Searching for new ferroelectrics and multiferroics : a user’s point of view

A perspective on computational studies of ferroelectrics and multiferroics is given that emphasises what has yet to be done, along with some subtleties in previously studied systems. Beginning with the extensive data-mining studies of Abrahams and more recently, Rabe, a survey is given of magnetostrictive effects in antiferromagnetic antiferroelectrics (after Toledano and Toledano), which has an nonmagnetic analogy in the antiferroelectric phase of tris-sarcosine calcium chloride and a reminder of the unusual spin–phonon coupling of Holden et al. in systems such as KCoF3 and EuTiO3. Attention is also paid to field-temperature phase diagrams, finite non-periodic boundary conditions, and processing-dependent structures.Publisher PDFPeer reviewe

Characterization of cermet fuel for nuclear thermal propulsion (NTP)

“A manned flight to Mars is met with many technical challenges, not the least of which is the development of propulsion technology capable of moving a transit vehicle from Earth orbit to Mars orbit. NASA is investigating Nuclear Thermal Propulsion (NTP) as a way of reducing flight time and providing the option for a mid-mission abort. NTP, which uses a high temperature nuclear reactor to heat a propellant, requires advanced fuel materials capable of withstanding temperatures well in excess of 2000 K. Among the fuel options are ceramic metal (cermet) composites composed of refractory metals and Ultra-High Temperature Ceramics (UHTCs). The mechanical and thermal properties of MoW-HfN, a surrogate cermet for MoW-UN, were characterized over a wide range of elevated temperatures. Thermal diffusivity, the coefficient of thermal expansion (CTE), elastic modulus, and heat capacity were measured. Optical and scanning electron microscopy (SEM) were performed to characterize the microstructure and draw structure-property correlations. The thermal diffusivity was obtained though the laser flash method. Values ranged from about 0.18 cm2/s at room temperature and decreased down to 0.15 cm2/s at 1800 °C. The CTE was measured using push rod dilatometry up to 1600 °C, giving average values from 6.0-9.0×10-6 K-1. Four-point bend tests were conducted from 25-1600 °C revealing systematic strengthening with temperature up to about 1400 °C where strength began to decrease, likely due to the increased ductility of the MoW matrix. A scientific rationalization of the effective material properties is made using the rule-of-mixtures and other effective properties models.”--Abstract, page iii

In the world but not of the world: A church\u27s relation to its environment

Research in general and inductive research in particular often begins from an unfocused curiosity. From this perplexity, emerges the problem of research, the collecting of relevant data, and the drawing of theoretical inferences from said data. The current research enterprise includes these major problems but is, in many respects, different. That is to say, the execution is different from that which is found in traditional patterns of investigation

Characterisation of terrestrial weathering products in ordinary and CM carbonaceous chondrites

Research investigating the terrestrial weathering experienced by ordinary and CM chondrites at high spatial resolution is sparse, with most published work using either bulk mineralogical or chemical analysis techniques. With asteroid sample return missions, Hayabusa 2 and OSIRIS-REx expected to return samples in near future, understanding the effects of terrestrial contamination and weathering in fine detail is of paramount importance. The research presented here sets out to investigate terrestrial weathering by analysing the alteration products found around Fe,Ni metal grains by coupled chemical and mineralogical analysis for the first time. Analysis is conducted using a suite of high spatial resolution imaging and spectroscopic techniques including EDS spectroscopy and Raman spectroscopy, an approach with very limited previous use in this field. Initially characterisation of the effects of terrestrial weathering on ordinary chondrites, which should have only experienced significant aqueous alteration in the terrestrial environment, is conducted. The effects of weathering in three climates (the Antarctic, Sahara and Western Australia) are investigated to compare the intensity of alteration between typical find environments. The results of ordinary chondrite analysis reveal Cl-bearing akaganeite is the first terrestrial alteration product to form, followed by goethite and a poorly crystallised hydrated iron III oxide or oxyhydroxide. Analysis also reveals that terrestrial weathering was least intense in cold desert environments (Antarctica) and most intense in semi-arid environments (Western Australia). Having characterised the terrestrial weathering products which form around Fe,Ni metal the effects of terrestrial weathering on CM chondrites, which have experienced significant aqueous alteration both terrestrially and on their parent bodies, is investigated. Analysis of the weathering products in CM chondrites revealed the terrestrial alteration products akaganeite and goethite eroding/replacing parent body alteration products tochilinite and magnetite. The work presented here highlights the need for high resolution, chemical and mineralogical analysis of the alteration products found in ordinary and CM chondrites in order to prevent misinterpretation of terrestrially derived alteration products as evidence of parent body alteration

