bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐resolution atmospheric profiling using combined spaced antenna and range imaging techniques
Authors: Yu T.‐Y. , Brown W. O. J.
Published: February 2004

A novel approach to high‐resolution wind profiling is presented using spaced antenna (SA) and range imaging (RIM) simultaneously. RIM was developed recently to improve the range resolution of pulsed radar by transmitting multiple frequencies. In this work, SA techniques are used to analyze RIM‐synthesized signals and obtain high‐resolution profiles of three‐dimensional wind field. This high‐resolution technique is termed RIM‐SA. Simulation results demonstrate the feasibility of RIM‐SA to measure wind shears embedded within the radar volume. The applications of RIM‐SA in the atmospheric boundary layer and lower free troposphere are demonstrated using the multiple antenna profiler radar (MAPR) of National Center for Atmospheric Research (NCAR). High‐resolution profiles using RIM‐SA are shown to be consistent with profiles measured by a radiosonde and MAPR using a single frequency and short pulse.
Characterizing the Earth's outer Van Allen zone using a radiation belt content index
Authors: Baker D. N. , Kanekal S. G. , Blake J. B.
Published: February 2004

We have utilized knowledge acquired from near‐Earth spacecraft missions to construct a “radiation belt content” (RBC) index. This index sums radiation belt electron fluxes above several chosen threshold energies (most commonly, E > 2 MeV) and over the range of magnetic L shells 2.5 ≤ L ≤ 6.5. The method takes account of pitch angle distribution effects and magnetic flux tube properties. As constructed, the RBC index gives a simple, robust, and readily utilized daily estimate of the total number of electrons throughout the entire outer Van Allen radiation belt. We show correlative comparisons with concurrent solar wind parameters, geomagnetic indices, and geostationary orbit (GOES) data sets. We also examine statistical and recurrence characteristics of the RBC index itself. Results are compared with some of the orbit‐integrated dose results from the Highly Elliptical Orbit (HEO) satellite 1997‐068 that covers the same L range. The correlation of the RBC index with various spacecraft data clearly illustrates the remarkable coherence of the outer Van Allen radiation belt previously described, for example, by Kanekal et al. [2001]. Although the RBC index may be viewed as suppressing much of the spatial information content of the direct electron measurements in the outer trapping zone, it nonetheless gives a useful tool for statistical and time series analysis. The utilization of such a long‐term, homogeneous index for space weather purposes is suggested.
Holocene to Pliocene tectonic evolution of the region offshore of the Los Angeles urban corridor, southern California
Authors: Bohannon Robert G. , Gardner James V. , Sliter Ray W.
Published: February 2004

Quaternary tectonism in the coastal belt of the Los Angeles urban corridor is diverse. In this paper we report the results of studies of multibeam bathymetry and a network of seismic reflection profiles that have been aimed at deciphering the diverse tectonism and at evaluating the relevance of published explanations of the region's tectonic history. Rapid uplift, subsidence in basins, folds and thrusts, extensional faulting, and strike‐slip faulting have all been active at one place or another throughout the Quaternary Period. The tectonic strain is reflected in the modern physiography at all scales. Los Angeles (LA) Basin has filled from a deep submarine basin to its present condition with sediment impounded behind a large sill formed behind uplifts near the present shoreline. Newport trough to the south‐southeast of LA Basin also accumulated a large volume of sediment, but remained at midbathyal depths throughout the Period. There is little or no evidence of Quaternary extensional tectonism in either basin although as much as 6 km of subsidence, which mainly occurred by sagging, has been recorded in places since the middle Miocene. The uplifts include folded and thrust faulted terranes in the Palos Verdes Hills and the shelves of Santa Monica and San Pedro Bays. The uplifted areas have been shortened in a southwest‐northeast direction by 10% or slightly more, and some folds are reflected in the bathymetry. Two large adjacent midbathyal basins, Santa Monica and San Pedro, show strong evidence of subsidence and slight west‐northwest extension (10%) during the same time folding was taking place in the uplifts. The tectonic boundaries between uplifts and basins are folded, normal faulted, reverse‐faulted, and strike‐slip faulted depending on location. The rapid Quaternary uplift and subsidence, along with the filling of LA Basin, have produced a reversal in the regional physiography. In the early Pliocene, LA Basin was a submarine deep, Palos Verdes and the shelves comprised a northeast basin slope, and the present offshore basins and Catalina Island formed an emergent or shallowly submerged shelf. Since extensional, compressional, and lateral strains are all locally in evidence, simple notions that this part of southern California underwent a change from Miocene transtension to Quaternary transpression fail to explain our observations.
Soil moisture retrieval during the Southern Great Plains Hydrology Experiment 1999: A comparison between experimental remote sensing data and operational products
Authors: Drusch Matthias , Wood Eric F. , Gao H. , Thiele Ariane
Published: February 2004

