bluuebunny/crossref_metadata_2025 huggingface dataset:
Profile Changes and Self-sputtering during Low Energy Ion Implantation.
Authors: Vandervorst W. , Janssens T. , Brijs B. , Lindsay R. , Collart E. J. H. , Kirkwood David A. , Mathot G. , Terwagne G.
Published: February 2013

Continued device scaling requires the formation of ever-shallower junctions with low resistance. A desirable option to form these junctions is still the use of conventional ion implantation. However in order to meet the junction depth/sheet resistance goals, a strong reduction in implant energy and increase in implant dose is required. Earlier work for B and BF2-implants, has suggested that during low energy ion implantation self-sputtering may become an important factor influencing/limiting the retained dose. The basic mechanism for the selfsputtering with increasing dose is the increasing dopant concentration at the surface leading to an increased probability for re-emission by the sputtering process. Simple models describing ion retention in combination with sputtering are based on this concept and indeed predict a selfsputtering process limiting the final retained dose. Unfortunately the theoretical calculations only predict a significant sputtering at doses >51016 at/cm2 whereas experimental results already show a limit in retained dose at 5 1015at/cm2.

In order to confirm the experimental data, low energy B, BF2, As and Sb implants have been made. Dose retention was monitored using nuclear reaction analysis and RBS whereby details of the dopant profile (redistribution) were studied using high resolution SIMS. For As and Sb no self-sputtering up to a dose of 1 1016at/cm2 can be found. For B a small dose loss (<10%) is seen significantly below the literature data. For BF2 a 20 % dose loss is observed. None of the SIMS profiles provide sufficient evidence for enhanced B-surface migration as required to explain the enhanced self-sputtering. On the other hand such a surface migration is reminiscent of the observations in SIMS whereby also an enhanced mobility of B during ion irradiation is required to explain the anomalous B-surface peak in many SIMS profiles. Based on the SIMS profiles a component sputter yield for B can be derived which is significantly higher than the matrix sputter yield suggesting a weak bonding of the segregated species leading to a reduced surface binding energy and thus enhanced sputtering yield.
Use of Multi-Objective Algorithms in History Matching of a Real Field
Authors: Christie Mike , Eydinov Dmitry , Demyanov Vasily , Talbot Jack , Arnold Dan , Shelkov Vassili
Published: February 2013

Conventionally, automated history matching methods operated on a single number (the misfit or match quality) which is obtained by summing the least square misfits for all the quantities of interest in a history match. Multi-objective history matching allows the algorithm to be guided by (usually groups of) match quality components, with the overall history match probability determined by summing the components at the end. This feature encourages diversity in the history match, as the algorithm can trade off matches in one area against good fits elsewhere, and has also been shown to speed up history matching in some cases.

This paper describes a comparison of single and multi-objective history matching of a medium-sized field in Western Siberia with nearly 100 wells and over 10 years of history. We compared the performance of both single and multi objective versions of Particle Swarm Optimization. We also assess the effectiveness of various different choices of history match parameters chosen based on reservoir engineering knowledge. Using these techniques, we are able to obtain a high-quality group level match with a relatively low number of simulation runs.

The paper also describes trade-offs between the parallelism of the history matching process and that of the simulator on a 12 core windows workstation. This is an important trade-off as the extreme choices of using of all the cores by the simulator or limiting each simulation to a single core and using each core for a separate history matching run may not be optimal.
Solver Preconditioning Using the Combinatorial Multilevel Method
Authors: Wang Yuhe , Killough John E.
Published: February 2013

The purpose of this paper is to report the first preliminary study of the recently introduced Combinatorial Multilevel (CML) method for solver preconditioning in large-scale reservoir simulation with coupled geomechanics. The CML method is a variant of the popular Algebraic Multigrid (AMG) method yet with essential differences. The basic idea of this new approach is to construct a hierarchy of matrices by viewing the underlying matrix as a graph and by using the discrete geometry of the graph such as graph separators and expansion. In this way, the CML method combines the merits of both geometric and algebraic multigrid methods. The resulting hybrid approach not only provides a simpler and faster set-up phase compared to AMG, but the method can be proved to exhibit strong convergence guarantees for arbitrary symmetric diagonally-dominant matrices. In addition, the underlying theoretical soundness of the CML method contrasts to the heuristic AMG approach, which often can show slow convergence for difficult problems.

This new approach is implemented in a reservoir simulator for both pressure and displacement preconditioners in the multi-stage preconditioning technique. We present results based on several known benchmark problems and provide a comparison of performance and complexity with the widespread preconditioning schemes used in large-scale reservoir simulation. An adaptation of CML for unsymmetric matrices is shown to exhibit excellent convergence properties for realistic cases.
Automatic Well Control and Decision Support in a massive parallel Simulation Environment
Authors: Wiegand Klaus D. , Beckner Bret L.
Published: February 2013

ExxonMobil’s proprietary reservoir simulator, EMpower, includes a programmable decision support system for manipulating well rates and wellhead pressures during simulation runs. The so-called well management component allows users to write algorithms that monitor simulation progress and steer the depletion process according to simulation objectives and constraints at well, platform, reservoir, and field levels. A built-in nonlinear optimization package can be used to determine well allocation under a set of constraints, including pressure and rate limits in the surface facility network. The strength of the system is its flexibility, which is limited only by the amount of programming a user is able and willing to do. Drawbacks of the system are its complexity, reliance on user expertise, and the requirement to write programs.

