• All-sky dynamical response of the Galactic halo to the Large Magellanic Cloud

      Conroy, Charlie; Naidu, Rohan P; Garavito-Camargo, Nicolás; Besla, Gurtina; Zaritsky, Dennis; Bonaca, Ana; Johnson, Benjamin D; Steward Observatory, University of Arizona (Nature Research, 2021-04-21)
      Gravitational interactions between the Large Magellanic Cloud (LMC) and the stellar and dark matter halo of the Milky Way are expected to give rise to disequilibrium phenomena in the outer Milky Way1-7. A local wake is predicted to trail the orbit of the LMC, and a large-scale overdensity is predicted to exist across a large area of the northern Galactic hemisphere. Here we report the detection of both the local wake and northern overdensity (hereafter the 'collective response') in a map of the Galaxy based on 1,301 stars at Galactocentric distances between 60 and 100 kiloparsecs. The location of the wake is in good agreement with an N-body simulation that includes the dynamical effect of the LMC on the Milky Way halo. The density contrast of the wake and collective response are stronger in the data than in the simulation. The detection of a strong local wake is independent evidence that the Magellanic clouds are on their first orbit around the Milky Way. The wake traces the path of the LMC, which will provide insight into the orbit of the LMC, which in turn is a sensitive probe of the mass of the LMC and the Milky Way. These data demonstrate that the outer halo is not in dynamical equilibrium, as is often assumed. The morphology and strength of the wake could be used to test the nature of dark matter and gravity.
    • An alternative domain-swapped structure of the Pyrococcus horikoshii PolII mini-intein

      Williams, J.E.; Jaramillo, M.V.; Li, Z.; Zhao, J.; Wang, C.; Li, H.; Mills, K.V.; Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona (Nature Research, 2021)
      Protein splicing is a post-translational process by which an intein catalyzes its own excision from flanking polypeptides, or exteins, concomitant with extein ligation. Many inteins have nested homing endonuclease domains that facilitate their propagation into intein-less alleles, whereas other inteins lack the homing endonuclease (HEN) and are called mini-inteins. The mini-intein that interrupts the DNA PolII of Pyrococcus horikoshii has a linker region in place of the HEN domain that is shorter than the linker in a closely related intein from Pyrococcus abyssi. The P. horikoshii PolII intein requires a higher temperature for catalytic activity and is more stable to digestion by the thermostable protease thermolysin, suggesting that it is more rigid than the P. abyssi intein. We solved a crystal structure of the intein precursor that revealed a domain-swapped dimer. Inteins found as domain swapped dimers have been shown to promote intein-mediated protein alternative splicing, but the solved P. horikoshii PolII intein structure has an active site unlikely to be catalytically competent. © 2021, The Author(s).
    • Analysis of the Coptis chinensis genome reveals the diversification of protoberberine-type alkaloids

      Liu, Y.; Wang, B.; Shu, S.; Li, Z.; Song, C.; Liu, D.; Niu, Y.; Liu, J.; Zhang, J.; Liu, H.; et al. (Nature Research, 2021)
      Chinese goldthread (Coptis chinensis Franch.), a member of the Ranunculales, represents an important early-diverging eudicot lineage with diverse medicinal applications. Here, we present a high-quality chromosome-scale genome assembly and annotation of C. chinensis. Phylogenetic and comparative genomic analyses reveal the phylogenetic placement of this species and identify a single round of ancient whole-genome duplication (WGD) shared by the Ranunculaceae. We characterize genes involved in the biosynthesis of protoberberine-type alkaloids in C. chinensis. In particular, local genomic tandem duplications contribute to member amplification of a Ranunculales clade-specific gene family of the cytochrome P450 (CYP) 719. The functional versatility of a key CYP719 gene that encodes the (S)-canadine synthase enzyme involved in the berberine biosynthesis pathway may play critical roles in the diversification of other berberine-related alkaloids in C. chinensis. Our study provides insights into the genomic landscape of early-diverging eudicots and provides a valuable model genome for genetic and applied studies of Ranunculales. © 2021, The Author(s).
    • Approximate Bayesian Computation of radiocarbon and paleoenvironmental record shows population resilience on Rapa Nui (Easter Island)

