Structural Congruence Research Articles

Automatically Proving Up–to Bisimulation

We present a tool for checking bisimilarities between π–calculus processes with the up–to techniques for bisimulation. These techniques are used to reduce the size of the relation one has to exhibit to prove a bisimulation. Not only is this interesting in terms of space management, but it also increases dramatically the expressive power of our system, by making in some cases the verification of infinite states space processes possible. Based on an algorithm to compute a unique normal form for structural congruence, we develop sound and complete methods to check bisimulation up to injective substitutions on free names, up to restriction and up to parallel composition. We show the usefulness of our results on a prototype implementation.

Flow Logic and Operational Semantics

Flow logic is a “fast prototyping” approach to program analysis that shows great promise of being able to deal with a wide variety of languages and calculi for computation. However, seemingly innocent choices in the flow logic as well as in the operational semantics may inhibit proving the analysis correct. Our main conclusion is that environment based semantics is more flexible than either substitution based semantics or semantics making use of structural congruences (like alpha-renaming).

The Cuboidal Fe3S4 Cluster: Synthesis, Stability, and Geometric and Electronic Structures in a Non-Protein Environment

Of the three known low-nuclearity iron−sulfur clusters in metallobiomolecules with the core units Fe2S2, Fe4S4, and Fe3S4, the last has not been obtained in stable form outside a protein environment. We describe a direct route to such clusters in the [Fe3S4]0 oxidation state, and demonstrate an effective stereochemical and electronic structural congruence with the native cluster. The synthesis is based on iron-site-differentiated clusters. Reaction of [Fe4S4(LS3)(SEt)]2- with (Et3NH)(OTf) affords [Fe4S4(LS3)(OTf)]2-, whose unique site is activated toward terminal ligand substitution. Treatment with 1 equiv of (Et4N)2(Meida) affords [Fe4S4(LS3)(Meida)]3-, which is readily converted to [Fe3S4(LS3)]3- with 1−2 equiv of additional reactant. The trinuclear cluster is formed by abstraction of Fe2+ from a precursor cubane-type [Fe4S4]2+ core and complexation as [Fe(Meida)2]2-. An analogous procedure starting with [Fe4Se4(LS3)(SEt)]2- yields [Fe3Se4(LS3)]3-. The compound (Et4N)3[Fe3S4(LS3)]·MeCN crystallizes in o...

Molecular modeling of the weak glycine antagonist iso‐THAO

When compared to strychnine, a potent glycine antagonist, iso-THAO, a bicyclic 5-isoxazolol zwitterion, has been reported to be a weak glycine antagonist. Since there are so few glycine antagonists, and there is a striking lack of similarity between the structures of these two antagonists, iso-THAO was studied using current molecular modeling techniques and quantum mechanical calculations in order to compare the structural features and charge distributions of iso-THAO with glycine. The results of this study confirm our earlier hypothesis that an antagonist to inhibitory neurotransmitters like glycine and GABA has at least three binding sites to the natural receptor that are very similar to three such binding sites in the transmitter and its agonists, and each antagonist has an additional negative binding site. We speculate that the latter negative binding site can attach to the top of the chloride channel within the receptor complex. The diminished inhibitory activity of iso-THAO is attributed to its poor structural congruence with the three atom attachment sites used by glycine at its natural recognition site.

Internship Strategy for Hospitality Management Programs

This paper shares an effective model for experiential education. This paradigm is unique because it represents a balanced triangular commitment from the univer sity, the industry and the student. Without this equal and committed partnership, the maximization of student development would be limited. The basic components of the model; quality commitment, structural congruence with the program mission state ment, competency based experiences, grading and evaluation mechanisms may be replicated in most academic settings.

