bluuebunny/crossref_metadata_2025 huggingface dataset:
Interleukin-1β up-regulates RGS4 through the canonical IKK2/IκBα/NF-κB pathway in rabbit colonic smooth muscle
Authors: Hu Wenhui , Li Fang , Mahavadi Sunila , Murthy Karnam S.
Published: April 2008

Initial Ca2+-dependent contraction of the intestinal smooth muscle mediated by Gq-coupled receptors is attenuated by RGS4 (regulator of G-protein signalling 4). Treatment of colonic muscle cells with IL-1β (interleukin-1β) inhibits acetylcholine-stimulated initial contraction through increasing the expression of RGS4. NF-κB (nuclear factor κB) signalling is the dominant pathway activated by IL-1β. In the present study we show that RGS4 is a new target gene regulated by IL-1β/NF-κB signalling. Exposure of cultured rabbit colonic muscle cells to IL-1β induced a rapid increase in RGS4 mRNA expression, which was abolished by pretreatment with a transcription inhibitor, actinomycin D, implying a transcription-dependent mechanism. Existence of the canonical IKK2 [IκB (inhibitor of NF-κB) kinase 2]/IκBα pathway of NF-κB activation induced by IL-1β in rabbit colonic muscle cells was validated with multiple approaches, including the induction of reporter luciferase activity and endogenous NF-κB-target gene expression, NF-κB-DNA binding activity, p65 nuclear translocation, IκBα degradation and the phosphorylation of IKK2 at Ser177/181 and p65 at Ser536. RGS4 up-regulation by IL-1β was blocked by selective inhibitors of IKK2, IκBα or NF-κB activation, by effective siRNA (small interfering RNA) of IKK2, and in cells expressing either the kinase-inactive IKK2 mutant (K44A) or the phosphorylation-deficient IκBα mutant (S32A/S36A). An IKK2-specific inhibitor or effective siRNA prevented IL-1β-induced inhibition of acetylcholine-stimulated PLC-β (phopsholipase C-β) activation. These results suggest that the canonical IKK2/IκBα pathway of NF-κB activation mediates the up-regulation of RGS4 expression in response to IL-1β and contributes to the inhibitory effect of IL-1β on acetylcholine-stimulated PLC-β-dependent initial contraction in rabbit colonic smooth muscle.
Structural biology of plasmid partition: uncovering the molecular mechanisms of DNA segregation
Authors: Schumacher Maria A.
Published: April 2008

DNA segregation or partition is an essential process that ensures stable genome transmission. In prokaryotes, partition is best understood for plasmids, which serve as tractable model systems to study the mechanistic underpinnings of DNA segregation at a detailed atomic level owing to their simplicity. Specifically, plasmid partition requires only three elements: a centromere-like DNA site and two proteins: a motor protein, generally an ATPase, and a centromere-binding protein. In the first step of the partition process, multiple centromere-binding proteins bind co-operatively to the centromere, which typically consists of several tandem repeats, to form a higher-order nucleoprotein complex called the partition complex. The partition complex recruits the ATPase to form the segrosome and somehow activates the ATPase for DNA separation. Two major families of plasmid par systems have been delineated based on whether they utilize ATPase proteins with deviant Walker-type motifs or actin-like folds. In contrast, the centromere-binding proteins show little sequence homology even within a given family. Recent structural studies, however, have revealed that these centromere-binding proteins appear to belong to one of two major structural groups: those that employ helix–turn–helix DNA-binding motifs or those with ribbon–helix–helix DNA-binding domains. The first structure of a higher-order partition complex was recently revealed by the structure of pSK41 centromere-binding protein, ParR, bound to its centromere site. This structure showed that multiple ParR ribbon–helix–helix motifs bind symmetrically to the tandem centromere repeats to form a large superhelical structure with dimensions suitable for capture of the filaments formed by the actinlike ATPases. Surprisingly, recent data indicate that the deviant Walker ATPase proteins also form polymer-like structures, suggesting that, although the par families harbour what initially appeared to be structurally and functionally divergent proteins, they actually utilize similar mechanisms of DNA segregation. Thus, in the present review, the known Par protein and Par–protein complex structures are discussed with regard to their functions in DNA segregation in an attempt to begin to define, at a detailed atomic level, the molecular mechanisms involved in plasmid segregation.
Trehalose 6-phosphate: a signal of sucrose status
Authors: Paul Matthew J.
Published: April 2008

T6P (trehalose 6-phosphate), the precursor of trehalose, has come out of obscurity over 10 years to be appreciated as an important regulator of plant metabolism and development, quite possibly linking the two. This information has been gained from analysis of mutant and transgenic plants, which show strong, diverse and strategically important phenotypes. Plant genes that encode the trehalose pathway are numerous and highly regulated transcriptionally and post-translationally, responding sensitively to the environment in a developmentally programmed and tissue-specific manner further suggestive of a vital function. Yet the precise role of T6P has not been clear. In an article published in the Biochemical Journal in 2006, John Lunn and colleagues addressed a major obstacle to understanding the function of T6P through development of a method capable of resolving femtomolar quantities of T6P from very small amounts of tissue. Using this technology, the authors showed large changes in T6P content that reflect tissue sucrose status. Overall, this elegant work makes an important contribution towards our understanding of the function of T6P in plants.
Situation of the whiteflies Bemisia tabaci and Trialeurodes vaporariorum in protected tomato crops in Algarve (Portugal)*
Authors: Ramos N. E. , Neto A. F. , Arsénio S. , Mangerico E. , Stigter L. , Fortunato E. , Fernandes J. E. , Lavadinho A. M. P. , Louro D.
Published: April 2008