The move towards massively parallel computing platforms, such as clusters with thousands of nodes, poses a major challenge to the well management environment as we know it. Its inherently sequential programming model, which is geared towards simulation users rather than software developers, cannot take advantage of the massive parallelization that is expected to dominate simulation technology in the next decade, and could be a roadblock for parallel scalability.

In the following, we describe our efforts to adapt the system to a massive parallel simulation environment. At the heart of the transformation lies an approach that parallelizes constraint management and work-overs at the well level, and uses numerical optimization to control material balance, production, and injection for well-groups. After laying out the approach and describing the mathematical derivation of the optimization problem, we provide examples for scalability and parallel efficiency.
New Locally Conservative Numerical Schemes for Hydrogeomechanical Couplings in Strongly Heterogeneous Presalt Reservoirs
Authors: Murad Marcio A. , Luizar-Obregon J. Alexei , Lopes Tuane V. , Garcia Eduardo , Radtke Luiz Carlos , Correa Maicon R. , Borges Marcio R. , de Lima Sidarta A.
Published: February 2013

We construct a new numerical modeling for two-phase immiscible flow in a strongly heterogeneous deformable carbonate underneath a rock salt composed by halite and anhydrite displaying creep behavior with the viscous strain ruled by a nonlinear constitutive law of power-law type. Within the framework of the so-called iteratively coupled methods and fixed-stress split algorithm we develop mixed finite element methods for the flow and geomechanics subsystems which furnish locally conservative Darcy velocity and transient porosity input fields for the transport problem for the water saturation. Such transport equation is decomposed within an operator splitting technique based on a predictor-corrector scheme with the predictor step discretized by a higher-order non-oscillatory finite volume central scheme. Numerical simulations of a water-flooding problem in secondary oil recovery are presented for different realizations of the input random fields (permeability, Young modulus and initial porosity). Comparisons between the accuracies of the proposed approach and the traditional one-way coupled hydro-geomechanical formulation are presented. In addition, simulations including the viscoelastic behavior of the overburden rock salt are performed showing the effects of salt stiffness and irreversible deformation upon finger grow and breakthrough curves. A notable feature of the formulation proposed herein is the accurate prediction of the influence of geomechanical effects upon the unstable movement of the water front, whose evolution is dictated by carbonate heterogeneity, unfavorable viscosity ratio and geomechanical effects without deteriorating the local conservative character of the numerical schemes.
Robust Semi-Implicit Three-Dimensional Upwind Techniques for Reducing Grid Orientation Effect in Thermal Simulations
Authors: Zheng Hongwen , Buchanan Wm. Lloyd
Published: February 2013

In field-scale thermal reservoir simulation, grid orientation is one important factor affecting the accuracy of numerical results. Traditionally thermal reservoir simulators adopt the nine-point method to handle this issue. However, the nine-point method introduces extra bandwidth of the Jacobian Matrix which significantly increases the storage and CPU requirements. Also, that method has limitations which make it difficult to integrate with advanced gridding techniques.

A new three-dimensional upwind technique was developed to reduce grid orientation effect without the disadvantages mentioned above. This new technique adopts a semi-implicit strategy such that no extra matrix bandwidth is added. Numerical results show that the new technique successfully reduces grid orientation effect while using much less CPU than the nine-point method.
Flexible and Efficient N-Porosity, Full-Featured Simulator Design, and Application
Authors: Hinkley R. E. , Wang Q. , Wang K. , Camilleri D. , Fleming G. , Watts J. W.
Published: February 2013

The need for flexible and efficient multi-porosity, reservoir-simulation capabilities has never been greater. Much of the world’s oil reserves are contained in highly variable fractured reservoirs. Moreover, there is now unprecedented interest in the simulation of unconventional gas reservoirs, where up to four porosity types may be required. This paper discusses the design of an N-porosity, full-featured reservoir simulator capable of handling these diverse scenarios. Essential to the design is the programming data-structure paradigm of the SubGrid. SubGrids represent collections of simulation nodes within spatial regions of interest and encapsulate all data and variables required. Any number of associated SubGrids may coexist, representing N-porosities. Inter- and intra-SubGrid connections may be arbitrarily specified. Because the linear solver operates on the associated SubGrids as distinct entities, the design has tremendous flexibility. For example, regions with simple connectivity, such as in dual-porosity, single-permeability models, can have simple pre-solver elimination performed while other regions with uniform intra-porosity connectivity require a merged SubGrid solution. The scheme efficiently treats regions with different numbers of porosities, levels of interconnectivity, and levels of implicitness. Applications may be applied across multiple reservoirs simultaneously. Treatment of missing "fracture" zones has always been an important feature in the dual-porosity, single-permeability simulation. The traditional approach is to treat the matrix within missing fracture zones effectively as though it were an interconnected portion of the fracture porosity. This preserves connectivity within the fracture-free zones and the more computationally efficient single-permeability solver pre-elimination step. A second missing "fracture" scheme is introduced, which differs in the way that the connections between the fracture and matrix blocks are computed at the boundary of fracture-free zones. Flexible transfer-function application and porosity dependency during equilibrium initialization are discussed.
High-Performance Modeling of CO2 Sequestration by Coupling Reservoir Simulation and Molecular Dynamics
Authors: Bao Kai , Yan Mi , Lu Ligang , Allen Rebecca , Salama Amgad , Jordan Kirk E. , Sun Shuyu
Published: February 2013

