Showing papers by "University of Rouen published in 2008"

On the experimental investigation on primary atomization of liquid streams

Abstract: The production of a liquid spray can be summarized as the succession of the following three steps; the liquid flow ejection, the primary breakup mechanism and the secondary breakup mechanism. The intermediate step—the primary breakup mechanism—covers the early liquid flow deformation down to the production of the first isolated liquid fragments. This step is very important and requires to be fully understood since it constitutes the link between the flow issuing from the atomizer and the final spray. This paper reviews the experimental investigations dedicated to this early atomization step. Several situations are considered: cylindrical liquid jets, flat liquid sheets, air-assisted cylindrical liquid jets and air-assisted flat liquid sheets. Each fluid stream adopts several atomization regimes according to the operating conditions. These regimes as well as the significant parameters they depend on are listed. The main instability mechanisms, which control primary breakup processes, are rather well described. This review points out the internal geometrical nozzle characteristics and internal flow details that influence the atomization mechanisms. The contributions of these characteristics, which require further investigations to be fully identified and quantified, are believed to be the main reason of experimental discrepancies and explain a lack of universal primary breakup regime categorizations.

Adaptations of higher plant cell walls to water loss: drought vs desiccation.

Abstract: Water-deficit stress poses unique challenges to plant cells dependent on a hydrostatic skeleton and a polysaccharide-rich cell wall for growth and development. How the plant cell wall is adapted to loss of water is of interest in developing a general understanding of water stress tolerance in plants and of relevance in strategies related to crop improvement. Drought tolerance involves adaptations to growth under reduced water potential and the concomitant restructuring of the cell wall that allow growth processes to occur at lower water contents. Desiccation tolerance, by contrast, is the evolution of cell walls that are capable of losing the majority of cellular water without suffering permanent and irreversible damage to cell wall structure and polymer organization. This minireview highlights common features and differences between these two water-deficit responses observed in plants, emphasizing the role of the cell wall, while suggesting future research avenues that could benefit fundamental understanding in this area.

Preventing unintended proteolysis in plant protein biofactories.

Abstract: Numerous reports have been published over the last decade assessing the potential of plants as useful hosts for the heterologous expression of clinically useful proteins. Significant progress has been made, in particular, in optimizing transgene transcription and translation in plants, and in elucidating the complex post-translational modifications of proteins typical of the plant cell machinery. In this article, we address the important issue of recombinant protein degradation in plant expression platforms, which directly impacts on the final yield, homogeneity and overall quality of the resulting protein product. Unlike several more stable and structurally less complex pharmaceuticals, recombinant proteins present a natural tendency to structural heterogeneity, resulting in part from the inherent instability of polypeptide chains expressed in heterologous environments. Proteolytic processing, notably, may dramatically alter the structural integrity and overall accumulation of recombinant proteins in plant expression systems, both in planta during expression and ex planta after extraction. In this article, we describe the current strategies proposed to minimize protein hydrolysis in plant protein factories, including organ-specific transgene expression, organelle-specific protein targeting, the grafting of stabilizing protein domains to labile proteins, protein secretion in natural fluids and the co-expression of companion protease inhibitors.

Differential effects of hyaluronan and its fragments on fibroblasts: relation to wound healing.

Abstract: Hyaluronan (HA) is involved in wound healing and its biological properties depend on its molecular size. The effects of native HA and HA-12 and HA-880 saccharide fragments on human fibroblast proliferation and expression of matrix-related genes were studied. The three HA forms promoted cell adhesion and proliferation. Matrix metalloproteinase-1 and -3 mRNA were increased by all HA forms, whereas only HA-12 stimulated the expression of the tissue inhibitor of metalloproteinase 1. HA-12 enhanced type I collagen and transforming growth factor-beta (TGF-beta) 1 expression. Interestingly, HA-12 and native HA stimulated type III collagen and TGF-beta3. HA and its fragments activated Akt and extracellular-regulated kinases 1/2 and p38. Inhibition of these signaling pathways suggested their implication in most of the effects. Only native HA activated nuclear factor-kappaB and activating protein 1. Use of CD44 siRNA suggests that this HA receptor is partly implicated in the effects, although it does not rule out the involvement of other receptors. Depending on its size, HA may exert differential regulation on the wound-healing process. Furthermore, the HA up-regulation of type III collagen and TGF-beta3 expression suggests that it may promote a fetal-like cell environment that favors scarless healing.

