Cell division in higher eukaryotes is mainly controlled by p34cdc2, a serine/ threonine protein kinase, and/or related kinases, and by other components of these kinase complexes. I present evidence that CDC2-like kinases also occur in the ciliate Paramecium tetraurelia. The protein encoded by the isolated Paramecium cdc2 homologue did not bind to pl3sucl , was localized in the macronucleus, its associated kinase activity was high at the initiation of macronuclear DNA synthesis, and it was active as a monomer. To study the relationship between the cellular and molecular events of cell cycle regulation, synchronous cultures are essential. However, in Paramecium, the only reliable technique for obtaining synchronous cell populations has been hand-selection of dividing cells. This technique is only useful for small samples and impractical for biochemical analysis. In this thesis, centrifugal ehxtriation, which fractionates the cell population on the basis of sedimentation properties with minimal perturbation of metabolic function, was applied to the ciliate Paramecium tetraurelia. Only the smallest cell fractions were well synchronized and exhibited synchrony and cell cycle duration equivalent to hand-selected samples. These small cell fractions consisted of a highly synchronous G1 cell population, which was easily obtained by this technique and used for all subsequent molecular and biochemical analysis. With a combination of various polymerase chain reaction (PCR) techniques, a cdc2 homologous sequence was isolated from Paramecium which is referred to as cdc2PtA. The genomic Paramecium cdc2PtA gene contained two short introns near the 5'-end. The corresponding amino acid sequence exhibited about 50 % identity to the cdc2 proteins of other eukaryotes. The Paramecium cdc2PtA gene-encoded protein was 11 amino acids longer than that of Schizosaccharomyces pombe. It had most of the catalytic sites required for CDC2 kinase activity, especially those phosphorylation sites which regulate CDC2 kinase activity in other organisms. There was one amino acid change in the highly conserved PSTAIRE region and other changes in regions which are required for interaction with other regulatory proteins, especially the pl3*"e / binding sites. Southern blot analysis as well as isolation of a second incomplete cDNA sequence from the 3'-end indicated that Paramecium has multiple cdc2 genes. Northern blotting results showed that the Paramecium cdc2PtA gene was much more strongly expressed in actively dividing cells than in starved stationary phase cells in which cdc2PtA mRNA was almost undetectable. There was no significant change in cdc2PtA mRNA level throughout the vegetative cell cycle. Polyclonal antibodies were produced against both a synthetic peptide from the C-tenninal region and a GSTCDC2PTA fusion protein which contained a third of the Paramecium cdc2PtA protein from the N-terminal region. Both antibodies recognized a 36 kDa polypeptide on Western blots. The antibodies did not cross-react with protein extracts from Tetrahymena or S. pombe, nor with the Paramecium 34 kDa polypeptide which was detected by anti- PSTATJRE antibody. The Paramecium CDC2PTA protein level decreased slightly when cells entered stationary phase and was invariant throughout the cell cycle, similar to its transcription pattern. Indirect immunofluorescence results showed that Paramecium CDC2PTA protein was located in the macronucleus, but not observed in the micronuclei or cytoplasm Upon starvation, the strength of the fluorescence signal in the macronucleus dropped slightly, consistent with the result from Western blotting. Native Paramecium CDC2PTA kinase was immunoprecipitated with the Paramecium CDC2PTA specific antibody. The precipitated CDC2PTA kinase phosphorylated both bovine histone HI and casein in vitro, but not retinoblastoma (Rb) protein. Using histone HI as substrate, CDC2PTA kinase activity was assayed in the ehitriation synchronized samples. Histone HI kinase activity was high during the early stages of the cell cycle and reached a peak at around 2.5 hr after ehitriation, which corresponded approximately to the time of the initiation of macronuclear DNA synthesis. This suggests that the isolated Paramecium CDC2PTA kinase may be associated with the regulation of macronuclear DNA synthesis. When Paramecium extracts were probed with anti-PSTAIRE antibody, two polypeptides were detected. The major one migrated at 36 kDa was apparently recognized by anti-CDC2PTA antibody. The minor one migrated at the same position as S. pombe p34cde2 protein. Only the faster migrating one showed affinity for p 13™c7 protein. The phosphotransferase activity of the p13sucl / precipitable protein was very low at early stages and increased at around 1.5 hr before cell division. This kinase activity increase corresponded to the point of commitment to division in Paramecium. Immunoprecipitation results showed that Paramecium CDC2PTA kinase occurred principally as monomers. This was further confirmed by glycerol density gradient centrifugation and gel filtration. These monomers were active as a histone HI kinase in vitro. These observations indicate that isolated Paramecium CDC2-like kinase differs from typical CDC2 kinases in terms of interaction with and regulation by other cell cycle regulatory components. / Science, Faculty of / Zoology, Department of / Graduate

