Viral infection dynamics with immune chemokines and CTL mobility modulated by the infected cell density.

We study a viral infection model incorporating both cell-to-cell infection and immune chemokines. Based on experimental results in the literature, we make a standing assumption that the cytotoxic T lymphocytes (CTL) will move toward the location with more infected cells, while the diffusion rate of CTL is a decreasing function of the density of infected cells. We first establish the global existence and ultimate boundedness of the solution via a priori energy estimates. We then define the basic reproduction number of viral infection R 0 and prove (by the uniform persistence theory, Lyapunov function technique and LaSalle invariance principle) that the infection-free steady state E 0 is globally asymptotically stable if R 0 < 1 . When R 0 > 1 , then E 0 becomes unstable, and another basic reproduction number of CTL response R 1 becomes the dynamic threshold in the sense that if R 1 < 1 , then the CTL-inactivated steady state E 1 is globally asymptotically stable; and if R 1 > 1 , then the immune response is uniform persistent and, under an additional technical condition the CTL-activated steady state E 2 is globally asymptotically stable. To establish the global stability results, we need to prove point dissipativity, obtain uniform persistence, construct suitable Lyapunov functions, and apply the LaSalle invariance principle.

[Effects of Different Topdressing Nitrogen Rates on Soil Fungal Community Structure and Ecological Network in Wheat Field Under Crop Residue Retention].

Crop residue retention and fertilizer application are the main sources of soil nutrient input in fields. Crop residue retention combined with appropriate fertilizer application rates could provide necessary nutrients for crop production under the premise of environmentally friendly conditions. The aim of this study was to clarify the influence of different topdressing nitrogen rates on the soil fungal community in a wheat field under crop residue retention and to evaluate the rationality of nitrogen fertilizer management in winter wheat from the perspective of soil ecological function. On the basis of full straw retention and 150 kg·hm-2 basal nitrogen, treatments with five topdressing nitrogen rates (0, 37.5, 75, 112.5, and 150 kg·hm-2) were set up. The abundance, diversity, structure, and ecological network of soil fungal communities were analyzed using real-time fluorescence quantitative PCR and high-throughput sequencing, and the main soil physical and chemical factors driving the change in soil fungal communities were explored. The results showed that, compared with the no topdressing nitrogen and low topdressing nitrogen rate treatments, high topdressing nitrogen rate treatments increased soil total nitrogen and mineral nitrogen and decreased soil pH, total phosphorus, available phosphorus, and available potassium. Compared with the no topdressing nitrogen treatments, the 37.5-150 kg·hm-2 topdressing nitrogen treatments significantly increased soil fungal community abundance (P<0.05), whereas there was no significant difference among different topdressing nitrogen treatments (P>0.05). The Heip index and Shannon index of soil fungal communities decreased gradually with the increase in topdressing nitrogen rate, and the Sobs index, Heip index, and Shannon index of soil fungal communities in the treatment with 150 kg·hm-2 topdressing nitrogen were significantly lower than those of 0-75 kg·hm-2 topdressing nitrogen treatments (P<0.05). Principal component analysis and similarity analysis showed that there were significant differences in soil fungal community structure under different topdressing nitrogen rate treatments (P<0.05). With the increase in topdressing nitrogen rate, the number of network edges and average number of neighbors of soil fungal ecological network increased first and then decreased, and the network complexity of 37.5 kg·hm-2 topdressing nitrogen treatments was the highest. Compared with 0-75 kg·hm-2 topdressing nitrogen treatments, 112.5 kg·hm-2 and 150 kg·hm-2 topdressing nitrogen treatments increased the characteristic path length of the soil fungal ecological network, whereas it decreased the network density. With the increase in topdressing nitrogen rate, the relative abundance of soil saprotrophs gradually increased, and the pathotroph-saprotroph-symbiotroph relative abundance gradually decreased. Redundancy analysis showed that soil pH, total phosphorus, mineral nitrogen, available phosphorus, and available potassium were the main soil physicochemical factors affecting the soil fungal community structure in the wheat field under different topdressing nitrogen rate treatments. In conclusion, on the basis of straw retention and basal nitrogen, topdressing nitrogen at the wheat jointing stage could change the diversity, structure, and species composition of the soil fungal community, in turn affecting the soil fungal ecological network and function, and high topdressing nitrogen rates could reduce soil fungal community diversity, ecological network complexity, and network density.

[Soil bacterial communities of different crop rotations and yield of succeeding wheat.] / 不同轮作茬口土壤细菌群落及后茬小麦产量.

Evaluating ecological sustainability and crop productivity of different crop rotation patterns could provide theoretical support for adjusting and optimizing crop planting structure. We set seven treatments with different rotation crops and periods. We used real-time quantitative PCR to determine the abundance of soil bacterial community and 16S rRNA gene amplicon high-throughput sequencing technology to analyze diversity and taxa composition of soil bacterial community. Both soil available nutrients and succeeding wheat yield were measured. The results showed that, compared with the rotation with summer maize, the rotations with summer peanut or soybean in diffe-rent periods reduced soil organic carbon, mineral nitrogen, and available potassium, but significantly increased soil available phosphorus. The 16S rRNA gene copy numbers of soil bacteria in the treatments of rotations with summer peanut or soybean in different periods were significantly decreased, while community richness and diversity were increased. Different rotation crops significantly changed the structure and taxonomic composition of soil bacterial community. Compared with the rotation with summer maize, the rotations with summer soybean in different periods significantly increased the 1000-grain weight and grain yield of succeeding winter wheat. In conclusion, rotations with summer peanut or soybean in different periods could increase soil available phosphorus content and bacterial diversity, and significantly change soil bacterial community structure. In particular, rotation with summer soybean performed best in promoting yield formation of succeeding winter wheat.

