117 research outputs found
STRUCTURAL DIAGNOSTICS OF GEOMATERIALS BY LASER ULTRASONIC SPECTROSCOPY
Abstract The possibilities of laser ultrasonic echoscopy for detection and diagnostics of rock structural imperfections are considered. It is shown, that calculating with the help of fast Fourier transformation spectra of the signals, arrived in a sample and multiple scattered, and carrying out a corresponding frequency filtration, it is possible to obtaine environment reflaction factor and on its basis to construct the sample structure image.The examples of forming images of structural changes under different influences on the rock samples are presented. The ferruginous quartzite samples were influenced by pulse electromagnetic field, the Karelian marble samples -thermal field
Bit Distribution Study and Implementation of Spatial Quality Map in the JPEG-AI Standardization
Currently, there is a high demand for neural network-based image compression
codecs. These codecs employ non-linear transforms to create compact bit
representations and facilitate faster coding speeds on devices compared to the
hand-crafted transforms used in classical frameworks. The scientific and
industrial communities are highly interested in these properties, leading to
the standardization effort of JPEG-AI. The JPEG-AI verification model has been
released and is currently under development for standardization. Utilizing
neural networks, it can outperform the classic codec VVC intra by over 10%
BD-rate operating at base operation point. Researchers attribute this success
to the flexible bit distribution in the spatial domain, in contrast to VVC
intra's anchor that is generated with a constant quality point. However, our
study reveals that VVC intra displays a more adaptable bit distribution
structure through the implementation of various block sizes. As a result of our
observations, we have proposed a spatial bit allocation method to optimize the
JPEG-AI verification model's bit distribution and enhance the visual quality.
Furthermore, by applying the VVC bit distribution strategy, the objective
performance of JPEG-AI verification mode can be further improved, resulting in
a maximum gain of 0.45 dB in PSNR-Y.Comment: 5 pages, 3 figures, 4 table
Bit Rate Matching Algorithm Optimization in JPEG-AI Verification Model
The research on neural network (NN) based image compression has shown
superior performance compared to classical compression frameworks. Unlike the
hand-engineered transforms in the classical frameworks, NN-based models learn
the non-linear transforms providing more compact bit representations, and
achieve faster coding speed on parallel devices over their classical
counterparts. Those properties evoked the attention of both scientific and
industrial communities, resulting in the standardization activity JPEG-AI. The
verification model for the standardization process of JPEG-AI is already in
development and has surpassed the advanced VVC intra codec. To generate
reconstructed images with the desired bits per pixel and assess the BD-rate
performance of both the JPEG-AI verification model and VVC intra, bit rate
matching is employed. However, the current state of the JPEG-AI verification
model experiences significant slowdowns during bit rate matching, resulting in
suboptimal performance due to an unsuitable model. The proposed methodology
offers a gradual algorithmic optimization for matching bit rates, resulting in
a fourfold acceleration and over 1% improvement in BD-rate at the base
operation point. At the high operation point, the acceleration increases up to
sixfold.Comment: Accepted at (IEEE) PCS 2024; 6 page
Noninvasive laser-induced photoacoustic tomography for structural and functional in vivo imaging of the brain
Imaging techniques based on optical contrast analysis can be used to visualize dynamic and functional properties of the nervous system via optical signals resulting from changes in blood volume, oxygen consumption and cellular swelling associated with brain physiology and pathology. Here we report in vivo noninvasive transdermal and transcranial imaging of the structure and function of rat brains by means of laser-induced photoacoustic tomography (PAT). The advantage of PAT over pure optical imaging is that it retains intrinsic optical contrast characteristics while taking advantage of the diffraction-limited high spatial resolution of ultrasound. We accurately mapped rat brain structures, with and without lesions, and functional cerebral hemodynamic changes in cortical blood vessels around the whisker-barrel cortex in response to whisker stimulation. We also imaged hyperoxia- and hypoxia-induced cerebral hemodynamic changes. This neuroimaging modality holds promise for applications in neurophysiology, neuropathology and neurotherapy
Temporal fluctuations of waves in weakly nonlinear disordered media
We consider the multiple scattering of a scalar wave in a disordered medium
with a weak nonlinearity of Kerr type. The perturbation theory, developed to
calculate the temporal autocorrelation function of scattered wave, fails at
short correlation times. A self-consistent calculation shows that for
nonlinearities exceeding a certain threshold value, the multiple-scattering
speckle pattern becomes unstable and exhibits spontaneous fluctuations even in
the absence of scatterer motion. The instability is due to a distributed
feedback in the system "coherent wave + nonlinear disordered medium". The
feedback is provided by the multiple scattering. The development of instability
is independent of the sign of nonlinearity.Comment: RevTeX, 15 pages (including 5 figures), accepted for publication in
Phys. Rev.
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