bluuebunny/crossref_metadata_2025 huggingface dataset:
High resolution electrical studies of vacancy-rich and interstitial-rich regions in ion-implanted silicon
Authors: Abdelgader N. , Evans-Freeman J. H.
Published: April 2003

A combination of high resolution Laplace deep level transient spectroscopy (LDLTS) and direct capture cross-section measurements has been used to investigate whether deep electronic states related to interstitial-type defects introduced by ion implantation originated from point or extended defects, prior to any annealing. n-type silicon was implanted with doses of 1×109 cm−2 of silicon, germanium, or erbium, and comparison was made with proton- and electron-irradiated material. When measured by LDLTS at 225 K, the region of the implant thought to contain mostly vacancy-type defects exhibited a complex spectrum with five closely spaced defect-related energy levels, with energies close to EC-400 meV. The region nearer the tail of the implant, which should be dominated by interstitial-type defects, exhibited a simpler LDLTS spectrum with three closely spaced levels being recorded, again with energies centered on EC-400 meV. Annealing at 180 °C did not completely remove any of the defect peaks, suggesting that the energy levels were not due to the simple vacancy-phosphorus center. Direct electron capture cross-section measurements revealed that the defects in the tail of the implanted volume, prior to any annealing, were not simple point defects, as they exhibited nonexponential capture properties. This is attributed to the presence of extended defects in this region. By contrast, defects with the same activation energy in proton- and electron-irradiated silicon exhibited point-defect-like exponential capture.
Magnetic and transport properties of alternately deposited Co-Bi films
Authors: Honda S. , Nagata Y.
Published: April 2003

Co-Bi films have been prepared on glass substrates by alternate electron-beam evaporation, and their magnetic and transport properties have been studied as a function of Co volume fraction x (vol %). When x increases, saturation magnetization increases linearly, while coercivity and resistivity decrease. The temperature dependence of resistivity is very weak. Both ordinary magnetoresistance (OMR) and anisotropic magnetoresistance (AMR) are observed. The OMR component, for which the Bi matrix is responsible, decreases with increasing x, while the AMR component, due to Co, increases. For x=17, the spontaneous Hall resistivity indicates strong temperature dependence. With the increase of temperature, polarity switches at 150 K from negative to positive. At room temperature, Hall resistivity exhibits a value as high as ∼1.6 μΩ cm or, in other words, a Hall coefficient of 5.25×10−10 Ω cm/G, which is larger than pure Co bulk by two orders of magnitude.
Ferroelectric properties of YMnO3 epitaxial films for ferroelectric-gate field-effect transistors
Authors: Ito Daisuke , Fujimura Norifumi , Yoshimura Takeshi , Ito Taichiro
Published: April 2003

Ferroelectric properties of YMnO3 epitaxial films were studied. The ferroelectric properties of epitaxially grown (0001) YMnO3 films on (111)Pt/(0001)sapphire (epi-YMO/Pt) with an excellent crystallinity were compared to (0001)-oriented poly crystalline films on (111)Pt/ZrO2/SiO2/Si. The epi-YMO/Pt had saturated polarization–electric-field (P–E) hysteresis loops, with a remanent polarization (Pr) of 1.7 μC/cm2 and a coercive field (Ec) of 80 kV/cm. The fatigue property showed no degradation up to 1010 measured cycles. These results suggested that the YMnO3 epitaxial films were suitable ferroelectric material for the ferroelectric-gate field-effect transistors. Consequently, epitaxially grown (0001)YMnO3 films on epitaxial Y2O3/Si (epi-YMO/Si) were fabricated. The epi-YMO/Si capacitor had almost equivalent crystallinity compared to epi-YMO/Pt. It was recognized that the epi-YMO/Si capacitor exhibited the ferroelectric type C–V hysteresis loop with the width of the memory window of 4.8 V, which was almost identical to the value of twice coercive voltage of the P–E hysteresis loops of the epi-YMO/Pt. A retention time exceeding 104 s was obtained in the epi-YMO/Si capacitor.
Datta–Das transistor with enhanced spin control
Authors: Egues J. Carlos , Burkard Guido , Loss Daniel
Published: April 2003

We consider a two-channel spin transistor with weak spin-orbit induced interband coupling. We show that the coherent transfer of carriers between the coupled channels gives rise to an additional spin rotation. We calculate the corresponding spin-resolved current in a Datta–Das geometry and show that a weak interband mixing leads to enhanced spin control.
Bonding structure in nitrogen doped ultrananocrystalline diamond
Authors: Birrell James , Gerbi J. E. , Auciello O. , Gibson J. M. , Gruen D. M. , Carlisle J. A.
Published: April 2003

The transport properties of diamond thin films are well known to be sensitive to the sp2/sp3-bonded carbon ratio, the presence of the grain boundaries and other defects, and to the presence of various impurities. In order to clarify the roles these factors play in the conduction mechanisms of nitrogen-doped ultrananocrystalline diamond (UNCD), Raman scattering, near edge x-ray absorption fine structure (NEXAFS), soft x-ray fluorescence (SXF), and secondary ion mass spectroscopy (SIMS) measurements were performed. Transmission electron microscopy analysis of nitrogen doped UNCD has previously indicated that the films are composed of crystalline diamond nano-grains with boundaries of amorphous carbon, and NEXAFS measurements reveal that the global amount of sp2-bonded carbon in these films increases slightly with nitrogen doping. The nitrogen content is quantified with high-resolution SIMS analysis, while NEXAFS and SXF indicates that the nitrogen exists primarily in tetrahedrally coordinated sites. These measurements indicate that the overall grain boundary volume of nitrogen-doped ultrananocrystalline diamond is increasing, while the grains themselves remain pure diamond. This supports our previously reported hypothesis that grain boundary conduction is the mechanism for the observed increase in conductivity in ultrananocrystalline diamond with nitrogen doping.
Structure and orientation of epitaxial titanium silicide nanowires determined by electron microdiffraction
Authors: Stevens M. , He Zhian , Smith David J. , Bennett P. A.
Published: April 2003

