bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficient treatment of the Hartree interaction in the relativistic Kohn-Sham problem
Authors: Matveev Alexei V. , Majumder Sonjoy , Rösch Notker
Published: October 2005

We elaborate the two-component Douglas-Kroll reduction of the Dirac-Kohn-Sham problem of relativistic density-functional theory as introduced by Matveev and Rösch [J. Chem. Phys. 118, 3997 (2003)]. That method retains corrections to the Coulomb self-interaction (or Hartree) term of the energy functional that are due to the picture change. Using analytic expressions for the matrix elements, one is able to abandon the resolution of the identity approach for a crucial step of the relativistic transformation. Thus, a major source of uncertainties of the method is eliminated because basis sets no longer have to be extended by functions of higher angular momentum, previously required to ensure kinetic balance. This approach also relies on the electron charge-density fitting scheme via an auxiliary basis set. An efficient approximate implementation results if one restricts the relativistic transformation to the spherically symmetric atom-centered auxiliary functions. It provides accurate results while simplifying greatly the expressions for the matrix elements of the relativistically transformed operators and significantly reducing the computational effort. We demonstrate the performance of the method for the fine structure of one-electron levels of the Hg atom, the g-tensor shifts of NO2, and the properties of the diatomic molecules Bi2, Pb2, PbO, and TlH.
Electron acceleration by lower hybrid waves in magnetic reconnection regions
Authors: Cairns Iver H. , McMillan B. F.
Published: October 2005

A new model for electron acceleration in magnetic reconnection regions is developed analytically, tested using quasilinear simulations, and the qualitative predictions compared with observations of reconnection in Earth’s magnetotail and the solar corona. The model involves lower hybrid (LH) waves, produced by a drift instability (LHDI) in reconnection regions, stochastically accelerating electrons parallel to the magnetic field by the Cherenkov resonance (LH drive or LHD). Analytic theory shows that LH waves produced by LHDI have the correct wave numbers to cause parallel electron acceleration from thermal to highly superthermal and even relativistic energies, for sufficiently low plasma β and long evolution times. Several previous Vlasov and particle-in-cell simulations show growth of LH waves by LHDI. Assuming that LHDI produces LH waves with the wave numbers and energy densities (≈50% that of the thermal ion plasma) found in the Vlasov simulations, quasilinear simulations with the correct mass ratio show creation of a superthermal electron tail resonant with the LH waves and parallel to B. The tail reaches about 20 electron thermal speeds in ≈600 lower hybrid times but extends to higher speeds with increasing time. When applied to Wind spacecraft data from Earth’s magnetotail, the model is qualitatively consistent with the occurrence of LH waves, primarily parallel electron acceleration, no ion acceleration, and overall time scale for the acceleration event. Similarly, it is not inconsistent with the primarily parallel electron acceleration, perpendicular ion heating, and time scales inferred from x-ray and radio observations of solar flares. Moreover, the conversion efficiencies from thermal and magnetic energies to semirelativistic electrons are estimated to be over 100 times lower for the magnetotail reconnection data than for the solar corona, not unexpected from the model since LH waves should be favored by the lower plasma beta conditions found in the corona.
Dynamics of glass-forming liquids. X. Dielectric relaxation of 3-bromopentane as molecular probes in 3-methylpentane
Authors: Huang Wei , Shahriari Shervin , Richert Ranko
Published: October 2005

The glass-forming liquids 3-bromopentane (3BP) and 3-methylpentane (3MP) are readily miscible across the entire composition range, although their polarities differ considerably. As noted by Berberian [J. Non-Cryst. Solids 131-133, 48 (1991)], the nearly matching molar volumes makes this binary system appear ideal for probe-sensitized measurements. We have performed a dielectric study of these mixtures in the range of 3BP mole fractions x from 2×10−4 to 0.75. In the limit of low concentrations, x<0.5%, the dielectric loss peak of 3BP is slower by a factor of 2.5 relative to that of 3MP. Additionally, the relaxation behavior of the guest is more exponential than that of the host liquid. We interpret the distinct dynamics of the guest as a result of temporal averaging over the heterogeneous host dynamics, with the exchange time being near the longest structural time constant of the system.
Spatial resolution limits in electron-beam-induced deposition
Authors: Silvis-Cividjian N. , Hagen C. W. , Kruit P.
Published: October 2005

Electron-beam-induced deposition (EBID) is a versatile micro- and nanofabrication technique based on electron-induced dissociation of metal-carrying gas molecules adsorbed on a target. EBID has the advantage of direct deposition of three-dimensional structures on almost any target geometry. This technique has occasionally been used in focused electron-beam instruments, such as scanning electron microscopes, scanning transmission electron microscopes (STEM), or lithography machines. Experiments showed that the EBID spatial resolution, defined as the lateral size of a singular deposited dot or line, always exceeds the diameter of the electron beam. Until recently, no one has been able to fabricate EBID features smaller than 15–20nm diameter, even if a 2-nm-diam electron-beam writer was used. Because of this, the prediction of EBID resolution is an intriguing problem. In this article, a procedure to theoretically estimate the EBID resolution for a given energetic electron beam, target, and gaseous precursor is described. This procedure offers the most complete approach to the EBID spatial resolution problem. An EBID model was developed based on electron interactions with the solid target and with the gaseous precursor. The spatial resolution of EBID can be influenced by many factors, of which two are quantified: the secondary electrons, suspected by almost all authors working in this field, and the delocalization of inelastic electron scattering, a poorly known effect. The results confirm the major influence played by the secondary electrons on the EBID resolution and show that the role of the delocalization of inelastic electron scattering is negligible. The model predicts that a 0.2-nm electron beam can deposit structures with minimum sizes between 0.2 and 2nm, instead of the formerly assumed limit of 15–20nm. The modeling results are compared with recent experimental results in which 1-nmW dots from a W(CO)6 precursor were written in a 200-kV STEM on a 30-nm SiN membrane.
Space-charge effects in the catcher gas cell of a rf ion guide
Authors: Takamine A. , Wada M. , Ishida Y. , Nakamura T. , Okada K. , Yamazaki Y. , Kambara T. , Kanai Y. , Kojima T. M. , Nakai Y. , Oshima N. , Yoshida A. , Kubo T. , Ohtani S. , Noda K. , Katayama I. , Hostain P. , Varentsov V. , Wollnik H.
Published: October 2005

