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Biomedical subjects

C Pan

Publications and source records attributed to C Pan.

At least 19 recordsLinked to original sources
PubMed2001

Pore-scale modeling of saturated permeabilities in random sphere packings.

We use two pore-scale approaches, lattice-Boltzmann (LB) and pore-network modeling, to simulate single-phase flow in simulated sphere packings that vary in porosity and sphere-size distribution. For both modeling approaches, we determine the size of the representative elementary volume with respect to the permeability. Permeabilities obtained by LB modeling agree well with Rumpf and Gupte's experiments in sphere packings for small Reynolds numbers. The LB simulations agree well with the empirical Ergun equation for intermediate but not for small Reynolds numbers. We suggest a modified form of Ergun's equation to describe both low and intermediate Reynolds number flows. The pore-network simulations agree well with predictions from the effective-medium approximation but underestimate the permeability due to the simplified representation of the porous media. Based on LB simulations in packings with log-normal sphere-size distributions, we suggest a permeability relation with respect to the porosity, as well as the mean and standard deviation of the sphere diameter.

Models, Theoretical↗
PubMed2001

[Study on different responses of rats' small intestine mucous membrane and bladder transitional epithelium in the same carcinogenic urine environment].

OBJECTIVE: To preliminarily verify the tentative idea of replacement of bladder transitional epithelium with small intestine mucous membrane to prevent recurrence of carcinoma of bladder. METHODS: A certain segment of small intestine was transplanted to the urinary bladder of the same body in 17 rats. Then N-butyl-N-(4-hydroxy-butyl) nitrosamine (BBN) was used to induce carcinoma of bladder. BBN was used to 11 control rats that did not undergo operation. RESULTS: Bladder carcinoma failed to be found in the transplanted small intestine mucous membrane in all experimental rats except one. After stimulation of BBN, carcinoma of urinary bladder occurred in all rats' bladder transitional epithelium. CONCLUSION: 1) The carcinogenic substances in the urine of rats suffering from BBN-induced bladder carcinoma are carcinogenic only to bladder transitional epithelium and have no effect on small intestine epithelium. 2) Bladder transitional epithelium may be more sensitive to the urine carcinogenic substances and easier to be cancerized than small intestine epithelium. 3) The tentative idea of substitution of small intestine mucous membrane for bladder transitional epithelium to prevent the recurrence of bladder carcinoma is worth further studying.

Animals↗
PubMed2001

Ligand-stabilized ruthenium nanoparticles: synthesis, organization, and dynamics.

The decomposition of the ruthenium precursor Ru(COD)(COT) (1, COD = 1,5-cyclooctadiene; COT = 1,3,5-cyclooctatriene) in mild conditions (room temperature, 1--3 bar H(2)) in THF leads, in the presence of a stabilizer (polymer or ligand), to nanoparticles of various sizes and shapes. In THF and in the presence of a polymer matrix (Ru/polymer = 5%), crystalline hcp particles of uniform mean size (1.1 nm) homogeneously dispersed in the polymer matrix and agglomerated hcp particles (1.7 nm) were respectively obtained in poly(vinylpyrrolidone) and cellulose acetate. The same reaction, carried out using various concentrations relative to ruthenium of alkylamines or alkylthiols as stabilizers (L = C(8)H(17)NH(2), C(12)H(25)NH(2), C(16)H(33)NH(2), C(8)H(17)SH, C(12)H(25)SH, or C(16)H(33)SH), leads to agglomerated particles (L = thiol) or particles dispersed in the solution (L = amine), both displaying a mean size near 2--3 nm and an hcp structure. In the case of amine ligands, the particles are generally elongated and display a tendency to form worm- or rodlike structures at high amine concentration. This phenomenon is attributed to a rapid amine ligand exchange at the surface of the particle as observed by (13)C NMR. In contrast, the particles stabilized by C(8)H(17)SH are not fluxional, but a catalytic transformation of thiols into disulfides has been observed which involves oxidative addition of thiols on the ruthenium surface. All colloids were characterized by microanalysis, infrared spectroscopy after CO adsorption, high-resolution electron microscopy, and wide-angle X-ray scattering.

Journal Article↗
PubMed2001

Monte Carlo simulation of morphologies of self-assembled amphiphilic diblock copolymers in solution.

The Monte Carlo method has been applied to simulate the process of the self-assembling of amphiphilic diblock copolymers in a selective solvent. The simulations illustrated that the aggregates morphologies of A-b-B diblock copolymers in solution strongly depend on the length of corona-forming segments, i.e., with the decrease of the corona-forming segments, the transition of spherical micelles to rodlike aggregates occurs, which are in accord with the experimental results of Eisenberg and co-workers [Science 268, 1728 (1995); Macromolecules 32, 2239 (1999); 31, 3509 (1998); 29, 6359 (1996); 31, 9399 (1998)].

