The aim of this paper is to derive a general AC/DC power flow model with Voltage Source Converter Multi-Terminal High-Voltage Direct Current Systems (VSC MTDCs). The equations of AC, DC grids, and ...VSCs are formulated in augmented rectangular coordinates. The proposed model is composed of two nodal equations and two power constraints for each AC bus, as well as one nodal equation and one power constraint for each DC bus. In this model, the VSC equations are included in the AC and DC grid model-its power balance equation and one of the control equations are regarded as the power constraints of the AC bus connected to it, whereas the other control equation is regarded as the power constraint of the DC bus connected to it. Therefore, the number of equations of the proposed model is determined only by that of AC and DC buses, and the model is systematically well organized; the variety of VSC control strategies and AC/DC linking configurations does not influence the overall structure. The proposed approach enables to solve the load flow of the most general AC/MTDC, consisting of multiple AC and DC grids connected by VSCs, and is suitable for control strategies including the droop control and any new ones in the future. The model also leads to higher computational efficiency. By demonstrations on AC/DC power systems with several VSCs, this method is proved to be effective, flexible, and efficient.
Nanoscale mechanical behavior of kaolinite as a fundamental failure mechanism has been investigated under uniaxial tension and compression using Molecular Dynamics (MD) simulation methods. External ...deformation has been applied on kaolinite with a strain rate of 5 × 10−7fs−1 for tensile and compressive tests in the directions parallel (x-, y-direction)/perpendicular (z-direction) to clay mineral layers. Results showed that better mechanical performance was presented in the directions parallel to clay mineral layers than the other direction due to its continuous lattice in this plane. However, the elastic modulus of kaolinite in the z-direction was almost half of that in the other directions, which nearly equals the overall elastic modulus of kaolinite with a value of about 72.6 GPa. Compression in the x- and y-directions resulted in the separation of clay mineral layers then bending toward the octahedral sheet till crack. Compression in the z-direction resulted in slippage of clay mineral layers at the first fracture then resistance till the second fracture at the strain of about 0.2. Tension would cause cracks in the direction perpendicular to the strain direction, which may be a cleavage fracture or cracks in clay mineral sheets. Different failure modes under tension and compression were originated from the layered structure of kaolinite.
•Compression along the direction perpendicular to kaolinite layers can lead to double fractures with slippage of layers.•To damage kaolinite layers needs more energy than to separate them.•Elastic modulus of kaolinite in the three directions is expressed as the average of tensile and compressive results.•The overall elastic modulus of kaolinite is dominated by that in the direction perpendicular to clay mineral layers.
Geometric phases are noise resilient, and thus provide a robust way towards high-fidelity quantum manipulation. Here we experimentally demonstrate arbitrary nonadiabatic holonomic single-qubit ...quantum gates for both a superconducting transmon qubit and a microwave cavity in a single-loop way. In both cases, an auxiliary state is utilized, and two resonant microwave drives are simultaneously applied with well-controlled but varying amplitudes and phases for the arbitrariness of the gate. The resulting gates on the transmon qubit achieve a fidelity of 0.996 characterized by randomized benchmarking and the ones on the cavity show an averaged fidelity of 0.978 based on a full quantum process tomography. In principle, a nontrivial two-qubit holonomic gate between the qubit and the cavity can also be realized based on our presented experimental scheme. Our experiment thus paves the way towards practical nonadiabatic holonomic quantum manipulation with both qubits and cavities in a superconducting circuit.
Using geometric phases to realize noise-resilient quantum computing is an important method to enhance the control fidelity. In this work, we experimentally realize a universal nonadiabatic geometric ...quantum gate set in a superconducting qubit chain. We characterize the realized single- and two-qubit geometric gates with both quantum process tomography and randomized benchmarking methods. The measured average fidelities for the single-qubit rotation gates and two-qubit controlled-Z gate are 0.9977(1) and 0.977(9), respectively. Besides, we also experimentally demonstrate the noise-resilient feature of the realized single-qubit geometric gates by comparing their performance with the conventional dynamical gates with different types of errors in the control field. Thus, our experiment proves a way to achieve high-fidelity geometric quantum gates for robust quantum computation.
Geometric phases induced in quantum evolutions have built‐in noise‐resilient characters, and thus can find applications in many robust quantum manipulation tasks. Here, a feasible and fast scheme for ...universal quantum computation on superconducting circuits with nonadiabatic non‐Abelian geometric phases is proposed, using resonant interaction of three‐level quantum system. In this scheme, arbitrary single‐qubit quantum gates can be implemented in a single‐loop scenario by shaping both the amplitudes and phases of the two driving microwave fields resonantly coupled to a transmon device. Moreover, nontrivial two‐qubit gates can also be realized with an auxiliary transmon simultaneously coupled to the two target transmons in an effective resonant way. In particular, this proposal can be compatible to various optimal control techniques, which further enhances the robustness of the quantum operations. Therefore, this proposal represents a promising way toward fault‐tolerant quantum computation on solid‐state quantum circuits.
Geometric phases have built‐in noise‐resilient characters, and thus are promising for robust quantum information processing. Now, a fast scheme for holonomic quantum computation on superconducting circuits is proposed, which is also compatible to optimal control techniques, and thus can further enhance the gate robustness. Therefore, it represents a promising way toward fault‐tolerant quantum computation on solid‐state quantum circuits.
