A New Proposal of an Index for Regional Cerebral Perfusion Pressure - A Theoretical Approach with Fluid Dynamics

Cerebral blood flow (CBF) / cerebral blood volume (CBV) ratio derived by [15O] H2O/ CO2 and CO positron emission tomography (PET) examination has been used empirically as an index for cerebral perfusion pressure (CPP). However, it lacks theoretical background and could not be confirmed to be proportionate to CPP, as measurement of local CPP is not practical. We have developed a new index for CPP from Poiseuille equation based on a simple model. Our model implies that CBF/CBV2 is proportionate to CPP. To estimate CPP, CBF/CBV2 would be a preferable index to CBF/CBV theoretically.

On the Tortuosity-Connectivity of Cement-Based Porous Materials

In this work, the transport equations of ionic species in concrete are studied. First, the equations at the porescale are considered, which are then averaged over a representative elementary volume. The so obtained transport equations at the macroscopic scale are thoroughly examined and each term is interpreted. Furthermore, it is shown that the tortuosity-connectivity does not slow the average speed of the ionic species down. The transport equations in the representative elementary volume are then compared with the equations obtained in an equivalent pore. Lastly, comparing Darcy’s law and the Hagen–Poiseuille equation in a cylindrical equivalent pore, the tortuosity-connectivity parameter is obtained for four different concretes. The proposed model provides very good results when compared with the experimentally obtained chloride profiles for two additional concretes.

On the Tortuosity-Connectivity of Porous Materials

In this work, the transport equations of ionic species in concrete are studied. First, the equations at the porescale are considered, which are then averaged over a representative elementary volume. The so obtained transport equations at the macroscopic scale are thoroughly examined and each term is interpreted. Furthermore, it is shown that the tortuosity-connectivity does not slow the average speed of the ionic species down. The transport equations in the representative elementary volume are then compared with the equations obtained in an equivalent pore. Lastly, comparing Darcy’s law and the Hagen-Poiseuille equation in a cylindrical equivalent pore, the tortuosity-connectivity parameter is obtained for four dierent concretes. The proposed model provides very good results when compared with the experimentally obtained chloride profiles for two additional concretes.

PRESERFLO MicroShunt

The PRESERFLO® MicroShunt (Santen Pharmaceutical Co. Ltd., Osaka, Japan), formerly called the InnFocus MicroShunt®, is a trans-scleral device that shunts aqueous humour from the anterior chamber to a filtering bleb under the conjunctiva and Tenon’s capsule. Manufactured from an inert biocompatible material called poly(styrene-block-isobutylene-block-styrene), or ‘SIBS’, the device elicits minimal foreign body reaction and inflammation; potentially reducing the risk of bleb-related fibrosis and failure. The MicroShunt is 8.5 mm long with a 70 μm lumen and is designed to minimize hypotony based on the Hagen–Poiseuille equation. Inserted via an ab-externo approach, the MicroShunt eliminates the need for creation of a scleral flap, sclerostomy, iridectomy, scleral flap suturing and postoperative suture lysis. Clinical trials show promising results with the MicroShunt achieving intraocular pressure reduction approaching that of trabeculectomy, the current gold standard for treating refractory glaucoma.

Analytical spontaneous imbibition model for confined nanofractures

The capillary spontaneous imbibition length of slick water in confined rectangular cross-sectional nanofractures is investigated in this paper. In the established model, the effective slip length, effective viscosity, wettability and nanofracture size are incorporated into the modified Hagen–Poiseuille equation. The calculated spontaneous imbibition length as a function of time, viscosity, wettability and pore size is qualitatively validated by experimental and previous theoretical Hagen–Poiseuille flow results. Our model calculation results agree well with the published experimental data. The ratio of the effective and bulk water viscosities is higher than one, and increases with an increase in the ratio of the nanofracture width to height and decreasing contact angle. The spontaneous imbibition capacity of confined water is enhanced ∼0.67–1.28 times, as determined by the Hagen–Poiseuille equation without the slip effect for various contact angles and nanofracture dimensions.

