bluuebunny/crossref_metadata_2025 huggingface dataset:
Interfacial electronic structure of a hybrid organic-inorganic optical upconverter device: The role of interface states
Authors: Tsai K. Y. F. , Helander M. G. , Lu Z. H.
Published: April 2009

Organic-inorganic hybrid heterojunctions are critical for the integration of organic electronics with traditional Si and III-V semiconductor microelectronics. The amorphous nature of organic semiconductors eliminates the stringent lattice-matching requirements in semiconductor monolithic growth. However, as of yet it is unclear what driving forces dictate the energy-level alignment at hybrid organic-inorganic heterojunctions. Using photoelectron spectroscopy we investigate the energy-level alignment at the hybrid organic-inorganic heterojunction formed between S-passivated InP(100) and several commonly used hole injection/transport molecules, namely, copper phthalocyanine (CuPc), N,N′-diphenyl-N,N′-bis-(1-naphthyl)-1-1′-biphenyl-4,4′-diamine (α-NPD), and fullerene (C60). The energy-level alignment at the hybrid organic-inorganic heterojunction is found to be consistent with traditional interface dipole theory, originally developed to describe Schottky contacts. Contrary to conventional wisdom, hole injection from S-passivated InP(100) into an organic semiconductor is found to originate from interface states at or near the Fermi level, rather than from the valance band maximum of the semiconductor. As a result the barrier height for hole injection is defined by the offset between the surface Fermi level of the S-passivated InP(100) and the highest occupied molecular orbital of the organic. This finding sheds new light on the unusual trend in device performance reported in literature for such hybrid organic-inorganic heterojunction devices.
Lattice location study of implanted In in Ge
Authors: Decoster S. , De Vries B. , Wahl U. , Correia J. G. , Vantomme A.
Published: April 2009

We report on emission channeling experiments to determine the lattice location and the thermal stability of implanted I111n atoms in Ge. The majority of the In atoms was found on the substitutional site, which is a thermally stable site at least up to 500 °C. We also found strong indication that directly after implantation, a fraction of the implanted I111n atoms occupies the bond-centered (BC) site. This fraction disappears after annealing at 300 °C. From comparison with ab initio calculations, electrical studies, and perturbed angular correlation experiments, the In atoms on the BC site can be related to In-vacancy and In-self-interstitial defect complexes. The activation energy for dissociation of this BC related defect was found to be below 1.6 eV.
Tunable GaN/AlGaN ultraviolet detectors with built-in electric field
Authors: Korona K. P. , Drabińska A. , Caban P. , Strupiński W.
Published: April 2009

We present the optical and the electrical properties of GaN/AlGaN structures that can be used as tunable ultraviolet photodetectors. The photosensitivity spectrum of the structures can be tuned in the range 3.5–3.85 eV by external voltage. The photosensitivity of the sample in the 3.5 eV spectral range increases about 500 times when the reverse bias changes from −2 to −6 V. The effect can be explained by changes in the electric field in the GaN/AlGaN structure. The field is generated by the internal electric polarization and the external bias. We present also a numerical modeling of the electric field, the potential profiles, and the current flow in such structures. Our modeling shows that at low bias a two-dimensional (2D)-electron gas at the AlGaN/GaN interface screens the electric field generated by spontaneous polarization. The lack of the field stops transport of photoexcited holes. The holes that are accumulated on the interface causes fast electron recombination and reduces photocurrent. The external electric field can move the 2D-electron gas and increase photocurrent from the GaN layer.
Phase separation in carbon-nickel films during hyperthermal ion deposition
Authors: Abrasonis G. , Kovács Gy. J. , Ryves L. , Krause M. , Mücklich A. , Munnik F. , Oates T. W. H. , Bilek M. M. M. , Möller W.
Published: April 2009

Microstructure evolution as a function of the substrate temperature and metal content of C:Ni nanocomposite films grown by hyperthermal ion deposition is investigated. The films were grown by pulsed filtered cathodic vacuum arc on thermally oxidized Si substrates held at temperatures in the range from room temperature (RT) to 500 °C and with the metal content ranging from 7 to 40 at. %. The elemental depth profiles and composition were determined by elastic recoil detection analysis. The film morphology and phase structure were studied by means of cross-sectional transmission electron microscopy and selected area electron diffraction. For RT deposition a transition from repeated nucleation dominated toward self-organized growth of alternating carbon and crystalline nickel carbide layers is observed at a Ni threshold content of ∼40 at. %. The surface diffusion increases concomitantly with the growth temperature resulting in the formation of elongated/columnar structures and a complete separation of the film constituents into the coexisting carbon and fcc Ni phases. At the highest growth temperature (500 °C) Ni shows a tendency to segregate at the surface of the growing film and to form a continuous layer for integrated Ni contents of ≥30 at. %. A corresponding structure zone model diagram is presented, and the results are discussed on the basis of the ion induced atomic displacement, temperature activated adatom diffusion, and the metallic island coalescence processes whose complex interplay results in the observed variety of the microstructures.
Highly stretchable, conductive, and transparent nanotube thin films
Authors: Hu Liangbing , Yuan Wei , Brochu Paul , Gruner George , Pei Qibing
Published: April 2009

