bluuebunny/crossref_metadata_2025 huggingface dataset:
Physicochemical Interactions During Surfactant Flooding of Fractured Carbonate Reservoirs
Authors: Seethepalli Anita , Adibhatla Bhargaw , Mohanty Kishore K.
Published: December 2007

Recovery from fractured, oil-wet/mixed-wet, carbonate reservoirs by waterflooding is poor. Dilute surfactant methods are being developed to improve oil recovery from fractured carbonates. This paper investigates the interactions of dilute alkaline anionic surfactant solutions with crude oil on carbonate mineral surfaces. Wettability, phase behavior, interfacial tension, and adsorption experiments have been conducted. Anionic surfactants have been identified that can change the wettability of the calcite surface to intermediate/water-wet condition as well or better than the cationic surfactant dodecyl trimethyl ammonium bromide (DTAB) with a west Texas crude oil. All the carbonate surfaces (lithographic limestone, marble, dolomite, and calcite) show similar behavior with respect to wettability alteration with an anionic surfactant. Anionic surfactants, which lower the interfacial tension with the crude oil to very low values (<10−2 mN/m), have also been identified. The adsorption of the sulphonate surfactants can be suppressed significantly by the addition of Na2CO3, because the addition of carbonate can change the zeta potential of calcite to a negative value. Greater than 50% OOIP can be recovered from oil-wet carbonate cores by spontaneous imbibition of 0.05 wt% anionic surfactant solutions in the laboratory scale.
Three-Phase Imbibition Relative Permeability
Authors: Naar J. , Wygal R.J.
Published: December 2007

An equation for three-phase (water, oil, gas) imbibition oil permeability is developed, assuming the water to be the dominant wetting fluid. Oil isoperms are obtained for consolidated sandstones characterized by. The evolution of an oil-gas system imbibing water from is shown to proceed along a line of constant oil saturation with increasing oil permeability and decreasing gas saturations. When the gas saturation cannot be reduced further, the system evolves along a line of constant with decreasing oil saturation and permeability. The initial gas saturation is shown to reduce markedly the effect of complete wetting by either oil or water on flow performance.

Introduction

Imbibition oil isoperms are required for performance prediction when a well is producing water, oil and gas. This situation occurs in multiphase displacements such as underground combustion, steam injection and the water flooding of highly depleted reservoirs. In a recent paper, a model was presented for the prediction of two-phase imbibition characteristics. This paper extends the imbibition model to the case of three phases by assuming that the water is the dominant wetting fluid. The following results were obtained from the model:an analytical expression of oil isoperms;oil isoperms as functions of reduced water, oil and gas saturations, valid for all sandstones having a capillary pressure curve which can be approximated by; andevaluation of the three-phase flow performance as dictated by complete wetting by either oil or water.

The agreement between predicted and observed oil recovery in the presence of a gas phase, reported in Ref. 1, is a partial support for the present development. However, experimental data are not available at this time to check fully the model predictions. Perhaps this paper will stimulate the collection of such data.

THEORETICAL

The imbibition model of a porous medium has been described previously, and the reader is referred to the paper of Naar and Henderson for details. In brief, the model is formed by the random interconnection of straight capillaries, with a provision for the blocking of the non-wetting phase by the invading wetting fluid.
Real Time Optimization: Classification and Assessment
Authors: Mochizuki Satoshi , Saputelli Luigi A. , Kabir C. Shah , Cramer Ron , Lochmann Mark , Reese Richard , Harms Larry , Sisk Carl , Hite J. Roger , Escorcia Alvaro
Published: December 2007

The Real-Time Optimization (RTO) Technical Interest Group (TIG) has endeavored to clarify the value of real-time optimization projects. RTO projects involve three critical components: People, Process, and Technology. Understanding these components will help establish a framework for determining the value of RTO projects. In this paper, the Technology component is closely examined and categorized.

Levels within each Technology category are illustrated by use of spider diagrams, which help decision makers understand the current status of operations and the future RTO status. The perception of uncertain value has been one of the critical issues in adopting RTO systems in our industry. Therefore, case histories are reviewed to demonstrate the impact of RTO projects.

To assist RTO project promotion further, we list lessons learned, suggest a justification process, and present a simple example of an economic-evaluation process.

Introduction

Industry case histories demonstrate many types of benefits from RTO such as production-volume increase; better return on investment (ROI); higher decision quality; health, safety, and environment (HSE) improvements; and operational expenditures (OPEX) reduction. However, they have lacked systematic project-evaluation processes for justification.