      DiNapoli, R.J.; Crema, E.R.; Lipo, C.P.; Rieth, T.M.; Hunt, T.L.; The Honors College and School of Anthropology, University of Arizona, Tucson, AZ, United States (Nature Research, 2021)
      Examining how past human populations responded to environmental and climatic changes is a central focus of the historical sciences. The use of summed probability distributions (SPD) of radiocarbon dates as a proxy for estimating relative population sizes provides a widely applicable method in this research area. Paleodemographic reconstructions and modeling with SPDs, however, are stymied by a lack of accepted methods for model fitting, tools for assessing the demographic impact of environmental or climatic variables, and a means for formal multi-model comparison. These deficiencies severely limit our ability to reliably resolve crucial questions of past human-environment interactions. We propose a solution using Approximate Bayesian Computation (ABC) to fit complex demographic models to observed SPDs. Using a case study from Rapa Nui (Easter Island), a location that has long been the focus of debate regarding the impact of environmental and climatic changes on its human population, we find that past populations were resilient to environmental and climatic challenges. Our findings support a growing body of evidence showing stable and sustainable communities on the island. The ABC framework offers a novel approach for exploring regions and time periods where questions of climate-induced demographic and cultural change remain unresolved. © 2021, The Author(s).
    • Augmenting ideational fluency in a creativity task across multiple transcranial direct current stimulation montages

      Chrysikou, E.G.; Morrow, H.M.; Flohrschutz, A.; Denney, L.; University of Arizona (Nature Research, 2021)
      Neuroimaging and transcranial direct current stimulation (tDCS) research has revealed that generating novel ideas is associated with both reductions and increases in prefrontal cortex (PFC) activity, and engagement of posterior occipital cortex, among other regions. However, there is substantial variability in the robustness of these tDCS‐induced effects due to heterogeneous sample sizes, different creativity measures, and methodological diversity in the application of tDCS across laboratories. To address these shortcomings, we used twelve different montages within a standardized tDCS protocol to investigate how altering activity in frontotemporal and occipital cortex impacts creative thinking. Across four experiments, 246 participants generated either the common or an uncommon use for 60 object pictures while undergoing tDCS. Participants also completed a control short-term memory task. We applied active tDCS for 20 min at 1.5 mA through two 5 cm × 5 cm electrodes over left or right ventrolateral prefrontal (areas F7, F8) or occipital (areas O1, O2) cortex, concurrent bilateral stimulation of these regions across polarities, or sham stimulation. Cathodal stimulation of the left, but not right, ventrolateral PFC improved fluency in creative idea generation, but had no effects on originality, as approximated by measures of semantic distance. No effects were obtained for the control tasks. Concurrent bilateral stimulation of the ventrolateral PFC regardless of polarity direction, and excitatory stimulation of occipital cortex did not alter task performance. Highlighting the importance of cross-experimental methodological consistency, these results extend our past findings and contribute to our understanding of the role of left PFC in creative thinking. © 2021, The Author(s).
    • Automated digital TIL analysis (ADTA) adds prognostic value to standard assessment of depth and ulceration in primary melanoma

