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Search Results: 1 - 10 of 7830 matches for " Christine Julien "
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Absolute evaporation rates of non-rotating neutral PAH clusters
Julien Montillaud,Christine Joblin
Physics , 2014, DOI: 10.1051/0004-6361/201323141
Abstract: Clusters of polycyclic aromatic hydrocarbons (PAHs) have been proposed as candidates for evaporating very small grains, which are thought to be precursors of free-flying PAHs. Evaporation rates have been calculated so far only for species containing up to a few 100 C atoms, whereas interstellar PAH clusters could contain up to ~1000 C atoms. We present a method that generalises the calculation of the statistical evaporation rate of large PAH clusters and provides rates for species containing up to ~1000 C-atoms. The evaporation of non-rotating neutral homo-molecular PAH clusters containing up to 12 molecules from a family of highly symmetric compact PAHs is studied. Statistical calculations were performed and completed with molecular dynamics simulations at high internal energies to provide absolute values for the evaporation rate and distributions of kinetic energy released. The calculations used explicit atom-atom Lennard-Jones potentials in the rigid molecule approximation. A new method is proposed to take both inter- and intra-molecular vibrations into account. Without any parameter adjustment, the calculated evaporation rates agree well with available experimental data. We find that the non-rotation assumption has a limited impact on the evaporation rates. The photostability of PAH clusters increases dramatically with the size of molecules in the clusters, and to a lesser extent with the number of molecules in the clusters. For values of the UV radiation field that are typical of the regions where evaporating very small grains are observed, the smallest clusters in this study (~50 C-atoms) are found to be quickly photo-evaporated, whereas the largest clusters (~1000 C-atoms) are photostable. Our results support the idea that large PAH clusters are good candidates for evaporating very small grains.
Effects of Feeding Programs Based on One or Two Milk Replacer Daily Meals on Growth, Solid Feed Intake and Rumen Fermentation and Development of Dairy Calves  [PDF]
Christine Julien, Corine Bayourthe, Caroline Lacroux, Francis Enjalbert
Agricultural Sciences (AS) , 2015, DOI: 10.4236/as.2015.612139
Abstract: Sixteen Holstein calves were used to study the effects of two feeding programs (FP) on growth, intake, rumen development and ruminal metabolism from birth to weaning. Two feeding programs based on milk replacer (MR) were tested: a once a day (OAD) MR (200 g/L) distribution vs. a standard twice a day (TAD) MR (125 g/L) distribution. All calves received water, wheat straw and a starter concentrate ad libitum. Four calves per group were slaughtered at weaning and rumen epithelium from the ventral sac was sampled for papillae (RP) density. Results showed that the FP had no effect on body weight of calves and total feed intake. From day 42 to day 56, ruminal pH was lower (P = 0.036) and ruminal oxydo-reducing potential was higher (P = 0.001) in OAD than TAD calves. Ruminal total volatile fatty acid (VFA) concentrations did not significantly differ between FP. From day 21 to day 63, butyrate ruminal concentration was significantly higher in OAD than TAD calves (5.17 vs 3.95 mmol/L). This probably explained the higher development of RP in calves fed once daily. Finally, the tested feeding system based on a once daily MR distribution affects the concentrate feeding pattern of calves.
Methodology Article: Can Ruminal Reducing Power Assessed in Batch Cultures be Comparable to in Vivo Measurements?  [PDF]
Christine Julien, Jean-Philippe Marden, Annabelle Troegeler-Meynadier, Corine Bayourthe
Journal of Analytical Sciences, Methods and Instrumentation (JASMI) , 2014, DOI: 10.4236/jasmi.2014.43011

In ruminant field of digestive research, the appeal to methods of less invasive studies and reproducing the in vivo conditions is essential. The objective of the present study was to determine whether the conditions created with the proposed in vitro batch culture was an accurate reproduction of the physico-chemical and fermentative ruminal conditions observed in vivo. Two experiments were conducted to compare ruminal reducing power measured in vitro, i.e. in batch cultures or, in vivo i.e. in live animals: dairy cows at maintenance (Experiment 1) and lactating dairy cows (Experiment 2). In Experiment 1, at the beginning of incubation period, in vitro redox potential (Eh), pH and Clark’s exponent (rH) values were significantly higher than in vivo (+42 mV, +0.25 and +1.9, respectively) whereas volatile fatty acids (VFA)

Interaction between Live Yeast and Dietary Rumen Degradable Protein Level: Effects on Diet Utilization in Early-Lactating Dairy Cows  [PDF]
Christine Julien, Jean Philippe Marden, Eric Auclair, Raymond Moncoulon, Laurent Cauquil, Jean Louis Peyraud, Corine Bayourthe
Agricultural Sciences (AS) , 2015, DOI: 10.4236/as.2015.61001
Abstract: Four early lactating Holstein cows were used to study the effect of live yeast (LY, Actisaf® CNCM I-4407, Lesaffre Feed Additives, Marcq en Baroeul, France) supplementation on diet digestive utilization of dairy cows receiving concentrated corn silage-based diets with two rumen-degradable protein (RDP) levels. For a 33 d period, cows were fed a total mixed ration (TMR) containing an adequate level (AL) of RDP or a low level (LL, 30% below AL) by using soybean meal or tanned soybean meal, respectively: for 21 d with no LY addition followed by 12 d during which LY was added to the diet. The pH and redox potential (Eh) were recorded and ruminal fluid samples were collected over 3 consecutive days. Feces were collected individually over 48 h and individual dry matter intake (DMI) was measured for determining apparent nutrient digestibility. The effective degradability of individual feed ingredients composing both diets was evaluated with nylon bags technique. Structure of the ruminal bacterial community was studied and diversity index was calculated. Digestibility of organic matter (OM) and crude protein (CP) were lower for LL than those for AL. With LY, digestibility of OM and CP was increased: +2.4 and +0.8 points, for AL, and +3.7 and +5.9 points for LL, respectively. Live yeast reduced dietary N ruminal degradation with both AL and LL. Ruminal pH and Eh were lower with AL compared to LL: 5.95 and –167 mV vs. 6.13 and –144 mV. Live yeast increased ruminal total volatile fatty acids (VFA) (+8.6%), C2 (+10%), and C4 (+35%) contents for LL and decreased that of C3 (?9.8%) for AL. Neither the structure of bacterial populations of the rumen nor the diversity index (Shannon) was altered by treatments. Those results suggested a specific interest in using LY in RDP deficient diets for early lactating cows.
