61 research outputs found
Seismic site effects in a deep alluvial basin: numerical analysis by the boundary element method
The main purpose of the paper is the numerical analysis of seismic site
effects in Caracas (Venezuela). The analysis is performed considering the
boundary element method in the frequency domain. A numerical model including a
part of the local topography is considered, it involves a deep alluvial deposit
on an elastic bedrock. The amplification of seismic motion (SH-waves, weak
motion) is analyzed in terms of level, occurring frequency and location. In
this specific site of Caracas, the amplification factor is found to reach a
maximum value of 25. Site effects occur in the thickest part of the basin for
low frequencies (below 1.0 Hz) and in two intermediate thinner areas for
frequencies above 1.0 Hz. The influence of both incidence and shear wave
velocities is also investigated. A comparison with microtremor recordings is
presented afterwards. The results of both numerical and experimental approaches
are in good agreement in terms of fundamental frequencies in the deepest part
of the basin. The boundary element method appears to be a reliable and
efficient approach for the analysis of seismic site effects
Numerical analysis of seismic wave amplification in Nice (France) and comparisons with experiments
The analysis of site effects is very important since the amplification of
seismic motion in some specific areas can be very strong. In this paper, the
site considered is located in the centre of Nice on the French Riviera. Site
effects are investigated considering a numerical approach (Boundary Element
Method) and are compared to experimental results (weak motion and
microtremors). The investigation of seismic site effects through numerical
approaches is interesting because it shows the dependency of the amplification
level on such parameters as wave velocity in surface soil layers, velocity
contrast with deep layers, seismic wave type, incidence and damping. In this
specific area of Nice, a one-dimensional (1D) analytical analysis of
amplification does not give a satisfactory estimation of the maximum reached
levels. A boundary element model is then proposed considering different wave
types (SH, P, SV) as the seismic loading. The alluvial basin is successively
assumed as an isotropic linear elastic medium and an isotropic linear
viscoelastic solid (standard solid). The thickness of the surface layer, its
mechanical properties, its general shape as well as the seismic wave type
involved have a great influence on the maximum amplification and the frequency
for which it occurs. For real earthquakes, the numerical results are in very
good agreement with experimental measurements for each motion component.
Two-dimensional basin effects are found to be very strong and are well
reproduced numerically
Multi-level fast multipole BEM for 3-D elastodynamics
To reduce computational complexity and memory requirement for 3-D elastodynamics using the boundary element method (BEM), a multi-level fast multipole BEM (FM-BEM) based on the diagonal form for the expansion of the elastodynamic fundamental solution is proposed and demonstrated on numerical examples involving single-region and multi-region configurations where the scattering of seismic waves by a topographical irregularity or a sediment-filled basin is examined
Clusterin Is Required for ÎČ-Amyloid Toxicity in Human iPSC-Derived Neurons
Our understanding of the molecular processes underlying Alzheimerâs disease (AD) is still limited, hindering the development of effective treatments, and highlighting the need for human-specific models. Advances in identifying components of the amyloid cascade are progressing, including the role of the protein clusterin in mediating ÎČ-amyloid (AÎČ) toxicity. Mutations in the clusterin gene (CLU), a major genetic AD risk factor, are known to have important roles in AÎČ processing. Here we investigate how CLU mediates AÎČ-driven neurodegeneration in human induced pluripotent stem cell (iPSC)-derived neurons. We generated a novel CLU-knockout iPSC line by CRISPR/Cas9-mediated gene editing to investigate AÎČ-mediated neurodegeneration in cortical neurons differentiated from wild type and CLU knockout iPSCs. We measured response to AÎČ using an imaging assay and measured changes in gene expression using qPCR and RNA sequencing. In wild type neurons imaging indicated that neuronal processes degenerate following treatment with AÎČ25-35 peptides and AÎČ1-42 oligomers, in a dose dependent manner, and that intracellular levels of clusterin are increased following AÎČ treatment. However, in CLU knockout neurons AÎČ exposure did not affect neurite length, suggesting that clusterin is an important component of the amyloid cascade. Transcriptomic data were analyzed to elucidate the pathways responsible for the altered response to AÎČ in neurons with the CLU deletion. Four of the five genes previously identified as downstream to AÎČ and Dickkopf-1 (DKK1) proteins in an AÎČ-driven neurotoxic pathway in rodent cells were also dysregulated in human neurons with the CLU deletion. AD and lysosome pathways were the most significantly dysregulated pathways in the CLU knockout neurons, and pathways relating to cytoskeletal processes were most dysregulated in AÎČ treated neurons. The absence of neurodegeneration in the CLU knockout neurons in response to AÎČ compared to the wild type neurons supports the role of clusterin in AÎČ-mediated AD pathogenesis
On-chip pressure measurements and channel deformation after oil absorption
