Publications

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https://hdl.handle.net/10217/100413

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Open Access
0.85 PW laser operation at 3.3 Hz and high-contrast ultrahigh-intensity λ = 400 nm second-harmonic beamline
(Colorado State University. Libraries, 2017-09-22) Wang, Yong, author; Wang, Shoujun, author; Rockwood, Alex, author; Luther, Bradley M., author; Hollinger, Reed, author; Curtis, Alden, author; Calvi, Chase, author; Menoni, Carmen S., author; Rocca, Jorge J., author; Optical Society of America, publisher
We demonstrate the generation of 0.85 PW, 30 fs laser pulses at a repetition rate of 3.3 Hz with a record average power of 85 W from a Ti:sapphire laser. The system is pumped by high-energy Nd:glass slab amplifiers frequency doubled in LiB3O5 (LBO). Ultrahigh-contrast λ = 400 nm femtosecond pulses were generated in KH2PO4 (KDP) with>40% efficiency. An intensity of 6.5 × 1021 W∕cm2 was obtained by frequency doubling 80% of the available Ti:sapphire energy and focusing the doubled light with an f∕2 parabola. This laser will enable highly relativistic plasma experiments to be conducted at high repetition rate.
Open Access
1-W cw Zn ion laser
(Colorado State University. Libraries, 1983) Meyer, J. D., author; Rocca, Jorge J., author; Collins, G. J., author; American Institute of Physics, publisher
We have obtained 1.2W of cw laser power on the 4911.6- and 4924.0-Å transitions of Zn II by exciting a He-Zn gas mixture with a dc glow discharge electron beam. In addition, 0.25-W output power has been obtained on the 6149.9-Å line of Hg+ using the same excitation scheme. The combination of electron beam ionization of rare gas atoms and subsequent charge transfer excitation to metal ion levels is shown to have the potential of significantly increasing the efficiency of ion lasers. cw multiwatt visible and ultraviolet ion lasers operating at efficiencies > 10-3 appear feasible using this excitation scheme.
Open Access
A 2-D filtering scheme for stereo image compression using sequential orthogonal subspace updating
(Colorado State University. Libraries, 2001) Seo, Sang-Hoon, author; Azimi-Sadjadi, Mahmood R., author; IEEE, publisher
Stereo image compression involves estimating the disparity vectors that represent the amount of binocular parallax. The mismatching problems between the left and right images greatly impact the accuracy of the reconstructed image, and hence the visual effects of the reproduced 3-D image. This paper presents a new method for compensating the mismatching effects in stereo image pairs. This 2-D filtering-based scheme uses a sequential orthogonal subspace updating (SOSU) process to project an image block onto a subset of best-basis vectors. The basis vectors are selected one by one from the neighboring blocks, as well as some typical edge blocks, forming an image-dependent set of basis vectors. This leads to the optimal representation of an image block with fewer coefficients. Simulation results on two different image pairs demonstrate the effectiveness of the SOSU scheme when compared to those of the standard least squares 2-D filtering and the hybrid disparity-compensated discrete cosine transform residual encoding schemes.
Open Access
A Bayesian correction approach for improving dual-frequency precipitation radar rainfall rate estimates
(Colorado State University. Libraries, 2020-01-27) Ma, Yingzhao, author; Chandrasekar, V., author; Biswas, Sounak K., author; Journal of Meteorological Society of Japan, publisher
The accurate estimation of precipitation is an important objective for the Dual-frequency Precipitation Radar (DPR), which is located on board the Global Precipitation Measurement (GPM) satellite core observatory. In this study, a Bayesian correction (BC) approach is proposed to improve the DPR’s instantaneous rainfall rate product. Ground dual-polarization radar (GR) observations are used as references, and a log-transformed Gaussian distribution is assumed as the instantaneous rainfall process. Additionally, a generalized regression model is adopted in the BC algorithm. Rainfall intensities such as light, moderate, and heavy rain and their variable influences on the model’s performance are considered. The BC approach quantifies the predictive uncertainties associated with the Bayesiancorrected DPR (DPR_BC) rainfall rate estimates. To demonstrate the concepts developed in this study, data from the GPM overpasses of the Weather Service Surveillance Radar (WSR-88D), KHGX, in Houston, Texas, between April 2014 and June 2018 are used. Observation errors in the DPR instantaneous rainfall rate estimates are analyzed as a function of rainfall intensity. Moreover, the best-performing BC model is implemented in three GPM-overpass cases with heavy rainfall records across the southeastern United States. The results show that the DPR_BC rainfall rate estimates have superior skill scores and are in better agreement with the GR references than with the DPR estimates. This study demonstrates the potential of the proposed BC algorithm for enhancing the instantaneous rainfall rate product from spaceborne radar equipment.
