bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a multilayered in vitro model for studying events associated with wound healing
Authors: Stephens Phil , Wood Edward J. , Raxworthy Michael J.
Published: September 2002

Simplified in vitro models such as cellular monolayer cultures have only limited usefulness in the study of cutaneous wound repair processes. This has stimulated the investigation of three‐dimensional tissue equivalent systems such as the dermal and skin equivalent models. With the use of a wound system constructed of rat tail type I collagen and human dermal fibroblasts, experimental wounding was accompanied by problems with mechanical scoring of the plastic substratum which prevented cell migration. These problems were overcome with the use of a multilayered model in which a punch biopsy‐wounded dermal equivalent (bilayered model) or skin equivalent (trilayered model) was placed onto an acellular collagen lattice and fixed in place with polymerizing collagen. This model permitted observation of the process of cellular repopulation of the “wound space,” into which both fibroblast and keratinocyte migration commenced within 1 day. The number of fibroblasts in this space increased dramatically over a period of 9 days, the cells appearing to migrate both over and through the acellular lower collagen layer. Keratinocyte reepithelialization of the “wound space” was completed after 5 days. With the model it was shown that platelet‐derived growth factor‐AB and epidermal growth factor had positive effects in increasing fibroblast number within the wound space. In conclusion, the model described here should facilitate the study of fibroblast and keratinocyte responses to a wound stimulus in vitro and be a plausible in vitro system for evaluating agents which may have a potential stimulatory or inhibitory effect on numerous cellular responses associated with wound healing.
Molecular mechanisms underlying wound healing acceleration by Staphylococcus aureus peptidoglycan
Authors: Liu Xiaoguang , Levenson Stanley M. , Chang Tsueng H. , Steinberg Jacob J. , Imegwu Obi , Rojkind Marcos
Published: September 2002

Molecular mechanisms involved in wound healing acceleration by Staphylococcus aureus peptidoglycan were investigated with the use of polyvinyl alcohol sponges implanted under the dorsal skin of rats. Total collagen and RNA content and messenger RNA levels of α1(I) and α1(III) procollagen, transforming growth factor‐β1, and matrix metalloproteinase‐1 were analyzed in saline solution‐ and S. aureus peptidoglycan‐inoculated sponges at 4, 7, 14, and 21 days after implantation. S. aureus peptidoglycan‐inoculated sponges on the fourth and seventh post‐operative day were surrounded and penetrated by a thick capsule of reparative connective tissue. They were considerably heavier and contained more collagen and total RNA than saline solution‐inoculated sponges. Histologically, the S. aureus peptidoglycan‐inoculated sponges early on contained a denser infiltrate of polymorphonuclear cells than saline solution‐inoculated sponges, and later fibroblasts, macrophages, collagen, and newly formed blood vessels were more abundant in the S. aureus peptidoglycan sponges. Matrix metalloproteinase‐1 messenger RNA expression was elevated at 4 days in both sponge types. However, although matrix metalloproteinase‐1 mRNA levels decreased to undetectable levels by 14 days in saline solution‐inoculated sponges, they remained elevated throughout the 21‐day study period in S. aureus peptidoglycan‐inoculated sponges. No other significant differences in the parameters analyzed were detected. These results suggest that S. aureus peptidoglycan induces an accelerated but normal wound healing process in which the markedly increased early deposition of connective tissue is rapidly remodeled likely because of a sustained expression of matrix metalloproteinase‐1.
Morphology and Dynamics of the Ulnar Nerve in the Cubital Tunnel
Authors: OKAMOTO M. , ABE M. , SHIRAI H. , UEDA N.
Published: September 2002

We examined 200 normal elbows to assess the usefulness of ultrasonography in examining the ulnar nerve in the cubital tunnel. On longitudinal images in elbow extension, the nerve changed its course at the fibrous band region 11.5 (SD 2.8) mm distal to the medial epicondyle. On axial images, the diameter of the major axis of the nerve was 3.1 (0.5) mm and that of the minor axis was 1.9 (0.4) mm in men. The respective values were 2.7 (0.4) mm and 1.8 (0.4) mm in women. Dynamic studies showed that in 53 elbows (27%), the nerve moved on to the tip of the epicondyle with the elbow flexed and in 39 elbows (20%), the nerve dislocated anteriorly. The diameters of the hypermobile nerves were significantly larger than nerves that did not displace.
Electrical impedance spectroscopy device for measurement of moisture gradients in wood
Authors: Tiitta M. , Olkkonen H.
Published: September 2002

A prototype of the electrical impedance spectroscopy (EIS) device for the measurement of internal moisture gradients in wood was developed. The EIS device consists of a hand-held probe connected to a control unit interfaced with a portable personal computer and a power unit. In the measurement, parallel flat electrodes of the measuring probe are laid against the wood specimen and the sine wave excitation is applied in the frequency range 1–100 kHz. The measured amplitude and phase spectral data were analyzed using the model based on constant phase elements. A spectral analysis software package was designed for measurement of subsurface transverse moisture gradients. The EIS device was tested with many types of uniform, desorption, and absorption gradients in lumber, pulpwood, and log specimens from spruce, pine, and birch. The EIS device can be easily transferred in a small case allowing field measurements.
Self-similarity of near-breaking short gravity wind waves
Authors: Caulliez Guillemette
Published: September 2002

