Cascaded ELM-Based Joint Frame Synchronization and Channel Estimation over Rician Fading Channel with Hardware Imperfections

Due to the interdependency of frame synchronization(FS)and channel estimation(CE),joint FS and CE(JFSCE)schemes are proposed to enhance their functionalities and therefore boost the overall performance of wireless communication systems.Although traditional JFSCE schemes alleviate the influence between FS and CE,they show deficiencies in dealing with hardware imperfection(HI)and deterministic line-of-sight(LOS)path.To tackle this challenge,we proposed a cascaded ELM-based JFSCE to alleviate the influence of HI in the scenario of the Rician fading channel.Specifically,the conventional JFSCE method is first employed to extract the initial features,and thus forms the non-Neural Network(NN)solutions for FS and CE,respectively.Then,the ELMbased networks,named FS-NET and CE-NET,are cascaded to capture the NN solutions of FS and CE.Simulation and analysis results show that,compared with the conventional JFSCE methods,the proposed cascaded ELM-based JFSCE significantly reduces the error probability of FS and the normalized mean square error(NMSE)of CE,even against the impacts of parameter variations.

Structural Imperfections Associated with Supersaturated Vacancies in an HPHT-Grown Diamond Single Crystal

A diamond single crystal, which was synthesized at a high temperature of 1570 K and a high pressure of 5.5 GPa in a Fe-Ni-C system, was directly and systematically examined by transmission electron microscopy (TEM). It is proposed that there exists a variety of imperfections such as dislocation loops, stacking faults, twins and stacking-fault tetrahedral in the diamond, which may be derived from the supersaturated vacancies generated during rapid cooling from high temperature. The formation process of the imperfections is discussed briefly.

First-principles study of the structural, electronic, and magnetic properties of double perovskite Sr2FeReO6 containing various imperfections

The structural, electronic, and magnetic properties of double perovskite Sr_2FeReO_6 containing eight different imperfections of FeReor ReFeantisites, Fe1–Re1 or Fe1–Re4 interchanges, V_（Fe）, V_（Re）, VOor V_（Sr） vacancies have been studied by using the first-principles projector augmented wave（PAW） within generalized gradient approximation as well as taking into account the on-site Coulomb repulsive interaction（GGA＋U）. No obvious structural changes are observed for the imperfect Sr_2FeReO_6 containing FeReor ReFeantisites, Fe1–Re1 or Fe1–Re4 interchanges, or VSrvacancy defects. However, the six（eight） nearest oxygen neighbors of the vacancy move away from（close to） VFeor V_（Re）（VO） vacancies. The half-metallic（HM） character is maintained for the imperfect Sr_2FeReO_6 containing FeReor ReFeantisites, Fe1–Re4 interchange, V_（Fe）,VO or V_（Sr） vacancies, while it vanishes when the Fe1–Re1 interchange or VRevacancy is presented. So the Fe1–Re1 interchange and the VRevacancy defects should be avoided to preserve the HM character of Sr_2FeReO_6 and thus usage in spintronic devices. In the FeReor ReFeantisites, Fe1–Re1 or Fe1–Re4 interchanges cases, the spin moments of the Fe（Re）cations situated on Re（Fe） antisites are in an antiferromagnetic coupling with those of the Fe（Re） cations on the regular sites. In the V_（Fe）, V_（Re）, VO, or V_（Sr） vacancies cases, a ferromagnetic coupling is obtained within each cation sublattice,while the two cation sublattices are coupled antiferromagnetically. The total magnetic moments μtot（μB/f.u.） of the imperfect Sr_2FeReO_6 containing eight different defects decrease in the sequence of VSrvacancy（3.50）, VRevacancy（3.43）,FeReantisite（2.74）, VOvacancy（2.64）, VFevacancy（2.51）, ReFeantisite（2.29）, Fe1–Re4 interchange（1.96）, Fe1–Re1interchange（1.87）, and the mechanisms of the saturation magnetization reduction have been analyzed.