Slow radioactive ion beams have been produced with an overall efficiency of 4% by thermalizing energetic ions produced by a projectile fragment separator in a He-gas cell and guiding them to a vacuum vessel by dc and rf fields. Space charge was observed to have a limiting effect. Since the ionization of He atoms by energetic ions creates a region of high space charge, many thermalized ions of interest are pushed toward the walls of the gas cell. Such losses have been investigated for different incoming ion intensities.
X-ray flux from filtered arrays of detectors without unfolding
Authors: Fehl D. L. , Stygar W. A. , Chandler G. A. , Cuneo M. E. , Ruiz C. L.
Published: October 2005

A simple computational method is proposed for estimating the time-dependent flux F[ΔE](t) of an x-ray spectrum S(E,t) over domain [ΔE] from data Dk(t)(k=1,…,N) obtained by an N-channel array of filtered detectors. It is assumed that the data are related to the spectrum by a discrete, inhomogeneous, first-kind Fredholm integral equation Dk=∫S(E,t)Rk(E)dE, where Rk(E) is the known response function for each detector channel of the diagnostic. The proposed method constructs a spectral sensitivity HLS(E) for the diagnostic array as a linear combination ∑k=1NakRk(E) of the responses, where the coefficients ak are obtained by a least-squares criterion plus a constraint. The ak values, once determined, apply as long as the responses are valid. The flux estimate is then simply FLS(t)=∑k=1NakDk(t), without a spectral unfold of the data. The method is useful for quick analyses of time-dependent data, for comparisons with other flux-measuring diagnostics, and for the experimental design of filtered-detector arrays. The method is applied to a five-channel array of filtered photoemissive x-ray detectors [G. A. Chandler et al., Rev. Sci. Instrum. 70, 561 (1999)], used for z-pinch measurements at the Z-accelerator facility [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)]. Comparisons with unfold results are made, and a first-order analysis of error propagation into FLS(t) is presented.
Size-dependent structures of NanIn−1+ cluster ions with a methanol adsorbate: A combined study by photodissociation spectroscopy and density-functional theory calculation
Authors: Misaizu Fuminori , Tsuruta Mamoru , Tsunoyama Hironori , Furuya Ari , Ohno Koichi , Lintuluoto Masami
Published: October 2005

Methanol adsorption sites on NanIn−1+ ions were investigated. Photoexcitation to charge-transfer states of NanIn−1+ (methanol) predominantly produces two fragment ions: Nan−1In−2+ (methanol) (neutral NaI loss) and Nan−1In−2+ (neutral NaI and methanol loss), without forming NanIn−1+ (methanol loss). The relative intensities of these fragments are correlated with the geometries and binding energies.
Colossal dielectric and electromechanical responses in self-assembled polymeric nanocomposites
Authors: Huang Cheng , Zhang Q. M. , Li Jiang Yu , Rabeony Manese
Published: October 2005

An electroactive polymer nanocomposite, in which high dielectric constant copper phthalocyanine oligomer (o-CuPc) nanoparticles are incorporated into the block polyurethane (PU) matrix by the combination of “top down” and “bottom up” approaches, was realized. Such an approach enables the nanocomposite to exhibit colossal dielectric and electromechanical responses with very low volume fraction of the high dielectric constant o-CuPc nanofillers (∼3.5%) in the composite. In contrast, a simple blend of o-CuPc and PU composite with much higher o-CuPc content (∼16% of o-CuPc) shows much lower dielectric and electromechanical responses.
Surface-plasmon resonance of Ag nanoparticles in polyimide
Authors: Lim Sung K. , Chung Keum J. , Kim C. K. , Shin Dong W. , Kim Young-Ho , Yoon Chong S.
Published: October 2005

Ag nanoparticles were fabricated by sandwiching a Ag thin film (2.5–15nm thick) between two polyimide precursor layers. During imidization, depending on the initial Ag film thickness, 10–20nm sized Ag nanoparticles arranged in a monolayer were formed within the polymer matrix. The Ag particles exhibited a pronounced localized surface-plasmon resonance effect. The resonance wavelength (460–540nm) can be easily tuned by ±40nm by simply changing the Ag film thickness which alters the mean particle diameter. The classical Mie model was introduced to explain the size dependence of the plasmon peaks.
Electron Bernstein wave excitation by counterpropagating electromagnetic waves in a plasma
Authors: Kumar Asheel , Tripathi V. K.
Published: October 2005

