Computational investigation of diffusion, flow, and multi-scale mass transport in disordered and ordered materials using high-performance computing

Flow and mass transport processes through porous materials are ubiquitous in nature and industry. In order to study these phenomena, we developed a computational framework for massively parallel supercomputers based on lattice-Boltzmann and random-walk particle tracking methods. Using this framework, we simulated the flow and mass transport (advection-diffusion problem) in several types of ordered and disordered porous materials. The pore network of the materials was either generated algorithmically (using Jodrey-Tory method) or reconstructed using confocal laser scanning microscopy or scanning electron microscopy. The simulated flow velocity field and dynamics of the random-walk tracer ensemble were used to study the transient and asymptotic behavior of macroscopic transport parameters: permeability, effective diffusion, and hydrodynamic dispersion coefficients. This work has three distinct topics developed and analyzed in four chapters. Each chapter has been published as a separate study. The date of publication and corresponding journal name are denoted at the beginning of each chapter. The first part of this work (Chapter 1) is addressing a timely question of high-performance liquid chromatography on whether particle size distribution of the modern packing materials gives any advantage in terms of separation efficiency. The second part (Chapters 2 and 3) is focused on the effects of dimensionality and geometry of the channels on the transport inside different types of chromatographic supports (particulate packings, monoliths, and pillar arrays). In order to analyze these effects, we recorded transient values of the longitudinal and transverse hydrodynamic dispersion coefficients in unconfined, partially, and fully confined structures and analyzed the time and length scales of the transport phenomena within. In the last part of this work (Chapter 4) we investigated the influence of the shell thickness and diffusivity on separation efficiency of the core--shell packings. Based on the simulation results, we extended the Giddings theory of coupled eddy dispersion and confirmed the validity of the Kaczmarski-Guiochon model of interparticle mass-transfer. Overall, this study extends the understanding of the connection of geometry and morphology of the porous materials with their macroscopic transport parameters

Lightness in Stereoscopic Depth

In the present study I tested the effect of stereoscopic depth on the lightness of two targets equal in size, presented simultaneously so that one target appeared in depth coplanar to the background and the other appeared floating in a frontal plane closer to the observer. When targets were equal in luminance, the target that appeared more distant from the observer appeared also more contrasted to the background: when targets were increments with respect to the luminance of the background the distant target appeared lighter than the closer one; vice versa when targets were decrements the distant target appeared darker. Results are discussed with respect to the Gestalt factor “belongingness”, and to more recent finding of the effect of perceived size on lightness in the Delboeuf and the Ebbinghaus Illusions

San Lorenzo and the Poggendorff illusion in Ravenna

In the Mausoleum of Galla Placidia (Ravenna, Italy), the San Lorenzo lunette shows two peculiar visual effects: a transparency effect of gold seen through gold and perceptual collinearity between two parts of a cross which are physically misaligned. Both effects are found within the area of the halo surrounding the saint’s head. In this work we addressed the problem posed by the physical misalignment of the cross. Our hypothesis is that the physical misalignment went unnoticed throughout history because the artist produced a perceptual alignment to correct for the Poggendorff illusion. Hence, we asked observers to align two ends of a cross in a reproduction showing the silhouette of San Lorenzo’s torso holding the cross. Results support our hypothesis: both direction and magnitude of adjustments comply with the alignment in the original mosaic

The influence of physical illumination on lightness perception in simultaneous contrast displays

Three experiments investigated the role of physical illumination on lightness perception in simultaneous lightness contrast (SLC). Four configurations were employed: the classic textbook version of the illusion and three configurations that produced either enhanced or reduced SLC. Experiment 1 tested the effect of ambient illumination on lightness perception. It simulated very dark environmental conditions that nevertheless still allowed perception of different shades of gray. Experiment 2 tested the effect of the intensity of Gelb lighting on lightness perception. Experiment 3 presented two conditions that integrated illumination conditions from Experiments 1 and 2. Our results demonstrated an illumination effect on both lightness matching and perceived SLC contrast: As the intensity of illumination increased, the target on the black background appeared lighter, while the target on the white background was little affected. We hypothesize the existence of two illumination ranges that affect lightness perception differently: low and normal. In the low range, the SLC contrast was reduced and targets appeared darker. In the normal range, the SLC contrast and lightness matchings for each background were little changed across illumination intensities

