On the effectiveness of flexible deterministic packet marking for DDoS defense

IP traceback is one of the defense mechanisms for Distributed Denial of Service (DDoS) attacks. However, most traceback schemes consume extensive resources such as CPU, memory, disk storage and bandwidth and require a large amount of IP packets to reconstruct sources, which makes them impractical and ineffective. In this paper, we present a new flexible IP traceback scheme called Flexible Deterministic Packet Marking (FDPM). The flexibilities of FDPM are in two ways, one is that it can adjust the length of marking field according to the network protocols deployed, thus it can work well even in an environment with different network protocols; the other is that it can adjust the marking rate according to the load of participating router, while it still can maintain the marking function. In order to verify the effectiveness of FDPM for DDoS defense in terms of marking efficiency, maximum forwarding rate, and number of packets for reconstruction, we tested FDPM by both simulation and Linux router implementation with an emphasis on the latter. The experiments demonstrate that the built-in overload prevention mechanism, flow-based marking, can isolate and mark the most possible DDoS attack packets, while keeping the load of the participating router in a reasonably low degree. The real hardware implementation confirms that this flexible capability is important when traceback mechanisms are used in a real DDoS defense scenario

For the aged: A novel PM2.5 concentration forecasting method based on spatial-temporal graph ordinary differential equation networks in home-based care parks

The immune ability of the elderly is not strong, and the functions of the body are in a stage of degeneration, the ability to clear PM2.5 is reduced, and the cardiopulmonary system is easily affected. Accurate prediction of PM2.5 can provide guidance for the travel of the elderly, thereby reducing the harm of PM2.5 to the elderly. In PM2.5 prediction, existing works usually used shallow graph neural network (GNN) and temporal extraction module to model spatial and temporal dependencies, respectively, and do not uniformly model temporal and spatial dependencies. In addition, shallow GNN cannot capture long-range spatial correlations. External characteristics such as air humidity are also not considered. We propose a spatial-temporal graph ordinary differential equation network (STGODE-M) to tackle these problems. We capture spatial-temporal dynamics through tensor-based ordinary differential equation, so we can build deeper networks and exploit spatial-temporal features simultaneously. In addition, in the construction of the adjacency matrix, we not only used the Euclidean distance between the stations, but also used the wind direction data. Besides, we propose an external feature fusion strategy that uses air humidity as an auxiliary feature for feature fusion, since air humidity is also an important factor affecting PM2.5 concentration. Finally, our model is evaluated on the home-based care parks atmospheric dataset, and the experimental results show that our STGODE-M can more fully capture the spatial-temporal characteristics of PM2.5, achieving superior performance compared to the baseline. Therefore, it can provide better guarantee for the healthy travel of the elderly

Activity and mechanism of vanadium sulfide for organic contaminants oxidation with peroxymonosulfate

Transition metal sulfides have been demonstrated to be effective for peroxymonosulfate (PMS) activation towards wastewater treatment. However, the activity of vanadium sulfide (VS4) and the role of the chemical state of V have not been revealed. Here, three types of VS4 with various morphologies and chemical states of V were synthesized by using methanol (M−VS4, nanosphere composed of nanosheets), ethanol (E-VS4, sea urchin like nanosphere) and ultrapure water (U-VS4, compact nanosphere) as hydrothermal solvent, respectively, and used as heterogeneous catalysts to activate PMS for the degradation of refractory organic pollutants. The effects of PMS concentration, temperature, pH, inorganic ions, and humic acid (HA) on the degradation efficiency of VS4/PMS system were investigated systematically. The results indicated that the highest specific surface area and lowest ratio of V5+ enable E-VS4/PMS system possessed the highest performance in degrading tetracycline hydrochloride (TCH), in which 100% TCH was removed after operating 10 min (0.805 min−1) under a relatively low concentration of PMS (1 mM) and catalyst (100 mg/L). It also revealed that the system exhibited a typical radical process in TCH degradation, which could be attributed to the redox cycles between V5+, V4+ and V3+ in the presence of PMS to generate various radicals. This radical process enabled the E-VS4/PMS system with a high activity in wide reaction conditions and high mineralization ratios in degrading various refractory organic pollutants within 10 min. In addition, the E-VS4/PMS system exhibited favorable reusability and stability with very less V and S ions leaching, and showed excellent performance in real water purification

Highly active and stable CuAlOx/WO3photoanode for simultaneous pollutant degradation, hydrogen and electricity generation

An unassisted solar water-energy nexus system (SWENS) based on an ultra-thin CuAlOx overlayer coated WO3 nanoplate array (CuAlOx/WO3) photoanode, a rear silicon solar cell and a Pt-black/Pt cathode was proposed to efficiently degrade refractory organic pollutants and simultaneously produce hydrogen and electricity. The formed p-n junction between p-type CuAlOx and n-type WO3 effectively facilitated the charge separation in the CuAlOx/WO3 photoanode. Moreover, the CuAlOx overlayer enhanced the capture of photogenerated holes and isolated WO3 from the solution, thereby improving the charge transfer and inhibiting the photocorrosion of WO3. Therefore, the optimized CuAlOx/WO3 photoanode showed a significantly enhanced and stable photocurrent density of ∼2.82 mA cm-2 at 1.0 V vs. Ag/AgCl, which was ∼4 times higher than that of the pristine WO3. Based on this outstanding photoelectrocatalytic performance, the assembled SWENS showed a degradation efficiency of nearly 100% for tetracycline, a hydrogen generation rate of ∼26.8 μmol·h-1·cm-2 and a power density of ∼593 μW cm-2 under simulated solar light illumination. Our SWENS also exhibited outstanding universality in degrading various refractory organic pollutants for green energy production