2,918 research outputs found
Nucleated dewetting in supported ultra-thin liquid films with hydrodynamic slip
This study reveals the influence of the surface energy and solid/liquid
boundary condition on the breakup mechanism of dewetting ultra-thin polymer
films. Using silane self-assembled monolayers, SiO substrates are rendered
hydrophobic and provide a strong slip rather than a no-slip solid/liquid
boundary condition. On undergoing these changes, the thin-film breakup
morphology changes dramatically -- from a spinodal mechanism to a breakup which
is governed by nucleation and growth. The experiments reveal a dependence of
the hole density on film thickness and temperature. The combination of lowered
surface energy and hydrodynamic slip brings the studied system closer to the
conditions encountered in bursting unsupported films. As for unsupported
polymer films, a critical nucleus size is inferred from a free energy model.
This critical nucleus size is supported by the film breakup observed in the
experiments using high speed \emph{in situ} atomic force microscopy.Comment: 8 pages, 9 figures, including supplementary materia
Capillary leveling of stepped films with inhomogeneous molecular mobility
A homogeneous thin polymer film with a stepped height profile levels due to
the presence of Laplace pressure gradients. Here we report on studies of
polymeric samples with precisely controlled, spatially inhomogeneous molecular
weight distributions. The viscosity of a polymer melt strongly depends on the
chain length distribution; thus, we learn about thin-film hydrodynamics with
viscosity gradients. These gradients are achieved by stacking two films with
different molecular weights atop one another. After a sufficient time these
samples can be well described as having one dimensional viscosity gradients in
the plane of the film, with a uniform viscosity normal to the film. We develop
a hydrodynamic model that accurately predicts the shape of the experimentally
observed self-similar profiles. The model allows for the extraction of a
capillary velocity, the ratio of the surface tension and the viscosity, in the
system. The results are in excellent agreement with capillary velocity
measurements of uniform mono- and bi-disperse stepped films and are consistent
with bulk polymer rheology.Comment: Accepted for publication in Soft Matter, Themed Issue on "The
Geometry and Topology of Soft Materials
Self-Similarity and Energy Dissipation in Stepped Polymer Films
The surface of a thin liquid film with nonconstant curvature is unstable, as
the Laplace pressure drives a flow mediated by viscosity. We present the
results of experiments on one of the simplest variable curvature surfaces: a
stepped polymer film. Height profiles are measured as a function of time for a
variety of molecular weights. The evolution of the profiles is shown to be
self-similar. This self-similarity offers a precise measurement of the
capillary velocity by comparison with numerical solutions of the thin film
equation. We also derive a master expression for the time dependence of the
excess free energy as a function of the material properties and film geometry.
The experiment and theory are in excellent agreement and indicate the
effectiveness of stepped polymer films to elucidate nanoscale rheological
properties.Comment: 5 pages, 4 figures, article accepted for publication in Physical
Review Letter
Capillary-driven flow induced by a stepped perturbation atop a viscous film
Thin viscous liquid films driven by capillarity are well described in the
lubrication theory through the thin film equation. In this article, we present
an analytical solution of this equation for a particular initial profile: a
stepped perturbation. This initial condition allows a linearization of the
problem making it amenable to Fourier analysis. The solution is obtained and
characterized. As for a temperature step in the heat equation, self-similarity
of the first kind of the full evolution is demonstrated and a long-term
expression for the excess free energy is derived. In addition, hydrodynamical
fields are described. The solution is then compared to experimental profiles
from a model system: a polystyrene nanostep above the glass transition
temperature which flows due to capillarity. The excellent agreement enables a
precise measurement of the capillary velocity for this polymeric liquid,
without involving any numerical simulation. More generally, as these results
hold for any viscous system driven by capillarity, the present solution may
provide a useful tool in hydrodynamics of thin viscous films.Comment: Accepted for publication in Physics of Fluid
Academic Perspectives on Agribusiness: An International Survey
