Impacts of the Tropical Pacific/Indian Oceans on the Seasonal Cycle of the West African Monsoon

The current consensus is that drought has developed in the Sahel during the second half of the twentieth century as a result of remote effects of oceanic anomalies amplified by local land–atmosphere interactions. This paper focuses on the impacts of oceanic anomalies upon West African climate and specifically aims to identify those from SST anomalies in the Pacific/Indian Oceans during spring and summer seasons, when they were significant. Idealized sensitivity experiments are performed with four atmospheric general circulation models (AGCMs). The prescribed SST patterns used in the AGCMs are based on the leading mode of covariability between SST anomalies over the Pacific/Indian Oceans and summer rainfall over West Africa. The results show that such oceanic anomalies in the Pacific/Indian Ocean lead to a northward shift of an anomalous dry belt from the Gulf of Guinea to the Sahel as the season advances. In the Sahel, the magnitude of rainfall anomalies is comparable to that obtained by other authors using SST anomalies confined to the proximity of the Atlantic Ocean. The mechanism connecting the Pacific/Indian SST anomalies with West African rainfall has a strong seasonal cycle. In spring (May and June), anomalous subsidence develops over both the Maritime Continent and the equatorial Atlantic in response to the enhanced equatorial heating. Precipitation increases over continental West Africa in association with stronger zonal convergence of moisture. In addition, precipitation decreases over the Gulf of Guinea. During the monsoon peak (July and August), the SST anomalies move westward over the equatorial Pacific and the two regions where subsidence occurred earlier in the seasons merge over West Africa. The monsoon weakens and rainfall decreases over the Sahel, especially in August.Peer reviewe

Search for heavy resonances decaying to two Higgs bosons in final states containing four b quarks

A search is presented for narrow heavy resonances X decaying into pairs of Higgs bosons (H) in proton-proton collisions collected by the CMS experiment at the LHC at root s = 8 TeV. The data correspond to an integrated luminosity of 19.7 fb(-1). The search considers HH resonances with masses between 1 and 3 TeV, having final states of two b quark pairs. Each Higgs boson is produced with large momentum, and the hadronization products of the pair of b quarks can usually be reconstructed as single large jets. The background from multijet and t (t) over bar events is significantly reduced by applying requirements related to the flavor of the jet, its mass, and its substructure. The signal would be identified as a peak on top of the dijet invariant mass spectrum of the remaining background events. No evidence is observed for such a signal. Upper limits obtained at 95 confidence level for the product of the production cross section and branching fraction sigma(gg -> X) B(X -> HH -> b (b) over barb (b) over bar) range from 10 to 1.5 fb for the mass of X from 1.15 to 2.0 TeV, significantly extending previous searches. For a warped extra dimension theory with amass scale Lambda(R) = 1 TeV, the data exclude radion scalar masses between 1.15 and 1.55 TeV

Untersuchung der Vertraulichkeit nach Obfuskierung durch Fountain Codes

Fountain Codes beschreiben eine Kodierungsform, in der die in Pakete unterteilten Daten nach einem bestimmten Schema miteinander verknüpft werden. Außerdem bieten sie gewisse Parameter, um Daten redundant über ein Netzwerk zu verschicken. Hierbei kann auf einen Rückkanal verzichtet werden. In dieser Arbeit wird untersucht, ob sich die Eigenschaften der Fountain-Kodierung nutzen lassen, um mit möglichst wenig zusätzlichen kryptographischen Verfahren Vertraulichkeit implizit zu gewährleisten. Unter diesem Aspekt werden zwei verschiedene Datentypen und ihre Merkmale sowie die Auswirkungen durch die Wahl der Parameter des Kodierungsalgorithmus genauer betrachtet. Ziel ist es, einem potentiellen Angreifer möglichst wenig Ansatzpunkte für eine er- folgreiche statistische Analyse zu bieten. Es werden verschiedene Konfigurationen in einer Testumgebung, welche ein spezielles Angreifermodell simuliert, auf ihre Praxistauglichkeit überprüft.Fountain codes discribe a coding form, in which the data is redundantly linked together into coded packages. They also define a set of parameters for sending these packages through a broadcast channel. This thesis is directed at analysing the obfuscating effect of the fountain coding process as well as pinpointing the extend of the possible resulting implicit privacy. For the analysis two different file formats are checked for characteristic structures and the resulting impact on the obfuscation of structural information enclosed in the data. The parameters of the fountain codes algorithm are varied to analyse their influence on the resulting implicit privacy. The experiments show whether it is more rewarding for a potential attacker to brute-forceattack the system than using a statistical analysis to uncover some structural information. Different configurations of the test environment are used in order to test the practical benefit of the fountain coding for implicit privacy

On Secure Routing in Low-Power and Lossy Networks: The Case of RPL

Diese Masterarbeit beschäftigt sich mit der Sicherheit des IPv6-basierten Routing Protokoll für „low-power and lossy networks“ RPL. Die durchgeführte Sicherheitsanalyse zeigt, dass ein Angreifer ohne Zugang zu den kryptographischen Schlüsseln weitestgehend abgewehrt wird. Es werden Topologie-Attacken aufgezeigt, welche erst durch den Besitz eben dieser Schlüssel möglich werden und eine ernste Bedrohung für die Sicherheit von RPL darstellen. Im Zuge dessen werden zwei Verfahren zur AuthentiVzierung der Topologie vorgestellt: VeRA und TRAIL. VeRA nutzt Hash-Ketten, um die Topologie zu sichern. TRAIL hingegen setzt auf das Hin- und Zurücksenden einer Nachricht, die Knoten für Knoten die Topologie veriVziert. Mit Hilfe der konkreten Umsetzung von TRAIL werden erste Studien zur Zeitverzögerung, die durch dieses VeriVzierungsverfahren entsteht, durchgeführt.This master-thesis engages in the security aspect of the newly introduced IPv6-based routing protocol for low-power and lossy networks RPL. In an analysis of the security of RPL, it is shown that RPL protects against most attacks launched by an adversary that does not have access to the security keys. The major threat lies within an attacker who has compromised these keys and who is consequently able to launch topology attacks. Two topology authentication schemes are presented and evaluated which deal with the prevention of such attacks: VeRA and TRAIL. The VeRA approach employs hash chains for veriVcation of the topology of RPL. TRAIL relies on the transmission of a round-trip message that veriVes the topology hop-by-hop. It is shown that these schemes can detect and isolate an insider attacker. A practical evaluation of TRAIL gives a Vrst impression of the delays that result from the veriVcation procedure

TRAIL: Topology Authentication in RPL

The IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) was recently introduced as the new routing standard for the Internet of Things. Although RPL defines basic security modes, it remains vulnerable to topological attacks which facilitate blackholing, interception, and resource exhaustion. We are concerned with analyzing the corresponding threats and protecting future RPL deployments from such attacks. Our contributions are twofold. First, we analyze the state of the art, in particular the protective scheme VeRA and present two new rank order attacks as well as extensions to mitigate them. Second, we derive and evaluate TRAIL, a generic scheme for topology authentication in RPL. TRAIL solely relies on the basic assumptions of RPL that (1) the root node serves as a trust anchor and (2) each node interconnects to the root as part of a hierarchy. Using proper reachability tests, TRAIL scalably and reliably identifies any topological attacker without strong cryptographic efforts.Unknow