Strukturuntersuchungen an einem Produkt der intramolekularen Diels-Alder-Reaktion Konfigurations- und Konformationsanalyse von 5-Methyl-2-phenyl-1H-2,3,3a,4,5,7a-hexahydroisoindol-1-on

Structure Elucidation of a Product of Intramolecular Diels-Alder-Reaction: Configurational and Conformational Analysis of 5-Methyl-2-phenyl-1H,2,3,3a,4,5,7a-hexahydroisoindol-1-one N-Allyl-N-phenylsorbamide 1 cyclizes at 160°C to give 5-methyl-2-phenyl-1H,2,3,3a,4,5,7a-hexahydroisoindol-1-one 2 . As a result of this intramolecular [4 + 2] cycloaddition four stereoisomeres 2a–2d can exist. The ¹H and ¹³C n.m.r. data are given. The ¹H n.m.r. studies demonstrate that the product of Diels-Alder cyclisation is the result of cis-fusion of the two rings. The nuclear Overhauser effect data provide further evidence for 2a in which the carbonyl group and methyl one are trans-arranged. The n.m.r. results are confirmed by X-ray studies.     

Condenser performance in a cylindrical humidification and dehumidification (HDH) system

In recent years, humidification and dehumidification (HDH) systems have garnered significant attention due to their enhanced effectiveness with packed beds, particularly for high-salinity waters. The direct-contact packed beds HDH system offers a more convenient and efficient installation compared with conventional HDH systems. This paper introduces a novel, compact cylindrical crossflow HDH system design that is easily constructed and scalable for industrial and residential applications. The compact crossflow-packed bed condenser employs perforated air tubes to distribute humidified air radially while cooling water drips vertically through the packed bed, coming into direct contact with the humidified air. To evaluate the system's performance, two-dimensional steady-state energy, and mass conservation equations were developed solving enthalpies instead of temperatures as dependents. The coupled partial differential equations were numerically solved to predict water temperature, air/vapor temperature, humidity ratio, and condenser effectiveness. Multiple designs were proposed, demonstrating that the proposed configuration can achieve effectiveness above 0.80 and a water production rate of 3.85 g/s under ideal operating conditions.     

Long-term reconstruction of energy fluxes in an alpine river: Effects of flow regulation and restoration

Flow regulation of montane and alpine headwater streams can fundamentally alter food web structure and energy flows through changes in productivity, resource availability, and community assembly. Dam flow-release schemes can be used to mitigate the environmental impacts of flow regulation via environmental flows, which can increase discharge variability and other ecologically important hydrological properties. In particular, managed floods can reintroduce disturbance to the system and stimulate the reactivation of physical habitat dynamics. However, how managed floods might restore ecosystem processes is virtually unknown. In this study, we examined patterns in potential energy fluxes before, during and after a long-term experimental flood program on the river Spöl, a regulated alpine River in southeast Switzerland. We used benthic samples collected during long-term monitoring and stable isotope analysis (δ¹³C and δ¹⁵N) of macroinvertebrates and their potential food sources to reconstruct secondary production, and potential energy fluxes, over a 20-year study period. The experimental floods did not alter the relative importance of basal resources but resulted in a considerable decline in secondary production, which remained low after the discontinuation of the floods. Our data suggest that a lack of recolonization by mosses following the discontinuation of the experimental flood program on the river Spöl may have driven patterns in energy fluxes by limiting macroinvertebrates using mosses for habitat. The effects of environmental flows on energy flows in this system thus depend on flood disturbance and the environmental context following the discontinuation of floods.     

