54 research outputs found
Study of the heating effect contribution to the nonlinear dielectric response of a supercooled liquid
No full textInternational audienceWe present a detailed study of the heating effects in dielectric measurements carried out on a liquid. Such effects come from the dissipation of the electric power in the liquid and give contribution to the nonlinear third harmonics susceptibility χ3χ3, which depends on the frequency and temperature. This study is used to evaluate a possible “spurious” contribution to the recently measured nonlinear susceptibility of an archetypical glassforming liquid (glycerol). Those measurements have been shown to give a direct evaluation of the number of dynamically correlated molecules temperature dependence close to the glass transition temperature Tg≈190Tg≈190 K [Crauste-Thibierge et al., Phys. Rev. Lett. 104, 165703 (2010)]. We show that the heating contribution is totally negligible (i) below 204 K at any frequency; (ii) for any temperature at the frequency where the third harmonics response χ3χ3 is maximum. Besides, this heating contribution does not scale as a function of f/fαf/fα, with fα(T)fα(T) the relaxation frequency of the liquid. In the high frequency range, when f/fα≥1f/fα≥1, we find that the heating contribution is damped because the dipoles cannot follow instantaneously the temperature modulation due to the heating phenomenon. An estimate of the magnitude of this damping is given
Third harmonics nonlinear susceptibility in supercooled liquids: A comparison to the box model
No full textInternational audienceThe box model, originally introduced to account for the nonresonant hole burning (NHB) dielectricexperiments in supercooled liquids, is compared to the measurements of the third harmonics P 3 of the polarisation, reported recently in glycerol, close to the glass transition temperature T g [C. Crauste-Thibierge, C. Brun, F. Ladieu, D. L’Hôte, G. Biroli, and J.-P. Bouchaud, Phys. Rev. Lett.104, 165703 (2010)]. In this model, each box is a distinct dynamical relaxing entity (hereafter called dynamical heterogeneity (DH)) which follows a Debye dynamics with its own relaxation time τ dh . When it is submitted to a strong electric field, the model posits that a temperature increase δT dh , depending on τ dh , arises due to the dissipation of the electrical power. Each DH has thus its own temperature increase, on top of the temperature increase of the phonon bath δT ph . Contrary to the “fast” hole burning experiments where δT ph is usually neglected, the P 3 measurements are, from a thermal point of view, fully in a stationary regime, which means that δT ph can no longer be neglected a priori. This is why the version of the box model that we study here takes δT ph into account, which implies that the δT dh of the DHs are all coupled together. The value of P 3, including both the “intrinsic” contribution of each DH as well as the “spurious” one coming from δT ph , is computed within this box model and compared to the P 3 measurements for glycerol, in the same range of frequencies and temperatures T. Qualitatively, we find that this version of the box model shares with experiments some nontrivial features, e.g., the existence of a peak at finite frequency in the modulus of P 3 as well as its order of magnitude. Quantitatively, however, some experimental features are not accounted for by this model. We show that these differences between the model and the experiments do not come from δT ph but from the “intrinsic” contribution of the DHs. Finally, we show that the interferences between the 3ω response of the various DHs are the most important issue leading to the discrepancies between the box model prediction and the experiments. We argue that this could explain why the box model is quite successful to account for some kinds of nonlinear experiments (such as NHB) performed close to T g , even if it does not completely account for all of them (such as the P 3 measurements). This conclusion is supported by an analytical argument which helps understanding how a “space-free” model as the box model is able to account for some of the experimental nonlinear features
Delay Model of Hematopoietic Stem Cell Dynamics: Asymptotic Stability and Stability Switch
No full textInternational audienceA nonlinear system of two delay differential equations is proposed to model hematopoietic stem cell dynamics. Each equation describes the evolution of a sub-population, either proliferating or nonproliferating. The nonlinearity accounting for introduction of nonproliferating cells in the proliferating phase is assumed to depend upon the total number of cells. Existence and stability of steady states are investigated. A Lyapunov functional is built to obtain the global asymptotic stability of the trivial steady state. The study of eigenvalues of a second degree exponential polynomial characteristic equation allows to conclude to the existence of stability switches for the unique positive steady state. A numerical analysis of the role of each parameter on the appearance of stability switches completes this analysis
Unravelling the capacity of hydroxytyrosol and its lipophenolic derivates to modulate the H2O2-induced isoprostanoid profile of THP-1 monocytes by UHPLC-QqQ-MS/MS lipidomic workflow
No full textPresently, the attention given to natural substances to counteract damage produced by oxidative stress (OS) has risen sharply. In this scenario, hydroxytyrosol (HT) derivatives, formed as a result of HT conjugation with fatty acids (FAs) (lipophenols), have been recently described in foodstuffs such as extra virgin olive oil, as being powerful bioactive compounds with a higher activity than the unesterified phenolic compound. The present work describes the capacity of HT lipophenols to act on the course of OS and secondary inflammatory processes, based on their capacity to modulate the isoprostanoid profile induced by H2O2 in THP-1 monocytic cells. A UHPLC-QqQ-ESI-MS/MS-based lipidomics workflow was applied over a range of 37 human oxylipins. The main outcomes retrieved suggest both HT and HT-lipophenols as regulators of the cellular redox balance, acting as pro-oxidants in vitro, which is highly dependent on the experimental conditions. Our outcomes suggest the anti-inflammatory potential of both HT and HT-lipophenols, where the type of the FAs on the HT core appears to be critical for defining the bioactivity of lipophenols, highlighting that a lipidomic approach, with the simultaneous analysis of multiple oxylipins, is critical for the understanding of the bioactivity of lipophenols on isoprostanoid generation and hence, on pathophysiological processes
