Relations Between Seepage Velocities in Immiscible,Incompressible Two-Phase Flow in Porous Media

Based on thermodynamic considerations, we derive a set of equations relating the seepage velocities of the fluid components in immiscible and incompressible two-phase flow in porous media. They necessitate the introduction of a new velocity function, the co-moving velocity. This velocity function is a characteristic of the porous medium. Together with a constitutive relation between the velocities and the driving forces, such as the pressure gradient, these equations form a closed set. We solve four versions of the capillary tube model analytically using this theory. We test the theory numerically on a network model.     

Analysis of the occurrence of stick-slip in AFM-based nano-pushing

The use of the Atomic Force Microscope (AFM) as a tool to manipulate matter at the nanoscale is promising. However, the complexity of the corresponding physics and mechanics makes such nanomanipulation difficult and not very accurate. In the present paper, we analyze the dynamics of AFM-based nano-pushing manipulation. Simulation results show that the choice of the manipulation speed and loading force highly affect the manipulation outcome. In addition, simulations predict the existence of several threshold manipulation speeds. These thresholds mark the transitions between no stick-slip motion and either unique or multiple coexisting stick-slip. The obtained results bear significant implications and help get more insight into AFM-based nano-pushing.     

Modelling of Unsteady Transition in Low-Pressure Turbine Blade Flows with Two Dynamic Intermittency Equations

A transition model for describing wake-induced transition is presented based on the SST turbulence model by Menter and two dynamic equations for intermittency: one for near-wall intermittency and one for free-stream intermittency. In the Navier-Stokes equations, the total intermittency factor, which is the sum of the two, multiplies the turbulent viscosity computed by the turbulence model. The quality of the transition model is illustrated on the T106A test cascade for two Reynolds numbers, using experimental results by Stieger and Hodson for transition mainly due to kinematic wake impact on a separation bubble. The quality of the model is also revealed on the T106D test cascade using experimental results from Hilgenfeld, Stadtmuller and Fottner for wake turbulence induced transition. The test cases differ in pitch to chord ratio, Reynolds number and inlet free-stream turbulence intensity, causing different transition mechanisms. The unsteady results are presented in space-time diagrams of shape factor and wall shear stress on the suction side. The results show the capability of the model to capture the physics of unsteady transition in separated state. Inevitable shortcomings are revealed as well.     

Transmission spectra of tunable dispersion filters of the type of small particles-liquid crystal

We propose a technique for the calculation of characteristics of tunable dispersion filters of infrared radiation of the type of small particles-liquid crystal. The relation between the structural parameters of filters and their transmission spectra is investigated. The dependence of the halfwidth of transmission spectral lines on the thickness of the filter, the concentration of particles, and their size and polydispersity is investigated.     

Studying Stabilization of PVC by Differential Thermal Analysis

A method for studying the thermal stability of PVC compounds by using differential thermal analysis (DTA) is presented. At isothermal conditions and in an oxygen-free nitrogen atmosphere, an exothermal maximum is observed at the moment when all stabilizer is consumed. The time until this maximum appears is taken as a measure of stability of the tested sample. Earlier DTA investigations on the thermal stability of PVC were done by Dunn and Ennis. They needed the addition of a destabilizer, such as ferric or zinc oxide to the PVC compound to get an easily determinable exothermal maximum. This means that applications of their method to industrial PVC compounds or end products were impossible, as neither should contain any of these oxides. Probably due to more sensitive equipment it is now possible to obtain an exothermal maximum without any destabilizer. A stabilizer such as tribasic lead sulfate (TBLS), for example, is still needed though. Plasticized or rigid compounds may be investigated. High amounts of some fillers cause the maximum to broaden, and the evaluation becomes more difficult. The method is easy and time saving. The very small amount of sample required (a few milligrams only) makes the sample preparation possible for all kinds of products.     

Long-Lived Triplet Excited State Accessed with Spin–Orbit Charge Transfer Intersystem Crossing in Red Light-Absorbing Phenoxazine-Styryl BODIPY Electron Donor/Acceptor Dyads

Orthogonal phenoxazine-styryl BODIPY compact electron donor/acceptor dyads were prepared as heavy atom-free triplet photosensitizers (PSs) with strong red light absorption (ϵ=1.33×10⁵ M⁻¹ cm⁻¹ at 630 nm), whereas the previously reported triplet photosensitizers based on the spin-orbit charge transfer intersystem crossing (SOCT-ISC) mechanism show absorption in a shorter wavelength range (<500 nm). More importantly, a long-lived triplet state (τ_T=333 μs) was observed for the new dyads. In comparison, the triplet state lifetime of the same chromophore accessed with the conventional heavy atom effect (HAE) is much shorter (τ_T=1.8 μs). Long triplet state lifetime is beneficial to enhance electron or energy transfer, the primary photophysical processes in the application of triplet PSs. Our approach is based on SOCT-ISC, without invoking of the HAE, which may shorten the triplet state lifetime. We used bisstyrylBodipy both as the electron acceptor and the visible light-harvesting chromophore, which shows red-light absorption. Femtosecond transient absorption spectra indicated the charge separation (109 ps) and SOCT-ISC (charge recombination, CR; 2.3 ns) for BDP-1 . ISC efficiency of BDP-1 was determined as Φ_T=25 % (in toluene). The dyad BDP-3 was used as triplet PS for triplet-triplet annihilation upconversion (upconversion quantum yield Φ_UC=1.5 %; anti-Stokes shift is 5900 cm⁻¹).