Conodont biostratigraphy of the Crawford Group, Southern Uplands, Scotland

Extensive new conodont collections from the Crawford Group, the oldest succession in the Southern Uplands of Scotland, support the previously documented biostratigraphical ages for the included formations. The Raven Gill Formation is lower Whitlandian, Arenig (comparable in age to the Dounans Limestone in the Highland Border Complex) and the Kirkton Formation is latest Llandeilian-Aurelucian, Llanvirn to Caradoc in age. It is concluded that there is a significant stratigraphical gap within the Crawford Group. The restricted and probably fault-bounded nature of the Raven Gill outcrops suggests that these may represent olistoliths within a mélange of Llandeilian-Aurelucian age. The chert-bearing succession of the Northern Belt of the Southern Uplands thus represents the juxtaposed sedimentary records of two entirely separate basins – the oldest pre-dates the Grampian assembly of the Laurentian margin, and the younger, the Northern Belt Basin sensu stricto, entirely post-dates this event

On the host galaxies of quasars

I present the results of three distinct, but inter-connected studies of the nature and evolution of the host galaxies of quasars. These three are: i) An HST V-band study of a sample of 17 quasars at z ≈ 0.4, with absolute magnitudes in the range -24 ≥ Mv ≥ -28; ii) An HST rest-frame U-band study of matched subsamples of radio-loud and radio-quiet quasars at z ≈ 1 and z ≈ 2; and iii) A UKIRT K-band imaging study of a sample of ULIRG’s and IR-bright QSO’s A 2-dimensional modelling technique has been developed, and used throughout to disentangle the host galaxies from the nucleardominated UV, optical and infrared images.The first study allows an investigation of host galaxy properties across a decade in quasar luminosity, but at a single redshift, and forms a crucial low-z baseline against which to compare future host galaxy studies at higher z- Previous imaging studies of AGN hosts have focussed primarily on quasars of moderate luminosity, but the most powerful objects in this sample have powers comparable to the most luminous quasars found at high redshifts. All the radio-loud quasars, and all the radio-quiet quasars with nuclear luminosities Mv < -24, are found to have massive bulge-dominated galaxies, confirming and extending the trends deduced from previous studies. From the best-fitting model host galaxies I have estimated spheroid and hence black-hole masses, and the efficiency (with respect to the Eddington luminosity) with which each quasar is emitting radiation. The largest inferred black-hole mass in our sample is mBH ≈ 3 x 10⁹m⨀, comparable to the mass of the black holes at the centres of M87 and Cygnus A. No evidence is found for super-Eddington accretion rates in even the most luminous objects. The role of the scatter in the black-hole:spheroid mass relation in determining the ratio of quasar to host-galaxy luminosity is addressed by generating simulated populations of quasars lying in hosts with a Schechter mass function. Within the subsample of the highest-luminosity quasars, the observed variation in nuclear-host luminosity ratio is consistent with being the result of the scatter in the black-hole:spheroid relation. Quasars with high nuclear-to-host luminosity ratios can be explained in terms of sub-Eddington accretion rates onto black holes in the high-mass tail of the black-hole:spheroid relation. The results imply that, owing to the Schechter function cutoff, host mass should not continue to increase linearly with quasar luminosity, at the very highest luminosities. Any quasars more luminous than Mv = -27 should be found in massive elliptical hosts which at the present day would have Mv ≈ -24.5.The second study is used in concert with existing rest-frame V-band data to calculate U - V colours for the host galaxies, and thus provide the first unbiased estimates of quasar host galaxy evolution out to cosmologically significant distances. The host galaxy colours are found to be broadly consistent with the assumption of passive evolution, but with a small amount (< 1%) of ongoing starformation. The hosts of the radio-quiet quasars are found to evolve slightly more rapidly than those of the radio-louds.Finally, the same modelling technique is applied to a sample of ULIRG’s and a control sample of IR-bright QSO’s, matched in terms of their 60μm luminosity. Using UKIRT K-band imaging to detect the presence of any well-evolved stellar population, the possibility of an evolutionary link between ULIRG’s and Quasars is explored. Large Tf-band bulges are found to be present in all of the quasars, with the majority of the ULIRG’s being best-fit by a disc. Despite the apparent difference, a significant overlap exists between the two populations in terms of their nuclear luminosity. A significant unresolved nuclear component is present in all of the objects, and this is found to correlate with the luminosity of the AT-band host across the sample. In general, the ULIRG’s do not appear to be on their way to becoming fully-fledged quasars, nor the first-ranked massive ellipticals that we have come to expect to find quasars situated in. It seems likely that such systems are the dusty equivalents of the Seyfert galaxies, and while some may end up as quite large (≤ L*) ellipticals, many have more in common with the disk galaxy populationTaken as a whole, this thesis pushes the study of Quasar Host Galaxies in three new directions, allowing a number of interesting questions on cosmology and galaxy evolution to be addressed

