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  • ItemOpen 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.
  • ItemOpen Access
    Wavefront improvement in an injection-seeded soft x-ray laser based on a solid-target plasma amplifier
    (Colorado State University. Libraries, 2013-10-15) Li, Lu, author; Wang, Yong, author; Wang, Shoujun, author; Oliva, Eduardo, author; Yin, Liang, author; Le, T. T. Thuy, author; Daboussi, Sameh, author; Ros, David, author; Maynard, Gilles, author; Sebban, Stephane, author; Hu, Bitao, author; Rocca, Jorge J, author; Zeitoun, Philippe, author; Optical Society of America, publisher
    The wavefront of an injection-seeded soft x-ray laser beam generated by amplification of high-harmonic pulses in a λ=18.9 nm molybdenum plasma amplifier was measured by a Hartmann wavefront sensor with an accuracy of λ/32 root mean square (rms). A significant improvement in wavefront aberrations of 0.51±0.03λ rms to 0.23±0.01λ rms was observed as a function of plasma column length. The variation of wavefront characteristic as a function time delay between the injection of the seed and peak of soft x-ray amplifier pump was studied. The measurements were used to reconstruct the soft x-ray source and confirm its high peak brightness.
  • ItemOpen Access
    Plasmoid ejection and secondary current sheet generation from magnetic reconnection in laser-plasma interaction
    (Colorado State University. Libraries, 2012-05-25) Dong, Quan-Li, author; Wang, Shou-Jun, author; Lu, Quan-Ming, author; Huang, Can, author; Yuan, Da-Wei, author; Liu, Xun, author; Lin, Xiao-Xuan, author; Li, Yu-Tong, author; Wei, Hui-Gang, author; Zhong, Jia-Yong, author; Shi, Jian-Rong, author; Jiang, Shao-En, author; Ding, Yong-Kun, author; Jiang, Bo-Bin, author; Du, Kai, author; He, Xian-Tu, author; Yu, M. Y., author; Liu, C. S., author; Wang, Shui, author; Tang, Yong-Jian, author; Zhu, Jian-Qiang, author; Zhao, Gang, author; Sheng, Zheng-Ming, author; Zhang, Jie, author; American Physical Society, publisher
    Reconnection of the self-generated magnetic fields in laser-plasma interaction was first investigated experimentally by Nilson et al. [Phys. Rev. Lett. 97, 255001 (2006)] by shining two laser pulses a distance apart on a solid target layer. An elongated current sheet (CS) was observed in the plasma between the two laser spots. In order to more closely model magnetotail reconnection, here two side-by-side thin target layers, instead of a single one, are used. It is found that at one end of the elongated CS a fanlike electron outflow region including three well-collimated electron jets appears. The (>1 MeV) tail of the jet energy distribution exhibits a power-law scaling. The enhanced electron acceleration is attributed to the intense inductive electric field in the narrow electron dominated reconnection region, as well as additional acceleration as they are trapped inside the rapidly moving plasmoid formed in and ejected from the CS. The ejection also induces a secondary CS.
  • ItemOpen Access
    Single-shot soft x-ray laser linewidth measurement using a grating interferometer
    (Colorado State University. Libraries, 2013-12-01) Wang, Y., author; Yin, L., author; Wang, S., author; Marconi, M. C., author; Dunn, J., author; Gullikson, E., author; Rocca, J. J., author; Optical Society of America, publisher
    The linewidth of a 14.7 nm wavelength Ni-like Pd soft x-ray laser was measured in a single shot using a soft x-ray diffraction grating interferometer. The instrument uses the time delay introduced by the gratings across the beam to measure the temporal coherence. The spectral linewidth of the 4d1S0-4p1P1 Ni-like Pd lasing line was measured to be Δλ/λ=3×10-5 from the Fourier transform of the fringe visibility. This single shot linewidth measurement technique provides a rapid and accurate way to determine the temporal coherence of soft x-ray lasers that can contribute to the development of femtosecond plasma-based soft x-ray lasers.