The present work describes a parallel computational framework for CO2 sequestration simulation by coupling reservoir simulation and molecular dynamics (MD) on massively parallel HPC systems. In this framework, a parallel reservoir simulator, Reservoir Simulation Toolbox (RST), solves the flow and transport equations that describe the subsurface flow behavior, while the molecular dynamics simulations are performed to provide the required physical parameters. Numerous technologies from different fields are employed to make this novel coupled system work efficiently.

One of the major applications of the framework is the modeling of large scale CO2 sequestration for long-term storage in the subsurface geological formations, such as depleted reservoirs and deep saline aquifers, which has been proposed as one of the most attractive and practical solutions to reduce the CO2 emission problem to address the global-warming threat. To effectively solve such problems, fine grids and accurate prediction of the properties of fluid mixtures are essential for accuracy. In this work, the CO2 sequestration is presented as our first example to couple the reservoir simulation and molecular dynamics, while the framework can be extended naturally to the full multiphase multicomponent compositional flow simulation to handle more complicated physical process in the future.

Accuracy and scalability analysis are performed on an IBM BlueGene/P and on an IBM BlueGene/Q, the latest IBM supercomputer. Results show good accuracy of our MD simulations compared with published data, and good scalability are observed with the massively parallel HPC systems. The performance and capacity of the proposed framework are well demonstrated with several experiments with hundreds of millions to a billion cells.

To our best knowledge, the work represents the first attempt to couple the reservoir simulation and molecular simulation for large scale modeling. Due to the complexity of the subsurface systems, fluid thermodynamic properties over a broad range of temperature, pressure and composition under different geological conditions are required, for which the experimental results are limited. Although equations of state can reproduce the existing experimental data within certain ranges of conditions, their extrapolation out of the experimental data range is still limited. The presented framework will definitely provide better flexibility and predictability compared with conventional methods.
Investigation of the Critical Velocity Required for a Gravity Stable Surfactant Flood
Authors: Tavassoli Shayan , Lu Jun , Pope Gary A. , Sepehrnoori Kamy
Published: February 2013

Classical stability theory predicts the critical velocity for a miscible fluid to be stabilized by gravity forces. This theory was tested for surfactant floods with ultra-low interfacial tension and found to be optimistic compared to both laboratory displacement experiments and fine-grid simulations. The inaccurate prediction of instabilities based on available analytical models is due to the complex physics of surfactant floods. First we simulated vertical sandpack experiments to validate the numerical model. Then we performed systematic numerical simulations in two and three dimensions to predict formation of instabilities in surfactant floods and to determine the velocity required to prevent instabilities by taking advantage of buoyancy. The 3D numerical grid was refined until the numerical results converged. A third-order TVD finite-difference method was used for these simulations. We investigated the effects of dispersion, heterogeneity, oil viscosity, relative permeability, microemulsion viscosity. These results indicate that it is possible to design a very efficient surfactant flood without any mobility control if the surfactant solution is injected at a low velocity in horizontal wells at the bottom of the geological zone and the oil captured in horizontal wells at the top of the zone. This approach is practical only if the vertical permeability of the geological zone is high. These experiments and simulations have provided new insight into how a gravity stable low-tension displacement behaves and in particular the importance of the microemulsion phase and its properties, especially its viscosity. Numerical simulations show high oil recovery efficiencies on the order of 60% of water flood residual oil saturation for gravity stable surfactant floods using horizontal wells. Thus under favorable reservoir conditions, gravity stable surfactant floods are very attractive alternatives to surfactant-polymer floods. Some of the world’s largest oil reservoirs are deep, high-temperature, high-permeability, light-oil reservoirs and thus candidates for gravity stable surfactant floods.
Fully Coupled Simulation of Multiple Compositional Reservoirs with a Shared Surface Facility Network
Authors: Fleming Graham , Wong Terry
Published: February 2013

When multiple reservoirs are produced through a common facility network, the capability to integrate the modeling of surface and subsurface can be critical to field development and optimization. The shared facility network imposes constraints that the combined production cannot exceed, determines the pressure drop in the flow lines, and the composition and volume of the sales and reinjection streams. Pressure drop in flow lines is particularly important in deepwater field development, where flow lines are long, and production from multiple reservoirs can flow through the same riser.

