13 research outputs found

    Viscous sintering of unimodal and bimodal cylindrical packings with shrinking pores

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    An elliptical-pore model for late-stage planar viscous sintering

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    Development, Verification, and Validation of Multiphase Models for Polydisperse Flows

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    The One-Dimensional Turbulence Model Applied to Spray Atomization

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    Numerical simulation of the spray behavior is an important part of engine research and is critical for combustion optimization. Successful implementation of the advanced modeling tools for sprays is strongly dependent on our current understanding of the physical processes involved. One of the main processes occurring close to the nozzle is primary atomization. It governs the initial size and velocity distribution of droplets formed at the liquid jet surface. This process is not yet fully understood due to challenges in experimental observation of the region close to the nozzle. This has kept the primary atomization as one of the least developed model components in spray simulation and in need of mprovement.In this dissertation, a new primary atomization model is proposed based on the One-Dimensional Turbulence (ODT) model framework. ODT is a stochastic turbulence model simulating turbulent flow evolution along a notional 1D line of sight by applying instantaneous maps to represent the effect of individual turbulent eddies on property profiles. This approach provides affordable high resolution at the liquid/gas interface, which is essential for capturing the local behavior of the breakup process.This new approach is assessed under different operating conditions parameterized by the liquid jet Reynolds and Weber numbers. ODT primary atomization results have been provided as an input to a spray model in conventional form to evaluate its predictive capability. These efforts are reported in several manuscripts attached to this dissertation.Furthermore, to better understand the physics behind primary atomization, a canonical simulation configuration is developed that isolates the interaction between surface tension and surrounding turbulence. The ability of the model to capture the breakup is assessed with the available Detailed Numerical Simulation (DNS) data for further improvements.Lastly, a new strategy is proposed to use ODT as a subgrid resolution model in LES/VOF simulations to describe/model unresolved subgrid interface dynamics

    Creation of Defined Single Cell Resolution Neuronal Circuits on Microelectrode Arrays

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    The way cell-cell organization of neuronal networks influences activity and facilitates function is not well understood. Microelectrode arrays (MEAs) and advancing cell patterning technologies have enabled access to and control of in vitro neuronal networks spawning much new research in neuroscience and neuroengineering. We propose that small, simple networks of neurons with defined circuitry may serve as valuable research models where every connection can be analyzed, controlled and manipulated. Towards the goal of creating such neuronal networks we have applied microfabricated elastomeric membranes, surface modification and our unique laser cell patterning system to create defined neuronal circuits with single-cell precision on MEAs. Definition of synaptic connectivity was imposed by the 3D physical constraints of polydimethylsiloxane elastomeric membranes. The membranes had 20μm clear-through holes and 2-3μm deep channels which when applied to the surface of the MEA formed microwells to confine neurons to electrodes connected via shallow tunnels to direct neurite outgrowth. Tapering and turning of channels was used to influence neurite polarity. Biocompatibility of the membranes was increased by vacuum baking, oligomer extraction, and autoclaving. Membranes were bound to the MEA by oxygen plasma treatment and heated pressure. The MEA/membrane surface was treated with oxygen plasma, poly-D-lysine and laminin to improve neuron attachment, survival and neurite outgrowth. Prior to cell patterning the outer edge of culture area was seeded with 5x105 cells per cm and incubated for 2 days. Single embryonic day 7 chick forebrain neurons were then patterned into the microwells and onto the electrodes using our laser cell patterning system. Patterned neurons successfully attached to and were confined to the electrodes. Neurites extended through the interconnecting channels and connected with adjacent neurons. These results demonstrate that neuronal circuits can be created with clearly defined circuitry and a one-to-one neuron-electrode ratio. The techniques and processes described here may be used in future research to create defined neuronal circuits to model in vivo circuits and study neuronal network processing