Today, promoting RTO is, in essence, a competition for capital within a company. The project teams that recognize this fact and then clearly outline the purpose, benefits, costs (direct or indirect), and strategic business alignment of their proposals will be in an advantageous position to secure funding. Because RTO is still an emerging discipline, classifying projects of this nature is still dependent on an individual's point of view. This paper provides classification of RTO to help provide a common vocabulary to address a multitude of issues.
Optimization of Horizontal Well-Completion Design With Cased/Perforated or Slotted Liner Completions
Authors: Furui K. , Zhu D. , Hill A. D. , Davis E. R. , Buck B. R.
Published: December 2007

A well completion is a critical interface between the productive formation and the wellbore. An effective completion must maintain the mechanical integrity of the borehole without creating any significant restrictions on the flow capacity of the well. In this paper, a process is outlined to design optimal completions for horizontal wells by applying comprehensive skin-factor models that include damage and turbulence effects for all common types of completions.

Slotted or perforated liner, cased, perforated, or gravel-pack completions have been used in horizontal wells for borehole stability and sand-control purposes. However, these completions may have lower productivity (as characterized by a positive skin) relative to an equivalent openhole completion, because the convergent flow to perforations or slots increases fluid velocity in the near-well vicinity. In addition, any reduced permeability zones (formation damage caused by drilling, completion, or other processes) magnify the convergent flow effects and therefore may result in substantially increased skin factors. Compound effects of formation damage around the well completion, a crushed zone because of perforating, plugging of slots, and turbulent flow, as well as interactions among these effects, are included in the model.

This paper illustrates how to use skin factor models to screen the available completion types for cased/perforated and slotted liner completions. This screening approach considers reservoir permeability, permeability anisotropy, fluid properties, formation damage effects, and rock mechanical characteristics as the key parameters. The types of completion that yield the most productive well performance for this matrix of properties are presented.

A more detailed completion design is then illustrated by showing how the skin-factor models were used to redesign the slot configuration of liner completions for viscous oil reservoirs on the North Slope of Alaska. Application of the slotted or perforated liner models to the readily available liners showed that the completion skin factor can vary by as much as 40%, depending on the detailed characteristics of the slots or perforations in the liner (slot or perforation size, density, and distribution). The example showed that optimizing the performance of the completion can increase well productivity at little or no cost and with no loss in liner mechanical strength.
Innovative, Integrated, and Cost-Effective Chemical Management on the Miller Platform
Authors: Wylde J. J. , Williams G. D. M. , Careil F.
Published: December 2007

The BP-operated Miller Field poses a unique chemical challenge as it has, arguably, the harshest oilfield scaling regime in the North Sea, if not the world. Some 3 million litres of chemical are consumed each year and the management, supply, use, and performance of every aliquot of chemical is imperative to see Miller through to its planned cessation of production.

The Miller Field is a mature North Sea asset and produces a potential of 80,000 BWPD with its 16,000 BOPD. The unique challenge posed by Miller is that the produced water contains very high concentrations of scale-forming components combined with a very high corrosivity potential. Chemicals are routinely deployed to control scale, corrosion, emulsions, foam, biological fouling, and hydrates.

Two major step changes have occurred in the past 12 months that have delivered significant improvement to chemical management processes. The first step is the use of a novel, best-in-class, scale-inhibitor chemistry. Two years were spent in an industrywide search as well as developing and extensively testing the chemical in the laboratory. The new chemical is now deployed on more than 75% of the Miller wells. The longevity of scale-prevention treatments has been doubled on some wells when compared to the incumbent products.

The second step change was the application of innovative relative permeability modifier chemistries that not only increase oil production but actually shut off water production. Cross-linked polymer gels are pumped down wells and inflate in the presence of water, effectively blocking the flow path, but deflate in the presence of oil, allowing flow.

By implementing these changes, significant steps have been taken toward ensuring that continuation of production to the proposed cessation of production remains a viable proposition.
The Dimensionless Productivity Index as a General Approach to Well Evaluation
Authors: Diyashev Iskander R. , Economides Michael J.
Published: December 2007

Petroleum-well performance and its evaluation are clearly some of the most important functions of modern production engineering. We present a general approach to the issue by employing the field-derived, dimensionless productivity index (JD), which we calculate from measured information including the production rate, reservoir and flowing pressures, and well and reservoir data.

The JD is independent of well completion (i.e., it transcends the geometry), whether the well is under radial flow, is hydraulically fractured, or whether it is vertical or horizontal. The determined JDs are then compared against benchmarks we have developed for optimized production, such as the concept of unified-fracture design (UFD) or maximized horizontal well performance. We have developed deterministic methods for this analysis and new means to depict the results graphically.

Such evaluations are important in concluding whether the well is underperforming or whether past engineering could have been improved and by how much. Decisions such as refracturing, the redesign and improvement of future treatments, and whether to fracture vertical or drill horizontal wells can be readily made.
Numerical and Analytical Modelling of the Gas Well Liquid Loading Process
Authors: Dousi Niek , Veeken Cornelis A.M. , Currie Peter K.
Published: December 2007

Liquid loading is a serious problem in areas where gas fields are maturing. This paper presents an analysis of the production behavior of liquid-loaded wells over time. This clearly shows that these wells can operate at two different rates—a stable rate, at which full production is taking place, and at a lower metastable rate, at which liquid-loading effects play a role.

