An efficient front‐tracking method for simulation of multi‐density bubbles

In this article, a masked bubble strategy is proposed using the front‐tracking method when simulation of multi‐density bubbles to reduce remarkably the computational cost from both the RAM usage and the number of computations at each time step comparing with the regular method. In the masked bubble strategy, instead of using full domain to update the properties at each time step, each bubble is considered as enclosed in the smallest box required to compute the properties based on the Peskin's function, which needs at least two full mesh sizes from both sides of the interface of each bubble in any directions. To show the performance of the masked bubble strategy in the front‐tracking method, we study the multi‐density bubbles motion in a curved duct flow induced by a pressure gradient in the absence of gravity. To solve the density Poisson equation, the parallel direct solver scheme is tested. The comparison of numerical simulations at the same conditions indicates that the parallel direct solver scheme under the masked bubble strategy considerably reduces the computational time and RAM usage relative to the regular full‐domain method, providing using simulations on finer grid resolutions. Copyright © 2016 John Wiley & Sons, Ltd.     

The transient buoyancy driven motion of bubbles across a two-dimensional quiescent domain

The transient buoyancy driven motion of two-dimensional bubbles across a domain bounded by two horizontal walls is studied by direct numerical simulations. The bubbles are initially released next to the lower wall and as they rise, they disperse. Eventually all the bubbles collect at the top wall. The goal of the study is to examine how a simple one-dimensional model for the averaged void fraction captures the unsteady bubble motion. By using void fraction dependent velocities, where the exact dependency is obtained from simulations of homogeneous bubbly flows, the overall dispersion of the bubbles is predicted. Significant differences remain, however. We suggest that bubble dispersion by the bubble induced liquid velocity must be included, and by using a simple model for the bubble dispersion we show improved agreement.     

Flow modulation of a planar free shear layer with large bubbles—direct numerical simulations

The flow of a planar free shear layer with cylindrical bubbles is simulated using a finite difference/front tracking scheme. This approach allows direct numerical simulation of the multiphase flow by wholly incorporating the local bubble flow field in conjunction with the large scale vortical structures of the liquid. The role of large bubbles in modifying low Reynolds number ( 250) shear flow structures is investigated, specifically for bubbles whose diameter approaches the scale of the largest liquid eddies. The results indicate that duration of eddy crossing is the main mechanism for flow modulation, which is typically characterized by decreased vortex coherency and size, modified fluctuation statistics and significant variations in pairing/merging phenomena. The comparison of fluctuating statistics and flow field visualization also allowed qualitative discrimination between the modulation of the non-linear eddy dynamics and fluctuations due simply to the random bubble induced perturbations.     

A novel microreactor approach for analysis of ketones and aldehydes in breath

We report a fabricated microreactor with thousands of micropillars in channels. Each micropillar surface is chemically functionalized to selectively preconcentrate gaseous ketones and aldehydes of exhaled breath and to enhance ultra-trace, rapid analysis by direct-infusion Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry (MS). The micropillar reactive coating contains the quaternary ammonium aminooxy salt 2-(aminooxy)ethyl-N,N,N-trimethylammonium iodide (ATM) for capturing trace carbonyl VOCs by means of an oximation reaction. We demonstrate the utility of this approach for detection of C(1) to C(12) aldehydes and ketones in exhaled breath, but the approach is applicable to any gaseous sample.     

A Precious‐Metal‐Free Hybrid Electrolyzer for Alcohol Oxidation Coupled to CO2‐to‐Syngas Conversion

Electrolyzers combining CO₂ reduction (CO₂R) with organic substrate oxidation can produce fuel and chemical feedstocks with a relatively low energy requirement when compared to systems that source electrons from water oxidation. Here, we report an anodic hybrid assembly based on a (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) electrocatalyst modified with a silatrane‐anchor ( STEMPO ), which is covalently immobilized on a mesoporous indium tin oxide (mesoITO) scaffold for efficient alcohol oxidation (AlcOx). This molecular anode was subsequently combined with a cathode consisting of a polymeric cobalt phthalocyanine on carbon nanotubes to construct a hybrid, precious‐metal‐free coupled AlcOx–CO₂R electrolyzer. After three‐hour electrolysis, glycerol is selectively oxidized to glyceraldehyde with a turnover number (TON) of ≈1000 and Faradaic efficiency (FE) of 83 %. The cathode generated a stoichiometric amount of syngas with a CO:H₂ ratio of 1.25±0.25 and an overall cobalt‐based TON of 894 with a FE of 82 %. This prototype device inspires the design and implementation of nonconventional strategies for coupling CO₂R to less energy demanding, and value‐added, oxidative chemistry.     

