bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential surface photovoltage spectroscopy characterization of a 1.3 μm InGaAlAs/InP vertical-cavity surface-emitting laser structure
Authors: Liang J. S. , Wang S. D. , Huang Y. S. , Malikova L. , Pollak Fred H. , Debray J. P. , Hoffman R. , Amtout A. , Stall R. A.
Published: February 2003

We have investigated a 1.3 μm InGaAlAs/InP vertical-cavity surface-emitting laser (VCSEL) structure using angle- and temperature-dependent wavelength-modulated differential surface photovoltage spectroscopy (DSPS). The DSPS measurements as functions of incident angle and temperature have been carried out in the ranges 0°⩽θ⩽60° and 300 K⩽T⩽420 K, respectively. Angle-dependent reflectance (R) and surface photovoltage spectroscopy (SPS) measurements have also been performed to illustrate the superior features of the DSPS technique. The differential surface photovoltage (DSPV) and SPV spectra exhibit both the fundamental conduction to heavy-hole excitonic transition of quantum well and cavity mode (CM) plus a rich interference pattern related to the mirror stacks, whereas in the R spectra only the CM and interference features are clearly visible. The energies of the excitonic transition and CM are accurately determined from the DSPV spectra. By changing the angle of incidence in the DSPS measurements the energy positions of the CM and distributed Bragg reflector features show a blueshift while the excitonic transition remains unchanged. At a fixed incident angle, the energy positions of the excitonic feature and CM show a different rate of redshift with increasing temperature, with the latter at a much slower pace. The results demonstrate considerable potential of DSPS for the nondestructive characterization of the VCSEL structures.
Pressure and temperature dependence of structural relaxation in diglycidylether of bisphenol A
Authors: Paluch M. , Roland C. M. , Gapinski J. , Patkowski A.
Published: February 2003

The structural (α-) relaxation in diglycidylether of bisphenol A (DGEBA) has been examined using three spectroscopic methods: dielectric spectroscopy (DS), dynamic light scattering–photon correlation spectroscopy (LS), and mechanical spectroscopy. The DS and LS measurements were carried out as a function of both temperature and pressure. Moreover, pressure-volumetemperature measurements were obtained for the DGEBA. These data allow an assessment of the relative contributions of thermal energy and free volume to structural relaxation in DGEBA. The results clearly show a substantial role for both thermal and free volume fluctuations in the dramatic slowing down of the dynamics. The combined temperature- and pressure-dependences of the dielectric and light scattering relaxation times were analyzed using the Avramov equation, implying that the fragility (normalized temperature dependence) is pressure independent over the studied range of pressures. The pressure dependence was the same as measured by the different spectroscopies. Conformance to the time-temperature-pressure superposition principle was also observed for all measurement techniques.
Linear gradient copolymer melt brushes
Authors: Pickett Galen T.
Published: February 2003

I consider a brush of gradient polymers, with the chains anchored at their pure A ends with the chemical composition changing linearly along the chain up to the untethered chain tips whose composition is pure B. Demixing of the A and B monomers results in the creation of a thermally-controllable zone from which free ends are excluded. For high temperatures, the zone is small and located near the grafting surface, but for lower temperatures the zone extends throughout the layer, giving a physical manifestation of an Alexander brush. This conclusion is supported by both scaling and numerical self-consistent field calculations.
On the bulk modulus of the cell model of charged macromolecules suspensions
Authors: Téllez Gabriel , Trizac Emmanuel
Published: February 2003

We study theoretically the bulk modulus (inverse of the compressibility) of a suspension of charged objects (macroions), making use of a cell model to account for the finite density of macroions. The diffuse layer of charged microspecies around a macroion is described by a generic local density functional theory. Within this general framework, we obtain the condition for a positive bulk modulus, which is fulfilled by several proposals made in the literature and rules out the possibility of a critical point. We show that a sufficient condition for a positive compressibility also ensures that the same theory produces repulsive effective pair potentials.
Kinetics of heterogeneous nucleation for low mean cluster populations
Authors: Bhatt Jayesh S. , Ford Ian J.
Published: February 2003

The process of nucleation is normally described using rate equations for the mean populations of molecular clusters. This approach can be justified for cases where these mean populations are large. However, it may be unsuitable in the case of heterogeneous nucleation on small particles if the mean populations are of the order of unity or less. In such a case, considering the average populations might be erroneous since the statistical fluctuations in the molecular populations should be taken into account. Here a stochastic treatment of heterogeneous nucleation kinetics is presented that is described by a set of master equations, and a modified expression for the nucleation rate has been deduced. Furthermore, a numerical method for solving the stochastic system has been examined, and the results show that the rate of nucleation can differ greatly from that obtained with the traditional kinetics.
Self-diffusion of linear and cyclic alkanes, measured with pulsed-gradient spin-echo nuclear magnetic resonance
Authors: von Meerwall E. , Ozisik R. , Mattice W. L. , Pfister P. M.
Published: February 2003

