871 research outputs found
Localized Modes in a Finite-Size Open Disordered Microwave Cavity
We present measurements of the spatial intensity distribution of localized
modes in a two-dimensional open microwave cavity randomly filled with
cylindrical dielectric scatterers. We show that each of these modes displays a
range of localization lengths and successfully relate the largest value to the
measured leakage rate at the boundary. These results constitute unambiguous
signatures of the existence of strongly localized electromagnetic modes in
two-dimensionnal open random media
Approximate equivalence between guided modes in a low-contrast photonic bandgap fiber and Maxwell TM modes of a high-contrast two-dimensional photonic structure
We present a formal analogy between the eigenvalue problem for guided scalar
modes in a low-contrast photonic bandgap fiber and quasi-stationary TM modes of
a two-dimensional (2D) photonic structure. Using this analogy, we numerically
study the confinement losses of disordered microstructured fibers through the
leakage rate of an open 2D system with high refractive index inclusions. Our
results show that for large values of the disorder, the confinement losses
increase. However, they also suggest that losses might be improved in strongly
disordered fibers by exploring ranges of physical parameters where Anderson
localization sets in
Control of anthocyanin biosynthesis pathway gene expression by eutypine, a toxin from Eutypa lata, in grape cell tissue cultures
Eutypine, 4-hydroxy-3-(3-methyl-3-butene-1-ynyl) benzaldehyde, is a toxin produced by Eutypa lata,
the causal agent of Eutypa dieback in grapevine. The effect of the toxin on anthocyanin synthesis has
been investigated in Vitis vinifera cv. Gamay cell cultures. At concentrations higher than 200 ÎĽmol/L,
eutypine reduced anthocyanin accumulation in cells. The reduction in anthocyanin accumulation was
proportional to the eutypine concentrations and HPLC analysis showed that eutypine affected the
levels of all anthocyanins. The effect of eutypine application on the expression of five genes of the
anthocyanin biosynthesis pathway, including chalcone synthase (CHS), flavonone-3-hydroxylase
(F3H), dihydroflavonol 4-reductase (DFR), leucoanthocyanidin dioxygenase (LDOX), and UDP glucose-
flavonoid 3-O-glucosyl transferase (UFGT) was determined. Expression of CHS, F3H, DFR and
LDOX was not affected by the addition of eutypine to grapevine cell cultures. In contrast, expression
of the UFGT gene was dramatically inhibited by the toxin. These results suggest that in grapevine cell
cultures, eutypine strongly affects anthocyanin accumulation by inhibiting UFGT gene expression.
The mechanism of action of eutypine is discussed
Brachyspira pilosicoli bloodstream infections: Case report and review of the literature
Brachyspira pilosicoli is the etiologic agent of human and animal intestinal spirochetosis and is rarely implicated as a cause of bacteremia. Here, we describe the case of a B. pilosicoli spirochetemia in a 53-year-old male patient suffering from cardiogenic shock. This fastidious bacterium was isolated from blood, likely after translocation from the intestinal tract. Blood cultures were positive after 5 days of incubation (one day after the patient's death), highlighting the problem of the recovery of such type of fastidious bacterium. Identification was achieved by molecular methods (16S rRNA sequencing). A review of the English literature found only 8 cases of bacteremia caused by B. pilosicoli, mostly in immunocompromised or critically ill patients. Finally, difficulties in rapid and accurate diagnosis of B. pilosicoli bloodstream infections, in vitro antimicrobial susceptibility of human clinical isolates, and therapeutic options are discussed
Geochemistry of Volcanic Rocks of Beka, North East of Ngaoundéré (Adamawa Plateau, Cameroon): Petrogenesis and Geodynamic Context
Beka area is situated in the Adamaoua Plateau of Cameroon in central Arica. Lavas in this area has not been studied before the present work.The volcanism of Beka is characterized by basalt, trachyte and phonolite domes and flows. The petrographic study shows that basaltic lavas have porphyritic microlitic textures. The felsic lavas indicate trachytic textures.The rocks are composed of olivine, clinopyroxene, plagioclase and irontitanium oxide minerals for the basalts; clinopyroxene, alkali feldspar (including foids), sphene and titanomagnetite for the felsic lavas. Chemical analyses show that basaltic lavas are basanites. Felsic lavas contain modal feldspathoid (nepheline in phonolites). All these lavas belong to the same series, because the felsic lavas are derived from the differentiation of basaltic lavas by fractional crystallization. They show an alkaline nature according to their geochemistry. Trace elements including Rare Earth Elements characteristics show that rocks emplaced in the Winthin Plate volcanic zone. They derived from an evolved parent magma showing a low degree of partial melting and characteristics closer to a modified and evolved primitive spinel lherzolite
Simple methods for crosstalk reduction in fiber optical parametric amplifiers
International audienceWe propose and numerically demonstrate two simple methods for reduction of the crosstalk caused by four-wave mixing between the pump and the wavelength-division multiplexed channels in single-pump fiber optical parametric amplifier. The first one is based on a proper tuning of the WDM system from the pump wavelength and the second one uses the Stokes side rather than the anti-Stokes side in the gain band
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