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Biomedical subjects

X M Meng

Publications and source records attributed to X M Meng.

16 recordsLinked to original sources
PubMed2006

Photoconductive characteristics of single-crystal CdS nanoribbons.

The photoconductive characteristics of CdS single nanoribbons were investigated. The device characteristics, including spectral response, light intensity response, and time response, were studied systematically. It is found that CdS nanoribbon has the response speed substantively faster than those ever reported for conventional film and bulk CdS materials and the size of nanoribbons has a significant influence on the response speed with smaller CdS nanoribbons showing higher response speed. The high photosensitivity and high photoresponse speed are attributable to the large surface-to-volume ratio and high single-crystal quality of CdS nanoribbons and the reduction of recombination barrier in nanostructures. Measurements in a different atmosphere demonstrate that the absorption of ambient gas (mainly oxygen) can significantly change the photosensitivity of CdS nanoribbons through trapping electrons from the nanoribbons.

Crystallization↗
PubMed2005

Interfacial study of cubic boron nitride films deposited on diamond.

We have studied the nucleation and growth of cubic boron nitride (cBN) films deposited on silicon and diamond-coated silicon substrates using fluorine-assisted chemical vapor deposition (CVD). These comparative studies substantiate that the incubation amorphous/turbostratic BN layers, essential for the cBN nucleation on silicon, are not vital precursors for cBN nucleation on diamond, and they are inherently eliminated. At vastly reduced critical bias voltage, down to -10 V, cBN growth is still maintained on diamond surfaces, and cBN and underlying diamond crystallites exhibit an epitaxial relationship. However, the epitaxial growth is associated with stress in the cBN-diamond interfacial region. In addition, some twinning of crystallites and small-angle grain boundaries are observed between the cBN and diamond crystallites because of the slight lattice mismatch of 1.36%. The small-angle grain boundaries could be eliminated by imposing a little higher bias voltage during the initial growth stage. The heteroepitaxial growth of cBN films on different substrate materials are discussed in the view of lattice matching, surface-energy compatibility, and stability of the substrate against ion irradiation.

Journal Article↗
PubMed2004

Visualization of diamond nucleation and growth from energetic species.

The mystery of diamond nucleation by energetic species is resolved via a special deposition scheme. The evolution of the precursor material for diamond nucleation and the development of the nanodiamond crystallites are visualized by high resolution electron microscopy and other spectroscopies. The diamond precipitation and growth are explained in terms of our recently proposed mechanism [Science 297, 1531 (2002)]]: (i) precipitation of sp(3) clusters a small fraction of which are perfect diamond; (ii) growth of diamond crystallites by preferential displacement of amorphous carbon atoms leaving diamond atoms intact. This general scheme is applicable to other materials such as cubic boron nitride.

Journal Article↗
PubMed2001

[Killing effect of human pulmonary adenocarcinoma cells with TK + CD/5-Fc + GCV coexpression suicide gene systems].

OBJECTIVE: To investigate the different killing effect to human pulmonary adenocarcinoma cell line cells GLC-82 with coexpressed double suicide genes compared with single gene. METHODS: Recombinant expression vectors containing CD (cytosine deaminase) and/or TK (thymidine kinase) gene under CMV promoter were constructed successfully. The vectors were transfected to GLC-82 tumor cell lines by use of lipofectamine. The clones were picked out after G418 selection. Extraneous gene integration and expression were confirmed by PCR and semi-quantitative RT-PCR. The cytotoxicity to these transgenic cells under treatment with 5-Fc and GCV were measured by MTT assays. RESULTS: Double and single suicide gene transfer were both stably expressed in GLC-82 cells. The cytotoxic effects of co-expressed TK-CD genes were superior than that of the single gene. CONCLUSION: The CD + TK/5-Fc + GCV co-expression system is more effective for killing effect of tumor cells than CD/5-Fc or TK/GCV system alone.

Cell Line, Tumor↗
PubMed1996

Image segmentation and bright contrast spot localization of the high resolution atomic image.

