bluuebunny/crossref_metadata_2025 huggingface dataset:
Small amplitude solitons in a warm plasma with smaller and higher order relativistic effects
Authors: Kalita B. C. , Das R.
Published: July 2007

Solitons have been investigated in a warm plasma through the Korteweg-de Vries (KdV) equation, considering a smaller relativistic effect for γ≈O(v2∕c2) and γe≈O(u2∕c2) and higher relativistic effects for γ≈O(v4∕c4) and γe≈O(u4∕c4). Compressive fast ion-acoustic solitons are observed to exist in the entire range (u0−v0) subject to a suitable mathematical condition satisfied by the initial streaming velocities u0,v0 of the electrons and the ions, respectively, electron to ion mass ratio Q(=me∕mi) and ion to electron temperature ratio σ(=Ti∕Te). Further, rarefactive solitons of pretty small amplitudes are observed in the small upper range of ∣u0−v0∣ for higher order relativistic effect which are found to change parabolically. It is essentially important to report in our model of plasma, that the higher order relativistic effect slows down the soliton speed to V⩽0.10 for all temperature ratios σ for small amplitude waves. On the other hand, the smaller order relativistic effect permits the soliton to exist even at a relatively much higher speed V<0.30. Solitons of high (negligible) amplitudes are found to generate at the smaller (greater) difference of initial streamings (u0−v0) corresponding to both the relativistic effects.
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ordering and magnetic interactions in FePt nanoparticles embedded in MgO and SiO2 shell matrices
Authors: Tomou Aphrodite , Panagiotopoulos Ioannis , Gournis Dimitrios , Kooi Bart
Published: July 2007

FePt nanoparticles have been encapsulated in insulating and protective MgO shells, using a two step chemical process, in order to prevent sintering during the heat-treatment process required for the L10 ordering. The FePt nanoparticles were initially prepared using a standard polyol process and then dispersed in a magnesium oxide solution. As a basis for comparison FePt∕SiO2 nanocomposites have been also synthesized using a modified aqueous sol-gel route as the second step. The magnetic and microstructural properties of FePt∕MgO and FePt∕SiO2 nanocomposites are compared with those of FePt nanoparticles. The presence of oxide matrices leads to more homogeneous microstructures and better magnetic properties. While higher coercivity values have been obtained in FePt∕SiO2, the MgO matrix is proven to provide better physical and magnetic isolations of the FePt nanoparticles. However, for FePt:MgO molar ratios exceeding 1:20 no L10 ordering has been achieved.
Simultaneous time and frequency detection in femtosecond coherent Raman spectroscopy. II. Application to acetonitrile
Authors: Nath Sukhendu , Urbanek Diana C. , Kern Sean J. , Berg Mark A.
Published: July 2007

The preceding paper showed that, in principle, a high-resolution coherent Raman spectrum can be recovered using femtosecond probe pulses by combined detection in both time and frequency. This measurement is possible even when the pulses are too broad in frequency for conventional frequency-domain spectroscopy and too broad in time for conventional time-domain spectroscopy. In this paper, the method is tested on experimental coherent anti-stokes Raman spectroscopy data from acetonitrile. Compared to theoretical models, experimental data are complicated by noise and incomplete knowledge of the pulse structure. Despite these complications, most of the information in the Raman spectrum is recovered from the data: weak transitions are detected and natural-linewidth resolution is achieved across an 800cm−1 spectral range. However, circumstances in which experimental limitations result in missed features or ambiguities in the recovered spectrum are also identified. These results suggest where improvements in measurement and data analysis can be made.
Transport of internal electronic energy in atomic hydrogen thermal plasmas
Authors: Bruno D. , Capitelli M. , Catalfamo C. , Laricchiuta A.
Published: July 2007

Reactive and internal thermal conductivities for equilibrium hydrogen plasma have been calculated by the Chapman-Enskog method. The equilibrium composition of the plasma is determined by taking consistently into account the number of allowed atomic electronic excited states (EES) as determined by the average interparticle distance. The coefficients depend on the inclusion of realistic cross sections for the interactions with EES. In particular, the interplay between the two coefficients that describe the transport of electronic and ionization energy is analyzed.
Neon in carbon nanopores: wetting, growth mechanisms, and cluster structures
Authors: Krainyukova N. V.
Published: July 2007

A low-temperature, high-energy (50keV) electron diffraction study of size-dependent structures and growth mechanisms of neon samples in multiporous “amorphous” carbon films is presented. Electron diffractograms are analyzed on the basis of the assumption that there exists a cluster size distribution in deposits formed in the substrate, and multi-shell structures such as icosahedra, decahedra, and fcc and hcp clusters are probed for different sizes up to approximately 3×104 atoms. The analysis is based on a comparison of precise experimental and calculated diffracted intensities with the help of a minimization procedure for the reliability factor R. Highly reproducible discrete distribution functions of sizes and structures are found. The time-dependent evolution of diffractograms at earlier stages of growth is revealed. Initially distinct diffraction peaks gradually “disappear,” although the total electron beam absorption attests that the deposited neon is preserved in the porous substrate. We ascribe this effect to diffusion-like gas penetration from larger to smaller pores, which results in a highly dispersed or even disordered substance. Evidently, the clusters that grow initially during deposition are later soaked up by a sponge-like substrate due to capillary forces.
Thermodynamics and microstructure of vacancies in rare gas crystals at high temperature
Authors: Karasevskii A. I. , Lubashenko V. V.
Published: July 2007