Protected tomato is the most important horticultural crop in the Algarve (south of Portugal). However, the growing area has decreased by almost 48% since 1995, mainly as a result of the pests Bemisia tabaci and Trialeurodes vaporariorum and the epidemics of Tomato yellow leaf curl virus (TYLCV), a Begomovirus transmitted by B. tabaci. Both whiteflies are vectors of economically important viruses. Recently, Tomato chlorosis virus (ToCV), a member of the genus Crinivirus, transmitted by both B. tabaci and T. vaporariorum, was reported infecting tomato crops in Algarve. A study was carried out to evaluate the dynamics of whitefly populations on tomato crops in Algarve. Population counts of B. tabaci were high in the first months of autumn, then decreased until January, when numbers of T. vaporariorum became higher. Counts of B. tabaci then increased again.
Optical and electrical study of deformed hydrogenated bulk Cd0.96Zn0.04Te single crystal
Authors: Lmai F. , Brihi N. , Takkouk Z. , Guergouri K. , Bouzerara F. , Hage-Ali M.
Published: April 2008

The effect of hydrogenation on defects associated with dislocations has been studied in the p-type Cd0.96Zn0.04Te (CZT) semiconductor, grown by the horizontal Bridgman method, with the help of current I(V), capacity C(V) measurements, photoluminescence spectra, and cathodoluminescence imaging. To generate dislocations by plastic deformation we have used a Vickers microhardness instrument on several cadmium (Cd)(111) and telluride (Te)(1¯1¯1¯)CZT faces. Hydrogenation was carried out by exposure of the samples to hydrogen plasma at 150 °C and 3 mbar for 3 h. The analysis of the results obtained confirms both the reduction of the acceptor concentration, that acceptors may be passivated by formation of neutral complexes with hydrogen, and that the majority defect on each face is the tellurium vacancy, VTe. A reduction of the broadband at 1.547 eV (VCd2−−D) is observed, while the donor bound exciton D0X is increased on the Cd face and finally, it seems that the hydrogen stabilizes dislocations and prevents their removal.
Photoelectron spectroscopy of the Cl−…H2∕D2 anions: A model beyond the rotationless and Franck–Condon approximations
Authors: Grinev Timur A. , Buchachenko Alexei A.
Published: April 2008

A model for simulating photoelectron spectra of the triatomic van der Waals complexes containing stable atomic anion and diatomic molecule is proposed and applied to the Cl−…H2 and Cl−…D2 anions. The model assumes adiabatic separation of the electronic and nuclear motions and localization of the photodetachment act at the atomic chromophore. Under these approximations, the electronic transition dipole moment matrix elements are evaluated using the atoms-in-molecule approach and explicit expressions for the rovibrational line strength factors are derived. The energies and intensities of a number of rovibronic photoelectron transitions are calculated for the Cl−…H2 and Cl−…D2 anions within the adiabatic bender model, i.e., with the full separation of the vibrational motions, whereas the simulations of the broad spectral envelopes are performed using the equilibrium conditions, asymmetric line shape function, and two choices of the relative abundances of the para- and ortho-forms of the complex. The simulations reproduce experimental spectra reasonably well allowing for their unambiguous assignment in terms of vibronic transitions fully consistent with the previous time-dependent calculations. Agreement with the previous theoretical works, manifestations of non-Franck–Condon effects, and implications to the assessment of the neutral potential energy surfaces are discussed.
Formation of (Ti,Al)N∕Ti2AlN multilayers after annealing of TiN∕TiAl(N) multilayers deposited by ion beam sputtering
Authors: Dolique V. , Jaouen M. , Cabioc’h T. , Pailloux F. , Guérin Ph. , Pélosin V.
Published: April 2008

By using ion beam sputtering, TiN∕TiAl(N) multilayers of various modulation wavelengths (Λ=8, 13, and 32nm) were deposited onto silicon substrates at room temperature. After annealing at 600°C in vacuum, one obtains for Λ=13nm a (Ti,Al)N∕Ti2AlN multilayer as it is evidenced from x-ray diffraction, high resolution transmission electron microscopy, and energy filtered electron imaging experiments. X-ray photoelectron spectroscopy (XPS) experiments show that the as-deposited TiAl sublayers contain a noticeable amount of nitrogen atoms which mean concentration varies with the period Λ. They also evidenced the diffusion of aluminum into TiN sublayers after annealing. Deduced from these observations, we propose a model to explain why this solid-state phase transformation depends on the period Λ of the multilayer.
Investigation of SnSe, SnSe2, and Sn2Se3 alloys for phase change memory applications
Authors: Chung Kyung-Min , Wamwangi Daniel , Woda Michael , Wuttig Matthias , Bensch Wolfgang
Published: April 2008

