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Full-Text Articles in Engineering

Test 1996b: New Holland T7070, Nebraska Tractor Test Lab Jan 2011

Test 1996b: New Holland T7070, Nebraska Tractor Test Lab

Nebraska Tractor Tests

ABOUT THE TEST REPORT AND USE OF THE DATA The test data contained in this report are a tabulation of the results of a series of tests. Due to the restricted format of these pages, only a limited amount of data and not all of the tractor specifications are included. The full OECD report contains usually about 30 pages of data and specifications. The test data were obtained for each tractor under similar conditions and therefore, provide a means of comparison of performance based on a limited set of reported data. EXPLANATION OF THE TEST PROCEDURES Purpose The purpose of …

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Test 1999a: John Deere 8335rt My12, Nebraska Tractor Test Lab Jan 2011

Test 1999a: John Deere 8335rt My12, Nebraska Tractor Test Lab

Nebraska Tractor Tests

ABOUT THE TEST REPORT AND USE OF THE DATA The test data contained in this report are a tabulation of the results of a series of tests. Due to the restricted format of these pages, only a limited amount of data and not all of the tractor specifications are included. The full OECD report contains usually about 30 pages of data and specifications. The test data were obtained for each tractor under similar conditions and therefore, provide a means of comparison of performance based on a limited set of reported data. EXPLANATION OF THE TEST PROCEDURES Purpose The purpose of …

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Goodput Maximization In Cooperative Networks With Arq, Qing Chen, M. Cenk Gursoy Jan 2011

Goodput Maximization In Cooperative Networks With Arq, Qing Chen, M. Cenk Gursoy

Department of Electrical and Computer Engineering: Faculty Publications

In this paper, the average successful throughput, i.e., goodput, of a coded 3-node cooperative network is studied in a Rayleigh fading environment. It is assumed that a simple automatic repeat request (ARQ) technique is employed in the network so that erroneously received packets are retransmitted until successful delivery. The relay is assumed to operate in either amplify-and-forward (AF) or decode-and-forward (DF) mode. Under these assumptions, retransmission mechanisms and protocols are described, and the average time required to send information successfully is determined. Subsequently, the goodput for both AF and DF relaying is formulated. The tradeoffs and interactions between the …

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Improving Safety And Mobility At High-Speed Intersections With Innovations In Sensor Technology, Anuj Sharma, Darcy M. Bullock, Senem Velipasalar, Mauricio Casares, Jacob Schmitz, Nathaniel P. Burnett Jan 2011

Improving Safety And Mobility At High-Speed Intersections With Innovations In Sensor Technology, Anuj Sharma, Darcy M. Bullock, Senem Velipasalar, Mauricio Casares, Jacob Schmitz, Nathaniel P. Burnett

Department of Civil and Environmental Engineering: Faculty Publications

A series of innovations has been made in the vehicle sensors field. Technologies such as IntelliDrive and radar-based smart sensors make it pos­sible to track each vehicle in proximity to an intersection. However, current technologies have limitations, such as lack of robustness, accuracy, or level of penetration. This paper assumes an accurate wide-area detector (WAD), which might be soon available, and highlights the potential benefits that might be derived in safety and efficiency of oper­ations at high-speed intersections from the deployment of the WAD. Two critical areas in which wide-area detection can lead to significant improvements are discussed: (a) location …

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Analysis Of Turbulent Hydraulic Jump Over A Transitional Rough Bed Of A Rectangular Channel: Universal Relations, Noor Afzal, A. Bushra, Abu Seena Jan 2011

Analysis Of Turbulent Hydraulic Jump Over A Transitional Rough Bed Of A Rectangular Channel: Universal Relations, Noor Afzal, A. Bushra, Abu Seena