Adequate knowledge of the ruminal degradation characteristics of feedstuffs fed to ruminants is paramount to successful ration formulation using the recently proposed protein rationing systems. In the first of two trials, in situ rumen degradation characteristics of cereal grains with or without steam rolling, roughages and agro-byproducts were evaluated. In vitro starch release of the cereals by the enzyme amyloglucosidase was also investigated. Steam rolling (SR) significantly reduced the in situ rate of degradation of DM, CP and starch of cereal grains. Compared to unprocessed cereals, in situ rate of degradation of these parameters was significantly lower for corn than for barley or wheat, for both the steam rolled and the unprocessed treatments. However, SR tended to increase the in vitro starch release by amyloglucosidase from cereal grains. In situ degradation characteristics varied significantly (P<0.01) among roughages and agro - byproducts, with alfalfa hay and rye distillers grains having higher rates of degradation. Beet pulp had the highest neutral detergent fiber (NDF) (P<0.01) effective degradability among the agro - byproducts. In the second trial, twelve lactating dairy cows were used to determine the effect of diets matched for rate of carbohydrate and protein degradation on feed intake, digestibility, rumen and blood components, and the yield and composition of milk. Four diets; steam - rolled corn - fish meal (SRC-FM), steam - rolled corn - canola meal (SRC-CM), steam - rolled barley - fish meal (SRB-FM) and steam - rolled barley - canola meal (SRB-CM) were all fed with alfalfa hay to the cows four times per day. Feed intake was not influenced by source of carbohydrate or protein (P>0.10), but the digestibility of most nutrients was significantly influenced (P<.10) by source of carbohydrate , being higher on the SRB diets than on the SRC diets. Total rumen volatile fatty acids and rumen ammonia nitrogen were significantly influenced by source of protein (P<0.10), with most other parameters, including blood parameters, showing significant interactions (P<0.01) between source of carbohydrate and source of protein. Milk production, and the yield of protein, total solids (TS), and solids - not - fat (SNF) were significantly influenced (P<.01) by source of carbohydrate, with the cows consuming SRB diets producing more of the above than those consuming SRC diets. Percent fat and percent SNF were higher and lower respectively on the SRC diets than the SRB diets. With alfalfa hay as roughage, SRB, when fed in combination with either FM or CM, resulted in more milk production than when SRC was fed with either FM or CM. Different starch and roughage sources and agro-byproducts degrade at different rates. This variability in degradation characteristics can be exploited in ration formulation in such a way that the provision of energy can be matched to the provision of nitrogen in order to optimize microbial production, maximize performance and minimize protein wastage. / Land and Food Systems, Faculty of / Graduate

The existing literature on household wealth accumulation has hitherto recognized the lifecycle effects, household socio-economic characteristics, bequest motives, and intergenerational transfers as important factors affecting household net wealth. The two empirical essays in this thesis expand the literature by emphasizing the likely roles that a household's tenure choice and home equity borrowing decisions have in its wealth accumulation process. The first essay, entitled "Homeownership and Household Wealth Accumulation", tests whether homeownership has placed the owner household on a more favorable wealth accumulation path, based on past observations that the values of owner-occupied housing have grown at a real rate greater than those of financial or other tangible assets. The premise is that, while the tenure choice decision is affected by a household's net wealth, the housing tenure chosen could place a household on different wealth accumulation paths over its life-cycle. Controlling for selection bias arising from tenure status, the results indicate that typical homeowners and renters have distinct wealth accumulation processes. While homeownership improves the wealth position of homeowners, the