  • ItemOpen Access
    Characteristic measurements of silicon dioxide aerogel plasmas generated in a Planckian radiation environment
    (Colorado State University. Libraries, 2010-01-06) Dong, Quan-Li, author; Wang, Shou-Jun, author; Li, Yu-Tong, author; Zhang, Yi, author; Zhao, Jing, author; Wei, Hui-Gang, author; Shi, Jian-Rong, author; Zhao, Gang, author; Zhang, Ji-Yan, author; Gu, Yu-Qiu, author; Ding, Yong-Kun, author; Wen, Tian-Shu, author; Zhang, Wen-Hai, author; Hu, Xin, author; Liu, Shen-Ye, author; Zhang, Lin, author; Tang, Yong-Jian, author; Zhang, Bao-Han, author; Zheng, Zhi-Jian, author; Nishimura, Hiroaki, author; Fujioka, Shinsuke, author; Wang, Fei-Lu, author; Takabe, Hideaki, author; Zhang, Jie, author; American Institute of Physics, publisher
    The temporally and spatially resolved characteristics of silicon dioxide aerogel plasmas were studied using x-ray spectroscopy. The plasma was generated in the near-Planckian radiation environment within gold hohlraum targets irradiated by laser pulses with a total energy of 2.4 kJ in 1 ns. The contributions of silicon ions at different charge states to the specific components of the measured absorption spectra were also investigated. It was found that each main feature in the absorption spectra of the measured silicon dioxide aerogel plasmas was contributed by two neighboring silicon ionic species.
  • ItemOpen Access
    Efficient picosecond x-ray pulse generation from plasmas in the radiation dominated regime
    (Colorado State University. Libraries, 2017-10-27) Hollinger, Reed, author; Bargsten, Clayton, author; Shlyaptsev, Vyacheslav N., author; Kaymak, Vural, author; Pukhov, Alexander, author; Capeluto, Maria Gabriela, author; Wang, Shoujun, author; Rockwood, Alex, author; Wang, Yong, author; Townsend, Amanda, author; Prieto, Amy, author; Stockton, Patrick, author; Curtis, Alden, author; Rocca, Jorge J., author; Optical Society of America, publisher
    The efficient conversion of optical laser light into bright ultrafast x-ray pulses in laser created plasmas is of high interest for dense plasma physics studies, material science, and other fields. However, the rapid hydrodynamic expansion that cools hot plasmas has limited the x-ray conversion efficiency (CE) to 1% or less. Here we demonstrate more than one order of magnitude increase in picosecond x-ray CE by tailoring near solid density plasmas to achieve a large radiative to hydrodynamic energy loss rate ratio, leading into a radiation loss dominated plasma regime. A record 20% CE into hν > 1 keV photons was measured in arrays of large aspect ratio Au nanowires heated to keV temperatures with ultrahigh contrast femtosecond laser pulses of relativistic intensity. The potential of these bright ultrafast x-ray point sources for table-top imaging is illustrated with single shot flash radiographs obtained using low laser pulse energy. These results will enable the deployment of brighter laser driven x-ray sources at both compact andlarge laser facilities.
