Electrical controlled rheology of a suspension of weakly conducting particles in dielectric liquid

The properties of suspensions of fine particles in dielectric liquid (electrorheological fluids) subjected to an electric field lead to a drastic change of the apparent viscosity of the fluid. For high applied fields (~ 3-5 kV/mm) the suspension congeals to a solid gel (particles fibrillate span the electrode gap) having a finite yield stress. For moderate fields the viscosity of the suspension is continuously controlled by the electric field strength. We have roposed that in DC voltage the field distribution in the solid (particles) and liquid phases of the suspension and so the attractive induced forces between particles and the yield stress of the suspension are controlled by the conductivities of the both materials. In this paper we report investigation and results obtained with nanoelectrorheological suspensions: synthesis of coated nanoparticles (size ~ 50 to 600 nm, materials Gd2O3:Tb, SiOx...), preparation of ER fluids (nanoparticles mixed in silicone oil), electrical and rheological characterization of the ER fluids. We also propose a possible explanation of the enhanced ER effect (giant ER fluids) taking into account the combined effects of the (nano)size of the particles, the Van der Waals forces between particles in contact and the electrostatic pressure in a very thin layer of insulating liquid.Comment: Article pour la conf\'{e}rence sur les charges d'espaces (CSC 6\`{e}me \'{e}dition) qui s'est d\'{e}roul\'{e}e \`{a} Tours du 3 au 7 juillet 2006. 6page

A simple model for the quenching of pairing correlations effects in rigidly deformed rotational bands

Using Chandrasekhar's S-type coupling between rotational and intrinsic vortical modes one may simply reproduce the HFB dynamical properties of rotating nuclei within Routhian HF calculations free of pairing correlations yet constrained on the relevant so-called Kelvin circulation operator. From the analogy between magnetic and rotating systems, one derives a model for the quenching of pairing correlations with rotation, introducing a critical angular velocity -- analogous to the critical field in supraconductors -- above which pairing vanishes. Taking stock of this usual model, it is then shown that the characteristic behavior of the vortical mode angular velocity as a function of the global rotation angular velocity can be modelised by a simple two parameter formula, both parameters being completely determined from properties of the band-head (zero-spin) HFB solution. From calculation in five nuclei, the validity of this modelised Routhian approach is assessed. It is clearly shown to be very good in cases where the evolution of rotational properties is only governed by the coupling between the global rotation and the pairing-induced intrinsic vortical currents. It therefore provides a sound ground base for evaluating the importance of coupling of rotation with other modes (shape distortions, quasiparticle degrees of freedom).Comment: 10 pages, 8 figures. Submited to PR

The Interplay of Defense Mechanisms Against Infectious Diseases

The total complex of immune expression is an interplay between nonspecific antimicrobial humoral systems plus specific antibodies and accessory factors. These systems are backstopped by the phagocytic functions of PMNs. If these fail, mononuclear phagocytes respond as a second line of defense to carry out chronic engagements. In addition to a direct activation process by substrate, macrophages may be activated and mobilized by a lymphocyte-mediated immunologic reaction which probably involves either a lymphotoxin and/or a specific antibody cytophilic for macrophages. Immunologically activated lymphocytes appear to be the primary effector cells of anti-tissue (transplantation) cellular immunity, whereas immunologically activated macrophages appear to be the primary effector cells of antibacterial cellular immunity

Are ships communities of practice?

The purpose of this paper is to explore the idea that a merchant ship aligns with the academic notion of a Community of Practice. Through secondary qualitative research, the paper identifies several characteristics which provide compelling evidence. Young seafarers face multiple challenges joining their first ship, not only in terms of mastering the technicalities of their roles but also in terms of social behaviour and interaction. As anyone contemplating the training of school leavers will realise, the people from whom they learn, will inevitably influence their conduct. Learning on the job is not exclusive to the apprentice. Ship staff will endeavour to learn the techniques of the future role they aspire to, by a similar process. Bandura (2001 p1) asserts that human behaviour may be “shaped and controlled automatically and mechanically by environmental stimuli” and this is a theme referenced by Nthia in her excellent 2018 paper relating the techniques of social learning at sea. Compelling evidence of this type of learning was provided and the next logical step is to pose the question Are ships Communities of Practice? based on the theories of Lave and Wenger (1991). Conclusions suggest the desire to improve is the one characteristic commonly missing

Time-delay and Doppler tests of the Lorentz symmetry of gravity

Modifications to the classic time-delay effect and Doppler shift in General Relativity (GR) are studied in the context of the Lorentz-violating Standard-Model Extension (SME). We derive the leading Lorentz-violating corrections to the time-delay and Doppler shift signals, for a light ray passing near a massive body. It is demonstrated that anisotropic coefficients for Lorentz violation control a time-dependent behavior of these signals that is qualitatively different from the conventional case in GR. Estimates of sensitivities to gravity-sector coefficients in the SME are given for current and future experiments, including the recent Cassini solar conjunction experiment.Comment: 13 pages, 4 figures, references added, matches PRD versio