The world of glass appears deceptively simple – a seemingly random network of atoms. However, recent research at the University of Tsukuba has shed light on the existence of a “hidden order” within this disorderly structure. This invisible arrangement plays a crucial role in determining vibrational fluctuations in the terahertz (THz) frequency range, which significantly impact the physical properties of glass.

At first glance, glass may seem like a jumbled mess of atomic structures. Yet, when subjected to X-ray and neutron beam analysis, a faint but consistent periodic feature known as the first sharp diffraction peak (FSDP) emerges. Concurrently, glass exhibits a boson peak (BP), a vibrational anomaly in the THz range that contributes to its low thermal conductivity, mechanical characteristics, and THz range light absorption. Despite extensive research, the precise relationship between the FSDP and BP has remained unclear – until now.

Using heterogeneous elasticity theory, researchers have identified a direct correlation between the emergence of the BP and the presence of the FSDP. The theoretical model indicates that the scale of elastic inhomogeneity necessary for BP manifestation aligns with that of the FSDP. This suggests that the FSDP is a determining factor in the vibrational behavior of glasses within the THz band.

These groundbreaking findings are expected to inform the development of novel glass materials with tunable boson peaks, enabling targeted control of their thermal and mechanical properties. By unlocking the secrets of the hidden order in glass, researchers can now explore new possibilities for creating materials with tailored properties, opening doors to innovative applications across various industries.

The world is on the cusp of a revolution in aviation, with emerging electric aircraft engines promising to change the game. However, a significant challenge remains – their noise levels can be gratingly unpleasant. A groundbreaking study conducted by scientists at the University of Bristol and the University of Salford has finally uncovered the root cause behind this issue and identified potential solutions.

The research, published in Nature npj Acoustics, delves into the physics of aerodynamic sound generation, revealing how turbulent boundary layer flow interacts with rotating fan and duct components to produce two distinct and perceptually unpleasant acoustic signatures. The team discovered that these noise patterns, known as “haystacking,” are caused by the interaction between turbulent flow and the internal acoustic field of the engine.

At low thrust levels, the weaker fan suction allows the airframe boundary layer flow to remain undisturbed, resulting in duct haystacking. In contrast, at high thrust levels, strong fan suction disrupts the airframe boundary layer flow, producing fan-induced flow distortion that draws in highly-unsteady turbulent flow structures across a larger portion of the blade span.

Lead researcher Dr. Feroz Ahmed highlighted the significance of this study: “These two hidden sound signatures – haystacking – make future embedded aircraft engines feel perceptually irritating, not just loud.” By understanding the aerodynamic origin of these noise patterns, engineers can now design quieter engines that truly sound as quiet as they look.

The implications of this research are far-reaching. The team’s findings offer actionable design guidance for both large-scale transport aircraft and manufacturers of next-generation electric vertical take-off and landing (eVTOL) aircraft in the urban air mobility sector. These insights could help reduce aircraft noise by 65% and support efforts to meet the EU’s FlightPath 2050 goal.

The researchers now plan to develop aerodynamic and acoustic control strategies to reduce both fan and duct haystacking, with the aim of shaping the future of quiet aviation.

Harnessing Microbubbles for Advanced Fluid Control
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Researchers at Kyoto University have made a groundbreaking discovery in the manipulation of microbubbles to control fluids. By precisely adjusting the distance between these tiny bubbles, scientists can fundamentally alter liquid flow, revolutionizing applications in medical and chemical fields.

The team’s innovative setup employs laser light to photothermally heat degassed water, allowing them to generate two microbubbles that spontaneously vibrate at sub-megahertz frequencies. These vibrations interact with each other, synchronizing their movements and influencing the surrounding fluid flow.

By adjusting the distance between the bubbles by just 10 micrometers, researchers observed a staggering change in vibration frequency of over 50%. This remarkable finding has significant implications for fluid control tools in various industries.

“We did not expect to observe such clear vibrational coupling between two oscillating bubbles,” says corresponding author Kyoko Namura. “The vibrations of the bubbles we generated were very stable over time and highly reproducible, allowing us to capture changes in their vibrations when their relative positions were even slightly adjusted.”

This breakthrough provides a new method for fluid control in various applications, including medical and chemical fields where faster analysis and data collection are essential. The research team plans to explore ways to actively select bubble vibration frequencies and modes, control larger arrays of bubbles, and analyze the sound waves and flows generated around them.

Harnessing microbubbles has the potential to revolutionize various industries, offering a more efficient and accurate way to manipulate fluids. As researchers continue to push the boundaries of this technology, we can expect to see exciting advancements in fields such as medicine, chemistry, and beyond.