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2012

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Articles 11731 - 11760 of 12196

Full-Text Articles in Physical Sciences and Mathematics

A Novel Approach For Optimal Allocation Of Distributed Generations Based On Static Voltage Stability Margin, Mohsen Rezaie Estabragh, Mohsen Mohammadian, Mehdi Shafiee Jan 2012

A Novel Approach For Optimal Allocation Of Distributed Generations Based On Static Voltage Stability Margin, Mohsen Rezaie Estabragh, Mohsen Mohammadian, Mehdi Shafiee

Turkish Journal of Electrical Engineering and Computer Sciences

This paper presents a newly developed approach to find the optimal location of distributed generations (DGs) to improve power system voltage stability margin and reduce losses incorporating the constraints. The loadability limit index is used to assess the static voltage stability security margin, which is associated with the point of voltage collapse limit. Based on this, a toolbox is developed to recognize the loadability margin in power networks. Finally, the mentioned problem is modeled as a nonlinear and multiobjective optimization problem. The proposed method establishes a tradeoff between the security index and power losses in DG placement using the hybrid …

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Application Of The Posicast Control Method To Static Shunt Compensators, Amir Ghorbani, Siamak Masoudi, Arash Shabani Jan 2012

Application Of The Posicast Control Method To Static Shunt Compensators, Amir Ghorbani, Siamak Masoudi, Arash Shabani

Turkish Journal of Electrical Engineering and Computer Sciences

In this paper, the Posicast control method is used for decreasing the reactive power oscillations of static shunt compensators. Shunt compensators such as the static synchronous compensator (STATCOM) and static VAR compensator (SVC) are considered to be FACTS devices. The applied control method decreases the amount of oscillations in the outputs of STATCOM and SVC considerably, with fast damping. In this paper, a PI controller is added to the model to decrease the sensitivity of the Posicast controller to the parameter variations and plant model mismatch. Simplicity and applicability are the main features of this controller. The model is simulated …

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Optimal Design Of Upfc-Based Damping Controller Using Imperialist Competitive Algorithm, Ali Ajami, Reza Gholizadeh Jan 2012

Optimal Design Of Upfc-Based Damping Controller Using Imperialist Competitive Algorithm, Ali Ajami, Reza Gholizadeh

Turkish Journal of Electrical Engineering and Computer Sciences

In this paper, the optimal design of supplementary controller parameters of a unified power flow controller (UPFC) to damp low-frequency oscillations in a weakly connected system is investigated. The individual design of the UPFC controller, using the imperialist competitive algorithm (ICA) technique over a wide range of operating conditions, is discussed. The effectiveness and validity of the proposed controller on damping low-frequency oscillations is tested through a time-domain simulation and eigenvalue analysis under 4 loading conditions and a large disturbance. The simulation results, carried out using MATLAB/Simulink software, reveal that the tuned ICA-based UPFC controller has an excellent capability of …

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Fractional Pid Controllers Tuned By Evolutionary Algorithms For Robot Trajectory Control, Zafer Bi̇ngül, Oğuzhan Karahan Jan 2012

Fractional Pid Controllers Tuned By Evolutionary Algorithms For Robot Trajectory Control, Zafer Bi̇ngül, Oğuzhan Karahan

Turkish Journal of Electrical Engineering and Computer Sciences

The aim of this paper is to compare the performances of a fractional order proportional integral derivative (FOPID) controller tuned with evolutionary algorithms for robot trajectory control. In order to make this comparison, a 2-degrees-of-freedom planar robot was controlled by a FOPID controller tuned with particle swarm optimization (PSO) and a real coded genetic algorithm (GA). In order to see the effects of the cost functions on the optimum parameters of the FOPID controller, 3 different cost functions were used: the root mean squared error (MRSE), mean absolute error (MAE), and mean minimum fuel and absolute error (MMFAE). In order …

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Identification Of Linear Dynamic Systems Using The Artificial Bee Colony Algorithm, Özden Erçi̇n, Ramazan Çoban Jan 2012

Identification Of Linear Dynamic Systems Using The Artificial Bee Colony Algorithm, Özden Erçi̇n, Ramazan Çoban

