Dynamics of bidisperse suspensions under stokes flows: linear shear flow and eedimentation

Sedimenting and sheared bidisperse homogeneous suspensions of non-Brownian particles are investigated by numerical simulations in the limit of vanishing small Reynolds number and negligible inertia of the particles. The numerical approach is based on the solution of the three-dimensional Stokes equations forced by the presence of the dispersed phase. Multi-body hydrodynamic interactions are achieved by a low order multipole expansion of the velocity perturbation. The accuracy of the model is validated on analytic solutions of generic flow configurations involving a pair of particles. The first part of the paper aims at investigating the dynamics of monodisperse and bidisperse suspensions embedded in a linear shear flow. The macroscopic transport properties due to hydrodynamic and non hydrodynamic interactions (short range repulsion force) show good agreement with previous theoretical and experimental works on homogeneous monodisperse particles. Increasing the volumetric concentration of the suspension leads to an enhancement of particle fluctuations and self-diffusion. The velocity fluctuation tensor scales linearly up to 15% concentration. Multi-body interactions weaken the correlation of velocity fluctuations and lead to a diffusion like motion of the particles. Probability density functions show a clear transition from Gaussian to exponential tails while the concentration decreases. The behavior of bidisperse suspensions is more complicated, since the respective amount of small and large particles modifies the overall response of the flow. Our simulations show that, for a given concentration of both species, when the size ratio varies from 1 to 2.5, the fluctuation level of the small particles is strongly enhanced. A similar trend is observed on the evolution of the shear induced self-diffusion coefficient. Thus for a fixed and total concentration, increasing the respective volume fraction of large particles can double the velocity fluctuation of small particles. In the second part of the paper, the sedimentation of a single test particle embedded in a suspension of monodisperse particles allows the determination of basic hydrodynamic interactions involved in a bidisperse suspension. Good agreement is achieved when comparing the mean settling velocity and fluctuations levels of the test sphere with experiments. Two distinct behaviors are observed depending on the physical properties of the particle. The Lagrangian velocity autocorrelation function has a negative region when the test particle has a settling velocity twice as large as the reference velocity of the surrounding suspension. The test particle settles with a zig-zag vertical trajectory while a strong reduction of horizontal dispersion occurs. Then, several configurations of bidisperse settling suspensions are investigated. Mean velocity depends on concentration of both species, density ratio and size ratio. Results are compared with theoretical predictions at low concentration and empirical correlations when the assumption of a dilute regime is no longer valid. For particular configurations, a segregation instability sets in. Columnar patterns tend to collect particles of the same species and eventually a complete separation of the suspension is observed. The instability threshold is compared with experiments in the case of suspensions of buoyant and heavy spheres. The basic features are well reproduced by the simulation model

Intraspecific trait variation and coordination: Root and leaf economics spectra in coffee across environmental gradients

Hypotheses on the existence of a universal “Root Economics Spectrum” (RES) have received arguably the least attention of all trait spectra, despite the key role root trait variation plays in resource acquisition potential. There is growing interest in quantifying intraspecific trait variation (ITV) in plants, but there are few studies evaluating (i) the existence of an intraspecific RES within a plant species, or (ii) how a RES may be coordinated with other trait spectra within species, such as a leaf economics spectrum (LES). Using Coffea arabica (Rubiaceae) as a model species, we measured seven morphological and chemical traits of intact lateral roots, which were paired with information on four key LES traits. Field collections were completed across four nested levels of biological organization. The intraspecific trait coefficient of variation (cv) ranged from 25 to 87% with root diameter and specific root tip density showing the lowest and highest cv, respectively. Between 27 and 68% of root ITV was explained by site identity alone for five of the seven traits measured. A single principal component explained 56.2% of root trait covariation, with plants falling along a RES from resource acquiring to conserving traits. Multiple factor analysis revealed significant orthogonal relationships between root and leaf spectra. RES traits were strongly orthogonal with respect to LES traits, suggesting these traits vary independently from one another in response to environmental cues. This study provides among the first evidence that plants from the same species differentiate from one another along an intraspecific RES. We find that in one of the world's most widely cultivated crops, an intraspecific RES is orthogonal to an intraspecific LES, indicating that above and belowground responses of plants to managed (or natural) environmental gradients are likely to occur independently from one another. (Résumé d'auteur

Particle self-diffusion in a viscous shear flow: from hydrodynamic interactions to collisional effects