Two high-power counterpropagating electromagnetic waves (ω1,k1x̂) and (ω2,−k2x̂) in a low-density plasma in the presence of a static magnetic field Bsẑ, drive an electron Bernstein wave at the beat frequency ω=ω1−ω2 and k=(k1+k2)x̂, when ω∼ωc⪡ω1,ω2 and kρ≥1, where ωc is the electron cyclotron frequency and ρ is the Larmor radius. The electromagnetic waves exert a ponderomotive force on the electrons and resonantly drive the Bernstein mode(ω,k). When the pump waves have finite z extent, the Bernstein wave has an effective kz and a component of group velocity in the direction of the magnetic field, leaking it out of the interaction region, limiting the level of the Bernstein mode. Plasma inhomogeneity also introduces convection losses. However, the electron Bernstein mode potential could still be significantly greater than the ponderomotive potential.
Nonlinear elasticity and yielding of depletion gels
Authors: Kobelev Vladimir , Schweizer Kenneth S.
Published: October 2005

A microscopic activated barrier hopping theory of the viscoelasticity of colloidal glasses and gels has been generalized to treat the nonlinear rheological behavior of particle-polymer suspensions. The quiescent cage constraints and depletion bond strength are quantified using the polymer reference interaction site model theory of structure. External deformation (strain or stress) distorts the confining nonequilibrium free energy and reduces the barrier. The theory is specialized to study a limiting mechanical description of yielding and modulus softening in the absence of thermally induced barrier hopping. The yield stress and strain show a rich functional dependence on colloid volume fraction, polymer concentration, and polymer-colloid size asymmetry ratio. The yield stress collapses onto a master curve as a function of the polymer concentration scaled by its ideal mode-coupling gel boundary value, and sufficiently deep in the gel is of an effective power-law form with a universal exponent. A similar functional and scaling dependence of the yield stress on the volume fraction is found, but the apparent power-law exponent is nonuniversal and linearly correlated with the critical gel volume fraction. Stronger gels are generally, but not always, predicted to be more brittle in the strain mode of deformation. The theoretical calculations appear to be in accord with a broad range of observations.
Dynamic yielding, shear thinning, and stress rheology of polymer-particle suspensions and gels
Authors: Kobelev Vladimir , Schweizer Kenneth S.
Published: October 2005

The nonlinear rheological version of our barrier hopping theory for particle-polymer suspensions and gels has been employed to study the effect of steady shear and constant stress on the alpha relaxation time, yielding process, viscosity, and non-Newtonian flow curves. The role of particle volume fraction, polymer-particle size asymmetry ratio, and polymer concentration have been systematically explored. The dynamic yield stress decreases in a polymer-concentration- and volume-fraction-dependent manner that can be described as apparent power laws with effective exponents that monotonically increase with observation time. Stress- or shear-induced thinning of the viscosity becomes more abrupt with increasing magnitude of the quiescent viscosity. Flow curves show an intermediate shear rate dependence of an effective power-law form, becoming more solidlike with increasing depletion attraction. The influence of polymer concentration, particle volume fraction, and polymer-particle size asymmetry ratio on all properties is controlled to a first approximation by how far the system is from the gelation boundary of ideal mode-coupling theory (MCT). This emphasizes the importance of the MCT nonergodicity transition despite its ultimate destruction by activated barrier hopping processes. Comparison of the theoretical results with limited experimental studies is encouraging.
Energy relaxation versus spectral diffusion of the OH-stretching vibration of HOD in liquid-to-supercritical deuterated water
Authors: Schwarzer Dirk , Lindner Jörg , Vöhringer Peter
Published: October 2005

The dynamics of vibrational energy relaxation (VER) of the OH-stretching vibration of HOD in liquid-to-supercritical heavy water is studied as a function of temperature and solvent density by femtosecond mid-infrared spectroscopy. Using the dielectric constant of the fluid both, the OH-stretching absorption frequency and the VER rate, can be correlated phenomenologically with the average hydrogen-bond connectivity within the random D2O network. This correlation enables the identification of thermodynamic conditions under which spectral diffusion due to hydrogen-bond breakage/formation is much faster than VER.
Physical model of retention and temperature-dependent polarization reversal in ferroelectric films
Authors: Stolichnov I. , Tagantsev A. K. , Colla E. , Setter N. , Cross J. S.
Published: October 2005

The phenomenon of time-dependent polarization loss in poled ferroelectric capacitors, also known as retention, represents one of the most important reliability issues for ferroelectric nonvolatile memories. In a number of publications different ways to control retention by varying ferroelectric material composition or processing have been proposed, but no quantitative physical model of this phenomenon is available so far. The goal of the present work is to fill this gap by proposing a retention model that describes the polarization loss as a function of time and temperature. This model considers polarization switching to be driven by the depolarization field occurring in a poled ferroelectric film capacitor. For this purpose the earlier-proposed nucleation-limited switching concept was extended to enable the description of polarization reversal versus temperature, time, and voltage. Temperature-dependent performance of ferroelectric nonvolatile memories is another important issue. The proposed approach employs the same concept for modeling the temperature dependence of polarization switching and retention loss. The theoretical predictions were verified using experimental data measured on Pb(Zr,TiO)3 ferroelectric film capacitors. Based on the proposed model we formulate a device-oriented algorithm that enables the following important predictions for the ferroelectric film capacitors based on relatively fast and simple tests: (a) Prediction of switching curves characterizing the reversed polarization versus time at different temperatures, based on room-temperature data only. (b) Prediction of retention properties for long periods up to ten years extrapolated from short 24-h test results. (c) Prediction of retention properties at elevated temperatures based on the room-temperature results, or, alternatively, use of the accelerated test at high temperature for characterization of the retention performance at room temperature.
Control of magnetic vortex chirality in square ring micromagnets
Authors: Libál A. , Grimsditch M. , Metlushko V. , Vavassori P. , Jankó B.
Published: October 2005

