Search results for "SPECTRA"
showing 10 items of 3542 documents
The influence of storage method on the transparency of pig crystalline lens
2019
Este artículo se ha publicado de forma definitiva en: http://www.scielo.br/pdf/abo/v82n1/0004-2749-abo-82-01-0056.pdf Purpose: The porcine eye is frequently used as a research model. This paper analyzes the effect of different storage methods on the transparency of pig crystalline lens. Methods: A spectral transmission curve (from 220 to 780 nm) for the crystalline lens was determined experimentally after storage in different conditions: saline solution, formalin, castor oil, and freezing at -80°C. The total transmission in the visible spectrum, which was used as an index of transparency, was calculated from these curves. For comparative purposes, fresh lenses were evaluated and used as con…
Tracking Polariton Relaxation with Multiscale Molecular Dynamics Simulations
2019
When photoactive molecules interact strongly with confined light modes in optical cavities, new hybrid light–matter states form. They are known as polaritons and correspond to coherent superpositions of excitations of the molecules and of the cavity photon. The polariton energies and thus potential energy surfaces are changed with respect to the bare molecules, such that polariton formation is considered a promising paradigm for controlling photochemical reactions. To effectively manipulate photochemistry with confined light, the molecules need to remain in the polaritonic state long enough for the reaction on the modified potential energy surface to take place. To understand what determine…
1H and13C n.m.r. spectra of dichloro(trans-2-chlorovinyl)arsine
1977
Proton and carbon magnetic resonance spectra of Lewisite or dichloro(trans-2-chlorovinyl)arsine have been measured and the results are compared with the n.m.r. spectral parameters of other trans-1,2-substituted ethylenes. The coupling constants can be rationalized by substituent electronegativity. The chemical shifts show an unusually large paramagnetic effect from the AsCl2 group.
Synthesis and chemical characterization of CuII, NiII and ZnII complexes of 3,5-bis(2′-pyridyl)-1,2,4-oxadiazole and 3-(2′-pyridyl)5-(phenyl)-1,2,4-o…
2011
Abstract The synthesis and structural characterization of Ni II , Cu II and Zn II complexes of two chelating 1,2,4-oxadiazole ligands, namely 3,5-bis(2′-pyridyl)-1,2,4-oxadiazole (bipyOXA) and 3-(2′-pyridyl)5-(phenyl)-1,2,4-oxadiazole (pyOXA), is here reported. The formed hexacoordinated metal complexes are [M(bipyOXA) 2 (H 2 O) 2 ](ClO 4 ) 2 and [M(pyOXA) 2 (ClO 4 ) 2 ], respectively (M = Ni, Cu, Zn). X-ray crystallography, 1 H and 13 C NMR spectroscopy and C, N, H elemental analysis data concord in attributing them an octahedral coordination geometry. The two coordinated pyOXA ligands assume a trans coplanar disposition, while the two bipyOXA ligands are not. The latter result is a possib…
He-I and He-II excited photoelectron spectra of cyclohepttatrienetricarbonyl complexes of group via metals
1979
Abstract Photoelectron spectra of Group VIA metal complexes M(CO) 3 (η 6 -C 7 H 8 ) have been assigned using experimental criteria along with quantum-mechanical calculations. A general agreement between computed and measured ionization energies has been found for molecular orbitas mainly ligand in character. Similar correlations do not hold for the highest orbitals, mainly metal d based. The energies associated with ionization processes are, in this case, largely dominated by the relaxation terms. The variations of intensities of these bands on changing the energy of ionizing radiation were of crucial significance in the assignment
Indoor artificial lighting: Prediction of the circadian effects of different spectral power distributions.
2014
The study presented in this paper aims to evaluate if and how the environment affects the circadian impact of a light source by predicting circadian stimulus (CS) resulting from the exposure to different light scenes, using equations reported in studies by Rea et al. The main findings are: (1) Above 600 lx at eye level the increase of CS is little; (2) Between 50 lx and 200 lx at the eye level an increase of only 50 lx determines a significant increase of CS; (3) Light sources with correlated colour temperatures between 2900 K and 4200 K have similar impacts on the circadian system according to the calculation method used; (4) Even an almost neutral environment affects the circadian impact…
Hyperspectral venous image quality assessment for optimum illumination range selection based on skin tone characteristics
2014
Background Subcutaneous veins localization is usually performed manually by medical staff to find suitable vein to insert catheter for medication delivery or blood sample function. The rule of thumb is to find large and straight enough vein for the medication to flow inside of the selected blood vessel without any obstruction. The problem of peripheral difficult venous access arises when patient’s veins are not visible due to any reason like dark skin tone, presence of hair, high body fat or dehydrated condition, etc. Methods To enhance the visibility of veins, near infrared imaging systems is used to assist medical staff in veins localization process. Optimum illumination is crucial to obt…
2-D mapping of skin chromophores in the spectral range 500 - 700 nm
2009
The multi-spectral imaging technique has been used for distant mapping of in-vivo skin chromophores by analyzing spectral data at each reflected image pixel and constructing 2-D maps of the relative concentrations of oxy-/deoxy-haemoglobin and melanin. Instead of using a broad visible-NIR spectral range, this study focuses on narrowed spectral band 500–700 nm, speeding-up the signal processing procedure. Regression analysis confirmed that superposition of three Gaussians is optimal analytic approximation for the oxy-haemoglobin absorption tabular spectrum in this spectral band, while superposition of two Gaussians fits well for deoxy-haemoglobin absorption and exponential function – for mel…
Spatio-Chromatic Adaptation via Higher-Order Canonical Correlation Analysis of Natural Images
2014
Independent component and canonical correlation analysis are two general-purpose statistical methods with wide applicability. In neuroscience, independent component analysis of chromatic natural images explains the spatio-chromatic structure of primary cortical receptive fields in terms of properties of the visual environment. Canonical correlation analysis explains similarly chromatic adaptation to different illuminations. But, as we show in this paper, neither of the two methods generalizes well to explain both spatio-chromatic processing and adaptation at the same time. We propose a statistical method which combines the desirable properties of independent component and canonical correlat…
Absence of lightness constancy as a deficit of monochromatic vision
1995
Dark-adapted human subjects arranged a collection of colored papers in a sequence according to their lightness. The sequence of the papers (which appeared gray to the subjects) varied under different illuminant spectra. These variations could be predicted quantitatively from the radiometric data and human scotopic spectral sensitivity. By substitution of natural daylight spectra in the computation it was shown that monochromats cannot perceive lightness reliably under the changing illuminant spectra of our planet. Animals need some degree of lightness constancy to detect figures against a background reliably. This can be achieved only with the help of additional light receptors of different…