Dusty plasma diffusion was applied to model the plasma response to perturbations in dust density, which yields small‐scale irregularities in electron density that are responsible for Polar Mesosphere ...Summer Echos. Previous diffusion models treated aerosols either as fixed‐charge dust or as multiple‐charge‐state dust using chemical rate equations. The growth of aerosol particles was previously considered in the study of layered structures in mesospheric clouds, but it has not been incorporated into dust diffusion. In this paper, a multicomponent diffusion of a dusty plasma, consisting of electrons, ions, and charged aerosols, is developed, accounting for the growth of the aerosols. It is shown that, for typical parameters in polar mesopause region, the evolution of the density structures of the dusty plasma undergoes an initial charging process (approximately 100 s), then an ambipolar diffusion process on ion time scale (approximately hundreds of seconds), and the aerosol diffusion on dust time scale (>104 s). Furthermore, the growth of the aerosols retards the dust diffusion and causes the transition from anticorrelation to correlation between the electron and ion density perturbations (contrary to only anticorrelation or correlation as in the case without considering the growth). The growth also bends the density profiles from upward shifting to downward sedimentation. In addition, larger initial grain radius and the width of the initial perturbation result in slower diffusion. The diffusion is much faster at 88 km than at 82 km.
Key Points
Multicomponent diffusion model including the growth of dust grains was established and numerically studied
Dust growth retards the diffusion and causes the transition from anticorrelation to correlation between electron and ion densities
Dust growth bends density profiles from upward shifting to downward sedimentation on a time scale of a few thousand seconds
An unprecedented asymmetric allenylic alkylation of readily available imine esters, which was enabled by a synergistic Cu/Pd catalysis, has been developed. This dual catalytic system possesses good ...substrate compatibility, delivering a diverse array of nonproteinogenic α‐allenylic α‐mono‐ or α,α‐disubstituted α‐amino acids (α‐AAs) with high yields and generally excellent enantioselectivities. Furthermore, the scalability and practicability of the current synthetic protocol were proven by performing gram‐scale reactions and by the first catalytic asymmetric synthesis of naturally occurring (S)‐γ‐allenic α‐amino acid, respectively.
Synergy for asymmetry: An unprecedented asymmetric allenylic alkylation of readily available imine esters enabled by a synergistic Cu/Pd catalysis has been developed. This dual catalytic system possesses good substrate compatibility, delivering a diverse array of nonproteinogenic α‐allenylic α‐mono‐ or α,α‐disubstituted α‐amino acids with high yields and generally excellent enantioselectivities. Gram‐scale reactions were performed, and the synthetic protocol allowed for the first catalytic asymmetric synthesis of naturally occurring (S)‐γ‐allenic α‐amino acids.
An intermolecular hydroalkylative dearomatization of naphthalenes with commercially available α‐amino acids is achieved via visible‐light photoredox catalysis. With an organic photocatalyst, a series ...of multi‐substituted 1,2‐dihydronaphthalenes are obtained in good‐to‐excellent yields. Intriguingly, by tuning the substituents at the C2 position of naphthalenes, formal dearomative 3+2 cycloadditions occur exclusively via a hydroalkylative dearomatization–cyclization sequence. This overall redox‐neutral method features mild reaction conditions, good tolerance of functionalities, and operational simplicity. Diverse downstream elaborations of the products are demonstrated. Preliminary mechanistic studies suggest the involvement of a radical–radical coupling pathway.
The development of dearomative functionalization strategies for arenes is intrinsically challenging and remains a largely unsolved synthetic problem owing to the particularly high resonance energy. We have now developed the first catalytic intermolecular hydroalkylative dearomatization of naphthalene derivatives with commercially available α‐amino acids by a photoredox‐neutral process.
To determine the abundance and distribution of bacterial and archaeal ammonia oxidizers in alpine and permafrost soils, 12 soils at altitudes of 4000-6550 m above sea level (m a.s.l.) were collected ...from the northern slope of the Mount Everest (Tibetan Plateau), where the permanent snow line is at 5800-6000 m a.s.l. Communities were characterized by real-time PCR and clone sequencing by targeting on amoA genes, which putatively encode ammonia monooxygenase subunit A. Archaeal amoA abundance was greater than bacterial amoA abundance in lower altitude soils (less-than or equal to5400 m a.s.l.), but this situation was reversed in higher altitude soils (≥5700 m a.s.l.). Both archaeal and bacterial amoA abundance decreased abruptly in higher altitude soils. Communities shifted from a Nitrosospira amoA cluster 3a-dominated ammonia-oxidizing bacteria community in lower altitude soils to communities dominated by a newly designated Nitrosospira ME and cluster 2-related groups and Nitrosomonas cluster 6 in higher altitude soils. All archaeal amoA sequences fell within soil and sediment clusters, and the proportions of the major archaeal amoA clusters changed between the lower altitude and the higher altitude soils. These findings imply that the shift in the relative abundance and community structure of archaeal and bacterial ammonia oxidizers may result from selection of organisms adapted to altitude-dependent environmental factors in elevated soils.
PDF
