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    Experiments cast doubts on the existence of quantum spin liquids

    When temperatures drop below zero degrees Celsius, water turns to ice. But does everything actually freeze if you just cool it down enough? In the classical picture, matter inherently becomes solid at low temperatures. Quantum mechanics can, however, break this rule. Therefore, helium gas, for example, can become liquid at -270 degrees, but never solid under atmospheric pressure: There is no helium ice.
    The same is true for the magnetic properties of materials: at sufficiently low temperatures, the magnetic moments known as ‘spins’, for example, arrange themselves in such a way that they are oriented opposite/antiparallel to their respective neighbors. One can think of this as arrows pointing alternating up and down along a chain or in a checkerboard pattern. It gets frustrating when the pattern is based on triangles: While two spins can align in opposite directions, the third is always parallel to one of them and not to the other — no matter how you turn it.
    For this problem, quantum mechanics suggests the solution that the orientation and bond of two spins are not rigid, but the spins fluctuate. The state formed is called a quantum spin liquid in which the spins constitute a quantum mechanically entangled ensemble. This idea was proposed almost fifty years ago by the American Nobel laureate Phil W. Anderson (1923-2020). After decades of research, only a handful of real materials remain in the search for this exotic state of matter. As a particularly promising “candidate” a triangular lattice in a complex organic compound was considered, in which no magnetic order with a regular up-down pattern could be observed, even at extremely low temperatures. Was this the proof that quantum spin liquids really exist?
    One problem is that it is extremely challenging to measure electron spins down to such extremely low temperatures, especially along different crystal directions and in variable magnetic fields. All previous experiments have been able to probe quantum spin liquids only more or less indirectly, and their interpretation is based on certain assumptions and models. Therefore, a new method of broadband electron spin resonance spectroscopy has been developed over many years at the Institute of Physics 1 at the University of Stuttgart.
    Using on-chip microwave lines, one can directly observe the properties of the spins down to a few hundredths of a degree above absolute zero. In doing so, the researchers found that the magnetic moments do not arrange themselves in the up-down pattern of a typical magnet, nor do they form a dynamic state resembling a liquid. “In fact, we observed the spins in spatially separated pairs. Thus, our experiments have shattered the dream of a quantum spin liquid for now, at least for this compound,” summarizes Prof. Martin Dressel, head of the Institute of Physics 1.
    But even though the pairs did not fluctuate as hoped, this exotic ground state of matter has lost none of its fascination for the physicists. “We want to investigate whether quantum spin liquids might be detectable in other triangular lattice compounds or even in completely different systems such as honeycomb structures,” Dressel outlines the next steps. However, it could also be that such a disordered, dynamic state simply does not exist in nature. Perhaps every kind of interaction leads in one way or another to a regular arrangement if the temperature is low enough. Spins just like to pair up.
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    A new book explores how military funding shaped the science of oceanography

    Science on a MissionNaomi OreskesUniv. of Chicago, $40

    In 2004, Japanese scientists captured the first underwater images of a live giant squid, a near-mythical, deep-ocean creature whose only interactions with humans had been via fishing nets or beaches where the animals lay dead or dying.

    Getting such a glimpse could have come much sooner. In 1965, marine scientist Frederick Aldrich had proposed studying these behemoths of the abyss using Alvin, a submersible funded by the U.S. Navy and operated by the Woods Hole Oceanographic Institution in Massachusetts. During the Cold War, however, studying sea life was not a top priority for the Navy, the main funder of U.S. marine research. Instead, the Navy urgently needed information about the terrain of its new theater of war and a thorough understanding of the medium through which submarines traveled.

    In Science on a Mission, science historian Naomi Oreskes explores how naval funding revolutionized our understanding of earth and ocean science — especially plate tectonics and deep ocean circulation. She also investigates the repercussions of the military’s influence on what we still don’t know about the ocean.

    The book begins just before World War II, when the influx of military dollars began. Oreskes describes how major science advances germinated and weaves those accounts with deeply researched stories of backstabbing colleagues, attempted coups at oceanographic institutions and daring deep-sea adventures. The story flows into the tumult of the 1970s, when naval funding began to dry up and scientists scrambled to find new backers. Oreskes ends with oceanography’s recent struggles to align its goals not with the military, but with climate science and marine biology.

