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Why Nanoscale Droplets Don’t Coalesce

A well-shaken mixture of oil and vinegar will separate as the oil droplets eventually coalesce. Droplet growth, or coarsening, usually evolves according to standard rules. But puzzling exceptions persist. When two polymers are mixed in water and the concentration is high enough, droplets containing one or both species form and can remain stable for hours or days. These loose molecular condensates otherwise behave like liquid droplets, and they abound in biological cells. Now Feipeng Chen of the University of Hong Kong and his colleagues have developed a predictive model for coarsening behavior that works across a range of droplet sizes and explains why coarsening may be suppressed in living systems [1].

The researchers derived their model from observations of a solution containing water and two different polymers, opposite in charge and having very different molecular chain lengths. Using light-scattering techniques, the researchers monitored condensate growth over 12 hours. The initial size and subsequent growth rate of the liquid-like droplets, rich in both polymers, turned out to depend on the solution’s overall initial concentration. In the most dilute solutions, condensates tens-of-nanometers in diameter formed and promptly stopped growing for the remaining 12-hour observation period. In solutions having slightly higher concentration, hundreds-of-nanometer condensates formed and remained stable, then underwent abrupt, rapid growth in the later stages. And in the most concentrated solutions, micrometer-scale condensates formed and grew according to a power-law model.

Applying an electric field to the solutions indicated that the nanoscale condensates had significant surface charge. Modeling these measurements revealed that the asymmetric chain lengths of oppositely charged polymers imparted a net charge to the droplet surfaces. These charges led to size-dependent electrostatic barriers that drastically reduced merging efficiency below a critical diameter. The finding offers a principle for controlling size stability in biology, nanotechnology, and soft-matter assembly.

Water-wave tweezers steer tiny ‘surfers’ without touching them

Summer brings with it the sight of surfers moving seamlessly across wave crests, with ocean waters carrying them along coastlines. A team of scientists has now created a similar phenomenon—with small objects rather than surfers—that can be controlled by humans rather than by nature.

Through a series of experiments on a replicated mini-beach, NYU researchers show how water waves can be used to move floating objects or hold them firmly in place—all without direct touch or contact.

“Our study shows how beaming water waves at a floating object can cause it to move sideways or be ‘tweezed’ and held precisely in place,” explains Leif Ristroph, a professor at New York University’s Courant Institute School of Mathematics, Computing, and Data Science and the senior author of the study, which appears in the journal Physical Review Fluids. “These surprising effects could be used to manipulate particles and structures, controlling their motions and positions.”

Genetically modified hookworms produce and deliver therapeutics

Hookworms, intestinal parasites that infect hundreds of millions of people in under-resourced tropical regions around the globe, have evolved to survive inside the human gut for years, secreting molecules that enable coexistence with their hosts. Now, researchers at Washington University School of Medicine in St. Louis have harnessed that biological mechanism for potential human benefit, engineering a hookworm to produce and deliver a drug within a living host.

In a new study, the team reports the first successful genetic modification of the human hookworm. It was designed to produce an antibody that neutralizes tetrodotoxin, a deadly neurotoxin produced by pufferfish and other marine animals. After colonizing an animal host with the modified hookworms, the parasites produced the antitoxin and secreted it into the bloodstream, partially inactivating the toxin. The findings are published in Nature Communications.

The work demonstrates that this drug production and delivery approach could be a long-term solution to any number of medical needs, from chronic conditions requiring continuous drug treatment to exposure to toxins in remote locations without medical care available.

Out-of-plane ice bridges reveal new way to suppress frost spreading

A research team led by Professor Nenad Miljkovic in The Grainger College of Engineering at the University of Illinois Urbana-Champaign has published a breakthrough study in Nature Physics. The work reports the first experimental discovery of a previously unknown frost propagation mechanism—a “suspended ice bridge”—offering new pathways for anti-frosting surface design.

Frost formation plays a critical role in many engineering systems, including air-source heat pumps, refrigeration systems and aerospace applications. At the microscopic level, frost mainly spreads through the formation of “ice bridges” that connect neighboring supercooled liquid droplets, enabling freezing to propagate rapidly across a surface. For decades, these ice bridges were widely assumed to grow along the solid surface.

This assumption, largely based on conventional top-view imaging, has shaped existing theoretical models and anti-frosting strategies. However, the Illinois team’s study reveals that this long-held view is incomplete.

