In this report, we fabricated a porous layer in amorphous SiC thin films by using constant-current anodic etching in an electrolyte of aqueous diluted hydrofluoric acid. The morphology of the porous amorphous SiC layer changed as the anodic current density changed: At low current density, the porous layer had a low pore density and consisted of small pores that branched downward. At moderate current density, the pore size and depth increased, and the pores grew perpendicular to the surface, creating a columnar pore structure. At high current density, the porous structure remained perpendicular, the pore size increased, and the pore depth decreased. We explained the changes in pore size and depth at high current density by the growth of a silicon oxide layer during etching at the tips of the pores.
This paper proposes an approach to assess and predict the seismic risk of existing concrete gravity dams (CGDs) considering the ageing effect. The combination of fragility function and cumulative absolute velocity (CAV) depending on two failure states has been used in the analysis. It represents the time-variant degradation of the concrete structure and the conditional change of structural vulnerability in the case of the seismic excitation. Therefore, the seismic risk assessment captures here the nonlinear dynamic behavior of a concrete gravity dam through the fragility analysis. Incremental dynamic analysis for the fragility curves is adopted to state the performance of the dam in terms of different intensity measures. To assess the capacity of the aged concrete gravity dam, this research introduces a way to estimate the CAVlimit of CGDs with varying time. For a case study, an existing concrete gravity dam in Korea has been taken into consideration to apply this approach. The numerical finite element model is validated by optimizing the recorded field data. The proposed approach and its findings will be helpful to CGDs operators to ensure whether a dam needs to stop after a specific time using the extracted mathematical model. Furthermore, as this mathematical model is the function of time, the operator can get an idea about dam conditions at any specific time and can take necessary steps.
Security administrators use network intrusion detection systems (NID systems) as a tool for detecting attacks and misuse, using passive monitoring techniques. However, there are sophisticated attacks which use ambiguities in protocol specifications to subvert detection. In these attacks, the destination endpoint reconstructs a malicious interpretation, whereas the passive NID system's protocol stack interprets the protocol as a benign exchange. There is a dire need for a new software element at the entry point of the network, which transparently modifies network traffic, so as to remove all possible ambiguities. This will ensure that all internal hosts and the NIDS interpret the traffic in a uniform way, hence removing all chances of an attack sneaking past the NIDS, unnoticed and unmonitored. In this paper, we will present the design and implementation of a normalizer whose job is to eliminate evasion and insertion attacks against an NIDS at the transport and network layers.
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