Mach Bands: How Many Models are Possible? Recent Experiemental Findings and Modeling Attempts

Mach bands are illusory bright and dark bands seen where a luminance plateau meets a ramp, as in half-shadows or penumbras. A tremendous amount of work has been devoted to studying the psychophysics and the potential underlying neural circuitry concerning this phenomenon. A number of theoretical models have also been proposed, originating in the seminal studies of Mach himself. The present article reviews the main experimental findings after 1965 and the main recent theories of early vision that have attempted to discount for the effect. It is shown that the different theories share working principles and can be grouped in three clsses: a) feature-based; b) rule-based; and c) filling-in. In order to evaluate individual proposals it is necessary to consider them in the larger picture of visual science and to determine how they contribute to the understanding of vision in general.Air Force Office of Scientific Research (F49620-92-J-0334); Office of Naval Research (N00014-J-4100); COPPE/UFRJ, Brazi

Modulation Transfer Function Compensation Through A Modified Wiener Filter For Spatial Image Quality Improvement.

Kebergunaan data imej yang diperolehi dari suatu sensor pengimejan amat bergantung kepada keupayaan sensor tersebut untuk meresolusikan perincian spatial ke satu tahap yang boleh diterima. The usefulness of image data acquired from an imaging sensor critically depends on the ability of the sensor to resolve spatial details to an acceptable level

Pulsed-waveform generator based on coupled oscillators

Waveform sharpening in nonlinear transmissionlines (NLTL) is analyzed in detail and applied to the design of apulse-generator based on two coupled oscillators. The maximumpropagation frequency through the NLTL is calculated with arealistic numerical technique, which enables an optimized design.By coupling two NLTL oscillators terminated in grounded stubsof different length, three design parameters are available, whichenables a flexible mechanism for pulse formation. A reducedordermodel is proposed for the efficient determination of thetuning voltage in one of the oscillator elements. The analysis anddesign techniques have been applied to a prototype at 0.8 GHz.Spanish project TEC20 11-29264-C03-01 for financial support

High magnetic field scales and critical currents in SmFeAs(O,F) crystals: promising for applications

Superconducting technology provides most sensitive field detectors, promising implementations of qubits and high field magnets for medical imaging and for most powerful particle accelerators. Thus, with the discovery of new superconducting materials, such as the iron pnictides, exploring their potential for applications is one of the foremost tasks. Even if the critical temperature Tc is high, intrinsic electronic properties might render applications rather difficult, particularly if extreme electronic anisotropy prevents effective pinning of vortices and thus severely limits the critical current density, a problem well known for cuprates. While many questions concerning microscopic electronic properties of the iron pnictides have been successfully addressed and estimates point to a very high upper critical field, their application potential is less clarified. Thus we focus here on the critical currents, their anisotropy and the onset of electrical dissipation in high magnetic fields up to 65 T. Our detailed study of the transport properties of optimally doped SmFeAs(O,F) single crystals reveals a promising combination of high (>2 x 10^6 A/cm^2) and nearly isotropic critical current densities along all crystal directions. This favorable intragrain current transport in SmFeAs(O,F), which shows the highest Tc of 54 K at ambient pressure, is a crucial requirement for possible applications. Essential in these experiments are 4-probe measurements on Focused Ion Beam (FIB) cut single crystals with sub-\mu\m^2 cross-section, with current along and perpendicular to the crystallographic c-axis and very good signal-to-noise ratio (SNR) in pulsed magnetic fields. The pinning forces have been characterized by scaling the magnetically measured "peak effect"

The use of liquid crystal adaptive optics devices in astronomy

Images obtained from large astronomical telescopes are distorted and blurred by the effects of the atmosphere. In order to compensate for this, an adaptive optics system can be incorporated downstream from the telescope focus. Conventional technology uses small piezo-driven mirrors to deviate the wavefronts through angles of the order of tens of arcseconds. This thesis is concerned with the possible replacement of these mirrors with liquid crystal phase control devices, in particular, small-angle prisms. The thesis considers the following fundamental optical properties of liquid crystals relevant to astronomy; dispersion, optical quality, dynamic range, and response times. Results of a novel approach to electrically addressing liquid crystals by a ramp voltage are given

Fabrication of Silicon Microneedles for Dermal Interstitial Fluid Extraction in Human Subjects

