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Biomedical subjects

P Shi

Publications and source records attributed to P Shi.

At least 19 recordsLinked to original sources
PubMed2004

Development of a fragment constant method for estimating the mixture toxicity.

Based on Group Contribution Theory, a fragment constant model to estimate mixture toxicity is proposed in this paper. The toxicity (EC50M) of 58 mixtures is determined using Photobacterium phosphoreum. Analysis of these EC50M and the mole fraction of the individual chemical fragments (Br, Cl, NO2, OH, NH2) helps work out the fragment toxicity contribution (deltaTi) to EC50M. Thus, a linear regression equation is established between the toxicity contribution deltaTi and the fragment constants of Hansch f(i), and this equation is so significant that it helps provide an approach for calculating EC50M.

Drug Interactions↗
PubMed2004

Tunable optical properties of colloidal quantum dots in electrolytic environments.

The absorption spectra of colloidal cadmium sulfide quantum dots in electrolytic solutions are found to manifest a shift in the absorption threshold as the concentration of the electrolyte is varied. These results are consistent with a shift in the absorption threshold that would be caused by electrolytic screening of the field caused by the intrinsic spontaneous polarisation of these würtzite structured quantum dots. These electrolyte-dependent absorption properties provide a potential means of gaining insights on the variable extracellular and intracellular electrolytic concentrations that are present in biological systems.

Journal Article↗
PubMed2001

Chaoslike behavior in nonchaotic systems at finite computation precision.

The dynamical behavior of a two-dimensional map is investigated numerically. A chaoslike behavior, i.e., a nonsmooth distribution of the attractor and seemly sensitive dependence of the motion on initial condition is found as the system state is nonchaotic (both Lyapunov exponents are nonpositive). The key point for this strange behavior is that the mode corresponding to the second negative Lyapunov exponent contains positive local Lyapunov exponent segments. It is argued that this kind of behavior may be typical and easily observed in practical numerical computations and experiments where small noise is inevitable.

Journal Article↗
PubMed2001

Quantification of 3-D regional myocardial deformation: shape-based analysis of magnetic resonance images.

A comprehensive three-dimensional (3-D) shape-based approach for quantification of regional myocardial deformations was evaluated in a canine model (n = 8 dogs) with the use of cine magnetic resonance imaging. The shape of the endocardial and epicardial surfaces was used to track the 3-D trajectories of a dense field of points over the cardiac cycle. The shape-based surface displacements are integrated with a continuum biomechanics model incorporating myofiber architecture to estimate both cardiac- and fiber-specific endocardial and epicardial strains and shears for 24 left ventricular regions. Whereas radial and circumferential end-systolic strains were fairly uniform, there was a significant apex-to-base gradient in longitudinal strain and radial-longitudinal shear. We also observed transmural epicardial-to-endocardial gradients in both cardiac- and fiber-specific strains. The increase in endocardial strain was accompanied by increases in radial-longitudinal shear and radial-fiber shears in the endocardium, supporting previous theories of regional myocardial deformation that predict considerable sliding between myocardial fibers.

Animals↗
PubMed2000

Point-tracked quantitative analysis of left ventricular surface motion from 3-D image sequences.

We propose and validate the hypothesis that we can use differential shape properties of the myocardial surfaces to recover dense field motion from standard three-dimensional (3-D) image sequences (MRI and CT). Quantitative measures of left ventricular regional function can be further inferred from the point correspondence maps. The noninvasive, algorithm-derived results are validated on two levels. First, the motion trajectories are compared to those of implanted imaging-opaque markers of a canine model in two imaging modalities, where subpixel accuracy is achieved. Second, the validity of using motion parameters (path length and thickness changes) for detecting myocardial injury area is tested by comparing algorithms derived results to postmortem analysis TTC staining of myocardial tissue, where the achieved Pearson product-moment correlation value is 0.968.

Algorithms↗
PubMed2000

Effect of lanthanum on ion absorption in cucumber seedling leaves.

Scanning electron microscope and energy-dispersive X-ray analysis were used to study the tissular distributions of elements Na, Mg, Cl, K, Ca, Mn, and Fe in leaves of cucumber seedlings in the absence or presence of La3+. The results showed that the atomic percentages of Na, Mg, Cl, K, and Ca were basically reduced and those of Mn and Fe were increased in the presence of La3+; in addition, at 0.02 mM La3+, the reduced or increased degrees were higher than those at 2.0 mM La3+. The effects of La3+ on ion absorption were similar to those of Ca2+, suggesting that the rare earth element lanthanum affects the plant physiological mechanism by regulating the Ca2+ level in plant cell.

Cucumis sativus↗
PubMed2000

[Fuzzy space based segmentation algorithm on periosteum medical image processing].

Object description in medical image often has the property of fuzziness, and with the development of computing, fuzzy logical theories are progressively used in medical image processing. Color medical images differ in spacial presentation and fuzzy description from grey-scale images and must be analyzed by special methods. In this paper, a new method of bone cell segmentation based on fuzzy logical theories is presented. With the utilization of fuzzy set theories in the steps of color enhancing, feature extraction and automatical segmentation, bone cells are detected from the background. The method has the advantages of high accuracy and flexibility to many situations. Experiments of bone cell images have proved that it is a fast and effective method.

Algorithms↗
PubMed2000

[A quantum chemical study of pi-back-donation bond and Raman intensity of 1 sigma + electronic state of Pt-CO molecule].

The Raman spectroscopic properties of Pt-CO molecule have been investigated based on the electronic state 1 sigma + determined by the HF and B3LYP methods. The result shows that the calculated stretching vibrational frequencies of the Pt-C and C-O bonds depend on the method and the basis sets used. It indicates that it is important to adopt an appropriate method to describe pi-donation and pi-back-donation bond. The result of the differential Raman scattering cross section for the stretching vibrations of the Pt-C and C-O bond shows that the latter is significantly larger value compared to the former.

