bluuebunny/crossref_metadata_2025 huggingface dataset:
Ribose 5-phosphate isomerase type B from Trypanosoma cruzi: kinetic properties and site-directed mutagenesis reveal information about the reaction mechanism
Authors: Stern Ana L. , Burgos Emmanuel , Salmon Laurent , Cazzulo Juan J.
Published: December 2006

Trypanosoma cruzi, the human parasite that causes Chagas disease, contains a functional pentose phosphate pathway, probably essential for protection against oxidative stress and also for R5P (ribose 5-phosphate) production for nucleotide synthesis. The haploid genome of the CL Brener clone of the parasite contains one gene coding for a Type B Rpi (ribose 5-phosphate isomerase), but genes encoding Type A Rpis, most frequent in eukaryotes, seem to be absent. The RpiB enzyme was expressed in Escherichia coli as a poly-His tagged active dimeric protein, which catalyses the reversible isomerization of R5P to Ru5P (ribulose 5-phos-phate) with Km values of 4 mM (R5P) and 1.4 mM (Ru5P).

4-Phospho-D-erythronohydroxamic acid, an analogue to the reaction intermediate when the Rpi acts via a mechanism involving the formation of a 1,2-cis-enediol, inhibited the enzyme competi-tively, with an IC50 value of 0.7 mM and a Ki of 1.2 mM. Site-directed mutagenesis allowed the demonstration of a role for His102, but not for His138, in the opening of the ribose furanosic ring. A major role in catalysis was confirmed for Cys69, since the C69A mutant was inactive in both forward and reverse directions of the reaction. The present paper contributes to the know-ledge of the mechanism of the Rpi reaction; in addition, the absence of RpiBs in the genomes of higher animals makes this enzyme a possible target for chemotherapy of Chagas disease.
Crystal structure of human phosphoribosylpyrophosphate synthetase 1 reveals a novel allosteric site
Authors: Li Sheng , Lu Yongcheng , Peng Baozhen , Ding Jianping
Published: December 2006

PRPP (phosphoribosylpyrophosphate) is an important metabolite essential for nucleotide synthesis and PRS (PRPP synthetase) catalyses synthesis of PRPP from R5P (ribose 5-phosphate) and ATP. The enzymatic activity of PRS is regulated by phosphate ions, divalent metal cations and ADP. In the present study we report the crystal structures of recombinant human PRS1 in complexes with SO42− ions alone and with ATP, Cd2+ and SO42− ions respectively. The AMP moiety of ATP binds at the ATP-binding site, and a Cd2+ ion binds at the active site and in a position to interact with the β- and γ-phosphates of ATP. A SO42− ion, an analogue of the activator phosphate, was found to bind at both the R5P-binding site and the allosteric site defined previously. In addi-tion, an extra SO42− binds at a site at the dimer interface between the ATP-binding site and the allosteric site. Binding of this SO42− stabilizes the conformation of the flexible loop at the active site, leading to the formation of the active, open conformation which is essential for binding of ATP and initiation of the catalytic reaction. This is the first time that structural stabilization at the active site caused by binding of an activator has been observed. Structural and biochemical data show that mutations of some residues at this site influence the binding of SO42− and affect the enzymatic activity. The results in the present paper suggest that this new SO42−-binding site is a second allosteric site to regulate the enzymatic activity which might also exist in other eukaryotic PRSs (except plant PRSs of class II), but not in bacterial PRSs.
Activation of the ATF3 gene through a co-ordinated amino acid-sensing response programme that controls transcriptional regulation of responsive genes following amino acid limitation
Authors: Pan Yuan-Xiang , Chen Hong , Thiaville Michelle M. , Kilberg Michael S.
Published: December 2006

Expression of ATF3 (activating transcription factor 3) is induced by a variety of environmental stress conditions, including nutrient limitation. In the present study, we demonstrate that the increase in ATF3 mRNA content following amino acid limitation of human HepG2 hepatoma cells is dependent on transcriptional activation of the ATF3 gene, through a highly co-ordinated amino acid-responsive programme of transcription factor synthesis and action. Studies using transient over-expression and knockout fibroblasts showed that several ATF and C/EBP (CCAAT/enhancer-binding protein) family members contribute to ATF3 regulation. Promoter analysis showed that a C/EBP-ATF composite site at −23 to −15 bp relative to the transcription start site of the ATF3 gene functions as an AARE (amino acid response element). Chromatin immunoprecipitation demonstrated that amino acid limitation increased ATF4, ATF3, and C/EBPβ binding to the ATF3 promoter, but the kinetics of each was markedly different. Immediately following histidine removal, there was a rapid increase in histone H3 acetylation prior to an enhancement in ATF4 binding and in histone H4 acetylation. These latter changes closely paralleled the initial increase in RNA pol II (RNA polymerase II) binding to the promoter and in the transcription rate from the ATF3 gene. The increase in ATF3 and C/EBPβ binding was considerably slower and more closely correlated with a decline in transcription rate. A comparison of the recruitment patterns between ATF and C/EBP transcription factors and RNA polymerase II at the AARE of several amino acid-responsive genes revealed that a highly co-ordinated response programme controls the transcriptional activation of these genes following amino acid limitation.
The diurnal metabolism of leaf starch
Authors: Zeeman Samuel C. , Smith Steven M. , Smith Alison M.
Published: December 2006