Open Access
A CAD driven multiscale approach to automated inspection
(Colorado State University. Libraries, 1994) Maciejewski, Anthony A., author; Khawaja, Khalid W., author; Bouman, Charles Addison, author; Tretter, Daniel, author; IEEE, publisher
In this paper we develop a general multiscale stochastic object detection algorithm for use in an automated inspection application. Information from a CAD model is used to initialize the object model and guide the training phase of the algorithm. An object is represented as a stochastic tree, where each node of the tree is associated with one of the various object components used to locate and identify the part. During the training phase a number of model parameters are estimated from a set of training images, some of which are generated from the CAD model. The algorithm then uses a fast multiscale search strategy to locate and identify the subassemblies making up the object tree. We demonstrate the performance of the algorithm on a typical mechanical assembly.
Open Access
A clarification of the index of refraction of beta-iron disilicide
(Colorado State University. Libraries, 1988) Bost, M. C., author; Mahan, John E., author; American Institute of Physics, publisher
Previously published values of the index of refraction of beta-iron disilicide are corrected. Based on improved measurements and analysis, the undispersed value of the refractive index is 5.6. The previously published analysis of the absorption coefficient showed that the material possesses a direct forbidden energy gap of approximately 0.87 eV. The type of the transition is unchanged, but the band-gap value is slightly shifted to 0.89 eV.
Open Access
A clustered yield model for SMT boards and MCM's
(Colorado State University. Libraries, 1995) Chen, Tom W., author; Tegethoff, Mick M. V., author; IEEE, publisher
This paper describes a clustered yield model for complex surface mount technology (SMT) assemblies and multichip modules (MCM's). Based on yield modeling techniques that have been proven in the manufacturing of integrated circuits (IC's), this model uses the negative binomial distribution of defects to calculate board yield after test. Manufacturing data validates that this model accurately predicts the clustering of defects and the yield predictions are significantly better than traditional binomial models.
Open Access
A comparative study of five parallel genetic algorithms using the traveling salesman problem
(Colorado State University. Libraries, 1998) Roychowdhury, Vwani P., author; Siegel, Howard Jay, author; Maciejewski, Anthony A., author; Wang, Lee, author; IEEE, publisher
Parallel genetic algorithms (PGAs) have been developed to reduce the large execution times that are associated with serial genetic algorithms (SGAs). They have also been used to solve larger problems and to find better solutions. In this paper, a comparative analysis of five different coarse-grained PGAs is conducted using the traveling salesman problem as the basis of this case study. To make fair comparisons, all of these PGAs are based on the same baseline SGA, implemented on the same parallel machine (IBM SP2), tested on the same set of traveling salesman problem instances, and started from the same set of initial populations. As a result of the experiments conducted in this study, a particular PGA that combines a new subtour technique with a known migration approach is identified to be the best for the traveling salesman problem among the five PGAs being compared.
Open Access
A comparison of eigendecomposition for sets of correlated images at different resolutions
(Colorado State University. Libraries, 2003) Roberts, Rodney G., author; Maciejewski, Anthony A., author; Saitwal, Kishor, author; IEEE, publisher
Eigendecomposition is a common technique that is performed on sets of correlated images in a number of computer vision and robotics applications. Unfortunately, the computation of an eigendecomposition can become prohibitively expensive when dealing with very high resolution images. While reducing the resolution of the images will reduce the computational expense, it is not known how this will affect the quality of the resulting eigendecomposition. The work presented here proposes a framework for quantifying the effects of varying the resolution of images on the eigendecomposition that is computed from those images. Preliminary results show that an eigendecomposition from low-resolution images may be nearly as effective in some applications as those from high-resolution images.
Open Access
A comparison of two methods for choosing repeatable control strategies for kinematically redundant manipulators
(Colorado State University. Libraries, 1992) Maciejewski, Anthony A., author; Roberts, Rodney G., author; IEEE, publisher
A kinematically redundant manipulator is a robotic system that has more than the minimum number of degrees of freedom that are required for a specified task. Due to this additional freedom, control strategies may yield solutions which are not repeatable in the sense that the manipulator may not return to its initial joint configuration for closed end effector paths. This paper presents two methods for choosing repeatable control strategies which minimize their distance from a non-repeatable inverse with desirable properties. The first method minimizes the integral norm of the difference of the desired inverse and a repeatable inverse. While this is the more appropriate criterion, it results in a difficult optimization. The second method, which minimizes the distance of the null vectors associated with the desired and the repeatable inverses, is somewhat easier to implement. As an illustrative example the pseudoinverse is approximated in a region of the joint space using both techniques.
