Is cell-to-cell scale variability necessary in reservoir models?

Reservoir models typically contain hundreds-of-thousands to millions of grid cells in which petrophysical properties such as porosity and permeability vary on a cell-to-cell basis. However, although the petrophysical properties of rocks do vary on a point-to-point basis, this variability is not equivalent to the cell-to-cell variations in models. We investigate the impact of removing cell-to-cell variability on predictions of fluid flow in reservoir models. We remove cell-to-cell variability from models containing hundreds of thousands of unique porosity and permeability values to yield models containing just a few tens of unique porosity and permeability values grouped into a few internally homogeneous domains. The flow behavior of the original model is used as a reference. We find that the impact of cell-to-cell variability on predicted flow is small. Cell-to-cell variability is not necessary to capture flow in reservoir models; rather, it is the spatially correlated variability in petrophysical properties that is important. Reservoir modelling effort should focus on capturing correlated geologic domains in the most realistic and computationally efficient manner

Human-like PB2 627K Influenza Virus Polymerase Activity Is Regulated by Importin-α1 and -α7

Influenza A viruses may cross species barriers and transmit to humans with the potential to cause pandemics. Interplay of human- (PB2 627K) and avian-like (PB2 627E) influenza polymerase complexes with unknown host factors have been postulated to play a key role in interspecies transmission. Here, we have identified human importin-α isoforms (α1 and α7) as positive regulators of human- but not avian-like polymerase activity. Human-like polymerase activity correlated with efficient recruitment of α1 and α7 to viral ribonucleoprotein complexes (vRNPs) without affecting subcellular localization. We also observed that human-like influenza virus growth was impaired in α1 and α7 downregulated human lung cells. Mice lacking α7 were less susceptible to human- but not avian-like influenza virus infection. Thus, α1 and α7 are positive regulators of human-like polymerase activity and pathogenicity beyond their role in nuclear transport

Influenza Polymerase Activity Correlates with the Strength of Interaction between Nucleoprotein and PB2 through the Host-Specific Residue K/E627

The ribonucleoprotein (RNP) complex is the essential transcription-replication machinery of the influenza virus. It is composed of the trimeric polymerase (PA, PB1 and PB2), nucleoprotein (NP) and RNA. Elucidating the molecular mechanisms of RNP assembly is central to our understanding of the control of viral transcription and replication and the dependence of these processes on the host cell. In this report, we show, by RNP reconstitution assays and co-immunoprecipitation, that the interaction between NP and polymerase is crucial for the function of the RNP. The functional association of NP and polymerase involves the C-terminal ‘627’ domain of PB2 and it requires NP arginine-150 and either lysine-627 or arginine-630 of PB2. Using surface plasmon resonance, we demonstrate that the interaction between NP and PB2 takes place without the involvement of RNA. At 33, 37 and 41°C in mammalian cells, more positive charges at aa. 627 and 630 of PB2 lead to stronger NP-polymerase interaction, which directly correlates with the higher RNP activity. In conclusion, our study provides new information on the NP-PB2 interaction and shows that the strength of NP-polymerase interaction and the resulting RNP activity are promoted by the positive charges at aa. 627 and 630 of PB2

Activation of Type I and III Interferon Signalling Pathways Occurs in Lung Epithelial Cells Infected with Low Pathogenic Avian Influenza Viruses

The host response to the low pathogenic avian influenza (LPAI) H5N2, H5N3 and H9N2 viruses were examined in A549, MDCK, and CEF cells using a systems-based approach. The H5N2 and H5N3 viruses replicated efficiently in A549 and MDCK cells, while the H9N2 virus replicated least efficiently in these cell types. However, all LPAI viruses exhibited similar and higher replication efficiencies in CEF cells. A comparison of the host responses of these viruses and the H1N1/WSN virus and low passage pH1N1 clinical isolates was performed in A549 cells. The H9N2 and H5N2 virus subtypes exhibited a robust induction of Type I and Type III interferon (IFN) expression, sustained STAT1 activation from between 3 and 6 hpi, which correlated with large increases in IFN-stimulated gene (ISG) expression by 10 hpi. In contrast, cells infected with the pH1N1 or H1N1/WSN virus showed only small increases in Type III IFN signalling, low levels of ISG expression, and down-regulated expression of the IFN type I receptor. JNK activation and increased expression of the pro-apoptotic XAF1 protein was observed in A549 cells infected with all viruses except the H1N1/WSN virus, while MAPK p38 activation was only observed in cells infected with the pH1N1 and the H5 virus subtypes. No IFN expression and low ISG expression levels were generally observed in CEF cells infected with either AIV, while increased IFN and ISG expression was observed in response to the H1N1/WSN infection. These data suggest differences in the replication characteristics and antivirus signalling responses both among the different LPAI viruses, and between these viruses and the H1N1 viruses examined. These virus-specific differences in host cell signalling highlight the importance of examining the host response to avian influenza viruses that have not been extensively adapted to mammalian tissue culture