The goal of this project is to design and develop a fabrication process for silicon microneedle arrays to extract dermal interstitial fluid (ISF) from human skin. ISF is a cell- free, living tissue medium that is known to contain many of the same, clinical biomarkers of general health, stress response and immune status as in blood. However, a significant barrier to adoption of ISF as a diagnostic matrix is the lack of a rapid, minimally invasive method of access and collection for analysis. Microfabricated chips containing arrays of microneedles that can rapidly and painlessly access and collect dermal ISF for bioassay could greatly facilitate point-of-care diagnosis and health monitoring, especially in times of crisis or in austere environments, where drawing venous blood poses an unnecessary infection or biohazard risk. Two different fabrication methods were explored. The first method borrows from a previously reported dicing saw process, where a series of parallel and perpendicular cuts of partial depth are made into a thicker silicon wafer, creating arrays of square columns, which are subsequently sharpened into needles. The second method uses a new, entirely-DRIE process to create the arrays of columns. The columns are sharpened into needles using an isotropic wet etch method (HNA etch) which preferentially enhances etching at the tips and diminishes etching at the base, creating remarkably sharp, conical shaped needles capable of piercing skin. The needles contain holes that pass through the wafer to the opposite side, where they connect to a series of microfluidic channels that lead to a reservoir. The back of the wafer is bonded to glass, providing a hydrophilic cap to the channels, as well as a way to see into the device to detect whether the channels are filling with liquid. The fabrication procedures for both methods are presented, along with 2D- and 3D-rendered schematics for the final devices. Needle geometric shape is crucial to their ability to extract ISF. To determine the appropriate pre-sharpened etched shape, needle columns with a variety of different shapes were designed, produced, sharpened, and examined under a scanning electron microscope. The most promising shapes were selected for further processing and testing. Resulting chips were first bench tested to ensure capillary filling capability, and then tested for ISF collection from human skin. Microneedle arrays which were successfully demonstrated to extract ISF are presented, and the unsuccessful shapes are also shown in the interest of completion. Potential means for improving performance and future research directions are discussed

Quantitative assessment for detection and monitoring of coastline dynamics with temporal RADARSAT images

© 2018 by the authors. This study aims to detect coastline changes using temporal synthetic aperture radar (SAR) images for the state of Kelantan, Malaysia. Two active images, namely, RADARSAT-1 captured in 2003 and RADARSAT-2 captured in 2014, were used to monitor such changes. We applied noise removal and edge detection filtering on RADARSAT images for preprocessing to remove salt and pepper distortion. Different segmentation analyses were also applied to the filtered images. Firstly, multiresolution segmentation, maximum spectral difference and chessboard segmentation were performed to separate land pixels from ocean ones. Next, the Taguchi method was used to optimise segmentation parameters. Subsequently, a support vector machine algorithm was applied on the optimised segments to classify shorelines with an accuracy of 98% for both temporal images. Results were validated using a thematic map from the Department of Survey and Mapping of Malaysia. The change detection showed an average difference in the shoreline of 12.5 m between 2003 and 2014. The methods developed in this study demonstrate the ability of active SAR sensors to map and detect shoreline changes, especially during low or high tides in tropical regions where passive sensor imagery is often masked by clouds

Temporal structure in spiking patterns of ganglion cells defines perceptual thresholds in rodents with subretinal prosthesis.

Subretinal prostheses are designed to restore sight in patients blinded by retinal degeneration using electrical stimulation of the inner retinal neurons. To relate retinal output to perception, we studied behavioral thresholds in blind rats with photovoltaic subretinal prostheses stimulated by full-field pulsed illumination at 20 Hz, and measured retinal ganglion cell (RGC) responses to similar stimuli ex-vivo. Behaviorally, rats exhibited startling response to changes in brightness, with an average contrast threshold of 12%, which could not be explained by changes in the average RGC spiking rate. However, RGCs exhibited millisecond-scale variations in spike timing, even when the average rate did not change significantly. At 12% temporal contrast, changes in firing patterns of prosthetic response were as significant as with 2.3% contrast steps in visible light stimulation of healthy retinas. This suggests that millisecond-scale changes in spiking patterns define perceptual thresholds of prosthetic vision. Response to the last pulse in the stimulation burst lasted longer than the steady-state response during the burst. This may be interpreted as an excitatory OFF response to prosthetic stimulation, and can explain behavioral response to decrease in illumination. Contrast enhancement of images prior to delivery to subretinal prosthesis can partially compensate for reduced contrast sensitivity of prosthetic vision