bluuebunny/crossref_metadata_2025 huggingface dataset:
Passive internal transport of aquatic organisms by waterfowl in Doñana, south‐west Spain
Authors: Figuerola Jordi , Green Andy J. , Santamaría Luis
Published: August 2003

Aim Waterbirds may play an important role in the maintenance of aquatic ecosystem biodiversity by transporting plants and invertebrate propagules between different wetlands. The aim of this study is to provide the first quantitative analysis of the transport of plant and animal propagules by a community of waterbirds.

Location Doñana marshes in south‐west Spain.

Methods We quantified the number of intact seeds and invertebrate eggs in 386 faecal samples from 11 migratory waterfowl species (10 ducks and coot), collected from 3 November to 3 December 1998 (when birds were arriving from further north), and 22–25 February 1999 (when birds were leaving Doñana).

Results Intact seeds of at least 7 plant genera, and invertebrate eggs (ephippia of at least 2 crustacea, statoblasts of at least 2 bryozoans and eggs of Corixidae) occurred in 65.6% of the faecal samples in early winter and 67.8% in late winter.

Main conclusions The abundance of different propagule types varied between waterfowl species in a seasonal and species specific manner, probably owing to differences in foraging strategies, bill and gut morphology, and seasonal shifts in propagule availability or distribution. Lamellar density was positively correlated with the abundance of intact propagules. Our results confirm that waterfowl play an important role in the dispersal of organisms in aquatic environments by internal transport. Wherever there is a propagule bank accessible to waterbirds, transport can occur even when propagule production and waterfowl movements do not overlap in time.
Latitudinal and altitudinal body size variation among north‐west European land snail species
Authors: Hausdorf Bernhard
Published: August 2003

Aim To investigate latitudinal and altitudinal patterns in body size variation among north‐west European land snail species, as well as factors influencing such patterns.

Location Latitudinal patterns were investigated in north‐west Europe from the British Isles and France in the west to Finland, Poland, Slovakia and Hungary in the east and from Norway in the north to France (with the exception of the Mediterranean part of the country), Switzerland, Austria and Hungary in the south. Altitudinal patterns were examined in the Alps in Austria and Switzerland.

Methods Data on latitudinal ranges of 366 north‐west European land snail species, on altitudinal ranges of 175 species from Austria and 150 species from Switzerland, and on their body sizes were used to test for the presence of interspecific latitudinal or altitudinal body size patterns. Four methods, Stevens’ method, the midpoint method, the across‐species method, and a phylogenetically controlled analysis (CAIC) were applied.

Results As a result of the predominance of some small bodied clades at higher latitudes and some large bodied clades at lower latitudes, body size of north‐west European land snails decreases significantly with increasing latitude. However, little of the body size variation across species is explained by latitude and the phylogenetically controlled analysis showed that the decrease of body size with increasing latitude is not a result of repeated and independent evolution of an association between body size and latitude in many clades. There is no significant correlation between body size of land snail species and altitude in the Alps although a negative correlation of body size and altitude is frequent within species.

Main conclusion If phylogenetic effects are controlled for, neither latitudinal nor altitudinal patterns in body size could be found. Bergmann's rule, which predicts a positive correlation between body size of species and latitude, could not be confirmed for north‐west European land snails.
Uphill shifts in distribution of butterflies in the Czech Republic: effects of changing climate detected on a regional scale
Authors: Konvicka Martin , Maradova Monika , Benes Jiri , Fric Zdenek , Kepka Pavel
Published: August 2003

Aim To assess whether altitude changes in the distribution of butterflies during the second half of the 20th century are consistent with climate warming scenarios.

Location The Czech Republic.

Methods Distributional data were taken from a recent butterfly distribution atlas, which maps all Czech butterflies using a grid of 10′ longitude to 6′ latitude, equivalent to about 11.1 × 12 km. Cell altitude was used as an independent variable, and altitudinal ranges of individual species (less migrants, extinct species, recent arrivals and extremely rare species) in 1950–80 vs. 1995–2001 and in 1950–80, 1981–94, 1995–2001 were compared using U‐tests and linear regressions.

Results Of 117 (U‐tests) and 119 (regressions) species, we found significant uphill increases in 15 and 12 species, respectively. The two groups were nested; none (U‐test) and one (regression) species showed a significant altitudinal decrease. Binomial tests of frequencies of signs of the U‐tests and regression coefficients, including nonsignificant ones, also showed that the increases prevailed. The mean and median of the significant shifts were 60 and 90 m, respectively, and the maximum shift per species was 148 m. The recording effort in individual time periods was not biased with respect to altitude.

Main conclusion Altitude shifts in the distribution of Czech butterflies are already detectable on the coarse scales of standard distribution maps. The increasing species do not show any consistent pattern in habitat affiliations, conservation status and mountain vs. nonmountain distribution, which renders climatic explanation as the most likely cause of the distributional shifts.
The Early Holocene treeline in the southern French Alps: new evidence from travertine formations
Authors: Ali Adam A. , Carcaillet Christopher , Guendon Jean‐Louis , Quinif Yves , Roiron Paul , Terral Jean‐Frédéric
Published: August 2003

Aims The present paper concerns the analysis of macro‐remains (plant imprints) from high altitude travertine deposits dating back to the early Holocene (9800 BP). Our results allow us to discuss treeline location and ecology, and to supplement previous data based on pollen from natural sediments and charcoal from natural soil.

