scholarly journals Analysis of Winter Concrete Construction in Water Conservation Project

2018 ◽  
Vol 2 (3) ◽  
Author(s):  
Wenzhong Sun
Keyword(s):  
Low Temperature ◽  
Water Conservation ◽  
Northern China ◽  
Control Measures ◽  
Atmospheric Conditions ◽  
Concrete Construction ◽  
Flood Season ◽  
Construction Techniques ◽  
Flood Period ◽  
Water Conservancy

The construction of water conservancy projects should commence during optimal atmospheric conditions and non-flood period to ensure completion before the flood season begin in summer. In most areas of Northern China, the temperature during winter remain at lower level, in which environmental factors play the most important role in the construction of water conservancy projects. In particular, low temperature directly affects the strength of concrete and delays its solidification, this highly affects the quality and progress of concrete construction. In order to overcome this barrier, better planning, for reasonable and effective construction techniques and targeted control measures should be adopted to reduce the adverse effects of low temperature to assure a strong and safe architecture.

scholarly journals Changes in Air Pollution Following the COVID-19 Epidemic in Northern China: The Role of Meteorology

2021 ◽  
Vol 9 ◽  
Author(s):  
Tian Xian ◽  
Zhanqing Li ◽  
Jing Wei
Keyword(s):  
Air Pollution ◽  
Large Scale ◽  
Human Life ◽  
Northern China ◽  
Control Measures ◽  
Economic Activities ◽  
Low Wind Speed ◽  
Seasonal Signals ◽  
Haze Formation ◽  
Holiday Effects

COVID-19 has a tremendous impact on both human life and the environment due to the unprecedented large-scale shutdown of economic activities at the beginning of 2020. While it was widely expected to see a dramatic reduction in air pollution, reality appears to be much more complex due to the joint influences of emissions and meteorology in dictating air pollution. By analyzing ample meteorological and environmental observational data, this study attempts to evaluate the contribution of an economic lockdown or at a well-below normal level across China to air pollution during the COVID-19 pandemic in the Beijing-Tianjin-Hebei region. Besides the unprecedented emission reductions that helped to improve air quality, multiple other factors came into play, such as high humidity and low wind speed that are favorable for haze formation. After separating long-term trends, seasonal signals, holiday effects, and meteorological contributions concerning climatology, we estimated that the relative contributions of human activities to changes in particulate matter with a diameter of less than 2.5 μm and nitrogen dioxide during the epidemic were −17.13 μg/m3 and −0.03 μg/m3, respectively, with negative quantities denoting reductions to air pollution. Furthermore, comparing the changes in PM2.5 and NO2 concentrations after lockdown revealed that for short-term control measures, meteorological factors mainly affected pollutant particles.

Low-temperature direct bonding of SiC and Ga2O3 substrates under atmospheric conditions

2021 ◽  
Vol 130 (8) ◽  
pp. 085303
Author(s):  
Takashi Matsumae ◽  
Yuichi Kurashima ◽  
Hideki Takagi ◽  
Hitoshi Umezawa ◽  
Eiji Higurashi
Keyword(s):  
Low Temperature ◽  
Atmospheric Conditions

scholarly journals Complete MDP convolutional codes

2019 ◽  
Vol 18 (06) ◽  
pp. 1950105 ◽  
Author(s):  
Julia Lieb
Keyword(s):  
Waiting Time ◽  
Recovery Rate ◽  
Convolutional Codes ◽  
Optimal Recovery ◽  
Base Field ◽  
Concrete Construction ◽  
Additional Advantage ◽  
Decoding Algorithms ◽  
Construction Techniques ◽  
Maximum Distance Profile

Maximum distance profile (MDP) convolutional codes have the property that their column distances are as large as possible. It has been shown that, transmitting over an erasure channel, these codes have optimal recovery rate for windows of a certain length. Reverse MDP convolutional codes have the additional advantage that they are suitable for forward and backward decoding algorithms. Beyond that the subclass of complete MDP convolutional codes has the ability to reduce the waiting time during decoding. The first main result of this paper is to show the existence and genericity of [Formula: see text] complete MDP convolutional codes for all code parameters with [Formula: see text] as well as that complete MDP convolutional codes cannot exist if [Formula: see text]. The second main contribution is the presentation of two concrete construction techniques to obtain complete MDP convolutional codes. These constructions work for all code parameters with [Formula: see text] but require that the size of the underlying base field is (sufficiently) large.

Aircraft Metallic Materials Under Low Temperature Conditions

1951 ◽  
Vol 55 (482) ◽  
pp. 61-86
Author(s):  
P. L. Teed
Keyword(s):  
Low Temperature ◽  
Water Content ◽  
Metallic Materials ◽  
Atmospheric Conditions ◽  
Ambient Conditions ◽  
Temperature Conditions ◽  
Engineering Problems

The ubiquity of aircraft in being and yet to be, whether civil or military, manned or unmanned, makes them liable to exposure to wide extremes of atmospheric conditions. The range of temperature to which they may be subjected may possibly be from +90° to –90°C. (+194° to –130°F.), that of pressure, from one atmosphere to something approximating to one-tenth of this amount, while the water content (aqueous vapour plus water in suspension; for example, in a very dense tropical cloud), can, on occasion, be as high as 2.5 per cent. by weight and, at stratospheric heights, at least as low as 0.001 per cent. Such variations in ambient conditions are not without chemical and physical repercussions. The engineering problems which arise will be examined, therefore, from both these view points, and attention will be drawn to potential dangers and means suggested for their avoidance.

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