A model has been constructed that enhances the understanding of the process of water buildup and drainage in gas wells. It assumes a single gas- and water-coproduction point and a single water reinjection point. As expected, a water column is built up in the well as soon as production takes place below the critical rate. As observed in the field, for good inflow performance, a metastable flow rate can be observed. At this state, the water-reinjection and water-coproduction rate are equal to one another, and the water-column height stabilizes.

A sensitivity analysis has been carried out to determine how well parameters influence the metastable flow rate, the time required to reach this metastable rate, the corresponding water-column height, and the shut-in time required to drain this water column. The results of the analysis indicate that significant metastable flow rates occur in wells that have good inflow performance, a low water/gas ratio, and a large distance between injection and production point.

Furthermore, a steady-state analytical solution has been derived for the metastable rate and stabilized water-column height confirming the numerical-analysis results.

Introduction

Many of the mature offshore gas fields in the southern North Sea have already experienced considerable pressure depletion resulting in significantly reduced gas flow rates and, eventually, liquid loading. Insight into the flow characteristics of these liquid-loaded wells will help manage tail-end production (i.e., will help define the most effective means of accelerating and maximizing their ultimate recovery.
Improved Reservoir Management With Intelligent Multizone Water-Alternating-Gas (WAG) Injectors and Downhole Optical Flow Monitoring
Authors: Sandøy B. , Tjomsland T. , Barton D. T. , Daae G. H. , Johansen E. S. , Vold G.
Published: December 2007

A four-zone intelligent water-alternating-gas (WAG) injector was installed at the Statoil Veslefrikk Field in the North Sea in May 2004. The completion includes one on/off and three variable downhole chokes for controlling injection rate into each of the four zones. The completion also includes three downhole optical flow-meters and three optical pressure and temperature gauges. Measurement of surface injection rate and the rate from each of the three flowmeters provides real-time measurement of injection rate into each zone, regardless of choke positions.

The well is on a WAG cycle in which one zone is primarily intended for gas injection and the other three zones are primarily intended for water injection. Therefore, equipment that can control and measure water flow and gas flow with no changes in hardware was critical for the success of this installation.

The combination of downhole chokes and flowmeters allows full control and monitoring of zonal injection rates and has proved to be a valuable tool for managing reservoir pressures and optimizing production. After more than 1 year of operation during water injection, all the valves and the optical monitoring equipment are functioning satisfactorily. It is estimated that up to half of the well's value creation during its expected lifetime is because of the DIACS (Downhole Instrumentation and Control System) installation.
Circulating Usage of Partial Produced Fluid as Power Fluid for Jet Pump in Deep Heavy-Oil Production
Authors: Chen Shengnan , Li Heng , Zhang Qi , He Jun , Yang Daoyong
Published: December 2007

Jet pumping driven by light oil is one of the preferred lift methods for producing heavy oil in a deep heavy-oil reservoir. Generally, the amount of light oil required is too large to be acceptable. One solution which reduces the amount of light oil required is to blend light oil with a portion of the produced fluid at a reasonable ratio. Then, the produced fluid/light-oil mixture is reinjected into the well as the power fluid. In this case, the viscosity of the blended power fluid keeps increasing and eventually reaches its equilibrium value, which has been found to be a function of reservoir-oil viscosity, light-oil viscosity, the ratio of light oil to blended power fluid (volumetric percentage), and the ratio of well rate to diluent rate (M ratio). Moreover, an optimal ratio of light oil to blended power fluid can be determined by using an iterative algorithm developed in this study. Variations in any of the previously mentioned parameters, especially the viscosity of light oil and the ratio of light oil to blended power fluid, result in a significant change in both the viscosity of the blended power fluid and the pressure loss in the production string. It has been shown in a field application that the amount of light oil used for driving the jet pumping operation can be reduced by more than 50%.
Rheology of Heavy-Oil Emulsions
Authors: Alboudwarej Hussein , Muhammad Moin , Shahraki Ardi , Dubey Sheila , Vreenegoor Loek , Saleh Jamal
Published: December 2007

Water is invariably produced with crude oil. If there is enough shear force when crude oil and produced water flow through the production path, stable emulsions may be formed. This scenario may particularly be present during the production of heavy oils, where steam is used to reduce the viscosity of heavy oil, or in cases in which submersible pumps are used to artificially lift the produced fluids. To efficiently design and operate heavy-oil production systems, knowledge of the realistic viscosities of the emulsified heavy oil, under the actual production conditions, is necessary. This study is an attempt to investigate the effect of water content, pressure, and temperature (i.e., operating conditions on the viscosity of live heavy-oil emulsions).

