LC/ESI‐MS/MS characterisation of lipopeptide biosurfactants produced by the Bacillus licheniformis V9T14 strain

Lipopeptide biosurfactants produced by the Bacillus licheniformis V9T14 strain showed an interesting anti‐adhesion activity against biofilm formation of human pathogenic bacterial strains. The chemical characterisation of the crude extract of V9T14 strain was first developed through electrospray ionisation mass spectrometry (ESI‐MS) and ESI‐MS/MS direct infusions: two sets of molecular ion species belonging to the fengycin and surfactin families were revealed and their structures defined, interpreting their product ion spectra. The LC/ESI‐MS analysis of the crude extract allowed to separate in different chromatogram ranges the homologues and the isoforms of the two lipopeptide families. The extract was then fractionated by silica gel chromatography in two main fractions, I and II. The purified biosurfactants were analysed through a new, rapid and suitable LC/ESI‐MS/MS method, which allowed characterising the composition and the structures of the produced lipopeptides. LC/ESI‐MS/MS analysis of fraction I showed the presence of C₁₃, C₁₄ and C₁₅ surfactin homologues, whose structures were confirmed by the product ion spectra of the sodiated molecules [M + Na]⁺ at m/z 1030, 1044 and 1058. LC/ESI‐MS/MS analysis of fraction II confirmed the presence of two main fengycin isoforms, with the protonated molecules [M + H]⁺ at m/z 1478 and 1506 corresponding to C₁₇ fengycin A and C₁₇ fengycin B, respectively. Other homologues (C₁₄ to C₁₆) were revealed and confirmed as belonging to fengycin A or B according to the retention times and the product ions generated, although with the same nominal mass. Finally, a relative percentage content of each homologue for both lipopeptides families in the whole extract was proposed. Copyright © 2010 John Wiley & Sons, Ltd.     

Pyroxene inclusions in paleo-Christian mosaic tesserae: a new tool for constraining the glass manufacturing temperature

The mineral inclusions of two orange glass tesserae from paleo-Christian mosaics were investigated in order to derive the melting temperature reached during their production (sourced from Padua and Vicenza, Veneto region, Italy). In particular, clinopyroxene crystals were studied by single-crystal X-ray diffraction and electron microprobe WDS analysis. The crystals show C2/c symmetry, typical of disordered Ca/Na and Mg/Al distributions indicating high-temperature of formation (>700°C). The cation site populations were obtained by combining results from the two experimental techniques enabled us to derive the following stoichiometric formula:

Characterization of an actively linearized ultrabroadband chirped laser with a fiber-laser optical frequency comb

The optical frequency sweep of an actively linearized, ultrabroadband, chirped laser source is characterized through optical heterodyne detection against a fiber-laser frequency comb. Frequency sweeps were measured over approximately 5 THz bandwidths from 1530 nm to 1570 nm. The dominant deviation from linearity resulted from the nonzero dispersion of the fiber delay used as a reference for the sweep linearization. Removing the low-order dispersion effects, the residual sweep nonlinearity was less than 60 kHz rms, corresponding to a constant chirp with less than 15 ppb deviation across the 5 THz sweep.     

The direct image of the relative dualizing sheaf needs not be semiample

We provide details for the proof of Fujita's second theorem and prove that for a Kähler fibre space f:X→B$f:X\to B$ over a smooth projective curve B  , the direct image of the relative dualizing sheaf V:=f_?ω_X/B$V:=f_{?}{\omega }_{X/B}$ is the direct sum of an ample and a unitary flat bundle. We also show that V needs not be semiample, which is our main result.     

Overconvergent modular sheaves and modular forms for GL 2/F

Given a totally real field F and a prime integer p which is unramified in F, we construct p-adic families of overconvergent Hilbert modular forms (of non-necessarily parallel weight) as sections of, so called, overconvergent Hilbert modular sheaves. We prove that the classical Hilbert modular forms of integral weights are overconvergent in our sense. We compare our notion with Katz’s definition of p-adic Hilbert modular forms. For F = ?, we prove that our notion of (families of) overconvergent elliptic modular forms coincides with those of R. Coleman and V. Pilloni.     

A Cauchy kernel for slice regular functions

In this article, we show how to construct a regular, non-commutative Cauchy kernel for slice regular quaternionic functions. We prove an (algebraic) representation formula for such functions, which leads to a new Cauchy formula. We find the expression of the derivatives of a regular function in terms of the powers of the Cauchy kernel, and we present several other consequent results.