    Multiwavelength studies of the blazars detected by AGILE

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    La scoperta dell’emissione nei raggi gamma da parti di numerosi Nuclei Galattici Attivi (AGN) con EGRET ed i telescopi Cherenkov è stata una delle più rivoluzionarie scoperte di astrofisica delle alte energie degli ultimi 20 anni, portando all’identificazione di una nuova classe di AGN: i blazar. I blazar sono la sottoclasse più estrema di AGN, caratterizzata da forte emissione di radiazione non-termica attraverso l'intero spettro elettromagnetico. Questa emissione è interpretata come il risultato della radiazione elettromagnetica da un getto relativistico allineato alla linea di vista dell'osservatore, causando una forte amplificazione relativistica dell’emissione osservata. Considerando che la maggiore frazione della potenza totale dei blazar è emessa nei raggi gamma, le informazioni in questa banda energetica sono fondamentali per studiare i diversi modelli di radiazione. Oltre dieci anni dopo l'epoca di EGRET, il satellite AGILE (e successivamente anche il satellite Fermi) ha colmato la lacuna nella banda MeV-GeV dando ulteriore impulso allo studio dei fenomeni di astrofisica delle alte energie nei blazar. Tuttavia, nonostante l'importanza delle informazioni fornite dalle osservazioni nei raggi gamma, studi correlati multifrequenza sono la chiave per raggiungere una migliore comprensione della struttura interna del getto, l'origine dei fotoni seme per il processo di Compton inverso ed i meccanismi di emissione che agiscono nei blazar. Dal suo lancio in Aprile 2007, il satellite AGILE ha rilevato diversi blazar in stato di alta attività: PKS 1510-089, S5 0716+714, 3C 454.3, 3C 273, 3C 279, W Comae, Mrk 421 e PG 1553+113. In questa Tesi saranno presentati i risultati più interessanti dell'analisi multifrequenza di queste sorgenti rilevate da AGILE in raggi gamma, insieme ai dati multifrequenza forniti da altri osservatori come Spitzer, Swift, RXTE, Suzaku, INTEGRAL, MAGIC, VERITAS, nonché dalle osservazioni dal radio all’ottico ottenute da GASP-WEBT e REM. Questa ampia copertura multifrequenza mi ha offerto l'opportunità di studiare le distribuzioni spettrali di energia di queste sorgenti dal radio ai raggi gamma, le variabilità correlata in diverse bande di energia e di indagare i meccanismi responsabili per la loro emissione, scoprendo in alcuni casi un comportamento più complesso rispetto ai modelli standard.The discovery of emission in the gamma-ray domain from many Active Galactic Nuclei (AGNs) by EGRET onboard Compton Gamma-Ray Observatory and the Cherenkov Telescopes was one of the most breakthrough of high energy astrophysics in the last 20 years, leading to the identification of a new class of AGNs: the blazars. Blazars are the most extreme subclass of AGNs, characterized by the emission of strong non-thermal radiation across the entire electromagnetic spectrum, from radio to very high gamma-ray energies. This emission is interpreted as the result of the electromagnetic radiation from a relativistic jet that is viewed closely aligned to the line of sight of the observer, thus causing strong relativistic amplification. Considering that the large fraction of the total power of blazars is emitted in the gamma-rays, information in this energy band is crucial to study the different radiation models. More than ten years after the EGRET era, the AGILE satellite (and subsequently also the Fermi satellite) filled the gap in the MeV-GeV band giving further impulse to the study of the high-energy astrophysics phenomena in blazars. However, notwithstanding the importance of the information provided by the gamma-ray observations, correlated multiwavelength studies are the key to achieve a better understanding of the structure of the inner jet, the origin of the seed photons for the inverse Compton process and the emission mechanisms at work in blazars. Since its launch in April 2007, the AGILE satellite detected several blazars in high activity state: PKS 1510–089, S5 0716+714, 3C 454.3, 3C 273, 3C 279, W Comae, Mrk 421 and PG 1553+113. In this Thesis I will present the most interesting results on multifrequency analysis of these sources detected by AGILE in gamma-rays, together with the multiwavelength data from other observatories such as Spitzer, Swift, RXTE, Suzaku, INTEGRAL, MAGIC, VERITAS, as well as radio-to-optical coverage by means of GASP-WEBT and REM. This large multifrequency coverage gave me the opportunity to study the Spectral Energy Distributions (SEDs) of these sources from radio to gamma-rays, the correlated variability in different energy bands and to investigate the mechanisms responsible for their emission, uncovering in some cases a more complex behaviour with respect to the standard models. The intense gamma-ray flares of S5 0716+714 observed by AGILE in September and October 2007 are among the highest fluxes detected by a BL Lac object and considering the redshift of the source (z = 0.31) the total power transported in the jet during these episodes approaches or slightly exceeds the maximum power generated by a spinning black hole of 10^9 solar masses, challenging the Blandford-Znajek mechanism and confirming the extreme energetics during these flares. The modeling of the SEDs of S5 0716+714 indicated as, even if the broad band emission appears in agreement with the synchrotron self Compton (SSC) paradigm, a more complex model with two SSC components is needed to interpret our data. The case of S5 0716+714 is not unique among the BL Lac objects, also for the multifrequency observation of Mrk 421 and W Comae in June 2008 a one-zone SSC model seems to be a good representation of the broad band spectrum, but the observations collected during the multiwavelength campaigns seem to open to more complex interpretations of the data. Moreover, the dominant emission mechanism in the gamma-ray band for Flat Spectrum Radio Quasars (FSRQs) is the inverse Compton scattering of external photons from the broad line region, but in some particular states also the contribution of seed photons from a hot corona (3C 454.3 in December 2007) or the accretion disk (3C 279) are shown to be important. Therefore, from the modeling of the different SEDs of BL Lacs and FSRQs observed by AGILE seems to emerge that the SSC and the external Compton (EC) frameworks, respectively, are good approximation for describing on average the high activity states of the two flavours of blazars, but going into details of the single observation more complex scenarios sometimes are requested. The possibility to obtain information over the entire electromagnetic spectrum during the multifrequency campaigns organized by AGILE gave me also the opportunity to investigate in some blazars the presence of Seyfert-like features, such as the little and big blue bumps (PKS 1510-089) and the Compton reflection component (3C 273). Moreover, we revealed in the FSRQ PKS 1510-089 some features typical of High-frequency peaked BL Lac objects, such a X-ray harder-when-brighter behaviour during March 2008 and a shift of the synchrotron peak towards higher frequencies during the huge flare of March 2009. Emission in optical and gamma-ray bands seems to be correlated during high activity states of blazars, but not strongly, with a possible lag of the gamma-ray flux with respect to optical one less than one day, both for FSRQs (e.g. 3C 454.3) and BL Lacs (S5 0716+714). On the other hand, during March 2009 a possible delay of the optical emission with respect to the gamma-ray one is detected for PKS 1510-089, suggesting a more complex behaviour in the optical/gamma-ray correlation, especially for FSRQs, where also a contribution of the thermal disk emission is clearly visible

