Similar Aperture Research Articles

Visual working memories are abstractions of percepts.

During perception, decoding the orientation of gratings depends on complex interactions between the orientation of the grating, aperture edges, and topographic structure of the visual map. Here, we aimed to test how aperture biases described during perception affect working memory (WM) decoding. For memoranda, we used gratings multiplied by radial and angular modulators to generate orthogonal aperture biases for identical orientations. Therefore, if WM representations are simply maintained sensory representations, they would have similar aperture biases. If they are abstractions of sensory features, they would be unbiased and the modulator would have no effect on orientation decoding. Neural patterns of delay period activity while maintaining the orientation of gratings with one modulator (e.g. radial) were interchangeable with patterns while maintaining gratings with the other modulator (e.g. angular) in visual and parietal cortex, suggesting that WM representations are insensitive to aperture biases during perception. Then, we visualized memory abstractions of stimuli using models of visual field map properties. Regardless of aperture biases, WM representations of both modulated gratings were recoded into a single oriented line. These results provide strong evidence that visual WM representations are abstractions of percepts, immune to perceptual aperture biases, and compel revisions of WM theory.

Visual working memories are abstractions of percepts

During perception, decoding the orientation of gratings depends on complex interactions between the orientation of the grating, aperture edges, and topographic structure of the visual map. Here, we aimed to test how aperture biases described during perception affect working memory (WM) decoding. For memoranda, we used gratings multiplied by radial and angular modulators to generate orthogonal aperture biases for identical orientations. Therefore, if WM representations are simply maintained sensory representations, they would have similar aperture biases. If they are abstractions of sensory features, they would be unbiased and the modulator would have no effect on orientation decoding. Neural patterns of delay period activity while maintaining the orientation of gratings with one modulator (e.g. radial) were interchangeable with patterns while maintaining gratings with the other modulator (e.g. angular) in visual and parietal cortex, suggesting that WM representations are insensitive to aperture biases during perception. Then, we visualized memory abstractions of stimuli using models of visual field map properties. Regardless of aperture biases, WM representations of both modulated gratings were recoded into a single oriented line. These results provide strong evidence that visual WM representations are abstractions of percepts, immune to perceptual aperture biases, and compel revisions of WM theory.

The theoretical approach of the solar organic Rankine cycle integrated with phase change material for the Hungarian region

AbstractHungary is not only dependent on imports of natural gas and fossil fuels, but Hungary is also the lowest in renewable energy utilization; otherwise, only 11.3% compared to other Central European countries in renewable energy utilization, above 13%. The percentage of renewables in power generation quadrupled from 8% to 16% between 2010 and 2020, with most of the gains coming from the rapid expansion of solar energy, particularly after 2016. Regarding solar energy resource potential, Hungary has a daily total of around 3.2–3.6 kWh/m2 and a yearly total of about 1168–1314 kW.h/m2. This makes it a suitable location for putting solar thermal collectors in conjunction with an organic Rankine cycle (ORC) system. In this study, the authors analyzed solar thermal as a heat source to generate electricity with ORC using two types of working fluids (R245fa and R123). Hungary's weather data for a whole year is used as primary data to look for solar radiation characteristics and ambient temperature. Based on the general solar collector equation, the parabolic tube collector was selected as the best solar collector to utilize solar radiation by producing a maximum heat of around 654.68 kW. Therefore, the evacuated flat plate collector was selected as the solar collector that can produce the maximum outlet temperature of around 372.15 K with a similar size aperture area. Producing a temperature output from the solar collector for heat transfer in the ORC system and from the performance showed that R245fa resulted in better Wnet performance compared with R123 with values of 45.82 and 28.17 kW, respectively, under the same solar collector. Meanwhile, the material suitable for the thermal energy storage‐evaporator combination is organic phase change material using N‐Octacosane, which in the same temperature range (350–375 K) has the smallest ζ(T) value (1.08–1.103), so the mass required for the system is very efficient.

Wavefront measurement of a large aperture high image quality off-axis Fresnel lens.

