Transceiver Optimization for Two-Hop AF MIMO Relay Systems With DFE Receiver and Direct Link

In this paper, we consider precoding and receiving matrices optimization for a two-hop amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay system with a decision feedback equalizer (DFE) at the destination node in the presence of the direct source-destination link. By adopting the minimum mean-squared error (MMSE) criterion, we develop two new transceiver design algorithms for such a system. The first one employs an iterative procedure to design the source, relay, feed-forward, and feedback matrices. The second algorithm is a non-iterative suboptimal approach which decomposes the optimization problem into two tractable subproblems and obtains the source and relay precoding matrices by solving the two subproblems sequentially. Simulation results validate the better MSE and bit-error-rate (BER) performance of the proposed algorithms and show that the non-iterative suboptimal method has a negligible performance loss when the ratio of the source node transmission power to the relay node transmission power is small. In addition, the computational complexity analysis suggests that the second algorithm and one iteration of the first algorithm have the same order of complexity. As the first algorithm typically converges within a few iterations, both proposed algorithms exhibit a low complexity order

WeChat Adoption among Older Adults and Urban-Rural Differences in China

At the intersection of social digitization and population aging, the challenge of older adults fitting into digital life is becoming more prominent. To understand how to help older adults adopt digital life, this study builds upon the Technology Acceptance Model (TAM) and developed the Digital Technology Motivation Interaction Model (DTMIM) to study the complex effects of autonomous motivation (perceived usefulness, perceived ease of use, perceived enjoyment), controlled motivation, and digital feedback on WeChat adoption among older adults, as well as the urban-rural differences. The results of the questionnaire survey and Fuzzy-set Qualitative Comparative Analysis (fsQCA) show that: First, no single construct is a necessary condition for a high (non-high) attitude toward using (ATU) or high (non-high) actual using (AU). Second, we identified two configurations that trigger high ATU including the autonomy-motivation type and digital feedback under motivational synergy, and three configurations that enable high AU including motivational synergy type, digital feedback under autonomous extrinsic motivation, and digital feedback under motivational synergy. Third, the configurations of high ATU and high AU show significant differences between urban and rural areas. Autonomy motivation plays a universal role in urban older adults’ WeChat adoption, while digital feedback is critical for rural older adults. The configuration analysis of DTMIM and urban-rural differences is not only an adaptive improvement of TAM but also provides new methods and perspectives for future research on the adoption of digital technology

Effects of Grazing Management on Grassland Production and Animal Performance

Five grazing treatments with a set of design for evaluation of seasonal grazing influencing grassland conditions and animal performance have been conducted across northern and western China, in order to identify the key solutions for degradation of grazing grasslands. Here, the effects of seasonal grazing within two systems-one based on current ‘survival’ practices and the other taking more of a ‘production’ focus in Bashang grasslands were reported. The experiment involved a factorial combination of alternative practices (survival vs. production systems) in spring, summer and autumn with a layout of 15 plots and 1.5 ha per plot. Results of consecutive two years studies showed that the vegetation composition changed significantly across grazing treatments, and spring rest treatments can significantly improve grassland production but with low LWG across all grazing seasons. Animal lost live weight on all grazing treatments in autumn indicating that the quality of grassland was lower and need supplementary feed in this season. In the meantime, the average LWG is lowest across the whole grazing season in the continuous survival grazing treatments, but highest in the continuous production treatment. In conclusion, spring rest is most important for grassland quality maintenance, and the continuous production grazing is more appropriate for animal production

A unified constitutive model for asymmetric tension and compression creep-ageing behaviour of naturally aged Al-Cu-Li alloy

A set of unified constitutive equations is presented that predict the asymmetric tension and compression creep behaviour and recently observed double primary creep of pre-stretched/naturally aged aluminium-cooper-lithium alloy AA2050-T34. The evolution of the primary micro- and macro-variables related to the precipitation hardening and creep deformation of the alloy during creep age forming (CAF) are analysed and modelled. Equations for the yield strength evolution of the alloy, including an initial reversion and subsequent strengthening, are proposed based on a theory of concurrent dissolution, re-nucleation and growth of precipitates during artificial ageing. We present new observations of so-called double primary creep during the CAF process. This phenomenon is then predicted by introducing effects of interacting microstructures, including evolving precipitates, diffusing solutes and dislocations, into the sinh-law creep model. In addition, concepts of threshold creep stress σth and a microstructure-dependant creep variable H, which behave differently under different external stress directions, are proposed and incorporated into the creep model. This enables prediction of the asymmetric tension and compression creep-ageing behaviour of the alloy. Quantitative transmission electron microscopy (TEM) and related small-angle X-ray scattering (SAXS) analysis have been carried out for selected creep-aged samples to assist the development and calibration of the constitutive model. A good agreement has been achieved between the experimental results and the model. The model has the potential to be applied to creep age forming of other heat-treatable aluminium alloys

