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101.
Jeppe Byskov-Nielsen Juha-Matti Savolainen Martin Snogdahl Christensen Peter Balling 《Applied Physics A: Materials Science & Processing》2010,98(1):97-101
In this paper we present femtosecond laser ablation studies of the metals copper, silver and tungsten. Measurements of the
threshold fluence determined from the hole diameters versus fluence provide incubation coefficients of the three materials,
which are found to be equal within one standard deviation. Furthermore, we have determined the single-shot threshold fluences
to be 1.7±0.3 J/cm2, 1.5±0.4 J/cm2 and 0.44±0.02 J/cm2 for copper, silver and tungsten, respectively. These are in good agreement with theoretical values calculated neglecting
heat diffusion. 相似文献
102.
We study systems with a continuous phase transition that tune their parameters to maximize a quantity that diverges solely at a unique critical point. Varying the size of these systems with dynamically adjusting parameters, the same finite-size scaling is observed as in systems where all relevant parameters are fixed at their critical values. This scheme is studied using a self-tuning variant of the Ising model. It is contrasted with a scheme where systems approach criticality through a target value for the order parameter that vanishes with increasing system size. In the former scheme, the universal exponents are observed in naïve finite-size scaling studies, whereas in the latter they are not. 相似文献
103.
104.
We provide explicit constructions of particularly convenient dual pairs of Gabor frames. We prove that arbitrary polynomials
restricted to sufficiently large intervals will generate Gabor frames, at least for small modulation parameters. Unfortunately,
no similar function can generate a dual Gabor frame, but we prove that almost any such frame has a dual generated by a B-spline.
Finally, for frames generated by any compactly supported function φ whose integer-translates form a partition of unity, e.g., a B-spline, we construct a class of dual frame generators, formed
by linear combinations of translates of φ. This allows us to chose a dual generator with special properties, for example, the one with shortest support, or a symmetric
one in case the frame itself is generated by a symmetric function. One of these dual generators has the property of being
constant on the support of the frame generator. 相似文献
105.
The link-cell (LC) algorithm is widely used in discrete element method (DEM) simulation, in order to increase computational efficiency. The common way is to divide the entire computational domain into a series of square sub-cells. A huge index matrix, Ω, is required to store the information of particles located in each of these sub-cells. However, most of these sub-cells are always empty for some anomalistic computational domain, such as particulate flow in a pipeline. These empty sub-cells also consume the limited memory bandwidth and lower the computational power. In order to reduce the size of the index matrix, a body fitted link-cell (BFLC) algorithm is established to identify the neighbors quickly. Furthermore, a simplified algorithm for simulation of two dimensional particulate flow in curved pipelines is presented. Lastly, an example is presented to validate the BFLC algorithm. 相似文献
106.
Dr. Evanildo G. Lacerda Jr. Dr. Fadhil S. Kamounah Prof. Dr. Kaline Coutinho Prof. Dr. Stephan P. A. Sauer Prof. Dr. Poul Erik Hansen Prof. Dr. Ole Hammerich 《Chemphyschem》2019,20(1):78-91
Prediction of chemical shifts in organic cations is known to be a challenge. In this article we meet this challenge for α-protonated alkylpyrroles, a class of compounds not yet studied in this context, and present a combined experimental and theoretical study of the 13C and 1H chemical shifts in three selected pyrroles. We have investigated the importance of the solvation model, basis set, and quantum chemical method with the goal of developing a simple computational protocol, which allows prediction of 13C and 1H chemical shifts with sufficient accuracy for identifying such compounds in mixtures. We find that density functional theory with the B3LYP functional is not sufficient for reproducing all 13C chemical shifts, whereas already the simplest correlated wave function model, Møller–Plesset perturbation theory (MP2), leads to almost perfect agreement with the experimental data. Treatment of solvent effects generally improves the agreement with experiment to some extent and can in most cases be accomplished by a simple polarizable continuum model. The only exception is the NH proton, which requires inclusion of explicit solvent molecules in the calculation. 相似文献
107.
Fourier transform infrared (FTIR) smog chamber techniques were used to investigate the atmospheric chemistry of the isotopologues of methane. Relative rate measurements were performed to determine the kinetics of the reaction of the isotopologues of methane with OH radicals in cm3 molecule−1 s−1 units: k(CH3D + OH) = (5.19 ± 0.90) × 10−15, k(CH2D2 + OH) = (4.11 ± 0.74) × 10−15, k(CHD3 + OH) = (2.14 ± 0.43) × 10−15, and k(CD4 + OH) = (1.17 ± 0.19) × 10−15 in 700 Torr of air diluent at 296 ± 2 K. Using the determined OH rate coefficients, the atmospheric lifetimes for CH4–xDx (x = 1–4) were estimated to be 6.1, 7.7, 14.8, and 27.0 years, respectively. The results are discussed in relation to previous measurements of these rate coefficients. 相似文献
108.
An integrated shape morphing and topology optimization approach based on the deformable simplicial complex methodology is developed to address Stokes and Navier‐Stokes flow problems. The optimized geometry is interpreted by a set of piecewise linear curves embedded in a well‐formed triangular mesh, resulting in a physically well‐defined interface between fluid and impermeable regions. The shape evolution is realized by deforming the curves while maintaining a high‐quality mesh through adaption of the mesh near the structural boundary, rather than performing global remeshing. Topological changes are allowed through hole merging or splitting of islands. The finite element discretization used provides smooth and stable optimized boundaries for simple energy dissipation objectives. However, for more advanced problems, boundary oscillations are observed due to conflicts between the objective function and the minimum length scale imposed by the meshing algorithm. A surface regularization scheme is introduced to circumvent this issue, which is specifically tailored for the deformable simplicial complex approach. In contrast to other filter‐based regularization techniques, the scheme does not introduce additional control variables, and at the same time, it is based on a rigorous sensitivity analysis. Several numerical examples are presented to demonstrate the applicability of the approach. 相似文献
109.
110.
Bodil Lousen Dr. Stephan K. Pedersen Pernille Bols Kasper H. Hansen Michelle R. Pedersen Prof. Ole Hammerich Dr. Sergey Bondarchuk Prof. Boris Minaev Dr. Glib V. Baryshnikov Prof. Hans Ågren Prof. Michael Pittelkow 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(22):4935-4940
This work describes a synthetic approach where a non-planar aromatic heterocyclic [7]helicene is compressed to yield a hetero[8]circulene containing an inner antiaromatic cyclooctatetraene (COT) core. This [8]circulene consists of four benzene rings and four heterocyclic rings, and it is the first heterocyclic [8]circulene containing three different heteroatoms. The synthetic pathway proceeds via a the flattened dehydro-hetero[7]helicene, which is partially a helicene and partially a circulene: it is non-planar and helically chiral as helicenes, and contains a COT motif like [8]circulenes. The antiaromaticity of the COT core is confirmed by nucleus independent chemical shift (NICS) calculations. The planarization from a helically π-conjugated [7]helicene to a fully planar heterocyclic [8]circulene significantly alters the spectroscopic properties of the molecules. Post-functionalization of the [7]helicenes and the [8]circulenes by oxygenation of the thiophene rings to the corresponding thiophene-sulfones allows an almost complete fluorescence emission coverage of the visible region of the optical spectrum (400–700 nm). 相似文献