bluuebunny/crossref_metadata_2025 huggingface dataset:
Time-slice velocity-map ion imaging studies of the photodissociation of NO in the vacuum ultraviolet region
Authors: Gao Hong , Pan Yang , Yang Lei , Zhou Jingang , Ng C. Y. , Jackson William M.
Published: April 2012

The time-slice velocity-map ion imaging and the resonant four-wave mixing techniques are combined to study the photodissociation of NO in the vacuum ultraviolet (VUV) region around 13.5 eV above the ionization potential. The neutral atoms, i.e., N(2Do), O(3P2), O(3P1), O(3P0), and O(1D2), are probed by exciting an autoionization line of O(1D2) or N(2Do), or an intermediate Rydberg state of O(3P0,1,2). Old and new autoionization lines of O(1D2) and N(2Do) in this region have been measured and newer frequencies are given for them. The photodissociation channels producing N(2Do) + O(3P), N(2Do) + O(1D2), N(2Do) + O(1S0), and N(2Po) + O(3P) have all been identified. This is the first time that a single VUV photon has been used to study the photodissociation of NO in this energy region. Our measurements of the angular distributions show that the recoil anisotropy parameters (β) for all the dissociation channels except for the N(2Do) + O(1S0) channel are minus at each of the wavelengths used in the present study. Thus direct excitation of NO by a single VUV photon in this energy region leads to excitation of states with Σ or Δ symmetry (ΔΩ = ±1), explaining the observed perpendicular transition.
Ultrafast structural and isomerization dynamics in the Rydberg-exited Quadricyclane: Norbornadiene system
Authors: Rudakov Fedor , Weber Peter M.
Published: April 2012

The quadricyclane – norbornadiene system is an important model for the isomerization dynamics between highly strained molecules. In a breakthrough observation for a polyatomic molecular system of that complexity, we follow the photoionization from Rydberg states in the time-domain to derive a measure for the time-dependent structural dynamics and the time-evolving structural dispersion even while the molecule is crossing electronic surfaces. The photoexcitation to the 3s and 3p Rydberg states deposits significant amounts of energy into vibrational motions. We observe the formation and evolution of the vibrational wavepacket on the Rydberg surface and the internal conversion from the 3p Rydberg states to the 3s state. In that state, quadricyclane isomerizes to norbornadiene with a time constant of τ2 = 136(45) fs. The lifetime of the 3p Rydberg state in quadricyclane is τ1 = 320(31) and the lifetime of the 3s Rydberg state in norbornadiene is τ3 = 394(32).
Computational study of the rovibrational spectrum of (OCS)2
Authors: Brown James , Wang Xiao-Gang , Dawes Richard , Carrington Tucker
Published: April 2012

In this paper, we report a new intermolecular potential energy surface and rovibrational transition frequencies and line strengths computed for the OCS dimer. The potential is made by fitting energies obtained from explicitly correlated coupled-cluster calculations and fit using an interpolating moving least squares method. The rovibrational Schroedinger equation is solved with a symmetry-adapted Lanczos algorithm and an uncoupled product basis set. All four intermolecular coordinates are included in the calculation. On the potential energy surface we find, previously unknown, cross-shaped isomers and also polar and non-polar isomers. The associated wavefunctions and energy levels are presented. To identify polar and cross states we use both calculations of line strengths and vibrational parent analysis. Calculated rotational constants differ from their experimental counterparts by less than 0.001 cm−1.
A self-consistent marginally stable state for parallel ion cyclotron waves
Authors: Isenberg Philip A.
Published: April 2012

We derive an equation whose solutions describe self-consistent states of marginal stability for a proton-electron plasma interacting with parallel-propagating ion cyclotron (IC) waves. Ion cyclotron waves propagating through this marginally stable plasma will neither grow nor damp. The dispersion relation of these waves, ω(k), smoothly rises from the usual MHD behavior at small |k| to reach ω = Ωp as k → ± ∞. The proton distribution function has constant phase-space density along the characteristic resonant surfaces defined by this dispersion relation. Our equation contains a free function describing the variation of the proton phase-space density across these surfaces. Taking this free function to be a simple “box function”, we obtain specific solutions of the marginally stable state for a range of proton parallel betas. The phase speeds of these waves are larger than those given by the cold plasma dispersion relation, and the characteristic surfaces are more sharply peaked in the υ⊥ direction. The threshold anisotropy for generation of ion cyclotron waves is also larger than that given by estimates which assume bi-Maxwellian proton distributions.
Ultrafast internal conversion in ethylene. II. Mechanisms and pathways for quenching and hydrogen elimination
Authors: Allison T. K. , Tao H. , Glover W. J. , Wright T. W. , Stooke A. M. , Khurmi C. , van Tilborg J. , Liu Y. , Falcone R. W. , Martínez T. J. , Belkacem A.
Published: April 2012

