Impact point prediction guidance of ballistic missile in high maneuver penetration condition

An impact point prediction(IPP) guidance based on supervised learning is proposed to address the problem of precise guidance for the ballistic missile in high maneuver penetration condition.An accurate ballistic trajectory model is applied to generate training samples,and ablation experiments are conducted to determine the mapping relationship between the flight state and the impact point.At the same time,the impact point coordinates are decoupled to improve the prediction accuracy,and the sigmoid activation function is improved to ameliorate the prediction efficiency.Therefore,an IPP neural network model,which solves the contradiction between the accuracy and the speed of the IPP,is established.In view of the performance deviation of the divert control system,the mapping relationship between the guidance parameters and the impact deviation is analysed based on the variational principle.In addition,a fast iterative model of guidance parameters is designed for reference to the Newton iteration method,which solves the nonlinear strong coupling problem of the guidance parameter solution.Monte Carlo simulation results show that the prediction accuracy of the impact point is high,with a 3 σ prediction error of 4.5 m,and the guidance method is robust,with a 3 σ error of 7.5 m.On the STM32F407 singlechip microcomputer,a single IPP takes about 2.374 ms,and a single guidance solution takes about9.936 ms,which has a good real-time performance and a certain engineering application value.

ADS Injector-I 2 K superfluid helium cryogenic system

The Accelerator Driven Sub-critical(ADS)system is a strategic plan to solve the nuclear waste problem for nuclear power plants in China.High-energy particle accelerators and colliders contain long strings of superconducting devices,superconducting radio frequency cavities,and magnets,which may require cooling by 2 K superfluid helium(HeliumⅡ).2 K superfluid helium cryogenic system has become a research hot spot in the field of superconducting accelerators.In this study,the ADS Injector-I 2 K cryogenic system is examined in detail.The cryogenic system scheme design,key equipment,and technology design,such as the 2 K Joule–Thomson(J–T)heat exchanger and cryomodules CM1+CM2 design,are examined,in addition to the commissioning and operation of the cryogenic system.The ADS Injector-I 2 K cryogenic system is the first 100 W superfluid helium system designed and built independently in China.The ADS proton beam reached 10 Me V at 10 m A in July 2016 and 10 Me V at 2 m A in continuous mode in January 2017 and has been operated reliably for over 15,000 h,proving that the design of ADS Injector-I 2 K cryogenic system,the key equipment,and technology research are reasonable,reliable,and meet the requirements.The research into key technologies provides valuable engineering experience that can be helpful for future projects such as CI-ADS(China Initiative Accelerator-Driven System),SHINE(Shanghai High Repetition Rate XFEL and Extreme Light Facility),PAPS(Platform of Advanced Photon Source Technology),and CEPC(Circular Electron-Positron Collider),thereby developing national expertise in the field of superfluid helium cryogenic systems.

Imaging presentation of biliary adenofibroma:A case report

BACKGROUND Biliary adenofibroma(BF)is a rare benign epithelial tumor with the possibility of malignant transformation.Its main pathological feature is a well-defined cystic or honeycomb mass.BF has no specific clinical manifestations or laboratory and imaging findings;thus,it is easily misdiagnosed before surgery.This report describes a case in which biliary cystadenoma was misdiagnosed preoperatively and BF was diagnosed postoperatively.The imaging features,particularly the magnetic resonance imaging(MRI)features,were analyzed and summarized.CASE SUMMARY A 68-year-old Chinese man was admitted to our hospital with a 2-mo history of abdominal discomfort.Following admission to our hospital,laboratory examinations showed normal tumor marker concentrations and liver function.Hepatocellular carcinoma was considered after contrast-enhanced ultrasound examination.MRI suggested the possibility of cystadenoma of the bile duct.However,postoperative pathological examination confirmed the diagnosis of BF.No local recurrence was found 1 mo after surgery.CONCLUSION Our objective is to highlight the imaging diagnostic value of BF,especially on an MRI enhanced scan with gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid.

Design, assembly, and pre-commissioning of cryostat for 3W1 superconducting wiggler magnet

One of the most important devices for the High Energy Photon Source Test Facility project,the 2.6 T 32-pole 3W1 superconducting wiggler,was designed by the Institute of High Energy Physics(IHEP);its magnetic gap is 68 mm,and its storage energy is 286 kJ.It will be installed at the storage ring of the Beijing Electron Positron Collider Upgrade Project at the IHEP to replace the old permanent wiggler.The primary purpose of the cryostat is to create a safe and reliable system and realize long-term operation with zero liquid helium consumption.To maintain liquid helium temperature,four identical two-stage cryocoolers are placed symmetrically at the wiggler ends.The cryostat has only one 60 K thermal shield,which is used to reduce the heat load to the liquid helium vessel.The cryostat has several novel features,including a suspension system with little heat leakage that is self-centered during cooling of the cryostat,a special copper liner and high-efficiency condensers,three pairs of binary current leads,and three-level safety design.The cryogenic system has been cooled three times,and the residual cooling capacity is approximately 0.41 W at 4.2 K without current.