We have studied the electrical and optical properties of transparent and conductive nanotube thin films subjected to extremely large strains, both isotropic and anisotropic. The films maintain electrical conductivity for strains up to 700% and the eventual loss of conductivity is due primarily to the buildup of cracks in the nanotube films. We also measured the change in optical transmittance and explain the observed haziness of the films by considering the micrometer sized cluster. This study of transparent nanotube films as stretchable electrodes is crucial for many applications, in particular, for medical implantation of electronic devices.
Improving the acousto-optical interaction in a Mach–Zehnder interferometer
Authors: Dühring Maria B. , Sigmund Ole
Published: April 2009

A method for modeling the interaction of the mechanical field from a surface acoustic wave and the optical field in the waveguides of a Mach–Zehnder interferometer is presented. The surface acoustic wave is generated by an interdigital transducer using a linear elastic plane model of a piezoelectric, inhomogeneous material, and reflections from the boundaries are avoided by applying perfectly matched layers. The optical modes in the waveguides are modeled by time-harmonic wave equations for the magnetic field. The two models are coupled using stress-optical relations and the change in effective refractive index introduced in the Mach–Zehnder interferometer arms by the stresses from the surface acoustic wave is calculated. It is then shown that the effective refractive index of the fundamental optical mode increases at a surface acoustic wave crest and decreases at a trough. The height and the width of the waveguides are varied for a silicon on insulator sample, and it is shown that the difference in effective refractive index between the waveguides can be increased 12 times for the right choice of waveguide size such that the optical modulation is improved. The difference is four times bigger if the waveguides are kept single moded. It is furthermore shown that the difference increases more than ten times when the waveguides are buried below the surface, where the mechanical stresses have their maximum, and in the case where two interdigital transducers are used the difference is increased 1.5 times.
Mean field limit for bosons and propagation of Wigner measures
Authors: Ammari Z. , Nier F.
Published: April 2009

We consider the N-body Schrödinger dynamics of bosons in the mean field limit with a bounded pair-interaction potential. According to the previous work [Ammari, Z. and Nier, F., “Mean field limit for bosons and infinite dimensional phase-space analysis,” Ann. Henri Poincare 9, 1503 (2008)], the mean field limit is translated into a semiclassical problem with a small parameter ε→0, after introducing an ε-dependent bosonic quantization. The limits of quantum correlation functions are expressed as a push forward by a nonlinear flow (e.g., Hartree) of the associated Wigner measures. These object and their basic properties were introduced by Ammari and Nier in the infinite dimensional setting. The additional result presented here states that the transport by the nonlinear flow holds for a rather general class of quantum states in their mean field limit.
Simulation of a particle-laden turbulent channel flow using an improved stochastic Lagrangian model
Authors: Arcen Boris , Tanière Anne
Published: April 2009

The purpose of this paper is to examine the Lagrangian stochastic modeling of the fluid velocity seen by inertial particles in a nonhomogeneous turbulent flow. A new Langevin-type model, compatible with the transport equation of the drift velocity in the limits of low and high particle inertia, is derived. It is also shown that some previously proposed stochastic models are not compatible with this transport equation in the limit of high particle inertia. The drift and diffusion parameters of these stochastic differential equations are then estimated using direct numerical simulation (DNS) data. It is observed that, contrary to the conventional modeling, they are highly space dependent and anisotropic. To investigate the performance of the present stochastic model, a comparison is made with DNS data as well as with two different stochastic models. A good prediction of the first and second order statistical moments of the particle and fluid seen velocities is obtained with the three models considered. Even for some components of the triple particle velocity correlations, an acceptable accordance is noticed. The performance of the three different models mainly diverges for the particle concentration and the drift velocity. The proposed model is seen to be the only one which succeeds in predicting the good evolution of these latter statistical quantities for the range of particle inertia studied.
A hybrid encapsulation method for organic electronics
Authors: Kim N. , Potscavage W. J. , Domercq B. , Kippelen B. , Graham S.
Published: April 2009

We report a thin-film encapsulation method for organic electronics that combines the deposition of a layer of SiOx or SiNx (100 nm) by plasma enhanced chemical vapor deposition followed by a layer of Al2O3 (10–50 nm) by atomic layer deposition and a 1-μm-thick layer of parylene by chemical vapor deposition. The effective water vapor transmission rates of the encapsulation was (2±1)×10−5 g/m2 day at 20 °C and 50% relative humidity (RH). The encapsulation was integrated with pentacene/C60 solar cells, which showed no decrease in conversion efficiency after 5800 h of exposure to air demonstrating the effectiveness of the encapsulation methodology.
Merging and colliding bores
Authors: Bestehorn Michael , Tyvand Peder A.
Published: April 2009

Interactions between two undular bores in a long rectangular channel are studied by solving the two-dimensional Laplace equation with fully nonlinear free-surface conditions. Each bore is generated by a steady bottom source or sink that is turned on impulsively. Two types of nonlinear interaction between bores are investigated: (1) The merging of two bores that move in the same direction. (2) The collision of two bores that move in opposite directions.
Coverage of dynamic correlation effects by density functional theory functionals: Density-based analysis for neon
Authors: Jankowski K. , Nowakowski K. , Grabowski I. , Wasilewski J.
Published: April 2009