Large aperture off-axis Fresnel lens will play an important role in the future 10 m scale aperture transmission space telescope system. Improving diffraction efficiency and wavefront image quality is always the goal of engineering applications. A 4-level off-axis fresnel lens with Ф350 mm effective aperture was fabricated through overlay etching technique by laser direct writing system. The wavefront aberration characteristics of the off-axis Fresnel lens at 632.8 nm wavelength are analyzed and discussed in detail, and the large aperture off-axis Fresnel lenses wavefront aberration measurement scheme, including a high-precision plane reflector, measured LAOFL, CGH, interferometer and laser tracker to compensate for certain low-order aberrations caused by LAOFL imperfect imaging, is proposed. Wavefront aberration of 0.020 λ(1/50 λ) RMS was achieved. This work presented the best results to our knowledge among the same field with similar aperture in open publications and provided a strong foundation for the future 10 m scale aperture transmission space telescope system.

Insect netting: effect of mesh size and shape on exclusion of some fruit pests and natural enemies under laboratory and orchard conditions

To improve exclusion systems for fruit trees, insect nets of various types were evaluated for their permeability to different beneficial and pest species, under laboratory and field conditions. Pests studied were the apple maggot, Rhagoletis pomonella (Diptera: Tephritidae) and the spotted wing drosophila, Drosophila suzukii (Diptera: Drosophilidae). Beneficials were Aphidoletes aphidimyza (Diptera: Cecidomyiidae), Aphidius matricariae (Hymenoptera: Braconidae) and Aphelinus abdominalis (Hymenoptera: Aphelinidae). Mesh nets with five different apertures (square, rectangle, triangle, rhombus and hexagon) and six different sizes (from 0.4 to 2.8 mm) were 3D-printed from strands of polylactic acid and tested in the laboratory along with two commercially available nets made of polyethylene. The physical and behavioral characteristics of the six studied species affected their ability to cross the nets. For an equal size (open area), the intrusion rate was generally greater through the square- and/or hexagonal-shaped meshes. Rectangular-shaped apertures totally excluded the apple maggot in both laboratory and field trials, provided their shortest side did not exceed 1.9 mm. For the spotted wing drosophila, a maximum of 1.0 mm was similarly required for exclusion in the laboratory. The shape factor (length/width ratio) of the apertures appeared to affect net selectivity. Field trials confirmed that more aphid predators and leafroller parasitoids colonized trees covered with larger mesh nets (2.3 × 3.4 mm), while still excluding the apple maggot. Thus, for a similar aperture size (area), an elongated rectangular-shaped mesh appears to facilitate access for beneficials, while continuing to provide effective protection against apple pests.

Large aperture high diffraction efficiency off-axis Fresnel lens fabrication and analysis.

Large aperture high diffraction efficiency off-axis Fresnel lens is one of the most important optical elements in future 10m scale aperture transmissive space telescope systems. Improving diffraction efficiency and effective aperture are long-term goals and bottlenecks for engineering applications. A 4-level off-axis fresnel lens with Ф350 mm effective aperture and 2 µm critical dimension was fabricated through overlay etching technique bylaser direct writing system. Average diffraction efficiency of 75.9% was achieved and certain distribution pattern was observed. Influence of alignment errors on diffraction efficiency distribution was analysed and discussed in detail. This work presented the best results to our knowledge among the same field with similar aperture and critical dimension in open publications, and layed a solid foundation for future large aperture diffractive telescope development.

Dust Production of Interstellar Comet 2I/Borisov Throughout Perihelion

Abstract The recently discovered comet 2I/Borisov quickly became a prime target for comet observers during its perihelion approach in 2019 December, after it was discovered to be the first comet of interstellar origin. We present our observations and measurements of the dust production between 2019 October, when the interstellar comet became bright enough for small aperture telescopes, and 2020 January, when the comet entered the plane of the Milky Way. We observed the comet for 24 nights using three telescopes in the public iTelescope network. The telescopes spanned both the Northern and Southern hemispheres, were of similar aperture size (0.43–0.51 m), and employed a Johnson–Cousins R C filter. Using these data, we measure an A(0°)f ρ range of 94 ± 14 to 139 ± 34 cm, a dust production rate Q dust range of 11.2 ± 4.4 to 16.4 ± 7.3 kg s−1, and a dust-brightness profile-parameter range of −0.95 ± 0.11 to −1.81 ± 0.20 for the interstellar comet. This work revealed low dust production rates from the comet that remained consistent throughout its apparition, with no notable brightening or increase in dust production throughout the observing campaign.

