Runtime analysis of applications can help to gain insight into control flow of applications as well as detect performance issues. This work presents efficient means for integrating runtime monitoring facilities into the DROPS operating system and uses these to analyse performance and behavior of L4-based applications such as L4Linux.

Thesis (MScEng)--University of Stellenbosch, 2008. / ENGLISH ABSTRACT: The performance of a natural draught wet-cooling tower can be improved by reducing the average drop size in the rain zone. In this thesis, the effect of installing different horizontal grids below the fill on drop size in the rain zone is investigated experimentally and theoretically. A specially designed horizontal grid consisting of evenly spaced slats and a grid made from expanded metal sheeting are tested. Drop size distribution measurements are taken below different cooling tower fills to determine the respective Sauter mean drop sizes and also below different configurations of splash grids to determine the reduction in drop size. Drop break-up through a grid of horizontally placed slats is modelled and compared to measured data to determine the optimum configuration in terms of spacing between the grid and fill, slat width and slat spacing. A cross flow rain zone is modelled under different air and water flow combinations with CFD for two distributions that represent the rain with and without splash grids and the results are compared. The Merkel transfer characteristic for all the flow conditions using both distributions are determined using a Lagrangian, Merkel, Poppe and e- NTU method in order to quantify the increase in rain zone Merkel number. Pressure drop over the cross flow rain zone is also determined and compared for the two distributions under considerations. / AFRIKAANSE OPSOMMING: Die verkoelingsvermoë van ‘n reënsone van ‘n natuurlike trek nat koeltoring kan verbeter word deur die verkleining van die gemiddelde druppelgrootte. In hierdie tesis word die effek wat horisontale roosters op die druppelgrootte het, wanneer dit onder die pakking geïnstalleer is, eksperimenteel en teoreties ondersoek. ‘n Spesiaal ontwerpte rooster bestaande uit horisontaal gepakte latte en ‘n gerolde metaal rooster word onderskeidelik vir hierdie doel gebruik. Druppelgrootte metings word geneem onder verskillende koeltoring pakkingsmateriaal om die Sauter gemiddelde diameter te bepaal, asook onder die verskillende rooster opstellings om die verkleinde druppelgrootte te bepaal wat die rooster veroorsaak. Druppelopbreking deur ‘n laag horisontaal gepakte latte word gemodelleer en vergelyk met gemete data om sodoende die beste kombinasie tussen die afstand onder die pakkingsmateriaal, latwydte en latspasiëring te bepaal. ‘n Kruisvloei reënsone word gemodelleer met CFD onder verkillende lug- en watervoeikombinasies vir twee druppelverdelings wat die reënsone met en sonder roosters verteenwoordig. Die Merkel oordragskoëffisiënt vir die twee verdelings word bereken en vergelyk deur van ‘n Lagrange- , Merkel- , Poppe- en e-NTU metode gebruik te maak om sodoende die verbetering in reënsone Merkelgetal te kwantifiseer. Drukvalle oor die reënsone word ook bereken en vergelyk vir die twee verdelings wat beskou is.

