Micromechanical constitutive modelling of granular media: Evolution and loss of contact in particle clusters

Micromechanical constitutive equations are developed which allow for the broad range of interparticle interactions observed in a real deforming granular assembly: microslip contact, gross slip contact, loss of contact and an evolution in these modes of contact as the deformation proceeds. This was accomplished through a synergetic use of contact laws, which account for interparticle resistance to both sliding and rolling, together withstrain-dependent anisotropies in contacts and the normal contact force. By applying the constitutive model to the bi-axial test it is demonstrated that the model can correctly predict the evolution of various anisotropies as well as the formation of a distinct shear band. Moreover, the predicted shear-band properties (e.g. thickness, prolonged localisation, void ratio) are an even better fit with experimental observations than were previously found by use of previously developed micromechanical models.     

The stress response of a semi-infinite micropolar granular material subject to a concentrated force normal to the boundary

We consider the problem of a two dimensional semi-infinite granular material subject to a concentrated or point force normal to the boundary. This boundary value problem was originally solved for a classical elastic material by Flamant in 1892 and, hence, is also known as the Flamant problem (Johnson [8]). In this paper, the granular material is considered as an elastic micropolar or Cosserat continuum and is represented by a particular form of the general constitutive law derived in Walsh and Tordesillas [29]. The stress distribution predicted by the model is in good agreement with experimental data for small strains. In particular, two important features that are captured by the proposed model are: (i) the presence of tensile stress response regions, and (ii) the dependence of the stresses on the microstructural properties, i.e. the particles normal, tangential and rotational stiffness constants. The proposed analysis utilizes two new stress functions, similar to Airys stress functions in classical elastic theory.The support of the US Army Research Office through a grant to AT (Grant No. DAAD19-02-1-0216) and the Melbourne Research and Development Grant scheme is gratefully acknowledged. We thank our reviewers for their useful suggestions and insightful comments.     

Design of Multiresponsive Hydrogel Particles and Assemblies

In the realm of soft nanotechnology, hydrogel micro‐ and nanoparticles represent a versatile class of responsive materials. Over the last decade, our group has investigated the synthesis and physicochemical properties of a variety of synthetic hydrogel particles. From these efforts, several particle types have emerged with potentially enabling features for biological applications, including nanogels for targeted drug delivery, microlenses for biosensing, and coatings for biomedical devices. For example, core/shell nanogels have been used to encapsulate and deliver small interfering RNA to ovarian cancer cells; nanogels used in this fashion may improve therapeutic outcomes for a variety of macromolecular therapeutics. Microgels arranged as multilayers on implantable biomaterials greatly minimize the host inflammatory response to the material. Furthermore, the triggered release of drugs (i.e., insulin) has been demonstrated from similar assemblies. The goal of this feature article is to highlight developments in the design of responsive microgels and nanogels in the context of our recent efforts and in relation to the community that has grown up around this fascinating class of materials.     

Empirical and clinical focus of child and adolescent psychotherapy research.

The present study evaluated the characteristics of research on child and adolescent psychotherapy. Published studies (N?=?223) of psychotherapy from 1970 to 1988 were codified to characterize research, clinical, and methodological characteristics. The major results indicate that (1) treatment research focuses almost exclusively on the impact of treatment techniques with scant attention to influences (child/adolescent, parent, family, therapist) that may moderate outcome and (2) several characteristics of the children/adolescents and methods of treatment delivery and approaches depart markedly from those evident in the practice of treatment. Priorities for treatment research to place clinical practice on firmer empirical footing are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bibliometrics as weapons of mass citation