Particle shear-induced self-diffusion is investigated at low Reynolds and variable Stokes (St) numbers. We simulated the suspension hydrodynamics for St<<1 by using the Force Coupling Method. For suspensions with finite particle inertia (finite St), we proposed a new Eulerian prediction based on the kinetic theory for granular flows which have been validated by discrete particle simulations assuming Stokes drag and binary collisions (for low to moderate solid concentration). On the microscopic level, the particle velocity fluctuations have a Gaussian distribution shape for both high and vanishing St, whereas they show a highly peaked distribution for suspensions characterized by St~O(1) and low solid volume fractions. On the macroscopic level, the self-diffusion tensor is strongly anisotropic and the diffusive behavior becomes more prominent when the particle inertia increases. The self-diffusion coefficients decrease with concentration at high St. The results will be analyzed in terms of analogies and differences between the two regimes investigated (hydrodynamic interactions or collisional effects)

The Statistics of the Number of Minima in a Random Energy Landscape

We consider random energy landscapes constructed from d-dimensional lattices or trees. The distribution of the number of local minima in such landscapes follows a large deviation principle and we derive the associated law exactly for dimension 1. Also of interest is the probability of the maximum possible number of minima; this probability scales exponentially with the number of sites. We calculate analytically the corresponding exponent for the Cayley tree and the two-leg ladder; for 2 to 5 dimensional hypercubic lattices, we compute the exponent numerically and compare to the Cayley tree case.Comment: 18 pages, 8 figures, added background on landscapes and reference

Knowledge-Attitudes-Practices About Malaria Among Communities in Southern Benin

Malaria still remains the main public health problem in Benin. We explored the determinants that influenced malaria treatment as well as protective behaviors, to generate a framework of useful ideas as alternative strategies against malaria. A cross-sectional survey of the knowledge, attitudes and practices (KAP) was conducted at Hozin, Vakon and Agblangandan districts in southern region of Benin. Descriptive statistics were computed and mixed logistic regression helped evaluating the relationship between frequency of each category of severity of malaria and sex group, educational level, treatment, means of self-protection against mosquitoes and identification of the cause of malaria. A significant proportion 750 (81.3%) (p&lt;0.001) of participants stated that malaria was caused by mosquitoes. The respondents who mentioned sun as the cause of malaria, have trivialized more malaria in a proportion of about 59.30% (OR=2.67 [95% CI 1.61-4.44]) followed by those who have reported the cause of body weakness (43.68%) (OR=2.97 [95% CI 1.68-5.28]). Poor knowledge justifies the trivialization of the disease and poor management of malaria control means. National Malaria Control Programs should improve access to education, especially for women and could help improving prevention and control behaviours against malaria in communities

Shadow of a Colossus: A z=2.45 Galaxy Protocluster Detected in 3D Ly-a Forest Tomographic Mapping of the COSMOS Field

Using moderate-resolution optical spectra from 58 background Lyman-break galaxies and quasars at $z\sim 2.3-3$ within a $11.5'\times13.5'$ area of the COSMOS field ($\sim 1200\,\mathrm{deg}^2$ projected area density or $\sim 2.4\,h^{-1}\,\mathrm{Mpc}$ mean transverse separation), we reconstruct a 3D tomographic map of the foreground Ly$\alpha$ forest absorption at $2.2<z<2.5$ with an effective smoothing scale of $\sigma_{3d}\approx3.5\,h^{-1}\,\mathrm{Mpc}$ comoving. Comparing with 61 coeval galaxies with spectroscopic redshifts in the same volume, we find that the galaxy positions are clearly biased towards regions with enhanced IGM absorption in the tomographic map. We find an extended IGM overdensity with deep absorption troughs at $z=2.45$ associated with a recently-discovered galaxy protocluster at the same redshift. Based on simulations matched to our data, we estimate the enclosed dark matter mass within this IGM overdensity to be $M_{\rm dm} (z=2.45) = (9\pm4)\times 10^{13}\,h^{-1}\,\mathrm{M_\odot}$, and argue based on this mass and absorption strength that it will form at least one $z\sim0$ galaxy cluster with $M(z=0) = (3\pm 2) \times 10^{14}\,h^{-1}\mathrm{M_\odot}$, although its elongated nature suggests that it will likely collapse into two separate clusters. We also point out a compact overdensity of six MOSDEF galaxies at $z=2.30$ within a $r\sim 1\,h^{-1}\,\mathrm{Mpc}$ radius and $\Delta z\sim 0.006$, which does not appear to have a large associated IGM overdensity. These results demonstrate the potential of Ly$\alpha$ forest tomography on larger volumes to study galaxy properties as a function of environment, as well as revealing the large-scale IGM overdensities associated with protoclusters and other features of large-scale structure.Comment: To be submitted to ApJ. Figure 3 can be viewed on Youtube: https://youtu.be/KeW1UJOPMY