Through a combined experimental and theoretical approach, we study the nonadiabatic dynamics of the prototypical ethylene (C2H4) molecule upon π → π* excitation with 161 nm light. Using a novel experimental apparatus, we combine femtosecond pulses of vacuum ultraviolet and extreme ultraviolet (XUV) radiation with variable delay to perform time resolved photo-ion fragment spectroscopy. In this second part of a two part series, the XUV (17 eV < hν < 23 eV) probe pulses are sufficiently energetic to break the C–C bond in photoionization, or to photoionize the dissociation products of the vibrationally hot ground state. The experimental data is directly compared to excited state ab initio molecular dynamics simulations explicitly accounting for the probe step. Enhancements of the CH2+ and CH3+ photo-ion fragment yields, corresponding to molecules photoionized in ethylene (CH2CH2) and ethylidene (CH3CH) like geometries are observed within 100 fs after π → π* excitation. Quantitative agreement between theory and experiment on the relative CH2+ and CH3+ yields provides experimental confirmation of the theoretical prediction of two distinct conical intersections and their branching ratio [H. Tao, B. G. Levine, and T. J. Martinez, J. Phys. Chem. A. 113, 13656 (2009)]. Evidence for fast, non-statistical, elimination of H2 molecules and H atoms is observed in the time resolved H2+ and H+ signals.
Differences in first neighbor orientation behind the anomalies in the low and high density trans-1,2-dichloroethene liquid
Authors: Rovira-Esteva M. , Murugan N. Arul , Pardo L. C. , Busch S. , Tamarit J. Ll. , Cuello G. J. , Bermejo F. J.
Published: April 2012

Trans-1,2-dichloroethene (HClC=CClH) has several structural and dynamic anomalies between its low- and high-density liquid, previously found through neutron scattering experiments. To explain the microscopic origin of the differences found in those experiments, a series of molecular dynamics simulations were performed. The analysis of molecular short-range order shows that the number of molecules in the first neighbor shell is 12 for the high-density liquid and 11 for the low-density one. It also shows that the angular position of the center of mass of the first neighbor is roughly the same although the molecular orientation is not. In both liquids the first neighbor and its reference molecule arrange mainly in two configurations, each being the most probable in one of the liquids. First neighbors in the configuration that predominates in the high-density liquid tend to locate themselves closer to the reference molecule, an evidence that they are more strongly bonded. This arrangement facilitates a better packing of the rest of molecules in the first neighbor shell so that on average an additional molecule can be included, and is proposed to be the key in the explanation of all the observed anomalies in the characteristics of both liquids.
Low energy charged particles interacting with amorphous solid water layers
Authors: Horowitz Yonatan , Asscher Micha
Published: April 2012

The interaction of charged particles with condensed water films has been studied extensively in recent years due to its importance in biological systems, ecology as well as interstellar processes. We have studied low energy electrons (3–25 eV) and positive argon ions (55 eV) charging effects on amorphous solid water (ASW) and ice films, 120–1080 ML thick, deposited on ruthenium single crystal under ultrahigh vacuum conditions. Charging the ASW films by both electrons and positive argon ions has been measured using a Kelvin probe for contact potential difference (CPD) detection and found to obey plate capacitor physics. The incoming electrons kinetic energy has defined the maximum measurable CPD values by retarding further impinging electrons. L-defects (shallow traps) are suggested to be populated by the penetrating electrons and stabilize them. Low energy electron transmission measurements (currents of 0.4–1.5 μA) have shown that the maximal and stable CPD values were obtained only after a relatively slow change has been completed within the ASW structure. Once the film has been stabilized, the spontaneous discharge was measured over a period of several hours at 103 ± 2 K. Finally, UV laser photo-emission study of the charged films has suggested that the negative charges tend to reside primarily at the ASW-vacuum interface, in good agreement with the known behavior of charged water clusters.
Optimal control of open quantum systems: A combined surrogate Hamiltonian optimal control theory approach applied to photochemistry on surfaces
Authors: Asplund Erik , Klüner Thorsten
Published: April 2012

In this paper, control of open quantum systems with emphasis on the control of surface photochemical reactions is presented. A quantum system in a condensed phase undergoes strong dissipative processes. From a theoretical viewpoint, it is important to model such processes in a rigorous way. In this work, the description of open quantum systems is realized within the surrogate Hamiltonian approach [R. Baer and R. Kosloff, J. Chem. Phys. 106, 8862 (1997)]10.1063/1.473950. An efficient and accurate method to find control fields is optimal control theory (OCT) [W. Zhu, J. Botina, and H. Rabitz, J. Chem. Phys. 108, 1953 (1998)10.1063/1.475576; Y. Ohtsuki, G. Turinici, and H. Rabitz, J. Chem. Phys. 120, 5509 (2004)]10.1063/1.1650297. To gain control of open quantum systems, the surrogate Hamiltonian approach and OCT, with time-dependent targets, are combined. Three open quantum systems are investigated by the combined method, a harmonic oscillator immersed in an ohmic bath, CO adsorbed on a platinum surface, and NO adsorbed on a nickel oxide surface. Throughout this paper, atomic units, i.e., ℏ = me = e = a0 = 1, have been used unless otherwise stated.
A multi-configurational time-dependent Hartree approach to the eigenstates of multi-well systems
Authors: Wodraszka Robert , Manthe Uwe
Published: April 2012

