130,506 research outputs found
Thin Film Breakup and Rivulet Evolution Modeling
No full textThe present paper is aimed at the modeling of a continuous film breakup into individual rivulets, leading to the formation of dry patches on the substrate surface. Following an approach already successfully applied to the prediction of still/moving droplet configuration, we attempt to model the details of a single possible film breakup and its evolution over a two-dimensional domain via a phenomenological model. Based on the momentum, energy and mass flow balance of the capillary ridge on the border of the dry patch, the proposed model is validated against both numerical prediction and experimental results from the open literature. Such a detailed prediction may not be practical for the simulation of complex geometrical configuration (which may include, as an example, multiple breakups on the surface of a the whole aircraft subject to icing condition), but can be used to look for statistically significant parameters that can be used to provide proper boundary conditions for fully 3D CFD computations
Numerical Modeling of Anti-Icing Operations Over Super-Hydrophobic Surfaces
No full textHydrophobic and super-hydrophobic coatings are currently considered promising tools to enhance the performances of thermal devices for in-flight icing protection. Icing protection is mostly obtained via heating of the critical surfaces: the simulation is quite complex, including the need for CFD solution of the flow around the wing, including the tracking of the cloud supercooled droplet, the simulation of the evolution of the interaction between droplets and airfoil (including coalescence into rivulets and continuous film, evaporation due to the de-icing heat flux, freezing on impact or later...). However, current commercial numerical prediction tools for in-flight icing simulation are based on the Messinger model [1], although extended to 3-D arbitrary surfaces [2], coupled with Lagrangian or Eulerian [3] droplet flow field analysis. Messinger's model assumes that the runback water layer is a continuous film driven by the shear stress and provides reliable and accurate results in several applications. Unfortunately, it intrinsically neglects any wettability effect and thus cannot assess hydrophobic coating performances. The main difficulty in the simulation of such coatings is that it involves an inherently multi-scale problem: wettability operates at a small scale, at most of the order of the single impinging droplet, but the local impinging mass flow, shear stresses, and heat transfer convective coefficients require state-of-the-art CFD computation around a whole wing or a whole aircraft. Since it is not practical to manage the large-scale computations with a grid fine enough to resolve the single droplet evolution (e.g., via VOF approach), a kind of intermediate bridge is required to derive average integral corrections from the small scale and transfer them to a coarser grid for the standard CFD solution of the large scale thermal and flow field. Here, a hierarchical approach is followed: first, a high-fidelity, small-scale model defines statistical distributions of relevant properties (rebounding droplet fractions, average runback water velocities, wet area fractions, coalesced droplet diameter distribution, including heat transfer and phase changes) as a function of the local fluid dynamic conditions; as a second step, statistical correlations are extracted by this small-scale computation campaign, providing integral corrections to the larger-scale CFD simulation. The high-fidelity simulation tool, an individual-based droplet phenomenological model, was described and validated in [4], and here is improved with regard to the phase change modeling (for both the ice beads freezing and the droplet evaporation due to de-icing system heat flux). The present work is then focused on the statistical models derived by the high- fidelity results, with special attention to the distribution of the small scale droplets (i.e., below the radius where coalescences become the main growth effect), following the approach described in [5] under different conditions. Such small droplets are of special interest for the antiicing devices, which ideally should operate mostly under such regime, allowing for quick evaporation and minimization of runback water rivulets. The statistical model is coupled with a CFD simulation of the heat and fluid flow around an airfoil under icing condition and a lagrangian droplet tracing code, allowing for thoughtful final validation versus literature experimental data provided in [6]. Finally, a parametrical analysis is conducted commenting on the usefulness of hydrophobic coatings of different properties for anti-icing operations under various environmental conditions. It demonstrates that it may offer a valuable aid in obtaining dry clean surfaces with no or little runback water with a relatively low energy consumption
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
A 2D simulation method for computing droplet size spectrum during the atomization of High-speeds liquid jets
No full textBased on both experimental observations and available numerical methods, an innovative 2D approach for determining droplet size during the atomisation process has been developed. Based on experimental evidences (Sallam and Faeth (2003); Fath, Munch and Leiperzt (1997)) atomisation of turbulent high speed jets is assumed to occur in a two stage process: ligaments detachment and droplet formation. The simulation method here proposed wants to take the advantages typical of the two most effective methods in spray investigation. It joins DNS approach and the Linear Stability Analysis: the first one is used to solve the liquid-air fluid dynamics interaction and in particular the instabilities leading to ligaments formation. The second one is finally adopted to compute the droplet size spectrum from ligament breakup. Therefore dynamics of ligament formation is directly computed while droplet formation is modelled by using a Linear Stability Analysis. The numerical simulation adopts a VOF method to track liquid-gas interface. Turbulence effects on liquid surface are accounted for by adding a turbulent flow field at the nozzle exit which represents a part of the boundary condition of the computational domain. A physical criterion is then applied to detach ligaments from liquid jet surface which will reduce in diameter during simulation. The droplet formation is then computed by applying the linear stability analysis to the ligaments, assumed being circular and subject to circulation. Liquid core length, droplet size spectrum and near cone angle are the determined. Then an extensive validation and sensitivity analysis has been carried out in order to assess method advantages and limits. The experimental results of Wu et al. (1986) and Hiroyasu et al. (1974) were used as test cases. The method exhibits promising attitude in the reconstruction of the droplet size spectrum depending on injection parameter or conditions
Use of yarrowia lipolytica strains for the treatment of olive mill wastewater
No full textThe principal aim of this research was to evaluate the ability of different Yarrowia lipolytica strains, having different origin, to
grow in olive mill wastewater (OMW) and reduce its COD level. All the strains were able to grow in undiluted OMW; the comparison
between the data obtained in a semi-synthetic medium and in OMW suggests that lipases with different specificity can be
produced in relation to the medium composition.
Under the adopted conditions, the reduction of the OMW COD values varied from 1.47% and 41.22% of the initial value. Some
strains determined a significant reduction of polyphenol content, while other ones caused its apparent increase. Moreover, some
Y. lipolytica strains, isolated from chilled foods, produced the highest citric acid concentrations. These results evidenced that some
Y. lipolytica strains are good candidates for the reduction of the pollution potential of OMW and for the production of enzymes and
metabolites such as lipase and citric acid
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Combination of multiplex PCR and PCR-DGGE for monitoring common sourdough-associated Lactobacillus species
No full textA combination of denaturing gradient gel electrophoresis (DGGE) and a previously described multiplex PCR approach was employed to detect sourdough lactobacilli. Primers specific for certain groups of Lactobacillus spp. were used to amplify fragments, which were analyzed by DGGE. DGGE profiles obtained from Lactobacillus type strains acted as standards to analyze lactobacilli from four regional Abruzzo (central Italy) sourdoughs
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