Nonlinear domain decomposition scheme for sequential fully implicit formulation of compositional multiphase flow

New sequential fully implicit (SFI) methods for compositional flow simulation have been recently investigated. These SFI schemes decouple the fully coupled problem into separate pressure and transport problems and have convergence properties comparable with those of the fully implicit (FI) method. The pressure system is a parabolic problem with fixed overall compositions and the transport system is a hyperbolic problem with fixed pressure and total velocity. We discuss some aspects of how to design optimal SFI schemes for compositional flow with general equation-of-states by localizing the computations. The different systems are solved sequentially and the fully implicit solution is recovered by controlling the a posteriori splitting errors due to the choice of decoupling. When the parabolic and the hyperbolic operators are separated, it is possible to design nonlinear domain decomposition schemes taking the advantage of the specific properties of each operator. Usually, for reservoir simulation models, most of the reservoir is converged with SFI methods in one outer iteration. However, in some localized regions with strong coupling between the pressure and the compositions, the SFI algorithms may need several outer iterations. Here, we propose a domain decomposition method based on a predictor-corrector strategy. As a first step, the nonlinear parabolic pressure equation is solved on the whole domain with the Multiscale Restriction-Smooth Basis (MsRSB) method used as a linear domain decomposition solver. In a second step, the compositions system is solved. At the end of this first outer iteration, most of the reservoir is converged. Based on a posteriori splitting errors of the SFI scheme in volume and velocity, we define local regions where additional global outer iterations would be required in the conventional SFI scheme. We then fix Dirichlet boundary conditions for the pressure and the compositions and solve local problems in these non converged regions. After convergence of these smaller nonlinear problems, if the boundary conditions are changed by the updated regions, the global pressure problem is revisited. An additional post-processing of local transport iterations makes sure mass is conserved everywhere. The resulting algorithm converges to the same solution as the FI solver, with all simultaneous updates to composition and pressure in localized regions. We demonstrate the robustness of this nonlinear domain decomposition algorithm across a wide parameter range. Realistic compositional models with gas and water injection are presented and discussed

Er3+ → Ho3+ energy transfer mechanisms at room temperature in YLiF4 single crystals

A detailed analysis of the energy transfer processes between Er3+ sensitizer ions and Ho3+ activator ions in YLiF4 : Er3+ , Ho3+ single crystals is reported. This study is carried out at room temperature on materials having different Ho3+ concentrations and for various selective laser excitations in the excited states of Er3+ in the visible and in the infrared optical regions. Emphasis is laid on the relative importance of the main channels of excitation of the 5I7 level of Ho3+ which is the initial state of the 5I7 → 5I8 transition of interest for the characteristic 2 μm laser emission.On présente une analyse détaillée des processus de transfert d'énergie entre les ions sensibilisateurs Er3+ et activateurs Ho3+ dans des monocristaux YLiF4 : Er3+ , Ho 3+ . Cette étude est réalisée à température ambiante sur des matériaux diversement concentrés en ions Ho3+ et utilisant différentes excitations laser dans les états excités de Er3+ situés dans les domaines optiques visible et proche infra-rouge. L'accent est mis sur l'importance relative des principales voies d'excitation du niveau 5I7 de Ho3+ qui constitue l'état initial de la transition 5I7 → 5I8 intéressante pour l'émission laser caractéristique vers 2 μm

Excited-state dynamics of the Tm3+ ions and Tm3+ → Ho3+ energy transfers in LiYF4