The crystal structure and epitaxial orientation of self-assembled titanium silicide nanowires (NWs) on Si (111) is determined using transmission electron microdiffraction. The NWs are formed by deposition of ∼1 monolayer Ti on Si(111) at ∼850 °C. Type 1 NWs are oriented with long axis along Si〈2-20〉 and are identified as C49 TiSi2. The most common orientation is C49 [01-3] || Si [112] and C49 (200) || Si (2-20), but several other orientations are also found. Type 2 NWs are oriented with long axis along Si〈224〉 and are identified as B27 TiSi, with orientation B27 [02-1] || Si [111] and B27 (-312) || Si (22-4) + 4°. Most of the NWs are incommensurate and fully strain relaxed. They generally extend below the surface with inclined incoherent interfaces.
Ceramic microdischarge arrays with individually ballasted pixels
Authors: von Allmen P. , McCain S. T. , Ostrom N. P. , Vojak B. A. , Eden J. G. , Zenhausern F. , Jensen C. , Oliver M.
Published: April 2003

Arrays of cylindrical microdischarge devices, ∼200 μm in diameter, have been fabricated with internally recessed annular electrodes in multilayer ceramic structures and operated both continuously and with pulsed excitation in the rare gases at pressures up to 800 Torr of Ne and 300 Torr of Xe. The overall thickness of the ceramic structure is ∼1.6 mm and each microdischarge is individually ballasted by a ∼225 kΩ resistor, produced and integrated into the structure by a thick film process. Arrays as large as 13×13 pixels have been tested to date. Spatially uniform glow discharges are generated in the pixels for all of the pressures investigated and strong emission from excited states of the singly charged Xe ion, lying ∼26–27 eV above the neutral (…5p6 1S0) ground state, is observed. For a 169 element array drawing a total current of 30 mA, the output power of the array in the 300–1000 nm spectral region falls to ∼55% of its initial value in ∼8.3 h of continuous operation with a static gas fill.
Ga/N flux ratio influence on Mn incorporation, surface morphology, and lattice polarity during radio frequency molecular beam epitaxy of (Ga,Mn)N
Authors: Haider Muhammad B. , Constantin Costel , Al-Brithen Hamad , Yang Haiqiang , Trifan Eugen , Ingram David , Smith Arthur R. , Kelly C. V. , Ijiri Y.
Published: April 2003

The effect of the Ga/N flux ratio on the Mn incorporation, surface morphology, and lattice polarity during growth by rf molecular beam epitaxy of (Ga,Mn)N at a sample temperature of 550 °C is presented. Three regimes of growth, N-rich, metal-rich, and Ga-rich, are clearly distinguished by reflection high-energy electron diffraction and atomic force microscopy. Using energy dispersive x-ray spectroscopy, it is found that Mn incorporation occurs only for N-rich and metal-rich conditions. For these conditions, although x-ray diffraction in third order does not reveal any significant peak splitting or broadening, Rutherford backscattering clearly shows that Mn is not only incorporated but also substitutional on the Ga sites. Hence, we conclude that a MnxGa1−xN alloy is formed (in this case x∼5%), but there is no observable change in the c-axis lattice constant. We also find that the surface morphology is dramatically improved when growth is just slightly metal rich. When growth is highly metal-rich, but not Ga-rich, we find that Ga polarity flips to N polarity. It is concluded that the optimal growth of Ga-polar MnGaN by rf N-plasma molecular beam epitaxy occurs in the slightly metal-rich regime.
Modeling of aluminum via filling by forcefill
Authors: Estrin Y. , Kim H. S. , Kovler M. , Berler G. , Shaviv R. , Rabkin E.
Published: April 2003

A simple constitutive model was used to predict the efficiency of the aluminum forcefill process. The constitutive description—adopted from the one developed for bulk material—was implemented in a finite-element code and applied to simulate the forcefill process. The results are summarized in the form of a “forcefill map” showing isochrones (constant via filling time lines) on the pressure–temperature plane. Using such a diagram, it is possible to identify the process conditions that warrant complete via filling within a specified time. Comparison of the simulation results with experimental data demonstrates a semiquantitative agreement.
Kinetics of defect creation in amorphous silicon thin film transistors
Authors: Wehrspohn R. B. , Powell M. J. , Deane S. C.
Published: April 2003

We have developed a theoretical model to account for the kinetics of defect state creation in amorphous silicon thin film transistors, subjected to gate bias stress. The defect forming reaction is a transition with an exponential distribution of energy barriers. We show that a single-hop limit for these transitions can describe the defect creation kinetics well, provided the backward reaction and the charge states of the formed defects are properly taken into account. The model predicts a rate of defect creation given by (NBT)α(t/t0)(β−1), with the key result that α=3β. The time constant t0 is also found to depend on band-tail carrier density. Both results are in excellent agreement with experimental data. The t0 dependence means that comparing defect creation kinetics for different thin film transistors can only be done for the same value of band-tail carrier density. Normalization of bias stress data on different thin film transistors made at different band-tail densities is not possible.
Compliant epitaxial growth of InxGa1−xAs and InxAl1−xAs on In0.25Ga0.75As pseudosubstrates
Authors: Pickrell G. W. , Xu C. F. , Chang K. L. , Hsieh K. C. , Cheng K. Y.
Published: April 2003