Adsorption↗
PubMed1999

[Computer-assisted identification of fundus lesions and a study of its reliability].

This study aimed at the use of computer for identifying fundus lesions quickly and reliably. We adopted the 'area filling' method to program in Visula C++, used the program to mesure the retina cotton-wool patches in diabetics (15 eyes), and then calculated the coefficient of variation to evaluate its reproducibility. The results showed that the coefficient of variation of the measurements ranged from 3.22% to 9.46%. In conclusion, this method is convient, quick and reliable.

Algorithms↗
PubMed1998

The COOH-terminal tyrosine phosphorylation sites on IRS-1 bind SHP-2 and negatively regulate insulin signaling.

Activation of tyrosine kinases by numerous growth factor and cytokine receptors leads to tyrosine phosphorylation of the insulin receptor substrate (IRS)-proteins. Tyrosine-phosphorylated motifs on the IRS proteins bind to the SH2 domains in proteins that mediate downstream signals, including phosphatidylinositol 3'-kinase, GRB-2, and SHP-2. We investigated the function of the two SHP-2 binding COOH-terminal tyrosines of IRS-1 by replacing them with phenylalanine (IRS-1(FCT)). IRS-1(FCT) failed to bind SHP-2 or mediate its tyrosine phosphorylation during insulin stimulation. Although several reports suggest a critical role for SHP-2 in insulin stimulated mitogen-activated protein kinase activation and cell proliferation, IRS-1(FCT) mediated these effects normally in 32D cells. Indeed, IRS-1(FCT) exhibited increased tyrosine phosphorylation, phosphatidylinositol 3'-kinase binding and activation of protein synthesis in response to insulin. These results suggest that SHP-2 attentuates the phosphorylation and downstream signal transmission of IRS-1 and that the interaction of IRS-1 and SHP-2 is an important regulatory event which attenuates insulin metabolic responses.

Animals↗
PubMed1998

Physical and geometrical modeling for image-based recovery of left ventricular deformation.

Information about left ventricular (LV) mechanical performance is of critical importance in understanding the etiology of ischemic heart disease. Regional measurements derived from non-invasive imaging to assist in assessing this performance have been in use for decades, and certain parameters derived from these measurements often are useful clinically, as they correlate to some extent with gross physiological hypotheses. However, relatively little work has been done to date to carefully understand the relationship of regional myocardial injury to the local mechanical performance of the heart as derived from image data acquired non-invasively for a particular patient in 3 spatial dimensions over time. This paper describes efforts to take advantage of recent developments in 3D non-invasive imaging and biomechanical modeling to design an integrated computational platform capable of assembling a variety of displacement and velocity data derived from each image frame to deform a volumetric model representation of a portion of the myocardium. A brief description of the reasoning behind this strategy an overview of the approach and some initial results are described.

Animals↗
PubMed1998

[Effects of opium peptide system on the temperature regulation of mice under dry-hot environment with different temperature].

The Kunming mice were selected as subjects. Animals were allowed to move and drink freely. The Naloxone(0.02 mg/g) was injected by abdominal cavity. The ability to body temperature stable by mice under the environment with high temperature (41 degrees C, 43 degrees C) was observed. The results showed that after obstructing opium receptor by Naloxone, the ability mentioned above was reduced obviously.

Animals↗
PubMed1995

Expression cloning of an AVP-activated, calcium-mobilizing receptor from rabbit kidney medulla.

Arginine vasopressin (AVP) is a nonapeptide that regulates body fluid and blood pressure homeostasis. We have used expression cloning in the Xenopus laevis oocyte system to identify cDNA clones from a rabbit renal medullary expression library encoding an AVP receptor linked to Ca2+ mobilization. cRNA generated from positive clones conferred upon oocytes the capacity to mobilize intracellular Ca2+ in response to AVP. A cDNA clone encoding a protein of 780 amino acids was isolated, sequenced, and subcloned into an SV40-based expression vector. Expression of the cloned protein [designated the vasopressin-activated, calcium-mobilizing (VACM-1) protein] in COS-1 cells, resulted in increased 125I-labeled AVP binding [dissociation constant (Kd) of approximately 2 nM] and increased AVP-induced mobilization of Ca2+. Importantly, 125I-AVP could be immunoprecipitated both from detergent-solubilized membranes from COS-1 cells expressing VACM-1 protein and from an in vitro translation system, in which VACM-1 protein was synthesized, using antibodies prepared against a synthetic peptide derived from the NH2-terminal sequence of VACM-1. Interestingly, immunohistochemical staining of rabbit kidney sections with this antibody showed specific staining of collecting tubule epithelia. The deduced amino acid sequence is not homologous with any nucleic acid or amino acid sequences reported to date, including those of the V1 and V2 AVP receptors. The VACM-1 protein may represent a novel AVP receptor.

Amino Acid Sequence↗
PubMed1995

Structure-function interrelation and clinical effect of atrial natriuretic peptide (ANP).

Atriopeptin III (AP III) and its six analogues were synthesized by solid phase method and their diuretic and hypotensive activities were determined. Among these analogues, analogue [D-Ala-5, D-Arg-23] AP III was nearly 10 times as potent as AP III in diuretic activity while its hypotensive activity increased only 50% of that of AP III. Analogue des [Ser-15Gly-16Leu-17Gly-18Asn-20Ser-21] AP III was 15% as potent as AP III in diuretic activity, but it still maintained about 60% of the hypotensive activity of AP III. Meanwhile, we tried analogue [D-Ala-5, D-Agr-23] AP III for the treatment of hypertensive syndrome in pregnancy and obtained some good results.

Adult↗