Self-diffusion coefficients of linear and cyclic alkanes in melt, in blends with equivalent linear alkanes, and dissolved in linear polyethylene, were measured by pulsed-gradient spin-echo nuclear magnetic resonance at various temperatures. The results indicate the following: (i) at the same carbon number, cyclic alkanes diffuse more slowly than linear alkanes in their respective melts, but linears and cyclics share a similar rapid rate of decrease with increasing carbon number; (ii) in blends of linear and cyclic alkanes at the same carbon number the single average diffusion coefficient observed varies monotonically as a function of composition; and (iii) two distinct diffusion coefficients are observed in the cycloalkane/linear polyethylene blends, with the extrapolated trace cycloalkane diffusion consistent with Rouse behavior. The results are compared with recent numerical simulations and with experiments in other polymer systems, forming a consistent picture of the effects of diffusant mass, molecular shape and flexibility, and the dynamic attributes of the host material.
Sphere-to-rod transitions of micelles in model nonionic surfactant solutions
Authors: Al-Anber Zaid A. , Bonet i Avalos Josep , Floriano M. Antonio , Mackie Allan D.
Published: February 2003

The transition of spherical to rod-like micelles is studied in a lattice model for amphiphiles using the single chain mean-field (SCMF) theory and grand-canonical Monte Carlo (GCMC) simulations. A linear combination of the free energy of spherical and infinite cylindrical geometries is assumed in the SCMF theory to estimate the free energy of rod-like micelles. The SCMF theory finds that the symmetric H4T4 amphiphile at a dimensionless temperature scale, T*, of T*=6.5 favors the formation of spherical micelles at all investigated overall amphiphile concentrations. On the other hand, the asymmetric H3T6 amphiphile at T* between 8.5 and 12.5 starts by forming spherical micelles (first cmc) at low overall amphiphile concentrations and then forms rod-like micelles (second cmc) as the overall amphiphile concentration increases. The GCMC simulations also find that the symmetric H4T4 amphiphile forms spherical micelles while the asymmetric H3T6 amphiphile tends to form rod-like micelles. The second cmc is found to increase with increasing T* whereas it decreases with increasing tail length. Our results are in good qualitative agreement with experimental observations.
Core level spectra of amorphous carbon nitride
Authors: Ripalda J. M. , Román E. , Galán L. , Montero I. , Lizzit S. , Baraldi A. , Comelli G. , Paolucci G. , Goldoni A.
Published: February 2003

The nature of bonding in amorphous carbon nitride was studied with core level spectroscopies such as x-ray absorption, photoemission, and Auger electron spectroscopy, using synchrotron radiation as the excitation source. The changes in local structure were systematically studied as a function of sample preparation conditions. The correspondence between nitrogen local environment and spectral features is discussed. It is found that thermal annealing increases the average coordination number and decreases bond multiplicity at nitrogen sites.
Corrections to the strong-stretching theory of polymer brushes due to the proximal layer
Authors: Matsen M. W. , Gardiner J. M.
Published: February 2003

Proximal-layer corrections to the strong-stretching theory (SST) for polymer brushes are tested against self-consistent field theory (SCFT). The corrections qualitatively account for a number of significant differences between SST and SCFT occurring next to the substrate. This includes severe deviations away from the parabolic field normally predicted by SST, and nonzero slopes in the single-chain segment distributions. When SST is also combined with corrections for the end-segment entropy, the quantitative agreement with SCFT becomes impressive, particularly in regards to the self-consistent field and the stretching energy of individual chains.
Ellipsometric characterization of damage profiles using an advanced optical model
Authors: Petrik P. , Polgár O. , Fried M. , Lohner T. , Khánh N. Q. , Gyulai J.
Published: February 2003

Damage created by ion implantation into single crystalline silicon was characterized with an optical model based on the coupled half-Gaussian model developed by Fried et al [J. Appl. Phys. 71, 2835 (1992)]. In the improved optical model the damage profile was described by sublayers with thicknesses inversely proportional to the slope of the profile. This method allows a better resolution at the quickly changing parts of the profile, and a better approximation of the Gaussian profile with the same number of sublayers. A fitting procedure, which we call “multipoint random search,” was applied to minimize the probability of getting in a local minimum. The capabilities of our method were demonstrated for amorphizing doses using different ions and energies. The improved fit quality and the correlation with results of backscattering spectrometry basically supported the optical model.
Incoherent neutron scattering and the dynamics of thin film photoresist polymers
Authors: Soles Christopher L. , Douglas Jack F. , Lin Eric K. , Lenhart Joseph L. , Jones Ronald L. , Wu Wen-Li , Goldfarb Darı́o L. , Angelopoulos Marie
Published: February 2003

Elastic incoherent neutron scattering is employed to parameterize changes in the atomic/molecular mobility in lithographic polymers as a function of film thickness. Changes in the 200 MHz and faster dynamics are estimated in terms of a harmonic oscillator model and the corresponding Debye–Waller factor mean-square atomic displacement 〈u2〉. We generally observe that relatively large 〈u2〉 values in the glassy state lead to a strong suppression of 〈u2〉 when the polymer is confined to exceedingly thin films. In contrast, this thin film suppression is diminished or even absent if 〈u2〉 in the glass is relatively small. We further demonstrate that highly localized side group or segmental dynamics of hydrogen-rich moieties, such as methyl groups, dominate 〈u2〉 and that thin film confinement apparently retards these motions. With respect to photolithography, we demonstrate that a reduced 〈u2〉 in exceedingly thin model resist films corresponds to a decrease in the reaction front propagation kinetics.
Efficient Monte Carlo sampling for long molecular chains using local moves, tested on a solvated lipid bilayer
Authors: Mezei Mihaly
Published: February 2003