    Each chapter could stand alone, but the book is best consumed as a web of stories about a group of people (mostly men, Oreskes notes), each of whom played a role in the history of oceanography. Oreskes uses these stories to explore the question of what difference it makes who pays for science. “Many scientists would say none at all,” she writes. She argues otherwise, demonstrating that naval backing led scientists to view the ocean as the Navy did — as a place where men, machines and sound travel. This perspective led oceanographers to ask questions in the context of what the Navy needed to know.

    One example Oreskes threads through the book is bathymetry. With the Navy’s support, scientists discovered seamounts and mapped mid-ocean ridges and trenches in detail. “The Navy did not care why there were ridges and escarpments; it simply needed to know, for navigational and other purposes, where they were,” she writes. But uncovering these features helped scientists move toward the idea that Earth’s outer layer is divided into discrete, moving tectonic plates (SN: 1/16/21, p. 16).

    Through the lens of naval necessity, scientists also learned that deep ocean waters move and mix. That was the only way to explain the thermocline, a zone of rapidly decreasing temperature that separates warm surface waters from the frigid deep ocean, which affected naval sonar. Scientists knew that acoustic transmissions depend on water density, which, in the ocean, depends on temperature and salinity. What scientists discovered was that density differences coupled with Earth’s rotation drive deep ocean currents that take cold water to warm climes and vice versa, which in turn create the thermocline.

    Unquestionably, naval funding illuminated physical aspects of the ocean. Yet many oceanographers failed to recognize that the ocean is also an “abode of life.” The Alvin’s inaugural years in the 1960s focused on salvage, acoustics research and other naval needs until other funding agencies stepped in. That switch facilitated startling discoveries of hydrothermal vents and gardens of life in the pitch black of the deep ocean.

    As dependence on the Navy lessened, many Cold War scientists and their trainees struggled to reorient their research. For instance, their view of the ocean, largely driven by acoustics and ignorant of how sound affects marine life, led to public backlash against studies that could harm sea creatures.

    “Every history of science is a history both of knowledge produced and of ignorance sustained,” Oreskes writes. “The impact of underwater sound on marine life,” she says, “was a domain of ignorance.”

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    Researcher uses bat-inspired design to develop new approach to sound location

    Inspired by the workings of a bat’s ear, Rolf Mueller, a professor of mechanical engineering at Virginia Tech, has created bio-inspired technology that determines the location of a sound’s origin.
    Mueller’s development works from a simpler and more accurate model of sound location than previous approaches, which have traditionally been modeled after the human ear. His work marks the first new insight for determining sound location in 50 years.
    The findings were published in Nature Machine Intelligence by Mueller and a former Ph.D. student, lead author Xiaoyan Yin.
    “I have long admired bats for their uncanny ability to navigate complex natural environments based on ultrasound and suspected that the unusual mobility of the animal’s ears might have something to do with this,” said Mueller.
    A new model for sound location
    Bats navigate as they fly by using echolocation, determining how close an object is by continuously emitting sounds and listening to the echoes. Ultrasonic calls are emitted from the bat’s mouth or nose, bouncing off the elements of its environment and returning as an echo. They also gain information from ambient sounds. Comparing sounds to determine their origin is called the Doppler effect. More

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    How to gain a sense of well-being, free and online