We show that the asymmetric profiles of the near-breaking wind waves observed in a large wind-wave tank do not depend on the wave scale. The experiments were performed for wind-generated waves of wavelength increasing with fetch. The wave crests just prior to breaking exhibit steep slopes exceeding 0.6 at the front and much smaller but remarkably constant slope at the rear. The statistics of wave geometric properties, such as the along-wind crest-slope distribution or the wavefront steepness, is found to be scale invariant. This implies that the shape of the near-breaking wind waves is self-similar. Similar experiments with paddle-generated waves amplified by wind reveal the same scale-independent features. These results suggest a certain universality of the underlying physical mechanisms leading to breaking for wave fields in equilibrium with wind.
The flow and solidification of a thin fluid film on an arbitrary three-dimensional surface
Authors: Myers T. G. , Charpin J. P. F. , Chapman S. J.
Published: September 2002

A model for the flow of a thin film, with and without solidification, on an arbitrary three-dimensional substrate is presented. The problem is reduced to two simultaneous partial differential equations for the film and solid layer thicknesses. The flow model (with the solidification rate set to zero) is the first such model to describe thin film flow on an arbitrary three-dimensional surface. Various limits are investigated to recover previous models for flow on flat, cylindrical and two-dimensional curved surfaces. With solidification a previous model for accretion on a flat substrate is retrieved. It is shown how the model may be reduced to standard forms, such as solidification on a flat surface, circular and non-circular cylinders, aerofoils and spheres. Numerical solutions are obtained by combining an ADI scheme with a shock capturing method. Results are presented for flow and accretion on a flat surface, aerofoil and sphere.
Characteristics of parallel electric fields in the downward current region of the aurora
Authors: Andersson L. , Ergun R. E. , Newman D. L. , McFadden J. P. , Carlson C. W. , Su Y.-J.
Published: September 2002

Direct measurements of parallel electric fields suggest that they are, in part, self-consistently supported as strong double layers in the auroral downward current region. The observed parallel electric fields have amplitudes reaching nearly 1 V/m and are confined to a thin layer of approximately 10 Debye lengths. The structures are moving at roughly the ion acoustic speed in the direction of the accelerated electrons, i.e., anti-earthward. On the high-potential side of the parallel electric field there is a clear signature of an accelerated electron beam which rapidly plateaus within a few hundred Debye lengths from the parallel electric field. Strong wave turbulence is observed in the vicinity of the plateaued electron distribution. Fast solitary waves, identified as a signature of electron phase-space holes, are seen farther away from the parallel electric field on the high-potential side. The observed ion distributions also indicate the presence of the parallel electric field. On the low-potential side of the double layer an ion beam is observed moving in the opposite direction of the electron beam and ion conics appear to be trapped between their mirror point and the moving double layer.
Carbonate formation on the O-enriched RuO2(110) surface
Authors: Lafosse A. , Wang Y. , Jacobi K.
Published: September 2002

The reaction of CO2 to carbonate CO3δ− is studied on the O-enriched RuO2(110) surface using thermal desorption spectroscopy and high-resolution electron energy-loss spectroscopy. It is known that the epitaxially grown RuO2(110) surface exposes coordinatively unsaturated sites, so-called Ru-cus and O-bridge, and can be O-enriched by dissociative adsorption of O2 giving rise to weakly bound O-cus atoms on top of Ru-cus. CO2 adsorption at 85 K and annealing up to 250 K, results in a stepwise increased carbonate CO3δ− formation which takes place only on Ru-cus sites. Based on isotope substitution experiments the carbonate-related losses are identified among them the symmetric stretching mode at 150.8 meV and the asymmetric one at 174.9 meV. Through interaction of CO2δ− with O-cus, both chemisorbed on neighboring Ru-cus sites, a bidentate transient state and finally a monodentate carbonate CO3δ− is formed. The molecular plane of monodentate CO3δ− is oriented perpendicular to the surface with a tilted RuO–CO2 axis. The maximum carbonate coverage is about 25%.
Characteristics of flow over a rotationally oscillating cylinder at low Reynolds number
Authors: Choi Sungho , Choi Haecheon , Kang Sangmo
Published: September 2002

Effects of rotary oscillation on unsteady laminar flow past a circular cylinder have been investigated in this study. Numerical simulations are performed for the flow at Re=100 in the range of 0.2⩽Ω⩽2.5 and 0.02⩽Stf⩽0.8, where Ω and Stf are, respectively, the maximum rotational speed and forcing oscillation frequency normalized by the free-stream velocity and cylinder diameter. Results show that the rotary oscillation has significant effects on the flow. The lock-on frequency range becomes wider as the rotational speed increases. In a non lock-on region, modulations in the velocity, lift and drag signals occur and the modulation frequency is expressed as a linear combination of the forcing frequency and vortex-shedding frequency. Also, the mechanism for the modulation phenomenon is presented in terms of the vortex merging process. Finally, it is found that the mean drag and amplitude of the lift fluctuations show local minima near the boundary between the lock-on and non lock-on regions.
Substrate bias dependence of Raman spectra for TiN films deposited by filtered cathodic vacuum arc
Authors: Cheng Y. H. , Tay B. K. , Lau S. P. , Kupfer H. , Richter F.
Published: September 2002