Starch is a primary product of photosynthesis in leaves. In most plants, a large fraction of the carbon assimilated during the day is stored transiently in the chloroplast as starch for use during the subsequent night. Photosynthetic partitioning into starch is finely regulated, and the amount of carbohydrate stored is dependent on the environmental conditions, particularly day length. This regulation is applied at several levels to control the flux of carbon from the Calvin cycle into starch biosynthesis. Starch is composed primarily of branched glucans with an architecture that allows the formation of a semi-crystalline insoluble granule. Biosynthesis has been most intensively studied in non-photosynthetic starch-storing organs, such as developing seeds and tubers. Biosynthesis in leaves has received less attention, but recent reverse-genetic studies of Arabidopsis (thale cress) have produced data generally consistent with what is known for storage tissues. The pathway involves starch synthases, which elongate the glucan chains, and branching enzymes. Remarkably, enzymes that partially debranch glucans are also required for normal amylopectin synthesis. In the last decade, our understanding of starch breakdown in leaves has advanced considerably. Starch is hydrolysed to maltose and glucose at night via a pathway that requires recently discovered proteins in addition to well-known enzymes. These sugars are exported from the plastid to support sucrose synthesis, respiration and growth. In the present review we provide an overview of starch biosynthesis, starch structure and starch degradation in the leaves of plants. We focus on recent advances in each area and highlight outstanding questions.
Localization at low temperature and infrared bounds
Authors: Bach Volker , Møller Jacob Schach
Published: December 2006

We consider a class of classical lattice spin systems, with Rn-valued spins and two-body interactions. Our main result states that the associated Gibbs measure localizes in certain cylindrical neighborhoods of the global minima of the unperturbed Hamiltonian. As an application we establish existence of a first order phase transition at low temperature, for a reflection positive mexican hat model on Zd, d⩾3, with a nonferromagnetic interaction.
The AΣu+1 state of K2 up to the dissociation limit
Authors: Falke St. , Sherstov I. , Tiemann E. , Lisdat Ch.
Published: December 2006

We report an experimental study of the K2 AΣu+1 state. Long-range levels up to the dissociation limit were observed in a two laser spectroscopic experiment using a highly collimated molecular beam. We derive an analytical potential energy curve for the complete A state including long-range dispersion terms. From these, we obtain radiative atomic lifetimes of 26.74(3)ns for the 4p1∕2 state and 26.39(3)ns for the 4p3∕2 state of K39. The dissociation energy of the XΣg+1 ground state with respect to v=0, J=0 is found to be D0=4404.808(4)cm−1.
X-ray magnetic circular dichroism studies of (001)-oriented NiFe∕Mn100−xPtx exchange bilayers
Authors: Yamato T. , Kume T. , Kato T. , Tsunashima S. , Nakamura T. , Fujiwara Y. , Iwata S.
Published: December 2006

(001)-oriented Ni80Fe20∕Mn100−xPtx and Co90Fe10∕Mn100−xPtx epitaxial bilayers were prepared using the molecular beam epitaxy method. Their exchange anisotropies were measured using a torque magnetometer, while their interfacial Mn uncompensated moments were measured by means of x-ray magnetic circular dichroism. The bilayers exhibited both one- and fourfold components in their anisotropy torque curves, which are difficult to explain using a simple model assuming the coherent rotation of ferromagnetic (F) and antiferromagnetic (AF) spins. Uncompensated Mn moments were confirmed to exist in the Mn100−xPtx layer due to exchange coupling with the adjacent F layer, and the Mn moment of CoFe∕Mn100−xPtx was found to be larger than that of NiFe∕Mn100−xPtx. In order to understand the experimental results, we extended the Mauri et al. [J. Appl. Phys. 62, 3047 (1987)] domain wall model by assuming cubic anisotropy in the AF and four AF domains whose interfacial moments are oriented along the principal axis of (001)-oriented Mn–Pt. The model predicted the uncompensated AF moment resulting from the domain wall formed in the AF layer and well reproduced the coexistence of one- and fourfold anisotropies in the in-plane torque curves. The uncompensated moment and torque curve were found to be dependent on the ratio of F/AF interfacial exchange coupling and the AF domain wall energy. By changing the ratio, it was possible to reproduce exchange anisotropy for various systems, such as NiFe∕MnPt, NiFe∕MnIr, and CoFe∕MnPt.
Temperature-dependent barrier characteristics of swift heavy ion irradiated Au∕n-Si Schottky structure
Authors: Kumar Sandeep , Katharria Y. S. , Kumar Sugam , Kanjilal D.
Published: December 2006

The electrical behavior of Au∕n-Si(100) structure, irradiated with 120MeV Ag8+107, has been investigated in a wide temperature range (50–300K). The forward bias current-voltage (I-V) and reverse bias capacitance-voltage (C-V) measurements have been used to extract the diode parameters. The variations in various parameters of the irradiated Schottky structure have been systematically studied as a function of temperature. It is found that the flatband barrier height is almost independent of the change in temperature. The ionized-donor concentration decreases while the ideality factor increases with decreasing temperatures. The behavior of Schottky parameters is explained by taking into account the role of the swift heavy ion irradiation induced defects at metal-semiconductor junction. The results are interpreted on the basis of recent models of Fermi level pinning.
Extension of the Conley-Zehnder index, a product formula, and an application to the Weyl representation of metaplectic operators
Authors: de Gosson Maurice A. , de Gosson Serge M.
Published: December 2006

