Viscosity of Colloidal Suspensions

Simple expressions are given for the Newtonian viscosity $\eta_N(\phi)$ as well as the viscoelastic behavior of the viscosity $\eta(\phi,\omega)$ of neutral monodisperse hard sphere colloidal suspensions as a function of volume fraction $\phi$ and frequency $\omega$ over the entire fluid range, i.e., for volume fractions $0 < \phi < 0.55$. These expressions are based on an approximate theory which considers the viscosity as composed as the sum of two relevant physical processes: $\eta (\phi,\omega) = \eta_{\infty}(\phi) + \eta_{cd}(\phi,\omega)$, where $\eta_{\infty}(\phi) = \eta_0 \chi(\phi)$ is the infinite frequency (or very short time) viscosity, with $\eta_0$ the solvent viscosity, $\chi(\phi)$ the equilibrium hard sphere radial distribution function at contact, and $\eta_{cd}(\phi,\omega)$ the contribution due to the diffusion of the colloidal particles out of cages formed by their neighbors, on the P\'{e}clet time scale $\tau_P$, the dominant physical process in concentrated colloidal suspensions. The Newtonian viscosity $\eta_N(\phi) = \eta(\phi,\omega = 0)$ agrees very well with the extensive experiments of Van der Werff et al and others. Also, the asymptotic behavior for large $\omega$ is of the form $\eta_{\infty}(\phi) + A(\phi)(\omega \tau_P)^{-1/2}$, in agreement with these experiments, but the theoretical coefficient $A(\phi)$ differs by a constant factor $2/\chi(\phi)$ from the exact coefficient, computed from the Green-Kubo formula for $\eta(\phi,\omega)$. This still enables us to predict for practical purposes the visco-elastic behavior of monodisperse spherical colloidal suspensions for all volume fractions by a simple time rescaling.Comment: 51 page

Dynamic structure factors of a dense mixture

We compute the dynamic structure factors of a dense binary liquid mixture. These describe dynamics on molecular length scales, where structural relaxation is important. We find that the presence of a few large particles in a dense fluid of small particles slows down the dynamics considerably. We also observe a deep narrowing of the spectrum for a disordered mixture composed of a nearly equal packing of the two species. In contrast, a few small particles diffuse easily in the background of a dense fluid of large particles. We expect our results to describe neutron scattering from a dense mixture

The role of area level social deprivation on childhood and adolescent consultation rate in primary care:a population based, cohort study

BACKGROUND: Studies show that children and adolescents in the most socially deprived areas (SDA) consult their general practitioner (GP) more often than those in the least socially deprived areas (Non-SDA). Given that GPs see a wide range of diseases, it is important to know which clinical diagnoses are shaped by socioeconomic factors. The primary objective was to determine the association between area level social deprivation and consultation rates in a pediatric population. The secondary objective was to explore this association across a wide range of clinical diagnoses. METHODS: A cohort study using the Rijnmond Primary Care Database (RPCD) was conducted. Between 2013 and 2020, a total of 69,861 patients aged 0 to 17 years registered with a GP were analysed. A consultation was defined as patient contact and entry of a diagnosis using the International Classification of Primary Care (ICPC-1) code. Associations between consultation rates, ICPC-1 codes and area level social deprivation were explored using a Poisson regression model. The incidence risk ratio (IRR) and 95% confidence interval (CI) were reported. RESULTS: Over the 7-year study period the consultation rate of the study population was 3.8 per person-years. The top 5 reasons for children and adolescents to consult their GP was related to skin, respiratory, general unspecified, musculoskeletal and digestive symptoms or diagnoses. Consultation rate was higher in SDA group compared to Non-SDA group (IRR 1.20, 95% CI 1.19–1.20). Consultation rate for ICPC-1 code related to pregnancy and family planning was significantly lower in SDA group compared to Non-SDA group. Upon further exploration of this code, SDA group were less likely to consult for oral contraception and more likely to contact a GP for induced termination of pregnancy compared to Non-SDA group (IRR 0.36; 95% CI 0.33–0.44 and IRR 2.94; 95% CI 1.58–5.46 respectively). CONCLUSIONS: Overall, SDA group had higher GP consultation rates for the majority of clinical diagnoses except for pregnancy and family planning. In this latter category, adolescent females in SDA consulted less frequently for oral contraception. This study illustrates the need to understand the underlying health seeking behaviors of children and adolescents at different development phases of their lives. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12875-022-01873-x

Fluctuating magnetic moments in liquid metals

We re-analyze literature data on neutron scattering by liquid metals to show that non-magnetic liquid metals possess a magnetic moment that fluctuates on a picosecond time scale. This time scale follows the motion of the cage-diffusion process in which an ion rattles around in the cage formed by its neighbors. We find that these fluctuating magnetic moments are present in liquid Hg, Al, Ga and Pb, and possibly also in the alkali metals.Comment: 17 pages, 5 figures, submitted to PR