bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Wood-Polypropylene Composite Sandwich System
Authors: Kumar Ganesan , Ramani Karthik
Published: August 2002

A new wood-polypropylene composite sandwich was made by bonding unidirectional continuous glass fiber reinforced polypropylene (UCGPP) composite to oak wood using a thermoplastic tie layer. In order to evaluate the practical utility of wood-composite sandwich systems, the effects of moisture changes in both continuous and cyclic manner were investigated by monitoring the modulus change. Dynamic mechanical analysis (DMA) of neat wood and wood-composite sandwich was carried out under controlled relative humidity (RH) and isothermal conditions to simulate moisture desorption/sorption processes. It is observed that under continuous desorption condition the modulus increase is less in the case of wood-sandwich (20%) when compared with neat wood (35%). However, under desorption/sorption cycle conditions the wood-sandwich undergoes significant modulus change when compared with neat wood. It is inferred that while bonding wood with UCGPP composite helps reduce the variation in modulus under continuous desorption, it is not the case under cyclic moisture condition. The modulus behavior of both dry and normal wood-sandwiches at different end-use temperatures is also studied using DMA. Optical and environmental scanning electron micrographs show the distribution and penetration pattern of tie layer into wood as well as UCGPP composite, thus demonstrating the significance of micro-mechanical interlocking for bonding.
A New Thermoelastic Model for Analysis of Shape Memory Alloy Hybrid Composites
Authors: Turner Travis L.
Published: August 2002

A constitutive model and a finite element formulation are developed for predicting the thermomechanical response of SMA hybrid composite structures subjected to combined thermal and mechanical loads. The constitutive model is valid for constrained, restrained, or free recovery behavior with appropriate measurements of basic SMA material properties. The model captures the material nonlinearity of the SMA with temperature and more accurately captures the mechanics of composites with embedded SMA actuators as compared to other recently developed approaches. The constitutive and finite element models are amenable to commercial code implementation. The fundamental thermoelastic behavior of such structures is described in physical terms and related to the governing equations. It is shown that alloy selection is imperative for achieving the desired performance with respect to the application environment. It is also shown that fundamental efforts to strategically place actuators can produce dramatic performance improvements. Numerical results are shown for glass-epoxy beam specimens with embedded Nitinol actuators. Control of critical buckling temperature, thermal post-buckling deflection, and random response are demonstrated.
Curing of Thick Angle-Bend Thermoset Composite Part: Curing Process Modification for Uniform Thickness and Uniform Fiber Volume Fraction Distribution
Authors: Naji Malak I. , Hoa Suong V.
Published: August 2002

The effect of existing cure cycles and processes on the quality of angle-bend thermoset parts was presented in a previous paper. In this paper, the 2-D finite difference scheme developed before was used to model the processing of arbitrary shaped composite laminates. The effect of different processing parameters on the final part was studied. An optimal curing process is defined as one which will produce uniform thickness and uniform fiber volume fraction distribution throughout the composite part including straight sections and curved sections. Based on the results of the model, a modified curing process was developed. This process was applied to a graphite/epoxy HerculesAS4/3501-6 curved laminate. Results obtained from simulation and experiment were compared. Good parts were obtained using an optimal curing process.
Influence of the Addition of Peach Dietary Fiber in Composition, Physical Properties and Acceptability of Reduced-Fat Muffins
Authors: Grigelmo-Miguel N. , Carreras-Boladeras E. , Martín-Belloso O.
Published: August 2002

Muffins were made with 2, 3, 4, 5 or 10% peach DF to study the feasibility of developing reduced-fat baked products with peach. DF was substituted for oil in a standard muffin recipe, and the resulting products were compared to control muffins (100% oil). Reduced-fat muffins with peach DF had more moisture, protein and minerals as well as fewer calories than the control. The addition of peach DF darkened the muffins and increased their hardness and chewiness. However, springiness and cohesiveness were not different in muffins with or without DF. On the other hand, there were no differences between the acceptability of reduced-fat muffins with peach DF up to 4% and control muffins.
Acidity, Proteolysis and Lipolysis Changes in Rapid-Cured Fermented Sausage Dried at Different Temperatures
Authors: Bolumar T. , Nieto P. , Flores J.
Published: August 2002

Two batches of dry-cured fermented sausage were made by industrial methods at pilot scale. The difference between them was the drying temperature applied (5 or 12 °C) for a period of time extending from the moment when pH = 5 was attained until a weight loss of 20% was achieved. The other conditions were the same for the two processes. Changes in pH, total acidity, D and L-lactic acids, acetic acid, total volatile basic nitrogen (TVBN), free amino acids (FAA) and free fatty acids (FFA) were studied, and a discriminatory sensory analysis of the ready-to-eat product was carried out. Only L-lactic acid and total acidity within the acidity parameters showed substantial differences halfway through the drying process. No significant differences were found in any of the acidity variables at the end of the process. The drying temperature encouraged the production of TVBN, but no direct relationship was established between it and the quantity of FAA. The three fractions of FFA [SFA (saturated fatty acids), MUFA (monounsaturated fatty acids) and PUFA (polyunsaturated fatty acids)] increased during the curing period, always higher at 12 °C than at 5 °C throughout the process. No differences between the two processes were detected by the discriminatory sensory analysis.
Differentiation Parameters of Ribera del Duero Wines from Other Spanish Denominations of Origin
Authors: Pérez-Magariño S. , Jos M. L. Gonzlez-San
Published: August 2002

