Search

Lag consensus is an essential dynamic behavior in nature and practical systems, which means that the trajectory of followers lags behind the leader owing to a track time-delay. In this paper, the lag consensus problem under event-triggered control is investigated for leader-following multi-agent systems with nonlinear dynamics. A novel static event-triggered control strategy based on combined measurement is presented to avoid continuous information interaction between agents by introducing a track time-delay. It should be emphasized that this control protocol is fully distributed, that is, the global information in the network is not involved. In addition, for each agent, the information transmission and the updates of control protocol only arise at its own triggering instants. Based on stability theory, a sufficient condition is derived for leader-following multi-agent systems with nonlinear dynamics to achieve lag consensus. Moreover, it is exhibited that Zeno behavior is excluded by proving the existence of a positive lower bound for the triggering interval. Finally, the correctness of theoretical results is verified via numerical simulations. [ABSTRACT FROM AUTHOR]

Microwave fracturing and assisted mechanical breakage of rocks has been demonstrated to be efficient and cost-effective, holding great potential in rock excavation. However, the size effect on the fracturing process using open-ended microwave antennas has not been well studied or understood. To address this issue, a dielectric-loaded converging antenna is used to heat and fracture diorite specimens of different dimensions. The study investigates the effect of specimen plane size and thickness, as well as microwave energy, on the crack characteristics. The results show that as specimen plane size increases, fracturing becomes more localized with shorter and narrower cracks. Conversely, specimen thickness is negatively correlated with crack characteristics on the microwave-treated surface. The study also defines and examines the representative elementary volume (REV) of microwave fracturing using the antenna. Regression models are developed and validated to predict crack characteristics such as number, density, total length, and maximum width. The paper concludes by discussing the arrangement of microwave radiations on rock masses with different joint spacings using the antenna. Highlights: The effect of specimen plane size and thickness, as well as microwave energy, on the crack characteristics is comprehensively studied. The representative elementary volume (REV) of microwave fracturing using the DLCWA is defined and studied. Regression models are developed to predict crack characteristics such as number, density, total length, and maximum width. The arrangement of microwave radiation points of rock masses with different joint spacings using the DLCWA is proposed. [ABSTRACT FROM AUTHOR]

Mechanical excavation in hard or very hard rocks is still challenging in rock engineering. One plausible solution is to reduce rock strength prior to mechanical excavation to increase excavation and cost-efficiency. The present study utilizes a 6 kW microwave to irradiate rock specimens and evaluates the variation in rock strength and indentation hardness. Since the contact between the drill bits of roadheaders and the rock surface is a dynamic impact process, dynamic tests are conducted and compared with the quasi-static results. The experimental results demonstrate that short microwave irradiation (30 s) can produce substantial damage to the rock. The reduction of uniaxial compressive strength, Brazilian tensile strength, and indentation hardness under quasi-static loading can be about 39%, 43%, and 44%, respectively, and 33%, 26%, and 50%, respectively, under dynamic loading. In addition, it is found that the tensile strength is the most sensitive to microwave, while the crack density is the least sensitive. More importantly, this reduction is not linear and not monotonic to the irradiation time. The fast reduction of rock strength and indentation hardness after microwave irradiation implies the reduction in the drill-bit wear and increase in the excavation rate, and vigorously demonstrates the great potential of microwave-assisted mechanical excavation of hard or very hard rocks. Highlights: The dynamic indentation test is used to simulate the impact between drill bits and rock surfaces. Short microwave irradiation (30 s) can largely reduce the diorite strength and indentation hardness. The reduction is not linear and not monotonic to the irradiation time, regardless of loading rates. Different physical properties have different sensitivities to the microwave. Experimental results demonstrate the great potential of the microwave technique in hard rock excavation. [ABSTRACT FROM AUTHOR]

