bluuebunny/crossref_metadata_2025 huggingface dataset:
A model for the azimuthal plasma velocity in Saturn's magnetosphere
Authors: Saur Joachim , Mauk Barry H. , Kaßner Arne , Neubauer Fritz M.
Published: May 2004

We present a model for Saturn's magnetospheric azimuthal plasma velocities measured by Voyager 1 and 2. The observed velocity profiles deviate from full corotation and show two dips slightly outside the orbits of Dione and Rhea. Our velocity model includes as sources for the deviation: radial mass transport, friction between magnetospheric ions and neutrals, and ion pickup. We combine the latter two processes in a quantity called magnetospheric conductance ΣM. We find that inside of 12 Saturn radii (RS) the magnetospheric conductance dominates the slowing of magnetospheric plasma as compared to the effect of radial mass transport. The magnetospheric conductance peaks twice, i.e., slightly outside the orbit of Dione (6.4 RS) and Rhea (8.8 RS), respectively. These two peaks result from a combination of the radially varying magnetic field magnitude, the radial plasma density distribution, and the neutral density distribution. A key finding of our work is that the two magnetospheric conductance maxima can explain the two dips in the observed azimuthal velocity profile that occur at roughly similar locations. Mismatches in the dip locations can be used to retrieve neutral gas profiles. We achieve reasonable agreement with the observations for very small effective Pedersen conductances, ΣI ∼ 0.014 S (Voyager 1) and ΣI ∼ 0.035 S (Voyager 2) in Saturn's ionosphere, for a total magnetospheric mass source of 40 kg s−1. Larger mass sources require appropriately higher ionospheric conductances. We also find that mass cannot leave, on average, the ≤10 RS regions as plasma. It must be mostly lost via conversion to neutrals.
Do Schumann resonance frequencies depend on altitude?
Authors: Morente Juan A. , Portí Jorge A. , Salinas Alfonso , Molina‐Cuberos Gregorio J. , Lichtenegger Herbert , Besser Bruno P. , Schwingenschuh Konrad
Published: May 2004

Schumann resonance frequencies are the resonance frequencies for an electromagnetic field inside the natural conducting cavity formed by the Earth's surface and its ionosphere. The spectrum peaks for the total electromagnetic energy stored inside the cavity define a unique value for each Schumann resonance. Because of the impossibility of measuring the total energy stored in the atmosphere, the experimental determination of Schumann resonances is carried out by a local measurement of the magnetic or electric field spectrum. However, peak frequencies in the amplitude of the electromagnetic field Fourier spectrum of a lightning discharge excited atmosphere may depend on height because this field depends on the atmosphere conductivity and this physical magnitude varies with height. Therefore it is reasonable to expect a slight shift between the peaks corresponding to the electric or magnetic field spectrum at a given height and those obtained by considering the total energy stored. In this paper the Earth's electromagnetic cavity is numerically modeled by using the transmission line matrix (TLM) numerical method. The altitude profile of the magnetic field spectrum remains constant from ground to 70‐km height; however, a decay between 1.5 and 4 Hz is observed for heights between 70 and 100 km, which represents a medium reduction of 10%.
Observations and modeling of the 6‐hour tide in the upper mesosphere
Authors: Smith Anne K. , Pancheva Dora V. , Mitchell Nicholas J.
Published: May 2004

This paper presents observations and modeling of the 6‐hour tide. Radar observations of horizontal winds at Esrange (68°N, 21°E) indicate that this tidal periodicity is a consistent part of the diurnal variation and is largest during midwinter. Vertical structure and phase coherence provide strong support that the observed oscillations are tidal. Model simulations generate a tide that has many similarities to the observed tide at Esrange. Diagnostic model tests indicate that the tide is forced primarily by the 6‐hour component of solar heating. Globally, the monthly mean simulated tide is dominated by the migrating component except near the poles, although the contribution from nonmigrating modes is not negligible. According to the model both migrating and nonmigrating 6‐hour tides have small amplitude in low latitudes.
Passive coherent scatter radar interferometer implementation, observations, and analysis
Authors: Meyer Melissa G. , Sahr John D.
Published: May 2004

We have recently extended the passive radar technique to permit interferometric observation of ionospheric irregularities. We discuss the implementation of a passive radar interferometer at VHF frequencies and show observations of field‐aligned irregularities in the high‐latitude E region ionosphere. The interferometer achieves very fine azimuthal resolution (as fine as 0.1°, or 2 km at a range of 1000 km); thus we can form two‐dimensional spatial images of the target volume. Many E region scatterers are compact, with transverse extent no greater than 10 km; this is significantly smaller than the beam width of most coherent radars. By tracking interferometric position, we can estimate the transverse drift of the scattering region. By coupling this information with the line of sight Doppler shift and using the dispersion relation for meter scale irregularities, we estimate electric fields and velocity shears within the scattering volume.
A clear case of radon anomaly associated with a micro‐earthquake event in a Stable Continental Region
Authors: Reddy D. V. , Sukhija B. S. , Nagabhushanam P. , Kumar Devender
Published: May 2004

Though many worldwide attempts to establish radon anomalies in soil and groundwater as precursors for major earthquakes are made, yet practically no such work has been reported for micro‐earthquakes in a Stable Continental Region (SCR). From the continuous radon measurements for five months at a depth of 1 m in fractured granitic area, we report for the first time that enhanced radon concentration preceded seventeen hours the occurrence of micro earthquake. The peak radon level (twice the normal concentration) was reached thirteen hours before the occurrence of the event and decayed exponentially during the next 5 days to come to normal level. This radon precursor pertains to a dry period, unaffected by meteorological factors, thus exemplifies clearly its association with micro earthquake.
Topology-based signal separation
Authors: Robins V. , Rooney N. , Bradley E.
Published: May 2004