Commercial wines (247 samples) from different Spanish Denomination of Origin (D.O.) and from three consecutive vintages were analyzed. Stepwise discriminant analyses (SDA) were applied to the differentiation and classification of young red and rose wines by geographic origin. Good discriminant models with a small number of variables were obtained. These models gave high percentages of correct classification and prediction for both red (84.6% and 76.7%) and rose wines (87.7% and 82.6%). The variables with greater discriminating power were the phenolic compounds and the chromatic parameters. The discriminant models obtained to differentiate wines from D.O. “Ribera del Duero” were adequate with percentages of classification and prediction around 98%. So, these wines have some characteristics that differentiate them from the wines from other D.O.
Optimal Design of Piezoelectric Materials for Vibration Damping in Mechanical Systems
Authors: Steffen Valder , Inman Daniel J.
Published: August 2002

This paper examines two different techniques for vibration control in mechanical systems using piezoceramics: the first one is based on a pure collocated damping control and the second uses resonant circuit shunting. Optimization techniques are used to determine the best design parameters with respect to performance indexes, which are associated with the dynamical behavior of the system, when several natural frequencies are present in the frequency band. The methodology presented in this paper is focused on the design aspects of vibration control devices and it can be extended to more complex structures.
Experimental Damage Mechanics of Microelectronics Solder Joints under Concurrent Vibration and Thermal Loading
Authors: Basaran Cemal , Cartwright Alexander , Zhao Ying
Published: August 2002

Concurrent vibration and thermal loading is commonly encountered in the service life of electronic packaging, such as in automotive, airplane, military and mobile electronic devices. Solder joint reliability has been a critical issue of the overall design of microelectronic devices. However, the contribution of vibration to thermal fatigue life of solder joints has rarely been investigated. Presently, vibration is taken as a loading case that only causes elastic material response. Literature is scarce on vibration plasticity and vibration caused fatigue for micron scale structures. The standard practice in the industry is to use Miner’s rule to calculate combined environment fatigue life. This study shows that using Miner’s rule for fatigue life under combined loading is inaccurate for micron scale solder joints. There are a number of constitutive models to simulate thermomechanical behavior of solder joints, yet few of these, if any, models are verified by test data obtained from actual microelectronics solder joints. The authors see the need of such tests for the purpose of better understanding of material behavior of micron scale solder joints under thermal and vibration loading and providing a solid basis for more accurate material modeling and fatigue life prediction. This paper reports observations from a series of concurrent thermal cycling and vibration tests on 63Sn/37Pb solder joints of an actual ball grid array (BGA) package. Moiré interferometry (MI) is used to measure the inelastic deformation field of solder joints with submicron resolution. A large capacity Super AGREE thermal chamber and a high acceleration electrodynamic shaker are assembled together to perform the concurrent cycling. The cyclic plasticity of solder joints and microstructure evolution are discussed and related to fatigue life prediction. The results obtained in this study agree with findings reported in the literature from micron scale material testing where it has been shown that “smaller is stronger.”
Significant Drug Interactions in the HIV Patient
Authors: Conry John M.
Published: August 2002

Current treatment guidelines advocate the use of triple combination antiretroviral therapy for the management of human immunodeficiency virus (HIV) infection with one protease inhibitor (PI) or nonnucleoside reverse transcriptase inhibitor (NNRTI) plus two nucleoside reverse transcriptase inhibitors (NRTIs). Additionally, patients often receive medications for prophylaxis and treatment of opportunistic infections and comorbid illnesses. Polypharmacy with potent medications places the patient with HIV at significant risk of drug interactions. The purpose of this review is to assist clinicians regarding awareness and management of clinically significant drug interactions frequently encountered in the HIV population.

Pharmacodynamic and pharmacokinetic interactions are discussed in depth with several tables of significant interactions encountered in the patient with HIV. Certain combinations of NRTIs have antagonistic antiretroviral action (e.g., zidovudine plus stavudine), and thus should be avoided. All of the currently available PIs and delavirdine are cytochrome (CYP) 450 inhibitors and can cause significant inhibition of concomitant drug metabolism. Nevirapine is a CYP 450 inducer and can cause induction of drug metabolism, whereas efavirenz may cause inhibition or induction. Drug-herbal interactions are reviewed, including the decreased concentrations of indinavir following the administration of St. John’s wort. Additionally, the pharmacist’s role as an integral member of the HIV patient care team is discussed.
Restrictions on the Rate of Absorption When Evaluating Sorption Isotherms Obtained Using a Micro-Calorimetric Technique
Authors: Johannesson BjÖrn
Published: August 2002