We investigate the effect of a deliberately introduced shape asymmetry on magnetization reversal in small, square-shaped, magnetic rings. The magnetization reversal process is investigated using the diffracted magneto-optical Kerr effect combined with micromagnetic simulations. Experimentally we find that the reversal path is sensitive to small (±1°) changes in the direction of the applied field. Micromagnetic simulations that reproduce the measured zeroth- and first-order loops allow us to identify the reversal mechanisms as due to different intermediate states, namely, the so-called vortex and horseshoe states. Based on our results we are now able to prescribe a methodology for writing a vortex state with specific chirality in these asymmetric rings. Such control will be necessary if patterned arrays of this kind are to be used as magnetic storage elements.
Mechanism for improvements of optical properties of 1.3-μm InAs∕GaAs quantum dots by a combined InAlAs–InGaAs cap layer
Authors: Liu H. Y. , Tey C. M. , Sellers I. R. , Badcock T. J. , Mowbray D. J. , Skolnick M. S. , Beanland R. , Hopkinson M. , Cullis A. G.
Published: October 2005

The optical and structural properties of InAs quantum dots (QDs) with a thin InAlAs–InGaAs composite cap layer have been systematically investigated by photoluminescence and transmission electron microscopy (TEM). A number of improvements in the optical properties are observed with the use of an InAlAs–InGaAs cap layer, instead of InGaAs. These include a redshift of the emission, a reduction of the photoluminescence linewidth, an increased separation between the ground- and first-excited-state transitions, and an enhancement of the photoluminescence intensity at room temperature. To understand these optical improvements, the structural characteristics of the dots are studied by cross-sectional TEM. The height of the QDs is found to increase with increasing InAlAs thickness in the InAlAs–InGaAs cap layer. In addition, scanning TEM is used to qualitatively map the Al distribution in the vicinity of the QDs. These studies indicate that Al atoms are not deposited directly above the QDs in the present structures and hence that the InAlAs cap layer mainly affects the lateral potential barrier of the QDs. The improvements of the QD optical properties can thus be explained in terms of the increased QD height and lateral potential barrier. A consideration of mass transport during the capping process provides a possible growth mechanism responsible for the formation of taller InAs dots when capped with a thin Al-containing layer.
Electronic spatial distribution of In0.53Ga0.47As∕AlAs0.56Sb0.44 quantum-cascade lasers
Authors: Vitiello Miriam S. , Scamarcio Gaetano , Spagnolo Vincenzo , Revin Dmitry G. , Cockburn John , Steer Matthew J. , Airey Robert J.
Published: October 2005

We have investigated the band-to-band photoluminescence of In0.53Ga0.47As∕AlAs0.56Sb0.44 quantum-cascade devices operating at λ∼4.3μm, based either on normally grown or nominally As-terminated interfaces. This technique allowed us to probe the spatial distribution of conduction electrons as a function of the applied voltage and to correlate the quantum design of devices with their thermal performance.
Electrical resistance of island-containing thin metal interconnects on polymer substrates under high strain
Authors: Wang D. P. , Biga Frederick Y. , Zaslavsky A. , Crawford Gregory P.
Published: October 2005

We have deposited thin metal films that include a granular indium layer on polymer substrates and observed the resistance of the film changed by a factor of less than 2, even as the sample is uniaxially stretched to the point of rupture (∼38% strain). The presence of a discontinuous layer of indium islands in these films maintains the electrical conductivity by providing a bridging mechanism across the cracks formed in the underlying continuous film layers. A simple model is used to relate the applied strain to the electrical resistance of the metal films. Furthermore, we present the data for these films under cyclic loading around a cylindrical mandrel which show that there is no change in resistance under these fatigue testing conditions for 10 000 loading cycles.
Development of a three-dimensional scanning microparticle image velocimetry system using a piezo actuator
Authors: Shinohara Kyosuke , Sugii Yasuhiko , Jeong Jae Hong , Okamoto Koji
Published: October 2005

A technique for measuring the full field (x,y,z,u,v,w) velocity distribution of fluid flow at a micrometer scale spatial resolution has been developed. To investigate three-dimensional (3D) flow structures on a microscopic scale, a 3D scanning microparticle image velocimetry system was developed by combining a high-speed camera, an epifluorescent microscope, a cw laser, and a piezo actuator. Both numerical simulations and an experiment were carried out in order to validate the measurement accuracy of the system. Optimum measurement conditions were determined by numerical simulations using synthetic images under epifluorescent microscope observation. As a demonstration, the three-dimensional velocity distribution of water flow inside a microround tube having a diameter of 95μm was measured at a spatial resolution of 5.4×2.7×4.2μm.
Tip-enhanced fluorescence imaging of quantum dots
Authors: Huang Fu Min , Festy Frederic , Richards David
Published: October 2005

