Picosecond Capture of Photoexcited Electrons Improves Photovoltaic Conversion in MAPbI3:C70‐Doped Planar and Mesoporous Solar Cells

In this work, solar cells based on methylammonium lead iodide (MAPbI₃) doped in solution with C₇₀ fullerene in a mesoporous as well as planar electron‐transporting layer (ETL)‐free architecture are realized, showcasing in the latter case a record efficiency of 15.7% and an improved open‐circuit voltage (V_OC). Contrary to the bulk heterojunction previously reported, the C₇₀ molecules do not phase segregate and they are rather finely dispersed in the perovskite film, possibly infiltrating at the grain boundaries, while assisting the growth of a highly uniform perovskite layer. By means of time‐resolved femtosecond‐to‐nanosecond optical spectroscopy, with an extended spectral coverage, it is observed that electrons photogenerated in the perovskite are transferred to C₇₀ with a time constant of 20 ps. Despite being captured by C₇₀, electrons are not deeply trapped and can potentially bounce back into the perovskite, as suggested by the high fill factor and enhanced V_OC of the MAPbI₃:C₇₀ solar cells, especially in the case of the ETL‐free device configuration.     

Surface functionalization of BiFeO<Subscript>3</Subscript>: A pathway for the enhancement of dielectric and electrical properties of poly(methyl methacrylate)–BiFeO<Subscript>3</Subscript> composite films

A novel two-phase composite film is prepared by the solvent casting method employing poly(methyl methacrylate) (PMMA) as polymer matrix and bismuth ferrite (BFO) as ceramic filler. The surfaces of BFO are functionalized by proper hydroxylating agents to activate their chemical nature. The structural analysis of the composite films confirms that the composites made up of functionalized BFO (BFO-OH) have a distorted rhombohedral structure. The morphological analysis shows that BFO-OH particles are equally distributed over the polymer matrix. The -OH functionality of BFO-OH is confirmed by FTIR. The dielectric and electrical studies at a frequency range from 100 Hz to 1 MHz reveal that PMMA-(BFO-OH) composites have enhanced dielectric constant as well as electrical conductivities, much higher than that of unmodified composites. According to the ferroelectric measurement result, the hydroxylated composite film shows a superior ferroelectric behavior than that of the unmodified one, with a remanent polarization (2P_r) of 2.764 μC/cm².     

Synthesis and photocatalysis study of multiwalled carbon nanotubes grown in a lead-based microspherical support

Plumbonacrite films were used as support material for growth of carbon nanotubes and the resulting nanocomposite was tested as photocatalysts for the degradation of methylene blue dye. The plumbonacrite films were deposited on silicon substrates by a simple alkaline chemical bath deposition process. After the CNT growth process, the resulting nanocomposite samples were analyzed by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The high temperature during the CNT growth process decomposed the plumbonacrite material into lead microspheres, which were covered by the CNT constituting the nanocomposite films. Afterwards, the nanocomposite films were applied for the photodegradation of methylene blue molecules using natural sunlight. The nanocomposite films were reused for up to three cycles obtaining efficiencies in the degradation of the dye superior to 92% and a first order kinetics with rate constants of 8.9 × 10^?3 min^?1 in a maximum irradiation time of 240 minutes.     

Model-free reinforcement learning from expert demonstrations: a survey

Reinforcement learning from expert demonstrations (RLED) is the intersection of imitation learning with reinforcement learning that seeks to take advantage of these two learning approaches. RLED uses demonstration trajectories to improve sample efficiency in high-dimensional spaces. RLED is a new promising approach to behavioral learning through demonstrations from an expert teacher. RLED considers two possible knowledge sources to guide the reinforcement learning process: prior knowledge and online knowledge. This survey focuses on novel methods for model-free reinforcement learning guided through demonstrations, commonly but not necessarily provided by humans. The methods are analyzed and classified according to the impact of the demonstrations. Challenges, applications, and promising approaches to improve the discussed methods are also discussed.

     

EP2LBS: efficient privacy-preserving scheme for location-based services

The Journal of Supercomputing - Mobile users frequently change their location and often desire to avail of location-based services (LBS). LBS server provides services to users at the service...     

Time series analysis of co-polarization phase difference (PPD) for winter field crops using polarimetric C-band SAR data

The utility of time series polarimetric C-band data for vegetation state monitoring was explored to understand the mechanism of growth and phenology for important winter crops in India. Parameters investigated were HH–VV phase difference (co-polarization phase difference, PPD), amplitude ratio, and polarization indices. Data were acquired during the entire growth phase categorized as early, mid/peak vegetative, and post-vegetative /flowering phase. The trend emerging in this study showed a shift in the phase difference distribution for agricultural areas relating to the growth rate for various crops. The time series data set revealed that the PPD is a function of frequency and was directly affected by crop type (planophile or erectophile), vigour, structure, and crop biophysical parameters, particularly biomass. The behaviour of crop biomass with PPD responded differentially across crop architectures and vigour classes. Co-polarization index was found to be a good measure for discrimination in early growth stages while cross-polarization index suited in advanced vegetative stages where geometrical orientation was uniform. The PPD captured the change in frequency distribution resulting in a peaked distribution at sowing changing to smooth, well-spread frequency distribution as the peak vegetation stage approaches. This histogram nature is observed to be gradual for high-biomass crops and peaked in case of the low-biomass crops. It is indicative of the rate of growth; a low peaked normal curve indicates faster growth rate and resulting in high biomass. The amplitude ratio in the later phase of growth as on the third date is similarly altered as in the VV returns from the crop. Intuition of the rate of growth and plant vigour is obtained from the temporal PPD pattern. The current study shows that while phase differences and amplitude ratio carry little information content on a single resolution cell basis, their spatial distribution over a wider time span can be used to derive quantitative relationships between SAR response and crop condition. The synergy of information involving the above parameters were used to derive useful information on the vegetation.     

Three-phase two-way relaying with imperfect channel estimation and asymmetric traffic requirements: performance analysis and optimization

We study the effect of imperfect channel estimation (ICE) and asymmetric traffic requirements (ATRs) on the performance of bidirectional relaying with a direct link by employing three-phase analog network coding under Nakagami-m fading. Under such a realistic scenario, a tight lower bound on the overall outage probability is derived in closed-form, while a useful expression is presented for the asymptotically low outage regime. We also deduce the tight closed-form expression for the ergodic sum-rate. Furthermore, we formulate and solve analytically three optimization problems viz., relay power allocation under fixed location of the relay, relay position with fixed relay power allocation, and joint optimization of relay power allocation and location. Our results reveal that for given ICE, the optimal relay location offers significant system performance enhancement under ATRs, whilst the optimal relay power allocation has a more noticeable impact under symmetric traffic. It is also shown that the joint optimization of relay power allocation and location can further enhance the system performance, regardless of ATRs and ICE. Above all, based on the direct link quality, we show that the considered scheme outperforms its two-phase counterpart, even in the low signal-to-noise ratio regime.