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Category: physics – Page 85

The Reconstructability of Networks

Network models provide a flexible way of representing objects and their multifaceted relationships. Deriving a network entails mapping hidden structures in inevitably noisy data—a critical task known as reconstruction. Now Gang Yan and Jia-Jie Qin of Tongji University in China have provided a mathematical proof showing what makes some networks easier to reconstruct than others [1].

Complex systems in biology, physics, and social sciences tend to involve a vast number of interacting entities. In a network model, these entities are represented by nodes, linked by connections weighted to describe the strength of each interaction. Yan and Qin took an empirical dataset and used a statistical inference method to calculate the likelihood that any pair of nodes is directly linked. Then, based on the true positive and false positive rates of these inferred connections, they analyzed the fidelity of the reconstructed networks. They found that the most faithful reconstructions are obtained with systems for which the number of connections per node varies most widely across the network. Yan and Qin saw the same tendency when they tested their model on synthetic and real networks, including metabolic networks, plant-pollinator webs, and power grids.

With the rapid increase in available data across research areas, network reconstruction has become an important tool for studying complex systems. Yan and Qin say their new result both solves the problem of what complex systems can be easily mapped into a network and provides a solid foundation for developing methods of doing so.

Faux gras? Scientists craft ‘more ethical’ version of French delicacy

Foie gras—the fattened liver of ducks or geese—is a French delicacy prized for its rich, buttery flavor. But its production, which involves force-feeding the animals, has led to bans in several countries.

Now, a team of scientists says they’ve developed a more ethical alternative: one that mimics the taste and texture of the dish, minus the controversy.

The results were published Tuesday in the journal Physics of Fluids.

Study resolves long-standing debate on low-pressure phase transitions in hafnium oxide

Researchers from the Institute of Solid State Physics, the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, in collaboration with Southwest Jiaotong University, have combined high-pressure electrical transport experiments, high-pressure Raman spectroscopy, and first-principles calculations to reveal the structural phase transition behavior of hafnium oxide (HfO2) under high pressure and its evolution mechanism in electrical properties.

The paper is published in the journal Physical Review B.

“This study resolves the previous controversies regarding the phase transitions of HfO2 in the low-pressure region,” said Pan Xiaomei, a member of the team.

Plant stomata pressure dynamics illuminated by laser-based method offer water efficiency insights

Every time the temperature drops, a cloud passes overhead, or the sun sets, a plant makes a choice: Keep its microscopic pores, called stomata, open to absorb carbon dioxide and continue photosynthesizing or close them to protect its precious stores of water. That capacity to open and close pores requires the plant to respond to subtle environmental changes by adjusting the pressure within the cells of the stomata—a complex ability that plants evolved over hundreds of millions of years.

An interdisciplinary team of biologists, physicists, and engineers, led by researchers at the Yale School of the Environment, has developed a method to observe those pressure changes. The new approach, detailed in a study published in PNAS, vastly expands the rate at which—and the number of species from which—scientists can take measurements, opening up new possibilities for research on and physiology with valuable applications for improving water efficiency, the researchers said.

“Almost every single land plant is using this principle of internal pressure in order to grow, reproduce, and do everything a plant does, but we previously had basically no access to this measurement,” said Craig Brodersen, the Howard and Maryam Newman Professor of Plant Physiological Ecology and the lead author of the study.

Beyond RGB: A new image file format efficiently stores invisible light data

Why would anyone need this level of wavelength detail in an image? There are many reasons. Car manufacturers want to predict exactly how paint will look under different lighting. Scientists use spectral imaging to identify materials by their unique light signatures. And rendering specialists need it to accurately simulate real-world optical effects like dispersion (rainbows from prisms, for example) and fluorescence.

For instance, past Ars Technica coverage has highlighted how astronomers analyzed spectral emission lines from a gamma-ray burst to identify chemicals in the explosion, how physicists reconstructed original colors in pioneering 19th century photographs, and how multispectral imaging revealed hidden, centuries-old text and annotations on medieval manuscripts like the Voynich Manuscript, sometimes even uncovering the identities of past readers or scribes through faint surface etchings.

The current standard format for storing this kind of data, OpenEXR, wasn’t designed with these massive spectral requirements in mind. Even with built-in lossless compression methods like ZIP, the files remain unwieldy for practical work as these methods struggle with the large number of spectral channels.

Experiment shows theory describing formation of interstellar benzene does not actually produce benzene

Astrophysicists at the University of Colorado’s JILA, National Institute of Science and Technology, have conducted an experiment to produce benzene the way theories have predicted it is produced in interstellar space and found it did not produce any benzene. The research by G. S. Kocheril, C. Zagorec-Marks and H. J. Lewandowski is published in the journal Nature Astronomy.

Research efforts in the 1990s led to theories suggesting that ion-molecule collisions could be one of the main ways that interstellar forms. Such theories are important for space research because it is believed that benzene is a precursor to the formation of interstellar , which are believed to hold cosmic carbon, which is important for many reasons but mainly because of the role it might have played in the development of carbon-based lifeforms.

Testing of theories that lead to the creation of benzene in has not been done before because of the difficulty in creating the conditions that exist in such an environment. In their paper, and during a speech at a recent symposium, the group stated that they had the equipment necessary to carry out such an experiment in their lab at JILA.

What Rules Actually Prohibit Us From Building a Warp Drive?

In 1994 Miguel Alcubierre was able to construct a valid solution to the equations of general relativity that enable a warp drive. But now we need to tackle the rest of relativity: How do we arrange matter and energy to make that particular configuration of spacetime possible?

Unfortunately for warp drives, that’s when we start running into trouble. In fact, right away, we run into three troubles. And these three troubles are called the energy conditions. Now, before I describe the energy conditions, I need to make a disclaimer. What I’m about to say are not iron laws of physics.

They are instead reasonable guesses as to how nature makes sense. General relativity is a machine. You put in various configurations of spacetime, various arrangements of matter and energy. You turn the handle and you learn how gravity works. General relativity on its own doesn’t tell you what’s real and what’s not.

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