Doctor of Philosophy

dissertationThe Mio-Pliocene geologic record is investigated along the southeastern margin of the Puna plateau in northwestern Argentina. The Puna plateau is the southernmost extension of the high elevation, internally drained, Central Andean plateau. A series of intermontane basins at the plateau margin preserve thick stratigraphic sections spanning ~10-3 Ma. The strata in these basins were investigated between 25°30?S and 28°S latitude, with geochronological and paleoenvironmental objectives. The stratigraphy, composition, and age of volcanic ash beds provide age control. Fossil vertebrates and soils interbedded with these volcanic ash beds provide material for stable isotopic proxies of environment. This approach permits analysis of spatial and temporal patterns in the tectonic and climatic evolution of the landscape at the Puna margin. Stable isotope analysis of fossil tooth enamel from the 2.5 km thick section at Puerta de Corral Quemado documents the late Miocene expansion of plants using the C4 photosynthetic pathway. Tooth enamel was analyzed by conventional methods, and by laser ablation which incorporates small bodied taxa in the study. These results indicate the presence of C4 plants in the region by at least 8.5 Ma and a shift to C4 diets among fossil notoungulates between 7-5.5 Ma. Fossil rodents exhibit a less dramatic diet change across this interval, and all taxa document transient enrichment in 13C and 18O approximately coincident with the Miocene-Pliocene boundary. Interbasin correlation of ash beds demonstrate that conglomeratic deposits are conformable with stratified sections and initiated between 4-3 Ma. These deposits lag uplift of basin margin mountain blocks by several million years and precede contractional deformation of Mio-Pliocene strata. This sequence is characteristic, but diachronous between basins. This Mio-Pliocene pulse of deformation typifies the evolution of a broken foreland at the plateau margin. Interbasin comparison of isotopic proxy data from fossil soils identifies regional 18O enrichment concurrent with topographic growth at the plateau margin. Carbon isotope data from fossil soils demonstrate strong ecological gradients at the landscape-scale and at local scales. The record of C4 expansion in fossil soils is significantly influenced by the growth of complex topography and possibly by regional reorganization of precipitation systems

Forced-convection, dispersed-flow film boiling

This report presents the latest results of an investigation of the characteristics of dispersed flow film boiling. Heat transfer data are presented for vertical upflow of nitrogen in an electrically heated tube, 0.4 in. I.D. and 8 ft long. Heat fluxes up to 18,000 Btu/ft 2-hr and mass fluxes up to 200,000 lbm/ft 2-hr were investigated. By variation of the startup procedure, it was possible to operate in two distinct regimes of film boiling. By preheating the tube before introducing the flow, film boiling was observed throughout the test tube. If the flow was established before applying power, film boiling was initiated downstream of the inlet. For similar conditions, the local heat transfer coefficients were different in the two cases due to the different degrees of thermal nonequilibrium. The data for both regimes were satisfactorily predicted by a modified version of the nonequilibrium model presented in earlier reports. The model was also applied to available data for methane, propane, and water. By modification of the empirical constant governing the direct wall-to-droplet heat transfer, these data were generally predicted to within 10 percent. The tests were repeated with tight-fitting, full-length twisted tapes installed in the test tube. Considerable augmentation of the heat transfer was achieved, with the heat transfer coefficient being increased by as much as a factor of 3 with the tightest tape twist. For the higher mass fluxes, it was observed that the tape promoted droplet deposition to such an extent that a continuous liquid film could be reestablished on the wall near the test section exit. The tape-generated swirl flow did not improve the "burnout" condition, primarily due to the fact that a liquid streamer forms on the twisted tape. The semiempirical model gave a reasonable prediction of the heat transfer coefficient when the effects of the swirl flow were included.Sponsored by the National Science Foundation D. S. R

