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Self-Assembly of Polyhedral Hybrid Colloidal Particles
We have developed a new method to produce hybrid particles with polyhedral shapes in very high yield (liter quantities at up to 70% purity) using a combination of emulsion polymerization and inorganic surface chemistry. The procedure has been generalized to create complex geometries, including hybrid line segments, triangles, tetrahedra, octahedra, and more. The optical properties of these particles are tailored for studying their dynamics and self-assembly. For example, we produce systems that consist of index-matched spheres allowing us to define the position of each elementary particle in three-dimensional space. We present some preliminary studies on the self-assembly of these complex shaped systems based on electron and optical microscopy.Engineering and Applied SciencesPhysic
Odd-even mass differences from self-consistent mean-field theory
We survey odd-even nuclear binding energy staggering using density functional
theory with several treatments of the pairing interaction including the BCS,
Hartree-Fock-Bogoliubov, and the Hartree-Fock-Bogoliubov with the Lipkin-Nogami
approximation. We calculate the second difference of binding energies and
compare with 443 measured neutron energy differences in isotope chains and 418
measured proton energy differences in isotone chains. The particle-hole part of
the energy functional is taken as the SLy4 Skyrme parametrization and the
pairing part of the functional is based on a contact interaction with possible
density dependence. An important feature of the data, reproduced by the theory,
is the sharp gap quenching at magic numbers. With the strength of the
interaction as a free parameter, the theory can reproduce the data to an rms
accuracy of about 0.25 MeV. This is slightly better than a single-parameter
phenomenological description but slightly poorer than the usual two-parameter
phenomenological form C/A^alpha . The following conclusions can be made about
the performance of common parametrization of the pairing interaction: (i) there
is a weak preference for a surface-peaked neutron-neutron pairing, which might
be attributable to many-body effects; (ii) a larger strength is required in the
proton pairing channel than in the neutron pairing channel; (iii) pairing
strengths adjusted to the well-known spherical isotope chains are too weak to
give a good overall fit to the mass differences.Comment: 13 pages, 9 figure
Microscopically-based energy density functionals for nuclei using the density matrix expansion: Implementation and pre-optimization
In a recent series of papers, Gebremariam, Bogner, and Duguet derived a
microscopically based nuclear energy density functional by applying the Density
Matrix Expansion (DME) to the Hartree-Fock energy obtained from chiral
effective field theory (EFT) two- and three-nucleon interactions. Due to the
structure of the chiral interactions, each coupling in the DME functional is
given as the sum of a coupling constant arising from zero-range contact
interactions and a coupling function of the density arising from the
finite-range pion exchanges. Since the contact contributions have essentially
the same structure as those entering empirical Skyrme functionals, a
microscopically guided Skyrme phenomenology has been suggested in which the
contact terms in the DME functional are released for optimization to
finite-density observables to capture short-range correlation energy
contributions from beyond Hartree-Fock. The present paper is the first attempt
to assess the ability of the newly suggested DME functional, which has a much
richer set of density dependencies than traditional Skyrme functionals, to
generate sensible and stable results for nuclear applications. The results of
the first proof-of-principle calculations are given, and numerous practical
issues related to the implementation of the new functional in existing Skyrme
codes are discussed. Using a restricted singular value decomposition (SVD)
optimization procedure, it is found that the new DME functional gives
numerically stable results and exhibits a small but systematic reduction of our
test function compared to standard Skyrme functionals, thus justifying
its suitability for future global optimizations and large-scale calculations.Comment: 17 pages, 6 figure
Instabilities in the Nuclear Energy Density Functional
In the field of Energy Density Functionals (EDF) used in nuclear structure
and dynamics, one of the unsolved issues is the stability of the functional.
Numerical issues aside, some EDFs are unstable with respect to particular
perturbations of the nuclear ground-state density. The aim of this contribution
is to raise questions about the origin and nature of these instabilities, the
techniques used to diagnose and prevent them, and the domain of density
functions in which one should expect a nuclear EDF to be stable.Comment: Special issue "Open Problems in Nuclear Structure Theory" of
Jour.Phys.G - accepted. 7 pages, 2 figure
Recent breakthroughs in Skyrme-Hartree-Fock-Bogoliubov mass formulas
We review our recent achievements in the construction of microscopic mass
tables based on the Hartree-Fock-Bogoliubov method with Skyrme effective
interactions. In the latest of our series of HFB-mass models, we have obtained
our best fit ever to essentially all the available mass data, by treating the
pairing more realistically than in any of our earlier models. The rms deviation
on the 2149 measured masses of nuclei with N and Z>8 has been reduced for the
first time in a mean field approach to 0.581 MeV. With the additional
constraint on the neutron-matter equation of state, this new force is thus very
well-suited for the study of neutron-rich nuclei and for the description of
astrophysical environments like supernova cores and neutron-star crusts.Comment: Proceedings of the Fifth International Conference on Exotic Nuclei
and Atomic Masses, September 7-13 2008, Ryn (Poland). To appear in the
European Physical Journal
Bare vs effective pairing forces. A microscopic finite-range interaction for HFB calculations in coordinate space
We propose a microscopic effective interaction to treat pairing correlations
in the channel. It is introduced by recasting the gap equation
written in terms of the bare force into a fully equivalent pairing problem.
