bluuebunny/crossref_metadata_2025 huggingface dataset:
A Damage Mechanics-Based Fatigue Life Prediction Model for Solder Joints
Authors: Tang Hong , Basaran Cemal
Published: March 2003

A thermomechanical fatigue life prediction model based on the theory of damage mechanics is presented. The damage evolution, corresponding to the material degradation under cyclic thermomechanical loading, is quantified thermodynamic framework. The damage, as an internal state variable, is coupled with unified viscoplastic constitutive model to characterize the response of solder alloys. The damage-coupled viscoplastic model with kinematic and isotropic hardening is implemented in ABAQUS finite element package to simulate the cyclic softening behavior of solder joints. Several computational simulations of uniaxial monotonic tensile and cyclic shear tests are conducted to validate the model with experimental results. The behavior of an actual ball grid array (BGA) package under thermal fatigue loading is also simulated and compared with experimental results.
Finite Element Analysis of Mechanical Shock Responses of RF Connectors
Authors: Zhu Z. Y. , Lee H. P. , Cheok B. T.
Published: March 2003

A numerical study of the effects of mechanical shock on Radio Frequency (RF) connectors is presented. The finite element method is used to analyze the mechanical shock responses of RF connectors. Three commonly used shock profiles, namely the rectangular, the triangular, and the half-sine profiles are considered. The effect of added mass as well as the direction of mechanical shock are also analyzed and discussed.
Open Defects in PBGA Assembly Solder Joints
Authors: Fan S. H. , Chan Y. C. , Lai J. K. L.
Published: March 2003

PBGA has the advantage of being compatible with existing surface-mount process. The eutectic solder balls collapse during reflow accommodates the lack of co-planarity, the surface tension between solder ball and associated pad creates a strong self-centering property to compensate for any placement offsets. However, some problems emerged in practice due to its special features. The major challenges for manufacturer are the inspection of solder joint and to perform touch-up. In most cases, the defect of solder joint cannot be found until in-circuit or functional testing is performed. At this stage, it becomes difficult to determine whether the defect is due to a solder joint or the component itself. Hence controlling the open defect is very important in the PBGA assembling process. It was found that three kinds of defective modes are responsible for the open defect; insufficient heating in the solder melting phase, poor thermal stability of PCB and PBGA and insufficient amount of printing solder paste. Based on the defect mechanism analysis, by optimizing the soldering process, very high assembly yield was achieved.
Thermoelectric Behavior of Solder
Authors: Kim and Taejin , Chung D. D. L.
Published: March 2003

The absolute thermoelectric power of tin-lead eutectic solder is −5μV/°C. The voltage generated by a temperature gradient in solder may affect the performance of microelectronics.
The Effect of Cooling Rate on the Growth of Cu-Sn Intermetallics in Annealed PBGA Solder Joints
Authors: Chan Y. C. , Fan S. H. , Lai J. K. L.
Published: March 2003

In this study, the diffusion behavior and microstructural evolution of Cu-Sn intermetallics at eutectic Sn-Pb solder/copper substrate interface of PBGA solder joints was studied. The PBGA solder joints were formed by different profiles, which was devised to have the same “heating factor”—the integral of the measured temperature above the liquidus (183°C) with respect to dwell time in the reflow profile, but to have different conveyor speeds. Using the theory of heat transmission, it is shown that the solder joint cooling rate during solidification increases with increasing conveyor speed. As a result, the “crystallization degree” of the solder joint microstructure decreased with the increasing of cooling rate. The thickness of IMC layer increased with extension of aging time. The growth of IMC is a diffusion-controlled process, i.e., tin diffuses into copper, and the diffusion coefficient in the “disordered region” Db is much bigger than that in the “crystallization region” Dl, so the IMC growth rate of solder joint with faster cooling rate was larger. On the other hand, although Db>Dl at all temperatures, the difference increases as temperature decrease, consequently, the difference of IMC thickness growth among different cooling rate solder joints varied according to the aging temperature.
Nano-Scale Fatigue Wear of Carbon Nitride Coatings: Part I—Wear Properties
Authors: Wang Dong F. , Kato Koji
Published: March 2003

This paper, the first of two companion papers, reports empirical data on wear properties in carbon nitride coatings by a spherical diamond counter-face in repeated sliding contacts through in situ examination and post-sliding observation, with an emphasis on the effects of friction cycles and normal load. In the repeated sliding, a specific wear amount of about 10−9mm3/Nm was observed on the wear track of the carbon nitride coating when no wear particles were detected. On the other hand, a specific wear amount of about 10−6mm3/Nm was observed on the wear track of the carbon nitride coating, where wear particles were generated after a certain number of friction cycles. Wear rate change corresponds to a wear mode change. From in situ examination, the critical number of friction cycles, Nc, for wear particle generation is proven to be related to a wear mode change.
Nano-Scale Fatigue Wear of Carbon Nitride Coatings: Part II—Wear Mechanisms
Authors: Wang Dong F. , Kato Koji
Published: March 2003

This is the second part of two companion papers, the first of which reported the empirical data on wear properties in carbon nitride coatings by a spherical diamond counter-face in repeated sliding contacts through in situ examination, with an emphasis on the effect of friction cycles and normal load. The second part will concentrate on wear mechanisms for the transition from “No observable wear particles” to “Wear particle generation.” The relationship between the critical number of friction cycles, Nc, and the representative plastic strain, Δεp, at asperity contact region was confirmed to follow the Manson-Coffin equation with two empirical constants, β and C. The observed generation of wear particles in carbon nitride coatings is therefore concluded to be a low cycle fatigue wear by surface flow and surface delamination in the ploughing mode. For further predicting lifespan, a simplified theoretical expression, combining the Manson-Coffin equation with the analytical solution of a proposed elastic perfectly-plastic indentation model, gives the relation between the critical number of friction cycles, Nc, and the coating thickness h, with respect to the contact pressure P, and the radius R of the asperity on the tip of the diamond pin.
New Experimental Results of a Single Ridge Passing Through an EHL Conjunction
Authors: Fe´lix-Quin˜onez Armando , Ehret Pascal , Summers Jonathan L.
Published: March 2003

