Analysis of polychlorinated n-alkanes in environmental samples

Polychlorinated n-alkanes (PCAs), also known as chlorinated paraffins (CPs), are highly complex technical mixtures that contain a huge number of structural isomers, theoretically more than 10,000 diastereomers and enantiomers. As a consequence of their persistence, tendency to bioaccumulation, and widespread and unrestricted use, PCAs have been found in aquatic and terrestrial food webs, even in rural and remote areas. Recently, these compounds have been included in regulatory programs of several international organizations, including the US Environmental Protection Agency and the European Union. Consequently, there is a growing demand for reliable methods with which to analyze PCAs in environmental samples. Here, we review current trends and recent developments in the analysis of PCAs in environmental samples such as air, water, sediment, and biota. Practical aspects of sample preparation, chromatographic separation, and detection are covered, with special emphasis placed on analysis of PCAs using gas chromatography–mass spectrometry. The advantages and limitations of these techniques as well as recent improvements in quantification procedures are discussed.     

1,4-Benzodiazepine N-nitrosoamidines: useful intermediates in the synthesis of tricyclic benzodiazepines

1,4-Benzodiazepine N-nitrosoamidines have been used as scaffolds for the preparation of different tricyclic derivatives. Replacement of the N-nitrosoamidine moiety through treatment with the nucleophiles acetylhydrazine, aminoacetaldehyde dimethylacetal and 1-amino-2-propanol, followed by an acid-catalyzed cyclization step, afforded triazolo and imidazobenzodiazepines 1, 6, and 7, respectively, in good yields. When acetylhydrazine is used as a nucleophile, the overall process provides an alternative route to alprazolam (1b) and triazolam (1c), respectively.     

Deformations of 2k-Einstein structures

It is shown that the space of infinitesimal deformations of 2k-Einstein structures is finite dimensional on compact non-flat space forms. Moreover, spherical space forms are shown to be rigid in the sense that they are isolated in the corresponding moduli space.     

Third-order nonlinearity of Er3+-doped lead phosphate glass

In a laser coherent combination, the phase detection and control is the most critical. Using the beat frequency method, consistence of the phase in output beams can be ensured through real-time detection and correction for the phase change. Phase noises are controlled by a liquid crystal phase modulator. At the same time, the liquid crystal polarization controller is used to make the polarization state stable, which is good for the improvement of the combining efficiency. The wave length of the main oscillation laser is 532 nm. The output power of laser can be adjusted continuously from 0 to 6 W. The shifted frequency of the system is 40 MHz. The accuracy for phase control is superior to λ/70 RMS. In the process of closed-loop control, using the liquid crystal phase and polarization controller, a better signal phase correction of optical path has been achieved for the coherent combination of high power laser arrays.     

Singular rational curves with points of nearly-maximal weight

In this article we study rational curves with a unique unibranch genus-g singularity, which is of κ-hyperelliptic type in the sense of [27]; we focus on the cases $\kappa =0$ and $\kappa =1$, in which the semigroup associated to the singularity is of (sub)maximal weight. We obtain a partial classification of these curves according to the linear series they support, the scrolls on which they lie, and their gonality.     

Some constructions of linearly optimal group codes

We continue here the research on (quasi)group codes over (quasi)group rings. We give some constructions of [n,n-3,3]_q-codes over F_q for n=2q and n=3q. These codes are linearly optimal, i.e. have maximal dimension among linear codes having a given length and distance. Although codes with such parameters are known, our main results state that we can construct such codes as (left) group codes. In the paper we use a construction of Reed-Solomon codes as ideals of the group ring F_qG where G is an elementary abelian group of order q.     

On deformations of spherical isometric foldings

The behavior of special classes of isometric foldings of the Riemannian sphere S ² under the action of angular conformal deformations is considered. It is shown that within these classes any isometric folding is continuously deformable into the standard spherical isometric folding f _s defined by f _s (x, y, z) = (x, y, |z|).     

Phonon-induced polariton superlattices

We show that the coherent interaction between microcavity polaritons and externally stimulated acoustic phonons forms a tunable polariton superlattice with a folded energy dispersion determined by the phonon population and wavelength. Under high phonon concentration, the strong confinement of the optical and excitonic polariton components in the phonon potential creates weakly coupled polariton wires with a virtually flat energy dispersion.