SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Aperture

168

The “just noticeable difference” (JND) represents the minimum amount by which a stimulus must change to produce a noticeable variation in one’s perceptual experience (i.e., Weber’s law). Recent work has shown that within-participant standard deviations of grip aperture (i.e., JNDs) increase linearly with increasing object size during the early, but not the late, stages of goal-directed grasping. A visually based explanation for this finding is that the early and late stages of grasping are respectively mediated by relative and absolute visual information and therefore render a time-dependent adherence to Weber’s law. Alternatively, a motor-based explanation contends that the larger aperture shaping impulses required for larger objects gives rise to a stochastic increase in the variability of motor output (i.e., impulse-variability hypothesis). To test the second explanation, we had participants grasp differently sized objects in grasping time criteria of 400 and 800 ms. Thus, the 400 ms condition required larger aperture shaping impulses than the 800 ms condition. In line with previous work, JNDs during early aperture shaping (i.e., at the time of peak aperture acceleration and peak aperture velocity) for both the 400 and 800 ms conditions scaled linearly with object size, whereas JNDs later in the response (i.e., at the time of peak grip aperture) did not. Moreover, the 400 and 800 ms conditions produced comparable slopes relating JNDs to object size. In other words, larger aperture shaping impulses did not give rise to a stochastic increase in aperture variability at each object size. As such, the theoretical tenets of the impulse-variability hypothesis do not provide a viable framework for the time-dependent scaling of JNDs to object size. Instead, we propose that a dynamic interplay between relative and absolute visual information gives rise to grasp trajectories that exhibit an early adherence and late violation to Weber’s law.

Concepts: Scientific method, Perception, Theory, Object, Pitch, Aperture, Psychophysics, Just-noticeable difference

152

It is essential for birds to be agile and aware of their immediate environment, especially when flying through dense foliage. To investigate the type of visual signals and strategies used by birds while negotiating cluttered environments, we presented budgerigars with vertically oriented apertures of different widths. We find that, when flying through narrow apertures, birds execute their maneuvers in an anticipatory fashion, with wing closures, if necessary, occurring well in advance of the aperture. When passing through an aperture that is narrower than the wingspan, the birds close their wings at a specific, constant distance before the aperture, which is independent of aperture width. In these cases, the birds also fly significantly higher, possibly pre-compensating for the drop in altitude. The speed of approach is largely constant, and independent of the width of the aperture. The constancy of the approach speed suggests a simple means by which optic flow can be used to gauge the distance and width of the aperture, and guide wing closure.

Concepts: Optics, Bird, Flight, Wing, Flying and gliding animals, Aperture, Bird flight, Denny Laine

45

Current optical microscope objectives of low magnification have low numerical aperture and therefore have too little depth resolution and discrimination to perform well in confocal and nonlinear microscopy. This is a serious limitation in important areas, including the phenotypic screening of human genes in transgenic mice by study of embryos undergoing advanced organogenesis. We have built an optical lens system for 3D imaging of objects up to 6 mm wide and 3 mm thick with depth resolution of only a few microns instead of the tens of microns currently attained, allowing sub-cellular detail to be resolved throughout the volume. We present this lens, called the Mesolens, with performance data and images from biological specimens including confocal images of whole fixed and intact fluorescently-stained 12.5-day old mouse embryos.

Concepts: Gene, Cell, Optics, Microscope, Magnification, Microscopy, Lens, Aperture

29

While metal halide perovskite solar cells (PSCs) presently attract enormous research interest because of their high solar to electric power conversion efficiency (PCE) and low fabrication costs, their practical development is hampered by difficulties to reach high performance on large size devices. Here we introduce a simple vacuum-flash solution processing method to obtain shiny, smooth and crystalline perovskite films of high electronic quality over large areas. This enables us to fabricate solar cells with an aperture area exceeding 1 cm(2) showing a maximum efficiency of 20.5% and a certified PCE of 19.6. This exceeds by far the current certified record of 15.6% for PSC of similar size. We demonstrate that the reproducibility of the method is excellent and that the cells show virtually no hysteresis. The success of this new approach paves the way to realize highly efficient large-area PSCs for practical deployment.

Concepts: Method acting, Solar cell, Energy conversion, Energy conversion efficiency, Energy development, Halide, Aperture, Metal halide lamp

27

BACKGROUND: Optimizing operational parameters of the digital microscope system is an important technique to acquire high quality cytogenetic images and facilitate the process of karyotyping so that the efficiency and accuracy of diagnosis can be improved. OBJECTIVE: This study investigated the impact of condenser on cytogenetic image quality and system working performance using a prototype digital microscope image scanning system. METHODS: Both theoretical analysis and experimental validations through objectively evaluating a resolution test chart and subjectively observing large numbers of specimen were conducted. RESULTS: The results show that the optimal image quality and large depth of field (DOF) are simultaneously obtained when the numerical aperture of condenser is set as 60%~70% of the corresponding objective. Under this condition, more analyzable chromosomes and diagnostic information are obtained. As a result, the system shows higher working stability and less restriction for the implementation of algorithms such as autofocusing especially when the system is designed to achieve high throughput continuous image scanning. CONCLUSIONS: Although the above quantitative results were obtained using a specific prototype system under the experimental conditions reported in this paper, the presented evaluation methodologies can provide valuable guidelines for optimizing operational parameters in cytogenetic imaging using the high throughput continuous scanning microscopes in clinical practice.

