In This Issue

September 7, 2021
118 (36) eiti3621118

ENGINEERING

An octopus-inspired, origami robotic arm.

Biomimetic origami robot arm

Compared with traditional, rigid robotic arms, the soft arms of an octopus are capable of more sophisticated movements and functional behavior. Shuai Wu, Qiji Ze, et al. engineered robotic arms using origami folds and magnetic fields to simulate the stretching, folding, bending, and twisting functions of octopus arms. The authors applied magnetic actuation to units of Kresling origami, which is formed from the buckling of a thin, hollow cylinder in response to torque. The authors programmed a magnetic field to expand, contract, bend, or twist the assembly and varied the patterns and magnetization of the Kresling units to expand the range of motion. By adding Kresling units to the assembly, the authors engineered arms up to 18 units in length with several degrees of freedom, enabling increasingly sophisticated motions and functions. The 18-unit arm was capable of omnidirectional bending to pick up and manipulate objects in a manner similar to an octopus. By separating the power sources and controllers from the robotic systems, the remote magnetic control enables miniaturized robotic arms to navigate environments with limited access, such as within the human body, promoting medical applications including endoscopy, intubation, and catheterization, according to the authors. — M.H.

APPLIED PHYSICAL SCIENCES

Granular forces (black lines) at the same location in the soil before (Left) and after (Right) ant tunneling. Image credit: José E. Andrade (California Institute of Technology, Pasadena, CA) and David R. Miller (artist).

Real-time 3D modeling of ant tunnels

Safely and efficiently excavating in an environment composed of solid, discrete particles is a complex engineering challenge. Yet ants have evolved to be proficient granular excavators. Robert Buarque de Macedo et al. used 3D X-ray imaging to map the force distributions and granular material attributes around tunnels dug by western harvester ants (Pogonomyrmex occidentalis) in real time. The authors prepared a container of soil and performed an initial high-resolution X-ray scan. Next, the authors introduced 15 western harvester ants to the container and captured additional scans every 10 minutes for 20 hours. From these 3D images, the authors created digital avatars of each soil particle to represent the shape, position, and orientation of individual particles and simulate the forces acting on the particles during excavation. The results suggest that, as the ants incrementally excavate, arches form in the soil that reduce the forces on particles surrounding the tunnel. Because of the force reduction, the ants can safely remove nearly any grain to extend the tunnel without reckoning the forces involved. According to the authors, the findings could inspire the development of improved robotic mining techniques. — M.H.

ENVIRONMENTAL SCIENCES

Global warming, aridity, and terrestrial biodiversity

Global aridity is expected to increase in the future, but its potential impact on species range has been unclear. Hao Shi et al. analyzed changes in the speed and direction of global aridity and the corresponding distributions of terrestrial vertebrates and plants in the past, from 1979 to 2016, and future, from 2050 to 2099. Using satellite observations, the authors also calculated spatial shifts in vegetation greenness from 1982 to 1986 and from 2011 to 2015. On average, the authors report, the future drying speed could reach up to 0.42 km per year worldwide and 0.72 km per year in natural protected areas. In general, the migration of vegetation greenness tracked changes in aridity velocity in northern Australia, Sahel Africa, and southern Africa. Among terrestrial taxa, amphibians are projected to be most harmed by changes in aridity velocity. Taken together, the findings suggest that future changes in water availability could drive the migration of terrestrial species and reduce the effectiveness of protected areas. According to the authors, the results could guide the allocation of limited conservation resources to high-risk regions and species and inform the design of protected area networks and ecological corridors to connect large nature reserves. — J.W.

EARTH, ATMOSPHERIC, AND PLANETARY SCIENCES

Researchers preparing to take a sample during the Megadunes, Antarctica, firn air sampling campaign in January 2004.

