bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of uniform InAs quantum dots on InGaAs surface structure modified superlattices on InP
Authors: Zhang Z. H. , Cheng K. Y.
Published: October 2003

We have developed a matrix layer structure, the InGaAs surface structure modified superlattice, to achieve high quality InAs quantum dots on (100) InP substrates. Formed by periodically repeating the group III- and group V-stabilized InGaAs layers, the InGaAs surface structure modified superlattice offers much greater advantages than the conventional InGaAs matrix layer for the growth of InAs quantum dots, where a thick InAs layer is required for the dot formation. By adjusting the number of period and the layer thickness of the superlattice structure, uniform InAs quantum dots are achieved even using an InAs deposition as thin as 2.5 monolayers. Photoluminescence measurements further verify a uniform size distribution of the achieved quantum dots.
Experimental and theoretical investigation on the structural properties of GaN grown on sapphire
Authors: Ohta J. , Fujioka H. , Oshima M. , Fujiwara K. , Ishii A.
Published: October 2003

We have investigated the growth mechanisms of group-III nitrides on c-plane sapphire substrates with experiments by pulsed-laser deposition and first-principles calculations. It has been experimentally revealed that the in-plane alignment between the nitrides and sapphire is [10-10]nitride//[11-20]sapphire and the nitride films have the N polarity for the most cases. We have found that the insertion of an Al-rich AlN buffer layer effectively turns over the GaN crystals from the N polarity to the Ga polarity, although the Ga-rich GaN buffer layer does not cause change in the polarity. The theoretical energy calculations of a sapphire slab with an adatom explain the experimental results, such as the in-plane alignment and the polarity change, quite well.
151
kA/cm
2
peak current densities in Si/SiGe resonant interband tunneling diodes for high-power mixed-signal applications
Authors: Jin Niu , Chung Sung-Yong , Rice Anthony T. , Berger Paul R. , Yu Ronghua , Thompson Phillip E. , Lake Roger
Published: October 2003

Room-temperature I–V characteristics of epitaxially grown Si/SiGe resonant interband tunneling diodes (RITDs) with extremely high peak current densities are presented. By optimizing the physical design, doping concentrations, and post-growth anneal temperatures, RITDs having peak current densities over 150 kA/cm2, peak-to-valley current ratios (PVCRs) greater than 2, and an estimated speed index of 34 mV/ps have been obtained. The interplay among the conditions to achieve maximum current density and highest PVCR is discussed. This result demonstrates the high potential of this type of Si-based tunnel diode for high-power mixed-signal applications.
Fabrication and characterization of high-quality waveguide-mode resonant optical filters
Authors: Priambodo P. S. , Maldonado T. A. , Magnusson R.
Published: October 2003

Optical filters containing resonant waveguide gratings are designed and fabricated using low-loss, robust materials. The double-layer filters contain a silicon dioxide diffractive element on a hafnium dioxide waveguide deposited on a fused silica substrate. Noise-pattern formation is minimized by use of an antireflective absorption layer during holographic grating recording in photoresist. Subsequent fabrication steps include metallization, lift-off, and oxygen plasma etch to create a metal etch mask for final CF4 plasma etching of a surface-relief grating. Spectral characterization with a tunable laser shows that the resulting filter exhibits 90% efficiency, 1.2 nm linewidth, and low sidebands.
Dilute nitride based double-barrier quantum-well infrared photodetector operating in the near infrared
Authors: Luna E. , Hopkinson M. , Ulloa J. M. , Guzmán A. , Muñoz E.
Published: October 2003

Near-infrared detection is reported for a double-barrier quantum-well infrared photodetector based on a 30-Å GaAs1−yNy (y≈0.01) quantum well. The growth procedure using plasma-assisted molecular-beam epitaxy is described. The as-grown sample exhibits a detection wavelength of 1.64 μm at 25 K. The detection peak strengthens and redshifts to 1.67 μm following rapid thermal annealing at 850 °C for 30 s. The detection peak position is consistent with the calculated band structure based on the band-anticrossing model for nitrogen incorporation into GaAs.
Thermal oxidation of gallium nitride nanowires
Authors: Tang Chengchun , Bando Yoshio , Liu Zongwen
Published: October 2003

The thermal oxidation of gallium nitride (GaN) nanowires in dry air was investigated by using thermogravimetric and transmission electron microscopy. The oxidation strongly depends on the oxidation temperature and the nanowire diameters. At temperatures lower than 700 °C, the oxidation is dominantly controlled by an oxygen absorption reaction. A chemical oxidation reaction occurs upon further increasing the temperature, accompanied by the formation of monoclinic gallium oxide (Ga2O3). The crystalline Ga2O3 can form a dense protective shell on the surfaces of GaN nanowires with large diameters, whereas Ga2O3 could not crystallize into one-dimensional morphology on the initial GaN nanowires with small diameters.
A study of the threshold voltage in pentacene organic field-effect transistors
Authors: Schroeder R. , Majewski L. A. , Grell M.
Published: October 2003

The threshold voltage and carrier mobilities were characterized in pentacene-based organic field-effect transistors with gold top-contact electrodes for different thickness of the pentacene film. The thickness of the semiconductor layer influences the values of the threshold voltage and, to a lesser extent, the saturation current. In this letter, we show that the thickness-dependent part of the threshold voltage results from the presence of an injection barrier at the gold–pentacene contact. We also show how the ratio between the gate insulator thickness and the semiconductor layer thickness alter the value for the saturation current, and therefore produces values for the field-effect mobility that are too low.
Planar polymer light-emitting electrochemical cells with extremely large interelectrode spacing
Authors: Gao Jun , Dane Justin
Published: October 2003