Asteroid Photometry with PIRATE: Optimizations and Techniques for Small Aperture Telescopes

Small aperture telescopes provide the opportunity to conduct high frequency, targeted observations of near-Earth Asteroids that are not feasible with larger facilities due to highly competitive time allocation requirements. Observations of asteroids with these types of facilities often focus on rotational brightness variations rather than longer-term phase angle-dependent variations (phase curves) due to the difficulty of achieving high precision photometric calibration. We have developed an automated asteroid light curve extraction and calibration pipeline for images of moving objects from the 0.43 m Physics Innovations Robotic Telescope Explorer. This allows for the frequency and quality of observations required to construct asteroid phase curves. Optimizations in standard data reduction procedures are identified that may allow for similar small aperture facilities, constructed from commercially available/off-the-shelf components, to improve the image and subsequent data quality. A demonstration of the hardware and software capabilities is expressed through observation statistics from a 10 months observing campaign, and through the photometric characterization of near-Earth Asteroids 8014 (1990 MF) and 19764 (2000 NF5).

Freeform based hYperspectral imager for MOisture Sensing (FYMOS).

We present FYMOS, an all-aluminum, robust, light weight, freeform based, near infrared hYperspectral imager for MOisture Sensing. FYMOS was designed and built to remotely measure moisture content using spectral features from 0.7-1.7µm integrating an InGaAs sensor. The imaging system, operating at F/2.8, is based on the three-concentric-mirror (Offner) spectrograph configuration providing a spectral resolution of 8 nm optimized for broad spectral coverage with sufficient resolution to make assessments of water levels. To optimize the optical performance, whilst minimizing weight and size, the design incorporates a bespoke freeform blazed grating machined on a commercial 5 axis ultra precision diamond machine. We achieve a 30% improvement on the RMS wavefront error in the spatial and spectral fields compared to a conventional Offner-Chrisp design with similar aperture and the monolithic Primary/Tertiary mirror eases the manufacturing assembly whilst minimizing weight. We demonstrate the performance of FYMOS by measuring the evaporation rate of water on a soil sample and results are processed with a physical multilayer radiative transfer model (MARMIT) to estimate the mean water thickness.

Modal control refractive Fresnel lens with uniform liquid crystal layer

We present the experimental and theoretical study of a refractive Fresnel lens design based on the “modal control” principle. Comparison of its performance with a similar but single aperture (6 mm) lens shows that the suggested Fresnel lens can achieve higher optical powers (above 3 diopters). A combined control mode is suggested to optimize its operation for different focal ranges. Theoretical modeling demonstrates the possibility of further improvement of its aberrations by means of an optimized driving technique.

Gaussian-like transverse-mode profile characteristics of high-power large-area red-emitting VCSELs.

We demonstrate a large-area red-emitting vertical-cavity surface-emitting laser (VCSEL) structure with significant improvement in the uniformity of charge carrier distribution by adopting a Si-doped $ {{\rm Al}_{0.20}}{\rm GaInP} $Al0.20GaInP current spreading layer and a bottom disk contact. The new structure emitting at 670 nm with a bottom disk contact diameter of 20 µm was compared with the conventional oxide-confined top-emitting structure with a similar aperture size. The maximum output peak power increased from 8.8 mW to 22.5 mW under pulsed-mode operation at room temperature. The far field improved from a strong multiple-mode pattern to a Gaussian-like profile. The corresponding divergence angle of the far-field pattern at $ 2{\rm {I}}_{\rm{th}} $2Ith injection current reduced from 16.2° to 10.9°.

