bluuebunny/crossref_metadata_2025 huggingface dataset:
Air plasma effect on dental disinfection
Authors: Duarte S. , Kuo S. P. , Murata R. M. , Chen C. Y. , Saxena D. , Huang K. J. , Popovic S.
Published: July 2011

A nonthermal low temperature air plasma jet is characterized and applied to study the plasma effects on oral pathogens and biofilms. Experiments were performed on samples of six defined microorganisms’ cultures, including those of gram-positive bacteria and fungi, and on a cultivating biofilm sample of Streptococcus mutans UA159. The results show that the plasma jet creates a zone of microbial growth inhibition in each treated sample; the zone increases with the plasma treatment time and expands beyond the entire region directly exposed to the plasma jet. With 30s plasma treatment twice daily during 5 days of biofilm cultivation, its formation was inhibited. The viability of S. mutans cells in the treated biofilms dropped to below the measurable level and the killed bacterial cells concentrated to local regions as manifested by the fluorescence microscopy via the environmental scanning electron microscope. The emission spectroscopy of the jet indicates that its plasma effluent carries an abundance of reactive atomic oxygen, providing catalyst for the observed plasma effect.
Figure of merit enhancement in bismuth telluride alloys via fullerene-assisted microstructural refinement
Authors: Gothard N. W. , Tritt T. M. , Spowart J. E.
Published: July 2011

Nanocomposite materials based on bismuth telluride with fullerene additions have been synthesized via ball milling and spark plasma sintering. The impact of fullerene addition upon the composites is studied with respect to both fullerene volume percentage and ball-mill duration. It is demonstrated that fullerenes can engage in significant microstructural refinement even when present in small quantities. The lattice thermal conductivity, electrical conductivity, Seebeck coefficient, and Hall coefficient are analyzed with a view to the impact of fullerene incorporation upon these properties. Fullerene-assisted microstructural refinement causes a decrease both in lattice thermal conductivity and electrical conductivity, but a corresponding increase in the Seebeck coefficient results in an enhancement in the figure of merit at low volume fractions.
Pseudo-bosons arising from standard ladder operators
Authors: Calabrese Fabio F. G.
Published: July 2011

Pseudo-bosons in the form: \documentclass[12pt]{minimal}\begin{document}$a_{\bf {s}}:=\check{\alpha }_{\bf {s}}a+ \hat{\alpha }_{\bf {s}}a^{\dag }$\end{document}as:=α̌sa+α̂sa†, \documentclass[12pt]{minimal}\begin{document}$b_{\bf {s}}:=\check{\beta }_{\bf { s}}a+\hat{\beta }_{\bf {s}}a^{\dag }$\end{document}bs:=β̌sa+β̂sa† with \documentclass[12pt]{minimal}\begin{document}$\left[ a_{\bf {s}},b_{ \bf {s}}\right]\break =\left[ a,a^{\dag }\right] =I$\end{document}as,bs=a,a†=I are considered, the α's and β's being real coefficients which depend on real parameters s1, …, sn. The eigenstates of the two number operators and their norm are explicitly obtained. Pseudo-bosons in Bagarello's sense are recovered: the states form two sets of biorthogonal bases of the full Hilbert space, but Riesz bases are obtained only in the ordinary bosonic case. Some examples of this setting are analyzed in detail.
Enhanced near band edge emission of ZnO via surface plasmon resonance of aluminum nanoparticles
Authors: Wu Kewei , Lu Yangfan , He Haiping , Huang Jingyun , Zhao Binghui , Ye Zhizhen
Published: July 2011

The enhanced near band edge emission from a ZnO thin film and nanorod array by capping aluminum nanoparticles has been studied by photoluminescence spectra. The enhancement is attributed to the resonant coupling between the bandgap transition of the semiconductor and the surface plasmon of metal nanoparticles. It is also found that the Al nanoparticles support the surface plasmon from the deep-UV to the visible region with different annealing temperatures. This cost-effective approach is useful for manufacturing highly efficient optoelectronic devices.
Characterization and calibration of piezoelectric polymers: In situ measurements of body vibrations
Authors: Kappel Marcel , Abel Markus , Gerhard Reimund
Published: July 2011

Piezoelectric polymers are known for their flexibility in applications, mainly due to their bending ability, robustness, and variable sensor geometry. It is an optimal material for minimal-invasive investigations in vibrational systems, e.g., for wood, where acoustical impedance matches particularly well. Many applications may be imagined, e.g., monitoring of buildings, vehicles, machinery, alarm systems, such that our investigations may have a large impact on technology. Longitudinal piezoelectricity converts mechanical vibrations normal to the polymer-film plane into an electrical signal, and the respective piezoelectric coefficient needs to be carefully determined in dependence on the relevant material parameters. In order to evaluate efficiency and durability for piezopolymers, we use polyvinylidene fluoride and measure the piezoelectric coefficient with respect to static pressure, amplitude of the dynamically applied force, and long-term stability. A known problem is the slow relaxation of the material towards equilibrium, if the external pressure changes; here, we demonstrate how to counter this problem with careful calibration. Since our focus is on acoustical measurements, we determine accurately the frequency response curve - for acoustics probably the most important characteristic. Eventually, we show that our piezopolymer transducers can be used as a calibrated acoustical sensors for body vibration measurements on a wooden musical instrument, where it is important to perform minimal-invasive measurements. A comparison with the simultaneously recorded airborne sound yields important insight of the mechanism of sound radiation in comparison with the sound propagating in the material. This is especially important for transient signals, where not only the long-living eigenmodes contribute to the sound radiation. Our analyses support that piezopolymer sensors can be employed as a general tool for the determination of the internal dynamics of vibrating systems.
Identifying low variance pathways for free energy calculations of molecular transformations in solution phase
Authors: Pham Tri T. , Shirts Michael R.
Published: July 2011

