Interactive specification acquisition via scenarios: A proposal

Some reactive systems are most naturally specified by giving large collections of behavior scenarios. These collections not only specify the behavior of the system, but also provide good test suites for validating the implemented system. Due to the complexity of the systems and the number of scenarios, however, it appears that automated assistance is necessary to make this software development process workable. Interactive Specification Acquisition Tool (ISAT) is a proposed interactive system for supporting the acquisition and maintenance of a formal system specification from scenarios, as well as automatic synthesis of control code and automated test generation. This paper discusses the background, motivation, proposed functions, and implementation status of ISAT

Arthur M. Okun, 1928-1980

tribute, rememberance

Mixed signals: central bank independence, coordinated wage bargaining, and European Monetary Union

Plans for European Monetary Union are based on the conventional postulate that increasing the independence of the central bank can reduce inflation without any real economic effects. However, the theoretical and empirical bases for this claim rest onmodels of the economy that make unrealistic information assumptions and omitinstitutional variables other than the central bank. When the signaling problems between the central bank and other actors in the political economy are considered,we find that the character of wage bargaining conditions the impact of central bankindependence by rendering the signals between the bank and the bargainers moreor less effective. Greater independence can reduce inflation without majoremployment effects where bargaining is coordinated, but it brings higher levels ofunemployment where bargaining is uncoordinated. Thus, currency unions like the EMU may require higher levels of unemployment to control inflation than their proponents envisage; they will have costs as well as benefits, costs which will bedistributed unevenly among and within the member nations based on the changesinduced in the status of the bank and of wage coordination -- Die Konzepte für die Europäische Währungsunion basieren auf dem allgemeinvertretenen Postulat, daß mit größerer Unabhängigkeit der Zentralbank die Inflationohne reale ökonomische Effekte verringert werden kann. Allerdings beruht die theoretische wie empirische Basis für diesen Anspruch auf Modellvorstellungen einer Volkswirtschaft, die auf unrealistischen Annahmen der Bedeutung von Informationen beruhen und institutionelle Variable - mit Ausnahme der Zentralbank - außer acht lassen. Wird allerdings die wechselseitige Wahrnehmung und Interpretation vonInformationen (signaling problems) zwischen Zentralbank und den anderenAkteuren in der politischen Ökonomie in die Analyse einbezogen, dann ist festzustellen, daß die Art der Lohnfindung die Intensität der Auswirkungen derZentralbankunabhängigkeit beeinflußt je nachdem, wie wirksam die wechselseitige Wahrnehmung und Interpretation von Informationen zwischen der Zentralbank und den Tarifpartnern vermittelt ist.Im Falle koordinierter Tarifverhandlungen kann eine größere Unabhängigkeit derZentralbank die Inflation in der Tat ohne größere Beschäftigungseffekte vermindern,im Falle unkoordinierter Tarifverhandlungen führt dies allerdings zu einem höherenNiveau der Arbeitslosigkeit. Daraus leitet sich die Überlegung ab, daß eineWährungsunion vom Typ Europäische Währungsunion ein höheres Maß an Arbeitslosigkeit erfordert, um die Inflation unter Kontrolle zu halten, als es ihre Befürworter erwarten. Bei den sich dann einstellenden Vor- und Nachteilen werden die Nachteile zwischen und innerhalb der Mitgliedstaaten ungleich verteilt sein, abhängig von dem letztendlich verwirklichten Grad der Unabhängigkeit derZentralbank und der Form der Lohnfindung.

Investigation of advanced counterrotation blade configuration concepts for high speed turboprop systems. Task 5: Unsteady counterrotation ducted propfan analysis

The primary objective of this study was the development of a time-marching three-dimensional Euler/Navier-Stokes aerodynamic analysis to predict steady and unsteady compressible transonic flows about ducted and unducted propfan propulsion systems employing multiple blade rows. The computer codes resulting from this study are referred to as ADPAC-AOAR\CR (Advanced Ducted Propfan Analysis Codes-Angle of Attack Coupled Row). This document is the final report describing the theoretical basis and analytical results from the ADPAC-AOACR codes developed under task 5 of NASA Contract NAS3-25270, Unsteady Counterrotating Ducted Propfan Analysis. The ADPAC-AOACR Program is based on a flexible multiple blocked grid discretization scheme permitting coupled 2-D/3-D mesh block solutions with application to a wide variety of geometries. For convenience, several standard mesh block structures are described for turbomachinery applications. Aerodynamic calculations are based on a four-stage Runge-Kutta time-marching finite volume solution technique with added numerical dissipation. Steady flow predictions are accelerated by a multigrid procedure. Numerical calculations are compared with experimental data for several test cases to demonstrate the utility of this approach for predicting the aerodynamics of modern turbomachinery configurations employing multiple blade rows

Knowledge Resources, Exploration, and Exploitation: A New Perspective on the Interplay Between Innovation and Application

Knowledge resources are the fundamental ingredients used in exploration and exploitation and an overlooked source of distinction and tension between these two processes. In this paper we use a strategic lens to differentiate evidence-based knowledge resources from tinkerable knowledge resources. This conceptualization provides the basis for a bridge between the literature on the resource-based view of the firm and research into exploration and exploitation. We suggest that an examination of knowledge resources offers a new perspective for understanding exploration and exploitation, and suggests new opportunities for achieving organizational ambidexterity. A proposed model indicates the application consequences of match and mismatch across knowledge resources and knowledge flow activities in terms of exploration and exploitation. An agenda for future research is proposed along with steps that managers can take to develop exploration and exploitation capabilities in their firms by managing their knowledge resources more precisely and effectively.knowledge resources, exploration, exploitation, knowledge management

