Untersuchung von Schwingungen einer Zweiphasenströmung durch Druckabfall und Dichtewellen mit Hilfe finiter Differenzen

The previous experimental analysis has indicated the existence to two major modes of oscillations, i.e., Density-Wave (high frequency) and Pressure-Drop (low frequency) Oscillations in single channel, electrically heated, forced convection upflow systems. In this work the stability of such a system is investigated theoretically and the results are compared with experimental findings obtained by the authors. The Homogeneous Phase Equilibrium model is used to describe the two-phase flow characteristics. The friction between the pipe wall and the expanding fluid is modeled using the Moody friction factor assuming an effective two-phase viscosity. Gravitational forces are included and heat transfer into the fluid is assumed to be the function of the wall temperature, fluid temperature and heat transfer coefficient which is also assumed to be a function of the flow rate. Though simple, this model is found to be very satisfactory in simulating both modes of oscillations with acceptable accuracy. The physical nature of each mode is different and distinct, therefore, separate solution methods are developed for each case. The Steady-State Flow Characteristics are obtained for various heat inputs and inlet temperatures by solving the conservation equations together with the equation of state by using an Implicit Finite- Difference technique. In the analysis of low frequency oscillations it is assumed that the quasi-steady state conditions prevail in the heater. The system equations obtained with this assumption are solved under constant exit pressure and constant container pressure boundary conditions using the finite-difference technique. Two methods of approach are adapted in solving the non-linear hyperbolic equations which describe the system at low mass flow rates where the density-wave type oscillations are observed. They are the Explicit Integral Momentum method (EIM) and the Explicit Finite-Difference method (EFD). A comparison of the results with experiments and other mathematical models is discussed.     

Measurement of LⅢ Subshell Absorption Jump Parameters of Hafnium

The L_Ⅲ subshell absorption jump ratio and jump factor of hafnium have been measured using two different ways which are X-ray attenuation method and Energy Dispersive X-ray Fluorescence technique. The results obtained both ways have been compared with theoretical values. They are in good agreement with each other.     

Mixing of miscible liquids in gas-segmented serpentine channels

The chaotic mixing of miscible liquids in gas-segmented serpentine channels is studied computationally in a two-dimensional setting. Passive tracer particles are used to visualize and quantify the mixing. The molecular diffusion is ignored and only the mixing due to chaotic stirring is considered. Mixing is quantified using the entropy and intensity of segregation measures. The effects of various non-dimensional parameters on the quality of mixing are investigated and it is found that the relative bubble size, the capillary number and the non-dimensional channel corrugation length are the most important parameters influencing the mixing. The mixing is found to be weakly dependent on Reynolds number and nearly independent of viscosity ratio.     

Photophysical behavior of a novel 4-aza-indole derivative in different solvents: reverse solvatochromism

Research on Chemical Intermediates - The photophysical properties of a new 4-aza-indole derivative [ethyl...     

Determination of surface tension of liquid ternary Ni–Cu–Fe and sub-binary alloys

Experimental data in the literature are almost limited to determine the thermophysical properties of multicomponent complex alloys, especially due to the inability of laboratories to achieve the desired ideal conditions, due to the difficulty of protection from oxidation at high temperatures and other contamination at high temperatures, due to time and cost in laboratory studies. Due to these reasons, the theoretical data obtained in this subject is of great importance. In this study, a series of geometric and physical models, such as Chou’s general solution model (GSM), Muggianu’s Model, Kohler’s Model, Toop’s Model, Hillert’s Model, Guggenheim’s Model, Butler’s Model, Egry’s Model and ideal solution model for quasi-binary alloy system for Section A: Ni_{0.4(1 – x)}Cu_xFe_{0.6(1 – x)}. and Section B: (Ni_xCu_0.2Fe_{0.8 – x}) are used to calculate the surface tension-composition and surface tension-temperature curves of the Cu-Fe-Ni ternary liquid system are plotted. The data for this process is evaluated by means of an extended Redlich-Kister-Muggianu polynomial fit to the experimental values of the surface tensions of the binary liquid alloy systems. The obtained results for these models are also compared with the available data in the literature and relatively good agreements are observed. In addition, the surface segregation having important key factor in determining surface tension of the liquid alloy Ni-Fe-Cu has also been investigated in this work.     

