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In human action recognition based on wearable sensors, most previous studies have focused on a single type of sensor and single classifier. This study aims to use a wearable sensor based on flexible sensors and a tri-axial accelerometer to collect action data of elderly people. It uses a statistical modeling approach based on the ensemble algorithm to classify actions and verify its validity.

Nine types of daily actions were collected by the wearable sensor device from a group of elderly volunteers, and the time-domain features of the action sequences were extracted. The dimensionality of the feature vectors was reduced by linear discriminant analysis. An ensemble learning method based on XGBoost was used to build a model of elderly action recognition. Its performance was compared with the action recognition rate of other algorithms based on the Boosting algorithm, and with the accuracy of single classifier models.

The effectiveness of the method was validated by three experiments. The results show that XGBoost is able to classify nine daily actions of the elderly and achieve an average recognition rate of 94.8 per cent, which is superior to single classifiers and to other ensemble algorithms.

The research could have important implications for health care, including the treatment and rehabilitation of the elderly, and the prevention of falls.

Instead of using a single type of sensor, this research used a wearable sensor to obtain daily action data of the elderly. The results show that, by using the appropriate method, the device can obtain detailed data of joint action at a low cost. Comparing differences in performance, it was concluded that XGBoost is the most suitable algorithm for building a model of elderly action recognition. This method, together with a wearable sensor, can provide key data and accurate feedback information to monitor the elderly in their rehabilitation activities.

The rising uncertainties in the macroeconomic environment exacerbate the challenges firms face in the export market. This study aims to explore which strategy is suitable for export enterprises to develop sustainably under COVID-19.

Based on the sample data of China’s A-stock listed manufacturing firms from 2010 to 2020, this study applies a survival analysis method to explore the impact of strategic flexibility on export firm survival. Furthermore, this study uses the difference-in-difference model to test the relationship between strategic flexibility and firms’ profits in the context of the pandemic.

The results show that strategic flexibility can increase firms’ survival time, improving dynamic production and innovation capabilities, which is favorable for their sustainable development. Meanwhile, after the spread of COVID-19, firms with strategic flexibility have higher profits than those without. This influence mechanism mainly involves exploring new markets that can improve the company revenue and the coordination capabilities of the supply chain; this reduces corporate costs.

This study expands relevant research on the factors affecting the survival of export enterprises and supplements research on the economic consequences of firms’ strategic flexibility; this also enriches the dynamic capability theory. Additionally, it provides important implications for firms to enhance strategic flexibility and recommends government implementation of policies that encourage the domestic sales of commodities originally produced for exports under COVID-19.

The study aims to display the bubbles' evolution in the shear layer and their relationship with the pressure fluctuations. Furthermore, the coherent structures of the first six modes are extracted, in order to provide insight into their temporal and spatial evolution and determine the relationship between cavitating bubbles and coherent structures.

In the present study, numerical simulations of submerged jet cavitating flow were carried out at a cavitation inception condition inside an axisymmetric cavity using the large eddy simulation (LES) turbulence model and the Schnerr–Sauer (S–S) cavitation model. Based on snapshots produced by the numerical simulation, dynamic mode decomposition (DMD) was performed to extract the three-dimensional coherent structures of the first six modes in the shear layer.

The cavitating bubbles in the shear layer are deformed to elongated ellipsoid shapes by shear forces. The significant pressure fluctuations are induced by the collapse of the biggest bubble in the group. The first mode illustrates the mean characteristics of the flow field. The flow in the peripheral region of the shear layer is mainly dominated by large-scale coherent structures revealed by the second and third modes, while different small-scale coherent structures are contained in the central region. The cavitating bubbles are associated with small size coherent structures as the sixth or higher modes.

This work demonstrates the feasibility of LES for high Reynolds number shear layer flow. The dynamic mode decomposition method is a novel method to extract coherent structures and obtain their dynamic information that will help us to optimize and control the flow.

(1) This paper first displays the three-dimensional coherent structures and their characteristics in the shear layer of confined jet flow. (2) The relationship of bubbles shape and pressure fluctuations is illustrated. (3) The visualization of coherent structures benefits the understanding of the mixing process and cavitation inception in jet shear layers.

