X-ray diffraction from protein crystals remains the most reliable way to determine the molecular structure of proteins, and how this structure relates to biological function. However, we still lack the ability to predict solution conditions that support the nucleation and growth of high-quality protein crystals for X-ray diffraction studies. The overall goal of this thesis is two-fold: (a) determine the nucleation behavior and solubilities for lysozyme crystals with two distinct crystal structures (orthorhombic vs. tetragonal) and (b) investigate whether these changes in crystal habit and crystal solubility correlate with any discontinuities in the liquid-liquid phase boundary of lysozyme that occurs under the same solution conditions. We measured lysozyme crystal solubility by nucleating and subsequently dissolving very small lysozyme crystals in highly supersaturated solutions. The presence of crystals in our samples is detected and monitored by measuring the light scattered off the micron-sized crystals. These "turbidity measurements" are repeated across a range of protein concentrations, for pH 4.6 and 5.6, thereby yielding the crystal solubility boundary. Changes in crystal structure are assessed at the end of the experiments by microscopic inspection of the distinct crystal habits. Attractive protein interactions in solution also induce liquid-liquid phase separation. Similar to the crystal solubility measurement, we use the turbidity increase associated with liquid-liquid phase separation to map out this phase boundary. Since both crystal formation and liquid-liquid phase separation are driven by attractive protein interactions, we investigated whether the dramatic changes in crystal solubility associated with different protein crystal structures lead to any discernable “discontinuities” in the liquid-liquid phase boundaries.

This thesis presents an in-depth study into the characterization and enhancement of a metastable neon laser cooled and trapped atomic beam. The apparatus consists of a standard Zeeman slowed atomic beam loaded into a magneto-optical trap and was designed for applications to electron scattering experiments and photoionization. The efficiency of the metastable neon atomic source was investigated to determine the ideal cathode type for maximum metastable production and optimal atomic beam velocity haracteristics. A series of characterization measurements were performed on the MOT, and the trap volume and population were investigated for a range of trapping and slowing laser intensities and detunings, together with the MOT and Zeeman slower magnetic fields. The volume measurements were compared to standard Doppler theory and it was found that the Doppler model inadequately explained the trap behaviour. It was found that the MOT population characteristics were governed by two processes: two-body losses that limit the trap population at high densities, and the efficiency of the atom capture process which limits the operational range of the MOT over the various parameters. The trap temperature was determined to be 1.3mK via a time-of-flight technique. This was nearly twice that predicted by Doppler theory and the lack of agreement once again suggests the inadequacies in the Doppler theory to correctly model the experiment. The application of the MOT to the photoionization cross-section measurement of the (2p53p)3D3 state of neon was investigated. The MOT decay technique was utilized to measure cross-section values of o351 = 2.9+0.2 -0.3 x 10 -18cm2 and o363 = 3.1 +0.3 -0.4 x 10-18cm2 at the wavelengths of 351nm and 363nm respectively. This is an increase in accuracy of around a factor of five from previous measurements and it was found that the results agreed well with the values predicted by current theories.

Ab Initio calculations suggest that partially lithiated layered LixMnO₂ transforms to spinel in a two-stage process. In the first stage, a significant fraction of the Mn and Li ions rapidly occupy tetrahedral sites, forming a metastable intermediate. The second stage involves a more difficult coordinated rearrangement of Mn and Li ions to form spinel. This behavior is contrasted to LixCoO₂. The susceptibility of Mn for migration into the Li layer is found to be controlled by oxidation state which suggests various means of inhibiting the transformation. These strategies could prove useful in the creation of superior Mn based cathode materials. / Singapore-MIT Alliance (SMA)

An atom or ion can change quantum state, usually through emission or absorption of a photon. The photon has the same energy as the energy difference between the states of the transition. The states, or energy levels, of an atom are quantized and light emitted, or absorbed, from the atom is therefore of specific wavelengths, giving spectral lines. The spectrum of an atomic ion is unique and contains information of the structure and energy levels of the ion. The spectrum of an atom can be used as a fingerprint in determinations of the abundance of the element in different objects. This thesis is focused on some weak effects observed by spectroscopy. Although the effects are weak, they turn out to be of great importance. According to quantum mechanics transitions between certain states are not allowed. Here the weak effects open the possibility for transitions. Spectral lines from forbidden transitions are very weak and difficult to observe under ordinary laboratorial conditions, but they are commonly observed from astrophysical objects and can be very useful for diagnostics of astrophysical plasmas. The first reported observation of forbidden lines was from an astrophysical object and at that time supposed to be from new, previous unknown, elements. If all possible decay channels from an energy level are forbidden, the energy level is metastable and has usually a lifetime 10$^8$ times longer than an ordinary excited state. Measurements of such long lifetimes are difficult since the ion need to be confined during the observation time. Confinement of ions can be achieved with a storage device, such as a storage ring or a trap, where the ions are stored without interacting with each other or the surroundings. A laser probing technique has been developed at the storage ring CRYRING, for measurements of lifetimes of metastable states. The technique has now been improved for measurement of longer lifetimes. The technique has also been modified to fit when measuring on negative ions. Results of lifetime measurements are reported and the techniques and methods used are described. Another weak effect is hyperfine interaction, which splits the energy levels of an atom or ion. Hyperfine splitting is very small and usually special spectral techniques are needed to resolve such structure. A laser can, in combination with an electromagnetic radio-frequency field, be used for accurate determination of hyperfine structures in atomic ions. Such measurements are also important for evaluation of astrophysical properties, since hyperfine structure can broaden the spectral lines. An experimental setup for such double resonance measurements has been developed and constructed. Results of experimental measurements are reported and the technique is described.