Location The travertine under study is located in the Queyras massif, in the southern French Alps, along the Italian border. The site is situated on a south‐facing slope.

Methods The travertine deposit has been dated by 230Th/234U. Taxonomic identification of plant imprints was achieved by comparison of the morphology of fossil specimens with extant material.

Results Imprints of Pinus uncinata (cones and needles), broad‐leaved trees (Betula cf. pubescens, Populus tremula and Salix spp.), and unidentified trunks have been found. The plant assemblage records the existence at a high altitude (2200 m) of shade‐intolerant vegetation at around 9800 BP. Our data indicate that the treeline limit was at least 100 m higher than previously thought. The morphological features of the travertine, the plant assemblage and trunk diameters indicate that during the travertinization process, vegetation around the site was probably dense with tall upright trees.

Main conclusions Our data show that Pinus uncinata and broad‐leaved trees developed at 2200 m, while regional pollen analyses locate the treeline at lower altitudes. Different research methods appear to provide different results. Around 9800 BP tree regeneration and growth were made possible up to at least 2200 m a.s.l., probably as a result of warmer and wetter summers. Warmer conditions are inferred from the predicted increase in incoming solar radiation based on calculated orbital variations, and wetter conditions are inferred from the build‐up of the travertine.
Stretch‐Induced Injury Alters Mitochondrial Membrane Potential and Cellular ATP in Cultured Astrocytes and Neurons
Authors: Ahmed Syed M. , Rzigalinski Beverly A. , Willoughby Karen A. , Sitterding Heather A. , Ellis Earl F.
Published: August 2003

Abstract: Energy deficit after traumatic brain injury (TBI) may alter ionic homeostasis, neurotransmission, biosynthesis, and cellular transport. Using an in vitro model for TBI, we tested the hypothesis that stretch‐induced injury alters mitochondrial membrane potential (Δ?m) and ATP in astrocytes and neurons. Astrocytes, pure neuronal cultures, and mixed neuronal plus glial cultures grown on Silastic membranes were subjected to mild, moderate, and severe stretch. After injury, Δ?m was measured using rhodamine‐123, and ATP was quantified with a luciferin‐luciferase assay. In astrocytes, Δ?m dropped significantly, and ATP content declined 43‐52% 15 min after mild or moderate stretch but recovered by 24 h. In pure neurons, Δ?m declined at 15 min only in the severely stretched group. At 48 h postinjury, Δ?m remained decreased in severely stretched neurons and dropped in moderately stretched neurons. Intracellular ATP content did not change in any group of injured pure neurons. We also found that astrocytes and neurons release ATP extracellularly following injury. In contrast to pure neurons, Δ?m in neurons of mixed neuronal plus glial cultures declined 15 min after mild, moderate, or severe stretch and recovered by 24‐48 h. ATP content in mixed cultures declined 22‐28% after mild to severe stretch with recovery by 24 h. Our findings demonstrate that injury causes mitochondrial dysfunction in astrocytes and suggest that astrocyte injury alters mitochondrial function in local neurons.
A Multimode Fibre‐coupled Compact Optical Wavelength Meter based on Wollaston Prisms
Authors: O'Dwyer M. J. , Padgett M. J.
Published: August 2003

Abstract: We present a compact, portable, and mechanically robust instrument for measuring optical wavelength based on an arrangement of four Wollaston prisms that forms spatially localised fringes in a plane perpendicular to the optic axis. The wavelength is determined from the fringe period. After calibration, the instrument had an accuracy of c. 1 of 106, and was immune to fluctuations in output intensity of a light source of up to 10 dB.
Plastic Optical Fibre Sensors for Environmental Monitoring: Biofouling and Strain Applications
Authors: Wong Y. M. , Scully P. J. , Bartlett R. J. , Kuang K. S. C. , Cantwell W. J.
Published: August 2003

Abstract: Two long‐term environmental monitoring plastic optical fibre (POF) sensors are described, using light intensity modulation. An evanescent field biofouling sensor was developed and characterised with sensitivity ±0.007 refractive index units or 0.5% below n = 1.4 and ±0.002 refractive index units or 0.15% above n = 1.4. A tapered POF was developed and tested as a strain sensor, which demonstrated a significant proportion of excellent linearity and exhibited good agreement with measured strain values. The POF strain sensor appeared to be well‐behaved in that it showed little data scatter and was able to monitor strains up to 1.4% without failure. These two applications clearly demonstrate the potential POF sensors have for cheap, on‐line continuous environmental monitoring.
On the Industrial Applications of Moiré and Fringe Projection Techniques
Authors: Heredia‐Ortiz M. , Patterson E. A.
Published: August 2003

