Publications by authors named "Alexandre Nicolas"

26 Publications

  • Page 1 of 1

A preliminary study to understand the effects of mask on tinted face cosmetics.

Skin Res Technol 2021 Mar 2. Epub 2021 Mar 2.

L'Oréal Research and Innovation, Tokyo, Japan.

Background: The recent COVID-19 pandemic has generalized the use of face mask in public area, and it is now common to wear it for long hours. But face mask interfere with cosmetics, and key concerns for tinted products are staining of the mask and degradation on face. Consumers have modified beauty routine by a decrease of makeup, but are now expecting new products adapted to face mask. Little is known about the mechanisms that affect most the makeup under the face mask, so that further studies are needed to develop adequate evaluation methods and products. In this study, the color transfer on mask and makeup degradation on face are assessed through a mixed approach of consumer and instrumental evaluation.

Materials And Methods: Two tinted face products (A and B) were applied by half face on 11 Japanese women, who conducted real-life activities with a face mask during 4 hours. Panelists evaluated the stain of their face mask by visual assessment, while the makeup degradation on face was evaluated by color measurement by instrumental method.

Results: No difference was observed between the two products for lasting on face, but consumer evaluation showed a better resistance of product A for color transfer on mask.

Conclusion: The mix of instrumental and consumer evaluation is a promising way to evaluate the makeup degradation on face and color transfer on mask, which are two key factors to develop mask resistant makeup products.
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http://dx.doi.org/10.1111/srt.13022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8014104PMC
March 2021

Japanese experiment of a complete and objective automatic grading system of facial signs from selfie pictures: Validation with dermatologists and characterization of changes due to age and sun exposures.

Skin Res Technol 2020 Dec 27. Epub 2020 Dec 27.

L'Oréal Research and Innovation, Clichy, France.

Objective: To evaluate the capacity of the automatic detection system to accurately grade, from smartphones' selfie pictures, the severity of ten facial signs in Japanese women and their changes due to age and sun exposures.

Methods: A three-step approach was conducted, based on self-taken selfie images. At first, to check on 310 Japanese women (18-69 years) enrolled in the northerner Hokkaido area (latitude 43.2°N), how, on ten facial signs, the A.I-based automatic grading system may correlate with dermatological assessments, taken as reference. Second, to assess and compare age changes in 310 Japanese and 112 Korean women. Third, as these Japanese panelists were recruited according to their usual behavior toward sun exposure, that is, non-sun-phobic (NSP, N = 114) and sun-phobic (SP, N = 196), and through their regular and early use of a photo-protective product, to characterize the facial photo-damages.

Results: (a) On the ten facial signs, detected automatically, nine were found significantly (P < .0001) highly correlated with the evaluations made by three Japanese dermatologists (Wrinkles: r = .75; Sagging: r = .80; Pigmentation: r = .75). (b) The automatic scores showed significant changes with age, by decade, of Wrinkles/Texture, Pigmentation, and Ptosis/Sagging (P < .05). (c) After 45 years, a significantly increased severity of Wrinkles/Texture and Pigmentation was observed in NSP vs. SP women (P < .05). A trend of an increased Ptosis/Sagging (P = .09) was observed.

Conclusion: This work illustrates, for the first time through investigations conducted at home, some impacts of aging and sun exposures on facial signs of Japanese women. Results significantly confirm the importance of sun avoidance coupled with photo-protective measures. In epidemiological studies, the AI-based system offers a fast, affordable, and confidential approach in detection and quantification of facial signs and their dependence with ages, environments and lifestyles.
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http://dx.doi.org/10.1111/srt.12982DOI Listing
December 2020

Contribution of Intrinsic Fluorescence to the Design of a New 3D-Printed Implant for Releasing SDABS.

Pharmaceutics 2020 Sep 26;12(10). Epub 2020 Sep 26.

GICC EA 7501, Faculty of Medicine, University of Tours, 37032 Tours, France.

Single-domain antibodies (sdAbs) offer great features such as increased stability but are hampered by a limited serum half-life. Many strategies have been developed to improve the sdAb half-life, such as protein engineering and controlled release systems (CRS). In our study, we designed a new product that combined a hydrogel with a 3D-printed implant. The results demonstrate the implant's ability to sustain sdAb release up to 13 days through a reduced initial burst release followed by a continuous release. Furthermore, formulation screening helped to identify the best sdAb formulation conditions and improved our understanding of our CRS. Through the screening step, we gained knowledge about the influence of the choice of polymer and about potential interactions between the sdAb and the polymer. To conclude, this feasibility study confirmed the ability of our CRS to extend sdAb release and established the fundamental role of formulation screening for maximizing knowledge about our CRS.
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http://dx.doi.org/10.3390/pharmaceutics12100921DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7601711PMC
September 2020

Role of RadA and DNA Polymerases in Recombination-Associated DNA Synthesis in Hyperthermophilic Archaea.

