AlSub: Fully Parallel and Modular Subdivision

In recent years, mesh subdivision---the process of forging smooth free-form surfaces from coarse polygonal meshes---has become an indispensable production instrument. Although subdivision performance is crucial during simulation, animation and rendering, state-of-the-art approaches still rely on serial implementations for complex parts of the subdivision process. Therefore, they often fail to harness the power of modern parallel devices, like the graphics processing unit (GPU), for large parts of the algorithm and must resort to time-consuming serial preprocessing. In this paper, we show that a complete parallelization of the subdivision process for modern architectures is possible. Building on sparse matrix linear algebra, we show how to structure the complete subdivision process into a sequence of algebra operations. By restructuring and grouping these operations, we adapt the process for different use cases, such as regular subdivision of dynamic meshes, uniform subdivision for immutable topology, and feature-adaptive subdivision for efficient rendering of animated models. As the same machinery is used for all use cases, identical subdivision results are achieved in all parts of the production pipeline. As a second contribution, we show how these linear algebra formulations can effectively be translated into efficient GPU kernels. Applying our strategies to $\sqrt{3}$, Loop and Catmull-Clark subdivision shows significant speedups of our approach compared to state-of-the-art solutions, while we completely avoid serial preprocessing.Comment: Changed structure Added content Improved description

On The Determination of MDI High-Degree Mode Frequencies

The characteristic of the solar acoustic spectrum is such that mode lifetimes get shorter and spatial leaks get closer in frequency as the degree of a mode increases for a given order. A direct consequence of this property is that individual p-modes are only resolved at low and intermediate degrees, and that at high degrees, individual modes blend into ridges. Once modes have blended into ridges, the power distribution of the ridge defines the ridge central frequency and it will mask the true underlying mode frequency. An accurate model of the amplitude of the peaks that contribute to the ridge power distribution is needed to recover the underlying mode frequency from fitting the ridge. We present the results of fitting high degree power ridges (up to l = 900) computed from several two to three-month-long time-series of full-disk observations taken with the Michelson Doppler Imager (MDI) on-board the Solar and Heliospheric Observatory between 1996 and 1999. We also present a detailed discussion of the modeling of the ridge power distribution, and the contribution of the various observational and instrumental effects on the spatial leakage, in the context of the MDI instrument. We have constructed a physically motivated model (rather than some ad hoc correction scheme) resulting in a methodology that can produce an unbiased determination of high-degree modes, once the instrumental characteristics are well understood. Finally, we present changes in high degree mode parameters with epoch and thus solar activity level and discuss their significance.Comment: 59 pages, 38 figures -- High-resolution version at http://www-sgk.harvard.edu:1080/~sylvain/preprints/ -- Manuscript submitted to Ap

Smart CMOS image sensor for lightning detection and imaging

We present a CMOS image sensor dedicated to lightning detection and imaging. The detector has been designed to evaluate the potentiality of an on-chip lightning detection solution based on a smart sensor. This evaluation is performed in the frame of the predevelopment phase of the lightning detector that will be implemented in the Meteosat Third Generation Imager satellite for the European Space Agency. The lightning detection process is performed by a smart detector combining an in-pixel frame-to-frame difference comparison with an adjustable threshold and on-chip digital processing allowing an efficient localization of a faint lightning pulse on the entire large format array at a frequency of 1 kHz. A CMOS prototype sensor with a 256×256 pixel array and a 60 μm pixel pitch has been fabricated using a 0.35 μm 2P 5M technology and tested to validate the selected detection approach

Comparison of the thin flux tube approximation with 3D MHD simulations

The structure and dynamics of small vertical photospheric magnetic flux concentrations has been often treated in the framework of an approximation based upon a low-order truncation of the Taylor expansions of all quantities in the horizontal direction, together with the assumption of instantaneous total pressure balance at the boundary to the non-magnetic external medium. Formally, such an approximation is justified if the diameter of the structure (a flux tube or a flux sheet) is small compared to all other relevant length scales (scale height, radius of curvature, wavelength, etc.). The advent of realistic 3D radiative MHD simulations opens the possibility of checking the consistency of the approximation with the properties of the flux concentrations that form in the course of a simulation. We carry out a comparative analysis between the thin flux tube/sheet models and flux concentrations formed in a 3D radiation-MHD simulation. We compare the distribution of the vertical and horizontal components of the magnetic field in a 3D MHD simulation with the field distribution in the case of the thin flux tube/sheet approximation. We also consider the total (gas plus magnetic) pressure in the MHD simulation box. Flux concentrations with super-equipartition fields are reasonably well reproduced by the second-order thin flux tube/sheet approximation. The differences between approximation and simulation are due to the asymmetry and the dynamics of the simulated structures

