The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform

Genevieve Massonnet - One of the best experts on this subject based on the ideXlab platform.

  • the evaluation of evidence for Microspectrophotometry data using functional data analysis
    Forensic Science International, 2019
    Co-Authors: Colin Aitken, Grzegorz Zadora, Patrick Buzzini, Yating Chang, Genevieve Massonnet
    Abstract:

    Microspectrophotometry data arise in the study of many forensically applicable situations. The situations here are those of ink and fibres. In a criminal investigation, data associated with a crime scene are compared with data associated with a person of interest. Methods based on the likelihood ratio are often used to evaluate such evidence. A technique known as functional data analysis for determining likelihood ratios using the full spectrum is described. It provides support comparing a proposition of common source with a proposition of different sources for data from the crime scene and from the person of interest. Data are available from ink, woollen and cotton fibres. The effectiveness of the method is assessed using false positive and false negative rates and Tippett plots in the comparison of data from known sources.

  • raman spectroscopy and Microspectrophotometry of reactive dyes on cotton fibres analysis and detection limits
    Forensic Science International, 2012
    Co-Authors: Genevieve Massonnet, Patrick Buzzini, F Monard, G Jochem, Louise A Fido, Steven E J Bell, M Stauber, T Coyle, Claude Roux, J Hemmings
    Abstract:

    A collaborative study on Raman spectroscopy and Microspectrophotometry (MSP) was carried out by members of the ENFSI (European Network of Forensic Science Institutes) European Fibres Group (EFG) on different dyed cotton fabrics. The detection limits of the two methods were tested on two cotton sets with a dye concentration ranging from 0.5 to 0.005% (w/w). This survey shows that it is possible to detect the presence of dye in fibres with concentrations below that detectable by the traditional methods of light microscopy and Microspectrophotometry (MSP). The MSP detection limit for the dyes used in this study was found to be a concentration of 0.5% (w/w). At this concentration, the fibres appear colourless with light microscopy. Raman spectroscopy clearly shows a higher potential to detect concentrations of dyes as low as 0.05% for the yellow dye RY145 and 0.005% for the blue dye RB221. This detection limit was found to depend both on the chemical composition of the dye itself and on the analytical conditions, particularly the laser wavelength. Furthermore, analysis of binary mixtures of dyes showed that while the minor dye was detected at 1.5% (w/w) (30% of the total dye concentration) using Microspectrophotometry, it was detected at a level as low as 0.05% (w/w) (10% of the total dye concentration) using Raman spectroscopy. This work also highlights the importance of a flexible Raman instrument equipped with several lasers at different wavelengths for the analysis of dyed fibres. The operator and the set up of the analytical conditions are also of prime importance in order to obtain high quality spectra. Changing the laser wavelength is important to detect different dyes in a mixture.

Patrick Buzzini - One of the best experts on this subject based on the ideXlab platform.

  • the evaluation of evidence for Microspectrophotometry data using functional data analysis
    Forensic Science International, 2019
    Co-Authors: Colin Aitken, Grzegorz Zadora, Patrick Buzzini, Yating Chang, Genevieve Massonnet
    Abstract:

    Microspectrophotometry data arise in the study of many forensically applicable situations. The situations here are those of ink and fibres. In a criminal investigation, data associated with a crime scene are compared with data associated with a person of interest. Methods based on the likelihood ratio are often used to evaluate such evidence. A technique known as functional data analysis for determining likelihood ratios using the full spectrum is described. It provides support comparing a proposition of common source with a proposition of different sources for data from the crime scene and from the person of interest. Data are available from ink, woollen and cotton fibres. The effectiveness of the method is assessed using false positive and false negative rates and Tippett plots in the comparison of data from known sources.

