Development of Creep Resistant Mg‐Gd‐Sc Alloys with Low Sc Content

High thermal stability and good mechanical properties are crucial for the wider future application of magnesium alloys. One of the most promising directions is the alloying of Mg with rare earth elements as Gd. The fine dispersion of metastable β′ phase (c‐base centred orthorhombic, a = 0.641 nm, b = 2.223 nm, c = 0.521 nm), already known from commercially successful WE alloys (Mg‐Y‐Nd‐Zr), precipitated in all three possible orientation modes during T6 treatment causes very pronounced age hardening in binary Mg‐Gd system and inhibits very effectively the dislocation motion during the creep. The stable β phase (Mg₅Gd, f.c.c. structure, a = 2.234 nm) ensures the creep resistance comparable to WE alloys. A high content of Gd (above 10 wt.%) is necessary to attain the required microstructure. The addition of Sc (below 1 wt.%) and Mn (about 1.5 wt.%) suppresses the solubility of Gd in Mg considerably. The complex precipitation process involving the precipitation of very stable Mn₂Sc, Mn and Gd containing phase and metastable β′ phase is responsible for superior creep properties of MgGd5Sc0.3Mn1 alloy at elevated temperatures. Even at 300°C the creep resistance is markedly better than for WE43 alloy. The increased Gd and Sc contents in MgGd10Sc0.8Mn1 alloy do not further improve the creep resistance.     

A TRNSYS-based simulation framework for the analysis of solar thermal and heat pump systems

The modeling and simulation of combined solar and heat pump (SHP) systems is a challenging task as it requires expert knowledge in modeling as well as in the behavior of the real systems. As an example of a SHP system, this work considers parallel solar thermal and heat pump systems with ground or air source heat pumps for the efficient energy supply of buildings. An introduction to SHP systems and the considered system concepts is given and the challenges in designing new models within the simulation environment TRNSYS are described. Finally, a TRNSYS-based stand-alone tool (SHP-SimFrame) ispresented which enables users to analyze predefined SHP concepts with hardly any knowledge in modeling and simulation itself.     

Hydrogen production by coupling pressurized high temperature electrolyser with solar tower technology

Solar hydrogen production by coupling of pressurized high temperature electrolyser with concentrated solar tower technology is studied. As the high temperature electrolyser requires constant temperature conditions, the focus is made on a molten salt solar tower due to its high storage capacity. A flowsheet was developed and simulations were carried out with Aspen Plus 8.4 software for MW-scale hydrogen production plants. The solar part was laid out with HFLCAL software. Two different scenarios were considered: the first concerns the production of 400 kg/d hydrogen corresponding to mobility use (fuel station). The second scenario deals with the production of 4000 kg/d hydrogen for industrial use. The process was analyzed from a thermodynamic point of view by calculating the overall process efficiency and determining the annual production. It was assumed that a fixed hydrogen demand exists in the two cases and it was assessed to which extent this can be supplied by the solar high temperature electrolysis process including thermal storage as well as hydrogen storage. For time periods with a potential over supply of hydrogen, it was considered that the excess energy is sold as electricity to the grid. For time periods where the hydrogen demand cannot be fully supplied, electricity consumption from the grid was considered. It was assessed which solar multiple is appropriate to achieve low consumption of grid electricity and low excess energy. It is shown that the consumption of grid electricity is reduced for increasing solar multiple but the efficiency is also reduced. At a solar multiple of 3.0 an annual solar-to-H₂ efficiency greater than 14% is achieved at grid electricity production below 5% for the industrial case (4000 kg/d). In a sensitivity study the paramount importance of electrolyser performance, i.e. efficiency and conversion, is shown.     

