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Search Results: 1 - 10 of 17893 matches for " Steven Tan "
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Functional Somatic Syndromes: Emerging Biomedical Models and Traditional Chinese Medicine
Steven Tan,Kirsten Tillisch,Emeran Mayer
Evidence-Based Complementary and Alternative Medicine , 2004, DOI: 10.1093/ecam/neh016
Abstract: The so-called functional somatic syndromes comprise a group of disorders that are primarily symptom-based, multisystemic in presentation and probably involve alterations in mind-brain-body interactions. The emerging neurobiological models of allostasis/allostatic load and of the emotional motor system show striking similarities with concepts used by Traditional Chinese Medicine (TCM) to understand the functional somatic disorders and their underlying pathogenesis. These models incorporate a macroscopic perspective, accounting for the toll of acute and chronic traumas, physical and emotional stressors and the complex interactions between the mind, brain and body. The convergence of these biomedical models with the ancient paradigm of TCM may provide a new insight into scientifically verifiable diagnostic and therapeutic approaches for these common disorders.
Spectrum of endoscopic findings among patients referred for colonoscopy in RIPAS Hospital.
Vui Heng CHONG,Steven TAN,Anand JALIHAL
Brunei International Medical Journal , 2012,
Abstract: Introduction: Colonoscopy is an investigation for the evaluation of lower gastrointestinal symptoms. Just like any other conditions, it is important to be aware of the spectrum of findings so that appropriate referral and decisions can be made. Materials and Methods: Patients (mean age 52.3 ± 15.3 years old with almost equal proportion of genders) referred for colonoscopy in RIPAS Hospital over a five year period (January 2003 to December 2007) were retrospectively identified and studied. Results: The most common indication for colonoscopy was bleeding per rectum (22.9%), followed by evaluation of abdominal pain (18.6%), anaemia (11.7%), colorectal cancer screening (11.7%), evaluation of constipation (5.9%) and altered bowel habits (3.8%). A large proportion (58.4%) colonoscopy was normal. The most common positive finding was haemorrhoids (30.3%), majority of which were categorised as grade I. This was followed by colonic polyps (17.6%), diverticular disease (12.1%), non-specific colitis (4.0%), colorectal cancers (4.0%) and ulcers (3.6%), melanosis coli (0.4%) and telangiectasia (0.1%). Colorectal cancer was most common among the Malays (4.4%), followed by the Chinese (4.0%), the indigenous (2.8) and the others (1.2%). Conclusions: Our study showed that the most common indication was for the evaluation of bleeding per rectum. Majority had normal colonoscopy and the most common positive finding was haemorrhoids. Importantly colorectal neoplasms accounted for one fifth of procedures with colorectal cancers accounting for four percent.
Enhanced Osteogenesis of Adipose Derived Stem Cells with Noggin Suppression and Delivery of BMP-2
Jiabing Fan, Hyejin Park, Steven Tan, Min Lee
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0072474
Abstract: Bone morphogenetic proteins (BMPs) are believed to be the most potent osteoinductive factors. However, BMPs are highly pleiotropic molecules and their supra-physiological high dose requirement leads to adverse side effects and inefficient bone formation. Thus, there is a need to develop alternative osteoinductive growth factor strategies that can effectively complement BMP activity. In this study, we intrinsically stimulated BMP signaling in adipose derived stem cells (ASCs) by downregulating noggin, a potent BMP antagonist, using an RNAi strategy. ASCs transduced with noggin shRNA significantly enhanced osteogenic differentiation of cells. The potency of endogenous BMPs was subsequently enhanced by stimulating ASCs with exogenous BMPs at a significantly reduced dose. The level of mineralization in noggin shRNA treated ASCs when treated with BMP-2 was comparable to that of control shRNA treated cell treated with 10-fold more BMP-2. The complementary strategy of noggin suppression + BMP-2 to enhance osteogenesis was further confirmed in 3D in vitro environments using scaffolds consisting of chitosan (CH), chondroitin sulfate (CS), and apatite layer on their surfaces designed to slowly release BMP-2. This finding supports the novel therapeutic potential of this complementary strategy in bone regeneration.