SnSe, SnSe2, and Sn2Se3 alloys have been studied to explore their suitability as new phase change alloys for electronic memory applications. The temperature dependence of the structural and electrical properties of these alloys has been determined and compared with that of GeTe. A large electrical resistance contrast of more than five orders of magnitude is achieved for SnSe2 and Sn2Se3 alloys upon crystallization. X-ray diffraction measurements show that the transition in sheet resistance is accompanied by crystallization. The activation energy for crystallization of SnSe, SnSe2, and Sn2Se3 has been determined. The microstructure of these alloys has been investigated by atomic force microscopy measurements. X-ray reflection measurements reveal density increases of 5.0%, 17.0%, and 9.1% upon crystallization for the different alloys.
Fast ignitor target studies for the HiPER project
Authors: Atzeni S. , Schiavi A. , Honrubia J. J. , Ribeyre X. , Schurtz G. , Nicolaï Ph. , Olazabal-Loumé M. , Bellei C. , Evans R. G. , Davies J. R.
Published: April 2008

Target studies for the proposed High Power Laser Energy Research (HiPER) facility [M. Dunne, Nature Phys. 2, 2 (2006)] are outlined and discussed. HiPER will deliver a 3ω (wavelength λ=0.35μm), multibeam, multi-ns pulse of about 250kJ and a 2ω or 3ω pulse of 70–100kJ in about 15ps. Its goal is the demonstration of laser driven inertial fusion via fast ignition. The baseline target concept is a direct-drive single shell capsule, ignited by hot electrons generated by a conically guided ultraintense laser beam. The paper first discusses ignition and compression requirements, and presents gain curves, based on an integrated model including ablative drive, compression, ignition and burn, and taking the coupling efficiency ηig of the igniting beam as a parameter. It turns out that ignition and moderate gain (up to 100) can be achieved, provided that adiabat shaping is used in the compression, and the efficiency ηig exceeds 20%. Using a standard ponderomotive scaling for the hot electron temperature, a 2ω or 3ω ignition beam is required to make the hot electron range comparable to the desired size of the hot spot. A reference target family is then presented, based on one-dimensional fluid simulation of compression, and two-dimensional fluid and hybrid simulations of fast electron transport, ignition, and burn. The sensitivity to compression pulse shape, as well as to hot electron source location, hot electron range, and beam divergence is also discussed. Rayleigh–Taylor instability at the ablation front has been addressed by a model and a perturbation code. Simplified simulations of code-guided target implosions have also been performed.
The vibrational proton potential in bulk liquid water and ice
Authors: Burnham C. J. , Anick D. J. , Mankoo P. K. , Reiter G. F.
Published: April 2008

We present an empirical flexible and polarizable water model which gives an improved description of the position, momentum, and dynamical (spectroscopic) distributions of H nuclei in water. We use path integral molecular dynamics techniques in order to obtain momentum and position distributions and an approximate solution to the Schrödinger equation to obtain the infrared (IR) spectrum. We show that when the calculated distributions are compared to experiment the existing empirical models tend to overestimate the stiffness of the H nuclei involved in H bonds. Also, these models vastly underestimate the enormous increase in the integrated IR intensity observed in the bulk over the gas-phase value. We demonstrate that the over-rigidity of the OH stretch and the underestimation of intensity are connected to the failure of existing models to reproduce the correct monomer polarizability surface. A new model, TTM4-F, is parametrized against electronic structure results in order to better reproduce the polarizability surface. It is found that TTM4-F gives a superior description of the observed spectroscopy, showing both the correct redshift and a much improved intensity. TTM4-F also has a somewhat improved dielectric constant and OH distribution function. It also gives an improved match to the experimental momentum distribution, although some discrepancies remain.
Elucidating the spectral and temporal contributions from the resonant and nonresonant response to femtosecond coherent anti-Stokes Raman scattering
Authors: Compton R. , Filin A. , Romanov D. A. , Levis R. J.
Published: April 2008

A theoretical expression is developed for femtosecond coherent anti-Stokes Raman scattering (CARS) to quantitatively account for the vibrational line shape in the presence of nonresonant signal. The contributions of the resonant and nonresonant components are extracted from the emitted signal line shape as a function of Stokes wavelength and as a function of the temporal overlap of the two pump pulses (for spectrally resolved femtosecond CARS). The theory is compared to the measured spectra of the oxygen vibrational transition ΔG01=1556.4cm−1 for temporal detunings of 0 and 700fs.
Specifics of solvation of sulfonated polyelectrolytes in water, dimethylmethylphosphonate, and their mixture: A molecular simulation study
Authors: Vishnyakov Aleksey , Neimark Alexander V.
Published: April 2008

Sulfonated polyelectrolyte membranes (PEMs), such as Nafion and styrene-olefin block copolymers, are explored as permselective membranes for fuel cells as well as suitable barrier materials against chemical agents. The permselective properties of PEM are determined by their microphase segregation into hydrophilic and hydrophobic domains. We performed classical molecular dynamics simulations of solvation of the hydrophilic fragments of PEM exemplified on sulfonated polystyrene (sPS) with potassium, calcium, and aluminum as counterions, in water, phosphor-organic nerve agent simulant dimethylmethylphosphonate (DMMP), and their binary mixture. The force field for the sulfonate group has been developed by optimizing the potential parameters to fit the benzenesulfonate conformations obtained from the density functional theory. For a comparison, we considered perfluorosulfonate oligomers representing fragments of Nafion polymer. We found a noticeable difference between the geometries of the polymer backbone in different solvents. The polymer backbone is stiffer in DMMP for both sPS and Nafion. An anisotropic structuring of the solvent around the phenylsulfonate group is substantially stronger than around the Nafion sidechain due to the rigidity and the anisotropy of the phenylsulfonate group. The counterion significantly affects the conformations of solvated sPS: the rigidity of the backbone increases when potassium or calcium ions are replaced by trivalent aluminum ions.
Higher excitations for an exponential multireference wavefunction Ansatz and single-reference based multireference coupled cluster Ansatz: Application to model systems H4, P4, and BeH2
Authors: Hanrath Michael
Published: April 2008

