A practical method for animating anisotropic elastoplastic materials

This paper introduces a simple method for simulating highly anisotropic elastoplastic material behaviors like the dissolution of fibrous phenomena (splintering wood, shredding bales of hay) and materials composed of large numbers of irregularly‐shaped bodies (piles of twigs, pencils, or cards). We introduce a simple transformation of the anisotropic problem into an equivalent isotropic one, and we solve this new “fictitious” isotropic problem using an existing simulator based on the material point method. Our approach results in minimal changes to existing simulators, and it allows us to re‐use popular isotropic plasticity models like the Drucker‐Prager yield criterion instead of inventing new anisotropic plasticity models for every phenomenon we wish to simulate

Use your illusion: the flash-lag effect as a tool for psychophysics

The flash-lag effect is an illusion in which a moving object is perceived advanced beyond an aligned flash. The majority of research into the effect has been directed at specifying its source, though a small body of literature simply makes use of flash-lag to answer diverse questions about perception – without necessarily arbitrating between competing accounts of its nature. The current thesis expands on this little-explored potential of the flash-lag effect with the presentation of three papers reporting programmes of research that exploit the phenomenon to address issues unrelated to its cause. In the first paper it is shown that, like in visual flash-lag, a similar motion direction based anisotropy is evident in the motor version of the effect, in which one’s unseen limb is perceived ahead of a flash. Specifically, the effect is greater for motion towards, rather than away from fixation. Furthermore, Paper I also demonstrates for the first time a motor flash-drag effect, in which one’s unseen moving hand ‘drags’ the perceived position of a nearby flash. It is argued that both of these findings are evidence of parallels between vision and action systems. Paper II takes advantage of the explicitly perceptual nature of the flash-lag effect to investigate whether the visuospatial perception of threatening objects is different to that of non-threatening objects. It is ultimately shown that when a moving stimulus is threatening, the flash-lag effect is greater, regardless of its direction of motion. Paper III shows that gamma movement (the apparent contraction of disappearing stimuli) adds to and subtracts from the forward displacement of contracting and expanding stimuli, respectively. Prior to these papers, however, an overview chapter reviews the flash-lag literature, and argues that the effect can be a useful tool for psychophysics, even without a consensus on its origin

Visualization of Tensor Fields in Mechanics

Tensors are used to describe complex physical processes in many applications. Examples include the distribution of stresses in technical materials, acting forces during seismic events, or remodeling of biological tissues. While tensors encode such complex information mathematically precisely, the semantic interpretation of a tensor is challenging. Visualization can be beneficial here and is frequently used by domain experts. Typical strategies include the use of glyphs, color plots, lines, and isosurfaces. However, data complexity is nowadays accompanied by the sheer amount of data produced by large-scale simulations and adds another level of obstruction between user and data. Given the limitations of traditional methods, and the extra cognitive effort of simple methods, more advanced tensor field visualization approaches have been the focus of this work. This survey aims to provide an overview of recent research results with a strong application-oriented focus, targeting applications based on continuum mechanics, namely the fields of structural, bio-, and geomechanics. As such, the survey is complementing and extending previously published surveys. Its utility is twofold: (i) It serves as basis for the visualization community to get an overview of recent visualization techniques. (ii) It emphasizes and explains the necessity for further research for visualizations in this context

Visual crowding in driving

Acknowledgments: This work was funded in part by NIH Grant 1R01CA236793-01.Peer reviewedPublisher PD

Magnetism, FeS colloids, and Origins of Life

A number of features of living systems: reversible interactions and weak bonds underlying motor-dynamics; gel-sol transitions; cellular connected fractal organization; asymmetry in interactions and organization; quantum coherent phenomena; to name some, can have a natural accounting via $physical$ interactions, which we therefore seek to incorporate by expanding the horizons of `chemistry-only' approaches to the origins of life. It is suggested that the magnetic 'face' of the minerals from the inorganic world, recognized to have played a pivotal role in initiating Life, may throw light on some of these issues. A magnetic environment in the form of rocks in the Hadean Ocean could have enabled the accretion and therefore an ordered confinement of super-paramagnetic colloids within a structured phase. A moderate H-field can help magnetic nano-particles to not only overcome thermal fluctuations but also harness them. Such controlled dynamics brings in the possibility of accessing quantum effects, which together with frustrations in magnetic ordering and hysteresis (a natural mechanism for a primitive memory) could throw light on the birth of biological information which, as Abel argues, requires a combination of order and complexity. This scenario gains strength from observations of scale-free framboidal forms of the greigite mineral, with a magnetic basis of assembly. And greigite's metabolic potential plays a key role in the mound scenario of Russell and coworkers-an expansion of which is suggested for including magnetism.Comment: 42 pages, 5 figures, to be published in A.R. Memorial volume, Ed Krishnaswami Alladi, Springer 201