Portable UV spectrometer can detect air pollutants across 2.5 km with high precision

Birgitta Schultze-Bernhardt and her team at the Institute of Experimental Physics at Graz University of Technology (TU Graz) have developed a new type of UV dual-comb spectrometer that detects gaseous air pollutants with unrivaled accuracy and sensitivity. Using ultraviolet double laser light, the device measures the concentration of harmful gases such as formaldehyde within half a second.

Thanks to its compact design and a measuring range of up to two and a half kilometers, the spectrometer is not only suitable for laboratory analyses, but also for mobile measurements in cities, industrial areas and agricultural regions.

The work is published in the journal PhotoniX.

Chip-scale ‘acoustic atom’ controls sound waves to imitate atomic energy levels and advance computing

For every action, there is an equal and opposite reaction. What goes up must come down. Physical laws like these govern all of the natural world—except for the tiny internal components of today’s microprocessors, which operate according to the unique and complicated rules of quantum physics.

As the microprocessors that power computers, medical equipment, sensors, and more continue to shrink in size, engineers face challenges controlling quantum-scale systems. But in a step forward for the technology, researchers at Virginia Tech have developed an “acoustic atom”—a chip-scale device that traps and controls sound waves in ways that mimic the behavior of real atoms. Long term, these advances could influence technologies connected to quantum artificial intelligence (AI), telecommunication, medical imaging, GPS, and more.

The research is published in Physical Review Letters by Linbo Shao, assistant professor in Virginia Tech’s Bradley Department of Electrical and Computer Engineering, along with colleagues at the university’s Center for Power Electronic Systems, Department of Physics, and Center for Quantum Information Science and Engineering and the Oak Ridge National Laboratory.

Ultrafast laser shrinks to chip scale, potentially lowering costs for diagnostics and atomic clocks

Ultrafast lasers emit pulses lasting only a few hundred femtoseconds (quadrillionths of a second). These flashes of light power applications from precision micromachining to eye surgery to optical frequency combs, the Nobel Prize-winning technology behind today’s most precise optical atomic clocks. Yet despite more than two decades of effort, ultrafast lasers have largely remained bulky, expensive systems confined to optical tables.

Now a team led by Professor Tobias J. Kippenberg at EPFL has brought them onto a photonic chip. Publishing in Nature, the researchers report the first integrated ultrafast laser to rival tabletop femtosecond lasers, delivering 1.05 nanojoules in pulses as short as 147 femtoseconds.

Photonic chips guide and process light in microscopic channels called waveguides patterned on a wafer, similar to how electronic microchips route electricity. Already widely used in telecommunications, photonic chips have miniaturized complex functions that once required much larger systems.

Temperature gaps help sneeze clouds stay denser and travel farther, experiments show

When a person coughs or sneezes, they expel a cloud of microscopic particles capable of carrying viruses and bacteria that act as vectors for respiratory diseases such as flu, COVID-19 or tuberculosis. Understanding how these aerosols disperse in the air is crucial for minimizing the transmission of pathogens in indoor spaces, but their dynamics are complex and depend on many factors: the force of the exhalation, the morphology of the respiratory system, the characteristics of the space, etc. Now, a new study led by researchers from the Universitat Rovira i Virgili has shown that temperature also plays an important role.

Their findings, published in Physics of Fluids, indicate that the difference between the temperature of exhaled air and that of the ambient air causes the cloud of particles to remain more concentrated and travel farther. The greater this difference, the more noticeable the effects are.

The research continues a line of work initiated by the URV’s ECoMMFiT research group, which developed a simulator capable of reproducing coughs and sneezes to study how respiratory aerosols disperse. As a result of that study, the team demonstrated that the nasal cavity significantly alters the trajectory of expelled particles. Now, the researchers have incorporated a new factor into the analysis: temperature.

‘Don’t scare the cat!’ Engineers find smarter way to measure quantum systems

UNSW Sydney engineers have riffed on the famous Schrödinger’s cat analogy to demonstrate a more efficient way to eliminate errors in quantum computing.

“Imagine you’re trying to find your cat hiding in one of eight identical cardboard boxes, in a dark and noisy room,” says UNSW Scientia Professor Andrea Morello.

“You are not allowed to enter the room—opening the door may kill the cat. What is the optimal strategy to find out where it’s hiding? Our team of quantum researchers have found an answer to this problem, and it might be an important milestone on the road to building a quantum computer.”

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