Journal Article↗
PubMed2001

Tissue tracking allows rapid and accurate visual evaluation of left ventricular function.

AIMS: To evaluate the ability of tissue tracking for rapid assessment of left ventricular function by determination of the systolic mitral annular displacement. Tissue tracking is a new echocardiographic modality based on Doppler Tissue imaging allowing rapid visual assessment of the systolic baso-apical displacement of each myocardial segment in apical views by a graded colour display. METHODS AND RESULTS: We studied 90 patients (69 male, age 60.4 +/- 10.1 years) with different left ventricular function (25 subjects with normal left ventricular function, 25 patients with homogeneous depression of left ventricular function and 40 patients with prior myocardial infarction). Systolic mitral annular displacement was determined by tissue tracking and M-mode echocardiography. Apical two-, three- and four-chamber views were used to determine the mitral annular displacement of six sites. Left ventricular ejection fraction was determined by two-dimensional echocardiography using Simpson's rule. Tissue tracking was possible in all patients. In the 50 patients with normal left ventricular function or homogeneous depression of left ventricular function, mean mitral annular displacement correlated closely with mitral annular displacement determined by M-mode (r=0.99,P <0.001) and with left ventricular ejection fraction (r=0.97, P<0.001). Left ventricular ejection fraction < or = 30% could be predicted with a sensitivity of 98% and a specificity of 78% using a cut-off value of 4.8mm for the mitral annular displacement determined by tissue tracking. In patients with prior myocardial infarction correlation between the mean mitral annular displacement and left ventricular ejection fraction was lower (r=0.87, P<0.001). CONCLUSION: Systolic mitral annular displacement determined by tissue tracking correlates closely with mitral annular displacement determined by M-mode and with left ventricular ejection fraction. Thus, tissue tracking allows rapid semiquantitative evaluation of global left ventricular function by assessment of systolic mitral annular displacement.

Aged↗
PubMed2001

Effect of benzene, toluene, xylene on the semen quality and the function of accessory gonad of exposed workers.

The effects on semen and the function of accessory gonad of workers after short and long term exposure to benzene, toluene, and xylene were examined. The semen and blood of 24 married workers exposed to benzene, toluene, and xylene were collected. Routine sperm characteristic, acrosin activity, and Lactate dehydrogenase C4 (LDH-C4) relative activity were detected. The results showed that benzene, toluene, and xylene were found in the blood and semen of some ex-workers at workplaces where the air concentration of benzene, toluene, and xylene exceeded the maximum allowable concentration (MAC). No such solvents were detected in the blood and semen of workers of the control group. The sperm vitality and sperm motility decreased in the exposed workers. The mean acrosin activity, gamma-GT activity and LDH-C4 relative activity in the exposed workers were lower, and fructose concentration was higher than those in the control. There were negative correlations between sperm vitality, sperm activity, acrosin activity, or LDH-C4 relative activity and working history. These results suggest that the mixture of these solvents could affect the sperm and the function of accessory gonad. This might be one reason of the abnormal pregnancy outcome among the wives of workers exposed to benzene, toluene, and xylene.

Acrosin↗
PubMed2001

[Coarse woody debris and its function in forest ecosystem].

Coarse woody debris (CWD) is an important structural and functional element in forest ecosystem. In this paper, the definition, dynamics, and role of CWD in a forest ecosystem were overviewed. CWD include all woody debris above and under the ground with a diameters > or = 2.5 cm, and mainly comes from the dead trees resulted from competition and disturbances. The biomass of CWD changes like "U" form along with the development of a forest community. The decay rate of CWD is determined by the compound course of the respiration and natural fragmentation. Insects and microorganisms play an important role in the course. CWD basically has two functions in an ecosystem. One is as the nutrition pool for some living creatures, and the other is that the large CWD can form some special habitats for animals and plants. Conclusively these two functions are helpful to reserve the biodiversity and the integrity of ecological process in a natural ecosystem. Gaps are formed while dead trees falling down, and all gaps in a forest succeed one another randomly in the development of a forest ecosystem, which pushes the inner circulation of the forest. Because of the vital roles of CWD in a forest ecosystem, much more attention should be paid in the management of forest ecosystem.

Ecosystem↗
PubMed2000

4-[3-(5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)phenyl]benzoic acid and heterocyclic-bridged analogues are novel retinoic acid receptor subtype and retinoid X receptor alpha agonists.

Aromatic retinoids having a meta-substituted aromatic ring bridge, such as 4-[3-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)phenyl]benzo ic acid and its 3,5-diaryl-substituted 4,5-dihydroisoxazole analogue, function as retinoid receptor panagonists by activating both retinoic acid and retinoid X receptors to induce gene transcription, and thereby provide novel scaffolds for retinoid drug development. Both classes of these ligand-inducible transcription factors are involved in mediating the inhibitory effects of retinoids on cancer cell growth.

