Showing papers by "University of Chicago published in 1982"

A Rasch Model for Partial Credit Scoring.

Abstract: A unidimensional latent trait model for responses scored in two or more ordered categories is developed. This “Partial Credit” model is a member of the family of latent trait models which share the property of parameter separability and so permit “specifically objective” comparisons of persons and items. The model can be viewed as an extension of Andrich's Rating Scale model to situations in which ordered response alternatives are free to vary in number and structure from item to item. The difference between the parameters in this model and the “category boundaries” in Samejima's Graded Response model is demonstrated. An unconditional maximum likelihood procedure for estimating the model parameters is developed.

Mass Extinctions in the Marine Fossil Record

Abstract: A new compilation of fossil data on invertebrate and vertebrate families indicates that four mass extinctions in the marine realm are statistically distinct from background extinction levels. These four occurred late in the Ordovician, Permian, Triassic, and Cretaceous periods. A fifth extinction event in the Devonian stands out from the background but is not statistically significant in these data. Background extinction rates appear to have declined since Cambrian time, which is consistent with the prediction that optimization of fitness should increase through evolutionary time.

The Effects of Macrobenthos on Chemical Properties of Marine Sediment and Overlying Water

Abstract: The composition of any environment or object is determined by a particular balance between material transport processes and chemical reactions within and around it. In the case of marine sedimentary deposits, the dominant agents of mass transport are often large bottom-dwelling animals that move particles and fluids during feeding, burrowing, tube construction, and irrigation. Such biogenic material transport has major direct and indirect effects on the composition of sediments and their overlying waters. In this chapter I review some of what is presently known about these effects, their implications for both chemical and biological properties of a deposit, and how they can be conceptualized in quantitative models.

Archaeology as human ecology : method and theory for a contextual approach

Abstract: Part I. Perspectives: 1. Context in archaeology 2. Environmental systems: spatial and temporal variability Part II. Foundations: 3. Geo-archaeology I: basic principles 4. Geo-archaeology II: landscape context 5. Geo-archaeology III: stratigraphic context 6. Geo-archaeology IV: site formation 7. Geo-archaeology V: site modification and destruction 8. Geo-archaeology VI: human impact on the landscape 9. Archaeometry: prospecting, provenance, dating 10. Archaeobotany: vegetation and plant utilization 11. Zoo-archaeology: faunas and animal procurement Part III. Synthesis: 12. Spatial integration I: quantitative models for pattern analysis 13. Spatial integration II: socioecological models for settlement analysis 14. Spatial integration III: reconstruction of settlement systems 15. Diachronic systems I: cultural adaptation 16. Diachronic systems II: continuity and change References Index.

Adaptive EAP Estimation of Ability in a Microcomputer Environment

Abstract: Expected a posteriori (EAP) estimation of ability, based on numerical evaluation of the mean and variance of the posterior distribution, is shown to have unusually good properties for computerized adaptive testing. The calculations are not complex, precede noniteratively by simple summation of log likelihoods as items are added, and require only values of the response function obtainable from precalculated tables at a limited number of quadrature points. Simulation studies are reported showing the near equivalence of the posterior standard deviation and the standard error of measurement. When the adaptive testings terminate at a fixed posterior standard deviation criterion of .90 or better, the regression of the EAP estimator on true ability is virtually linear with slope equal to the reliability, and the measurement error homogeneous, in the range ± 2.5 standard deviations.

A neo-darwinian commentary on macroevolution.

