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2007

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Articles 3241 - 3270 of 3831

Full-Text Articles in Engineering

Investigation On Miniature Wideband Patch Antenna For Portable Wireless And Cellular Applications, Xiulong Bao, Max Ammann Jan 2007

Investigation On Miniature Wideband Patch Antenna For Portable Wireless And Cellular Applications, Xiulong Bao, Max Ammann

Conference papers

A low-profile miniature antenna with very wide bandwidth is proposed for emerging multimode devices. It comprises a small circular patch antenna loaded by a metallic annular-ring and located on a laminate with a slotted ground plane. The design achieves a very compact low-profile antenna with broadband performance. By optimizing the parameters of the annular-ring patch antenna, very broadband characteristics can be obtained. The measured results show that the antenna achieves a 10 dB return loss from 1.383 GHz to 2.210 GHz, (827 MHz) ie about 47% with respect to the centre frequency 1.796 GHz. The measured results are in good …

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Investigation Of Fast Light In Long Optical Fibers Based On Stimulated Brillouin Scattering, Kai-Uwe Lauterback, Thomas Schneider, Ronny Henker, Marcus Junker, Max Ammann, Andreas Schwarzbacher Jan 2007

Investigation Of Fast Light In Long Optical Fibers Based On Stimulated Brillouin Scattering, Kai-Uwe Lauterback, Thomas Schneider, Ronny Henker, Marcus Junker, Max Ammann, Andreas Schwarzbacher

Conference papers

A simple method to generate a negative time delay in SBS-based fast-light systems using Brillouin gain and loss is shown. We achieved a maximum negative time delay of 32.4 ns in one long fiber segment.

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Investigation On Proximity-Coupled Microstrip Integrated Pv Antenna, Maria Roo Ons, S. Shynu, Max Ammann, Sarah Mccormack, Brian Norton Jan 2007

Investigation On Proximity-Coupled Microstrip Integrated Pv Antenna, Maria Roo Ons, S. Shynu, Max Ammann, Sarah Mccormack, Brian Norton

Conference papers

The use of polycrystalline silicon solar cells (156 times156 mm) as a groundplane for a proximity-coupled microstrip square patch antenna (30 times 30 mm) is investigated. Four different models that arise from the different possible positions of the cell with respect to patch, were simulated, fabricated and compared to an ideal PEC ground plane antenna of the same size. It was found that the use of the solar cell as ground plane is feasible, yielding similar impedance bandwidth (around 4%, 3.5% for the PEC) with reasonable gain. The feasibility of using poly-crystalline solar cells as a ground plane, instead of …

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High Quality Millimeter Wave Generation Via Stimulated Brillouin Scattering, Marcus Junker, Thomas Schneider, Kai-Uwe Lauterbach, Ronny Henker, Max Ammann, Andreas Schwarzbacher Jan 2007

High Quality Millimeter Wave Generation Via Stimulated Brillouin Scattering, Marcus Junker, Thomas Schneider, Kai-Uwe Lauterbach, Ronny Henker, Max Ammann, Andreas Schwarzbacher

Conference papers

A new and simple method for the generation and modulation of Millimeter waves is presented. Based on frequency upconversion via Stimulated Brillouin Scattering, it is very flexible in its output frequency and modulation bandwidth.

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Some Techniques To Improve Small Groundplane Printed Monopole Performance, Max Ammann, Matthias John Jan 2007

Some Techniques To Improve Small Groundplane Printed Monopole Performance, Max Ammann, Matthias John

Conference papers

Printed planar monopole antennas are enjoying considerable popularity and publicity to their low-profile, wide bandwidth, quasi-omnidirectional radiation characteristics and their ease of integratability into devices. The impedance bandwidth and radiation properties of a strip monopole have been shown to be heavily dependent on groundplane size. The groundplane (GP) is of primary importance and when miniaturised, the antenna properties change significantly. Techniques to improve the performance of printed antennas on small groundplanes are presented.

