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Now showing items 1 - 16 of 18

  • The mean flow of a laminar wall‐jet subjected to blowing or suction

    Amitay, M.   Cohen, J.  

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  • [American Institute of Aeronautics and Astronautics 38th Aerospace Sciences Meeting and Exhibit - Reno,NV,U.S.A. (10 January 2000 - 13 January 2000)] 38th Aerospace Sciences Meeting and Exhibit - Control of internal flow separation using synthetic jet actuators

    Amitay, M.   Parekh, D.   Pitt, D.   Kibens, V.   Glezer, A.  

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  • [American Institute of Aeronautics and Astronautics 37th Aerospace Sciences Meeting and Exhibit - Reno,NV,U.S.A. (11 January 1999 - 14 January 1999)] 37th Aerospace Sciences Meeting and Exhibit - The dynamics of flow reattachment over a thick airfoil controlled by synthetic jet actuators

    Amitay, M.   Kibens, V.   Parekh, D.   Glezer, A.  

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  • [American Institute of Aeronautics and Astronautics 15th AIAA Computational Fluid Dynamics Conference - Anaheim,CA,U.S.A. (11 June 2001 - 14 June 2001)] 15th AIAA Computational Fluid Dynamics Conference - Virtual aerodynamic shape modification at low angles of attack using synthetic jet actuators

    Amitay, M.   Horvath, M.   Michaux, M.   Glezer, A.  

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  • Early enteral feeding and nosocomial sepsis in very low birthweight infants

    Flidel-Rimon, O.   Friedman, S.   Lev, E.   Juster-Reicher, A.   Amitay, M.  

    Background: The interrelations between early enteral feeding, necrotising enterocolitis (NEC), and nosocomial sepsis (NS) remain unclear. Objective: To evaluate the effect of age at the introduction of enteral feeding on the incidence of NS and NEC in very low birthweight (VLBW 1500 g) infants. Methods: Data were collected on the pattern of enteral feeding and perinatal and neonatal morbidity on all VLBW infants born in one centre during 1995 - 2001. Enteral feeding was compared between infants with and without NS and/or NEC. Results: The study sample included 385 infants. Of these, 163 (42%) developed NS and 35 (9%) developed NEC. Enteral feeding was started at a significantly earlier mean (SD) age in infants who did not develop nosocomial sepsis (2.8 (2.6) v 4.8 (3.7) days, p = 0.0001). Enteral feeding was introduced at the same age in babies who did or did not develop NEC (3.1 ( 2) v 3.7 ( 3) days, p = 0.28). Over the study period, the mean annual age at the start of enteral feeding fell consistently, and this correlated with the mean annual incidence of NS (r2 = 0.891, p = 0.007). Multiple logistic regression analysis showed age at start of enteral feeding, respiratory distress syndrome, and birth weight to be the most significant predictors of risk of NS ( p = 0.0005, p = 0.024, p = 0.011). Conclusions: Early enteral feeding was associated with a reduced risk of NS but no change in the risk of NEC in VLBW infants. These findings support the use of early enteral feeding in this high risk population, but this needs to be confirmed in a large randomised controlled trial.
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  • Prediction of Shigellosis outcomes in Israel using machine learning classifiers

    Adamker, G.   Holzer, T.   Karakis, I.   Amitay, M.   Anis, E.   Singer, S. R.   Barnett-Itzhaki, Z.  

    Shigellosis causes significant morbidity and mortality in developing and developed countries, mostly among infants and young children. The World Health Organization estimates that more than one million people die from Shigellosis every year. In order to evaluate trends in Shigellosis in Israel in the years 2002-2015, we analysed national notifiable disease reporting data. Shigella sonnei was the most commonly identified Shigella species in Israel. Hospitalisation rates due to Shigella flexenri were higher in comparison with other Shigella species. Shigella morbidity was higher among infants and young children (age 0-5 years old). Incidence of Shigella species differed among various ethnic groups, with significantly high rates of S. flexenri among Muslims, in comparison with Jews, Druze and Christians. In order to improve the current Shigellosis clinical diagnosis, we developed machine learning algorithms to predict the Shigella species and whether a patient will be hospitalised or not, based on available demographic and clinical data. The algorithms' performances yielded an accuracy of 93.2% (Shigella species) and 94.9% (hospitalisation) and may consequently improve the diagnosis and treatment of the disease.
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  • Instability of a two-dimensional plane wall jet subjected to blowing or suction

    Amitay, M.   Cohen, J.  