This article reports on the convergence of the exponential multireference wavefunction Ansatz (MRexpT) [J. Chem. Phys. 123, 84102 (2005)] and the single-reference based multireference coupled cluster Ansatz [J. Chem. Phys. 94, 1229 (1991)] with respect to higher cluster excitations. The approaches are applied to the H4, P4, and BeH2 model systems according to the recently published analysis by Evangelista et al. [J. Chem. Phys. 125, 154113 (2006)]. The results show both MRexpT and SRMRCC to be highly accurate although SRMRCC shows problems due to its lack of Fermi vacuum invariance (symmetry breaking).
Mechanisms of photoinduced CαCβ bond breakage in protonated aromatic amino acids
Authors: Lucas B. , Barat M. , Fayeton J. A. , Perot M. , Jouvet C. , Grégoire G. , Brøndsted Nielsen S.
Published: April 2008

Photoexcitation of protonated aromatic amino acids leads to CαCβ bond breakage among other channels. There are two pathways for the CαCβ bond breakage, one is a slow process (microseconds) that occurs after hydrogen loss from the electronically excited ion, whereas the other is a fast process (nanoseconds). In this paper, a comparative study of the fragmentation of four molecules shows that the presence of the carboxylic acid group is necessary for this fast fragmentation channel to occur. We suggest a mechanism based on light-induced electron transfer from the aromatic ring to the carboxylic acid, followed by a fast internal proton transfer from the ammonium group to the negatively charged carboxylic acid group. The ion formed is a biradical since the aromatic ring is ionized and the carbon of the COOH group has an unpaired electron. Breakage of the weak CαCβ bond gives two even-electron fragments and is expected to quickly occur. The present experimental results together with the ab initio calculations support the interpretation previously proposed.
One-dimensional model for water and aqueous solutions. III. Solvation of hard rods in aqueous mixtures
Authors: Ben-Naim Arieh
Published: April 2008

A simple one-dimensional model for aqueous solution is applied to study the solvation thermodynamics of a simple solute (here, a hard-rod particle) in mixtures of waterlike particles and a cosolvent. Two kinds of cosolvents are considered, one that stabilizes and one that destabilizes the “structure of water.” The results obtained for the Gibbs energy, entropy, enthalpy, and heat capacity of solvation are in qualitative agreement with experimental data on the solvation of argon and methane in mixtures of water and ethanol and of water and p-dioxane.
Mechanisms of solute orientational order in nematic liquid crystals
Authors: Elliott Burnell E. , ter Beek Leon C. , Sun Zhengmin
Published: April 2008

The order parameters of a number of different solutes dissolved in a number of different nematic liquid-crystal solvents are measured and compared. It is shown that the order parameters can all be rationalized with the ansatz that there exist two independent ordering mechanisms operating in the liquid crystals employed. With this ansatz it is possible to fit the experimental order parameters to better than 5%. This opens the possibility of the accurate prediction of order parameters in ordered liquids.
Thermodynamics and kinetics of oxygen-induced segregation of 3d metals in Pt–3d–Pt(111) and Pt–3d–Pt(100) bimetallic structures
Authors: Menning Carl A. , Chen Jingguang G.
Published: April 2008

The stability of subsurface 3d transition metals (3d represents Ni, Co, Fe, Mn, Cr, V, and Ti) in Pt(111) and Pt(100) was examined in vacuum and with 0.5 ML atomic oxygen by a combined experimental and density functional theory (DFT) approach. DFT was used to predict the trends in the binding energy of oxygen and in the stability of 3d metals to remain in the subsurface layer. DFT calculations predicted that for both (111) and (100) crystal planes the subsurface Pt–3d–Pt configurations were thermodynamically preferred in vacuum and that the surface 3d–Pt–Pt configurations were preferred with the adsorption of 0.5 ML atomic oxygen. Experimentally, the DFT predictions were verified by using Auger electron spectroscopy to monitor the segregation of Ni and Co in Pt–3d–Pt structures on polycrystalline Pt foil, composed of mainly (111) and (100) facets. The activation barrier for the oxygen-induced segregation of Ni was found to be 17±1kcal∕mol attributed to the Pt(111) areas and 27±1kcal∕mol attributed to the Pt(100) areas of the Pt foil. For Pt–Co–Pt, the activation barrier was found to be 10±1kcal∕mol and was attributed to the Pt(111) areas of the Pt foil. The Brønsted–Evans–Polanyi relationship was utilized to predict the activation barriers for segregation of the other Pt–3d–Pt(111) and Pt–3d–Pt(100) systems. These results are further discussed in connection to the activity and stability for cathode bimetallic electrocatalysts for proton exchange membrane fuel cells.
Indium induced band gap tailoring in AgGa1−xInxS2 chalcopyrite structure for visible light photocatalysis
Authors: Jang Jum Suk , Borse Pramod H. , Lee Jae Sung , Choi Sun Hee , Kim Hyun Gyu
Published: April 2008