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Slow And Fast-Light In Optical Fibers: An Overview, Ronny Henker, Thomas Schneider, Kai-Uwe Lauterbach, Markus Junker, Max Ammann, Andreas Schwarzbacher Jan 2007

Slow And Fast-Light In Optical Fibers: An Overview, Ronny Henker, Thomas Schneider, Kai-Uwe Lauterbach, Markus Junker, Max Ammann, Andreas Schwarzbacher

Conference papers

Slow- and fast-light is the control of the velocity of light in a medium by light. As a fascinating new field in physics there is a fundamental interest on this effect on the one side, but on the other side there exist a lot of practical applications for telecommunication and information systems. Among these are optical signal processing, the radio frequency-photonics, nonlinear optics and spectroscopy in time domain. Furthermore, the slow- and fast-light effect can be seen as a key technology for optical delay lines, buffers, equalizers and synchronizers in packed switched networks. To realize the effect there are different …

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A Pda Based Recording System To Investgate Heart Rate, Marcos Efren Bolanos Jan 2007

A Pda Based Recording System To Investgate Heart Rate, Marcos Efren Bolanos

Open Access Theses & Dissertations

Diabetes is one of most afflicting diseases in society which is caused by the inability of the body to appropriately use insulin to balance sugar levels. Type 1 diabetics require monitoring of their glucose levels to ensure a normal glucose level is maintained between 90 and 130 mg/dL (milligrams per deciliter). Unfortunately, current methods of monitoring are based on invasive and painful sampling of the blood. It was imperative that noninvasive and painless methods of monitoring glucose should be explored. A proven noninvasive technique utilizing infrared light to detect the fluctuations in the heart rate was used to determine if …

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Using Pareto Fronts To Evaluate Polyp Detection Algorithms For Ct Colonography, Adam Huang, Jiang Li, Ronald M. Summers, Nicholas Petrick, Amy K. Hara Jan 2007

Using Pareto Fronts To Evaluate Polyp Detection Algorithms For Ct Colonography, Adam Huang, Jiang Li, Ronald M. Summers, Nicholas Petrick, Amy K. Hara

Electrical & Computer Engineering Faculty Publications

We evaluate and improve an existing curvature-based region growing algorithm for colonic polyp detection for our CT colonography (CTC) computer-aided detection (CAD) system by using Pareto fronts. The performance of a polyp detection algorithm involves two conflicting objectives, minimizing both false negative (FN) and false positive (FP) detection rates. This problem does not produce a single optimal solution but a set of solutions known as a Pareto front. Any solution in a Pareto front can only outperform other solutions in one of the two competing objectives. Using evolutionary algorithms to find the Pareto fronts for multi-objective optimization problems has been …

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Error Performance Of Double Space Time Transmit Diversity Systems, Jingxian Wu, Y. Rosa Zheng, Ashwin Gumaste, Chengshan Xiao Jan 2007

Error Performance Of Double Space Time Transmit Diversity Systems, Jingxian Wu, Y. Rosa Zheng, Ashwin Gumaste, Chengshan Xiao

Electrical and Computer Engineering Faculty Research & Creative Works

The theoretical error performance of double space time transmit diversity (DSTTD) system with optimum combining receiver is analyzed in this paper. by employing both spatial multiplexing and transmit diversity in one system, DSTTD provides practical tradeoff between system spectral efficiency and diversity gain. We derive exact analytical expressions to describe the symbol error rate for DSTTD systems. The effects of both diversity gain and antenna interference introduced by spatial multiplexing are quantified in the results. In addition, the performance of DSTTD system with successive interference cancellation is also investigated. Simulation results are in excellent agreement with the theoretical results obtained …

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Hybrid Ac/Dc Power Distribution Solution For Future Space Applications, Sushant Barave, Badrul H. Chowdhury Jan 2007

Hybrid Ac/Dc Power Distribution Solution For Future Space Applications, Sushant Barave, Badrul H. Chowdhury