renter households are, however, better off in their existing tenure than otherwise. It appears that households self-select themselves into the appropriate tenure that optimizes their wealth accumulation paths. The second essay on "Household Consumption/Investment Behavior and Home Equity Loans" investigates which behavioral model underpins the homeowners' consumption and investment decisions of home equity loan funds, and how these decisions impact portfolio decisions and wealth accumulation. It concludes that the 'life-cycle model' and the 'precautionary savings model' prevail over the 'bequest motive model' in motivating the household consumption/investment decisions of home equity loans. Home equity loans alter the illiquid nature of housing investment through convenient tapping of housing equity, and reduce household preference to hold liquid assets to meet precautionary needs. Their presence encourages loan users to hold smaller shares of liquid cash and financial assets in total assets, and to diversify from housing asset to business, real estate and illiquid nonhousing assets. They generally reduce homeowners' net wealth, reflecting a tendency for borrowed funds to be consumed or invested in loss-incurring assets. / Business, Sauder School of / Graduate

Commodity futures markets are often thought of as good examples of perfectly competitive markets. However, there are many commodities that are produced in concentrated industries and traded on large commodity exchanges. Nickel, aluminum, lead, zinc, tin, oil, and coffee are some examples. This thesis examines the effects of concentrated production on output and prices in these markets. The analysis includes the possibility that firms can trade futures contracts for their output and also store their output. A dynamic model is developed that examines how a duopoly could use futures trading and storage strategically to affect outcomes in subsequent periods. I examine futures trading for a perishable good and storage with no futures trading separately in order to highlight the potential stategic use of these activities on their own. I also analyse a model in which both futures trading and storage are allowed. I show that both futures positions and storage would be used strategically by the duopolists, in contrast to the results of previous work that used two-period models only. By allowing for uncertainty in the form of demand and cost shocks, the solution to the model can be used to provide some implications for correlations among industry level variables. These correlations are examined for the world lead, zinc, and copper industries. Weak support for the model is found, however, estimation of the vector auotregression implied by the model suggests the model in its present form is unable to fit the data very well. / Arts, Faculty of / Vancouver School of Economics / Graduate

The time required to identify a common object depends on several factors, especially pre-existing knowledge and episodic representations newly established as a result of a prior study. My research examined how these factors contribute to identification of objects (both studied and non-studied) and to performance on explicit memory tests. The overall goal was to explore the link between memory and object perception. One series of experiments examined influences due to object orientation in the plane of the page. Subjects were shown color photos of objects, and memory was assessed either with an old/new recognition test or with a test that required them to identify objects that were slowly faded in on a computer monitor. The critical variables were the type of photo — each showing either an object with a predominant or cardinal orientation (e.g., helicopter) or a non-cardinal object (e.g., pencil), and the orientation at which the photos were displayed at study and at test (e.g., rotated 0°, 120°, or 240°). For non-studied targets, identification test performance showed a large effect due to display orientation, but only for cardinal objects. For studied targets, study-to-test changes in orientation influenced priming for both non-cardinal and cardinal objects, but orientation specific priming effects (larger priming when study and test orientations matched rather than mismatched) were much larger with cardinal than non-cardinal objects, especially, when their display orientation, at test was unusual (i.e., 120°, 240°). A second series of experiments examined influences due to object size (size of an object presented alone) and relative size (size of an object relative to another object). Size manipulations had a large effect on identification of non-studied objects but study-to- test changes in size had only a minimal effect on priming. In contrast, study1to-test changes in relative size influenced recognition decision speed which is an index of priming. The combined findings suggest that both semantic and episodic representations behave as if they coded orientation but only for cardinal objects. They also suggest that episodic representations code relative size but not size information. The findings are explained by the instance views of memory. / Arts, Faculty of / Psychology, Department of / Graduate