Traditional noise-filtering techniques are known to significantly alter features of chaotic data. In this paper, we present a noncausal topology-based filtering method for continuous-time dynamical systems that is effective in removing additive, uncorrelated noise from time-series data. Signal-to-noise ratios and Lyapunov exponent estimates are dramatically improved following the removal of the identified noisy points.
Irreversible adsorption of particles at random-site surfaces
Authors: Adamczyk Zbigniew , Jaszczółt Katarzyna , Siwek Barbara , Weroński Paweł
Published: May 2004

Irreversible adsorption of negatively charged polystyrene latex particles (averaged diameter 0.9 μm) at heterogeneous surfaces was studied experimentally. The substrate bearing a controlled number of adsorption sites was produced by precovering mica sheets by positively charged polystyrene latex (averaged diameter of 0.45 μm). Positive latex (site) deposition was carried out under diffusion-controlled transport conditions and its coverage was determined by direct particle counting using the optical microscopy. Deposition kinetics of larger latex particles (averaged diameter 0.9 μm) at heterogeneous surfaces produced in this way was studied by direct optical microscope observations in the diffusion cell (under no-convection transport conditions). It was demonstrated that the structure of larger particle monolayers, characterized in terms of the pair correlation function, showed much more short-range ordering than it was predicted for homogeneous surface monolayers at the same coverage. This was found in agreement with theoretical predictions derived from the Monte Carlo simulations. On the other hand, particle adsorption kinetics was quantitatively interpreted in terms of numerical solutions of the governing diffusion equation with the nonlinear boundary condition derived from Monte Carlo simulations. From these kinetic measurements maximum (jamming) coverage of particles was determined in an accurate way by extrapolation. It was concluded that both the monolayer structure and jamming coverage were strongly influenced by the site multiplicity (coordination) effect.
Non-Lipschitzian control algorithms for extended mechanical systems
Authors: Protopopescu V. , Barhen J.
Published: May 2004

We derive the properties of a general control algorithm [Braiman et al., Phys. Rev. Lett. 90, 094301 (2003)] for quantities describing global features of nonlinear extended mechanical systems. The control algorithm is based on the concepts of non-Lipschitzian dynamics and global targeting. We show that (i) certain average quantities of the controlled system can be driven—exactly or approximately—towards desired targets which become linearly stable attractors for the system’s dynamics; (ii) the basins of attraction of these targets are reached in very short times; and (iii) while within reasonably broad ranges the time-scales of the control and of the intrinsic dynamics may be quite different, this disparity does not affect significantly the overall efficiency of the proposed scheme, up to natural fluctuations.
Wave chaos and mode–medium resonances at long-range sound propagation in the ocean
Authors: Smirnov I. P. , Virovlyansky A. L. , Zaslavsky G. M.
Published: May 2004

We study how the chaotic ray motion manifests itself at a finite wavelength at long-range sound propagation in the ocean. The problem is investigated using a model of an underwater acoustic waveguide with a periodic range dependence. It is assumed that the sound propagation is governed by the parabolic equation, similar to the Schrödinger equation. When investigating the sound energy distribution in the time–depth plane, it has been found that the coexistence of chaotic and regular rays can cause a “focusing” of acoustic energy within a small temporal interval. It has been shown that this effect is a manifestation of the so-called stickiness, that is, the presence of such parts of the chaotic trajectory where the latter exhibit an almost regular behavior. Another issue considered in this paper is the range variation of the modal structure of the wave field. In a numerical simulation, it has been shown that the energy distribution over normal modes exhibits surprising periodicity. This occurs even for a mode formed by contributions from predominantly chaotic rays. The phenomenon is interpreted from the viewpoint of mode–medium resonance. For some modes, the following effect has been observed. Although an initially excited mode due to scattering at the inhomogeneity breaks up into a group of modes its amplitude at some range points almost restores the starting value. At these ranges, almost all acoustic energy gathers again in the initial mode and the coarse-grained Wigner function concentrates within a comparatively small area of the phase plane.
Chiral symmetry breaking and the Josephson current in a ballistic superconductor–quantum wire–superconductor junction
Authors: Krive I. V. , Gorelik L. Y. , Shekhter R. I. , Jonson M.
Published: May 2004

We evaluate the Josephson current through a quasi-1D quantum wire coupled to bulk superconductors. It is shown that the interplay of Rashba spin–orbit interaction and Zeeman splitting results in the appearance of a Josephson current even in the absence of any phase difference between the superconductors. In a transparent junction (D≃1) at low temperatures this anomalous supercurrent Jan appears abruptly for a Zeeman splitting of the order of the Andreev level spacing as the magnetic field is varied. In a low-transparency (D≪1) junction one has Jan∝D under special (resonance) conditions. In the absence of Zeeman splitting the anomalous supercurrent disappears. We have investigated the influence of dispersion asymmetry induced by the Rashba interaction in quasi-1D quantum wires on the critical Josephson current and have shown that the breakdown of chiral symmetry enhances the supercurrent.
Modeling of dry sliding friction dynamics: From heuristic models to physically motivated models and back
Authors: Al-Bender Farid , Lampaert Vincent , Swevers Jan
Published: May 2004