An improved acceptance criterion for local move Monte Carlo method (in which trial steps change only seven consecutive torsion angles of a polymer) is introduced. In contrast to previous methods, not all possible loop closures are considered, but only the most structurally conservative one. By filtering such moves with the “reverse proximity criterion” introduced here, detailed balance is satisfied. Furthermore, the new method is ergodic, and is shown to be significantly more efficient than previous methods when applied to a fully solvated hydrocarbon chain with bulky sidechains as well as a fully solvated lipid bilayer.
Solvent effect on single-chain collapse of poly(methyl methacrylate) in tert-butyl alcohol
Authors: Nakamura Yoshiki , Sasaki Naoki , Nakata Mitsuo
Published: February 2003

Kinetic and static properties of the coil–globule transition of poly(methyl methacrylate) (PMMA) in pure tert-butyl alcohol were determined by static light scattering and compared with those of PMMA in the mixed solvent tert-butyl alcohol+water(2.5 vol %) in order to examine the effect of water on the chain collapse. The measurements were carried out for the molecular weight M×10−6=4.1 and 12.2 in the concentration range of 0.6×10−4–2.6×10−4 g/cm3, and the mean-square radius of gyration 〈s2〉 was determined as a function of the time after an abrupt decrease of temperature. PMMA chains collapsed to equilibrium globules within 90 min after quenching for M=1.22×107 and within 30 min for M=4.1×106. Chain aggregation due to phase separation became noticeable after the collapse of the chain because of an increase of observed molecular weight. For PMMA in the mixed solvent tert-butyl alcohol+water(2.5 vol %), the chain collapse process has been observed for periods from hours to weeks depending on the molecular weight and temperature, and the chain aggregation was negligibly small in the chain collapse process. The expansion factor α2=〈s2〉/〈s2〉0 obtained for fully collapsed chains in pure tert-butyl alcohol was represented by the theoretical prediction α3−α−C(α−3−1)=B(1−θ/T)M1/2 with the coefficients of B=0.0179 and C=0.054. For PMMA in the mixed solvent, the coil–globule transition curve has been expressed by the same equation with B=0.0164 and C=0.049, close to the above values. The small amount of water in the mixed solvent caused a drastic slowdown in the chain-collapse rate but had little effect on the coil–globule transition curve.
Osmotic pressure of isotropic solutions of rodlike polymers
Authors: Yethiraj Arun
Published: February 2003

The osmotic pressure of isotropic solutions of athermal rodlike polymers is studied using Monte Carlo simulations. The simulation results show that scaling theory is in qualitative error for the dependence of pressure on concentration. The virial expansion truncated after the second virial coefficient, however, is in quantitative agreement with the simulation results.
Emission spectra of TiH and TiD near 938 nm
Authors: Andersson Nils , Balfour Walter J. , Bernath Peter F. , Lindgren Bo , Ram Ram S.
Published: February 2003

High resolution, near infrared emission spectra of TiH and TiD have been recorded with a Fourier transform spectrometer. The TiH and TiD molecules were made in a titanium hollow cathode lamp operated with a mixture of neon and hydrogen or deuterium gases. A heavily perturbed band system near 938 nm is assigned as a Φ4–X 4Φ electronic transition. Line positions and approximate spectroscopic constants are reported for the 0–0 band of the new transition. The Φ4–X 4Φ TiH transition might potentially be observed in late M-type stars and in L-type brown dwarfs.
The electrostatic potential profile along a biased molecular wire: A model quantum-mechanical calculation
Authors: Pleutin Stéphane , Grabert Hermann , Ingold Gert-Ludwig , Nitzan Abraham
Published: February 2003

We study the electrostatic potential of a molecular wire bridging two metallic electrodes in the limit of weak contacts. With the use of a tight-binding model including a fully three-dimensional treatment of the electrostatics of the molecular junction, the potential is shown to be poorly screened, dropping mostly along the entire molecule. In addition, we observe pronounced Friedel oscillations that can be related to the breaking of electron–hole symmetry. Our results are in semiquantitative agreement with recent state-of-the-art ab initio calculations and point to the need of a three-dimensional treatment to properly capture the behavior of the electrostatic potential. Based on these results, current-voltage curves are calculated within the Landauer formalism. It is shown that Coulomb interaction partially compensates the localization of the charges induced by the electric field and consequently tends to suppress zones of negative differential resistance.
Two-vibron bound states lifetime in a one-dimensional molecular lattice coupled to acoustic phonons
Authors: Pouthier V.
Published: February 2003

The lifetime of two-vibron bound states in the overtone region of a one-dimensional anharmonic molecular lattice is investigated. The anharmonicity, introduced within an attractive Hubbard Hamiltonian for bosons, is responsible for the formation of bound states which belong to a finite linewidth band located below the continuum of two-vibron free states. The decay of these bound states into either bound or free states is described by considering the coupling between the vibrons and a thermal bath formed by a set of low-frequency acoustic phonons. The relaxation rate is expressed in terms of the spectral distribution of the vibron/phonon coupling and of the two-vibron Green operator which is calculated exactly by using the number states method. The behavior of the two-vibron bound states relaxation rate is analyzed with a special emphasis on the influence of the anharmonicity. It is shown that the rate exhibits two distinct regimes depending on the thermal bath dimension. When the bath dimension is equal to unity, the rate increases with the anharmonicity and the decay of the two-vibron bound states into the other bound states appears as the main contribution of the rate. By contrast, when the bath dimension is equal to 2 and 3, the rate decreases as the anharmonicity increases, indicating that the two-vibron bound states decay into the two-vibron free states continuum.
Orbital rehybridization in n-octane adsorbed on Cu(110)
Authors: Öström H. , Triguero L. , Weiss K. , Ogasawara H. , Garnier M. G. , Nordlund D. , Nyberg M. , Pettersson L. G. M. , Nilsson A.
Published: February 2003

