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Abstract 30 min of moderate-intensity aerobic exercise per day is recommended, but the response and adaptation of endothelial function (EF) to this exercise remains controversial. The purpose of this study was to determine the changes in EF in endurance trained and untrained individuals before and after this exercise and to compare the differences between trained and untrained individuals. Twelve endurance-trained male college athletes (trained group) and 12 untrained male college students (untrained group) performed a 30-min run at an intensity of 60% VO2max. Brachial artery flow-mediated dilation (FMD) was measured before exercise, 30 min and 60 min after exercise, and the following morning. Resting diameter and maximum diameter showed large time effects (p

A large amount of pulverized coal is easy to be produced in the process of hydraulic fracturing of coalbed methane reservoir. The accumulation and settlement of pulverized coal will cause serious blockage to the fractures formed by fracturing, and reduce the permeability and conductivity of fractures and affect the effect of fracturing stimulation of coalbed methane wells. Therefore, a new type of coal powder dispersant MFFS-2 was developed through a large number of laboratory experiments and combined with the reservoir characteristics of the target CBM block, and its comprehensive performance was evaluated. The experimental results show that when the mass concentration of MFFS-2 reaches 0.3%, the surface tension of water solution can be reduced to less than 25 mN/m, and the contact angle of coal surface can be reduced from 115.3° to less than 60° with good surface activity and wettability; when the suspension of coal powder is standing for 10 hours, the suspension rate of coal powder can reach more than 30% with the addition of 0.3% MFFS-2. When 0.3% MFFS-2 solution is used to displace for 2 hours, the yield of pulverized coal can reach more than 60%, which indicates that MFFS-2 has good suspension dispersion and carrying effect on pulverized coal; in addition, the damage rate of MFFS-2 to the matrix permeability of block coal core in the target area is less than 10%, and the damage degree of fracturing fluid system to the permeability of coal core is reduced after adding MFFS-2 into the active hydraulic fracturing fluid. The field fracturing operation results of coalbed methane well show that the fracturing operation of S-1 well is smooth after adding new coal powder dispersant MFFS-2, a large amount of coal powder is carried out in the backflow fluid, and the gas production is high, which achieves the expected fracturing effect. Moreover, the construction effect of the new active hydraulic fracturing fluid in the same block is significantly better than that of the conventional active hydraulic fracturing fluid.

Background: Identifying the correlates of exercise behavior is essential to combating physical inactivity as a public health concern. The purpose of this study is to identify the correlates of physical activity among urban Chinese adults under the social-ecological theoretical model in order to facilitate targeted interventions to promote physical activity. Methods: Using the socio-ecological model, we conducted a questionnaire survey among 1459 urban residents in Zhejiang and Shaanxi provinces of China, collecting data on individual demographic factors, sociological factors, environmental perception, and exercise behavior. Binary logistic regression models were employed to analyze the relationships between exercise behavior and socio-ecological factors. Results: Male gender (p < 0.01), advanced age (p < 0.001), higher education level (p < 0.05), living independently from parents (p < 0.05), absence of childcare responsibilities (p < 0.01), residence in a county/prefecture-level city (p < 0.001), favorable neighborhood esthetics (p < 0.001), available greenways/parks (p < 0.001), and family support for exercise participation (p < 0.05) were significantly correlated with an increased likelihood of participating in physical activity. Male gender (p < 0.001), advanced age (p < 0.001), absence of childcare responsibilities (p < 0.05), good neighborhood vegetation (p < 0.01), availability of free neighborhood exercise facilities (p < 0.05), and support from friends for exercise participation (p < 0.01) were significantly correlated with an increased likelihood of engaging in physical activity for more than 150 min per week. BMI, community air quality, traffic safety, public safety, and level of social development were not major correlates. Conclusions: To promote exercise behavior, more attention should be paid to individuals who are female, young, have lower levels of education, bear childcare responsibilities, or reside in provincial capitals in China. Improving the habitat environment and providing convenient and affordable facilities should also be considered. Furthermore, support from family and friends can positively reinforce exercise behavior.

The compressor speed, expansion valve opening and drying temperature are critical to the thermal performance improvement and control logic optimization of the closed heat pump drying (CHPD) system. This paper investigates the effects of the three parameters on the thermal performance of the CHPD system by the single factor experiment method. According to the experimental findings, as the compressor speed of the system increased, the heating capacity grew by 11.4%, but the coefficient of performance (COP) declined by 41.3%. As the expansion valve opening of the system increased, the heating capacity and COP grew by 73.5% and 82.9%, respectively. As the drying temperature of the system rose, the heating capacity grew by 3.1%, but the COP dropped by 25.3%. It can be concluded that reducing the compressor speed and drying temperature, and increasing the expansion valve opening could effectively enhance the thermal performance of the CHPD system.

This paper experimentally studied the effects of different factors of electrohydrodynamics-heat pump combined drying on the drying characteristics of banana slices. Results showed that: The introduction of high-voltage electric field in heat pump drying could increase the drying rate of banana slices, and it would increased with the increasing of voltage. Banana slices showed better drying quality under combined drying. Compared with 60 ℃ single heat pump, the energy consumption of 60 ℃, 75 kV electrohydrodynamics-heat pump drying was reduced by 7.61 kJ/g. In addition, by fitting different drying models, the fitting effect of the Page model was the best, which could better describe the moisture change rule of banana slices during electrohydrodynamics-heat pump combined drying. It was suggested that, the electrohydrodynamics could help speed up the drying rate while improving the drying quality, reducing drying energy consumption, and save energy, which could provide reference value for the application of electrohydrodynamics drying technology.

