| RESEARCH HIGHLIGHTS |


Comparative analyses presented more


surprises. In samples not infected with liver fluke, tumor tissue had significantly higher levels of Stenotrophomonas bacteria. Several Stenotrophomonas species are known to trigger inflammation, which is a common mecha- nism by which bacteria cause cancer. The researchers could not, however,


clearly distinguish between normal and tumor tissue in samples infected by liver f luke. But they did notice that, compared


to the parasite-free subset, the infected samples had an abundance of intestinal Bifidobacteriaceae, Enterobacteriaceae and Enterococcaceae. Further computational anal- ysis revealed that these bacteria metabolize ammonia and bile acids, which are known to promote colorectal cancer. The researchers plan to conduct further


genomic analyses on a much larger sample size and study these processes in cell culture experi- ments. “We want to grow human bile duct cell


lines, expose them to the various bacteria and see how they respond,” says Nagarajan. “Even if it does not lead to the initiation of the cancer, bacteria could be accelerating the process of tumor formation.”


1. Chng, K. R., Chan, S. H., Ng, A. H. Q, Li, C., Jusakul, A. et al. Tissue microbiome profiling identifies an enrichment of specific enteric bacteria in Opisthorchis viverrini associated cholangiocarcinoma. EBioMedicine 8, 195–202 (2016).


Fluid dynamics:


VISUALIZING VORTICES


PREVIOUSLY TOO COMPLEX TO TACKLE, COMPUTER SIMULATIONS CAN NOW SHOW HOW ELLIPTICAL VORTEX RINGS FORM


Understanding how smoke rings form and dissipate could lead to technology allowing airplanes to soar more efficiently and blood to flow more freely through the human heart. Smoke rings and the airflows surrounding


airplanes are two examples of vortex rings, which occur when a fast-moving fluid — liquid or air — flows within a slower moving environment. As this faster fluid slows down at the fringes, whirls are created that start to develop into stable vortex rings. Vortex rings were previously considered to


be too complicated to solve. But researchers at A*STAR have now developed a computational model to simulate the motion of an elliptical


10 A*STAR RESEARCH Y


Y Z T = 24 X


T = 0 X


2


6 10 16 18 Z


Evolution of a vortex ring at different times as it moves from the left to the right.


22 26


vortex ring in a slow-moving fluid in a range of different situations, allowing for a more realistic description of vortex rings1. Vortex rings present issues in fields


such as engineering as they can hamper fluid flow. For example, they can increase the fuel consumption of a car by reducing its aerodynamic efficiency. Understanding the formation of vortex rings under different circumstances is therefore important to improve the mass flow in fluidic devices and around moving vehicles. Previous studies of vortex rings focused mainly on perfectly circular structures, as they are much easier to mathematically model than the more common and realistic


elliptical ones, explains Cheng Ming from the A*STAR Institute of High Performance Computing (IHPC). This challenge did not deter Cheng and


the IHPC team. To investigate elliptical vortex rings, the researchers used a simulation technique called the lattice Boltzmann method, which divides space into a lattice of coordinates and calculates the particle flow for each set of coordinates individually. This approach is often used to model large and complex systems, such as those in weather forecasts. The simulations allow for a detailed study


of the evolution of vortex rings as they move through space, and the shape changes that


ISSUE 5 | OCTOBER – DECEMBER 2016


Modified with permission from Ref. 1. Copyright 2016, AIP Publishing LLC.


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