576
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Chen G, Lin W, Feng X. Relationship between serum apolipoprotein levels and coronary heart disease in the Hainanese province of China. Atherosclerosis 1994. [DOI: 10.1016/0021-9150(94)93578-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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577
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Feng X, Epstein S. Climatic Implications of an 8000-Year Hydrogen Isotope Time Series from Bristlecone Pine Trees. Science 1994; 265:1079-81. [PMID: 17832901 DOI: 10.1126/science.265.5175.1079] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Tree rings from three dendrochronologically dated bristlecone pines were analyzed for stable hydrogen isotopic composition. These trees give a continuous time series from 8000 years ago to the present that indicates the presence of a postglacial climate optimum 6800 years ago and a continuous cooling since then. The qualitative agreement between this record and records from other sources, such as ice cores, pollen, and treeline fluctuations, indicates that these climate changes were global. This record can serve as a reference for other climate indicators throughout the past 8000 years.
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578
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Mares JJ, Feng X, Koch F, Kohl A, Kristofik J. Magnetotransport in InP-based dilute single delta layers. PHYSICAL REVIEW. B, CONDENSED MATTER 1994; 50:5213-5220. [PMID: 9976860 DOI: 10.1103/physrevb.50.5213] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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579
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Zhang S, Feng X, Koga H, Ichikawa T, Abe S, Kumanishi T. p53 gene mutations in pontine gliomas of juvenile onset. Biochem Biophys Res Commun 1993; 196:851-7. [PMID: 8240361 DOI: 10.1006/bbrc.1993.2327] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Using polymerase chain reaction-single strand polymorphism(PCR-SSCP) and nucleotide analyses, p53 gene mutation was examined in 13 pontine gliomas many of which were of juvenile onset. A total of 15 mutations were detected in 8 cases, of which 5 revealed multiple or tandem mutations. The mutations included 6 G:C-A:T and 4 A:T-G:C transitions and 4 G:C-T:A and 1 A:T-T:A transversions. There was only 1 transition at the CpG site. Normal tissues of the same patients revealed no mutation, suggesting that these mutations were somatic, but not of germ line, in nature. The pattern of mutation characterized by frequent multiple or tandem occurrence, predominancy of transition at non-CpG sites and relatively frequent transversions suggested that pontine glioma might be related with some mutagenic or carcinogenic agents.
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580
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Song Z, Antzutkin ON, Feng X, Levitt MH. Sideband suppression in magic-angle-spinning NMR by a sequence of 5 pi pulses. SOLID STATE NUCLEAR MAGNETIC RESONANCE 1993; 2:143-146. [PMID: 7812752 DOI: 10.1016/0926-2040(93)90032-i] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
We report a symmetrical sequence of 5 pi pulses for total sideband suppression in magic-angle-spinning NMR. The sequence is almost evenly spaced and shorter than previous 4 and 6 pi pulse methods.
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581
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Katagiri T, Feng X, Ichikawa T, Usui H, Takahashi Y, Kumanishi T. Neuron-specific enolase (NSE) and non-neuronal enolase (NNE) mRNAs are co-expressed in neurons of the rat cerebellum: in situ hybridization histochemistry. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1993; 19:1-8. [PMID: 8361331 DOI: 10.1016/0169-328x(93)90142-c] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Using in situ hybridization histochemistry, we analysed the localization of mRNAs for neuron-specific enolase (NSE) and non-neuronal enolase (NNE) in the rat cerebellum at various postnatal developmental stages. Synthetic 45 meric oligonucleotides corresponding to partial sequences of the non-coding region of rat NSE or NNE mRNA were 35S-labeled to approximately the same specific activity and used as hybridization probes. On examination of the adult rat cerebellum, both NSE and NNE signals were detected in all identified and presumed neurons which included Purkinje cells, internal granule cells and presumed stellate/basket cells in the cerebellar cortex and neurons of the dentate nucleus. Examination of the cerebellum during postnatal development also revealed coexistence of NSE and NNE signals in these neurons from early stages. During development, both signals coincidentally increased in Purkinje cells and neurons of the dentate nucleus, while only NSE signals showed a gradual increase in the internal granule cells in which NNE signals remained at the same level from early postnatal to adult stages. The external granule cells showed NNE signals until postnatal day 7 but thereafter the signals became less distinct, especially in cells if the inner zone of the external granule cell layer. Thus, it was shown that NSE and NNE were commonly coexpressed at the mRNA level in various neurons of the cerebellum except for very undifferentiated external granule cells which expressed only NNE mRNA.
