359 research outputs found
Nanostructures and Thin Films of Poly(Ethylene Glycol)-Based Surfactants and Polystyrene Nanocolloid Particles on Mica: An Atomic Force Microscopy Study
Eliminating cracking during drying
When colloidal suspensions dry, stresses build up and cracks often occur - a
phenomenon undesirable for important industries such as paint and ceramics. We
demonstrate an effective method which can completely eliminate cracking during
drying: by adding emulsion droplets into colloidal suspensions, we can
systematically decrease the amount of cracking, and eliminate it completely
above a critical droplet concentration. Since the emulsion droplets eventually
also evaporate, our technique achieves an effective function while making
little changes to the component of final product, and may therefore serve as a
promising approach for cracking elimination. Furthermore, adding droplets also
varies the speed of air invasion and provides a powerful method to adjust
drying rate. With the effective control over cracking and drying rate, our
study may find important applications in many drying and cracking related
industrial processes.Comment: 5 pages, 5 figure
Multiparty Electoral Competition in the Netherlands and Germany: A Model Based on Multinomial Probit
A typical assumption of electoral models of party competition is that parties adopt policy positions so as to maximize expected vote share. Here we use Euro-barometer survey data and European elite-study data from 1979 for the Netherlands and Germany to construct a stochastic model of voter response, based on multinomial probit estimation. For each of these countries, we estimate a pure spatial electoral voting model and a joint spatial model. The latter model also includes individual voter and demographic characteristics. The pure spatial models for the two countries quite accurately described the electoral response as a stochastic function of party positions. We use these models to perform a thought experiment so as to estimate the expected vote maximizing party positions. We go on to propose a model of internal party decision-making based both on pre-election electoral estimation and postelection coalition bargaining. This model suggests why the various parties in the period in question did not adopt vote maximizing positions. We argue that maximizing expected vote will not, in general, be a rational party strategy in multiparty political systems which are based on proportional representation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/116246/1/pc98.pd
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Human gut Bacteroides capture vitamin B12 via cell surface-exposed lipoproteins.
Human gut Bacteroides use surface-exposed lipoproteins to bind and metabolize complex polysaccharides. Although vitamins and other nutrients are also essential for commensal fitness, much less is known about how commensal bacteria compete with each other or the host for these critical resources. Unlike in Escherichia coli, transport loci for vitamin B12 (cobalamin) and other corrinoids in human gut Bacteroides are replete with conserved genes encoding proteins whose functions are unknown. Here we report that one of these proteins, BtuG, is a surface-exposed lipoprotein that is essential for efficient B12 transport in B. thetaiotaomicron. BtuG binds B12 with femtomolar affinity and can remove B12 from intrinsic factor, a critical B12 transport protein in humans. Our studies suggest that Bacteroides use surface-exposed lipoproteins not only for capturing polysaccharides, but also to acquire key vitamins in the gut
Bicontinuous Soft Solids with a Gradient in Channel Size
We present examples of bicontinuous interfacially jammed emulsion gels
("bijels") with a designed gradient in the channel size along the sample. These
samples are created by quenching binary fluids which have a gradient in
particle concentration along the sample, since the channel size is determined
by the local particle concentration. A gradient in local particle concentration
is achieved using a two-stage loading process, with different particle volume
fractions in each stage. Confocal microscopy and image analysis were used to
quantitatively measure the channel size of the bijels. Bijels with a gradient
in channel size of up to 2.8%/mm have been created. Such tailored soft
materials could act as templates for energy materials optimised for both high
ionic transport rates (high power) and high interfacial area (high energy
density), potentially making them useful in novel energy applications.Comment: 9 pages, 5 figure
What is second-order vision for? Discriminating illumination versus material changes
The human visual system is sensitive to second-order modulations of the local contrast (CM) or amplitude (AM) of a carrier signal. Second-order cues are detected independently of first-order luminance signals; however, it is not clear why vision should benet from second-order sensitivity. Analysis of the first-and second-order contents of natural images suggests that these cues tend to occur together, but their phase relationship varies. We have shown that in-phase combinations of LM and AM are perceived as a shaded corrugated surface whereas the anti-phase combination can be seen as corrugated when presented alone or as a flat material change when presented in a plaid containing the in-phase cue. We now extend these findings using new stimulus types and a novel haptic matching task. We also introduce a computational model based on initially separate first-and second-order channels that are combined within orientation and subsequently across orientation to produce a shading signal. Contrast gain control allows the LM + AM cue to suppress responses to the LM-AM when presented in a plaid. Thus, the model sees LM -AM as flat in these circumstances. We conclude that second-order vision plays a key role in disambiguating the origin of luminance changes within an image. © ARVO
Drying of complex suspensions
We investigate the 3D structure and drying dynamics of complex mixtures of
emulsion droplets and colloidal particles, using confocal microscopy. Air
invades and rapidly collapses large emulsion droplets, forcing their contents
into the surrounding porous particle pack at a rate proportional to the square
of the droplet radius. By contrast, small droplets do not collapse, but remain
intact and are merely deformed. A simple model coupling the Laplace pressure to
Darcy's law correctly estimates both the threshold radius separating these two
behaviors, and the rate of large-droplet evacuation. Finally, we use these
systems to make novel hierarchical structures.Comment: 4 pages, 4 figure
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