The aim of this paper is to express the Conley-Zehnder index of a symplectic path in terms of an index due to Leray and which has been studied by one of us in a previous work. This will allow us to prove a formula for the Conley-Zehnder index of the product of two symplectic paths in terms of a symplectic Cayley transform. We apply our results to a rigorous study of the Weyl representation of metaplectic operators, which plays a crucial role in the understanding of semiclassical quantization of Hamiltonian systems exhibiting chaotic behavior.
Using the thermal Gaussian approximation for the Boltzmann operator in semiclassical initial value time correlation functions
Authors: Liu Jian , Miller William H.
Published: December 2006

The thermal Gaussian approximation (TGA) recently developed by Frantsuzov et al. [Chem. Phys. Lett. 381, 117 (2003)] has been demonstrated to be a practical way for approximating the Boltzmann operator exp(−βĤ) for multidimensional systems. In this paper the TGA is combined with semiclassical (SC) initial value representations (IVRs) for thermal time correlation functions. Specifically, it is used with the linearized SC-IVR (LSC-IVR, equivalent to the classical Wigner model), and the “forward-backward semiclassical dynamics” approximation developed by Shao and Makri [J. Phys. Chem. A 103, 7753 (1999); 103, 9749 (1999)]. Use of the TGA with both of these approximate SC-IVRs allows the oscillatory part of the IVR to be integrated out explicitly, providing an extremely simple result that is readily applicable to large molecular systems. Calculation of the force-force autocorrelation for a strongly anharmonic oscillator demonstrates its accuracy, and calculation of the velocity autocorrelation function (and thus the diffusion coefficient) of liquid neon demonstrates its applicability.
Modeling organic light-emitting diodes incorporating nanocrystal quantum dots
Authors: Kohary K. , Burlakov V. M. , Pettifor D. G. , Burlakov V. M. , Pettifor D. G.
Published: December 2006

Based on a rate equation model, we have investigated theoretically the performance of a model organic light-emitting diode (OLED), which is activated by a single emissive layer of nanocrystals (NCs) embedded between electron- and hole-transporting organic films. Our model combines a unified description of diffusion-controlled charge transport in the organic semiconductors, exciton formation and kinetics at the organic-organic interface, and Förster injection of the excitons into the nanocrystals. We have used the resultant rate equation model to study the light intensity and quantum efficiency of the NC-OLED as a function of the concentration of the nanocrystals, assuming the latter are arranged on a regular two-dimensional lattice in the emissive layer. We have identified an optimal nanocrystal density and shown that the NC-OLED performance is affected mainly by the efficiency of the Förster injection of excitons into the nanocrystals, whereas it is much less sensitive to the exciton kinetics at the organic-organic interface.
Application of photoluminescence characterization to the development and manufacturing of high-efficiency silicon solar cells
Authors: Abbott M. D. , Cotter J. E. , Chen F. W. , Trupke T. , Bardos R. A. , Fisher K. C.
Published: December 2006

Characterization techniques based on quasi-steady-state photoluminescence have recently emerged as accurate, fast, and powerful tools for developing high-efficiency silicon solar cells. These techniques are contactless and provide complementary spatial and injection level dependent information about recombination. In this paper, we demonstrate the application of different photoluminescence techniques to several important aspects of high-efficiency solar cell fabrication: wafer handling, furnace contamination, process-induced defects, cell design, and cell process monitoring. The experimental results demonstrate that photoluminescence characterization techniques are excellent tools for laboratory experiments and also potentially for industrial process monitoring.
Restructuring and modification of metallic nanorod arrays using femtosecond laser direct writing
Authors: Reinhardt C. , Passinger S. , Chichkov B. N. , Dickson W. , Wurtz G. A. , Evans P. , Pollard R. , Zayats A. V.
Published: December 2006

Local restructuring of metallic nanorod arrays and the fabrication of metallodielectric microstructures using direct femtosecond laser writing technologies have been studied. Femtosecond laser ablation has demonstrated the possibility to create sharp boundaries (down to a single nanorod) on the nanorod array. Polymer structures on the nanorods can be used to control the resonance wavelengths and thus the effective refractive index of surface plasmons supported by the array. The structured nanorods and their polymer composites are important for applications in light guiding and the development of nonlinear optical nanodevices.
Kinetically modified parametric instabilities of circularly polarized Alfvén waves: Ion kinetic effects
Authors: Nariyuki Y. , Hada T.
Published: December 2006

Parametric instabilities of parallel propagating, circularly polarized, finite amplitude Alfvén waves in a uniform background plasma is studied, within a framework of one-dimensional Vlasov description for ions and massless electron fluid, so that kinetic perturbations in the longitudinal direction (ion Landau damping) are included. The present formulation also includes the Hall effect. The obtained results agree well with relevant analysis in the past, suggesting that kinetic effects in the longitudinal direction play essential roles in the parametric instabilities of Alfvén waves when the kinetic effects react “passively.” Furthermore, existence of the kinetic parametric instabilities is confirmed for the regime with small-wave-number daughter waves. Growth rates of these instabilities are sensitive to ion temperature. The formulation and results demonstrated here can be applied to Alfvén waves observed in the solar wind and in the earth’s foreshock region.
Room-temperature single charge sensitivity in carbon nanotube field-effect transistors
Authors: Peng H. B. , Hughes M. E. , Golovchenko J. A.
Published: December 2006

