Design and Implementation of a TDD-Based 128-Antenna Massive MIMO Prototype System

Owing to the dramatic mobile IP growth,the emerging Internet of Things,and cloud-based applications,wireless networking is witnessing a paradigm shift.By fully exploiting spatial degrees of freedom,massive multiple-input-multiple-output(MIMO) systems promise significant gains in data rates and link reliability.Although the research community has recognized the theoretical benefits of these systems,building the hardware of such complex systems is a challenge in practice.This paper presents a time division duplex(TDD)-based 128-antenna massive MIMO prototype system from theory to reality.First,an analytical signal model is provided to facilitate the setup of a feasible massive MIMO prototype system.Second,a link-level simulation consistent with practical TDDbased massive MIMO systems is conducted to guide and validate the massive MIMO system design.We design and implement the TDDbased 128-antenna massive MIMO prototype system with the guidelines obtained from the link-level simulation.Uplink real-time video transmission and downlink data transmission under the configuration of multiple single-antenna users are achieved.Comparisons withstate-of-the-art prototypes demonstrate the advantages of the proposed system in terms of antenna number,bandwidth,latency,and throughput.The proposed system is also equipped with scalability,which makes the system applicable to a wide range of massive scenarios.

Morphological Heredity of Intermetallic Nb_(5)Si_(3)Dendrites in Hypereutectic Nb-Si Based Alloys via Non-Equilibrium Solidification

For hypereutectic Nb-Si based alloys,primary Nb_(5)Si_(3)phases typically grow in a faceted mode during equilibrium or near-equilibrium solidification,which damages the ductility and toughness.To address this issue,here we artificially manipulate the growth morphology of Nb_(5)Si_(3)using electron beam surface melting(EBSM)and subsequent annealing treatments.Results show that such a non-equilibrium solidification pathway enables the transition from faceted growth to non-faceted dendritic growth of Nb_(5)Si_(3),along with evident microstructure refinement,generation of metastableβ-Nb_(5)Si_(3)phases and elimination of chemical segregation.The transformation fromβ-Nb_(5)Si_(3)toα-Nb_(5)Si_(3)and Nb solid solution(Nbss)particles is triggered by the annealing treatment at 1450°C for 5 h.Also,we find the annealing-mediated formation of inherited Nb_(5)Si_(3)dendrites that maintain the dendritic morphology of the original as-solidifiedβ-Nb_(5)Si_(3)dendrites.This work thus provides a feasible routine to obtain thermally stable and refinedα-Nb_(5)Si_(3)dendrites in hypereutectic Nb-Si based alloys.

Study on Freshmen’Metacognitive Knowledge of Business English-Majors in English Writing

Based on the investigation of freshmen’metacognitive knowledge of business English-majors in English writing,the results show that:(1)the metacognitive subject knowledge of business English freshmen is at the middle level,the metacognitive task knowledge is at a high level,the strategy of seeking teachers'help is at a high level,and the use of other strategies is at a middle or lower level;(2)There is no significant differences between high and low group learners in their views on Chinese writing level and in their strategies of seeking help from classmates;(3)Multiple regression analysis shows that the main factors affecting English writing achievement are the views on writing standard,the utilization of strategies in writing process and strategies of seeking help from teachers.

On the Necessity and Significance of Strengthening Business English Teachers' Scientific Research Capability

This research reviews the construction process of business English teachers in China,and puts forward the notion that business English teachers should establish correct scientific research concept,correctly understand the dialectical relationship between scientific research capability and teaching,the role of scientific research capability and the necessity for teachers to carry out scientific research in teaching.Business English teachers should realize the deficiency of their own scientific research capability,and the necessity of strengthening it.They should learn to combine scientific research theory with teaching practice.Business English teachers in different colleges and universities should learn how to improve their research capability according to reality.Only in this way can they improve their understanding of the necessity of strengthening their scientific research capability and promoting their own professional quality as well as improving students’learning ability and cultivating high-level business English personnel for the society.

The Effective Path of the Connotative Development in Higher Education

At present,higher education in China has entered the stage of popularization,and the"connotative development of higher education"has become the inevitable choice for the development of colleges and universities in China.In the process of"connotative development"in higher education,we must realize the importance of discipline construction and optimize discipline layout and specialty construction,improve the quality of personnel trained by colleges and universities in order to satisfy the needs of social and economic development.On this basis,colleges and universities should,according to the market demand for talents,reform and innovate the talent training mode,continuously strengthen the construction of teaching staff,improve the quality of classroom teaching,effectively improve students'social practice capability,improve the quality of talent training,and take a connotative development path through school-enterprise cooperation and integration of production and teaching.