After giving an overview of the different approaches found in the literature to model dry friction force dynamics, this paper presents a generic friction model based on physical mechanisms involved in the interaction of a large population of surface asperities and discusses the resulting macroscopic friction behavior. The latter includes the hysteretic characteristic of friction in the presliding regime, the velocity weakening and strengthening in gross-sliding regime, the frictional lag and the stick-slip behavior. Out of the generic model, which is shown to be a good, but rather computationally intensive, simulation tool, a simpler heuristic model, which we call the generalized Maxwell-slip friction, is deduced. This model is appropriate for quick simulation and control purposes being easy to implement and to identify. Both of the generic and heuristic model structures are compared, through simulations, with each other and with experimental data.
Calculation of the 𝓐 term of magnetic circular dichroism based on time dependent-density functional theory I. Formulation and implementation
Authors: Seth Michael , Ziegler Tom , Banerjee Arup , Autschbach Jochen , van Gisbergen Stan J. A. , Baerends Evert J.
Published: May 2004

A procedure for calculating the 𝒜 term and the 𝒜/𝒟 ratio of magnetic circular dichroism (MCD) within time-dependent density functional theory (TD–DFT) is described. Utilizing an implementation of the MCD theory within the Amsterdam Density Functional program, the 𝒜 term contributions to the MCD spectra of MnO4−, CrO42−, VO43−, MoO42−, VO43−, MoS42−, Se42+, Te42+, Fe(CN)64−, Ni(CN)42−, trichlorobenzene, hexachlorobenzene, tribromobenzene, and hexabromobenzene are calculated. For the most part, agreement between theory and experiment for 𝒜/𝒟 ratios and the relative magnitude of 𝒜 terms is found to be good, leading to simulated spectra that are similar in appearance to those derived from measurements. The 𝒜 terms are found to be too small whenever comparison with experiment was possible, probably due to the neglect of environment effects on the incident radiation and the relative low accuracy of dipole strengths calculated within TD–DFT.
Dynamic interacting bubble simulation (DIBS): An agent-based bubble model for reacting fluidized beds
Authors: Pannala Sreekanth , Daw C. Stuart , Halow John S.
Published: May 2004

In this paper we explore the global dynamics of an agent-type model for bubbles in gas-fluidized beds and demonstrate that these features are consistent with experimentally observed behavior. The model accounts for the simultaneous interactions of thousands of individual bubbles and includes mass-transfer and first-order reactions between the gas and solids so that the impact of the dynamics is reflected in reactant conversion. We start with model parameters that have been demonstrated to produce time average behavior consistent with experimental reactor measurements. By observing the temporal variations of spatially averaged bubble properties, we are able to clearly distinguish the onset of global low-dimensional features that appear to be consistent with previous observations. The most prominent of these features is a large-scale oscillation that exhibits intermittency with power-law scaling in the vicinity of a critical gas flow. We show that the oscillation occurs as the result of a globally synchronized horizontal movement of the bubbles toward the center of the reactor. The oscillation appears to be consistent with the occurrence of the so-called “slugging” phenomenon, which is known to have large effects on fluidized bed reactor performance. Although this model can clearly be further improved, its success in replicating several of the key features of slugging indicates that this approach can serve as a useful tool for understanding and possibly controlling fluidized bed dynamics. We also conjecture that this model may be useful for more generally understanding the occurrence of global features in high-dimensional, multi-agent systems.
Three terminal capacitance technique for magnetostriction and thermal expansion measurements
Authors: Kundys B. , Bukhantsev Yu. , Vasiliev S. , Kundys D. , Berkowski M. , Dyakonov V. P.
Published: May 2004

An instrument has been constructed to measure a large range of magnetostriction and thermal expansion between room temperature and 4 K in a superconductive split-coil magnet, that allows investigation in magnetic fields up to 12 T. The very small bulk samples (up to 1 mm in size) as well as big ones (up to 13 mm) of the irregular form can be measured. The possibility of magnetostriction investigation in thin films is shown. A general account is given of both electrical and the mechanical aspects of the design of capacitance cell and their associated electronic circuitry. A simple lever device is proposed to increase the sensitivity twice. The resulting obtained sensitivity is 0.5 Å. The performance of the technique is illustrated by some preliminary measurements of the magnetostriction of superconducting MgB2, thermal expansion of (La0.8Ba0.2)0.93MnO3 single crystal and magnetoelastic behavior of the Ni/Si(111) and La0.7Sr0.3CoO3/SAT0.7CAT0.1LA0.2(001) cantilevers.
Using 15 fs, LINAC-generated electron bunches for naturally synchronized infrared pump x-ray probe experiments with coherent synchrotron radiation
Authors: Adams Bernhard W.
Published: May 2004

It is proposed to use highly compressed 15 fs bunches from a linear accelerator, such as the Stanford Linear Accelerator, for the production of both ultrashort x rays and mid-infrared coherent synchrotron radiation (CSR). The two types of radiation are synchronized with each other on the femtosecond time scale and can be used for pump–probe experiments in the study of ultrafast phenomena. A possible extension to 3 fs bunches is discussed, where the CSR serves both, as a source of pump radiation and as an indicator for those bunches that are perfectly compressed.
A spin rotator for spin-polarized scanning electron microscopy
Authors: Kohashi Teruo , Konoto Makoto , Koike Kazuyuki
Published: May 2004

