Spatial inhomogeneities in the sedimentation of biogenic particles in ocean flows: analysis in the Benguela region

Sedimentation of particles in the ocean leads to inhomogeneous horizontal distributions at depth, even if the release process is homogeneous. We study this phenomenon considering a horizontal sheet of sinking particles immersed in an oceanic flow, and determine how the particles are distributed when they sediment on the seabed (or are collected at a given depth). The study is performed from a Lagrangian viewpoint attending to the properties of the oceanic flow and the physical characteristics (size and density) of typical biogenic sinking particles. Two main processes determine the distribution, the stretching of the sheet caused by the flow and its projection on the surface where particles accumulate. These mechanisms are checked, besides an analysis of their relative importance to produce inhomogeneities, with numerical experiments in the Benguela region. Faster (heavier or larger) sinking particles distribute more homogeneously than slower ones.Comment: 24 pages, 8 figures. To appear in J. Geophys. Res.-Ocean

A Method for Patching Interleaving-Replay Attacks in Faulty Security Protocols

AbstractThe verification of security protocols has attracted a lot of interest in the formal methods community, yielding two main verification approaches: i) state exploration, e.g. FDR [Gavin Lowe. Breaking and fixing the needham-schroeder public-key protocol using FDR. In TACAs'96: Proceedings of the Second International Workshop on Tools and Algorithms for Construction and Analysis of Systems, pages 147–166, London, UK, 1996. Springer-Verlag] and OFMC [A.D. Basin, S. Mödersheim, and L. Viganò. An on-the-fly model-checker for security protocol analysis. In D. Gollmann and E. Snekkenes, editors, ESORICS'03: 8th European Symposium on Research in Computer Security, number 2808 in Lecture Notes in Computer Science, pages 253–270, Gjøvik, Norway, 2003. Springer-Verlag]; and ii) theorem proving, e.g. the Isabelle inductive method [Lawrence C. Paulson. The inductive approach to verifying cryptographic protocols. Journal in Computer Security, 6(1-2):85–128, 1998] and Coral [G. Steel, A. Bundy, and M. Maidl. Attacking the asokan-ginzboorg protocol for key distribution in an ad-hoc bluetooth network using coral. In H. König, M. Heiner, and A. Wolisz, editors, IFIP TC6 /WG 6.1: Proceedings of 23rd IFIP International Conference on Formal Techniques for Networked and Distributed Systems, volume 2767, pages 1–10, Berlin, Germany, 2003. FORTE 2003 (work in progress papers)]. Complementing formal methods, Abadi and Needham's principles aim to guide the design of security protocols in order to make them simple and, hopefully, correct [M. Abadi and R. Needham. Prudent engineering practice for cryptographic protocols. IEEE Transactions on Software Engineering, 22(1):6–15, 1996]. We are interested in a problem related to verification but far less explored: the correction of faulty security protocols. Experience has shown that the analysis of counterexamples or failed proof attempts often holds the key to the completion of proofs and for the correction of a faulty model. In this paper, we introduce a method for patching faulty security protocols that are susceptible to an interleaving-replay attack. Our method makes use of Abadi and Needham's principles for the prudent engineering practice for cryptographic protocols in order to guide the location of the fault in a protocol as well as the proposition of candidate patches. We have run a test on our method with encouraging results. The test set includes 21 faulty security protocols borrowed from the Clark-Jacob library [J. Clark and J. Jacob. A survey of authentication protocol literature: Version 1.0. Technical report, Department of Computer Science, University of York, November 1997. A complete specification of the Clark-Jacob library in CAPSL is available at http://www.cs.sri.com/millen/capsl/]

Prueba De Habilidades Prácticas CCNP

La técnica multi-VRF (Virtual Routing and Forwarding) es una técnica de enrutamiento que permite la creación de múltiples instancias de enrutamiento en una red. Esto se logra mediante la creación de tablas de enrutamiento virtuales, que se utilizan para enrutar el tráfico entre diferentes redes o VLANs. La principal ventaja de la técnica multi-VRF es que permite separar el tráfico de diferentes redes o VLANs, lo que mejora el rendimiento y la seguridad de la red. Al separar el tráfico, se pueden aplicar políticas de seguridad y de calidad de servicio (QoS) específicas para cada red o VLAN, lo que ayuda a garantizar que el tráfico crítico se priorice y se entregue de manera eficiente. Además, la técnica multi-VRF permite una mayor eficiencia en el uso de los recursos de la red. Al separar el tráfico, se pueden utilizar enlaces y recursos de red específicos para cada red o VLAN, lo que reduce la congestión de la red y mejora la disponibilidad de los recursos.The multi-VRF technique (Virtual Routing and Forwarding) is a routing technique that allows the creation of multiple routing instances in a network. This is accomplished by creating virtual routing tables, which are used to route traffic between different networks, or VLANs. The main advantage of the multi-VRF technique is that it allows the traffic of different networks or VLANs to be separated, which improves the performance and security of the network. By separating traffic, specific security and quality of service (QoS) policies can be applied to each network or VLAN, helping to ensure that critical traffic is prioritized and delivered efficiently. In addition, the multi-VRF technique allows greater efficiency in the use of network resources. By separating traffic, specific network links and resources can be used for each network or VLAN, reducing network congestion and improving resource availability

DAEH N-terminal sequence of avian serum albumins as catalytic center of Cu (II)-dependent organophosphorus hydrolyzing A-esterase activity

O-hexyl O-2,5-dichlorophenyl phosphoramidate (HDCP) induces delayed neuropathy. The R (+)-HDCP inhibits and caused the so call “aging reaction” on inhibited-NTE. This enantiomer is not hydrolyzed by Ca(II)-dependent A-esterases in mammal tissues but is hydrolyzed by Cu(II)-dependent chicken serum albumin (CSA). With the aim of identifying HDCP hydrolysis by other vertebrate albumins, we incubated albumin with 400 μM racemic HDCP in the presence of 100 μM copper sulfate. HDCPase activity was assessed by measurement of HDCP with chiral chromatography. Human, sheep, dog, pig, lamprey or cobra serum albumin did not show a significant activity (~10%). Rabbit and bovine albumins hydrolyzed both enantiomers of HDCP (25% and 50% respectively). Turkey serum albumin had more HDCPase activity (~80 μM remaining) than the chicken albumin (~150 μM remaining). No animal albumins other than chicken showed stereoselective hydrolysis. Preincubation of chicken albumin with 1 mM the histidine modifying agents, 100 μM N-bromosuccinimide (NBS) and Zn(II), inhibited its Cu(II)-dependent R (+)-HDCPase activity, where as other mM amino acids modifiers had no inhibitory effects. . These results confirm that the stereoselective hydrolysis of (+)-HDCP is a specific A-esterase catalytic property of chicken albumin. The higher HDCPase activity by turkey albumin suggests the amino-terminal sequence of avian albumins (DAEHK) is the active center of this Cu(II)-dependent A-esterase activity