Improvement of Explosive Detection with a Fluorescent Sensor Using a Heating Device

AbstractThere is a strong demand for a fast and reliable detection of explosives because of their use in most terrorist attacks. Chemical sensors, especially fluorescent ones, seem to fill the need in terms of reliability, cost and handling ability. In this paper, the detection of 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX or hexogen) using a heating device of the particles was studied. Two fluorescent sensitive materials were compared: diimine [1] and polycarbosilane functionalised with pyrene moieties at 50% (PCS-Py-50%) [2]. Both materials were shown to be sensitive to TNT and RDX vapours. The PCS-Py-50% material was the most promising for the detection of RDX because of a higher kinetics of interaction

Structural activation of the transcriptional repressor EthR from Mycobacterium tuberculosis by single amino acid change mimicking natural and synthetic ligands

Ethionamide is an antituberculous drug for the treatment of multidrug-resistant Mycobacterium tuberculosis. This antibiotic requires activation by the monooxygenase EthA to exert its activity. Production of EthA is controlled by the transcriptional repressor EthR, a member of the TetR family. The sensitivity of M. tuberculosis to ethionamide can be artificially enhanced using synthetic ligands of EthR that allosterically inactivate its DNA-binding activity. Comparison of several structures of EthR co-crystallized with various ligands suggested that the structural reorganization of EthR resulting in its inactivation is controlled by a limited portion of the ligand-binding-pocket. In silico simulation predicted that mutation G106W may mimic ligands. X-ray crystallography of variant G106W indeed revealed a protein structurally similar to ligand-bound EthR. Surface plasmon resonance experiments established that this variant is unable to bind DNA, while thermal shift studies demonstrated that mutation G106W stabilizes EthR as strongly as ligands. Proton NMR of the methyl regions showed a lesser contribution of exchange broadening upon ligand binding, and the same quenched dynamics was observed in apo-variant G106W. Altogether, we here show that the area surrounding Gly106 constitutes the molecular switch involved in the conformational reorganization of EthR. These results also shed light on the mechanistic of ligand-induced allosterism controlling the DNA binding properties of TetR family repressors

Molecular mechanism by which the nucleoid occlusion factor, SlmA, keeps cytokinesis in check

Nucleoid occlusion (NO) restricts bacterial cell division to prevent chromosome guillotining in the cell midzone when replication or segregation is delayed. Structural work suggests that the NO factor SlmA (synthetic lethal with a defective Min system) interferes with formation of the cytokinetic Z-ring by altering associations between FtsZ protofilaments

Étude du temps de relaxation T2 des échos de phonons dans les poudres cristallines

The relaxation time T2 for phonon echoes has been studied in crystalline powders as a function of the diameter of the grains.Le temps de relaxation T2 des échos de phonons a été étudié dans les poudres cristallines en fonction du diamètre des grains

Échos de phonons et transitions de phase

The experiments described in this paper show that the phonon echo method applied to crystalline powders is well suited to study critical phenomena. The case of K.D.P. is reported and the results are compared with those obtained by standard acoustical methods.Ces expériences montrent que la méthode des échos de phonons appliquée à des poudres cristallines peut être utilisée pour examiner les propriétés critiques du matériau ; on a pris l'exemple du K.D.P. et les résultats sont comparés à des expériences standard d'acoustique

Les échos de phonons. II

The effect of an electromagnetic wave of frequency 2 ω on the generation of dipolar phonon echoes at frequency ω is directly demonstrated by using a subsidiary source at 2 ω. As a consequence, when the source is strong enough, the echoes may be excited in most piezoelectric crystals.Le rôle d'une onde électromagnétique de fréquence 2 ω dans la production des échos de phonons dipolaires de fréquence ω est directement mis en évidence par l'utilisation d'une source auxiliaire à 2 ω. De ce fait, si la source est intense, ces échos peuvent être observés dans la plupart des cristaux piézoélectriques

Effect of the electric field on the elastic and dielectric properties of a lithium-potassium tantalate crystal

We have measured in a K$_{1-x}$Li$_{x}$TaO$_3$ crystal with x = 1.7 % the elastic constant with longitudinal acoustic waves of frequency between 30 and 330 MHz and the dielectric constant between 10 Hz and 1 MHz in the temperature range from 4 to 200 K under an electric field applied upon cooling. The main effect of the applied field on the dielectric constant is attributed to space charges. The real part of the elastic constant (the sound velocity) was found to increase when the field was applied perpendicular to the acoustic wave vector and to decrease when it was applied parallel to the wave vector. The effect of the cooling rate was also studied. These results are explained by the occurrence of clusters of oriented dipoles borne by the Li$^+$ ions, favoured by the field

A polycrystalline model for stress-strain behaviour of tantalum at 300 K

A polycrystalline model is proposed to model the large plastic deformation and texture evolutions in tantalum over a wide range of strain rates at room temperature. The mechanical behaviour is discussed in terms of back and effective stresses with the help of qualitative and quantitative TEM observations, Using these observations, an elasto-visco-plastic formulation for b.c.c. crystals is developed in the thermal activation framework

Stimulated phonon echoes in resonant powders

Experiments on stimulated phonon echoes in resonant quartz powders are reported. Angular dependence and power dependence studies give new information about their behaviour. Sieving the powder does not completely destroy the echo. The nature of the frozen state is not yet understood.On présente diverses expériences sur l'écho de phonons à T + τ (ou écho stimulé) dans des poudres de quartz à la résonance mécanique. L'étude des dépendances angulaires et en puissances apporte de nouvelles informations sur son comportement. L'écho persiste même après tamisage de la poudre. La nature de l'état figé demeure inconnue

On the ultrasonic absorption and dispersion in amorphous superconductors

We explain the unexpected behaviour of the ultrasonic absorption observed in the amorphous superconductor Pd30Zr70. It is assumed that the relaxation of the tunnelling states present in amorphous metals, is determined by their strong coupling to electrons as well as to thermal phonons. The distribution of the corresponding coupling strengths as invoked in the tunnelling model leads to a smooth temperature dependence of the absorption when passing through the superconducting transition temperature Tc. In contrast, the dispersion should exhibit a change of slope at Tc.Nous expliquons le comportement inattendu de l'absorption ultrasonore observé dans le supraconducteur amorphe Pd30Zr70. Nous supposons que la relaxation des états tunnel, présents dans les amorphes métalliques, est déterminée par leur fort couplage avec les électrons aussi bien qu'avec les phonons thermiques. La distribution des constantes de couplage correspondantes telle que la prévoit le modèle des états tunnel conduit à une variation faible de l'absorption avec la température lorsque la température de transition supraconductrice Tc est franchie. A l'opposé, la variation de vitesse devrait montrer un changement à Tc