Inverted faces benefit from whole-face processing

Upright faces are thought to engage holistic processing whereby local regions are integrated into a unified whole for the purposes of rapid, efficient analysis. In contrast, inverted faces are thought to recruit a slower, less-accurate serial analysis of local features. Aperture paradigms, whereby a target face is revealed by a dynamic viewing window that shifts over the stimulus image, offer a compelling test of this view. If upright faces are processed holistically, perceptual judgements ought to be substantially disrupted when stimuli are viewed through apertures. In contrast, aperture viewing should produce little or no decrement in perceptual decisions when judging inverted faces, as they are thought to be subjected to serial feature-based analysis. Here we present four experiments that elucidate the effects of aperture viewing on the perception of upright and inverted faces. In our first two experiments, we find evidence of disproportionate aperture effects for upright faces relative to inverted faces. However, these findings are qualified by the fact that observers found it harder to discriminate inverted faces presented in the ‘baseline’ whole-face condition. When observers’ ability to discriminate faces in the whole-face condition was matched for difficulty (Experiments 3 and 4), we show that upright and inverted faces produce very similar aperture effects. These findings indicate that both upright and inverted faces benefit from whole-face processing and accord with other lines of evidence that faces engage qualitatively similar types of processing in both orientations.

Fast 3-D Imaging of Brain Organoids With a New Single-Objective Planar-Illumination Two-Photon Microscope.

Human inducible pluripotent stem cells (hiPSCs) hold a large potential for disease modeling. hiPSC-derived human astrocyte and neuronal cultures permit investigations of neural signaling pathways with subcellular resolution. Combinatorial cultures, and three-dimensional (3-D) embryonic bodies (EBs) enlarge the scope of investigations to multi-cellular phenomena. The highest level of complexity, brain organoids that—in many aspects—recapitulate anatomical and functional features of the developing brain permit the study of developmental and morphological aspects of human disease. An ideal microscope for 3-D tissue imaging at these different scales would combine features from both confocal laser-scanning and light-sheet microscopes: a micrometric optical sectioning capacity and sub-micrometric spatial resolution, a large field of view and high frame rate, and a low degree of invasiveness, i.e., ideally, a better photon efficiency than that of a confocal microscope. In the present work, we describe such an instrument that uses planar two-photon (2P) excitation. Its particularity is that—unlike two- or three-lens light-sheet microscopes—it uses a single, low-magnification, high-numerical aperture objective for the generation and scanning of a virtual light sheet. The microscope builds on a modified Nipkow-Petráň spinning-disk scheme for achieving wide-field excitation. However, unlike the Yokogawa design that uses a tandem disk, our concept combines micro lenses, dichroic mirrors and detection pinholes on a single disk. This new design, advantageous for 2P excitation, circumvents problems arising with the tandem disk from the large wavelength difference between the infrared excitation light and visible fluorescence. 2P fluorescence excited by the light sheet is collected with the same objective and imaged onto a fast sCMOS camera. We demonstrate 3-D imaging of TO-PRO3-stained EBs and of brain organoids, uncleared and after rapid partial transparisation with triethanolamine formamide (RTF) and we compare the performance of our instrument to that of a confocal laser-scanning microscope (CLSM) having a similar numerical aperture. Our large-field 2P-spinning disk microscope permits one order of magnitude faster imaging, affords less photobleaching and permits better depth penetration than a confocal microscope with similar spatial resolution.

Morphological Anomalies Observed on Vertebralina striata dOrbigny, 1826 Test in the Northern Coast of Karaburun Peninsula (Izmir-Turkey)

Morphological abnormalities have been observed on the test of recent foraminifer samples and locally different ecological conditions are suggested to be the cause of this phenomenon. Hypersalinity, presence of heavy metals, thermal springs, chemicals carried by the coastal and submarine springs found in karstic regions and rapid change in ecological parameters are suggested to play a major role in changing the ecological conditions that leads to abnormal test morphology in foraminifers. Abnormal test development, as well as twins and triplets are commonly observed in natural and artificial saltpans which form hypersaline environments. Submarine freshwater springs can cause extreme seasonal salinity variations on the coastal regions which affects the benthic foraminifer species and results in the abnormal test development. Vertebralina striata d Orbigny individuals with abnormal aperture morphology have been found in samples collected around the thermal springs in Çeşme-Ilıca Bay. More surprisingly, specimens with similar aperture abnormality have also been observed in samples collected from other two stations on the Karaburun Peninsula. Five of the abnormal specimens had two apertures the others had three. A specimen collected from Ilıca Bay had two apertures, one of which is the typical Vertebralina striata d Orbigny aperture, but the other was distantly located and rounded. Vertebralina striata d Orbigny is widely distributed in world s seas, however such aperture abnormalities has not been reported elsewhere. Observation of similar morphological abnormalities in three distinct locations suggests a common cause. The submarine spring found in Ilıca Bay supports the idea that spring waters affect the chemical composition of the seawater locally, leading to this aperture abnormality.

