Dinoflagellate bioluminescence in response to mechanical stimuli in water flows

Bioluminescence of plankton organisms induced by water movements has long been observed and is still under investigations because of its great complexity. In particular, the exact mechanism occurring at the level of the cell has not been yet fully understood. This work is devoted to the study of the bioluminescence of the dinoflagellates plankton species Pyrocystis noctiluca in response to mechanical stimuli generated by water flows. Several experiments were performed with different types of flows in a Couette shearing apparatus. All of them converge to the conclusion that stationary homogeneous laminar shear does not trigger massive bioluminescence, but that acceleration and shear are both necessary to stimulate together an intense bioluminescence response. The distribution of the experimental bioluminescence thresholds is finally calculated from the light emission response for the Pyrocystis noctiluca species

Effects of wall compliance on the laminar–turbulent transition of torsional Couette flow

Torsional Couette flow between a rotating disk and a stationary wall is studied experimentally. The surface of the disk is either rigid or covered with a compliant coating. The influence of wall compliance on characteristic flow instabilities and on the laminar–turbulent flow transition is investigated. Data obtained from analysing flow visualizations are discussed. It is found that wall compliance favours two of the three characteristic wave patterns associated with the transition process and broadens the parameter regime in which these patterns are observed. The results for the effects of wall compliance on the third pattern are inconclusive. However, the experiments indicate that the third pattern is not a primary constituent of the laminar–turbulent transition process of torsional Couette flow

Investigation of nosocomial pneumocystis infections: usefulness of longitudinal screening of epidemic and post-epidemic pneumocystis genotypes

BACKGROUND: Twenty-five patients, of whom 22 were renal transplant recipients, developed Pneumocystis jirovecii infections at the nephrology department of Reims University Hospital (France) from September 2008 to October 2009, whereas only four sporadic cases had been diagnosed in this department over the 14 previous years. AIM: This outbreak was investigated by analysing patient encounters and P. jirovecii types. METHODS: A transmission map was drawn up. P. jirovecii typing at DHPS, ITS and mtLSU rRNA sequences was performed in the patients of the cluster (18 patients with Pneumocystis pneumonia (PCP) and seven colonized patients), 10 unlinked control patients (six PCP patients and four colonized patients), as well as 23 other patients diagnosed with P. jirovecii (nine PCP patients and 14 colonized patients) in the same department over a three-year post-epidemic period. FINDINGS: Eleven encounters between patients harbouring the same types were observed. Three PCP patients and one colonized patient were considered as possible index cases. The most frequent types in the cluster group and the control group were identical. However, their frequency was significantly higher in the first than in the second group (P < 0.01). Identical types were also identified in the post-epidemic group, suggesting a second outbreak due to the same strain, contemporary to a disruption in prevention measures. CONCLUSIONS: These results provide additional data on the role of both PCP and colonized patients as infectious sources. Longitudinal screening of P. jirovecii types in infected patients, including colonized patients, is required in the investigation of the fungus\u27s circulation within hospitals

Magnetic field induced by elliiptical instability in a rotating tidally distorded sphere

It is usually believed that the geo-dynamo of the Earth or more generally of other planets, is created by the convective fluid motions inside their molten cores. An alternative to this thermal or compositional convection can however be found in the inertial waves resonances generated by the eventual precession of these planets or by the possible tidal distorsions of their liquid cores. We will review in this paper some of our experimental works devoted to the elliptical instability and present some new results when the experimental fluid is a liquid metal. We show in particular that an imposed magnetic field is distorted by the spin- over mode generated by the elliptical instability. In our experiment, the field is weak (20 Gauss) and the Lorenz force is negligible compared to the inertial forces, therefore the magnetic field does not modify the fluid flow and the pure hydrodynamics growth rates of the instability are recovered through magnetic measurements

