Force transmission in a packing of pentagonal particles

We perform a detailed analysis of the contact force network in a dense confined packing of pentagonal particles simulated by means of the contact dynamics method. The effect of particle shape is evidenced by comparing the data from pentagon packing and from a packing with identical characteristics except for the circular shape of the particles. A counterintuitive finding of this work is that, under steady shearing, the pentagon packing develops a lower structural anisotropy than the disk packing. We show that this weakness is compensated by a higher force anisotropy, leading to enhanced shear strength of the pentagon packing. We revisit "strong" and "weak" force networks in the pentagon packing, but our simulation data provide also evidence for a large class of "very weak" forces carried mainly by vertex-to-edge contacts. The strong force chains are mostly composed of edge-to-edge contacts with a marked zig-zag aspect and a decreasing exponential probability distribution as in a disk packing

Nitrogen sorption as a tool for the characterisation of polysaccharide aerogels

Supercritically dried aerogels of several polysaccharides (chitin, chitosan, alginate, alginic acid, k- carrageenan, and agar) have been characterised by physisorption ofN2. Surface areas as high as 570m2 g−1 have been measured. The nature of the functional groups of the polysaccharide significantly influences the adsorption of N2 on the surface of the aerogel. The net enthalpy of adsorption increases with the polarity of the surface groups of the polymer, in the order chitin < agar≤chitosan < carrageenan < alginic acid∼alginate. The surface area and the mesopore distribution of the aerogels depend both on the dispersion of the parent hydrogel and on the behaviour of each polymer in the drying treatment. Aerogels which retain the dispersion of the parent hydrogel are mainly macroporous (pores larger than 50 nm) while materials liable to shrink upon solvent exchange form mesoporous structures

Measurement of Turbulence in Superfluid 3He-B

The experimental investigation of superfluid turbulence in 3He-B is generally not possible with the techniques which have been developed for 4He-II. We describe a new method by which a transient burst of turbulent vortex expansion can be generated in 3He-B. It is based on the injection of a few vortex loops into rotating vortex-free flow. The time-dependent evolution of the quantized vorticity is then monitored with NMR spectroscopy. Using these techniques the transition between regular (i.e. vortex number conserving) and turbulent vortex dynamics can be recorded at T ~ 0.6 Tc and a number of other characteristics of turbulence can be followed down to a temperature of T ~ 0.4 Tc.Comment: 31 pages, 10 figure

Experimental study on stability and rheological properties of aqueous foam in the presence of reservoir natural solid particles

The authors would like to acknowledge the school of engineering at the University of Aberdeen and University Technology Malaysia (UTM) to provide required materials and facilities to complete this research.Peer reviewedPostprin

Importance of low-angle grain boundaries in YBa2Cu3O7-delta coated conductors

Over the past ten years the perception of grain boundaries in YBa2Cu3O7-δ conductors has changed greatly. They are no longer a problem to be eliminated but an inevitable and potentially favourable part of the material. This change has arisen as a consequence of new manufacturing techniques which result in excellent grain alignment, reducing the spread of grain boundary misorientation angles. At the same time there is considerable recent evidence which indicates that the variation of properties of grain boundaries with mismatch angle is more complex than a simple exponential decrease in critical current. This is due to the fact that low-angle grain boundaries represent a qualitatively different system to high angle boundaries. The time is therefore right for a targetted review of research into low-angle YBa2Cu3O7-δ grain boundaries. This article does not purport to be a comprehensive review of the physics of grain boundaries as found in YBa2Cu3O7-δ in general; for a broader overview we would recommend that the reader consult the comprehensive review of Hilgenkamp and Mannhart (Rev. Mod. Phys., 74, 485, 2002). The purpose of this article is to review the origin and properties of the low-angle grain boundaries found in YBa2Cu3O7-δ coated conductors both individually and as a collective system.EPSR

Neural dynamics of feedforward and feedback processing in figure-ground segregation

Determining whether a region belongs to the interior or exterior of a shape (figure-ground segregation) is a core competency of the primate brain, yet the underlying mechanisms are not well understood. Many models assume that figure-ground segregation occurs by assembling progressively more complex representations through feedforward connections, with feedback playing only a modulatory role. We present a dynamical model of figure-ground segregation in the primate ventral stream wherein feedback plays a crucial role in disambiguating a figure's interior and exterior. We introduce a processing strategy whereby jitter in RF center locations and variation in RF sizes is exploited to enhance and suppress neural activity inside and outside of figures, respectively. Feedforward projections emanate from units that model cells in V4 known to respond to the curvature of boundary contours (curved contour cells), and feedback projections from units predicted to exist in IT that strategically group neurons with different RF sizes and RF center locations (teardrop cells). Neurons (convex cells) that preferentially respond when centered on a figure dynamically balance feedforward (bottom-up) information and feedback from higher visual areas. The activation is enhanced when an interior portion of a figure is in the RF via feedback from units that detect closure in the boundary contours of a figure. Our model produces maximal activity along the medial axis of well-known figures with and without concavities, and inside algorithmically generated shapes. Our results suggest that the dynamic balancing of feedforward signals with the specific feedback mechanisms proposed by the model is crucial for figure-ground segregation