We have investigated the local electronic structure of n-octane adsorbed on the Cu(110) surface using symmetry-resolved x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES) in combination with density functional theory (DFT) spectrum calculations. We found new adsorption-induced states in the XE spectra, which we assign to interaction between the bonding CH orbitals and the metal surface. By performing a systematic investigation of the influence of different structural parameters on the XA and XE spectra, we conclude that the molecular geometry is significantly distorted relative to the gas-phase structure. The bonding to the surface leads to a strengthening of the carbon–carbon bonds and a weakening of the carbon–hydrogen bonds, consistent with a rehybridization of the carbons from sp3 to sp2.8.
High pressure effect on structural and electrical properties of glassy carbon
Authors: Wang X. , Bao Z. X. , Zhang Y. L. , Li F. Y. , Yu R. C. , Jin C. Q.
Published: February 2003

The structural evolutions of glassy carbon (GC) and graphitized glassy carbon (GGC) treated under high temperatures and high pressures have been studied by energy-dispersive x-ray diffraction in a diamond anvil cell. The equations of state of GC and GGC are determined from x-ray density data. GC has a higher bulk modulus than that of GGC. It is found that the two-dimensional order of stacked layers in GC decreases with increasing the stresses, and the orientated layers merge with the disorientated layers at higher pressures, in which it can also be attributed to the appearance of a bump in the electrical resistance measurements under high pressures.
Free energy landscapes of model peptides and proteins
Authors: Evans David A. , Wales David J.
Published: February 2003

A parallel searching algorithm based on eigenvector-following is used to generate databases of minima and transition states for an all-atom model of the peptide Ac(ala)3NHMe and for a simplified bead model of a protein. We analyze the energy landscapes of both systems using disconnectivity graphs based upon both potential energy and free energy. This approach highlights the role of vibrational entropy in determining the relative free energy of local minima. Thermodynamic properties for Ac(ala)3NHMe calculated using the superposition approach are in reasonable agreement with parallel-tempering Monte Carlo simulations.
Computer simulation of structural properties of dilute aqueous solutions of argon at supercritical conditions
Authors: De Grandis V. , Gallo P. , Rovere M.
Published: February 2003

Computer simulation studies of aqueous solutions of argon are performed from ambient to supercritical conditions by using a recent polarizable potential model and the nonpolarizable simple point charge extended model. At T=673 K we compare the water-solute pair correlation functions of the argon-water mixture with recent experimental results obtained from neutron scattering experiments. The comparison shows that the introduction of the polarizable effects decreases the solute-water repulsion and improves the agreement with the experiment at supercritical conditions. In particular we find that the water-solute structure predicted by the polarizable model is in good agreement with the experiment.
Formation mechanism of nanocatalysts for the growth of silicon nanowires on a hydrogen-terminated Si {111} surface template
Authors: Takeda S. , Ueda K. , Ozaki N. , Ohno Y.
Published: February 2003

We have observed the formation process of nanocatalysts that act for the growth of Si nanowires by means of UHV scanning tunneling microscopy. Gold–silicon nanocatalysts that we have examined were thought to form on a hydrogen (H)-terminated [111] silicon surface and to expel Si nanowires of extremely high aspect ratio via the vapor-liquid-solid mechanism. We have observed that a nanocatalyst, that is, a droplet of melted gold–silicon alloy of about 5 nm in diameter, is actually formed in a pit on a H-terminated surface in the narrow temperature range around 500 °C. We have concluded that, in this specific temperature range, nanocatalysts can be melted, remain mutually isolated, absorb silicon effectively, and expel Si nanowires. Based on the result, we have proposed a method of making a thin template, which facilitates to decide the nucleation sites and the sizes of nanocatalysts, resulting in the precise control of those of Si nanowires.
Mechanism of vortex switching in magnetic nanodots under a circular magnetic field. II. Dynamics of a spin plaquette containing a vortex
Authors: Kovalev A. S. , Prilepsky J. E.
Published: February 2003

For a theoretical explanation of the mechanism of switching of the polarization of magnetic vortices in an external circular magnetic field, a small spin plaquette in a vortex configuration is considered. An analytical investigation of the initial (linear) stage of the vortex switching process is carried out. The analytical results obtained confirm the data of a numerical calculation of the plaquette dynamics. Both the numerical simulation and an analytical treatment of the initial stage of activation show the importance of taking the azimuthal modes of the system into account. It is at the frequencies of these modes that the most rapid growth of the vortex energy and the total intraplane projection of the magnetization occur. Increasing the amplitude of these modes leads to parametric excitation of a low-frequency symmetric mode, and that causes vortex switching. The results provide a qualitative explanation of the data of a numerical simulation of vortex switching in large magnetic systems and can be used in experiments on the directed influencing of the polarization of vortices in magnetic nanodots.
Induced magnetic anisotropy in amorphous ribbons by applying a magnetic field during the quenching process
Authors: Tejedor M. , Garcı́a J. A. , Carrizo J. , Elbaile L. , Santos J. D.
Published: February 2003