Electrical current fluctuation studies are reported for coaxial p-type and n-type single-wall carbon nanotube field-effect transistors (FETs). Abrupt discrete switching of the source-drain current is observed at room temperature. The authors attribute these random telegraph signals to charge fluctuating electron traps near the FET conduction channels. Evolution of the current-switching behavior associated with the occupancy of individual electron traps is demonstrated and analyzed statistically. The result strongly indicates room temperature single charge sensitivity in carbon nanotube FETs, which may offer potential applications for single molecule sensors based on suitably prepared FET devices.
Large cone angle magnetization precession of an individual nanopatterned ferromagnet with dc electrical detection
Authors: Costache M. V. , Watts S. M. , Sladkov M. , van der Wal C. H. , van Wees B. J.
Published: December 2006

The on-chip resonant driving of large cone-angle magnetization precession of an individual nanoscale Permalloy element is demonstrated. Strong driving is realized by locating the element in close proximity to the shorted end of a coplanar strip waveguide, which generates a microwave magnetic field. A frequency modulation method is used to accurately measure resonant changes of the dc anisotropic magnetoresistance. Precession cone angles up to 9° are determined with better than 1° of resolution. The resonance peak shape is well described by the Landau-Lifshitz-Gilbert equation.
Measuring activity in ant colonies
Authors: Noda C. , Fernández J. , Pérez-Penichet C. , Altshuler E.
Published: December 2006

Ants, as paradigm of social insects, have become a recurrent example of efficient problem solvers via self-organization. In spite of the simple behavior of each individual, the colony as a whole displays “swarm intelligence:” the organization of ant trails for foraging is a typical output of it. But conventional techniques of observation can hardly record the amount of data needed to get a detailed understanding of self-organization of ant swarms in the wild. Here we are presenting a measurement system intended to monitor ant activity in the field comprising massive data acquisition and high sensitivity. A central role is played by an infrared sensor devised specifically to monitor relevant parameters to the activity of ants through the exits of the nest, although other sensors detecting temperature and luminosity are added to the system. We study the characteristics of the activity sensor and its performance in the field. Finally, we present massive data measured at one exit of a nest of Atta insularis, an ant endemic to Cuba, to illustrate the potential of our system.
Reduced density matrix quantum approach for particle trapping and sticking on corrugated moving surfaces
Authors: Medina Zuleika , Jackson Bret
Published: December 2006

A short time propagation algorithm for the reduced density matrix is derived to model the interaction of a quantum particle with a moving corrugated surface. The algorithm includes dissipative terms, which can be derived directly from the full Hamiltonian. The scattering of He from a corrugated Cu surface is examined as a function of incident energy and angle and the temperature of the substrate, with a focus on the nature of trapping. It is found that corrugation can make a significant contribution to trapping, even on a metal surface. Energy exchange with the phonons is shown to significantly modify the nature of diffraction mediated selective adsorption.
Potential energy surface and MULTIMODE vibrational analysis of C2H3+
Authors: Sharma Amit R. , Wu Jiayan , Braams Bastiaan J. , Carter Stuart , Schneider Ralf , Shepler Ben , Bowman Joel M.
Published: December 2006

A full dimensional, ab initio-based semiglobal potential energy surface for C2H3+ is reported. The ab initio electronic energies for this molecule are calculated using the spin-restricted, coupled cluster method restricted to single and double excitations with triples corrections [RCCSD(T)]. The RCCSD(T) method is used with the correlation-consistent polarized valence triple-zeta basis augmented with diffuse functions (aug-cc-pVTZ). The ab initio potential energy surface is represented by a many-body (cluster) expansion, each term of which uses functions that are fully invariant under permutations of like nuclei. The fitted potential energy surface is validated by comparing normal mode frequencies at the global minimum and secondary minimum with previous and new direct ab initio frequencies. The potential surface is used in vibrational analysis using the “single-reference” and “reaction-path” versions of the code MULTIMODE.
Highly efficient GaN-based light emitting diodes with micropits
Authors: Hao M. , Egawa T. , Ishikawa H.
Published: December 2006

Light emitting diodes (LEDs) on GaN templates with high-density V-shaped micropits have been grown and characterized by transmission electron microscopy, scanning electron microscopy, and photoluminescence. Higher emission efficiency has been obtained for the fabricated LEDs compared with those without V-shaped pits. The high efficiency of the LEDs is mainly attributed to the increase in light extraction efficiency due to the light extraction from the sidewalls of the V-shaped pits. The improved internal quantum efficiency of the device resulting from the reduction of the dislocation density in the light emitting area also contributes to the high efficiency of the LEDs.
Dynamical diffraction peak splitting in time-of-flight neutron diffraction
Authors: Üstündag E. , Karnesky R. A. , Daymond M. R. , Noyan I. C.
Published: December 2006

Time-of-flight neutron diffraction data from 20 and 0.7mm thick perfect Si single crystal samples, which exhibit dynamical diffraction effects associated with finite crystal size, are presented. This effect is caused by constructive interference occurring solely from thin layers bounded by the front (entry) and back (exit) surfaces of the sample with no scattering originating from the layers in between, resulting in two distinct peaks observed for each reflection. If the sample is thin and/or the instrument resolution is insufficient, these two peaks can convolve and cause peak shape aberrations which can lead to significant errors in the strain and peak-broadening parameters obtained from a kinematical diffraction analysis.
Random telegraph signals and noise behaviors in carbon nanotube transistors
Authors: Liu Fei , Wang Kang L. , Zhang Daihua , Zhou Chongwu
Published: December 2006