A distinction between ruminative and reflective forms of dispositional self-focus is introduced and the theoretical utility of this distinction is evaluated in a program of eight studies. Study 1 examined for the presence of this distinction among natural language trait descriptors. Study 2 evaluated whether this distinction provided a sufficient summary of relations between the Fenigstein, Scheier and Buss (1975) Self-Consciousness scales and the Five Factor Model of personality (FFM). In Study 3, two brief questionnaire measures of ruminative and reflective tendencies were developed, and their convergent and discriminant validity evaluated with respect to the FFM, and the Fenigstein et al. (1975) Public Self- Consciousness (PUSC) and Private Self-Consciousness (PRSC) scales. Study 4 investigated the extent to which rumination and reflection separately account for PRSC associations with measures of psychological distress (e.g., Beck Depression scale) and intellective dispositions (e.g., Need for Cognition scale), respectively. Study 5 evaluated, using a sample of dormitory roommates, the extent to which self-estimates of ruminativeness and reflectiveness correspond with the judgments of a knowledgeable observer. Studies 6, 7, and 8 evaluated the extent to which the traits of rumination and reflection separately account for previously reported PRSC associations with three theoretically relevant criteria of private self-consciousness: state indices of self-focused attention (Study 6), the asymmetry effect in self-other similarity judgments (Study 7), and research volunteerism (Study 8). Findings suggest that the PRSC scale confounds two relatively independent, and motivationally distinct dispositions, rumination and reflection, and that latent ruminative and reflective components of PRSC scores separately and fully account for PRSC correlates and effects. These findings provide a straight forward explanation of the "self-absorption" paradox implicit in the PRSC research literature, i.e., the consistent but apparently contradictory finding of more accurate and extensive self-knowledge, yet higher levels of subjective psychological distress, among persons high in private self-consciousness. It is likely that the PRSC's associations with psychological distress are uniquely due to its neurotic component (rumination), and that the PRSC's self-knowledge effects are uniquely due its intellective component (reflection). It is argued that rumination and reflection represent statistically and functionally independent self-focusing tendencies. Their strong and unique associations with the FFM dimensions of neuroticism and openness, respectively, imply a basic dichotomy of self-attentive motives: anxiety/fear and curiosity/exploration: rumination represents a useful summary conception of self-attentiveness motivated by perceived threats, losses, or injustices to the self; reflection represents a useful summary conception of self-attentiveness motivated by intrinsic curiosity, or epistemic interest in the self. It is concluded that the spatial metaphor of "direction" may not be an appropriate basis for a useful scientific conception of dispositional self-consciousness. The concept of a purely cognitive tendency to have attention chronically directed toward the self versus away from the self, construed independently of the emotional and motivational determinants of such a tendency, is probably untenable. / Arts, Faculty of / Psychology, Department of / Graduate

Various explanations have been proposed for the strong visible luminescence from porous silicon (PS), the most widely accepted being quantum confinement. In the quantum confinement model the bandgap of PS depends on the size of the microstructure. Double crystal x-ray diffraction on PS shows a narrow peak and a broad peak consistent with a two phase model for the structure of PS in which there is a macroporous backbone supporting a nanoporous surface layer. From the width of the diffuse peak we estimate the size of the silicon structures in the nanoporous region to range between 30-60A depending on the preparation conditions. Synchrotron radiation based techniques such as x-ray absorption spectroscopy (XAS) and photoemission spectroscopy (PES) allow direct measurement of the quantum shift in the conduction and valence band edges in porous silicon. High resolution measurements of the silicon L and K-edge absorption in porous silicon show that the absorption