Raman spectroscopy was used to characterize TiN films deposited by using an off-plane double bend filtered cathodic vacuum arc technique. The influence of substrate bias on the Raman spectra was systematically studied. Four peaks at 235, 320, 440, and 570 cm−1, related to transverse acoustic (TA), longitudinal acoustic (LA), second-order acoustic (2A), and transverse optical (TO) modes of TiN, respectively, were observed in the Raman spectra of TiN films. The intensity of all four peaks and the area fraction as well as the full width at half maximum (FWHM) of the TO peak increase drastically with increasing substrate bias, reaching a maximum at −100 V, and then decrease greatly. However, the area fraction of TA, LA, and 2A peaks, the FWHM of TA and 2A peaks, as well as the frequency of all four peaks decrease rapidly with increasing substrate bias to −100 V, and then increase greatly. At a bias above −200 V, only a slight change in the Raman spectra of TiN films were observed. The change in the N/Ti ratio is the main reason for the evolution in the Raman spectra of TiN films with increasing substrate bias. The internal stress and the crystal size play only a minor role in the Raman spectra of TiN films in the present study.
Density functional study of structural and electronic properties of bimetallic silver–gold clusters: Comparison with pure gold and silver clusters
Authors: Bonačić-Koutecký Vlasta , Burda Jaroslav , Mitrić Roland , Ge Maofa , Zampella Giuseppe , Fantucci Piercarlo
Published: September 2002

Bimetallic silver–gold clusters offer an excellent opportunity to study changes in metallic versus “ionic” properties involving charge transfer as a function of the size and the composition, particularly when compared to pure silver and gold clusters. We have determined structures, ionization potentials, and vertical detachment energies for neutral and charged bimetallic AgmAun [3⩽(m+n)⩽5] clusters. Calculated VDE values compare well with available experimental data. In the stable structures of these clusters Au atoms assume positions which favor the charge transfer from Ag atoms. Heteronuclear bonding is usually preferred to homonuclear bonding in clusters with equal numbers of hetero atoms. In fact, stable structures of neutral Ag2Au2, Ag3Au3, and Ag4Au4 clusters are characterized by the maximum number of hetero bonds and peripheral positions of Au atoms. Bimetallic tetramer as well as hexamer are planar and have common structural properties with corresponding one-component systems, while Ag4Au4 and Ag8 have 3D forms in contrast to Au8 which assumes planar structure. At the density functional level of theory we have shown that this is due to participation of d electrons in bonding of pure Aun clusters while s electrons dominate bonding in pure Agm as well as in bimetallic clusters. In fact, Aun clusters remain planar for larger sizes than Agm and AgnAun clusters. Segregation between two components in bimetallic systems is not favorable, as shown in the example of Ag5Au5 cluster. We have found that the structures of bimetallic clusters with 20 atoms Ag10Au10 and Ag12Au8 are characterized by negatively charged Au subunits embedded in Ag environment. In the latter case, the shape of Au8 is related to a pentagonal bipyramid capped by one atom and contains three exposed negatively charged Au atoms. They might be suitable for activating reactions relevant to catalysis. According to our findings the charge transfer in bimetallic clusters is responsible for formation of negatively charged gold subunits which are expected to be reactive, a situation similar to that of gold clusters supported on metal oxides.
A global potential energy surface of Ar2H+ based on ab initio calculations
Authors: Qu Jun Yan , Li Wei , Guo Rui , Zhao Xin Sheng
Published: September 2002

Results of the QCICD/6-311++G(3df,3pd) ab initio calculations on the ground state of Ar2H+ are presented. With accurate method and basis sets, the potential energy surface for the ground state was scanned with more than 7000 points, and an analytic global potential energy surface was constructed based on these points. The properties such as the potential minima, the transition state, and the dissociating paths of [Ar–H–Ar]+ were discussed. The influence of the three-body interaction in this system was also investigated, and it is found that a potential based on the two-body additive interaction is not good to represent the Ar2H+ system.
Percolation of water in aqueous solution and liquid–liquid immiscibility
Authors: Oleinikova A. , Brovchenko I. , Geiger A. , Guillot B.
Published: September 2002

The first simulation study of the percolation of hydrogen bonded water clusters in the vicinity of the region of immiscibility of an aqueous solution (of tetrahydrofuran) is reported. Percolation of water is found in a wide concentration range on both sides of the liquid–liquid coexistence curve. An infinite cluster appears with a probability of 50% at a water fraction significantly lower than the one corresponding to the organic-rich branch of the coexistence curve. The fractal dimension df of the infinite clusters at this threshold is found close to the two-dimensional (2D) value, df(2D)≅1.9. Three-dimensional (3D) percolation clusters form at the organic-rich branch of the coexistence curve. At this water concentration the fractal dimension of an infinite cluster reaches the 3D value df(3D)≅2.5 and the cluster size distribution follows a power law with an exponent τ≅2.2. The analysis of the clustering of the organic (tetrahydrofuran) molecules indicates that the immiscibility gap of an aqueous solution corresponds to the concentration interval where both components are above their respective percolation threshold.
Experimental study of the high frequency relaxation process in monohydroxy alcohols
Authors: Murthy S. S. N. , Tyagi Madhusudan
Published: September 2002

