Low-Rate DoS Attack Flows Filtering Based on Frequency Spectral Analysis

In frequency domain,the power spectrum of Low-rate denial of service(LDoS) attacks is totally spread into the spectrum of normal traffic.It is a challenging task to detect and filter LDoS attack flows from the normal traffic.Based on the analysis of LDoS attack flows and legitimate TCP traffic in time and frequency domains,the periodicity of the TCP traffic and LDoS attack flows is explored to facilitate the research of network traffic processing.Hence,an approach of LDoS attack flow filtering based on frequency spectrum analysis is proposed.In this approach,the TCP traffic and LDoS attack flows are transformed from the time domain into the frequency domain.Then the round-trip time(RTT) is estimated by using frequency domain search method.Analysis of amplitude spectrum shows that TCP traffic energy is mainly concentrated on the points of n/RTT.Therefore,a comb filter using infinite impulse response(IIR) filter is designed to filter out the LDoS attack flows in frequency domain,while most legitimate TCP traffic energy at the points of n/RTT are pass through.Experimental results show that the maximum pass rate for legitimate TCP traffic reaches 92.55%,while the maximum filtration rate of LDoS attack flows reaches 81.36%.The proposed approach can effectively filter the LDoS attack flows while less impact on the legitimate TCP traffic.

Local density of states around two nonmagnetic impurities in cuprate superconductors

The local density of states （LDOS） around two nonmagnetic impurities which are located at different sites is studied within the two-dimensional t-J-U model. The order parameters are determined in a self-consistent way with the Gutzwiller projected mean-field approximation and the Bogoliubov-de Gennes theory. When the two impurities are located one or two sites away, we find the supercon- ductivity coherence peaks are more strongly suppressed and the zero-energy peak （ZEP） has split into two peaks. Whereas when the two impurities are located next to each other, the ZEP vanished, and LDOS does not change a lot compared with the case away from the impurities.

Local density of states in photonic crystal cavity

Local radiative density of optical states （LDOS） offers a tool to control the radiative rate of spontaneous emission from molecules, atoms, and quan- tum dots, which is proportional to LDOS. This paper presents that LDOS how to make the population of excited-state decay exponentially in time, and how these dynamics can be affected. By adopting the plane-wave expansion method, properties of an inverse-opal photonic crystal are studied with the help of photonic dispersion relations. Results in this paper show that the LDOS is radically modified in photonic crystal, and the rate of spontaneous emission can be described by the functions of position in the crystal and orientation of transition dipole moment.