bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect on stellarator neoclassical transport of a fluctuating electrostatic spectrum
Authors: Mynick H. E. , Boozer A. H.
Published: June 2005

A study is presented of the effect on neoclassical transport of a fluctuating electrostatic spectrum, such as produced either by plasma turbulence, or imposed externally. For tokamaks, it is usually assumed that the neoclassical and “anomalous” contributions to the transport roughly superpose, D=Dnc+Dan, an intuition also used in modeling stellarators. An alternate intuition, however, is one where it is the collisional and anomalous scattering frequencies which superpose, νef=ν+νan. For nonaxisymmetric systems, in regimes where ∂D∕∂ν<0, this “νef picture” implies that turning on the fluctuations can decrease the total radial transport. Using numerical and analytic means, it is found that the total transport has contributions conforming to each of these intuitions, either of which can dominate. In particular, for stellarators, the νef picture is often valid, producing transport behavior differing from tokamaks.
Modulation of magnetized multidimensional waves in dusty plasma
Authors: Xue Ju-Kui
Published: June 2005

The modulation of weakly three-dimensional (3D) dust-ion acoustic waves (DIAW) in a magnetized dusty plasma is studied. By using the standard reductive perturbation method, a three-dimensional nonlinear Schödinger equation (3D NLSE) in magnetized dusty plasma is obtained. The modulational instability of weakly 3D DIAW described by the 3D NLSE is investigated. Some new and important explicit criteria are obtained. It is shown that the modulation properties of weakly 3D DIAWs in magnetized and unmagnetized dusty plasmas are very different.
Spin waves in dusty plasmas
Authors: Shokri B. , Alavi S. Kh.
Published: June 2005

Taking into account the spin of dust particles in a dusty plasma, the bulk and surface spin oscillations in an isotropic one are studied. The dispersion relation and frequency spectra for bulk and surface spin waves are obtained.
Self-expansion patterns of charged particulates and ionic assemblies
Authors: Zimmels Y. , Kojevnikova S. , Agnon Y.
Published: June 2005

Self-expansion patterns of unconstrained assemblies of charged particulates are considered. As the assemblies cannot be described, in general, in the context of a continuum comprising massless charged entities, the complete equation of motion is applied for each member of the assembly. It is shown that irrespective of the initial positions of the particulates, when expanding in free space or else they are identical in size and mass, the assembly tends toward a spherical shape, with characteristic inner structure. Examples of simulations are presented to this end.
Effect of frequency variation on electromagnetic pulse interaction with charges and plasma
Authors: Khachatryan A. G. , van Goor F. A. , Verschuur J. W. J. , Boller K.-J.
Published: June 2005

The effect of frequency variation (chirp) in an electromagnetic (EM) pulse on the pulse interaction with a charged particle and plasma is studied. Various types of chirp and pulse envelopes are considered. In vacuum, a charged particle receives a kick in the polarization direction after interaction with a chirped EM pulse. Interaction of a one-dimensional chirped pulse with uniform plasma is considered. We found that the amplitude of the wake wave generated in plasma by an EM pulse can be significantly higher when the pulse is chirped.
Receptivity of stationary transient disturbances to surface roughness
Authors: White Edward B. , Rice Justin M. , Gökhan Ergin F.
Published: June 2005

Recent experiments on transient disturbance growth in boundary layers indicate that disturbances generated by surface roughness undergo suboptimal growth. The implication is that the receptivity mechanism governing the distribution of disturbance energy among the continuous spectrum of damped Orr–Sommerfeld/Squire modes produces energy distributions that are significantly different from the theoretical optimum. Experiments presented here are intended to investigate how the amplitude and diameter of cylindrical roughness elements arranged in a spanwise array affect various features of transient growth. The objective is to infer how or to what extent the roughness features affect the continuous spectrum and to use this information as a foundation for future receptivity models. The results show that the energy of stationary disturbances varies as Rek2 and that the streamwise distance over which the disturbances grow increases slightly with increasing Rek. As the roughness diameter is varied, dramatic changes in the qualitative nature of the resulting transient growth occur. Both the variation of the growth length with Rek and the behavioral changes with roughness diameter indicate that the energy distribution among the continuous modes is a strong function of roughness features and that an accurate and sophisticated receptivity model will be necessary to accurately predict transient growth.
Analysis of the drop weight method
Authors: Yildirim Ozgur E. , Xu Qi , Basaran Osman A.
Published: June 2005

