bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface energy maps of nanostructures: Atomic force microscopy and numerical simulation study
Authors: Mechler Ádám , Kokavecz Janos , Heszler Peter , Lal Ratnesh
Published: May 2003

Topography and surface energy distribution of etched graphite were examined by atomic force microscopy (AFM). AFM images show atomic monolayer deep circular holes (etch pits). At certain imaging conditions, these etch pits appear surrounded by rims. Numerical simulation of AFM images reveals that the rims are formed due to an increased surface energy zone at the edges. The vertical dimension of the rim correlates with the magnitude of the local surface energy. Such a correlation between the imaging features and the surface energy profiles can be used to demarcate local chemical constituents in a composite nanomaterial.
Metalorganic chemical vapor deposition of highly conductive Al0.65Ga0.35N films
Authors: Cantu P. , Keller S. , Mishra U. K. , DenBaars S. P.
Published: May 2003

Highly conductive Al0.65Ga0.35N films were fabricated using indium–silicon codoping and a low growth temperature of 920 °C in the metalorganic chemical vapor deposition process. The Al0.65Ga0.35N:(Si,In) layers exhibited an n-type carrier density as high as 2.5×1019 cm−3 with an electron mobility of 22 cm2/V s, corresponding to a resistivity of 1.1×10−4 Ω cm. Significantly higher resistivity values were measured for AlxGa1−xN:Si doped films with x⩾0.49 deposited at 1150 °C without indium, e.g., the Al0.62Ga0.38N:Si samples exhibited a maximum carrier concentration of 1.3×1017 cm−3 and a resistivity of 6.2×10−2 Ω cm. The electrical properties of the films are discussed in relation to the chemical concentrations of silicon and residual impurities in the films.
Fabrication of a vector Hall sensor for magnetic microscopy
Authors: Gregušová D. , Cambel V. , Fedor J. , Kúdela R. , Šoltýs J. , Lalinský T. , Kostič I. , Bending S. J.
Published: May 2003

We have developed a micromachined Hall sensor for scanning the entire magnetic field vector whose active dimensions are an order of magnitude smaller (∼5 μm) than the smallest existing vector field sensor. It is realized by patterning three Hall probes on the tilted faces of epitaxy-overgrown GaAs-based pyramidal-shaped mesa structures. Data from these “tilted” Hall probes are used to reconstruct the full magnetic field vector.
Photoinduced phase transition of metallic SmS thin films by a femtosecond laser
Authors: Kitagawa R. , Takebe H. , Morinaga K.
Published: May 2003

Metallic SmS thin films with 100–2000 nm in thickness were prepared by rf magnetron sputtering. The metallic- to semiconductor-phase transition was induced by a regeneratively amplified mode-locked Ti:sapphire laser. The shifts of the (200) peak due to the phase transition were observed by grazing incidence x-ray diffraction (GIXD) analysis. This phase transition was accompanied by the significant reflectance change of the thin films up to 45% in the near-infrared region. The depth of the phase transition layer from the surface of the film irradiated by a femtosecond laser pulse was estimated ∼200 nm from the depth profile of GIXD.
Tuning the structural and optical properties of 1.3-μm InAs/GaAs quantum dots by a combined InAlAs and GaAs strained buffer layer
Authors: Liu H. Y. , Hopkinson M.
Published: May 2003

A combined InAlAs and GaAs strained buffer layer was presented to tailor the structural and optical properties of 1.3-μm InAs/GaAs quantum dots. This growth technique exhibits an increment of InAs quantum-dot density from 1.6×1010 to 2.8×1010 cm−2 and an improvement of energy separation between the quantum-dot ground and first-excited states from 84 to 93 meV upon adjusting the thickness of GaAs in InAlAs–GaAs buffer layer. We also investigate the effect of an InAlAs layer surrounding InAs quantum dots on photoluminescence intensity with increasing the thickness of InAlAs layer in a 6-nm InAlAs–InGaAs composite cap layer, and no negative effect has been observed.
Enhanced single-photon emission from a quantum dot in a micropost microcavity
Authors: Vučković Jelena , Fattal David , Santori Charles , Solomon Glenn S. , Yamamoto Yoshihisa
Published: May 2003

We demonstrate a single-photon source based on a quantum dot in a micropost microcavity that exhibits a large Purcell factor together with a small multiphoton probability. For a quantum dot on resonance with the cavity, the spontaneous emission rate is increased by a factor of 5, while the probability to emit two or more photons in the same pulse is reduced to 2% compared to a Poisson-distributed source of the same intensity. In addition to the small multiphoton probability, such a strong Purcell effect is important in a single-photon source for improving the photon outcoupling efficiency and the single-photon generation rate, and for bringing the emitted photon pulses closer to the Fourier transform limit.
High-intensity regime of x-ray generation from relativistic laser plasmas
Authors: Pretzler Georg , Brandl Felix , Stein Jürgen , Fill Ernst , Kuba Jaroslav
Published: May 2003

We report experiments exhibiting specific features in generating hard x rays with femtosecond laser plasmas as relativistic intensities are approached. Copper foils are irradiated with 1-J/130-fs Ti:sapphire laser pulses, and the x rays are detected with spatial resolution. The results demonstrate a dramatic reduction in the x-ray-emitting spot size at intensities around 1019 W/cm2, and a corresponding increase in the x-ray flux density. These findings are explained in terms of forward acceleration of electrons due to relativistic effects.
A 2.78-μm laser diode based on hybrid AlGaAsSb/InAs/CdMgSe double heterostructure grown by molecular-beam epitaxy
Authors: Ivanov S. V. , Kaygorodov V. A. , Sorokin S. V. , Meltser B. Ya. , Solov’ev V. A. , Terent’ev Ya. V. , Lyublinskaya O. G. , Moiseev K. D. , Grebenshchikova E. A. , Mikhailova M. P. , Toropov A. A. , Yakovlev Yu. P. , Kop’ev P. S. , Alferov Zh. I.
Published: May 2003

