Further results on controllability properties of discrete-time nonlinear systems

Controllability questions for discrete-time nonlinear systems are addressed in this paper. In particular, we continue the search for conditions under which the group-like notion of transitivity implies the stronger and semigroup-like property of forward accessibility. We show that this implication holds, pointwise, for states which have a weak Poisson stability property, and globally, if there exists a global attractor for the system.This research was supported in part by US Air Force Grant AFOSR-91-0346, and also by an INDAM (Istituto Nazionale di Alta Matematica Francesco Severi, Italy) fellowship.     

Recommendation of RILEM Technical Committee 250-CSM: Test method for Textile Reinforced Mortar to substrate bond characterization

Textile Reinforced Mortar (TRM), also known as Fabric Reinforced Mortar or Fabric Reinforced Cementitious Matrix, composites are an emerging technology for the external repair and strengthening of existing structures. For most applications, the effectiveness of the TRM reinforcement relies on its bond performance. This recommendation identifies the best practice to characterize the bond behaviour of TRM. A shear bond test method is proposed to determine the peak axial stress (associated with the maximum load that can be transferred from the structural member to the externally bonded TRM reinforcement), the stress–slip relationship and the failure mode that controls the TRM-to-substrate load transfer capacity. Guidelines on specimen manufacturing, experimental setup, test execution, and determination of test results are provided.     

Secondary bioreceptivity of granite: effect of salt weathering on subaerial biofilm growth

Salt crystallisation is a very common and powerful weathering agent that can modify the petrophysical properties of building stone such as granite. In addition, the weathering can affect the susceptibility of the stone to biological colonisation. The aims of the present study were to examine the properties of a granite weathered by sodium chloride crystallisation and to evaluate the effects of the weathering on the secondary bioreceptivity of the stone to subaerial phototrophic biofilms. For this purpose, granite samples were subjected to a laboratory-based accelerated salt weathering test, and changes in weight, open porosity, bulk density, capillary water content, abrasion pH and surface roughness of the samples were determined. Samples of both weathered and non-weathered granite were then inoculated with a multi-species phototrophic culture derived from a natural subaerial biofilm and incubated under standardised laboratory conditions for 3 months. The weight loss produced by the weathering process was consistent with significant changes in abrasion pH and surface roughness. The bioreceptivity of the stone was also altered. According to the bioreceptivity index, the granite under study was characterised by ‘mild primary bioreceptivity’, but ‘high secondary bioreceptivity’ after the salt weathering process. Study of the secondary bioreceptivity of stone materials can provide very useful information about response to weathering effects, and the findings can be used to improve the selection of materials for building purposes.     

Abstract argumentation

In this paper we explore the thesis that the role of argumentation in practical reasoning in general and legal reasoning in particular is to justify the use of defeasible rules to derive a conclusion in preference to the use of other defeasible rules to derive a conflicting conclusion. The defeasibility of rules is expressed by means of non-provability claims as additional conditions of the rules.We outline an abstract approach to defeasible reasoning and argumentation which includes many existing formalisms, including default logic, extended logic programming, non-monotonic modal logic and auto-epistemic logic, as special cases. We show, in particular, that the admissibility semantics for all these formalisms has a natural argumentation-theoretic interpretation and proof procedure, which seem to correspond well with informal argumentation.In the admissibility semantics there is only one way for one argument to attack another, namely by undermining one of its non-provability claims. In this paper, we show how other kinds of attack between arguments, specifically how rebuttal and priority attacks, can be reduced to the undermining of non-provability claims.     

An enhanced exact procedure for the absolute robust shortest path problem

The aim of this paper is to investigate the use of heuristic information to efficiently solve to optimality the robust shortest path problem. Starting from the exact algorithm proposed by Murty and Her, we describe how this algorithm can be enhanced by using heuristic rules and evaluation functions to guide the search. The efficiency of the proposed enhanced approach is tested over a range of random generated instances. Our computational results indicate that the use of heuristic criteria is able to speed up considerably the search and that the enhanced exact solution method outperforms the state‐of‐the‐art algorithm proposed by Murty and Her in most of the instances.     

Automatic selection of arterial input function on dynamic contrast-enhanced MR images

Dynamic susceptibility contrast-magnetic resonance imaging (DSC-MRI) data analysis requires the knowledge of the arterial input function (AIF) to quantify the cerebral blood flow (CBF), volume (CBV) and the mean transit time (MTT). AIF can be obtained either manually or using automatic algorithms. We present a method to derive the AIF on the middle cerebral artery (MCA). The algorithm draws a region of interest (ROI) where the MCA is located. Then, it uses a recursive cluster analysis on the ROI to select the arterial voxels. The algorithm had been compared on simulated data to literature state of art automatic algorithms and on clinical data to the manual procedure. On in silico data, our method allows to reconstruct the true AIF and it is less affected by partial volume effect bias than the other methods. In clinical data, automatic AIF provides CBF and MTT maps with a greater contrast level compared to manual AIF ones. Therefore, AIF obtained with the proposed method improves the estimate reliability and provides a quantitatively reliable physiological picture.     

Dufour Gland Contents of Ants of the Cataglyphis bicolor Group

The species of desert-dwelling ants of the Cataglyphis bicolor (Hymenoptera: Formicidae) group are difficult to distinguish by morphological features. Analysis of the secretion from the Dufour glands of workers of a number of colonies was undertaken to see if it provided a clear test of species. Linked 6c-ms showed in all samples straight and branched-chain alkanes, linear alkenes, ketones, aldehydes, acetates, and a group of C₂₂ to C₂₈ esters not previously identified in this genus. Contents of the Dufour glands of C. savignyi from Tunisia and Egypt were similar, and comprised straight and branched-chain alkanes, alkenes and small amounts of esters. C. bicolor from Tunisia contained compounds similar to C. savignyi but was distinguished from the latter by larger amounts of the esters. The major compound in the glands of C. viaticus was tridecane, in contrast to the pentadecane of other species. It also contained a branched alkane, 3-methyltridecane as a major component. Branched-chain esters and a wide variety of acetates were also found in this species. C. diehlii had a limited range of compounds, with branched alkanes almost completely absent and high proportions of pentadecene and dodecyl acetate. C. bombycinus, a sympatric species, but recognized as not belonging to the bicolor group by its different mandibular gland substances, was notable in having butanoate esters in its Dufour glands. Despite these differences among species, both the great variability of individuals from a single colony and the among between conspecific colonies make species diagnosis from a few individuals difficult, in contrast with postpharyngeal glands, which, as recently reported, give a clearer indication of species.     

Discovering invariants via simple component analysis

We propose a new technique combining dynamic and static analysis of programs to find linear invariants. We use a statistical tool, called simple component analysis, to analyze partial execution traces of a given program. We get a new coordinate system in the vector space of program variables, which is used to specialize numerical abstract domains. As an application, we instantiate our technique to interval analysis of simple imperative programs and show some experimental evaluations.