Although pretrained Transformers such as BERT achieve high accuracy on indistribution examples, do they generalize to new distributions? We systematically measure out-of-distribution (OOD) generalization for seven NLP datasets by constructing a new robustness benchmark with realistic distribution shifts. We measure the generalization of previous models including bag-of-words models, ConvNets, and LSTMs, and we show that pretrained Transformers' performance declines are substantially smaller. Pretrained transformers are also more effective at detecting anomalous or OOD examples, while many previous models are frequently worse than chance. We examine which factors affect robustness, finding that larger models are not necessarily more robust, distillation can be harmful, and more diverse pretraining data can enhance robustness. Finally, we show where future work can improve OOD robustness.
The high density of heat generated in power electronics and optoelectronic devices is a critical bottleneck in their application. New materials with high thermal conductivity are needed to effectively dissipate heat and thereby enable enhanced performance of power controls, solid-state lighting, communication, and security systems. We report the experimental discovery of high thermal conductivity at room temperature in cubic boron arsenide (BAs) grown through a modified chemical vapor transport technique. The thermal conductivity of BAs, 1000 ± 90 watts per meter per kelvin meter-kelvin, is higher than that of silicon carbide by a factor of 3 and is surpassed only by diamond and the basal-plane value of graphite. This work shows that BAs represents a class of ultrahigh-thermal conductivity materials predicted by a recent theory, and that it may constitute a useful thermal management material for high-power density electronic devices.
Gefitinib, a small molecule inhibitor of the epidermal growth factor receptor tyrosine kinase, has been shown to induce autophagy as well as apoptosis in tumor cells. Yet, how to exploit autophagy and apoptosis to improve therapeutic efficacy of this drug against cancer remains to be explored. We reported here that MK-2206, a potent allosteric Akt inhibitor currently in Phase I trials in patients with solid tumors, could reinforce the cytocidal effect of gefitinib against glioma. We found that co-treatment with gefitinib and MK-2206 increased the cytotoxicity of this growth factor receptor inhibitor in the glioma cells, and the Compusyn synergism/antagonism analysis showed that MK-2206 acted synergistically with gefitinib. The benefit of the combinatorial treatment was also demonstrated in an intracranial glioma mouse model. In the presence of MK-2206, there was a significant increase in apoptosis in glioma cells treated with gefitinib. MK-2206 also augmented the autophagy-inducing effect of gefitinib, as evidenced by increased levels of the autophagy marker, LC3-II. Inhibition of autophagy by silencing of the key autophagy gene, beclin 1 or 3-MA, further increased the cytotoxicity of this combinatorial treatment, suggesting that autophagy induced by these agents plays a cytoprotective role. Notably, at 48 hours following the combinatorial treatment, the level of LC3-II began to decrease but Bim was significantly elevated, suggesting a switch from autophagy to apoptosis. Based on the synergistic effect of MK-2206 on gefitinib observed in this study, the combination of these two drugs may be utilized as a new therapeutic regimen for malignant glioma.
Although perovskite solar cells (PSCs) have attracted enormous attention owing to their fascinating optoelectronic properties and solution processability, defects in PSCs, which adversely affect efficiency and stability, are still not completely resolved. Herein, a novel indacenodithieno[3,2‐b]thiophene‐based small molecule (SM) additive (IDTT‐ThCz), capable of interacting with perovskite layers, is developed. In particular, the IDTT‐ThCz, which can perform a surface passivation, is introduced into the perovskite layer to significantly suppress perovskite defects via antisolvent treatment. Furthermore, this facile surface passivation not only significantly improves the charge extraction capability, but also prevents perovskite degradation. The IDTT‐ThCz‐treated PSCs exhibits a power conversion efficiency (PCE) of 22.5% and retains 95% of its initial PCE after 500 h storage under thermal condition (85 °C), representing the most remarkable efficiency as well as stability among the SM additives reported to date.