Spatial scaling of soil microbial co-occurrence networks in a fragmented landscape

Impact statement Habitat loss has been a primary threat to biodiversity.However,species do not function in isolation but often associate with each other and form complex networks.Thus,revealing how the network complexity and stability scale with habitat area will give us more insights into the effects of habitat loss on ecosystems.In this study,we explored the relationships between the island area and the network complexity and stability of soil microbes.We found that the complexity and stability of soil microbial co‐occurrence networks scale positively with island area,indicating that habitat loss will potentially simplify and destabilize soil microbial networks.

物种定殖和丧失驱动近70年森林演替进程中的群落结构动态

在过去的几十年中,揭示群落谱系和功能性状结构如何随着演替变化引起了广泛关注。但长期动态数据的缺乏限制了我们对于群落格局和构建机制的理解,这一问题在森林群落中尤为突出。本研究基于南京灵谷寺森林1951、1981、2002和2019年的定点样带调查数据,分析了这一中国东南部亚热带森林68年的次生演替动态。研究发现,随着演替的深入,群落谱系和性状结构呈现相反的变化趋势。尽管近缘物种间的谱系距离在下降,物种间的平均谱系距离却在增加,群落谱系结构整体上趋于发散。相反,无论用平均还是最近距离作为度量,物种间的性状距离均随着演替逐渐下降,群落功能性状结构趋于聚集。我们进一步拆分了物种定殖和丧失对群落谱系和性状结构动态的相对贡献。结果表明:谱系结构趋于发散主要是由于定殖的物种本身亲缘关系较远,也和群落中原有的物种有着较远的亲缘距离;性状结构趋于聚集主要是因为那些与群落中原有的物种性状相似的物种具有更高的定殖机会但从群落中丧失的概率却更低。这一研究结果表明,拆分物种定殖和丧失过程是解开长期演替进程中群落动态和构建机制的关键。

近十年植物入侵生态学重要研究进展

外来植物入侵对本地生物多样性、生态安全、社会经济发展和人类健康造成了严重威胁。因此,探究植物入侵机制及其生态效应对我国生态可持续发展具有重要意义,也是植物入侵生态学的主要研究内容。过去10年,生态学家开展了大量研究,取得了丰硕成果,为推动入侵植物防控与生物多样性保护提供了理论指导。为深入解析外来植物入侵机制,为其防控管理提供依据,本文从以下3个方面综述了植物入侵生态学重要进展:首先是外来植物生物学特性、生物和非生物环境对植物入侵的调控作用;其次是外来植物入侵对本地生态系统的影响;最后介绍了外来植物入侵的类比研究范式——本地植物入侵,以及多组学技术在入侵生态学研究中的应用。基于这些研究进展,本文展望了该领域的未来发展趋势,包括:(1)研究对象从单一物种扩展到多物种比较;(2)研究地理范围从局域尺度扩大到纬度梯度格局;(3)入侵机制从单一理论验证到综合阐释多个假说。

回顾与讨论气动导纳函数

目的:提出一种识别桥面气动导纳函数的理论框架并验证其合理性。方法:1.提出一种考虑来流脉动风和气动力全部交叉分量贡献的全分量导纳函数的识别算法。2.利用风洞试验与数值分析结合的方法,对一组流线型和钝体断面的气动导纳进行验证。3.对一桥梁断面进行抖振响应分析,验证其等效气动导纳。结论:1.通过数值计算,系统地验证了本文所提出的等效气动导纳函数具有较高的保真度。2.风洞中流线型断面的等效气动导纳函数的辨识结果与随机子空间辨识方法的结果吻合良好。3.通过对一组流线型和钝体断面进行气动导纳识别表明,某些断面的气动导纳高于基于准定常理论的所得值。4.根据准定常理论下的气动导纳函数、Sears函数和实验验证的函数计算抖振响应并与风洞试验结果进行比较发现,对于流线型断面,采用Sears函数或等效气动导纳函数都是合理的,而用准定常理论得到的抖振响应则过于保守。5.灵敏度分析表明,抖振响应对平均风速、气动导纳函数、静风力系数及其导数和颤振导数等参数非常敏感。

Dynamically Tunable and High-Contrast Graphene-Based Terahertz Electro-Optic Modulator

We propose and discuss terahertz(THz) electro-optic modulator induced by periodically patterned graphene microcavity. Due to the joint effect of graphene plasmon resonances and Fabry-Perot(F-P) oscillations, plasmon-induced transparency(PIT) effect is achieved and the operation frequency can be dynamically tuned by graphene Fermi energies and structural parameters. The results reveal that modulation depth(MD) larger than 80% is obtained across a wide frequency range from 4.2 THz to 9.4 THz, and the largest MD and Q factor reaches 95% and 15.8, respectively. In addition, operation frequency range and MD can also be tuned by optimizing the structure parameters. This investigation promises the development of high-performance widely tunable THz modulator in chip integrated photonic circuits.