High-efficiency Blue Phase Liquid Crystal Displays

Blue phase liquid crystals (BPLCs) have a delicate lattice structure existing between chiral nematic and isotropic phases, with a stable temperature range of about 2 K. But due to short coherent length, these self-assembled nano-structured BPLCs have a fast response time. In the past three decades, the application of BPLC has been rather limited because of its narrow temperature range. In 2002, Kikuchi et al. developed a polymer stabilization method to extend the blue-phase temperature range to more than 60 K. This opens a new gateway for display and photonic applications. In this dissertation, I investigate the material properties of polymer-stabilized BPLCs. According the Gerber’s model, the Kerr constant of a BPLC is linearly proportional to the dielectric anisotropy of the LC host. Therefore, in the frequency domain, the relaxation of the Kerr constant follows the same trend as the dielectric relaxation of the host LC. I have carried out experiments to validate the theoretical predictions, and proposed a model called extended Cole-Cole model to describe the relaxation of the Kerr constant. On the other hand, because of the linear relationship, the Kerr constant should have the same sign as the dielectric anisotropy of the LC host; that is, a positive or negative Kerr constant results from positive (∆ε \u3e 0) or negative host LCs (∆ε \u3c 0), respectively. BPLCs with a positive Kerr constant have been studied extensively, but there has been no study on negative ∆ε polymer-stabilized BPLCs. Therefore, I have prepared a BPLC mixture using a negative ∆ε LC host and investigated its electro-optic properties. I have demonstrated that indeed the induced birefringence and Kerr constant are of negative sign. Due to the fast response time of BPLCs, color sequential display is made possible without color breakup. By removing the spatial color filters, the optical efficiency and resolution density are both tripled. With other advantages such as alignment free and wide viewing angle, polymer-stabilized BPLC is emerging as a promising candidate for next-generation displays. However, the optical efficiency of the BPLC cell is relatively low and the operating voltage is quite high using conventional in-plane-switching electrodes. I have proposed several device structures for improving the optical efficiency of transmissive BPLC cells. Significant improvement in transmittance is achieved by using enhanced protrusion electrodes, and a 100% transmittance is achievable using complementary enhanced protrusion electrode structure. For a conventional transmissive blue phase LCD, although it has superb performances indoor, when exposed to strong sunlight the displayed images could be washed out, leading to a degraded contrast ratio and readability. To overcome the sunlight readability problem, a common approach is to adaptively boost the backlight intensity, but the tradeoff is in the increased power consumption. Here, I have proposed a transflective blue phase LCD where the backlight is turned on in dark surroundings while ambient light is used to illuminate the displayed images in bright surroundings. Therefore, a good contrast ratio is preserved even for a strong ambient. I have proposed two transflective blue phase LCD structures, both of which have single cell gap, single gamma driving, reasonably wide view angle, low power consumption, and high optical efficiency. Among all the 3D technologies, integral imaging is an attractive approach due to its high efficiency and real image depth. However, the optimum observation distance should be adjusted as the displayed image depth changes. This requires a fast focal length change of an adaptive lens array. BPLC adaptive lenses are a good candidate because of their intrinsic fast response time. I have proposed several BPLC lens structures which are polarization independent and exhibit a parabolic phase profile in addition to fast response time. To meet the low power consumption requirement set by Energy Star, high optical efficiency is among the top lists of next-generation LCDs. In this dissertation, I have demonstrated some new device structures for improving the optical efficiency of a polymerstabilized BPLC transmissive display and proposed sunlight readable transflective blue-phase LCDs by utilizing ambient light to reduce the power consumption. Moreover, we have proposed several blue-phase LC adaptive lenses for high efficiency 3D displays

