Drift tube ion mobility spectrometry (IMS) is a powerful, post-ionization separation that yields structural information of ions through an ion-neutral collision cross section. The ion-neutral collision cross section is governed by the collision frequency of the ion with the neutral drift gas. Consequently, ions of different size will have different collision frequencies with the gas and be separated in the drift cell. A significant challenge for IMS, however, is to separate ions with very similar collision cross sections, requiring higher resolution ion mobility spectrometers. Resolution in IMS is of utmost importance for the separation of complex mixtures, e.g. crude oil samples, proteolytic digests, positional isomers, and ion conformers. However, most methods employed to increase mobility resolution significantly decrease ion transmission through the mobility device. Herein, a periodic-focusing DC ion guide drift cell (PDC IG) is presented to display its potential capabilities for higher mobility resolution with increased ion transmission. The PDC IG utilizes unique electrode geometry compared to the conventional uniform field electrode design. Electrode geometry can be defined by the electrode inner diameter (d), thickness (t), and spacing (s). Specifically, the ratio of d : t : s is equal to, or very near, 1:1:1. The PDC IG electrode design creates a non-uniform (fringing) electric field-especially near the electrode walls. The design also causes variations in the radial electric field which provides an effective RF as ions move through the device and a radially confining effective potential that improves ion transmission through the device. In this dissertation the analytical utility of the PDC IG drift cell for ion mobility separations will be explored. The radial focusing properties of the device will be presented along with studies of electrode geometry and its effect on ion mobility resolution and ion transmission through the drift cell. PDC IG drift cell length is also examined to determine its effect on mobility resolution and ion transmission. Finally, the PDC IG drift cell device is coupled to an orthogonal-acceleration time-of-flight mass spectrometer as well as a modular, PDC IG drift cell being adapted to a commercial qTOF mass spectrometer for IM-MS experiments.

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This paper presents the results of servo designs for optical disk drives which consist of a dual-input/single-output (DISO) actuator; both a sledge actuator and a voice coil motor contribute to a radial movement of the spot on the disk. DISO systems are subset of multi-input/multi-output (MIMO) systems and thus the servo engineer can apply the design methods developed for MIMO controller design to the DISO compensator problems. These techniques include H2 , H¡Û and £g-synthesis. However, in order to obtain insights into the controller elements, in this study we prefer the H¡Û loop-shaping approach. Here, the focus is on stability and disturbance rejection. The method is presented for a master-slave control scheme in tracking servo, a parallel scheme in seeking servo, and a unit-feedback scheme in focusing servo. The maximum stability margin can be obtained in H¡Û loop-shaping algorithm. Furthermore, a robust controller guarantees to stabilize it would be carried out. Finally, computer simulation results are provided to show that the shaking disturbance due to the run-out of disk can be significantly attenuated and a good tracking performance can be achieved by the developed controller.

A reflective type Fresnel lens using an array of micromirrors is designed and fabricated using the MUMPs?? surface micromachining process. The focal length of the lens can be rapidly changed by controlling both the rotation and translation of electrostatically actuated micromirrors. The suspension spring, pedestal and electrodes are located under the mirror to maximize the optical efficiency. The micromirror translation and rotation are plotted versus the applied voltage. Relations are provided for the fill-factor and the numerical aperture as functions of the lens diameter, the mirror size, and the tolerances specified by the MUMPs?? design rules. Linnik interferometry is used to measure the translation, rotation, and flatness of a fabricated micromirror. The reflective type Fresnel lens is controlled by independent DC voltages of 16 channels with a 0 to 50V range, and translational and torsional stiffness are calibrated with measured data. The spot diameter of the point source by the fabricated and electrostatically controlled reflective type Fresnel lens is measured to test focusing quality of the lens.

<p>Focusing of strong shock waves in a gas-filled thin test section with various forms of the reflector boundary is investigated. The test section is mounted at the end of the horizontal co-axial shock tube. Two different methods to produce shock waves of various forms are implemented. In the first method the reflector boundary of the test section is exchangeable and four different reflectors are used: a circle, a smooth pentagon, a heptagon and an octagon. It is shown that the form of the converging shock wave is influenced both by the shape of the reflector boundary and by the nonlinear dynamic interaction between the shape of the shock and the propagation velocity of the shock front. Further, the reflected outgoing shock wave is affected by the shape of the reflector through the flow ahead of the shock front. In the second method cylindrical obstacles are placed in the test section at various positions and in various patterns, to create disturbances in the flow that will shape the shock wave. It is shown that it is possible to shape the shock wave in a desired way by means of obstacles. The influence of the supports of the inner body of the co-axial shock tube on the form of the shock is also investigated. A square shaped shock wave is observed close to the center of convergence for the circular and octagonal reflector boundaries but not in any other setups. This square-like shape is believed to be caused by the supports for the inner body. The production of light, as a result of shock convergence, has been preliminary investigated. Flashes of light have been observed during the focusing and reflection process.</p>

