Biomedical subjects

J H Chen

Publications and source records attributed to J H Chen.

At least 19 recordsLinked to original sources

PubMed2006

Preparation and electrocatalytic properties of Pt-SiO2 nanocatalysts for ethanol electrooxidation.

Due to their high stability in general acidic solutions, SiO(2) nanoparticles were selected as the second catalyst for ethanol oxidation in sulfuric acid aqueous solution. Pt-SiO(2) nanocatalysts were prepared in this paper. The micrography and elemental composition of Pt-SiO(2) nanoparticles were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. The electrocatalytic properties of Pt-SiO(2) nanocatalysts for ethanol oxidation were investigated by cyclic voltammetry. Under the same Pt loading mass and experimental conditions for ethanol oxidation, Pt-SiO(2) nanocatalysts show higher activity than PtRu/C (E-Tek), Pt/C (E-Tek), and Pt catalysts. Additionally, Pt-SiO(2) nanocatalysts possess good anti-poisoning ability. The results indicate that Pt-SiO(2) nanocatalysts may have good potential applications in direct ethanol fuel cells.

Journal Article↗

PubMed2006

Direct observation of dijets in central Au+Au collisions at sqrt[sNN]=200 GeV.

The STAR Collaboration at the Relativistic Heavy Ion Collider reports measurements of azimuthal correlations of high transverse momentum (pT) charged hadrons in Au+Au collisions at higher pT than reported previously. As (pT) is increased, a narrow, back-to-back peak emerges above the decreasing background, providing a clear dijet signal for all collision centralities studied. Using these correlations, we perform a systematic study of dijet production and suppression in nuclear collisions, providing new constraints on the mechanisms underlying partonic energy loss in dense matter.

Journal Article↗

PubMed2006

Identified baryon and meson distributions at large transverse momenta from Au + Au collisions at square root sNN=200 GeV.

Transverse momentum spectra of pi+/-, p, and p up to 12 GeV/c at midrapidity in centrality selected Au + Au collisions at square root sNN=200 GeV are presented. In central Au + Au collisions, both pi +/- and p(p) show significant suppression with respect to binary scaling at pT approximately >4 GeV/c. Protons and antiprotons are less suppressed than pi+/-, in the range 1.5 approximately < pT approximately < 6 GeV/c. The pi-/pi+ and p/p ratios show at most a weak pT dependence and no significant centrality dependence. The p/pi ratios in central Au + Au collisions approach the values in p + p and d + Au collisions at pT approximately >5 GeV/c. The results at high pT indicate that the partonic sources of pi+/-, p, and p have similar energy loss when traversing the nuclear medium.

Journal Article↗

PubMed2006

Forward neutral pion production in p + p and d + Au collisions at square root sNN=200 GeV.

Measurements of the production of forward pi0 mesons from p + p and d + Au collisions at square root sNN=200 GeV are reported. The p + p yield generally agrees with next-to-leading order perturbative QCD calculations. The d + Au yield per binary collision is suppressed as eta increases, decreasing to approximately 30% of the p + p yield at eta =4.00, well below shadowing expectations. Exploratory measurements of azimuthal correlations of the forward pi0 with charged hadrons at eta approximately 0 show a recoil peak in p + p that is suppressed in d + Au at low pion energy. These observations are qualitatively consistent with a saturation picture of the low-x gluon structure of heavy nuclei.

Journal Article↗

PubMed2006

Strange baryon resonance production in sqrt s NN=200 GeV p+p and Au+Au collisions.

We report the measurements of Sigma(1385) and Lambda(1520) production in p+p and Au+Au collisions at sqrt[s{NN}]=200 GeV from the STAR Collaboration. The yields and the p(T) spectra are presented and discussed in terms of chemical and thermal freeze-out conditions and compared to model predictions. Thermal and microscopic models do not adequately describe the yields of all the resonances produced in central Au+Au collisions. Our results indicate that there may be a time span between chemical and thermal freeze-out during which elastic hadronic interactions occur.