A large fraction of unclassified variants of the mismatch repair genes MLH1 and MSH2 is associated with splicing defects.

Abstract: Numerous unclassified variants (UVs) have been found in the mismatch repair genes MLH1 and MSH2 involved in hereditary nonpolyposis colorectal cancer (HNPCC or Lynch syndrome). Some of these variants may have an effect on pre-mRNA splicing, either by altering degenerate positions of splice site sequences or by affecting intronic or exonic splicing regulatory sequences such as exonic splicing enhancers (ESEs). In order to determine the consequences of UVs on splicing, we used a functional assay of exon inclusion. For each variant, mutant and wild-type exons to be tested were PCR-amplified from patient genomic DNA together with ∼150 bp of flanking sequences and were inserted into a splicing reporter minigene. After transfection into HeLa cells, the effects on splicing were evaluated by RT-PCR analysis and systematic sequencing. A total of 22 UVs out of 85 different variant alleles examined in 82 families affected splicing, including four exonic variants that affected putative splicing regulatory elements. We analyzed short stretches spanning the latter variants by cloning them into the ESE-dependent central exon of a three-exon splicing minigene and we showed in cell transfection experiments that the wild-type sequences indeed contain functional ESEs. We then used this construct to query for ESE elements in the MLH1 or MSH2 regions affected by 14 previously reported exonic splicing mutations and showed that they also contain functional ESEs. These splicing assays represent a valuable tool for the interpretation of UVs and should contribute to the optimization of the molecular diagnosis of the Lynch syndrome and of other genetic diseases. Hum Mutat 0,1–13, 2008. © 2008 Wiley-Liss, Inc.

Support Vector Machines with a Reject Option

Abstract: We consider the problem of binary classification where the classifier may abstain instead of classifying each observation. The Bayes decision rule for this setup, known as Chow's rule, is defined by two thresholds on posterior probabilities. From simple desiderata, namely the consistency and the sparsity of the classifier, we derive the double hinge loss function that focuses on estimating conditional probabilities only in the vicinity of the threshold points of the optimal decision rule. We show that, for suitable kernel machines, our approach is universally consistent. We cast the problem of minimizing the double hinge loss as a quadratic program akin to the standard SVM optimization problem and propose an active set method to solve it efficiently. We finally provide preliminary experimental results illustrating the interest of our constructive approach to devising loss functions.

Nanostructure and related mechanical properties of an Al–Mg–Si alloy processed by severe plastic deformation

Abstract: Microstructural features and mechanical properties of an Al–Mg–Si alloy processed by high-pressure torsion (HPT) have been investigated using transmission electron microscopy, X-ray diffraction, three-dimensional atom probe, tensile tests and micro-hardness measurements. It is shown that HPT processing of the Al–Mg–Si alloy leads to a much stronger grain size refinement than of pure aluminium (down to 100 nm). Moreover, massive segregation of alloying elements along grain boundaries is observed. This nanostructure exhibits a yield stress even two times higher than that after a standard T6 heat treatment of the coarse-grained alloy.

