Effects of Different Motion Parameters on the Interaction of Fish School Subsystems.

For a long time, fish school swimming has attracted a great deal of attention in biological systems, as fish schools can have complex hydrodynamic effects on individuals. This work adopted a non-iterative, immersed boundary-lattice Boltzmann method (IB-LBM). A numerical simulation of two-dimensional three-degree-of-freedom self-propelled fish, in side-by-side, staggered, and triangle formations, was conducted by adjusting spacing and motion parameters. A comprehensive analysis of individual speed gains and energy efficiencies in these formations was carried out. Furthermore, an analysis of the hydrodynamic characteristics of fish schools was performed, using instantaneous vorticity profiles and pressure fields. Certain studies have shown that passive interactions between individuals cannot always bring hydrodynamic benefits. The swimming efficiency of side-by-side formations in the same phase gradually increases as the distance decreases, but it also brings certain burdens to individuals when the phases are different. This paper also shows that the roles of passive interactions, spacing, and deflections affect fish school subsystems differently. When the low-pressure areas created by a wake vortex act on one side of an individual's body, the tail-end fish are good at gaining hydrodynamic benefits from it. This effect is not universal, and the degree to which individuals benefit from changes in exercise parameters varies. This study provides a theoretical basis for bioinspired robots, as well as providing certain insights into the mechanism of collective biological movement.

Learning to school in dense configurations with multi-agent deep reinforcement learning.

Fish are observed to school in different configurations. However, how and why fish maintain a stable schooling formation still remains unclear. This work presents a numerical study of the dense schooling of two free swimmers by a hybrid method of the multi-agent deep reinforcement learning and the immersed boundary-lattice Boltzmann method. Active control policies are developed by synchronously training the leader to swim at a given speed and orientation and the follower to hold close proximity to the leader. After training, the swimmers could resist the strong hydrodynamic force to remain in stable formations and meantime swim in desired path, only by their tail-beat flapping. The tail movement of the swimmers in the stable formations are irregular and asymmetrical, indicating the swimmers are carefully adjusting their body-kinematics to balance the hydrodynamic force. In addition, a significant decrease in the mean amplitude and the cost of transport is found for the followers, indicating these swimmers could maintain the swimming speed with less efforts. The results also show that the side-by-side formation is hydrodynamically more stable but energetically less efficient than other configurations, while the full-body staggered formation is energetically more efficient as a whole.

Study on SO2 and Cl2 sensor application of 2D PbSe based on first principles calculations.

In this paper, we use 2D PbSe to design a gas sensor to monitor the presence of SO2 and Cl2. We use first principles to verify the feasibility of this material, such as atomic structure, band gap, differential charge density and Bader charge. The results show that 2D PbSe can distinctly adsorb SO2 and Cl2. Furthermore, the adsorption of SO2 and Cl2 will affect the electronic structure of 2D PbSe, and some electrons in the PbSe are transferred to gas atoms. The band gap of the system after adsorption is smaller than that of the PbSe before adsorption. The band gap of single layer PbSe decreases by 41.92% after SO2 adsorption and 60.61% after Cl2 adsorption. The band gap of multi-layer PbSe decreases by 72.97% after SO2 adsorption and 43.24% after Cl2 adsorption. This shows that single layer PbSe is more sensitive to Cl2 and multi-layer PbSe is more sensitive to SO2. It provides a potential possibility for designing gas sensors for SO2 and Cl2 based on 2D PbSe.

Recent Progress of Fluxgate Magnetic Sensors: Basic Research and Application.

Fluxgate magnetic sensors are especially important in detecting weak magnetic fields. The mechanism of a fluxgate magnetic sensor is based on Faraday's law of electromagnetic induction. The structure of a fluxgate magnetic sensor mainly consists of excitation windings, core and sensing windings, similar to the structure of a transformer. To date, they have been applied to many fields such as geophysics and astro-observations, wearable electronic devices and non-destructive testing. In this review, we report the recent progress in both the basic research and applications of fluxgate magnetic sensors, especially in the past two years. Regarding the basic research, we focus on the progress in lowering the noise, better calibration methods and increasing the sensitivity. Concerning applications, we introduce recent work about fluxgate magnetometers on spacecraft, unmanned aerial vehicles, wearable electronic devices and defect detection in coiled tubing. Based on the above work, we hope that we can have a clearer prospect about the future research direction of fluxgate magnetic sensor.

