Explicit Contact Research Articles

A comparative study of conflict resolution in macaques: insights into the nature of trait covariation

Conflict resolution is an essential component of primate sociality that has been studied extensively within primate social groups, but few studies have examined how conflict resolution behaviours covary at evolutionary scales. We assembled a standardized data set on social interactions of sexually mature females to analyse patterns of conflict resolution in 15 groups of nine macaque species. Between-group comparisons revealed no significant difference in nonkin reconciliation levels between groups of the same species, whereas substantial interspecific differences were found. We tested for associations between four behavioural traits involving reconciliation and dominance asymmetry that play a central role in primate social systems. Regression analyses using group values indicated that these traits (conciliatory tendencies, proportions of explicit reconciliatory contacts, kin bias and levels of counteraggression) exist as an integrated suite of characters. We found strong phylogenetic signal in most traits, which further indicates that they evolved during the adaptive radiation of macaques. Using the method of independent contrasts, relationships between conciliatory tendencies and proportions of explicit reconciliatory contacts and between kin bias and levels of counteraggression remained consistent after controlling for phylogeny. This reveals that evolutionary change in one trait leads to correlated changes in other traits. Collectively, these results show how comparative studies of detailed behavioural interactions can be used to elucidate primate socioecology.

How disease models in static networks can fail to approximate disease in dynamic networks

In the modeling of infectious disease spread within explicit social contact networks, previous studies have predominantly assumed that the effects of shifting social associations within groups are small. These models have utilized static approximations of contact networks. We examine this assumption by modeling disease spread within dynamic networks where associations shift according to individual preference based on three different measures of network centrality. The results of our investigations clearly show that this assumption may not hold in many cases. We demonstrate that these differences in association dynamics do yield significantly different disease outcomes both from each other and also from models using graph-theoretically accurate static network approximations. Further work is therefore needed to explore under which circumstances static models accurately reflect constantly shifting natural populations.

Optimizing the control of disease infestations at the landscape scale.

Using a contact-process model for the spread of crop disease over a regional scale, we examine the importance of the time scale for control with respect to the cost of the epidemic. The costs include the direct cost of treating infected sites as well as the indirect costs incurred through lost yield. We first use a mean-field approximation to derive analytical results for the optimal treatment regimes that minimize the total cost of the epidemic. We distinguish short- and long-term epidemics. and show that seasonal control (short time scale) requires extreme treatment, either treating all sites or none or switching between the two at some stage during the season. The optimal long-term strategy requires an intermediate level of control that results in near eradication of the disease. We also demonstrate the importance of incorporating economic constraints by deriving a critical relationship between the epidemiological and economic parameters that determine the qualitative nature of the optimal treatment strategy. The set of optimal strategies is summarized in a policy plot, which can be used to determine the nature of the optimal treatment regime given prior knowledge of the epidemiological and economic parameters. Finally, we test the robustness of the analytical results, derived from the mean-field approximation, on the spatially explicit contact process and demonstrate robustness to implementation errors and misestimation of crucial parameters.

Disease evolution across a range of spatio-temporal scales

Traditional explorations of infectious disease evolution have considered the competition between two cross-reactive strains within the standard framework of disease models. Such techniques predict that diseases should evolve to be highly transmissible, benign to the host and possess a long infectious period: in general, diseases do not conform to this ideal. Here we consider a more holistic approach, suggesting that evolution is a trade-off between adaptive pressures at different scales: within host, between hosts and at the population level. We present a model combining within-host pathogen dynamics and transmission between individuals governed by an explicit contact network, where transmission dynamics between hosts are a function of the interaction between the pathogen and the hosts’ immune system, though ultimately constrained by the contacts each infected host possesses. Our results show how each of the scales places constraints on the evolutionary behavior, and that complex dynamics may emerge due to the feedbacks between epidemiological and evolutionary dynamics. In particular, multiple stable states can occur with switching between them stochastically driven.

