The crossover from single file to Fickian diffusion

The crossover from single-file diffusion, where the mean-square displacement scales as ~t^(1/2), to normal Fickian diffusion, where ~t$, is studied as a function of channel width for colloidal particles. By comparing Brownian dynamics to a hybrid molecular dynamics and mesoscopic simulation technique, we can study the effect of hydrodynamic interactions on the single file mobility and on the crossover to Fickian diffusion for wider channel widths. For disc-like particles with a steep interparticle repulsion, the single file mobilities for different particle densities are well described by the exactly solvable hard-rod model. This holds both for simulations that include hydrodynamics, as well as for those that don't. When the single file constraint is lifted, then for particles of diameter \sigma and pipe of width$L$ such that (L- 2 \sigma)/\sigma = \delta_c << 1 the particles can be described as hopping past one-another in an average time t_{hop}. For shorter times t << t_{hop} the particles still exhibit sub-diffusive behaviour, but at longer times t > t_{hop}, normal Fickian diffusion sets in with an effective diffusion constant D_{hop} ~ t_{hop}^(1/2). For the Brownian particles, t_{hop} ~ 1/\delta_c^(2) when \delta << 1, but when hydrodynamic interactions are included, we find a stronger dependence than \delta_c^{-2}. We attribute this difference to short-range lubrication forces that make it more difficult for particles to hop past each other in very narrow channels

Four-strand hamstring tendon autograft for ACL reconstruction in patients aged 50years or older

SummaryIntroductionReconstruction of the anterior cruciate ligament using a four-strand hamstring tendon autograft in symptomatic patients aged 50years or older is an accepted treatment option.HypotesisFour-strand hamstring tendon autograft although not universally utilized in patients who are at least 50years old is an efficient procedure to control knee instability.Material and methodsIn this retrospective, we analyzed the clinical outcomes of 18patients treated from September 1998 to September 2003. Criteria for inclusion were the following: age above 50years at surgery, chronic anterior laxity associated or not with meniscal damage; one or more episodes of knee instability and no prior ligament surgery on the involved knee. A same operative technique (arthroscopic single-bundle four-strand hamstring reconstruction, blind femoral tunnel, through anteromedial portals), a same fixation type (absorbable interference screws in femur and tibia) and a same rehabilitation protocol were used for all these knees. The IKDC 93scores were determined pre- and postoperatively combined with anteroposterior and lateral views, single leg stance, 30° flexion stance, and passive Lachman test (Telos) postoperatively.ResultsAt mean 30month-follow-up (range 12–59months), there were no graft failure and no loss of extension for any of these knees. Three patients complained of hypoesthesia in the medial saphenous nerve territory and one patient experienced posterior knee pain. All patients graded their knee as normal or nearly normal, all were satisfied or very satisfied with their operation. None of the patients reported instability. The Lachman-Trillat test was noted “firm end point” in 14knees and “delayed firm end point” in four. The pivot-shift test was negative in 16knees and mild positive in two. The mean residual differential laxity was 3.1mm (0 to +6mm) for the passive Lachman test. At last follow-up, the overall IKDC score was 7A, 7B, 3C, and 1 D. Patients with preserved meniscus (nine patients) reported a lesser degree of pain and a better residual laxity control compared with patients who had undergone a meniscectomy.ConclusionAge over 50years is not a contraindication to select a hamstring tendon autograft for ACL reconstruction. This surgery can restore knee stability but does not modify the pain pattern in patients, who had a medial meniscectomy prior to the ACL reconstruction.Level of evidence: level IV, therapeutic study

11 W narrow linewidth laser source at 780nm for laser cooling and manipulation of Rubidium

We present a narrow linewidth continuous laser source with over 11 Watts of output power at 780nm, based on single-pass frequency doubling of an amplified 1560nm fibre laser with 36% efficiency. This source offers a combination of high power, simplicity, mode quality and stability. Without any active stabilization, the linewidth is measured to be below 10kHz. The fibre seed is tunable over 60GHz, which allows access to the D2 transitions in 87Rb and 85Rb, providing a viable high-power source for laser cooling as well as for large-momentum-transfer beamsplitters in atom interferometry. Sources of this type will pave the way for a new generation of high flux, high duty-cycle degenerate quantum gas experiments.Comment: 5 pages, 3 figure

