bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigating the Stress and Crystal Quality of AlN Air-Bridges through Micro-Raman Scattering
Authors: Kuchibhatla Sridhar , Rodak L. E. , Korakakis D. 
Published: February 2009

AbstractIn this work, we report the post-growth investigation of the microstructure and stress in the AlN films grown on patterned amorphous dielectrics through micro-Raman spectroscopy. The surface texture of AlN/SiO2 structures was characterized by randomly oriented crystallites typical of polycrystalline films. Post growth analysis of the AlN/SiO2 structures using micro Raman spectroscopy did not reveal phonon modes corresponding to wurtzite AlN. The presence of randomly oriented crystallites with a possibility of oxidized Al phase in the AlN film could have suppressed the appearance of wurtzite AlN phonon peaks in the Raman spectrum. Profiling the stress and the microstructure of AlN/SiO2 structures across the width of the bridges is thus limited by these factors. AlN structures on SiO2 when subjected to wet etching in buffered HF (10:1) showed a clear change in texture. Micro-raman spectroscopy on the etched areas revealed wurtzite AlN like phonon modes. The appearance of wurtzite AlN modes can be attributed to the removal of oxidized Al phase in the AlN film after wet etching.
Micro Tensile Tests on Aluminium Thin Films: Tensile Device and In Situ Observations
Authors: Ignat Michel T. , Lay Sabine , Roussel d'Herbey Francine , Seguineau Cedric , Malhaire Christophe , Lafontan Xavier , Desmarres Jean Michel , Brida Sebastiano 
Published: February 2009

AbstractThe results of micromechanical tensile experiments performed on thin aluminum samples are presented and discussed. The micro tensile test system and the design of the samples, based on finite element modeling (FEM), and their production by micromachining are briefly described. Some examples of the stress strain curves are presented. The Young's modulus and critical parameters (flow and rupture stress and strains) are reported. The micro structural changes induced by the tensile experiment were observed during and after the testing by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).The results of micromechanical tensile experiments performed on thin aluminum samples are presented and discussed. The micro tensile test system and the design of the samples, based on finite element modeling (FEM), and their production by micromachining are briefly described. Some examples of the stress strain curves are presented. The Young's modulus and critical parameters (flow and rupture stress and strains) are reported. The micro structural changes induced by the tensile experiment were observed during and after the testing by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
Poly(3-hexythiophene)/multi-walled carbon nanotube composites: electrochemical and optical characterization
Authors: Calado Hállen D. R. , Valadares Marcelo , Musumeci Anthony W. , Waclawik Eric R. , Cury Luiz A. , Silva Glaura Goulart 
Published: February 2009

ABSTRACTCarbon nanotubes (CNT) / conjugated polymer composites have been used for the preparation of thin film-modified electrodes. Thin, short, multi-walled CNT (MWNT) (purity higher than 95%) was completely coated by regioregular poly(3-hexylthiophene) (P3HT) through precipitation of a mixture of both in the non-solvent methanol. This work reports the electrochemical and optical characterization of P3HT and composites after dissolution in xylene and spin casting of films with thickness <1 micrometer. Cyclic voltammetry showed that all samples were characterized by a semi-reversible behavior. The samples with 0% and 2% of MWNT, for instance, present anodic peak potential at +0.67 and +0.68V respectively when cycling at 100 mV/s. Optical properties, such as optical absorption and photoluminescence (PL), have been investigated. The samples showed maximum of absorption at ˜530 nm and intense PL in the orange. PL spectra of nanocomposites exhibited a new band at lower energy characteristic of a structure with higher conjugation length when compared to P3HT.
Annealing of Nanocrystalline Silicon Micro-bridges with Electrical Stress
Authors: Bakan Gokhan , Cywar Adam , Boztug Cicek , Akbulut Mustafa Bilal , Silva Helena , Gokirmak Ali 
Published: February 2009

