Green’s Function Approach to the Bose-Hubbard Model

We use a diagrammatic hopping expansion to calculate finite-temperature Green functions of the Bose-Hubbard model which describes bosons in an optical lattice. This technique allows for a summation of subsets of diagrams, so the divergence of the Green function leads to non-perturbative results for the boundary between the superfluid and the Mott phase for finite temperatures. Whereas the first-order calculation reproduces the seminal mean-field result, the second order goes beyond and shifts the phase boundary in the immediate vicinity of the critical parameters determined by high-precision Monte-Carlo simulations of the Bose-Hubbard model. In addition, our Green’s function approach allows for calculating the excitation spectrum both for zero and finite temperature and for determining the effective masses of particles and holes.

Artificial gauge field switching using orbital angular momentum modes in optical waveguides

The discovery of artificial gauge fields controlling the dynamics of uncharged particles that otherwise elude the influence of standard electromagnetic fields has revolutionised the field of quantum simulation.Hence,developing new techniques to induce these fields is essential to boost quantum simulation of photonic structures.Here,we experimentally demonstrate the generation of an artificial gauge field in a photonic lattice by modifying the topological charge of a light beam,overcoming the need to modify the geometry along the evolution or impose external fields.In particular,we show that an effective magnetic flux naturally appears when a light beam carrying orbital angular momentum is injected into a waveguide lattice with a diamond chain configuration.To demonstrate the existence of this flux,we measure an effect that derives solely from the presence of a magnetic flux,the Aharonov-Bohm caging effect,which is a localisation phenomenon of wavepackets due to destructive interference.Therefore,we prove the possibility of switching on and off artificial gauge fields just by changing the topological charge of the input state,paving the way to accessing different topological regimes in a single structure,which represents an important step forward for optical quantum simulation.

DEM-CFD study of the filter cake formation process due to non-spherical particles

The formation of a filter cake during the filtration of a suspension with non-spherical particles is studied using a multi-sphere model in a simulation that couples the discrete element method with computational fluid dynamics.The implementation of the coupling with a drag model that considers orientation,sphericity,and the presence of surrounding particles for non-spherical particles is tested for single particles and suspensions by comparing the terminal velocities with empirical results.Phenomena predicted in the simulations,such as the presence or absence of initial oscillations and changes in the orientation of a particle,are consistent with experimental observations reported in the literature.The variation in the void fraction of a filter cake with respect to the particle sphericity is obtained and compared with experimental trends reported in the literature.Furthermore,complex interdependencies of the particle sphericity,void fraction,and pressure drop of a filter cake for a wide range of fluid conditions are investigated.

Photosensitive Material Enabling Direct Fabrication of Filigree 3D Silver Microstructures via Laser-Induced Photoreduction

Dear Editor Laser-induced photoreduction(LPR)as a direct fabrication technique that promises to be one of the most versatile routes for fabricating highly conductive 3D metallic microstructures on-chip(e.g.,metamaterials,electro-mechanical systems,and high-frequency components like antennas).

Microstructuring of titanium surfaces with plasma-modified titanium particles by cold spraying

Although the deposition mechanisms of the cold spray process are well studied, few reports regarding the use of surface-modified particles exist. Herein, titanium particles 3-39 μm in size and with an angular shape were modified in a plasma-enhanced chemical vapor deposition process in Ar, Ar-C2H2, and N2 plasmas. After Ar-C2H2 and N2 treatments, the respective presence of TiC and TiN on the particle surface was confirmed via transmission electron microscopy and energy-dispersive X-ray, X-ray photoelectron, and Raman spectroscopies. The powders were deposited on titanium substrates by cold spray experiments, where unmodified particles up to 10(xm in size exhibited a successful surface bon ding. This finding was described by an existing analytical model, whose parameters were achieved by computational fluid dynamics simulations taking the particle shape factor into account:. A good deposition of plasma-modified particles up to 30 μm in size was experimentally observed, exhibiting an upper size limit larger than that predicted by the model. Higher surface roughness values were found for plasmamodified particles, as determined by 3D scanning electron microscopy. The water contact angle indicated that argon treatment influenced the wettability. Tribological tests showed a decrease of the initial friction coefficient from 0.53 to 0.47 by microstructuring.