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See detailDetermination of charge carrier transport properties in organic devices by admittance spectroscopy : application to hole mobility in α-NPD
Nguyen, Ngoc Duy ULg; Schmeits, Marcel; Loebl, Hans-Peter

in Physical Review. B : Condensed Matter (2007), 75

Hole mobility in N,N′-diphenyl-N,N′-bis(1-naphtylphenyl)-1,1′-biphenyl-4,4′-diamine (α-NPD) is evaluated by electrical characterization in the ac regime. The frequency-dependent complex admittance and ... [more ▼]

Hole mobility in N,N′-diphenyl-N,N′-bis(1-naphtylphenyl)-1,1′-biphenyl-4,4′-diamine (α-NPD) is evaluated by electrical characterization in the ac regime. The frequency-dependent complex admittance and impedance of the structure consisting of the organic layer, grown by thermal evaporation, sandwiched by indium tin oxide and aluminum electrodes, are measured as functions of the applied dc voltage. The capacitance response shows negative values for frequencies below a characteristic value depending on the bias and ranging from 0.1 Hz up to 20 Hz. It increases with the modulation frequency and reaches a peak, the magnitude and position of which are functions of the applied voltage. For higher frequencies, a minimum can be observed before the capacitance increases again up to a constant value. A final decreasing occurs at frequency of 4×106 Hz. The analysis of the experimental data is performed by a detailed theoretical study of the steady-state and small-signal electrical characteristics of the device. Numerical calculations are based on the solution of the basic semiconductor equations for the system consisting of two electrodes connected by the semiconducting channel formed by the organic layer. The description explicitly includes a continuous distribution of trap density of states and a field-dependent carrier mobility. The spatially dependent charge carrier and occupied trap concentrations, as well as the various components to the total current density, are obtained for the dc and ac regimes and are analyzed for given bias and frequency. Based on a formalism used in the study of inorganic semiconductors, the results of the simulation show that the inductive contribution to the capacitance response originates from the modulation of the hole concentration in the organic material, leading to the corresponding carrier transit time. Moreover, the low-frequency behavior of the capacitance curves could be explained by the presence of a band of defect states which modifies the charge distribution within the organic layer and the injection of electrons from the cathode. We show that the latter contribution is also responsible for the negative values of the capacitance measured below 10 Hz. Good agreement is observed between the experimental and theoretical electrical characteristics, in particular for the differential susceptance results and the subsequent hole mobility values. Our approach can be a useful contribution for the methodology of obtaining mobilities from admittance measurements as it allows one to clarify the physical origin of the measured frequency-dependent capacitance and to check for the experimental procedure. This work finally leads to the formulation of the conditions under which small-signal ac measurements can be used to determine carrier mobility in organic devices. [less ▲]

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See detailDetermination of chloramphenicol in honey, shrimp and poultry meat with liquid chromatography-mass spectrometry. Validation of the method according to Commission Decision 2002/657/EC
Douny, Caroline ULg; Widart, Joëlle ULg; De Pauw, Edwin ULg et al

in Food Analytical Methods (2013), 6(5), 1458-1465

Chloramphenicol (CAP) is an antibiotic used for the treatment of bacterial infections in human and veterinary medicine. The use of CAP was prohibited in the European Union in 1994. Control laboratories ... [more ▼]

