A multivariate distribution for sub-images

2008 ◽  
Vol 465 (2103) ◽  
pp. 983-1001
Author(s):  
S.J Maybank
Keyword(s):  
Gaussian Distribution ◽  
Random Projection ◽  
Natural Images ◽  
Correct Match ◽  
Discrete Cosine Transforms ◽  
Multivariate Distributions ◽  
Uhlenbeck Process ◽  
Measurement Vector ◽  
Unique Match ◽  
Good Agreement

A new method for obtaining multivariate distributions for sub-images of natural images is described. The information in each sub-image is summarized by a measurement vector in a measurement space. The dimension of the measurement space is reduced by applying a random projection to the truncated output of the discrete cosine transforms of the sub-images. The measurement space is then reparametrized, such that a Gaussian distribution is a good model for the measurement vectors in the reparametrized space. An Ornstein–Uhlenbeck process, associated with the Gaussian distribution, is used to model the differences between measurement vectors obtained from matching sub-images. The probability of a false alarm and the probability of accepting a correct match are calculated. The accuracy of the resulting statistical model for matching sub-images is tested using images from the Middlebury stereo database with promising results. In particular, if the probability of accepting a correct match is relatively large, then there is good agreement between the calculated and the experimental probabilities of obtaining a unique match that is also a correct match.

scholarly journals Separate Universe calibration of the dependence of halo bias on cosmic web anisotropy

2020 ◽  
Vol 499 (3) ◽  
pp. 4418-4431 ◽  
Author(s):  
Sujatha Ramakrishnan ◽  
Aseem Paranjape
Keyword(s):  
Dark Matter ◽  
High Precision ◽  
Gaussian Distribution ◽  
Initial Perturbation ◽  
Analytical Framework ◽  
Web Environment ◽  
Wide Range ◽  
Galaxy Assembly ◽  
Very High ◽  
Good Agreement

ABSTRACT We use the Separate Universe technique to calibrate the dependence of linear and quadratic halo bias b1 and b2 on the local cosmic web environment of dark matter haloes. We do this by measuring the response of halo abundances at fixed mass and cosmic web tidal anisotropy α to an infinite wavelength initial perturbation. We augment our measurements with an analytical framework developed in earlier work that exploits the near-lognormal shape of the distribution of α and results in very high precision calibrations. We present convenient fitting functions for the dependence of b1 and b2 on α over a wide range of halo mass for redshifts 0 ≤ z ≤ 1. Our calibration of b2(α) is the first demonstration to date of the dependence of non-linear bias on the local web environment. Motivated by previous results that showed that α is the primary indicator of halo assembly bias for a number of halo properties beyond halo mass, we then extend our analytical framework to accommodate the dependence of b1 and b2 on any such secondary property that has, or can be monotonically transformed to have, a Gaussian distribution. We demonstrate this technique for the specific case of halo concentration, finding good agreement with previous results. Our calibrations will be useful for a variety of halo model analyses focusing on galaxy assembly bias, as well as analytical forecasts of the potential for using α as a segregating variable in multitracer analyses.

Particle Resuspension in a Wall-Bounded Turbulent Flow

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
S. C. Fu ◽  
C. Y. H. Chao ◽  
R. M. C. So ◽  
W. T. Leung
Keyword(s):  
Angular Velocity ◽  
Uhlenbeck Process ◽  
Particle Resuspension ◽  
Air Stream ◽  
Safety And Health ◽  
Wide Range ◽  
Resuspension Rate ◽  
Mc Simulation ◽  
Using Data ◽  
Good Agreement

Resuspension is of common occurrence in a wide range of industrial and environmental processes. Excessive resuspension in these processes could have a severe impact on human safety and health. Therefore, it is necessary to develop a practical, yet reasonably accurate model to describe the resuspension phenomenon. It has been identified that rolling is the dominant mechanism for particle resuspension in the presence of an air stream, be it laminar or turbulent. Existing models predict the resuspension rate by regarding particles as being resuspended once they are set in motion; only a few of these models attempt to describe the full scenario, including rolling motion and the effect of turbulence. The objective of this paper is to propose a stochastic model to simulate the resuspension rate in the presence of a near-wall turbulent stream, and where the rolling mechanism is assumed to dominate the resuspension process. The fluctuating part of the angular velocity of a rolling particle is modeled by the Langevin equation (i.e., an Ornstein–Uhlenbeck process); thus, the overall angular velocity is modeled as a diffusion process. A free parameter of the proposed resuspension model is determined using data obtained from a Monte Carlo (MC) simulation of the problem. Once determined, the parameter is found to be universal for different materials and different sizes of particles tested. The modeling results obtained using this parameter are found to be in good agreement with experimental data, and the model performs better compared to other models.

