3,059 research outputs found
A multichannel thiacalix[4]arene-based fluorescent chemosensor for Zn²⁺, F⁻ ions and imaging of living cells
The fluorescent sensor (3) based on the 1,3-alternate conformation of the thiacalix[4]arene bearing the coumarin fluorophore, appended via an imino group, has been synthesised. Sensing properties were evaluated in terms of a colorimetric and fluorescence sensor for Zn 2+ and F - . High selectivity and excellent sensitivity were exhibited, and off-on optical behaviour in different media was observed. All changes were visible to the naked eye, whilst the presence of the Zn 2+ and F - induces fluorescence enhancement and the formation of a 1:1 complex with 3. In addition, 3 exhibits low cytotoxicity and good cell permeability and can readily be employed for assessing the change of intracellular levels of Zn 2+ and F -
Magnetic susceptibility and specific heat of the spin-1/2 Heisenberg model on the kagome lattice and experimental data on ZnCu3(OH)6Cl2
We compute the magnetic susceptibility and specific heat of the spin-1/2
Heisenberg model on the kagome lattice with high-temperature expansions and
exact diagonalizations. We compare the results with the experimental data on
ZnCu3(OH)6Cl2 obtained by Helton et al. [Phys. Rev. Lett. 98, 107204 (2007)].
Down to k_BT/J~0.2, our calculations reproduce accurately the experimental
susceptibility, with an exchange interaction J~190K and a contribution of 3.7%
of weakly interacting impurity spins. The comparison between our calculations
of the specific heat and the experiments indicate that the low-temperature
entropy (below ~20K) is smaller in ZnCu3(OH)6Cl2 than in the kagome Heisenberg
model, a likely signature of other interactions in the system.Comment: Minor revisions in the text and references. To appear in Eur. Phys.
J.
Thermal coupling analysis for a multi-chip paralleled IGBT module in a doubly fed wind turbine power converter
Thermal coupling between adjacent IGBT or diode chips is the result of non-uniform temperature distribution in a multi-chip IGBT module. This affects the junction temperatures and hence the total power loss predicted for the module. The study first investigates the impact of thermal coupling effect on the junction temperatures through finite element method (FEM), and then develops a thermal coupling impedance model to represent such effect. The effect is shown to reduce with the distance exponentially. The model result agrees well with test. The validated model is then used to predict the junction temperature swings during operational power cycling in a DFIG wind turbine, showing the difference between the rotor and grid side converters. The model presented and the results obtained may be important for reliability evaluation and condition monitoring in the wind turbine power converters as well as in other multi-chip paralleled power electronic systems
NeurAR: Neural Uncertainty for Autonomous 3D Reconstruction
Implicit neural representations have shown compelling results in offline 3D
reconstruction and also recently demonstrated the potential for online SLAM
systems. However, applying them to autonomous 3D reconstruction, where robots
are required to explore a scene and plan a view path for the reconstruction,
has not been studied. In this paper, we explore for the first time the
possibility of using implicit neural representations for autonomous 3D scene
reconstruction by addressing two key challenges: 1) seeking a criterion to
measure the quality of the candidate viewpoints for the view planning based on
the new representations, and 2) learning the criterion from data that can
generalize to different scenes instead of hand-crafting one. For the first
challenge, a proxy of Peak Signal-to-Noise Ratio (PSNR) is proposed to quantify
a viewpoint quality. The proxy is acquired by treating the color of a spatial
point in a scene as a random variable under a Gaussian distribution rather than
a deterministic one; the variance of the distribution quantifies the
uncertainty of the reconstruction and composes the proxy. For the second
challenge, the proxy is optimized jointly with the parameters of an implicit
neural network for the scene. With the proposed view quality criterion, we can
then apply the new representations to autonomous 3D reconstruction. Our method
demonstrates significant improvements on various metrics for the rendered image
quality and the geometry quality of the reconstructed 3D models when compared
with variants using TSDF or reconstruction without view planning.Comment: 8 pages, 6 figures, 2 table
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