The drop weight method is an accurate yet simple technique for determining surface tension σ. It relies on dripping a liquid of density ρ at a low flow rate Q̃ from a capillary of radius R into air and measuring the combined volumes of the primary and satellite drops that are formed. The method’s origin can be traced to Tate, who postulated that the volume Ṽideal of the drop that falls from the capillary should be given by ρgṼideal=2πRσ, where g is the gravitational acceleration. Since Tate’s law is only an approximation and the actual drop volume Ṽf<Ṽideal, in practice the surface tension of the liquid-air interface is determined from the experimental master curve due to Harkins and Brown (HB). The master curve is a plot of the fraction of the ideal drop volume, Ψ≡Ṽf∕Ṽideal, as a function of the dimensionless tube radius, Φ≡R∕Ṽf1∕3. Thus, once the actual drop volume Ṽf, and hence Φ, is known, σ is readily calculated upon determining the value of Ψ from the master curve and that Ψ=ρgṼf∕2πRσ. Although HB proposed their master curve more than 80 years ago, a sound theoretical foundation for the drop weight method has heretofore been lacking. This weakness is remedied here by determining the dynamics of formation of many drops and their satellites in sequence by solving numerically the recently popularized one-dimensional (1–d) slender-jet equations. Computed solutions of the 1-d equations are shown to be in excellent agreement with HB’s master curve when Q̃ is low. Moreover, a new theory of the drop weight method is developed using the computations and dimensional analysis. The latter reveals that there must exist a functional relationship between the parameter Φ, where Φ−3 is the dimensionless drop volume, and the gravitational Bond number G≡ρgR2∕σ, the Ohnesorge number Oh≡μ∕(ρRσ)1∕2, where μ is the viscosity, and the Weber number We≡ρQ̃2∕π2R3σ. When We→0, the computed results show that Φ depends solely on G. In this limit, a new correlation is deduced which has a simple functional form, G=3.60Φ2.81, and is more convenient to use than that of HB. The computed results are also used to show how the original drop weight method can be extended to situations where We is finite and resulting drop volumes are not independent of Oh.
On the use of one-dimensional position sensitive detector for x-ray diffraction reciprocal space mapping: Data quality and limitations
Authors: Masson Olivier , Boulle Alexandre , Guinebretière René , Lecomte André , Dauger Alain
Published: June 2005

A homemade x-ray diffractometer using one-dimensional position sensitive detector (PSD) and well suited to the study of thin epitaxial layer systems is presented. It is shown how PSDs can be advantageously used to allow fast reciprocal space mapping, which is especially interesting when analyzing poor crystalline and defective layers as usually observed with oxides and ceramics films. The quality of the data collected with such a setup and the limitations of PSDs in comparison with the use of analyzer crystals are discussed. In particular, the effects of PSD on angular precision, instrument resolution and corrections that must be applied to raw data are presented.
Multilayer coating for 30.4nm
Authors: Yoshikawa Ichiro , Murachi Tetsunori , Takenaka Hisataka , Ichimaru Satoshi
Published: June 2005

A multilayer coating of Mo∕Si is usually used for space science in the spectral range of extreme ultraviolet, especially for He-II (30.4nm) radiation, because it is highly stable under vacuum and atmosphere. The fairly high reflectivity of 15%–20% is achieved. But the space science community needs a higher reflective coating at 30.4nm for the future satellite missions. In this work, we report the design of a multilayer, consisting of a pair of Mg and SiC, and its fabrication, and result of the reflectance.
A magnetohydrodynamic model for quantum plasmas
Authors: Haas F.
Published: June 2005

The quantum hydrodynamic model for charged particle systems is extended to the cases of nonzero magnetic fields. In this way, quantum corrections to magnetohydrodynamics are obtained starting from the quantum hydrodynamical model with magnetic fields. The importance of the quantum corrections is described by a parameter H which can be significant in dense astrophysical plasmas. The quantum magnetohydrodynamic model is analyzed in the infinite conductivity limit. The conditions for equilibrium in ideal quantum magnetohydrodynamics are established. Translationally invariant exact equilibrium solutions are obtained in the case of the ideal quantum magnetohydrodynamic model.
Broadband efficient nonlinear difference generation in a counterpropagating configuration
Authors: Martorell Jordi
Published: June 2005

A counterpropagating parametric nonlinear interaction is considered in the framework of a short one-dimensional photonic crystal. This interaction, otherwise highly inefficient, is shown to be efficient in the framework of such one-dimensional photonic crystal. The large momentum mismatch of this counterpropagating interaction is shown to be compensated for a broad range of frequencies when difference generation is considered. The numerical results presented indicate that such nonlinear photonic crystals are a very good material to consider the observation of backward parametric oscillation without mirror feedback.
Accurate measurements of thermal radiation from a tungsten photonic lattice
Authors: Seager C. H. , Sinclair M. B. , Fleming J. G.
Published: June 2005

Recently, photonic lattice structures have become available that are fabricated from refractory materials such as tungsten and thus stable in vacuo at high temperatures. Such structures can be tailored to exhibit optical properties that are not achievable with ordinary optical materials. In particular, photonic lattices can be designed to suppress thermal emission in undesired spectral regions, and can thereby enhance the overall energy efficiency of emission at useful wavelengths. We report measurements of the thermal emission spectra of tungsten photonic lattices in the wavelength range 3to24μm. Suppression of thermal emission at wavelengths longer than the photonic bandedge (∼6μm) is observed, along with significant emission at shorter wavelengths. We show that from 404to546K the spectral emissivity E(λ) is temperature independent and approaches [1−R(λ)], where R(λ) is the measured specular reflectance spectrum. These results are in accord with Kirchhoff’s law.
2.8 and 1.55μm emission from diode-pumped Er3+-doped and Yb3+ co-doped lead lanthanum zirconate titanate transparent ferroelectric ceramic
Authors: de Camargo A. S. S. , Botero É. R. , Andreeta É. R. M. , Garcia D. , Eiras J. A. , Nunes L. A. O.
Published: June 2005

This work reports the observation of intense emissions at 2.8 and 1.55μm from optical quality diode-pumped Er3+-doped lead lanthanum zirconate titanate (PLZT) transparent ferroelectric ceramic. Radiative properties were calculated using the Judd Ofelt theory, and the respective values of η=0.09 and η=0.94 were obtained. The effect of ytterbium co-doping the PLZT: Er3+ samples was investigated in an attempt to increase intensities. It was found that Yb3+→Er3+ energy transfer processes, that favor Er3+ upconversion, are detrimental to the efficiency of midinfrared emissions. Even so, the advantageous spectroscopic characteristics of PLZT: Er3+ associated with its excellent thermal and mechanical properties, indicate it is a potential cost-effective laser active media.
Step erosion during nucleation of InAs∕GaAs(001) quantum dots
Authors: Placidi E. , Arciprete F. , Sessi V. , Fanfoni M. , Patella F. , Balzarotti A.
Published: June 2005