High-quality regrowth of InxGa1−xAs and In0.25Al0.75As layers on In0.25Ga0.75As pseudosubstrates was demonstrated. These pseudosubstrates were formed using lateral oxidation of an underlying Al0.98Ga0.02As layer to improve the material quality of a relaxed In0.25Ga0.75As seeding layer. Using transmission electron microscopy, dislocation densities in the regrown layers were measured and found to be equal to that of the underlying pseudosubstrates (⩽106 cm−2). Doping characterization of these regrown films, using Hall-effect measurements, was also performed for both Si-doped and Be-doped materials. The doped In0.25Ga0.75As films showed normal carrier concentration trends as compared to doped GaAs films and In0.53Ga0.47As films grown on InP substrates. The doped In0.25Al0.75As films, however, showed lower-carrier concentrations than expected. In addition, room-temperature photoluminescence (PL) measurements of thick (∼1 μm) In0.25Ga0.75As layers show emission near 1.1 μm indicating the high quality of the regrown material. Strained In0.40Ga0.60As quantum wells (QWs) were also grown in an In0.25Ga0.75As matrix. PL measurements taken at a temperature of 77 K show emission from the strained QWs at a wavelength near 1.23 μm. With further optimization, these materials promise room-temperature emission at wavelengths near 1.3 μm.
Cooperative upconversion as the gain-limiting factor in Er doped miniature Al2O3 optical waveguide amplifiers
Authors: Kik P. G. , Polman A.
Published: April 2003

Erbium doped Al2O3 waveguide amplifiers were fabricated using two different doping methods, namely Er ion implantation into sputter deposited Al2O3, and co-sputtering from an Er2O3/Al2O3 target. Although the Er concentration in both materials is almost identical (0.28 and 0.31 at. %), the amplifiers show a completely different behavior. Upon pumping with 1.48 μm, the co-sputtered waveguide shows a strong green luminescence from the S3/24 level, indicating efficient cooperative upconversion in this material. This is confirmed by pump power dependent measurements of the optical transmission at 1.53 μm and the spontaneous emission at 1.53 and 0.98 μm. All measurements can be accurately modeled using a set of rate equations that include first order and second order cooperative upconversion. The first order cooperative upconversion coefficient C24 is found to be 3.5×10−16 cm3 s−1 in the co-sputtered material, two orders of magnitude higher than the value obtained in Er implanted Al2O3 of 4.1×10−18 cm3 s−1. It is concluded that the co-sputtering process results in a strongly inhomogeneous atomic scale spatial distribution of the Er ions. As a result, the co-sputtered waveguides do not show optical gain, while the implanted waveguides do.
Grain boundary electric characterization of Zn7Sb2O12 semiconducting ceramic: A negative temperature coefficient thermistor
Authors: Nobre M. A. L. , Lanfredi S.
Published: April 2003

The electrical properties of the grain boundary region of electroceramic sensor temperature based on inverse spinel Zn7Sb2O12 were investigated at high temperature. The zinc antimoniate was synthesized by a chemical route based on the modified Pechini method. The electric properties of Zn7Sb2O12 were investigated by impedance spectroscopy in the frequency range from 5 Hz to 13 MHz and from 250 up to 600 °C. The grain boundary conductivity follows the Arrhenius law, with two linear branches of different slopes. These branches exhibit activation energies with very similar values; the low-temperature (⩽350 °C) and high-temperature (⩾400 °C) regions are equal to 1.15 and 1.16 eV, respectively. Dissimilar behavior is observed on the relaxation time (τ) curve as a function of temperature, where a single slope is identified. The negative temperature coefficient parameters and nature of the polarization phenomenon of the grain boundary are discussed.
Effects of tensile strain in barrier on optical gain spectra of GaInNAs/GaAsN quantum wells
Authors: Fan W. J. , Ng S. T. , Yoon S. F. , Li M. F. , Chong T. C.
Published: April 2003

The band structures, optical gain spectra, and transparency radiative current densities of compressive-strained GaInNAs quantum wells (QWs) with different tensile-strained GaAsN (N composition from 0 to 3%) barriers are systematically investigated using a modified 6×6 k⋅p Hamiltonian including the heavy hole, light hole, and spin-orbit splitting bands. We found that the transition energy decreases when increasing the N composition in the barrier. The optical gain spectra and maximum optical gain as a function of carrier density and radiative current density are obtained for the GaInNAs/GaAsN QWs with well width of 5 nm, InW=28%, and NW=2.66% emitting around 1.55 μm. The transparency carrier density increases with the nitrogen composition in the GaAsN barrier. The transparency radiative current density decreases with more nitrogen being added into the barrier, which is in agreement with the recent experimental observation.
Effect of microstructure on diffusion of copper in TiN films
Authors: Gupta A. , Wang H. , Kvit A. , Duscher G. , Narayan J.
Published: April 2003

