Compaction of polymer powders and polymer-based nanocomposites by uniaxial high-velocity cold compaction (HVC), by high-energy ball milling (HEBM) and using a novel technique, relaxation assists, was investigated with a focus on the process parameters, the compactibility characteristics, surface morphology and friction. The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain the pull-out phenomenon, springback gradient, delay time, relative time of the pressure wave, and stick-slip phenomenon during the compaction process. Experimental results for different compaction profiles, different particle size distributions and different milling system for polymer-based nanocomposite are presented, showing the effect of varying the process parameters on the compacted material; the compactibility in the compacted bed, the uniformity of the compacted surface, the pull-out phenomenon, the springback gradient, the stick-slip phenomenon and the homogeneity of the dispersions of nanoparticles in the polymer powders in the solid state. It was found that the high-velocity compaction process is an interruption process and that the opposite velocity and pressure loss during the compaction process have a major influence on the quality of the compacted material. The relaxation assist device is a novel technique that has been successfully developed to improve the compaction process. The relaxation assists are parts of the piston and they are regarded as projectile supports. They are constructed of the same material as the piston, and the diameters are the same but the lengths are different. The relaxation assist device leads to an improvement in the compaction of powders, polymer powders and polymer-based nanocomposites by giving a more homogeneous opposite velocity and a better locking of the powder bed in the compacted form during the compaction process with less change in dimensions in the case of both homogeneous and heterogeneous materials. If the movement of the particles is restricted the powder bed attains a higher density and the total elastic springback is minimized. In addition, there is a more homogeneous dispersion of nanoparticles in the case of a heterogeneous material. A much better transfer of the pressure through the powder bed and a smaller loss of pressure lead to a more homogenous stick-slip of the particles and a higher sliding coefficient due to the overall friction during the compaction process. / QC 20100630

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (p. 161-167).

