Yuwang Wang

Controllable gas-liquid phase flow patterns and monodisperse microbubbles in a microfluidic T-junction device

This letter describes the gas-liquid phase flow patterns and the mechanism of generation of monodisperse microbubbles in a T-junction microfluidic device using the crossflowing shear-rupturing technique. The bubble size is ranged from 100 to 500μm. The air phase states as isolate air slugs, “pearl necklaces,” periodic isolate bubbles, zig-zag bubble patterns, and multiple-bubble layer can be observed in the wider measured channel. The bubble size relates with the continuous phase flow velocity and viscosity as Vb∝1∕(μcuc), while being almost independent of surface tension γ and air phase flow rate Qg, for the conditions used in this work. The bubble formation mechanism by using the crossflowing shear-rupturing technique is different from the hydrodynamic flow focusing and both geometry-dominated breakup techniques. Our system provides independent control of both the size and volume fraction of dispersed bubbles.

Oxidative desulfurization of DBT with H2O2 catalysed by TiO2/porous glass

Aimed at ultra-deep oxidative desulfurization (ODS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) to control air pollution, we specially designed and prepared porous glass supported with TiO2 nanoparticles acting as an amphiphilic catalyst. Hydrogen peroxide which is considered as the “green” oxidant was used, and for the extreme liquid–liquid phase ratio (usually larger than 1500) reaction system, a pore volume of 0.19 mL g−1 of the catalyst provides enough space for the storage of hydrogen peroxide. The as-prepared catalyst offers a high interfacial surface area of 116.9 m2 g−1 and enhances the reaction by facilitating the mass transfer. The mono-dispersed TiO2 exhibited good crystallinity. The mean diameter varied from 2.1 to 7.8 nm with the loading amount increasing from 1.27 wt% to 9.85 wt%. The catalyst showed high activity and good stability for producing ultra-clean fuels: 100% conversion was obtained within 2 min and the conversion just decreased from 100.0 ± 1.0% to 94.3 ± 0.6% after 5 cycles. Overall, this new reusable catalyst provided an alternative for highly efficient ultra-deep desulfurization in a green way.

Hyperspectral Computational Ghost Imaging via Temporal Multiplexing

Computational ghost imaging has made large progress in both spatial resolution and acquisition efficiency, but so far still cannot resolve the spectral reflectance well. This letter proposes a spectrum encoded acquisition scheme to achieve computational ghost imaging of hyperspectral data. Taking advantage of the speed gap between the extremely fast response of the bucket detector and magnitudes lower spatial illumination modulation, our approach temporally multiplexes a group of diverse spectra into the elapse of each 2-D illumination pattern. The number and the type of the multiplexed spectra are optimized utilizing the low intrinsic dimension of the hyperspectral data and based on the reconstruction quality on a diverse range of nature materials. After data acquisition, we infer the top principal component analysis projections of the hyperspectral image from the demultiplexed correlated measurements and the illumination patterns, and then reconstruct the final hyperspectral data. As far as we know, we are the first one to achieve computational hyperspectral ghost imaging with high accuracy in a few seconds.

High Speed Computational Ghost Imaging via Spatial Sweeping

Computational ghost imaging (CGI) achieves single-pixel imaging by using a Spatial Light Modulator (SLM) to generate structured illuminations for spatially resolved information encoding. The imaging speed of CGI is limited by the modulation frequency of available SLMs, and sets back its practical applications. This paper proposes to bypass this limitation by trading off SLM’s redundant spatial resolution for multiplication of the modulation frequency. Specifically, a pair of galvanic mirrors sweeping across the high resolution SLM multiply the modulation frequency within the spatial resolution gap between SLM and the final reconstruction. A proof-of-principle setup with two middle end galvanic mirrors achieves ghost imaging as fast as 42 Hz at 80 × 80-pixel resolution, 5 times faster than state-of-the-arts, and holds potential for one magnitude further multiplication by hardware upgrading. Our approach brings a significant improvement in the imaging speed of ghost imaging and pushes ghost imaging towards practical applications.

Single-shot thermal ghost imaging using wavelength-division multiplexing

Ghost imaging (GI) is an emerging technique that reconstructs the target scene from its correlated measurements with a sequence of patterns. Restricted by the multi-shot principle, GI usually requires long acquisition time and is limited in observation of dynamic scenes. To handle this problem, this paper proposes a single-shot thermal ghost imaging scheme via a wavelength-division multiplexing technique. Specifically, we generate thousands of correlated patterns simultaneously by modulating a broadband light source with a wavelength dependent diffuser. These patterns carry the scenes spatial information and then the correlated photons are coupled into a spectrometer for the final reconstruction. This technique increases the speed of ghost imaging and promotes the applications in dynamic ghost imaging with high scalability and compatibility.

In situ dispersion of oil-based Ag nanocolloids by microdroplet coalescence and their applications in SERS detection

Monodispersity and size uniformity of the nanoparticles coated on film-like nanosensors are critical for detection efficiency. However, there is limited controllability in the dispersion of these nanoparticles during their preparation and surface modification processes. Herein, we have developed a method for the in situ dispersion of surface-modified Ag nanoparticles by controlling microdroplet coalescence, and fabricated surface-enhanced Raman scattering (SERS) films by spin-coating the nano-Ag suspensions. In the dispersion process, a two-plate type microchannel was employed to promote microdroplet coalescence. Under the experimentally optimized conditions, about 88% surface-modified Ag nanoparticles with an average size of 16–19 nm could be in situ dispersed. Upon the deposition of the resulting nanosuspensions on PDMS film surfaces, the films could be used to detect a target analyte, rhodamine 6G (R6G), at a detection limit of approximately 1.0 × 10−8 mol L−1. The Ag-coated films were also confirmed to be stable and highly reusable.

Single-pixel hyperspectral imaging

Conventional multispectral imaging methods detect photons of a 3D hyperspectral data cube separately either in the spatial or spectral dimension using array detectors, and are thus photon inefficient and spectrum range limited. Besides, they are usually bulky and highly expensive. To address these issues, this paper presents single-pixel multispectral imaging techniques, which are of high sensitivity, wide spectrum range, low cost and light weight. Two mechanisms are proposed, and experimental validation are also reported.