Truly On-The-Fly LTL Model Checking

We propose a novel algorithm for automata-based LTL model checking that interleaves the construction of the generalized B\"{u}chi automaton for the negation of the formula and the emptiness check. Our algorithm first converts the LTL formula into a linear weak alternating automaton; configurations of the alternating automaton correspond to the locations of a generalized B\"{u}chi automaton, and a variant of Tarjan's algorithm is used to decide the existence of an accepting run of the product of the transition system and the automaton. Because we avoid an explicit construction of the B\"{u}chi automaton, our approach can yield significant improvements in runtime and memory, for large LTL formulas. The algorithm has been implemented within the SPIN model checker, and we present experimental results for some benchmark examples

Finite Element Modeling of the Plantar Fascia: A Viscohyperelastic Approach

The present work details the creation and analysis of a finite element model of the foot, wherein the plantar fascia was modeled as a viscohyperelastic solid. The objective of this work was to develop a fully functional CAD and Finite Element Model of the foot and plantar fascia for analysis by examining the transient stresses on the plantar fascia through the use of a viscohyperelastic material model. The model’s geometry was developed through the use of image processing techniques with anatomical images provided by the National Institutes of Health. The finite element method was used to analyze the transient response of the plantar fascia during loading. As a first step towards modeling the transient response of the mechanical behavior of the plantar fascia under dynamic loadings, standing conditions were used to analyze the relaxation of the plantar fascia over a time period of 120 seconds (which is the steady-state relaxation time of the plantar fascia). This study resulted in a fully functional model with transient stress data on the behavior of the plantar fascia during loading, along with stress and deformation data for the bones and soft tissue of the foot. The results obtained were similar to that recorded in literature. This model is the first step towards fully characterizing the mechanics of the plantar fascia so as to develop novel treatment methods for plantar fasciitis, and can be applied to future studies to develop novel orthotic devices and surgical techniques for the treatment of and prevention of plantar fasciitis

UML Interactions Meet State Machines - An Institutional Approach

UML allows the multi-viewpoint modelling of systems. One important question is whether an interaction as specified by a sequence diagram can be actually realised in the system. Here, the latter is specified as a combination of several state machines (one for each lifeline in the interaction) by a composite structure diagram. In order to tackle this question, we formalise the involved UML diagram types as institutions, and their relations as institution (co)morphisms

Executing Underspecified OCL Operation Contracts with a SAT Solver

Executing formal operation contracts is an important technique for requirements validation and rapid prototyping. Current approaches require additional guidance from the user or exhibit poor performance for underspecified contracts that describe the operation results non-constructively. We present an efficient and fully automatic approach to executing OCL operation contracts which uses a satisfiability (SAT) solver. The operation contract is translated to an arithmetic formula with bounded quantifiers and later to a satisfiability problem. Based on the system state in which the operation is called and the arguments to the operation, an off-the-shelf SAT solver computes a new state that satisfies the postconditions of the operation. An effort is made to keep the changes to the system state as small as possible. We present a tool for generating Java method bodies for operations specified with OCL. The efficiency of our method is confirmed by a comparison with existing approaches

Forecasting office capitalization rates and risk premia in emerging markets

Thesis (S.M. in Real Estate Development)--Massachusetts Institute of Technology, Dept. of Architecture, Center for Real Estate, 2008 [first author]; and, (S.M. in Real Estate Development)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, Center for Real Estate, 2008 [second author].Includes bibliographical references (leaves 70-72).As international property investors increasingly understand and appreciate the benefits of diversification and look to achieve higher returns, cross-border real estate investment has increased. In this context, the issue of the country risk premium is crucial as these types of investments present a wide range of risk and return opportunities that need to be understood and, ideally, quantified. Naturally, the decision of whether or not to invest begins with an assessment of how much additional return is required to compensate for the additional risk associated with a particular country. Establishing these risk premiums is particularly difficult since cross-border investors often lack local market knowledge and encounter transparency issues when trying to gain an understanding of the market. These questions matter particularly to institutional investors looking to make allocation decisions across geographically diversified holdings. Given the problem of appropriate pricing in emerging markets, this study will attempt to forecast capitalization rates for these markets using widely available macroeconomic data and property-related market ratings. This cross-sectional study will employ univariate and multivariate regressions. We will initially identify various factors with a significant relationship to cap rates in markets where real estate pricing data is available. Office cap rate data from Real Capital Analytics (RCA), Jones Lang LaSalle-LaSalle Investment Management and Investment Property Databank (IPD) for sets of 23 to 25 overlapping countries will be used as dependent variables in the analysis. Once the significant factors have been established, we will extrapolate the model out to markets that have the necessary background data, but lack usable cap rate information. In other words, we will forecast cap rates for countries that lack data - as is typical for emerging markets.(cont.) Using this forecast, we can then estimate a "risk factor" by subtracting an appropriate risk-free rate and by adding a income growth proxy - the country's GDP growth. This study hopes to reveal key factors that will help institutional investors looking to invest in countries other than their own. It will attempt to provide a basic guideline of cap rates and risk-factors for office properties in emerging markets. Understanding the drivers behind pricing differences can help us better predict how cap rates would change with underlying changes in local macroeconomic, political, and property market factors.by Vipasha Dasgupta and Alexander Ward Nathaniel Knapp.S.M.in Real Estate Developmen

An Index for Software Engineering Models

International audienc