Planar polymer light-emitting electrochemical cells have been demonstrated with interelectrode spacings nearly 100 times larger than previously reported. Striking details of the p–i–n junction structure have been imaged directly using a digital camera. With an interelectrode spacing of 1.5 mm, a well-defined emission zone over 70 μm wide is observed near the cathode. Imaging under UV excitation reveals that the p-doped region migrates towards the cathode during operation, causing the emission zone at its frontier to shift. The width of the p-doped region is found to have a large variance, giving rise to an irregularly shaped emission zone.
High-resolution near-field spectroscopy of InAs single quantum dots at 70 K
Authors: Yu Young-Jun , Jhe Wonho , Arakawa Yasuhiko
Published: October 2003

We have performed high-resolution near-field laser spectroscopy and microscopy of single InAs/GaAs quantum dots near liquid nitrogen temperature. By simultaneous use of 100-nm shadow mask apertures and a 30-nm-aperture fiber probe, we have achieved photoluminescence (PL) resolution comparable to that available at liquid helium temperature. In particular, we have obtained a PL linewidth of 0.6 meV for single exciton states, and observed biexciton states with quadratic power dependence.
Field-induced electric switching in sol–gel-derived SiO2 films
Authors: Hu J. , Ward S. , Wang Q.
Published: October 2003

The switching dynamics of sol–gel-derived SiO2 films is investigated using voltage pulses over durations from 300 ns to 1 s and amplitudes from 1 to 20 V. The SiO2 film was fabricated using a spin-coating technique and annealed at 100 °C. The shortest switching transit time is found to be on the order of 10 ns. A delay time ranging from 100 ns to 500 ms is usually observed prior to switching, which changes exponentially with the electric field at switching, and also depends strongly on the area of the device.
Polyelectrolyte nanolayers as diffusion barriers for Cu metallization
Authors: Ganesan P. G. , Gamba J. , Ellis A. , Kane R. S. , Ramanath G.
Published: October 2003

Cu interconnect technology requires the use of <5-nm-thick interfacial layers to inhibit Cu transport into adjacent dielectric layers. We demonstrate the use of 3.5-nm-thick polyelectrolyte layers comprising polyethyleneimine (PEI) and polyacrylic acid (PAA) for this application. Cu/PAA/PEI/SiO2/Si structures show more than a factor-of-5 greater failure time compared to that observed in Cu/SiO2/Si structures. Increasing the number of PAA/PEI bilayers does not show any further improvement in barrier properties. Spectroscopic probing of the Cu/PAA interface reveals that polychelation of Cu with carboxyl groups in PAA is the primary reason for Cu immobilization. Our study suggests that polyelectrolyte nanolayers are attractive for applications such as tailoring barrierless low-k polymeric dielectrics, and for isolating nanoscale components in future device systems.
Low-energy electron-beam irradiation and yellow luminescence in activated Mg-doped GaN
Authors: Gelhausen O. , Klein H. N. , Phillips M. R. , Goldys E. M.
Published: October 2003

The effect of low-energy electron-beam irradiation (LEEBI) on native defects and residual impurities in metalorganic-vapor-phase-epitaxy-grown, lightly Mg-doped, p-type GaN was studied by temperature-resolved and excitation power density-resolved cathodoluminescence spectroscopy. Following the LEEBI treatment, the ubiquitous shallow donor–acceptor-pair emission at 3.27 eV decreased, while a deeper DAP emission at ∼3.1 eV dramatically increased in intensity, and a broad yellow luminescence band centered at 2.2 eV evolved. The results clearly indicate that the centers involved in the 3.27 eV transition are not stable during irradiation by low-energy electrons. Further, we report that the LEEBI-treatment not only dissociates neutral Mg-H complexes as intended, but simultaneously dissociates other hydrogenated defect complexes, giving rise to additional radiative recombination channels.
Frequency converters from visible to mid-infrared with periodically poled RbTiOPO4
Authors: Fragemann A. , Pasiskevicius V. , Nordborg J. , Hellström J. , Karlsson H. , Laurell F.
Published: October 2003

Electric-field poling has been used to fabricate quasi-phase-matched frequency converters in RbTiOPO4. A more accurate Sellmeier equation has been obtained for wavelengths between 0.43 and 3.4 μm. The dispersion of the thermo-optic coefficient for nz refractive index has been derived in the near- to mid-infrared spectral region. The nonlinear performance of periodically poled RbTiOPO4 obtained in the infrared optical parametric devices is comparable to that of periodically poled KTiOPO4.
Temperature-dependent optical studies of Ti1−xCoxO2
Authors: Guha S. , Ghosh K. , Keeth J. G. , Ogale S. B. , Shinde S. R. , Simpson J. R. , Drew H. D. , Venkatesan T.
Published: October 2003

We present the results of Raman and photoluminescence studies on epitaxial anatase phase Ti1−xCoxO2 films for x=0–0.07, grown by pulsed-laser deposition. The low-doped system (x=0.01 and 0.02) shows a Curie temperature of 700 K in the as-grown state. The Raman spectra from the doped and undoped films confirm their anatase phase. The photoluminescence spectrum is characterized by a broad emission from self-trapped excitons (STE) at 2.3 eV at temperatures below 120 K. This peak is characteristic of the anatase-phase TiO2 and shows a small blueshift with increasing doping concentration. The Co-doped samples show two spin-flip emission lines at 2.77 and 2.94 eV.
Generation of information theoretic secure keys using a chaotic semiconductor laser
Authors: Uchida A. , Davis P. , Itaya S.
Published: October 2003