Program Improvement by Automatic Redistribution of Intermediate Results

This paper was originally a Ph.D. thesis proposal.The problem of automatically improving the performance of computer programs has many facets. A common source of program inefficiency is the use of abstraction techniques in program design: general tools used in a specific context often do unnecessary or redundant work. Examples include needless copy operations, redundant subexpressions, multiple traversals of the same datastructure and maintenance of overly complex data invariants. I propose to focus on one broadly applicable way of improving a program's performance: redistributing intermediate results so that computation can be avoided. I hope to demonstrate that this is a basic principle of optimization from which many of the current approaches to optimization may be derived. I propose to implement a system that automatically finds and exploits opportunities for redistribution in a given program. In addition to the program source, the system will accept an explanation of correctness and purpose of the code. Beyond the specific task of program improvement, I anticipate that the research will contribute to our understanding of the design and explanatory structure of programs. Major results will include (1) definition and manipulation of representation of correctness and purpose of a program's implementation, and (2) definition, construction, and use of a representation of a program's dynamic behavior.MIT Artificial Intelligence Laborator

Investigation of advanced counterrotation blade configuration concepts for high speed turboprop systems, task 1: Ducted propfan analysis

The time-dependent three-dimensional Euler equations of gas dynamics were solved numerically to study the steady compressible transonic flow about ducted propfan propulsion systems. Aerodynamic calculations were based on a four-stage Runge-Kutta time-marching finite volume solution technique with added numerical dissipation. An implicit residual smoothing operator was used to aid convergence. Two calculation grids were employed in this study. The first grid utilized an H-type mesh network with a branch cut opening to represent the axisymmetric cowl. The second grid utilized a multiple-block mesh system with a C-type grid about the cowl. The individual blocks were numerically coupled in the Euler solver. Grid systems were generated by a combined algebraic/elliptic algortihm developed specifically for ducted propfans. Numerical calculations were initially performed for unducted propfans to verify the accuracy of the three-dimensional Euler formulation. The Euler analyses were then applied for the calculation of ducted propfan flows, and predicted results were compared with experimental data for two cases. The three-dimensional Euler analyses displayed exceptional accuracy, although certain parameters were observed to be very sensitive to geometric deflections. Both solution schemes were found to be very robust and demonstrated nearly equal efficiency and accuracy, although it was observed that the multi-block C-grid formulation provided somewhat better resolution of the cowl leading edge region

Bounded gaps between primes in number fields and function fields

The Hardy--Littlewood prime $k$-tuples conjecture has long been thought to be completely unapproachable with current methods. While this sadly remains true, startling breakthroughs of Zhang, Maynard, and Tao have nevertheless made significant progress toward this problem. In this work, we extend the Maynard-Tao method to both number fields and the function field $\mathbb{F}_q(t)$

Conditional Spectral Analysis of Replicated Multiple Time Series with Application to Nocturnal Physiology

This article considers the problem of analyzing associations between power spectra of multiple time series and cross-sectional outcomes when data are observed from multiple subjects. The motivating application comes from sleep medicine, where researchers are able to non-invasively record physiological time series signals during sleep. The frequency patterns of these signals, which can be quantified through the power spectrum, contain interpretable information about biological processes. An important problem in sleep research is drawing connections between power spectra of time series signals and clinical characteristics; these connections are key to understanding biological pathways through which sleep affects, and can be treated to improve, health. Such analyses are challenging as they must overcome the complicated structure of a power spectrum from multiple time series as a complex positive-definite matrix-valued function. This article proposes a new approach to such analyses based on a tensor-product spline model of Cholesky components of outcome-dependent power spectra. The approach flexibly models power spectra as nonparametric functions of frequency and outcome while preserving geometric constraints. Formulated in a fully Bayesian framework, a Whittle likelihood based Markov chain Monte Carlo (MCMC) algorithm is developed for automated model fitting and for conducting inference on associations between outcomes and spectral measures. The method is used to analyze data from a study of sleep in older adults and uncovers new insights into how stress and arousal are connected to the amount of time one spends in bed

Takeoff/approach noise for a model counterrotation propeller with a forward-swept upstream rotor

A scale model of a counterrotating propeller with forward-swept blades in the forward rotor and aft-swept blades in the aft rotor (designated F39/A31) has been tested in the NASA Lewis 9- by 15-Foot Anechoic Wind Tunnel. This paper presents aeroacoustic results at a takeoff/approach condition of Mach 0.20. Laser Doppler velocimeter results taken in a plane between the two rotors are also included to quantify the interaction flow field. The intention of the forward-swept design is to reduce the magnitude of the forward rotor tip vortex and/or wakes which impinge on the aft rotor, thus lowering the interaction tone levels. A reference model propeller (designated F31/A31), having aft-swept blades in both rotors, was also tested. Aeroelastic performance of the F39/A31 propeller was disappointing. The forward rotor tip region tended to untwist toward higher effective blade angles under load. The forward rotor also exhibited steady state blade flutter at speeds and loadings well below the design condition. The noise results, based on sideline acoustic data, show that the interaction tone levels were up to 8 dB higher with the forward-swept design compared to those for the reference propeller at similar operating conditions, with these tone level differences extending down to lower propeller speeds where flutter did not occur. These acoustic results are for a poorly-performing forward-swept propeller. It is quite possible that a properly-designed forward-swept propeller would exhibit substantial interaction tone level reductions