Journal articles: 'Spatial channel'

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Jinno, Masahiko. "Spatial Channel Cross-Connect Architectures for Spatial Channel Networks." IEEE Journal of Selected Topics in Quantum Electronics 26, no. 4 (July 2020): 1–16. http://dx.doi.org/10.1109/jstqe.2020.2975660.

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Iqbal, Zahid, Fei Ji, and Yun Liu. "Virtual Spatial Channel Number and Index Modulation." Wireless Communications and Mobile Computing 2021 (September 11, 2021): 1–10. http://dx.doi.org/10.1155/2021/2982226.

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This paper proposes a novel precoding-aided and efficient data transmission scheme called virtual spatial channel number and index modulation (VS-CNIM), which conveys extra data by changing both the number and index of active virtual parallel channels of multiple-input multiple-output (MIMO) channels, obtained through the singular value decomposition (SVD) in each time slot. Unlike the conventional virtual spatial modulation (VSM), where extra data bits are transmitted only using index of active virtual parallel channels, the VS-CNIM scheme, depending on incoming information bits, transmits extra bits utilizing both the number and indices of active parallel channels along the bits carried by M -ary constellation symbols. Therefore, VS-CNIM provides significantly superior spectral efficiency (SE) compared to VSM. Considering the influence of imperfect channel estimation, a closed-form upper bound is derived on average bit error probability (ABEP). The asymptotic performance is also analyzed, which gives the coding gain and diversity order and describes error floor under the consideration of perfect and imperfect channel estimation, respectively. Monte Carlo simulations exhibit that the VS-CNIM scheme achieves considerably better error performance and high SE than precoding-aided SM (PSM) and VSM schemes.

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DENNIS, S. C. R., W. H. H. BANKS, P. G. DRAZIN, and M. B. ZATURSKA. "Flow along a diverging channel." Journal of Fluid Mechanics 336 (April 10, 1997): 183–202. http://dx.doi.org/10.1017/s0022112096004648.

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This paper treats the two-dimensional steady flow of a viscous incompressible fluid driven through a channel bounded by two walls which are the radii of a sector and two arcs (the ‘inlet’ and ‘outlet’), with the same centre as the sector, at which inflow and outflow conditions are imposed. The computed flows are related to both a laboratory experiment and recent calculations of the linearized ‘spatial’ modes of Jeffery–Hamel flows. The computations, at a few values of the angle between the walls of the sector and several values of the Reynolds number, show how the first bifurcation of the flow in a channel is related to spatial instability. They also show how the end effects due to conditions at the inlet and outlet of the channel are related to the spatial modes: in particular, Saint-Venant's principle breaks down when the flow is spatially unstable, there being a temporally stable steady flow for which small changes at the inlet or outlet create substantial effects all along the channel. The choice of a sector as the shape of the channel is to permit the exploitation of knowledge of the spatial modes of Jeffery–Hamel flows, although we regard the sector as an example of channels with walls of moderate curvature.

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Cogalan, T., H. Haas, and E. Panayirci. "Optical spatial modulation design." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 378, no. 2169 (March 2, 2020): 20190195. http://dx.doi.org/10.1098/rsta.2019.0195.

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Visible light communication (VLC) systems are inherently signal-to-noise ratio (SNR) limited due to link budget constraints. One favourable method to overcome this limitation is to focus on the pre-log factors of the channel capacity. Multiple-input multiple-output (MIMO) techniques are therefore a promising avenue of research. However, inter-channel interference in MIMO limits the achievable capacity. Spatial modulation (SM) avoids this limitation. Furthermore, the performance of MIMO systems in VLC is limited by the similarities among spatial channels. This limitation becomes particularly severe in intensity modulation/direct detection (IM/DD) systems because of the lack of phase information. The motivation of this paper is to propose a system that results in a multi-channel transmission system that enables reliable multi-user optical MIMO SM transmission without the need for a precoder, power allocation algorithm or additional optics at the receiver. A general bit error performance model for the SM system is developed for an arbitrary number of light-emitting diodes (LEDs) in conjunction with pulse amplitude modulation. Based on this model, an LED array structure is designed to result in spatially separated multiple channels by manipulating the transmitter geometry. This article is part of the theme issue ‘Optical wireless communication’.

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Saleem, Ayesha Bint, Syed Ali Hassan, and Haejoon Jung. "Channel Estimation for Spatial Modulation Schemes in Spatially Correlated Time Varying Channels." IEEE Transactions on Vehicular Technology 70, no. 5 (May 2021): 5143–48. http://dx.doi.org/10.1109/tvt.2021.3075734.

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Abouda, A. A., and N. G. Tarhuni. "MIMO Channel Gain Mechanisms Relative to SISO Channel." Journal of Engineering Research [TJER] 7, no. 2 (December 1, 2010): 40. http://dx.doi.org/10.24200/tjer.vol7iss2pp40-47.

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In contrast to the rest of wireless communication technologies, multiple-input multiple-output (MIMO) technology enjoys different gain mechanisms that make it very attractive for reliable high data rate wireless communications. This paper presents a study on these gain mechanisms with particular emphasis on the case of high average received signal to noise ratio (SNR) where the MIMO system deployment is most promising. We write the MIMO channel capacity in terms of gains relative to a single- input single-output (SISO) wireless channel. Doing so, spatial multiplexing gain and power gain of MIMO wireless channels become more insightful. Based on this analysis a switching scheme between spatial multiplexing and transmit diversity is proposed. We support our discussion with numerical results which show that under a high data rate spatial multiplexing scheme the contribution of each gain mechanism to the total channel capacity depends on the channel Ricean factor, the average received SNR, and the MIMO system size. The proposed switching scheme gives about 2 dB gain in bit error rate performance relative to the spatial multiplexing mode.

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Davis, Mark Franklin. "Audio channel spatial translation." Journal of the Acoustical Society of America 128, no. 1 (2010): 509. http://dx.doi.org/10.1121/1.3472297.

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Fan, Wei, Pekka Kyösti, Jesper Ø. Nielsen, Lassi Hentilä, and Gert F. Pedersen. "Emulating Realistic Bidirectional Spatial Channels for MIMO OTA Testing." International Journal of Antennas and Propagation 2015 (2015): 1–13. http://dx.doi.org/10.1155/2015/289843.