Consideration is given to the conditions under which floating drops of water, here referred to as water boules, form, exist and coalesce. Particular emphasis is placed on the part played by electric charge and electric fields in these processes. The literature is reviewed in terms of both the phenomenon of floating drops and of the development of hydrostatics, hydrodynamics and electrohydrodynamics as applicable to the subject. . Experimental investigations to ascertain the boundary conditions to the influence of such electrical forces are described, together with observations of the connected electrical events. It is confirmed that boules will fail to form at all, i) under conditions of high humidity, and ii) in the presence of an electric field greater than a certain value. This is investigated experimentally, and shown to be approximately 34kV/m, this figure being about two-thirds that previously reported. Boules traversing a plane water surface are demonstrated to acquire additional charge in the process. In the case of drops dispensed from a grounded source, forming boules and crossing a bulk water surface some 15cm wide, the additional charge gathered is significant. Boules of 0.055g mass were found to have a mean charge of 1.6 x 10-12C on leaving a water surface, having arrived as drops with an average charge of 5.8 x 10-14C. Possible charging mechanisms are discussed. The origin of the initial drop charge is considered, and measurements of this are presented from (i), conventional Faraday cup determinations, and (ii), induction methods applied to free-falling drops. Experimental investigation of the time-dependent electrical records of the coalescence of a dispensed drop with a plane water surface shows the whole coalescence process to have a two-part form. This detail is commonly hidden within more conventional charge-transfer measurements. For the coalescences investigated experimentally an small initial event is shown to occur, involving a charge transfer in the range 1.2 – 4.8 x 10-12C. Oscillograms taken from a large number of coalescences show this preliminary event to be a general feature of the coalescence process, with a number of such traces being appended to the thesis. This initial event is followed by a larger one where the signs of the signals from the drop and the bulk surface are opposite to those of the initial event, and whose potential magnitude is broadly in agreement with that anticipated by double layer disruption. The interfacial potential difference necessary for the onset of instability and subsequent coalescence in the case of closely opposed drops is shown to be dependent on the relative humidity of the ambient air. Consideration is given to G I Taylor’s equation describing the critical potential for the onset of instability between closely spaced drops, and this is shown experimentally to require correction for different humidities. It is demonstrated that the critical potential, Vc, at a relative humidity of 100% is approximately 50% of that at 40% RH. Possible reasons for this are discussed, drawing attention to the problem of establishing an accurate DC relative permittivity value for vapour-laden air in small interfacial gaps. The rôle of evaporation in modifying the system geometry is considered experimentally and theoretically, and shown to be significant only for humidities < 50%. The complex nature of the interface in the case of very small air-gaps is discussed, together with the implications of these investigations for the interfacial stability of a floating drop or boule system. A theoretical model based on a consideration of the complex liquid-air-liquid interface as a capacitive system is developed, and shown to be in good agreement with practical observations. This model demonstrates that the parts played by electrical forces, together with environmental factors, are likely to be significant in terms of coalescence at stages prior to gap thinning to the point where London/van-der-Waals forces become dominant. Interfacial potentials are calculated in a boule system at a number of times between 0.1 and 10 seconds, and shown to be sufficient to promote instability and coalescence. Full data based on a number of values of instability potentials is appended to the thesis. Development of the model raises questions concerning the validity of currently accepted values both for interfacial stability in small gaps and for the relative permittivity of humid air in similar situations. Suggestions are made for future work in such areas, together with possible methodologies. The phenomenon of floating water drops is therefore shown to be compatible with the general coalescence process, the event time being modified by such diverse factors as the impact energy with the surface, the ambient humidity and the magnitude of the initial drop charge. The latter is shown to be the dominant factor in the case of drops arriving on a clean surface with low kinetic energies, with the small charge inherent on any water drop being sufficient to produce potentials adequate to promote eventual instability.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Lawrence M. Hull. / Ph.D.

Excerpt: Dom Flemons, Rhiannon Giddens, and Justin Robinson met at the Black Banjo Gathering at Appalachian State University in 2005. Inspired by this meeting in Appalachia, the trio worked to connect the legacy of Cumberland Plateau fiddler Howard Armstrong (of the 1920s band the Tennessee Chocolate Drops) with musical material they learned from their mentor, North Carolina Piedmont fiddler Joe Thompson. As the Carolina Chocolate Drops (CCD), these musicians explored a variety of black string band traditions.

We investigate the dynamics of spontaneous jumps of water drops from electrically charged superhydrophobic dielectric substrates during a sudden step reduction in gravity level. In the brief free-fall environment of a drop tower, with a non-homogeneous external electric field arising due to dielectric surface charges (with surface potentials 0.4-1.8 kV), body forces acting on the jumped drops are primarily supplied by polarization stress and Coulombic attraction instead of gravity. This electric body force leads to a drop bouncing behavior similar to well-known phenomena in 1-g0, though occurring for much larger drops (~0.5 mL). We show a simple model for the phenomenon, its scaling, and asymptotic estimates for drop time of flight in two regimes: at short-times close to the substrate when drop inertia balances Coulombic force due to net free charge and image charges in the dielectric substrate and at long-times far from the substrate when drop inertia balances free charge Coulombic force and drag. The drop trajectories are controlled primarily by the dimensionless electrostatic Euler number Eu, which is a ratio of inertial to electrostatic forces. To experimentally determine values of Eu we conduct a series of drop tower experiments where we observe the effects of drop volume, net free charge, and static surface potential of the superhydrophobic substrate on drop trajectories. We use a direct search optimization to obtain a Maximum Likelihood Estimate for drop net charge, as we do not measure it directly in experiment. For φEu/8π > 1 drops escape the electric field, where φ is a drop to substrate aspect ratio. However, we do not observe any escapes in our dataset. With an eye towards engineering applications we consider the results in light of the so-called low-gravity phase separation problem with a worked example.

