On the Effect of Ions on Water Dynamics in Dilute and Concentrated Aqueous Salt Solutions

International audienceAqueous ionic solutions are ubiquitous in chemistry and in biology. Experiments show that ions affect water dynamics, but a full understanding of several questions remains needed: why some salts accelerate water dynamics while others slow it down, why the effect of a given salt can be concentration dependent, whether the effect of ions is rather local or more global. Numerical simulations are particularly suited to disentangle these different effects, but current force fields suffer from limitations and often lead to a poor description of dynamics in several aqueous salt solutions. Here, we develop an improved classical force field for the description of alkali halides which yields dynamics in excellent agreement with experimental measurements for water reorientational and translational dynamics. These simulations are analyzed with an extended jump model, which allows to compare the effects of ions on local hydrogen-bond exchange dynamics and on more global properties like viscosity. Our results unambiguously show that the ion-induced changes in water dynamics are usually mostly due to a local effect on the hydrogen-bond exchange dynamics; in contrast , the change in viscosity leads to a smaller effect, which governs the retardation only for a minority of salts and at high concentrations. We finally show how the respective importance of these two effects can be directly determined from experimental measurements alone, thus providing guidelines for the selection of an elec-trolyte with specific dynamical properties

Clock Genes in Depression

Data demonstrate that abnormal regulation of the circadian system can result in cardiovascular disease, metabolic syndrome, obesity, immune dysfunction, increased risk for cancer, reproductive complications, etc. It is highly individual among depressed patients and may be expressed as a phase advance or phase delay of rhythms and/or increase or decrease in the amplitude. The stress-induced anhedonic-like state characterizes by hypothermia, hypercortisolemia, and hypermelatoninemia associated with disturbances in the circadian system. Mainly Per2 and Bmal1 demonstrate altered expression in the brain and liver: expression of Per2 is sensitive to stress and changes in Bmal1 mostly associated with depressive behavior. The Per1 expression is sustainable in maintaining the circadian rhythm. A normalization of the expression patterns is likely to be essential for the recovery from the pathological state. Depression is a high prevalent disorder. The number of incidents is rising due to changes in lifestyle. The symptomatology is inconsistent and it is difficult to agree on one hypothesis. The disturbances of the 24 h circadian rhythm may be a factor in the development of major depressive disorder. The molecular biology underlying a causal relationship between circadian rhythm and mood disorders is slowly being unraveled. However, many questions still need to be answered

Are there dynamical effects in enzyme catalysis? Some thoughts concerning the enzymatic chemical step

AbstractWe offer some thoughts on the much debated issue of dynamical effects in enzyme catalysis, and more specifically on their potential role in the acceleration of the chemical step. Since the term ‘dynamics’ has been used with different meanings, we find it useful to first return to the Transition State Theory rate constant, its assumptions and the choices it involves, and detail the various sources of deviations from it due to dynamics (or not). We suggest that much can be learned about the key current questions for enzyme catalysis from prior extensive studies of dynamical and other effects in the case of reactions in solution. We analyze dynamical effects both in the neighborhood of the transition state and far from it, together with the situation when quantum nuclear motion is central to the reaction, and we illustrate our discussion with various examples of enzymatic reactions

Establishing SME–university collaboration through innovation support programmes

Purpose – The research purpose is to analyse when and how innovation support programmes (ISPs) can affectcollaboration between universities and established small and medium sized enterprises (SMEs). The paperspecifically considers SME’s absorptive capacity.Design/methodology/approach – A Swedish research centre is studied in the context of innovation supportand two of its SME-ISPs are examined with regards to industry–university collaboration and impact on firminnovation capabilities. Data collection and analysis are performed, using interviews, survey answers,document search and reflectional analysis to evaluate processes and effects of the centre and the programmes.Findings – A developed research centre, integrated into both academia and industry, can supporttranslational collaboration and promote SME innovation absorptive capacity. The action learning elementsand the organisational development approaches used when coaching in the ISPs contribute to the SMEsinternal absorption capacity and collaborational skills. Organising collaboration into ISPs can provide arelational path to future collaboration with universities, which, for example start with student projects.Research limitations/implications – The study, though limited to one Swedish region, adds to empiricalinnovation research as it connects industry–university collaboration and absorptive capacity to organisationallearning.Practical implications – The empirical results indicate possible long-term gains for industry anduniversities in building collaborative innovation into SME-ISPs.Originality/value – The contribution of this study pertains to the practice of innovation support forestablished SMEs with the inclusion of absorption capacity and collaborative innovation development

