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Biomedical subjects

S Y Chen

Publications and source records attributed to S Y Chen.

At least 19 recordsLinked to original sources
PubMed2006

Characteristics of neoplasm occurrence and the therapeutic effect of sirolimus in South Chinese kidney transplant recipients.

Kidney transplantation (KTx) recipients are at a higher risk of oncogenesis when compared to the general population. Sirolimus (SRL), a potent immunosuppressant, has shown promising antineoplastic effects in vitro and in vivo. This study retrospectively analyzed the neoplasm occurrence and the efficiency of SRL on unresectable malignancies in South Chinese KTx recipients. Thirty-three (1.64%) of 2017 patients who received KTx from January 1984 to December 2004 developed neoplasms at 4 to 117 months posttransplant, mostly in digestive organs (33.3%), the hematologic system (15.2%), or the skin (12.1%). The most common type was liver cancer (24.2%), followed by skin cancer, lymphoma, and thyroid cancer (9.1%). The median survival times were 41.5 and 6.0 months for those who did (n = 10) receive radical surgery or did not (n = 23), respectively. The 20-month survival rates were 70.0% versus 13.0% (P < .01). For unresectable patients, the median survival time of those treated with SRL (n = 8) was 14.5 months compared to 3.0 months for those who did not (n = 15). The survival rates at 12(th) and 20(th) months were 75.0% and 37.5% in the SRL group and 6.7% and 0% in the non-SRL group (P < .05). In conclusion, when compared with Western studies, a lower incidence and unique location pattern (liver cancer-dominant) are characteristics of de novo posttransplant neoplasms in South Chinese KTx recipients. Early diagnosis and feasible radical surgery are favorable for prognosis, and SRL is a treatment of choice for KTx recipients with neoplasms.

China↗
PubMed2006

Managing the disposition of potentially radioactive scrap metal.

In 2002, the National Council on Radiation Protection and Measurements (NCRP) issued Report No. 141, Managing Potentially Radioactive Scrap Metal. The report evaluates management policy and related issues regarding scrap metal generated in regulated facilities that have been under radiological control or have radiological concerns. It has been estimated that more than 9 million metric tons of scrap metal of all types that have been associated with the production or use of radioactive materials will be generated during the coming decades at various facilities across the United States. Currently, disposition of such metal has encountered particular obstacles, primarily because of the lack of a consistent disposition policy, systematic regulatory provisions, and, above all, public understanding. Without clarity in the regulatory passage, much of the scrap metal, including metal that has not been contaminated, could be mischaracterized as low-level radioactive waste, resulting in a costly disposition operation. NCRP Report No. 141 identifies this general category of metal as "potentially radioactive scrap metal" (PRSM) and discusses the viable disposition options for facilitating its management. Because much of the PRSM has been found to contain very low residual radioactivity or even none at all, one consideration is to release such metal outside of the radiological control framework. This would require the development and implementation of a set of strict release standards in the United States that would necessarily be risk-based and supported by a comprehensive management scheme. Developing a policy of this kind, however, would entail the resolution of many issues, not the least of which would be public acceptance, including that of the metal industry, of the possible recycling of PRSM in the general commerce.

Decision Making↗
PubMed2005

Progressive decrease of proinsulin secretion in sulphonylurea-treated type 2 diabetes.

Progressive deterioration of beta-cell function is proposed as a disease-related factor of sulphonylurea (SU) failure in type 2 diabetes. If it gradually worsens over time then disease duration may mirror the progressive beta-cell deterioration. The aim of the present study is to assess whether or not disease duration is influential in remodelling the secretion pattern of insulin-like molecules and in glucose control of SU-treated type 2 diabetes. A research model is used to investigate proinsulin secreting capacity over time, using two groups of patients: i) disease duration <5 years (n=62), comprising SU responders (SUr; n=48) and SU failures (SUf; n=14); and ii) disease duration > or = 5 years (n= 37), comprising an SUr group (n=17) and an SUf group (n=20). Blood samples are taken at 0 h, 0.5 h 1 h, 2 h and 3 h during a standard oral glucose tolerance test and measured for glucose, total proinsulin (TPI), intact proinsulin (IPI) and specific insulin (SI) concentrations. Pairwise comparison of estimated marginal means of blood glucose, SI, IPI and TPI levels at each time point are carried out between groups and subgroups. (SUr vs. SUf). Homa insulin resistance index (IR index) is applied to analyse IR between the groups. It was found that patients with shorter disease duration had higher proinsulin (TPI and IPI) levels at all time points (P<0.05), together with a lower glucose level at 2 h and 3 h (P<0.05). Homa insulin index analysis showed no difference between the two groups (P=0.26). Results also showed that the SUr group had a significantly lower glucose level at Oh and 3h (P<0.05), although no significant difference in insulin and proinsulin levels was found between the SUr and SUf groups. In conclusion, proinsulin may play an important role in glucose control in SU-treated type 2 diabetes, but the effect is reduced in SUf patients.