Improving the efficiency of free energy calculations is important for many biological and materials design applications, such as protein-ligand binding affinities in drug design, partitioning between immiscible liquids, and determining molecular association in soft materials. We show that for any pair potential, moderately accurate estimation of the radial distribution function for a solute molecule is sufficient to accurately estimate the statistical variance of a sampling along a free energy pathway. This allows inexpensive analytical identification of low statistical error free energy pathways. We employ a variety of methods to estimate the radial distribution function (RDF) and find that the computationally cheap two-body “dilute gas” limit performs as well or better than 3D–RISM theory and other approximations for identifying low variance free energy pathways. With a RDF estimate in hand, we can search for pairwise interaction potentials that produce low variance. We give an example of a search minimizing statistical variance of solvation free energy over the entire parameter space of a generalized “soft core” potential. The free energy pathway arising from this optimization procedure has lower curvature in the variance and reduces the total variance by at least 50% compared to the traditional soft core solvation pathway. We also demonstrate that this optimized pathway allows free energies to be estimated with fewer intermediate states due to its low curvature. This free energy variance optimization technique is generalizable to solvation in any homogeneous fluid and for any type of pairwise potential and can be performed in minutes to hours, depending on the method used to estimate g(r).
Note: Optical fiber milled by focused ion beam and its application for Fabry-Pérot refractive index sensor
Authors: Yuan Wu , Wang Fei , Savenko Alexey , Petersen Dirch Hjorth , Bang Ole
Published: July 2011

We introduce a highly compact fiber-optic Fabry-Pérot refractive index sensor integrated with a fluid channel that is fabricated directly near the tip of a 32 μm in diameter single-mode fiber taper. The focused ion beam technique is used to efficiently mill the microcavity from the fiber side and finely polish the end facets of the cavity with a high spatial resolution. It is found that a fringe visibility of over 15 dB can be achieved and that the sensor has a sensitivity of ∼1731 nm/RIU (refractive index units) and a detection limit of ∼5.78 × 10−6 RIU. This miniature integrated all-in-fiber optofludic sensor may find use in minimal-invasive biomedical applications.
Experimental and theoretical investigation on the high frequency dielectric properties of Ag/Al2O3 composites
Authors: Shi Z. C. , Fan R. H. , Zhang Z. D. , Gong H. Y. , Ouyang J. , Bai Y. J. , Zhang X. H. , Yin L. W.
Published: July 2011

The impedance and dielectric properties of Ag/Al2O3 composites are investigated experimentally in the frequency range from 100 MHz to 1 GHz. Besides, equivalent circuit analysis and numerical simulations were carried out. For the composites with sufficiently high silver loading, current paths were formed and negative permittivity appeared. The negative permittivity can be well described by lossy Drude model. Moreover, the negative permittivity sample manifests inductive characteristic and shunt inductors are added to its equivalent circuit. Numerical simulations show that the interconnection of silver particles results in negative permittivity, hence the serious attenuation of electromagnetic waves.
Quantum chemical analysis of the unfolding of a penta-glycyl 310-helix initiated by HO•, HO2•, and O2−•
Authors: Owen Michael C. , Viskolcz Bela , Csizmadia Imre G.
Published: July 2011

In this study, the thermodynamic functions of hydrogen abstraction from the Cα and amide nitrogen of Gly3 in a homo-pentapeptide (N-Ac–GGGGG–NH2; G5) by HO•, HO2•, and O2−• were computed using the Becke three-parameter Lee-Yang-Parr (B3LYP) density functional. The thermodynamic functions, standard enthalpy (ΔH°), Gibbs free energy (ΔG°), and entropy (ΔS°), of these reactions were computed with G5 in the 310-helical (G5Hel) and fully-extended (G5Ext) conformations at the B3LYP/6-31G(d) and B3LYP/6-311+G(d,p) levels of theory, both in the gas phase and using the conductor-like polarizable continuum model implicit water model. H abstraction is more favorable at the Cα than at the amide nitrogen. The secondary structure of G5 affects the bond dissociation energy of the H–Cα, but has a negligible effect on the dissociation energy of the H–N bond. The HO• radical is the strongest hydrogen abstractor, followed by HO2•, and finally O2−•. The secondary structure elements, such as H-bonds in the 310-helix, protect the peptide from radical attack by disabling the potential electron delocalization at the Cα, which is possible when G5 is in the extended conformation. The unfolding of the peptide radicals is more favorable than the unfolding of G5Hel; however, only the HO• can initiate the unfolding of G5Hel and the formation of G5Ext•. These results are relevant to peptides that are prone to undergoing transitions from helical structures to β-sheets in the cellular condition known as “oxidative stress” and the results are discussed in this context.
Fe solubility, growth mechanism, and luminescence of Fe doped ZnO nanowires and nanorods grown by evaporation-deposition
Authors: Alemán Belén , Ortega Yanicet , García José Ángel , Fernández Paloma , Piqueras Javier
Published: July 2011

