Artykuły w czasopismach na temat „Spatial jitter”
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Khademi, Fatemeh, Chih-Yang Chen i Ziad M. Hafed. "Visual feature tuning of superior colliculus neural reafferent responses after fixational microsaccades". Journal of Neurophysiology 123, nr 6 (1.06.2020): 2136–53. http://dx.doi.org/10.1152/jn.00077.2020.
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Despite being diminutive, microsaccades still jitter retinal images. We investigated how such jitter affects superior colliculus (SC) activity. We found that SC neurons exhibit short-latency visual reafferent bursts after microsaccades. These bursts reflect not only the spatial luminance profiles of visual patterns but also how such profiles are shifted by eye movement size and direction. These results indicate that the SC continuously represents visual patterns, even as they are jittered by the smallest possible saccades.
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Nagasako, Elna, Robert Boyd i Girish Saran Agarwal. "Vacuum-induced jitter in spatial solitons". Optics Express 3, nr 5 (31.08.1997): 171. http://dx.doi.org/10.1364/oe.3.000171.
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WANG, WENQIN. "CLOCK TIMING JITTER ANALYSIS AND COMPENSATION FOR BISTATIC SYNTHETIC APERTURE RADAR SYSTEMS". Fluctuation and Noise Letters 07, nr 03 (wrzesień 2007): L341—L350. http://dx.doi.org/10.1142/s0219477507003982.
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Bistatic synthetic aperture radar (SAR) operates with distinct transmit and receive antennas that are mounted on separate platforms. Such a spatial separation has several operational advantages, which will increase the capability, reliability and flexibility of future SAR missions. However, this configuration results that there is no cancelation of low frequency oscillator noise as in the monostatic cases. As a consequence, high accurate time synchronization or clock timing jitter compensation must be provided. Literature search reveals little time synchronization work for bistatic SAR has been reported. As such, the use of a new range alignment algorithm to quantify and compensate clock timing jitter is proposed. The impact of clock timing jitter on bistatic SAR is analyzed, and the performance of the proposed algorithm is evaluated. Simulation results show that successful clock timing jitter compensation for bistatic SAR is achieved by using the proposed algorithm.
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Shinohara, K., K. Fukuda i K. Uchikawa. "Jitter detection exceeds spatial frequency limit of the visual system". Journal of Vision 11, nr 11 (23.09.2011): 1186. http://dx.doi.org/10.1167/11.11.1186.
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Watson, Lynne M., Niall C. Strang, Fraser Scobie, Gordon D. Love, Dirk Seidel i Velitchko Manahilov. "Image Jitter Enhances Visual Performance when Spatial Resolution Is Impaired". Investigative Opthalmology & Visual Science 53, nr 10 (6.09.2012): 6004. http://dx.doi.org/10.1167/iovs.11-9157.
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Gripeos, Panagiotis J., Hector E. Nistazakis, Andreas D. Tsigopoulos, Vasilis Christofilakis i Evgenia Roditi. "Time and Spatial Jitter Influence on the Performance of FSO Links with DF Relays and OC Diversity Over Turbulence Channels". Photonics 8, nr 8 (7.08.2021): 318. http://dx.doi.org/10.3390/photonics8080318.
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FSO communication is a viral technology among optical wireless communications, gathering the interest of both researchers and manufacturers. This is because of the many advantages associated with FSO communication, including high data rates, reliability, safety, and economy. However, there are several unavoidable drawbacks that shadow the performance of FSO systems. For example, atmospheric turbulence is a well-known problem related to the weather conditions of the channel, which causes the scintillation effect. Also, spatial jitter due to pointing errors is a critical factor of the link’s performance, caused by occasional misalignments between the transmitter and the receiver. Moreover, time jitter is another limiting agent that deteriorates the total throughput, inducing bit stream misdetections, caused by the arrival of out-of-sync pulses. All three effects have been exhaustively studied and many statistical models and interesting solutions have been proposed in the literature to estimate their magnitude and compensate for their impact. In this work, the turbulence effect was treated by Málaga distribution, the spatial jitter effect was regulated by the non-zero boresight model, and the time jitter effect was modeled by the generalized Gaussian distribution. Various modulation schemes were studied, along with DF multi-hop and optimal combining diversity techniques at the receiver’s end. New, accurate mathematical expressions of average BER performance have been obtained, and valuable conclusions were drawn thanks to the presented numerical results.
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Franz, Marcel, Moritz M. Nickel, Alexander Ritter, Wolfgang H. R. Miltner i Thomas Weiss. "Somatosensory spatial attention modulates amplitudes, latencies, and latency jitter of laser-evoked brain potentials". Journal of Neurophysiology 113, nr 7 (kwiecień 2015): 2760–68. http://dx.doi.org/10.1152/jn.00070.2015.
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Several studies provided evidence that the amplitudes of laser-evoked potentials (LEPs) are modulated by attention. However, previous reports were based on across-trial averaging of LEP responses at the expense of losing information about intertrial variability related to attentional modulation. The aim of this study was to investigate the effects of somatosensory spatial attention on single-trial parameters (i.e., amplitudes, latencies, and latency jitter) of LEP components (N2 and P2). Twelve subjects participated in a sustained spatial attention paradigm while noxious laser stimuli (left hand) and noxious electrical stimuli (right hand) were sequentially delivered to the dorsum of the respective hand with nonnoxious air puffs randomly interspersed within the sequence of noxious stimuli. Participants were instructed to mentally count all stimuli (i.e., noxious and nonnoxious) applied to the attended location. Laser stimuli, presented to the attended hand (ALS), elicited larger single-trial amplitudes of the N2 component compared with unattended laser stimuli (ULS). In contrast, single-trial amplitudes of the P2 component were not significantly affected by spatial attention. Single-trial latencies of the N2 and P2 were significantly smaller for ALS vs. ULS. Additionally, the across-trial latency jitter of the N2 component was reduced for ALS. Conversely, the latency jitter of the P2 component was smaller for ULS compared with ALS. With the use of single-trial analysis, the study provided new insights into brain dynamics of LEPs related to spatial attention. Our results indicate that single-trial parameters of LEP components are differentially modulated by spatial attention.
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Guo, Ru Hai, Kui Shi, Jun Ma, Run Qiang Jiang i Shuai Bei Yu. "Built-Up Alignment System by Four-Quadrant Detector in High Power Laser System". Key Engineering Materials 552 (maj 2013): 415–19. http://dx.doi.org/10.4028/www.scientific.net/kem.552.415.
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Spatial stability is an important property of a laser beam for a laser system. Because four-quadrant detector has more high damage threshold than CCD, it can be applied in a high laser system to monitor the direction of laser beam. In this article, the four-quadrant detector as pointing monitor device is used for a 532nm semiconductor laser, which can obtain the center position of laser spot quickly. In the experiment, the amount of shift and jitter for laser beam is measured at first. Next step is combining rotating stage and lens to measure the alignment error for three angles. The results show that the top amount of shift and jitter is 3.6″ and the average of combined pointing error is around 6″. The data can support the spatial beam pointing stability system which needs feedback system with fast steering mirrors.
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Sutton, S. S., A. K. Boyd, R. L. Kirk, D. Cook, J. W. Backer, A. Fennema, R. Heyd, A. S. McEwen i S. D. Mirchandani. "CORRECTING SPACECRAFT JITTER IN HIRISE IMAGES". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-3/W1 (25.07.2017): 141–48. http://dx.doi.org/10.5194/isprs-archives-xlii-3-w1-141-2017.