      Moore, Michael R.; Friesner, Isabel D.; Rizk, Emanuelle M.; Fullerton, Benjamin T.; Mondal, Manas; Trager, Megan H.; Mendelson, Karen; Chikeka, Ijeuru; Kurc, Tahsin; Gupta, Rajarsi; et al. (Nature Research, 2021-02-02)
      Accurate prognostic biomarkers in early-stage melanoma are urgently needed to stratify patients for clinical trials of adjuvant therapy. We applied a previously developed open source deep learning algorithm to detect tumor-infiltrating lymphocytes (TILs) in hematoxylin and eosin (H&E) images of early-stage melanomas. We tested whether automated digital (TIL) analysis (ADTA) improved accuracy of prediction of disease specific survival (DSS) based on current pathology standards. ADTA was applied to a training cohort (n = 80) and a cutoff value was defined based on a Receiver Operating Curve. ADTA was then applied to a validation cohort (n = 145) and the previously determined cutoff value was used to stratify high and low risk patients, as demonstrated by Kaplan–Meier analysis (p ≤ 0.001). Multivariable Cox proportional hazards analysis was performed using ADTA, depth, and ulceration as co-variables and showed that ADTA contributed to DSS prediction (HR: 4.18, CI 1.51–11.58, p = 0.006). ADTA provides an effective and attainable assessment of TILs and should be further evaluated in larger studies for inclusion in staging algorithms. © 2021, The Author(s).
    • Belief propagation with quantum messages for quantum-enhanced classical communications

      Rengaswamy, N.; Seshadreesan, K.P.; Guha, S.; Pfister, H.D.; Department of Electrical and Computer Engineering, The University of Arizona; College of Optical Sciences, The University of Arizona (Nature Research, 2021)
      For space-based laser communications, when the mean photon number per received optical pulse is much smaller than one, there is a large gap between communications capacity achievable with a receiver that performs individual pulse-by-pulse detection, and the quantum-optimal “joint-detection receiver” that acts collectively on long codeword-blocks of modulated pulses; an effect often termed “superadditive capacity”. In this paper, we consider the simplest scenario where a large superadditive capacity is known: a pure-loss channel with a coherent-state binary phase-shift keyed (BPSK) modulation. The two BPSK states can be mapped conceptually to two non-orthogonal states of a qubit, described by an inner product that is a function of the mean photon number per pulse. Using this map, we derive an explicit construction of the quantum circuit of a joint-detection receiver based on a recent idea of “belief-propagation with quantum messages” (BPQM). We quantify its performance improvement over the Dolinar receiver that performs optimal pulse-by-pulse detection, which represents the best “classical” approach. We analyze the scheme rigorously and show that it achieves the quantum limit of minimum average error probability in discriminating 8 (BPSK) codewords of a length-5 binary linear code with a tree factor graph. Our result suggests that a BPQM receiver might attain the Holevo capacity of this BPSK-modulated pure-loss channel. Moreover, our receiver circuit provides an alternative proposal for a quantum supremacy experiment, targeted at a specific application that can potentially be implemented on a small, special-purpose, photonic quantum computer capable of performing cat-basis universal qubit logic. © 2021, The Author(s).
    • Bidirectional interconversion of microwave and light with thin-film lithium niobate

      Xu, Y.; Sayem, A.A.; Fan, L.; Zou, C.-L.; Wang, S.; Cheng, R.; Fu, W.; Yang, L.; Xu, M.; Tang, H.X.; et al. (Nature Research, 2021)
      Superconducting cavity electro-optics presents a promising route to coherently convert microwave and optical photons and distribute quantum entanglement between superconducting circuits over long-distance. Strong Pockels nonlinearity and high-performance optical cavity are the prerequisites for high conversion efficiency. Thin-film lithium niobate (TFLN) offers these desired characteristics. Despite significant recent progresses, only unidirectional conversion with efficiencies on the order of 10−5 has been realized. In this article, we demonstrate the bidirectional electro-optic conversion in TFLN-superconductor hybrid system, with conversion efficiency improved by more than three orders of magnitude. Our air-clad device architecture boosts the sustainable intracavity pump power at cryogenic temperatures by suppressing the prominent photorefractive effect that limits cryogenic performance of TFLN, and reaches an efficiency of 1.02% (internal efficiency of 15.2%). This work firmly establishes the TFLN-superconductor hybrid EO system as a highly competitive transduction platform for future quantum network applications. © 2021, The Author(s).
    • Cannabis sativa terpenes are cannabimimetic and selectively enhance cannabinoid activity