Fe doped ZnO nanowires, nanorods, and urchin-like nanostructures have been grown using an evaporation-deposition method with compacted mixtures of ZnS and Fe2O3 powders, with different Fe contents as precursors. Treatments at 950 °C under argon flow lead to the growth of iron doped nanowires, nanorods, and other nanostructures on the surface of the compacted sample. The incorporation of iron into the nanostructures has been investigated via energy dispersive spectroscopy as well as by cathodoluminescence in a scanning electron microscope and photoluminescence in an optical microscope. The iron content in the structures is limited to the range of 0.5–0.7 at.% and does not depend on the content in the precursor. Bright and dark field imaging and twist contour analysis via transmission electron microscopy support the possibility of a dislocation driven growth of the nanowires.
Synthetic three-dimensional turbulent passive scalar fields via the minimal Lagrangian map
Authors: Rosales Carlos
Published: July 2011

A method for simple but realistic generation of three-dimensional synthetic turbulent passive scalar fields is presented. The method is an extension of the minimal turnover Lagrangian map approach (MTLM) [C. Rosales and C. Meneveau, Phys. Rev. E 78, 016313 (2008)] formulated for the generation of synthetic turbulent velocity fields. In this development, the minimal Lagrangian map is applied to deform simultaneously a vector field and an advected scalar field. This deformation takes place over a hierarchy of spatial scales encompassing a range from integral to dissipative scales. For each scale, fluid particles are mapped transporting the scalar property, without interaction or diffusional effects, from their initial configuration to new positions determined only by their velocity at the beginning of the motion and a parameter chosen to accumulate deformation for the equivalent of the phenomenological “turn-over” time scale. The procedure is studied for the case of inertial-convective regime. It is found that many features of passive scalar turbulence are well reproduced by this simple kinematical construction. Fundamental statistics of the resulting synthetic scalar fields, evaluated through the flatness and probability density functions of the scalar gradient and scalar increments, reproduce quite well the known statistical characteristics of passive scalars in turbulent fields. High-order statistics are also consistent with those observed in real hydrodynamic turbulence. The anomalous scaling of real turbulence is well reproduced for different kind of structure functions, with good quantitative agreement in general, for the scaling exponents. The spatial structure of the scalar field is also quite realistic, as well as several characteristics of the dissipation fields for the scalar variance and kinetic energy. Similarly, the statistical geometry at dissipative scales that ensues from the coupling of velocity and scalar gradients behaves in agreement with what is already known for real scalar turbulence in the considered regime. The results indicate that the multiscale self-distortion of the velocity field is an important factor to capture realistically turbulent scalar features beyond low-order statistics.
Optimal excitation of two dimensional Holmboe instabilities
Authors: Constantinou Navid C. , Ioannou Petros J.
Published: July 2011

Highly stratified shear layers are rendered unstable even at high stratifications by Holmboe instabilities when the density stratification is concentrated in a small region of the shear layer. These instabilities may cause mixing in highly stratified environments. However, these instabilities occur in limited bands in the parameter space. We perform Generalized Stability analysis of the two dimensional perturbation dynamics of an inviscid Boussinesq stratified shear layer and show that Holmboe instabilities at high Richardson numbers can be excited by their adjoints at amplitudes that are orders of magnitude larger than by introducing initially the unstable mode itself. We also determine the optimal growth that is obtained for parameters for which there is no instability. We find that there is potential for large transient growth regardless of whether the background flow is exponentially stable or not and that the characteristic structure of the Holmboe instability asymptotically emerges as a persistent quasi-mode for parameter values for which the flow is stable.
Note: Reflection-type micro multipoint laser Doppler velocimeter for measuring velocity distributions in blood vessels
Authors: Ishida H. , Kobayashi D. , Shirakawa H. , Andoh T. , Akiguchi S. , Wakisaka T. , Ishizuka M. , Hachiga T.
Published: July 2011

We have developed a laser Doppler velocimeter (LDV) for measuring velocity distributions in blood vessels. We converted a transmission-based LDV into a reflection-based LDV to make it suitable for clinical applications. The velocity distribution image of a serpentine flow channel obtained could be qualitatively explained by the numerical results. Finally, we evaluated the system by using it to measure injection of blood into a glass tube by a syringe pump. The results obtained demonstrate that erythrocytes can be used as seeding particles for the reflection-type micro multipoint LDV. The results obtained are useful as basic data for clinical applications.
RG+ formation following photolysis of NO–RG via the $\tilde{A}$Ã–$\tilde{X}$X̃ transition: A velocity map imaging study
Authors: Hopkins W. Scott , Lipciuc M. Laura , Gardiner Sara H. , Vallance Claire
Published: July 2011

