Halide perovskites have emerged as promising candidates for various applications, such as photovoltaic, optoelectronic and thermoelectric applications. The knowledge of the thermal transport of ...halide perovskites is essential for enhancing the device performance for these applications and improving the understanding of heat transport in complicated material systems with atomic disorders. In this work, the current understanding of the experimentally and theoretically obtained thermal transport properties of halide perovskites is reviewed. This study comprehensively examines the reported thermal conductivity of methylammonium lead iodide, which is a prototype material, and provides theoretical frameworks for its lattice vibrational properties. The frameworks and discussions are extended to other halide perovskites and derivative structures. The implications for device applications, such as solar cells and thermoelectrics, are discussed.
This study seeks to analyze the trends in research studies in the past decade which have utilized Google Trends, a new source of big data, to examine how the scope of research has expanded. Our ...purpose is to conduct a comprehensive and objective research into how the public use of Big Data from web searches has affected research, and furthermore, to discuss the implications of Google Trends in terms of Big Data utilization and application. To this end, we conducted a network analysis on 657 research papers that used Google Trends. We also identified the important nodes of the networks and reviewed the research directions of representative papers. The study reveals that Google Trends is used to analyze various variables in a wide range of areas, including IT, communications, medicine, health, business and economics. In addition, this study shows that research using Google Trends has increased dramatically in the last decade, and in the process, the focus of research has shifted to forecasting changes, whereas in the past the focus had been on merely describing and diagnosing research trends, such as surveillance and monitoring. This study also demonstrates that in recent years, there has been an expansion in analysis in linkage with other social Big Data sources, as researchers attempt to overcome the limitations of using only search information. Our study will provide various insights for researchers who utilize Google Trends as well as researchers who rely on various other sources of Big Data in their efforts to compare research trends and identify new areas for research.
•Google Trends already been used to analyse user's interests across various fields.•The purpose of Big Data utilization is now shifting toward forecasting from monitoring.•For accurate forecasting, additional analyses such as sentiment will be required.•Diverse sources (ex, SNS) are being analysed together to overcome various limitations•To conduct precise analysis using Big Data, access to raw data should be expanded
Bimolecular and trap‐assisted recombination mechanisms are investigated in small molecule‐based phosphorescent organic light emitting diodes (PhOLEDs) using the current−voltage−luminance ...characteristics in the diffusion current region, along with transient electroluminescence and capacitance measurements. Two different PhOLEDs, one with a single host, 4,4′‐Bis(carbazol‐9‐yl)biphenyl, and the other with an exciplex‐forming co‐host, are studied. Trap‐assisted recombination with a large number of trapped charges is dominant in the PhOLED with the single host because of the large energy gap between the host and the dopant state. In contrast, bimolecular Langevin recombination is dominant in the PhOLED with the exciplex forming co‐host, where a phosphorescent dye is doped in the co‐host. As a result, the accumulated charge density is lower in the co‐host system than in the single host emission layer, leading to high efficiency that approaches the theoretical limit, with an extremely low efficiency roll‐off.
The origin
of the ultimate efficiency with extremely low efficiency roll‐off in a PhOLED with exciplex‐forming co‐host (quasi‐single host) is unveiled. Unlike the other PhOLEDs with single host which is dominantly governed by trap assisted recombination, Langevin assisted recombination is dominated in the PhOLED with quasi‐single host system, resulting in low accumulation of charges in the device.
Anosmia, the loss of smell, is a common and often the sole symptom of COVID-19. The onset of the sequence of pathobiological events leading to olfactory dysfunction remains obscure. Here, we have ...developed a postmortem bedside surgical procedure to harvest endoscopically samples of respiratory and olfactory mucosae and whole olfactory bulbs. Our cohort of 85 cases included COVID-19 patients who died a few days after infection with SARS-CoV-2, enabling us to catch the virus while it was still replicating. We found that sustentacular cells are the major target cell type in the olfactory mucosa. We failed to find evidence for infection of olfactory sensory neurons, and the parenchyma of the olfactory bulb is spared as well. Thus, SARS-CoV-2 does not appear to be a neurotropic virus. We postulate that transient insufficient support from sustentacular cells triggers transient olfactory dysfunction in COVID-19. Olfactory sensory neurons would become affected without getting infected.
