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Articles by J. Liu
Total Records ( 8 ) for J. Liu
  X. Zou , Z. Deng , M. Ge , G. Dick , W. Jiang and J. Liu
  In order to obtain crustal deformations of higher spatial resolution, existing GPS networks must be densified. This densification can be carried out using single-frequency receivers at moderate costs. However, ionospheric delay handling is required in the data processing. We adapt the Satellite-specific Epoch-differenced Ionospheric Delay model (SEID) for GPS networks with mixed single- and dual-frequency receivers. The SEID model is modified to utilize the observations from the three nearest dual-frequency reference stations in order to avoid contaminations from more remote stations. As data of only three stations are used, an efficient missing data constructing approach with polynomial fitting is implemented to minimize data losses. Data from large scale reference networks extended with single-frequency receivers can now be processed, based on the adapted SEID model. A new data processing scheme is developed in order to make use of existing GPS data processing software packages without any modifications. This processing scheme is evaluated using a sub-network of the German SAPOS network. The results verify that the new scheme provides an efficient way to densify existing GPS networks with single-frequency receivers.
  J. Liu
  High-rate GPS positioning has been recognized as a powerful tool in estimating epoch-wise station displacement which is particularly useful for seismology. In this study, station displacements during the 12 May 2008 Mw 8.0 Wenchuan earthquake are derived from the 1-Hz GPS data collected at a set of stations in China. The impacts of integer ambiguity resolution and station environment-dependent effects are investigated in order to yield more accurate results. The position accuracy of horizontal components of better than 1 cm suggests that GPS can sense the rapid position oscillation of about 2 cm in amplitude. Temporal and spatial analysis is applied to the surface displacement at station XANY and the characteristics of the movements due to Rayleigh and Love waves are detected and discussed. The comparison of GPS-derived displacement with relevant synthetic data computed based on a recently published rapture model shows a reasonable agreement in waveform. The various differences in amplitude need further investigation and also imply that rapture inversion might be improved if GPS-derived displacement is assimilated.
  W. L St. Peter , Q Fan , E Weinhandl and J. Liu
 

Background and objectives: A secondary analysis of the Dialysis Clinical Outcomes Revisited (DCOR) trial suggested that sevelamer reduced hospitalizations relative to calcium-based phosphate binders. However, whether changed medical costs associated with reduced hospitalizations or other medical services offset the higher cost of sevelamer is unclear. This DCOR secondary analysis aimed to (1) evaluate Medicare total, inpatient, outpatient, skilled nursing facility, and other costs in sevelamer-treated versus calcium-treated patients; (2) examine Medicare costs in specific categories to determine cost drivers; and (3) estimate and incorporate sevelamer and calcium binder costs.

Design, setting, participants, & measurements: DCOR trial participants were linked to the Centers for Medicare & Medicaid Services ESRD database. Medicare costs for 1895 dosed Medicare-primary-payer participants were evaluated. Phosphate binder costs were incorporated. Costs were indexed to 2001 (study base year). Sensitivity analyses were performed with randomized participants, two follow-up periods, and 2004 as index year.

Results: Inflation-adjusted Medicare per member per month (PMPM) costs were lower for sevelamer-treated than for calcium-treated participants by a mean differential of $199 PMPM (mean, $5236 versus $5435; median, $4653 versus $4933), mainly because of lower inpatient costs for the sevelamer group (mean, $1461 versus $1644; median, $909 versus $1144). However, after phosphate binder costs were incorporated, costs trended lower for calcium-treated than for sevelamer-treated patients (differential –$81, 95% confidence interval –$321 to $157 PMPM, using average wholesale price; –$25, –$256 to $213 PMPM, using wholesale acquisition cost).

Conclusions: Sevelamer reduced inpatient Medicare costs compared with calcium binders. However, when binder costs were added, overall PMPM costs favored calcium-treated over sevelamer-treated participants.