Kr+ and Xe+ formation following photodissociation of NO–RG (RG = Kr or Xe) molecules via the $\tilde{A}$Ã–$\tilde{X}$X̃ electronic transition in the 44 150–44 350 cm−1 region has been investigated using velocity map imaging. Nuclear kinetic energy release (nKER) spectra indicate that the NO cofragment is produced in multiple vibrational states of the electronic ground state, with a high degree of rotational excitation. Photofragment angular distributions and nKERs are consistent with photo-induced charge transfer at the two-photon level followed by dissociative ionization at the three-photon level. RG+ angular distributions showing highly parallel character relative to the laser polarization axis are indicative of a high degree of molecular alignment in the dissociating species.
Does amino acid sequence determine the properties of Aβ dimer?
Authors: Lockhart Christopher , Kim Seongwon , Kumar Rashmi , Klimov Dmitri K.
Published: July 2011

The effect of random reshuffling of amino acids on the properties of dimers formed by Aβ peptides is studied using replica exchange molecular dynamics and united atom implicit solvent model. We show that thermodynamics of dimer assembly and the dimer globule-like state are not affected by sequence permutation. Furthermore, sequence reshuffling does not change the distributions of non-local interactions and, to a large extent, amino acids in the dimer volume. To rationalize these results, we demonstrate that Gaussian statistics applies surprisingly well to the end-to-end distances of the peptides in the dimer implying that non-bonded interactions between distant along the chain amino acids are effectively screened. This observation suggests that peptides in the dimer behave as ideal chains in polymer melt, in which amino acids lose their “identity” and therefore the memory of sequence position. As a result large-scale properties of the dimer become universal or sequence independent. Comparison of our simulations with the prior theoretical studies and their implications for experiments are discussed.
Theory of crosslinked bundles of helical filaments: Intrinsic torques in self-limiting biopolymer assemblies
Authors: Heussinger Claus , Grason Gregory M.
Published: July 2011

Inspired by the complex influence of the globular crosslinking proteins on the formation of biofilament bundles in living organisms, we study and analyze a theoretical model for the structure and thermodynamics of bundles of helical filaments assembled in the presence of crosslinking molecules. The helical structure of filaments, a universal feature of biopolymers such as filamentous actin, is shown to generically frustrate the geometry of crosslinking between the “grooves” of two neighboring filaments. We develop a coarse-grained model to investigate the interplay between the geometry of binding and mechanics of both linker and filament distortion, and we show that crosslinking in parallel bundles of helical filaments generates intrinsic torques, of the type that tend to wind the bundle superhelically about its central axis. Crosslinking mediates a non-linear competition between the preference for bundle twist and the size-dependent mechanical cost of filament bending, which in turn gives rise to feedback between the global twist of self-assembled bundles and their lateral size. Finally, we demonstrate that above a critical density of bound crosslinkers, twisted bundles form with a thermodynamically preferred radius that, in turn, increases with a further increase in crosslinking bonds. We identify the stiffness of crosslinking bonds as a key parameter governing the sensitivity of bundle structure and assembly to the availability and affinity of crosslinkers.
Hot electron transmission in metals using epitaxial NiSi2/n-Si(111) interfaces
Authors: Parui S. , Wit B. , Bignardi L. , Rudolf P. , Kooi B. , van Wees B. J. , Banerjee T.
Published: July 2011

We have investigated hot electron transmission across epitaxial metal-disilicide/n-Si(111) interfaces using ballistic electron emission microscopy (BEEM). Different crystal orientations of epitaxial NiSi2 were grown on a Si(111) substrate using molecular beam epitaxy. The presence of different interfaces of NiSi2 on Si(111) were confirmed by high resolution transmission electron microscopy. Electrical transport measurements reveal a clear rectifying Schottky interface with a barrier height of 0.69 eV. However, using BEEM, three different regions with different transmissions and Schottky barrier heights of 0.65 eV, 0.78 eV, and 0.71 eV are found. The addition of a thin Ni film on the NiSi2 layer strongly reduces the transmission in all the three regions and interestingly, almost equalizes the transmission across them.
Voltage-controlled tuning of an organic semiconductor distributed feedback laser using liquid crystals
Authors: Klinkhammer Sönke , Heussner Nico , Huska Klaus , Bocksrocker Tobias , Geislhöringer Felix , Vannahme Christoph , Mappes Timo , Lemmer Uli
Published: July 2011

Voltage-controlled continuous tuning of the laser wavelength of an organic distributed feedback laser is demonstrated by incorporation of liquid crystals (LCs) in the top cladding layer. Orientation of the LCs and hence the modal refractive index are controlled by applying a lateral electrical field. Laser emission shifts by 4 nm at an applied voltage of 675 V. The device showed lasing thresholds of about 286 nJ per pulse. The tuning behaviour is analyzed by implementation of a voltage-dependent spatial LC director orientation profile in a slab waveguide model and solving the Bragg condition to obtain the voltage-dependent lasing wavelength.
Dye-sensitized solar cell with a titanium-oxide-modified carbon nanotube transparent electrode
Authors: Kyaw A. K. K. , Tantang H. , Wu T. , Ke L. , Peh C. , Huang Z. H. , Zeng X. T. , Demir H. V. , Zhang Q. , Sun X. W.
Published: July 2011