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This paper discusses over the air (OTA) testing for multiple input multiple output (MIMO) capable terminals with emphasis on modeling bidirectional spatial channel models in multiprobe anechoic chamber (MPAC) setups. In the literature, work on this topic has been mainly focused on how to emulate downlink channel models, whereas uplink channel is often modeled as free space line-of-sight channel without fading. Modeling realistic bidirectional (i.e., both uplink and downlink) propagation environments is essential to evaluate any bidirectional communication systems. There have been works stressing the importance of emulating full bidirectional channel and proposing possible directions to implement uplink channels in the literature. Nevertheless, there is no currently published work reporting an experimental validation of such concepts. In this paper, a general framework to emulate bidirectional channels for time division duplexing (TDD) and frequency division duplexing (FDD) communication systems is proposed. The proposed technique works for MPAC setups with arbitrary uplink and downlink probe configurations, that is, possibly different probe configurations (e.g., number of probes or their configurations) in the uplink and downlink. The simulation results are further supported by measurements in a practical MPAC setup. The proposed algorithm is shown to be a valid method to emulate bidirectional spatial channel models.

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Ndzi, David L., Nick Savage, and Boris Gremont. "Spatial and Temporal Variation of Wideband Indoor Channels." International Journal of Antennas and Propagation 2010 (2010): 1–11. http://dx.doi.org/10.1155/2010/735434.

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Extensive studies of the impact of temporal variations induced by people on the characteristics of indoor wideband channels are reported. Singular Value Decomposition Prony algorithm has been used to compute the impulse response from measured channel transfer functions. The high multipath resolution of the algorithm has allowed a detailed assessment of the shapes of individual multipath clusters and their variation in time and space in indoor channels. Large- and small-scale analyses show that there is a significant dependency of the channel response on room size. The presence of people in the channel has been found to induce both signal enhancements and fading with short-term dynamic variations of up to 30 dB, depending on the number of people and their positions within the room. A joint amplitude and time of arrival model has been used to successfully model measured impulse response clusters.

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Jain, Faquir, Bander Saman, Raja Hari Gudlavalleti, John Chandy, and Evan Heller. "Multi-State 2-Bit CMOS Logic Using n- and p- Quantum Well Channel Spatial Wavefunction Switched (SWS) FETs." International Journal of High Speed Electronics and Systems 27, no. 03n04 (September 2018): 1840020. http://dx.doi.org/10.1142/s0129156418400207.

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Unlike conventional FETs, spatial wavefunction switched (SWS)-FETs are comprised of two or more vertically stacked coupled quantum well or quantum dot channels, and the spatial location of carriers within these channels is used to encode the logic states (00), (01), (10) and (11). The aim of this paper is to present 4-states/2-bit output-input transfer characteristics using two Si/SiGe quantum well channels configured as CMOS using n- and p-channel spatial wavefunction switched field-effect transistors (SWS-FETs). Quantum simulations show switching of wavefunctions as the gate voltage is increased from lower Si quantum well to the upper well in n-channel and from upper SiGe quantum well to lower well in the p-channel. The inverter transfer characteristic and current switching are obtained by integrating BSIM (Berkeley Short-channel IGFET Model) and the Analog Behavioral Model (ABM). The simulation shows current flow only during switching.

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Wu, Jian, Lei Ye, Chenchen Wu, Qingrui Chang, Zhuohang Xin, Chi Zhang, and Huicheng Zhou. "Spatial variation of channel head curvature in small mountainous watersheds." Hydrology Research 50, no. 5 (July 5, 2019): 1251–66. http://dx.doi.org/10.2166/nh.2019.036.

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Abstract High-resolution digital elevation models (DEMs) offer opportunities for channel network extraction due to its representation of realistic topography. Channels are generally surrounded by well-defined banks that have a distinct signature in the contour lines. Contour curvature is one of the important topographic attributes usually used for channel head identification; however, the curvature at channel heads may vary considerably between and even within watersheds. Therefore, uncertainty exists in the extracted channel heads due to the specified curvature threshold. In this paper, the locations of channel heads in 14 small mountainous watersheds are obtained using a nonparametric method based on the shape of contour lines generated from DEMs with a spatial resolution of 1 m, and the channel head curvature is computed from the extracted channel heads. The spatial distributions of the channel head curvature in these 14 watersheds have been analyzed, and another two watersheds with field-mapped channel heads are selected for validation. The results indicate that: (1) the channel head curvature is sensitive to the local terrain and varies within and between watersheds; (2) the Gamma distribution effectively fits the spatial distribution of the channel head curvature in all the selected watersheds; and (3) constant threshold-based methods for channel head identification gain significant location errors even within a single watershed.

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Wang, Zhang, and Wang. "Attention Bilinear Pooling for Fine-Grained Classification." Symmetry 11, no. 8 (August 9, 2019): 1033. http://dx.doi.org/10.3390/sym11081033.

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Fine-grained image classification is a challenging problem because of its large intra-class differences and low inter-class variance. Bilinear pooling based models have been shown to be effective at fine-grained classification, while most previous approaches neglect the fact that distinctive features or modeling distinguishing regions usually have an important role in solving the fine-grained problem. In this paper, we propose a novel convolutional neural network framework, i.e., attention bilinear pooling, for fine-grained classification with attention. This framework can learn the distinctive feature information from the channel or spatial attention. Specifically, the channel and spatial attention allows the network to better focus on where the key targets are in the image. This paper embeds spatial attention and channel attention in the underlying network architecture to better represent image features. To further explore the differences between channels and spatial attention, we propose channel attention bilinear pooling (CAB), spatial attention bilinear pooling (SAB), channel spatial attention bilinear pooling (CSAB), and spatial channel attention bilinear pooling (SCAB) as four alternative frames. A variety of experiments on several datasets show that our proposed method has a very impressive performance compared to other methods based on bilinear pooling.

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Li, Zhongwei, Xingshuai Cui, Leiquan Wang, Hao Zhang, Xue Zhu, and Yajing Zhang. "Spectral and Spatial Global Context Attention for Hyperspectral Image Classification." Remote Sensing 13, no. 4 (February 19, 2021): 771. http://dx.doi.org/10.3390/rs13040771.

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Recently, hyperspectral image (HSI) classification has attracted increasing attention in the remote sensing field. Plenty of CNN-based methods with diverse attention mechanisms (AMs) have been proposed for HSI classification due to AMs being able to improve the quality of feature representations. However, some of the previous AMs squeeze global spatial or channel information directly by pooling operations to yield feature descriptors, which inadequately utilize global contextual information. Besides, some AMs cannot exploit the interactions among channels or positions with the aid of nonlinear transformation well. In this article, a spectral-spatial network with channel and position global context (GC) attention (SSGCA) is proposed to capture discriminative spectral and spatial features. Firstly, a spectral-spatial network is designed to extract spectral and spatial features. Secondly, two novel GC attentions are proposed to optimize the spectral and spatial features respectively for feature enhancement. The channel GC attention is used to capture channel dependencies to emphasize informative features while the position GC attention focuses on position dependencies. Both GC attentions aggregate global contextual features of positions or channels adequately, following a nonlinear transformation. Experimental results on several public HSI datasets demonstrate that the spectral-spatial network with GC attentions outperforms other related methods.

