Velocity profiles in shear-banding wormlike micelles

Using Dynamic Light Scattering in heterodyne mode, we measure velocity profiles in a much studied system of wormlike micelles (CPCl/NaSal) known to exhibit both shear-banding and stress plateau behavior. Our data provide evidence for the simplest shear-banding scenario, according to which the effective viscosity drop in the system is due to the nucleation and growth of a highly sheared band in the gap, whose thickness linearly increases with the imposed shear rate. We discuss various details of the velocity profiles in all the regions of the flow curve and emphasize on the complex, non-Newtonian nature of the flow in the highly sheared band.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let

A transient network of telechelic polymers and microspheres : structure and rheology

We study the structure and dynamics of a transient network composed of droplets of microemulsion connected by telechelic polymers. The polymer induces a bridging attraction between droplets without changing their shape. A viscoelastic behaviour is induced in the initially liquid solution, characterised in the linear regime by a stretched exponential stress relaxation. We analyse this relaxation in the light of classical theories of transient networks. The role of the elastic reorganisations in the deformed network is emphasized. In the non linear regime, a fast relaxation dynamics is followed by a second one having the same rate as in the linear regime. This behaviour, under step strain experiments, should induce a non monotonic behaviour in the elastic component of the stress under constant shear rate. However, we obtain in this case a singularity in the flow curve very different from the one observed in other systems, that we interpret in terms of fracture behaviour.Comment: 9 pages, 4 figure

Cohomological tautness for Riemannian foliations

In this paper we present some new results on the tautness of Riemannian foliations in their historical context. The first part of the paper gives a short history of the problem. For a closed manifold, the tautness of a Riemannian foliation can be characterized cohomologically. We extend this cohomological characterization to a class of foliations which includes the foliated strata of any singular Riemannian foliation of a closed manifold

The galaxy environment in GAMA G3C groups using the Kilo Degree Survey Data Release 3

We aim to investigate the galaxy environment in GAMA Galaxy Groups Catalogue (G3C) using a volume-limited galaxy sample from the Kilo Degree Survey Data Release 3. The k-Nearest Neighbour technique is adapted to take into account the probability density functions (PDFs) of photometric redshifts in our calculations. This algorithm was tested on simulated KiDS tiles, showing its capability of recovering the relation between galaxy colour, luminosity and local environment. The characterization of the galaxy environment in G3C groups shows systematically steeper density contrasts for more massive groups. The red galaxy fraction gradients in these groups is evident for most of group mass bins. The density contrast of red galaxies is systematically higher at group centers when compared to blue galaxy ones. In addition, distinct group center definitions are used to show that our results are insensitive to center definitions. These results confirm the galaxy evolution scenario which environmental mechanisms are responsible for a slow quenching process as galaxies fall into groups and clusters, resulting in a smooth observed colour gradients in galaxy systems.Comment: 14 pages, Accepted to MNRA

“Everything Will Be Fine”: A Study on the Relationship between Employees’ Perception of Sustainable HRM Practices and Positive Organizational Behavior during COVID19

Sustainable human resource management practices represent one of the main organizational strategy to survive and to prosper within the fast-moving current scenario. According to this view, sustainability is strictly linked to the consideration of the unique and distinctive value that each human resource means for organizations. The recent COVID19 pandemic is having a serious impact on organizations and on their employees, it is profoundly changing the working modalities, mainly introducing smart working practices that were showed to have significant consequences on workers’ wellbeing. This study aims to investigate employees’ perception of sustainable HRM in the frame of the COVID19 emergency, exploring if and to what extent perceptions of involvement and organizational support together with individual coping strategies associated with organizational change could influence positive organizational behaviors, namely organizational engagement and extra-role behavior. The research involved 549 participants who completed a self-report online questionnaire encompassing psycho-social measures of the abovementioned variables. Results confirmed the important role played by sustainable HRM practices both for the capitalization of human resources and of organizational performance in a time of great uncertainty and global crisis. Implications for theory and HRM practice development were also discussed

Entropic phase separation of linked beads

We study theoretically a model system of a transient network of microemulsion droplets connected by telechelic polymers and explain recent experimental findings. Despite the absence of any specific interactions between either the droplets or polymer chains, we predict that as the number of polymers per drop is increased, the system undergoes a first order phase separation into a dense, highly connected phase, in equilibrium with dilute droplets, decorated by polymer loops. The phase transition is purely entropic and is driven by the interplay between the translational entropy of the drops and the configurational entropy of the polymer connections between them. Because it is dominated by entropic effects, the phase separation mechanism of the system is extremely robust and does not depend on the particlular physical realization of the network. The discussed model applies as well to other polymer linked particle aggregates, such as nano-particles connected with short DNA linkers

Does the end justify the means? The role of organizational communication among work‐from‐home employees during the covid‐19 pandemic

During the first months of 2020, the world, and Italy at an early stage, went through the Covid‐19 emergency that had a great impact on individual and collective health, but also on working processes. The mandatory remote working and the constant use of technology for employees raised different implications related to technostress and psycho‐physical disorders. This study aimed to detect, in such a period of crisis and changes, the role of organizational communication considering the mediating role of both technostress and self‐efficacy, with psycho‐physical disorders as outcome. The research involved 530 workers working from home. A Structural Equations Model was estimated, revealing that organizational communication is positively associated with self‐efficacy and negatively with technostress and psycho‐physical disorders. As mediators, technostress is positively associated with psycho‐physical disorders, whereas self‐efficacy is negatively associated. As regards mediated effects, results showed negative associations between organizational communication and psycho‐physical disorders through both technostress and self‐efficacy. This study highlighted the potential protective role of organizational communication that could buffer the effect of technostress and enhance a personal resource, self‐efficacy, which is functional to the reduction of psycho‐physical disorders. This study contributed to literature underlying the role of communication in the current crisis and consequent reorganization of the working processes

Influence of surfactants on the structure of titanium oxide gels : experiments and simulations

We report here on experimental and numerical studies of the influence of surfactants on mineral gel synthesis. The modification of the gel structure when the ratios water-precursor and water-surfactant vary is brought to the fore by fractal dimension measures. A property of {\em polydispersity of the initial hydrolysis} is proposed to explain these results, and is successfuly tested through numerical experiments of three dimensional chemically limited aggregation.Comment: 12 pages, 4 Postscript figures, uses RevTe