Journal Article↗

PubMed2006

The removal and recovery of Cr(VI) by Li/Al layered double hydroxide (LDH).

Hexavalent Cr has been identified as one of the toxic metals commonly present in industrial effluents. Among the treatment techniques developed for removing Cr(VI) from waste waters, sorption is most commonly applied, due to its simplicity and efficiency. However, few adsorbents can be recycled and reused cost-effectively. In this study, the removal and recovery of Cr(VI) from water using Li/Al LDH was investigated. The removal of Cr(VI) by Li/Al LDH was evaluated in a batch mode. The results demonstrated that Cr(VI) adsorption onto Li/Al LDH occurs by replacing the Cl(-) that originally exists in the interlayer of the adsorbent. The degree of Cr(VI) adsorption observed for Li/Al LDH was relatively high and the process occurred rapidly; however, a portion of adsorbed Cr(VI) was gradually desorbed, due to the Li de-intercalation of Li/Al LDH. Lithium de-intercalation from Li/Al LDH with interlayer Cl(-) and interlayer Cr(VI) follows the first order kinetics and has the activation energies of 76.6 and 41.5 kJ mol(-1), respectively. The properties of thermal unstability and the high adsorption capacity of Li/Al LDH may lead to the development of an innovative technique for the removal of Cr(VI) from Cr(VI)-containing wastewater. That is, Li/Al LDH may be used as an effective adsorbent for the adsorption of Cr(VI) in an ambient environment. Following the adsorptive process, the adsorbed Cr(VI) may be released, using heated water to treat the Cr(VI)-containing Li/Al LDH particles. Through this hydrothermal treatment of the used adsorbent, Cr(VI) can be recovered and the solid product (gibbsite) can be recycled for further use.

Aluminum Hydroxide↗

PubMed2006

Atomic pillar-based nanoprecipitates strengthen AlMgSi alloys.

Atomic-resolution electron microscopy reveals that pillarlike silicon double columns exist in the hardening nanoprecipitates of AlMgSi alloys, which vary in structure and composition. Upon annealing, the Si2 pillars provide the skeleton for the nanoparticles to evolve in composition, structure, and morphology. We show that they begin as tiny nuclei with a composition close to Mg2Si2Al7 and a minimal mismatch with the aluminum matrix. They subsequently undergo a one-dimensional growth in association with compositional change, becoming elongated particles. During the evolution toward the final Mg5Si6 particles, the compositional change is accompanied by a characteristic structural change. Our study explains the nanoscopic reasons that the alloys make excellent automotive materials.

Journal Article↗

PubMed2006

Image deconvolution in spherical aberration-corrected high-resolution transmission electron microscopy.

The method of image deconvolution developed previously for FEG high-resolution transmission electron microscope (HRTEM) without a spherical aberration (C(s)) corrector was for the first time applied to FEG HRTEM with a C(s)-corrector. The principle and the procedure of image deconvolution are briefly described. Four qualified [1 1 0] images of Si were selected from a through-focus series to perform image deconvolution. The projected potential is successfully derived from all the images, and the obtained "dumbbell" structure maps of Si [1 1 0] are in good agreement with the calculated potential map. The criterion of selecting qualified images for performing image deconvolution is indicated. The possibility of applying image deconvolution to defect study and to ab initio crystal structure determination is discussed.

Journal Article↗

PubMed2006

Inhibition of glutamate uptake in the spinal cord induces hyperalgesia and increased responses of spinal dorsal horn neurons to peripheral afferent stimulation.