Turkish Journal of Electrical Engineering and Computer Sciences

This paper presents an investigation into the development of system identification using the artificial bee colony (ABC) algorithm. A system identification task can be formulated as an optimization problem where the objective is to obtain a model and a set of parameters that minimize the prediction error between the measured plant outputs and the model outputs. The most common existing system identification approaches, such as the recursive least squares method and autoregressive exogenous method, are substantially analytical and based on a mathematical derivation of the system's model. Evolutionary computation, which seems to be a very promising approach, is an alternative …

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An Implementation Of Modified Scatter Search Algorithm To Transmission Expansion Planning, Majid Zeinaddini Maymand, Masoud Rashidinejad, Hamid Khorasani, Mohsen Rahmani, Amin Mahmoudabadi Jan 2012

An Implementation Of Modified Scatter Search Algorithm To Transmission Expansion Planning, Majid Zeinaddini Maymand, Masoud Rashidinejad, Hamid Khorasani, Mohsen Rahmani, Amin Mahmoudabadi

Turkish Journal of Electrical Engineering and Computer Sciences

Transmission network expansion planning (TNEP) is one of the most important tasks in the field of power systems, especially in deregulated power system environments. TNEP is a nonlinear mixed integer programming problem that can be solved via hybrid heuristic algorithms. This paper presents a modified scatter search algorithm (MSSA) to reinforce the ordinary scatter search algorithm (SSA) to be equipped for handling large scale transmission expansion planning (TEP) problems. The proposed methodology is based on the SSA, incorporating some improved strategies so as to decrease the number of linear programming problems required to be solved iteratively. In this study, it …

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Analysis And Characterization Of Longitudinal Flux Single-Sided Linear Switched Reluctance Machines, Lenin Chokkalingam, Arumugam Rengasamy Jan 2012

Analysis And Characterization Of Longitudinal Flux Single-Sided Linear Switched Reluctance Machines, Lenin Chokkalingam, Arumugam Rengasamy

Turkish Journal of Electrical Engineering and Computer Sciences

Linear switched reluctance motors (LSRMs) have recently gained more popularity for propulsion drives. This paper contributes a certain design improvement to reduce the force ripple in LSRMs. By affixing a pole cap in the stator pole, the target is achieved. Finite element analysis has been carried out to predict the performance of the basic and proposed structures. Motor performances for different load conditions are simulated. The application of fast Fourier transform has been utilized to envisage the vibration frequencies. The experimental results are well correlated with the predicted results.

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Analysis, Nonlinear Control, And Chaos Generator Circuit Of Another Strange Chaotic System, İhsan Pehli̇van, Zhouchao Wei Jan 2012

Analysis, Nonlinear Control, And Chaos Generator Circuit Of Another Strange Chaotic System, İhsan Pehli̇van, Zhouchao Wei

Turkish Journal of Electrical Engineering and Computer Sciences

In this paper, we introduce a new 3-dimensional quadratic continuous autonomous chaotic system. This system can generate strange and interesting attractors. Some basic dynamical properties, such as bifurcations, and chaotic behaviors of the new chaotic system are investigated analytically and numerically. We propose a nonlinear control scheme to discuss codimension 1 and 2 Hopf bifurcations. In addition, a new circuit implementation of the chaotic attractor is reported and examined in PSpice. The new system is suitable for purposefully generating chaos in chaos-based engineering applications.

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A Neural-Based Electromagnetic Inverse Scattering Approach To The Detection Of A Conducting Cylinder Coated With A Dielectric Material, Senem Makal, Ahmet Kizilay Jan 2012

A Neural-Based Electromagnetic Inverse Scattering Approach To The Detection Of A Conducting Cylinder Coated With A Dielectric Material, Senem Makal, Ahmet Kizilay

Turkish Journal of Electrical Engineering and Computer Sciences

In this study, a radial basis function neural network approach is applied for the estimation of the localization and the radius of a conducting cylinder with a circular cross-section coated with a dielectric material. A set of features, the radar cross-section (RCS) values, are derived from scattered fields, which are calculated using the surface equivalence principle and the method of moment. RCS values are obtained using 10 different scattering angles that are fed into the network. The outputs of the network are the location (x_0, y_0) and the radius (r_p) of the conducting cylinder. This is an application of the …