Department of Civil and Environmental Engineering: Faculty Publications

The streamwise flow structure of a turbulent hydraulic jump over a rough bed rectangular channel has been investigated. The flow is divided into inner and outer layers, where upstream supercritical flow changes to downstream subcritical flow. The analysis is based on depth averaged Reynolds momentum equations. The molecular viscosity on the rough bed imposes the no slip boundary condition, but close to the wall the turbulent process in inner layer provides certain matching conditions with the outer layer, where molecular viscosity has no dominant role. It is shown that the bed roughness in the inner layer has a passive role …

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On The Performance Limits Of Cognitive Mimo Channels, Sami Akin, M. Cenk Gursoy Jan 2011

On The Performance Limits Of Cognitive Mimo Channels, Sami Akin, M. Cenk Gursoy

Department of Electrical and Computer Engineering: Faculty Publications

In this paper, throughput of cognitive multiple-input multiple-output (MIMO) systems operating under quality-of service (QoS) constraints is studied. It is assumed that transmission power and the covariance of the input signal vector are varied depending on the sensed activities of primary users in the system. Considering the reliability of the transmission and channel sensing results, a state-transition model is provided. Effective capacity is determined, and expressions for the first and second derivatives of the effective capacity are obtained at SNR = 0. The minimum bit energy requirements in the presence of QoS limitations are identified. Numerical results are provided.

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Energy-Efficient Feedback Tracking On Embedded Smart Cameras By Hardware-Level Optimization, Mauricio Casares, Senem Velipasalar, Paolo Santinelli, Rita Cucchiara, Reggio Emilia, Andrea Prati Jan 2011

Energy-Efficient Feedback Tracking On Embedded Smart Cameras By Hardware-Level Optimization, Mauricio Casares, Senem Velipasalar, Paolo Santinelli, Rita Cucchiara, Reggio Emilia, Andrea Prati

Department of Electrical and Computer Engineering: Faculty Publications

Embedded systems have limited processing power, memory and energy. When camera sensors are added to an embedded system, the problem of limited resources becomes even more pronounced. In this paper, we introduce two methodologies to increase the energy-efficiency and battery-life of an embedded smart camera by hardware-level operations when performing object detection and tracking. The CITRIC platform is employed as our embedded smart camera. First, down-sampling is performed at hardware level on the micro-controller of the image sensor rather than performing software-level down-sampling at the main microprocessor of the camera board. In addition, instead of performing object detection and tracking …

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Risk-Based Failure Mode And Effect Analysis For Wind Turbines (Rb-Fmea), Salman Kahrobaee, Sohrab Asgarpoor Jan 2011

Risk-Based Failure Mode And Effect Analysis For Wind Turbines (Rb-Fmea), Salman Kahrobaee, Sohrab Asgarpoor

Department of Electrical and Computer Engineering: Faculty Publications

Failure Mode and Effect Analysis (FMEA) has already been used as a qualitative measure for identifying failure modes and causes, in order to mitigate the effects of failure in different sectors of power systems. This paper presents a quantitative approach called Risk-Based-FMEA, based on the failure probabilities and incurred failure costs instead of rating scales. As a case study, this approach has been applied to a direct drive wind turbine. The results show that the definition of failure modes priorities based on their contribution to the total failure cost of the wind turbine is more realistic and practical than the …

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Series-Connected Self-Reconfigurable Multicell Battery, Taesic Kim, Wei Qiao, Liyan Qu Jan 2011

Series-Connected Self-Reconfigurable Multicell Battery, Taesic Kim, Wei Qiao, Liyan Qu

Department of Electrical and Computer Engineering: Faculty Publications

This paper proposes a novel series-connected, self-reconfigurable, multi-cell battery design. A new cell switching circuit topology is proposed and implemented by using high efficiency semiconductor devices for dynamic configuration of the multi-cell battery. Each cell in the battery only uses two switches to fully control its operation independently. The proposed design can maximally utilize the battery’s capacity and is tolerant to failures of single or multiple cells. These prolong the operating time and lifespan and enhance the reliability of the battery system. By using the proposed design, additional monitoring, control, protection and optimization functions can be readily added to each …

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A Dual-Network Testbed For Wireless Sensor Applications, Jedrzej Kowalczuk, Mehmet C. Vuran, Lance C. Pérez Jan 2011

