Design Considerations for Voltage Sensorless Control of a PFC Single-Phase Rectifier Without Electrolytic Capacitors

In this paper, a voltage sensorless controller is developed for a two-switch single-phase rectifier that involves power factor correction and active pulsating power buffering without electrolytic capacitors. While a two-switch rectifier normally requires four sensed signals for control, only one current sensor is required in this proposal, thereby offering advantages such as low cost, high compactness, isolation between control and power circuits, and improved reliability. While the basic operating principle follows that of a conventional voltage sensorless controller for single-switch converters, several critical design considerations are the key to the success of the implementation which is explained in detail. The feasibilities of the controller are experimentally testified with a 100-W rectifier prototype regarding both steady state and dynamic performance.</p

High-Power-Density Single-Phase Three-Level Flying-Capacitor Buck PFC Rectifier

Active pulsating-power-buffering (PPB) is an effective technique to reduce the energy storage requirement of a single-phase power-factor-correction (PFC) rectifier. Existing single-phase solutions with active PPB, however, generally suffer from high voltage stresses, leading to increased power losses as well as the need for high-voltage-rating semiconductor switches. Previous works have been focusing on two-level switching converter configurations, and thus have failed to address the high-voltage-stress problem. In this paper, a single-phase three-level flying-capacitor PFC rectifier with PPB embedded switching is proposed. The flying capacitor not only clamps the voltage stresses of all power devices but also functions as a PPB capacitor. The operating principles, control methods, and design guidelines are detailed and the feasibility of the proposed converter is verified through a 48-W (48-V/1-A) hardware prototype. The proposed rectifier is shown to achieve nearly 50% reduction of the voltage stresses, 72% reduction of the buffering capacitor's volume and 23.8% reduction of the magnetic core size, as compared to a state-of-the-art two-level solution recently proposed. This new approach of formulating single-phase PFC rectifiers with active PPB could dramatically boost the system's efficiency and power density whilst reducing cost

Developing hierarchically ultra-micro/mesoporous biocarbons for highly selective carbon dioxide adsorption

Activated carbons represent one of the important categories of the adsorbent materials for CO2 capture currently under development. However, the low adsorption capacity and selectivity at low CO2 partial pressure or relatively high flue gas temperatures is the main barrier for carbons to be applied in post-combustion CO2 capture under practical conditions. Here, we report the successful preparation of hierarchical ultra-micro/mesoporous bio-carbons from using a facile one-step method with a low-grade biomass waste as the feedstock. The bio-carbons exhibit high adsorption capacities (1.90 mmol/g) and record-high Henry’s law CO2/N2 selectivities up to 212 at ambient temperature and low CO2 partial pressure. Unlike conventional chemical activation process for manufacturing carbon materials, the integrated compaction-carbonization-activation method proposed endows the biowaste-derived carbons with unique hierarchical bio-modal pore structures, which is highly characterised by their high mesoporosity and high ultra-microporosity with narrow pore size distributions. The results demonstrated that the unique surface textural properties along with the enhanced surface chemistry due to the simultaneously achieved potassium intercalation created favourable conditions for CO2 adsorption with high CO2/N2 selectivity at low CO2 partial pressures, whilst the presence of mesoporosity greatly increased the CO2 adsorption kinetics. Measurements of CO2 adsorption heat confirmed the strong surface affinity of the prepared bio-carbons to CO2 molecules

Spherical Indicatrices of a Bertrand Curve in Three Lie Groups

In this paper, new representations of a Bertrand curve pair in three dimensional Lie groups with bi-invariant metric are given. Besides, the spherical indicatrices of a Bertrand curve pair are obtain and the relations between the spherical indicatrices and new representations of Bertrand curve pair are shown.Comment: 12 page

