B2B E Commerce is one of the most potential electronic commerce forms at present. But since traditional B2 B E Commerce system lacks an unified standard and solution of basic architectur e a nd interface, it has m...B2B E Commerce is one of the most potential electronic commerce forms at present. But since traditional B2 B E Commerce system lacks an unified standard and solution of basic architectur e a nd interface, it has many shortcomings such as poor reusability and poor extensi bility. In order to solve the problem, combined with Web Service technology, a B 2B E Commerce system model based on Web Service is proposed and analyzed. The m odel can combine relatively independent Web Service on Intranet and Internet by constructing core application program. As a part of supply chain, it can also pr ovide a standard interface for other applications such as ERP/CRM/SCM, etc. Th er efore, B2B E Commerce system with this form is easy for development, integratio n and maintenance. Finally, a solution of B2B E Commerce system based on Web Se rvice is propounded by introducing an instance.展开更多
Computer simulation models are widely applied in various areas of the health care sector, including the spread of infectious diseases. Patch models involve explicit movements of people between distinct locations. The ...Computer simulation models are widely applied in various areas of the health care sector, including the spread of infectious diseases. Patch models involve explicit movements of people between distinct locations. The aim of the present work has been designed and explored a patch model with population mobility between different patches and between each patch and an external population. The authors considered a SIR (susceptible-infected-recovered) scheme. The model was explored by computer simulations. The results show how endemic levels are reached in all patches of the system. Furthermore, the performed explorations suggest that the people mobility between patches, the immigration from outside the system and the infection rate in each patch, are factors that may influence the dynamics of epidemics and should be considered in health policy planning.展开更多
To solve nutrient flux and budget among waters with distinct salinity difference for water-salt- nutrient budget, a traditional method is to build a stoichiometrically linked steady state model. However, the tradition...To solve nutrient flux and budget among waters with distinct salinity difference for water-salt- nutrient budget, a traditional method is to build a stoichiometrically linked steady state model. However, the traditional way cannot cope appropriately with those without distinct salinity difference that parallel to coastline or in a complex current system, as the results would be highly affected by box division in time and space, such as the Changjiang (Yangtze) River estuary (CRE) and adjacent waters (30.75°-31.75°N, 122°10′-123°20′E). Therefore, we developed a hydrodynamic box model based on the traditional way and the regional oceanic modeling system model (ROMS). Using data from four cruises in 2005, horizontal, vertical and boundary nutrient fluxes were calculated in the hydrodynamic box model, in which flux fields and the major controlling factors were studied. Results show that the nutrient flux varied greatly in season and space. Water flux outweighs the nutrient concentration in horizontal flux, and upwelling flux outweighs upward diffusion flux in vertical direction (upwelling flux and upward diffusion flux regions overlap largely all the year). Vertical flux in spring and summer are much greater than that in autumn and winter. The maximum vertical flux for DIP (dissolved inorganic phosphate) occurs in summer. Additional to the fluxes of the ChanNiang River discharge, coastal currents, the Taiwan Warm Current, and the upwelling, nutrient flux inflow from the southern Yellow Sea and outflow southward are found crucial to nutrient budgets of the study area. Horizontal nutrient flux is controlled by physical dilution and confined to coastal waters with a little into the open seas. The study area acts as a conveyer transferring nutrients from the Yellow Sea to the East China Sea in the whole year. In addition, vertical nutrient flux in spring and summer is a main source of DIP. Therefore, the hydrodynamic ROMS-based box model is superior to the traditional one in estimating nutrient fluxes in a complicated hydrodynamic current system and provides a modified box model approach to material flux research.展开更多
S-ALOHA (Slotted ALOHA) random access protocol is a widely used protocol mainly for the transmission of short packets in wireless networks. Most papers consider either an infinite population model where the impact o...S-ALOHA (Slotted ALOHA) random access protocol is a widely used protocol mainly for the transmission of short packets in wireless networks. Most papers consider either an infinite population model where the impact of the backoff protocol cannot be adequately evaluated or a finite population model where the number of nodes is fixed. In this letter, a combination of both models is proposed using the time-scale decomposition technique. This methodology allows to study the system under more realistic conditions where the dynamics of users enter and leaving the system are reflected on the performance of the system as well as the impact of the backoff protocol. Also, it allows studying the system in non-saturation conditions. The proposed methodology divides the analysis in two parts: packet-level and connection-level. This analysis renders suitable results when the time scale of the packet level and connection level statistics is different. On the other hand, when these scales are similar, the proposed methodology is no longer suited.展开更多