The micro-elastohydrodynamic lubrication of a single transverse ridge is revisited using an experimental technique, which combines an optical interferometry technique and a high-speed color video camera. The purpose of this study is to augment prior experimental analyses, by providing a complete and detailed history of the ridge associated with changes in film thickness as it passes through a high-pressure conjunction. An enhanced experimental procedure has been developed to enable an automatic analysis of the interferograms. In particular, the methodology allows abrupt changes in film thickness and rapid variations of interference orders to be taken into account. The observations presented in this paper exhibit interesting and fascinating features that have not been previously reported. In particular, it is observed that under rolling/sliding conditions the ridge undergoes further deformations as it proceeds to the exit to the contact. In addition, there appears to be an important contribution of pressure flow to the transport of lubricant and, contrary to current understanding, entrapped lubricant is seen to accompany the ridge as it passes through the contact, therefore appearing not to move at the entraining velocity.
Indentation of an Orthotropic Half-Space by a Rigid Ellipsoidal Indenter
Authors: Shi Dongai , Lin Yuan , Ovaert Timothy C.
Published: March 2003

Anisotropic materials represent a unique class of materials, including crystals, wood, thin-films, and composites. Existing work in the literature has provided the engineering community with an in-depth understanding of isotropic contact mechanics, and the methodologies for solving isotropic contact problems have been fully developed. Anisotropic material systems, however, are more complex and their analysis is less fully-developed in the literature. Presented here is the analysis of indentation by a rigid ellipsoidal indenter against an orthotropic half-space, with the surface of the half-space parallel to two of the axes of material symmetry, derived from stress equilibrium. A numerical method has been used to solve for the contact parameters (contact dimensions and normal approach) for both orthotropic and transversely isotropic material systems.
Particle Flow and Contamination in Slider Air Bearings for Hard Disk Drives
Authors: Shen Xinjiang , Bogy David B.
Published: March 2003

For a particle entrained in an air bearing, various forces, such as the viscous drag force, Saffmann and Magnus lift forces and gravity force, will act on it. Such particles may pass through the air bearing or impact the slider or disk and then adhere to the surface or bounce off. In this paper, particle flow in an air bearing is simulated. The contamination of particles on a slider’s surface is analyzed using the assumption of adhesion upon impact. The effect of particle size and density on particle paths in the air bearing is studied. The numerical results show that particles are likely to contaminate slider surfaces in the transition regions on the rails. The density of the particles and the pitch angle of the slider are also found to strongly affect the flying path of the particles, and therefore, the accumulation of the particles on slider surfaces.
Measurement of Temperature Field in Surface Grinding Using Infra-Red (IR) Imaging System
Authors: Hwang Jihong , Kompella Sridhar , Chandrasekar Srinivasan , Farris Thomas N.
Published: March 2003

An experimental technique is described for measuring the temperature field in a workpiece during surface grinding. The technique involves measurement of the radiation emitted by a side of the workpiece immediately adjoining the wheel-workpiece contact region using a Charge-Coupled Device (CCD) based Infra-Red imaging system. By using an appropriate calibration procedure, measured radiation values are converted to temperatures. Novel aspects of the experimental technique are full-field measurement of temperature at high spatial and temporal resolution, high sensitivity and non-intrusive measurement. The repeatability of temperature measurement is found to be very good. The experiments have provided an accurate estimate of the surface and sub-surface temperatures in the workpiece. Furthermore, by grinding along a taper with a continuously increasing depth of cut, the effect of material removal rate on temperature field has been characterized. Measurements of the temperature field in taper grinding have been found to correlate well with those made in conventional constant depth grinding thereby, establishing taper grinding as a viable, accelerated test for studying grinding temperatures. Full-field measurements of workpiece temperature should facilitate study of thermal damage and multi-scale validation of thermal models in grinding.
Polypyrrole Latex: Surface Analysis by XPS
Authors: Tarcha Peter J. , Salvati Lawrence , Johnson Robert W.
Published: March 2003

Polypyrrole colloids are synthesized by an oxidative polymerization of pyrrole by ferric chloride in aqueous media containing a steric stabilizer. Polyvinyl alcohol (125,000 to 186,000 mol. wt., 99% hydrolyzed) was used as the stabilizer to prepare the particles for this study. Depending on the synthesis conditions, polypyrrole colloids typically have diameters between 100 and 200 nm, as evidenced by transmission electron microscopy and disk centrifuge photosedimentometry. The conjugated pyrrole polymer imparts intense black coloration to the colloid. Molecules of biological interest, such as antibodies, can be immobilized in active form on the particle surface. Thus these nanoparticles can be used as colored “markers” for immunodiagnostic assays.
Carboxylated Polypyrrole-Silica Nanocomposite: Surface Analysis by XPS
Authors: Armes Steven P. , Tarcha Peter J. , Salvati Lawrence , Johnson Robert W.
Published: March 2003