scholarly journals A study of the approaches used to retrieve aerosol extinction, as applied to limb observations made by OSIRIS and SCIAMACHY

2018 ◽  
Author(s):  
Landon A. Rieger ◽  
Elizaveta P. Malinina ◽  
Alexei V. Rozanov ◽  
John P. Burrows ◽  
Adam E. Bourassa ◽  
...  
Keyword(s):  
Particle Size ◽  
Radiative Transfer ◽  
A Priori ◽  
Stratospheric Aerosol ◽  
Aerosol Extinction ◽  
Measurement Vector ◽  
Transfer Modelling ◽  
Inversion Techniques ◽  
And Inversion ◽  
Good Agreement

Abstract. Limb scatter instruments in the UV-Vis spectral range have provided longterm global records of stratospheric aerosol extinction important for climate records and modelling. While comparisons with occultation instruments show generally good agreement, the source and magnitude of the biases arising from retrieval assumptions, approximations in the radiative transfer modelling, and inversion techniques has not been thoroughly characterized. This paper explores the biases between SCIAMACHY v1.4, OSIRIS v5.07 and SAGE II v7.00 aerosol extinctions through a series of coincident comparisons as well as simulation and retrieval studies to investigate the cause and magnitude of the various systematic differences. The effect of a priori profiles, particle size assumptions, radiative transfer modelling, inversion techniques, and the different satellite datasets are explored. It is found that the assumed a priori profile can have a large effect near the normalization point, as well as systematic influence at lower altitudes. The error due to particle size assumptions is relatively small when averaged over a range of scattering angles, but individual errors depend on the particular scattering angle, particle size and measurement vector definition. Differences due to radiative transfer modelling introduce differences between the retrieved products of less than 10 % on average, but can introduce vertical structure. The combination of the different scenario simulations and the application of both algorithms to both datasets enable the origin of some of the systematic features such as high altitude differences when compared to SAGE II to be explained.

Die Umwandlung des Cristobalits

1959 ◽  
Vol 14 (10) ◽  
pp. 912-919
Author(s):  
O. Krisement ◽  
G. Trömel
Keyword(s):  
Gaussian Distribution ◽  
Free Energies ◽  
Transformation Temperatures ◽  
Additional Information ◽  
Distribution Of Values ◽  
Good Agreement

The α ⇋ β inversion of cristobalite has been investigated by observing optically the transformation of a sufficiently great number of single cristais of microscopic size. The derived transformationtemperature-function (Mengenkurve) is in good agreement with data from microcalorimetric measurements. Additional information is obtained from the distribution of the transformation temperatures of individual cristais. The behavior of the α ⇋ β inversion is determined by the superposition of two effects: the GAussian distribution of the temperatures, for which the free energies of a- and β-phases are equal, and the GAussian distribution of values for the hysteresis.

Unsupervised Learning of Generative and Discriminative Weights Encoding Elementary Image Components in a Predictive Coding Model of Cortical Function

2012 ◽  
Vol 24 (1) ◽  
pp. 60-103 ◽  
Author(s):  
M. W. Spratling
Keyword(s):  
Cortical Neurons ◽  
Predictive Coding ◽  
Natural Images ◽  
Cortical Function ◽  
Processing Stage ◽  
Computational Theory ◽  
Neurophysiological Data ◽  
Feedback Connections ◽  
First Time ◽  
Good Agreement

A method is presented for learning the reciprocal feedforward and feedback connections required by the predictive coding model of cortical function. When this method is used, feedforward and feedback connections are learned simultaneously and independently in a biologically plausible manner. The performance of the proposed algorithm is evaluated by applying it to learning the elementary components of artificial and natural images. For artificial images, the bars problem is employed, and the proposed algorithm is shown to produce state-of-the-art performance on this task. For natural images, components resembling Gabor functions are learned in the first processing stage, and neurons responsive to corners are learned in the second processing stage. The properties of these learned representations are in good agreement with neurophysiological data from V1 and V2. The proposed algorithm demonstrates for the first time that a single computational theory can explain the formation of cortical RFs and also the response properties of cortical neurons once those RFs have been learned.

scholarly journals On measuring the local perceived blur in natural scenes both in the lab and online

2018 ◽  
Author(s):  
Christopher Patrick Taylor ◽  
Peter J. Bex
Keyword(s):  
Three Dimensional ◽  
Natural Images ◽  
Amazon Mechanical Turk ◽  
Retinal Images ◽  
Natural Scenes ◽  
Local Slope ◽  
Image Blur ◽  
Band Limited ◽  
Local Image ◽  
Good Agreement