We investigated the effect of the microstructure of TiN films on the diffusion behavior of Cu. Cu/TiN films were synthesized on Si(100) substrate by the pulsed laser deposition (PLD) technique. Three different microstructures of TiN were achieved by growing the films at different substrate temperatures, where higher deposition temperatures (∼650 °C) led to epitaxial growth by the mechanism of domain matching epitaxy and lower temperature depositions resulted in polycrystalline and nanocrystalline TiN films. These structures were characterized using x-ray diffraction and high-resolution transmission electron microscopy. Cu was deposited in situ on the samples with three different microstructures of TiN films on Si(100) by PLD. All three samples were simultaneously annealed at 500 °C for 30 min in high vacuum to study the effect of diffusion characteristics of Cu as a function of microstructure of the TiN films. Secondary ion mass spectroscopy, Z-contrast imaging and electron energy-loss spectroscopy were used to understand the diffusion mechanisms and rationalize results in different microstructures.
The red σ2/kT spectral shift in partially disordered semiconductors
Authors: Eliseev P. G.
Published: April 2003

In connection with some spectral anomalies of the luminescence in III–V semiconductors, we consider here the red spectral shift in partially disordered semiconductors, namely, in heavily doped GaAs and in alloys of InGaP and InGaN. The shift (of the Stokes type) between the Gaussian absorption peak and the quasi-equilibrium low-intensity luminescence peak is equal to σ2/kT, where σ2 is the dispersion of the Gaussian. As this shift is strongly temperature dependent, the temperature-induced blueshift anomaly appears in the temperature dependence of the luminescence peak position in III–V materials. The broadening parameter σ can be derived from spectral measurements. It is determined by the Coulomb-related fluctuations in heavily doped materials or by composition variations in disordered alloys (in bulk materials). In nanostructured materials additional factor of the disordering appears due to roughness of interfaces.
Exploring two-dimensional soap-foam films using fullerene (C60) nanosensors
Authors: Maguire John F. , Amer Maher S. , Busbee John
Published: April 2003

A large number of studies have been devoted to the investigation of foam structure formation, characteristics, and stability. In this paper, we use fullerene (C60) spheres as Raman active nanosensors to probe the local chemical environment in a two-dimensional soap foam. It has been found that the position of the Raman active pentagon pinch mode around 1469 cm−1 shifts to lower wave numbers with the increase in the angle between foam-cell boundaries. The observed shift is due to changes in the local chemical interaction between the nanosensor and its environment. The study demonstrates that fullerenes may be used as sensitive nanoscale sensors to probe the local chemical potential in soft and interfacial materials, and more importantly in thermodynamically small systems.
Large polarization change in two-dimensional metallic photonic crystals in subterahertz region
Authors: Miyamaru Fumiaki , Kondo Takashi , Nagashima Takeshi , Hangyo Masanori
Published: April 2003

Interesting polarization characteristics of two-dimensional metallic photonic crystals (2D-MPC) in the subterahertz region have been found. We measured the temporal wave form of the THz wave transmitted thorough the 2D-MPC using a THz time domain spectroscopic system. The linear polarization of the incident THz wave transmitted through the 2D-MPC becomes elliptical with a slight tilting of the incident angle from the normal incidence. This result indicates that the 2D-MPC behaves not only as a band-pass filter already reported, but also as a wave plate. This large polarization change is attributed to the strong TE–TM polarization mixing in the 2D-MPC.
Relaxor behavior in sol–gel-derived BaZr(0.40)Ti(0.60)O3 thin films
Authors: Dixit A. , Majumder S. B. , Katiyar R. S. , Bhalla A. S.
Published: April 2003

In the present work, we have reported the phase transition behavior of sol–gel-derived BaZr0.4Ti0.6O3 (BZT40) thin films. The dielectric properties of these films were measured as a function of temperature in the frequency range of 1 kHz to 1 MHz. A broad dielectric anomaly coupled with the shift of dielectric maxima toward a higher temperature with increasing frequency indicates the relaxor-type behavior in the films. The index of relaxation (γ) and the broadening parameter (Δ) were estimated from a linear fit of the modified Curie–Weiss law. The value of γ≈1.79 and Δ≈76 K indicates the strong relaxor nature of these films. A remarkably good fit to the Vogel–Fulcher relation further supports such a relaxor nature. The films showed good polarization hysteresis at a low temperature, though that slims down yet persists even above the dielectric maximum temperature (Tm), which is about 170 K.
Ultrafast optical nonlinearity in poly(methylmethacrylate)-TiO2 nanocomposites
Authors: Elim H. I. , Ji W. , Yuwono A. H. , Xue J. M. , Wang J.
Published: April 2003

With 780-nm, 250-fs laser pulses, ultrafast optical nonlinearity has been observed in a series of thin films containing poly(methyl methacrylate) (PMMA)-TiO2 nanocomposites, which are synthesized by a simple technique of in-situ sol-gel/polymerization. The best figures of merit are found in one of the films prepared with a 60 wt % of titanium isopropoxide. Transmission electron microscopy shows the presence of 5-nm-diameter particles in the film. The observed optical nonlinearity has a recovery time of ∼1.5 ps. These findings suggest the strong potential of PMMA-TiO2 nanocomposites for all-optical switching.
Thermoelectric properties of a clathrate compound Ba8Cu16P30
Authors: Huo Dexuan , Sasakawa Tetsuya , Muro Yuji , Takabatake Toshiro
Published: April 2003