A rigorous and efficient approach for the calculation of eigenstates in polyatomic molecular systems with potentials displaying multiple wells is introduced. The scheme is based on the multi-configurational time-dependent Hartree (MCTDH) approach and uses multiple MCTDH wavefunctions with different single-particle function bases to describe the quantum dynamics in the different potential wells. More specifically, an iterative block Lanczos-type diagonalization scheme utilizing state-averaged MCTDH wavefunctions localized in different wells is employed to obtain the energy eigenvalues and eigenstates. The approach does not impose any formal restriction on the symmetry of the potential or the number of wells. A seven-dimensional model system of tetrahedral symmetry, which is inspired by A·CH4 type complexes and displays four equivalent potential minima, is used to study the numerical performance of the new approach. It is found that the number of configurations in the MCTDH wavefunctions required to obtain converged results is decreased by roughly one order of magnitude compared to standard MCTDH calculations employing a block-relaxation scheme.
Dissipation range turbulent cascades in plasmas
Authors: Terry P. W. , Almagri A. F. , Fiksel G. , Forest C. B. , Hatch D. R. , Jenko F. , Nornberg M. D. , Prager S. C. , Rahbarnia K. , Ren Y. , Sarff J. S.
Published: April 2012

Dissipation range cascades in plasma turbulence are described and spectra are formulated from the scaled attenuation in wavenumber space of the spectral energy transfer rate. This yields spectra characterized by the product of a power law and exponential fall-off, applicable to all scales. Spectral indices of the power law and exponential fall-off depend on the scaling of the dissipation, the strength of the nonlinearity, and nonlocal effects when dissipation rates of multiple fluctuation fields are different. The theory is used to derive spectra for MHD turbulence with magnetic Prandtl number greater than unity, extending previous work. The theory is also applied to generic plasma turbulence by considering the spectrum from damping with arbitrary wavenumber scaling. The latter is relevant to ion temperature gradient turbulence modeled by gyrokinetics. The spectrum in this case has an exponential component that becomes weaker at small scale, giving a power law asymptotically. Results from the theory are compared to three very different types of turbulence. These include the magnetic plasma turbulence of the Madison Symmetric Torus, the MHD turbulence of liquid metal in the Madison Dynamo Experiment, and gyrokinetic simulation of ion temperature gradient turbulence.
High-stiffness driven micromechanical resonators with enhanced power handling
Authors: Hou Li-Jen , Li Sheng-Shian
Published: April 2012

A two-port silicon-based micromechanical beam resonator driven at its high-stiffness locations has been proposed with enhanced power handling as compared with the same resonator but using conventional drive/sense configurations. The key to attaining superior power handling relies on the electrode arrangements where critical handling power (or Duffing-nonlinear bifurcation power) becomes much higher by driving the resonator at its high-stiffness locations than low-stiffness areas. In this work, resonators using high-stiffness driving approach exhibit around 20× (20 times) power handling improvement as compared to low-stiffness driving counterpart while the motional impedances in both cases are the same under linear operation.
Direction switching and beam steering of cholesteric liquid crystal gratings
Authors: Jau Hung-Chang , Lin Tsung-Hsien , Chen Yan-Yu , Chen Chun-Wei , Liu Jui-Hsiang , Fuh Andy Y.-G.
Published: April 2012

This work proposes two mechanisms for switching the direction of stripes in cholesteric liquid crystal (CLC) gratings. The stripe direction depends on the ratio of cell gap to the natural pitch length (d/P0) of a CLC sample. Electrical switching is based on the different pitches at the planar and the transient planar states. Optical switching, however, changes pitch by using the photo-isomerization effect of the azobenzene doped in a CLC sample. Using the two mechanisms, we can switch the stripe directions in two orthogonal directions. Furthermore, the beam-steering capability of CLC gratings also remains effective after switching directions.
Correlation between interface traps and paramagnetic defects in c-Si/a-Si:H heterojunctions
Authors: Thoan N. H. , Jivanescu M. , O’Sullivan B. J. , Pantisano L. , Gordon I. , Afanas’ev V. V. , Stesmans A.
Published: April 2012

Low-temperature (77 K) capacitance-voltage measurements are proposed as a technique to quantify the densities of traps in c-Si/a-Si:H heterojunction solar cell structures. By comparing the inferred trap densities to the results of electron spin resonance spectroscopy, we found that the dangling bonds of silicon atoms at the surface of the (100)Si substrate (Pb0 centers) and in a-Si:H layer (D-centers) provide the most significant contributions to the density of traps.
Tunable clover-shaped GaN photonic bandgap structures patterned by dual-step nanosphere lithography
Authors: Li K. H. , Ma Zetao , Choi H. W.
Published: April 2012

The fabrication of close-packed clover-shaped photonic crystal structure on GaN by dual-step nanosphere lithography is demonstrated. By shrinkage of spheres prior to pattern transfer, a non-closed-packed clover-shaped photonic bandgap (PBG) structure, as designed by modified 3D finite-difference time-domain simulation, is also realized. The PBG of the close-packed and non-close-packed clover-shaped structures is verified through optical transmission spectroscopy, found to agree well with simulated results. A threefold enhancement in photoluminescence (PL) intensity is observed from the optimized structure, when the PBG is tuned to overlap with the emission band of the InGaN/GaN multi-quantum wells. From time-resolved PL measurements, shortened decay lifetimes are observed.
Extraction of the sub-bandgap density-of-states in polymer thin-film transistors with the multi-frequency capacitance-voltage spectroscopy
Authors: Jang Jaeman , Kim Jaehyeong , Bae Minkyung , Lee Jaewook , Myong Kim Dong , Hwan Kim Dae , Lee Jiyoul , Lee Bang-Lin , Koo Bonwon , Wan Jin Yong
Published: April 2012

