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Search Results: 1 - 10 of 34596 matches for " Ping-Heng Tan "
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Acute morphine induces matrix metalloproteinase-9 up-regulation in primary sensory neurons to mask opioid-induced analgesia in mice
Yen-Chin Liu, Temugin Berta, Tong Liu, Ping-Heng Tan, Ru-Rong Ji
Molecular Pain , 2012, DOI: 10.1186/1744-8069-8-19
Abstract: Subcutaneous morphine induced a marked up-regulation of MMP-9 protein in DRGs but not spinal cords. Morphine also increased MMP-9 activity and mRNA expression in DRGs. MMP-9 up-regulation peaked at 2 h but returned to the baseline after 24 h. In DRG tissue sections, MMP-9 is expressed in small and medium-sized neurons that co-express mu opioid receptors (MOR). In DRG cultures, MOR agonists morphine, DAMGO, and remifentanil each increased MMP-9 expression in neurons, whereas the opioid receptor antagonist naloxone and the MOR-selective antagonist D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP) suppressed morphine-induced MMP-9 expression. Notably, subcutaneous morphine-induced analgesia was enhanced and prolonged in Mmp9 knockout mice and also potentiated in wild-type mice receiving intrathecal injection of MMP-9 inhibitors. Consistently, intrathecal injection of specific siRNA targeting MMP-9 reduced MMP-9 expression in DRGs and enhanced and prolonged morphine analgesia. Subcutaneous morphine also produced heat hyperalgesia at 24 h, but this opioid-induced hyperalgesia was not enhanced after MMP-9 deletion or inhibition.Transient MMP-9 up-regulation in DRG neurons can mask opioid analgesia, without modulating opioid-induced hyperalgesia. Distinct molecular mechanisms (MMP-9 dependent and independent) control acute opioid-induced pronociceptive actions (anti-analgesia in the first several hours and hyperalgesia after 24 h). Targeting MMP-9 may improve acute opioid analgesia.Opioids especially mu opioid receptor (MOR) agonists remain to be the most effective treatment for moderate to severe pain. MOR is expressed by primary sensory neurons including small-sized (C-fiber) and medium-sized (Aδ-fiber) neurons in the dorsal root ganglia (DRGs) [1-5]. MOR is also expressed in primary afferent terminals and lamina II interneurons in the spinal cord [1,6-8]. MOR agonist, such as [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO) elicits potent presynaptic inhibition via suppress
Evolution of Electronic Structure in Atomically Thin Sheets of WS2 and WSe2
Weijie Zhao,Zohreh Ghorannevis,Leiqiang Chua,Minglin Toh,Christian Kloc,Ping-Heng Tan,Goki Eda
Physics , 2012, DOI: 10.1021/nn305275h
Abstract: Geometrical confinement effect in exfoliated sheets of layered materials leads to significant evolution of energy dispersion with decreasing layer thickness. Molybdenum disulphide (MoS2) was recently found to exhibit indirect to direct gap transition when the thickness is reduced to a single monolayer. This leads to remarkable enhancement in the photoluminescence efficiency, which opens up new opportunities for the optoelectronic applications of the material. Here we report differential reflectance and photoluminescence (PL) spectra of mono- to few-layer WS2 and WSe2 that indicate that the band structure of these materials undergoes similar indirect to direct transition when thinned to a single monolayer. Strong enhancement in PL quantum yield is observed for monoayer WS2 and WSe2 due to exciton recombination at the direct band edge. In contrast to natural MoS2 crystals extensively used in recent studies, few-layer WS2 and WSe2 show comparatively strong indirect gap emission along with distinct direct gap hot electron emission, suggesting high quality of synthetic crystals prepared by chemical vapor transport method. Fine absorption and emission features and their thickness dependence suggest strong effect of Se p-orbitals on the d electron band structure as well as interlayer coupling in WSe2.
Tailoring Plasmonic Metamaterials for DNA Molecular Logic Gates
Jun Zhang,Cuong Cao,Xinlong Xu,Chihao Liow,Shuzhou Li,Ping-Heng Tan,Qihua Xiong
Physics , 2013,
Abstract: Structural and functional information encoded in DNA combined with unique properties of nanomaterials could be of use for the construction of novel biocomputational circuits and intelligent biomedical nanodevices. However, at present their practical applications are still limited by either low reproducibility of fabrication, modest sensitivity, or complicated handling procedures. Here, we demonstrate the construction of label-free and switchable molecular logic gates that use specific conformation modulation of a guanine- and thymine- rich DNA, while the optical readout is enabled by the tunable alphabetical metamaterials, which serve as a substrate for surface enhanced Raman spectroscopy (MetaSERS). By computational and experimental investigations, we present a comprehensive solution to tailor the plasmonic responses of MetaSERS with respect to the metamaterial geometry, excitation energy, and polarization. Our tunable MetaSERS-based DNA logic is simple to operate, highly reproducible, and can be stimulated by ultra-low concentration of the external inputs, enabling an extremely sensitive detection of mercury ions.
Accurate determination of electronic transition energy of carbon nanotubes from the resonant behavior of radial breathing modes and their overtones

