No description available.

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. / QC 20101126

We investigate the spatial evolution of an intense laser pulse as it generates high-order harmonics in a long gas cell, filled with 80 torr of helium. A thin foil separates the gas-filled region of the cell from a subsequent evacuated region. The exit plane of the gas cell can be scanned along the laser axis so that the evolution of the laser throughout the focus can be observed (full scanning range of 9 cm). We constructed an apparatus that images the laser radial energy profile as it exits the cell. The high harmonics, odd orders ranging from 45 to 91, are observed at the same time that the laser spot is characterized. Re-absorption of the harmonics within the gas cell restricts the region of harmonic emission to the final centimeter (or less) of the cell. We present the first direct evidence (to our knowledge) of laser filamentation under conditions ideal for high-order harmonic generation. The 30 fs, 4 mJ, laser pulses were observed to undergo double focusing within the gas cell, with about 4 cm separating the two foci. The region with best harmonic emission occurs midway between the two foci. The radial profile of the laser focus, 150-200 microns in diameter, evolves from a Gaussian-like profile to a more square-top profile as it propagates over several centimeters. The filamentation phenomenon as well as the brightness of the harmonics improves when an aperture is partially closed on the laser beam before reaching the focusing mirror. A spectral sampling of the imaged laser focus revealed a 4 nm blue-shift associated with the generation of plasma in the gas cell. The blue-shifting occurs primarily in the center of the laser beam and less at the wider radii. The initial laser pulse had a spectrum centered at 800 nm with a 35 nm bandwidth. The energy associated with each of the observed 26 harmonic beams was found to be approximately 1 nJ, yielding a conversion efficiency of approximately 2e−7.

Electric field gradient focusing (EFGF) utilizes a hydrodynamic flow and an electric field gradient to focus and concentrate charged analytes and order them in a separation channel according to electrophoretic mobility. Elution can be achieved by decreasing the applied voltage or increasing the hydrodynamic flow. EFGF has the advantages of concentrating a large volume (100 micro-L) of target proteins without significant band broadening and simultaneously removing unwanted components from the sample. Two types of EFGF devices have been investigated to concentrate and separate proteins: a fiber-based EFGF device and a hydrogel-based EFGF device. Using fiber-based EFGF with UV detection, a concentration factor as high as 15,000 and a concentration limit of detection as low as 30 pM were achieved using bovine serum albumin as a model protein. I also demonstrated the potential of using fiber-based EFGF for quantitative protein analysis. Simultaneous desalting and protein concentration as well as online concentration of ferritin and simultaneous removal of albumin from a sample matrix were also performed using this fiber-based EFGF system. In the approach of utilizing hydrogel-based EFGF, online concentration of amyloglucosidase indicated a concentration limit of detection of approximately 20 ng/mL (200 pM) from a sample volume of 100 micro-L. Both voltage-controlled and flow-controlled elution methods were demonstrated using a 3-component protein mixture. Concentration of human α1-acid glycoprotein with simultaneous removal of human serum albumin was also described. A tandem EFGF system, which integrates fiber-based and hydrogel-based EFGF sections, was also investigated to selectively concentrate and separate proteins in a mixture. By carefully controlling the voltages applied to both sections, charged analytes with high mobilities were trapped in the fiber-based section, analytes with intermediate mobilities in the hydrogel-based section, and analytes with low mobilities not at all. A 3-way switching valve was incorporated in the system to purge the analytes with high mobilities periodically. Selective concentration and separation of myoglobin from a mixture were performed using the tandem EFGF system. Based on the experimental results described in this dissertation, EFGF shows potential for selective isolation, concentration, and quantitation of trace analytes such as proteins in biomedical samples.

No description available.