Two heavy oil samples from South America were used for this study. The stock tank oil (STO) samples were recombined with the corresponding flash gases to reconstitute the original reservoir oil compositions. Live oil/water emulsions were prepared in a concentric cylinder shear cell using synthetic formation water, under predetermined pressure, temperature, and shear conditions. The stability of live emulsions was investigated using a fully visual pressure/volume/temperature (PVT) cell, while viscosities were measured using a precalibrated, high-pressure capillary viscometer. Viscosities were measured at least in three different flow rates at the testing conditions. In addition to live-oil emulsion studies, the stability and droplet size distribution of STO emulsions were also determined.

Experimental results indicated that the inversion point for the STO emulsions was approximately 60% water cut (volume), and the average droplet size was increasing with water content. For all measured cases, viscosities varied with temperature according to an Arrhenius relation, while viscosities did not indicate any variation with flow rate (shear) within the range of tested flow rates. Measured viscosities also increased as pressure decreased below the bubblepoint of the sample as lighter hydrocarbon components evolved. The measured viscosities increased as much as 500% because of the presence of emulsions before a sharp drop in viscosity beyond the inversion point. The variation of viscosity with water content for live emulsion samples indicated that the inversion point for live emulsions is similar to that of STO samples.

The experimental results are also used to analyze and evaluate the performance of an ESP system when water cut increases and causes emulsion in a well.
Behavior of a Scale Inhibitor Water-in-Oil Emulsion in Porous Media
Authors: Romero C. , Bazin B. , Zaitoun A. , Leal-Calderon F.
Published: December 2007

The use of water-in-oil emulsions (WO) to deploy scale inhibitors has been reported in the literature as an alternative to water-based squeeze treatments. The non-aqueous nature of these emulsions has the advantage of preventing water blocking, which adversely affects oil production in aqueous squeeze treatments. Placing the scale inhibitor in a WO or "invert" emulsion has shown in some cases the additional advantage of enhancing treatment lifetime. However, results from the literature seem contradictory and highlight a poor understanding of this technology.

The present paper aims at providing further insight on emulsified scale inhibitor placement in porous media. We focus on studying the retention mechanisms of the emulsion droplets containing the scale inhibitor (SI), whilst SI release and, consequently, the performance of the emulsified squeeze is not discussed. Preliminary experiments were conducted using a low molecular-weight biopolymer as a SI. They evidenced a low adsorption/retention of this SI in aqueous solution. Reformulation of the product under invert emulsion was investigated to measure inhibitor retention.

Results from coreflood experiments using well-characterized silicon carbide (SiC) packs provided preliminary evidence of aqueous droplet adsorption as the main retention mechanism in porous media. This was expected considering the average droplet size of 0.3 µm (300 nm). The mother formulation of the WO emulsion is a concentrate, containing 80% of water phase and 8% of active SI. The product can be diluted down to 2% water phase by adding the desired oil phase. Dilution does not affect emulsion stability or increase the emulsion's droplet size. These results represent a promising first step towards the development of a technically and commercially viable, environment-friendly SI technology based on WO emulsions. Future work to study the emulsified SI release mechanisms and its consequent performance are being prepared to compare with conventional aqueous squeeze treatments.
Proppant Placement Using Reverse-Hybrid Fracs
Authors: Liu Yajun , Gadde Phani B. , Sharma Mukul M.
Published: December 2007

In conventional gel-fracturing treatments, the damage induced by the gel can have a significant impact on well performance, particularly in low-permeability gas formations. Slick-water fracs have been shown to be more successful in some tight gas formations because of reduced gel damage and limited height growth. Proppant placement is a major concern in water fracs. Hybrid water fracs (i.e., using slick water as the pad fluid and gel to place the proppant) provide improvements to the performance of water fracs.

This paper proposes a new method, reverse-hybrid fracs (RHF), for the efficient placement of proppant deep into created fractures while minimizing gel-induced damage. Experiments were conducted in a simulated fracture (i.e., slot cell) to study the transport of proppant. Slick water was injected first into the slot, followed by gel. Finally, slick water containing proppant was injected to displace the gel. The water that carried the proppant quickly formed viscous fingers through the gel. The gel was observed to form long, thin layers that effectively hindered proppant settling and helped transport the proppant further into the slot. This resulted in the formation of proppant packs above the gel layers.

In this paper, experimental results are presented to show how the gel layers distribute in the slot and how proppant distribution is affected by the gel layers. A transparent cell composed of rough walls was set up to investigate the effect of fracture wall roughness. The effects of fluid viscosity ratio, fracture wall roughness, and gel pad volume were investigated. Based on the experiments and scaling relations, recommendations are made for the pumping sequence and the size of the gel and slick-water stages in reversehybrid fracture treatments.