A mid-IR laser based on a hybrid pseudomorphic AlGaAsSb/InAs/CdMgSe heterostructure with a III–V/II–VI heterovalent interface at the 0.6-μm-InAs active region has been fabricated by molecular-beam epitaxy on p+-InAs substrate. It provides ∼1.5-eV asymmetric barriers for both electrons and holes in InAs, inhibiting carrier leakage from the active region. Despite a nonoptimal defect density at the CdMgSe/InAs interface (106–107 cm−2), the structure demonstrates lasing at ∼2.78 μm (up to 100 K) under pulse injection pumping with the threshold current density of 3–4 kA/cm2. The proposed design is promising for high-power mid-IR lasers operating at room temperature.
A new method for wave packet dynamics: Derivative propagation along quantum trajectories
Authors: Trahan Corey J. , Hughes Keith , Wyatt Robert E.
Published: May 2003

A new method is proposed for computing the time evolution of quantum mechanical wave packets. Equations of motion for the real-valued functions C and S in the complex action S=C(r,t)+iS(r,t)/ℏ, with ψ(r,t)=exp(S), involve gradients and curvatures of C and S. In previous implementations of the hydrodynamic formulation, various time-consuming fitting techniques of limited accuracy were used to evaluate these derivatives around each fluid element in an evolving ensemble. In this study, equations of motion are developed for the spatial derivatives themselves and a small set of these are integrated along quantum trajectories concurrently with the equations for C and S. Significantly, quantum effects can be included at various orders of approximation, no spatial fitting is involved, there are no basis set expansions, and single quantum trajectories (rather than correlated ensembles) may be propagated, one at a time. Excellent results are obtained when the derivative propagation method is applied to anharmonic potentials involving barrier transmission.
The energy barriers in antiferromagnetically coupled media
Authors: Margulies D. T. , Berger A. , Moser A. , Schabes M. E. , Fullerton Eric E.
Published: May 2003

We study the physics of the energy barriers for magnetization reversal in antiferromagnetically coupled (AFC) media by means of temperature dependent magnetometry as well as modeling. We find that the energy barrier of the lower layer is fairly low, and mainly given by its anisotropy–volume product (KV). This means the lower layer magnetization is actually in thermal equilibrium, but the presence of the interlayer coupling makes the state with AF alignment of both layers thermodynamically so much more probable, that AFC media are thermally stable overall. The model further predicts that for typical values of the exchange coupling constant, the energy barrier of the composite system at zero field is essentially equal to the upper layer KV with the additional energy from the interlayer coupling being only a small perturbation.
Highly uniform (Cd,Mn,Zn)Se/(Zn,Mn)Se quantum dot array formation by means of thermal treatments
Authors: Topuria T. , Möck P. , Lei Y. , Browning N. D.
Published: May 2003

Thermal treatments of (Cd,Mn,Zn)Se/(Zn,Mn)Se multiquantum well heterostructures inside the electron microscope resulted in the formation of three-dimensional CdSe based quantum dots (QDs). The array uniformity of the QDs was investigated by means of the Z-contrast imaging technique in the scanning transmission electron microscope and found to be superior to that of Stranski–Krastanow grown CdSe based QDs. The outcome of the heating experiment demonstrated that thermal treatments might be considered as one of the ways in obtaining highly ordered QD arrays. Possible mechanisms of the QD formation by means of thermal treatments are also discussed.
Increasing medium-range order in amorphous silicon with low-energy ion bombardment
Authors: Gerbi J. E. , Voyles P. M. , Treacy M. M. J. , Gibson J. M. , Abelson J. R.
Published: May 2003

We have observed the existence of medium–range order in amorphous silicon with the fluctuation electron microscopy technique. We hypothesize that this structure is produced during the highly nonequilibrium deposition process, during which nuclei are formed and subsequently buried. We test this hypothesis by altering the deposition kinetics during magnetron sputter deposition by bombarding the growth surface with a variable flux of low-energy (20 eV) Ar+ ions. We observe that medium–range order increases monotonically as the ion/neutral flux ratio increases. We suggest that this low-energy bombardment increases adspecie surface mobility or modifies local structural rearrangements, resulting in enhanced medium–range order via increases in the size, volume fraction, and/or internal order of the nuclei.
Detwinning YBa2Cu3O7−δ thin films
Authors: Nam J. , Hughes R. A. , Dabkowski A. , Preston J. S.
Published: May 2003

Single crystals of YBa2Cu3O7-δ (YBCO) have been detwinned under the simultaneous application of heat and uniaxial stress. This approach, however, has proved futile in thin films as they become heavily twinned due to strain from the underlying substrate as well as the orthorhombic unit cell. This lack of control over twinning has made it difficult to determine the role that twins play in determining the transport properties of films. Here, we present a technique for detwinning YBCO thin films. The detwinning in YBCO thin film is achieved by suspending a portion of the YBCO film above the underlying substrate. The suspended material is no longer influenced by the confining effects of the substrate and this allows it to detwin under the application of a uniaxial stress brought about by an anneal. With this technique, we are able to produce high-quality detwinned regions that will help aid the understanding of transport mechanisms in YBCO.
Ultrafast carrier and plasmon-phonon dynamics in ion-irradiated n-GaAs
Authors: Hase Muneaki , Ishioka Kunie , Kitajima Masahiro , Ushida Kiminori
Published: May 2003