We have imaged the fluorescence from a single quantum dot cluster using an apertureless scanning near-field optical microscope. When a sharp gold tip is brought within a few nanometers from the sample surface, the resulting enhancement in quantum dot fluorescence in the vicinity of the tip leads to a resolution of about 60nm. We determine this enhancement of the fluorescence to be about fourfold in magnitude, which is consistent with the value expected as a result of competition between fluorescence quenching and electromagnetic field enhancement.
Double-handed circular Bragg phenomena in polygonal helix thin films
Authors: van Popta Andy C. , Brett Michael J. , Sit Jeremy C.
Published: October 2005

Oblique-incidence physical vapor deposition has been used to create optical thin films with a polygonal helix-shaped nanostructure. A series of titanium dioxide thin films are investigated, including triangle, square, pentagon, and star-shaped polygonal helices. Experimental optical measurements reveal a double-handed circular Bragg response: at one frequency band a polygonal helix reflects left-handed circularly polarized light, and at a second frequency band reflects right-handed circularly polarized light. The relative wavelength dependence of each reflection band is determined by the physical structure of the polygonal helix, a property that is set during the thin-film deposition process. Spectral-hole polarization filters, produced by adding twist and spacing layer defects to polygonal helix thin films, are also reported.
Shear flow driven drift waves and the counter-rotating vortices
Authors: Haque Q. , Saleem H. , Mirza Arshad M.
Published: October 2005

It is shown that the drift waves can become unstable due to the shear flow produced by externally applied electric field. The modified Rayleigh instability condition is obtained which is applicable to both electron-ion and electron-positron-ion plasmas. It is proposed that the shear flow driven drift waves can be responsible for large amplitude electrostatic fluctuations in tokamak edges. In the nonlinear regime the stationary structures may appear in electron-positron-ion plasmas as well as electron-ion plasmas. A particular form of the shear flow can give rise to counter-rotating dipole vortices and vortex chains. The speed and amplitude of the structures are affected by the presence of positrons in the electron ion plasma. The relevance of this investigation to laboratory and astrophysical plasmas is pointed out.
Pressure-induced structural phase transition in CaCrO4: Evidence from Raman scattering studies
Authors: Long Y. W. , Zhang W. W. , Yang L. X. , Yu Y. , Yu R. C. , Ding S. , Liu Y. L. , Jin C. Q.
Published: October 2005

Raman spectroscopic studies have been carried out on CaCrO4 under pressure up to 26.2GPa at ambient temperature. The Raman spectra showed that CaCrO4 underwent a continuous structural phase transition started near 6GPa, and finished at about 10GPa. It was found that the high-pressure phase could be quenched to ambient conditions. Pressure dependence of the Raman peaks suggested that there existed four pressure regions related to different structural characters. We discussed these characters and inferred that the nonreversible structural transition in CaCrO4, most likely was from a zircon-type (I41∕amd) ambient phase to a scheelite-type high-pressure structure (I41∕a).
Modeling of electric energy harvesting using piezoelectric windmill
Authors: Priya Shashank
Published: October 2005

This letter reports a theoretical model for determination of generated electric power from piezoelectric bimorph transducers in low frequency range far from the piezoelectric resonance. The model is divided into two parts. In the first part the open circuit voltage response of the transducer under the ac stress is computed based on the bending beam theory for bimorph. In the second part, this open circuit voltage acts as the input to the equivalent circuit of the capacitor connected across a pure resistive load. The results of the theoretical model were verified by comparing it with the measured response of a prototype windmill. The prototype piezoelectric windmill consisting of ten piezoelectric bimorph transducers was operated in the wind speed of 1–12 mph. A power of 7.5 mW at the wind speed of 10 mph was measured across a matching load of 6.7kΩ. The theoretical model was found to give very accurate prediction of the generated power and matching load and an excellent matching was found with the experimental results.
Organic field-effect transistors based on a crosslinkable polymer blend as the semiconducting layer
Authors: Yan He , Yoon Myung-Han , Facchetti Antonio , Marks Tobin J.
Published: October 2005

For fabrication of top-gate polymer-based organic field-effect transistors (OFETs), it is essential that the semiconducting layer remain intact during spin coating of the overlying dielectric layer. This requirement severely limits the applicable solvent and materials combinations. We show here that a crosslinkable polymer blend consisting of a p-type semiconducting polymer {e.g., TFB; poly[9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine]} and an electroactive crosslinkable silyl reagent {e.g., TPDSi2; 4,4′-bis[(p-trichloro-silylpropylphenyl)phenylamino]biphenyl} is effective as the semiconducting layer in a top-gate bottom-contact OFET device. The TFB+TPDSi2 semiconducting blend is prepared by spin-coating in ambient. The crosslinking process occurs during spin-coating in air and is completed by curing at 90 °C, which renders the resulting film insoluble in common organic solvents and allows subsequent deposition of dielectric layers from a wide range of organic solvents. We also show that the presence of TPDSi2 in the semiconductor layer significantly reduces typical TFB-source-drain threshold voltages in bottom-contact devices, likely due to favorable interfacial TPDSi2-gold electrode interactions.
Charge injection and trapping in silicon nanocrystals
Authors: Rafiq M. A. , Tsuchiya Y. , Mizuta H. , Oda S. , Uno Shigeyasu , Durrani Z. A. K. , Milne W. I.
Published: October 2005