We report the electrical resistivity (ρ), thermoelectric power (S), thermal conductivity (κ), and specific heat (C) for the clathrate compound Ba8Cu16P30, in which polyhedral cages are composed of Cu and P atoms. Being in contrast to the n-type conduction in most of clathrate compounds, a p-type metallic conduction in this compound is indicated by the positive S, which monotonically increases up to 65 μV/K at 460 K. The analysis of C(T) gives indirect evidence for low-frequency local vibrations of Ba atoms with two Einstein temperatures 120 and 90 K, respectively. These local vibrations lead to a low lattice thermal conductivity of 2.9 W/K m at 300 K. The combination of the metallic resistivity, large thermoelectric power, and low thermal conductivity, makes this compound be a prospective thermoelectric material.
Compound cavity measurement of transmission and reflection of a tapered single-line photonic-crystal waveguide
Authors: Talneau A. , Mulot M. , Anand S. , Lalanne Ph.
Published: April 2003

Measurements on a single-line defect photonic crystal waveguide demonstrate propagation losses as low as 140 cm−1 and coupling efficiency to a ridge access guide increased from 20% to 50% thanks to a tapered access. These results are obtained by analyzing the internal cavities created by residual reflections, hence, requiring a single sample. They are nevertheless crosschecked by measurements on distinct samples by the Fabry–Pérot resonance method.
Size-independent spin switching field using synthetic antiferromagnets
Authors: Inomata K. , Koike N. , Nozaki T. , Abe S. , Tezuka N.
Published: April 2003

The arrays of the synthetic antiferromagnetic (SyAF) patterned bits consisting of Co90Fe10 (t1nm)/Ru (d nm)/Co90Fe10 (t2 nm) were successfully fabricated with micron to submicron sizes and different aspect ratios. Magnetization switching field Hsw and magnetic domain structure were investigated using magneto-optical Kerr effect and magnetic force microscopy (MFM), respectively. It was demonstrated that the strongly AF-coupled SyAF with aspect ratio k=1 creates size-independent Hsw down to submicron sizes fabricated, which is understood by zero demagnetization field for k=1 and single domain structure, observed by MFM. The size-independent switching field demonstrates the predominance of the SyAF for spintronics devices, requiring a low switching field and stabilized single domain structure for small bit sizes such as ultrahigh density magnetic random access memories and spin transistors.
Thermal lens model of Sb thin film in super-resolution near-field structure
Authors: Wei Jingsong , Gan Fuxi
Published: April 2003

Using a time-resolved dual-beam mode-mismatched thermal lens method, the refractive index change of the Sb thin film with a thickness of 20 nm at the wavelength of 632.8 nm with temperature is measured. According to the results measured and the radial distribution law of the refractive index within the aperture, by considering the aperture as a thermal lens and setting the thickness of Sb thin film being 20 nm, recording or readout laser power 10 mW, the radius of the aperture 200 nm, and laser irradiation time on the Sb thin film 20 ns, the focal length of thermal lens of Sb thin film is 38.5 nm, correspondingly, the focused spot size through the thermal lens can be reduced to about 80 nm, at the same time, the intensity can be approximately increased to 20 times as compared to that of the primary focused spot by lens.
Diode-pumped Yb:Y2O3 ceramic laser
Authors: Kong J. , Lu J. , Takaichi K. , Uematsu T. , Ueda K. , Tang D. Y. , Shen D. Y. , Yagi H. , Yanagitani T. , Kaminskii A. A.
Published: April 2003

We report on a diode-pumped polycrystalline Yb:Y2O3 ceramic laser. We demonstrate that, with a pump power of 11 W at 937 nm, 0.75-W cw laser output at 1078 nm can be obtained from the laser. The laser had a threshold of 4.7 W and a slope efficiency of 12.6% when an output coupler of R=98% was used.
InAs/GaAs quantum dots optically active at 1.5 μm
Authors: da Silva M. J. , Quivy A. A. , Martini S. , Lamas T. E. , da Silva E. C. F. , Leite J. R.
Published: April 2003

InAs quantum dots grown by molecular-beam epitaxy on GaAs substrates are demonstrated to be suitable structures to achieve an optical emission in the 1.3–1.5-μm range. Their tuning towards such long wavelengths was made possible by combining an extreme reduction of the InAs growth rate and a fast growth of the GaAs cap layer at low temperature. Our results create perspectives for the fabrication of GaAs-based devices operating in the most important telecommunications window.
Nonradiative recombination in quantum dots via Coulomb interaction with carriers in the barrier region
Authors: Solov’ev Igor Yu. , Zegrya Georgy G.
Published: April 2003

A mechanism of nonradiative recombination of nonequilibrium carriers in semiconductor quantum dots (QDs) is suggested and discussed. Recombination of an electron-hole pair localized in a QD occurs via Coulomb (Auger) interaction with carriers in the barrier region. It is shown that the characteristic time of such an Auger process depends on QD parameters, temperature, and carrier density in the barrier region and, under certain conditions, is shorter than the characteristic time of radiative recombination.
Composition anisotropy compensation and spontaneous magnetostriction in Tb0.2Dy0.8−xPrx(Fe0.9B0.1)1.93 alloys
Authors: Ren W. J. , Zhang Z. D. , Song X. P. , Zhao X. G. , Jin X. M.
Published: April 2003

