14,208 research outputs found
Aggregation kinetics of stiff polyelectrolytes in the presence of multivalent salt
Using molecular dynamics simulations, the kinetics of bundle formation for
stiff polyelectrolytes such as actin is studied in the solution of multivalent
salt. The dominant kinetic mode of aggregation is found to be the case of one
end of one rod meeting others at right angle due to electrostatic interactions.
The kinetic pathway to bundle formation involves a hierarchical structure of
small clusters forming initially and then feeding into larger clusters, which
is reminiscent of the flocculation dynamics of colloids. For the first few
cluster sizes, the Smoluchowski formula for the time evolution of the cluster
size gives a reasonable account for the results of our simulation without a
single fitting parameter. The description using Smoluchowski formula provides
evidence for the aggregation time scale to be controlled by diffusion, with no
appreciable energy barrier to overcome.Comment: 6 pages, 5 figures, Phys. Rev. E (Accepted
Continuous and discrete Clebsch variational principles
The Clebsch method provides a unifying approach for deriving variational
principles for continuous and discrete dynamical systems where elements of a
vector space are used to control dynamics on the cotangent bundle of a Lie
group \emph{via} a velocity map. This paper proves a reduction theorem which
states that the canonical variables on the Lie group can be eliminated, if and
only if the velocity map is a Lie algebra action, thereby producing the
Euler-Poincar\'e (EP) equation for the vector space variables. In this case,
the map from the canonical variables on the Lie group to the vector space is
the standard momentum map defined using the diamond operator. We apply the
Clebsch method in examples of the rotating rigid body and the incompressible
Euler equations. Along the way, we explain how singular solutions of the EP
equation for the diffeomorphism group (EPDiff) arise as momentum maps in the
Clebsch approach. In the case of finite dimensional Lie groups, the Clebsch
variational principle is discretised to produce a variational integrator for
the dynamical system. We obtain a discrete map from which the variables on the
cotangent bundle of a Lie group may be eliminated to produce a discrete EP
equation for elements of the vector space. We give an integrator for the
rotating rigid body as an example. We also briefly discuss how to discretise
infinite-dimensional Clebsch systems, so as to produce conservative numerical
methods for fluid dynamics
Characterization of eukaryotic microbial diversity in hypersaline Lake Tyrrell, Australia.
This study describes the community structure of the microbial eukaryotic community from hypersaline Lake Tyrrell, Australia, using near full length 18S rRNA sequences. Water samples were taken in both summer and winter over a 4-year period. The extent of eukaryotic diversity detected was low, with only 35 unique phylotypes using a 97% sequence similarity threshold. The water samples were dominated (91%) by a novel cluster of the Alveolate, Apicomplexa Colpodella spp., most closely related to C. edax. The Chlorophyte, Dunaliella spp. accounted for less than 35% of water column samples. However, the eukaryotic community entrained in a salt crust sample was vastly different and was dominated (83%) by the Dunaliella spp. The patterns described here represent the first observation of microbial eukaryotic dynamics in this system and provide a multiyear comparison of community composition by season. The lack of expected seasonal distribution in eukaryotic communities paired with abundant nanoflagellates suggests that grazing may significantly structure microbial eukaryotic communities in this system
E-recruitment: Towards an ubiquitous recruitment process and candidate relationship management