A self-consistent statistical method is used to calculate the Gibbs free energy of vacancy formation in heavy rare gas crystals at high temperature. It is shown that the vacancy formation free energy falls rapidly in the vicinity of the melting point of the crystal. Such behavior is attributed to the approach of the system to an anharmonic instability point of the vibrational subsystem of the solid.
Thermal conductivity of solid CF2Cl2
Authors: Pursky O. I. , Konstantinov V. A.
Published: July 2007

The thermal conductivity of solid CF2Cl2 is measured by the linear-flow method in the temperature range 80–115K under saturated vapor pressure. Special attention is given to the explanation of the heat transfer process under constant density. The temperature dependence of the isochoric thermal conductivity is analyzed within a model in which heat is transferred by phonons and, above the phonon mobility edge, by “diffusive” modes migrating randomly from site to site.
Observation of relaxation of molecular spins in CH4 and CD4 crystals in thermal conductivity experiment
Authors: Pisarska E. , Stachowiak P. , Jeżowski A.
Published: July 2007

Preliminary results are reported on the kinetics of the molecular spin conversion in solid methane (CH4) and deuterated methane (CD4), obtained through thermal conductivity measurements in the temperature range 2–10K.
FTIR spectra and conformations of 2′-deoxyuridine in Kr matrices
Authors: Ivanov A. Yu. , Karachevtsev V. A.
Published: July 2007

The Fourier transform infrared spectra in the range 4000–200cm−1 of pyrimidine nucleoside 2′-deoxyuridine (dU) are obtained in low-temperature inert Kr matrices. For the first time, instead of a usual flat mirror, a low-temperature, one-coordinate retroreflector is used as the matrix substrate. Owing to this, the matrix setup is insensitive to dip angle vibrations of the cryostat and is favorable to work with thinner matrix layers. Of two syn-conformers with dU_s1 and dU_s2 (stabilized by the intramolecular hydrogen bond O5′H…O2), only the dT_s2 conformer with C2′-endo structure of the ribose ring is uniquely quenched. The height of the interconversion barrier of the minor syn-conformer dU_s1 was estimated to be below 0.7kcal∕mole. It is shown that the energy relaxation of impurities in Kr is slower than in Ar matrices.
The peculiarities of heat transfer in CO2 and N2O solids at low temperatures
Authors: Sumarokov V. V. , Stachowiak P. , Jeżowski A.
Published: July 2007

The thermal conductivities of CO2 and N2O solids are investigated in the low-temperature range 1–40K. The thermal conductivities of CO2 and N2O are large compared with those of simple molecular crystals such as N2, CO, or O2 in the whole investigated temperature range. Analysis of the experimental data by the Callaway method shows that a relatively large size of the crystalline grains, low density of dislocations, and weak phonon–phonon interaction might be the reasons for the good thermal conduction in these crystals at temperatures near the maxima. A comparison between calculated values of the intensity of normal phonon scattering processes and experiment gives evidence that in N2O there is an additional (in comparison with CO2) giant scattering of phonons. This scattering is described in the frameworks of the soft potential model by the resonance phonon scattering on tunneling states and low-energy vibrations.
Orientational order parameter in CO2-based alloys with rare gases from THEED data: pure CO2
Authors: Danchuk V. V. , Solodovnik A. A. , Strzhemechny M. A.
Published: July 2007

Using the transmission high-energy electron diffraction technique, we study the temperature dependence of the diffraction reflection intensities from the solid phase of CO2. To deduce absolute values of the orientational order parameter, we modify the existing reconstruction method to take into account the triatomic shape of the molecule. It is shown that for triatomic solids a higher-rank order parameter, η4, is important and cannot be neglected. Application of the modified approach yield η and η4 values as a function of temperature over the range from 6 to 70K. Both orientational order parameters prove to be a nonmonotone function of temperature.
Cluster relaxation dynamics in liquids and solids near the glass-transformation temperature
Authors: Kokshenev V. B.
Published: July 2007

The structural relaxation in glass-forming materials is studied near the glass transformation temperature Tg indicated by the heat capacity maximum. The late-time asymptote of the Kohlrausch–Williams–Watts form of the relaxation function is rationalized via the mesoscopic-scale correlated regions in terms of the Debye-type clusters following the dynamic scaling law. It is repeatedly shown that regardless of underlying microscopic realizations in glass formers with site disorder the structural relaxation is driven by local random fields, described via the directed random walks model. The relaxation space dimension ds=3 at Tg is suggested for relaxing units of fractal dimension df=5∕2 for quadrupolar-glass clusters in ortho–parahydrogen mixtures, that is compared with entangled-chain clusters in polymers (df=1) and solid-like clusters relaxing in supercooled molecular liquids (with ds=6 and df=3). The relaxation dynamics of orientational-glass clusters in plastic crystals is attributed to the model of continuous-time random walks in space ds=6. As a by-product, the expansivity in polymers, molecular liquids, and networks is predicted.
Energy of a single electron in gaseous media
Authors: Shikin V. B. , Nazin S. S.
Published: July 2007

The so-called “optical” approximation in the theory of the electron energy spectrum in the presence of scattering centers with positive scattering length randomly distributed with the average density ng is considered for a number of inert gases. The average minimal energy W of a single electron calculated beyond the optical approximation reveals behavior qualitatively different from that of the same quantity W0 derived within the optical approximation. Results of calculations are in qualitative agreement with experimental data available for the W(ng) dependence for different cryogenic gases.
Theoretical studies on photoelectron and IR spectral properties of Br2∙−(H2O)n clusters
Authors: Pathak A. K. , Mukherjee T. , Maity D. K.
Published: July 2007

