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- Electrical and Computer Engineering Faculty Research and Publications (12)
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Articles 1 - 30 of 39
Full-Text Articles in Computer Engineering
Real-Time 3d Image Visualization System For Digital Video On A Single Chip, Nader I. Rafla
Real-Time 3d Image Visualization System For Digital Video On A Single Chip, Nader I. Rafla
Electrical and Computer Engineering Faculty Publications and Presentations
Implementation of a real-time image visualization system on a reconfigurable chip (FPGA) is proposed. The system utilizes an innovative stereoscopic image capture, processing and visualization technique. Implementation is done as a two stage process. In the first stage, the stereo pair is captured using two image sensors. The captured images are then synchronized and sent to the second stage for fusion. A controller module is developed, designed, and placed on the FPGA for this purpose. The second stage is used for reconstruction and visualization of the 3D image. An innovative technique employing dual-processor architecture on the same single FPGA is …
H-Infinity Estimation For Fuzzy Membership Function Optimization, Daniel J. Simon
H-Infinity Estimation For Fuzzy Membership Function Optimization, Daniel J. Simon
Electrical and Computer Engineering Faculty Publications
Given a fuzzy logic system, how can we determine the membership functions that will result in the best performance? If we constrain the membership functions to a specific shape (e.g., triangles or trapezoids) then each membership function can be parameterized by a few variables and the membership optimization problem can be reduced to a parameter optimization problem. The parameter optimization problem can then be formulated as a nonlinear filtering problem. In this paper we solve the nonlinear filtering problem using H∞ state estimation theory. However, the membership functions that result from this approach are not (in general) sum normal. …
Dynamic Voltage Scaling Techniques For Power Efficient Video Decoding, Ben Lee, Eriko Nurvitadhi, Reshma Dixit, Chansu Yu, Myungchul Kim
Dynamic Voltage Scaling Techniques For Power Efficient Video Decoding, Ben Lee, Eriko Nurvitadhi, Reshma Dixit, Chansu Yu, Myungchul Kim
Electrical and Computer Engineering Faculty Publications
This paper presents a comparison of power-aware video decoding techniques that utilize dynamic voltage scaling (DVS). These techniques reduce the power consumption of a processor by exploiting high frame variability within a video stream. This is done through scaling of the voltage and frequency of the processor during the video decoding process. However, DVS causes frame deadline misses due to inaccuracies in decoding time predictions and granularity of processor settings used. Four techniques were simulated and compared in terms of power consumption, accuracy, and deadline misses. In addition, this paper proposes the frame-data computation aware (FDCA) technique, which is …
Partition-Based Interpolation For Color Filter Array Demosaicking And Super-Resolution Reconstruction, Min Shao, Kenneth E. Barner, Russell C. Hardie
Partition-Based Interpolation For Color Filter Array Demosaicking And Super-Resolution Reconstruction, Min Shao, Kenneth E. Barner, Russell C. Hardie
Electrical and Computer Engineering Faculty Publications
A class of partition-based interpolators that addresses a variety of image interpolation applications are proposed. The proposed interpolators first partition an image into a finite set of partitions that capture local image structures. Missing high resolution pixels are then obtained through linear operations on neighboring pixels that exploit the captured image structure. By exploiting the local image structure, the proposed algorithm produces excellent performance on both edge and uniform regions. The presented results demonstrate that partition-based interpolation yields results superior to traditional and advanced algorithms in the applications of color filter array (CFA) demosaicking and super-resolution reconstruction.
Applicationofspectroscopic Ellipsometry To In-Stu. Real-Time Fabrication Of Multiple Layer Alternating High/Low Refractive Index Filters, Blaine D. Johs, Jeffery S. Hale, John A. Woollam, Craig M. Herzinger
Applicationofspectroscopic Ellipsometry To In-Stu. Real-Time Fabrication Of Multiple Layer Alternating High/Low Refractive Index Filters, Blaine D. Johs, Jeffery S. Hale, John A. Woollam, Craig M. Herzinger
Department of Electrical and Computer Engineering: Faculty Publications
Disclosed is application of oblique angle of incidence, reflection and/or transmission mode spectroscopic ellipsometry PSI and/or DELTA, (including combinations thereof and/or mathematical equivalents), vs. wavelength data to monitor and/or control fabrication of multiple layer high/low refractive index band-pass, band-reject and varied attenuation vs. wavelength filters, either alone or in combination with transmissive non-ellipsometric electromagnetic beam turning point vs. layer data obtained at an essentially normal angle of incidence.