Soil moisture images for the Southern Great Plains Hydrology Experiment (SGP99) were derived from airborne passive microwave measurements obtained from the electronically scanned thinned array radiometer (ESTAR) and the polarimetric scanning radiometer (PSR) at L‐band and C‐band, respectively. In order to mimic operational products, a robust retrieval method is chosen and the corrections for vegetation and surface roughness are based on average values from the literature. Validation against field measurements results in root‐mean‐square errors and biases of 2.9% and 4.2% in volumetric soil moisture for the ESTAR data set and 4.6% and 6.0% for the PSR product. For this sparsely vegetated experiment region, the quality of the C‐band derived soil moisture is therefore comparable to the corresponding L‐band product. The accuracies of the operational data sets, namely, the European Centre for Medium‐Range Weather Forecasts (ECMWF) 40 year reanalysis product (ERA40) and the European Remote Sensing Satellite (ERS) scatterometer derived soil moisture, are quantified based on the high‐resolution PSR soil moisture images for the SGP99 region. The ERA40 reanalysis comprises soil moisture data for four soil layers at the T159 spectral resolution. The top 7 cm layer soil moisture product is in reasonable agreement with the C‐band derived soil moisture data sets. Temporal and spatial patterns are well represented, but a significant wet bias of up to 14.4% (ERA40) is present in dry conditions. In order to evaluate the quality of the operational data sets on a longer temporal timescale, in situ soil moisture measurements at the Little Washita National Oceanic and Atmospheric Administration/Atmospheric Turbulence and Diffusion Division (NOAA/ATDD) site are used to analyze time series for June 1997 to December 1998. The temporal evolution of soil moisture is captured reasonably well by the ERA40 product and the ERS scatterometer derived surface soil moisture data set. RMS errors were found to be 5.6% and 5.7%, respectively. The study shows that passive microwave remote sensing has the potential to improve operational products.
Nonadiabatic unimolecular reaction kinetic theory based on l th-order semi-Markov model
Authors: Kawano Akio , Takahashi Osamu , Saito Ko
Published: February 2004

We present a microcanonical kinetic theory, which we refer to as the lth-order semi-Markov phase space theory (SMl-PST), for nonadiabatic unimolecular dissociations dominated by standard surface hopping dynamics. In this theory, reaction dynamics is considered as a stochastic transport, which is described as an lth-order Markov chain, among cells produced from partition of the available phase space. Kinetic equations are derived by importing residence time of stay cells as a random variable into the Markov chain. An efficient method to determine the parameters of the kinetic equations is developed, which is made up of Monte Carlo phase space integration and short-time trajectory calculations. As a test calculation, the SMl-PST has been applied to a model system for the predissociation of collinear N2O. We show that the SMl-PST works well, giving rate coefficients of much better accuracy than conventional statistical theory and of comparable accuracy to standard trajectory calculations with a lower computational effort.
Hamiltonians separable in Cartesian coordinates and third-order integrals of motion
Authors: Gravel Simon
Published: February 2004

We present in this article all Hamiltonian systems in E(2) that are separable in Cartesian coordinates and that admit a third-order integral, both in quantum and in classical mechanics. Many of these superintegrable systems are new, and it is seen that there exists a relation between quantum superintegrable potentials, invariant solutions of the Korteweg–de Vries equation and the Painlevé transcendents.
Bound states in two spatial dimensions in the noncentral case
Authors: Martin André , Wu Tai Tsun
Published: February 2004

We derive a bound on the total number of negative energy bound states in a potential in two spatial dimensions by using an adaptation of the Schwinger method to derive the Birman–Schwinger bound in three dimensions. Specifically, counting the number of bound states in a potential gV for g=1 is replaced by counting the number of gi’s for which zero energy bound states exist, and then the kernel of the integral equation for the zero-energy wave functon is symmetrized. One of the keys of the solution is the replacement of an inhomogeneous integral equation by a homogeneous integral equation.
Soliton solutions on noncommutative orbifold T2/Z4
Authors: Deng Hui , Hou Bo-Yu , Shi Kang-Jie , Yang Zhan-Ying , Yue Rui-Hong
Published: February 2004

In this paper, we explicitly construct a series of projectors on integrable noncommutative orbifold T2/Z4 by extended GHS construction. They include integration of two arbitary functions with Z4 symmetry. Our expression possesses manifest Z4 symmetry. It is proven that the expression includes all projectors with minimal trace and in their standard expansions, the eigenvalue functions of coefficient operators are continuous with respect to the arguments k and q. Based on the integral expression, we alternately show the derivative expression in terms of the similar kernal to the integral one. Since projectors correspond to soliton solutions of the field theory on the noncommutative orbifold, we thus present a series of corresponding solitons.
Casimir energy inside a cavity with triangular cross section
Authors: Ahmedov H. , Duru I. H.
Published: February 2004

For a certain class of triangles (with angles proportional to π/N, N⩾3) we formulate an image method by making use of the group GN generated by reflections with respect to the three lines which form the triangle under consideration. We formulate the regularization procedure by classification of subgroups of GN and corresponding fixed points in the triangle. We then also calculate Casimir energy for a cavity of infinite height with triangular cross section for scalar massless fields. More detailed calculation is given for odd N.
Mathematical properties of a new Levin-type sequence transformation introduced by Čı́žek, Zamastil, and Skála. I. Algebraic theory
Authors: Weniger Ernst Joachim
Published: February 2004