Transparent and conductive carbon-based materials are promising for window electrodes in solid-state optoelectronic devices. However, the catalytic activity to redox reaction limits their application as a working electrode in a liquid-type dye-sensitized solar cell (DSSC). In this letter, we propose and demonstrate a transparent carbon nanotubes (CNTs) film as the working electrode in a DSSC containing iodide/triiodide redox couples. This implementation is realized by inhibiting the charge-transfer kinetics at CNT/redox solution interface with an aid of thin titanium oxide film that facilitates the unidirectional flow of electrons in the cell without sacrificing the electrical and optical properties of CNT.
Gold nanoresistors with near-constant resistivity in the cryogenic-to-room temperature range
Authors: Yajadda M. M. A. , Levchenko I. , Ostrikov K.
Published: July 2011

Using a multiple plasma deposition-annealing (MDA) technique, we have fabricated an Au nanoisland-based thin film nanoresistor with a very low temperature coefficient of electrical resistivity in a cryogenic-to-room temperature range of 10 to 300 K. The nanoislanded gold film was deposited on a SiO2/Si wafer (500 nm SiO2 thickness) between two 300 nm thick Au electrodes which were separated by 100 m. A sophisticated selection of the thickness of the nanoislanded gold film, the annealing temperature, as well as the number of deposition/annealing cycles resulted in the fabrication of a nanoresistor with a temperature coefficient of electrical resistivity of 2.1 × 10−3 K−1 and the resistivity deviation not exceeding 2% in a cryogenic-to-room temperature range. We have found that the constant resistivity regime of the nanoisland-based thin film nanoresistor corresponds to a minimized nanoisland activation energy (approximately 0.3 meV). This energy can be minimized by reducing the nearest neighbor distance and increasing the size of the Au nanoislands in the optimized nanoresistor structure. It is shown that the constant resistivity nanoresistor operates in the regime where the thermally activated electron tunneling is compensated by the negative temperature dependence of the metallic-type conductivity of nanoislands. Our results are relevant to the development of commercially viable methods of nanoresistor production for various nanoelectronics-based devices. The proposed MDA technique also provides the opportunity to fabricate large arrays of metallic nanoparticles with controllable size, shapes and inter-nanoparticle gaps.
First-principles study of field emission from carbon nanotubes and graphene nanoribbons
Authors: Driscoll Joseph A. , Cook Brandon , Bubin Sergiy , Varga Kálmán
Published: July 2011

A real-space, real-time implementation of time-dependent density functional theory is used to study electron field emission from nanostructures. Carbon nanotubes and graphene nanoribbons are used as model systems. The calculations show that carbon nanotubes with iron adsorbates have spin-polarized emission currents. Graphene nanoribbons are shown to be good field emitters with spatial variation of the emission current influenced by the presence of passivating hydrogen.
Inhomogeneous low temperature epitaxial breakdown during Si overgrowth of GeSi quantum dots
Authors: Petz C. W. , Floro J. A.
Published: July 2011

The low temperature epitaxial breakdown of inhomogeneously strained Si capping layers is investigated. By growing Si films on coherently strained GeSi quantum dot surfaces, we differentiate the effects of surface roughness, strain, and growth orientation on the mechanism of epitaxial breakdown. Using atomic force microscopy and high resolution cross-sectional transmission electron microscopy, we find that whereas local lattice strain of up to 2% has a negligible effect, growth on higher-index facets such as {113} significantly reduces the local breakdown thickness. Nanoscale growth mound formation is observed above all facet orientations. Because diffusion lengths depend directly on the surface orientation, we relate the variation in epitaxial thickness to the low temperature stability of specific growth facets and the average size of kinetically limited growth mounds.
Drop size control in electro-coflow
Authors: Vilanova N. , Gundabala V. R. , Fernandez-Nieves A.
Published: July 2011

We introduce electro-coflow as a way to generate emulsion drops with an average size that can be larger, comparable, and smaller than the smallest geometric feature of the device. The method relies on using three immiscible liquids, two of them having a finite electrical conductivity. There are three regimes of operation that allow the steady generation of drops: dripping, electro-dripping, and an electrically dominated regime. We transit from one to the other by increasing the applied voltage and describe the changes in drop size by balancing the relevant forces in each regime.
Field-free molecular orientation enhanced by two dual-color laser subpulses
Authors: Zhang Shian , Lu Chenhui , Jia Tianqing , Wang Zugeng , Sun Zhenrong
Published: July 2011

In this paper, we theoretically show that the field-free molecular orientation created by a single dual-color laser pulse can be significantly enhanced by separating it into two time-delayed dual-color subpulses. It is indicated that the maximum enhancement of the molecular orientation created by two time-delayed dual-color subpulses can be achieved with their intensity ratio of about 1:2 and by simultaneously applying the second one at the beginning of the rotational wave packet rephasing or the end of the rotational wave packet dephasing induced by the first one. It is also shown that the enhancement or suppression of the molecular orientation can be coherently manipulated by varying the relative phase between the fundamental field and its second harmonic field of the second dual-color subpulse, and its enhancement is obtained around half rotational period.
Open-circuit voltage dependency on hole-extraction layers in planar heterojunction organic solar cells
Authors: Kulshreshtha Chandramouli , Choi Jin Woo , Kim Jeong-kyu , Jeon Woo Sik , Suh Min Chul , Park Yougsup , Kwon Jang Hyuk
Published: July 2011

