground and transition state structures at the B3LYP/6–31G* level.
Metal-binding loop length and not sequence dictates structure
Authors: Sato Katsuko , Li Chan , Salard Isabelle , Thompson Andrew J. , Banfield Mark J. , Dennison Christopher
Published: March 2009

The C-terminal copper-binding loop in the β-barrel fold of the cupredoxin azurin has been replaced with a range of sequences containing alanine, glycine, and valine residues to assess the importance of amino acid composition and the length of this region. The introduction of 2 and 4 alanines between the coordinating Cys, His, and Met results in loop structures matching those in naturally occurring proteins with the same loop lengths. A loop with 4 alanines between the Cys and His and 3 between the His and Met ligands has a structure identical to that of the WT protein, whose loop is the same length. Loop structure is dictated by length and not sequence allowing the properties of the main surface patch for interactions with partners, to which the loop is a major contributor, to be optimized. Loops with 2 amino acids between the ligands using glycine, alanine, and valine residues have been compared. An empirical relationship is found between copper site protection by the loop and reduction potential. A loop adorned with 4 methyl groups is sufficient to protect the copper ion, enabling most sequences to adequately perform this task. The mutant with 3 alanine residues between the ligands forms a strand-swapped dimer in the crystal structure, an arrangement that has not, to our knowledge, been seen previously for this family of proteins. Cupredoxins function as redox shuttles and are required to be monomeric; therefore, none have evolved with a metal-binding loop of this length.
Solution-processed, high-performance n-channel organic microwire transistors
Authors: Oh Joon Hak , Lee Hang Woo , Mannsfeld Stefan , Stoltenberg Randall M. , Jung Eric , Jin Yong Wan , Kim Jong Min , Yoo Ji-Beom , Bao Zhenan
Published: March 2009

The development of solution-processable, high-performance n-channel organic semiconductors is crucial to realizing low-cost, all-organic complementary circuits. Single-crystalline organic semiconductor nano/microwires (NWs/MWs) have great potential as active materials in solution-formed high-performance transistors. However, the technology to integrate these elements into functional networks with controlled alignment and density lags far behind their inorganic counterparts. Here, we report a solution-processing approach to achieve high-performance air-stable n-channel organic transistors (the field-effect mobility (μ) up to 0.24 cm
2
/Vs for MW networks) comprising high mobility, solution-synthesized single-crystalline organic semiconducting MWs (μ as high as 1.4 cm
2
/Vs for individual MWs) and a filtration-and-transfer (FAT) alignment method. The FAT method enables facile control over both alignment and density of MWs. Our approach presents a route toward solution-processed, high-performance organic transistors and could be used for directed assembly of various functional organic and inorganic NWs/MWs.
Predictors of stillbirth among HIV‐infected Tanzanian women
Authors: KUPKA ROLAND , KASSAYE TARIK , SAATHOFF ELMAR , HERTZMARK ELLEN , MSAMANGA GERNARD I. , FAWZI WAFAIE W.
Published: March 2009

