The source of a majority (more than 80%) of high-consequence marine accidents can be attributed to compounded human and organizational errors (HOE). Recent examples include the Exxon Valdez tanker grounding (258,000 barrels of oil spilled), and the Occidental Piper Alpha platform explosions and fires (167 men killed). Currently, there is no structured quantitative approach to assist engineers, operators, and regulators of marine systems to either design HOE tolerant systems or to include considerations of HOE as an integral part of the design, construction, and operation of marine systems. The human element has generally been ignored.

The objective of this dissertation is to introduce a quantitative modeling methodology to assess the impacts of HOE in operation of tankers and offshore platforms. This methodology includes a systematic approach to structuring critical elements that lead to accident scenarios and a quantitative modeling procedure to assess the impacts of operational risks under various operating conditions that can lead to these scenarios.

The modeling methodology incorporates structuring accident scenarios into underlying, direct, and compounding factors. Diagrammatic representations of the unique factors leading to accident scenarios using influence diagrams are proposed. The diagrams are used to develop simplified general "templates" for that particular class of accident. The function of the templates are to form a basis that preserve the central causative mechanisms for a similar operation, yet do not preserve the unique aspects of the disaster being modeled.

Insufficient and unreliable data linking complex effects of human errors to marine casualties has led to limitations in quantitative human error modeling. A quantitative measuring technique, the Human Error Safety Index Method (HESIM), has been proposed that measures organizational, task and system complexities, and environmental factors that affect operators abilities to perform decisions and actions to mitigate or aggravate accident events. These measurement techniques rely upon judgments and experiences of those familiar with the operations being modeled and objective data to formulate a "safety index". A methodology for coiiection of the objective data, the Human and Organizational Error Data Quantification System (HOEDQS), is also proposed. The HOEDQS allows updating of human errors such that there becomes a greater reliance upon objective data and less upon the judgmental indexing procedure.

Two marine casualties were identified as case study examples for confirmation of the modeling procedures: the Exxon Valdez and Piper Alpha disasters. These casualties were selected because of the quality, completeness, accessibility, and availability of information related to the accident events. The unique aspects of each disaster are modeled and templates are developed. Quantitative analyses were performed on each operation to confirm that high risk levels were measured conditional upon the operating factors for each disaster. The results from this dissertation will be of interest to engineers, operators, managers, and regulators concerned with preventing and mitigating the effects of HOE to increase safety of marine systems.

Plants form a variety of endosymbiotic relationships with bacteria and fungi that promote plant growth and fitness through reciprocal nutrient exchange. Central to the development and function of endosymbiotic relationships is the synthesis of a specialized host-derived membrane, which compartmentalizes the endosymbiont inside plant cells, and creates a dynamic interface for the exchange of nutrients and information. The development of these interfaces is dependent upon bidirectional signaling between the plant and microorganism, and is highly coordinated with the morphological differentiation of the endosymbiont within plant cells. Previous studies using glycan-directed monoclonal antibodies indicated that glycoproteins, glycolipids, and pectic polysaccharides localize to periarbuscular and symbiosome membranes. Among these epitopes were arabinogalactan proteins (AGPs) and glycosyl inositolphophorylceramides (GIPCs), which have potent signaling properties in plants. These epitopes appeared to be developmentally regulated, which led to the hypothesis that a membrane-associated glycocalyx of glycoproteins and glycolipids might be important for mediating interactions through these membrane interfaces. However, AGPs have not been well documented outside of Arabidosis thaliana and are intrinsically disordered, which make them difficult to identify and study in plants species capable of forming endosymbiosis. Here, we have developed a new bioinformatic search tool that identifies AGP-encoding genes based on the noncontiguous hydroxyproline motifs that direct AGP glycosylation. We used this tool to identify all putative AGP-encoding genes in the Medicago truncatula genome, which were cross-referenced to transcriptomic studies of roots engaged in symbiosis with Sinohizobium meliloti and the arbuscular mycorrhizal (AM) fungus Rhizohagus irregularis. Using this approach we identified a small three-member family of tandemly duplicated SYMBIOSIS-ASSOCIATED ARABINOGALACTAN PEPTIDES (SAPs) that were differentially expressed in root nodules and AM colonized roots. SAPs localized to symbiotic membranes and knockdown of SAP expression using RNAi-mediated gene silencing impaired the growth and differentiation of Sinorhizobium meliloti and Rhizphagus irregularis within these compartments. In parallel we also identified a glycosyltransferase gene highly expressed in root nodules and AM colonized roots as GIPC GLUCOSAMINE TRANSFERASE 1 (GINT1), and showed that the corresponding GINT1 enzyme functions in the synthesis of HexN(Ac) decorated GIPCs in planta. Silencing of GINT1 using RNAi impaired the development of symbiotic membranes, which resulted in the senescence of symbiosomes and arbuscules. Taken together these results provide genetic evidence to support that reprogramming of the membrane-associated glycocalyx with specific AGPs and GIPCs is necessary for endosymbiosis.