THE INFLUENCE OF IMPERFECTIONS UPON THE CRITICAL LOAD OF STRUCTURES

By means of the theory of universal unfolding, the influence of multi-imperfections upon the critical load of structure in engineering is analysed in this paper. For the pitchfork problem, a lower bound of increments of the critical loads caused by imperfections of the structures is given. A simple and available numerical method for computing the lower bound is described.

Numerical Analysis of Physical and Geometrical Imperfections in Cellular Beams

Cellular beams are appropriate for large spans with relatively small loads or for conditions in which strain dictates dimensioning. Another important advantage of cellular beams is the possibility of passing utility ducts through the openings, which avoids cutting through the web of the beam or increasing the construction height, which occurs when the ducts pass under the beams. Geometrical imperfections result from a lack of straightness during fabrication of rolled profiles. Geometric imperfections are represented numerically by an initial curvature. Additionally, the physical imperfections of rolled profiles result from the appearance of residual stresses. The condition that creates residual stresses in steel is the result of thermal and mechanical industrial processes. In this study, numerical analyses are performed with cellular beams using Finite Element Method software. During the simulations, through non-linear geometric and physical analyses, geometric imperfections were varied, where lateral torsional buckling in cellular beams was considered as a function of the unrestrained length. In the boundary, conditions were restrained displacements in the axis X, Y, Z and rotation about X-axis, thus simulating the fork support. The beams are submitted to uniform bending and concentrated load. The results from the numerical analyses were compared with the calculation procedures, which verified that the results were significant.

New insight into the stability and dynamics of fluid-conveying supported pipes with small geometric imperfections

In several previous studies,it was reported that a supported pipe with small geometric imperfections would lose stability when the internal flow velocity became sufficiently high.Recently,however,it has become clear that this conclusion may be at best incomplete.A reevaluation of the problem is undertaken here by essentially considering the flow-induced static deformation of a pipe.With the aid of the absolute nodal coordinate formulation(ANCF)and the extended Lagrange equations for dynamical systems containing non-material volumes,the nonlinear governing equations of a pipe with three different geometric imperfections are introduced and formulated.Based on extensive numerical calculations,the static equilibrium configuration,the stability,and the nonlinear dynamics of the considered pipe system are determined and analyzed.The results show that for a supported pipe with the geometric imperfection of a half sinusoidal wave,the dynamical system could not lose stability even if the flow velocity reaches an extremely high value of 40.However,for a supported pipe with the geometric imperfection of one or one and a half sinusoidal waves,the first-mode buckling instability would take place at high flow velocity.Moreover,based on a further parametric analysis,the effects of the amplitude of the geometric imperfection and the aspect ratio of the pipe on the static deformation,the critical flow velocity for buckling instability,and the nonlinear responses of the supported pipes with geometric imperfections are analyzed.

Band structures of transverse waves in nanoscale multilayered phononic crystals with nonlocal interface imperfections by using the radial basis function method

A radial basis function collocation method based on the nonlocal elastic continuum theory is developed to compute the band structures of nanoscale multilayered phononic crystals. The effects of nonlocal imperfect interfaces on band structures of transverse waves propagating obliquely or vertically in the system are studied. The correctness of the present method is verified by comparing the numerical results with those obtained by applying the transfer matrix method in the case of nonlocal perfect interface. Furthermore, the influences of the nanoscale size, the impedance ratio and the incident angle on the cut-off frequency and band structures are investigated and discussed in detail. Numerical results show that the nonlocal interface imperfections have significant effects on the band structures in the macroscopic and microscopic scale.

Analysis on column-bracing forces considering random initial imperfections

A large number of column-bracing systems were modeled and analyzed by second-order analysis using finite element program ANSYS,in which the random combination of the initial imperfections between columns and horizontal braces was well considered by Monte Carlo Method.According to the analysis results,four kinds of instability modes of column-bracing systems were found,the probability density function of the mid-height horizontal bracing forces was established based on probability statistics,and the design bracing forces were also obtained.The results indicated that the above design bracing forces are smaller than that proposed by the "Code for design of steel structures"(GB50017-2003) when the top axial compressions on the braced columns are equal,and much smaller than the latter when the top axial compressions on the braced columns are unequal.The results also indicated that the random combination of the initial imperfections between columns and horizontal braces leads to the randomness of the mid-height horizontal bracing forces in compression or in tension,so that the design bracing forces can be reduced.