Statistical mechanics of error exponents for error-correcting codes

Error exponents characterize the exponential decay, when increasing message length, of the probability of error of many error-correcting codes. To tackle the long standing problem of computing them exactly, we introduce a general, thermodynamic, formalism that we illustrate with maximum-likelihood decoding of low-density parity-check (LDPC) codes on the binary erasure channel (BEC) and the binary symmetric channel (BSC). In this formalism, we apply the cavity method for large deviations to derive expressions for both the average and typical error exponents, which differ by the procedure used to select the codes from specified ensembles. When decreasing the noise intensity, we find that two phase transitions take place, at two different levels: a glass to ferromagnetic transition in the space of codewords, and a paramagnetic to glass transition in the space of codes.Comment: 32 pages, 13 figure

Assessment of Xenoestrogens Using Three Distinct Estrogen Receptors and the Zebrafish Brain Aromatase Gene in a Highly Responsive Glial Cell System

The brain cytochrome P450 aromatase (Aro-B) in zebrafish is expressed in radial glial cells and is strongly stimulated by estrogens (E(2)); thus, it can be used in vivo as a biomarker of xenoestrogen effects on the central nervous system. By quantitative real-time polymerase chain reaction, we first confirmed that the expression of Aro-B gene is robustly stimulated in juvenile zebrafish exposed to several xenoestrogens. To investigate the impact of environmental estrogenic chemicals on distinct estrogen receptor (ER) activity, we developed a glial cell-based assay using Aro-B as the target gene. To this end, the ER-negative glial cell line U251-MG was transfected with the three zebrafish ER subtypes and the Aro-B promoter linked to a luciferase reporter gene. E(2) treatment of U251-MG glial cells cotransfected with zebrafish ER-α and the Aro-B promoter–luciferase reporter resulted in a 60- to 80-fold stimulation of luciferase activity. The detection limit was < 0.05 nM, and the EC(50) (median effective concentration) was 1.4 nM. Interestingly, in this glial cell context, maximal induction achieved with the Aro-B reporter was three times greater than that observed with a classical estrogen-response-element reporter gene (ERE-tk-Luc). Dose–response analyses with ethynylestradiol (EE(2)), estrone (E(1)), α-zeralenol, and genistein showed that estrogenic potency of these agents markedly differed depending on the ER subtype in the assay. Moreover, the combination of these agents showed an additive effect according to the concept of concentration addition. This confirmed that the combined additive effect of the xenoestrogens leads to an enhancement of the estrogenic potency, even when each single agent might be present at low effect concentrations. In conclusion, we demonstrate that our bioassay provides a fast, reliable, sensitive, and efficient test for evaluating estrogenic potency of endocrine disruptors on ER subtypes in a glial context

INSIG1 influences obesity-related hypertriglyceridemia in humans

In our analysis of a quantitative trait locus (QTL) for plasma triglyceride (TG) levels [logarithm of odds (LOD) = 3.7] on human chromosome 7q36, we examined 29 single nucleotide polymorphisms (SNPs) across INSIG1, a biological candidate gene in the region. Insulin-induced genes (INSIGs) are feedback mediators of cholesterol and fatty acid synthesis in animals, but their role in human lipid regulation is unclear. In our cohort, the INSIG1 promoter SNP rs2721 was associated with TG levels (P = 2 × 10−3 in 1,560 individuals of the original linkage cohort, P = 8 × 10−4 in 920 unrelated individuals of the replication cohort, combined P = 9.9 × 10−6). Individuals homozygous for the T allele had 9% higher TG levels and 2-fold lower expression of INSIG1 in surgical liver biopsy samples when compared with individuals homozygous for the G allele. Also, the T allele showed additional binding of nuclear proteins from HepG2 liver cells in gel shift assays. Finally, the variant rs7566605 in INSIG2, the only homolog of INSIG1, enhances the effect of rs2721 (P = 0.00117). The variant rs2721 alone explains 5.4% of the observed linkage in our cohort, suggesting that additional, yet-undiscovered genes and sequence variants in the QTL interval also contribute to alterations in TG levels in humans