Indium was substituted at gallium site in chalcopyrite AgGaS2 structure by using a simple solid solution method. The spectroscopic analysis using extended x-ray absorption fine structure and x-ray photoelectron spectroscopy confirmed the indium substitution in AgGaS2 lattice. The band gap energy of AgGa1−xInxS2 (x=0–1) estimated from the onset of absorption edge was found to be reduced from 2.67eV (x=0) to 1.9eV (x=1) by indium substitution. The theoretical and experimental studies showed that the indium s orbitals in AgGa1−xInxS2 tailored the band gap energy, thereby modified the photocatalytic activity of the AgGa1−xInxS2.
Structural changes in chemical solution deposited lanthanum doped bismuth ferrite thin films
Authors: Singh V. R. , Garg A. , Agrawal D. C.
Published: April 2008

Here, we report on the lanthanum (La) doping induced structural changes in chemical solution grown Bi1−xLaxFeO3 (0.0⩽x⩾0.30) thin films on indium tin oxide coated glass substrates and influence on film’s properties. Films show gradual structural changes from rhombohedral towards a pseudocubic structure as the La content increases, also evident from changes in the lattice constant and disappearance of peak splitting upon increasing the doping level. This was also accompanied by an increase in the dielectric constant, magnetization and a marginal decrease in the leakage current density up to x=0.20 followed by a reverse trend at higher doping levels.
Event-driven dynamics of rigid bodies interacting via discretized potentials
Authors: van Zon Ramses , Schofield Jeremy
Published: April 2008

A framework for performing event-driven, adaptive time step simulations of systems of rigid bodies interacting under stepped or terraced potentials in which the potential energy is only allowed to have discrete values is outlined. The scheme is based on a discretization of an underlying continuous potential that effectively determines the times at which interaction energies change. As in most event-driven approaches, the method consists of specifying a means of computing the free motion, evaluating the times at which interactions occur, and determining the consequences of interactions on subsequent motion for the terraced potential. The latter two aspects are shown to be simply expressible in terms of the underlying smooth potential. Within this context, algorithms for computing the times of interaction events and carrying out efficient event-driven simulations are discussed. The method is illustrated on a system composed of rigid rods in which the constituents interact via a terraced potential that depends on the relative orientations of the rods.
A novel gas-loading system for mechanically closing of various types of diamond anvil cells
Authors: Kurnosov Alexander , Kantor Innokenty , Boffa-Ballaran Tiziana , Lindhardt Sven , Dubrovinsky Leonid , Kuznetsov Alexei , Zehnder Beat H.
Published: April 2008

Loading of gases in diamond anvil cells is a complicated but necessary task to obtain hydrostatic conditions for high-pressure measurements. A simple in operation, safe, and universal gas-loading system has been designed and constructed. Innovations were introduced to simplify the loading procedure up to the “three-button” mode.
Fixed-node diffusion Monte Carlo study of the structures of m-benzyne
Authors: Al-Saidi W. A. , Umrigar C. J.
Published: April 2008

Diffusion Monte Carlo (DMC) calculations are performed on the monocyclic and bicyclic forms of m-benzyne, which are the equilibrium structures at the CCSD(T) and CCSD levels of coupled cluster theory. We employed multiconfiguration self-consistent field trial wave functions which are constructed from a carefully selected eight-electrons-in-eight-orbitals complete active space [CAS(8,8)], with configuration state function coefficients that are reoptimized in the presence of a Jastrow factor. The DMC calculations show that the monocyclic structure is lower in energy than the bicyclic structure by 1.9(2)kcal∕mole, which is in excellent agreement with the best coupled cluster results.
Inhibition of fast electron energy deposition due to preplasma filling of cone-attached targets
Authors: Baton S. D. , Koenig M. , Fuchs J. , Benuzzi-Mounaix A. , Guillou P. , Loupias B. , Vinci T. , Gremillet L. , Rousseaux C. , Drouin M. , Lefebvre E. , Dorchies F. , Fourment C. , Santos J. J. , Batani D. , Morace A. , Redaelli R. , Nakatsutsumi M. , Kodama R. , Nishida A. , Ozaki N. , Norimatsu T. , Aglitskiy Y. , Atzeni S. , Schiavi A.
Published: April 2008

We present experimental and numerical results on the propagation and energy deposition of laser-generated fast electrons into conical targets. The first part reports on experimental measurements performed in various configurations in order to assess the predicted benefit of conical targets over standard planar ones. For the conditions investigated here, the fast electron-induced heating is found to be much weaker in cone-guided targets irradiated at a laser wavelength of 1.057μm, whereas frequency doubling of the laser pulse permits us to bridge the disparity between conical and planar targets. This result underscores the prejudicial role of the prepulse-generated plasma, whose confinement is enhanced in conical geometry. The second part is mostly devoted to the particle-in-cell modeling of the laser-cone interaction. In qualitative agreement with the experimental data, the calculations show that the presence of a large preplasma leads to a significant decrease in the fast electron density and energy flux near the target rear side.
Effect of ZnS coating on the photovoltaic properties of CdSe quantum dot-sensitized solar cells
Authors: Shen Qing , Kobayashi Junya , Diguna Lina J. , Toyoda Taro
Published: April 2008

CdSe quantum dots (QDs) were adsorbed onto nanostructured TiO2 films for different times by using a chemical bath deposition method in order to produce QD-sensitized solar cells (QDSSCs). Surface modification was done by coating ZnS onto the CdSe QDs. The optical absorption and current-voltage characteristics of these devices were studied. The size of the CdSe QDs increased with increasing adsorption time, and there was an optimum CdSe adsorption time for achieving the best photovoltaic conversion efficiency. The photovoltaic properties of short-circuit current density, open-circuit voltage, and photovoltaic conversion efficiency were significantly improved after modifying the surface with ZnS. Under a solar illumination of 100 mW/cm2, an efficiency as high as 2.02% was achieved for the CdSe QDSSCs that were made by using this method.
Injection-seeded internal-reflection-mode p-Ge laser exceeds 10W peak terahertz power
Authors: Muravjov A. V. , Saxena H. , Peale R. E. , Fredricksen C. J. , Edwards O. , Shastin V. N.
Published: April 2008