threshold is shifted to higher energy relative to bulk silicon, and the shift is dependent on how the porous silicon is prepared. The blue shift of the conduction band minimum in PS is understood qualitatively using a simple LCAO model. The x-ray absorption spectra also show an excitonic enhancement at the Si L edge in PS which increases with the quantum shift in the L-edge absorption. The enhanced excitonic absorption, is in agreement with the expectation that electron-hole interactions increase in silicon nanocrystals because of confinement effects. PES data show that the valence band of porous silicon is also shifted relative to the bands for bulk silicon. The quantum shift in the valence band is larger than the shift in the conduction band and is proportional to it with a proportionality constant of 2.0 that is independent of preparation conditions. An independent conformation of the relationship between the quantum shifts in the valence and conduction band edges is obtain from PS annealing experiments. The quantum shifts in the conduction and valence band edges of PS relative to bulk Si are found to decrease with progressively higher annealing temperatures, up to 550°C, at which point the band edge energies revert to the values for bulk Si. The ratio of the shift in the valence band edge to the shift in the conduction band edge remains approximately constant with annealing and equal to 1.9, in agreement with the ratio determined as a function of preparation conditions. This result suggests that the PS microstructure progressively becomes larger when heated between 400 and 500°C where the surface hydrogen evolves. The ratio of the valence band shift to conduction band shift is predicted to be 1.5 using an effective mass model for the quantum shifts. Measurements of the Si L-edge were used to probe the effects of different preparation procedures on the electronic structure of PS. When the porous silicon is made from n-type material with light exposure, the blue shift increases logarithmically with the anodizing current and anodization time. We explore the hypothesis that the etching reaction self-limits and that the quantum size effect is a key part of the self-limiting mechanism. Two models have been proposed to explain the light intensity and time dependence of the quantum shift in anodized n-type PS. The peak energy of the room temperature photoluminescence of PS is compared with the bandgap determined from the XAS and PES measurements for a series of PS sample prepared under different conditions. The photoluminescence bandgap is found to be smaller than the photoelectron spectroscopy bandgap, but exhibits the same trend with preparation conditions. The width of both the photoluminescence spectrum and the L- absorption edge increase with increasing blue shift, consistent with a distribution of quantum confinement energies. An alternative explanation for the visible PL in PS is emission from a surface siloxene (Si6H6O3) layer which is peaked near 550 nm. The structure of siloxene is known to consist of Si (111) layers terminated above and below by OH groups and H atoms. This is difficult to reconcile with photoelectron experiments which show that freshly prepared PS does not contain oxygen. Recently an oxygen-free form of siloxene (Si6H6) called layered polysilane has been synthesized. The x-ray absorption of the layered polysilane and PS are found to be remarkably similar. In particular, the K absorption edge of layered polysilane is shifted by 0.6 eV the same as that of the PS samples with the maximum conduction band shift. Conceivably PS could consist of (111) oriented layers of Si terminated with hydrogen with a chemical formula Si6nH6, where n is the number of layers and it depends on the preparation conditions. In this picture layered polysilane (n=l) is the limiting form of PS. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A number of decisions confront both the public and private sectors when considering the use of a Public-Private Partnership (PPP) approach for a given project. They include: identifying the design alternatives which best satisfy public needs and the project's constraint set; what PPP approach is best suited for the alternatives selected; and, for a given PPP approach, how should risks be mitigated, residual risks assigned, and what compensation is justified. Additional decisions from a private-sector viewpoint deal with whether to pursue a proposal or not, and under what conditions should a consortium withdraw from the process. In seeking help with these decision problems, one finds that the knowledge base required is highly fragmented, little objective assessment of the pros and cons of various approaches is available, few real life experiences have been analysed and documented in the form of case studies, and, formal tools to