Screening BRCA1 and BRCA2 unclassified variants for splicing mutations using reverse transcription PCR on patient RNA and an ex vivo assay based on a splicing reporter minigene

Abstract: Background: Many unclassified variants (UV) of BRCA1 or BRCA2 may have an effect on pre-mRNA splicing. Patient blood samples suitable for RNA extraction are not always available for testing UVs at the RNA level. Methods: We have compared analyses of RNA from patient peripheral blood, using a one-step reverse transcription-PCR (RT-PCR) protocol, and an ex vivo splicing assay based on PCR-amplified patient DNA inserted into a splicing reporter minigene. We have examined with both methods 20 variants found in 17 patients. Results: Data from patient RNA and from the minigene assay were fully concordant, but the ex vivo splicing assay, which is monoallelic, clarified several ambiguities of patient RNA data. Two intronic variants induced strong splicing defects: BRCA1 c.4987-5T>A (IVS16-5T>A) induced exon 17 skipping and BRCA2 c.316+5G>C (IVS3+5G>C) induced complete skipping of exon 3. Among exonic variants, BRCA2 c.7805G>C (p.Arg2602Thr), at the last base of exon 16, induced both exon skipping and activation of a cryptic exonic donor site and BRCA2 c.8023A>G (p.Ile2675Val) generated a strong donor site within exon 18. These four variants were thus classified as pathogenic, because of total absence of a normal transcript from the corresponding allele. Variant BRCA2 c.9501+3A>T (IVS25+3A>T) induced incomplete skipping of exon 25, suggesting a mutation with incomplete penetrance and BRCA2 c.8257_8259del (p.Leu2753del) modified the alternative splicing of exons 17 and 18. Conclusions: We show that functional analysis using a splicing reporter minigene is sensitive and specific and should be used for initial screening of potential splicing defects, especially when patient RNA is not readily available.

Influence of chemical modifications on water-sorption and mechanical properties of Agave fibres

Abstract: Because of their good mechanical properties and low density, natural fibres are more and more considered as reinforcement in composite materials. In this work, to improve the adhesion between a polyester matrix (unsaturated polyester resin) and Agave (Agave Americana L .) fibres and to increase their moisture resistance, chemical surface treatments have been performed on the fibres. These different treatments were performed with acetic anhydride (Ac), styrene (S), acrylic acid (AA) and maleic anhydride (MA). The modified Agave fibres were characterized by means of infrared spectroscopy, surface energy, and microscopic analysis. The effect of these treatments on water sorption was investigated by using a gravimetric static equilibrium method. Water sorption isotherms have been deduced from kinetic data. The Park model based on the three sorption modes: Langmuir, Henry’s law, and clustering, was successfully used to simulate the experimental sorption data. It was found that the chemical treatments used reduced the overall water uptake of the Agave fibres. In particular, the acetylation treatment allows to significantly increase the moisture resistance of these fibres. The mechanical properties of the treated fibres were analyzed from tensile tests. The tensile modulus, the breaking strength and the breaking strain depend on the chemical treatment used.

Nanostructure and related mechanical properties of an Al-Mg-Si alloy processed by severe plastic deformation

Abstract: Microstructural features and mechanical properties of an Al-Mg-Si alloy processed by high-pressure torsion have been investigated using transmission electron microscopy, X-ray diffraction, three-dimensional atom probe, tensile tests and microhardness measurements. It is shown that HPT processing of the Al-Mg-Si alloy leads to a much stronger grain size refinement than of pure aluminium (down to 100 nm). Moreover, massive segregation of alloying elements along grain boundaries is observed. This nanostructure exhibits a yield stress even two times higher than that after a standard T6 heat treatment of the coarse grained alloy

Incorporation of a Hydrophobic Antibacterial Peptide into Amphiphilic Polyelectrolyte Multilayers : A Bioinspired Approach to Prepare Biocidal Thin Coatings