Recursive Approximation of Complex Behaviours With IoT-Data Imperfections

This paper presents an approach to recursively estimate the simplest linear model that approximates the time-varying local behaviors from imperfect(noisy and incomplete) measurements in the internet of things(IoT) based distributed decision-making problems. We first show that the problem of finding the lowest order model for a multi-input single-output system is a cardinality(l0) optimization problem, known to be NP-hard.To solve the problem a simpler approach is proposed which uses the recently developed atomic norm concept and the modified Frank-Wolfe(mFW) algorithm is introduced. Further, the paper computes the minimum data-rate required for computing the models with imperfect measurements. The proposed approach is illustrated on a building heating, ventilation, and air-conditioning(HVAC) control system that aims at optimizing energy consumption in commercial buildings using IoT devices in a distributed manner. The HVAC control application requires recursive thermal dynamical model updates due to frequently changing conditions and non-linear dynamics. We show that the method proposed in this paper can approximate such complex dynamics on single-board computers interfaced to sensors using unreliable communication channels. Real-time experiments on HVAC systems and simulation studies are used to illustrate the proposed method.

Simulation of the influence of imperfections on dynamical decoupling of a superconducting qubit

Dynamical decoupling is widely used in many quantum computing systems to combat decoherence. In a practical superconducting quantum system, imperfections can plague decoupling performance. In this work, imperfections in a superconducting qubit and its control system are modeled via modified Hamiltonian and collapse operator. A master equation simulation is carried out on the qubit under 1/f environment noise spectrum. The average dephasing rate of qubit is extracted to characterize the impact of different imperfections on the decoupling from dephasing. We find that the precision of pulse position, on–off ratio, and filtering effect are most critical. Bounded pulses have weaker impact,while variation in pulse width and qubit relaxation are insignificant. Consequently, alternative decoupling protocols, jitter mitigation, cascaded mixers, and pulse shaping can be conducive to the performance of decoupling. This work may assist the analysis and optimization of dynamical decoupling on noisy superconducting quantum systems.

ANALYSIS OF STABILITY ON ELASTIC PLATES WITH INITIAL IMPERFECTIONS

On the basis of Marguerre equations ,the influence on a bifurcation diagram of an elastic plate affected by initial deflection imperfection and transverse loading is studiedwith the help of the singularity theory This paper applies universal unfolding principles,it is put forward that the unstable analysis of this problem can transforminto the study of a triple algebraic equation in the neighborhood of a simple eigenvalue .Thus the bifurcated stated are decided,and the bifurcation diagrams aredrawn up following distinct parameters.Then the quantitative seriesof interfering witheigenvalues are discussed.

Analysis of Stability on Elastic Plates with Initial Imperfections

On the basis of Marguerre equations,the influence on a bifurcation diagram of am elatic plate affected by initial deflection imperfection and transverse loading is studied with the help of the singularity theory .Thes paper applies universal unfoldingprinciples,it is put forward that the unstable analysis of thes problem can transform into the study of a triple algebraic equation in the neighborhood of a simple eigenvalue .Thus the bifurcated states are decided,and the bifurcation diagrams are drawn up following distinct paramentrs. Then the quantitative series of interfering with eigenvalues are discussed.

