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Search Results: 1 - 10 of 18413 matches for " Shiang Fang "
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Quantum and Thermal Transitions Out of the Pair-Supersolid Phase of Two-Species Bosons in Lattice
Chia-Min Chung,Shiang Fang,Pochung Chen
Physics , 2012, DOI: 10.1103/PhysRevB.85.214513
Abstract: We investigate two-species bosons in a two-dimensional square lattice by quantum Monte Carlo method. We show that the inter-species attraction and nearest-neighbor intra-species repulsion results in the pair-supersolid phase, where a diagonal solid order coexists with an off-diagonal pair-superfluid order. The quantum and thermal transitions out of the pair-supersolid phase are characterized. It is found that there is a direct first order transition from the pair-supersolid phase to the double-superfluid phase without an intermediate region. Furthermore, the melting of the pair-supersolid occurs in two steps. Upon heating, first the pair-superfluid is destroyed via a KT transition then the solid order melts via an Ising transition
Quantum fluctuations and condensate fraction during the time-of-flight expansion
Shiang Fang,Ray-Kuang Lee,Daw-Wei Wang
Physics , 2009, DOI: 10.1103/PhysRevA.82.031601
Abstract: The quantum fluctuation effects in the time-of-flight (TOF) experiment for a condensate released from an optical lattice potential is studied within the truncated Wigner approximation. By investigating both the spatial and momentum density distributions, we find that the condensate fraction decreases monotonically in time and hence cannot be measured in the standard TOF image. We then propose a semi-quantitative analysis for such dynamical quantum depletion process. Our study shows a universal algebraic decay of the true condensate fraction, and have a very good agreement with numerical results. We also discuss possible methods to determine the condensate fraction inside the optical lattice, and its implication to the TOF experiments in higher dimensional systems.
IL-22 Negatively Regulates Helicobacter pylori-Induced CCL20 Expression in Gastric Epithelial Cells
Jia-Perng Chen, Ming-Shiang Wu, Sung-Hsin Kuo, Fang Liao
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0097350
Abstract: Helicobacter pylori is a Gram-negative bacterium that infects the human gastric mucosa and causes various gastric diseases. H. pylori infection induces the production of inflammatory chemokine CCL20 in gastric mucosa and leads to gastric inflammation. Given that the IL-22/IL-22R axis plays a critical role in the regulation of homeostasis and inflammation of epithelial cells at barrier surfaces, we investigated the effect of IL-22 on CCL20 expression induced by H. pylori. We demonstrated that H. pylori infection of the gastric epithelia-derived AGS cells significantly induced CCL20 expression and the induction was inhibited by IL-22. Functional analysis of the CCL20 promoter revealed that the H. pylori-induced CCL20 expression required the activation of NF-κB, and that IL-22 inhibited the induction by attenuating NF-κB activation. Knockdown of endogenous STAT3 by either short interfering RNAs or a short hairpin RNA significantly reduced the inhibitory effect of IL-22. Furthermore, STAT3 phosphorylation elicited by IL-22 was crucial for the inhibition of H. pylori-induced CCL20 expression. Consistent with the in vitro data showing that IL-22 negatively regulated H. pylori-induced CCL20 expression in gastric epithelial cells, studies on the tissue sections from patients with H. pylori infection also revealed an inverse association of IL-22 expression and CCL20 expression in vivo. Together, our findings suggest that IL-22 plays a role in the control of overproduction of the inflammatory chemokine and thus may protect the gastric mucosa from inflammation-mediated damage.
