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Sudden Decrease (sudden + decrease)
Selected AbstractsShear wave splitting changes associated with the 2001 volcanic eruption on Mt EtnaGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2006Francesca Bianco SUMMARY The time delays and polarizations of shear wave splitting above small earthquakes show variations before the 2001 July 17,August 9 2001 flank eruption on Mt Etna, Sicily. Normalized time delays, measured by singular value decomposition, show a systematic increase starting several days before the onset of the eruption. On several occasions before the eruption, the polarization directions of the shear waves at Station MNT, closest to the eruption, show 90°-flips where the faster and slower split shear waves exchange polarizations. The last 90°-flip being 5 days before the onset of the eruption. The time delays also exhibit a sudden decrease shortly before the start of the eruption suggesting the possible occurrence of a ,relaxation' phenomena, due to crack coalescence. This behaviour has many similarities to that observed before a number of earthquakes elsewhere. [source] Laminar separation bubble on an Eppler 61 airfoilINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2010Samir B. Savaliya Abstract Laminar separation bubble that occurs on the suction side of the Eppler 61 airfoil at Re=46000 is studied. The incompressible flow equations are solved using a stabilized finite element method. No turbulence model is used. The variation of the bubble length and its location, with the angle of attack (,), is studied in detail. An abrupt increase in the lift coefficient is observed at ,,4.5°. It is found to be related to a sudden decrease in the separation bubble length at the trailing edge of the airfoil. Significant differences are observed in the results from the 2D and 3D computations. Stall is observed in 3D simulations, but is found to be absent in 2D. The laminar bubble, which fails to reattach in 3D for ,>14°, continues to reattach for , as large as 20° in the 2D computations. Reynolds stress calculations in both 2D and 3D indicate the extent to which the outer flow is affected by the presence of bubble. It is found that the Reynolds stress components and are of comparable order of magnitude indicating that spanwise fluctuations are significant. The effect of the time window used to compute the time-averaged aerodynamic coefficients is studied. The time-averaged and root mean square (rms) value of the aerodynamic coefficients are calculated for both 2D and 3D computations and compared with the previously published experimental results. The 3D computations show good agreement with the earlier data. The variation of the rms value of the aerodynamic coefficients with angle of attack shows certain peaks. The cause of their appearance is investigated. The effect of Reynolds number is studied. The increase in Re at ,=10° is found to reduce the bubble length and cause it to move closer to the leading edge. Copyright © 2009 John Wiley & Sons, Ltd. [source] Incubation period in the 2,2,4,4-tetramethyl-1-piperidinyloxy-mediated thermal autopolymerization of styrene: Kinetics and simulationsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2006Enrique Saldívar-Guerra Abstract Mechanisms and simulations of the induction period and the initial polymerization stages in the nitroxide-mediated autopolymerization of styrene are discussed. At 120,125 °C and moderate 2,2,4,4-tetramethyl-1-piperidinyloxy (TEMPO) concentrations (0.02,0.08 M), the main source of radicals is the hydrogen abstraction of the Mayo dimer by TEMPO [with the kinetic constant of hydrogen abstraction (kh)]. At higher TEMPO concentrations ([N,] > 0.1 M), this reaction is still dominant, but radical generation by the direct attack against styrene by TEMPO, with kinetic constant of addition kad, also becomes relevant. From previous experimental data and simulations, initial estimates of kh , 1 and kad , 6 × 10,7 L mol,1 s,1 are obtained at 125 °C. From the induction period to the polymerization regime, there is an abrupt change in the dominant mechanism generating radicals because of the sudden decrease in the nitroxide radicals. Under induction-period conditions, the simulations confirm the validity of the quasi-steady-state assumption (QSSA) for the Mayo dimer in this regime; however, after the induction period, the QSSA for the dimer is not valid, and this brings into question the scientific basis of the well-known expression kth[M]3 (where [M] is the monomer concentration and kth is the kinetic constant of autoinitiation) for the autoinitiation rate in styrene polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6962-6979, 2006 [source] The Effect of Decreasing Temperature up to Chilling Values on the in vivo F685/F735 Chlorophyll Fluorescence Ratio in Phaseolus vulgaris and Pisum sativum: The Role of the Photosystem I Contribution to the 735 nm Fluorescence Band ,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2000Giovanni Agati ABSTRACT The effect of leaf temperature (T), between 23 and 4°C, on the chlorophyll (Chl) fluorescence spectral shape was investigated under moderate (200 ,E m,2 s,1) and low (30,35 ,E m,2 s,1) light intensities in Phaseolus vulgaris and Pisum sativum. With decreasing temperature, an increase in the fluorescence yield at both 685 and 735 nm was observed. A marked change occurred at the longer emission band resulting in a decrease in the Chl fluorescence ratio, F685/F735, with reducing T. Our fluorescence analysis suggests that this effect is due to a temperature-induced state 1,state 2 transition that decreases and increases photosystem II (PSII) and photosystem I (PSI) fluorescence, respectively. Time-resolved fluorescence lifetime measurements support this interpretation. At a critical temperature (about 6°C) and low light intensity a sudden decrease in fluorescence intensity was observed, with a larger effect at 685 than at 735 nm. This is probably linked to a modification of the thylakoid membranes, induced by chilling temperatures, which can alter the spillover from PSII to PSI. The contribution of photosystem I to the long-wavelength Chl fluorescence band (735 nm) at room temperature was estimated by both time-resolved fluorescence lifetime and fluorescence yield measurements at 685 and 735 nm. We found that PSI contributes to the 735 nm fluorescence for about 40, 10 and 35% at the minimal (F0), maximal (Fm) and steady-state (Fs) levels, respectively. Therefore, PSI must be taken into account in the analysis of Chl fluorescence parameters that include the 735 nm band and to interpret the changes in the Chl fluorescence ratio that can be induced by different agents. [source] Effect of the applied organic load rate on biodegradable polymer production by mixed microbial cultures in a sequencing batch reactorBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2006Davide Dionisi Abstract This article studies the operation of a new process for the production of biopolymers (polyhydroxyalkanoates, PHAs) at different applied organic load rates (OLRs). The process is based on the aerobic enrichment of activated sludge to obtain mixed cultures able to store PHAs at high rates and yields. A mixture of acetic, lactic, and propionic acids at different concentrations (in the range 8.5,31.25 gCOD/L) was fed every 2 h in a sequencing batch reactor (SBR). The resulting applied OLR was in the range 8.5,31.25 gCOD/L/day. Even though, as expected, the increase in the OLR caused an increase in biomass concentration (up to about 8.7 g COD/L), it also caused a relevant decrease of maximal polymer production rate. This decrease in polymer production rate was related to the different extent of "feast and famine" conditions, as function of the applied OLR and of the start-up conditions. As a consequence the best performance of the process was obtained at an intermediate OLR (20 gCOD/L/day) where both biomass productivity and PHA storage were high enough. However, at this high OLR the process was unstable and sudden decrease of performance was also observed. The sludge characterized by the highest PHA storage response was investigated by 16S rDNA clone library. The clone library contained sequences mostly from PHA producers (e.g., Alcaligenes and Comamonas genera); however many genera and among them, one of the dominant (Thauera), were never described before in relation to PHA storage response. © 2005 Wiley Periodicals, Inc. [source] | ||||||||||