Chloramphenicol (CAP) is an antibiotic used for the treatment of bacterial infections in human and veterinary medicine. The use of CAP was prohibited in the European Union in 1994. Control laboratories are required to use suitably validated analytical methods to check sample compliance with the regulation. A quantitative method based on liquid chromatography coupled to isotopic dilution tandem mass spectrometry (LC–IDMS/MS) was developed for the determination of chloramphenicol in honey, shrimp and poultry meat. The experimental protocol consisted of a liquid-liquid extraction with ethyl acetate. Separation and detection were realized respectively by a 2690 Waters HPLC (Milford, MA, USA) and a Micromass Triple Quadrupole mass spectrometer (Micromass, Manchester, UK), equipped with an Electrospray source. The effects of mobile phase additives on the response of LC/ESI/MS were examined. Two different HPLC columns were tested: the X-Terra from Waters and the Alltima HP C18 HL from Alltech (Deerfield, IL, USA). A validation of the method was conducted according to the EU criteria for the analysis of chloramphenicol in foods. The decision limits (CCα) were 0.04, 0.03, 0.07 µg kg-1 and the detection capabilities (CCβ) were 0.05, 0.04, 0.08 µg kg-1 for honey, shrimp and poultry meat respectively. Those values are below the minimum required performance limit (MRPL) set at 0.3 µg kg-1 by the EU and 0.1 µg kg-1 by Belgium. Our protocol has the advantage to propose a unique extraction method working as well for honey, shrimp and poultry meat, contrary to similar published methods in which a different extraction method is used for each type of matrix. [less ▲]

Detailed reference viewed: 97 (12 ULg)
See detailDetermination of CK-MB mass in clinical practice
Chapelle, Jean-Paul ULg

Conference (1997, February 03)

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See detailDetermination of COBALT in patients with metal hip prosthesis
MISTRETTA, Virginie ULg; Charlier, Corinne ULg

Poster (2014, October 18)

Detailed reference viewed: 20 (2 ULg)
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See detailDetermination of COF2 vertical distributions above Jungfraujoch by FTIR and multi-spectra fitting
Duchatelet, Pierre ULg; Mahieu, Emmanuel ULg; Demoulin, Philippe ULg et al

Poster (2007, April)

The major sources of fluorine in the stratosphere are CFC-11 and CFC-12. Photolysis of these compounds leads to release of chlorine atoms, while the fluorine is, in a first step, present in the form of ... [more ▼]

The major sources of fluorine in the stratosphere are CFC-11 and CFC-12. Photolysis of these compounds leads to release of chlorine atoms, while the fluorine is, in a first step, present in the form of carbonyl compounds like COClF and COF2. Their further photolysis liberates fluorine atoms, which are quickly converted to HF. Given its long life time, COF2 is the second stratospheric fluorine reservoir. The first COF2 vertical distributions were derived from occultation measurements performed by the ATMOS instrument during the SPACELAB-3 Space Shuttle mission in 1985. The Canadian FTIR spectrometer ACE-FTS, onboard the SCISAT-1 satellite, is the first instrument since the last ATMOS flight in 1994, to record COF2 vertical profiles from space. All these observations show that, at mean latitudes, COF2 concentration is maximum between 30 and 35 km. Several COF2 IR absorption lines located either in the so-called InSb (1-5 µm) and MCT (2-16 µm) spectral ranges can be used to determine its total column from ground-based FTIR observations. In this context, several studies concerning the evolution of COF2 total column above various stations were published during the nineties. At this time, no study concerning the inversion of COF2 vertical distributions from ground-based FTIR spectra has been published. This report deals with the feasibility of such inversions, using, simultaneously, via the SFIT-2 v3.91 algorithm, a multi-microwindows and a multi-spectra fitting procedure. The multi-spectra method consists of combining several FTIR observations, recorded during the same day, to increase the information content. A selection of microwindows in InSb and MCT ranges, a complete discussion about the data characterization (e.g. information content) and typical examples of COF2 retrieved profiles from high resolution solar spectra recorded with the University of Liège Jungfraujoch FTS will be revealed. [less ▲]

Detailed reference viewed: 71 (7 ULg)
See detailDetermination of critical current in bulk high temperature superconductors by magnetic flux profile measuring methods
Vanderbemden, Philippe ULg

Doctoral thesis (1999)

In this thesis, the emphasis is placed on determining the critical current density in bulk high-temperature superconductors by magnetic flux profile measuring methods. The thesis involves three different ... [more ▼]

