Most stable structure of fullerene[20] and its novel activity toward addition of alkene: A theoretical study

Structures and stabilities of fullerene C-20 and C-20(-) have been investigated by the density functional theory and CCSD(T) calculations. In consideration of the Jahn-Teller distortion of I-h-symmetric C-20, possible subgroup symmetries have been used in the full geometry optimization. On the basis of relative energetics, vibrational analyses, and electron affinities, fullerenes C-20 and C-20(-) have most stable D-2h and C-i structures, respectively. The controversy on the relative stability of fullerene[20] arises from the use of different subgroups in calculation and the basis set dependence in vibrational analysis. Predicted nucleus-independent chemical shift values show that the most stable fullerene C-20 and its derivatives C-20(C2H2)(n) and C-20(C2H4)(n) (n=1-3) exhibit remarkable aromaticity, while C-20(C2H2)(4) and C-20(C2H4)(4) have no spherical aromaticity. The C-20 (D-2h) cage has remarkable activity toward the addition of olefin, and such feasibility of the addition reaction is ascribed to strong bonding interactions among frontier molecular orbitals from C-20 and olefin. Calculations indicate that both C-20(C2H2)(n) and C-20(C2H4)(n) have similar features in electronic spectra. (c) 2007 American Institute of Physics

Association between ecological risks and ecosystem services in an urban agglomeration in arid China

Rapid urbanization leads to changes in ecosystem services and may exacerbate ecological risks. Clarifying the relationship between these two factors in a specific context is essential to explore the integrated management model and achieve sustainable regional development. However, previous studies mainly lack an integrated analysis, fail to clearly explain the mechanism of ecosystem change, and can neither support landscape ecological security construction nor spatial planning and management. This study, using the urban agglomeration on the northern slope of the Tianshan Mountains (UANSTM) as an example, applied multi-source data from 2010 to 2020, investigated the changes and relationships between ecological risks and ecosystem services, and proposes an assessment framework. The total ecosystem services (TES) of the studied agglomeration showed a decreasing trend, with an overall loss of 0.43%. Corresponding to the decrease of ecosystem services, the ecological risk was higher in the south and north of the UANSTM and lower in the northwestern, central, and eastern regions. The proportion of ecological high-risk areas was expanding. The key to the relationship between ecological risks and ecosystem services is the change in hydrological conditions. Therefore, we suggest that the UANSTM actively transforms the development and use mode of water resources and coordinates their allocation, aiming to reduce regional ecological risks and optimize the pattern of ecosystem services

Discerning Spatiotemporal Patterns and Policy Drivers of Rural Settlement Changes from 1962 to 2020

Despite two centuries of urbanisation worldwide, 45% of the world’s people still live in rural areas. Driven by urban development, the form and structure of rural settlements have undergone drastic changes. Reasonable planning according to the scale of the land and spatial layout of rural settlements is particularly important for the development of rural areas. The continuous development of the economy means that the housing needs of farmers and the macro policy background will inevitably change. We create a relationship curve for the “policy-scale of rural settlements” in different periods according to the laws of Maslow’s psychological demand theory and game theory and conduct an empirical study on Dingzhou City, China. The limited availability of remote sensing data means it is difficult to map the evolution patterns of rural settlements on medium and long time scales, and therefore, this paper explores and decrypts military satellite images, reveals the spatial evolution characteristics of rural settlements in Dingzhou, China from 1962 to 2020, and discusses the impact of policy factors on changes to rural settlements in different periods. The study found that from 1962 to 2020, the total area of rural settlements in Dingzhou showed a trend of continual increase, with a total increase of 8354.97 ha (73%). The average annual growth rates in 1962–1972, 1972–1990, 1990–2000, 2000–2010, and 2010–2020 were 0.29%, 1.17%, 1.81%, 1.26%, and 0.05%, respectively. The growth rate of rural settlements was relatively slow from 1962 to 1972. The policy was mainly because rural homesteads (land for building rural residences) were transformed from private ownership to “one homestead, two systems”, and the expansion of rural settlements was inhibited. From 1972 to 1990, with the deepening of reform and opening up, there was a boom in building houses in rural areas, and the growth rate of rural settlements increased. From 1990 to 2000, although the state strengthened the management of rural settlement use, there was still an increasing trend in the area of rural settlements; from 2000 to 2020 the implementation of policies such as “one house for one household" and “connecting increase and decrease" meant that the growth rate of rural settlements slowed