A method to induce magnetic anisotropy in amorphous magnetic ribbons has been developed. The anisotropy is induced in the high Curie temperature Fe80B20 and Co70Mn5Fe1Mo1Si14B9 amorphous magnetic ribbons by applying a magnetic field at the moment of the solidification of the melt. This method does not affect the excellent mechanical properties of these materials. The induced magnetic anisotropy has been measured by torque magnetometry and its strength and easy axis are compared with the results obtained by other authors using static magnetic annealing in similar samples.
Composite cathode based on yttria stabilized bismuth oxide for low-temperature solid oxide fuel cells
Authors: Xia Changrong , Zhang Yuelan , Liu Meilin
Published: February 2003

Composites consisting of silver and yttria stabilized bismuth oxide (YSB) have been investigated as cathodes for low-temperature honeycomb solid oxide fuel cells with stabilized zirconia as electrolytes. At 600 °C, the interfacial polarization resistances of a porous YSB–Ag cathode is about 0.3 Ω cm2, more than one order of magnitude smaller than those of other reported cathodes on stabilized zirconia. For example, the interfacial resistances of a traditional YSZ–lanthanum maganites composite cathode is about 11.4 Ω cm2 at 600 °C. Impedance analysis indicated that the performance of an YSB–Ag composite cathode fired at 850 °C for 2 h is severely limited by gas transport due to insufficient porosity. The high performance of the YSB–Ag cathodes is very encouraging for developing honeycomb fuel cells to be operated at temperatures below 600 °C.
Piezoacoustic modulation of gain and distributed feedback for quantum cascade lasers with widely tunable emission wavelength
Authors: Kisin Mikhail V. , Luryi Serge
Published: February 2003

Due to the piezoelectric properties of III–V materials, an acoustic wave propagating along the optical axis of a unipolar laser produces a periodic modulation of the carrier density and the optical gain, sufficient for providing distributed feedback (DFB) with a mode suppression ratio exceeding 30 dB. In contrast to bipolar lasers, the piezoelectric modulation of unipolar carrier density is not accompanied by a degradation of the average gain. Inasmuch as the acoustic frequency can be easily changed, the wavelength of the main DFB mode can be tuned in a wide range. This property should be very attractive for spectroscopic applications of the quantum cascade laser.
Temperature dependence of superconductor-correlated metal–superconductor Josephson junctions
Authors: Freericks J. K. , Nikolić B. K. , Miller P.
Published: February 2003

Josephson junctions, with the barrier composed of a correlated metal (or insulator) tuned to lie close to the metal–insulator transition, show promise to provide the fastest operating speeds for digital electronics based on rapid single-flux quantum logic. We provide theoretical calculations that indicate that these devices have a small enough temperature derivative of Ic(T) within the junction operating range to allow them to be employed as elements in complex digital circuits.
Electro-optical properties of a polymer light-emitting diode with an injection-limited hole contact
Authors: van Woudenbergh T. , Blom P. W. M. , Huiberts J. N.
Published: February 2003

The electro-optical characteristics of a polymer light-emitting diode with a strongly reduced hole injection have been investigated. A silver contact on poly-dialkoxy-p-phenylene vinylene decreases the hole injection by five orders of magnitude, resulting in both a highly reduced light output and current. However, at high applied voltages, the current and light output strongly exceed the predictions based on the reduced hole injection, which is explained by an enhanced electric field near the hole-injection contact due to trapped electrons.
Electron-beam-induced damage in wurtzite InN
Authors: Mkhoyan K. A. , Silcox J.
Published: February 2003

Knock-on type damage with ejection of nitrogen atoms from a sample was observed in wurtzite InN during irradiation by 100 keV electron beam in scanning transmission electron microscope. Comparison of the measured integrated intensities of nitrogen K and indium M4,5 edges with calculated mass-loss provided a method to measure the energy of vacancy-enhanced displacement in InN for nitrogen atoms, which was found to be 4.6 eV. The results were also applied to predict the rate of electron beam induced damage that will occur in InN specimens with different thicknesses.
Nonlinear hole transport through a submicron-size channel
Authors: Makarovsky O. , Neumann A. , Martin A. M. , Turyanska L. , Patanè A. , Eaves L. , Henini M. , Main P. C. , Thoms S. , Wilkinson C. D. W. , Maude D. K. , Portal J. C.
Published: February 2003

We investigate hole transport through a submicron-size channel fabricated from a modulation-doped p-type GaAs/(AlGa)As single-quantum-well heterostructure. The intense electric field in the channel accelerates the holes beyond the inflection point of the lowest energy subband dispersion curve. This leads to current saturation and negative differential conduction effects in the current–voltage characteristics.
Nanoscale stiffness of individual dendritic molecules and their aggregates
Authors: Tsukruk Vladimir V. , Shulha Hennady , Zhai Xiaowen
Published: February 2003

We demonstrate that carefully designed micromapping of the surface stiffness with nanoscale resolution could reveal quantitative data on the elastic properties of compliant, dendritic organic molecules with nanoparticulate dimensions below 3 nm. Much higher elastic modulus was observed for individual, fourth generation dendritic molecules due to their more shape persistent conformation. Large, reversible, elastic deformation is a distinct characteristic of the nanomechanical response observed for individual dendritic molecules. Such a “rubbery” response could be an indication of spatial constraints imposed on vitrification of dendritic molecules tethered to the functionalized interface. Surprisingly, an increased stiffness was also found for the third generation dendritic molecules within long aggregates.
Nonlinear optical crystal-line writing in glass by yttrium aluminum garnet laser irradiation
Authors: Honma Tsuyoshi , Benino Yasuhiko , Fujiwara Takumi , Komatsu Takayuki , Sato Ryuji
Published: February 2003