One interestingway of measuring sorption isotherms and heats of sorption is the newly developed micro-calorimetric method. It turns out, however, that the adsorption kinetics must be proven to be rapid enough to fulfill the assumptions behind the theory for the determination of the isotherm to be valid. Here, the lower limit of the accepted rate of adsorption will be analyzed by making calculations of the diffusion behavior in the calorimetric vessel. The evaluation of the adsorption isotherms is based on assumptions of a quasi-static nature. If the adsorption kinetics are slow the behavior in the calorimeter will turn to a more or less transient process. When the heat of adsorption is of interest and the sorption isotherm and kinetics of sorption can be determined by other methods, compensation for the transient effects can be made.
Thermo-Hygrometric Evaluations in the Recovery of Rocky Buildings of the “Sassi of Matera”(Italy)
Authors: Cardinale Nicola , Guida Antonella , Ruggiero Francesco
Published: August 2002

The Sassi of Matera are a very interesting example of a rocky settlement. The limestone walls often present high moisture content which negatively influences the room microclimate. In the first part of this paper, rooms without evident problems of moisture were analyzed for the purpose of carrying out a statistical analysis, to be repeated in analogous situations and to identify the distribution of what we can define as background moisture of the rocky installation. The knowledge of moisture, however, greatly influences the evaluation of heat loss since thermal conductivity of a material increases with an increase in the percentage of water that is contained within it. Consequently, the second part of the paper deals with thermal conductivity and other thermal physical properties related to the moisture of the calcareous sandstone present in the installation of the “Sassi,” continuing the analysis initiated in a previous work.
An Electrorheological Fluid in Squeeze Mode
Authors: Nilsson Magnus , Ohlson Nils G.
Published: August 2002

Electrorheological (ER) fluids may be regarded as smart materials, in the sense that their mechanical properties can be affected by an applied electrical field. This paper describes experiments performed in a unit containing circular plates which are placed in parallel, with an ER fluid (silicone oil with dispersed plastic spheres) between them, so that the fluid is forced in the radial direction when plates move towards each other. This is termed “squeeze mode operation.” Force obtained is at least one order of magnitude larger than in shear mode (plates moving parallel to each other). Results show that damping as well as stiffness are affected by the electrical field. A constitutive equation is derived, describing the force as a function of displacement and velocity of plates. Models of the micro-mechanical behaviour of the ER fluid are proposed. They provide an efficient tool for interpreting test results and their predictions are shown to agree well with these. Only DC fields were studied. The response to harmonic motion of plates was analysed for frequencies below 50 Hz.
An Investigation on Buckling of Laminated Plates with Central Square Hole
Authors: Akbulut H. , Sayman O.
Published: August 2002

In this paper buckling analysis of rectangular composite laminates with a central square hole is investigated. Using the first order shear deformation theory, the buckling loads of rectangular laminated plates under the inplane loads are found for various hole sizes. The four-mode finite element method is used to obtain critical loads. The critical loads of symmetric angle-ply, antisymmetric cross-ply or angle-ply laminates are found for constant or various thicknesses, simple or clamped boundary conditions, various modules ratios, simple or biaxial loading versus hole sizes. Some results are compared with those of given references.
A Method for Establishing Hybrid Piezoelectric Composite Plate Theories with Continuous Interlaminar Stresses
Authors: Lu Pin , Tan M. J. , Chen Haibo , Liew K. M.
Published: August 2002

In the present paper, a regular method is proposed to establish approximate piezoelectric composite plate theories with continuous interlaminar stresses. As an application of the treatment, a hybrid piezoelectric composite plate model with eight unknown displacement and electric potential parameters is developed. The theory satisfies the continuity conditions of transverse shear stresses at layer interfaces and is adequate for both global and ply level analysis. Furthermore, for a composite plate with any number of piezoelectric and fiber-reinforced layers, the number of unknown displacement and electric potential parameters in the governing equations is fixed for a specific approximate model. The methodology suggested in the paper can be used to construct approximate piezoelectric composite plate theories with various degrees of accuracy and unknown parameters.
Irreversibility, Stability and Maximum Dissipation in Elastoplastic Damage
Authors: Hesebeck O.
Published: August 2002

The relation between the maximum dissipation principle, the irreversibility condition of Ilyushin and Drucker's stability postulate is studied in the present paper. For simple elastoplastic material models, it is well known that these three postulates require orthogonality between the plastic strain rate and the yield surface. The objective of this work is to investigate this relation for more general material models containing internal variables coupled with the elastic strains. It can be shown that the irreversibility and stability conditions pose the same restriction on the directions of dissipative fluxes, but do not determine uniquely this direction. The postulate of maximum dissipation is a stronger restriction to the evolution equations than Ilyushin's condition. The results are applied to damage mechanics models. For models describing elasticity and damage, a normality law in damage force space is obtained. In the case of plasticity with damage, the postulates imply orthogonality neither in the stress space nor in the damage force space. Usual non-associated flow rules for elastoplasticity with damage violate Drucker's stability postulate. The only convenient way to formulate a model, which fulfills the postulates of Ilyushin and Drucker a priori, is the use of an associated flow rule.
Resistance Welding of Metal/Thermoplastic Composite Joints
Authors: Ageorges Christophe , Ye Lin
Published: August 2002