The passive particle separation method of elasto-inertial microfluidics have greatpotential in the field of physics, biology and chemistry. The objective of thisdegree project was to understand particle behavior in curved microchannels fornon-Newtonian fluids. This in order to optimize the separation of 1 µm and 2 µmparticles where the end goal is to create an efficient sample preparation method fordiagnosing sepsis. Fluorescent beads were spiked into PEO solutions of differentconcentrations and used in microfluidic PDMS-glass chips with various radii toexamine the influence of curvature and elasticity as well as the flow rate. Theresult indicated an independence of both curvature and elasticity. Reynoldsnumber and Dean number are dependent on the flow rate which results in atrade-off between a high and low flow rate. A low Reynolds number is not enoughto create Dean vortices that can be used to separate particles while a highReynolds number creates strong Dean vortices that can obstruct the focusing. Later, microfluidic silicon-glass chips were used to separate 1 µm and 2 µm beads.The 2 µm particles were able to focus in two different PEO concentrations whereasthe 1 µm particles did not have time to focus entirely. This makes it possible toseparate 2 µm particles along with some 1 µm particles towards one outlet whileleaving another outlet with only 1 µm particles. This is a promising start butfurther optimization is required before being applied to real bacteria separation. / Den passiva partikelseparationsmetoden elastisk tröghetsmikrofluidik har storapotential inom fysik, biologi och kemi. Målet med examensarbetet var att förståpartiklars förflyttning i krökta mikrokanaler för icke-newtonska vätskor. Dettagjordes för att optimera separering av 1 µm och 2 µm partiklar där slutmålet är attskapa en effektiv provberedningsmetod för att diagnostisera sepsis. Fluorescerandepartiklar tillsatta i PEO-l¨osningar av olika koncentrationer anv¨andes imikrofluidiska PDMS-glas chip med olika radier för att undersöka inverkan avkrökning och elasticitet samt flödeshastigheten. Resultatet indikerade ettoberoende av både krökning och elasticitet. Reynolds nummer och Deans nummerär beroende av flödeshastigheten vilket resulterar i en avvägning mellan en hög ochlåg flödeshastighet. Ett lågt Reynolds nummer är inte tillräckligt för att skapaDean virvlar vilket kan utnyttjas för att separera partiklar medan ett högtReynolds nummer framkallar starka Dean virvlar vilket kan hindra fokuseringen. Sedan användes mikrofluidiska kisel-glas chip för att separera 1 µm and 2 µmpartiklar. 2 µm partiklarna lyckades fokusera i två olika PEO-koncentrationermedan partiklarna av 1 µm inte fokuserade fullt ut. Detta gör det möjligt attseparera 2 µm partiklar tillsammans med ett antal 1 µm partiklar mot ett utloppsamtidigt som ett annat utlopp endast innehåller 1 µm partiklar. Det är enlovande start men ytterligare optimering krävs innan det kan tillämpas på faktiskbakterieseparation.

The innovative technology behind production of strong biofilaments involves the process of spinning filaments from nanoparticles extracted from wood. These nanoparticles are called cellulose nanofibrils (CNFs). The spun filaments can have high mechanical properties, rivaling many other plant based materials, and could be an environmentally friendly replacement for many materials in the future such as fabrics and composites. Before mass production might be possible, the optimal dispersion properties must be determined for the intended use, with regard to concentration, method of oxidation (TEMPO-oxidation or carboxymethylation) and pretreatment through sonication and centrifugation. In this bachelor’s thesis attributes of spun filaments were investigated in order to find a correlation between mechanical properties and the effects of concentration, method of oxidation as well as sonication and centrifugation of the dispersions. The mechanical properties were also compared to the fibrils’ ability to entangle and align during flow-focusing. A variety of analytical methods: flow-stop, tensile testing, scanning electron microscopy (SEM) and wide angle X-ray scattering (WAXS) were implemented for the dispersions and filaments. The results from this study show that flow-stop analysis could be used to determine which CNF dispersions are spinnable and which are non-spinnable, along with which spinnable dispersion would yield the strongest filament. It was also concluded that crystallinity of fibrils affects the mechanical properties of filaments and that TCNFs are generally more crystalline than CMCs. Pretreatment through sonication and centrifugation seems to have a negative impact on spinnability and sonication in combination with low concentration seems to lead to non-spinnable conditions. On the other hand, sonicated dispersions seem to yield a greater number of samples without aggregates than non-sonicated ones. Aggregates, however, seem to only affect ultimate stress out of the measured mechanical properties. Furthermore, concentration and viscosity affect spinnability and CMC dispersions seem to yield thicker filaments than TCNF dispersions. However, due to lack of statistically validated data any definitive conclusions could not be drawn.