assist with these decisions are few and invariably lack the depth commensurate with the magnitude of the commitments and risks involved. This work presents an analysis framework designed to address several of these decisions. This framework was derived based on a thorough review and analysis of the literature, a case study of the Northumberland Strait Crossing project (The Fixed Link to Prince Edward Island), and significant interaction with the B.C. Ministry of Transportation and Highways (MoTH-B.C). As part of this framework, an economic evaluation model which provides a mechanism for unifying the phases, and the cost and time consequences of the performance/risk dimensions which characterize a project is developed. This model can be used for both deterministic and probabilistic analyses, from which valuable insights dealing with the behavior of PPP projects can be drawn. They include: quantification of overall economic and financial performance as a function of different variable values; estimation of overall risks, their composition and probabilities of failure; bounds on rates of return; tradeoffs between rates of return and risk assignment strategies; and, the relative effectiveness of different strategies for project speed-up (e.g. fast-tracking versus construction acceleration). A hypothetical case study is used to illustrate the power of the developed framework and the diversity of issues that must be addressed for PPP projects. Key findings in this research include: - Each project is a unique case and has to be assessed based on its merits and constraints. However, documentation of the experience gained in every project, especially in terms of risks is essential for enhancing the scant knowledge base that currently exists; - In general, and given the government's capability to acquire financing at a lower price than can the private sector, BOT's could be more expensive from a user-charge perspective, unless savings can be achieved in other project inputs such as capital costs and operating and maintenance costs. However, they can be potentially viable in cases when no funds are available, or for projects that have near monopoly situations; and, - Acceleration strategies such as fast-tracking design and construction and acceleration of construction exhibit only marginal benefits. The greatest benefits of adopting these strategies are expected when penalties are imposed for untimely completion of construction. The thesis highlights some of the knowledge gaps that exist in the literature and concludes with several recommendations for further research to enhance the developed framework. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

This thesis consists of three parts. In Part I, a two-Liouville space theory of reactive gases is formulated in an effort to understand and by-pass the strong orthogonality approximation standardly used in reactive gas kinetic theories. The formulation is based on a two-Liouville space scattering formalism developed in this thesis. The present work follows an approach very similar to the presentation by Lowry and Snider (J. Chem. Phys. 61, 2320 (1974)). Kinetic equations for arbitrary bound clusters are derived within the structure of the two-Liouville space scattering theory. Bound clusters for an arbitrary number of particles are systematically treated in the present work and defined as the asymptotic bound fragments in the N-particle asymptotic Liouville space. A method of closure, which is quite different from the conventional BBGKY procedure, is introduced to yield a compact set of kinetic equations for the clusters. A comparison with the Lowry-Snider theory is given. In Part II, a Hilbert-Schmidt representation of Ursell operators is given. It is found that the connected quantum Ursell operators are closely related to the Hilbert-Schmidt kernel of Faddeev (for three particles), and its generalization to the description of the collision of an arbitrary number of particles. This important feature permits the formulation of a general Hilbert-Schmidt representation of Ursell operators by expressing the latter in terms of Hilbert- Schmidt kernels. As a consequence, it is seen how the virial coefficients can be evaluated using Hilbert-Schmidt expansions. In particular, second virial coefficient is explicitly expressed in terms of the Hilbert-Schmidt expansion of the resolvent operator. Square integrable states associated with the resonance poles have been found of use in carrying out this expansion. The method depends on distinguishing between the functional analysis properties of the resolvent operator and the analytic function properties of its matrix elements. In Part III, a renormalized quantum Boltzmann equation (R. F. Snider, J. Stat. Phys. 61, 443 (1990)) has been generalized to include the presence of bound states. This