Boom and bust of bike sharing industry in China: a case study of ofo

From 2016 to the first half of 2017, shared bicycles experienced explosive growth in China, rapidly spreading from first- and second-tier cities to third- and fourth-tier cities, and even began to expand to some foreign cities. The advancement of Internet technology, the popularity of new consumption habits, and the large population size have provided the basic conditions for the development of the sharing economy. The sharing of bicycles as a pioneer of the sharing economy came into being. Sharing bicycles as a new force to solve “the last mile” problem of urban traffic has great significance. However, in the second half of 2017, after the feast of capital, the shared bicycles quickly entered the stage of a big reshuffle. The exposure of the weakness of the shared bike platform’s profit model made the shared bicycle companies closures always appear in the newspapers, and the whole industry fell into a cold winter. The article will take a series of dynamic industrial analysis tool like PEST, Michael Porter's Five Forces Model to give a clear framework of sharing bike industry. In addition, SWOT and Sensitive analysis have been used in the select company “ofo” to dissect the real situation they are facing. It is found from the results that the existing risks of ofo bicycle platform mainly include social, legal, financial and strategical aspects. Therefore, it is necessary to construct a risk and profit guarantee mechanism from the perspective of government and platform.De 2016 até o primeiro semestre de 2017, as bicicletas compartilhadas tiveram um crescimento explosivo na China, espalhando-se rapidamente de cidades de primeiro e segundo níveis para cidades de terceiro e quarto níveis, e até começaram a se expandir para algumas cidades estrangeiras. O avanço da tecnologia da Internet, a popularidade de novos hábitos de consumo e o grande tamanho da população proporcionaram as condições básicas para o desenvolvimento da economia compartilhada. O compartilhamento de bicicletas como um pioneiro da economia compartilhada surgiu. Compartilhar bicicletas como uma nova força para resolver o problema da "última milha" do tráfego urbano tem um grande significado. No entanto, no segundo semestre de 2017, após a festa da capital, as bicicletas compartilhadas rapidamente entraram no palco de uma grande remodelação. A exposição da fraqueza do modelo de lucro da plataforma de bicicleta compartilhada fez com que os fechamentos de empresas de bicicletas compartilhadas aparecessem sempre nos jornais, e toda a indústria caiu em um inverno frio. O artigo levará uma série de ferramentas dinâmicas de análise industrial, como a PEST, o Five Forces Model, de Michael Porter, para fornecer uma estrutura clara de compartilhamento da indústria de bicicletas. Além disso, análises SWOT e Sensitive foram usadas na empresa escolhida “ofo” para dissecar a situação real que estão enfrentando. Verifica-se a partir dos resultados que os riscos existentes da plataforma ofo bicycle incluem principalmente aspectos sociais, legais, financeiros e estratégicos. Portanto, é necessário construir um mecanismo de garantia de risco e lucro na perspectiva do governo e da plataforma

A Superdirective Beamforming Approach with Impedance Coupling and Field Coupling for Compact Antenna Arrays

In most multiple-input multiple-output (MIMO) communication systems, the antenna spacing is generally no less than half a wavelength. It helps to reduce the mutual coupling and therefore facilitate the system design. The maximum array gain equals the number of antennas in this settings. However, when the antenna spacing is made very small, the array gain of a compact array can be proportional to the square of the number of antennas - a value much larger than the traditional array. To achieve this so-called ``superdirectivity" however, the calculation of the excitation coefficients (beamforming vector) is known to be a challenging problem. In this paper, we address this problem with a novel double coupling-based superdirective beamforming method. In particular, we categorize the antenna coupling effects to impedance coupling and field coupling. By characterizing these two coupling in model, we derive the beamforming vector for superdirective arrays. In order to obtain the field coupling matrix, we propose a spherical wave expansion approach, which is effective in both simulations and realistic scenarios. Moreover, a prototype of the independently controlled superdirective antenna array is developed. Full-wave electromagnetic simulations and real-world experiments validate the effectiveness of our proposed approaches, and superdirectivity is achieved in reality by a compact array with 4 and 5 dipole antennas.Comment: arXiv admin note: text overlap with arXiv:2204.1154

Mesenchymal stem cells improve mouse non-heart-beating liver graft survival by inhibiting Kupffer cell apoptosis via TLR4-ERK1/2-Fas/FasL-caspase3 pathway regulation