Abstract: This paper describes a set of tools and procedures based on the moiré and fringe projection techniques, which were developed to suit the requirements of real industrial situations. Particular attention was paid to flexibility, robustness and reliability, ease of use and calibration, and cost efficiency. Three case studies are being discussed in the paper. The first case describes a prototype shadow moiré instrument, which was developed for the detection of surface defects such as barely visible impact damage or corrosion inside lap‐joints, during maintenance inspections of aeronautical structures. The second case presents a portable instrument based on the fringe projection technique for the automatic, full‐field measurement of the shape and deformation of an arbitrary object. The system has applications ranging from deformation measurement of bioprostheses to correction of shape effects in the photoelastic analysis of complex aerospace components. Finally, a portable instrument was developed for the measurement of the location, orientation, shape and deformation of an arbitrary object, by combining the fringe projection technique with the laser spot technique for distance measurement. The system was used to assist in the integration of non‐destructive evaluation techniques throughout the life cycle of an aircraft.
Complete Fringe Order Determination in Digital Photoelasticity using Fringe Combination Matching
Authors: Jones I. A. , Wang P.
Published: August 2003

Abstract:  A novel approach is presented for obtaining the complete (integer and fractional) value of isochromatic parameters in digital imaging photoelasticity. This takes the form of a new variant on the existing technique of RGB photoelasticity, involving the matching of combinations of isochromatic fringe value measured on the three colour planes or channels rather than the usual RGB method of matching colour combinations directly. The new variant of RGB photoelasticity avoids the need for calibration for specific materials. This approach is demonstrated with real photoelastic data and compared with results from a conventional unwrapping process and from manual readings.
Local Cooling: A Therapy for Intractable Neocortical Epilepsy
Authors: Rothman Steven , Yang Xiao-Feng
Published: August 2003

Therapy for many of the neocortical epilepsies remains unsatisfactory. Recent research has demonstrated that focal cooling, using thermoelectric (Peltier) devices, may be capable of terminating, or possibly even preventing, some types of seizures.
The Ermanno–Bernoulli constants and representations of the complete symmetry group of the Kepler problem
Authors: Leach P. G. L. , Andriopoulos K. , Nucci M. C.
Published: August 2003

The expression of the components of the equation of motion of the classical Kepler problem in terms of the natural variables associated with the Ermanno–Bernoulli constants leads naturally to the same equations as are obtained by the technique of reduction of order developed by Nucci [J. Math. Phys. 37, 1772 (1996)], reported by Nucci and Leach [J. Math. Phys. 42, 746 (2001)]. Three representations of the complete symmetry group of the Kepler problem are obtained from the three standard representations of the complete symmetry group of the simple harmonic oscillator. The algebra of the complete symmetry group of the two-dimensional Kepler problem is identified to be A1⊕{A3,3}. The applicability of the results to other classes of problem, such as the Kepler problem with drag, which possess a conserved vector of Laplace–Runge–Lenz type, is indicated. The three-dimensional Kepler problem is shown to be completely specified by six symmetries rather than the eight previously reported by Krause [J. Math. Phys. 35, 5734 (1994)].
Entropy production fluctuations of finite Markov chains
Authors: Jiang Da-Quan , Qian Min , Zhang Fu-Xi
Published: August 2003

For almost every trajectory segment over a finite time span of a finite Markov chain with any given initial distribution, the logarithm of the ratio of its probability to that of its time-reversal converges exponentially to the entropy production rate of the Markov chain. The large deviation rate function has a symmetry of Gallavotti–Cohen type, which is called the fluctuation theorem. Moreover, similar symmetries also hold for the rate functions of the joint distributions of general observables and the logarithmic probability ratio.
Terahertz magnetospectroscopy of transient plasmas in semiconductors
Authors: Zudov M. A. , Mitchell A. P. , Chin A. H. , Kono J.
Published: August 2003

Using synchronized near-infrared (NIR) and terahertz (THz) lasers, we have performed picosecond time-resolved THz spectroscopy of transient carriers in semiconductors. Specifically, we measured the temporal evolution of THz transmission and reflectivity after NIR excitation. We systematically investigated transient carrier relaxation in GaAs and InSb with varying NIR intensities and magnetic fields. Using this information, we were able to determine the evolution of the THz absorption to study the dynamics of photocreated carriers. We developed a theory based on a Drude conductivity with time-dependent density and density-dependent scattering lifetime, which reproduced the observed plasma dynamics. Detailed comparison between experimental and theoretical results revealed a linear dependence of the scattering frequency on density, which suggests that electron–electron scattering is the dominant scattering mechanism for determining the scattering time. In InSb, plasma dynamics was dramatically modified by the application of a magnetic field, showing rich magnetoreflection spectra, while GaAs did not show any significant magnetic field dependence. We attribute this to the small effective masses of the carriers in InSb compared to GaAs, which made the plasma, cyclotron, and photon energies all comparable in the density, magnetic field, and wavelength ranges of the current study.
Spectral curve and Hamiltonian structure of isomonodromic SU(2) Calogero–Gaudin system
Authors: Takasaki Kanehisa
Published: August 2003

