Influence of long-range cation order on relaxor properties of doped Pb(Mg1/3Nb2/3)O3 ceramics

The 1:1 B-site cation order in Pb(Mg1/3Nb2/3)O3 relaxor ferroelectric ceramics was significantly enhanced by doping of minor amounts of La3+, Sc3+, or W6+ (less than 3 at. %) combined with a slow cooling procedure. Transmission electron microscopy examination confirmed the size increase of the cation-ordered regions embedded in a disordered matrix in the samples that were slowly cooled after sintering. The average cation ordering parameter (S) determined from x-ray diffraction data in these partially ordered samples was about 0.3–0.4. The ferroelectric properties and dielectric relaxation were compared in partially ordered and disordered (S=0) samples with the same composition. It was found that typical relaxor behavior was preserved in partially ordered ceramics. Furthermore, the temperature and diffuseness of the characteristic relaxor permittivity peak and the parameters of dielectric relaxation (in particular, the distribution of relaxation times and the Vogel-Fulcher freezing temperature) were practically independent of S. In contrast, the diffuseness of the phase transition from the ferroelectric phase (induced by external electric field) to the ergodic relaxor phase appeared to be much larger in the disordered samples than in the partially ordered ones (this diffuseness was assessed using pyroelectric current and ferroelectric hysteresis loops). These results suggest that cation ordering did not influence the behavior of polar nanoregions which are responsible for the dielectric response in the ergodic relaxor phase but significantly influenced the ferroelectric phase transition. The results are interpreted in terms of different types of polar regions in the disordered matrix and cation-ordered domains

Electric field-induced phase transitions in (111)-, (110)-, and (100)-oriented Pb(Mg1∕3Nb2∕3)O3 single crystals

Electric field-induced phase transitions were investigated in (111), (110), and (100) thin platelets of relaxor ferroelectric Pb(Mg1∕3Nb2∕3)O3 single crystals with electric fields applied along the ⟨111⟩, ⟨110⟩, and ⟨100⟩ directions, respectively. Temperature dependences of complex dielectric permittivity, pyroelectric current and dielectric hysteresis loops were investigated. Electric field-temperature (E-T) phase diagrams were proposed for the different directions of the field. Alongside with the high-temperature ergodic relaxor phase and the low-temperature glassy nonergodic relaxor phase existing at E=0, the ferroelectric phase may appear in the diagram at the fields higher than the threshold field (Eth). The temperature of the first-order transition between ergodic relaxor and ferroelectric phases (TC) was located in field cooling and field heating after field-cooling regimes. For the ⟨111⟩ field direction, TC is higher and Eth is lower than for the other directions. For the ⟨100⟩ direction, TC is the lowest and Eth is the highest. The critical point bounding the TC(E) line when the field is applied in ⟨111⟩ direction [ Z. Kutnjak, J. Petzelt and R. Blinc Nature 441 956 (2006)] is not observed in the ⟨110⟩ and ⟨100⟩ directions up to the highest applied field of 7.5 kV∕cm. Extrapolation of experimental data suggests that the critical point for the ⟨110⟩ and ⟨100⟩ directions (if any) can be expected only at much higher fields. In the hysteresis loops experiments performed after zero-field cooling, the lower temperature limit is determined above which a ferroelectric phase can be induced from the frozen glassy state at a given field strength or the polarization of the induced ferroelectric phase can be reversed. This limit is located at much lower temperatures in the (100) platelet than in the (110) or (111) platelets. An additional ferroelectric rhombohedral to ferroelectric orthorhombic phase transition occurs in the (110) platelet at high electric fields (∼20 kV∕cm). The mechanisms of the field-induced transformation from the glassy nonergodic relaxor phase or the ergodic relaxor phase to the ferroelectric phase are discussed

High-precision Absolute Distance Measurement using Dual-Laser Frequency Scanned Interferometry Under Realistic Conditions

In this paper, we report on new high-precision absolute distance measurements performed with frequency scanned interferometry using a pair of single-mode optical fibers. Absolute distances were determined by counting the interference fringes produced while scanning the frequencies of the two chopped lasers. High-finesse Fabry-Perot interferometers were used to determine frequency changes during scanning. Dual lasers with oppositely scanning directions, combined with a multi-distance-measurement technique previously reported, were used to cancel drift errors and to suppress vibration effects and interference fringe uncertainties. Under realistic conditions, a precision about 0.2 microns was achieved for a distance of 0.41 meters.Comment: 14 pages, 5 figures, submitted to Applied Optic

M6AMRFS: Robust Prediction of N6-Methyladenosine Sites With Sequence-Based Features in Multiple Species

As one of the well-studied RNA methylation modifications, N6-methyladenosine (m6A) plays important roles in various biological progresses, such as RNA splicing and degradation, etc. Identification of m6A sites is fundamentally important for better understanding of their functional mechanisms. Recently, machine learning based prediction methods have emerged as an effective approach for fast and accurate identification of m6A sites. In this paper, we proposed “M6AMRFS”, a new machine learning based predictor for the identification of m6A sites. In this predictor, we exploited a new feature representation algorithm to encode RNA sequences with two feature descriptors (dinucleotide binary encoding and Local position-specific dinucleotide frequency), and used the F-score algorithm combined with SFS (Sequential Forward Search) to enhance the feature representation ability. To predict m6A sites, we employed the eXtreme Gradient Boosting (XGBoost) algorithm to build a predictive model. Benchmarking results showed that the proposed predictor is competitive with the state-of-the art predictors. Importantly, robust predictions for multiple species by our predictor demonstrate that our predictive models have strong generalization ability. To the best of our knowledge, M6AMRFS is the first tool that can be used for the identification of m6A sites in multiple species. To facilitate the use of our predictor, we have established a user-friendly webserver with the implementation of M6AMRFS, which is currently available in http://server.malab.cn/M6AMRFS/. We anticipate that it will be a useful tool for the relevant research of m6A sites

Gene expression profile indicates involvement of NO in Camellia sinensis pollen tube growth at low temperature

DEGs identified from the comparison between control (CsPT-CK) and 4 °C-treated (CsPT-LT) pollen tbues. All of the samples were replicated three times. CK and LT FPKM: fragments per kb per million reads for each unigene in the CK and LT libraries, respectively. The log2Ratio (LT/CK): ratio between the FPKM of LT and CK. The absolute values of log2Ratio > 1 and probability > 0.7 were used as threshold for assigning significance. Annotation of DEGs against NR, NT, Swiss-Prot protein, KEGG, COG and GO were all reported in the tables. “-”: no hit. (XLS 381 kb