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Resolution Enhancement Of Video Sequences By Using Discrete Wavelet Transform And Illumination Compensation, Sara Izadpanahi, Çağri Özçinar, Gholamreza Anbarjafari, Hasan Demirel Jan 2012

Resolution Enhancement Of Video Sequences By Using Discrete Wavelet Transform And Illumination Compensation, Sara Izadpanahi, Çağri Özçinar, Gholamreza Anbarjafari, Hasan Demirel

Turkish Journal of Electrical Engineering and Computer Sciences

This research paper proposes a new technique for video resolution enhancement that employees an illumination compensation procedure before the registration process. After the illumination compensation process, the respective frames are registered using the Irani and Peleg technique. In parallel, the corresponding frame is decomposed into high-frequency (low-high, high-low, and high-high) and low-frequency (low-low) subbands using discrete wavelet transform (DWT). The high-frequency subbands are superresolved using bicubic interpolation. Afterwards, the interpolated high-frequency subbands and superresolved low-frequency subband obtained by registration are used to construct the high-resolution frame using inverse DWT. The superiority of the proposed resolution enhancement method over well-known video …

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Model Selection And Score Normalization For Text-Dependent Single Utterance Speaker Verification, Osman Büyük, Mustafa Levent Arslan Jan 2012

Model Selection And Score Normalization For Text-Dependent Single Utterance Speaker Verification, Osman Büyük, Mustafa Levent Arslan

Turkish Journal of Electrical Engineering and Computer Sciences

In this paper, we investigate model selection and channel variability issues on a text-dependent single utterance (TDSU) speaker verification application. Due to the lack of an appropriate database for the task, a multichannel speaker recognition database, which consists of multiple recordings of a single Turkish utterance, is collected. The first set of experiments is devoted to model selection. Phonetic hidden Markov model (HMM)-based, sentence HMM-based, and Gaussian mixture model (GMM)-based methods are compared to find the most appropriate modeling approach for the target application. Based on the experimental results, the HMM-based methods outperform the GMM. The sentence HMM yields the …

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Using A Game-Based Learning Model As A New Teaching Strategy For Computer Engineering, Kristijan Kuk, Dragica Jovanovic, Dusan Jokanovic, Petar Spalevic, Marko Caric, Stefan Panic Jan 2012

Using A Game-Based Learning Model As A New Teaching Strategy For Computer Engineering, Kristijan Kuk, Dragica Jovanovic, Dusan Jokanovic, Petar Spalevic, Marko Caric, Stefan Panic

Turkish Journal of Electrical Engineering and Computer Sciences

Interactive multimedia simulations and computer game elements can be successfully combined in order to create new advanced educational resources for teaching today's generation of students. Such a learning environment, a game-based learning model (GBLm), has been designed as a research prototype. This paper describes one type of GBLm for computer engineering, which we have used in the subject of computer graphics for the teaching unit Z-buffer algorithm, in order to facilitate the learning process. The implementation of a GBLm for graphical algorithms (GBL4CAl) is presented in detail as a multimedia interactive learning module designed to motivate students by making learning …

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Symbolic Regression Of Crop Pest Forecasting Using Genetic Programming, Basim Alhadidi, Alaa Alafeef, Heba Al-Hiari Jan 2012

Symbolic Regression Of Crop Pest Forecasting Using Genetic Programming, Basim Alhadidi, Alaa Alafeef, Heba Al-Hiari

Turkish Journal of Electrical Engineering and Computer Sciences

In this paper, we propose and evaluate a mathematical model that describes the reported data on crop pests to get an accurate prediction of production costs, food safety, and the protection of the environment. Meteorological factors are not the only things that affect a bumper harvest; it is also affected by crop plant diseases and insect pests. Studies show that relying solely on the naked-eye observations of experts to forecast well-planned agriculture is not always sufficient to achieve effective control. Providing fast, automatic, cheap, and accurate artificial intelligence-based solutions for that task can be of great realistic significance. The proposed …

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Adaptive Optimization Of Edca Parameters For Improved Qos In Multi-Media Applications, Alparslan Çi̇l, Mehmet Akar, Emi̇n Anarim Jan 2012