Čı́žek, Zamastil, and Skála [J. Math. Phys. 44, 962–968 (2003)] introduced in connection with the summation of the divergent perturbation expansion of the hydrogen atom in an external magnetic field a new sequence transformation which uses as input data not only the elements of a sequence {sn}n=0∞ of partial sums, but also explicit estimates {ωn}n=0∞ for the truncation errors. The explicit incorporation of the information contained in the truncation error estimates makes this and related transformations potentially much more powerful than, for instance, Padé approximants. Special cases of the new transformation are sequence transformations introduced by Levin [Int. J. Comput. Math. B 3, 371–388 (1973)] and Weniger [Comput. Phys. Rep. 10, 189–371 (1989), Secs. 7–9; Numer. Algor. 3, 477–486 (1992)] and also a variant of Richardson extrapolation [Philos. Trans. R. Soc. London, Ser. A 226, 299–349 (1927)]. The algebraic theory of these transformations—explicit expressions, recurrence formulas, explicit expressions in the case of special remainder estimates, and asymptotic order estimates satisfied by rational approximants to power series—is formulated in terms of hitherto unknown mathematical properties of the new transformation introduced by Čı́žek, Zamastil, and Skála. This leads to a considerable formal simplification and unification.
The irreducible unitary representations of the extended Poincaré group in (1+1) dimensions
Authors: de Mello R. O. , Rivelles V. O.
Published: February 2004

We prove that the extended Poincaré group in (1+1) dimensions P̄ is non-nilpotent solvable exponential, and therefore that it belongs to type I. We determine its first and second cohomology groups in order to work out a classification of the two-dimensional relativistic elementary systems. Moreover, all irreducible unitary representations of P̄ are constructed by the orbit method. The most physically interesting class of irreducible representations corresponds to the anomaly-free relativistic particle in (1+1) dimensions, which cannot be fully quantized. However, we show that the corresponding coadjoint orbit of P̄ determines a covariant maximal polynomial quantization by unbounded operators, which is enough to ensure that the associated quantum dynamical problem can be consistently solved, thus providing a physical interpretation for this particular class of representations.
An extension of the classical theory of algebraic invariants to pseudo-Riemannian geometry and Hamiltonian mechanics
Authors: McLenaghan Raymond G. , Smirnov Roman G. , The Dennis
Published: February 2004

We develop a new approach to the study of Killing tensors defined in pseudo-Riemannian spaces of constant curvature that is ideologically close to the classical theory of invariants. The main idea, which provides the foundation of the new approach, is to treat a Killing tensor as an algebraic object determined by a set of parameters of the corresponding vector space of Killing tensors under the action of the isometry group. The spaces of group invariants and conformal group invariants of valence two Killing tensors defined in the Minkowski plane are described. The group invariants, which are the generators of the space of invariants, are applied to the problem of classification of orthogonally separable Hamiltonian systems defined in the Minkowski plane. Transformation formulas to separable coordinates expressed in terms of the parameters of the corresponding space of Killing tensors are presented. The results are applied to the problem of orthogonal separability of the Drach superintegrable potentials.
Band spectroscopy of colloidal photonic crystal films
Authors: Mı́guez H. , Kitaev V. , Ozin G. A.
Published: February 2004

Here we report on the optical properties associated with photonic bands of three-dimensional photonic colloidal crystals. Optical spectroscopy analysis shows fluctuations of the transmitted and reflected light intensity in photon frequency regions where no stop bands open up. The different optical features observed at low and high photon energy ranges are analyzed in terms of the band structure of the crystal. A relationship is found between dispersion of the bands and the features observed experimentally. On these premises, we show it is possible to map the higher-energy band region along nonprincipal directions of the first Brillouin zone by transmission spectroscopy.
Soft molding lithography of conjugated polymers
Authors: Pisignano Dario , Persano Luana , Cingolani Roberto , Gigli Giuseppe , Babudri Francesco , Farinola Gianluca M. , Naso Francesco
Published: February 2004

We report on the nanopatterning of conjugated polymers by soft molding, and exploit the glass transition of the organic compound in conformal contact with an elastomeric element. We succeeded in printing different compounds with resolution down to 300 nm at temperatures up to 300 °C in vacuum. No significant variation of the photoluminescence (PL) spectra nor heavy degradation of the PL quantum yield was observed after the lithography process. Based on the high resolution achieved and on the well-retained luminescence properties of the patterned compounds, we conclude that high-temperature soft lithography is a valid, flexible and straightforward technique for one-step realization of organic-based devices.
Contextual approach to quantum mechanics and the theory of the fundamental prespace
Authors: Khrennikov Andrei
Published: February 2004

We constructed a Hilbert space representation of a contextual Kolmogorov model. This representation is based on two fundamental observables—in the standard quantum model these are the position and momentum observables. This representation has all distinguishing features of the quantum model. Our representation is not standard model with hidden variables. In particular, this is not a reduction of the quantum model to the classical one.
Equal rank embedding and its related construction to superconformal field theories
Authors: Pengpan Teparksorn
Published: February 2004

The lowest lines of Euler multiplets corresponding to massless and massive supersymmetric representations are classified. At the level of representation theory, the Euler multiplets constructed by the GKRS method of equal rank embedding of semisimple complex Lie algebras are found to be the intrinsic ground states of superconformal field theories according to the Kazama–Suzuki construction.
On linearity of separating multiparticle differential Schrödinger operators for identical particles
Authors: Svetlichny George
Published: February 2004