The most robust method for solving the combined surface-subsurface system is to fully couple and simultaneously solve the reservoir and facility equations. However, if the reservoirs fluids are represented with compositional equation of state models, and different pseudo-components are used in some or all of the reservoirs, then the reservoir fluid must be delumped into a common set of pseudo-components in the network. In this paper, we describe a method to consistently and efficiently model such a system with a fully coupled surface-subsurface simulator. At every point in the network, where fluid from only a single reservoir is present, the phase behavior calculations can use the fluid characterization for that reservoir and exactly reproduce the result that would have been obtained if the fluid had not been delumped into the network pseudo-components. However, at any point in the network, the characterization of the common network fluid can be used. In addition, if more compositional accuracy is required, the network fluid can be further delumped into more pseudo-components, or if accuracy is not critical, the fluid can be lumped into fewer pseudo-components for more computational efficiency. Examples demonstrating the flexibility, efficiency, and consistency of the method are provided.
Reduced-Order Modeling for Compositional Simulation Using Trajectory Piecewise Linearization
Authors: He Jincong , Durlofsky Louis J.
Published: February 2013

Compositional simulation can be very demanding computationally as a result of the potentially large number of system unknowns and the intrinsic nonlinearity of typical problems. In this work, we develop a reduced-order mod- eling procedure for compositional simulation. The technique combines trajectory piecewise linearization (TPWL) and proper orthogonal decomposition (POD) to provide a highly efficient surrogate model. The compositional POD-TPWL method represents new solutions in terms of linearizations around states generated (and saved) during previously simulated ‘training’ runs. High-dimensional states are projected (optimally) into a low-dimensional subspace using POD. The compositional POD-TPWL model is based on a molar formulation that uses pressure and overall component mole fractions as the primary unknowns. Several new features, including the use of a Petrov-Galerkin projection to reduce the number of equations (rather than the commonly used Galerkin projection), and a new procedure for determining which saved state to use for linearization, are incorporated into the method. Results are presented for heterogeneous three-dimensional reservoir models containing oil and gas phases with up to four hydrocarbon components. Reasonably close agreement between full-order reference solutions and compositional POD-TPWL simulations is demonstrated for the cases considered. Construction of the POD-TPWL model requires preprocessing overhead computations equivalent to about three full-order runs. Runtime speedups using POD-TPWL are, however, very significant – about a factor of 500 for the cases considered. The POD-TPWL model thus appears to be well suited for use in applications such as production optimization or uncertainty assessment, in which many simulations must be performed.
Fast-Marching Methods for Complex Grids and Anisotropic Permeabilities: Application to Unconventional Reservoirs
Authors: Zhang Yanbin , Yang Changdong , King Michael J. , Datta-Gupta Akhil
Published: February 2013

Unconventional reservoirs are characterized by sufficiently low permeabilities so that the pressure depletion from a producing well may not propagate far from the well during the life of a development. This is in contrast to conventional plays where the pressure transients may probe the entire reservoir in weeks to months. The concept of depth of investigation and its application to unconventional reservoirs provide the understanding necessary to describe and optimize the interaction between complex multi-stage fractured wells, reservoir heterogeneity, drainage volumes, pressure depletion, well rates, and the estimated ultimate recovery.

Previous studies have performed unconventional reservoir analysis using more conventional reservoir simulation techniques. High resolution local PEBI grids and global corner point grids have been used to represent complex fracture geometry and conductivity and estimate subsequent well performance. However, these techniques do not provide the more geometric understanding provided by the depth of investigation and drainage volumes.

The application of the depth of investigation to heterogeneous reservoirs can be obtained from an asymptotic expansion of the diffusivity equation leading to the Eikonal equation which describes the propagation of the pressure front. This equation is solved using a Fast Marching Method to calculate a diffusive time of flight at every location within the domain. The diffusive time of flight is directly related to pressure front propagation. Unlike in a reservoir simulator, this frontal propagation is determined in a single non-iterative calculation, which is extremely fast. Once the pressure fronts are determined spatially, we may apply a pseudo-steady state pressure approximation within the moving front to determine pressure depletion and well rates.

In the current study, we extend the Fast Marching Method for solution of the Eikonal equation to complex simulation grids including corner point and unstructured grids. This allows the rapid approximation of reservoir simulation results without the need for flow simulation, and also provides the time-evolution of the well drainage volume for visualization. Understanding the drainage volume alone is useful for well spacing and multi-stage fracture spacing optimization. Additional potential applications include well trajectory and hydraulic fracture location optimization, reservoir model screening and ranking, matrix/fracture parameter estimation, uncertainty analysis and production data integration.
Representing Hydraulic Fractures Using a Multilateral, Multisegment Well in Simulation Models
Authors: Edwards D. A. , Cheng N. , Dombrowsky T. P. , Bowen G. , Nasvik H.
Published: February 2013

Hydraulic fracturing is a stimulation treatment routinely performed on oil and gas wells in low-permeability reservoirs. However, simulating fractured wells is still challenging and impractical using local grid refinement in full-field models with a large number of wells each with multiple fractures.