Carboxylated polypyrrole-silica colloids are synthesized in aqueous media by the oxidative copolymenzation of molar equivalents of pyrrole and 1-(2-carboxyethyl) pyrrole in the presence of ultrafine (20 nm) silica particles [see Maeda et al., Macromolecules 28, 2901 (1995)]. The resulting nanoparticles have a diameter of ∼100 nm as evidenced by transmission electron microscopy and disk centrifuge photosedimentometry and obtain 24–43 wt. % of silica. The conducting polymer component imparts intense coloration to the nanoparticle and the silica component ensures good colloidal stability. The surface carboxylic groups allow the covalent attachment of biological ligands of interest, such as antibodies. Thus these functional nanoparticles can be used as colored “markers” for immunodiagnostic assays.
Carboxylated Polypyrrole Latex: Surface Analysis by XPS
Authors: Tarcha Peter J. , Salvati Lawrence , Johnson Robert W.
Published: March 2003

Carboxylated polypyrrole colloids are synthesized by post-modification of polypvrrole latex in organic media. The modification begins with solvent exchange of the aqueous colloid into N-methyl pyrrolidone, followed by reaction with bromoacetyl bromide. The last reaction is a nulceophilic substitution on the bromoacetyl pendant group with mercaptoacetic acid. After reaction the particles are solvent-exchanged into water. Depending on the synthesis conditions of the base polypvrrole colloid, the resulting nanoparticles can have diameters between 100 and 200 nm, as evidenced by transmission electron microscopy and disk centrifuge photosedimentometry. The conjugated pyrrole polymer imparts intense, intrinsic coloration to the colloid. The surface carboxylic groups allow the covalent attachment of biological ligands of interest such as antibodies. Thus these functional nanoparticles can be used as colored “markers” for immunodiagnostic assays.
Surface Segregation Study of Transparent ZnGa2O4 Films by XPS
Authors: Delichere Pierre , Daniele Stephane , Hubert-Pfalzgraf Liliane G.
Published: March 2003

Sol-gel colloidal suspensions were used to elaborate ZnGa2O4 films by spin coating on glass and MgO substrates. Those films were annealed at 600 °C (10°/min) for l h in air and showed good mechanical resistance as well as very good transparency. XPS spectra recorded from 0 to 1200 eV indicated that the films contained zinc, gallium, oxygen, and a significant amount of carbon. In the absence of depth profiling analysis of the film composition, it has been impossible to determine whether this is due to surface contamination or film incorporation. Surprisingly, the data show that the Zn:Ga stochiometry of ZnGa2O4 is disrupted by interaction with the glass substrate with a Ga/Zn ratio of 4. The result is a multiphasic material namely crystallites of ZnGa2O4 (as shown by AFM measurements) in an amorphous matrix of zinc and gallium oxides. This interaction was confirmed by the fact that deposition on MgO substrate and thermal annealing in similar conditions than for the previous deposits gave XPS data confirming the retention of the Zn:Ga 1:2 stoichiometry.
Alkyl Monolayers on Silica Surfaces Prepared from Neat, Heated ClSi(CH3)2(CH2)17CH3 Analyzed by XPS
Authors: Husseini Ghaleb A. , Zilch Lloyd W. , Sevy Eric T. , Asplund Matthew C. , Linford Matthew R.
Published: March 2003

Silane monolayers on silica, prepared from mono-, di- and trichlorosilanes, are widely used in industry for surface functionalization and modification. However, unlike di- and trichlorosilanes, monochlorosilanes are particularly easy to work with because they can dimerize, but not polymerize, upon reaction with water. Typically, an organic solvent is used when depositing a silane monolayer. Here we show XPS spectra of monolayers of ClSi(CH3)2(CH2)17CH3 (octadecyldimethylchlorosilane, CAS# 18643-08-8) on silicon oxide (silicon wafer) prepared using a rapid, solvent-free approach. Reaction conditions are 120 °C for 10 min using the neat (pure) compound, and no inert atmosphere or special treatment of the compound is required.
Alkyl Monolayers on Silica Surfaces Prepared from Neat, Heated ClSi(CH3)2(CH2)6CH=CH2 Analyzed by XPS
Authors: Husseini Ghaleb A. , Sathyapalan Amarchand , Sevy Eric T. , Linford Matthew R. , Asplund Matthew C.
Published: March 2003

Silane monolayers on silica, prepared from mono-, di-, and trichlorosilanes, are widely used in industry for surface functionalization and modification. However, unlike di-and trichlorosilanes, monochlorosilanes are particularly easy to work with because they can dimerize, but not polymerize, upon reaction with water. Typically, an organic solvent is used when depositing a silane monolayer. Here we show XPS spectra of monolayers of ClSi(CH3)2(CH2)6CH=CH2 (octenyldimethylchlorosilane, CAS# 17196-12-2) on silicon oxide (silicon wafer) prepared using a rapid, solvent-free approach. Reaction conditions are 120 °C for 10 min using the neat (pure) compound, and no inert atmosphere or special treatment of the compound is required.
Alkyl Monolayers on Silica Surfaces Prepared from Neat, Heated 3-Glycidoxypropyldimethylethoxysilane Analyzed by XPS
Authors: Husseini Ghaleb A. , Linford Matthew R. , Asplund Matthew C. , Peacock Justin , Sevy Eric T.
Published: March 2003

Silane monolayers on silica, prepared from mono-, di-, and trichlorosilanes, are widely used in industry for surface functionalization and modification. However, unlike di- and trichlorosilanes, monochlorosilanes are particularly easy to work with because they can dimerize, but not polymerize, upon reaction with water. Typically, an organic solvent is used when depositing a silane monolayer. Here we show XPS spectra of monolayers of 3-glycidoxypropyldimethylethoxysilane (CAS# 17963-04-1) on silicon oxide (silicon wafer) prepared using a rapid, solvent-free approach. Reaction conditions are 100 °C for 10 min using the neat (pure) compound, and no inert atmosphere or special treatment of the compound is required.
Plasma-Enhanced CVD CeO2 Nanocrystalline Thin Films Analyzed by XPS
Authors: Armelao Lidia , Barreca Davide , Bottaro Gregorio , Gasparotto Alberto , Tondello Eugenio
Published: March 2003

