bluuebunny/crossref_metadata_2025 huggingface dataset:
A new simplified high radio frequency power amplifier
Authors: Ogawa Y. , Okutsu H. , Kobayashi N. , Hayakawa A.
Published: October 2004

In order to simplify a present standard high rf power amplifier of ion cyclotron range of frequency plasma heating system, a new amplifier arrangement composed of a tetrode with a grounded cathode and a field effect transistor (FET) switching circuit providing an input rf power is proposed. The FET switching circuit is so small that it can be installed close to the tetrode in one cubicle. It might be called a single tube high rf power amplifier. A test amplifier composed of the tetrode (8F76R) and the FET (2SK-1310) switching circuit is constructed. The maximum output rf power of 8.5 kW was stably obtained at 70 MHz. The feasibility of the single tube high rf power amplifier was experimentally proved.
Optical investigation of Zn1−xFexO films grown on Al2O3(0001) by radio-frequency sputtering
Authors: Kim Kwang Joo , Park Young Ran
Published: October 2004

Zn 1 − x Fe x O thin films were grown on Al2O3(0001) substrates by radio-frequency magnetron sputtering. The alloys show wurtzite crystal structure up to x=0.24 with reduced c-axis lattice constant compared to that of pure ZnO. Fe 2p core-level photoemission measurements reveal the evidence for the coexistence of the Fe3+ and Fe2+ ions substituting the tetrahedral the Zn2+ sites. The optical properties of the samples were measured by the spectroscopic ellipsometry at room temperature in the 1.5–5eV photon energy region. With increasing x, the optical band-gap (E0) absorption edge is found to shift slightly to lower energies (70meV for x=0.24) than that of the pure ZnO. Below the E0 edge, optical absorption structures are observed at about 1.7, 2.4, and 2.8eV. These structures are interpreted as due to the d-d transitions from the A16 ground state to the excited states, T14 (1.7eV), T24 (2.4eV), and E4 and A14 (2.8eV), of the crystal-field-split 3d5 multiplets of the tetrahedral Fe3+ ion.
Germanium effect on oxygen precipitation in Czochralski silicon
Authors: Li Hong , Yang Deren , Ma Xiangyang , Yu Xuegong , Que Duanlin
Published: October 2004

The oxygen precipitation in germanium-doped Czochralski (GCZ) silicon has been investigated. After a prolonged annealing at 800 and 1000°C, it was found that the Ge-doping enhanced the formation of oxygen precipitates with a higher density and modified their morphology and size. Furthermore, the existing oxygen precipitates in the GCZ silicon were readily dissolved, because the Ge-doping facilitated the formation of smaller oxygen precipitates. Based on the facts, the mechanism for the enhancement effect of Ge-doping on oxygen precipitation has been preliminarily discussed.
Introduction of Si∕SiO2 interface states by annealing Ge-implanted films
Authors: Marstein E. S. , Gunnæs A. E. , Olsen A. , Finstad T. G. , Turan R. , Serincan U.
Published: October 2004

Nanocrystals embedded in SiO2 films are the subject of a number of recent works, mainly because of their potential usefulness in the fabrication of optoelectronic devices and nanocrystal memory structures. One interesting method for the fabrication of such nanocrystals is the ion implantation of segregating species into SiO2 films followed by heat treatment in order to induce nanocrystal formation. This method is both relatively simple and also compatible with the current MOS (metal-oxide-semiconductor) device technology. An unintentional effect can occur during the fabrication of nanocrystals using this method, namely a significant diffusion of the implanted species during annealing, away from the regions with the highest concentration. The Si∕SiO2 interface can be exposed to this diffusion flux. This can result in an altered interface and have a significant influence on electronic devices. Here, we report on ion implantation of Ge into SiO2 on Si followed by annealing under conditions, resulting in Ge accumulation at the Si∕SiO2 interface as determined by secondary-ion mass spectroscopy analysis, transmission electron microscopy with energy dispersive analysis of x-rays, and Rutherford backscattering spectrometry. The accumulation of Ge at the Si∕SiO2 interface has also been reported before. The resulting effect on the electronic structure of the interface is a priori unknown. We have fabricated MOS capacitors on the sample structures and their capacitance-voltage characteristics were measured and analyzed. We measure an interface state density around 1×1012cm−2, which is high compared to standard Si MOS devices. We discuss the results in terms of the previous electrical measurements on Ge-oxide interfaces and SiGe interfaces, which also can yield a high interface state density. The specific conditions we report result in a sufficiently low Ge concentration that nanocrystals are not segregated in the SiO2 film, while Ge still accumulates at the Si∕SiO2 interface after annealing.
Dielectric behavior of polymer-stabilized-liquid-crystal cells made from hosts with different ultraviolet absorptions
Authors: Dessaud Nathalie , Raynes Peter , Bonnett Paul
Published: October 2004

Small concentrations (<7%) of reactive mesogen were introduced into liquid-crystal materials and filled into standard homogeneous planar-aligned cells, and the physical properties of the resulting polymer-stabilized-liquid-crystal cells were deduced from capacitance measurements. Two nematic liquid-crystal hosts were compared (E7 and ML1001), the former with significant ultraviolet absorption and the latter with negligible absorption. This paper uses capacitance results to find a model, which describes best the cells’ dielectric switching properties measured for both liquid-crystal hosts. Several models, considering the polymer network formed is totally rigid, totally elastic, or with mixed properties, are compared. Using a specific fitting routine, the unknown parameters for each model are determined to provide the best agreement between the observed and predicted electro-optic behavior. The quality of the fit is discussed for each model and that based on the well-known continuum energy expression for a simple nematic liquid crystal is found to give the best results.
Microlensed red and violet diode lasers in an extended cavity geometry
Authors: Carruthers A. E. , Lake T. K. , Shah A. , Allen J. W. , Sibbett W. , Dholakia K.
Published: October 2004

