Anatomy of a polarization switch of a vertical-cavity semiconductor laser

Using a streak camera we have measured the three Stokes polarization parameters during a polarization switch of a vertical-cavity semiconductor laser. The switch occurs along a corkscrew path on the Poincare sphere and takes on average a few nanoseconds; this value agrees with a theoretical treatment based upon the Fokker-Planck equation.     

Structurally Diverse π‐Extended Conjugated Polycarbo‐ and Heterocycles through Pd‐Catalyzed Autotandem Cascades

The Pd‐catalyzed reaction between 2,2′‐dibromobiphenyls and related systems with tosylhydrazones gives rise to new π‐extended conjugated polycarbo‐ and heterocycles through an autotandem process involving a cross‐coupling reaction followed by an intramolecular Heck cyclization. The reaction shows wide scope regarding both coupling partners. Cyclic and acyclic tosylhydrazones can participate in the process. Additionally, a variety of aromatic and heteroaromatic dibromoderivatives have been employed, leading to an array of diverse scaffolds featuring a fluorene or acridine central nucleus, and containing binaphthyl, thiophene, benzothiophene and indole moieties. The application to appropriate tetrabrominated systems led to greater structural complexity through two consecutive autotandem cascades. The photophysical properties of selected compounds were studied through their absorption and emission spectra. Fluorescence molecules featuring very high quantum yields were identified, showing the potential of this methodology in the development of molecules with interesting optoelectronic properties.     

Spectrochemical study for the in situ detection of oil spill residues using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has been used to identify the differences or similarities between crude oil and fuel residues. Firstly, a man portable LIBS analyzer was used for the on-site environmental control and analysis of the oil spill from The Prestige. An exhaustive analysis of crude oil and oil spill residues (collected during the field campaign in the Galician Coast) was performed in the laboratory. Characteristics elements in petroleum such as C, H, N, O, Mg, Na, Fe and V were detected. In addition, contributions from Ca, Si and Al in the composition of residues have been found. The use of intensity ratios of line and band emissions in the original fuel (crude oil) and in the aged residues allowed a better characterization of the samples than the simple use of peak intensities. The chemical composition between the crude oil and the fuel residues was found completely different. As well, a statistical method was employed in order to discriminate residues. Although significant differences were observed, no conclusions in terms of age and provenance could be reached due to the unknowledgment in the origin of the samples.     

Preparation of quinolinium salts differing in the length of the alkyl side chain

Quaternary quinolinium salts differing in alkyl chain length are members of a widespread group of cationic surfactants. These compounds have numerous applications in various branches of industry and research. In this work, the preparation of quinoline-derived cationic surface active agents differing in the length of the side alkyl chains (from C? to C??) is described. An HPLC method was successfully developed for distinction of all members of the series of prepared long-chain quinolinium derivatives. In conclusion, some possibilities of intended tests or usage have been summarized. In vitro testing using a microdilution broth method showed good activity of a substance with a C12 chain length against Gram-positive cocci and Candida species.     

Proton magnetic relaxation process during the polymerization of hemoglobin S

The proton spin-lattice and spin-spin magnetic relaxation times are investigated at 4 MHz in samples of hemoglobin A and S with intracellular concentrations, at 36 °C, and during spontaneous deoxygenation. Magnetic relaxation behaves differently in the solutions of hemoglobin A and S. The possible causes of this behavior are discussed: changes in molecular mobility, the variations of hemoglobin magnetism, and the appearance of microinhomogeneities in the solutions of hemoglobin S at the end of the polymerization process.     

Possibilities of energy-resolved X-ray radiography for the investigation of paintings

X-ray radiographic images of paintings often show little or no contrast. In order to increase the contrast in radiographic images we measured the X-ray spectrum of a low power X-ray tube, after passing through the painting, with a high energy-resolution SDD detector. To obtain images, the detector is collimated with a 400 μm diameter pinhole and the painting was moved through the beam in the x and y-direction using a dwell time of a few seconds per pixel. The data obtained consists of a data cube of, typically, 200 × 200 pixels and a 512-channel X-ray spectrum for each pixel, spanning the energy range from 0 to 40 keV. Having the absorbance spectrum available for each pixel, we are able, a posteriori, to produce images by edge subtraction for any given element. In this way high contrast, element-specific, images can be obtained. Because of the high energy-resolution a much simpler edge subtraction algorithm can be applied. We also used principal-component imaging to obtain, in a more automated way, images with high contrast. Some of these images can easily be attributed to specific elements. It turns out that preprocessing of the spectral data is crucial for the success of the multivariate image processing.