In this thesis, the emphasis is placed on determining the critical current density in bulk high-temperature superconductors by magnetic flux profile measuring methods. The thesis involves three different aspects : a brief theoretical investigation of the flux profile methods, the practical realization of an experimental set-up intended for measuring such profiles and a discussion of flux profile measurements in several bulk high-temperature superconductors. [less ▲]

Detailed reference viewed: 54 (9 ULg)
See detailDetermination of divinyl ether synthase activity during storage of potato tubers
Hoyaux, P.; Delcarte, J.; du Jardin, Patrick ULg et al

Poster (2001, April 18)

Detailed reference viewed: 10 (0 ULg)
See detailDetermination of electron and proton auroral energy inputs from FUV-IMAGE
Gérard, Jean-Claude ULg; Hubert, Benoît ULg; Meurant, M. et al

Conference (2001, May 01)

The FUV experiment onboard the IMAGE spacecraft offers the unique possibility to obtain simultaneous snapshots of the global north aurora every 2 minutes in three different spectral channels. The WIC ... [more ▼]

The FUV experiment onboard the IMAGE spacecraft offers the unique possibility to obtain simultaneous snapshots of the global north aurora every 2 minutes in three different spectral channels. The WIC camera has a broadband channel covering the 135-190 nm interval including the N[SUB]2[/SUB] LBH bands, part of which may be absorbed by O[SUB]2[/SUB]. The SI13 channel is centered on the OI 135.6 nm line which is optically thin and includes a ~ 40% LBH contribution. Finally, the SI12 camera images the Doppler-shifted Ly-α emission excited by the proton aurora. This set of instrumentation is combined with auroral models to determine the electron and the proton energy fluxes from the magnetosphere. Examples will be presented and compared with the values deduced from the NOAA satellites. Simultaneous in-situ measurements of the particle characteristic energy have been combined with the data extracted from the FUV images to validate the models and derive empirical relationships between the particle flux measured by the detectors and the brightness observed by FUV-IMAGE at the footprint of the same magnetic field line. Finally, we will assess the ability to deduce the characteristic energy of the auroral particles from the ratio of co-registered images in the WIC and SI13 cameras. This method is based on the difference of vertical distribution of the LBH and the OI 135.6 nm emissions. It offers the potential to globally remotely sense not only the energy flux from the magnetosphere but also the main features of the electron characteristic energy. [less ▲]

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See detailDetermination of Electrostatic Potential Differences Between Coexisting Phases in Aqueous Two-Phase Systems
Bringmann, J; Gaube, J; Keil, B et al

Conference (1993)

Detailed reference viewed: 3 (0 ULg)
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See detailDetermination of enantiomeric purity of S-amlodipine by chiral LC with emphasis on reversal of enantiomer elution order.
Dossou, Katina Sourou Sylvestre ULg; Edorh, P. A.; Chiap, Patrice ULg et al

in Journal of Separation Science (2011), 34

An LC method was developed and prevalidated for the enantiomeric purity determination of S-amlodipine in polar organic solvent chromatography using a chlorine-containing cellulose-based chiral stationary ... [more ▼]

An LC method was developed and prevalidated for the enantiomeric purity determination of S-amlodipine in polar organic solvent chromatography using a chlorine-containing cellulose-based chiral stationary phase (CSP). The concentration of formic acid (FA) (0.01-0.2%) in the mobile phase containing acetonitrile as the main solvent was found to influence the elution order of amlodipine enantiomers as well as the enantioresolution. A reversal of the enantiomer elution order of amlodipine was only observed with chiral stationary phases with both electron-withdrawing (chloro) and electron-donating groups (methyl) on the phenyl moieties of the chiral selector, namely cellulose tris(3-chloro-4-methylphenylcarbamate) and cellulose tris(4-chloro-3-methylphenylcarbamate). The highest enantioresolution (R(s) : 4.1) value was obtained at the lowest FA concentration (0.01%) using cellulose tris(4-chloro-3-methylphenylcarbamate) as the chiral selector and the enantiomeric impurity, R-amlodipine, eluted first under these conditions. Therefore, the mobile phase selected for the prevalidation of the method consisted of ACN/0.1% DEA/0.01% FA and the temperature was set at 25 degrees C. The method was prevalidated by means of the strategy based on the total measurement error and the accuracy profile. The method was found to be selective and the limit of quantification was found to be about 0.05% for R-amlodipine, while the limit of detection was close to 0.02%. [less ▲]