We examine the behavior of two microlensed diode lasers at 413 and 661 nm placed in both free-running and extended cavity geometries. The 25 mW free-running 413 nm diode shows current tuning over 40 GHz and the 50 mW, 661 nm diode shows tuning of 55 GHz. In extended cavity the 413 nm diode coarsely tunes 5 nm and finely tunes 6 GHz, with a linewidth of 4 MHz. The 661 nm diode coarsely tunes 11 nm with fine tuning of 6 GHz. Beam profile ratios for the 413 and 661 nm microlensed diodes are 1:1.06 and 1:1.10 respectively.
Compact microwave imaging system to measure spatial distribution of plasma density
Authors: Ito H. , Oba R. , Yugami N. , Nishida Y.
Published: October 2004

We have developed an advanced microwave interferometric system operating in the K band (18–27 GHz) with the use of a fan-shaped microwave based on a heterodyne detection system for measuring the spatial distribution of the plasma density. In order to make a simple, low-cost, and compact microwave interferometer with better spatial resolution, a microwave scattering technique by a microstrip antenna array is employed. Experimental results show that the imaging system with the microstrip antenna array can have finer spatial resolution than one with the diode antenna array and reconstruct a good spatially resolved image of the finite size dielectric phantoms placed between the horn antenna and the micro strip antenna array. The precise two-dimensional electron density distribution of the cylindrical plasma produced by an electron cyclotron resonance has been observed. As a result, the present imaging system is more suitable for a two- or three-dimensional display of the objects or stationary plasmas and it is possible to realize a compact microwave imaging system.
In-plane measurements of microelectromechanical systems vibrations with nanometer resolution using the correlation of synchronous images
Authors: Serio B. , Hunsinger J. J. , Cretin B.
Published: October 2004

We report on the development of a versatile vibrometer for characterizing in-plane microelectromechanical systems (MEMS) motion. It combines conventional optical components (microscope objective or macrozoom lens) and a home-made light-emitting diode (LED) stroboscope with incremental phase shifts. The system drives a digital charge-coupled device camera to record a video sequence of the moving MEMS “frozen” by the strobe LED at four equally spaced phases. The periodic motion of the specimen is accurately estimated by computing the values of displacements between successive images. We obtained the subpixel accuracy using an interpolation and correlation motion estimation algorithm. By using this technique, we analyzed vibrations of a silicon microprobe made for scanning probe microscopy. We determined both its natural vibration and mode shapes. The nanometer resolution of the displacement is reached using a microscope, and the mode shapes are imaged using a macrolens with a large field of view (10 mm). The experiments showed a good agreement with analytical predictions.
Development of a new two color far infrared laser interferometer for future fusion devices
Authors: Kawahata K. , Tanaka K. , Tokuzawa T. , Akiyama T. , Ito Y. , Okajima S. , Nakayama K. , Wylde R. J.
Published: October 2004

A new two color far infrared (FIR) laser interferometer under development for future fusion devices will be presented. The laser wavelength is optimized from the consideration of the beam refraction effect due to plasma density gradient and signal-to-noise ratio for an expected phase shift due to plasmas. Laser lines of 57.2 and 47.6 μm are found to be suitable for the applications to high performance plasmas of Large Helical Device and future fusion devices such as the International Thermonuclear Experimental Reactor. The output power of 57.2 μm CH3OD laser is estimated to be ∼1.6 W, which is the highest laser power in the FIR wavelength regime. The optical configuration of a new interferometer system using two colors will be proposed. In the system, one detector simultaneously detects the beat signals of the 57.2 and 47.6 μm laser lines, and each interference signal can be separated electronically (1 MHz for 57.2 μm and 0.84 MHz expected for 47.6 μm). Mechanical vibration can be compensated by using the two color interferometer. The present status of the development of the system is also presented.
Energy spectra of backscattered electrons in Auger electron spectroscopy: comparison of Monte Carlo simulations with experiment
Authors: Ding Z. J. , Li H. M. , Goto K. , Jiang Y. Z. , Shimizu R.
Published: October 2004

The primary energy dependecne and atomic-number dependence of backscattered electrons in Auger electron spectroscopy in the EN(E) mode have been investigated both theoretically and experimentally. A Monte Carlo simulation method with inclusion of cascade-secondary-electron production has been used to calculate the full energy distribution of backscattered electrons from the elastic peak down to the true-secondary-electron peak. The simulation model is based on the use of a dielectric function for describing inelastic scattering and secondary excitation, and on the use of Mott cross sections for elastic scattering. A systematic comparison between the calculated and experimental spectra measured with a cylindrical mirror analyzer has been made for Au, Ag, and Cu and for primary energies ranging from 0.5 to 5keV. Reasonable agreement was obtained for the backscattering background at primary energies in the keV region. A significant contribution of cascade-secondary electrons to the measured spectra on the low-energy side (less than 200eV ) was found. Experiments performed on elements with a wide range of atomic numbers have shown a quantitative common curve of the backscattering continuum when plotted on a logarithmic intensity scale in the intermediate energy region between 200eV and the low-loss peaks.
Low density GaAs∕AlGaAs quantum dots grown by modified droplet epitaxy
Authors: Mantovani V. , Sanguinetti S. , Guzzi M. , Grilli E. , Gurioli M. , Watanabe K. , Koguchi N.
Published: October 2004