Some basic quantitative analysis techniques of digitized high resolution atomic image are developed in this paper. We describe how to divide the atomic image into small independent areas with special structure information by the valley mesh segmentation method. The procedure is with regard to the bright contrast spot segmentation of atomic images. We suggest several ways for bright contrast spot localization in images. Calculation routines for peak detection and weighted local position average methods for this purpose are given.

Microscopy, Electron↗
PubMed1995

[Applied study on MRI diagnosis of the oral and maxillofacial masses.].

38 cases of Oral and Maxillofacial masses were selected to be studied by MRI,combined with fine neddle aspiration cytologic examination,compared with CT scan.The authors thought that MRI was clear,high resolving power of soft tissue,able to find out the bone infiltration of the Oral Maxillofacial masses and hemangioma or lymphoangioma etc,those which were suspected to invade the crania base,tip of orbit,pterygopalatine fossa,parapharyngeal,the vital blood vessel of the neck,primary study on MRI supervising local recur after the maxillofacial tumors being resected was also done.

English Abstract↗
PubMed1992

Functional compartments in the portal system. An experimental study.

The pressure of the portal trunk, the left gastric vein, the left and right gastroepiploic veins, the mesenteric vein and the abdominal aorta was measured experimentally at the same time in 10 normal dogs. The levels of the raised pressure in the different compartments with their outflow tracts obstructed respectively were observed and the potentials of the functional barriers between these compartments were quantitatively evaluated. The findings showed that the average power of the functional barriers was 45.1 +/- 5.7% between the different compartments in the gastrosplenic area and 74.3% in the mesenteric region. The weakness of the functional barriers' capacity limiting the collateral diversion between the lesser and greater splanchnic systems may be one of the causes making the distal splenorenal shunt lose its selectivity.

Animals↗
PubMed1991

[Mechanism of damage to erythrocytes after burn injury in rat--changes in lipid peroxidation, antioxidant function and sulfhydryl groups].

Thermal burn on the back of rat (20% TBSA full-thickness burn) was used to study the changes in free radicals and lipid peroxidation and function of the antioxidation of erythrocytes postburn. It was found that there were increase in the concentration of lipid peroxides and decrease in activity of glutathione peroxidase (GSHpx) in plasma. The activity of RBC GSHpx increased significantly on day 1 postburn. When RBC GSHpx could not resist the injury, the function of antioxidation decreased, such as the activities of G6PD, GSHpx and the concentration of GSH and NPSH. RBC LPO increased, which cross-linked with sulfhydryl proteins and inflicted injury to RBC membrane. It might be concluded that the mechanism of damage of RBC after burn injury is due to chain reactions of free radicals and lipid peroxidation of the cell membrane. It also proved that there were changes in functional capability of antioxidation in vivo after burn injury. Further study is needed to locate the site of production of free radicals within or/and in the neighborhood of RBC and elucidate the transfer of the messages which cause the change.

Animals↗
PubMed1980

Studies on the ultrastructure of envelope of elementary bodies of Chlamydia trachomatis.

Electron microscopy of purified Chlamydia trachomatis treated by various physical and chemical means shows that the envelope of the elementary bodies (EB) consists of the outer cell wall layer, the inner cell wall layer, and the inner membrane. The outer cell wall layer is mainly made up of granular subunits arranged in a hexagonal pattern and may be called the "mural structural protein layer". It forms together with the inner cell wall layer the rigid cell wall. The inner or protoplasmic membrane is not easily shown in the young EB. In the negatively stained specimen, a frail and easily removable superficial layer is seen adhering to the "mural structural protein layer". But in ultra-thin sections this superficial layer is not shown separately. There are fold-like grooves which are special structures probably related to reproduction. There are seen some EB's in binary fission, and a number of bodies very big in size yet having morphological characteristics of the EB's, which are in various processes of multiplication, such as binary fission, budding, and "multicentered germination". These observations give a challenge to the current opinion that only the initial bodies have the power of reproduction.

Cell Membrane↗
PubMedDate not supplied

Two components of long-term depression are impaired by chronic lead exposure in area CA1 and dentate gyrus of rat hippocampus in vitro.