A matheuristic approach for the minimum broadcast time problem using a biased random-key genetic algorithm

The Minimum Broadcast Time (MBT) is a well-known data dissemination problem whose goal is to find a broadcast scheme that minimizes the number of steps needed to execute the broadcast operation. The problem has many applications in distributed systems and, in particular, the Industry 4.0 domain. Because Industry 4.0 applications rely primarily on the use of large-scale machine to machine communications, they need data dissemination techniques that combine high reliability with low communication latency. This work proposes a Biased Random-Key Genetic Algorithm and a matheuristic for the MBT. We carry out experiments with our algorithms on instances commonly used in the literature (hypercube, shuffle exchange, cube-connected cycles, de Bruijn, Harary graphs), and also on massive synthetic instances (up to 1000 vertices), allowing to cover many possibilities of real industry topologies. Our proposal is also compared with state-of-the-art exact methods and heuristics. Experimental results show that our algorithm is able to outperform the best-known heuristics for the MBT, and also that it is a very good alternative for large instances that cannot be solved by current exact methods.     

It's time for an update—A perspective on fuel cell electrodes

Hydrogen fuel cell technology is gaining significant attention as a promising alternative for decarbonizing automotive vehicles. At the heart of hydrogen fuel cell technology is the electrode, composed of catalysts, supports, binders, and pores, which facilitates the half-cell reactions and often governs the efficiency of fuel cells. Over the last decade, scientists have made great strides in discovering catalyst, support, and binder materials featuring unique nanostructures and compositions that significantly enhance the efficiency of those devices. While innovations must continue, we must not overlook how these materials are put together to form an electrode and how it impacts the overall efficiency. This perspective article discusses the urgent need for developing alternative electrodes for designing next generation hydrogen fuel cells.     

Radiofrequency antenna concepts for human cardiac MR at 14.0 T

Objective

To examine the feasibility of human cardiac MR (CMR) at 14.0 T using high-density radiofrequency (RF) dipole transceiver arrays in conjunction with static and dynamic parallel transmission (pTx).

Materials and methods

RF arrays comprised of self-grounded bow-tie (SGBT) antennas, bow-tie (BT) antennas, or fractionated dipole (FD) antennas were used in this simulation study. Static and dynamic pTx were applied to enhance transmission field (B₁⁺) uniformity and efficiency in the heart of the human voxel model. B₁⁺ distribution and maximum specific absorption rate averaged over 10 g tissue (SAR_10g) were examined at 7.0 T and 14.0 T.

Results

At 14.0 T static pTx revealed a minimum B₁⁺_ROI efficiency of 0.91 μT/√kW (SGBT), 0.73 μT/√kW (BT), and 0.56 μT/√kW (FD) and maximum SAR_10g of 4.24 W/kg, 1.45 W/kg, and 2.04 W/kg. Dynamic pTx with 8 kT points indicate a balance between B₁⁺_ROI homogeneity (coefficient of variation < 14%) and efficiency (minimum B₁⁺_ROI > 1.11 µT/√kW) at 14.0 T with a maximum SAR_10g < 5.25 W/kg.

Discussion

MRI of the human heart at 14.0 T is feasible from an electrodynamic and theoretical standpoint, provided that multi-channel high-density antennas are arranged accordingly. These findings provide a technical foundation for further explorations into CMR at 14.0 T.

     

Material Properties and Glass Transition Temperatures of Different Thermoplastic Starches After Extrusion Processing

Four different starch sources, namely waxy maize, wheat, potato and pea starch were extruded with the plasticizer glycerol, the latter in concentrations of 15, 20 and 25% (w/w). The glass transition temperatures of the resulting thermoplastic products were measured by Dynamic Mechanical Thermal Analysis (DMTA). Beside mechanical and structural properties also the transition temperatures of the materials were evaluated during tensile and impact tests. Above certain glycerol contents, dependent on the starch source, a lower glass transition temperature T_g resulted in decreased modulus and tensile strengths and increased elongations. Lowering the T_g at different glycerol contents did not influence the impact strength. When the amylose/amylopectin ratio increased a decrease in T_g was found. For pea, wheat, potato and waxy maize starch the T_g was 75 °C, 143 °C, 152 °C and 158 °C, respectively. Therefore products with higher percentages of amylose are more flexible. The shrinkage of the specimens made by injection molding was considerable compared to the specimens made by pressing.