Simulation of transport and deposition of nanoparticles in a gas phase by particle-Monte-Carlo and Lattice-Boltzmann methods

Die Arbeit behandelt ein numerisches Lösungskonzept zur Simulation der Transport und Depositionsvorgänge von Nanopartikeln in der Gasphase um komplexe Geometrien. Diese beinhalten neben der Geometrie eines beliebigen Faserfilters auch die Oberflächenänderungen infolge deponierter Partikel, die sehr unregelmäßige Dendritenähnliche Strukturen bilden. Die relativ einfache Behandlung solch komplexer Ränder ist ein Vorteil der Lattice-Boltzmann-(LBGK)-Methoden. Diese werden zur Lösung des Strömungsfeldes (Navier-Stokes-Gleichungen) und zur Lösung eines elektrostatischen oder magnetostatischen Potentials (Poisson-Gleichung) verwendet. Über externe Kräfte und Momente nehmen die so bestimmten Lösungen des Fluidfeldes und der Kraftpotentiale Einfluss auf die Translations- und die Rotationsbewegung der Partikel. Haben die Nanopartikel einen hinreichend kleinen Durchmesser spielt die zufallsverteilte Brownsche Bewegung, deren Ursache im Impulsaustausch der Partikel mit den Molekülen der Gasphase liegt, eine entscheidende Rolle. Die Trajektorien einzelner Partikel werden mit der Partikel-Monte-Carlo-Methode durch Integration der Langevin- Gleichungen sowohl für die Translations- als auch für die Rotationsbewegung bestimmt. In Oberflächennähe werden zusätzlich die dort wesentlichen Kräfte, z.B. die van-der-Waals-Kraft, berücksichtigt. Durch deponierte Partikel werden Wechselwirkungen zwischen den Phasen hervorgerufen. Sie ändern die Kontur der Oberfläche und somit den Verlauf der kontinuierlichen Felder, was wiederum zu einer Beeinflussung der nachfolgenden Partikeltrajektorien führt. Berücksichtigt wird dieser Vorgang durch eine iterative Prozedur zwischen beiden Lösungsverfahren.A numerical solution concept is presented for simulating the transport and deposition to surfaces of discrete nanoparticles. The motion of single particles is calculated from the Langevin equation by Lagrangian integration under consideration of different forces such as drag force, van-der-Waals forces, Coulomb force, magnetic force and not negligible for small particles, under stochastic diffusion (Brownian diffusion). This so called particle Monte-Carlo method enables the computation of macroscopic filter properties as well the detailed resolution of the structure of deposited particles. The external forces and torques depend on solutions of continuum equations. Solutions of these equations are computed here using Lattice-Boltzmann methods. Essential advantage of this methods are the easy and efficient treatment of three-dimensional complex geometries, given by filter geometries or particle covered surfaces. The interaction between the deposited particle layer and the external fields is included by recomputing of these fields with changed boundaries

Vorticity Confinement methods for cavitating flows

Present work deals with investigations of numerical aspects of cavitating vortex dominated flows. Computations of the viscous flow on realistic, technical configurations require efficient methods and high grid resolution, which is not sufficient in most cases to capture important details of the flow. Insufficient resolution increases the numerical dissipation of vortices generated at the tip region of lifting surfaces. One possible solution to reduce the unphysical decay of the strength of the vortices (despite of moderate resolution) is the application of vorticity confinement methods. Aim of the paper is the development and the comparison of Vorticity Confinement (VC) methods for cavitating flows on unstructured grids. Applications are proposed to control devices and marine propulsion systems. The numerical dissipation of vortices is compared for different VC formulations. Especially the influence of the source terms on cavitating flows is investigated. The numerical computations are carried out by the finite volume solution method FreSCo on arbitrary grids. In the study vorticity confinement techniques are combined with different cavitation models available in the applied numerical method to investigate tip vortex flow. The cavitation models are based on Volume-of-Fluid (VoF). A NACA16020 elliptical wing is selected as a validation case. The combination of vorticity confinement formulations and cavitation models enables a better and a more detailed study of cavitation effects.http://deepblue.lib.umich.edu/bitstream/2027.42/84314/1/CAV2009-final139.pd

Relation between activity‐induced intracellular sodium transients and ATP dynamics in mouse hippocampal neurons