The multi-frequency capacitance-voltage (C-V) spectroscopy is proposed for extracting the sub-bandgap density-of-states (DOS) of polymer semiconductors and demonstrated in three different thiophene-based organic thin-film transistors including poly(3-hexylthiophene), poly(3,3′′′-didodecylquaterthiophene), and poly(didodecylquaterthiophene-alt-didodecylbithiazole). The density of exponential tail and exponential deep states are extracted to be in the range of 3.0 × 1018 ∼ 1.5 × 1019 cm−3 eV−1 and 3.0 × 1016 ∼ 3.0 × 1017 cm−3 eV−1, respectively. The extracted DOS correspond to the polymer semiconductor-dependence of the measured crystallinity and mobility. In addition, the extracted DOS values are verified by comparing the measured I-V characteristics with the simulated results through a technology computer-aided design tool.
Interface barriers at the interfaces of polar GaAs(111) faces with Al2O3
Authors: Chou H. Y. , O’Connor E. , Hurley P. K. , Afanas’ev V. V. , Houssa M. , Stesmans A. , Ye P. D. , Newcomb S. B.
Published: April 2012

Internal photoemission measurements of barriers for electrons at interfaces between GaAs(111) and atomic-layer deposited Al2O3 indicate that changing the GaAs polar crystal face orientation from the Ga-terminated (111)A to the As-terminated (111)B has no effect on the barrier height and remains the same as at the non-polar GaAs(100)/Al2O3 interface. Moreover, the presence of native oxide on GaAs(111) or passivation of this surface with sulphur also have no measurable influence on the GaAs(111)/Al2O3 barrier. These results suggest that the orientation and composition-sensitive surface dipoles conventionally observed at GaAs surfaces are effectively compensated at GaAs/oxide interfaces.
Optical generation of polarized photoluminescence from GaAs(100)
Authors: Hu Zhan , Singha Sima , H. Rich Daniel , J. Gordon Robert
Published: April 2012

Polarized photoluminescence from GaAs(100) was generated using shaped ultrashort laser pulses. A train of three pulses separated by an integer multiple of the longitudinal optical phonon period produced p-polarized continuum emission, whereas trains with half-integer multiples of the phonon period as well as single Gaussian pulses produced s-polarized emission. The p-polarized emission is attributed to recombination of carriers in the L-valley, resulting from plasma generation and coherent phonon-excitation by the pulse train, whereas the s-polarized emission is caused by reflection by the melted surface of unpolarized plasma emission.
Sheared polymer glass and the question of mechanical rejuvenation
Authors: Chung Yongchul G. , Lacks Daniel J.
Published: April 2012

There has been much recent debate as to whether mechanical deformation reverses the aging of a material, and returns it to a structure characteristic of the system at a higher temperature. We use molecular dynamics simulation to address this problem by carrying out shear and temperature increase simulation on atactic glassy polystyrene. Our results show explicitly that the structure (as quantified by the torsion population) changes associated with shear and temperature increase are quantitatively – and in some cases qualitatively – different. This is due to the competition between rejuvenation and physical aging, and we show this by carrying out a relaxation simulation. The conclusion agrees with those from previous experiments and simulations, which were suggestive of mechanical deformation moving the system to structures distinct from those reached during thermal treatment.
Large-scale first-principles molecular dynamics for electrochemical systems with O(N) methods
Authors: Ohwaki Tsukuru , Otani Minoru , Ikeshoji Tamio , Ozaki Taisuke
Published: April 2012

A method for large-scale first-principles molecular dynamics (MD) simulations on electrochemical systems has been developed by combining the effective screening medium (ESM) method with O(N) density functional theory (DFT). This implementation has been significantly simplified by the introduction of neutral atom potentials, which minimizes the modifications to existing DFT code. In order to demonstrate ability of this implementation, it has been applied to an electrochemical system consisting of a H-Si(111) electrode, which is a candidate anode for high-capacity Li-ion secondary batteries, and a propylene carbonate (PC) solvent to simulate how PC molecules in the vicinity of the electrode surface respond to an imposed electric field. The large-scale MD simulation clearly demonstrates that the combination of the ESM and O(N) DFT methods provides a useful tool for first-principles investigation of complicated electrochemical systems such as high-capacity batteries.
Explicitly correlated Gaussian calculations of the 2P
o Rydberg spectrum of the lithium atom
Authors: Bubin Sergiy , Adamowicz Ludwik
Published: April 2012

Accurate quantum-mechanical nonrelativistic variational calculations are performed for the nine lowest members of the 2Po Rydberg series (1s2np1, n = 2, …, 10) of the lithium atom. The effect of the finite nuclear mass is included in the calculations allowing for determining the isotopic shifts of the energy levels. The wave functions of the states are expanded in terms of all-electron explicitly correlated Gaussian functions. The exponential parameters of the Gaussians are variationally optimized with the aid of the analytical energy gradient determined with respect to those parameters. The calculated state energies are compared with the available experimental data.
Collision frequency dependence of polarization current in neoclassical tearing modes
Authors: Imada K. , Wilson H. R.
Published: April 2012