The problem of linking the dynamic electron correlation effects defined in traditional ab initio methods [or wave function theories (WFTs)] with the structure of the individual density functional theory (DFT) exchange and correlation functionals has been analyzed for the Ne atom, for which nondynamic correlation effects play a negligible role. A density-based approach directly hinged on difference radial-density (DRD) distributions defined with respect the Hartree–Fock radial density has been employed for analyzing the impact of dynamic correlation effects on the density. Attention has been paid to the elimination of basis-set incompleteness errors. The DRD distributions calculated by several ab initio methods have been compared to their DFT counterparts generated for representatives of several generations of broadly used exchange-correlation functionals and for the recently developed orbital-dependent OEP2 exchange-correlation functional [Bartlett et al., J. Chem. Phys. 122, 034104 (2005)]. For the local, generalized-gradient, and hybrid functionals it has been found that the dynamic correlation effects are to a large extend accounted for by densities resulting from exchange-only calculations. Additional calculations with self-interaction corrected exchange potentials indicate that this finding cannot be explained as an artifact caused by the self-interaction error. It has been demonstrated that the VWN5 and LYP correlation functionals do not represent any substantial dynamical correlation effects on the electron density, whereas these effects are well represented by the orbital-dependent OEP2 correlation functional. Critical comparison of the present results with their counterparts reported in literature has been made. Some attention has been paid to demonstrating the differences between the energy- and density-based perspectives. They indicate the usefulness of density-based criteria for developing new exchange-correlation functionals.
On the robustness of NK-Kauffman networks against changes in their connections and Boolean functions
Authors: Zertuche Federico
Published: April 2009

N K -Kauffman networks LKN are a subset of the Boolean functions on N Boolean variables to themselves, ΛN={ξ:Z2N→Z2N}. To each NK-Kauffman network it is possible to assign a unique Boolean function on N variables through the function Ψ:LKN→ΛN. The probability PK that Ψ(f)=Ψ(f′), when f′ is obtained through f by a change in one of its K-Boolean functions (bK:Z2K→Z2), and/or connections, is calculated. The leading term of the asymptotic expansion of PK, for N⪢1, turns out to depend on the probability to extract the tautology and contradiction Boolean functions, and in the average value of the distribution of probability of the Boolean functions, the other terms decay as O(1/N). In order to accomplish this, a classification of the Boolean functions in terms of what I have called their irreducible degree of connectivity is established. The mathematical findings are discussed in the biological context, where Ψ is used to model the genotype-phenotype map.
Two-dimensional hybrid simulations of the oblique electromagnetic alpha/proton instability in the solar wind
Authors: Lu Quanming , Du Aimin , Li Xing
Published: April 2009

In the solar wind, alpha particles are observed to flow faster than the core protons. In this paper, two-dimensional hybrid simulations are performed to investigate the nonlinear evolution of oblique Alfvén waves excited by an alpha/proton beam instability in a low beta plasma. The propagation angles of the excited waves are within a finite range suggesting the generation of oblique Alfvén waves. During the nonlinear evolution, both the wave numbers and frequencies of the waves drift to smaller values, and the propagation angles decrease. At the same time, the propagation angle of the dominant mode also changes. Eventually the plasma system reaches a marginally stable state according to linear theory.
Tailoring the hydraulic impedance of out-of-plane micromachined electrospray sources with integrated electrodes
Authors: Krpoun R. , Smith K. L. , Stark J. P. W. , Shea H. R.
Published: April 2009

Hydraulic impedance is a critical parameter for the operation of electrospray emitters, and for preventing flooding when spraying from arrays of emitters. Controlling flow rate by tuning the flow impedance allows accessing different operating modes, such as droplet, ionic, or pulsating. We report on a method to tailor the hydraulic impedance of micromachined capillary out-of-plane emitters with integrated extractor electrodes by filling them with silica microspheres. Spraying the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), we demonstrate the ability to tune from droplet emission to pure ion emission depending on microbead diameter, obtaining stable emission from single emitters and from arrays of 19 emitters.
Rapidly pulsed helium droplet source
Authors: Pentlehner Dominik , Riechers Ricarda , Dick Bernhard , Slenczka Alkwin , Even Uzi , Lavie Nachum , Brown Raviv , Luria Kfir
Published: April 2009

A pulsed valve connected to a closed-cycle cryostat was optimized for producing helium droplets. The pulsed droplet beam appeared with a bimodal size distribution. The leading part of the pulse consists of droplets suitable for doping with molecules. The average size of this part can be varied between 104 and 106 helium atoms, and the width of the distribution is smaller as compared to a continuous-flow droplet source. The system has been tested in a single pulse mode and at repetition rates of up to 500 Hz with almost constant intensity. The droplet density was found to be increased by more than an order of magnitude as compared to a continuous-flow droplet source.
Apparatus and method to measure dielectric properties (ε′ and ε″) of ionic liquids
Authors: Göllei Attila , Vass András , Pallai Elisabeth , Gerzson Miklós , Ludányi Lajos , Mink János
Published: April 2009