The open-circuit voltage (Voc) dependency on hole-extraction layers (HELs) with different energy levels and mobility was investigated in a single stack heterojunction subphthalocyanine chloride (SubPc)/C60 organic solar cells. The HELs having about 0.2–0.3 eV higher highest occupied molecular orbital (HOMO) level than that of a donor material can significantly enhance the Voc in SubPc/C60 device due to a corresponding built-in potential increase. The high mobility of HELs can also increase Voc with increasing Jsc according to the simple diode equation. Among all HELs we utilized, N,N,N′,N′-tetra(biphenyl-4-yl)biphenyl-4,4′-diamine (TBBD) illustrates a largest increase in Voc (from 0.90 to 1.15 V) with an improvement in efficiency compared to a reference SubPc/C60 device without HEL. This increase is mainly attributed to easy and rapid extraction of holes by TBBD due to its proper HOMO level and high mobility.
Superlattices of Bi2Se3/In2Se3: Growth characteristics and structural properties
Authors: Wang Z. Y. , Guo X. , Li H. D. , Wong T. L. , Wang N. , Xie M. H.
Published: July 2011

Superlattices (SLs) consisted of alternating Bi2Se3 and In2Se3 layers are grown on Si(111) by molecular-beam epitaxy. Bi2Se3, a three-dimensional topological insulator (TI), showed good chemical and structural compatibility with In2Se3, a normal band insulator with large energy bandgap. The individual layers in the SLs are very uniform, and the hetero-interfaces are sharp. Therefore, such SL structures are potential candidates for explorations of the quantum size effects of TIs.
Extraction of trapped charge in 4H-SiC metal oxide semiconductor field effect transistors from subthreshold characteristics
Authors: DasGupta Sandeepan , Brock Reinhard , Kaplar Robert , Marinella Matthew , Smith Mark , Atcitty Stanley
Published: July 2011

A technique for characterizing trapped charge in silicon carbide (SiC) metal oxide semiconductor field effect transistors (MOSFETs) based only on the subthreshold I-V characteristics and its degradation under bias temperature stress is described. The method utilizes the large departure of the subthreshold slope from a constant value, due to large and exponentially rising DIT (density of interface traps) near band edges for SiC/SiO2 interface. Elevated bias-temperature stress experiments demonstrate the feasibility of separating ΔNIT (increase in interface trapped charge) from slow trapping components like ΔNOT (increase in oxide trapped charge) with minimal error due to extrapolation of subthreshold current to midgap potentials. A slow trap, dissimilar to either interface or oxide states close to the interface, dominates degradation at elevated temperature.
Submillisecond-response polymer network liquid crystal phase modulators at 1.06-μm wavelength
Authors: Sun Jie , Xianyu Haiqing , Chen Yuan , Wu Shin-Tson
Published: July 2011

A fast-response and scattering-free polymer network liquid crystal (PNLC) light modulator is demonstrated at λ = 1.06 μm wavelength. A decay time of 117 μs for 2π phase modulation is obtained at 70 °C, which is ∼ 650 × faster than that of the host nematic LCs. The major tradeoff is the increased operating voltage. Potential applications include spatial light modulators and adaptive optics.
Symmetry exploitation in closed-shell coupled-cluster theory with spin-orbit coupling
Authors: Tu Zheyan , Yang Dong-Dong , Wang Fan , Guo Jingwei
Published: July 2011

In the present work, we report exploitation of spatial symmetry in calculations of ground state energy and analytic first derivatives of closed-shell molecules based on our previously developed coupled-cluster (CC) approach with spin-orbit coupling. Both time-reversal symmetry and spatial symmetry for D2h and its subgroups are exploited in the implementation. The symmetry of a certain spin case for the amplitude, intermediate, or density matrix is determined by the symmetry of the corresponding spin functions and the direct product decomposition method is employed in computations involving these quantities. The reduction in computational effort achieved through the use of spatial symmetry is larger than the order of the molecular single point group. Symmetry exploitation renders application of the CC approaches with spin-orbit coupling to larger closed-shell molecules containing heavy elements with high accuracy.
A low emittance and high efficiency visible light photocathode for high brightness accelerator-based X-ray light sources
Authors: Vecchione T. , Ben-Zvi I. , Dowell D. H. , Feng J. , Rao T. , Smedley J. , Wan W. , Padmore H. A.
Published: July 2011

Free-electron lasers and energy recovery linacs represent a new generation of ultra-high brightness electron accelerator based x-ray sources. Photocathodes are a critical performance-limiting component of these systems. Here, we describe the development of photocathodes based on potassium-cesium-antimonide that satisfy many of the key requirements of future light sources, such as robustness, high quantum efficiency when excited with visible light, and low transverse emittance.
The diatomic dication CuZn2+ in the gas phase
Authors: Diez Reinaldo Pis , Franzreb Klaus , Alonso Julio A.
Published: July 2011