Is Chinese urbanization going to take a long time, or can its development goal be achieved by the government in a short time? What is the highest stable urbanization level that China can reach? When can China complete...Is Chinese urbanization going to take a long time, or can its development goal be achieved by the government in a short time? What is the highest stable urbanization level that China can reach? When can China complete its urbanization? To answer these questions, this paper presents a system dynamic(SD) model of Chinese urbanization, and its validity and simulation are justified by a stock-flow test and a sensitivity analysis using real data from 1998 to 2013. Setting the initial conditions of the simulation by referring to the real data of 2013, the multi-scenario analysis from 2013 to 2050 reveals that Chinese urbanization will reach a level higher than 70% in 2035 and then proceed to a slow urbanization stage regardless of the population policy and GDP growth rate settings; in 2050, Chinese urbanization levels will reach approximately 75%, which is a stable and equilibrium level for China. Thus, it can be argued that Chinese urbanization is a long social development process that will require approximately20 years to complete and that the ultimate urbanization level will be 75–80%, which means that in the distant future, 20–25% of China's population will still settle in rural regions of China.展开更多
Electromagnetic transient simulation for large-scale power system is a time-consuming problem.A new frequency-dependent equivalence method is presented in the paper,which might significantly accelerate power system el...Electromagnetic transient simulation for large-scale power system is a time-consuming problem.A new frequency-dependent equivalence method is presented in the paper,which might significantly accelerate power system electromagnetic transient simulation.In the method,an effective algorithm is designed to directly transfer the port admittance determinant of external system's mixing matrix into admittance rational function;and the step-by-step strategy for the equivalence of actual large system is put forward,which further reduces the calculation quantities needed.Moreover,the study of multiple real root pole characteristics of admittance transfer function of two-port network is performed and a proposition is achieved.Based on the proposition and residue theorem,the equivalence system for external system corresponding to the admittance rational function is obtained.The computation complexity of the step-by-step equivalence method is about o(┌n/np×T┐)(┌┐ is upper integral operation,n is the total buses number of external system,N P is the total buses number of single step equivalence network,T is single step equivalence time),which indicates that the computation complexity of the method proposed has nearly linear relationship with the buses number of external system,and the method proposed has satisfactory computation speed.Since the mixing matrix of external system includes all the information of external system,therefore,port admittance rational function derived from it can reflect its full frequency characteristic and the equivalence network achieved has high equivalence precision.Moreover,since the port rational function is gained at the condition of the external system without source,which equals stable passive network,it could not show any unstable pole and need not extra measure to make the equivalence system stable.The test results of the samples and comparison with other methods demonstrate that the new method proposed is valid and effective.展开更多
One of eight gates of the Pearl River Estuary,the Yamen Inlet is a bedrock channel mouth connecting the Huangmao Sea and Yamen Channel.The wider water surfaces of the upper and lower reaches of the entrance produce a ...One of eight gates of the Pearl River Estuary,the Yamen Inlet is a bedrock channel mouth connecting the Huangmao Sea and Yamen Channel.The wider water surfaces of the upper and lower reaches of the entrance produce a unique bidirectional asymmetrical jet system.Using observed hydrology and historical charts,the ECOMSED model was applied in morphodynamic analysis of the dynamic structures and dynamic equilibrium of the Yamen jet system and its effect on sedimentation.It was found that (1) the nonlinear interaction of Yamen dynamic structures could not be ignored,as while the Coriolis force and friction force were generally of the same order of magnitude,the effect of friction force was greater;(2) the bidirectional asymmetrical jet system was flood preferential flow to the north of the channel mouth and ebb preferential flow to the south;and (3) the bidirectional asymmetrical jet system was the dominant factor in the long term stability of the Yamen deep trough.展开更多
Internet-based virtual computing environment (iVCE) has been proposed to combine data centers and other kinds of computing resources on the Internet to provide efficient and economical services. Virtual machines (...Internet-based virtual computing environment (iVCE) has been proposed to combine data centers and other kinds of computing resources on the Internet to provide efficient and economical services. Virtual machines (VMs) have been widely used in iVCE to isolate different users/jobs and ensure trustworthiness, but traditionally VMs require a long period of time for booting, which cannot meet the requirement of iVCE's large-scale and highly dynamic applications. To address this problem, in this paper we design and implement VirtMan, a fast booting system for a large number of virtual machines in iVCE. VirtMan uses the Linux Small Computer System Interface (SCSI) target to remotely mount to the source image in a scalable hierarchy, and leverages the homogeneity of a set of VMs to transfer only necessary image data at runtime. We have implemented VirtMan both as a standalone system and for OpenStack. In our 100-server testbed, VirtMan boots up 1000 VMs (with a 15 CB image of Windows Server 2008) on 100 physical servers in less than 120 s, which is three orders of magnitude lower than current public clouds.展开更多
文摘B2B E Commerce is one of the most potential electronic commerce forms at present. But since traditional B2 B E Commerce system lacks an unified standard and solution of basic architectur e a nd interface, it has many shortcomings such as poor reusability and poor extensi bility. In order to solve the problem, combined with Web Service technology, a B 2B E Commerce system model based on Web Service is proposed and analyzed. The m odel can combine relatively independent Web Service on Intranet and Internet by constructing core application program. As a part of supply chain, it can also pr ovide a standard interface for other applications such as ERP/CRM/SCM, etc. Th er efore, B2B E Commerce system with this form is easy for development, integratio n and maintenance. Finally, a solution of B2B E Commerce system based on Web Se rvice is propounded by introducing an instance.
