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In this work, the dual effect of Na in the copper indium gallium diselenide (CIGS) absorber is studied. Na doping exhibits a drastic improvement of the cell efficiency mainly by an increase in the open‐circuit current and fill factor. However, when the Na content is too high, it can deteriorate the cell properties and performance. Nonetheless, it is still beneficial when compared with a cell without Na inside. Here, we therefore use electron backscatter diffraction, atom probe tomography, and admittance spectroscopy to understand why Na starts to deteriorate the properties when inserted excessively. More exactly, it is shown that a moderate addition of Na strongly decreases the open‐circuit voltage (VOC) deficit, whereas the opposite happens when the Na content is too high. Interestingly, this cell with deteriorated VOC value and characterized by a very high Na content exhibits a high density of not only grain boundaries and dislocations but also of Na‐rich clusters. These clusters may host a high concentration of deep defects and trap the electrons within the CIGS bulk. At this stage, Na still has its beneficial effects, but the cell properties start to deteriorate compared to the cell with a moderate content of Na, especially when found as clusters in the bulk. In conclusion, this work clearly demonstrates the dual effect of Na in the CIGS absorber. [ABSTRACT FROM AUTHOR]

Unmanned underwater vehicles which use biomimetic mechanisms are becoming increasingly useful in the realisation of tasks requiring silent and efficient propulsion. Complex fish kinematics are simplified to some extent and implemented in such vehicles. One of the essential fish behaviours is their ability to adjust their buoyancy using a swim bladder. This paper covers the issues concerning the implementation of artificial swim bladders as well as depth regulators in two underwater vehicles: biomimetic and hybrid. The control of vehicle depth through buoyancy change was examined in the computer simulation and in the experiment. Two types of artificial swim bladder were tested – a rigid cylinder with a piston and an elastic container with a water pump.

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This paper presents a mathematical model of the heat and mass transfer processes for a rotary-spray honey dehydrator with a heat pump and a closed air circuit. An analytical calculation model, based on the energy balance equations of the dehydrator and heat pump, was used to model the transient dehydration process of honey in a dehydrator. The presented article includes a different approach to modelling both the dryer and the heat pump assisting the drying process. The novel quality of this study lies in the use of original equations to determine the heat and mass transfer coefficients between honey and air and using an actual model of a cooling unit to model the honey dehydration process. The experimentally verified calculation algorithm enables an analysis of the effects of air flow rate, mixer rotation speed, and cooling unit power on the efficiency of the drying process. The dehydrator calculation model was used to minimize the drying time by selecting the optimal evaporative temperature values of the cooling unit. For fixed mixer speed and air flow rates, optimal values of evaporation temperatures allow for 8–13% reduction in honey drying time and an increase in the specific moisture extraction rate (SMER) by 4–32%. [ABSTRACT FROM AUTHOR]

Thin‐film solar cells based on Cu(In,Ga)Se2 (CIGSe) absorber layers reach conversion efficiencies of above 20%. One key to this success is the incorporation of alkali metals, such as Na and K, into the surface and the volume of the CIGSe thin film. The present work discusses the impact of Na and K on the grain‐boundary (GB) properties in CIGSe thin films, i.e., on the barriers for charge carriers, Φb, and on the recombination velocities at the GBs, sGB. First, the physics connected with these two quantities as well as their impact on the device performance are revised, and then the values for the barrier heights and recombination velocities are provided from the literature. The sGB values are measured by means of a cathodoluminescence analysis of Na‐/K‐free CIGSe layers as well as on CIGSe layers on Mo/sapphire substrates, which are submitted to only NaF or only KF postdeposition treatments. Overall, passivating effects on GBs by neither Na nor K can be confirmed. The GB recombination velocities seem to remain on the same order of magnitude, in average about 103–104 cm s−1, irrespective of whether CIGSe thin films are Na‐/K‐free or Na‐/K‐containing. [ABSTRACT FROM AUTHOR]

Background: Data on routine hypothermic machine perfusion of livers procured from donors after brain death (DBD) are scarce, and the benefits of the method have only been demonstrated in extended criteria grafts. The aim of this study was to assess if end-ischemic dual hypothermic oxygenated machine perfusion (dHOPE) is superior to static cold storage (SCS) in preservation of livers procured from DBD donors with respect to long-term outcomes. Existing data on short-term outcomes favours dHOPE in patients receiving high-risk grafts., Methods: This prospective randomized controlled trial included 104 recipients of DBD livers randomly assigned to static cold storage arm (78 patients) and dHOPE arm (26 patients). Endpoints of interest were occurrence of biliary complications (biliary fistula, anastomotic, and nonanastomotic strictures) and overall patient (OS) and graft survival (GS) during two-year follow-up., Results: A total of 36 patients developed biliary complications (at least one event) - 6 events in dHOPE arm and 30 in SCS arm. There was no significant difference in biliary complications between groups (23.7% vs. 43.4% [P=0.11]). No differences were found significant with respect to anastomotic (19.9% vs. 33.7% [P=0.20]) and non-anastomotic strictures (0% vs. 11.1% [P=0.10]) as well as biliary fistulas (11.7% vs. 12.2% [P=0.93]). Survival analysis did not show significantly different result in the study population - OS: 92.3% in dHOPE and 83.9% in SCS (P=0.35), and GS: 92.3% and 81.4% (P=0.23), respectively. However, significant difference in GS was noted in recipients of high-risk grafts - 100% in dHOPE and 73.1% in SCS, respectively (P=0.038)., Conclusions: The long-term outcome data suggest that the routine use of dHOPE may be beneficial for recipients of high-risk grafts from DBD donors. The present study does not provide any evidence for benefits of dHOPE in low-risk grafts., (Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc.)