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Biomedical subjects

S C Wang

Publications and source records attributed to S C Wang.

At least 19 recordsLinked to original sources
PubMed2006

Differential cross section and photon-beam asymmetry for the gamma n --> K+ Sigma- reaction at E gamma = 1.5-2.4 GeV.

Differential cross sections and photon-beam asymmetries have been measured for the gamma n --> K+ Sigma- and gamma p --> K+Sigma0 reactions separately using liquid deuterium and hydrogen targets with incident linearly polarized photon beams of E gamma = 1.5-2.4 GeV at 0.6 < cos ThetacmK< 1. The cross section ratio of sigma K+ Sigma-/sigma K+ Sigma0, expected to be 2 on the basis of the isospin 1/2 exchange, is found to be close to 1. For the K+ Sigma- reaction, large positive asymmetries are observed, indicating the dominance of K* exchange. The large difference between the asymmetries for the K+ Sigma- and K+ Sigma0 reactions cannot be explained by simple theoretical considerations based on Regge model calculations.

Journal Article↗
PubMed2006

Heterogeneous meshing and biomechanical modeling of human spine.

We aim to develop a patient-specific biomechanical model of human spine for the purpose of surgical training and planning. In this paper, we describe the development of a finite-element model of the spine from the VHD Male Data. The finite-element spine model comprises volumetric elements suitable for deformation and other finite-element analysis using ABAQUS. The mesh generation solution accepts segmented radiological slices as input, and outputs three-dimensional (3D) volumetric finite element meshes that are ABAQUS compliant. The proposed mesh generation method first uses a grid plane to divide the contours of the anatomical boundaries and its inclusions into discrete meshes. A grid frame is then built to connect the grid planes between any two adjacent planes using a novel scheme. The meshes produced consist of brick elements in the interior of the contours and with tetrahedral and wedge elements at the boundaries. The nodal points are classified according to their materials and hence, elements can be assigned different properties. The resultant spine model comprises a detailed model of the 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, and S1. Each of the vertebrae and intervertebral disc has between 1200 and 6000 elements, and approximately 1200 elements, respectively. The accuracy of the resultant VHD finite element spine model was good based on visual comparison of volume-rendered images of the original CT data, and has been used in a computational analysis involving needle insertion and static deformation. We also compared the mesh generated using our method against two automatically generated models; one consists of purely tetrahedral elements and the other hexahedral elements.

Adult↗
PubMed2006

[A mixture of antimicrobial peptides and fibrin glue in treatment of partial-thickness burn wounds].

BACKGROUND: Antimicrobial peptides are naturally occurring cationic peptides. The first-line of defense in infected burns is the innate immune system, of which antimicrobial peptides are essential parts. To facilitate their topical use in infected partial-thickness burns, the efficacy of a mixture with fibrin glue in vitro and in vivo was tested. METHODS: After in vitro tests, 15 male Sprague-Dawley rats received partial-thickness burns. Afterwards, the wounds were infected with multiresistant Pseudomonas aeruginosa. The animals received PG-1 (100 microg/ml, n=5), fibrin glue (n=5), or a mixture of both (n=5) topically. The efficacy of the materials was previously proven by radial diffusion assay. After 24 h, the infected and burned skin was harvested and quantitative bacterial counts per gram of skin performed. RESULTS: The biologic effect of the peptides was confirmed in vitro. The PG-1 and fibrin glue groups did not show significant differences in bacterial numbers, whereas the mixture group showed significant reduction in Pseudomonas in vivo (P<0.04 and P<0.01). CONCLUSION: A mixture of an antimicrobial peptide and commercially available fibrin glue is capable of significantly reducing bacteria in infected partial thickness burns in vivo compared to controls.

Animals↗
PubMed2006

Liver transplantation for hepatocellular carcinoma in Singapore.

