Modeling and Analysis of Bifurcation in a Delayed Worm Propagation Model

A delayed worm propagation model with birth and death rates is formulated. The stability of the positive equilibrium is studied. Through theoretical analysis, a critical value τ0 of Hopf bifurcation is derived. The worm propagation system is locally asymptotically stable when time delay is less than τ0. However, Hopf bifurcation appears when time delay τ passes the threshold τ0, which means that the worm propagation system is unstable and out of control. Consequently, time delay should be adjusted to be less than τ0 to ensure the stability of the system stable and better prediction of the scale and speed of Internet worm spreading. Finally, numerical and simulation experiments are presented to simulate the system, which fully support our analysis

A Reputation-based Mechanism to Stimulate Cooperation in Wireless Sensor Networks

In wireless sensor networks, the sensor nodes need to collaborate with each other to transmit packets to the destination. However, some malicious nodes are not cooperative. The paper introduces a new reputation-based mechanism to stimulate nodes to forward packets for other nodes and enforce the security of the networks. All nodes are encouraged to maintain a good reputation so that their packets can be forwarded by other nodes, and a node will be isolated and punished if it acts maliciously. The impact of collisions and interference on nodes' reputation is reduced, and nodes can have chance to restore cooperation after being mistaken for the selfish ones. The low competitive nodes that do not have enough energy to help other nodes can also be treated well. While searching a route to the destination, the factors of reputation, remaining energy and the distance to the destination are taken into consideration. Simulation results show that our strategy can achieve relatively high throughput even when there are malicious nodes in the networks

Modeling and Bifurcation Research of a Worm Propagation Dynamical System with Time Delay

Both vaccination and quarantine strategy are adopted to control the Internet worm propagation. By considering the interaction infection between computers and external removable devices, a worm propagation dynamical system with time delay under quarantine strategy is constructed based on anomaly intrusion detection system (IDS). By regarding the time delay caused by time window of anomaly IDS as the bifurcation parameter, local asymptotic stability at the positive equilibrium and local Hopf bifurcation are discussed. Through theoretical analysis, a threshold τ0 is derived. When time delay is less than τ0, the worm propagation is stable and easy to predict; otherwise, Hopf bifurcation occurs so that the system is out of control and the containment strategy does not work effectively. Numerical analysis and discrete-time simulation experiments are given to illustrate the correctness of theoretical analysis

Identification of Heat-Tolerant Genes in Non-Reference Sequences in Rice by Integrating Pan-Genome, Transcriptomics, and QTLs.

The availability of large-scale genomic data resources makes it very convenient to mine and analyze genes that are related to important agricultural traits in rice. Pan-genomes have been constructed to provide insight into the genome diversity and functionality of different plants, which can be used in genome-assisted crop improvement. Thus, a pan-genome comprising all genetic elements is crucial for comprehensive variation study among the heat-resistant and -susceptible rice varieties. In this study, a rice pan-genome was firstly constructed by using 45 heat-tolerant and 15 heat-sensitive rice varieties. A total of 38,998 pan-genome genes were identified, including 37,859 genes in the reference and 1141 in the non-reference contigs. Genomic variation analysis demonstrated that a total of 76,435 SNPs were detected and identified as the heat-tolerance-related SNPs, which were specifically present in the highly heat-resistant rice cultivars and located in the genic regions or within 2 kbp upstream and downstream of the genes. Meanwhile, 3214 upregulated and 2212 downregulated genes with heat stress tolerance-related SNPs were detected in one or multiple RNA-seq datasets of rice under heat stress, among which 24 were located in the non-reference contigs of the rice pan-genome. We then mapped the DEGs with heat stress tolerance-related SNPs to the heat stress-resistant QTL regions. A total of 1677 DEGs, including 990 upregulated and 687 downregulated genes, were mapped to the 46 heat stress-resistant QTL regions, in which 2 upregulated genes with heat stress tolerance-related SNPs were identified in the non-reference sequences. This pan-genome resource is an important step towards the effective and efficient genetic improvement of heat stress resistance in rice to help meet the rapidly growing needs for improved rice productivity under different environmental stresses. These findings provide further insight into the functional validation of a number of non-reference genes and, especially, the two genes identified in the heat stress-resistant QTLs in rice

Thermo-Economic Analysis of a Bottoming Kalina Cycle for Internal Combustion Engine Exhaust Heat Recovery