Low temperature photoluminescence spectroscopy is used to analyze the effects of the Ga coverage and of the postgrowth thermal annealing on the electronic properties of low density (≈1×109cm−2) self-assembled GaAs∕AlGaAs quantum dots (QDs) grown by modified droplet epitaxy (MDE). We demonstrate that with the MDE method it is possible to obtain low density and high efficiency QD samples with high photoluminescence efficiency. Large modifications of the photoluminescence band, which depend on Ga coverage and thermal annealing, are found and quantitatively interpreted by means of a simple model based on the Al-Ga interdiffusion.
Photoluminescence and deep levels in lattice-matched InGaAsN∕GaAs
Authors: Fischer C. H. , Bhattacharya P.
Published: October 2004

Temperature-dependent photoluminescence measurements and deep level transient spectroscopy have been made to identify defects and deep level traps in InGaAsN alloys lattice-matched to GaAs. The epitaxial layers were grown by molecular beam epitaxy at different substrate temperatures. Defect levels responsible for the quenching of luminescence with increase of temperature have been identified. Several electron trap levels have been identified and characterized in the alloys. The concentrations of all of these increase with N content in the alloy. A dominant center, with an activation energy of ET=0.44eV, is present in all the samples and its concentration is inversely proportional to photoluminescence intensity. H2O and O present in the source nitrogen are believed to be responsible for the presence of this trap, which also has characteristics similar to the E3 and E4 levels in molecular beam epitaxial GaAs.
In situ high pressure-temperature Raman spectroscopy technique with laser-heated diamond anvil cells
Authors: Lin Jung-Fu , Santoro Mario , Struzhkin Viktor V. , Mao Ho-kwang , Hemley Russell J.
Published: October 2004

We describe an in situ high pressure-temperature Raman technique for studying materials in laser-heated diamond anvil cells using a Nd:YLF laser (1053 nm) as the heating source and an ion laser as the Raman exciting source. Here we introduce the method of laser heating transparent samples using a metallic foil (Pt,Re, or W) as the laser absorber (internal heating furnace) in a diamond cell. The YLF laser is used to effectively laser-heat one side of a metal foil 5–15 μm thick with a small hole of 10–20 μm in diameter at the center. The foil, in turn, heats a transparent sample while the Raman signals excited by an Ar+ or Kr+ laser are measured. Temperature of the laser-heated foil is measured by means of spectroradiometry whereas the average temperature of the heated sample is independently determined from the intensity ratios of the anti-Stokes/Stokes excitation pairs. The intrinsic temperature-dependent asymmetry of the Raman spectra arises from the principle of the detailed balance and is independent of sample properties other than the temperatures. The average determined by the signal-to-noise ratio of anti-Stokes/Stokes excitation pairs gives the sample temperature with the statistical accuracy of the Raman spectra. Transparent samples such as CO2 have been heated up to 1600 K and 65 GPa and Raman spectra have been measured with temperature uncertainty of 50–100 K. In situ Raman spectroscopy by laser heating represents a powerful technique to characterize high pressure-temperature properties of materials including molecular systems present in planetary interiors.
Elastic flow instability, curved streamlines, and mixing in microfluidic flows
Authors: Pathak Jai A. , Ross David , Migler Kalman B.
Published: October 2004

Flow instabilities are well known to occur in macroscopic flows when elastic fluids flow along curved streamlines. In this work we use flow visualization to study the mechanism underlying a purely elastic flow instability for Poiseuille flow in a micro (μ)channel having a zigzag path (curved streamlines) and quantitatively investigate its implications for fluid mixing (studied by fluorescence microscopy) in the μchannel. We find that the instability enhances mixing over the range of applied flow rates. For Newtonian streams, mixing occurs by molecular diffusion, and, as expected, mixing worsens with increasing flow rate because of decreasing residence time. However, for elastic fluid streams, we find substantial enhancement of mixing at sufficiently high throughputs, which indicates a strategy to counter the loss of diffusive mixing at high throughputs by exciting an elastic flow instability. Flow visualization is done using neutrally buoyant non-Brownian tracer particles added to the elastic fluids and also to the Newtonian fluids. In the Newtonian fluids, the tracer particles follow the streamlines. In the elastic fluids, the particles are radially displaced while flowing around bends in the zigzag μchannel, revealing the presence of secondary flow. This radial secondary flow, which promotes mixing between adjacent fluid streams, motivates us to draw an analogy between the instability observed here for the elastic fluids in the μchannel and the elastic instability that occurs in systems with curved streamlines, e.g., in the viscoelastic (non-inertial) Taylor–Couette, Dean, and Taylor–Dean instabilities.
Vortex state stability in soft magnetic cylindrical nanodots
Authors: Guslienko K. Yu. , Novosad V.
Published: October 2004

The stability of the vortex magnetization state in circular cylindrical soft magnetic dots is calculated analytically and by micromagnetic simulations. For the cases considered the dot thickness is comparable to the material exchange length and dot radii are in the submicron range. The equation for the vortex magnetization distribution is analyzed taking exact account of the magnetostatic field inside dot. The limitations and applicability of a previously proposed “exchange-dominated” vortex ansatz are discussed. It is shown that for the transition from the vortex to perpendicular single-domain state the magnetization distribution changes continuously while retaining the axial symmetry. The zero-field critical line of the transition is calculated analytically as a function of dot size and is compared with micromagnetic simulations of the vortex magnetization profile.
Perturbation of charges in AlGaN∕GaN heterostructures by ultraviolet laser illumination
Authors: Koley G. , Cha Ho-Young , Hwang Jeonghyun , Schaff W. J. , Eastman L. F. , Spencer M. G.
Published: October 2004

