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Gizmorama - December 20, 2017

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Have you ever wondered about the physics of a café latte? Well, wonder no more! Gizmorama is where we ask the hard science questions.

Learn about this and more interesting stories from the scientific community in today's issue.

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*-- Study details the physics of a café latte --*

New research by scientists sat Princeton University has revealed the physics underlying the delicious layers of a café latte.

"The structure formation in a latte is surprising because it evolves from the chaotic, initial pouring and mixing of fluids into a very organized, distinct arrangement of layers," researcher Nan Xue said in a news release.

Xue is a grad student student working in the lab of Howard Stone, professor of mechanical and aerospace engineering at Princeton.

Though inspired by an everyday drink order, Xue's investigation yielded insights into the layering of fluids -- insights that could have a variety of useful applications.

"From a manufacturing perspective, a single pouring process is much simpler than the traditional sequential stacking of layers in a stratified product," Stone said. "In one application of this study, we are exploring the physics behind making a whole layered structure with one step, rather than one-by-one stacking of the layers."

Xue initially experimented with store-bought coffee and milk but struggled to maintain consistency as he attempted to recreate a latte's layers. To simplify the experimentation process, he used dyed water as stand-in for hot coffee and salty, denser water as a substitute for warm milk.

Xue and his research partners mixed racer particles into the two liquids and used light-emitting diodes and a camera to track the movement of fluids during the mixing and layering process. The collected data -- which scientists compared with models of intermixing liquids -- revealed the physical principles underlying the phenomenon.

As revealed by their analysis, the most important mechanism is double-diffusive convection. The mechanism describes the flow patterns as different density liquids mix and heat is diffused. At first vertical flows occur, but as temperature and density differences begin to reach equilibrium, flows begin to move horizontally and layers develop.

The mechanism is dependent on the temperature and density difference of the liquids and -- in the case of a café latte -- the speed at which the milk is poured into the coffee. If poured too slowly, the milk and coffee mix too evenly and distinct layers fail to form.

Researchers are now working on understanding how double-diffusive convection might work in other liquids and semi-solids.

That Xue was able to replicate the layering process of a café latte using water with different levels of salt suggests the findings -- published this week in the journal Nature Communications -- could help scientists better understand currents and upwelling in the ocean.

*- Lasers could soon trigger fusion energy, researchers predict -*

Laser-driven fusion energy is a realistic goal and one within reach, according to a new paper published this week in the journal Laser and Particle Beams.

An international team of scientists argue laser and fusion technologies are advancing at such a pace that self-sustaining hydrogen-boron fusion reactions will become a reality sooner rather than later.

The quest for hydrogen-boron fusion, the researchers posit, is more likely to prove fruitful than related efforts, such as attempts to trigger deuterium-tritium fusion.

"I think this puts our approach ahead of all other fusion energy technologies," Heinrich Hora, a researcher at the University of New South Wales in Sydney said in a news release.

Researchers at the U.S. National Ignition Facility and the International Thermonuclear Experimental Reactor in France are working to trigger fusion by heating plasma inside a doughnut-shaped toroidal chamber to the temperature of the sun using high-powered magnets.

The authors of the newest paper believe hydrogen-boron fusion could be more easily triggered with a laser. In their preferred model, brief but powerful laser pulses trigger non-linear forces, which squeeze the nuclei together.

Unlike nuclear energy, hydrogen-boron fusion yields no atomic waste, toxic or otherwise. And unlike fossil fuel energy, hydrogen-boron fusion, which converts directly to electricity, is carbon neutral.

Despite its potential, scientists have been skeptical that laser technology can yield the high temperatures and intense pressures necessary to trigger hydrogen-boron fusion.

In the latest paper, however, scientists argue advancements in laser technology prove such dramatic capacities are within reach.

"It is a most exciting thing to see these reactions confirmed in recent experiments and simulations," said Hora, a professor of theoretical physics at UNSW. "Not just because it proves some of my earlier theoretical work, but they have also measured the laser-initiated chain reaction to create one billion-fold higher energy output than predicted under thermal equilibrium conditions."

In addition to detailing the latest relevant technological breakthroughs, the new paper lists the kinds of research necessary to bring hydrogen-boron fusion to fruition.

Barring an unforeseen challenges, a spin-off company working with Hora believes it could build a working prototype within a decade.

"From an engineering perspective, our approach will be a much simpler project because the fuels and waste are safe," said Warren McKenzie, managing director of HB11 Energy. "The reactor won't need a heat exchanger and steam turbine generator, and the lasers we need can be bought off the shelf.


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