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Song, Qi, Jie Li, Chenghong Li, Hao Guo, and Rui Huang. "Fully Attentional Network for Semantic Segmentation." Proceedings of the AAAI Conference on Artificial Intelligence 36, no. 2 (June 28, 2022): 2280–88. http://dx.doi.org/10.1609/aaai.v36i2.20126.

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Recent non-local self-attention methods have proven to be effective in capturing long-range dependencies for semantic segmentation. These methods usually form a similarity map of R^(CxC) (by compressing spatial dimensions) or R^(HWxHW) (by compressing channels) to describe the feature relations along either channel or spatial dimensions, where C is the number of channels, H and W are the spatial dimensions of the input feature map. However, such practices tend to condense feature dependencies along the other dimensions, hence causing attention missing, which might lead to inferior results for small/thin categories or inconsistent segmentation inside large objects. To address this problem, we propose a new approach, namely Fully Attentional Network (FLANet), to encode both spatial and channel attentions in a single similarity map while maintaining high computational efficiency. Specifically, for each channel map, our FLANet can harvest feature responses from all other channel maps, and the associated spatial positions as well, through a novel fully attentional module. Our new method has achieved state-of-the-art performance on three challenging semantic segmentation datasets, i.e., 83.6%, 46.99%, and 88.5% on the Cityscapes test set, the ADE20K validation set, and the PASCAL VOC test set, respectively.

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Wu, Xiping, Holger Claussen, Marco Di Renzo, and Harald Haas. "Channel Estimation for Spatial Modulation." IEEE Transactions on Communications 62, no. 12 (December 2014): 4362–72. http://dx.doi.org/10.1109/tcomm.2014.2366750.

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Chen, Xin, Yong Fang, Weidong Xiang, and Liang Zhou. "Research on Spatial Channel Model for Vehicle-to-Vehicle Communication Channel in Roadside Scattering Environment." International Journal of Antennas and Propagation 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/3098198.

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In this paper, an extension of spatial channel model (SCM) for vehicle-to-vehicle (V2V) communication channel in roadside scattering environment is investigated for the first time theoretically and by simulations. Subsequently, to efficiently describe the roadside scattering environment and reflect the nonstationary properties of V2V channels, the proposed SCM V2V model divides the scattering objects into three categories of clusters according to the location of effective scatterers by introducing critical distance. We derive general expressions for the most important statistical properties of V2V channels, such as channel impulse response, power spectral density, angular power density, autocorrelation function, and Doppler spread of the proposed model. The impact of vehicle speed, traffic density, and angle of departure, angle of arrival, and other statistical performances on the V2V channel model is thoroughly discussed. Numerical simulation results are presented to validate the accuracy and effectiveness of the proposed model.

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Jagadeesan, Neeraja, B. Saman, M. Lingalugari, P. Gogna, and F. Jain. "Sequential Logic Circuits Using Spatial Wavefunction Switched (SWS) FETs." International Journal of High Speed Electronics and Systems 24, no. 03n04 (September 2015): 1550011. http://dx.doi.org/10.1142/s0129156415500111.

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The spatial wavefunction-switched field-effect transistor (SWSFET) is one of the promising quantum well devices that transfers electrons from one quantum well channel to the other channel based on the applied gate voltage. This eliminates the use of more transistors as we have coupled channels in the same device operating at different threshold voltages. This feature can be exploited in many digital integrated circuits thus reducing the count of transistors which translates to less die area. The simulations of basic sequential circuits like SR latch, D latch and flip flop are presented here using SWSFET based logic gates. The circuit model of a SWSFET was developed using Berkeley short channel IGFET model (BSIM 3).

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Hou, Shuai, Yafeng Wang, Tianyi Zeng, and Sheng Wu. "Sparse Channel Estimation for Spatial Non-Stationary Massive MIMO Channels." IEEE Communications Letters 24, no. 3 (March 2020): 681–84. http://dx.doi.org/10.1109/lcomm.2019.2961079.

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Deneke, H. M., and R. Roebling. "Downscaling of METEOSAT SEVIRI 0.6 and 0.8 micron channel radiances utilizing the high-resolution visible channel." Atmospheric Chemistry and Physics Discussions 10, no. 4 (April 23, 2010): 10707–40. http://dx.doi.org/10.5194/acpd-10-10707-2010.

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Abstract. An algorithm is introduced to downscale the 0.6 and 0.8 micron spectral channels of the METEOSTAT SEVIRI satellite imager from 3×3 km2 (LRES) to 1×1 km2 (HRES) resolution utilizing SEVIRI's high-resolution visible channel (HRVIS). Intermediate steps include the coregistration of low- and high-resolution images, lowpass filtering of the HRVIS channel with the spatial response function of the narrowband channels, and the estimation of a least-squares linear regression model for linking high-frequency variations in the HRVIS and narrowband images. The importance of accounting for the sensor spatial response function for matching reflectances at different spatial resolutions is demonstrated, and an estimate of the accuracy of the downscaled reflectances is provided. Based on a 1-year dataset of Meteosat SEVIRI images, it is estimated that on average, the reflectance of a HRES pixel differs from that of an enclosing LRES pixel by standard deviations of 0.049 and 0.052 in the 0.6 and 0.8 micron channels, respectively. By applying our downscaling algorithm, explained variance of 98.2 and 95.3 percent are achieved for estimating these deviations, corresponding to residual standard deviations of only 0.007 and 0.011 for the respective channels. For this dataset, a minor misregistration of the HRVIS channel relative to the narrowband channels of 0.36±0.11 km in East and 0.06±0.10 km in South direction is observed and corrected for, which should be negligible for most applications.

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Deneke, H. M., and R. A. Roebeling. "Downscaling of METEOSAT SEVIRI 0.6 and 0.8 μm channel radiances utilizing the high-resolution visible channel." Atmospheric Chemistry and Physics 10, no. 20 (October 18, 2010): 9761–72. http://dx.doi.org/10.5194/acp-10-9761-2010.

