The breakup of liquid jets is ubiquitous with rich underpinning physics and widespread applications. The natural breakup of liquid jets originates from small ambient perturbations, which can grow exponentially until the amplitude as large as the jet radius is reached. For unelectrified inviscid jets, surface energy analysis shows that only the axisymmetric perturbation is possibly unstable, and this mode is referred as varicose instability. For electrified jets, the presence of surface charge enables additional unstable modes, among which the most common one is the whipping (or kink) instability that bends and stretches the charged jet that is responsible for the phenomena of electrospinning. A closer examination of the two instabilities suggests that due to mass conservation, the uneven jet stretching from whipping may translate into radial perturbations and trigger varicose instabilities. Although the varicose and whipping instabilities of electrified micro-jets have both been extensively studied separately, there is little attention paid to the combined effect of these two, which may lead to new jet breakup phenomena. This dissertation investigates the dynamic response of electrified jets under transverse electrohydrodynamic (EHD) perturbations which were introduced by exciters driven by alternating voltage of sweeping frequency. Three different jetting mechanisms are used to generate jets with various ranges of jet diameters: ~150 micrometer inertial jets from liquid pressurized through a small orifice, ~50 micrometer flow focused jets, and ~20 micrometer electrified Taylor-cone jets. The transverse perturbations enable systematic triggering of varicose and whipping instabilities, and consequently a wide range of remarkable phenomena emerge. For inertial jets with zero or low charge levels, only varicose instability is observable due to suppressed whipping instability. At modest charge levels, inertia jets can respond to the fundamental perturbation frequency as well as the second harmonic of the perturbation frequency. Highly charged jets such as fine jets generated from Taylor cones exhibit distinct behavior for different perturbation wavenumber x. Typical behavior include: whipping jets with superimposed varicose instability at small x, jet bifurcation from crossover of whipping and varicose instabilities at x~0.5, Coulombic fission owing to the surge of surface charge density as the slender liquid segments recover spherical shapes at x~0.7, and simple varicose mode near wave numbers of unity. The phenomena observed in this work may be explained by a linear model and rationalized by the phase diagram in the space of wave number and dimensionless charge levels. The experimental apparatus used in this dissertation is simple, non-intrusive, and scalable to a linear array of jets. The rich phenomena combined with the versatile apparatus may spawn new research directions such as regulated electrospinning, generating strictly monodisperse micro/nano droplets, and manufacturing of non-spherical particles from drying droplets that undergo controlled Coulombic fissions.

A description of a Dempster type double focusing mass spectrograph, converted to a mass spectrometer is reported. The latter part of the thesis deals with an investigation of a Shaw type solid ion source. Ten microgram samples of VaCl2 and SrCl2 yielded measurable ion currents of 1.0 x 10-11 amperes. Results with UF4 and PbI2 are also reported. / Thesis / Master of Science (MS)

TRANSIMS is a disaggregate, behavioral, regional transportation planning package developed by Los Alamos National Laboratory (LANL) under funding from US DOT, EPA, and Department of Energy. It is an integrated system of travel forecasting models designed to give transportation planners accurate, complete information on traffic impacts, congestion, and pollution by simulating on a second-by-second basis the movements of every person and every vehicle through the transportation network of a large metropolitan area. This regional microsimulation approach provides a better assessment of the performance of a large network than the current link performance functions utilized in the current planning procedures. On the other hand, their microsimulation approach on a regional scale requires a lot of data that may not be readily available, and utilize a low fidelity microsimulation in order to make it operational. Some agencies may be interested in performing a more detailed investigation of traffic patterns within a sub area, such as the downtown area. The author implemented a subarea focusing methodology within TRANSIMS and also developed an interface that allows the investigator to use a high-fidelity, small-size network efficient traffic operational software package — CORSIM to perform sub area traffic operational analysis with demand and network extracted from applications of TRANSIMS. This methodology will allow TRANSIMS to take advantage of higher fidelity models for sub-network analysis and allow CORSIM to use planning inputs such as individual 24 hour travel activities and trip chains. An evacuation model is also built and applied to Virginia Tech main campus, Blacksburg, VA to evaluate this sub area focusing methodology. / Master of Science

No description available.