We show that hierarchies of differential Schrödinger operators for identical particles which are separating for the usual (anti-)symmetric tensor product, are necessarily linear, and offer some speculations on the source of quantum linearity.
Nb–Au bilayer hot-electron bolometers for low-noise THz heterodyne detection
Authors: Siddiqi I. , Prober D. E.
Published: February 2004

The sensitivity of present Nb diffusion-cooled hot-electron bolometer (HEB) mixers is not quantum limited, and can be improved by reducing the superconducting transition temperature TC. Lowering TC reduces thermal fluctuations, resulting in a decrease of the mixer noise temperature TM. However, lower TC mixers have reduced dynamic range and saturate more easily due to background noise. We present 30 GHz microwave measurements on a bilayer HEB system, Nb–Au, in which TC can be tuned with Au layer thickness to obtain the maximum sensitivity for a given noise background. These measurements are intended as a guide for the optimization of THz mixers. Using a Nb–Au mixer with TC=1.6 K, we obtain TM=50 K with 2 nW of local oscillator (LO) power. Good mixer performance is observed over a wide range of LO power and bias voltage and such a device should not exhibit saturation in a THz receiver.
Amplified spontaneous emission under optical pumping from an organic semiconductor laser structure equipped with transparent carrier injection electrodes
Authors: Yamamoto Hidetoshi , Oyamada Takahito , Sasabe Hiroyuki , Adachi Chihaya
Published: February 2004

We succeeded in observing amplified spontaneous emissions (ASEs) from an organic semiconductor laser structure equipped with transparent carrier injection electrodes under optical pumping. We employed a transparent indium-tin-oxide (ITO) anode and cathode, which significantly minimized light propagation loss compared with that in conventional metal electrodes. In particular, we incorporated an ultrathin MgAg layer between the organic electron transport layer and ITO cathode to enhance electron injection efficiency, while maintaining low light propagation loss, and also to protect the organic layer from plasma damage when forming the ITO. By optically pumping the ITO [30 nm]/4,4′-bis[N(1-naphthyl)-N-phenyl-amino]biphenyl (α-NPD) [20 nm]/ 4,4′-di(N-carbazolyl)biphenyl (CBP) doped with 1,4-dimethoxy-2,5-bis[p-{N-phenyl-N(m-tolyl)amino}styryl]benzene (BSB) [70 nm]/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) [20 nm]/tris-(8-hydroxy-quinoline)aluminum (Alq3) [20 nm]/MgAg [2.5 nm]/ITO [20 nm] device, a low ASE threshold of Eth=5.1±1.0 μJ/cm2 with a full width at half maximum of 11 nm was obtained under optical excitation. We also evaluated electrical pumping with this device. Although we observed high efficiency electroluminescence at an external quantum efficiency (ηext) of 3.6% at a low current density of J=0.1 mA/cm2, a rapid decrease in ηext was observed with an increase in current density, suggesting the presence of large exciton-polaron annihilation.
Charge storage and photoluminescence characteristics of silicon oxide embedded Ge nanocrystal trilayer structures
Authors: Das K. , NandaGoswami M. , Mahapatra R. , Kar G. S. , Dhar A. , Acharya H. N. , Maikap S. , Lee Je-Hun , Ray S. K.
Published: February 2004

Metal-oxide-semiconductor capacitors with a trilayer structure consisting of the cap gate oxide, sputtered SiGe layers and thermally grown tunnel oxide were fabricated on p-Si substrates. The trilayer structures were rapid thermal annealed at 1000 °C in nitrogen atmosphere for different durations. Cross-sectional transmission electron micrographs revealed the complete isolation of Ge nanocrystals in the sandwiched structure annealed for a longer duration. The optical and charge storage characteristics of trilayer structures were studied through photoluminescence spectroscopy and capacitance-voltage measurements, respectively. Under optimized annealing conditions, an enhancement of the charge storage capability of nanocrystals was observed in agreement with the optical emission characteristics.
Abiotic synthesis of high-molecular-weight organics from an inorganic gas mixture of carbon monoxide, ammonia, and water by 3 MeV proton irradiation
Authors: Takano Yoshinori , Ohashi Akihiro , Kaneko Takeo , Kobayashi Kensei
Published: February 2004

The abiotic formation of high-molecular-weight organics from an inorganic gas mixture of carbon monoxide, ammonia, and water as a result of 3 MeV proton irradiation from a Van de Graaff accelerator was experimentally verified. The inorganic gas mixture was simulated for representative of interstellar medium. The irradiation products included amino acid (AA) precursors, and the molecular weight distribution ranged from several hundred to a maximum of 3000 Da. Both proteinous and nonproteinous AAs were detected after acid hydrolysis. Thus, the primary irradiation products were not free AA analogs, but were AA precursors having high molecular weight. The present results have significant implications regarding the extraterrestrial origins of AA precursors, such as meteoritic organic compounds and the organic composition of interstellar dust particles.
Control of polytype formation in silicon carbide heteroepitaxial films by pulsed-laser deposition
Authors: Kusumori Takeshi , Muto Hachizo , Brito Manuel E.
Published: February 2004