      LaVigne, J.E.; Hecksel, R.; Keresztes, A.; Streicher, J.M.; Department of Pharmacology, College of Medicine, University of Arizona (Nature Research, 2021)
      Limited evidence has suggested that terpenes found in Cannabis sativa are analgesic, and could produce an “entourage effect” whereby they modulate cannabinoids to result in improved outcomes. However this hypothesis is controversial, with limited evidence. We thus investigated Cannabis sativa terpenes alone and with the cannabinoid agonist WIN55,212 using in vitro and in vivo approaches. We found that the terpenes α-humulene, geraniol, linalool, and β-pinene produced cannabinoid tetrad behaviors in mice, suggesting cannabimimetic activity. Some behaviors could be blocked by cannabinoid or adenosine receptor antagonists, suggesting a mixed mechanism of action. These behavioral effects were selectively additive with WIN55,212, suggesting terpenes can boost cannabinoid activity. In vitro experiments showed that all terpenes activated the CB1R, while some activated other targets. Our findings suggest that these Cannabis terpenes are multifunctional cannabimimetic ligands that provide conceptual support for the entourage effect hypothesis and could be used to enhance the therapeutic properties of cannabinoids. © 2021, The Author(s).
    • Ceramide kinase regulates TNF-α-induced immune responses in human monocytic cells

      Al-Rashed, F.; Ahmad, Z.; Snider, A.J.; Thomas, R.; Kochumon, S.; Melhem, M.; Sindhu, S.; Obeid, L.M.; Al-Mulla, F.; Hannun, Y.A.; et al. (Nature Research, 2021)
      Ceramide kinase (CERK) phosphorylates ceramide to produce ceramide-1-phosphate (C1P), which is involved in the development of metabolic inflammation. TNF-α modulates inflammatory responses in monocytes associated with various inflammatory disorders; however, the underlying mechanisms remain not fully understood. Here, we investigated the role of CERK in TNF-α-induced inflammatory responses in monocytes. Our results show that disruption of CERK activity in monocytes, either by chemical inhibitor NVP-231 or by small interfering RNA (siRNA), results in the defective expression of inflammatory markers including CD11c, CD11b and HLA-DR in response to TNF-α. Our data show that TNF-α upregulates ceramide phosphorylation. Inhibition of CERK in monocytes significantly reduced the secretion of IL-1β and MCP-1. Similar results were observed in CERK-downregulated cells. TNF-α-induced phosphorylation of JNK, p38 and NF-κB was reduced by inhibition of CERK. Additionally, NF-κB/AP-1 activity was suppressed by the inhibition of CERK. Clinically, obese individuals had higher levels of CERK expression in PBMCs compared to lean individuals, which correlated with their TNF-α levels. Taken together, these results suggest that CERK plays a key role in regulating inflammatory responses in human monocytes during TNF-α stimulation. CERK may be a relevant target for developing novel therapies for chronic inflammatory diseases. © 2021, The Author(s).
    • Chromosome Xq23 is associated with lower atherogenic lipid concentrations and favorable cardiometabolic indices

      NHLBI Trans-Omics for Precision Medicine (TOPMed) Consortium; University of Arizona (Nature Research, 2021)
      Autosomal genetic analyses of blood lipids have yielded key insights for coronary heart disease (CHD). However, X chromosome genetic variation is understudied for blood lipids in large sample sizes. We now analyze genetic and blood lipid data in a high-coverage whole X chromosome sequencing study of 65,322 multi-ancestry participants and perform replication among 456,893 European participants. Common alleles on chromosome Xq23 are strongly associated with reduced total cholesterol, LDL cholesterol, and triglycerides (min P = 8.5 × 10−72), with similar effects for males and females. Chromosome Xq23 lipid-lowering alleles are associated with reduced odds for CHD among 42,545 cases and 591,247 controls (P = 1.7 × 10−4), and reduced odds for diabetes mellitus type 2 among 54,095 cases and 573,885 controls (P = 1.4 × 10−5). Although we observe an association with increased BMI, waist-to-hip ratio adjusted for BMI is reduced, bioimpedance analyses indicate increased gluteofemoral fat, and abdominal MRI analyses indicate reduced visceral adiposity. Co-localization analyses strongly correlate increased CHRDL1 gene expression, particularly in adipose tissue, with reduced concentrations of blood lipids. © 2021, The Author(s).
    • Climate change and tree growth in the Khakass-Minusinsk Depression (South Siberia) impacted by large water reservoirs

