23,385 research outputs found
Solvent coarsening around colloids driven by temperature gradients
Using mesoscopic numerical simulations and analytical theory we investigate
the coarsening of the solvent structure around a colloidal particle emerging
after a temperature quench of the colloid surface. Qualitative differences in
the coarsening mechanisms are found, depending on the composition of the binary
liquid mixture forming the solvent and on the adsorption preferences of the
colloid. For an adsorptionwise neutral colloid, as function of time the phase
being next to its surface alternates. This behavior sets in on the scale of the
relaxation time of the solvent and is absent for colloids with strong
adsorption preferences. A Janus colloid, with a small temperature difference
between its two hemispheres, reveals an asymmetric structure formation and
surface enrichment around it, even if the solvent is within its one-phase
region and if the temperature of the colloid is above the critical demixing
temperature of the solvent. Our phenomenological model turns out to
capture recent experimental findings according to which, upon laser
illumination of a Janus colloid and due to the ensuing temperature gradient
between its two hemispheres, the surrounding binary liquid mixture develops a
concentration gradient.Comment: 8 pages, 4 figure
Vampires, Viruses and Verbalisation: Bram Stoker’s Dracula as a genealogical window into fin-de-siècle science
This paper considers Bram Stoker’s novel Dracula, published in 1897, as a window into techno-scientific and sociocultural developments of the fin-de-siècle era, ranging from blood transfusion and virology up to communication technology and brain research, but focusing on the birth of psychoanalysis in 1897, the year of publication. Stoker’s literary classic heralds a new style of scientific thinking, foreshadowing important aspects of post-1900 culture. Dracula reflects a number of scientific events which surfaced in the 1890s but evolved into major research areas that are still relevant today. Rather than seeing science and literature as separate realms, moreover, Stoker’s masterpiece encourages us to address the ways in which techno-scientific and psycho- cultural developments mutually challenge and mirror one another, so that we may use his novel to deepen our understanding of emerging research practices and vice versa (Zwart 2008, 2010). Psychoanalysis plays a double role in this. It is the research field whose genealogical constellation is being studied, but at the same time (Lacanian) psychoanalysis guides my reading strategy.
Dracula, the infectious, undead Vampire has become an archetypal cinematic icon and has attracted the attention of numerous scholars (Browning & Picart 2009). The vampire complex built on various folkloristic and literary sources and culminated in two famous nineteenth-century literary publications: the story The Vampyre by John Polidori (published in 1819)2 and Stoker’s version. Most of the more than 200 vampire movies released since Nosferatu (1922) are based on the latter (Skal 1990; Browning & Picart 2009; Melton 2010; Silver & Ursini 2010). Yet, rather than on the archetypal cinematic image of the Vampire, I will focus on the various scientific ideas and instruments employed by Dracula’s antagonists to overcome the threat to civilisation he represents. Although the basic storyline is well-known, I will begin with a plot summary
Note on Generalized Janus Configurations
We study several aspects of generalized Janus configuration, which includes a
theta term. We investigate the vacuum structure of the theory and find that
unlike the Janus configuration without theta term there is no nontrivial
vacuum. We also discuss BPS soliton configuration both by supersymmetry
analysis and from energy functional. The half BPS configurations could be
realized by introducing transverse (p,q)-strings in original brane
configuration corresponding to generalized Janus configuration. It turns out
the BPS soliton could be taken as modified dyon. We discuss the solution of
half BPS equations for the sharp interface case. Moreover we construct less
supersymmetric Janus configuration with theta term.Comment: 27 pages; References adde
The Janus Intertextuality Search Engine: A Research Tool of (and for) the Electronic Manipulus florum Project
This article demonstrates how the search engine developed for this online edition not only serves the research purposes of users of this digital resource, but is also a valuable tool for refining and improving the edition while also aiding the author’s research on the construction of this text. An example of its utility for the edition project is provided which calls into question previous theories regarding the influence John of Wales may have had on this collection of Latin quotations
Dynamics of self-propelled Janus particles in viscoelastic fluids
We experimentally investigate active motion of spherical Janus colloidal
particles in a viscoelastic fluid. Self-propulsion is achieved by a local
concentration gradient of a critical polymer mixture which is imposed by laser
illumination. Even in the regime where the fluid's viscosity is independent
from the deformation rate induced by the particle, we find a remarkable
increase of up to two orders of magnitude of the rotational diffusion with
increasing particle velocity, which can be phenomenologically described by an
effective rotational diffusion coefficient dependent on the Weissenberg number.
We show that this effect gives rise to a highly anisotropic response of
microswimmers in viscoelastic media to external forces depending on its
orientation.Comment: 5 pages, 4 figures, Physical Review Letters (accepted
Emergent behavior in active colloids
Active colloids are microscopic particles, which self-propel through viscous
fluids by converting energy extracted from their environment into directed
motion. We first explain how articial microswimmers move forward by generating
near-surface flow fields via self-phoresis or the self-induced Marangoni
effect. We then discuss generic features of the dynamics of single active
colloids in bulk and in confinement, as well as in the presence of gravity,
field gradients, and fluid flow. In the third part, we review the emergent
collective behavior of active colloidal suspensions focussing on their
structural and dynamic properties. After summarizing experimental observations,
we give an overview on the progress in modeling collectively moving active
colloids. While active Brownian particles are heavily used to study collective
dynamics on large scales, more advanced methods are necessary to explore the
importance of hydrodynamic and phoretic particle interactions. Finally, the
relevant physical approaches to quantify the emergent collective behavior are
presented.Comment: 31 pages, 14 figure
Phototaxis of synthetic microswimmers in optical landscapes
Many microorganisms, with phytoplankton and zooplankton as prominent
examples, display phototactic behaviour, that is, the ability to perform
directed motion within a light gradient. Here we experimentally demonstrate
that sensing of light gradients can also be achieved in a system of synthetic
photo-activated microparticles being exposed to an inhomogeneous laser field.
We observe a strong orientational response of the particles because of
diffusiophoretic torques, which in combination with an intensity-dependent
particle motility eventually leads to phototaxis. Since the aligning torques
saturate at high gradients, a strongly rectified particle motion is found even
in periodic asymmetric intensity landscapes. Our results are in excellent
agreement with numerical simulations of a minimal model and should similarly
apply to other particle propulsion mechanisms. Because light fields can be
easily adjusted in space and time, this also allows to extend our approach to
dynamical environments.Comment: 10 pages, 7 figure
Effect of a surface tension imbalance on a partly submerged cylinder
We perform a static analysis of a circular cylinder that forms a barrier
between surfactant-laden and surfactant-free portions of a liquidgas
interface. In addition to determining the general implications of the balances
for forces and torques, we quantify how the imbalance
between the uniform surface tension
of the surfactant-free portion of the interface and the uniform surface tension
of the surfactant-laden portion of the interface influences the
load-bearing capacity of a hydrophobic cylinder. Moreover, we demonstrate that
the difference between surface tensions on either side of a cylinder with a
cross-section of arbitrary shape induces a horizontal force component
equal to in magnitude, when measured per unit length of the
cylinder. With an energetic argument, we show that this relation also applies
to rod-like barriers with cross-sections of variable shape. In addition, we
apply our analysis to amphiphilic Janus cylinders and we discuss practical
implications of our findings for Marangoni propulsion and surface pressure
measurements
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