Conventional techniques for measurement of dielectric properties of ionic liquids or electrolyte solutions fail because the samples are largely short circuited by the high electrical conductance. The object of the author’s research activity was to elaborate an apparatus (microwave dielectrometer) and method suitable to measure the dielectric constant (ε′) and loss factor (ε″) of well conducting ionic liquids and other solvents. This process is based on a revised waveguide method completed with an automatic calibration possibility. Contrary to conventional measuring methods this technique uses about 20 W/g power density. The measurements were carried out at 2.45 GHz frequency in the temperature range from 10 up to 100 °C. The obtained (ε′) and (ε″) values of different solvents were compared with several published (calculated and measured) data. Statistical analysis was used to determine the error of measurements and distilled water was chosen as a standard for study of data dispersion. To accomplish statistical analysis, namely, the dielectric characteristics have to be determined at the same temperature. The values of variances were less or equal 1 in case of ε′ and decrease with increasing temperature. In case of ε″ the variance data were much smaller.
Spin-charge-lattice coupling through resonant multimagnon excitations in multiferroic BiFeO3
Authors: Ramirez M. O. , Kumar A. , Denev S. A. , Chu Y. H. , Seidel J. , Martin L. W. , Yang S.-Y. , Rai R. C. , Xue X. S. , Ihlefeld J. F. , Podraza N. J. , Saiz E. , Lee S. , Klug J. , Cheong S. W. , Bedzyk M. J. , Auciello O. , Schlom D. G. , Orenstein J. , Ramesh R. , Musfeldt J. L. , Litvinchuk A. P. , Gopalan V.
Published: April 2009

Spin-charge-lattice coupling mediated by multimagnon processes is demonstrated in multiferroic BiFeO3. Experimental evidence of two- and three-magnon excitations as well as multimagnon coupling at electronic energy scales and high temperatures are reported. Temperature dependent Raman experiments show up to five resonant enhancements of the two-magnon excitation below the Néel temperature. These are shown to be collective interactions between on-site Fe d-d electronic resonance, phonons, and multimagnons.
Collisionless plasma expansion into vacuum: Two new twists on an old problem
Authors: Arefiev Alexey V. , Breizman Boris N.
Published: April 2009

The paper deals with a generic problem of collisionless plasma expansion into vacuum in the regimes where the expanding plasma consists of hot electrons and cold ions. The expansion is caused by electron pressure and serves as an energy transfer mechanism from electrons to ions. This process is often described under the assumption of Maxwellian electrons, which easily fails in the absence of collisions. The paper discusses two systems with a naturally occurring non-Maxwellian distribution: an expanding laser-irradiated nanoplasma and a supersonic jet coming out of a magnetic nozzle. The presented rigorous kinetic description demonstrates how the deviation from the Maxwellian distribution fundamentally alters the process of ion acceleration during plasma expansion. This result points to the critical importance of a fully kinetic treatment in problems with collisionless plasma expansion.
Nanoporous silica-water interfaces studied by sum-frequency vibrational spectroscopy
Authors: Zhang Luning , Singh Seema , Tian Chuanshan , Shen Y. Ron , Wu Yan , Shannon Mark A. , Brinker C. Jeffery
Published: April 2009

Using sum-frequency vibrational spectroscopy, we found that water structure at nanoporous silica/water interfaces depended on the nanoporous film structure. For a periodic, self-assembled nanoporous film with monosized 2 nm pores occupying 20% of the top surface area, the surface vibrational spectrum was dominated by water in contact with silica, bare or covered by silane, at the top surface. It resembled the spectral characteristic of the hydrophilic water/silica or the hydrophobic water/silane interface. For a fractal nanoporous film with pores ranging from 5 to 50 nm in size occupying 90% of the top surface, the spectrum for a trimethyl silane-coated superhydrophobic porous film resembled largely that of a water/air interface. Only when the silane was completely removed would the spectrum revert to that characteristic of a hydrophilic water/silica interface. The surface charging behaviors of the bare nanoporous films in water with different pH were monitored by spectroscopic measurements and atomic force microscopy force measurements. The point of zero charge for the periodic porous film is around pH 2, similar to that of the flat silica surface. The point of zero charge could only be determined to be pH<6 for the fractal porous film because the thin fractal solid network limited the amount of surface charge and therefore, the accuracy of the measurements.
Comment on three-point function in AdS(3)/CFT(2)
Authors: Giribet Gaston , Nicolás Lorena
Published: April 2009

Recently, exact agreement has been found between bulk and boundary three-point functions in AdS3×S3×T4 with Neveu-Schwarz-Neveu-Schwarz (NSNS) fluxes. This represents a nontrivial check of AdS/CFT correspondence beyond the supergravity approximation as it corresponds to an exact worldsheet computation. When taking a closer look at this computation, one notices that a crucial point for the bulk-boundary agreement to hold is an intriguing mutual cancellation between worldsheet contributions corresponding to the AdS3 and to the S3 pieces of the geometry, that results in a simple factorized form for the final three-point function. In this note we review this cancellation and clarify some points about the analytic relation between the SU(2) and the SL(2,R) structure constants. In particular, we dicuss the connection to the Coulomb gas representation. We also make some comments on the four-point function.
Conformational behavior of diblock comb copolymers
Authors: Konovalov M. A. , Kramarenko E. Yu. , Khokhlov A. R. , Reineker P.
Published: April 2009