Microwave fracturing of hard rocks holds great promise in the civil, mining and tunnelling industries. The role of heating and cooling in the fracturing of rocks and when and where cracks initiate from and propagate to remain unclear and need to be addressed for future field applications of the technology. This study treated an alkali feldspar granite using a 6 kW industrial microwave source and a customised open-ended dielectric-loaded converging waveguide antenna. The real-time acoustic emission (AE) characteristics in the microwave heating and natural cooling phases were recorded and investigated. The surface temperature and P-wave velocity reduction of the specimens were also measured to quantify the thermal damage. The fracturing of granite is found to be tensile failure and is heating-dominated. Although a considerable amount of AE hits and events was detected in the cooling phase, they were of low energy, and therefore, the role of cooling in rock fracturing by open-ended microwave can be neglected. Fractures initiated from the exterior of the antenna and propagated towards the edges and the interior of the specimens. The cracks obtained from the AE localisation were in good agreement with those observed. With the increase of power level, the time for crack initiation was shortened, confirming the high-power effect. Highlights: Acoustic emission activities were measured in the microwave heating and cooling phases on granite blocks. Microwave fracturing of the granite is found to be heating-dominated. The microwave-induced rock fracturing is primarily tensile failure. The test results confirm the high-power effect in microwave fracturing of rocks. [ABSTRACT FROM AUTHOR]

Microwave fracturing has a great potential in assisting the breakage of hard rocks using impact hammers by inducing artificial cracks and downgrading the rock mass quality. In this article, the techno-economy of microwave-assisted impact hammer breakage of hard rocks was investigated. Microwave heating tests of 50-cm cubic biotite diorite blocks were carried out, followed by temperature measurement, ultrasonic velocity tests, Schmidt hammer rebound tests and rock breakage tests. The fracturing characteristics, the interaction between the radiation locations and the rock breaking by impact hammer were comprehensively investigated. The results show that the microwave system is efficient in fracturing the diorite. Cracks generated by the subsequent radiation tend to develop toward the centre of, or the cracks generated by, the previous radiation. Cracks produced by the previous radiations can be widened and extended by a following radiation. The maximum length and width of crack increase with the increase of the microwave power and heating time. Rock breakage tests demonstrate that microwave treatment greatly weakens the specimens and improves the efficiency of rock breaking by impact hammer. It is technologically feasible and economically viable to conduct microwave-assisted rock breakage by impact hammers. [ABSTRACT FROM AUTHOR]

This work developed a composite (Pe-FeLs) which loaded ferric lignin on polyethylene film (PE film) by chemical modification and physico-chemically characterized by Microscope, FESEM with elemental mapping analysis, and XRD. Microscope pictures showed that chemical modification did not destroy the appearance of PE film. The FESEM images of Pe-FeLs showed the well-distributed clusters could be clearly seen and most of the particles were spherical morphology. Elemental mapping of individual element on Pe-FeLs clearly indicated the existing of iron. The XRD pattern showed the amorphous hydroxides of iron on Pe-FeLs. In arsenic solution, the total arsenic adsorption capacity of Pe-FeLs was much higher than that of ferric lignin and PE, which showed Pe-FeLs had the ability to adsorb arsenic. For making Pe-FeLs work well in the soil, a Pe-FeLs system was set up with plastic grid plate, PE film with holes, Pe-FeLs, PE film, and plastic grid plate from the upper to bottom in order. With applying Pe-FeLs system under the soil, arsenic was significantly reduced by 25.5 ~ 53.4% in heavily, moderately, and lower arsenic-polluted soils, the biomass of the romaine lettuce increased and arsenic accumulation in the romaine lettuce decreased. [ABSTRACT FROM AUTHOR]

Microwave heating is a promising technique in assisting the breakage of hard and abrasive rocks. It features rapid heating and selective heating, enabling generation of large enough thermal stresses to induce damage in rocks. This paper investigated the effect of microwave treatment on the heating rate, spatial temperature distribution, ultrasonic wave velocity, elastic modulus and load bearing capacity of three igneous rocks (i.e., gabbro, monzonite and granite). The crack pattern and crack density were also studied using petrographic thin-section observations. Experimental results indicate that the single-mode microwave system can effectively and efficiently weaken the three rocks by generating cracks or melting/shattering the specimens. The heating rates and thermal gradients increase as either exposure time or power level increases. When heated at 2 kW for 120 s, the P-wave velocities of gabbro and monzonite can be reduced to 44% and 51%, respectively, S-wave velocities reduced to 34% and 62%, Young's modulus reduced to 13% and 27%, load bearing capacity reduced to 34% and 43%. In contrast, granite specimens were more prone to violent failures at high power levels. Petrographic observations imply that the dominant crack types in gabbro, monzonite and granite are intergranular & transgranular cracks, intergranular cracks, and transgranular cracks, respectively. [ABSTRACT FROM AUTHOR]