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Mechanical oscillations or vibrations on spacecraft, also called pointing jitter, cause geometric distortions and/or smear in high resolution digital images acquired from orbit. Geometric distortion is especially a problem with pushbroom type sensors, such as the High Resolution Imaging Science Experiment (HiRISE) instrument on board the Mars Reconnaissance Orbiter (MRO). Geometric distortions occur at a range of frequencies that may not be obvious in the image products, but can cause problems with stereo image correlation in the production of digital elevation models, and in measuring surface changes over time in orthorectified images. The HiRISE focal plane comprises a staggered array of fourteen charge-coupled devices (CCDs) with pixel IFOV of 1 microradian. The high spatial resolution of HiRISE makes it both sensitive to, and an excellent recorder of jitter. We present an algorithm using Fourier analysis to resolve the jitter function for a HiRISE image that is then used to update instrument pointing information to remove geometric distortions from the image. Implementation of the jitter analysis and image correction is performed on selected HiRISE images. Resulting corrected images and updated pointing information are made available to the public. Results show marked reduction of geometric distortions. This work has applications to similar cameras operating now, and to the design of future instruments (such as the Europa Imaging System).
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Wang, Shengxiang, Jianhong Liu, Yinghao Li, Jian Chen, Yong Guan i Lei Zhu. "Jitter correction for transmission X-ray microscopy via measurement of geometric moments". Journal of Synchrotron Radiation 26, nr 5 (19.08.2019): 1808–14. http://dx.doi.org/10.1107/s1600577519008865.
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Transmission X-ray microscopes (TXMs) have become one of the most powerful tools for imaging 3D structures of nano-scale samples using the computed tomography (CT) principle. As a major error source, sample jitter caused by mechanical instability of the rotation stage produces shifted 2D projections, from which reconstructed images contain severe motion artifacts. In this paper, a jitter correction algorithm is proposed, that has high accuracy and computational efficiency for TXM experiments with or without nano-particle markers. Geometric moments (GMs) are measured on segmented projections for each angle and fitted to sinusoidal curves in the angular direction. Sample jitter is estimated from the difference between the measured and the fitted GMs for image correction. On a digital phantom, the proposed method removes jitter errors at different noise levels. Physical experiments on chlorella cells show that the proposed GM method achieves better spatial resolution and higher computational efficiency than the re-projection method, a state-of-the-art algorithm using iterative correction. It even outperforms the approach of manual alignment, the current gold standard, on faithfully maintaining fine structures on the CT images. Our method is practically attractive in that it is computationally efficient and lowers experimental costs in current TXM studies without using expensive nano-particles markers.
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Dimitrov, Alexander G., Melissa A. Sheiko, Jonathan Baker i Shih-Cheng Yen. "Spatial and temporal jitter distort estimated functional properties of visual sensory neurons". Journal of Computational Neuroscience 27, nr 3 (8.04.2009): 309–19. http://dx.doi.org/10.1007/s10827-009-0144-8.
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Torta, Diana M. E. "Understanding the mechanisms through which spatial attention acts on nociception". Journal of Neurophysiology 114, nr 5 (listopad 2015): 2561–63. http://dx.doi.org/10.1152/jn.00450.2015.
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Previous studies have shown that spatial attention can influence the magnitude of brain responses to nociceptive inputs. In their recent article (Franz M, Nickel MM, Ritter A, Miltner WH, Weiss T. J Neurophysiol 113: 2760–2768, 2015), Franz and colleagues expand this observation by showing that spatial attention is further able to modify the chronometry of nociceptive processing by modulating the latency and temporal jitter of the recorded responses. The mechanisms through which attention could possibly modulate nociceptive processing are discussed here, with a particular focus on novel findings and future perspectives.
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Girod, Luc, Christopher Nuth i Andreas Kääb. "GLACIER VOLUME CHANGE ESTIMATION USING TIME SERIES OF IMPROVED ASTER DEMS". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B8 (23.06.2016): 489–94. http://dx.doi.org/10.5194/isprsarchives-xli-b8-489-2016.
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Volume change data is critical to the understanding of glacier response to climate change. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) system embarked on the Terra (EOS AM-1) satellite has been a unique source of systematic stereoscopic images covering the whole globe at 15m resolution and at a consistent quality for over 15 years. While satellite stereo sensors with significantly improved radiometric and spatial resolution are available to date, the potential of ASTER data lies in its long consistent time series that is unrivaled, though not fully exploited for change analysis due to lack of data accuracy and precision. Here, we developed an improved method for ASTER DEM generation and implemented it in the open source photogrammetric library and software suite MicMac. The method relies on the computation of a rational polynomial coefficients (RPC) model and the detection and correction of cross-track sensor jitter in order to compute DEMs. ASTER data are strongly affected by attitude jitter, mainly of approximately 4 km and 30 km wavelength, and improving the generation of ASTER DEMs requires removal of this effect. Our sensor modeling does not require ground control points and allows thus potentially for the automatic processing of large data volumes. <br><br> As a proof of concept, we chose a set of glaciers with reference DEMs available to assess the quality of our measurements. We use time series of ASTER scenes from which we extracted DEMs with a ground sampling distance of 15m. Our method directly measures and accounts for the cross-track component of jitter so that the resulting DEMs are not contaminated by this process. Since the along-track component of jitter has the same direction as the stereo parallaxes, the two cannot be separated and the elevations extracted are thus contaminated by along-track jitter. Initial tests reveal no clear relation between the cross-track and along-track components so that the latter seems not to be easily modeled analytically from the first one. We thus remove the remaining along-track jitter effects in the DEMs statistically through temporal DEM stacks to finally compute the glacier volume changes over time. Our method yields cleaner and spatially more complete elevation data, which also proved to be more in accordance to reference DEMs, compared to NASA’s AST14DMO DEM standard products. <br><br> The quality of the demonstrated measurements promises to further unlock the underused potential of ASTER DEMs for glacier volume change time series on a global scale. The data produced by our method will help to better understand the response of glaciers to climate change and their influence on runoff and sea level.
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Girod, Luc, Christopher Nuth i Andreas Kääb. "GLACIER VOLUME CHANGE ESTIMATION USING TIME SERIES OF IMPROVED ASTER DEMS". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B8 (23.06.2016): 489–94. http://dx.doi.org/10.5194/isprs-archives-xli-b8-489-2016.
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Volume change data is critical to the understanding of glacier response to climate change. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) system embarked on the Terra (EOS AM-1) satellite has been a unique source of systematic stereoscopic images covering the whole globe at 15m resolution and at a consistent quality for over 15 years. While satellite stereo sensors with significantly improved radiometric and spatial resolution are available to date, the potential of ASTER data lies in its long consistent time series that is unrivaled, though not fully exploited for change analysis due to lack of data accuracy and precision. Here, we developed an improved method for ASTER DEM generation and implemented it in the open source photogrammetric library and software suite MicMac. The method relies on the computation of a rational polynomial coefficients (RPC) model and the detection and correction of cross-track sensor jitter in order to compute DEMs. ASTER data are strongly affected by attitude jitter, mainly of approximately 4 km and 30 km wavelength, and improving the generation of ASTER DEMs requires removal of this effect. Our sensor modeling does not require ground control points and allows thus potentially for the automatic processing of large data volumes. <br><br> As a proof of concept, we chose a set of glaciers with reference DEMs available to assess the quality of our measurements. We use time series of ASTER scenes from which we extracted DEMs with a ground sampling distance of 15m. Our method directly measures and accounts for the cross-track component of jitter so that the resulting DEMs are not contaminated by this process. Since the along-track component of jitter has the same direction as the stereo parallaxes, the two cannot be separated and the elevations extracted are thus contaminated by along-track jitter. Initial tests reveal no clear relation between the cross-track and along-track components so that the latter seems not to be easily modeled analytically from the first one. We thus remove the remaining along-track jitter effects in the DEMs statistically through temporal DEM stacks to finally compute the glacier volume changes over time. Our method yields cleaner and spatially more complete elevation data, which also proved to be more in accordance to reference DEMs, compared to NASA’s AST14DMO DEM standard products. <br><br> The quality of the demonstrated measurements promises to further unlock the underused potential of ASTER DEMs for glacier volume change time series on a global scale. The data produced by our method will help to better understand the response of glaciers to climate change and their influence on runoff and sea level.