  • ItemOpen Access
    Micro-scale fusion in dense relativistic nanowire array plasmas
    (Colorado State University. Libraries, 2018-03-14) Curtis, Alden, author; Calvi, Chase, author; Tinsley, James, author; Hollinger, Reed, author; Kaymak, Vural, author; Pukhov, Alexander, author; Wang, Shoujun, author; Rockwood, Alex, author; Wang, Yong, author; Shlyaptsev, Vyacheslav N., author; Rocca, Jorge J., author; Nature Research, publisher
    Nuclear fusion is regularly created in spherical plasma compressions driven by multi-kilojoule pulses from the world’s largest lasers. Here we demonstrate a dense fusion environment created by irradiating arrays of deuterated nanostructures with joule-level pulses from a compact ultrafast laser. The irradiation of ordered deuterated polyethylene nanowires arrays with femtosecond pulses of relativistic intensity creates ultra-high energy density plasmas in which deuterons (D) are accelerated up to MeV energies, efficiently driving D–D fusion reactions and ultrafast neutron bursts. We measure up to 2 × 106 fusion neutrons per joule, an increase of about 500 times with respect to flat solid targets, a record yield for joule-level lasers. Moreover, in accordance with simulation predictions, we observe a rapid increase in neutron yield with laser pulse energy. The results will impact nuclear science and high energy density research and can lead to bright ultrafast quasi-monoenergetic neutron point sources for imaging and materials studies.
  • ItemOpen 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.
  • ItemOpen Access
    Compact gain-saturated x-ray lasers down to 6.85 nm and amplification down to 5.85 nm
    (Colorado State University. Libraries, 2018-03-02) Rockwood, Alex, author; Wang, Yong, author; Wang, Shoujun, author; Berrill, Mark, author; Shlyaptsev, Vyacheslav N., author; Rocca, Jorge J., author; Optical Society of America, publisher
    Plasma-based x-ray lasers allow single-shot nano-scale imaging and other experiments requiring a large number of photons per pulse to be conducted in compact facilities. However, compact repetitively fired gain-saturated x-ray lasers have been limited to wavelengths above λ = 8.85 nm. Here we extend their range to λ = 6.85 nm by transient traveling wave excitation of Ni-like Gd ions in a plasma created with an optimized pre-pulse followed by rapid heating with an intense sub-picosecond pump pulse. Isoelectronic scaling also produced strong lasing at 6.67 nm and 6.11 nm in Ni-like Tb and amplification at 6.41 nm and 5.85 nm in Ni-like Dy. This scaling to shorter wavelengths was obtained by progressively increasing the pump pulse grazing incidence angle to access increased plasma densities. We experimentally demonstrate that the optimum grazing incidence angle increases linearly with atomic number from 17 deg for Z = 42 (Mo) to 43 deg for Z = 66 (Dy). The results will enable applications of sub-7 nm lasers at compact facilities.
  • ItemOpen Access
    Accurate characterization of winter precipitation using multi-angle snowflake camera, visual hull, advanced scattering methods and polarimetric radar
    (Colorado State University. Libraries, 2016-06-11) Notaroš, Branislav M., author; Bringi, Viswanathan N., author; Kleinkort, Cameron, author; Kennedy, Patrick, author; Huang, Gwo-Jong, author; Thurai, Merhala, author; Newman, Andrew J., author; Bang, Wonbae, author; Lee, GyuWon, author; MDPI, publisher
    This article proposes and presents a novel approach to the characterization of winter precipitation and modeling of radar observables through a synergistic use of advanced optical disdrometers for microphysical and geometrical measurements of ice and snow particles (in particular, a multi-angle snowflake camera-MASC), image processing methodology, advanced method-of-moments scattering computations, and state-of-the-art polarimetric radars. The article also describes the newly built and established MASCRAD (MASC + Radar) in-situ measurement site, under the umbrella of CSU-CHILL Radar, as well as the MASCRAD project and 2014/2015 winter campaign. We apply a visual hull method to reconstruct 3D shapes of ice particles based on high-resolution MASC images, and perform "particle-by-particle" scattering computations to obtain polarimetric radar observables. The article also presents and discusses selected illustrative observation data, results, and analyses for three cases with widely-differing meteorological settings that involve contrasting hydrometeor forms. Illustrative results of scattering calculations based on MASC images captured during these events, in comparison with radar data, as well as selected comparative studies of snow habits from MASC, 2D video-disdrometer, and CHILL radar data, are presented, along with the analysis of microphysical characteristics of particles. In the longer term, this work has potential to significantly improve the radar-based quantitative winter-precipitation estimation.