Delay Differential Equations and Autonomous Oscillations in Hematopoietic Stem Cell Dynamics Modeling
No full textInternational audienceWe illustrate the appearance of oscillating solutions in delay differential equations modeling hematopoietic stem cell dynamics. We focus on autonomous oscillations, arising as consequences of a destabilization of the system, for instance through a Hopf bifurcation. Models of hematopoietic stem cell dynamics are considered for their abilities to describe periodic hematological diseases, such as chronic myelogenous leukemia and cyclical neutropenia. After a review of delay models exhibiting oscillations, we focus on three examples, describing different delays: a discrete delay, a continuous distributed delay, and a state-dependent delay. In each case, we show how the system can have oscillating solutions, and we characterize these solutions in terms of periods and amplitudes
A New Journal in the Field of Pharmaceutical Technology Is Born
No full textLaunching a new journal is always an adventure. There are so many tasks, so many people to convince from the publisher to the authors. After many discussions at the GERPAC’s meetings every year in the south of France, we decided that the game was worth the candle. In fact, few journals are dedicated to the field of Pharmaceutical Technology in Hospitals. Very often the scopes of the scientific journals are wider and it is difficult for authors to communicate over much focused technical questions in those papers. This is why Pharmaceutical Technology in Hospital Pharmacy (PTHP) was launched. We are committed to produce a high-quality scientific international journal because our profession really needs it. This journal will be dedicated to all angles of pharmaceutical technologies in hospitals from sterile compounding to electronic devices related to drug production or distribution. Sterilization and radiopharmacy are also considered in this new journal. Detailed aims and scope are provided in this issue along with the instructions to authors. The editorial board of the journal gather hospital pharmacists and scientific researchers all having a strong background in applied research and scientific publishing, holding also a PhD and being for most of them professors of pharmaceutical technology in Universities from European and extra European Universities. [...
Dynamics of erythroid progenitors and erythroleukemia
No full textInternational audienceThe paper is devoted to mathematical modelling of erythropoiesis, production of red blood cells in the bone marrow. We discuss intra-cellular regulatory networks which determine self-renewal and differentiation of erythroid progenitors. In the case of excessive self-renewal, immature cells can fill the bone marrow resulting in the development of leukemia. We introduce a parameter characterizing the strength of mutation. Depending on its value, leukemia will or will not develop. The simplest model of treatment of acute myeloid leukemia with chemotherapy allows us to determine the conditions of successful treatment or of its failure. We show that insufficient treatment can worsen the situation. In some cases curing may not be possible even without resistance to treatment. Modelling presented in this work is based on ordinary differential equations, reaction-diffusion systems and individual based approach
Investigating the role of the experimental protocol in phenylhydrazine-induced anemia on mice recovery
No full textInternational audienceProduction of red blood cells involves growth-factor mediated regulation of erythroid progenitor apoptosis and self-renewal. During severe anemia, characterized by a strong fall of the hematocrit followed by a recovery phase, these controls allow a fast recovery of the hematocrit and survival of the organism. Using a mathematical model of stress erythropoiesis and an ad hoc numerical method, we investigate the respective roles of anemia-inducing phenylhydrazine injections and physiological regulation on the organism's recovery. By explicitly modeling the experimental protocol, we show that it mostly characterizes the fall of the hematocrit following the anemia and its severeness, while physiological process regulation mainly controls the recovery. We confront our model and our conclusions to similar experiments inducing anemia and show the model's ability to reproduce several protocols of phenylhydrazine-induced anemia. In particular, we establish a link between phenylhydrazine effect and the severeness of the anemia
Numerical integration of an erythropoiesis model with explicit growth factor dynamics
No full textInternational audienceErythropoiesis, the red blood cell production process, involves interactions between cell populations with different differentiation states, mainly immature progenitor cells and mature erythrocytes, and growth factors such as erythropoietin and glucocorticoids, known to respectively inhibit cell apoptosis, stimulate proliferation and differentiation, and stimulate self-renewal. The feedback regulation of this process allows a very fast and efficient recovery in the case of a severe anemia. We consider an age-structured model of red blood cell production accounting for these feedback regulations and the dynamics of growth factors. We theoretically show the existence of a unique positive steady state for the model and we propose a numerical method to obtain an approximation to its solution. Experiments are reported to show numerically, on one hand, the optimal convergence order of the numerical scheme and, on the other hand, a fine approximation to real experimental data, with a suitable selection of the parameters involved
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