Zhang Jun,Tan Ping-Heng,Zhao Wei-Jie,

物理学报 , 2010,
Abstract: The resonant Raman behavior of the radial breathing modes are very useful to analyze the electronic property of carbon nanotubes. We investigated the resonant behaviors of Stokes and anti-Stokes radial breathing mode and its overtone of a metallic nanotube, and show how to accurately determine the electronic transition energy of carbon nanotubes from radial breathing modes and their overtones. Based on the present results, the previously reported resonant Raman behavior of the radial breathing modes of SWNT bundles can be interpreted very well.
Phonon and Raman scattering of two-dimensional transition metal dichalcogenides from monolayer, multilayer to bulk material
Xin Zhang,Xiao-Fen Qiao,Wei Shi,Jiang-Bin Wu,De-Sheng Jiang,Ping-Heng Tan
Physics , 2015, DOI: 10.1039/c4cs00282b
Abstract: Two-dimensional (2D) transition metal dichalcogenide (TMD) nanosheets exhibit remarkable electronic and optical properties. The 2D features, sizable bandgaps, and recent advances in the synthesis, characterization, and device fabrication of the representative MoS$_2$, WS$_2$, WSe$_2$, and MoSe$_2$ TMDs make TMDs very attractive in nanoelectronics and optoelectronics. Similar to graphite and graphene, the atoms within each layer in 2D TMDs are joined together by covalent bonds, while van der Waals interactions keep the layers together. This makes the physical and chemical properties of 2D TMDs layer dependent. In this review, we discuss the basic lattice vibrations of monolayer, multilayer, and bulk TMDs, including high-frequency optical phonons, interlayer shear and layer breathing phonons, the Raman selection rule, layer-number evolution of phonons, multiple phonon replica, and phonons at the edge of the Brillouin zone. The extensive capabilities of Raman spectroscopy in investigating the properties of TMDs are discussed, such as interlayer coupling, spin--orbit splitting, and external perturbations. The interlayer vibrational modes are used in rapid and substrate-free characterization of the layer number of multilayer TMDs and in probing interface coupling in TMD heterostructures. The success of Raman spectroscopy in investigating TMD nanosheets paves the way for experiments on other 2D crystals and related van der Waals heterostructures.
Interlayer Interactions in Anisotropic Atomically-thin Rhenium Diselenide
Huan Zhao,Jiangbin Wu,Hongxia Zhong,Qiushi Guo,Xiaomu Wang,Fengnian Xia,Li Yang,Ping-Heng Tan,Han Wang
Physics , 2015,
Abstract: Recently, two-dimensional (2D) materials with strong in-plane anisotropic properties such as black phosphorus have demonstrated great potential for developing new devices that can take advantage of its reduced lattice symmetry with potential applications in electronics, optoelectronics and thermoelectrics. However, the selection of 2D material with strong in-plane anisotropy has so far been very limited and only sporadic studies have been devoted to transition metal dichalcogenides (TMDC) materials with reduced lattice symmetry, which is yet to convey the full picture of their optical and phonon properties, and the anisotropy in their interlayer interactions. Here, we study the anisotropic interlayer interactions in an important TMDC 2D material with reduced in-plane symmetry - atomically thin rhenium diselenide (ReSe2) - by investigating its ultralow frequency interlayer phonon vibration modes, the layer dependent optical bandgap, and the anisotropic photoluminescence (PL) spectra for the first time. The ultralow frequency interlayer Raman spectra combined with the first study of polarization-resolved high frequency Raman spectra in mono- and bi-layer ReSe2 allows deterministic identification of its layer number and crystal orientation. PL measurements show anisotropic optical emission intensity with bandgap increasing from 1.26 eV in the bulk to 1.32 eV in monolayer, consistent with the theoretical results based on first-principle calculations. The study of the layer-number dependence of the Raman modes and the PL spectra reveals the relatively weak van der Waals interaction and 2D quantum confinement in atomically-thin ReSe2.
Monolayer Molybdenum Disulfide Nanoribbons with High Optical Anisotropy
Jiang-Bin Wu,Huan Zhao,Yuanrui Li,Douglas Ohlberg,Wei Shi,Wei Wu,Han Wang,Ping-Heng Tan
Physics , 2015,
Abstract: Two-dimensional Molybdenum Disulfide (MoS2) has shown promising prospects for the next generation electronics and optoelectronics devices. The monolayer MoS2 can be patterned into quasi-one-dimensional anisotropic MoS2 nanoribbons (MNRs), in which theoretical calculations have predicted novel properties. However, little work has been carried out in the experimental exploration of MNRs with a width of less than 20 nm where the geometrical confinement can lead to interesting phenomenon. Here, we prepared MNRs with width between 5 nm to 15 nm by direct helium ion beam milling. High optical anisotropy of these MNRs is revealed by the systematic study of optical contrast and Raman spectroscopy. The Raman modes in MNRs show strong polarization dependence. Besides that the E' and A'1 peaks are broadened by the phonon-confinement effect, the modes corresponding to singularities of vibrational density of states are activated by edges. The peculiar polarization behavior of Raman modes can be explained by the anisotropy of light absorption in MNRs, which is evidenced by the polarized optical contrast. The study opens the possibility to explore quasione-dimensional materials with high optical anisotropy from isotropic 2D family of transition metal dichalcogenides.
Optical properties of the E0+△0 energy level higher than the bandgap of GaAs studied by micro-photoluminescence technique