We have investigated, by means of atomic force microscopy, the complete evolution of InAs∕GaAs(001) quantum dots as a function of deposited InAs. Direct evidence is found for step erosion by quantum dots nucleated onto the step edge and an estimate of the eroded volume is provided. By studying the quantum dots volume as a function of InAs coverage, we show that the wetting layer contribution is confined within a narrow range of coverage around the two- and three-dimensional transition.
Surface passivation of InAs(001) with thioacetamide
Authors: Petrovykh D. Y. , Long J. P. , Whitman L. J.
Published: June 2005

We describe the passivation of InAs(001) surfaces with thioacetamide (CH3CSNH2 or TAM) as an alternative to the standard sulfur passivation using inorganic sulfide (NH4)2Sx. Quantitative comparison using x-ray photoelectron spectroscopy (XPS) demonstrates that TAM passivation dramatically improves the stability against reoxidation in air compared with the inorganic sulfide, with little to no etching during the treatment. We find that TAM passivation preserves the intrinsic surface charge accumulation layer, as directly confirmed with laser-induced photoemission. Overall, TAM appears to provide superior passivation for electronic device and sensing applications.
Efficient photovoltaic energy conversion in tetracene-C60 based heterojunctions
Authors: Chu Chih-Wei , Shao Yan , Shrotriya Vishal , Yang Yang
Published: June 2005

We report organic solar cells fabricated with small-molecule organic semiconductor tetracene∕C60 heterojunction as the photoactive layer. The external power conversion efficiency of the devices under AM 1.5 solar illumination at 100mW∕cm2 (1 sun) is 2.3±0.5% with relatively high open-circuit voltage (Voc=0.58±0.06V) compared to most of the other small-molecular donor-acceptor (D-A) heterojunction solar cells reported so far. Using atomic force microscopy and x-ray diffraction we found that tetracene thin films consist of submicron-sized grains with rough surface and well defined molecular order. Therefore, using high mobility polycrystalline tetracene thin films for D-A heterojunction devices dramatically increases area of tetracene and C60 interface for exciton diffusion to reduce the recombination.
Open-type magnetocardiograph with cylindrical magnetic shield
Authors: Seki Yusuke , Kandori Akihiko , Suzuki Daisuke , Ohnuma Mitsuru
Published: June 2005

We have developed an open-type magnetocardiograph (MCG) with a cylindrical magnetic shield—having an auxiliary magnetic shield—and 64 gradiometers based on low-transition temperature (Tc) superconducting quantum interference devices (SQUIDs). A revolving door is applied to the magnetic shield with the aim of providing easy access to a subject and easy operation. The cryostat attached to the MCG contains 64 low-Tc SQUIDs and is about 1m in height, so there must be an opening through the cylindrical surface of the magnetic shield. The properties of the magnetic shield were simulated using finite-element-method simulations and experiments. The results of the simulations indicated that the auxiliary magnetic shield recovers enough of the shielding performance of a magnetic shield with an opening that it performs like a magnetic shield without an opening. The shielding factor of the developed magnetic shield is above 46dB in the vicinity of the magnetic shield. Accordingly, the open-type MCG can clearly measure magnetocardiograms.
Picosecond photoelectric characteristic in La0.7Sr0.3MnO3∕Si p-n junctions
Authors: Lu Hui-Bin , Jin Kui-Juan , Huang Yan-Hong , He Meng , Zhao Kun , Cheng Bo-Lin , Chen Zheng-Hao , Zhou Yue-Liang , Dai Sou-Yu , Yang Guo-Zhen
Published: June 2005

Ultrafast photoelectric effects have been observed in La0.7Sr0.3MnO3∕Si p-n junctions fabricated by laser molecular-beam epitaxy. The rise time was ∼210ps and the full width at half-maximum was ∼650ps for the photovoltaic pulse when the junction was irradiated by a 1064nm laser pulse of 25ps duration. The photovoltaic sensitivity was as large as 435mV∕mJ for a 1064nm laser pulse. No such photovoltaic signal was observed with irradiation from a 10.6μm CO2 laser pulse. The results reveal that this phenomenon is an ultrafast photoelectric effect.
Design for mixing using bubbles in branched microfluidic channels
Authors: Garstecki Piotr , Fischbach Michael A. , Whitesides George M.
Published: June 2005

This letter describes a method for producing chaotic transport trajectories in planar, microfluidic networks prepared by standard, single-step lithography and operated with a steady-state inflow of the fluids into the device. Gaseous slugs flowing through the network produce temporal variation of pressure distribution and lead to stretching and folding of the continuous fluid. Stabilization of the bubbles by surface-active agents is not necessary, and the method is compatible with the wide range of reactions performed in on-chip bioassays.
Multiple-band-edge quantum-well intermixing in the InGaAs∕InGaAsP∕InGaP material system
Authors: Skogen Erik J. , Coldren Larry A. , Raring James W. , DenBaars Steven P.
Published: June 2005

The development of photonic integrated circuits lattice matched to GaAs are desirable for the manufacture of high-power, high-efficiency optical components. In this letter we investigate and describe a process technique based on quantum-well intermixing to achieve multiple band edges in the Al-free 980nm InGaAs∕InGaAsP∕InGaP material system.
Negative differential resistance in mesoscopic manganite structures
Authors: Wu T. , Mitchell J. F.
Published: June 2005