Glutamate is a primary excitatory neurotransmitter in the mammalian CNS. Glutamate released from presynaptic neurons is cleared from the synaptic cleft passively by diffusion and actively by glutamate transporters. In this study, the role of glutamate transporters in sensory processing in the spinal cord has been investigated in behavioral, in vivo and in vitro experiments. Intrathecal application of a non-selective glutamate transport inhibitor, L-trans-pyrrolidine-2,4-dicarboxylic acid (10 microl of 100 microM solution) induced hypersensitivity to peripheral mechanical and thermal stimuli. Topical application of L-trans-pyrrolidine-2,4-dicarboxylic acid (100 microM) onto the dorsal surface of the L3-L6 spinal cord increased spontaneous activities, innocuous and noxious stimulus-evoked responses and after-discharges of wide dynamic range neurons in the L4-5 spinal segments. Whole cell recordings made from superficial dorsal horn neurons in an isolated whole spinal cord from newborn rats (2-3 weeks old) revealed that bath-applied L-trans-pyrrolidine-2,4-dicarboxylic acid (100 microM) produced partial membrane depolarization, increased spontaneous action potentials with decreased neuronal membrane resistance and time constant, but without significant changes of capacitance. Finally, the amplitude and duration of primary afferent evoked-excitatory postsynaptic currents recorded from neurons in the substantia gelatinosa in the spinal slices from young adult rats (6-8 weeks old) were increased in the presence of L-trans-pyrrolidine-2,4-dicarboxylic acid (100 microM). This study indicates that glutamate transporters regulate baseline excitability and responses of dorsal horn neurons to peripheral stimulation, and suggests that dysfunction of glutamate transporters may contribute to certain types of pathological pain.

Action Potentials↗

PubMed2006

Changes in the expression of Fas on T lymphocytes after allogeneic fetal thymus transplantation in systemic lupus erytematosus mice.

BACKGROUND: Systemic lupus erythematosus (SLE) is an autoimmune disorder that can produce inflammation in many organ systems. The rate of spontaneous apoptosis in lymphocytes from human SLE patients has been reported to be increased both in vivo and in vitro. Studies of fetal thymus transplantation in an autoimmune syndrome indicate that cellular immunity can be reconstituted and regulatory T cell functions can be normalized. OBJECTIVES: The aim of this study was to assess changes in Fas expression on T lymphocytes following fetal thymus transplant. METHODS: (B/CxB6) F1 (H-2d/h) female F1 mice were assigned to groups designated transplantation, normal, and control. Mice in the transplantation and control groups received parental BALB/c lymphocytes intravenously. Thirty days after injection of the lymphocytes, each F1 mouse in the transplantation group received a fetal thymus graft under the right renal capsule. Mice in the control group did not receive thymus transplant and mice in the normal group received neither parental lymphocytes nor a fetal thymus graft. All mice received cyclosporin A at 2 mg/kg daily for the first 12 days after transplantation or starting on the corresponding day. Thirty days after thymus transplantation, F1 mice were sacrificed and expression of Fas in peripheral blood lymphocytes was analyzed by flow cytometry. RESULTS: The percentage of CD4Fas+ T lymphocytes was significantly increased in the control group and the transplantation group compared with the normal group. Corresponding significant differences were observed for CD8Fas+, CD4CD25Fas', and CD45RB(low)Fas+ T lymphocytes. CONCLUSIONS: In this study, we found that fetal thymus transplantation had a significant effect on the expression of Fas by T cell subtypes in SLE mice.

Animals↗

PubMed2005

Multistrange Baryon elliptic flow in Au+Au collisions at square root of sNN=200 GeV.

We report on the first measurement of elliptic flow v2(pT) of multistrange baryons Xi- +Xi+ and Omega- + Omega+ in heavy-ion collisions. In minimum-bias Au+Au collisions at square root of s(NN)=200 GeV, a significant amount of elliptic flow, comparable to other nonstrange baryons, is observed for multistrange baryons which are expected to be particularly sensitive to the dynamics of the partonic stage of heavy-ion collisions. The pT dependence of v2 of the multistrange baryons confirms the number of constituent quark scaling previously observed for lighter hadrons. These results support the idea that a substantial fraction of the observed collective motion is developed at the early partonic stage in ultrarelativistic nuclear collisions at the Relativistic Heavy Ion Collider.

Journal Article↗

PubMed2005

Translocation of double-strand DNA through a silicon oxide nanopore.