Cette thèse se situe à la frontière de deux domaines : celui de la rhéologie des mousses et celui de la microfluidique. On présente comment créer une mousse dans un système microfluidique avec une taille minimale de bulle autour de 100 μm et on étudie son écoulement. Après un rappel de l'état de l'art en microfluidique biphasique et dans le domaine de l'écoulement de mousse 2D, on présente l'ensemble de techniques expérimentales qui permettent de produire le système microfluidique et d'imager l'écoulement résultant. Ensuite, on étudie la génération de mousse microfluidique avec la méthode du pincement liquide. On mesure la dépendance des propriétés de la mousse (fraction liquide, topologie) envers les paramètres de contrôle et la géométrie. Nous montrons que la rhéologie de l'écoulement est fortement non-linéaire. La relation pression-débit présente en effet un seuil, une loi de puissance et des discontinuités liés aux transitions de topologie. On met en évidence un effet rétroactif de l'écoulement dans le canal sur la formation de la mousse, qui entraîne un comportement dynamique très riche. On trouve notamment une oscillation entre différentes topologies reliée à une instabilité qui peut être de type advectif, stationnaire ou absolu. Finalement on étudie une méthode pour l'application de forces acoustiques sur un écoulement biphasique, afin de manipuler les bulles de la mousse depuis l'extérieur.

This thesis describes electronic transport experiments in graphene from the hopping to the ballistic regime. The first experiment studies dual-gated bilayer graphene devices. By applying an electric field with these dual gates, we can open a band gap in bilayer graphene and observe an increase in resistance of over six orders of magnitude as well as a strongly non-linear behavior in the transport characteristics. A temperature-dependence study of resistance at large electric field at the charge neutrality point shows the change in the transport mechanism from a hopping dominated regime at low temperature to a diffusive regime at high temperature. / Physics

The ability to control the motion of particles and cells in microchannels has been a center of fascination since the advent of microfluidics. Entire fields have been created in order to accomplish separation, volume reduction and overall positioning of particles and cells within microfluidic devices in the fastest and most accurate manner possible. While most of these technologies rely on low Reynolds number operation, one technique entitled inertial focusing takes advantage of the inertia of the surrounding fluid and the interaction between a particle and the channel itself which cause the lateral migration of particles across streamlines to equilibrium positions within a flow. The major advantage of inertial microfluidics in biomedical and microfluidic applications is that it is inherently high throughput being dependent on inertia whereas most microfluidic concepts are dependent on low Reynolds number operation. / Engineering and Applied Sciences

In the disertation, the self-focusing phenomenon of intense femtosecond light pulses in media with cubic nonlinearity is investigated and the origin of formation of light filaments is revealed. In this work, new measurement techniques are introduced and applied experimentally, which allowed high resolution temporal, spatial and spectral mapping of light wave-packet dynamics during the nonlinear propagation in transparent media, and enabled to observe and make accurate quantitative evaluation of the ultrafast change of medium properties. By means of high temporal (20 fs) and spatial (1 μm) resolution laser 3D mapping technique, it was shown that the initial Gaussian wave packet during self-action in Kerr media redistributes its energy in a way that in spatio-temporal domain the wave packet takes a complex X-type intensity distribution. This transformation is universal and is determined by temporal and spatial spectral broadening (as a consequence of self-focusing and self phase modulation), conical emission (as a consequence of four-wave mixing) and nonlinear losses caused by multiphoton absorption. By means of imaging spectrometer technique it was shown that in the medium with normal group velocity dispersion the far-field angular spectrum of the wave packet takes a characteristic X shape, whereas in anomalous group velocity dispersion regime – a characteristic O shape. In both cases the localization of the wave packet is observed, however the quantitative differences of the... [to full text] / Disertacijoje nagrinėjamas intensyvių femtosekundinių šviesos impulsų fokusavimosi reiškinys kubinio netiesiškumo terpėse bei atskleidžiama šviesos gijų formavimosi prigimtis. Darbe yra pasiūlytos ir eksperimentiškai realizuotos šviesos bangų paketų registravimo metodikos, kurios leidžia su didele skyra fiksuoti laikinę, erdvinę bei spektrinę šviesos bangų paketų dinamiką netiesinio sklidimo metu, taip pat stebėti bei itin tiksliai kiekybiškai įvertinti terpės savybių sparčius pokyčius. Pasitelkus didelės laikinės (20 fs) ir erdvinės (1 μm) skyros lazerinės tomografijos metodiką, parodyta, kad pradinio Gauso formos bangų paketo energija saviveikos Kero terpėje metu persiskirsto taip, kad erdvėlaikyje jis įgauna sudėtingą X tipo intensyvumo skirstinį. Ši transformacija yra universali, ir ją nulemia laikinis ir erdvinis spektro plitimas (dėl fokusavimosi ir fazės moduliavimosi), kūginė spinduliuotė (dėl keturbangio maišymosi) bei nuostoliai dėl daugiafotonės sugerties. Remiantis atvaizduojančio spektrometro metodika parodyta, kad formuojantis šviesos gijai normalios grupinių greičių dispersijos terpėje bangų paketo tolimojo lauko kampinis spektrinis skirstinys yra X formos, o anomalios grupinių greičių dispersijos terpės atveju – O formos. Abiem atvejais stebima bangų paketo lokalizacija, tačiau kiekybinius kampinių spektrinių skirstinių skirtumus nulemia keturbangio dažnių maišymo fazinio sinchronizmo sąlygos. Ir galiausiai, naudojant didelės laikinės (23 fs) ir erdvinės (1,5... [toliau žr. visą tekstą]