      Zhirnova, D.F.; Belokopytova, L.V.; Meko, D.M.; Babushkina, E.A.; Vaganov, E.A.; Laboratory of Tree-Ring Research, University of Arizona (Nature Research, 2021)
      Regional and local climate change depends on continentality, orography, and human activities. In particular, local climate modification by water reservoirs can reach far from shore and downstream. Among the possible ecological consequences are shifts in plant performance. Tree-ring width of affected trees can potentially be used as proxies for reservoir impact. Correlation analysis and t-tests were applied to climatic data and tree-ring chronologies of Pinus sylvestris L. and Larix sibirica Ledeb. from moisture-deficit habitats in the intermontane Khakass-Minusinsk Depression, to assess modification of climate and tree growth by the Krasnoyarsk and Sayano-Shushenskoe Reservoirs on the Yenisei River. Abrupt significant cooling in May–August and warming in September-March occurred after the launch of the turbines in dams, more pronounced near the Sayano-Shushenskoe dam (up to – 0.5 °C in summer and to + 3.5 °C in winter) than near the Krasnoyarsk Reservoir headwaters (– 0.3 °C and + 1.4 °C). Significant lengthening of the warm season was also found for temperature thresholds 0–8 °C. Shifts of seasonality and intensity occurred in climatic responses of all tree-ring chronologies after development of water reservoirs. Patterns of these shifts, however, depended on species-specific sensitivity to climatic modification, distance from reservoirs, and physiographic regions. Mitigation of climate continentality and extremes by reservoirs appears to have offset possible negative effects of warming on tree growth. © 2021, The Author(s).
    • Coevolutionary transitions from antagonism to mutualism explained by the Co-Opted Antagonist Hypothesis

      Johnson, C.A.; Smith, G.P.; Yule, K.; Davidowitz, G.; Bronstein, J.L.; Ferrière, R.; Dept. of Ecology and Evolutionary Biology, University of Arizona; Dept. of Entomology, University of Arizona (Nature Research, 2021)
      There is now good evidence that many mutualisms evolved from antagonism; why or how, however, remains unclear. We advance the Co-Opted Antagonist (COA) Hypothesis as a general mechanism explaining evolutionary transitions from antagonism to mutualism. COA involves an eco-coevolutionary process whereby natural selection favors co-option of an antagonist to perform a beneficial function and the interacting species coevolve a suite of phenotypic traits that drive the interaction from antagonism to mutualism. To evaluate the COA hypothesis, we present a generalized eco-coevolutionary framework of evolutionary transitions from antagonism to mutualism and develop a data-based, fully ecologically-parameterized model of a small community in which a lepidopteran insect pollinates some of its larval host plant species. More generally, our theory helps to reconcile several major challenges concerning the mechanisms of mutualism evolution, such as how mutualisms evolve without extremely tight host fidelity (vertical transmission) and how ecological context influences evolutionary outcomes, and vice-versa. © 2021, The Author(s).
    • CRISPR-mediated mutations in the ABC transporter gene ABCA2 confer pink bollworm resistance to Bt toxin Cry2Ab