ABSTRACTNanocrystalline silicon (nc-Si) micro-bridges are melted and crystallized through Joule heating by applying high-amplitude short duration voltage pulses. Full crystallization of nc-Si bridges is achieved by adjusting the voltage-pulse amplitude and duration. If the applied pulse cannot deliver enough energy to the bridges, only surface texture modification is observed. On the contrary, if the pulse is not terminated after the entire bridge melts, molten silicon diffuses on to the contact pads and the bridge tapers in the middle. Melting of the bridges can be monitored through current-time (I-t) and voltage-time (V-t) measurements during the electrical stress. Conductance of the bridges is enhanced after the electrical stress.
Luminescence characterization of InGaN/GaN vertical heterostructures grown on GaN nanocolumns
Authors: Armitage Robert 
Published: February 2009

ABSTRACTThe photoluminescence of MBE-grown InGaN/GaN vertical heterostructures on c-axis oriented GaN nanocolumns is investigated. Nanocolumnar InGaN heterostructures exhibit luminescence efficiencies greater than 20% for peak emission wavelengths as long as 540 nm. Compared to otherwise identical InGaN samples with larger median column diameters, the luminescence is blue-shifted and exhibits reduced efficiency for diameters less than about 50 nm. Growth of InGaN on GaN columns with a broad distribution of diameters results in broad-band photoluminescence that appears white to the eye and has efficiency as high as 23%.
Monitoring Organic Thin Film Growth In Aqueous Solution In-situ With A Combined Quartz Crystal Microbalance and Ellipsometry
Authors: Sarkar Amitabha , Viitala Tapani , Hofmann Tino , Tiwald Tom E. , Woollam John A. , Kjerstad Ann , Laderian Bahar , Schubert Mathias 
Published: February 2009

AbstractThe change of the visible light ellipsometric parameters and mechanical harmonic frequencies of a hydrophobic gold surface attached to a quartz crystal are measured in aqueous solution during deposition of synperonic polymer thin film. The ellipsometry data reveal the amount of polymer mass attached to the surface, while the mechanical resonance shifts are caused by the total mass attached to the surface. Analysis of the combined ellipsometry and quartz crystal microbalance data reveal that the polymer thin film has a high water content, and we determine in-situ, for the first time, the porosity, or the water content, of a polymer thin film in aqueous solution.
Surface functionalized mesoporous silicas as adsorbents for aromatic contaminants in aqueous solution
Authors: Zhu Dongqiang , Zhang Hua , Tao Qi , Xu Zhaoyi , Zheng Shourong 
Published: February 2009

Abstract
A hexagonal mesoporous silica (HMS) and its postfunctionalized counterparts with propyl (P-HMS) and aminopropyl (AMP-HMS) were prepared and characterized by elemental analysis, N2 adsorption, powder x-ray diffraction, Fourier-transform infrared, and surface charge measurements. Batch experiments were further performed to systematically investigate adsorption properties of these materials toward two nonpolar aromatic compounds (pyrene and pentachlorobenzene) and three phenolic compounds (2,4-dichlorophenol, pentachlorophenol, and 4-methyl-2,6-dinitrophenol) in aqueous solutions. The adsorption isotherms were well described by the Freundlich model and varied in adsorption linearity. For HMS and P-HMS, the adsorption of pyrene and pentachlorobenzene was much stronger than that of pentachlorophenol at pH slightly greater than 6. Alternatively, for AMP-HMS, pentachlorophenol and 4-methyl-2,6-dinitrophenol showed comparable or stronger adsorption affinity than the other target compounds did, suggesting that a major role is played by electrostatic interactions of the two phenols. Furthermore, adsorption decreased with increasing pH for all adsorbate-adsorbent combinations except that of pentachlorophenol and 4-methyl-2,6-dinitrophenol on AMP-HMS, which showed bell-shaped curves with the maximum adsorption at pH close to the pKa. The advantages of reversible adsorption and fast adsorption/desorption kinetics (&lt;15 min), as compared to commercial microporous activated carbons, make AMP-HMS a promising candidate to remove selected phenolic compounds in water treatment.
Towards a New Generation of Physics-Driven Solvers for Black-Oil and Compositional Flow Simulation
Authors: Klie Hector , Monteagudo Jorge , Hoteit Hussein , Rodriguez Adolfo 
Published: February 2009