We demonstrate a method for information theoretic secure key generation based on practical physical limits of continuous data acquisition from a rapidly fluctuating random signal generated by a chaotic semiconductor laser and transmitted over an optical fiber. Users independently and randomly grab sections of the chaotic waveform, separate into tag and key parts, and exchange tag parts to identify the common key parts which can be used to make secure keys. The frequency of trigger pulses in the waveform is used to control the security of the scheme which depends on the small probability of a third party coincidentally acquiring samples acquired by two other users.
Thermal conductivity of Si/SiGe superlattice nanowires
Authors: Li Deyu , Wu Yiying , Fan Rong , Yang Peidong , Majumdar Arun
Published: October 2003

The thermal conductivities of individual single crystalline Si/SiGe superlattice nanowires with diameters of 58 and 83 nm were measured over a temperature range from 20 to 320 K. The observed thermal conductivity shows similar temperature dependence as that of two-dimensional Si/SiGe superlattice films. Comparison with the thermal conductivity data of intrinsic Si nanowires suggests that alloy scattering of phonons in the Si–Ge segments is the dominant scattering mechanism in these superlattice nanowires. In addition, boundary scattering also contributes to thermal conductivity reduction.
Co distribution in ferromagnetic rutile Co-doped TiO2 thin films grown by laser ablation on silicon substrates
Authors: Hong Nguyen Hoa , Sakai Joe , Prellier W. , Hassini Awatef
Published: October 2003

Pure rutile Co-doped TiO2 films were fabricated by the pulsed-laser-deposition technique on silicon substrates from a ceramic target. Under the right fabrication conditions, Co concentration in the films could be almost the same as in the target, and films under various conditions all are ferromagnetic well above room temperature. Even though Rutherford backscattering spectroscopy measurements show that Co atoms mostly localize near the surface of the films and exist less in deeper levels, other experimental evidence shows that the ferromagnetism does not come from Co segregations, but from the Co-doped TiO2 matrix. Rutile Ti1−xCoxO2 thin films grown by a very simple technique on low-cost silicon substrates showing a Curie temperature (TC) above 400 K appear to be very attractive to applications.
Field emission from various CuO nanostructures
Authors: Hsieh Chien-Te , Chen Jin-Ming , Lin Hung-Hsiao , Shih Han-Chang
Published: October 2003

Three types of CuO nanostructures—the nanorod, nanofiber, and nanoparticle—have been grown by using a self-catalytic growth process at 400, 500, and 600 °C, respectively. Field-emission (FE) properties of the CuO nanostructures were investigated. The results indicated that the FE current was significantly affected by the morphologies of the CuO samples. Typical turn-on voltage for the CuO nanofiber array was detected at about 6–7 V/μm with an emission area of 1 mm2. Based on Fowler–Nordheim plot, the values of work function for the nanofiber array were estimated in ranges of 0.56 to 2.62 and 0.30 to 1.39 eV from a two-stage linearity plot. X-ray photoelectron spectroscopy analysis showed no obvious changes in chemical composition of the nanofiber array before and after FE tests. According to the analyses, the highly ordered CuO nanofiber array can be a promising candidate for FE emitters.
Quantum-size-effect-enhanced dynamic magnetic interactions among doped spins in Cd1−xMnxSe nanocrystals
Authors: Jian W. B. , Fang Jiye , Ji Tianhao , He Jibao
Published: October 2003

Dynamic magnetic properties of spins from Mn ions doped in semiconductor nanocrystals (Cd1−xMnxSe) have been studied using an electron paramagnetic resonance method based on two different crystalline sizes and a series of Mn concentrations. By decreasing the size of the quantum dots, the electron spin-nuclear spin interactions are reduced due to enhanced magnetic interactions between Mn ions. A linewidth analysis was also carried out, showing longer spin relaxation times and supporting the enhancement of spin coherence. We suggest that the enhancement of Mn–Mn interactions results from the quantized electrons which have longer coherence length in quantum dots. Quantum size effects may benefit to control and manipulation of spins in a semiconductor nanocrystalline system in which the magnetic ions are incorporated.
Physical properties of single-crystalline fibers of the colossal-magnetoresistance manganite La0.7Ca0.3MnO3
Authors: Cardoso C. A. , Araujo-Moreira F. M. , Andreeta M. R. B. , Hernandes A. C. , Leite E. R. , de Lima O. F. , Mombrú A. W. , Faccio R.
Published: October 2003

We have grown high-quality single crystals of the colossal-magnetoresistance (CMR) material La0.7Ca0.3MnO3 by using the laser heated pedestal growth method. Samples were grown as fibers of different diameters, and with lengths of the order of centimeters. Their composition and structure were verified through x-ray diffraction, scanning electron microcopy with energy dispersive x-ray analysis and by Rietveld analysis. The quality of the crystalline fibers was confirmed by Laue and electron backscatter diffraction patterns. Rocking curves performed along the fiber axis revealed a half-height width of 0.073°. The CMR behavior was confirmed by electrical resistivity and magnetization measurements as a function of temperature.
Optical and structural analysis of ZnCdO layers grown by metalorganic vapor-phase epitaxy
Authors: Gruber Th. , Kirchner C. , Kling R. , Reuss F. , Waag A. , Bertram F. , Forster D. , Christen J. , Schreck M.
Published: October 2003

The development of ZnO-based semiconductor devices requires band gap engineering. Ternary Zn1−xCdxO allows reduction of the band gap relative to ZnO, which would be necessary for devices emitting visible light. We have analyzed the structural and optical properties of Zn1−xCdxO layers grown by metalorganic vapor-phase epitaxy. A narrowing of the fundamental band gap of up to 300 meV has been observed, while introducing a lattice mismatch of only 0.5% with respect to binary ZnO. Photoluminescence, high-resolution x-ray diffraction, and spatially resolved cathodoluminescence measurements revealed a lateral distribution of two different cadmium concentrations within the Zn1−xCdxO layers.
Nuclear magnetic resonance in a ferromagnet–semiconductor heterostructure
Authors: Strand J. , Isakovic A. F. , Lou X. , Crowell P. A. , Schultz B. D. , Palmstrøm C. J.
Published: October 2003

