Biomedical subjects

S B Zhang

Publications and source records attributed to S B Zhang.

At least 37 records · Page 2Linked to original sources

PubMed2002

Bipolar doping and band-gap anomalies in delafossite transparent conductive oxides.

Doping wide-gap materials p type is highly desirable but often difficult. This makes the recent discovery of p-type delafossite oxides, CuM(III)O2, very attractive. The CuM(III)O2 also show unique and unexplained physical properties: Increasing band gap from M(III) = Al,Ga, to In, not seen in conventional semiconductors. The largest gap CuInO2 can be mysteriously doped both n and p type but not the smaller gaps CuAlO2 and CuGaO2. Here, we show that both properties are results of a large disparity between the fundamental gap and the apparent optical gap, a finding that could lead to a breakthrough in the study of bipolarly dopable wide-gap semiconductor oxides.

Journal Article↗

PubMed2002

Spontaneous assembly of perfectly ordered identical-size nanocluster arrays.

A method, by which periodic two-dimensional arrays of identical metal clusters of nanometer size and spacing could be spontaneously obtained by taking advantage of surface mediated clustering, is reported. The versatility of the method is demonstrated for a broad range of metals on Si(111)-(7 x 7) substrates. In situ scanning tunneling microscopy analysis of In clusters, combined with first-principles total energy calculations, unveils unique initial-stage atomic structures of the surface-supported clusters and the vital steps that lead to the success of this method. A strong interaction between the clusters and the surface holds the key to the observed cluster sizes.

Journal Article↗

PubMed2001

Steps on As-terminated Ge(001) revisited: theory versus experiment.

We examine the double-layer B-type steps on As-terminated vicinal Ge(001) surfaces. The currently accepted structure is a chemically inert bulklike structure without any gap state, and with all the chemical bonds of the Ge and As atoms being satisfied. However, we show that the need for optimizing the p(3) pyramidal angles of the threefold coordinated As atoms drives unusual atomic rearrangement. This leads to a more stable reconstruction involving odd-membered (5-7-5) rings at the step edge. Comparison between theoretical and experimental scanning tunneling microscopy images yields excellent agreement.

Journal Article↗

PubMed2001

Hydrogen above saturation at silicon vacancies: H-pair reservoirs and metastability sites.

We propose that hydrogen-passivated multivacancies which appear to be fully saturated with H can actually capture additional H in electrically inactive sites. In silicon, first-principles total energy calculations show that splitting an (m>or=2) multivacancy into a mono- and an (m-1) vacancy provides a low-strain pairing site for H, 0.4 eV per H lower than any known bulk pairing site. This monovacancy ejection mechanism is an excellent candidate for the H reservoir found both in crystalline and amorphous Si. A distinct H pairing on the fully saturated m vacancies, by forming an internal surface Si-Si dimer, provides the final state of light-induced metastable degradation of hydrogenated amorphous silicon.

Journal Article↗

PubMed2001

Control of doping by impurity Cchemical potentials: predictions for p-type ZnO.

Theoretical work has so far focused on the role of host-element chemical potentials in determining defect formation energies that control doping levels in semiconductors. Here, we report on our analysis of the role of the dopant-impurity chemical potential, which depends on the source gas. We present first-principles total-energy calculations that demonstrate a wide variation in the possible effective chemical potential of N. We account in detail for the recent puzzling observations of doping ZnO using N2 and N2O and predict that the use of dilute NO or NO2 gas would resolve the long-standing problem of achieving p-type ZnO.

Journal Article↗

PubMed2001

Nitrogen solubility and induced defect complexes in epitaxial GaAs:N.

Thermodynamic calculation suggests that the formation of bulk GaN pins N chemical potential mu(N)< or =mu(max)(N), resulting in low equilibrium N solubility [N] in bulk GaAs:N. In epitaxial growth, however, a fully relaxed GaN phase cannot form prior to the spontaneous formation of a N-rich layer on the surface. First-principles total-energy calculations show that in the epitaxial regime one can increase mu(max)(N) considerably from equilibrium mu(max)(N) without triggering the spontaneous formation of such a N-rich layer. This enhances [N] by 8 orders of magnitude to about 4% at T = 650 degrees C in agreement with experiments. The dominant defects at high N concentration are qualitatively different from those at low [N].

Journal Article↗

PubMed2001

Function of GATA transcription factors in hydroxyurea-induced HEL cells.