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Watten, Reidulf G., Svein Magnussen i Mark W. Greenlee. "Spatial-Frequency Discrimination, Brain Lateralisation, and Acute Intake of Alcohol". Perception 27, nr 6 (czerwiec 1998): 729–36. http://dx.doi.org/10.1068/p270729.
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The effect of alcohol (breath-alcohol level of 0.1%) on perceptual discrimination of low (1.5 cycles deg−1) and high (8 cycles deg−1) spatial frequencies in the left and right visual field was measured in eighteen right-handed males, in a double-blind, balanced placebo design. Discrimination thresholds for briefly (180 ms) presented sinusoidal gratings were determined by two-alternative forced-choice judgments with four interleaving psychophysical staircases providing random trial-to-trial variation of reference spatial frequency and visual field, in addition to a random (±10%) jitter of reference spatial frequency. Alcohol produced overall higher discrimination thresholds but did not alter the visual-field balance: no main effect of visual field was observed, but in both placebo and alcohol conditions spatial frequency interacted with visual field in the direction predicted by the spatial-frequency hypothesis of hemispheric asymmetry in visual-information processing, with left-visual-field/right-hemisphere superiority in discrimination of low spatial frequencies and right-visual-field/left-hemisphere superiority in discrimination of high spatial frequencies.
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Yang, Jie, Markus Guehr, Theodore Vecchione, Matthew S. Robinson, Renkai Li, Nick Hartmann, Xiaozhe Shen i in. "Femtosecond gas phase electron diffraction with MeV electrons". Faraday Discussions 194 (2016): 563–81. http://dx.doi.org/10.1039/c6fd00071a.
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We present results on ultrafast gas electron diffraction (UGED) experiments with femtosecond resolution using the MeV electron gun at SLAC National Accelerator Laboratory. UGED is a promising method to investigate molecular dynamics in the gas phase because electron pulses can probe the structure with a high spatial resolution. Until recently, however, it was not possible for UGED to reach the relevant timescale for the motion of the nuclei during a molecular reaction. Using MeV electron pulses has allowed us to overcome the main challenges in reaching femtosecond resolution, namely delivering short electron pulses on a gas target, overcoming the effect of velocity mismatch between pump laser pulses and the probe electron pulses, and maintaining a low timing jitter. At electron kinetic energies above 3 MeV, the velocity mismatch between laser and electron pulses becomes negligible. The relativistic electrons are also less susceptible to temporal broadening due to the Coulomb force. One of the challenges of diffraction with relativistic electrons is that the small de Broglie wavelength results in very small diffraction angles. In this paper we describe the new setup and its characterization, including capturing static diffraction patterns of molecules in the gas phase, finding time-zero with sub-picosecond accuracy and first time-resolved diffraction experiments. The new device can achieve a temporal resolution of 100 fs root-mean-square, and sub-angstrom spatial resolution. The collimation of the beam is sufficient to measure the diffraction pattern, and the transverse coherence is on the order of 2 nm. Currently, the temporal resolution is limited both by the pulse duration of the electron pulse on target and by the timing jitter, while the spatial resolution is limited by the average electron beam current and the signal-to-noise ratio of the detection system. We also discuss plans for improving both the temporal resolution and the spatial resolution.
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Androutsos, Nistazakis, Khalid, Muhammad i Tombras. "Serial DF Relayed FSO Links over Mixture Gamma Turbulence Channels and Nonzero Boresight Spatial Jitter". Computation 7, nr 3 (5.07.2019): 34. http://dx.doi.org/10.3390/computation7030034.
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Over the past few years, terrestrial free space optical (FSO) communication systems have demonstrated increasing research and commercial interest. However, due the signal’s propagation path, the operation of FSO links depends strongly on atmospheric conditions and related phenomena. One such significant phenomenon is the scintillation caused by atmospheric turbulence effects; in order to address the significant performance degradation that this causes, several statistical models have been proposed. Here, turbulence-induced fading of the received optical signal is investigated through the recently presented mixture Gamma distribution, which accurately describes the irradiance fluctuations at the receiver’s input of the FSO link. Additionally, at the same time, it significantly reduces the mathematical complexity of the expressions used for the description of composite channels with turbulence along with nonzero boresight pointing error-induced fading. In order to counterbalance the performance mitigation due to these effects, serial decode-and-forward relays are employed, and the performance of the system is estimated through derived mathematical expressions.
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Watanabe, Masataka, Andreas Bartels, Jakob H. Macke, Yusuke Murayama i Nikos K. Logothetis. "Temporal Jitter of the BOLD Signal Reveals a Reliable Initial Dip and Improved Spatial Resolution". Current Biology 23, nr 21 (listopad 2013): 2146–50. http://dx.doi.org/10.1016/j.cub.2013.08.057.
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Wei, Ming Zhe, i Wan Wei Tang. "The Design of Real-Time and High-Speed Video Processing Platform for Aerial UAV Based on DM642". Advanced Materials Research 1061-1062 (grudzień 2014): 1186–89. http://dx.doi.org/10.4028/www.scientific.net/amr.1061-1062.1186.
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With the rapid development of aerial UAV (Unmanned Aerial Vehicle), the design of real-time data acquisition and transmission system for the video signal has a new applied field. It is different from traditional video acquisition and processing system, aerial video signal has the problems of screen jitter and spatial interference. The processing algorithm of aerial UAV airborne video signal is put forward in the paper, and the platform of high speed procession is constructed based on chip TMS320DM642, and get a good effect.
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Kiasaleh, Kamran. "Statistical Profile of Hermite–Gaussian Beam in the Presence of Residual Spatial Jitter in FSO Communications". IEEE Communications Letters 20, nr 4 (kwiecień 2016): 656–59. http://dx.doi.org/10.1109/lcomm.2016.2517624.
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Androutsos, Nikolaos A., Hector E. Nistazakis, Efstratios V. Chatzikontis, Argyris N. Stassinakis i George S. Tombras. "Spatial Jitter Influence on the Average BLER Performance of SIMO FSO Links over Atmospheric Turbulence Channels". Electronics 10, nr 16 (22.08.2021): 2033. http://dx.doi.org/10.3390/electronics10162033.
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In the recent years, Free Space Optics (FSO) technology has attracted significant research and commercial interest mostly because of its many advantages in comparison with other radio systems used for point-to-point connections. However, the reliable operation of these systems significantly depends on the conditions of the atmosphere in the area in which the optical beam propagates. The most important of these conditions are atmospheric turbulence and the misalignment between the optical beam and the receiver, which is also known as the pointing errors effect. In this work, in order to obviate the performance mitigation caused by these phenomena, we examined the most widely accepted and one of the most effective techniques, i.e., the implementation of receivers’ diversity. Various metrics have been investigated to evaluate the performance of such systems, but most of them do not take into account that the ultra-fast modern optical communication systems use blocks of bits for the transmission and codes for the detection and/or correction of erroneous bits. Thus, by taking these aspects into account, in this work, we investigated the combined impact of spatial jitter and atmospheric turbulence on the total average block error rate of an optical wireless system with receivers’ diversity. Novel closed-form analytical formulas were derived.