Ultrafast dynamics of plasmon-phonon coupled modes and photoexcited carriers in He ion irradiated n-GaAs has been investigated with a femtosecond pump-probe technique. The frequencies of the coupled modes shift as the ion dose increases, and after 1.9×1013 He+/cm2 irradiation the coherent oscillation of the coupled modes disappear. The relaxation time of the photoexcited carriers decreases with increasing ion dose, which is explained quantitatively by trapping of carriers via the deep levels related to single vacancies. The dose dependence of the dephasing time of the coupled modes and the relaxation time of the photoexcited carriers reveal that the trapping of the majority carriers dominates the disappearance as well as the frequency shift of the coupled mode oscillation.
Comparison of radiative and structural properties of 1.3 μm InxGa(1−x)As quantum-dot laser structures grown by metalorganic chemical vapor deposition and molecular-beam epitaxy: Effect on the lasing properties
Authors: Passaseo A. , De Vittorio M. , Todaro M. T. , Tarantini I. , De Giorgi M. , Cingolani R. , Taurino A. , Catalano M. , Fiore A. , Markus A. , Chen J. X. , Paranthoen C. , Oesterle U. , Ilegems M.
Published: May 2003

We have studied the radiative and structural properties of identical InxGa(1−x)As quantum dot laser structures grown by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). Despite the comparable emission properties found in the two devices by photoluminescence, electroluminescence, and photocurrent spectroscopy, efficient lasing from the ground state is achieved only in the MBE sample, whereas excited state lasing is obtained in the MOCVD device. Such a difference is ascribed to the existence of the internal dipole field in the MOCVD structure, induced by the strong faceting of the dots, as observed by high-resolution transmission electron microscopy.
Fabrication and transport characterization of a primary thermometer formed by Coulomb islands in a suspended silicon nanowire
Authors: Tilke Armin T. , Pescini Laura , Lorenz Heribert , Blick Robert H.
Published: May 2003

We realized bolometers in suspended highly n-doped silicon nanowires with lateral dimensions down to about 40 nm. Random dopant fluctuations in the suspended wires lead to the formation of multiple tunnel junctions, utilized for Coulomb blockade thermometry. In the low bias regime, we observe relaxation via discrete acoustic phonon modes to give a lower bound for the sensitivity.
Correlation between fractal dimension and reversal behavior of magnetic domain in Co/Pd nanomultilayers
Authors: Kim Dong-Hyun , Cho Yoon-Chul , Choe Sug-Bong , Shin Sung-Chul
Published: May 2003

We report the experimental finding that there is a close correlation between fractal geometry and reversal mechanism of magnetic domain in Co/Pd nanomultilayers. We have measured the fractal dimension Df of magnetic domain as well as the wall-motion speed V, the nucleation rate R, and the reversal ratio V/R in Co/Pd nanomultilayer films during magnetization reversal via time-resolved direct domain observation. Interestingly enough, Df is inversely related to the reversal ratio V/R, which could be quantitatively explained using a micromagnetic simulation based on thermally activated relaxation model. We find that the fractal dimension is a crucial parameter to characterize magnetization reversal behavior as well as jaggedness of domain geometry.
Dynamically tuning properties of epitaxial colossal magnetoresistance thin films
Authors: Dale Darren , Fleet Aaron , Brock J. D. , Suzuki Y.
Published: May 2003

The strain state of epitaxial La0.5Sr0.5MnO3 thin films on BaTiO3 are dynamically tuned by temperature and substrate bias. The resistivity of the La0.5Sr0.5MnO3 thin films is particularly sensitive to changes in structure. Fractional changes in magnetization and resistivity as a function of temperature reveal a direct correlation with fractional changes in the structure, as measured by out-of-plane x-ray diffraction. Fractional changes in resistivity, as large as 30%, are observed for strain induced by the structural phase transitions of the BaTiO3 substrate, and a 12% change is induced by an inverse piezoelectric effect at room temperature.
Boron uphill diffusion during ultrashallow junction formation
Authors: Duffy R. , Venezia V. C. , Heringa A. , Hüsken T. W. T. , Hopstaken M. J. P. , Cowern N. E. B. , Griffin P. B. , Wang C. C.
Published: May 2003

The recently observed phenomenon of boron uphill diffusion during low-temperature annealing of ultrashallow ion-implanted junctions in silicon has been investigated. It is shown that the effect is enhanced by preamorphization, and that an increase in the depth of the preamorphized layer reduces uphill diffusion in the high-concentration portion of boron profile, while increasing transient enhanced diffusion in the tail. The data demonstrate that the magnitude of the uphill diffusion effect is determined by the proximity of boron and implant damage to the silicon surface.
Cathodoluminescence studies of the electron injection-induced effects in GaN
Authors: Chernyak Leonid , Burdett William , Klimov Mikhail , Osinsky Andrei
Published: May 2003

Local irradiation of p-type GaN with the electron beam of a scanning electron microscope resulted in up to a threefold decrease of the peak cathodoluminescence intensity at ∼379 nm, as was observed in the variable temperature measurements. The cathodoluminescence results are consistent with an increase of the minority carrier diffusion length in the material, as is evident from the electron-beam-induced current measurements. The activation energy for the electron injection effect, estimated from the temperature-dependent cathodoluminescence, is in agreement with the thermal ionization energy of the Mg-acceptor in GaN.
Interface structures in FePt/Fe3Pt hard-soft exchange-coupled magnetic nanocomposites
Authors: Li Jing , Wang Zhong Lin , Zeng Hao , Sun Shouheng , Ping Liu J.
Published: May 2003

