124 research outputs found
Novel C-Shaped Shape Memory Alloy Connectors for Vacuum Flanges: Modeling and Tests
No full textShape memory alloy (SMA)-based fasteners and connectors represent a class of successful SMA components that are increasingly used especially in marine or aerospace applications. The present paper aims to investigate novel C-Shaped SMA connectors for room-temperature vacuum pipes within particle accelerators. The proposed connectors exhibit the two-way shape memory effect (TW-SME), so they can generate significant axial recovery forces and they can be dismounted by temperature variations. Proper thermo-mechanical training procedures were performed to tune the mechanical and functional response of the connectors to make them suitable for the investigated application. The thermo-mechanical and functional response of the SMA fasteners in both free and constrained recovery conditions were assessed by strain gauge and extensometer tests as well as by finite element analyses based on a constitutive model, recently developed by the authors, accounting for TW-SME and plasticity. Comparison between experimental and numerical results validates the proposed model. Moreover, results give useful, important information in terms of SMA transformation temperatures, generated recovery forces as well as shape recovery capabilities
Distribution of goals addressed to a group of agents
No full textThe problem investigated in this paper is the distribution of goals addressed to a group of rational agents. Those agents are characterized by their ability (i.e. what they can do), their knowledge about the world and their commitments. The goals of the group are represented by conditional preferences. In order to deduce the actual goals of the group, we determine its ability using each agent’s ability and we suppose that the agents share a common knowledge about the world. The individual goals of an agent are deduced using its ability, the knowledge it has about the world, its own commitments and the commitments of the other agents of the group
BEAUVILLE SURFACES AND PROBABILISTIC GROUP THEORY
No full textAbstract. A Beauville surface is a complex algebraic surface that can be presented as a quotient of a product of two curves by a suitable action of a finite group. Bauer, Catanese and Grunewald have been able to intrinsically characterize the groups appearing in minimal presentations of Beauville surfaces in terms of the existence of a so-called ”Beauville structure“. They conjectured that all finite simple groups, except A5, admit such a structure. This conjecture has recently been proved by Guralnick-Malle and Fairbairn-Magaard-Parker. In this survey we demonstrate another approach towards the proof of this conjecture, based on probabilistic group-theoretical methods, by describing the following three works. The first is the work of Garion, Larsen and Lubotzky, showing that the above conjecture holds for almost all finite simple groups of Lie type. The second is the work of Garion and Penegini on Beauville structures of alternating groups, based on results of Liebeck and Shalev, and the third is the case of the group PSL2(p e), in which we give bounds on the probability of generating a Beauville structure. We also discuss other related problems regarding finite simple quotients of hyperbolic triangle groups and present some open questions and conjectures. 1. Beauville surfaces and Beauville structures A Beauville surface S (over C) is a particular kind of surface isogenous to a higher product of curves, i.e., S = (C1 × C2)/G is a quotient of a product of two smooth curves C1 and C2 of genus at least two, modulo a free action of a finite group G which acts faithfully on each curve. For Beauville surfaces the quotients Ci/G are isomorphic to P 1 and both projections Ci → Ci/G ∼ = P 1 are coverings branched over three points. A Beauville surface is in particular a minimal surface of general type. Beauville [4] constructed a minimal surface of general type S with K 2 S = 8 and pg = q = 0 in the following way: take two curves C1 = C2 given by the Fermat equation x 5 +y 5 +z 5 = 0 and G the group (Z/5Z) 2 acting on C1 × C2 b
Strategies for distributing goals in a team of cooperative agents
No full textThis paper addresses the problem of distributing goals to individual agents inside a team of cooperative agents. It shows that several parameters determine the goals of particular agents. The first parameter is the set of goals allocated to the team; the second parameter is the description of the real actual world; the third parameter is the description of the agents' ability and commitments. The last parameter is the strategy the team agrees on: for each precise goal, the team may define several strategies which are orders between agents representing, for instance, their relative competence or their relative cost. This paper also shows how to combine strategies. The method used here assumes an order of priority between strategie
A three-dimensional phenomenological model for shape memory alloys including two-way shape memory effect and plasticity
No full textThe one-way and two-way shape memory effects (SMEs) as well as the thermal hysteresis represent fundamental properties when dealing with the design of detachable and thermally-stable connection systems based on shape memory alloys (SMAs). Such properties can be induced and tuned by thermo-mechanical processes that include thermal treatments and severe pre-deformation in martensitic state, causing the onset of plastic strains. In such complex conditions, material modeling is of great importance to support the design. This paper proposes a generalization of the three-dimensional phenomenological constitutive model by Souza et al. (1998), in order to describe the behavior of severely pre-strained NiTi-based SMAs. The proposed model allows to describe pseudoelasticity, one-way and two-way SMEs, as well as additional physical phenomena evidenced experimentally, such as transformation temperatures’ evolution, thermal hysteresis, phase transformations at low stresses, thermal strains, and phase-dependent elastic properties. Several numerical simulations, ranging from uniaxial tests to the finite element analysis of two case-studies, are performed. Model results are in good agreement with the results of a performed experimental campaign and allow to discuss SMA behavior under such complex loading conditions
