原子层制造的研究现状与科学挑战

原子层制造是指加工精度达到原子层量级的可控制造技术,包括原子层去除、添加、迁移等。针对信息、能源、航空航天等领域核心零部件超高性能构建的发展需求,通过原子层可控去除制造全频段原子级精度无损表面,并结合原子层增材制造原子级新结构,有望实现特殊功能的有效创成,保证超高性能的安全可靠。另外,后摩尔时代先进芯片的制造工艺将迈入亚纳米物理极限,原子层制造需求贯穿芯片制造工艺的全流程。本文阐述了原子层制造技术的发展需求与研究进展,围绕原子层抛光、原子层沉积/刻蚀、原子层损伤控制、原子层工艺与装备等领域,梳理了原子层制造的发展方向及研究目标,凝练了原子层制造领域未来的关键科学问题及面临的挑战,探讨了前沿研究方向和发展战略。

A preliminary study of the effects of plastic film-mulched raised beds on soil temperature and crop performance of early-sown short-season spring maize(Zea mays L.) in the North China Plain

To identify a strategy for earlier sowing and harvesting of spring maize(Zea mays L.) in an alternative maize–maize double cropping system, a 2-year field experiment was performed at Quzhou experimental station of China Agricultural University in 2014 and 2015. A short-season cultivar, Demeiya number 1(KX7349), was used in the experiment. Soil temperature to 5 cm depth in the early crop growth stage, crop growth, crop yield, and water use of different treatments(plastic film-mulched raised bed(RF) and flat field without plastic film mulching(CK) in 2014; RF, plastic film-mulched flat field(FF), and CK in 2015)were measured or calculated and compared. Soil temperature in the film-mulched treatments was consistently higher than that in CK(1.6–3.5 °C in average) during the early growth stage. Crops in plastic film-mulched treatments used 214 fewer growing-degree days(GDDs) in 2014 and 262 fewer GDDs in 2015. In 2014, the RF treatment yielded 32.7%higher biomass than CK, although its 9.4% higher grain yield was not statistically significant. Also, RF used 17.9% less water and showed 33.1% higher water use efficiency(WUE) than CK. In 2015, RF and FF showed 56.2% and 49.5% higher yield, 15.0% and 4.5%lower water use(ET), and 63.4% and 75.7% higher WUE, respectively, than CK. RF markedly increased soil temperature in the early crop season, accelerated crop growth, reduced ET,and greatly increased crop yield and WUE. Compared with FF, RF had no obvious effect on crop growth rate, although soil temperature during the period between sowing and stem elongation was slightly increased. However, RF resulted in lower ET and higher WUE than FF. Effects of RF on soil water dynamics as well as its cost-effectiveness remain topics for further study.

Topology optimization method of metamaterials design for efficient enhanced transmission through arbitrary-shaped sub-wavelength aperture

The electromagnetic wave enhanced transmission(ET)through the sub-wavelength aperture was an unconventional physical phenomenon with great application potential.It was important to find a general design method which can realize efficient ET for arbitrary-shaped apertures.For achieving ET with maximum efficiency at specific frequency through arbitrary-shaped subwavelength aperture,a topology optimization method for designing metamaterials(MTM)microstructure was proposed in this study.The MTM was employed and inserted vertically in the aperture.The description function for the arbitrary shape of the aperture was established.The optimization model was founded to search the optimal MTM microstructure for maximum enhanced power transmission through the aperture at the demanded frequency.Several MTM microstructures for ET through the apertures with different shapes at the demanded frequency were designed as examples.The simulation and experimental results validate the feasibility of the method.The regularity of the optimal ET microstructures and their advantages over the existing configurations were discussed.

Advanced Agriculture of Israel Roots in its Decision Making Mechanism

In the past 70 years, Israel has not only realized the self-sufficiency of agricultural products, but also make its way to becoming one of leading exporters of agricultural products in the world rapidly. Undoubtedly, there are many reasons for this world famous "Miracle of Negev Desert" [1], but we consider the decision making mechanism as one of the most important reasons, because such a perfect integrated system consisting of researching system, experimental system and extension system is well organized and it booms the development of agriculture in Israel.