BTG2 suppresses renal cell carcinoma progression through N6-methyladenosine

The biological functions of N6-methyladenosine (m6A) modification of mRNA have recently received a great deal of attention. In previous studies, m6A methylation modification has been shown to regulate mRNA fate and to be crucial for the progression and development of tumors. BTG2 (B-cell translocation gene 2) is a member of BTG/TOB anti-proliferative protein family. BTG2 could inhibit cell proliferation and migration and regulate the cell cycle progression. In this study, we confirm that BTG2 is frequently down-regulated in renal cell carcinoma (RCC) tissues and its low expression is associated with unfavorable prognosis and decreased m6A level. Moreover, we found that m6A methylation modifies the 5’UTR of BTG2 to promote its mRNA stability by binding to IGF2BP2. It has been shown that CRISPR/dCas13b-METLL3 can specifically increase BTG2 m6A modification to significantly increase its m6A and expression levels. Then m6A hypermethylation in BTG2 mRNA could dramatically inhibit RCC cells proliferation and migration, and induce cells apoptosis. Taken together, our data show that BTG2 functions as a tumor suppressor and is frequently silenced via m6A modification in RCC

Flat optical conductivity in topological kagome magnet TbMn6_6Sn6_6

Kagome magnet TbMn$_6$Sn$_6$ is a new type of topological material that is known to support exotic quantum magnetic states. Experimental work has identified that TbMn$_6$Sn$_6$ hosts Dirac electronic states that could lead to topological and Chern quantum phases, but the optical response of the Dirac fermions of TbMn$_6$Sn$_6$ and its properties remain to be explored. Here, we perform optical spectroscopy measurement combined with first-principles calculations on single-crystal sample of TbMn$_6$Sn$_6$ to investigate the associated exotic phenomena. TbMn$_6$Sn$_6$ exhibits a frequency-independent optical conductivity spectra in a broad range from 1800 to 3000 cm$^{-1}$ (220-370 meV) in experiments. The theoretical band structures and optical conductivity spectra are calculated with several shifted Fermi energy to compare with the experiment. The theoretical spectra with 0.56 eV shift for Fermi energy are well consistent with our experimental results. Besides, the massive quasi-two-dimensional (quasi-2D) Dirac bands, which have linear band dispersion in $k_x$-$k_y$ plane and no band dispersion along the $k_z$ direction, exist close to the shifted Fermi energy. According to tight-bond model analysis, we find that quasi-2D Dirac bands give rise to a flat optical conductivity, while its value is smaller than the result by calculations and experiments. It indicates that the other trivial bands also contribute to the flat optical conductivity

Examining the generalizability of research findings from archival data

This initiative examined systematically the extent to which a large set of archival research findings generalizes across contexts. We repeated the key analyses for 29 original strategic management effects in the same context (direct reproduction) as well as in 52 novel time periods and geographies; 45% of the reproductions returned results matching the original reports together with 55% of tests in different spans of years and 40% of tests in novel geographies. Some original findings were associated with multiple new tests. Reproducibility was the best predictor of generalizability—for the findings that proved directly reproducible, 84% emerged in other available time periods and 57% emerged in other geographies. Overall, only limited empirical evidence emerged for context sensitivity. In a forecasting survey, independent scientists were able to anticipate which effects would find support in tests in new samples

Photonic Weyl points due to broken time-reversal symmetry in magnetized semiconductor

Weyl points are discrete locations in the three-dimensional momentum space where two bands cross linearly with each other. They serve as the monopoles of Berry curvature in the momentum space, and their existence requires breaking of either time-reversal or inversion symmetry. Although various non-centrosymmetric Weyl systems have been reported, demonstration of Weyl degeneracies due to breaking of the time-reversal symmetry remains scarce and is limited to electronic systems. Here, we report the experimental observation of photonic Weyl degeneracies in a magnetized semiconductor—InSb, which behaves as a magnetized plasma19 for electromagnetic waves at the terahertz band. By varying the magnetic field strength, Weyl points and the corresponding photonic Fermi arcs have been demonstrated. Our observation establishes magnetized semiconductors as a reconfigurable terahertz Weyl system, which may prompt research on novel magnetic topological phenomena such as chiral Majorana-type edge states and zero modes in classic systems