We report vertical detachment energy (VDE) and IR spectra of Br2∙−∙(H2O)n clusters (n=1–8) based on first principles electronic structure calculations. Cluster structures and IR spectra are calculated at Becke’s half-and-half hybrid exchange-correlation functional (BHHLYP) with a triple split valence basis function, 6-311++G(d,p). VDE for the hydrated clusters is calculated based on second order Moller-Plesset perturbation (MP2) theory with the same set of basis function. On full geometry optimization, it is observed that conformers having interwater hydrogen bonding among solvent water molecules are more stable than the structures having double or single hydrogen bonded structures between the anionic solute, Br2∙−, and solvent water molecules. Moreover, a conformer having cyclic interwater hydrogen bonded network is predicted to be more stable for each size hydrated cluster. It is also noticed that up to four solvent H2O units can reside around the solute in a cyclic interwater hydrogen bonded network. The excess electron in these hydrated clusters is localized over the solute atoms. Weighted average VDE is calculated for each size (n) cluster based on statistical population of the conformers at 150K. A linear relationship is obtained for VDE versus (n+3)−1∕3 and bulk VDE of Br2∙− aqueous solution is calculated as 10.01eV at MP2 level of theory. BHHLYP density functional is seen to make a systematic overestimation in VDE values by ∼0.5eV compared to MP2 data in all the hydrated clusters. It is observed that hydration increases VDE of bromine dimer anion system by ∼6.4eV. Calculated IR spectra show that the formation of Br2∙−-water clusters induces large shifts from the normal O–H stretching bands of isolated water keeping bending modes rather insensitive. Hydrated clusters, Br2∙−∙(H2O)n, show characteristic sharp features of O–H stretching bands of water in the small size clusters.
Microhydration of Cs+ ion: A density functional theory study on Cs+–(H2O)n clusters (n=1–10)
Authors: Ali Sk. M. , De S. , Maity D. K.
Published: July 2007

Structure, energy enthalpy, and IR frequency of hydrated cesium ion clusters, Cs+–(H2O)n (n=1–10), are reported based on all electron calculations. Calculations have been carried out with a hybrid density functional, namely, Becke’s three-parameter nonlocal hybrid exchange-correlation functional B3LYP applying cc-PVDZ correlated basis function for H and O atoms and a split valence 3-21G basis function for Cs atom. Geometry optimizations for all the cesium ion-water clusters have been carried out with several possible initial guess structures following Newton-Raphson procedure leading to many conformers close in energy. The calculated values of binding enthalpy obtained from present density functional based all electron calculations are in good agreement with the available measured data. Binding enthalpy profile of the hydrated clusters shows a saturation behavior indicating geometrical shell closing in hydrated structure. Significant shifts of O–H stretching bands with respect to free water molecule in IR spectra of hydrated clusters are observed in all the hydrated clusters.
Electron beam machining of nanometer-sized tips from multiwalled boron nitride nanotubes
Authors: Celik-Aktas Ayten , Stubbins James F. , Zuo Jian-Min
Published: July 2007

We report here that high energy electron irradiation of multiwalled boron nitride nanotubes can be used to form sharp, crystalline, conical tips, or to cut boron nitride nanotubes by controlling the electron beam size. Electron beam cutting is observed when a focused electron beam with a diameter much smaller than the tube diameter is used. The tip formation is observed when a shaped, disklike, electron beam is used to irradiate the tube; the diameter of the beam in this case is similar to the tube diameter. In situ electron microscopy observation shows that the tip formation effect is driven by layer peeling and the collapse of the inner walls of the nanotube. This is very different from the formation of nanoarches observed during cutting. The combination of shaping and cutting can be used to fabricate atomically sharp tips for field emitters, nanoimaging, and manipulations.
Conduction band energies and hot-electron transport characteristics of epitaxial Sc2O3∕Si (111) studied by ballistic electron emission microscopy and internal photoemission
Authors: Cai W. , Stone S. E. , Pelz J. P. , Edge L. F. , Schlom D. G.
Published: July 2007

Ballistic electron emission microscopy (BEEM) and internal photoemission measurements on a 20-nm-thick epitaxial Sc2O3 film on Si (111) show the existence of a lower “tail state” conduction band (CB) extending ∼0.9eV below the upper CB (similar to that reported for amorphous Sc2O3 films), indicating that these states are not simply due to disorder in amorphous films. This lower CB is also found to support elastic hot-electron transport even against an applied electric field, indicating transport via extended rather than localized states.
Laser scanning thermoreflectance imaging system using galvanometric mirrors for temperature measurements of microelectronic devices
Authors: Grauby S. , Salhi A. , Rampnoux J.-M. , Michel H. , Claeys W. , Dilhaire S.
Published: July 2007

We present a thermoreflectance imaging system using a focused laser sweeping the device under test with a scanner made of galvanometric mirrors. We first show that the spatial resolution of this setup is submicrometric, which makes it adapted to microelectronic thermal measurements. Then, we studied qualitative temperature variations on two dissipative structures constituted of thin (0.35μm) dissipative resistors, the distance between two resistors being equal to 0.8 or 10μm. This technique combines sensitivity and speed: it is faster than a point classical thermoreflectance technique and, in addition, more sensitive than a charge-coupled device thermoreflectance imaging technique.
Effects of pulse duration upon the plume formation by the laser ablation of Cu in water
Authors: Oguchi Hisayuki , Sakka Tetsuo , Ogata Yukio H.
Published: July 2007