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Abstract. An algorithm is introduced to downscale the 0.6 and 0.8 μm spectral channels of the METEOSTAT SEVIRI satellite imager from 3×3 km2 (LRES) to 1×1 km2 (HRES) resolution utilizing SEVIRI's high-resolution visible channel (HRV). Intermediate steps include the coregistration of low- and high-resolution images, lowpass filtering of the HRV channel with the spatial response function of the narrowband channels, and the estimation of a least-squares linear regression model for linking high-frequency variations in the HRV and narrowband images. The importance of accounting for the sensor spatial response function for matching reflectances at different spatial resolutions is demonstrated, and an estimate of the accuracy of the downscaled reflectances is provided. Based on a 1-year dataset of Meteosat SEVIRI images, it is estimated that on average, the reflectance of a HRES pixel differs from that of an enclosing LRES pixel by standard deviations of 0.049 and 0.052 in the 0.6 and 0.8 μm channels, respectively. By applying our downscaling algorithm, explained variance of 98.2 and 95.3 percent are achieved for estimating these deviations, corresponding to residual standard deviations of only 0.007 and 0.011 for the respective channels. For this dataset, a minor misregistration of the HRV channel relative to the narrowband channels of 0.36±0.11 km in East and 0.06±0.10 km in South direction is observed and corrected for, which should be negligible for most applications.

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Shailender, Shelej Khera, Sajjan Singh, and Jyoti. "Estimation of Channel for Millimeter-Wave Hybrid Massive MIMO Systems using Orthogonal Matching Pursuit (OMP)." Journal of Physics: Conference Series 2327, no. 1 (August 1, 2022): 012040. http://dx.doi.org/10.1088/1742-6596/2327/1/012040.

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Abstract In a millimeter-wave (mm-Wave) large MIMO system, hybrid precoding is a critical component for lowering radio-frequency hardware costs as compared to the traditional full-digital precoding strategy. Knowledge of channels is required for hybrid precoding. Though, estimation of the channel is problematic for the mm-Wave system because of the usage of a massive array of antenna and hybrid architecture with analog precoding. Due to the extremely directed nature of wireless propagation, wireless channels have spatial sparsity. In this paper, we exploit this spatial sparsity nature of wireless channels to develop orthogonal matching pursuit technique-based estimation of channels for hybrid millimeter-wave (mm-Wave) wireless systems. Genie (Ideal) channel estimation is also performed in which we presume that actual angle of departures (AoD) and angle of arrivals (AoA) are known to us. Finally, the simulation results reveal that suggested OMP algorithm-based channel estimation has a significant advantage over conventional approaches like least-squares channel estimation.

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Amadid, Jamal, Abdelfettah Belhabib, Asma Khabba, Zakaria El Ouadi, and Abdelouhab Zeroual. "Channel Estimation Evaluation For a Massive MIMO System Considering Spatially Correlated Channels in an Urban Network." E3S Web of Conferences 351 (2022): 01055. http://dx.doi.org/10.1051/e3sconf/202235101055.

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Channel estimation (CE) is an important process that is done during the pilot transmission phase in each base station. This work addresses this process for the massive multiple-input multiple-output systems by studying the scenario where the channels are spatially correlated. Throughout this work, the spatial correlation between channels is modeled using the exponential correlation model. The minimum mean square error (MMSE) estimator’s performance for uncorrelated and correlated channels is compared and examined using the normalized mean square error (NMSE) metric, where the correlated scenario is presented through two array designs, namely proposed uniform planar array (UPA) and uniform linear array (ULA). In comparison to the uncorrelated situation, the correlated channels scenario is a more practical scenario that represents the real- world environment and provides superior channel estimate quality since the spatial correlation is advantageous for CE. Hence, we proposed a proposed UPA arrangement for correlated channels based on the Kronecker product of the ULA arrangement that outperforms the ULA arrangement and offers superior performance comparedto ULA. Numerical results are offered in order to support our analytical study.

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Basnayaka, Dushyantha A., and Harald Haas. "MIMO Interference Channel Between Spatial Multiplexing and Spatial Modulation." IEEE Transactions on Communications 64, no. 8 (August 2016): 3369–81. http://dx.doi.org/10.1109/tcomm.2016.2580146.

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Hanegan, K., and I. Georgiou. "Tidal modulated flow and sediment flux through Wax Lake Delta distributary channels: Implications for delta development." Proceedings of the International Association of Hydrological Sciences 367 (March 3, 2015): 391–98. http://dx.doi.org/10.5194/piahs-367-391-2015.

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Abstract. In this study, a Delft3D model of the Wax Lake Delta was developed to simulate flow and sediment flux through delta distributary channels. The model was calibrated for tidal constituents as well as velocity and sediment concentration across channel transects. The calibrated model was then used to simulate full spring–neap tidal cycles under constant low flow upstream boundary conditions, with grain size variation in suspended load represented using two sediment fractions. Flow and sediment flux results through distributary channel cross-sections were examined for spatial and temporal variability with the goal of characterizing the role of tides in sediment reworking and delta development. The Wax Lake Delta has prograded through channel extension, river mouth bar deposition, and channel bifurcation. Here we show that tidal modulation of currents influences suspended sand transport, and spatial acceleration through distributary channels at low tides is sufficient to suspend sand in distal reaches during lower flows. The basinward-increasing transport capacity in distributary channels indicates that erosive channel extension could be an important process, even during non-flood events.

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Helm, Carina, Marwan A. Hassan, and David Reid. "Characterization of morphological units in a small, forested stream using close-range remotely piloted aircraft imagery." Earth Surface Dynamics 8, no. 4 (November 4, 2020): 913–29. http://dx.doi.org/10.5194/esurf-8-913-2020.

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Abstract. Forested, gravel-bed streams possess complex channel morphologies which are difficult to objectively characterize. The spatial scale necessary to adequately capture variability in these streams is often unclear, as channels are governed by irregularly spaced features and episodic processes. This issue is compounded by the high cost and time-consuming nature of field surveys in these complex fluvial environments. In larger streams, remotely piloted aircraft (RPA) have proven to be effective tools for characterizing channels at high resolutions over large spatial extents, but to date their use in small, forested streams with closed forest canopies has been limited. This paper seeks to demonstrate an effective method for classifying channel morphological units in small, forested streams and for providing information on the spatial scale necessary to capture the dominant spatial morphological variability of these channels. This goal was achieved using easily extractable data from close-range RPA imagery collected under the forest canopy (flying height of 5–15 m above ground level; ma.g.l.) in a small (width of 10–15 m) stream along its 3 km of salmon-bearing channel. First, the accuracy and coverage of RPA for extracting channel data were investigated through a subcanopy survey. From these survey data, relevant cross-sectional variables (hydraulic radius, sediment texture, and channel slope) were extracted from high-resolution point clouds and digital elevation models (DEMs) of the channel and used to characterize channel unit morphology using a principal component analysis-clustering (PCA-clustering) technique. Finally, the length scale required to capture dominant morphological variability was investigated from an analysis of morphological diversity along the channel. The results demonstrate that subcanopy RPA surveys provide a viable alternative to traditional ground-based survey approaches for mapping morphological units, with 87 % coverage of the main channel stream bed achieved. The PCA-clustering analysis provided a comparatively objective means of classifying channel unit morphology with a correct classification rate of 85 %. An analysis of the morphological diversity along the surveyed channel indicates that reaches of at least 15 bankfull width equivalents are required to capture the channel's dominant morphological heterogeneity. Altogether, the results provide a precedent for using RPA to characterize the morphology and diversity of forested streams under dense canopies.

