Showing papers by "Carnegie Mellon University published in 1974"

Reaching a Consensus

Abstract: Consider a group of individuals who must act together as a team or committee, and suppose that each individual in the group has his own subjective probability distribution for the unknown value of some parameter. A model is presented which describes how the group might reach agreement on a common subjective probability distribution for the parameter by pooling their individual opinions. The process leading to the consensus is explicitly described and the common distribution that is reached is explicitly determined. The model can also be applied to problems of reaching a consensus when the opinion of each member of the group is represented simply as a point estimate of the parameter rather than as a probability distribution.

Accuracy of AH n equilibrium geometries by single determinant molecular orbital theory

Abstract: A simple level of ab initio molecular orbital theory with a split-valence shell basis with d-type polarization functions (6–31G*) is used to predict equilibrium geometries for the ground and some low-lying excited states of AHn molecules and cations where A is carbon, nitrogen, oxygen or fluorine. The results are shown to be close to the limit for single determinant wave functions in cases where corresponding computations with more extensive bases are available. Comparison with experimental results also shows good agreement although a systematic underestimation of bond lengths up to 3 per cent is evident. For systems where no experimental data are available, the results provide predictions of equilibrium geometry.

How Big Is a Chunk?: By combining data from several experiments, a basic human memory unit can be identified and measured

Abstract: I have explored some of the interactions between research on higher mental processes over the past decade or two and laboratory experiments on simpler cognitive processes. I have shown that, by viewing experimentation in a parameter-estimating paradigm instead of a hypothesis-testing paradigm, one can obtain much more information from experiments-information that, combined with contemporary theoretical models of the cognitive processes, has implications for human performance on tasks quite different from those of the original experiments. The work of identifying and measuring the basic parameters of the human information processing system has just begun, but already important information has been gained. The psychological reality of the chunk has been fairly well demonstrated, and the chunk capacity of short-term memory has been shown to be in the range of five to seven. Fixation of information in longterm memory has been shown to take about 5 or 10 seconds per chunk. Some other "magical numbers" have been estimated-for example, visual scanning speeds and times required for simple grammatical transformations-and no doubt others remain to be discovered. But even the two basic constants discussed in this article-short-term memory capacity and rate of fixation in long-term memory-organize, systematize, and explain a wide range of findings, about both simple tasks and more complex cognitive performances that have been reported in the psychological literature over the past 50 years or more.

Optimal Order of One-Point and Multipoint Iteration

Abstract: The problem is to calculate a simple zero of a nonlinear function ƒ by iteration. There is exhibited a family of iterations of order 2n-1 which use n evaluations of ƒ and no derivative evaluations, as well as a second family of iterations of order 2n-1 based on n — 1 evaluations of ƒ and one of ƒ′. In particular, with four evaluations an iteration of eighth order is constructed. The best previous result for four evaluations was fifth order.It is proved that the optimal order of one general class of multipoint iterations is 2n-1 and that an upper bound on the order of a multipoint iteration based on n evaluations of ƒ (no derivatives) is 2n.It is conjectured that a multipoint iteration without memory based on n evaluations has optimal order 2n-1.

Non-linear age-dependent population dynamics

Abstract: where P( t ) is the total population at time t and 5 is the growth modulus. This law is clearly inapplicable to situations in which the population competes for resources (e.g., space and food), for in these situations 5 should depend on the size of the population: the larger the population, the slower should be its rate of growth. To overcome this deficiency in the Malthusian law, VERHULST [1845, 1847] assumed that f i= (6o-co0 P ) P (5o, COo=constant). (1.2)

HYDRA: the kernel of a multiprocessor operating system

Abstract: This paper describes the design philosophy of HYDRA—the kernel of an operating system for C.mmp, the Carnegie-Mellon Multi-Mini-Processor. This philosophy is realized through the introduction of a generalized notion of “resource,” both physical and virtual, called an “object.” Mechanisms are presented for dealing with objects, including the creation of new types, specification of new operations applicable to a given type, sharing, and protection of any reference to a given object against improper application of any of the operations defined with respect to that type of object. The mechanisms provide a coherent basis for extension of the system in two directions: the introduction of new facilities, and the creation of highly secure systems.

An investigation of the plastic fracture of AISI 4340 and 18 Nickel-200 grade maraging steels

Abstract: The mechanisms of plastic fracture (dimpled rupture) in high-purity and commercial 18 Ni, 200 grade maraging steels and quenched and tempered AISI 4340 steels have been studied. Plastic fracture takes place in the maraging alloys through void initiation by fracture of titanium carbo-nitride inclusions and the growth of these voids until impingement results in coalescence and final fracture. The fracture of AISI 4340 steel at a yield strength of 200 ksi (1378 MN/mm2) occurs by nucleation and subsequent growth of voids formed by fracture of the interface between manganese sulfide inclusions and the matrix. The growth of these inclusion-nucleated voids is interrupted long before coalescence by impingement, by the formation of void sheets which connect neighboring sulfide-nucleated voids. These sheets are composed of small voids nucleated by the cementite precipitates in the quenched and tempered structures. The sizes of non-metallic inclusions are an important aspect of the fracture resistance of these alloys since the investigation demonstrates that void nuclea-tion occurs more readily at the larger inclusions and that void growth also proceeds more rapidly from the larger inclusions. Using both notched and smooth round tensile specimens, it was demonstrated that the level of tensile stress triaxiality does not effect the void nu-cleation process in these alloys but that increased levels of triaxial tension do result in greatly increased rates of void growth and a concomitant reduction in the resistance to plastic fracture.