A Wien filter, which is a common energy analyzer, was modified as a spin rotator for use in a spin-polarized scanning electron microscope. By switching the spin rotator on and off, magnetic domain images of all three magnetization vectors can be produced in one scan. The electrodes and the magnetic pole pieces were specially designed by using a three-dimensional computer simulation for electric and magnetic fields, electron trajectories, and spin rotation; the broad beam of the secondary electrons passes through to the spin detector with a 90° rotation. The structure is simple with only two electrodes that have hyperbolically curved surfaces to create a stigmatic focusing effect, while the surfaces of the magnetic pole pieces are flat to enable a uniform rotation of all electron spins. The performance was tested and confirmed to be effective by observing the magnetic domain structures of Fe(001) with in-surface-plane magnetization and a TbFeCo magneto-optical medium with surface normal magnetization.
Push–pull fiber optic inclinometer based on a Mach–Zehnder optical low-coherence reflectometor
Authors: Yuan Li-Bo
Published: May 2004

A push–pull inclinometer based on the gravity-referenced rotation fiber optic sensing system is demonstrated by using a specially designed parallelogram pendulum. It measures the angle variations between a nominally vertical reference line in the civil structure and the direction of gravity. By using a low-coherence fiber optic Mach–Zehnder interferometric technique, rotation sensitivity in the two perpendicular vertical planes of 0.2′ can be achieved. The total measurement range is ±5° and the temperature cross-sensitivity is expected to be very low. These values compare favorably to the high-end of electronic inclinometers and are well suited for the monitoring of civil structures such as bridges, towers, and anchored walls. The small size of the sensors and the mechanical design make them suitable for open-air use, while the low temperature sensitivity makes them ideal for eliminating temperature-induced rotations. The proposed inclinometer has a resolution of 0.2′ and a precision of 1′ full scale.
Localization of firearm projectiles in the human body using a superconducting quantum interference device magnetometer: A theoretical study
Authors: Hall Barbosa C.
Published: May 2004

A technique had been previously developed, based on magnetic field measurements using a superconducting quantum interference device sensor, to localize in three dimensions steel needles lost in the human body. In all six cases that were treated until now, the technique allowed easy surgical localization of the needles with high accuracy. The technique decreases, by a large factor, the surgery time for foreign body extraction, and also reduces the generally high odds of failure. The method is accurate, noninvasive, and innocuous, and with clear clinical importance. Despite the importance of needle localization, the most prevalent foreign body in the modern society is the firearm projectile (bullet), generally composed of lead, a paramagnetic material, thus not presenting a remanent magnetic field as steel needles do. On the other hand, since lead is a good conductor, eddy current detection techniques can be employed, by applying an alternating magnetic field with the aid of excitation coils. The primary field induces eddy currents on the lead, which in turn generate a secondary magnetic field that can be detected by a magnetometer, and give information about position and volume of the conducting foreign body. In this article we present a theoretical study for the development of a localization technique for lead bullets inside the human body. Initially, we present a model for the secondary magnetic field generated by the bullet, given a known applied field. After that, we study possible excitation systems, and propose a localization algorithm based on the detected magnetic field.
Electromechanical coupling coefficient for surface acoustic waves in single-crystal bulk aluminum nitride
Authors: Bu G. , Ciplys D. , Shur M. , Schowalter L. J. , Schujman S. , Gaska R.
Published: May 2004

The electromechanical coupling coefficient K2 for surface acoustic waves propagating on c and a surfaces of bulk AlN single crystals has been measured using the S11-parameter method in the frequency range of 160–360 MHz. The extracted values of K2 are 0.11% and 0.47% for the c and a surfaces, respectively. By fitting our experimental data to our numerical simulation results, we have estimated piezoelectric constants, which are in a reasonable agreement with literature data. Our results are consistent with the negative sign of the e15 constant.
Transparent conducting metal electrode for top emission organic light-emitting devices: Ca–Ag double layer
Authors: Pode R. B. , Lee C. J. , Moon D. G. , Han J. I.
Published: May 2004

We have fabricated a transparent conducting double-layer metal electrode for top emission organic light-emitting devices which consists of thin layers of Ca and Ag metals of different thicknesses, deposited by the vacuum evaporation technique. The process is clean and does not damage the underlaying organic layers. High optical transparency over 70%, low reflectivity (14%) in the visible region, and low electrical sheet resistance (12 ohms/square) in Ca(10 nm)–Ag(10 nm) structures are reported. This transparent conducting Ca–Ag metal electrode opens a practical way to fabricate top-emitting organic displays without generating damage-induced states.
Diffraction gratings and diffusion coefficient determination of acrylamide and polyacrylamide in sol-gel glass
Authors: Blaya S. , Murciano A. , Acebal P. , Carretero L. , Ulibarrena M. , Fimia A.
Published: May 2004

We describe the recording of holographic gratings in a photopolymerizable sol-gel glass based on acrylamide as monomer, triethanolamine as coinitiator, and yellowish eosin as photoinitiator. Although acrylic monomers have been introduced in silica glass by Cheben and Calvo [Appl. Phys. Lett. 78, 1490 (2001)], the well-known acrylamide based composition has not yet been produced by this method. Diffraction efficiencies close to 55% were obtained with an exposure of 8 mJ/cm2. The holographic gratings were not stable and we made use of this instability to determine the diffusion coefficients of acrylamide and polyacrylamide inside this glass.
Specific heat of single-walled boron nitride nanotubes
Authors: Xiao Y. , Yan X. H. , Xiang J. , Mao Y. L. , Zhang Y. , Cao J. X. , Ding J. W.
Published: May 2004