    Sports Materials

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    To further improve the level of correlation between these finite element models and lab-simulated bat/ball impacts, the material behavior for these wood species must also be characterized at strain rates comparable to those experienced ..

    Medical Robotics

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    The first generation of surgical robots are already being installed in a number of operating rooms around the world. Robotics is being introduced to medicine because it allows for unprecedented control and precision of surgical instruments in minimally invasive procedures. So far, robots have been used to position an endoscope, perform gallbladder surgery and correct gastroesophogeal reflux and heartburn. The ultimate goal of the robotic surgery field is to design a robot that can be used to perform closed-chest, beating-heart surgery. The use of robotics in surgery will expand over the next decades without any doubt. Minimally Invasive Surgery (MIS) is a revolutionary approach in surgery. In MIS, the operation is performed with instruments and viewing equipment inserted into the body through small incisions created by the surgeon, in contrast to open surgery with large incisions. This minimizes surgical trauma and damage to healthy tissue, resulting in shorter patient recovery time. The aim of this book is to provide an overview of the state-of-art, to present new ideas, original results and practical experiences in this expanding area. Nevertheless, many chapters in the book concern advanced research on this growing area. The book provides critical analysis of clinical trials, assessment of the benefits and risks of the application of these technologies. This book is certainly a small sample of the research activity on Medical Robotics going on around the globe as you read it, but it surely covers a good deal of what has been done in the field recently, and as such it works as a valuable source for researchers interested in the involved subjects, whether they are currently “medical roboticists” or not

    FGK stars and T Tauri stars: Monograph series on nonthermal phenomena in stellar atmospheres

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    The purpose of this book, FGK Stars and T Tauri Stars, like all other volumes of this series, is to exhibit and describe the best space data and ground based data currently available, and also to describe and critically evaluate the status of current theoretical models and physical mechanisms that have been proposed to interpret these data. The method for obtaining this book was to collect manuscripts from competent volunteer authors, and then to collate and edit these contributions to form a well structured book, which will be distributed to an international community of research astronomers by NASA and by the French CNRS
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