ABSTRACT
The conventional tracking control of mechanical systems is generally based on the stabilization of error dynamics and most of the results can only guarantee asymptotic tracking of the desired trajectories. Since error dynamics are generally time-varying, it is very difficult to find appropriate Lyapunov functions or control Lyapunov functions to complete stability analysis and controller design. To address this limitation, the novel constructive exponential tracking control method is proposed to mechanical systems by utilizing the Hamiltonian realization and contraction analysis in this paper. Firstly, based on the Hamiltonian realization and use the structural characteristics of port-Hamiltonian systems, the exponential tracking controllers are constructed for fully actuated and under-actuated mechanical systems by combining the pre-feedback with feedback control. The proposed tracking control strategies can be used to discuss fully actuated and under-actuated mechanical systems in a unified framework. Then the exponential decay-rate of tracking controllers and procedure for selecting control parameters for fully actuated and under-actuated mechanical systems are given. Finally, comparative simulations and experiments are carried out to illustrate the effectiveness and robustness of the proposed control strategy.
ABSTRACT
BACKGROUND: To conduct an in vitro investigation into the effect of different concentrations of levocetirizine hydrochloride on the growth of human dermal papilla cells (hDPCs) the underlying mechanisms involved. METHODS: hDPCs were cultured in Dulbecco's Modified Eagle Medium (DMEM) containing different concentrations of levocetirizine hydrochloride for 48 h. The growth of hDPCs was observed by immunofluorescence staining, and the cell proliferation was detected by MTT assay. After the hDPCs were cultured in DMEM containing 1, 10, 100, 1,000, and 10,000 ng/mL levocetirizine hydrochloride for 48 h, the mRNA expressions of cyclooxygenase 2 (COX-2), prostaglandin D2 synthase (PTGDS), prostaglandin E2 (PGE2), prostaglandin F2α (PGF2α), G protein-coupled receptor 44 (GPR44), protein kinase B (AKT), and glycogen synthase kinase 3ß (GSK3ß) were determined by real-time fluorescence-based quantitative polymerase chain reaction (PCR), and the protein expressions of PTGDS, phosphorylated protein kinase B (pAKT), and phosphorylated glycogen synthase kinase 3ß (pGSK3ß) were detected by Western blotting. After the hDPCs were cultured in DMEM containing 1, 10, 100, 1,000, 10,000 ng/mL levocetirizine hydrochloride for 24 h, the secretion levels of prostaglandin D2 (PGD2) and PGD2 receptor (PGD2R) in the culture supernatant were determined by enzyme-linked immunosorbent assay (ELISA). One-way analysis of variance (ANOVA) was performed using SPSS 17.0 software, and the LSD-t test was used for pairwise comparisons. RESULTS: Immunofluorescence staining showed that hDPCs in the 100 ng/mL group grew well, with over 90% confluency. Methyl thiazolyl tetrazolium (MTT) method showed that the proliferation rate of hDPCs significantly differed between different levocetirizine hydrochloride groups and the blank control group (F=42.22, P<0.05), while the proliferation rate was significantly higher in the 100 ng/mL group (115.80%±5.10%) than in the blank control group (100%) (t=28.26, P<0.05). The relative mRNA expressions of COX-2, PGF2a, PTGDS, GPR44, and AKT showed significant differences in different levocetirizine hydrochloride groups (the F values were 1.97, 3.66, 2.17, 2.66, and 7.32, respectively; all P<0.05), whereas the mRNA expressions of PGE2 and GSK3ß showed no significant difference (F=0.87, F=1.19, respectively; both P>0.05). The mRNA expressions of COX-2, PTGDS, and GPR44 in the 100 ng/mL group (0.840.08, 0.810.10, and 0.85±0.09, respectively) were significantly lower than those in the blank control group (t=1.97, t=2.17, and t=2.65, respectively; all P<0.05), whereas the mRNA expressions of PGF2α and AKT in the 100 ng/mL group (1.96±0.25 and 1.74±0.32, respectively) were significantly higher than those in the blank control group (t=3.662 and t=7.325, respectively; both P<0.05). There were significant differences in the levels of PTGDS, pAKT, pGSK3ß, PGD2, and PGD2R proteins between the different levocetirizine hydrochloride groups (the F values were 11.84, 3.89, 4.07, 66.15, and 44.33, respectively). The protein expressions of PTGDS, PGD2, and PGD2R in the 100 ng/mL group (0.32±0.05, 141.62±5.44, and 215.08±9.55, respectively) were significantly lower than those in the blank control group (0.73±0.06, 180.08±6.15, and 273.24±3.18, respectively) (the t values were 5.66, 45.07, and 92.05, respectively; all P<0.05), whereas the protein expressions of pAKT and pGSK3ß in the 100 ng/mL group (0.59±0.05 and 0.46±0.03, respectively) were significantly higher than those in the blank control group (0.46±0.02 and 0.35±0.042, respectively) (t=16.59, t=7.73, respectively; both P<0.05). CONCLUSIONS: Levocetirizine hydrochloride may promote the growth and proliferation of hDPC in vitro by inhibiting the PGD2-GPR44 pathway and activating the AKT signaling pathway.