A kinetic study of wild-type and mutant dihydrofolate reductases from Lactobacillus casei

A kinetic scheme is presented for Lactobacillus casei dihydrofolate reductase that predicts steady-state kinetic parameters. This scheme was derived from measuring association and dissociation rate constants and pre-steady-state transients by using stopped-flow fluorescence and absorbance spectroscopy. Two major features of this kinetic scheme are the following: (i) product dissociation is the rate-limiting step for steady-state turnover at low pH and follows a specific, preferred pathway in which tetrahydrofolate (H4F) dissociation occurs after NADPH replaces NADP+ in the ternary complex; (ii) the rate constant for hydride transfer from NADPH to dihydrofolate (H2F) is rapid (khyd = 430 s-1), favorable (Keq = 290), and pH dependent (pKa = 6.0), reflecting ionization of a single group. Not only is this scheme identical in form with the Escherichia coli kinetic scheme [Fierke et al. (1987) Biochemistry 26, 4085] but moreover none of the rate constants vary by more than 40-fold despite there being less than 30% amino acid homology between the two enzymes. This similarity is consistent with their overall structural congruence. The role of Trp-21 of L. casei dihydrofolate reductase in binding and catalysis was probed by amino acid substitution. Trp-21, a strictly conserved residue near both the folate and coenzyme binding sites, was replaced by leucine. Two major effects of this substitution are on (i) the rate constant for hydride transfer which decreases 100-fold, becoming the rate-limiting step in steady-state turnover, and (ii) the affinities for NADPH and NADP+ which decrease by approximately 3.5 and approximately 0.5 kcal mol-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Social Determinants of Perception: Power, Equity, and Status Effects in an Exchange Situation

Emphasizing the perceptual interdependence of social exchange partners, this study tests hypotheses derived from assumptions about self-enhancing social categorization coupled with the perspective adopted by the perceiver. Subjects assumed the role of a typist who, as described in a vignette, conducts a transaction with a student seeking typing services. Social factors defining categories included structural power position (typist lowlother high; typist highlother low), outcome equity (underreward, equity, overreward), and status congruence between the task and the sex composition of the dyad (female typistlmale other; male typistlfemale other). Evaluation and rationality components emerged from factor analysis involving indicators of perceptions of self and other. Results confirm the expected positive relationship between power and favorable self-perceptions. Outcome equity affected perceptions differentially, influencing self's rationality and other's evaluation. Status congruence effects were nonsignificant. Implications for reactions to inequity are discussed.

Catalytic Antibodies

Monoclonal antibodies elicited to haptens that are analogs of the transition state for hydrolysis of carboxylic esters behaved as enzymic catalysts with the appropriate substrates. These substrates are distinguished by the structural congruence of both hydrolysis products with haptenic fragments. The haptens were potent inhibitors of this esterolytic activity, in agreement with their classification as transition state analogs. Mechanisms are proposed to account for the different chemical behavior of these antibodies with two types of ester substrates. The generation of an artificial enzyme through transition state stabilization by antibodies was thus demonstrated. These studies indicate a potentially general approach to catalyst design.

The anatomy of a corporate venturing program: Factors influencing success

The author proposes a classification framework for factors that affect corporate venture success. Then, a database of 37 new venture investments by Exxon, including 18 venture capital investments, is analyzed for insight into the relative affect of these factors on venture technical and financial success. This article presents a statistical analysis of those factors which were quantified. As a group the venture capital investments were financially far more successful for Exxon than the internally initiated ventures. This striking difference stimulated the retrospective analysis reported here. The author was in a position to observe the program over its entire life span and had first-hand knowledge of each venture's technology, markets, and personnel. Because of the mix of venture capital and internal investments, the author was also in a position to compare the two modes of investment. Factors affecting venture success are broadly classified as extrinsic and intrinsic. Extrinsic or environmental factors are those determined by the form of investment sponsorship (e.g., corporate or venture capital) and the characteristics of the investment sponsor. Extrinsic factors are segregated into two categories: structural and procedural. These factors are defined as the degree of difference between the corporate and venture environment in each category. The four structural factors (technology, market, organization, and people) are summed up as the overall degree of structural congruence. The author postulates that the degree of congruence is directly related to venture success within the corporation. To take the corporation into new markets some incongruence is required. Too much incongruence probably pushes the risk of failure too high. The corporation's procedures for management of this incongruence will determine the degree to which it can successfully diversify its business. The four procedural factors (control, selection of venture managers, incentive compensation, and financing) are dealt with as differences between the corporate environment and an independent venture environment. Major differences in procedural factors usually exist between corporate and venture capital sponsored ventures. They probably explain to some extent the relative greater financial success of the Exxon venture capital investments as a group. However, the statistical analysis results indicate that the identified intrinsic factors are more important in explaining relative venture success. Intrinsic factors are those inherent to the venture itself, and are subdivided into two categories: product related (market and technical risk levels) and managerial (relative experience levels). Each of the 37 Exxon ventures was rated for success and for the intrinsic factors using a simple ordinal range of 3 to 6 values. The product related risk factors showed a significant inverse correlation with financial success. The level of venture managers' prior experience in the venture's target market area and their level of prior general managerial experience showed an even greater correlation with financial success. The sample correlation coefficient between the financial success rating SF and the sum of the ratings for prior marketing and managerial experience (XS + XM) was 0.809 with a standard error of only 0.105. Selection of the influential extrinsic and intrinsic factors is largely within the control of corporate management. An approach to selection of these factors similar to that used by private venture capital fund managers should greatly improve the overall success of internal corporate ventures.