We report double-strand DNA translocation experiments using silicon oxide nanopores with a diameter of about 10 nm . By monitoring the conductance of a voltage-biased pore, we detect molecules with a length ranging from 6557 to 48 500 base pairs. We find that the molecules can pass the pore both in a straight linear fashion and in a folded state. Experiments on circular DNA further support this picture. We sort the molecular events according to their folding state and estimate the folding position. As a proof-of-principle experiment, we show that a nanopore can be used to distinguish the lengths of DNA fragments present in a mixture. These experiments pave the way for quantitative analytical techniques with solid-state nanopores.

Biocompatible Materials↗

PubMed2005

Maximum likelihood estimation of structure parameters from high resolution electron microscopy images. Part II: a practical example.

This paper is the second part of a two-part paper on maximum likelihood (ML) estimation of structure parameters from electron microscopy images. In order to show the practical applicability of the theoretical methods described in the first part of this two-part paper, an experimental study of an aluminium crystal is presented. In this study, structure parameters, atom column distances in particular, are estimated from high-resolution transmission electron microscopy (HRTEM) images using the ML method. The necessary steps to be made in the application of this method will be worked out one by one, including model assessment, the computation of the ML parameter estimates, and the construction of confidence intervals for these parameter estimates.

Journal Article↗

PubMed2005

Bayesian models for population-based case-control studies when the population is in Hardy-Weinberg equilibrium.

Association analysis of genetic polymorphisms has been mostly performed in a case-control setting with unrelated affected subjects compared with unrelated unaffected subjects. In this paper, we present a Bayesian method for analyzing such case-control data when the population is in Hardy-Weinberg equilibrium. Our Bayesian method depends on the informative prior which is the retrospective likelihood based on historical data, raised to a power a. By modeling the retrospective likelihood properly, different prior information about the studied population can be incorporated into the specification of the prior. The scalar a is a precision parameter quantifying the heterogeneity between current and historical data. A guide value for a is discussed in this paper. The informative prior and posterior distributions are proper under very general conditions. Therefore, our method can be applied in most case-control studies. Further, for assessing gene-environment interactions, our approach will naturally lead to a Bayesian model depending only on the case data, when genotype and environmental factors are independent in the population. Thus our approach can be applied to case-only studies. A real example is used to show the applications of our method.

Bayes Theorem↗

PubMed2005

Stage migration influences on stage-specific survival comparison between D1 and D3 gastric cancer surgeries.

AIMS: We evaluate the influency stage migration in a randomised trial comparing D1 (N 1 lymphadenectomy) and D3 (N 1, 2 and 3 lymphadenectomy) dissections. METHODS: Two hundred and thirteen curatively resected patients were analysed, with this TNM data. RESULTS: After applying D3 patients' data according to simulated D1 staging, D3 resections were associated with up-staging to N2-3 levels in 8% of patients according to the N stage. The likelihood of N-status migration increased with increasing depth of invasion into the gastric wall. The increases in the calculated survival rate after stage migration on known 5-year survival rates were: 2% in stage IB, 1% in stage II, 4% in stage IIIA, and 1% in stage IIIB. CONCLUSIONS: Stage migration secondary to meticulous lymph node dissection affects stage-specific survival rates. True therapeutic survival benefit of D3 resection can only be assessed in this context.

Gastrectomy↗

PubMed2005

The impact of pretransplant cytomegalovirus infection on acute renal allograft rejection.