Today, it is well known that galaxies like the Milky Way consist not only of stars but also of gas and dust. The galactic halo, a sphere of gas that surrounds the stellar disk of a galaxy, is especially interesting. It provides a wealth of information about in and outflowing gaseous material towards and away from galaxies and their hierarchical evolution. For the Milky Way, the so-called high-velocity clouds (HVCs), fast moving neutral gas complexes in the halo that can be traced by absorption-line measurements, are believed to play a crucial role in the overall matter cycle in our Galaxy. Over the last decades, the properties of these halo structures and their connection to the local circumgalactic and intergalactic medium (CGM and IGM, respectively) have been investigated in great detail by many different groups. So far it remains unclear, however, to what extent the results of these studies can be transferred to other galaxies in the local Universe. In this thesis, we study the absorption properties of Galactic HVCs and compare the HVC absorption characteristics with those of intervening QSO absorption-line systems at low redshift. The goal of this project is to improve our understanding of the spatial extent and physical conditions of gaseous galaxy halos in the local Universe. In the first part of the thesis we use HST /STIS ultraviolet spectra of more than 40 extragalactic background sources to statistically analyze the absorption properties of the HVCs in the Galactic halo. We determine fundamental absorption line parameters including covering fractions of different weakly/intermediately/highly ionized metals with a particular focus on SiII and MgII. Due to the similarity in the ionization properties of SiII and MgII, we are able to estimate the contribution of HVC-like halo structures to the cross section of intervening strong MgII absorbers at z = 0. Our study implies that only the most massive HVCs would be regarded as strong MgII absorbers, if the Milky Way halo would be seen as a QSO absorption line system from an exterior vantage point. Combining the observed absorption-cross section of Galactic HVCs with the well-known number density of intervening strong MgII absorbers at z = 0, we conclude that the contribution of infalling gas clouds (i.e., HVC analogs) in the halos of Milky Way-type galaxies to the cross section of strong MgII absorbers is 34%. This result indicates that only about one third of the strong MgII absorption can be associated with HVC analogs around other galaxies, while the majority of the strong MgII systems possibly is related to galaxy outflows and winds. The second part of this thesis focuses on the properties of intervening metal absorbers at low redshift. The analysis of the frequency and physical conditions of intervening metal systems in QSO spectra and their relation to nearby galaxies offers new insights into the typical conditions of gaseous galaxy halos. One major aspect in our study was to regard intervening metal systems as possible HVC analogs. We perform a detailed analysis of absorption line properties and line statistics for 57 metal absorbers along 78 QSO sightlines using newly-obtained ultraviolet spectra obtained with HST /COS. We find clear evidence for bimodal distribution in the HI column density in the absorbers, a trend that we interpret as sign for two different classes of absorption systems (with HVC analogs at the high-column density end). With the help of the strong transitions of SiII λ1260, SiIII λ1206, and CIII λ977 we have set up Cloudy photoionization models to estimate the local ionization conditions, gas densities, and metallicities. We find that the intervening absorption systems studied by us have, on average, similar physical conditions as Galactic HVC absorbers, providing evidence that many of them represent HVC analogs in the vicinity of other galaxies. We therefore determine typical halo sizes for SiII, SiIII, and CIII for L = 0.01L∗ and L = 0.05L∗ galaxies. Based on the covering fractions of the different ions in the Galactic halo, we find that, for example, the typical halo size for SiIII is ∼ 160 kpc for L = 0.05L∗ galaxies. We test the plausibility of this result by searching for known galaxies close to the QSO sightlines and at similar redshifts as the absorbers. We find that more than 34% of the measured SiIII absorbers have galaxies associated with them, with the majority of the absorbers indeed being at impact parameters ρ ≤160 kpc. / Galaxien bestehen nicht nur aus Planeten und Sternen, sondern sind u.a. auch von einer Hülle aus Gas und Staub, dem Halo, umgeben. Dieser Halo spielt für die Entwicklung der Galaxie eine zentrale Rolle, da er mit der galaktischen Scheibe wechselwirken kann. Für das Verständnis des galaktischen Materiekreislaufs ist es daher entscheidend, die Prozesse und Vorgänge sowie das Zusammenspiel der verschiedenen Gasphasen in diesem Übergangsbereich zum intergalaktischen Medium charakterisieren und verstehen zu können. In der vorliegenden Arbeit werden lokale Phänomene, die sogenannten Hochgeschwindigkeitswolken (HVCs), im Halo der Milchstraße mit Hilfe des Hubble-Weltraumteleskops analysiert und ausgewertet. Im Gegensatz zu dem normalen Halo Gas bewegen sich diese HVCs mit ungewöhnlich hohen Geschwindigkeiten durch die ̈ äußeren Bereiche der Milchstraße. Sie passen daher nicht in das Galaktische Ge- schwindigkeitsmodell und stellen eine eigene, wichtige Klasse von Objekten dar, welche mit der Galaxie wechselwirken und diese beeinflussen. Für die Analyse dieser HVCs werden mehr als 40 Spektren von extragalaktischen Hintergrundquellen statistisch untersucht, um u.a. den Bedeckungsanteil von verschiedenen niedrig-/mittel- und hochionisierten Metallen zu ermitteln. Wegen der Ähnlichkeit der Ionisationsparameter von einfach ionisiertem Silizium, SiII, und einfach ionisiertem Magnesium, MgII, ist es möglich, den Beitrag von HVCs zum Wirkungsquerschnitt von starken MgII Absorbern im lokalen Universum zu bestimmen. Es stellt sich heraus, dass, würde man von außen auf die Milchstraße schauen, Galaktische HVCs etwa 52 % zum totalen Wirkungsquerschnitt von starken MgII Absorptionssystemen in der Milchstraße beitragen. Weiterhin ergibt sich, dass nur etwa ein Drittel der starken MgII Absorptionssysteme in der Umgebung von Milchstraßen-ähnlichen Galaxien als HVC Gegenstücke identifziert werden kann. Betrachtet man die große Anzahl an bekannten MgII Absorptionssystemen folgt daraus, dass das HVC-Phänomen nicht alleine auf unsere Galaxie beschränkt ist, sondern im Gegenteil, weit verbreitet zu sein scheint. Weiterhin werden die Eigenschaften von Metallsystemen bei niedriger Rotverschiebung in Quasarspektren analysiert. Die Suche nach extragalaktischen Metallsystemen in einer Vielzahl von Spektren und deren statistische Auswertung bezogen auf ihre Ursprungsgalaxien ermöglicht es, neue Erkenntnisse über die typische Struktur von Halos Milchstraßen-ähnlicher Galaxien zu erlangen. Eine der Hauptfragestellungen ist die Identifizierung von entfernten Metallsystemen als HVC-Analoga. Dazu wurden weitere Quasarspektren des Hubble-Teleskops ausgewertet und mit den Ergebnissen über Galaktische HVCs verglichen. Es zeigt sich hierbei, dass z.B. in der Säulendichteverteilung von neutralem Wasserstoff eine deutliche zweikomponentige Struktur zu erkennen ist. Diese könnte das Resultat von zwei verschiedenen Absorber Populationen sein, wobei eine HVC-ähnliche Eigenschaften aufweist. Diese Absorptionssysteme besitzen im Mittel sehr ähnliche Eigenschaften wie Galaktische Absorber, z.B. in Bezug auf die Eigenschaften des Gases oder dessen Zusammensetzung. Das impliziert u.a., dass sich auch dazugehörige Galaxien innerhalb eines bestimmten Abstandes um diese Absorber befinden sollten. Diese Vermutung wird anhand der Daten exemplarisch für zweichfach ionisiertes Silizium, SiII, untersucht. Es stellt sich heraus, dass sich in mehr als 34 % der Fälle zugehörige Galaxien bei SiIII Absorbern befinden, wobei die Mehrheit sogar innerhalb des von uns ermittelten mittleren Detektionsradius von 160 kpc zu finden ist. Allgemein können wir viele Hinweise darauf finden, dass das HVC-Phänomen nicht nur auf die Milchstraße beschränkt, sondern weit verbreitet ist. Zusätzlich scheinen Metallsysteme in Quasarspektren gute Indikatoren für HVC-Analoga in der Umgebung von anderen entfernten Galaxien zu sein.