文摘Computer simulation models are widely applied in various areas of the health care sector, including the spread of infectious diseases. Patch models involve explicit movements of people between distinct locations. The aim of the present work has been designed and explored a patch model with population mobility between different patches and between each patch and an external population. The authors considered a SIR (susceptible-infected-recovered) scheme. The model was explored by computer simulations. The results show how endemic levels are reached in all patches of the system. Furthermore, the performed explorations suggest that the people mobility between patches, the immigration from outside the system and the infection rate in each patch, are factors that may influence the dynamics of epidemics and should be considered in health policy planning.
基金Supported by the National Nature Science Foundation of China(Nos.41121064,41276116)the National Basic Research Program of China(973 Program)(No.2010CB428706)
文摘To solve nutrient flux and budget among waters with distinct salinity difference for water-salt- nutrient budget, a traditional method is to build a stoichiometrically linked steady state model. However, the traditional way cannot cope appropriately with those without distinct salinity difference that parallel to coastline or in a complex current system, as the results would be highly affected by box division in time and space, such as the Changjiang (Yangtze) River estuary (CRE) and adjacent waters (30.75°-31.75°N, 122°10′-123°20′E). Therefore, we developed a hydrodynamic box model based on the traditional way and the regional oceanic modeling system model (ROMS). Using data from four cruises in 2005, horizontal, vertical and boundary nutrient fluxes were calculated in the hydrodynamic box model, in which flux fields and the major controlling factors were studied. Results show that the nutrient flux varied greatly in season and space. Water flux outweighs the nutrient concentration in horizontal flux, and upwelling flux outweighs upward diffusion flux in vertical direction (upwelling flux and upward diffusion flux regions overlap largely all the year). Vertical flux in spring and summer are much greater than that in autumn and winter. The maximum vertical flux for DIP (dissolved inorganic phosphate) occurs in summer. Additional to the fluxes of the ChanNiang River discharge, coastal currents, the Taiwan Warm Current, and the upwelling, nutrient flux inflow from the southern Yellow Sea and outflow southward are found crucial to nutrient budgets of the study area. Horizontal nutrient flux is controlled by physical dilution and confined to coastal waters with a little into the open seas. The study area acts as a conveyer transferring nutrients from the Yellow Sea to the East China Sea in the whole year. In addition, vertical nutrient flux in spring and summer is a main source of DIP. Therefore, the hydrodynamic ROMS-based box model is superior to the traditional one in estimating nutrient fluxes in a complicated hydrodynamic current system and provides a modified box model approach to material flux research.
文摘S-ALOHA (Slotted ALOHA) random access protocol is a widely used protocol mainly for the transmission of short packets in wireless networks. Most papers consider either an infinite population model where the impact of the backoff protocol cannot be adequately evaluated or a finite population model where the number of nodes is fixed. In this letter, a combination of both models is proposed using the time-scale decomposition technique. This methodology allows to study the system under more realistic conditions where the dynamics of users enter and leaving the system are reflected on the performance of the system as well as the impact of the backoff protocol. Also, it allows studying the system in non-saturation conditions. The proposed methodology divides the analysis in two parts: packet-level and connection-level. This analysis renders suitable results when the time scale of the packet level and connection level statistics is different. On the other hand, when these scales are similar, the proposed methodology is no longer suited.