The neoclassical polarization current, generated when a magnetic island propagates through a tokamak plasma, is believed to influence the initial stage of the neoclassical tearing mode evolution. Understanding the strength of its contribution in the relevant plasma collision frequency regimes for future tokamaks such as ITER is crucial for the successful control and/or avoidance of the neoclassical tearing mode. A nonlinear drift kinetic theory is employed to determine the full collision frequency dependence of the neoclassical polarization current in the small island limit, comparable to the trapped ion orbit width. Focusing on the region away from the island separatrix (where a layer with a complex mix of physics processes exists), we evaluate for the first time the variation of the neoclassical ion polarization current in the transition regime between the analytically tractable collisionless and collisional limits. In addition, the island propagation frequency-dependence of the neoclassical polarization current and its contribution to the island evolution is revealed. For a range of propagation frequencies, we find that the neoclassical polarization current is maximum in the intermediate collision frequency regime analyzed here—a new and unexpected result.
Phase sensitive monitoring of electron bunch form and arrival time in superconducting linear accelerators
Authors: Kaya C. , Schneider C. , Al-Shemmary A. , Seidel W. , Kuntzsch M. , Bhattacharyya J. , Mittendorff M. , Evtushenko P. , Winnerl S. , Staats G. , Helm M. , Stojanovic N. , Michel P. , Gensch M.
Published: April 2012

In this Letter, we present a simple approach for monitoring electron bunch form and arrival time combining electro-optic sampling and phase and frequency sensitive signal detection. The sensitivity of the technique has the potential to allow online diagnostics to be performed down to bunch charges in the femto coulomb regime. The concept has high impact for the developments of the next generation of 4th generation x-ray light sources working with long pulse trains or continuous wave mode of operation.
Thermoelectric and magnetic properties of nanocrystalline La0.7Sr0.3CoO3
Authors: Durá O. J. , Rogl P. , Falmbigl M. , Hilscher G. , Bauer E.
Published: April 2012

This work reports on the effect of grain size on the electrical, thermal, and magnetic properties of La0.7Sr0.3CoO3 samples obtained by solid-state reaction combined with ball milling. Electrical characterization made for samples with grain sizes ranging from 26 nm to 0.57 μm shows a size-induced metal-to-insulator transition for the sample with smallest grain size. As a consequence of the grain size reduction, there is a change of the thermopower sign and the thermal conductivity displays extremely low values. Interestingly, the thermoelectric figure of merit displays an enhancement as a consequence of the grain size reduction. The Curie temperature was found to be constant whereas the saturation magnetization decreases as grain size decreases. Thereby electrical and magnetic properties of nanocrystalline samples are interpreted in terms of a core-shell structure in which grain boundaries display an insulating behavior while the core region of each grain exhibits the bulk properties.
Highly ionized physical vapor deposition plasma source working at very low pressure
Authors: Stranak V. , Herrendorf A.-P. , Drache S. , Cada M. , Hubicka Z. , Tichy M. , Hippler R.
Published: April 2012

Highly ionized discharge for physical vapor deposition at very low pressure is presented in the paper. The discharge is generated by electron cyclotron wave resonance (ECWR) which assists with ignition of high power impulse magnetron sputtering (HiPIMS) discharge. The magnetron gun (with Ti target) was built into the single-turn coil RF electrode of the ECWR facility. ECWR assistance provides pre-ionization effect which allows significant reduction of pressure during HiPIMS operation down to p = 0.05 Pa; this is nearly more than an order of magnitude lower than at typical pressure ranges of HiPIMS discharges. We can confirm that nearly all sputtered particles are ionized (only Ti+ and Ti++ peaks are observed in the mass scan spectra). This corresponds well with high plasma density ne ∼ 1018 m−3, measured during the HiPIMS pulse.
Facile preparation of nanofibrous polyaniline thin film as counter electrodes for dye sensitized solar cells
Authors: Guo Feng , Hu Hao , Tai Qi-Dong , Chen Bo-Lei , Sebo Bobby , Bu Cheng-Hao , Xu Jun-Hua , Zhao Xing-Zhong
Published: April 2012

A fibrous polyaniline (PANI) thin film has been fabricated from prepared PANI nanofiber solution by Marangoni flow. The PANI retained its original fiber morphology after being deposited into films and formed highly interconnected network structures, which leads to an excellent electrochemical catalytic activity. This PANI thin film was applied in dye sensitized solar cell (DSSC) as counter electrode. A power conversion efficiency (PCE) of 3.8% of the DSSC by this PANI counter electrode was obtained without optimization of synthesis conditions, compared with 5.1% PCE by traditional Pt counter electrode. Better performances are attainable by improving the conductivity of PANI with acid doping process to decrease the sheet resistance of this electrode. Facile synthesis process and good performance of these nanofibrous PANI thin films highlight the potential large scale applications for low-cost counter electrode in DSSCs.
Spinodal decomposition in particle-laden Landau-Levich flow
Authors: Kao Justin C. T. , Hosoi A. E.
Published: April 2012

We examine Landau-Levich coating by a suspension of spherical particles. For particles larger than the liquid film thickness, capillary forces lead to self-assembly of monolayer particle aggregates. We observe two regimes of deposition, find coating fraction as a function of wall speed, and propose a spinodal decomposition (Cahn-Hilliard) model for this pattern formation process.
Polymorphism in 3-Pyridylsydnone: Preparative and Structural Aspects
Authors: Bernhardt Paul V. , Kvaskoff David , Veedu Rakesh Naduvile , Wentrup Curt
Published: April 2012

