Influence of a Counterion on the Ion Atmosphere of an Anion: A Molecular Dynamics Study of LiX and CsX (X = F-, Cl-, I-) in Methanol

We report molecular dynamics (MD) simulations to explore the influence of a counterion on the structure and dynamics of cationic and anionic solvation shells for various ions in methanol at 298 K. We show that the variation in ionic size of either the cation or the anion in an ion pair influences the solvation structure of the other ion as well as the diffusivity in an electrolyte solution of methanol. The extent of ionic association between the cation and its counteranion of different ionic sizes has been investigated by analyzing the radial distribution functions (RDFs) and the orientation of methanol molecules in the first solvation shell (FSS) of ions. It is shown that the methanol in the FSS of the anion as well the cation exhibit quite different radial and orientational structures as compared to methanol which lie in the FSS of either the anion or the cation but not both. We find that the coordination number (CN) of F-, Cr-, and I- ions decreases with increasing size of the anion which is contrary to the trend reported for the anions in H2O. The mean residence time (MRT) of methanol molecules in the FSS of ions has been calculated using the stable states picture (SSP) approach. It is seen that the ion-counterion interaction has a considerable influence on the MRT of methanol molecules in the FSS of ions. We also discuss the stability order of the ion-counterion using the potentials of mean force (PMFs) for ion pairs with ions of different sizes. The PMF plots reveal that the Li+-F- pair (small-small) is highly stable and the Li+-I- pair is least stable (small-large) in electrolyte solutions.

PCB desorption kinetics under realistic shear and turbulence [progress report]

We hypothesize that the impact of PCB desorption from resuspended sediments depends upon the intensity of the resuspension (which scales to bottom stress in the absence of organisms), the rate at which each congener desorbs (which depends on the size and hydrophobicity of the chemical, the relative amount of 'labile' and 'resistant' forms, and the size distribution of the suspended particles), and the residence time of the particles in the water column (which depends on the time-variable water column turbulence regime and the particle settling velocities). In order to accurately quantify the impact of PCB desorption from Hudson River sediments, we are conducting experiments that realistically mimic bottom shear stress and water column turbulence and rapidly measure PCB congener release. The objectives of this study are to measure the kinetics of PCB congener desorption from Hudson River sediments under realistic bottom shear and water column turbulence conditions and to quantify the impact of shear stress and contaminant aging on PCB desorption kinetics.

Markovian bulk-arriving queues with state-dependent control at idle time

This paper considers a Markovian bulk-arriving queue modified to allow both mass arrivals when the queue is idle and mass departures which allow for the possibility of removing the entire workload. Properties of queues which terminate when the server becomes idle are developed first, since these play a key role in later developments. Results for the case of mass arrivals, but no mass annihilation, are then constructed with specific attention being paid to recurrence properties, equilibrium queue-size structure, and waiting-time distribution. A closed-form expression for the expected queue size and its Laplace transform are also established. All of these results are then generalised to allow for the removal of the entire workload, with closed-form expressions being developed for the equilibrium size and waiting-time distributions.

Investigating the impact of occupant response time on computer simulations of the WTC North Tower evacuation

This work explores the impact of response time distributions on high-rise building evacuation. The analysis utilises response times extracted from printed accounts and interviews of evacuees from the WTC North Tower evacuation of 11 September 2001. Evacuation simulations produced using these “real” response time distributions are compared with simulations produced using instant and engineering response time distributions. Results suggest that while typical engineering approximations to the response time distribution may produce reasonable evacuation times for up to 90% of the building population, using this approach may underestimate total evacuation times by as much as 61%. These observations are applicable to situations involving large high-rise buildings in which travel times are generally expected to be greater than response times

Treatment of effluents contaminated with prions. Chemical reactor design

The control and elimination of prionic infective agents that may be present in the effluents, turns out to be a complicated mechanism inside a High Containment bological Facility. There are two ways to carry out this neutralization: Installation of thermal systems to ensure achieve a minimum temperature of 134 ° C sterilization plateau for a residence time of 18 minutes, and the use of chemical reactors based on the addition of sodium hypochlorite so the mixture maintained 2% of free chlorine during the reaction period. This study presents the design phases, elements and benefits, of a chemical reactor that allows the treatment of prion effluents in order to serve as a model to biocontainment facilities with areas of animal experimentation, who want to develop their work with prions.