Biomolecules 2020 07 14;10(7). Epub 2020 Jul 14.

Laboratoire de Microbiologie des Environnements Extrêmes, Ifremer, CNRS, Univ Brest, 29280 Plouzané, France.

Among the three domains of life, the process of homologous recombination (HR) plays a central role in the repair of double-strand DNA breaks and the restart of stalled replication forks. Curiously, main protein actors involved in the HR process appear to be essential for hyperthermophilic Archaea raising interesting questions about the role of HR in replication and repair strategies of those Archaea living in extreme conditions. One key actor of this process is the recombinase RadA, which allows the homologous strand search and provides a DNA substrate required for following DNA synthesis and restoring genetic information. DNA polymerase operation after the strand exchange step is unclear in Archaea. Working with proteins, here we show that both DNA polymerases, family-B polymerase (PolB) and family-D polymerase (PolD), can take charge of processing the RadA-mediated recombination intermediates. Our results also indicate that PolD is far less efficient, as compared with PolB, to extend the invaded DNA at the displacement-loop (D-loop) substrate. These observations coincide with previous genetic analyses obtained on species showing that PolB is mainly involved in DNA repair without being essential probably because PolD could take over combined with additional partners.
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http://dx.doi.org/10.3390/biom10071045DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7407445PMC
July 2020

Patient exposure data and operator dose in coronary interventional procedures: Impact of body-mass index and procedure complexity.

Phys Med 2020 Aug 24;76:38-43. Epub 2020 Jun 24.

CHU UCL Namur site Sainte Elisabeth, Department of Cardiology, 5000 Namur, Belgium.

Purpose: The aim of this study was to assess patient exposure data and operator dose in coronary interventional procedures, when considering patient body-mass index and procedure complexity.

Methods: Total air kerma area product (P), Air-Kerma (AK), Fluoroscopy time (FT), operator dose and patient body-mass index (BMI) from 97 patients' procedures (62 coronary angiography (CA) and 35 Percutaneous Coronary Intervention (PCI) were collected for one year. For PCI procedures, also the complexity index-CI was collected. Continuous variables for each of the 2 groups procedures (CA and PCI) were compared as medians with interquartile range and using Mann-Whitney U test. Multiple group data were compared using Kruskal-Wallis test (significance: p < 0.05).

Results: Median P was 63 and 125 Gy cm for CA and PCI respectively (p < 0.001); FT was 3 and 14 min, respectively (p < 0.001). P and FT significantly increased (p < 0.05) with BMI class for CA procedures. P and FT also increased in function of CI class for PCI, thought significantly only for FT (p < 0.001), possibly because of the low number of PCI procedures included; cine mode contributed most to P. Significant dose variability was observed among cardiologists for CA procedures (p < 0.001).

Conclusions: Dose references levels for P and FT in interventional cardiology should be defined - on a sufficient number of procedures- in function of CI and BMI classes. These could provide an additional tool for refining a facility's quality assurance and optimization processes. Dose variability associated with cardiologists underlines the importance of continuous training.
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http://dx.doi.org/10.1016/j.ejmp.2020.05.006DOI Listing
August 2020

VHH characterization.Recombinant VHHs: Production, characterization and affinity.

Anal Biochem 2020 01 30;589:113491. Epub 2019 Oct 30.

PEX Biotechnologies, Chimie, Biologie, Institut de Recherches Servier, 125 Chemin de Ronde, 78290, Croissy-sur-Seine, France; Institut de Recherches Internationales Servier, 50 rue Carnot, 92284, Suresnes Cedex, France. Electronic address:

Among the biological approaches to therapeutics, are the cells, such as CAR-T cells engineered or not, the antibodies armed or not, and the smaller protein scaffolds that can be modified to render them specific of other proteins, à la façon of antibodies. For several years, we explored ways to substitute antibodies by nanobodies (also known as VHHs), the smallest recognizing part of camelids' heavy-chain antibodies: production of those small proteins in host microorganisms, minute analyses, characterization, and qualification of their affinity towards designed targets. Here, we present three standard VHHs described in the literature: anti-albumin, anti-EGF receptor and anti-HER2, a typical cancer cell surface -associated protein. Because they differ slightly in global structure, they are good models to assess our body of analytical methodologies. The VHHs were expressed in several bacteria strains in order to identify and overcome the bottlenecks to obtain homogeneous preparations of this protein. A large panel of biophysical tools, ranging from spectroscopy to mass spectrometry, was here combined to assess VHH structural features and the impact of the disulfide bond. The routes are now ready to move to more complex VHHs raised against specific targets in numerous areas including oncology.
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http://dx.doi.org/10.1016/j.ab.2019.113491DOI Listing
January 2020

Genetically Defined Functional Modules for Spatial Orienting in the Mouse Superior Colliculus.

