Virtual acoustic rendering by state wave synthesis

International audienceIn the context of the class of virtual acoustic simulation techniques that rely on traveling wave rendering as dictated by path-tracing methods (e.g, image-source, ray-tracing, beam-tracing) we introduce State Wave Synthesis (SWS), a novel framework for the efficient rendering of sound traveling waves as exchanged between multiple directional sound sources and multiple directional sound receivers in time-varying conditions.The proposed virtual acoustic rendering framework represents sound-emitting and sound-receiving objects as multiple-input, multiple-output dynamical systems. Each input or output corresponds to a sound traveling wave received or emitted by the object from/to different orientations or at/from different positions of the object. To allow for multiple arriving/departing waves from/to different orientations and/or positions of an object in dynamic conditions, we introduce a discrete-time state-space system formulation that allows the inputs or the outputs of a system to mutate dynamically. The SWS framework treats virtual source or receiver objects as time-varying dynamical systems in state-space modal form, each allowing for an unlimited number of sound traveling wave inputs and outputs.To model the sound emission and/or reception behavior of an object, data may be collected from measurements. These measurements, which may comprise real or virtual impulse or frequency responses from a real physical object or a numerical physical model of an object, are jointly processed to design a multiple-input, multiple-output state-space model with mutable inputs and/or outputs. This mutable state-space model enables the simulation of direction- and/or position-dependent, frequency-dependent sound wave emission or reception of the object. At run-time, each of the mutable state-space object models may present any number of inputs or outputs, with each input or output associated to a received/emitted sound traveling wave from/to specific arrival/departure position or orientation. In a first formulation, the sound wave form, the traveling of sound waves between object models is simulated by means of delay lines of time-varying length. In a second formulation, the state wave form, the traveling of sound waves between object models is simulated by way of propagating the state variables of source objects along delay lines of time-varying length. SWS allows the accurate simulation of frequency-dependent source directivity and receiver directivity in time-varying conditions without any time-domain or frequency-domain explicit convolution processing. In addition, the framework enables time-varying, obstacle-induced frequency-dependent attenuation of traveling waves without any dedicated digital filters. SWS facilitates the implementation of efficient virtual acoustic rendering engines either as software or in dedicated hardware, allowing realizations in which the number of delay lines is independent of the number of traveling wave paths being simulated. Moreover, the method enables a straightforward dynamic coupling between virtual acoustic objects and their physics-based simulation counterparts as performed by computer for animation, virtual reality, video-games, music synthesis, or other applications.In this presentation we will introduce the foundations of SWS and employ a real acoustic violin and a real human head as illustrative examples for a source object and a receiver object respectively. In light of available implementation possibilities, we will examine the basic memory requirements and computational cost of the rendering framework and suggest how to conveniently include minimum-phase diffusive elements to procure additional diffuse field contributions if necessary. Finally, we will expose limitations and discuss future opportunities for development

Effect of total pressure on the formation and size evolution of silicon quantum dots in silicon nitride films

The size of silicon quantum dots (Si QDs) embedded in silicon nitride (SiN(x)) has been controlled by varying the total pressure in the plasma-enhanced chemical vapor deposition (PECVD) reactor. This is evidenced by transmission electron microscopy and results in a shift in the light emission peak of the quantum dots. We show that the luminescence in our structures is attributed to the quantum confinement effect. These findings give a strong indication that the quality (density and size distribution) of Si QDs can be improved by optimizing the deposition parameters which opens a route to the fabrication of an all-Si tandem solar cell

Charge photo-carrier transport from silicon nanocrystals embedded in SiO_2-based multilayer structures

© 2012 American Institute of Physics This work was supported by the French National Agency for Research (ANR) through the DUOSIL project. Financial support has also been partly funded by the RhôneAlpes region in the frame of the PHOSIL project.Experimental investigation of photoconductivity in Si-rich silicon oxide (SRSO)/SiO_2 multilayer (ML) structures prepared by magnetron reactive sputtering is reported. Photocurrent (PC) measurements show that the PC threshold increases with decreasing the thickness of SRSO layer. Photo-conduction processes in our samples are shown to be dominated by carrier transport through quantum-confined silicon nanocrystals embedded in the SiO_2 host. In addition, the observed bias-dependence of photocurrent intensity is consistent with a model in which carrier transport occurs by both tunneling and hopping through defect states in the silicon oxide matrix. A photocurrent density J_(ph) of 1-2mA cm^(-2) is extracted from our results. Although this photocurrent density along the ML absorber film is relatively low, the results presented in this work are believed to be a valuable contribution toward the implementation of all-Si tandem solar cells.French National Agency for Research (ANR)Rhône-AlpesDepto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu

