170,385 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Decoding of complex isothermal chromatograms recovered from space missions - Identification of molecular structure
No full textIn gas chromatographic isothermal separations of multicomponent mixtures, i.e., mixtures where the number of components is high and unknown, the efficiency is low and
not enough to allow a complete separation with a consequent severe peak overlapping in the chromatogram. The consequence is a significant loss in analytical information content. Therefore it is practically mandatory to use a chemometric procedure to
decode the complex chromatogram, i. e. to deconvolve the overlapping signal to extract from it information on the mixture and the separation system. Isothermal separations
are not very popular, due to their low efficiency, but they are very common inin situ analyses during space missions, as a consequence of flight constraints on instrumentation complexity and power (energy saving). In this work a chemometric
approach based on Fourier analysis is applied to chromatograms obtained under isothermal or low temperature programming conditions. These conditions simulate those
employed in space missions. The procedure has been applied to standard mixtures containing compounds representative of the planetary atmospheres that will be investigated
in the near future: in particular, those related to Titan’s atmosphere (Cassini- Huygens mission) and a cometary nucleus (Rosetta mission), i. e., hydrocarbons and oxygenated compounds with carbon atom numbers ranging from 2 to 8.
The original approach, developed for constant peak width, is extended to variable peak width, in particular to the case of peak width linearly increasing with retention time, representing
isothermal separations. The proposed approach is able to characterise complex isothermal chromatograms in terms of number of components present in the mixture and of separation efficiency: such results are useful in interpreting data recovered
from space missions and for optimising analysis conditions compatible with flight constraints
Decoding of complex isothermal chromatograms: Application to chromatograms recovered from space missions
No full textIn gas chromatographic isothermal separations of multicomponent mixtures, i.e., mixtures where the number of components is high and unknown, the efficiency is low and not enough to allow a complete separation with a consequent severe peak overlapping in the chromatogram. The consequence is a significant loss in analytical information content. Therefore it is practically mandatory to use a chemometric procedure to decode the complex chromatogram, i.e. to deconvolve the overlapping signal to extract from it information on the mixture and the separation system. Isothermal separations are not very popular, due to their low efficiency, but they are very common in in situ analyses during space missions, as a consequence of flight constraints on instrumentation complexity and power (energy saving). In this work a chemometric approach based on Fourier analysis is applied to chromatograms obtained under isothermal or low temperature programming conditions. These conditions simulate those employed in space missions. The procedure has been applied to standard mixtures containing compounds representative of the planetary atmospheres that will be investigated in the near future: in particular, those related to Titan's atmosphere (Cassini-Huygens mission) and a cometary nucleus (Rosetta mission), i.e., hydrocarbons and oxygenated compounds with carbon atom numbers ranging from 2 to 8. The original approach, developed for constant peak width, is extended to variable peak width, in particular to the case of peak width linearly increasing with retention time, representing isothermal separations. The proposed approach is able to characterise complex isothermal chromatograms in terms of number of components present in the mixture and of separation efficiency: such results are useful in interpreting data recovered from space missions and for optimising analysis conditions compatible with flight constraints
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
GC-MS analysis of amino acid enantiomers: application to detection of chemical biomarkers in space analysis
No full text
GC-MS analysis of amino acid enantiomers, as their N(O,S)-perfluoroacyl perfluoroalkyl esters: Application to space analysis
No full textThe target of the in-situ research of optical activity in extraterrestrial
samples stimulated an extended investigation of a GC-MS method based on the derivatization
of amino acids by using a mixture of perfluorinated alcohols and perfluorinated
anhydrides. Amino acids are converted to their N(O,S)-perfluoroacyl perfluoroalkyl
esters in a single-step procedure, using different combinations of the derivatization
reagents trifluoroacetic anhydride (TFAA)-2,2,2-trifluoro-1-ethanol (TFE), TFAA-
2,2,3,3,4,4,4-heptafluoro-1-butanol (HFB), and heptafluorobutyric anhydride (HFBA)-
HFB. The derivatives obtained are analyzed using two different chiral columns: Chirasil-
L-Val and g-cyclodextrin (Rt-g-DEXsa) stationary phases which show different and
complementary enantiomeric selectivity. The mass spectra of the derivatives are
studied, and mass fragmentation patterns are proposed: significant fragment ions can
be identified to detect amino acid derivatives. The obtained results are compared in
terms of the enantiomeric separation achieved and mass spectrometric response. Linearity
studies and the measurement of the limit of detection (LOD) show that the proposed
method is suitable for a quantitative determination of enantiomers of several
amino acids. The use of the programmed temperature vaporiser (PTV) technique for
the injection of the untreated reaction mixture is a promising method for avoiding
manual treatment of the sample and decreasing the LOD
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