The use of a Kalina cycle (KC) with a superheater to recover waste heat from an internal combustion engine (ICE) is described in this paper. The thermodynamic and economic analyses are performed for KC. The results indicate that using KC with a superheater is a feasible method to recover waste heat from ICE. The maximum thermal efficiency of KC is 46.94% at 100% ICE percentage load. The improvement of thermal efficiency is greater than 10% at all ICE loads, and the maximum improvement of thermal efficiency is 21.6% at 100% ICE load. Both the net power output and thermal efficiency of the KC subsystem increase with ICE percentage load and ammonia mass fraction. A lower turbine inlet pressure leads to a higher net power output of KC and a greater improvement of thermal efficiency when the ammonia mass fraction of the mixture is greater than 0.34. In the paper, if the same KC, which uses the largest capital investment, is used at different ICE loads, the payback period decreases with ICE load and ammonia mass fraction. In addition, both longer annual operation times and lower interest rates lead to shorter payback periods. However, it is worth noting that the payback period will be longer than the ICE’s lifetime if the ICE load is low and the annual operation time is too short

Research on the dissipation of green tide and its influencing factors in the Yellow Sea based on Google Earth Engine

Since 2007, the outbreak of green tides has become the most serious ecological problem in the Yellow Sea. In this study, a new method was used to identify green tides in multi-source satellite data from 2007 to 2020, and the relationship between the conditions necessary for green tide dissipation and other environmental factors was discussed. We found a "wavy" trend of green tide scales over the 14-year dissipation period. The dissipation direction was influenced by sea surface wind (SSW) and sea surface circulation (SSC). Under the action of northeast moving SSW and SSC, green tides move away from the shore and drift northward; under the action of northwest or southwest moving SSW and SSC, they moved towards the shore and drift southward. The date of dissipation was influenced by sea surface temperature (SST) and precipitation, and high SST accelerated the process of green tide dissipation, while precipitation slowed it down

Analysis of relationships between land surface temperature and land use changes in the Yellow River Delta

This study analyzed land use and land cover changes and their impact on land surface temperature using Landsat 5 Thematic Mapper and Landsat 8 Operational Land Imager and Thermal Infrared Sensor imagery of the Yellow River Delta. Six Landsat images comprising two time series were used to calculate the land surface temperature and correlated vegetation indices. The Yellow River Delta area has expanded substantially because of the deposited sediment carried from upstream reaches of the river. Between 1986 and 2015, approximately 35% of the land use area of the Yellow River Delta has been transformed into salterns and aquaculture ponds. Overall, land use conversion has occurred primarily from poorly utilized land into highly utilized land. To analyze the variation of land surface temperature, a mono-window algorithm was applied to retrieve the regional land surface temperature. The results showed bilinear correlation between land surface temperature and the vegetation indices (i.e., Normalized Difference Vegetation Index, Adjusted-Normalized Vegetation Index, Soil-Adjusted Vegetation Index, and Modified Soil-Adjusted Vegetation Index). Generally, values of the vegetation indices greater than the inflection point mean the land surface temperature and the vegetation indices are correlated negatively, and vice versa. Land surface temperature in coastal areas is affected considerably by local seawater temperature and weather conditions

Challenges and Progress in Lead-Free Halide Double Perovskite Solar Cells

Lead-free halide double perovskites (HDPs) with a chemical formula of A(2)B(+)B(3+)X(6) are booming as attractive alternatives to solve the toxicity issue of lead-based halide perovskites (APbX(3)). HDPs show excellent stability, a wide range of possible combinations, and attractive optoelectronic features. Although a number of novel HDPs have been studied, the power conversion efficiency of the state-of-the-art double perovskite solar cell is still far inferior to that of the dominant Pb-based ones. Understanding the fundamental challenges is essential for further increasing device efficiency. In this review, HDPs with attractive electronic and optical properties are focused on, and current challenges in material properties and device fabrication that limit high-efficiency photovoltaics are analyzed. Finally, the promising approaches and views to overcome these bottlenecks are highlighted.Funding Agencies|Swedish Research Council [2018-04809]; Carl Tryggers Stiftelse; Olle Engkvist Byggmastare Stiftelse; STINT grant [CH2018-7655]; Jiangsu Key Laboratory for Carbon-Based Functional Materials &amp; Devices (Soochow University); aforsk [21-32]</p