Characterization of organic packing materials in the removal of ammonia gas in automated biofilters

A fully-automated pilot-scale biofilter filled with coconut fiber as packing material was investigatedfor treatment of ammonia-containing off-gas streams. Coconut fiber was completely characterized forphysical and chemical parameters and biological activity. Biofilter performance was assessed in a pilot-scale unit in a set of continuous experiments varying the inlet ammonia concentration in a range of 45 to240 ppmv at a gas contact time of 36 seconds. Samples taken along the bed height as well as inlet and outletammonia concentrations were used to determine a maximum elimination capacity of 12 g NH3m?3h?1ata 80% removal efficiency. Some features related to nitrification inhibition encountered in the experimentsare also discussed.Peer ReviewedPostprint (published version

Structural and optoelectronical characterization of Si-SiO_2/SiO_2 multilayers with applications in all Si tandem solar cells

SiO_2 multilayers with embedded Si nanocrystals (Si-ncs) were investigated as an approach for developing highly efficient all Si tandem solar cells. The nanostructured samples, fabricated by means of a reactive magnetron sputtering, were structurally and optoelectronically characterized using different techniques. High resolution transmission electron microscopy (TEM) and energy filtered images in TEM show a high density of Si-nc with uniform sizes below 4 nm, while electrical characterization indicates high resistance values (10^2 kΩ) of these samples. In order to develop a better understanding of the optoelectronical behavior, photocurrent I-V curves were measured, obtaining variations under "dark" or "illumination" conditions. Recombination lifetimes in the order of tenths of nanoseconds were estimated by applying the transverse pump/probe technique

Nonalcoholic fatty liver disease, liver fibrosis, and structural brain imaging: The Cross-Cohort Collaboration

Background and purpose Prior studies reported conflicting findings regarding the association of nonalcoholic fatty liver disease (NAFLD) and liver fibrosis with measures of brain health. We examined whether NAFLD and liver fibrosis are associated with structural brain imaging measures in middle- and old-age adults. Methods In this cross-sectional study among dementia- and stroke-free individuals, data were pooled from the Offspring and Third Generation cohorts of the Framingham Heart Study (FHS), the Rotterdam Study (RS), and the Study of Health in Pomerania. NAFLD was assessed through abdominal imaging. Transient hepatic elastography (FibroScan) was used to assess liver fibrosis in FHS and RS. Linear regression models were used to explore the relation of NAFLD and liver fibrosis with brain volumes, including total brain, gray matter, hippocampus, and white matter hyperintensities, adjusting for potential confounders. Results were combined using fixed effects meta-analysis. Results In total, 5660 and 3022 individuals were included for NAFLD and liver fibrosis analyses, respectively. NAFLD was associated with smaller volumes of total brain (β = −3.5, 95% confidence interval [CI] = −5.4 to −1.7), total gray matter (β = −1.9, 95% CI = −3.4 to −0.3), and total cortical gray matter (β = −1.9, 95% CI = −3.7 to −0.01). In addition, liver fibrosis (defined as liver stiffness measure ≥8.2 kPa) was related to smaller total brain volumes (β = −7.3, 95% CI = −11.1 to −3.5). Heterogeneity between studies was low. Conclusions NAFLD and liver fibrosis may be directly related to brain aging. Larger and prospective studies are warranted to validate these findings and identify liver-related preventive strategies for neurodegeneration

Experimental and Numerical Investigation for Predicting the Performance of Voluteless Centrifugal Fan Rotors

A better understanding of the flow field is crucial for improving the design of a turbomachine. In this work we investigate the performance of voluteless centrifugal fan rotors. The study includes two parts: experiments and numerical simulations through Computational Fluid Dynamics (CFD) techniques. Our test system allows the analysis of the flow behavior of centrifugal fan rotors maintaining the meridional shape without making substantial changes to their internal structure, but with different blade shapes, sizes, and blade numbers. To avoids irregular interference with the rotor flow from external components such as the collector a radial channel composed by two parallel discs was placed concentrically on the rotor axis at its outer periphery with special interest in measuring flow characteristics at the rotor outlet with a reliable accuracy. As an application case a typical centrifugal fan rotor with ten blades of single curvature in the circular arc shape has been investigated. Two types of measuring systems were used: one, with an aerodynamic probe located in the centrifugal rotor outlet and, the other, with a load cell for measuring the rotor shaft power. A comparison of the results by these two measuring arrangements shows some important characteristics, such as the phenomenon of the flow recirculation within the rotor. The experimental performance curves related to non-dimensional flow such as the slip factor, and pressure coefficient, revealed good matching with numerical simulations, highlighting the remarkable reliability of our experimental setup