Diffusion and localization of cold atoms in 3D optical speckle

In this work we re-formulate and solve the self-consistent theory for localization to a Bose-Einstein condensate expanding in a 3D optical speckle. The long-range nature of the fluctuations in the potential energy, treated in the self-consistent Born approximation, make the scattering strongly velocity dependent, and its consequences for mobility edge and fraction of localized atoms have been investigated numerically.     

Rigorous interpretation of electronic density functions of axial and equatorial conformers of dimethylphosphinoylcyclohexane, 2-(dimethylphosphinoyl)-1,3,5-trithiane, and 2-(dimethylphosphinoyl)-1,3-dithiane-1,1,3,3-tetraoxide

Theoretical analysis within the frame of the Topological Theory of Atoms in Molecules confirms the repulsive steric interaction between an axial dimethylphosphinoyl group and the syn-diaxial hydrogens in cyclohexane derivative 2-ax. In seemingly good agreement with experiment, equatorial isomer 2-eq was calculated to be 1.49 kcal/mol more stable than 2-ax. (Experimental energy difference in (diphenylphosphinoyl)cyclohexane, Delta H(o) = 1.96 kcal/mol.) In contrast, axial 2-(dimethylphosphinoyl)-1,3,5-trithiane, 3-ax, was calculated to be 6.38 kcal/mol more stable than 3-eq. (Experimentally, the axial conformer of 2-(diphenylphosphinoyl)-1,3,5-trithiane, was found to be 1.43 kcal/mol more stable than the equatorial conformer, in solvent chloroform.) Theoretical analysis, in particular the electron density at the bond critical point within the C(4,6)-H...O=P bonding trajectory, implies significant bonding in this segment of interacting atoms. By the same token, substantial positive charge is acquired by the C--H bonds adjacent to the sulfonyl groups in disulfone 4. Hydrogen bonding between the phosphoryl group and H(4,6) leads to stabilization of 4-ax, which is estimated to be 5.0 kcal/mol lower in energy than 4-eq. This conclusion is supported by examination of P==O...H--C(4,6) bond trajectories, as well as from evaluation of the critical point properties along those interacting moieties. By contrast, fluorinated derivative 5 is more stable in the equatorial conformation, indicating a repulsive electrostatic interaction of the C--F...O-P entity in 5-ax.     

The role of conditioning film formation and surface chemical changes on Xylella fastidiosa adhesion and biofilm evolution

Biofilms are complex microbial communities with important biological functions including enhanced resistance against external factors like antimicrobial agents. The formation of a biofilm is known to be strongly dependent on substrate properties including hydrophobicity/hydrophilicity, structure, and roughness. The adsorption of (macro)molecules on the substrate, also known as conditioning film, changes the physicochemical properties of the surface and affects the bacterial adhesion. In this study, we investigate the physicochemical changes caused by Periwinkle wilt (PW) culture medium conditioning film formation on different surfaces (glass and silicon) and their effect on X. fastidiosa biofilm formation. Contact angle measurements have shown that the film formation decreases the surface hydrophilicity degree of both glass and silicon after few hours. Atomic force microscopy (AFM) images show the glass surface roughness is drastically reduced with conditioning film formation. First-layer X. fastidiosa biofilm on glass was observed in the AFM liquid cell after a period of time similar to that determined for the hydrophilicity changes. In addition, attenuation total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy supports the AFM observation, since the PW absorption spectra increases with time showing a stronger contribution from the phosphate groups. Although hydrophobic and rough surfaces are commonly considered to increase bacteria cell attachment, our results suggest that these properties are not as important as the surface functional groups resulting from PW conditioning film formation for X. fastidiosa adhesion and biofilm development.     

Optical Metrology by Fringe Processing on Independent Windows Using a Genetic Algorithm

We present a method to retrieve the phase of a fringe pattern based on the window fringe pattern demodulation technique (WFPD). The overlapped phase similarity criterion is avoided in the proposed method, and it is substituted by a second order smoothness criterion. The fringe processing on independent windows (FPIW) method can measure physical quantities from closed and near sub-sampled fringe patterns by a simplified cost or fitness function. The fringe image is divided into a set of partially overlapping windows. In these sub-images the estimated phase is modelled as a parametric analytic-function, and its parameters are optimized using a genetic algorithm (GA). This analytic-function is used to estimate the phase in the area framed by the window. Phases from all windows are sequentially spliced to retrieve the whole phase field. A media filter is applied over the entire phase field to smooth the irregularities that appear in the junctures between windows.     

Density of states for a disordered system of interacting dipoles

The density of states for a system of interacting Ising dipoles in the presence of diagonal disorder is obtained by computer simulation. Two models are considered, one with the true dipole-dipole interaction and another in which the angular dependence of the interaction is not included. Results for different values of the disorder energy are obtained for the two models, fitting quite well to previous analytical calculations.     

Subharmonic shapiro steps and assisted tunneling in superconducting point contacts

We analyze the current in a superconducting point contact of arbitrary transmission in the presence of a microwave radiation. The interplay between the ac Josephson current and the microwave signal gives rise to Shapiro steps at voltages V = (m/n)h(omega)(r)/2e, where n,m are integer numbers and omega(r) is the radiation frequency. The subharmonic steps (n not equal 1) are a consequence of multiple Andreev reflections (MAR) and provide a signature of the peculiar ac Josephson effect at high transmission. Moreover, the dc current exhibits a rich subgap structure due to photon-assisted MARs.     

Monitoring structural damage of components using an effective modulus approach

This paper describes a novel nondestructive damage detection method that was developed to study the influence of a crack on the dynamic properties of a cantilever beam subjected to bending. Experimental measurements of transfer functions for the cracked cantilever beam revealed a change in the natural frequency with increasing crack length. A finite element model of a cracked element was created to compute the influence of severity and location of damage on the structural stiffness. The proposed model is based on the response of the cracked beam element under a static load. The change in beam deflection as a result of the crack is used to calculate the reduction in the global component stiffness. The reduction of the beam stiffness is then used to determine its dynamic response employing a modal analysis computational model. Euler–Bernoulli and Timoshenko beam theories are used to quantify the elastic stiffness matrix of a finite element. The transfer functions from both theories compare well with the experimental results. The experimental and computational natural frequencies decreased with increasing crack length. Furthermore the Euler–Bernoulli and Timoshenko beam theories resulted in approximately the same decrease in the natural frequency with increasing crack length as experimentally measured.