Hydrodynamics of confined colloidal fluids in two dimensions

We apply a hybrid Molecular Dynamics and mesoscopic simulation technique to study the dynamics of two dimensional colloidal discs in confined geometries. We calculate the velocity autocorrelation functions, and observe the predicted $t^{-1}$ long time hydrodynamic tail that characterizes unconfined fluids, as well as more complex oscillating behavior and negative tails for strongly confined geometries. Because the $t^{-1}$ tail of the velocity autocorrelation function is cut off for longer times in finite systems, the related diffusion coefficient does not diverge, but instead depends logarithmically on the overall size of the system.Comment: RevTex 13 pages, 9 figure

How do tsetse recognise their hosts? The role of shape in the responses of tsetse (Glossina fuscipes and G. palpalis) to artificial hosts

Palpalis-group tsetse, particularly the subspecies of Glossina palpalis and G. fuscipes, are the most important transmitters of human African trypanomiasis (HAT), transmitting .95% of cases. Traps and insecticide-treated targets are used to control tsetse but more cost-effective baits might be developed through a better understanding of the fly’s host-seeking behaviour.Electrocuting grids were used to assess the numbers of G. palpalis palpalis and G. fuscipes quanzensis attracted to and landing on square or oblong targets of black cloth varying in size from 0.01 m2 to 1.0 m2. For both species, increasing the size of a square target from 0.01 m2 (dimensions = 0.1 x 0.1 m) to 1.0 m2 (1.0 x 1.0 m) increased the catch ,4x however the numbers of tsetse killed per unit area of target declined with target size suggesting that the most cost efficient targets are not the largest. For G. f. quanzensis, horizontal oblongs, (1 m wide x 0.5 m high) caught, 1.8x more tsetse than vertical ones (0.5 m wide x 1.0 m high) but the opposite applied for G. p. palpalis. Shape preference was consistent over the range of target sizes. For G. p. palpalis square targets caught as many tsetse as the oblong; while the evidence is less strong the same appears to apply to G. f. quanzensis. The results suggest that targets used to control G. p. palpalis and G. f. quanzensis should be square, and that the most cost-effective designs, as judged by the numbers of tsetse caught per area of target, are likely to be in the region of 0.25 x 0.25 m2. The preference of G. p. palpalis for vertical oblongs is unique amongst tsetse species, and it is suggested that this response might be related to its anthropophagic behaviour and hence importance as a vector of HAT

The crossover from single file to Fickian diffusion.

The crossover from single-file diffusion, where the mean-square displacement scales as (x2) to approximately t(1/2), to normal Fickian diffusion, where (x2) to approximately t, is studied as a function of channel width for colloidal particles. By comparing Brownian dynamics to a hybrid molecular dynamics and mesoscopic simulation technique, we can study the effect of hydrodynamic interactions on the single file mobility and on the crossover to Fickian diffusion for wider channel widths. For disc-like particles with a steep interparticle repulsion, the single file mobilities for different particle densities are well described by the exactly solvable hard-rod model. This holds both for simulations that include hydrodynamics, as well as for those that do not. When the single file constraint is lifted, then for particles of diameter sigma and pipe of width L such that (L - 2sigma)/sigma = deltac &lt;&lt; 1, the particles can be described as hopping past one-another in an average time t(hop). For shorter times t &lt;&lt; t(hop) the particles still exhibit sub-diffusive behaviour, but at longer times t &gt;&gt; t(hop), normal Fickian diffusion sets in with an effective diffusion constant Dhop to approximately 1/ mean square root of t(hop). For the Brownian particles, t(hop) to approximately deltac(-2) when deltac &lt;&lt; 1, but when hydrodynamic interactions are included, we find a stronger dependence than deltac(-2). We attribute this difference to short-range lubrication forces that make it more difficult for particles to hop past each other in very narrow channels

