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Biomedical subjects

G Z Yao

Publications and source records attributed to G Z Yao.

10 recordsLinked to original sources
PubMed2004

Characterization of vibration and acoustic noise in a gradient-coil insert.

High-speed switching of current in gradient coils within high magnetic field strength magnetic resonance imaging (MRI) scanners results in high acoustic sound pressure levels (SPL) in and around these machines. To characterize the vibration properties as well as the acoustic noise properties of the gradient coil, a finite-element (FE) model was developed using the dimensional design specifications of an available gradient-coil insert and the concentration of the copper windings in the coil. This FE model was then validated using experimentally collected vibration data. A computational acoustic noise model was then developed based on the validated FE model. The validation of the finite-element analysis results was done using experimental modal testing of the same gradient coil in a free-free state (no boundary constraints). Based on the validated FE model, boundary conditions (supports) were added to the model to simulate the operating condition when the gradient-coil insert is in place in an MRI machine. Vibration analysis results from the FE model were again validated through experimental vibration testing with the gradient-coil insert installed in the MRI scanner and excited using swept sinusoidal time waveforms. The simulation results from the computational acoustic noise model were also validated through experimental noise measurement from the gradient-coil insert in the MRI scanner using swept sinusoidal time waveform inputs. Comparisons show that the FE model predicts the vibration properties and the computational acoustic noise model predicts the noise characteristic properties extremely accurately.

Acoustics↗
PubMed1994

Connection ensemble model of local neural circuits.

A connection ensemble model (CEM) of local neural circuits in central nervous system (CNS) is proposed in this work. Neuronal interactions are investigated at two levels, i.e. the synaptic connection between single neurons and the macro-connections between different neuronal groups. The efficacy of macro-connection is quantitatively determined by the efficacies of constituent synapses, and is asymptotically stable. This model provides a reasonable description for the functional invariance of local neural circuits with structural diversities, which is a widely observed fact in neurobiology. It is expected that the works in CEM model would enrich the current research in neural dynamics.

Animals↗
PubMed1993

Effects of combined administration of FK 506 and the purine biosynthesis inhibitors mizoribine or mycophenolic acid on lymphocyte DNA synthesis and T cell activation molecule expression in human mixed lymphocyte cultures.

Our objective was to obtain new information on the in vitro antilymphocytic action of the cytokine synthesis inhibitor FK 506 and the purine biosynthesis inhibitors mycophenolic acid (MPA; the active moiety of RS61443) and mizoribine (MZB) when used alone or in combination. When added at the initiation of six-day human mixed lymphocyte cultures (MLC), FK 506, MPA or MZB exhibited dose-dependent inhibition of T-lymphocyte DNA synthesis. FK 506, however, was 100-fold more potent than MPA, and 10,000-fold more potent than MZB. Combination of FK 506 with either MPA or MZB, each at suboptional concentrations, produced no more than additive inhibitory effects on 3H thymidine incorporation. Two-colour flow cytometric analysis of lymphocytes revealed that none of the drugs affected cell surface activation molecule expression (CD25 = IL-2R 55 kD alpha-chain, HLA-DR or CD71 = transferrin receptor [TR]) on allostimulated CD4+ or CD8+ cells harvested at three days of culture. By day six, however, all three agents, at levels which markedly inhibited proliferation, suppressed the expression of activation markers on both CD4+ and CD8+ cells. Also at day six, inhibition of activation molecule expression on CD4+ cells was achieved with the combination of FK 506 and either MPA or MZB at concentrations which, on their own, were ineffective. These data provide new, additional information on the in vitro antilymphocytic action of FK 506, MPA and MZB when used alone and in combination.

Cells, Cultured↗
PubMed1993

Neural wave representation in early vision.

The neural wave representation which describes spatiotemporal information in early vision is proposed in terms of extended Gabor functions in this paper. Its reasonability, completeness and uncertainty in spatiotemporal domains and their frequency domains were investigated. The ranges of these parameters in this representation were estimated on electrophysiological and psychophysical data. We derived the partial differential equations which the neural wave satisfied. The general significance of 3D neural wave representation has been explored.

Animals↗
PubMed1988

Pregnancy interruption with RU 486 in combination with dl-15-methyl-prostaglandin-F2 alpha-methyl ester: the Chinese experience.

In a multicenter study taking place in four centers in Beijing (People's Republic of China), pregnancies up to 49 days of amenorrhea (DA) were interrupted with RU 486 (RU 38486, mifepristone, 600 mg orally once), followed 36-60 hours later by administration of dl-15-methyl-PGF 2 alpha-methyl ester (PG05, 1 mg vaginal suppository). One-hundred-and-sixty women were included in the study, three of whom being excluded from efficacy assessment because of non-compliance to the protocol. Complete pregnancy interruption without additional surgical procedure (success) was obtained in 136 women (86.6%, 95% confidence interval: 81.3-91.9%). The success rate was significantly (P = 0.013) higher for pregnancies below (91.3%), than for pregnancies above 42 days of amenorrhea (DA) (76.6%). The time elapsed between RU 486 intake and complete expulsion was 2.8 +/- 1.5 (sd) days (range: 1-12 days). Expulsion took place at the latest 4 days after RU 486 in 125 women (94.7%), and in 107 of these women, it occurred 3.1 +/- 1.7 (sd) hours after PG05 administration. Uterine bleeding occurred in all women after RU 486 intake whatever the outcome of treatment and lasted 11.5 +/- 4.8 (sd) days (range: 3-36 days). It was judged more or much more abundant than usual periods in 6.15% of the women. It led to a slight but significant decrease in hemoglobin as measured eight and 14 days after RU 486 intake. In five women, hemoglobin decreased by 4 g/dl or more, but no patient required a blood transfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

A randomized comparative clinical evaluation of the Steel Ring, the VCu200 and the TCu220c IUDs.

A randomized comparative clinical study of the Steel Ring, VCu200 and TCu220c IUDs was carried out in Beijing. Six-hundred subjects were recruited and each group of 200 was inserted with one of the three devices. The TCu220c and the VCu200 had statistically significantly lower pregnancy and expulsion rates at one and two years of use than the Steel Ring. However, the Steel Ring consistently had the lowest rate of removal for pain and/or bleeding. At two years, the early differences of use-related discontinuation and continuation between the higher rates of the Steel Ring and the lower rates of the VCu200 and TCu220c were significantly reduced. There were no statistically significant differences of net event rates between VCu200 and TCu220c.

Adult↗