2,799 research outputs found
Color homography
We show the surprising result that colors across a change in viewing
condition (changing light color, shading and camera) are related by a
homography. Our homography color correction application delivers improved color
fidelity compared with the linear least-square.Comment: Accepted by Progress in Colour Studies 201
A Semi-Blind Source Separation Method for Differential Optical Absorption Spectroscopy of Atmospheric Gas Mixtures
Differential optical absorption spectroscopy (DOAS) is a powerful tool for
detecting and quantifying trace gases in atmospheric chemistry
\cite{Platt_Stutz08}. DOAS spectra consist of a linear combination of complex
multi-peak multi-scale structures. Most DOAS analysis routines in use today are
based on least squares techniques, for example, the approach developed in the
1970s uses polynomial fits to remove a slowly varying background, and known
reference spectra to retrieve the identity and concentrations of reference
gases. An open problem is to identify unknown gases in the fitting residuals
for complex atmospheric mixtures.
In this work, we develop a novel three step semi-blind source separation
method. The first step uses a multi-resolution analysis to remove the
slow-varying and fast-varying components in the DOAS spectral data matrix .
The second step decomposes the preprocessed data in the first step
into a linear combination of the reference spectra plus a remainder, or
, where columns of matrix are known reference spectra,
and the matrix contains the unknown non-negative coefficients that are
proportional to concentration. The second step is realized by a convex
minimization problem ,
where the norm is a hybrid norm (Huber estimator) that helps to
maintain the non-negativity of . The third step performs a blind independent
component analysis of the remainder matrix to extract remnant gas
components. We first illustrate the proposed method in processing a set of DOAS
experimental data by a satisfactory blind extraction of an a-priori unknown
trace gas (ozone) from the remainder matrix. Numerical results also show that
the method can identify multiple trace gases from the residuals.Comment: submitted to Journal of Scientific Computin
The electrokinetic behavior of calcium oxalate monohydrate in macromolecular solutions
Electrophoretic mobilities were measured for calcium oxalate monohydrate (COM) in solutions containing macromolecules. Two mucopolysaccharides (sodium heparin and chrondroitin sulfate) and two proteins (positively charged lysozyme and negatively charged bovine serum albumin) were studied as adsorbates. The effects of pH, calcium oxalate surface charge (varied by calcium or oxalate ion activity), and citrate concentration were investigated. All four macromolecules showed evidence for chemical adsorption. The macromolecule concentrations needed for reversing the surface charge indicated that the mucopopolysacchrides have greater affinity for the COM surface than the proteins. The amount of proteins that can chemically adsorb appears to be limited to approximately one monomolecular layer. When the surface charge is high, an insufficient number of proteins can chemically adsorb to neutralize or reverse the surface charge. The remaining surface charge is balanced by proteins held near the surface by longer range electrostatic forces only. Citrate ions at high concentrations appear to compete effectively with the negative protein for surface sites but show no evidence for competing with the positively charged protein
Diagnosis and incidence of neisseria gonorrhoeae in Cape coloured females in the Western Cape
Specimens were taken, using carbon-impregnated swabs, from the cervix, urethra and rectum of 945 Cape Coloured gynaecological patients, and from the cervix only of 1 276 pregnant Cape Coloured women. These specimens were submitted to the laboratory in a modified Stuart transport medium and cultured on Thayer-Martin medium. Neisseria gonorrhoeae was cultured in 5,3% of the specimens from the gynaecological patients and in 5,3% of specimens from the pregnant women. All cultures showed type I or 11 colony pattern. No strains showed resistance to any of the antibiotics tested.S. Afr. Med. J., 48, 259 (1974)
Color Homography Color Correction
Homographies -- a mathematical formalism for relating image points across different camera viewpoints -- are at the foundations of geometric methods in computer vision and are used in geometric camera calibration, image registration, and stereo vision and other tasks. In this paper, we show the surprising result that colors across a change in viewing condition (changing light color, shading and camera) are also related by a homography. We propose a new color correction method based on color homography. Experiments demonstrate that solving the color homography problem leads to more accurate calibration
Prevention of food poisoning in hospital patients
CITATION: Horwitz, B. M., Finlayson, M. H. & Brede, H. D. 1974. Prevention of food poisoning in hospital patients. South African Medical Journal, 48(26):1109-1111.The original publication is available at http://www.samj.org.zaBacteriological investigations of raw and cooked foods and of food handlers in abattoirs, food factories and hospital kitchens show that they are potential sources of food poisoning organisms. The use of reheated (reconstituted) frozen foods is recommended as an ideal means of preventing food poisoning among hospital patients.http://archive.samj.org.za/index.php?path=%2F1974+VOL+XLVIII+Jan-Jun%2FArticles%2F06+JunePublisher’s versio
Updated world map of the Köppen-Geiger climate classification
International audienceAlthough now over 100 years old, the classification of climate originally formulated by Wladimir Köppen and modified by his collaborators and successors, is still in widespread use. It is widely used in teaching school and undergraduate courses on climate. It is also still in regular use by researchers across a range of disciplines as a basis for climatic regionalisation of variables and for assessing the output of global climate models. Here we have produced a new global map of climate using the Köppen-Geiger system based on a large global data set of long-term monthly precipitation and temperature station time series. Climatic variables used in the Köppen-Geiger system were calculated at each station and interpolated between stations using a two-dimensional (latitude and longitude) thin-plate spline with tension onto a 0.1°×0.1° grid for each continent. We discuss some problems in dealing with sites that are not uniquely classified into one climate type by the Köppen-Geiger system and assess the outcomes on a continent by continent basis. Globally the most common climate type by land area is BWh (14.2%, Hot desert) followed by Aw (11.5%, Tropical savannah). The updated world Köppen-Geiger climate map is freely available electronically in the Supplementary Material Section
Heat Capacity in Magnetic and Electric Fields Near the Ferroelectric Transition in Tri-Glycine Sulfate
Specific-heat measurements are reported near the Curie temperature (~=
320 K) on tri-glycine sulfate. Measurements were made on crystals whose
surfaces were either non-grounded or short-circuited, and were carried out in
magnetic fields up to 9 T and electric fields up to 220 V/cm. In non-grounded
crystals we find that the shape of the specific-heat anomaly near is
thermally broadened. However, the anomaly changes to the characteristic sharp
-shape expected for a continuous transition with the application of
either a magnetic field or an electric field. In crystals whose surfaces were
short-circuited with gold, the characteristic -shape appeared in the
absence of an external field. This effect enabled a determination of the
critical exponents above and below , and may be understood on the basis
that the surface charge originating from the pyroelectric coefficient, ,
behaves as if shorted by external magnetic or electric fields.Comment: 4 Pages, 4 Figures. To Appear in Applied Physics Letters_ January
200
The low dimensional dynamical system approach in General Relativity: an example
In this paper we explore one of the most important features of the Galerkin
method, which is to achieve high accuracy with a relatively modest
computational effort, in the dynamics of Robinson-Trautman spacetimes.Comment: 7 pages, 5 figure
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