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582
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Coyle P, Feng X. Risk area and infarct area relations in the hypertensive stroke-prone rat. Stroke 1993; 24:705-9; discussion 710. [PMID: 8488526 DOI: 10.1161/01.str.24.5.705] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
BACKGROUND AND PURPOSE Our purpose was to characterize the surface area of the infarct and the surface area at risk of infarction as defined spatially by arterial anastomoses to determine whether position, size, or shape of the infarct and the area at risk were related in stroke-prone rats or hybrid rats. METHODS Stroke-prone rats (n = 18; mean +/- SEM blood pressure, 182 +/- 8 mm Hg) and hybrid rats (n = 18; mean +/- SEM blood pressure, 147 +/- 6 mm Hg; p < 0.05) were anesthetized and the left middle cerebral artery was occluded with a ligature. The rats were killed 7 days later, arterial anastomoses were made visible with latex, the brains were fixed in formalin, and film recorded the infarct and anastomoses. Anastomoses and infarcts were digitized for measurements of risk area, luminal width, and infarct area. RESULTS Mean risk area was similar in size, length, width, and variability in stroke-prone rats (area, 85 +/- 5 mm2) and hybrid rats (area, 84 +/- 7 mm2; p > 0.05), whereas mean infarct area was larger, longer, wider, and less variable in stroke-prone rats (area, 53 +/- 6 mm2) than in hybrid rats (area, 15 +/- 11 mm2; p < 0.05). Infarct length was appreciably greater than infarct width in both groups, indicating that infarct shape was not amorphous. Spatial overlap maps indicated that the infarct area common to all stroke-prone rats was positioned centrally in the risk area and was surrounded by a variable infarct area, which indicated that the likelihood of infarction increased with distance from the anastomoses. Shape factors for both risk area and infarct area were significantly different within each rat group, which indicated that infarct shape did not uniformly parallel the anastomotic sites that determined risk area shape (p < 0.05). Risk area anastomoses and border zone width were linearly correlated in size and both were significantly wider in hybrid rats than in stroke-prone rats (p < 0.05), which suggests that the narrower border zone tissue was perfused by narrower anastomoses. CONCLUSIONS We conclude that the position of the infarct within the risk area relates to luminal widths of conterminous anastomoses that define the risk area, but not to the size or shape of the area at risk of infarction defined spatially by the anastomoses.
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583
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Chodzko-Zajko W, Caruso A, Vaca V, Griffin W, Feng X, Heist M, McWhorter D. 252 BLOOD PRESSURE RESPONSES OF OLDER ADULTS TO EXERCISE, COGNITIVE, AND DAILY-LIFE STRESS. Med Sci Sports Exerc 1993. [DOI: 10.1249/00005768-199305001-00254] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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584
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Ruchti TL, Brown RH, Jeutter DC, Feng X. Identification algorithm for systemic arterial parameters with application to total artificial heart control. Ann Biomed Eng 1993; 21:221-36. [PMID: 8328722 DOI: 10.1007/bf02368178] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
A new algorithm for estimating systemic arterial parameters from systolic pressure and flow measurements at the root of the aorta is developed and tested through a systems identification approach. The resulting procedure has direct application to a total artificial heart (TAH) control system currently under development. Identification models, representing the systemic arterial system, are developed from existing work in the area of cardiovascular modeling. The resistive and compliance components of these models are physically significant, representing overall hydraulic properties of the systemic arterial system. A unique method of parameterizing the identification models is designed which operates on the basis of aortic pressure and flow measurements taken exclusively during systole. The estimator is a modified recursive least squares algorithm which utilizes covariance modification to track time-varying parameters and a dead-zone to improve the robustness. Performance of the estimation algorithm was tested on data generated by a higher-order distributed model of the systemic arterial bed using normal canine parameters. Results from model-to-model experiments verify the consistency of the estimates and the ability of the estimator to converge quickly and track dynamically varying parameters.