Rapid solidification experiment on Fe-Cr-Mo-Mn-Si-C alloy was performed to investigate metastable phases formed during the solidification. A wide range of cooling rate was used to analyse the sample from melt spinning technique (~107 K/s) to water quenching method (~102 K/s). A single phase featureless structure was obtaind initially in the melt spinning experiment for 77Fe-8Cr-6Mn-5Si-4C alloy. Reduction of C and addition of Mo led to form a complete featureless structure for 2.85 mm rod for 72.8Fe-8Cr-5Mo-6Mn-5Si-3.2C. Subsequent investigation of influence of Mo, Cr and Mn on the single phase featureless structure concludes that 7.5 mm thick complete featureless phase could be formed at 63.8Fe-15Cr-7Mo-6Mn-5Si-3.2C alloy composition. In a separate attempt, powder samples of 40 μm dia. size complete featureless powders were produced for three slightly different compostions for the same alloy system. Characterisation of the featureless phases reveals that it could be a single phase metastable structure of ε phase or austenitic solid solution with high amount of alloying element dissolved in it. Subsequent heat treatment of this featureless phase of the rod and the powder at different temperatures formed bainitic ferrite with fine carbides dispersed in the austenitic matrix. Hardness values measured on featureless phase found to have influenced by the alloying element specially Mo, Cr and Mn. In an attempet to improve clean melting condition to extend the featureless phase and to form amorphous, an elliptic short arc lamp vaccum furnace was designed with 10 kW lamp power. Around 30 g of iron based alloy system was melted and cast as a 7 mm rod sample in a copper mould. Design details of new mirror and the lamp furnace are presented. In a separate study, influence of the melt temperature on Al-Y and Al-Si alloys were investigated by levitaion casting in a silver mould at around 2000 K/s cooling rate. Plate like structure of Al8Y3 primary phase was observed at low melt temperature with small percentage of peritectic transformation of Al8Y3 and liquid melt into Al9Y2. A pre-dentritic star like crystal of Al3Y was observed in a fine eutectic matrix at very high melt temperature. Amount and number of primary Si crystals formed in a unit area during the solidification increases as the melt temperature increases. / QC 20100805

Das hier vorgestellte Vorhaben hat die Entwicklung eines neuartigen Sensor- und Messtechnikkonzepts zur Erfassung der Maximalwerte mechanischer Belastungen von Bauteilen bestehend aus Kohlenstofffaserverbundwerkstoffen mit polymerer Matrix (CFK) zum Ziel. Dazu wurden Untersuchungen zur Anwendbarkeit der spontanen Magnetisierung durch die martensitische Gefügeumwandlung metastabiler Stähle als möglicher Sensoreffekt durchgeführt. Als ein einfaches passives Sensorverfahren hat die Ausbildung einer spontanen Magnetisierung durch die Gefügeumwandlung ein denkbares Anwendungspotenzial. Es ist keine permanente Energieversorgung des Messsystems erforderlich, der Sensor ist vollständig und ohne Kontakt zur Umgebung im Bauteil einbettbar und eine äquivalente Information der maximalen Last ist unauslöschbar im Sensor eingeprägt. Durch kontakt- und zerstörungsfreie Verfahren kann das Auslesen erfolgen. Um die Eignung des Effekts zu überprüfen, erfolgten verschiedene Untersuchungen. Die Ergebnisse von Zugversuchen, durchgeführt an eingebetteten und nicht eingebetteten Sensorproben, und die Messwerte magnetischer Messungen der Sensormagnetisierung wurden zur Ermittlung einer Abhängigkeit zwischen dem Grad der Belastung und der Änderung der Magnetisierung infolge der martensitischen Transformation korreliert. Mittels metallografischer Untersuchungen sowie durch Röntgenbeugung erfolgte zudem der Vergleich zwischen dem Martensitgehalt und den Messergebnissen zur spontanen Magnetisierung. Der vorliegende Artikel beschreibt die Grundlagen des ausgewählten Sensorprinzips, die durchgeführten Arbeiten und erläutert die Ergebnisse der Untersuchungen.