Reorientation dynamics of nanoconfined water: Power-law decay, hydrogen-bond jumps, and test of a two-state model

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/136/4/10.1063/1.3679404.The reorientation dynamics of water confined within nanoscale, hydrophilicsilica pores are investigated using molecular dynamics simulations. The effect of surface hydrogen-bonding and electrostatic interactions are examined by comparing with both a silica pore with no charges (representing hydrophobic confinement) and bulk water. The OH reorientation in water is found to slow significantly in hydrophilic confinement compared to bulk water, and is well-described by a power-law decay extending beyond one nanosecond. In contrast, the dynamics of water in the hydrophobic pore are more modestly affected. A two-state model, commonly used to interpret confined liquid properties, is tested by analysis of the position-dependence of the water dynamics. While the two-state model provides a good fit of the orientational decay, our molecular-level analysis evidences that it relies on an over-simplified picture of water dynamics. In contrast with the two-state model assumptions, the interface dynamics is markedly heterogeneous, especially in the hydrophilic pore and there is no single interfacial state with a common dynamics

Liberalisierung des Fernbusverkehrs 2013 – Wie umweltfreundlich ist der deutsche Fernbusverkehr und welche Folgen hat er für Städte wie Dresden?

Der Fernbus ist eines der attraktivsten Verkehrsmittel, das den Fernreisenden im deutschen Fernverkehrsangebot seit dem Jahr 2013 zur Verfügung steht. Das steigende Bedürfnis nach flexibler und intermodaler Mobilität kann der Fernbus vor allem bei jungen Menschen auf eine bequeme und kostengünstige Art befriedigen. Als Teil des öffentlichen Personenverkehrs und als Massenverkehrsmittel wird er dabei als besonders umweltfreundlich wahrgenommen und ihm ein besonders geringer CO2-Ausstoß unterstellt. Im Hinblick auf die durch den Staat gesetzten Ziele einer nachhaltigen Mobilität und dem Umdenken in der Verkehrsmittelwahl hin zu öffentlichen Verkehrsmitteln sollte er daher helfen können, diese Ziele zu erreichen. Im Zuge einer ersten Analyse des Fernbusmarktes, welche aktuelle Marktentwicklungen, Folgen für deutsche Kommunen und umweltrelevante Rahmenbedingungen beschreibt, konnte jedoch festgestellt werden, dass die statistischen Grundlagen für eine ausführliche Bewertung, verkehrlich wie auch ökologisch, nicht ausreichend vorhanden sind. Diese Arbeit hat es sich daher zum Ziel gesetzt, ein grundlegendes Erhebungskonzept für den Fernbusverkehr zu erstellen. Dabei wurden notwendige Kenngrößen, wie z.B. die Herkunft der Fernbusnutzer oder die Auslastung der Fernbusse, als Schwerpunkte der Erhebung identifiziert und ein Konzept unter der Zuhilfenahme aktueller wissenschaftlicher Erkenntnisse erstellt. Um die praktische Anwendbarkeit des Erhebungskonzepts zu prüfen und erste Erkenntnisse zu erlangen, wurde das Konzept in einem Testrahmen für den Standort Dresden erprobt. Im Anschluss der Erhebung wurden die gesammelten Daten einer ersten Auswertung unterzogen und im Rahmen einer Analyse aufbereitet vorgestellt. Abschließend konnte unter der Verwendung der erhobenen Auslastungen eine vereinfachte Umweltbilanz ermittelt und in einen Vergleich zu vorangegangenen Studien gestellt werden. Es zeigte sich dabei, dass der Fernbus auch unter den aktuell sehr harten Wettbewerbsbedingungen mit vielen parallelen Angeboten und Konkurrenten durchaus einen ökologischen und umweltschonenden Verkehr anbieten kann

Optimisation de l’affichage des itinéraires dans le système interne de réservation d’une compagnie aérienne

