16 research outputs found
Incompatible Deformations of Elastic Plates
No full textThis article considers the methods for mathematical modeling of incompatible finite deformations of elastic plates by using the principles of the differential geometry theory underlying continuously distributed defects. Equilibrium equations were derived by asymptotic expansions of the finite strain measures with respect to two small parameters. One parameter defines the order of smallness of displacements from the reference shape (self-stressed state), while the other specifies the thickness. Asymptotic orders were different for the deflections and displacements in the plate plane, as well as for their derivatives. They were selected in such a way that, with additional assumptions on the possibility of ignoring certain terms in the resulting expressions and the compatibility of deformations, the equations could be reduced to the system of F¨oppl–von Ka´rm´an equations
Provable Security of S-BGP and other Path Vector Protocols: Model, Analysis and Extensions
Get PDFThis paper provides the provable-security treatment of path vector routing protocols. We first design a security definition for routing path vector protocols by studying, generalizing, and formalizing numerous known threats. Our model incorporates three major security goals. It is quite strong, yet simple to use. We prove by reduction that S-BGP satisfies two out of the security model’s three goals, assuming the underlying signature scheme is secure. Under the same assumption, we next show how the protocol can be modified to meet all three security goals simultaneously. We also analyze SoBGP and show that it fails to meet two security goals. Finally, we study security of partial PKI deployment of path vector protocols when not all nodes have public keys. We investigate the possibilities of relaxing the PKI requirement and relying on non-cryptographic physical security of networks that use the protocol in order to achieve possibly weaker, but still well-defined, notions of security. We also present the necessary and sufficient conditions to achieve full security in the partial PKI deployment scenario. We believe our conclusions will prove useful for protocol developers, standards bodies and government agencies
Double periodicity of mechanical properties of a thin ice field formed under conditions of lateral constraint
Get PDFExperimental data and results of theoretical modeling of the bending of a viscoelastic floating ice plate formed under constrained deformation are analyzed. When a thin plate of ice is frozen on the water surface under conditions of constrained deformation, which may be caused, for example, by the rigid walls of the pool, periodic changes in physical properties occur in it, in particular, periodic penetration resistance. Experimental results confirming this fact were obtained during tests of a thin ice cover at the Krylov State Research Center (Saint-Petersburg, Russia). A characteristic feature of the test results is that their spatial distributions can be represented with sufficient accuracy as an overlap of two periodic functions with significantly different periods: long-wave and short-wave components. In this paper, a detailed analysis of experimental data is given, which makes it possible to isolate these components. Furthermore, the theoretical model that explains the physical causes for double periodicity is proposed. The model assumes viscoelastic quasi-static deformation of the ice plate caused by small fluctuations of the water level in the basin and random disturbances of its surface. An analytical solution for the model case of cylindrical bending is derived. The solution is presented in the form of an expansion in terms of eigenfunctions of differential operators generated by the boundary value problem under study. It has been established that when a thin plate of ice freezes under conditions of constrained deformation, there are at least two reasons for the appearance of a periodic structure: a general loss of stability as an elastic structure and a local loss of stability by a viscoelastic-plastic mechanism. The results obtained can be used in the development of the theory of ice compression, in assessing the causes of variation in the local strength of ice fields and the possibility of their artificial destruction
Rethinking security for internet routing
No full textS.48-57ON JUNE 12, 2015, an incident in the Asia-Pacific region caused network performance problems for hundreds of thousands of Internet destinations, including Facebook and Amazon. 24,37 It was not the result of a natural disaster, a failed transatlantic cable, or a malicious attack. Instead, it resulted from a misconfiguration at a Malaysian ISP that inadvertently exploited the Internet's Border Gateway Protocol (BGP) to disrupt connectivity at networks in Malaysia and beyond. BGP establishes Internet connectivity by setting up routes between independently operated networks. Over the past two decades, several high-profile routing incidents (often resulting from misconfigurations(4,8,28,30,37)) have regularly demonstrated that BGP is highly vulnerable to malicious attacks. BGP attacks cause a victim network Internet traffic to be rerouted to the attacker's own network. The rerouted traffic might then be dropped before it reaches its legitimate destination(4,28,30,37) or, more deviously, be subject to eavesdropping,(2,32) traffic analysis,(36) or tampering.(15,21,34)59Nr.1
M.: Bgp security in partial deployment: Is the juice worth the squeeze
No full textAs the rollout of secure route origin authentication with the RPKI slowly gains traction among network operators, there is a push to standardize secure path validation for BGP (i.e., S*BGP: S-BGP, soBGP, BGPSEC, etc.). Origin authentica-tion already does much to improve routing security. More-over, the transition to S*BGP is expected to be long and slow, with S*BGP coexisting in “partial deployment ” along-side BGP for a long time. We therefore use theoretical and experimental approach to study the security benefits pro-vided by partially-deployed S*BGP, vis-a-vis those already provided by origin authentication. Because routing policies have a profound impact on routing security, we use a survey of 100 network operators to find the policies that are likely to be most popular during partial S*BGP deployment. We find that S*BGP provides only meagre benefits over origin au-thentication when these popular policies are used. We also study the security benefits of other routing policies, pro-vide prescriptive guidelines for partially-deployed S*BGP, and show how interactions between S*BGP and BGP can introduce new vulnerabilities into the routing system
GEOMETRIC ASPECTS OF THE THEORY OF INCOMPATIBLE DEFORMATIONS. PART I. UNIFORM CONFIGURATIONS
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Transient Temperature Fields in Growing Bodies Subject to Discrete and Continuous Growth Regimes
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