Surface Tension and Viscosity of Blood

Blood has certain significant physical properties, which the authors investigated. This paper provides values of surface tension and viscosity of blood at 37 °C, as well as relationship between them plotted on a cross-plot. By applying Hagen- Poiseuille equation and Jurin's law to the experimentally obtained data, the authors calculated with great accuracy viscosity and surface tension of blood. Evaluating both of the properties using described methods required from the authors to know the density of investigated liquid, which was found to be on average $\rho=1063,56 \frac{kg}{m^3}$. The authors took blood samples from 30 healthy subjects and determined aforementioned physical properties. There has been made a distinction in regard of a sex of the blood donor. Results indicate that both surface tension and viscosity are independent from sex of a subject, as well as indicate that there is no correlation between viscosity and surface tension of blood at 37\degree C. Average values of surface tension and viscosity were found to be $\sigma=5,241\pm 0,262 \cdot 10^{-2}\frac{J}{m^2}$ and $\eta=3,352\pm0,360 \cdot 10^{-3} Pa \cdot s$, respectively.

Significance of Brownian Motion for Nanoparticle and Virus Capture in Nanocellulose-Based Filter Paper

Pressure-dependent breakthrough of nanobioparticles in filtration was observed and it was related to depend on both convective forces due to flow and diffusion as a result of Brownian motion. The aim of this work was to investigate the significance of Brownian motion on nanoparticle and virus capture in a nanocellulose-based virus removal filter paper through theoretical modeling and filtration experiments. Local flow velocities in the pores of the filter paper were modeled through two different approaches (i.e., with the Hagen–Poiseuille equation) and by evaluating the superficial linear flow velocity through the filter. Simulations by solving the Langevin equation for 5 nm gold particles and 28 nm ΦX174 bacteriophages showed that hydrodynamic constraint is favored for larger particles. Filtration of gold nanoparticles showed no difference in retention for the investigated fluxes, as predicted by the modeling of local flow velocities. Filtration of ΦX174 bacteriophages exhibited a higher retention at higher filtration pressure, which was predicted to some extent by the Hagen–Poiseuille equation but not by evaluation of the superficial linear velocity. In all, the hydrodynamic theory was shown able to explain some of the observations during filtration.

A Numerical Approach for the Evaluation of a Capillary Viscometer Experiment

The dynamic viscosity of a fluid is an important input parameter for the investigation of elastohydrodynamic contacts within tribological simulation tools. In this paper, a capillary viscometer is used to analyse the viscosity of a calibration fluid for diesel injection pumps. Capillary viscometers are often used for the determination of viscosities that show a significant dependence on shear rate, pressure and temperature such as polymer melts or blood. Therefore most of the research on corrections of measured viscosities have been made using polymer melts. A new method is presented to shorten the effort in evaluating the capillary experiment. The viscosity itself can be calculated from experimental data. Essential parameters are the radius of the capillary, its length, the capillary flow and the pressure difference over the capillary. These quantities are used in the Hagen-Poiseuille equation to calculate the viscosity, assuming laminar and monodirectional flow. According to said equation, the viscosity depends on the geometry and the pressure gradient. A typical capillary viscometer contains three main flow irregularities. First the contraction of the flow at the capillary inlet, second the expansion of the flow at the capillary outlet and third the inlet section length of the flow after which the velocity profile is fully developed. These flow phenomena cause pressure losses, which have to be taken into account, as well as the altered length of the laminar flow in the capillary. Furthermore, the temperature difference over the capillary also affects the outlet flow. Therefore, in this paper, a newly developed method is proposed, which shortens the effort in pressure and length correction. The method is valid for viscometers, which provide a single phase flow of the sampling fluid. Furthermore, the proposed correction is suited for arbitrary geometries. A numerical approach is chosen for the analysis of the experiment. In order to facilitate the experimental procedure of a capillary viscometer, a special algorithm was developed. The numerical approach uses a static CFD simulation, which is recursively passed through. If a termination condition, regarding the pressure difference between two cycles, is fulfilled, the real viscosity can be calculated in the usual way from the Hagen-Poiseuille equation. A special advantage of the proposed experimental evaluation is the general applicability for arbitrary geometries. In this paper, the procedure is validated with a well-known reference fluid and compared to data, which was gathered from a quartz viscometer experiment with the same fluid. Therefore, experiments are conducted with the capillary viscometer and compared at various pressure and temperature levels.

Superpermeable nanoporous carbon-based catalytic membranes for electro-Fenton driven high-efficiency water treatment

Based on the Hagen–Poiseuille equation, theoretical membrane permeability is inversely and directly proportional to its thickness and pore-radius, respectively, indicating that a thin membrane with an effective pore-radius is extremely permeable.