Abstract
In recent years, there has been a resurgence in developing new solver technologies for addressing highly complex and large-scale flow simulations on specialized parallel and multicore architectures in a very effective manner. Methods such as algebraic multigrid (AMG), Krylov recycling (e.g., deflation, Krylov-secant) and extensions to two-stage preconditioners (e.g., GPR) have been copping the scene in latest solver advances. Nevertheless, there is still a long way to transit to be able to reduce the gap between achieving maximum robustness and parallel efficiency of these solvers in a wide range of problems that the oil industry is currently pursuing on. A new generation of solvers seems to require capabilities to recapture part of the masked physics that is overlooked by strictly algebraic procedures in order to retrieve part of the loss efficiency and furthermore, to obtain insights that make them adaptable to different reservoir situations. In this work, we show that this physical information may be possible by aggregation of system coefficients via percolation. The process can be efficiently encapsulated into a two-stage preconditioner that relies on the solution of the identified highly connected blocks (i.e., aggregates) followed by a deflation preconditioner. The proposed approach is coined as two-stage percolation aggregation (2SPA) and emerges as a representative member of a new family of physics-driven solvers to exploit connectivity (and consequently, flow trends) on highly heterogeneous media. We compare the performance of 2SPA preconditioner against ILU and conclude that the method could be promising to tackle a wider range of reservoir scenarios.
Embedding a Petroelastic Model in a Multipurpose Flow Simulator to Enhance the Value of 4D Seismic
Authors: Fanchi John R. 
Published: February 2009

Abstract
Time-lapse (4D) seismic can be effectively integrated into the reservoir management process by embedding the calculation of seismic attributes in a flow simulator. This paper describes a petroelastic model embedded in a multi-purpose flow simulator. The flow simulator may be used to model gas, black oil, compositional, and thermal systems. The petroelastic model can calculate such reservoir geophysical attributes as P-wave and S-wave velocities and impedances, dynamic and static Young's moduli, and dynamic and static Poisson's ratios. Examples illustrate how to use the petroelastic model to facilitate the integratation of 4D seismic and reservoir flow modeling.
Determination of Active Constraints in a Network
Authors: Watts J. W. , Fleming G. C. , Lu Q. 
Published: February 2009

Abstract
There is increasing interest in modeling networks of wells, including subsurface components of complex wells and surface facilities. Such modeling requires setting constraints at various points in the network. Typical constraints are maximum phase flow rates and minimum flowing pressures. A major difficulty in network calculations is determining which of these constraints is active.
This paper presents a method that uses slack variables in determining active constraints. The equations of interest generally come in pairs, with each pair consisting of a base equation and a constraint equation. The base equation is the equation that normally applies. The constraint equation replaces it if the constraint is active. Normally, only one of these two equations can be satisfied. The slack variable provides a way to ensure that both are satisfied, regardless of which is active. If the constraint is inactive, the slack variable is added to the constraint equation and accounts for the slack. By definition, "slack" is the amount by which the inactive equation is not satisfied. On the other hand, if the constraint is active, the slack variable is instead added to the base equation, and the constraint equation as originally written is satisfied. To obtain this behavior, we define a parameter w and add w times the slack variable to the base equation and (1 – w) times the slack variable to the constraint equation. Thus, if w = 1, the slack variable is added to the base equation, and the constraint is active. On the other hand, if w = 0, the slack variable is added to the constraint equation, and the base equation is inactive. The slack is always in the inactive equation. There is a w associated with each slack variable.
Determining the parameter w is an iterative process. The efficiency of the process is improved by manipulating the network matrix such that a Schur complement can be created that has the slack variables as its unknowns and contains the only references to the w‘s. To determine the slack variables, we need only to work with this matrix, which typically is much smaller than the network matrix.
The resulting method is implemented within a general-purpose reservoir simulator. Testing of the method in more than 700 cases has shown it to be much more robust than an earlier heuristic procedure.
Practical and Robust Isenthalpic/Isothermal Flashes for Thermal Fluids
Authors: Stone Terry W. , Nolen James S. 
Published: February 2009