Two polymorphs of 3-(3′-pyridyl)sydnone 4 have been investigated. It was established that the metastable P2/c form is the kinetically favoured product formed by recrystallization from solution, but this may be converted to the new, more stable, P21/c polymorph by sublimation or heating in the solid state.
An extended γ-tubulin ring functions as a stable platform in microtubule nucleation
Authors: Erlemann Sarah , Neuner Annett , Gombos Linda , Gibeaux Romain , Antony Claude , Schiebel Elmar
Published: April 2012

γ-Tubulin complexes are essential for microtubule (MT) nucleation. The γ-tubulin small complex (γ-TuSC) consists of two molecules of γ-tubulin and one molecule each of Spc97 and Spc98. In vitro, γ-TuSCs oligomerize into spirals of 13 γ-tubulin molecules per turn. However, the properties and numbers of γ-TuSCs at MT nucleation sites in vivo are unclear. In this paper, we show by fluorescence recovery after photobleaching analysis that γ-tubulin was stably integrated into MT nucleation sites and was further stabilized by tubulin binding. Importantly, tubulin showed a stronger interaction with the nucleation site than with the MT plus end, which probably provides the basis for MT nucleation. Quantitative analysis of γ-TuSCs on single MT minus ends argued for nucleation sites consisting of approximately seven γ-TuSCs with approximately three additional γ-tubulin molecules. Nucleation and anchoring of MTs required the same number of γ-tubulin molecules. We suggest that a spiral of seven γ-TuSCs with a slight surplus of γ-tubulin nucleates MTs in vivo.
The enduring enigma of nuclear translation
Authors: Reid David W. , Nicchitta Christopher V.
Published: April 2012

Although the physical separation of transcription in the nucleus and translation in the cytoplasm has presided as a fundamental tenet of cell biology for decades, it has not done so without recurring challenges and contentious debate. In this issue, David et al. (2012. J. Cell Biol. http://dx.doi.org/10.1083/jcb.201112145) rekindle the controversy by providing convincing experimental evidence for nuclear translation.
Structural transformation and improved dielectric and magnetic properties in Ti-substituted Bi0.8La0.2FeO3 multiferroics
Authors: Reetu  , Agarwal Ashish , Sanghi Sujata , Ashima  , Ahlawat Neetu
Published: April 2012

Ti-substituted BiLaFeO3 ceramics having compositions Bi0.8La0.2Fe1−x
Ti
x
O3 (x = 0.0, 0.05, 0.1, 0.15) were synthesized by the conventional solid-state reaction method. Powder x-ray diffraction investigations performed at room temperature show that the crystal structure is rhombohedral for x = 0.0, 0.05; tetragonal for x = 0.15; and a phase boundary occurs at x = 0.1. In the Rietveld refinement good agreement between the observed and calculated pattern was observed. Dielectric response of these samples was analysed in the frequency range 1 kHz–5 MHz at different temperatures. A decrease in the values of real (ε′) and imaginary (ε″) parts of dielectric constant with Ti substitution indicates reduced conductivity and hence enhanced resistivity in doped samples. Stability of dielectric constant and conductivity with temperature is considerably improved with Ti substitution. Magnetic measurements were carried out at room temperature up to a field of 20 kOe. Magnetic properties of Bi0.8La0.2FeO3 ceramics are considerably improved on Ti substitution along with a significant opening in the room temperature M–H hysteresis loop. Higher values of remanent magnetization (M
r) 0.1373 and 0.1487 emu g−1; coercivity (H
c) 4.856 and 5.904 kOe are observed for samples with x = 0.1 and 0.15, respectively. This is due to the structural phase transition from rhombohedral to tetragonal.
Ultra-wide bandwidth measurement of partial discharge current pulses in SF6
Authors: Reid A J , Judd M D
Published: April 2012

This paper presents ultra-wide bandwidth measurements of partial discharge (PD) current pulses. Using a 33 GHz bandwidth oscilloscope together with a direct, matched coaxial connection to the PD source, pulses have been characterized with a greater degree of accuracy than has previously been achieved, with a minimum observed rise time of 24 ps. The PD source consists of a sharp protrusion in pressurized sulfur hexaflouride (SF6) with a tip radius of 25 µm. Both positive and negative corona pulses were recorded, revealing previously indistinguishable frequency content and features such as the appearance of groups of multiple component pulses occurring within a nanosecond time scale. The upper bandwidth limitation of the complete measurement set-up was established. This was calculated by cross-correlating current pulses with corresponding pulses filtered at lower frequencies to determine their similarity. The tendency for multiple consecutive pulses to occur within a short time period was evident. The results provide valuable data for researchers investigating fundamental physical phenomena of SF6 ionization and PD activity.
Ordering and segregation in isolated Au–Pd icosahedral nanoclusters and nanowires and the consequences of their encapsulation inside carbon nanotubes
Authors: Zhu B , Wang Y , Atanasov I S , Cheng D , Hou M
Published: April 2012

Metropolis Monte Carlo sampling in the semi-grand canonical ensemble with empirical potentials is used to predict equilibrium ordered structures and segregation properties of small icosahedral Au–Pd nanoclusters and helical nanowire segments over the whole range of compositions at low temperatures. The cases of free-standing clusters and wires are compared with the same systems encapsulated in carbon nanotubes.