Capacity‐enhancement in MIMO systems using biomimetic electrically small antenna arrays

The authors investigate the performance of multi-input-multi-output (MIMO) communications systems that exploit biomimetic antenna arrays (BMAAs) with electrically small-aperture dimensions. By exploiting the mutual coupling between closely spaced radiating elements and extracting the maximum available power from all excitation modes of the array, BMAAs can significantly outperform conventional antenna arrays with similar aperture sizes. As a proof of concept demonstration, they examine the use of two-element BMAAs consisting of two $\lambda /4$λ/4 monopole antennas with variable element spacing in an MIMO system. The capacity of MIMO systems using such BMAAs is compared with those that use conventional antenna arrays with the same element types and spacing. Their simulation results demonstrate that using BMAAs can offer considerable capacity enhancements in an MIMO system. To experimentally verify these results, a prototype of a two-element BMAA operating at 615 MHz with element spacing of $\lambda /10$λ/10 and a regular array prototype with similar antenna elements and dimensions are fabricated and characterised. The performance of MIMO systems using these two antennas is modelled using numerical channel modelling using the measured antenna responses. These results are found to be in good agreement with theoretical predictions.

A Comparison of Hybrid Beamforming and Digital Beamforming With Low-Resolution ADCs for Multiple Users and Imperfect CSI

For 5G it will be important to leverage the available millimeter wave spectrum. To achieve an approximately omni- directional coverage with a similar effective antenna aperture compared to state of the art cellular systems, an antenna array is required at both the mobile and basestation. Due to the large bandwidth and inefficient amplifiers available in CMOS for mmWave, the analog front-end of the receiver with a large number of antennas becomes especially power hungry. Two main solutions exist to reduce the power consumption: hybrid beam forming and digital beam forming with low resolution Analog to Digital Converters (ADCs). In this work we compare the spectral and energy efficiency of both systems under practical system constraints. We consider the effects of channel estimation, transmitter impairments and multiple simultaneous users. Our power consumption model considers components reported in literature at 60 GHz. In contrast to many other works we also consider the correlation of the quantization error, and generalize the modeling of it to non-uniform quantizers and different quantizers at each antenna. The result shows that as the SNR gets larger the ADC resolution achieving the optimal energy efficiency gets also larger. The energy efficiency peaks for 5 bit resolution at high SNR, since due to other limiting factors the achievable rate almost saturates at this resolution. We also show that in the multi-user scenario digital beamforming is in any case more energy efficient than hybrid beamforming. In addition we show that if different ADC resolutions are used we can achieve any desired trade-offs between power consumption and rate close to those achieved with only one ADC resolution.

Processor dependent bias of spatial spectral estimates from coprime sensor arrays.

Coprime sensor arrays (CSAs) can estimate the directions of arrival of O(MN) narrowband plane wave sources using only O(M+N) sensors with the CSA product processor. Processing data from a finite aperture array effectively smears the true spatial power spectral density (PSD) with a kernel function determined by both the array geometry and the processing of the signals observed by the array. This paper examines the asymptotic behaviors of the kernel functions resulting from two different processors applied to a CSA sampling geometry in the limit of large aperture. The kernel functions of the product processed CSA and conventionally beamformed coprime sensor arrays (CBF CSA) are compared to the baseline of the kernel of a densely populated uniform line array (ULA) of similar aperture. At the limit of large aperture, the product processed CSA estimate is asymptotically unbiased like the ULA, while the CBF CSA estimate is not. The PSD estimates computed from the CSA processors are compared when spatially correlated Gaussian noise is an input to the array to highlight the bias issues.