Quantitative Analysis of the Relationship between Ruminal Redox Potential and pH in Dairy Cattle: Influence of Dietary Characteristics  [PDF]
Yayu Huang, Jean Philippe Marden, Chaouki Benchaar, Christine Julien, Eric Auclair, Corine Bayourthe
Agricultural Sciences (AS) , 2017, DOI: 10.4236/as.2017.87047
Abstract: The ruminal redox potential (Eh) can reflect the microbiological activity and dynamics of fermentation in the rumen. It might be an important indicator of rumen fermentation in combination with pH. However, the ruminal Eh has been rarely studied in dairy cows due to the difficulty of its measurement, and the relationship between ruminal Eh and pH is not clear. The objective of this study was to investigate the relationship between ruminal Eh and pH of dairy cows by meta-analysis of systematic measurements from different experiments. A database was constructed from 22 experiments on cannulated dairy cattle including 57 dietary treatments. The ruminal pH and Eh were measured without air contact between 0 and 8 h post-feeding. The results demonstrated a quadratic correlation between ruminal Eh and pH with a reliable within-animal variation (Eh = -1697 + 540.7 pH -47.7 pH2, nobservation = 70, nanimal = 26, P < 0.001, RMSE = 56, AIC = 597). The dietary characteristics (NDF, NDFf, OM, starch, degradable starch, soluble sugars contents, and the dietary ionic balance) influencing the ruminal pH also affected the ruminal Eh, but not always to the same extent. Some of them still influenced the relationship between ruminal Eh and pH. While the mechanism of the interaction between ruminal Eh and pH remains to be elucidated, it would be interesting to associate Eh to microbial profile, ruminal VFA concentration and milk production performance in future studies.
Field Study of the Impact of Supplementation with Probiotic Yeast (Saccharomyces cerevisiae Sc47-CNCM I-4407) on Reproductive Performance in Dairy Cows  [PDF]
Christine Julien, Maxime Briche, Hélo?se Legendre, Vincent Delcloy, Gérard Heumez
Agricultural Sciences (AS) , 2018, DOI: 10.4236/as.2018.912116
Abstract: Probiotic yeasts are used widely today in the diets of dairy cows with a high production potential. Various studies have researched the effects of live yeasts, in particular Saccharomyces cerevisiae, on digestion, metabolism and performance in dairy cows. The present study aims at evaluating the beneficial effects of using probiotic yeast in dairy cattle farms as a means of improving the breeding performance of milking cows. A group of 14 dairy cattle farms, with at least 40 dairy cows, was selected for the study, all of them using artificial insemination (AI) and that had not used probiotics in the two milking years preceding the study. On these farms, the lactating cows received probiotic yeast supplementation (5 g/cow/day, Actisaf®, Saccharomyces cerevisiae Sc47-CNCM I-4407, 1.1010 CFU/g, Phileo Lesaffre Animal Care, Marcq-en-Baroeul, France) over 13 months including a 4-week period of adaptation to the product and then the observation period lasting a full year. The analysis was therefore based on 2421 Holstein females inseminated with a total of 4230 doses of conventional Holstein semen at 14 farms over three consecutive years: the period of observation and the two preceding years stated as reference period. Use of daily supplementation with probiotic yeast resulted in a significant improvement of 4 points on average in the success rate of artificial insemination and of 5 points in the success rate of first artificial insemination in multiparous dairy cows. The number of inseminations required to obtain a pregnancy was therefore reduced from 3.1 in the reference period to 2.7 in the probiotic yeast supplementation period (p = 0.007). In parallel, the fat and protein yield by these same animals tended to improve (+5%, p = 0.07) between these two periods, demonstrating that it is possible to combine milk performance and maintenance of an effective reproductive system.