Hydrogen levels preserved in Antarctic ice

Hydrogen is not considered a greenhouse gas, but it affects the ability of other atmospheric components to trap methane and ozone. John Patterson et al. analyzed air trapped in Antarctic ice and report that atmospheric concentrations of hydrogen have increased more than 70% in the last 150 years. To uncover the role of hydrogen and human impacts on the hydrogen atmospheric budget, the authors reconstructed historical levels from 1852 to 2003. The authors drilled a 70-m firn core in Megadunes, Antarctica, to collect firn air samples, which were trapped at the time the snow was deposited. Analysis and reconstruction revealed that atmospheric hydrogen levels were consistent during the mid- to late-1800s, around 330 parts per billion, and rose steadily to 550 parts per billion by 2003. Unlike carbon monoxide, atmospheric hydrogen did not decline in concert with decreasing automobile emissions toward the end of the 20th century but instead continued to rise. The authors note that an additional source of hydrogen, or a reduction in its natural sinks, is needed to explain the rise. According to the authors, the reconstruction provides a baseline to understand historical human impacts on atmospheric hydrogen, especially given the increasing use of hydrogen as an energy source. — T.H.D.

PSYCHOLOGICAL AND COGNITIVE SCIENCES

A common big-eared bat (Micronycteris microtis) eating a dragonfly. Image credit: Christian Ziegler (photographer).

Bat hearing sensitivity and niche differentiation

Adaptations for differentiated niches allow species to coexist in ecosystems with high biodiversity, such as tropical forests. Research into niche differentiation has mostly focused on behavioral and morphological adaptations, whereas differences in species’ sensory capabilities are poorly understood. Inga Geipel, Ella Lattenkamp, et al. measured auditory brainstem responses to a wide range of sound frequencies in 12 co-occurring species of Neotropical leaf-nosed bats (Phyllostomidae) with similar foraging strategies to compare the species’ hearing sensitivities. The graphs of each leaf-nosed bat species’ auditory brainstem responses had similar overall shapes, but the results differed substantially for frequencies below 9 kilohertz. Leaf-nosed bat species that primarily hunt by listening for prey-produced sounds, such as prey mating calls and prey locomotion noise, had sensitivity peaks at low frequencies, corresponding to frequencies produced by prey. In comparison, species that largely rely on echolocation for hunting were more sensitive at high frequencies. The authors also measured sound parameters of echolocation calls from each leaf-nosed bat species and found that each species was sensitive to the frequencies of its own echolocation calls. According to the authors, differences in the sensory abilities of ecologically similar species may represent overlooked drivers of niche differentiation. — M.H.

GENETICS

Istanbul, Turkey. Image credit: Pixabay/smuldur.

Genetic structure of the Turkish population

Turkey has been at the crossroads of numerous historical human migrations. Despite its complex ancestry, the Turkish population has been underrepresented in genomic databases. M. Ece Kars et al. analyzed whole-exome and whole-genome sequencing data from 3,362 unrelated Turkish individuals to generate a large-scale database of genetic variation in Turkey. Consistent with Turkey’s common practice of consanguineous marriage, half of the participants showed strong signs of inbreeding, with contiguous lengths of homozygous genotypes longer than four megabases. Approximately 21% of all variants identified were unique to the Turkish population, as were 28% of the whole-exome variants and 49% of the whole-genome variants classified as very rare. The results revealed 704 rare homozygous variants that would likely result in gene inactivation. Between one and four of these variants, which affected a total of 626 genes, were present in 20% of the participants. In addition, 6,537 variants in 2,188 genes were classified as disease-causing pathological mutations in the Human Gene Mutation Database. All participants harbored between 1 and 30 of these variants, with an average of 12. According to the authors, the high-resolution genomic database may provide an invaluable resource for prioritizing variants and identifying disease-causing genes. — J.W.

COMPUTER SCIENCES

A swarm of 50 robots adapted better to change when each robot had a small number of neighbors. Image credit: Andreagiovanni Reina.

Robot swarms communicate best when messages spread neighbor to neighbor

Posted on August 27, 2021
Amy McDermott
In the not-so-distant future, swarms of robots could help contain environmental disasters such as wildfires, by locating and dousing the most dangerous patches, even as flames move and spread. But how would these individual robots coordinate effectively to pull off such a complex task? A recent paper suggests a surprising answer: a smaller, less-connected social network. According to the work, published in Science Robotics, a flock of simple robots is better at homing in on a dynamic target when individual bots communicate only with their close neighbors, rather than globally across the network.

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Proceedings of the National Academy of Sciences
Vol. 118 | No. 36
September 7, 2021

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