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585
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Feng X, Schott JR, Gallagher T. Comparison of methods for generation of absolute reflectance-factor values for bidirectional reflectance-distribution function studies. APPLIED OPTICS 1993; 32:1234-1242. [PMID: 20820258 DOI: 10.1364/ao.32.001234] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Currently, spectrophotometric standard reference materials are calibrated only by using the illumination and viewing geometries recommended by the Commission Internationale de l'Eclairage, and for some geometries the spectral range is limited to the visible wavelengths. A need exists for procedures that calibrate standards at many other geometries and for a broader spectral range. Two methods for calibrating the spectral bidirectional reflectance factor are described. The absolute bidirectional reflectance factor of a sintered polytetrafluoroethylene (PTFE) sample is determined for nearly all the possible illumination and viewing geometries from 400 nm to 2500 nm. The references are a 45/0 reflectance standard calibrated by the National Institute of Standards and Technology and a sintered PTFE sample with a directional, hemispherical reflectance factor traceable to the Institute. The results of the two methods agree to within 0.01 in reflectance factor values. With this PTFE sample as a transfer standard, the instrument described can also be used to measure the absolute bidirectional reflectance factor at nearly all the illumination and viewing geometries from 400 nm to 2500 nm.
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586
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Coyle P, Feng X. Spatial features of focal infarction after hydralazine treatment in stroke-prone spontaneously hypertensive rats. Stroke 1993; 24:253-7; discussion 257-8. [PMID: 8421828 DOI: 10.1161/01.str.24.2.253] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
BACKGROUND AND PURPOSE Rapid occlusion of the middle cerebral artery above the rhinal fissure produces a large ischemic infarct in hypertensive rats, but this occlusion results in a minimal lesion in young normotensive rats. Our purpose was to attenuate rising blood pressure in young stroke-prone spontaneously hypertensive rats with hydralazine before the occlusion to determine if the gross infarct volume is smaller, and if it is, to determine whether length, width, depth, or surface area of the infarct changes, which could suggest a mechanism of protection. METHODS Untreated rats (n = 6) and rats receiving hydralazine for 1.5 (n = 6) or 5 (n = 5) weeks were anesthetized, and the middle cerebral artery was rapidly occluded with a ligature. One day later the rats were killed and the brains were fixed in formalin. Fine-grain-release film that is sensitive to spectral properties of the infarct was used to photograph the tissue. Infarcted areas were traced on paper and then digitized for measurements and computations with a microcomputer. RESULTS Compared with untreated rats, tail systolic blood pressure (120 +/- 3 versus 138 +/- 4 mm Hg), infarct volume (61 +/- 4 versus 93 +/- 6 mm3), infarct surface area (39 +/- 1 versus 54 +/- 2 mm2), infarct width (3.8 +/- 0.1 versus 4.8 +/- 0.2 mm), and infarct length (6.0 +/- 0.3 versus 8.1 +/- 0.3 mm) were less in rats receiving hydralazine for 5 weeks (p < 0.05). No change was detected in infarct depth. CONCLUSIONS Treatment of young stroke-prone spontaneously hypertensive rats with hydralazine for 5 weeks before middle cerebral artery occlusion results in a smaller infarct. The narrower, shorter dimensions indicate increased protection against lateral enlargement of the infarct and the possibility that protection was due to increased collateral blood flow through modified blood vessels.
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587
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Feng X, Yip GL. Simple technique for determining substrate indices of isotropic materials by a multisheet Brewster angle measurement. APPLIED OPTICS 1992; 31:7570-7574. [PMID: 20802635 DOI: 10.1364/ao.31.007570] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
When an H-polarized light is incident upon a substrate at the Brewster angle, the reflected light becomes zero. Stacking many identical substrates together forms a multisheet structure. The valley of this reflected intensity pattern centered at the Brewster angle becomes narrower owing to the overlap of these similar reflections from many parallel interfaces of air and substrates. Therefore measuring the Brewster angle of this multisheet structure leads to an accurate determination of the substrate index, which is up to the third decimal place (0.00075).
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588
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Parrish DD, Feng X, Lambert MW. Isolation of a DNA endonuclease complex in XPD cells which is defective in ability to incise nucleosomal DNA containing pyrimidine dimers. Biochem Biophys Res Commun 1992; 189:782-9. [PMID: 1472050 DOI: 10.1016/0006-291x(92)92270-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
A DNA endonuclease complex which recognizes predominantly pyrimidine dimers in UVC irradiated DNA has been isolated from the chromatin of normal human and xeroderma pigmentosum, complementation group D (XPD) lymphoblastoid cells. The activity of the normal complex on UVC irradiated DNA was increased approximately 2.5 and 1.5 fold over activity on damaged naked DNA, when core (histones H2A, H2B, H3, H4) and total (core+histone H1) nucleosomal DNA, respectively, was used. In contrast, the XPD complex showed no increase in activity on UVC irradiated total and only a 1.4 fold increase on UVC irradiated core nucleosomal DNA, indicating that the XPD complex is defective in its ability to incise UVC irradiated nucleosomal DNA. The normal complex was able to correct this defect in the XPD complex at the nucleosomal level.