      Fabrick, J.A.; LeRoy, D.M.; Mathew, L.G.; Wu, Y.; Unnithan, G.C.; Yelich, A.J.; Carrière, Y.; Li, X.; Tabashnik, B.E.; Department of Entomology, University of Arizona (Nature Research, 2021)
      Crops genetically engineered to produce insecticidal proteins from Bacillus thuringiensis (Bt) have many benefits and are important globally for managing insect pests. However, the evolution of pest resistance to Bt crops reduces their benefits. Understanding the genetic basis of such resistance is needed to better monitor, manage, and counter pest resistance to Bt crops. Previous work shows that resistance to Bt toxin Cry2Ab is associated with mutations in the gene encoding the ATP-binding cassette protein ABCA2 in lab- and field-selected populations of the pink bollworm (Pectinophora gossypiella), one of the world’s most destructive pests of cotton. Here we used CRISPR/Cas9 gene editing to test the hypothesis that mutations in the pink bollworm gene encoding ABCA2 (PgABCA2) can cause resistance to Cry2Ab. Consistent with this hypothesis, introduction of disruptive mutations in PgABCA2 in a susceptible strain of pink bollworm increased the frequency of resistance to Cry2Ab and facilitated creation of a Cry2Ab-resistant strain. All Cry2Ab-resistant individuals tested in this study had disruptive mutations in PgABCA2. Overall, we found 17 different disruptive mutations in PgABCA2 gDNA and 26 in PgABCA2 cDNA, including novel mutations corresponding precisely to single-guide (sgRNA) sites used for CRISPR/Cas9. Together with previous results, these findings provide the first case of practical resistance to Cry2Ab where evidence identifies a specific gene in which disruptive mutations can cause resistance and are associated with resistance in field-selected populations. © 2021, The Author(s).
    • Decoding individual identity from brain activity elicited in imagining common experiences

      Anderson, A.J.; McDermott, K.; Rooks, B.; Heffner, K.L.; Dodell-Feder, D.; Lin, F.V.; Neuroscience, University of Arizona (Nature Research, 2020)
      Everyone experiences common events differently. This leads to personal memories that presumably provide neural signatures of individual identity when events are reimagined. We present initial evidence that these signatures can be read from brain activity. To do this, we progress beyond previous work that has deployed generic group-level computational semantic models to distinguish between neural representations of different events, but not revealed interpersonal differences in event representations. We scanned 26 participants’ brain activity using functional Magnetic Resonance Imaging as they vividly imagined themselves personally experiencing 20 common scenarios (e.g., dancing, shopping, wedding). Rather than adopting a one-size-fits-all approach to generically model scenarios, we constructed personal models from participants’ verbal descriptions and self-ratings of sensory/motor/cognitive/spatiotemporal and emotional characteristics of the imagined experiences. We demonstrate that participants’ neural representations are better predicted by their own models than other peoples’. This showcases how neuroimaging and personalized models can quantify individual-differences in imagined experiences. © 2020, The Author(s).
    • Decrypting bacterial polyphenol metabolism in an anoxic wetland soil

      McGivern, B.B.; Tfaily, M.M.; Borton, M.A.; Kosina, S.M.; Daly, R.A.; Nicora, C.D.; Purvine, S.O.; Wong, A.R.; Lipton, M.S.; Hoyt, D.W.; et al. (Nature Research, 2021)
      Microorganisms play vital roles in modulating organic matter decomposition and nutrient cycling in soil ecosystems. The enzyme latch paradigm posits microbial degradation of polyphenols is hindered in anoxic peat leading to polyphenol accumulation, and consequently diminished microbial activity. This model assumes that polyphenols are microbially unavailable under anoxia, a supposition that has not been thoroughly investigated in any soil type. Here, we use anoxic soil reactors amended with and without a chemically defined polyphenol to test this hypothesis, employing metabolomics and genome-resolved metaproteomics to interrogate soil microbial polyphenol metabolism. Challenging the idea that polyphenols are not bioavailable under anoxia, we provide metabolite evidence that polyphenols are depolymerized, resulting in monomer accumulation, followed by the generation of small phenolic degradation products. Further, we show that soil microbiome function is maintained, and possibly enhanced, with polyphenol addition. In summary, this study provides chemical and enzymatic evidence that some soil microbiota can degrade polyphenols under anoxia and subvert the assumed polyphenol lock on soil microbial metabolism. © 2021, The Author(s).
    • Development of a Genetic Risk Score to predict the risk of overweight and obesity in European adolescents from the HELENA study