The conformational behavior of a single diblock copolymer chain with comb blocks is studied by computer simulation. The comb blocks have equal lengths of the backbones and side chains and differ only by the degree of grafting of the side chains. The collapse behavior is studied for two cases: (i) comb diblock copolymer with attracting backbones of the blocks and swollen side chains and (ii) comb diblock copolymer with attracting monomer units of the side chains of the blocks and swollen backbones. In both cases the conformation of a globule with a tail is observed when one of the block collapses while the other stays swollen. At high attraction micellar-type globules are formed. The core of the micelle consists of attracting monomeric units and the soluble segments (side chains or backbones) comprise the corona. It is shown that separation of monomeric units belonging to different blocks can take place both in the core and in the corona regions of the micelle.
Density functional theory for adsorption of colloids on the polymer-tethered surfaces: Effect of polymer chain architecture
Authors: Xu Xiaofei , Cao Dapeng
Published: April 2009

A density functional theory is used to investigate adsorption of colloids on the surfaces grafted by polymers of different architectures, including linear, star, branched, and dendritic structures. In order to calculate the direct bonding connectivity integral, a new numerical algorithm is proposed for polymers with complex architecture. A good agreement of the calculated results and the simulation and experimental data in studying grafted hard chain brushes confirm that our approach does lead a correct prediction. Accordingly, adsorption of colloids in the negative exponential attractive surface was studied. The effects of grafting density, attractive strength, molecular concentration, and size on adsorption were considered. The contour maps of excluded rate show that a complex architecture of polymer chains is much more effective in preventing adsorption than linear polymer brush. The results also show that the grafting density and complex architecture are two key factors to prevent colloidal adsorption, while the surface attractive strength only exhibits slight effect on colloidal adsorption. For polymer brushes with complex architecture, the height of potential of mean force is strongly dependent on the colloidal size. The larger the size, the higher is the potential of mean force, which means that the larger colloidal molecules are harder to penetrate the brush. In short, to prevent colloidal adsorption, it is more suitable to use the polymer brushes with complex architecture.
Defect reduction in (112¯2) semipolar GaN grown on m-plane sapphire using ScN interlayers
Authors: Johnston C. F. , Moram M. A. , Kappers M. J. , Humphreys C. J.
Published: April 2009

The effect of ScN interlayer thickness on the defect density of (112¯2) semipolar GaN grown on m-plane sapphire was studied by transmission electron microscopy. The interlayers comprised Sc metal deposited on a GaN seedlayer that was nitrided before GaN overgrowth by metal-organic vapor-phase epitaxy. Both interlayer thicknesses reduced the dislocation density by a factor of 100 to low-108 cm−2. The 8.5 nm interlayer produced regions that were free from basal plane stacking faults (BSF) and dislocations. The overall BSF density here was reduced by a factor of 5, to (6.49±0.07)×104 cm−1, without the need for an ex situ mask patterning step.
Amorphous silicon thin-film transistors with field-effect mobilities of 2 cm2/V s for electrons and 0.1 cm2/V s for holes
Authors: Han Lin , Mandlik Prashant , Cherenack Kunigunde H. , Wagner Sigurd
Published: April 2009

A new gate dielectric material is used to fabricate hydrogenated amorphous-silicon (a-Si:H) thin-film transistors (TFTs) with high field-effect mobilities. The dielectric is a homogeneous SiO2-silicone hybrid, which is deposited by plasma-enhanced chemical vapor deposition system at nominal room temperature. This new dielectric results in a-Si:H TFTs with measured field-effect mobilities of ∼2 cm2/V s for electrons and ∼0.1 cm2/V s for holes.
On dynamic heterogeneity in supercooled liquids
Authors: Graessley William W.
Published: April 2009

A simplified molecular theory for the dynamics of liquids near the glass transition temperature Tg is developed and compared with experimental viscosity and diffusion behavior. Its basis is the spatial fluctuations of local density, a property that depends on isothermal compressibility and thus occurs naturally in all liquids at equilibrium. Instantaneous liquid structure is approximated by randomly distributed arrays of two domains having either higher or lower density than the average. The time dependence of fluctuations is represented by a sequence of such structures, each having a lifetime that varies with the macroscopic density. The dynamic environment of a molecule within a domain (slow or fast) depends on the density of its domain (high or low). Translational diffusion and orientational relaxation depend on different averages of the slow and fast domain contributions and lead, on approaching Tg, to a progressive departure from the Stoke–Einstein relationship. Predictions are made using macroscopic viscosity-density relationships within the individual domains. They depend only on the choice of domain size, which, according to this formulation, is insensitive to temperature. The data for three well-studied nonpolymeric liquids were found to be in reasonable accord with NMR assessments of domain size.
Plasmonic Bloch oscillations in chirped metal-dielectric structures
Authors: Davoyan Artur R. , Shadrivov Ilya V. , Sukhorukov Andrey A. , Kivshar Yuri S.
Published: April 2009

We study the propagation of plasmon polaritons in one-dimensional chirped metal-dielectric layered structures. We find an optical Wannier–Stark ladder in the mode spectrum and analyze Bloch oscillations associated with the coupling of surface plasmons localized at the metal-dielectric interfaces. For long structures, we find that the energy flow may dramatically change its direction, thus providing possibilities for the beam steering in the transmission band.
Nonlinear oscillators for vibration energy harvesting
Authors: Gammaitoni L. , Neri I. , Vocca H.
Published: April 2009