Control of silicon carbide (SiC) polytype formation has been achieved. 3C, 2H, and 4H SiC heteroepitaxial films are fabricated on a sapphire (0001) substrate at a low temperature of 1100 °C using a pulsed-laser deposition (PLD) method. Images made by transmission electron microscopy clearly show that each film consists of a single polytype. The polytype of the SiC films can be changed by varying just two easily controlled parameters: the laser pulse frequency and the substrate temperature. These results suggest that precise control of growth conditions, which is essential for polymorphic materials, is possible using the PLD method.
Imaging scanning tunneling microscope-induced electroluminescence in plasmonic corrals
Authors: Egusa Shunji , Liau Yish-Hann , Scherer Norbert F.
Published: February 2004

An approach to image localized and propagating surface plasmon (SP) modes is introduced. It is shown that scanning tunneling microscope (STM)-electroluminescence, the radiative decay of SPs induced by inelastically tunneling electrons, observed in Fourier space yields distinct features that reflect the degree of delocalization and spatial distribution of SP modes. The propagating SP is isolated from the localized mode by way of this Fourier space imaging approach. Furthermore, a cylindrically symmetric spatial interference pattern is obtained when the STM-induced plasmon is created within a circular “corral” boundary condition.
Enhancement of visible second-harmonic generation in epitaxial GaN-based two-dimensional photonic crystal structures
Authors: Vecchi Gabriele , Torres Jérémi , Coquillat Dominique , Le Vassor d’Yerville Marine , Malvezzi Andrea Marco
Published: February 2004

Second-harmonic (SH) radiation generated in reflection is measured from the surface of a two-dimensional triangular photonic crystal in a GaN layer. A very large SH enhancement is observed when the incident radiation is resonant with a leaky photonic mode. The potential of second-harmonic generation as a tool for photonic band mapping is also envisaged. The extended transparency window of III-nitride wide band gap semiconductors coupled with large nonlinearities is an appealing feature pointing toward light control and manipulation in photonic structures.
A pressure-tuned blue-violet InGaN/GaN laser diode grown on bulk GaN crystal
Authors: Suski T. , Franssen G. , Perlin P. , Bohdan R. , Bercha A. , Adamiec P. , Dybala F. , Trzeciakowski W. , Prystawko P. , Leszczyński M. , Grzegory I. , Porowski S.
Published: February 2004

We demonstrate efficient wavelength tuning by means of hydrostatic pressure of an InGaN/GaN laser diode grown on bulk GaN crystal. Energy shifts of the emitted light with pressure have been found to be about 36 meV/GPa, which are high magnitudes for nitride-based device structures. This result is interpreted as being indicative of efficient screening of built-in electric fields in the studied device. Furthermore, the threshold current of the laser diode was found to be independent of applied pressure. The high magnitude of the pressure coefficient allowed for the achievement of a laser tuning range of up to 10 nm in the blue/violet region, using compact pressure equipment.
Strain-tunable silicon photonic band gap microcavities in optical waveguides
Authors: Wong Chee Wei , Rakich Peter T. , Johnson Steven G. , Qi Minghao , Smith Henry I. , Ippen Erich P. , Kimerling Lionel C. , Jeon Yongbae , Barbastathis George , Kim Sang-Gook
Published: February 2004

We report the design, device fabrication, and measurements of tunable silicon photonic band gap microcavities in optical waveguides, using direct application of piezoelectric-induced strain to the photonic crystal. We show, through first-order perturbation computations and experimental measurements, a 1.54 nm shift in cavity resonances at 1.56 μm wavelengths for an applied strain of 0.04%. The strain is applied through integrated piezoelectric microactuators. For operation at infrared wavelengths, we combine x-ray and electron-beam lithography with thin-film piezoelectric processing. This level of integration permits realizable silicon-based photonic chip devices, such as high-density optical filters, with active reconfiguration.
Carrier redistribution in organic/inorganic (poly(3,4-ethylenedioxy thiophene/poly(styrenesulfonate)polymer)-Si) heterojunction determined from infrared ellipsometry
Authors: Schubert M. , Bundesmann C. , Wenckstern H. v. , Jakopic G. , Haase A. , Persson N.-K. , Zhang F. , Arwin H. , Inganäs O.
Published: February 2004

Charge redistribution in organic/inorganic heterojunction between poly(3,4-ethylenedioxy thiophene)/poly(styrenesulfonate) polymer (PEDOT/PSS) is observed contact-less by infrared spectroscopic ellipsometry. Hole accumulation or depletion layer formation is detected according to the different work functions of n- and p-type silicon. Dielectric function, optical conductivity, sheet resistance, and vibration modes at wave numbers from 300 to 3000 cm−1 are determined for PEDOT/PSS thin films. We propose use of infrared ellipsometry for investigation of structure and free-charge-carrier properties in layered polymer device heterostructures.
Hydrogen–deuterium exchange in KD2PO4
Authors: Kucheyev S. O. , Felter T. E. , Siekhaus W. J. , Nelson A. J. , Hamza A. V.
Published: February 2004

