Coexistence and harvesting control policy in a food chain model with mutual defense of prey

A model is proposed to understand the dynamics in a food chain (one predator‐two prey). Unlike many approaches, we consider mutualism (for defense against predators) between the two groups of prey. We investigate the conditions for coexistence and exclusion. Unlike Elettreby's (2009) results, we show that prey can coexist in the absence of predators (as expected since there is no competition between prey). We also show the existence of Hopf bifurcation and limit cycle in the model, and numerically present bifurcation diagrams in terms of mutualism and harvesting. When the harvest is practiced for profit making, we provide the threshold effort value that determines the profitability of the harvest. We show that there is zero profit when the constant effort is applied. Below (resp. above) , there will always be gain (resp. loss). In the case of gain, we provide the optimal effort and optimal steady states that produce maximum profit and ensure coexistence. Recommendations for resource managers As a result of our investigation, we bring the following to the attention of management:

• 1. In the absence of predators, different groups of prey can coexist if they mutually help each other (no competition among them).
• 2. There is a maximal effort to invest in order to gain profit from the harvest. Above , the investment will result in a loss.
• 3. In the case of profit from harvest, policy makers should recommend the optimal effort to be applied and the optimal stock to harvest. This will guarantee maximum profit while ensuring sustainability of all species.

     

Free boundary problem for a fully nonlinear and degenerate parabolic equation in an angular domain

This paper concerns with the problem of how to running an insurance company to maximize his total discounted expected dividends. In our model, the dividend rate is limited in $[0,M]$ and the company is allowed to transfer any proportion of risk by reinsuring. So there are two strategies which we call dividend strategy and reinsurance strategy. The objective function and the corresponding optimal two strategies are the solution and the two free boundaries of the following Barenblatt parabolic equation

$v_t?\underset{0\le a\le 1}{\max }?(\frac{1}{2}{a}^2{\sigma }^2{v}_{xx}+a\mu v_x)+cv?\underset{0\le l\le M}{\max }?[(1?v_x)l]=0$

under certain boundary conditions on an angular domain

$Q_T=\{(x,t)|0<x<Mt,0<t\le T\}.$

The main effort is to analyze the properties of the solution and the free boundaries to show the optimal decision for the insurance company.     

Quantitative NMR (qNMR) for pharmaceutical analysis: The pioneering work of George Hanna at the US FDA

In the last two decades, quantitative NMR (qNMR) has become increasingly important for the analysis of pharmaceuticals, chemicals, and natural products including dietary supplements. For the purpose of quality control and chemical standardization of a large variety of pharmaceutical, chemical, and medicinal products, qNMR has proven to be a valuable orthogonal quantification method and a compelling alternative to chromatographic techniques. This work reviews a fundamental component of the early development of qNMR, reflected in the pioneering work of the late George M. Hanna during the years between 1984 and 2006 at the US Food and Drug Administration (FDA). Because Hanna performed the majority of his groundbreaking work on a 90‐MHz instrument, his legacy output connects with recent progress in low‐field benchtop NMR instrumentation. Hanna gradually established the utility of qNMR for the routine quality control analyses practiced in pharmaceutical and related operations well ahead of his peers. His work has the potential to inspire new developments in qNMR applied to small molecules of biomedical importance.     

Co‐syndiospecific Alternating Copolymerization of Functionalized Propylenes and Styrene by Rare‐Earth Catalysts

The precise control of monomer sequence and stereochemistry in copolymerization is of much interest and importance for the synthesis of functional polymers, but studies toward this goal have met with only limited success to date. Now, the co‐syndiospecific alternating copolymerization of methoxyphenyl‐ and N,N‐dimethylaminophenyl‐functionalized propylenes with styrene by half‐sandwich rare‐earth catalysts is reported. This reaction efficiently afforded the corresponding functionalized propylene‐alt‐styrene copolymers with a perfect alternating sequence and excellent co‐syndiotacticity (rrrr >99 %), thus constituting the first example of co‐stereospecific alternating copolymerization of polar and non‐polar olefins.     