Adaptive Optimization Of Edca Parameters For Improved Qos In Multi-Media Applications, Alparslan Çi̇l, Mehmet Akar, Emi̇n Anarim

Turkish Journal of Electrical Engineering and Computer Sciences

IEEE 802.11e Enhanced Distributed Channel Access (EDCA) has been incorporated into the standard as an effective medium access mechanism in order to provide the desired QoS for multimedia applications such as VoIP and IPTV. This paper presents an adaptive optimization algorithm in EDCA which strives to provide improved QoS from both delay and throughput perspectives. As a first step towards this goal, a Markov model of the EDCA mechanism has been introduced, which is subsequently used to compute the estimates of throughput and delay. Based on the analytical model that is validated via real-time simulations in OPNET, a new algorithm …

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Hybrid Mpi+Upc Parallel Programming Paradigm On An Smp Cluster, Zeki̇ Bozkuş Jan 2012

Hybrid Mpi+Upc Parallel Programming Paradigm On An Smp Cluster, Zeki̇ Bozkuş

Turkish Journal of Electrical Engineering and Computer Sciences

The symmetric multiprocessing (SMP) cluster system, which consists of shared memory nodes with several multicore central processing units connected to a high-speed network to form a distributed memory system, is the most widely available hardware architecture for the high-performance computing community. Today, the Message Passing Interface (MPI) is the most widely used parallel programming paradigm for SMP clusters, in which the MPI provides programming both for an SMP node and among nodes simultaneously. However, Unified Parallel C (UPC) is an emerging alternative that supports the partitioned global address space model that can be again employed within and across the nodes …

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Robust Distributed Scheduling Via Time Period Aggregation, Shih-Fen Cheng, John Tajan, Hoong Chuin Lau Jan 2012

Robust Distributed Scheduling Via Time Period Aggregation, Shih-Fen Cheng, John Tajan, Hoong Chuin Lau

Research Collection School Of Computing and Information Systems

In this paper, we evaluate whether the robustness of a market mechanism that allocates complementary resources could be improved through the aggregation of time periods in which resources are consumed. In particular, we study a multi-round combinatorial auction that is built on a general equilibrium framework. We adopt the general equilibrium framework and the particular combinatorial auction design from the literature, and we investigate the benefits and the limitation of time-period aggregation when demand-side uncertainties are introduced. By using simulation experiments on a real-life resource allocation problem from a container port, we show that, under stochastic conditions, the performance variation …

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Evaluating The Use Of A Mobile Annotation System For Geography Education, Dion Hoe-Lian Goh, Khasfariyati Razikin, Chei Sian Lee, Ee Peng Lim, Kalyani Chatterjea, Chew-Hung Chang Jan 2012

Evaluating The Use Of A Mobile Annotation System For Geography Education, Dion Hoe-Lian Goh, Khasfariyati Razikin, Chei Sian Lee, Ee Peng Lim, Kalyani Chatterjea, Chew-Hung Chang

Research Collection School Of Computing and Information Systems

Mobile devices used in educational settings are usually employed within a collaborative learning activity in which learning takes place in the form of social interactions between team members while performing a shared task. The authors aim to introduce MobiTOP (Mobile Tagging of Objects and People), a mobile annotation system that allows users to contribute and share geospatial multimedia annotations via mobile devices. Field observations and interviews were conducted. A group of trainee teachers involved in a geography field study were instructed to identify rock formations by collaborating with each other using the MobiTOP system. The trainee teachers who were in …

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Who Is Retweeting The Tweeters? Modeling, Originating, And Promoting Behaviors In The Twitter Network, Achananuparp Palakorn, Ee Peng Lim, Jing Jiang, Tuan Anh Hoang Jan 2012

Who Is Retweeting The Tweeters? Modeling, Originating, And Promoting Behaviors In The Twitter Network, Achananuparp Palakorn, Ee Peng Lim, Jing Jiang, Tuan Anh Hoang