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589
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Feng X, Li GZ, Werth G. High-precision hyperfine spectroscopy in M1-M1 double-resonance transitions on trapped 207Pb+. PHYSICAL REVIEW. A, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 1992; 46:2959-2961. [PMID: 9908459 DOI: 10.1103/physreva.46.2959] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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590
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Feng X, Li GZ, Alheit R, Werth G. Hyperfine-structure measurements on trapped Pb II. PHYSICAL REVIEW. A, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 1992; 46:327-329. [PMID: 9907867 DOI: 10.1103/physreva.46.327] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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591
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Xia Q, Tan P, Feng X, Chen M, Kajihara N, Minai M, Hosaka Y. Assessment of the molluscicidal activities of Tribromosalan, Cartap and Chlorothalonil against Oncomelania hupensis. JAPANESE JOURNAL OF MEDICAL SCIENCE & BIOLOGY 1992; 45:75-80. [PMID: 1434068 DOI: 10.7883/yoken1952.45.75] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Molluscicidal activities of Tribromosalan, Cartap and Chlorothalonil were evaluated in the laboratory and the field against Oncomelania hupensis, the intermediate host of Schistosoma japonicum in China. The three chemicals were very effective against O. hupensis in the laboratory. The molluscicidal activities found in the field trials suggest that Tribromosalan and Cartap may be used as practical molluscicides. Dosage of 10 g/m2 of Tribromosalan in spring only and 20 g/m2 of Cartap in both spring and autumn would be recommendable as practical mollusciciding doses for the control of O. hupensis.
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592
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Cunnane JC, Bates JK, Ebert WL, Feng X, Mazer JJ, Wronkiewicz DJ, Sproull J, Bourcier WL, Mcgrail BP. High-Level Nuclear-Waste Borosilicate Glass: A Compendium of Characteristics. ACTA ACUST UNITED AC 1992. [DOI: 10.1557/proc-294-225] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
ABSTRACTWith the imminent startup, in the United States, of facilities for vitrification of high-level nuclear waste, a document has been prepared that compiles the scientific basis for understanding the alteration of the waste glass products under the range of service conditions to which they may be exposed during storage, transportation, and eventual geologic disposal. A summary of selected parts of the content of this document is provided.Waste glass alterations in a geologic repository may include corrosion of the glass network due to groundwater and/or water vapor contact. Experimental testing results are described and interpreted in terms of the underlying chemical reactions and physical processes involved. The status of mechanistic modeling, which can be used for long-term predictions, is described and the remaining uncertainties associated with long-term simulations are summarized.
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593
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Feng X, Feng J. [The natural variance of transient myocardial ischemia in coronary artery patients]. ZHONGHUA XIN XUE GUAN BING ZA ZHI 1990; 18:343-6, 382. [PMID: 2093553] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Sixty patients of CAD were studied with 24 and 48 hours ambulatory electrocardiogram monitoring. The day-to-day natural variances of transient myocardial ischemia in this group were analysed. The ranges of variation of myocardial ischemia based on a 95% confidence interval were confirmed. The results showed that the day-to-day variances of ischemia between the different days were: (1) 43% in number of ischemia episodes, (2) 76% in duration, (3) 53% in integration, and (4) 48% in maximal degree of ST depression.
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594
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Wang JL, Miao FM, Fan XJ, Feng X, Wang JT. Diethoxybis(4,4,4-trifluoro-1-phenyl-1,3-butanedionato)titanium(IV). Acta Crystallogr C 1990. [DOI: 10.1107/s0108270189013909] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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595
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Feng X, Estep RJ, Dropesky BJ. Cross section for the 27Al(p,2 pi +)28Mg reaction at 800 MeV. PHYSICAL REVIEW. C, NUCLEAR PHYSICS 1990; 42:451-452. [PMID: 9966729 DOI: 10.1103/physrevc.42.451] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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596
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Feng X. [Studies on the identification of mineral medicine wumingyi]. ZHONGGUO ZHONG YAO ZA ZHI = ZHONGGUO ZHONGYAO ZAZHI = CHINA JOURNAL OF CHINESE MATERIA MEDICA 1989; 14:331-3, 382. [PMID: 2511857] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
In the paper the morphological characters, physical properties and spectral analyses(IR,AES) of seven samples collected from different regions are investigated by means of comparison with reference standard pyrolusite. The result indicates that the domestic commercial traditional medicine Wumingyi is practically limonite, therefore further investigations should be made to find out the correct mineral sources.