The IFAMR is published by (IFAMA) the International Food and Agribusiness Management Review. www.ifama.orgpromotion and tenure, agribusiness, teaching, grantsmanship, research, Agribusiness, Institutional and Behavioral Economics, Productivity Analysis, Teaching/Communication/Extension/Profession, Q130,
Influence of Slip on the Plateau-Rayleigh Instability on a Fibre
The Plateau-Rayleigh instability of a liquid column underlies a variety of
fascinating phenomena that can be observed in everyday life. In contrast to the
case of a free liquid cylinder, describing the evolution of a liquid layer on a
solid fibre requires consideration of the solid-liquid interface. In this
article, we revisit the Plateau-Rayleigh Instability of a liquid coating a
fibre by varying the hydrodynamic boundary condition at the fibre-liquid
interface, from no-slip to slip. While the wavelength is not sensitive to the
solid-liquid interface, we find that the growth rate of the undulations
strongly depends on the hydrodynamic boundary condition. The experiments are in
excellent agreement with a new thin film theory incorporating slip, thus
providing an original, quantitative and robust tool to measure slip lengths
UC-248 GTRI: IT Management Web Application
This application was part of an industry Capstone project with Georgia Tech Research Institute, with Mr. Matthew Pinkston as the industry sponsor, Ms. Allison Boyle as the industry Capstone coordinator, and Mr. Donald Privitera as the Capstone professor. Our team worked on creating the framework for an opensource, web-based IT management application that future developers can add various features and sub-applications onto for purposes such as asset and budget management. The application is PHP-based with its backend, utilizing the Laravel framework and several of its built-in features for routing, database management, login authentication with bcrypt hash security, and session tracking. The frontend design of the web application was done using HTML, Bootstrap, and jQuery. MySQL was used for the database, which is currently used primarily for the user authentication system. We have chosen the MIT licensing model to ensure future developers can easily add onto the code and incorporate sub-applications into our framework, which was created with the intent of being a basis for developers to add functionality to as they see fit. It also ensures the application serves as a free, opensource solution for small IT management departments
Recombination and its impact on the genome of the haplodiploid parasitoid wasp Nasonia
Homologous meiotic recombination occurs in most sexually reproducing organisms, yet its evolutionary advantages are elusive. Previous research explored recombination in the honeybee, a eusocial hymenopteran with an exceptionally high genome-wide recombination rate. A comparable study in a non-social member of the Hymenoptera that would disentangle the impact of sociality from Hymenoptera-specific features such as haplodiploidy on the evolution of the high genome-wide recombination rate in social Hymenoptera is missing. Utilizing single-nucleotide polymorphisms (SNPs) between two Nasonia parasitoid wasp genomes, we developed a SNP genotyping microarray to infer a high-density linkage map for Nasonia. The map comprises 1,255 markers with an average distance of 0.3 cM. The mapped markers enabled us to arrange 265 scaffolds of the Nasonia genome assembly 1.0 on the linkage map, representing 63.6% of the assembled N. vitripennis genome. We estimated a genome-wide recombination rate of 1.4-1.5 cM/Mb for Nasonia, which is less than one tenth of the rate reported for the honeybee. The local recombination rate in Nasonia is positively correlated with the distance to the center of the linkage groups, GC content, and the proportion of simple repeats. In contrast to the honeybee genome, gene density in the parasitoid wasp genome is positively associated with the recombination rate; regions of low recombination are characterized by fewer genes with larger introns and by a greater distance between genes. Finally, we found that genes in regions of the genome with a low recombination frequency tend to have a higher ratio of non-synonymous to synonymous substitutions, likely due to the accumulation of slightly deleterious non-synonymous substitutions. These findings are consistent with the hypothesis that recombination reduces interference between linked sites and thereby facilitates adaptive evolution and the purging of deleterious mutations. Our results imply that the genomes of haplodiploid and of diploid higher eukaryotes do not differ systematically in their recombination rates and associated parameters.Publisher PDFPeer reviewe
- …