Based on a force constant model, we have calculated the phonon spectrum and specific heat of single-walled boron nitride nanotubes. Compared with carbon nanotubes, boron nitride nanotubes have a larger specific heat. The fitting formulas for diameter and chirality dependence of specific heat at 300 K are given.
Electromagnetic study of the quality factor of pillar microcavities in the small diameter limit
Authors: Lalanne Ph. , Hugonin J. P. , Gérard J. M.
Published: May 2004

A thorough electromagnetic study of pillar microcavities reveals a surprising behavior for their Q factors in the strong confinement limit. Q displays a fast oscillatory variation as a function of the pillar diameter, and reaches values well in excess of the quality factor of the reference planar cavity. This behavior is explained by the hybrid character of the cavity mode in the small diameter limit, which results mainly from the electromagnetic coupling of the HE11 (i.e., fundamental) and EH11 guided modes of the cavity spacer through the associated Bloch modes in the Bragg mirrors.
Thermal diffusivity and conductivity of supercooled liquid in Zr41Ti14Cu12Ni10Be23 metallic glass
Authors: Yamasaki Michiaki , Kagao Shinya , Kawamura Yoshihito , Yoshimura Kenji
Published: May 2004

We measured the thermal diffusivity of amorphous solid and supercooled liquid in a Zr41Ti14Cu12Ni10Be23 bulk metallic glass (BMG) and its crystalline counterpart alloy at temperatures ranging from room temperature to 700 K, using a laser flash method. The thermal diffusivity and conductivity of the amorphous solid were weakly temperature dependent and increased with increasing temperature up to the glass transition temperature. The thermal diffusivity of the supercooled liquid was approximately 3.5×10−6 m2 s−1 and quite constant with temperature. The amorphous solid and supercooled liquid of Zr41Ti14Cu12Ni10Be23 BMG showed lower thermal diffusivity and conductivity than the crystalline counterpart in the range from room temperature to crystallization temperature.
Asymmetric AlAsSb/InAs/CdMgSe quantum wells grown by molecular-beam epitaxy
Authors: Ivanov S. V. , Lyublinskaya O. G. , Vasilyev Yu. B. , Kaygorodov V. A. , Sorokin S. V. , Sedova I. V. , Solov’ev V. A. , Meltser B. Ya. , Sitnikova A. A. , L’vova T. V. , Berkovits V. L. , Toropov A. A. , Kop’ev P. S.
Published: May 2004

Asymmetric (6.7–300)-nm-thick InAs quantum wells (QWs) confined between AlAsSb and CdMgSe barriers have been fabricated by molecular-beam epitaxy. A special procedure of the CdMgSe-on-InAs growth initiation, exploiting an ex situ S passivation of InAs and in situ deposition of an ultrathin ZnTe buffer layer, results in the fabrication of high quality structures with a density of extended defects below 106 cm2. QW photoluminescence studies demonstrate a confinement effect and confirm the type I band alignment at the heterovalent InAs/CdMgSe interface mediated by the ZnTe interlayer. Observation of Shubnikov de Haas oscillations of magnetoresistance for an asymmetric 19-nm-thick InAs QW indicates an existence of the two-dimensional electron gas with the low-temperature sheet electron density of 1.3×1012 cm−2 and the mobility as high as ∼10 000 cm2/V s.
Double focusing of hard x rays using combined multilayer and Bragg–Fresnel optics
Authors: Yasa M. , Li Y. , Mammen C. B. , Als-Nielsen J. , Hoszowska J. , Mocuta C. , Freund A.
Published: May 2004

A multilayer Bragg–Fresnel x-ray lens (MBFL) structure that combines diffraction and geometric focusing on a single device is presented. With the MBFL, the linear BFL focuses the x-ray beam vertically while the bent multilayer focuses x rays horizontally. This combination eliminates the need for a second mirror in the conventional Kirkpatrick–Baez-based microprobe, which will be advantageous in x-ray fluorescence microscopy as well as microdiffraction applications. The characterization of the MBFL was carried out at the European Synchrotron Radiation Facility and a 1.6 μm (vertical)×12 μm (horizontal) focus was obtained from a 250 μm (V)×200 μm (H) incident beam. With a binary Fresnel lens efficiency of about 35% this yields a gain of almost three orders of magnitude compared to obtaining the same spot size by a raw aperture.
NbO as gate electrode for n-channel metal-oxide-semiconductor field-effect-transistors
Authors: Gao W. , Conley J. F. , Ono Y.
Published: May 2004

Niobium mono-oxide (NbO) is investigated as a potential candidate for gate electrode to replace poly-silicon gate in metal-oxide-semiconductor field-effect transistors. NbO was found to have a work function of 4.18±0.05 eV on SiO2 and to be stable up to 1000 °C with SiO2 and HfO2 gate dielectrics. The low work function and high stability make NbO suitable for n-channel metal-oxide-semiconductor field-effect transistors devices. The method of deposition is critical during the fabrication to minimize the incorporation of Nb, NbO2, and Nb2O5 which are detrimental to the stability and conductivity of the gate electrode and extra care is needed to avoid further oxidation of NbO.
Persistence of (In,Ga)As quantum-dot chains under index deviation from GaAs(100)
Authors: Wang Z. M. , Mazur Yu. I. , Salamo G. J. , Lytvin P. M. , Strelchuk V. V. , Valakh M. Ya.
Published: May 2004

