The Evolution of Online Short-Term Rental Enterprises’ Ecosystem and Legitimacy: A Longitudinal Interpretive Case Study

As an emerging field, the online short-term rental in China appears with poor national policy and industry general regulations. All enterprises in this industry are constantly groping for sustainable strategy of legitimacy. Previous studies on the online short-term rental mainly focus on the positive influence, the business model, and policy and regulation. However, there is currently little research on how the online short-term rental enterprises develop ecosystem and legitimacy during different phases involved, which provides a good reference for other emerging organization in sharing economy.This study applied business ecosystem and legitimacy to analyze the development of a typical online short-term rental company via a longitudinal interpretive case study. A process model of how an online short-term rental company’s sub-ecosystems is inductively derived and elucidates the regulative challenges, normative challenges, and cognitive challenges in each phase. The findings of this case study provide a comprehensive and empirically supported framework and demonstrate a successful process model

Numerical Modelling of the Dynamic Voltage in HTS Materials under the Action of DC Transport Currents and Different Oscillating Magnetic Fields.

The dynamic voltage is a unique phenomenon of superconducting materials. It arises when the superconductor is carrying a DC transport current and spontaneously in subject to an AC magnetic field. This study excavates the aspects that previous studies have not comprehensively investigated: the dynamic voltage in a DC-carrying superconducting tape exposed to different oscillating AC magnetic fields. First, the fundamental physics of dynamic voltage/flux of superconductors is reviewed and further analysed in detail. We used the superconducting modelling method using the H-formulation merged into the finite-element method (FEM) software, to re-produce the typical dynamic voltage behaviour of a superconducting tape. The modelling was verified by both the analytical and experimental results, in order to precisely prove the reliability of the modelling. Afterwards, the modelling was performed for a DC-carrying superconducting tape under four different oscillating magnetic fields (sine, triangle, sawtooth and square), and their corresponding dynamic voltages and energy losses were analysed and compared. Results show the sinusoidal magnetic field can lead to the optimal combination of reasonable dynamic voltage but relatively lower loss, which is suitable for those superconducting applications requiring dynamic voltage as the energy source, e.g., flux pumps. This article presents novel investigation and analysis of the dynamic voltage in superconducting materials, and both the methodology and results can provide useful information for the future design/analysis of superconducting applications with DC transport currents and AC magnetic fields

QMCPACK: Advances in the development, efficiency, and application of auxiliary field and real-space variational and diffusion Quantum Monte Carlo

We review recent advances in the capabilities of the open source ab initio Quantum Monte Carlo (QMC) package QMCPACK and the workflow tool Nexus used for greater efficiency and reproducibility. The auxiliary field QMC (AFQMC) implementation has been greatly expanded to include k-point symmetries, tensor-hypercontraction, and accelerated graphical processing unit (GPU) support. These scaling and memory reductions greatly increase the number of orbitals that can practically be included in AFQMC calculations, increasing accuracy. Advances in real space methods include techniques for accurate computation of band gaps and for systematically improving the nodal surface of ground state wavefunctions. Results of these calculations can be used to validate application of more approximate electronic structure methods including GW and density functional based techniques. To provide an improved foundation for these calculations we utilize a new set of correlation-consistent effective core potentials (pseudopotentials) that are more accurate than previous sets; these can also be applied in quantum-chemical and other many-body applications, not only QMC. These advances increase the efficiency, accuracy, and range of properties that can be studied in both molecules and materials with QMC and QMCPACK

A high-current and low-loss high-temperature superconducting cable for nuclear fusion applications

The primary challenge in applying high-temperature superconducting (HTS) coated conductors (CCs) to AC energy applications, including motors, power transmission, and fusion magnets, is their relatively high AC loss. In this dissertation, a novel high-current and low-loss HTS cable, Patterned superconductors for AC loss minimization and current maximization (PSALM), is proposed and investigated to tackle the AC loss problem. Compared with the existing HTS cables, PSALMs are more compact, more capable of carrying large currents with minimized losses, and easier to manufacture. A 3D finite element method (FEM) model of the PSALM based on the T-A formulation is built to optimize the structure and verify the performance. Samples of PSALMs with a single superconducting layer are manufactured, tested, modeled, and analyzed. In the experiments, the critical current degradation and the transport AC losses are measured. In the simulation, the transport AC losses are calculated and compared with the experimental data, and the current distribution is analyzed in detail. The results show that compared with normal REBCO CCs, PSALMs with optimum patterns can reduce AC transport losses by 60\% through field-canceling and can reduce magnetization losses by the factor of the filament number through patterning. This model is then used to simulate long PSALMs which could be used in practice and calculate the transport AC losses. The losses are found over 30\% lower than that of the normal HTS REBCO tapes, which verifies the loss-reduction performance of the PSALMs. To explore the underlying physics of the PSALM, we then focus on the field-canceling effect of the PSALM introduced by the specially designed patterns on the buffer layers and superconducting layers. From the results obtained by the 2D and 3D models using the T-A formulation, we find this effect can make the current distributed more uniformly and can significantly reduce AC losses. The reasons and the basic principles behind are revealed and analyzed. To sufficiently exploit it to reduce losses, the structure parameters of the PSALM are optimized and an optimum solution is obtained. Then we extend the study to the PSALM with a multiple-layer structure. Current distribution and AC losses of the PSALMs with up to 10 REBCO layers are calculated. The results show that the tapes with even numbers of layers generate lower losses than those with odd numbers, which indicates the superconducting layers should always appear in pairs. Increasing layers can increase the engineering current density of the tape, but the average loss per layer also rises. Therefore, we suggest increasing the distance between the layer pairs or using double-layer PSALM stacks instead. This work provides both experimental and simulation proof of the advantage of the PSALM as a high-current and low-loss HTS cable. It could potentially become the key to compact fusion magnets, which require high power density and suppressed losses

Numerical Modelling of the Dynamic Voltage in HTS Materials under the Action of DC Transport Currents and Different Oscillating Magnetic Fields

The dynamic voltage is a unique phenomenon of superconducting materials. It arises when the superconductor is carrying a DC transport current and spontaneously in subject to an AC magnetic field. This study excavates the aspects that previous studies have not comprehensively investigated: the dynamic voltage in a DC-carrying superconducting tape exposed to different oscillating AC magnetic fields. First, the fundamental physics of dynamic voltage/flux of superconductors is reviewed and further analysed in detail. We used the superconducting modelling method using the H-formulation merged into the finite-element method (FEM) software, to re-produce the typical dynamic voltage behaviour of a superconducting tape. The modelling was verified by both the analytical and experimental results, in order to precisely prove the reliability of the modelling. Afterwards, the modelling was performed for a DC-carrying superconducting tape under four different oscillating magnetic fields (sine, triangle, sawtooth and square), and their corresponding dynamic voltages and energy losses were analysed and compared. Results show the sinusoidal magnetic field can lead to the optimal combination of reasonable dynamic voltage but relatively lower loss, which is suitable for those superconducting applications requiring dynamic voltage as the energy source, e.g., flux pumps. This article presents novel investigation and analysis of the dynamic voltage in superconducting materials, and both the methodology and results can provide useful information for the future design/analysis of superconducting applications with DC transport currents and AC magnetic fields