Crystal lines with second-order optical nonlinearity have been successfully fabricated at the surface of 10Sm2O3.35Bi2O3.55B2O3 glass by continuous irradiation of Nd:YAG laser. The laser-induced crystalline phase was confirmed to be Bi0.7Sm0.3BO3 by x-ray diffraction measurements, and second-harmonic generation (SHG) from the phase was clearly observed. An array structure of crystal lines was fabricated by laser writing under automatic computer control, and Maker fringe patterns of SHG were observed, indicating that the direction of polarization in the structure with a crystal line array was parallel to the sample surface. In addition, we measured polarization optical microphotographs, and found uniform phase retardation for a whole length of crystal lines. It is strongly suggested from these results that crystal lines by laser irradiation are formed in single-domain crystalline phase (single crystal) with second-order nonlinearity.
Highly-ordered GaAs/AlGaAs quantum-dot arrays on GaAs (001) substrates grown by molecular-beam epitaxy using nanochannel alumina masks
Authors: Mei X. , Blumin M. , Sun M. , Kim D. , Wu Z. H. , Ruda H. E. , Guo Q. X.
Published: February 2003

Highly-ordered GaAs/AlGaAs quantum-dot arrays (QDA) were grown by molecular-beam epitaxy on GaAs (001) using masks of anodic nanochannel alumina (NCA). The QDA replicated the hexagonal lattice pattern of the NCA masks with period spacing of 100 nm. The circular disk-like dots were defined by the nanohole channels of NCA masks with size adjustable between 45 and 85 nm. Both single- and double-well GaAs/AlGaAs QDA exhibited strong photoluminescence. The single-well QDA showed a narrow peak at 1.64 eV with full width at half maximum of only 16 meV, indicating good size uniformity and crystal quality for the QDA. NCA masked epitaxial growth is thus shown to be a promising general approach for fabricating various heterostructure QDA, including both strained and lattice-matched heterostructures.
Enhanced oxidation and segregation in plasma source ion implanted alloy
Authors: Bolduc M. , Terreault B.
Published: February 2003

Segregation of surprising magnitude and depth was discovered in oxygen plasma-implanted Mg-containing Al alloys. In order to identify the respective roles of diffusional kinetics and oxidation energetics in the effect, pure Al and an Al–Mg–Zn–Cu–Cr alloy were implanted for various times, or oxidized in air, at 700 K. Examination of depth profiles and chemical states of O, Al, and Mg by x-ray photoelectron spectroscopy reveals a potent synergy between the chemical potential drive and the radiation-enhanced diffusion.
Excitonic emissions observed in ZnO single crystal nanorods
Authors: Park W. I. , Jun Y. H. , Jung S. W. , Yi Gyu-Chul
Published: February 2003

We report on the photoluminescent characteristics of ZnO single crystal nanorods grown by catalyst-free metalorganic vapor phase epitaxy. From photoluminescence (PL) spectra of the nanorods at 10 K, several PL peaks were observed at 3.376, 3.364, 3.360, and 3.359 eV. The PL peak at 3.376 eV is attributed to a free exciton peak while the other peaks are ascribed to neutral donor bound exciton peaks. The observation of the free exciton peak at 10 K indicates that ZnO nanorods prepared by the catalyst-free method are of high optical quality.
Relativistic, nearly basis-set-limit nuclear magnetic shielding constants of the rare gases He–Rn: A way to absolute nuclear magnetic resonance shielding scales
Authors: Vaara Juha , Pyykkö Pekka
Published: February 2003

Relativistic four-component ab initio calculations using the Dirac–Coulomb Hamiltonian and converged, very large Gaussian one-particle basis sets are carried out for the nuclear magnetic shielding constants of rare gas atoms He–Rn in their ground state. A discrepancy between two earlier sets of theoretical results for He–Xe is attributed to the basis. Absolute nuclear magnetic resonance shielding scales for the investigated elements are established because electron correlation effects are negligible in this case. Future atomic-beam experiments are discussed.
Nuclear magnetic resonance noise spectroscopy using two-photon excitation
Authors: Michal Carl A.
Published: February 2003

Two-photon excitation is employed in conjunction with stochastic nuclear magnetic resonance (NMR) at high magnetic field to acquire pulsed NMR spectra with high sensitivity in the absence of an on-resonance radio-frequency excitation. These conditions allow the NMR receiver to be active during excitation and therefore eliminate the receiver dead-time. Examples are presented demonstrating the direct observation of nuclear magnetization under nutation and spin-locking conditions. Applications of the techniques are discussed.
Existence verification for singular and nonsmooth zeros of real nonlinear systems
Authors: Dian Jianwei , Kearfott R.
Published: February 2003