Injection seeding of a large active p-Ge laser crystal operating on total internal reflection modes is demonstrated with peak output power at the level of 40W in the 1.5–4.2THz spectral range. The improvement over traditional 1W axial mode p-Ge lasers is due both to spatially and temporally more efficient use of the available population inversion.
Electronic transport in outer-wall disordered carbon nanotube molecular devices
Authors: Xu N. , Ding J. W. , Xing D. Y.
Published: April 2008

Two device models of outer-wall disordered carbon nanotube with lead contacts of multi- and single-wall nanotubes are proposed for both measurement and control of carrier mobility in multiwall carbon nanotubes. By developing a decomposition elimination method for Green’s function, we have explored the outer-wall disorder effects on the electronic transport in such surface-doped-like molecular devices. It is found that the average conductance and localization length largely exceed those in the bulk disorder, showing the relative robustness of the model device to surface disorder. Especially, the fashion of the conductance variations with disorder depends strongly on the Fermi energy and the makeup of lead contacts. In the absence of the contact scattering, a nonmonotonic behavior, first decreasing then increasing, is observed in the conductance variations with disorder. In the presence of the contact scattering, an abnormal growth of the conductance is obtained at much lower disorder, due to the destroyed coherence by the introduction of disorder. The results present a new approach for the design and application of the nanotube molecular devices and device wiring.
A self-oscillating ionic polymer-metal composite bending actuator
Authors: Pugal Deivid , Kim Kwang J. , Punning Andres , Kasemägi Heiki , Kruusmaa Maarja , Aabloo Alvo
Published: April 2008

This paper presents an electromechanical model of an ionic polymer-metal composite (IPMC) material. The modeling technique is a finite element method (FEM). An applied electric field causes the drift of counterions (e.g., Na+), which, in turn, drags water molecules. The mass and charge imbalance inside the polymer is the main cause of the bending motion of the IPMC. The studied physical effects have been considered as time dependent and modeled with FEM. The model takes into account the mechanical properties of the Nafion polymer as well as the thin coating of the platinum electrodes and the platinum diffusion layer. The modeling of the electrochemical reactions, in connection with the self-oscillating behavior of an IPMC, is also considered. Reactions occurring on the surface of the platinum electrode, which is immersed into formaldehyde (HCHO) solution during the testing, are described using partial differential equations and also modeled using FEM. By coupling the equations with the rest of the model, we are able to simulate the self-oscillating behavior of an IPMC sheet.
Algebraic approach to electronic spectroscopy and dynamics
Authors: Toutounji Mohamad
Published: April 2008

Lie algebra, Zassenhaus, and parameter differentiation techniques are utilized to break up the exponential of a bilinear Hamiltonian operator into a product of noncommuting exponential operators by the virtue of the theory of Wei and Norman [J. Math. Phys. 4, 575 (1963); Proc. Am. Math. Soc., 15, 327 (1964)]. There are about three different ways to find the Zassenhaus exponents, namely, binomial expansion, Suzuki formula, and q-exponential transformation. A fourth, and most reliable method, is provided. Since linearly displaced and distorted (curvature change upon excitation/emission) Hamiltonian and spin-boson Hamiltonian may be classified as bilinear Hamiltonians, the presented algebraic algorithm (exponential operator disentanglement exploiting six-dimensional Lie algebra case) should be useful in spin-boson problems. The linearly displaced and distorted Hamiltonian exponential is only treated here. While the spin-boson model is used here only as a demonstration of the idea, the herein approach is more general and powerful than the specific example treated. The optical linear dipole moment correlation function is algebraically derived using the above mentioned methods and coherent states. Coherent states are eigenvectors of the bosonic lowering operator a and not of the raising operator a+. While exp(a+) translates coherent states, exp(a+a+) operation on coherent states has always been a challenge, as a+ has no eigenvectors. Three approaches, and the results, of that operation are provided. Linear absorption spectra are derived, calculated, and discussed. The linear dipole moment correlation function for the pure quadratic coupling case is expressed in terms of Legendre polynomials to better show the even vibronic transitions in the absorption spectrum. Comparison of the present line shapes to those calculated by other methods is provided. Franck–Condon factors for both linear and quadratic couplings are exactly accounted for by the herein calculated linear absorption spectra. This new methodology should easily pave the way to calculating the four-point correlation function, F(τ1,τ2,τ3,τ4), of which the optical nonlinear response function may be procured, as evaluating F(τ1,τ2,τ3,τ4) is only evaluating the optical linear dipole moment correlation function iteratively over different time intervals, which should allow calculating various optical nonlinear temporal/spectral signals.
A simple theoretical approach to calculate the electrical conductivity of nonideal copper plasma
Authors: Zaghloul Mofreh R.
Published: April 2008