Abstract: The neo-Darwinian synthesis that resulted from the integration of Mendelian genetics into evolutionary theory has dominated evolutionary biology for the last 30 to 40 years, due largely to its agreement with a huge body of experimental and observational data. The classic works representative of this school of thought come from the fields of genetics (Fisher, 1930; Wright, 1931; Haldane, 1932; Dobzhansky, 1937; Muller, 1940), development (de Beer, 1940), zoology, (Huxley, 1942; Mayr, 1942; Rensch, 1959), botany (Stebbins, 1950), and paleontology (Simpson, 1944, 1953). These authors broadly agree with Darwin's view that most important evolutionary changes at the level of the visible phenotype, as revealed by paleontological and systematic studies, have resulted from natural selection acting on variation within populations. This variation is ultimately due to mutations that arise at random with respect to the direction of selection. A role for evolutionary forces other than selection and mutation, such as random genetic drift, is of course recognized by neo-Darwinists, but selection is regarded as the main guiding force of phenotypic evolution. Within this general framework, there has been plenty of room for vigorous disagreements about the relative importance of different processes, such as the Wright-Fisher debate on the significance of random genetic drift. Recently, however, certain elements of neo-Darwinism have been sharply challenged by advocates of the "punctuated equilibria" theory of evolution (Eldredge and Gould, 1972; Gould, 1977, 1980; Stanley, 1975, 1979; Gould and Eldredge, 1977). Indeed, Gould (1980) states:

Reheating an inflationary universe

Abstract: A numerical analysis of the evolution of the Higgs expectation value and the temperature of the universe during the symmetry-breaking phase transition in an SU(5) theory with radiatively induced symmetry breaking is presented. It is shown that there is sufficient inflation (exponential expansion) to explain the cosmological homogeneity, isotropy, flatness, and monopole puzzles, and also that the universe reheats to a temperature $O({10}^{14} \mathrm{GeV})$ so that the usual scheme for baryogenesis can proceed.

Exploiting rank ordered choice set data within the stochastic utility model.

Abstract: The authors report on a procedure for exploiting the information content of rank ordered choice sets to estimate efficiently the parameters of the multinomial logit model formulation of the stochas...

An Experimental Comparison of Different Approaches to Determining Weights in Additive Utility Models

Abstract: Several studies this past decade have examined differences between holistic and decomposed approaches to determining weights in additive utility models. Some have argued that it matters little which procedure is used, whereas others strongly favored particular methods. In this paper we address this controversy experimentally by comparing five conceptually different approaches in terms of their weights and predictive ability. The five methods are 1 multiple linear and non-linear regression analyses of ten and fifteen holistic assessments, 2 direct decomposed tradeoffs as proposed by Keeney and Raiffa Keeney, R. L., H. Raiffa. 1977. Decisions with Multiple Objectives. Wiley, New York., 3 a recent eigen-vector technique of Saaty Saaty, T. L. 1977. A scaling method for priorities in hierarchical structures. J. Math. Psych.15 3 234-281. involving redundant pairwise comparisons of attributes, 4 a straightforward allocation of hundred importance points, and 5 unit weighting i.e., equal weighting after standardizing the attributes. The decision task involved college admissions. Subjects were asked to evaluate hypothetical college applicants on the basis of verbal SAT, quantitative SAT, high-school grade point average, and a measure of extra-curricular activity. Linear as well as nonlinear attribute utility functions were used in constructing the additive models. The nonlinear functions were specified graphically by the subjects through selection from five different shapes i.e., one per attribute. To test the predictive ability of the various models, each subject made twenty separate pairwise comparisons of alternatives including direction and strength of preference. The prediction criteria were percentage correct predictions as well as correlations using these twenty pairs. Seventy subjects were tested, using an order-controlled within-subject design, in comparing the different methods of weight determination. Monetary incentives were used to enhance motivation. In terms of findings, the methods generally differed systematically concerning the weights given to the various attributes, as well as the variances of the resulting predictions. On average, however, the methods predicted about equally well, except for unit weighting which was clearly inferior. The findings differ in this regard from the general literature. Furthermore, nonlinear models were found to be inferior to linear ones. Finally, subjects judged the methods to differ significantly in difficulty and trustworthiness, which were found to correlate inversely. The overall results raise various applied and theoretical issues, which are discussed.

Mammalian evolution and the great american interchange.

Abstract: A reciprocal and apparently symmetrical interchange of land mammals between North and South America began about 3 million years ago, after the appearance of the Panamanian land bridge. The number of families of land mammals in South America rose from 32 before the interchange to 39 after it began, and then back to 35 at present. An equivalent number of families experienced a comparable rise and decline in North America during the same interval. These changes in diversity are predicted by the MacArthur-Wilson species equilibrium theory. The greater number of North American genera (24) initially entering South America than the reverse (12) is predicted by the proportions of reservoir genera on the two continents. However, a later imbalance caused by secondary immigrants (those which evolved from initial immigrants) is not expected from equilibrium theory.