CeO2 nanocrystalline films were deposited on SiO2 and SiO2/Si(100) substrates by plasma enhanced-chemical vapor deposition (PE-CVD) in Ar–O2 atmospheres. Ce(dpm)4 (dpm = 2,2-6,6-tetramethyl-3,5-heptanedionate) was used as a precursor, which allows a clean conversion into CeO2 due to the presence of Ce–O bonds. The coatings were pale yellow in color, homogeneous and crack-free. In this study, an x-ray photoelectron spectroscopy (XPS) investigation of the principal core levels (O ls, Ce 3d) of CeO2 films was performed. The relative Ce(III)/Ce(IV) amount was estimated by evaluating the ratio of the Ce 3d3/2(u′″) satellite to the total Ce 3d integral area. The relative content of Ce(III) and Ce(IV) amount can be tailored by controlling the O2 partial pressure and substrate temperature during the depositions. The reported results represent the extension of a recently published article (Ref. 1).
A Study of Nanophase Tungsten Oxides Thin Films by XPS
Authors: Barreca Davide , Carta Giovanni , Gasparotto Alberto , Rossetto Gilberto , Tondello Eugenio , Zanella Pierino
Published: March 2003

Nanophasic tungsten oxides thin films have been deposited at 500 °C on quartz and glass substrates starting from W(CO)6 using the metal organic chemical vapor deposition technique (MOCVD). Two series of deposition experiments were carried out to make a comparison between the results obtained employing, as reactant gases, O2 mixed with water vapor and a dry mixture of N2 with 25% H2, respectively. The obtained tungsten oxides were analyzed by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) in order to investigate their microstructure, chemical composition, and surface morphology. In this work, XPS analyses of two tungsten oxides thin films deposited in different atmospheres are presented. Besides the wide scan spectra, charge corrected binding energies for the W 4f7/2, W 4f5/2, O ls, and C 1s surface photoelectron signals are reported. In particular, the film obtained in H2 atmosphere shows the presence of W in an oxidation state lower than VI.
Signaling Life and Death in the Thymus: Timing Is Everything
Authors: Werlen Guy , Hausmann Barbara , Naeher Dieter , Palmer Ed
Published: March 2003

T lymphocytes are generated in the thymus, where developing thymocytes must accept one of two fates: They either differentiate or they die. These fates are chiefly determined by signals that originate from the T cell receptor (TCR), a single receptor complex with a remarkable capacity to decide between distinct cell fates. This review explores TCR signaling in thymocytes and focuses on the kinetic aspects of ligand binding, coreceptor involvement, protein phosphorylation, and mitogen-activated protein kinase (MAPK) activation. Understanding the logic of TCR signaling may eventually explain how thymocytes and T cells distinguish self from nonself, a phenomenon that has fascinated immunologists for 50 years.
Discrete Coding of Reward Probability and Uncertainty by Dopamine Neurons
Authors: Fiorillo Christopher D. , Tobler Philippe N. , Schultz Wolfram
Published: March 2003

Uncertainty is critical in the measure of information and in assessing the accuracy of predictions. It is determined by probability
P
, being maximal at
P
= 0.5 and decreasing at higher and lower probabilities. Using distinct stimuli to indicate the probability of reward, we found that the phasic activation of dopamine neurons varied monotonically across the full range of probabilities, supporting past claims that this response codes the discrepancy between predicted and actual reward. In contrast, a previously unobserved response covaried with uncertainty and consisted of a gradual increase in activity until the potential time of reward. The coding of uncertainty suggests a possible role for dopamine signals in attention-based learning and risk-taking behavior.
Hexapod Origins: Monophyletic or Paraphyletic?
Authors: Nardi Francesco , Spinsanti Giacomo , Boore Jeffrey L. , Carapelli Antonio , Dallai Romano , Frati Francesco
Published: March 2003

Recent morphological and molecular evidence has changed interpretations of arthropod phylogeny and evolution. Here we compare complete mitochondrial genomes to show that Collembola, a wingless group traditionally considered as basal to all insects, appears instead to constitute a separate evolutionary lineage that branched much earlier than the separation of many crustaceans and insects and independently adapted to life on land. Therefore, the taxon Hexapoda, as commonly defined to include all six-legged arthropods, is not monophyletic.
Role of EphA4 and EphrinB3 in Local Neuronal Circuits That Control Walking
Authors: Kullander Klas , Butt Simon J. B. , Lebret James M. , Lundfald Line , Restrepo Carlos E. , Rydström Anna , Klein Rüdiger , Kiehn Ole
Published: March 2003

Local circuits in the spinal cord that generate locomotion are termed central pattern generators (CPGs). These provide coordinated bilateral control over the normal limb alternation that underlies walking. The molecules that organize the mammalian CPG are unknown. Isolated spinal cords from mice lacking either the EphA4 receptor or its ligand ephrinB3 have lost left-right limb alternation and instead exhibit synchrony. We identified EphA4-positive neurons as an excitatory component of the locomotor CPG. Our study shows that dramatic locomotor changes can occur as a consequence of local genetic rewiring and identifies genes required for the development of normal locomotor behavior.
Small-Diameter Silicon Nanowire Surfaces
Authors: Ma D. D. D. , Lee C. S. , Au F. C. K. , Tong S. Y. , Lee S. T.
Published: March 2003