中国聚变工程实验堆水冷包层钢构件流道成形控制研究

针对CFETR水冷包层流道钢构件热等静压制备时易变形压塌问题，利用单轴扩散焊设备开展了焊接工艺参数优化试验。在此基础上，重新设计了流道焊接界面位置和尺寸，用两步热等静压扩散焊法制备出了流道变形可控的平板型第一壁钢构件模块。优化试验表明，低活化钢试样的固相扩散焊温度需高于950℃，焊后经过760℃/60min回火热处理试样力学性能可以得到有效回复。     

基于虚拟中心电流法的 HL-2M快控电源数学模型

针对中国环流器2号M(HL-2M)装置中用于核聚变物理实验等离子体的垂直不稳定性控制的快控电源拓扑结构，充分考虑线圈的自感与互感对输出的影响，构建出数学模型，首次提出并运用虚拟中心电流法，使得控制算法更加简单，采用多输入多输出的控制方法，利用2个参量控制3个变量。本文基于基本供电方案得到多线圈耦合电压，基于快控电源拓扑推导出快控电源电路方程，再将其合并得到最终的线圈电压数学模型，最后进行仿真验证。结果表明数学模型搭建正确，为今后进行进一步计算提供了坚实的基础。     

基于EKF的水下LD通信精对准控制算法

高速激光通信中接收机与光斑中心很难处于精对准状态,导致水下光通信链路难以稳定建立.首先采用蒙特卡洛仿真统计法分析激光光子在海水中传输的接收光强分布规律,再通过实验对接收端的光斑图像进行采样分析,利用曲线拟合得到接收器位置与接收光强的关系.仿真与实验结果表明:光束经过25 m的水下传输,接收光强分布仍近似为高斯分布.采用非线性估计算法(扩展卡尔曼滤波)与基本状态控制反馈理论,根据接收光强度估计接收器当前位置与最大光强处的距离,通过反馈算法实现接收端与光斑中心的主动跟踪对准.算法仿真结果显示,接收端对准误差在2 mm以下,稳定后接收效率超过98%.     

Advances of phononics in 2012—2022

Due to its great potential applications in thermal management, heat control, and quantum information, phononics has gained increasing attentions since the first publication in Rev. Mod. Phys. 84 1045 (2012). Many theoretical and experimental progresses have been achieved in the past decade. In this paper, we first give a critical review of the progress in thermal diodes and transistors, especially in classical regime. Then, we give a brief introduction to the new developing research directions such as topological phononics and quantum phononics. In the third part, we discuss the potential applications. Last but not least, we point out the outlook and challenges ahead.     

Re-Analysis of Abdominal Gland Volatilome Secretions of the African Weaver Ant,Oecophylla longinoda (Hymenoptera: Formicidae)

The African weaver ant, Oecophylla longinoda, is used as a biological control agent for the management of pests. The ant has several exocrine glands in the abdomen, including Dufour’s, poison, rectal, and sternal glands, which are associated with pheromone secretions for intra-specific communication. Previous studies have analyzed the gland secretions of Dufour’s and poison glands. The chemistry of the rectal and sternal glands is unknown. We re-analyzed the secretions from Dufour’s and poison glands plus the rectal and sternal glands to compare their chemistries and identify additional components. We used the solid-phase microextraction (SPME) technique to collect gland headspace volatiles and solvent extraction for the secretions. Coupled gas chromatography–mass spectrometry (GC-MS) analysis detected a total of 78 components, of which 62 were being reported for the first time. These additional components included 32 hydrocarbons, 12 carboxylic acids, 5 aldehydes, 3 alcohols, 2 ketones, 4 terpenes, 3 sterols, and 1 benzenoid. The chemistry of Dufour’s and poison glands showed a strong overlap and was distinct from that of the rectal and sternal glands. The different gland mixtures may contribute to the different physiological and behavioral functions in this ant species.