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Varotsos, G. K., H. E. Nistazakis, K. Aidinis, F. Jaber i K. K. Mujeeb Rahman. "Transdermal subcarrier L-PSK or DBPSK optical wireless links with time diversity, skin attenuation and spatial jitter". Journal of Modern Optics 67, nr 14 (15.08.2020): 1233–40. http://dx.doi.org/10.1080/09500340.2020.1825848.
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Xie, Jing, Erik Stensrud i Torbjørn Skramstad. "Detection-Based Object Tracking Applied to Remote Ship Inspection". Sensors 21, nr 3 (23.01.2021): 761. http://dx.doi.org/10.3390/s21030761.
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We propose a detection-based tracking system for automatically processing maritime ship inspection videos and predicting suspicious areas where cracks may exist. This system consists of two stages. Stage one uses a state-of-the-art object detection model, i.e., RetinaNet, which is customized with certain modifications and the optimal anchor setting for detecting cracks in the ship inspection images/videos. Stage two is an enhanced tracking system including two key components. The first component is a state-of-the-art tracker, namely, Channel and Spatial Reliability Tracker (CSRT), with improvements to handle model drift in a simple manner. The second component is a tailored data association algorithm which creates tracking trajectories for the cracks being tracked. This algorithm is based on not only the intersection over union (IoU) of the detections and tracking updates but also their respective areas when associating detections to the existing trackers. Consequently, the tracking results compensate for the detection jitters which could lead to both tracking jitter and creation of redundant trackers. Our study shows that the proposed detection-based tracking system has achieved a reasonable performance on automatically analyzing ship inspection videos. It has proven the feasibility of applying deep neural network based computer vision technologies to automating remote ship inspection. The proposed system is being matured and will be integrated into a digital infrastructure which will facilitate the whole ship inspection process.
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KOZMA, PETRA, i LYNNE KIORPES. "Contour integration in amblyopic monkeys". Visual Neuroscience 20, nr 5 (wrzesień 2003): 577–88. http://dx.doi.org/10.1017/s0952523803205113.
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Amblyopia is characterized by losses in a variety of aspects of spatial vision, such as acuity and contrast sensitivity. Our goal was to learn whether those basic spatial deficits lead to impaired global perceptual processing in strabismic and anisometropic amblyopia. This question is unresolved by the current human psychophysical literature. We studied contour integration and contrast sensitivity in amblyopic monkeys. We found deficient contour integration in anisometropic as well as strabismic amblyopic monkeys. Some animals showed poor contour integration in the fellow eye as well as in the amblyopic eye. Orientation jitter of the elements in the contour systematically decreased contour-detection ability for control and fellow eyes, but had less effect on amblyopic eyes. The deficits were not clearly related to basic losses in contrast sensitivity and acuity for either type of amblyopia. We conclude that abnormal contour integration in amblyopes reflects disruption of mechanisms that are different from those that determine acuity and contrast sensitivity, and are likely to be central to V1.
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Shinohara, Koichiro, Kazuho Fukuda i Keiji Uchikawa. "P1-29: Banding Detection Exceeds Spatial Frequency Limit of the Visual System by Single Frequency Grating and Jitter". i-Perception 3, nr 9 (październik 2012): 643. http://dx.doi.org/10.1068/if643.
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Muzalevsky, I., V. Chudoba, S. Belogurov, O. Kiselev, A. Bezbakh, A. Fomichev, S. Krupko i in. "NeuRad detector prototype pulse shape study". EPJ Web of Conferences 177 (2018): 03003. http://dx.doi.org/10.1051/epjconf/201817703003.
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The EXPERT setup located at the Super-FRS facility, the part of the FAIR complex in Darmstadt, Germany, is intended for investigation of properties of light exotic nuclei. One of its modules, the high granularity neutron detector NeuRad assembled from a large number of the scintillating fiber is intended for registration of neutrons emitted by investigated nuclei in low-energy decays. Feasibility of the detector strongly depends on its timing properties defined by the spatial distribution of ionization, light propagation inside the fibers, light emission kinetics and transition time jitter in the multi-anode photomultiplier tube. The first attempt of understanding the pulse formation in the prototype of the NeuRad detector by comparing experimental results and Monte Carlo (MC) simulations is reported in this paper.
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Pensyl, William Russell, Tran C. T. Qui, Pei Fang Hsin, Shang Ping Lee i Daniel K. Jernigan. "Large Area Robust Hybrid Tracking with Life-size Avatar in Mixed Reality Environment for Cultural and Historical Installation". International Journal of Virtual Reality 8, nr 2 (1.01.2009): 13–18. http://dx.doi.org/10.20870/ijvr.2009.8.2.2719.
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We have developed a system which enables us to track participant-observers accurately in a large area for the purpose of immersing them in a mixed reality environment. This system is robust even under uncompromising lighting conditions. Accurate tracking of the observer�s spatial and orientation point of view is achieved by using hybrid inertial sensors and computer vision techniques. We demonstrate our results by presenting a life-size, animated human avatar sitting in a real chair, in a stable and low-jitter manner. The system installation allows the observers to freely walk around and navigate themselves in the environment even while still being able to see the avatar from various angles. The project installation provides an exciting way for cultural and historical narratives to be presented vividly in the real present world.
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Ninos, M. P., H. E. Nistazakis i G. S. Tombras. "On the BER performance of FSO links with multiple receivers and spatial jitter over gamma-gamma or exponential turbulence channels". Optik 138 (czerwiec 2017): 269–79. http://dx.doi.org/10.1016/j.ijleo.2017.03.009.
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Pan, Rui, Ekaterina Zapolnova, Torsten Golz, Aleksandar J. Krmpot, Mihailo D. Rabasovic, Jovana Petrovic, Vivek Asgekar i in. "Photon diagnostics at the FLASH THz beamline". Journal of Synchrotron Radiation 26, nr 3 (26.04.2019): 700–707. http://dx.doi.org/10.1107/s1600577519003412.
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The THz beamline at FLASH, DESY, provides both tunable (1–300 THz) narrow-bandwidth (∼10%) and broad-bandwidth intense (up to 150 uJ) THz pulses delivered in 1 MHz bursts and naturally synchronized with free-electron laser X-ray pulses. Combination of these pulses, along with the auxiliary NIR and VIS ultrashort lasers, supports a plethora of dynamic investigations in physics, material science and biology. The unique features of the FLASH THz pulses and the accelerator source, however, bring along a set of challenges in the diagnostics of their key parameters: pulse energy, spectral, temporal and spatial profiles. Here, these challenges are discussed and the pulse diagnostic tools developed at FLASH are presented. In particular, a radiometric power measurement is presented that enables the derivation of the average pulse energy within a pulse burst across the spectral range, jitter-corrected electro-optical sampling for the full spectro-temporal pulse characterization, spatial beam profiling along the beam transport line and at the sample, and a lamellar grating based Fourier transform infrared spectrometer for the on-line assessment of the average THz pulse spectra. Corresponding measurement results provide a comprehensive insight into the THz beamline capabilities.
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Salama i Saatchi. "Evaluation of Wirelessly Transmitted Video Quality Using a Modular Fuzzy Logic System". Technologies 7, nr 3 (14.09.2019): 67. http://dx.doi.org/10.3390/technologies7030067.
