147 research outputs found
On positive scalar curvature and moduli of curves
In this article we first show that any finite cover of the moduli space of
closed Riemann surfaces of genus with does not admit any
Riemannian metric of nonnegative scalar curvature such that where is the Teichm\"uller metric.
Our second result is the proof that any cover of the moduli space
of a closed Riemann surface does not admit any
complete Riemannian metric of uniformly positive scalar curvature in the
quasi-isometry class of the Teichm\"uller metric, which implies a conjecture of
Farb-Weinberger.Comment: J. Differential Geom, to appear; 24 page
Exploring the Impact of Ions on Oxygen K-Edge X-ray Absorption Spectroscopy in NaCl Solution using the GW-Bethe-Salpeter-Equation Approach
X-ray absorption spectroscopy (XAS) is a powerful experimental tool to probe
the local structure in materials with the core hole excitations. Here, the
oxygen K-edge XAS spectra of the NaCl solution and pure water are computed by
using a recently developed GW-BSE approach, based on configurations modeled by
path-integral molecular dynamics with the deep-learning technique. The neural
network is trained on ab initio data obtained with SCAN density functional
theory. The observed changes in the XAS features of the NaCl solution, compared
to those of pure water, are in good agreement between experimental and
theoretical results. We provided detailed explanations for these spectral
changes that occur when NaCl is solvated in pure water. Specifically, the
presence of solvating ion pairs leads to localization of electron-hole
excitons. Our theoretical XAS results support the theory that the effects of
the solvating ions on the H-bond network are mainly confined within the first
hydration shell of ions, however beyond the shell the arrangement of water
molecules remains to be comparable to that observed in pure water.Comment: 18 pages, 4 figure
Exploring the supersymmetric U(1) U(1) model with dark matter, muon and mass limits
We study the low scale predictions of supersymmetric standard model extended
by symmetry, obtained from breaking via a
left-right supersymmetric model, imposing universal boundary conditions. Two
singlet Higgs fields are responsible for the radiative symmetry breaking, and a singlet fermion is introduced to
generate neutrino masses through inverse seesaw mechanism. The lightest
neutralino or sneutrino emerge as dark matter candidates, with different low
scale implications. We find that the composition of the neutralino LSP changes
considerably depending on the neutralino LSP mass, from roughly half
bino, half MSSM bino, to singlet higgsino, or completely dominated by MSSM
higgsino. The sneutrino LSP is statistically much less likely, and when it
occurs it is a 50-50 mixture of right-handed sneutrino and the scalar . Most of the solutions consistent with the relic density constraint survive
the XENON 1T exclusion curve for both LSP cases. We compare the two scenarios
and investigate parameter space points and find consistency with the muon
anomalous magnetic moment only at the edge of deviation from the
measured value. However, we find that the sneutrino LSP solutions could be
ruled out completely by strict reinforcement of the recent mass
bounds. We finally discuss collider prospects for testing the model
Secure server-aided data sharing clique with attestation
National Research Foundation (NRF) Singapor
A Dimensionality Reduction-Based Multi-Step Clustering Method for Robust Vessel Trajectory Analysis
The Shipboard Automatic Identification System (AIS) is crucial for navigation safety and maritime surveillance, data mining and pattern analysis of AIS information have attracted considerable attention in terms of both basic research and practical applications. Clustering of spatio-temporal AIS trajectories can be used to identify abnormal patterns and mine customary route data for transportation safety. Thus, the capacities of navigation safety and maritime traffic monitoring could be enhanced correspondingly. However, trajectory clustering is often sensitive to undesirable outliers and is essentially more complex compared with traditional point clustering. To overcome this limitation, a multi-step trajectory clustering method is proposed in this paper for robust AIS trajectory clustering. In particular, the Dynamic Time Warping (DTW), a similarity measurement method, is introduced in the first step to measure the distances between different trajectories. The calculated distances, inversely proportional to the similarities, constitute a distance matrix in the second step. Furthermore, as a widely-used dimensional reduction method, Principal Component Analysis (PCA) is exploited to decompose the obtained distance matrix. In particular, the top k principal components with above 95% accumulative contribution rate are extracted by PCA, and the number of the centers k is chosen. The k centers are found by the improved center automatically selection algorithm. In the last step, the improved center clustering algorithm with k clusters is implemented on the distance matrix to achieve the final AIS trajectory clustering results. In order to improve the accuracy of the proposed multi-step clustering algorithm, an automatic algorithm for choosing the k clusters is developed according to the similarity distance. Numerous experiments on realistic AIS trajectory datasets in the bridge area waterway and Mississippi River have been implemented to compare our proposed method with traditional spectral clustering and fast affinity propagation clustering. Experimental results have illustrated its superior performance in terms of quantitative and qualitative evaluation
A Non-Equilibrium Sediment Transport Model for Dam Break Flow over Moveable Bed Based on Non-Uniform Rectangular Mesh
The use of multiple-level non-uniform rectangular mesh in coupled flow and sediment transport modeling is preferred to achieve high accuracy in important region without increasing computational cost greatly. Here, a robust coupled hydrodynamic and non-equilibrium sediment transport model is developed on non-uniform rectangular mesh to simulate dam break flow over movable beds. The enhanced shallow water and sediment transport equations are adopted to consider the mass and momentum exchange between the flow phase and sediment phase. The flux at the interface is calculated by the positivity preserving central upwind scheme, which belongs to Godunov-type Riemann-problem-solver-free central schemes and is less expensive than other popular Riemann solvers while still capable of tracking wet/dry fronts accurately. The nonnegative water depth reconstruction method is used to achieve second-order accuracy in space. The model was first verified against two laboratory experiments of dam break flow over irregular fixed bed. Then the quantitative performance of the model was further investigated by comparing the computational results with measurement data of dam break flow over movable bed. The good agreements between the measurements and the numerical simulations are found for the flow depth, velocity and bed changes
NDRG2 Ameliorates Hepatic Fibrosis by Inhibiting the TGF-Ξ²1/Smad Pathway and Altering the MMP2/TIMP2 Ratio in Rats
Liver fibrosis is a worldwide clinical issue. It has been well established that activated hepatic stellate cells (HSCs) are responsible for excessive extracellular matrix (ECM) deposition in chronically damaged livers. The identification of key elements that control HSCs activation will help to further our understanding of liver fibrosis and improve the outcome of clinical treatment. This study demonstrates that N-Myc downstream-regulated gene 2 (NDRG2) is a potential regulator of liver fibrosis as NDRG2 mRNA and protein levels were reduced during HSCs activation. In addition, enhanced NDRG2 expression reduced Smad3 transcription and phosphorylation, which inhibited HSCs activation by blocking the TGF-Ξ²1 signal. Moreover, NDRG2 contributed to an increase in the ratio of matrix metalloproteinase 2 (MMP2) to tissue inhibitor of matrix metalloproteinase 2 (TIMP2), which may facilitate the degradation of the ECM. In dimethylnitrosamine (DMN)-induced fibrotic rat livers, adenovirus-mediated NDRG2 overexpression resulted in decreased ECM deposition and improved liver function compared with controls. In conclusion, the present findings indicate that the modulation of NDRG2 is a promising strategy for the treatment of liver fibrosis
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