A Dual-Network Testbed For Wireless Sensor Applications, Jedrzej Kowalczuk, Mehmet C. Vuran, Lance C. Pérez

Department of Electrical and Computer Engineering: Faculty Publications

A dual-network Cyber-physical Networking (CPN) testbed developed at the University of Nebraska-Lincoln is described. The CPN testbed consists of two geographically disparate wireless sensor networks connected by a traditional TCP/IP network and enables peer-to-peer communication between each sensor in the network. The functionality of the testbed is enhanced by a range of software tools that support remote programming and network monitoring, and real-time visualization of sensor data. The resulting architecture supports easy deployment and evaluation of applications for both traditional and interconnected wireless sensor networks. To demonstrate the features of this testbed, a novel ping application was developed and deployed …

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Analysis Of The Accuracy-Latency-Energy Tradeoff For Wireless Embedded Camera Networks, Alvaro Pinto, Zhe Zhang, Xin Dong, Senem Velipasalar, Mehmet C. Vuran, M. Cenk Gursoy Jan 2011

Analysis Of The Accuracy-Latency-Energy Tradeoff For Wireless Embedded Camera Networks, Alvaro Pinto, Zhe Zhang, Xin Dong, Senem Velipasalar, Mehmet C. Vuran, M. Cenk Gursoy

Department of Electrical and Computer Engineering: Faculty Publications

Wireless embedded smart cameras provide flexibility in camera deployment in terms of the locations and number of the cameras. However, these battery-powered embedded vision sensors have very limited energy, memory, and processing power. Energy consumption and latency are two major concerns in wireless embedded camera networks. In multi-camera tracking applications, the amount of data exchanged between cameras has an effect on the tracking accuracy, the energy consumption of the camera nodes and the latency. In this paper, we provide a detailed quantitative analysis of the accuracy-latency-energy tradeoff for overlapping and non-overlapping camera setups when different-sized data packets are transferred in …

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Channel Coding Over Multiple Coherence Blocks With Queueing Constraints, Deli Qiao, M. Cenk Gursoy, Senem Velipasalar Jan 2011

Channel Coding Over Multiple Coherence Blocks With Queueing Constraints, Deli Qiao, M. Cenk Gursoy, Senem Velipasalar

Department of Electrical and Computer Engineering: Faculty Publications

This paper investigates the performance of wireless systems that employ finite-blocklength channel codes for transmission and operate under queueing constraints in the form of limitations on buffer overflow probabilities. A block fading model, in which fading stays constant in each coherence block and change independently between blocks, is considered. It is assumed that channel coding is performed over multiple coherence blocks. An approximate lower bound on the transmission rate is obtained from Feintein’s Lemma. This lower bound is considered as the service rate and is incorporated into the effective capacity formulation, which characterizes the maximum constant arrival rate that can …

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On The Effective Capacity Of Two-Hop Communication Systems, Deli Qiao, M. Cenk Gursoy, Senem Velipasalar Jan 2011

On The Effective Capacity Of Two-Hop Communication Systems, Deli Qiao, M. Cenk Gursoy, Senem Velipasalar

Department of Electrical and Computer Engineering: Faculty Publications

In this paper, two-hop communication between a source and a destination with the aid of an intermediate relay node is considered. Both the source and intermediate relay node are assumed to operate under statistical quality of service (QoS) constraints imposed as limitations on the buffer overflow probabilities. It is further assumed that the nodes send the information at fixed power levels and have perfect channel side information. In this scenario, the maximum constant arrival rates that can be supported by this two-hop link are characterized by finding the effective capacity. Through this analysis, the impact upon the throughput of having …

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Support Vector Machine-Based Short-Term Wind Power Forecasting, Jianwu Zeng, Wei Qiao Jan 2011

Support Vector Machine-Based Short-Term Wind Power Forecasting, Jianwu Zeng, Wei Qiao