Electrical and Computer Engineering Faculty Research & Creative Works

As NASA readies itself for new space exploration initiatives starting with a human return to the Moon by the year 2020 eventually leading to human exploration of Mars, the requirements for a safe and reliable power system will become important issues. A preliminary study of a proposed hybrid AC/DC distribution system with a power electronic interface is investigated. A Static synchronous Compensator (STATCOM) is considered as the power electronic interface between the AC and the DC portions of the hybrid AC/DC distribution system. The system is modeled in EMTDC/PSCAD and tested for certain operating conditions and contingencies. High reliability and …

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Implementation Of Static And Semi-Static Versions Of A Bit-Wise Pipelined Dual-Rail Ncl 2s Complement Multiplier, R. Sankar, V. Kadiyala, Ravi Bonam, S. Kumar, S. Mohan, F. Kacani, Waleed K. Al-Assadi, Scott C. Smith Jan 2007

Implementation Of Static And Semi-Static Versions Of A Bit-Wise Pipelined Dual-Rail Ncl 2s Complement Multiplier, R. Sankar, V. Kadiyala, Ravi Bonam, S. Kumar, S. Mohan, F. Kacani, Waleed K. Al-Assadi, Scott C. Smith

Electrical and Computer Engineering Faculty Research & Creative Works

This paper focuses on implementing a 2s complement 8x8 dual-rail bit-wise pipelined multiplier using the asynchronous NULL Convention Logic (NCL) paradigm. The design utilizes a Wallace tree for partial product summation, and is implemented and simulated in VHDL, the transistor level, and the physical level, using a 1.8V 0.18,um TSMC CMOS process.The multiplier is realized using both static and semi-static Dualversions of the NCL gates; and these two implementations are compared in terms of area, power, and speed.

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Improvement Of Can Bus Performance By Using Error-Correction Codes, Krishna Chaitanya Emani, Maciej Jan Zawodniok, Y. Rosa Zheng, Jagannathan Sarangapani, Keong W. Kam Jan 2007

Improvement Of Can Bus Performance By Using Error-Correction Codes, Krishna Chaitanya Emani, Maciej Jan Zawodniok, Y. Rosa Zheng, Jagannathan Sarangapani, Keong W. Kam

Electrical and Computer Engineering Faculty Research & Creative Works

In this paper, two variants of the Hybrid Automatic Repeat Request (HARQ) scheme for CAN bus are presented. The basic HARQ uses error-correction code based on the Reed- Solomon (RS) technique and the Cyclic Redundancy Check (CRC) method to detect errors. The second scheme uses the cyclic error-correction method instead of the CRC error-detection method to further improve the throughput. Moreover, the second scheme uses no additional bit overhead when compared with the basic HARQ scheme. This paper presents the performance of the proposed schemes using MATLAB and NS2 simulations. Experimental data of error patterns were used for realistic evaluation. …

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Multiclass Cancer Classification Using Semisupervised Ellipsoid Artmap And Particle Swarm Optimization With Gene Expression Data, Georgios C. Anagnostopoulos, Donald C. Wunsch, Rui Xu Jan 2007

Multiclass Cancer Classification Using Semisupervised Ellipsoid Artmap And Particle Swarm Optimization With Gene Expression Data, Georgios C. Anagnostopoulos, Donald C. Wunsch, Rui Xu

Electrical and Computer Engineering Faculty Research & Creative Works

It is crucial for cancer diagnosis and treatment to accurately identify the site of origin of a tumor. with the emergence and rapid advancement of DNA microarray technologies, constructing gene expression profiles for different cancer types has already become a promising means for cancer classification. In addition to research on binary classification such as normal versus tumor samples, which attracts numerous efforts from a variety of disciplines, the discrimination of multiple tumor types is also important. Meanwhile, the selection of genes which are relevant to a certain cancer type not only improves the performance of the classifiers, but also provides …

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Near Optimal Output-Feedback Control Of Nonlinear Discrete-Time Systems In Nonstrict Feedback Form With Application To Engines, Peter Shih, Brian C. Kaul, Jagannathan Sarangapani, J. A. Drallmeier Jan 2007