A random telegraph signal appears at a smaller absolute gate bias for a larger absolute drain-source bias in a carbon nanotube transistor. Its mechanism is attributed to a defect located in the drain side of the Schottky barrier carbon nanotube transistor with Ti∕Au as contact material. Furthermore, room temperature random telegraph signal is presented for both semiconducting and metallic carbon nanotubes, indicating the need to include random telegraph signal as a noise source for carbon nanotube transistors.
Coercive fields in ultrathin BaTiO3 capacitors
Authors: Jo J. Y. , Kim Y. S. , Noh T. W. , Yoon Jong-Gul , Song T. K.
Published: December 2006

Thickness-dependence of coercive field (EC) was investigated in ultrathin BaTiO3 capacitors with thicknesses (d) between 30 and 5.0nm. The EC appears nearly independent of d below 15nm, and decreases slowly as d increases above 15nm. This behavior can be explained not by effects of interfacial passive layers or strain relaxation, but by domain nuclei formation models. Based on domain nuclei formation models, the observed EC behavior is explainable via a quantitative level. A crossover of domain shape from a half-prolate spheroid to a cylinder is also suggested at d∼15nm, exhibiting good agreement with experimental results.
Highly efficient inverted organic photovoltaics using solution based titanium oxide as electron selective contact
Authors: Waldauf C. , Morana M. , Denk P. , Schilinsky P. , Coakley K. , Choulis S. A. , Brabec C. J.
Published: December 2006

The challenge to reversing the layer sequence of organic photovoltaics (OPVs) is to prepare a selective contact bottom cathode and to achieve a suitable morphology for carrier collection in the inverted structure. The authors report the creation of an efficient electron selective bottom contact based on a solution-processed titanium oxide interfacial layer on the top of indium tin oxide. The use of o-xylene as a solvent creates an efficient carrier collection network with little vertical phase segregation, providing sufficient performance for both regular and inverted solar cells. The authors demonstrate inverted layer sequence OPVs with AM 1.5 calibrated power conversion efficiencies of over 3%.
Microfluidic model of bubble lodging in microvessel bifurcations
Authors: Calderón Andrés J. , Heo Yun Seok , Huh Dongeun , Futai Nobuyuki , Takayama Shuichi , Fowlkes J. Brian , Bull Joseph L.
Published: December 2006

The lodging mechanisms and dynamics of cardiovascular gas bubbles are investigated in microfluidic model bifurcations made of poly(dimethylsiloxane). This work is motivated by gas embolotherapy for the potential treatment of cancer by tumor infarction. The results show that the critical driving pressure below which a bubble will lodge in a bifurcation is significantly less than the driving pressure required to dislodge it. From the results the authors estimate that gas bubbles from embolotherapy can lodge in vessels 20μm or smaller in diameter, and conclude that bubbles may potentially be used to reduce blood flow to tumor microcirculation.
Mapping of dopant concentration in a GaAs semiconductor by off-axis phase-shifting electron holography
Authors: Sasaki H. , Yamamoto K. , Hirayama T. , Ootomo S. , Matsuda T. , Iwase F. , Nakasaki R. , Ishii H.
Published: December 2006

This letter presents a method to map dopant concentration in compound semiconductors by off-axis electron holography. Using the microsampling technique of a focused ion beam, the authors prepared a cross sectional test specimen with n+(3.0×1018cm−3), n−(1.3×1016cm−3), and p gallium arsenide thin films. A phase map was obtained by off-axis phase-shifting electron holography, and the dopant distributions across a p-n junction are clearly observed. Furthermore, the low and high dopant concentration regions are remarkably distinguished in high contrast.
Work function tuning of n-channel metal-oxide field-effect transistors using interfacial yttrium layer in fully silicided nickel gate
Authors: Yu H. P. , Pey K. L. , Choi W. K. , Antoniadis D. A. , Fitzgerald E. A. , Chi D. Z. , Tung C. H.
Published: December 2006

The authors propose to tune the nickel (Ni) fully silicided (FUSI) metal gate work function via an yttrium/Si∕Ni gate stack structure. The work function of such structure indicates that the Y interlayer can effectively tune the Ni FUSI work function from the midgap to the conduction band edge of silicon by controlling the interlayer thickness. The gate stack work function starts to saturate to the pure yttrium value when the yttrium interlayer is >1.6nm. This indicates that the chemical potential of the material adjacent to gate electrode/gate insulator plays an important role in the determination of the work function.
Radial cavity mode excitation in fluorescent core-shell microcavities
Authors: Weller Andreas , Himmelhaus Michael
Published: December 2006

In this letter the authors show that the optical mode spectrum of fluorescent dielectric microparticles can be entirely altered by coating the particles with a semitransparent gold layer. While the particles show the frequently observed whispering gallery mode (WGM) excitations without the metal shell, WGMs are suppressed after the coating procedure. Instead, the observed mode spectra can be explained by the evolution of radial modes, which the authors refer to as “spherical Fabry-Pérot modes” in analogy to the mode patterns observed in planar Fabry-Pérot interferometers.
Thermoreflectance imaging of current dynamics in high power SiGe heterojunction bipolar transistors
Authors: Chan Paddy K. L. , Pipe Kevin P. , Qin Guoxuan , Ma Zhenqiang
Published: December 2006