An investigation of the resistance welding between carbon fiber (CF) rein-forced polyetherimide (PEI) and aluminium substrates (7075-T6 grade alloy) is presented. A three-dimensional transient finite element model (FEM) featuring heat transfer, consolidation and thermal degradation was used for simulating the process. Two mechanisms are distinguished in the consolidation model: (1) removal of the initial surface profile of the laminate modelled by the establishment of intimate contact between the two substrate surfaces and (2) penetration of the thermoplastic (TP) polymer in the micro-pores of the aluminium oxide surface modelled using a capillary flow model. The “optimal” welding time based on the maximum lap shear strength (LSS) was determined for various power levels and correlated to the bonding time predicted by the FEM. Consolidation quality and failure mechanisms were discussed in relation to processing parameters. The effect of the welding operation on overaging (annealing) of the aluminium alloy also was investigated. Experimental and simulated processing windows were constructed and correlated to each other. However, thermal degradation of PEI as predicted by the model did not correlate to a reduction in performance of the joint.
Thermal Degradation of Pinus pinaster Needles by DSC. Part 1: Dehydration Kinetics
Authors: Leoni E. , Tomi P. , Khoumeri B. , Balbi N. , Bernardini A. F.
Published: August 2002

Fire behaviour prediction models, required for controlling wild-land fires, can be calculated from a mathematical approach, taking the thermal and chemical properties of forest fuels into account. To improve and extend applications ofthe model, we need a better understanding ofthe different phenomena involved in the thermal decomposition of forest fuels. Three steps have been observed during thermal degradation of Pinus pinaster needles: dehydration, oxidization of evolved gases and char combustion. Kinetic parameters of the first step were determined from DSC curves using various known methods which enable the determination of activation energy, pre-exponential Arrhenius factor and order of reaction.
Study on the Flame-retardance and Thermal Stability of the Acid Anhydride-cured Epoxy Resin Flame-retarded by Triphenyl Phosphate and Hydrated Alumina
Authors: Xiao Weidong , He Peixin , Hu Gaoping , He Benqiao
Published: August 2002

The effect of hydrated alumina and triphenyl phosphate on the flame-retardance and thermal stability of the acid anhydride-cured epoxy resin was studied by thermogravimetry and limiting oxygen index determination. The results show that both the hydrated alumina and triphenyl phosphate act as flame-retardants for epoxy resin in gas phase and display condensed phase flame-retardant synergism when they are used together. However, they have little influence on the cured resin’s thermal stability.
Effects of Chemical Blowing Agents on Swelling Properties of Expanded Elastomers
Authors: Sombatsompop N. , Lertkamolsin P.
Published: August 2002

Two commercial chemical blowing agents, azodicarbonamide (ADC) and oxybisenzenesulphonylhydrazide (OBSH), were used alone and in blends for expanded natural rubber vulcanisates. The expanded rubber vulcanisates were characterised with respect to the apparent foam density, degree of crosslinking, tensile properties and swelling behaviour. For a given blowing agent, the apparent foam density and crosslink density were found to change with blowing agent content. The swelling behaviour greatly changed with OBSH content, but was unaffected by ADC content. The OBSH blowing agent seemed to generate more voids in the vulcanisates as compared to the ADC blowing agent and thus increased swelling. The swelling ratio of the NR vulcanisates having blended blowing agents tended to be more influenced by OBSH than ADC blowing agents.
Growth of Pb[(Zn1/3Nb2/3)0.91Tio.09]03 Single Crystal of Ultrasonic Transducer for Medical Application
Authors: Harada K. , Shimanuki S. , Kobayashi T. , Saitoh S. , Yamashita Y.
Published: August 2002

Single crystals of Pb[(Znl/3Nb2/3)0o91Tio009]03 (PZNT 91/9) were grown by the Solution Bridgman method using a PbO-based flux. The crystals were about 40 m min diameter X 25 mm in size and had a light brown color. The properties of these single crystals satisfy the requirements for array-type transducers in echocardio-graphs, a type of medical diagnostic equipment. Compared with other piezoelectric materials, PZNT 91/9 is a superior piezoelectric material for ultrasonic diagnostic cardiac probes.
The Response of Fiber-Reinforced Elastomers under Simple Tension
Authors: Peel Larry D. , Jensen David W.
Published: August 2002

The mechanical behavior and basic response mechanisms of fiberreinforced elastomers (flexible composites) can be significantly different from those of typical advanced “stiff” composites. This paper presents experimental results of elastomer (rubber) matrices, dry and impregnated fibers, and four sets of fiber-reinforced elastomeric composite, summarizes the corresponding initial and nonlinear orthotropic constitutive properties, and sheds light on fundamental response mechanisms. Silicone and urethane rubber were combined with fiberglass and cotton reinforcing fibers. Balanced angle-ply laminates of each material system were fabricated with off-axis angles ranging from 0° to 90° in 15° increments. Dog-boned test specimens, 76 mm (3 in) long, were fabricated with fiber volume fractions ranging from 12% to 62% using a previously documented non-calendering fabrication method [1–3]. The average extensional stiffness of individual twisted cotton fibers increased 74% to 128% when impregnated with an elastomer. Fiber-reinforced elastomer laminate stiffness and nonlinearity can vary significantly with fiber angle. The nonlinear stiffening or softening trends of the silicone and urethane rubbers are reflected in their respective fiber-reinforced elastomers. Longitudinal stiffness at low off-axis angles is a function of the reinforcement stiffness. At high off-axis angles, longitudinal stiffness and strength are functions of fiber type, fiber volume fraction and elastomer.
On the Design of Some Particular Orthotropic Plates with Non-Standard Ply Orientations
Authors: Grediac M.
Published: August 2002