The main aim of this project is to model the effects of varied injection parameters on the gas dynamics and droplet dynamics of the HVSFS and SP- HVOFS processes for improving the droplet breakup and evaporation to enhance the nanoparticles heating and deposition efficiency. Thermal spraying processes are widely used to generate thermal-, corrosion-, and wear-resistant layers over the machine parts, to increase the durability of the equipment under severe environmental conditions. The liquid feedstock is used to achieve nanostructured coatings. It is used either in the form of a suspension or a solution precursor. The suspension is a mixture of solid nanoparticles suspended in a liquid medium consisting, for instance, of water, ethanol, or isopropanol. This dispersion mechanism in a liquid carrier provides adequate flowability to the nanoparticles, which cannot be handled by conventional gas- based feeding systems, whereas the solution precursor is mixed at the molecular level; hence, more uniform phase composition and properties are expected in the sprayed coatings as compared to the suspension and conventional powder spraying. Firstly, experiments are conducted to analyse the effects of different precursor concentrations, solvent types and injection nozzles on the size and morphology of synthesized nanoparticles. The results indicate that the particle size increased with increasing precursor concentration due to the variations in the physical properties of the mixture solution. The higher precursor concentrations had an adverse effect on the droplet atomization and evaporation process that led to bigger size particle formation. The use of aqueous solvent has some limits and with higher precursor concentration the surface tension increases that resulted in the reduction of droplets’ disintegration, and thus bigger size precursor droplets generate larger nanoparticles. A mixture of aqueous-organic solvents and pure organic precursors are preferred to improve the process efficiency of the nanoparticles size and morphology. Furthermore, the nanoparticles size can be controlled by using liquid feedstock atomization before injecting into the HVOF torch. A new effervescent injection nozzle is designed and compared to different types of existing injection nozzles, to see the variations in the droplet disintegration, and its effects on the performance of the HVOF torch processes. It is detected that the atomization would result in smaller size particles with homogeneous morphology. In a numerical study, different droplet injection types are analysed to see their effects on the gas and droplet dynamics inside the HVOF torch. The group-type injection (GTI) and effervescent-type atomization (ETI) are used effectively to overcome the heat losses and delays in the droplet evaporation. These approaches reduce the thermal and kinetic energy losses in the suspension-fed-HVOF torch, thereby improving the coating formation. The effects of using multicomponent water-ethanol mixture injection in the HVOF torch are also modelled, and its impact on the droplet breakup and evaporation are studied. The organic solvents have a low heat of vaporization and surface tension, and can effectively be used in the HVOF spraying process over the water-based solvents. Furthermore, nanoparticles are suspended in the liquid feedstock and injected into the HVOF torch. The effect of increasing nanoparticles’ concentration in the feedstock and its consequence on the gas dynamics, droplet breakup and evaporation are analysed. The augmentation in the nanoparticles loading in the suspension droplets can decrease the droplet breakup and evaporation rate because the required heat of vaporization increases significantly. Moreover, the size of injection droplet affects the droplet fragmentation process; bigger sized droplets observed a delay in their evaporation that resulted in coating porosity. The results suggest that smaller droplet sizes are preferred in coating applications involving a higher concentration of nanoparticles with high melting point. Further, the gas flow rates (GFRs) are regulated to control the droplet dispersion, atomization and evaporation inside the solution precursor fed-HVOF torch. The size of the droplet diameter is decreased by an increment in the GFR, as higher combustion rates increase the combustion flame enthalpy and kinetic energy. Moreover, the increase in the oxygen/fuel flow rates dilutes the injected precursor. It reduces ZrO2 concentration in the process and decreases the rate of particle collision; as a result, non-agglomerated nanoparticles can be obtained.