This paper describes a novel modeling technique by which hydraulic fractures are represented as part of the well model, rather than any form of refinement in the simulation grid. In this approach a planar fracture is modeled by the mesh formed from the interconnected branches of a multilateral, multisegment well. The main advantages are: 1) the fracture mesh is made independent of the simulation grid and thus model building is simpler; 2) fractures can be added and altered at any simulation time; 3) fractures can intersect the reservoir grid lines at any angle; 4) fracture geometry and properties can be fully honored. This technique is designed to model long-term pseudo-steady state fracture flows and uses Darcy flow equations in the lateral well branches that represent the fracture.

The accuracy, stability, and practicality of this new technique have been investigated using a suite of simulation models ranging from a single well in a homogeneous reservoir to a real field sector model with numerous wells, each with multiple fractures. Where possible, the behavior of a reference model—built using traditional grid-refinement techniques—is compared against the multilateral, multisegment well model equivalent. The results of these experiments presented in this paper show a close agreement between the reference gridded fractures and the well model fractures when the system reaches a pseudo-steady state. They also show that the new approach suffers from a lesser degree of numerical instability when modeling extremely thin and highly conductive fractures. Finally, the results confirm the practicality and flexibility of this approach.
Multiscale method for simulating two and three-phase flow in porous media
Authors: Pal Mayur , Lamine Sadok , Lie Knut-Andreas , Krogstad Stein
Published: February 2013

Multiscale methods developed to solve coupled flow equations for reservoir simulation are based on a hierarchical strategy in which the pressure equation is solved on a coarsened grid and transport equation is solved on the fine grid as a decoupled system. The multiscale mixed finite-element (MsMFE) method attempts to capture sub-grid geological heterogeneity directly into the coarse-scale via mathematical basis functions. These basis functions are able to capture important multiscale information and are coupled through a global formulation to provide good approximation of the subsurface flow solution.

In the literature, the general formulation of the MsMFE method for incompressible two-phase and compressible three-phase flow has mainly addressed problems with idealized flow physics. In this paper, we present a new formulation that accounts for compressibility, gravity, and spatially-dependent capillary and relative-permeability effects.

We evaluate the computational efficiency and accuracy of the method by reporting the result of series of representative benchmark tests that have a high degree of realism with respect to flow physics, heterogeneity in petrophysical model, and geometry/topology of the corner-point grids. In particular, the MsMFE method is validated and compared against Shell’s in-house simulator MoReS. The fine-scale flux, pressure, and saturation fields computed by the multiscale simulation show a noteworthy improvement in resolution and accuracy compared with coarse-scale models.
Rapid Updating of Stochastic Models Using an Ensemble Filter Approach
Authors: Tavakoli Reza , Srinivasan Sanjay , Wheeler Mary F.
Published: February 2013

Ensemble Kalman filtering (EnKF) is an effective method for reservoir history matching. The underlying principle is that an initial ensemble of stochastic models can be progressively updated to reflect the measured values as they become available. However, the ensemble Kalman filter updating scheme restricts the method to multivariate Gaussian random fields. Therefore, it is challenging to implement the filtering scheme for non-Gaussian random fields such as reservoirs where there is a strong contrast in permeability between different geological facies. In this paper, we develop a methodology to combine multidimensional scaling and the ensemble Kalman filter for rapidly updating models for a channelized reservoir. A dissimilarity matrix is computed using the dynamic responses of ensemble members. This dissimilarity matrix is transformed to a lower dimensional space using multidimensional scaling. The responses mapped in the lower dimension space are clustered and based on distances between the models in a cluster and the actual observed response, the closest models to the observed response are retrieved. Updating of models within the closest cluster are performed using EnKF equations. The results of the update are used to re-sample new models for the next step. A two dimensional water flooding example of a channelized reservoir is set up to demonstrate the applicability of the proposed method. The obtained results demonstrate that the proposed algorithm is viable for sequentially updating reservoir models and for preserving the channel features after the data assimilation process.
History-Matching Production and Seismic Data in a Real Field Case Using the Ensemble Smoother With Multiple Data Assimilation
Authors: Emerick Alexandre A. , Reynolds Albert C.
Published: February 2013

In a recent paper, we introduced a data assimilation procedure based on the application of the ensemble smoother (ES) with multiple data assimilation (MDA). The method, which has the acronym ES-MDA, was theoretically motivated by the equivalence between single and multiple data assimilation for the linear-Gaussian case and an approximate relationship between ES and one iteration of the Gauss-Newton method. ES-MDA is easy to combine with any commercial simulator, in fact, much easier than it is to couple the ensemble Kalman filter (EnKF) with a commercial simulator. Here, we apply EnKF and ES-MDA to generate multiple realizations of the porosity, net-to-gross ratio (NTG) and permeability fields by history matching production and seismic impedance data (3D and 4D) in a turbidite reservoir in the Campos Basin. 3D seismic data are integrated first and then 4D and production data are assimilated together, either simultaneously with ES-MDA or sequentially in time with EnKF.
Thermal energy from drinking water and cost benefit analysis for an entire city
Authors: Blokker E. J. M. , van Osch A. M. , Hogeveen R. , Mudde C.
Published: February 2013