HEL cells, a human erythroleukemia cell line, mainly express the fetal (gamma) globin gene and trace amount of the embryonic (epsilon) globin gene, but not adult (beta) globin gene. Here we show that hydroxyurea (HU) can induce HEL cells to express adult (beta) globin gene and lead these cells to terminal differentiation. Results showed in Gel mobility shift assays that GATA factors could specifically bind to the regulatory elements of human beta-globin gene, including the proximal regulatory element (the beta-promoter) and the distal regulatory elements (the DNase I hypersensitive sites in the LCR, HS2-HS4 core sequences). However, the DNA binding patterns of GATA factors were quite different between HU-induced and uninduced HEL cells. Western-blot analysis of nuclear extracts from both the uninduced and HU-induced HEL cells revealed that the level of GATA-2 transcription factor decreased, whereas the level of GATA-1 transcription factor increased following the time of hydroxyurea induction. Furthermore, using RT-PCR analysis the expression of human beta-globin gene in HU-induced HEL cells could be blocked again when HEL cells were incubated in the presence of antisense oligonucleotides for hGATA-1, suggesting that the upregulation of hGATA-1 transcription factor might be critical for the expression of human beta-globin gene in HU-induced HEL cells.

Cell Differentiation↗

PubMed2001

[A comparative study on cytochemistry between spring and fall peanut seeds].

A comparative study was conducted on cytochemistry of spring and fall crop seeds in peanut cultivars Quanhua No. 10 and Shanyou 71 respectively. Lipids, protein, and polysaccharides in cells of axis and coteledon were simultaneously shown in the Epon812 buried section by means of cytochemistry, and their morphology, quantity and distribution were compared. Embryo cells of spring crop seed develop fully with big cell more vivid contrasting texture and more regularly disposed organelle, but the counterpart cells in fall crop seeds were not as much mature and their organelle arrangement appeared somewhat irregular. In cotyledon storage cells, there were also some difference between spring crop seed and fall crop seed. Cells of spring crop seeds were full of reserves, with more lipid and protein bodies that were closely ranged and extruded with each other. However, the cell structure in fall crop seeds was more loosely arranged, vacuoles had not been filled with protein, but starch grains accumulated more. Therefore, it was shown clearly that spring crop seeds have some advantages over fall crop seeds on production application. Moreover, some cytochemical techniques for demonstration of lipid, polysaccharide and protein in thick resin section and the stain protection were discussed in the paper.

Arachis↗

PubMed2000

[Measurement for relative molecular mass distribution of lignin dispersants].

Gel chromatography was employed to measure relative molecular mass distribution of lignin dispersants. The results show that relative molecular mass distribution of Reax-85A(I) and M-9(II) are respectively to be from 500 to 35,000 and from 1,000 to 50,000. The fractions separated from (I) and (II) by thin layer chromatography were also investigated through gel chromatography to prove that these fractions were mainly separated depending on relative molecular mass.

Chromatography, Gel↗

PubMed1999

The structure of the nucleosome core particle of chromatin in chicken erythrocytes visualized by using atomic force microscopy.

The structure of the nucleosome core particle of chromatin in chicken erythrocytes has been examined by using AFM. The 146 bp of DNA wrapped twice around the core histone octamer are clearly visualized. Both the ends of entry/exit of linker DNA are also demonstrated. The dimension of the nucleosome core particles is approximately 1-4 nm in height and approximately 13-22 nm in width. In addition, superbeads (width of approximately 48-57 nm, height of approximately 2-3 nm) are occasionally revealed, two turns of DNA around the core particles are also detected.

Animals↗

PubMed1999

[Analysis of the binding of GATA factors to the regulatory elements of human beta-globin gene in hydroxyurea-induced and uninduced HEL cells].