Studying the mechanical properties of rock mass plays a critical role in reducing the frequency of accidents such as large deformation and rock bursts that often occur in tunnels. In this study, a series of phyllites with different bedding structures and mineral compositions were drilled from different tunnels firstly, then the effects of different bedding angles and mineral compositions on the mechanical properties and failure modes of phyllites under unloading confining pressure conditions were studied. The results show that the deformation characteristics of phyllite have complex relations with confining pressure, bedding angle and mineral composition, and the influence of other parameters cannot be ignored to quantitatively analyze the influence of a certain parameter. The strength of phyllite shows an increases trend as the increase of confining pressure, while the strength shows a trend of first decreases and then increases as the increase of bedding angle. Under the same confining pressure and bedding angle, the strength of phyllite with more quartz is generally the largest, followed by phyllite with more chlorite. With the constant release of confining pressure (unloading), the elastic modulus of phyllite decreases and the Poisson's ratio increases, and the rate of decrease and increase varies with the tunnel bedding angle and mineral composition. The bedding angle, mineral composition and confining pressure have great influence on the unloading failure mode of phyllite, but the influence degree is different. The bedding angle has the greatest influence on the failure mode of phyllite, followed by the mineral composition, and finally the mechanical environment. [ABSTRACT FROM AUTHOR]

This study proposes a probabilistic approach based on blind data theory and a k-means clustering algorithm to analyze the wedge stability problem considering multiple failure modes. The method evaluates the stability of the wedge by constructing a blind data model that can comprehensively consider the various uncertainties of the wedge parameters. The construction of the blind data evaluation model of wedge stability is described, and the blind evaluation model used to determine the wedge stability with wedge failure dominated by a prone-sliding face and double-face failure is given. The model is applied to analyze the stability of a classical double-face wedge. The results are compared with the probability of failure evaluated by a Monte-Carlo simulation, as well as the results obtained from deterministic analysis, including the mean safety factor and SWEDGE numerical analysis methods. The probability distribution for the safety factor of the wedge determined by this method is fairly consistent with those from the Monte-Carlo simulation method, verifying the reliability and efficiency of the new method. Finally, the method is applied to the stability evaluation of the wedge in Huludao city, Liaoning Province, China. The probability of safety factors less than 1 is 89.8%, and the probability that the safety factor is less than 1.2 is 100%, which is consistent with the actual situation. This result demonstrates that the blind data model for evaluating wedge stability exhibits good generalization performance. [ABSTRACT FROM AUTHOR]

In this paper, a new concept of cluster-delay consensus is defined, which means that all agents in the same cluster reach identical consensus and that any two agents in the different clusters reach delay consensus simultaneously. In fact, cluster-delay consensus is a kind of dynamics between identical consensus and cluster consensus. And then, the problem of leader-following cluster-delay consensus in a nonlinear multi-agent system is investigated. By using graph theory, Lyapunov stability theory and matrix theory, a control protocol for cluster-delay consensus is given, which is based on intrinsic dynamics of each agent and the topology of multi-agent system. Finally, some numerical simulations are also given to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

Competitive coexistence of different microorganism species is a fundamental ecological process in the evolution and maintenance of biodiversity. This work studied the interactions happened in the competitive coexistence process of actinomycete Streptomyces sp. and Escherichia coli from morphological and secondary metabolites perspective. We found three important interactions occurred in their successful coexistence process: medium pH was elevated, indole alkaloids with dual inhibiting effects were produced, and culture environment was spatially structured. For the weed-like superior competitor E. coli, its massive growth was suppressed by the elevated pH and the newly produced novel bisindole alkaloid hepchrome. For the inferior Streptomyces sp., its mycelium floated to the medium surface for further colonization, and the growth in liquid medium was inhibited by its self-produced alkaloids such as halichrome A, 1,1,1-Tris (3-indolyl) methane, vibrindole A, and hepchrome. The coexistence of E. coli and Streptomyces sp. was thereby achieved through reduction of spatial and energy resource overlapping and suppression of competition. [ABSTRACT FROM AUTHOR]