Depth profiles of H1 and D2 in rapidly grown KD2xH2(1−x)PO4 single crystals are studied by elastic recoil detection analysis. Results show that, under ambient conditions, deuteration in the first ∼500 nm from the sample surface significantly decreases within the first several days after D2O surface polishing. This effect is attributed to deuterium–hydrogen exchange. The effective diffusion coefficient of this process is strongly dependent on both the degree of deuteration and the sample growth conditions. Physical mechanisms of D/H exchange are discussed.
Observation of spontaneous ordering in the optoelectronic material GaInNP
Authors: Su Y. K. , Wu C. H. , Hsu S. H. , Chang S. J. , Chen W. C. , Huang Y. S. , Hsu H. P.
Published: February 2004

We report a detailed structural and optical characterization of high-quality GaInNP films. These films were grown by gas-source molecular-beam epitaxy on GaAs (100) substrates. These epitaxial layers were then characterized by a high-resolution x-ray rocking curve (HRXRC) and photoluminescence (PL) measurements. With nitrogen incorporation, the PL peak redshifts, indicating bandgap reduction and the line-width broadening increases due to alloy scattering. The anisotropic properties of the polarized HRXRC and polarized piezoreflectance spectra are used to prove the spontaneous ordering in GaInP incorporating nitrogen. Furthermore, ordering-induced superlattice-like microstructure shown in high-resolution transmission electron microscope images is used to confirm the spontaneous ordering in Ga0.44In0.56NxP1−x epitaxial layers.
Direct transport imaging in planar structures
Authors: Haegel N. M. , Fabbri J. D. , Coleman M. P.
Published: February 2004

Direct imaging of transport behavior between planar contacts has been demonstrated in a scanning electron microscope, using an optical microscope and a high sensitivity charge coupled device to image the motion of free carriers in epitaxial GaAs. After generating charge at a fixed point, subsequent transport can be observed by imaging carrier recombination. Results as a function of applied electric field show excellent agreement to predicted Bessel function distributions for combined drift and diffusion from a point source. The approach can be applied to any luminescent material and allows for direct observation of transport across contacts and other internal boundaries.
Valence band structure and band alignment at the ZrO2/Si interface
Authors: Puthenkovilakam Ragesh , Chang Jane P.
Published: February 2004

X-ray photoelectron spectroscopy combined with first-principles simulations are used to determine the band alignments of ZrO2 thin films on silicon. Theoretical band offsets were calculated by simulating the ZrO2/Si interface by means of plane-wave pseudopotential calculations. Experimental band offsets were determined by measuring the core-level to valence-band maximum binding energy differences. Excellent agreement was obtained between the theoretical (3.5–3.9 eV) and experimental (3.65 eV) valence band offsets. Both theoretical and experimental analyses predict the conduction band offset to be ∼0.6–1.0 eV which indicates the intrinsic limitation of ZrO2 to be considered as a viable alternative gate dielectric.
Measurement of tunneling time via electron interferometry
Authors: Martinez J. C. , Polatdemir E.
Published: February 2004

After many decades, our understanding of the tunneling time across a barrier at the theoretical and experimental levels remains unsatisfactory and subject to debate. We describe an electron interference experiment by which the tunneling time across a symmetric potential barrier can be obtained from the phase shift introduced by the barrier to the interference pattern. We compare these phase shifts as predicted by three competing views of the tunneling time.
Chirality assignment of individual single-walled carbon nanotubes in carbon nanotube field-effect transistors by micro-photocurrent spectroscopy
Authors: Ohno Yutaka , Kishimoto Shigeru , Mizutani Takashi , Okazaki Toshiya , Shinohara Hisanori
Published: February 2004

We have proposed a possibility of chirality assignment of individual single-walled carbon nanotubes in nanotube field-effect transistors (FETs) by micro-photocurrent spectroscopy. The nanotube FETs were fabricated by utilizing position-controlled nanotube growth technique using alcohol chemical vapor deposition. Photocurrent signal that originated from a single single-walled carbon nanotube was obtained by using microscopic optical measurement system. A peak was observed at 1.73 eV in the photocurrent excitation spectrum. This corresponds to optical absorption by van Hove singularity of the nanotube with a diameter of ∼2 nm. Chirality of the nanotube in the nanotube FET was assigned to be (18, 10) by comparing the experimental results with theoretical calculation.
Influence of particle oxide coating on light scattering by submicron metal particles on silicon wafers
Authors: Kim Jung Hyeun , Ehrman Sheryl H. , Germer Thomas A.
Published: February 2004

We report the effect of room-temperature oxidation on scattering of 633 nm light by copper particles deposited on a silicon wafer. The results provide a validation for a theory of light scattering by coated particles on a substrate and establish the lifetime of these particles as light scattering standards to be on the order of a few months. The results also suggest that the room-temperature oxidation of copper particles proceeds in a continuous manner, rather than approaching an asymptotic thickness as found by Cabrera and Mott [Rep. Prog. Phys. 12, 163 (1948)] on copper films.
Enhancement of fracture toughness in nanostructured diamond–SiC composites
Authors: Zhao Yusheng , Qian Jiang , Daemen Luke L. , Pantea Cristian , Zhang Jianzhong , Voronin Georgiy A. , Zerda T. Waldek
Published: February 2004