A number of chemically ordered structures and segregation states are identified and found to be consistent with the same interplay between size mismatch, mixing enthalpy and surface energies of elemental metals which determines the thermodynamic equilibrium of binary metal alloys. Encapsulation has the effect of modifying the surface energies of nanoclusters and wires, with considerable consequences on their thermodynamic states, although the metal–graphite interaction strength is low as compared with the metal cohesive energy and the carbon–carbon binding energy.
Szegő and para-orthogonal polynomials on the real line: Zeros and canonical spectral transformations
Authors: Castillo Kenier , Lamblém Regina , Rafaeli Fernando , Ranga Alagacone
Published: April 2012

We study polynomials which satisfy the same recurrence relation as the Szegő polynomials, however, with the restriction that the (reflection) coefficients in the recurrence are larger than one in modulus. Para-orthogonal polynomials that follow from these Szegő polynomials are also considered. With positive values for the reflection coefficients, zeros of the Szegő polynomials, para-orthogonal polynomials and associated quadrature rules are also studied. Finally, again with positive values for the reflection coefficients, interlacing properties of the Szegő polynomials and polynomials arising from canonical spectral transformations are obtained.
A convergence analysis of regularization by discretization in preimage space
Authors: Kaltenbacher Barbara , Offtermatt Jonas
Published: April 2012

In this paper we investigate the regularizing properties of discretization in preimage space for linear and nonlinear ill-posed operator equations with noisy data. We propose to choose the discretization level, that acts as a regularization parameter in this context, by a discrepancy principle. While general convergence has been shown not to hold, we provide convergence results under appropriate conditions on the exact solution.
River history
Authors: Vita-Finzi Claudio
Published: April 2012

During the last half century, advances in geomorphology—abetted by conceptual and technical developments in geophysics, geochemistry, remote sensing, geodesy, computing and ecology—have enhanced the potential value of fluvial history for reconstructing erosional and depositional sequences on the Earth and on Mars and for evaluating climatic and tectonic changes, the impact of fluvial processes on human settlement and health, and the problems faced in managing unstable fluvial systems.
Microsatellite Markers for Linkage and Association Studies
Authors: Gulcher Jeffrey
Published: April 2012

During the 1990s and the first several years of this century, microsatellites or short tandem repeats were the workhorse genetic markers for hypothesis-independent studies in human genetics, facilitating genome-wide linkage studies and allelic imbalance studies. However, the rise of higher throughput and cost-effective single-nucleotide polymorphism (SNP) platforms led to the era of the SNP for genome scans. Nevertheless, it is important to note that microsatellites remain highly informative and useful measures of genomic variation for linkage and association studies. Their continued advantage in complementing SNPs lies in their greater allelic diversity than biallelic SNPs as well as in their population history, in which single-step expansion or contraction of the tandem repeat on the background of ancestral SNP haplotypes can break up common haplotypes, leading to greater haplotype diversity within the linkage disequilibrium block of interest. In fact, microsatellites have starred in association studies leading to widely replicated discoveries of type 2 diabetes (TCF7L2) and prostate cancer genes (the 8q21 region). At the end of the day, it will be important to catalog all variation, including SNPs, microsatellites, copy number variations, and polymorphic inversions in human genetic studies. This article describes the utilities of microsatellites and experimental approaches in their use.
In Vivo Imaging of Drosophila Larval Neuromuscular Junctions to Study Synapse Assembly
Authors: Andlauer Till F.M. , Sigrist Stephan J.
Published: April 2012

In the past decade, a significant number of proteins involved in the developmental assembly and maturation of synapses have been identified. However, detailed knowledge of the molecular processes underlying developmental synapse assembly is still sparse. Here, we discuss an approach that makes extended in vivo imaging of selected proteins in live Drosophila larvae feasible at a single-synapse resolution. The intact larvae are anesthetized and neuromuscular junctions (NMJs) are noninvasively imaged with confocal microscopy. This method allows for both protein trafficking and protein turnover kinetics to be studied at various points in time during the development of an animal. These data contribute to our understanding of synaptic assembly under in vivo conditions.
Developing reading comprehension through collaborative learning
Authors: Rojas‐Drummond Sylvia , Mazón Nancy , Littleton Karen , Vélez Maricela
Published: April 2012

The present study explores the development and promotion of reading comprehension in primary school students, in the context of the implementation of an educational programme called ‘Learning Together’ (LT). The programme, which centred on collaborative learning activities, was designed to promote oral and written communication in primary school Mexican children. Analyses revealed that children who participated in the LT programme, in comparison with students in a control condition, produced higher‐quality written summaries of texts they had read, both when working in teams and when working individually. This suggests that the LT participants appropriated and transferred the text comprehension strategies promoted, so that they could apply these strategies effectively not only in collaborative contexts but also independently, that is, in a self‐regulated and autonomous fashion. The theoretical and practical implications of the work are discussed in relation to understanding and promoting oracy and literacy processes in primary school students.
Cloning and characterization of trypsin- and chymotrypsin-like genes in the striped rice stem borer,Chilo suppressalis
Authors: Ge Zhao-Yu , Wan Pin-Jun , Han Zhao-Jun
Published: April 2012