When confined within containers or conduits, drops and bubbles migrate to regions of minimum energy by the combined effects of surface tension, surface wetting, system geometry, and initial conditions. Such capillary phenomena are exploited for passive phase separation operations in micro-fluidic devices on earth and macro-fluidic devices aboard spacecraft. Our study focuses on the migration and ejection of large inertial-capillary drops confined between tilted planar hydrophobic substrates. In our experiments, the brief nearly weightless environment of a drop tower allows for the study of such capillary dominated behavior for up to 10 mL water drops with migration velocities up to 12 cm/s. We control ejection velocities as a function of drop volume, substrate tilt angle, initial confinement, and fluid properties. We then demonstrate how such geometries may be employed as passive no-moving-parts droplet generators for very large drop dynamics investigations. The method is ideal for hand-held non-oscillatory drop generation for fun, educational, and insightful astronaut demonstrations aboard the International Space Station.

<p>The interaction between liquid drops and textured surfaces not only offers fundamental challenges in capillarity and wetting, but also enables new applications ranging from self-cleaning materials to self-sustaining condensers. The first part of this dissertation deals with the fundamental wetting and dewetting dynamics of drops on textured surfaces, and the self-propelled jumping of dropwise condensate on superhydrophobic surfaces. The second part builds upon these findings in dynamical superhydrophobicity to develop a jumping-drop thermal diode that rectifies heat flow between textured superhydrophilic and superhydrophobic surfaces. </p><p>On the fundamental side, anti-dew is an essential property of robust superhydrophobic surfaces, particularly those deployed in ambient environments or phase-change systems. A superhydrophobic lotus leaf retains water repellency after repeated condensation in nature but becomes sticky to water drops after condensation on a fixed cold plate. To solve this mystery, we first study the possible wetting states of superhydrophobic surfaces possessing two-tier surface roughness mimicking that on the lotus leaf. By incrementally increasing the ethanol concentration of water/ethanol drops, two distinct wetting transitions are observed on two-tier surfaces. Drops in the intermediate wetting state uniformly wet the microscale roughness but not the nanoscale roughness. Dew drops exhibited a similar intermediate wetting state. Our experiments show that mechanical vibration can be used to overcome the energy barrier for transition from the intermediate wetting (Partial Wenzel) state to the fully dewetted (Cassie) state, and the threshold for the dewetting transition follows a scaling law comparing the kinetic energy imparted to the drop with the work of adhesion. </p><p>Although vibration-induced dewetting is effective for removing millimetric condensate from the surface, micrometric condensate cannot be removed as surface energy dominates at small scales. We report a new discovery in which the micrometric condensate can spontaneously dewet and jump off the superhydrophobic surface. The spontaneous jumping results from the surface energy released upon drop coalescence, which leads to the rapid out-of-plane jumping motion of the coalesced drops. The jumping drops follow an inertial-capillary scaling and give rise to self-sustained dropwise condensation with a micrometric average diameter. Using two approaching Leidenfrost drops suspended on a vapor layer to simulate superhydrophobicity, we show that the out-of-plane directionality results from the impingement of the expanding liquid bridge against the heated Leidenfrost surface, which is initially formed between coalescing drops above the substrate.</p><p>On the practical side, textured surfaces offer new possibilities for phase-change heat transfer. Taking advantage of the self-propelled jumping condensate, we developed a planar phase-change thermal diode that transports heat in a preferential direction. The jumping-drop diode is composed of parallel superhydrophobic and superhydrophilic plates, and the thermal rectification is enabled by spontaneously jumping dropwise condensate which only occurs when the superhydrophobic surface is colder. The superhydrophobic surface has nanoscale surface roughness that is anti-dew, while the superhydrophilic surface consists of porous copper wick borrowed from heat pipes. Our planar thermal diode with asymmetric wettability is scalable to large areas with an orientation-independent diodicity of over a hundred. </p><p>More broadly speaking, the self-propelled jumping offers an alternative means to return liquid condensate in phase-change systems. We systematically investigate the heat transfer performance of a vapor chamber enabled by the jumping condensate. When the non-condensable gases are removed, the effective heat transfer coefficient is mainly governed by the interfacial resistance of the phase-change processes and the conduction resistance across the superhydrophilic wick. Potential routes for improving the heat transfer performance are discussed, including the optimization of the superhydrophilic wick and its separation with the opposing superhydrophobic surface. The new jumping return mechanism is unique in that it neither relies on external forces nor requires wick structures along the return path, and is expected to be applicable to a variety of phase-change heat transfer systems.</p> / Dissertation