The temperature dependence of the conduction mechanism in thin films of ∼8nm diameter silicon nanocrystals is investigated using Al∕Sinanocrystal∕p-Si∕Al diodes. A film thickness of 300 nm is used. From 300 to 200 K, space charge limited current, in the presence of an exponential distribution of trapping states, dominates the conduction mechanism. Using this model, a trap density Nt=2.3×1017cm−3 and a characteristic trap temperature Tt=1670K can be extracted. The trap density is within an order of magnitude of the nanocrystal number density, suggesting that most nanocrystals trap single or a few carriers at most.
Two-dimensional numerical simulation of the splitting and uniting of current-carrying zones in a dielectric barrier discharge
Authors: Zhang Yuan Tao , Wang De Zhen , Wang Yan Hui
Published: October 2005

In this paper, the splitting and uniting of the current-carrying zones in a dielectric barrier discharge are investigated at atmospheric pressure, and the motion of such zone is also referred while the discharge is developing. These phenomena are examined by the two-dimensional computational simulation with uniform initial conditions. The generation and annihilation of such zones are discussed according to the simulation results. The charges accumulated on the barrier surface are shown to play a dominant role in the global spatial-temporal evolution of filamentary discharge.
Pentacene transistor encapsulated by poly-para-xylylene behaving as gate dielectric insulator and passivation film
Authors: Tsukagoshi Kazuhito , Yagi Iwao , Shigeto Kunji , Yanagisawa Keiichi , Tanabe Jun , Aoyagi Yoshinobu
Published: October 2005

We present pentacene thin-film transistors with poly-para-xylylene gate dielectric and passivation films for plastic electronics. Both the poly-para-xylylene films are formed by dry chemical vapor deposition at room temperature. An organic pentacene channel is fully encapsulated by poly-para-xylylene films, except in the area of electrode connection. Passivation induces little degradation of the organic transistor properties. In addition, a small amount of charge transfer molecules are introduced between the pentacene channel and the metal electrodes to improve device performance. Contact resistance is sufficiently reduced by the employment of the charge transfer molecules, which is analyzed using a transmission-line model.
Surfactant-mediated epitaxy of relaxed low-doped Ge films on Si(001) with low defect densities
Authors: Wietler T. F. , Bugiel E. , Hofmann K. R.
Published: October 2005

Fully relaxed, high-quality Ge layers were grown directly on Si(001) substrates by surfactant-mediated epitaxy at high temperature with large Sb flux. We attribute the low dislocation densities in our films to an abrupt strain relief via the formation of a regular array of 90° dislocations at the interface during the initial, microrough stage of growth. This mechanism of abrupt strain relaxation occurs exclusively under high Sb coverage at temperatures ∼700°C. The high growth temperature also enhances Sb segregation leading to a low background doping level of only (3–4×1016)cm−3. Thus, we regard surfactant-mediated epitaxy of relaxed Ge on Si(001) as a promising candidate for device application.
High-performance operation of single-mode terahertz quantum cascade lasers with metallic gratings
Authors: Mahler Lukas , Tredicucci Alessandro , Köhler Rüdeger , Beltram Fabio , Beere Harvey E. , Linfield Edmund H. , Ritchie David A.
Published: October 2005

A periodic array of thin slits opened on a metallic surface can act as a one-dimensional photonic crystal for the propagation of surface-plasmon waves. We have used such structure for the implementation of distributed feedback resonators in quantum cascade lasers emitting near 2.5THz. Single-mode emission, stable at all injection currents and operating temperatures, was achieved both in pulsed and continuous wave. The devices exhibited output powers of several milliwatts with low threshold current densities of ∼100A∕cm2.
Observation of the interferences between the emitted beams in a 4Pi microscope by partial coherence interferometry
Authors: Sandeau N. , Giovannini H. , Lenne P.-F. , Rigneault H.
Published: October 2005

We propose a modified 4Pi microscope setup for observing solely the interference resulting from the superposition of the beams emitted by fluorescent species placed between two microscope objectives. A scanning Michelson interferometer is coupled to the 4Pi microscope. Interferences between the beams emitted by fluorophores deposited on a cover glass are observed, thanks to partial coherence interferometry technique.
Observation of interdot correlation in single pair of electromagnetically coupled quantum dots
Authors: Yamauchi Shohgo , Komori Kazuhiro , Morohashi Isao , Goshima Keishiro , Sugaya Takeyoshi , Takagahara Toshihide
Published: October 2005

The interdot correlation in a single pair of InAs∕GaAs barrier-coupled quantum dots (QDs) is investigated by microphotoluminescence spectroscopy, in which each QD is individually excited at unique energy levels. Surprisingly, we observe an anomalous increase in the luminescence intensity when the two QDs are excited simultaneously. This remarkable finding can be interpreted in terms of the electromagnetic coupling between QDs with thick barrier layers.
Bending of magnetic avalanches in MgB2 thin films
Authors: Albrecht J. , Matveev A. T. , Djupmyr M. , Schütz G. , Stuhlhofer B. , Habermeier H.-U.
Published: October 2005

The penetration of magnetic flux into a superconductor above the lower critical field does not necessarily happen in a regular way. It is found that under particular conditions, a chaotic penetration in form of magnetic avalanches occurs. These avalanches are closely related to the so-called thermomagnetic instability, which identifies local heating due to flux line movement as the origin of the effect. In case of MgB2 thin films, these avalanches are found only below T=10K and are suppressed by a covering metallic layer with high thermal conductivity and sufficient thickness. These avalanches are observed in the case of partly gold covered MgB2 films by the magneto-optical Faraday effect. The investigation of avalanches propagating into a gold-covered region revealed a change of the propagation direction depending on the incident angle of these avalanches.
Capsule endoscopy – comparison of two strategies of bowel preparation
Authors: NIV Y. , NIV G. , WISER K. , DEMARCO D. C.
Published: October 2005

Background:  Capsule endoscopy can identify lesions of the small bowel that cannot be detected by other techniques. In addition to patient safety, quality of care and cost‐efficiency, good preparation is an important factor for good visualization.