Serine proteinases including trypsins and chymotrypsins play various important roles in insects, including food digestion, immune defense, and zymogen activation. Studies on insect serine proteinases could reveal their feeding preference (polyphagous and monophagous) and facilitate identification of protease inhibitors, which can be engineered for pest management. In this paper, 11 transcripts encoding trypsin- and chymotrypsin-like proteins were cloned from the striped rice stem borer, Chilo suppressalis (Walker). All the predicted proteins share high sequence similarity with known trypsin- and chymotrypsin-like proteins from either lepidopterans or dipterans, and most of the proteins have conserved motifs that are characteristics of serine proteinases. Among the 11 cloned genes, six were expressed predominantly and one exclusively in the midgut of the insect, three were expressed relatively evenly in examined tissues, and one was not expressed in either the gut or hemolymph based on RT–PCR results. The seven genes that were predominantly or exclusively expressed in the gut were also affected by feeding on different host plants. The genes that were expressed in the gut and were affected by host plants are likely to encode digestive proteinases. The identification of trypsin- and chymotrypsin-like genes in this insect species is the first step towards further comparative studies and for identification of insect-specific proteinase inhibitors, which might be engineered to protect rice plants against the striped rice stem borer, which is one of the destructive pests of rice.
Influence of Electrolyte Refreshing on the Photoelectrochemical Performance of Fiber-Shaped Dye-Sensitized Solar Cells
Authors: Lv Zhibin , Wu Hongwei , Cai Xin , Fu Yongping , Wang Dan , Chu Zengze , Zou Dechun
Published: April 2012

Given the convenient sealing of fiber-shaped dye-sensitized solar cells (FDSSCs), the electrolyte refreshing effect on the photo-electrochemical performance of FDSSCs was studied. The electron transport and interfacial recombination kinetics were also systematically investigated by electrochemical impedance spectroscopy. With increased electrolyte refreshing times from 0 to 10, the open-circuit voltage (Voc) and fill factor (FF) increased, whereas the photocurrent density (Jsc) and power conversion efficiency (PCE) significantly decreased. The increasedVocwas mainly ascribed to the electron recombination resistance (Rct, WE) at the TiO2/electrolyte interface and electron lifetime. The decreasedJscand PCE were due to dye desorption and the increase of series resistance. Further investigation proved that Li+played a vital role in increasingVocas electrolyte refreshing and Li+had more significant impact than TBP (tert-butyl pyridine) on maintaining highVoc.
A Fast Numerical Method for the Calculation of the Equilibrium Isotopic Composition of a Transmutation System in an Advanced Fuel Cycle
Authors: Álvarez-Velarde F. , González-Romero E. M.
Published: April 2012

A fast numerical method for the calculation in a zero-dimensional approach of the equilibrium isotopic composition of an iteratively used transmutation system in an advanced fuel cycle, based on the Banach fixed point theorem, is described in this paper. The method divides the fuel cycle in successive stages: fuel fabrication, storage, irradiation inside the transmutation system, cooling, reprocessing, and incorporation of the external material into the new fresh fuel. The change of the fuel isotopic composition, represented by an isotope vector, is described in a matrix formulation. The resulting matrix equations are solved using direct methods with arbitrary precision arithmetic. The method has been successfully applied to a double-strata fuel cycle with light water reactors and accelerator-driven subcritical systems. After comparison to the results of the EVOLCODE 2.0 burn-up code, the observed differences are about a few percents in the mass estimations of the main actinides.
Temporal Dynamics and Electronic Nose Detection of Stink Bug-Induced Volatile Emissions from Cotton Bolls
Authors: Degenhardt David C. , Greene Jeremy K. , Khalilian Ahmad
Published: April 2012

Management decisions for stink bugs (Pentatomidae) inBtcotton are complicated by time-consuming sampling methods, and there is a need for more efficient detection tools. Volatile compounds are released from cotton bolls in response to feeding by stink bugs, and electronic nose (E-nose) technology may be useful for detecting boll damage. In this study, we investigated the temporal dynamics of volatile emissions in response to feeding by stink bugs and tested the ability of E-nose to discriminate between odors from healthy and injured bolls. Feeding by stink bugs led to an approximate 2.4-fold increase in volatile organic compound (VOC) emissions. Principal components analysis of E-nose sensor data showed distinct (100%) separation between stink bug-injured and healthy bolls after two days of feeding. However, when E-nose was used to randomly identify samples, results were less accurate (80–90%). These results suggest that E-nose is a promising technology for rapid detection of stink bug injury to cotton.
Chloride Penetration through Cracks in High-Performance Concrete and Surface Treatment System for Crack Healing
Authors: Yoon In-Seok
Published: April 2012

For enhancing the service life of concrete structures, it is very important to minimize crack at surface. Even if these cracks are very small, the problem is to which extend these cracks may jeopardize the durability of these decks. It was proposed that crack depth corresponding with critical crack width from the surface is a crucial factor in view of durability design of concrete structures. It was necessary to deal with chloride penetration through microcracks characterized with the mixing features of concrete. This study is devoted to examine the effect of high strength concrete and reinforcement of steel fiber on chloride penetration through cracks. High strength concrete is regarded as an excellent barrier to resist chloride penetration. However, durability performance of cracked high strength concrete was reduced seriously up to that of ordinary cracked concrete. Steel fiber reinforcement is effective to reduce chloride penetration through cracks because steel fiber reinforcement can lead to reduce crack depth significantly. Meanwhile, surface treatment systems are put on the surface of the concrete in order to seal the concrete. The key-issue is to which extend a sealing is able to ensure that chloride-induced corrosion can be prevented. As a result, penetrant cannot cure cracks, however, coating and combined treatment can prevent chloride from flowing in concrete with maximum crack width of 0.06 mm and 0.08 mm, respectively.