Missile Modeling and Simulation of Nominal and Abnormal Scenarios Resulting from External Damage

This thesis presents the development of a six-degree-of-freedom flight simulation environment for missiles and the application thereof to investigate the flight performance of missiles when exposed to external damage. The simulation environment was designed to provide a realistic representation of missile flight dynamics including aerodynamic effects, flight control systems, and self-guidance. The simulation environment was designed to be modular, expandable, and include realistic models of external damage to the missile body obtained by adversarial counteraction. The primary objective of this research was to examine missile flight performance when subjected to unspecified external damage, including changes in trajectory, stability, and controllability, and to provide a basis for the future development of fault tolerant control laws to improve target tracking and overall flight performance when experiencing abnormal conditions. To accomplish this, a variety of scenarios were developed to simulate damage to different parts of the missile, such as the fuselage, wings, and control surfaces. Three types of damage are considered: arbitrary failures which affect the major overall missile dynamic force and moment coefficients, structural failures including wings and fin breakage, and stuck fin failures where a given fin is arbitrarily fixed to a specified deflection. The missile behavior in response to these scenarios was analyzed and compared to the baseline behavior of an undamaged missile. The results of this research demonstrate how simulated missiles behave during flight, under both nominal and abnormal scenarios resulting from external damage. The simulation environment is shown to be a useful tool in examining the performance of missiles under real-world scenarios, such as during combat, in the event of an accident, or when exposed to other adversarial counteractions. This is done by producing envelopes for mission success for each tested scenario and analyzing the results. The results of this research can be used to assist in and improve the design and performance of missiles and enhance their survivability in the field. These results can also be used to determine the amount of damage necessary to prevent a given missile from reaching its target

Using DSpace for Publishing Electronic Theses and Dissertations

The IUScholarWorks Repository is a DSpace-based institutional repository for the dissemination and preservation of Indiana University's scholarly output. Some time ago, our team made a decision to incorporate electronic theses and dissertations (ETD's) into our DSpace repository, and this created several technical challenges for us. Getting ETD's into DSpace is a challenge that a number of institutions have tackled recently, and several innovative solutions have been found, such as Vireo, the ETD submission management tool from the Texas Digital Library. However, we were faced with a number of requirements in our ETD workflow that had not yet been encountered by other institutions, and required some interesting solutions. In this proposal, we will provide an outline for a presentation that will discuss these challenges, and the solutions that were envisioned. We will also provide an update on our current progress towards implementing our plans, and discuss the future work that is left to be done