Benzoates↗
PubMed2000

Synovial tissue in rheumatoid arthritis is a source of osteoclast differentiation factor.

OBJECTIVE: Osteoclast differentiation factor (ODF; also known as osteoprotegerin ligand, receptor activator of nuclear factor kappaB ligand, and tumor necrosis factor-related activation-induced cytokine) is a recently described cytokine known to be critical in inducing the differentiation of cells of the monocyte/macrophage lineage into osteoclasts. The role of osteoclasts in bone erosion in rheumatoid arthritis (RA) has been demonstrated, but the exact mechanisms involved in the formation and activation of osteoclasts in RA are not known. These studies address the potential role of ODF and the bone and marrow microenvironment in the pathogenesis of osteoclast-mediated bone erosion in RA. METHODS: Tissue sections from the bone-pannus interface at sites of bone erosion were examined for the presence of osteoclast precursors by the colocalization of messenger RNA (mRNA) for tartrate-resistant acid phosphatase (TRAP) and cathepsin K in mononuclear cells. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to identify mRNA for ODF in synovial tissues, adherent synovial fibroblasts, and activated T lymphocytes derived from patients with RA. RESULTS: Multinucleated cells expressing both TRAP and cathepsin K mRNA were identified in bone resorption lacunae in areas of pannus invasion into bone in RA patients. In addition, mononuclear cells expressing both TRAP and cathepsin K mRNA (preosteoclasts) were identified in bone marrow in and adjacent to areas of pannus invasion in RA erosions. ODF mRNA was detected by RT-PCR in whole synovial tissues from patients with RA but not in normal synovial tissues. In addition, ODF mRNA was detected in cultured adherent synovial fibroblasts and in activated T lymphocytes derived from RA synovial tissue, which were expanded by exposure to anti-CD3. CONCLUSION: TRAP-positive, cathepsin K-positive osteoclast precursor cells are identified in areas of pannus invasion into bone in RA. ODF is expressed by both synovial fibroblasts and by activated T lymphocytes derived from synovial tissues from patients with RA. These synovial cells may contribute directly to the expansion of osteoclast precursors and to the formation and activation of osteoclasts at sites of bone erosion in RA.

Arthritis, Rheumatoid↗
PubMed2000

Identification of CD72 as a lymphocyte receptor for the class IV semaphorin CD100: a novel mechanism for regulating B cell signaling.

We have identified the lymphocyte semaphorin CD100/Sema4D as a CD40-inducible molecule by subtractive cDNA cloning. CD100 stimulation significantly enhanced the effects of CD40 on B cell responses. Administration of soluble CD100 markedly accelerated in vivo antigen-specific antibody responses. CD100 receptors with different binding affinities were detected on renal tubular cells (K(d) = approximately 1 x 10(-9)M) and lymphocytes (K(d) = approximately 3 x 10(-7)M). Expression cloning revealed that the CD100 receptor on lymphocytes is CD72, a negative regulator of B cell responsiveness. CD72 thus represents a novel class of semaphorin receptors. CD100 stimulation induced tyrosine dephosphorylation of CD72 and dissociation of SHP-1 from CD72. Our findings indicate that CD100 plays a critical role in immune responses by the novel mechanism of turning off negative signaling by CD72.

Animals↗
PubMed2000

CD72, a negative regulator of B-cell responsiveness.

The ability of lymphocytes to respond to antigenic or mitogenic stimulation is regulated not only by specific receptor proteins, but also by both positive and negative regulatory proteins that set or fine-tune the threshold for responsiveness. CD72 is one such regulatory protein on B lymphocytes. It is a member of the C-type lectin superfamily and is expressed on the surface of B cells from the pro-B through the mature B-cell stage. Studies with anti-CD72 antibodies have suggested a positive regulatory role for CD72 in B-cell activation. However, the cytoplasmic tail of CD72 contains two potential immunoreceptor tyrosine-based inhibitory motifs, one of which has been shown to recruit the tyrosine phosphatase SHP- 1. These features suggest a negative regulatory role for CD72. We have generated CD72-deficient mice to elucidate the physiological role of CD72 in B-lymphocyte development and activation. Our analyses of these mice and their B-cell compartment demonstrate that CD72 is a nonredundant regulator of B-cell development and a negative regulator of B-cell responsiveness.

Animals↗
PubMed2000

[A study of ventricular repolarization duration variability and dependence of RTm/RR].

