Hydrogen storage in 1D nanotube-like channels metal–organic frameworks: Effects of free volume and heat of adsorption on hydrogen uptake

Metal–organic Frameworks generate significant interest for their potential application as Hydrogen storage materials. Grand Canonical Monte Carlo (GCMC) simulations were performed at two different temperatures 77 and 300 K over a wide range of pressures to describe H₂ adsorption in 7 metal–organic frameworks (MOFs), which all have the same framework topology but different surface chemistry and different pore sizes. DREIDING and UFF force fields were identified to be able to predict adsorption isotherms for H₂ in MOFs in a reasonable agreement with the experimental data from the literature. This work reveals that at 77 K the total amount of H₂ adsorbed correlates mainly with: the heat of adsorption at low pressure and the free volume at high pressure. While at 300 K the amount adsorbed mainly correlates with the available free volume at both low and high pressure. None of the MOFs studied fulfils DOE requirement, this is due to their low heat of adsorption. The required adsorption energy to meet the DOE targets is estimated to be 34 kJ/mol.     

Crystallographic anisotropy of growth and etch rates of CVD diamond

The investigation of orientation dependent crystal growth and etch processes can provide deep insights into the underlying mechanisms and thus helps to validate theoretical models. Here, we report on homoepitaxial diamond growth and oxygen etch experiments on polished, polycrystalline CVD diamond wafers by use of electron backscatter diffraction (EBSD) and white-light interferometry (WLI). Atomic force microscopy (AFM) was applied to provide additional atomic scale surface morphology information. The main advantage of using polycrystalline diamond substrates with almost random grain orientation is that it allows determining the orientation dependent growth (etch) rate for different orientations within one experiment. Specifically, we studied the effect of methane concentration on the diamond growth rate, using a microwave plasma CVD process. At 1% methane concentration a maximum of the growth rate near <100> and a minimum near <111> is detected. Increasing the methane concentration up to 5% shifts the maximum towards <110> while the minimum stays at <111>. Etch rate measurements in a microwave powered oxygen plasma reveal a pronounced maximum at <111>. We also made a first attempt to interpret our experimental data in terms of local micro-faceting of high-indexed planes.     

A hybrid genetic algorithm for solving no-wait flowshop scheduling problems

A hybrid genetic algorithm is proposed in this paper to minimize the makespan and the total flowtime in the no-wait flowshop scheduling problem, which is known to be NP-hard for more than two machines. The Variable Neighborhood Search is used as an improvement procedure in the last step of the genetic algorithm. First, comparisons are provided with respect to several techniques that are representative of the previous works in the area. Then, we compare the results given by three proposed algorithms. For the makespan criterion as well as for the total flowtime, the computational results show that our algorithms are able to provide competitive results and new best upper bounds.     

Importance of in-plane shear rigidity in finite element analyses of woven fabric composite preforming

A finite element made of woven unit cells under biaxial tension and in-plane shear is proposed for the simulation of fabric forming. The simulation is made within an explicit dynamic approach and is based on a simplified dynamic equation accounting for tension and in-plane shear strain energy. The biaxial tensile properties (given by two surfaces) and the in-plane shear properties (given by a curve) can be determined both by biaxial tensile tests and picture frame experiments or obtained by mesoscopic 3D finite element analyses of the woven unit cell. The interior load components of the proposed finite element are calculated explicitly and simply from the tensions and shear torque on four woven cells. The results obtained by the simulations of a hemispherical forming process on a very unbalanced fabric are compared to experiments. It is shown that the tension strain energy permits to describe the asymmetry of the response but that the computation of wrinkles and of the deformed states when the locking angle is exceeded needs to take the in-plane shear stiffness and its evolution with shear angle into account.     

Verformungsverhalten weicher Böden im spannungsgesteuerten Kompressionsversuch

Anhand von spannungsgesteuerten Kompressionsversuchen kann das Verformungsverhalten weicher Böden wirklichkeitsnäher beschrieben werden, da durch die Wahl einer geeigneten Spannungsrate eine Ähnlichkeit zu den Belastungsbedingungen in situ vorliegt. Die Versuchsergebnisse werden in kontinuierlichen Kurven dargestellt, die eine lückenlose Interpretation der Versuchsergebnisse ermöglichen. Die Versuchsdauer wird dabei maßgeblich reduziert. Im vorliegenden Beitrag werden die mathematischen Grundlagen in kontinuierlichen Kurven dargestellt, die eine lückenlose Interpretation der Versuchsergebnisse ermöglichen. Außerdem werden die Versuchsdauer, labor‐ und bodenmechanischen Grundlagen zur Ausführung von spannungsgesteuerten Kompressionsversuchen dargestellt. Versuchsergebnisse von aufbereiteten Kaolin‐ und ungestörten Seetonproben werden ebenfalls präsentiert und mit den Ergebnissen des Standardkompressionsversuchs verglichen. Schließlich wird eine Modellierung des geschwindigkeitsabhängigen Kompressionsverhaltens vorgestellt. Constant rate of loading consolidation tests on soft soils. The one‐dimensional consolidation tests under constant rate of loading (CRL‐test) have the ability to describe the behaviour of soft soils realistically because of its similarity to the field loading conditions. The test results can be presented in continues curves, which enable a steeples Interpretation of the test results. Moreover the testing time will be enormously reduced. In the present paper the mathematical and the procedural basics are presented in order to carry out the CRL‐test. Test results of remoulded kaolin as well as undisturbed lacustrine clay are shown and compared to the results from the incremental loading consolidation tests (IL‐Test). Finally a modelling of the compressibility behaviour depending on the loading rate will be presented.