Microfluidic channels moulded from the soft polymer poly(dimethylsiloxane) (PDMS) are widely used as a platform for mimicking biological environments, and can be used for the simulation of fluid filled structures such as blood and lung vessels. The control of pressure and flow rate within these structures is vital to mimic physiological conditions. The flexibility of PDMS leads to pressure-induced deformation under flow, leading to variable flow profiles along a device. Here, we investigate the change in Youngâs modulus of microfluidic channels due to infiltration of mineral oil, a PDMS permeable fluid, and how this affects the resulting pressure profile using a novel pressure measurement method. We found a 53% decrease in Youngâs modulus of PDMS due to mineral oil absorption over the course of 3 h accounted for lower internal pressure and larger channel deformation compared to fresh PDMS at a given flow rate. Confocal fluorescence microscopy used to image channel profiles before and after the introduction of mineral oil showed a change in pressure-induced deformation after infiltration of the oil. Atomic force microscopy (AFM) nanoindentation was used to measure Youngâs modulus of PDMS before (2.80±0.032.80±0.03 MPa) and after (1.32±0.041.32±0.04 MPa) mineral oil absorption. Raman spectroscopy showed the infiltration of mineral oil into PDMS from channel walls and revealed the diffusion coefficient of mineral oil in PDMS
Compact ECL gate design for double mesa HBT process
Emitter Coupled Logic (ECL) gate is a good candidate for gigabit logic when one uses GaAs/GaAlAs Heterojunction Bipolar Transistor (HBT). With the double mesa process, interconÂnections between the 5 transistors of the elemental gate have to climb the emitter and base mesas, leading to lack of density. A more compact design of the ECL gate has been achieved, in which the transistors are directly connected on the top of the base mesa. The DC characteristics of this gate are similar to these obtained with conventional gate design and the surface is reduced by a factor 1.6
A Poromechanical Model for Coal Seams Injected with Carbon Dioxide: From an Isotherm of Adsorption to a Swelling of the Reservoir Un modĂ©le poromĂ©canique pour lâinjection de dioxyde de carbone dans des veines de charbon : dâune isotherme dâadsorption Ă un gonflement du rĂ©servoir
Injecting carbon dioxide into deep unminable coal seams can enhance the amount of methane recovered from the seam. This process is known as CO2-Enhanced Coal Bed Methane production (CO2-ECBM). The seam is a porous medium whose porous system is made of cleats (small natural fractures) and of coal pores (whose radius can be as small as a few angström). During the injection process, the molecules of CO2 get adsorbed in the coal pores. Such an adsorption makes the coal swell, which, in the confined conditions that prevail underground, induces a closure of the cleat system of the coal bed reservoir and a loss of injectivity. In this work, we develop a poromechanical model which, starting from the knowledge of an adsorption isotherm and combined with reservoir simulations, enables to estimate the variations of injectivity of the coal bed reservoir over time during the process of injection. The model for the coal bed reservoir is based on poromechanical equations that explicitly take into account the effect of adsorption on the mechanical behavior of a microporous medium. We consider the coal bed reservoir as a dual porosity (cleats and coal porosity) medium, for which we derive a set of linear constitutive equations. The model requires as an input the adsorption isotherm on coal of the fluid considered. Reversely, the model provides a way to upscale an adsorption isotherm into a meaningful swelling of the coal bed reservoir at the macroscopic scale. The parameters of the model are calibrated on data on coal samples available in the literature. Reservoir simulations of an injection of carbon dioxide in a coal seam are performed with an in-house finite volume and element code. The variations of injection rate over time during the process of injection are obtained from the simulations. The effect of the compressibility of the coal matrix on those variations is discussed. Lâinjection de dioxyde de carbone dans des veines de charbon profondes peut augmenter la quantitĂ© de mĂ©thane rĂ©cupĂ©rĂ©e de ces veines. Ce processus de production de mĂ©thane est appelĂ© CO2-ECBM (Enhanced Coal Bed Methane). La veine est un milieu poreux dont le rĂ©seau poreux est constituĂ© de fissures et des pores de la matrice de charbon (ces pores pouvant ĂȘtre aussi petits que quelques Angströms). Pendant le processus dâinjection, les molĂ©cules de CO2 sont adsorbĂ©es dans les pores de la matrice de charbon, ce qui la fait gonfler. Un tel gonflement conduit, dans les conditions de confinement qui prĂ©valent sous terre, Ă une fermeture du systĂšme de fissures de la veine rĂ©servoir et par consĂ©quent Ă une baisse de lâinjectivitĂ©. Dans ce travail, nous dĂ©veloppons un modĂšle poromĂ©canique qui, Ă partir dâune utilisation dâisothermes dâadsorption dans des simulations Ă lâĂ©chelle du rĂ©servoir, permet dâestimer les variations dâinjectivitĂ© de la veine rĂ©servoir au cours du temps pendant le processus dâinjection. Le modĂšle pour la veine rĂ©servoir est basĂ© sur des Ă©quations poromĂ©caniques qui prennent explicitement en compte lâeffet de lâadsorption sur le comportement mĂ©canique dâun milieu microporeux. Nous considĂ©rons la veine rĂ©servoir comme un systĂšme Ă double porositĂ© (fissures et porositĂ© du charbon), pour lequel nous dĂ©rivons un ensemble dâĂ©quations constitutives linĂ©aires. Le modĂšle nĂ©cessite en entrĂ©e lâisotherme dâadsorption sur le charbon du fluide considĂ©rĂ©. Inversement, le modĂšle permet de transformer une isotherme dâadsorption en un gonflement ayant un sens Ă lâĂ©chelle macroscopique de la veine rĂ©servoir. Les paramĂštres du modĂšle sont calibrĂ©s sur des donnĂ©es expĂ©rimentales dâadsorption sur des charbons. Des simulations dâinjection de dioxyde de carbone dans une veine de charbon sont exĂ©cutĂ©es avec un logiciel aux Ă©lĂ©ments et volumes finis dĂ©veloppĂ© en interne. Ainsi, les variations de taux dâinjection pendant le processus dâinjection sont obtenues. Lâinfluence de la compressibilitĂ© de la matrice de charbon sur ces variations est discutĂ©e
- âŠ