We report the observation of nuclear magnetic resonance in a ferromagnet–semiconductor heterostructure in the presence of a spin-polarized current. Spin-polarized electrons injected from a metallic ferromagnet dynamically polarize a large nuclear spin population in a GaAs quantum well. The characteristic time for the polarization process is approximately 20 s, and the nuclear polarization can persist for several minutes after the current is turned off. Resonant depolarization is observed in the presence of an ac magnetic field or when the injection current is modulated at the nuclear magnetic resonance frequency.
Photonic-crystal 180° power splitter based on coupled-cavity waveguides
Authors: Martinez Alejandro , Cuesta Francisco , Griol Amadeu , Mira David , Garcia Jaime , Sanchis Pablo , Llorente Roberto , Marti Javier
Published: October 2003

We propose a structure that allows the splitting of electromagnetic waves with a phase shift of 180° between output signals based on photonic crystals. The structure consists of two parallel coupled-cavity waveguides placed in proximity. The performance of the splitting structure is theoretically discussed, evaluated by means of finite-difference time-domain method simulations and experimentally demonstrated at microwave frequencies. As both output paths have the same physical length, the two output signals are synchronized, which is very attractive for splitting high-speed optical signals in photonic-crystal-based integrated circuits.
Fabrication of nonepitaxially grown double-layered FePt:C/FeCoNi thin films for perpendicular recording
Authors: Yan M. L. , Li X. Z. , Gao L. , Liou S. H. , Sellmyer D. J. , van de Veerdonk R. J. M. , Wierman K. W.
Published: October 2003

A noneptaxially grown double-layered thin-film medium of nanocompsite FePt:C with a FeCoNi soft underlayer for high-density perpendicular magnetic recording was fabricated and investigated. Square-shaped perpendicular loops with a remanance ratio nearly equal to one and a coercivity as large as 8.5 kOe were obtained for this ordered FePt:C double-layered medium. The formation of the ordered L10 phase is confirmed by electron diffraction experiments. Transmission electron microscope observations reveal that FePt grains with a uniform size less than 5 nm are embedded in the C matrix and appear to be well isolated. Our results show that nonepitaxially grown (001) textured double-layered nanocomposite L10 FePt-based films with perpendicular anisotropy are a promising candidate to realize extremely high-density perpendicular recording.
Dense hydrogen adsorption on carbon subnanopores at 77 K
Authors: Kadono K. , Kajiura H. , Shiraishi M.
Published: October 2003

Hydrogen adsorption measurements on two types of different carbon nanomaterials were carried out at 77 K up to hydrogen pressures of 2 MPa using the volumetric method modified for low-temperature experiments. The adsorption property was concluded as dense hydrogen physisorption in subnanometer-sized pores because of the Langmuir-type isotherm, reversible adsorption/desorption, and large hydrogen uptake exceeding 2 wt %. The estimated density of adsorbed hydrogen was comparable to the density of bulk liquid hydrogen, indicating that hydrogen filling would be attainable when both the chemical potential of hydrogen and adsorption potential of carbon were optimized.
Enhanced adhesion and performance of the source/drain electrode using a single-layered Ag(Cu) film for an amorphous silicon thin-film transistor
Authors: Hong S. J. , Lee S. , Park J. B. , Yang H. J. , Ko Y. K. , Lee J. G. , Cho B. S. , Jeong C. O. , Chung K. H.
Published: October 2003

The feasibility of using a Ag(Cu) alloy film as a source/drain electrode for thin-film transistor (TFT) liquid-crystal displays has been investigated. The annealing of a Ag(Cu)/Si structure, for 30 min at 200 °C, produced a uniform Cu3Si layer at the Ag(Cu)–Si interface, as a result of the reaction of the segregated Cu with Si. This lowered the resistivity from 5.3 to 3.2 μΩ cm, which also led to improved adhesion properties. A hydrogenated amorphous silicon (a-Si:H) TFT was fabricated using a single layer of Ag (19 at. % Cu) alloy film as the source/drain metal. The subthreshold slope, mobility, and threshold voltage obtained from the fabricated a-Si:H TFT were 0.78 V/dec, 0.79 cm2/V s, and 2 V, respectively, revealing a reduction in the process steps, with excellent performance.
Optimization of semiconductor–metal hybrid structures for application in magnetic-field sensors and read heads
Authors: Holz Matthias , Kronenwerth Oliver , Grundler Dirk
Published: October 2003

Semiconductor–metal hybrid structures can exhibit a very large geometrical magnetoresistance effect, the so-called extraordinary magnetoresistance (EMR) effect. Using the finite element method, we study the EMR effect in rectangular semiconductor–metal hybrid structures and investigate the effects of material parameters and of device geometry. We find that the EMR device exhibits inverse scalability, i.e., the output characteristics improve with decreasing device width. This is promising for miniaturized magnetic-field sensors like, e.g., read heads. Using realistic device parameters, we predict an optimized performance as a sensor for a width-to-length ratio of 0.025.
Rapid measurement of surface acoustic wave velocity on single crystals using an all-optical adaptive scanning acoustic microscope
Authors: Hong Y. , Sharples S. D. , Clark M. , Somekh M. G.
Published: October 2003