By generating high resolution two dimensional temperature images of electronic devices and linking heat dissipation to electrical current, the authors demonstrate that thermoreflectance measurements employing a charge-coupled device can provide a useful and nondestructive method for profiling current density in electronic devices. Here they apply this method to high power SiGe heterojunction bipolar transistors (HBTs) integrated in a commercial SiGe bipolar complementary metal-oxide-semiconductor platform, measuring the current carried by each subcell and quantifying current collapse under high-bias operation. They show that current hogging for a HBT with two emitter subcells can lead to one subcell carrying 81% of the total current.
Analytical model for studying how environmental factors influence protein conformational stability in solution
Authors: Cheung Jason K. , Raverkar Prajakta S. , Truskett Thomas M.
Published: December 2006

We introduce an analytical modeling strategy for probing the conformational stability of globular proteins in aqueous solution. In this approach, the intrinsic (i.e., infinite dilution) thermodynamic stability and coarse structural properties of the proteins, as well as the effective protein-protein interactions, derive from a heteropolymer collapse theory that incorporates predicted temperature- and pressure-dependent hydrophobic interactions. Protein concentration effects are estimated by integrating this information into a molecular thermodynamic model, which is an ad hoc generalization of the exact equilibrium theory of a one-dimensional binary mixture of square-well particles that interconvert through an isomerization (i.e., folding) reaction. The end result is an analytical multiscale modeling approach which, although still schematic, can predict that folded proteins exhibit a closed-loop region of stability in the pressure-temperature plane and that protein concentration has a nonmonotonic effect on protein stability, results consistent with qualitative trends observed in both experiments of protein solutions and simulations of coarse-grained protein models.
Tunneling electron transport of silicon nanochains studied by in situ scanning electron microscopy
Authors: Kohno Hideo , Takeda Seiji , Akita Tomoki
Published: December 2006

Electron transport and field emission properties of silicon nanochains are studied by in situ scanning electron microscopy at bias voltages up to 120V using a micromanipulator system. The current-voltage (I-V) characteristics follow the Fowler-Nordheim law when the anode is in contact with the silicon nanochains as well as when separated by about 1μm. This result suggests that the field-induced tunneling current is dominant even when the microprobe is in contact with the silicon nanochains.
Effect of gate metal on polymer transistor with glass substrate
Authors: Meng Hsin-Fei , Liu Chien-Cheng , Jiang Chin-Jung , Yeh Yu-Lin , Horng Sheng-Fu , Hsu Chain-Shu
Published: December 2006

Poly(3-hexylthiophene) (P3HT) field-effect transistors (FETs) are fabricated on glass substrates with SiO2 as a gate dielectric over the gate. Indium tin oxide (ITO), Al, and Cr are employed as gate metals. For spin-coated FET, the mobility increases from 10−4–10−5cm2∕Vs for ITO and Al gates to 10−2cm2∕Vs for Cr gate. After O2 plasma treatment, the SiO2 roughness can be made as low as 0.7nm. The mobility is further improved up to 0.3cm2∕Vs by dip-coating P3HT. "Crossed rods" such as morphology can be observed in dip-coated FET with high mobility, indicating high degree of self-assembly facilitated by the flat SiO2 surface over Cr gate.
Tunable slow light in Bragg-spaced quantum wells
Authors: Prineas J. P. , Johnston W. J. , Yildirim M. , Zhao J. , Smirl Arthur L.
Published: December 2006

The group velocity of light is continuously varied in the intermediate band of a Bragg-spaced quantum well structure by tuning the pulse frequency. Delays of 0–0.4bit, without significant pulse distortion, are measured. The high group index is found to lead to large Fresnel reflection coupling losses and Fabry-Pérot fringing. Antireflection (AR) coatings deposited on both sides of the Bragg-spaced quantum well structure are shown to improve coupling of light into the intermediate band but to be sensitive to small errors (∼1%) in the AR coating layer thicknesses.
Epitaxial growth of single-crystalline AlN films on tungsten substrates
Authors: Li Guoqiang , Kim Tae-Won , Inoue Shigeru , Okamoto Koichiro , Fujioka Hiroshi
Published: December 2006

The authors have grown single-crystalline AlN(0001) films on W(110) substrates with an in-plane alignment AlN[11–20]‖W[001] at temperatures ranging from 450to600°C by pulsed laser deposition. These AlN films have a clear sixfold symmetry without 30° rotational domains. When AlN films are grown at 450°C, the interfacial reaction between AlN and W(110) is fully suppressed and a flat surface with a root-mean-square value as low as 0.20nm for AlN films is obtained. These single-crystalline AlN films grown on W(110) open a good opportunity for the high performance film bulk acoustic wave resonators of the next generation.
Resistivity and resistive switching properties of Pr0.7Ca0.3MnO3 thin films
Authors: Fujimoto Masayuki , Koyama Hiroshi , Kobayashi Shinji , Tamai Yukio , Awaya Nobuyoshi , Nishi Yuji , Suzuki Toshimasa
Published: December 2006

The authors studied the relationship between electrical resistivity and resistive switching properties in various stoichiometric and nonstoichiometric Pr1−xCaxMnO3 (PCMO) (x=0.3) thin films fabricated by pulsed laser deposition. The resistivity of Pt/PCMO/Pt structured thin films depended mainly on the PCMO deposition temperature, which was related to the crystallinity of the thin films. The highest resistivity was obtained from the lowest deposition temperature (300°C) specimen, and it was amorphous, while higher temperature deposition specimens (500–800°C) showed specific crystallographic orientation depending on the deposition temperature but showed quite low resistivity. Amorphous film deposited at 350°C exhibited monopolar resistive switching when pulses were applied.
Influence of sample compaction on the thermoelectric performance of Zn4Sb3
Authors: Pedersen B. L. , Birkedal H. , Iversen B. B. , Nygren M. , Frederiksen P. T.
Published: December 2006