The possibility of the composition anisotropy compensating in Dy1−xPrxFe2 is discussed phenomenologically, based on a single ion approach. The crystal structure, the easy magnetization direction, and the spontaneous magnetostriction of Tb0.2Dy0.8−xPrx(Fe0.9B0.1)1.93 (0⩽x⩽0.7) alloys are studied. Single-phase Tb0.2Dy0.8−xPrx(Fe0.9B0.1)1.93 with cubic MgCu2-type structure forms up to x=0.4 and the magnetostrictive phase exists in all the alloys studied. A single (440) peak of x-ray diffraction of the Laves phase exists when 0⩽x⩽0.3, but becomes doubly split when 0.4⩽x⩽0.7 because of a large spontaneous magnetostriction along its easy magnetization direction 〈111〉. Composition anisotropy compensation is realized in Tb0.2Dy0.8−xPrx(Fe0.9B0.1)1.93 alloys. Tb0.2Dy0.4Pr0.4(Fe0.9B0.1)1.93 alloy with the single Laves phase has a large magnetostriction (λ111≈1200 ppm) and a low anisotropy, which may be a good candidate material for magnetostriction application.
Low-temperature thermal oxide to plasma-enhanced chemical vapor deposition oxide wafer bonding for thin-film transfer application
Authors: Tan C. S. , Fan A. , Chen K. N. , Reif R.
Published: April 2003

Low-temperature direct plasma-enhanced chemical vapor deposition (PECVD) oxide to thermal oxide bonding is described. The PECVD oxide is densified at 350 °C and chemical-mechanically polished to obtain reasonably smooth surface for bonding. The PECVD oxide wafer is bonded to the thermal oxide wafer at room temperature after piranha clean that leaves the wafer surfaces hydrophilic. A postbonding anneal at 300 °C completes the bonding. A void-free bonding interface is observed from infrared imaging and the bonding strength is estimated to be 432 mJ/m2. This bonding method can be used in a variety of applications, including three-dimensional integration.
Genomic instability and endoreduplication triggered byRAD17deletion
Authors: Wang Xin , Zou Lee , Zheng Huyong , Wei Qingyi , Elledge Stephen J. , Li Lei
Published: April 2003

Cell cycle checkpoints are critical for genomic stability. Rad17, a component of the checkpoint clamp loader complex (Rad17/Rfc2-5), is required for the response to DNA damage and replication stress. To explore the role of Rad17 in the maintenance of genomic integrity, we established somatic conditional alleles ofRAD17in human cells. We find thatRAD17is not only important for the Atr-mediated checkpoint but is also essential for cell viability. Cells lackingRAD17exhibited acute chromosomal aberrations and underwent endoreduplication at a high rate. Therefore,RAD17links the checkpoint to ploidy control and is essential for the maintenance of chromosomal stability.
The β-globinlocus control region (LCR) functions primarily by enhancing the transition from transcription initiation to elongation
Authors: Sawado Tomoyuki , Halow Jessica , Bender M.A. , Groudine Mark
Published: April 2003

To investigate the molecular basis of β-globingene activation, we analyzed factor recruitment and histone modification at the adult β-globingene in wild-type (WT)/locus control region knockout (ΔLCR) heterozygous mice and in murine erythroleukemia (MEL) cells. Although histone acetylation and methylation (Lys 4) are high before and after MEL differentiation, recruitment of the erythroid-specific activator NF-E2 to the promoter and preinitiation complex (PIC) assembly occur only after differentiation. We reported previously that targeted deletion of the LCR reduces β-globingene expression to 1%–4% of WT without affecting promoter histone acetylation. Here, we report that NF-E2 is recruited equally efficiently to the adult β-globinpromoters of the ΔLCR and WT alleles. Moreover, the LCR deletion reduces PIC assembly only twofold, but has a dramatic effect on Ser 5 phosphorylation of RNA polymerase II and transcriptional elongation. Our results suggest at least three distinct stages in β-globingene activation: (1) an LCR-independent chromatin opening stage prior to NF-E2 recruitment to the promoter and PIC assembly; (2) an intermediate stage in which NF-E2 binding (LCR-independent) and PIC assembly (partially LCR-dependent) occur; and (3) an LCR-dependent fully active stage characterized by efficient pol II elongation. Thus, in its native location the LCR functions primarily downstream of activator recruitment and PIC assembly.
Functional interactions between the transcription and mRNA 3′ end processing machineries mediated by Ssu72 and Sub1
Authors: He Xiaoyuan , Khan Asad U. , Cheng Hailing , Pappas Donald L. , Hampsey Michael , Moore Claire L.
Published: April 2003

Transcription and processing of pre-mRNA are coupled events. By using a combination of biochemical, molecular, and genetic methods, we have found that the phylogenetically conserved transcription factor Ssu72 is a component of the cleavage/polyadenylation factor (CPF) ofSaccharomyces cerevisiae. Our results demonstrate that Ssu72 is required for 3′ end cleavage of pre-mRNA but is dispensable for poly(A) addition and RNAP II termination. The in vitro cleavage defect caused by depletion of Ssu72 from cells can be rescued by addition of recombinant Ssu72. Ssu72 interacts physically and genetically with the Pta1 subunit of CPF. Overexpression ofPTA1causes synthetic lethality in anssu72-3mutant. Moreover, Sub1, which has been implicated in transcription initiation and termination, also interacts with Pta1, and overexpression ofSUB1suppresses the growth and processing defect of apta1mutation. Physical interactions of Ssu72 and Sub1 with Pta1 are mutually exclusive. Based on the interactions of Ssu72 and Sub1 with both the Pta1 of CPF and the TFIIB component of the initiation complex, we present a model describing how these novel connections between the transcription and 3′ end processing machineries might facilitate transitions in the RNAP II transcription cycle.
ICE1: a regulator of cold-induced transcriptome and freezing tolerance inArabidopsis
Authors: Chinnusamy Viswanathan , Ohta Masaru , Kanrar Siddhartha , Lee Byeong-ha , Hong Xuhui , Agarwal Manu , Zhu Jian-Kang
Published: April 2003

