Micro Solid Oxide Fuel Cells on Glass Ceramic Substrates

Miniaturized solid oxide fuel cells are fabricated on a photostructurable glass ceramic substrate (Foturan) by thin film and micromachining techniques. The anode is a sputtered platinum film and the cathode is made of a spray pyrolysis (SP)‐deposited lanthanum strontium cobalt iron oxide (LSCF), a sputtered platinum film and platinum paste. A single‐layer of yttria‐stabilized zirconia (YSZ) made by pulsed laser deposition (PLD) and a bilayer of PLD–YSZ and SP–YSZ are used as electrolytes. The total thickness of all layers is less than 1 µm and the cell is a free‐standing membrane with a diameter up to 200 µm. The electrolyte resistance and the sum of polarization resistances of the anode and cathode are measured between 400 and 600 °C by impedance spectroscopy and direct current (DC) techniques. The contribution of the electrolyte resistance to the total cell resistance is negligible for all cells. The area‐specific polarization resistance of the electrodes decreases for different cathode materials in the order of Pt paste > sputtered Pt > LSCF. The open circuit voltages (OCVs) of the single‐layer electrolyte cells ranges from 0.91 to 0.56 V at 550 °C. No electronic leakage in the PLD–YSZ electrolyte is found by in‐plane and cross‐plane electrical conductivity measurements and the low OCV is attributed to gas leakage through pinholes in the columnar microstructure of the electrolyte. By using a bilayer electrolyte of PLD–YSZ and SP–YSZ, an OCV of 1.06 V is obtained and the maximum power density reaches 152 mW cm⁻² at 550 °C.     

Real-time simulation and visualization of robotic belt grinding processes

Real time simulation and visualization are important for robot programmers to verify and optimize the path planning for the robotic belt grinding process. A new free-form surface representation based on discrete surfel element is developed to facilitate the system implementation, which exploits the advantage of the new development of point-based rendering technology in computer graphics. A local process model is integrated to calculate the material removal rate by considering the local geometry information and non-uniform force distribution. The final surface grinding error is easy to be assessed and visualized for quality evaluation. The experiments show that the simulation error is below 15%, even for a non-uniform contact under stable cutting conditions.     

Modeling the material behavior of magnesium alloy AZ31 using different yield criteria

Nowadays, the finite element analysis (FEA) is playing a main rule in fields of sheet metal forming for designing processes and dimensioning parts. The most frequent yield criteria used in the FE commercial programs for the sheet-metal-forming simulation, like AUTOFORM, PAMSTAMP, etc., are Hill’48 for common steels or Barlat’89 and various BBC models for some aluminum alloys. In this paper, different yield loci for biaxial tensile stress conditions of the magnesium sheet metal alloy AZ31 are investigated. The experimental investigations have been done using the specimen geometry for the experimental setup developed at the Chair of Manufacturing Technology (LFT) of the University of Erlangen. The yielding behavior is determined basing exclusively on real material data out of experiments so that no FE calculations are necessary to detect strains and stresses. Using these data, several yield criteria are applied to approximate the real material characteristics, whereas the model of BBC’2005 leads to the best agreement for uniaxial yield stresses, the anisotropy coefficients, and the yield locus.     

Eradication of Helicobacter pylori by a 1-week course of famotidine, amoxicillin and clarithromycin

OBJECTIVES: The combination of a proton pump inhibitor (PPI) such as omeprazole with amoxicillin and clarithromycin constitutes one of the most effective treatments for the eradication of Helicobacter pylori. Nevertheless, the mechanisms of interaction between these drugs remain unclear. It has been shown that minimal inhibitory concentration values of both antibiotics are considerably lower at neutral pH levels than in an acid environment. Further, omeprazole possesses bacteriostatic activity. To evaluate the significance of these mechanisms we replaced omeprazole with famotidine, a drug which only suppresses acid production, but has no intrinsic antimicrobial activity. METHODS: We evaluated the efficacy of a 1-week course of famotidine 80 mg b.i.d., amoxicillin 1000 mg b.i.d. and clarithromycin 500 mg b.i.d. in a pilot study (20 patients), and then confirmed our results in a larger replication study (87 patients). A total of 107 patients with H. pylori-associated duodenal ulcer (n = 54), gastric ulcer (n = 14) or non-ulcer dyspepsia (n = 39) were included. Endoscopy was performed at baseline and 4-6 weeks after discontinuation of treatment. H. pylori status was assessed by the urease test and histology. RESULTS: H. pylori was successfully eradicated in 94 of 104 patients who completed the study (90.4%; CI 95%, 83.0-95.3%). By intention-to-treat analysis, the eradication rate was 87.9% (CI 95%, 80.1-93.4%). Ulcer healing was observed in 98.1% of duodenal ulcers and 92.9% of gastric ulcers (based on per-protocol analysis). Mild side effects that did not require termination of treatment were reported by seven patients (6.7%). CONCLUSION: A 1-week course of famotidine, amoxicillin and clarithromycin is a highly effective, simple and safe eradication regimen. Our data indicate that acid suppression is the crucial mechanism by which the activity of amoxicillin and clarithromycin against H. pylori is enhanced, whereas additional antimicrobial activity or other specific effects of PPIs seem to be less important.     