A Policy-Oriented Theory of Corruption

Perspectives from political science and economics are drawn on to suggest an integrated theory of governmental corruption. The theory is oriented toward policy choices, and corruption is viewed as a product of individual and structural variables that interact to produce both positive and negative consequences. Individual-level considerations such as greed and the likelihood of detection and prosecution suggest one set of policies for reducing corruption. Bureaucratic constraints, citizen participation, and the congruence of legal structures and social demands offer a competing set of concerns that must be dealt with in analyzing corrupt practices. We show that corruption, as a process, influences the optimal level of social welfare. Alternative conceptions are examined, and a model is developed to evaluate policy choices related to corruption from the perspective of welfare optimization. Applied to the analysis of corruption, the model integrates general equilibrium theory, deterrence theory, and structural conditions. Finally, policy implications are considered.

Dynamic and Structural Relationships Among Leaves, Roots, and Storage Tissue in the Sugar Beet

Clearing 1-5-mm-thick cross sections of growing storage roots indicated that number and development of vascular rings in the storage root are consequences of the increasing number of leaves. The vascular bundle rings are originally spirals derived from the spiral arrangement of leaves. The new clearing method also revealed that leaf traces can traverse each other in the stem without forming many vascular connections. Inversion of the vasculature, e.g., traces from peripheral leaves extending to the root center and traces from young leaves extending to the root periphery, takes place within the stem and also partly in the hypocotyl. Evidence is provided that (1) each vascular ring is in direct connection with a certain number of leaves, and (2) leaves are preferentially connected with regions of the root belonging to the same orthostichon. Our results support the hypothesis of a structural congruence in the development of leaves and of the storage root.

Dulness Unbound: Rhetoric and Pope'sDunciad

It has long been recognized that the American formalists' rehabilitation of Alexander Pope depended on a renewed interest in rhetoric. In fact, there is a remarkable structural congruence between the formalists image of Pope's poetry and their conception of rhetoric, for both are item-centered, combinatory, and ultimately unifying. A single model of unified diversity, then, governs not only the formalist image of Pope's couplet rhetoric and theodicean scheme but formalist conceptions of rhetoric and “organic form” as well. An alternative (and complementary) model of rhetoric, however, insisting on creation as an act of structuring through differentiation rather than through unification, can help us to a fuller understanding ofThe Dunciad, and especially of the place of Dulness in that poem. Such a model can also generate a poetics capable of granting to satire and mock forms an appropriately primary status. (FVB)

An Algorithm for Assessing Factor Structure Congruence

The coefficient of congruence is a quantitative measure of the similarity of factor structures for different samples of subjects. This paper is intended to inform interested readers of the availability of a computer program capable of computing coefficients of congruence of factor structures.

The Congruence of Factor-Analytic Structures: Comparisons of Four Procedures and Their Solutions

Use of factor analytic techniques for the analysts of organizational data is increasing. Four readily available techniques are described. Results derived from application of each technique to a common data set are compared.

The Congruence of Factor-Analytic Structures: Comparisons of Four Procedures and Their Solutions.

The Congruence of Factor-Analytic Structures: Comparisons of Four Procedures and Their Solutions.