Abstract Background Liver transplantation is the optimal treatment option for end-stage liver disease, but organ shortages dramatically restrict its application. Donation after cardiac death (DCD) is an alternative approach that may expand the donor pool, but it faces challenges such as graft dysfunction, early graft loss, and cholangiopathy. Moreover, DCD liver grafts are no longer eligible for transplantation after their warm ischaemic time exceeds 30 min. Mesenchymal stem cells (MSCs) have been proposed as a promising therapy for treatment of certain liver diseases, but the role of MSCs in DCD liver graft function remains elusive. Methods In this study, we established an arterialized mouse non-heart-beating (NHB) liver transplantation model, and compared survival rates, cytokine and chemokine expression, histology, and the results of in vitro co-culture experiments in animals with or without MSC infusion. Results MSCs markedly ameliorated NHB liver graft injury and improved survival post-transplantation. Additionally, MSCs suppressed Kupffer cell apoptosis, Th1/Th17 immune responses, chemokine expression, and inflammatory cell infiltration. In vitro, PGE2 secreted by MSCs inhibited Kupffer cell apoptosis via TLR4-ERK1/2-caspase3 pathway regulation. Conclusion Our study uncovers a protective role for MSCs and elucidates the underlying immunomodulatory mechanism in an NHB liver transplantation model. Our results suggest that MSCs are uniquely positioned for use in future clinical studies owing to their ability to protect DCD liver grafts, particularly in patients for whom DCD organs are not an option according to current criteria

Sacral terminal filar cyst: a distinct variant of spinal meningeal cyst and midterm clinical outcome following combination resection surgery

ObjectiveSpinal meningeal cysts (SMCs) are currently classified into three types: extradural cysts without nerve root fibers (Type I), extradural cysts with nerve root fibers (Type II), and intradural cysts (Type III). However, the sacral terminal filar cyst is a distinct subtype with the filum terminale rather than nerve roots within the cyst. This study aimed to investigate the clinicoradiological characteristics and surgical outcomes of sacral terminal filar cysts.MethodsA total of 32 patients with sacral terminal filar cysts were enrolled. Clinical and radiological profiles were collected. All patients were surgically treated, and preoperative and follow-up neurological functions were evaluated.ResultsChronic lumbosacral pain and sphincter dysfunctions were the most common symptoms. On MRI, the filum terminale could be identified within the cyst in all cases, and low-lying conus medullaris was found in 23 (71.9%) cases. The filum terminale was dissociated and cut off in all cases, and the cyst wall was completely resected in 23 (71.9%) cases. After a median follow-up period of 26.5 ± 15.5 months, the pain and sphincter dysfunctions were significantly improved (both P < 0.0001). The cyst recurrence was noted in only 1 (3.1%) case.ConclusionsSacral terminal filar cysts are rare, representing a distinct variant of SMCs. Typical MRI features, including filum terminale within the cyst and low-lying conus medullaris, may suggest the diagnosis. Although the optimal surgical strategy remains unclear, we recommend a combination of resection of the cyst wall and dissociation of the filum terminale. The clinical outcomes can be favorable

Revealing intrinsic domains and fluctuations of moir\'e magnetism by a wide-field quantum microscope

Moir\'e magnetism featured by stacking engineered atomic registry and lattice interactions has recently emerged as an appealing quantum state of matter at the forefront condensed matter physics research. Nanoscale imaging of moir\'e magnets is highly desirable and serves as a prerequisite to investigate a broad range of intriguing physics underlying the interplay between topology, electronic correlations, and unconventional nanomagnetism. Here we report spin defect-based wide-field imaging of magnetic domains and spin fluctuations in twisted double trilayer (tDT) chromium triiodide CrI3. We explicitly show that intrinsic moir\'e domains of opposite magnetizations appear over arrays of moir\'e supercells in low-twist-angle tDT CrI3. In contrast, spin fluctuations measured in tDT CrI3 manifest little spatial variations on the same mesoscopic length scale due to the dominant driving force of intralayer exchange interaction. Our results enrich the current understanding of exotic magnetic phases sustained by moir\'e magnetism and highlight the opportunities provided by quantum spin sensors in probing microscopic spin related phenomena on two-dimensional flatland

The interplay of interstitial and substitutional copper in zinc oxide

Cu impurities are reported to have significant effects on the electrical and optical properties of bulk ZnO. In this work, we study the defect properties of Cu in ZnO using hybrid quantum mechanical/molecular mechanical (QM/MM)–embedded cluster calculations based on a multi-region approach that allows us to model defects at the true dilute limit, with polarization effects described in an accurate and consistent manner. We compute the electronic structure, energetics, and geometries of Cu impurities, including substitutional and interstitial configurations, and analyze their effects on the electronic structure. Under ambient conditions, CuZn is the dominant defect in the d9 state and remains electronically passive. We find that, however, as we approach typical vacuum conditions, the interstitial Cu defect becomes significant and can act as an electron trap

Dynamic Prognosis Prediction for Patients on DAPT After Drug-Eluting Stent Implantation: Model Development and Validation