Desires, norms and constraints
No full textThis paper deals with modeling mental states of a rational agent, in particular states based on agent’s desires. It shows that the world the agent belongs to forces it to restrict its desires. More precisely, desires of a rational agent are restricted by the constraints that exist in the world and which express what is possible or necessary. Furthermore, if the agent is law-abiding, its desires are restricted by the regulations that are defined in the world and which express what is obligatory, permitted or forbidden. This paper characterizes how desires are restricted depending on the fact that the agent is law-abiding or not. This work considers the general case when the agent orders its own desires according to a preference order. The solution is based on modeling desires, regulations and constraints in an unique formal system which is a logic of conditional preferences
Deriving individual obligations from collective obligations
No full textA collective obligation is an obligation directed to a group of agents so that the group, as a whole, is obliged to achieve a given task. The problem investigated here is the impact of collective obligations on individual obligations,i.e. obligations directed to single agents of the group. In this case, we claim that the derivation of individual obligations from collective obligations depends on several parameters among which the ability of the agents (i.e. what they can do) and their own personal commitments (i.e. what they are determined to do). As for checking if these obligations are fulfilled or not, we need to know what are the actual actions performed by the agents
Combined model of strain-induced phase transformation and orthotropic damage in ductile materials at cryogenic temperatures
No full textDuctile materials (like stainless steel or copper) show at cryogenic temperatures three principal phenomena: serrated yielding (discontinuous in terms of dsigma/depsilon), plastic strain-induced phase transformations and evolution of ductile damage. The present paper deals exclusively with the two latter cases. Thus, it is assumed that the plastic flow is perfectly smooth. Both in the case of damage evolution and for the gamma-alpha prime phase transformation, the principal mechanism is related to the formation of plastic strain fields. In the constitutive modeling of both phenomena, a crucial role is played by the accumulated plastic strain, expressed by the Odqvist parameter p. Following the general trends, both in the literature concerning the phase transformation and the ductile damage, it is assumed that the rate of transformation and the rate of damage are proportional to the accumulated plastic strain rate. The gamma-alpha prime phase transformation converts the initially homogenous material to a two-phase heterogeneous "composite ". The kinetics of phase transformation is described by the relevant linearized law of evolution of the volume fraction of alpha prime martensite in the austenitic gamma matrix left bracket Garion, C. and Skoczen, B. (2002a). The evolution of orthotropic damage is characterized by the fact that the principal directions of damage are generally not colinear with the principal directions of stress. The damage rate tensor depends linearly on the strain energy density release rate tensor (conjugate force) and on the material properties tensor C, that reflects the orthotropy level. The relevant kinetic law of damage evolution and the combined constitutive model, including phase transformation, are developed in the present paper. The model is particularly suitable to describe the evolution of highly localized damage fields in thin-walled shells, subjected at cryogenic temperatures to the loads far beyond the yield point. It has been applied to the prediction of the response of the belows expansion joints (corrugated thin-walled shells) designed for the interconnections of the Large Hadron Collider at CERN
Testing Alternative Theories of the Property Price-Trading Volume Correlation
No full textThis article examines the correlation between the real housing price and trading volume. Contrary to the predictions of standard rational expectation models, a robust positive correlation between the two variables is identified. While no clear lead-lag relationship is found in the raw data, which is more consistent with the downpayment effect model, the medium-run component of the trading volume tends to lead (and Granger cause) the corresponding component of the property price, which is more consistent with the search theoretic model. An explanation for this difference in behavior is suggested and several future research directions are provided.
Isotrivially Fibred Surfaces and Their Numerical Invariants
No full textWe give a survey of our previous work on relatively minimal isotrivial fibrations α: X → C, where X is a smooth, projective surface and C is a curve. In particular, we consider two inequalities involving the numerical invariants K2 X and χ(OX) and we illustrate them by means of several examples and counter examples
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