Electrical discharge machining of B4C-TiB2 composites

The interrelationships between the microstructure and electrical discharge machining (EDM) behaviour of B₄C-TiB₂ composites with respectively 30, 40 and 60 vol.% TiB₂ are investigated. Special attention was given to the influence of the grain size on the EDM behaviour by producing composites with an ultrafine TiB₂ phase using in situ synthesis during PECS. The experimental work revealed that 40 vol.% of TiB₂ results in an optimal material removal rate while the surface roughness for rough cut EDM decreases with increasing TiB₂ content. The finer microstructure of the ultrafine composite shows higher MRR's and lower R_a values than the commercial powder based composites. The major material removal mechanism for the PECS based composites was melting. The 3 point bending strength of all composites after grinding, EDM rough cut and EDM finish cut was not statistically different and about 800 MPa. The EDM recast layer was analysed by X-ray photoelectron spectroscopy.     

Do Matrix Metalloproteases and Tissue Inhibitors of Metalloproteases in Tenocytes of the Rotator Cuff Differ with Varying Donor Characteristics?

An imbalance between matrix metalloproteases (MMPs) and the tissue inhibitors of metalloproteases (TIMPs) may have a negative impact on the healing of rotator cuff tears. The aim of the project was to assess a possible relationship between clinical and radiographic characteristics of patients such as the age, sex, as well as the degenerative status of the tendon and the MMPs and TIMPs in their tenocyte-like cells (TLCs). TLCs were isolated from ruptured supraspinatus tendons and quantitative Real-Time PCR and ELISA was performed to analyze the expression and secretion of MMPs and TIMPs. In the present study, MMPs, mostly gelatinases and collagenases such as MMP-2, -9 and -13 showed an increased expression and protein secretion in TLCs of donors with higher age or degenerative status of the tendon. Furthermore, the expression and secretion of TIMP-1, -2 and -3 was enhanced with age, muscle fatty infiltration and tear size. The interaction between MMPs and TIMPs is a complex process, since TIMPs are not only inhibitors, but also activators of MMPs. This study shows that MMPs and TIMPs might play an important role in degenerative tendon pathologies.     

Synthesis of Novel Nitroxoline Analogs with Potent Cathepsin B Exopeptidase Inhibitory Activity

Nitroxoline, a well-known antimicrobial agent, has been identified in several independent studies, and on different molecular targets, as a promising candidate to be repurposed for cancer treatment. One specific target of interest concerns cathepsin B, a lysosomal peptidase involved in the degradation of the extracellular matrix (ECM), leading to tumor invasion, metastasis and angiogenesis. However, dedicated optimization of the nitroxoline core is needed to actually deliver a nitroxoline-based antitumor drug candidate. Within that context, 34 novel nitroxoline analogs were synthesized and evaluated for their relative cathepsin B inhibitory activity, their antiproliferative properties and their antimicrobial activity. More than twenty analogs were shown to exert a similar or even slightly higher cathepsin B inhibitory activity compared to nitroxoline. The implemented modifications of the nitroxoline scaffold and the resulting SAR information can form an eligible basis for further optimization toward more potent cathepsin B inhibitors in the quest for a clinical nitroxoline-based antitumor agent.     

Alumina-Protected,Durable and Photostable Zinc Sulfide Particles from Scalable Atomic Layer Deposition

Zinc sulfide has unique and easily modifiable photophysical properties and is a promising candidate for photocatalysis and optoelectronic devices. However, ZnS suffers from corrosive decomposition during excitation processes like UV irradiation, which drastically limits its field of potential applications. For the first time, complete photostabilization of individual ZnS particles by a dense, durable, and only 3-nm-thick Al₂O₃ layer, produced by rotary atomic layer deposition (ALD) is reported. In contrast to bare ZnS, the coated particles do not suffer from photocorrosive degradation even under long-term or high power UV irradiation. The presence of a protection layer covering the entire ZnS surface is additionally confirmed by microscopic and spectroscopic investigations of particle cross-sections. Further, complete inhibition of the reaction between Ag⁺ ions added as the analyte and the ZnS surface is observed. Durability tests of the as-prepared Al₂O₃ layer upon prolonged exposure to water reveal a significant decrease in the protection capability of the layer, which is ascribed to the hydrolysis of the amorphous Al₂O₃. A calcination step at 1000 °C after the ALD treatment, which leads to crystallization of the amorphous Al₂O₃ layer, successfully suppresses this hydrolysis and produces an insulating, dense, and inert protection layer.     

Identification of boundary heat fluxes in a falling film experiment using high resolution temperature measurements

In this paper, we consider a three-dimensional inverse heat conduction problem (IHCP) in a falling film experiment. The wavy film is heated electrically by a thin constantan foil and the temperature on the back side of this foil is measured by high resolution infrared (IR) thermography. The transient heat flux at the inaccessible film side of the foil is determined from the IR data and the electrical heating power. The IHCP is formulated as a mathematical optimization problem, which is solved with the conjugate gradient method. In each step of the iterative process two direct transient heat conduction problems must be solved. We apply a one step θ-method and piecewise linear finite elements on a tetrahedral grid for the time and space discretization, respectively. The resulting large sparse system of equations is solved with a preconditioned Krylov subspace method. We give results of simulated experiments, which illustrate the performance and tuning of the solution method, and finally present the estimation results from temperature measurements obtained during falling film experiments.