Biomedical subjects

Lei Yuan

Publications and source records attributed to Lei Yuan.

6 recordsLinked to original sources

PubMed2006

Truncation effects in SENSE reconstruction.

Finite sampling is an important practical issue in Fourier imaging systems. Although data truncation effects are well understood in conventional Fourier imaging where a single uniform receiver channel is used for data acquisition, this issue is not yet fully addressed in parallel imaging where an array of nonuniform receiver channels is used for sensitivity encoding to enable sub-Nyquist sampling of k-space. This article presents a systematic analysis of the problem by comparing the truncation effects in parallel imaging with those in conventional Fourier imaging. Specifically, it derives a convolution kernel function to characterize the truncation effects, which is shown to be approximately equal to that associated with the conventional Fourier imaging scheme. This article also describes a set of conditions under which significant differences between the truncation effects in parallel imaging and conventional Fourier imaging occur. The results should provide useful insight into interpreting and reducing data truncation effects in parallel imaging.

Fourier Analysis↗

PubMed2006

Use of a biologically active cover to reduce landfill methane emissions and enhance methane oxidation.

Biologically-active landfill cover soils (biocovers) that serve to minimize CH4 emissions by optimizing CH4 oxidation were investigated at a landfill in Florida, USA. The biocover consisted of 50 cm pre-composted yard or garden waste placed over a 10-15 cm gas distribution layer (crushed glass) over a 40-100 cm interim cover. The biocover cells reduced CH4 emissions by a factor of 10 and doubled the percentage of CH4 oxidation relative to control cells. The thickness and moisture-holding capacity of the biocover resulted in increased retention times for transported CH4. This increased retention of CH4 in the biocover resulted in a higher fraction oxidized. Overall rates between the two covers were similar, about 2g CH4 m(-2)d(-1), but because CH4 entered the biocover from below at a slower rate relative to the soil cover, a higher percentage was oxidized. In part, methane oxidation controlled the net flux of CH4 to the atmosphere. The biocover cells became more effective than the control sites in oxidizing CH4 3 months after their initial placement: the mean percent oxidation for the biocover cells was 41% compared to 14% for the control cells (p<0.001). Following the initial 3 months, we also observed 29 (27%) negative CH4 fluxes and 27 (25%) zero fluxes in the biocover cells but only 6 (6%) negative fluxes and 22 (21%) zero fluxes for the control cells. Negative fluxes indicate uptake of atmospheric CH4. If the zero and negative fluxes are assumed to represent 100% oxidation, then the mean percent oxidation for the biocover and control cells, respectively, for the same period would increase to 64% and 30%.

Air Pollutants↗

PubMed2006

Quantitative analysis of cytochrome C released from rice mitochondria using the adsorptive polarographic wave of guanidine modified Co(II)-cytochrome C complex.

A new, simple and sensitive method for the quantitative analysis of cytochrome C (Cyt C) based on the reduction wave of guanidine modified Co(II)-Cyt C complex at about -1.74 V (vs. SCE) by single sweep polarography in the solution containing 8 x 10(-6) mol L(-1) CoCl2, 0.04 mol L(-1) guanidine hydrochloride, 0.2 mol L(-1) NaOH and 0.5% Na2SO3. The peak height is linearly proportional to the concentration of Cyt C in the range of 0.005 approximately 1.500 mg L(-1) (correlation coefficient 0.999). Common amino acids, saccharide, organic acid and metal ions of appropriate concentrations have no interference on the Cyt C determination. The released Cyt C in the process of mitochondrial permeability transition of Hong-Lian cytoplasmic male sterile line of rice has been measured by the method, and the result is satisfactory.

Amino Acids↗

PubMed2005

XGef mediates early CPEB phosphorylation during Xenopus oocyte meiotic maturation.

Polyadenylation-induced translation is an important regulatory mechanism during metazoan development. During Xenopus oocyte meiotic progression, polyadenylation-induced translation is regulated by CPEB, which is activated by phosphorylation. XGef, a guanine exchange factor, is a CPEB-interacting protein involved in the early steps of progesterone-stimulated oocyte maturation. We find that XGef influences early oocyte maturation by directly influencing CPEB function. XGef and CPEB interact during oogenesis and oocyte maturation and are present in a c-mos messenger ribonucleoprotein (mRNP). Both proteins also interact directly in vitro. XGef overexpression increases the level of CPEB phosphorylated early during oocyte maturation, and this directly correlates with increased Mos protein accumulation and acceleration of meiotic resumption. To exert this effect, XGef must retain guanine exchange activity and the interaction with CPEB. Overexpression of a guanine exchange deficient version of XGef, which interacts with CPEB, does not enhance early CPEB phosphorylation. Overexpression of a version of XGef that has significantly reduced interaction with CPEB, but retains guanine exchange activity, decreases early CPEB phosphorylation and delays oocyte maturation. Injection of XGef antibodies into oocytes blocks progesterone-induced oocyte maturation and early CPEB phosphorylation. These findings indicate that XGef is involved in early CPEB activation and implicate GTPase signaling in this process.

Animals↗

PubMed2004

[Technical improvement of mechanical suture of bronchial stumps in pneumonectomy].

OBJECTIVE: To prevent or reduce such postoperative complications of pneumonectomy as bronchopleural fistula and promote the curative effect of the surgery by improving the technique for handling the bronchial stumps. METHODS: In 107 patients, bronchial stapler was adopted for closure of the bronchial stump and pneumonectomy was subsequently performed on the side of the staples. A 1-0 polyester suture was used to for suture in the shape of "U" deep in the mechanical suture on the bronchial stump. The postoperative complications were observed. RESULTS: The operations were performed easily and the bronchial stumps were short and sutured firmly. No fluid retention or granuloma occurred in the stumps after the operation, nor were the complications such as intractable cough and infection of thoracic cavity observed. No bronchopleural fistula was found in these patients. CONCLUSION: This new method is safe and effective for treatment of the bronchial stumps.

Adolescent↗

PubMed2003

XGef is a CPEB-interacting protein involved in Xenopus oocyte maturation.

XGef was isolated in a screen for proteins interacting with CPEB, a regulator of mRNA translation in early Xenopus development. XGef is a Rho-family guanine nucleotide exchange factor and activates Cdc42 in mammalian cells. Endogenous XGef (58 kDa) interacts with recombinant CPEB, and recombinant XGef interacts with endogenous CPEB in Xenopus oocytes. Injection of XGef antibodies into stage VI Xenopus oocytes blocks progesterone-induced oocyte maturation and prevents the polyadenylation and translation of c-mos mRNA; injection of XGef rescues these events. Overexpression of XGef in oocytes accelerates progesterone-induced oocyte maturation and the polyadenylation and translation of c-mos mRNA. Overexpression of a nucleotide exchange deficient version of XGef, which retains the ability to interact with CPEB, no longer accelerates oocyte maturation or Mos synthesis, suggesting that XGef exchange factor activity is required for the influence of overexpressed XGef on oocyte maturation. XGef overexpression continues to accelerate c-mos polyadenylation in the absence of Mos protein, but does not stimulate MAPK phosphorylation, MPF activation, or oocyte maturation, indicating that XGef may function through the Mos pathway to influence oocyte maturation. These results suggest that XGef may be an early acting component of the progesterone-induced oocyte maturation pathway.

Amino Acid Sequence↗