Self-assembly of FePt and Fe3O4 nanoparticles of different sizes led to various FePt–Fe3O4 nanocomposites. Annealing the composite under reducing atmosphere at 650 and 700 °C induced magnetically hard FePt phase and magnetically soft Fe3Pt phase. The FePt and Fe3Pt phases were either linked by a common interface or coexisted within one grain as domains with sizes <10 nm. This ensures the effective exchange coupling of magnetically hard and soft phases. High-resolution transmission electron microscopy studies provide detailed structural characterization for the FePt based nanocomposites.
Magnetic domain structure in a ferromagnetic shape memory alloy Ni51Fe22Ga27 studied by electron holography and Lorentz microscopy
Authors: Murakami Y. , Shindo D. , Oikawa K. , Kainuma R. , Ishida K.
Published: May 2003

Behaviors of magnetic domains with cooling in a Ni51Fe22Ga27 ferromagnetic shape memory alloy were examined by electron holography and Lorentz microscopy. A peculiar meshy pattern was observed in the Lorentz microscope image of the parent phase, being concurrent with the anomaly in the thermomagnetization curve. The meshy pattern was found to stem from the heavily bent lines of magnetic flux. The dramatic change in the magnetic domains is presumably due to some intrinsic magnetic instability that is pronounced by cooling, rather than a phenomenon triggered by the lattice modulation as the precursor effect of martensitic transformations or formation of the intermediate phase as observed in other systems.
Spherical Nb single crystals containerlessly grown by electrostatic levitation
Authors: Sung Y. S. , Takeya H. , Hirata K. , Togano K.
Published: May 2003

Spherical Nb (Tm=2750 K) single crystals were grown via containerless electrostatic levitation (ESL). Samples became spherical at melting in levitation and undercooled typically 300–450 K prior to nucleation. As-processed samples were still spherical without any macroscopic shape change by solidification showing a uniform dendritic surface morphology. Crystallographic {111} planes exposed in equilateral triangular shapes on the surface by preferential macroetching and spotty back-reflection Laue patterns confirm the single crystal nature of the ESL-processed Nb samples. No hysteresis in magnetization between zero field and field cooling also implies a clean defect-free condition of the spherical Nb single crystals.
Fabrication of flexible field emitter arrays of carbon nanotubes using self-assembly monolayers
Authors: Lee Ok-Joo , Lee Kun-Hong
Published: May 2003

This letter reports on flexible field emitter arrays of single-walled carbon nanotubes (SWNTs) aligned on organic polymer substrates. An array of gold electrodes was patterned on the Ti-coated polymer substrate by sputtering gold through a shadow mask. A self-assembly monolayer of organic molecules was then formed on the gold electrodes using thiol chemistry. Cut SWNTs prepared by acidic treatment were attached to the end of the organic molecules. The field emission measurement showed that the turn-on field was 3.88 V/μm at the emission current density of 10 μA/cm2. The current density was 1.6 mA/cm2 at 6 V/μm. This room temperature process is suitable for the fabrication of flexible electronic devices with carbon nanotubes.
Nitrogen-doped gallium phosphide nanobelts
Authors: Seo Hee Won , Bae Seung Yong , Park Jeunghee , Yang Hyunik , Kang Myungil , Kim Sangsig , Park Ju Chul , Lee Soun Young
Published: May 2003

Nitrogen-doped gallium phosphide nanobelts were directly synthesized via a sublimation of ball-milled powders under ammonia flow. The average width of the nanobelts is 300 nm and the thickness is about 1/10 of the width. They consist of single-crystalline zinc blende structure crystal with the [111] direction parallel to the belt axis. Electron energy-loss spectroscopy reveals that the nitrogen doping occurs mainly in the surface region. Photoluminescence shows the typical isoelectronic bound exciton peaks in the range of 2.11–2.25 eV, suggesting a concentration of ∼1018 cm−3 nitrogen atoms.
Temperature-dependent emission intensity and energy shift in InGaN/GaN multiple-quantum-well light-emitting diodes
Authors: Cao X. A. , LeBoeuf S. F. , Rowland L. B. , Yan C. H. , Liu H.
Published: May 2003

Temperature-dependent electroluminescence (EL) of InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) has been investigated to illustrate the role of localization effects in carrier capture and recombination. The devices have identical structure but with varying indium content in the active region. A large redshift of the emission peak with decreasing temperature is observed in the UV and blue LEDs over the temperature range of 77–200 K, accompanying a pronounced decrease of EL intensity. This redshift reflects carrier relaxation into lower energy localized states and the change in carrier recombination dynamics at low temperatures. In contrast, the peak energy of the green LEDs exhibits a smaller temperature-induced shift, and the emission intensity increases monotonically with decreasing temperature down to 5 K. Based on a rate equation analysis, we find that the densities of the localized states in the green LEDs are more than two orders of magnitude higher than that in the UV LED.
Uniaxial magnetic anisotropy and magnetic switching in La0.67Sr0.33MnO3 thin films grown on vicinal SrTiO3(100)
Authors: Wang Zhi-Hong , Cristiani G. , Habermeier H.-U.
Published: May 2003