System And Method Enabling Simultaneous Investigation Of Sample With Two Beams Of Electromagnetic Radiation, John A. Woollam, Galen L. Pfeiffer, Daniel W. Thompson, Blaine D. Johs, Craig M. Herzinger
System And Method Enabling Simultaneous Investigation Of Sample With Two Beams Of Electromagnetic Radiation, John A. Woollam, Galen L. Pfeiffer, Daniel W. Thompson, Blaine D. Johs, Craig M. Herzinger
Department of Electrical and Computer Engineering: Faculty Publications
Disclosed are system and method for a characterizing system consisting of a fluid sample on a two-sided stage, utilizing data obtained by applying, from both sides thereof, beams of electromagnetic radiation to a fluid coated surface in a containing cell volume. The beams can have the same or different wavelength content and/or polarization state and can be applied at the same or different magnitude angles-of-incidence, and a third typically unpolarized beam can be applied at a normal angle-of-incidence.
System And Method Enabling Simultaneous Investigation Of Sample With Two Beams Of Electromagnetic Radation, John A. Woollam, Galen L. Pfeiffer, Daniel W. Thompson, Blaine D. Johs, Craig M. Herzinger
System And Method Enabling Simultaneous Investigation Of Sample With Two Beams Of Electromagnetic Radation, John A. Woollam, Galen L. Pfeiffer, Daniel W. Thompson, Blaine D. Johs, Craig M. Herzinger
Department of Electrical and Computer Engineering: Faculty Publications
Disclosed are System and method for characterizing a System consisting of a fluid Sample on a two sided Stage, utilizing data obtained by applying, from both sides thereof, beams of electromagnetic radiation to a fluid coated Surface in a containing cell Volume. The beams can have the same or different wavelength content and/or polarization State, and can be applied at the same or different magnitude angles-of-incidence, and a third typically unpolarized beam can be applied at a normal angle-of-incidence.
Study Of System Parameters And Control Design For A Flexible Manipulator Using Piezoelectric Transducers, Mehrdad Kermani Ph.D., P.Eng., Mehrdad Moallem, Rajni Patel
Study Of System Parameters And Control Design For A Flexible Manipulator Using Piezoelectric Transducers, Mehrdad Kermani Ph.D., P.Eng., Mehrdad Moallem, Rajni Patel
Electrical and Computer Engineering Publications
No abstract provided.
The Case For Thoroughly Testing Complex System Dynamic Models, Wayne Wakeland, Megan Hoarfrost
The Case For Thoroughly Testing Complex System Dynamic Models, Wayne Wakeland, Megan Hoarfrost
Systems Science Faculty Publications and Presentations
In order to determine whether model testing is as useful as suggested by modeling experts, the full battery of model tests recommended by Forrester, Senge, Sterman, and others was applied retrospectively to a complex previously-published system dynamics model. The time required to carry out each type of test was captured, and the benefits that resulted from applying each test was determined subjectively. The resulting benefit to cost ratios are reported. These ratios suggest that rather than focusing primarily on sensitivity testing, modelers should consider other types of model tests such as extreme condition tests and family member tests. The study …
Time-Domain Isolated Phoneme Classification Using Reconstructed Phase Spaces, Michael T. Johnson, Richard J. Povinelli, Andrew C. Lindgren, Jinjin Ye, Xiaolin Liu, Kevin M Indrebo
Time-Domain Isolated Phoneme Classification Using Reconstructed Phase Spaces, Michael T. Johnson, Richard J. Povinelli, Andrew C. Lindgren, Jinjin Ye, Xiaolin Liu, Kevin M Indrebo
Electrical and Computer Engineering Faculty Research and Publications
This paper introduces a novel time-domain approach to modeling and classifying speech phoneme waveforms. The approach is based on statistical models of reconstructed phase spaces, which offer significant theoretical benefits as representations that are known to be topologically equivalent to the state dynamics of the underlying production system. The lag and dimension parameters of the reconstruction process for speech are examined in detail, comparing common estimation heuristics for these parameters with corresponding maximum likelihood recognition accuracy over the TIMIT data set. Overall accuracies are compared with a Mel-frequency cepstral baseline system across five different phonetic classes within TIMIT, and a …
