CHIMP: A SIMPLE POPULATION MODEL FOR USE IN INTEGRATED ASSESSMENT OF GLOBAL ENVIRONMENTAL CHANGE

We present the Canberra-Hamburg Integrated Model for Population (CHIMP), a new global population model for long-term projections. Distinguishing features of this model, compared to other model for secular population projections, are that (a) mortality, fertility, and migration are partly driven by per capita income; (b) large parts of the model have been estimated rather than calibrated; and (c) the model is in the public domain. Scenario experiments show similarities but also differences with other models. Similarities include rapid aging of the population and an eventual reversal of global population growth. The main difference is that CHIMP projects substantially higher populations, particularly in Africa, primarily because our data indicate a slower fertility decline than assumed elsewhere. Model runs show a strong interaction between population growth and economic growth, and a weak feedback of climate change on population growth.population model, long term projections, global change, integrated assessment

SAT-based Explicit LTL Reasoning

We present here a new explicit reasoning framework for linear temporal logic (LTL), which is built on top of propositional satisfiability (SAT) solving. As a proof-of-concept of this framework, we describe a new LTL satisfiability tool, Aalta\_v2.0, which is built on top of the MiniSAT SAT solver. We test the effectiveness of this approach by demonnstrating that Aalta\_v2.0 significantly outperforms all existing LTL satisfiability solvers. Furthermore, we show that the framework can be extended from propositional LTL to assertional LTL (where we allow theory atoms), by replacing MiniSAT with the Z3 SMT solver, and demonstrating that this can yield an exponential improvement in performance

Efficient Emptiness Check for Timed B\"uchi Automata (Extended version)

The B\"uchi non-emptiness problem for timed automata refers to deciding if a given automaton has an infinite non-Zeno run satisfying the B\"uchi accepting condition. The standard solution to this problem involves adding an auxiliary clock to take care of the non-Zenoness. In this paper, it is shown that this simple transformation may sometimes result in an exponential blowup. A construction avoiding this blowup is proposed. It is also shown that in many cases, non-Zenoness can be ascertained without extra construction. An on-the-fly algorithm for the non-emptiness problem, using non-Zenoness construction only when required, is proposed. Experiments carried out with a prototype implementation of the algorithm are reported.Comment: Published in the Special Issue on Computer Aided Verification - CAV 2010; Formal Methods in System Design, 201

O conceito de consumidor direto e a jurisprudência do Superior Tribunal de Justiça

- Texto de autoria de Ministra do Superior Tribunal de Justiça.Trata, sob o enfoque jurídico e econômico, o conceito de consumidor direto, contextualizando-o, de um lado, com as duas escolas de pensamento formuladas sobre o tema, e, de outro, com os recentes avanços jurisprudenciais desenvolvidos pelo Superior Tribunal de Justiça (STJ). Comenta que a Escola Subjetiva considera que a aquisição ou uso de bem ou serviço para o exercício de atividade econômica, civil ou empresária (CC/02, art. 966, caput e parágrafo único), descaracteriza requisito essencial à formação da relação de consumo, qual seja, ser o consumidor o destinatário final da fruição do bem. Informa que a linha de precedentes adotada pela Quarta e Sexta Turmas deste STJ coaduna-se com os pressupostos da teoria subjetiva ou finalista, restringindo a exegese do art. 2º do CDC ao destinatário final fático e também econômico do bem ou serviço. Apresenta ainda a teoria da Escola Objetiva que considera que a aquisição ou uso de bem ou serviço na condição de destinatário final fático caracteriza a relação de consumo, por força do elemento objetivo, qual seja, o ato de consumo. Informa também que a linha de precedentes adotada pela Primeira e Terceira Turmas deste STJ coaduna-se com os pressupostos da teoria objetiva (ou maximalista), considerando-se consumidor o destinatário final fático do bem ou serviço, ainda que venha a utilizá-lo no exercício de profissão ou de empresa. Indica a tendência jurisprudencial do STJ de prevalência da Escola Objetiva. Apresenta precedente recente (Conflito de Competência nº. 41056/SP, julgado em 23/06/2004), em que a Segunda Seção do STJ acolheu, por maioria, o conceito de consumidor direto eleito pela escola objetiva

A Fully Verified Executable LTL Model Checker

International audienceWe present an LTL model checker whose code has been completely verified using the Isabelle theorem prover. The checker consists of over 4000 lines of ML code. The code is produced using recent Isabelle technology called the Refinement Framework, which allows us to split its correctness proof into (1) the proof of an abstract version of the checker, consisting of a few hundred lines of “formalized pseudocode”, and (2) a verified refinement step in which mathematical sets and other abstract structures are replaced by implementations of efficient structures like red-black trees and functional arrays. This leads to a checker that, while still slower than unverified checkers, can already be used as a trusted reference implementation against which advanced implementations can be tested. We report on the structure of the checker, the development process, and some experiments on standard benchmarks

Senescent ground tree rewrite systems

Ground Tree Rewrite Systems with State are known to have an undecidable control state reachability problem. Taking inspiration from the recent introduction of scope-bounded multi-stack pushdown systems, we define Senescent Ground Tree Rewrite Systems. These are a restriction of ground tree rewrite systems with state such that nodes of the tree may no longer be rewritten after having witnessed an a priori fixed number of control state changes. As well as generalising scope-bounded multi-stack pushdown systems, we show --- via reductions to and from reset Petri-nets --- that these systems have an Ackermann-complete control state reachability problem. However, reachability of a regular set of trees remains undecidable

Analyzing recursive programs using a fixed-point calculus

We show that recursive programs where variables range over finite domains can be effectively and efficiently analyzed by describing the analysis algorithm using a formula in a fixed-point calculus. In contrast with programming in traditional languages, a fixed-point calculus serves as a high-level programming language to easily, correctly, and succinctly describe model-checking algorithms While there have been declarative high-level formalisms that have been proposed earlier for analysis problems (e.g., Datalog the fixed-point calculus we propose has the salient feature that it also allows algorithmic aspects to be specified.We exhibit two classes of algorithms of symbolic (BDD-based) algorithms written using this framework-- one for checking for errors in sequential recursive Boolean programs, and the other to check for errors reachable within a bounded number of context-switches in a concurrent recursive Boolean program. Our formalization of these otherwise complex algorithms is extremely simple, and spans just a page of fixed-point formulae. Moreover, we implement these algorithms in a tool called Getafix which expresses algorithms as fixed-point formulae and evaluates them efficiently using a symbolic fixed-point solver called Mucke. The resulting model-checking tools are surprisingly efficient and are competitive in performance with mature existing tools that have been fine-tuned for these problems