Discerning Spatiotemporal Patterns and Policy Drivers of Rural Settlement Changes from 1962 to 2020

Despite two centuries of urbanisation worldwide, 45% of the world’s people still live in rural areas. Driven by urban development, the form and structure of rural settlements have undergone drastic changes. Reasonable planning according to the scale of the land and spatial layout of rural settlements is particularly important for the development of rural areas. The continuous development of the economy means that the housing needs of farmers and the macro policy background will inevitably change. We create a relationship curve for the “policy-scale of rural settlements” in different periods according to the laws of Maslow’s psychological demand theory and game theory and conduct an empirical study on Dingzhou City, China. The limited availability of remote sensing data means it is difficult to map the evolution patterns of rural settlements on medium and long time scales, and therefore, this paper explores and decrypts military satellite images, reveals the spatial evolution characteristics of rural settlements in Dingzhou, China from 1962 to 2020, and discusses the impact of policy factors on changes to rural settlements in different periods. The study found that from 1962 to 2020, the total area of rural settlements in Dingzhou showed a trend of continual increase, with a total increase of 8354.97 ha (73%). The average annual growth rates in 1962–1972, 1972–1990, 1990–2000, 2000–2010, and 2010–2020 were 0.29%, 1.17%, 1.81%, 1.26%, and 0.05%, respectively. The growth rate of rural settlements was relatively slow from 1962 to 1972. The policy was mainly because rural homesteads (land for building rural residences) were transformed from private ownership to “one homestead, two systems”, and the expansion of rural settlements was inhibited. From 1972 to 1990, with the deepening of reform and opening up, there was a boom in building houses in rural areas, and the growth rate of rural settlements increased. From 1990 to 2000, although the state strengthened the management of rural settlement use, there was still an increasing trend in the area of rural settlements; from 2000 to 2020 the implementation of policies such as “one house for one household" and “connecting increase and decrease" meant that the growth rate of rural settlements slowed

Dynamic Analysis and Fault Diagnosis for Gear Transmission of a Vibration Exciter of a Mine-Used Vibrating Screen under Different Conditions

The helical gear pair of a box-type vibration exciter of a mine-used linear vibrating screen is subjected to complex excitation and prone to broken tooth failures. At present, investigation regarding the difference and particularity between gear transmission in vibrating screens (i.e., vibration machinery) and that in rotating machinery is still a challenge, which is the key to revealing the performance and failure mechanism of gear transmission in the premise of application to vibrating screens. In order to intuitively display the peculiarity of gear transmission on the exciter, an innovative virtual prototype model of a gear pair of a vibrating screen exciter is proposed. This model considers the effects of internal and external excitation, such as the friction and lubrication of the gear, strong alternating load produced by a large eccentric block, the reciprocating motion of the screen body, the large clearance of bearing and so on, and its correctness is verified. Based on the comparison, the inducement for the high fatigue rate of exciter gears is revealed. Models of a vibrating screen’s excitation system with different degrees of broken teeth are also established, and tooth fault features are proposed for fault detection. Sensitive indicators for the degradation degree of tooth damage are put forward, and the monitoring strategy is presented that with the increase of damage degree, the waveform index and pulse index of axial vibration acceleration increase. The analysis results provide powerful support for the optimal design of the vibrating screen’s exciter gears and fault diagnosis

Dynamic Analysis and Fault Diagnosis for Gear Transmission of a Vibration Exciter of a Mine-Used Vibrating Screen under Different Conditions