The municipality of Almere is planning to develop a new carbon neutral neighbourhood. The area is located close to a treated water storage facility. By extracting enough thermal energy to provide 900 homes with energy for space heating and heating tap water, the temperature of the treated water is lowered by 1.16 °C. This could lead to an increase in the energy required to heat water for domestic purposes. The temperature of tap water is influenced by the temperature of the soil surrounding the drinking water distribution system. The rate at which the water temperature will reach the soil temperature depends on the pipe material, the pipe diameter and the flow velocity. With the help of a network model, the effect of a lower initial water temperature on every customer in Almere was determined. On average, all 75,000 connections would receive slightly cooler water. The energy to heat the extra 0.125 °C is equivalent to the energy required to heat approximately 85 homes. As the extracted thermal energy enables heating of 900 homes, the energy balance is very positive.
Occurrence and environmental risk assessment of PAEs in Weihe River near Xi'an City, China
Authors: Guo Xiaofeng , Wang Lei , Wang Xudong , Liu Hanli
Published: February 2013

The occurrence and distribution of phthalate acid esters (PAEs) in surface water of the Weihe River basin (eight mainstream sampling points and 15 tributary sampling points) in the Shaanxi section were investigated during the dry season, level period (spring), wet season and level period (autumn). The PAEs tested for were diethyl phthalate (DEP), di-n-butyl phthalate (DBP), dicyclohexyl phthalate (DCHP) and di-(2-ethylhexyl) phthalate (DEHP). The testing proceeded by millipore filtration, then solid phase extraction and then gas chromatography-mass spectrometry determination for all examined PAEs. The monitoring results indicated that, in terms of seasonal changes, concentration of the PAEs in the mainstream is: Dry season > Level period (spring) > Wet season ≈ Level period (autumn). An environmental risk assessment was then performed on PAE pollution levels of the Weihe River basin. This paper employed a risk assessment methodology to evaluate the potential adverse health effects of the individual PAE compounds according to their carcinogenicities. For DEP, DBP and DEHP, a low Risk Index (all of them were lower than the specified level of 1.0) reveals that small non-carcinogenic risks exist resulting from the presence of trace concentrations in the surface water of the Weihe River basin.
A simple and flexible field-tested device for housing water monitoring sensors at point discharges
Authors: Exner-Kittridge Michael , Niederreiter Richard , Eder Alexander , Zessner Matthias
Published: February 2013

The Water Monitoring Enclosure (WME) provides a simple and flexible housing for many types of sensors for continuous measurements of water parameters (physical, chemical, or biological) and provides the opportunity of representative sampling for external analyses. The WME ensures a minimum internal water level and this ensures that the internal monitoring equipment remains submerged even when there is no flow into the enclosure. The limited diameter of the inflow pipe and water volume in the WME buffers the flow velocity from dramatic changes. The device ensures that the sediment entering the enclosure from the inflow will be conveyed through the enclosure with minimal sediment accumulation. The device is powered purely from natural hydraulic forces, so it requires no power source, and requires little additional maintenance beyond periodic cleaning. If desired, the WME can also measure discharge entering the device through additional modifications. Water samples were taken throughout the year to validate the effectiveness of the WME. The comparisons of the influent water to the water in the WME for all parameters were below the laboratory analysis standard error or below the limit of quantification, indicating that the water in the WME is representative of the influent water.
Performance of plastic- and sponge-based trickling filters treating effluents from an UASB reactor
Authors: Almeida P. G. S. , Marcus A. K. , Rittmann B. E. , Chernicharo C. A. L.
Published: February 2013

The paper compares the performance of two trickling filters (TFs) filled with plastic- or sponge-based packing media treating the effluent from an upflow anaerobic sludge blanket (UASB) reactor. The UASB reactor was operated with an organic loading rate (OLR) of 1.2 kgCOD m−3 d−1, and the OLR applied to the TFs was 0.30–0.65 kgCOD m−3 d−1 (COD: chemical oxygen demand). The sponge-based packing medium (Rotosponge) gave substantially better performance for ammonia, total-N, and organic matter removal. The superior TF-Rotosponge performance for NH4+-N removal (80–95%) can be attributed to its longer biomass and hydraulic retention times (SRT and HRT), as well as enhancements in oxygen mass transfer by dispersion and advection inside the sponges. Nitrogen removals were significant (15 mgN L−1) in TF-Rotosponge when the OLRs were close to 0.75 kgCOD m−3 d−1, due to denitrification that was related to solids hydrolysis in the sponge interstices. For biochemical oxygen demand removal, higher HRT and SRT were especially important because the UASB removed most of the readily biodegradable organic matter. The new configuration of the sponge-based packing medium called Rotosponge can enhance the feasibility of scaling-up the UASB/TF treatment, including when retrofitting is necessary.
Adsorption of methylene blue and methyl red dyes from aqueous solutions onto modified zeolites
Authors: Ioannou Z. , Karasavvidis Ch. , Dimirkou A. , Antoniadis V.
Published: February 2013