Perturbation of charges in AlGaN∕GaN heterostructures by ultraviolet (UV) laser illumination has been studied by Kelvin probe microscopy. It is observed that the charge dipole formed across the AlGaN barrier decreases under UV laser illumination, and typically takes a few days to a few weeks to revert back to the original equilibrium value. Bare surface barrier height of AlGaN∕GaN heterostructures has been calculated based on the observed recovery transients after the UV illumination is switched off, and found to increase with Al alloy composition as well as thickness of the AlGaN layer. After SiNx passivation, the surface barrier is reduced, and the charges cannot be perturbed to a significant extent. It is further observed that by UV illumination through a quartz mask, surface barrier patterns can be imprinted on AlGaN∕GaN heterostructures, which stay for several hours to several days. It is proposed that the imprinted patterns, with a spatial resolution ∼1–2μm, are caused by surface trapping of photogenerated holes.
Monte Carlo modeling of spin injection through a Schottky barrier and spin transport in a semiconductor quantum well
Authors: Shen Min , Saikin Semion , Cheng Ming-C.
Published: October 2004

We develop a Monte Carlo model to study injection of spin-polarized electrons through a Schottky barrier from a ferromagnetic metal contact into a nonmagnetic low-dimensional semiconductor structure. Both mechanisms of thermionic emission and tunneling injection are included in the model. Due to the barrier shape, the injected electrons are nonthermalized. Spin dynamics in the semiconductor heterostructure is controlled by the Rashba and Dresselhaus spin-orbit interactions and described by a single electron spin density matrix formalism. In addition to the linear term, the third-order term in momentum for the Dresselhaus interaction is included. Effect of the Schottky potential on the spin dynamics in a two-dimensional semiconductor device channel is studied. It is found that the injected current can maintain substantial spin polarization to a length scale in the order of 1μm at room temperature without external magnetic fields.
High-pressure phase transition of mullite under shock compression
Authors: Kawai Nobuaki , Nakamura Kazutaka G. , Kondo Ken-ichi
Published: October 2004

Hugoniot measurements have been performed on mullite polycrystals in the pressure range up to 80GPa by using a two-stage light-gas gun and a Doppler laser interferometer. The Hugoniot elastic limit is determined to be 16.1±2.2GPa. The Hugoniot data show that the phase transition occurs at 30.4±3.6GPa. Comparison of the Hugoniot data with calculated theoretical Hugoniots suggests that the high-pressure phase transition of mullite is its disproportionation to corundum and stishovite. The mixed phase region is between 30 and 70GPa. It is indicated that this phase transition is very sluggish.
Conditions for waveguide decoupling in square-lattice photonic crystals
Authors: Koponen T. , Huttunen A. , Törmä P.
Published: October 2004

We study coupling and decoupling of parallel waveguides in two-dimensional square-lattice photonic crystals. We show that the waveguide coupling is prohibited at some wavelengths when there is an odd number of rows between the waveguides. In contrast, decoupling does not take place when there is an even number of rows between the waveguides. Decoupling can be used to avoid cross talk between adjacent waveguides.
Experimental analysis of the coalescence process via head-on collisions in a time-dependent flow
Authors: Borrell Marcos , Yoon Y. , Leal L. Gary
Published: October 2004

The present study experimentally investigates the mechanisms involved in the flow-induced coalescence process for two equal-sized drops (polybutadiene drops suspended in a polydimethylsiloxane matrix), by taking advantage of the capability of the computer-controlled “four-roll mill” to carry out head-on collisions. In this work, head-on collision experiments have been carried out for a time-dependent flow that is designed so that the force along the line of centers mimics the force history due to rotation of the two droplets in a glancing collision. One primary goal of these experiments is to assess the importance of global deformation of the drops in the coalescence process. Specifically, we seek to determine whether global deformation plays a role in the observation that coalescence often occurs during the portion of a glancing collision when the drops are actually being pulled apart by the external flow. By comparison of the results for head-on and glancing collisions, we find that coalescence occurs in an apparently identical fashion in spite of the fact that the overall shape of the drops must be different since the velocity gradient is steady during the glancing collision but time dependent in the head-on collision. Specifically, the (near) axisymmetric film drainage process achieved in a head-on collision is apparently a very good approximation to the same process in a nonaxisymmetric glancing collision, suggesting that the coalescence process is dominated by the time history of the force along the line of centers and is at least approximately independent of the degree of asymmetry in the overall collision process.
Recurrence time statistics for finite size intervals
Authors: Altmann Eduardo G. , da Silva Elton C. , Caldas Iberê L.
Published: October 2004

We investigate the statistics of recurrences to finite size intervals for chaotic dynamical systems. We find that the typical distribution presents an exponential decay for almost all recurrence times except for a few short times affected by a kind of memory effect. We interpret this effect as being related to the unstable periodic orbits inside the interval. Although it is restricted to a few short times it changes the whole distribution of recurrences. We show that for systems with strong mixing properties the exponential decay converges to the Poissonian statistics when the width of the interval goes to zero. However, we alert that special attention to the size of the interval is required in order to guarantee that the short time memory effect is negligible when one is interested in numerically or experimentally calculated Poincaré recurrence time statistics.
A fractional equation for anomalous diffusion in a randomly heterogeneous porous medium
Authors: Logvinova Kira , Néel Marie-Christine
Published: October 2004