Review and Reflection on Business English Translation Researches in China

This research analyzes business English translation articles published in Chinese Translators Journal,Shanghai Journal of Translators and Chinese Science and Technology Translators journal from 2000 to 2019.The result shows that descriptive and applied articles occupy the dominant position in all business English translation research articles.By comparison,the number of business English theoretical research articles is relatively less than the former two types of articles.In addition,the number of business English translation research articles published in recent years shows a downward trend.Compared with the descriptive and applied research of business English,there is still much room for further improvement in the theoretical research of business English Translation.In addition,research methodologies of business English translation need to be further standardized,and the research content needs to be further innovated.

Landslide Damming Threats Along the Jinsha River,China

The 2280 km long Jinsha River has been blocked at least four times in the past 30 years.A landslide dam-ming hazard chain can endanger communities and infrastructures hundreds of kilometers downstream from the damming site in alpine gorges.Past damming events have resulted in severe consequences,demanding a thorough assessment of damming threats along the entire Jinsha River.This study digitizes the Jinsha River and visualizes its topographic,tectonic,hydrologic,and climate characteristics in detail.A two-stage full-probability method is proposed for assessing the damming threats along this river,mak-ing it possible to identify potential damming hotspots and high-priority zones for hazard mitigation.It is found that the upper reach of the Jinsha River poses the greatest damming threat,and the threat level gradually decreases downstream.Approximately 33.4%,36.7%,20.5%,and 9.4%of the entire length of the Jinsha River are classified as low,moderate,high,and very high threat levels,respectively.Compared with existing hydropower projects,future projects in the upper reach are more likely to be exposed to landslide damming.We highlight the value of basin-scale spatial threat analysis and envisage that our findings will promote more targeted local-scale risk assessments for potential damming hot-spots.These outcomes provide the basis for managing the risks of river damming and hydropower infras-tructure along the Jinsha River.

A Novel High-Entropy Amorphous Thin Film with High Electrical Resistivity and Outstanding Corrosion Resistance

This study explores a novel WNbMoTaV high-entropy thin film(HETF)in amorphous structure via pulsed laser deposition system.The formation of amorphous structure of this high-entropy alloy is ascribed to the high cooling rate during the deposition process.The HETF shows a smooth surface with a height fl uctuation of less than 13 nm.This film has a high electrical resistivity of~320.6μΩ·cm and a low corrosion current density of 0.088μA/cm 2.The corrosion resistance of the HETF at ambient temperature is superior to the conventional AISI 316 L stainless steel.The high electrical resistivity and excellent corrosion resistance of the HETF are mainly attributed to its chemical disorder,cocktail effect and homogeneous amorphous structure.This experimental phenomenon not only provides a basis for the preparation of amorphous alloy films with low glass forming ability by pulsed laser deposition system,also promotes the potential application of WNbMoTaV HETF in the microelectronic components as resistivity sensors.

Modeling and Prediction of Fatigue Properties of Additively Manufactured Metals

Additive manufacturing(AM)has emerged as an advanced technique for the fabrication of complex near-net shaped and lightweight metallic parts with acceptable mechanical performance.The strength of AM metals has been confirmed comparable or even superior to that of metals manufactured by conventional processes,but the fatigue performance is still a knotty issue that may hinder the substitution of currently used metallic components by AM counterparts when the cyclic loading and thus fatigue failure dominates.As essential complements to high-cost and time-consuming experimental fatigue tests of AM metals,models for fatigue performance prediction are highly desirable.In this review,different models for predicting the fatigue properties of AM metals are summarized in terms of fatigue life,fatigue limit and fatigue crack growth,with a focus on the incorporation of AM characteristics such as AM defect and processing parameters into the models.For predicting the fatigue life of AM metals,empirical models and theoretical models(including local characteristic model,continuum damage mechanics model and probabilistic method)are presented.In terms of fatigue limit,the introduced models involve the Kitagawa–Takahashi model,the Murakami model,the El-Haddad model,etc.For modeling the fatigue crack growth of AM metals,the summarized methodologies include the Paris equation,the Hartman-Schijve equation,the NASGRO equation,the small-crack growth model,and numerical methods.Most of these models for AM metals are similar to those for conventionally processed materials,but are modified and pay more attention to the AM characteristics.Finally,an outlook for possible directions of the modeling and prediction of fatigue properties of AM metals is provided.