Effects Of Load Magnitude On Diagnosing Broken Bar Faults In Induction Motors Using The Pendulous Oscillation Of The Rotor Magnetic Field Orientation, Behrooz Mirafzal, Nabeel Demerdash
Effects Of Load Magnitude On Diagnosing Broken Bar Faults In Induction Motors Using The Pendulous Oscillation Of The Rotor Magnetic Field Orientation, Behrooz Mirafzal, Nabeel Demerdash
Electrical and Computer Engineering Faculty Research and Publications
The effects of load level on the ability to diagnose broken bar faults in squirrel-cage induction motors are studied in this paper. The pendulous oscillation of the rotor magnetic field orientation is implemented as a fault signature for rotor fault diagnostic purposes at steady-state operations. Moreover, the effects of load level on the low-side band component of the stator current spectrum, and associated diagnostic difficulties in this approach particularly in the presence of motor operation from pulsewidth-modulation drives, are reported as well. These investigations were performed through testing 2-hp and 5-hp induction motors over a wide range of load levels …
Optimal Flux Weakening In Surface Pm Machines Using Fractional-Slot Concentrated Windings, Ayman M. El-Refaie, Thomas M. Jahns
Optimal Flux Weakening In Surface Pm Machines Using Fractional-Slot Concentrated Windings, Ayman M. El-Refaie, Thomas M. Jahns
Electrical and Computer Engineering Faculty Research and Publications
A design approach is presented for achieving optimal flux-weakening operation in surface permanent-magnet (SPM) synchronous machines by properly designing the machine's stator windings using concentrated, fractional-slot stator windings. This technique makes it possible to significantly increase the machine inductance in order to achieve the critical condition for providing wide speed ranges of constant-power operation. The conditions for optimal flux weakening can be achieved while simultaneously delivering sinusoidal line-to-line back-electromotive-force waveforms and low cogging torque. A closed-form analytical model is described that can be used to design SPM machines to achieve optimal flux-weakening conditions. This technique is applied to design a …
Capacity And Complexity Of Hmm Duration Modeling Techniques, Michael T. Johnson
Capacity And Complexity Of Hmm Duration Modeling Techniques, Michael T. Johnson
Electrical and Computer Engineering Faculty Research and Publications
The ability of a standard hidden Markov model (HMM) or expanded state HMM (ESHMM) to accurately model duration distributions of phonemes is compared with specific duration-focused approaches such as semi-Markov models or variable transition probabilities. It is demonstrated that either a three-state ESHMM or a standard HMM with an increased number of states is capable of closely matching both Gamma distributions and duration distributions of phonemes from the TIMIT corpus, as measured by Bhattacharyya distance to the true distributions. Standard HMMs are easily implemented with off-the-shelf tools, whereas duration models require substantial algorithmic development and have higher computational costs when …
Nanoindentation Technique For Characterizing Cantilever Beam Style Rf Microelectromechanical Systems (Mems) Switches, Hyukjae Lee, Ronald A. Coutu Jr., Shankar Mall, Paul E. Kladitis
Nanoindentation Technique For Characterizing Cantilever Beam Style Rf Microelectromechanical Systems (Mems) Switches, Hyukjae Lee, Ronald A. Coutu Jr., Shankar Mall, Paul E. Kladitis
Electrical and Computer Engineering Faculty Research and Publications
A nanoindentation technique was used to mechanically actuate a radio frequency micro-switch along with the measurement of contact resistance to investigate its applicability to characterize deflection and contact resistance behaviors of micro-sized cantilever beam switches. The resulting load–displacement relationship showed a discontinuity in slope when the micro-switch closed. The measured spring constants reasonably agreed with theoretical values obtained from the simple beam models. The change in contact resistance during test clearly indicated micro-switch closure but it did not coincide exactly with the physical contact between two electric contacts due to a resistive contaminated film.