Magnetosensitive e-skins for interactive electronics

The rapid progress of electronics and computer science in the last years has brought humans and machines closer than ever before. Current trends like the Internet of Things and artificial intelligence are closing the gap even further, by providing ubiquitous data processing and sensing. As this ongoing revolution advances, novel forms of human-machine interactions are required in an ever more connected world. A crucial component to enable these interactions is the field of flexible electronics, which aims to establish a seamless link between living and artificial entities using electronic skins (e-skins). E-skins combine the functionality of commercial electronics with the soft, stretchable and biocompatible characteristics of human skin or tissue. Until lately, the focus had been to replicate the standard functions associated with human skin, such as, temperature, pressure and chemical detection. Yet, recent developments have also introduced non-standard sensing capabilities like magnetic field detection to create the field of magnetosensitive e-skins. The addition of a supplementary information channel—an electronic sixth sense—has sparked a wide range of applications in the fields of cognitive psychology and human-machine interactions. In this thesis, we expand the concept of magnetosensitive e-skins to include the notion of directionality, which utilizes the full interaction potential of the magnetic field vector. Also, we introduce the use of flexible magnetoelectronics in virtual/augmented reality and human-computer interfaces. Three main results are attained in the course of this work: (i) we first demonstrate how magnetosensitive e-skins can be used as humanmachine interfaces driven by permanent magnet sources in the range of 5 mT. (ii) Building upon this milestone, we realize the first magnetosensitive e-skins which are driven by the earth’s magnetic field of 50 μT. (iii) We fabricate magnetosensitive e-skins which push the detection limit below 1 μT. The magnetosensitive e-skins in this work open exciting possibilities for sensory substitution experiments and sensory processing disorder therapies. Futhermore, for human-machine interactions, they provide a new interactive platform for touchless and gestural control in virtual and augmented reality scenarios beyond the limitations of optics-based systems.Der rasante Fortschritt der Elektronik und der Informatik in den letzten Jahren hat Mensch und Maschine nähergebracht als je zuvor. Aktuelle Trends wie das Internet der Dinge und künstliche Intelligenz schließen die Lücke noch weiter, indem sie eine allgegenwärtige Datenverarbeitung und -erfassung ermöglichen. Mit fortschreitender Revolution sind neue Formen der Mensch-Maschine-Interaktion in einer immer vernetzter werdenden Welt erforderlich. Eine entscheidende Komponente, um diese Interaktionen zu ermöglichen, ist das Gebiet der flexiblen Elektronik, das darauf abzielt, mithilfe elektronischer Häute (e-skins) eine nahtlose Verbindung zwischen lebenden und künstlichen Entitäten herzustellen. E-skins verbinden die Funktionalität kommerzieller Elektronik mit den weichen, dehnbaren und biokompatiblen Eigenschaften menschlicher Haut oder menschlichen Gewebes. Bis vor kurzem lag der Schwerpunkt auf der Nachbildung der mit der menschlichen Haut verbundenen Standardfunktionen wie Temperatur-, Druck- und Chemikalienerkennung. Jüngste Entwicklungen haben jedoch auch nicht standardmäßige Erfassungsfähigkeiten wie die Magnetfelderkennung eingeführt, um das Feld magnetoempfindlicher e-skins zu erzeugen. Die Hinzufügung eines zusätzlichen Informationskanals - eines elektronischen sechsten Sinns - hat eine breite Palette von Anwendungen auf den Gebieten der kognitiven Psychologie und der Mensch-Maschine-Interaktionen ausgelöst. In dieser Arbeit erweitern wir das Konzept der magnetoempfindlichen e-skins um den Begriff der Richtwirkung, bei dem das volle Wechselwirkungspotential des Magnetfeldvektors genutzt wird. Außerdem führen wir die Verwendung flexibler Magnetoelektronik in der virtuellen Realität / erweiterten Realität und in Mensch-Computer-Schnittstellen ein. Im Verlauf dieser Arbeit werden drei Hauptergebnisse erzielt: (i) Wir demonstrieren erstmals, wie magnetoempfindliche e-skins als Mensch-Maschine-Schnittstellen verwendet werden können, die von Permanentmagnetquellen im Bereich von 5 mT angetrieben werden. (ii) Aufbauend auf diesem Meilenstein realisieren wir die ersten magnetoempfindlichen e-skins, die vom Erdmagnetfeld von 50 μT angetrieben werden. (iii) Wir fertigen magnetoempfindliche e-skins, bei denen die Nachweisgrenze unter 1 μT liegt. Die magnetoempfindlichen e-skins in dieser Arbeit eröffnen aufregende Möglichkeiten für sensorische Substitutionsexperimente und Therapien bei sensorischen Verarbeitungsstörungen. Darüber hinaus bieten sie für die Mensch-Maschine-Interaktion eine neue interaktive Plattform für die berührungslose und gestische Steuerung in virtuellen und Augmented Reality-Szenarien, die über die Grenzen optikbasierter Systeme hinausgehen

Diffusion tensor magnetic resonance imaging-derived myocardial fiber disarray in hypertensive left ventricular hypertrophy: visualization, quantification and the effect on mechanical function

Left ventricular hypertrophy induced by systemic hypertension is generally regarded a morphological precursor of unfortunate cardiovascular events. Myocardial fiber disarray has been long recognized as a prevalent hallmark of this pathology. In this chapter, ex vivo diffusion tensor magnetic resonance imaging is employed to delineate the regional loss of myocardial organization that is present in the excised heart of a spontaneously hypertensive rat, as opposed to a control. Fiber tracking results are provided that illustrate in great detail the alterations in the integrity of cardiac muscle microstructure due to the disease. A quantitative analysis is also performed. Another contribution of this chapter is the model-based assessment of the role of the myofiber disarray in modulating the mechanical properties of the myocardium. The results of this study improve our understanding of the structural remodeling mechanisms that are associated with hypetensive left ventricular hypertrophy and their role

共晶粒界拡散プロセスによる熱間加工ネオジム系永久磁石の高性能化

筑波大学 (University of Tsukuba)201