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•A postmortem bedside surgical procedure was developed for COVID-19 and control patients•Ciliated cells are the main target cell type for SARS-CoV-2 in the respiratory mucosa•Sustentacular cells (non-neuronal) are the main target cell type in the olfactory mucosa•No evidence for infection of olfactory sensory neurons or olfactory bulb parenchyma
Postmortem samples of respiratory and olfactory mucosa and whole olfactory bulbs are harvested immediately after the death of COVID-19 patients revealing ciliated cells and sustentacular cells but not olfactory sensory neurons as the main target cell types for SARS-CoV-2 infection and replication.
The exciplex forming co‐host with phosphorescent dopant system has potential to realize highly efficient phosphorescent organic light emitting didoes (PhOLEDs). However, the exciplex forming co‐host ...for blue phosphorescent OLEDs has been rarely introduced because of higher triplet level of the blue dopant than green and red dopants. In this work, a novel exciplex forming co‐host with high triplet energy level is developed by mixing a phosphine oxide based electron transporting material, PO‐T2T, and a hole transporting material, N,N′‐dicarbazolyl‐3,5‐benzene (mCP). Photo‐physical analysis shows that the exciplexes are formed efficiently in the host and the energy transfer from the exciplex to blue phosphorescent dopant (iridium(III)bis(4,6‐difluorophenyl)‐pyridinato‐N,C2′picolinate; FIrpic) is also efficient, enabling the triplet harvest without energy loss. As a result, an unprecedented high performance blue PhOLED with the exciplex forming co‐host is demonstrated, showing a maximum external quantum efficiency (EQE) of 30.3%, a maximum power efficiency of 66 lm W−1, and low driving voltage of 2.75 at 100 cd m−2, 3.29 V at 1000 cd m−2, and 4.65 V at 10 000 cd m−2, respectively. The importance of the exciton confinement in the exciplex forming co‐host is further investigated which is directly related to the performance of PhOLEDs.
A novel exciplex forming host, composed of mCP and PO‐T2T, is realized. Using the host and efficient energy transfer to FIrpic, unprecedented high performance blue phosphorescent OLED is demonstrated, showing a maximum EQE of 30.3%, power efficiency of 66 lm W−1, and extremely low operating voltages of 2.75 at 100 cd m−2, and 4.65 V at 10 000 cd m−2.
A high‐efficiency blue‐emitting organic light‐emitting diode (OLED) approaching theoretical efficiency using an exciplex‐forming co‐host composed of N,N′‐dicarbazolyl‐3,5‐benzene (mCP) and ...bis‐4,6‐(3,5‐di‐3‐pyridylphenyl)‐ 2‐methylpyrimidine (B3PYMPM) is fabricated. Iridium(III)bis(4,6‐difluorophenyl)‐ pyridinato‐N,C2′picolinate (FIrpic) is used as the emitter, which turns out to have a preferred horizontal dipole orientation in the emitting layer. The OLED shows a maximum external quantum efficiency of 29.5% (a maximum current efficiency of 62.2 cd A−1), which is in perfect agreement with the theoretical prediction.
This article reviews recent progress on charge generation by doping and its influence on the carrier mobility in organic semiconductors (OSs). The doping induced charge generation efficiency is ...generally low in OSs which was explained by the integer charge transfer model and the hybrid charge transfer model. The ionized dopants formed by charge transfer between hosts and dopants can act as Coulomb traps for mobile charges, and the presence of Coulomb traps in OSs broadens the density of states (DOS) in doped organic films. The Coulomb traps strongly reduce the carrier hopping rate and thereby change the carrier mobility, which was confirmed by experiments in recent years. In order to fully understand the doping mechanism in OSs, further quantitative and systematic analyses of charge transport characteristics must be accomplished.
