Safe stopping of running component-based distributed systems

Continuous availability of services and low degree of disruption are two inherent necessities for mission-critical software systems. These systems could not be stopped to perform updates because disruption in their services consequent irretrievable losses. Additionally, compared to offline update, the changes should preserve the correct completion of ongoing activities. In order to place the affected elements in a safe state before dynamic changes take place, the notion of tranquility has been proposed to make quiescence criterion less disruptive and easier to obtain. Additionally, some other approaches have been proposed in order to tackle the shortcomings of these seminal proposals. However, these approaches impose some challenges to the safe dynamic reconfiguration of component-based systems. In this paper, existing challenges to preserve global consistency during runtime software reconfiguration in distributed contexts are described. The contribution of this paper is to propose a number of guidelines which can be served as agenda for future direction of research to enable a dependable safe stopping of running component-based systems

An architectural approach to ensure globally consistent dynamic reconfiguration of component-based systems

One of the key issues that should be considered when addressing reliable evolution is to place a software system in a consistent status before and after change. This issue becomes more critical at runtime because it may lead to the failure on running missioncritical systems. In order to place the affected elements in a safe state before dynamic changes take place, the notion of tranquility has been proposed to make quiescence criterion less disruptive and easier to obtain. However, it only ensures consistency in applications with restrictive black-box design. In this paper, an architecture-based approach is proposed to preserve global consistency during runtime reconfiguration of component-based systems in distributed contexts. An initial evaluation through a prototypical implementation shows that this approach not only enables tranquility to be applicable for distributed transactions, but also significantly reduces required time to achieve a safe state and increases system availability during runtime evolution

Development of Novel Mixed Halide/Superhalide Tin-Based Perovskites for Mesoscopic Carbon-Based Solar Cells

Tin perovskites suffer from poor stability and a self-doping effect. To solve this problem, we synthesized novel tin perovskites based on superhalide with varied ratios of tetrafluoroborate to iodide and implemented them into solar cells based on a mesoscopic carbon-electrode architecture because film formation was an issue in applying this material for a planar heterojunction device structure. We undertook quantum-chemical calculations based on plane-wave density functional theory (DFT) methods and explored the structural and electronic properties of tin perovskites FASnI3–x(BF4)x in the series x = 0, 1, 2, and 3. We found that only the x = 2 case, FASnI­(BF4)2, was successfully produced, beyond the standard FASnI3. The electrochemical impedance and X-ray photoelectron spectra indicate that the addition of tin tetrafluoroborate instead of SnI2 suppressed trap-assisted recombination by decreasing the Sn4+ content. The power conversion efficiency of the FASnI­(BF4)2 device with FAI and Sn­(BF4)2 in an equimolar ratio improved 72% relative to that of a standard FASnI3 solar cell, with satisfactory photostability under ambient air conditions

Ag Doping of Organometal Lead Halide Perovskites: Morphology Modification and p‑Type Character

We report a simple synthetic approach to grow uniform CH₃NH₃PbI₃ perovskite (PSK) layers free of pinholes via varied portions of silver iodide (AgI) added to the precursor solution. XRD/EDS elemental mapping experiments demonstrated nearly uniform Ag distribution inside the perovskite film. When the 1% AgI-assisted perovskite films were fabricated into a p-i-n planar device, the photovoltaic performance was enhanced by ∼30% (PCE increased from 9.5% to 12.0%) relative to the standard cell without added AgI. Measurement of electronic properties using a hall setup indicated that perovskite films show p-type character after Ag doping, whereas the film is n-type without Ag. Transients of photoluminescence of perovskite films with and without AgI additive deposited on glass, p-type (PEDOT:PSS), and n-type (TiO₂) contact layers were recorded with a time-correlated single-photon counting (TCSPC) technique. The TCSPC results indicate that addition of AgI inside perovskite in contact with PEDOT:PSS accelerated the hole-extraction motion whereas that in contact with TiO₂ led to a decelerated electron extraction, in agreement with the trend observed from the photovoltaic results. The silver cationic dopant inside the perovskite films had hence an effect of controlling the morphology to improve photovoltaic performance for devices with p-i-n configuration