Šviesos netiesinio fokusavimosi reiškinys tyrinėjamas jau nuo pat lazerio sukūrimo. Ypatingai aktyviai nagrinėjamas šviesos gijų susidarymas bei jų dinamika skirtingos fazinės būsenos medžiagose. Šviesos gijos įdomios tuo, kad šviesa jose sklinda beveik nepatirdama difrakcijos ir dispersijos. Mokslininkai pasiūlė nemažai šviesos gijos taikymų, kaip pvz. atmosferos sluoksnių spektrinė analizė, atosekundinių impulsų generacija inertinėse dujose ar bangolaidžių užrašymas kietose skaidriose terpėse. Šviesos saviveikos metu pradinė bangų paketų forma erdvėje bei laike gali stipriai pakisti. Standartiniai impulsų charakterizavimo metodai, kurie remiasi erdvėje integruotų autokoreliacinių ir kryžminių koreliacinių funkcijų matavimu, įgalina gauti tik dalinę informaciją apie vykstančias šviesos impulso bei terpės savybių transformacijas ir jų fizikinę prigimtį. Todėl, norint gerai įvaldyti minėtus taikymus bei suprasti vykstančius fizikinius reiškinius, visiškam šviesos impulsų sąveikos su medžiaga ir šviesos gijų formavimo proceso charakterizavimui reikalingi nauji matavimo metodai, kuriuos pasitelkus būtų galima išmatuoti bangų paketo intensyvumo pasiskirstymą trijų matmenų erdvėje bet kuriuo laiko momentu bei registruoti momentinius terpės struktūros pokyčius. Antra vertus, šviesos ir medžiagos sąveikos procesai yra labai spartūs, tad jų tyrimui reikalinga labai didelė tiek erdvinė (μm eilės), tiek laikinė (fs eilės) skyra. Šiame darbe pasiūlėme didelės laikinės (20 fs) ir... [toliau žr. visą tekstą] / In the disertation, the self-focusing phenomenon of intense femtosecond light pulses in media with cubic nonlinearity is investigated and the origin of formation of light filaments is revealed. In this work, new measurement techniques are introduced and applied experimentally, which allowed high resolution temporal, spatial and spectral mapping of light wave-packet dynamics during the nonlinear propagation in transparent media, and enabled to observe and make accurate quantitative evaluation of the ultrafast change of medium properties. By means of high temporal (20 fs) and spatial (1 μm) resolution laser 3D mapping technique, it was shown that the initial Gaussian wave packet during self-action in Kerr media redistributes its energy in a way that in spatio-temporal domain the wave packet takes a complex X-type intensity distribution. This transformation is universal and is determined by temporal and spatial spectral broadening (as a consequence of self-focusing and self phase modulation), conical emission (as a consequence of four-wave mixing) and nonlinear losses caused by multiphoton absorption. By means of imaging spectrometer technique it was shown that in the medium with normal group velocity dispersion the far-field angular spectrum of the wave packet takes a characteristic X shape, whereas in anomalous group velocity dispersion regime – a characteristic O shape. In both cases the localization of the wave packet is observed, however the quantitative differences of the... [to full text]