Mechanical Characterization of Two-Segment Free-Standing ZnO Nanowires Using Lateral Force Microscopy.

Mechanical characterization of quasi one-dimensional nanostructures is essential for the design of novel nanoelectromechanical systems. However, the results obtained on basic mechanical quantities, such as Young's modulus and fracture strength, show significant standard deviation in the literature. This is partly because of diversity in the quality of the nanowire, and partly because of inappropriately performed mechanical tests and simplified mechanical models. Here we present orientation-controlled bending and fracture studies on wet chemically grown vertical ZnO nanowires, using lateral force microscopy. The lateral force signal of the atomic force microscope was calibrated by a diamagnetic levitation spring system. By acquiring the bending curves of 14 nanowires, and applying a two-segment mechanical model, an average bending modulus of 108 ± 17 GPa was obtained, which was 23% lower than the Young's modulus of bulk ZnO in the [0001] direction. It was also found that the average fracture strain and stress inside the nanowire was above 3.1 ± 0.3 % and 3.3 ± 0.3 GPa, respectively. However, the fracture of the nanowires was governed by the quality of the nanowire/substrate interface. The demonstrated technique is a relatively simple and productive way for the accurate mechanical characterization of vertical nanowire arrays.

Calibration of random dot stereograms and correlograms free of monocular cues.

Dynamic random dot stereograms (DRDSs) and correlograms (DRDCs) are cyclopean stimuli containing binocular depth cues that are ideally, invisible by one eye alone. Thus, they are important tools in assessing stereoscopic function in experimental or ophthalmological diagnostic settings. However, widely used filter-based three-dimensional display technologies often cannot guarantee complete separation of the images intended for the two eyes. Without proper calibration, this may result in unwanted monocular cues in DRDSs and DRDCs, which may bias scientific or diagnostic results. Here, we use a simple mathematical model describing the relationship of digital video values and average luminance and dot contrast in the two eyes. We present an optimization algorithm that provides the set of digital video values that achieve minimal crosstalk at user-defined average luminance and dot contrast for both eyes based on photometric characteristics of a given display. We demonstrated in a psychophysical experiment with color normal participants that this solution is optimal because monocular cues were not detectable at either the calculated or the experimentally measured optima. We also explored the error by which a range of luminance and contrast combinations can be implemented. Although we used a specific monitor and red-green glasses as an example, our method can be easily applied for other filter based three-dimensional systems. This approach is useful for designing psychophysical experiments using cyclopean stimuli for a specific display.

Correction: Simple reaction times to cyclopean stimuli reveal that the binocular system is tuned to react faster to near than to far objects.

[This corrects the article DOI: 10.1371/journal.pone.0188895.].

Simple reaction times to cyclopean stimuli reveal that the binocular system is tuned to react faster to near than to far objects.

Binocular depth perception is an important mechanism to segregate the visual scene for mapping relevant objects in our environment. Convergent evidence from psychophysical and neurophysiological studies have revealed asymmetries between the processing of near (crossed) and far (uncrossed) binocular disparities. The aim of the present study was to test if near or far objects are processed faster and with higher contrast sensitivity in the visual system. We therefore measured the relationship between binocular disparity and simple reaction time (RT) as well as contrast gain based on the contrast-RT function in young healthy adults. RTs were measured to suddenly appearing cyclopean target stimuli, which were checkerboard patterns encoded by depth in dynamic random dot stereograms (DRDS). The DRDS technique allowed us to selectively study the stereoscopic processing system by eliminating all monocular cues. The results showed that disparity and contrast had significant effects on RTs. RTs as a function of disparity followed a U-shaped tuning curve indicating an optimum at around 15 arc min, where RTs were minimal. Surprisingly, the disparity tuning of RT was much less pronounced for far disparities. At the optimal disparity, we measured advantages of about 80 ms and 30 ms for near disparities at low (10%) and high (90%) contrasts, respectively. High contrast always reduced RTs as well as the disparity dependent differences. Furthermore, RT-based contrast gains were higher for near disparities in the range of disparities where RTs were the shortest. These results show that the sensitivity of the human visual system is biased for near versus far disparities and near stimuli can result in faster motor responses, probably because they bear higher biological relevance.

Spiral-Shaped Piezoelectric MEMS Cantilever Array for Fully Implantable Hearing Systems.

Fully implantable, self-powered hearing aids with no external unit could significantly increase the life quality of patients suffering severe hearing loss. This highly demanding concept, however, requires a strongly miniaturized device which is fully implantable in the middle/inner ear and includes the following components: frequency selective microphone or accelerometer, energy harvesting device, speech processor, and cochlear multielectrode. Here we demonstrate a low volume, piezoelectric micro-electromechanical system (MEMS) cantilever array which is sensitive, even in the lower part of the voice frequency range (300⁻700 Hz). The test array consisting of 16 cantilevers has been fabricated by standard bulk micromachining using a Si-on-Insulator (SOI) wafer and aluminum nitride (AlN) as a complementary metal-oxide-semiconductor (CMOS) and biocompatible piezoelectric material. The low frequency and low device footprint are ensured by Archimedean spiral geometry and Si seismic mass. Experimentally detected resonance frequencies were validated by an analytical model. The generated open circuit voltage (3⁻10 mV) is sufficient for the direct analog conversion of the signals for cochlear multielectrode implants.