Zeolite, hematite, modified zeolite and commercial activated charcoal were examined for their ability to remove methylene blue (MB) and methyl red (MR) from their aqueous solutions. Modified zeolite and hematite were produced according to the Schwertmann and Cornell method while zeolite and commercial activated charcoal were obtained from S&B and Fluka AG companies, respectively. Adsorption experiments were conducted at three different adsorbent-to-solution ratios, namely 8, 16 and 24 g/L under environmental conditions and continuous stirring. Equilibrium isotherms of MB and MR were studied at different initial concentrations (from 5 × 10−4 to 5 × 10−3 g/L). MB adsorption kinetics were also studied. The maximum adsorption of MB and MR from their aqueous solutions was achieved at 24 g/L (adsorbent-to-dye solution ratio) after 1 h and was equal to 100% (MB) on modified zeolite and 99% (MR) on commercial activated charcoal, respectively. All the other materials achieved intermediate values of dye adsorption. From the applied kinetic models, the pseudo-second-order equation best described the adsorption of MB and MR. Consequently, modified zeolite showed the highest adsorption capacity for MB, while commercial activated charcoal showed the highest adsorption capacity of MR. The studied adsorbents can be used as filters to remove dyes from wastewaters.
Reductions in greenhouse gas (GHG) generation and energy consumption in wastewater treatment plants
Authors: Yerushalmi L. , Ashrafi O. , Haghighat F.
Published: February 2013

Greenhouse gas (GHG) emission and energy consumption by on-site and off-site sources were estimated in two different wastewater treatment plants that used physical–chemical or biological processes for the removal of contaminants, and an anaerobic digester for sludge treatment. Physical–chemical treatment processes were used in the treatment plant of a locomotive repair factory that processed wastewater at 842 kg chemical oxygen demand per day. Approximately 80% of the total GHG emission was related to fossil fuel consumption for energy production. The emission of GHG was reduced by 14.5% with the recovery of biogas that was generated in the anaerobic digester and its further use as an energy source, replacing fossil fuels. The examined biological treatment system used three alternative process designs for the treatment of effluents from pulp and paper mills that processed wastewater at 2,000 kg biochemical oxygen demand per day. The three designs used aerobic, anaerobic, or hybrid aerobic/anaerobic biological processes for the removal of carbonaceous contaminants, and nitrification/denitrification processes for nitrogen removal. Without the recovery and use of biogas, the aerobic, anaerobic, and hybrid treatment systems generated 3,346, 6,554 and 7,056 kg CO2-equivalent/day, respectively, while the generated GHG was reduced to 3,152, 6,051, and 6,541 kg CO2-equivalent/day with biogas recovery. The recovery and use of biogas was shown to satisfy and exceed the energy needs of the three examined treatment plants. The reduction of operating temperature of the anaerobic digester and anaerobic reactor by 10°C reduced energy demands of the treatment plants by 35.1, 70.6 and 62.9% in the three examined treatment systems, respectively.
Omega 3 fatty acids in psychiatry
Authors: Pavlovic D.M. , Pavlovic Aleksandra , Lackovic Maja
Published: February 2013

Omega-3 long-chain polyunsaturated fatty acids (?-3 LC-PUFAs) are thought to
be important for normal dopaminergic, glutamatergic and serotonergic
neurotransmission. Depression is less prevalent in societies with high fish
consumption, and depressed patients have significantly lower red blood cell
?-3 levels. Studies with ?-3 supplementation have led to controversial
results. A significantly longer remission of bipolar symptomatology has been
confirmed from a high-dose DHA and EPA mixture. Greater seafood consumption
per capita has been connected with a lower prevalence of bipolar spectrum
disorders. Reduced levels of ?-6 and ?-3 PUFAs were found in patients with
schizophrenia.
eNOS Glu298Asp polymorphism is associated with development of complicated plaques in patients from Serbia with advanced carotid atherosclerosis
Authors: Djuric Tamara , Djordjevic Ana , Lukic N. , Andjelevski Magdalena , Zivkovic Maja , Stankovic Aleksandra
Published: February 2013

Nitric oxide inhibits adhesion of thrombocytes, proliferation and migration
of smooth muscle cells and restricts oxidation of atherogenic low-density
lipoproteins. Therefore, decreased production or activity of NO may play a
role in the initiation, progression or complications of atherosclerosis. The
aim of this study was to estimate the effect of Glu298Asp eNOS gene
polymorphism on the individual risk for development of complicated carotid
atherosclerotic plaque in patients from Serbia with advanced carotid
atherosclerosis (CA) who had undergone endarterectomy. The study population
included 233 patients. eNOS G894T gene polymorphism was identified by PCR and
RFLP methods. Multivariate logistic regression analysis showed that Asp298Asp
is an independent risk factor for the presence of complicated plaques in CA
patients. Patients who were homozygous for the Asp298 allele had an adjusted
OR of 4.36 for the development of complicated plaques compared to those that
carry the Glu298 allele. Further validation and replication studies are
needed.
Micromorphology and ultrastructure of trichomes of Libyan Salvia fruticosa Mill.
Authors: Al Sheef , Duletic-Lausevic Sonja , Janosevic Dusica , Budimir Snezana , Marin Marija , Alimpic Ana , Giweli A.A.M. , Marin P.D.
Published: February 2013