  • raman spectroscopy and Microspectrophotometry of reactive dyes on cotton fibres analysis and detection limits
    Forensic Science International, 2012
    Co-Authors: Genevieve Massonnet, Patrick Buzzini, F Monard, G Jochem, Louise A Fido, Steven E J Bell, M Stauber, T Coyle, Claude Roux, J Hemmings
    Abstract:

    A collaborative study on Raman spectroscopy and Microspectrophotometry (MSP) was carried out by members of the ENFSI (European Network of Forensic Science Institutes) European Fibres Group (EFG) on different dyed cotton fabrics. The detection limits of the two methods were tested on two cotton sets with a dye concentration ranging from 0.5 to 0.005% (w/w). This survey shows that it is possible to detect the presence of dye in fibres with concentrations below that detectable by the traditional methods of light microscopy and Microspectrophotometry (MSP). The MSP detection limit for the dyes used in this study was found to be a concentration of 0.5% (w/w). At this concentration, the fibres appear colourless with light microscopy. Raman spectroscopy clearly shows a higher potential to detect concentrations of dyes as low as 0.05% for the yellow dye RY145 and 0.005% for the blue dye RB221. This detection limit was found to depend both on the chemical composition of the dye itself and on the analytical conditions, particularly the laser wavelength. Furthermore, analysis of binary mixtures of dyes showed that while the minor dye was detected at 1.5% (w/w) (30% of the total dye concentration) using Microspectrophotometry, it was detected at a level as low as 0.05% (w/w) (10% of the total dye concentration) using Raman spectroscopy. This work also highlights the importance of a flexible Raman instrument equipped with several lasers at different wavelengths for the analysis of dyed fibres. The operator and the set up of the analytical conditions are also of prime importance in order to obtain high quality spectra. Changing the laser wavelength is important to detect different dyes in a mixture.

J Hemmings - One of the best experts on this subject based on the ideXlab platform.

  • raman spectroscopy and Microspectrophotometry of reactive dyes on cotton fibres analysis and detection limits
    Forensic Science International, 2012
    Co-Authors: Genevieve Massonnet, Patrick Buzzini, F Monard, G Jochem, Louise A Fido, Steven E J Bell, M Stauber, T Coyle, Claude Roux, J Hemmings
    Abstract:

    A collaborative study on Raman spectroscopy and Microspectrophotometry (MSP) was carried out by members of the ENFSI (European Network of Forensic Science Institutes) European Fibres Group (EFG) on different dyed cotton fabrics. The detection limits of the two methods were tested on two cotton sets with a dye concentration ranging from 0.5 to 0.005% (w/w). This survey shows that it is possible to detect the presence of dye in fibres with concentrations below that detectable by the traditional methods of light microscopy and Microspectrophotometry (MSP). The MSP detection limit for the dyes used in this study was found to be a concentration of 0.5% (w/w). At this concentration, the fibres appear colourless with light microscopy. Raman spectroscopy clearly shows a higher potential to detect concentrations of dyes as low as 0.05% for the yellow dye RY145 and 0.005% for the blue dye RB221. This detection limit was found to depend both on the chemical composition of the dye itself and on the analytical conditions, particularly the laser wavelength. Furthermore, analysis of binary mixtures of dyes showed that while the minor dye was detected at 1.5% (w/w) (30% of the total dye concentration) using Microspectrophotometry, it was detected at a level as low as 0.05% (w/w) (10% of the total dye concentration) using Raman spectroscopy. This work also highlights the importance of a flexible Raman instrument equipped with several lasers at different wavelengths for the analysis of dyed fibres. The operator and the set up of the analytical conditions are also of prime importance in order to obtain high quality spectra. Changing the laser wavelength is important to detect different dyes in a mixture.

Ellis R. Loew - One of the best experts on this subject based on the ideXlab platform.

  • photopigment spectral absorbance of lake malawi cichlids
    Journal of Fish Biology, 2006
    Co-Authors: Rebecca Jordan, Karen Kellogg, David V Howe, Francis Juanes, Jay R Stauffer, Ellis R. Loew
    Abstract:

    To predict spectral sensitivity, Microspectrophotometry (MSP) was used to measure absorbance of photoreceptor cells from 15 species of Lake Malaŵi cichlids. Each fish had one rod and at least three cone pigments. UV-sensitive pigments were common, but spectral sensitivity did not clearly correlate with feeding mode or habitat.