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Video transmission over wireless computer networks is increasingly popular as new applications emerge and wireless networks become more widespread and reliable. An ability to quantify the quality of a video transmitted using a wireless computer network is important for determining network performance and its improvement. The process requires analysing the images making up the video from the point of view of noise and associated distortion as well as traffic parameters represented by packet delay, jitter and loss. In this study a modular fuzzy logic based system was developed to quantify the quality of video transmission over a wireless computer network. Peak signal to noise ratio, structural similarity index and image difference were used to represent the user's quality of experience (QoE) while packet delay, jitter and percentage packet loss ratio were used to represent traffic related quality of service (QoS). An overall measure of the video quality was obtained by combining QoE and QoS values. Systematic sampling was used to reduce the number of images processed and a novel scheme was devised whereby the images were partitioned to more sensitively localize distortions. To further validate the developed system, a subjective test involving 25 participants graded the quality of the received video. The image partitioning significantly improved the video quality evaluation. The subjective test results correlated with the developed fuzzy logic approach. The video quality assessment developed in this study was compared against a method that uses spatial efficient entropic differencing and consistent results were observed. The study indicated that the developed fuzzy logic approaches could accurately determine the quality of a wirelessly transmitted video.
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Álvarez, Inés, Ignasi Furió, Julián Proenza i Manuel Barranco. "Design and Experimental Evaluation of the Proactive Transmission of Replicated Frames Mechanism over Time-Sensitive Networking". Sensors 21, nr 3 (23.01.2021): 756. http://dx.doi.org/10.3390/s21030756.
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In recent years the Time-Sensitive Networking (TSN) Task Group (TG) has been working on proposing a series of standards to provide Ethernet with hard real-time guarantees, online management of the traffic and fault tolerance mechanisms. In this way the TG expects to create the network technology of future novel applications with real-time and reliability requirements. TSN proposes using spatial redundancy to increase the reliability of Ethernet networks, but using spatial redundancy to tolerate temporary faults is not a cost-effective solution. For this reason, we propose to use time redundancy to tolerate temporary faults in the links of TSN-based networks. Specifically, we have proposed the Proactive Transmission of Replicated Frames (PTRF) mechanism, which consists in transmitting several copies of each frame in a preventive manner. In this article we present for the first time a detailed description of the mechanism, with the three different approaches we have designed. We also present the implementation of PTRF in a real TSN prototype. Furthermore, we carry out a qualitative comparison of the different approaches of the mechanism and we experimentally evaluate the approaches of the mechanism in a quantitative manner from three perspectives: the end-to-end delay, the jitter and the bandwidth consumption.
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Zhu, Y., S. Jin, Y. Tian i M. Wang. "ROI-ORIENTATED SENSOR CORRECTION BASED ON VIRTUAL STEADY REIMAGING MODEL FOR WIDE SWATH HIGH RESOLUTION OPTICAL SATELLITE IMAGERY". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-2/W7 (12.09.2017): 587–92. http://dx.doi.org/10.5194/isprs-archives-xlii-2-w7-587-2017.
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To meet the requirement of high accuracy and high speed processing for wide swath high resolution optical satellite imagery under emergency situation in both ground processing system and on-board processing system. This paper proposed a ROI-orientated sensor correction algorithm based on virtual steady reimaging model for wide swath high resolution optical satellite imagery. Firstly, the imaging time and spatial window of the ROI is determined by a dynamic search method. Then, the dynamic ROI sensor correction model based on virtual steady reimaging model is constructed. Finally, the corrected image corresponding to the ROI is generated based on the coordinates mapping relationship which is established by the dynamic sensor correction model for corrected image and rigours imaging model for original image. Two experimental results show that the image registration between panchromatic and multispectral images can be well achieved and the image distortion caused by satellite jitter can be also corrected efficiently.
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Eitan, O., G. Kosa i Y. Yovel. "Sensory gaze stabilization in echolocating bats". Proceedings of the Royal Society B: Biological Sciences 286, nr 1913 (16.10.2019): 20191496. http://dx.doi.org/10.1098/rspb.2019.1496.
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Sensing from a moving platform is challenging for both man-made machines and animals. Animals' heads jitter during movement, so if the sensors they carry are not stabilized, any spatial estimation might be biased. Flying animals, like bats, seriously suffer from this problem because flapping flight induces rapid changes in acceleration which moves the body up and down. For echolocating bats, the problem is crucial. Because they emit a sound to sense the world, an unstable head means sound energy pointed in the wrong direction. It is unknown how bats mitigate this problem. By tracking the head and body of flying fruit bats, we show that they stabilize their heads, accurately maintaining a fixed acoustic-gaze relative to a target. Bats can solve the stabilization task even in complete darkness using only echo-based information. Moreover, the bats point their echolocation beam below the target and not towards it, a strategy that should result in better estimations of target elevation.
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Ali, Ali Mohd, Mahmoud Dhimish, Malek M. Alsmadi i Peter Mather. "Algorithmic Identification of the Best WLAN Protocol and Network Architecture for Internet-Based Applications". Journal of Information & Knowledge Management 19, nr 01 (marzec 2020): 2040011. http://dx.doi.org/10.1142/s0219649220400110.
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This research developed a novel algorithm to evaluate internet-based services such as VoIP, Video Conferencing, HTTP and FTP, of different IEEE 802.11 technologies in order to identify the optimum network architecture among Basic Service Set (BSS), Extended Service Set (ESS) and the Independent Basic Service Set (IBSS). The proposed algorithm will yield the rank order of different IEEE 802.11 technologies. By selecting the optimum network architecture and technology, the best overall network performance that provides good voice, video and data quality is guaranteed. Furthermore, it meets the acceptance threshold values for the VoIP, Video Conferencing, HTTP and FTP quality metrics. This algorithm was applied to various room sizes ranging from [Formula: see text][Formula: see text]m to [Formula: see text][Formula: see text]m and the number of nodes ranged from 1 to 65. The spatial distributions considered were circular, uniform and random. The Quality of Service (QoS) metrics used were delay, jitter, throughput and packet loss.
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Hamer, Russell D., i Anthony M. Norcia. "The Jitter Spatial Frequency Sweep VEP: A new paradigm to study spatiotemporal development of pattern- and motion-processing mechanisms in human infants." Psychology & Neuroscience 2, nr 2 (lipiec 2009): 163–77. http://dx.doi.org/10.3922/j.psns.2009.2.008.
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Buonomano, Dean V. "A Learning Rule for the Emergence of Stable Dynamics and Timing in Recurrent Networks". Journal of Neurophysiology 94, nr 4 (październik 2005): 2275–83. http://dx.doi.org/10.1152/jn.01250.2004.
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Neural dynamics within recurrent cortical networks is an important component of neural processing. However, the learning rules that allow networks composed of hundreds or thousands of recurrently connected neurons to develop stable dynamical states are poorly understood. Here I use a neural network model to examine the emergence of stable dynamical states within recurrent networks. I describe a learning rule that can account both for the development of stable dynamics and guide networks to states that have been observed experimentally, specifically, states that instantiate a sparse code for time. Across trials, each neuron fires during a specific time window; by connecting the neurons to a hypothetical set of output units, it is possible to generate arbitrary spatial-temporal output patterns. Intertrial jitter of the spike time of a given neuron increases as a direct function of the delay at which it fires. These results establish a learning rule by which cortical networks can potentially process temporal information in a self-organizing manner, in the absence of specialized timing mechanisms.
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Maccarone, Aurora, Giulia Acconcia, Ulrich Steinlehner, Ivan Labanca, Darryl Newborough, Ivan Rech i Gerald S. Buller. "Custom-Technology Single-Photon Avalanche Diode Linear Detector Array for Underwater Depth Imaging". Sensors 21, nr 14 (16.07.2021): 4850. http://dx.doi.org/10.3390/s21144850.