Electrical doping effects in disordered organic semiconductors are reviewed focusing on the charge generation and carrier mobility. The dopant materials and their charge generation efficiency are introduced firstly. Then the charge transfer processes are described based on two different models, namely the integer charge transfer model and the hybrid charge transfer complex model. The broadening of the Gaussian density‐of‐states upon doping is discussed and experimental results of the charge mobility in doped organic semiconductors are reviewed.
The external quantum efficiencies (EQEs) of the fluorescent organic light-emitting diodes (OLEDs) using exciplex as emitters are much lower than fluorescent OLEDs based on single-molecular thermally ...activated delayed fluorescent (TADF) emitters, even though exciplex can, in principle, realize 100% internal quantum efficiency (IQE). In addition, there are no clear guidelines to improve the efficiency in exciplex-based fluorescent OLEDs. Here, we quantitatively analyze the exciton dynamics influencing IQE of exciplex and demonstrate a fluorescent OLED with IQE of 100% and EQE of 25.2% at 150 K, which are improved from IQE of 48.3% and EQE of 11.0% at room temperature by reducing nonradiative transition of exciplex. This study shows that a high reverse intersystem crossing rate does not necessarily lead to efficient harvesting of triplet exciplex if it occurs with a high nonradiative transition rate (k nr). We harvested more triplet exciplex by adopting exciplex with low k nr and further suppressed the k nr by freezing the exciplex to achieve IQE of 100%.
Emerging evidence indicates that angiopoietin-2 (Angpt2), a well-recognized vascular destabilizing factor, is a biomarker of poor outcome in ischemic heart disease. However, its precise role in ...postischemic cardiovascular remodeling is poorly understood. Here, we show that Angpt2 plays multifaceted roles in the exacerbation of cardiac hypoxia and inflammation after myocardial ischemia. Angpt2 was highly expressed in endothelial cells at the infarct border zone after myocardial infarction (MI) or ischemia/reperfusion injury in mice. In the acute phase of MI, endothelial-derived Angpt2 antagonized Angpt1/Tie2 signaling, which was greatly involved in pericyte detachment, vascular leakage, increased adhesion molecular expression, degradation of the glycocalyx and extracellular matrix, and enhanced neutrophil infiltration and hypoxia in the infarct border area. In the chronic remodeling phase after MI, endothelial- and macrophage-derived Angpt2 continuously promoted abnormal vascular remodeling and proinflammatory macrophage polarization through integrin α5β1 signaling, worsening cardiac hypoxia and inflammation. Accordingly, inhibition of Angpt2 either by gene deletion or using an anti-Angpt2 blocking antibody substantially alleviated these pathological findings and ameliorated postischemic cardiovascular remodeling. Blockade of Angpt2 thus has potential as a therapeutic option for ischemic heart failure.
•Quantitative investigation of curing temperature for FA-based geopolymer strength.•Various micro-observation results through EDA, XRD, SEM, MIP.•Strength grading contour considering ...alkali-activators, Ms values, and curing temperatures.•Relationship between strength and changes in macro-pore structure.•Pre-curing effect with different temperature and duration on strength.
Many researches have been performed on performance improvement of geopolymer considering low calcium materials and alkaline solutions. In the binder of geopolymer, OPC (Ordinary Portland Cement) which can cause environmental load such as CO2 emission is not used. The mechanical properties of geopolymer are directly affected by various parameters like binder types, SiO2/Na2O molar ratios, alkali activator concentrations, and curing conditions (temperature and period), but very limited researches have been performed on comprehensive evaluation of the influencing parameters.
In the work, compressive strength in FA (Fly Ash)-based geopolymer is evaluated considering four test variables covering Na2O content, SiO2/Na2O molar ratios, curing temperature/period, and pre-curing temperature/period. The results reveal that higher compressive strength can be obtained with higher Na2O content, higher curing temperatures, and longer pre-curing periods at the relatively low temperature (23°C). On the other hand, an extension of curing period at high temperatures leads to strength reduction due to increasing macro-pores over 50nm. Through the various tests, strength grade contours considering SiO2/Na2O molar ratios, Na2O content, and curing temperatures are obtained, which can be utilized for an effective mix design for FA-based geopolymer.
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