Time-resolved images of an ablation plume obtained at different pulse durations have been measured for the liquid-phase laser ablation of a Cu plate, and the emission intensity and size of the plume have been discussed. In some plume images, high-density bright spots were observed. The size of the light-emitting region increases and the bright spots disappear for the irradiation with a 150-ns pulse. We conclude that consecutive excitation by the later part of a longer pulse expands the plume and reduces plume density. These results are consistent with our previous result that less-broadened atomic line spectra with high emission intensity were obtained with a 150-ns-pulse irradiation.
Effects of doped dye on the charge carrier injection, transport, and electroluminescent performance in polymeric light-emitting diodes
Authors: Chen Zhenyu , Ma Dongge
Published: July 2007

The effects of doped fluorescent dye 4-(dicyanomethylene)-2-i-propyl-6-(1, 1, 7, 7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTI) on the charge carrier injection, transport and electroluminescence (EL) performance in polyfluorene (PFO)-based polymer light-emitting diodes (PLEDs) were investigated by steady-state current-voltage (I−V) characteristics and transient EL measurements. A red EL from DCJTI was observed and the EL performance depended strongly on the DCJTI concentration. The analysis of the steady-state I−V characteristics at different DCJTI concentrations found that three regions was shown in the I−V characteristics, and each region was controlled by different processes depending on the applied electric field. The effect of the dopant concentration on the potential-barrier height of the interface is estimated using the Fowler–Nordheim model. The dopant concentration dependence of the current-voltage relationship indicated clearly the carrier trapping by the DCJTI molecules. The mobility in DCJTI: PFO changed significantly with the DCJTI concentration, and showed a nontrivial dependence on the doping level. The behavior may be understood in terms of the formation of an additional energy disorder due to potential fluctuation caused by the Coulomb interaction of the randomly distributed doping molecules.
Ge-on-glass detectors
Authors: Lin C.-H. , Chiang Y.-T. , Hsu C.-C. , Lee C.-H. , Huang C.-F. , Lai C.-H. , Cheng T.-H. , Liu C. W.
Published: July 2007

A single crystalline thin film of Ge on glass is fabricated using wafer bonding and smart cut. A simple metal-insulator-semiconductor detector is demonstrated for visible light and telecommunication wavelength. The implantation damage of separated Ge film bonded on glass is removed by chemical etching, and the surface roughness is reduced from 14to4nm. The defect removal reduces the dark current by a factor of 30 and increases the responsivity by a factor of 1.85 at visible wavelength. The responsivity of 0.27A∕W at 1.3μm wavelength for an unetched device does not increase after damage removal due to the decrease of the absorption layer thickness.
Shape transformation during overgrowth of InGaAs∕GaAs(001) quantum rings
Authors: Hanke M. , Mazur Yu. I. , Marega E. , AbuWaar Z. Y. , Salamo G. J. , Schäfer P. , Schmidbauer M.
Published: July 2007

The authors have investigated a shape transformation during the vertical stacking of InGaAs quantum rings (QRs) on GaAs(001). Samples have been grown by means of molecular beam epitaxy. The initial QR layer exhibits nearly round-shaped, flat disks. Especially for a very thin spacer layer of 2nm, the topmost QRs in a twofold stack tend to be of ellipsoidal shape with preferential elongation along the [11¯0] direction. Grazing incidence diffraction and corresponding x-ray scattering simulations prove an asymmetry in the shape of the buried QRs with respect to different ⟨110⟩ directions. This clearly indicates a significant shape transformation during the overgrowth process from circular toward ellipsoidal QRs.
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and CrB2 diffusion barriers for Ni∕Au contacts to p-GaN
Authors: Voss L. F. , Stafford L. , Wright J. S. , Pearton S. J. , Ren F. , Kravchenko I. I.
Published: July 2007

Ohmic contacts to p-type GaN were fabricated using W2B and CrB2 as diffusion barriers for a traditional Ni∕Au contact scheme. The annealing temperature dependence (25–1000°C) of contact resistance and the thermal aging characteristics at 200°C were examined. A minimum contact resistance of ∼2×10−4Ωcm2 was achieved after annealing at 700°C for 60s. These contacts also showed excellent stability as a function of aging at 200°C. Auger electron depth profiles reveal a large degree of intermixing at the GaN interface between Ni and Au.
Proximity electron lithography using permeable electron windows
Authors: Cho Wonje , Ono Takahito , Esashi Masayoshi
Published: July 2007

This letter reports on an electron source consisting of thin electron-permeable windows and a carbon nanocoil emitter. Electron windows with diameters of 250nm were fabricated using silicon micromachining technology. Carbon nanocoils that are selectively grown from silicon were used as emitters. Field-emitted electrons from the emitters are transmitted through the thin silicon electron windows with thicknesses in the range of 15–50nm. The electron transmittance of the electron windows was evaluated and it was demonstrated that transmittances higher than 60% are achievable for the case of electron energies higher than 5keV. Proximity electron lithography is demonstrated using 1.5×1.5μm2 electron windows with a thickness of 50nm.
Electrochemical corrosion behavior of a Zr-based bulk-metallic glass
Authors: Jiang W. H. , Jiang F. , Green B. A. , Liu F. X. , Liaw P. K. , Choo H. , Qiu K. Q.
Published: July 2007