[Response of Soil Fungal Communities in Diversified Rotations of Wheat and Different Crops].

Crop-soil microorganism interactions and feedback are critical to soil health and crop production. The aim of this study was to clarify the difference in soil fungal communities under diversified rotations of wheat and different crops in the North China Plain and to provide a theoretical basis for the construction and optimization of ecological sustainable planting systems. The soil fungal community abundance, composition, and diversity of continuous winter wheat-summer maize M, winter wheat-summer peanut (summer maize) PM, and winter wheat-summer soybean (summer maize) SM treatments were studied using real-time quantitative PCR and high-throughput sequencing technology. The results showed that, compared with those of the continuous winter wheat-summer maize treatment, the peanut rotation treatment PM2 and soybean rotation treatment SM2 significantly reduced soil fungal ITS sequence copy numbers (P<0.05); there was no significant difference in soil fungal ITS sequence copy numbers between other rotation treatments and those of the control (P>0.05). Rotation treatments with peanut or soybean increased soil fungal community richness (Chao1 and ACE indices) and diversity (Shannon and InvSimson indices), in which the community richness of all rotation treatments and the community diversity of SM1/SM2 treatments varied significantly (P<0.05). The result of non-metric multidimensional scaling (NMDS) analysis showed that the soil fungal community among different rotation crops were obviously separated. The rotation crops significantly affected soil fungal community structure (PERMANOVA:r2=0.350, P=0.001; ANOSIM:r=0.478, P=0.001). Ascomycota (73.67%-85.48%) was the dominant phylum, whereas Sordariomycetes (30.53%-48.19%) and Eurotiomycetes (11.12%-31.19%) were the dominant classes of the fungal communities of sandy-loam fluvo-aquic soil in the North China Plain. There were significantly different taxa of soil fungal communities in different rotations. Potential pathogens such as Neocosmospora, Plectosphaerella, and Gibellulopsis were significantly enriched in the rotations of winter wheat-summer peanut (summer maize), whereas potential beneficial fungi such as Penicillium and Zopfiella were significantly enriched in the rotations of winter wheat-summer soybean (summer maize). Compared with that under the continuous winter wheat-summer maize treatment, rotations with peanut or soybean increased the relative abundance of pathotroph, pathotroph-symbiotroph, and saprotroph-symbiotroph fungi and decreased the relative abundance of saprotroph fungi. The soil fungal community richness and structure were significantly related to soil organic carbon and available nutrients, and the Shannon diversity index was significantly related to soil mineral nitrogen and available phosphorus. In summary, on the basis of continuous winter wheat-summer maize rotation in the North China Plain, adding summer peanut or summer soybean instead of summer maize for rotations with different interval years could increase the richness and diversity of soil fungal communities and significantly change soil fungal community structure. In particular, summer soybean as the preceding crop had a positive effect on the enrichment of potential beneficial fungi.

Predator-prey systems with defense switching and density-suppressed dispersal strategy.

In this paper, we consider the following predator-prey system with defense switching mechanism and density-suppressed dispersal strategy $ \begin{equation*} \begin{cases} u_t = \Delta(d_1(w)u)+\frac{\beta_1 uvw}{u+v}-\alpha_1 u, & x\in \Omega, \; \; t>0, \\ v_t = \Delta(d_2(w)v)+\frac{\beta_2 uvw}{u+v}-\alpha_2 v, & x\in \Omega, \; \; t>0, \\ w_t = \Delta w-\frac{\beta_3 uvw}{u+v}+\sigma w\left(1-\frac{w}{K}\right), & x\in \Omega, \; \; t>0, \\ \frac{\partial u}{\partial \nu} = \frac{\partial v}{\partial \nu} = \frac{\partial w}{\partial \nu} = 0, & x\in\partial\Omega, \; \; t>0, \\ (u, v, w)(x, 0) = (u_0, v_0, w_0)(x), & x\in\Omega, \ \end{cases} \end{equation*} $ where $ \Omega\subset{\mathbb{R}}^2 $ is a bounded domain with smooth boundary. Based on the method of energy estimates and Moser iteration, we establish the existence of global classical solutions with uniform-in-time boundedness. We further prove the global stability of co-existence equilibrium by using the Lyapunov functionals and LaSalle's invariant principle. Finally we conduct linear stability analysis and perform numerical simulations to illustrate that the density-suppressed dispersal may trigger the pattern formation.

Real-time mandibular angle reduction surgical simulation with haptic rendering.

Mandibular angle reduction is a popular and efficient procedure widely used to alter the facial contour. The primary surgical instruments, the reciprocating saw and the round burr, employed in the surgery have a common feature: operating at a high-speed. Generally, inexperienced surgeons need a long-time practice to learn how to minimize the risks caused by the uncontrolled contacts and cutting motions in manipulation of instruments with high-speed reciprocation or rotation. A virtual reality-based surgical simulator for the mandibular angle reduction was designed and implemented on a CUDA-based platform in this paper. High-fidelity visual and haptic feedbacks are provided to enhance the perception in a realistic virtual surgical environment. The impulse-based haptic models were employed to simulate the contact forces and torques on the instruments. It provides convincing haptic sensation for surgeons to control the instruments under different reciprocation or rotation velocities. The real-time methods for bone removal and reconstruction during surgical procedures have been proposed to support realistic visual feedbacks. The simulated contact forces were verified by comparing against the actual force data measured through the constructed mechanical platform. An empirical study based on the patient-specific data was conducted to evaluate the ability of the proposed system in training surgeons with various experiences. The results confirm the validity of our simulator.