The Influence of Lubricating Agents on the Formation of a Film of a Styrene/Butadiene Latex

The interactions between paper coating lubricants and a carboxylated styrene/butadiene latex emulsion and their effect on latex film morphology have been studied. Calcium stearate, non-ionic polyethylene emulsion and organic triglyceride lubricants showed different interaction characteristics with the latex emulsion according to viscosity, zeta potential and isothermal calorimetric measurements. Calcium stearate lowered the viscosity of the dilute latex emulsion at low concentration suggesting a strong interaction with the latex particles due to a change in the hydrodynamic dimensions of the latex particles. The exothermic enthalpy change supported the assumption of a dissociative interaction. In contrast, both non-ionic polyethylene and organic triglyceride emulsion showed less pronounced enthalpy changes, indicating lower affinity for the latex particles. The reduction in viscosity showed, however, that at low lubricant concentrations there is an interaction between the latex particles and particularly the organic triglyceride emulsion. This suggests a selective adsorption of stabilizing agents and species from the lubricant emulsion which alters the hydrodynamic radius of the latex particles. The effects of the colloidal interactions on the morphology of the latex films monitored by Atomic Force Microscopy (AFM) indicated that specific surface interaction occurring in aqueous media influenced the topography and the surface chemical heterogeneity of the latex films. Especially in the case of calcium stearate, it seems that the dissolved species arrange themselves around the latex particles inhibiting film formation. The organic triglyceride, on the other hand, showed a lower interaction potential in the aqueous phase and it had a different impact on the film formation.     

Design of dynamic Hohlraum opacity samples to increase measured sample density on Z

We are attempting to measure the transmission of iron on Z at plasma temperatures and densities relevant to the solar radiation and convection zone boundary. The opacity data published by us to date has been taken at an electron density about a factor of 10 below the 9×10(22)/cm(3) electron density of this boundary. We present results of two-dimensional (2D) simulations of the heating and expansion of an opacity sample driven by the dynamic Hohlraum radiation source on Z. The aim of the simulations is to design foil samples that provide opacity data at increased density. The inputs or source terms for the simulations are spatially and temporally varying radiation temperatures with a Lambertian angular distribution. These temperature profiles were inferred on Z with on-axis time-resolved pinhole cameras, x-ray diodes, and bolometers. A typical sample is 0.3?μm of magnesium and 0.078?μm of iron sandwiched between 10?μm layers of plastic. The 2D LASNEX simulations indicate that to increase the density of the sample one should increase the thickness of the plastic backing.     

Validation of convection-limited cooling of samples for freeze-fracture electron microscopy

Rapid freezing is the most important step in sample preparation for freeze-fracture and other cryotechniques for electron microscopy. A simple heat transfer model is experimentally validated to show that convection from the cryogen to the specimen is the limiting step in rapid freezing of small samples [Biot modulus, (hd/k) < 1] by measuring cooling rates in a variety of samples, materials, and cryogens. In comparison to the commonly accepted conduction-limited model, the convection-limited model predicts, and our experiments show, that cooling rates are proportional to the surface area to volume ratio, independent of the sample thermal conductivity, and inversely proportional to the product of sample density and heat capacity. We show that almost any material can be frozen at similar rates if the sample thickness, the cryogen, and the method and velocity of contact with cryogen are similar. Liquid ethane or propane cooled to liquid nitrogen temperature are shown to give the best results.     

Self-build communities: the rationale and experiences of group-build (Baugruppen) housing development in Germany

Group-build housing developments can bring together the cost and customisation benefits regularly attributed to self-build housing with a communitarian ethos associated with ‘intentional’ communities. This paper presents an initial examination of the rationale, motivations and social experiences of group-build housing from Germany, where over half of all new homes are produced independently from volume-build developers. The paper aims, firstly, to test the hypothesis that group-build delivers general ‘community’ benefits; secondly, to contribute to an understanding of the processes leading to successful schemes; and lastly, to demonstrate that by making individual home building dependent on the success of a larger group, collective interests can prevail over personal pursuit. This research draws attention to the motivations, the social experiences through the development process and the social legacy – aspects of particular interest for policy-makers as well as prospective builders – of group-build housing projects.     