We synthesized diamond–SiC nanocomposites with superhardness and greatly enhanced fracture toughness through a synthetic approach based on high-energy ball milling to form amorphous Si precursors followed by rapid reactive sintering at high pressure (P) and high temperature (T). We show how the simultaneous P–T application allows for better control of the reactive sintering of a nanocrystalline SiC matrix in which diamond crystals are embedded. The measured fracture toughness KIC of the synthesized composites has been enhanced greatly, as much as 50% from 8.2 to 12.0 MPa m1/2, as the crystal size of the SiC matrix decreases from 10 μm to 20 nm. Our result contradicts a commonly held belief of an inverse correlation between hardness and fracture toughness. We demonstrate the importance of nanostructure for the enhancement of mechanical properties of the composite materials.
Luminescence enhancement in Eu3+-doped α- and γ-Al2O3 produced by pressure-assisted low-temperature combustion synthesis
Authors: Ozuna O. , Hirata G. A. , McKittrick J.
Published: February 2004

Intense red luminescence in Eu3+-doped gamma (γ) and alpha (α) alumina (Al2O3) phosphors obtained by direct and indirect combustion synthesis at low-temperatures is reported. γ and α-(Al1−xEux)2O3 are easily produced by combustion synthesis at 280 °C in the range of x=0.001–0.06 at. %. The well-defined direct synthesis allows europium ions to incorporate into the α or γ alumina lattice in spite of the large size difference between these ions and the aluminum cations in Al2O3. These materials yield a strong fluorescence at room temperature due to f–f transition lines within Eu3+ (4f6) electron emission configuration. Furthermore, from luminescence measurements, it is deduced that Eu3+ occupy low-symmetry sites in the Al2O3 lattice.
Quadrimolecular recombination kinetics of photogenerated charge carriers in regioregular poly(3-alkylthiophene)/fullerene composites
Authors: Marumoto K. , Muramatsu Y. , Kuroda S.
Published: February 2004

The recombination kinetics of photogenerated charge carriers in composites of regioregular poly(3-alkylthiophene)s and C60 have been investigated by a transient response of light-induced electron spin resonance (LESR). The dependence of the prompt decay component on excitation-light intensity Iex shows that quadrimolecular recombination (QR) is dominant at higher Iex while bimolecular recombination is relatively important at lower Iex. The time decay of the LESR intensity is also well explained by the QR model. The temperature dependence of the QR rate constant clearly shows a crossover from hopping to tunneling behavior with decrease of temperature; the activation energy for the hopping of 0.10 eV is obtained.
Pseudo-periodic partitions of biological sequences
Authors: Li Lugang , Jin Renchao , Kok Poh-Lin , Wan Honghui
Published: February 2004

Motivation: Algorithm development for finding typical patterns in sequences, especially multiple pseudo-repeats (pseudo-periodic regions), is at the core of many problems arising in biological sequence and structure analysis. In fact, one of the most significant features of biological sequences is their high quasi-repetitiveness. Variation in the quasi-repetitiveness of genomic and proteomic texts demonstrates the presence and density of different biologically important information. It is very important to develop sensitive automatic computational methods for the identification of pseudo-periodic regions of sequences through which we can infer, describe and understand biological properties, and seek precise molecular details of biological structures, dynamics, interactions and evolution.

Results: We develop a novel, powerful computational tool for partitioning a sequence to pseudo-periodic regions. The pseudo-periodic partition is defined as a partition, which intuitively has the minimal bias to some perfect-periodic partition of the sequence based on the evolutionary distance. We devise a quadratic time and space algorithm for detecting a pseudo-periodic partition for a given sequence, which actually corresponds to the shortest path in the main diagonal of the directed (acyclic) weighted graph constructed by the Smith–Waterman self-alignment of the sequence. We use several typical examples to demonstrate the utilization of our algorithm and software system in detecting functional or structural domains and regions of proteins. A big advantage of our software program is that there is a parameter, the granularity factor, associated with it and we can freely choose a biological sequence family as a training set to determine the best parameter. In general, we choose all repeats (including many pseudo-repeats) in the SWISS-PROT amino acid sequence database as a typical training set. We show that the granularity factor is 0.52 and the average agreement accuracy of pseudo-periodic partitions, detected by our software for all pseudo-repeats in the SWISS-PROT database, is as high as 97.6%.

Availability: The program is available upon request from Honghui Wan and will be also available at http://www.mindgen.org
affy—analysis of Affymetrix GeneChip data at the probe level
Authors: Gautier Laurent , Cope Leslie , Bolstad Benjamin M. , Irizarry Rafael A.
Published: February 2004

Motivation: The processing of the Affymetrix GeneChip data has been a recent focus for data analysts. Alternatives to the original procedure have been proposed and some of these new methods are widely used.

Results: The affy package is an R package of functions and classes for the analysis of oligonucleotide arrays manufactured by Affymetrix. The package is currently in its second release, affy provides the user with extreme flexibility when carrying out an analysis and make it possible to access and manipulate probe intensity data. In this paper, we present the main classes and functions in the package and demonstrate how they can be used to process probe-level data. We also demonstrate the importance of probe-level analysis when using the Affymetrix GeneChip platform.
Hybrid simulation of cellular behavior
Authors: Kiehl Thomas R. , Mattheyses Robert M. , Simmons Melvin K.
Published: February 2004

Motivation: To be valuable to biological or biomedical research, in silico methods must be scaled to complex pathways and large numbers of interacting molecular species. The correct method for performing such simulations, discrete event simulation by Monte Carlo generation, is computationally costly for large complex systems. Approximation of molecular behavior by continuous models fails to capture stochastic behavior that is essential to many biological phenomena.

