Fault-Tolerant Control for a Class of Uncertain Systems with Actuator Faults

The problem of fault-tolerant controller design for a class of polytopic uncertain systems with actuator faults is studied in this paper. The actuator faults are presented as a more general and practical continuous fault model. Based on the affine quadratic stability (AQS), the stability of the polytopic uncertain system is replaced by the stability at all corners of the polytope. For a wide range of problems including H∞ and mixed H 2 /H∞ controller design, sufficient conditions are derived to guarantee the robust stability and performance of the closed-loop system in both normal and fault cases. In the framework of the linear matrix inequality (LMI) method, an iterative algorithm is developed to reduce conservativeness of the design procedure. The effectiveness of the proposed design is shown through a flight control example.     

Doping inorganic ions to regulate bioactivity of Ca –P coating on bioabsorbable high purity magnesium

Performance of biomaterials was strongly affected by their surface properties and could be designed artificially to meet specific biomedical requirements. In this study, F(F), Si O2 4(Si), or HCO 3(C)-doped Ca–P coatings were fabricated by biomimetic deposition on the surface of biodegradable high-purity magnesium(HP Mg). The crystalline phases, morphologies and compositions of Ca–P coatings had been characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and energy-dispersive spectroscopy(EDS). The biomineralization and corrosion resistance of doped Ca–P coatings had also been investigated. The results showed that the Ca–P coating with or without doped elements mainly contained the plate-like dicalcium phosphate dehydrate(DCPD) phase. The doped F, Si, or C changed the surface morphology of Ca–P coatings after mineralization. Doped F enhanced the mineralization of Ca–P coating, and doped Si retarded the mineralization of Ca–P coating.However, H2 evolution of HP Mg discs with different Ca–P coatings was close to 0.4–0.7 ml/cm2 after two-week immersion. That meant that the corrosion resistance of the Ca–P coatings with different or without doped elements did not change significantly.     

A Note on Trace Polynomial

In this paper, we mainly study the relation of two cyclically reduced words w and w ′on the condi- tion they have the same trace polynomial (i.e., tr w= trw ′). By defining an equivalence relation through such operators on words as inverse, cyclically left shift, and mirror, it is straightforward to get that w ~ w ′ implies tr w = tr w ′. We show by a counter example that tr w = tr w ′ does not imply w ~ w ′. And in two special cases, we prove that tr w = tr w ′ if and only if w ~ w ′.     

Modeling the hot working behavior of near-α tita nium alloy IMI 834

The hot working behavior of near-a titanium alloy IMI 834 with a duplex starting microstructure was studied using the technique of processing map.The processing map was interpreted in terms of the microstrucmral processes occurring during deformation,based on the values of dimensionless parameter η which represents the energy dissipation through microstructural processes.An instability criterion（ξ<0） was also applied to demarcate the flow instability regions in the processing map.Both the parameters（η and ξ） were computed using the experimental data generated by carrying out hot compression tests over a range of temperatures（850-1060℃） and strain rates(3×10^-4-1/s).The deterministic domains observed under the investigated temperature and strain rate conditions were attributed to continuous dynamic recrystallization or globularisation of a lamellae,dynamic recrystallization and growth of β grains through microstructural observations.An unified strain compensated constitutive equation was established to describe the hot working behavior of the material in the selected temperature-strain rate range.The established constitutive equation was validated using standard statistical parameters such as correlation coefficient and average absolute relative error.     

Microstructure evolution and mechanical properties of Ti-8Nb-2Fe-0.2O alloy with high elastic admissible strain for orthopedic implant applications

A Ti-8Nb-2Fe-0.2O(wt.%) alloy with high strength,high elastic admissible strain(δ) and low cost was designed using d-electron theory combined with electron-to-atom ratio(e/a) approach.Interstitial oxygen was introduced to strengthen the matrix of the alloy.The β-solution treated alloy was mainly composed of α " martensite with internal {111}_(α") type Ⅰ nano-twins.The α " martensite with hexagonal-like crystal structure caused by interstitial oxygen showed a high strength of 1.1 GPa but limited ductility.The alloy generated equiaxed fine-grained a phase embedded by β matrix via hot rolling and subsequent annealing in α+β phase field.The obtained alloy indicated a good combination of mechanical properties with ultimate tensile strength,Young's modulus,ductility and δ value of 1029 MPa,74 GPa,21% tensile elongation and 1.32%,respectively.These findings demonstrate that interstitial oxygen and martensitic nano-twins can be used to strengthen the soft α" martensite and high elastic admissible strain can be obtained by formation of equiaxed fine-grained α phase embedded by βmatrix in this Ti-8Nb-2Fe-0.2O alloy for orthopedic implant.     