Near Optimal Output-Feedback Control Of Nonlinear Discrete-Time Systems In Nonstrict Feedback Form With Application To Engines, Peter Shih, Brian C. Kaul, Jagannathan Sarangapani, J. A. Drallmeier

Electrical and Computer Engineering Faculty Research & Creative Works

A novel reinforcement-learning based output-adaptive neural network (NN) controller, also referred as the adaptive-critic NN controller, is developed to track a desired trajectory for a class of complex nonlinear discrete-time systems in the presence of bounded and unknown disturbances. The controller includes an observer for estimating states and the outputs, critic, and two action NNs for generating virtual, and actual control inputs. The critic approximates certain strategic utility function and the action NNs are used to minimize both the strategic utility function and their outputs. All NN weights adapt online towards minimization of a performance index, utilizing gradient-descent based rule. …

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Optimal Wide Area Controller And State Predictor For A Power System, Salman Mohagheghi, Ganesh K. Venayagamoorthy, Ronald G. Harley Jan 2007

Optimal Wide Area Controller And State Predictor For A Power System, Salman Mohagheghi, Ganesh K. Venayagamoorthy, Ronald G. Harley

Electrical and Computer Engineering Faculty Research & Creative Works

An optimal wide area controller is designed in this paper for a 12-bus power system together with a Static Compensator (STATCOM). The controller provides auxiliary reference signals for the automatic voltage regulators (AVR) of the generators as well as the line voltage controller of the STATCOM in such a way that it improves the damping of the rotor speed deviations of the synchronous machines. Adaptive critic designs theory is used to implement the controller and enable it to provide nonlinear optimal control over the infinite horizon time of the problem and at different operating conditions of the power system. Simulation …

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Rfid Instrumentation In A Field Application, Theresa M. Swift, Martha J. Molander, Steve Eugene Watkins Jan 2007

Rfid Instrumentation In A Field Application, Theresa M. Swift, Martha J. Molander, Steve Eugene Watkins

Electrical and Computer Engineering Faculty Research & Creative Works

The behavior of radio-frequency identification (RFID) tags is investigated in a field application. The RFID instrumentation is used to mark the position of point strain sensors in a fiber-reinforced polymer (FRP), short-span bridge. The tags are surface mounted on carbon FRP structural elements and covered with a resin wear layer, i.e. the deck of the bridge. The smart composite bridge was installed in 2000 and serves as a field testbed for various sensor technologies including the RFID tags. The operation of the RFID network is tested in the field and compared to laboratory tags. Specific research issues include long-term survivability …

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Understanding Behavior Of System Of Systems Through Computational Intelligence Techniques, Nil H. Kilicay, Cihan H. Dagli Jan 2007

Understanding Behavior Of System Of Systems Through Computational Intelligence Techniques, Nil H. Kilicay, Cihan H. Dagli

Engineering Management and Systems Engineering Faculty Research & Creative Works

The world is facing an increasing level of systems integration leading towards systems of systems (SoS) that adapt to changing environmental conditions. The number of connections between components, the diversity of the components and the way the components are organized can lead to different emergent system behavior. Therefore, the need to focus on overall system behavior is becoming an unavoidable issue. The problem is to develop methodologies appropriate for better understanding behavior of system of systems before the design and implementation phase. This paper focuses on computational intelligence techniques used for analysis of complex adaptive systems with the aim of …

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Breaking The Cycle-Preventing Failures By Leveraging Historical Data During Conceptual Design, Daniel A. Krus, Katie Grantham Jan 2007

Breaking The Cycle-Preventing Failures By Leveraging Historical Data During Conceptual Design, Daniel A. Krus, Katie Grantham