Step-like negative differential resistance is observed in patterned Pr0.65(Ca0.75Sr0.25)0.35MnO3 structures with mesoscopic (micrometer) length scales. Key to the appearance of the steps is a field- and temperature-dependent mixture of ferromagnetic metal (FMM) and charge ordered insulating (COI) phases found in this material. Notably, such steps in the current-voltage curves have not been observed in bulk or unpatterned films of this material, suggesting that the commensurability between device dimensions and the size of competing FMM and COI domains are important conditions for observing this effect. We offer a semiquantitative resistor-network model of the steps that posits a local Joule heating-induced phase transition of FMM to COI.
Generation of ultrashort Kα radiation from quasipoint interaction area of femtosecond pulses with thin foils
Authors: Zhavoronkov N. , Gritsai Y. , Bargheer M. , Woerner M. , Elsaesser T.
Published: June 2005

We demonstrate a concept for short x-ray generation at 1kHz repetition rate from a thin-foil target in a very compact configuration, which allows one, essentially, to decrease the distance between x-ray source and investigated object. The scaling for the hard x-ray yield and the hot electron temperature with the pulse intensity are determined and best described by a power law. The useful photon fluxes of 3.4×109 and 3.3×109phot∕(ssrad) are generated for the Ni- and Cu Kα lines, respectively. The size of the x-ray source was detected to be 10μm.
Experimental confirmation of negative phase change in negative index material planar samples
Authors: Vier D. , Fredkin D. R. , Simic A. , Schultz S. , Tanielian Minas
Published: June 2005

We use far-field range measurements to determine and confirm the negative phase change through a planar negative index material as a function of frequency. The metamaterial is composed of wires and split ring resonators. At frequencies for which the surface impedance Z∕Z0=1, we determine the index (n) from the measured phase change (relative to a vacuum) and via numerical simulation. In addition to confirming the simulated negative phase change at the frequency where n=−1, we find good agreement with prior Snell’s law measurements from n=−2.5 to −0.5. This illustrates that measuring the phase change of the transmitted signal can be a practical means of identifying the existence of negative index in planar test samples.
Dynamic avalanche breakdown of a p-n junction: Deterministic triggering of a plane streamer front
Authors: Rodin Pavel , Grekhov Igor
Published: June 2005

We discuss the dynamic impact ionization breakdown of a high voltage p-n junction which occurs when the electric field is increased above the threshold of avalanche impact ionization on a time scale smaller than the inverse thermogeneration rate. The avalanche-to-streamer transition characterized by generation of dense electron-hole plasma capable of screening the applied external electric field occurs in such regimes. We argue that the experimentally observed deterministic triggering of the plane streamer front at the electric-field strength above the threshold of avalanche impact ionization, yet below the threshold of band-to-band tunneling, is generally caused by field-enhanced ionization of deep-level centers. We suggest that the process-induced sulfur centers and native defects such as EL2, HB2, and HB5 centers initiate the front in Si and GaAs structures, respectively. In deep-level-free structures the plane streamer front is triggered by Zener band-to-band tunneling.
Random conductivity of δ-Bi2O3 films
Authors: Skorodumova N. V. , Jonsson A. K. , Herranen M. , Strømme M. , Niklasson G. A. , Johansson B. , Simak S. I.
Published: June 2005

The experimental investigation of the cubic δ-Bi2O3 phase grown on a (110) Au substrate at low temperature has disclosed a chaotic character of the conductivity at low voltage and temperature. Based on first-principles calculations, we show that the conductivity of this oxide strongly depends on the distribution of oxygen ions and that oxygen migration is able to cause a momentary switch of the conduction mechanism.
Indium redistribution in an InGaN quantum well induced by electron-beam irradiation in a transmission electron microscope
Authors: Li T. , Hahn E. , Gerthsen D. , Rosenauer A. , Strittmatter A. , Reißmann L. , Bimberg D.
Published: June 2005

The change of the morphology and indium distribution in an In0.12Ga0.88N quantum well embedded in GaN was investigated depending on the duration of electron-beam irradiation in a transmission electron microscope. Strain-state analysis based on high-resolution lattice-fringe images was used to determine quantitatively the local and average indium concentration of the InGaN quantum well. In-rich clusters were found already in the first image taken after 20 s of irradiation. The indium concentration in the clusters tends to increase with prolonged irradiation time. In contrast, the locally averaged indium concentration and the quantum-well width do not change within the first minute.
Tunneling spectroscopy studies of treated aluminum oxide tunnel barrier layers
Authors: Mather P. G. , Perrella A. C. , Tan E. , Read J. C. , Buhrman R. A.
Published: June 2005

We report scanning tunneling microscopy and ballistic electron emission microscopy studies of the electronic states of the uncovered and chemisorbed-oxygen covered surface of AlOx tunnel barrier layers. These states change when chemisorbed oxygen ions are moved into the oxide by either flood gun electron bombardment or by thermal annealing. While untreated samples exhibit band tails extending to zero bias, the former, if sufficiently energetic, results in locally well defined conduction band onsets at ∼1V, while the latter results in a progressively higher local conduction band onset, exceeding 2.3 V for 500 and 600 °C thermal anneals.
Radiative ballistic phonon transport in silicon-nitride membranes at low temperatures
Authors: Hoevers H. F. C. , Ridder M. L. , Germeau A. , Bruijn M. P. , de Korte P. A. J. , Wiegerink R. J.
Published: June 2005