Et Facta Est Lux: Experiencing Luminosity in Art and in the Real World

The experience of light determined some of the most intriguing cultural universals, yet it is an underrepresented problem in vision sciences. In their attempt to represent cultural universals, artists adopted empirical solutions to the representation of light sources. We believe that such graphic solutions are showcases of visual indexes related to the phenomenology of light, and therefore they already constitute a level of explanation for luminosity perception. This claim is supported by psychophysical experiments on the ‘glare effect’, an illusion that generates a vivid impression of self-luminosity only by means of quasi-linear luminance ramps. Recent studies show that a similar illusion can be obtained in absence of physically continuous luminance ramps. Results from several experiments suggest that: 1) the key features for luminosity perception lie within the photo-geometric structure of the proximal stimulus; 2) the processes involved in luminosity perception are intrinsically different from those involved in surface color perception

Mishaps, errors, and cognitive experiences: on the conceptualization of perceptual illusions

Although a visual illusion is often viewed as an amusing trick, for the vision scientist it is a question that demands an answer, which leads to even more questioning. All researchers hold their own chain of questions, the links of which depend on the very theory they adhere to. Perceptual theories are devoted to answering questions concerning sensation and perception, but in doing so they shape concepts such as reality and representation, which necessarily affect the concept of illusion. Here we consider the macroscopic aspects of such concepts in vision sciences from three classic viewpoints—Ecological, Cognitive, Gestalt approaches—as we see this a starting point to understand in which terms illusions can become a tool in the hand of the neuroscientist. In fact, illusions can be effective tools in studying the brain in reference to perception and also to cognition in a much broader sense. A theoretical debate is, however, mandatory, in particular with regards to concepts such as veridicality and representation. Whether a perceptual outcome is considered as veridical or illusory (and, consequently, whether a class of phenomena should be classified as perceptual illusions or not) depends on the meaning of such concepts

Can music be figurative? Exploring the possibility of crossmodal similarities between music and visual arts

According to both experimental research and common sense, classical music is a better fit for figurative art than jazz. We hypothesize that similar fits may reflect underlying crossmodal structural similarities between music and painting genres. We present two preliminary studies aimed at addressing our hypothesis. Experiment 1 tested the goodness of the fit between two music genres (classical and jazz) and two painting genres (figurative and abstract). Participants were presented with twenty sets of six paintings (three figurative, three abstract) viewed in combination with three sound conditions: 1) silence, 2) classical music, or 3) jazz. While figurative paintings scored higher aesthetic appreciation than abstract ones, a gender effect was also found: the aesthetic appreciation of paintings in male participants was modulated by music genre, whilst music genre did not affect the aesthetic appreciation in female participants. Our results support only in part the notion that classical music enhances the aesthetic appreciation of figurative art. Experiment 2 aimed at testing whether the conceptual categories ‘figurative’ and ‘abstract’ can be extended also to music. In session 1, participants were first asked to classify 30 paintings (10 abstract, 10 figurative, 10 ambiguous that could fit either category) as abstract or figurative and the to rate them for pleasantness; in session 2 participants were asked to classify 40 excerpts of music (20 classical, 20 jazz) as abstract or figurative and to rate them for pleasantness. Paintings which were clearly abstract or figurative were all classified accordingly, while the majority of ambiguous paintings were classified as abstract. Results also show a gender effect for painting’s pleasantness: female participants rated higher ambiguous and abstract paintings. More interestingly, results show an effect of music genre on classification, showing that it is possible to classify music as figurative or abstract, thus supporting the hypothesis of cross-modal similarities between the two sensory-different artistic expressions

The Poggendorff illusion in Ruben's Descent from the Cross in Antwerp: Does the illusion even matter?

Two experiments are described, the purpose of which was to investigate the presence of a misalignment illusion caused by Poggendorff-like conditions in two paintings by Peter Paul Rubens, both depicting the Descent from the Cross, one located in Antwerp (Belgium), the other in Lille (France). The first shows a geometrical misalignment made by Rubens in a minor detail, which is considered proof that the artist observed the Poggendorff illusion. The second painting, instead, shows a perfect geometrical alignment in a similar detail. In experiment 1, participants were asked to align a top segment to a lower one in two types of stimuli: a full-size digitally manipulated reproduction of the painting and a Poggendorff-like configuration that recalled the painting's lines displacement and tilt. Adjustments were performed from two distances, one up close (painting distance) and one from below and far (observation distance). Results confirmed the presence of the Poggendorff illusion, but mean adjustments significantly differed from the misalignment perpetrated by Rubens. Experiment 2 was set up in a similar fashion with the Lille painting. Results confirmed the presence of the Poggendorff illusion also in this painting; however, the alignment by Rubens coincides with the geometrical one. Results from both experiments do not support the claim that Rubens observed the Poggendorff illusion and therefore corrected for it in the Antwerp painting. An alternative account is discussed, which relates to the structural layout of the painting