Engineering Management and Systems Engineering Faculty Research & Creative Works

Major engineering accidents are often caused by seemingly minor failures propagating through complex systems. One example of this is an accident involving a Bell 206 Rotorcraft where a fuel pump failure led to the severing of the tail boom. Cataloguing and communicating the knowledge of potential failures and failure propagations is critical to prevent further accidents. The need for effective failure prevention tools is not specific to rotorcrafts, however. Failure reporting systems have been adopted by various industries to aid and promote failure prevention. The catalogued failures usually consist of narratives describing which part of a product failed, how it …

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Analysis Of Interaction Between A Crystallographically Uniaxial Ferrite Resonator And A Hall-Effect Transducer, Marina Koledintseva, Alexander A. Kitaytsev Jan 2007

Analysis Of Interaction Between A Crystallographically Uniaxial Ferrite Resonator And A Hall-Effect Transducer, Marina Koledintseva, Alexander A. Kitaytsev

Electrical and Computer Engineering Faculty Research & Creative Works

In this paper, a number of physical phenomena taking place at the interaction of a crystallographically uniaxial ferrite resonator (UFR) with a semiconductor element, such as a Hall-effect transducer (HET), are analyzed. The UFR in this study is in a direct contact with an unpackaged HET. The interaction is studied in the vicinity of the ferromagnetic resonance in the UFR. The analytical model based on the combination of the problem of interaction of an arbitrarily orientated and shaped UFR with electromagnetic field of a multimode transmission line (waveguide) and thermal balance equations is proposed. A number of thermo/electro/magnetic phenomena that …

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Reinforcement Learning Neural-Network-Based Controller For Nonlinear Discrete-Time Systems With Input Constraints, Pingan He, Jagannathan Sarangapani Jan 2007

Reinforcement Learning Neural-Network-Based Controller For Nonlinear Discrete-Time Systems With Input Constraints, Pingan He, Jagannathan Sarangapani

Electrical and Computer Engineering Faculty Research & Creative Works

A novel adaptive-critic-based neural network (NN) controller in discrete time is designed to deliver a desired tracking performance for a class of nonlinear systems in the presence of actuator constraints. The constraints of the actuator are treated in the controller design as the saturation nonlinearity. The adaptive critic NN controller architecture based on state feedback includes two NNs: the critic NN is used to approximate the "strategic" utility function, whereas the action NN is employed to minimize both the strategic utility function and the unknown nonlinear dynamic estimation errors. The critic and action NN weight updates are derived by minimizing …

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A Normalized Fractionally Lower-Order Moment Algorithm For Space-Time Adaptive Processing, Y. Rosa Zheng, Genshe Chen, Erik Blasch Jan 2007

A Normalized Fractionally Lower-Order Moment Algorithm For Space-Time Adaptive Processing, Y. Rosa Zheng, Genshe Chen, Erik Blasch

Electrical and Computer Engineering Faculty Research & Creative Works

A new space-time adaptive processing algorithm is proposed for clutter suppression in phased array radar systems. In contrast to the commonly used normalized least mean square (NLMS) algorithm which uses the second order moments of the data for adaptation, the proposed method uses the lower order moments of the data to adapt the weight coefficients. The normalization is also performed based on the data sample dispersion rather than the variance. Processing results using simulated and measured data show that the proposed algorithm converges faster than the NLMS algorithms in Gaussian and non-Gaussian clutter environments. It also provides better clutter suppression …

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A Proportional-Integrator Type Adaptive Critic Design-Based Neurocontroller For A Static Compensator In A Multimachine Power System, Salman Mohagheghi, Ganesh K. Venayagamoorthy, Yamille Del Valle, Ronald G. Harley Jan 2007

A Proportional-Integrator Type Adaptive Critic Design-Based Neurocontroller For A Static Compensator In A Multimachine Power System, Salman Mohagheghi, Ganesh K. Venayagamoorthy, Yamille Del Valle, Ronald G. Harley