We have critically examined the possibility of the existence of yet another process (often referred to as process II in the literature) of much smaller magnitude on the high frequency side in the case of 2-ethyl-1-hexanol and 4-methyl-3-heptanol using the dielectric relaxation technique. We have also studied the mixtures of 2-ethyl-1-hexanol with nonpolar methylcyclohexane and a mixture of 1-bromobutane in 4-methyl-3-heptanol for this purpose. In addition, the differential scanning calorimetry (DSC) has been used to study the structural relaxation in the vicinity of the glass transition temperature using the Tool–Narayanaswami–Moynihan procedure as discussed by Sartor et al. [J. Phys. Chem. 100, 6801 (1996)]. Our results show the presence of a clear process II on the higher frequency side whose freezing-out corresponds to the glass transition event at Tg in the DSC studies. It is suggested that process II is associated with free alcohol molecules and is connected to the structural relaxation in alcohols. The dielectric data have been analyzed to understand the thermodynamics of hydrogen bonding using the model of Dannhauser [J. Chem. Phys. 48, 1911 (1968)]. An attempt has been made to correlate the ratio of relaxation rates of processes I and II and the observed deviation from Debye behavior in the case of alcohols.
Experimental realization of the Brüschweiler’s algorithm in a homonuclear system
Authors: Xiao Li , Long G. L. , Yan Hai-Yang , Sun Yang
Published: September 2002

Compared with classical search algorithms, Grover quantum algorithm [L. K. Grover, Phys. Rev. Lett. 79, 325 (1997)] achieves quadratic speedup and Brüschweiler hybrid quantum algorithm [R. Brüschweiler, Phys. Rev. Lett. 85, 4815 (2000)] achieves an exponential speedup. In this paper, we report the experimental realization of the Brüschweiler algorithm in a three-qubit nuclear magnetic resonance ensemble system. The pulse sequences are used for the algorithms and the measurement method used here is improved on that used by Brüschweiler, namely, instead of quantitatively measuring the spin projection of the ancilla bit, we utilize the shape of the ancilla bit spectrum. By simply judging the downwardness or upwardness of the corresponding peaks in an ancilla bit spectrum, the bit value of the marked state can be read out, especially the geometric nature of this read-out can make the results more robust against errors.
Multiconfigurational nuclear-electronic orbital approach: Incorporation of nuclear quantum effects in electronic structure calculations
Authors: Webb Simon P. , Iordanov Tzvetelin , Hammes-Schiffer Sharon
Published: September 2002

The nuclear-electronic orbital (NEO) method for the calculation of mixed nuclear-electronic wave functions is presented. Both electronic and nuclear molecular orbitals are expressed as linear combinations of Gaussian basis functions. In the NEO-HF (Hartree-Fock) method, the energy corresponding to the single-configurational mixed nuclear-electronic wave function is minimized with respect to the molecular orbitals. Multiconfigurational approaches are implemented to include significant correlation effects. In the NEO-CI (configuration interaction) method, the energy corresponding to the multiconfigurational mixed nuclear-electronic wave function is minimized with respect to the CI coefficients. In the NEO-MCSCF (multiconfigurational self-consistent-field) method, the energy is minimized with respect to the molecular orbitals as well as the CI coefficients. Analytic gradient expressions are presented for NEO-HF and NEO-MCSCF. These analytic gradients allow the variational optimization of the centers of the nuclear basis functions. They also enable the location and characterization of geometry stationary points and the generation of minimum energy paths and dynamic reaction paths. The advantages of the NEO approach are that nuclear quantum effects are incorporated during the electronic structure calculation, the Born-Oppenheimer separation of electrons and nuclei is avoided, excited vibrational-electronic states may be calculated, and its accuracy may be improved systematically. Initial applications are presented to illustrate the computational feasibility and accuracy of this approach.
Significant suppression of leakage current in (Ba,Sr)TiO3 thin films by Ni or Mn doping
Authors: Ahn Kun Ho , Baik Sunggi , Kim Sang Sub
Published: September 2002

Effects of Ni or Mn doping in (Ba0.5Sr0.5)TiO3 thin films on leakage current behaviors of Pt/(Ba0.5Sr0.5)TiO3/Pt capacitors were investigated. The leakage current level was found to reduce significantly after the doping over a wide range of voltages and temperatures. The leakage current in an undoped capacitor was largely governed by the Fowler–Nordheim tunneling, and its onset voltage was greatly increased in doped capacitors. The suppression of leakage current in doped capacitors appeared to be caused by a widened depletion layer, which decreases the likelihood of tunneling.
Bulk and interfacial properties of quadrupolar fluids
Authors: Warshavsky V. B. , Zeng X. C.
Published: September 2002

We extend Teixeira and Telo da Gama’s density-functional approach [J. Phys.: Condens. Matter 3, 111 (1991)] to study the vapor–liquid phase equilibria and planar interfacial properties of quadrupolar fluids. The density profile, surface ordering, surface polarization, and surface tension of quadrupolar fluids are evaluated. Particular attention is given to the temperature and quadrupole-strength dependence. It is found that the interfacial molecular ordering can arise entirely due to the quadrupole–quadrupole interaction. It is also found that the bulk-phase properties of the quadrupolar fluids satisfy the law of correspondence states. The reduced surface potential and surface tension can be well correlated by power laws of the scaled temperature τ≡1−T/Tc, where Tc is the critical temperature of the fluids.
Structural and magnetic transformation of monodispersed iron oxide particles in a reducing atmosphere
Authors: Varanda L. C. , Jafelicci M. , Tartaj P. , O’ Grady K. , González-Carreño T. , Morales M. P. , Muñoz T. , Serna C. J.
Published: September 2002