Cold temperatures trigger the expression of the CBF family of transcription factors, which in turn activate many downstream genes that confer chilling and freezing tolerance to plants. We report here the identification ofICE1(inducer ofCBFexpression1), an upstream transcription factor that regulates the transcription ofCBFgenes in the cold. AnArabidopsis ice1mutant was isolated in a screen for mutations that impair cold-induced transcription of aCBF3promoter-luciferase reporter gene. Theice1mutation blocks the expression ofCBF3and decreases the expression of many genes downstream ofCBFs, which leads to a significant reduction in plant chilling and freezing tolerance.ICE1encodes a MYC-like bHLH transcriptional activator. ICE1 binds specifically to the MYC recognition sequences in theCBF3promoter.ICE1is expressed constitutively, and its overexpression in wild-type plants enhances the expression of theCBFregulon in the cold and improves freezing tolerance of the transgenic plants.
Crystal structure of theDrosophilaMago nashi–Y14 complex
Authors: Shi Hang , Xu Rui-Ming
Published: April 2003

Pre-mRNA splicing is essential for generating mature mRNA and is also important for subsequent mRNA export and quality control. The splicing history is imprinted on spliced mRNA through the deposition of a splicing-dependent multiprotein complex, the exon junction complex (EJC), at ∼20 nucleotides upstream of exon–exon junctions. The EJC is a dynamic structure containing proteins functioning in the nuclear export and nonsense-mediated decay of spliced mRNAs. Mago nashi (Mago) and Y14 are core components of the EJC, and they form a stable heterodimer that strongly associates with spliced mRNA. Here we report a 1.85 Å-resolution structure of theDrosophilaMago–Y14 complex. Surprisingly, the structure shows that the canonical RNA-binding surface of the Y14 RNA recognition motif (RRM) is involved in extensive protein–protein interactions with Mago. This unexpected finding provides important insights for understanding the molecular mechanisms of EJC assembly and RRM-mediated protein–protein interactions.
Mathematical development: a theory of natural creation
Authors: Sabelli H.
Published: April 2003

The physical universe is the embodiment of necessary mathematical forms by ever‐present flux. Interaction of these forms generates diversity, novelty, complexity, and higher levels of organization. Lattice order, group opposition, and topological transformation are generators necessary and sufficient to construct mathematics. Homologous cognitive structures generate human mental development. Process theory proposes that these mathematical generators also create nature. Lattice order is embodied as action, group opposition as two‐valued information, and topological transformation as spatial organization.
Aging and social systems
Authors: Sabelli H. , Patel M. , Carlson‐Sabelli L. , Konecki J. , Nagib J. , Sugerman A.
Published: April 2003

In our society, medical care and economic progress have improved the duration and quality of life, but aging is accelerated by social norms and their psychological introjection. Healthy aging involves the continuing pursuit of creative activity. Changes in self‐view and behavior will require and promote a change in social roles, and the emancipatory mobilization of senior adults of both sexes and all classes.
Novelty, diversification and nonrandom complexity define creative processes
Authors: Sugerman A. , Sabelli H.
Published: April 2003

We describe a theory of creative activity through the development and use of mathematical tools in the analysis of time series. The time series analyzed include empirical series and biotic and chaotic series generated by recurrent functions. Embeddings are used to measure the dimensionality of a series, and analyses of isometries of Euclidean norms at various embeddings reveal the relatively simple processes that generate and combine with complex structures. These tools identify and measure diversity, novelty, and complexity in complex natural processes and in mathematical bios. The presence of these properties shows that creative processes result from deterministic interactions among relatively simple components, not only from random accident.
Cybernetics and systems, from past to future
Authors: Vallée Robert
Published: April 2003

The founders of cybernetics and systems are presented, among them N. Wiener, W.S. McCulloch and L. von Bertalanffy. Some precursors are cited from antiquity to 20th century. The basic concepts are exposed: feedback, quantity of information, requisite variety, homeostasis, local and global points of view, oprn systems, autopoiesis. The roles of the observer and of the actor are emphasized. Future is considered in three directions: development of epistemology and of praxiology, symbiosis of man and machine, role of requisite variety in the survival of mankind.
Parameter Identification of a Large Floating Body in Random Ocean Waves by Reverse MISO Method
Authors: Bhattacharyya S. K. , Selvam R. Panneer
Published: April 2003

Dynamics of a large moored floating body in ocean waves involves frequency dependent added mass and radiation damping as well as the linear and nonlinear mooring line characteristics. Usually, the added mass and radiation damping matrices can be estimated either by potential theory-based calculations or by experiments. The nonlinear mooring line properties are usually quantified by experimental methods. In this paper, we attempt to use a nonlinear system identification approach, specifically the Reverse Multiple Inputs-Single Output (R-MISO) method, to a single-degree-of-freedom system with linear and cubic nonlinear stiffnesses. The system mass is split into a frequency independent and a frequency dependent component and its damping is frequency dependent. This can serve as a model of a moored floating system with a dominant motion associated with the nonlinear stiffness. The wave diffraction force, the excitation to the system, is assumed known. This can either be calculated or obtained from experiments. For numerical illustration, the case of floating semi-ellipsoid is adopted with dominant sway motion. The motion as well as the loading are simulated with and without noise assuming PM spectrum and these results have been analyzed by the R-MISO method, yielding the frequency dependent added mass and radiation damping, linear as well as the nonlinear stiffness coefficients quite satisfactorily.
Part Dimensional Error and Its Propagation Modeling in Multi-Operational Machining Processes
Authors: Huang Qiang , Shi Jianjun , Yuan Jingxia
Published: April 2003

