This Week in Science

Science  15 Nov 2019:
Vol. 366, Issue 6467, pp. 833
  1. Solar Physics

    Magnetic fields can generate spicules

    1. Keith T. Smith

    Spicules (small dark streaks) around sunspots (large dark regions) in a hydrogen alpha image of the solar surface

    CREDIT: GREG PIEPOL/SCIENCE SOURCE

    Spicules are small jets of plasma from the surface of the Sun that last a few minutes. Around a million are occurring at any moment, even during periods of low solar activity. The mechanism responsible for launching spicules remains unknown, as is their contribution to heating the solar corona. Samanta et al. observed emerging spicules and the magnetic fields in the adjacent solar surface. They found that many spicules appear a few minutes after a patch of reverse-polarity magnetic field and that the overlying corona is heated shortly afterward. This result provides evidence that magnetic reconnection can generate spicules, which then transfer energy to the corona.

    Science, this issue p. 890

  2. Biomedicine

    Tuning stress protects cognition

    1. Stella M. Hurtley

    Down syndrome (DS) is a chromosomal disorder that occurs when a person has an extra copy of chromosome 21. DS causes intellectual disabilities, among other health issues, but little is known about the mechanisms underlying the memory deficits in DS. Zhu et al. used a multidisciplinary approach to show that a defect in integrated stress response, a conserved pathway that controls protein homeostasis, can explain the cognitive and neuronal deficits in a mouse model of DS (see the Perspective by Halliday and Mallucci). These insights into the biological basis underlying DS could potentially help in the design of treatments for this condition.

    Science, this issue p. 843; see also p. 797

  3. Structural Biology

    The architecture of the RSC complex

    1. Steve Mao

    RSC is a Snf2-family chromatin remodeler complex that controls the promoter architecture of most of the genes in yeast. Using single-particle cryo–electron microscopy, Ye et al. determined the structure of RSC bound to the nucleosome. The structure reveals the modular architecture of RSC, shows how RSC engages the nucleosome, and explains the remodeling directionality. RSC shows strong similarities to homologous human complexes that are frequently mutated in cancers, and this structure provides valuable information for understanding these systems.

    Science, this issue p. 838

  4. Quantum Optics

    Irreversible splitting of light

    1. Ian S. Osborne

    Prisms and dielectric beam splitters tend to be unitary and reversible optical elements, with the quantum properties of the photons largely irrelevant. Kurtscheid et al. introduce a method of irreversibly, but coherently, populating a split state with photons by thermalizing the photons into a low-energy ground state by repeated absorption-emission interaction with a fluorescent dye within a double-dimple optical cavity. Generation of such a coherent split state could be used as a precursor step to the quasi-continuous creation of many-body entangled states of light, which could be useful in applications in quantum communication, computing, and simulation.

    Science, this issue p. 894

  5. Immunology

    Peptide mimicry breaks the heart

    1. Seth Thomas Scanlon

    Myocarditis, a prolonged chronic inflammation of heart muscle, can eventually progress to inflammatory cardiomyopathy, a serious condition associated with heart failure. Activated T helper (TH) cells that recognize myosin heavy chain 6–derived peptides are thought to play a central role in this pathogenesis. Using a mouse model of myocarditis, Gil-Cruz et al. found that cardiac myosin–reactive TH cells are initially primed by myosin-peptide mimics derived from commensal Bacteroides species in the gut (see the Perspective by Epelman). Unlike heathy controls, human myocarditis patients also showed detectable immune reactivity to both Bacteroides and cardiac myosin antigens. Treatment with antibiotics dampened inflammatory responses and prevented lethal heart disease.

    Science, this issue p. 881; see also p. 806

  6. Nutrient Delivery

    Mitigating micronutrient deficiency

    1. Caitlin Czajka

    Micronutrient deficiencies that impair growth and contribute to disease remain leading public health concerns, particularly within the developing world. Although fortification of food can help treat deficiencies, heat used during cooking and other conditions can degrade vitamins, preventing adequate absorption. Anselmo et al. developed a polymer coating to encapsulate micronutrients, 11 of which showed improved stability against oxidation, heat, and other conditions. Micronutrients were absorbed by the intestine when microparticles were administered to rodents. The researchers used data from two clinical trials and experiments using human intestinal tissue to optimize microparticle formulations, enhance iron loading, improve bioavailability, retain stability during cooking, and allow for scale-up. This microparticle platform could help improve oral delivery of micronutrients.

