Ostwald ripening in Two Dimensions: Correlations and Scaling Beyond Mean Field

We present a systematic quasi-mean field model of the Ostwald ripening process in two dimensions. Our approach yields a set of dynamic equations for the temporal evolution of the minority phase droplets' radii. The equations contain only pairwise interactions between the droplets; these interactions are evaluated in a mean- field type manner. We proceed to solve numerically the dynamic equations for systems of tens of thousands of interacting droplets. The numerical results are compared with the experimental data obtained by Krichevsky and Stavans for the relatively large volume fraction $\phi=0.13$. We found good agreement with experiment even for various correlation functions.Comment: 29 pages, RevTex, 5 eps figure

Lifshitz-Slyozov Scaling For Late-Stage Coarsening With An Order-Parameter-Dependent Mobility

The coarsening dynamics of the Cahn-Hilliard equation with order-parameter dependent mobility, $\lambda(\phi) \propto (1-\phi^2)^\alpha$, is addressed at zero temperature in the Lifshitz-Slyozov limit where the minority phase occupies a vanishingly small volume fraction. Despite the absence of bulk diffusion for $\alpha>0$, the mean domain size is found to grow as $\propto t^{1/(3+\alpha)}$, due to subdiffusive transport of the order parameter through the majority phase. The domain-size distribution is determined explicitly for the physically relevant case $\alpha = 1$.Comment: 4 pages, Revtex, no figure

How important is on-site adequacy assessment for thyroid FNA? An evaluation of 883 cases

Immediate adequacy assessment (IADA) during fine-needle aspiration (FNA) is not universal and the optimal numberof passes has not been well determined. The aim of this study was to evaluate the nondiagnostic rates (NDR) with and without the IADA forthyroid aspirates. Subsequent cytological and surgical follow-upwere reviewed for nondiagnostic cases. In addition, we evaluated the numberof passes performed in each FNA to determine the optimal number. Retrospective analysis of NDR was performed on 883 thyroid FNA specimens retrievedthrough a Computer SNOMED Search from our files between January 2001 toDecember 2003. For FNAs with IADA, one Diff-Quick and one fixedsmear for each pass were prepared, and the needle was rinsed in CytoLytsolution for a ThinPrep and/or a cell-block. FNAs without IADAwere received in CytoLyt solution, from which a ThinPrep and a cell-block were prepared for each case. Of the total 883 cases, 443 wereperformed with IADA, of which 417 cases were diagnostic. The remaining440 cases were performed without IADA, of which 300 cases were diagnostic.NDR for IADA was 5.9% (26 cases-group-I)compared to 31.8% (140 cases-group-II)without IADA. In group-I, 5 cases were followed-upby repeat FNA, 10 cases by surgical resection, and 11 cases received notissue follow-up. In group-II, 23 cases were followed-up by repeat FNA, 36 by surgical resection, and 82 cases received notissue follow-up. Interestingly, follow-up in group-Idid not reveal any missed malignancy, while that in group-II resultedin a malignant diagnosis in 13.8% (8 cases). We alsofound that the optimal number of passes with least NDR was 4–6 passes.NDR was 25% for < 3 passes, 11% for 4 passes, 5.2% for 5 passes, 1.4% for 6 passes, and 2.5% for 7 passesor more. IADA significantly reduces the NDR and increases the sample adequacy for diagnosis. Optimal number of passes is 4–6 passes, and additionalpasses did not improve the diagnostic rate. Our study also emphasizesthe significance of repeat FNA or histological follow-up for nondiagnostic cases, especially for those without IADA. Diagn. Cytopathol. 2007;35:183–186. © 2007 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/55982/1/20552_ftp.pd

Ultrasonic study of the gelation of gelatin: phase diagram, hysteresis and kinetics

We map the ultrasonic (8 MHz) speed and attenuation of edible-grade gelatin in water, exploring the key dependencies on temperature, concentration and time. The ultrasonic signatures of the sol-gel transition, confirmed by rheological measurements, and incomplete gel formation at low concentrations, enable a phase diagram of the system to be constructed. Sensitivity is also demonstrated to the kinetics of gel formation and melting, and associated hysteresis effects upon cyclic temperature sweeps. Furthermore, simple acoustic models of the sol and gel state enable estimation of the speed of sound and compressibility of gelatin. Our results demonstrate the potential of ultrasonic measurements to characterise the structure and visco-elasticity of gelatin hydrogels.Comment: 15 pages, 8 figure

Geometry and symmetry presculpt the free-energy landscape of proteins

We present a simple physical model which demonstrates that the native state folds of proteins can emerge on the basis of considerations of geometry and symmetry. We show that the inherent anisotropy of a chain molecule, the geometrical and energetic constraints placed by the hydrogen bonds and sterics, and hydrophobicity are sufficient to yield a free energy landscape with broad minima even for a homopolymer. These minima correspond to marginally compact structures comprising the menu of folds that proteins choose from to house their native-states in. Our results provide a general framework for understanding the common characteristics of globular proteins.Comment: 23 pages, 5 figure

The heat released during catalytic turnover enhances the diffusion of an enzyme

Recent studies have shown that the diffusivity of enzymes increases in a substrate-dependent manner during catalysis,. Although this observation has been reported and characterized for several different systems–, the precise origin of this phenomenon is unknown. Calorimetric methods are often used to determine enthalpies from enzyme-catalysed reactions and can therefore provide important insight into their reaction mechanisms,. The ensemble averages involved in traditional bulk calorimetry cannot probe the transient effects that the energy exchanged in a reaction may have on the catalyst. Here we obtain single-molecule fluorescence correlation spectroscopy data and analyse them within the framework of a stochastic theory to demonstrate a mechanistic link between the enhanced diffusion of a single enzyme molecule and the heat released in the reaction. We propose that the heat released during catalysis generates an asymmetric pressure wave that results in a differential stress at the protein–solvent interface that transiently displaces the centre-of-mass of the enzyme (chemoacoustic effect). This novel perspective on how enzymes respond to the energy released during catalysis suggests a possible effect of the heat of reaction on the structural integrity and internal degrees of freedom of the enzyme