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Park, Yongkoo, and Wonzoo Chung. "Selective Feature Generation Method Based on Time Domain Parameters and Correlation Coefficients for Filter-Bank-CSP BCI Systems." Sensors 19, no. 17 (August 30, 2019): 3769. http://dx.doi.org/10.3390/s19173769.

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This paper presents a novel motor imagery (MI) classification algorithm using filter-bank common spatial pattern (FBCSP) features based on MI-relevant channel selection. In contrast to existing channel selection methods based on global CSP features, the proposed algorithm utilizes the Fisher ratio of time domain parameters (TDPs) and correlation coefficients: the channel with the highest Fisher ratio of TDPs, named principle channel, is selected and a supporting channel set for the principle channel that consists of highly correlated channels to the principle channel is generated. The proposed algorithm using the FBCSP features generated from the supporting channel set for the principle channel significantly improved the classification performance. The performance of the proposed method was evaluated using BCI Competition III Dataset IVa (18 channels) and BCI Competition IV Dataset I (59 channels).

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Mirdha, Pial, Murali Lingalugari, Evan K. Heller, John A. Chandy, and Faquir C. Jain. "Novel Multiplexer Design Using Multi-State Spatial Wavefunction-Switched (SWS) FETs." International Journal of High Speed Electronics and Systems 24, no. 03n04 (September 2015): 1520011. http://dx.doi.org/10.1142/s0129156415200116.

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In this paper, we propose a multiplexer design based on use of a twin channel and twin drain spatial wavefunction-switched field-effect transistors (SWSFETs). SWSFET comprises of vertically stacked coupled quantum wells devices, which are the channels, where depending on the gate voltage only one of the channels is in conduction mode. Using SWSFET in multi-channel and single drain configuration operates as a multi-valued logic device. 2:1 and 4:2 multiplexer designs are proposed which are compatible with current CMOS technology and with all SWSFET. Both designs lead to greater than 4X reduction in transistor count. Ngspice simulation of circuits is also presented.

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Tan, Yi, Jesper Ødum Nielsen, and Gert Frølund Pedersen. "Spatial Stationarity of Ultrawideband and Millimeter Wave Radio Channels." International Journal of Antennas and Propagation 2016 (2016): 1–7. http://dx.doi.org/10.1155/2016/3212864.

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For radio channels with broad bandwidth resource, such as those often used for ultrawideband (UWB) and millimeter wave (mmwave) systems, the Wide-Sense Stationary Uncorrelated Scattering (WSSUS) and spatial stationary assumptions are more critical than typical cellular channels with very limited bandwidth resource. This paper studies spatial stationarity and bandwidth dependency of the Multipath Component (MPC) parameters, and the concept of local region of stationarity (LRS) is used as the measure of the physical stationarity region. LRS calculation results based on channel measurements show that the size of LRS is bandwidth dependent in all measured bands, 2–4 GHz, 14–16 GHz, and 28–30 GHz. The results in this paper point out that an inappropriate choice of bandwidth in channel parameter estimation could violate spatial stationary assumptions. The paper indicates LRS sizes for different bandwidths in the three bands.

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Cui, Xuelian, Zhanjie Zhang, Tao Zhang, Zhuoqun Yang, and Jie Yang. "Attention graph: Learning effective visual features for large-scale image classification." Journal of Algorithms & Computational Technology 16 (January 2022): 174830262110653. http://dx.doi.org/10.1177/17483026211065375.

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In recent years, the research of deep learning has received extensive attention, and many breakthroughs have been made in various fields. On this basis, a neural network with the attention mechanism has become a research hotspot. In this paper, we try to solve the image classification task by implementing channel and spatial attention mechanism which improve the expression ability of neural network model. Different from previous studies, we propose an attention module consisting of channel attention module (CAM) and spatial attention module (SAM). The proposed module derives attention graphs from channel dimension and spatial dimension respectively, then the input features are selectively learned according to the importance of the features. Besides, this module is lightweight and can be easily integrated into image classification algorithms. In the experiment, we combine the deep residual network model with the attention module and the experimental results show that the proposed method brings higher image classification accuracy. The channel attention module adds weight to the signals on different convolution channels to represent the correlation. For different channels, the higher the weight, the higher the correlation which required more attention. The main function of spatial attention is to capture the most informative part in the local feature graph, which is a supplement to channel attention. We evaluate our proposed module based on the ImageNet-1K and Cifar-100 respectively. Through a large number of comparative experiments, our proposed model achieved outstanding performance.

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ZHANG, Hui-ping, Ping WU, and Ai-jun LIU. "Ergodic channel capacity of the spatial correlated rayleigh MIMO channel." Journal of China Universities of Posts and Telecommunications 14, no. 4 (December 2007): 32–35. http://dx.doi.org/10.1016/s1005-8885(08)60034-5.

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Chen, Jia, Yibo Ai, Yuhan Qian, and Weidong Zhang. "A novel Siamese Attention Network for visual object tracking of autonomous vehicles." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 235, no. 10-11 (March 29, 2021): 2764–75. http://dx.doi.org/10.1177/09544070211006520.

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In the environment perception stage of autonomous driving, vehicles need to track its surrounding objects quickly and accurately to avoid dangerous behaviors. Therefore, visual object tracking has important practical application value in autonomous driving system. However, the performance of most hierarchical convolutional feature trackers are limited by ignoring the complex environment of autonomous driving. In this paper, a novel Siamese Attention Network to explore the rich spatial and channel information of objects was proposed. Because of the lack of important information between the channel and the spatial position, the tracking performance is reduced by the challenges of illumination change and deformation. The spatial attention block and channel attention block focus on the importance of different spatial positions and channels, respectively. The effective fusion of the two makes our tracker achieve the state-of-the art performance of 0.300 in the EAO criterion of 2017, which exceeds the baseline by 5.7%.

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Beaudot, W. H. A. "Dynamics in Parvocellular and Magnocellular Pathways: Consequences for Luminance and Colour Processing Streams." Perception 25, no. 1_suppl (August 1996): 9. http://dx.doi.org/10.1068/v96l0710.