This research presents an experimental study of the formation of drops of suspensions consisting of a viscous liquid and spherical, neutrally buoyant, noncolloidal particles. Pendant drop formation and low Reynolds number jetting of suspensions are investigated, as is the transition between the two. Throughout, the particles utilized are on the order of 100 μm and the orifice from which the drops are formed is on the order of 1 mm. The presence of the particulate phase causes the structure at pinch-off in the pendant drop regime to change noticeably from that of pure liquids. Thick cone-like structures, termed "spindles" here, form at either end of the slender thread and are the result of particle motions during necking. These spindles become more pronounced with increasing particle concentration. Depending on particle concentration, the particles can have either a destabilizing effect (low concentration) on drop formation or a stabilizing one (high concentration). At low concentrations, the particles lead to earlier rupture of the thread and much shorter jet lengths, while at elevated concentrations the particles stabilize the thread after rupture and lead to fewer satellite drops as well as induce jetting at lower flower rates. A two-stage model has been proposed to describe the necking process for particle-laden suspensions in the pendant drop regime. The first stage occurs when the thread is thick relative to the particles and the effect of the particles can be attributed solely to a change in the effective viscosity of the mixture. The second stage occurs nearer pinch-off when the thread has thinned to only a few particle diameters. In this stage the individual particle motions within the thread determine the behavior and the thread ultimately ruptures over a region of the thread devoid of particles.

Wireless technology has become the most interesting field in the area of communications and networking. Video transmission plays a major role in this area. Data transmission via wireless communications is a major task, especially to send the data without loss of packets. The digital video decoder produces dropped or repeated frames from the encoded video due to packet loss. Brief frame drops of one frame duration are referred as dips. This research work investigates how to identify these frame dips and drops and also to measure the quality of the video which contain frame dips and frame drops. A dynamic threshold estimator is implemented to identify these frame dips. The qualitative analysis of a video is performed using a No Reference metric. In this metric the quality assessment can be achieved by identification of frame dips and drops and calculating Modified Fraction of Dropped Frames. Dips and abrupt temporal variation occurring at the end of frame freezing event of a video fluidity impairment caused by frame dropping will be taken into account using this metric. The parameters which are generated from Structural Similarity Index Metric (SSIM) analysis are efficient enough to compare the video quality and estimate the metric performance objectively. Our proposed metric has predicted the SSIM with a Pearson correlation coefficient of 0.99 in test1, 0.92 in test2 and 0.99 in test3. Therefore in terms of prediction accuracy the proposed metric has a good correlation with the deployed metric and obtained robustness to our approach. / Trådlös teknik har blivit den mest intressanta fältet inom kommunikation och nätverk. Videoöverföring spelar en viktig roll på detta område. Dataöverföring via trådlös kommunikation är en stor uppgift, särskilt för att skicka data utan förlust av paket. Den digitala videoavkodare producerar tappade eller upprepade bildrutor från den kodade videon grund paketförluster. Kort ram droppar en ram varaktighet kallat dips. Denna forskning undersöker hur man identifierar dessa ram dips och droppar och även att mäta kvaliteten på video som innehåller ram dips och droppar ram. En dynamisk tröskel estimatorn genomförs för att identifiera dessa ram dips. Den kvalitativa analysen av ett videoklipp utförs med hjälp av en No Reference metrisk. I denna statistik kvalitetsbedömningen kan uppnås genom identifiering av ram nedgångar och droppar och beräkning modifierad Andel bildrutor. Dips och abrupt temporal variation inträffar i slutet av ramen frysning händelse av en video flytbarhet orsakats av ram släppa kommer att beaktas med denna metrik. De parametrar som genereras från strukturell likhet Index Metric (SSIM) analys är effektiva nog att jämföra videokvalitet och uppskatta det metriska prestanda objektivt. Vår föreslagna värdet har förutspådde SSIM med Pearson korrelationskoefficient av 0,99 i test1, 0,92 i test2 och 0,99 i test3. Därför gäller förutsägelse noggrannhet föreslagna måttet har en god korrelation med utplacerade metriska och fick robusthet till vår strategi. / Vydik Mopidevi, D.No: 5-162, Sri Vijetha Public School, Tallapudi, West Godavari District, Pin Code: 534341 Phone Number: Home: 00813282979 Work: 0046734784445 Email: vydik.mopidevi@gmail.com