This paper presents a new approach to the Hamiltonian structure of isomonodromic deformations of a matrix system of ordinary differential equations (ODEs) on a torus. An isomonodromic analogue of the SU(2) Calogero–Gaudin system is used for a case study of this approach. A clue of this approach is a mapping to a finite number of points on the spectral curve of the isomonodromic Lax equation. The coordinates of these moving points give a new set of Darboux coordinates called the spectral Darboux coordinates. The system of isomonodromic deformations is thereby converted to a nonautonomous Hamiltonian system in the spectral Darboux coordinates. The Hamiltonians turn out to resemble those of a previously known isomonodromic system of a second-order scalar ODE. The two isomonodromic systems are shown to be linked by a simple relation.
Insights into dynamics of the F+CD4 reaction via product pair correlation
Authors: Zhou Jingang , Lin Jim J. , Shiu Weicheng , Liu Kopin
Published: August 2003

To unravel the “extra-atom” complexity of the title reaction, we exploit an experimental approach which, by taking advantage of the correlated information of coincident product pairs, allows us to peel off judiciously the intrinsic complications of a six-atom reaction, extracting the underlying backbone of three-atom dynamics. Examining the collisional energy dependencies of the pair-correlated attributes for a given state(s) of CD3 products from the title reaction, several of major observations can qualitatively be understood, whereas others await further theoretical investigations. An intriguing possibility for the existence of reactive resonances in this six-atom reaction is surmised.
Structural stability and magnetic properties in X2AlX′ (X=Fe, Co, Ni; X′=Ti, Cr) Heusler alloys from quantum mechanical calculations
Authors: Kellou A. , Fenineche N. E. , Grosdidier T. , Aourag H. , Coddet C.
Published: August 2003

We present quantum mechanical calculations of structural, electronic, and magnetic properties of X2AlX′ (X=Fe, Co, Ni; X′=Ti, Cr) Heusler alloys within the generalized gradient approximation. Structural properties, magnetic moments, and stable ground states are well described by the present method and are in good agreement with available experimental and theoretical results. Also, electronic properties are predicted and related to stability and conductivity mechanisms. We also report the polarized densities of states and shown the half metallicity character among these materials.
Explicit calculations of homoclinic tangles in tokamaks
Authors: Roeder R. K. W. , Rapoport B. I. , Evans T. E.
Published: August 2003

Explicit numerical calculations of homoclinic tangles are presented for a physically realistic model of a resonantly perturbed magnetic field in a tokamak. The structure of these tangles is consistent with that expected from the general theory of near-integrable Hamiltonian systems commonly studied with simple algebraic twist map models. In addition, understanding the structure of homoclinic tangles corresponding to the primary separatrix of a poloidally diverted tokamak allows one to make predictions of the locations and structure of magnetic footprints and heat buildup on the tokamak wall. These separatrix tangles undergo an interesting bifurcation sequence as the current through a set of error field correction coils is increased. Since this model of the magnetic field is very realistic, these features are expected to be experimentally verifiable.
Algebraic classification of the curvature of three-dimensional manifolds with indefinite metric
Authors: Torres del Castillo G. F. , Gómez-Ceballos L. F.
Published: August 2003

The curvature of a three-dimensional Riemannian manifold with Lorentzian signature is algebraically classified using the fact that the spinor equivalent of the traceless part of the Ricci tensor is a totally symmetric four-index spinor. Following G. S. Hall and M. S. Capocci [J. Math. Phys. 40, 1466 (1999)] it is shown that at each point of the manifold there exists four, possibly complex, null vectors which are analogous to the Debever–Penrose vectors and also satisfy the condition Rablalb=0. It is also shown that a similar conclusion holds for the Cotton–York tensor.
Electron–phonon heat transport and electronic thermal conductivity in heavily doped silicon-on-insulator film
Authors: Kivinen P. , Savin A. , Zgirski M. , Törmä P. , Pekola J. , Prunnila M. , Ahopelto J.
Published: August 2003

Electron–phonon interaction and electronic thermal conductivity have been investigated in heavily doped silicon at subKelvin temperatures. The heat flow between electron and phonon systems is found to be proportional to T6. Utilization of a superconductor–semiconductor–superconductor thermometer enables a precise measurement of electron and substrate temperatures. The electronic thermal conductivity is consistent with the Wiedemann–Franz law.
Electrical contact resistance theory for conductive rough surfaces
Authors: Kogut L. , Komvopoulos K.
Published: August 2003

A general electrical contact resistance (ECR) theory for conductive rough surfaces was derived from first principles. The analysis is based on fractal geometry for the surface topography description, elastic-plastic deformation of contacting asperities, and size-dependent constriction resistance of microcontacts. Relations for the ECR in terms of contact load and apparent contact area are obtained for isotropic, homogeneous, conductive surfaces with known material properties and surface topography. Useful design guidelines for electrical contacts are extracted from the numerical results. A general relation between the dimensionless real contact area and the dimensionless ECR is introduced for lightly loaded contacts that depends only on the electron mean free path. Approaches for determining the surface roughness, material properties, and real contact area are discussed in the context of relatively simple ECR measurements.
Monotone Riemannian metrics on density matrices with non-monotone scalar curvature
Authors: Andai Attila
Published: August 2003