Dynamiques urbaines

Au-delà d’une communauté de localisation continentale, rien d’autre que la communauté d’une situation urbaine et la contemporanéité du regard porté ne rapprochent les quatre espaces considérés. Aucune des situations ne relève d’une quelconque africanité ni d’une quelconque exceptionnalité : on ne parle pas ici de villes africaines mais de villes ordinaires, en Afrique, qui obéissent à des dynamiques universelles (Robinson, 2006). Ces mécanismes renvoient cependant aux caractères déterminants de l’urbain dans un Sud qui, hormis quelques isolats miniers industriels menacés, n’est pas près de connaître le phénomène des shrinking cities : l’accroissement démographique urbain y détermine, et pour quelque temps encore semble-t-il, étalement et densification, déclenchant la dialectique de l’inclusion et de l’exclusion, de la spécialisation et de la fragmentation et, au-delà, posant aux autorités le défi de la gestion de « l’urbanocénose », considérée ici surtout dans sa dimension hydrologique

Is machine learning efficient for mango yield estimation when used under heterogeneous field conditions?

International audienceIn the last decade, image analysis using machine learning algorithms proved its potential for the detection and counting of plant organs. Numerous studies provided fruit tree yield estimates based on machine learning with high levels of efficiency. However, most of these studies were conducted under homogeneous conditions of fruit aspect. The aim of this study was to develop an efficient machine learning method for ripe mango fruit detection from RGB images and to test it under heterogeneous field conditions for tree yield estimation in Senegal. The algorithm consisted in a k-nearest neighbours classification based on colour and texture features followed by a post-treatment based on shape indices. The F1 score, which accounts for both precision and recall performances, reached 0.73 for a set of 42 images of ‘Kent’ trees in homogeneous conditions. When performed on a second set of 128 images representing the actual heterogeneity in tree structure (height, canopy volume) and cultivars (‘Kent’, ‘Keitt’ and ‘Boucodiékhal’) found in the Niayes region of Senegal, the F1 score fell to 0.48. This decrease resulted from the heterogeneous field conditions in terms of fruit size, fruit colour and light exposure caused by different tree structures among cultivars. Despite the algorithm was less efficient under these conditions, significant linear relationships were evidenced between the number of detected fruits and the actual number of fruits per tree for each cultivar (‘Kent’: R2=0.92, ‘Keitt’: R2=0.93, and ‘Boucodiékhal’: R2=0.90). These models were cross-validated and reached a relative RMSE of 14%. Those results offer new opportunities to accurately and rapidly estimate mango yield and to further identify the parameters that drive its variability at the tree and orchard scales

Sar1b mutant mice recapitulate gastrointestinal abnormalities associated with chylomicron retention disease

International audienceChylomicron retention disease (CRD) is an autosomal recessive disorder associated with biallelic Sar1b mutations leading to defects in intracellular chylomicron (CM) trafficking and secretion. To date, a direct cause-effect relationship between CRD and Sar1b mutation has not been established, but genetically modified animal models provide an opportunity to elucidate unrecognized aspects of these mutations. To examine the physiological role and molecular mechanisms of Sar1b function, we generated mice expressing either a targeted deletion or mutation of human Sar1b using the CRISPR-Cas9 system. We found that deletion or mutation of Sar1b in mice resulted in late-gestation lethality of homozygous embryos. Moreover, compared with WT mice, heterozygotes carrying a single disrupted Sar1b allele displayed lower plasma levels of triglycerides, total cholesterol, and HDL-cholesterol, along with reduced CM secretion following gastric lipid gavage. Similarly, decreased expression of apolipoprotein B and microsomal triglyceride transfer protein was observed in correlation with the accumulation of mucosal lipids. Inefficient fat absorption in heterozygotes was confirmed via an increase in fecal lipid excretion. Furthermore, genetically modified Sar1b affected intestinal lipid homeostasis as demonstrated by enhanced fatty acid β-oxidation and diminished lipogenesis through the modulation of transcription factors. This is the first reported mammalian animal model with human Sar1b genetic defects, which reproduces some of the characteristic CRD features and provides a direct cause-effect demonstration