Curr Biol 2019 09 29;29(17):2892-2904.e8. Epub 2019 Aug 29.

MRC Laboratory of Molecular Biology, Neurobiology Division, Francis Crick Avenue, Cambridge CB2 0QH, UK. Electronic address:

In order to explore and interact with their surroundings, animals need to orient toward specific positions in space. Throughout the animal kingdom, head movements represent a primary form of orienting behavior. The superior colliculus (SC) is a fundamental structure for the generation of orienting responses, but how genetically distinct groups of collicular neurons contribute to these spatially tuned behaviors remains largely to be defined. Here, through the genetic dissection of the murine SC, we identify a functionally and genetically homogeneous subclass of glutamatergic neurons defined by the expression of the paired-like homeodomain transcription factor Pitx2. We show that the optogenetic stimulation of Pitx2 neurons drives three-dimensional head displacements characterized by stepwise, saccade-like kinematics. Furthermore, during naturalistic foraging behavior, the activity of Pitx2 neurons precedes and predicts the onset of spatially tuned head movements. Intriguingly, we reveal that Pitx2 neurons are clustered in an orderly array of anatomical modules that tile the entire intermediate layer of the SC. Such a modular organization gives origin to a discrete and discontinuous representation of the motor space, with each Pitx2 module subtending a defined portion of the animal's egocentric space. The modularity of Pitx2 neurons provides an anatomical substrate for the convergence of spatially coherent sensory and motor signals of cortical and subcortical origins, thereby promoting the recruitment of appropriate movement vectors. Overall, these data support the view of the superior colliculus as a selectively addressable and modularly organized spatial-motor register.
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http://dx.doi.org/10.1016/j.cub.2019.07.083DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6739420PMC
September 2019

Habitat preference of an herbivore shapes the habitat distribution of its host plant.

Ecosphere 2018 Sep 13;9(9). Epub 2018 Sep 13.

Department of Integrative Biology, University of California, Berkeley, California 94720 USA.

Plant distributions can be limited by habitat-biased herbivory, but the proximate causes of such biases are rarely known. Distinguishing plant-centric from herbivore-centric mechanisms driving differential herbivory between habitats is difficult without experimental manipulation of both plants and herbivores. Here we tested alternative hypotheses driving habitat-biased herbivory in bittercress (), which is more abundant under shade of shrubs and trees (shade) than in nearby meadows (sun) where herbivory is intense from the specialist fly . This system has served as a textbook example of habitat-biased herbivory driving a plant's distribution across an ecotone, but the proximate mechanisms underlying differential herbivory are still unclear. First, we found that higher herbivory in sun habitats contrasts sharply with their preference to attack plants from shade habitats in laboratory choice experiments. Second, strongly preferred leaves in simulated sun over simulated shade habitats, regardless of plant source habitat. Thus, herbivore preference for brighter, warmer habitats overrides their preference for more palatable shade plants. This promotes the sun-biased herbivore pressure that drives the distribution of bittercress into shade habitats.
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http://dx.doi.org/10.1002/ecs2.2372DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6392191PMC
September 2018

Mechanical response of dense pedestrian crowds to the crossing of intruders.

Sci Rep 2019 01 14;9(1):105. Epub 2019 Jan 14.

LPT UMR 8627, CNRS, Université Paris-Sud, Université Paris-Saclay, 91405, Orsay, France.

The increasing number of mass events involving large crowds calls for a better understanding of the dynamics of dense crowds. Inquiring into the possibility of a mechanical description of these dynamics, we experimentally study the crossing of dense static crowds by a cylindrical intruder, a mechanical test which is classical for granular matter. The analysis of our experiments reveals robust features in the crowds' response, comprising both similarities and discrepancies with the response of granular media. Common features include the presence of a depleted region behind the intruder and the short-range character of the perturbation. On the other hand, unlike grains, pedestrians anticipate the intruder's passage by moving much before contact and their displacements are mostly lateral, hence not aligned with the forces exerted by the intruder. Similar conclusions are reached when the intruder is not a cylinder, but a single crossing pedestrian. Thus, our work shows that pedestrian interactions even at high densities (3 to 6 ped/m) do not reduce to mechanical ones. More generally, the avoidance strategies evidenced by our findings question the incautious use of force models for dense crowds.
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http://dx.doi.org/10.1038/s41598-018-36711-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6331639PMC
January 2019

Orientation of plastic rearrangements in two-dimensional model glasses under shear.

Phys Rev E 2018 Jun;97(6-1):063002

Department of Physics and Astronomy and Quantum Matter Institute, University of British Columbia, Vancouver BC V6T 1Z1, Canada.