This method of proppant placement requires less gel than conventional gel fracs. Other possible advantages include: (1) less gel damage to the proppant pack, (2) limited height growth, and (3) less penetration of the pad fluid into the formation resulting in shorter cleanup time following fracture treatment.
How uncertain is model-based prediction of copper loads in stormwater runoff?
Authors: Lindblom E. , Ahlman S. , Mikkelsen P.S.
Published: December 2007

In this paper, we conduct a systematic analysis of the uncertainty related with estimating the total load of pollution (copper) from a separate stormwater drainage system, conditioned on a specific combination of input data, a dynamic conceptual pollutant accumulation-washout model and measurements (runoff volumes and pollutant masses). We use the generalized likelihood uncertainty estimation (GLUE) methodology and generate posterior parameter distributions that result in model outputs encompassing a significant number of the highly variable measurements. Given the applied pollution accumulation-washout model and a total of 57 measurements during one month, the total predicted copper masses can be predicted within a range of ±50% of the median value. The message is that this relatively large uncertainty should be acknowledged in connection with posting statements about micropollutant loads as estimated from dynamic models, even when calibrated with on-site concentration data.
A new design of flocculation tank: the Turbomix® applied to weighted flocculation
Authors: Levecq C. , Breda C. , Ursel V. , Marteil P. , Sauvignet P.
Published: December 2007

As far as flocculation is concerned, the agglomeration of suspended particles into flocs is highly linked to the hydraulic behaviour of the agitation. The Turbomix® is a special design of mixing tank; its design was developed to better control the flow during the flocculation stage. It enables a significant decrease in footprint of the process. The combination of the Turbomix® and ballasted flocculation has been studied during pilot trials in terms of treatment efficiency. Its controlled hydraulic behaviour explains the efficiency of the process as proved by CFD investigation.
Natural attenuation potential of downwelling streams for perfluorochemicals and other emerging contaminants
Authors: Hoehn E. , Plumlee M.H. , Reinhard M.
Published: December 2007

Stream augmentation with tertiary treated municipal wastewater—i.e., recycled water—is increasingly considered as an ecologically beneficial way to utilize recycled water, especially in semi-arid regions of the American Southwest. There is concern that emerging contaminants, i.e. unregulated but biologically active organic compounds, may be present in recycled water and will impact on the aquatic environment and the underlying groundwater. Emerging contaminants include a wide variety of chemically disparate compounds, including pharmaceuticals, endocrine disruptors, and residues of perfluorochemical surfactants (PFCs). This paper presents background data on the occurrence and transport of PFC in Upper Silver Creek (USC) and Coyote Creek, in San Jose, California. USC feeds into Coyote Creek, which discharges into San Francisco Bay. Augmenting the natural flow of Coyote Creek with highly treated recycled water is currently being considered as a means to provide more freshwater to the river ecosystem. The reach of interest is approximately 1,000 m where USC flows on alluvial fan deposits. Data indicate that some PFCs are refractory
Ozonation and reductive deiodination of iopromide to reduce the environmental burden of iodinated X-ray contrast media
Authors: Putschew A. , Miehe U. , Tellez A.S. , Jekel M.
Published: December 2007

The potential of ozonation for the removal of iodinated X-ray contrast media (ICM) with focus on the oxidation products was examined. Iopromide used as model compound was dissolved in tap water, respectively in the effluent of a membrane bioreactor and was ozonated. Ozone (10 mg/L) was continuously introduced into a semi-batch reactor (35 L/h). After 30 minutes the ozone concentration was increased to 30 mg/L. In all experiments the iopromide concentration decreased very fast, whereas the decrease of the amount of organic bound iodine (AOI) was much lower. The concentration of iodate, the inorganic oxidation product increases with time, depending on the AOI decrease. The data clearly show that the ozonation of iopromide using a common applied ozone dosage leads to the formation of numerous iodinated transformation products, which are detectable by LC-ESI-MS.

As an alternative treatment, especially for the treatment of urine or hospital waste water, the source for the contamination, it was tested if iopromide can be deiodinated by zero-valent iron. First experiments done in stirred batch reactors using iopromide dissolved in ultra pure water and urine with an initial pH of 2 showed that iopromide can be deiodinated completely by zero-valent iron. Even in contaminated urine collected in a hospital a deiodination of ICM was possible. Kinetic studies at constant pH showed that the deiodination can be described by pseudo-first order for equal iopromide and iron concentrations. The observed rate constant kobs increased with decreasing pH with a maximum at pH 3 with 4.76 × 10−4 s−1.

