786 research outputs found
Numerical solution of steady-state groundwater flow and solute transport problems: Discontinuous Galerkin based methods compared to the Streamline Diffusion approach
In this study, we consider the simulation of subsurface flow and solute
transport processes in the stationary limit. In the convection-dominant case,
the numerical solution of the transport problem may exhibit non-physical
diffusion and under- and overshoots. For an interior penalty discontinuous
Galerkin (DG) discretization, we present a -adaptive refinement strategy
and, alternatively, a new efficient approach for reducing numerical under- and
overshoots using a diffusive -projection. Furthermore, we illustrate an
efficient way of solving the linear system arising from the DG discretization.
In -D and -D examples, we compare the DG-based methods to the streamline
diffusion approach with respect to computing time and their ability to resolve
steep fronts
Discontinuous Galerkin based Geostatistical Inversion of Stationary Flow and Transport Processes in Groundwater
The hydraulic conductivity of a confined aquifer is estimated using the quasi-linear geostatistical approach (QLGA), based on measurements of dependent quantities such as the hydraulic head or the arrival time of a tracer. This requires the solution of the steady-state groundwater flow and solute transport equations, which are coupled by Darcy's law. The standard Galerkin finite element method (FEM) for the flow equation combined with the streamline diffusion method (SDFEM) for the transport equation is widely used in the hydrogeologists' community. This work suggests to replace the first by the two-point flux cell-centered finite volume scheme (CCFV) and the latter by the Discontinuous Galerkin (DG) method. The convection-dominant case of solute (contaminant) transport in groundwater has always posed a special challenge to numerical schemes due to non-physical oscillations at steep fronts. The performance of the DG method is experimentally compared to the SDFEM approach with respect to numerical stability, accuracy and efficient solvability of the occurring linear systems. A novel method for the reduction of numerical under- and overshoots is presented as a very efficient alternative to local mesh refinement. The applicability and software-technical integration of the CCFV/DG combination into the large-scale inversion scheme mentioned above is realized. The high-resolution estimation of a synthetic hydraulic conductivity field in a 3-D real-world setting is simulated as a showcase on Linux high performance computing clusters. The setup in this showcase provides examples of realistic flow fields for which the solution of the convection-dominant transport problem by the streamline diffusion method fails
Coordinated Container Migration and Base Station Handover in Mobile Edge Computing
Offloading computationally intensive tasks from mobile users (MUs) to a
virtualized environment such as containers on a nearby edge server, can
significantly reduce processing time and hence end-to-end (E2E) delay. However,
when users are mobile, such containers need to be migrated to other edge
servers located closer to the MUs to keep the E2E delay low. Meanwhile, the
mobility of MUs necessitates handover among base stations in order to keep the
wireless connections between MUs and base stations uninterrupted. In this
paper, we address the joint problem of container migration and base-station
handover by proposing a coordinated migration-handover mechanism, with the
objective of achieving low E2E delay and minimizing service interruption. The
mechanism determines the optimal destinations and time for migration and
handover in a coordinated manner, along with a delta checkpoint technique that
we propose. We implement a testbed edge computing system with our proposed
coordinated migration-handover mechanism, and evaluate the performance using
real-world applications implemented with Docker container (an
industry-standard). The results demonstrate that our mechanism achieves 30%-40%
lower service downtime and 13%-22% lower E2E delay as compared to other
mechanisms. Our work is instrumental in offering smooth user experience in
mobile edge computing.Comment: 6 pages. Accepted for presentation at the IEEE Global Communications
Conference (Globecom), Taipei, Taiwan, Dec. 202
Activation of the 2-5OAS/RNase L pathway in CVB1 or HAV/18f infected FRhK-4 cells does not require induction of OAS1 or OAS2 expression
AbstractThe latent, constitutively expressed protein RNase L is activated in coxsackievirus and HAV strain 18f infected FRhK-4 cells. Endogenous oligoadenylate synthetase (OAS) from uninfected and virus infected cell extracts synthesizes active forms of the triphosphorylated 2-5A oligomer (the only known activator of RNase L) in vitro and endogenous 2-5A is detected in infected cell extracts. However, only the largest OAS isoform, OAS3, is readily detected throughout the time course of infection. While IFNβ treatment results in an increase in the level of all three OAS isoforms in FRhK-4 cells, IFNβ pretreatment does not affect the temporal onset or enhancement of RNase L activity nor inhibit virus replication. Our results indicate that CVB1 and HAV/18f activate the 2-5OAS/RNase L pathway in FRhK-4 cells during permissive infection through endogenous levels of OAS, but contrary to that reported for some picornaviruses, CVB1 and HAV/18f replication is insensitive to this activated antiviral pathway
Slice-level Detection of Intracranial Hemorrhage on CT Using Deep Descriptors of Adjacent Slices
The rapid development in representation learning techniques such as deep
neural networks and the availability of large-scale, well-annotated medical
imaging datasets have to a rapid increase in the use of supervised machine
learning in the 3D medical image analysis and diagnosis. In particular, deep
convolutional neural networks (D-CNNs) have been key players and were adopted
by the medical imaging community to assist clinicians and medical experts in
disease diagnosis and treatment. However, training and inferencing deep neural
networks such as D-CNN on high-resolution 3D volumes of Computed Tomography
(CT) scans for diagnostic tasks pose formidable computational challenges. This
challenge raises the need of developing deep learning-based approaches that are
robust in learning representations in 2D images, instead 3D scans. In this
work, we propose for the first time a new strategy to train \emph{slice-level}
classifiers on CT scans based on the descriptors of the adjacent slices along
the axis. In particular, each of which is extracted through a convolutional
neural network (CNN). This method is applicable to CT datasets with per-slice
labels such as the RSNA Intracranial Hemorrhage (ICH) dataset, which aims to
predict the presence of ICH and classify it into 5 different sub-types. We
obtain a single model in the top 4% best-performing solutions of the RSNA ICH
challenge, where model ensembles are allowed. Experiments also show that the
proposed method significantly outperforms the baseline model on CQ500. The
proposed method is general and can be applied to other 3D medical diagnosis
tasks such as MRI imaging. To encourage new advances in the field, we will make
our codes and pre-trained model available upon acceptance of the paper.Comment: Accepted for presentation at the 22nd IEEE Statistical Signal
Processing (SSP) worksho
- …