Evaluation of cyclic inelastic response in fretting based on unified Chaboche model

Fretting in high strength metalline materials is one of primary failure mechanics that reduces the structural integrity of engineering component. The cyclic deformation response in the region experiencing fretting plays a central role. A unified cyclic viscoplasticity Chaboche model at finite deformations that incorporates fully explicit contact analysis is used to investigate the plastic strain history in fretting process. The analyses are accompanied by finite element simulations using a non-linear kinematic hardening rule with isotropic cyclic hardening and the full details of contact behavior are solved for at all stages of the loading. Numerical evaluations have explored the nature of subsurface cyclic plasticity and interface contact stress fields for realistic fretting fatigue geometries for an applied bulk stress amplitude with a stress ratio of R=−1, two tangential loads, and two different values of coefficient of friction. The characteristics of the fretting fatigue, including local cyclic stress strain and cumulative plastic strain are all better described. Owing to the fact that the plastic anisotropy in the scale of grain size plays a significant role especially in the very local region near the contact edge, an analysis of plastic anisotropy is presented in fretting problem. In the case of fretting configuration considered here, the plastic history combines cyclic plasticity and plastic ratcheting when plastic anisotropy is considered, while the ratcheting plasticity dominates during the fretting process without consideration of plastic anisotropy.

Commentary on Intrapersonal, Interpersonal, and Contextual Factors in Extramarital Involvement.

Extramarital Involvements (EMIs) attract significant societal attention, as exemplified by the revelation of former President Clinton's EMI. Depression, anxiety, and divorce are important sequelae of EMIs, though it will be important to learn which couples successfully cope with EMIs. Allen et al. (this issue) provide an excellent overview of the prevalence of EMIs and the problems in trying to ascertain accurate estimates thereof. The impact of a very close relationship even without explicit sexual contact was noted, and Allen et al. present a useful framework for organizing theoretical positions and data on EMIs. It is an excellent review for a clinician or researcher addressing EMIs.

Decomposition contact response (DCR) for explicit finite element dynamics

We propose a new explicit contact algorithm for finite element discretized solids and shells with smooth and non-smooth geometries. The equations of motion are integrated in time with a predictor-corrector-type algorithm. After each predictor step, the impenetrability constraints and the exchange of momenta between the impacting bodies are considered and enforced independently. The geometrically inadmissible penetrations are removed using closest point projections or similar updates. Penetration is measured using the signed volume of intersection described by the contacting surface elements, which is well-defined for both smooth and non-smooth geometries. For computing the instantaneous velocity changes that occur during the impact event, we introduce the decomposition contact response method. This enables the closed-form solution of the jump equations at impact, and applies to non-frictional as well as frictional contact, as exemplified by the Coulomb frictional model. The overall algorithm has excellent momentum and energy conservation characteristics, as several numerical examples demonstrate. Copyright © 2005 John Wiley & Sons, Ltd.

Arctic research at three levels

This paper is a posthumous publication of a Steven McNabb’s presentation to the 1993 annual meeting of the American Anthropological Association. In it he described how the Social Transitions in the North research project involved explicit cross-cultural contact or participation at three levels: between scientists and public agencies; between scientists and study populations; and between research teams themselves. He explored a few of the entanglements and opportunities that arise in those interactions. Dr. McNabb urged northern researchers to avoid embracing rigid standards, for they will result in more entanglements and fewer opportunities. On the otherhand, if researchers are open-minded, they will be able to treat each dilemma as an opportunity that will make for better science.

Discrete fracture in quasi-brittle materials under compressive and tensile stress states

A method for modelling discrete fracture in geomaterials under tensile and compressive stress fields has been developed based on a Mohr–Coulomb failure surface in compression and three independent anisotropic rotating crack models in tension. Extension fracturing is modelled by coupling the softening of the anisotropic rotating crack failure criterion to the compressive plastic strain evolution. Modifications were introduced into an explicit discrete element/finite element code with an explicit Lagrangian contact algorithm to enforce non-penetration of the surfaces created when the tensile strength is depleted. The model is applied to triaxial and plane strain tests, as well as punch tests and borehole breakouts to show that the model is able to quantitatively predict the appropriate load–displacement response of the system in addition to the observed evolution of discrete fracturing in situations comprising a variety of compressive and tensile stress states.

