Shear-thinning drop formation

A volume-of-fluid numerical method is used to predict the dynamics of drop formation from a nozzle with a circular exit, directed vertically downwards in air, when the drop fluid is shear-thinning. The validity of the numerical calculation is first confirmed for a Newtonian fluid by comparison with experimental measurements. For the cases considered, predictions for a shear-thinning drop fluid result in more rapid pinch-off and a smaller final neck length consistent with a related study of liquid bridges

Modulation of stem cell adhesion and morphology via facile control over surface presentation of cell adhesion molecules

To encourage cell adhesion on biomaterial surfaces in a more facile, safe, and low-cost fashion, we have demonstrated a noncovalent approach to spatially conjugate β-cyclodextrin (β-CD) modified peptide sequences onto self-assembled adamantane-terminated polystyrene-b-poly(ethylene oxide) (PS-PEO-Ada) films through inclusion complexing interactions between β-CDs and adamantane. By simply blending various ratios of unmodified PS-PEO with a newly synthesized PS-PEO-Ada, we produced PS polymer films that displayed well-organized adamantine-decorated cylindrical PEO domains with varying average interdomain spacings ranging from 29 to 47 nm. The presence of the adamantane moiety at the terminal end of the PEO chain permitted rapid, and importantly, oriented attachment of β-CD functionalized peptides onto these surfaces. This one-step process not only converted these proven nonadherent PS-PEO surfaces into adherent surfaces, but also permitted precisely controlled presentation and surface distribution of the conjugated peptides. The utility of these surfaces as cell culture substrates was confirmed with human mesenchymal stem cells (hMSCs). We observed that with increasing PS-PEO-Ada content in the PEO cylindrical domains, these novel polymer films displayed improved cell attachment and spreading, with notable differences in hMSC morphology. We further confirmed that this novel PS-PEO-Ada surface provides a flexible platform for facile conjugation of mixtures of β-CDs functionalized with different peptides, specifically RGD and IKVAV peptides. The cell adhesion and spreading assays on these surfaces indicated that the morphologies of hMSCs can be easily manipulated, while no significant changes in cell attachment were observed. The lock-and-key peptide conjugation technique presented in this work is applicable to any substrate that incorporates a moiety capable of forming inclusion complexes with α-, β-, and γ-CDs, providing a facile and flexible method by which to construct peptide-conjugated biomaterial substrates for a multitude of applications in fields ranging from cell bioprocessing and regenerative medicine to cell-based assays

Symposium in Celebration of the Fixed Target Program with the Tevatron

This document is an abridgement of the commemorative book prepared on the occasion of the symposium "In Celebration of the Fixed Target Program with the Tevatron" held at Fermilab on June 2, 2000. The full text with graphics contains, in addition to the material here, a section for each experiment including a "plain text" description, lists of all physics publications, lists of all degree recipients and a photo from the archives. The full text is available on the web at: http://conferences.fnal.gov/tevft/book

The Dark Matter Problem in Light of Quantum Gravity

We show how, by considering the cumulative effect of tiny quantum gravitational fluctuations over very large distances, it may be possible to: ($a$) reconcile nucleosynthesis bounds on the density parameter of the Universe with the predictions of inflationary cosmology, and ($b$) reproduce the inferred variation of the density parameter with distance. Our calculation can be interpreted as a computation of the contribution of quantum gravitational degrees of freedom to the (local) energy density of the Universe.Comment: 13 pages, LaTeX, (3 figues, not included

Transgenic human ES and iPS reporter cell lines for identification and selection of pluripotent stem cells in vitro

Optimization of pluripotent stem cell expansion and differentiation is facilitated by biological tools that permit non-invasive and dynamic monitoring of pluripotency, and the ability to select for an undifferentiated input cell population. Here we report on the generation and characterisation of clonal human embryonic stem (HES3, H9) and human induced pluripotent stem cell lines (UQEW01i-epifibC11) that have been stably modified with an artificial EOS(C3+) promoter driving expression of EGFP and puromycin resistance-conferring proteins. We show that EGFP expression faithfully reports on the pluripotency status of the cells in these lines and that antibiotic selection allows for an efficient elimination of differentiated cells from the cultures. We demonstrate that the extinction of the expression of the pluripotency reporter during differentiation closely correlates with the decrease in expression of conventional pluripotency markers, such as OCT4 (POU5F1), TRA-1-60 and SSEA4 when screening across conditions with various levels of pluripotency-maintaining or differentiation-inducing signals. We further illustrate the utility of these lines for real-time monitoring of pluripotency in embryoid bodies and microfluidic bioreactors. (C) 2014 The Authors. Published by Elsevier B. V