We studied the phonon transport in free-standing 1μm thick silicon-nitride membranes at temperatures around 100 mK. By varying the geometry of the membranes and the dimensions of the heater element, we are able to distinguish between radiative and diffuse phonon transport. The data indicate that the transport is radiative ballistic with a lower limit to a phonon mean-free path of about 1 mm and that the probability for specular reflection from the surface is at least 0.99. The tested silicon-nitride membranes were grown on Si(100), Si(110), and polycrystalline-Si and the transport properties show no dependency on the substrate.
Optical properties of single droplet of photonic crystal assembled by ink-jet printing
Authors: Wang Dake , Park Minseo , Park Jungho , Moon Jooho
Published: June 2005

An array of droplets of photonic crystal with polystyrene colloidal particles was assembled on silicon using ink-jet printing. A microreflectance spectrum from a single droplet was collected using an optical microscope and a spectrometer. It was observed that the photonic band gap of these droplets shifts as a function of the size of the colloidal particle. The reflectance peak position predicted from the model based on Bruggeman and Maxwell–Garnett effective medium approximations agrees well with those of the experimentally observed peak.
Photoinduced doping effect of pentacene field effect transistor in oxygen atmosphere studied by displacement current measurement
Authors: Ogawa Satoshi , Naijo Tatsuo , Kimura Yasuo , Ishii Hisao , Niwano Michio
Published: June 2005

It is widely accepted that atmospheric oxygen can work as an electron-accepting dopant mainly to p-type organic semiconductors. We have examined the effect of oxygen on a pentacene field effect transistor (FET) with and without exposure to light using the displacement current measurement. Under vacuum conditions, the change in the displacement current due to hole injection from the source and drain electrodes to the pentacene layer is clearly observed, suggesting that the origin of the mobile carriers in the pentacene FET is carrier injection. When the FET is exposed to oxygen under dark conditions, a very small change in the threshold gate voltage for hole injection is observed. In contrast, with exposure to both oxygen and light, we observed that the threshold voltage is lowered and shifted across the zero bias and even to the polarity against hole injection. This photoinduced doping effect induces a distinct increase in the drain current of the FET, and it is maintained for at least several hours even after the irradiation is turned off. This finding suggests that the performance of organic semiconductor devices is affected not only by atmospheric oxygen but also by ambient light even during the processing and storage of the devices.
Analysis of high-power packages for phosphor-based white-light-emitting diodes
Authors: Luo Hong , Kim Jong Kyu , Schubert E. Fred , Cho Jaehee , Sone Cheolsoo , Park Yongjo
Published: June 2005

An optimized packaging configuration for high-power white-light-emitting diode (LED) lamps that employs a diffuse reflector cup, a large separation between the primary emitter (the LED chip) and the wavelength converter (the phosphor) and a hemispherically shaped encapsulation is presented. Ray tracing simulations for this configuration show that the phosphor efficiency can be enhanced by up to 50% over conventional packages. Dichromatic LED lamps with phosphor layers on the top of a diffuse reflector cup were fabricated and studied experimentally. The experimental enhancement of phosphor efficiency is 15.4% for blue-pumped yellow phosphor and 27% for ultraviolet-pumped blue phosphor. Those improvements are attributed to reduced absorption of the phosphorescence by the LED chip and the reduction of deterministic optical modes trapped inside the encapsulant.
Self-assembled nanobridge formation and spontaneous growth of metal-induced nanowires
Authors: Kim Joondong , Anderson Wayne A. , Song Young-Joo , Kim Gi Bum
Published: June 2005

Self-assembled nanobridges, 30–80 nm in diameter and 1–2μm in length, have been fabricated using spontaneously grown nanowires by the metal-induced growth method at 575 °C. Ni as a catalyst was first deposited on SiO2-coated Si wafers. Si was sputtered from a Si target in a dc magnetron system. A solid-state reaction of Si with Ni provided highly linear nanowires. These nanowires have a single-crystal NiSi composition. Laterally propagated nanowires formed nanobridges passing through a vertically trenched region, without nanowires on the trench sidewall. The nanobridge formation is repeatably governed by the Ni deposition. The self-assembled nanobridge can be applied to form nanocontacts at relatively low temperatures.
Distinctive current-induced magnetization switching in a current-perpendicular-to-plane giant-magnetoresistance nanopillar with a synthetic antiferromagnet free layer
Authors: Ochiai T. , Jiang Y. , Hirohata A. , Tezuka N. , Sugimoto S. , Inomata K.
Published: June 2005

We investigated current-induced magnetization switching (CIMS) in two types of pseudo-spin-valve nanopillars with current-perpendicular-to-plane giant magnetoresistance (CPP-GMR); Co90Fe10(10nm)∕Cu(10nm)∕Co90Fe10(2.5nm) (conventional type) and Co90Fe10(10nm)∕Cu(10nm)∕Co90Fe10(1.5nm)∕Ru(0.45nm)∕Co90Fe10(2.5nm) (synthetic antiferromagnet; SyAF type). We observed the CIMS in the both CPP-GMR structures at room temperature. In particular for the SyAF type nanopillars, the CIMS was observed only in a negative current regime. We also discovered that the applied magnetic field dependence of the CIMS shows absolutely different behavior from that of the conventional type. These peculiar CIMS behaviors with the SyAF free layer are attributed to majority electron spin transfer torque from the thick to the thin Co90Fe10 layers, enhanced by the presence of a Ru layer.
Amorphous silicon thin-film transistors with 90° vertical nanoscale channel
Authors: Chan Isaac , Nathan Arokia
Published: June 2005