Utilizing the naturally curved surface contours provided by oval defects on a GaAs(100) surface, we demonstrate that alignment of quantum-dot chains formed during the growth of (In,Ga)As multilayers is unyielding to a modest deviation of surface orientation from (100) of about 0.7° along [01-1] and 8° along [011]. This finding suggests that the strain-driven kinetic anisotropy responsible for the formation of the quantum dot chains dominates over selective island formation at steps due to surface misorientation. The robustness of the quantum dot chain adds to its potential for its future application.
Observation of resonant energy transfer in Au:CdS nanocomposite
Authors: Ma G. H. , He J. , Rajiv K. , Tang S. H. , Yang Y. , Nogami M.
Published: May 2004

Au:CdS nanocomposite film was investigated using femtosecond pump–probe measurement at 800 nm. Time dependence of transmittance shows a two-photon absorption followed by a saturable absorption and recovery process, which clearly demonstrates that resonant energy transfer between CdS and Au nanocomposite systems occur with excitation at 800 nm. In addition, enhancement of the two-photon absorption coefficient in Au:CdS nanocomposite with a factor of more than 6 was observed compared to that of bulk CdS.
Arbitrary angle waveguiding applications of two-dimensional curvilinear-lattice photonic crystals
Authors: Zarbakhsh Javad , Hagmann Frank , Mingaleev Sergei F. , Busch Kurt , Hingerl Kurt
Published: May 2004

We introduce a fresh class of photonic band-gap materials, curvilinear-lattice photonic crystals, whose distinctive feature is that their individual scatterers are arranged in a curvilinear lattice. We show that adhering to some restrictions in the acceptable lattice transformations, one can achieve omnidirectional photonic band gaps for an entire subclass of such structures. We demonstrate, designing an efficient arbitrary-angle waveguide bend, that curvilinear-lattice photonic crystals can be employed for creation of original types of nanophotonic devices.
Single-ensemble nonequilibrium path-sampling estimates of free energy differences
Authors: Ytreberg F. Marty , Zuckerman Daniel M.
Published: May 2004

We introduce a straightforward, single-ensemble, path sampling approach to calculate free energy differences based on Jarzynski’s relation. For a two-dimensional “toy” test system, the new (minimally optimized) method performs roughly one hundred times faster than either optimized “traditional” Jarzynski calculations or conventional thermodynamic integration. The simplicity of the underlying formalism suggests the approach will find broad applicability in molecular systems.
Gd
5
Si
2
Ge
2
composite for magnetostrictive actuator applications
Authors: Nersessian Nersesse , Or Siu Wing , Carman Gregory P. , McCall Scott K. , Choe Wonyoung , Radousky Harry B. , McElfresh Mike W. , Pecharsky Vitalij K. , Pecharsky Alexandra O.
Published: May 2004

A composite system containing particles of Gd5Si2Ge2, which exhibit a colossal magnetic-field-induced strain, has been prepared. The composite is manufactured by embedding ball-milled Gd5Si2Ge2 particles with a size distribution of <600 μm in a resin matrix. The thermally induced volume strain in the composite resulting from phase transformation is found to be 1300 ppm. The magnetically induced linear strain resulting from phase transformation is also measured, from which the volume strain is deduced to be 1650 ppm. The volume strain from the composite is significantly lower than phase transformation strain of the bulk Gd5Si2Ge2 (8000 ppm) and is mainly attributed to nonalignment of the particles in the matrix. An analytical model for a 1–3 composite (particles aligned in a single direction in a polymer matrix) and a 0–3 composite (particles dispersed randomly in a polymer matrix) predicts significantly higher strains in a 1–3 composite.
Growth and pyroelectric property of 0.2 mol % Fe-doped Pb(Mg1/3Nb2/3)O3-0.38PbTiO3 single crystals measured by a dynamic technique
Authors: Wan Xinming , Tang Xingui , Wang Jie , Chan H. L. W. , Choy C. L. , Luo Haosu
Published: May 2004

To develop a high-performance pyroelectric infrared detector, large-size and high-quality 0.2 mol % Fe-doped Pb(Mg1/3Nb2/3)O3-0.38PbTiO3 single crystals have been grown by a modified Bridgman technique with a seed crystal. At 50 Hz, the doped single crystal showed a lower dielectric constant of 310 compared with the pure one. A low dielectric loss of 0.0067 was also obtained by doping with small concentration of iron ions. Piezoelectric coefficient (d33) of 〈001〉 oriented sample was ∼260 pC/N. The pyroelectric properties and their temperature dependence were measured by the dynamic technique. At room temperature, the pyroelectric coefficient and calculated detectivity figure of merit FD are 568 μC/m2 K and 53 μPa−1/2, respectively. The values of current response figure of merit Fi and voltage response figure of merit Fv are 227.2 pm/V and 0.083 m2/C, respectively. These excellent pyroelectric properties as well as being able to produce large-size and high-quality single crystals make this kind of single crystal very promising for high-performance infrared detectors and other pyroelectric applications.
Deletion of macrophage-inflammatory protein 1α retards neurodegeneration in Sandhoff disease mice
Authors: Wu Yun-Ping , Proia Richard L.
Published: May 2004