This paper deals with the design of thin orthotropic plates exhibiting required stiffness properties. An optimization programme based on the well-known gradient method is used to obtain stacking sequences in which lamination parameters are very close to a set of target lamination parameters. Some examples are studied. The stacking sequences found are not symmetric while the coupling matrix is zero and the ply angles are not standard.
Characterization of Magnetorheological Suspension for Seal
Authors: Fujita Toyohisa , Yoshimura Kei , Seki Yoshikazu , Dodbiba Gjergj , Miyazaki Toshio , Numakura Satoshi
Published: August 2002

Magnetorheological suspension (MRS) dispersing spherical several gm of iron particles in the low vapor pressure of dimethylpolysiloxane has been prepared. Yield stress has been proportional to square of magnetic field intensity and increases as containing larger volume fraction of iron particles and using solvent that is more viscous. The plastic viscosity increased linearly as a function of volume fraction of iron particles. The burst pressure of MRF seal is related on the dispersed iron particle size. The burst pressure is related on the magnetization curve in the MRS dispersing less than several gm of iron particles. On the other hand, the surface tension of solvent influences on the burst pressure in the MRS dispersing more than several gm of iron particles. Also the burst pressure is affected on the seal gap. In the large gap, the burst pressure in stationary condition adds the pressure by the yield stress of MRS. However, in the small gap the burst pressure of rotating condition is almost the same as that of stationary condition because the arranged iron particles cannot be reconstructed in a small gap. The larger viscosity of solvent and volume of iron in MRS increases the burst pressure.
Processing and Performance of Continuous Fiber Ceramic Composites by Preceramic Polymer Pyrolysis: I—Filament Winding
Authors: Ghasemi Nejhad Mehrdad N. , Chandramouli Mahesh V. , Yousefpour Ali
Published: August 2002

Continuous Fiber Ceramic Composite (CFCC) tubes have been manufactured using cure-on-the-fly and no cure-on-the-fly filament winding by preceramic polymer pyrolysis route. Processing guidelines to effectively use the cure-on-the-fly filament winding technique for the manufacture of CFCCs are introduced in this paper. The preceramic polymer used in thiswork is Blackglas™ (a siloxane polymer). Afilament winding machine was designed to adapt to the brittle nature of the fibers and the relatively low temperature cure of the polymer. Seven reinfiltration/pyrolysis cycles, with about 17 hours per cycle, were necessary to reach a convergence by weight. C-ring tests at both room and high temperature were performed to assess the quality of the manufactured parts. Scanning Electron Microscopy (SEM) was used to further examine the microstructure and quality of the parts. Effects of infrared cure-on-the-fly, fiber coating/material system, part thickness, and service temperature on the processing and mechanical performance of the manufactured CFCCs were studied.
Xanthan Gum as a Carrier for Controlled Release of Drugs
Authors: Andreopoulos A. G. , Tarantili P. A.
Published: August 2002

Systems based on xanthan gum matrix containing 1%, 2% and 5% salicylic acid were prepared and studied as controlled release devices. Swelling of the matrix in distilled water and buffer solutions showed that the ionic strength of the liquid has a strong effect on the sorptive properties of the matrix. From the release experiments, conductedin distilled water at 37±0.5°C, it was found that the drug delivery process was accomplished within the first 10 hours after immersion and salicylic acid was always released via a non-Fickian transport. The phenomenon can be described by a release exponent (n) in the area of 0.77 independently of the initial concentration of salicylic acid in the xanthan matrix. These results can be interpreted taking into consideration the dimensional and physical changes of the polymeric matrix during swelling.
Numerical and Experimental Studies of 3-Dimensional Thermoforming Process
Authors: Nam G. J. , Lee J. W.
Published: August 2002

Two Acrylonitrile-Butadiene-Styrene (ABS) polymers were thermoformed, and their behavior was compared with numerical simulation. Hot tensile and dynamic oscillatory shear tests were performed at various temperatures to characterize the polymers. Hot tensile test results were used to obtain the material parameters for simulation and to check the relative usefulness of these test parameters in the actual thermoforming process. The thickness distribution obtained from experiments was compared with simulation results. It shows that simulation results based on hyperelastic rubber like model can predict the deformation behavior of a sheet reasonably well. We could also find that the temperature sensitive polymer in hot tensile test shows more temperature sensitive thickness distribution in actual thermoforming process.
A Plane Strain Model for Process-Induced Deformation of Laminated Composite Structures
Authors: Johnston Andrew , Vaziri Reza , Poursartip Anoush
Published: August 2002