This letter reports 100nm channel length vertical thin-film transistors (VTFTs) in hydrogenated amorphous silicon (a-Si:H) technology. The channel length is defined by means of a dielectric film thickness, realized by an anisotropic reactive ion etching process to yield a 90° vertical transistor structure. Furthermore, the device area of the vertical TFT structure is less than ∼1∕3 that of the ubiquitous lateral TFT structure. The 100nm channel length VTFTs exhibit an ON/OFF current ratio of 108, a threshold voltage of 2.8V, and a subthreshold slope of 0.8V∕dec.
Laser ablated Ni-doped HfO2 thin films: Room temperature ferromagnets
Authors: Hong Nguyen Hoa , Sakai Joe , Poirot Nathalie , Ruyter Antoine
Published: June 2005

Laser ablated Ni-doped HfO2 thin films fabricated under a wide range of growth conditions all showed ferromagnetism above room temperature. However, the films deposited at 800°C under an oxygen partial pressure of 10−6Torr have the largest magnetic moment of 2.7μB∕Ni. Ni-doped HfO2 films also well demonstrate a large anisotropy. Magnetic force microscopy measurements confirmed that Ni-doped HfO2 films are real room temperature ferromagnets with a domain structure, and that the size of magnetic domains is larger than 10μm.
Terahertz heterodyne receiver based on a quantum cascade laser and a superconducting bolometer
Authors: Gao J. R. , Hovenier J. N. , Yang Z. Q. , Baselmans J. J. A. , Baryshev A. , Hajenius M. , Klapwijk T. M. , Adam A. J. L. , Klaassen T. O. , Williams B. S. , Kumar S. , Hu Q. , Reno J. L.
Published: June 2005

We report the first demonstration of an all solid-state heterodyne receiver that can be used for high-resolution spectroscopy above 2THz suitable for space-based observatories. The receiver uses a NbN superconducting hot-electron bolometer as mixer and a quantum cascade laser operating at 2.8THz as local oscillator. We measure a double sideband receiver noise temperature of 1400K at 2.8THz and 4.2K, and find that the free-running QCL has sufficient power stability for a practical receiver, demonstrating an unprecedented combination of sensitivity and stability.
Band structure modification of Al oxide by Ti-alloying and magnetoresistance behavior of magnetic tunnel junctions with Ti-alloyed Al oxide barrier
Authors: Song Jin-Oh , Lee Seong-Rae , Shin Hyun-Joon
Published: June 2005

We investigated the composition dependence of the band structure of Ti-alloyed Al oxide (TiAlOx), tunneling magnetoresistance (TMR) behavior of the magnetic tunnel junctions (MTJs) with TiAlOx barrier, and the microstructural evolution of Ti–Al alloy films. X-ray absorption spectroscopy indicated that TiAlOx had localized d states in the band gap below the conduction band. As the Ti concentration increased, the resistance×area value and effective barrier height of the MTJs were reduced owing to the band-gap reduction of TiAlOx caused by the formation of extra bands, mainly composed of Ti3d orbitals, within the band gap. The TMR ratio increased up to 49% at 5.33at.% Ti. Ti alloying enhanced the barrier∕electrode interface uniformity and reduced microstructural defects. These structural improvements enhanced not only the TMR effect but also the thermal stability of the MTJs.
Photoresponse of n-ZnO∕p-SiC heterojunction diodes grown by plasma-assisted molecular-beam epitaxy
Authors: Alivov Ya. I. , Özgür Ü. , Doğan S. , Johnstone D. , Avrutin V. , Onojima N. , Liu C. , Xie J. , Fan Q. , Morkoç H.
Published: June 2005

High quality n-ZnO films on commercial p-type 6H–SiC substrates have been grown by plasma-assisted molecular-beam epitaxy, and n-ZnO∕p-SiC heterojunction mesa structures have been fabricated. Current-voltage characteristics of the structures had a very good rectifying diode-like behavior with a leakage current less than 2×10−4A∕cm2 at −10V, a breakdown voltage greater than 20V, a forward turn on voltage of ∼5V, and a forward current of ∼2A∕cm2 at 8V. Photosensitivity of the diodes was studied at room temperature and a photoresponsivity of as high as 0.045A∕W at −7.5V reverse bias was observed for photon energies higher than 3.0eV.
Tunneling spectroscopy of metal-oxide-semiconductor field-effect transistor at low temperature
Authors: Bao Mingqiang , Liu Fei , Baron Filipp , Wang Kang L. , Li Ruigang
Published: June 2005

Electron tunneling spectroscopy is used to study drain-source current spectra of metal-oxide-semiconductor field-effect transistors (MOSFETs). Measured at liquid helium temperature (4.2 K), experimental results reveal that as drain-source voltage (Vds) increases, the first derivative of drain-source current (or conductance) first decreases, then increases to a maximum and finally decreases again at higher Vds, which is different from the monotonous decreasing feature described by the conventional MOSFET theory. In addition, the measured MOSFET spectra show that there are fine features on the second derivative spectra, and these features may be used to extract trap information.
Switchable single c-domain formation in a heteroepitaxial PbTiO3 thin film on a (001) Nb–SrTiO3 substrate fabricated by means of hydrothermal epitaxy
Authors: Jung W. W. , Lee H. C. , Ahn W. S. , Ahn S. H. , Choi S. K.
Published: June 2005