Using cyclic-anodic-polarization tests, the corrosion behaviors of the as-cast, deformed, and relaxed Zr52.5Cu17.9Ni14.6Al10.0Ti5.0 bulk-metallic glasses were investigated. Their corrosion behaviors are related to the amount of free volume. As the free volume decreased, the glasses became more corrosion resistant. The as-cast and the deformed glasses are less resistant to pit propagation, while the relaxed one is more vulnerable to pit nucleation. It is thought that an increase in free volume favors the pit propagation, and the chemical ordering caused by the relaxation may promote the pit nucleation.
Gate oxide scaling down in HfO2–GaAs metal-oxide-semiconductor capacitor using germanium interfacial passivation layer
Authors: Kim Hyoung-Sub , Ok Injo , Zhang Manhong , Zhu F. , Park S. , Yum J. , Zhao Han , Lee Jack C.
Published: July 2007

The primary goal of this work is to investigate the capability of gate oxide scaling down in HfO2-based GaAs metal-oxide-semiconductor capacitor (MOSCAP) using a thin germanium (Ge) interfacial passivation layer (IPL). With HfO2 of 45–50Å, an equivalent oxide thickness (EOT) of 8.7Å was achieved with a low gate oxide leakage current density (Jg) of (2–4)×10−3A∕cm2 at VG−VFB=1.0V. This is the thinnest EOT thickness ever reported for high-k III-V MOSCAPs. On the other hand, with thicker HfO2 of 100–110Å, an EOT of 20–22Å with Jg of (2–4)×10−6A∕cm2 at VG−VFB=1.0V was attained. In addition, breakdown voltages of gate oxide and hysteresis characteristics according to different thicknesses of HfO2 were studied. The results indicate that a Ge IPL and thin HfO2 enable excellent gate oxide scaling down in GaAs system.
Morphotropic phase boundary in (1−x)BiFeO3–xPbTiO3: phase coexistence region and unusually large tetragonality
Authors: Bhattacharjee Shuvrajyoti , Tripathi Saurabh , Pandey Dhananjai
Published: July 2007

It is shown that the tetragonal (T) and rhombohedral (R) structures of (1−x)BiFeO3–xPbTiO3 are stable for xT⩾0.31 and xR⩽0.27, respectively, giving the narrowest width of 0.03, reported so far, for the morphotropic phase boundary region in this system. The Rietveld refined structure of the T phase for x=0.31 reveals partial covalent character of the Ti∕Fe–O and Pb∕Bi–O bonds which may be responsible for the unusually large tetragonality.
Dissolution of metal precipitates in multicrystalline silicon during annealing and the protective effect of phosphorus emitters
Authors: Tan J. , Macdonald D. , Bennett N. , Kong D. , Cuevas A. , Romijn I.
Published: July 2007

The degradation of the carrier lifetime in multicrystalline silicon due to the dissolution of metal precipitates during high temperature annealing is well known. This letter presents evidence indicating that the presence of phosphorus emitters during annealing can help reduce this recontamination. Part of the degradation observed is due to increased interstitial iron concentrations caused by the dissolution of iron precipitates during annealing. However, dissolution of other metals also seems to contribute to the reduced carrier lifetimes observed.
Growth of polycrystalline Cu(In,Ga)Se2 thin films using a radio frequency-cracked Se-radical beam source and application for photovoltaic devices
Authors: Ishizuka Shogo , Shibata Hajime , Yamada Akimasa , Fons Paul , Sakurai Keiichiro , Matsubara Koji , Niki Shigeru
Published: July 2007

Cu ( In , Ga ) Se 2 (CIGS) thin films were grown using a rf-cracked Se-radical beam source. A unique combination of film properties, a highly dense and smooth surface with large grain size, is shown. These features seem to have no significant influence on the photovoltaic performance. Defect control in bulk CIGS leading to corresponding variations in the electrical and photoluminescence properties was found to be possible by regulating the Se-radical source parameters. A competitive energy conversion efficiency of 17.5%, comparable to that of a Se-evaporative source grown CIGS device, has been demonstrated from a solar cell fabricated using a Se-radical source grown CIGS absorber.
Measurement of the clustering energy for manganese silicide islands on Si(001) by Ostwald ripening
Authors: Krause M. R. , Stollenwerk A. J. , Licurse M. , LaBella V. P.
Published: July 2007

The rate of growth during annealing of manganese silicide islands in the submonolayer coverage regime on the Si(001) surface has been measured by scanning tunneling microscopy. The fourth power of the growth rate is linearly dependent upon the annealing time, consistent with a diffusion limited Ostwald ripening mechanism for island growth. The growth rate has been determined for four different annealing temperatures to extract the activation energy for clustering, which has been found to be 2.6±0.2eV.
On the role of H2O2 in the recovery of grapevine (Vitis vinifera cv. Prosecco) from Flavescence dorée disease
Authors: Musetti Rita , Marabottini Rosita , Badiani Maurizio , Martini Marta , Sanità di Toppi Luigi , Borselli Stefano , Borgo Michele , Osler Ruggero
Published: July 2007