Fabrication and Characterization of Single-Aperture 3.5-MHz BNT-Based Ultrasonic Transducer for Therapeutic Application.

This paper discusses the fabrication and characterization of 3.5-MHz single-element transducers for therapeutic applications in which the active elements are made of hard lead-free BNT-based and hard commercial PZT (PZT-841) piezoceramics. Composition of (BiNa0.88K0.08Li0.04)0.5(Ti0.985Mn0.015)O3 (BNKLT88-1.5Mn) was used to develop lead-free piezoelectric ceramic. Mn-doped samples exhibited high mechanical quality factor ( ) of 970, thickness coupling coefficient ( ) of 0.48, a dielectric constant ( ) of 310 (at 1 kHz), depolarization temperature ( ) of 200 °C, and coercive field ( ) of 52.5 kV/cm. Two different unfocused single-element transducers using BNKLT88-1.5Mn and PZT-841 with the same center frequency of 3.5 MHz and similar aperture size of 10.7 and 10.5 mm were fabricated. Pulse-echo response, acoustic frequency spectrum, acoustic pressure field, and acoustic intensity field of transducers were characterized. The BNT-based transducer shows linear response up to the peak-to-peak voltage of 105 V in which the maximum rarefactional acoustic pressure of 1.1 MPa, and acoustic intensity of 43 W/cm2 were achieved. Natural focal point of this transducer was at 60 mm from the surface of the transducer.

Achievable Rate and Energy Efficiency of Hybrid and Digital Beamforming Receivers With Low Resolution ADC

For 5G, it will be important to leverage the available millimeter wave spectrum. To achieve an approximately omnidirectional coverage with a similar effective antenna aperture compared with the state-of-the-art cellular systems, an antenna array is required at both the mobile and base stations. Due to the large bandwidth, the analog front-end of the receiver with a large number of antennas becomes especially power hungry. Two main solutions exist to reduce the power consumption: Hybrid BeamForming (HBF) and Digital BeamForming (DBF) with low resolution Analog to Digital Converters (ADCs). An HBF system can also be combined with low resolution ADCs. This paper compares the spectral and energy efficiency based on the RF-frontend configuration. A channel with multipath propagation is used. In contrast to previous publication, we take the spatial correlation of the quantization noise into account. We show that the low resolution ADC DBF is robust to small Automatic Gain Control (AGC) imperfections. We showed that in the low SNR regime, the performance of DBF even with 1–2 bit resolution outperforms HBF. If we consider the relationship of spectral and energy efficiency, DBF with 3–5 bit resolution achieves the best ratio of spectral efficiency per power consumption of the RF receiver frontend over a wide SNR range. The power consumption model is based on components reported in the literature.

Parametric Trough Solar Collector With Commercial Evacuated Receiver: Performance Comparison at Plant Level

A new anidolic parametric trough solar collector (PmTC) having 8.12 m net width aperture has been recently proposed for a commercial evacuated receiver tube with an absorber diameter of 70 mm. Since the collector was designed ignoring transmission, absorption, and reflection optical losses, calculations of the optical efficiency and the incidence angle modifier (IAM) by means of Monte Carlo spectral raytracing simulations using real slope errors distributions and taking into account Fresnel reflection losses were done. Comparison with an Eurotrough parabolic trough collector (PTC) shows an optical penalization of 5.1% due to the reflectivity and additional soiling of the secondary mirror, to an increase in the end losses and to the Fresnel reflection losses. The National Renewable Energy Laboratory (NREL) system advisor model (SAM) was used to perform annual simulations of two commercial 50 MWe oil power plants without thermal energy storage located in Seville. A PTC solar field consisting of 90 loops, each one having four Eurotrough solar collector assemblies (SCA) with 150 m length was first modeled resulting in a gross production of 386 kWh/(m2 yr). A PmTC solar field with the same module length and similar SCA net aperture area was also simulated. A final configuration of 94 loops and four SCAs with 100 m length per loop yields a gross production of 379 kWh/(m2 yr) showing no improvement compared to the reference PTC plant. The present study allows to advance in the understanding of the potential of the anidolic optic to produce optical geometries able to effectively improve the PTC technology in the short-term projecting results at a commercial plant level.