A simple theoretical approach to calculate the electrical conductivity of partially ionized nonideal copper plasma is introduced. The densities of plasma species are calculated, to machine accuracy, including electronic excitation and allowing for high ionization states up to the atomic number of the element. Depression of ionization energies is taken into account using an interpolation formula that is valid over a wide range of densities. The formula yields the results of the Debye–Hückel and the ion-sphere models at the limiting boundaries of low and high densities, respectively. The nonideal Coulomb logarithm is represented by an analytic wide-range formula supplemented by a specially tailored cutoff parameter. Effects of excluding excited and high ionization states on the calculation of ionization equilibrium and electrical conductivity of copper are investigated and assessed. Computational results of the electrical conductivity are compared with results from other theoretical models and available experimental measurements and showed reasonable agreement. A discussion about the choice of the ion-sphere radius is included and concerns about thermodynamic inconsistency when using the modified nonideal Saha equations are discussed and cleared.
Effects of dust size distribution on dust acoustic waves in two-dimensional unmagnetized dusty plasma
Authors: He Guang-jun , Duan Wen-shan , Tian Duo-xiang
Published: April 2008

For unmagnetized dusty plasma with many different dust grain species containing both hot isothermal electrons and ions, both the linear dispersion relation and the Kadomtsev–Petviashvili equation for small, but finite amplitude dust acoustic waves are obtained. The linear dispersion relation is investigated numerically. Furthermore, the variations of amplitude, width, and propagation velocity of the nonlinear solitary wave with an arbitrary dust size distribution function are studied as well. Moreover, both the power law distribution and the Gaussian distribution are approximately simulated by using appropriate arbitrary dust size distribution functions.
Nanocrystalline coating design for extreme applications based on the concept of complex adaptive behavior
Authors: Fox-Rabinovich G. S. , Veldhuis S. C. , Dosbaeva G. K. , Yamamoto K. , Kovalev A. I. , Wainstein D. L. , Gershman I. S. , Shuster L. S. , Beake B. D.
Published: April 2008

The development of effective hard coatings for high performance dry machining, which is associated with high stress/temperatures during friction, is a major challenge. Newly developed synergistically alloyed nanocrystalline adaptive Ti0.2Al0.55Cr0.2Si0.03Y0.02N plasma vapor deposited hard coatings exhibit excellent tool life under conditions of high performance dry machining of hardened steel, especially under severe and extreme cutting conditions. The coating is capable of sustaining cutting speeds as high as 600 m/min. Comprehensive investigation of the microstructure and properties of the coating was performed. The structure of the coating before and after service has been characterized by high resolution transmission electron microscopy. Micromechanical characteristics of the coating have been investigated at elevated temperatures. Oxidation resistance of the coating has been studied by using thermogravimetry within a temperature range of 25–1100 °C in air. The coefficient of friction of the coatings was studied within a temperature range of 25–1200 °C. To determine the causes of excellent tool life and improved wear behavior of the TiAlCrSiYN coatings, its surface structure characteristics after service have been investigated by using x-ray photoelectron spectroscopy and extended energy-loss fine spectroscopy. One of the major features of this coating is the dynamic formation of the protective tribo-oxide films (dissipative structures) on the surface during friction with a sapphire and mullite crystal structure. Aluminum- and silicon-rich tribofilms with dangling bonds form on the surface as well. These tribofilms act in synergy and protect the surface so efficiently that it is able to sustain extreme operating conditions. Moreover, the Ti0.2Al0.55Cr0.2Si0.03Y0.02N coating possesses some features of a complex adaptive behavior because it has a number of improved characteristics (tribological adaptability, ultrafine nanocrystalline structure, hot hardness and plasticity, and oxidation stability) that work synergistically as a whole. Due to the complex adaptive behavior, this coating represents a higher ordered system that has an ability to achieve unattainable wear resistance under strongly intensifying and extreme tribological conditions.
Implications of hydrophobic interactions and consequent apparent slip phenomenon on the entrance region transport of liquids through microchannels
Authors: Chakraborty Suman , Anand Kumar Dinkar
Published: April 2008

The implications of entrance region transport in hydrophobic microchannels are theoretically and experimentally investigated in this work. Detailed analytical solutions are derived, depicting the dependences of the liquid phase velocity profiles, entrance lengths, and friction factor variations on the relative thickness of a nanobubble-dispersed layer formed in the vicinity of the microchannel wall as a consequence of localized hydrophobic interactions. It is revealed that even for a layer of nanobubbles formed with a typical thickness in the tune of three orders of magnitude lower than the characteristic microchannel dimensions, the entrance length can be enhanced to the limit of about 1.5 times than that for the cases devoid of any hydrophobic interactions. The pressure drop characteristics in the entrance region, as obtained for such cases, can turn out to be of significant consequence with regard to the design of typical pressure-driven microflow systems involving hydrophobic substrates. Closed-form expressions for the effective friction factor are also derived so that more accurate and scientific guidelines can be provided for design of hydrophobic microchannels, rather than trivially overruling the consequences of entrance region transport that is commonly exercised on a routine basis.
Application of compact neural network for drag reduction in a turbulent channel flow at low Reynolds numbers
Authors: Lorang Li Vodinh , Podvin Bérengère , Le Quéré Patrick
Published: April 2008