The concentration of iopromide can be decreased by ozonation and by the reductive dehalogenation. In case of ozonation iodinated organic compounds are the main reaction products, whereas the reductive dehalogenation leads to transformation products which are not iodinated and are thus most probable biodegradable.
Predictors of Incretin Concentrations in Subjects With Normal, Impaired, and Diabetic Glucose Tolerance
Authors: Vollmer Kirsten , Holst Jens J. , Baller Birgit , Ellrichmann Mark , Nauck Michael A. , Schmidt Wolfgang E. , Meier Juris J.
Published: December 2007

OBJECTIVE—Defects in glucagon-like peptide 1 (GLP-1) secretion have been reported in some patients with type 2 diabetes after meal ingestion. We addressed the following questions: 1) Is the quantitative impairment in GLP-1 levels different after mixed meal or isolated glucose ingestion? 2) Which endogenous factors are associated with the concentrations of GLP-1? In particular, do elevated fasting glucose or glucagon levels diminish GLP-1 responses?

RESEARCH DESIGN AND METHODS—Seventeen patients with mild type 2 diabetes, 17 subjects with impaired glucose tolerance, and 14 matched control subjects participated in an oral glucose tolerance test (75 g) and a mixed meal challenge (820 kcal), both carried out over 240 min on separate occasions. Plasma levels of glucose, insulin, C-peptide, glucagon, triglycerides, free fatty acids (FFAs), gastric inhibitory polypeptide (GIP), and GLP-1 were determined.

RESULTS—GIP and GLP-1 levels increased significantly in both experiments (P < 0.0001). In patients with type 2 diabetes, the initial GIP response was exaggerated compared with control subjects after mixed meal (P < 0.001) but not after oral glucose ingestion (P = 0.98). GLP-1 levels were similar in all three groups in both experiments. GIP responses were 186 ± 17% higher after mixed meal ingestion than after the oral glucose load (P < 0.0001), whereas GLP-1 levels were similar in both experiments. There was a strong negative association between fasting glucagon and integrated FFA levels and subsequent GLP-1 concentrations. In contrast, fasting FFA and integrated glucagon levels after glucose or meal ingestion and female sex were positively related to GLP-1 concentrations. Incretin levels were unrelated to measures of glucose control or insulin secretion.

CONCLUSIONS—Deteriorations in glucose homeostasis can develop in the absence of any impairment in GIP or GLP-1 levels. This suggests that the defects in GLP-1 concentrations previously described in patients with long-standing type 2 diabetes are likely secondary to other hormonal and metabolic alterations, such as hyperglucagonemia. GIP and GLP-1 concentrations appear to be regulated by different factors and are independent of each other.
Artifical Intelligence Languages
Authors: Vranes Sanja
Published: December 2007

Programming languages have had a crucial impact on the development of the artificial intelligence (AI) branch of computer science for at least two reasons. First, they allow convenient implementation and modification of programs that demonstrate and test AI ideas. Second, they provide vehicles of thought and they allow the user to concentrate on higher level concepts. Frequently, new ideas in AI are accompanied by a new language in which it is natural to apply these ideas.
Bioinformatics
Authors: Akutsu Tatsuya
Published: December 2007

Bioinformatics is an interdisciplinary area between biology and computer science. One of the major goals of bioinformatics is to develop methods and tools for analyzing huge amounts of biological data, including genomic sequences, protein structures, and gene expression data, whereas another major goal of bioinformatics is to discover new biological knowledge using such kinds of tools. We focus on the former goal and review important computational problems and computational techniques for solving these problems. In particular, we explain the following topics: pairwise and multiple sequence alignment, hidden Markov models and their applications to bioinformatics, protein structure prediction, kernel methods for bioinformatics, and analysis of gene expression patterns.
Computer Architecture
Authors: Flynn Michael
Published: December 2007

Computer architecture represents the programming model of the computer, including the instruction set and the definition of register file, memory, and so on. Over time, the concept of computer architecture has evolved to include both the functional specification and the hardware implementation. At the system level, it defines the processor‐level building blocks, such as processors and memories, and the interconnection among the building blocks. At the microprocessor level, computer architecture determines the processor's programming model and its detailed implementation. The implementation of a microprocessor is also known asmicroarchitecture.
Computerized Dictionaries: Integrating Portable Devices, Translation Software, and Web Dictionaries to Maximize Learning
Authors: Loucky John Paul
Published: December 2007

This article looks first at background studies on bilingual and electronic dictionaries, then surveys their use, followed by a look at the state of the art in technical features employed by various translation programs and devices. After briefly reviewing the history of electronic lexicography, their place in language and self‐access learning is discussed, with many references given for further in‐depth study. Overall, 75 companies are listed that produce a wide variety of various computerized dictionaries and translation software programs. Finally, their potential for maximizing language learning is discussed, with pedagogical recommendations given that apply to improving the integration of these devices with both classroom and self‐access, independent online learning in all fields.
Concurrent Programming
Authors: Gomaa Hassan
Published: December 2007