Open Access
A computational feasibility study of failure-tolerant path planning
(Colorado State University. Libraries, 2004) Maciejewski, Anthony A., author; Jamisola, Rodrigo S., author; Roberts, Rodney G., author; American Nuclear Society, publisher
This work considers the computational costs associated with the implementation of a failure-tolerant path planning algorithm proposed in [1]. The algorithm makes the following assumptions: a manipulator is redundant relative to its task, only a single joint failure occurs at any given time, the manipulator is capable of detecting a joint failure and immediately locks the failed joint, and the environment is static and known. The algorithm is evaluated on a three degree-of-freedom planar manipulator for a total of eleven thousand different scenarios, randomly varying the robot's start and goal positions and the number and locations of obstacles in the environment. Statistical data are presented related to the computation time required by the different steps of the algorithm as a function of the complexity of the environment.
Open Access
A description of the CSU–CHILL National Radar Facility
(Colorado State University. Libraries, 2000) Bowie, Robert K., author; Mueller, E. A., author; Chandrasekar, V., author; Rutledge, Steven A., author; Kennedy, Patrick C., author; Bringi, V. N., author; Brunkow, David, author; American Meteorological Society, publisher
The subject of this paper is the Colorado State University-University of Chicago-Illinois State Water Survey (CSU-CHILL) National Radar Facility's S-band polarimetric research radar. Key features of this system include polarization agility (provided by the dual-transmitter, dual-receiver design), a recently updated signal processor, and a low (-34 dB, two way) integrated cross-polar ratio (ICPR2) antenna system. After reviewing the technical description of the radar, the authors present a new differential reflectivity (ZDR) calibration technique and data examples collected in different polarization modes. Although the CSU-CHILL radar is transportable, it can also be operated in a dual-Doppler configuration with the CSU-Pawnee radar, an 11-cm Doppler radar system situated 48 km north of the CSU-CHILL Greeley field site. Used together, these radars provide three-dimensional kinematic and hydrometeor information in precipitating cloud systems.
Open Access
A different mirror
(Colorado State University. Libraries, 1994) Schneider, Richard P., author; Lear, Kevin L., author; Gourley, Paul L., author; IEEE, publisher
Mirrors grown in the crystalline structure ease manufacture of vertical-cavity lasers, which emit collimated circular beams and can form large two-dimensional arrays. The authors discuss the fabrication of the surface emitting laser mirrors. By means of techniques such as molecular beam epitaxy and metal-organic vapor phase epitaxy, hundreds of layers of semiconductor materials can be grown one on top of the other. By mixing and matching the materials to create "designer" alloys, it is possible to grow a crystalline structure with all the electrical and optical properties desired for its various parts. This method of tailoring semiconductor structures is called bandgap engineering. The principles of the mirrors and their applications are discussed.
Open Access
A fast learning algorithm for Gabor transformation
(Colorado State University. Libraries, 1996) Ibrahim, Ayman, author; Azimi-Sadjadi, Mahmood R., author; IEEE, publisher
An adaptive learning approach for the computation of the coefficients of the generalized nonorthogonal 2-D Gabor transform representation is introduced in this correspondence. The algorithm uses a recursive least squares (RLS) type algorithm. The aim is to achieve minimum mean squared error for the reconstructed image from the set of the Gabor coefficients. The proposed RLS learning offers better accuracy and faster convergence behavior when compared with the least mean squares (LMS)-based algorithms. Applications of this scheme in image data reduction are also demonstrated.
Open Access
A full-plane block Kalman filter for image restoration
(Colorado State University. Libraries, 1992) Citrin, Stuart, author; Azimi-Sadjadi, Mahmood R., author; IEEE, publisher
A new two-dimensional (2-D) block Kalman filtering method is presented which uses a full-plane image model to generate a more accurate filtered estimate of an image that has been corrupted by additive noise and full-plane blur. Causality is maintained within the filtering process by employing multiple concurrent block estimators. In addition, true state dynamics are preserved, resulting in an accurate Kalman gain matrix. Simulation results on a test image corrupted by additive white Gaussian noise are presented for various image models and compared to those of the previous block Kalman filtering methods.
Open Access
A global motion planner for curve-tracing robots
(Colorado State University. Libraries, 1994) Neidigk, David D., author; Maciejewski, Anthony A., author; Chen, Pang C., author; Hwang, Yong K., author; IEEE, publisher
We present a global motion planner for tracing curves in three dimensions with robot manipulator tool frames. This planner generates an efficient motion satisfying three types of constraints: constraints on the tool tip for curve tracing, robot kinematic constraints and robot link collision constraints. Motions are planned using a global search algorithm and a local planner based on a potential-field approach. This planner can be used with any robots including redundant manipulators, and can control the trade-offs between its algorithmic completeness and computation time. It can be applied in many robotic tasks such as seam welding, caulking, edge deburring and chamfering, and is expected to reduce motion programming times from days to minutes.