An experimental method has been developed to measure the phase velocity of laser-generated and detected surface acoustic waves. An optical grating produced by a spatial light modulator was imaged onto the sample surface to generate the ultrasound whose frequency and wave front were controlled electrically by tailoring the grating. When the grating period matched the surface acoustic wavelength, strong excition of the surface wave was observed. Thus, the wavelength and, thereby, the phase velocity were determined. We present results with this method that allow the phase velocity and the angular dispersion of the generalized surface wave as well as the pseudosurface wave on the (100) nickel and (111) silicon single crystals to be measured, with the precision of approximately 0.2%. Those factors affecting the measurement precision are discussed.
Nanowatt chemical vapor detection with a self-sensing, piezoelectric microcantilever array
Authors: Adams J. D. , Parrott G. , Bauer C. , Sant T. , Manning L. , Jones M. , Rogers B. , McCorkle D. , Ferrell T. L.
Published: October 2003

The portability, compactness, price, and deployment of sensing systems are determined in large part by the power consumption and simplicity of the sensing platform used. We demonstrate a microcantilever chemical detection platform based on an array of piezoelectric microcantilevers. The sensor-element array power consumption, including actuation, is measured in nanowatts, with impedance of the order of megohms. This is four to five orders of magnitude lower power dissipation than current cantilever chemical detection platforms using optical or piezoresistive detection. The sensor is further characterized in the picowatt regime. The platform comprises three cantilevers wired in series, where variations in the resonant frequency and quality factor of selectively coated cantilevers, during successive impedance measurements, enable detection of ethanol vapor.
Multiband subwavelength magnetic reflectors based on fractals
Authors: Zhou Lei , Wen Weijia , Chan C. T. , Sheng Ping
Published: October 2003

We use theory and experiment to demonstrate that a composite material, consisting of a metallic planar fractal and a metal sheet separated by a thin dielectric layer, can reflect electromagnetic wave in-phase at a series of frequencies, with some of the corresponding wavelengths much longer than the reflector’s own size. We show that the physics is governed by a series of intrinsic magnetic resonances and can be well described by an effective-media of frequency-dependent permeability.
Electrodeposition of (001) oriented CoPt L10 columns into anodic alumina films
Authors: Yasui N. , Imada A. , Den T.
Published: October 2003

Anodic alumina films are known to have perpendicular holes normal to the film surface. This character is favorable to perpendicular magnetic recording and patterned media. L10-ordered CoPt columns are filled into anodic alumina nanoholes by an electrodeposition method and a subsequent thermal annealing process. Two kinds of metal (W and Pt) were used as underlayers at the bottom of nanoholes, which acts as electrode layer for electrodeposition. We show that while the embedded L10-ordered CoPt columns have random c-axis orientations for W underlayer samples, the c-axis orientation can be controlled by using the underlayer with Pt(001) surface. This orientation controlled sample has a perpendicular anisotropy with Hc=7.4 kOe, and Mr/Ms=0.96. This approach has the potential to become one of the important methods for the fabrication of recording media with ultrahigh areal density.
Highly directive radiation from sources embedded inside photonic crystals
Authors: Bulu Irfan , Caglayan Humeyra , Ozbay Ekmel
Published: October 2003

In this work, we have experimentally and theoretically studied the angular distribution of power emitted from a radiation source embedded inside a photonic crystal. Our results show that it is possible to obtain highly directive radiation sources operating at the band edge of the photonic crystal. Half power beam widths as small as 6° have been obtained. Our results also show that the angular distribution of power strongly depends on the frequency and on the size of the photonic crystal.
Steroid hormones augment nitric oxide synthase activity and expression in rat uterus
Authors: Ogando D. , Farina M. , Ribeiro M. L. , Perez Martinez S. , Cella M. , Rettori V. , Franchi A.
Published: October 2003

Nitric oxide (NO) is synthesized in a variety of tissues, including rat uterus, from L-arginine by NO synthase (NOS), of which there are three isoforms, namely neuronal, endothelial and inducible NOS (nNOS, eNOS and iNOS, respectively). Nitric oxide is an important regulator of the biology and physiology of the organs of the reproductive system, including the uterus. Some studies have shown increased variation in NO production and NOS expression during the oestrous cycle. However, the factors that regulate NO production in the uterus remain unclear. Therefore, in the present study, we investigated the effect of sex steroids on NOS expression and activity in the ovariectomized rat uterus. Ovariectomized rats received progesterone (4 mg per rat) or 17β-oestradiol (1 μg per rat). All rats were killed 18 h after treatment. Both progesterone and oestradiol were able to augment NOS activity. The effect of oestradiol was abolished by pre-incubation with 500 μM aminoguanidine, an iNOS inhibitor, or by coadministration of oestradiol with 3 mg kg−1 dexamethasone, but the effect of progesterone was not affected by these treatments. Uterine nNOS, eNOS and iNOS protein levels were assessed using Western blots. Ovariectomized rat uteri expressed iNOS and eNOS. Progesterone increased the expression of eNOS and iNOS, whereas oestradiol increased iNOS expression only. These results suggest that oestradiol and progesterone are involved in the regulation of NOS expression and activity during pregnancy and implantation in the rat.
Anatomy and chromosomes of two intersexual dasyurid marsupials
Authors: Woolley P. A. , Guedelha N. , Graves J. A. M.
Published: October 2003