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An achromatic neuromorphic model of the vertebrate retina has already accounted for X and Y pathways (Beaudot and Hérault, 1994 Perception23 Supplement, 25) and has shown a temporal ‘coarse-to-fine’ processing of spatial information (Beaudot et al, 1995 Perception24 Supplement, 93). This model has been extended to colour vision. By taking into account the chromatic sensitivities of cones, functional properties of the parvocellular pathway are modelled. Approximating the responses of colour-opponent cells, the model provides a spatial multiplexing of luminance and chrominance information: sustained responses show spatial band-pass behaviour to luminance variations and low-pass behaviour to equiluminant colour changes. In addition the spatiotemporal inseparability for luminance in the parvocellular model leads to a temporal multiplexing of spatial luminance information: at higher temporal frequencies the spatial filtering is low-pass, conveying only luminance information. Demultiplexing this mixed information suggests interactions between retinal channels. By locally combining additive and subtractive mechanisms between opposite parvocellular pathways (eg G+/ R−± R+/ G−), and an inhibition from the magnocellular pathway, the existence of at least three functional subchannels is predicted: (i) a transient, spatially low-pass channel, (ii) a sustained, spatially band-pass channel, dedicated to the analysis of luminance information in a spatiotemporally separable way (eg moving shadows and static textures), and (iii) a spatiotemporally low-pass, colour-opponent channel leading to colour induction, which is little affected by the presence of shadows and is more representative of objects. This hypothesis of spatiotemporal demultiplexing of luminance and chrominance information, which should presumably occur at an early cortical level, is in accordance with the multiple-processing-streams organisation of the primate visual system.

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Xiao, Yang, and Jinfeng Kou. "Cooperative Spatial Multiplexing for CR Users Sharing a Common Channel with Primary Users*." WSEAS TRANSACTIONS ON SIGNAL PROCESSING 17 (December 31, 2021): 127–31. http://dx.doi.org/10.37394/232014.2021.17.18.

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To enable mobile stations (MSs) of secondary users (SUs) in cognitive radio (CR) networks sharing a common channel with MSs of primary users (PUs) is an important but challenging issue. In this paper, a cooperative spatial multiplexing (CSM) scheme is proposed, where base station (BS) in CR network has K antennas and each SU or PU has one antenna only, and BS supports PUs and SUs by K spatial channels. To ensure communication quality of the network, the paper applies LDPC as the channel coding for BS, PUs and SUs. Simulations verify the proposed scheme with good spatial multiplexing capacity and BER performance.

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Alhassoun, Mohammad, and Gregory D. Durgin. "A Theoretical Channel Model for Spatial Fading in Retrodirective Backscatter Channels." IEEE Transactions on Wireless Communications 18, no. 12 (December 2019): 5845–54. http://dx.doi.org/10.1109/twc.2019.2939323.

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Brante, Glauber, Richard Demo Souza, and Javier Garcia-Frias. "Spatial Diversity Using Analog Joint Source Channel Coding in Wireless Channels." IEEE Transactions on Communications 61, no. 1 (January 2013): 301–11. http://dx.doi.org/10.1109/tcomm.2012.091212.110773.

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Acar, Yusuf, Hakan Doğan, and Erdal Panayırcı. "On channel estimation for spatial modulated systems over time-varying channels." Digital Signal Processing 37 (February 2015): 43–52. http://dx.doi.org/10.1016/j.dsp.2014.11.004.

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Xu, Xiangyang, Qiao Chen, and Ruixin Xu. "The Study of Spatial Frequency Channels for Human Visual System." International Journal of Pattern Recognition and Artificial Intelligence 33, no. 06 (April 21, 2019): 1955007. http://dx.doi.org/10.1142/s0218001419550073.

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Similar to auditory perception of sound system, color perception of the human visual system also presents a multi-frequency channel property. In order to study the multi-frequency channel mechanism of how the human visual system processes color information, the paper proposed a psychophysical experiment to measure the contrast sensitivities based on 17 color samples of 16 spatial frequencies on CIELAB opponent color space. Correlation analysis was carried out on the psychophysical experiment data, and the results show obvious linear correlations of observations for different spatial frequencies of different observers, which indicates that a linear model can be used to model how human visual system processes spatial frequency information. The results of solving the model based on the experiment data of color samples show that 9 spatial frequency tuning curves can exist in human visual system with each lightness, R–G and Y–B color channel and each channel can be represented by 3 tuning curves, which reflect the “center-around” form of the human visual receptive field. It is concluded that there are 9 spatial frequency channels in human vision system. The low frequency tuning curve of a narrow-frequency bandwidth shows the characteristics of lower level receptive field for human vision system, the medium frequency tuning curve shows a low pass property of the change of medium frequent colors and the high frequency tuning curve of a width-frequency bandwidth, which has a feedback effect on the low and medium frequency channels and shows the characteristics of higher level receptive field for human vision system, which represents the discrimination of details.

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Tang, Qing, Raul Benítez, and Fan-Gang Zeng. "Spatial channel interactions in cochlear implants." Journal of Neural Engineering 8, no. 4 (July 13, 2011): 046029. http://dx.doi.org/10.1088/1741-2560/8/4/046029.

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Kang, Dong Wook. "Two-channel spatial interpolation of images." Signal Processing: Image Communication 16, no. 4 (November 2000): 395–99. http://dx.doi.org/10.1016/s0923-5965(00)00004-7.

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Charlton, Clive. "Spatial perspectives on the channel tunnel." Journal of Transport Geography 2, no. 4 (December 1994): 280. http://dx.doi.org/10.1016/0966-6923(94)90054-x.

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Huang, Mengxing, Shi Liu, Zhenfeng Li, Siling Feng, Di Wu, Yuanyuan Wu, and Feng Shu. "Remote Sensing Image Fusion Algorithm Based on Two-Stream Fusion Network and Residual Channel Attention Mechanism." Wireless Communications and Mobile Computing 2022 (January 11, 2022): 1–14. http://dx.doi.org/10.1155/2022/8476000.

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A two-stream remote sensing image fusion network (RCAMTFNet) based on the residual channel attention mechanism is proposed by introducing the residual channel attention mechanism (RCAM) in this paper. In the RCAMTFNet, the spatial features of PAN and the spectral features of MS are extracted, respectively, by a two-channel feature extraction layer. Multiresidual connections allow the network to adapt to a deeper network structure without the degradation. The residual channel attention mechanism is introduced to learn the interdependence between channels, and then the correlation features among channels are adapted on the basis of the dependency. In this way, image spatial information and spectral information are extracted exclusively. What is more, pansharpening images are reconstructed across the board. Experiments are conducted on two satellite datasets, GaoFen-2 and WorldView-2. The experimental results show that the proposed algorithm is superior to the algorithms to some existing literature in the comparison of the values of reference evaluation indicators and nonreference evaluation indicators.

