CALD : surviving various application-layer DDoS attacks that mimic flash crowd

Distributed denial of service (DDoS) attack is a continuous critical threat to the Internet. Derived from the low layers, new application-layer-based DDoS attacks utilizing legitimate HTTP requests to overwhelm victim resources are more undetectable. The case may be more serious when suchattacks mimic or occur during the flash crowd event of a popular Website. In this paper, we present the design and implementation of CALD, an architectural extension to protect Web servers against various DDoS attacks that masquerade as flash crowds. CALD provides real-time detection using mess tests but is different from other systems that use resembling methods. First, CALD uses a front-end sensor to monitor thetraffic that may contain various DDoS attacks or flash crowds. Intense pulse in the traffic means possible existence of anomalies because this is the basic property of DDoS attacks and flash crowds. Once abnormal traffic is identified, the sensor sends ATTENTION signal to activate the attack detection module. Second, CALD dynamically records the average frequency of each source IP and check the total mess extent. Theoretically, the mess extent of DDoS attacks is larger than the one of flash crowds. Thus, with some parameters from the attack detection module, the filter is capable of letting the legitimate requests through but the attack traffic stopped. Third, CALD may divide the security modules away from the Web servers. As a result, it keeps maximum performance on the kernel web services, regardless of the harassment from DDoS. In the experiments, the records from www.sina.com and www.taobao.com have proved the value of CALD

Web3D learning framework for 3D shape retrieval based on hybrid convolutional neural networks

With the rapid development of Web3D technologies, sketch-based model retrieval has become an increasingly important challenge, while the application of Virtual Reality and 3D technologies has made shape retrieval of furniture over a web browser feasible. In this paper, we propose a learning framework for shape retrieval based on two Siamese VGG-16 Convolutional Neural Networks (CNNs), and a CNN-based hybrid learning algorithm to select the best view for a shape. In this algorithm, the AlexNet and VGG-16 CNN architectures are used to perform classification tasks and to extract features, respectively. In addition, a feature fusion method is used to measure the similarity relation of the output features from the two Siamese networks. The proposed framework can provide new alternatives for furniture retrieval in the Web3D environment. The primary innovation is in the employment of deep learning methods to solve the challenge of obtaining the best view of 3D furniture, and to address cross-domain feature learning problems. We conduct an experiment to verify the feasibility of the framework and the results show our approach to be superior in comparison to many mainstream state-of-the-art approaches

Novel Brønsted-acidic ionic liquids based on benzothiazolium cations as catalysts for esterification reactions

Three novel Brønsted-acidic ionic liquids based on benzothiazolium cations were prepared, which served as catalysts for the synthesis of benzoic esters. All three gave good yields of the target esters in esterification reactions. Moreover, they combine the advantages of both homogeneous and heterogeneous solid catalysts in esterification reactions, which enabled them to serve as homogeneous catalysts to catalyze the reactions and be conveniently recovered by simple filtration after the reactions. They could be reused several times without noticeable decrease in efficiency

VIE-FG-FFT for Analyzing EM Scattering from Inhomogeneous Nonmagnetic Dielectric Objects

A new realization of the volume integral equation (VIE) in combination with the fast Fourier transform (FFT) is established by fitting Green’s function (FG) onto the nodes of a uniform Cartesian grid for analyzing EM scattering from inhomogeneous nonmagnetic dielectric objects. The accuracy of the proposed method is the same as that of the P-FFT and higher than that of the AIM and the IE-FFT especially when increasing the grid spacing size. Besides, the preprocessing time of the proposed method is obviously less than that of the P-FFT for inhomogeneous nonmagnetic dielectric objects. Numerical examples are provided to demonstrate the accuracy and efficiency of the proposed method