High-throughput sorting of mosquito larvae for laboratory studies and for future vector control interventions
Marois Eric,Scali Christina,Soichot Julien,Kappler Christine
Malaria Journal , 2012, DOI: 10.1186/1475-2875-11-302
Abstract: Background Mosquito transgenesis offers new promises for the genetic control of vector-borne infectious diseases such as malaria and dengue fever. Genetic control strategies require the release of large number of male mosquitoes into field populations, whether they are based on the use of sterile males (sterile insect technique, SIT) or on introducing genetic traits conferring refractoriness to disease transmission (population replacement). However, the current absence of high-throughput techniques for sorting different mosquito populations impairs the application of these control measures. Methods A method was developed to generate large mosquito populations of the desired sex and genotype. This method combines flow cytometry and the use of Anopheles gambiae transgenic lines that differentially express fluorescent markers in males and females. Results Fluorescence-assisted sorting allowed single-step isolation of homozygous transgenic mosquitoes from a mixed population. This method was also used to select wild-type males only with high efficiency and accuracy, a highly desirable tool for genetic control strategies where the release of transgenic individuals may be problematic. Importantly, sorted males showed normal mating ability compared to their unsorted brothers. Conclusions The developed method will greatly facilitate both laboratory studies of mosquito vectorial capacity requiring high-throughput approaches and future field interventions in the fight against infectious disease vectors.
Modélisation multi-niveaux dans AA4MM
Benjamin Camus,Julien Siebert,Christine Bourjot,Vincent Chevrier
Computer Science , 2012,
Abstract: In this article, we propose to represent a multi-level phenomenon as a set of interacting models. This perspective makes the levels of representation and their relationships explicit. To deal with coherence, causality and coordination issues between models, we rely on AA4MM, a metamodel dedicated to such a representation. We illustrate our proposal and we show the interest of our approach on a flocking phenomenon.
Assessment of Human Multi-Potent Hematopoietic Stem/Progenitor Cell Potential Using a Single In Vitro Screening System
Julien Calvo, Aissa BenYoucef, Jan Baijer, Marie-Christine Rouyez, Francoise Pflumio
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0050495
Abstract: Hematopoietic stem cells are responsible for the generation of the entire blood system through life. This characteristic relies on their ability to self renew and on their multi-potentiality. Thus quantification of the number of hematopoietic stem cells in a given cell population requires to show both properties in the studied cell populations. Although xenografts models that support human hematopoietic stem cells have been described, such in vivo experimental systems remain restrictive for high throughput screening purposes for example. In this work we developed a conditional tetracycline inducible system controlling the expression of the human NOTCH ligand Delta-like 1 in the murine stromal MS5 cells. We cultured hematopoietic immature cells enriched in progenitor/stem cells in contact with MS5 cells that conditionally express Delta-like 1, in conditions designed to generate multipotential lineage differentiation. We show that upon induction or repression of DL1 expression during co-culture, human immature CD34+CD38?/low(CD45RA?CD90+) cells can express their B, T, NK, granulo/monocytic and erythroid potentials in a single well, and at the single cell level. We also document the interference of low NOTCH activation with human B and myelo/erythroid lymphoid differentiation. This system represents a novel tool to precisely quantify human hematopoietic immature cells with both lymphoid and myeloid potentials.
Electroporation of cDNA/Morpholinos to targeted areas of embryonic CNS in Xenopus
Julien Falk, Jovana Drinjakovic, Kin Leung, Asha Dwivedy, Aoife G Regan, Michael Piper, Christine E Holt
BMC Developmental Biology , 2007, DOI: 10.1186/1471-213x-7-107
Abstract: We describe here an electroporation procedure that can be used with high efficiency and low toxicity for targeting DNA and antisense morpholino oligonucleotides (MOs) into spatially restricted regions of the Xenopus CNS at a critical time-window of development (22–50 hour post-fertilization) when axonal tracts are first forming. The approach relies on the design of "electroporation chambers" that enable reproducible positioning of fixed-spaced electrodes coupled with accurate DNA/MO injection. Simple adjustments can be made to the electroporation chamber to suit the shape of different aged embryos and to alter the size and location of the targeted region. This procedure can be used to electroporate separate regions of the CNS in the same embryo allowing separate manipulation of growing axons and their intermediate and final targets in the brain.Our study demonstrates that electroporation can be used as a versatile tool to investigate molecular pathways involved in axon extension during Xenopus embryogenesis. Electroporation enables gain or loss of function studies to be performed with easy monitoring of electroporated cells. Double-targeted transfection provides a unique opportunity to monitor axon-target interaction in vivo. Finally, electroporated embryos represent a valuable source of MO-loaded or DNA transfected cells for in vitro analysis. The technique has broad applications as it can be tailored easily to other developing organ systems and to other organisms by making simple adjustments to the electroporation chamber.Xenopus laevis is a model system widely used to study vertebrate development. Much of our understanding of early embryo patterning and tissue induction has come from this model, and Xenopus has provided many important insights into neuronal development. However, many of the molecules involved in neuronal differentiation also play crucial roles in early development [1,2]. Therefore, the classical approach of injecting blastomeres with DNA/mRNA or
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