The specification of process synchronization by path expressions

Abstract: A new method of expressing synchronization is presented and the motivations and considerations which led to this method are explained. Synchronization rules, given by ‘path expressions’, are incorporated into the type definitions which are used to introduce data objects shared by several asynchronous processes. It is shown that the method's ability to express synchronization rules is equivalent to that of P and V operations, and a means of automatically translating path expressions to existing primitive synchronization operations is given.

β ℕ Revisited

Abstract: We have obtained two results since leaving Chapter 3 which make this return to βℕ possible. The first of these was Corollary 4.30 in which we found, under the assumption of the Continuum Hypothesis, that ℕ* contains a dense subset of 2C P-points. The second was Corollary 6.30 in which we saw that no point of ℕ* has its own type as a relative type with respect to any copy of ℕ contained in ℕ*. Here we will make use of these two properties of ℕ* to continue the investigation of βℕ and especially of ℕ*.

Intraspecies aggression in rats: effects of d-amphetamine and chlordiazepoxide.

Abstract: d-Amphetamine sulfate and chlordiazepoxide hydrochloride, administered to either the dominant or subordinate rat, altered several components of fighting behavior in a dose-dependent biphasic manner. Stereotypic sequences of attack, threat, defense, and submission were generated between pairs of previously isolated Sprague-Dawley rats by extinction of a food-reinforced response. Low doses of amphetamine (0.05, 0.1 mg/kg) and chlordiazepoxide (2.5, 5.0 mg/kg) given i.m. to the dominant rat 30 min prior to 15 min tests increased attack bites and leaps and the display of aggressive postures and threats, whereas higher doses of both drugs (0.5, 1.0 mg/kg amphetamine; 20 mg/kg chlordiazepoxide) suppressed attacks and threats. Amphetamine and chlordiazepoxide, administered to the subordinate rat, caused a more prolonged display of submissive-supine and defensive-upright postures; chlordiazepoxide (10.0, 20.0 mg/kg) prolonged immobile crouching whereas amphetamine (0.5, 1.0 mg/kg) greatly reduced this response. Drugged subordinate rats also provoked more attacks and threats by the non-drugged opponents. The multi-response analysis of fighting reveals that various elements of aggressive and defensive-submissive behavior patterns are differentially sensitive to drug action. The results indicate that amphetamine and chlordiazepoxide can facilitate or inhibit attack or defense depending on the dose level and which of the opponents was injected, but do not reverse dominance-subordination relationships.

An Exploratory Study of Computer Program Debugging

Abstract: This experiment represents a new approach to the study of the psychology of programming, and demonstrates the feasibility of studying an isolated part of the programming process in the laboratory. Thirty experienced FORTRAN programmers debugged 12 one-page FORTRAN listings, each of which was syntactically correct but contained one non-syntactic error (bug). Three classes of bugs (Array bugs, Iteration bugs, and bugs in Assignment Statements) in each of four different programs were debugged. The programmers were divided into five groups, based upon the information, or debugging “aids”, given them. Key results were that debug times were short (median = 6 min.). The aids groups did not debug faster than the control group; programmers adopted their debugging strategies based upon the information available to them. The results suggest that programmers often identify the intended state of a program before they find the bug. Assignment bugs were more difficult to find than Array and Iteration bugs, probably beca...

Perceptual coding strategies in the formation and verification of descriptions.

Abstract: Three experiments were carried out to study the “picture coding” process implicit both in making up descriptions of pictures and in verifying descriptions against pictures. In the first experiment, Ss were asked simply to describe pictures of one object above another; some pictures were symmetrical vertically and some were not. In the other two experiments, other Ss were timed as they judged whether sentences likeStar isn’t below line were true or false of such pictures. According to the results, Ss comply to three ordered “preference” rules in describing the two objects, rules that are conditional on characteristics of the picture and demands of the task. Furthermore, Ss in the verification task comply to the same three rules when they view and encode the picturebefore they read the sentence to be verified, but to only one of the rules when they view the pictureafter they read the sentence. The results also reconfirm two recently proposed models for the process of verifying sentences against pictures.

The equivalence problem for deterministic finite-turn pushdown automata

Abstract: It is proved that there is an effective procedure for deciding whether two deterministic finite-turn pushdown automata are equivalent.

The calculation of spin-restricted single-determinant wavefunctions

Abstract: A procedure is described for the calculation of spin-restricted single-determinant molecular orbital wavefunctions for systems such as free radical ground states and lowest triplet states. It is a further development of ‘partitioning techniques’, which divide the available one-electron space (for a given basis) into three mutually orthogonal subspaces for doubly-occupied, singly-occupied and empty orbitals respectively. Necessary and sufficient conditions are derived for the calculated total energy to be stationary with respect to changes in these subspaces. These lead to an iterative procedure for the determination of self-consistent molecular orbitals. Some preliminary applications to hydrocarbon radicals are described and compared with corresponding spin-unrestricted results.

Identification of Multi-Input Biological Systems

Abstract: The Wiener theory of nonlinear system identification is extended to multi-input-output systems and experimentally applied. The experimental applicability of the method is discussed with regard to biological systems. It is shown that the method is well suited for the treatment of the idiosyncratic features of such systems: nonlinearities, short lifetimes of experimental preparations, and high noise content. A preliminary analysis is outlined, taking into account the characteristics of the system under study, which results in the determination of the parameters of the identifying experiment. An error analysis is made which can be used to increase the accuracy of the derived model within certain constraints. Several examples are given of the experimental application of the method to certain neural networks in a vertebrate retina (the catfish, Ictalurus punctatus, retina was used for these experiments). In addition to functional identification through white-noise stimulation, these same retinal neurons are identified morphologically through intracellular dye injection. The performance of the derived functional models, as compared to the physical system, is evaluated through a variety of tests and it is found to be very satisfactory.