高性能罗兰-C接收天线设计

为了提高罗兰-C磁天线的接收能力,设计了一种顺接串联多层线圈的磁天线。理论推导了顺接串联多层线圈磁天线的信噪比和灵敏度,最终设计的磁天线大小为150 mm×150 mm。远场测试接收到了较高信噪比的罗兰-C信号,在相同信号调理电路条件下,与单层单组线圈的磁天线相比,顺接串联多层线圈的磁天线接收到3.47 V的电压信号,且信噪比高达30.87 dB,灵敏度和信噪比分别提高了82.42%和63.20%。顺接串联多层线圈磁天线提高了罗兰-C磁天线的灵敏度和信噪比,对罗兰-C系统在定位方面的应用具有重要意义。     

Epitaxial growth and thermal-conductivity limit of single-crystalline Bi2Se3/In2Se3 superlattices on mica

Nano Research - Thermal transport in superlattices is governed by various phonon-scattering processes. For extracting the phonon-scattering contribution of hetero-interfaces in chalcogenide...     

Application potential of bone marrow mesenchymal stem cell (BMSCs) based tissue-engineering for spinal cord defect repair in rat fetuses with spina bifida aperta

Spina bifida aperta are complex congenital malformations resulting from failure of fusion in the spinal neural tube during embryogenesis. Despite surgical repair of the defect, most patients who survive with spina bifida aperta have a multiple system handicap due to neuron deficiency of the defective spinal cord. Tissue engineering has emerged as a novel treatment for replacement of lost tissue. This study evaluated the prenatal surgical approach of transplanting a chitosan–gelatin scaffold seeded with bone marrow mesenchymal stem cells (BMSCs) in the healing the defective spinal cord of rat fetuses with retinoic acid induced spina bifida aperta. Scaffold characterisation revealed the porous structure, organic and amorphous content. This biomaterial promoted the adhesion, spreading and in vitro viability of the BMSCs. After transplantation of the scaffold combined with BMSCs, the defective region of spinal cord in rat fetuses with spina bifida aperta at E20 decreased obviously under stereomicroscopy, and the skin defect almost closed in many fetuses. The transplanted BMSCs in chitosan–gelatin scaffold survived, grew and expressed markers of neural stem cells and neurons in the defective spinal cord. In addition, the biomaterial presented high biocompatibility and slow biodegradation in vivo. In conclusion, prenatal transplantation of the scaffold combined with BMSCs could treat spinal cord defect in fetuses with spina bifida aperta by the regeneration of neurons and repairmen of defective region.     

Preliminary Study on Quantitative Research Methods of Discussion-based Teaching: CAD/CAM Course

Computer-aided design and manufacturing,or CAD/CAM,in a narrow sense,is the use of a computer for component design and machining. As a specialized course for students,CAD/CAM course is a required course for undergraduates majoring in mechanical engineering and related engineering majors and also the core technical skills to be mastered during the undergraduate study. Based on the teaching practices of CAD/CAM course,this paper tries to introduce the discussion-based method in curriculum design and the implementation of the course,and enhance the interaction between teachers and students through using new information interaction tools such as We Chat group and course homepage to stimulate students' interest,and also expand the learning space and time. Thus,the problems students have will be solved in real time. In this study,for the first time,the statistical methods are used to record detailed the speaking time,keywords and the frequency of teachers and students' interaction,and also carries out quantitative analysis in order to explore the interactive patterns between teacher and students in discussion-based teaching,so as to improve communication and learning efficiency between teacher and students. Meanwhile,this paper also discussed the advantages and the disadvantages of using discussion-based teaching in the hope that it can provide reference for the following discussion-based teaching of CAD/CAM course in mechanical or related engineering majors.     

Graphene quantum dots derived from hollow carbon nano-onions

Herein, carbon nano-onions (CNOs) with different structures have been investigated as precursors for the synthesis of graphene quantum dots (GQDs). It was found that hollow CNOs yield GQDs with a uniform size distribution, whereas metal encapsulation in the CNO structure is disadvantageous for the same. Furthermore, the hollow CNOs are also advantageous for the synthesis of GQDs with a yellow-green hybrid luminescence and long-ranged excitation wavelength (λ _ex)-independent photoluminescent (PL) behavior, in which the λ _ex upper limit was 480 nm. These features enable safe sensing and cell tracking applications with a longer excitation wavelength in the visible light region. The potential applications of the synthesized GQDs as fluorescent sensing probes for detecting Cu(II) ions and non-toxic cell imaging under visible light excitation have been demonstrated. This means that sensing and bioimaging can be accomplished in the natural environment with no need for UV excitation. This work provides a reference to researchers in tailoring CNO structures in terms of their inner space to synthesize GQDs with the desired luminescence behavior.

