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Impressive performance of hybrid perovskite solar cells reported in recent years still awaits a comprehensive understanding of its microscopic origins. In this work, the intrinsic Hall mobility and photocarrier recombination coefficient are directly measured in these materials in steady-state transport studies. The results show that electron-hole recombination and carrier trapping rates in hybrid perovskites are very low. The bimolecular recombination coefficient (10 −11 to 10 −10  cm 3  s −1 ) is found to be on par with that in the best direct-band inorganic semiconductors, even though the intrinsic Hall mobility in hybrid perovskites is considerably lower (up to 60 cm 2  V −1  s −1 ). Measured here, steady-state carrier lifetimes (of up to 3 ms) and diffusion lengths (as long as 650 μm) are significantly longer than those in high-purity crystalline inorganic semiconductors. We suggest that these experimental findings are consistent with the polaronic nature of charge carriers, resulting from an interaction of charges with methylammonium dipoles. Hybrid perovskites exhibit long carrier diffusion lengths and lifetimes. Here, Chen et al . show experimentally that carrier recombination in perovskites is far from Langevin and closer to the best direct-bandgap semiconductors, which can be explained by the dipolar polaronic nature of charge carriers.

Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force acting on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor.

Hexagonal YMnO 3 shows a unique improper ferroelectricity induced by structural trimerization. Extensive research on this system is primarily due to its candidacy for ferroelectric memory as well as the intriguing coexistence of ferroelectricity and magnetism. Despite this research, the true ferroelectric domain structure and its relationship with structural domains have never been revealed. Using transmission electron microscopy and conductive atomic force microscopy, we observed an intriguing conductive ‘cloverleaf’ pattern of six domains emerging from one point—all distinctly characterized by polarization orientation and structural antiphase relationships. In addition, we discovered that the ferroelectric domain walls and structural antiphase boundaries are mutually locked and this strong locking results in incomplete poling even when large electric fields are applied. Furthermore, the locked walls are found to be insulating, which seems consistent with the surprising result that the ferroelectric state is more conducting than the paraelectric state. These fascinating results reveal the rich physics of the hexagonal system with a truly semiconducting bandgap where structural trimerization, ferroelectricity, magnetism and charge conduction are intricately coupled. The ability to exert control over domains in multiferroic materials is important in terms of the potential use of these materials. In the multiferroic YMnO 3 , structural considerations lead to an unusual cloverleaf pattern of ferroelectric domains, where the domain walls are electrically insulating.

Fundamental studies of intrinsic charge transport properties of organic semiconductors are often hindered by charge traps associated with static disorder present even in optimized single-crystal devices. Here, we report a method of surface functionalization using an inert non-conjugated polymer, perfluoropolyether (PFPE), deposited at the surface of organic molecular crystals, which results in accumulation of mobile holes and a ‘trap healing’ effect at the crystal/PFPE interface. As a consequence, a remarkable ultralow-noise, trp-free conduction regime characterized by intrinsic mobility and transport anisotropy emerges in organic single crystals, and Hall effect measurements with an unprecedented signal-to-noise ratio are demonstrated. This general method to convert trap-dominated organic semiconductors to intrinsic systems may enable the determination of intrinsic transport parameters with high accuracy and make Hall effect measurements in molecular crystals ubiquitous. In organic semiconductors, disorder-induced traps can alter the mobility of the charges and introduce noise in transport measurements. It is now shown that simple drop-casting of perfluoropolyether on top of organic single-crystals is an effective strategy for healing charge traps. This method allows the intrinsic transport properties of these materials to be recovered as well as suppressing noise in Hall effect measurements.

Insulating magnets can display novel signatures of quantum fluctuations as similar to the case of metallic magnets. However, their weak spin-lattice coupling has made such observations challenging. Here we find that antiferromagnetic (AF) quantum fluctuations manifest in the dielectric properties of multiferroic Ba 2 CoGe 2 O 7 , where a ferroelectric polarization develops concomitant to an AF ordering. Upon application of a magnetic field ( H ), dielectric constant shows a characteristic power-law dependence near absolute zero temperature and close to the critical field H c =37.1 T due to enhanced AF quantum fluctuations. When H > H c , the dielectric constant shows the temperature-dependent anomalies that reflect a crossover from a field-tuned quantum critical to a gapped spin-polarized state. We uncover theoretically that a linear relation between AF susceptibility and dielectric constant stems from the generic magnetoelectric coupling and directly explains the experimental findings, opening a new pathway for studying quantum criticality in condensed matter. Although quantum fluctuations of the spins occur on a local scale, they can have a macroscopic impact on the properties of magnets. Here, the authors observe the macroscopic influence of magnetic quantum fluctuations on the dielectric properties of a multiferroic oxide.