In the present combined experimental and theoretical study we report the observation of the novel gas-phase dication CuZn2+ and provide some theoretical insight into the electronic binding of this exotic metastable molecule and its formation mechanism. Using mass spectrometry we have detected four isotopomer signals of CuZn2+ at half-integer m/z values for ion flight times of about 14 μs. CuZn2+ was unambiguously identified by its isotopic abundance. High-current energetic Ar+ ion bombardment of a brass surface was used for its production. Subsequent dication formation was found to take place in the ion extraction region of our mass spectrometer several tens of microns in front of the sputtered brass surface. The dication formation mechanism appears to be resonant electron transfer in soft gas-phase collisions between sputter-ejected singly charged CuZn+ molecular ions and incoming Ar+ projectiles. This conclusion is supported by our theoretical study that obtained an ionization energy of CuZn+ of 15.75 eV, in excellent agreement with both the experimental and calculated ionization energy of Ar (15.76 and 15.67 eV, respectively). The ground state of CuZn2+ is found to be a metastable one with a very shallow potential well at an internuclear equilibrium distance of about 2.7 Å, the dissociation energy being very difficult to estimate. Interestingly, spin-orbit corrections are found to be necessary to get an adequate description of the metastable state of CuZn2+, whereas relativistic corrections have no effects on neutral CuZn nor on CuZn+.
Carbon-assisted nucleation and vertical growth of high-quality ZnO nanowire arrays
Authors: Cheng Chun , Wong Tai Lun , Li Wei , Zhu Chao , Xu Shuigang , Wang Lin , Fung Kwok Kwong , Wang Ning
Published: July 2011

We developed a carbon-assisted physical-vapor-deposition method for the growth of highly aligned ZnO nanowire arrays on any flat substrates in large area. Amorphous carbon (a-C) films acted as the preferential nucleation sites to facilitate the growth of high-quality ZnO nanowire array patterns. The ultrathin a-C films can effectively retard the inclined growth of ZnO nanowires at the edge of the a-C patterns. The investigations of the nanowire structures, photoluminescence and electrical transport properties have shown that the ZnO nanowires were well crystallized and the formation of defects in the nanowires was largely suppressed.
Temperature dependence of ice critical nucleus size
Authors: Pereyra Rodolfo G. , Szleifer Igal , Carignano Marcelo A.
Published: July 2011

We present a molecular dynamics study of ice growth from supercooled water. By performing a series of simulations with different initial conditions, we have quantitative established the relationship existing between the critical nucleus size and the temperature. The results show that ice embryos containing hundreds or thousands of molecules are needed for the system to crystallize macroscopically, even at high degrees of supercooling. Our findings explain the difficulty in observing spontaneous ice nucleation in atomistic simulations and the relative ease with which water droplets can be supercooled under controlled experiments.
Effect of membrane charge density on the protein corona of cationic liposomes: Interplay between cationic charge and surface area
Authors: Caracciolo Giulio , Pozzi Daniela , Candeloro De Sanctis Sofia , Laura Capriotti Anna , Caruso Giuseppe , Samperi Roberto , Laganà Aldo
Published: July 2011

Here we investigate the effect of membrane charge density on the protein corona that forms upon exposure of cationic liposomes to human plasma. We show that the protein corona around cationic liposomes is not uniquely defined by membrane charge density, but it is deeply affected by both the overall cationic charge and the available surface area. Remarkably, changes in protein composition are largely removed when a correcting quantity accounting for the ratio between the cationic charge and the surface area of different cationic liposome formulations is considered.
Optical absorption in c-Si/a-Si:H core/shell nanowire arrays for photovoltaic applications
Authors: Xie W. Q. , Liu W. F. , Oh J. I. , Shen W. Z.
Published: July 2011

The optical properties have been numerically investigated in crystalline Si (c-Si)/hydrogenated amorphous Si (a-Si:H) core/shell nanowire (CSNW) arrays for various structural parameters. We have demonstrated that the light absorption can be greatly enhanced in c-Si/a-Si:H CSNW arrays especially for the weak absorption solar band (1.5–2.5 eV) of crystalline silicon nanowire (c-SiNW) arrays. We have also obtained the optimal parameters for photovoltaic applications, at which the photocurrent enhancement factors have been achieved to be 14% and 345% per volume material compared to in c-SiNW arrays and c-Si films, respectively. Furthermore, the underlying mechanism of the absorption enhancement in CSNW arrays has been discussed.
Communication: Momentum-resolved quantum interference in optically excited surface states
Authors: Chan Wai-Lun , Tritsch John , Dolocan Andrei , Ligges Manuel , Miaja-Avila Luis , Zhu X.-Y.
Published: July 2011