Department of Electrical and Computer Engineering: Faculty Publications

This paper proposes a support vector machine (SVM)-based statistical model for wind power forecasting (WPF). Instead of predicting wind power directly, the proposed model first predicts the wind speed, which is then used to predict the wind power by using the power-wind speed characteristics of the wind turbine generators. Simulation studies are carried out to validate the proposed model for very short-term and short term WPF by using the data obtained from the National Renewable Energy Laboratory (NREL). Results show that the proposed model is accurate for very short-term and short-term WPF and outperforms the persistence model as well as …

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An Achievable Rate Region For Imperfectly-Known Two-Way Relay Fading Channels, Junwei Zhang, M. Cenk Gursoy Jan 2011

An Achievable Rate Region For Imperfectly-Known Two-Way Relay Fading Channels, Junwei Zhang, M. Cenk Gursoy

Department of Electrical and Computer Engineering: Faculty Publications

In this paper, achievable rates and resource allocation strategies for imperfectly known two-way relay fading channels are studied. Decode-and-forward (DF) relaying is considered. It is assumed that communication starts with the network training phase in which the users and the relay estimate the fading coefficients, albeit imperfectly. Subsequently, data transmission is performed in multiple-access and broadcast phases. In both phases, achievable rate regions are identified by treating the terms that arise due to channel estimation errors and imperfect interference cancellation as Gaussian distributed noise components. The achievable rate region of the two-way relay channel is given by the intersection of …

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Energy-Efficient Foreground Object Detection On Embedded Smart Cameras By Hardware-Level Operations, Mauricio Casares, Paolo Santinelli, Senem Velipasalar, Andrea Prati, Rita Cucchiara Jan 2011

Energy-Efficient Foreground Object Detection On Embedded Smart Cameras By Hardware-Level Operations, Mauricio Casares, Paolo Santinelli, Senem Velipasalar, Andrea Prati, Rita Cucchiara

Department of Electrical and Computer Engineering: Faculty Publications

Embedded smart cameras have limited processing power, memory and energy. In this paper, we introduce two methodologies to increase the energy-efficiency and the battery-life of an embedded smart camera by hardware level operations when performing foreground object detection. We use the CITRIC platform as our embedded smart camera. We first perform down-sampling at hardware level on the micro-controller of the image sensor rather than performing software-level down-sampling at the main microprocessor of the camera board. In addition, we crop an image frame at hardware level by using the HREF and VSYNC signals at the micro-controller of the image sensor to …

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On The Interplay Between Channel Sensing And Estimation In Cognitive Radio Systems, M. Cenk Gursoy, Sinan Gezici Sinan Gezici Jan 2011

On The Interplay Between Channel Sensing And Estimation In Cognitive Radio Systems, M. Cenk Gursoy, Sinan Gezici Sinan Gezici

Department of Electrical and Computer Engineering: Faculty Publications

Cognitive radio transmissions in the presence of channel uncertainty are considered. In practical scenarios, cognitive secondary users need to perform both channel sensing in order to identify whether the channel is being occupied by the primary users or not, and also channel estimation in order to learn the channel fading coefficients. Generally, errors occur in both channel sensing and estimation, and this leads to a coupling between the two. More specifically, imperfect sensing affects both the structure and the performance of channel estimation schemes. With this motivation, the interactions between channel sensing and estimation are studied in this paper. In …

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Location Cheating: A Security Challenge To Location-Based Social Network Services, Wenbo He, Xue Liu, Mai Ren Jan 2011

Location Cheating: A Security Challenge To Location-Based Social Network Services, Wenbo He, Xue Liu, Mai Ren

Department of Electrical and Computer Engineering: Faculty Publications

Location-based mobile social network services such as foursquare and Gowalla have grown exponentially over the past several years. These location-based services utilize the geographical position to enrich user experiences in a variety of contexts, including location-based searching and location-based mobile advertising. To attract more users, the location-based mobile social network services provide real-world rewards to the user, when a user checks in at a certain venue or location. This gives incentives for users to cheat on their locations. In this paper, we investigate the threat of location cheating attacks, find the root cause of the vulnerability, and outline the possible …

