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Category: physics – Page 59

Numerical simulation of deformable droplets in three-dimensional, complex-shaped microchannels

The physics of drop motion in microchannels is fundamental to provide insights when designing applications of drop-based microfluidics. In this paper, we develop a boundary-integral method to simulate the motion of drops in microchannels of finite depth with flat walls and fixed depth but otherwise arbitrary geometries. To reduce computational time, we use a moving frame that follows the droplet throughout its motion. We provide a full description of the method, including our channel-meshing algorithm, which is a combination of Monte Carlo techniques and Delaunay triangulation, and compare our results to infinite-depth simulations. For regular geometries of uniform cross section, the infinite-depth limit is approached slowly with increasing depth, though we show much faster convergence by scaling with maximum vs average velocities. For non-regular channel geometries, features such as different branch heights can affect drop partitioning, breaking the symmetric behavior usually observed in regular geometries. Moreover, non-regular geometries also present challenges when comparing the results for deep and infinite-depth channels. To probe inertial effects on drop motion, the full Navier–Stokes equations are first solved for the entire channel, and the tabulated solution is then used as a boundary condition at the moving-frame surface for the Stokes flow inside the moving frame. For moderate Reynolds numbers up to Re = 5, inertial effects on the undisturbed flow are small even for more complex geometries, suggesting that inertial contributions in this range are likely small. This work provides an important tool for the design and analysis of three-dimensional droplet-based microfluidic devices.

Scientists achieve unprecedented control of active matter

An international research team led by Brandeis University has achieved a major breakthrough in the field of active matter physics, as detailed in a study published this week in Physical Review X. This pioneering research offers the first experimental validation of a key theoretical prediction about 3D active nematic liquid crystals by trapping them within cell-sized spherical droplets.

Rotating cylinder amplifies electromagnetic fields

Physicists have observed the Zel’dovich effect in an electromagnetic system – something that was thought to be incredibly difficult to do until now. This observation, in a simplified induction generator, suggests that the effect could in fact be quite fundamental in nature.

In 1971, the Russian physicist Yakov Zel’dovich predicted that electromagnetic waves scattered by a rotating metallic cylinder should be amplified by gaining mechanical rotational energy from the cylinder. The effect, explains Marion Cromb of the University of Southampton, works as follows: waves with angular momentum – or twist – that would usually be absorbed by an object, instead become amplified by that object. However, this amplification only occurs if a specific condition is met: namely, that the object is rotating at an angular velocity that’s higher than the frequency of the incoming waves divided by the wave angular momentum number. In this specific electromagnetic experiment, this number was 1, due to spin angular momentum, but it can be larger.

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Looking back at President Jimmy Carter’s science policy

As President, Jimmy Carter established several science-related initiatives and policies.

Carter also sought to promote scientific research and development in a number of areas. He increased funding for basic science research in fields such as physics and chemistry, and established the National Commission on Excellence in Education to promote improvements in science and math education in American schools.

On top of that, Carter sought to address environmental issues through science policy. He established the Superfund program, which was created to clean up hazardous waste sites, and signed the Alaska National Interest Lands Conservation Act, which protected millions of acres of land in Alaska.

Carter’s science policy emphasized the importance of science and technology in addressing pressing issues such as energy, the environment, and education.

Revisiting the Moon’s Origin: A New Capture Theory

“No one knows how the moon was formed,” said Dr. Darren Williams. “For the last four decades, we have had one possibility for how it got there. Now, we have two. This opens a treasure trove of new questions and opportunities for further study.”

How did the Moon form? Was it from a collision, as has been the longstanding theory, or could it have been captured by the Earth early in our planet’s formation? This is what a recent study published in The Planetary Science Journal hopes to address as two researchers from Penn State investigated a new model for how our Moon came to reside within its present orbit around the Earth. This study holds the potential to help researchers better understand the origin of our Moon, which could help explain how some moons throughout our solar system came to be orbiting their respective planets, as well.

For the study, the researchers performed a series of calculations aimed at ascertaining if a simulated binary object could end up in the Moon’s orbit. The argument the researchers make is that if the Moon was formed from a collision, then it would orbit above the Earth’s equator. In contrast, the Moon’s orbit follows a different orbit.

“The moon is more in line with the sun than it is with the Earth’s equator,” said Dr. Darren Williams, who is a professor of astronomy and astrophysics at Penn State Behrend and lead author of the study.

From branches to loops: The physics of transport networks in nature

An international team of researchers described how loops, crucial for the stability of such networks, occur in transport networks found in nature. The researchers observed that when one branch of the network reaches the system’s boundary, the interactions between the branches change drastically. Previously repelling branches begin to attract each other, leading to the sudden formation of loops.

Smashing heavy ions together could produce the world’s strongest electric fields

Lab experiments around the globe that are gearing up to recreate the mysterious phase of matter found in the early universe could also produce the world’s strongest electromagnetic fields, according to a theoretical analysis by a RIKEN physicist and two colleagues. This unanticipated bonus could enable physicists to investigate entirely new phenomena.