Delayed Newton-based multivariable extremum seeking with sequential predictors

We provide a new method for Newton-based multivariable extremum seeking which allows different delays in each of the input channels. We allow arbitrarily long input delays. Our sequential predictor delay compensation method eliminates the need for the distributed terms that were required in earlier methods. We illustrate our method in a source seeking example

Microscopic characterization of pretransition oxide formed on Zr-Nb-Sn alloy under various Zn and dissolved hydrogen concentrations

Microstructure of oxide formed on Zr-Nb-Sn tube sample was intensively examined by scanning transmission electron microscopy after exposure to simulated primary water chemistry conditions of various concentrations of Zn (0 or 30 ppb) and dissolved hydrogen (H-2) (30 or 50 cc/kg) for various durations without applying desirable heat flux. Microstructural analysis indicated that there was no noticeable change in the microstructure of the oxide corresponding to water chemistry changes within the test duration of 100 days (pretransition stage) and no significant difference in the overall thickness of the oxide layer. Equiaxed grains with nano-size pores along the grain boundaries and microcracks were dominant near the water/oxide interface, regardless of water chemistry conditions. As the metal/oxide interface was approached, the number of pores tended to decrease. However, there was no significant effect of H-2 concentration between 30 cc/kg and 50 cc/kg on the corrosion of the oxide after free immersion in water at 360 degrees C. The adsorption of Zn on the cladding surface was observed by X-ray photoelectron spectroscopy and detected as ZnO on the outer oxide surface. From the perspective of OH - ion diffusion and porosity formation, the absence of noticeable effects was discussed further

On the continuous and discontinuous precipitation of the L12 phase in Cu-Ni-Al alloys

L12 precipitate hardened Cu-Ni-Al alloys offer high strength, corrosion resistance and anti-biofouling properties, making them useful in marine engineering applications. Optimisation of their mechanical properties requires a full understanding of their complex precipitate nucleation and coarsening mechanisms. In this work, the microstructural characteristics and hardness of three Cu-Ni-Al alloys with compositions of Cu(95-x)NixAl5 (x = 5, 15, 25 at%) were investigated in the homogenised state and following heat treatments at 700˚C for 1, 10, 100 and 1000 hours. L12 precipitates were observed in the alloys containing ≥ 15 at% Ni. In these alloys, the L12 phase was found to precipitate via both continuous and discontinuous routes following all exposures at 700˚C. The coarsening behaviours of the continuous and discontinuous L12 distributions were characterised and correlated to measurements of hardness and lattice misfit. The alloys containing 15 and 25 at% Ni exhibited peak hardness after 1 h at 700˚C, which corresponded to average particle diameters of 30 nm, respectively. These results were rationalised through calculations of the change in the critical resolved shear stress associated with the transition from weakly to strongly coupled superpartial dislocations. The discontinuous reaction was observed to be led by L12 phase formation, which extended into the neighbouring grain, ahead of the reorientation front of the matrix

Sintering and compensation effect of donor- and acceptor-codoped 3mol% Y 2 O 3 -ZrO 2

Addition of ∼0.15–0.5 mol% acceptor oxide, Al 2 O 3 , to 3 mol% Y 2 O 3 -ZrO 2 results in enhanced densification at 1350 °C. The enhancement is accounted for by a liquid phase sintering mechanism. The addition of donor oxide, Ta 2 O 5 , of 0.15–2.5 mol % at 1300–1600 °C results in the destabilization of tetragonal (t-) phase and the decrease of final density in 3 mol% Y 2 O 3 -TZP (tetragonal ZrO 2 polycrystals). X-ray diffractometry (XRD) reveals that the Ta 2 O 5 -added 3 mol% Y 2 O 3 -ZrO 2 contains monoclinic (m-) ZrO 2 and a second phase of Ta 2 Zr 6 O 17 . The decreasing in final density is attributed to the increase of m-ZrO 2 content. Complete destabilization of t-ZrO 2 to m-ZrO 2 in samples added with 2.5 mol% Ta 2 O 5 is interpreted by the compensation effect based on donor- and acceptor-codoping defect chemistry.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44714/1/10853_2005_Article_BF01166021.pd

Backstepping observer design for parabolic PDEs with measurement of weighted spatial averages

This paper is concerned with the observer design for one-dimensional linear parabolic partial differential equations whose output is a weighted spatial average of the state over the entire spatial domain. We focus on the backstepping approach, which provides a systematic procedure to design an observer gain for systems with boundary measurement. If the output is not a boundary value of the state, the backstepping approach is not directly applicable to obtaining an observer gain that stabilizes the error dynamics. Therefore, we attempt to convert the error system into another system to which backstepping is applicable. The conversion is successfully achieved for a class of weighting functions, and the resultant observer realizes exponential convergence of the estimation error with an arbitrary decay rate in terms of the L2 norm. In addition, an explicit expression of the observer gain is available in a special case. The effectiveness of the proposed observer is also confirmed by numerical simulations