BACKGROUND: The rapid evolution of artificial intelligence (AI) in conjunction with recent updates in dual antiplatelet therapy (DAPT) management guidelines emphasizes the necessity for innovative models to predict ischemic or bleeding events after drug-eluting stent implantation. Leveraging AI for dynamic prediction has the potential to revolutionize risk stratification and provide personalized decision support for DAPT management. METHODS AND RESULTS: We developed and validated a new AI-based pipeline using retrospective data of drug-eluting stent-treated patients, sourced from the Cerner Health Facts data set (n=98 236) and Optum\u27s de-identified Clinformatics Data Mart Database (n=9978). The 36 months following drug-eluting stent implantation were designated as our primary forecasting interval, further segmented into 6 sequential prediction windows. We evaluated 5 distinct AI algorithms for their precision in predicting ischemic and bleeding risks. Model discriminative accuracy was assessed using the area under the receiver operating characteristic curve, among other metrics. The weighted light gradient boosting machine stood out as the preeminent model, thus earning its place as our AI-DAPT model. The AI-DAPT demonstrated peak accuracy in the 30 to 36 months window, charting an area under the receiver operating characteristic curve of 90% [95% CI, 88%-92%] for ischemia and 84% [95% CI, 82%-87%] for bleeding predictions. CONCLUSIONS: Our AI-DAPT excels in formulating iterative, refined dynamic predictions by assimilating ongoing updates from patients\u27 clinical profiles, holding value as a novel smart clinical tool to facilitate optimal DAPT duration management with high accuracy and adaptability

A comprehensive review on flow field properties in polymer mixing processes: a focus on applications in energetic materials

The mixing process is a critical step in the production of energetic materials and has a profound impact on product performance. As modern formulations for energetic materials continue to advance, the needs placed on the mixing process have become increasingly complex. Understanding and mastering the properties of the mixing flow field are essential for achieving optimal mixing function, ensuring process safety, and optimizing the parameters of both the mixing process and equipment specifically for energetic materials. In this comprehensive review, we analyze the influence of flow field properties on the mixing process of energetic materials by examining the mixing mechanism of two types of flow within the flow field. Additionally, we provide evidence to support the advantages of elongational flow in achieving effective mixing. We also discuss the application of mixing flow field properties in the processing of energetic materials, including advancements in mixing equipment and methods designed to optimize flow fields. Finally, we address the current shortcomings in energetic material mixing and offer an outlook for future developments in this field

Quasi-Bound States in the Continuum Enabled Strong Terahertz Chiroptical Response in Bilayer Metallic Metasurfaces

Bound state in the continuum (BIC) as a novel non-radiating state of light in the continuum of propagating modes has received great attention in photonics. Recently, chiral BICs have been introduced in the terahertz regime. However, strong chiroptical effects of transmitted waves remain challenging to achieve in metallic terahertz metasurfaces, especially for intrinsic chirality at normal incidences. Here, we propose a chiral quasi-BIC by simultaneously breaking the out-of-plane mirror and in-plane C2 rotation symmetries in a bilayer metallic metasurface, in which spin-selective terahertz transmittance is successfully realized. Benefiting from the symmetry-protected nature of our proposed BIC, precise tuning of structural parameters can lead to anticipated chiroptical performance. As a degree of freedom, the rotation angle of the split ring gaps can fully determine the handedness, linewidth, and working frequency with strong circular dichroism. Besides, the sensing performance shows a surrounding refractive index sensitivity of 200 GHz/RIU, which is similar to those of previous works based on terahertz metasurfaces. Taking advantage exclusively of symmetry-protected BICs to realize transmitted terahertz chiroptical response provides fresh insights into the creation of novel BICs, which enables profound advancements in the surging field of novel terahertz devices

Multiple Photonic Bound States in the Continuum in an Electromagnetically Induced Transparency Metasurface

Bound state in the continuum (BIC), as a novel eigenmode with infinitely high-quality factor, has received great attention in modern optical science. Mode coupling in dielectric metasurfaces opens possibilities in searching for robust BICs. Here, we discover multiple BICs in periodic dielectric resonators composed of a silicon rectangular bar and a silicon ring in one lattice. For the symmetry-protected BIC at-Γ point, a sharp electromagnetically induced transparency window can be formed by either tilting incident angle to induce the ‘bright-bright’ mode coupling, or by displacing the ring to generate the ‘bright-dark’ mode coupling. Besides, the coupling between two resonators leads to a new energy band in the dielectric metasurface. As a result, two off-Γ BICs are formed owing to avoided crossings with two energy bands, and another one belongs to the single-resonance parametric BIC. Thus, our coupled resonators possess superior abilities to judiciously engineer BICs via versatile physical mechanisms. Taking advantage exclusively of coupled resonators in dielectric metasurfaces provides fresh insights into the creation of both symmetry-protected and accidental BICs, which enables profound advancements in designing novel photonic devices