Voltage-activated and calcium-activated currents studied in solitary rod inner segments from the salamander retina.

Abstract: 1. Solitary rod inner segments were obtained by enzymatic dissociation of the tiger salamander (Ambystoma tigrinum) retina. Their membrane currents were studied with the single-pipette voltage-clamp technique. Individual currents were isolated with the aid of pharmacological agents. 2. Extracellular caesium blocked a current activated by hyperpolarization from -30 mV. Changing external sodium and potassium concentrations altered the value of the reversal potential in a manner consistent with the current being carried equally by both ions. 3. Extracellular tetraethylammonium (TEA) blocked a current activated by depolarization from -70 mV. In normal medium this current had a reversal potential of -72 mV. Changing the external potassium concentration altered the value of the reversal potential in a manner consistent with the current being carried predominantly by potassium. 4. Extracellular cobalt blocked a current activated by depolarization that had an initial inward and a later outward component. 5. After EGTA was injected into an inner segment the outward component was suppressed. Cobalt then blocked an inward current. This current is believed to be carried predominantly by calcium. The conductance increased with depolarization from -45 mV and reached a maximum at approximately 0 mV. Following a step of depolarization the current activated rapidly (< 20 msec) and then remained constant for at least several seconds without evidence of inactivation. 6. Injecting caesium into an inner segment eliminated a calcium-activated outward current believed to be carried by potassium ions. 7. After the injection of caesium there remained another calcium-activated current with a reversal potential of -17 mV. Changing extracellular chloride concentration altered the value of the reversal potential in a manner consistent with chloride carrying at least 70% of the current. Another anion may carry the balance. 8. When the five currents mentioned in items 2, 3, 5, 6 and 7 were blocked, the membrane resistance between -90 and -25 mV was linear, time-independent, and had a high value (2·1 GΩ). 9. The five identified currents can all be activated in the physiological range of voltage in which salamander rods normally operate.

Rapid origin of sexual isolation and character divergence in a cline.

Abstract: The recent revival of interest in modes of speciation without geographic isolation (reviewed by Bush, 1975; Endler, 1977; White, 1978) makes it appropriate to reinvestigate mechanisms for clinal speciation first outlined in genetic terms by Fisher (1930, Ch. 6). He noted that following adaptive divergence of geographical or ecological races, if hybrids are at a disadvantage, genetic variation in mating preferences (and/or habitat preferences) could lead to the evolution of a decreased frequency of hybridization. This mechanism for the evolution of sexual isolation was popularized by Dobzhansky (1940, 1951, 197 0 , Ch. 11) who believed it could occur only after secondary contact between races which had become partially reproductively isolated by postmating mechanisms (see also Sturtevant, 1938; Muller, 1940; Sibley, 1961; Mayr, 1963, p. 525-526, 548-559). Fisher (1915, 1930) also described a process of "runaway" sexual selection which can produce exponentially increasing rates of evolution in male secondary sexual characters and female mating preferences. As argued below, the latter mechanism is potentially much more powerful for initiating sexual isolation and character divergence along a cline than is selection against hybridization. Population genetic models have shown that when hybrids between geographic races are at a substantial disadvantage a narrow hybrid zone will evolve, followed perhaps by formation of reversed clines (i.e., reproductive character displacement) around the contact zone, and slow or limited diffusion of the genetic differences to remote regions by migration (Crosby, 1970; Endler, 1977; Caisse and Antonovics, 1978). However, if populations in the contact zone have comparatively low mean fitness, in part due to hybrid disadvantage, and if there is a net immigration from surrounding regions, gene flow may prevent the evolution of sexual isolation or may limit it to the contact zone (Littlejohn, 1969; Hall, 1973). Hybrid zones of apparent long standing are known in various animal taxa where neither widespread sexual isolation nor localized reproductive character displacement has occurred (Mayr, 1963, p. 548-550; Bigelow, 1965; White, 1978, Ch. 6). In contrast with the localized origin and slow or restricted spread of sexual isola-

Mechanism and stereoselectivity of asymmetric hydrogenation.