The theory of monotone Riemannian metrics on the state space of a quantum system was established by Dénes Petz in 1996. In a recent paper he argued that the scalar curvature of a statistically relevant—monotone—metric can be interpreted as an average statistical uncertainty. The present paper contributes to this subject. It is reasonable to expect that states which are more mixed are less distinguishable than those which are less mixed. The manifestation of this behavior could be that for such a metric the scalar curvature has a maximum at the maximally mixed state. We show that not every monotone metric fulfils this expectation, some of them behave in a very different way. A mathematical condition is given for monotone Riemannian metrics to have a local minimum at the maximally mixed state and examples are given for such metrics.
Magnetic force microscopy and simulations of colloidal iron nanoparticles
Authors: Pedreschi F. , Sturm J. M. , O’Mahony J. D. , Flipse C. F. J.
Published: August 2003

Colloidal iron nanoparticles with a core size of 10.6 nm were examined using magnetic force microscopy. Surprisingly, single nanoparticles were more prominently visible in magnetic force gradient images than clusters. A simple qualitative model is proposed to explain this observation, speculating that the local field produced by a cluster of particles may be sufficient to align their moments in the plane of the cluster, even though the particles are superparamagnetic. An alternative possibility of spin glass formation within clusters is also considered. Calculations performed with nanoparticles represented as single dipoles appear to match experimental data quite well.
Finite element method for electronic properties of semiconductor nanocrystals
Authors: Qu Fanyao , Alcalde A. M. , Almeida C. G. , Dantas Noelio Oliveira
Published: August 2003

The finite element method (FEM) has been implemented in order to investigate the electronic structure of spherical quantum dots (SQDs) in an external magnetic field. The Schrödinger equation has been discretized by means of Galerkin’s weighted residue method with a nonuniform mesh of triangular elements. Unlike other approaches, the computational effort required to obtain converged results is independent of the strength of the magnetic field. Since the basis functions are given by strictly local polynomials in real space, FEM allows a controlled convergence of the solutions. The effects of the diamagnetic term on the energy levels and their reordering produced by state crossing for semiconductor metal oxide quantum dots in alkaline aqueous colloids, and CdTe SQDs embedded in a glass matrix, have been discussed. The efficiency and accuracy of FEM have been shown by its successful applications to a single SQD, two-coupled SQDs, and a hydrogenic impurity in SQDs.
Infrared spectra of photochemically grown suboxides at the Si/SiO2 interface
Authors: Lambers Jochen , Hess Peter
Published: August 2003

Infrared (IR) spectra of ultrathin silicon-oxide layers, grown by pulsed F2-laser (157 nm) photoinduced oxidation of H-terminated Si(111) and Si(110) in an oxygen atmosphere, were monitored in situ with monolayer sensitivity. Oxygen atoms play an essential role in this laser-induced oxidation process occurring at room temperature. The IR spectra of the various oxidation states of silicon (suboxides) in the interfacial region recorded for oxides grown by the self-limiting photochemical oxidation process are compared with those of thermal oxide layers of 22 nm thickness obtained by a top-down wet-chemical thinning procedure. The characteristic features of the suboxide spectra recorded for normal and oblique incidence of the analyzing IR beam are discussed.
Characterization of the erosion plume after ablation of copper and tantalum targets by excimer laser irradiation
Authors: Novodvorsky O. A. , Khramova O. D. , Wenzel C. , Bartha J. W. , Filippova E. O.
Published: August 2003

The erosion plume resulting from ablation of copper and tantalum targets in vacuum with excimer laser irradiation (308 nm) was studied using Langmuir probe and optical emission spectroscopy. The ion and electron probe currents were obtained in the range of energy densities from 0.2 to 2.2 J/cm2 at the target with a probe-to-target distance from 10 to 133 mm. The ion velocity distribution calculated from the time-of-flight measurements has been revealed as a multimodal kind. Curves of the spatial and time dependence of electron probe current were obtained in real time. The electron temperature of different plume regions was determined from a series of I-U characteristics taken at different distances between the Langmuir probe and target. It was established that the plume electron temperature is nonuniform and it has a maximum in front of the plume. The optical emission spectra were used to study the plume composition qualitatively. In addition, the optical emission spectroscopy allowed us to measure both the ion and atom velocities by time-of-flight measurements. The electron temperature was calculated from the continuum part of the optical spectrum of the plume radiation. The results obtained were compared with probe measurements of electron temperature and ion velocity. An acceleration of tantalum ions has been performed successfully with CO2 laser irradiation perpendicular to the plume expansion. An increase of about 25 eV was observed in the middle ion energy.
Impulsive fracture of fused quartz and silicon crystals by nonlinear surface acoustic waves
Authors: Lehmann G. , Lomonosov A. M. , Hess P. , Gumbsch P.
Published: August 2003

During nonlinear evolution of laser-generated surface acoustic wave (SAW) pulses the stress increases with distance of propagation, and causes fracturing of brittle materials. This effect was used to evaluate the strength of isotropic fused quartz and anisotropic crystalline silicon with respect to impulsive loading in the nanosecond range and spontaneous cracking without using seed cracks. Crack nucleation and propagation along the surface was studied by optical microscopy and into the depth of the bulk by the focused ion beam technique and confocal microscopy. In fused quartz, fracturing produced characteristic regular patterns at the surface with cracks extending into the bulk at an angle of 30°–35° to the surface in the direction of SAW propagation. On Si(111) surfaces cracks extended at the surface in the 〈110〉 direction and propagated along the weak {111¯}̄ cleavage plane into the bulk. Other crack planes were observed in only a few cases, e.g., at a larger depth and on the Si(100) surfaces. The observed fracture behavior was rationalized by the complex displacement and stress tensor fields induced by elliptically polarized SAWs.
Interaction of laser-induced cavitation bubbles with composite surfaces
Authors: Tomita Y. , Kodama T.
Published: August 2003