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Fabrication of Titanium Aluminides via Powder-Cored Wire Arc Additive Manufacturing: Microstructural and Mechanical Characterization

Herein, an innovative powder-cored wire arc additive manufacturing (PC-WAAM) process is proposed to fabricate γ-TiAl thin-walled intermetallic alloy. The metallography, phase composition, and mechanical properties at different thin-wall locations are characterized. The results show that the alternatively distributed layer-like microstructure composed of α₂ (Ti₃Al) and γ (TiAl) phases is obtained along the building direction. The content of α₂ phase exhibits the tendency of decreasing from the bottom to top region. This unique microstructure characteristic is closely related to the typical thermal cycling history during deposition. Moreover, the tensile strength and microhardness of the top region are lower than the middle and bottom region. In general, the current PC-WAAM technique shows promising capability of fabricating γ-TiAl intermetallic alloy with low cost. This work becomes a valuable reference for understanding the evolution mechanism of microstructure and paves the way for the flexible and customized additive manufacturing of γ-TiAl alloy.     

一种快速自适应谱估计算法

通过对梯度格型快速自适应算法的研究,结合最大熵谱外推目前存在的缺点,将梯度格型算法应用于最大熵谱外推中,并将其与伯格算法进行了比较。     

On the definition of the intuitionistic fuzzy subgroups

In this paper, a new kind of intuitionistic fuzzy subgroup theory, which is different from that of Ma, Zhan and Davvaz (2008) [22], [23], is presented. First, based on the concept of cut sets on intuitionistic fuzzy sets, we establish the neighborhood relations between a fuzzy point $x_a$ and an intuitionistic fuzzy set $A$. Then we give the definitions of the grades of $x_a$ belonging to $A$, $x_a$ quasi-coincident with $A$, $x_a$ belonging to and quasi-coincident with $A$ and $x_a$ belonging to or quasi-coincident with $A$, respectively. Second, by applying the 3-valued Lukasiewicz implication, we give the definition of $(\alpha ,\beta )$-intuitionistic fuzzy subgroups of a group $G$ for $\alpha ,\beta \in \{\in ,q,\in \wedge q,\in \vee q\}$, and we show that, in 16 kinds of $(\alpha ,\beta )$-intuitionistic fuzzy subgroups, the significant ones are the $(\in ,\in )$-intuitionistic fuzzy subgroup, the $(\in ,\in \vee q)$-intuitionistic fuzzy subgroup and the $(\in \wedge q,\in )$-intuitionistic fuzzy subgroup. We also show that $A$ is a $(\in ,\in )$-intuitionistic fuzzy subgroup of $G$ if and only if, for any $a\in (0,1]$, the cut set $A_a$ of $A$ is a 3-valued fuzzy subgroup of $G$, and $A$ is a $(\in ,\in \vee q)$-intuitionistic fuzzy subgroup (or $(\in ,\in \vee q)$-intuitionistic fuzzy subgroup) of $G$ if and only if, for any $a\in (0,0.5]$(or for any $a\in (0.5,1]$), the cut set $A_a$ of $A$ is a 3-valued fuzzy subgroup of $G$. At last, we generalize the $(\in ,\in )$-intuitionistic fuzzy subgroup, $(\in ,\in \vee q)$-intuitionistic fuzzy subgroup and $(\in \wedge q,\in )$-intuitionistic fuzzy subgroup to intuitionistic fuzzy subgroups with thresholds, i.e., $(s,t]$-intuitionistic fuzzy subgroups. We show that $A$ is a $(s,t]$-intuitionistic fuzzy subgroup of $G$ if and only if, for any $a\in (s,t]$, the cut set $A_a$ of $A$ is a 3-valued fuzzy subgroup of $G$. We also characterize the $(s,t]$-intuitionistic fuzzy subgroup by the neighborhood relations between a fuzzy point $x_a$ and an intuitionistic fuzzy set $A$.