Small-diameter (1 to 7 nanometers) silicon nanowires (SiNWs) were prepared, and their surfaces were removed of oxide and terminated with hydrogen by a hydrofluoric acid dip. Scanning tunneling microscopy (STM) of these SiNWs, performed both in air and in ultrahigh vacuum, revealed atomically resolved images that can be interpreted as hydrogen-terminated Si (111)-(1 × 1) and Si (001)-(1 × 1) surfaces corresponding to SiH
3
on Si (111) and SiH
2
on Si (001), respectively. These hydrogen-terminated SiNW surfaces seem to be more oxidation-resistant than regular silicon wafer surfaces, because atomically resolved STM images of SiNWs were obtained in air after several days' exposure to the ambient environment. Scanning tunneling spectroscopy measurements were performed on the oxide-removed SiNWs and were used to evaluate the electronic energy gaps. The energy gaps were found to increase with decreasing SiNW diameter from 1.1 electron volts for 7 nanometers to 3.5 electron volts for 1.3 nanometers, in agreement with previous theoretical predictions.
"Plugging into Enzymes": Nanowiring of Redox Enzymes by a Gold Nanoparticle
Authors: Xiao Yi , Patolsky Fernando , Katz Eugenii , Hainfeld James F. , Willner Itamar
Published: March 2003

The reconstitution of an apo-flavoenzyme, apo–glucose oxidase, on a 1.4-nanometer gold nanocrystal functionalized with the cofactor flavin adenine dinucleotide and integrated into a conductive film yields a bioelectrocatalytic system with exceptional electrical contact with the electrode support. The electron transfer turnover rate of the reconstituted bioelectrocatalyst is ∼5000 per second, compared with the rate at which molecular oxygen, the natural cosubstrate of the enzyme, accepts electrons (∼700 per second). The gold nanoparticle acts as an electron relay or “electrical nanoplug” for the alignment of the enzyme on the conductive support and for the electrical wiring of its redox-active center.
Coherent Quantum Dynamics of a Superconducting Flux Qubit
Authors: Chiorescu I. , Nakamura Y. , Harmans C. J. P. M. , Mooij J. E.
Published: March 2003

We have observed coherent time evolution between two quantum states of a superconducting flux qubit comprising three Josephson junctions in a loop. The superposition of the two states carrying opposite macroscopic persistent currents is manipulated by resonant microwave pulses. Readout by means of switching-event measurement with an attached superconducting quantum interference device revealed quantum-state oscillations with high fidelity. Under strong microwave driving, it was possible to induce hundreds of coherent oscillations. Pulsed operations on this first sample yielded a relaxation time of 900 nanoseconds and a free-induction dephasing time of 20 nanoseconds. These results are promising for future solid-state quantum computing.
Accumulation of Phosphorylated Repressor for Gibberellin Signaling in an F-box Mutant
Authors: Sasaki Akie , Itoh Hironori , Gomi Kenji , Ueguchi-Tanaka Miyako , Ishiyama Kanako , Kobayashi Masatomo , Jeong Dong-Hoon , An Gynheung , Kitano Hidemi , Ashikari Motoyuki , Matsuoka Makoto
Published: March 2003

Gibberellin (GA) regulates growth and development in plants. We isolated and characterized a rice GA-insensitive dwarf mutant,
gid2
. The
GID2
gene encodes a putative F-box protein, which interacted with the rice Skp1 homolog in a yeast two-hybrid assay. In
gid2
, a repressor for GA signaling, SLR1, was highly accumulated in a phosphorylated form and GA increased its concentration, whereas SLR1 was rapidly degraded by GA through ubiquitination in the wild type. We conclude that GID2 is a positive regulator of GA signaling and that regulated degradation of SLR1 is initiated through GA-dependent phosphorylation and finalized by an SCF
GID2
-proteasome pathway.
Self-Aligned, Vertical-Channel, Polymer Field-Effect Transistors
Authors: Stutzmann Natalie , Friend Richard H. , Sirringhaus Henning
Published: March 2003

The manufacture of high-performance, conjugated polymer transistor circuits on flexible plastic substrates requires patterning techniques that are capable of defining critical features with submicrometer resolution. We used solid-state embossing to produce polymer field-effect transistors with submicrometer critical features in planar and vertical configurations. Embossing is used for the controlled microcutting of vertical sidewalls into polymer multilayer structures without smearing. Vertical-channel polymer field-effect transistors on flexible poly(ethylene terephthalate) substrates were fabricated, in which the critical channel length of 0.7 to 0.9 micrometers was defined by the thickness of a spin-coated insulator layer. Gate electrodes were self-aligned to minimize overlap capacitance by inkjet printing that used the embossed grooves to define a surface-energy pattern.
Identifying Kinetic Barriers to Mechanical Unfolding of the
T. thermophila
Ribozyme
Authors: Onoa Bibiana , Dumont Sophie , Liphardt Jan , Smith Steven B. , Tinoco Ignacio , Bustamante Carlos
Published: March 2003

Mechanical unfolding trajectories for single molecules of the
Tetrahymena thermophila
ribozyme display eight intermediates corresponding to discrete kinetic barriers that oppose mechanical unfolding with lifetimes of seconds and rupture forces between 10 and 30 piconewtons. Barriers are magnesium dependent and correspond to known intra- and interdomain interactions. Several barrier structures are “brittle,” breakage requiring high forces but small (1 to 3 nanometers) deformations. Barrier crossing is stochastic, leading to variable unfolding paths. The response of complex RNA structures to locally applied mechanical forces may be analogous to the responses of RNA during translation, messenger RNA export from the nucleus, and viral replication.
Identified Sources and Targets of Slow Inhibition in the Neocortex
Authors: Tamás Gábor , Simon Andrea Lőrincz, Anna , Szabadics János
Published: March 2003