Design,development, construction and operation of a novel metal hydride compressor

Metal Hydride Compressors (MHC) is a promising technology for thermal compression of hydrogen. Besides the absence of a necessity for significant mechanical or electrical energy input, this type of compressor has the advantage that no moving parts are involved. A brief review on the reported experimental set ups of metal hydride compressors is carried out and compared to the metal hydride compressor developed and constructed by HYSTORE Technologies Ltd in Cyprus. The compressor built by HYSTORE consists of 6 stages using AB₂ and AB₅ – type metal hydride alloys. The MHC is operated between 10 C and 80 °C, which is a temperature range that can be supplied by solar thermal collectors. Furthermore, the experimental results showed, that even lower temperatures of 17 C are sufficient thus reducing the demand for cooling capacity. During the operation, the compressor achieved stable compression of hydrogen from 7 bar more than 220 bar. The specific productivity of the compressor achieved values up to 67.2 l_H2 kg^?1 h^?1.     

Wax esters and triglycerides as storage substances in seeds of Buxus sempervirens

The seeds of the evergreen Buxus‐tree, Buxus sempervirens, contain a yellowish oil which represents up to 42% of the dry weight. The oil consists, in comparison to the lipids of jojoba fruits (Simmondsia chinensis), of only 3.6% wax esters. 95% of the oil consist of triglycerides, the typical storage substances of oil fruits. Phospholipids occur with 0.4% and glycolipids with 0.13%. The fatty acid patterns of these lipids correspond to the typical fatty acid compositions of the respective lipid classes. In the wax esters monoenoic fatty acids and saturated fatty acids with 16 and 18 carbon atoms prevail. The glycolipid and phospholipid fractions are characterized by a high portion of dienoic and monoenoic as well as saturated fatty acids having 16 and 18 carbon acids.     

Effect of fault distribution and execution patterns on fault exposure in software: a simulation study

Execution patterns and fault distribution characteristics of a program will affect the failure process and thus reliability estimates. The failure process of a software system is influenced by many factors, and traditional software reliability engineering has found it difficult to isolate the effect of each individual factor. A simulation approach is used to investigate the effects of fault distribution, execution pattern and program structure on software reliability estimates. A reliability simulation environment (RSIM) is extended by introducing variable fault distribution patterns in its code generation phase. Flow control points allow varying the execution frequency of different parts of a program. The simulation results show that fault distribution patterns and execution patterns have dramatic effects on fault exposure rate. If the fault distribution is non‐uniform, a non‐uniform code execution exposes faults more efficiently and effectively than uniform execution. Results also show that the structure of a program affects fault exposure rate and testing time required. Copyright © 2000 John Wiley & Sons, Ltd.     

Overcoming Microenvironment-Mediated Chemoprotection through Stromal Galectin-3 Inhibition in Acute Lymphoblastic Leukemia

Environmentally-mediated drug resistance in B-cell precursor acute lymphoblastic leukemia (BCP-ALL) significantly contributes to relapse. Stromal cells in the bone marrow environment protect leukemia cells by secretion of chemokines as cues for BCP-ALL migration towards, and adhesion to, stroma. Stromal cells and BCP-ALL cells communicate through stromal galectin-3. Here, we investigated the significance of stromal galectin-3 to BCP-ALL cells. We used CRISPR/Cas9 genome editing to ablate galectin-3 in stromal cells and found that galectin-3 is dispensable for steady-state BCP-ALL proliferation and viability. However, efficient leukemia migration and adhesion to stromal cells are significantly dependent on stromal galectin-3. Importantly, the loss of stromal galectin-3 production sensitized BCP-ALL cells to conventional chemotherapy. We therefore tested novel carbohydrate-based small molecule compounds (Cpd14 and Cpd17) with high specificity for galectin-3. Consistent with results obtained using galectin-3-knockout stromal cells, treatment of stromal-BCP-ALL co-cultures inhibited BCP-ALL migration and adhesion. Moreover, these compounds induced anti-leukemic responses in BCP-ALL cells, including a dose-dependent reduction of viability and proliferation, the induction of apoptosis and, importantly, the inhibition of drug resistance. Collectively, these findings indicate galectin-3 regulates BCP-ALL cell responses to chemotherapy through the interactions between leukemia cells and the stroma, and show that a combination of galectin-3 inhibition with conventional drugs can sensitize the leukemia cells to chemotherapy.