119 research outputs found
Nonequilibrium Green's functions and atom-surface dynamics: Simple views from a simple model system
We employ Non-equilibrium Green's functions (NEGF) to describe the real-time
dynamics of an adsorbate-surface model system exposed to ultrafast laser
pulses. For a finite number of electronic orbitals, the system is solved
exactly and within different levels of approximation. Specifically i) the full
exact quantum mechanical solution for electron and nuclear degrees of freedom
is used to benchmark ii) the Ehrenfest approximation (EA) for the nuclei, with
the electron dynamics still treated exactly. Then, using the EA, electronic
correlations are treated with NEGF within iii) 2nd Born and with iv) a recently
introduced hybrid scheme, which mixes 2nd Born self-energies with
non-perturbative, local exchange-correlation potentials of Density Functional
Theory (DFT). Finally, the effect of a semi-infinite substrate is considered:
we observe that a macroscopic number of de-excitation channels can hinder
desorption. While very preliminary in character and based on a simple and
rather specific model system, our results clearly illustrate the large
potential of NEGF to investigate atomic desorption, and more generally, the non
equilibrium dynamics of material surfaces subject to ultrafast laser fields.Comment: 10 pages, 5 figure
Influence of Filler Metals in Welding Wires on the Phase and Chemical Composition of Weld Metal
The influence of filler metals used in welding wires on the phase and chemical composition of the metal, which is surfaced to mining equipment exposed to abrasive wear, has been investigated. Under a laboratory environment, samples of Mo-V-B and Cr-Mn-Mo-V wires were made. The performed experiments have revealed that fillers of the Cr-Mn-Mo-V system used in powder wire show better wear resistance of the weld metal than that of the Mn-Mo-V-B system; the absence of boron, which promotes grain refinement in the Mn-Mo-V-B system, significantly reduces wear resistance; the Mn-Mo-V-B weld metal has a finer structure than the Cr-Mn-Mo-V weld metal
Collective modes and the broken symmetry of a rotating attractive Bose gas in an anharmonic trap
We study the rotational properties of an attractively interacting Bose gas in
a quadratic + quartic potential. The low-lying modes of both rotational ground
state configurations, namely the vortex and the center of mass rotating states,
are solved. The vortex excitation spectrum is positive for weak interactions
but the lowest modes decrease rapidly to negative values when the interactions
become stronger. The broken rotational symmetry involved in the center of mass
rotating state induces the appearance of an extra zero-energy mode in the
Bogoliubov spectrum. The excitations of the center of mass rotational state
also demonstrate the coupling between the center of mass and relative motions.Comment: 4 pages, 3 eps figures (2 in color) v2: changes in Title, all
figures, in text (especially in Sec III) and in Reference
Fabrication of Omniphobic‐Omniphilic Micropatterns using GPOSS‐PDMS Coating
Surfaces with special wettability properties, such as omniphobicity or omniphilicity, are essential for functional devices that use both aqueous and organic media. Micropatterning of omniphobic and omniphilic properties can provide a wide range of applications, including miniaturized experiments using both aqueous and organic media. Herein, an approach for creating omniphobic-omniphilic micropatterns based on selective photoacid polymerization of octa(3-glycidyloxypropyl) polyhedral oligomeric silsesquioxane modified with mono-aminopropyl-terminated polydimethylsiloxane is reported. The composition of the polymeric coatings using infrared spectroscopy; patterning accuracy using atomic force microscopy and scanning electron microscopy; wettability characteristics of the omniphobic, and omniphilic surfaces using contact angle measurements are studied. The proposed approach allows for single-step micropatterning (sub-10 µm) or macropatterning (3 mm). Liquids with surface tensions >22.8 mN m−1 can be confined to the omniphilic areas by the omniphobic borders. C2C12 cells are successfully cultivated in omniphilic areas, demonstrating their cell compatibility. The cells adhere to and grow on the entire surface of the pattern, without any signs of cytotoxicity. However, the strongest adhesion is observed in the omniphilic areas, making it possible to create cell micropatterns in a single step. The proposed method for the fabrication of omniphobic-omniphilic transparent, mechanically robust, biocompatible patterns can find applications in microfluidics, biotechnology or miniaturized biological screening experiments
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