Abstract
This paper describes in detail computational techniques and formulations for constructing a phase envelope and/or subsequent isenthalpic/isothermal flash calculations that are practical for multiphase fluids in a non-isothermal environment. These methods were designed especially for heavy oil applications and use in numerical simulators. The methods are based on a fluid characterized by pressure and temperature dependent K-values. Although these procedures may be extended to more general N-phase systems, the paper gives full details for a 3-phase oil/gas/water system. Any number of hydrocarbon components may be present and water may exist as a liquid and/or a vapor. The presence of non-volatile and/or non-condensable hydrocarbon components is treated.
Automatic History Matching of Production and Facies Data with Non-stationary Proportions using EnKF
Authors: Agbalaka Chinedu C. , Oliver Dean S. 
Published: February 2009

Abstract
Most geostatistical methods for generating plausible facies models require prior knowledge of the facies proportions distribution to account for heterogeneity within the reservoir. This parameter affects the flow behavior, predictive performance and fluid volume distribution of the model. In practice, it is hardly known with certainty and it is important to account for this uncertainty in the modeling and history matching phases.
The ensemble Kalman filter (EnKF), when modified appropriately, to account for non-linearity and non-Gaussianity, is quite robust for automatic history matching problems. However, because the problem of history matching applied to facies is complex, most attempts at solving this problem typically assume constant petrophysical properties and stationary facies proportions. However, realistic representation of facies distribution requires incorporating the variation in petrophysical properties in the geologic model, in addition to any associated uncertainty. This is critical to correctly defining the flow connectivity within the model and the variations in storativity within facies.
In this paper, we investigate a number of practical issues in history matching applied to facies with heterogeneous petrophysical properties and non-stationary proportions: (1) Can we account for heterogeneity in facies petrophysical properties during history matching and subsequently reduce any associated uncertainty in them by sequential calibration to data? To the best of our knowledge, this is the first time that heterogeneity in facies petrophysical properties has ever been applied to problems of this kind; (2) What is the EnKF performance when the facies proportions are stationary but implicitly uncertain? (3) Can EnKF efficiently adjust the facies boundaries and distributions when the prior proportions are assumed known but non-stationary?
To answer these questions we designed three different test problems. We show that when the facies proportion is non-stationary the EnKF is a robust in estimating the facies properties and distribution.
Massively Parallel Sector Scale Discrete Fracture and Matrix Simulations
Authors: Geiger S. , Huangfu Q. , Reid F. , Matthäi S. , Coumou D. , Belayneh M. , Fricke C. , Schmid K. 
Published: February 2009

Abstract
We have been able to solve a reservoir simulation problem which was previously thought of as intractable: We simulated multiphase displacement, including viscous, capillary, and gravitational forces, for highly resolved and geologically realistic models of naturally fractured reservoirs (NFR) at the sector, i.e. kilometre, scale with very reasonable runtime. This has been possible because we used massive parallelisation and hierarchical solvers in conjunction with a new discrete fracture and matrix modelling (DFM) technique that is based on mixed-dimensional unstructured hybrid-element discretisations.
High-resolution DFM simulations are important to resolve the non-linear coupling of small scale capillary – viscous and large scale gravitational – viscous processes adequately for sector scale NFR. Cross-scale process coupling in NFR controls oil recovery and NFR often exhibit power-law fracture length distributions, i.e. they do not possess an REV, and highly permeable fractures can extend over the full hydrocarbon column height. As a consequence, emergent displacement patterns have been observed which are difficult to quantify using traditional means of upscaling. However, such patterns could now be used as benchmarks to reach a better consensus on the correctness of promising new upscaling techniques. The parallel DFM technologies presented here allow us to to obtain these results much more efficiently and hence explore the parameter space in greater detail.
We observed a linear scaling behaviour for up to 64 processes and a significant decrease in runtime when applying our parallel DFM approach to three highly refined NFR simulations. These contain thousands of fractures, up to 5 million elements, and have local grid-refinements below 1 m for model dimensions between 1 and 10 kilometres. We achieved this excellent speedup because we reduced inter-processor communication by minimising the overlap between individual domains and decreased idle time of individual processors by distributing the number of unknowns equally among the processors.
Stochastic Collocation Methods for Efficient and Accurate Quantification of Uncertainty in Multiphase Reservoir Simulations
Authors: Li Heng , Chang Haibin , Zhang Dongxiao 
Published: February 2009