We used hydrothermal epitaxy to fabricate a heteroepitaxial PbTiO3 (PTO) thin film on a Nb-doped (001) cubic SrTiO3 (NSTO) substrate while avoiding the phase transition. By means of transmission electron microscopy and piezoresponse force microscopy analyses, it was confirmed that no a domain formed in the heteroepitaxial PTO film; the film had a single +c-domain structure at an as-synthesized state. From the measurement of the polarization-voltage hysteresis curve, large remanent polarization (2Pr:144μC∕cm2) resulting from the single +c-domain structure and an imprint induced by an asymmetric electrode configuration were observed. It is suggested that the single +c-domain structure was caused by the interface of the PTO film and solution rather than the interface of the PTO film and NSTO electrode under the hydrothermal conditions. This hydrothermally synthesized PTO film is anticipated to be very suitable for high-performance engineering applications.
HEXIM1 forms a transcriptionally abortive complex with glucocorticoid receptor without involving 7SK RNA and positive transcription elongation factor b
Authors: Shimizu Noriaki , Ouchida Rika , Yoshikawa Noritada , Hisada Tetsuya , Watanabe Hajime , Okamoto Kensaku , Kusuhara Masatoshi , Handa Hiroshi , Morimoto Chikao , Tanaka Hirotoshi
Published: June 2005

The HEXIM1 protein has been shown to form a protein–RNA complex composed of 7SK small nuclear RNA and positive transcription elongation factor b (P-TEFb), which is composed of cyclin-dependent kinase 9 (CDK9) and cyclin T1, and to inhibit the kinase activity of CDK9, thereby suppressing RNA polymerase II-dependent transcriptional elongation. Here, we biochemically demonstrate that HEXIM1 forms a distinct complex with glucocorticoid receptor (GR) without RNA, CDK9, or cyclin T1. HEXIM1, through its arginine-rich nuclear localization signal, directly associates with the ligand-binding domain of GR. Introduction of HEXIM1 short interfering RNA and adenovirus-mediated exogenous expression of HEXIM1 positively and negatively modulated glucocorticoid-responsive gene activation, respectively. In the nucleus, HEXIM1 was shown to localize in a distinct compartment from that of the p160 coactivator transcriptional intermediary factor 2. Overexpression of HEXIM1 decreased ligand-dependent association between GR and transcriptional intermediary factor 2. Antisense-mediated disruption of 7SK blunted the negative effect of HEXIM1 on arylhydrocarbon receptor-dependent transcription but not on GR-mediated one, indicating that a class of transcription factors are direct targets of HEXIM1. These results indicate that HEXIM1 has dual roles in transcriptional regulation: inhibition of transcriptional elongation dependent on 7SK RNA and positive transcription elongation factor b and interference with the sequence-specific transcription factor GR via a direct protein–protein interaction. Moreover, the fact that the central nuclear localization signal of HEXIM1 is essential for both of these actions may argue the crosstalk of these functions.
Development of a unique system for spatiotemporal and lineage-specific gene expression in mice
Authors: Yu Hsiao-Man Ivy , Liu Bo , Chiu Shang-Yi , Costantini Frank , Hsu Wei
Published: June 2005

We have developed an advanced method for conditional gene expression in mice that integrates the Cre-mediated and tetracycline-dependent expression systems. An rtTA gene, preceded by a loxP-flanked STOP sequence, was inserted into the ROSA26 locus to create a R26STOPrtTA mouse strain. When the STOP sequence is excised by Cre-mediated recombination, the rtTA is expressed in the Cre-expressing cells and all of their derivatives. Therefore, cell type-, tissue-, or lineage-specific expression of rtTA is achieved by the use of an appropriate Cre transgenic strain. In mice also carrying a target gene under the control of the tetracycline response element, inducible expression of the target gene is temporally regulated by administration of doxycycline. Our results demonstrate that this universal system is uniquely suited for spatiotemporal and lineage-specific gene expression in an inducible fashion. Gene expression can be manipulated in specific cell types and lineages with a flexibility that is difficult to achieve with conventional methods.
Signal peptide–chaperone interactions on the twin-arginine protein transport pathway
Authors: Hatzixanthis Kostas , Clarke Thomas A. , Oubrie Arthur , Richardson David J. , Turner Raymond J. , Sargent Frank
Published: June 2005

The twin-arginine transport (Tat) system is a protein-targeting pathway of prokaryotes and chloroplasts. MostEscherichia coliTat substrates are complex metalloenzymes that must be correctly folded and assembled before transport, and a preexport chaperone-mediated “proofreading” process is therefore in operation. The paradigm proofreading chaperone is TorD, which coordinates maturation and export of the key respiratory enzyme trimethylamineN-oxide reductase (TorA). It is demonstrated here that purified TorD binds tightly and with exquisite specificity to the TorA twin-arginine signal peptidein vitro. It is also reported that the TorD family constitutes a hitherto unexpected class of nucleotide-binding proteins. The affinity of TorD for GTP is enhanced by initial signal peptide binding, and it is proposed that GTP governs signal peptide binding-and-release cycles during Tat proofreading.
Gelatinase A and membrane-type matrix metalloproteinases 1 and 2 are responsible for follicle rupture during ovulation in the medaka
Authors: Ogiwara Katsueki , Takano Naoharu , Shinohara Masakazu , Murakami Masahiro , Takahashi Takayuki
Published: June 2005