Vibration to electricity energy conversion strategies are discussed by using nonlinear stochastic dynamics. General principles for the exploitation of nonlinear oscillators in energy harvesting that provide useful leads for the realization of micropower generators of practical interest are presented.
Pure rotational spectra of the CCCF radical
Authors: Yoshikawa Takashi , Sumiyoshi Yoshihiro , Endo Yasuki
Published: April 2009

Pure rotational transitions of a new carbon-chain radical CCCF in a supersonic jet have been observed for the first time using a Fourier-transform microwave spectrometer with a pulsed-discharge nozzle. The radical was produced by a pulsed electric discharge in a C2H2 and CF4 mixture diluted to 0.1% and 0.1% with Ne, respectively. Rotational transitions with spin and hyperfine splittings have been observed in the region from 9.1 GHz for NKaKc=101−000 to 27.3 GHz for NKaKc=303−202. The rotational constant, the spin-rotation interaction constant, and the hyperfine coupling constants due to the F nucleus have been precisely determined from the least-squares analysis, yielding B¯=4555.8043(44), γeff=−7.105(16), bF,eff=368(19), and ceff=−284.832(61) MHz. The determined molecular constants were compared with those obtained from high-level ab initio calculations and concluded that the CCCF radical has a bent ground state X̃A2′.
A variable torque motor compatible with magnetic resonance imaging
Authors: Roeck W. W. , Ha S-H. , Farmaka S. , Nalcioglu O.
Published: April 2009

High magnetic fields used in magnetic resonance imaging (MRI) do not allow the employment of conventional motors due to various incompatibility issues. This paper reports on a new motor that can operate in or near high field magnets used for MRI. The motor was designed to be operational with the MRI equipment and could be used in a rotating imaging gantry inside the magnet designed for dual modality imaging. Furthermore, it could also be used for image guided robotic interventional procedures inside a MRI system if so desired. The prototype motor was developed using magnetic resonance (MR) compatible materials, and its functionality with MR imaging was evaluated experimentally by measuring the performance of the motor and its effect on the MR image quality. Since in our application, namely, single photon emission tomography, the motor has to perform precise stepping of the gantry in small angular steps the most important parameter is the start-up torque. The experimental results showed that the motor has a start-up torque up to 1.37 Nm and rotates at 196 rpm when a constant voltage difference of 12 V is applied at a magnetic field strength of 1 T. The MR image quality was quantified by measuring the signal-to-noise of images acquired under different conditions. The results presented here indicate that the motor is MR compatible and could be used for rotating an imaging gantry or a surgical device inside the magnet.
Superhydrophobic cellulose-based bionanocomposite films from Pickering emulsions
Authors: Bayer Ilker S. , Steele Adam , Martorana Philip J. , Loth Eric , Miller Lance
Published: April 2009

Inherently superhydrophobic and flexible cellulose-based bionanocomposites were fabricated from solid stabilized (Pickering) emulsions. Emulsions were formed by dispersing cyclosiloxanes in water stabilized by layered silicate particles and were subsequently modified by blending into a zinc oxide nanofluid. The polymer matrix was a blend of cellulose nitrate and fluoroacrylic polymer (Zonyl 8740) precompatibilized in solution. Coatings were spray cast onto aluminum substrates from polymer blends dispersed in modified Pickering emulsions. No postsurface treatment was required to induce superhydrophobicity. Effect of antiseptic additives on bionanocomposite superhydrophobicity is also discussed. Replacing cellulose nitrate with commercial liquid bandage solutions produced identical superhydrophobic coatings.
Twist defect in an imprinted cholesteric elastomer
Authors: Castro-Garay P. , Reyes J. Adrian , Corella-Madueño A.
Published: April 2009

We have found that a chiral twist defect inserted in a cholesteric elastomer gives rise to circularly polarized localized modes of both handedness. This defect enhances the resonant mode amplitude whose handedness is opposite to that of the cholesteric helix for high cross-linked density, whereas for low cross-linked density, the same mode is decoupled with the defect and thus the resonant mode disappears. Finally, the resonant mode of the same handedness as the elastomer helix is maintained for both high and low cross-linked density.
Phase-resolved two-dimensional spectroscopy based on collinear n-wave mixing in the ultrafast time domain
Authors: Kuehn W. , Reimann K. , Woerner M. , Elsaesser T.
Published: April 2009

We present a novel approach for femtosecond two-dimensional (2D) spectroscopy in the midinfrared combining a collinear beam geometry and phase-resolved detection. Two phase-locked pulses of variable time delay τ interact with the sample. The transmitted electric fields are measured in real time t by electro-optic sampling. 2D spectra are generated by Fourier transforming the signal along the two time axes τ and t. In the 2D spectra, nonlinear signals originating from different orders n in the electric field are separated. Such decomposition of the overall response is demonstrated by mapping the nonlinear response of intersubband transitions in GaAs/AlGaAs multiple quantum wells.
On the unsteady behavior of turbulence models
Authors: Rubinstein R. , Bos W. J. T.
Published: April 2009

Periodically forced turbulence is used as a test case to evaluate the predictions of two-equation and multiple-scale turbulence models in unsteady flows. The limitations of the two-equation model are shown to originate in the basic assumption of spectral equilibrium. A multiple-scale model based on a picture of stepwise energy cascade overcomes some of these limitations, but the absence of nonlocal interactions proves to lead to poor predictions of the time variation of the dissipation rate. A new multiple-scale model that includes nonlocal interactions is proposed and shown to reproduce the main features of the frequency response correctly.
Extracting energetically dominant flow features in a complicated fish wake using singular-value decomposition
Authors: Ting Shang-Chieh , Yang Jing-Tang
Published: April 2009