An approximate nonlinear modified Mohr-Coulomb shear strength criterion with critical state for intact rocks

In this paper, the Mohr-Coulomb shear strength criterion is modified by mobilising the cohesion and internal friction angle with normal stress, in order to capture the nonlinearity and critical state concept for intact rocks reported in the literature. The mathematical expression for the strength is the same as the classical form, but the terms of cohesion and internal friction angle depend on the normal stress now, leading to a nonlinear relationship between the strength and normal stress. It covers both the tension and compression regions with different expressions for cohesion and internal friction angle. The strengths from the two regions join continuously at the transition of zero normal stress. The part in the compression region approximately satisfies the conditions of critical state, where the maximum shear strength is reached. Due to the nonlinearity, the classical simple relationship between the parameters of cohesion, internal friction angle and uniaxial compressive strength from the linear Mohr-Coulomb criterion does not hold anymore. The equation for determining one of the three parameters in terms of the other two is supplied. This equation is nonlinear and thus a nonlinear equation solver is needed. For simplicity, the classical linear relationship is used as a local approximation. The approximate modified Mohr-Coulomb criterion has been implemented in a fracture mechanics based numerical code FRACOD, and an example case of deep tunnel failure is presented to demonstrate the difference between the original and modified Mohr-Coulomb criteria. It is shown that the nonlinear modified Mohr-Coulomb criterion predicts somewhat deeper and more intensive fracturing regions in the surrounding rock mass than the original linear Mohr-Coulomb criterion. A more comprehensive piecewise nonlinear shear strength criterion is also included in Appendix B for those readers who are interested. It covers the tensile, compressive, brittle-ductile behaviour transition and the critical state, and gives smooth transitions.     

The Social Value of Second Homes in Rural Communities

Analyses of the impacts of second home ownership in rural areas, around the world, regularly align with a “loss of community” thesis, linking second homes to a range of negative socio-economic consequences. This article looks again at the second home issue, developing a perspective that attributes a particular social value to temporary and seasonal rural residence. It proposes a framework for thinking about this phenomenon that brings together writings on the nature of place dwelling with ideas of social capital accumulation, and the potential interconnectors that temporary residents provide between the otherwise closed (or more limited) social networks of some rural communities and wider socio-economic and professional worlds. It argues that second homes may give communities a potential store of “bridging” social capital. Moreover, it proposes that second homes have a clear social value within rural community structures, and aims to open a research agenda and debate around the measurement and likely extent of this value.     

Ambivalent geographies of encounter inside and around the fortified homes of middle class Whites in Cape Town

Drawing on in-depth interviews with 78 middle class Whites in two neighborhoods of Cape Town, this paper focuses on domestic geographies of encounter. By looking at the motivations to fortify houses with walls, gates and alarms, it will be demonstrated, first, that seemingly banal actions to secure the residential environment are not only dependent upon the socio-spatial exclusion of poor people, but also specifically targeting it. Secondly, it will be argued that fortified homes provide, nevertheless, one of the rare places where White, middle class South Africans interact across class and race lines. Precisely because of the perceived absence of a crime threat, encounters with domestic workers, builders and homeless people inside and around fortified homes do not only help middle class Whites to shatter their naive assumptions about crime, poverty and privilege, but to set up small-scale acts of generosity as well. Based on these findings, the conclusion raises three issues to take up in the geographies of encounter literature. They relate to the nature of interactions, the conditions under which they emerge and their potential effects.     

Change and Continuity:Chinese Villages in Transition (I)–Longmei Village

This is the first in a series of four articles ethnographically exploring instances of village transformation in peri-urban China.Each article presents an in-depth case study of a single village and its unique combination of change and continuity.Together,these case studies demonstrate the specificity and idiosyncrasy of village transformation and the need for planners to"take actions that suit local conditions"(yindi zhiyi).This first installment investigates Longmei Village in the Panyu District of Guangzhou Municipality.Longmei’s leaders have encouraged economic transformation through industrialization and real estate development while seeking to maintain the village’s socio-spatial continuity.These competing priorities have led to contradictions in Longmei’s development,as integration into economic networks brings new people,goods,and ideas to the village.This tension has intensified as both registered villagers and migrant workers have pursued divergent visions for Longmei’s future transformation.