There are two types of inhibitory postsynaptic potentials in the cerebral cortex. Fast inhibition is mediated by ionotropic γ-aminobutyric acid type A (GABA
A
) receptors, and slow inhibition is due to metabotropic GABA
B
receptors. Several neuron classes elicit inhibitory postsynaptic potentials through GABA
A
receptors, but possible distinct sources of slow inhibition remain unknown. We identified a class of GABAergic interneurons, the neurogliaform cells, that, in contrast to other GABA-releasing cells, elicited combined GABA
A
and GABA
B
receptor–mediated responses with single action potentials and that predominantly targeted the dendritic spines of pyramidal neurons. Slow inhibition evoked by a distinct interneuron in spatially restricted postsynaptic compartments could locally and selectively modulate cortical excitability.
MONTE CARLO SIMULATION OF ADSORPTION PROBABILITIES: THE CASE OF CO/DISORDERED–Cu(110) AND CO/O–Ir(110)
Authors: BURGHAUS U.
Published: March 2003

Recently [M. Kunat et al., Surf. Sci.474, 114 (2001)] a quenching of adsorbate-assisted adsorption ("autocatalytic adsorption") by defects has been observed for the system CO/Cu(110). A conceptually similar effect for CO adsorption on O–Ir(110) had additionally been reported before [U. Burghaus et al., Surf. Sci.384, L869 (1997)]. Presented is a simple Monte Carlo simulation (MCS) scheme which includes basically one free fit parameter and can reproduce both effects consistently.
MEASUREMENT OF CRITICAL EXPONENTS OF PLATINUM THIN FILMS
Authors: SALVADORI M. C. , MELO L. L. , CATTANI M. , MONTEIRO O. R. , BROWN I. G.
Published: March 2003

We have fabricated platinum thin films by metal plasma ion deposition on silicon substrates. The roughness of these films has been measured by a scanning tunneling microscope (STM) and we have determined the growth dynamics critical exponents.
THEORY OF NONLINEAR GUIDED AND SURFACE PLASMON–POLARITONS IN DIELECTRIC FILMS
Authors: BAHER S. , COTTAM M. G.
Published: March 2003

Calculations are presented for the dispersion relations of nonlinear plasmon–polariton modes in a layered dielectric structure consisting of a film bounded on each side by another medium. At least one of the media is a metal or semiconductor (such as InSb) with a real, isotropic, frequency-dependent dielectric function, characteristic of an electron plasma. In addition, both media may have a Kerr-type nonlinearity in their dielectric functions. Hence the resulting plasmon–polaritons, which we study in s polarization, are nonlinear and are found to occur in multiple branches. The theory is illustrated by numerical solutions of the dispersion relations for several geometries and physical parameters, and a comparison is made with previous plasmon–polariton results for linear dielectric media as a special case.
MESOSCOPIC PATTERN FORMATION IN CATALYTIC PROCESSES BY AN EXTENSION OF THE MEAN FIELD APPROACH
Authors: MOLA E. E. , IRURZUN I. M. , VICENTE J. L. , KING D. A.
Published: March 2003

For some years it has been known that a number of catalytic reactions, under specified steady operating conditions, exhibit oscillations, in the rate of product formation. These are often related to beautiful spatiotemporal patterns, including targets and spirals, on the metal surface.

These examples of self-organizational phenomena have attracted considerable interest, because they are proving to be theoretically amenable.

Here we review different approximations to model heterogeneous surface chemical reactions, which exhibit oscillatory behavior.

A focal point is the use of a detailed knowledge of the dynamics of surface structural phase transition for modeling kinetic oscillations, which represent a severe test of our understanding of chemical processes at surfaces.

Advantages and disadvantages of the Monte Carlo approach are presented to model heterogeneous oscillatory chemical reactions, with special emphasis if a Monte Carlo method is going to be applied to study the time evolution of a surface chemical reaction, as there should be a linear relationship between the time unit called the Monte Carlo step (MCS) and actual time. We conclude that special care must be taken when two or more processes are included in a simulation, because now overall MCS should be compatible with every individual process.

The mean field approach (MFA) takes into account only reaction processes and completely neglects spatial correlation and fluctuations. Therefore, this approach is not adequate for describing the rich variety of spatial patterns that are experimentally observed. On the other hand, Monte Carlo approaches are severely limited by computational capabilities. To overcome MFA limitations we propose to extend the earlier work of King and coworkers [J. Chem. Phys.100, 14417 (1996)], which did not include spatial dependence, by adding diffusion processes and gas global coupling to the coupled reaction equations.

The extended MFA can now be used as a new tool for the analysis of pattern formation in surface chemistry.
MODELING OF SURFACE STRESS OF SEMICONDUCTORS
Authors: JIANG Q. , ZHAO D. S. , ZHAO M.
Published: March 2003

A general equation for surface stress is established based on a thermodynamic consideration of the size dependence of solid–liquid interface energy under an assumption that the solid–liquid interface of a particle immersed in surrounding liquid disappears when almost all atoms of the particle are located on its surface. The predicted surface stresses of semiconductors in terms of the model are in agreement with the first principles calculations and calculations based on forces associated with the elastic distortion of the covalent bonds.
MORPHOLOGICAL ELEMENTS OF THE RuO2·TiO2 COATING AS DISPLAYED AT DIFFERENT SCALE LEVELS AND POSSIBLE MODELS OF ITS CONDUCTIVITY
Authors: KONDRIKOV N. B. , SHCHITOVSKAYA E. V. , VASILYEVA M. S. , KURYAVY V. G. , BOUZNIK V. M.
Published: March 2003