Research Collection School Of Computing and Information Systems

Real-time microblogging systems such as Twitter offer users an easy and lightweight means to exchange information. Instead of writing formal and lengthy messages, microbloggers prefer to frequently broadcast several short messages to be read by other users. Only when messages are interesting, are they propagated further by the readers. In this article, we examine user behavior relevant to information propagation through microblogging. We specifically use retweeting activities among Twitter users to define and model originating and promoting behavior. We propose a basic model for measuring the two behaviors, a mutual dependency model, which considers the mutual relationships between the two …

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A New Efficient Optimistic Fair Exchange Protocol Without Random Oracles, Qiong Huang, Guomin Yang, Duncan S. Wong, Willy Susilo Jan 2012

A New Efficient Optimistic Fair Exchange Protocol Without Random Oracles, Qiong Huang, Guomin Yang, Duncan S. Wong, Willy Susilo

Research Collection School Of Computing and Information Systems

Optimistic fair exchange (OFE) is a kind of protocols to solve the problem of fair exchange between two parties. Most of the previous work on this topic are provably secure in the random oracle model. In this work, we propose a new construction of OFE from another cryptographic primitive, called time capsule signature. The construction is efficient and brings almost no overhead other than the primitive itself. The security of our new construction is based on that of the underlying primitive without relying on the random oracle heuristic. Applying our generic construction to the time capsule signature scheme recently proposed …

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An Improved K-Nearest-Neighbor Algorithm For Text Categorization, Shengyi Jiang, Guansong Pang, Meiling Wu, Limin Kuang Jan 2012

An Improved K-Nearest-Neighbor Algorithm For Text Categorization, Shengyi Jiang, Guansong Pang, Meiling Wu, Limin Kuang

Research Collection School Of Computing and Information Systems

Text categorization is a significant tool to manage and organize the surging text data. Many text categorization algorithms have been explored in previous literatures, such as KNN, Naive Bayes and Support Vector Machine. KNN text categorization is an effective but less efficient classification method. In this paper, we propose an improved KNN algorithm for text categorization, which builds the classification model by combining constrained one pass clustering algorithm and KNN text categorization. Empirical results on three benchmark corpora show that our algorithm can reduce the text similarity computation substantially and outperform the-state-of-the-art KNN, Naive Bayes and Support Vector Machine classifiers. …

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Topic Based Query Suggestions For Video Search, Kong-Wah Wan, Ah-Hwee Tan, Joo-Hwee Lim, Liang-Tien Chia Jan 2012

Topic Based Query Suggestions For Video Search, Kong-Wah Wan, Ah-Hwee Tan, Joo-Hwee Lim, Liang-Tien Chia

Research Collection School Of Computing and Information Systems

Query suggestion is an assistive technology mechanism commonly used in search engines to enable a user to formulate their search queries by predicting or completing the next few query words that the user is likely to type. In most implementations, the suggestions are mined from query log and use some simple measure of query similarity such as query frequency or lexicographical matching. In this paper, we propose an alternative method of presenting query suggestions by their thematic topics. Our method adopts a document-centric approach to mine topics in the corpus, and does not require the availability of a query log. …

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A Hybridized Lagrangian Relaxation And Simulated Annealing Method For The Course Timetabling Problem, Aldy Gunawan, Kim Leng Poh Jan 2012

A Hybridized Lagrangian Relaxation And Simulated Annealing Method For The Course Timetabling Problem, Aldy Gunawan, Kim Leng Poh

Research Collection School Of Computing and Information Systems

This paper describes a timetabling problem at universities, where a master course timetable is given extrinsically and conflicts due to students' course enrollment do not need to be considered. A solver for the problem, which integrates both teacher assignment and course scheduling, is described. An initial solution is obtained by a mathematical programming approach based on Lagrangian relaxation. This solution is further improved by a simulated annealing algorithm. The proposed method has been tested on instances from a university in Indonesia, as well as on several randomly generated datasets, and the corresponding computational results are reported.