Uniform metal iron ellipsoidal particles of around 200 nm in length were obtained by reduction and passivation of alumina-coated α–Fe2O3 (hematite) particles under different conditions of temperature and hydrogen flow rate. The monodispersed hematite particles were prepared by the controlled hydrolysis of ferric sulfate and further coated with a homogeneous thin layer of Al2O3 by careful selection of the experimental conditions, mainly pH and aluminum salt concentration. The reduction mechanism of α–Fe2O3 into α–Fe was followed by x-ray and electron diffraction, and also by the measurements of the irreversible magnetic susceptibility. The transformation was found to be topotactic with the [001] direction of hematite particles, which lies along the long axis of the particles, becoming the [111] direction of magnetite and finally the [111] direction of metal iron. Temperature and hydrogen flow rate during the reduction have been found to be important parameters, which determine not only the degree of reduction but also the crystallite size of the final particles. Magnetic characterization of the samples shows that the only parameters affected by the crystallite size are the saturation magnetization and magnetic time-dependence effect, i.e., activation volume.
Electronic properties of multiwalled carbon nanotubes in an embedded vertical array
Authors: Li Jun , Stevens Ramsey , Delzeit Lance , Ng Hou Tee , Cassell Alan , Han Jie , Meyyappan M.
Published: September 2002

We demonstrate integration of carbon nanotubes into large scale vertically aligned electrode arrays, by filling the as-grown samples with conformal SiO2 using chemical vapor deposition. Subsequent mechanical polishing yields a flat surface with only the very ends of the nanotube array exposed. The electronic properties of individual carbon nanotubes in the array are measured using current-sensing atomic force microscopy. These vertical nanotube arrays are suitable for fabricating various electronic devices and sensors.
Recombination-enhanced extension of stacking faults in 4H-SiC p-i-n diodes under forward bias
Authors: Galeckas A. , Linnros J. , Pirouz P.
Published: September 2002

The extension of stacking faults in a forward-biased 4H-SiC PiN diodes by the recombination-enhanced motion of leading partial dislocations has been investigated by the technique of optical emission microscopy. From the temperature dependence of the measured velocity of the partials, an activation energy of 0.27 eV is obtained. Based on this and analysis of the emission spectra, a radiative recombination level of 2.8 eV for the stacking fault, and two energy levels for the partial dislocation, a radiative one at 1.8 eV and a nonradiative at 2.2 eV, have been determined.
Anomalous magnetic and dynamic behavior in magnetoresistive compounds: origin of bulk colossal magnetoresistivity
Authors: Chechersky V. , Nath A.
Published: September 2002

We present the results of our extensive Mössbauer effect studies carried out on a wide variety of mixed valence manganites as well as other types of magnetoresistive materials, including pyrochlore Tl2Mn2O7 and the chalcospinels Fe0.5Cu0.5Cr2S4 and FeCr2S4 with absolutely different natures of the magnetism, in a search for similarities linked to their magnetoresistive behavior. The double exchange electron transfer and coupling between the electrons and Jahn–Teller lattice distortions invoked by most theories to explain the colossal magnetoresistivity and associated metal–insulator transition in manganites are not applicable to pyrochlore nor to chalcospinels. Nevertheless, we find intriguing similarities in the anomalous magnetic and dynamic behavior among these widely different systems at, above, and below the Curie temperature TC, which shed light on the origin of bulk magnetoresistivity in general. All these compounds share the following features. The long-range ferromagnetic order breaks down even below the Curie temperature, with the formation of nano-size spin clusters. Softening of the lattice was observed near TC. The short-range interactions in these spin clusters survive well above TC. When an external magnetic field is applied, the spin clusters coalesce to form large clusters, with considerable lowering of the resistivity. There is a strong evidence that the existence of nano-size spin clusters with superparamagnetic-like behavior near TC is a prerequisite for the occurrence of bulk magnetoresistivity.
Orientation-dependent density fingering in an acidity front
Authors: Horváth Dezső , Bánsági Tamás , Tóth Ágota
Published: September 2002

Density fingering of the chlorite–tetrathionate reaction is studied experimentally in a Hele-Shaw cell. It is shown that the dispersion curve describing the linear regime of the evolution of pattern formation is strongly affected by the orientation of the cell. Both the growth rate and the range of wave numbers associated with the unstable modes decrease on increasing the tilt angle from the vertical. From the dispersion curves, the dependence of the most unstable mode on the tilt angle is determined experimentally and compared with that of existing theories. The ratio of the marginal wave number, separating the stable and unstable modes, to the wave number with the maximum growth rate indicates that the high-frequency disturbances are stabilized by the diffusion of the components in the reaction.
Electrochromism in Ir–Mg oxide films
Authors: Azens A. , Granqvist C. G.
Published: September 2002

Thin films of IrMgyOz with 2<y<5 were produced by reactive dc magnetron sputtering. Electrochromism was investigated by voltammetric cycling in proprionic acid and by spectrophotometry. The Mg addition yielded enhanced optical modulation and bleached state transparency, while good cycling durability prevailed.
Mean rise rate of droplets in isotropic turbulence
Authors: Friedman P. D. , Katz J.
Published: September 2002