Discrete fracture in quasi-brittle materials under compressive and tensile stress states

A method for modelling discrete fracture in geomaterials under tensile and compressive stress fields has been developed based on a Mohr–Coulomb failure surface in compression and three independent anisotropic rotating crack models in tension. Extension fracturing is modelled by coupling the softening of the anisotropic rotating crack failure criterion to the compressive plastic strain evolution. Modifications were introduced into an explicit discrete element/finite element code with an explicit Lagrangian contact algorithm to enforce non-penetration of the surfaces created when the tensile strength is depleted. The model is applied to triaxial and plane strain tests, as well as punch tests and borehole breakouts to show that the model is able to quantitatively predict the appropriate load–displacement response of the system in addition to the observed evolution of discrete fracturing in situations comprising a variety of compressive and tensile stress states.

Three-body problem in a dilute bose-Einstein condensate.

We derive the explicit three-body contact potential for a dilute condensed Bose gas from microscopic theory. The three-body coupling constant exhibits the general form predicted by Wu [Phys. Rev. 115, 1390 (1959)]] and is determined in terms of the amplitudes of two- and three-body collisions in vacuum. In the present form, the coupling constant becomes accessible to quantitative studies which should provide the crucial link between few-body collisions and the stability of condensates with attractive two-body forces.

Numerical treatment of contact and friction in FE simulation of forming processes

The problem of contact between a part and a tool or between two deforming bodies is analysed in view of metal forming processes. For simplicity, only the case of viscoplastic materials is considered. The velocity formulation is presented, with different time integration schemes. The contact with a rigid tool is considered first and various forms of contact formulations are described: nodal contact, integral formulation with a penalty or with a Lagrange multiplier method. Time integration is considered which results in various explicit or implicit contact formulations. Special attention is paid to the contact between two deforming bodies or to the self contact when a fold is generated in the workpiece.

Origin of the lognormal shape in the boson-peak of globular proteins

We propose an explanation for the origin of the lognormal shape in the boson-peak anomaly of globular proteins. The origin is ascribed to a distribution of quasi-localization lengths for acoustic waves within the protein. The local densities of states for different sites display logarithmic singularities in this range. The distribution of these singularities, however, follows a lognormal distribution. This seems to be a universal characteristic for quasi-two dimensional random networks, which are used to model the protein dynamics. This interpretation makes explicit contact with well established models for the boson-peak anomaly in glasses and/or amorphous solids.

The sexual habits of males who molest.

To gain better understanding into the causes of molesting behaviour in males, we examined a prison cohort of molesters and compared them with a control group comprising thieves. The molesters were older, had attained a higher educational level and were more likely to be married. They had their initial sexual intercourse at an older age but tended to have multiple sexual relationships and were less likely to report having viewed pornographic material. Three months prior to committing their offences, molesters seemed to engage in less sexual activity. The implications are that molesters had a need for more explicit sexual contact but were unable to sustain ongoing, stable, intimate sexual relationships.

Numerical formulations and algorithms for solving contact problems in metal forming simulation

The problem of contact between a part and a tool or between two deforming bodies is analysed in view of metal-forming processes. For simplicity, only the case of viscoplastic materials is considered. The velocity formulation is presented. The contact with a rigid tool is considered first and various forms of contact formulations are described: nodal contact, integral or discrete formulation with a penalty or with a Lagrange multiplier method. The time integration is considered which results in various explicit or implicit contact formulations. A special attention is paid to the contact between two deforming bodies or to the self-contact when a fold is generated in the work-piece. Some 2-D and 3-D application examples illustrate the effectiveness of the proposed formulations and algorithms. Copyright © 1999 John Wiley & Sons, Ltd.