  J. Liu , H. Gao and Z. Deng
  For optimizing wheel configuration of planetary rover, the effect analysis of straight grousers on motion performance of a small rigid wheel was conducted in loose sand bin. All tests were done at a free wheel sinkage and 0 to 60% slip in a single-wheel test bed. By the qualitative analysis and comparisons of tractive and steering performance between smooth wheel and the wheels with different straight grousers, the results show that the grouser height and slip more significantly influence the motion performance than grouser spacing and thickness. Through applying the evaluation indexes of tractive and steering performance to the experimental results, the preferable grouser parameters for actual applications are 15° grouser spacing, 10 mm grouser height and 1.5 mm grouser thickness; the optimum value of wheel slip is 13% for the similar sand used in the experiment.
  J. Liu , J. Hua , B. Liu , F. Chen and L. Meng
  With the rapid development of wireless communications, there will be many communication standards in the future, which may cost much to buy the corresponding vector microwave signal generator. Hence, this study investigated a novel vector microwave signal generation method, which modeled the vector baseband signal by the CAD software (Agilent ADS) and then control the conventional microwave signal generation hardware to output vector microwave signals. Compared with the specified vector microwave signal generator developed by Agilent, Anritsu, etc., our software-controllable microwave signal source is cheaper, more flexible and more convenient. Moreover, as an application of our method, we model and realize the TD-SCDMA baseband signal corrupted by multipath channel and Additive White Gaussian Noise (AWGN) in ADS software and then control the hardware (Agilent E4432B) to generate the TD-SCDMA microwave signals. The measurements of the TD-SCDMA microwave signals approve the validity of our method.
  X. Mao , Y. Xu , J. Liu , H. Ma and R. Gao
  In this paper, we develop an algorithm for tracking the center of swarm systems to a desired trajectory by using the sliding-mode control method. The algorithm is robust with respect to system perturbations and external disturbance. Simulation further shows the effectiveness very well.
  T Yu , W. G Junger , C Yuan , A Jin , Y Zhao , X Zheng , Y Zeng and J. Liu
 

Shockwaves elicited by transient pressure disturbances are used to treat musculoskeletal disorders. Previous research has shown that shockwave treatment affects T-cell function, enhancing T-cell proliferation and IL-2 expression by activating p38 mitogen-activated protein kinase (MAPK) signaling. Here we investigated the signaling pathway by which shockwaves mediate p38 MAPK phosphorylation. We found that shockwaves at an intensity of 0.18 mJ/mm2 induce the release of extracellular ATP from human Jurkat T-cells at least in part by affecting cell viability. ATP released into the extracellular space stimulates P2X7-type purinergic receptors that induce the activation of p38 MAPK and of focal adhesion kinase (FAK) by phosphorylation on residues Tyr397 and Tyr576/577. Elimination of released ATP with apyrase or inhibition of P2X7 receptors with the antagonists KN-62 or suramin significantly weakens FAK phosphorylation, p38 MAPK activation, IL-2 expression, and T-cell proliferation. Conversely, addition of exogenous ATP causes phosphorylation of FAK and p38 MAPK. Silencing of FAK expression also reduces these cell responses to shockwave treatment. We conclude that shockwaves enhance p38 MAPK activation, IL-2 expression, and T-cell proliferation via the release of cellular ATP and feedback mechanisms that involve P2X7 receptor activation and FAK phosphorylation.

  W Xu , L Yi , Y Feng , L Chen and J. Liu
 

Pancreatic phospholipase A2 (phospholipase A2 group 1B, G1B) belongs to the superfamily of secreted phospholipase A2 (PLA2) enzymes. G1B has been proposed to be a potential target for diseases such as hypertension, obesity, and diabetes. Human pancreatic prophospholipase A2 (pro-hG1B) is activated by cleavage of the first seven-residue propeptide (phospholipase A2 propeptide, PROP). However, questions still remain on the mode of action for pro-hG1B. In this work, we expressed pro-hG1B in Pichia pastoris and determined the crystal structure at 1.55-Å resolution. The x-ray structure demonstrates that pro-hG1B forms a trimer. In addition, PROP occupies the catalytic cavity and can be self-cleaved at 37 °C. A new membrane-bound surface and activation mechanism are proposed based on the trimeric model of pro-hG1B. We also propose a new autoproteolytic mechanism for pro-hG1B by the reaction triad Asp49-Arg0-Ser(-2) that is similar to the serine protease catalytic triad.

 
 
 
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