Probabilistic analysis of secant piles with random geometric imperfections

The failure to achieve minimum design overlap between secant piles compromises the ability of a structure to perform as designed,resulting in water leakage or even ground collapse.To establish a more realistic simulation and provide guidelines for designing a safe and cost-effective secant-pile wall,a three-dimensional model of a secant pile,considering the geometric imperfections of the diameter and direction of the borehole,is introduced.An ultrasonic cross-hole test was performed during the construction of secant piles in a launching shaft in Beijing,China.Based on the test results,the statistical characteristics of the pile diameters and orientation parameters were obtained.By taking the pile diameter D,inclination angleβ,and azimuth angleαas random variables,Monte Carlo simulations were performed to discuss the influence of different design parameters on the probability density functions of the overlap of secant piles.The obtained results show that the randomness of the inclination angle and pile diameter can be well described by a normal distribution,whereas the azimuth angle is more consistent with a uniform distribution.The integrity of the secant-pile wall can be overestimated without considering the uncertainty of geometric imperfections.The failure of the secant-pile wall increases substantially with increasing spatial variability in drilling inclination and diameter.A design flowchart for pile spacing under the target safety level is proposed to help engineers design a safe and economical pile wall.

Power Allocation for SE Maximization in Uplink Massive MIMO System Under Minimum Rate Constraint

In this paper,we optimize the spectrum efficiency(SE)of uplink massive multiple-input multiple-output(MIMO)system with imperfect channel state information(CSI)over Rayleigh fading channel.The SE optimization problem is formulated under the constraints of maximum power and minimum rate of each user.Then,we develop a near-optimal power allocation(PA)scheme by using the successive convex approximation(SCA)method,Lagrange multiplier method,and block coordinate descent(BCD)method,and it can obtain almost the same SE as the benchmark scheme with lower complexity.Since this scheme needs three-layer iteration,a suboptimal PA scheme is developed to further reduce the complexity,where the characteristic of massive MIMO(i.e.,numerous receive antennas)is utilized for convex reformulation,and the rate constraint is converted to linear constraints.This suboptimal scheme only needs single-layer iteration,thus has lower complexity than the near-optimal scheme.Finally,we joint design the pilot power and data power to further improve the performance,and propose an two-stage algorithm to obtain joint PA.Simulation results verify the effectiveness of the proposed schemes,and superior SE performance is achieved.

Effective Capacity of URLLC over Parallel Fading Channels with Imperfect Channel State Information

This paper investigates the effective capacity of a point-to-point ultra-reliable low latency communication(URLLC)transmission over multiple parallel sub-channels at finite blocklength(FBL)with imperfect channel state information(CSI).Based on reasonable assumptions and approximations,we derive the effective capacity as a function of the pilot length,decoding error probability,transmit power and the sub-channel number.Then we reveal significant impact of the above parameters on the effective capacity.A closed-form lower bound of the effective capacity is derived and an alternating optimization based algorithm is proposed to find the optimal pilot length and decoding error probability.Simulation results validate our theoretical analysis and show that the closedform lower bound is very tight.In addition,through the simulations of the optimized effective capacity,insights for pilot length and decoding error probability optimization are provided to evaluate the optimal parameters in realistic systems.

Influence of manufacturing process-induced geometrical defects on the energy absorption capacity of polymer lattice structures

Modern additive manufacturing processes enable fabricating architected cellular materials of complex shape,which can be used for different purposes.Among them,lattice structures are increasingly used in applications requiring a compromise among lightness and suited mechanical properties,like improved energy absorption capacity and specific stiffness-to-weight and strength-to-weight ratios.A dedicated modeling strategy to assess the energy absorption capacity of lattice structures under uni-axial compression loading is presented in this work.The numerical model is developed in a non-linear framework accounting for the strain rate effect on the mechanical responses of the lattice structure.Four geometries,i.e.,cubic body centered cell,octet cell,rhombic-dodecahedron and truncated cuboctahedron 2+,are investigated.Specifically,the influence of the relative density of the representative volume element of each geometry,the strain-rate dependency of the bulk material and of the presence of the manufacturing process-induced geometrical imperfections on the energy absorption capacity of the lattice structure is investigated.The main outcome of this study points out the importance of correctly integrating geometrical imperfections into the modeling strategy when shock absorption applications are aimed for.