On the dynamics of one-prey-n-predator impulsive reaction-diffusion predator-prey system with ratio-dependent functional response.

In this paper, a one-prey-n-predator impulsive reaction-diffusion periodic predator-prey system with ratio-dependent functional response is investigated. On the basis of the upper and lower solution method and comparison theory of differential equation, sufficient conditions on the ultimate boundedness and permanence of the predator-prey system are established. By constructing an appropriate auxiliary function, the conditions for the existence of a unique globally stable positive periodic solution are also obtained. Examples and numerical simulations are presented to verify the feasibility of our results. A discussion is conducted at the end.

The Dynamical Behaviors for a Class of Immunogenic Tumor Model with Delay.

This paper aims at studying the model proposed by Kuznetsov and Taylor in 1994. Inspired by Mayer et al., time delay is introduced in the general model. The dynamic behaviors of this model are studied, which include the existence and stability of the equilibria and Hopf bifurcation of the model with discrete delays. The properties of the bifurcated periodic solutions are studied by using the normal form on the center manifold. Numerical examples and simulations are given to illustrate the bifurcation analysis and the obtained results.

Surgical treatment of gynecomastia: mastectomy compared to liposuction technique.

BACKGROUND: Gynecomastia is a benign enlargement of the male breast. Yet enlarged breasts cause anxiety, embarrassment, psychosocial discomfort, and fear of breast cancer. The aim of this study was to assess the experience of gynecomastia patients undergoing mastectomy and liposuction surgery. METHODS: Seven hundred thirty-three patients were analyzed for age, chief complaint, position, grade, operation approach, biopsy, and complication between mastectomy group and liposuction group, from 1990 to 2010. RESULTS: Four hundred two patients (436 breasts) were treated with mastectomy and 331 patients (386 breasts) were treated with liposuction techniques. Three hundred thirty (82%) patients complained of breast lump and lump with pain in mastectomy group, and 204 (61%) patients complained of enlargement breast and enlargement with pain in liposuction group (P < 0.05). All excision specimens were performed for routine histological analysis which showed pathologic diagnosis in patients with mastectomy (100%). One hundred fifty-nine (41%) patients with liposuction acquired pathologic diagnosis through fine needle aspiration and/or core biopsy (P < 0.05). The reoperation rates in mastectomy group and liposuction group were 1.4% and 0.5%, respectively. There were no nipple/areola necrosis and scars in liposuction group. CONCLUSIONS: The surgical treatment of gynecomastia required an individual approach, depending on symptoms (lump or enlargement) and requirements of patients. Patients who chose mastectomy were looking for reassurance that their pathologic diagnosis was benign. The increase in the number of liposuction patients was reflected in our study because it was associated with superior esthetic results and few complications.

Dynamical behavior of a hepatitis B virus transmission model with vaccination.

Hepatitis B virus (HBV) infection is a globally health problem. In 2005, the WHO Western Pacific Regional Office set a goal of reducing chronic HBV infection rate to less than 2% among children five years of age by 2012, as an interim milestone towards the final goal of less than 1%. Many countries made some plans (such as free HBV vaccination program for all neonates in China now) to control the transmission HBV. We develop a model to explore the impact of vaccination and other controlling measures of HBV infection. The model has simple dynamical behavior which has a globally asymptotically stable disease-free equilibrium when the basic reproduction number R(0)< or =1, and a globally asymptotically stable endemic equilibrium when R(0)>1. Numerical simulation results show that the vaccination is a very effective measure to control the infection and they also give some useful comments on controlling the transmission of HBV.