Observation d'une transition conformationnelle dans le PMMA

Intrinsic viscosity and light scattering measurements on fractionated samples of atactic poly (methyl methacrylate) show a conformational transition around 45–50° in toluene and benzene but not in 2-heptanone. The transition is detected by a stepwise change in K_θ (i.e. the unperturbed dimensions) with increasing temperature.     

Autocorrelation measurement of femtosecond laser pulses by use of a ZnSe two-photon detector array

We demonstrate autocorrelation measurements of 85-fs Ti:sapphire laser pulses, using a 32-pixel ZnSe detector array in a single-shot geometry. The two-photon photoconductor is fabricated by deposition of an array of interdigitated gold fingers on a single-crystal ZnSe substrate.     

Closed principal lines and bifurcation

The simplest pattern through which the closed principal lines (cycles) of a one parameter family of immersed surfaces bifurcate, while being apart from umbilical points, is studied in this paper. Partially supported by the J.S. Guggenheim Foundation.     

Selective desulfurization of 1,3-dithianes, -oxathiolanes and -thiazolidines by tributyltin hydride

Selective desulfurization of 2-alkyl-1,3-dithianes, -oxathiolanes, or -thiazolidines 1 with one equivalent of tri-n-butyltin hydride yields acyclic compounds R¹R²CHX(CH₂)_nSSnBu₃ (X = S,O,NH; N= 2,3), (2) which can be destannylated to the corresponding mercaptans 3.     

Ultrafiltration for proteomic sample preparation

Proteome analysis represents significant challenges to the existing sample preparation techniques. Traditional methods, such as two-dimensional electrophoresis, typically separate high-molecular-weight proteins while discarding low-molecular-weight species. This approach is well justified considering the complexity of any proteome. However, it is desirable to extract the maximum amount of information from each sample to investigate the entire range of biomolecules. We have demonstrated that ultrafiltration not only improves two-dimensional electrophoresis (2-DE) resolution of the protein fraction but also yields the low-molecular-weight fraction amenable for further analysis by high-resolution mass spectrometry. This approach was successfully adapted to the variety of biological samples including cell and tissue lysates and serum. Therefore, ultrafiltration offers an alternative sample preparation technique that enables more thorough analysis of a proteome.     

Photoacoustic Spectroscopy to determine <Emphasis Type="Italic">in vitro</Emphasis> the non radiative relaxation time of protoporphyrin IX solution containing gold metallic nanoparticles

In order to compare the non radiative relaxation time (NRRT) between standard protoporphyrin IX (PpIX) and protoporphyrin PpIX(1) solution containing gold metallic nanoparticles, we measured the photoacoustic spectroscopy (PAS) signal phase to determine, for each solution, the NRRT by using the Rosencwaig-Gesho theory, modified to include the effect of a finite non radiative deexcitation time. A NRRT average value, obtained for each solution, is reported and compared with some NRRT of triplet states reported in the literature for molecules with the same tetrapyrrolic structure. In the study was used PpIX disodium salt (DS) solution of 25% HCL. From each solution it was obtained its optical absorption spectrum, by using a UV-Vis spectrophotometer. After this, in the maximum observed optical absorption peak (404 nm), it was obtained the Photoacoustic (PA) signal phase as a function of the light modulation frequency, from 17 to 80 Hz. Our investigations are devoted to the improvement of the thermal treatments of drugs for medical applications.     

Suppression of plasma turbulence during optimized shear configurations in JET

Correlation of density turbulence suppression and reduced plasma transport is observed in the internal transport barrier (ITB) region of JET tokamak discharges with optimized magnetic shear. The suppression occurs in two stages. First, low frequency turbulence and ion transport are reduced across the plasma core by a toroidal velocity shear generated by intense auxiliary heating. Then with the ITB formation, high frequency turbulence and electron transport are reduced locally within the steep pressure gradient region of the ITB.