Recently,sand fences,made of high density polyethylene(HDPE)board,which is resistant against harsh plateau environmental conditions,could possibly be used to control the wind-blown sand along the Qinghai section of th...Recently,sand fences,made of high density polyethylene(HDPE)board,which is resistant against harsh plateau environmental conditions,could possibly be used to control the wind-blown sand along the Qinghai section of the Golmud-Korla Railway.In this paper,wind tunnel simulation was performed on the protective effect of multiple rows of HDPE board sand fences on wind-blown sand.Two parameters have been used to reflect the protective effect of sand fences,that is,windproof efficiency and sand control efficiency,referring to the reduction rates of wind speed at a height of 0.04 m and sand flux in a run of test with the fence compared those in the control run of test without it,respectively.The test results showed that when the porosity was 30%,the single-row sand fence had the best wind proof and sand control efficiency with respective values of 46%and 65.3%.The windproof efficiencies of double-row and triple-row sand fences at 20H were 59%and 62%,respectively.Compared with the windproof effi-ciency of the single-row sand fence,those of the two-row and three-row fences increased by 13%and 16%,respectively:The maximum sand control efficiency of the double-row and triple-row sand fences were 92.1%and 96.5%,increased by 26.8%and 31.2%,respectively,compared with that of the single-row sand fence.This study indicates that the sand control efficiency after adding one or two rows was not double or triple that of the single-row fence,while the first-row sand fence played a major protective role.Compared with the double-row sand fences,the effect of the third row sand fence in triple-row sand fences is limited,and thus double-row HDPE board sand fences with the porosity of 30%are rec-ommended to control wind-blown sand along the Qinghai section of the Golmud-Korla Railway.展开更多
The theory of （n） truth degrees of formulas is proposed in modal logic for the first time. A consistency theorem is obtained which says that the （n） truth degree of a modality-free formula equals the truth degree ...The theory of （n） truth degrees of formulas is proposed in modal logic for the first time. A consistency theorem is obtained which says that the （n） truth degree of a modality-free formula equals the truth degree of the formula in two-valued propositional logic. Variations of （n） truth degrees of formulas w.r.t. n in temporal logic is investigated. Moreover, the theory of （n） similarity degrees among modal formulas is proposed and the （n） modal logic metric space is derived therefrom which contains the classical logic metric space as a subspace. Finally, a kind of approximate reasoning theory is proposed in modal logic.展开更多
基金supported by the Young Scholars Science Foundation of Lanzhou Jiaotong University,China(2018016)the Chang Jiang Scholar and Innovation Team Development Plan of China(IRT_15R29)。
文摘Recently,sand fences,made of high density polyethylene(HDPE)board,which is resistant against harsh plateau environmental conditions,could possibly be used to control the wind-blown sand along the Qinghai section of the Golmud-Korla Railway.In this paper,wind tunnel simulation was performed on the protective effect of multiple rows of HDPE board sand fences on wind-blown sand.Two parameters have been used to reflect the protective effect of sand fences,that is,windproof efficiency and sand control efficiency,referring to the reduction rates of wind speed at a height of 0.04 m and sand flux in a run of test with the fence compared those in the control run of test without it,respectively.The test results showed that when the porosity was 30%,the single-row sand fence had the best wind proof and sand control efficiency with respective values of 46%and 65.3%.The windproof efficiencies of double-row and triple-row sand fences at 20H were 59%and 62%,respectively.Compared with the windproof effi-ciency of the single-row sand fence,those of the two-row and three-row fences increased by 13%and 16%,respectively:The maximum sand control efficiency of the double-row and triple-row sand fences were 92.1%and 96.5%,increased by 26.8%and 31.2%,respectively,compared with that of the single-row sand fence.This study indicates that the sand control efficiency after adding one or two rows was not double or triple that of the single-row fence,while the first-row sand fence played a major protective role.Compared with the double-row sand fences,the effect of the third row sand fence in triple-row sand fences is limited,and thus double-row HDPE board sand fences with the porosity of 30%are rec-ommended to control wind-blown sand along the Qinghai section of the Golmud-Korla Railway.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 10331010 and 10771129)the Foundation of 211 Constructionof Shaanxi Normal University
文摘The theory of （n） truth degrees of formulas is proposed in modal logic for the first time. A consistency theorem is obtained which says that the （n） truth degree of a modality-free formula equals the truth degree of the formula in two-valued propositional logic. Variations of （n） truth degrees of formulas w.r.t. n in temporal logic is investigated. Moreover, the theory of （n） similarity degrees among modal formulas is proposed and the （n） modal logic metric space is derived therefrom which contains the classical logic metric space as a subspace. Finally, a kind of approximate reasoning theory is proposed in modal logic.
