We have used large-eddy simulation with an immersed boundary method to study turbulent flows over distributions of uniform height, staggered cubes. The computational domains were designed such that both the roughness sublayer and a region of the inertial layer are resolved. With this, we record vertical profiles of time series of fluctuating streamwise and vertical velocity at different locations throughout the domain. Contour images of these fluctuating quantities shown relative to elevation and time are studied; contour images of Reynolds shear stresses owing to 'sweeps' and 'ejections' are also studied. These images show that periods of momentum excess (deficit) in the inertiallayer precede excitation (subdual) of cube-scale coherent vortices in the roughness sublayer. We compute this time lag (termed advective lag) and demonstrate that it scales linearly with wall-normal elevation. The advective lag is attributed to coherent, lowand high-momentum regions in the aloft inertial layer. Vortex identification is used to illustrate the presence of hairpin packets encapsulating low-momentum regions. Based on this, the reported inclination angle associated with hairpin packets is used to guide the development of a model for prediction of advective lag with height. The model captures the advective lag profiles reasonably well. In the interest of generality, additional cases of flow over homogeneous roughness (aerodynamic drag imposed with the equilibrium logarithmic law) are considered. We again observe that advective lag scales linearly with wall-normal elevation. Advective lag predictions from the aforementioned model agree well with results for these cases.

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To controllably deflect the Airy beam in a wide range dynamic, the method of combining the classical Airy cubic phase with a diffraction blazed grating phase was adopted in this paper. By dynamically adjusting the grating parameters, the transverse self-accelerating Airy beam allows arbitrary deflection, and the deflected position can be controlled precisely. The mathematical model of the Airy beam optical field distributions generated by the combined phase patterns were proposed to explain the feasibility. Its correctness was ultimately demonstrated by the experimental results. It is significant to use this method for the Airy beam deflection control in high-precision closed-loop aiming systems.

Formation mass density is directly related to porosity, fluid type, fluid saturation, and matrix mineral composition. The change of the reservoir parameters can cause the change of density and then the seismic velocity, impedance and amplitude. We discussed the characteristics of the changes by theoretical calculation and presented a method for estimating density and porosity based on full acoustic waveform inversion. Because of avoiding the signal distortion caused by more processing, the method can improve the inversion accuracy of density and porosity. It also can eliminate noise by integrating the derivative of wave field along time and summing multi-shot data. The method has been tested successfully by a synthetic example and gas-field data from western China. The density and porosity provided by the method agree with the logging result. It also supplies reliable data for prediction of effective reservoir and calculation of reserves.

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In this paper, two series of poly­(sulfobetaine methacrylate)-b-poly­(lauryl methacrylate) (PSBMA-b-PLMA) diblock copolymers were prepared to investigate the core–shell reversion of amphiphilic copolymers. Experimental results proved that the PSBMA-b-PLMA copolymers can be self-assembled as core–shell nanoparticles in chloroform. Moreover, 1H NMR spectra and contact angle measurements revealed that there is a transitional PSBMA/PLMA block ratio of 0.6, above which the nanoparticles are capable of switching their core and shell in aqueous solution. Consequently, nanoparticles with PSBMA/PLMA block ratios above 0.6 showed superior antifouling and antibacterial abilities to those with block ratios below 0.4. Moreover, it was also found that the block chain length plays an important role in core–shell reversion as evidenced by 1H NMR spectra, water contact angle, and antifouling tests. As a result, coatings fabricated with the PLMA100 series of nanoparticles showed better antifouling abilities than those of the PLMA150 series at the same block ratio probably because of the thinner shell of PLMA100 copolymers. PSBMA100-b-PLMA100 was proved to be the best candidate for the fabrication of antifouling coatings as it exhibited the highest efficacy in antibacterial adhesion and antiprotein adsorption. This study provided a facile method to fabricate antifouling coatings by developing amphiphilic diblock copolymers with tuned hydrophobic/hydrophilic block ratio, block chain length, etc.