Electrical and Computer Engineering Faculty Research & Creative Works

A novel nonlinear optimal controller for a static compensator (STATCOM) connected to a power system, using artificial neural networks, is presented in this paper. The action dependent heuristic dynamic programming, a member of the adaptive critic designs family is used for the design of the STATCOM neurocontroller. This neurocontroller provides optimal control based on reinforcement learning and approximate dynamic programming. Using a proportional-integrator approach, the proposed neurocontroller is capable of dealing with actual rather than deviation signals. Simulation results are provided to show that the proposed controller outperforms a conventional PI controller for a STATCOM in a small and large …

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Adaptive Power Control Protocol With Hardware Implementation For Wireless Sensor And Rfid Reader Networks, Kainan Cha, Jagannathan Sarangapani, David Pommerenke Jan 2007

Adaptive Power Control Protocol With Hardware Implementation For Wireless Sensor And Rfid Reader Networks, Kainan Cha, Jagannathan Sarangapani, David Pommerenke

Electrical and Computer Engineering Faculty Research & Creative Works

The development and deployment of radio frequency identification (RFID) systems render a novel distributed sensor network which enhances visibility into manufacturing processes. In RFID systems, the detection range and read rates will suffer from interference among high-power reading devices. This problem grows severely and degrades system performance in dense RFID networks. Consequently, medium access protocols (MAC) protocols are needed for such networks to assess and provide access to the channel so that tags can be read accurately. In this paper, we investigate a suite of feasible power control schemes to ensure overall coverage area of the system while maintaining a …

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Analysis Of Radiated Emissions From A Printed Circuit Board Using Expert System Algorithms, Yan Fu, Todd H. Hubing Jan 2007

Analysis Of Radiated Emissions From A Printed Circuit Board Using Expert System Algorithms, Yan Fu, Todd H. Hubing

Electrical and Computer Engineering Faculty Research & Creative Works

Three algorithms developed for expert system electromagnetic compatibility tools are used to evaluate a printed circuit board design. The maximum radiated emissions estimated by the algorithms are compared to the measured data for various board configurations. The algorithms identify the most important electromagnetic interference source mechanisms, drawing attention to the design parameters that have the most significant effect on the radiated emissions.

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Comparison Of Nonuniform Optimal Quantizer Designs For Speech Coding With Adaptive Critics And Particle Swarm, Ganesh K. Venayagamoorthy, Wenwei Zha Jan 2007

Comparison Of Nonuniform Optimal Quantizer Designs For Speech Coding With Adaptive Critics And Particle Swarm, Ganesh K. Venayagamoorthy, Wenwei Zha

Electrical and Computer Engineering Faculty Research & Creative Works

This paper presents the design of a companding nonuniform optimal scalar quantizer for speech coding. The quantizer is designed using two neural networks to perform the nonlinear transformation. These neural networks are used in the front and back ends of a uniform quantizer. Two approaches are presented in this paper namely adaptive critic designs and particle swarm optimization, aiming to maximize the signal-to-noise ratio. The comparison of these optimal quantizer designs over a bit-rate range of 3-6 is presented. The perceptual quality of the coding is evaluated by the International Telecommunication Union's Perceptual Evaluation of Speech Quality standard

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Coordinated Machine Learning And Decision Support For Situation Awareness, Timothy Draelos, Pengchu Zhang, Donald C. Wunsch, John E. Seiffertt Iv, Gregory Conrad, Nathan Brannon Jan 2007

Coordinated Machine Learning And Decision Support For Situation Awareness, Timothy Draelos, Pengchu Zhang, Donald C. Wunsch, John E. Seiffertt Iv, Gregory Conrad, Nathan Brannon

Electrical and Computer Engineering Faculty Research & Creative Works

For applications such as force protection, an effective decision maker needs to maintain an unambiguous grasp of the environment. Opportunities exist to leverage computational mechanisms for the adaptive fusion of diverse information sources. The current research employs neural networks and Markov chains to process information from sources including sensors, weather data, and law enforcement. Furthermore, the system operator's input is used as a point of reference for the machine learning algorithms. More detailed features of the approach are provided, along with an example force protection scenario.