Reducing the Foreign Body Reaction by Surface Modification with Collagen/Hyaluronic Acid Multilayered Films
Cindy Yi Chi Hsieh,Fang-Wei Hu,Wen-Shiang Chen,Wei-Bor Tsai
ISRN Biomaterials , 2014, DOI: 10.1155/2014/718432
Abstract: Biological response against foreign implants often leads to encapsulation, possibly resulting in malfunction of implants devices. The aim of this study was to reduce the foreign body reaction by surface modification of biomaterials through layer-by-layer deposition of type I collagen (COL)/hyaluronic acid (HA) multilayer films. Polydimethylsiloxane (PDMS) samples were coated with alternative COL and HA layers with different layers. We found that the in vitro adhesion, proliferation, and activation of macrophage-like cells were greatly decreased by COL/HA multilayered deposition. The PDMS samples modified with 20 bilayers of COL/HA were implanted in rats for 3 weeks, and the thickness of encapsulation surrounding the samples was decreased by 29–57% compared to the control unmodified PDMS. This study demonstrates the potential of COL/HA multilayer films to reduce foreign body reaction. 1. Introduction Biological response against artificial implants leads to encapsulation of implants, which often causes malfunction of implants or patients’ agonies due to capsular contracture [1–3]. For example, capsule contracture of fibrous tissues overlying silicone breast implants may cause the implant rupture and become painful [3]. When a foreign material is implanted into a host, the interaction between the material and the surrounding injured tissues causes acute inflammation, similar to the natural healing process that usually lasts for a week [1, 2]. Chronic inflammation with the participation of monocytes, macrophages, and foreign body giant cells (FBGCs) may occur with a duration of less than 3 weeks if the wound is not healed [1]. Macrophages try to eliminate the foreign object from the host. However, the implant is too large to be phagocytosized, so activated macrophages fuse together to form multinucleated FBGCs [1]. The inability of FGBCs in eliminating the foreign object will lead to a route to encapsulation of the implant with dense collagen matrix that is secreted by fibroblasts in order to wall the foreign object off the host [1, 2]. Macrophages can be considered as a hallmark due to their critical roles in guiding through the entire wound healing process [2, 4]. Activated macrophages release biosignals such as interleukins to induce the formation of FBGCs as well as collagen synthesis from fibroblasts. To prevent these undesirable events from occurring, scientists have sought suitable surface modifications on biomaterials to prevent capsule formation by altering the hydrophilicity, topology, roughness, and surface chemistry of surfaces [5, 6].
Quantum Criticality from in-situ Density Imaging
Shiang Fang,Chia-Ming Chung,Ping Nang Ma,Pochung Chen,Daw-Wei Wang
Physics , 2010, DOI: 10.1103/PhysRevA.83.031605
Abstract: We perform large-scale Quantum Monte Carlo (QMC) simulations for strongly interacting bosons in a 2D optical lattice trap, and confirm an excellent agreement with the benchmarking in-situ density measurements by the Chicago group [1]. We further present a general finite temperature phase diagram both for the uniform and the trapped systems, and demonstrate how the universal scaling properties near the superfluid(SF)-to-Mott insulator(MI) transition can be observed by analysing the in-situ density profile. The characteristic temperature to find such quantum criticality is estimated to be of the order of the single-particle bandwidth, which should be achievable in the present or near future experiments. Finally, we examine the validity regime of the local fluctuation-dissipation theorem (FDT), which can be a used as a thermometry in the strongly interacting regime.
\textit{Ab-initio} Tight-Binding Hamiltonian for Transition Metal Dichalcogenides
Shiang Fang,Rodrick Kuate Defo,Sharmila N. Shirodkar,Simon Lieu,Georgios A. Tritsaris,Efthimios Kaxiras
Physics , 2015, DOI: 10.1103/PhysRevB.92.205108
Abstract: We present an accurate \textit{ab-initio} tight-binding hamiltonian for the transition-metal dichalcogenides, MoS$_2$, MoSe$_2$, WS$_2$, WSe$_2$, with a minimal basis (the \textit{d} orbitals for the metal atoms and \textit{p} orbitals for the chalcogen atoms) based on a transformation of the Kohn-Sham density function theory (DFT) hamiltonian to a basis of maximally localized Wannier functions (MLWF). The truncated tight-binding hamiltonian (TBH), with only on-site, first and partial second neighbor interactions, including spin-orbit coupling, provides a simple physical picture and the symmetry of the main band-structure features. Interlayer interactions between adjacent layers are modeled by transferable hopping terms between the chalcogen \textit{p} orbitals. The full-range tight-binding hamiltonian (FTBH) can be reduced to hybrid-orbital k $\cdot$ p effective hamiltonians near the band extrema that captures important low-energy excitations. These \textit{ab-initio} hamiltonians can serve as the starting point for applications to interacting many-body physics including optical transitions and Berry curvature of bands, of which we give some examples.
Tuning the Kosterlitz-Thouless transition to zero temperature in Anisotropic Boson Systems
Jhih-Shih You,Hao Lee,Shiang Fang,Miguel A. Cazalilla,Daw-Wei Wang
Physics , 2012, DOI: 10.1103/PhysRevA.86.043612
Abstract: We study the two-dimensional Bose-Hubbard model with anisotropic hopping. Focusing on the effects of anisotropy on the superfluid properties such like the helicity modulus and the normal-to-superfluid (Berezinskii-Kosterlitz-Thouless, BKT) transition temperature, two different approaches are compared: Large-scale Quantum Monte Carlo simulations and the self-consistent harmonic approximation (SCHA). For the latter, two different formulations are considered, one applying near the isotropic limit and the other applying in the extremely anisotropic limit. Thus we find that the SCHA provides a reasonable description of superfluid properties of this system provided the appropriate type of formulation is employed. The accuracy of the SCHA in the extremely anisotropic limit, where the BKT transition temperature is tuned to zero (i.e. into a Quantum critical point) and therefore quantum fluctuations play a dominant role, is particularly striking.