The intersexual phenotypes of marsupials with XXY and XO chromosome constitutions imply that not all sexual dimorphisms are under the control of testicular hormones and, ultimately, the SRY gene on the Y chromosome. It has been hypothesised that there is a gene on the X chromosome that determines whether either a scrotum will form (one copy of the gene) or a pouch with teats (two copies of the gene). Here, we describe the anatomy and chromosomes of two intersexual dasyurid marsupials. One, a Dasyuroides byrnei, had a pouch, but the reproductive tract was essentially male. The other, a Sminthopsis douglasi, had a hemipouch and a hemiscrotum and the reproductive tract was essentially female. The S. douglasi was a mosaic for cells with an apparently normal 2n = 14, XX female karyotype and cells with 2n = 14 plus (usually) two dot-like supernumerary elements 2n = 14, XX + 2B. The D. byrnei cells examined also had a 2n = 14, XX + 2B karyotype. In fibroblasts from the male and female sides of the S. douglasi, it was possible to assign the 2n = 14, XX karyotype to the male side and the 2n = 14, XX + 2B to the female side.
Obesity among children attending elementary public schools in São Paulo, Brazil: a case–control study
Authors: da Costa Ribeiro Isabela , Taddei José Augusto AC , Colugnatti Fernando
Published: October 2003

Objective:

To describe obesity among students of public schools in São Paulo and to identify risk factors for this nutritional and physical activity disorder.

Design:

Case– control study of obese and non-obese schoolchildren to study risk factors for obesity.

Setting:

Anthropometric survey including 2519 children attending eight elementary public schools in Sã o Paulo, Brazil.

Subjects:

Schoolchildren aged 7–10 years, of whom 223 were obese (cases; weight-for-height greater than or equal to two standard deviations(≥2SD) above the median of the National Center for Health Statistics (NCHS) reference population) and 223 were eutrophic (controls; weight-for-height ±1SD from NCHS median).

Measurements:

Parents or guardians of the 446 cases and controls were interviewed about the children's eating behaviours and habits.

Results:

The prevalence of obesity (weight-for-height ≥2SD) in the surveyed population was 10.5%. A logistic regression model fitted to the case–control dataset showed that obesity was positively associated with the following factors: birth weight ≥3500 g (odds ratio (OR) 1.83, 95% confidence interval (CI) 1.21–2.78), child's appetite at meals (OR 3.81, 95% CI 2.49–5.83), watching television for 4h per day or longer (OR 2.07, 95% CI 1.32–3.24), mother's schooling>4 years (OR 1.85, 95% CI 1.25–2.75) and parents' body mass index ≥ 30 kgm−2(OR 2.50, 95% CI 1.43–4.37).

Conclusion:

The explanatory multivariate model points to preventive measures that would encourage knowledge of the children and their guardians in relation to a balanced diet and a less sedentary lifestyle, such as reducing television viewing. Schoolchildren with a birth weight of 3500g or more or whose parents are obese should receive special attention in the prevention of obesity.
The importance of composite foods for estimates of vegetable and fruit intakes
Authors: O'Brien MM , Kiely M , Galvin M , Flynn A
Published: October 2003

Objective:

To evaluate the contribution of composite foods to vegetable and fruit intakes in Irish adults and to compliance with dietary guidelines for vegetable and fruit intake.

Design:

Data were analysed from the North/South Ireland Food Consumption Survey of 18–64-year-old adults (n= 1379; 662 men, 717 women), which used a 7-day food diary to estimate food intake.

Results:

The mean intake of vegetables (excluding potatoes) was 140g day−1(men 149g day−1; women 132g day−1), of fruit was 136 g day−1(men 133g day−1; women 140 g day−1) and of potatoes was 227 g day−1(men 296g day−1; women 163 g day−1). The mean daily intakes of vegetables, fruit and potatoes from composite foods were 37 g (26%), 6 g (5%) and 17 g (7%), respectively. The mean intake of vegetables from composite foods was unrelated to age or gender, but increased with increasing social class and level of education attained. The proportions of men and women meeting the recommendation for ≥400g day−1(5 servings of 80 g per day) of vegetables and fruit were 21% (15% excluding composite foods) and 19% (12% excluding composite foods), respectively. Compliance with the dietary recommendation decreased with decreasing levels of educational attainment and social class.

Conclusion:

Intakes of vegetables and fruit are low compared with current dietary recommendations, particularly in those of lower levels of educational attainment and social class. Composite foods are an important source of vegetables (less importantly of fruit) and should be included when estimating vegetable intakes. Failure to do so may result in bias in estimates of intake and of compliance with dietary guidelines for population groups, as well as misclassification of individuals by level of intake.
Two approaches to derive a proposal for added sugars intake for German children and adolescents
Authors: Alexy Ute , Kersting Mathilde , Schultze-Pawlitschko Verena
Published: October 2003

Objective:

Intake of sugars is restricted in most international food guides. However, in recent recommendations quantified limits of added sugars intake have not been given, although deemed necessary by those who criticised the recommendations.

Design:

Two approaches to derive a scientifically based quantified limit of added sugars intake for German children and adolescents are suggested. For the first dietary survey approach, 5120 three-day weighed dietary records from the Dortmund Nutritional and Anthropometric Longitudinally Designed (DONALD) Study were used. Added sugars intakes in records of high vs. low dietary quality, measured by a nutrient intake score, were compared. For the second approach, a total dietary concept for German children and adolescents developed and evaluated by the Research Institute of Child Nutrition – the Optimised Mixed Diet – was used.

Results:

Whereas in the latter dietary concept an added sugars intake of about 6% of energy intake is tolerated, the dietary survey approach resulted in only small differences between high and low dietary quality, with a median added sugars intake of 12% of energy in records with high dietary quality.

Conclusions:

A reasonable dietary quality is possible within higher ranges of added sugars intake than derived from the dietary concept approach. Therefore we suggest a range of intake of added sugars for German children and adolescents, from 6% to 12% of energy.
Relationship of tobacco smoking with serum vitamin B12, folic acid and haematological indices in healthy adults
Authors: Tungtrongchitr Rungsunn , Pongpaew Praneet , Soonthornruengyot Malida , Viroonudomphol Duangkamol , Vudhivai Niyomsri , Tungtrongchitr Anchalee , Phonrat Benjaluck , Pooudong Somchai , Schelp Frank Peter
Published: October 2003

Objectives:

To investigate the effects of tobacco smoking on serum vitamin B12, folic acid and haematological parameters in healthy Thai smokers and non-smokers.

