2,863 research outputs found
A model for effective interactions in binary colloidal systems of soft particles
While the density functional theory with integral equations techniques are
very efficient tools in numerical analysis of complex fluids, an analytical
insight into the phenomenon of effective interactions is still limited. In this
paper we propose a theory of binary systems which results in a relatively
simple analytical expression combining arbitrary microscopic potentials into
the effective interaction. The derivation is based on translating many particle
Hamiltonian including particle-depletant and depletant-depletant interactions
into the occupation field language. Such transformation turns the partition
function into multiple Gaussian integrals, regardless of what microscopic
potentials are chosen. In result, we calculate the effective Hamiltonian and
discuss when our formula is a dominant contribution to the effective
interactions. Our theory allows us to analytically reproduce several important
characteristics of systems under scrutiny. In particular, we analyze the
effective attraction as a demixing factor in the binary systems of Gaussian
particles, effective interactions in the binary mixtures of Yukawa particles
and the system of particles consisting of both repulsive core and
attractive/repulsive Yukawa interaction tail, for which we reproduce the
'attraction-through-repulsion' and 'repulsion-through-attraction' effects.Comment: Second version of article, after major revision due to the comments
from reviewers. Includes overhauled introductory section, new, more compact
derivation and more elaborate examples than previousl
Thermodynamically consistent Langevin dynamics with spatially correlated noise predicts frictionless regime and transient attraction effect
While the origin of temporal correlations in Langevin dynamics have been
thoroughly researched, the understanding of Spatially Correlated Noise (SCN) is
rather incomplete. In particular, very little is known about the relation
between friction and SCN. In this article, we derive the formal formula for the
spatial correlation function in the particle-bath interactions. This expression
shows that SCN is the inherent component of binary mixtures, originating from
the effective (entropic) interactions. Further, employing this spatial
correlation function, we postulate the thermodynamically consistent Langevin
equation driven by SCN and the adequate Fluctuation-Dissipation Relation. The
thermodynamical consistency is achieved by introducing the spatially variant
friction coefficient, which can be also derived analytically. This coefficient
exhibits a number of intriguing properties, e.g. the singular behavior for
certain interaction types. Eventually, we apply this new theory to the system
of two charged particles in the presence of counter-ions. Such particles
interact via the screened-charge Yukawa potential and the inclusion of SCN
leads to the emergence of the anomalous frictionless regime. In this regime the
particles can experience active propulsion leading to the transient attraction
effect. This effect suggests a non-equilibrium mechanism facilitating the
molecular binding of the like-charged particles.Comment: expanded and revised version resubmitted to Phys. Rev.
Non-Gaussian polymers described by alpha-stable chain statistics: model, applications and effective interactions in binary mixtures
The Gaussian chain model is the classical description of a polymeric chain,
which provides the analytical results regarding end-to-end distance, the
distribution of segments around the mass center of a chain, coarse grained
interactions between two chains and effective interactions in binary mixtures.
This hierarchy of results can be calculated thanks to the alpha stability of
the Gaussian distribution. In this paper we show that it is possible to
generalize the model of Gaussian chain to the entire class of alpha stable
distributions, obtaining the analogous hierarchy of results expressed by the
analytical closed-form formulas in the Fourier space. This allows us to
establish the alpha-stable chain model. We begin with reviewing the
applications of Levy flights in the context of polymer sciences, which include:
chains with heavy-tailed distributions of persistence length, polymers adsorbed
to the surface and the chains driven by a noise with power-law spatial
correlations. Further, we derive the distribution of segments around the mass
center of the alpha-stable chain and the coarse-grained interaction potential
between two chains is constructed. These results are employed to discuss the
model of binary mixture consisting of the alpha-stable chains. On what follows,
we establish the spinodal decomposition condition generalized to the particles
described by the shape of alpha-stable distributions. This condition is finally
applied to analyze the on-surface phase separation of adsorbed polymers, which
are known to be described with heavy tailed statistics.Comment: Complete version prepared for submission to Phys. Rev.
