The Experts below are selected from a list of 165 Experts worldwide ranked by ideXlab platform

C. H. Fernando - One of the best experts on this subject based on the ideXlab platform.

  • Seasonality and abundance of some dominant crustacean zooplankton in Lake Awasa, a tropical rift valley lake in Ethiopia
    Hydrobiologia, 1991
    Co-Authors: Seyoum Mengestou, C. H. Fernando
    Abstract:

    The zooplankton of a Rift Valley lake in Ethiopia, Awasa, was sampled at 3 stations for 2 years (1986 and 1987) concurrently with various meteorological and limnological measurements. The spatial and temporal variation in abundance of some numerically dominant crustaceans, Mesocyclops aequatorialis similis (Copepoda), Thermocyclops consimilis (Copepoda) and Diaphanosoma excisum (Cladocera) is discussed. Temporal (months, sampling dates) rather than spatial (station) variability accounts for more than 50% of the total variance in zooplankton abundance but horizontal patchiness exists during periods of high zooplankton density. Sampling errors were generally low, except for counts of cyclopoid nauplii (subsampling) and Diaphanosoma (inter-replicate variance). Zooplankton showed distinct seasonality associated with the Mixing Cycle of the lake. Total numbers increased to more than 200 000 m^−3 during the unstratified period (July to September). Low numbers were evident during stratification (February to May) when zooplankton numbers did not exceed 15 000 m^−3. Individual zooplankton species and age classes showed variable seasonal amplitudes, ranging from 6.4 (nauplius 3) to 44.8 (copepodite 3 of Mesocyclops ). We discuss some possible causes for zooplankton seasonality in Lake Awasa, and also review zooplankton seasonal Cycles in other tropical lakes, especially African ones.

Luca Galletti - One of the best experts on this subject based on the ideXlab platform.

  • Twin-Shaft Mixers’ Mechanical Behavior Numerical Simulations of the Mix and Phases
    Machines, 2019
    Co-Authors: Maria Cristina Valigi, Silvia Logozzo, Luca Landi, Claudio Braccesi, Luca Galletti
    Abstract:

    In this paper, the mechanical behavior of concrete twin-shaft mixers is analyzed in terms of power consumption and exchanged forces between the mixture and the Mixing organs during the Mixing Cycle. The Mixing Cycle is divided into two macro phases, named transient and regime phase, where the behavior of the mixture is modeled in two different ways. A force estimation and power consumption prediction model are presented for both the studied phases and they are validated by experimental campaigns. From the application of this model to different machines and by varying different design parameters, the optimization of the power consumption of the concrete twin-shaft mixers is analyzed. Results of this work can be used to increase productivity and profitability of concrete mixers and reduce energy waste in the industries which involve Mixing processes.

  • effect of design parameters and operating conditions in concrete twin shaft mixers
    The International Conference of IFToMM ITALY, 2018
    Co-Authors: Maria Cristina Valigi, Silvia Logozzo, Luca Galletti
    Abstract:

    In the sector of construction industry, research aims at designing new products, with better and better performance and able to guarantee a reduction in production times, costs and energy consumption. This paper deals with the optimization of concrete twin shaft mixers with the aim of proposing a model able to evaluate the influence of design parameters on the machine’s power consumption during the different phases of the Mixing Cycle. Mixers of different size have been analysed to propose geometrical changes in terms of length and width of the tanks, keeping the working volumes as constant parameters. The model has been validated by means of experimental campaigns performed on real twin shaft mixers. The results demonstrate how the power consumption varies during the different Mixing phases when geometrical parameters are changed.

B. R. Gupta - One of the best experts on this subject based on the ideXlab platform.

  • Rheology of HTPB propellant: Development of generalized correlation and evaluation of pot life
    Propellants Explosives Pyrotechnics, 1996
    Co-Authors: Rajendran Muthiah, V.n. Krishnamurthy, B. R. Gupta
    Abstract:

    Composite solid propellants based on hydroxy-terminated poly-butadiene\n(HTPB) have become the workhorse propellants in the present-day solid\nrocket motors world-wide. Because of the high solid loading. the\nrheological behaviour of such propellants is quite complex. The effect\nof solid loading, oxidizer particle size and aluminium content has teen\nstudied and reported. Similarly, the effect of temperature and mixer\nkinematics and Mixing Cycle time have also been studied and reported. In\nthe present paper it generalized correlation tins been developed For\nshear stress-shear rate based on the rheological parameters like yield\nstress, consistency index and pseudoplasticity index which am in turn\nfunctions of solid volume fraction, cure time, t, and temperature, and\nhas a correlation coefficient of 0.94 with the experimental values. Also\na commonly used term in propellant industries, pot lire, has been\ndefined and evaluated for the HTPB propellant system.