Abstract
Reservoir simulation is subject to uncertainties, which may stem from inaccurate and imprecise measurements or inadequate characterization of spatially or temporally varying medium properties. Such uncertainties render the model parameters random and the equations describing flow and transport in the media stochastic. There exist several stochastic approaches for quantifying uncertainties, which, however, are either incompatible with existing deterministic simulators or are too demanding computationally. In this study, an alternative approach is proposed that is both accurate and efficient. In this approach, the uncertainty quantities such as permeability and porosity fields are represented by the Karhunen-Loeve expansions while the fluid saturations and reservoir production quantities are expressed by the polynomial chaos or Lagrange polynomial expansions. Two collocation-based methods, i.e. probabilistic collocation method (PCM) and Smolyak method are used to determine the coefficients of the polynomials expansions by solving for the fluid saturations and pressures at different collocation points via the original partial differential equations. This approach is non-intrusive in that it results in independent deterministic differential equations, which similar to the Monte Carlo method, can be implemented with existing codes or simulators. However, the required number of simulations in PCM or Smolyak method is much smaller than that in the Monte Carlo method. The approach is demonstrated with three-phase flow problems in heterogeneous reservoirs using Eclipse. The accuracy, efficiency, and compatibility of this approach are compared against Monte Carlo simulations. This study reveals that while their computational efforts are greatly reduced compared to Monte Carlo method, the stochastic collocation methods are able to accurately estimate the statistical moments and probability density functions of the fluid saturations, pressures, and production quantities of interest.
Results of the Brugge Benchmark Study for Flooding Optimization and History Matching
Authors: Peters E. , Arts R. J. , Brouwer G. K. , Geel C. K. 
Published: February 2009

AbstractIn preparation for the SPE-ATW held in Brugge in June 2008 a unique benchmark project to test the use of flooding optimization and history-matching methods was organized in the form of an interactive competition during the months preceding the ATW. In total nine different groups participated and presented their results during the workshop.Prior to the Brugge workshop, early 2008, a 3D synthetic dataset was made available to the participants by TNO. The dataset consisted of 104 upscaled realizations of a 3D geological model, well-log data from wells with fixed positions, the first 10 years of the production history of the field (including measurement errors), inverted time-lapse seismic data in terms of (uncertain) pressures and saturations, and economic parameters for oil and water (price and discount rate).Participants were asked to provide a history match (either a single matched "best" model or a matched ensemble) based on the available data, and an optimal production strategy (without infill drilling) for the next period (10-20 years). Their strategy was tested on the "real field" to obtain additional production data over the 10-year period. Using these production data, the participants updated their reservoir model and revised their optimal production strategy for the final period of production (20-30 year).The final objective of the exercise was to optimize, within a time constraint, the NPV of a waterflooded oilfield having smart wells that can be controlled by an inflow control valve per completed layer. The results of the nine participants are compared to an optimization of the "real field" as performed by TNO.This paper gives an overview of the results obtained from this benchmark study. After the Brugge workshop the participants that were not able to finalize the exercise in time were given an additional two months time. The results of this additional exercise are reported in this paper as well.