  • ItemOpen Access
    A study of cloud classification with neural networks using spectral and textural features
    (Colorado State University. Libraries, 1999) Bian, Bin, author; Shaikh, Mukhtiar A., author; Azimi-Sadjadi, Mahmood R., author; Vonder Haar, Thomas H., author; Reinke, Donald L., author; IEEE, publisher
    The problem of cloud data classification from satellite imagery using neural networks is considered in this paper. Several image transformations such as singular value decomposition(SVD) and wavelet packet (WP) were used to extract the salient spectral and textural features attributed to satellite cloud data in both visible and infrared (IR) channels. In addition, the well-known gray-level cooccurrence matrix (GLCM) method and spectral features were examined for the sake of comparison. Two different neural-network paradigms namely probability neural network (PNN) and unsupervised Kohonen self-organized feature map (SOM) were examined and their performance were also benchmarked on the geostationary operational environmental satellite (GOES) 8 data. Additionally, a postprocessing scheme was developed which utilizes the contextual information in the satellite images to improve the final classification accuracy. Overall, the performance of the PNN when used in conjunction with these feature extraction and postprocessing schemes showed the potential of this neural-network-based cloud classification system.
  • ItemOpen Access
    Real-time SVD for the control of redundant robotic manipulators
    (Colorado State University. Libraries, 1989) Maciejewski, Anthony A., author; IEEE, publisher
    By taking advantage of the well-behaved nature of singular values and vectors, the computational expense of determining the SVD of the Jacobian matrix can be reduced to such an extent that on-line calculation becomes feasible. This permits more intelligent use of the extra degrees of freedom present with redundant manipulators, particularly with respect to the optimization of various secondary criteria, including obstacle avoidance, under the constraint of a specified end effector trajectory.
  • ItemOpen Access
    Identifying the failure-tolerant workspace boundaries of a kinematically redundant manipulator
    (Colorado State University. Libraries, 2007) Roberts, Rodney G., author; Jamisola, Rodrigo S., author; Maciejewski, Anthony A., author; IEEE, publisher
    In addition to possessing a number of other important properties, kinematically redundant manipulators are inherently more tolerant to locked-joint failures than nonredundant manipulators. However, a joint failure can still render a kinematically redundant manipulator useless if the manipulator is poorly designed or controlled. This paper presents a method for identifying a region of the workspace of a redundant manipulator for which task completion is guaranteed in the event of a locked-joint failure. The existence of such a region, called a failure-tolerant workspace, will be guaranteed by imposing a suitable set of artificial joint limits prior to a failure. Conditions are presented that characterize end-effector locations in this region. Based on these conditions, a method is presented that identifies the boundaries of the failure-tolerant workspace. Optimized failure-tolerant workspaces for a three degree-of-freedom planar robot are presented.
  • ItemOpen Access
    Using genetic algorithms to optimize social robot behavior for improved pedestrian flow
    (Colorado State University. Libraries, 2005) Eldridge, Bryce D., author; Maciejewski, Anthony A., author; IEEE, publisher
    This paper expands on previous research on the effect of introducing social robots into crowded situations in order to improve pedestrian flow. In this case, a genetic algorithm is applied to find the optimal parameters for the interaction model between the robots and the people. Preliminary results indicate that adding social robots to a crowded situation can result in significant improvement in pedestrian flow. Using the optimized values of the model parameters as a guide, these robots can be designed to be more effective at improving the pedestrian flow. While this work only applies to one situation, the technique presented can be applied to a wide variety of scenarios.