Surface states play essential roles in condensed matter physics, e.g., as model two-dimensional (2D) electron gases and as the basis for topological insulators. Here, we demonstrate quantum interference in the optical excitation of 2D surface states using the model system of C60/Au(111). These surface states are transiently populated and probed in a femtosecond time- and angle-resolved two-photon photoemission experiment. We observe quantum interference within the excited populations of these surface states as a function of parallel momentum vector. Such quantum interference in momentum space may allow one to control 2D transport properties by optical fields.
Development of microfabricated TiO2 channel waveguides
Authors: Furuhashi Masayuki , Fujiwara Masazumi , Ohshiro Takahito , Tsutsui Makusu , Matsubara Kazuki , Taniguchi Masateru , Takeuchi Shigeki , Kawai Tomoji
Published: July 2011

An optical channel waveguide is a key solution to overcome signal propagation delay. For the benefits of miniaturization, development of microfabrication process for waveguides is demanded. TiO2 is one of the suitable candidates for the microfabricated waveguide because of the high refractive index and the transparency. In the present study, conventional microfabrication processes manufactured TiO2 channel waveguides with 1–20 μm width on oxidized Si substrates and the propagation loss was measured. The prepared channels successfully guided light of 632.8 nm along linear and Y-branched patterns. The propagation loss for the linear waveguide was 9.7 dB/cm.
Student ambassador experience in higher education: Skills and competencies for the future?
Authors: Ylonen Annamari
Published: July 2011

Lifelong learning, where individuals keep modifying, renewing and updating their existing skills and competencies, is an essential requirement in the knowledge economy. Yet research has shown that employers often find it hard to hire individuals who are equipped with sufficiently rounded competencies in areas such as commitment, enthusiasm and timekeeping. The Student Ambassador (SA) scheme offers university students the opportunity to undertake relatively well‐paid and flexible part‐time jobs around widening participation initiatives, which, in general, focus on raising aspiration and attainment of young people from more disadvantaged backgrounds. This article examines research evidence into the SA scheme in South‐East London and, in particular, focuses on analysing whether the scheme offers students an ideal part‐time job opportunity while in higher education. It will be seen that SAs not only gain complex transferable skills while earning money, but also engage in something that they perceive to be a highly rewarding and valuable experience.
Thirty years of 14–19 education and training in England: reflections on policy, curriculum and organisation
Authors: Higham Jeremy , Yeomans David
Published: July 2011

This article traces and analyses some of the key features of 14–19 education and training in England over the 30 years since such a phase was first mooted. It does this through an introductory narrative outlining the key policies and initiatives and the development of six themes
drawing on analysis of a body of research and policy. The themes are: the waxing and waning of policy in relation to a 14–19 phase; policy imperatives driving 14–19 education and training; curricular commonality, differentiation and unification; pathways and progression; qualifications-led
curriculum change and partnership, institutional autonomy and competition. The article concludes by outlining the implications of the analysis for the current political and policy context in relation to education and training for 14- to 19-year-olds.
Educating 14- to 19-year-olds in England: a UK lens on possible futures
Authors: Hodgson Ann , Spours Ken
Published: July 2011

Here we draw on recent research and on earlier contributions on convergence and divergence across Great Britain to consider possible future trajectories for 14–19 education and training in England. We use a UK-wide lens to reflect on 14–19 strategies in England by showing
how common issues can be tackled in different ways in Scotland, Wales and Northern Ireland. The article identifies what could be seen as three models of upper secondary education – Type 1 (England); Type 2 (Scotland and Wales); and Type 3 (Northern Ireland) – that have been part
of the picture of divergence. We conclude that the process of divergence is likely to continue in the short-term but, in the longer term, wider political factors could produce post-devolution convergence.
Relativistic time transfer in the vicinity of the Earth and in the solar system
Authors: Nelson Robert A
Published: July 2011

The algorithms for relativistic time transfer in the vicinity of the Earth and in the solar system are derived. The concepts of proper time and coordinate time are distinguished. The coordinate time elapsed during the transport of a clock and the propagation of an electromagnetic signal is analysed in three coordinate systems: an Earth-Centred Inertial (ECI) coordinate system, an Earth-Centred Earth-Fixed (ECEF) coordinate system and a barycentric coordinate system. The timescales of Geocentric Coordinate Time (TCG), Terrestrial Time (TT) and Barycentric Coordinate Time (TCB) are defined and their relationships are discussed. Some numerical examples are provided to illustrate the magnitudes of the effects.
GNSS times and UTC
Authors: Lewandowski W , Arias E F
Published: July 2011

Global Navigation Satellite Systems (GNSSs) use internal reference time scales: GPS Time, GLONASS Time, Galileo System Time and BeiDou System Time. Constructed from a clock ensemble, they are designed for internal system synchronization, necessary to produce a navigation solution. They are usually steered to an external stable reference time scale, for example UTC(USNO), modulo 1 s, for GPS time. To achieve safe operation of a GNSS, a system time should preferably be a uniform time scale not affected by the leap seconds of Coordinated Universal Time (UTC). But this is not compatible with international recommendations that radio broadcast time signals should conform as closely as possible to UTC. This paper describes the various approaches chosen by GNSS providers and the relation between GNSS system times and UTC in terms of numbering of seconds. Different solutions for numbering seconds do not help the GNSS interoperability. This paper also explains why, on some occasions, GNSS system times play a role of alternative time scales with the consequent risk of confusion.