This paper investigates the rise rate of droplets that are slightly lighter than the surrounding fluid. We experimentally investigate the effect of three parameters: Stokes number, turbulence intensity, and droplet Reynolds number. Droplets were injected into a chamber with nearly isotropic turbulence and little mean flow. The results show that at high turbulence intensity, the mean droplet rise rate is 25% of the root-mean-square velocity regardless of the Stokes number, while at low turbulence intensity, the droplets rise at a rate equal to the rise rate in a quiescent fluid. At intermediate turbulence intensity, the rise rate is strongly dependent on the Stokes number. Qualitative discussions explain these trends.
Improvement in light-output efficiency of InGaN/GaN multiple-quantum well light-emitting diodes by current blocking layer
Authors: Huh Chul , Lee Ji-Myon , Kim Dong-Joon , Park Seong-Ju
Published: September 2002

The fabrication and characterization of an InGaN/GaN multiple-quantum well (MQW) light-emitting diode (LED) with a SiO2 current blocking layer inserted beneath the p-pad electrode is described. The light-output power and external quantum efficiency for the InGaN/GaN MQW LED chip with a current blocking layer were significantly increased compared to those for the conventional InGaN/GaN MQW LED chip. The increase in the light-output power can be attributed to the injection of additional current into the light-emitting quantum well layer of the LED by the SiO2 current blocking layer and a reduction in parasitic optical absorption in the p-pad electrode.
Exploration of multidimensional variational Gaussian wave packets as a simulation tool
Authors: Buch Victoria
Published: September 2002

Variational Gaussian wave packets are investigated as a simulation tool. The method is tested on the Ne13 cluster in the liquid- and solid-like regimes. Feasibility of fully correlated 39-dimensional wave packets is demonstrated for the latter system. The problems associated with long-time wave packet dynamics in the liquid range are identified and discussed. The usefulness of the method is limited by wave packet broadening in the course of the trajectory. A procedure is suggested employing consecutive segments of variational wave packet trajectories.
Solubility of KF in water by molecular dynamics using the Kirkwood integration method
Authors: Ferrario Mauro , Ciccotti Giovanni , Spohr Eckhard , Cartailler Thierry , Turq Pierre
Published: September 2002

We have studied the solubility of potassium fluoride in aqueous solution at near ambient condition, using a simple modeling for the ion and water interactions and computing the values of the chemical potential by molecular dynamics within the framework of Kirkwood generalized thermodynamic integration approach for the evaluation of free energy differences. We report the details of the procedure we used, which is based—at variance with previous attempts—on the individual determination of the chemical potential for the ions in solution. We explore a wide range of salt concentrations up to more than 25 M and determine the solubility. The agreement with the experimental value is reasonable, taking account of the rather crude model used.
Stokes slip flow through a grid of circular cylinders
Authors: Wang C. Y.
Published: September 2002

The Stokes flow through a row of equally spaced circular cylinders with partial slip on the boundaries is studied by domain decomposition and matching. The pressure drop or resistance across the grid is found for various slip and normalized cylinder radii. Asymptotic formulas are found for sparcely and closely spaced cylinders.
Heterostructures of ZnO–Zn coaxial nanocables and ZnO nanotubes
Authors: Wu Jih-Jen , Liu Sai-Chang , Wu Chien-Ting , Chen Kuei-Hsien , Chen Li-Chyong
Published: September 2002

The heterostructures of Zn–ZnO coaxial nanocables and ZnO nanotubes with an average diameter of 30 nm have been synthesized by simple pyrolysis of zinc acetylacetonate. High-resolution transmission electron microscopy analyses reveal that the Zn core and the ZnO sheath of the nanocables have an epitaxial relationship with their longitudinal axis oriented along the 〈001〉 direction. ZnO nanotubes with a wall thickness of 4 nm possess a single-crystal structure and appear to be the extension of the ZnO sheath of the coaxial nanocables. It is suggested that the ZnO nanotubes are formed by partial evaporation of Zn core of the Zn–ZnO coaxial nanocables.
Evidence of ductile response of alumina ceramic under shock wave compression
Authors: Zaretsky E. B. , Kanel G. I.
Published: September 2002

An experimental technique for controlled variation of the transversal stress in specimens subjected to planar impact has been developed to study the inelastic response mode of materials under one-dimensional shock compression. That technique was employed in order to test alumina ceramic at zero and 0.3 GPa confining pressure. The results unambiguously exhibit the ductile response of the ceramic under conditions of one-dimensional shock compression.
Influence of a thin GaAs cap layer on structural and optical properties of InAs quantum dots
Authors: Ferdos Fariba , Wang Shumin , Wei Yongqiang , Larsson Anders , Sadeghi Mahdad , Zhao Qingxiang
Published: September 2002

In this letter we investigate the changes in the surface morphology and emission wavelength of InAs quantum dots (QDs) during initial GaAs encapsulation by atomic force microscopy and photoluminescence. The density (2.9×1010 cm−2) and height (7.9±0.4 nm) of the uncapped QDs decrease and saturate at 0.6×1010 cm−2 and 4 nm, respectively, after the deposition of 4 monolayers (MLs) of GaAs. A model for the evolution of surface morphology is proposed. Photoluminescence spectra of the surface dots show a wavelength shift from 1.58 to 1.22 μm when the GaAs capping layer thickness increases from 0 to 8 MLs.
Self-assembly of globular particles in a nematic dispersion of colloidal rods
Authors: van der Schoot Paul
Published: September 2002