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A Current-Sensorless Mppt Quasi-Double-Boost Converter For Pv Systems, Christopher J. Lohmeier, Jianwu Zeng, Wei Qiao, Liyan Qu, Jerry L. Hudgins Jan 2011

A Current-Sensorless Mppt Quasi-Double-Boost Converter For Pv Systems, Christopher J. Lohmeier, Jianwu Zeng, Wei Qiao, Liyan Qu, Jerry L. Hudgins

Department of Electrical and Computer Engineering: Faculty Publications

This paper proposes a current-sensorless maximum power point tracking (MPPT) quasi-double-boost converter for photovoltaic (PV) systems. Instead of using sensors, the output current of the PV system is obtained from the measured voltage ripple in the input capacitor of the DC-DC converter. The estimated current is used by a hill-climbing (HC) MPPT algorithm to determine the optimal duty ratio for controlling the DC-DC converter. The operating principle, theoretical analysis, and design guidelines of the quasi-double-boost converter are provided in the paper. Simulation studies are carried out in MATLAB Simulink by using real solar radiation data obtained from the National Renewable …

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Effective Capacity Region And Optimal Power Control For Fading Broadcast Channels, Deli Qiao, M. Cenk Gursoy, Senem Velipasalar Jan 2011

Effective Capacity Region And Optimal Power Control For Fading Broadcast Channels, Deli Qiao, M. Cenk Gursoy, Senem Velipasalar

Department of Electrical and Computer Engineering: Faculty Publications

Transmission over fading broadcast channels in the presence of quality of service (QoS) constraints is studied. Effective capacity, which provides the maximum constant arrival rate that a given service process can support while satisfying statistical QoS constraints, is employed as the performance metric. The effective capacity region achieved with superposition coding and successive interference cancellation is identified and is shown to be convex. Subsequently, optimal power control policies that achieve the boundary points of the effective capacity region are investigated, and an algorithm for the numerical computation of the optimal power adaptation schemes for the two-user case is provided. Additionally, …

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A Hybrid Battery Model Capable Of Capturing Dynamic Circuit Characteristics And Nonlinear Capacity Effects, Taesic Kim, Wei Qiao Jan 2011

A Hybrid Battery Model Capable Of Capturing Dynamic Circuit Characteristics And Nonlinear Capacity Effects, Taesic Kim, Wei Qiao

Department of Electrical and Computer Engineering: Faculty Publications

A high-fidelity battery model capable of accurately predicting battery performance is required for proper design and operation of battery-powered systems. However, the existing battery models have at least one of the following drawbacks: 1) requiring intensive computation due to high complexity; 2) not applicable for electrical circuit design and simulation; and 3) not capable of accurately capturing the state of charge (SOC) and predicting run time of the battery due to neglecting the nonlinear capacity effects. This paper proposes a novel hybrid battery model, which takes the advantages of an electrical circuit battery model to accurately predicting the dynamic circuit …

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Wide-Area Multi-Object Tracking With Non-Overlapping Camera Views, Youlu Wang, Senem Velipasalar, M. Cenk Gursoy Jan 2011

Wide-Area Multi-Object Tracking With Non-Overlapping Camera Views, Youlu Wang, Senem Velipasalar, M. Cenk Gursoy

Department of Electrical and Computer Engineering: Faculty Publications

We present a system for wide-area multi-object tracking across disjoint camera views. We employ a probabilistic Petri Net-based approach to account for the uncertainties of the vision algorithms (such as unreliable background subtraction, and tracking failure) and to incorporate the available domain knowledge. We combine appearance features of objects as well as the travel-time evidence for target matching and consistent labeling across disjoint camera views. 3D color histogram, Histogram of Oriented Gradients, object size and aspect ratio are used as the appearance features. The distribution of the travel time is modeled by a Gaussian Mixture Model. By incorporating the domain …

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Bearing Fault Detection For Direct-Drive Wind Turbines Via Stator Current Spectrum Analysis, Xiang Gong, Wei Qiao Jan 2011