Concurrent programming refers to the development of programs that address the parallel execution of several tasks. A
process
or
task
represents the execution of a sequential program or a sequential component in a concurrent program. Each task deals with one sequential thread of execution; thus, no concurrency is allowed within a task. However, overall system concurrency is obtained by having multiple tasks executing in parallel. The tasks often execute asynchronously (i.e., at different speeds) and are relatively independent of each other for significant periods of time. From time to time, the tasks need to communicate and synchronize their operations with each other. Concurrent programming has been applied extensively in the development of operating systems, database systems, real‐time systems, interactive systems, and distributed systems.
Data Analysis
Authors: Wu Yi‐Hung , Chen Arbee L. P.
Published: December 2007

In this article, we describe the concepts and techniques of data analysis. Two categories, supervised data analysis and unsupervised data analysis, are first presented according to their different initial conditions and resultant uses. Two methods for data analysis are then described and illustrated by examples, which are based on probability theory and fuzzy‐set theory, respectively. Following this introduction of the fundamental data analysis methods, the methods for data analysis on two types of Internet data, web page and web log, are presented. Further discussions on advanced methods for Internet data analysis are then provided, which are based on rough‐set theory and association mining concepts. Finally, we bring this article to a conclusion with the research trends highlighted.
Data Structures and Algorithms
Authors: Oliveira Carlos A.S. , Pardalos Panos M. , Prokopyev Oleg A.
Published: December 2007

Algorithms and data structures are the basic building blocks employed in computer sciences research and applications. We present the fundamental concepts in the area of analysis of algorithms and data structures. The concept of abstract data type is introduced, along with some useful data types such as lists, queues, stacks, trees, and graphs. More advanced data structures are also mentioned along with applications where they occur. Techniques for algorithm construction, including divide and conquer, dynamic programming, and backtracking, are introduced. Standard algorithms are presented, such as sorting, searching, and matrix multiplication. Finally, more advanced topics such as approximation algorithms, parallel algorithms, and randomized algorithms are discussed.
Deductive Databases
Authors: Grant John , Minker Jack
Published: December 2007

In this article define the concept of deductive database including the formal definition of a query and an answer to a query; we provide an historical background for deductive databases; we explain the different types of deductive databases starting with Datalog and including stratified, nonstratified, extended, and disjunctive deductive databases; we discuss various semantics for deductive databases; we list the prototypes and implementations of deductive databases; we also give several applications that cannot be handled by relational and databases and require deductive databases.
Embedded Operating Systems
Authors: Mo Albert , Cheng Kim
Published: December 2007

Many of the systems and devices used in our modern society must provide a response that is both correct and timely. More and more computer systems are built as integral parts of many
of these systems to monitor and control their functions and operations. These embedded systems often operate in environments where safety is a major concern. For real‐time embedded applications in which task deadlines must be satisfied, a real‐time operating system (RTOS) with an appropriate scheduler for scheduling tasks with timing constraints must be used. This article introduces the basics of RTOSs, covering task synchronization, scheduling, memory management, and input/output.
Home Automation
Authors: Douligeris Christos
Published: December 2007

Home automation is expected to increase comfort and security around the house and provide economic benefits through energy conservation. An ideal home automation system would relieve the inhabitant of a house of any unwanted manual control of every appliance and electrical or gas equipment in the house and would provide for an automated environment that would be aware of specific user needs and habits and program the operation of these appliances accordingly. Given the recent advances and drop in costs in computers, fiber optics, and multimedia communications, the concept of home automation systems has been extended to include data, voice, and visual communications inside a home. The recent expansion of the Internet and the World Wide Web (WWW) coupled with efficient home automation systems may provide an additional added value to the concepts of telecommuting; home schooling; interaction between students, teachers, and parents; home entertainment; and remote efficient resource management of home appliances.
Logic Synthesis
Authors: Barriga Angel , Jimenez Carlos J. , Valencia Manuel
Published: December 2007

This article addresses logic synthesis, which involves the generation of a circuit at the logic level based on an RT level design specification. The article deals with aspects associated with logic design such as data types, system components, and modes of operation. The hardware description languages will be presented as tools to specify digital systems. Two standard languages (VHDL and Verilog) will be examined in detail, and the use of VHDL for automatic synthesis will be explained to illustrate specific aspects of logic synthesis descriptions. The article ends with an illustrative example of the principal concepts discussed.
Biologically Inspired Neural Computation
Authors: Leondopulos Stathis , Micheli‐Tzanakou Evangelia
Published: December 2007

The development of intelligent machines that are capable of robust sensory perception has been an elusive task for those involved in machine intelligence. Indeed, although machines have been developed for performing on the order of 10
12
floating‐point operations per second, they have not been able to outperform human infants at such simple tasks as face recognition. As a result, many researchers have turned their sights to the inner workings of the biological brain itself in the hope of finding clues to the development of more robust machine perception, thus spawning the field of biologically inspired computation.

It should be noted that biologically inspired computation includes many topics that are not directly related to the function of the nervous system, such as genetic algorithms and molecular or DNA computing. However, within the context of neural networks, biologically inspired computation can be described as the development and implementation of models and algorithms that imitate the behavior of individual nerve cells (or neurons) as well as groups or nuclei of synaptically interconnected neurons.