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Demodulation Of Fiber-Optic Sensors For Frequency Response Measurement, Abdeq M. Abdi, Steve Eugene Watkins Jan 2007

Demodulation Of Fiber-Optic Sensors For Frequency Response Measurement, Abdeq M. Abdi, Steve Eugene Watkins

Electrical and Computer Engineering Faculty Research & Creative Works

The neural-network-based processing of extrinsic Fabry-Perot interferometric (EFPI) strain sensors was investigated for the special case of sinusoidal strain. The application area is modal or cyclic testing of structures in which the frequency response to periodic actuation must be demodulated. The nonlinear modulation characteristic of EFPI sensors produces well-defined harmonics of the actuation frequency. Relationships between peak strain and harmonic content were analyzed theoretically. A two-stage demodulator was implemented with a Fourier series neural network to separate the harmonic components of an EFPI signal and a backpropagation neural network to predict the peak-to-peak strain from the harmonics. The system performance …

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Reactive Oxygen Emission From Microwave Discharge Plasmas, S. Popovic, M. Rašković, S. P. Kuo, L. Vuskovic Jan 2007

Reactive Oxygen Emission From Microwave Discharge Plasmas, S. Popovic, M. Rašković, S. P. Kuo, L. Vuskovic

Physics Faculty Publications

Metastable oxygen atoms and molecules have received increased interest because of their function in surface modification, bio-decontamination and many other industrial applications, in addition to the role in the upper atmospheric layer chemistry. We review work on production and detection of metastable oxygen and we describe our experiments, including the development of techniques for measurement of metastable molecular oxygen. We show that either metastable oxygen molecules or metastable oxygen atoms can be produced in large quantities in electrical discharges, carefully tailored to promote the required kinetics. Although the two species may coexist, colder discharge regimes favor production of molecules, while …

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Plasma Treatment Of Bulk Nb Surface In The Ar/Cl2 Discharge, M. Rašković, L. Vuskovic, S. Popovic, A.-M. Valente-Feliciano, L. Phillips Jan 2007

Plasma Treatment Of Bulk Nb Surface In The Ar/Cl2 Discharge, M. Rašković, L. Vuskovic, S. Popovic, A.-M. Valente-Feliciano, L. Phillips

Physics Faculty Publications

The preparation of the cavity walls has been one of the major challenges in the superconducting radio-frequency (SRF) accelerator technology. Therefore, constant research and development effort is devoted to develop surface preparation processes that will improve roughness and lower the level of impurities, like hydrogen or oxygen, embedded in bulk Nb, having in the same time reasonable etching rates. Plasma based surface modification provides an excellent opportunity to achieve these goals. We present Ar/Cl2 discharge treatment of bulk Nb where we achieved etching rates comparable to the rates obtained with the electropolishing method without introducing impurities in Nb. The …

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An Evaluation Of Supercritical Drying And Peg/Freeze Drying Of Waterlogged Archaeological Wood, Eric Schindelholz, Robert Blanchette, Desmond C. Cook, Michael Drews, Steve Hand, Benjamin Held, Joel Jurgens, Betty Seifert Jan 2007

An Evaluation Of Supercritical Drying And Peg/Freeze Drying Of Waterlogged Archaeological Wood, Eric Schindelholz, Robert Blanchette, Desmond C. Cook, Michael Drews, Steve Hand, Benjamin Held, Joel Jurgens, Betty Seifert

Physics Faculty Publications

This study was undertaken to evaluate the physical effects of drying waterlogged archaeological wood using supercritical carbon dioxide as compared to air drying and the popular polyethylene glycol (PEG)/freeze drying method. Previous studies have shown supercritical drying to be a potentially advantageous alternative to current methods of drying waterlogged wood through reduced processing time, minimal shrinkage, and increased success for reversibility. Samples in the form of blocks and planks of a few centimeters in size were prepared from two archaeological waterlogged wood sources and grouped into three treatment sets: one for air drying, one for PEG/freeze drying, and the other …

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