The dynamics of a laser-induced cavitation bubble near a composite surface, consisting of either a thin rigid plate glued on a foam rubber (composite surface A) or a deformable rubber plate glued on a foam rubber (composite surface B), was investigated experimentally with high-speed photography. To understand the interaction between a cavitation bubble and a composite surface, the dynamic properties of the composite surfaces were measured with a modal analysis by providing a maximum frequency to 5 kHz, since the period of the bubble motion with the radius of 1 mm is about 200 μs. It was found that bubble migration was significantly influenced by the dynamic property of composite surfaces, showing a range of response between the free surface and rigid boundary cases. For one of the composite surfaces with a deformable rubber, bubble splitting was generated for γ<1.1, where γ=L/Rmax with L being the initial bubble location and Rmax the maximum bubble radius. A neutral bubble collapse occurred at a specified bubble location defined as γN that was fairly correlated with the compliance, Gn, of the composite surfaces. The value of γN decreased with increasing Gn.
Transport in a gated Al0.18Ga0.82N/GaN electron system
Authors: Juang J. R. , Huang Tsai-Yu , Chen Tse-Ming , Lin Ming-Gu , Kim Gil-Ho , Lee Y. , Liang C.-T. , Hang D. R. , Chen Y. F. , Chyi Jen-Inn
Published: August 2003

We have investigated the low-temperature transport properties of front-gated Al0.18Ga0.82N/GaN heterostructures. At zero gate voltage, the Hall mobility increases with decreasing temperature (20 K⩽T⩽190 K) due to a reduction in phonon scattering. For T⩽20 K, the mobility decreases with decreasing temperature. This is due to weak localization in a weakly disordered two-dimensional system. By changing the applied gate voltage, we can vary the carrier density n from 3.11×1012 to 6.95×1012 cm−2 in our system. The carrier density shows a linear dependence on the applied gate voltage, consistent with a simple parallel-plate capacitor model. The average distance between the GaN electron system and the AlGaN/GaN interface is estimated to be 240 Å. At high carrier densities (n>4.65×1012 cm−2), the measured mobility (μ) is found to be a decreasing function of carrier density as μ∼n−0.31. Loss of mobility with increasing carrier density is dominated by interface roughness scattering. At low carrier densities (n<4.24×1012 cm−2), the measured mobility is found to be an increasing function of carrier density as μ∼n0.34. This is consistent with remote ionized impurity scattering, although the measured exponent 0.34 is smaller than the typical value (0.7–1.5) observed in an AlGaN/GaN electron system. A possible reason is that our sample mobility is approximately five times lower than those in other devices for a similar electron density.
Riemannian geometry of bicovariant group lattices
Authors: Dimakis Aristophanes , Müller-Hoissen Folkert
Published: August 2003

Group lattices (Cayley digraphs) of a discrete group are in natural correspondence with differential calculi on the group. On such a differential calculus geometric structures can be introduced following general recipes of noncommutative differential geometry. Despite the noncommutativity between functions and (generalized) differential forms, for the subclass of “bicovariant” group lattices considered in this work it is possible to understand central geometric objects like metric, torsion and curvature as “tensors” with (left) covariance properties. This ensures that tensor components (with respect to a basis of the space of 1-forms) transform in the familiar homogeneous way under a change of basis. There is a natural compatibility condition for a metric and a linear connection. The resulting (pseudo-) Riemannian geometry is explored in this work. It is demonstrated that the components of the metric are indeed able to properly describe properties of discrete geometries like lengths and angles. A simple geometric understanding of torsion and curvature in particular is achieved. The formalism has much in common with lattice gauge theory. For example, the Riemannian curvature is determined by parallel transport of vectors around a plaquette (which corresponds to a biangle, a triangle or a quadrangle).
Indium nitride (InN): A review on growth, characterization, and properties
Authors: Bhuiyan Ashraful Ghani , Hashimoto Akihiro , Yamamoto Akio
Published: August 2003

During the last few years the interest in the indium nitride (InN) semiconductor has been remarkable. There have been significant improvements in the growth of InN films. High quality single crystalline InN film with two-dimensional growth and high growth rate are now routinely obtained. The background carrier concentration and Hall mobility have also improved. Observation of strong photoluminescence near the band edge is reported very recently, leading to conflicts concerning the exact band gap of InN. Attempts have also been made on the deposition of InN based heterostructures for the fabrication of InN based electronic devices. Preliminary evidence of two-dimensional electron gas accumulation in the InN and studies on InN-based field-effect transistor structure are reported. In this article, the work accomplished in the InN research, from its evolution to till now, is reviewed. The In containing alloys or other nitrides (AlGaInN, GaN, AlN) are not discussed here. We mainly concentrate on the growth, characterization, and recent developments in InN research. The most popular growth techniques, metalorganic vapor phase epitaxy and molecular beam epitaxy, are discussed in detail with their recent progress. Important phenomena in the epitaxial growth of InN as well as the problems remaining for future study are also discussed.
Eigenmodes of a reflective twisted-nematic liquid-crystal cell
Authors: Zhu Xinyu , Hong Qi , Huang Yuhua , Wu Shin-Tson
Published: August 2003