We developed a method to extract the energetically dominant flow features in a complicated fish wake according to an energetic point of view, and applied singular-value decomposition (SVD) to two-dimensional instantaneous fluid velocity, vorticity and λ2 (vortex-detector) data. We demonstrate the effectiveness and merits of the use of SVD through an example regarding the wake of a fish executing a fast-start turn. The energy imparted into the water by a swimming fish is captured and portrayed through SVD. The analysis and interpretation of complicated data for the fish wake are greatly improved, and thus help to characterize more accurately a complicated fish wake. The velocity vectors and Galilean invariants (i.e., vorticity and λ2) resulting from SVD extraction are significantly helpful in recognizing the energetically dominant large-scale flow features. To obtain successful SVD extractions, we propose useful criteria based on the Froude propulsion efficiency, which is biologically and physically related. We also introduce a novel and useful method to deduce the topology of dominant flow motions in an instantaneous fish flow field, which is based on combined use of the topological critical-point theory and SVD. The concept and approach proposed in this work are useful and adaptable in biomimetic and biomechanical research concerning the fluid dynamics of a self-propelled body.
Si nanowire ion-sensitive field-effect transistors with a shared floating gate
Authors: Nishiguchi Katsuhiko , Clement Nicolas , Yamaguchi Toru , Fujiwara Akira
Published: April 2009

Ion-sensitive field-effect transistors (ISFETs) arrayed in parallel were fabricated on a silicon-on-insulator substrate. Since the nanoscale wire channels of the ISFETs are bridged with a floating gate on which molecules are preferably immobilized, signals originating from charged materials only on the floating gate can appear and can therefore be distinguished from background noise, which leads to noise-robust sensing. Additionally, the nanoscale channels provide the ISFETs with single-electron-resolution charge sensitivity as well as a reduction in background noise induced in the wider channels used as electrical leads. These features promise the detection of a small number of molecules.
Pseudo spin valves based on L1 (111)-oriented FePt fixed layers with tilted anisotropy
Authors: Zha C. L. , Persson J. , Bonetti S. , Fang Y. Y. , Åkerman Johan
Published: April 2009

We demonstrate magnetoresistance (MR) in excess of 4% in FePt/CoFe/Cu/CoFe/NiFe pseudo spin valves based on L10 (111)-oriented FePt fixed layers with a 36° out-of-plane tilted magnetization. The high MR is achieved by increasing the spin polarization at the Cu interfaces, using thin CoFe, and optimizing the FePt growth and Cu interface quality using Ta and Ta/Pt underlayers. We observe well-separated switching of the FePt/CoFe fixed layer and the CoFe/NiFe free layer, suggesting that CoFe is rigidly exchange coupled to FePt and NiFe in the respective layers.
Ferromagnetism of undoped GaN mediated by through-bond spin polarization between nitrogen dangling bonds
Authors: Jin Hao , Dai Ying , Huang BaiBiao , Whangbo M.-H.
Published: April 2009

Room-temperature ferromagnetism occurs in GaN nanoparticles even without any doped magnetic ions. The cause for this finding was examined by performing density functional calculations for the bulk GaN and the nonpolar surface of GaN with Ga- and N-vacancies. Our work indicates that the room-temperature ferromagnetism of undoped GaN nanoparticles originates from the nitrogen dangling bonds associated with the surface Ga-vacancies. The spins of the nitrogen dangling bonds couple ferromagnetically by through-bond spin polarization, and this ferromagnetic coupling is effective even when the vacancy separation is as long as ∼8 Å.
Ultradense phosphorus in germanium delta-doped layers
Authors: Scappucci G. , Capellini G. , Lee W. C. T. , Simmons M. Y.
Published: April 2009

Phosphorus (P) in germanium (Ge) δ-doped layers are fabricated in ultrahigh vacuum by adsorption of phosphine molecules onto an atomically flat clean Ge(001) surface followed by thermal incorporation of P into the lattice and epitaxial Ge overgrowth by molecular beam epitaxy. Structural and electrical characterizations show that P atoms are confined, with minimal diffusion, into an ultranarrow 2-nm-wide layer with an electrically active sheet carrier concentration of 4×1013 cm−2 at 4.2 K. These results open up the possibility of ultranarrow source/drain regions with unprecedented carrier densities for Ge n-channel field effect transistors.
Highly phosphorescent organic mixed films: The effect of aggregation on triplet-triplet annihilation
Authors: Reineke Sebastian , Schwartz Gregor , Walzer Karsten , Falke Meiken , Leo Karl
Published: April 2009

The efficiency roll-off at high brightness levels is a key factor limiting the application of organic light emitting diodes. We investigate triplet-triplet annihilation in an archetype phosphorescent host-guest system. We show that the currently used host-guest systems are not at the physical limit set by intrinsic annihilation, but have an increased roll-off due to aggregate formation. The existence of these aggregates is directly proven by transmission electron microscopy.
Surface charge dynamics on ferroelectric PbZr0.48Ti0.52O3 films responding to the switching bias of electric force microscope
Authors: Son J. Y. , Lee Geunhee , Shin Y.-H.
Published: April 2009