    In 2018, when Professor Laurie Santos introduced her course “Psychology and the Good Life,” a class on the science of happiness, it became the most popular in the history of Yale, attracting more than 1,200 undergraduate enrollees that first semester. An online course based on those teachings became a global phenomenon. By latest count, 3.38 million people have enrolled to take the free course, called “The Science of Well Being.”
    But the popularity of the course posed an interesting question. Does taking the course and participating in homework assignments — which include nurturing social connections, compiling a gratitude list, and meditation — really help improve a sense of well-being?
    The answer is yes, according to two new studies that measured the psychological impact on individuals who took Santos’s or a similar course. The findings suggest that free online courses that teach principles of positive psychology can enrich the lives of millions of people.
    In the latest study, published April 14 in the journal PLOS ONE, researchers at Johns Hopkins University and Yale found that people who took the online “Science of Well Being” course reported a greater sense of well-being than those enrolled in another Yale Coursera course, “Introduction to Psychology.” Although learners in both classes said they experienced significant improvement in their well-being after taking the courses, those who took the “Science of Well-Being” course reported greater mental health benefits than those learning about the basics of psychology.
    Unlike the psychology course, “The Science of Well Being” requires participants to do exercises known to improve psychological health, such as improving sleep patterns, developing exercise routines, and practicing meditation, the authors say. Before and after taking the course, participants answered questions designed to measure factors related to psychological health such as positive emotions, engagement, and strength of relationships.
    “Knowledge is great but it isn’t enough. You also have to do the work,” said lead author David Yaden, research fellow in the Department of Psychiatry and Behavioral Sciences at Johns Hopkins.
    A similar study in Health Psychology Open, conducted by researchers at Yale and the University of Bristol, surveyed people who took either a live or an online credit-bearing course based on Santos’s original class and found similar psychological benefits for enrollees.
    Yaden stressed, however, that the classes are not a substitute for professional treatment for those who suffer from diagnosed mental illness. “These courses are not a panacea or replacement for psychotherapy or medication,” he said.
    However, both Yaden and Santos, who co-authored the study, say the findings show that massive open online courses can provide at least modest value to millions of people at no cost.
    “We wanted to know if we could scale these benefits and we can,” Santos said. “Even bringing a small mental health benefit to millions of people can have a huge value.”
    Other authors of the PLOS ONE paper are Jennifer Claydon,, Meghan Bathgate, and Belinda Platt of the Yale Poorvu Center for Teaching and Learning.
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    Materials provided by Yale University. Original written by Bill Hathaway. Note: Content may be edited for style and length. More

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    Research breakthrough in understanding how neural systems process and store information

    Research breakthrough in understanding how neural systems process and store information.
    A team of scientists from the University of Exeter and the University of Auckland have made a breakthrough in the quest to better understand how neural systems are able to process and store information.
    The researchers, including lead author Dr Kyle Wedgwood from the University of Exeter’s Living Systems Institute, have made a significant discovery in how a single cell can store electrical patterns, similar to memories.
    They compared sophisticated mathematical modelling to lab-based experiments to determine how different parameters, such as how long it takes for neuronal signals to be processed and how sensitive a cell is to external signals, affect how neural systems encode information.
    The research team found that a single neuron is able to select between different patterns, dependent on the properties of each individual stimulus.
    The research offers a new step towards developing a greater understanding of how information is encoded and stored in the brain, which could open up fresh insights into the cause and treatment of conditions such as dementia.
    The research is published in the Journal of the Royal Society Interface on Wednesday, April 14th 2021.
    Dr Wedgwood, from the University of Exeter’s Living Systems Institute said: “This work highlights how mathematical analysis and wet-lab experiments can be closely integrated to shed new light on fundamental problems in neuroscience.
    “That the theoretical predictions were so readily confirmed in experiments gives us great confidence in the mathematical approach as a tool for understanding how individual cells store patterns of activity. In the long run, we hope that this is the first step to a better understanding of memory formation in neural networks.”
    According to Professor Krauskopf from the University of Auckland: “The research shows that a living neuron coupled to itself is able to sustain different patterns in response to a stimulus. This is an exciting first step towards understanding how groups of neurons are able to respond to external stimuli in a precise temporal manner.”
    “Communication between neurons occurs over large distances. The communication delay associated with this plays an important role in shaping the overall response of a network. This insight is crucial to how neural systems encode memories, which is one of the most fundamental questions in neuroscience,” adds Professor Tsaneva form the University of Exeter’s Living Systems Institute.
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    New method measures super-fast, free electron laser pulses

    New research shows how to measure the super-short bursts of high-frequency light emitted from free electron lasers (FELs). By using the light-induced ionization itself to create a femtosecond optical shutter, the technique encodes the electric field of the FEL pulse in a visible light pulse so that it can be measured with a standard, slow, visible-light camera.
    “This work has the potential to lead to a new online diagnostic for FELs, where the exact pulse shape of each light pulse can be determined. That information can help both the end-user and the accelerator scientists,” said Pamela Bowlan, Los Alamos National Laboratory’s lead researcher on the project. The paper was published April 12, 2021 in Optica. “This work also paves the way for measuring x-ray pulses or femtosecond time-resolved x-ray images.”
    Free electron lasers, which are driven by kilometer-long linear accelerators, emit bursts of short-wavelength light lasting one quadrillionth of a second. As a result, they can act as strobe lights for viewing the fastest events in nature — atomic or molecular motion — and therefore promise to revolutionize our understanding of almost any kind of matter.
    Measuring such a vanishingly rapid burst of ionizing radiation has previously proved challenging. But while electronics are too slow to measure these light pulses, optical effects can be essentially instantaneous. Squeezing all of the energy of a continuous laser into short pulses means that femtosecond laser pulses are extremely bright and have the ability to modify a material’s absorption or refraction, creating effectively instantaneous “optical shutters.”
    This idea has been widely used for measuring visible-light femtosecond laser pulses. But the higher-frequency extreme ultraviolet light from FELs interacts with matter differently; this light is ionizing, meaning that it pulls electrons out of their atoms. The researchers showed that ionization itself can be used as a “femtosecond optical shutter” for measuring extreme ultraviolet laser pulses at 31 nanometers.
    “Ionization typically changes the optical properties of a material for nanoseconds, which is 10,000 times slower than the FEL pulse duration,” Bowlan said. “But the duration of the rising edge of ionization, determined by how long it takes the electron to leave the atom, is significantly faster. This resulting change in the optical properties can act as the fast shutter needed to measure the FEL pulses.”
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    Transforming circles into squares