The eigenmodes of a reflective twisted-nematic liquid-crystal (TN LC) cell are analyzed based on the Jones matrix method. Two models are developed to describe the LC system in the low- and high-voltage regimes. The simulated transmission spectra of LC Fabry–Perot etalons are used to investigate the eigenmodes. In a general reflective TN LC cell, the eigenmodes are two orthogonal linear polarization states. Under some specific conditions, these two linear polarization states will approach the bisector or orthogonal to the bisector of the TN LC cell. This bisector effect is useful for reducing the operating voltage and enhancing the contrast ratio of LC display devices and for eliminating the mode coupling of the tunable Fabry–Perot etalons.
Alignment mechanism of liquid crystal in a stretched porous polymer film
Authors: Fujikake Hideo , Kuboki Masashi , Murashige Takeshi , Sato Hiroto , Kikuchi Hiroshi , Kurita Taiichiro
Published: August 2003

This article discusses the mechanism of nematic liquid crystal alignment in stretched porous polymer films. The polymer films were formed by extreme stretching of an isotropic porous polyolefin, such that the draw ratio was 12:1. A 6-μm-thick porous film with a high porosity coefficient of 92% revealed fine string-shaped areas that exhibited optical anisotropy due to their possessing a high degree of molecular alignment. The porous film was filled with nematic liquid crystal and then the composite film was sandwiched between transparent electrodes coated onto glass substrates, without the use of conventional alignment layers. From polarizing microscopy observations it was found that the string-like polymer areas induce liquid crystal molecular alignment. The liquid crystal cells can exhibit an electrically controlled birefringence effect. This alignment technique enables us to realize three-dimensional control of liquid crystal alignment.
Control of micromagnetics in Permalloy nanomagnets by means of indentation
Authors: Koltsov D. K. , Welland M. E.
Published: August 2003

The competition of exchange and magnetostatic interaction in nanomagnets is known to lead to the formation of configurational anisotropy. We present an effective method of controlling the configurational anisotropy and underlying micromagnetic configurations in isotropic Permalloy square prisms by edge indentation. Finite difference micromagnetic modeling of such indented square prisms gives five ground state micromagnetic configurations, the relative energies of which are determined by the structure size and depth of indentation. A micromagnetic phase diagram for the system is constructed on a size-indentation plane and is confirmed by direct magneto-optical measurements on nanofabricated Permalloy structures. The effect of indentation is to suppress curling micromagnetic configurations resulting in single domain behavior in indented structures as large as 400 nm.
Extrinsic models for the dielectric response of CaCu3Ti4O12
Authors: Cohen Morrel H. , Neaton J. B. , He Lixin , Vanderbilt David
Published: August 2003

The large, temperature-independent, low-frequency dielectric constant recently observed in single-crystal CaCu3Ti4O12 is most plausibly interpreted as arising from spatial inhomogenities of its local dielectric response. Probable sources of inhomogeneity are the various domain boundaries endemic in such materials: twin, Ca ordering, and antiphase boundaries. The material in, and neighboring, such boundaries can be insulating or conducting. We construct a decision tree for the resulting six possible morphologies, and derive or present expressions for the dielectric constant for models of each morphology. We conclude that all six morphologies can yield dielectric behavior consistent with observations. Thus, present experimental findings are insufficient to establish the internal morphology responsible for the remarkable properties of CaCu3Ti4O12, and we suggest further experiments to distinguish among them.
Extension of the semiclassical theory of current-perpendicular-to-plane giant magnetoresistance including spin flip to any multilayered magnetic structures
Authors: Strelkov N. , Vedyaev A. , Dieny B.
Published: August 2003

In the framework of the Valet and Fert theory of current perpendicular to plane (CPP) giant magnetoresistance (GMR) in metallic multilayers [Valet and Fert, Phys. Rev. B 48, 7099 (1993)], the calculation of the CPP resistance and magnetoresistance has been generalized to any multilayered stacks including spin valves with synthetic free layers, laminated free and pinned layers, and dual spin valves. The theory takes into account bulk and interfacial spin-dependent scattering as well as spin flip in all layers. It also considers the effect of scattering at lateral edges of submicron multilayered pillars which can be viewed as a current in plane effect intruding on CPP transport. This latter effect plays a role when the diameter of the pillar becomes of the order of the elastic mean-free paths (i.e., below ∼30 nm). Based on the theory, a code has been developed to compute the CPP resistance and CPP magnetoresistance from the transport parameters of each material involved in the stack (spin-dependent resistivities, spin-dependent interfacial resistances, and spin-diffusion length in each layers). As examples, we compare the results of the calculations with various already published CPP experiments. In particular, we interpret experiments previously carried out on (NiFe/Cu/Co/Cu)N and (Co 6 nm/Cu/Co 1 nm/Cu)N multilayers in which the order of the layers in the stack had been shown to affect the CPP resistance and magnetoresistance, a property which could not be explained in a simple two-channel serial resistance model. We also investigate the influence of the thickness of the various layers and underline the key role of the spin diffusion length in these thickness variations. Unexpected predictions are made with this theory such as the existence of a maximum in CPP–MR as a function of the thickness of the antiferromagnetic pinned layer. This type of calculations should allow a faster optimization of CPP–GMR in metallic multilayers.
Crystal and domain structure of the BiFeO3–PbTiO3 solid solution
Authors: Woodward David I. , Reaney Ian M. , Eitel Richard E. , Randall Clive A.
Published: August 2003

