Showing papers by "University of Texas at Dallas published in 1980"

On visible surface generation by a priori tree structures

Abstract: This paper describes a new algorithm for solving the hidden surface (or line) problem, to more rapidly generate realistic images of 3-D scenes composed of polygons, and presents the development of theoretical foundations in the area as well as additional related algorithms. As in many applications the environment to be displayed consists of polygons many of whose relative geometric relations are static, we attempt to capitalize on this by preprocessing the environment's database so as to decrease the run-time computations required to generate a scene. This preprocessing is based on generating a “binary space partitioning” tree whose in order traversal of visibility priority at run-time will produce a linear order, dependent upon the viewing position, on (parts of) the polygons, which can then be used to easily solve the hidden surface problem. In the application where the entire environment is static with only the viewing-position changing, as is common in simulation, the results presented will be sufficient to solve completely the hidden surface problem.

Situational Constraints and Work Outcomes: The Influences Of a Frequently Overlooked Construct

Abstract: We present a conceptual framework specifying the hypothesized influences of situational constraints on work outcomes and individual difference to work outcome associations. In addition to reviewing the relevant literature and discussing the implications for researchers and practitioners, we suggest a systematic program of needed research.

Consistency in Hierarchical Database Systems

Abstract: The problems of locking and consistency m database systems are examined It is assumed that each transacuon, when executed alone, transforms a consistent state into a consistent state A set of conditions is derived to guarantee that when transactions are processed concurrently, the results are the same as would be obtained by processing the transactmns serially These conditions are used to estabhsh a locking protocol in Merarchmal database systems The locking protocol allows transaeuons to request new locks after releasing a lock. However, a data item may be locked at most once as a result of each transacUon It ~s shown that the protocol ensures consistency and that tt ts deadlock free.

Causality Analysis and Multivariate Autoregressive Modelling with an Application to Supermarket Sales Analysis

Abstract: This paper describes a modelling methodology for multivariate stochastic processes. The concept of multiple causality is discussed and a procedure to detect multiple causality is suggested. The data of a major Canadian supermarket is analyzed and a multivariate autoregressive model for this supermarket is constructed and estimated. Several empirical findings are reported.

Strategy Formulation in Declining Industries

Abstract: Because the environments of declining industries differ, many different strategies could be appropriate for coping with declining demand. Demand and customer traits, product traits, supplier behavior, competitor traits, and exit barriers must be taken into account by a firm in a declining industry. Strategy alternatives include early exit, milking the company's investment, shrinking selectively, holding the present position, and increasing investments. Some possible strategies must be adopted early if they are to succeed.

Measuring Personal Values: An Evaluation of Alternative Methods:

Abstract: Three methods of gathering and evaluating value profiles for use in market segmentation are compared. Different reliability estimates are found to produce different conclusions as to the relative t...

The effect of exit barriers upon strategic flexibility

Abstract: The conceptual construct, exit barriers, is expanded using both statistical findings and the results of field studies. The immobility of resources, it is suggested, can be overcome by helping marginal competitors to exit from potentially volatile businesses. The implementation of such tactics can be adapted to the firm's own strategic commitment and to the nature of the business in question, although it is expected that firms which might consider purchasing the physical and intangible assets of competitors in order to help them to scale high exit barriers, must themselves perceive the business to be of sufficiently high strategic importance to do so.

Characterization of thin films of the palladium-hydrogen system.

Abstract: In this paper we present a study of the pressure-concentration ( P − C ) isotherms and the resistance properties of evaporated palladium films to which hydrogen has been added in situ at 27 °C. Hydrogen was introduced into the samples via the gas phase and the equilibrium H Pd ratio was determined using a quartz-crystal mass monitor. We find that the P − C function is highly dependent on film thickness, with the slope of the α + β coexistence region increasing and the limiting β-phase concentration decreasing with decreasing film thickness. However, the P − C function does approach bulk behavior for thick films ( t > 1000 A ). Film resistance was measured as hydrogen was cycled in and out of annealed and unannealed films. The annealed films show reversible electrical behavior with respect to hydrogen cycling; unannealed films are also electrically reversible in the α phase but show a monotonie decrease in resistance with cycling of hydrogen concentration through the β phase. For the unannealed films the ratio of the film resistance after maximum hydrogen uptake (β phase at a hydrogen pressure of 60 Torr) to the vacuum film resistance increases with cycling. This ratio never exceeds that for the annealed films.