  • Scanning electron microscopy and Microspectrophotometry of the photoreceptors of ictalurid catfishes
    Journal of Comparative Physiology A, 1993
    Co-Authors: A J Sillman, Stephen J. Ronan, Ellis R. Loew
    Abstract:

    The retinal photoreceptors from larval channel catfish ( Ictalurus punctatus ) were studied using single cell, in situ Microspectrophotometry. Rods appear at 5 days after hatch; cones are present from day one. The rods contain a visual pigment which absorbs light maximally at 540 nm. The cones contain either a green sensitive visual pigment with peak absorbance at 535 nm or a red sensitive visual pigment with peak absorbance at 608 nm. All pigments are based on vitamin A_2. Visual pigment complement does not change with age, as photoreceptors from adult I. punctatus, I. catus and I. melas contain visual pigments virtually identical to those of the larval I. punctatus . Regardless of age, no visual pigment with peak absorbance in the short wavelength region of the spectrum was ever observed. Scanning electron microscopy of adult I. punctatus retinas showed large rods with long, cylindrical outer segments and smaller cones with short, tapered outer segments. The myoids of both rods and cones are extensable. The rods, embedded in a granular tapetal material, comprise from 50 to 60% of the photoreceptors. Only single cones are present. The data are consistent with the idea that the ictalurid catfishes spend their entire lives in an environment deficient in blue light.

  • Histology and Microspectrophotometry of the photoreceptors of a crocodilian, Alligator mississippiensis
    Proceedings of The Royal Society B: Biological Sciences, 1991
    Co-Authors: A J Sillman, Stephen J. Ronan, Ellis R. Loew
    Abstract:

    The photoreceptors in the retina of Alligator mississippiensis were examined by means of in situ , single cell Microspectrophotometry and scanning electron microscopy (SEM). The retina is characterized by a system of four cone visual pigments. One type of single cone contains a visual pigment with absorbance maximum ( λ max ) at 535 nm. A second type contains a visual pigment absorbing maximally at 444 nm. The principal member of the double cone has a visual pigment with λ max at 566 nm whereas the accessory member’s visual pigment absorbs maximally at 503 nm. There is only one rod pigment and it is virtually identical to that within the accessory cone, absorbing maximally at 501 nm. All visual pigments are based on the retinal or vitamin A 1 chromophore. SEM confirms that the alligator retina is duplex with rods dominating but cones present in significant numbers. There is a wide range of photoreceptor shapes and sizes throughout the retina

Thomas Ursby - One of the best experts on this subject based on the ideXlab platform.

  • a microspectrophotometer for uv visible absorption and fluorescence studies of protein crystals
    Journal of Applied Crystallography, 2002
    Co-Authors: Dominique Bourgeois, Xavier Vernede, Virgile Adam, E Fioravanti, Thomas Ursby
    Abstract:

    Absorption Microspectrophotometry has been shown to be of considerable help to probe crystalline proteins containing chromophores, metal centres, or coloured substrates/co-factors. Absorption spectra contribute to the proper interpretation of crystallographic structures, especially when transient intermediate states are studied. Here it is shown that fluorescence Microspectrophotometry might also be used for such purposes if endogenous fluorophores are present in the macromolecule or when exogenous fluorophores are added and either bind to the protein or reside in the solvent channels. An off-line microspectrophotometer that is able to perform low-temperature absorption and fluorescence spectroscopy on crystals mounted in cryo-loops is described. One-shot steady-state emission spectra of outstanding quality were routinely collected from several samples. In some cases, crystals with optical densities that are too low or too high for absorption studies can still be tackled with fluorescence Microspectrophotometry. The technique may be used for simple controls such as checking the presence, absence or redox state of a fluorescent substrate/co-factor. Potential applications in the field of kinetic crystallography are numerous. In addition, the possibility to probe key physico-chemical parameters of the crystal, such as temperature, pH or solvent viscosity, could trigger new studies in protein dynamics.