As an important electrophysiological parameter that reflects cardiac depolarization and repolarization process, ventricular repolarization duration has been drawing growing attention. It is influenced by several physiological and pathological factors and associated with several cardiac diseases. We studied repolarization duration variability (RDV) and dependence of RTm/RR among normal subjects of different age-groups, as well as between normal subjects and subjects with cardiac diseases. It was found that RDV and dependence of RTm/RR are related to age. There are significant differences in the slope of RTm/RR, coherence, CV ratio and RDV between normal subjects and subjects with cardiac diseases. The RDV and dependence of RTm/RR can be employed in providing a more useful evaluation of cardiac disease and function in clinical care.

Adult↗
PubMed2000

[Analysis of influence of axial length and keratometric value on the curative effects of excimer laser photorefractive keratectomy for myopia].

OBJECTIVE: To evaluate the influence of axial length (AL) and keratometric value (KV) on the curative effects of excimer laser photorefractive keratectomy (PRK) for myopia. METHOD: A Keracor-17 excimer laser was used to treat 80 patients (121 eyes) with myopia. The cases were divided into three groups according to the AL and KV: The first group AL > 26 mm, KV 45 D, 36 eyes; the third group AL 0.05). The cases with uncorrected visual acuity >or= 0.5 had significant difference between the first and the second group and between the first and the third group (chi(2) = 6.30, P < 0.05). Multiple linear regression and correlative analysis showed that the increase in ocular axis was an unfavorable factor to visual acuity, while the increase in keratometric value was a favorable factor to visual acuity. CONCLUSION: PRK for treatment of myopia is an effective and safe refractive surgery. When the myopic degrees are identical, the postoperative outcome of myopia with increase in keratometric value as the main pathogeny is better than the myopia with increase in axial length as the main pathogeny.

Adolescent↗
PubMed1999

Three-dimensional pharmacophore hypotheses for the locust neuronal octopamine receptor (OAR3). Part 2: agonists.

Three-dimensional pharmacophore hypotheses were built from a set of 43 agonists against octopamine receptor class 3 (OAR3) in locust nervous tissue. Among the 10 chemical-featured models generated by program Catalyst/Hypo, a hypothesis including hydrogen-bond acceptor (HBA), hydrophobic (Hp), and hydrophobic aliphatic (HpA1) features was considered to be important and predictive in evaluating OAR3 agonists. While the ideal and null hypotheses had a cost of 156.40 and 239.20, respectively, the 10 resulting hypotheses possessed costs from 169.89 to 175.81. The best hypothesis that was confirmed to have a 95% chance of true correlation yielded a low RMS of 0.757 and high regression r of 0.933. Active agonists mapped well onto all the features of the hypothesis such as HBA, Hp, and HpA1. On the other hand, inactive compounds were shown to be difficult to achieve the energetically favorable conformation which is found in the active molecules in order to fit the 3-D chemical feature pharmacophore models.

Animals↗
PubMed1999

CD72-deficient mice reveal nonredundant roles of CD72 in B cell development and activation.

CD72, a B cell surface protein of the C-type lectin superfamily, recruits the tyrosine phosphatase SHP-1 through its ITIM motif(s). Using CD72-deficient (CD72-/-) mice, we demonstrate that CD72 is a nonredundant regulator of B cell development. In the bone marrow of CD72-/- mice, there was a reduction in the number of mature recirculating B cells and an accumulation of pre-B cells. In the periphery of CD72-/- mice, there were fewer mature B-2 cells and more B-1 cells. In addition, CD72 is a negative regulator of B cell activation, as CD72-/- B cells were hyperproliferative in response to various stimuli and showed enhanced kinetics in their intracellular Ca2+ response following IgM cross-linking.

Animals↗
PubMed1999

Effect of benzene, toluene, xylene on the semen quality of exposed workers.

OBJECTIVE: To examine the effects on semen and sperm quality of workers after a short and long term exposure to benzene, toluene, and xylene. METHODS: The semen and blood of 24 married workers exposed to benzene, toluene, and xylene from shoemaking, spray painting, or paint manufacturing factories were collected. The concentration of benzene, toluene, and xylene in the blood and semen was determined by using headspace chromatographic method. Routine sperm test was carried out and acrosin activity detected. RESULTS: The results showed that benzene, toluene, and xylene were found in the blood and semen of some ex-workers in a working environment where the air concentration of benzene, toluene, and xylene exceeded the maximum allowable concentration (MAC). This result was not found in workers of the control group. There were also some effects on the quality of semen in the exposed workers. For example, the percentage of semen with liquefaction time exceeding 30 minutes increased. The sperm vitality, motility and acrosin activity decreased. At the same time, there were a positive correlation between liquefaction time and the level of toluene in semen, and a negative correlation between sperm vitality, sperm activity or acrosin activity and working history. CONCLUSIONS: The results suggested that the mixture could affect the quality of semen and sperm, which might be the main reason of the abnormal pregnancy outcome among the wives of workers exposed to benzene, toluene, and xylene. Further studies are, however, required to confirm these findings.

Acrosin↗