102 research outputs found
Wigner crystals for a planar, equimolar binary mixture of classical, charged particles
We have investigated the ground state configurations of an equimolar, binary
mixture of classical charged particles (with nominal charges and )
that condensate on a neutralizing plane. Using efficient Ewald summation
techniques for the calculation of the ground state energies, we have identified
the energetically most favourable ordered particle arrangements with the help
of a highly reliable optimization tool based on ideas of evolutionary
algorithms. Over a large range of charge ratios, , we identify
six non-trivial ground states, some of which show a remarkable and unexpected
structural complexity. For the system undergoes a phase
separation where the two charge species populate in a hexagonal arrangement
spatially separated areas.Comment: 14 pages, 8 figure
Taking one charge off a two-dimensional Wigner crystal
A planar array of identical charges at vanishing temperature forms a Wigner
crystal with hexagonal symmetry. We take off one (reference) charge in a
perpendicular direction, hold it fixed, and search for the ground state of the
whole system. The planar projection of the reference charge should then evolve
from a six-fold coordination (center of a hexagon) for small distances to a
three-fold arrangement (center of a triangle), at large distances from the
plane. The aim of this paper is to describe the corresponding non-trivial
lattice transformation. For that purpose, two numerical methods (direct energy
minimization and Monte Carlo simulations), together with an analytical
treatment, are presented. Our results indicate that the and
limiting cases extend for finite values of from the respective starting
points into two sequences of stable states, with intersecting energies at some
value ; beyond this value the branches continue as metastable states.Comment: 17 pages, 11 figure
Structures ordonnées dans les systèmes avec des interactions à longue portée
The central paradigm in the emerging field of metamaterials is that the properties of a material are in certain cases governed rather by the well-ordered spatial arrangement of its constituent particles than by the properties of those particles themselves. Since such highly ordered patterns can act as waveguides for acoustic, elastic, or electromagnetic waves, they can give rise to novel material properties, opening up new avenues in materials design. The central problem of how to produce the required ordered particle arrangements, e.g., via self-assembly, has received significant attention both from the experimental and theoretical sides.In theoretical studies, the interactions between particles are modeled via potential functions, whose shape and range have a profound impact on the formed structures. These potentials are often short-ranged, i.e., they are characterized by a rapid decay with distance. In this thesis, we focus on systems featuring long-range interactions, where particles interact over significantly larger distances than the mean inter-particle separation. Typical examples for such potentials are charged or multipolar interactions.In our approach, we first determine the ordered structures formed by the particles at vanishing temperature by minimizing the relevant thermodynamic potential. We observe a surprising plethora of different structural archetypes as well as novel phase transition scenarios. Then, we investigate the stability of these structures at low temperatures using Monte Carlo simulations.L'un des concepts fondamentaux dans l'étude des métamatériaux est que, dans certains cas, les propriétés du milieu sont déterminées par l'arrangement structurel de ses composants plutôt que par les propriétés intrinsèques des particules. De telles structures hautement ordonnées peuvent servir de guide d'onde en acoustique, ainsi que pour des ondes élastiques ou électromagnétiques ; elles peuvent aussi induire de nouvelles propriétés, ouvrant ainsi de nouvelles perspectives dans la conception des matériaux. Dans ce champ de recherche, la question centrale est de trouver comment produire ces arrangements ordonnés de particules et de molécules ; par exemple, un grand nombre d'études expérimentales et théoriques s'appuient sur des mécanismes d'auto-assemblage.Dans les études théoriques, ainsi que dans les simulations numériques, les interactions entre les constituants sont déterminées par des potentiels modèles ou effectifs dont la portée et la forme déterminent les structures collectives. Les potentiels utilisés sont souvent à courte portée, c'est-à-dire qu'ils ont une décroissance très rapide avec la distance ; typiquement, des molécules séparées de quelques diamètres moléculaires n'interagissent pas directement. Dans cette thèse, nous nous intéressons à ces structures ordonnées qu'il est possible d'obtenir, non pas avec des interactions à courte portée, mais avec des interactions à très longue portée (Coulomb, etc.). Notre démarche consiste dans un premier temps à déterminer les structures optimales à température nulle (états fondamentaux) en minimisant le potentiel thermodynamique adéquat ; puis, nous étudions la stabilité thermique de ces structures à basse température à l'aide de simulations numériques de Monte-Carlo. Nous observons une pléthore de structures prototypes, ainsi que des transitions de phases entre elles
Self-assembly scenarios of patchy colloidal particles
The rapid progress in precisely designing the surface decoration of patchy
colloidal particles offers a new, yet unexperienced freedom to create building
entities for larger, more complex structures in soft matter systems. However,
it is extremely difficult to predict the large variety of ordered equilibrium
structures that these particles are able to undergo under the variation of
external parameters, such as temperature or pressure. Here we show that, by a
novel combination of two theoretical tools, it is indeed possible to predict
the self-assembly scenario of patchy colloidal particles: on one hand, a
reliable and efficient optimization tool based on ideas of evolutionary
algorithms helps to identify the ordered equilibrium structures to be expected
at T = 0; on the other hand, suitable simulation techniques allow to estimate
via free energy calculations the phase diagram at finite temperature. With
these powerful approaches we are able to identify the broad variety of emerging
self-assembly scenarios for spherical colloids decorated by four patches and we
investigate and discuss the stability of the crystal structures on modifying in
a controlled way the tetrahedral arrangement of the patches.Comment: 11 pages, 7 figures, Soft Matter Communication (accepted
Heart Failure with Preserved and Reduced Ejection Fraction in Hemodialysis Patients: Prevalence, Disease Prediction and Prognosis
CMV Late Phase-Induced mTOR Activation Is Essential for Efficient Virus Replication in Polarized Human Macrophages : Antiviral Effects of mTOR Inhibitors
Human cytomegalovirus (CMV) remains one of the
most important pathogens following solid-organ
transplantation. Mounting evidence indicates that
mammalian target of rapamycin (mTOR) inhibitors
may decrease the incidence of CMV infection in solid-
organ recipients. Here we aimed at elucidating the
molecular mechanisms of this effect by employing
a human CMV (HCMV) infection model in human
macrophages, since myeloid cells are the principal
in
vivo
targets of HCMV. We demonstrate a highly di-
vergent host cell permissiveness for HCMV with opti-
mal infection susceptibility in M2 but not M1 polarized
macrophages. Employing an ultrahigh purified HCMV
stock we observed rapamycin-independent viral entry
and induction of IFN-b transcripts, but no proinflam-
matory cytokines or mitogen-activated protein kinases
and mTOR activation early after infection. However,
in the late infection phase, sustained mTOR activa-
tion was observed in HCMV-infected cells and was
required for efficient viral protein synthesis including
the viral late phase proteins pUL-44 and pp65. Accord-
ingly, rapamycin strongly suppressed CMV replication
3 and 5 days postinfection in macrophages. In conclu-
sion, these data indicate that mTOR is essential for
virus replication during late phases of the viral cycle in
myeloid cells and might explain the potent anti-CMV
effects of mTOR inhibitors after organ transplantatio
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