A tale of two solvers: Eager and lazy approaches to bit-vectors

The standard method for deciding bit-vector constraints is via eager reduction to propositional logic. This is usually done after first applying powerful rewrite techniques. While often efficient in practice, this method does not scale on problems for which top-level rewrites cannot reduce the problem size sufficiently. A lazy solver can target such problems by doing many satisfiability checks, each of which only reasons about a small subset of the problem. In addition, the lazy approach enables a wide range of optimization techniques that are not available to the eager approach. In this paper we describe the architecture and features of our lazy solver (LBV). We provide a comparative analysis of the eager and lazy approaches, and show how they are complementary in terms of the types of problems they can efficiently solve. For this reason, we propose a portfolio approach that runs a lazy and eager solver in parallel. Our empirical evaluation shows that the lazy solver can solve problems none of the eager solvers can and that the portfolio solver outperforms other solvers both in terms of total number of problems solved and the time taken to solve them.

Extending the theory of Owicki and Gries with a logic of progress

This paper describes a logic of progress for concurrent programs. The logic is based on that of UNITY, molded to fit a sequential programming model. Integration of the two is achieved by using auxiliary variables in a systematic way that incorporates program counters into the program text. The rules for progress in UNITY are then modified to suit this new system. This modification is however subtle enough to allow the theory of Owicki and Gries to be used without change.

Formalising progress properties of non-blocking programs

A non-blocking program is one that uses non-blocking primitives, such as load-linked/store-conditional and compare-and-swap, for synchronisation instead of locks so that no process is ever blocked. According to their progress properties, non-blocking programs may be classified as wait-free, lock-free or obstruction-free. However, a precise description of these properties does not exist and it is not unusual to find a definition that is ambiguous or even incorrect. We present a formal definition of the progress properties so that any confusion is removed. The formalisation also allows one to prove the widely believed presumption that wait-freedom is a special case of lock-freedom, which in turn is a special case of obstruction-freedom.

The use and meanings of 'time of wetness' in understanding stone decay

Moisture is a well documented, and crucial, control on the nature of stone decay. The term time of wetness has frequently been adopted to describe how long a stone block is wet, with a view to understanding the impact of this on decay processes. Although this term has proved conceptually useful, it has been used in different ways, by different groups to mean mean quite different things. For example, the time of wetness for a stone block surface (the traditional understanding) may be quite different from that of a block interior, controlled by the different dynamics of wetting and drying in those zones. Thus, surface wetting will occur regularly (sometimes swiftly followed by drying, depending on the time of year), with block interior wetting requiring the accumulation of surface moisture to penetrate to depth (more likely in autumn and winter months), and drying out much more slowly. This relatively new but important perspective, framed in the context of climate change, is crucial to understanding the length of time stone may remain damp at depth following a period of prolonged precipitation. The nature and speed of drying is also relevant in quantifying time of wetness of both surfaces and the interior of building stones.
These ideas related to time of wetness have implications for decay processes, specifically how a prolonged time of deep wetness may re-focus the emphasis of salt weathering in natural building stones toward chemical action. Literature on chemical change is discussed, suggesting that chemical change occurring during periods of prolonged wetness is likely to be significant in itself, with implications for weakening the stone (in terms of, for example, cement dissolution or grain boundary weakening) and exacerbating physical damage from salt crystallisation when blocks finally dry out.

ADHD and medicalization: consideration of the senses and meanings of symptoms presented by children diagnosed

The present paper is a reflection on the diagnosis of Attention Deficit Hyperactivity Disorder (ADHD) and its relations to the process of medicalization as well as the meanings and perspectives apprehended through three case studies of children diagnosed with such disorder in a doctoral research in which the main purpose was to understand the meanings and peculiarities of ADHD symptomatology .We’ve utilized the model of qualitative research, grounded in psychoanalytic perspective, and conducted the psychodiagnosis for three children who were referred for psychological treatment. The survey found that those children had few experiences of both continence and frustration tolerance. It was evidenced how the school uses the logic of medicalization to try solving the problems with their children when it came to the school dimension. The variety of symptomatic manifestations and psychic dynamics presented by the cases that were studied revealed the weaknesses and inconsistencies of the referred diagnosis.

"Framing Counterspaces: Forms and Meanings of Graffiti in Berlin's Linguistic Landscape"

Street art and graffiti are integral parts of Berlin’s urban space, which has undergone dramatic transformations in the past two decades. Graffiti texts constitute a critical comment on these urban transformations. This talk analyzes the connection between the phenomenon of street art and trajectories in urban planning in post-wall Berlin. My current research explores the meaning of various forms of street art (such as graffiti, posters, sticker art, stencils) as texts in Berlin’s linguistic landscape. Linguistic Landscape research pays critical attention to language, words, and images displayed and exposed in public spaces. The field of Linguistic Landscapes has only recently begun to include graffiti texts in analyses of text and space to fully comprehend the semiotics of the street. In the case of Germany’s capital, graffiti writing enters into a critical dialogue with the environment and provides a readable text to understand the city.

Transformation�based implementation and optimization of programs exploiting the basic Andorra model.

The characteristics of CC and CLP systems are in principle very dierent However a recent trend towards convergence in the implementation techniques for these systems can be observed While CLP and Prolog systems have been incorporating capabilities to deal with userdened suspension and coroutining CC compilers have been trying to coalesce negrained tasks into coarsergrained sequential threads This convergence of techniques opens up the possibility of having a general purpose kernel language and abstract machine to serve as a compilation target for a variety of userlevel languages We propose a transformation technique directed towards such an objective In particular we report on techniques to support the Andorra computational model essentially emulating the AndorraI system via program transformation into a sequential language with delay primitives The system is automatic comprising an optional program analyzer and a basic transformer to the kernel language It turns out that a simple parallel CLP or Prolog system with dynamic scheduling is sucient as a kernel language for this purpose The preliminary results are quite encouraging performance of the resulting system is comparable to the current AndorraI implementation.

Perceptual factors and meanings of symbolic information elements. Volume I, executive summary.

Mode of access: Internet.

Perceptual factors and meanings of symbolic information elements. Volume II, technical report.

Mode of access: Internet.

Residential treatment for the disturbed child: basic principles in planning and design of programs and facilities.

Includes index.