HEL cells, a human erythroleukemia cell line, expressing mainly the gamma-globin genes, small amount of epsilon-globin gene, but not beta-globin gene. Our previous studies demonstrated that beta-globin gene could be expressed in HEL cells induced by hydroxyurea. However, the molecular mechenism is still unknown. Here the binding patterns of GATA factors (GATA-1 and GATA-2) to the regulatory elements of human beta-globin gene were examined with the nuclear extracts from hydroxyurea-induced and uninduced HEL cells. Our results showed in EMSA assay that GATA factors could bind to the core sequence of HS2(-10681 to -10971 bp), the 3' flanking sequence of HS2 core(-10323 to -10680 bp) and the promoter of human beta-globin gene(+20 to -112 bp). However, the binding patterns between hydroxyurea-induced and uninduced HEL cells were different. Furthermore, by using Western-blot analysis, our data showed that the amount of GATA-2 was decreased in hydroxyurea-induced HEL cells. In contrast to GATA-2, the amount of GATA-1 was increased in hydroxyurea-induced HEL cells. These results showed that the different members of GATA family might play different roles during the differentiation of erythrocytes. GATA-1 may stimulate the differentiation of HEL cells, while GATA-2 can probably inhibit the differentiation of HEL cells.

Cell Differentiation↗

PubMed1993

Replication of the DNA A component of African cassava mosaic virus in a heterologous system.

The capacity for autonomous replication of the DNA A of African cassava mosaic virus (ACMV), a member of the bipartite geminiviruses infecting dicotyledonous plants, has been compared in host and non-host cells. A derivative of the ACMV DNA A was transfected into tobacco and maize protoplasts. Although ACMV is not able to infect maize, replication of the DNA A in maize protoplasts was observed to occur. The efficiency of replication was 10 to 20% of that seen in tobacco protoplasts. In both plant systems, replication was detected after the onset of cell division. ACMV replication in maize cells was compared to that of wheat dwarf virus and found to be 10 to 20% of that observed with the monocotyledon-specific virus. Insertion of 1165 bp of non-viral DNA into the ACMV DNA A prevented replication in maize but not in tobacco.

Blotting, Southern↗

PubMed1993

[Cardiac amyloidosis: an analysis of five cases].

Five patients with the diagnosis of cardiac amyloidosis established by autopsy and biopsy of noncardiac tissue were reported. All of the patients had cardiac dysfunction. Echocardiogram showed symmetrical thickness of left ventricle, increase of heart weight and reduction of left ventricular ejection fraction. Only two cases had "granular sparkling" on the ventricular wall. The clinical findings of cardiac amyloidosis are arrhythmias, conduction disturbances and intractable heart failure. Echocardiographic examination may reveal cardiac involvement and severity of pathological involvement and predict prognosis. The "granular sparkling" is not a specific feature for the diagnosis of cardiac amyloidosis. Biopsy of either noncardiac or cardiac tissue is required for correct diagnosis.

Amyloidosis↗

PubMed1992

The size of the mature membrane receptor for follicle-stimulating hormone is larger than that predicted from its cDNA.

A 240 kDa protein isolated from bovine calf testis has been shown to have properties characteristic of an FSH receptor. However, rat testis FSH receptor has, on the basis of cloning experiments, been found to have a much lower molecular mass of 75 kDa (peptide only). To examine this point, the size of the FSH receptor in membranes obtained from cultured Sertoli cells of immature rats was determined after polyacrylamide gel electrophoresis under non-reducing conditions, followed by transfer to polyvinylidene difluoride membranes and direct identification of the FSH receptor by ligand blot analysis utilizing radioiodinated human FSH. In this system, the rat Sertoli cell membrane FSH receptor also showed a molecular mass of 240 kDa. Bovine testis contains LH and FSH receptors. We compared the sizes of FSH and LH receptors present in the same bovine testis membrane preparation by ligand blot analysis. The FSH receptor again showed a molecular mass of 240 kDa, whereas the LH receptor showed a molecular mass of 90 kDa. The latter value is similar to that deduced by cloning techniques (75 kDa, peptide only). The evidence seems to suggest that, whereas the molecular mass deduced for the LH receptor on the basis of its cDNA is similar to that of the mature membrane receptor, the size of the FSH membrane receptor is considerably different from that deduced on the basis of its cDNA, presumably as a result of post-translational processing. The marked difference in size between mature FSH (240 kDa) and LH (90 kDa) receptors may reflect significant structural differences of importance with regard to mechanisms of signal transduction.

Animals↗

PubMed1991

Differential roles of high and low affinity guanosine 5'-triphosphate binding sites in the regulation of follicle-stimulating hormone binding to receptor and signal transduction in bovine calf testis membranes.