Aircraft disasters during take-off and landing by the impact of foreign object debris (FOD) have always been an important issue. When the wing is lifted, its upper and bottom surfaces are subjected to compressive and tensile stresses, respectively. The bottom surface of the aircraft wing is vulnerable due to the threat of runway debris, which may travel at high speed, leading to the catastrophic failure of structures under tension. This thesis studies the ballistic performance of a structural panel subjected to projectile impact when the influence of in-plane pretension is considered. An experimental program was proposed to obtain the laboratory testing results where a special rig was designed to apply pretension to the panel as it is being hit by a projectile launched from a gas gun at velocities between 60 to 160 m/s. Instrumentation was used to record impact and residual velocities at different stages of the impact process. The panel was supported on opposing sides in one direction with two free sides in the other direction. Two target materials related to aircraft structure were considered, i.e., aluminium alloy, 2014-T6 and carbon fiber reinforced plastic (CFRP). Two projectile nose shapes - including flat and hemisphere - were used to account for the influence of debris on the ballistic performance of the target. Target materials were fully characterized in the experimental program. Finite element (FE) models were established and validated, and were used to simulate the response and damage of the panels in the experiments when the influence of pretension is considered. The damage of aluminium alloy, 2014-T6 was modeled using shear failure criterion with damage evolution. For CFRP, the in-plane damage initiation was modeled using Hashin’s damage criterion with damage evolution in terms of fracture energy. Parametric studies were done for both aluminium alloy 2014-T6 and CFRP panels with various pretensions of up to 50% of the material ultimate strength. It has been shown that the pretension has more profound effect on the ballistic behavior of the CFRP panel in comparison with its influence on the ballistic behavior of aluminium alloy panel. The simplified analyses and the numerical modeling reflect the physical nature of the impact response and damage of aluminium alloy and CFRP target panels. Hashin’s damage model for CFRP needs to be extended from in-plane to out-of-plane in order to include shear failure, which may happen for the flat nose projectile impact.

京都大学 / 0048 / 新制・課程博士 / 博士(人間健康科学) / 甲第17981号 / 人健博第10号 / 新制||人健||1(附属図書館) / 80825 / 京都大学大学院医学研究科人間健康科学系専攻 / (主査)教授 坪山 直生, 教授 椎名 毅, 教授 松田 秀一 / 学位規則第4条第1項該当 / Doctor of Human Health Sciences / Kyoto University / DFAM

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Image-charge detection is an analytical technique in which a highly-charged particle is detected by the magnitude of the image current that it generates in a detecting electrode. This current is represented as a voltage between the charged particle and the sensing electrode. It is a single particle detection method, ideal for the analysis of large, variable mass particles such as biological cells. Some of the physical properties of Bacillus subtilis spores were explored using different applications of image-charge detection. B. subtilis is a gram-negative spore-forming bacteria that has been shown to exhibit extremophile behavior. The particular extremophile behavior that was investigated in this study is the resistance to extreme mechanical stress. The effects of high-velocity impacts upon these spores were studied using image-charge detection. The elastic properties of these spores as well as spore survivability to high-velocity impacts were investigated. Spores were shown to survive impacts at velocities up to 299 ± 28 m/s. The average kinetic energy loss experienced by impacting spores, regardless of velocity at impact, was between 71 and 72%. Both conventional and novel image-charge detection techniques were used for these studies. The novel version of a charge detector that was demonstrated was fabricated using patterned metal electrodes on printed circuit boards. The simplicity and versatility of this method was demonstrated with a multi-stage charge detector, a unique bouncing detector, and charge-detection mass spectrometry detector which is capable of measuring the absolute mass of a single highly-charged particle.

The identification and characterization of molecular biomarkers using mass spectrometry on an orbiting or fly-by spacecraft is one of the preferred analytical techniques in the search for life beyond the Earth. However, analysis is complicated by unwanted molecular dissociation occurring when sampled native molecules impact the instrument at high velocity. The mechanisms of chemical changes produced in high velocity impacts have been studied experimentally in some cases; however, there are significant experimental limitations to these techniques. Here I present the design, construction, and testing of a new experimental technique to produce high velocity molecular and microparticle collisions under a controlled lab setting using a high-speed spinning rotor. Chapter 1 of this manuscript gives a scientific review of the astrobiological importance of this project for future and current space missions as well as describing previous techniques used to produced hypervelocity impacts and their limitations. Chapter 2 presents the design, construction, calibration, and preliminary experiments of the new technique involving the high-speed rotor. Chapter 3 describes the fabrication of a molecular beam system from the ground up to be coupled with the high-speed rotor. Chapter 4, describes future project directions and presents future experiments using the rotor as a stand-alone instrument. Lastly, the appendix contains the standard operation procedures and design notes regarding the operation of these two instruments.