Sandhoff disease is a prototypical lysosomal storage disorder in which a heritable deficiency of a lysosomal enzyme, β-hexosaminidase, results in the storage of the enzyme's substrates in lysosomes. As with many of the other lysosomal storage diseases, neurodegeneration is a prominent feature. Although the cellular and molecular pathways that underlie the neurodegenerative process are not yet fully understood, macrophage/microglial-mediated inflammation has been suggested as one possible mechanism. We now show that the expanded macrophage/microglial population in the CNS of Sandhoff disease mice is compounded by the infiltration of cells from the periphery. Coincident with the cellular infiltration was an increased expression of macrophage-inflammatory protein 1α (MIP-1α), a leukocyte chemokine, in astrocytes. Deletion of MIP-1α expression resulted in a substantial decrease in infiltration and macrophage/microglial-associated pathology together with neuronal apoptosis in Sandhoff disease mice. These mice without MIP-1α showed improved neurologic status and a longer lifespan. The results indicate that the pathogenesis of Sandhoff disease involves an increase in MIP-1α that induces monocytes to infiltrate the CNS, expand the activated macrophage/microglial population, and trigger apoptosis of neurons, resulting in a rapid neurodegenerative course.
Nuclear receptor corepressor RIP140 regulates fat accumulation
Authors: Leonardsson Göran , Steel Jenny H. , Christian Mark , Pocock Victoria , Milligan Stuart , Bell Jimmy , So Po-Wah , Medina-Gomez Gema , Vidal-Puig Antonio , White Roger , Parker Malcolm G.
Published: May 2004

Nuclear receptors and their coactivators have been shown to function as key regulators of adipose tissue biology. Here we show that a ligand-dependent transcriptional repressor for nuclear receptors plays a crucial role in regulating the balance between energy storage and energy expenditure. Mice devoid of the corepressor protein RIP140 are lean, show resistance to high-fat diet-induced obesity and hepatic steatosis, and have increased oxygen consumption. Although the process of adipogenesis is unaffected, expression of certain lipogenic enzymes is reduced. In contrast, genes involved in energy dissipation and mitochondrial uncoupling, including uncoupling protein 1, are markedly increased. Therefore, the maintenance of energy homeostasis requires the action of a transcriptional repressor in white adipose tissue, and ligand-dependent recruitment of RIP140 to nuclear receptors may provide a therapeutic target in the treatment of obesity and related disorders.
Can a simple measure of vigorous physical activity predict future mortality? Results from the OXCHECK study
Authors: Hillsdon Melvyn , Thorogood Margaret , Murphy Mike , Jones Lesley
Published: May 2004

Background:

As epidemiological studies have become more complex, demands for short, easily administered measures of risk factors have increased. This study investigates whether such a measure of physical activity is associated with the risk of death from all causes and death from specific causes.

Methods:

A prospective follow-up study of 11 090 men and women, aged 35–64 years, recruited from five UK general practices who responded to a postal questionnaire in 1989. Self-reported frequency of vigorous-intensity physical activity and data on confounding factors were collected at baseline survey. Death notifications up to 31 December 2001 were provided by the Office for National Statistics. The relative risk (and 95% confidence interval) of dying associated with each level of exposure to physical activity was estimated by the hazard ratio in a series of Cox regression models.

Results:

After > 10 years' follow-up there were 825 deaths among the 10 522 subjects with no previous history of angina or myocardial infarction. Participation in vigorous exercise was associated with a significantly lower risk of all-cause mortality. Similar associations were found for ischaemic heart disease and cancer mortality, although the relationships were not significant at the 5% level.

Conclusions:

Simple measures of self-reported vigorous physical activity are associated with the risk of future mortality, at least all-cause mortality in a somewhat selected group. Interpretation of the finding should be treated with caution due to the reliance on self-report and the possibility that residual confounding may underlie the associations. Because moderate-intensity physical activity is also beneficial to health, short physical activity questionnaires should include measures of such physical activity in the future.
Evaluation of Simplified Kinetic Analyses for Measurement of Brain Acetylcholinesterase Activity Using N-[11C]Methylpiperidin-4-yl Propionate and Positron Emission Tomography
Authors: Sato Koichi , Fukushi Kiyoshi , Shinotoh Hitoshi , Nagatsuka Shinichiro , Tanaka Noriko , Aotsuka Akiyo , Ota Tsuneyoshi , Shiraishi Tetsuya , Tanada Shuji , Iyo Masaomi , Irie Toshiaki
Published: May 2004

The applicability of two reference tissue-based analyses without arterial blood sampling for the measurement of brain regional acetylcholinesterase (AChE) activity using N-[11C]methylpiperidin-4-yl propionate ([11C]MP4P) was evaluated in 12 healthy subjects. One was a linear least squares analysis derived from Blomqvist's equation, and the other was the analysis of the ratio of target-tissue radioactivity relative to reference-tissue radioactivity proposed by Herholz and coworkers. The standard compartment analysis using arterial input function provided reliable quantification of k3 (an index of AChE activity) estimates in regions with low (neocortex and hippocampus), moderate (thalamus), and high (cerebellum) AChE activity with a coefficient of variation (COV) of 12% to 19%. However, the precise k3 value in the striatum, where AChE activity is the highest, was not obtained. The striatum was used as a reference because its time-radioactivity curve was proportional to the time integral of the arterial input function. Reliable k3 estimates were also obtained in regions with low-to-moderate AChE activity with a COV of less than 21% by striatal reference analyses, though not obtained in the cerebellum. Shape analysis, the previous method of direct k3 estimation from the shape of time-radioactivity data, gave k3 estimates in the cortex and thalamus with a somewhat larger COV. In comparison with the standard analysis, a moderate overestimation of k3 by 9% to 18% in the linear analysis and a moderate underestimation by 2% to 13% in the Herholz method were observed, which were appropriately explained by the results of computer simulation. In conclusion, simplified kinetic analyses are practical and useful for the routine analysis of clinical [11C]MP4P studies and are nearly as effective as the standard analysis for detecting regions with abnormal AChE activity.
Altered Biosynthesis of Neuropeptide Processing Enzyme Carboxypeptidase E after Brain Ischemia: Molecular Mechanism and Implication
Authors: Zhou An , Minami Manabu , Zhu Xiaoman , Bae Sylvia , Minthorne John , Lan Jingquan , Xiong Zhi-gang , Simon Roger P.
Published: May 2004