    The effects of wall blowing or suction on the stability characteristics of a laminar incompressible two-dimensional plane wall jet are investigated both experimentally and theoretically. A quantitative comparison between linear stability calculations and phase-locked experimental data, obtained when the wall jet is subjected to two-dimensional excitations, confirms the co-existence of the viscous and inviscid instability modes and the theoretically predicted effects of blowing and suction on the stability of the wall jet. According to these predicted effects, blowing stabilizes the inviscid mode while destabilizing the viscous one; suction has the opposite effect. Furthermore, blowing and suction tend to increase and decrease, respectively, the ratio between the outer and inner amplitude maxima of the streamwise velocity fluctuation. When wall blowing is applied, the instability domain is enlarged and includes higher-frequency waves. In addition, the region where both unstable modes co-exist simultaneously begins at a lower local Reynolds number. Opposite effects are caused when suction is applied. The quantitative comparison between the theory and experiment includes the cross-stream structure and the downstream growth of the streamwise velocity fluctuations. In order to accurately account for the effect of the mean flow divergence in the stability analysis, the second-order corrections to the mean flow solutions are obtained for all wall conditions. Spectral distributions, obtained when natural wall-jets are subjected to blowing and suction, support qualitatively the above results
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  • Interaction of a liquid flow around a micropillar with a gas jet

    Elcock, D.   Jung, J.   Kuo, C. -J.   Amitay, M.   Peles, Y.  

    An experimental study was conducted to investigate two-phase flow characteristics resulting from gas jet injection into a 225 mu m high by 1500 mu m wide microchannel. The jet was injected from a 25 mu m wide slit on the downstream side of a 150 mu m diameter pillar. The liquid Reynolds number (Re =3D rho UD/mu) based on pillar diameter ranged from 100 to 700, and the average gas momentum coefficient (rho(jet)U(jet)A(jet)/rho(main)U(main)A(ref)), defined as the ratio of gas momentum to liquid momentum, ranged from 1.6 x 10(-5) to 3.368 x 10(-1). Flow visualization, micro particle image velocimetry (mu PIV), and micro particle tracing velocimetry (mu PTV) were used to elucidate the two-phase flow patterns, liquid velocity field, and bubble dynamics. Two modes of gas jets were observed in which bubbles either formed and detached at the pillar or formed an attached ligament that sheared bubbles from its trailing edge. The modes were determined to be primarily Reynolds number dependent. Both modes were observed to positively affect turbulent kinetic energy in the microchannel. The momentum coefficient of the gas jet had the most significant effect at low Reynolds numbers, when bubble formation took place at the pillar. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3662436]
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  • Bubble dynamics and interactions with a pair of micro pillars in tandem

    Elcock, D.   Honkanen, M.   Kuo, C.   Amitay, M.   Peles, Y.  

    This study investigates flow patterns and bubble dynamics of two-phase flow around two 100 mu m diameter circular pillars in tandem, which were entrenched inside a horizontal micro channel. Bubble velocity, trajectory, size, and void fraction were measured using a high speed camera and analyzed using a particle tracking velocimetry method. A range of gas and liquid superficial velocities were tested, resulting in different bubbly flow patterns, which were consistent with previous studies. These flow patterns were altered as they interacted with the pillars. Depending on the relative transverse location of bubbles to the pillars, and through bubble-bubble interaction, the flow sometimes returned to its original state. It was also determined that the pillars altered both the bubble trajectory and void fraction, especially in the pillars region. (C) 2010 Elsevier Ltd. All rights reserved.
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  • Evaluating the peptide structure prediction capabilities of a purely ab-initio method

    Amitay, M.   Goldstein, M.  

