1,721,131 research outputs found
Laboratory study of orifice jets from a pressurized pipe
No full textOrifice jet through a small opening or orifice into a surrounding fluid exhibits intricate fluid dynamics, encompassing the interaction of the jet with the fluid. Although the dynamics of simple jets has been extensively studied, there are still unresolved issues that need to be addressed. In this study, we experimentally investigated the characteristics of non-buoyant jets emerging from a sharp-edged orifice located in the wall of a pipe with a constant flow rate. Specifically, we examined how the ratio between the variable jet flow rate to the constant pipe flow rate upstream of the orifice influences not only the jet trajectory but (for the first time to the authors' knowledge) also the jet velocity-related features. Particle image velocimetry measurements were performed to explore the velocity fields in the near and intermediate regions of the jet and data were analyzed in terms of fields of time-averaged velocity components, turbulent intensities, Reynolds shear stresses, vorticity, and Q-criterion. The transversal velocity profiles were shown and their Gaussianity investigated via skewness and kurtosis. Thus, second-order statistics of turbulence of the velocity fluctuations were carried out. Moreover, a spectral analysis was performed after the Taylor hypothesis verification was proved and a net scale separation was guaranteed to develop the inertial sub-range. The influence of variable jet flow rate and the constant pipe flow rate on the jet behavior is shown and, in particular, how, as this parameter decreases, the jet moves away from the typical axisymmetric features of a round simple jet. In addition, the spectra analysis is used to identify the jet potential core and the large-scale organization zones, highlighting the effect of variable jet flow rate and the constant pipe flow rate on the extension of the potential core region and on the mixing layer
Near-bed eddy scales and clear-water local scouring around vertical cylinders
No full textIn the last five decades much research has been devoted to the development of predictive formulae to quantify the maximum local-scour depth developing around hydraulic structures (e.g bridge piers). Owing to the complexity of the problem, most of the proposed formulae were developed on empirical grounds, which made them susceptible to scale issues. Recently, a new theoretical approach was proposed to develop a better understanding of the physics of local scouring around piers. The analysis rested on two stringent hypotheses whereby the momentum-transport rate at the sediment–water interface was dominated by eddies belonging to the inertial range and the sediment critical bed shear stress was independent from roughness Reynolds number and relative roughness effects. The present paper builds upon that previous work and explores the scaling of the equilibrium scour depth when these two hypotheses are relaxed. Results from theoretical considerations and empirical evidence are then combined to derive a new formula for maximum local-scour depth prediction
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Antibiotics and artificial nutrition in the cardiac intensive care unit
No full textPatients admitted to cardiac intensive care units are at high risk for infections, particularly nosocomial pneumonia, pacemaker's pocket and sternotomic wound infections. These complications delay recovery, prolong hospitalization, time on mechanical ventilation, and increase mortality. Both behavioral and pharmacological measures are needed to prevent and control infections in these patients, as well as specific antibiotic treatment and nutritional support. In infected critically ill patients, pathophysiological alterations modify distribution and clearance of antibiotics, and hypercatabolic state leads to malnutrition and immune paralysis, which both contribute to increased infectious risk and worsened outcome. A deep understanding of antibacterial agents pharmacology in the critically ill is essential in order to treat severe infections; moreover, it is necessary to know routes of administration and composition of artificial nutrition solutions. The aim of this review is to define main and specific aspects of antibiotic therapy and nutritional support in cardiac critical care patients in light of recent literature data. © 2010 AIM Publishing Srl
Hydrodynamics of a bordered collar as a countermeasure against pier scouring: Hydrodynamics countermeasure scouring
No full textAn experimental campaign on long-term clear-water scour at bridge piers with different configurations was performed in a laboratory to investigate the effects of different countermeasures. Tests were performed in a flume with a movable sediment bed for an unprotected cylindrical pier, a cylindrical pier with a standard collar and a cylindrical pier with a bordered collar. The scoured beds at the equilibrium stage were acquired through the photogrammetry technique and the efficiencies of the tested countermeasures were measured. Results showed a reduction in the maximum scour depth as well as in the scour hole volume with respect to the unprotected pier. The maximum scour depth was reduced by 59.63% with the standard collar and by 63.51% with the bordered collar. The scoured volume was reduced by 43.80% with the standard collar and by 60.00% with the bordered collar. The three-dimensional Reynolds-averaged Navier-Stokes equations were solved numerically to reproduce the hydrodynamics of the experiments. The volume of fluid technique was used to reproduce the free surface. For each test, the results of the simulations were analysed to investigate the flow field around the pier both at the initial (flat-bed) and at the equilibrium stages, highlighting the changes in the velocity field owing to the presence of the standard collar and of the bordered collar
Microbes in rocks and meteorites: A new form of life unaffected by time, temperature, pressure
No full textCrystals, rocks and mineral ores of different origins contain viable microbial life that appears actively swimming under the microscope when the sample is properly fragmented and suspended in a nutrient medium. This form of life in rocks is unaffected by time, since microbes have been found in samples of all geological ages, from about 2.8 Ga to recent rocks, and by pressure and temperature, since it is present in metamorphic and in igneous rocks. From the tests performed, among which those to secure from sample pollution, it emerges that this form of life is not destroyed, as indeed expected, when the rock is heated above 500 °C in a kiln. However, all cloned microbes are sensitive to growth inhibition by specific antibiotics. A similar search, for the presence of microbes in meteorites, shows that also these materials are rich in microorganisms, indicating that these already existed in early Earth formation stages. Some different microbial species, derived from different samples of rocks and meteorites, have been cultured, cloned and classified by 16S rDNA typing and found to be not essentially different from present day organisms An interesting consequence of these findings, among others, is the support to the hypothesis that life came from outside Earth with the additional indication that it was already present in those materials that accreted to form the solar planetary system
- …