The purpose of this paper is to elucidate the detailed flow field and cavitation effect in the centrifugal pump volute at partial load condition.

Unsteady flows in a centrifugal pump volute at non-cavitation and cavitation conditions are investigated by using a computation fluid dynamics framework combining the re-normalization group k-e turbulence model and the mass transport cavitation model.

The flow field in pump volute is very complicated at part load condition with large pressure gradient and intensive vortex movement. Under cavitation conditions, the dominant frequency for most of the monitoring points in volute transit from the blade passing frequency to a lower frequency. Generally, the maximum amplitudes of pressure fluctuations in volute at serious cavitation condition is twice than that at non-cavitation condition because of the violent disturbances caused by cavitation shedding and explosion.

The detailed flow field and cavitation effect in the centrifugal pump volute at partial load condition are revealed and analysed.

Resilience concepts in integrated urban transport refer to the performance of dealing with external shock and the ability to continue to provide transportation services of all modes. A robust transportation resilience is a goal in pursuing transportation sustainability. Under this specified context, while before the perturbations, robustness refers to the degree of the system’s capability of functioning according to its design specifications on integrated modes and routes, redundancy is the degree of duplication of traffic routes and alternative modes to maintain persistency of service in case of perturbations. While after the perturbations, resourcefulness refers to the capacity to identify operational problems in the system, prioritize interventions and mobilize necessary material/ human resources to recover all the routes and modes, rapidity is the speed of complete recovery of all modes and traffic routes in the urban area. These “4R” are the most critical components of urban integrated resilience.

The trends of transportation resilience's connotation, metrics and strategies are summarized from the literature. A framework is introduced on both qualitative characteristics and quantitative metrics of transportation resilience. Using both model-based and mode-free methodologies that measure resilience in attributes, topology and system performance provides a benchmark for evaluating the mechanism of resilience changes during the perturbation. Correspondingly, different pre-perturbation and post-perturbation strategies for enhancing resilience under multi-mode scenarios are reviewed and summarized.

Cyber-physic transportation system (CPS) is a more targeted solution to resilience issues in transportation. A well-designed CPS can be applied to improve transport resilience facing different perturbations. The CPS ensures the independence and integrity of every child element within each functional zone while reacting rapidly.

This paper provides a more comprehensive understanding of transportation resilience in terms of integrated urban transport. The fundamental characteristics and strategies for resilience are summarized and elaborated. As little research has shed light on the resilience concepts in integrated urban transport, the findings from this paper point out the development trend of a resilient transportation system for digital and data-driven management.

Regarding the global development of the wine industry, China has gained a notable share in terms of wine consumption, and its domestic wine production has increased steadily since 2000. The wine production process requires close coordination between growers and processors to avoid disruption and instability in the supply chain of the wine grapes. However, vertical coordination in the Chinese wine regions has received little attention. Based on the existing theoretical background on vertical coordination, this study aims to detect the evolution processes of vertical coordination in the Chinese grape market.

Exploratory qualitative research fits with the aim of this study. From December 2018 to January 2019, interviews with grape growers and wine processors of various Chinese wine-producing areas took place. After transcribing all recorded files into text, a qualitative data analysis following the approach of Mayring (2015) was used to analyse and interpret the data.

The models of vertical coordination in the grape supply in China vary between the producer's requirements on grape quality/quantity and the arrangements of grape supply chains, which are diverse depending on regional strategies of the local government.

However, in this research, the authors did not get into details on the organization of the contractual coordination, and due to the limited access to grape growers, the relationship between farmers and processors cannot be analysed in detail. With a better understanding of the coordination relationship and enhanced contract enforcement, the vineyard management and grape supply chain management can be better performed, inducing a steady industrial development.

Regarding the global development of the wine industry, China has gained a notable share in terms of wine consumption, and its domestic wine production has increased steadily since 2000. However, vertical coordination in the Chinese wine regions has received little attention. The study provides a first insight into the grape market structures, as very little is known.