A fractional partial differential equation is derived for the spreading of matter in a saturated porous medium starting from precise hypotheses concerning the medium itself, which is a collection of intertwisted tubes with randomly distributed slopes, filled with quiescent fluid. Examining the fundamental solution of the fractional equation indicates that the second moment is not proportional to time, which is the signature of anomalous diffusion. The equation derived preserves non-negativity and also the total mass of matter.
Coplanar two vortex filaments without change of form
Authors: Ohtsuka Kazumichi , Takaki Ryuji , Watanabe Shinsuke
Published: October 2004

Shapes of a coplanar vortex pair rotating around a central axis without change of a shape is obtained by solving an equation governing an entanglement motion of a corotating vortex pair. The governing equation, called an entanglement equation, is derived from the Biot-Savart law with an assumption of the local induction. It is shown that the solution exist within a finite range of the radial coordinate perpendicular to the central axis, and that vortex pair takes a shape of horn type or barrel one depending on an intervortex separation at boundary.
Air-damping effects on developing velocity profiles in flowing soap films
Authors: Huang M.-J. , Wen C.-Y. , Lee I.-C. , Tsai C.-H.
Published: October 2004

The continuously running gravity-driven soap-film tunnel is a device suitable for the study of two-dimensional flows. In this innovative device, the films start from a reservoir, run over a vertical wire frame and get pulled by the gravity force. Despite its simple design and successful applications in two-dimensional flows, its working mechanisms are not fully understood. In the present work, the laminar velocity profiles of freely suspended flowing soap films are examined theoretically and experimentally. A complete momentum integral analysis is performed including boundary layers developed within the channel on the film as well as beside the film in the air. The theoretical results are compared with the experimental measurements via laser Doppler velocimetry. Reasonable agreements are observed. Although the gravity force speeds up the film motion, the acceleration is significantly slowed down, but not completely, by the air friction. The growth of the boundary layers developed on the film is also damped by the air friction so that across the film channel the velocity profile is mostly uniform. Moreover, a saturated boundary layer thickness seemingly exists when the thinning due to acceleration and the thickening due to viscous diffusion are in balance.
On the sensitivity of dynamo action to the system’s magnetic diffusivity
Authors: Müller U. , Stieglitz R. , Busse F. H.
Published: October 2004

An experiment at the Karlsruhe dynamo test facility has shown that the intensity of the dynamo magnetic field decreases significantly with increasing temperature of the test fluid, liquid sodium, while keeping the other control parameters constant. This is explained by the increasing magnetic diffusivity with increasing temperatures utilizing results from a weakly nonlinear analysis of Tilgner and Busse [“Saturation mechanism in a model of the Karlsruhe dynamo,” in Dynamo and Dynamics, a Mathematical Challenge, NATO Science Series, II. Mathematics, Physics and Chemistry, Vol. 26, edited by P. Chossat, D. Armbruster, and I. Oprea (Kluwer, Dordrecht, 2001)] for the transcritical regime of the Karlsruhe dynamo experiment. The observations are also interpreted by dimensional reasoning utilizing previous experimental results.
Current Controlled Current Differencing Buffered Amplifier: Implementation and Applications
Authors: Maheshwari Sudhanshu , Khan Iqbal A.
Published: October 2004

A new four terminal current‐controlled active element is introduced, where parasitic resistances at two current input ports are controlled leading to the definition of current‐controlled current differencing buffered amplifier. Bipolar implementation and as application current‐mode band‐pass filter circuits are proposed. Simulation results using real device parameters are included, which show device bandwidth of 35 MHz, low total harmonic distortions, and tuning over a wide current range.
GATA-2 Plays Two Functionally Distinct Roles during the Ontogeny of Hematopoietic Stem Cells
Authors: Ling Kam-Wing , Ottersbach Katrin , van Hamburg Jan Piet , Oziemlak Aneta , Tsai Fong-Ying , Orkin Stuart H. , Ploemacher Rob , Hendriks Rudi W. , Dzierzak Elaine
Published: October 2004

GATA-2 is an essential transcription factor in the hematopoietic system that is expressed in hematopoietic stem cells (HSCs) and progenitors. Complete deficiency of GATA-2 in the mouse leads to severe anemia and embryonic lethality. The role of GATA-2 and dosage effects of this transcription factor in HSC development within the embryo and adult are largely unexplored. Here we examined the effects of GATA-2 gene dosage on the generation and expansion of HSCs in several hematopoietic sites throughout mouse development. We show that a haploid dose of GATA-2 severely reduces production and expansion of HSCs specifically in the aorta-gonad-mesonephros region (which autonomously generates the first HSCs), whereas quantitative reduction of HSCs is minimal or unchanged in yolk sac, fetal liver, and adult bone marrow. However, HSCs in all these ontogenically distinct anatomical sites are qualitatively defective in serial or competitive transplantation assays. Also, cytotoxic drug-induced regeneration studies show a clear GATA-2 dose–related proliferation defect in adult bone marrow. Thus, GATA-2 plays at least two functionally distinct roles during ontogeny of HSCs: the production and expansion of HSCs in the aorta-gonad-mesonephros and the proliferation of HSCs in the adult bone marrow.
CXCR2- and E-Selectin–induced Neutrophil Arrest during Inflammation In Vivo
Authors: Smith Michael L. , Olson Timothy S. , Ley Klaus
Published: October 2004