Aim:  To evaluate the efficacy of oral sodium phosphate preparation.

Methods:  Forty‐six consecutive patients scheduled for capsule endoscopy in two medical centres. The patients treated in Dallas were prepared by 12 h fasting (group A), and those treated in Israel were also asked to drink 45 mL of sodium phosphate with water (group B). An experienced endoscopist, blinded to the method used, graded the quality of preparation according to visual capability, and to relative durations of each grade.

Results:  The quality of the preparation was poor in 35% of group A compared with 4% of group B (P = 0.023). The mean duration of good preparation with excellent visualization was 122 ± 110 min in group A and 180 ± 96 min in group B (P = 0.006). Preparation with sodium phosphate and lower patient weight were significant predictive factors for good visualization.

Conclusions:  Bowel preparation offers better visualization than overnight fasting alone and is associated with fewer disturbances by intraluminal turbid fluid.
Outlet type constipation in Parkinson's disease: results of botulinum toxin treatment
Authors: CADEDDU F. , BENTIVOGLIO A. R. , BRANDARA F. , MARNIGA G. , BRISINDA G. , MARIA G.
Published: October 2005

Background : Constipation is one of the most common autonomic dysfunctions observed in Parkinson's disease.

Aim : To investigate the efficacy of injections of botulinum toxin in improving rectal emptying in these patients.

Methods : Eighteen Parkinson's disease patients with outlet constipation were included in the study. The patients were treated with type A botulinum toxin, injected into two sites on either side of the puborectalis muscle under ultrasonographic guidance.

Results : Symptomatic improvement was noted in 10 patients, at 2 months evaluation. In these subjects, anorectal manometry demonstrated decreased tone during straining from 96.2 ± 17.1 to 45.9 ± 16.2 mmHg at 1 month evaluation (P = 0.00001) and to 56.1 ± 10.7 mmHg at 2 months (P = 0.00001). Pressure during straining was lower than resting anal pressure at the same times in all patients. Defecography after the treatment showed improvement in anorectal angle during straining, which increased from 99.1 ± 8.4° to 121.7 ± 12.7° (P = 0.00001) at 2 months.

Conclusions : Botulinum toxin injections may be a useful treatment for Parkinson's disease patients affected by outlet‐obstruction constipation. The treatment is safe and simple. However, because the effects of the toxin wear off within 3 months of administration, repeated injections could be necessary to maintain the clinical improvement.
Prevalence and demographics of irritable bowel syndrome: results from a large web‐based survey
Authors: ANDREWS E. B. , EATON S. C. , HOLLIS K. A. , HOPKINS J. S. , AMEEN V. , HAMM L. R. , COOK S. F. , TENNIS P. , MANGEL A. W.
Published: October 2005

Background : Irritable bowel syndrome is a common gastrointestinal disorder, and its prevalence and demographics have been evaluated by different methodologies with varying results.

Aim : To evaluate irritable bowel syndrome demographic and prevalence characteristics utilizing a web‐enabled panel.

Methods : From an existing 150 000‐member panel, 31 829 individuals were randomly selected and sent screening questionnaires to evaluate irritable bowel syndrome symptoms. Individuals who agreed to participate and completed the screening questionnaire received a second questionnaire related to a diagnosis of irritable bowel syndrome, a more detailed symptom description, and additional burden of illness data.

Results : Irritable bowel syndrome prevalence was 7%. Prevalence was higher in women vs. men, unmarried individuals vs. married individuals and unemployed individuals vs. employed individuals. Of those completing the second questionnaire, 51% had seen their physicians for irritable bowel syndrome symptoms in the past year and most had an episode within the past 3 months. During the past year, approximately half of the participants had used a prescription medication, and over 90% had used an over‐the‐counter medication for irritable bowel syndrome. Participants with irritable bowel syndrome demonstrated quality‐of‐life reductions relative to norms of the United States population.

Conclusions : Web‐enabled data collection represents a novel tool for rapidly surveying a large population of individuals with irritable bowel syndrome symptoms.
Melatonin improves bowel symptoms in female patients with irritable bowel syndrome: a double‐blind placebo‐controlled study
Authors: LU W. Z. , GWEE K. A. , MOOCHHALLA S. , HO K. Y.
Published: October 2005

Background : Melatonin is involved in the regulation of gastrointestinal motility and sensation.

Aim : To determine the potential therapeutic effects of melatonin in irritable bowel syndrome (IBS).