Vanishing Hall Constant in the Stripe Phase of Cuprates

The Hall constant R_H is considered for the stripe structures. In order to explain the vanishing of R_H in LNSCO at x = 1/8, we use the relation of R_H to the Drude weight D as well as direct numerical calculation, to obtain results within the t-J model, where the stripes are imposed via a charge potential and a staggered magnetic field. The origin of R_H ~ 0 is related to a maximum in D and the minimal kinetic energy in stripes with a hole filling ~ 1/2. The same argument indicates on a possibility of R_H ~ 0 in the whole range of static stripes for x < 1/8.Comment: RevTeX, 4 pages, 5 figure

Adding Environmental Gas Physics to the Semi-Analytic Method for Galaxy Formation: Gravitational Heating

We present results of an attempt to include more detailed gas physics motivated from hydrodynamical simulations within semi-analytic models (SAM) of galaxy formation, focusing on the role that environmental effects play. The main difference to previous SAMs is that we include 'gravitational' heating of the intra-cluster medium (ICM) by the net surplus of gravitational potential energy released from gas that has been stripped from infalling satellites. Gravitational heating appears to be an efficient heating source able to prevent cooling in environments corresponding to dark matter halos more massive than $\sim 10^{13}$M$_{\odot}$. The energy release by gravitational heating can match that by AGN-feedback in massive galaxies and can exceed it in the most massive ones. However, there is a fundamental difference in the way the two processes operate. Gravitational heating becomes important at late times, when the peak activity of AGNs is already over, and it is very mass dependent. This mass dependency and time behaviour gives the right trend to recover down-sizing in the star-formation rate of massive galaxies. Abridged...Comment: replaced by accepted version to ApJ, some sections have been dropped and text has been added to others to include the referee's comments, several typos have been correcte

Drop Formation and Breakup of Low Viscosity Elastic Fluids: Effects of Molecular Weight and Concentration

Submitted to Phys. FluidsThe dynamics of drop formation and pinch-off have been investigated for a series of low viscosity elastic fluids possessing similar shear viscosities, but differing substantially in elastic properties. On initial approach to the pinch region, the viscoelastic fluids all exhibit the same global necking behaviour that is observed for a Newtonian fluid of equivalent shear viscosity. For these low viscosity dilute polymer solutions, inertial and capillary forces form the dominant balance in this potential flow regime, with the viscous force being negligible. The approach to the pinch point, which corresponds to the point of rupture for a Newtonian fluid, is extremely rapid in such solutions, with the sudden increase in curvature producing very large extension rates at this location. In this region the polymer molecules are significantly extended, causing a localised increase in the elastic stresses, which grow to balance the capillary pressure. This prevents the necked fluid from breaking off, as would occur in the equivalent Newtonian fluid. Alternatively, a cylindrical filament forms in which elastic stresses and capillary pressure balance, and the radius decreases exponentially with time. A (0+1)-dimensional FENE dumbbell theory incorporating inertial, capillary and elastic stresses is able to capture the basic features of the experimental observations. Before the critical ‘pinch time’ tp , an inertial-capillary balance leads to the expected 2/3-power scaling of the minimum radius with time, Rmin ∼ (tp − t)^2/3. However, the diverging deformation rate results in large molecular deformations and rapid crossover to an elasto-capillary balance for times t > tp. In this region the filament radius decreases exponentially with time Rmin ~exp[(tp - t) / λ1], where λ1 is the characteristic time constant of the polymer molecules. Measurements of the relaxation times of PEO solutions of varying concentrations and molecular weights obtained from high speed imaging of the rate of change of filament radius are significantly higher than the relaxation times estimated from Rouse-Zimm theory, even though the solutions are within the dilute concentration region as determined using intrinsic viscosity measurements. The effective relaxation times exhibit the expected scaling with molecular weight but with an additional dependence on the concentration of the polymer in solution. This is consistent with the expectation that the polymer molecules are in fact highly extended during the approach to the pinch region (i.e. prior to the elasto-capillary filament thinning regime) and subsequently as the filament is formed they are further extended by filament stretching at a constant rate until full extension of the polymer coil is achieved. In this highly-extended state, inter-molecular interactions become significant producing relaxation times far above theoretical predictions for dilute polymer solutions under equilibrium conditions.Australian Research Counci