Novel Slurry Solutions For Thick Cu Cmp, Peter A. Miranda, Jerome A. Imonigie, Aaron L. Erbe, Amy J. Moll
Novel Slurry Solutions For Thick Cu Cmp, Peter A. Miranda, Jerome A. Imonigie, Aaron L. Erbe, Amy J. Moll
Electrical and Computer Engineering Faculty Publications and Presentations
Electro-plating methods currently used to deposit Cu in through-wafer interconnect applications result in the formation of a thick Cu layer with large amounts of topographical variation. In this paper, alternative methods for thick Cu removal are investigated using a two-step slurry CMP approach.
Multi-Aoi-System For Easy Changing Angles Of Incidence In Ellipsometer, Polarimeter And Reflectometer Systems, Blaine D. Johs, Ping He, Martin M. Liphardt, Christopher A. Goeden, John A. Woollam, James D. Welch
Multi-Aoi-System For Easy Changing Angles Of Incidence In Ellipsometer, Polarimeter And Reflectometer Systems, Blaine D. Johs, Ping He, Martin M. Liphardt, Christopher A. Goeden, John A. Woollam, James D. Welch
Department of Electrical and Computer Engineering: Faculty Publications
Disclosed is a system for enabling easy sequential setting of different Angles-of-Incidence of a beam of electromagnetic radiation to a surface of a sample system, and to regression based methodology for evaluating and compensating the effects of the presence of electromagnetic beam intercepting angle-of-incidence changing systems, including where desired, parameterization of calibration parameters.
Generalized Phase Space Projection For Nonlinear Noise Reduction, Michael T. Johnson, Richard J. Povinelli
Generalized Phase Space Projection For Nonlinear Noise Reduction, Michael T. Johnson, Richard J. Povinelli
Electrical and Computer Engineering Faculty Research and Publications
Improved phase space projection methods, adapted from related work in the linear signal processing field based on subspace decomposition, are presented for application to the problem of additive noise reduction in the context of phase space analysis. These methods improve upon existing methods such as Broomhead–King singular spectrum analysis projection by minimizing overall signal distortion subject to constraints on the residual error, rather than using a direct least-squares fit. This results in a range of weighted projections which estimate and compensate for the portion of the principal component's singular values corresponding to noise rather than signal energy, and which include …
Automatic Classification And Speaker Identification Of African Elephant (Loxodonta Africana) Vocalizations, Patrick J. Clemins, Michael T. Johnson, Kirsten Leong, Anne Savage
Automatic Classification And Speaker Identification Of African Elephant (Loxodonta Africana) Vocalizations, Patrick J. Clemins, Michael T. Johnson, Kirsten Leong, Anne Savage
Electrical and Computer Engineering Faculty Research and Publications
A hidden Markov model (HMM) system is presented for automatically classifying African elephant vocalizations. The development of the system is motivated by successful models from human speech analysis and recognition. Classification features include frequency-shifted Mel-frequency cepstral coefficients (MFCCs) and log energy, spectrally motivated features which are commonly used in human speech processing. Experiments, including vocalization type classification and speaker identification, are performed on vocalizations collected from captive elephants in a naturalistic environment. The system classified vocalizations with accuracies of 94.3% and 82.5% for type classification and speaker identification classification experiments, respectively. Classification accuracy, statistical significance tests on the model parameters, …
Gain-Bandwidth Product Optimization Of Heterostructure Avalanche Photodiodes, Oh-Hyun Kwon, Majeed M. Hayat, Joe C. Campbell, Bahaa E.A. Saleh, Malvin Carl Teich
Gain-Bandwidth Product Optimization Of Heterostructure Avalanche Photodiodes, Oh-Hyun Kwon, Majeed M. Hayat, Joe C. Campbell, Bahaa E.A. Saleh, Malvin Carl Teich
Electrical and Computer Engineering Faculty Research and Publications