The development and characterization of bipolar electrode (BPE) focusing is described. BPE focusing is an electrokinetic equilibrium technique in which charged analytes are focused and locally enriched on an electric field gradient in the presence of a counter-flow. This electric field gradient is formed at the boundary of an ion depletion zone – the direct result of faradaic reactions occurring at the BPE in the presence of an externally applied electric field. Direct measurement of the electric field strength in the ion depletion region shows that the electric field is enhanced in this region and takes on a gradient shape, confirming the results of numerical simulations. Transient electric field measurements with simultaneous monitoring of a focused fluorescent tracer reveal that the field gradient forms rapidly upon application of the external field and remains stable over time with the tracer focused at a local field strength predicted by simple electrokinetic equations. These transient electric field measurements probe the effect of individual experimental parameters on the electric field gradient and the focused band. The results of these studies indicate that a steeper field gradient leads to enhanced concentration enrichment of the analyte. The slope of the gradient is increased with higher concentration of the running buffer and higher applied field strength. The addition of pressure driven flow across the microchannel moves the location of the field gradient and the position of the focused band. Further enhancement of enrichment is achieved through the suppression of Taylor dispersion after coating the microchannel with a non-ionic surfactant. The findings of these studies have motivated the transition of BPE focusing to smaller microchannels. A decrease in microchannel size not only decreases Taylor dispersion, but also provides access to higher buffer concentration and higher applied field strength, both of which enhance enrichment. The result is a three-order-of-magnitude increase in total analyte enrichment at a much higher enrichment rate. Furthermore, a dual channel configuration for BPE focusing is introduced which provides greater control over focusing conditions. Finally, the formation of ion depletion and enrichment zones at a BPE in a microchannel is shown to mimic ion concentration polarization (ICP) at micro-/nano-channel junctions. This is significant because this faradaic ICP provides a model to which traditional ICP can be compared and is achieved in a more easily fabricated device. In summary, the fundamental principles of BPE focusing are described. A greater understanding of the effect of experimental parameters on the focusing process leads to an unprecedented magnitude and rate of enrichment in a simple device architecture. / text

Incomplete data, unknown source-receiver signatures and free-surface reflectivity represent challenges for a successful prediction and subsequent removal of multiples. In this paper, a new method will be represented that tackles these challenges by combining what we know about wavefield (de-)focussing, by weighted convolutions/correlations, and recently developed curvelet-based recovery by sparsity-promoting inversion (CRSI). With this combination, we are able to leverage recent insights from wave physics towards a nonlinear formulation for the multiple-prediction problem that works for incomplete data and without detailed knowledge on the surface effects.

Extensive research on amino acids, and even other biochemical assays usually present in low concentration and volume face challenges using known analytical techniques for analysis of traces amounts. Some limiting factors are the achievable efficiency, sensitivity (resulting from instrument limit of detection and/or experimental methods), volume requirement, and total analysis time. Counterflow electrofocusing techniques combining forces of electrophoresis and bulk flow (pressure driven flow and/or electroosmotic flow) provides a basis for the development of alternative detection techniques geared towards improving peak efficiency, sensitivity and time. The work presented gives a vivid description of recently developed capillary counterflow techniques: gradient elution isotachophoresis (GEITP) using UV detection, GEITP coupled to Capillary Zonal Electrophoresis (GEITP-CZE), temperature gradient focusing (TGF), and temperature gradient denaturing focusing (TGDF). A first demonstration of GEITP using UV detection was applied to enrichment and separation of tyrosine and tryptophan under optimized conditions. Primarily, separation is achieved as the result of the difference in electrophoretic velocity of analytes in a discontinuous buffer system. First, a plug of sample is allowed to preconcentrate (or enrich) between high mobility leading electrolyte (LE) and low mobility trailing electrolyte (TE) under controlled hydrodynamic pressure and continuous injection. This preconcentration is initiated outside the capillary in a conductivity bubble. Although analyte focus according to their electrophoretic velocity, the inclusion of spacer molecule in sample matrix was instrumental in achieving separation with tradeoff between analyte resolution and enrichment. Gradient produced results from reduction in pressure as sample is loaded on column. Separation using this technique is a one step process. A hybrid method marking the first successful coupling of GEITP to CZE with laser induced fluorescence detection was used for separation of six fluorescently labeled amino acids (which formulates the Mars-7). An eleven minute separation was achieved under optimized conditions. A proof-of-concept demonstration of TGF with LIF detection showed focusing and separation of fluorescein and carboxyfluorescein dye molecules, and carboxyfluorescein-labeled glutamate and aspartate. The generation of null focusing points along the thermal separation column (set between 80-20oC) was produced in collaboration with continuous sample injection, discontinuous buffer system and balancing of counterflows (electrophoresis and bulk flow). Preliminary results showed stability in instrument. The TGDF method carried out on a TGF apparatus is a modification to the temperature gradient gel electrophoresis and denaturing gradient gel electrophoresis methods. In principle, TGDF primarily achieves focusing and separation on a thermal separation column (set between 20 to 80 oC) as a result of conformational changes. It is currently being developed for the detection and simultaneous separation of single and double stranded DNA. Preliminary results show enrichment of wildtype and mutant synthetic DNA strands (containing twenty-four base pairs in sequence) in different buffer matrices. / Chemistry