Objective. To determine maternal risk factors for stillbirth among pregnant HIV‐infected women in sub‐Saharan Africa. Design. Prospective cohort study nested within a micronutrient trial. At enrollment, maternal sociodemographic, obstetric, immunologic, clinical, and nutritional variables were measured. Women were followed through monthly clinic visits until delivery. Multivariate predictors of stillbirth were identified in Poisson regression models. Setting. Antenatal clinic in a tertiary care hospital in urban Dar es Salaam, Tanzania. Population. N = 1,078 women enrolled between 12 and 27 weeks of gestation. Main outcome measures. Stillbirth (delivery of dead baby ≥ 28 weeks’ gestation), fresh stillbirth, and macerated stillbirth. Results. Among 1,017 singleton pregnancies, there were 49 stillbirths, yielding a stillbirth risk of 50.0 per 1,000 deliveries (95% Confidence Interval(CI) = 37.2, 65.6). Of stillbirths with known type, 53.7% were fresh and 46.3% macerated. In multivariate analyses, baseline measures of late (≥ 21 weeks’ gestation) study entry (Relative Risk (RR) = 2.13, 95% CI = 1.17, 3.87), CD3 count ≥ 1,179 cells/ml (RR = 2.15, 95% CI = 1.16, 4.01), stillbirth history (RR = 3.53, 95% CI = 1.30, 9.59), primiparity (RR = 3.65, 95% CI = 1.83, 7.29), and syphilis infection (RR = 2.06, 95% CI = 1.09, 3.88) predicted increased stillbirth risk. Late study entry, illiteracy, stillbirth history, primiparity, CD3 count ≥ 1,179 cells/ml, gonorrhea infection, and previous hospitalization predicted increased risk of fresh stillbirth, while living alone and syphilis infection predicted increased risk of macerated stillbirth. Conclusions. Applying antenatal screening and preventive tools for the socioeconomic, obstetric, immunologic, and clinical risk factors identified may assist in reducing the high incidence of stillbirth among HIV‐infected women in urban sub‐Saharan Africa.
Book Review
Authors: Cwikiel Wojciech
Published: March 2009

Image-Guided Interventions. Edited by M. Maura, K. Murphy, K. Thomson, A. Venbrux, & C. Zollikofer. Philadelphia, PA: Saunders Elsevier, 2008. ISBN 978-1-4160-2964-9. Two volumes. 1777 pages. Price (hardback): USD 339
Ralstonia solanacearum Race 3 Biovar 2 Causes Tropical Losses and Temperate Anxieties
Authors: Champoiseau Patrice G. , Jones Jeffrey B. , Allen Caitilyn
Published: March 2009

R. solanacearum Race 3 biovar 2, which causes potato brown rot and Southern wilt of geranium, is a high-consequence quarantine pathogen in Europe and North America and causes large crop losses in tropical highlands. This practical review emphasizes prevention, detection, diagnosis, and effective management of diseases caused by this destructive pathogen.

Accepted for publication 17 January 2009. Published 13 March 2009.
Pharmacokinetics and response of obese patients with chronic hepatitis C treated with different doses of PEG‐IFN α‐2a (40KD) (PEGASYS®)
Authors: Bressler Brian , Wang Ka , Grippo Joseph F. , Heathcote E. Jenny
Published: March 2009

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• Obesity is a negative predictor of successful treatment in patients with chronic hepatitis C treated with peginterferon (PEG‐IFN) and ribavirin.

• Obese patients may have suboptimal exposure of PEG‐IFN contributing to the poor responses seen in this patient population.

• In non‐obese patients doses of PEG‐IFN α‐2a (40KD) up to 360 µg week−1 have shown dose proportional pharmacokinetics.

WHAT THIS STUDY ADDS

• Here we show that among obese patients treated with the standard dose of PEG‐IFN α‐2a (40KD) (180 µg week−1) drug exposure was lower than that found in a large set of unpublished data among non‐obese patients, but was generally similar to exposures found in a large set of unpublished data among similarly obese patients receiving the same dose of PEG‐IFN α‐2a (40KD).

• By increasing the dose of PEG‐IFN α‐2a (40KD) from 180 µg week−1 to 270 µg week−1 one can increase PEG‐IFN α‐2a (40KD) exposure, thereby potentially compensating for the apparent reduction in drug exposure in obese patients.

AIMS To evaluate whether higher doses of peginterferon α‐2a (40KD) [PEG‐IFN α‐2a (40KD)] can compensate for lower exposure observed among obese patients with chronic hepatitis C (CHC) treated with the standard dose of PEG‐IFN α‐2a (40KD).

METHODS Noncirrhotic, obese (body mass index ≥30 kg m−2) patients with CHC participated in a single‐centre, open‐label study. Patients were randomized to 180 or 270 µg week−1 PEG‐IFN α‐2a (40KD) + ribavirin (1000/1200 mg day−1) for 48 weeks. Blood samples were collected predose and up to 168 h after the first dose and at week 12 for pharmacokinetic analysis. Trough serum concentrations (Ctrough) were determined up to week 24.