Identification of the hydrolytic enzymes involved in follicle rupture during vertebrate ovulation remains a central challenge for research in reproductive biology. Here, we report a previously uncharacterized approach to this problem by using an
in vitro
ovulation system in the medaka,
Oryzias latipes
, which is a small freshwater teleost. We found that follicle rupture in the medaka ovary involves the cooperation of at least three matrix metalloproteinases (MMPs), together with the tissue inhibitor of metalloproteinase-2b protein. We determined the discrete roles of each of these proteins during follicle rupture. Our results indicated that gelatinase A induces the hydrolysis of type IV collagen constituting the basement membrane, membrane-type 2 MMP degrades type I collagen present in the theca cell layer, and MT1-MMP and the tissue inhibitor of metalloproteinase-2b are involved in the production and regulation of gelatinase A. These findings will help clarify the mechanism of follicle wall degradation during ovulation in mammalian species.
Global and Hox-specific roles for the MLL1 methyltransferase
Authors: Guenther Matthew G. , Jenner Richard G. , Chevalier Brett , Nakamura Tatsuya , Croce Carlo M. , Canaani Eli , Young Richard A.
Published: June 2005

The mixed-lineage leukemia (MLL1/ALL-1/HRX) histone methyltransferase is involved in the epigenetic maintenance of transcriptional memory and the pathogenesis of human leukemias. To understand its role in cell type specification, we determined the human genomic binding sites of MLL1. We found that MLL1 functions as a human equivalent of yeast Set1. Like Set1, MLL1 localizes with RNA polymerase II (Pol II) to the 5′ end of actively transcribed genes, where histone H3 lysine 4 trimethylation occurs. Consistent with this global role in transcription, MLL1 also localizes to microRNA (miRNA) loci that are involved in leukemia and hematopoiesis. In contrast to the 5′ proximal binding behavior at most protein-coding genes, MLL1 occupies an extensive domain within a transcriptionally active region of the HoxA cluster. The ability of MLL1 to serve as a start site-specific global transcriptional regulator and to participate in larger chromatin domains at the Hox genes reveals dual roles for MLL1 in maintenance of cellular identity.
The turbulent wall jet: A triple-layered structure and incomplete similarity
Authors: Barenblatt G. I. , Chorin A. J. , Prostokishin V. M.
Published: June 2005

We demonstrate using the high-quality experimental data that turbulent wall jet flows consist of two self-similar layers: a top layer and a wall layer, separated by a mixing layer where the velocity is close to maximum. The top and wall layers are significantly different from each other, and both exhibit incomplete similarity, i.e., a strong influence of the width of the slot that had previously been neglected.
Prehistoric contacts over the Straits of Gibraltar indicated by genetic analysis of Iberian Bronze Age cattle
Authors: Anderung Cecilia , Bouwman Abigail , Persson Per , Carretero José Miguel , Ortega Ana Isabel , Elburg Rengert , Smith Colin , Arsuaga Juan Luis , Ellegren Hans , Götherström Anders
Published: June 2005

The geographic situation of the Iberian Peninsula makes it a natural link between Europe and North Africa. However, it is a matter of debate to what extent African influences via the Straits Gibraltar have affected Iberia's prehistoric development. Because early African pastoralist communities were dedicated to cattle breeding, a possible means to detect prehistoric African–Iberian contacts might be to analyze the origin of cattle breeds on the Iberian Peninsula. Some contemporary Iberian cattle breeds show a mtDNA haplotype, T1, that is characteristic to African breeds, generally explained as being the result of the Muslim expansion of the 8th century A.D., and of modern imports. To test a possible earlier African influence, we analyzed mtDNA of Bronze Age cattle from the Portalón cave at the Atapuerca site in northern Spain. Although the majority of samples showed the haplotype T3 that dominates among European breeds of today, the T1 haplotype was found in one specimen radiocarbon dated 1800 calibrated years B.C. Accepting T1 as being of African origin, this result indicates prehistoric African–Iberian contacts and lends support to archaeological finds linking early African and Iberian cultures. We also found a wild ox haplotype in the Iberian Bronze Age sample, reflecting local hybridization or backcrossing or that aurochs were hunted by these farming cultures.
Optical frequency standards
Authors: Gill Patrick
Published: June 2005

The evolution of atomic frequency standards since Essen's atomic clock fifty years ago has been considerable both in respect of microwave and optical standards. In particular, the development of trapping and laser cooling techniques for both atoms and ions has played a major role. This paper reviews the status of the development of single cold trapped ion and cold trapped atom optical frequency standards. Recent results show comb measurements of trapped ion optical frequency standards with accuracies close to Cs fountain limited operation. The factors affecting future stability and reproducibility are discussed. The opportunities for future standards capable of approaching reproducibility at the 10−18level are outlined, together with the likely limitations arising.
A new progressive-iterative algorithm for multiple structure alignment
Authors: Lupyan Dmitry , Leo-Macias Alejandra , Ortiz Angel R.
Published: June 2005

Motivation: Multiple structure alignments are becoming important tools in many aspects of structural bioinformatics. The current explosion in the number of available protein structures demands multiple structural alignment algorithms with an adequate balance of accuracy and speed, for large scale applications in structural genomics, protein structure prediction and protein classification.

Results: A new multiple structural alignment program, MAMMOTH-mult, is described. It is demonstrated that the alignments obtained with the new method are an improvement over previous manual or automatic alignments available in several widely used databases at all structural levels. Detailed analysis of the structural alignments for a few representative cases indicates that MAMMOTH-mult delivers biologically meaningful trees and conservation at the sequence and structural levels of functional motifs in the alignments. An important improvement over previous methods is the reduction in computational cost. Typical alignments take only a median time of 5 CPU seconds in a single R12000 processor. MAMMOTH-mult is particularly useful for large scale applications.

Availability:  http://ub.cbm.uam.es/mammoth/mult

Contact:  aro@cbm.uam.es