Fast methods to solve the unloading problem of a cylindrical cavity or tunnel excavated in elasto-perfectly plastic, elasto-brittle or strain-softening materials under a hydrostatic stress feld can be derived based on...Fast methods to solve the unloading problem of a cylindrical cavity or tunnel excavated in elasto-perfectly plastic, elasto-brittle or strain-softening materials under a hydrostatic stress feld can be derived based on the self-similarity of the solution. As a consequence, they only apply when the rock mass is homogeneous and so exclude many cases of practical interest. We describe a robust and fast numerical technique that solves the tunnel unloading problem and estimates the ground reaction curve for a cylindrical cavity excavated in a rock mass with properties depending on the radial coordinate, where the solution is no longer self-similar. The solution is based on a continuation-like approach(associated with the unloading and with the incremental formulation of the elasto-plastic behavior), fnite element spatial discretization and a combination of explicit sub-stepping schemes and implicit techniques to integrate the constitutive law, so as to tackle the diffculties associated with both strong strain-softening and elasto-brittle behaviors. The developed algorithm is used for two practical ground reaction curve computation applications. The frst application refers to a tunnel surrounded by an aureole of material damaged by blasting and the second to a tunnel surrounded by a ring-like zone of reinforced(rock-bolted) material.展开更多
The decrease of runoff in the Luanhe river basin, which caused water crisis in Tian-jin for several times, was investigated using discharge data covering the period 1956-2002. The data from the differential integral c...The decrease of runoff in the Luanhe river basin, which caused water crisis in Tian-jin for several times, was investigated using discharge data covering the period 1956-2002. The data from the differential integral curves of the annual runoff indicate that the decreasing point began in 1979 in the six sub-basins. The decrease of runoff in the Luanhe river basin resulted from the combination of climate effects and human activities, in which the latter plays an important role. This can be illustrated by noting that after 1979 the runoff generated by similar precipitation decreased under the condition that the total precipitation did not decrease in the entire basin. As a result, the annual runoff of the Luanhe river basin after 1979 decreased by about 6.46×10^8 m^3 each year. To analyze the runoff characteristics, it is inadequate to seek the runoff trends only and the identification of cyclical component of the runoff as accurate as possible is necessary. From the natural annual runoff discharge time series, we can see the annual runoff fluctuates around the long-term average. Analyzed by VRL （Variable Record Length） method, the main periods of 3, 5-6, 7, 9, 16-20 and 37-39 years were found. The last decade causing water crisis was the driest period in the history, and this condition will last several years from trend analysis and power spectrum analysis. So finding new water sources is urgent to solve water crisis in Tianjin city, and the South-North Water Transfer is a feasible option.展开更多
Atrial fibrillation(AF) has been considered as a growing epidemiological problem in the world,with a substantial impact on morbidity and mortality.Ambulatory electrocardiography(e.g.,Holter) monitoring is commonly use...Atrial fibrillation(AF) has been considered as a growing epidemiological problem in the world,with a substantial impact on morbidity and mortality.Ambulatory electrocardiography(e.g.,Holter) monitoring is commonly used for AF diagnosis and therapy and the automated detection of AF is of great significance due to the vast amount of information provided.This study presents a combined method to achieve high accuracy in AF detection.Firstly,we detected the suspected transitions between AF and sinus rhythm using the delta RR interval distribution difference curve,which were then classified by a combination analysis of P wave and RR interval.The MIT-BIH AF database was used for algorithm validation and a high sensitivity and a high specificity(98.2% and 97.5%,respectively) were achieved.Further,we developed a dataset of 24-h paroxysmal AF Holter recordings(n=45) to evaluate the performance in clinical practice,which yielded satisfactory accuracy(sensitivity=96.3%,specificity=96.8%).展开更多
Taking a block of an oilfield as the engineering background, by analyzing the relationship between lithology and electrical properties, physical properties and electrical properties, as well as the relationship betwee...Taking a block of an oilfield as the engineering background, by analyzing the relationship between lithology and electrical properties, physical properties and electrical properties, as well as the relationship between oil-producing properties and electrical properties, four diagrams, namely, well right diagram, spontaneous potential curve, natural gamma curve, microelectrode curve, acoustic time difference curve, 4.0 m apparent resistance curve (2.5 m) and induction curve, were obtained, and porosity data (acoustic time difference) and induction curve were determined. It is suggested to establish an empirical formula by using acoustic time difference curve and tank porosity analysis, and further determine the limit thickness as fine sandstone. Through comprehensive analysis of the lower limit thickness of effective lithology and the lower limit electrical property of oil-bearing category, it is concluded that the oil-bearing category is oil-bearing category. The effective thickness is determined by using geological records of adjacent wells, laboratory analysis and oil testing (production) data and interlayer is subtracted, which provides an important reference link for determining the thickness of such tanks.展开更多