The plastic deformation of amorphous solids is mediated by localized shear transformations involving small groups of particles rearranging irreversibly in an elastic background. We introduce and compare three different computational methods to extract the size and orientation of these shear transformations in simulations of a two-dimensional athermal model glass under simple shear. We find that the shear angles are broadly distributed around the macroscopic shear direction, with a more or less Gaussian distribution with a standard deviation of around 20^{∘}. The distributions of sizes and orientations of shear transformations display no substantial sensitivity to the shear rate. These results can notably be used to refine the description of rearrangements in elastoplastic models.
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http://dx.doi.org/10.1103/PhysRevE.97.063002DOI Listing
June 2018

Trap Model for Clogging and Unclogging in Granular Hopper Flows.

Phys Rev Lett 2018 May;120(19):198002

Departamento de Física y Matemática Aplicada, Facultad de Ciencias, Universidad de Navarra, 31080 Pamplona, Spain.

Granular flows through narrow outlets may be interrupted by the formation of arches or vaults that clog the exit. These clogs may be destroyed by vibrations. A feature which remains elusive is the broad distribution p(τ) of clog lifetimes τ measured under constant vibrations. Here, we propose a simple model for arch breaking, in which the vibrations are formally equivalent to thermal fluctuations in a Langevin equation; the rupture of an arch corresponds to the escape from an energy trap. We infer the distribution of trap depths from experiments made in two-dimensional hoppers. Using this distribution, we show that the model captures the empirically observed heavy tails in p(τ). These heavy tails flatten at large τ, consistently with experimental observations under weak vibrations. But, here, we find that this flattening is systematic, which casts doubt on the ability of gentle vibrations to restore a finite outflow forever. The trap model also replicates recent results on the effect of increasing gravity on the statistics of clog formation in a static silo. Therefore, the proposed framework points to a common physical underpinning to the processes of clogging and unclogging, despite their different statistics.
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http://dx.doi.org/10.1103/PhysRevLett.120.198002DOI Listing
May 2018

Three-Dimensional Representation of Motor Space in the Mouse Superior Colliculus.

Curr Biol 2018 06 17;28(11):1744-1755.e12. Epub 2018 May 17.

MRC Laboratory of Molecular Biology, Cambridge, UK. Electronic address:

From the act of exploring an environment to that of grasping a cup of tea, animals must put in register their motor acts with their surrounding space. In the motor domain, this is likely to be defined by a register of three-dimensional (3D) displacement vectors, whose recruitment allows motion in the direction of a target. One such spatially targeted action is seen in the head reorientation behavior of mice, yet the neural mechanisms underlying these 3D behaviors remain unknown. Here, by developing a head-mounted inertial sensor for studying 3D head rotations and combining it with electrophysiological recordings, we show that neurons in the mouse superior colliculus are either individually or conjunctively tuned to the three Eulerian components of head rotation. The average displacement vectors associated with motor-tuned colliculus neurons remain stable over time and are unaffected by changes in firing rate or the duration of spike trains. Finally, we show that the motor tuning of collicular neurons is largely independent from visual or landmark cues. By describing the 3D nature of motor tuning in the superior colliculus, we contribute to long-standing debate on the dimensionality of collicular motor decoding; furthermore, by providing an experimental paradigm for the study of the metric of motor tuning in mice, this study also paves the way to the genetic dissection of the circuits underlying spatially targeted motion.
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http://dx.doi.org/10.1016/j.cub.2018.04.021DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5988568PMC
June 2018

Correction: Soft modes and strain redistribution in continuous models of amorphous plasticity: the Eshelby paradigm, and beyond?

Soft Matter 2018 May;14(18):3652

LPTMS, CNRS, Univ. Paris-Sud, Université Paris Saclay, Orsay, France.

Correction for 'Soft modes and strain redistribution in continuous models of amorphous plasticity: the Eshelby paradigm, and beyond?' by Xiangyu Cao et al., Soft Matter, 2018, DOI: 10.1039/c7sm02510f.
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http://dx.doi.org/10.1039/c8sm90066cDOI Listing
May 2018

Soft modes and strain redistribution in continuous models of amorphous plasticity: the Eshelby paradigm, and beyond?

Soft Matter 2018 May;14(18):3640-3651

LPTMS, CNRS, Univ. Paris-Sud, Université Paris Saclay, Orsay, France.