Periodicity-dependent long range coulomb on-site repulsion in hydrogen adsorbed graphene:A DFT+U study

The long rang Coulomb on-site repulsion between u electrons in hydrogen (H) adsorbed graphene has been studied based on DFT+U calculations.This study demonstrates that the rigidity of n electronic structure of graphene is partially destroyed in the cases of H adsorption due to the introduction of un-paired electron in this system.The softness of n conjugation is largely depending on the concentrations as well as the periodicity of H adsorption.Due to the destruction of the rigidity of n conjugation,the Coulomb on-site repulsion increases.The results show that the Coulomb on-site repulsion between n electrons is very sensitive to the periodicity of H adsorption.A considerable enhancement of Coulomb on-site repulsion occurs for the systems with 3n×3n peroidcity.More importantly,the strength and the patterns of Coulomb on-site repulsion in the graphene plane are significantly size-dependent,which further induces the band gap opening at Fermi level.Especially for 6 x 6 system,the on-site repulsion induces a stabilized non-ferromagnetic state.Our results reveal for the first time that the considerable long rang Coulomb onsite repulsion between n electrons exists which plays an important role in the electronic characteristics of H adsorbed graphene.The finding in this investigation provides new insight into the many-body interaction between localized impurities with delocalized n electrons in graphene related materials.     

Microstructure/texture evolution maps to optimize hot deformation process of near-α titanium alloy

The microstructure/texture evolution(MTE,for short) map and processing map of a new near a titanium alloy Ti65 were constructed in order to investigate the workability and microstructure evolution of hot deformation.The processing map illustrated four domains,two summit domains and two instability domains.The morphologies of the a phase changed from the spheroidization(α+β region) to the deformed and elongated β grains(near the βtransus temperature T_β),and then to the obvious dynamic recrystallization(DRX)(β region) with the temperature rising from 930 ℃ to 1140℃.Deformation in the α+β field mainly generated the texture component with [0001]or [0223] parallel to radial directions(RDs).While deformation in the β phase field formed two types of texture component with [0001] parallel to RDs and [2110] parallel to compression direction.An optimized processing map was summarized by overlaying the macro-instability map on the original processing map,and the instability domain of Ti65 alloy was confirmed in the area with the strain rate higher than 0.01 s~(-1).     

Thermal shock resistance and crack growth behavior of Aurivillius phase Bi_4Ti_3O_(12)-based ferroelectric ceramics

A type of W/Cr co-doped Bi_4Ti_3O_(12)(ab. BTWC) ceramics were synthesized utilizing the traditional solid-state reaction process, and its thermal shock resistance(TSR) as well as the crack growth behavior was systematically investigated by water quenching technology. It can be found by the succeeded fractographic analysis that many edge thermal cracks began to appear in the samples subjected to thermal shock with ΔT=400°C. According to an integrated TSR model, the critical thermal-shock temperature difference ΔTCwas calculated to be 356°C. Moreover, it can be noticed that the indenter induced crack growth behaviors under thermal shock loads presented three stages, i.e. no growth, large growth, and moderate growth, along with ΔT increasing from 0°C to 700°C. Finally, the asymmetry of P-E hysteresis loops was observed and understood by the orientated polarization of defect dipoles after the sample was thermally shocked, while the water-quenching process above the Curie temperature of the ceramics could lead to a random orientation of the defect dipoles. This research can not only evaluate the service conditions of Bi_4Ti_3O_(12) high-temperature piezoceramics, but also understand the failure mechanism of bismuth layer structured ferroelectric ceramics in the case of thermal shock.     