基金the Spanish Ministry of Science and Technology for fnancial support awarded under Contract Reference Numbers BIA2009-09673 and MTM2010-21235-C02-02
文摘Fast methods to solve the unloading problem of a cylindrical cavity or tunnel excavated in elasto-perfectly plastic, elasto-brittle or strain-softening materials under a hydrostatic stress feld can be derived based on the self-similarity of the solution. As a consequence, they only apply when the rock mass is homogeneous and so exclude many cases of practical interest. We describe a robust and fast numerical technique that solves the tunnel unloading problem and estimates the ground reaction curve for a cylindrical cavity excavated in a rock mass with properties depending on the radial coordinate, where the solution is no longer self-similar. The solution is based on a continuation-like approach(associated with the unloading and with the incremental formulation of the elasto-plastic behavior), fnite element spatial discretization and a combination of explicit sub-stepping schemes and implicit techniques to integrate the constitutive law, so as to tackle the diffculties associated with both strong strain-softening and elasto-brittle behaviors. The developed algorithm is used for two practical ground reaction curve computation applications. The frst application refers to a tunnel surrounded by an aureole of material damaged by blasting and the second to a tunnel surrounded by a ring-like zone of reinforced(rock-bolted) material.
基金China Education Foundation National Natural Science Foundation of China, No.50579049
文摘The decrease of runoff in the Luanhe river basin, which caused water crisis in Tian-jin for several times, was investigated using discharge data covering the period 1956-2002. The data from the differential integral curves of the annual runoff indicate that the decreasing point began in 1979 in the six sub-basins. The decrease of runoff in the Luanhe river basin resulted from the combination of climate effects and human activities, in which the latter plays an important role. This can be illustrated by noting that after 1979 the runoff generated by similar precipitation decreased under the condition that the total precipitation did not decrease in the entire basin. As a result, the annual runoff of the Luanhe river basin after 1979 decreased by about 6.46×10^8 m^3 each year. To analyze the runoff characteristics, it is inadequate to seek the runoff trends only and the identification of cyclical component of the runoff as accurate as possible is necessary. From the natural annual runoff discharge time series, we can see the annual runoff fluctuates around the long-term average. Analyzed by VRL （Variable Record Length） method, the main periods of 3, 5-6, 7, 9, 16-20 and 37-39 years were found. The last decade causing water crisis was the driest period in the history, and this condition will last several years from trend analysis and power spectrum analysis. So finding new water sources is urgent to solve water crisis in Tianjin city, and the South-North Water Transfer is a feasible option.
文摘Atrial fibrillation(AF) has been considered as a growing epidemiological problem in the world,with a substantial impact on morbidity and mortality.Ambulatory electrocardiography(e.g.,Holter) monitoring is commonly used for AF diagnosis and therapy and the automated detection of AF is of great significance due to the vast amount of information provided.This study presents a combined method to achieve high accuracy in AF detection.Firstly,we detected the suspected transitions between AF and sinus rhythm using the delta RR interval distribution difference curve,which were then classified by a combination analysis of P wave and RR interval.The MIT-BIH AF database was used for algorithm validation and a high sensitivity and a high specificity(98.2% and 97.5%,respectively) were achieved.Further,we developed a dataset of 24-h paroxysmal AF Holter recordings(n=45) to evaluate the performance in clinical practice,which yielded satisfactory accuracy(sensitivity=96.3%,specificity=96.8%).
文摘Taking a block of an oilfield as the engineering background, by analyzing the relationship between lithology and electrical properties, physical properties and electrical properties, as well as the relationship between oil-producing properties and electrical properties, four diagrams, namely, well right diagram, spontaneous potential curve, natural gamma curve, microelectrode curve, acoustic time difference curve, 4.0 m apparent resistance curve (2.5 m) and induction curve, were obtained, and porosity data (acoustic time difference) and induction curve were determined. It is suggested to establish an empirical formula by using acoustic time difference curve and tank porosity analysis, and further determine the limit thickness as fine sandstone. Through comprehensive analysis of the lower limit thickness of effective lithology and the lower limit electrical property of oil-bearing category, it is concluded that the oil-bearing category is oil-bearing category. The effective thickness is determined by using geological records of adjacent wells, laboratory analysis and oil testing (production) data and interlayer is subtracted, which provides an important reference link for determining the thickness of such tanks.