This thesis is devoted to the deposition of intermetallic thin films by laser ablation deposition (LAD) and their characterization. Pulsed laser ablation and subsequent deposition of the ablated vapours produces films under conditions very far away from equilibrium. Besides the film, which forms directly by quenching the vapour or plasma on substrate, one also obtains under certain conditions micron and sub-micron sized spherical droplets of alloy melt on to the film. The latter travel at very high velocities and impinge on the substrate resulting in a very high rate of heat transfer during solidification from liquid state. Therefore, in this work it was possible to study the microstructure evolution depending on quenching rates of different sized droplets and compare with the extreme case of vapour/plasma quenching. The compositions selected correspond to the intermetallic compounds in Al-Fe, Al-Ni and Ti-Si binary systems. Pre-alloyed targets of the appropriate intermetallic compositions were used for ablation by laser. The deposition system has been designed and built in-house. The characterization is mainly done by transmission electron microscopy (TEM). The study focuses on microstructure and phase evolution within these intermetallic films at room temperature, at elevated temperature and during heating the room temperature deposited films in heating stage inside the TEM.

Le but de ce travail de thèse est de mieux comprendre les mécanismes de déformation à température ambiante dans les alliages de titane bêta-métastable Ti17 et Ti5553. Les microstructures étudiées sont composées de grains bêta transformé, dans lesquels la phase alpha peut précipiter, selon les relations de Burgers, sous la forme de douze variants différents. Une approche multi-échelles est donc préconisée avec trois niveaux représentatifs: macroscopique, mésoscopique (ex-grains bêta), et microscopique (variants alpha et matrice bêta de chaque grain). Différents modèles à champs moyens sont adaptés pour reproduire le comportement mécanique du Ti17 et du Ti5553. Ces modèles impliquent deux transitions d'échelle, et sont basés sur l'homogénéisation des comportements locaux, avec plusieurs manières de représenter les interactions intergranulaires. Les relations entre microstructures et propriétés mécaniques sont également considérées. Les modèles les plus complexes développés dans cette étude vont permettre de simuler l'anisotropie élastique et l'écoulement visqueux de chaque variant alpha (hcp) et de chaque matrice bêta (bcc), en employant la plasticité cristalline avec des écrouissages de type cinématique et isotrope. L'identification des paramètres matériaux est faite à partir d'une vaste base de données expérimentale provenant du projet PROMITI. Pour comprendre le rôle de chaque phase dans le processus de déformation, un calcul EF a également été fait afin de reproduire l'essai de traction sur une très fine éprouvette plate. Dans cette étude, le niveau mésoscopique est explicitement représenté en reprenant fidèlement la géométrie et l'orientation cristallographique de chaque grain bêta transformé. Des comparaisons entre expérience et simulation sont faites à l'échelle macroscopique pour les courbes contrainte - déformation, ainsi qu'au niveau mésoscopique, en considérant les champs de déplacement hors-plan et les champs de déformation.

Collapse in soils occur when a partially unstable, partially saturated open fabric under high enough stress causing a metastable structure with large soil suction, or in the presence of a bonding or cementing agent, is allowed to free access to additional water. Such excess water reduces soil suction and weakens or destroys the bonding, this causing shear failure at the interaggregate or intergranular contacts, consequently, the soil collapses. In this study, the collapsible soils found in the &Ccedil / ayirhan Thermal Power Plant area has been stabilized by using the desulphogypsum, and fly ash obtained from the &Ccedil / ayirhan Thermal Power Plant. An extensive laboratory testing program has been undertaken to provide information on the geotechnical properties of collapsible soil treated by &Ccedil / ayirhan fly ash and desulphogypsum. At the end of the test program, it has been seen that the collapsible soil (compacted) can be stabilized by adding fly ash and desulphogypsum. Although a significant change on the collapse potential was not observed when fly ash and desulphogypsum added samples were compared with compacted sample without stabilization, but there is an increase in unconfined compressive strength values due to stabilization.

A new methodology is developed to calculate density of states of interstellar and atmospheric clusters that takes account of their loosely bound nature and incorporates kinetically important angular momentum constraints explicitly. The method is based on classical phase space integration for the intermonomer modes of the cluster with imposition of the constraints of selected total energy and total angular momentum. It achieves considerable efficiency via essentially analytic evaluation of the momentum space integrals coupled with efficient Monte Carlo sampling of configurations. The derivation for the equation for the density of states is outlined and all steps in the simplification of the accessible momentum space volume are detailed. The method is tested rigorously against an entirely analytic result obtained for the ideal case of a dimer with spherical top fragments and no interaction potential. Interstellar applications of the new approach are presented for (HCN)2 and (CO)2. The new intermononmer density of states has been integrated over metastable states to obtain the intermonomer partition function, which in turn is used to calculate the metastable equilibrium constants for interstellar clusters, which in turn is used tocalculate the second order rate constant of overall dimer formation in the interstellar environment. Atmospheric applications of the new approach are presented for (H2O)2. The new intermonomer density of states is convoluted with the intramonomer density of states to obtain the convoluted density of states. This convoluted density of states is then integrated over total energy and angular momentum to obtain the anharmonic partition function, which in turn is used to calculate the equilibrium constant for atmospheric clusters, which in turn is used to calculate the third order rate constant for overall dimer formation in the atmospheric environment. Kinetic quantities are also calculated with the intermonomer and convoluted density of states for interstellar and atmospheric clusters, respectively. These densities of states are combined with RRKM theory to compute unimolecular dissociation rate constants, which are then averaged with respect to the thermal capture flux distribution to compute average lifetimes as a function of temperature.