Bioinspired and hydrophobic alkyl-silanized protective polymer coating for Mg alloy

The modification of silica coating surfaces by trimethylsilylation has contributed to enhanced hydrophobicity(θ_w~o90°)against fluid permeation and corrosion in Na Cl.These alkyl-silanized coatings were deployed to protect Mg alloy after reinforcing their internal structures with nanosilica powder.The reduced wetness of coating surfaces is attributed to their chemically-modified surface morphology,and this has been compared to the reticulate leaf structures of lotus plant.The optimum amount of silylating additive(hexamethyldisilazane)required to prepare a hydrophobic coating with minimum water adhesion has been established.Barrier performance of coatings were examined by electrochemical and surface analyses in 5 wt%Na Cl.The corrosion resistance of these coatings is a result of the direct contribution of their bulk stability and surface hydrophobicity,and this is expressed in terms of the variation of electrochemical parameters with exposure time.These coatings may have emerging industrial applications,including a future in metal surface treatments and anticorrosion paints.     

Evolutions of diffusion activation energy and Zener–Hollomon parameter of ultra-high strength Al-Zn-Mg-Cu-Zr alloy during hot compression

The changes of stress level for the ultra-high strength Al-Zn-Mg-Cu-Zr alloy were described by constitutive equation with considering lattice diffusion of aluminum, zinc, magnesium and copper. Zener–Hollomon(Z)parameter expression based on the constitutive equation with considering lattice diffusion was used to reflect the changes of microstructure. The critical stress σcfor the initiation of dynamic recrystallization(DRX) was introduced to calculate the Z parameter. Steady-state dislocation density ρsatand critical dislocation density ρcfor the initiation of DRX decreased with the increase of deformation temperature. The dependence of diffusion activation energy Q on temperature and strain rate was given and the effects of deformation conditions on Q were discussed in detail. Microstructural evolution revealed that low angle boundaries(2–5°) created in the process of dynamic recovery(DRV) could convert into subgrain boundary, thus the original grains were divided into subgrains, and then subgrains transformed into DRX grains by the way of progressive rotation. When the Z value was high(ln Z 30.9), DRV was the main softening mechanism. With the decrease of Z value, both of DRV and DRX played an important roles in softening effect, while with the further decrease of Z value(ln Z 28.6), DRX became the main softening mechanism. Continuous dynamic recrystallization(CDRX) and discontinuous dynamic recrystallization(DDRX) operated together under the condition of lower Z value, but CDRX was confirmed as the dominant DRX mechanism.     

Effects of Gd solutes on hardness and yield strength of Mg alloys

Relative contribution of individual strengthening mechanisms to the yield strength of Mg–0–15 wt%Gd alloys were investigated.Alloys with different grain size were prepared by adding Zr and hot extrusion.Hardness and tensile/compression yield strength were tested on the alloys after solid solution treatment and extrusion.HallPetch constants were calculated with hardness and tensile/compressive data.The results showed that the hardness of Mg–Gd alloys with similar Gd content and different grain size were almost the same,which indicates that grain size had little effect on hardness.The hardness linearly increased with rising Gd content(d H_v/dc≈25 kg mm~(-2)/at%Gd).The tensile and compressive yield strengths enhanced with the increase of Gd content for all alloys in different conditions.In addition,the tensile/compressive(t/c)yield asymmetry of extruded alloys decreased with increasing Gd content.Large t/c yield asymmetry ratio(1.77)was observed for pure Mg,and with increasing Gd content this value decreased to 1.With the increasing of tensile strength,the stress intensity factor,k_y,decreased from 0.27 MPa m~(1/2)for Mg–2 wt%Gd alloy to 0.19 MPa m~(1/2) for Mg–5 wt%Gd alloy,then increased to 0.29 MPa m~(1/2) for Mg–15 wt%Gd alloy.However,k_yincreased linearly form 0.16–0.31 MPa for compression test.The influence of grain size strengthening was eliminated,and the yield strength of tension and compression both linearly increased with c~n,where c is the atom concentration of Gd,and n=1/2 or 2/3.     

Influence of slip system combination models on crystal plasticity finite element simulation of NiTi shape memory alloy undergoing uniaxial compression

The influence of various slip system combination models on crystal plasticity finite element simulation of Ni Ti shape memory alloy subjected to uniaxial compression deformation is investigated according to three combinations of slip systems, including combination of {010}100and {110}111slip modes, combination of {110}100and {110}111slip modes and combination of {110}100, {010}100and {110}111slip modes, which consist of 18, 18 and 24 slip systems, respectively. By means of simulating mechanical response,strain distribution, stress distribution and Schmid factor, it can be found that in terms of simulation accuracy,combination of {110}100and {110}111slip modes is in good agreement with combination of {110}100,{010}100and {110}111slip modes. The contribution of {110}100slip mode to plastic strain is primary in plastic deformation of Ni Ti shape memory alloy, whereas {010}100slip mode, which makes small contribution to plastic deformation, can be regarded as the unfavorable slip mode. In the case of large plastic strain, the {010}100slip mode contributes to the formation of(001) [010] texture component, while {110}100and {110}111slip modes facilitate the formation of γ-fibre(111) texture.     