In the present work, we compared hydrogen peroxide (H2O2) localisation and the activities/contents of antioxidant enzymes and metabolites in the leaf tissues of grapevine (Vitis vinifera L. cv. Prosecco) plants showing different sanitary status, namely diseased by Flavescence dorée, healthy or recovered. Polymerase chain reaction analysis revealed that the pathogen associated with Flavescence dorée (proposed as ‘Candidatus Phytoplasma vitis’) was detected in the leaf tissues of symptomatic plants, but was not observed in either the healthy or recovered plants. Hydrogen peroxide accumulated in the phloem plasmalemma of recovered grapevine leaves, but was not detected in either healthy or diseased material. When compared to diseased or healthy plants, recovered plants had distinctly lower extractable levels of catalase and ascorbate peroxidase, two enzymes primarily involved in the scavenging of excess H2O2 generated in different cell compartments. Among healthy, diseased and recovered leaves there was no significant difference in the amount of 2-thiobarbituric acid-reactive substances, which are assumed to reflect the extent of peroxidative breakdown of membrane lipids. Therefore, it is suggested that recovery from Flavescence dorée disease in grapevine might be associated with a long-term, sustained and tissue-specific accumulation of H2O2 in leaves, which reduces numbers or prevents further infection by Flavescence dorée phytoplasma. Recovered grapevine plants might be able to achieve such H2O2 accumulation through a selective and presumably stable downregulation of enzymatic H2O2 scavengers, without altering the levels of other antioxidant systems and without incurring an increased oxidative risk.
Microarray analysis of bast fibre producing tissues of Cannabis sativa identifies transcripts associated with conserved and specialised processes of secondary wall development
Authors: De Pauw Mary A. , Vidmar John J. , Collins JoAnn , Bennett Rick A. , Deyholos Michael K.
Published: July 2007

The mechanisms underlying bast fibre differentiation in hemp (Cannabis sativa L.) are largely unknown. We hybridised a cDNA microarray with RNA from fibre enriched tissues extracted at three different positions along the stem axis. Accordingly, we identified transcripts that were enriched in tissues in which phloem fibres were elongating or undergoing secondary wall thickening. These results were consistent with a dynamic pattern of cell wall deposition involving tissue specific expression of a large set of distinct glycosyltransferases and glycosylhydrolases apparently acting on polymers containing galactans, mannans, xylans, and glucans, as well as raffinose-series disaccharides. Putative arabinogalactan proteins and lipid transfer proteins were among the most highly enriched transcripts in various stem segments, with different complements of each expressed at each stage of development. We also detected stage-specific expression of brassinosteroid-related transcripts, various transporters, polyamine and phenylpropanoid related genes, and seven putative transcription factors. Finally, we observed enrichment of many transcripts with unknown biochemical function, some of which had been previously implicated in fibre development in poplar or cotton. Together these data complement and extend existing biochemical models of bast fibre development and secondary wall deposition and highlight uncharacterised, but conserved, components of these processes.
Regulation of lutein biosynthesis and prolamellar body formation in Arabidopsis
Authors: Cuttriss Abby J. , Chubb Alexandra C. , Alawady Ali , Grimm Bernhard , Pogson Barry J.
Published: July 2007

Carotenoids are critical for photosynthetic function in chloroplasts, and are essential for the formation of the prolamellar body in the etioplasts of dark-grown (etiolated) seedlings. They are also precursors for plant hormones in both types of plastids. Lutein is one of the most abundant carotenoids found in both plastids. In this study we examine the regulation of lutein biosynthesis and investigate the effect of perturbing carotenoid biosynthesis on the formation of the lattice-like membranous structure of etioplasts, the prolamellar body (PLB). Analysis of mRNA abundance in wildtype and lutein-deficient mutants, lut2 and ccr2, in response to light transitions and herbicide treatments demonstrated that the mRNA abundance of the carotenoid isomerase (CRTISO) and epsilon-cyclase (ϵLCY) can be rate limiting steps in lutein biosynthesis. We show that accumulation of tetra-cis-lycopene and all-trans-lycopene correlates with the abundance of mRNA of several carotenoid biosynthetic genes. Herbicide treatments that inhibit carotenoid biosynthetic enzymes in wildtype and ccr2 etiolated seedlings were used to demonstrate that the loss of the PLB in ccr2 mutants is a result of perturbations in carotenoid accumulation, not indirect secondary effects, as PLB formation could be restored in ccr2 mutants treated with norflurazon.
Contribution of anthocyanins to the antioxidant capacity of juvenile and senescing sugar maple (Acer saccharum) leaves
Authors: van den Berg Abby K. , Perkins Timothy D.
Published: July 2007

Foliar anthocyanins are hypothesised to provide an additional source of photoprotection from photooxidative stress to the leaves in which they occur through their ability to scavenge excess free radical species. Although demonstrated to significantly enhance the antioxidant status of red morphs of fully expanded leaves of some species, the contribution of anthocyanins to the antioxidant capacity of the juvenile and senescing leaves in which they frequently occur has not been examined. Antioxidant activity of extracts from anthocyanic and non-anthocyanic juvenile and senescing sugar maple (Acer saccharum Marsh.) leaves from similar light environments was assessed using the stable free radical 1,1-diphenyl-2-picryl hydrazyl (DPPH). Anthocyanin content was significantly correlated with antioxidant activity in extracts of anthocyanic juvenile leaves but only weakly correlated in extracts of anthocyanic senescing leaves. In addition, the antioxidant activity of anthocyanic and non-anthocyanic leaves was equal in both juvenile and senescing leaves. Thus, although anthocyanins may contribute to the antioxidant capacity of anthocyanic juvenile and senescing sugar maple leaves, these results are not consistent with the hypothesis that anthocyanins provide an enhancement to the photoprotection available in either leaf type through free radical scavenging. The results suggest anthocyanins may be part of alternative strategies employed by anthocyanic juvenile and senescing maple leaves to achieve similar levels of antioxidant capacity as their non-anthocyanic counterparts to cope with the same set of environmental challenges.
Plant isotopic composition provides insight into mechanisms underlying growth stimulation by AM fungi in a semiarid environment
Authors: Querejeta José I. , Allen Michael F. , Alguacil María M. , Roldán Antonio
Published: July 2007