Adult↗
PubMed2005

Toward the framework and implementation for clearance of materials from regulated facilities.

The disposition of solid materials from nuclear facilities has been a subject of public debate for several decades. The primary concern has been the potential health effects resulting from exposure to residual radioactive materials to be released for unrestricted use. These debates have intensified in the last decade as many regulated facilities are seeking viable management decisions on the disposition of the large amounts of materials potentially containing very low levels of residual radioactivity. Such facilities include the nuclear weapons complex sites managed by the U.S. Department of Energy, commercial power plants licensed by the U.S. Nuclear Regulatory Commission (NRC), and other materials licensees regulated by the NRC or the Agreement States. Other facilities that generate radioactive material containing naturally occurring radioactive materials (NORM) or technologically enhanced NORM (TENORM) are also seeking to dispose of similar materials that may be radioactively contaminated. In contrast to the facilities operated by the DOE and the nuclear power plants licensed by the U.S. Nuclear Regulatory Commission, NORM and TENORM facilities are regulated by the individual states. Current federal laws and regulations do not specify criteria for releasing these materials that may contain residual radioactivity of either man-made or natural origin from regulatory controls. In fact, the current regulatory scheme offers no explicit provision to permit materials being released as "non-radioactive," including those that are essentially free of contamination. The only method used to date with limited success has been case-by-case evaluation and approval. In addition, there is a poorly defined and inconsistent regulatory framework for regulating NORM and TENORM. Some years ago, the International Atomic Energy Agency introduced the concept of clearance, that is, controlling releases of any such materials within the regulatory domain. This paper aims to clarify clearance as an important disposition option for solid materials, establish the framework and basis of release, and discuss resolutions regarding the implementation of such a disposition option.

Decontamination↗
PubMed2005

Vision sensor planning for 3-D model acquisition.

A novel method is proposed in this paper for automatic acquisition of three-dimensional (3-D) models of unknown objects by an active vision system, in which the vision sensor is to be moved from one viewpoint to the next around the target to obtain its complete model. In each step, sensing parameters are determined automatically for incrementally building the 3-D target models. The method is developed by analyzing the target's trend surface, which is the regional feature of a surface for describing the global tendency of change. While previous approaches to trend analysis are usually focused on generating polynomial equations for interpreting regression surfaces in three dimensions, this paper proposes a new mathematical model for predicting the unknown area of the object surface. A uniform surface model is established by analyzing the surface curvatures. Furthermore, a criterion is defined to determine the exploration direction, and an algorithm is developed for determining the parameters of the next view. Implementation of the method is carried out to validate the proposed method.

Algorithms↗
PubMed2005

Growth of carbon nanotubes at low powers by impedance-matched microwave plasma enhanced chemical vapor deposition method.

A solo carbon nanotube (CNT) was successfully grown on nickel electrodes by a microwave plasma enhanced chemical vapor deposition (MPECVD) method equipped with an impedance-matched substrate holder with the reaction gases composed of hydrogen (H2), carbon dioxide (CO2), and methane (CH4) mixtures. An introduction of carbon dioxide gas before CNTs growth, the substrate temperature can easily be reached above 610 degrees C even heated at a low microwave power. This can be enunciated from fact that carbon dioxide inherits with higher bond energy for molecular dissociation, lower thermal conductivity, and higher heat capacity in comparing to other gases. The electron field emissions for randomly aligned CNTs and well-aligned CNTs grown by MPECVD and by radio frequency assisted hot-filament methods, respectively, are measured and compared. The higher field emission characteristic of the randomly aligned CNTs is presumed to be due to the protruded CNTs, which inheriting with less screening effect and manifesting with defects are crucial to play the effective emission sites.