Cu-FeOx@AC活化PMS体系除藻效能与机制

为探究富营养化水体中藻类的新型治理技术，通过水热法和高温煅烧法，使颗粒活性炭（AC）表层上负载铜铁双金属氧化物Cu-FeO_x，制得可回收的Cu-FeO_x@AC复合催化剂。以XRD、SEM、FTIR和XPS对Cu-FeO_x@AC的表征为基础，研究Cu-FeO_x占AC的负载比、过一硫酸盐（PMS）使用量、初始pH及不同反应体系对除藻的影响，探究Cu-FeO_x@AC活化过一硫酸盐体系的除藻效能。Cu-FeO_x@AC活化过一硫酸盐体系反应机理，通过自由基淬灭实验、XPS表征进行探究。结果可知，初始pH为6，初始藻细胞密度为1.4×10⁹个/L，使用催化剂0.5 g/L，PMS 0.2 g/L时，反应90 min，该体系对藻的降解率有97.25%。在该体系中，藻细胞能被吸附在Cu-FeO_x@AC复合催化剂表面，在铜、铁不同价态离子的转换及AC的协同作用下，产生空穴、·O2-、·OH、SO4-·，单线态氧等多种氧化基团而被去除。     

Controllable synthesis,XPS investigation and magnetic property of multiferroic BiMn_2O_5 system: The role of neodyme doping

In this work, a novel series of multiferroic materials BiMn_2O_5 doped by Neodyme has been prepared by a sol-gel method at low temperature. The crystallographic studies using X-ray diffraction and Rietveld Refinement techniques showed the formation of single-phase samples for all compositions, crystallizing in a mullite-type orthorhombic perovskite structure, space group Pbam(Z = 4). The SEM techniques confirmed the formation of single-phase materials with excellent mapping distribution. Raman and infrared spectroscopic measurements were performed and combined with lattice dynamics simulations to describe the room-temperature vibrational properties of all samples. The X-ray Photoelectron Spectroscopy(XPS) were measured in the energy range of 0–1400 eV at room temperature. The Fermi level E_F was defined with the accuracy of 0.127, 0.32 and 0.48 eV for BiMn_2O_5, Bi_(0.9)Nd_(0.1)Mn_2O_5 and Bi_(0.8)Nd_(0.2)Mn_2O_5 respectively. The X-ray photoelectron spectroscopy shows the existence of Mn~(4+) state. Magnetic measurements indicate Neél temperature T_N at 31, 40 and 61 K for BiMn_2O_5,Bi_(0.9)Nd_(0.1)Mn_2O_5 and Bi_(0.8)Nd_(0.2)Mn_2O_5 respectively.     

CoPt-Co hybrid supported on amino modified SiO_2 nanospheres as a high performance catalyst for hydrogen generation from ammonia borane

CoPt-Co hybrids were successfully supported on amino modified SiO_2 nanospheres by a chemical reduction method at a temperature of 278 K.The solid carrier i.e.amino modified SiO_2,provides numerous anchoring sites for the metal nanoparticles(NPs)to improve the dispersion while reducing the size of metal NPs.The supported NPs displayed a narrow particle size distribution on the SiO_2 surface with an average diameter of 12 nm.The XRD results alongside with the binary alloy phase diagram suggest that the resulted NPs are bimetallic,composed of CoPt and amorphous Co.Among the prepared materials,the solid with the specific composition of SiO_2@Pt_(0.1)Co_(0.9)was proved to be effective catalyst for ammonia borane(AB)hydrolysis in aqueous solution.The turnover frequency(TOF)value of the supported nanocatalyst was 25.59mol_(H_2)min~(-1)·mol_M~(-1),almost twice as that of unsupported Pt_(0.1)Co_(0.9)NPs while the activation energy was 37.05 kJ mol~(-1).Furthermore,the SiO_2@Pt_(0.1)Co_(0.9)composite manifested high catalytic activity even after five cycles of reuse.