A general conjugate-gradient-based predictor-corrector solver for explicit finite-element contact

A Lagrange-multiplier based approach is presented for the general solution of multi-body contact within an explicit finite element framework. The technique employs an explicit predictor step to permit the detection of interpenetration and then utilizes a corrector step, whose solution is obtained with a pre-conditioned matrix-free conjugate gradient projection method, to determine the Lagrange multipliers necessary to eliminate the predicted penetration. The predictor–corrector algorithm is developed for deformable bodies based upon the central difference method, and for rigid bodies from momentum and energy conserving approaches. Both frictionless and Coulomb-based frictional contact idealizations are addressed. The technique imposes no time-step constraints and quickly mitigates velocity discontinuities across closed interfaces. Special attention is directed toward contact between rigid bodies. Algorithmic moment arms conserve the translational and angular momentums of the system in the absence of external loads. Elastic collisions are captured with a two-phase predictor–corrector approach and a geometrically approximate velocity jump criterion. The first step solves the inelastic contact problem and identifies inactive constraints between rigid bodies, while the second step generates the necessary velocity jump condition on the active constraints. The velocity criterion is shown to algorithmically preserve the system kinetic energy for two unconstrained rigid bodies. Copyright © 1999 John Wiley & Sons, Ltd. This paper was produced under the auspices of the U.S. Government and it is therefore not subject to copyright in the U.S.

An explicit finite difference procedure for contact-impact analysis of crack edges

A finite difference procedure is proposed to simulate the frictional contact-impact response of crack edges. The procedure takes into account in an explicit way separation, stick contact and slip contact of the crack edges. Numerical examples are presented to show the influence of the contactimpacting of crack edges on the history of dynamic stress intensity factors.

THEORY OF SELF-INTERACTING SCALAR FIELDS AND GRAVITATION

The theory of self-interacting scalar fields and gravitation is discussed using Robertson-Walker metric in conformal time. The theory is formulated in terms of a metric compatible connection with torsion. Analytic solutions are derived and in some cases we make explicit contact with the conventional Brans-Dicke theory.

Internal, External, and Generalized Symmetries

Bácklund′s theorem, which characterizes contact transformations, is generalized to give an analogous characterization of "internal symmetries" of systems of differential equations. For a wide class of systems of differential equations, we prove that every internal symmetry comes from a first order generalized symmetry and, conversely, every first order generalized symmetry satisfying certain explicit contact conditions determines an internal symmetry. We analyze the contact conditions in detail, deducing powerful necessary conditions for a system of differential equations that admit "genuine" internal symmetries, i.e., ones which do not come from classical "external" symmetries. Applications include a direct proof that both the internal symmetry group and the first order generalized symmetries of a remarkable differential equation due to Hilbert and Cartan are the noncompact real form of the exceptional simple Lie group G 2.

The growth of microstructurally small fatigue cracks in a ferriticpearlitic steel: Tokaji, K., Ogawa, T. and Osako, S.Fatigue Fract. Eng. Mater. Struct. 1988, 11, (5), 331–342

This article presents a parallel algorithm to model the nonlinear dynamic interactions between ultrasonic guided waves and fatigue cracks. The Local Interaction Simulation Approach (LISA) is further developed to capture the contact-impact clapping phenomena during the wave crack interactions based on the penalty method. Initial opening and closure distributions are considered to approximate the 3-D rough crack microscopic features. A Coulomb friction model is integrated to capture the stick-slip contact motions between the crack surfaces. The LISA procedure is parallelized via the Compute Unified Device Architecture (CUDA), which enables parallel computing on powerful graphic cards. The explicit contact formulation, the parallel algorithm, as well as the GPU-based implementation facilitate LISA’s high computational efficiency over the conventional finite element method (FEM). This article starts with the theoretical formulation and numerical implementation of the proposed algorithm, followed by the solution behavior study and numerical verification against a commercial finite element code. Numerical case studies are conducted on Lamb wave interactions with fatigue cracks. Several nonlinear ultrasonic phenomena are addressed. The classical nonlinear higher harmonic and DC response are successfully captured. The nonlinear mode conversion at a through-thickness and a half-thickness fatigue crack is investigated. Threshold behaviors, induced by initial openings and closures of rough crack surfaces, are depicted by the proposed contact LISA model.