THE MARINE RADIOCARBON BOMB PULSE ACROSS THE TEMPERATE NORTH ATLANTIC: A COMPILATION OF Delta C-14 TIME HISTORIES FROM ARCTICA ISLANDICA GROWTH INCREMENTS

Marine radiocarbon bomb-pulse time histories of annually resolved archives from temperate regions have been underexploited. We present here series of Delta C-14 excess from known-age annual increments of the long-lived bivalve mollusk Arctica islandica from 4 sites across the coastal North Atlantic (German Bight, North Sea; Tromso, north Norway; Siglufjordur, north Icelandic shelf; Grimsey, north Icelandic shelf) combined with published series from Georges Bank and Sable Bank (NW Atlantic) and the Oyster Ground (North Sea). The atmospheric bomb pulse is shown to be a step-function whose response in the marine environment is immediate but of smaller amplitude and which has a longer decay time as a result of the much larger marine carbon reservoir. Attenuation is determined by the regional hydrographic setting of the sites, vertical mixing, processes controlling the isotopic exchange of C-14 at the air-sea boundary, C-14 content of the freshwater flux, primary productivity, and the residence time of organic matter in the sediment mixed layer. The inventories form a sequence from high magnitude-early peak (German Bight) to low magnitude-late peak (Grimsey). All series show a rapid response to the increase in atmospheric Delta C-14 excess but a slow response to the subsequent decline resulting from the succession of rapid isotopic air-sea exchange followed by the more gradual isotopic equilibration in the mixed layer due to the variable marine carbon reservoir and incorporation of organic carbon from the sediment mixed layer. The data constitute calibration series for the use of the bomb pulse as a high-resolution dating tool in the marine environment and as a tracer of coastal ocean water masses.

BitTorrent based transmission of real-time scalable video over P2P networks

The number of software applications available on the Internet for distributing video streams in real time over P2P networks has grown quickly in the last two years. Typical this kind of distribution is made by television channel broadcasters which try to make their content globally available, using viewer's resources to support a large scale distribution of video without incurring in incremental costs. However, the lack of adaptation in video quality, combined with the lack of a standard protocol for this kind of multimedia distribution has driven content providers to basically ignore it as a solution for video delivery over the Internet. While the scalable extension of the H. 264 encoding (H.264/SVC) can be used to support terminal and network heterogeneity, it is not clear how it can be integrated in a P2P overlay to form a large scale and real time distribution. In this paper, we start by defining a solution that combines the most popular P2P file-sharing protocol, the BitTorrent, with the H. 264/SVC encoding for a real-time video content delivery. Using this solution we then evaluate the effect of several parameters in the quality received by peers.

Mise au point de nanoparticules polymères pour l'administration parentérale d'agents anticancéreux hydrophobes