A generalized history-dependent recurrence theory for the time-response analysis is derived for avalanche photodiodes with multilayer, heterojunction multiplication regions. The heterojunction multiplication region considered consists of two layers: a high-bandgap Al/sub 0.6/Ga/sub 0.4/As energy-buildup layer, which serves to heat up the primary electrons, and a GaAs layer, which serves as the primary avalanching layer. The model is used to optimize the gain-bandwidth product (GBP) by appropriate selection of the width of the energy-buildup layer for a given width of the avalanching layer. The enhanced GBP is a direct consequence of the heating of primary electrons in the energy-buildup layer, which …
An Electro-Oculogram Based System For Communication And Control Using Target Position Variation, Ronan Fitzmaurice, Ted Burke, Annraoi De Paor
An Electro-Oculogram Based System For Communication And Control Using Target Position Variation, Ronan Fitzmaurice, Ted Burke, Annraoi De Paor
Conference Papers
In this paper we describe a novel mode of human computer interaction based on gaze tracking using the electro-oculogram (EOG). Despite the relative simplicity of recording this signal, it is often discounted as a reliable method of gaze tracking because of problems arising from changing sensitivity and DC drift. We describe an original technique, Target Position Variation (TPV), which addresses this issue by presenting moving icons which, when followed with the eye, create a corresponding pattern in the EOG signal which can be used to infer the correct gaze position and to compensate for variations in sensitivity.
Design Of Mobile Phone Applications For Point-Of-Care Test Result Validation., John Mcgrory, Owen Lynch, Eugene Coyle
Design Of Mobile Phone Applications For Point-Of-Care Test Result Validation., John Mcgrory, Owen Lynch, Eugene Coyle
Conference Papers
Patients with many different conditions are required to take the management of their condition into their own hands and perform Point of Care Testing (POCT) at home. However, this raises quality control issues that would not arise in a clinical setting, since the sample acquisition and testing procedures are not overseen by professional hospital staff. Another major issue, the main focus of this research, is that results from such tests are not clinically validated to ensure that they are plausible for that patient at the time of testing. In hospital, tests taken by clinicians are validated by hi-tech computerised validation …
Editorial, Robert W. Stewart, Michael W. Hoffman, Stephan Weiss
Editorial, Robert W. Stewart, Michael W. Hoffman, Stephan Weiss
Department of Electrical and Computer Engineering: Faculty Publications
In the past years, digital signal processing (DSP) algorithms and architectures for baseband communication systems have fuelled the delivery of applications such as 3G mobile communications and wireless LAN to mass markets. This was made possible by a tremendous growth in the performance of computational devices such as digital signal processors and FPGAs, as well as an increase in sampling rates of conversion devices to potentially several 100 MHz. While the development of both computational devices and ADCs/DACs continues, thus permitting DSP to be applied at IF sampling rates and possibly beyond, the opportunities for further enhancing radio devices by …
Comparison Of Antenna Array Systems Using Ofdm For Software Radio Via The Sibic Model, Khoi D. Le, Michael W. Hoffman, Robert D. Palmer
Comparison Of Antenna Array Systems Using Ofdm For Software Radio Via The Sibic Model, Khoi D. Le, Michael W. Hoffman, Robert D. Palmer
Department of Electrical and Computer Engineering: Faculty Publications
This paper investigates the performance of two candidates for software radio WLAN, reconfigurable OFDM modulation and antenna diversity, in an indoor environment. The scenario considered is a 20m × 10m × 3m room with two base units and one mobile unit. The two base units use omnidirectional antennas to transmit and the mobile unit uses either a single antenna with equalizer, a fixed beamformer with equalizer, or an adaptive beamformer with equalizer to receive. The modulation constellation of the data is QPSK and 16-QAM. The response of the channel at the mobile unit is simulated using a three-dimensional indoor WLAN …