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A Sentiment Analysis Of Singapore Presidential Election 2011 Using Twitter Data With Census Correction, Murphy Junyu Choy, Michelle Lee Fong Cheong, Nang Laik Ma, Ping Shung Koo Jan 2012

A Sentiment Analysis Of Singapore Presidential Election 2011 Using Twitter Data With Census Correction, Murphy Junyu Choy, Michelle Lee Fong Cheong, Nang Laik Ma, Ping Shung Koo

Research Collection School Of Computing and Information Systems

Sentiment analysis is a new area in text analytics where it focuses on the analysis and understanding of the human emotions from the text patterns. This new form of analysis has been widely adopted in customer relationship management especially in the context of complaint management. However, sentiment analysis using Twitter data has remained extremely difficult to manage due to sampling biasness. In this paper, we will discuss about the application of reweighting techniques in conjunction with online sentiment divisions to predict the vote percentage that individual presidential candidate in Singapore will receive in the Presidential Election 2011. There will be …

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In Situ And Ex Situ Studies Of Molybdenum Thin Films Deposited By Rf And Dc Magnetron Sputtering As A Back Contact For Cigs Solar Cells, K. P. Aryal, H. Khatri, R. W. Collins, S. Marsillac Jan 2012

In Situ And Ex Situ Studies Of Molybdenum Thin Films Deposited By Rf And Dc Magnetron Sputtering As A Back Contact For Cigs Solar Cells, K. P. Aryal, H. Khatri, R. W. Collins, S. Marsillac

Electrical & Computer Engineering Faculty Publications

Molybdenum thin films were deposited by rf and dc magnetron sputtering and their properties analyzed with regards to their potential application as a back contact for CIGS solar cells. It is shown that both types of films tend to transition from tensile to compressive strain when the deposition pressure increases, while the conductivity and the grain size decreas. The nucleation of the films characterized by in situ and real time spectroscopic ellipsometry shows that both films follow a Volmer-Weber growth, with a higher surface roughness and lower deposition rate for the rf deposited films. The electronic relaxation time was then …

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Growth Analysis Of (Ag,Cu)Inse2 Thin Films Via Real Time Spectroscopic Ellipsometry, S. A. Little, V. Ranjan, R. W. Collins, S. Marsillac Jan 2012

Growth Analysis Of (Ag,Cu)Inse2 Thin Films Via Real Time Spectroscopic Ellipsometry, S. A. Little, V. Ranjan, R. W. Collins, S. Marsillac

Electrical & Computer Engineering Faculty Publications

In situ and ex situ characterization methods have been applied to investigate the properties of (Ag,Cu)InSe2 (ACIS) thin films. Data acquired from real time spectroscopic ellipsometry (RTSE) experiments were analyzed to extract the evolution of the nucleating, bulk, and surface roughness layer thicknesses. The evolution of these layer thicknesses suggests a transition from Volmer-Weber to Stranski-Krastanov type behavior when Cu is replaced by Ag. The complex dielectric functions of ACIS at both deposition and room temperature as a function of film composition were also extracted from the RTSE data, enabling parameterization of the alloy optical properties.

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High Resolution Determination Of Nanomolar Concentrations Of Dissolved Reactive Phosphate In Ocean Surface Waters Using Long Path Liquid Waveguide Capillary Cells (Lwcc) And Spectrometric Detection, Louise A. Zimmer, Gregory A. Cutter Jan 2012

High Resolution Determination Of Nanomolar Concentrations Of Dissolved Reactive Phosphate In Ocean Surface Waters Using Long Path Liquid Waveguide Capillary Cells (Lwcc) And Spectrometric Detection, Louise A. Zimmer, Gregory A. Cutter

OES Faculty Publications

In the last decade, long path length, low volume, liquid waveguide capillary cells (LWCC) in conjunction with conventional nutrient auto-analyzers have been applied to determinations of nanomolar levels of phosphate, nitrate, and nitrite in oligotrophic waters. This article reports a high resolution, real-time, continuous method for nanomolar dissolved reactive phosphate measurements in ocean surface waters with data logging every 30 seconds for up to 16 consecutive hours. Surface seawater is pumped continuously from a shipboard underway tow-fish unit to a helium gas-segmented, continuous-flow, nutrient auto-analyzer modified with a 250 cm LWCC. To circumvent baseline instability due to reagents, a parallel …

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Rapid And Noncontaminating Sampling System For Trace Elements In Global Ocean Surveys, Gregory A. Cutter, Kenneth W. Bruland Jan 2012