RÉSUMÉ : Les revenus des compagnies aériennes sont principalement issus des ventes de billets d’avions aux passagers, optimiser les systèmes de réservation fait donc partie de leurs principales préoccupations. On considère dans notre étude un passager qui effectue une réservation par le centre d’appel d’un transporteur nord américain. Les itinéraires disponibles lui sont proposés dans l’ordre d’affichage du système interne de réservation de la compagnie. Notre objectif est de trouver, pour chaque réservation, l’affichage optimal des itinéraires qui maximise le revenu espéré de la compagnie. On suppose que la position de l’itinéraire dans l’affichage fait partie des critères de choix du passager ainsi que le nombre d’escales, la durée, l’heure de départ, le prix, et la cabine de l’avion. Le programme d’optimisation est bi-niveau : le premier niveau correspond à la maximisation des revenus espérés du transporteur et le deuxième niveau à la maximisation de la fonction d’utilité du passager, linéaire en ses critères de choix. Deux modèles de choix discret sont testés pour estimer les poids associés aux différents attributs des itinéraires. Le modèle multinomial logit suppose que les différentes alternatives sont en concurrence uniforme et le modèle nested logit regroupe les alternatives que l’on suppose en concurrence plus étroite en plusieurs nids. Les paramètres de la fonction d’utilité sont estimés à partir de données fournies par le transporteur et les deux modèles donnent des résultats similaires qui valident l’hypothèse de départ. La position dans l’affichage est un critère de choix du passager et son utilité diminue si l’itinéraire est moins bien placé. Le prix a une influence moins significative sur la décision du passager que les autres critères, des passagers plus sensibles au prix se rendent sur des plateformes adaptées à la comparaison de tarifs. On résout ensuite le programme d’optimisation de premier niveau dont la fonction objectif contient les probabilités d’achat des itinéraires. Celles-ci sont calculées avec le modèle multinomial logit et varient selon la position dans l’affichage. On résout le programme avec une métaheuristique de recherche taboue dont les paramètres sont calibrés par une première simulation sur des ensembles de choix restreints à 10 itinéraires. Deux structures de voisinage sont étudiées : la première, plus petite, où les voisins sont obtenus par la permutation de deux itinéraires adjacents dans l’affichage et la seconde par la permutation de deux quelconques. Cette dernière atteint une meilleure solution en très peu d’itérations quelque soit les valeurs des autres paramètres, que l’on peut supposer être la solution optimale. L’autre structure de voisinage en revanche n’atteint jamais cette solution. Sur l’échantillon des réservations considérées, l’algorithme génère en environ 0,1 seconde des affichages qui augmentent en moyenne le revenu espéré de 19,8%. Ces résultats sont prometteurs et une étude complémentaire sur des réservations depuis d’autres plateformes permettrait de définir plusieurs profils de passagers et accéder à des informations plus fines.----------ABSTRACT : With most of their revenue coming from flight ticket sales, one of the main concerns of Airlines is optimizing booking systems. In this thesis, a passenger is willing to book a flight with a north american carrier and a travel agent enumerates him all possible alternatives in the same order as the internal booking system display. Our objective is to find optimal displays for each booking which maximize airline expected revenue. Passenger preferences are included in the bi-level optimization program. The upper level aims to maximize airline expected revenue while the lower lovel describe the passenger utility maximization problem. Our main hypothesis is that the position of an itinerary in the display is a criteria in the passenger decision making as well as the connections number, the elapsed time of the itinerary, the departure time, the fare and cabin in the plane. The utility function is linear in these variables. We study two discrete choice models to estimate the importance of different attributes on the passenger choice. The multinomial logit model suppose an uniform competition between alternatives while the nested logit model allows for the possibility of correlation for groups of alternatives. Data from previous bookings are used to estimate passenger utility function parameters and both models show similar results which verify the main hypothesis. Position Over the sample of bookings used for the estimations, displays generated by the algorithm increase the expected revenue by 19.8% on average in about 0.1 second. This promising results should be compared with a study on bookings from other systems to characterise several passenger profiles and draw more accurate behaviours. of itineraries in the display is indeed affecting the passenger choice and the utility is increasing with a better rank. The ticket fare however is less important than the other criteria because price sensitive passengers might prefer to book flights on more suited booking systems. The upper level of the optimization program is then solved with a tabu search metaheuristic. Its objective function is defined with the revenue and the choice probability from multinomial logit model of each itinerary and variables are their position in the display. Algorithm parameters are first estimated with simulations on choice sets restricted to 10 alternatives. We study two different structures of a neighborhood : in the first one neighbors arise from the permutation of two adjacent itineraries in the display and of any two itineraries in the second one which produces better results. It reaches the optimal solution in very few iterations for all values of the other criteria and a best solution when simulating over full choice sets. The other structure of a neighborhood never reaches this best solution