Neural mechanisms underlying specific visual tasks during self-motion

Object movement detection during observers’ self-motion is critical in navigation. Given ample optical available variables, which of them would be used would help us reveal the strategies being employed. In this work, using functional magnetic resonance imaging (fMRI) methods, we investigated the neural substrate underlying specific visual motion related tasks, such as time to passage (TTP), depth parallax, and collision. Using a visual search paradigm implemented with MATLAB, we developed a psychophysical task to investigate how the target characteristics (initial depth, initial eccentricity, and independent velocity), spatial attention, and heading estimation would affect visual search, for better understanding the mechanisms involved in object movement detection during self-motion. The fMRI analysis shows that: 1. Bilateral precentral sulcus (PreCS), postcentral sulcus (PostCS) and bilateral hMT are strongly activated during the TTP task. 2. Cortical regions along the dorsal visual processing pathway, including bilateral hMT, superior parietal gyrus (SPG), PostCS, PreCS and superior frontal gyrus (SFG), play important roles in our depth perception test. 3. In the collision test, similar activation pattern has been found in normal controls and stroke patients with visual deficits, intraparietal sulcus (IPS), SPG, supplementary area (SMA) and premotor regions are highly activated. The psychophysical results in visual search tasks indicate targets located in central visual field and target placed closer to the observer are easier to detect, looming distractor demands attention, the detrimental effect increases with the increasing of the target eccentricity level, no preference has been found in visual search among different heading directions in this test. In summary, cortical regions along visual motion processing pathway are highly involved in object movement detection during self-motion, the observers will take flexible strategies when different optical cues are provided

Functional neuroanatomy of time-to-passage perception

The time until an approaching object passes the observer is referred to as time-to-passage (TTP). Accurate judgment of TTP is critical for visually guided navigation, such as when walking, riding a bicycle, or driving a car. Previous research has shown that observers are able to make TTP judgments in the absence of information about local retinal object expansion. In this paper we combine psychophysics and functional MRI (fMRI) to investigate the neural substrate of TTP processing. In a previous psychophysical study, we demonstrated that when local retinal expansion cues are not available, observers take advantage of multiple sources of information to judge TTP, such as optic flow and object retinal velocities, and integrate these cues through a flexible and economic strategy. To induce strategy changes, we introduced trials with motion but without coherent optic flow (0% coherence of the background), and trials with coherent, but noisy, optic flow (75% coherence of the background). In a functional magnetic resonance imaging (fMRI) study we found that coherent optic flow cues resulted in better behavioral performance as well as higher and broader cortical activations across the visual motion processing pathway. Blood oxygen-level-dependent (BOLD) signal changes showed significant involvement of optic flow processing in the precentral sulcus (PreCS), postcentral sulcus (PostCS) and middle temporal gyrus (MTG) across all conditions. Not only highly activated during motion processing, bilateral hMT areas also showed a complex pattern in TTP judgment processing, which reflected a flexible TTP response strategy.Accepted manuscrip

Pixelating Structural Color with Cholesteric Spherical Reflectors

While structural color is a powerful means of obtaining saturated and durable pigments that minimize absorption, scattering, and negative environmental impact, appearing naturally in animals and plants as well as in carefully designed artificial composites, it is fundamentally limited to spectral colors, leaving white and other mixed colors elusive. It also normally suffers from a strong viewing angle dependence, making color definition difficult. Herein, it is demonstrated that these challenges can be overcome by using cholesteric spherical reflectors (CSRs), spheres of polymerized cholesteric liquid crystal with radial alignment of the self-assembled helical structure. Exhibiting omnidirectional selective retroreflectivity of well-defined color, CSRs are discrete “packages” of structural color. This allows them to be used as pixels for generating nonspectral colors, following the principle of digital displays. A method of creating densely packed monolayers of CSRs with red (R), green (G), and blue (B) retroreflection is developed. Mixing them in equal proportions gives a white surface. By embedding the CSRs in an index matching transparent medium, nonselective specular reflections and scattering are avoided. The approach can be used to create arbitrary colors, including nonspectral ones, without any absorption or nonselective scattering, opening doors to decorating surfaces as desired while minimizing light loss

Unclonable human-invisible machine vision markers leveraging the omnidirectional chiral Bragg diffraction of cholesteric spherical reflectors

The seemingly simple step of molding a cholesteric liquid crystal into spherical shape, yielding a Cholesteric Spherical Reflector (CSR), has profound optical consequences that open a range of opportunities for potentially transformative technologies. The chiral Bragg diffraction resulting from the helical self-assembly of cholesterics becomes omnidirectional in CSRs. This turns them into selective retroreflectors that are exceptionally easy to distinguish— regardless of background—by simple and low-cost machine vision, while at the same time they can be made largely imperceptible to human vision. This allows them to be distributed in human-populated environments, laid out in the form of QR-code-like markers that help robots and Augmented Reality (AR) devices to operate reliably, and to identify items in their surroundings. At the scale of individual CSRs, unpredictable features within each marker turn them into Physical Unclonable Functions (PUFs), of great value for secure authentication. Via the machines reading them, CSR markers can thus act as trustworthy yet unobtrusive links between the physical world (buildings, vehicles, packaging,...) and its digital twin computer representation. This opens opportunities to address pressing challenges in logistics and supply chain management, recycling and the circular economy, sustainable construction of the built environment, and many other fields of individual, societal and commercial importance

History and Overview of Proton Therapy

The use of proton therapy in oncology is not a new idea. The unique physical properties of protons and potential advantages in radiation therapy were initially recognized in the 1940s. Since the first patients were treated in the 1950s, technology and clinical applications have evolved as evidenced by the increasing number of proton therapy centers and patients being treated throughout the world. This chapter will review the history of proton therapy providing a detailed overview of the cyclotron and synchrotron techniques used and how they have advanced with time

Ignition and energy release characteristics of energetic high-entropy alloy HfZrTiTa0.2Al0.8 under dynamic loading

Steel-like density HfZrTiTa0.2Al0.8 high entropy alloy (HEA) with a density of 7.78 g/cm3 is designed and fabricated as a novel energetic structural material (ESM). The microstructure, thermal analysis, compressive mechanical properties, ignition and energy release under dynamic loading are systemically investigated. The experimental results show that the HfZrTiTa0.2Al0.8 HEA has a single BCC solid solution structure, and spinodal decomposition with elements segregation in the nanoscale is observed. Thermal analysis shows the HEA keeps stable in the Ar atmosphere and the oxidizing reaction occurs in the Air atmosphere. The mechanical properties show brittle characteristics with maximum strength with 1520 MPa and fracture strain 0.07 and strain rate effect from 0.001s−1 to 3000s−1 is observed. Under high strain rate loading, the fracture-induced spark is observed, which is caused by an oxidizing reaction due to the rise. By direct ballistic test, the energy release velocity threshold is measured as 980 m/s, and the energy release intensity is more violent in higher velocity impact conditions. Moreover, the impact reaction degree is increased with increasing fragmentation degree and adiabatic temperature rise induced by impact. The designed HEA-ESM is a promising candidate that simultaneously possesses both high strength, high reactive heat and excellent energetic characteristics in the application field of high-strength ESM fragment