Mesoscopic model for colloidal particles, powders and granular solids

A simulation model is presented, comprising elastic spheres with a short range attraction. Besides conservative forces, radial- and shear friction, and radial noise are added. The model can be used to simulate colloids, granular solids and powders, and the parameters may be related to experimental systems via the range of attraction and the adhesion energy. The model shares the simplicity and speed of Dissipative Particle Dynamics (DPD), yet the predictions are rather non-trivial. We demonstrate that the model predicts the correct scaling relations for fracture of granular solids, and we present a schematic phase diagram. This shows liquid-vapor coexistence for sufficiently large interaction range, with a surface tension that follows Ising criticality. For smaller interaction range only solid-vapor coexistence is found, but for very small attractive interaction range stable liquid-vapor coexistence reappears due to pathological stability of the solid phase. At very low temperature the model forms a glassy state.Comment: 12 pages, 6 figures, accepted by Physical Review E, typos correcte

Fuelwood Exploitation and its Impacts on Residents of Kakau Daji Village, Chikun Local Government Area, Kaduna State, Nigeria

Communication in Physical Sciences 2019, 4(1): 39-48 Authors: Dogo Simeon, B. N. Wendock, B. Friday & M. Madaka  Majority of rural dwellers in Nigeria still depend on fuelwood as their main source of energy for cooking and heating. The rate of exploitation of fuelwood and its impact on the environment especially in rural areas has attracted much interest recently than evere. This study examines the nature of fuelwood exploitation, quantity of fuelwood consumed per household, quantity sold perhousehold and environmental problems associated with fuelwood exploitation. Primary data obtained in a cross-section survey of 100 household selected across the settlements of the area together with observation and measurements of quality of woodexploited were used. Data were analyzed through the use of descriptive statistical technique tools such as tables and graphs. Key findings show that 57% of fuelwood exploiters in the village are farmers. The fuelwood used by 85% of respondents came fromboth bush and farmlands. Results also show that 95% of the villagers used fuelwood as primary source of fuel, cooking and heating on daily basis as there is little alternative availability and affordability.. About 84% of the respondents said the experience shifts in their income and expenditure level while exploiting and selling fuelwood. The study concludes that the impact offuelwood exploitation is becoming increasingly glaring and cannot be overlooked. Rapid efforts should be employed in providing alternative cheap and accessible type of fuel/energy for rural use

Commodity-based Trade and Market Access for Developing Country Livestock Products: The Case of Beef Exports from Ethiopia

While Ethiopia is Africa’s largest livestock producer, sanitary and phytosanitary (SPS) barriers and animal diseases have traditionally constrained market access. A system dynamics model examined the feasibility of a proposed SPS certification system under a number of scenarios. Model results indicate that the system may not be viable for beef exports to Middle Eastern markets. However, the binding constraint is high domestic input costs rather than the costs of SPS compliance. Sensitivity analyses reveal that while investments in feed efficiency and animal productivity would enhance Ethiopia’s export competitiveness, the competitive nature of international beef markets may still prevent market access.SPS, livestock, market access, system dynamics, Ethiopia, Livestock Production/Industries, Marketing, Q10, Q13,

\u27Horae\u27 in Roman Funerary Inscriptions

References to hours on Roman tombstones, long assumed to be a means of displaying affection for children, are shown to be the basis for horoscopes of the afterlife. Statistical analysis argues for the accuracy of the figures of hours recorded. Close study of the inscriptions demonstrates that all references, whether to points in time or durations are records of times of death. Such inscriptions were set up from the first-sixth centuries CE and were most prevalent in Rome, Italy, and North Africa. Among both pagans and Christians these times allow for the casting of horoscopes of the afterlife. The individual hours would have been associated with signs of the Zodiac, gods of the Pantheon, or the Apostles. The hours recorded also indicate the tutelar who would watch over the deceased in the afterlife. This practice develops in the late Republic as Rome encounters Hellenistic ideas of astrology and time measurement

Cell shape recognition by colloidal cell imprints: Energy of the cell-imprint interaction

The results presented in this study are aimed at the theoretical estimate of the interactions between a spherical microbial cell and the colloidal cell imprints in terms of the Derjaguin, Landau, Vervey, and Overbeek (DLVO) surface forces. We adapted the Derjaguin approximation to take into account the geometry factor in the colloidal interaction between a spherical target particle and a hemispherical shell at two different orientations with respect to each other. We took into account only classical DLVO surface forces, i.e., the van der Waals and the electric double layer forces, in the interaction of a spherical target cell and a hemispherical shell as a function of their size ratio, mutual orientation, distance between their surfaces, their respective surface potentials, and the ionic strength of the aqueous solution. We found that the calculated interaction energies are several orders higher when match and recognition between the target cell and the target cell imprint is achieved. Our analysis revealed that the recognition effect of the hemispherical shell towards the target microsphere comes from the greatly increased surface contact area when a full match of their size and shape is produced. When the interaction between the surfaces of the hemishell and the target cell is attractive, the recognition greatly amplifies the attraction and this increases the likelihood of them to bind strongly. However, if the surface interaction between the cell and the imprint is repulsive, the shape and size match makes this interaction even more repulsive and thus decreases the likelihood of binding. These results show that the surface chemistry of the target cells and their colloidal imprints is very important in controlling the outcome of the interaction, while the shape recognition only amplifies the interaction. In the case of nonmonotonous surface-to-surface interaction we discovered some interesting interplay between the effects of shape match and surface chemistry which is discussed in the paper. The results from this study establish the theoretical basis of cell shape recognition by colloidal cell imprints which, combined with cell killing strategies, could lead to an alternative class of cell shape selective antimicrobials, antiviral, and potentially anticancer therapies