Open Access
A least-squares-based 2-D filtering scheme for stereo image compression
(Colorado State University. Libraries, 2000) Tian, Bin, author; Azimi-Sadjadi, Mahmood R., author; Seo, Sang-Hoon, author; IEEE, publisher
A two-dimensional (2-D) least squares (LS)-based filtering scheme for high fidelity stereo image compression applications is introduced in this correspondence. This method removes the effects of mismatching in a stereo image pair by applying the left image as the reference input to a 2-D transversal filter while the right image is used as the desired output. The weights of the filter are computed using a block-based LS method. A reduced order filtering scheme is also introduced to find the optimum number of filter coefficients. The principal coefficients and the disparity vectors are used together with left image to reconstruct the right image at the receiver. The proposed schemes were examined on a real stereo image pair for 3DTV applications and the results were benchmarked against those of the block-matching method.
Open Access
A local measure of fault tolerance for kinematically redundant manipulators
(Colorado State University. Libraries, 1996) Maciejewski, Anthony A., author; Roberts, Rodney G., author; IEEE, publisher
When a manipulator suffers a joint failure, its performance can be significantly affected. If the failed joint is locked, the resulting manipulator Jacobian is given by the original Jacobian, except that the column associated with the failed joint is removed. The rank of the resulting Jacobian then determines if the manipulator still has the ability to perform arbitrary end-effector motions. Unfortunately, even at an operating configuration that has a relatively high manipulability index, a joint failure may still result in a singular Jacobian. This work examines the problem of determining the reduced manipulability of a manipulator after one or more joint failures. Configurations that result in a minimal reduction of the manipulability index for any set of joint failures are determined.
Open Access
A methodology for estimating the parameters of a gamma raindrop size distribution model from polarimetric radar data: application to a squall-line event from the TRMM/Brazil campaign
(Colorado State University. Libraries, 2002) Bringi, V. N., author; Chandrasekar, V., author; Huang, Gwo-Jong, author; Gorgucci, E., author; American Meteorological Society, publisher
A methodology is proposed for estimating the parameters of a gamma raindrop size distribution model from radar measurements of Zh, Zdr, and Kdp at S band. Previously developed algorithms by Gorgucci et al. are extended to cover low rain-rate events where both Zdr and Kdp are noisy. Polarimetric data from the S band Dual-Polarization Doppler Radar (S-Pol) during the Tropical Rainfall Measuring Mission (TRMM)/Brazil campaign are analyzed; specifically, the gamma parameters are retrieved for samples of convective and trailing stratiform rain during the 15 February 1999 squall-line event. Histograms of Nw and Do are retrieved from radar for each rain type and compared with related statistics reported in the literature. The functional behavior of Nw and Do versus rain rate retrieved from radar is compared against samples of 2D-video and RD-69 disdrometer data obtained during the campaign. The time variation of Nw, Do, and μ averaged over a 5 km × 5 km area (within which a network of gauges and a profiler were situated) is shown to illustrate temporal changes associated with the gamma parameters as the squall line passed over the network. The gauge-derived areal rainfall over the network is compared against radar using the areal ϕdp method, and the concept of an effective slope of a linear axis ratio versus diameter model is shown to significantly reduce the bias in radar-derived rainfall accumulation.
Open Access
A methodology for exploiting concurrency among independent tasks in partitionable parallel processing systems
(Colorado State University. Libraries, 1993) Siegel, Howard J., author; Maciejewski, Anthony A., author; Nation, Wayne G., author; Academic Press, publisher
One benefit of partitionable parallel processing systems is their ability to execute multiple, independent tasks simultaneously. Previous work has identified conditions such that, when there are tasks to be processed, partitioning the system so that all k tasks are processed simultaneously results in a minimum overall execution time. An alternate condition is developed that provides additional insight into the effects of parallelism on execution time. This result and previous results, however, assume that execution times are data independent. It is shown that data-dependent tasks do not necessarily execute faster when processed simultaneously even if the condition is met. A model is developed that provides for the possible variability of a task's execution time and is used in a new framework to study the problem of finding an optimal mapping for identical, independent data-dependent execution time tasks onto partitionable systems. Executing one, some, or all of the k tasks simultaneously is considered. Because this new framework is general, it can also serve as a new method for the study of data-independent tasks. Extension of this framework to situations where the k tasks are nonidentical is discussed.