  • Rheology of HTPB Propellant: Effect of Mixing Speed and Mixing Time
    Defence Science Journal, 1993
    Co-Authors: Rm. Muthaiah, V.n. Krishnamurthy, R. Manjari, B. R. Gupta
    Abstract:

    The effect of mixer blade speed and Mixing Cycle time on the rheological behaviour of an optimized HTPB-based propellant formulations has been studied keeping the temperature constant. Variations in yield stress and viscosity at unit shear rate have been determined as a function of time for different Mixing speeds. The effect of Mixing on the extent of pseudoplasticity has been represented in the form of a bar chart. A correlation in terms of shear and yield stresses has been developed for viscosity index, i.e., the viscosity at unit shear rate as a function of mixer blade speed.

Subrata Mukherjee - One of the best experts on this subject based on the ideXlab platform.

  • CHAOTIC Mixing IN RIGID, PERFECTLY PLASTIC MATERIAL
    International Journal of Bifurcation and Chaos, 1995
    Co-Authors: Brian F. Feeny, Francis C. Moon, P.y. Chen, Subrata Mukherjee
    Abstract:

    An example of Lagrangian chaos or Mixing in a solid material is presented here. The Mixing due to cyclic torques of rigid, perfectly plastic sheet is simulated. The plastic flow results in an area-preserving map. Results are displayed as Poincaré maps, the stretching and folding of an initial line of material points, the Mixing of initial regions, and the eigenvalues about initial points during one Mixing Cycle. The Poincaré sections show iterates of sets of points after each Cycle of deformation. The Mixing diagrams provide evidence for horseshoe-like processes in the dynamics. Single-Cycle eigenvalues exhibit self similarity in the spatial structure.

  • CHAOTIC Mixing IN RIGID, PERFECTLY PLASTIC MATERIAL
    International Journal of Bifurcation and Chaos, 1995
    Co-Authors: Brian F. Feeny, Francis C. Moon, P.y. Chen, Subrata Mukherjee
    Abstract:

    An example of Lagrangian chaos or Mixing in a solid material is presented here. The Mixing due to cyclic torques of rigid, perfectly plastic sheet is simulated. The plastic flow results in an area-preserving map. Results are displayed as Poincare maps, the stretching and folding of an initial line of material points, the Mixing of initial regions, and the eigenvalues about initial points during one Mixing Cycle. The Poincare sections show iterates of sets of points after each Cycle of deformation. The Mixing diagrams provide evidence for horseshoe-like processes in the dynamics. Single-Cycle eigenvalues exhibit self similarity in the spatial structure.

Annecarlijn Alderkamp - One of the best experts on this subject based on the ideXlab platform.

  • can photoinhibition control phytoplankton abundance in deeply mixed water columns of the southern ocean
    Limnology and Oceanography, 2010
    Co-Authors: Annecarlijn Alderkamp, Hein J W De Baar, Ronald J W Visser, Kevin R Arrigo
    Abstract:

    To study how natural Southern Ocean phytoplankton communities acclimate to rapid fluctuations in irradiance levels that result from deep wind-driven Mixing of the upper water column, we measured their fluorescence properties (Fv:Fm, maximum quantum yield of photosystem II; and qN, non-photochemical quenching) and pigment composition. Values of Fv:Fm were low (, 0.46) and qN was high (. 0.67) throughout the upper mixed layer (UML). Short-term (20-min) exposure to incident surface irradiance strongly reduced Fv:Fm and recovery was slow under subsequent incubation at low irradiance. This suggests that phytoplankton cells are frequently photodamaged when mixed up to the surface from depth. Recovery of Fv:Fm was suppressed when lincomycin was added, inhibiting synthesis of the photosystem II reaction center D1 protein. This indicates that D1 protein repair is crucial in maintaining photosynthetic performance under fluctuating irradiance levels. Regions within the Antarctic Circumpolar Current (ACC) with a deep UML had lower depth-integrated phytoplankton biomass than regions close to the Antarctic continent with a shallow UML. Surprisingly, the depth-averaged light level within the UML in these latter regions was lower than in the ACC. Thus, it appears that photodamage incurred during the high irradiance portion of the vertical Mixing Cycle, rather than light limitation, controls phytoplankton growth in regions of the Southern Ocean with a deep UML. This concept represents a shift from the widely accepted paradigm that phytoplankton growth in the open Southern Ocean is limited by low levels of light or inadequate iron supply. The Southern Ocean (south of 44uS) is an important component of the global carbon Cycle due to its large size and unique physical and chemical characteristics. Recent studies indicate that some regions of the Southern Ocean are a strong sink for anthropogenic CO2 (Arrigo et al. 2008; Gruber et al. 2009) and that its lower latitudes are important areas of anthropogenic CO2 storage (Sabine et al. 2004). In regions south of the Polar Front, major inorganic nutrients such as nitrate, phosphate, and silicate are seldom fully utilized, but low trace metal concentrations, especially of iron (Fe), limit phytoplankton growth in large areas of the Southern Ocean (Martin et al. 1990; Boyd et al. 2007), making it the largest of the three high nutrient– low chlorophyll (HNLC) regions of the global ocean. In addition, phytoplankton productivity is light limited in many areas of the Southern Ocean because weak water column stratification and strong winds create deep mixed layers, especially in the vicinity of the Antarctic Circumpo