Design:

Cross-sectional study of smokers and non-smokers in a military unit in Bangkok, Thailand.

Setting:

A military unit in Thailand.

Subjects:

One hundred and twenty-three male smokers from a military unit in Bangkok, who participated voluntarily in the study, were investigated. Sixty-six male non-smokers from the same unit were selected as controls. Fasting blood samples were collected for investigation of vitamin B12, folic acid and haematological variables.

Results:

The serum folic acid concentration of smokers was lower than that of non-smokers, but was not statistically significantly different. Haemoglobin was lower in smokers than in non-smokers; 16.3% of smokers were anaemic compared with only 3.0% of non-smokers. Anaemia was not related to folate deficiency. The white blood cell count was found to be higher in smokers than in non-smokers.

Conclusion:

The results of this study suggest that there were low serum folic acid concentrations in smokers compared with non-smokers, which might contribute to the development of vascular and cardiovascular diseases. The higher white blood cell count might be indicative alterations in the immune functions of smokers.
Association of education with dietary intake among young adults in the bi-ethnic Coronary Artery Risk Development in Young Adults (CARDIA) cohort
Authors: Archer SL , Hilner JE , Dyer AR , Greenlund KJ , Colangelo LA , Kiefe CI , Liu K
Published: October 2003

Objective:

To examine associations of changes in dietary intake with education in young black and white men and women.

Design:

The Coronary Artery Risk Development in Young Adults (CARDIA) study, a multi-centre population-based prospective study. Dietary intake data at baseline and year 7 were obtained from an extensive nutritionist-administered diet history questionnaire with 700 items developed for CARDIA.

Setting:

Participants were recruited in 1985–1986 from four sites: Birmingham, Alabama; Chicago, Illinois; Minneapolis, Minnesota; and Oakland, California.

Subjects:

Participants were from a general community sample of 703 black men (BM), 1006 black women (BW), 963 white men (WM) and 1054 white women (WW) who were aged 18–30 years at baseline. Analyses here include data for baseline (1985–1986) and year 7 (1992–1993).

Results:

Most changes in dietary intake were observed among those with high education (≥ 12 years) at both examinations. There was a significant decrease in intake of energy from saturated fat and cholesterol and a significant increase in energy from starch for each race-gender group (P< 0.001). Regardless of education, taste was considered an important influence on food choice.

Conclusion:

The inverse relationship of education with changes in saturated fat and cholesterol intakes suggests that national public health campaigns may have a greater impact among those with more education.
CD151 regulates epithelial cell–cell adhesion through PKC- and Cdc42-dependent actin cytoskeletal reorganization
Authors: Shigeta Masaki , Sanzen Noriko , Ozawa Masayuki , Gu Jianguo , Hasegawa Hitoshi , Sekiguchi Kiyotoshi
Published: October 2003

CD151, a member of the tetraspanin family proteins, tightly associates with integrin α3β1 and localizes at basolateral surfaces of epithelial cells. We found that overexpression of CD151 in A431 cells accelerated intercellular adhesion, whereas treatment of cells with anti-CD151 mAb perturbed the integrity of cortical actin filaments and cell polarity. E-Cadherin puncta formation, indicative of filopodia-based adhesion zipper formation, as well as E-cadherin anchorage to detergent-insoluble cytoskeletal matrix, was enhanced in CD151-overexpressing cells. Levels of GTP-bound Cdc42 and Rac were also elevated in CD151-overexpressing cells, suggesting the role of CD151 in E-cadherin–mediated cell–cell adhesion as a modulator of actin cytoskeletal reorganization. Consistent with this possibility, engagement of CD151 by the substrate-adsorbed anti-CD151 mAb induced prominent Cdc42-dependent filopodial extension, which along with E-cadherin puncta formation, was strongly inhibited by calphostin C, a protein kinase C (PKC) inhibitor. Together, these results indicate that CD151 is involved in epithelial cell–cell adhesion as a modulator of PKC- and Cdc42-dependent actin cytoskeletal reorganization.
APP processing is regulated by cytoplasmic phosphorylation
Authors: Lee Ming-Sum , Kao Shih-Chu , Lemere Cynthia A. , Xia Weiming , Tseng Huang-Chun , Zhou Ying , Neve Rachael , Ahlijanian Michael K. , Tsai Li-Huei
Published: October 2003

Amyloid-β peptide (Aβ) aggregate in senile plaque is a key characteristic of Alzheimer's disease (AD). Here, we show that phosphorylation of amyloid precursor protein (APP) on threonine 668 (P-APP) may play a role in APP metabolism. In AD brains, P-APP accumulates in large vesicular structures in afflicted hippocampal pyramidal neurons that costain with antibodies against endosome markers and the β-secretase, BACE1. Western blot analysis reveals increased levels of T668-phosphorylated APP COOH-terminal fragments in hippocampal lysates from many AD but not control subjects. Importantly, P-APP cofractionates with endosome markers and BACE1 in an iodixanol gradient and displays extensive colocalization with BACE1 in rat primary cortical neurons. Furthermore, APP COOH-terminal fragments generated by BACE1 are preferentially phosphorylated on T668 verses those produced by α-secretase. The production of Aβ is significantly reduced when phosphorylation of T668 is either abolished by mutation or inhibited by T668 kinase inhibitors. Together, these results suggest that T668 phosphorylation may facilitate the BACE1 cleavage of APP to increase Aβ generation.
Identification of a novel antiapoptotic protein that antagonizes ASK1 and CAD activities
Authors: Cho Ssang-Goo , Kim Jin Woo , Lee Yong Hee , Hwang Hyun Sub , Kim Mi-Sung , Ryoo Kanghyun , Kim Myung Jin , Noh Kyung Tae , Kim Eun Kyung , Cho Jun-Ho , Yoon Kyoung Wan , Cho Eun-Gyung , Park Hee-Sae , Chi Sung Wook , Lee Min-Jae , Kang Sang Sun , Ichijo Hidenori , Choi Eui-Ju
Published: October 2003