We present a plane strain finite element model for simulation of the development of process-induced deformation during autoclave processing of complex-shaped composite structures. A “cure-hardening, instantaneously linear elastic” constitutive model is employed to represent the mechanical behaviour of the composite matrix resin, and micromechanics models are used to determine composite ply mechanical properties and behaviour, including thermal expansion and cure-shrinkage. Structures with multiple composite and non-composite components can be simulated through the use of such strategies as adaptive time-stepping and incorporation of multiple composite plies into each finite element. The effect of process tooling can also be directly modelled through simulation of tool/part interfaces and post-processing tool removal. Integration of the residual deformation model with models for heat transfer and resin cure and resin flow permits analysis of all major identified sources of process-induced deformation during the autoclave process. Model application is demonstrated through prediction of process-induced deformation of a number of variations of a simple L-shaped laminate. The model is shown to provide accurate predictions of both spring-back angle and warped shape of the final part.
GUIDELINES FOR DATA-PARALLEL CYCLE-STEALING IN NETWORKS OF WORKSTATIONS II: ON MAXIMIZING GUARANTEED OUTPUT
Authors: ROSENBERG ARNOLD L.
Published: August 2002

We derive efficient guidelines for scheduling data-parallel computations within a draconian mode of cycle-stealing in networks of workstations. In this computing regimen, (the owner of) workstation A contracts with (the owner of) workstation B to take control of B's processor for a guaranteed total of U time units, punctuated by up to some prespecified number p of interrupts which kill any work A has in progress on B. On the one hand, the high overhead — of c time units — for setting up the communications that supply workstation B with work and receive its results recommends that A communicate with B infrequently, supplying B with large amounts of work each time. On the other hand, the risk of losing work in progress when workstation B is interrupted recommends that A supply B with a long sequence of small bundles of work. In this paper, we derive two sets of scheduling guidelines that balance these conflicting pressures in a way that optimizes, up to low-order additive terms, the amount of work that A is guaranteed to accomplish during the cycle-stealing opportunity. Our non-adaptive guidelines, which employ a single fixed strategy until all p interrupts have occurred, produce schedules that achieve at least [Formula: see text] units of work. Our adaptive guidelines, which change strategy after each interrupt, produce schedules that achieve at least [Formula: see text] (low-order terms) units of work. By deriving the theoretical underpinnings of our guidelines, we show that our non-adaptive schedules are optimal in guaranteed work-output and that our adaptive schedules are within low-order additive terms of being optimal.
THE INTERSECTION GRAPH CONJECTURE FOR LOOP DIAGRAMS
Authors: MELLOR BLAKE
Published: August 2002

The study of Vassiliev invariants for knots can be reduced to the study of the algebra of chord diagrams modulo certain relations (as done by Bar-Natan). Chmutov, Duzhin and Lando defined the idea of the intersection graph of a chord diagram, and conjectured that these graphs determine the equivalence class of the chord diagrams. They proved this conjecture in the case when the intersection graph is a tree. This paper extends their proof to the case when the graph contains a single loop, and determines the size of the subalgebra generated by the associated "loop diagrams." While the conjecture is known to be false in general, the extent to which it fails is still unclear, and this result helps to answer that question.
Accidental surfaces in knot complements
Authors: Ichihara Kazuhiro , Ozawa Makoto
Published: August 2002

It is well known that for many knot classes in the 3-sphere, every closed incompressible surface in their complements contains an essential loop which is isotopic into the boundary of the knot exterior. In this paper, we investigate closed incompressible surfaces in knot complements with this property. We show that if a closed, incompressible, non-boundary-parallel surface in a knot complement has such loops, then they determine the unique slope on the boundary of the knot exterior. Moreover, if the slope is non-meridional, then such loops are mutually isotopic in the surface. As an application, a necessary and sufficient condition for knots to bound totally knotted Seifert surfaces is given.
ESTIMATION OF EXTREME QUANTILES: EMPIRICAL TOOLS FOR METHODS ASSESSMENT AND COMPARISON
Authors: DIEBOLT J. , EL-AROUI M.-A. , DURBEC V. , VILLAIN B.
Published: August 2002

When extreme quantiles have to be estimated from a given data set, the classical parametric approach can lead to very poor estimations. This has led to the introduction of specific methods for estimating extreme quantiles (MEEQ's) in a nonparametric spirit, e.g., Pickands excess method, methods based on Hill's estimate of the Pareto index, exponential tail (ET) and quadratic tail (QT) methods. However, no practical technique for assessing and comparing these MEEQ's when they are to be used on a given data set is available. This paper is a first attempt to provide such techniques. We first compare the estimations given by the main MEEQ's on several simulated data sets. Then we suggest goodness-of-fit (Gof) tests to assess the MEEQ's by measuring the quality of their underlying approximations. It is shown that Gof techniques bring very relevant tools to assess and compare ET and excess methods. Other empirical criterions for comparing MEEQ's are also proposed and studied through Monte-Carlo analyses. Finally, these assessment and comparison techniques are experimented on real-data sets issued from an industrial context where extreme quantiles are needed to define maintenance policies.
REFINEMENT OF THE Pt(111)+c(4×2)-2CO STRUCTURE USING AUTOMATED TENSOR LEED
Authors: ZASADA I. , VAN HOVE M. A.
Published: August 2002

