This article is concerned with assessment of changes in two critical characteristics of lake and river ice regime, namely ice cover duration and maximum ice thickness, in the period from the beginning of the 80s to th...This article is concerned with assessment of changes in two critical characteristics of lake and river ice regime, namely ice cover duration and maximum ice thickness, in the period from the beginning of the 80s to the present, which is characterized by higher temperatures in the Northern Hemisphere compared with the previous period. The above ice regime characteristics are often limiting factors in winter operation of lakes and rivers (navigation, hydraulic construction works in cold period, construction of ice roads etc.). Assessment of changes in ice characteristics of lakes and rivers has been made for 52 river and five lake gauging sites of the Asian part of Russia (APR) using long-term observation data from the Russian observing network. Long-term series of the above characteristics were divided into two periods: from 1955 to 1979 (the period of stationary climate) and from 1980 to 2014 (non-stationary climate) and assessed from the point of view of their homogeneity and trend significance by Student’s t-test. The research has found that at most of the sites in the APR, both ice cover duration and maximum ice thickness decreased during non-stationary climate period compared with the previous one. The greatest quantitative changes have occurred in the Eastern Siberia (average net decrease in ice cover duration amounted to 7 days.decade-1 and in maximum ice thickness-20 cm.decade-1) and in the Amur River basin (7 days.decade-1 and 17 cm.decade-1 respectively).展开更多
This paper focuses on the last stock problem of substitutive service parts, which is a hot problem in practice. Considering that a firm faces two types of service parts with a certain substitution coefficient, we stud...This paper focuses on the last stock problem of substitutive service parts, which is a hot problem in practice. Considering that a firm faces two types of service parts with a certain substitution coefficient, we study the optimization problem of minimizing the total expected cost. Using the non-linear programming theory and method, we find the optimal preserved quantities for the optimization problem. The relation between the product substitution characteristic and the total cost of service parts is analyzed. And an example is given to show the application of our model.展开更多
文摘This article is concerned with assessment of changes in two critical characteristics of lake and river ice regime, namely ice cover duration and maximum ice thickness, in the period from the beginning of the 80s to the present, which is characterized by higher temperatures in the Northern Hemisphere compared with the previous period. The above ice regime characteristics are often limiting factors in winter operation of lakes and rivers (navigation, hydraulic construction works in cold period, construction of ice roads etc.). Assessment of changes in ice characteristics of lakes and rivers has been made for 52 river and five lake gauging sites of the Asian part of Russia (APR) using long-term observation data from the Russian observing network. Long-term series of the above characteristics were divided into two periods: from 1955 to 1979 (the period of stationary climate) and from 1980 to 2014 (non-stationary climate) and assessed from the point of view of their homogeneity and trend significance by Student’s t-test. The research has found that at most of the sites in the APR, both ice cover duration and maximum ice thickness decreased during non-stationary climate period compared with the previous one. The greatest quantitative changes have occurred in the Eastern Siberia (average net decrease in ice cover duration amounted to 7 days.decade-1 and in maximum ice thickness-20 cm.decade-1) and in the Amur River basin (7 days.decade-1 and 17 cm.decade-1 respectively).
文摘This paper focuses on the last stock problem of substitutive service parts, which is a hot problem in practice. Considering that a firm faces two types of service parts with a certain substitution coefficient, we study the optimization problem of minimizing the total expected cost. Using the non-linear programming theory and method, we find the optimal preserved quantities for the optimization problem. The relation between the product substitution characteristic and the total cost of service parts is analyzed. And an example is given to show the application of our model.