RESULTS In the 180 µg week−1 group mean ± SD steady‐state (week 12) estimates of AUC0–168 (ng h−1 ml−1), Cmax (ng ml−1) and CL/F (l h−1) were 2154 ± 919, 13.8 ± 6.7 and 0.102 ± 0.051, respectively. In the 270 µg week−1 group, estimates were 3374 ± 1844, 23.4 ± 10.7 and 0.090 ± 0.042, respectively. The mean (range) Ctrough (ng ml−1) was 11.2 (4.4–18.5) in the 180 µg week−1 group and 16.1 (0.4–44.2) in the 270 µg week−1 group. Overall, 14 of 20 (70%) and 16 of 20 (80%) patients in the 180 µg week−1 and 270 µg week−1 groups were infected with hepatitis C virus genotype 1 or 4. In the 180 µg week−1 and 270 µg week−1 groups 14 of 20 (70%) and 15 of 19 (79%) patients, respectively, achieved a sustained viral response. Safety was similar between groups.

CONCLUSIONS Mean PEG‐IFN α‐2a (40KD) exposure was dose proportional from 180 to 270 µg week−1. Increasing PEG‐IFN α‐2a (40KD) from 180 to 270 µg week−1 achieves higher serum drug exposure in obese patients.
A pharmacokinetic evaluation of five H1 antagonists after an oral and intravenous microdose to human subjects
Authors: Madan Ajay , O'Brien Zhihong , Wen Jianyun , O'Brien Chris , Farber Robert H. , Beaton Graham , Crowe Paul , Oosterhuis Berend , Garner R. Colin , Lappin Graham , Bozigian Haig P.
Published: March 2009

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• Human microdosing studies with novel drug candidates offer an opportunity to evaluate their pharmacokinetic (PK) behaviour early in drug development and before committing to the expense of clinical Phase I‐enabling activities.

• Such studies assume linearity of exposure with dose all the way down to a subtherapeutic dose.

• Previous studies have reported partial success in the use of this technique for assessing human PK of marketed drugs.

WHAT THIS STUDY ADDS

• The present study describes the application of the microdosing concept in early drug development for an H1 antagonist programme where having good estimates of human PK and information about the shape of the concentration–time curve was critical for compound selection.

• Microdosing data were generated for four novel compounds and one reference compound, and the data were used for advancing the compound with the most favourable PK properties.

• To our knowledge, this is the first example of the use microdosing technique for compound selection.

AIMS To evaluate the pharmacokinetics (PK) of five H1 receptor antagonists in human volunteers after a single oral and intravenous (i.v.) microdose (0.1 mg).

METHODS Five H1 receptor antagonists, namely NBI‐1, NBI‐2, NBI‐3, NBI‐4 and diphenhydramine, were administered to human volunteers as a single 0.1‐mg oral and i.v. dose. Blood samples were collected up to 48 h, and the parent compound in the plasma extract was quantified by high‐performance liquid chromatography and accelerator mass spectroscopy.

RESULTS The median clearance (CL), apparent volume of distribution (Vd) and apparent terminal elimination half‐life (t1/2) of diphenhydramine after an i.v. microdose were 24.7 l h−1, 302 l and 9.3 h, and the oral Cmax and AUC0–∞ were 0.195 ng ml−1 and 1.52 ng h ml−1, respectively. These data were consistent with previously published diphenhydramine data at 500 times the microdose. The rank order of oral bioavailability of the five compounds was as follows: NBI‐2 > NBI‐1 > NBI‐3 > diphenhydramine > NBI‐4, whereas the rank order for CL was NBI‐4 > diphenhydramine > NBI‐1 > NBI‐3 > NBI‐2.