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We present an optical depth imaging system suitable for highly scattering underwater environments. The system used the time-correlated single-photon counting (TCSPC) technique and the time-of-flight approach to obtain depth profiles. The single-photon detection was provided by a linear array of single-photon avalanche diode (SPAD) detectors fabricated in a customized silicon fabrication technology for optimized efficiency, dark count rate, and jitter performance. The bi-static transceiver comprised a pulsed laser diode source with central wavelength 670 nm, a linear array of 16 × 1 Si-SPAD detectors, with a dedicated TCSPC acquisition module. Cylindrical lenses were used to collect the light scattered by the target and image it onto the sensor. These laboratory-based experiments demonstrated single-photon depth imaging at a range of 1.65 m in highly scattering conditions, equivalent up to 8.3 attenuation lengths between the system and the target, using average optical powers of up to 15 mW. The depth and spatial resolution of this sensor were investigated in different scattering conditions.
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Kayser, Christoph, Rodrigo F. Salazar i Peter König. "Responses to Natural Scenes in Cat V1". Journal of Neurophysiology 90, nr 3 (wrzesień 2003): 1910–20. http://dx.doi.org/10.1152/jn.00195.2003.
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Studies on processing in primary visual areas often use artificial stimuli such as bars or gratings. As a result, little is known about the properties of activity patterns for the natural stimuli processed by the visual system on a daily basis. Furthermore, in the cat, a well-studied model system for visual processing, most results are obtained from anesthetized subjects and little is known about neuronal activations in the alert animal. Addressing these issues, we measure local field potentials (lfp) and multiunit spikes in the primary visual cortex of awake cats. We compare changes in the lfp power spectra and multiunit firing rates for natural movies, movies with modified spatio-temporal correlations as well as gratings. The activity patterns elicited by drifting gratings are qualitatively and quantitatively different from those elicited by natural stimuli and this difference arises from both spatial as well as temporal properties of the stimuli. Furthermore, both local field potentials and multiunit firing rates are most sensitive to the second-order statistics of the stimuli and not to their higher-order properties. Finally, responses to natural movies show a large variability over time because of activity fluctuations induced by rapid stimulus motion. We show that these fluctuations are not dependent on the detailed spatial properties of the stimuli but depend on their temporal jitter. These fluctuations are important characteristics of visual activity under natural conditions and impose limitations on the readout of possible differences in mean activity levels.
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SAUL, ALAN B. "Effects of fixational saccades on response timing in macaque lateral geniculate nucleus". Visual Neuroscience 27, nr 5-6 (8.10.2010): 171–81. http://dx.doi.org/10.1017/s0952523810000258.
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AbstractEven during active fixation, small eye movements persist that might be expected to interfere with vision. Numerous brain mechanisms probably contribute to discounting this jitter. Changes in the timing of responses in the visual thalamus associated with fixational saccades are considered in this study. Activity of single neurons in alert monkey lateral geniculate nucleus (LGN) was recorded during fixation while pseudorandom visual noise stimuli were presented. The position of the stimulus on the display monitor was adjusted based on eye position measurements to control for changes in retinal locations due to eye movements. A method for extracting nonstationary first-order response mechanisms was applied, so that changes around the times of saccades could be observed. Saccade-related changes were seen in both amplitude and timing of geniculate responses. Amplitudes were greatly reduced around saccades. Timing was retarded slightly during a window of about 200 ms around saccades. That is, responses became more sustained. These effects were found in both parvocellular and magnocellular neurons. Timing changes in LGN might play a role in maintaining cortical responses to visual stimuli in the presence of eye movements, compensating for the spatial shifts caused by saccades via these shifts in timing.
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Jackson, M. C., R. D. Long, D. Lee i N. J. Freeman. "Development of X-ray streak camera electronics at AWRE". Laser and Particle Beams 4, nr 1 (luty 1986): 145–56. http://dx.doi.org/10.1017/s0263034600001695.
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The paper reviews a number of X-ray streak cameras developed at AWRE. These cameras are used to provide temporal and one-dimensional spatial or spectral information on X-rays emitted from laser produced plasmas. Two of these cameras have been designed to be combined with other diagnostic instrumentation; one with a Wolter X-ray microscope (×22 magnification) and the other with a Bragg diffraction crystal spectrometer. This latter instrument provides a few eV spectral resolution and ∼15 ps temporal resolution; a typical experimental application at the AWRE HELEN laser facility will be described. The paper describes the circuitry of the bipolar avalanche transistor ramp generator used to drive the streak plates of the cameras. Improvements to this include: (a) increasing the fastest streak rate to ∼10 ps mm−1 by a distributed capacitance network across each of the bipolar stacks of transistors, and (b) reducing the trigger jitter to approximately ±10 ps by the use of a new mix of transistors in the stack and a Raytheon RS 3500 avalanche transistor. Additional improvements have now been added. These include a ‘half-scan’ user facility to aid initial camera timing and direct switching to select the sweep rate of the camera.
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Meinecke, C. "Texture Segmentation and the Familiarity Effect". Perception 26, nr 1_suppl (sierpień 1997): 265. http://dx.doi.org/10.1068/v970078.
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Texture segmentation performance is usually defined as being data-driven and bottom - up: visual features of the stimulus—like orientation differences between target and background texture elements—are then evaluated automatically. The question investigated in the experiments reported here is: Are there some hints that not only ‘pure visual features’ determine segmentation performance, but other factors like the familiarity of the stimulus material already exert an influence at these early stages of information processing? The familiarity effect is revealed by better performance when detecting an unfamiliar element embedded in familiar elements (eg an inverted letter ‘N’ among correct ‘N's) compared with the familiar element embedded in unfamiliar elements (see, eg, Frith, 1974 Perception & Psychophysics16 113 – 116). In a series of experiments, spatial and temporal factors of the stimulus conditions (eg density, jitter, display size, presentation time) have been varied, so as to determine the constraints under which the familiarity effect influences texture-segmentation performance. Results showed that the familiarity of texture elements had a rather strong influence on early visual processes. This influence disappeared only under very restricted display conditions (very short presentation time, very high density). This provides further information on which framing conditions are typical for data-driven early vision processes.
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Durant, Szonya, i Johannes M. Zanker. "Variation in the Local Motion Statistics of Real-Life Optic Flow Scenes". Neural Computation 24, nr 7 (lipiec 2012): 1781–805. http://dx.doi.org/10.1162/neco_a_00294.
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Optic flow motion patterns can be a rich source of information about our own movement and about the structure of the environment we are moving in. We investigate the information available to the brain under real operating conditions by analyzing video sequences generated by physically moving a camera through various typical human environments. We consider to what extent the motion signal maps generated by a biologically plausible, two-dimensional array of correlation-based motion detectors (2DMD) not only depend on egomotion, but also reflect the spatial setup of such environments. We analyzed the local motion outputs by extracting the relative amounts of detected directions and comparing the spatial distribution of the motion signals to that of idealized optic flow. Using a simple template matching estimation technique, we are able to extract the focus of expansion and find relatively small errors that are distributed in characteristic patterns in different scenes. This shows that all types of scenes provide suitable motion information for extracting ego motion despite the substantial levels of noise affecting the motion signal distributions, attributed to the sparse nature of optic flow and the presence of camera jitter. However, there are large differences in the shape of the direction distributions between different types of scenes; in particular, man-made office scenes are heavily dominated by directions in the cardinal axes, which is much less apparent in outdoor forest scenes. Further examination of motion magnitudes at different scales and the location of motion information in a scene revealed different patterns across different scene categories. This suggests that self-motion patterns are not only relevant for deducing heading direction and speed but also provide a rich information source for scene structure and could be important for the rapid formation of the gist of a scene under normal human locomotion.