In a multi-operational machining process (MMP), the final product variation is an accumulation or stack-up of variation from all machining operations. Modeling and control of the variation propagation is essential to improve product dimensional quality. This paper presents a state space model and its modeling strategies to describe the variation stack-up in MMPs. The physical relationship is explored between part variation and operational errors. By using the homogeneous transformation approach, kinematic modeling of setup and machining operations are developed. A case study with real machined parts is presented in the model validation.
A Lagrangian Model for Irregular Waves and Wave Kinematics
Authors: Gjøsund Svein Helge
Published: April 2003

It has proven difficult to describe the kinematics in irregular waves satisfactorily, in particular for the surface zone in broad-banded waves. A Lagrangian approach offers distinct advantages in this respect, eliminating the need for extrapolation of solutions or “stretching” of coordinates. This paper presents a model of irregular waves based on superposition of linear Lagrangian wave components, using an iterative method to obtain the Eulerian solution. This approach yields theoretically consistent results everywhere in the waves, and comparisons with wave flume measurements show good agreement. Also, the linear Lagrangian model includes wave interactions that would be nonlinear in an Eulerian formulation.
A Response-Based Method for Developing Joint Metocean Criteria for On-Bottom Pipeline Stability
Authors: Ewans Kevin C.
Published: April 2003

A response-based method for deriving joint metocean criteria for the on-bottom stability design of submarine pipelines is described. The method consists of applying a response function to convert a long time history of ocean wave and current conditions into a corresponding pipe response time history, from which extreme values and the joint metocean criteria can be obtained. In the case of designing for the 100-year return period conditions, the joint criteria are defined as either the value of the steady current to associate with the wave conditions that have a return period of 100 years or the value of the wave conditions to associate with the value of the steady current that has a return period of 100 years. The method involves first determining the extreme values, of the waves, currents and the responses, such as those with a 100-year return period, and then deriving the pair of wave and current combinations by inverting the response function at the 100-year return period level. Response functions for both the traditional static design approach and the state-of-the-art dynamic simulation design approach are presented. Both response functions are expressed in terms of the pipe weight per unit pipe length required for the pipe to be stable. In the case of the traditional approach, this is the weight required to keep the pipe static on the sea bed; but in the case of the dynamic approach, it is the weight that will allow a maximum lateral pipe displacement of three pipe diameters. The dynamic response function was developed from the AGA Level-3 pipeline stability software, by performing pipeline response simulations for many combinations of different sea state and steady current conditions. Joint wave and current criteria obtained from the response functions, for two test locations, are compared and evaluated against both the independent wave and current criteria and the joint criteria values recommended in design codes. A method is also outlined on how the response functions may be used to make estimates of the pipeline reliability with respect to on-bottom stabilization.
Cost-Effective Design Criteria for Australian Monopod Platforms
Authors: Pinna Rodney , Ronalds Beverley F. , Andrich Mark A.
Published: April 2003

Assessments of structural reliability under storm overload have been performed on various monopod configurations located on Australia’s North West Shelf (NWS). The results have shown that these monopods have lower reliabilities than typical platforms in other petroleum provinces, due to a number of factors. In itself, this may not be a concern, as it may be argued that minimum facilities platforms have relatively low consequences of failure. Reasons for this could center around these monopods being satellites with small production throughput, having short service lives, being not-normally-manned, and having environmental protection features which minimize the possibility of a hydrocarbon spill resulting from a structural failure. A suitable target probability of failure for monopod platforms may be computed using a cost-benefit approach, where the total platform cost, including the cost of failure, is minimized. This analysis is developed for four distinct monopod configurations involving single pile, pile cluster and outrigger foundations in water depths ranging between 9-52m LAT. The relationship between platform CAPEX and probability of failure is derived from first principles for cases of appurtenances located within and external to the main caisson.
Laying Modeling of Submarine Pipelines Using Contact Elements into a Corotational Formulation
Authors: Marti´nez Cora E. , Goncalves Rau´l
Published: April 2003

A new finite element formulation to analyze stresses and displacements in submarine pipelines during laying operations is presented in this paper. The method is based on the corotational formulation using Bernoulli nonlinear beam elements to model the large displacements and rotations of the pipeline. The penalty method is used with spring-contact elements to accurately represent the actual boundary conditions on both the stinger and the sea floor. A comparison with a finite element formulation introduced by the authors in a previous paper is presented in order to verify the accuracy and computational effectiveness of the proposed method. A real laying case of an oil transportation submarine pipeline is also presented at the end of the paper to validate the results obtained with the developed formulation.
Microstructure-Level Force Prediction Model for Micro-milling of Multi-Phase Materials
Authors: Vogler Michael P. , DeVor Richard E. , Kapoor Shiv G.
Published: April 2003

A mechanistic model for the micro-endmilling process is developed that explicitly accounts for the different phases while machining heterogeneous materials. It is shown that frequencies in the cutting force signal higher than those that can be explained by the kinematics of the process can be explained by considering the multiple phases in the material. Experiments are performed on two compositions of ductile iron, pure ferrite and pearlite workpieces. These experiments show that the nature of the variation in the ductile iron cutting force signals can be attributed to the mixture of the phases. Additionally, simulation studies show that the frequency component of the variation is related to the spacing of the secondary (ferrite) phase and the magnitude of this component is determined by the size of the secondary phase particles.