    Sci. Transl. Med. 11, eaaw3680 (2019).

  7. Anthropology

    Change in climate withered an empire

    1. Kip Hodges

    From roughly 912 to 609 BCE, the Neo-Assyrian Empire rose as one of the most powerful superpowers of its time, dominating much of the Near East. Sinha et al. propose that megadroughts played an important role in the rapid decline in the empire's power, from its height around 670 BCE to its collapse only six decades later. Precisely dated cave deposits from northern Iraq preserved a record of precipitation and effective moisture over a 4000-year period that includes the span of the Neo-Assyrian Empire. This record demonstrates that the rise of the empire occurred during a roughly 200-year interval of abundant rainfall. Subsequently, severe megadroughts characterized the climate across the empire, likely contributing to the empire's rapid decline.

    Sci. Adv. 10.1126/sciadv.aax6656 (2019).

  8. Electrochemistry

    Nanocage-chain fuel cell catalysts

    1. Phil Szuromi

    The expense and scarcity of platinum has driven efforts to improve oxygen-reduction catalysts in proton-exchange membrane fuel cells. Tian et al. synthesized chains of platinum-nickel alloy nanospheres connected by necking regions. These structures can be etched to form nanocages with platinum-rich surfaces that are highly active for oxygen reduction. In fuel cells running on air and hydrogen, these catalysts operated for at least 180 hours.

    Science, this issue p. 850

  9. Developmental Biology

    In vitro development of monkey embryos

    1. Beverly A. Purnell

    Owing to technical and ethical limitations, the molecular and cellular mechanisms underlying primate gastrulation are far from clear (see the Perspective by Tam). Two independent studies used an in vitro culture system to study cynomolgus monkey embryo postimplantation development up to and beyond gastrulation (day 9 to day 20). Niu et al. observed in vivo morphogenetic events and used single-cell RNA sequencing and single-cell chromatin accessibility to study the distinct cell lineages in developing embryos. Ma et al. also observed that key events of in vivo early development were recapitulated in their system, and single-cell RNA-sequencing analysis revealed molecular signatures of postimplantation cell types. These systems will help elucidate the dynamics and regulation of gastrulation in primates, including possible relevance to human development.

    Science, this issue p. eaaw5754, p. eaax7890; see also p. 798

  10. Laser Physics

    Filling the terahertz gap

    1. Ian S. Osborne

    Compared with other wavelengths, coherent sources of electromagnetic radiation in the terahertz regime are relatively scarce. Despite a number of applications in security imaging, spectroscopy, and chemical analysis, it has been experimentally challenging to produce such light. Chevalier et al. demonstrate an approach involving the excitation of a molecular gas with a quantum cascade laser. They show that they can tune into a broad range of desired wavelengths by carefully selecting the required molecular transition. A compact platform—the size of a shoe box—and widely tunable source of coherent terahertz radiation should find immediate application across a number of fields.

    Science, this issue p. 856

  11. Glasses

    A glass that won't break

    1. Brent Grocholski

    Oxide glasses are important for applications ranging from smartphone screens to window panes. One familiar feature of glass is that it fractures and shatters when rapidly deformed, limiting the number of potential uses. However, Frankberg et al. found that they could deform thin films of glassy alumina (Al2O3) with high strain rates at room temperature (see the Perspective by Wondraczek). This surprising observation is supported by simulations of the material that show that dense and flawless glassy alumina samples can deform this way. The discovery provides important insight into designing new glasses that might be more fracture resistant.