Targeting cancer stem cell pathways for cancer therapy

Since cancer stem cells(CSCs)were first identified in leukemia in 1994,they have been considered promising therapeutic targets for cancer therapy.These cells have self-renewal capacity and differentiation potential and contribute to multiple tumor malignancies,such as recurrence,metastasis,heterogeneity,multidrug resistance,and radiation resistance.The biological activities of CSCs are regulated by several pluripotent transcription factors,such as OCT4,Sox2,Nanog,KLF4,and MYC.In addition,many intracellular signaling pathways,such as Wnt,NF-κB(nuclear factor-κB),Notch,Hedgehog,JAK-STAT(Janus kinase/signal transducers and activators of transcription),PI3K/AKT/mTOR(phosphoinositide 3-kinase/AKT/mammalian target of rapamycin),TGF(transforming growth factor)/SMAD,and PPAR(peroxisome proliferator-activated receptor),as well as extracellular factors,such as vascular niches,hypoxia,tumor-associated macrophages,cancer-associated fibroblasts,cancer-associated mesenchymal stem cells,extracellular matrix,and exosomes,have been shown to be very important regulators of CSCs.Molecules,vaccines,antibodies,and CAR-T(chimeric antigen receptor T cell)cells have been developed to specifically target CSCs,and some of these factors are already undergoing clinical trials.This review summarizes the characterization and identification of CSCs,depicts major factors and pathways that regulate CSC development,and discusses potential targeted therapy for CSCs.

Generalized spatial representation for digital modulation and its potential application

Constellation mapping has provided a great convenience to measure the performance of digital signal modulation in Euclid space. However, traditional in-phase and quadrature(IQ) plane is difficult to express the frequency modulation scheme such as minimum shift keying(MSK) and the time domain modulation such as cyclic code shift keying(CCSK). How to represent the digital signal modulation visually through constellation mapping is an attractive problem. To address this issue, in this paper, the combined frequency and phase modulation are utilized to define a new kind of constellation mapping, where the phase and frequency are quantized to the same elements. The uniform geometric construction for combined phase and frequency modulation is redefined in the 3D cylindrical coordinate system based on frequency(f), in-phase component(I) and quadrature component(Q). In the new coordinates, the quadrature frequency-phase shift keying(QFPSK) is produced by the QPSK with dimensional rotation matrix and denoted by the reduced dual quaternion. Furthermore, the spatial extension from QFPSK to chirp cyclic shift keying(Chirp CSK) is analyzed with bandwidth efficiency and energy efficiency. At last, the QFPSK is combined with the 2D OFDM, yielding the image OFDM system.Experimental results verify the effectiveness of QFPSK in the proposed system with the time-varying wireless channel and frequency selective fading channel respectively.

Running-in behavior of a H‒DLC/Al_(2)O_(3) pair at the nanoscale

Diamond-like carbon(DLC)film has been developed as an extremely effective lubricant to reduce energy dissipation;however,most films should undergo running-in to achieve a super-low friction state.In this study,the running-in behaviors of an H–DLC/Al_(2)O_(3) pair were investigated through a controllable single-asperity contact study using an atomic force microscope.This study presents direct evidence that illustrates the role of transfer layer formation and oxide layer removal in the friction reduction during running-in.After 200 sliding cycles,a thin transfer layer was formed on the Al2O3 tip.Compared with a clean tip,this modified tip showed a significantly lower adhesion force and friction force on the original H–DLC film,which confirmed the contribution of the transfer layer formation in the friction reduction during running-in.It was also found that the friction coefficient of the H–DLC/Al_(2)O_(3) pair decreased linearly as the oxygen concentration of the H–DLC substrate surface decreased.This phenomenon can be explained by a change in the contact surface from an oxygen termination with strong hydrogen bond interactions to a hydrogen termination with weak van der Waals interactions.These results provide new insights that quantitatively reveal the running-in mechanism at the nanoscale,which may help with the design optimization of DLC films for different environmental applications.

读徐艺乙先生《风筝史话》有感

《风筝史话》是徐艺乙先生于1991年完成的一本民间文化著作,书中汇集整理风筝文化的史籍资料、诗文写作、图案样式,并从技术演进的角度,讨论了风筝起源问题以及对于现代飞行技术的影响。三十余年来,在艺术界产生了广泛的影响。时移势迁,新版《风筝史话》已由江苏凤凰美术出版社出版发行,在科技、艺术与民艺深度关联的当下,《风筝史话》正阐扬着全新的时代价值。