Experimental and laboratory research into residual physical and mechanical characteristics of historical masonry structures (GAČR 2008; Witzany 2008), in particular the determination of residual strength and modulus of elasticity in compression, included research oriented towards the effect of moisture and porosity on the respective characteristics of masonry units – bricks, sandstone and arenaceous marl. Partial results published in (Witzany et al. 2008) and in this paper testify to the need for further research into the effects of porosity, moisture and chemism on the development of characteristics of building materials applied on historical structures.
The Domain Name System (DNS) belongs to crucial services in a computer network. Because of its importance, DNS is usually allowed in security policies. That opens a way to break policies and to transfer data from/to restricted area due to misusage of a DNS infrastructure. This paper is focused on a detection of communication tunnels and other anomalies in a DNS traffic. The proposed detection module is designed to process huge volume of data and to detect anomalies at near real-time. It is based on combination of statistical analysis of several observed features including application layer information. Our aim is a stream-wise processing of huge volume of DNS data from backbone networks. To achieve these objectives with minimal resource consumption, the detection module uses efficient extended data structures. The performance evaluation has shown that the detector is able to process approximately 511 thousand DNS flow records per second. In addition, according to experiments, a tunnel that lasts over 30 seconds can be detected in a minute. During the on-line testing on a real traffic from production network, the module signalized on average over 60 confirmed alerts including DNS tunnels per day.
The most frequent damage and collapse of some of the spans of Charles Bridge during floods occurred namely in its central part which was exposed to an intense flow of backwater and erosion of the bridge pier footing bottom, which the originally relatively shallow foundations of the piers on boxes were not able to resist for a longer time (the floods of 1432, 1496, 1784, 1890). The stone vault bridge structure was damaged due to scouring of the bridge piers foundations, their successive tilting and settlement accompanied by degradation, and finally collapse of the adjoining bridge vaults. The foundation of piers on caissons and execution of caisson rings in 1892 and 1902 to 1904 in this part of the bridge, together with measures avoiding the piling up of objects in front of the bridge, enabled the bridge to withstand the impact of more than a hundred‐year flood during the events of August 2002. The numerical analysis proved an extreme sensitivity of the stone vault bridge structure to the effects of changes in the footing bottom shape. Due to the changes in the footing bottom (angular rotation, subsidence, shifting), normal and shear stresses arise in the stone vault bridge structure, and exceed the load‐bearing capacity of the masonry causing its disintegration. The fundamental measure to prevent the bridge vaults from failure due to the changes in the footing bottom shape is to secure reliably the bridge piers foundations. The increased rigidity of the stone bridge structure achieved by the interaction with the additionally inserted reinforcing structure and by bracing the bridge body filler does not ensure the reliability and safety of the bridge structure from flood‐related failures.
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