34 research outputs found
Spontaneous honeybee behaviour is altered by persistent organic pollutants
The effect of environmental pollutants on honeybee behaviour has focused mainly on currently used pesticides. However, honeybees are also exposed to persistent organic pollutants (POPs). The aim of this laboratory based study was to determine if exposure to sublethal field-relevant concentrations of POPs altered the spontaneous behaviour of foraging-age worker honeybees. Honeybees (Apis mellifera) were orally exposed to either a sublethal concentration of the polychlorinated biphenyl (PCB) mixture Aroclor 1254 (100âng/ml), the organochlorine insecticide lindane (2.91âng/ml) or vehicle (0.01% DMSO, 0.00015% ethanol in 1M sucrose) for 1â4 days. The frequency of single event behaviours and the time engaged in one of four behavioural states (walking, flying, upside down and stationary) were monitored for 15âmin after 1, 2, 3 and 4 days exposure. Exposure to Aroclor 1254 but not lindane increased the frequency and time engaged in honeybee motor activity behaviours in comparison to vehicle. The Aroclor 1254âinduced hyperactivity was evident after 1 day of exposure and persisted with repeated daily exposure. In contrast, 1 day of exposure to lindane elicited abdominal spasms and increased the frequency of grooming behaviours in comparison to vehicle exposure. After 4 days of exposure, abdominal spasms and increased grooming behaviours were also evident in honeybees exposed to Aroclor 1254. These data demonstrate that POPs can induce distinct behavioural patterns, indicating different toxicokinetic and toxicodynamic properties. The changes in spontaneous behaviour, particularly the PCB-induced chronic hyperactivity and the associated energy demands, may have implications for colony health
Being treated in higher volume hospitals leads to longer progression-free survival for epithelial ovarian carcinoma patients in the Rhone-Alpes region of France
Stability Derivatives in a Parallel Triangular Tube Bundle Subject to Cross-Flow at Moderated Reynolds Number
Effect of Reynolds number on the stability of a single flexible tube predicted by the quasi-steady model in tube bundles
Incorporation Of Water-Soluble Porphyrins In Sol-Gel Matrices And Application To pH Sensing
The incorporation of HâTPPSâŽ- into sol-gel materials has been used to determine the pH inside a sol-gel matrix
Two-phase damping for internal flow: Physical mechanism and effect of excitation parameters
International audienceTwo-phase flow induced-vibration is a major concern for the nuclear industry. This paper provides experimental data on two-phase damping that is crucial to predict vibration effects in steam generators. An original test section consisting of a tube subjected to internal two-phase flow was built. The tube is supported by linear bearings and compression springs allowing it to slide in the direction transverse to the flow. An excitation system provides external sinusoidal force. The frequency and magnitude of the force are controlled through extension springs. Damping is extracted from the frequency response function of the system. It is found that two-phase damping depends on flow pattern and is fairly proportional to volumetric fraction for bubbly flow. Measurements are completed by the processing of high-speed videos which allow to characterize the transverse relative motion of the gas phase with respect to the tube for bubbly flow. It is shown that the bubble drag forces play a significant role in the dissipation mechanism of two-phase damping.Les vibrations induites par les Ă©coulements diphasiques sont une prĂ©occupation majeure pour l'industrie nuclĂ©aire. Cet article prĂ©sente des expĂ©riences de mesure de lâamortissement diphasique. La connaissance de lâamortissement diphasique est cruciale pour prĂ©dire les vibrations dans les gĂ©nĂ©rateurs de vapeur. Une section dâessai composĂ©e d'un tube de section carrĂ© soumis Ă Ă©coulement interne diphasique a Ă©tĂ© construite. Le tube est soutenu par des roulements linĂ©aires et des ressorts de compression lui permettant de se dĂ©placer dans la direction transversale Ă l'Ă©coulement. Un systĂšme d'excitation fournit une force sinusoĂŻdale externe. La frĂ©quence et l'amplitude de la force excitatrice forces sont contrĂŽlĂ©es par des ressorts d'extension. L'amortissement est extrait de la fonction de transfert du systĂšme. Il est constatĂ© que l'amortissement diphasique dĂ©pend du rĂ©gime d'Ă©coulement. Pour un Ă©coulement Ă bulles, l'amortissement diphasique est quasiment proportionnel Ă la qualitĂ© volumĂ©trique. De plus un traitement des vidĂ©os Ă haute vitesse ont permis de caractĂ©riser le mouvement relatif transversale de la phase gazeuse par rapport au tube pour un Ă©coulement Ă bulles. Il est montrĂ© que la trainĂ©e de la bulle joue un rĂŽle essentiel dans le mĂ©canisme de d'amortissement diphasique
Two-phase damping in vertical pipe flows: Effect of void fraction, flow rate and external excitation
Predicting vibration effects in steam generators requires good knowledge of two-phase damping ζ2Ï. The purpose of this work is to correlate two-phase damping in axial flow with tube transversal excitation frequency and magnitude. The test section consists of a stiff square tube subjected to internal axial flow of air-water mixture. The hydraulic diameter is 3 inches. The tube is supported with linear bearings and fitted with flexible tubing on both ends to allow motion in the transverse direction. Compression springs allow setting the natural frequency of the tube oscillation. A motor provides transverse sinusoidal excitation to the tube assembly. ζ2Ï is determined from the frequency response function. As a result of this study, ζ2Ï is represented as a function of excitation frequency and amplitude, void fraction and flow rate. Specific information is gained through high frame rate videos of the oscillating tube, including bubble transverse velocity and size for low void fraction, and flow pattern transitions. Indeed, it is suspected that two-phase damping is partly caused by the work rate of virtual mass forces of the gas phase. Better knowledge of the physical process involved in two-phase damping will allow better modeling and prediction of tube behavior.</jats:p
In Situ Characterization of Redox Properties of WaterâSoluble Porphyrins Irreversibly Adsorbed on Gold Electrode Using the Electroreflectance Technique
Electrochemical preparation of anthraquinone and zinc porphyrin coated electrodes: redox activity and film stability
This study concerns some aspects of the electrochemical design and characterization of zinc porphyries and anthraquinone-based polymers. The electro-formation of the films on the electrode surface has been achieved by cyclic voltammetry in organic solvents such as dichloromethane and acetonitrile. It is based on the electrochemical oxidative polymerization of the pyrrole or hydroxy-substituted phenyl groups attached to the porphyrin or anthraquinone molecules. The redox characteristics of the polymer films as well as their stability were studied by cyclic voltammetry and spectrophotometry and are compared to those of the starting monomers. The conditions of the electropolymerization of stable and reproducible multicomponent films are also discussed