INTRODUCTION: The prognosis of patients with hepatocellular carcinoma (HCC) is poor. Surgical resection offers the benefit of removal of the tumour but is associated with liver decompensation and tumour recurrence, even after successful surgery. Liver transplantation offers the benefits of complete tumour removal with prevention of both decompensation and recurrence post-operation. This paper aims to review results of liver transplantation for patients with HCC in Singapore. METHODS: All adult patients with HCC accepted on the waiting list for liver transplantation (based on the Milan criteria) from 1996 to 2004 in Singapore were reviewed. Patients' HCC were managed with either transarterial chemoembolisation or percutaneous radiofrequency ablation while they were on the waiting list. Post-transplant survival and factors associated with mortality were analysed by Cox regression analysis. RESULTS: 41 patients with HCC were accepted onto the waiting list over the nine-year period. 22 underwent transplantation and 19 did not, with a one-year survival of 91 percent versus 24 percent, respectively. (p-value is less than 0.001). Mean waiting time for transplant was 39 weeks. Post-transplant HCC recurrence was 2/22 (nine percent). Among all patients, mortality was significantly related to baseline white cell counts, prothrombin time, age, alpha-foetoprotein level, Child-Pugh score, and whether patients underwent transplant. CONCLUSION: Despite the relatively long waiting time of a mean of 39 weeks, post-transplant recurrence of HCC was relatively low at nine percent. Liver transplant is an effective treatment for patients with a HCC, with a reasonable long-term survival.

Carcinoma, Hepatocellular↗
PubMed2006

Cancer screening in Singapore, with particular reference to breast, cervical and colorectal cancer screening.

Cancer is the leading cause of mortality in Singapore, accounting for 27.1% of deaths in 2004. The most common cancers are those of the lung, colon and rectum, liver, stomach, and prostate in men; and breast, colon and rectum, lung, ovary and cervix in women. Singapore has the highest age-adjusted breast cancer incidence in Asia. National population screening programmes have been implemented for breast and cervical cancer. BreastScreen Singapore (BSS), the first population-based nationwide mammographic breast-screening programme in Asia, was launched in 2002, incorporating international standards and practice guidelines. For improved quality assurance, two-view screening mammography is carried out. From January 2002 until March 2004, BSS conducted over 84,000 screens, with an overall recall rate of 9.5%, and an overall invasive cancer detection rate of 4.48 per 1000 screened. Close to 30% of the cancers diagnosed was ductal carcinoma in situ. Papanicolaou (Pap) smear screening for cervical cancer has been available opportunistically since 1964. The national CervicalScreen Singapore programme was launched in 2004, aiming to achieve coverage of 80% of targeted women by 2010. Colorectal cancer currently has the highest incidence of all cancers in Singapore. The health authorities advocate colorectal cancer screening for the average risk population, starting from age 50 years, but in the absence of a national screening programme, the reliance is on opportunistic screening.

Adult↗
PubMed2005

Near-threshold diffractive psi-meson photoproduction from the proton.

Photoproduction of a phi meson on protons was studied by means of linearly polarized photons at forward angles in the low-energy region from threshold to Egamma = 2.37 GeV. The differential cross sections at t = -|t|min do not increase smoothly as Egamma increases but show a local maximum at around 2.0 GeV. The angular distributions demonstrate that phi mesons are photoproduced predominantly by helicity-conserving processes, and the local maximum is not likely due to unnatural-parity processes.

Journal Article↗
PubMed2005

Generation of synchronized femtosecond and picosecond pulses in a dual-wavelength femtosecond Ti:sapphire laser.

We obtain synchronized 45-fs and 0.848-ps pulses by achieving cross-mode locking in a double-cavity dual-wavelength femtosecond Ti:sapphire laser. Autocorrelation and cross correlation show that the femtosecond and picosecond pulses are well synchronized, with a timing jitter of 41 fs. Cross-phase modulation dominates the processes of cross-mode locking and synchronization.

Journal Article↗
PubMed2005

Computational biomechanical modelling of the lumbar spine using marching-cubes surface smoothened finite element voxel meshing.

