18,809 research outputs found
Alignment of cylindrical colloids near chemically patterned substrates induced by critical Casimir torques
Recent experiments have demonstrated a fluctuation-induced lateral trapping
of spherical colloidal particles immersed in a binary liquid mixture near its
critical demixing point and exposed to chemically patterned substrates.
Inspired by these experiments, we study this kind of effective interaction,
known as the critical Casimir effect, for elongated colloids of cylindrical
shape. This adds orientational degrees of freedom. When the colloidal particles
are close to a chemically structured substrate, a critical Casimir torque
acting on the colloids emerges. We calculate this torque on the basis of the
Derjaguin approximation. The range of validity of the latter is assessed via
mean-field theory. This assessment shows that the Derjaguin approximation is
reliable in experimentally relevant regimes, so that we extend it to Janus
particles endowed with opposing adsorption preferences. Our analysis indicates
that critical Casimir interactions are capable of achieving well-defined,
reversible alignments both of chemically homogeneous and of Janus cylinders.Comment: 24 pages, 12 figures; v2: 22 pages, 12 figure
Liquid bridging of cylindrical colloids in near-critical solvents
Within mean field theory, we investigate the bridging transition between a
pair of parallel cylindrical colloids immersed in a binary liquid mixture as a
solvent which is close to its critical consolute point . We determine the
universal scaling functions of the effective potential and of the force between
the colloids. For a solvent which is at the critical concentration and close to
, we find that the critical Casimir force is the dominant interaction at
close separations. This agrees very well with the corresponding Derjaguin
approximation for the effective interaction between the two cylinders, while
capillary forces originating from the extension of the liquid bridge turn out
to be more important at large separations. In addition, we are able to infer
from the wetting characteristics of the individual colloids the first-order
transition of the liquid bridge connecting two colloidal particles to the
ruptured state. While specific to cylindrical colloids, the results presented
here provide also an outline for identifying critical Casimir forces acting on
bridged colloidal particles as such, and for analyzing the bridging transition
between them.Comment: 23 pages, 12 figure
Central Bank Forex Interventions Assessed Using Realized Moments
This paper studies and assesses the impact of G3 Central Bank interventions on the DEM/USD exchange rate properties using daily realized moments of exchange rate returns (obtained from intraday data) for the period 1989-2001. Event studies in terms of the realized moments for the intervention day, the days preceding and following the intervention day illustrate the shape of this impact. Rolling regressions results for an ARFIMA model for realized moments are used to measure the intervention impact and characterize its significance.The analysis confirms previous findings of an increase of volatility after a coordinated Central Bank intervention. It highlights new findings on the timing and the persistence of coordinated interventions on exchange rate volatility, on important volatility spillovers, on the impact on exchange rate covariances and correlations and on skewness coefficients.Economics ;
Trace anomaly of the conformal gauge field
The proposed by Bastianelli and van Nieuwenhuizen new method of calculations
of trace anomalies is applied in the conformal gauge field case. The result is
then reproduced by the heat equation method. An error in previous calculation
is corrected. It is pointed out that the introducing gauge symmetries into a
given system by a field-enlarging transformation can result in unexpected
quantum effects even for trivial configurations.Comment: 9 pages, LaTeX file, BI-TP 93/3
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