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Harrison, Matthew T., Asohan Amarasingham i Wilson Truccolo. "Spatiotemporal Conditional Inference and Hypothesis Tests for Neural Ensemble Spiking Precision". Neural Computation 27, nr 1 (styczeń 2015): 104–50. http://dx.doi.org/10.1162/neco_a_00681.
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The collective dynamics of neural ensembles create complex spike patterns with many spatial and temporal scales. Understanding the statistical structure of these patterns can help resolve fundamental questions about neural computation and neural dynamics. Spatiotemporal conditional inference (STCI) is introduced here as a semiparametric statistical framework for investigating the nature of precise spiking patterns from collections of neurons that is robust to arbitrarily complex and nonstationary coarse spiking dynamics. The main idea is to focus statistical modeling and inference not on the full distribution of the data, but rather on families of conditional distributions of precise spiking given different types of coarse spiking. The framework is then used to develop families of hypothesis tests for probing the spatiotemporal precision of spiking patterns. Relationships among different conditional distributions are used to improve multiple hypothesis-testing adjustments and design novel Monte Carlo spike resampling algorithms. Of special note are algorithms that can locally jitter spike times while still preserving the instantaneous peristimulus time histogram or the instantaneous total spike count from a group of recorded neurons. The framework can also be used to test whether first-order maximum entropy models with possibly random and time-varying parameters can account for observed patterns of spiking. STCI provides a detailed example of the generic principle of conditional inference, which may be applicable to other areas of neurostatistical analysis.
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MILLER, J. A., K. S. DENNING, J. S. GEORGE, D. W. MARSHAK i G. T. KENYON. "A high frequency resonance in the responses of retinal ganglion cells to rapidly modulated stimuli: A computer model". Visual Neuroscience 23, nr 5 (wrzesień 2006): 779–94. http://dx.doi.org/10.1017/s0952523806230104.
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Brisk Y-type ganglion cells in the cat retina exhibit a high frequency resonance (HFR) in their responses to large, rapidly modulated stimuli. We used a computer model to test whether negative feedback mediated by axon-bearing amacrine cells onto ganglion cells could account for the experimentally observed properties of HFRs. Temporal modulation transfer functions (tMTFs) recorded from model ganglion cells exhibited HFR peaks whose amplitude, width, and locations were qualitatively consistent with experimental data. Moreover, the wide spatial distribution of axon-mediated feedback accounted for the observed increase in HFR amplitude with stimulus size. Model phase plots were qualitatively similar to those recorded from Y ganglion cells, including an anomalous phase advance that in our model coincided with the amplification of low-order harmonics that overlapped the HFR peak. When axon-mediated feedback in the model was directed primarily to bipolar cells, whose synaptic output was graded, or else when the model was replaced with a simple cascade of linear filters, it was possible to produce large HFR peaks but the region of anomalous phase advance was always eliminated, suggesting the critical involvement of strongly non-linear feedback loops. To investigate whether HFRs might contribute to visual processing, we simulated high frequency ocular tremor by rapidly modulating a naturalistic image. Visual signals riding on top of the imposed jitter conveyed an enhanced representation of large objects. We conclude that by amplifying responses to ocular tremor, HFRs may selectively enhance the processing of large image features.
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Ibrahim, R. A., V. N. Pilipchuk i T. Ikeda. "Recent Advances in Liquid Sloshing Dynamics". Applied Mechanics Reviews 54, nr 2 (1.03.2001): 133–99. http://dx.doi.org/10.1115/1.3097293.
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A liquid free surface in partially filled containers can experience a wide spectrum of motions such as planar, non-planar, rotational, quasi-periodic, chaotic, and disintegration. Civil engineers and seismologists have been studying liquid sloshing effects on large dams, oil tanks and elevated water towers under ground motion. Since the early 1960’s, the problem of liquid sloshing dynamics has been of major concern to aerospace engineers studying the influence of liquid propellant sloshing on the flight performance of jet vehicles. Since then, new areas of research activities have emerged. The modern theory of nonlinear dynamics has indeed promoted further studies and uncovered complex nonlinear phenomena. These include rotary sloshing, Faraday waves, nonlinear liquid sloshing interaction with elastic structures, internal resonance effects, stochastic sloshing dynamics, hydrodynamic sloshing impact dynamics, g-jitter under microgravity field, cross-waves, and spatial resonance. The dynamic stability of liquid gas tankers and ship cargo tankers, and liquid hydrodynamic impact loading are problems of current interest to the designers of such systems. This article will address the means of passive control of liquid sloshing and the use of liquid sloshing forces to control vibratory structures. Other important contributions include the development of digital computer codes to solve complex problems that were difficult to handle in the past. The purpose of this article is to review the research work developed in different applications. It will highlight the major achievements and results reported in the literature. Some early work will be cited very briefly in order to provide an updated bibliography of liquid sloshing dynamics. This review article contains 1,319 references.
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Straka, Małgorzata M., Samuel Schmitz i Hubert H. Lim. "Response features across the auditory midbrain reveal an organization consistent with a dual lemniscal pathway". Journal of Neurophysiology 112, nr 4 (15.08.2014): 981–98. http://dx.doi.org/10.1152/jn.00008.2014.
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The central auditory system has traditionally been divided into lemniscal and nonlemniscal pathways leading from the midbrain through the thalamus to the cortex. This view has served as an organizing principle for studying, modeling, and understanding the encoding of sound within the brain. However, there is evidence that the lemniscal pathway could be further divided into at least two subpathways, each potentially coding for sound in different ways. We investigated whether such an interpretation is supported by the spatial distribution of response features in the central nucleus of the inferior colliculus (ICC), the part of the auditory midbrain assigned to the lemniscal pathway. We recorded responses to pure tone stimuli in the ICC of ketamine-xylazine-anesthetized guinea pigs and used three-dimensional brain reconstruction techniques to map the location of the recording sites. Compared with neurons in caudal-and-medial regions within an isofrequency lamina of the ICC, neurons in rostral-and-lateral regions responded with shorter first-spike latencies with less spiking jitter, shorter durations of spiking responses, a higher proportion of spikes occurring near the onset of the stimulus, lower thresholds, and larger local field potentials with shorter latencies. Further analysis revealed two distinct clusters of response features located in either the caudal-and-medial or the rostral-and-lateral parts of the isofrequency laminae of the ICC. Thus we report substantial differences in coding properties in two regions of the ICC that are consistent with the hypothesis that the lemniscal pathway is made up of at least two distinct subpathways from the midbrain up to the cortex.
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Zhong, Qiang, Fazle Hussain i Harindra J. S. Fernando. "Quantification of turbulent mixing in colliding gravity currents". Journal of Fluid Mechanics 851 (19.07.2018): 125–47. http://dx.doi.org/10.1017/jfm.2018.488.