The signaling events leading to the activation of integrins and firm arrest of rolling neutrophils in inflamed venules have yet to be elucidated. In vitro assays suggest that both E-selectin and chemokines can trigger arrest of rolling neutrophils, but E-selectin−/− mice have normal levels of adherent neutrophils in inflamed venules. To test whether chemokine-induced neutrophil arrest in vivo can be unmasked by blocking E-selectin, we investigated neutrophil adhesion in inflamed cremaster muscle venules in tumor necrosis factor (TNF)-α–treated CXCR2−/− or wild-type (WT) mice injected with E-selectin blocking monoclonal antibody (mAb) 9A9. To block chemokine receptor signaling, we investigated E-selectin−/− or WT mice treated with pertussis toxin (PTx) intravenously. Neutrophil adhesion was unchanged in CXCR2−/−, E-selectin−/−, PTx-treated WT, or mAb 9A9–treated WT mice. However, TNF-α–induced neutrophil adhesion was almost completely abrogated in E-selectin−/− mice treated with PTx and significantly reduced in CXCR2−/− mice treated with the E-selectin blocking mAb. In thioglycollate-induced peritonitis, PTx treatment blocked neutrophil recruitment into the peritoneum of E-selectin−/− mice, but had only a partial effect in WT animals. These data show that E-selectin– and chemokine-mediated arrest mechanisms are overlapping in this model and identify CXCR2 as an important neutrophil arrest chemokine in vivo.
Basophils Initiate IL-4 Production during a Memory T-dependent Response
Authors: Khodoun Marat V. , Orekhova Tatyana , Potter Crystal , Morris Suzanne , Finkelman Fred D.
Published: October 2004

Experiments were performed to characterize and identify the cellular sources of the secondary interleukin (IL)-4 response to a T cell–dependent antigen. Mice were primed by immunization with goat anti–mouse immunoglobulin (Ig)D antibody (GaMD), which stimulates naive CD4+ T cells to secrete IL-4 in 3–4 d. When challenged with goat serum 14 d after immunization, GaMD-primed mice generated an IL-4 response that exceeded the primary response by ∼100-fold, started in <2 h, and lasted for 4 d. Studies with 4get mice, in which cells with an accessible Il4 gene express a green fluorescent protein (GFP), revealed CD4+ memory T cells, natural killer T cells, basophils, mast cells, and eosinophils as possible rapid producers of IL-4. GFP+CD4+ T cells and basophils expanded more in the spleen than the other cell types during the primary response to GaMD. Quantitation of in vivo IL-4 production by the in vivo cytokine capture assay after individual cell types were selectively stimulated or deleted demonstrated that basophils and memory CD4+ T cells account for most of the secondary IL-4 response, with basophils initiating that response through IgE/FcεRI-mediated signaling but secreting IL-4 for <4 h and memory T cells secreting IL-4 within 4 h and continuing to secrete this cytokine for 4 d.
Bruton's Tyrosine Kinase Is Essential for Human B Cell Tolerance
Authors: Ng Yen-Shing , Wardemann Hedda , Chelnis James , Cunningham-Rundles Charlotte , Meffre Eric
Published: October 2004

Most polyreactive and antinuclear antibodies are removed from the human antibody repertoire during B cell development. To elucidate how B cell receptor (BCR) signaling may regulate human B cell tolerance, we tested the specificity of recombinant antibodies from single peripheral B cells isolated from patients suffering from X-linked agammaglobulinemia (XLA). These patients carry mutations in the Bruton's tyrosine kinase (BTK) gene that encode an essential BCR signaling component. We find that in the absence of Btk, peripheral B cells show a distinct antibody repertoire consistent with extensive secondary V(D)J recombination. Nevertheless, XLA B cells are enriched in autoreactive clones. Our results demonstrate that Btk is essential in regulating thresholds for human B cell tolerance.
Cyclic GMP-dependent protein kinase II is a molecular switch from proliferation to hypertrophic differentiation of chondrocytes
Authors: Chikuda Hirotaka , Kugimiya Fumitaka , Hoshi Kazuto , Ikeda Toshiyuki , Ogasawara Toru , Shimoaka Takashi , Kawano Hirotaka , Kamekura Satoru , Tsuchida Atsuko , Yokoi Norihide , Nakamura Kozo , Komeda Kajuro , Chung Ung-il , Kawaguchi Hiroshi
Published: October 2004

The Komeda miniature rat Ishikawa (KMI) is a naturally occurring mutant caused by an autosomal recessive mutation mri, which exhibits longitudinal growth retardation. Here we identified the mri mutation as a deletion in the rat gene encoding cGMP-dependent protein kinase type II (cGKII). KMIs showed an expanded growth plate and impaired bone healing with abnormal accumulation of postmitotic but nonhypertrophic chondrocytes. Ex vivo culture of KMI chondrocytes reproduced the differentiation impairment, which was restored by introducing the adenovirus-mediated cGKII gene. The expression of Sox9, an inhibitory regulator of hypertrophic differentiation, persisted in the nuclei of postmitotic chondrocytes of the KMI growth plate. Transfection experiments in culture systems revealed that cGKII attenuated the Sox9 functions to induce the chondrogenic differentiation and to inhibit the hypertrophic differentiation of chondrocytes. This attenuation of Sox9 was due to the cGKII inhibition of nuclear entry of Sox9. The impaired differentiation of cultured KMI chondrocytes was restored by the silencing of Sox9 through RNA interference. Hence, the present study for the first time shed light on a novel role of cGKII as a molecular switch, coupling the cessation of proliferation and the start of hypertrophic differentiation of chondrocytes through attenuation of Sox9 function.
Epidermal detachment, desmosomal dissociation, and destabilization of corneodesmosin in Spink5-/- mice
Authors: Yang Tao , Liang Dongcai , Koch Peter J. , Hohl Daniel , Kheradmand Farrah , Overbeek Paul A.
Published: October 2004