The allocation of resources for research is increasingly based on so-called 'bibliometrics'. Scientists are now deemed to be successful on the sole condition that their work be abundantly cited. This world-wide trend appears to enjoy support not only by granting agencies (whose task is obviously simplified by extensive recourse to bibliometrics), but also by the scientists themselves (who seem to enjoy their status of celebrities). This trend appears to be fraught with dangers, particularly in the area of social sciences, where bibliometrics are less developed, and where monographs (which are not taken into account in citation indexes) are often more important than articles published in journals. We argue in favour of a return to the values of 'real science', in analogy to the much-promised return to a 'real economy'. While economists may strive towards a more objective evaluation of the prospects of a company, a market, or an industrial sector, we scientists can only base our appraisal on a responsible practice of peer review. Since we fear that decision-takers of granting agencies such as the FNRS, CTI, EPFL, ETHZ, ANR, CNRS, NIH, NSF, DOE, etc. will be too busy to read our humble paper in Chimia, we appeal to scientists of all countries and disciplines to unite against the tyranny of bibliometrics.     

Bioorganic and bioinorganic chemistry

The interdisciplinary projects in bioinorganic and bioorganic chemistry of the Department of Chemistry, University of Basel led to the preparation of new systems that mimic biologically important processes and to the discovery of compounds from natural sources which are very promising with respect to medical applications. The advances in these areas are reported here.     

Attitude strength and resistance processes.

This study examined whether multiple indicators of attitude strength form general dimensions that foster differential pathways to resistance. Ego involvement, certainty, personal importance, knowledge, and extremity were assessed. Resistance processes and outcomes were measured in a selective judgment paradigm. Intentions to act on attitudes and information-seeking proclivities were also assessed. Factor analyses of the strength measures revealed 2 factors. Both fostered intentions to act but were associated with differential resistance processes and outcomes. Heightened levels of the factor representing commitment to one's position were associated with increased selective elaboration, selective judgment, and attitude polarization. Embeddedness, the linkage of the attitude to one's self-concept, value system, and knowledge structure, was associated with decreased selective elaboration and increased information seeking and selective memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spectral fuzzy classification: an application

Geographical information (including remotely sensed data) is usually imprecise, meaning that the boundaries between different phenomena are fuzzy. In fact, many classes in nature show internal gradual differences in species, health, age, moisture, as well other factors. If our classification model does not acknowledge that those classes are heterogeneous, and crisp classes are artificially imposed, a final careful analysis should always search for the consequences of such an unrealistic assumption. We consider the unsupervised algorithm presented by A. del Amo et al. (2000), and its application to a real image in Sevilla province (south Spain). Results are compared with those obtained from the ERDAS ISO-DATA classification program on the same image, showing the accuracy of our fuzzy approach. As a conclusion, it is pointed out that whenever real classes are natural fuzzy classes, with gradual transition between classes, then its fuzzy representation will be more easily understood, and therefore accepted by users     

Peer models: Influence on children's self-efficacy and achievement.

Investigated how the self-efficacy and achievement of 72 children (aged 8 yrs 6 mo to 10 yrs 10 mo) were influenced by their observing peer models learn a cognitive skill. Within this context, the effects of modeled mastery and coping behaviors were explored. Ss were children who had experienced difficulties learning subtraction with regrouping operations in their classes. Ss were pre- and posttested on measures of subtraction self-efficacy, skill, and persistence. Ss observed a same-sex peer demonstrate either rapid (mastery model) or gradual (coping model) acquisition of subtraction skills, observed a teacher model demonstrate subtraction operations, or did not observe a model. Ss then judged self-efficacy for learning to subtract and received subtraction training. Observing a peer model led to higher self-efficacy for learning, posttest self-efficacy, and achievement than did observing the teacher model or not observing a model. Ss who observed the teacher model scored higher than no-model Ss on these measures. No significant differences due to type of peer modeled behavior (mastery/coping) were obtained on any measure. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cross-correlation frequency-resolved optical gating for studying ultrashort-pulse nonlinear dynamics in arbitrary fibers

We describe a cross-correlation frequency-resolved optical-gating system specifically designed for studying nonlinear pulse-propagation dynamics in fibers of arbitrary length at telecommunication wavelengths. The formation of optical solitons and the appearance of temporal phase slips are observed in 100 m of fiber. The wide phase-matching bandwidth and high sensitivity of this system allow us to visualize femtosecond-pulse evolution in a range of linear and nonlinear propagation regimes.