    DEEPSAM is a relatively new global optimization algorithm aimed to predict the structure of biomolecules from sequence, without any additional preliminary assumption. It is an evolutionary algorithm whose mutation operators are built by hybridizing the diffusion equation method, molecular dynamics simulated annealing, and a quasi- Newton local minimization method. The goal of this study was to evaluate the structure prediction capabilities of DEEPSAM by running it upon NMR structures of linear peptides (10-20 residues). The results indicate that DEEPSAM successfully predicted the conformations of these peptides, using modest computing resources.
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  • Modification of the near wake behind a finite-span cylinder by a single synthetic jet

    DeMauro, E. P.   Leong, C. M.   Amitay, M.  

    Modification to the flow field about a finite-span cylinder of low-aspect ratio (AR =3D 3) by a single synthetic jet, mounted normal to the cylinder axis, was studied experimentally using surface-mounted pressure taps, stereoscopic particle image velocimetry (SPIV), and constant-temperature anemometry. The synthetic jet altered the circulation about the cylinder and created a large spanwise change to the surface pressure, much greater than the dimensions of its orifice. SPIV measurements in the near wake showed that the synthetic jet enhances mixing of the downwash from the cylinder free end with the wake deficit, vectoring and narrowing the wake. The synthetic jet penetrates through the streamwise vorticity, enhancing mixing within the wake and reducing the power associated with the shedding frequency, St =3D 0.155, except below the vortex dislocation, where the shedding frequency was increased to that corresponding to a quasi-two-dimensional cylinder, St =3D 0.22.
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  • Energetic scales in a bluff body shear layer

    Moore, D. M.   Letchford, C. W.   Amitay, M.  

    A detailed experimental campaign into separated shear layers stemming from rectangular sections (having aspect ratios of 5 : 1, 3 : 1 and 1 : 1) was carried out at Reynolds numbers range between 1.34 X 10(4) and 1.18 X 10(5) based on the body thickness. Particle image velocimetry was used to locate the highest concentration of fluctuations in the velocity field and subsequent hot-wire measurements at those locations provided adequate spectral resolution to follow the evolution of various instabilities that are active within the separated shear layer. Similar to recent findings by this same group, the shear layer behaviour is observed to contain a combination of Reynolds invariant characteristics, including its time-averaged position, while other properties demonstrate clear Reynolds number dependency, including the spatial amplification of turbulent kinetic energy. Additional results here show that the ratio of side lengths of the body is a key parameter in revealing these effects. One reason for this is the level of coupling between modes of instability, which is evaluated using two-point correlation methods. These findings indicate that the separated shear layer on a bluff body is highly nonlinear. A specific set of scales responsible for these unique behaviours is identified and discussed, along with their relationship to other scales in the flow.
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  • Dynamic stall process on a finite span model and its control via synthetic jet actuators

    Taylor, K.   Amitay, M.  

    An experimental study of the process by which dynamic stall occurs on a finite span S809 airfoil was conducted at the Center for Flow Physics and Control at Rensselaer Polytechnic Institute. Understanding the flow field around a dynamically pitching airfoil helped in controlling the dynamic stall process through active flow control via synthetic jet actuators. The three component, two dimensional flow fields were measured with a stereoscopic particle image velocimetry system. This study demonstrated that, through the introduction of periodic momentum near the leading edge of this model, the evolution of the dynamic stall vortex, which forms and convects downstream under dynamic conditions, could be delayed or suppressed in favor of the preservation of a trailing edge vortex that arises due to trailing edge separation and recirculation in the time averaged sense. This process seems to be the result of changing how the flow field transitions from trailing edge separation to a fully separated flow. In a phase-averaged sense, absent of flow control, this process is defined by the creation of a phase averaged leading edge recirculation region, which interacts with the trailing edge separation. Through the introduction of momentum near the leading edge, this process can be altered, such that the phase averaged trailing edge separation region is the dominant structure present in the flow. Additionally, a cursory investigation into the instantaneous flow fields was conducted, and a comparison between the phase averaged flow field and instantaneous fields demonstrated that while similar effects can be observed, there is a significant difference in the flow field observed in the instantaneous fields versus the phase averaged sense. This would imply that a different method of analyzing dynamic stall from PIV measurements may be necessary. (C) 2015 AIP Publishing LLC.
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  • Boundary layer suction through rectangular orifices:effects of aspect ratio and orientation