The deformation of disordered solids relies on swift and localised rearrangements of particles. The inspection of soft vibrational modes can help predict the locations of these rearrangements, while the strain that they actually redistribute mediates collective effects. Here, we study soft modes and strain redistribution in a two-dimensional continuous mesoscopic model based on a Ginzburg-Landau free energy for perfect solids, supplemented with a plastic disorder potential that accounts for shear softening and rearrangements. Regardless of the disorder strength, our numerical simulations show soft modes that are always sharply peaked at the softest point of the material (unlike what happens for the depinning of an elastic interface). Contrary to widespread views, the deformation halo around this peak does not always have a quadrupolar (Eshelby-like) shape. Instead, for finite and narrowly-distributed disorder, it looks like a fracture, with a strain field that concentrates along some easy directions. These findings are rationalised with analytical calculations in the case where the plastic disorder is confined to a point-like 'impurity'. In this case, we unveil a continuous family of elastic propagators, which are identical for the soft modes and for the equilibrium configurations. This family interpolates between the standard quadrupolar propagator and the fracture-like one as the anisotropy of the elastic medium is increased. Therefore, we expect to see a fracture-like propagator when extended regions on the brink of failure have already softened along the shear direction and thus rendered the material anisotropic, but not failed yet. We speculate that this might be the case in carefully aged glasses just before macroscopic failure.
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http://dx.doi.org/10.1039/c7sm02510fDOI Listing
May 2018

Multidrug transporters and organic anion transporting polypeptides protect insects against the toxic effects of cardenolides.

Insect Biochem Mol Biol 2017 02 21;81:51-61. Epub 2016 Dec 21.

Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA; Department of Integrative Biology, University of California, Berkeley, 3040 Valley Life Sciences Building, Berkeley, CA 94720, USA. Electronic address:

In the struggle against dietary toxins, insects are known to employ target site insensitivity, metabolic detoxification, and transporters that shunt away toxins. Specialized insects across six taxonomic orders feeding on cardenolide-containing plants have convergently evolved target site insensitivity via specific amino acid substitutions in the Na/K-ATPase. Nonetheless, in vitro pharmacological experiments have suggested a role for multidrug transporters (Mdrs) and organic anion transporting polypeptides (Oatps), which may provide a basal level of protection in both specialized and non-adapted insects. Because the genes coding for these proteins are evolutionarily conserved and in vivo genetic evidence in support of this hypothesis is lacking, here we used wildtype and mutant Drosophila melanogaster (Drosophila) in capillary feeder (CAFE) assays to quantify toxicity of three chemically diverse, medically relevant cardenolides. We examined multiple components of fitness, including mortality, longevity, and LD50, and found that, while the three cardenolides each stimulated feeding (i.e., no deterrence to the toxin), all decreased lifespan, with the most apolar cardenolide having the lowest LD50 value. Flies showed a clear non-monotonic dose response and experienced high levels of toxicity at the cardenolide concentration found in plants. At this concentration, both Mdr and Oatp knockout mutant flies died more rapidly than wildtype flies, and the mutants also experienced more adverse neurological effects on high-cardenolide-level diets. Our study further establishes Drosophila as a model for the study of cardenolide pharmacology and solidifies support for the hypothesis that multidrug and organic anion transporters are key players in insect protection against dietary cardenolides.
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http://dx.doi.org/10.1016/j.ibmb.2016.12.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5428987PMC
February 2017

Statistical fluctuations in pedestrian evacuation times and the effect of social contagion.

Phys Rev E 2016 Aug 23;94(2-1):022313. Epub 2016 Aug 23.

Consejo Nacional de Investigaciones Científicas y Técnicas, Centro Atómico Bariloche, and Instituto Balseiro, R8400AGP Bariloche, Argentina.

Mathematical models of pedestrian evacuation and the associated simulation software have become essential tools for the assessment of the safety of public facilities and buildings. While a variety of models is now available, their calibration and test against empirical data are generally restricted to global averaged quantities; the statistics compiled from the time series of individual escapes ("microscopic" statistics) measured in recent experiments are thus overlooked. In the same spirit, much research has primarily focused on the average global evacuation time, whereas the whole distribution of evacuation times over some set of realizations should matter. In the present paper we propose and discuss the validity of a simple relation between this distribution and the microscopic statistics, which is theoretically valid in the absence of correlations. To this purpose, we develop a minimal cellular automaton, with features that afford a semiquantitative reproduction of the experimental microscopic statistics. We then introduce a process of social contagion of impatient behavior in the model and show that the simple relation under test may dramatically fail at high contagion strengths, the latter being responsible for the emergence of strong correlations in the system. We conclude with comments on the potential practical relevance for safety science of calculations based on microscopic statistics.
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http://dx.doi.org/10.1103/PhysRevE.94.022313DOI Listing
August 2016

Population structure of a vector-borne plant parasite.

Mol Ecol 2016 Jul 15;25(14):3332-43. Epub 2016 Jun 15.

Department of Ecology and Evolutionary Biology, University of Arizona, 1041 E Lowell St, Tucson, AZ, 85721, USA.