The roughness elements displayed at different scales on the RuO 2· TiO 2 (ORTA) coating obtained by means of calcination on a titanium support were studied with the methods of electronic scanning microscopy and scanning tunneling microscopy. Two models for the emergence of the electronic conductivity, possible for different ORTA components, were discussed on the basis of the scanning tunneling microscopy data. One of the models, formerly known as the "islet" model, assumes the simultaneous presence of conducting nanoclusters of RuO 2 and nonconducting clusters of TiO 2 separated in space. Another model assumes the presence of similar volume-conducting nanoclusters of cross-size ~ 1 nm, every one of which is a solid solution of RuO 2· TiO 2 composed in such a way as to have the Fermi level common for RuO 2 and TiO 2.
INVESTIGATION OF THE INTERFACE OF THE DCB SUBSTRATE
Authors: NING HONGLONG , MA USHENG , HUANG FUXIANG , WANG YONGGANG , ZHU JIMAN , GENG ZHITING
Published: March 2003

DCB means direct copper bonding and denotes a process in which copper and a ceramic material are directly bonded. Between the temperature of the metal's melting point and the eutectic temperature of the metal-oxygen, DCB depends on the eutectic compound to join the copper and the ceramic. We do some research to investigate the interface between the copper foils and Al2O3 ceramics; it is the key factor in influencing the performance of the DCB substrate. We also discuss how to get good microstructure of the DCB interface.
PROPERTIES OF ULTRATHIN Sb LAYERS ON THE Ni(111) FACE
Authors: KRUPSKI A. , MRÓZ S.
Published: March 2003

We present the first results concerning the atomic structure and morphology of ultrathin Sb layers deposited on the Ni(111) face in ultrahigh vacuum at the substrate temperature ranging from 150 to 700 K obtained with the use of Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and directional elastic peak electron spectroscopy (DEPES). The AES results indicate that the antimony layer on the Ni(111) at T < 200 K grows in the Frank–van der Merwe mode. For temperature around 250 K, the flat two atomic layer islands ("wedding cakes") seem to grow after completion of the first antimony monolayer. At T ≥ 300 K , a Sb–Ni surface alloy is formed. DEPES measurements indicate that the atomic structure of Sb layers deposited at T = 150 K is completely amorphous, while better and better pronounced maxima appear in DEPES profiles when the sample temperature increases from 300 to 450 K. LEED patterns corresponding to p(1 × 1), p(2 × 2) and [Formula: see text] structures have been observed for 150 K ≤ T ≤ 250 K . A possible model for the last structure is proposed. After annealing the deposited layer at T > 500 K , the [Formula: see text] structure appears.
A MODEL FOR COAXIAL ABLATION BY PLASMA AT THE HEAT FLUX THRESHOLD
Authors: VALLÉE O. , CAILLARD J. , DE IZARRA C.
Published: March 2003

The purpose of this paper is to present a model for ablation due to a plasma flash in cylindrical symmetry. The model of ablation speed of the coaxial material is based on the integral method of the heat equation which basically involves the idea of a thermal layer. It is first shown that an important step in the process is the heating of the material. When the material comes up to melt, it is found that the mass ablated by the plasma flux appears only beyond a threshold.
HIGHLY ORIENTED DIAMOND FILMS ON HETEROSUBSTRATES: CURRENT STATE OF THE ART AND REMAINING CHALLENGES
Authors: ARNAULT J. C.
Published: March 2003

The potential applications of diamond in the field of electronics working under high power and high temperature (aeronautic, aerospace, etc.) require highly oriented films on heterosubstrates. This is the key motivation of the huge research efforts that have been carried out during the last ten years. Very significant progress has been accomplished and nowadays diamond films with misorientations close to 1.5° are elaborated on β-SiC monocrystals. Moreover, an excellent crystalline quality with polar and azimuthal misalignments lower than 0.6° is reported for diamond films grown on iridium buffer layers. Unfortunately, these films are still too defective for high power electronics applications. To achieve higher crystalline quality, further improvements of the deposition methods are needed. Nevertheless, a deeper knowledge of the elemental mechanisms occurring during the early stages of growth is also essential. The first part of this paper focuses on the state of the art of the different investigated ways towards heteroepitaxy. Secondly, the present knowledge of the early stages of diamond nucleation and growth on silicon substrates for both classical nucleation and bias-assisted nucleation (BEN) is reviewed. Finally, the remaining questions concerning the understanding of the nucleation processes are discussed.
Mevastatin Can Cause G
1
Arrest and Induce Apoptosis in Pulmonary Artery Smooth Muscle Cells Through a p27
Kip1
-Independent Pathway
Authors: Fouty Brian W. , Rodman David M.
Published: March 2003

Advanced pulmonary arterial hypertension is characterized by extensive vascular remodeling that is usually resistant to vasodilator therapy. Mevastatin is an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, the rate-limiting step for cholesterol synthesis. HMG-CoA reductase inhibitors have been shown to upregulate the cyclin-dependent kinase inhibitor p27
Kip1
and to block cell proliferation through cholesterol-independent pathways. The aim of this study was to determine the effect of mevastatin on DNA synthesis, cell cycle progression, and cell proliferation in rat pulmonary artery smooth muscle cells (PASMCs). We found that mevastatin induced G
1
arrest and decreased DNA synthesis in rat PASMCs and did so in association with an increase in both total and cyclin E-bound p27
Kip1
. This caused a marked decrease in cyclin E kinase activity, which suggests an important role for p27
Kip1
in the ability of mevastatin to induce G
1
arrest. However, in PASMCs lacking functional p27
Kip1
, mevastatin still decreased cyclin E kinase activity, caused G
1
arrest, and decreased DNA synthesis. In p27
Kip1
-deficient PASMCs, mevastatin induced a greater reduction of cyclin E protein levels (to 35% of control) than in wild-type cells (to 70% of control) and also reduced the phosphorylation of cdk2 on threonine 160. Mevastatin also caused apoptosis in both wild-type and p27
Kip1
-deficient PASMCs and was able to do so at a dose that did not induce cell cycle arrest. These data suggest that HMG-CoA reductase inhibitors can both inhibit cell proliferation and induce apoptosis in PASMCs through p27
Kip1
-independent pathways and may be important therapeutic agents in pulmonary arterial hypertension.
Involvement of the Fibroblast Growth Factor System in Adaptive and Chemokine-Induced Arteriogenesis
Authors: Deindl Elisabeth , Hoefer Imo E. , Fernandez Borja , Barancik Miroslav , Heil Matthias , Strniskova Monika , Schaper Wolfgang
Published: March 2003