Traditional computational fixed point theorems, such as the Kantorovich theorem (made rigorous with directed roundings), Krawczyk’s meth- od, or interval Newton methods use a computer’s floating-point hardware computations to mathematically prove existence and uniqueness of a solution to a nonlinear system of equations within a given region of

n
n

-space. Such computations require the Jacobi matrix of the system to be nonsingular in a neighborhood of a solution. However, in previous work we showed how we could mathematically verify existence of singular solutions in a small region of complex

n
n

-space containing an approximate real solution. We verified existence of such singular solutions by verifying that the topological degree of a small region is nonzero; a nonzero topological degree implies existence of a solution in the interior of the region. Here, we show that, when the actual topological degree in complex space is odd and the rank defect of the Jacobi matrix is one, the topological degree of a small region containing the singular solution can be verified to be plus or minus one in real space. The algorithm for verification in real space is significantly simpler and more efficient. We demonstrate this efficiency with numerical experiments. Since our verification procedure uses only values on the surfaces of a bounding box that contains the solution, the method can also be applied to cases where the system is nonsmooth at the solution.
A computation of minimal polynomials of special values of Siegel modular functions
Authors: Itoh Tsuyoshi
Published: February 2003

Recently, Fukuda and Komatsu constructed units of a certain abelian extension of

Q

(
exp
⁡
(
2
π

−
1

/

5
)
)

\mathbb {Q}(\exp (2 \pi \sqrt {-1}/5))

using special values of Siegel modular functions. In this paper, we determine the minimal polynomials of these units.
Strong tractability of multivariate integration using quasi–Monte Carlo algorithms
Authors: Wang Xiaoqun
Published: February 2003

We study quasi–Monte Carlo algorithms based on low discrepancy sequences for multivariate integration. We consider the problem of how the minimal number of function evaluations needed to reduce the worst-case error from its initial error by a factor of

ε
\varepsilon

depends on

ε

−
1

{\varepsilon }^{-1}

and the dimension

s
s

. Strong tractability means that it does not depend on

s
s

and is bounded by a polynomial in

ε

−
1

{\varepsilon }^{-1}

. The least possible value of the power of

ε

−
1

{\varepsilon }^{-1}

is called the

ε
\varepsilon

-exponent of strong tractability. Sloan and Woźniakowski established a necessary and sufficient condition of strong tractability in weighted Sobolev spaces, and showed that the

ε
\varepsilon

-exponent of strong tractability is between 1 and 2. However, their proof is not constructive. In this paper we prove in a constructive way that multivariate integration in some weighted Sobolev spaces is strongly tractable with

ε
\varepsilon

-exponent equal to 1, which is the best possible value under a stronger assumption than Sloan and Woźniakowski’s assumption. We show that quasi–Monte Carlo algorithms using Niederreiter’s

(
t
,
s
)

(t,s)

-sequences and Sobol sequences achieve the optimal convergence order

O
(

N

−
1
+
δ

)

O(N^{-1+\delta })

for any

δ
>
0

\delta >0

independent of the dimension with a worst case deterministic guarantee (where

N
N

is the number of function evaluations). This implies that strong tractability with the best

ε
\varepsilon

-exponent can be achieved in appropriate weighted Sobolev spaces by using Niederreiter’s

(
t
,
s
)

(t,s)

-sequences and Sobol sequences.
On the linear independence measure of logarithms of rational numbers
Authors: Wu Qiang
Published: February 2003

In this paper we give a general theorem on the linear independence measure of logarithms of rational numbers and, in particular, the linear independence measure of

1
,
log
⁡
2
,
log
⁡
3
,
log
⁡
5

1,\log 2, \log 3, \log 5

and of

1
,
log
⁡
2
,
log
⁡
3
,
log
⁡
5
,
log
⁡
7

1,\log 2, \log 3, \log 5, \log 7

. We also give a method to search for polynomials of smallest norm on a real interval

[
a
,
b
]

[a,b]

which may be suitable for computing or improving the linear independence measure of logarithms of rational numbers.
The class number one problem for some non-abelian normal CM-fields of degree 48
Authors: Chang Ku-Young , Kwon Soun-Hi
Published: February 2003

We prove that there is precisely one normal CM-field of degree 48 with class number one which has a normal CM-subfield of degree 16: the narrow Hilbert class field ofQ(5,101,θ)\mathbb {Q}(\sqrt {5}, \sqrt {101}, \theta )withθ3−θ2−5θ−1=0\theta ^3 - \theta ^2 -5 \theta -1=0.
The smallest solutions to the diophantine equation 𝑥⁶+𝑦⁶=𝑎⁶+𝑏⁶+𝑐⁶+𝑑⁶+𝑒⁶
Authors: Resta Giovanni , Meyrignac Jean-Charles
Published: February 2003

In this paper we discuss a method used to find the smallest nontrivial positive integer solutions to

a
1
6

+

a
2
6

=

b
1
6

+

b
2
6

+

b
3
6

+

b
4
6

+

b
5
6

a_1^6+a_2^6=b_1^6+b_2^6+b_3^6+b_4^6+b_5^6

. The method, which is an improvement over a simple brute force approach, can be applied to search the solution to similar equations involving sixth, eighth and tenth powers.
Near optimality of the sinc approximation
Authors: Sugihara Masaaki
Published: February 2003

Near optimality of the sinc approximation is established in a variety of spaces of functions analytic in a strip region about the real axis, each space being characterized by the decay rate of their elements (functions) in the neighborhood of the infinity.
Nontrivial Galois module structure of cyclotomic fields
Authors: Conrad Marc , Replogle Daniel
Published: February 2003

We say a tame Galois field extension

L

/

K

L/K

with Galois group

G
G

has trivial Galois module structure if the rings of integers have the property that

O

L

\mathcal {O}_{L}

is a free

O

K

[
G
]

\mathcal {O}_{K}[G]

-module. The work of Greither, Replogle, Rubin, and Srivastav shows that for each algebraic number field other than the rational numbers there will exist infinitely many primes

l
l

so that for each there is a tame Galois field extension of degree

l
l

so that

L

/

K

L/K

has nontrivial Galois module structure. However, the proof does not directly yield specific primes

l
l

for a given algebraic number field

K
.