This article discusses the relationship between the biological neuron and popular artificial neural networks that have been used in the scientific literature. In addition, applications of neural networks that are exemplary of their biological origin will be presented.
Cognitive Systems and Cognitive Architectures
Authors: Sun Ron , Bringsjord Selmer
Published: December 2007

Cognitive systems refer to computational models and systems that are in some way inspired by human (or animal) cognition as we understand it. There is a variety of forms of cognitive systems. Among cognitive systems, cognitive architectures are generic models of cognition, inspired by psychological studies and aimed for capturing human cognition in a rather comprehensive fashion. Another common approach is specifying cognitive processes through logics and logic‐based systems. Many theoretical tools and perspectives have been developed along these lines. In this article, example cognitive systems will be described, and general issues in developing cognitive systems and cognitive architectures will also be discussed along the way.
Optimizing Compilers
Authors: Chapman Barbara M. , Leiss Ernst L.
Published: December 2007

Optimizing compilers are designed to modify (automatically and at compile time) the code of a given program in such a way that

The semantics of the program are maintained (i.e., the results of the original program and the modified program are identical), and

The new program is an improved one with respect to some predefined goal.

This goal is usually a reduction in execution time, but may be a reduction in memory or power consumption. Although these goals are distinct, and occasionally conflicting, programs that consume fewer resources tend to be a little faster and we do not consider other goals explicitly in the following.
Queueing Theory
Authors: Lee Ho Woo , Kumar Santosh
Published: December 2007

Waiting is pervasive in most computer systems—packets wait to be routed by a router, threads wait to be scheduled on a CPU, disk requests wait to be served by the disk subsystem, and so on. Queueing theory is used in to analyze the expected performance of all such systems. At design time, it is used to determine the optimal level of resources to provision. During operation, queueing theory is used to predict the performance expected of the system and to provide quality‐of‐service guarantees to the users of the system. Consequently, queueing theory is an indispensable tool for computer system designers and analysts. This article provides an introduction to queueing theory, key concepts, a summary of key results, and a discussion of current research issues in this area.
Relational Databases
Authors: Laurent Dominique
Published: December 2007

Database management systems (DBMSs) aim to provide users with an efficient tool for good modeling and for easy and efficient manipulation of data. The first DBMSs were based on a hierarchical and then network‐like conceptual data organization, which actually reflects the physical organization of the underlying files. These systems, although efficient, have some important drawbacks.

The relational model, proposed by Codd in 1970, avoids these drawbacks by distinguishing explicitly between the physical and the conceptual levels of data organization. This basic property of the relational model is a consequence of the fact that, in this model, users see the data as tables. The tables of a relational database are accessed and manipulated as a whole, contrary to languages based on hierarchical or network models, according to which data are manipulated on a record‐by‐record basis. As a consequence, data manipulation languages for relational databases are set‐oriented, and so, they fall into the category of declarative languages. On the other hand, because relations are a well‐known mathematical concept, the relational model stimulated a lot of theoretical research that led to successful implementations.

In this article, we focus on the theory of the relational model and on basic aspects of dependency theory. Then, we address problems related to updates and transaction management, and we briefly describe the structure of relational systems and the associated reference language called SQL. We conclude with a brief discussion on extensions of the relational model.
Software Architecture
Authors: Garlan David
Published: December 2007

As the size and complexity of software systems increase, the design, specification, and analysis of overall system structure becomes a critical issue. Structural issues include the organization of a system as a composition of components; global control structures, the protocols for communication, synchronization, and data access; the assignment of functionality to design elements; the composition of design elements; physical distribution; scaling and performance, and dimensions of evolution. This is the
software architecture
level of design.
CoXML: Cooperative XML Query Answering?
Authors: Chu Wesley W. , Liu Shaorong
Published: December 2007

The heterogeneity nature of XML data creates the need for approximate query answering. Approximate answers may be derived by relaxing query conditions to less restricted forms, i.e.,query relaxation. In this article, we first present an approach to XML query relaxation based on schema conversion, which leverages on the value relaxation techniques in the relational model. This approach, however, does not support structure relaxation. Also, information may be lost during schema conversion. To remedy these shortcomings, we then present a cooperative XML (CoXML) system provides user‐specific approximate query answers directly in the XML model. The key features of the system include:

a query language that allows users to specify approximate query conditions and relaxation control requirements;

a relaxation index structure, XTAH, that enables the system to provide user‐desired relaxations as specified in the queries; and

a ranking model that incorporates both content and structure similarities in evaluating the relevancy of approximate answers.

We also present a scalable and extensible architecture for the CoXML system based on mediators. Finally, we evaluate the system using the INEX test collections. The evaluation results demonstrate the effectiveness of the system in providing user‐specific relaxation.