Plusieurs agents anticancéreux très puissants sont caractérisés par une solubilité aqueuse limitée et une toxicité systémique importante. Cette dernière serait liée d’une part à la solubilisation des agents anticancéreux à l’aide de surfactifs de bas poids moléculaire, connus pour leur toxicité intrinsèque, et d’autre part, par le manque de spécificité tissulaire des anticancéreux. Les vecteurs colloïdaux à base de polymères permettraient de résoudre certains défis liés à la formulation d’agents anticancéreux hydrophobes. D’abord, les polymères peuvent être sélectionnés afin de répondre à des critères précis de compatibilité, de dégradation et d’affinité pour le médicament à formuler. Ensuite, le fait d’encapsuler l’agent anticancéreux dans un vecteur peut améliorer son efficacité thérapeutique en favorisant son accumulation au niveau du tissu cible, i.e. la tumeur, et ainsi limiter sa distribution au niveau des tissus sains. Des travaux antérieurs menés au sein de notre laboratoire ont mené à la mise au point de micelles à base de poly(N-vinyl-pyrrolidone)-bloc-poly(D,L-lactide) (PVP-b-PDLLA) capables de solubiliser des agents anticancéreux faiblement hydrosolubles dont le PTX. Ce dernier est commercialisé sous le nom de Taxol® et formulé à l’aide du Crémophor EL (CrEL), un surfactif de bas poids moléculaire pouvant provoquer, entre autres, des réactions d’hypersensibilité sévères. Bien que les micelles de PVP-b-PDLLA chargées de PTX aient démontré une meilleure tolérance comparée au Taxol®, leur potentiel de ciblage tumoral et leur efficacité thérapeutique étaient similaires à la forme commerciale à doses égales. Ceci était possiblement dû au fait que les micelles étaient rapidement déstabilisées et ne pouvaient retenir leur cargo suite à leur administration intraveineuse. Nous avons donc décidé de poursuivre les travaux avec un autre type de vecteur, soit des nanoparticules, qui possèdent une stabilité intrinsèque supérieure aux micelles. L’objectif principal de cette thèse de doctorat était donc de mettre au point des nanoparticules polymères pour l’administration parentérale d’agents anticancéreux faiblement solubles dans l’eau. Les nanoparticules devaient permettre d’encapsuler des agents anticancéreux hydrophobes et de les libérer de manière contrôlée sur plusieurs jours. De plus, elles devaient démontrer un temps de circulation plasmatique prolongée afin de favoriser l’accumulation passive du médicament encapsulé au niveau de la tumeur. La première partie du travail visait à employer pour la première fois le copolymère amphiphile PVP-b-PDLLA comme émulsifiant dans la préparation de nanoparticules polymères. Ainsi, une méthode de fabrication des nanoparticules par émulsion huile-dans-eau a été appliquée afin de produire des nanoparticules à base de PDLLA de taille inférieure à 250 nm. Grâce aux propriétés lyoprotectrices de la couronne de PVP présente à la surface des nanoparticules, celles-ci pouvaient retrouver leur distribution de taille initiale après lyophilisation et redispersion en milieu aqueux. Deux anticancéreux hydrophobes, soit le PTX et l’étoposide (ETO), ont été encapsulés dans les nanoparticules et libérés de ces dernières de façon contrôlée sur plusieurs jours in vitro. Une procédure de « salting-out » a été appliquée afin d’améliorer le taux d’incorporation de l’ETO initialement faible étant donnée sa solubilité aqueuse légèrement supérieure à celle du PTX. Le second volet des travaux visait à comparer le PVP comme polymère de surface des nanoparticules au PEG, le polymère le plus fréquemment employé à cette fin en vectorisation. Par le biais d’études d’adsorption de protéines, de capture par les macrophages et de biodistribution chez le rat, nous avons établi une corrélation in vitro/in vivo démontrant que le PVP n’était pas un agent de surface aussi efficace que le PEG. Ainsi, malgré la présence du PVP à la surface des nanoparticules de PDLLA, ces dernières étaient rapidement éliminées de la circulation sanguine suite à leur capture par le système des phagocytes mononucléés. Par conséquent, dans le troisième volet de cette thèse, le PEG a été retenu comme agent de surface, tandis que différents polymères biodégradables de la famille des polyesters, certains synthétiques (PDLLA et copolymères d’acide lactique/acide glycolique), d’autres de source naturelle (poly(hydroxyalkanoates)(PHAs)), ont été investiguées comme matériaux formant le cœur des nanoparticules. Il en est ressorti que les propriétés physicochimiques des polyesters avaient un impact majeur sur l’efficacité d’encapsulation du PTX et son profil de libération des nanoparticules in vitro. Contrairement aux PHAs, les polymères synthétiques ont démontré des taux d’incorporation élevés ainsi qu’une libération contrôlée de leur cargo. Des études de pharmacocinétique et de biodistribution ont démontré que les nanoparticules de PDLLA dotées d’une couronne de PEG conféraient un temps de circulation plasmatique prolongé au PTX et favorisaient son accumulation tumorale. Les nanoparticules polymères représentent donc une alternative intéressante au Taxol®.