    Van Buren, T.   Smits, A. J.   Amitay, M.  

    The flow field generated by suction through a rectangular orifice within a laminar boundary layer is investigated using stereoscopic particle image velocimetry. For orifice aspect ratios of 6, 12, and 18, the impact of suction on the surrounding flow field appears to be self-similar, scaling with aspect ratio and suction velocity. Changing the orifice pitch angle had almost no impact on the surrounding boundary layer, but, as expected, changing the skew angle significantly altered the extent of the suction impact on the flow field.
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  • Scaling of square-prism shear layers

    Lander, D. C.   Moore, D. M.   Letchford, C. W.   Amitay, M.  

    Scaling characteristics, essential to the mechanisms of transition in square-prism shear layers, were explored experimentally. In particular, the evolution of the dominant instability modes as a function of Reynolds number were reported in the range 1.5 x 10(4) less than or similar to Re-D less than or similar to 7.5 x 10(4). It was found that the ratio between the shear layer frequency and the shedding frequency obeys a power-law scaling relation. Adherence to the power-law relationship, which was derived from hot-wire measurements, has been supported by two additional and independent scaling considerations, namely, by particle image velocimetry measurements to observe the evolution of length and velocity scales in the shear layer during transition, and by comparison to direct numerical simulations to illuminate the properties of the front-face boundary layer. The nonlinear dependence of the shear layer instability frequency is sustained by the influence of Re-D on the thickness of the laminar front-face boundary layer. In corroboration with the original scaling argument for the circular cylinder, the length scale of the shear layer was the only source of nonlinearity in the frequency ratio scaling, within the range of Reynolds numbers reported. The frequency ratio scaling may therefore be understood by the influence of Re-D on the appropriate length scale of the shear layer. This length scale was observed to be the momentum thickness evaluated at a transition point, defined where the Kelvin-Helmholtz instability saturates.
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  • Bio-mimicry inspired tall buildings:The response of cactus-like buildings to wind action at Reynolds Number of 10(4)

    Letchford, C. W.   Lander, D. C.   Case, P.   Dyson, A.   Amitay, M.  

    Applying bio-mimicry intelligence to the aerodynamic performance of tall slender buildings has potential to lead to not only improved response to wind loading, but generate savings in material and construction costs, affect energy consumption by providing self-shading and controlling local air flow to promote local wind energy generation and ventilation strategies. To this end, the alongwind and crosswind responses of high aspect ratio (15:1) cylinders, (smooth, roughened and grooved) were obtained from wind tunnel tests in simulated smooth and rough atmospheric boundary layer flows. The influence of top, flat or domed was also studied. The Saguaro cactus-inspired cylinder with 24 circumferential grooves was seen to have large reductions (similar to 20%) for mean and fluctuating alongwind base shear (drag) and overturning moments in comparison with smooth cylinders and is in agreement with 2D studies in uniform low turbulence flow. Domed tops also led to reduced drag over flat tops. Differences in fluctuating crosswind base shear (lift) and overturning moment were much less marked. In spectral terms the amplitudes of response near the pronounced vortex shedding frequency were almost unchanged, however the cactus-shape had a higher Strouhal Number indicating a shift to a higher frequency as might be attributed to a narrowing of the wake. (C) 2016 Elsevier Ltd. All rights reserved.
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