In recent years, China has been undergoing a metro railway construction boom in order to alleviate the urban traffic congestion problem resulting from the rapid urbanization and population growth in many metropolises. In the construction of metro systems, deep excavations and continuous dewatering for construction of the metro tunnels and stations remain a challenging and high risk task in densely populated urban areas. Intelligent computational methods and techniques have exhibited the exceptional talent in dealing with the complicated problems inherent in the deep excavation and dewatering practice. In this paper, an intelligent risk assessment system for deep excavation dewatering is developed and has been applied in the project of Hangzhou Metro Line 1 which is the first metro line of the urban rapid rail transit system in Hangzhou, China. The specific characteristics and great challenges in deep excavation dewatering of the metro-tunnel airshaft of Hangzhou Metro Line 1 are addressed. A novel design method based on the coupled three-dimensional flow theory for dewatering of the deep excavation is introduced. The modularly designed system for excavation dewatering risk assessment is described, and the field observations in dewatering risk assessment of the airshaft excavation of Hangzhou Metro Line 1 are also presented.

Summary Decreased sperm quality was caused by oxidative stress in semen from patients with leucocytospermia. Curcumin is a traditional Chinese herbal monomer extracted from Zingiberaceae turmeric and zedoary turmeric and has antioxidative and anti‐inflammatory effects. This study aimed to investigate the effects and specific molecular mechanisms of curcumin on sperm quality in patients diagnosed with leucocytospermia. Forty cases of semen samples were collected from patients with leucocytospermia and 35 cases from normal fertile male. Computer‐assisted semen analysis (CASA) was used to detect sperm motility after curcumin incubation. ELISA was used to measure the changes in H2O2, sperm mitochondrial DNA (mtDNA), cytochrome B (Cyt B) and NADH dehydrogenase 5 (NADH5) contents before and after curcumin treatment. The results indicate that curcumin can significantly improve sperm motility from the patients with leucocytospermia. After curcumin treatment, the level of the H2O2 was significantly decreased in the supernatant of curcumin‐incubated spermatozoa from leucocytospermic patients. The content of mtDNA was significantly decreased, while the content of Cyt B and NADH5 in spermatozoa was significantly increased. In conclusion, curcumin can significantly improve sperm motility of leucocytospermic patients, against the oxidative damage induced by H2O2. Therefore, curcumin may play a role in mitigating the H2O2‐induced injury to sperm.

The project of Hangzhou Metro Line 1 is the first metro line of the urban rapid rail transit system in Hangzhou, China, which is one of the largest municipal projects of Hangzhou and is being constructed commencing from March 28, 2007 and expected to be completed by October 1, 2012. This metro line has a total length of 48 km and 34 stations, connecting Hangzhou downtown with the suburban area of the city. Owing to the complex geological condition, harsh construction situation, and immature computational methodology, construction of metro systems is often subjected to considerable sources of uncertainties. To ensure the safety of the adjacent building structures, it is a vital necessity to monitor deep excavations of metro tunnels at their in-construction stage. This paper introduces the instrumentation system for settlement monitoring of a metro-tunnel airshaft of the project of Hangzhou Metro Line 1 during the construction of deep excavation. The long-term settlement data monitored by the measurement markers installed at the surface ground and in the depth direction of the airshaft excavation construction site are analyzed and presented in detail. The obtained results indicate that the settlements at the instrumented locations of the construction site during different construction steps vary steadily in an allowable variation range.

Modal parameters, such as frequency, damping ratio and modal shape, play a key role to reflect the structural behaviour. Eigensystem realization algorithm (ERA) has been effectively utilized to many applications to identify the modal parameters. However, the noises in practical environment can influent the effectiveness of ERA, which can introduce spurious modes. This paper proposes a modified ERA to distinguish the spurious modes. It is first proved that any two Hankel matrices with one time step shift used in ERA can obtain the state matrix. The singular values in the singular value matrix obtained by singular value decomposition of Hankel matrix are populated by noises. The truncated order for the singular value matrix cannot be determined. It is proposed that singular value changing can be observed through moving data, which help to identify the spurious mode. The stabilization diagram is employed to obtain the interested modes. Then the proposed moving data diagram can demonstrate the singular value changing which is spurious. Finally, the performance of the proposed method is verified through a numerical example.

In structural vibration tests, one of the main factors which disturb the reliability and accuracy of the results are the noise signals encountered. To overcome this deficiency, this paper presents a discrete wavelet transform (DWT) approach to denoise the measured signals. The denoising performance of DWT is discussed by several processing parameters, including the type of wavelet, decomposition level, thresholding method, and threshold selection rules. To overcome the disadvantages of the traditional hard- and soft-thresholding methods, an improved thresholding technique called the sigmoid function-based thresholding scheme is presented. The procedure is validated by using four benchmarks signals with three degrees of degradation as well as a real measured signal obtained from a three-story reinforced concrete scale model shaking table experiment. The performance of the proposed method is evaluated by computing the signal-to-noise ratio (SNR) and the root-mean-square error (RMSE) after denoising. Results reveal that the proposed method offers superior performance than the traditional methods no matter whether the signals have heavy or light noises embedded.