The excited-state dynamics of the Tm3+ ions in a singly doped crystal of LiYF4 is analysed. The Stokes fluorescence processes are interpreted by taking into account the numerous coincidences between the fluorescences emitted by the Tm3+ ions and by considering two kinds of sites. The anti-Stokes fluorescence dynamics which are more complicated are only briefly described. The Tm3+ → Ho3+ energy transfers are then analysed in codoped systems. Very efficient 3F 4 → 5I7 energy transfers are reported at room temperature whereas the 5I7 → 3F 4 back-transfer is completely quenched at low temperatures (T < 200 K ). When the Tm3+ ions are excited in their 3H 4 level, it is shown that three channels of de-excitation have to be considered : a Tm3+ intra-center de-excitation, a cross-relaxation process between adjacent Tm3+ ions of type 3H 4, 3H6 → 3F4, 3F4 and a direct Tm3+ → Ho3+ energy transfer. The former mechanism is very weak while the other two compete, the latter being largely dominant at high Ho3+ concentrations.La dynamique des états excités de LiYF4 faiblement dopé en ions Tm3+ est tout d'abord analysée. Les processus de fluorescence Stokes sont interprétés en tenant compte des nombreuses coïncidences entre les fluorescences émises par les ions Tm3+ et en considérant deux types de sites. Plus compliquée, la dynamique de fluorescence anti-Stokes est décrite seulement très brièvement. Les transferts d'énergie Tm3+ ⇄ Ho3+ sont ensuite étudiés dans des systèmes codopés. Des transferts 3F4 → 5I 7 très efficaces à température ambiante sont rapportés alors que le transfert retour 5I7 → 3F4 disparaît complètement aux basses températures (T < 200 K). Lorsque les ions Tm3+ sont excités dans leur niveau 3H 4, on montre que trois voies de désexcitation sont possibles : une désexcitation à l'intérieur d'un même centre Tm3+, une relaxation croisée entre ions Tm3+ adjacents du type 3H 4 , 3H6 → 3F4, 3F4 et un transfert direct Tm3+ → Ho 3+. Le premier mécanisme est très faible et les deux autres sont en compétition, le dernier dominant largement à haute concentration en ions Ho3+

Excited-state absorption and fluorescence dynamics of Er3+Er^{3+}:KY3KY_{3}F10F_{10}

International audienceWe report here on a complete investigation of the excited-state absorption and fluorescence dynamics of $Er^{3+}$ doped $KY_{3}$$F_{10}$ single crystals versus dopant concentrations and optical excitation conditions. Radiative and effective (including non-radiative relaxations) emission lifetimes and branching ratios are determined from a Judd-Ofelt analysis of the absorption spectra and via specific fluorescence experiments using wavelength selective laser excitations. Excited-state absorption and emission spectra are registered within seven spectral domains, i.e. 560 nm, 650 nm, 710 nm, 810 nm, 970 nm, 1550 nm and 2750 nm. A maximum gain cross-section of 0.93 × $10^{−21}$ $cm^{2}$ is determined at the potential laser wavelength of 2.801 μm for a population ratio of 0.48. Saturation of fluorescence intensities and variations of population ratios versus pumping rates are registered and confronted with a rate equation model to derive the rates of the most important up-conversion and cross-relaxation energy transfers occurring at high dopant concentrations

Mutual quenching of Er3+ photolurninescence under two laser excitation in GaN : Er

Erbium photoluminescence in GaN:Er was studied with above-band-gap excitation, provided by a He-Cd (lambda = 325 nm) laser and below-band-gap excitation by a tunable Ti-Sa laser. The spectra obtained with these two lasers exhibit different spectral shapes. When both lasers are used at the same time, we observe that the Er3+ photoluminescence induced by each of the lasers is partly quenched by the illumination of the other laser. In this experiment, one of the lasers is modulated and a lockin amplifier is used to filter the corresponding photoluminescence signal. The spectra recorded this way are found to be linear combinations of spectra obtained with each of the lasers used separately. This effect is explained by the presence of defects mediating the excitation towards the Er3+ ions. These defects act as electron traps, which can be populated by one specific laser excitation and are photo-ionized by the other laser leading to a large quenching of Er3+ emission. (C) 2004 Elsevier Ltd. All rights reserved