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Zhang, Jianhua, and Chun Pan. "Validation of Antenna Modeling Methodology in IMT-Advanced Channel Model." International Journal of Antennas and Propagation 2012 (2012): 1–9. http://dx.doi.org/10.1155/2012/282797.

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In this paper, the antenna modeling method in the International Mobile Telecommunications-Advanced (IMT-Advanced) channel model is validated by field channel measurements in the indoor scenario at 2.35 GHz. First, the 2 × 2 MIMO channel impulse responses (CIRs) are recorded with practical antennas as references. Second, the CIRs are reconstructed from the available IMT-Advanced channel model with field patterns of the practical antennas and updated spatial parameters extracted from the similar scenario measurements. Then comparisons between the field CIRs and the reconstructed CIRs are made from coherent bandwidth, eigenvalue dispersion, outage capacity, and ergodic channel capacity. It is found that the reconstructed results closely approximate real results in the coherent bandwidth and correctly describe the statistical characteristics in frequency domain. Compared to the field CIRs, the spatial correlation of the reconstructed CIRs with both types of antenna have a wider range that causes the underestimation of the 5% channel outage capacity. Due to the negligence of the coupling among the antennas and the near field effect of antenna, this modeling method will have a great impact on the characteristics of radio channels, especially on the spatial characteristics.

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Luo, Fujun, Markus Dittrich, Soyoun Cho, Joel R. Stiles, and Stephen D. Meriney. "Transmitter release is evoked with low probability predominately by calcium flux through single channel openings at the frog neuromuscular junction." Journal of Neurophysiology 113, no. 7 (April 2015): 2480–89. http://dx.doi.org/10.1152/jn.00879.2014.

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The quantitative relationship between presynaptic calcium influx and transmitter release critically depends on the spatial coupling of presynaptic calcium channels to synaptic vesicles. When there is a close association between calcium channels and synaptic vesicles, the flux through a single open calcium channel may be sufficient to trigger transmitter release. With increasing spatial distance, however, a larger number of open calcium channels might be required to contribute sufficient calcium ions to trigger vesicle fusion. Here we used a combination of pharmacological calcium channel block, high-resolution calcium imaging, postsynaptic recording, and 3D Monte Carlo reaction-diffusion simulations in the adult frog neuromuscular junction, to show that release of individual synaptic vesicles is predominately triggered by calcium ions entering the nerve terminal through the nearest open calcium channel. Furthermore, calcium ion flux through this channel has a low probability of triggering synaptic vesicle fusion (∼6%), even when multiple channels open in a single active zone. These mechanisms work to control the rare triggering of vesicle fusion in the frog neuromuscular junction from each of the tens of thousands of individual release sites at this large model synapse.

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Schiller, Peter H., Nikos K. Logothetis, and Eliot R. Charles. "Role of the color-opponent and broad-band channels in vision." Visual Neuroscience 5, no. 04 (October 1990): 321–46. http://dx.doi.org/10.1017/s0952523800000420.

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AbstractThe functions of the primate color-opponent and broad-band channels were assessed by examining the visual capacities of rhesus monkeys following selective lesions of parvocellular and magnocellular lateral geniculate nucleus, which respectively relay these two channels to the cortex. Parvocellular lesions impaired color vision, high spatial-frequency form vision, and fine stereopsis. Magnocellular lesions impaired high temporal- frequency flicker and motion perception but produced no deficits in stereopsis. Low spatial-frequency form vision, stereopsis, and brightness perception were unaffected by either lesion. Much as the rods and cones of the retina can be thought of as extending the range of vision in the intensity domain, we propose that the color-opponent channel extends visual capacities in the wavelength and spatial-frequency domains whereas the broad-band channel extends them in the temporal domain.

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Piccolini, Matteo, Farzam Nosrati, Giuseppe Compagno, Patrizia Livreri, Roberto Morandotti, and Rosario Lo Franco. "Entanglement Robustness via Spatial Deformation of Identical Particle Wave Functions." Entropy 23, no. 6 (June 3, 2021): 708. http://dx.doi.org/10.3390/e23060708.

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We address the problem of entanglement protection against surrounding noise by a procedure suitably exploiting spatial indistinguishability of identical subsystems. To this purpose, we take two initially separated and entangled identical qubits interacting with two independent noisy environments. Three typical models of environments are considered: amplitude damping channel, phase damping channel and depolarizing channel. After the interaction, we deform the wave functions of the two qubits to make them spatially overlap before performing spatially localized operations and classical communication (sLOCC) and eventually computing the entanglement of the resulting state. This way, we show that spatial indistinguishability of identical qubits can be utilized within the sLOCC operational framework to partially recover the quantum correlations spoiled by the environment. A general behavior emerges: the higher the spatial indistinguishability achieved via deformation, the larger the amount of recovered entanglement.

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Sun, Jun, Junbo Zhang, Xuesong Gao, Mantao Wang, Dinghua Ou, Xiaobo Wu, and Dejun Zhang. "Fusing Spatial Attention with Spectral-Channel Attention Mechanism for Hyperspectral Image Classification via Encoder–Decoder Networks." Remote Sensing 14, no. 9 (April 19, 2022): 1968. http://dx.doi.org/10.3390/rs14091968.

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In recent years, convolutional neural networks (CNNs) have been widely used in hyperspectral image (HSI) classification. However, feature extraction on hyperspectral data still faces numerous challenges. Existing methods cannot extract spatial and spectral-channel contextual information in a targeted manner. In this paper, we propose an encoder–decoder network that fuses spatial attention and spectral-channel attention for HSI classification from three public HSI datasets to tackle these issues. In terms of feature information fusion, a multi-source attention mechanism including spatial and spectral-channel attention is proposed to encode the spatial and spectral multi-channels contextual information. Moreover, three fusion strategies are proposed to effectively utilize spatial and spectral-channel attention. They are direct aggregation, aggregation on feature space, and Hadamard product. In terms of network development, an encoder–decoder framework is employed for hyperspectral image classification. The encoder is a hierarchical transformer pipeline that can extract long-range context information. Both shallow local features and rich global semantic information are encoded through hierarchical feature expressions. The decoder consists of suitable upsampling, skip connection, and convolution blocks, which fuse multi-scale features efficiently. Compared with other state-of-the-art methods, our approach has greater performance in hyperspectral image classification.

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Al-Faiz, Mohammed Z., and Ammar A. Al-hamadani. "IMPLEMENTATION OF EEG SIGNAL PROCESSING AND DECODING FOR TWO-CLASS MOTOR IMAGERY DATA." Biomedical Engineering: Applications, Basis and Communications 31, no. 04 (June 27, 2019): 1950028. http://dx.doi.org/10.4015/s1016237219500285.