NUMERICAL INVESTIGATION OF INFLUENCING PARAMETER OF IMPERFECTIONS ON THIN SHORT CARBON STEEL CYLINDRICAL SHELL UNDER AXIAL COMPRESSION

Thin cylindrical shell structures have wide variety of applications due to their favorable stiffness-to-mass ratio and under axial compressive loading,these shell structures fail by their buckling instability.Hence,their load carrying capacity is decided by its buckling strength which in turn predominantly depends on the geometrical imperfections present on the shell structure.The main aim of the present study is to determine the more influential geometrical parameter out of two geometrical imperfection parameters namely,“the extent of imperfection present over a surface area”and its“amplitude”.To account for these geometrical parameters simultaneously,the imperfection pattern is assumed as a dent having the shape of extent of surface area as a nearly square.The side length of extent of surface area can be considered as proportional to extent of imperfection present over an area and the dent depth can be considered as proportional to amplitude of imperfections.For the present numerical study,FE models of thin short carbon steel perfect cylindrical shells with different sizes of dent are generated at 1/3rd and half the height of cylindrical shells and analyzed using ANSYS nonlinear FE buckling analysis.

Secure Short-Packet Transmission in Uplink Massive MU-MIMO Assisted URLLC Under Imperfect CSI

Ultra-reliable and low-latency communication(URLLC)is still in the early stage of research due to its two strict and conflicting requirements,i.e.,ultra-low latency and ultra-high reliability,and its impact on security performance is still unclear.Specifically,short-packet communication is expected to meet the delay requirement of URLLC,while the degradation of reliability caused by it makes traditional physical-layer security metrics not applicable.In this paper,we investigate the secure short-packet transmission in uplink massive multiuser multiple-inputmultiple-output(MU-MIMO)system under imperfect channel state information(CSI).We propose an artificial noise scheme to improve the security performance of the system and use the system average secrecy throughput(AST)as the analysis metric.We derive the approximate closed-form expression of the system AST and further analyze the system asymptotic performance in two regimes.Furthermore,a one-dimensional search method is used to optimize the maximum system AST for a given pilot length.Numerical results verify the correctness of theoretical analysis,and show that there are some parameters that affect the tradeoff between security and latency.Moreover,appropriately increasing the number of antennas at the base station(BS)and transmission power at user devices(UDs)can increase the system AST to achieve the required threshold.

Remaining useful life prediction based on nonlinear random coefficient regression model with fusing failure time data

Remaining useful life(RUL) prediction is one of the most crucial elements in prognostics and health management(PHM). Aiming at the imperfect prior information, this paper proposes an RUL prediction method based on a nonlinear random coefficient regression(RCR) model with fusing failure time data.Firstly, some interesting natures of parameters estimation based on the nonlinear RCR model are given. Based on these natures,the failure time data can be fused as the prior information reasonably. Specifically, the fixed parameters are calculated by the field degradation data of the evaluated equipment and the prior information of random coefficient is estimated with fusing the failure time data of congeneric equipment. Then, the prior information of the random coefficient is updated online under the Bayesian framework, the probability density function(PDF) of the RUL with considering the limitation of the failure threshold is performed. Finally, two case studies are used for experimental verification. Compared with the traditional Bayesian method, the proposed method can effectively reduce the influence of imperfect prior information and improve the accuracy of RUL prediction.

Numerical Study on Lateral Buckling Mode of Pipelines Laid on A Sleeper

Because non-buried submarine pipelines under cyclic thermal loading are prone to global buckling,sleepers are commonly laid along the pipeline route to induce a series of relatively small and controllable lateral buckling.A finite element model which can simulate the transformation of pipeline laid on a sleeper from vertical buckling to lateral buckling is established in this work.The parameters of sleeper affecting pipeline buckling modes are analysed,and a new kind of sleeper is proposed aimed at avoiding antisymmetric buckling.Results show that the lateral trigger force can avoid antisymmetric lateral buckling when acting between 1℃and 13℃before the critical buckling temperature.The range increases slightly with increasing trigger force.Compared with an ordinary sleeper,the proposed new sleeper with slider can reduce the critical buckling temperature by 25%,which significantly improves the success rate of sleepers.