X-ray diffraction and transmission electron microscopy have been performed on samples in the solid solution series (BiFeO3)x–(PbTiO3)1−x in which a morphotropic phase boundary occurs at x≈0.7. BiFeO3 exhibits superlattice reflections at 12{hkl}p positions in some electron diffraction patterns, the distribution of which unambiguously demonstrates that the FeO6 octahedra are rotated in anti-phase about the pseudocubic [111] axis, consistent with the rhombohedral (R) space group R3c. The amplitude of the rotations decreases in the R phase as PbTiO3 content increases and superlattice reflections are absent in electron diffraction patterns from the tetragonal (T) phase (x=0.6), indicating that it is untilted with space group P4mm. Electron diffraction patterns from samples where x=0.7 reveal superlattice reflections not associated with octahedral rotations and consistent with an intermediate phase with lower symmetry than T and R.
Thermodynamics and kinetics of room-temperature microstructural evolution in copper films
Authors: Detavernier C. , Rossnagel S. , Noyan C. , Guha S. , Cabral C. , Lavoie C.
Published: August 2003

We studied the energetics and kinetics of microstructural evolution in copper films by estimating the magnitude of various possible driving forces for microstructural change that can be present in the as-deposited film. A driving force of at least 100 J/cm3 is required to account for the speed at which the grain boundaries move at room temperature. This value cannot be accounted for by only considering the minimization of grain-boundary energy and possible effects related to surface and strain energy as the main driving mechanisms. It is suggested that the additional driving force which is needed to explain the speed at which the grains recrystallize, is originating from a high density of defects within the as-deposited grains.
Contrast in friction and its inversion observed on metal deposited SrTiO3(100) surfaces
Authors: Shiraki Susumu , Nantoh Masashi , Wakatsuchi Masayuki , Kawai Maki
Published: August 2003

Local variation of frictional properties associated with adatoms of Sr and Cu with SrTiO3(100) surfaces was investigated by friction force microscopy. On the surfaces partially covered with Sr, strong friction was observed on Sr adlayers. In contrast, the areas covered with Cu showed weaker friction than the substrates. We found that a thick Cu layer became easily worn by scanning, so the stepped surface of the substrate appeared in the scanned area. Furthermore, inversion of the contrast in friction between the SrO and TiO2 terraces was observed in the same region during measurement. The origins of this friction behavior will be discussed in terms of the interaction between adsorbates and the substrate.
A theoretical study of the conversion of gas phase methanediol to formaldehyde
Authors: Kent David R. , Widicus Susanna L. , Blake Geoffrey A. , Goddard William A.
Published: August 2003

Methanediol, or methylene glycol, is a product of the liquid phase reaction of water and formaldehyde and is a predicted interstellar grain surface species. Detection of this molecule in a hot core environment would advance the understanding of complex organic chemistry in the interstellar medium, but its laboratory spectroscopic characterization is a prerequisite for such observational searches. This theoretical study investigates the unimolecular decomposition of methanediol, specifically the thermodynamic and kinetic stability of the molecule under typical laboratory and interstellar conditions. Methanediol was found to be thermodynamically stable at temperatures of <100 K, which is the characteristic temperature range for interstellar grain mantles. The infinite-pressure RRKM unimolecular decomposition rate was found to be <10−18 s−1 at 300 K, indicating gas phase kinetic stability for typical laboratory and hot core temperatures. Therefore, both laboratory studies of and observational searches for this molecule should be feasible.
Stabilization of global movement on a field-reversed configuration due to fast neutral beam ions
Authors: Asai T. , Inomoto M. , Iwasawa N. , Okada S. , Goto S.
Published: August 2003

Experimental evidence for the global stabilization effect of neutral beam injection on field-reversed configuration (FRC) plasma has been found for the first time. The translation of FRC plasma, i.e., transferring the formed plasma into another vessel along a gradient of guiding magnetic field, is an important technique for both the current FRC experiments and a future fusion reactor to separate formation and confinement regions. However, the translation’s dynamic process causes global wobble movement of the plasma column. The stabilization effect induced by obliquely injected neutral beams on this global movement has been observed by both interferometry and magnetic measurement. The behavior of injected beam ions has been calculated numerically and suggests that the injected beam ions confined under a strong mirror field could produce effective ring-current at both ends of the plasma column. The stabilization effect of this ring-current on the global movement has been discussed by using a rigid body model.