Effect of substrate thermal resistance on space-domain microchannel

In recent years, Fluorescent Melting Curve Analysis (FMCA) has become an almost ubiquitous feature of commercial quantitative PCR (qPCR) thermal cyclers. Here a micro-fluidic device is presented capable of performing FMCA within a microchannel. The device consists of modular thermally conductive blocks which can sandwich a microfluidic substrate. Opposing ends of the blocks are held at differing temperatures and a linear thermal gradient is generated along the microfluidic channel. Fluorescent measurements taken from a sample as it passes along the micro-fluidic channel permits fluorescent melting curves to be generated. In this study we measure DNA melting temperature from two plasmid fragments. The effects of flow velocity and ramp-rate are investigated, and measured melting curves are compared to those acquired from a commercially available PCR thermocycler

Anisotropic shear melting and recrystallization of a two-dimensional complex (dusty) plasma

A two-dimensional plasma crystal was melted by suddenly applying localized shear stress. A stripe of particles in the crystal was pushed by the radiation pressure force of a laser beam. We found that the response of the plasma crystal to stress and the eventual shear melting depended strongly on the crystal's angular orientation relative to the laser beam. Shear stress and strain rate were measured, from which the spatially resolved shear viscosity was calculated. The latter was shown to have minima in the regions with high velocity shear, thus demonstrating shear thinning. Shear-induced reordering was observed in the steady-state flow, where particles formed strings aligned in the flow direction.Comment: 7 pages, 8 figures, submitted to Physical Review

Colloidal interactions in an alternate make cheese : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, (Manawatū), New Zealand

The role of emulsion structure and interactions on the material and technical functionality of an alternate make cheese (AMC) was investigated. Lab scale cheese samples (25 g comprising 23 wt.% fat and 20 wt.%) were prepared by recombining model emulsions with a separate protein phase under controlled temperature, shear speed and residence time in a rapid visco analyser (RVA). Sodium caseinate and Tween 20 were used respectively to stabilize fat globules for the model emulsions. Preliminary experiments were carried out for samples prepared using either calcium caseinate or sodium caseinate as protein phase. Structural characterisation of samples showed emulsion structure and distribution within these phases to be dependent on protein type. It was inferred that the calcium from calcium caseinate matrix modified the interfacial layer of the emulsions stabilised by sodium caseinate, as indicated by the increased fat globule size distribution after cheese making. In comparison, the size of fat globules covered with sodium caseinate appeared relatively stable in cheese produced form cheese curd. Based on these observations, caseinates were subsequently replaced by cheese curd as the protein phase for the remainder of the study. For cheese samples prepared with low fat cheese curd, fat droplets stabilised with sodium caseinate were hypothesised as binding with the surrounding protein matrix, and thereby these fat globules could be considered as ‘active fillers’. Confocal laser scanning microscopy supported this hypothesis showing homogeneously dispersed fat droplets within the protein network. This emulsion system did not show fat-protein phase separation in baking (170 °C 10 minutes) as droplets were prevented from coalescing as a consequence of entrapment within the protein phase. Fat globules covered with Tween 20 were hypothesised as behaving as ‘inactive fillers’, with the adsorbed layer not anticipated to form bonds with the surrounding protein network. Confocal and scanning electron microscopy instead showed localised domains of fat droplets within the protein structure that underwent partial coalescence on cooling of the cheese after manufacture. Cheeses comprising Tween stabilised droplets exhibited phase separation on baking and visible oil-off on the surface of cheese arising from extensive coalescence taking place within the localised regions of fat due to melting of the partially coalesced structures. Additional rheological analysis of cheeses was carried out to determine the effect of droplet-protein interactions on the material properties of the cheese samples. Notably, findings were presented in relation to a non-fat control cheese. Findings showed that, at temperatures below 30 °C when fat was crystallized, both inactive and active fillers had a higher relative modulus to the non-fat sample. However, at elevated temperature without fat crystals, inactive fillers resulted in a relative reduction in storage modulus when compared to the non-fat cheese, while active fillers increased relative storage modulus. Model cheeses prepared with either sodium caseinate or Tween 20 stabilised emulsions were then compared to cheese samples comprising non-homogenised cream as the emulsion phase. Structural analysis of samples determined that cheeses comprising fat globules stabilized with native milk fat globule membrane behaved in a manner analogous to samples prepared with the Tween stabilised emulsion, indicating the presence of inactive droplets. However, it was also observed that increasing the residence time of cheese production within the RVA caused a transition of the interaction behaviour of the emulsion from inactive to active, as evidenced by corresponding changes to structural, material and functional properties of the cheese. Further exploration of this transition determined that the mechanical work applied during cheese preparation was sufficient to homogenise fat droplets during extended shearing, resulting in a reduction to fat droplet size. Droplet homogenisation during shearing was also found to have disrupted the native milk fat globule membrane, allowing protein adsorption to take place. It was also determined that whey proteins were the predominant interfacial fraction adsorbed as a consequence of extended shearing, and were considered responsible for the transition of droplets from inactive to active. Combined findings have shown that the material and functional properties of an alternate make cheese composition could be strongly influenced by the interactions of the emulsion phase with the surrounding protein network. These interactions could, in turn, be manipulated through formulation and/or process design, providing greater control over product properties

Anomalous evolution of the near-side jet peak shape in Pb-Pb collisions with ALICE

Two-particle angular correlations are sensitive probes to study the interaction of jets with the flowing medium produced in heavy-ion collisions. These interactions may appear as modifications of the near-side jet peak compared to pp collisions. In these measurements, the associated per-trigger yield is calculated from the relative azimuthal angle and pseudorapidity between a trigger particle with higher $p_{\rm T}$ (1 GeV/c $< p_{\rm T} < 8$ GeV/c) and an associated particle. Subsequently, the near-side peak width and shape are extracted as a function of $p_{\rm T}$ and centrality. Results obtained by the ALICE detector from Pb-Pb and pp collisions are presented. In Pb-Pb collisions, a significant broadening of the peak in central events at low $p_{\rm T}$ is observed in the data, and is more pronounced in the $\Delta\eta$ direction than in the $\Delta\varphi$ direction. A novel feature is also observed at low $p_{\rm T}$ in central events: the peak departs from the Gaussian shape, and a depletion around its center appears. To put the broadening and the depletion in context with the strength of longitudinal, radial and elliptic flow, the results are compared to AMPT simulations, which suggest that radial and longitudinal flow play a significant role in the appearance of the observed features.Comment: 4 pages, 3 figures. Submitted to the proceedings of Rencontres de Moriond QCD and High Energy Interactions 201

Analytical and Experimental Investigation of Ice Melting in Power Line Ground Wires

The present case study, using computer modeling technology, is to investigate the process of ice melting (de-icing) on iced ground wires due to current flowing through the ground wire. Using the AC model, the time course of heating of the given ground wire has been determined, and treating the results as input to the thermal model, the ice melting process has also been investigated by finite element thermal analysis. After comparing the elements by computer analysis to laboratory measurements, the results obtained were validated with numerical analysis