The helical gear pair of a box-type vibration exciter of a mine-used linear vibrating screen is subjected to complex excitation and prone to broken tooth failures. At present, investigation regarding the difference and particularity between gear transmission in vibrating screens (i.e., vibration machinery) and that in rotating machinery is still a challenge, which is the key to revealing the performance and failure mechanism of gear transmission in the premise of application to vibrating screens. In order to intuitively display the peculiarity of gear transmission on the exciter, an innovative virtual prototype model of a gear pair of a vibrating screen exciter is proposed. This model considers the effects of internal and external excitation, such as the friction and lubrication of the gear, strong alternating load produced by a large eccentric block, the reciprocating motion of the screen body, the large clearance of bearing and so on, and its correctness is verified. Based on the comparison, the inducement for the high fatigue rate of exciter gears is revealed. Models of a vibrating screen’s excitation system with different degrees of broken teeth are also established, and tooth fault features are proposed for fault detection. Sensitive indicators for the degradation degree of tooth damage are put forward, and the monitoring strategy is presented that with the increase of damage degree, the waveform index and pulse index of axial vibration acceleration increase. The analysis results provide powerful support for the optimal design of the vibrating screen’s exciter gears and fault diagnosis

Fault Feature Enhanced Extraction and Fault Diagnosis Method of Vibrating Screen Bearings

For mechanical equipment, bearings have a high incidence area of faults. A problem for bearings is that their fault characteristics include a vibrating screen exciter which is weak and thus easily covered in strong background noise, hence making the noise difficult to remove. In this paper, a noise reduction method based on singular value decomposition, improved by singular value’s unilateral ascent method (SSVD), and a fault feature enhancement method, i.e., variational mode decomposition, improved by revised whale algorithm optimization (RWOA-VMD), are proposed. These two methods are used in vibration signal processing with early faults of bearings having a vibrating screen and they have achieved significant application results. This paper also aims to construct a multi-modal feature matrix composed of energy entropy, singular value entropy, and power spectrum entropy, and then the early fault diagnosis of bearings of a vibrating screen exciter bearing is realized by using the proposed support vector machine, improved by the aquila optimizer algorithm (AO-SVM)

Fault Feature Enhanced Extraction and Fault Diagnosis Method of Vibrating Screen Bearings

For mechanical equipment, bearings have a high incidence area of faults. A problem for bearings is that their fault characteristics include a vibrating screen exciter which is weak and thus easily covered in strong background noise, hence making the noise difficult to remove. In this paper, a noise reduction method based on singular value decomposition, improved by singular value’s unilateral ascent method (SSVD), and a fault feature enhancement method, i.e., variational mode decomposition, improved by revised whale algorithm optimization (RWOA-VMD), are proposed. These two methods are used in vibration signal processing with early faults of bearings having a vibrating screen and they have achieved significant application results. This paper also aims to construct a multi-modal feature matrix composed of energy entropy, singular value entropy, and power spectrum entropy, and then the early fault diagnosis of bearings of a vibrating screen exciter bearing is realized by using the proposed support vector machine, improved by the aquila optimizer algorithm (AO-SVM)

Cardiac rehabilitation knowledge in patients with coronary heart disease in Baoding city of China: A cross-sectional study

Objective: The purpose of this study is to assess the awareness on cardiac rehabilitation (CR) in patients with coronary heart disease (CHD). Methods: Inpatients diagnosed with coronary heart disease were recruited from 3 hospitals in this study. The study employed a cardiac structured questionnaire to assess respondents' level of awareness, and bivariate to analyze the sociodemographic factors that influence the awareness on CR. Results: Of all 500 participants, 66.40% were male and the mean age was 62.51 ± 9.96 years. The mean score of knowledge was 44.00 ± 17.00 (score range: 0–93), and the mean level of awareness was 47.31% (awareness range: 0–100%). The highest mean level of awareness was in the reexamination subscale (98%) and the lower were in the basic information about CR program, SP optimized medication and heart rate subscale. Bivariate analysis showed that higher age was associated with less knowledge. Patients with higher education level and better income status had better knowledge. And patients who lived in rural and had no jobs had less knowledge. Conclusions: This study showed low levels of awareness on CR program in CHD patients in Baoding. Therefore, the need for health education is indicated in this study to improve the awareness on CR among CHD patients. Keywords: Coronary heart disease, Cardiac rehabilitation, Awareness, Influencing factor