Abstract: A non-water-soluble natural antibacterial peptide, gramicidin A, has been successfully incorporated into polyelectrolyte assemblies to elaborate biocidal thin films. For this, we used a double strategy, the first step of which consists of complexing the peptide by a non-denaturing anionic amphiphilic polysaccharide, namely a hydrophobically modified carboxymethylpullulan. We demonstrate that the use of this amphiphilic anionic derivative allows to efficiently solubilize the peptide in aqueous solution, without denaturation. The amount of peptide solubilized by the amphiphilic polysaccharide was optimized by systematically varying the hydrophobicity and the molar mass of the CMP derivative. In a second step, the negatively charged complex was layer-by-layer assembled with cationic poly(L-lysine) to form biofunctionalized thin films. The amount of peptide incorporated in the multilayers was controlled by changing the number of deposited complex layers, and was quantified by UV spectroscopy. The antibacterial activity of the resulting biofunctionalized films was I evidenced against a gram-positive bacterium, E. faecalis. We demonstrated that the biocidal activity resulted from a double mechanism: contact between bacteria and the film surface, and release of the peptide into the solution surrounding the film. We also showed that the peptide was not completely removed from the film after rinsing, which insured preservation of the biocidal activity of the film surface.

A role for pectin-associated arabinans in maintaining the flexibility of the plant cell wall during water deficit stress

Abstract: One of the main components of pectin, a primary constituent of higher plant cell walls, is rhamnogalacturonan I. This polymer comprised of linked alternating rhamnose and galacturonic acid residues is decorated with side chains composed of arabinose and galactose residues. At present, the function of these side chains is not fully understood. Our research on Southern African resurrection plants, plants that are capable of surviving severe dehydration (desiccation), has revealed that their cell walls are capable of extreme flexibility in response to water loss. One species, Myrothamnus flabellifolia, has evolved a constitutively protected leaf cell wall, composed of an abundance of arabinose polymer side chains, suggested to be arabinans and/or arabinogalactans, associated with the pectin matrix. In this article, we propose a hypothetical model that explains how the arabinan rich pectin found in the leaves of this desiccation-tolerant plant permits almost complete water loss without deleterious consequences, such as irreversible polymer adhesion, from occurring. Recent evidence suggesting a role for pectin-associated arabinose polymers in relation to water dependent processes in other plant species is also discussed.

Palladium-catalyzed direct (hetero)arylation of ethyl oxazole-4-carboxylate: an efficient access to (hetero)aryloxazoles.

Abstract: A straightforward route toward 2-(hetero)arylated and 2,5-di(hetero)arylated oxazoles through regiocontrolled palladium-catalyzed direct (hetero)arylation of ethyl oxazole-4-carboxylate with iodo-, bromo-, and chloro(hetero)aromatics followed by a two-step hydrolysis/decarboxylation sequence was described. The method was applied here to a neat synthesis of two 2,5-di(hetero)aryloxazole natural products, balsoxin and texaline.

Discordance between measured postural instability and absence of clinical symptoms in Parkinson's disease patients in the early stages of the disease.

Abstract: We compared postural performances in early stage Parkinson's disease (PD) patients and healthy subjects, and to determine if PD patients have infraclinical postural instability. Nine PD patients and 18 age- and sex-matched control subjects were recorded with open eyes (OE) and closed eyes (CE) using a force platform in static and dynamic conditions with a mobile platform allowing antero posterior and medio lateral oscillations. Oscillations of the mobile platform and balance strategy were quantified using both a force platform and the Vicon system. Under static conditions with both OE and CE, PD patients had a larger center foot pressure sway area than the control subjects (P = 0.007 and P = 0.04, respectively). Under dynamic conditions, the PD patients' sway area was greater than that of the control subjects in the CE antero posterior position (P = 0.04). Oscillations of the mobile platform were not different between the two groups. Lastly, all subjects used an ankle strategy, but PD patients had larger head oscillations than the control subjects. Early stage PD patients have an infraclinical postural instability which is compensated when it is more difficult to maintain good balance, suggesting that the neurological mechanisms of balance are partially still operating at this stage of the disease.