Concepts: Scientific method, Optics, Evaluation, Microscope, Aperture, F-number, Depth of field, Microscopes

26

The ever-increasing brightness of synchrotron radiation sources demands improved X-ray optics to utilise their capability for imaging and probing biological cells, nanodevices, and functional matter on the nanometer scale with chemical sensitivity. Here we demonstrate focusing a hard X-ray beam to an 8 nm focus using a volume zone plate (also referred to as a wedged multilayer Laue lens). This lens was constructed using a new deposition technique that enabled the independent control of the angle and thickness of diffracting layers to microradian and nanometer precision, respectively. This ensured that the Bragg condition is satisfied at each point along the lens, leading to a high numerical aperture that is limited only by its extent. We developed a phase-shifting interferometric method based on ptychography to characterise the lens focus. The precision of the fabrication and characterisation demonstrated here provides the path to efficient X-ray optics for imaging at 1 nm resolution.

Concepts: DNA, Diffraction, X-ray, Optics, Light, X-ray crystallography, Synchrotron radiation, Aperture

17

Unlike the electrostatic and electromagnetic lenses used in electron microscopy, most X-ray focusing optical systems have fixed optical parameters with constant numerical apertures (NAs). This lack of adaptability has significantly limited application targets. In the research described herein, we developed a variable-NA X-ray focusing system based on four deformable mirrors, two sets of Kirkpatrick-Baez-type focusing mirrors, in order to control the focusing size while keeping the position of the focus unchanged. We applied a mirror deformation procedure using optical/X-ray metrology for offline/online adjustments. We performed a focusing test at a SPring-8 beamline and confirmed that the beam size varied from 108 nm to 560 nm (165 nm to 1434 nm) in the horizontal (vertical) direction by controlling the NA while maintaining diffraction-limited conditions.

Concepts: Electron, Diffraction, Optics, Light, Electromagnetic radiation, Mirror, Aperture, F-number

15

Field of view and accommodative focus are two fundamental attributes of many imaging systems, ranging from human eyes to microscopes. Here, we present arrays of Fresnel zone plates fabricated on a flexible substrate, which allows for the adjustment of both the field of view and optical focus. Such zone plates function as compact and lightweight microlenses and are fabricated using silicon nanowires. Inspired by compound eyes in nature, these microlenses are designed to point along various angles in order to capture images, offering an exceptionally wide field of view. Moreover, by flexing the substrate, the lens position can be adjusted, thus achieving axial focus scanning. An array of microlenses on a flexible substrate was incorporated into an optical system to demonstrate high resolution imaging of objects located at different axial and angular positions. These silicon based microlenses could be integrated with electronics and have a wide range of potential applications, from medical imaging to surveillance.

Concepts: Diffraction, Optics, Eye, Lens, Focal length, Science of photography, Aperture, Fresnel diffraction

7

The iris, found in many animal species, is a biological tissue that can change the aperture (pupil) size to regulate light transmission into the eye in response to varying illumination conditions. The self-regulation of the eye lies behind its autofocusing ability and large dynamic range, rendering it the ultimate “imaging device” and a continuous source of inspiration in science. In optical imaging devices, adjustable apertures play a vital role as they control the light exposure, the depth of field, and optical aberrations of the systems. Tunable irises demonstrated to date require external control through mechanical actuation, and are not capable of autonomous action in response to changing light intensity without control circuitry. A self-regulating artificial iris would offer new opportunities for device automation and stabilization. Here, this paper reports the first iris-like, liquid crystal elastomer device that can perform automatic shape-adjustment by reacting to the incident light power density. Similar to natural iris, the device closes under increasing light intensity, and upon reaching the minimum pupil size, reduces the light transmission by a factor of seven. The light-responsive materials design, together with photoalignment-based control over the molecular orientation, provides a new approach to automatic, self-regulating optical systems based on soft smart materials.

Concepts: Optics, Eye, Geometrical optics, Photography, Pupil, Aperture, F-number, Depth of field

7

Plant glutamate receptor homologs (GLRs) have long been proposed to function as ligand-gated Ca(2+) channels, but no in planta evidence has been provided. Here, we present genetic evidence that Arabidopsis GLR3.1 and GLR3.5 form Ca(2+) channels activated by L-methionine (L-Met) at physiological concentrations and regulate stomatal apertures and plant growth. The glr3.1/3.5 mutations resulted in a lower cytosolic Ca(2+) level, defective Ca(2+)-induced stomatal closure, and Ca(2+)-deficient growth disorder, all of which involved L-Met. Patch-clamp analyses of guard cells showed that GLR3.1/3.5 Ca(2+) channels are activated specifically by L-Met, with the activation abolished in glr3.1/3.5. Moreover, GLR3.1/3.5 Ca(2+) channels are distinct from previously characterized ROS-activated Ca(2+) channels and act upstream of ROS, providing Ca(2+) transients necessary for the activation of NADPH oxidases. Our data indicate that GLR3.1/3.5 constitute L-Met-activated Ca(2+) channels responsible for maintaining basal [Ca(2+)]cyt, play a pivotal role in plant growth, and act upstream of ROS, thereby regulating stomatal aperture.

Concepts: Photosynthesis, Eukaryote, NMDA receptor, Regulation, Ligand-gated ion channel, Stoma, Aperture, Function object