Carbon Dioxide↗
PubMed2004

Factors affecting the accuracy of elastometric impression materials.

OBJECTIVES: The purpose of this study was to evaluate the effects of (1) various impression materials, (2) different storage times and (3) the proportion of inorganic filler on the accuracy and stability of elastometric impression materials. METHODS: The impression materials studied included three alginate impression materials (Algiace Z, CAVEX and Jeltrate), five commercial silicone impression materials (Aquasil, Exaflex regular type, Express, Coltex fine and Rapid liner) and two experimental silicone impression materials designed for this study (KE106A and KE106B). Impressions were made of 10 metal dies that mimicked prepared crowns. After an impression was taken, dental stone was immediately poured into the alginate impressions, while the silicone impressions was poured 30 min later and waited for 1 h for setting. The second and third stone dies were made 1 and 24 h later, respectively. The diameters of the occlusal surfaces of the metal dies and stone casts were determined using photographs of the surfaces taken with a Kodak DC 290 digital camera. The pictures were then measured using a photomicrograph digitized integration system to calculate any discrepancy. Because each impression was used to make three rounds of stone dies, two-factor mixed factorial ANOVA was used to evaluate the effect of materials and storage time on the accuracy of the stone casts. The simple effects analysis, combined with multiple comparisons considering the per family type I error rate, was performed following confirmation that an interaction between the two factors was significant. RESULTS: The results showed that: (1) there was a significant interaction effect between materials and storage times on the accuracy of the impressions. (2) Two addition type silicone materials, Aquasil and Exaflex, had the greatest accuracy and stability. (3) The experimental material KE106A had the least accuracy in the first and second rounds and the alginate impression material CAVEX had the least accuracy in the third round. (4) The stabilities of CAVEX and Jeltrate were the least consistent of the 10 materials and decreased significantly with storage time. (5) When the experimental material had a low proportion of filler (KE106A), there was a significantly greater dimensional discrepancy compared to the same material with a higher proportion of filler (KE106B). CONCLUSIONS: The accuracies varied among the 10 impression materials over three rounds. Of all the materials, the addition type silicone materials, Aquasil and Exaflex, had relatively greater accuracy and stability. The discrepancy of the alginate impression materials increased with storage time. The large loading of filler showed less discrepancy.

Alginates↗
PubMed2004

The cytological mechanism of low fertility in the naked seed rice.

The low fertility of naked seed rice (NSR) was investigated by the following observations: somatic chromosome constitute, behavior of pollen mother cells (PMCs), the germination of mature pollen grains, the development of male and female gametes and the structure of the anther opening. The results indicated that somatic chromosomal number was 2n = 24, behavior of PMCs were normal and most of pollen grains could regularly develop further to mature male gametophytes in NSR. And dehiscence chamber and thickened endothecium cell (TEC) in numerous anthers of the NSR were developed abnormally after dicaryotic phase, result in few anthers complete opening and most partly opening or failure to opening, therefore much fewer of pollen grains attach on the stigma as compared with normal variety. Furthermore most of embryo sacs possessed abnormal structure and were sterile. All of above illustrated that the failure of the anther opening and the abortion of female gametophyte were main factors controlling the low seed-setting rate of the NSR.

China↗
PubMed2004

Automatic sensor placement for model-based robot vision.

This paper presents a method for automatic sensor placement for model-based robot vision. In such a vision system, the sensor often needs to be moved from one pose to another around the object to observe all features of interest. This allows multiple three-dimensional (3-D) images to be taken from different vantage viewpoints. The task involves determination of the optimal sensor placements and a shortest path through these viewpoints. During the sensor planning, object features are resampled as individual points attached with surface normals. The optimal sensor placement graph is achieved by a genetic algorithm in which a min-max criterion is used for the evaluation. A shortest path is determined by Christofides algorithm. A Viewpoint Planner is developed to generate the sensor placement plan. It includes many functions, such as 3-D animation of the object geometry, sensor specification, initialization of the viewpoint number and their distribution, viewpoint evolution, shortest path computation, scene simulation of a specific viewpoint, parameter amendment. Experiments are also carried out on a real robot vision system to demonstrate the effectiveness of the proposed method.