This dissertation describes a variety of reduction techniques applied towards the synthesis and characterization of low oxidation state rare-earth metal compounds in order to determine the techniques’ efficacy and the ability of these methods to yield species with interesting properties different from those generated from the widely used potassium-based reduction systems. The research results described herein add to the fundamental knowledge base on the coordination and redox chemistry of the rare-earth metals, which are scandium, yttrium, and the lanthanides. In Chapter 1, an array of alkali metal (M) and organic chelate (L) combinations were used to generate nine [M(L)][Cp′3YII] (Cp′ = C5H4SiMe3) complexes in order to determine whether K/crypt (crypt = 2.2.2-cryptand) is indeed the most suitable for reducing Cp′3YIII and isolating Y(II) complexes. During the process, two new Y(II) complexes were crystallographically characterized, namely [(THF)Na2(18c6)2][Cp′3YII]2 and [Na(crypt)][Cp′3YII]. EPR, UV-visible absorbance, and IR spectroscopies revealed minimal differences in the spectroscopic characeristics of these complexes. Interestingly, the decomposition profiles of these species at room temperature show marked differences. This Chapter initiates a discussion of the factors that determine the stability of these low oxidation state-complexes. In Chapter 2, cesium metal smears were used to reduce Cp′3YbIII and Cp′3TmIII and generate a series of ytterbium(II) and thulium(II) complexes that display an extended structure by single crystal X-ray diffraction (XRD). The structures are composed of layers of hexagonal nets with alternating vertices of Cs(I) and Ln(II) ions. This structure is robust with respect to the level of THF-solvation, as compounds with 0, 1, and 2 bound THF molecules per monomer unit were characterized. The Tm-containing species, [(THF)Cs(µ–η5:η5–Cp′)3TmII]n, was synthesized in order to investigate whether the trigonal arrangement of S = ½ Tm(II) ions yielded spin frustration at low temperatures and whether single crystals were exfoliatable. By collaborating with Alexandre Vincent from the lab of Professor Jeffrey R. Long at the University of California, Berkeley, SQUID measurements were collected to show that the thulium ions are in the +2 oxidation state and non-interacting. And by collaborating with TJ McSorley from the lab of Professor Luis A. Jauregui in the Department of Physics at the University of California, Irvine, exfoliation of single crystals was successful down to approximately 50 layers. In Chapter 3, a method was adapted to induce the reduction of Ln(III) organometallic complexes (Ln = Sc, Y, La) by exposing them to γ-irradiation in a glassy matrix. The method was first utilized to reduce Ln(III) complexes to known [Ln(II)]1− anions, which were identified by EPR and UV-visible spectroscopies. That γ-irradiation method was extended to generate and characterize a new anion, namely [LaII(NR2)3]1− (R = SiMe3). Furthermore, the formation of [Cp′3YII]1− was monitored over time to show the low conversion rate of the method (<1% over 6.5 hours). This method may have broader implications for the generation and characerization of low oxidation state species otherwise unisolable by chemical means. In Chapter 4, an attempt to generate a bridging [C≡C]2− unit for reduction to the magnetically interesting, previously unknown [C≡C]3− bridge is described. The reaction of (C5Me5)2Y(μ–Ph)2BPh2 with NaC≡CH did not yield the desired (C5Me5)2Y(CC)Y(C5Me5)2 and instead forms an interesting C–C coupled product, namely (C5Me5)2Y(μ–η3:η1–CCCCH2)Y(C5Me5)2. This represents the second crystallographically characterized butatrienylidene dianion. The product was characterized by 1H, 13C, and HMQC NMR, UV-visible absorbance, and IR spectroscopies. Theoretical calculations were conducted to investigate the nature of the C–C bonding in the butatrienylidene bridge. In Chapter 5, results are reported on separate approaches to reduce organometallic rare-earth metal complexes using photoredox reactions and using barium powder. The photoredox approach focused on reducing Cp′3YIII in collaboration with Professor Harry B. Gray and his graduate student Dr. Javier Fajardo Jr. at the California Institute of Technology using a powerful photoreductant developed in their lab, namely W(CNdipp)6. Upon excitation with UV-visible light, the reduction potential is shifted approximately 2.3 V more negative {E1/2 of W(CNdipp)6 = −0.72 V vs Fc+/0, E1/2 of [W(CNdipp)6]* ≈ −3.0 V vs Fc+/0}. The reduction of Cp′3YIII by this species was attempted in toluene with the inclusion of a suite of sacrificial reductants. No isolation or characterization of Y(II) product was observed. Regarding the use of barium as a reductant, barium powder was generated in order to maximize its surface area and improve the speed at which a reduction reaction would occur. Reductions were attempted in the presence of crypt with Cp′3Ln (Ln = Y, Tm, Yb). Reductions were observed for thulium and ytterbium. Crystals isolated from a sample dissolved in wet acetonitrile demonstrate the electrostatic attraction of Ba(II) and anionic ligands, yielding the structure [Ba(crypt)Cp][Cp2Yb(μ–OSiMe3)2YbCp2].

Introduction

Methods

Results

Discussion