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This work decodes two-class motor imagery (MI) based on four main processing steps: (i) Raw electroencephalographic (EEG) signal is decomposed to single trials and spatial filters are estimated for each trial by common spatial filtering (CSP) method; (ii) features are extracted by taking the log transformation (normal distribution) of the spatially filtered EEG signal; (iii) optimal channel selection algorithm is proposed to reduce the number of EEG channels, such approach is regarded as key technological advantage in the implementation of brain–computer interface (BCI) to reduce the system processing time; (iv) finally, support vector machine (SVM) is employed to discriminate two classes of left and right hand MI. Two variations of SVM were proposed: polynomial function kernel and radial-based function RBF kernel. The results revealed that CSP succeeded in removing the strong correlation bound between the EEG samples by maximizing the variance of class 2 samples while minimizing the variance of class 1 samples. The channel selection algorithm achieved its goal to reduce the data dimension by selecting two channels out of three having the lowest variance entropies of 0.239 and 0.261 for channel 1 and channel 2, respectively. The features vector was divided into 80% train and 20% test with five-fold cross validation. The classification performance of SVM-polynomial kernel was 87.86% while it is 95.72% for SVM-RBF kernel as average accuracy of five-folds for both. Thus SVM-RBF is superior to SVM-Poly in the proposed framework.

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Demuro, Angelo, and Ian Parker. "“Optical Patch-clamping”." Journal of General Physiology 126, no. 3 (August 15, 2005): 179–92. http://dx.doi.org/10.1085/jgp.200509331.

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We describe an optical technique using total internal reflection fluorescence (TIRF) microscopy to obtain simultaneous and independent recordings from numerous ion channels via imaging of single-channel Ca2+ flux. Muscle nicotinic acetylcholine (ACh) receptors made up of αβγδ subunits were expressed in Xenopus oocytes, and single channel Ca2+ fluorescence transients (SCCaFTs) were imaged using a fast (500 fps) electron-multiplied c.c.d. camera with fluo-4 as the indicator. Consistent with their arising through openings of individual nicotinic channels, SCCaFTs were seen only when a nicotinic agonist was present in the bathing solution, were blocked by curare, and increased in frequency as roughly the second power of [ACh]. Their fluorescence amplitudes varied linearly with membrane potential and extrapolated to zero at about +60 mV. The rise and fall times of fluorescence were as fast as 2 ms, providing a kinetic resolution adequate to characterize channel gating kinetics; which showed mean open times of 7.9 and 15.8 ms when activated, respectively, by ACh or suberyldicholine. Simultaneous records were obtained from >400 channels in the imaging field, and we devised a novel “channel chip” representation to depict the resultant large dataset as a single image. The positions of SCCaFTs remained fixed (<100 nm displacement) over tens of seconds, indicating that the nicotinic receptor/channels are anchored in the oocyte membrane; and the spatial distribution of channels appeared random without evidence of clustering. Our results extend single-channel TIRFM imaging to ligand-gated channels that display only partial permeability to Ca2+, and demonstrate an order-of-magnitude improvement in kinetic resolution. We believe that functional single-channel imaging opens a new approach to ion channel study, having particular advantages over patch-clamp recording in that it is massively parallel, and provides high-resolution spatial information that is inaccessible by electrophysiological techniques.

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Falcini, F., and E. Salusti. "Friction and mixing effects on potential vorticity for bottom current crossing a marine strait: an application to the Sicily Channel (central Mediterranean Sea)." Ocean Science 11, no. 3 (May 21, 2015): 391–403. http://dx.doi.org/10.5194/os-11-391-2015.

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Abstract. We discuss here the evolution of vorticity and potential vorticity (PV) for a bottom current crossing a marine channel in shallow-water approximation, focusing on the effect of friction and mixing. The purpose of this research is indeed to investigate the role of friction and vertical entrainment on vorticity and PV spatial evolution in channels or straits when along-channel morphology variations are significant. To pursue this investigation, we pose the vorticity and PV equations for a homogeneous bottom water vein and we calculate these two quantities as an integral form. Our theoretical findings are considered in the context of in situ hydrographic data related to the Eastern Mediterranean Deep Water (EMDW), i.e., a dense, bottom water vein that flows northwestward, along the Sicily Channel (Mediterranean Sea). Indeed, the narrow sill of this channel implies that friction and entrainment need to be considered. Small tidal effects in the Sicily Channel allow for a steady theoretical approach. We argue that bottom current vorticity is prone to significant sign changes and oscillations due to topographic effects when, in particular, the current flows over the sill of a channel. These vorticity variations are, however, modulated by frictional effects due to seafloor roughness and morphology. Such behavior is also reflected in the PV spatial evolution, which shows an abrupt peak around the sill region. Our diagnoses on vorticity and PV allow us to obtain general insights about the effect of mixing and friction on the pathway and internal structure of bottom-trapped currents flowing through channels and straits, and to discuss spatial variability of the frictional coefficient. Our approach significantly differs from other PV-constant approaches previously used in studying the dynamics of bottom currents flowing through rotating channels.

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Jiang, Xin, Chunlei Zhao, Ming Zhu, Zhicheng Hao, and Wen Gao. "Residual Spatial and Channel Attention Networks for Single Image Dehazing." Sensors 21, no. 23 (November 27, 2021): 7922. http://dx.doi.org/10.3390/s21237922.

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Single image dehazing is a highly challenging ill-posed problem. Existing methods including both prior-based and learning-based heavily rely on the conceptual simplified atmospheric scattering model by estimating the so-called medium transmission map and atmospheric light. However, the formation of haze in the real world is much more complicated and inaccurate estimations further degrade the dehazing performance with color distortion, artifacts and insufficient haze removal. Moreover, most dehazing networks treat spatial-wise and channel-wise features equally, but haze is practically unevenly distributed across an image, thus regions with different haze concentrations require different attentions. To solve these problems, we propose an end-to-end trainable densely connected residual spatial and channel attention network based on the conditional generative adversarial framework to directly restore a haze-free image from an input hazy image, without explicitly estimation of any atmospheric scattering parameters. Specifically, a novel residual attention module is proposed by combining spatial attention and channel attention mechanism, which could adaptively recalibrate spatial-wise and channel-wise feature weights by considering interdependencies among spatial and channel information. Such a mechanism allows the network to concentrate on more useful pixels and channels. Meanwhile, the dense network can maximize the information flow along features from different levels to encourage feature reuse and strengthen feature propagation. In addition, the network is trained with a multi-loss function, in which contrastive loss and registration loss are novel refined to restore sharper structures and ensure better visual quality. Experimental results demonstrate that the proposed method achieves the state-of-the-art performance on both public synthetic datasets and real-world images with more visually pleasing dehazed results.

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Journal articles on the topic 'Spatial channel'

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