Graphene Dirac fermions in one-dimensional inhomogeneous field profiles: Transforming magnetic to electric field
Liang Zheng Tan,Cheol-Hwan Park,Steven G. Louie
Physics , 2009, DOI: 10.1103/PhysRevB.81.195426
Abstract: We show that the low-energy electronic structure of graphene under a one-dimensional inhomogeneous magnetic field can be mapped into that of graphene under an electric field or vice versa. As a direct application of this transformation, we find that the carrier velocity in graphene is isotropically reduced under magnetic fields periodic along one direction with zero average flux. This counterintuitive renormalization has its origin in the pseudospin nature of graphene electronic states and is robust against disorder. In magnetic graphene superlattices with a finite average flux, the Landau level bandwidth at high fields exhibits an unconventional behavior of decreasing with increasing strength of the average magnetic field due to the linear energy dispersion of graphene. As another application of our transformation relation, we show that the transmission probabilities of an electron through a magnetic barrier in graphene can directly be obtained from those through an electrostatic barrier or vice versa.
Theory of the electronic and transport properties of graphene under a periodic electric or magnetic field
Cheol-Hwan Park,Liang Zheng Tan,Steven G. Louie
Physics , 2011, DOI: 10.1016/j.physe.2010.07.022
Abstract: We discuss the novel electronic properties of graphene under an external periodic scalar or vector potential, and the analytical and numerical methods used to investigate them. When graphene is subjected to a one-dimensional periodic scalar potential, owing to the linear dispersion and the chiral (pseudospin) nature of the electronic states, the group velocity of its carriers is renormalized highly anisotropically in such a manner that the velocity is invariant along the periodic direction but is reduced the most along the perpendicular direction. Under a periodic scalar potential, new massless Dirac fermions are generated at the supercell Brillouin zone boundaries. Also, we show that if the strength of the applied scalar potential is sufficiently strong, new zero-energy modes may be generated. With the periodic scalar potential satisfying some special conditions, the energy dispersion near the Dirac point becomes quasi one-dimensional. On the other hand, for graphene under a one-dimensional periodic vector potential (resulting in a periodic magnetic field perpendicular to the graphene plane), the group velocity is reduced isotropically and monotonically with the strength of the potential.
Towards a query language for annotation graphs
Steven Bird,Peter Buneman,Wang-Chiew Tan
Computer Science , 2000,
Abstract: The multidimensional, heterogeneous, and temporal nature of speech databases raises interesting challenges for representation and query. Recently, annotation graphs have been proposed as a general-purpose representational framework for speech databases. Typical queries on annotation graphs require path expressions similar to those used in semistructured query languages. However, the underlying model is rather different from the customary graph models for semistructured data: the graph is acyclic and unrooted, and both temporal and inclusion relationships are important. We develop a query language and describe optimization techniques for an underlying relational representation.
Metatranscriptomics and Pyrosequencing Facilitate Discovery of Potential Viral Natural Enemies of the Invasive Caribbean Crazy Ant, Nylanderia pubens
Steven M. Valles, David H. Oi, Fahong Yu, Xin-Xing Tan, Eileen A. Buss
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0031828
Abstract: Background Nylanderia pubens (Forel) is an invasive ant species that in recent years has developed into a serious nuisance problem in the Caribbean and United States. A rapidly expanding range, explosive localized population growth, and control difficulties have elevated this ant to pest status. Professional entomologists and the pest control industry in the United States are urgently trying to understand its biology and develop effective control methods. Currently, no known biological-based control agents are available for use in controlling N. pubens. Methodology and Principal Findings Metagenomics and pyrosequencing techniques were employed to examine the transcriptome of field-collected N. pubens colonies in an effort to identify virus infections with potential to serve as control agents against this pest ant. Pyrosequencing (454-platform) of a non-normalized N. pubens expression library generated 1,306,177 raw sequence reads comprising 450 Mbp. Assembly resulted in generation of 59,017 non-redundant sequences, including 27,348 contigs and 31,669 singlets. BLAST analysis of these non-redundant sequences identified 51 of potential viral origin. Additional analyses winnowed this list of potential viruses to three that appear to replicate in N. pubens. Conclusions Pyrosequencing the transcriptome of field-collected samples of N. pubens has identified at least three sequences that are likely of viral origin and, in which, N. pubens serves as host. In addition, the N. pubens transcriptome provides a genetic resource for the scientific community which is especially important at this early stage of developing a knowledgebase for this new pest.