Natural retinal images contain blur. Image blur varies across the visual field depending on the three dimensional image structure and the observers’ point of accommodation. There is currently no consensus in the field on how to quantify local perceived blur in natural images. We developed a biologically-plausible measure of local image blur, local slope, which is computed from the output of a set spatial frequency and orientation band-limited filters. To determine if local slope captured the perception of image blur variation, we used a task in which observers traced regions in natural images that matched the perceived blur of a standard blur. We ran our tracing task both under controlled laboratory conditionswith a small number of observers and online using a large sample of Amazon Mechanical Turk Workers. There was good agreement across observes on image regions with matched perceived blur and a correlation between local slopes of blur-matching areas of natural and standard images for data collected in the lab and online. These data indicate that local slope may provide a rapid and simple metric of perceived blur in natural scenes for human observers.

Oscillator Strength Measurements in the Vacuum-Ultraviolet by the Emission Method

1988 ◽  
Vol 102 ◽  
pp. 353-356
Author(s):  
C. Goldbach ◽  
G. Nollez
Keyword(s):  
Oscillator Strength ◽  
Vacuum Ultraviolet ◽  
Oscillator Strengths ◽  
Emission Method ◽  
Absolute Scale ◽  
Good Agreement

AbstractThe principles and the realization of an experiment devoted to oscillator strength measurements in the vacuum-ultraviolet by the emission method are briefly presented. The results obtained for the strong multiplets of neutral nitrogen and carbon in the 1200-2000 Å range yield an absolute scale of oscillator strengths in good agreement with the most recent calculations.

A High Voltage Electron Microscopy Study of Sub-Oxide Formation in Vanadium

1971 ◽  
Vol 29 ◽  
pp. 212-213
Author(s):  
R. H. Geiss ◽  
R. L. Ladd ◽  
K. R. Lawless
Keyword(s):  
High Vacuum ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Ultra High Vacuum ◽  
Pure Oxygen ◽  
Pressure Oxidation ◽  
High Voltage Electron Microscopy ◽  
Oxidation Study ◽  
Voltage Electron ◽  
Good Agreement

Detailed electron microscope and diffraction studies of the sub-oxides of vanadium have been reported by Cambini and co-workers, and an oxidation study, possibly complicated by carbon and/or nitrogen, has been published by Edington and Smallman. The results reported by these different authors are not in good agreement. For this study, high purity polycrystalline vanadium samples were electrochemically thinned in a dual jet polisher using a solution of 20% H2SO4, 80% CH3OH, and then oxidized in an ion-pumped ultra-high vacuum reactor system using spectroscopically pure oxygen. Samples were oxidized at 350°C and 100μ oxygen pressure for periods of 30,60,90 and 160 minutes. Since our primary interest is in the mechanism of the low pressure oxidation process, the oxidized samples were cooled rapidly and not homogenized. The specimens were then examined in the HVEM at voltages up to 500 kV, the higher voltages being necessary to examine thick sections for which the oxidation behavior was more characteristic of the bulk.

Diagnostic Value of Electron Microscopy in Soft Tissue Tumors

1970 ◽  
Vol 28 ◽  
pp. 220-221
Author(s):  
Gerald Fine ◽  
Azorides R. Morales
Keyword(s):  
Cardiac Myxoma ◽  
Osteogenic Sarcoma ◽  
Diagnostic Value ◽  
Soft Tissue Tumors ◽  
Amelanotic Melanoma ◽  
Growth Patterns ◽  
Light Microscopic Level ◽  
Mesenchymal Tumors ◽  
Good Agreement

For years the separation of carcinoma and sarcoma and the subclassification of sarcomas has been based on the appearance of the tumor cells and their microscopic growth pattern and information derived from certain histochemical and special stains. Although this method of study has produced good agreement among pathologists in the separation of carcinoma from sarcoma, it has given less uniform results in the subclassification of sarcomas. There remain examples of neoplasms of different histogenesis, the classification of which is questionable because of similar cytologic and growth patterns at the light microscopic level; i.e. amelanotic melanoma versus carcinoma and occasionally sarcoma, sarcomas with an epithelial pattern of growth simulating carcinoma, histologically similar mesenchymal tumors of different histogenesis (histiocytoma versus rhabdomyosarcoma, lytic osteogenic sarcoma versus rhabdomyosarcoma), and myxomatous mesenchymal tumors of diverse histogenesis (myxoid rhabdo and liposarcomas, cardiac myxoma, myxoid neurofibroma, etc.)

Sign in / Sign up

Export Citation Format

Share Document