Strong decays of low-lying DD-wave Ξb/Ξb′\Xi_b/\Xi_b' baryons with QPC model

For further decoding the inner structure of the two excited $\Xi_b$ states observed by LHCb, we perform a systematical study of the strong decays of the low-lying $1D$-wave $\Xi_b$ and $\Xi_b'$ excitations using the quark pair creation model within the $j-j$ coupling scheme. Combining with the measured masses and decay properties of $\Xi_{b}(6327)^{0}$ and $\Xi_{b}(6327)^{0}$, the two excited states can be explained as $1D$ $\lambda$-mode $\Xi_b$ states $\Xi_{b}|J^{P}=\frac{3}{2}^{+},2\rangle_{\lambda\lambda}$ and $\Xi_{b}|J^{P}=\frac{5}{2}^{+},2\rangle_{\lambda\lambda}$, respectively. If such a view were correct, $\Xi_b'\pi$ and $\Xi_b'^*\pi$ could be another interesting channels for experimental exploring of the $\Xi_{b}(6327)^{0}$ and $\Xi_{b}(6327)^{0}$, respectively. Those calculations are good consistent with the results within the chiral quark model. In addition, for the other missing $1D$-wave $\Xi_b$ and $\Xi_b'$ excitations, our predictions indicate that:(i) the two $\rho$-mode $1D$ $\Xi_b$ states are likely to be moderate states with a width of $\Gamma\sim50$ MeV. The $J^P=3/2^+$ state dominantly decays into $\Sigma_bK$ and $\Xi_b'\pi$, while the $J^P=5/2^+$ state decays primarily through $\Sigma_b^*K$ and $\Xi_b'^*\pi$. (ii) The $\lambda$-mode $1D$ $\Xi_b'$ states may be moderate states with a widths of about several to dozens of MeV. Most of the $\lambda$-mode $1D$ $\Xi_b'$ states mainly decay into the $1P$-wave bottomed baryon via the pionic decay processes. Meanwhile, several $\lambda$-mode $1D$ $\Xi_b'$ states have significant decay rates into $\Lambda B$. (iii) While, the $\rho$-mode $1D$ $\Xi_b'$ states are predicted to be very broad states with a width of about several hundreds MeV. It will be a great challenge to explore the $\rho$-mode $1D$ $\Xi_b'$ states in experiments for their broad widths.Comment: 11 pages, 5 figure

Strong decays of the low-lying 1P1P- and 1D1D-wave Σc\Sigma_c baryons

In this work, we systematically study the OZI-allowed two-body strong decay properties of $1P$- and $1D$-wave $\Sigma_c$ baryons within the $j$-$j$ coupling scheme in the framework of the quark pair creation model. For a comparison, we also give the predictions of the chiral quark model. Some model dependencies can be found in the predictions of two models. The calculations indicate that: (i) The $1P$-wave $\lambda$-mode $\Sigma_c$ states most likely to be relatively narrow states with a width of $\Gamma<80$ MeV. Their main decay channels are $\Lambda_c\pi$, or $\Sigma_c\pi$, or $\Sigma_c^*\pi$. The $1P$-wave $\rho$-mode states most might be broad states with a width of $\Gamma\sim 100-200$ MeV. They dominantly decay into $\Sigma_c\pi$ and $\Sigma_c^*\pi$ channels. Some evidences of these $1P$-wave states are most likely to be observed in the $\Lambda_c\pi$ and $\Lambda_c\pi\pi$ invariant mass spectra around the energy range of $2.75-2.95$ GeV. (ii) The $1D$-wave $\lambda$-mode $\Sigma_c$ excitations may be moderate states with a width of about dozens of MeV. The $1D$-wave $\lambda$-mode states mainly decay into the $1P$-wave charmed baryon via the pionic decay processes. Meanwhile, several $1D$-wave $\lambda$-mode states have significant decay rates into $DN$ or $D^*N$. Hence, the $DN$ and $D^*N$ are likely to be interesting channels for experimental exploration. (iii) Furthermore, the two $1D$-wave $\rho$-mode excitations $\Sigma_c|J^P=5/2^+,3\rangle_{\rho\rho}$ and $|J^P=7/2^+,3\rangle_{\rho\rho}$ are most likely to be fairly narrow state with a width of dozens of MeV, and they mainly decay into $\Lambda_c\pi$. Some evidences of them might be observed in the $\Lambda_c\pi$ invariant mass spectra around the energy range of $3.1-3.2$ GeV.Comment: 12 pages,5 figures, 4 tables. arXiv admin note: text overlap with arXiv:2208.1011

Patterns and driving forces of dimensionality-dependent charge density waves in 2H-type transition metal dichalcogenides

Two-dimensional (2D) materials have become a fertile playground for the exploration and manipulation of novel collective electronic states. Recent experiments have unveiled a variety of robust 2D orders in highly-crystalline materials ranging from magnetism to ferroelectricity and from superconductivity to charge density wave (CDW) instability. The latter, in particular, appears in diverse patterns even within the same family of materials with isoelectronic species. Furthermore, how they evolve with dimensionality has so far remained elusive. Here we propose a general framework that provides a unfied picture of CDW ordering in the 2H polytype of four isoelectronic transition metal dichalcogenides 2H-MX$_2$ (M=Nb, Ta and X=S, Se). We first show experimentally that whilst NbSe$_2$ exhibits a strongly enhanced CDW order in the 2D limit, the opposite trend exists for TaSe$_2$ and TaS$_2$, with CDW being entirely absent in NbS$_2$ from its bulk to the monolayer. Such distinct behaviours are then demonstrated to be the result of a subtle, yet profound, competition between three factors: ionic charge transfer, electron-phonon coupling, and the spreading extension of the electronic wave functions. Despite its simplicity, our approach can, in essence, be applied to other quasi-2D materials to account for their CDW response at different thicknesses, thereby shedding new light on this intriguing quantum phenomenon and its underlying mechanisms