Parasites are among the most diverse groups of life on Earth, yet complex natural histories often preclude studies of their speciation processes. The biology of parasitic plants facilitates in situ collection of data on both genetic structure and the mechanisms responsible for that structure. Here, we studied the role of mating, dispersal and establishment in host race formation of a parasitic plant. We investigated the population genetics of a vector-borne desert mistletoe (Phoradendron californicum) across two legume host tree species (Senegalia greggii and Prosopis velutina) in the Sonoran desert using microsatellites. Consistent with host race formation, we found strong host-associated genetic structure in sympatry, little genetic variation due to geographic site and weak isolation by distance. We hypothesize that genetic differentiation results from differences in the timing of mistletoe flowering by host species, as we found initial flowering date of individual mistletoes correlated with genetic ancestry. Hybrids with intermediate ancestry were detected genetically. Individuals likely resulting from recent, successful establishment events following dispersal between the host species were detected at frequencies similar to hybrids between host races. Therefore, barriers to gene flow between the host races may have been stronger at mating than at dispersal. We also found higher inbreeding and within-host individual relatedness values for mistletoes on the more rare and isolated host species (S. greggii). Our study spanned spatial scales to address how interactions with both vectors and hosts influence parasitic plant structure with implications for parasite virulence evolution and speciation.
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http://dx.doi.org/10.1111/mec.13693DOI Listing
July 2016

Aversion and attraction to harmful plant secondary compounds jointly shape the foraging ecology of a specialist herbivore.

Ecol Evol 2016 05 8;6(10):3256-68. Epub 2016 Apr 8.

Ecology and Evolutionary Biology University of Arizona Tucson Arizona 85721; Rocky Mountain Biological Laboratory Gothic Colorado 81224; Present address: Department of Integrative Biology University of California Berkeley California 94720.

Most herbivorous insect species are restricted to a narrow taxonomic range of host plant species. Herbivore species that feed on mustard plants and their relatives in the Brassicales have evolved highly efficient detoxification mechanisms that actually prevent toxic mustard oils from forming in the bodies of the animals. However, these mechanisms likely were not present during the initial stages of specialization on mustard plants ~100 million years ago. The herbivorous fly Scaptomyza nigrita (Drosophilidae) is a specialist on a single mustard species, bittercress (Cardamine cordifolia; Brassicaceae) and is in a fly lineage that evolved to feed on mustards only in the past 10-20 million years. In contrast to many mustard specialists, S. nigrita does not prevent formation of toxic breakdown products (mustard oils) arising from glucosinolates (GLS), the primary defensive compounds in mustard plants. Therefore, it is an appealing model for dissecting the early stages of host specialization. Because mustard oils actually form in the bodies of S. nigrita, we hypothesized that in lieu of a specialized detoxification mechanism, S. nigrita may mitigate exposure to high GLS levels within plant tissues using behavioral avoidance. Here, we report that jasmonic acid (JA) treatment increased GLS biosynthesis in bittercress, repelled adult female flies, and reduced larval growth. S. nigrita larval damage also induced foliar GLS, especially in apical leaves, which correspondingly displayed the least S. nigrita damage in controlled feeding trials and field surveys. Paradoxically, flies preferred to feed and oviposit on GLS-producing Arabidopsis thaliana despite larvae performing worse in these plants versus non-GLS-producing mutants. GLS may be feeding cues for S. nigrita despite their deterrent and defensive properties, which underscores the diverse relationship a mustard specialist has with its host when lacking a specialized means of mustard oil detoxification.
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http://dx.doi.org/10.1002/ece3.2082DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4829532PMC
May 2016

Effects of Inertia on the Steady-Shear Rheology of Disordered Solids.

Phys Rev Lett 2016 Feb 5;116(5):058303. Epub 2016 Feb 5.

Department of Physics and Astronomy, The University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia V6T 1Z4, Canada.

We study the finite-shear-rate rheology of disordered solids by means of molecular dynamics simulations in two dimensions. By systematically varying the damping strength ζ in the low-temperature limit, we identify two well-defined flow regimes, separated by a thin (temperature-dependent) crossover region. In the overdamped regime, the athermal rheology is governed by the competition between elastic forces and viscous forces, whose ratio gives the Weissenberg number Wi∝ζγ[over ˙]; the macroscopic stress Σ follows the frequently encountered Herschel-Bulkley law Σ=Σ_{0}+ksqrt[Wi], with yield stress Σ_{0}>0. In the underdamped (inertial) regime, dramatic changes in the rheology are observed for low damping: the flow curve becomes nonmonotonic. This change is not caused by longer-lived correlations in the particle dynamics at lower damping; instead, for weak dissipation, the sample heats up considerably due to, and in proportion to, the driving. By thermostating more or less underdamped systems, we are able to link quantitatively the rheology to the kinetic temperature and the shear rate, rescaled with Einstein's vibration frequency.
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http://dx.doi.org/10.1103/PhysRevLett.116.058303DOI Listing
February 2016

A Microfluidic Diffusion Cell for Fast and Easy Percutaneous Absorption Assays.