There is a need for the development of finite element (FE) models based on medical datasets, such as magnetic resonance imaging and computerized tomography in computation biomechanics. Direct conversion of graphic voxels to FE elements is a commonly used method for the generation of FE models. However, conventional voxel-based methods tend to produce models with jagged surfaces. This is a consequence of the inherent characteristics of voxel elements; such a model is unable to capture the geometries of anatomical structures satisfactorily. We have developed a robust technique for the automatic generation of voxel-based patient-specific FE models. Our approach features a novel tetrahedronization scheme that incorporates marching-cubes surface smoothing together with a smooth-distortion factor (SDF). The models conform to the actual geometries of anatomical structures of a lumbar spine segment (L3). The resultant finite element analysis (FEA) at the surfaces is more accurate compared to the use of conventional voxel-based generated FE models. In general, models produced by our method were superior compared to that obtained using the commercial software ScanFE.

Biomechanical Phenomena↗
PubMed2005

Estimation of dislocation densities in cold rolled Al-Mg-Cu-Mn alloys by combination of yield strength data, EBSD and strength models.

Al-Mg-Cu-Mn alloys have been developed for the packaging industry, in which large cold-working deformations are normally applied that can produce high dislocation densities. In this study, we present a simplified model for the yield strength contributions and apply that to obtain the dislocation densities by determining the orientation factors, which can be obtained via the crystal information of electron backscatter diffraction (EBSD). One alloy subjected to three cold-rolling reductions (10%, 40% and 90%) has been analysed by EBSD, and the density of dislocations are estimated using the strengthening model. This assessment suggests that dislocation densities by the Taylor model are roughly consistent but slightly lower than those determined by transmission electron microscopy.

Alloys↗
PubMed2004

Host defense peptides in burns.

Overuse of antibiotics and failure to apply basic infection control policies and procedures have contributed to the increasing multi-drug resistance of many nosocomial pathogens. The alarming increase of multi-drug-resistant bacteria (e.g. Pseudomonas aeruginosa, methicilin-resistant Staphylococci, vancomycin-resistant Enterococci) causes infected wounds associated with high mortality and morbidity in burned patients and focuses attention on the need for better treatment and prevention of wound infections. The review points out and discusses some emerging alternatives to antibiotics used in clinical practice, with special emphasis on the role of the innate immune response and potential application of human host defense peptides in thermal injury.

Antimicrobial Cationic Peptides↗
PubMed2003

Beam-polarization asymmetries for the p(gamma-->, K+)Lambda and p(gamma-->, K+)Sigma(0) reactions for E(gamma)=1.5-2.4 GeV.

Beam polarization asymmetries for the p(gamma-->,K+)Lambda and p(gamma-->,K+)Sigma(0) reactions are measured for the first time for E(gamma)=1.5-2.4 GeV and 0.6<cos((theta(c.m.)(K+))<1.0 by using linearly polarized photons at the Laser-Electron-Photon facility at SPring-8 (LEPS). The observed asymmetries are positive and gradually increase with rising photon energy. The data are not consistent with theoretical predictions based on tree-level effective-Lagrangian approaches. Including the new results in the development of the models is, therefore, crucial for understanding the reaction mechanism and to test the presence of baryon resonances which are predicted in quark models but are thus far undiscovered.

Journal Article↗
PubMed2003

Evidence for a narrow S = +1 baryon resonance in photoproduction from the neutron.

The gamman-->K(+)K(-)n reaction on 12C has been studied by measuring both K+ and K- at forward angles. A sharp baryon resonance peak was observed at 1.54+/-0.01 GeV/c(2) with a width smaller than 25 MeV/c(2) and a Gaussian significance of 4.6sigma. The strangeness quantum number (S) of the baryon resonance is +1. It can be interpreted as a molecular meson-baryon resonance or alternatively as an exotic five-quark state (uuddsmacr;) that decays into a K+ and a neutron. The resonance is consistent with the lowest member of an antidecuplet of baryons predicted by the chiral soliton model.

Journal Article↗
PubMed2003

Limit on the electron neutrino magnetic moment from the kuo-sheng reactor neutrino experiment.