Five compacted samples of thermoelectric Zn4Sb3 have been prepared from the same synthesis batch by spark plasma sintering. Four samples were made from powder with a grain size <45μm, and one sample from powder with grain size >45μm. Thermoelectric properties were evaluated, and an apparent strong correlation with sample density is found. ZnSb impurity contents obtained from powder x-ray diffraction cannot explain the variation in properties, which the authors’ suggest may be caused by slight changes in Zn content. The results show that minute changes in sample compaction conditions can have a larger effect on ZT than doping.
Infrared photodissociation spectroscopy of protonated ammonia cluster ions, NH4+(NH3)n (n=5–8), by using infrared free electron laser
Authors: Tono Kensuke , Bito Kotatsu , Kondoh Hiroshi , Ohta Toshiaki , Tsukiyama Koichi
Published: December 2006

Infrared photodissociation action spectra of protonated ammonia cluster ions, NH4+(NH3)n (n=5–8), were measured in the range of 1020–1210cm−1 by using a tunable infrared free electron laser. Analyses by the density functional theory (DFT) show that the spectral features observed can be assigned to the ν2 vibrational mode of the NH3 molecules in NH4+(NH3)n. Size dependence of the spectra supports structural models obtained by the DFT calculations, in which the NH4+ ion is solvated by the four nearest-neighbor NH3 molecules. For NH4+(NH3)5, the spectrum between 1000 and 1700cm−1 was measured. The ν4 bands of the NH3 molecules and the NH4+ ion were found in the range of 1420–1700cm−1.
Hysteresis in electric polarization of InP doped with Mn
Authors: Park C. S. , Kang T. W.
Published: December 2006

InP:Mn was grown by liquid phase epitaxy method. Ferroelectric characterization of the InMnP based capacitor revealed a clear hysteresis in its polarization-voltage curves. The remnant polarization of InP:Mn amounts to 3.84μC∕cm2 at 300Hz. Current-voltage hysteresis demonstrated a variation of built-in voltage, and capacitance versus voltage revealed a hysteresis as well. Imprint, electric conductivity, and hysteretic asymmetry of sample were enhanced after annealing at 800°C for 30s. It is considered that the hysteresis is originated from the displacement of phosphorus vacancy by Jahn-Teller distortion of [MnIn−VP] complex defect.
Displacement measurement of the depth migration of transparent cells
Authors: Yoshida Makoto , Ishimaru Ichirou , Ishizaki Katsumi , Yasokawa Toshiki , Kuriyama Shigeki , Masaki Tsutomu , Nakai Seiji , Takegawa Kaoru , Tanaka Naoyuki
Published: December 2006

This letter reports a method for displacement measurement of the depth migration of transparent cells. This proposed optical spatial filtering method allows visualization of the transparent cells and determination of depth migration as a horizontal displacement positive or negative first order diffracted light on the detector surface. When the sample is displaced upward or downward from the focal plane, first and negative first order diffracted light form images at a different point as a light circle. The coordinates of these two light circles on the detector surface change places when the displacement of depth migration moves to the opposite direction.
Enhanced low-temperature magnetoresistance in facing-target reactive sputtered Ni–CNx composite films
Authors: Wang X. C. , Mi W. B. , Jiang E. Y. , Bai H. L.
Published: December 2006

Ni – C N x films with ∼23at.% Ni, fabricated using facing-target reactive sputtering, are composed of metallic Ni, Ni–N, Ni–C, and CN compounds, showing the morphology of ∼1–5nm Ni-rich particles embedded in amorphous CN matrix. The films exhibit superparamagnetism with an average blocking temperature of ∼100K. Below 20K the tunneling magnetoresistance MR=[R(H)−R(0)]∕R(0) increases rapidly, following log∣MR∣∝−T relation with decreasing temperature. By optimizing the nitrogen partial pressure, the 3K MR maximum can reach −59% at 90kOe field, which can be mainly ascribed to the high-order tunneling process.
Log DOW: Key to Understanding and Regulating Wastewater-Derived Contaminants
Authors: Wells Martha J. M.
Published: December 2006

Environmental Context. Worldwide, surface water is a source of drinking water and is a recipient of wastewater effluents and pollutants. Many surface water bodies undergo a natural, cyclical, diurnal variation in pH between 7 and 9. Most drinking water and wastewater treatment in the United States is conducted between pH 7 and 8. The pH of water undergoing treatment processes directly impacts the ratio of nonionized to ionized chemical form(s) present, which in turn impacts the success rate of contaminant removal. Many organic wastewater-derived contaminants are very water soluble at pH 7–8 and are inadequately treated.
Abstract. Wastewater-derived contaminants (WWDCs) occur in surface water due to inadequate wastewater treatment and subsequently challenge the capabilities of drinking water treatment. Fundamental chemical properties must be understood to reduce the occurrence of known WWDCs and to better anticipate future chemical contaminants of concern to water supplies. To date, examination of the fundamental properties of WWDCs in surface water appears to be completely lacking or inappropriately applied. In this research, the hydrophobicity–ionogenicity profiles of WWDCs reported to occur in surface water were investigated, concentrating primarily on pharmaceuticals and personal care products (PPCPs), steroids, and hormones. Because most water treatment is conducted between pH 7 and 8 and because DOW, the pH-dependent n-octanol–water distribution ratio embodies simultaneously the concepts of hydrophobicity and ionogenicity, DOW at pH 7–8 is presented as an appropriate physicochemical parameter for understanding and regulating water treatment. Although the pH-dependent chemical character of hydrophobicity is not new science, this concept is insufficiently appreciated by scientists, engineers, and practitioners currently engaged in chemical assessment. The extremely hydrophilic character of many WWDCs at pH 7–8, indicated by DOW (the combination of KOW and pKa) not by KOW of the neutral chemical, is proposed as an indicator of occurrence in surface water.
Rate of Cd2+ Release from Dissolved Fulvic Acid and Natural Dissolved Organic Carbon as a Function of UVB Dose
Authors: Néron R. , Auclair J. C. , Fortin C.
Published: December 2006