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Collision between two identical counterflowing gravity currents was studied in the laboratory with the goal of understanding the fundamental turbulent mixing physics of flow collisions in nature, for example katabatic flows and thunderstorm outflows. The ensuing turbulent mixing is a subgrid process in mesoscale forecasting models, and needs to be parameterized using eddy diffusivity. Laboratory gravity currents were generated by simultaneously removing two identical locks, located at both ends of a long rectangular tank, which separated dense and lighter water columns with free surfaces of the same depth $H$. The frontal velocity $u_{f}$ and the velocity and density fields of the gravity currents were monitored using time-resolved particle image velocimetry and planar laser-induced fluorescence imaging. Ensemble averaging of identical experimental realizations was used to compute turbulence statistics, after removing inherent jitter via phase alignment of successive data realizations by iteratively maximizing the cross-correlation of each realization with the ensemble average. Four stages of flow evolution were identified: initial (independent) propagation of gravity currents, their approach while influencing one another, collision and resulting updraughts, and postcollision slumping of collided fluid. The collision stage, in turn, involved three phases, and produced the strongest turbulent mixing as quantified by the rate of change of density. Phase I spanned $-0.2\leqslant tu_{f}/H<0.5$, where collision produced a rising density front (interface) with strong shear and intense turbulent kinetic energy production ($t$ is a suitably defined time coordinate such that gravity currents make the initial contact at $tu_{f}/H=-0.2$). In Phase II ($0.5\leqslant tu_{f}/H<1.2$), the interface was flat and calm with negligible vertical velocity. Phase III ($1.2\leqslant tu_{f}/H<2.8$) was characterized by slumping which led to hydraulic bores propagating away from the collision area. The measurements included root mean square turbulent velocities and their decay rates, interfacial velocity, rate of change of fluid-parcel density, and eddy diffusivity. These measures depended on the Reynolds number $Re$, but appeared to achieve Reynolds number similarity for $Re>3000$. The eddy diffusivity $K_{T}$, space–time averaged over the spatial extent ($H\times H$) and the lifetime ($t\approx 3H/u_{f}$) of collision, was $K_{T}/u_{f}H=0.0036$ for $Re>3000$, with the area $A$ of active mixing being $A/H^{2}=0.037$.
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Keller, Clifford H., i Terry T. Takahashi. "Representation of Temporal Features of Complex Sounds by the Discharge Patterns of Neurons in the Owl's Inferior Colliculus". Journal of Neurophysiology 84, nr 5 (1.11.2000): 2638–50. http://dx.doi.org/10.1152/jn.2000.84.5.2638.
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The spiking pattern evoked in cells of the owl's inferior colliculus by repeated presentation of the same broadband noise was found to be highly reproducible and synchronized with the temporal features of the noise stimulus. The pattern remained largely unchanged when the stimulus was presented from spatial loci that evoke similar average firing rates. To better understand this patterning, we computed the pre-event stimulus ensemble (PESE)—the average of the stimuli that preceded each spike. Computing the PESE by averaging the pressure waveforms produced a noisy, featureless trace, suggesting that the patterning was not synchronized to a particular waveform in the fine structure. By contrast, computing the PESE by averaging the stimulus envelope revealed an average envelope waveform, the “PESE envelope,” typically having a peak preceded by a trough. Increasing the overall stimulus level produced PESE envelopes with higher amplitudes, suggesting a decrease in the jitter of the cell's response. The effect of carrier frequency on the PESE envelope was investigated by obtaining a cell's response to broadband noise and either estimating the PESE envelope for each spectral band or by computing a spectrogram of the stimulus prior to each spike. Either method yielded the cell's PESE spectrogram, a plot of the average amplitude of each carrier-frequency component at various pre-spike times. PESE spectrograms revealed surfaces with peaks and troughs at certain frequencies and pre-spike times. These features are collectively called the spectrotemporal receptive field (STRF). The shape of the STRF showed that in many cases, the carrier frequency can affect the PESE envelope. The modulation transfer function (MTF), which describes a cell's ability to respond to time-varying amplitudes, was estimated with sinusoidally amplitude-modulated (SAM) noises. Comparison of the PESE envelope with the MTF in the time and frequency domains showed that the two were closely matched, suggesting that a cell's response to SAM stimuli is largely predictable from its response to a noise-modulated carrier. The STRF is considered to be a model of the linear component of a system's response to dynamic stimuli. Using the STRF, we estimated the degree to which we could predict a cell's response to an arbitrary broadband noise by comparing the convolution of the STRF and the envelope of the noise with the cell's post-stimulus time histogram to the same noise. The STRF explained 18–46% of the variance of a cell's response to broadband noise.
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Meunier, N., i A. M. Lagrange. "Radial-velocity variations due to meridional flows in the Sun and solar-type stars: impact on exoplanet detectability". Astronomy & Astrophysics 638 (czerwiec 2020): A54. http://dx.doi.org/10.1051/0004-6361/201937354.
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Context. Stellar variability due to magnetic activity and flows at different spatial scales strongly impacts radial velocities. This variability is seen as oscillations, granulation, supergranulation, and meridional flows. The effect of this latter process is currently poorly known but could affect exoplanet detectability. Aims. We aim to quantify the amplitude of the meridional flow integrated over the disc and its temporal variability, first for the Sun, as seen with different inclinations, and then for other solar-type stars. We then want to compare these amplitudes with low-mass exoplanetary amplitudes in radial velocity. Methods. We used long time series (covering two 11-yr cycles) of solar latitudinal meridional circulation to reconstruct its integrated contribution and study its properties. We then used scaling laws from hydrodynamical simulations relating the amplitude of the meridional flow variability with stellar mass and rotation rate to estimate the typical amplitude expected for other solar-type stars. Results. We find typical rms of the order of 0.5–0.7 m s−1 (edge-on) and 1.2–1.7 m s−1 (pole-on) for the Sun (peak-to-peak amplitudes are typically 1–1.4 m s−1 and 2.3–3.3 m s−1 resp.), with a minimal jitter for an inclination of 45–55°. This signal is significant compared to other stellar activity contributions and is much larger than the radial-velocity signal of the Earth. The variability is strongly related to the activity cycle, with maximum flows during the descending phase of the cycle, and possible variability on timescales lower than the cycle period. Extension to other solar-type stars shows that the variability due to meridional flows is dominated by the amplitude of the cycle of those stars (compared with mass and rotation rate), and that the peak-to-peak amplitudes can reach 4 m s−1 for the most variable stars when seen pole-on. The meridional flow contribution sometimes represents a high fraction of the convective blueshift inhibition signal, especially for quiet, low-mass stars. For fast-rotating stars, the presence of multi-cellular patterns should significantly decrease the meridional flow contribution to the radial-velocity signal. Conclusions. Our study shows that these meridional flows could be critical for exoplanet detection. Low inclinations are more impacted than edge-on configurations, but these latter still exhibit significant variability. Meridional flows also degrade the correlation between radial velocities due to convective blueshift inhibition and chromospheric activity indicators. This will make the correction from this signal challenging for stars with no multi-cellular patterns, such as the Sun for example, although there may be some configurations for which the line shape variations may be used if the precision is sufficient.
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Shanbhogue, Santosh J., Michael Seelhorst i Tim Lieuwen. "Vortex Phase-Jitter in Acoustically Excited Bluff Body Flames". International Journal of Spray and Combustion Dynamics 1, nr 3 (wrzesień 2009): 365–87. http://dx.doi.org/10.1260/175682709789141528.
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This paper describes an experimental study of the effect of acoustic excitation on bluff body stabilized flames, specifically on the flow field characteristics. The Kelvin-Helmholtz (KH) instability of the shear layer is excited due to the incident acoustics. In turn, the KH instability imposes a convecting, harmonic excitation on the flame, which leads to spatially periodic flame wrinkling and heat-release oscillations. Understanding the factors influencing these heat release oscillations requires an understanding of the generation, convection, and dissipation of these vortical disturbances. Phase locked particle image velocimetry was carried out over a range of conditions to characterize the vortical dynamics. It was found that the vortex core location exhibits “phase jitter”, manifested as cycle-to-cycle variation in flame and vorticity field at the same excitation phase. Phase jitter is shown to be a function of separation point dynamics, downstream convection time, and amplitude of acoustic excitation. It leads to fairly significant differences between instantaneous and ensemble averaged flow fields and, in particular, the decay rate of the vorticity in the axial direction.