Within this approach, the proposed interaction reproduces the pairing
properties provided by the realistic force very accurately. Written in
the canonical basis of the actual Bogolyubov transformation, the force takes
the form of an off-shell in-medium two-body matrix in the superfluid phase
multiplied by a BCS occupation number . This interaction is finite
ranged, non local, total-momentum dependent and density dependent. The factor
emerging from the recast of the gap equation provides a natural
cut-off and makes zero-range approximations of the effective vertex meaningful.
Performing such an approximation, the roles of the range and of the density
dependence of the interaction can be disentangled. The isoscalar and isovector
density-dependences derived ab-initio provide the pairing force with a strong
predictive power when extrapolated toward the drip-lines. Although finite
ranged and non local, the proposed interaction makes HFB calculations of finite
nuclei in coordinate space tractable. Through the two-basis method, its
computational cost is of the same order as for a zero-range force.Comment: 43 pages, 13 figures. Published versio
Observation of the lowest energy gamma-ray in any superdeformed nucleus : 196Bi
New results on the superdeformed Bi nucleus a re reported. We have
observed with the EUROBALL IV -ray spectrometer array a superdeformed
trans ition of 124 keV which is the lowest observed energy -ray in any
superdeformed nucleus. We have de velopped microscopic cranked
Hartree-Fock-Bogoliubov calculations using the SLy4 effective force and a
realistic surface p airing which strongly support the
([651]1/2[752]5/2) assignment of this su
perdeformed band
On the decay of turbulence in plane Couette flow
The decay of turbulent and laminar oblique bands in the lower transitional
range of plane Couette flow is studied by means of direct numerical simulations
of the Navier--Stokes equations. We consider systems that are extended enough
for several bands to exist, thanks to mild wall-normal under-resolution
considered as a consistent and well-validated modelling strategy. We point out
a two-stage process involving the rupture of a band followed by a slow
regression of the fragments left. Previous approaches to turbulence decay in
wall-bounded flows making use of the chaotic transient paradigm are
reinterpreted within a spatiotemporal perspective in terms of large deviations
of an underlying stochastic process.Comment: ETC13 Conference Proceedings, 6 pages, 5 figure
Recent Duplication and Functional Divergence in Parasitic Nematode Levamisole-Sensitive Acetylcholine Receptors
Helminth parasites rely on fast-synaptic transmission in their neuromusculature to experience the outside world and respond to it. Acetylcholine plays a pivotal role in this and its receptors are targeted by a wide variety of both natural and synthetic compounds used in human health and for the control of parasitic disease. The model, Caenorhabditis elegans is characterized by a large number of acetylcholine receptor subunit genes, a feature shared across the nematodes. This dynamic family is characterized by both gene duplication and loss between species. The pentameric levamisole-sensitive acetylcholine receptor has been characterized from C. elegans, comprised of five different subunits. More recently, cognate receptors have been reconstituted from multiple parasitic nematodes that are found to vary in subunit composition. In order to understand the implications of receptor composition change and the origins of potentially novel drug targets, we investigated a specific example of subunit duplication based on analysis of genome data for 25 species from the 50 helminth genome initiative. We found multiple independent duplications of the unc-29, acetylcholine receptor subunit, where codon substitution rate analysis identified positive, directional selection acting on amino acid positions associated with subunit assembly. Characterization of four gene copies from a model parasitic nematode, Haemonchus contortus, demonstrated that each copy has acquired unique functional characteristics based on phenotype rescue of transgenic C. elegans and electrophysiology of receptors reconstituted in Xenopus oocytes. We found evidence that a specific incompatibility has evolved for two subunits co-expressed in muscle. We demonstrated that functional divergence of acetylcholine receptors, driven by directional selection, can occur more rapidly than previously thought and may be mediated by alteration of receptor assembly. This phenomenon is common among the clade V parasitic nematodes and this work provides a foundation for understanding the broader context of changing anthelmintic drug targets across the parasitic nematodes
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