We investigated the role of surface charges in writing and reading ferroelectric bits on an epitaxial PbZr0.48Ti0.52O3 thin film by electric force microscopy (EFM). The sign of EFM surface potential was reversed within several hundred microseconds for 10 V. For a negative bias voltage of −10 V, EFM surface potential was reversed in several milliseconds. The different time scales of the EFM surface potential reversals originate from the screening of the ferroelectric polarization charges by the surface charges which pass over two different Schottky barriers depending on the applied bias polarity.
Muscle hypertrophy driven by myostatin blockade does not require stem/precursor-cell activity
Authors: Amthor Helge , Otto Anthony , Vulin Adeline , Rochat Anne , Dumonceaux Julie , Garcia Luis , Mouisel Etienne , Hourdé Christophe , Macharia Raymond , Friedrichs Melanie , Relaix Frederic , Zammit Peter S. , Matsakas Antonios , Patel Ketan , Partridge Terence
Published: April 2009

Myostatin, a member of the TGF-β family, has been identified as a powerful inhibitor of muscle growth. Absence or blockade of myostatin induces massive skeletal muscle hypertrophy that is widely attributed to proliferation of the population of muscle fiber-associated satellite cells that have been identified as the principle source of new muscle tissue during growth and regeneration. Postnatal blockade of myostatin has been proposed as a basis for therapeutic strategies to combat muscle loss in genetic and acquired myopathies. But this approach, according to the accepted mechanism, would raise the threat of premature exhaustion of the pool of satellite cells and eventual failure of muscle regeneration. Here, we show that hypertrophy in the absence of myostatin involves little or no input from satellite cells. Hypertrophic fibers contain no more myonuclei or satellite cells and myostatin had no significant effect on satellite cell proliferation in vitro, while expression of myostatin receptors dropped to the limits of detectability in postnatal satellite cells. Moreover, hypertrophy of dystrophic muscle arising from myostatin blockade was achieved without any apparent enhancement of contribution of myonuclei from satellite cells. These findings contradict the accepted model of myostatin-based control of size of postnatal muscle and reorient fundamental investigations away from the mechanisms that control satellite cell proliferation and toward those that increase myonuclear domain, by modulating synthesis and turnover of structural muscle fiber proteins. It predicts too that any benefits of myostatin blockade in chronic myopathies are unlikely to impose any extra stress on the satellite cells.
Three related receptor-like kinases are required for optimal cell elongation in
Arabidopsis thaliana
Authors: Guo Hongqing , Li Lei , Ye Huaxun , Yu Xiaofei , Algreen Alexandria , Yin Yanhai
Published: April 2009

Cell elongation in plants is controlled by environmental cues such as light and internal growth regulators including plant steroid hormones, brassinosteroids (BRs). In this study, we found that 3 related receptor-like kinases (RLKs), HERCULES1, THESEUS1, and FERONIA, are transcriptionally induced by BRs and are down-regulated in the loss-of-function BR mutant
bri1
and up-regulated in the constitutive BR-response mutant
bes1-D
. These RLKs belong to the CrRLK family that has 17 members in
Arabidopsis
. We hypothesize that these RLKs are involved in BR-regulated processes. Although 2 of the RLKs were recently found to mediate male-female interaction during pollen tube reception (FERONIA) and to sense cell wall integrity (THESEUS1), our genetic studies demonstrated that they are required for cell elongation during vegetative growth as
herk1 the1
double and
fer
RNAi mutants displayed striking dwarf phenotypes. The
herk1 the1
double mutant enhances the dwarf phenotype of
bri1
and partially suppresses
bes1-D
phenotype, supporting a role of HERK1/THE1 in BR-mediated cell elongation. Microarray experiments demonstrated that these RLKs control the expression of a unique set of genes including those implicated in cell elongation and 16% of the genes affected in
herk1 the1
are regulated by BRs. Our results, therefore, identify a previously unknown pathway that functions cooperatively with, but largely independent of the BR pathway to regulate cell elongation. The work establishes a platform to identify other signaling components in this important pathway for plant growth and provides a paradigm to study the coordination of independent pathways in the regulation of a common biological process.
Earliest domestication of common millet (
Panicum miliaceum
) in East Asia extended to 10,000 years ago
Authors: Lu Houyuan , Zhang Jianping , Liu Kam-biu , Wu Naiqin , Li Yumei , Zhou Kunshu , Ye Maolin , Zhang Tianyu , Zhang Haijiang , Yang Xiaoyan , Shen Licheng , Xu Deke , Li Quan
Published: April 2009

The origin of millet from Neolithic China has generally been accepted, but it remains unknown whether common millet (
Panicum miliaceum
) or foxtail millet (
Setaria italica
) was the first species domesticated. Nor do we know the timing of their domestication and their routes of dispersal. Here, we report the discovery of husk phytoliths and biomolecular components identifiable solely as common millet from newly excavated storage pits at the Neolithic Cishan site, China, dated to between
ca.
10,300 and
ca.
8,700 calibrated years before present (cal yr BP). After
ca.
8,700 cal yr BP, the grain crops began to contain a small quantity of foxtail millet. Our research reveals that the common millet was the earliest dry farming crop in East Asia, which is probably attributed to its excellent resistance to drought.