Bearing Fault Detection For Direct-Drive Wind Turbines Via Stator Current Spectrum Analysis, Xiang Gong, Wei Qiao

Department of Electrical and Computer Engineering: Faculty Publications

Bearing faults constitute a significant portion of all faults in wind turbine generators (WTGs). Current-based bearing fault detection has significant advantages over traditional vibration-based methods in terms of cost, implementation, and system reliability. This paper proposes a method based on stator current power spectral density (PSD) analysis for bearing fault detection of direct-drive WTGs. In the proposed method, appropriate interpolation/up-sampling and down-sampling algorithms are designed to convert the variable fundamental frequency of the stator current to a fixed frequency according to the estimated fundamental speed of the WTG. Consequently, the characteristic frequencies of bearing faults can be clearly identified form …

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Non-Binary Joint Network-Channel Decoding Of Correlated Sensor Data In Wireless Sensor Networks, Arindra Guha, Eric T. Psota, Lance C. Pérez Jan 2011

Non-Binary Joint Network-Channel Decoding Of Correlated Sensor Data In Wireless Sensor Networks, Arindra Guha, Eric T. Psota, Lance C. Pérez

Department of Electrical and Computer Engineering: Faculty Publications

The performance of non-binary joint network channel decoding (NB-JNCD) is examined in wireless sensor networks with correlated sensors. The operating assumption is that systems containing multiple sensors in close proximity obtain correlated measurements. It is shown that, when the correlation model between sensors is known at the sink, the addition of a correlation based decoder within the decoding framework greatly improves the error rate performance. Simulation results also indicate that the proposed correlation-based decoder is comparable to source coding across the correlated sensors in terms of error rate, while eliminating the need for costly sensor-to-sensor communication.

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A Novel Sol-Gel Route To Pinhole-Free Iron Sulfide Thin Films, S. Kment, H. Kmentova, A. Sarkar, Rodney J. Soukup, Natale J. Ianno, J. Krysa, Z. Hubicka, J. Olejnicek, C. L. Exstrom, S. A. Darveau Jan 2011

A Novel Sol-Gel Route To Pinhole-Free Iron Sulfide Thin Films, S. Kment, H. Kmentova, A. Sarkar, Rodney J. Soukup, Natale J. Ianno, J. Krysa, Z. Hubicka, J. Olejnicek, C. L. Exstrom, S. A. Darveau

Department of Electrical and Computer Engineering: Faculty Publications

The general purpose of the study is to fabricate and improve upon FeS2 thin films which can be used as the photon absorber layer for a heterojunction or homojunction solar cell. This work deals with the preparation of the pyrite by an unconventional sol-gel approach. Thin pyrite films were prepared by sulfurizing the iron oxide films previously deposited through the sol-gel method using iron (III) chloride as a precursor. The structural, morphological, electronic and optical properties of the deposited films were determined using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy, Auger electron spectroscopy (AES), UV-Vis absorption spectroscopy, Hall …

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Computational Intelligence For Control Of Wind Turbine Generators, Wei Qiao, Jiaqi Liang, Ganesh K. Venayagamoorthy, Ronald Harley Jan 2011

Computational Intelligence For Control Of Wind Turbine Generators, Wei Qiao, Jiaqi Liang, Ganesh K. Venayagamoorthy, Ronald Harley

Department of Electrical and Computer Engineering: Faculty Publications

This paper summarizes past and ongoing research in the area of the application of computational intelligence (CI) for control of wind turbine generators (WTGs). Several intelligent design approaches and control strategies, including optimal design of WTG controllers using particle swarm optimization (PSO) and mean-variance optimization (MVO) algorithms and adaptive critic design-based coordinated optimal adaptive control for wind plants and shunt FACTS devices, are presented for dynamic performance and fault ride-through enhancement of WTGs and the associated power grid. The effectiveness of these intelligent design approaches and control strategies are demonstrated by nonreal- and real-time simulations in PSCAD/EMTDC and RSCAD/RTDS, respectively.

