Microstructural and microwave dielectric properties of LZT (Li2ZnTi3O8) ceramics sintered in presence of bismuth borate glass for LTCC applications

In the present research, the Li₂ZnTi₃O₈(LZT) ceramics were synthesized throughout solid-state ceramic processing, then mixed with bismuth borate (BiBO) glass prepared based on conventional melt quenching method. Wetting behavior of BiBO glass on the LZT ceramic substrate was monitored by hot stage microscopy. Afterward, dielectric LZT ceramics containing different amounts of BiBO glass (0.25–6 wt%) were sintered at various temperatures. X-ray diffraction and electron back scatter diffraction examinations revealed the presence of two crystalline phases of Li₂ZnTi₃O₈ and Bi₂Ti₂O₇. The maximum value of relative density (above 95%) was obtained in the case of specimens contained more than 5 wt% glass. The microwave dielectric properties of the finally sintered BiBO glass containing LZT ceramics were as follows: dielectric constant (ε_r) = 21.44–25.09, quality factor (Q × f) = 10839–54708 GHz and temperature coefficient of resonant frequency (τ_f) = (? 15.58) ? (? 12.86)ppm/°C.     

Thermal actuators featuring large displacements for passive temperature sensing

The thermal actuator presented in this paper consists of two symmetrically V-shaped beam stacks, where each stack consists of six beams in parallel. The stacks are coupled facing each other and slightly shifted along the mirror axis. Both stacks are connected to a lever beam and fixed at four anchor regions to the substrate. Due to the difference in the coefficient of thermal expansion of the material of the beams and the one of the substrate, the tip of the lever moves perpendicular to the mirror axis. The device is fabricated from galvanic deposited nickel on a silicon substrate. Finite element simulations were carried out to optimize the design with respect to the sensitivity and the maximum mechanical stress. The stress needs to be lower than the yield strength of the material. Otherwise, plastic deformations of the beams would lead to irreversible deflections of the beam tip. This limits the overall sensitivity of the design. First results of the device with 400 μm long bent beams show a linear behavior and a sensitivity of 0.5 μm/K and forces of 66 μN/K for a temperature range of ?30 °C up to +40 °C.     

An approach to mechanistic event recognition applied on monitoring organic matter depletion in SBRs

A fundamental practice in process engineering is monitoring the state dynamics of a system. Unfortunately, observability of some states is related to high costs, time, and efforts. The mechanistic event recognition (MER) aims to detect an event (defined as a change of the system with specific significance to the operation of the process) that cannot be directly observed but has some predictable effect on the dynamics of the systems. MER attempts to apply fault diagnosis techniques using mechanistic “recognition” models to describe the process. A systematic method for building recognition models using optimal experimental design tools is presented. As proof of concept, the MER approach to detect organic matter depletion in sequencing batch reactors, measuring only ammonia, dissolved oxygen, and nitroxides is applied. The event, that is, consumption of organic matter to a level below 50 gCOD/m³, was successfully detected even though microbial activity is known to continue after organic matter depletion. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3460–3472, 2014     

Creep compliance mapping by atomic force microscopy

We present a method for mapping the spatial distribution of viscoelastic properties of heterogeneous samples using the atomic force microscope (AFM). By applying a force step load protocol to induce time dependent sample indentations we measured the local creep compliance of the sample. The creep compliance was quantified in terms of the standard linear solid model to give maps of the instant glassy modulus, the equilibrium rubbery modulus, and the retardation time. To reduce the influence of plastic deformations, the sample was preformed with an initial preload step. Different polymer samples with a homogeneous or a heterogeneous material composition on a microscopic scale were investigated.     

2‐(1‐Ethynylpyrene)‐Adenosine as a Folding Probe for RNA—Pyrene in or out

A series of short RNA duplexes containing one or two 1‐ethynylpyrene‐modified adenine bases was synthesised. The melting behaviour of these duplexes was examined by monitoring temperature‐dependent pyrene fluorescence. In the singly modified RNA duplexes, the bases flanking the ethynylpyrene‐rA were varied to examine the sequence specificity of the fluorescence change of pyrene upon RNA hybridisation. Because an increase in pyrene fluorescence upon melting of the duplex can be correlated with intercalation of pyrene, and a decrease is usually associated with the position of pyrene outside the strand, a relationship between the flanking bases and the tendency of the dye to intercalate has been established. It was found that pyrene intercalation is less likely to take place if the modified base is flanked only by A–U base pairs. Flanking G–C base pairs, even only in the 5′‐direction of the modified base, will favour intercalation. In addition, we examined a doubly modified compound that had a pyrene located on each strand. The spectra indicated that the two pyrenes were close enough for interaction. Upon melting of the strand, a fluorescence blue shift corresponding to the dissociation of the pyrene–pyrene complex could be observed in addition to the intensity effect already known from the singly modified compounds. Two melting curves based on the different properties of the fluorophore could be extracted, leading to different melting points corresponding to the global duplex melting and to the change of local pyrene environment, respectively.     

Finite element methods for the Stokes problem on complicated domains

It is a standard assumption in the error analysis of finite element methods that the underlying finite element mesh has to resolve the physical domain of the modeled process. In case of complicated domains which appear in many applications such as ground water flows this requirement sometimes becomes a bottleneck. The resolution condition links the computational complexity to the number (and size) of geometric details although the accuracy requirements, possibly, are moderate and would allow a (locally) coarse mesh width. Therefore even the coarsest available discretization can lead to a huge number of unknowns. The composite mini element is a remedy to this dilemma because the degrees of freedom are not linked to the number of geometric details. The basic concept for the Stokes problem with uniform no-slip boundary conditions has been introduced and analyzed in [D. Peterseim, S. Sauter, The composite mini element – coarse mesh computation of Stokes flows on complicated domains, SINUM, 46(6) (2008) 3181–3206]. Here, we generalize the composite mini element to slip, leak and Neumann boundary conditions so that it becomes applicable to this much larger and more important problem class. The main results are (a) the algorithmic concept remains unchanged and the new boundary conditions can be implemented as a weighted quadrature rule, (b) the stability and convergence can be proved under very mild assumption on the domain geometries, (c) the analysis is far from trivial and requires the development of substantially new tools compared to the simple case of uniform no-slip boundary conditions.