Results: We present a novel approach to building hybrid simulations in which some processes are simulated discretely, while other processes are handled in a continuous simulation by differential equations. This approach preserves the stochastic behavior of cellular pathways, yet enables scaling to large populations of molecules. We present an algorithm for synchronizing data in a hybrid simulation and discuss the trade-offs in such simulation. We have implemented the hybrid simulation algorithm and have validated it by simulating the statistical behavior of the well-known lambda phage switch. Hybrid simulation provides a new method for exploring the sources and nature of stochastic behavior in cells.

Supplementary information: The SBML file for the lambda phage tests will be made available at the OUP site.
A benchmark for Affymetrix GeneChip expression measures
Authors: Cope Leslie M. , Irizarry Rafael A. , Jaffee Harris A. , Wu Zhijin , Speed Terence P.
Published: February 2004

Motivation: The defining feature of oligonucleotide expression arrays is the use of several probes to assay each targeted transcript. This is a bonanza for the statistical geneticist, who can create probeset summaries with specific characteristics. There are now several methods available for summarizing probe level data from the popular Affymetrix GeneChips, but it is difficult to identify the best method for a given inquiry.

Results: We have developed a graphical tool to evaluate summaries of Affymetrix probe level data. Plots and summary statistics offer a picture of how an expression measure performs in several important areas. This picture facilitates the comparison of competing expression measures and the selection of methods suitable for a specific investigation. The key is a benchmark data set consisting of a dilution study and a spike-in study. Because the truth is known for these data, we can identify statistical features of the data for which the expected outcome is known in advance. Those features highlighted in our suite of graphs are justified by questions of biological interest and motivated by the presence of appropriate data.

Availability: In conjunction with the release of a graphics toolbox as part of the Bioconductor project (http://www.bioconductor.org), a webtool is available at http://affycomp.biostat.jhsph.edu. Supplemental material is available at http://www.biostat.jhsph.edu/~ririzarr/papers/suppaffycomp.pdf
Model-based methods for identifying periodically expressed genes based on time course microarray gene expression data
Authors: Luan Y. , Li H.
Published: February 2004

Motivation: The expressions of many genes associated with certain periodic biological and cell cycle processes such as circadian rhythm regulation are known to be rhythmic. Identification of the genes whose time course expressions are synchronized to certain periodic biological process may help to elucidate the molecular basis of many diseases, and these gene products may in turn represent drug targets relevant to those diseases.

Results: We propose in this paper a statistical framework based on a shape-invariant model together with a false discovery rate (FDR) procedure for identifying periodically expressed genes based on microarray time-course gene expression data and a set of known periodically expressed guide genes. We applied the proposed methods to the α-factor, cdc15 and cdc28 synchronized yeast cell cycle data sets and identified a total of 1010 cell-cycle-regulated genes at a FDR of 0.5% in at least one of the three data sets analyzed, including 89 (86%) of 104 known periodic transcripts. We also identified 344 and 201 circadian rhythmic genes in vivo in mouse heart and liver tissues with FDR of 10 and 2.5%, respectively. Our results also indicate that the shape-invariant model fits the data well and provides estimate of the common shape function and the relative phases for these periodically regulated genes.

Availability: Matlab programs are available on request from the authors.

Supplementary information:  http://dna.ucdavis.edu/~hli/period.html
Functional topology in a network of protein interactions
Authors: Pržulj N. , Wigle D.A. , Jurisica I.
Published: February 2004

Motivation: The building blocks of biological networks are individual protein–protein interactions (PPIs). The cumulative PPI data set in Saccharomyces cerevisiae now exceeds 78 000. Studying the network of these interactions will provide valuable insight into the inner workings of cells.

Results: We performed a systematic graph theory-based analysis of this PPI network to construct computational models for describing and predicting the properties of lethal mutations and proteins participating in genetic interactions, functional groups, protein complexes and signaling pathways. Our analysis suggests that lethal mutations are not only highly connected within the network, but they also satisfy an additional property: their removal causes a disruption in network structure. We also provide evidence for the existence of alternate paths that bypass viable proteins in PPI networks, while such paths do not exist for lethal mutations. In addition, we show that distinct functional classes of proteins have differing network properties. We also demonstrate a way to extract and iteratively predict protein complexes and signaling pathways. We evaluate the power of predictions by comparing them with a random model, and assess accuracy of predictions by analyzing their overlap with MIPS database.

Conclusions: Our models provide a means for understanding the complex wiring underlying cellular function, and enable us to predict essentiality, genetic interaction, function, protein complexes and cellular pathways. This analysis uncovers structure–function relationships observable in a large PPI network.

Supplementary information: We are placing the full predicted tables on the web page: http://www.cs.utoronto.ca/~juris/data/b03/SuppDataTables.zip