Algorithms↗
PubMed2004

Dynamic three-dimensional reconstruction and modeling of cardiovascular anatomy in children with congenital heart disease using biplane angiography.

Modeling and simulation of cardiovascular biomechanics and fluid dynamics from patient-specific data is a continuing topic of research investigation. Several methodologies utilizing CT, MRI and ultrasound to re-create the three-dimensional anatomy of the cardiovascular system have been examined. Adaptation of these models to pediatric applications has not been studied as extensively. There is significant need for such techniques in pediatric congenital heart disease since local anatomy may exhibit highly unusual geometry, and three-dimensional information would be of significant use for surgical and interventional planning, biomechanical and fluid dynamic simulation, and patient counseling. We report here on the adaptation and application of a three-dimensional reconstruction technique that utilizes bi-plane angiographic images as the base data sets. The method has been validated in a variety of adult imaging situations including coronary artery imaging and intervention. The method uses a skeletonization approach whereby local centerline, diameter, branching and tortuosity of the vasculature are obtained to create the three-dimensional model. Ten patients with a variety of etiology were imaged and 3D reconstructions were obtained. Excellent images were obtained of complex anatomy including the highly branched pulmonary vasculature and Fontan surgical connections. The data were then translated into solid and surface models to facilitate viewing, export into computational fluid dynamic grids, and into files suitable for stereo lithography fabrication (STL). This method appears promising for the dynamic study of complex cardiovascular anatomy found in congenital heart disease. Optimization of the method to facilitate on-line reconstruction and simulation are currently ongoing.

Algorithms↗
PubMed2004

Inhibition of the proliferation of smooth muscle cells from human coronary bypass vessels by vasonatrin peptide.

Abnormal proliferation of vascular smooth muscle cells (VSMCs) is known to be a key event in the development of atherosclerosis and restenosis. The present study examined the effect of a novel synthetic natriuretic peptide, vasonatrin peptide (VNP), on norepinephrine (NE)-induced proliferation of VSMCs from coronary bypass vessels. Human VSMCs were isolated from an internal mammary artery (IMA) and saphenous vein (SV) by explant culture and stimulated with NE. MTT assay and [3H] thymidine-incorporation were undertaken to analyze cell proliferation and radioimmunoassay was used to determine the level of intracellular cyclic 3',5'-guanosine monophosphate (cyclic GMP). NE (10(-8) - 10(-7) mol/l) had a mitogenic effect in human VSMCs from both SV and IMA. However, NE-stimulated proliferation of VSMCs from SV was greater than that from IMA. Furthermore, low concentration of NE (10(-10) mol/l) promoted cell growth in SV-derived cells but not in IMA-derived cells. VNP (10(-8) - 10(-6) mol/l) reduced NE-induced cell proliferation and increased intracellular cyclic GMP, which were abrogated by HS-142-1. In addition, the growth inhibition of VNP was mimicked by 8-bromo-cGMP. These results indicate that VNP has a significant inhibitory effect on NE-stimulated proliferation of human VSMCs from both IMA and SV, which is mediated by guanylate cyclase-linked receptors by increasing cyclic GMP.

Analysis of Variance↗
PubMed2003

Energy and enstrophy transfer in decaying two-dimensional turbulence.

We present experimental data on the direct enstrophy cascade in decaying two-dimensional turbulence. Velocity and vorticity fields are obtained using particle tracking velocimetry. From those fields we directly compute the enstrophy and energy flux by using a filtering technique inspired by large-eddy simulations. This allows considerable insight into the physical processes of turbulence when compared with structure-function or spectral analysis. The direct cascade of enstrophy is weakly forward, with almost as much backscatter as down-scale enstrophy transfer, whereas the inverse energy cascade is strongly upscale with a modest amount of backscatter.

Journal Article↗
PubMed2003

Secondary sulphonylurea failure: what pathogenesis is responsible?