Netherton syndrome (NS) is a human autosomal recessive skin disease caused by mutations in the SPINK5 gene, which encodes the putative proteinase inhibitor LEKTI. We have generated a transgenic mouse line with an insertional mutation that inactivated the mouse SPINK5 ortholog. Mutant mice exhibit fragile stratum corneum and perinatal death due to dehydration. Our analysis suggests that the phenotype is a consequence of desmosomal fragility associated with premature proteolysis of corneodesmosin, an extracellular desmosomal component. Our mouse mutant provides a model system for molecular studies of desmosomal stability and keratinocyte adhesion, and for designing therapeutic strategies to treat NS.
The activity of the Nodal antagonist Cerl-2 in the mouse node is required for correct L/R body axis
Authors: Marques Sara , Borges Ana Cristina , Silva Ana Cristina , Freitas Sandra , Cordenonsi Michelangelo , Belo José António
Published: October 2004

Correct establishment of the left/right (L/R) body asymmetry in the mouse embryo requires asymmetric activation of the evolutionarily conserved Nodal signaling cascade in the left lateral plate mesoderm (L-LPM). Furthermore, the presence of Nodal in the node is essential for its own expression in the L-LPM. Here, we have characterized the function of cerl-2, a novel Nodal antagonist, which displays a unique asymmetric expression on the right side of the mouse node. cerl-2 knockout mice display multiple laterality defects including randomization of the L/R axis. These defects can be partially rescued by removing one nodal allele. Our results demonstrate that Cerl-2 plays a key role in restricting the Nodal signaling pathway toward the left side of the mouse embryo by preventing its activity in the right side.
Participation of CYP2A in Cocaine‐Induced Hepatotoxicity in Female Mice
Authors: Aoki Kimiko , Takimoto Masafumi , Ota Hidekazu , Yoshida Takemi
Published: October 2004

Female ICR mice were treated with cocaine either alone or in combination with one of several cytochrome P450 (CYP) inducers, i.e. phenobarbital, β‐ionone, dexamethasone and β‐naphthoflavone. Cocaine‐induced hepatotoxicity was first observed by pretreatment with phenobarbital, β‐ionone or dexamethasone in accordance with significant elevation of cocaine N‐demethylation, the first step of cocaine bioactivation. The hepatic lesions occured in the periportal region (zone 1) by phenobarbital and β‐ionone and in the perivenular region (zone 3) by dexamethasone. The activities of the enzyme specific for CYP isozyme were determined to elucidate the effects of pretreatment with CYP inducers. β‐Naphthoflavone induced CYP1A and 2B but had no effects on hepatotoxicity by cocaine. On the other hand, β‐ionone enhanced hepatotoxicity without induction of CYP3A. Activities of cocaine N‐demethylase correlated well with CYP2A (r=0.83) and CYP2B (r=0.81). Cocaine N‐demethylation was inhibited particularly by addition of the CYP2A specific inhibitor, 8‐methoxypsoralen. Moreover, pretreatment with 8‐methoxypsoralen produced a marked inhibition of the hepatotoxicity induced by cocaine in phenobarbital‐treated mice. These results suggest that cocaine‐induced hepatotoxicity in female mice was mediated in part by CYP2A, participating in cocaine N‐demethylation.
Age‐Related Differences on Aluminium Mobilization by Chelating Agents in Aluminium‐Loaded Uraemic Rats
Authors: Esparza Jose L. , Gómez Mercedes , Domingo Jose L. , Del Castillo Daniel , Hernández Mercedes
Published: October 2004

The efficacy of deferoxamine, deferiprone, and a combination of these chelating agents in the mobilization and promotion of aluminium (Al) excretion was compared in two age groups of uraemic rats which had previously received Al nitrate nonahydrate intraperitoneally in a daily dose of 45 mg/kg for 5 weeks. At the end of the period of Al exposure, Al‐loaded rats of each age (young and adult) group were given one of the following treatments for 5 days: 0.90 mmol/kg/day of deferoxamine (subcutaneously), 0.90 mmol/kg/day of deferiprone (orally), and 0.45 mmol/kg/day of deferoxamine (subcutaneously) plus 0.45 mmol/kg/day of deferiprone (orally). Control rats were given 0.9% saline (subcutaneously) and deionized water (orally). Total urines were collected 24 hr after each chelator administration. Although young rats treated with deferoxamine, deferiprone, or deferoxamine plus deferiprone showed significant increases in the total amount of Al excreted into urine during 5 consecutive days, the effect of combined administration of deferoxamine and deferiprone was lower than that caused by deferoxamine or deferiprone only. On the other hand, after administration of deferoxamine and deferiprone, a significant reduction of Al was noted only in the liver of young rats, while no significant effects of the chelators were seen in any of the examined tissues of adult animals. The results of the current study show that a combined therapy with deferoxamine and deferiprone (at half‐doses of each drug) can also be effective in mobilizing Al from the body of Al‐loaded uraemic rats.
Lithium has No Direct Effect on Cardiac Function in the Isolated, Perfused Rat Heart
Authors: Linakis James G. , Savitt Daniel L. , Schuyler Joy E. , Simon Peter M. , Raymond Richard M.
Published: October 2004