CONCLUSIONS Human microdosing provided estimates of clinical PK of four structurally related compounds, which were deemed useful for compound selection.
Opposite effect of fluticasone and salmeterol on fibronectin and tenascin‐C expression in primary human lung fibroblasts
Authors: Degen M. , Goulet S. , Ferralli J. , Roth M. , Tamm M. , Chiquet‐Ehrismann R.
Published: March 2009

Background
Airway remodelling is a key feature of asthma and chronic obstructive pulmonary disease (COPD). The remodelling process involves the deposition of extracellular matrix (ECM) proteins within the airways. Current therapies for asthma and COPD consist of inhaled corticosteroids and long‐acting β2‐agonists (LABA). However, their effect on airway remodelling is not well understood so far.

Objective
In this study we investigated the effect of fluticasone and salmeterol, either alone or in combination, on fibronectin and tenascin‐C protein, isoform, and mRNA levels in primary human lung fibroblasts.

Methods
In our model, fibroblasts cultured in serum‐free medium represented a non‐inflammatory condition and stimulation with 5% fetal calf serum and/or TGF‐β1 mimicked a pro‐fibrotic environment with activation of tissue repair. Using these two different conditions, the effects of fluticasone and salmeterol on fibronectin and tenascin‐C protein and mRNA levels were analysed by immunoblotting and semi‐quantitative RT‐PCR.

Results
In both conditions, fluticasone increased fibronectin transcript and protein levels, whereas it decreased those of tenascin‐C. Salmeterol neither affected fibronectin and tenascin‐C synthesis significantly nor did it influence the effect of fluticasone when applied in combination. Furthermore, we found that treatment with fluticasone had an opposite effect on extra domain A and B containing fibronectin isoforms generated by alternative splicing compared with total fibronectin transcript levels, whereas tenascin‐C isoforms were not differently modulated by fluticasone.

Conclusions
Our results indicate that standard therapies for inflammatory lung disorders influence ECM protein composition and relative expression levels. In contrast to corticosteroids, LABA did not significantly alter the expression of tenascin‐C and fibronectin in cultures of primary human lung fibroblasts.
Sampling groundwater fauna: efficiency of rapid assessment methods tested in bores in eastern Australia
Authors: HANCOCK PETER J. , BOULTON ANDREW J.
Published: March 2009

1. Growing recognition of the ecological significance and biodiversity of groundwater fauna in Australia has led to statutory requirements for monitoring these communities prior to resource development. However, the efficiency of methods for assessing community composition and taxa richness remains untested, hampering the collection of reliable data for compliance.

2. We assessed the efficiency of two commonly‐used methods to sample groundwater fauna (net hauls and pumping) in bores in two contrasting regions (Dubbo and upper Hunter Valley) of eastern Australia. Repeated sets of seasonal samples from the upper Hunter Valley bores were used to test whether once‐off sampling was sufficient for compliance purposes.

3. All taxa collected by the net method were also captured in pump samples. In addition, pumping yielded more taxa, higher total abundances, and higher numbers of the two most common taxa (syncarids and copepods) than the net. Ten net hauls in the upper Hunter Valley bores collected, on average, 64% of the taxa and 44% of total abundance. When combined with the first 100 L from pumping, cumulative totals rose to 92.5% and 74.5% respectively. Similar trends occurred in bores near Dubbo, indicating that net hauls alone under‐sampled groundwater faunal communities. Multivariate analyses revealed substantial differences in community composition as each incremental subsample was added.

4. Temporal changes in community composition in the Hunter Valley aquifer were marked yet inconsistent across the bores. Initial once‐off sampling collected 30–87% of the total taxa from each bore and new taxa were still being collected after four sampling periods in over half the bores. This shows that more than one sampling occasion is needed for comprehensive assessments of groundwater biodiversity.

5. Successful compliance monitoring of groundwater fauna requires cost‐effective sampling that will not overlook potentially vulnerable taxa or miss ecologically relevant changes in community composition. Currently, a lack of suitable bores seems to be the main constraint on accurate assessment of groundwater invertebrate community composition in these two areas of eastern Australia.