  • ItemOpen Access
    A path planning strategy for kinematically redundant manipulators anticipating joint failures in the presence of obstacles
    (Colorado State University. Libraries, 2003) Jamisola, Rodrigo S., author; Maciejewski, Anthony A., author; Roberts, Rodney G., author; IEEE, publisher
    This work considers the failure tolerant operation of a kinematically redundant manipulator in an environment containing obstacles. In particular, the article addresses the problem of planning a collision-free path for a manipulator operating in a static environment such that the manipulator can reach its desired goal despite a single locked-joint failure and the presence of obstacles in the environment. A method is presented that searches for a continuous obstacle-free space between the starting configuration and the desired final end-effector position which is characterized in the joint space by the goal self-motion manifold. This method guarantees completion of critical tasks in the event of a single locked-joint failure in the presence of obstacles.
  • ItemOpen Access
    Eigendecomposition of correlated images characterized by three parameters
    (Colorado State University. Libraries, 2006) Saitwal, Kishor, author; Maciejewski, Anthony A., author; Roberts, Rodney G., author; IEEE, publisher
    Most eigendecomposition algorithms operate on correlated images that are characterized by only one parameter. Hence they lack the required specifications of fully general 3D image data sets, in which the images need to be characterized by three parameters. In this paper, an extension of one of the fastest known eigendecomposition algorithms is successfully implemented to improve the computational efficiency of computing the eigendecomposition of such 3D image sets. This algorithm can be used in pattern recognition applications such as fully general 3D pose estimation of objects.
  • ItemOpen Access
    The effect of spatial resolution reduction techniques on the temporal properties of video sequences
    (Colorado State University. Libraries, 2005) Saitwal, Kishor, author; Maciejewski, Anthony A., author; Roberts, Rodney G., author; IEEE, publisher
    Singular value decomposition (SVD) is a common technique that is performed on video sequences in a number of computer vision and robotics applications. The left singular vectors represent the eigenimages, while the right singular vectors represent the temporal properties of the video sequence. It is obvious that spatial reduction techniques affect the left singular vectors, however, the extent of their effect on the right singular vectors is not clear. Understanding how the right singular vectors are affected is important because many SVD algorithms rely on computing them as an intermediate step to computing the eigenimages. The work presented here quantifies the effects of different spatial resolution reduction techniques on the right singular vectors that are computed from those video sequences. Examples show that using random sampling for spatial resolution reduction rather than a low-pass filtering technique results in less perturbation of the temporal properties.
  • ItemOpen Access
    A simulation of attempts to influence crowd dynamics
    (Colorado State University. Libraries, 2003) Kirkland, Joel A., author; Maciejewski, Anthony A., author; IEEE, publisher
    An understanding of how to alter crowd dynamics would have a significant impact in a number of scenarios, e.g., during riots or evacuations. The social force model, where individuals are self-driven particles interacting through social and physical forces, is one approach that has been used to describe crowd dynamics. This work uses the framework of the social force model to study the effects of introducing autonomous robots into crowds. Two simple pedestrian flow problems are used as illustrative examples, namely flow in varying width hallways and lane formation in bidirectional pedestrian flow. Preliminary results indicate that robots capable of inducing an attractive social force are effective at improving pedestrian flow in both of these scenarios.
  • ItemOpen Access
    Analysis of eigendecomposition for sets of correlated images at different resolutions
    (Colorado State University. Libraries, 2004) Saitwal, Kishor, author; Maciejewski, Anthony A., author; Roberts, Rodney G., 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 gives the theoretical background for quantifying the effects of varying the resolution of images on the eigendecomposition that is computed from those images. A computationally efficient algorithm for this eigendecomposition is proposed using derived analytical expressions. Examples show that this algorithm performs very well on arbitrary video sequences.
  • ItemOpen Access
    Fast eigenspace decomposition of correlated images using their low-resolution properties
    (Colorado State University. Libraries, 2004) Saitwal, Kishor, author; Maciejewski, Anthony A., author; Roberts, Rodney G., 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 a priori how this will affect the quality of the resulting eigendecomposition. The work presented here provides an analysis of how different resolution reduction techniques affect the eigendecomposition. A computationally efficient algorithm for calculating the eigendecomposition based on this analysis is proposed. Examples show that this algorithm performs very well on arbitrary video sequences.