On the Doppler Shift and Asymmetry of Stokes Profiles of Photospheric FeI and Chromospheric MgI Lines

We analyzed the full Stokes spectra using simultaneous measurements of the photospheric (FeI 630.15 and 630.25 nm) and chromospheric (MgI b2 517.27 nm) lines. The data were obtained with the HAO/NSO Advanced Stokes Polarimeter, about a near disc center sunspot region, NOAA AR 9661. We compare the characteristics of Stokes profiles in terms of Doppler shifts and asymmetries among the three spectral lines, which helps us to better understand the chromospheric lines and the magnetic and flow fields in different magnetic regions. The main results are: (1) For penumbral area observed by the photospheric FeI lines, Doppler velocities derived from Stokes I (Vi) are very close to those derived from linear polarization profiles (Vlp) but significantly different from those derived from Stokes V profiles (Vzc), which provides direct and strong evidence that the penumbral Evershed flows are magnetized and mainly carried by the horizontal magnetic component. (2) The rudimentary inverse Evershed effect observed by the MgI b2 line provides a qualitative evidence on its formation height that is around or just above the temperature minimum region. (3) Vzc and Vlp in penumbrae and Vzc in pores generally approach their Vi observed by the chromospheric MgI line, which is not the case for the photospheric FeI lines. (4) Outer penumbrae and pores show similar behavior of the Stokes V asymmetries that tend to change from positive values in the photosphere (FeI lines) to negative values in the low chromosphere (MgI line). (5) The Stokes V profiles in plage regions are highly asymmetric in the photosphere and more symmetric in the low chromosphere. (6) Strong red shifts and large asymmetries are found around the magnetic polarity inversion line within the common penumbra of the Delta spot. This study thus emphasizes the importance of spectro-polarimetry using chromospheric lines.Comment: 10 pages, 7 figures, accepted to The Astrophysical Journa

Stokes diagnostics of simulated solar magneto-convection

We present results of synthetic spectro-polarimetric diagnostics of radiative MHD simulations of solar surface convection with magnetic fields. Stokes profiles of Zeeman-sensitive lines of neutral iron in the visible and infrared spectral ranges emerging from the simulated atmosphere have been calculated in order to study their relation to the relevant physical quantities and compare with observational results. We have analyzed the dependence of the Stokes-I line strength and width as well as of the Stokes-V signal and asymmetries on the magnetic field strength. Furthermore, we have evaluated the correspondence between the actual velocities in the simulation with values determined from the Stokes-I (Doppler shift of the centre of gravity) and Stokes-V profiles (zero-crossing shift). We confirm that the line weakening in strong magnetic fields results from a higher temperature (at equal optical depth) in the magnetic flux concentrations. We also confirm that considerable Stokes-V asymmetries originate in the peripheral parts of strong magnetic flux concentrations, where the line of sight cuts through the magnetopause of the expanding flux concentration into the surrounding convective donwflow.Comment: Astronomy & Astrophysics, in pres

Universal Usability of Virtual Reality

Virtual Reality (VR) is envisioned to be a mainstream medium that would change how we work, connect, and play. For this vision to be realized, however, VR must be equally accessible and enjoyable for all users irrespective of their differences. This dissertation addresses two research themes that are concerned with the universal usability of VR.In the first theme, the gap in user experience quality between high-end VR platforms (PC VR) and low-end VR platforms (mobile VR) is addressed through the development of two low-cost acoustic interaction techniques for mobile VR. The first technique, PAWdio, appropriates a regular earbud and the smartphone's microphone to enable hand input for mobile VR. PAWdio was found to increase the immersiveness of the user experience compared to the traditional input of mobile VR. StereoTrack is another acoustic tracking technique that enables real walking in mobile VR using a pair of regular speakers and the smartphone's microphone. The interaction fidelity of StereoTrack was evaluated in terms of accuracy, precision, and latency. The potential of StereoTrack to augment existing locomotion techniques for mobile VR was also demonstrated in the context of two VR games.In the second theme, the effect of dynamic field-of-view (FOV) restriction as a technique to mitigate VR sickness on the sex gap in VR user experience was investigated through two studies that considered sex and FOV restriction as the variables under analysis. In the first study, the effect of dynamic FOV restriction on participants' route knowledge was examined using a triangle completion task. In the second study, participants' spatial learning as a response to changing the FOV was evaluated using a virtual version of the Morris Water Maze. Both studies aim to expand our understanding of the relationship between sex differences in spatial abilities, VR sickness, and FOV restriction in VR