La 0.67 Sr 0.33 MnO 3 ultrathin films grown on vicinal SrTiO3(100) surface show an in-plane uniaxial magnetic anisotropy with easy axis along the substrate atomic steps generated by a 10° miscut off the (100) plane. Over a large angular range, the angular dependence of magnetic switching field is found to obey the 1/cos φ law, indicating that the magnetic reversal is completed by a 180° domain nucleation and sweeping along the easy axis. However, when the applied field is perpendicular to the hard axis (φ=90°), the magnetization reversal is found to be well described by the Stoner–Wohlfarth model, in which the magnetization coherently rotates from the easy axis to hard axis.
The fabrication of photonic band gap materials with a two-dimensional defect
Authors: Zhao Yuxia , Wostyn Kurt , de Schaetzen Gaetan , Clays Koen , Hellemans Louis , Persoons Andre , Szekeres Marta , Schoonheydt Robert A.
Published: May 2003

Colloidal crystals with three-dimensional periodicities in the refractive index have a photonic band gap (PBG) in which electromagnetic waves are forbidden. We present a method to fabricate stacked colloidal crystals containing a two-dimensional defect as a middle layer by combining vertical deposition method with the Langmuir–Blodgett (LB) technique. The defect layer introduces an impurity mode within the optical stop band, which is observed as a defect peak (pass band) in the optical density spectrum. The result shows that the combination of vertical deposition with LB technique provides a way for introducing defect modes in PBG materials.
Approach to optimize the pinning effect of a NiMn layer with reduced thickness under a much shortened annealing process
Authors: Dai B. , Cai J. W. , Lai W. Y. , Shen F. , Zhang Z. , Yu G. H.
Published: May 2003

We investigated the magnetic properties of sputtered Ni0.8Fe0.2/Ni1−xMnx (0.43⩽x⩽0.70) bilayers and found that an antiferromagnetic equiatomic NiMn layer could be formed through Mn diffusion with reduced thickness and a much shortened annealing time if the Ni1−xMnx layer is off-stoichiometric with suitable excess Mn. An overdose of Mn in a NiMn precursor layer was demonstrated to enhance the migration and the diffusion of Mn atoms, which seemed to promote the formation of antiferromagnetic NiMn of the θ phase, but in the mean time led to the deterioration of the adjacent ferromagnetic layer. We thus introduced the nano-oxide layer in the ferromagnetic layer near the interface of ferromagnetic and antiferromagnetic layers, which was proven to be very efficient to prevent Mn atoms from further intruding into the ferromagnetic layer even in the case that a large amount of Mn atoms were involved. As a result, a ferromagnetic layer pinned by a NiMn layer with excellent performance has been developed in a much simplified process.
Effects of discrete energy levels on single-electron tunneling in coupled metal particles
Authors: Wang Bing , Wang Kedong , Lu Wei , Wang Haiqian , Li Zhenyu , Yang Jinlong , Hou J. G.
Published: May 2003

We report the measurements of single-electron tunneling (SET) spectra for individual and coupled ultrasmall palladium nanoparticles using scanning tunneling microscopy. Extra fine structures, in addition to the Coulomb blockade and staircases in current–voltage curves, was observed for individual Pd particles of about 2 nm in diameter, which is attributed to the interplay of the SET effect and the effects of discrete energy levels due to significant quantum confinement effects in nanoparticles. The origination of the negative differential resistance effect in series-coupled Pd particles is also attributed to the discreteness of energy levels of both the coupled Pd particles.
Nanostructured silicon formations as a result of ionized N2 gas reactions on silicon with native oxide layers
Authors: Jung Min-Cherl , Lee Tae Gyoung , Park Young Ju , Jun Sung Ho , Lee Joosang , Han Moonsup , Jeong Jong Seok , Lee Jeong Yong
Published: May 2003

Nanostructured silicon was formed by means of the ionized N2 gas reaction on SiO2/Si, and the electronic structure, surface morphology, and optical properties were investigated. The physicochemically modified thin layers were resolved to SiNy and SiOxNy through the observation of Si 2p, O 1s, and N 1s core-level spectra in x-ray photoelectron spectroscopy. The formations of SiOxNy and SiO2 nanostructures (3–4 nm in size), performed by the etching process followed by adsorption of ionized nitrogen, were confirmed by atomic force microscopy. The nanocrystalline Si (6 nm in size) distributed within the modified layer (approximately 10 nm thick) was observed after the in situ rapid thermal annealing processes, using high-resolution transmission electron microscopy. Photoluminescence with a wavelength peaking at around 400 nm was emitted from the nanocrystalline Si formed from the SiOxNy/SiO2/Si structures. This work suggests that the nanocrystalline-Si formation and the nanostructured surface modification method, using the controlled ionized gas, were simple and efficient methods requiring low energy and low temperatures.
Cyanine dye acting both as donor and acceptor in heterojunction photovoltaic devices
Authors: Meng Fanshun , Chen Kongchang , Tian He , Zuppiroli Libero , Nuesch Frank
Published: May 2003

The use of cyanine dyes in thin-film heterojunction photovoltaic devices is investigated. It is demonstrated that a carbocyanine dye acts as donor in conjunction with buckminsterfullerene (C60). Due to its high electron affinity, the cyanine can also act as acceptor when using copoly(dicyano-phenylvinylene-triphenylamine) as donor. H and J aggregates of the cyanine dye play a determining role both in the photocurrent spectrum and in the open circuit voltage. Open-circuit voltages ranging from 0.25 to 1.28 V are obtained for devices using the cyanine as donor and acceptor, respectively. When the cyanine layer is sandwiched between the polymer donor and the C60 acceptor, incident photon to current conversion efficiencies greater than 10% are observed. The possibility of using cyanine dyes at the same time as donors and acceptors is a promising strategy to improve conversion efficiency.
An economic comparison of organic and conventional grain crops in a long-term agroecological research (LTAR) site in lowa
Authors: Delate Kathleen , Duffy Michael , Chase Craig , Holste Ann , Friedrich Heather , Wantate Noreen
Published: May 2003