    Reconfigurable materials can do amazing things. Flat sheets transform into a face. An extruded cube transforms into dozens of different shapes. But there’s one thing a reconfigurable material has yet to be able to change: its underlying topology. A reconfigurable material with 100 cells will always have 100 cells, even if those cells are stretched or squashed.
    Now, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a method to change a cellular material’s fundamental topology at the microscale. The research is published in Nature.
    “Creating cellular structures capable of dynamically changing their topology will open new opportunities in developing active materials with information encryption, selective particle trapping, as well as tunable mechanical, chemical and acoustic properties,” said Joanna Aizenberg, the Amy Smith Berylson Professor of Materials Science at SEAS and Professor of Chemistry & Chemical Biology and senior author of the paper.
    The researchers harnessed the same physics that clumps our hair together when it gets wet — capillary force. Capillary force works well on soft, compliant material, like our hair, but struggles with stiff cellular structures that require the bending, stretching or folding of walls, especially around strong, connected nodes. Capillary force is also temporary, with materials tending to return to their original configuration after drying.
    In order to develop a long-lasting yet reversible method to transform the topology of stiff cellular microstructures, the researchers developed a two-tiered dynamic strategy. They began with a stiff, polymeric cellular microstructure with a triangular lattice topology, and exposed it to droplets of a volatile solvent chosen to swell and soften the polymer at the molecular scale. This made the material temporarily more flexible and in this flexible state, the capillary forces imposed by the evaporating liquid drew the edges of the triangles together, changing their connections with one another and transforming them into hexagons. Then, as the solvent rapidly evaporated, the material dried and was trapped in its new configuration, regaining its stiffness. The whole process took a matter of seconds.
    “When you think about applications, it’s really important not to lose a material’s mechanical properties after the transformation process,” said Shucong Li, a graduate student in the Aizenberg Lab and co-first author of the paper. “Here, we showed that we can start with a stiff material and end with a stiff material through the process of temporarily softening it at the reconfiguration stage.”
    The new topology of the material is so durable it can withstand heat or be submerged in some liquids for days without disassembling. Its robustness actually posed a problem for the researchers who had hoped to make the transformation reversible. More

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    Auxin makes the spirals in gerbera inflorescences follow the Fibonacci sequence

    When people are asked to draw the flower of a sunflower plant, almost everyone draws a large circle encircled by yellow petals.
    “Actually, that structure is the flower head, or the capitulum, which may be composed of hundreds of flowers, also known as florets. The surrounding ‘petals’ are florets different in structure and function to those closer to the centre,” says Professor of Horticulture Paula Elomaa from the Faculty of Agriculture and Forestry, University of Helsinki, Finland.
    A giant inflorescence is beneficial, as it is effective in attracting pollinators. When pollinators move around the inflorescence, they pollinate hundreds of individual florets over the course of their journey.
    The order of the florets in a flower head is not random. Instead, they are patterned into regular spirals whose number follows the Fibonacci sequence familiar from mathematics. Fibonacci numbers are the sum of the two preceding numbers in the sequence: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144…
    In the flower head, the number of left- and right-winding spirals is always two consecutive Fibonacci numbers. Sunflower flower heads can have as many as 89 right-winding and 144-left winding spirals, while the gerbera, another much-studied plant from the Asteraceae plant family, has fewer spirals (34/55).
    The geometric regularity of nature has fascinated both biologists and mathematicians for centuries. More