Poly(N‐isopropylacrylamide)‐Based Polymers as Additive for Rapid Generation of Spheroid via Hanging Drop Method

Multicellular tumor spheroid (MCTS) mimics microenvironment for tumor formation and provides predictive insight for in vivo tests. The hanging drop (HD) method of spheroid generation is cost effective, but it is limited by a long time duration for spheroid development and a low rate of formation of larger spheroids. Toward addressing those limitations, thermoresponsive copolymers with poly(N‐isopropylacrylamide) (p(NIPA)) backbone are developed, to be used as additives in the MCTS formation via HD method. Upon investigation it is found that in the presence of the polymer, robust and compact spheroids are formed in a short duration of 48 h. Larger spheroids (350–600 µm) can be formed by increasing the number of cells. Spheroids are characterized for their 3D shape and different cellular layers, and drug uptake study is done to prove the efficacy of the spheroids generated in drug screening.     

Rh(III)‐Catalyzed Denitrogenative [4+2] Annulation of Benzamides and 3‐Diazoindolin‐2‐imines: Expedient Access to Indolo[2,3‐c] isoquinolin‐5‐ones

An effective and pragmatic strategy for the synthesis of structurally diverse indolo[2,3‐c]isoquinolin‐5‐ones has been developed via a Rh(III)‐catalyzed C?H activation and [4+2] annulation reaction of N‐methoxybenzamides and 3‐diazoindolin‐2‐imines. The reaction involves the efficient formation of two new (one C?C and one C?N) bonds under operationally simple conditions and has the benefits of a broad substrate scope.     

Interaction between 14mer DNA oligonucleotide and cationic surfactants of various chain lengths

In the recent genomic era, a novel gene silencing approach has been introduced based on the use of small synthetic oligonucleotides, such as antisense RNAs, siRNAs, to inhibit the expression of a specific target gene. Successful implementation of this methodology calls for the development of efficient systems to deliver small oligonucleotides into the cells using various natural and synthetic cationic agents. While extensive studies have focused on the interaction of various natural and synthetic cationic surfactants with long DNA, less attention has been paid to surfactant interaction with small oligonucleotides. In this study, the interaction between 14mer double stranded DNA and alkyltrimethylammonium bromides of C16 (cetyl, CTAB), C14 (tetradecyl, TTAB), and C12 (dodecyl, DTAB) chain lengths was investigated at different charge ratios by gel electrophoresis, ethidium bromide exclusion, circular dichroism, and UV melting. Our gel studies at 1 microM oligonucleotide concentration showed that CTAB, TTAB, and DTAB neutralize the oligonucleotides at a charge ratio (Z+/-) of 1, 14, and 50, respectively. At lower charge ratios, CTAB and TTAB interact with oligonucleotides, and the complexes show electrophoretic mobility shifts in the gel, while such mobility shifts were completely absent in the case of DTAB. UV melting experiments revealed that interaction with all three surfactants increased the thermostability of the oligonucleotide. The extent of thermal stabilization was highest in the case of CTAB, moderate in the case of TTAB, and extremely low in the case of DTAB. Oligonucleotides within fully neutralized complexes denatured at further higher temperatures, and again, stabilization was the highest in the case of CTAB followed by TTAB and DTAB, hence revealing that the oligonucleotides interacted more strongly with CTAB than with the other two surfactants. Ethidium bromide exclusion studies also supported our UV melting studies, confirming that CTAB binds most strongly to the oligonucleotide. CD titrations of oligonucleotides with increasing amounts of surfactants revealed common spectral patterns consisting of the progressive loss of CD signals for native helical DNA conformations. Overall, our results demonstrate that interaction between oligonucleotides and cationic surfactants, although qualitatively similar to long double stranded DNA, shows subtle differences that need to be understood to improve small oligonucleotide delivery into the cells by using common delivery agents that have been used to deliver long pieces of DNA.     

Are we ready for industrial production of bioactive plant secondary metabolites utilizing endophytes?

The prospect of endophytes capable of producing associated plant natural products with therapeutic potential is undeniable. However, the unyielding struggle so far to transform these potential sources into sustainable microbial manufacturers on a commercial scale has been disappointing. In this Viewpoint, we address this trade-off between endophyte discovery and viable industrial application.