535 research outputs found
Automated fragment identification for electron ionisation mass spectrometry: application to atmospheric measurements of halocarbons
Non-target screening consists in searching a sample for all present
substances, suspected or unknown, with very little prior knowledge about the
sample. This approach has been introduced more than a decade ago in the field
of water analysis, together with dedicated compound identification tools, but
is still very scarce for indoor and atmospheric trace gas measurements, despite
the clear need for a better understanding of the atmospheric trace gas
composition.For a systematic detection of emerging trace gases in the
atmosphere, a new and powerful analytical method is gas chromatography (GC) of
preconcentrated samples, followed by electron ionisation, high resolution mass
spectrometry (EI-HRMS). In this work, we present data analysis tools to enable
automated fragment formula annotation for unknown compounds measured by
GC-EI-HRMS. Based on co-eluting mass/charge fragments, we developed an
innovative data analysis method to reliably reconstruct the chemical formulae
of the fragments, using efficient combinatorics and graph theory. The method
does not require the presence of the molecular ion, which is absent in ~40% of
EI spectra. Our method has been trained and validated on \textgreater50
halocarbons and hydrocarbons, with 3 to 20 atoms and molar masses of 30 to 330
g mol-1, measured with a mass resolution of approx.~3500. For 90% of the
compounds, more than 90% of the annotated fragment formulae are correct. Cases
of wrong identification can be attributed to the scarcity of detected fragments
per compound or the lack of isotopic constraint (no minor isotopocule
detected).Our method enables to reconstruct most probable chemical formulae
independently from spectral databases. Therefore, it demonstrates the
suitability of EI-HRMS data for non-target analysis and paves the way for the
identification of substances for which no EI mass spectrum is registered in
databases. We illustrate the performances of our method for atmospheric trace
gases and suggest that it may be well suited for many other types of samples.
The L-GPL licenced Python code is released under the name ALPINAC for
ALgorithmic Process for Identification of Non-targeted Atmospheric Compounds.Comment: Journal of Cheminformatics, Chemistry Central Ltd. and BioMed
Central, 202
David Hockney: The Yosemite Suite
Acidulées et singulières. Tels sont les premiers qualificatifs qui viennent à l’esprit lorsque l’on regarde les œuvres de la série Yosemite Suite de David Hockney. Le catalogue éponyme est édité à l’occasion de l’exposition à la Galerie Lelong (Paris, 20 mai-13 juillet 2017) et le lecteur avisé fera le lien avec la rétrospective consacrée à l’œuvre de l’artiste au Centre Pompidou (21 juin-23 octobre 2017). Avec un format vertical, l’artiste peint inlassablement des arbres jaunes et vert acide..
Unconstrained handwriting recognition applied to the processing of bank cheques
Develops a French and English database with a fully trainable word recognizer which bypasses the notion of character recognition
Computing Individual Discrete Logarithms Faster in
The Number Field Sieve (NFS) algorithm is the best known method to
compute discrete logarithms (DL) in finite fields
, with medium to large and small. This algorithm
comprises four steps: polynomial selection, relation collection,
linear algebra and finally, individual logarithm computation. The
first step outputs two polynomials defining two number fields, and a
map from the polynomial ring over the integers modulo each of these
polynomials to .
After the relation collection and linear algebra
phases, the (virtual) logarithm of a subset of elements in each number
field is known. Given the target element in , the fourth
step computes a preimage in one number field. If one can write the
target preimage as a product of elements of known (virtual) logarithm,
then one can deduce the discrete logarithm of the target.
As recently shown by the Logjam attack, this final step can be
critical when it can be computed very quickly.
But we realized that computing an individual DL is much slower in medium-
and large-characteristic non-prime fields with ,
compared to prime fields and quadratic fields . We optimize
the first part of individual DL: the \emph{booting step}, by reducing
dramatically the size of the preimage norm.
Its smoothness probability is higher, hence the running-time of the
booting step is much improved.
Our method is very efficient for small extension fields with and applies to any , in medium and large characteristic
A l’Ouest, toute ! Travailleuses de Bretagne et d’ailleurs (sous la dir. de Fabienne Dumont, Sylvie Ungauer)
« A l’Ouest, toute ! » est le résultat d’un travail initié par Fabienne Dumont et Sylvie Ungauer, toutes deux enseignantes à l’Ecole supérieure d’art de Bretagne – la première à Quimper et la seconde à Brest. Il fallut trois ans et la participation d’artistes et d’étudiants dans le cadre de différents ateliers, projections publiques, conférences, workshops et séminaires, pour faire évoluer et aboutir la réflexion des participants. Des artistes comme Margaret Harrison, Marie Preston ou Mierle ..
Valérie Mréjen : images en quête d’histoires
Une enveloppe cartonnée. A l’intérieur, trente-six photos en noir et blanc. Photos de famille, instants volés, portraits figés, sourires, solennité, exotisme ou familiarité. Des photos souvenirs qui pourraient être les nôtres et qui suscitent tour à tour l’amusement ou la nostalgie. Au dos, chaque photo est divisée en deux parties, comme une carte postale. En haut de chaque partie, un titre devancé d’un numéro. Et sous chaque titre une phrase. On comprend alors qu’il s’agit de remettre les ph..
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