We hypothesised that improved plant water status and enhanced transpiration are key mechanisms involved in plant growth stimulation by native arbuscular mycorrhizal fungi (AMF) in semiarid calcareous soils. Seedlings of the dryland shrubs Pistacia lentiscus L. and Retama sphaerocarpa L. were pre-inoculated with a mixture of eight native Glomus spp. fungi, or left un-inoculated, before transplanting into a degraded site in south-eastern Spain. Pre-inoculated Pistacia and Retama shrubs grew faster after transplanting, despite spontaneous colonisation of control plants by local AMF. Pre-inoculation enhanced shoot water content and shoot δ15N in both shrub species. Increased potassium uptake and improved water relations were key mechanisms behind growth stimulation by native AMF in Pistacia. Shoot δ18O (a proxy measure of stomatal conductance) was significantly less negative in AMF-inoculated than in control Pistacia seedlings, indicating enhanced cumulative transpiration in the former. In contrast, shoot δ18O was unaffected by AMF inoculation in Retama, a leafless leguminous shrub with photosynthetic stems. Growth stimulation by native AMF in Retama was attributed to increased phosphorus uptake, enhanced atmospheric nitrogen fixation and a largely nutrient-mediated improvement of plant water status. Shoot δ13C was not significantly influenced by AMF inoculation in either shrub species, thus suggesting roughly parallel upshifts in photosynthetic and transpiration rates which did not affect plant water use efficiency.
Impairment of leaf hydraulics in young plants of Citrus aurantium (sour orange) infected by Phoma tracheiphila
Authors: Raimondo Fabio , Raudino Francesco , Cacciola Santa Olga , Salleo Sebastiano , Lo Gullo Maria Assunta
Published: July 2007

Phoma trachephila (Petri) Kantschaveli et Gikachvili causes dieback of several Citrus species. The impact of this fungus on leaf hydraulics was studied in Citrus aurantium L. (sour orange) with the aim of identifying the primary mechanism of damage to leaves. Leaves inoculated with a conidial suspension were measured for conductance to water vapor (gL) and specific hydraulic conductance (Kleaf) every 3 days after inoculation. The earliest symptom of infection consisted of vein chlorosis. Functional vein density (FVD) was monitored and microscopic observations were made of major vein conduits. Impairment of vein hydraulics started 25 days after inoculation with a losses of Kleaf of 40% and gL of ~60%. Most minor veins within chlorotic areas were no longer functioning and some conduits of the major veins showed digested interconduit pits leading to vein cavitation. The close Kleaf–FVD relationship revealed that vein impairment caused drop of Kleaf and, consequently, of gL at chlorotic areas. Leaf infection was focused to veins that were first forced to embolise and then invaded by fungal hyphae. The vein embolism due to the Phoma amplifies the native dominant hydraulic resistance of leaf veins, and leads ultimately to early shedding of infected leaves.
Sumoylation in axons triggers retrograde transport of the RNA-binding protein La
Authors: van Niekerk Erna A. , Willis Dianna E. , Chang Jay H. , Reumann Kerstin , Heise Tilman , Twiss Jeffery L.
Published: July 2007

A surprisingly large population of mRNAs has been shown to localize to sensory axons, but few RNA-binding proteins have been detected in these axons. These axonal mRNAs include several potential binding targets for the La RNA chaperone protein. La is transported into axonal processes in both culture and peripheral nerve. Interestingly, La is posttranslationally modified in sensory neurons by sumoylation. In axons, small ubiquitin-like modifying polypeptides (SUMO)-La interacts with dynein, whereas native La interacts with kinesin. Lysine 41 is required for sumoylation, and sumoylation-incompetent La
K41R
shows only anterograde transport, whereas WT La shows both anterograde and retrograde transport in axons. Thus, sumoylation of La determines the directionality of its transport within the axonal compartment, with SUMO-La likely recycling to the cell body.
Design of protein–membrane interaction inhibitors by virtual ligand screening, proof of concept with the C2 domain of factor V
Authors: Segers Kenneth , Sperandio Olivier , Sack Markus , Fischer Rainer , Miteva Maria A. , Rosing Jan , Nicolaes Gerry A. F. , Villoutreix Bruno O.
Published: July 2007