Synergetic deformation mechanism in hierarchical twinned high-entropy alloys

The mechanical properties of crystalline materials can be efficiently optimized using a hierarchical twinned structure.Conventional deformation mechanisms for coherentΣ3 boundaries generally involve three basic models:cross-slip,partial dislocation step,and full dislocation step.In this study,we report a novel deformation mechanism that allows the co-existence of twin-separation,phase transformations,grain rotation,and cracking,around a triple junction of twin boundaries in a hierarchical twinned highentropy alloy.The deformation mechanisms in the reference high-entropy alloy(Fe-30 Mn-10 Co-10 Cr at.%)were investigated using LAADF-STEM.The triple junction of the hierarchical twinned structure gradually deformed during in-situ strain and showed mechanisms significantly different from that observed in the purely twinned structures.These new mechanisms are referred to as“novel synergetic deformation mechanisms of hierarchical twin boundaries”.Understanding the fundamental mechanisms of the hierarchical twin boundaries under deformation could assist the design of strong and ductile bulk materials with hierarchical twinned structure.

Shear instability in heterogeneous nanolayered Cu/Zr composites

Ultrastrong nanolayered metallic composites are usually subjected to low ductility due to plastic instability during deformation.Here we investigated the shear instability of a newly designed heterogeneous nanolayered Cu/Zr composites by microindentation.The heterogeneity in size was generated by inserting a few thin Cu-Zr bilayers with an individual layer thickness of 2.5-10 nm into the interface region of the Cu/Zr layered composites with an individual layer thickness of 100 nm.The microindentation tests showed that multiple shear bands appeared in the heterogeneous composite with one bilayer,whereas only a single shear band was formed in that with two or three bilayers.Most importantly,the layer strain in the multi-shear band region is much smaller than that in the single-shear band area.For example,the strain of the 100 nm layers within the shear band in the composite with one 10 nm bilayer could reach as low as 2.8,which was less than half of that in the composite with three 10 nm bilayers,i.e.,6.1.These fndings demonstrated that strain delocalization can be achieved through shear band multiplication if an appropriate number of thin bilayers were used as interlayers in the 100 nm Cu/Zr composites.Besides,compared with the homogeneous composite with an individual layer thickness of 100 nm and the bimodal composite which is composed of alternating one 100 nm Cu-Zr bilayer and two 10 nm CuZr bilayers,the heterogeneous composite with one bilayer displayed a higher strength(2.15 GPa)and a favorable resistance to strain localization.

Characterization of Compositionally Complex Hydrides in a Metastable Refractory High-Entropy Alloy

Here,we study the hydride formation in a metastable Ti-33Zr-22Hf-11Ta(at.%)refractory high entropy alloy(RHEA).Deviating to non-equiatomic compositions of RHEAs promotes the formation of transformation-induced plasticity where the body-centered cubic phase transforms to hexagonal close-packed(HCP)phase.It is found that the phase transformation capability assists the hydride formation due to the low solubility of hydrogen within the HCP phase.In this study,hydrogen is charged via electrochemical polishing and the corresponding phase transformation is activated in the metastable RHEAs.The newly formed HCP phase interacts with hydrogen to form a face-centered cubic hydride verified by electron energy loss spectroscopy.This work provides a primary exploration of the formation of compositionally complex metal hydrides in the metastable RHEAs,which are potential candidates for future hydrogen storage material design.

Speech Dictation System Based on Character Recognition

To solve students’ dictation problems, a speech dictation system basedon character recognition is proposed in this paper. The system applied offlinehandwritten Chinese character recognition technology, denoised the imagethrough Gaussian filter, segmented the text through projection method, and convertedthe image to text through OCR technology. The straight line mark in thepicture was detected by Hough transform technology, and then SKB-FSS algorithmand WST algorithm were used for speech synthesis. Experiments show thatthe system can effectively assist students in dictation.

Intelligent Express Delivery System Based on Video Processing

Although the scale of the express industry is large, it is difficult toachieve the function of fully intelligent receiving and sending express. In thispaper, the intelligent express delivery system is proposed based on the imageand video processing technology of OpenCV, the Faster R-CNN object detectionalgorithm and other technologies. Through the depth camera and electronic scale,it can identify the object category, volume and weight of the items placed on thescale by the sender and store the video of the objects packed into the cabinet. Theoverall framework of the systemwas constructed;key technologies were applied torealize the system;the function of the system was tested. The experimental resultsshow that it achieves the intelligent automation of delivery and delivery throughthe integrated express delivery system of intelligent identification and informationtraceability, which promotes the development of express delivery industry.