Czech version of the Outcome Rating Scale : Selected psychometric properties

Objectives. The Outcome Rating Scale (ORS) is an ultra-brief self-report scale designed to measure change during psychotherapy. The goal of this study was to test (a) the factor structure of the ORS, (b) the measurement invariance between a clinical and a non-clinical sample, between pre-therapy and post-therapy assessment (within the clinical sample), and between online and paper-and-pencil forms of administration (within the non-clinical sample), (c) concurrent validity with other outcome measures, and (d) sensitivity to therapeutic change. Sample and settings. N = 256 patients, N = 210 non-clinical respondents, and N = 89 students participated in the study. Patients responded to the ORS before and after psychotherapy. Statistical analysis. The factor structure and measurement invariance were tested using confirmatory factor analysis. Concurrent validity and test-retest reliability were assessed using correlational analysis. Sensitivity to change was assessed using the Reliable Change Index and pre-post effect size. Results. The unidimensional structure was supported. The best-fitting model was a partially tau-equivalent model with the first and the fourth items’ loadings fixed to the same value. While only metric invariance was demonstrated between the clinical and non-clinical samples, the ORS demonstrated scalar invariance between pre- and post-therapy assessment and strict invariance between the paper-and-pencil and online forms of administration. Internal consistency, as well as concurrent validity, were satisfactory. The sensitivity to the therapeutic change was adequate. Furthermore, internal consistency and sensitivity to change were increased if the score was computed as a weighted sum of items. Study limitation. The samples were not representative

A branching, positive relief network in the middle member of the Medusae Fossae Formation, Equatorial Mars - evidence for sapping?

The Medusae Fossae Formation (MFF) is a geological formation comprising three geological units (members) spread across five principal lobes. It dominates a quarter of the longitudinal extent of the equatorial region of Mars. Positive relief features referred to as ‘sinuous ridges' (commonly interpreted as inverted paleoflow channel or valley fills) have been observed in the lowest member of the western MFF, but have not been identified within the central and eastern portions of the formation, in the middle and upper members. This paper presents the identification and analysis of a branching, positive relief system which occurs in the central lobe of the MFF in what appears to be an exposure of the middle member. A simple geomorphological map of the system is presented, from which we have adopted the working hypothesis that this is an inverted fill of a branching fluvial channel or valley system. A suite of morphological and topographic evidence supporting this hypothesis is presented, including analysis of the network using a~15 m per pixel digital terrain model derived from a Context Imager (CTX) stereo image pair. The evidence supporting this hypothesis includes: 1) The local slope and topography of the upper surface of the network are consistent with a contributory network, 2) The braided, fan-like form at the termination of the branching network is consistent in morphology with it being a depositional fan at the end of a fluvial system, 3) The terminal fan and surrounding deposits show layering and polygonization, 4) There is strong association between the lower order branches and amphitheater shaped scarps in the depression walls. We evaluate the possible origins of this fluvial system and suggest that seepage sapping is the most probable. Two possible models for the evolution of the network and related features are presented; both require melt of ice within the MFF to form liquid water. We conclude that at least some portions of the Medusae Fossae Formation, if not the entire formation, were once volatile-rich. Finally, we note that our observations do not rule out the case that this network formed before MFF emplacement, and has since been exhumed. However, this conclusion would suggest that much of the surrounding terrain, currently mapped as middle-member MFF, is not in fact MFF material at all

New simulants for martian regolith: Controlling iron variability

Existing martian simulants are predominantly based on the chemistry of the average ‘global’ martian regolith as defined by data on chemical and mineralogical variability detected by orbiting spacecraft, surface rovers and landers. We have therefore developed new martian simulants based on the known composition of regolith from four different martian surface environments: an early basaltic terrain, a sulfur-rich regolith, a haematite-rich regolith and a contemporary Mars regolith. Simulants have been developed so that the Fe2+/Fe3+ ratios can be adjusted, if necessary, leading to the development of four standard simulants and four Fe-modified simulants. Characterisation of the simulants confirm that all but two (both sulfur-rich) are within 5 wt% of the martian chemistries that they were based on and, unlike previous simulants, they have Fe2+/Fe3+ ratios comparable to those found on Mars. Here we outline the design, production and characterisation of these new martian regolith simulants. These are to be used initially in experiments to study the potential habitability of martian environments in which Fe may be a key energy source