Micromorphological and ultrastructural analyses of the leaf trichomes of
Salvia fruticosa Mill. were performed by light and electron microscopy. The
leaves bear numerous non-glandular unbranched trichomes, and peltate,
capitate and digitiform glandular trichomes. Very elongated flagelliform
non-glandular trichomes densely covered the leaf surfaces, with especially
abundance on the leaf margins. Peltate trichomes consist of a basal epidermal
cell, a very short stalk cell and a large round head of eight secretory cells
arranged in a circle. Capitate trichomes can be divided into two main types,
short-stalked and long-stalked, and further into five subtypes according to
the number of stalk cells, morphology and number of glandular head cells.
Digitiform trichomes consist of one basal cell, one or two stalk cells and
one apical secretory cell, which are of similar diameter and approximately
equal length.
Confocal microscopy in the diagnosis of melanoma
Authors: Apostolovic-Stojanovic Milica , Dobrosavljevic-Vukojevic Danijela , Lackovic Vesna , Stojanovic A. , Markovic I. , Dzodic R.
Published: February 2013

Melanoma is the most deadly form of skin cancer of melanocytic origin. The
tumor has a high malignant potential and early metastasis. Prognosis is
directly linked to the stage of the disease. Diagnosing thin melanoma at an
early stage offers patients their best chance for survival. The crucial
innovation in the early recognition of melanoma was the development of in
vivo examination of the skin in high-resolution, by confocal microscopy.
Confocal microscopy and its modifications provides a ?virtual biopsy?, owing
to melanosomes and melanin, which are a source of endogenous contrast.
Confocal scanning laser microscopy (CSLM) provides visualization of
microanatomical structures and cellular detail in real time (pigmented
keratinocytes, melanocytes, melanosomes and melanophages) in the epidermis,
dermoepidermal junction and superficial dermis at a resolution equivalent to
the resolution of conventional microscopes.
Analytical application of the reaction system phenyl fluorone-hydrogen peroxide for the kinetic determination of cobalt and tin traces by spectrophotometry in ammonia buffer media
Authors: Rancic Sofija , Nikolic-Mandic Snezana , Bojic Aleksandar
Published: February 2013

The present paper describes two new, simple, rapid, selective and sensitive
kinetic spectrophotometric methods for Co(II) and Sn(II) determination in
solution at room temperature, based on their effect on phenyl fluorone (PF)
oxidation by hydrogen peroxide in ammonia buffer. The new method was
elaborated for nano amounts of Co(II) determination, based on its catalytic
effect on the oxidation of PF by H2O2 in the presence of citric acid (CA) as
an activator. Also, the new method for micro amounts of Sn(II) determination
was developed based on its inhibitory effect upon the same reaction.
Comparison of the results showed that the activated catalytic reaction has
better sensitivity than the inhibitory one. Methods were validated by the
analyze of chemical substances and results were improved by examining the
same samples by AAS method.
Cardiovascular disease risk factors in patients with non-alcoholic fatty liver disease
Authors: Novakovic Tatjana , Inic-Kostic Biljana , Milinic Srbislava , Jovicevic Ljiljana , Dzeletovic Gordana
Published: February 2013

Introduction. Clinical, epidemiological and biochemical studies strongly
support the concept that the non-alcoholic fatty liver disease is a hepatic
manifestation of the metabolic syndrome. Insulin resistance is a common
factor connecting obesity, diabetes, hypertension and dyslipidemia with fatty
liver and the progression of hepatic disease to steatohepatitis, fibrosis,
cirrhosis and hepatocellular carcinoma. Since identification of
cardiovascular risk factors is the first step in their prevention, the aim of
this study was to analyze the prevalence of some risk factors in patients
with fatty liver. Material and Methods. The study included 130 patients who
met metabolic syndrome criteria; their demographic and anthropometric
characteristics were analyzed and some clinical characteristics were
determined, such as smoking habit, arterial pressure and alcohol intake.
Routine biochemical analyses were carried out by a standard laboratory
procedure. Hepatic steatosis was detected by the abdominal ultrasound.
Modified criteria of the National Cholesterol Education Program Adult
Treatment Panel III were used to describe the metabolic syndrome. Results.
The study group consisted of 72 subjects (55.38%), who had been found by
ultrasound to have fatty liver, whereas the control group included 58
respondents (44.62%) without pathological ultrasound findings. Differences in
the number of fatty liver were highly statistically significant between the
groups. The values of body mass index (33.56?6.05 vs 30.56?4.23 kg/m2; p =
0.001), glucose (6.23?0.95 vs 5.76?0.88 mmol/l; p<0.01) and cholesterol
(6.66?1.30 vs 6.23?0.95; p <0.05) were significantly higher in the patients
with fatty liver than in those without fatty liver. Conclusion. Our results
indicate that the patients from the study group had a high percentage of
cardiovascular risk factors.