Pharm Res 2015 Aug 28;32(8):2704-12. Epub 2015 Feb 28.

LIMMS/CNRS-IIS (UMI 2820), Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, 153-8505, Tokyo, Japan,

Purpose: Percutaneous absorption assays of molecules for pharmaceutical and cosmetology purposes are important to determine the bioavailability of new compounds, once topically applied. The current method of choice is to measure the rate of diffusion through excised human skin using a diffusion cell. This method however entails significant drawbacks such as scarce availability and poor reproducibility of the sample, low sampling rate, and tedious assay setup.

Methods: The objective of the present work is to propose an alternative method that overcomes these issues by integrating an experimental model of the skin (artificial stratum corneum) and online optical sensors into a microfluidic device.

Results: The measurement of the diffusion profile followed by the calculation of the permeability coefficients and time lag were performed on seven different molecules and obtained data positively fit with those available from literature on human skin penetration. The coating of the lipid mixture to generate the artificial stratum corneum also proved robust and reproducible. The results show that the proposed device is able to give fast, real-time, accurate, and reproducible data in a user-friendly manner, and can be produced at a large scale.

Conclusion: These assets should help both the cosmetics and pharmaceutics fields where the skin is the target or a pathway of a formulated compound, by allowing more candidate molecules or formulations to be assessed during the various stages of their development.
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http://dx.doi.org/10.1007/s11095-015-1654-xDOI Listing
August 2015

Spatiotemporal correlations between plastic events in the shear flow of athermal amorphous solids.

Eur Phys J E Soft Matter 2014 Jun 26;37(6). Epub 2014 Jun 26.

LIPhy, Univ. Grenoble Alpes, F-38000, Grenoble, France,

The slow flow of amorphous solids exhibits striking heterogeneities: swift localised particle rearrangements take place in the midst of a more or less homogeneously deforming medium. Recently, experimental as well as numerical work has revealed spatial correlations between these flow heterogeneities. Here, we use molecular dynamics (MD) simulations to characterise the rearrangements and systematically probe their correlations both in time and in space. In particular, these correlations display a four-fold azimuthal symmetry characteristic of shear stress redistribution in an elastic medium and we unambiguously detect their increase in range with time. With increasing shear rate, correlations become shorter-ranged. In addition, we study a coarse-grained model motivated by the observed flow characteristics and challenge its predictions directly with the MD simulations. While the model captures both macroscopic and local properties rather satisfactorily, the agreement with respect to the spatiotemporal correlations is at most qualitative. The discrepancies provide important insight into relevant physics that is missing in all related coarse-grained models that have been developed for the flow of amorphous materials so far, namely the finite shear wave velocity and the impact of elastic heterogeneities on stress redistribution.
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http://dx.doi.org/10.1140/epje/i2014-14050-1DOI Listing
June 2014

Universal and non-universal features in coarse-grained models of flow in disordered solids.

Soft Matter 2014 Jul;10(26):4648-61

Univ. Grenoble Alpes, LIPhy, F-38000 Grenoble, France.

We study the two-dimensional (2D) shear flow of amorphous solids within variants of an elastoplastic model, paying particular attention to spatial correlations and time fluctuations of, e.g., local stresses. The model is based on the local alternation between an elastic regime and plastic events during which the local stress is redistributed. The importance of a fully tensorial description of the stress and of the inclusion of (coarse-grained) convection in the model is investigated; scalar and tensorial models yield similar results, while convection enhances fluctuations and breaks the spurious symmetry between the flow and velocity gradient directions, for instance when shear localisation is observed. Besides, correlation lengths measured with diverse protocols are discussed. One class of such correlation lengths simply scale with the spacing between homogeneously distributed, simultaneous plastic events. This leads to a scaling of the correlation length with the shear rate as γ̇(-1/2) in 2D in the athermal regime, regardless of the details of the model. The radius of the cooperative disk, defined as the near-field region in which plastic events induce a stress redistribution that is not amenable to a mean-field treatment, notably follows this scaling. On the other hand, the cooperative volume measured from the four-point stress susceptibility and its dependence on the system size and the shear rate are model-dependent.
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http://dx.doi.org/10.1039/c4sm00395kDOI Listing
July 2014

RAD51 deficiency disrupts the corticospinal lateralization of motor control.

Brain 2013 Nov 20;136(Pt 11):3333-46. Epub 2013 Sep 20.