Experimental studies and constitutive modelling of anelastic creep recovery during creep age forming

This paper presents a study of anelastic creep recovery during creep-ageing of an aluminium alloy AA7050-TAF. Uniaxial Creep-Ageing and Recovery Test (CART) was used to characterise the influence of anelastic creep strain on total creep deformation for determining the actual amount of springback in creep age forming (CAF) process. CART was performed on aluminium alloy AA7050-TAF at 174°C between the stress levels of 137.5 to 162.5 MPa. A constitutive model was developed for the prediction of the creep-ageing and recovery response of material in creep age forming. A 'back stress' variable was used to represent the net effect of the internal stresses of the material which causes anelastic creep recovery. Other microstructural variables were introduced to model complex micro-mechanisms and hardening effects including solid solution hardening, dislocation hardening, and age hardening. It has been found that the permanent strain after creep-ageing depends not only on total creep strain but also on anelastic strain. Simulation results from the constitutive model developed in this study show a good agreement with experimental data

The development of ovary in quail’s embryo

The experiment was conducted to study the development of ovary in quails’ embryos which were incubated for 4 to 17 days and incubated out for 1 day. The quails’ embryos or gonads were cut out and HE staining was carried out. The results showed that when embryo was hatched for 4 days, lots of primordial germ cells (PGCs) clustered in the region where gonad would be formed. On the 5th day of hatching, the gonad of the embryo began to be formed and exhibited the feature of ovary or testis. On the 7th hatching day, the right ovary began to degenerate, just a few PGCs began to differentiate into oogonia. On the 10th day, there were many oogonia in the ovary, some of which were surrounded by some other cells distributed like circles. On the 11th day, there were more oogonia, the skinniness became thicker while the medulla was thinner. On the 13th day, the division between skinniness and medulla was obvious and the ovary formed the early original ovum. On the 14th day, more original ovums were seen in the skinniness. On the 17th hatching day and on the 1st day of hatching out, the shape of ovary tended to be mature, also the ovum was clear and more; the medulla was full of vessels. On the 5th hatching day, gonad began to differentiate. On the 7th hatching day and later, thedifferentiation of gonad was obvious; the right ovary began to degenerate. On the 13th hatching day, early original ovum began to be formed in the skinniness of ovary. The results established groundwork for the research of the development of gonads of quail and other poultry.Key words: Quail, embryo, gonad, ovary

3D Trajectory Optimization for Energy-Efficient UAV Communication: A Control Design Perspective

This paper studies the three-dimensional (3D) trajectory optimization problem for unmanned aerial vehicle (UAV) aided wireless communication. Existing works mainly rely on the kinematic equations for UAV's mobility modeling, while its dynamic equations are usually missing. As a result, the planned UAV trajectories are piece-wise line segments in general, which may be difficult to implement in practice. By leveraging the concept of state-space model, a control-based UAV trajectory design is proposed in this paper, which takes into account both of the UAV's kinematic equations and the dynamic equations. Consequently, smooth trajectories that are amenable to practical implementation can be obtained. Moreover, the UAV's controller design is achieved along with the trajectory optimization, where practical roll angle and pitch angle constraints are considered. Furthermore, a new energy consumption model is derived for quad-rotor UAVs, which is based on the voltage and current flows of the electric motors and thus captures both the consumed energy for motion and the energy conversion efficiency of the motors. Numerical results are provided to validate the derived energy consumption model and show the effectiveness of our proposed algorithms

Dominant Physicochemical Properties of SF6/N2 Thermal Plasmas with a Two-temperature Chemical Kinetic Model

It's increasingly clear that the existence of thermodynamic equilibrium is an exception rather than the role in SF6/N2 thermal plasmas. We intended to investigate the dominant physicochemical properties of SF6/N2 thermal plasmas at 4  atm from 12000 K to 1000 K with considering the thermal non-equilibrium. A two-temperature chemical kinetic model containing all the available reactions is developed. The temperature difference between the electron and the heavy species is defined as a function of the electron number density. The molar fractions of species are compared to the equilibrium composition predicted by Gibbs free energy minimization. By analyzing the main reactions in the generation and loss of a dominant species, the chemistry set is simplified and characterized by a few species and reactions. Then, the dominant physicochemical properties are captured and the computing time of complicated chemical kinetic model is dramatically shortened at the same time