基金supported by the Key Project of the National Natural Science Foundation of China “the SD model and threshold value prediction of the interactive coupled effects between urbanization and eco-environment in mega-urban agglomerations” (Grant No. 41590844)the Independent Research Program of Tsinghua University (Grant No. 2015THZ01)
文摘Is Chinese urbanization going to take a long time, or can its development goal be achieved by the government in a short time? What is the highest stable urbanization level that China can reach? When can China complete its urbanization? To answer these questions, this paper presents a system dynamic(SD) model of Chinese urbanization, and its validity and simulation are justified by a stock-flow test and a sensitivity analysis using real data from 1998 to 2013. Setting the initial conditions of the simulation by referring to the real data of 2013, the multi-scenario analysis from 2013 to 2050 reveals that Chinese urbanization will reach a level higher than 70% in 2035 and then proceed to a slow urbanization stage regardless of the population policy and GDP growth rate settings; in 2050, Chinese urbanization levels will reach approximately 75%, which is a stable and equilibrium level for China. Thus, it can be argued that Chinese urbanization is a long social development process that will require approximately20 years to complete and that the ultimate urbanization level will be 75–80%, which means that in the distant future, 20–25% of China's population will still settle in rural regions of China.
基金supported by the National Natural Science Foundation ofChina (Grant No. 51177107)
文摘Electromagnetic transient simulation for large-scale power system is a time-consuming problem.A new frequency-dependent equivalence method is presented in the paper,which might significantly accelerate power system electromagnetic transient simulation.In the method,an effective algorithm is designed to directly transfer the port admittance determinant of external system's mixing matrix into admittance rational function;and the step-by-step strategy for the equivalence of actual large system is put forward,which further reduces the calculation quantities needed.Moreover,the study of multiple real root pole characteristics of admittance transfer function of two-port network is performed and a proposition is achieved.Based on the proposition and residue theorem,the equivalence system for external system corresponding to the admittance rational function is obtained.The computation complexity of the step-by-step equivalence method is about o(┌n/np×T┐)(┌┐ is upper integral operation,n is the total buses number of external system,N P is the total buses number of single step equivalence network,T is single step equivalence time),which indicates that the computation complexity of the method proposed has nearly linear relationship with the buses number of external system,and the method proposed has satisfactory computation speed.Since the mixing matrix of external system includes all the information of external system,therefore,port admittance rational function derived from it can reflect its full frequency characteristic and the equivalence network achieved has high equivalence precision.Moreover,since the port rational function is gained at the condition of the external system without source,which equals stable passive network,it could not show any unstable pole and need not extra measure to make the equivalence system stable.The test results of the samples and comparison with other methods demonstrate that the new method proposed is valid and effective.
基金supported by Guangdong Natural Science Foundation (Grant No. 9151027501000111)‘908’ Marine Survey Project (Grant No. 908-02-01-04)National Natural Science Foundation of China (Grant No. 50839005)
文摘One of eight gates of the Pearl River Estuary,the Yamen Inlet is a bedrock channel mouth connecting the Huangmao Sea and Yamen Channel.The wider water surfaces of the upper and lower reaches of the entrance produce a unique bidirectional asymmetrical jet system.Using observed hydrology and historical charts,the ECOMSED model was applied in morphodynamic analysis of the dynamic structures and dynamic equilibrium of the Yamen jet system and its effect on sedimentation.It was found that (1) the nonlinear interaction of Yamen dynamic structures could not be ignored,as while the Coriolis force and friction force were generally of the same order of magnitude,the effect of friction force was greater;(2) the bidirectional asymmetrical jet system was flood preferential flow to the north of the channel mouth and ebb preferential flow to the south;and (3) the bidirectional asymmetrical jet system was the dominant factor in the long term stability of the Yamen deep trough.
基金supported by the National Natural Science Foundation of China(Nos.61379055 and 61379053)
文摘Internet-based virtual computing environment (iVCE) has been proposed to combine data centers and other kinds of computing resources on the Internet to provide efficient and economical services. Virtual machines (VMs) have been widely used in iVCE to isolate different users/jobs and ensure trustworthiness, but traditionally VMs require a long period of time for booting, which cannot meet the requirement of iVCE's large-scale and highly dynamic applications. To address this problem, in this paper we design and implement VirtMan, a fast booting system for a large number of virtual machines in iVCE. VirtMan uses the Linux Small Computer System Interface (SCSI) target to remotely mount to the source image in a scalable hierarchy, and leverages the homogeneity of a set of VMs to transfer only necessary image data at runtime. We have implemented VirtMan both as a standalone system and for OpenStack. In our 100-server testbed, VirtMan boots up 1000 VMs (with a 15 CB image of Windows Server 2008) on 100 physical servers in less than 120 s, which is three orders of magnitude lower than current public clouds.