BACKGROUND: The role of cytomegalovirus (CMV) infection in renal allograft rejection remains controversial; moreover, there are few studies on pretransplant infections. This study sought to investigate whether pretransplant CMV infections had negative effects on acute rejection episodes (ARE) and to evaluate the effect of preemptive treatment. METHODS: This retrospective single-center study of 416 transplant recipients from October 1, 2000 to September 1, 2003 had CMV infections diagnosed by CMV antigenemia tests. The incidences of ARE were compared between CMV-infected and noninfected groups. Risk factors for ARE were analyzed. Based on preemptive treatment, pretransplant CMV-infected recipients were divided into ganciclovir-treated and nontreated groups and the incidence of ARE was compared between the two groups. RESULTS: One hundred eighty four recipients had CMV infections pretransplant; the infection rate was 44.2%. Fifty five recipients had ARE among the pretransplant CMV-positive group, which was significantly higher than that in the noninfected group (29.9% vs 19.5%, P = .014). But the rejection subgroups and renal function recovery had no significant differences. While the presence of pretransplant infection was an independent predictor of ARE (RR = 1.807), severity showed no significant impact on ARE. Among 184 pretransplant CMV infection recipients, the incidences of ARE were 14.3% and 18.0% in ganciclovir-treated versus nontreated patients, respectively (P = .650). CONCLUSIONS: Pretransplant CMV-positive recipients were at greater risk of ARE. Pretransplant CMV infection was an independent risk factor for ARE. Preemptive antiviral treatment did not show protective effects against ARE related to CMV infection-mediated immunological injuries.

Acute Disease↗

PubMed2004

Transcriptional regulation of human osteopontin promoter by C/EBPalpha and AML-1 in metastatic cancer cells.

Osteopontin (OPN) is a secreted glycoprotein produced by osteoclasts, macrophages, T cells, hematopoietic cells, and vascular smooth muscle cells. It contributes to macrophage homing and cellular immunity. It also mediates neovascularization, inhibits apoptosis, and plays important roles in extracellular matrix remodeling and angiogenesis. These properties are also characteristics of metastatic cancer cells. Consequently, the OPN gene was found to be upregulated among various metastatic cancer cells. This suggests that OPN is involved in tumor metastasis. How the OPN gene is upregulated in metastatic cancer cells remains to be illustrated. Thus, we investigated the transcriptional activation of the OPN promoter in the human metastatic cancer cell line A2058. We cloned the OPN promoter, and serial deletion analysis of the OPN promoter showed that the region between -170 and -127 may act as an enhancer to control the OPN gene in metastatic tumor cells. This region was found to contain overlapped AML-1 and C/EBP binding site motifs. Gel-mobility-shift assays using the A2058 nuclear extract and AML-1a or C/EBPalpha (CCAAT/enhancer binding protein alpha) recombinant protein indicated that these two transcription factors can bind to the overlapped AML-1 /C/EBP binding site motifs on the OPN regulatory sequence from -147 to -127. Surprisingly, the gel-shift experiments did not show supershift complex formation between AML-1 and C/EBPalpha. Functional analysis showed that the C/EBPalpha was more potent than the complex of AML-1 and its cofactor CBFbeta to upregulate the OPN promoter. In addition, AML-1 and C/EBPalpha did not exhibit transactivation additively or synergistically. Our results suggest that AML-1 and C/EBPalpha play an important role in the upregulation of the OPN gene in metastatic tumor cells.

Binding Sites↗

PubMed2004

The pre-styloid compartment of the parapharyngeal space: a three-dimensional digitized model based on the Chinese Visible Human.

To build a digitized visible model of the parapharyngeal space of the Chinese Visible Human and to provide a sectional anatomic basis for radiological and clinical diagnosis of the parapharyngeal space, sectional anatomy data of the parapharyngeal space were selected from the Chinese Visible Human male and female to compare with MR imaging findings in the axial planes. From these data the parapharyngeal space and surrounding structures were segmented. They were then reconstructed in three dimensions on PC. In the axial planes of the sectional anatomy and MR imaging, the shape, content and relations of the parapharyngeal space were clearly displayed and the dominant plane for showing the parapharyngeal space was elicited. The three-dimensional reconstructed images displayed perfectly the anatomic relationships of the parapharyngeal space, parotid, muscles, mandible and vessels. All reconstructed structures can be displayed singly, in groups or as a whole; any diameter or angle of the reconstructed structures can be easily measured. The Chinese Visible Human male and female data set can provide complete and accurate data. The digitized model of the parapharyngeal space and its surroundings offers unique insights into the complex anatomy of the area, providing morphologic data for imaging diagnosis and surgery of the parapharyngeal space.

Anatomy, Cross-Sectional↗