Abstract: Rhodium complexes containing chiral phosphine ligands catalyze the hydrogenation of olefinic substrates such as alpha-aminoacrylic acid derivatives, producing chiral products with very high optical yields. Elucidation of the mechanisms of such reactions leads to the conclusion that the stereoselection is dictated not by the preferred initial binding of the substrate to the chiral catalyst, but rather by the much higher reactivity of the minor diastereomer of the catalyst-substrate adduct corresponding to the less favored binding mode.

The life cycle of thunderstorm gust fronts as viewed with Doppler radar and rawinsonde data

Abstract: This paper presents the time-dependent analysis of the thunderstorm gust front with the use of Project NIMROD data. RHI cross sections of reflectivity and Doppler velocity are constructed to determine the entire vertical structure. The life cycle of the gust front is divided into four stages: (1) the formative stage; (2) the early mature stage; (3) the late mature stage; and (4) the dissipation stage. A new finding is a horizontal roll detected in the reflectivity pattern resulting from airflow that is deflected upward by the ground, while carrying some of the smaller precipitation ahead of the main echo core of the squall line. This feature is called a 'precipitation roll'. As determined from rawinsonde data, the cold air behind the gust front accounts for the observed surface pressure rise. Calculations confirm that the collision of two fluids produce a nonhydrostatic pressure at the leading edge of the outflow. The equation governing the propagation speed of a density current accurately predicts the movement of the gust front.

The transformation of amphibolite facies gneiss to charnockite in southern Karnataka and northern Tamil Nadu, India

Abstract: Amphibolite facies metamorphic grade gives way southward to the granulite grade in southern Karnataka, as acid gneisses develop charnockite patches and streaks and basic enclaves develop pyroxenes. Petrologic investigations in the transitional zone south of Mysore have established the following points: 1) The transition is prograde. Amphibole-bearing gneisses intimately associated with charnockite at Kabbal and several similar localities are not retrogressive after charnockite, as proved by patchy obliteration of their foliation by transgressive, very coarse-grained charnockite, high fluorine content of biotite and amphibole in gneisses, and high large-ion lithophile element contents in gneisses and charnockites. These features are in contrast to very low fluorine in retrogressive amphiboles and biotites, very low large-ion lithophile element contents, and zonal bleaching of charnockite, in clearly retrogressive areas, as at Bhavani Sagar, Tamil Nadu. 2) Metamorphic temperatures in the transitional areas were 700°–800° C, pressures were 5–7 kbar, and H2O pressures were 0.1–0.3 times total pressures, based on thermodynamic calculations using mineral analyses. Dense CO2-rich fluid inclusions in the Kabbal rocks confirm the low H2O pressures at the first appearance of orthopyroxene. Farther to the south, in the Nilgiri Hills and adjacent granulite massif areas, peak metamorphic temperatures were 800°–900° C, pressures were 7–9 kbar, and water pressures were very low, so that primary biotites and amphiboles (those with high F contents) are rare. 3) The incipient granulite-grade metamorphism of the transitional areas was introduced by a wave of anatexis and K-metasomatism. This process was arrested by drying out under heavy CO2 influx. Charnockites so formed are hybrids of anatectic granite and metabasite, of metabasite and immediately adjacent gneiss, or are virtually isochemical with pre-existing gneiss despite gross recrystallization to granulite mineralogy. These features show that partial melting and metasomatism are attendant, rather than causative, in charnockite development. Copious CO2 from a deep-crustal or mantle source pushed ahead of it a wave of more aqueous solutions which promoted anatexis. Granulite metamorphism of both neosome and paleosome followed. The process is very similar to that deduced for the Madras granulites by Weaver (1980). The massif charnockites, for the most part extremely depleted in lithophile minor elements, show many evidences of having gone through the same process.