Incorporation of extracellular polysaccharide produced by Xanthomonas campestris into milk powders : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Technology at Massey University

The purpose of the research was to investigate the functional properties of milk powders following exopolysaccharide (EPS) addition to milk solutions and their subsequent spray-drying. The aim was to replace some of the milk proteins with polysaccharide in dairy products while maintaining or improving the functional characteristics. Both commercial xanthan EPS and ferment xanthan EPS were incorporated into whole milk powder (WMP), skim milk powder (SMP), and milk protein concentrate (MPC). Ferment EPS was produced from a by-product of the dairy industry, milk permeate, through the hydrolysis of the lactose and fermentation with a strain of Xanthomonas campestris. Ferment EPS had a characteristic and unpleasant odour. The main compound responsible for this odour was p-cresol which, in milk, is largely bound in the conjugate form. Xanthomonas campestris hydrolyses these conjugates releasing the odour compounds. Ultrafiltration (UF) of the ferment or passing the ferment through a bed of activated carbon was effective in reducing the odour. UF was proven to reduce the levels of p-cresol in the ferment from 138ppb to less than 5ppb after 98 concentration factors. Milk powders made with UF ferment were more acceptable to the consumer sensory panel than those made with untreated ferment. The incorporation of EPS into milk powders has beneficial effects on the product with small additions increasing the viscosity of reconstituted SMP and WMP considerably. The EPS addition could result in a thickened milk product or alternatively, substitute for some of the milk solids. Sensory testing showed that 13.3% WMP solution, containing 0.02% commercial EPS, was not detectably different from a 15% WMP solution. The addition of both commercial and ferment EPS into milk powders leads to the formation of separate flocculated casein and polysaccharide phases with reconstituted milk. Confocal microscopy showed that casein flocculation occurred at all EPS concentrations tested, but this only resulted in sedimentation at intermediate EPS concentrations. At high EPS concentrations of approximately 0.2% the high viscosity limited flocculation and prevented sedimentation. At low EPS concentrations of approximately 0.05% flocculation was insufficient to overcome Brownian motion. Fresh cheese (Panela) made from MPC containing either ferment or commercial EPS showed greatly decreased whey loss. This was attributed to (i) the increased viscosity of the continuous phase limiting the flow of liquid through the pores of the cheese, and (ii) diminished casein interaction in the presence of EPS leading to a looser curd and lower contraction forces. For example the incorporation of 0.161% ferment EPS decreased the whey lost by approximately 75%. Negative effects were also apparent. The addition of EPS led to a granular appearance, which became more apparent with increasing EPS concentration. Cheese firmness was also decreased by approximately 40% by the addition of the ferment EPS at 0.161%. This could also be attributed to the localised aggregation of protein during renneting and the increased heterogeneity of the network. Sensory testing of cheeses made with 15.6% MPC + 0.045% commercial EPS compared with cheese made with 17.37% MPC alone showed that the consumers had no significant preference for one cheese over the other, but did notice a difference in texture. For reasons of safety and health, the sensory testing of milk and cheese in this research was confined to commercial xanthan. Future sensory testing of milk and cheese should be conducted with ferment EPS after odour removal rather than commercial EPS, and use consumers familiar with these cheese and milk products. For commercial production of dairy powders containing UF ferment EPS it is vital that either the xanthan or casein micelle structure be altered to prevent casein flocculation. If this is not feasible then an alternative use of the product may need to be found. A potential option involves the addition of the powder containing UF ferment EPS into food products as a minor food constituent. This may limit the occurrence of phase separation while improving the functionality of the product. Commercialisation is also limited by the increasing costs caused by ferment EPS purification and the lower solids concentrations required for spray-drying. As such the viability of the powder production must be determined

Assessing the microstructural and rheological changes induced by food additives on potato puree

The effects of agar, alginate, lecithin and glycerol on the rheological properties of commercial potato puree were investigated and interpreted in terms of starch microstructural changes, and the applicability of the Cox-Merz rule was evaluated. Each additive was applied separately at two concentrations (0.5 and 1%). Microscopic observations revealed more swollen starch aggregations in lecithin and glycerol compared with those of potato puree and agar, consequently affecting the rheological properties of potato puree. All samples exhibited shear thinning non-Newtonian behaviour. Rheological measurements were strongly concentration dependent. At 0.5% concentration, additives exerted decreases in all the rheological properties of potato puree in the order of glycerol > alginate > lecithin > agar, while at 1% concentration, the order changed to glycerol > lecithin > alginate, whereas 1% agar behaved differently, increasing all rheological values. This study also showed that agar and alginate in addition to potato puree could be valuable and advantageous for further technological processes, such as 3D printing.Peer ReviewedPostprint (updated version