Sulphonylurea (SU) stimulates insulin secretion by pancreatic beta-cells and is generally used as a first-line treatment for type 2 diabetes. However, after long-term SU treatment (six months or over), some patients begin to show an increase in blood glucose once again (secondary SU failure). Two theories have been put forward to explain this failure--dysfunction of the proinsulin conversion machinery or insulin resistance. However, the primary pathogenesis behind secondary SU failure still needs to be investigated. Using a reliable technique that specifically identifies intact proinsulin (IPI), total proinsulin (TPI) and specific insulin (SI), this study aims to discover if a defect in the proinsulin converting mechanism plays a role in SU failure. Three groups were recruited for this study: healthy controls (n=8), SU responders (n=38) and secondary SU failures (n= 46). Serum concentrations of insulin-related molecules released in response to a standard glucose challenge test were compared between the groups. It was found that total SI was lower in the patient groups (P<0.05 compared to the control group), while TPI and IPI showed no distinct difference between the three groups (P>0.05). TPI:SI ratio and IPI:SI ratio showed marked increases in the patient groups (P<0.05 compared to control group), with no obvious quantitative difference between SU responders and secondary SU failures (P>0.05). Similar results for the Homa Insulin Resistant Index were found between the two patient groups. Interestingly, blood glucose at 180 mins after glucose challenge was significantly higher in the secondary SU failure group (P<0.05), with no correlation to SI, while the SU responder group showed good correlation between the parameters (P<0.05). We conclude that type 2 diabetes is associated with obvious dysfunction in the proinsulin-converting process and shows severe SI deficiency in responding to glucose challenge. Dysfunction of the proinsulin conversion mechanism was not an extra cause responsible for SU failure.

Adult↗
PubMed2003

Case report: diabetic mastopathy.

Diabetic mastopathy is a source of confusion with breast carcinoma. The association between mastopathy and Type I diabetes of long duration has been reported, but this clinical condition is poorly recognized since breast examination is not routinely performed in young diabetic patients. Radiologists' awareness of the constellation of findings in diabetic mastopathy may spare patients from undergoing unwarranted surgical biopsies.

Adult↗
PubMed2003

Assessment of sediment toxicity by metal speciation in different particle-size fractions of river sediment.

Mobility and toxicity of metals associated with sediments are generally affected by metal speciation and granular compositions. Due to the various speciation patterns of heavy metals in sediments, it is not reliable to assess the potential toxicity of heavy metals on the aquatic environment with the total concentrations of heavy metals in sediments. The purposes of this study were to investigate the distribution of metal speciation in different particle-size fractions of sediments collected from two rivers (the Ke-Ya River and Ell-Ren River) in Taiwan, and to assess their potential toxicity to the aquatic ecosystem. Metals in the exchangeable, carbonate-bound and Fe/Mn oxide-bound forms obtained by sequential extraction were considered to be mobile and related with anthropogenic pollution. The degree of metal pollution and potential toxicity of sediments were higher in the lower reaches of both rivers. The metal speciation in sediments had a bimodal distribution over particle-size fractions. Heavy metals were subject to accumulation in the silt/clay fraction (< 25 microm) and coarse sand (420-2,000 microm). By normalizing the sum of the exchangeable, carbonate-bound, and Fe/Mn oxide-bound metals, it suggested that the potential toxicity to the aquatic ecosystem was caused by the fine sediments as well as coarse sediments.

Ecosystem↗
PubMed2003

Effects of ferric ion on bioleaching of heavy metals from contaminated sediment.

Bioleaching is one of the promising procedures for removal of heavy metals from contaminated sediments. The advantages of this biotechnology are that it is easy, efficient, less costly and friendly to the environment. However, the principal disadvantage of this process is its slow kinetics in metal solubilization, which may limit practical application of the bioleaching process. In order to enhance the rate and efficiency of metal solubilization, the ferric ion was used as a catalytic agent in the bioleaching process. It was found that the sediment pH apparently decreased in the bioleaching after addition of ferric ion. The metal solubilization increased quickly after the addition of ferric ion. The rate of metal solubilization was enhanced by the addition of ferric ion, especially for Cr and Pb. An increase in the amount of ferric ion added increased the final efficiency of metal solubilization. The highest final efficiency of metal solubilization was obtained in the bioleaching with 1 g/L of ferric ion. Besides, the growth of sulfur-oxidizing bacteria was not affected by addition of ferric ion in the bioleaching. It was concluded that the kinetics of metal solubilization were enhanced by addition of ferric ion in the bioleaching process.

Bacteria↗