Ultraviolet downconverting phosphor for use with silicon CCD imagers

Abstract: The properties and application of a UV downconverting phosphor (coronene) to silicon charge coupled devices are discussed. Measurements of the absorption spectrum have been extended to below 1000 A, and preliminary results indicate the existence of useful response to at least 584 A. The average conversion efficiency of coronene was measured to be approximately 20% at 2537 A. Imagery at 3650 A using a backside illuminated 800 x 800 CCD coated with coronene is presented.

Aggregation-dependent turnover of flagellar adhesion molecules in chlamydomonas gametes

Abstract: Previous studies on flagellar adhesion in chlamydomonas (Snell, W. and S. Roseman. 1979. J. Biol. Chem. 254:10820-10829.) have shown that as gametes adhere to flagella isolated from gametes of the opposite mating type, the adhsiveness of the added flagella but not of the gametes is lost. The studies reported here show that the addition of protein synthesis inhibitors (cycloheximide [CH] or anisomycin) to the medium of such cell- flagella mixtures causes the cells to lose their adhesiveness. This loss, however, occurs only after the cells have interacted with 4-8 flagella/cell and does not occur if the cells are kept in CH (7 h) without aggregating. The availability of an impotent (imp) mating type plus (MT(+)) mutant (provided by U.W. Goodenough), which adheres but is unable to undergo the fusion that normally follows adhesion, made it possible to determine whether a similar loss of adhesiveness occurs in mixtures of matting type minus (mt(-)) and imp mt(+) gametes. In the absence of inhibitor, mt(-) and imp mt(+) gametes adhered to each other (without fusing) for several hours; however, in the presence of CH or anisomycin, the gametes began to de-adhere 35 min after mixing, and, by 90 min, 100 percent of the cells were single again. This effect was reversible, and the rapid turnover of cells were single again. This effect was reversible, and the rapid turnover of molecules involved in adhesion occurred only during adhesion inasmuch as gametes pretreated for 4 h with CH were able to aggregate in CH for the same length of time as nonpretreated cells aggregated in CH. By the addition of CH at various times after the mt(-) and imp mt(+) gametes were mixed, measurements were made of the "pool size" of the molecules involved in adhesion. The pool reached a minimum after 25 min of aggregation, rapidly increased for the next 25 min, and then leveled off at the premixing level. These results suggest that flagellar adhesion in chlamydomonas causes modification of surface molecules (receptors, ligands), which brings about their inactivation and stimulates their replacement.

An Analysis of Fish Genomes by Density Gradient Centrifugation

Abstract: DNA was prepared from 33 species of fishes representing 12 of the 31 orders of Teleostei and one order of Chondrichthyes. DNA samples were investigated to determine modal and mean buoyant densities in CsCl (q0 and 〈q〉), main-band asymmetry, intermolecular compositional heterogeneity and base composition. Modal buoyant densities ranged over 1.697–1.704 g/cm3, generally with identical or close values for DNAs from species belonging to the same order. Main bands were practically symmetrical in most cases; when present, asymmetries were on the heavy side of the band and rather modest. In most cases, compositional heterogeneities were equal to, or lower than, those of bacterial DNAs. Both the CsCl band symmetry and the low compositional heterogeneity strikingly distinguish fish DNAs from the DNAs of warm-blooded vertebrates and indicate a major discontinuity in genome organization in the vertebrates. The overall properties of the main bands of fish DNAs are very similar to those exhibited by the light components of DNAs from mammals and birds.

The Contribution of Crime to Urban Decline

Abstract: The fact that crime is higher in the larger urban centers and in the central cities of metropolitan areas suggests that crime has contributed to suburbanisation. Previous studies have been unable to extricate crime from other causes of suburbanisation and central city decline. The present study of residential mobility isolates the effect of property crime from other neighborhood characteristics, such as accessibility to workplace and social composition. In Dallas it is found that the repelling effects of crime for potential movers is greater for families with children than without and for more affluent families, white and black.

On Whitney's 2‐isomorphism theorem for graphs

Abstract: Let G and H be 2-connected 2-isomorphic graphs with n nodes. Whitney's 2-isomorphism theorem states that G may be transformed to a graph G* isomorphic to H by repeated application of a simple operation, which we will term “switching”. We present a proof of Whitney's theorem that is much shorter than the original one, using a graph decomposition by Tutte. The proof also establishes a surprisingly small upper bound, namely n-2, on the minimal number of switchings required to derive G* from G. The bound is sharp in the sense that for any integer N there exist graphs G and H with n ≥ N nodes for which the minimal number of switchings is n-2.

