Use of inverse gas chromatography to quantify interactions in amine cured epoxy resins

Flory–Huggins interaction parameters, λ, were determined for a series of probes in an amine cured epoxy resin matrix (433–493 K) and its precursors (324–363 K) by inverse gas chromatography (IGC). Hildebrand–Scatchard theory was combined with Flory–Huggins theory in order to estimate infinte dilution solubility parameters (δ₂) for the matrix and its precursors at 298 K. It was shown that the value of the solubility parameter for the cured resin matrix lies between those of its precursors. Compared to the majority of published work, an unusual aspect of this application of IGC is that solubility parameters have been determined when the stationery phases are (i) small molecules and (ii) a highly crosslinked polymer. Moreover, all possible attempts have been made to ensure equilibrium conditions between probe and stationary phase, and compensation for asymmetry of peak profile has been applied in determining δ₂. The solubility parameters estimated by IGC are in good agreement with those calculated by other methods.     

Methane/natural gas storage and delivered capacity for activated carbons in dry and wet conditions

Methane/natural gas storage and delivered capacity for three different activated carbons in dry and wet conditions were measured. In all tests the temperature of the bed was maintained constant at 277.15 K and pressure was increased up to 10 MPa. Natural gas storage capacity was less than methane storage capacity in dry conditions for all the three activated carbons tested, while the gas delivery was almost the same. One of activated carbon tested (NC120) showed the possibility of hydrate forming for pressures higher than 4 MPa but the amount of gas stored still was less than the amount stored in dry conditions over the whole range of pressure. The analysis of the gas delivered at each pressure steps shows that considerable amount of heavy components do not come out from the bed even at very low pressures in both dry and wet condition tests. Repeatability of the sorption/desorption processes - vital for possible commercial/industrial use - has been examined over various cycles.     

Three-dimensional simulation of sacrificial etching

Sacrificial etching is one of the most important process steps in micro-electro-mechanical systems technology, since it enables the generation of free-standing structures. These structures are often the main part of micro-mechanical devices, intended to sense or induce a mechanical movement. The etching process transforms an initial multi-segmented geometry and depends on material properties and several process conditions. One of the crucial issues for etching is the etching selectivity on different materials. The major task for the simulation is to give an answer, how sacrificial layer surfaces regress in time under the influence of process parameters and to which magnitude surrounding material segments are affected by the etching process. For this purpose we have developed a fully three-dimensional topography simulation tool, Etcher-Topo3D, which is capable to deal with realistic process conditions. The main concept is demonstrated in this work. During simulation the topography of the initial multi-segment geometry is changed which is handled by a level-set algorithm. After a simulation is finished, the level-set representation has usually to be converted back to a mesh representation to enable further analysis. To illustrate the main features of our simulation tool several examples of MEMS structures with a sacrificial layer are presented.     

Comprehensive Performance Analysis of ZigBee Technology Based on Real Measurements

Although the ZigBee technology is massively deployed the performance question still remains unanswered. There is a lack of serious performance evaluations and thus this paper provides a comprehensive and unbiased study of the ZigBee PRO technology. An extensive real measurement was conducted to accomplish this task. We found out a big performance gap among ZigBee implementations even though they are compliant with the ZigBee standard. The presented results and analysis could be beneficial for many wireless sensor network developers.     

On the crystallographic anisotropy of nanoindentation in pseudoelastic NiTi

We use a nanoindenter with a Berkovich tip to study local mechanical properties of two polycrystalline intermetallics with a B2 crystal structure, NiAl and NiTi. We use orientation imaging scanning electron microscopy to select a relevant number of grains with appropriate sizes and surface normals parallel to 〈0 0 1〉, 〈1 0 1〉 and 〈1 1 1〉. As a striking new result, we find a strong crystallographic orientation dependence for NiTi. This anisotropy is less pronounced in the case of NiAl. For NiTi, the indentation force required to impose a specific indentation depth is highest for indentation experiments performed in the 〈0 0 1〉 direction and lowest along the 〈1 1 1〉 direction. We consider transmission electron microscopy results from cross-sections below the indents and use molecular dynamics simulations and resolved shear stress calculations to discuss how this difference can be accounted for in terms of elementary deformation and transformation processes, related to dislocation plasticity (NiAl and NiTi), and in terms of the stress-induced formation and growth of martensite (NiTi). Our results show that the crystallographic anisotropy during nanoindentation of NiTi is governed by the orientation dependence of the martensitic transformation; dislocation plasticity appears to be less important.     

One-radius triplets

The one-radius triplet is an optical system that consists of three lenses. Either the radii of curvature of the lenses have the same absolute value or one radius of curvature has an infinitely large value. The advantage of such optical systems is that their production cost is less than that of systems with ordinary triplets. Here a theory of one-radius triplets is described and tables of parameters for their modification are provided. Residual aberrations are given for several selected triplets. One-radius triplets are suitable for use in laser technology and metrology.     

Graphene substrates promote adherence of human osteoblasts and mesenchymal stromal cells

The biocompatibility of large single layer graphene produced by chemical vapour deposition was investigated using human osteoblasts and mesenchymal stromal cells. The study was focused on cellular adhesion, morphology and the ability to proliferate on graphene substrates. It was found that both of the cell types which were tested adhered and proliferated better when cultured on graphene films than on a SiO₂ substrate.     

Modeling of deep-submicron silicon-based MISFETs with calcium fluoride dielectric

We model the main characteristics of metal-insulator-silicon field-effect transistors (MISFETs) with different gate insulators using the carrier energy distribution function calculated with a Spherical Harmonics Expansion method. In addition to standard devices with Silicon Dioxide or Oxynitride we study a hypothetical MISFET with a rather new crystalline dielectric-Calcium Fluoride. The real physical parameters of the \(\hbox {CaF}_{2}\) /Si tunnel barrier are used in our simulations. The obtained characteristics of the transistors with \(\hbox {CaF}_{2}\) are, in some details, better than those of the devices with traditional oxides. Being a step forward in the context of the industrial implementation of fluorite, this work opens the possibility of simulating the characteristics of different silicon-based devices with crystalline insulators.