269 research outputs found
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
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
Palindromic complexity of codings of rotations
International audienceWe study the palindromic complexity of infinite words obtained by coding rotations on partitions of the unit circle by inspecting the return words. The main result is that every coding of rotations on two intervals is full, that is, it realizes the maximal palindromic complexity. As a byproduct, a slight improvement about return words in codings of rotations is obtained: every factor of a coding of rotations on two intervals has at most 4 complete return words, where the bound is realized only for a finite number of factors. We also provide a combinatorial proof for the special case of complementary-symmetric Rote sequences by considering both palindromes and antipalindromes occurring in it
Bridging transitions and capillary forces for colloids in a slit
Capillary bridges can form between colloids immersed in a two phase fluid,
e.g., in a binary liquid mixture, if the surface of the colloids prefers the
species other than the one favored in the bulk liquid. Here, we study the
formation of liquid bridges induced by confining colloids to a slit, with the
slit walls having a preference opposite to the one of the colloid surface.
Using mean field theory, we show that there is a line of first-order phase
transitions between the bridge and the no-bridge states, which ends at a
critical point. By decreasing the slit width, this critical point is shifted
towards smaller separations between the colloids. However, at very small
separations, and far from criticality, we observe only a minor influence of the
slit width on the location of the transition. Monte Carlo simulations of the
Ising model, which mimics incompressible binary liquid mixtures, confirm the
occurrence of the bridging transitions, as manifested by the appearance of
bistable regions where both the bridge and the no-bridge configurations are
(meta)stable. Interestingly, we find no bistability in the case of small
colloids, but we observe a sharpening of the transition when the colloid size
increases. In addition, we demonstrate that the capillary force acting between
the colloids can depend sensitively on the slit width, and varies drastically
with temperature, thus achieving strengths orders of magnitude higher than at
criticality of the fluid
Tour d'horizon du potentiel de développement de l'aquaponie en France : présentation et regard critique sur cette voie de développement alternative pour les productions piscicoles et horticoles
L'aquaponie repose sur l'intégration de process de production aquacole et hydroponique permettant le recyclage et la valorisation des nutriments émis par l'élevage aquacole par des cultures végétales. Cette démarche innovante attire à la fois les filiÚres aquacoles, car la co-production permet de réutiliser l'eau en permanence pour l'élevage ; mais également les filiÚres horticoles en réduisant l'emploi d'intrants chimiques dans la conduite de production végétale. Le projet APIVAŸ (Aquaponie Innovation Végétale et Aquaculture) vise à développer et caractériser des pilotes aquaponiques fonctionnels, d'étudier leur faisabilité économique, leur impact environnemental et la qualité des produits obtenus, tout en modélisant les flux se produisant entre les compartiments (bassins d'élevage, surfaces de culture, filtre biologique). AprÚs une rapide présentation de l'origine de l'aquaponie, cet article vise à définir les avantages et inconvénients de cette pratique innovante, les différentes formes qu'elle peut prendre, les diverses modalités de conception envisageables, ainsi que les aspects techniques à appréhender. En France, trÚs peu de systÚmes d'aquaponie commerciale sont actifs, mais beaucoup de projets émergent depuis quelques années, notamment en milieu urbain. Des exemples d'entreprises d'aquaponie commerciale à l'international sont présentés, avant de définir une typologie des porteurs de projet français. (Résumé d'auteur
Enhanced individual selection for selecting fast growing fish: the "PROSPER" method, with application on brown trout (Salmo trutta fario)
Growth rate is the main breeding goal of fish breeders, but individual selection has often shown poor responses in fish species. The PROSPER method was developed to overcome possible factors that may contribute to this low success, using (1) a variable base population and high number of breeders (Ne > 100), (2) selection within groups with low non-genetic effects and (3) repeated growth challenges. Using calculations, we show that individual selection within groups, with appropriate management of maternal effects, can be superior to mass selection as soon as the maternal effect ratio exceeds 0.15, when heritability is 0.25. Practically, brown trout were selected on length at the age of one year with the PROSPER method. The genetic gain was evaluated against an unselected control line. After four generations, the mean response per generation in length at one year was 6.2% of the control mean, while the mean correlated response in weight was 21.5% of the control mean per generation. At the 4th generation, selected fish also appeared to be leaner than control fish when compared at the same size, and the response on weight was maximal (â130% of the control mean) between 386 and 470 days post fertilisation. This high response is promising, however, the key points of the method have to be investigated in more detail
Theoretical study of highly strained InAs material from first-principles modelling: application to an ideal QD
International audienceWe study the properties of highly strained InAs material calculated from first principles modeling using ABINIT packages. We first simulate the characteristic of bulk InAs crystal and compare them with both experimental and density functional theory (DFT) results. Secondly, we focus our attention on the strain effects on InAs crystal with a gradual strain reaching progressively the lattice matched parameters of InP, GaAs and GaP substrates. The final part is dedicated to the study of a hypothetic spherical InAs/GaP quantum dot. The effect of hydrostatic deformations for both InAs Zinc-Blende phase and InAs RockSalt phase is discussed
PTP1B Is an Androgen ReceptorâRegulated Phosphatase That Promotes the Progression of Prostate Cancer
Hepatitis C Virus Infection in Guinea-Bissau: A Sexually Transmitted Genotype 2 with Parenteral Amplification?
BACKGROUND: Sub-Saharan Africa is the continent with the highest prevalence of Hepatitis C virus (HCV) infection. Genotype 2 HCV is thought to have originated from West Africa several hundred years ago. Mechanisms of transmission remain poorly understood. METHODOLOGY/PRINCIPAL FINDINGS: To delineate mechanisms for HCV transmission in West Africa, we conducted a cross-sectional survey of individuals aged â„50 years in Bissau, Guinea-Bissau. Dried blood spots were obtained for HCV serology and PCR amplification. Prevalence of HCV was 4.4% (47/1066) among women and 5.0% (27/544) among men. In multivariate analysis, the independent risk factors for HCV infection were age (baseline: 50â59 y; 60â69 y, adjusted odds ratio [AOR]: 1.67, 95% CI: 0.91â3.06; â„70 y, AOR: 3.47, 95% CI: 1.89â6.39), belonging to the Papel, Mancanha, Balanta or Mandjako ethnic groups (AOR: 2.45, 95% CI:1.32â4.53), originating from the Biombo, Cacheu or Oio regions north of Bissau (AOR: 4.16, 95% CI: 1.18â14.73) and having bought or sold sexual services (AOR: 3.60, 95% CI: 1.88â6.89). Of 57 isolates that could be genotyped, 56 were genotype 2. CONCLUSIONS: Our results suggest that transmission of HCV genotype 2 in West Africa occurs through sexual intercourse. In specific locations and subpopulations, medical interventions may have amplified transmission parenterally
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