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Wind/Solar Hybrid Generation-Based Roadway Microgrids, Wei Qiao, Anuj Sharma, Jerry L. Hudgins, Elizabeth G. Jones, Laurence Rilett Jan 2011

Wind/Solar Hybrid Generation-Based Roadway Microgrids, Wei Qiao, Anuj Sharma, Jerry L. Hudgins, Elizabeth G. Jones, Laurence Rilett

Department of Electrical and Computer Engineering: Faculty Publications

This paper presents the concept and design of a novel roadway microgrid. It operates as a smart microgrid that optimally utilizes the public right-of-way and roadway infrastructure to provide cost-effective, highly efficient, and reliable wind/solar electric power production, distribution, storage, and utilization. The fundamental unit of the microgrid is called the energy-plus roadway/traffic signal light (EPRTL), which contains a grid-connected wind/solar hybrid generation system installed on the pole of a roadway/traffic signal light for clean electric power production. The term “energy-plus” stands for annual energy consumption that is less than production. The generated electric power will be consumed locally by …

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Secure Relay Beamforming Over Cognitive Radio Channels, Junwei Zhang, Mustafa Cenk Gursoy Jan 2011

Secure Relay Beamforming Over Cognitive Radio Channels, Junwei Zhang, Mustafa Cenk Gursoy

Department of Electrical and Computer Engineering: Faculty Publications

In this paper, a cognitive relay channel is considered, and amplify-and-forward (AF) relay beam forming designs in the presence of an eavesdropper and a primary user are studied. Our objective is to optimize the performance of the cognitive relay beamforming system while limiting the interference in the direction of the primary receiver and keeping the transmitted signal secret from the eavesdropper. We show that under both total and individual power constraints, the problem becomes a quasiconvex optimization problem which can be solved by interior point methods. We also propose two sub-optimal null space beamforming schemes which are obtained in a …

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A Third-Order Sliding-Mode Controller For Dcmc Converters With Constant Power Loads, Yue Zhao, Wei Qiao Jan 2011

A Third-Order Sliding-Mode Controller For Dcmc Converters With Constant Power Loads, Yue Zhao, Wei Qiao

Department of Electrical and Computer Engineering: Faculty Publications

Incorporating a medium-voltage DC (MVDC) integrated power system is a goal for future surface combatants and submarines. In a MVDC shipboard power system, DCIDC converters are commonly employed to supply constant power to electric loads. These constant-power loads have a characteristic of negative incremental impedance, which may cause system instability during disturbances if the system is not properly controlled. This paper proposes a third-order sliding-mode controller (SMC) for DCIDC buck converters with constant power loads. The SMC is able to stabilize the DC power systems over the entire operating range in the presence of significant variations in the load power …

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Formation Of Graphene Sheets Through Laser Exfoliation Of Highly Ordered Pyrolytic Graphite, Min Qian, Yun-Shen Zhou, Yang Gao, Jong Bok Park, Tao Feng, Su Mei Huang, Zhuo Sun, Lan Jiang, Yongfeng Lu Jan 2011

Formation Of Graphene Sheets Through Laser Exfoliation Of Highly Ordered Pyrolytic Graphite, Min Qian, Yun-Shen Zhou, Yang Gao, Jong Bok Park, Tao Feng, Su Mei Huang, Zhuo Sun, Lan Jiang, Yongfeng Lu

Department of Electrical and Computer Engineering: Faculty Publications

Freestanding two-dimensional (2D) few-layer graphene was formed through laser exfoliation of highly ordered pyrolytic graphite, using a pulsed neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. Graphene sheets of several nanometers in thickness and micrometers in size were obtained. The laser exfoliation process was investigated at different laser fluences and distances between target and substrate. Three different phases, amorphous carbon, few-layer graphene sheets, and thin graphite films, were obtained as the laser fluence increased. This study reveals an existing route of forming freestanding 2D nanostructures through laser exfoliation.

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