Towards ultra-high resolution 3D reconstruction of a whole rat brain from 3D-PLI data
3D reconstruction of the fiber connectivity of the rat brain at microscopic
scale enables gaining detailed insight about the complex structural
organization of the brain. We introduce a new method for registration and 3D
reconstruction of high- and ultra-high resolution (64 m and 1.3 m
pixel size) histological images of a Wistar rat brain acquired by 3D polarized
light imaging (3D-PLI). Our method exploits multi-scale and multi-modal 3D-PLI
data up to cellular resolution. We propose a new feature transform-based
similarity measure and a weighted regularization scheme for accurate and robust
non-rigid registration. To transform the 1.3 m ultra-high resolution data
to the reference blockface images a feature-based registration method followed
by a non-rigid registration is proposed. Our approach has been successfully
applied to 278 histological sections of a rat brain and the performance has
been quantitatively evaluated using manually placed landmarks by an expert.Comment: 9 pages, Accepted at 2nd International Workshop on Connectomics in
NeuroImaging (CNI), MICCAI'201
Properties of Exotic Matter for Heavy Ion Searches
We examine the properties of both forms of strange matter, small lumps of
strange quark matter (strangelets) and of strange hadronic matter (Metastable
Exotic Multihypernuclear Objects: MEMOs) and their relevance for present and
future heavy ion searches. The strong and weak decays are discussed separately
to distinguish between long-lived and short-lived candidates where the former
ones are detectable in present heavy ion experiments while the latter ones in
future heavy ion experiments, respectively. We find some long-lived strangelet
candidates which are highly negatively charged with a mass to charge ratio like
a anti deuteron (M/Z=-2) but masses of A=10 to 16. We predict also many
short-lived candidates, both in quark and in hadronic form, which can be highly
charged. Purely hyperonic nuclei are bound and have a negative charge while
carrying a positive baryon number. We demonstrate also that multiply charmed
exotics (charmlets) might be bound and can be produced at future heavy ion
colliders.Comment: 10 pages, 4 figures, uses IOP style and epsf.sty, to be published in
Journal of Physics, Proceedings of the International Symposium on Strangeness
in Quark Matter 1997, April 14-18, Thera (Santorini), Hellas. Corrected
typos, added comment about bag constant
The presence of B7-H4+ macrophages and CD25+CD4+ and FOXP3+ regulatory T cells in the microenvironment of nasal polyps - a preliminary report.
The nasal polyp (NP) seems to represent the end-stage of longstanding inflammation in patients with chronic rhinosinusitis. The aim of our study has been to evaluate the presence of two regulatory cell populations in the microenvironment of NP: CD4+CD25high Foxp3+ (Treg) cells and B7-H4-expressing macrophages. Treg cells are actively able to inhibit T lymphocytes, while the population of B7-H4-expressing macrophages has recently been described as characterized by a regulatory function similar to that of Treg cells. For our study, we evaluated 14 NP tissue samples. The samples were divided into two main groups, eosinophilic (NP) and lymphocytic (NP), according to the predominant type of immune cell infiltration. The presence of Treg cells and B7-H4 positive macrophages in the samples was analyzed by FACS. Treg cells and B7-H4-expressing macrophages were identified in all the examined nasal polyps. The percentages of both Treg cells and of B7H4 positive cells found in the eosinophilic nasal polyps were higher than those found in the lymphocytic nasal polyps. Treg cells and B7H4+ macrophage subpopulations were present in the NP microenvironment and the alterations in their percentages were related to a distinct pattern of immune cell infiltration
Whole-brain metallomic analysis of the common marmoset (: Callithrix jacchus)
© 2017 The Royal Society of Chemistry. Despite the importance of transition metals for normal brain function, relatively little is known about the distribution of these elemental species across the different tissue compartments of the primate brain. In this study, we employed laser ablation-inductively coupled plasma-mass spectrometry on PFA-fixed brain sections obtained from two adult common marmosets. Concurrent cytoarchitectonic, myeloarchitectonic, and chemoarchitectonic measurements allowed for identification of the major neocortical, archaecortical, and subcortical divisions of the brain, and precise localisation of iron, manganese, and zinc concentrations within each division. Major findings across tissue compartments included: (1) differentiation of white matter tracts from grey matter based on manganese and zinc distribution; (2) high iron concentrations in the basal ganglia, cortex, and substantia nigra; (3) co-localization of high concentrations of iron and manganese in the primary sensory areas of the cerebral cortex; and (4) high manganese in the hippocampus. The marmoset has become a model species of choice for connectomic, aging, and transgenic studies in primates, and the application of metallomics to these disciplines has the potential to yield high translational and basic science value
Halogen-bearing metasomatizing melt preserved in high-pressure (HP) eclogites of Pfaffenberg, Bohemian Massif
Primary granitic melt inclusions are trapped in garnets of eclogites in the garnet peridotite body of Pfaffenberg, Granulitgebirge (Bohemian Massif, Germany). These polycrystalline inclusions, based on their nature and composition, can be called nanogranitoids and contain mainly phlogopite/biotite, kumdykolite, quartz/rare cristobalite, a phase with the main Raman peak at 412 cm−1, a phase with the main Raman peak at 430 cm−1, osumilite and plagioclase. The melt is hydrous, peraluminous and granitic and significantly enriched in large ion lithophile elements (LILE), Th, U, Li, B and Pb. The melt major element composition resembles that of melts produced by the partial melting of metasediments, as also supported by its trace element signature characterized by elements (LILE, Pb, Li and B) typical of the continental crust. These microstructural and geochemical features suggest that the investigated melt originated in the subducted continental crust and interacted with the mantle to produce the Pfaffenberg eclogite. Moreover, in situ analyses and calculations based on partition coefficients between apatite and melt show that the melt was also enriched in Cl and F, pointing toward the presence of a brine during melting.
The melt preserved in inclusions can thus be regarded as an example of a metasomatizing agent present at depth and responsible for the interaction between the crust and the mantle. Chemical similarities between this melt and other metasomatizing melts measured in other eclogites from the Granulitgebirge and Erzgebirge, in addition to the overall similar enrichment in trace elements observed in other metasomatized mantle rocks from central Europe, suggest an extended crustal contamination of the mantle beneath the Bohemian Massif during the Variscan orogeny.</p
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