Method : Seventeen female patients satisfying the Rome II criteria for IBS were randomized to receive either melatonin 3 mg nocte or identically appearing placebo 1 nocte for 8 weeks, followed by a 4‐week washout period and placebo or melatonin in the reverse order for another 8 weeks. Three validated questionnaires – the GI symptom, the sleep questionnaires and the Hospital Anxiety and Depression Scale – were used to assess symptom severity and to compute the IBS, sleep and anxiety/depression scores, respectively.

Results : Improvements in mean IBS scores were significantly greater after treatment with melatonin (3.9 ± 2.6) than with placebo (1.3 ± 4.0, P = 0.037). Percent response rate, defined as percentage of subjects achieving mild‐to‐excellent improvement in IBS symptoms, was also greater in the melatonin‐treated arm (88% vs. 47%, P = 0.04). The changes in mean sleep, anxiety, and depression scores were similar with either melatonin or placebo treatment.

Conclusions : Melatonin is a promising therapeutic agent for IBS. Its therapeutic effect is independent of its effects on sleep, anxiety or depression.
The association of body mass index with Barrett's oesophagus
Authors: STEIN D. J. , EL‐SERAG H. B. , KUCZYNSKI J. , KRAMER J. R. , SAMPLINER R. E.
Published: October 2005

Background:  Obesity has been linked to gastro‐oesophageal reflux disease symptoms and oesophageal adenocarcinoma; however, there is no published evidence for an association with Barrett's oesophagus.

Aim:  To investigate the association between obesity and Barrett's oesophagus.

Methods:  We conducted a retrospective cross‐sectional study of patients who underwent upper endoscopy at the Southern Arizona Veteran's Affairs Healthcare System between 1998 and 2004. We examined male patients without malignancy, with available information on weight and height. Based on endoscopic and histological findings, patients were classified as cases with Barrett's oesophagus or non‐cases without Barrett's oesophagus. Multivariable logistic regression analysis was conducted to examine the association of body mass index and obesity with Barrett's oesophagus and Barrett's oesophagus length while adjusting for age and race.

Results:  There were 65 cases with Barrett's oesophagus and 385 non‐cases without Barrett's oesophagus. The mean body mass index was significantly higher in cases than in non‐cases (29.8 vs. 28.0, P = 0.03). Cases had significantly greater mean weight than controls (206 lb vs. 190,P = 0.005). The proportions of cases with body mass index 25–30 and body mass index ≥30 were greater than those in non‐cases (44.6% vs. 37.7%) and (40.0% vs. 33.5%), respectively (P = 0.08). In the multivariable logistic regression model adjusting for race and age, when compared with body mass index < 25, the odds ratio was 2.43 (95% confidence interval: 1.12–5.31) for body mass index 25–30 and 2.46 (1.11–5.44) for body mass index ≥30. When examined as a continuous variable the adjusted odd ratio for each five‐point increase in body mass index was 1.35 (95% confidence interval: 1.06–1.71, P = 0.01). The association between weight and Barrett's oesophagus was also statistically significant (adjusted odd ratio for each 10 pound increase = 1.10, 1.03–1.17, P =0.002). Among the 65 cases of Barrett's oesophagus, there was no correlation between the length of Barrett's oesophagus at the time of diagnosis and the body mass index (correlation coefficient = 0.03, P = 0.79).

Conclusion:  This retrospective cross‐sectional study in male veterans shows that overweight is associated with a two‐and‐half‐fold increased risk of Barrett's oesophagus. Larger studies of the underlying mechanism are warranted to better understand how and why obese patients are at greater risk for Barrett's oesophagus.
Normal values and day‐to‐day variability of 24‐h ambulatory oesophageal impedance‐pH monitoring in a Belgian–French cohort of healthy subjects
Authors: ZERBIB F. , BRULEY DES VARANNES S. , ROMAN S. , POUDEROUX P. , ARTIGUE F. , CHAPUT U. , MION F. , CAILLOL F. , VERIN E. , BOMMELAER G. , DUCROTTÉ P. , GALMICHE J.‐P. , SIFRIM D.
Published: October 2005

Background : Impedance‐pH monitoring is the most sensitive method for detection and characterization of gastro‐oesophageal reflux episodes. Normal values from European subjects are lacking.

Aim : To build a database of gastro‐oesophageal reflux patterns from French and Belgian healthy subjects.

Methods : Seventy‐two healthy subjects (35 men, mean age 35 years, 18–72) underwent 24‐h ambulatory impedance‐pH studies. Gastro‐oesophageal reflux episodes were detected using impedance and characterized by pH as acid, weakly acidic, or weakly alkaline. Analysis was performed visually and effects of age, gender and intra‐individual reproducibility were evaluated.

Results : The total number of gastro‐oesophageal reflux episodes was 44 (25,58,75) of which 59% were acid, 28% were weakly acidic and 10% weakly alkaline. Half of gastro‐oesophageal reflux episodes were mixed (liquid/gas) and 22% reached 15 cm above the lower oesophageal sphincter. The bolus clearance time was 11 s while acid was chemically cleared in 34 s. Male gender was associated with increased number and proximal extent of total and acid gastro‐oesophageal reflux. Repeated studies in 27 subjects showed good reproducibility for number, acidity and air–liquid composition of reflux (Kendall's W‐values = 0.72–0.85).

Conclusions : This study demonstrates good reproducibility of 24‐h ambulatory impedance‐pH studies and provides values of reflux patterns in healthy subjects for comparisons with European gastro‐oesophageal reflux disease patients.