K.

For

K
K

any cyclotomic field we find an explicit

l
l

so that there is a tame degree

l
l

extension

L

/

K

L/K

with nontrivial Galois module structure.
Newman polynomials with prescribed vanishing and integer sets with distinct subset sums
Authors: Borwein Peter , Mossinghoff Michael
Published: February 2003

We study the problem of determining the minimal degreed(m)d(m)of a polynomial that has all coefficients in{0,1}\{0,1\}and a zero of multiplicitymmat−1-1. We show that a greedy solution is optimal precisely whenm≤5m\leq 5, mirroring a result of Boyd on polynomials with±1\pm 1coefficients. We then examine polynomials of the form∏e∈E(xe+1)\prod _{e\in E} (x^e+1), whereEEis a set ofmmpositive odd integers with distinct subset sums, and we develop algorithms to determine the minimal degree of such a polynomial. We determine thatd(m)d(m)satisfies inequalities of the form2m+c1m≤d(m)≤10396⋅2m+c22^m + c_1 m \leq d(m) \leq \frac {103}{96}\cdot 2^m + c_2. Last, we consider the related problem of finding a set ofmmpositive integers with distinct subset sums and minimal largest element and show that the Conway-Guy sequence yields the optimal solution form≤9m\leq 9, extending some computations of Lunnon.
Effects of Water Flow Rate on Fatigue Life of Carbon Steel in Simulated LWR Environment Under Low Strain Rate Conditions
Authors: Hirano Akihiko , Yamamoto Michiyoshi , Sakaguchi Katsumi , Shoji Tetsuo , Iida Kunihiro
Published: February 2003

The flow rate of water flowing on a steel surface is considered to be one of the important factors strongly influencing the fatigue life of the steel, because the water flow produces difference in the local environmental conditions. The effect of the water flow rate on the fatigue life of a carbon steel was thus investigated experimentally. Fatigue testing of the carbon steel was performed at 289°C for various dissolved oxygen contents (DO) of less than 0.01 and 0.05, 0.2, and 1 ppm, and at various water flow rates. Three different strain rates of 0.4, 0.01, and 0.001 %/s were used in the fatigue tests. At the strain rate of 0.4 %/s, no significant difference in fatigue life was observed under the various flow rate conditions. On the other hand, at 0.01 %/s, the fatigue life increased with increasing water flow rate under all DO conditions, such that the fatigue life at a 7 m/s flow rate was about three times longer than that at a 0.3 m/s flow rate. This increase in fatigue life is attributed to increases in the crack initiation life and small-crack propagation life. The major mechanism producing these increases is considered to be the flushing effect on locally corrosive environments at the surface of the metal and in the cracks. At the strain rate of 0.001 %/s, the environmental effect seems to be diminished at flow rates higher than 0.1 m/s. This behavior does not seem to be explained by the flushing effect alone. Based on this experimental evidence, it was concluded that the existing fatigue data obtained for carbon steel under stagnant or relatively low flow rate conditions may provide a conservative basis for fatigue life evaluation. This approach seems useful for characterizing fatigue life evaluation by expressing increasing fatigue life in terms of increasing water flow rate.
Elasticity Solutions for Laminated Orthotropic Cylindrical Shells Subjected to Localized Longitudinal and Circumferential Moments
Authors: Bhaskar K. , Ganapathysaran N.
Published: February 2003

The purpose of this work is to present baseline elasticity solutions for laminated composite shells subjected to localized moments. For simply supported cross-ply cylindrical shells, the problem reduces to one of coupled ordinary differential equations which are solved in terms of Taylor’s series. Results, in the form of tables and graphs, are presented for the cases of longitudinal and circumferential moments. These results would be very useful for judging the accuracy of approximate two-dimensional shell theories. They are used herein to study the errors of a shell theory based on the classical Love-Kirchhoff hypothesis.
Prediction of Crack Initiation Direction for Surface Flaws Under Biaxial Loading
Authors: Seibi Abdennour C. , Zamrik Sam Y.
Published: February 2003

This paper presents a simple method based on the strain energy density factor ΔS to study the fatigue characteristics of rhombic plates with induced angled flaws under biaxial stress field. The paper discusses in detail the procedures followed to predict the fracture crack initiation angle, θo, as a function of induced crack angle, β, the path of the crack trajectory at the initial stage of fracture and develop an expression for the crack growth rate. This method assumes that the crack extends in a radial direction and that the initial fracture crack angle, θo, is obtained by maximizing the hoop stress along a circumference of a radius r. Expressions for the stress-state near the crack tip were developed for computing the crack trajectory and the strain energy density factor. The crack trajectory path was estimated by computing the new values of the crack angle and a fictitious crack length. These computed values were in turn used to determine the strain energy density factor. The developed method revealed two important observations: i) The crack trajectory was in close agreement with the experimental data for the first 20% of the lifetime to failure, ii) the crack propagation rate is dependent on the crack angle using the stress intensity factor and exhibited no variation with respect to the crack angle when the strain energy density factor is used.