Small spherical guest particles added to a nematic liquid-crystalline dispersion of colloidal rods self-assemble linearly into chain-like aggregates. We argue that the formation of these chains is induced by the excluded-volume coupling of the globules to the nematic matrix, and that pretransitional fluctuations in the mixture give rise to the structural reorganization of the linear aggregates observed in experiment. Ultimately, the repulsive interactions between the globules and the rods either promote large-scale demixing or a transition to a microphase-separated lamellar state, depending on the concentration of rods in the host dispersion.
Deformation potentials of the E2(high) phonon mode of AlN
Authors: Sarua A. , Kuball M. , Van Nostrand J. E.
Published: September 2002

AlN layers grown on (111)-oriented silicon substrates were studied by Raman spectroscopy. The deformation potentials of the nonpolar E2(high) phonon mode of hexagonal AlN were derived from phonon frequency shifts under biaxial stress applied to the layer. Stress was applied by mechanical bending of the wafer with resulting in-plane biaxial stress in AlN. The technique allows one to avoid the uncertainty of x-ray diffraction strain determination inherent to experimental methods commonly used for deformation potentials determination in III–V nitrides. The obtained values for the phonon deformation potentials are in reasonably good agreement with previous theoretical calculations. For pure biaxial stress, we determine a phonon frequency shift of 3 cm−1/GPa.
Bi
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Sr
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whiskers with high thermoelectric figure of merit
Authors: Funahashi Ryoji , Shikano Masahiro
Published: September 2002

Bi 2 Sr 2 Co 2 O y (BC-222) whiskers were grown with an excellent Seebeck coefficient (S) and electrical resistivity (ρ) for power generation applications at high temperatures in air. The S value of these long BC-222 whiskers reached almost 300 μV K−1 at 973 K. Thermal conductivity (κ) was measured and found to be suppressed to a low value of about 2.0 W m−1 K−1. This is considered due not only to a phonon–phonon interaction but also other scattering processes. The resulting dimensionless thermoelectric figure of merit ZT(=S2T/ρκ) was more than 1.1, which corresponds to a conversion efficiency of almost 10% at 973 K in air.
Assessing freshwater inflows to the hypersaline lower Laguna Madre Estuary of Texas using spectral radiometry, aerial videography, and in situ physicochemistry
Authors: Webster Charles F. , Repic Randall L. , Escobar David , Everitt James , Davis M. R.
Published: September 2002

The Lower Laguna Madre is a biologically productive, subtropical, hypersaline estuary on the southern Texas Coast. Its shallow waters tend to be relatively clear, over extensive seagrass beds that serve as important nursery areas for many Gulf of Mexico species and as food for the largest wintering population of redhead ducks (Aytha americana) in North America. The Arroyo Colorado and its distributary arm, the North Floodway, are the only two freshwater streams entering the Lower Laguna Madre. Both streams are turbid and deliver significant particulate, nutrient, and chlorophyll/pheophytin loads to the estuary. Water reflectance, airborne videography, and in situ physicochemical data were acquired from two above-tidal and two tidal stations in the Arroyo Colorado and from one station in the estuary, at the confluence of the Arroyo Colorado with the Gulf Intracoastal Waterway, during the summer of 1995. Analysis of the spectral data, collected imagery, and physicochemistry confirm that near-surface chlorophyllous aggregates (chlorophyll a and pheophytin) can be imaged, yielding both qualitative and quantitative results. Correlation coefficients greater than 0.90 were obtained when digital data from specified spectral bands and band ratios were compared to chlorophyll a, total suspended solids and total dissolved solids concentrations. Results demonstrate the potential of rapid airborne video image acquisition for detecting and mapping effluent discharges into rivers and estuaries. Video remote sensing could be used for environmental monitoring by government agencies, managers, planners, and others making decisions about land and water use, disposition, and development.
Ren
Authors: Gallo Rita , Zazzeroni Francesca , Alesse Edoardo , Mincione Claudia , Borello Ugo , Buanne Pasquale , D'Eugenio Roberta , Mackay Andrew R. , Argenti Beatrice , Gradini Roberto , Russo Matteo A. , Maroder Marella , Cossu Giulio , Frati Luigi , Screpanti Isabella , Gulino Alberto
Published: September 2002

Expansion and fate choice of pluripotent stem cells along the neuroectodermal lineage is regulated by a number of signals, including EGF, retinoic acid, and NGF, which also control the proliferation and differentiation of central nervous system (CNS) and peripheral nervous system (PNS) neural progenitor cells. We report here the identification of a novel gene, REN, upregulated by neurogenic signals (retinoic acid, EGF, and NGF) in pluripotent embryonal stem (ES) cells and neural progenitor cell lines in association with neurotypic differentiation. Consistent with a role in neural promotion, REN overexpression induced neuronal differentiation as well as growth arrest and p27Kip1 expression in CNS and PNS neural progenitor cell lines, and its inhibition impaired retinoic acid induction of neurogenin-1 and NeuroD expression. REN expression is developmentally regulated, initially detected in the neural fold epithelium of the mouse embryo during gastrulation, and subsequently throughout the ventral neural tube, the outer layer of the ventricular encephalic neuroepithelium and in neural crest derivatives including dorsal root ganglia. We propose that REN represents a novel component of the neurogenic signaling cascade induced by retinoic acid, EGF, and NGF, and is both a marker and a regulator of neuronal differentiation.
Gene replacement in mice reveals that the heavily phosphorylated tail of neurofilament heavy subunit does not affect axonal caliber or the transit of cargoes in slow axonal transport
Authors: Rao Mala V. , Garcia Michael L. , Miyazaki Yukio , Gotow Takahiro , Yuan Aidong , Mattina Salvatore , Ward Chris M. , Calcutt Nigel A. , Uchiyama Yasuo , Nixon Ralph A. , Cleveland Don W.
Published: September 2002