To determine if lithium exerts direct cardiac toxicity, using an isolated, perfused rat heart model, paced and unpaced beating rat hearts were perfused with Krebs‐Henseleit bicarbonate solution and left ventricular pressures were measured via a balloon‐tipped catheter positioned in the left ventricle via the mitral valve. Following a stabilization period, hearts were then perfused with Krebs‐Henseleit bicarbonate solution containing 1, 10, and 100 mM ionized lithium chloride or lithium carbonate in an antecedent dose‐response protocol and perfused for 10 min. at each dose. To control for the possibility of osmotic effects from the high dose of lithium, an additional group was studied in which hearts were perfused with Krebs‐Henseleit bicarbonate solution for an initial stabilization period, then perfused for an additional 20 min. with Krebs‐Henseleit bicarbonate solution alone, and finally with Krebs‐Henseleit bicarbonate solution containing mannitol (200 mOsm/l) for 10 min. Lithium did not have any effect on left ventricular peak systolic pressure, left ventricular end diastolic pressure, heart rate or coronary haemodynamics at concentrations of 1 or 10 mM. At 100 mM LiCl and Li2CO3, left ventricular peak systolic pressure decreased transiently during the first minute of lithium infusion, but recovered significant function by 10 min. Heart rate decreased significantly by 10 min. of infusion. These effects were also seen in the osmotic controls and thus do not appear to be a direct effect of lithium. At the doses tested, lithium had no direct effect on cardiac function which could not be explained by an osmotic effect.
Supernatants from Macrophages Stimulated with Microcystin‐LR Induce Electrogenic Intestinal Response in Rabbit Ileum
Authors: Rocha Marcos F. G. , Sidrim José J. C. , Soares Alberto M. , Jimenez George C. , Guerrant Richard L. , Ribeiro Ronaldo A. , Lima Aldo A. M.
Published: October 2004

Microcystin‐LR is a cyclic heptapeptide hepatotoxin produced by the cyanobacterium Microcystis aeruginosa. This microorganism often forms toxic blooms in freshwater lakes and reservoirs for drinking water supply, producing serious disorders in humans and animals. Some have suggested that certain biological activities of microcystin may depend upon the stimulation of immune cells. Therefore, the aims of this research were to examine electrogenic intestinal secretion, in vitro, caused by the supernatants from macrophages stimulated with microcystin‐LR, as well as to investigate the presence of interleukin‐1β and tumour necrosis factor‐α in these supernatants. We found that the supernatants of macrophages stimulated with microcystin‐LR (0.1, 0.3 and 1.0 μg/ml) caused electrogenic intestinal effects (change in short‐circuit currents (Δ SCC)=57.6, 50.8 and 73.3, respectively, versus control=19.6 μA.cm−2) in a time‐dependent way (microcystin‐LR (1.0 μg/ml)=63.2, 108.8, 120.4 and 132.3 μA.cm−2 at time 0, 40, 50 and 60 min., respectively). In addition, the intestinal secretory activity present in these supernatants was blocked (57%) by the prior treatment of macrophages with dexamethasone. We also demonstrated that microcystin‐LR (0.1, 0.3 and 1.0 μg/ml) is capable of stimulating the synthesis of tumour necrosis factor‐α (375.4, 369.0 and 610.8 pg/ml, respectively, versus control=165.0 pg/ml) and interleukin‐1β (198.9, 189.3 and 522.1 pg/ml, respectively, versus control=39.7 pg/ml). These findings demonstrate that microcystin‐LR induces the release of interleukin‐1β and tumour necrosis factor‐α by peritoneal macrophages in vitro, and that the supernatants from these macrophages induce electrogenic secretion in rabbit ileal mucosa.
Citizen Response to Disasters: a Survey of Literature and Some Practical Implications
Authors: Helsloot I. , Ruitenberg A.
Published: October 2004

It is most likely that the modern citizen responds to disasters in the same fashion as his ancestor. Contrary to widespread belief, citizens do not panic in disaster situations. In fact, research into different aspects of citizen response shows that most citizens act in a rather rational way. Indeed, citizens often prove to be the most effective kind of emergency personnel. Disaster evaluations invariably show that most lives are actually saved by the ‘average’ citizen. On the other hand, it seems little can be done to improve citizen preparedness. A modern western citizen is not likely to invest time or money in preparing for ‘acceptable’ risks.

The above results stem for the greater part from research already conducted as long ago as the nineteen‐eighties. Limitations and implications however seem as yet unclear. One important limitation is the cultural bias in most studies. One important implication is that in western countries government should step in to improve citizen response by preparing to facilitate it in times of disaster.
Genetic basis of blood group diversity
Authors: Storry Jill R. , Olsson Martin L.
Published: October 2004

In the last 18 years the genes that encode all but one of the 29 blood group systems present on red blood cells (RBCs) have been identified. This body of knowledge has permitted the application of molecular techniques to characterize the common blood group antigens and to elucidate the background for some of the variant phenotypes. Just as the RBC was used as a model for the biochemical characterization of cell membranes, so the genes encoding blood groups provide a readily accessible model for the study of gene expression and diversity. The application of genotyping techniques to identify fetuses at risk of haemolytic disease of the newborn is now the standard of care, and the expansion of nucleic acid testing platforms to include both disease testing and blood typing in the blood centre is on the horizon. This review summarizes the molecular basis of blood groups and illustrates the mechanisms that generate diversity through specific examples.