Fracture toughness of unidirectional fiber-metal laminates: crack orientation effect

Fiber-metal laminates (FMLs) are structural composites developed for aeronautical applications. The application of FMLs to structures demands a deep knowledge of a wide set of properties, including fracture toughness. The objective of this work was to evaluate the effect of crack orientation on the fracture toughness (critical J-integral and CTOD δ₅) of unidirectional FMLs. Small C(T) and SE(B) specimens with notches parallel and perpendicular to the fibers direction were tested. A study of the relation and equivalence between J_C and δ_5C, which heavily depend on the yield strength and on the stress state, was performed motivated by apparently contradictory experimental results. These results can be explained by the direction-dependent yielding properties of unidirectional FMLs. The best overall equivalence between J_C and δ_5C was obtained considering plane stress state and using the effective yield strength, both for unidirectional FMLs notched parallel and perpendicular to the fibers direction.     

Optimized Design of Plasmonic MSM Photodetector

We present an optimized design for a plasmonic metal-semiconductor-metal photodetector with interdigitated electrodes with subwavelength dimensions and a single GaInNAs quantum well (QW) as an absorbing layer. The excitation of surface plasmons at the metal-semiconductor interface leads to a strong field enhancement near the metallic electrodes. This results in an increased absorption in the QW, allowing both fast electrical response of the photodetector and high quantum efficiencies. With a grating periodicity of 820 nm and electrode finger width of 460 nm a 16-fold increase in the absorption of p-polarized light in the QW is achieved in comparison to the case without electrodes.     

Synthesis and nanoindentation study of high-velocity oxygen fuel thermal-sprayed nanocrystalline and near-nanocrystalline Ni coatings

In the present work, the nanoindentation technique was used to study the behavior of nanocrystalline Ni coatings. Two different types of Ni coatings were synthesized. One of the coatings was prepared with a commercial-grade Ni powder (as received, near-nanocrystalline), and the second coating was sprayed with the same powder, after having been mechanically milled in liquid nitrogen for 15 hours (nanocrystalline). Identical high-velocity oxygen fuel (HVOF) spray parameters were used for both types of coatings. The oxide-phase content in each coating was analyzed. The microstructure and properties of the milled powders and as-sprayed coatings were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nanoindentation. The average grain size of the as-received powder was 140±52 nm, and that of the as milled powders was 15.7±5.1 nm. The near-nanocrystalline coating microstructure was composed of grains with an average grain size of 280±39 nm, and the nanocrystalline coating was composed of nanocrystalline grains with an average grain size of 92±41 nm. The nanoindentation technique was applied to characterize the coating hardness under different penetration depths. The indentation size effect (or ISE) has been observed and correlated to the microstructure of the coatings. The results show that the assumption of geometrically necessary dislocations was valid for this study. A critical indentation depth was identified for measuring the intrinsic properties of the constituent material of the coating (≲500 nm).     

System Level Modeling of Microsystems Using Order Reduction Methods

The dynamic element matching (DEM) techniques for digital-to-analog converters(DACs) has been suggested as a promising method to improve matching between the DAC's referencelevels. However, no work has so far taken the dynamic effects that limit the performance for higher frequenciesinto account. In this paper we present a model describing the dynamic properties of a DEM DAC and compare thesimulated results with measurements of a 14-bit current-steering DEM DAC implemented in a 0.35-m CMOSprocess. The measured data agrees well with the results predicted by the used model. It is also shown that theDEM technique does not necessarily increase the performance of a DAC when dynamic errors are dominating theachievable performance.     