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597
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Chen ZF, Feng X, Sheng ZJ. [The role of the uvrA gene in the screening of genotoxins in the SOS chromotest]. WEI SHENG WU XUE BAO = ACTA MICROBIOLOGICA SINICA 1988; 28:313-8. [PMID: 3073575] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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598
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Xie JT, Xie LH, Li CL, Liang N, Feng X. [Effects of resibufogenin on monophasic action potential and contractile force of rabbit heart in situ]. ZHONGGUO YAO LI XUE BAO = ACTA PHARMACOLOGICA SINICA 1988; 9:536-8. [PMID: 3256217] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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599
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Xie JT, Xie LH, Li CL, Liang N, Feng X. Resibufogenin-induced delayed afterdepolarization in rabbit heart in situ. METHODS AND FINDINGS IN EXPERIMENTAL AND CLINICAL PHARMACOLOGY 1988; 10:475-6. [PMID: 3419251] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The pharmacological effects of resibufogenin (RGB), an effective cardiotonic obtained from a famous traditional Chinese medicine, on the electrical activity of the rabbit heart (n = 12) in situ were studied by using a new technique of recording monophasic action potential (MAP). RBG (0.3 mg/kg IV) induced DAD in 3/12 animals. DAD appeared within the first 0.5 to 1 min after RBG and lasted about 20-30 min. The position of DAD was in the end of phase 3 of MAP. The DADs of rabbit epicardium showed a transient, regular and phasic depolarization process. The triggered arrhythmias were not recorded in these experiments, as amplitudes of DAD were lower and did not reach the threshold. The results indicate that DADs are induced by RBG at first time in situ in rabbits. The characteristics of DAD were similar to those previously described in single cardiac fibers in vitro.
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600
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Richter E, Richter-Cooberg U, Feng X, Schulze J, Wiessler M. Intestinal metabolism of nitrosamines. 1. Transport and metabolism of six nitrosamines in isolated perfused rat small intestinal segments. Carcinogenesis 1986; 7:1207-13. [PMID: 3087650 DOI: 10.1093/carcin/7.7.1207] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Possible relationships between structure and metabolism of nitrosamines have been investigated in the rat small intestine. Isolated segments of jejunum and ileum were perfused from the luminal side for 2 h with a Tyrode solution containing one of four symmetrical dialkylnitrosamines with 2-5 carbon atoms per side chain, all 14C-labeled at the alpha position, or one of two unsymmetrical nitrosamines, N-nitroso-tert-butylmethylamine and N-nitrosomethylbenzylamine, 14C-labeled in the methyl group. Besides measurement of 14CO2 production and covalent binding of 14C to intestinal tissue, the absorbed fluid (absorbate) as well as the perfusion medium and tissue homogenates were analysed by h.p.l.c. for the presence of polar metabolites to assess the intestinal metabolism of nitrosamines. Neither N-nitrosodiethylamine nor the two unsymmetrical nitrosamines were metabolized to any significant extent. With increasing chain length of symmetrical dialkylnitrosamines small intestinal metabolism increased dramatically. At a concentration of 1 microM up to 60% and 30% of N-nitrosodipropylamine (NDPA) in jejunal and ileal segments, respectively, and greater than 90% of N-nitrosodibutylamine (NDBA) and N-nitrosodipentylamine (NDAA) in both intestinal segments were metabolized during absorption. Metabolites were found also in perfusate and tissue homogenate but generally at lower percentages as compared with the absorbate. With increasing concentrations the percentage of metabolites decreased, the decrease being more pronounced in ileal as compared with jejunal segments. CO2 production and covalent binding were negligible in ileal segments but amounted up to 5-8% and 0.1-0.4% of the dose in jejunal segments perfused with NDPA, NDBA or NDAA. With NDBA and NDAA no concentration-dependent decrease could be observed, the highest amounts of 14CO2 and bound 14C being found at intermediate concentrations. At concentrations below 10 microM metabolic pathways other than alpha-hydroxylation seem to be of greater importance. The toxicological evaluation of the high intestinal first-pass metabolism of NDPA, NDBA and NDAA must await the identification and quantitation of the metabolites formed.
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