Previous studies have demonstrated that low-level lead exposure can impair the induction of long-term depression (LTD) in area CA1 and dentate gyrus (DG) of rat hippocampus in vitro and in vivo. The induction of LTD in area CA1 and DG has been shown to associate with N-methyl-D-aspartate receptors (NMDARs) and voltage-gated calcium channel (VGCC). In this study, the relative contributions of NMDARs-dependent and VGCC-dependent components in the induction of LTD in the hippocampus and the impairments of these two components of LTD by chronic low-level lead exposure were investigated. Neonatal Wistar rats were exposed to lead from parturition to weaning via milk of dams drinking 0.2% lead acetate solution. Field excitatory postsynaptic potentials (EPSPs) were recorded in area CA1 and DG before and after two 15-min trains of 1-Hz low-frequency stimulation (LFS) (2x900 pulses). In area CA1, the amplitude of NMDARs-dependent LTD (NMDA-LTD), in the presence of 10 microM nimodipine (a blocker of L-type Ca(2+) channels), was 80.05+/-2.54% (n=8) and 94.58+/-10.57% (n=8) in the control and lead-exposed rats, respectively. The amplitude of VGCC-dependent LTD (VGCC-LTD), in the presence of 50 microM (-)-2-amino-5-phosphonopentanoic acid (AP5), was 80.36+/-4.08% (n=10) and 93.91+/-7.85% (n=10) in the control and lead-exposed rats, respectively. In area DG the amplitude of NMDA-LTD, with both 50 microM Ni(2+) (a blocker of T-type Ca(2+) channels) and 10 microM nimodipine present, in the control rats (79. 97+/-4.30%, n=8) was significantly larger than that in the lead-exposed rats (91.24+/-11.08%, n=10, P<0.001). The amplitude of VGCC-LTD, with 50 microM AP5 present, was significantly larger in the control rats (70.80+/-3.64%, n=9) than that in the lead-exposed rats (87.60+/-9.00%, n=10, P<0.001). The results suggested that chronic lead exposure affected two components of LTD induction in area CA1 and DG. Furthermore, the impairment of two components by lead exposure might be similar in area CA1, while the impairment of VGCC-LTD might be more serious in DG of hippocampus.

2-Amino-5-phosphonovalerate↗
PubMedDate not supplied

Effects of lead exposure on long-term potentiation induced by 2-deoxy-D-glucose in area CA1 of rat hippocampus in vitro.

Chronic developmental lead exposure is known to be associated with cognitive dysfunction in children. Previous studies have demonstrated that chronic lead exposure could impair the induction and maintenance of long-term potentiation induced by high-frequency stimulation (HFS-LTP). In area CA1 of rat hippocampus, long-term potentiation could also be induced following temporary replacement of 10 mM 2-deoxy-D-glucose (2-DG) for 10 mM glucose in the normal perfusate (artificial cerebrospinal fluid). The present study was carried out to investigate whether chronic lead exposure affected long-term potentiation induced by 2-DG (2-DG-LTP). Neonatal Wistar rats were exposed to lead from parturition to weaning via milk of dams whose drinking water contained 0.2% lead acetate. Field excitatory postsynaptic potentials (EPSPs) in area CA1 of hippocampus were recorded on postnatal days 25-30. 2-DG application was followed by an increase in EPSP slopes in a time-course-dependent manner in both control and lead-exposed rats, while the amplitude of 2-DG-LTP in the lead-exposed rats (225.9+/-19.0%, n=12) was significantly greater than that in controls (155.2+/-9.8%, n=12). In contrast to the effects of lead exposure on 2-DG-LTP, the amplitude of HFS-LTP in the lead-exposed rats (121.5+/-13.7%, n=12) was significantly less than that in controls (183.9+/-18.6%, n=12). These results indicate that chronic lead exposure had opposite effects on the two types of LTP induced by HFS and 2-DG. This would suggest that the effects of lead on HFS-LTP and 2-DG-LTP are the result of different sites of lead toxicity.

Animals↗