Excitatory neuronal activity results in the influx of Na+ through voltage- and ligand-gated channels. Recovery from accompanying increases in intracellular Na+ concentrations ([Na+]i) is mainly mediated by the Na+/K+-ATPase (NKA) and is one of the major energy-consuming processes in the brain. Here, we analysed the relation between different patterns of activity-induced [Na+]i signalling and ATP in mouse hippocampal CA1 pyramidal neurons by Na+ imaging with sodium-binding benzofurane isophthalate (SBFI) and employing the genetically encoded nanosensor ATeam1.03YEMK (ATeam). In situ calibrations demonstrated a sigmoidal dependence of the ATeam Förster resonance energy transfer ratio on the intracellular ATP concentration ([ATP]i) with an apparent KD of 2.6 mm, indicating its suitability for [ATP]i measurement. Induction of recurrent network activity resulted in global [Na+]i oscillations with amplitudes of ∼10 mm, encompassing somata and dendrites. These were accompanied by a steady decline in [ATP]i by 0.3–0.4 mm in both compartments. Global [Na+]i transients, induced by afferent fibre stimulation or bath application of glutamate, caused delayed, transient decreases in [ATP]i as well. Brief focal glutamate application that evoked transient local Na+ influx into a dendrite, however, did not result in a measurable reduction in [ATP]i. Our results suggest that ATP consumption by the NKA following global [Na+]i transients temporarily overrides its availability, causing a decrease in [ATP]i. Locally restricted Na+ transients, however, do not result in detectable changes in local [ATP]i, suggesting that ATP production, together with rapid intracellular diffusion of both ATP and Na+ from and to unstimulated neighbouring regions, counteracts a local energy shortage under these conditions

E3L and F1L Gene Functions Modulate the Protective Capacity of Modified Vaccinia Virus Ankara Immunization in Murine Model of Human Smallpox

The highly attenuated Modified Vaccinia virus Ankara (MVA) lacks most of the known vaccinia virus (VACV) virulence and immune evasion genes. Today MVA can serve as a safety-tested next-generation smallpox vaccine. Yet, we still need to learn about regulatory gene functions preserved in the MVA genome, such as the apoptosis inhibitor genes F1L and E3L. Here, we tested MVA vaccine preparations on the basis of the deletion mutant viruses MVA-F1L and MVA-E3L for efficacy against ectromelia virus (ECTV) challenge infections in mice. In non-permissive human tissue culture the MVA deletion mutant viruses produced reduced levels of the VACV envelope antigen B5. Upon mousepox challenge at three weeks after vaccination, MVA-F1L and MVA-E3L exhibited reduced protective capacity in comparison to wildtype MVA. Surprisingly, however, all vaccines proved equally protective against a lethal ECTV infection at two days after vaccination. Accordingly, the deletion mutant MVA vaccines induced high levels of virus-specific CD8+ T cells previously shown to be essential for rapidly protective MVA vaccination. These results suggest that inactivation of the anti-apoptotic genes F1L or E3L modulates the protective capacity of MVA vaccination most likely through the induction of distinct orthopoxvirus specific immunity in the absence of these viral regulatory proteins

Gcn5 facilitates Pol II progression, rather than recruitment to nucleosome-depleted stress promoters, in Schizosaccharomyces pombe

In the fission yeast, the MAP kinase Sty1 and the transcription factor Atf1 regulate up to 400 genes in response to environmental signals, and both proteins have been shown to bind to their promoters in a stress-dependent manner. In a genetic search, we have isolated the histone H3 acetyltransferase Gcn5, a component of the SAGA complex, as being essential for oxidative stress survival and activation of those genes. Upon stress, Gcn5 is recruited to promoters and coding sequences of stress genes in a Sty1- and Atf1-dependent manner, causing both an enhanced acetylation of histone H3 and nucleosome eviction. Unexpectedly, recruitment of RNA polymerase II (Pol II) is not impaired in Δgcn5 cells. We show here that stress genes display a 400-bp long nucleosome depleted region upstream of the transcription start site even prior to activation. Stress treatment does not alter promoter nucleosome architecture, but induces eviction of the downstream nucleosomes at stress genes, which is not observed in Δgcn5 cells. We conclude that, while Pol II is recruited to nucleosome-free stress promoters in a transcription factor dependent manner, Gcn5 mediates eviction of nucleosomes positioned downstream of promoters, allowing efficient Pol II progression along the genes