Based on the interest of organic and conventional farmers in Iowa in long-term analysis of organic systems, the Neely-Kinyon Long-Term Agroecological Research (LTAR) site was established in 1998 to examine the agronomic and economic performance of conventional and organic systems, using certified organic production practices. We report the results of the economic analysis from 3 years of production (1999–2001). Using organic price premiums for organic crops, returns for corn within the organic corn-soybean-oat and corn-soybean-oat-alfalfa rotations were significantly greater than conventional corn-soybean rotation returns (US$126 ha−1). Com returns were not significantly different between the two organic rotations, at US$655 ha−1 and US$674 ha−1, respectively. Returns for soybean within the organic corn-soybean-oat and com-soybean-oat-alfalfa rotations were not significantly different, at US$1233 ha−1 and US$1326 ha−1, respectively. Organic soybean returns were significantly greater than conventional soybean crop returns (US$235 ha−1) in the corn-soybean rotation. Rotational 3-year average returns were US$180 ha−1 for the conventional corn-soybean rotation, compared to US$734 ha−1 for the organic corn-soybean-oat and US$739 ha−1 for the organic com-soybean-oat-alfalfa rotation.
The mission of land grant colleges of agriculture
Authors: Zimdahl Robert L.
Published: May 2003

This paper examines what land grant colleges of agriculture were designed to be and do and, using their published mission statements, discusses what they now claim to be and do. Teaching ‘such branches of learning as are related to the agriculture and the mechanic arts’ and ‘to promote the liberal and practical education of the industrial classes’ is what land grant colleges were designed to do; it is the land grant mission. The paper asks whether these things are what land grant colleges of agriculture do now. The original mission has been amended with new challenges that must be met in a time of declining public support for higher education, societal distrust of science and a negative public perception of agricultural technology, in a culture that wants cheap food. The agricultural community, including colleges of agriculture, has been slow to accept the challenges and opportunities inherent in the questions agriculture now faces. Agriculture remains an essential human activity in our post-industrial, information-age society. Colleges of agriculture are in trouble, and this paper suggests that the sensible thing to do may be to turn away from self-interest in survival to take a leadership role with emphasis on the obligations of service and humanism.
Na+/glucose co-transporter abundance and activity in the small intestine of lambs: enhancement by abomasal infusion of casein
Authors: Mabjeesh Sameer J. , Guy Dafna , Sklan David
Published: May 2003

The purpose of the present study was to determine the effect of abomasal casein infusion on glucose uptake and abundance of the Na+/glucose co-transporter (SGLT1) 1 in the ovine small intestine. Lambs (body weight 35 (SEM 1·0) kg) were surgically fitted with abomasal infusion catheters and were fed diets containing equal portions of wheat hay and cracked maize. Lambs were infused with either 500 g water/d or with 500 g water containing 35 g casein/d. The infusion period lasted 10 d, after which lambs were killed, exsanguinated and eviscerated. Brush border membrane vesicles (BBMV) were prepared using mucosa from different small intestinal regions. Intake and total tract digestibility of nutrients were similar between treatments and averaged 1134, 1142 and 486 g/d and 67, 70, and 94 % for DM, organic matter and non-structural carbohydrates respectively. Crude protein (N×6·25) digestibility was 15 % greater in the casein-infused than control lambs. Glucose uptake to BBMV ranged from 101 to 337 pmol/mg protein per s along the small intestine and was greatest in the mid-section of the small intestine. In the mid-jejunum, glucose uptake was greater (P<0·07) in lambs infused with casein and averaged 120 pmol/mg protein per s compared with 68 pmol/mg protein per s in the control group. SGLT1 affinity was similar between treatments and averaged 104 μM in the different segments of the small intestine of lambs. However, lambs infused with casein exhibited similar values along the small intestine and affinity averaged 106 μm, while in the control group a greater affinity (85 μm) was measured in the mid-jejunum. SGLT1 protein abundance was correlated with glucose uptake in the BBMV in the casein-treated lambs, but not in the control group. These results suggest that glucose uptake along the small intestine of lambs is influenced by casein or its derivatives in the small intestine via SGLT1 affinity and activity at the brush border membrane, and that SGLT1 activity may be regulated by post-translational events affected by amino acids and peptides.
Nutritional status of Japanese-Brazilian subjects: comparison across gender and generation
Authors: Freire Renata D. , Cardos Marly A. , Shinzato Alexandre R. , Ferreira Sandra R. G. ,   for the Japanese-Brazilian Diabetes Study Group
Published: May 2003