Stepped fans and facies-equivalent phyllosilicates in Coprates Catena, Mars

Stepped fan deposits and phyllosilicate mineralogies are relatively common features on Mars but have not previously been found in association with each other. Both of these features are widely accepted to be the result of aqueous processes, but the assumed role and nature of any water varies. In this study we have investigated two stepped fan deposits in Coprates Catena, Mars, which have a genetic link to light-toned material that is rich in Fe–Mg phyllosilicate phases. Although of different sizes and in separate, but adjacent, trough-like depressions, we identify similar features at these stepped fans and phyllosilicates that are indicative of similar formation conditions and processes. Our observations of the overall geomorphology, mineralogy and chronology of these features are consistent with a two stage formation process, whereby deposition in the troughs first occurs into shallow standing water or playas, forming fluvial or alluvial fans that terminate in delta deposits and interfinger with interpreted lacustrine facies, with a later period of deposition under sub-aerial conditions, forming alluvial fan deposits. We suggest that the distinctive stepped appearance of these fans is the result of aeolian erosion, and is not a primary depositional feature. This combined formation framework for stepped fans and phyllosilicates can also explain other similar features on Mars, and adds to the growing evidence of fluvial activity in the equatorial region of Mars during the Hesperian and Amazonian

Saltatory remodeling of Hox chromatin in response to rostrocaudal patterning signals

Hox genes controlling motor neuron subtype identity are expressed in rostrocaudal patterns that are spatially and temporally collinear with their chromosomal organization. Here we demonstrate that Hox chromatin is subdivided into discrete domains that are controlled by rostrocaudal patterning signals that trigger rapid, domain-wide clearance of repressive histone H3 Lys27 trimethylation (H3K27me3) polycomb modifications. Treatment of differentiating mouse neural progenitors with retinoic acid leads to activation and binding of retinoic acid receptors (RARs) to the Hox1–Hox5 chromatin domains, which is followed by a rapid domain-wide removal of H3K27me3 and acquisition of cervical spinal identity. Wnt and fibroblast growth factor (FGF) signals induce expression of the Cdx2 transcription factor that binds and clears H3K27me3 from the Hox1–Hox9 chromatin domains, leading to specification of brachial or thoracic spinal identity. We propose that rapid clearance of repressive modifications in response to transient patterning signals encodes global rostrocaudal neural identity and that maintenance of these chromatin domains ensures the transmission of positional identity to postmitotic motor neurons later in development.Leona M. and Harry B. Helmsley Charitable TrustNational Institutes of Health (U.S.) (Grant P01 NS055923)Smith Family Foundatio

Phenome-wide association analysis of LDL-cholesterol lowering genetic variants in PCSK9

Abstract: Background: We characterised the phenotypic consequence of genetic variation at the PCSK9 locus and compared findings with recent trials of pharmacological inhibitors of PCSK9. Methods: Published and individual participant level data (300,000+ participants) were combined to construct a weighted PCSK9 gene-centric score (GS). Seventeen randomized placebo controlled PCSK9 inhibitor trials were included, providing data on 79,578 participants. Results were scaled to a one mmol/L lower LDL-C concentration. Results: The PCSK9 GS (comprising 4 SNPs) associations with plasma lipid and apolipoprotein levels were consistent in direction with treatment effects. The GS odds ratio (OR) for myocardial infarction (MI) was 0.53 (95% CI 0.42; 0.68), compared to a PCSK9 inhibitor effect of 0.90 (95% CI 0.86; 0.93). For ischemic stroke ORs were 0.84 (95% CI 0.57; 1.22) for the GS, compared to 0.85 (95% CI 0.78; 0.93) in the drug trials. ORs with type 2 diabetes mellitus (T2DM) were 1.29 (95% CI 1.11; 1.50) for the GS, as compared to 1.00 (95% CI 0.96; 1.04) for incident T2DM in PCSK9 inhibitor trials. No genetic associations were observed for cancer, heart failure, atrial fibrillation, chronic obstructive pulmonary disease, or Alzheimer’s disease – outcomes for which large-scale trial data were unavailable. Conclusions: Genetic variation at the PCSK9 locus recapitulates the effects of therapeutic inhibition of PCSK9 on major blood lipid fractions and MI. While indicating an increased risk of T2DM, no other possible safety concerns were shown; although precision was moderate