77 research outputs found
Improved convergence of fast integral equation solvers for acoustic scattering by inhomogeneous penetrable media with discontinuous material interface
In recent years, several fast solvers for the solution of the
Lippmann-Schwinger integral equation that mathematically models the scattering
of time-harmonic acoustic waves by penetrable inhomogeneous obstacles, have
been proposed. While many of these fast methodologies exhibit rapid convergence
for smoothly varying scattering configurations, the rate for most of them
reduce to either linear or quadratic when material properties are allowed to
jump across the interface. A notable exception to this is a recently introduced
Nystr\"{o}m scheme [J. Comput. Phys., 311 (2016), 258--274] that utilizes a
specialized quadrature in the boundary region for a high-order treatment of the
material interface. In this text, we present a solution framework that relies
on the specialized boundary integrator to enhance the convergence rate of other
fast, low order methodologies without adding to their computational complexity
of for an -point discretization. In particular, to demonstrate
the efficacy of the proposed framework, we explain its implementation to
enhance the order to convergence of two schemes, one introduced by Duan and
Rokhlin [J. Comput. Phys., 228(6) (2009), 2152--2174] that is based on a
pre-corrected trapezoidal rule while the other by Bruno and Hyde [J. Comput.
Phys., 200(2) (2004), 670--694] which relies on a suitable decomposition of the
Green's function via Addition theorem. In addition to a detailed description of
these methodologies, we also present a comparative performance study of the
improved versions of these two and the Nystr\"{o}m solver in [J. Comput. Phys.,
311 (2016), 258--274] through a wide range of numerical experiments
An efficient high-order Nystr\"om scheme for acoustic scattering by inhomogeneous penetrable media with discontinuous material interface
This text proposes a fast, rapidly convergent Nystr\"{o}m method for the
solution of the Lippmann-Schwinger integral equation that mathematically models
the scattering of time-harmonic acoustic waves by inhomogeneous obstacles,
while allowing the material properties to jump across the interface. The method
works with overlapping coordinate charts as a description of the given
scatterer. In particular, it employs "partitions of unity" to simplify the
implementation of high-order quadratures along with suitable changes of
parametric variables to analytically resolve the singularities present in the
integral operator to achieve desired accuracies in approximations. To deal with
the discontinuous material interface in a high-order manner, a specialized
quadrature is used in the boundary region. The approach further utilizes an FFT
based strategy that uses equivalent source approximations to accelerate the
evaluation of large number of interactions that arise in the approximation of
the volumetric integral operator and thus achieves a reduced computational
complexity of for an -point discretization. A detailed
discussion on the solution methodology along with a variety of numerical
experiments to exemplify its performance in terms of both speed and accuracy
are presented in this paper
Experimental demonstration of 25 GHz wideband chaos in symmetric dual port EDFRL
We study dynamics of chaos in dual port erbium-doped fiber ring laser (EDFRL). The laser consists of
two erbium-doped fibers, intracavity filters at 1549.30 nm, isolators, and couplers. At both ports, the laser
transitions into the chaotic regime for pump currents greater than 100 mA via period doubling route. We
calculate the Lyapunov exponents using Rosenstein’s algorithm. We obtain positive values for the largest
Lyapunov exponent (≈0.2) for embedding dimensions 5, 7, 9 and 11 indicating chaos. We compute the
power spectrum of the photocurrents at the output ports of the laser. We observe a bandwidth of ≈ 25
GHz at both ports. This ultra wideband nature of chaos obtained has potential applications in high speed
random number generation and communication
Performance analysis of a compact heat exchanger
Compact heat exchangers are one of the most critical components of many cryogenic components; they are characterized by a high heat transfer surface area per unit volume of the exchanger. The heat exchangers having surface area density (β) greater than 700 m2/m3 in either one or more sides of two-stream or multi stream heat exchanger is called as a compact heat exchanger. Plate fin heat exchanger is a type of compact heat exchanger which is widely used in automobiles, cryogenics, space applications and chemical industries. The plate fin heat exchangers are mostly used for the nitrogen liquefiers, so they need to be highly efficient because no liquid nitrogen is produced, if the effectiveness of heat exchanger is less than 87%. So it becomes necessary to test the effectiveness of these heat exchangers before putting them in to operation
Effect of Attention and Self-Supervised Speech Embeddings on Non-Semantic Speech Tasks
Human emotion understanding is pivotal in making conversational technology
mainstream. We view speech emotion understanding as a perception task which is
a more realistic setting. With varying contexts (languages, demographics, etc.)
different share of people perceive the same speech segment as a non-unanimous
emotion. As part of the ACM Multimedia 2023 Computational Paralinguistics
ChallengE (ComParE) in the EMotion Share track, we leverage their rich dataset
of multilingual speakers and multi-label regression target of 'emotion share'
or perception of that emotion. We demonstrate that the training scheme of
different foundation models dictates their effectiveness for tasks beyond
speech recognition, especially for non-semantic speech tasks like emotion
understanding. This is a very complex task due to multilingual speakers,
variability in the target labels, and inherent imbalance in the regression
dataset. Our results show that HuBERT-Large with a self-attention-based
light-weight sequence model provides 4.6% improvement over the reported
baseline.Comment: Accepted to appear at ACM Multimedia 2023 Multimedia Grand Challenges
Trac
Improved convergence of fast integral equation solvers for acoustic scattering by inhomogeneous penetrable media with discontinuous material interface
In recent years, several fast solvers for the solution of the Lippmann–Schwinger integral equation that mathematically models the scattering of time-harmonic acoustic waves by penetrable inhomogeneous obstacles, have been proposed. While many of these fast methodologies exhibit rapid convergence for smoothly varying scattering configurations, the rate for most of them reduce to either linear or quadratic when material properties are allowed to jump across the interface. A notable exception to this is a recently introduced Nyström scheme (Anand et al., 2016 [22]) that utilizes a specialized quadrature in the boundary region for a high-order treatment of the material interface. In this text, we present a solution framework that relies on the specialized boundary integrator to enhance the convergence rate of other fast, low order methodologies without adding to their computational complexity of O(N log N) for an N-point discretization. In particular, to demonstrate the efficacy of the proposed framework, we explain its implementation to enhance the order to convergence of two schemes, one introduced by Duan and Rokhlin (2009) [13] that is based on a pre-corrected trapezoidal rule while the other by Bruno and Hyde (2004) [12] which relies on a suitable decomposition of the Green's function via Addition theorem. In addition to a detailed description of these methodologies, we also present a comparative performance study of the improved versions of these two and the Nyström solver in Anand et al. (2016) [22] through a wide range of numerical experiments
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