The glycerol enol ether, fecapentaene-12, is a direct acting fecal mutagen that is formed in the lower portion of the gastrointestional tract by anaerobic bacteria. The biological precursor to fecapentaene-12 is a natural product of mammalian origin whose role in the etiology of colon cancer is unknown. Preliminary evidence indicated that the precursor may be a plasmalogen with an intact pentaenol ether moiety. Further structural studies by means of degradative methods and chromatographic techniques enabled the structure of the precursor to be elucidated. Based on the structure of the precursor, the name plasmalopentaene-12 was coined. Synthetic methodology was developed for obtaining synthetic plasmalopentaene12. This was necessary in order to confirm the structure and to determine the precursor's biological role. The synthetic methodology proceeded through a novel "acyl migration" which enables the highly labile pentaenol ether to be generated late in the synthesis. Model studies indicated that this was a feasible pathway. It was also determined that this methodology may be highly adaptable to the synthesis of other plasmalogens and may also provide a new synthetic route to fecapentaene-12. / Ph. D.

The Layerwise Shell Theory is used to model discretely stiffened laminated composite cylindrical shells for stress, vibration, pre-buckling and post-buckling analysis. The layerwise theory reduces a three-dimensional problem to a two-dimensional problem by expanding the three-dimensional displacement field as a function of a surface-wise two-dimensional displacement field and a one-dimensional interpolation through the shell thickness. Any required degree of accuracy can be obtained by an appropriate, independent selection of the one-dimensional interpolation functions through the thickness and the two-dimensional interpolation of the variables on the surface. Using a layerwise format, discrete axial and circumferential stiffeners are modeled as two-dimensional beam elements. Similar displacement fields are prescribed for both the stiffener and shell elements. The contribution of the stiffeners to the membrane stretching, bending and twisting stiffnesses of the laminated shell is accounted for by forcing compatibility of strains and equilibrium of forces between the stiffeners and the shell skin. The layerwise theory is also used to model initial imperfections of the unstressed configuration. A finite element scheme of the layerwise model is developed and applied here to investigate the effect of imperfections on the response of laminated cylindrical shells. Using a finite element model of the layerwise theory for shells and shell stiffener elements, the accuracy and reliability of the elements is investigated through a wide variety of examples. The examples include laminated stiffened and unstiffened plates and shells and stand-alone beams under different types of external destabilizing loads. Finally, the study identifies the particular types of problems where the layerwise elements possess a clear advantage and superiority over the conventional equivalent single-layer models. / Ph. D.

The CO dehydrogenase~linked ferredoxin from acetate-grown <i>Methanosarcina thermophiIa</i> was characterized to determine the structure and biochemical properties of the iron-sulfur clusters. Chemical and spectroscopic analyses indicated that the ferredoxin contained two [4Fe-4S] clusters per monomer of 6,790 Da, although a [3Fe-4S] species was also detected in the oxidized protein. The midpoint potentials of the [4Fe-4S] and [3Fe~4S] clusters at pH 7 were -407 m V and + 103 m V, respectively. Evidence from biochemical and spectroscopic studies indicated that the [3Fe-4S] species may have been formed from [4Fe-4S] clusters when ferredoxin was oxidized. The gene encoding the CO dehydrogenase-linked ferredoxin (<i>fdxA</i>) in <i>Ms. thermophila</i> had the coding capacity for a 6,230-Da protein which contained eight cysteines with spacings typical of 2[4Fe-4S] ferredoxins. A second open reading frame (ORF1) was also identified which had the potential to encode a 2[4Fe-4S] bacterial-like ferredoxin (5,850 Da). The deduced proteins from <i>fdxA</i> and ORF1 were 62% identical. <i>fdxA</i> and ORFI were present as single copies in the genome and each was transcribed on a monocistronic mRNA. Both <i>fdxA</i> and ORF1 were transcribed in cells grown on methanol and trimethylamine, but only the <i>fdxA</i> -specific transcript was detected in acetate-grown cells. The apparent transcriptional start sites of <i>fdxA</i> and ORFI were downstream of sequences which had high identity with the consensus methanogen promoter. The heterodisulfide of two cofactors unique to the methanogenic microorganisms, HS-HTP and HS-CoM, was enzymatically reduced in cell extracts of <i>Ms. thermophila</i> using electrons from the oxidation of either H₂ or CO. The homodisulfides of either HS-HTP or HS-CoM were not reduced under the same conditions. The results indicated that methane is formed by reductive demethylation of CH₃-S-CoM using HS-HTP as a reductant in <i>Ms. thermophila</i>. Coupling of CO oxidation with reduction of the heterodisulfide suggested that the CO dehydrogenase-linked ferredoxin may be involved, although the details of electron flow are not known. / Ph. D.