Most orally bioavailable drugs on the market are competitive inhibitors of catalytic sites, but a significant number of targets remain undrugged, because their molecular functions are believed to be inaccessible to drug-like molecules. This observation specifically applies to the development of small-molecule inhibitors of macromolecular interactions such as protein–membrane interactions that have been essentially neglected thus far. Nonetheless, many proteins containing a membrane-targeting domain play a crucial role in health and disease, and the inhibition of such interactions therefore represents a very promising therapeutic strategy. In this study, we demonstrate the use of combined
in silico
structure-based virtual ligand screening and surface plasmon resonance experiments to identify compounds that specifically disrupt protein–membrane interactions. Computational analysis of several membrane-binding domains revealed they all contain a druggable pocket within their membrane-binding region. We applied our screening protocol to the second discoidin domain of coagulation factor V and screened >300,000 drug-like compounds
in silico
against two known crystal structure forms. For each C2 domain structure, the top 500 molecules predicted as likely factor V-membrane inhibitors were evaluated
in vitro
. Seven drug-like hits were identified, indicating that therapeutic targets that bind transiently to the membrane surface can be investigated cost-effectively, and that inhibitors of protein–membrane interactions can be designed.
Elevated NF-κB responses and FLIP levels in leukemic but not normal lymphocytes: reduction by salicylate allows TNF-induced apoptosis
Authors: Rae Colin , Langa Susana , Tucker Steven J. , MacEwan David J.
Published: July 2007

As its name suggests, tumor necrosis factor (TNF) is known to induce cytotoxicity in a wide variety of tumor cells and cell lines. However, its use as a chemotherapeutic drug has been limited by its deleterious side effects of systemic shock and widespread inflammatory responses. Some nonsteroidal antiinflammatory drugs, such as sodium salicylate, have been shown to have a chemopreventive role in certain forms of cancer. Here, we reveal that sodium salicylate selectively enhances the apoptotic effects of TNF in human erythroleukemia cells but does not affect primary human lymphocytes or monocytes. Sodium salicylate did not affect the intracellular distribution of TNF receptors (TNFRs) but stimulated cell surface TNFR2 shedding. Erythroleukemia cells were shown to possess markedly greater basal NF-κB responses and elevated Fas-associated protein with death domain-like IL-1converting enzyme (FLIP) levels. Sodium salicylate achieved its effects by reducing the elevated NF-κB responsiveness and FLIP levels and restoring the apoptotic response of TNF rather than the proliferative/proinflammatory effects of the cytokine in these cancer cells. Inhibition of NF-κB or FLIP levels in human erythroleukemia cells by pharmacological or molecular-biological means also resulted in switching the character of these cells from a TNF-responsive proliferative phenotype into an apoptotic one. These findings expose that the enhanced proliferative nature of human leukemia cells is caused by elevated NF-κB and FLIP responses and basal levels, reversible by sodium salicylate to allow greater apoptotic responsiveness of cytotoxic stimuli such as TNF. Such findings provide insight into the molecular mechanisms by which human leukemia cells can switch from a proliferative into an apoptotic phenotype.
Energy transport in peptide helices
Authors: Botan Virgiliu , Backus Ellen H. G. , Pfister Rolf , Moretto Alessandro , Crisma Marco , Toniolo Claudio , Nguyen Phuong H. , Stock Gerhard , Hamm Peter
Published: July 2007

We investigate energy transport through an α-aminoisobutyric acid-based 3
10
-helix dissolved in chloroform in a combined experimental-theoretical approach. Vibrational energy is locally deposited at the N terminus of the helix by ultrafast internal conversion of a covalently attached, electronically excited, azobenzene moiety. Heat flow through the helix is detected with subpicosecond time resolution by employing vibrational probes as local thermo meters at various distances from the heat source. The experiment is supplemented by detailed nonequilibrium molecular dynamics (MD) simulations of the process, revealing good qualitative agreement with experiment: Both theory and experiment exhibit an almost instantaneous temperature jump of the reporter units next to the heater which is attributed to the direct impact of the isomerizing azobenzene moiety. After this impact event, helix and azobenzene moiety appear to be thermally decoupled. The energy deposited in the helix thermalizes on a subpicosecond timescale and propagates along the helix in a diffusive-like process, accompanied by a significant loss into the solvent. However, in terms of quantitative numbers, theory and experiment differ. In particular, the MD simulation seems to overestimate the heat diffusion constant (2 Å
2
ps
−1
from the experiment) by a factor of five.
Single A326G mutation converts human CYP24A1 from 25-OH-D
3
-24-hydroxylase into -23-hydroxylase, generating 1α,25-(OH)
2
D
3
-26,23-lactone
Authors: Prosser David E. , Kaufmann Martin , O'Leary Brendan , Byford Valarie , Jones Glenville
Published: July 2007

Studies of 25-hydroxyvitamin D
3
-24-hydroxylase (CYP24A1) have demonstrated that it is a bifunctional enzyme capable of the 24-hydroxylation of 1α,25-(OH)
2
D
3
, leading to the excretory form, calcitroic acid, and 23-hydroxylation, culminating in 1α,25-(OH)
2
D
3
-26,23-lactone. The degree to which CYP24A1 performs either 23- or 24-hydroxylation is species-dependent. In this paper, we show that the human enzyme that predominantly 24-hydroxylates its substrate differs from the opossum enzyme that 23-hydroxylates it at only a limited number of amino acid residues. Mutagenesis of the human form at a single substrate-binding residue (A326G) dramatically changes the regioselectivity of the enzyme from a 24-hydroxylase to a 23-hydroxylase, whereas other modifications have no effect. Ala-326 is located in the I-helix, close to the terminus of the docked 25-hydroxylated side chain in a CYP24A1 homology model, a result that we interpret indicates that substitution of a glycine at 326 provides extra space for the side chain of the substrate to move deeper into the pocket and place it in a optimal stereochemical position for 23-hydroxylation. We discuss the physiological ramifications of these results for species possessing the A326G substitution, as well as implications for optimal vitamin D analog design.