Up to now, there has been little research on the impact of e-recruitment on the recruitment process as a whole. The present study fills part of this gap by investigating the effect of e-recruitment on the design of the recruitment process. Three explorative case studies were carried out in three large organisations in Denmark in 2008-2010. The findings indicate that e-recruitment transforms the traditional recruitment process into a time- and space-independent, collaborative hiring process. The most significant changes are recorded in the sequence and increased divisibility of main recruitment tasks and subtasks. For management, the main task is now that of communicating with candidates. In addition, a new on-going task of maintaining a corporate career website has become an integral part of the new recruitment process. The new design is presented in the following, and its implications briefly discussed.Bis heute wurden die Auswirkungen von E-Recruiting auf den gesamten Rekrutierungsprozess wenig erforscht. Die vorliegende Studie zielt darauf ab, diese Forschungslücke durch die Untersuchung der Auswirkung von E-Recruiting auf die Gestaltung des Rekrutierungsprozesses teilweise zu schließen. Der Beitrag basiert dabei auf drei explorativen Fallstudien in drei großen dänischen Organisationen in den Jahren 2008-2010. Die Ergebnisse lassen darauf schließen, dass E-Recruiting den traditionellen Rekrutierungsprozess in einen zeit- und raumunabhängigen, kollaborativen Prozess transformiert. Dies stellt sich insbesondere in der Modifikation der Aufgabenabfolge und der erhöhten Teilbarkeit der Rekrutierungsaufgaben heraus. Zudem ist hervorzuheben, dass sich die Kommunikation mit den Bewerbern als eine zentrale neue Managementaufgabe herausbildet. Darüber hinaus bildet die permanente Pflege der Karriere-Website einen integralen Teil des neuen Rekrutierungsprozesses. Damit stellt dieser Beitrag generell die technologische Neugestaltung von Rekrutierungsprozessen vor und diskutiert deren Auswirkungen
Finite Size Polyelectrolyte Bundles at Thermodynamic Equilibrium
We present the results of extensive computer simulations performed on
solutions of monodisperse charged rod-like polyelectrolytes in the presence of
trivalent counterions. To overcome energy barriers we used a combination of
parallel tempering and hybrid Monte Carlo techniques. Our results show that for
small values of the electrostatic interaction the solution mostly consists of
dispersed single rods. The potential of mean force between the polyelectrolyte
monomers yields an attractive interaction at short distances. For a range of
larger values of the Bjerrum length, we find finite size polyelectrolyte
bundles at thermodynamic equilibrium. Further increase of the Bjerrum length
eventually leads to phase separation and precipitation. We discuss the origin
of the observed thermodynamic stability of the finite size aggregates
Variational Principles for Lagrangian Averaged Fluid Dynamics
The Lagrangian average (LA) of the ideal fluid equations preserves their
transport structure. This transport structure is responsible for the Kelvin
circulation theorem of the LA flow and, hence, for its convection of potential
vorticity and its conservation of helicity.
Lagrangian averaging also preserves the Euler-Poincar\'e (EP) variational
framework that implies the LA fluid equations. This is expressed in the
Lagrangian-averaged Euler-Poincar\'e (LAEP) theorem proven here and illustrated
for the Lagrangian average Euler (LAE) equations.Comment: 23 pages, 3 figure
Development of moored oceanographic spectroradiometer
Biospherical Instruments has successfully completed a NASA sponsored SBIR (Small Business Innovational Research Program) project to develop spectroradiometers capable of being deployed in the ocean for long periods of time. The completion of this project adds a valuable tool for the calibration of future spaceborne ocean color sensors and enables oceanographers to extend remote sensing optical techniques beyond the intermittent coverage of spaceborne sensors. Highlights of the project include two moorings totalling 8 months generating extensive sets of optical, biological, and physical data sets in the ocean off La Jolla, California, and a 70 day operational deployment of the resulting commercial product by the ONR and NASA sponsored BIOWATT program. Based on experience gained in these moorings, Biospherical Instruments has developed a new line of spectroradiometers designed to support the oceanographic remote sensing missions of NASA, the Navy, and various oceanographers
An integrable shallow water equation with peaked solitons
We derive a new completely integrable dispersive shallow water equation that
is biHamiltonian and thus possesses an infinite number of conservation laws in
involution. The equation is obtained by using an asymptotic expansion directly
in the Hamiltonian for Euler's equations in the shallow water regime. The
soliton solution for this equation has a limiting form that has a discontinuity
in the first derivative at its peak.Comment: LaTeX file. Figure available from authors upon reques
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