The drying characteristics of yam slices using heat pump-electrohydrodynamics (EHD) combined drying were studied under the conditions of the drying temperatures of 50–60 °C, the voltages of 80–100 kV and the wind speeds of 1∼3 m/s. The results show that compared with the single heat pump drying, the combined drying can effectively reduce the drying temperature by approximately 5 °C. This is relatively friendly to heat sensitive materials and can also improve the running performance of the heat pump system. Furthermore, the sensory score is increased by approximately 21.4% and the specific energy consumption of combined drying at the voltage of 100 kV is reduced by approximately 27.8%. Under the later stage of the combined drying, the wind speed can be reduced to save energy consumption. Through the analysis of model parameters, Page model is more consistent with the variation law of drying experimental data. This paper provides practical guidance for optimizing the process of yam slices using heat pump-EHD combined drying.

The performance of an enhanced vapor-injection heat-pump drying system was designed and theoretically studied in cold areas. According to the simulation findings, the ideal vapor-injection charge of the system ranges from 12.3 to 13.9%, and its ideal intermediate pressure is between 1.278 and 1.498 MPa when the evaporation temperature is above 0 °C. The ideal vapor-injection charge of the system ranges from 13 to 20%, and its optimal intermediate pressure ranges from 1.078 to 1.278 MPa when the evaporation temperature is −15–0 °C. The ideal vapor-injection charge of the system ranges from 20 to 24%, and the intermediate pressure ranges from 0.898 to 1.078 MPa when the evaporation temperature is below −15 °C. The heat and humidity exhausted air source heat-pump drying (HHE–ASHPD) system has higher dehumidification efficiency than the closed heat-pump drying (CHPD) system under the same air temperature, humidity, and volume parameters.

In this paper, a solar-assisted enhanced vapor injection air-source heat pump (SC-EVIHP) system was built to investigate its heating performance in cold regions. A typical-weather day in Harbin was selected for the experiment, and the heating characteristics of the SC-EVIHP system were explored under variable working conditions. The experimental results showed that the system was greatly affected by solar radiation intensity. On typical-weather days in winter, the maximum values for the heating capacity and COP of the system appeared at the time of maximum radiation intensity. Compared with conventional enhanced vapor injection air-source heat pump systems (EVI-ASHPs), the heating capacity and COP were increased by 24.9% and 12.5% at most, respectively. The COP of the system increased by at most 11.1% under conditions where the outdoor temperature was −12 °C and the outlet hot air temperature of the solar air collector was 40 °C. The SC-EVIHP system works well in a low-temperature environment and can be widely applied in cold regions.

In this article, R1234ze(E), R152a, and three mixtures M1, M2, and M3 composed of R152a and R1234ze(E) (in the ratio of 60:40, 50:50, and 40:60, by mass, respectively) as drop-in replacements of R134a in vapor compression system were theoretically analyzed. The performance of the vapor compression system was compared in terms of compressor discharge temperature, volumetric cooling capacity, cooling capacity, compressor power consumption, and coefficient of performance. The results showed that R152a had better coefficient of performance as well as nearly equal volumetric cooling capacity and cooling capacity compared to R134a; however, flammable R152a running with high compressor discharge temperature was restricted. Cooling capacity of R1234ze(E) was far lower than that of R134a. M2 was selected as the best alternative for R134a. Volumetric cooling capacity of M2 and R134a was similar so that M2 can be used in R134a vapor compressor system without modifying compressor. Coefficient of performance of M2 was higher than that of R134a by about 3% with 7% lower cooling capacity and 10% lower compressor power consumption. Compressor discharge temperature of M2 was higher than that of R134a by about 2°C–5°C. It was concluded that M2 can primely be an energy conservation and environmental protection alternative to R134a in vapor compression system.

The performance of a new mixed refrigerant R1234yf/R13I1 with a mass ratio of 90/10 under basic refrigeration cycle and refrigeration cycle with internal heat exchanger is calculated in comparison with the performance of R134a under basic refrigeration cycle at different condensation temperature and evaporation temperature. The results show that R1234yf/R13I1 is virtually non-flammable with global warming potential of less than 4. Under basic refrigeration cycle, the compressor power consumption, cooling capacity and COP of R1234yf/R13I1 are lower than these of R134a by about 4.5%, 9.5%, and 7.5%, respectively. Under refrigeration cycle with internal heat exchanger, the compressor power consumption, cooling capacity, and COP of R1234yf/R13I1 are lower than these of R134a by about 2%, 4.5%, and 3%, respectively. The R1234yf/R13I1 is a beneficial refrigerant of replacing R134a in vapor compression system. [ABSTRACT FROM AUTHOR]

In this paper, the feasibility of two low global warming potential refrigerants R513A and R1234yf as alternatives to R134a was tested in an automotive air conditioning system in winter. The test results showed that the heating capacities of R513A and R1234yf were 2% and 4% lower than that of R134a, and their COP were 3-9% and 6-19% lower than that of R134a, respectively. It revealed that R513A can be used as a transition product to replace R134a, and R1234yf required further improvements to improve the energy efficiency. [ABSTRACT FROM AUTHOR]

Refrigerants with low global warming potential (GWP) are much needed in automotive air conditioning systems. This paper compares two refrigerants, R134a (GWP=1300) and R513A (GWP = 573) experimentally. The results show that the latter has lower cooling capacity, lower COP and lower discharge temperature than the former, revealing that R513A is a promising replacement of its high GWP partner. [ABSTRACT FROM AUTHOR]