The aim of the present work is to develop neural networks for flow estimation and control in a turbulent channel flow at low Reynolds number. The control strategy considered here is the opposition strategy of Choi et al. [“Active turbulence control for drag reduction in wall-bounded flows,” J. Fluid Mech. 267, 75 (1994)]. The idea is to identify which velocity length scales are associated with substantial drag reduction, and to determine how the flow at these length scales can be estimated from a grid of sensors with limited extent and finite spacing. Numerical experiments are carried out in a restricted computational domain at Rτ=140 as well as in a full flow unit at Rτ=180. Evidence is shown that the flow is more complex in the larger domain than in the reduced one. In the larger domain, the estimation is performed on independent subdomains spanning at most a few coherent structures. We obtain up to 13% drag reduction in the simplified flow and 12% in the full flow unit. The essential scales for control are found to roughly match the characteristic dimensions of the coherent structures: On the order of a few hundred wall units in the streamwise direction and about 25 to 50 wall units in the spanwise direction. Controlling the flow with a Fourier-filtered estimate for the velocity resulted in about the same drag reduction as was obtained with the exact, Fourier-filtered velocity field. In addition, we found that the neural-based estimation remained adequate in the presence of moderate aliasing.
Electron transport in open systems from finite-size calculations: Examination of the principal layer method applied to linear gold chains
Authors: Beste Ariana , Meunier Vincent , Harrison Robert J.
Published: April 2008

We describe the occurrence of computational artifacts when the principal layer method is used in combination with the cluster approximation for the calculation of electronic transport properties of nanostructures. For a one-dimensional gold chain, we observe an unphysical band in the band structure. The artificial band persists for large principal layers and for large buffer sizes. We demonstrate that the assumption of equality between Hamiltonian elements of neighboring layers is no longer valid and that a discontinuity is introduced in the potential at the layer transition. The effect depends on the basis set. When periodic boundary conditions are imposed and the k-space sampling is converged, the discontinuity disappears and the principal layer method can be correctly applied by using a linear combination of atomic orbitals as basis set.
Analyzing NMR shielding tensors calculated with two-component relativistic methods using spin-free localized molecular orbitals
Authors: Autschbach Jochen
Published: April 2008

A recently developed analysis method [J. Chem. Phys. 127, 124106 (2007)] for NMR spin-spin coupling constants employing two-component (spin-orbit) relativistic density functional theory along with scalar relativistic natural localized molecular orbitals (NLMOs) and natural bond orbitals (NBOs) has been extended for analyzing NMR shielding tensors. Contributions from a field-dependent basis set (gauge-including atomic orbitals) have been included in the formalism. The spin-orbit NLMO/NBO nuclear magnetic shielding analysis has been applied to methane, plumbane, hydrogen iodide, tetracholoplatinate(II), and hexachloroplatinate(IV).
Synthesis and characterization of Zn1−xMnxO nanowires
Authors: Zhang Xiaomei , Zhang Yue , Wang Zhong Lin , Mai Wenjie , Gu Yudong , Chu Wangsheng , Wu Ziyu
Published: April 2008

Mn doped ZnO nanowires (NWs) were fabricated by a one-step vapor-solid process at 500°C. The doped Mn exists in the wurtzite lattice as substitutional atom without forming secondary phases. X-ray absorption near-edge structure reveals that the doped Mn atoms occupy the Zn sites, and they lead to an expansion in lattice constants. The I-V characteristic of a single Zn1−xMnxO NW shows a typical Ohmic contact with gold electrodes. The as-received NWs could be suitable for studying spintronics in one-dimensional diluted magnetic semiconductors.
Conversion of just-continuous metallic films to large particulate substrates for metal-enhanced fluorescence
Authors: Aslan Kadir , Malyn Stuart N. , Zhang Yongxia , Geddes Chris D.
Published: April 2008

We report the effects of thermally annealing, non-, just-, and thick continuous silver films for their potential applications in metal-enhanced fluorescence, a near-field concept which can alter the free-space absorption and emissive properties of close-proximity fluorophores (excited states). We have chosen to anneal a noncontinuous particulate film 5nm thick and two thicker continuous films, 15 and 25nm thick, respectively. Our results show that the annealing of the 25nm film has little effect on close-proximity fluorescence when coated with a monolayer of fluorophore-labeled protein. However, the 15nm continuous film cracks upon annealing, producing large nanoparticles which are ideal for enhancing the fluorescence of close-proximity fluorophores that are indeed difficult to prepare by other wet-chemical deposition processes. The annealing of 5nm noncontinuous particulate films (a control sample) has little influence on metal-enhanced fluorescence, as expected.
Semiconductor-doped glass saturable absorbers for near-infrared solid-state lasers
Authors: Malyarevich A. M. , Yumashev K. V. , Lipovskii A. A.
Published: April 2008

A survey of results on use of semiconductor-doped glass saturable absorbers for near-infrared passively mode-locked and Q-switched solid-state lasers is presented. Nanosized semiconductor particles (quantum dots) belong to quantum confined systems where motion of an electron and a hole is defined by the finite size of the nanoparticle. Dependence of the excitonic transition energy on the QDs size provides the possibility to tune the absorption of the glasses embedded with such particles to wavelength of specific light source. IV-VI semiconductor QDs (PbS, PbSe) are of interest for IR application due to their narrow band gap and large exciton Bohr radii. These allow for exciton absorption band at the wavelength through 1–3μm. Nonlinear optical properties of PbS, PbSe, and CuxSe nanoparticles embedded in glass matrices necessary for saturable absorber applications are analyzed. It is shown that these materials can be efficiently used for passive mode locking and Q switching of solid-state lasers based on Nd3+, Yb3+, Cr4+, Tm3+, and Ho3+ ions emitting through 1–2.1μm spectral range.