Preconditioning Of Primary Human Endothelial Cells With Inflammatory Mediators Alters The “Set Point” Of The Cell, Youichiro Wada, Hasan H. Otu, Shengqian Wu, Md. Ruhul Abid, Hitomi Okada, Towia Libermann, Tatsuhiko Kodama, Shu-Ching Shih, Takashi Minami, William C. Aird
Preconditioning Of Primary Human Endothelial Cells With Inflammatory Mediators Alters The “Set Point” Of The Cell, Youichiro Wada, Hasan H. Otu, Shengqian Wu, Md. Ruhul Abid, Hitomi Okada, Towia Libermann, Tatsuhiko Kodama, Shu-Ching Shih, Takashi Minami, William C. Aird
Department of Electrical and Computer Engineering: Faculty Publications
Endothelial cells are highly sensitive to changes in the extracellular milieu. Sepsis results in activation of inflammatory and coagulation pathways. We hypothesized that sepsis-associated mediators may alter the response capacity (so-called “set point”) of endothelial cells. Human umbilical vein endothelial cells (HUVEC) were preincubated in the presence or absence of tumor necrosis factor (TNF)-α, lipopolysaccharide (LPS), hypoxia, hyperthermia, and/or high glucose; treated with or without thrombin for 4 h; and then processed for RNase protection assays of selected activation markers. Priming with TNF-α and LPS significantly inhibited thrombin-mediated induction of vascular cell adhesion molecule-1, intercellular adhesion molecule-1, tissue factor, and …
A Novel Role For Gadd45Β As A Mediator Of Mmp-13 Gene Expression During Chondrocyte Terminal Differentiation, Kosei Ijiri, Luiz F. Zerbini, Haibing Peng, Ricardo G. Correa, Binfeng Lu, Nicole Walsh, Yani Zhao, Noboru Taniguchi, Xu-Ling Huang, Hasan H. Otu, Hong Wang, Jian Fei Wang, Setsuro Komiya, Patricia Ducy, Mahboob U. Rahman, Richard A. Flavell, Ellen M. Gravallese, Peter Oettgen, Towia A. Libermann, Mary B. Goldring
A Novel Role For Gadd45Β As A Mediator Of Mmp-13 Gene Expression During Chondrocyte Terminal Differentiation, Kosei Ijiri, Luiz F. Zerbini, Haibing Peng, Ricardo G. Correa, Binfeng Lu, Nicole Walsh, Yani Zhao, Noboru Taniguchi, Xu-Ling Huang, Hasan H. Otu, Hong Wang, Jian Fei Wang, Setsuro Komiya, Patricia Ducy, Mahboob U. Rahman, Richard A. Flavell, Ellen M. Gravallese, Peter Oettgen, Towia A. Libermann, Mary B. Goldring
Department of Electrical and Computer Engineering: Faculty Publications
The growth arrest and DNA damage-inducible 45β (GADD45β) gene product has been implicated in the stress response, cell cycle arrest, and apoptosis. Here we demonstrated the unexpected expression of GADD45β in the embryonic growth plate and uncovered its novel role as an essential mediator of matrix metalloproteinase-13 (MMP-13) expression during terminal chondrocyte differentiation. We identified GADD45β as a prominent early response gene induced by bone morphogenetic protein-2 (BMP-2) through a Smad1/Runx2-dependent pathway. Because this pathway is involved in skeletal development, we examined mouse embryonic growth plates, and we observed expression of Gadd45β mRNA coincident with Runx2 protein …
Range Imaging Observations Of Pmse Using The Eiscat Vhf Radar: Phase Calibration And First Results, J. R. Fernandez, R. D. Palmer, P. B. Chilson, I. Haggstrom, M. T. Rietveld
Range Imaging Observations Of Pmse Using The Eiscat Vhf Radar: Phase Calibration And First Results, J. R. Fernandez, R. D. Palmer, P. B. Chilson, I. Haggstrom, M. T. Rietveld
Department of Electrical and Computer Engineering: Faculty Publications
A novel phase calibration technique for use with the multiple-frequency Range IMaging (RIM) technique is introduced based on genetic algorithms. The method is used on data collected with the European Incoherent SCATter (EISCAT) VHF radar during a 2002 experiment with the goal of characterizing the vertical structure of Polar Mesosphere Summer Echoes (PMSE) over northern Norway. For typical Doppler measurements, the initial phases of the transmitter and receiver are not required to be the same. The EISCAT receiver systems exploit this fact, allowing a multistatic configuration. However, the RIM method relies on the small phase differences between closely spaced frequencies. …
