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[Display omitted] • Standard solar collectors' absorber geometry modification by inserting V-grooves. • Optimizing solar collectors based on the geometric modification was demonstrated. • Importance of the absorbing surface geometry combined with spectral selectivity. • Improvement of the efficiency of the collectors despite increasing the thermal losses. • Efficiency improvement up to 5.61%, considering a V-groove opening angle of 60°. Solar energy plays an essential role in the process of the energy transition to renewable sources, and so too do technological innovations for exploring these energy sources, and for improving the thermal efficiency of conventional flat solar collectors. This study set out to model, simulate, and investigate the effect of modifying the geometry of the absorber plate of standard solar collectors for heating liquids, by inserting V corrugations. This leads to making consequent modifications to geometrical and optical parameters that improve the efficiency of the equipment. This paper presents the application of a mathematical-graphical model that seeks an optimum incidence angle to corrugate an absorber plate. This model, based on available optical experimental data, was built to improve the efficiency of solar collectors. During its application, an investigation could be made of the effect of the corrugation on the radiation and on the convection coefficients, the correlations of which were introduced into the mathematical model, and some of them were neither mentioned nor used in previous publications. A case study was carried out to investigate the behavior of three different collectors and the improvement in the efficiency of these collectors. It was shown that by using V grooves the efficiency was improved for all three flat solar collectors studied. As seen, the geometric modification contributes to improving efficiency when associated with selective absorption layers of solar collectors. The combination of both strategies can enhance the thermal efficiency of solar collectors and this can be further explored by researchers and manufacturers. [ABSTRACT FROM AUTHOR]

The pretectum of vertebrates contains neurons responsive to global visual motion. These signals are sent to the cerebellum, forming a subcortical pathway for processing optic flow. Global motion neurons exhibit selectivity for both direction and speed, but this is usually assessed by first determining direction preference at intermediate velocity (16-32°/s) and then assessing speed tuning at the preferred direction. A consequence of this approach is that it is unknown if and how direction preference changes with speed. We measured directional selectivity in 114 pretectal neurons from 44 zebra finches ( Taeniopygia guttata ) across spatial and temporal frequencies, corresponding to a speed range of 0.062-1,024°/s. Pretectal neurons were most responsive at 32-64°/s with lower activity as speed increased or decreased. At each speed, we determined if cells were directionally selective, bidirectionally selective, omnidirectionally responsive, or unmodulated. Notably, at 32°/s, 60% of the cells were directionally selective, and 28% were omnidirectionally responsive. In contrast, at 1,024°/s, 20% of the cells were directionally selective, and nearly half of the population was omnidirectionally responsive. Only 15% of the cells were omnidirectionally excited across most speeds. The remaining 85% of the cells had direction tuning that changed with speed. Collectively, these results indicate a shift from a bias for directional tuning at intermediate speeds of global visual motion to a bias for omnidirectional responses at faster speeds. These results suggest a potential role for the pretectum during flight by detecting unexpected drift or potential collisions, depending on the speed of the optic flow signal., Competing Interests: The authors declare no competing financial interests., (Copyright © 2024 Dash et al.)

Block frames called directional analytic discrete cosine frames (DADCFs) are proposed for sparse image representation. In contrast to conventional overlapped frames, the proposed DADCFs require a reduced amount of 1) computational complexity, 2) memory usage, and 3) global memory access. These characteristics are strongly required for current high-resolution image processing. Specifically, we propose two DADCFs based on discrete cosine transform (DCT) and discrete sine transform (DST). The first DADCF is constructed from parallel separable transforms of DCT and DST, where the DST is permuted by row. The second DADCF is also designed based on DCT and DST, while the DST is customized to have no DC leakage property which is a desirable property for image processing. Both DADCFs have rich directional selectivity with slightly different characteristics each other and they can be implemented as non-overlapping block-based transforms, especially they form Parseval block frames with low transform redundancy. We perform experiments to evaluate our DADCFs and compare them with conventional directional block transforms in image recovery.

Angular tuning is preferential sensory response to a directional stimulus and is observed in the whisker tactile system. In whisker hair follicles, there are at least three types of low threshold mechanoreceptors (LTMRs): rapidly adapting (RA), slowly adapting type 1 (SA1), and slowly adapting type 2 (SA2). These LTMRs display angular tuning but their properties remain incompletely studied. Here, we used isolated rat whisker hair follicles and pressure-clamped single-fiber recordings to study angular tuning of these LTMRs. Angular tuning was determined with impulses elicited by ramp-and-hold deflection of whisker hair in 24 directions each at 15° for a total of 360°. We show that RA display impulses during ramp-up, both ramp-up and ramp-down, or ramp-down dynamic phases. Both SA1 and SA2 respond to angular stimuli with slowly adapting impulses in most angles. However, SA1 and SA2 show rapidly adapting responses in other angles. All the three types of LTMRs display strong angular tuning, and there is no significant difference in angular tuning index among them. Population wise, the majority of SA1 are tuned in the caudal direction, a large part of SA2 is tuned in the rostral direction, and RAs are tuned in multiple directions. In the angles showing strong tuning, the three LTMRs respond to increased stimulation amplitudes with increased impulse numbers in a hyperbola relationship, and the responsiveness based on impulse numbers is SA2 > SA1 > RA. Our findings provide new information on angular tuning properties of LTMRs in whisker hair follicles and help to understand directional encoding., Competing Interests: The authors declare no competing financial interests., (Copyright © 2022 Yamada et al.)