Chlorophyll-a in the rivers of eastern England

Chlorophyll-a concentration variations are described for two major river basins in England, the Humber and the Thames and related to catchment characteristics and nutrient concentrations across a range of rural, agricultural and urban/industrial settings. For all the rivers there are strong seasonal variations, with concentrations peaking in the spring and summer time when biological activity is at its highest. However, there are large variations in the magnitude of the seasonal effects across the rivers. For the spring-summer low-flow periods, average concentrations of chlorophyll-a correlate with soluble reactive phosphor-us (SRP). Chlorophyll-a is also correlated with particulate nitrogen (PN), organic carbon (POC) and suspended sediments. However, the strongest relationships are with catchment area and flow, where two straight line relationships are observed. The results indicate the importance of residence times for determining planktonic growth within the rivers. This is also indicated by the lack of chlorophyll-a response to lowering of SRP concentrations in several of the rivers in the area due to phosphorus stripping of effluents at major sewage treatment works. A key control on chlorophyll-a concentration may be the input of canal and reservoir waters during the growing period: this too relates to issues of residence times. However, there may well be a complex series of factors influencing residence time across the catchments due to features such as inhomogeneous flow within the catchments, a fractal distribution of stream channels that leads to a distribution of residence times and differences in planktonic inoculation sources. Industrial pollution on the Aire and Calder seems to have affected the relationship of chlorophyll-a with PN and POC. The results are discussed in relation to the Water Framework Directive. (c) 2006 Elsevier B.V. All rights reserved.

Kinetics analysis and automated online screening of aminocarbonylation of aryl halides in flow

Temperature, pressure, gas stoichiometry, and residence time were varied to control the yield and product distribution of the palladium-catalyzed aminocarbonylation of aromatic bromides in both a silicon microreactor and a packed-bed tubular reactor. Automation of the system set points and product sampling enabled facile and repeatable reaction analysis with minimal operator supervision. It was observed that the reaction was divided into two temperature regimes. An automated system was used to screen steady-state conditions for offline analysis by gas chromatography to fit a reaction rate model. Additionally, a transient temperature ramp method utilizing online infrared analysis was used, leading to more rapid determination of the reaction activation energy of the lower temperature regimes. The entire reaction spanning both regimes was modeled in good agreement with the experimental data.

Investigation and optimization of parameters affecting the multiply charged ion yield in AP-MALDI MS

Liquid matrix-assisted laser desorption/ionization (MALDI) allows the generation of predominantly multiply charged ions in atmospheric pressure (AP) MALDI ion sources for mass spectrometry (MS) analysis. The charge state distribution of the generated ions and the efficiency of the ion source in generating such ions crucially depend on the desolvation regime of the MALDI plume after desorption in the AP-tovacuum inlet. Both high temperature and a flow regime with increased residence time of the desorbed plume in the desolvation region promote the generation of multiply charged ions. Without such measures the application of an electric ion extraction field significantly increases the ion signal intensity of singly charged species while the detection of multiply charged species is less dependent on the extraction field. In general, optimization of high temperature application facilitates the predominant formation and detection of multiply charged compared to singly charged ion species. In this study an experimental setup and optimization strategy is described for liquid AP-MALDI MS which improves the ionization effi- ciency of selected ion species up to 14 times. In combination with ion mobility separation, the method allows the detection of multiply charged peptide and protein ions for analyte solution concentrations as low as 2 fmol/lL (0.5 lL, i.e. 1 fmol, deposited on the target) with very low sample consumption in the low nL-range.