has involved the introduction of three coupled equations, one each for the renormalized particle, the bound pair and the unbound pair correlations. The latter is responsible, at equilibrium, for the unbound part of the second virial coefficient. Chapman Enskog solutions to this set of equations are obtained in two schemes. One for moderately dense gas in which there are no bound states, the other in the presence of bound states. The Wigner representation for quantum mechanical operators are used throughout to separate the macroscopic and microscopic properties of the state of system. The resulting expressions for the transport coefficients in the first scheme have contributions arising from particles that are free and from pair correlations. In the second, there are also contributions from the bound pairs. / Science, Faculty of / Chemistry, Department of / Graduate

Surface crystallographic analyses have been undertaken with the tensor LEED approach in low-energy electron diffraction (LEED) in order to contribute to the development of the principles of surface structural chemistry. For the Rh(110)-c(2x2)-S surface structure, each S atom chemisorbs on a center site of the Rh(110) surface. It bonds to the second layer Rh atom directly below, with a bond distance equal to about 2.27 A, and to four neighboring First layer Rh atoms at close to 2.47 A. A significant feature of this structure is that the second metal layer is buckled; those Rh atoms directly below the S atoms relax down by about 0.11 A compared with the other second layer Rh atoms. This buckling is apparently driven by the need to reduce the difference that would otherwise occur between these two types of S-Rh bond lengths. A component in the observed difference between the S-Rh distances appears to be dependent on the metallic coordination number for the Rh atoms. For the corresponding higher coverage Rh(110)-(3x2)-S surface, the result supports an arrangement of chemisorbed S atoms at 2/3 monolayer (ML) coverage on a basically unreconstructed metallic structure. Alternating [110] channels in the metal surface are occupied differently, although each has two S atoms per unit mesh. In one set, the S atoms occupy long-bridge and center sites with a constant separation along the channel of 4.03 A. In the other set of channels, all S atoms occupy equivalent positions, displaced from regular center sites by 0.39 A, to give successive S to S separations of 3.47 and 4.60 A. The long-bridge site bonding is a novel feature which is facilitated by the neighboring topmost Rh atoms relaxing laterally by about 0.27 A perpendicular to the [110] row. Bucklings of 0.20 and 0.10 A are indicated to occur in the first and the second Rh layers respectively; the latter value essentially equals that (0.11 A) in the corresponding c(2x2) surface. For S atoms at or near center sites in the (3x2) structure, the average S-Rh bond distances to the first and the second Rh layer atoms are 2.42 and 2.29 A respectively; the corresponding values at the long-bridge sites are 2.20 and 2.27 A. New analyses for the Rh(111)-(>^x>/3)R30o-S and Rh(111)-c(4x2)-S surface structures indicate S coverages of 1/3 and 1/2 M L respectively. For the lower-coverage form, S adsorbs on the regular three-coordinate sites which continue the fcc packing sequence; the S-Rh bond lengths are indicated to equal 2.23 A, and relaxations in the metallic structure are negligible. In the c(4x2) form, the adsorption occurs equally on both types of three-coordinate site (fcc and hcp), although some surface Rh atoms bond to two S atoms while others bond to only one, and this sets up some interesting relaxations. Specifically, the S atoms displace laterally from the center of the threefold sites by 0.20 to 0.29 A, and the first metal layer is buckled by about 0.23 A. The first-to-second interlayer spacing in the metal expands to 2.26 A from the bulk value of 2.20 A. The average S-Rh bond length equals 2.22 A, and is not significantly changed from that in the low-coverage form. The structural evolution with increasing coverage for S chemisorbed on the (111) surface of Rh shows a close relation to the corresponding evolution on the Rh(110) surface. ln the Rh(111)-(2x1)-0 surface structure formed by chemisorption of O on the Rh(111) surface, O atoms chemisorb close to the regular fee sites. The structure shows significant relaxations; for example, a buckling of about 0.07 A is indicated in the first metal layer and O appears to displace laterally by about 0.05 A. The individual O-Rh bond lengths are around 2.01 and 1.92 A to top layer Rh atoms which bond to two and one O atoms respectively. Comparison is made with O-Rh bond lengths determined recently by another group for the Rh(110)-p2mg(2x1)-0 surface structure. / Science, Faculty of / Chemistry, Department of / Graduate