Obscured Starburst Activity in High Redshift Clusters and Groups

Using Spitzer-MIPS 24um imaging and Keck spectroscopy we examine the nature of the obscured star forming population in three clusters and three groups at z~0.9. These six systems are components of the Cl1604 supercluster, the largest structure imaged by Spitzer at redshifts near unity. We find that the average density of 24um-detected galaxies within the Cl1604 clusters is nearly twice that of the surrounding field and that this overdensity scales with the cluster's dynamical state. The 24um-bright members often appear optically unremarkable and exhibit only moderate [OII] line emission due to severe obscuration. Their spatial distribution suggests they are an infalling population, but an examination of their spectral properties, morphologies and optical colors indicate they are not simply analogs of the field population that have yet to be quenched. Using stacked composite spectra, we find the 24um-detected cluster and group galaxies exhibit elevated levels of Balmer absorption compared to galaxies undergoing normal, continuous star formation. A similar excess is not observed in field galaxies with equivalent infrared luminosities, indicating a greater fraction of the detected cluster and group members have experienced a burst of star formation in the recent past compared to their counterparts in the field. Our results suggest that gas-rich galaxies at high redshift experience a temporary increase in their star formation activity as they assemble into denser environments. Using HST-ACS imaging we find that disturbed morphologies are common among the 24um-detected cluster and group members and become more prevalent in regions of higher galaxy density. We conclude that mergers are the dominant triggering mechanism responsible for the enhanced star formation found in the Cl1604 groups, while a mix of harassment and mergers are likely driving the activity of the cluster galaxies.Comment: 18 pages, 19 figures, submitted to Ap

A sulfur-rich pi-electron acceptor derived from 5,5 '-bithiazolidinylidene: charge-transfer complex vs. charge-transfer salt

International audienceNovel pi-electron acceptors are still highly desirable for the formation of conducting salts or as n-dopable semiconductors. We describe here two synthetic approaches to substitute a dicyanovinylidene group, C=C(CN)(2) to a thioketone (C=S) in the recently described DEBTTT acceptor where DEBTTT stands for (E)-3,3'-diethyl-5,5'-bithiazolidinylidene-2,4,2',4'-tetrathione. These electron withdrawing groups enhance the electron accepting ability as demonstrated through electrochemical investigations, without hindering the formation of short intra-and intermolecular S center dot center dot center dot S contacts in the solid state. Association of this acceptor 1 with tetramethyltetrathiafulvalene (TMTTF) and decamethylferrocene (Fe(Cp*)(2)) afforded 1 : 1 adducts which were analyzed by single crystal X-ray diffraction. Combined with vibrational and magnetic properties, it appears that [TMTTF][1] behaves as a neutral charge-transfer complex while [Fe(Cp*)(2)][1] is an ionic salt. The concentration of the spin density on the exocyclic sulfur atoms in 1(-center dot) favors the setting of direct anti-ferromagnetic interactions in [Fe(Cp*)(2)][1

Ecology of Scedosporium Species: Present Knowledge and Future Research

The genus Scedosporium, which comprises at least five clinically relevant species, i.e. Scedosporium apiospermum, Scedosporium boydii, Scedosporium aurantiacum, Scedosporium dehoogii and Scedosporium minutisporum, ranks the second among the filamentous fungi colonizing the airways of patients with cystic fibrosis (CF). This colonization of the airways is thought to contribute to the inflammatory reaction leading to a progressive deterioration of the lung function. Additionally, these colonizing fungi may lead to severe disseminated infections in case of lung transplantation. Therefore, considering the low susceptibility of Scedosporium species to all current antifungal drugs, preventive measures should be defined to reduce the risk of exposure to these fungi for non-colonized CF patients. With this in mind, several studies have been conducted to elucidate the ecology of these fungi and to define possible sources of patient contamination. This review will summarize the major outcomes of those studies, including: the clear demonstration that ecological niches of Scedosporium species are strongly impacted by human activities, and the ability of Scedosporium species to degrade aliphatic and aromatic pollutants which supports the high occurrence of these species in contaminated soils and polluted waters and makes them promising candidates for bioremediation purposes. Finally, prospects for future research in this field are proposed