How accurate are volcanic ash simulations of the 2010 Eyjafjallajökull eruption?

In the event of a volcanic eruption the decision to close airspace is based on forecast ash maps, produced using volcanic ash transport and dispersion models. In this paper we quantitatively evaluate the spatial skill of volcanic ash simulations using satellite retrievals of ash from the Eyja allajökull eruption during the period from 7 to 16 May 2010. We find that at the start of this period, 7–10 May, the model (FLEXible PARTicle) has excellent skill and can predict the spatial distribution of the satellite-retrieved ash to within 0.5∘ × 0.5∘ latitude/longitude. However, on 10 May there is a decrease in the spatial accuracy of the model to 2.5∘× 2.5∘ latitude/longitude, and between 11 and 12 May the simulated ash location errors grow rapidly. On 11 May ash is located close to a bifurcation point in the atmosphere, resulting in a rapid divergence in the modeled and satellite ash locations. In general, the model skill reduces as the residence time of ash increases. However, the error growth is not always steady. Rapid increases in error growth are linked to key points in the ash trajectories. Ensemble modeling using perturbed meteorological data would help to represent this uncertainty, and assimilation of satellite ash data would help to reduce uncertainty in volcanic ash forecasts.

Computational simulation of gas flow and heat transfer near an immersed object in fluidized beds

To improve the understanding of the heat transfer mechanism and to find a reliable and simple heat-transfer model, the gas flow and heat transfer between fluidized beds and the surfaces of an immersed object is numerically simulated based on a double particle-layer and porous medium model. The velocity field and temperature distribution of the gas and particles are analysed during the heat transfer process. The simulation shows that the change of gas velocity with the distance from immersed surface is consistent with the variation of bed voidage, and is used to validate approximately dimensional analysing result that the gas velocity between immersed surface and particles is 4.6Umf/εmf. The effects of particle size and particle residence time on the thermal penetration depth and the heat-transfer coefficients are also discussed.

Adaptive, Decentralized, And Real-Time Sampling Strategies For Resource Constrained Hydraulic And Hydrologic Sensor Networks

We discuss the development and performance of a low-power sensor node (hardware, software and algorithms) that autonomously controls the sampling interval of a suite of sensors based on local state estimates and future predictions of water flow. The problem is motivated by the need to accurately reconstruct abrupt state changes in urban watersheds and stormwater systems. Presently, the detection of these events is limited by the temporal resolution of sensor data. It is often infeasible, however, to increase measurement frequency due to energy and sampling constraints. This is particularly true for real-time water quality measurements, where sampling frequency is limited by reagent availability, sensor power consumption, and, in the case of automated samplers, the number of available sample containers. These constraints pose a significant barrier to the ubiquitous and cost effective instrumentation of large hydraulic and hydrologic systems. Each of our sensor nodes is equipped with a low-power microcontroller and a wireless module to take advantage of urban cellular coverage. The node persistently updates a local, embedded model of flow conditions while IP-connectivity permits each node to continually query public weather servers for hourly precipitation forecasts. The sampling frequency is then adjusted to increase the likelihood of capturing abrupt changes in a sensor signal, such as the rise in the hydrograph – an event that is often difficult to capture through traditional sampling techniques. Our architecture forms an embedded processing chain, leveraging local computational resources to assess uncertainty by analyzing data as it is collected. A network is presently being deployed in an urban watershed in Michigan and initial results indicate that the system accurately reconstructs signals of interest while significantly reducing energy consumption and the use of sampling resources. We also expand our analysis by discussing the role of this approach for the efficient real-time measurement of stormwater systems.

Spontaneous Interblink Time Distributions in Patients with Graves' Orbitopathy and Normal Subjects

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)