Copper-catalyzed asymmetric conjugate addition of diethylzinc to substituted chalcones using a chiral phosphine ligand

A series of chiral phosphine PFAM and phosphine oxide POFAM ligands were studied for the copper-catalyzed asymmetric diethylzinc addition to enones. One of these ligands, PFAM2, was an efficient catalyst with a variety of enones to give conjugate addition products in up to 96% yield and 92% ee.     

Neuroactive Peptide Nanofibers for Regeneration of Spinal Cord after Injury

The highly complex nature of spinal cord injuries (SCIs) requires design of novel biomaterials that can stimulate cellular regeneration and functional recovery. Promising SCI treatments use biomaterial scaffolds, which provide bioactive cues to the cells in order to trigger neural regeneration in the spinal cord. In this work, the use of peptide nanofibers is demonstrated, presenting protein binding and cellular adhesion epitopes in a rat model of SCI. The self‐assembling peptide molecules are designed to form nanofibers, which display heparan sulfate mimetic and laminin mimetic epitopes to the cells in the spinal cord. These neuroactive nanofibers are found to support adhesion and viability of dorsal root ganglion neurons as well as neurite outgrowth in vitro and enhance tissue integrity after 6 weeks of injury in vivo. Treatment with the peptide nanofiber scaffolds also show significant behavioral improvement. These results demonstrate that it is possible to facilitate regeneration especially in the white matter of the spinal cord, which is usually damaged during the accidents using bioactive 3D nanostructures displaying high densities of laminin and heparan sulfate‐mimetic epitopes on their surfaces.     

Comparative study of boron compounds and aluminum trihydroxide as flame retardant additives in epoxy resin

The aim of this study was to investigate and compare the flame retardant properties of boron compounds with respect to aluminum trihydroxide (ATH) in an epoxy system based on bisphenol A epichlorohydrin‐based epoxy resin and cycloaliphatic polyamine‐based hardener. Six different boron compounds including colemanite (C), ulexite (U), boric acid (BA), boric oxide (BO), melamine borate (MB) and guanidinium nonaborate (GB) were used as flame retardant additive. The flame retardant properties of epoxy‐based composites were investigated using limiting oxygen index (LOI), UL 94 standards both in vertical and horizontal position, thermogravimetric analysis, cone calorimeter and scanning electron microscopy. According to flammability test results, boron compounds except for C and U showed better performance than ATH. According to the LOI results, 40% BA containing sample had the highest LOI value of 28.5, while 30% MB, 35% GB and 40% BA containing samples had the highest UL 94V rating (V0). According to the cone calorimeter test results, all boron containing samples had better fire performances than ATH containing sample; 40 wt% BO containing sample showed the lowest peak heat release rate, average heat release rate and total heat release values. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermal stability and flame retardancy of guanidinium and imidazolium borate finished cotton fabrics

Dark chocolate is a complex food product in which sugar crystals and cocoa particles are surrounded by cocoa butter. Thermogravimetry and derivative thermogravimetry are proposed as fast, cheap, and sensitive tools to determine the composition of dark chocolate and consequently to confirm the cocoa percent declared by the producer or to check the production cycle.     

Experiments on yielding of tension specimens with notches and holes

The yield loads of various ST-37 steel strips with notches and holes, subjected to tension, are determined experimentally. All samples have the same thickness and the same net cross-sectional area. Their width-to-thickness ratio is such that they are assumed to be in a state of plane stress. Essentially, the experiments are performed to find the effect of the angle of the V-notched specimens on the yield load, the most efficient shape of cut-outs and the effect of eccentricity of circular holes on the carrying capacities of the strips. The results are then compared, whenever possible, to the existing theoretical results.