The COOH-terminal tail of mammalian neurofilament heavy subunit (NF-H), the largest neurofilament subunit, contains 44-51 lysine–serine–proline repeats that are nearly stoichiometrically phosphorylated after assembly into neurofilaments in axons. Phosphorylation of these repeats has been implicated in promotion of radial growth of axons, control of nearest neighbor distances between neurofilaments or from neurofilaments to other structural components in axons, and as a determinant of slow axonal transport. These roles have now been tested through analysis of mice in which the NF-H gene was replaced by one deleted in the NF-H tail. Loss of the NF-H tail and all of its phosphorylation sites does not affect the number of neurofilaments, alter the ratios of the three neurofilament subunits, or affect the number of microtubules in axons. Additionally, it does not reduce interfilament spacing of most neurofilaments, the speed of action potential propagation, or mature cross-sectional areas of large motor or sensory axons, although its absence slows the speed of acquisition of normal diameters. Most surprisingly, at least in optic nerve axons, loss of the NF-H tail does not affect the rate of transport of neurofilament subunits.
Conditional control of selectin ligand expression and global fucosylation events in mice with a targeted mutation at the FX locus
Authors: Smith Peter L. , Myers Jay T. , Rogers Clare E. , Zhou Lan , Petryniak Bronia , Becker Daniel J. , Homeister Jonathon W. , Lowe John B.
Published: September 2002

Glycoprotein fucosylation enables fringe-dependent modulation of signal transduction by Notch transmembrane receptors, contributes to selectin-dependent leukocyte trafficking, and is faulty in leukocyte adhesion deficiency (LAD) type II, also known as congenital disorder of glycosylation (CDG)-IIc, a rare human disorder characterized by psychomotor defects, developmental abnormalities, and leukocyte adhesion defects. We report here that mice with an induced null mutation in the FX locus, which encodes an enzyme in the de novo pathway for GDP–fucose synthesis, exhibit a virtually complete deficiency of cellular fucosylation, and variable frequency of intrauterine demise determined by parental FX genotype. Live-born FX(−/−) mice exhibit postnatal failure to thrive that is suppressed with a fucose-supplemented diet. FX(−/−) adults suffer from an extreme neutrophilia, myeloproliferation, and absence of leukocyte selectin ligand expression reminiscent of LAD-II/CDG-IIc. Contingent restoration of leukocyte and endothelial selectin ligand expression, general cellular fucosylation, and normal postnatal physiology is achieved by modulating dietary fucose to supply a salvage pathway for GDP–fucose synthesis. Conditional control of fucosylation in FX(−/−) mice identifies cellular fucosylation events as essential concomitants to fertility, early growth and development, and leukocyte adhesion.
The road less traveled
Authors: Roy Craig R. , Tilney Lewis G.
Published: September 2002

Phagosomes containing the bacterial pathogen Legionella pneumophila are transported to the ER after macrophage internalization. To modulate phagosome transport, Legionella use a specialized secretion system that injects bacterial proteins into eukaryotic cells. This review will focus on recent studies that have identified bacterial proteins and host processes that play a concerted role in transporting Legionella to the ER.
FGF signaling targets the pRb-related p107 and p130 proteins to induce chondrocyte growth arrest
Authors: Laplantine Emmanuel , Rossi Ferdinand , Sahni Malika , Basilico Claudio , Cobrinik David
Published: September 2002

Unregulated FGF signaling affects endochondral ossification and long bone growth, causing several genetic forms of human dwarfism. One major mechanism by which FGFs regulate endochondral bone growth is through their inhibitory effect on chondrocyte proliferation. Because mice with targeted mutations of the retinoblastoma (Rb)-related proteins p107 and p130 present severe endochondral bone defects with excessive chondrocyte proliferation, we have investigated the role of the Rb family of cell cycle regulators in the FGF response. Using a chondrocyte cell line, we found that FGF induced a rapid dephosphorylation of all three proteins of the Rb family (pRb, p107, and p130) and a blockade of the cells in the G1 phase of the cell cycle. This cell cycle block was reversed by inactivation of Rb proteins with viral oncoproteins such as polyoma large T (PyLT) antigen and Adenovirus E1A. Expression of a PyLT mutant that efficiently binds pRb, but not p107 and p130, allowed the cells to be growth inhibited by FGF, suggesting that pRb itself is not involved in the FGF response. To investigate more precisely the role of the individual Rb family proteins in FGF-mediated growth inhibition, we used chondrocyte micromass culture of limb bud cells isolated from mice lacking Rb proteins individually or in combination. Although wild-type as well as Rb−/− chondrocytes were similarly growth inhibited by FGF, chondrocytes null for p107 and p130 did not respond to FGF. Furthermore, FGF treatment of metatarsal bone rudiments obtained from p107−/−;p130−/− embryos failed to inhibit proliferation of growth plate chondrocytes, whereas rudiments from p107-null or p130-null embryos showed only a slight inhibition of growth. Our findings indicate that p107 and p130, but not pRb, are critical effectors of FGF-mediated growth inhibition in chondrocytes.