Antecedents of the perceived organizational justice: An aggregated theoretical framework

The interest of the perceived organizational justice realm remains an increased manifold. It is a behavioral concept that emphasizes how people subjectively assess the ethical and moral norms of organizational management. Perceived organizational justice (OJ) is sometimes studied as a dependent variable, but often as an independent variable. For that reason, various OJ antecedents are examined in this paper, such as factors related to individual characteristics (Demographic characteristics, personality traits), culture (Individualism/collectivism, uncertainty avoidance, power distance, long, term/court term orientation, masculinity/femininity), organizational processes (organizational structure, HR practices, CSR initiatives), and interpersonal relationship (Leader-member-exchange and social contagion). Besides, the current paper presents an analytic review of the existing perceived organizational justice literature, and attempts to respond to the following question: What contributes to framing a fairness perception? Because of the multidisciplinary and interdisciplinarity of this field, we consolidated more than 125 theoretical and empirical papers, to portray firstly a holistic overview of fairness theories (cognitive/process and content theories), and highlight secondly the different relationships between perceived organizational justice and an array of predictors. Thereby, this review aims to contribute to the enrichment of the state of knowledge of justice or fairness, by providing a clear roadmap and deeper insight for researchers and practitioners concerned with perceived organizational justice, and enabling them to understand how and why people make such fairness perceptions in the workplace. To do so, we discuss its relationships with various antecedent aspects and propose an aggregated theoretical framework to identify multiple areas for future investigation and guide the field forward.The interest of the perceived organizational justice realm remains an increased manifold. It is a behavioral concept that emphasizes how people subjectively assess the ethical and moral norms of organizational management. Perceived organizational justice (OJ) is sometimes studied as a dependent variable, but often as an independent variable. For that reason, various OJ antecedents are examined in this paper, such as factors related to individual characteristics (Demographic characteristics, personality traits), culture (Individualism/collectivism, uncertainty avoidance, power distance, long, term/court term orientation, masculinity/femininity), organizational processes (organizational structure, HR practices, CSR initiatives), and interpersonal relationship (Leader-member-exchange and social contagion). Besides, the current paper presents an analytic review of the existing perceived organizational justice literature, and attempts to respond to the following question: What contributes to framing a fairness perception? Because of the multidisciplinary and interdisciplinarity of this field, we consolidated more than 125 theoretical and empirical papers, to portray firstly a holistic overview of fairness theories (cognitive/process and content theories), and highlight secondly the different relationships between perceived organizational justice and an array of predictors. Thereby, this review aims to contribute to the enrichment of the state of knowledge of justice or fairness, by providing a clear roadmap and deeper insight for researchers and practitioners concerned with perceived organizational justice, and enabling them to understand how and why people make such fairness perceptions in the workplace. To do so, we discuss its relationships with various antecedent aspects and propose an aggregated theoretical framework to identify multiple areas for future investigation and guide the field forward

Parent-Implemented Pivotal Response Treatment to Promote Social Communication Skills in Children with Autism

Providing children with autism with early intensive behavioral interventions has become a research priority. Specifically, early and intensive behavioral intervention of Pivotal Response Training (PRT) has been targeted as an effective natural behavioral intervention. The present study extended the use of PRT to teaching parents to implement this intervention in their home natural settings and was hypothesized to intensify and increase the time access to the intervention; hence, enhance maintenance and generalization of social communication skills for children with autism. A multiple-probe-across-setting design was used in this study to determine if training parents of children with autism to use Pivotal Response Treatment (PRT), specifically teaching their children to label and use query responses, enhanced social communication skills and also led to generalization in other settings. The results of this study of three distinct families who participated in this study showed that parents were able to learn, implement, and generalize the Pivotal Response Treatment (PRT) intervention. Also, the children of these parents significantly increased their communication responses at home and generalized these communication responses across different settings. Implications of the findings of this study were discussed and further lines of research were suggested. The implications included that social conversation could be enhanced through the implementation of naturalistic behavioral intervention that included motivational variables