The present paper describes a nutritional survey carried out among Japanese-Brazilian subjects living in Bauru, south-eastern Brazil. Data were from a cross-sectional population-based study of 1283 first-generation Japanese-Brazilian subjects (Japan-born; 127 men and 121 women) and second-generation Japanese-Brazilian subjects (Brazil-born; 456 men and 573 women) aged 30–90 years. Anthropometric measurements and % body fat were measured and BMI and waist:hip ratio calculated. Dietary assessment was performed using a validated food-frequency questionnaire. A considerable proportion of men (51 %) and women (47 %) had excess weight (BMI>24·9 kg/m2). A greater waist circumference in men and women (age-adjusted by covariance analysis) was observed among Brazil-born participants. In general, only 10 % of the participants reported current practice of sports or other vigorous physical activity. Age-adjusted mean energy intakes and % energy from macronutrients were found to be similar across generations. The age-adjusted mean daily % energy intake from fat were similar across generations: among Japan-born participants, they were 31·5 (95 % CI 30·6, 32·4) % for men and 32·6 (95 % CI 31·7, 33·5) % for women. The respective figures for Brazil-born subjects were 32·1 (95 % CI 31·6, 32·6) % and 33·2 (95 % CI 32·7, 33·5) %. These values are quite different from the usual intakes reported in Japan during the last decades (about 25 %). Taking into account the traditional Japanese diet, a high energy density diet and a sedentary lifestyle may be implicated in the high prevalence of central obesity and metabolic syndrome observed among Japanese-Brazilian subjects across gender and generations.
Interaction between vitamins C and E affects their tissue concentrations, growth, lipid oxidation, and deficiency symptoms in yellow perch (Perca flavescens)
Authors: Lee Kyeong-Jun , Dabrowski Konrad
Published: May 2003

We have conducted studies with juvenile yellow perch (Perca flavescens) over a period of 20 weeks to address the question of the interaction between water- and lipid-soluble antioxidant vitamins. Fish (2·25±0·14 g) were divided into twelve groups, and triplicate groups were fed one of four casein-based, semi-purified diets formulated to contain low or high vitamin E levels of either 5 or 160 mg/kg without or with vitamin C supplementation (250 mg/kg). Diets were designated as −C−E, −C+E, +C−E, or +C+E, respectively. The fish fed the +C+E diet showed significantly higher weight gain, feed intake, and feed efficiency than the groups fed vitamin C-deficient diets. Total ascorbate concentrations of liver were significantly higher in fish fed vitamin C-supplemented diets than in fish fed the vitamin C-deficient diet after 16 and 20 weeks. The liver α-tocopherol concentrations were increased by supplemental vitamin C in vitamin E-deficient dietary groups which indicates a sparing or regenerating effect of vitamin C on vitamin E. Fish fed vitamin C-deficient diets (−C−E and −C+E) exhibited severe deficiency symptoms, such as scoliosis, lens cataracts, anorexia, and haemorrhages. The cumulative mortality was significantly higher in the −C−E groups. The thiobarbituric acid-reactive substances value was significantly higher in blood plasma of fish fed a diet unsupplemented with both vitamins. The findings in the present study with yellow perch support the hypothesis that vitamin C regenerates and/or spares vitamin Ein vivo.
Effect of genistein and daidzein on platelet aggregation and monocyte and endothelial function
Authors: Gottstein Nicole , Ewins Benjamin A. , Eccleston Clair , Hubbard Gary P. , Kavanagh Ian C. , Minihane Anne-Marie , Weinberg Peter D. , Rimbach Gerald
Published: May 2003

There has been much recent interest in the cardiovascular benefits of dietary isoflavones. The aim of the presentin vitrostudies was to investigate potential anti-thrombogenic and anti-atherogenic effects of the isoflavones genistein and daidzein in platelets, macrophages and endothelial cells. Pre-treatment with either isoflavone inhibited collagen-induced platelet aggregation in a dose-dependent manner. In a macrophage cell line (RAW 264·7) activated with interferon γ plus lipopolysaccharide, both isoflavones were found to inhibit NO production and tumour necrosis factor α (TNF-α) secretion dose-dependently, but they did not affect mRNA levels for inducible nitric oxide synthase and cyclo-oxygenase-2. Both isoflavones also dose-dependently decreased monocyte chemoattractant protein-1 secretion induced by TNF-α in human umbilical vein endothelial cells. Compared with daidzein, genistein exerted greater inhibitory effects for all parameters studied. The present data contributes to our knowledge on the molecular mechanisms by which isoflavones may protect against coronary artery disease. Further studies are required to determine whether the effects of isoflavones observed in the currentin vitrostudies are relevant to the aetiology of coronary artery diseasein vivo.
Zinc supplementation has no effect on circulating levels of peripheral blood leucocytes and lymphocyte subsets in healthy adult men
Authors: Bonham Maxine , O'Connor Jacqueline M. , Alexander H. Denis , Coulter James , Walsh Paula M. , McAnena Liadhan B. , Downes C. Stephen , Hannigan Bernadette M. , Strain J. J.
Published: May 2003

As a result of evidence documenting harmful effects of Zn supplementation on immune function and Cu status, thirty-eight men were recruited onto a Zn supplementation trial. The aim was to examine the effects of chronic Zn supplementation on circulating levels of peripheral blood leucocytes and lymphocyte subsets. Subjects (n19) took 30 mg Zn/d for 14 weeks followed by 3 mg Cu/d for 8 weeks to counteract adverse effects, if any, of Zn supplementation on immune status resulting from lowered Cu status. A control group (n19) took placebo supplements for the duration of the trial. Dietary intakes of Zn approximated 10 mg/d. Blood samples, taken throughout the trial, were assessed for full blood profiles and flow cytometric analyses of lymphocyte subsets. Putative indices of Cu status were also examined. Results indicate that there was no effect of Zn supplementation on circulating levels of peripheral blood leucocytes or on lymphocyte subsets. Cu status was also unaltered. Independent of supplement, there appeared to be seasonal variations in selected lymphocyte subsets in both placebo and supplemented groups. Alterations in circulating levels of B cells (cluster of differentiation (CD) 19), memory T cells (CD45RO) and expression of the intracellular adhesion molecule-1 (CD54) on T cells were observed. Findings indicated no adverse effects of Zn supplementation on immune status or Cu status and support the US upper level of Zn tolerance of 40 mg/d. The seasonal variations observed in lymphocyte subsets in the group as a whole could have implications for seasonal variability in the incidence of infectious diseases.
Oxidation of essential amino acids by the ovine gastrointestinal tract
Authors: Lobley Gerald E. , Shen Xiangzhen , Le Guowei , Bremner David M. , Milne Eric , Calder A. Graham , Anderson Susan E. , Dennison Ngaire
Published: May 2003