Bao Zhi-Hu,Jing Wei-Ping,Luo Xiang-Dong,Tan Ping-Heng,

物理学报 , 2007,
Abstract: 通过显微光致发光技术和显微拉曼(Raman)技术研究了半绝缘GaAs(SI-GaAs)晶体的带边附近的发光.在光荧光谱中,观察到在高于GaAs带边0.348eV处有一个新的荧光峰.结合Raman谱指认此发光峰来源于GaAs的E。+△。能级的非平衡荧光发射.同时,通过研究E0+△0能级的偏振、激发光强度依赖关系,以及温度依赖关系说明E0+△0能级与带边‰共享了共同的导带位置Г6,同时这也说明在GaAs中主要是导带的性质决定了材料的光学行为.同时,通过与n-GaAs和δ掺杂GaAs相比较,半绝缘GaAs晶体的E0+△0能级的发光峰更能反映GaAs电子能级高临界点E0+△0的能量位置和物理性质.研究结果说明显微光致发光技术是研究半导体材料带边以上能级光学性质的一种非常有力的研究工具.

CHENG Wen-Chao,XIA Jian-Bai,LI Guo-Hu,TAN Ping-Heng,ZHENG Hou-Zhi,

红外与毫米波学报 , 1999,
Abstract: 低温下观察了弱耦合δ掺杂GaAs超晶格的辐射复合发光.实验结果表明:除观察到基态的复合发光外,还观察到激发态的复合发光.基于有效质量近似理论,计算了能带结构和发光光谱,理论结果与实验结果符合得很好.

LUO Xiang-Dong,XU Zhong-Ying,TAN Ping-Heng,GE Wei-Kun,

红外与毫米波学报 , 2005,
Abstract: GaNAs/GaAs single quantum wells (SQWs) and dilute GaNAs bulk grown by molecular beam epitaxy(MBE) were studied by photoluminescence (PL), selectively-excited PL, and time-resolved PL. Exciton localization and delocalization were investigated in detail. Under short pulse laser excitation, the delocalization exciton emission was revealed in GaNAs/GaAs SQWs. It exhibits quite different optical properties from N-related localized states. In dilute GaNAs bulk, a transition of alloy band related recombination was observed by measuring the PL dependence on temperature and excitation intensity and time-resolved PL as well. This alloy-related transition presents intrinsic optical properties. These results are very important for realizing the abnomal features of Ⅲ-Ⅴ-N semiconductors.
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