1 Centre de Neuro-imagerie de Recherche (CENIR) de l'Institut du Cerveau et de la Moëlle Epiniere (ICM), Paris, France.

Mirror movements are involuntary symmetrical movements of one side of the body that mirror voluntary movements of the other side. Congenital mirror movement disorder is a rare condition characterized by mirror movements that persist throughout adulthood in subjects with no other clinical abnormalities. The affected individuals have mirror movements predominating in the muscles that control the fingers and are unable to perform purely unimanual movements. Congenital mirror movement disorder thus provides a unique paradigm for studying the lateralization of motor control. We conducted a multimodal, controlled study of patients with congenital mirror movements associated with RAD51 haploinsufficiency (n = 7, mean age 33.3 ± 16.8 years) by comparison with age- and gender-matched healthy volunteers (n = 14, mean age 33.9 ± 16.1 years). We showed that patients with congenital mirror movements induced by RAD51 deficiency had: (i) an abnormal decussation of the corticospinal tract; (ii) abnormal interhemispheric inhibition and bilateral cortical activation of primary motor areas during intended unimanual movements; and (iii) an abnormal involvement of the supplementary motor area during both unimanual and bimanual movements. The lateralization of motor control thus requires a fine interplay between interhemispheric communication and corticospinal wiring. This fine interplay determines: (i) the delivery of appropriate motor plans from the supplementary motor area to the primary motor cortex; (ii) the lateralized activation of the primary motor cortex; and (iii) the unilateral transmission of the motor command to the limb involved in the intended movement. Our results also unveil an unexpected function of RAD51 in corticospinal development of the motor system.
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http://dx.doi.org/10.1093/brain/awt258DOI Listing
November 2013

Spatial cooperativity in microchannel flows of soft jammed materials: a mesoscopic approach.

Phys Rev Lett 2013 Mar 27;110(13):138304. Epub 2013 Mar 27.

Laboratoire Interdisciplinaire de Physique, Université Joseph Fourier Grenoble, CNRS UMR 5588, BP 87, 38402 Saint-Martin d'Hères, France.

The flow of amorphous solids results from a combination of elastic deformation and local structural rearrangements, which induce nonlocal elastic deformations. These elements are incorporated into a mechanically consistent mesoscopic model of interacting elastoplastic blocks. We investigate the specific case of channel flow with numerical simulations, paying particular attention to situations of strong confinement. We find that the simple picture of plastic events embedded in an elastic matrix successfully accounts for manifestations of spatial cooperativity. Shear rate fluctuations are observed in seemingly quiescent regions, and the velocity profiles in confined flows at high applied pressure deviate from those expected in the absence of nonlocal effects, in agreement with experimental data. However, we suggest a different physical origin for the large deviations observed when walls have rough surfaces, associated with "bumps" of the particles against the asperities of the walls.
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http://dx.doi.org/10.1103/PhysRevLett.110.138304DOI Listing
March 2013

A mesoscopic model for the rheology of soft amorphous solids, with application to microchannel flows.

Faraday Discuss 2013 ;167:567-600

We have studied a mesoscopic model for the flow of amorphous solids. The model is based on key features identified at the microscopic level, namely periods of elastic deformation interspersed with localised rearrangements of particles that induce long-range elastic deformations. These long-range deformations are derived following a continuum mechanics approach, in the presence of solid boundaries, and are included in full in the model. Indeed, they mediate spatial cooperativity in the flow, whereby a localised rearrangement may lead a distant region to yield. In particular, we have simulated a channel flow and found manifestations of spatial cooperativity that are consistent with published experimental observations for concentrated emulsions in microchannels. Two categories of effects are distinguished. On the one hand, the coupling of regions subject to different shear rates, for instance, leads to finite shear rate fluctuations in the seemingly unsheared "plug" in the centre of the channel. On the other hand, there is convincing experimental evidence of a specific rheology near rough walls. We discuss the diverse possible physical origins for this effect, and we suggest that it may be associated with the bumps of particles into surface asperities as they slide along the wall.
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http://dx.doi.org/10.1039/c3fd00067bDOI Listing
March 2015

Nonaxisymmetric instability of shear-banded Taylor-Couette flow.

Phys Rev Lett 2012 Feb 22;108(8):088302. Epub 2012 Feb 22.

SUPA, School of Physics & Astronomy, University of Edinburgh, JCMB, Edinburgh, United Kingdom.

Recent experiments show that shear-banded flows of semidilute wormlike micelles in Taylor-Couette geometry exhibit a flow instability in the form of Taylor-like vortices. Here we perform the nonaxisymmetric linear stability analysis of the diffusive Johnson-Segalman model of shear banding and show that the nature of this instability depends on the applied shear rate. For the experimentally relevant parameters, we find that at the beginning of the stress plateau the instability is driven by the interface between the bands, while most of the stress plateau is occupied by the bulk instability of the high-shear-rate band. Our work significantly alters the recently proposed stability diagram of shear-banded flows based on axisymmetric analysis.
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http://dx.doi.org/10.1103/PhysRevLett.108.088302DOI Listing
February 2012