The structure of Pt(111)+c(4×2)-2CO has been refined using the powerful capabilities of automated tensor LEED, in particular to determine hitherto-unexplored adsorbate-induced relaxations in the substrate. The refinement considerably improves the fit to experiment obtained in a previous structural analysis performed with low-energy electron diffraction (LEED). This study confirms that CO occupies both top and bridge sites. It finds a buckling of the outermost Pt layer, such that the Pt atoms bonded to CO molecules are raised out of the surface by 0.06±0.04 Å relative to the Pt atoms which do not bond to CO. The raised atoms have a spacing of 2.28±0.04 Å to the next Pt layer, expanded from the bulk spacing of 2.2655 Å, while the depressed Pt atoms have a reduced spacing of 2.22±0.04 Å to the next Pt layer. The second Pt layer itself shows minor buckling of 0.03±0.04 Å. No lateral relaxations in the substrate are detected within 0.1 Å. The CO molecules are perpendicular to the surface, with bond lengths of 1.12±0.04 Å and 1.19±0.04 Å in top and bridge sites, respectively. The C–Pd spacings, measured between bonding atoms, are 1.92±0.04 Å and 1.40±0.04 Å in top and bridge sites, respectively.
ATOMIC STRUCTURE AND ENERGETICS OF VACANCIES IN A SUBLAYER OF GaAs(110)
Authors: YI JAE-YEL , KOO JA-YONG , LEE SEKYUNG , SHIN DONG-HYUK , HA JEONG SOOK
Published: August 2002

The energetics and structure of vacancies in the second layer of GaAs(110) were examined using the ab initio total energy calculation method. Structural changes due to the presence of the vacancies are substantial. The changes are different in shape, depending on the type of vacancy and charged states. Both the Ga vacancy and the As vacancy in the second layer of the surface favor negatively charged states.
PHENOMENOLOGICAL VIEW OF NUCLEATION AND GROWTH OF Si ON THE Si(111)-(7×7) SUPERLATTICE
Authors: SHIGETA YUKICHI
Published: August 2002

The influence of surface structure on epitaxial growth, which has not been considered before in the crystal growth theory, is discussed for the case of epitaxial growth of Si on Si(111)-(7×7) substrate. Since the rearrangement of surface structure is essential for progressing the epitaxial growth, the activation energy for the rearrangement is considered into the free energy change in the nucleation and growth processes. From a phenomenological consideration, some features of island shape and size distribution, which had been observed, are clearly explained. The size distribution is discontinuous according to the size of the unit cell of the superlattice and the shape will be almost triangular. These features are caused by prevention of the lateral growth at the faulted half in the 7×7 structure. After the evaporation has been stopped, the detachment of atoms from corners of the triangular island starts and the island shows a rounded shape. The detachment after the deposition is also explained by the difference in the free energy changes between during and after deposition. It is suggested that the activation energy for the rearrangement process of the 7×7 structure with island growth is much higher than that for the formation process with thermal decay of the Si island.
OPTICALLY NONLINEAR S-POLARIZED ELECTROMAGNETIC WAVES IN MULTILAYERED SYMMETRIC DIELECTRICS
Authors: VASSILIEV O. N. , COTTAM M. G.
Published: August 2002

A theory is presented for the nonlinear s-polarized electromagnetic waves in multilayer systems with an arbitrary number of planar interfaces. Each of the individual layers may be characterized by either a linear or a Kerr-type nonlinear dielectric constant, and we examine the coupled nonlinear waves at both linear/nonlinear and nonlinear/nonlinear interfaces. An analysis of the phase trajectories (in terms of an electric field amplitude and its spatial derivative) is employed to enumerate the modes of the system in a systematic manner and to facilitate the derivation of dispersion relations. In particular, numerical examples are given for two-interface systems (for example, a thin film sandwiched between two semi-infinite media) and for periodic superlattices (with effectively infinite interfaces), thereby extending previous calculations.
TRANSMISSION RESONANCES IN MAGNETIC STRUCTURES BASED ON NARROW-GAP SEMICONDUCTORS
Authors: MALKOVA M. , DOMINGUEZ-ADAME F.
Published: August 2002

In this work we are concerned with magnetic junction structures in which a homogeneous narrow-gap semiconductor is subjected to an inhomogeneous magnetic field, in an attempt to elucidate the band-structure effect on the resonance tunneling. Careful investigation of the transmission as a function of the energy shows that the resonances in the spectrum can appear. These are remnants of the Landau levels localized near the interface boundary. Comparing the solutions obtained within two-band and single-band models we found the allowed values of the momentum to be quite different, resulting in different resonant values of the transmission coefficient of electron transport through the magnetic interface.
KINETICS OF THIN OXIDE FILM GROWTH ON METAL CRYSTALS
Authors: ZHDANOV V. P. , NORTON P. R.
Published: August 2002

A seminal model describing the kinetics of growth of thin oxide films on metal crystals was proposed by Cabrera and Mott (CM). The model is based on the assumption that the growth is limited by the field-facilitated activated jumps of metal ions located in steps on the metal–oxide interface. We generalize the CM model by (i) exploring the interplay of jumps of metal ions from the step and terrace sites at the metal–oxide interface, and (ii) scrutinizing the processes at the oxide–gas-phase interface. The former factor is found to change the physical meaning of the parameters in the CM growth law. The latter factor results in modification of the growth law. In particular, the oxidation kinetics becomes dependent on the O2 pressure. More specifically, the oxidation rate is predicted to increase with increasing pressure. This effect is, however, rather weak and becomes progressively weaker with increasing oxide film thickness.
XPS INVESTIGATIONS OF TWO METAL–PET INTERFACES FORMED BY Zr and Al
Authors: WONG P. C. , KONO M. , LI Y. S. , ZHOU M. Y. , MITCHELL K. A. R.
Published: August 2002