Electrospray is an atomization method subject to intense study recently due to its monodispersity and the wide size range of droplets it can produce, from nanometers to hundreds of micrometers. This thesis focuses on the numerical and theoretical modeling of the interaction of charged droplets from the single and multiplexed electrospray. We studied two typical scenarios: large area film depositions using multiplexed electrospray and fine pattern printings assisted by linear electrostatic quadrupole focusing. Due to the high computation power requirement in the unsteady n-body problem, graphical processing unit (GPU) which delivers 10 Tera flops in computation power is used to dramatically speed up the numerical simulation both efficiently and with low cost. For large area film deposition, both the spray profile and deposition number density are studied for different arrangements of electrospray and electrodes. Multiplexed electrospray with hexagonal nozzle configuration can not give us uniform deposition though it has the highest packing density. Uniform film deposition with variation < 5% in thickness was observed with the linear nozzle configuration combined with relative motion between ES source and deposition substrate. For fine pattern printing, linear quadrupole is used to focus the droplets in the radial direction while maintaining a constant driving field at the axial direction. Simulation shows that the linear quadrupole can focus the droplets to a resolution of a few nanometers quickly when the interdroplet separation is larger than a certain value. Resolution began to deteriorate drastically when the inter-droplet separation is smaller than that value. This study will shed light on using electrospray as a scalable nanomanufacturing approach.

The goal of this project is to eliminate electroosmotic flow (EOF) in a microfluidic chip. EOF is a naturally occurring phenomenon at the fluid-surface interface in microfluidic chips when an electric field is applied across the fluid. When isoelectric focusing (IEF) is carried out to separate proteins based on their surface charge, the analytes must remain in the separation chamber, and not migrate to adjacent features in the microfluidic chip, which happens with EOF. For this project, a microfluidic chip was designed and commissioned to be photolithographically transferred onto a Si wafer. A PDMS component was then casted on the Si wafer and plasma bonded to a glass substrate. This chip was initially designed to carry out continuous IEF, and the focus of the project was shifted to the analysis of eliminating EOF in a microfluidic chamber. Per previous research test methods, methylcellulose will be used to analyze the phenomenon of electroosmotic flow in the chamber. A COMSOL model is used a theoretical basis of comparison when analyzing the flow velocities of the treated versus untreated microfluidic chips. The purpose of this project is to use the research performed in on this chip as a precursor to future analyses of continuous IEF on microfluidic chips in the Cal Poly Microfluidics group.

Sociala medieplattformar har blivit en integrerad del av våra dagliga liv och kopplar samman miljarder människor världen över för kommunikation, informationsspridning och underhållning. Trots att de erbjuder många fördelar har sociala medier också kopplats till negativa effekter på mental hälsa, välbefinnande och akademisk prestation. Syftet med denna forskning är att undersöka sambandet mellan användningen av sociala medier och uppmärksamhetsfokusering, samt sambandet mellan uppmärksamhetsskiftning och uppmärksamhetsfokusering.Genom att använda en kvantitativ forskningsmetod genomfördes en webbaserad enkät bland svenska universitetsstudenter. Enkäten bestod av 28 noggrant formulerade frågor om användning av sociala medier, uppmärksamhetsfokusering och uppmärksamhetsskiftning. Multipel linjär regression användes för att identifiera signifikanta prediktorer och få insikter i datasetets relationer.Resultaten bekräftar en negativ korrelation mellan frekvent användning av sociala medier och uppmärksamhetsfokusering, vilket tyder på att långvarigt engagemang på dessa plattformar påverkar förmågan att bibehålla uppmärksamhet. Dock fanns ingen signifikant relation mellan uppmärksamhetsskiftning och uppmärksamhetsfokus, vilket antyder att förmågan att växla uppmärksamhet mellan uppgifter inte nödvändigtvis påverkar förmågan att fokusera vid behov. De nämnda resultaten ovan gäller oavsett syftet eller sammanhanget för användningen av sociala medier och ger antydningar om de skadliga effekterna på uppmärksamhetsfokusering hos olika studentprofiler. Den allmängiltighet som dessa effekter visar belyser behovet av ytterligare forskning för att förstå uppmärksamhetens dynamik i samband med sociala medier.Rekommendationer för framtida studier inkluderar att utvidga urvalsstorleken för att förbättra validiteten och generaliserbarheten av resultaten. Dessutom bör man undersöka de underliggande mekanismerna och genomföra longitudinella studier för att få en mer heltäckande förståelse av de långsiktiga effekterna av sociala medier på uppmärksamheten. Sådan forskning kan bidra till utvecklingen av effektiva strategier och interventioner för att minska de negativa konsekvenserna av överdriven användning av sociala medier på uppmärksamheten hos universitetsstudenter.