Theory of Graphene Raman Spectroscopy
Eric J. Heller,Yuan Yang,Lucas Kocia,Wei Chen,Shiang Fang,Mario Borunda,Efthimios Kaxiras
Physics , 2015,
Abstract: Raman spectroscopy plays a key role in studies of graphene and related carbon systems. Graphene is perhaps the most promising material of recent times for many novel applications, including electronics. In this paper, the traditional and well established Kramers-Heisenberg-Dirac (KHD) Raman scattering theory (1925-1927) is extended to crystalline graphene for the first time. It demands different phonon production mechanisms and phonon energies than does the popular "double resonance" Raman scattering model. The latter has never been compared to KHD. Within KHD, phonons are produced instantly along with electrons and holes, in what we term an electron-hole-phonon triplet, which does not suffer Pauli blocking. A new mechanism for double phonon production we name "transition sliding" explains the brightness of the 2D mode and other overtones, as a result of linear (Dirac cone) electron dispersion. Direct evidence for sliding resides in hole doping experiments performed in 2011 \cite{chenCrommie}. Whole ranges of electronic transitions are permitted and may even constructively interfere for the same laser energy and phonon q, explaining the dispersion, bandwidth, and strength of many two phonon Raman bands. Graphene's entire Raman spectrum, including dispersive and fixed bands, missing bands not forbidden by symmetries, weak bands, overtone bands, Stokes anti-Stokes anomalies, individual bandwidths, trends with doping, and D-2D band spacing anomalies emerge naturally and directly in KHD theory.
Action of Intertwining operators on pseudospherical K-types
Shiang Tang
Mathematics , 2015,
Abstract: In this paper, we give a concrete description of the two-fold cover of a simply connected, split real reductive group and its maximal compact subgroup as Chevalley groups. We define a representation of the maximal compact subgroup called pseudospherical representation, it appears with multiplicity one in the principal series representation. We introduce a family of canonically defined intertwining operators and compute the action of them on pseudospherical K-types, obtaining explicit formulas of the Harish-Chandra c-function.
Expression of Kruppel-Like Factor KLF4 in Mouse Hair Follicle Stem Cells Contributes to Cutaneous Wound Healing
Juan Li, Hai Zheng, Junfeng Wang, Fang Yu, Rebecca J. Morris, Timothy C. Wang, Shiang Huang, Walden Ai
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0039663
Abstract: Background Kruppel-like factor KLF4 is a transcription factor critical for the establishment of the barrier function of the skin. Its function in stem cell biology has been recently recognized. Previous studies have revealed that hair follicle stem cells contribute to cutaneous wound healing. However, expression of KLF4 in hair follicle stem cells and the importance of such expression in cutaneous wound healing have not been investigated. Methodology/Principal Findings Quantitative real time polymerase chain reaction (RT-PCR) analysis showed higher KLF4 expression in hair follicle stem cell-enriched mouse skin keratinocytes than that in control keratinocytes. We generated KLF4 promoter-driven enhanced green fluorescence protein (KLF4/EGFP) transgenic mice and tamoxifen-inducible KLF4 knockout mice by crossing KLF4 promoter-driven Cre recombinase fused with tamoxifen-inducible estrogen receptor (KLF4/CreER?) transgenic mice with KLF4(flox) mice. KLF4/EGFP cells purified from dorsal skin keratinocytes of KLF4/EGFP transgenic mice were co-localized with 5-bromo-2'-deoxyuridine (BrdU)-label retaining cells by flow cytometric analysis and immunohistochemistry. Lineage tracing was performed in the context of cutaneous wound healing, using KLF4/CreER? and Rosa26RLacZ double transgenic mice, to examine the involvement of KLF4 in wound healing. We found that KLF4 expressing cells were likely derived from bulge stem cells. In addition, KLF4 expressing multipotent cells migrated to the wound and contributed to the wound healing. After knocking out KLF4 by tamoxifen induction of KLF4/CreER? and KLF4(flox) double transgenic mice, we found that the population of bulge stem cell-enriched population was decreased, which was accompanied by significantly delayed cutaneous wound healing. Consistently, KLF4 knockdown by KLF4-specific small hairpin RNA in human A431 epidermoid carcinoma cells decreased the stem cell population and was accompanied by compromised cell migration. Conclusions/Significance KLF4 expression in mouse hair bulge stem cells plays an important role in cutaneous wound healing. These findings may enable future development of KLF4-based therapeutic strategies aimed at accelerating cutaneous wound closure.
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