An ultra melt-resistant hydrogel from food grade carbohydrates

© 2017 The Royal Society of Chemistry. We report a binary hydrogel system made from two food grade biopolymers, agar and methylcellulose (agar-MC), which does not require addition of salt for gelation to occur and has very unusual rheological and thermal properties. It is found that the storage modulus of the agar-MC hydrogel far exceeds those of hydrogels from the individual components. In addition, the agar-MC hydrogel has enhanced mechanical properties over the temperature range 25-85 °C and a maximum storage modulus at 55 °C when the concentration of methylcellulose was 0.75% w/v or higher. This is explained by a sol-gel phase transition of the methylcellulose upon heating as supported by differential scanning calorimetry (DSC) measurements. Above the melting point of agar, the storage modulus of agar-MC hydrogel decreases but is still an elastic hydrogel with mechanical properties dominated by the MC gelation. By varying the mixing ratio of the two polymers, agar and MC, it was possible to engineer a food grade hydrogel of controlled mechanical properties and thermal response. SEM imaging of flash-frozen and freeze-dried samples revealed that the agar-MC hydrogel contains two different types of heterogeneous regions of distinct microstructures. The latter was also tested for its stability towards heat treatment which showed that upon heating to temperatures above 120 °C its structure was retained without melting. The produced highly thermally stable hydrogel shows melt resistance which may find application in high temperature food processing and materials templating

Analytical modeling of micelle growth. 2. Molecular thermodynamics of mixed aggregates and scission energy in wormlike micelles

Hypotheses: Quantitative molecular-thermodynamic theory of the growth of giant wormlike micelles in mixed nonionic surfactant solutions can be developed on the basis of a generalized model, which includes the classical phase separation and mass action models as special cases. The generalized model describes spherocylindrical micelles, which are simultaneously multicomponent and polydisperse in size. Theory: The model is based on explicit analytical expressions for the four components of the free energy of mixed nonionic micelles: interfacial-tension, headgroup-steric, chain-conformation components and free energy of mixing. The radii of the cylindrical part and the spherical endcaps, as well as the chemical composition of the endcaps, are determined by minimization of the free energy. Findings: In the case of multicomponent micelles, an additional term appears in the expression for the micelle growth parameter (scission free energy), which takes into account the fact that the micelle endcaps and cylindrical part have different compositions. The model accurately predicts the mean mass aggregation number of wormlike micelles in mixed nonionic surfactant solutions without using any adjustable parameters. The endcaps are enriched in the surfactant with smaller packing parameter that is better accommodated in regions of higher mean surface curvature. The model can be further extended to mixed solutions of nonionic, ionic and zwitterionic surfactants used in personal-care and house-hold detergency

From Molecular Dynamics to hydrodynamics - a novel Galilean invariant thermostat

This article proposes a novel thermostat applicable to any particle-based dynamic simulation. Each pair of particles is thermostated either (with probability P) with a pairwise Lowe-Andersen thermostat, or (with probability 1-P) with a thermostat that is introduced here, which is based on a pairwise interaction similar to the Nose-Hoover thermostat. When the pairwise Nose-Hoover thermostat dominates (low P), the liquid has a high diffusion coefficient and low viscosity, but when the Lowe-Andersen thermostat dominates, the diffusion coefficient is low and viscosity is high. This novel Nose-Hoover-Lowe-Andersen thermostat is Galilean invariant and preserves both total linear and angular momentum of the system, due to the fact that the thermostatic forces between each pair of the particles are pairwise additive and central. We show by simulation that this thermostat also preserves hydrodynamics. For the (non-interacting) ideal gas at P=0, the diffusion coefficient diverges and viscosity is zero, while for P>0 it has a finite value. By adjusting probability P, the Schmidt number can be varied by orders of magnitude. The temperature deviation from the required value is at least an order of magnitude smaller than in Dissipative Particle Dynamics (DPD), while the equilibrium properties of the system are very well reproduced. Applications of this thermostat include all standard molecular dynamic simulations of dense liquids and solids with any type of force field, as well as hydrodynamic simulation of multi-phase systems with largely different bulk viscosities, including surface viscosity, and of dilute gases and plasmas

Fabrication of living soft matter by symbiotic growth of unicellular microorganisms

We report the fabrication of living soft matter made as a result of the symbiotic relationship of two unicellular microorganisms. The material is composed of bacterial cellulose produced in situ by acetobacter (Acetobacter aceti NCIMB 8132) in the presence of photosynthetic microalgae (Chlamydomonas reinhardtii cc-124), which integrates into a symbiotic consortium and gets embedded in the produced cellulose composite. The same concept of growing living materials can be applied to other symbiotic microorganism pairs similar to the combination of algae and fungi in lichens, which is widespread in Nature. We demonstrate the in situ growth and immobilisation of the C. reinhardtii cells in the bacterial cellulose matrix produced by the simultaneous growth of acetobacter. The effect of the growth media composition on the produced living materials was investigated. The microstructure and the morphology of the produced living biomaterials were dependent on the shape of the growth culture container and media stirring conditions, which control the access to oxygen. As the photosynthetic C. reinhardtii cells remain viable and produce oxygen as they spontaneously integrate into the matrix of the bacterial cellulose generated by the acetobacter, such living materials have the potential for various applications in bio-hydrogen generation from the immobilised microalgae. The proposed approach for building living soft matter can provide new ways of immobilising other commercially important microorganisms in a bacterial cellulose matrix as a result of symbiosis with acetobacter without the use of synthetic binding agents and in turn increase their production efficiency