Informational Cues and Individual Differences as Determinants of Subjective Perceptions of Task Enrichment

Abstract: The influences of both manipulated enrichment informational cues and individual differences on subjective job perceptions were examined. Results indicate that both the manipulation and individual d...

Global Context Recovery: A New Strategy for Syntactic Error Recovery by Table-Drive Parsers

Abstract: Described is a method for syntactic error recovery that is compatible with deterministic parsing methods and that is able to recover from many errors more quickly than do other schemes because it performs global context recovery. The method relies on fiducial symbols, which are typically reserved key words of a language, to provide mileposts for error recovery. The method has been applied to LL(1) parsers, for which a detailed algorithm is given, and informally proved correct. The algorithm will always recover and return control to the parser if the text being analyzed satisfies only minimal requirements: that it contains one or more occurrences of fiducial symbols following the point at which an error is detected. Tables needed for error recovery have been automatically generated, along with parsing tables, by a parser constructor for the LL(1) grammars.A theoretical characterization of fiducial symbols is given, and the utility of this characterization in practice is discussed. It has been applied to a grammar for the programming language Pascal to aid in selection of a set of fiducial symbols. The error recovery scheme has been tested on a set of student-written Pascal program texts and is compared with other error recovery strategies.

Streptomycin-Induced Defects of the Otocon1al Membrane

Abstract: Damage to the neuro-epithelium caused by the vestibulotoxic drugs has been well described in previous reports; however, little is known about the effect of such drugs on the otoconia. In this inves...

Behavior of aggregate state variables in ecosystem models

Abstract: Our lack of complete knowledge concerning ecosystems necessitates the use of aggregate (lumped) state variables in ecosystems models. Solutions to the state equations describing these aggregates typically deviate from reference true values found by solving equivalent disaggregated systems. Since the true value is unknown in practice, it is necessary to understand how aggregate state variables behave, so as to (1) understand the error they will generate and (2) be able to minimize unacceptably high error. Analyses are restricted to the ecologically most meaningful case of aggregating within single trophic levels. Results include a general solution for aggregate dynamics under free and forced simulation, other general and specific solutions for nonequilibrium behavior, a recursive method for reducing aggregation error, and a suggested strategy for aiding in sample design.

Effects of Changes in Job Characteristics on Some Theory-Specific Attitudinal Outcomes: Results from a Naturally Occurring Quasi-Experiment

Abstract: The present research examined changes in motivational properties of jobs as measured in the theoretical context of Hackman and Oldham's [19761 job characteristics model through a quasi-experimental design. In an effort to reduce utility costs, a manufacturing organization underwent a planned change from a 5-to a 4-day work week. Changes in characteristics ofjobs in the organization which resulted from the shortened work week were introduced without regard for the motivational consequences of the new schedule. Neither "expectation levels" (King, 1974) nor organizational policies pertaining to the reward system were changed when the 4-day work week was implemented. The overall design of the planned change resembled that of a quasi-experiment, permitting examination of the causal impact of changes in core job dimensions on employee attitudinal outcomes. Measures of core job dimensions and outcome variables were collected before and after the change. Results showed that the group characterized by an increase ...

Stochastic modeling in computer graphics

Abstract: A recurrent problem in generating realistic pictures by computers is to represent natural irregular objects and phenomena without undue time or space overhead. We develop a new and powerful solution to this problem by modeling objects as sample paths of stochastic processes. Of particular interest are those stochastic processes which previously have been found to be useful models of the natural phenomena to be represented. One such model applicable to the representation of terrains, known as “fractional Brownian motion”, has been proposed by B. Mandelbrot.The value of a new approach to object modeling in Computer Graphics depends largely on the efficiency of the techniques used to implement the model. We introduce here a new, efficient algorithm for rendering realistic surfaces defined using the stochastic process mentioned above. A major advantage of this technique is that it allows us to compute the surface to arbitrary levels of detail without increasing the database. Thus objects with complex appearance can be displayed from a very small database. The character of the surface can be controlled by merely modifying a few parameters. A similar change allows complex motion to be created inexpensively.

Individual Differences and Job Design Reconsidered: Where Do We Go from Here?

Abstract: White [1978], in a recent review, has focused attention on the modest and inconsistent findings often evident in earlier job design moderator research. In this paper, we discuss several conceptual and methodological inadequacies that may account for these results and we review evidence supporting the potential value of individual-difference research within the job design field.