A cable dome has no stiffness or load carrying capacity unless it has been prestressed.Analyses of cable domes are based on successful prestressing designs,making force finding analysis very important.A new force find...A cable dome has no stiffness or load carrying capacity unless it has been prestressed.Analyses of cable domes are based on successful prestressing designs,making force finding analysis very important.A new force finding method named the imbal-ance force iterative method is proposed,which can overcome some limitations of the integrity feasible prestressing method.For instance,even if groups are assigned by mistake,the pretension distribution that satisfies the known geometry form can also be found.This method possess good stability and calculation efficiency,and a case study indicates that it is applicable to the force finding of large and complicated cable domes.On the other hand,form finding analysis of cable domes is also a key engineering problem.However,rigid displacement occurs in this process,which makes the analysis more complex.In this pa-per,the dynamic relaxation method was selected,and the problem of rigid displacement was therefore effectively solved.The method includes two steps:first,the stretching cables are released,and secondly,an axial force is imposed on the two ends of each released cable.This method is convenient in its calculation and clear in its conception.A case study indicates that the method is suitable for the simulation of the construction process of various cable domes and cable-strut tension structures.Moreover,a form finding experiment was conducted on a model of a cable dome with a diameter of 4.8 m by tensing diagonal cables.The behavior of the model in the form finding process was investigated.The experimental results indicate that the ini-tial lengths of members and prestress loss are key issues in cable domes design.The results also prove that the methods of form finding and force finding proposed in this paper are reliable and effective.展开更多
The popularity of cloud hosting services also brings in new security chal-lenges:it has been reported that these services are increasingly utilized by miscreants for their malicious online activities.Mitigating this e...The popularity of cloud hosting services also brings in new security chal-lenges:it has been reported that these services are increasingly utilized by miscreants for their malicious online activities.Mitigating this emerging threat,posed by such“bad repositories”(simply Bar),is challenging due to the different hosting strategy to traditional hosting service,the lack of direct observations of the repositories by those outside the cloud,the reluctance of the cloud provider to scan its customers’repositories without their consent,and the unique evasion strategies employed by the adversary.In this paper,we took the first step toward understanding and detecting this emerging threat.Using a small set of“seeds”(i.e.,confirmed Bars),we identified a set of collective features from the websites they serve(e.g.,attempts to hide Bars),which uniquely characterize the Bars.These features were utilized to build a scanner that detected over 600 Bars on leading cloud platforms like Amazon,Google,and 150 K sites,including popular ones like groupon.com,using them.Highlights of our study include the pivotal roles played by these repositories on malicious infrastructures and other important discoveries include how the adversary exploited legitimate cloud repositories and why the adversary uses Bars in the first place that has never been reported.These findings bring such malicious services to the spotlight and contribute to a better understanding and ultimately eliminating this new threat.展开更多
文摘A cable dome has no stiffness or load carrying capacity unless it has been prestressed.Analyses of cable domes are based on successful prestressing designs,making force finding analysis very important.A new force finding method named the imbal-ance force iterative method is proposed,which can overcome some limitations of the integrity feasible prestressing method.For instance,even if groups are assigned by mistake,the pretension distribution that satisfies the known geometry form can also be found.This method possess good stability and calculation efficiency,and a case study indicates that it is applicable to the force finding of large and complicated cable domes.On the other hand,form finding analysis of cable domes is also a key engineering problem.However,rigid displacement occurs in this process,which makes the analysis more complex.In this pa-per,the dynamic relaxation method was selected,and the problem of rigid displacement was therefore effectively solved.The method includes two steps:first,the stretching cables are released,and secondly,an axial force is imposed on the two ends of each released cable.This method is convenient in its calculation and clear in its conception.A case study indicates that the method is suitable for the simulation of the construction process of various cable domes and cable-strut tension structures.Moreover,a form finding experiment was conducted on a model of a cable dome with a diameter of 4.8 m by tensing diagonal cables.The behavior of the model in the form finding process was investigated.The experimental results indicate that the ini-tial lengths of members and prestress loss are key issues in cable domes design.The results also prove that the methods of form finding and force finding proposed in this paper are reliable and effective.
基金supported in part by the National Science Foundation(grants CNS-1223477,1223495,1527141 and 1618493)。
文摘The popularity of cloud hosting services also brings in new security chal-lenges:it has been reported that these services are increasingly utilized by miscreants for their malicious online activities.Mitigating this emerging threat,posed by such“bad repositories”(simply Bar),is challenging due to the different hosting strategy to traditional hosting service,the lack of direct observations of the repositories by those outside the cloud,the reluctance of the cloud provider to scan its customers’repositories without their consent,and the unique evasion strategies employed by the adversary.In this paper,we took the first step toward understanding and detecting this emerging threat.Using a small set of“seeds”(i.e.,confirmed Bars),we identified a set of collective features from the websites they serve(e.g.,attempts to hide Bars),which uniquely characterize the Bars.These features were utilized to build a scanner that detected over 600 Bars on leading cloud platforms like Amazon,Google,and 150 K sites,including popular ones like groupon.com,using them.Highlights of our study include the pivotal roles played by these repositories on malicious infrastructures and other important discoveries include how the adversary exploited legitimate cloud repositories and why the adversary uses Bars in the first place that has never been reported.These findings bring such malicious services to the spotlight and contribute to a better understanding and ultimately eliminating this new threat.