Cette étude vise à comparer des mères à risques psychosociaux à des mères non à risque relativement à la connaissance qu'elles ont du développement de l'enfant et à leurs attentes envers les enfants. Trente-deux mères à risques et 30 mères non à risque sont rencontrées et répondent au C.D.Q. ( Child Development Questionnaire) et au P.O.Q. ( Parent Opinion Questionnaire). Les résultats indiquent une connaissance moindre du développement de l'enfant ainsi que des attentes plus irréalistes envers les enfants de la part des mères à risques comparativement aux mères non à risque. Par ailleurs, un lien entre les connaissances des mères et leurs attentes concernant les enfants ne semble pas être présent.

No description available.

Ph. D.

This study was undertaken to evaluate the dewatering characteristics of a bench-scale belt filter press and a full-scale screw press, and to develop a suitable bench-scale test to simulate dewatering in a full-scale screw press. Tests were conducted to determine the effect of pressure and shear on dewatering of anaerobically digested, alum, waste activated, and pulp and paper sludges. The first part of the study involved tests conducted on a bench-scale belt filter press. Pressure was varied to develop performance characteristics with respect to cake and filtrate solids, and polymer demand. The second part of the study consisted of mixing intensity tests conducted to evaluate the effect of shear on dewatering in sludges. The third part of the study involved field evaluation of dewatering performance using a full-scale screw press. Tests were conducted to determine the shear produced in the dewatering process and to assess its effect on polymer conditioning requirements. The tests indicated that the polymer demand produced by the belt filter press simulator and the screw device was minimal. Rather, a substantial polymer demand was observed as a result of shear in the pipes and pumps during full-scale screw press dewatering operations. A combination of a high speed mixing device and a free drainage tester was capable of predicting polymer conditioning requirements for a full-scale screw press. Individual sludge performance characteristics varied with pressure producing changes in cake solids and filtrate quality. / M.S.

The problem of optimal guidance design for the low altitude, subsonic, vertical plane approach maneuver of an air vehicle constrained to maintain view of a fixed final position is studied using a nonlinear, constrained, optimal control problem formulation. Multiple, competing optimization criteria are included separately as performance goals and in combination as state equality constraints for design tradeoff analysis. In conjunction with vehicle flight constraints, a sensor line-of -sight (LOS) angle limit is imposed as a control variable inequality constraint to provide a sensor field of regard influence on the guidance design. Numerical results are provided that illustrate the optimal guidance for different performance criteria, the sensor LOS profile along the optimal maneuvers, and the influence of the sensor limit on the guidance law design. A near-optimal, closed-loop feedback guidance law that incorporates the sensor constraint is developed based on neighboring extremals. / Ph. D.

This research specifically addresses the issue of construct validity as it applies to past research in the study of services. Existing empirical research efforts examining the services sector have largely produced mixed results and have consistently failed to support a theoretical framework from which a greater understanding of service organizations could be developed. This has been the case in spite of the seemingly correctness and strong theoretical support for existing models. Thus, this study did not undertake an attempt to develop a new model for understanding services, rather, the goal was to extend existing theory through operationalizing a construct valid definition of the service concept. / Ph. D.

Sales management researchers apply various leadership measures and theories taken from conventional work-group settings. These applications may be questionable given the unique boundary-spanning context in which the field sales force must operate. This study raises the questions and offers an approach which may be more appropriate. Specifically, this study questions the assumption that the manager acts and the salesperson reacts, and the focus of sales management studies which study managerial behavior in isolation from those of the salesperson he or she is supervising. The Leader-member Exchange theory (and the basis for this theory, social exchange) is offered as an approach which may be more consistent with the work-setting and obstacles faced by the field sales manager. This study offers a conceptual model of salesperson-manager relationships as a guide to explaining effective leadership in the field sales setting. A study was conducted on a subset of this conceptual model. Using the survey responses of industrial field salespeople and their managers, this study tested (1) the exchange relationships between the perceived behaviors of both the manager and salesperson, (2) the degree to which these exchanges influence the salesperson’s overall assessment of the salesperson-manager relationship, (3) the degree to which this assessment affects job-related outcomes and (4) the impact of environmental uncertainty on this boundary spanning link between salesperson and manager. The results of this study provides some support for the notion of an exchange relationship between the salesperson and manager. An exchange relationship may exist between the salesperson’s competency and the manager’s latitude. The salesperson’s assessment of the working relationship is based on the latitude received and the loyalty felt toward the manager {rather than his or her contributions of competency). This approach to studying the effects of leader behavior was effective in explaining salesperson satisfaction levels. It was less effective in predicting the goal achievement levels of the field sales force. Finally, the results of this study indicate the amount of uncertainty in the environment may have a direct effect on goal achievement levels of the salespeople, but lacks a moderating influence over the link between salesperson-manager relationships and outcomes. / Ph. D.