We have previously shown that FSH receptors are physically and functionally associated with a guanine nucleotide regulatory protein (Gs) in membranes of calf testis. Using N-ethylmaleimide (NEM), forskolin, and cholera toxin as probes, we have investigated the role of low and high affinity GTP-binding sites of stimulatory guanine nucleotide-binding protein of adenylate cyclase (Gs) in the activation of adenylate cyclase. When calf testis membranes were exposed to NEM (1 mM), FSH binding to receptors was slightly (30%) decreased, but the receptors showed continued sensitivity to GTP, resulting in a further decrease in [125I]human FSH binding to receptors. Pretreatment of membranes with NEM (up to 20 microM) produced no effect on GTP-binding. A dose-dependent decrease in high affinity GTP-binding sites, however, was observed at higher (greater than 50 microM) NEM. Adenylate cyclase activity was reduced in response to GTP gamma S or NaF concomitant to a decrease in high affinity GTP-binding sites in membranes treated with 50-100 microM NEM, or completely abolished in membranes exposed to 300 microM NEM. Stimulation by forskolin indicated that the significant inhibition of adenylate cyclase activity occurring in membranes exposed to low NEM (50-100 microM) was not due to inactivation of catalytic unit of adenylate cyclase by NEM. Pretreatment of membranes with 100 micrograms/ml cholera toxin and NAD slightly (18%) reduced specific FSH binding but did not affect Gpp(NH)p-binding. However, adenylate cyclase stimulation by GTP plus FSH in these membranes was significantly enhanced. When membranes were treated with higher concentration of cholera toxin (250 micrograms/ml), the adenylate cyclase stimulation by GTP plus FSH was abolished due to uncoupling of FSH receptors from Gs and a significant decrease in high affinity GTP-binding sites. Our results suggest that high affinity GTP-binding sites of Gs coupled to FSH receptors are essential for FSH and guanine nucleotide activation of adenylate cyclase. The low affinity binding sites bind GTP and thereby regulate FSH binding but are not involved in the activation of adenylate cyclase.

Adenylyl Cyclases↗

PubMed1991

[Internal intussusception of the rectum. An analysis of 62 cases].

In 62 cases of internal intussusception of the rectum, 21 were treated surgically. Their clinical features included serious dyschesia demanding longer time and strength, tenesmus, and slender stool. Digital examination of the rectum, proctoscopy, and colonoscopy usually showed no abnormalities, while defecography could show the presence and severity of internal intussusception. Parenchymal diseases of the rectum such as carcinomas should be ruled out before surgical correction. Operative measures included rectal suspension raising of the pelvic floor, resection of the redundant sigmoid colon, and the pathogenesis of the disease.

Adult↗

PubMed1991

[Multiple primary colo-rectal carcinoma--an analysis of 28 cases].

Of 226 cases with colo-rectal carcinoma treated, 21 (7.89%) had synchronous and 7 (2.63%) had metachronous multiple primary lesions. In these 28 cases, 13 (46.43%) were complicated by adenomatous polyp, in which 7 cases (53.85%) became malignant. The tumor in 9 cases (18.75%) of synchronous carcinoma was less than 1 cm in diameter and could not be palpated during operation. The early metachronous carcinoma could be detected by fiberendoscopy during follow-up. Its diagnostic accuracy can be improved by fiberendoscopy before operation and during follow-up.

Adenocarcinoma↗

PubMed1990

Purification of follitropin receptor from bovine calf testes.

Follitropin (FSH) receptors were solubilized from pure light membranes of bovine calf testis, using an optimum detergent to protein ratio of 0.01. The soluble FSH receptor fraction was gel filtered through Sepharose 6B to isolate an active fraction (6B-Fr-1) which behaved as a complex of FSH receptor and Gs protein. The 6B-Fr-1 was concentrated by ultrafiltration and further purified by sequential Sepharose 4B gel filtration, DEAE-cellulose chromatography (to separate the receptor from Gs protein), and wheat germ lectin affinity chromatography. The purified receptor had an FSH-binding capacity of approximately 3.47 nmol/mg of protein with a Kd of 1.9 X 10(-10) M. Yield was 526 micrograms/11.5 kg tested. Radioiodinated, as well as unlabeled purified FSH receptor, migrated on sodium dodecyl sulfate-polyacrylamide gels as a single major band of Mr approximately 240,000. This band was not affected by 8 M urea treatment prior to analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but treatment with dithiothreitol induced the loss of the 240-kDa band, with appearance of an Mr approximately 60,000 band. The availability of highly purified, stable FSH receptor should allow direct studies on its structure-function relationships.

Animals↗