    Science, this issue p. 864; see also p. 804

  12. Optoelectronics

    Switching light on-chip

    1. Ian S. Osborne

    The development of practical, reconfigurable photonics requires a platform that can be scaled to large circuits and driven by low-voltage complementary metal-oxide semiconductor (CMOS) electronics. Such a platform requires that switching devices possess a compact footprint, low driving voltages, fast switching, low optical losses, and low power consumption. Haffner et al. demonstrate that the combination of opto-electro-mechanical effects with plasmonic devices can provide a platform that meets all the above criteria. The results are promising for developing on-chip integrated optical networks that can be switched by CMOS-level voltages.

    Science, this issue p. 860

  13. Polymer Chemistry

    Cross-linking a range of alkyl polymers

    1. Marc S. Lavine

    Some alkyl polymers, such as polyethylene, can be cross-linked by using peroxides or high-energy radiation or through the addition of a radical forming agent. Others, like polypropylene, are likely to undergo chain scission, and this process tends to be uncontrolled in the distribution of the cross-links. Lepage et al. developed a widely applicable approach using bis-diazirine molecules as cross-linking agents (see the Perspective by de Zwart et al.). These molecules can be thermally or photochemically activated to form carbenes that readily insert into the polymer carbon-hydrogen bonds, thus leading to cross-linking. The bis-diazirine is nonexplosive, nonvolatile, and easily activated at relatively mild temperatures and thus could be used to fine-tune the properties of existing polymers through small chemical modifications.

    Science, this issue p. 875; see also p. 800

  14. Freshwater Ecology

    Change in plants as bicarbonate rises

    1. Andrew M. Sugden

    Freshwater plants can be broadly divided into two major categories according to their photosynthetic traits: Some use carbon dioxide as their carbon source, whereas others use bicarbonate. Iversen et al. found that the relative concentrations of these two inorganic carbon forms in water determine the functional composition of plant communities across freshwater ecosystems (see the Perspective by Marcé and Obrador). They created global maps revealing that community composition is structured by catchment geology and not climate (in contrast to the terrestrial realm, where the trait composition is structured by temperature and rainfall). Anthropogenic influences from land-use change are causing large-scale increases in bicarbonate concentrations in freshwater catchments and are thus leading to wholesale changes in the composition of their aquatic plant communities.

    Science, this issue p. 878; see also p. 805

  15. Soil Ecology

    Many factors influence global change

    1. Andrew M. Sugden

    Global environmental change is driven by multiple natural and anthropogenic factors. With a focus on global change as it affects soils, Rillig et al. point out that nearly all published studies consider just one or two factors at a time (see the Perspective by Manning). In a laboratory experiment, they tested 10 drivers of global change both individually and in combination, at levels ranging from 2 to 10 factors. They found that soil properties, processes, and microbial communities could not be predicted from single-effect responses and that multiple factors in combination produced unsuspected responses. They concluded that single-factor studies remain important for uncovering mechanisms but that global change biology needs to embrace more fully the multitude of drivers impinging on ecosystems.

    Science, this issue p. 886; see also p. 801

  16. Asthma

    Neutrophils keep the peace

    1. Anand Balasubramani

    Allergic airway inflammation is a complex disease, and multiple immune and nonimmune factors contribute to its development and progression. Using a house dust mite–induced mouse model of allergic inflammation, Patel et al. found that depletion of neutrophils worsens airway inflammation and enhances myelopoiesis—the proliferation of bone marrow cells—driven by granulocyte colony-stimulating factor (G-CSF). Experiments demonstrate a previously unsuspected link between this hormone and type 2 innate lymphoid cells (ILC2s). G-CSF acts directly on both human and mouse ILC2s to promote production of the cytokines interleukin-5 and -13.

    Sci. Immunol. 4, eaax7006 (2019).

  17. 2D Materials

    Taking electrical control

    1. Jelena Stajic

    Excitons—bound pairs of electrons and holes in a solid—can, in principle, be used as information carriers. However, their lifetime is limited because the electrons and holes tend to quickly recombine. One way to extend this lifetime is to physically separate electrons and holes—for example, by having them reside in different layers of a van der Waals heterostructure. Jauregui et al. used this strategy to form long-lived interlayer excitons in a heterostructure made out of monolayers of molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2). Through electrical control of the layers in the heterostructure, the researchers further increased exciton lifetime and formed and manipulated charged excitons.

    Science, this issue p. 870

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