Determination of boswellic acids in brain and plasma by high-performance liquid chromatography/tandem mass spectrometry

Peritumoral edema, one of the major causes for neurological disorders in brain tumor patients, is mainly treated with steroids, which unfortunately have significant side effects and interfere with the efficacy of chemotherapy. Boswellic acids, the main active ingredients of Boswellia serrata, are antiinflammatory agents, inhibiting 5-lipoxygenase, the key enzyme of leukotriene biosynthesis and one of the pathophysiological mechanisms of peritumoral edema. Based on positive results in clinical trials and animal studies, B. serrata resin dry extract was designated an orphan drug by the European Commission for the treatment of peritumoral edema resulting from brain tumors. Thus boswellic acids may be alternative drugs to corticosteroids. However, the question of the availability of boswellic acids in brain has not been addressed until now. Accordingly, a highly sensitive LC/MS method has been developed for the simultaneous determination of KBA and AKBA, the most potent boswellic acids, in plasma and brain. This method involves matrix-assisted liquid-liquid extraction on Extrelut NT followed by separation on reversed-phase high-performance liquid chromatography and tandem mass spectrometry detection using atmospheric pressure chemical ionization. Excellent linearity was obtained for the entire calibration range from 5 to 1500 ng/mL KBA and AKBA in plasma and 5 to 1000 ng/mL KBA and AKBA in brain. Validation assays of the lower limit of quantification as well as for the intra- and interday precision and accuracy met the international acceptance criteria for bioanalytical method validation. Moreover, the interchangeability of calibration curves generated in pork and rat brain homogenates could be demonstrated. Using the developed analytical method, KBA and AKBA could be detected for the first time in brain up to a concentration of 99 and 95 ng/g of brain, respectively, 3 h after the single oral administration of 240 mg/kg of dry B. serrata resin extract to Wistar rats. The developed method represents an appropriate tool to further study the time-dependent distribution of KBA and AKBA in plasma and brain as well as the absolute brain concentration after multiple doses and contributes thus to the optimization of the dosage regimen and to a better understanding of the therapeutic effects of B. serrata.     

Comparison of 14 PCR systems for the detection and subtyping of stx genes in Shiga-toxin-producing Escherichia coli

The specificity of 14 polymerase chain reaction (PCR) systems designed for the detection and subtyping of stx genes was tested on a set of Escherichia coli strains with known sequences of stx genes. Systems designed for the detection of genes of the stx1 type did not detect any variant genes of the stx2 type and conversely, no stx2 type-specific systems detected stx1 variant genes. Among five stx2 type-specific systems, none detected the stx2ev gene, and two detected the stx2e gene. Among systems designed for screening genes of the both stx1 and stx2 types with a single primer pair, only one system (the Lin system) was able to detect stx genes in all studied strains. Shiga-toxin-producing E. coli frequently carry more than one stx variant gene. Coamplification of stx genes present in the same strain was demonstrated by restriction of PCR products with endonucleases generating fragments of variant-specific size. The amplification product obtained by the Lin system restricted by Hincll yielded fragments of different size for stx1, stx2, stx2c, stx2e and stx2ev. Thus it was possible to identify different genes carried in a single strain with a simple two-step PCR/endonuclease restriction protocol.     

Inhibition by salmon calcitonin (SCT) of desoxycorticosterone acetate (DOCA) induced hypertension in the rat

Two cases of a continuous murmur following an acute pulmonary embolic episode are presented, and eight previously reported cases with an acquired postembolic continuous murmur (found in a review of the literature) are discussed. This finding is present in both chronic and acute pulmonary embolism and is suggestive of significant embolic obstruction. Although the continuous murmur is an unusual sign in patients with pulmonary embolism, its auscultation is often quite distinctive, and its appearance may lead to more definitive diagnostic studies when the presentation or associated clinical findings are nonspecific.     

Heterogeneously Catalyzed Hydrogenation of Supercritical CO2 to Methanol

Interest in energy storage technologies is still increasing in times of excess of electricity generated by wind farms or solar plants. A key part of the energy storage technologies plays the efficient conversion of H₂ and CO₂ from renewable resources. Here, the process conditions for continuous catalytic hydrogenation of CO₂ to CH₃OH under supercritical conditions over lab‐synthesized Cu/ZnO/Al₂O₃ catalysts were investigated. A possible in situ phase separation of reaction products within the reactor due to the higher densities of the reaction mixture by the higher pressure could affect the kinetics and simplify downstream processing. The combination of thermodynamic studies and catalytic performance tests for CO₂ hydrogenation under supercritical conditions is discussed and a process concept is presented.