It is not known if the ruminant animal gastrointestinal tract (GIT) can oxidise essential amino acids (AA) other than leucine. Therefore, the oxidation of four essential AA (leucine, lysine, methionine and phenylalanine), supplied systemically as labelled 1-13C forms, was monitored across the mesenteric-drained viscera (MDV; small intestine) and portal-drained viscera (PDV; total GIT), as part of a 4×4 Latin square design, in four wether sheep (35–45 kg) fed at 1·4 × maintenance. Oxidation was assessed primarily by appearance of13CO2,corrected for sequestration of [13C]bicarbonate. The GIT contributed 25 % (P<0·001) and 10 % (P<0·05) towards whole-body AA oxidation for leucine and methionine respectively. This reduced net appearance across the PDV by 23 and 11 % respectively. The contribution of MDV metabolism to total PDV oxidation was 40 % for leucine and 60 % for methionine. There was no catabolism of systemic lysine or phenylalanine across the GIT. Production and exchange of secondary metabolites (e.g. 4-methyl-2-oxo-pentanoate, homocysteine, 2-aminoadipate) across the GIT was also limited. Less AA appeared across the PDV than MDV (P<0·001), indicative of use by tissues such as the forestomach, large intestine, spleen and pancreas. The PDV: MDV net appearance ratios varied (P<0·001) between AA, e.g. phenylalanine (0·81), lysine (0·71), methionine (0·67), leucine (0·56), histidine (0·71), threonine (0·63) and tryptophan (0·48). These differences probably reflect incomplete re-absorption of endogenous secretions and, together with the varied oxidative losses measured, will alter the pattern of AA net supply to the rest of the animal.
The effect of nutrient profiles of the Dietary Approaches to Stop Hypertension (DASH) diets on blood pressure and bone metabolism and composition in normotensive and hypertensive rats
Authors: Doyle Lorna , Cashman Kevin D.
Published: May 2003

Hypertension has been associated with abnormalities of Ca and bone metabolism. Consequently, dietary strategies aimed at reducing blood pressure may also benefit bone health; however, this issue has received little attention. Therefore, the objective of the present study was to investigate the effect of two antihypertensive-type diets on blood pressure and bone metabolism and composition in normotensive (Wistar-Kyoto NHsd, WKY) and hypertensive (spontaneously hypertensive NHsd, SHR) rats. Thirty WKY and thirty SHR male rats, 14 weeks old, were separately randomized by weight into three groups of ten rats each. One group from each strain was given a control diet while the other two groups were fed two anti-hypertensive (high fruit and vegetable (F/V) and high fruit and vegetable and low-fat dairy produce (combination)) diets for 8 weeks. SHR rats were significantly (P<0·01) heavier than WKY rats. Blood pressure and femoral length, width, dry weight, ash, Ca, Mg, P and bone mineral mass were significantly (P<0·0001) greater in SHR than WKY rats, but were unaffected by diet, irrespective of strain. While markers of bone formation (serum osteocalcin) and bone resorption (urinary pyridinoline and deoxypyridinoline) were similar in both strains, these markers were significantly (P<0·05) lower (28–31, 16–23, 31–33 % respectively) in the SHR rats fed the combination diet relative to those fed the control and F/V diets. Bone turnover in WKY rats was unaffected by diet. In conclusion, these findings suggest that the combination diet may benefit bone metabolism in hypertensive animals. However, as blood pressure was unaffected by this diet, the mechanism by which it reduced bone turnover requires further investigation.
Metabolic effects oftransfatty acids on an experimental dietary model
Authors: Colandré María E. , Diez Rosaura S. , Bernal Claudio A.
Published: May 2003

The aim of the present study was to investigate the potential nutritional and metabolic impact oftrans(t) fatty acids (FA) on an appropriate experimental dietary model. Since previously reported experimental designs have been matter of concern, we developed a dietary model to compare the effect oftisomers and/or the saturation of FA independently of other variables. Wistar rats were fed diets containing identical amounts of nutrients and high levels of dietary fats (200 g/kg) for 30 d. Dietary fat rich int-FA was compared with fat rich in saturated (s) FA or rich incis(c) FA, maintaining the same length of C chain of the FA. The fats were obtained through isomerization or hydrogenation of thec-FA present in the control fat. Apparent fat absorption, energy efficiency and triacylglycerol levels in serum and liver were different in rats fedt-FA or s-FA thanc-FA. The apparent fat absorption was (%): s-FA 85·7 (SD 3·4)<T-FA 93·1 (sd 0·4)<c-FA 96·7 (sd 1·1) (P<0·05). The efficiency of energy utilization was lower int-FA (11·7 %) and s-FA (18·5 %) diets, reaching statistical significance only between s-FA andc-FA. A striking finding was the change in the lipid profile in serum and liver. Serum and hepatic triacylglycerol levels were greater fort-FA and s-FA diets than inc-FA; however, the increases on serum triacylglycerol concentrations were greater with the s-FA diet and the increases on hepatic triacylglycerol content were greater witht-FA. Knowledge of thet-FA effects on this kind of experimental dietary model could contribute to determine the potential risk oft-FA intake for man.