Diverse stimuli initiate the activation of apoptotic signaling pathways that often causes nuclear DNA fragmentation. Here, we report a new antiapoptotic protein, a caspase-activated DNase (CAD) inhibitor that interacts with ASK1 (CIIA). CIIA, by binding to apoptosis signal-regulating kinase 1 (ASK1), inhibits oligomerization-induced ASK1 activation. CIIA also associates with CAD and inhibits the nuclease activity of CAD without affecting caspase-3–mediated ICAD cleavage. Overexpressed CIIA reduces H2O2- and tumor necrosis factor-α–induced apoptosis. CIIA antisense oligonucleotides, which abolish expression of endogenous CIIA in murine L929 cells, block the inhibitory effect of CIIA on ASK1 activation, deoxyribonucleic acid fragmentation, and apoptosis. These findings suggest that CIIA is an endogenous antagonist of both ASK1- and CAD-mediated signaling.
How VASP enhances actin-based motility
Authors: Samarin Stanislav , Romero Stéphane , Kocks Christine , Didry Dominique , Pantaloni Dominique , Carlier Marie-France
Published: October 2003

The function of vasodilator-stimulated phosphoprotein (VASP) in motility is analyzed using a biomimetic motility assay in which ActA-coated microspheres propel themselves in a medium containing actin, the Arp2/3 complex, and three regulatory proteins in the absence or presence of VASP. Propulsion is linked to cycles of filament barbed end attachment-branching-detachment-growth in which the ActA-activated Arp2/3 complex incorporates at the junctions of branched filaments. VASP increases the velocity of beads. VASP increases branch spacing of filaments in the actin tail, as it does in lamellipodia in living cells. The effect of VASP on branch spacing of Arp2/3-induced branched actin arrays is opposed to the effect of capping proteins. However, VASP does not compete with capping proteins for binding barbed ends of actin filaments. VASP enhances branched actin polymerization only when ActA is immobilized on beads or on Listeria. VASP increases the rate of dissociation of the branch junction from immobilized ActA, which is the rate-limiting step in the catalytic cycle of site-directed filament branching.
Skeletal myosin heavy chain function in cultured lung myofibroblasts
Authors: Rice Nancy A. , Leinwand Leslie A.
Published: October 2003

Myofibroblasts are unique contractile cells with both muscle and nonmuscle properties. Typically myofibroblasts are identified by the expression of α smooth muscle actin (ASMA); however some myofibroblasts also express sarcomeric proteins. In this study, we show that pulmonary myofibroblasts express three of the eight known sarcomeric myosin heavy chains (MyHCs) (IIa, IId, and embryonic) and that skeletal muscle myosin enzymatic activity is required for pulmonary myofibroblast contractility. Furthermore, inhibition of skeletal myosin activity and myofibroblast contraction results in a decrease in both ASMA and skeletal MyHC promoter activity and ASMA protein expression, suggesting a potential coupling of skeletal myosin activity and ASMA expression in myofibroblast differentiation. To understand the molecular mechanisms whereby skeletal muscle genes are regulated in myofibroblasts, we have found that members of the myogenic regulatory factor family of transcription factors and Ca2+-regulated pathways are involved in skeletal MyHC promoter activity. Interestingly, the regulation of skeletal myosin expression in myofibroblasts is distinct from that observed in muscle cells and suggests that cell context is important in its control.
APP-BP1 mediates APP-induced apoptosis and DNA synthesis and is increased in Alzheimer's disease brain
Authors: Chen Yuzhi , Liu Wenyun , McPhie Donna L. , Hassinger Linda , Neve Rachael L.
Published: October 2003

APP-BP1, first identified as an amyloid precursor protein (APP) binding protein, is the regulatory subunit of the activating enzyme for the small ubiquitin-like protein NEDD8. We have shown that APP-BP1 drives the S- to M-phase transition in dividing cells, and causes apoptosis in neurons (Chen, Y., D.L. McPhie, J. Hirschberg, and R.L. Neve. 2000. J. Biol. Chem. 275:8929–8935). We now demonstrate that APP-BP1 binds to the COOH-terminal 31 amino acids of APP (C31) and colocalizes with APP in a lipid-enriched fraction called lipid rafts. We show that coexpression of a peptide representing the domain of APP-BP1 that binds to APP, abolishes the ability of overexpressed APP or the V642I mutant of APP to cause neuronal apoptosis and DNA synthesis. A dominant negative mutant of the NEDD8 conjugating enzyme hUbc12, which participates in the ubiquitin-like pathway initiated by APP-BP1, blocks neuronal apoptosis caused by APP, APP(V642I), C31, or overexpression of APP-BP1. Neurons overexpressing APP or APP(V642I) show increased APP-BP1 protein levels in lipid rafts. A similar increase in APP-BP1 in lipid rafts is observed in the Alzheimer's disease brain hippocampus, but not in less-affected areas of Alzheimer's disease brain. This translocation of APP-BP1 to lipid rafts is accompanied by a change in the subcellular localization of the ubiquitin-like protein NEDD8, which is activated by APP-BP1.