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Flow in discrete networks can be observed in biological, geological, or technical systems. Often, the number of individual segments is very large. Therefore, discrete pressure and flow calculation in each single segment becomes very time consuming, and a continuum model becomes attractive. We apply a global upscaling method based on a spatial average to investigate a porous media network model with heterogeneous pore length distribution. For this purpose, the porous media was modeled by triangular networks. For such networks, we characterize the representative elementary volume (REV) size and show that using window sizes smaller than the REV requires an heterogeneous Darcian description. We find that the permeability has to be distributed according to a log-Gaussian distribution with variance and correlation length depending on the window size and the porous microstructure. Finally, we apply the procedure to an anisotropic regular network for which an analytical solution can be found and show that using this method leads to the correct analytical behavior. DOI: 10.1061/(ASCE)0733-9429(2008)134:6(784) CE Database subject headings: Porous media; Hydraulic networks; Heterogeneity.

A viscous lock-exchange gravity current corresponds to the reciprocal exchange of two fluids of different densities in a horizontal channel. The resulting front between the two fluids spreads as the square root of time, with a diffusion coefficient reflecting the buoyancy, viscosity, and geometrical configuration of the current. On the other hand, an autocatalytic reaction front between a reactant and a product may propagate as a solitary wave, namely, at a constant velocity and with a stationary concentration profile, resulting from the balance between molecular diffusion and chemical reaction. In most systems, the fluid left behind the front has a different density leading to a lock-exchange configuration. We revisit, with a chemical reaction, the classical situation of lock-exchange. We present an experimental analysis of buoyancy effects on the shape and the velocity of the iodate arsenous acid autocatalytic reaction fronts, propagating in horizontal rectangular channels and for a wide range of aspect ratios (1/3 to 20) and cylindrical tubes. We do observe stationary-shaped fronts, spanning the height of the cell and propagating along the cell axis. Our data support the contention that the front velocity and its extension are linked to each other and that their variations scale with a single variable involving the diffusion coefficient of the lock-exchange in the absence of chemical reaction. This analysis is supported by results obtained with lattice Bathnagar-Gross-Krook (BGK) simulations Jarrige et al. [Phys. Rev. E 81, 06631 (2010)], in other geometries (like in 2D simulations by Rongy et al. [J. Chem. Phys. 127, 114710 (2007)] and experiments in cylindrical tubes by Pojman et al. [J. Phys. Chem. 95, 1299 (1991)]), and for another chemical reaction Schuszter et al. [Phys. Rev. E 79, 016216 (2009)]. [ABSTRACT FROM AUTHOR]

We address the issue of the convective or absolute nature of the instability of core-annular pipe flows, in experiments using two miscible fluids of equal density but different viscosities, the core fluid being much less viscous than the wall one. We use a concentric co-current injection of the two fluids. An axisymmetric parallel base state is obtained downstream the injector. The core radius R -I and the Reynolds number Re of the so-obtained base state are varied independently due to the control of the flow rate of each fluid. However, a downstream destabilization of this base state was observed within the explored range of the two control parameters R-I and Re . Moreover, the fixed location of this destabilization, observed for some particular parameters, suggests an absolute nature of the instability. We present a tentative delineation of the nature (convective or absolute) of the instability and discuss the accessible measurements to experimentally address this issue. [ABSTRACT FROM AUTHOR]

We report on experiments with two miscible fluids of equal density but different viscosities. The fluids were injected co-currently and concentrically into a cylindrical pipe. The resulting base state is an axisymmetric parallel flow. The ratio of the two fluid flow rates determines the relative amount of the fluids, thus the radius of the inner core fluid. Depending on this radius and the total flow rate, two different and unstable axisymmetric patterns, denoted by mushrooms and pearls, were observed. We delineate the diagram of occurrence of the two patterns as a function of the various parameters. [ABSTRACT FROM AUTHOR]

Background: The incidence of cardiovascular diseases is increasing in persons with hemophilia A (HA). Therefore, anticoagulant therapy based on direct oral anticoagulants (DOACs) may be needed, despite the bleeding risk. In case of surgery or bleeding, such patients may be concomitantly treated with emicizumab (routine prophylaxis), factor (F)VIII products, and DOAC. Their concomitant presence constitutes a hemostatic challenge. Recent international guidelines stated that data are scarce on the hemostatic balance of plasma samples from patients with HA receiving emicizumab and DOAC., Objectives: The aim of this observational study was to assess the coagulation of FVIII-deficient plasma spiked with DOAC and emicizumab and to evaluate the effects of FVIII addition., Methods: Prothrombin time, activated partial thromboplastin time, and thrombin generation (TG) using the calibrated automated thrombogram method were evaluated in aliquots of a commercial severe HA plasma supplemented with emicizumab (0, 12.5, 25, 50, and 100 ng/mL), DOAC (0, 50, 100, 200, and 400 ng/mL of apixaban, rivaroxaban, edoxaban, or dabigatran) and FVIII (0%, 5%, 15%, 50%, and 100%)., Results: DOAC rapidly induced a TG decrease. Emicizumab could counter this effect only for the lowest DOAC dose. FVIII addition to the FVIII-deficient plasma containing a DOAC and emicizumab improved TG and countered the anticoagulant effect of DOAC at ≤100 ng/mL., Conclusion: Our findings indicate that FVIII can be safely used with emicizumab to counter the anticoagulant effect of DOAC at ≤100 ng/mL. The TG assay is an efficient tool to monitor plasma containing anti-FXa DOAC, but not dabigatran (anti-FIIa)., (© 2024 The Authors.)