X-ray photoelectron spectroscopy (XPS) was used to study two interfaces formed between polyethyleneterephthalate (PET) and thin layers of aluminum and zirconium deposited under ultrahigh vacuum conditions. The thicknesses of these layers were estimated to be about 10 and 4 Å respectively. The interpretations were guided by difference spectra, especially for the Zr system, and it was concluded that different interactions operate at these two PET–metal interfaces. For the amounts deposited, Zr bonds especially to O atoms in PET, whereas Al bonds to both C and O atoms; the latter metal shows both bonding to carbonyl groups and direct Al–C bonding to the benzene-like rings. Comparisons were made for the behaviors of these systems on exposure to oxygen, and they were compared further with related systems.
ANALYSIS OF THE ARRHENIUS SHAPE OF THE DIFFUSION COEFFICIENT ON AN fcc (111) SURFACE
Authors: MAŠÍN M. , CHVOJ Z.
Published: August 2002

We study the temperature and coverage dependence of an effective diffusion barrier assuming an Arrhenius shape of the chemical diffusion coefficient for a system of interacting particles. The previously published model of the diffusion of an fcc (111) surface with bivariate trap is used. The presence of two nonequivalent occupation sites and interaction result in a non-Arrhenius shape of the diffusion coefficient and a coverage- and temperature-dependent effective diffusion barrier. The temperature dependence of effective energy Ea shows a minimum at low temperatures (at approximately 150 K) for strong interactions. The coverage dependence of Ea has a deep minimum in the vicinity of Θ=1/2, even in a system without interaction.
MASS TRANSPORT OF GaN AND REDUCTION OF THREADING DISLOCATIONS
Authors: NITTA S. , KASHIMA T. , NAKAMURA R. , IWAYA M. , AMANO H. , AKASAKI I.
Published: August 2002

Mass transport of patterned GaN at around 1100°C in nitrogen with an ammonia atmosphere has been discovered for the first time. The mass transport process is found to be affected by the anisotropy of surface energy of GaN. Behaviors of threading dislocations which are predominantly of the mixed type and the pure edge type are affected by the anisotropy during mass transport. Mixed type dislocations are bent keeping the geometrical relationship normal to the surfaces, while pure edge type dislocations are bent horizontally. This new-found process, the so-called "mass transport epitaxy," is one of the best methods for achieving low dislocation density GaN on the highly lattice-mismatched substrate.
GROWTH AND CHARACTERIZATION OF ATOMIC AND NANOMETER SCALE WIRES ON THE SILICON SURFACE
Authors: NOGAMI J.
Published: August 2002

Growth of metals on semiconductor surfaces can result in the self-assembly of a variety of 1D or 2D structures whose lateral dimensions range from one atom to tens of atoms. Over this range in length scales, STM gives information about the structure, the growth behavior and the electronic properties of these small structures. STM and STS data on several different systems are presented. In addition, ongoing and future efforts to measure the transport properties of these small structures are described.
ASSESSMENT OF CORRELATED THERMAL DIFFUSE SCATTERING AS A DIRECT STRUCTURAL METHOD ON THE MULTIELEMENT SURFACE SYSTEM OF ${\rm Si}(111)(\sqrt3\times\sqrt3)\mbox{-}{\rm In}$
Authors: ABUKAWA T. , YOSHIMURA K. , KONO S.
Published: August 2002

Correlated thermal diffuse scattering (CTDS), a direct structural technique using a simple oscillatory intensity variation in the medium energy electron diffraction, has been applied to the biatomic surface system of [Formula: see text]. A problem with the application of CTDS to multicomposition systems arises from the element-specific atomic scattering factors. The difference in atomic scattering factors disturbs the diffraction phase originating from the path length difference and causes the shift from the true atomic position in Patterson analysis. In order to recover the true atomic position, a numerical calibration method has been introduced. With the aid of the calibration, structural parameters for the topmost three layers of the [Formula: see text] surface have been determined with 0.1 Å accuracy. This shows that CTDS is applicable to multicomposition surface systems.
MICRO-FOUR-POINT PROBES IN A UHV SCANNING ELECTRON MICROSCOPE FOR IN-SITU SURFACE-CONDUCTIVITY MEASUREMENTS
Authors: SHIRAKI ICHIRO , NAGAO TADAAKI , HASEGAWA SHUJI , PETERSEN CHRISTIAN L. , BØGGILD PETER , HANSEN TORBEN M. , HANSEN FRANÇOIS
Published: August 2002

For in-situ measurements of surface conductivity in ultrahigh vacuum (UHV), we have installed micro-four-point probes (probe spacings down to 4 μm) in a UHV scanning electron microscope (SEM) combined with scanning reflection–high-energy electron diffraction (RHEED). With the aid of piezoactuators for precise positioning of the probes, local conductivity of selected surface domains of well-defined superstructures could be measured during SEM and RHEED observations. It was found that the surface sensitivity of the conductivity measurements was enhanced by reducing the probe spacing, enabling the unambiguous detection of surface-state conductivity and the influence of surface defects on the electrical conduction.