New Green-Kubo formulas for transport coefficients in hard sphere-, Langevin fluids and the likes

We present generalized Green-Kubo expressions for thermal transport coefficients $\mu$ in non-conservative fluid-type systems, of the generic form, $\mu$ $= \mu_\infty$ +\int^\infty_0 dt V^{-1} \av{I_\epsilon \exp(t {\cal L}) I}_0 where $\exp(t{\cal L})$ is a pseudo-streaming operator. It consists of a sum of an instantaneous transport coefficient $\mu_\infty$, and a time integral over a time correlation function in a state of thermal equilibrium between a current $I$ and its conjugate current $I_\epsilon$. This formula with $\mu_\infty \neq 0$ and $I_\epsilon \neq I$ covers vastly different systems, such as strongly repulsive elastic interactions in hard sphere fluids, weakly interacting Langevin fluids with dissipative and stochastic interactions satisfying detailed balance conditions, and "the likes", defined in the text. For conservative systems the results reduce to the standard formulas.Comment: 7 pages, no figures. Version 2: changes in the text and references adde

Monitoring of dioxin levels in cow's milk in Zeeuws-Vlaanderen

In 1196/1997, the Belgian government measured dioxin levels in cow's milk from dairy farms in the neighborhood of a metal reclamation plant in Zelzate above the Belgian standard of 5 pg (i) TEQ/g of milkfat. In the same period they measured high dioxin emissions at the metal reclamation plant concerned. Predictions by the dioxin chain model in the basis of the emissions didn't exclude a exceeding of the Dutch standard of 6 pg (i) TEQ/gram milkfat for cow's milk from diary farms on the Dutch side of the border. Therefore, the Dutch government decided to start a monitoring program to measure the dioxin levels in cow's milk from two selected diary farms in the neighborhood of Sas van Gent, 5 km North-east of the metal reclamation plant, on a monthly basis. In the period October 1998 - June 2000 dioxin levels in cow's milk from these two diary farms were measured. None of the values exceeded the Dutch standard. The highest levels were measured at the start of the monitoring program; 3.0 +/- 0.2 and 5.1 +/- 0.3 pg (i)-TEQ/g milkfat, for the two farms respectively, in October 1998. During the same period, October-December 1998, the dioxin levels of consumers milk, sampled on a monthly basis were monitored. The samples were collected per region of the Netherlands (North, East, South and West). The measured dioxin levels in this period resulted in a background level of 0.5-0.8 pg (i)-TEQ/g of fat. At the end of the period, in June 2000, dioxin levels were decreased to a level round 1 pg (i) TEQ/g of fat. These values are in the same order of magnitude as the back ground level of 0.3-0.4 pg (i) TEQ/g of fat found for consumers milk in the second quarter of 2000. It can be concluded that the measures taken by the metal reclamation plant, imposed by the Belgian government, presumably have led to decreasing dioxin levels in locally produced cow's milk. Therefore, in August 2000, the monitoring program in Zeeuws Vlaanderen was discontinued.In 1996/1997 is door de Belgische overheid aangetoond dat de dioxine-gehalten in koemelk, uit de omgeving van een metaalsmelterij te Zelzate, de Belgische norm van 5 pg (i) TEQ/g melkvet overschreden. Tevens werd in die periode aangetoond dat de dioxine-emissie van de betreffende metaalsmelterij verhoogd was. Berekeningen met het ketenmodel sloten een overschrijding van de Nederlandse warenwetnorm van 6 pg (i) TEQ/g melkvet aan de Nederlandse zijde van de grens niet uit. Daarom is besloten koemelk van twee geselecteerde melkveebedrijven in de omgeving van Sas van Gent, 5 km ten noord-oosten van de metaalsmelterij, te monitoren op basis van maandgemiddelde monsters. In de periode oktober 1998-juni 2000 zijn dioxinegehalten gemeten in koemelk van deze twee melkveebedrijven. De dioxinegehalten in de monsters liggen allen beneden de warenwetnorm van 6 pg (i)-TEQ/g vet. De dioxinegehalten waren aan het begin van de meetperiode het hoogst; 3.0 +/- 0.2 en 5.1 +/- 0.3 pg (i)-TEQ/g melkvet voor respectievelijk melkveebedrijf SvG-1 en SvG-2. In dezelfde periode, oktober-december 1998, werden, in het kader van een ander deelprojekt (639102-9802), ook gehalten gemeten van maandgemiddelde consumptiemelkmonsters. De monsters zijn samengesteld per regio (Noord, Oost, Zuid en West) van Nederland. De gemeten waarden lagen in deze periode op een achtergrondniveau van 0.5-0.8 pg (i)-TEQ/g vet. Aan het eind van de periode, in juni 2000, zijn de waarden gedaald tot een niveau van rond de 1 pg (i) TEQ/g vet. Deze waarden hebben dezelfde orde van grootte als het achtergrondniveau van 03.-0.4 pg (i) TEQ/g vet in consumptiemelk bemonsterd in het tweede kwartaal van 2000. Geconcludeerd kan worden dat door de genomen maatregelen bij de metaalsmelterij, opgelegd door de Belgische overheid, de dioxineconcentraties in koemelk uit de omgeving waarschijnlijk structureel tot een waarde royaal onder de norm hebben geleid. Per augustus 2000 is dan ook, door de Inspectie Gezondheidsbescherming, Waren en Veterinaire Zaken besloten het monitoren van koemelk in de omgeving van Sas van Gent stop te zetten