In this study, using both in vivo and in vitro ischemia models, the authors investigated the impact of brain ischemia on the biosynthesis of a key neuropeptide-processing enzyme, carboxypeptidase E (CPE). The response to brain ischemia of animals that lacked an active CPE was also examined. Combined in situ hybridization and immunocytochemical analyses for CPE showed reciprocal changes of CPE mRNA and protein, respectively, in the same cortical cells in rat brains after focal cerebral ischemia. Western blot analysis revealed an accumulation of the precursor protein of CPE in the ischemic cortex in vivo and in ischemic cortical neurons in vitro. Detailed metabolic labeling experiments on ischemic cortical neurons showed that ischemic stress caused a blockade in the proteolytic processing of CPE. When mice lacking an active CPE protease were subjected to a sublethal episode of focal cerebral ischemia, abundant TUNEL-positive cells were seen in the ischemic cortex whereas only a few were seen in the cortex of wild-type animals. These findings suggest that ischemia has an adverse impact on the neuropeptide-processing system in the brain and that the lack of an active neuropeptide-processing enzyme exacerbates ischemic brain injury.
Bayesian Inference for a Random Tessellation Process
Authors: Blackwell P. G.
Published: May 2004

Summary.This article describes an inhomogeneous Poisson point process in the plane with an intensity function based on a Dirichlet tessellation process and a method for using observations on the point process to make fully Bayesian inferences about the underlying tessellation. The method is implemented using a Markov chain Monte Carlo approach. An application to modeling the territories of clans of badgers,Meles meles, is described.
Inference Procedures for Assessing Interobserver Agreement among Multiple Raters
Authors: Altaye Mekibib , Dormer Allan , Klar Neil
Published: May 2004

Summary. We propose a new procedure for constructing inferences about a measure of interobserver agreement in studies involving a binary outcome and multiple raters. The proposed procedure, based on a chi‐square goodness‐of‐fit test as applied to the correlated binomial model (Bahadur, 1961, in Studies in Item Analysis and Prediction, 158–176), is an extension of the goodness‐of‐fit procedure developed by Donner and Eliasziw (1992, Statistics in Medicine11, 1511–1519) for the case of two raters. The new procedure is shown to provide confidence‐interval coverage levels that are close to nominal over a wide range of parameter combinations. The procedure also provides a sample‐size formula that may be used to determine the required number of subjects and raters for such studies.
Frailty Models with Missing Covariates
Authors: Herring Amy H. , Ibrahim Joseph G. , Lipsitz Stuart R.
Published: May 2004

Summary.We present a method for estimating the parameters in random effects models for survival data when covariates are subject to missingness. Our method is more general than the usual frailty model as it accommodates a wide range of distributions for the random effects, which are included as an offset in the linear predictor in a manner analogous to that used in generalized linear mixed models. We propose using a Monte Carlo EM algorithm along with the Gibbs sampler to obtain parameter estimates. This method is useful in reducing the bias that may be incurred using complete‐case methods in this setting. The methodology is applied to data from Eastern Cooperative Oncology Group melanoma clinical trials in which observations were believed to be clustered and several tumor characteristics were not always observed.
On Estimation and Prediction for Spatial Generalized Linear Mixed Models
Authors: Zhang Hao
Published: May 2004

Summary.We use spatial generalized linear mixed models (GLMM) to model non‐Gaussian spatial variables that are observed at sampling locations in a continuous area. In many applications, prediction of random effects in a spatial GLMM is of great practical interest. We show that the minimum mean‐squared error (MMSE) prediction can be done in a linear fashion in spatial GLMMs analogous to linear kriging. We develop a Monte Carlo version of the EM gradient algorithm for maximum likelihood estimation of model parameters. A by‐product of this approach is that it also produces the MMSE estimates for the realized random effects at the sampled sites. This method is illustrated through a simulation study and is also applied to a real data set on plant root diseases to obtain a map of disease severity that can facilitate the practice of precision agriculture.
High‐resolution wide‐field surface plasmon microscopy
Authors: STABLER G. , SOMEKH M. G. , SEE C. W.
Published: May 2004

This paper describes the application of a Köhler illuminated high‐resolution wide‐field microscope using surface plasmons to provide the image contrast. The response of the microscope to a grating structure in both the Fourier and the image planes is presented to demonstrate image formation by surface waves. The effect of spatial filtering in the back focal (Fourier) plane to enhance image constrast is described. We also discuss how the surface wave contrast mechanism affects the imaging performance of the microscope and discuss factors that can be expected to lead to even greater improvements in lateral resolution and sensitivity.