Finite-Time Stabilization Control for a Rigid Spacecraft under Parameter Uncertainties

A novel finite-time control scheme is investigated for a rigid spacecraft in present of parameter uncertainties and external disturbances. Firstly, the spacecraft mathematical model is transformed into a cascading system by introducing an adaptive variable. Then a novel finite-time attitude stabilization control scheme for a rigid spacecraft is proposed based on the homogeneous method. Lyapunov stability analysis shows that the resulting closed-loop attitude system is proven to be stable in finite time without parameter uncertainties and asymptotically stable with parameter uncertainties. Finally, numerical simulation examples are also presented to demonstrate that the control strategy developed is feasible and effective for spacecraft attitude stabilization mission

Finite-time control for attitude tracking maneuver of rigid satellite

Published version of an article in the journal: Abstract and Applied Analysis. Also available from the publisher at: http://dx.doi.org/10.1155/2014/302982 Open AccessThe problem of finite-time control for attitude tracking maneuver of a rigid spacecraft is investigated. External disturbance, unknown inertia parameters are addressed. As stepping stone, a sliding mode controller is designed. It requires the upper bound of the lumped uncertainty including disturbance and inertia matrix. However, this upper bound may not be easily obtained. Therefore, an adaptive sliding mode control law is then proposed to release that drawback. Adaptive technique is applied to estimate that bound. It is proved that the closed-loop attitude tracking system is finite-time stable. The tracking errors of the attitude and the angular velocity are asymptotically stabilized. Moreover, the upper bound on the lumped uncertainty can be exactly estimated in finite time. The attitude tracking performance with application of the control scheme is evaluated through a numerical example

World J. Microbiol. Biotechnol.

Corn stover is a potential feedstock for biofuel production. This work investigated physical and chemical changes in plant cell-wall structure of corn stover due to hot compressed water (HCW) pretreatment at 170-190 A degrees C in a tube reactor. Chemical composition analysis showed the soluble hemicellulose content increased with pretreatment temperature, whereas the hemicellulose content decreased from 29 to 7 % in pretreated solids. Scanning electron microscopy revealed the parenchyma-type second cell-wall structure of the plant was almost completely removed at 185 A degrees C, and the sclerenchyma-type second cell wall was greatly damaged upon addition of 5 mmol/L ammonium sulfate during HCW pretreatment. These changes favored accessibility for enzymatic action. Enzyme saccharification of solids by optimized pretreatment with HCW at 185 A degrees C resulted in an enzymatic hydrolysis yield of 87 %, an enhancement of 77 % compared to the yield from untreated corn stover.Corn stover is a potential feedstock for biofuel production. This work investigated physical and chemical changes in plant cell-wall structure of corn stover due to hot compressed water (HCW) pretreatment at 170-190 A degrees C in a tube reactor. Chemical composition analysis showed the soluble hemicellulose content increased with pretreatment temperature, whereas the hemicellulose content decreased from 29 to 7 % in pretreated solids. Scanning electron microscopy revealed the parenchyma-type second cell-wall structure of the plant was almost completely removed at 185 A degrees C, and the sclerenchyma-type second cell wall was greatly damaged upon addition of 5 mmol/L ammonium sulfate during HCW pretreatment. These changes favored accessibility for enzymatic action. Enzyme saccharification of solids by optimized pretreatment with HCW at 185 A degrees C resulted in an enzymatic hydrolysis yield of 87 %, an enhancement of 77 % compared to the yield from untreated corn stover

Enhanced saccharification of lignocellulosic biomass with 1-allyl-3-methylimidazolium chloride (AmimCl) pretreatment

1-Allyl-3-methylimidazolium chloride pretreatment is used to enhance biomass saccharification. Softwood, hardwoods, and agricultural wastes were exploited. PW reached as high as 85.4% hydrolysis ratio after IL pretreatment. Biomass structure plays a key role in enzymatic hydrolysis ratio

Experimental Study on Optimal Recycling Mechanical Parameters of Cotton Field Mulch film based on Small Soil Trough System

Film mulching agriculture in arid areas is faced with pollution caused by film mulching, and currently mainly adopts the mechanized recycling of mulch film. However, residual mulch film in the soil will bind with soil under the farming environment, which affects the recycling effect. The main factors affecting the recycling of mulch film in the soil are not clear. In order to find out the specific factors, the actual dry-wet cycle water environment was simulated by using a small soil trough system based on the film lifting, separation and recycling problem of residual mulch film in the soil. The film lifting force and recycling efficiency of the residual mulch film under the action of wet-dry cycle were studied. The following results were obtained: soil compaction, film lifting angle, and the dry-wet cycle had a significant influence on the film lifting force value, indicating that the dry-wet cycle including water fertilizer had an impact on the soil structure. After mechanical loosening, the film lifting force decreased and the recycling rate of residual mulch film increased obviously. The optimal film recycling effect could be obtained under the following conditions, namely, a film lifting angle of 21.37–45.37°, the number of dry-wet cycles <3.8, a soil moisture of 22.43–23.18%, a soil compaction of 132.51–144.06 KPa, and a residual mulch film area of 45.85–64.5 cm2. The experimental results can provide technical reference for residual mulch film pollution control and mechanized recycling

Saccharification of the Pretreated Corn Stover by Microwave Assisted DMSO/AmimCl Co-solvents

In order to enhance the enzymatic saccharification efficiency of corn stover, microwave assisted treatment with dimethyl sulfoxide (DMSO) and 1-ally-3-methylimidazolium (AmimCl) co-solvents was designed to break up the complicated chemical structure of corn stover. The pretreatment conditions were studied to increase the dissolution ratio, extraction ratio and cellulose I crystallinity index (Crl) variation. With the increase of AmimCl concentration, time and temperature of the pretreatment, the dissolution ratio, extraction ratio increased and Crl decreased. Considering the costs of high AmimCl concentration, degradation of biomass at high temperature and long time, the optimum conditions were DMSO/AmimCl co-solvents with a DMSO concentration of 15% (w) and 4 g corn stover per 100 g co-solvents. The optimum temperature and time were 110 degrees C and 60 min, respectively. Under the optimal conditions, the ratios of corn stover dissolution and extraction were as high as 46.6% and 22.9%, respectively. The cellulose saccharification ratio had a great increase within 14 h of enzymatic hydrolysis with an enzyme loading amount of 14 FPU/g solids. The saccharification ratio for the extracts was 71.4% in 14 h, while the ratio was only 12.5% for the raw corn stover in 20 h. Powder X-ray diffraction was used to determine the cellulose crystal structure. The cellulose I crystallinity index of corn stover residues decreased obviously and the crystal form of AmimCl extracts were transformed from I to II. From the SEM pictures of the materials, it could be seen that the outer surface of corn stover residues became rough, which was good for enzyme accessibility and saccharification. The AmimCl extracts had lost their natural status completely. By simple vacuum distillation, AmimCl could be recycled and its solubility kept almost constant. According to H-1 NMR spectroscopy analysis, the structures of fresh and recycled AmimCl were almost the same. From the results mentioned above, it can be concluded that microwave assisted treatment with DMSO AmimCl co-solvents was a feasible method for corn stover pretreatment