Generalized Green-Kubo formulas for fluids with impulsive, dissipative, stochastic and conservative interactions

We present a generalization of the Green-Kubo expressions for thermal transport coefficients $\mu$ in complex fluids of the generic form, $\mu= \mu_\infty +\int^\infty_0 dt V^{-1} _0$, i.e. a sum of an instantaneous transport coefficient $\mu_\infty$, and a time integral over a time correlation function in a state of thermal equilibrium between a current $J$ and a transformed current $J_\epsilon$. The streaming operator $\exp(t{\cal L})$ generates the trajectory of a dynamical variable $J(t) =\exp(t{\cal L}) J$ when used inside the thermal average $_0$. These formulas are valid for conservative, impulsive (hard spheres), stochastic and dissipative forces (Langevin fluids), provided the system approaches a thermal equilibrium state. In general $\mu_\infty \neq 0$ and $J_\epsilon \neq J$, except for the case of conservative forces, where the equality signs apply. The most important application in the present paper is the hard sphere fluid.Comment: 14 pages, no figures. Version 2: expanded Introduction and section II specifying the classes of fluids covered by this theory. Some references added and typos correcte

Capillary Rise in Nanopores: Molecular Dynamics Evidence for the Lucas-Washburn Equation

When a capillary is inserted into a liquid, the liquid will rapidly flow into it. This phenomenon, well studied and understood on the macroscale, is investigated by Molecular Dynamics simulations for coarse-grained models of nanotubes. Both a simple Lennard-Jones fluid and a model for a polymer melt are considered. In both cases after a transient period (of a few nanoseconds) the meniscus rises according to a $\sqrt{\textrm{time}}$-law. For the polymer melt, however, we find that the capillary flow exhibits a slip length $\delta$, comparable in size with the nanotube radius $R$. We show that a consistent description of the imbibition process in nanotubes is only possible upon modification of the Lucas-Washburn law which takes explicitly into account the slip length $\delta$.Comment: 4 pages 4 figure

Mesoscopic model for the fluctuating hydrodynamics of binary and ternary mixtures

A recently introduced particle-based model for fluid dynamics with continuous velocities is generalized to model immiscible binary mixtures. Excluded volume interactions between the two components are modeled by stochastic multiparticle collisions which depend on the local velocities and densities. Momentum and energy are conserved locally, and entropically driven phase separation occurs for high collision rates. An explicit expression for the equation of state is derived, and the concentration dependence of the bulk free energy is shown to be the same as that of the Widom-Rowlinson model. Analytic results for the phase diagram are in excellent agreement with simulation data. Results for the line tension obtained from the analysis of the capillary wave spectrum of a droplet agree with measurements based on the Laplace's equation. The introduction of "amphiphilic" dimers makes it possible to model the phase behavior and dynamics of ternary surfactant mixtures.Comment: 7 pages including 6 figure

Evolution of displacements and strains in sheared amorphous solids

The local deformation of two-dimensional Lennard-Jones glasses under imposed shear strain is studied via computer simulations. Both the mean squared displacement and mean squared strain rise linearly with the length of the strain interval $\Delta \gamma$ over which they are measured. However, the increase in displacement does not represent single-particle diffusion. There are long-range spatial correlations in displacement associated with slip lines with an amplitude of order the particle size. Strong dependence on system size is also observed. The probability distributions of displacement and strain are very different. For small $\Delta \gamma$ the distribution of displacement has a plateau followed by an exponential tail. The distribution becomes Gaussian as $\Delta \gamma$ increases to about .03. The strain distributions consist of sharp central peaks associated with elastic regions, and long exponential tails associated with plastic regions. The latter persist to the largest $\Delta \gamma$ studied.Comment: Submitted to J. Phys. Cond. Mat. special volume for PITP Conference on Mechanical Behavior of Glassy Materials. 16 Pages, 8 figure