Fibroblast growth factors (FGFs) have been applied in a variety of therapeutic and experimental studies to improve collateral blood flow. However, the pathophysiological role and the temporospatial expression of the FGFs and their receptors during arteriogenesis have never been elucidated in vivo. Here, we report that collateral artery growth in its early phase is associated with an increased expression of FGF receptor-1 (FGFR-1) and syndecan-4 on mRNA and protein levels as well as with an increased kinase activity of FGFR-1 in a rabbit model of arteriogenesis. However, the mRNA levels of FGF-1 and -2 remained constant. Our data suggest that these growth factors are supplied by endothelial attracted monocytes that, in turn, produce and deliver the FGFs to growing collateral arteries. Monocyte chemoattractant protein-1-stimulated arteriogenesis was strongly reduced in rabbits by application of the FGF inhibitor polyanetholesulfonic acid, indicating that the monocyte-related arteriogenesis (as well as the unstimulated adaptation proper) is promoted by FGFs. In summary, this study shows that arteriogenesis is associated with an increased expression of the FGFRs at the site of the vessel, whereas the growth-promoting ligands are supplied by monocytes in a paracrine way.
Vasomodulation by Skeletal Muscle–Derived Nitric Oxide Requires α-Syntrophin–Mediated Sarcolemmal Localization of Neuronal Nitric Oxide Synthase
Authors: Thomas Gail D. , Shaul Philip W. , Yuhanna Ivan S. , Froehner Stanley C. , Adams Marvin E.
Published: March 2003

Neuronal nitric oxide synthase (nNOS) is abundantly expressed in skeletal muscle where it associates with the dystrophin complex at the sarcolemma by binding to the PDZ domain of α-syntrophin. Nitric oxide (NO) produced by skeletal muscle nNOS is proposed to regulate blood flow in exercising muscle by diffusing from the skeletal muscle fibers to the nearby microvessels where it attenuates α-adrenergic vasoconstriction. In the present study, we hypothesized that sarcolemmal localization of nNOS is a critical determinant of the vasoregulatory effect of skeletal muscle–derived NO. To test this hypothesis, we performed experiments in α-syntrophin null mice and in transgenic mice expressing a mutated α-syntrophin lacking the PDZ domain (ΔPDZ), both of which are characterized by reduced sarcolemmal nNOS. We found that modulation of α-adrenergic vasoconstriction was greatly impaired in the contracting muscles of the α-syntrophin null mice and transgenic ΔPDZ mice compared with wild-type mice and transgenic mice expressing full-length α-syntrophin. These in vivo mouse studies highlight the functional importance of appropriate membrane targeting of nNOS by the dystrophin-associated protein α-syntrophin and may have implications for the development of potential gene therapy strategies to treat muscular dystrophy or other muscle-related diseases.
Urokinase-Type Plasminogen Activator Plays a Critical Role in Angiotensin II–Induced Abdominal Aortic Aneurysm
Authors: Deng Gary G. , Martin-McNulty Baby , Sukovich Drew A. , Freay Ana , Halks-Miller Meredith , Thinnes Therese , Loskutoff David J. , Carmeliet Peter , Dole William P. , Wang Yi-Xin
Published: March 2003

We have previously demonstrated that urokinase-type plasminogen activator (uPA) is highly expressed in the aneurysmal segment of the abdominal aorta (AAA) in apolipoprotein E–deficient (apoE
−/−
) mice treated with angiotensin II (Ang II). In the present study, we tested the hypothesis that uPA is essential for AAA formation in this model. An osmotic minipump containing Ang II (1.44 mg/kg per day) was implanted subcutaneously into 7- to 11-month-old male mice for 1 month. Ang II induced AAA in 9 (90%) of 10 hyperlipidemic mice deficient in apoE (apoE
−/−
/uPA
+/+
mice) but in only 2 (22%) of 9 mice deficient in both apoE and uPA (apoE
−/−
/uPA
−/−
mice) (
P
<0.05). Although the expansion of the suprarenal aorta was significantly less in apoE
−/−
/uPA
−/−
mice than in apoE
−/−
/uPA
+/+
mice, the aortic diameters of the aorta immediately above or below the suprarenal aorta were similar between the 2 groups. Ang II induced AAA in 7 (39%) of 18 strain-matched wild-type C57 black/6J control mice. The incidence was significantly higher in atherosclerotic apoE-deficient (apoE
−/−
) mice, in which 8 (100%) of 8 mice developed AAA. Only 1 (4%) of 27 uPA
−/−
mice developed AAA after Ang II treatment. We conclude the following: (1) uPA plays an essential role in Ang II–induced AAA in mice with or without preexisting hyperlipidemia and atherosclerosis; (2) uPA deficiency does not affect the diameter of the nonaneurysmal portion of the aorta; and (3) atherosclerosis and/or hyperlipidemia promotes but is not essential for Ang II–induced AAA formation in this model.