A search of neutrino magnetic moment was carried out at the Kuo-Sheng Nuclear Power Station at a distance of 28 m from the 2.9 GW reactor core. With a high purity germanium detector of mass 1.06 kg surrounded by scintillating NaI(Tl) and CsI(Tl) crystals as anti-Compton detectors, a detection threshold of 5 keV and a background level of 1 kg(-1) keV(-1) day(-1) at 12-60 keV were achieved. Based on 4712 and 1250 h of reactor ON and OFF data, respectively, the limit on the neutrino magnetic moment of mu(nu;(e))<1.3x10(-10)mu(B) at 90% confidence level was derived. An indirect bound of the nu;(e) radiative lifetime of m(3)(nu)tau(nu)>2.8x10(18) eV(3) s can be inferred.

Journal Article↗
PubMed2003

Immunocytochemistry versus molecular fingerprinting of metastases.

Examination of cytological samples of cancer to suggest a possible primary site of origin is one of the commonest and most difficult tasks of diagnostic cytopathologists. Currently, both cytomorphology and immunocytochemistry are the main approaches to this diagnostic dilemma. We report the application of microsatellite analysis in cytological samples in a patient with a primary colonic tumour and two subsequent lung nodules, which were suspected on CT scans of the chest, and compared the findings with those obtained with conventional immunocytochemistry. The molecular results were in agreement with the radiological impression and conflicted with the immunocytochemistry. We conclude that immunocytochemical and molecular biology approaches to the diagnosis of tumours may give rise to contradictory results.

Adenocarcinoma↗
PubMed2003

A simple approach to the determination of the crystallographic orientation: applications and accuracy.

A simple analytical solution for the crystallographic orientation is described. This method is based on one indexed Kikuchi pair in a known zone rather than the corresponding diffraction spots. The accuracy of this method is shown to be better than 0.1 degrees even for cases in which a zone axis deviates by a large angle (e.g. 10 degrees ) from the centre of the beam direction. This approach simplifies experiments because only one pair of Kikuchi lines and a zone axis are needed, and is especially suited when it is difficult or cumbersome to resolve a second pair of Kikuchi lines with sufficient accuracy.

Journal Article↗
PubMed2003

The Singapore National Breast Screening Programme: principles and implementation.

The Singapore Breast Screening Project (1993-1996) showed that mammographic screening in Singaporean women shifts the size and stage of screen-detected breast cancers downwards and markedly increases the rate of detection of ductal carcinoma in situ, with acceptable recall, needle biopsy and interval cancer rates. Breast cancer is the leading cause of death in Singaporean women. Singapore has one of the highest age-adjusted breast cancer incidences in Asia. Although this is much lower than in the West, for women aged 45-49 years, the breast cancer incidence in Singapore is the same as for women in Australia, Canada or the United States. The latest Singapore Cancer Registry data shows that the age of peak incidence of breast cancer in Singaporean women has risen from 45-49 years in the period 1993-1997 to 50-55 years in the period 1998-1999. This suggests that the age-specific incidence of breast cancer in Singaporean women is shifting more to a pattern usually seen in Western nations. These factors, together with reconfirmed evidence of mortality benefit from breast cancer screening trials, led the Singapore government to establish the first population-based mammographic breast screening programme in Asia, the Singapore National Breast Screening Programme (BreastScreen Singapore). It uses a distributed model of mammography service, with centralised reading and assessment, co-ordinated by the Singapore Health Promotion Board. It is unique in that women co-pay at each step of the screening and assessment process. The programme, launched in January 2002, has adopted international standards of breast screening practice and breast cancer detection. To date, the initial targets for the first year have been met. Several key policies and issues over the programme's implementation are presented.

Adult↗
PubMed2002

Penetrating injury of the cheek requiring skull base exploration.

We report a case of a very unusual penetrating injury of the middle third of the face. The patient was involved in a road traffic accident, and the indicator control lever became impaled in his right cheek. There was contralateral orbital damage resulting in loss of sight. The cribriform plate was breached and a pneumoencephalocele ensued. We discuss the modern management of such injuries including injury assessment. We emphasize the importance of crash scene information gathering and analysis of injury mechanisms. Facial injury zonal classification and imaging are reviewed in the context of the case. We discuss the reasons that led us to treat this patient via the subcranial approach.

Accidents, Traffic↗