The long-lived latently infected cells persist in spite of prolonged highly active anti-retroviral therapy and present a major barrier to a cure of human immunodeficiency virus type 1 (HIV-1) infection. Elimination of this reservoir requires reactivation of the latent virus. None of the current agents can safely and effectively reactivate latent HIV-1 reservoirs. Dilazep, a nucleoside transport inhibitor, is used to treat ischemic dysfunction. However, little is known about the effect of dilazep in inducing HIV expression in latently infected cells. Using the Jurkat T cell model of HIV-1 latency, we found that dilazep effectively reactivates latent HIV-1 gene expression in a dose manner. We observed that dilazep synergistically reactivated latent HIV-1 transcription with valproic acid. We also found that dilazep activates viral latency without inducing cell surface activation markers CD25 and CD69 activation. In summary, dilazep, alone or in combination with VPA, could be useful in future eradication strategies. [ABSTRACT FROM AUTHOR]

In this paper, effect of the coupling matrix with a weight parameter on synchronization pattern in a globally coupled network is investigated. On the basis of matrix theory, the threshold values of the coupling strength and the weight parameter for cluster synchronization have been obtained by utilizing the attractiveness criteria of the invariant synchronization manifold. It shows that cluster synchronization bifurcation comes forth, which concept is first put forward. That is to say, via changing the weight parameter and the coupling strength, the purpose of controlling the number of clusters is achieved, which provides a new idea for control the number of clusters in a network. Numerical simulations are given to demonstrate the theoretical results. In addition, the theoretical results and the numerical simulations also show that full synchronization may not be realized even if the network is globally coupled when there are some negative couplings. [ABSTRACT FROM AUTHOR]

In this paper, the dynamical behavior of a linear Hamiltonian system under two kinds of impulsive control is discussed by means of both theoretical and numerical ways. The existence and stability of the periodic solution are investigated. Moreover, the conditions of existence for a Neimark-Sacker bifurcation are derived by using a discrete map. Numerical results for phase portraits, periodic solutions, and bifurcation diagrams are in good agreement with the theoretical analysis. [ABSTRACT FROM AUTHOR]

Under the assumption that the incidence rate of the infection and the removal rate of the infective by cytotoxic T lymphocytes are nonlinear, we study the global dynamics of a HIV infection model with the response of the immune system using characteristic equation, the Fluctuation lemma, and the direct Lyapunov method. The existence of a threshold parameter, i.e., the basic reproduction number or basic reproductive ratio is established and the global stability of the equilibria is discussed. [ABSTRACT FROM AUTHOR]

Sulfonamide is present in many important drugs, due to its unique chemical and biological properties. In contrast, naturally occurring sulfonamides are rare, and their biosynthetic knowledge are scarce. Here we identify the biosynthetic gene cluster of sulfonamide antibiotics, altemicidin, SB-203207, and SB-203208, from Streptomyces sp. NCIMB40513. The heterologous gene expression and biochemical analyses reveal unique aminoacyl transfer reactions, including the tRNA synthetase-like enzyme SbzA-catalyzed L-isoleucine transfer and the GNAT enzyme SbzC-catalyzed β-methylphenylalanine transfer. Furthermore, we elucidate the biogenesis of 2-sulfamoylacetic acid from L-cysteine, by the collaboration of the cupin dioxygenase SbzM and the aldehyde dehydrogenase SbzJ. Remarkably, SbzM catalyzes the two-step oxidation and decarboxylation of L-cysteine, and the subsequent intramolecular amino group rearrangement leads to N-S bond formation. This detailed analysis of the aminoacyl sulfonamide antibiotics biosynthetic machineries paves the way toward investigations of sulfonamide biosynthesis and its engineering. Sulfonamide is in many important drugs yet is rare in nature and little is known about the synthesis of sulfonamide containing antibiotics. Here, the authors report on a detailed analysis of the biosynthesis machineries of the aminoacyl sulfonamide antibiotics. [ABSTRACT FROM AUTHOR]