No description available.

Thesis (MSc (Biochemistry))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: This study describes: a) the isolation and purification of horseradish peroxidase isoenzymes from horseradish roots, b) the characterization of various forms and components of the enzyme by cation-exchange and reversed-phase high performance liquid chromatography, c) the preparation of antibodies against horseradish peroxidase isoenzymes, d) immunological studies for the development of an isoenzyme quantification method and e) the formation of an enzyme-melamine conjugate for use in a melamine quantification immunoassay. / AFRIKAANSE OPSOMMING: Hierdie studie beskryf: a) die isolering en suiwering van peperwortel-peroksidase-isoënsieme vanuit die peperwortel, b) die karakterisering van verskillende vorme en komponente van dié ensiem deur katioonuitruilings en omgekeerde-fase HPLC c) die voorbereiding van teenliggaampies vir peperwortel-peroksidase-isoënsieme, d) immunologiese studies vir die ontwikkeling van 'n isoënsiem-kwantifiseringsmetode; en e) die vorming van 'n ensiem-melamien-konjugaat vir gebruik in 'n melamienkwantifiseringsmetode.

Single frame ultrasound B-mode image quality is largely governed by the ability to focus the ultrasound beam over a range in depths both in transmission and reception. By developing a comprehensive understanding of acoustic wave propagation two signal processing methods were identified for solving the transmission problem. We made use of both the impulse response using the classical point spread function (PSF) and the spatial sensitivity function (SSF) which describes the spatial distribution at a particular time. Using the angular spectrum method, an accurate analytical model was developed for the field distribution arising from a finite geometry, apodized and focused, plane piston transducer. While there is a thorough understanding of the radiated field arising from uniformly excited plane piston transducers, the focused equivalent (i.e., one that allows a continuous change in phase over the plane piston surface) is incomplete and assumes the Fresnel approximation. Our model addresses the effects of diffraction and evanescent waves without the use of the Fresnel approximation and is applicable at all near- and far-field locations in a lossless medium. The model was analyzed to identify new insights into wave propagation and compared with the Fresnel approximation and the spherically-focused, concave transducer. The piston transducer model was then extended to an attenuating and dispersive medium. After analysing existing models of power-law frequency dependent attenuation, a causal, spherical wave Green’s function was derived from the Navier-Stokes equation for a classical viscous medium. Modifications to the angular spectrum method were presented and used to analyze the radiated field of a focused, planar piston transducer. Finally, after presenting our signal processing strategy for improving imaging spatial resolution through minimization of the SSF, two signal processing methods were derived and analysed in simulation: a deconvolution technique to remove the effects of the ultrasound excitation wave and suppress additive noise from the received ultrasound signal, and a retrospective transmit focusing method that changed the response from a predefined transmit focus to an arbitrary transmit focal depth. Proof-of-concept simulations were presented using a variable number of scatterers and compared with the traditional matched filtering and envelope detection technique.