Rapid And Noncontaminating Sampling System For Trace Elements In Global Ocean Surveys, Gregory A. Cutter, Kenneth W. Bruland

OES Faculty Publications

A system for the rapid and noncontaminating sampling of trace elements with volumes of up to 36 L per depth and including the dissolved and particulate phases has been developed for ocean sections that are a crucial part of programs such as International GEOTRACES. The system uses commercially available components, including an aluminum Seabird Carousel with all titanium pressure housings for electronics and sensors to eliminate zinc sacrificial anodes and holding twenty-four 12 L GO-FLO bottles, and a 7500 m, 14 mm Vectran conducting cable (passing over an A-frame with nonmetallic sheave) spooled onto a traction winch. The GO-FLO bottles …

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Controls On Dissolved Cobalt In Surface Waters Of The Sargasso Sea: Comparisons With Iron And Aluminum, R. U. Shelley, Peter N. Sedwick, T. S. Bibby, P. Cabedo-Sanz, T. M. Church, R. J. Johnson, A. I. Macey, C. M. Marsay, E. R. Sholkovitz, S. J. Ussher, P. J. Worsfold, M. C. Lohan Jan 2012

Controls On Dissolved Cobalt In Surface Waters Of The Sargasso Sea: Comparisons With Iron And Aluminum, R. U. Shelley, Peter N. Sedwick, T. S. Bibby, P. Cabedo-Sanz, T. M. Church, R. J. Johnson, A. I. Macey, C. M. Marsay, E. R. Sholkovitz, S. J. Ussher, P. J. Worsfold, M. C. Lohan

OES Faculty Publications

Dissolved cobalt (dCo), iron (dFe) and aluminum (dAl) were determined in water column samples along a meridional transect (∼31°N to 24°N) south of Bermuda in June 2008. A general north-to-south increase in surface concentrations of dFe (0.3-1.6 nM) and dAl (14-42 nM) was observed, suggesting that aerosol deposition is a significant source of dFe and dAl, whereas no clear trend was observed. for near-surface dCo concentrations. Shipboard aerosol samples indicate fractional solubility values of 8-100% for aerosol Co, which are significantly higher than corresponding estimates of the solubility of aerosol Fe (0.44-45%). Hydrographic observations and analysis of time series rain …

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The Role Of Larval Dispersal In Metapopulation Gene Flow: Local Population Dynamics Matter, Daphne M. Munroe, John M. Klinck, Eileen E. Hofmann, Eric N. Powell Jan 2012

The Role Of Larval Dispersal In Metapopulation Gene Flow: Local Population Dynamics Matter, Daphne M. Munroe, John M. Klinck, Eileen E. Hofmann, Eric N. Powell

OES Faculty Publications

The degree of genetic connectivity among populations in a metapopulation has direct consequences for species evolution, development of disease resistance, and capacity of a metapopulation to adapt to climate change. This study used a metapopulation model that integrates population dynamics, dispersal, and genetics within an individual-based model framework to examine the mechanisms and dynamics of genetic connectivity within a metapopulation. The model was parameterized to simulate four populations of oysters (Crassostrea virginica) from Delaware Bay on the mid-Atlantic coast of the United States. Differences among the four populations include a strong spatial gradient in mortality, a spatial gradient …

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An Introduction To Ecology Of Infectious Diseases - Oysters And Estuaries, Eileen E. Hofmann, Susan E. Ford Jan 2012

An Introduction To Ecology Of Infectious Diseases - Oysters And Estuaries, Eileen E. Hofmann, Susan E. Ford

OES Faculty Publications

Infectious diseases are recognized as an important factor regulating marine ecosystems (Harvell et al., 1999, 2002, 2004; Porter et al., 2001; McCallum et al., 2004; Ward and Lafferty, 2004; Stewart et al., 2008; Bienfang et al., 2011). Many of the organisms affected by marine diseases have important ecological roles in estuarine and coastal environments and some are also commercially important. Outbreaks of infectious diseases in these environments, referred to as epizootics, can produce significant population declines and extinctions, both of which threaten biodiversity, food web interactions, and ecosystem productivity (Harvell et al., 2002, 2004).

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