MgB2 nonlinear properties investigated under localized high rf magnetic field excitation-report 2
Tamin Tai,B. G. Ghamsari,T. Tan,C. G. Zhuang,X. X. Xi,Steven M. Anlage
Physics , 2013, DOI: 10.1103/PhysRevSTAB.15.122002
Abstract: The high transition temperature and low surface resistance of MgB2 attracts interest in its potential application in superconducting radio frequency accelerating cavities. However, compared to traditional Nb cavities, the viability of MgB2 at high rf fields is still open to question. Our approach is to study the nonlinear electrodynamics of the material under localized rf magnetic fields. Because of the presence of the small superconducting gap in the $\pi$ band, the nonlinear response of MgB2 at low temperature is potentially complicated compared to a single-gap s-wave superconductor such as Nb. Understanding the mechanisms of nonlinearity coming from the two-band structure of MgB2, as well as extrinsic sources of nonlinearity, is an urgent requirement. A localized and strong rf magnetic field, created by a magnetic write head, is integrated into our nonlinear-Meissner-effect scanning microwave microscope [Tamin Tai, X. X. Xi, C. G. Zhuang, D. I. Mircea, and S. M. Anlage, IEEE Trans. Appl. Supercond. 21, 2615 (2011)]. MgB2 films with thickness 50 nm, fabricated by a hybrid physical-chemical vapor deposition technique on dielectric substrates, are measured at a fixed location and show a strongly temperature-dependent third harmonic response. We propose that several possible mechanisms are responsible for this nonlinear response.
Near-Field Microwave Magnetic Nanoscopy of Superconducting Radio Frequency Cavity Materials
Tamin Tai,Behnood G. Ghamsari,Thomas R. Bieler,Teng Tan,X. X. Xi,Steven M. Anlage
Physics , 2013, DOI: 10.1063/1.4881880
Abstract: A localized measurement of the RF critical field on superconducting radio frequency (SRF) cavity materials is a key step to identify specific defects that produce quenches of SRF cavities. Two new measurements are performed to demonstrate these capabilities with a novel near-field scanning probe microwave microscope. The first is a third harmonic nonlinear measurement on a high Residual- Resistance-Ratio bulk Nb sample showing strong localized nonlinear response for the first time, with surface RF magnetic field $B_{surface} \sim 10^{2}$ $mT$. The second is a raster scanned harmonic response image on a high quality $MgB_{2}$ thin film demonstrating a quench defect-free surface over large areas.
Theory of the Raman spectrum of rotated double-layer graphene
Sinisa Coh,Liang Z. Tan,Steven G. Louie,Marvin L. Cohen
Physics , 2013, DOI: 10.1103/PhysRevB.88.165431
Abstract: We study theoretically the Raman spectrum of the rotated double-layer graphene, consisting of two graphene layers rotated with respect to each other by an arbitrary angle \theta. We find a relatively simple dependence of the Raman G peak intensity on the angle \theta. On the other hand, the Raman 2D peak position, intensity, and width show a much more complicated dependence on the angle \theta. We account for all of these effects, including dependence on the incoming photon energy, in good agreement with the experimental data. We find that it is sufficient to include the interaction between the graphene layers on the electronic degrees of freedom (resulting in the occurrence of van Hove singularities in the density of states). We assume that the phonon degrees of freedom are unaffected by the interaction between the layers. Furthermore, we decompose the Raman 2D peak into two components having very different linewidths; these widths are almost independent of the angle \theta. The change in the intensity and the peak position of one of these two components gives insight into the dependence of the overall Raman 2D peak features as a function of the angle \theta. Additionally, we show regions in the phonon spectrum giving rise to the Raman 2D peak signal. This work provides an insight into the interplay between the mechanical degree of freedom (angle \theta) and the electronic degrees of freedom (singularities in the density of states) in rotated double-layer graphene. Additionally, this work provides a way to establish experimentally the value of the rotation angle \theta using Raman spectroscopy measurement. This procedure becomes even more robust if one repeats the Raman spectroscopy measurement with a different incoming photon energy.
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