Detailed reference viewed: 52 (4 ULg)
See detailDetermination of equilibrium association constants of ligand-DNA complexes by electrospray mass spectrometry
Gabelica, Valérie ULg

in Keith R., Fox (Ed.) Drug-DNA Interaction Protocols (2010)

Electrospray mass spectrometry can be used to detect ligand-DNA noncovalent complexes formed in solution. This chapter describes how to determine equilibrium association constants of the complexes ... [more ▼]

Electrospray mass spectrometry can be used to detect ligand-DNA noncovalent complexes formed in solution. This chapter describes how to determine equilibrium association constants of the complexes. Particular attention is devoted to describing how to tune an electrospray mass spectrometer using a 12-mer oligodeoxynucleotides duplex in order to perform these experiments. This protocol can then be applied to any nucleic acid structure that can be ionized with electrospray mass spectrometry. [less ▲]

Detailed reference viewed: 91 (13 ULg)
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See detailDetermination of equivalent material characteristics for parasitic effects in electrical apparatus
Hedia, Hakim; Henrotte, François; Dular, Patrick ULg et al

in IEEE Transactions on Magnetics (1996), 32(5), 4341-4343

For linear systems excited with sinusoidal constraints, an exact dynamical modelling can be performed with a phasor (complex number) approach. For nonlinear systems (exhibiting saturation, hysteresis and ... [more ▼]

For linear systems excited with sinusoidal constraints, an exact dynamical modelling can be performed with a phasor (complex number) approach. For nonlinear systems (exhibiting saturation, hysteresis and higher harmonics), a time stepping model is very time consuming. A method to model such nonlinear systems with an approximated phasor approach is presented. Determination of equivalent material characteristics is discussed and applications are given. [less ▲]

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See detailDetermination of flurbiprofen enantiomers in plasma using a single-isomer amino cyclodextrin derivative in nonaqueous capillary electrophoresis.
Rousseau, Anne ULg; Pedrini, Matteo; Chiap, Patrice ULg et al

in Electrophoresis (2008), 29(17), 3641-8

A nonaqueous capillary electrophoresis (NACE) assay was developed for the separation and determination of flurbiprofen enantiomers in plasma samples using 6-monodeoxy-6-mono(3-hydroxy)propylamino-beta ... [more ▼]

A nonaqueous capillary electrophoresis (NACE) assay was developed for the separation and determination of flurbiprofen enantiomers in plasma samples using 6-monodeoxy-6-mono(3-hydroxy)propylamino-beta-cyclodextrin as chiral selector. The nonaqueous background electrolyte was made up of 40 mM ammonium acetate in methanol (MeOH), and flufenamic acid was employed as internal standard. Solid-phase extraction was used for sample cleanup prior to the NACE separation.The NACE method reproducibility was optimized by evaluating different capillary washing sequences between runs. After having tested various conditions, trifluoroacetic acid (1 M) in MeOH was finally selected. Concerning the solid-phase extraction procedure, good and reproducible analyte recoveries were obtained using MeOH for protein denaturation and a polymeric phase combining hydrophobic interactions with anion exchange properties (Oasis) MAX) was selected as extraction sorbent. The method selectivity was not only demonstrated toward a blank plasma sample but also toward other non-steroidal anti-inflammatory drugs. The method was then successfully validated with respect to response function, trueness, precision, accuracy, linearity and limit of quantification. [less ▲]

Detailed reference viewed: 57 (6 ULg)