Dissipative Particle Dynamics with Energy Conservation

The stochastic differential equations for a model of dissipative particle dynamics with both total energy and total momentum conservation in the particle-particle interactions are presented. The corresponding Fokker-Planck equation for the evolution of the probability distribution for the system is deduced together with the corresponding fluctuation-dissipation theorems ensuring that the ab initio chosen equilibrium probability distribution for the relevant variables is a stationary solution. When energy conservation is included, the system can sustain temperature gradients and heat flow can be modeled.Comment: 7 pages, submitted to Europhys. Let

Ontwikkeling signalering / vangsysteem voor schadelijke wantsen met lokstoffen en lokplanten": Onderzoek aan geurstoffen en lokplanten in laboratorium, veld en kassen

Referaat Behaarde wants, Lygus rugulipennis, en brandnetelwants, Liocoris tripustulatis, staan bekend als plagen in uiteenlopende kasgewassen waaronder paprika, komkommer, aubergine, chrysant. In het laboratorium is bepaald welke geurstoffen mogelijk bruikbaar zouden zijn om deze wantsen te monitoren met behulp van een val in combinatie met een geurstof. Tevens is een lijst van planten opgesteld, die aantrekkelijk zijn voor deze wantsen. Uit een keuzeproef met 16 plantensoorten in een kas bleek dat behaarde wants een voorkeur heeft voor kattenstaartamarant, zonnebloem, aardappel en tuinmelde boven de eerder genoemde gewassen. In een kasproef met 2000 m2 paprika werden zowel behaarde wantsen als brandnetel wantsen losgelaten gedurende 12 weken. Zowel deltavallen, als witte en blauwe signaalplaten werden opgehangen in combinatie met verschillende geurstoffen. Geen van deze combinaties van vallen en geurstoffen resulteerde in grote vangsten van de wantsen. Hoewel duizenden gekweekte wantsen werden losgelaten, trad geen schade op in het gewas.Na het loslaten vlogen wantsen niet naar het glas maar waren uren na het loslaten terug te vinden in de planten bij de loslaatpunten. Na een week waren nog enkele exemplaren op het loslaat punt aanwezig, maar in het gewas waren ze moeilijk te vinden. In de praktijk werden zowel behaarde wantsen als brandnetelwantsen verzameld in gewassen (paprika, aubergine, komkommer, gerbera) waarin schade optrad. Deze wantsen gaven op een jonge paprikaplant in een kooi geen schade. Het blijkt dat het optreden van wantsen en het al dan niet optreden van schade vragen oproept. Uit een vervolgstudie zou moeten blijken onder welke voorwaarden schade optreedt en wanneer niet. Abstract The tarnished plant bug, Lygus ruulipennis, and the coomon nettle capsid, Liocoris tripustulatis, are pests in a variety of crops in greenhouses, including sweet pepper, cucumber, eggplant and chrysantemum. Odours which were possibly attractive to the bugs were established in the laboratory.The aim was to find pheromones, which can be used in combination with a trap for monitoring the bugs.Further a list was composed of plants which are attractive for the bugs.From a choice test with 16 plant species it appeared that the tarnished plant bug us attrackted more to Amaranthus caudatus, Helianthus annuus, Sollanum tuburosum and Atriplex hortensis than to the greenhouse crops. In a greenhouse trial planted with 2000 m2 sweet pepper both tarnished plant bugs and common nettle capsids were introduced during a period of 12 weeks. Delta traps were installed and also white or blue sticky traps in combination with several lures. None of these combinations of traps and lures resulted in large catches of bugs. Although thousands of bugs were released, no symptoms were noticed in the crop. The bugs did not fly to the top of the grennhouse when they were released, but were presemt pn the plants near the releasing point for several hours. After a week some specimens were still present on the releasing point, but they were difficult to find in the crop. In commercial greenhouses both tarnished plant bugs and common nettle bugs were sampled in sweet pepper, egg plant, cucumber and gerbera were symptoms were present. These bugs did not cause any symptoms on a young sweet pepper plant in a cage. It is obvious that the occurrence of bugs and the showing or not-showing of symptoms raises questions. Further studies are necessary in order to reveal the conditions is which symptoms will occur or not

Particle-Based Mesoscale Hydrodynamic Techniques

Dissipative particle dynamics (DPD) and multi-particle collision (MPC) dynamics are powerful tools to study mesoscale hydrodynamic phenomena accompanied by thermal fluctuations. To understand the advantages of these types of mesoscale simulation techniques in more detail, we propose new two methods, which are intermediate between DPD and MPC -- DPD with a multibody thermostat (DPD-MT), and MPC-Langevin dynamics (MPC-LD). The key features are applying a Langevin thermostat to the relative velocities of pairs of particles or multi-particle collisions, and whether or not to employ collision cells. The viscosity of MPC-LD is derived analytically, in very good agreement with the results of numerical simulations.Comment: 7 pages, 2 figures, 1 tabl