Three-dimensional inversion of self-potential data used to constrain the pattern of groundwater flow in geothermal fields

Abstract: We propose an algorithm to invert self-potential signals measured at the ground surface of the Earth to localize hydromechanical disturbances or to the pattern of groundwater flow in geothermal systems. The self-potential signals result from the divergence of the streaming current density. Groundwater flow can be either driven by topography of the water table, free convection, or deformation of the medium. The algorithm includes the electrical resistivity distribution of the medium obtained independently by DC resistance tomography or electromagnetic methods or by coding the assumed geology in terms of distribution of the electrical resistivity accounting for the effect of the temperature and salinity distributions and possibly constraints from borehole measurements. Inversion of the distribution of the source current density from ground surface and borehole self-potential measurements is achieved by solving the inverse problem using Tikhonov regularization solutions that are compatible with the physics of the primary flow problem. By introducing assumptions regarding the smoothness or the compactness of the source and the three-dimensional distribution of the electrical resistivity of the system, the inverse problem can be solved in obtaining the three-dimensional distribution of the current source density in the ground. However, an annihilator can be added to the inverted source geometry without affecting the measured self-potential field. Annihilators can be obtained from boundary conditions. Synthetic models and a sandbox experiment are discussed to demonstrate the validity of the algorithm. An application is presented to the geothermal field of Cerro Prieto, Baja California, Mexico, using literature data. Inversion of the self-potential and resistivity data allows observing a plume of hot groundwater rising to the ground surface in the central part of the investigated area and discharging to the ground surface in the southwest part. The temperature anomaly associated with the existence of this plume is independently observed by interpolating borehole temperature measurements. We found a good agreement between the distribution of the temperature and the inverted source current density. The proposed method appears therefore as a noninvasive method for remote detection and three-dimensional mapping of subsurface groundwater flow.

Impact on disinfection efficiency of cell load and of planktonic/adherent/detached state: case of Hafnia alvei inactivation by Plasma Activated Water

Abstract: This paper describes the effects of initial microbial concentration and planktonic/adherent/detached states on the efficiency of plasma-activated water. This disinfecting solution was obtained by treating distilled water with an atmospheric pressure plasma produced by gliding electric discharges in humid air. The inactivation kinetics of planktonic cells of Hafnia alvei (selected as a bacterial model) were found to be of the first order. They were influenced by the initial microbial concentration. Efficiency decreased when the initial viable population N0 increased, and the inactivation rate kmax was linearly modified as a function of Log10 (N0). This relation was used to compare planktonic, adherent, and detached cells independently from the level of population. Bacteria adhering to stainless steel and high-density polyethylene were also sensitive to treatment, but at a lower rate than their free-living counterparts. Moreover, cells detached from these solid substrates exhibited an inactivation rate lower than that of planktonic cells but similar to adherent bacteria. This strongly suggests the induction of a physiological modification to bacteria during the adhesion step, rendering adherent—and further detached—bacteria less susceptible to the treatment, when compared to planktonic bacteria.

Sound level of environmental music and drinking behavior: A field experiment with beer drinkers.

Abstract: Objective: It had been found that environmental music was associated with an increase in alcohol consumption. The presence versus absence of music, high versus slow tempo and the different styles of environmental music is associated with different level of alcohol consumption. However, the effect of the level of the environmental music played in a bar still remained in question. Methods: Forty male beer drinkers were observed in a bar. According to a random distribution, patrons were exposed to the usual level of environmental music played in 2 bars where the experiment was carried out or were exposed to a high level. Results: The results show that high level volume led to increase alcohol consumption and reduced the average amount of time spent by the patrons to drink their glass. Conclusions: The impact of environmental music on consumption was discussed and the “arousal” hypothesis and the negative effect of loud music on social interaction were used to explain our results.

Dissipative solitons in a passively mode-locked Er-doped fiber with strong normal dispersion.

Abstract: We report on ultrashort pulse generation from a passively mode-locked erbium fiber laser operating in the highly positive dispersion regime. Highly-chirped pulses with 5.3 ps duration and spectral bandwidth of 8.3 nm are generated. They are extra-cavity compressed down to 757 fs. Numerical simulations confirm the experimental results and show that these pulses could be interpreted as dissipative solitons.