Detection of DNA sequence variations in homo- and heterozygous samples via molecular mass measurements by electrospray ionization time-of-flight mass spectrometry

The potential of ion-pair reversed-phase high-performance liquid chromatography on-line hyphenated to electrospray ionization time-of-flight mass spectrometry for the characterization of polymerase chain reaction (PCR) amplified nucleic acids was evaluated. For that purpose, a "SNP toolbox" was constructed by cloning and PCR-mediated site-directed in vitro mutagenesis at nucleotide position (ntp) 16,519 of a sequence-verified fragment of the human mitochondrial genome (ntps 15,900-599). Confirmatory sequencing demonstrated that within the sequences of the clones one and the same base was mutated to all other bases. Using these clones or equimolar mixtures of these clones as PCR templates, 51-401-bp-long amplicons were generated, which were used to determine the upper size limits of PCR products for the unequivocal detection of sequence variations in homo- and heterozygous samples. Based on the high mass spectrometric performance of the applied time-of-flight mass spectrometer, the unequivocal genotyping of all kinds of single base exchanges in PCR amplicons from heterozygous samples with lengths up to 254 base pairs (bp) was demonstrated. Considering homozygous samples, the successful genotyping of single base substitutions in up to 401-bp-long PCR products was possible. Consequently, the described hyphenated technique represents one of the most powerful mass spectrometric genotyping assays available today.     

Characterization of zopiclone crystal forms found among generic raw materials

This paper deals with the occurrence of polymorphs and pseudopolymorphs and their effect on the solid-state properties of zopiclone, a poorly water soluble nondiazepine sedative and hypnotic drug. X-ray powder diffraction (XRPD), infrared spectroscopy (IR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), particle size analysis, dissolution studies, and solubility determinations were used to characterize the zopiclone raw materials. An anhydrated form, a dihydrated form, and a mixture of these two crystal forms were found and characterized among the zopiclone powders.     

How the shape of pre- and postsynaptic signals can influence STDP: a biophysical model

Spike-timing-dependent plasticity (STDP) is described by long-term potentiation (LTP), when a presynaptic event precedes a postsynaptic event, and by long-term depression (LTD), when the temporal order is reversed. In this article, we present a biophysical model of STDP based on a differential Hebbian learning rule (ISO learning). This rule correlates presynaptically the NMDA channel conductance with the derivative of the membrane potential at the synapse as the postsynaptic signal. The model is able to reproduce the generic STDP weight change characteristic. We find that (1) The actual shape of the weight change curve strongly depends on the NMDA channel characteristics and on the shape of the membrane potential at the synapse. (2) The typical antisymmetrical STDP curve (LTD and LTP) can become similar to a standard Hebbian characteristic (LTP only) without having to change the learning rule. This occurs if the membrane depolarization has a shallow onset and is long lasting. (3) It is known that the membrane potential varies along the dendrite as a result of the active or passive backpropagation of somatic spikes or because of local dendritic processes. As a consequence, our model predicts that learning properties will be different at different locations on the dendritic tree. In conclusion, such site-specific synaptic plasticity would provide a neuron with powerful learning capabilities.     

Estimation of doses to personnel and patients during endovascular brachytherapy applications

In the last few years coronary endovascular brachytherapy using gamma- and beta-emitting radionuclides has been established as a standard treatment procedure to prevent restenosis after percutaneous coronary interventions. Direct measurements and calculations were made to determine personnel doses and organ doses of patients due to gamma rays of 192Ir and beta rays of 90Sr/90Y and 32P sources. In general, our results show that the dose levels are low compared with the X-ray exposure from angiography. The dose rate from bremsstrahlung at 1 m distance from a device containing a 90Sr/90Y source of 2.3 GBq is 4 micro Sv h(-1). The skin dose from beta rays during source transfer into and from the patient was estimated with the directional dose equivalent H'(0.07) of 10 micro Sv at 1 m distance from the catheter. By maintaining safe distances, the dose levels can be kept well within annual dose limits.     

Neural field model of receptive field restructuring in primary visual cortex

Receptive fields (RF) in the visual cortex can change their size depending on the state of the individual. This reflects a changing visual resolution according to different demands on information processing during drowsiness. So far, however, the possible mechanisms that underlie these size changes have not been tested rigorously. Only qualitatively has it been suggested that state-dependent lateral geniculate nucleus (LGN) firing patterns (burst versus tonic firing) are mainly responsible for the observed cortical receptive field restructuring. Here, we employ a neural field approach to describe the changes of cortical RF properties analytically. Expressions to describe the spatiotemporal receptive fields are given for pure feedforward networks. The model predicts that visual latencies increase nonlinearly with the distance of the stimulus location from the RF center. RF restructuring effects are faithfully reproduced. Despite the changing RF sizes, the model demonstrates that the width of the spatial membrane potential profile (as measured by the variance sigma of a gaussian) remains constant in cortex. In contrast, it is shown for recurrent networks that both the RF width and the width of the membrane potential profile generically depend on time and can even increase if lateral cortical excitatory connections extend further than fibers from LGN to cortex. In order to differentiate between a feedforward and a recurrent mechanism causing the experimental RF changes, we fitted the data to the analytically derived point-spread functions. Results of the fits provide estimates for model parameters consistent with the literature data and support the hypothesis that the observed RF sharpening is indeed mainly driven by input from LGN, not by recurrent intracortical connections.