Point-of-care testing (POCT) for D-dimer is an alternative to -laboratory testing for the exclusion of venous thromboembolism (VTE). This critical review by the "CEC et biologie délocalisée" working group of the "Société Française de Thrombose et d'Hémostase" (French Society of -Thrombosis and Haemostasis) aims to present the characteristics of six POCT D-dimer assays available in France in 2023. The article highlights the need to define VTE -exclusion thresholds specific to each technique and validated by clinical studies. There is insufficient data to validate the use of cut off suggested by manufacturers, and age-adjusted thresholds. The article discusses the role of laboratories in justifying and prescribing POCT D-dimer, according to objective criteria, such as the availability and turnaround time of classical laboratory tests. They should also encourage rational prescribing, limited to patients with low risk of venous thromboembolism, following an assessment of clinical probability according to national and international guidelines.

Understanding the flow of yield stress fluids in porous media is a major challenge. In particular, experiments and extensive numerical simulations report a nonlinear Darcy law as a function of the pressure gradient. In this letter we consider a treelike porous structure for which the problem of the flow can be resolved exactly due to a mapping with the directed polymer (DP) with disordered bond energies on the Cayley tree. Our results confirm the nonlinear behavior of the flow and expresses its full pressure dependence via the density of low-energy paths of DP restricted to vanishing overlap. These universal predictions are confirmed by extensive numerical simulations.

Background: Patients with cirrhosis are at high risk of thrombotic events, including portal vein thrombosis and venous thromboembolism. In such patients, hypercoagulability is not detected by conventional coagulation tests, but only by the thrombin generation assay (TGA) that integrates the role of pro- and anticoagulant factors. However, TGA use to predict clinical events depends on thrombin generation variability over time., Objectives: The aim of this study was to compare TGA intraindividual variability over time in patients with cirrhosis and in healthy controls., Methods: Blood samples were prospectively collected from 34 healthy controls and 52 patients with cirrhosis at week 0 (inclusion), 6, and 12. TGA was performed with the calibrated automated thrombogram method, tissue factor (5 pM), phospholipids, and with and without thrombomodulin (4 nM) or activated protein C (1 nM)., Results: When TGA was performed with thrombomodulin, endogenous thrombin potential in patients with cirrhosis was higher compared with controls and increased with cirrhosis severity. Stability over time of all thrombin generation parameters was excellent in healthy controls, good in Child-Turcotte-Pugh (CTP)-A patients, and poor in CTP-B/C patients (severe cirrhosis). In CTP-B/C patients, the phenotype was more variable because one-third of patients switched to normal or hypercoagulability during the 3-month follow-up., Conclusion: A study with longer monitoring is needed to correlate the hypercoagulable phenotype of patients with cirrhosis with the occurrence of thrombotic events., Competing Interests: Declaration Of Competing Interest There are no competing interests to disclose., (Copyright © 2023. Published by Elsevier Inc.)

Background: Storage of frozen plasma samples for hemostasis testing is a key step to obtain reliable results. Variables that can affect the quality of plasma during storage include the cryotube type and volume and the tube filling level that conditions the residual air volume. To date, there are only few data on which to base recommendations., Objectives: The aim of this study was to investigate the influence of the tube filling volume (20%, 40%, and 80%) of 2-mL microtubes on frozen plasma for a large panel of hemostasis assays., Methods: For this study, 85 subjects were included, and blood samples were collected from them by venipuncture. After double centrifugation, each sample was aliquoted in 3 2-mL microtubes with different volumes (0.4, 0.8, and 1.6 mL) and stored at -80 °C. At the end of the frozen storage period (3 months ± 1 week), all aliquots from the sample were tested in the same analytical series for a large panel of hemostasis analyses., Results: Compared with completely filled microtubes (1.6/2 mL), storing frozen plasma in smaller volumes (0.4/2 mL) significantly decreased prothrombin time and activated partial thromboplastin time. Conversely, factor II, V, VII, and X levels were increased. Antithrombin, Russell's viper venom time, and anti-Xa activity in patients treated with heparin were also increased., Conclusion: To store plasma at -80 °C for hemostasis analysis, samples should be frozen in small-volume microtubes (<2 mL) with screw caps that are filled to 80% of their volume., (© 2023 The Authors.)