Phased-Array Design For Biological Clutter Rejection: Simulation And Experimental Validation, B.L. Cheong, Michael Hoffman, R.D. Palmer, Stephen J. Frasier, F.J. Lopez-Dekker
Phased-Array Design For Biological Clutter Rejection: Simulation And Experimental Validation, B.L. Cheong, Michael Hoffman, R.D. Palmer, Stephen J. Frasier, F.J. Lopez-Dekker
Department of Electrical and Computer Engineering: Faculty Publications
This paper highlights recent results obtained with the Turbulent Eddy Profiler (TEP), which was devel- oped by the University of Massachusetts. This unique 915-MHz radar has up to 64 spatially separated receiving elements, each with an independent receiver. The calibrated raw data provided by this array could be processed using sophisticated imaging algorithms to resolve the horizontal structures within each range gate. After collecting all of the closely spaced horizontal slices, the TEP radar can produce three- dimensional images of echo power, radial velocity, and spectral width. From the radial velocity measure- ments, it is possible to estimate the three-dimensional …
Observations Of The Small-Scale Variability Of Precipitation Using An Imaging Radar, Robert D. Palmer, Boon Leng Cheong, Michael Hoffman, Stephen J. Frasier, F.J. Lopez-Dekker
Observations Of The Small-Scale Variability Of Precipitation Using An Imaging Radar, Robert D. Palmer, Boon Leng Cheong, Michael Hoffman, Stephen J. Frasier, F.J. Lopez-Dekker
Department of Electrical and Computer Engineering: Faculty Publications
For many years, spatial and temporal inhomogeneities in precipitation fields have been studied using scanning radars, cloud radars, and disdrometers, for example. Each measurement technique has its own advantages and disadvantages. Conventional profiling radars point vertically and collect data while the atmosphere advects across the field of view. Invoking Taylor’s frozen turbulence hypothesis, it is possible to construct time-history data, which are used to study the structure and dynamics of the atmosphere. In the present work, coherent radar imaging is used to estimate the true three-dimensional structure of the atmosphere within the field of view of the radar. The 915-MHz …
Exponential Time Response In Analogue And Geiger Mode Avalanche Photodiodes, C. Groves, C. H. Tan, J. P.R. David, G. J. Rees, Majeed M. Hayat
Exponential Time Response In Analogue And Geiger Mode Avalanche Photodiodes, C. Groves, C. H. Tan, J. P.R. David, G. J. Rees, Majeed M. Hayat
Electrical and Computer Engineering Faculty Research and Publications
The mean avalanche current impulse response in an avalanche photodiode exhibits an initial transient and then grows or decays, above or below breakdown, at exponential rates which depend only on the probability distributions of the electron and hole ionization events. The process continues while the electric field profile remains unchanged by the applied bias or the evolving space charge. Below breakdown the distribution in the avalanche duration also exhibits an initial transient and then decays exponentially at the same rate as the mean current. Below breakdown the standard deviation in current decays exponentially at one half of the rate of …
Theoretical Investigation Of Quantum-Dot Avalanche Photodiodes For Mid-Infrared Applications, Sanjay Krishna, Oh-Hyun Kwon, Majeed M. Hayat
Theoretical Investigation Of Quantum-Dot Avalanche Photodiodes For Mid-Infrared Applications, Sanjay Krishna, Oh-Hyun Kwon, Majeed M. Hayat
Electrical and Computer Engineering Faculty Research and Publications
A novel midinfrared sensor, called the quantum-dot avalanche photodiode (QDAP), is proposed which is expected to have improved signal-to-noise ratio (SNR) in the presence of Johnson noise over its quantum-dot (QD) counterpart. In the QDAP, an intersubband QD detector is coupled with a thin, low-noise GaAs avalanche layer through a tunnel barrier. The avalanche layer provides the necessary photocurrent gain required to overcome Johnson noise and nearly achieve the dark-current-limited SNR of the QD detector. In the proposed three-terminal device, the applied biases of the QD-detector and the avalanche-photodiode sections of the QDAP are controlled separately. This feature permits the …