Environmental Context. Atmospheric ozone depletion results in an increase of UVB radiation impinging on the surface waters of aquatic ecosystems. Radiative absorption by dissolved humic substances results in bleaching and photochemical decomposition to smaller molecular weight dissolved components. With respect to the lake biota, this can reduce the effectiveness of a natural absorptive protective UV screen, as well as enrich the surface waters with microbial substrates and previously bound biologically unavailable trace metals. In controlled experiments using low-level Cd-contaminated dissolved fulvic acids and natural lakewater dissolved organic carbon, we examine the relationship between increasing UV dose and cadmium free-ion (Cd2+) concentrations.
Abstract. Using controlled UVB exposures in a laboratory incubator, the photolytic release of bound cadmium from cadmium-contaminated dissolved fulvic acid and cadmium-amended natural lakewater dissolved organic carbon was examined using an ion-exchange technique, developed to measure the cadmium free-ion concentration (Cd2+). In the fulvic acid experiments, with increasing UVB dose, the increasing cadmium free-ion concentration followed an exponential saturation function, whereas the decrease in dissolved organic carbon was linear. Experiments using natural lakewaters did not reveal any increase in Cd2+, even at high UVB exposures. Given the much greater dissolved iron concentration in humic natural lakewaters, relative to the fulvic acid medium, iron photoreduction and reoxidation produces fresh amorphous iron oxide surfaces. We hypothesize that these bind the cadmium free-ion, thus reducing its aqueous concentration. Depending on Cd2+ affinity to biological surfaces, this mechanism might thus competitively further protect the biota from trace metal toxicity.
Bursts of nonsynonymous substitutions in HIV-1 evolution reveal instances of positive selection at conservative protein sites
Authors: Bazykin Georgii A. , Dushoff Jonathan , Levin Simon A. , Kondrashov Alexey S.
Published: December 2006

The fixation of a new allele can be driven by Darwinian positive selection or can be due to random genetic drift. Identifying instances of positive selection is a difficult task, because its impact is routinely obscured by the action of negative selection. The nature of the genetic code dictates that positive selection in favor of an amino acid replacement should often cause a burst of two or three nucleotide substitutions at a single codon site, because a large fraction of amino acid replacements cannot be achieved after just one nucleotide substitution. Here, we study pairs of successive nonsynonymous substitutions at one codon in the course of evolution of HIV-1 genes within HIV-1 populations inhabiting infected individuals. Such pairs are more numerous and more clumped than expected if different substitutions were independent and than what is observed for pairs of successive synonymous substitutions. Bursts of nonsynonymous substitutions in HIV-1 evolution cannot be explained by mutational biases and must, therefore, be due to positive selection. Both reversals, exact or imprecise, of fixed deleterious mutations and acquisitions of amino acids with new properties are responsible for the bursts. Temporal clumping is strongest at codon sites with a low overall rate of nonsynonymous evolution, implying that a substantial fraction of replacements of conservative amino acids are driven by positive selection. We identified many conservative sites of HIV-1 proteins that occasionally experience positive selection.
Confronting Categorical Assumptions About the Power of Religion in Africa
Authors: Green Maia
Published: December 2006

This article examines the place of religion in social science accounts of Africa, particularly as they relate to politics and culture. It explores the significance of representational continuities across the twentieth century and across disciplines which present African social life as religiously determined, and considers the political implications of African exceptionalism as a mode of analysis and policy rationale. Finally, the article considers some directions of institutional change in southern Tanzania and the consequences for understanding religion.

This paper is based on a workshop organised by ROAPE on religion and politics in Africa held at the University of Leeds in February 2006. Some of the arguments made in the paper concerning detotalisation and deconversion were developed through discussions at a workshop on history and anthropology held at the University of Manchester in November 2005.
Environmental education, national curriculum and primary school teachers. Findings of a research study in England and possible implications upon education for sustainable development
Authors: Chatzifotiou Athanasia
Published: December 2006

This article reports the results of a research study on the impact of environmental education (EE) upon English primary school teachers, and it then discusses the findings of the study in relation to education for sustainable development, as EE is considered one of the two precursors of education for sustainable development. The article begins by considering the development of EE in the English national curriculum of primary schools and then briefly outlines and reports two major findings of the study, comparing them against the new context of education for sustainable development. Overall, the article demonstrates how EE, the national curriculum and teachers have interacted with each other, while arguing that there seems to be a parallel course among education for sustainable development and EE in the national curriculum, with no apparent crossroad to link the two and explain how education for sustainable development is partly based on EE as well.