Rapid progress achieved on perovskite solar cells raises the expectation for their further development toward practical applications. Moisture sensitivity of perovskite materials is one of the major obstacles which limits the long-term durability of the perovskite solar cells, especially in outdoor operation where rainfall and water accumulation on the solar panels often occur. Micro/nanopinholes within the functional layers of the devices usually lead to water vapor penetration, thus subsequent decomposition of perovskites, and finally poor device performance and shortened operational lifetime. In this work, low-temperature atomic layer deposition (ALD) technique was utilized to incorporate pinhole-free metal oxide layers (TiO and AlO) into an inverted perovskite solar cell consisting of indium tin oxide/NiO/perovskite/PCBM/TiO/Ag. The interface properties between the inserted TiO layer and the perovskite layer were investigated by X-ray photoelectron spectroscopy. The results showed that TiO ALD fabrication process had made negligible degradation to the perovskite layer. The TiO layer can significantly reduce interfacial charge recombination loss, improve interfacial contact, and enhance water resistance. A maximum power conversion efficiency (PCE) of 18.3% was achieved for devices with TiO interface layers. A stacked AlO encapsulation layer was designed and deposited on top of the devices to further improve device stability under harsh environmental conditions. The encapsulated devices with the best performance retained 97% of the initial PCE after being stored in ambient condition for a thousand hours. They also showed great water resistance, and no significant degradation in terms of PCE and photocurrent of the devices was observed after they were immersed in deionized water for as long as 2 h. Our approach offers a promising way of developing highly efficient and stable perovskite solar cells under real-world operational conditions.
Zinc blende boron arsenide (BAs), boron phosphide (BP), and boron nitride (BN) have attracted significant interest in recent years due to their high thermal conductivity (Λ) predicted by first-principles calculations. This research reports the study of the temperature dependence of Λ (120 K < T < 600 K) for natural isotope-abundance BP and isotopically enriched 11 BP crystals grown from modified flux reactions. Time-domain thermoreflectance is used to measure Λ of sub-millimeter-sized crystals. At room temperature, Λ for BP and 11 BP is 490 and 540 W m −1 K −1 , respectively, surpassing the values of conventional high Λ materials such as Ag, Cu, BeO, and SiC. The Λ of BP is smaller than only cubic BN, diamond, graphite, and BAs among single-phase materials. The measured Λ for BP and 11 BP is in good agreement with the first-principles calculations above 250 K. The quality of the crystals is verified by Raman spectroscopy, X-ray diffraction, and scanning transmission electron microscopy. By combining the first-principles calculations and Raman measurements, a previously misinterpreted Raman mode is reassigned. Thus, BP is a promising material not only for heat spreader applications in high-power microelectronic devices but also as an electronic material for use in harsh environments.
This article reviews various dopant-free hole transporting materials (HTMs) used in perovskite solar cells (PSCs) in three main categories including inorganic, polymeric, and small molecule HTMs. PSCs have undergone rapid progress, achieving power conversion efficiencies (PCEs) above 22%. With their low production cost and high efficiencies, PSCs are considered promising next-generation solar cell technology. In all developed architectures for PSCs, including planar and mesoscopic with conventional and inverted structures, HTMs play a significant role in determining the photovoltaic performance of PSCs. Using p-type dopants, however, is considered a common strategy to increase the hole conductivity of HTM, which is usually compensated by a more complicated fabrication procedure, higher production costs, and lower stability of PSC. Although several reviews on HTMs have been published, progress on dopant free HTMs needs to be reviewed and analyzed. Here, a review covering most of the published reports on dopantfree HTMs is presented, and the device structure and fabrication method, HTM layer deposition techniques, and the efficiency and the stability of PSCs are addressed during discussions in each main category. Finally, an outlook on stability and PCE growth in PSCs based on dopant-free HTMs is presented.
we are reporting a new synthetic strategy to grow large size black phosphorus (Black-P) crystals through a ternary clathrate Sn24P22-xI8, under lower synthetic temperature and pressure. The Black-P crystals are found grown in situ at the site where the solid clathrate originally resides, which suggests chemical vapor mineralizer does not play a critical role for the Black-P formation. More detailed systematical studies has indicated the P vacancies in the framework of ternary clathrate Sn24P22-xI8 is important for the subsequent Black-P from phosphorus vapors, and a likely Vapor-Solid-Solid (VSS) model is responsible for the Black-P crystal growth. The obtained room temperature mobility μ is ~350 cm 2 /V•s from Hall measurements at mechanically-cleaved flake, where noticeable micro-cracks are visible. The obtained high mobility value further suggest the high quality of the Black-P crystals synthesized through this route.Introduction:
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