      Seral-Cortes, Miguel; Sabroso-Lasa, Sergio; De Miguel-Etayo, Pilar; Gonzalez-Gross, Marcela; Gesteiro, Eva; Molina-Hidalgo, Cristina; De Henauw, Stefaan; Gottrand, Frederic; Mavrogianni, Christina; Manios, Yannis; et al. (Nature Research, 2021-02-04)
      Obesity is the result of interactions between genes and environmental factors. Since monogenic etiology is only known in some obesity-related genes, a genetic risk score (GRS) could be useful to determine the genetic predisposition to obesity. Therefore, the aim of our study was to build a GRS able to predict genetic predisposition to overweight and obesity in European adolescents. A total of 1069 adolescents (51.3% female), aged 11–19 years participating in the Healthy Lifestyle in Europe by Nutrition in Adolescence (HELENA) cross-sectional study were genotyped. The sample was divided in non-overweight (non-OW) and overweight/obesity (OW/OB). From 611 single nucleotide polymorphisms (SNP) available, a first screening of 104 SNPs univariately associated with obesity (p < 0.20) was established selecting 21 significant SNPs (p < 0.05) in the multivariate model. Unweighted GRS (uGRS) was calculated by summing the number of risk alleles and weighted GRS (wGRS) by multiplying the risk alleles to each estimated coefficient. The area under curve (AUC) was calculated in uGRS (0.723) and wGRS (0.734) using tenfold internal cross-validation. Both uGRS and wGRS were significantly associated with body mass index (BMI) (p <.001). Both GRSs could potentially be considered as useful genetic tools to evaluate individual’s predisposition to overweight/obesity in European adolescents. © 2021, The Author(s).
    • Discovery of a tsunami deposit from the Bronze Age Santorini eruption at Malia (Crete): impact, chronology, extension

      Lespez, L.; Lescure, S.; Saulnier-Copard, S.; Glais, A.; Berger, J.-F.; Lavigne, F.; Pearson, C.; Virmoux, C.; Müller Celka, S.; Pomadère, M.; et al. (Nature Research, 2021)
      A geomorphological survey immediately west of the Minoan town of Malia (Crete) shows that a tsunami resulting from the Bronze Age Santorini eruption reached the outskirts of the Palatial center. Sediment cores testify a unique erosional event during the Late Minoan period, followed locally by a high energy sand unit comprising marine fauna. This confirms that a tsunami impacted northern Crete and caused an inundation up to 400 m inland at Malia. We obtained a radiocarbon range of 1744–1544 BCE for the secure pre-tsunami context and an interval 1509–1430 BCE for the post-event layer. Examination of tsunami deposits was used to constrain run-up not exceeding 8 m asl. The results open the field for new research on the Bronze Age Santorini tsunami regarding both impact and consequences for the Minoan civilization. © 2021, The Author(s).
    • A dusty veil shading Betelgeuse during its Great Dimming

      Montargès, M; Cannon, E; Lagadec, E; de Koter, A; Kervella, P; Sanchez-Bermudez, J; Paladini, C; Cantalloube, F; Decin, L; Scicluna, P; et al. (Nature Research, 2021-06-16)
      Red supergiants are the most common final evolutionary stage of stars that have initial masses between 8 and 35 times that of the Sun1. During this stage, which lasts roughly 100,000 years1, red supergiants experience substantial mass loss. However, the mechanism for this mass loss is unknown2. Mass loss may affect the evolutionary path, collapse and future supernova light curve3 of a red supergiant, and its ultimate fate as either a neutron star or a black hole4. From November 2019 to March 2020, Betelgeuse-the second-closest red supergiant to Earth (roughly 220 parsecs, or 724 light years, away)5,6-experienced a historic dimming of its visible brightness. Usually having an apparent magnitude between 0.1 and 1.0, its visual brightness decreased to 1.614 ± 0.008 magnitudes around 7-13 February 20207-an event referred to as Betelgeuse's Great Dimming. Here we report high-angular-resolution observations showing that the southern hemisphere of Betelgeuse was ten times darker than usual in the visible spectrum during its Great Dimming. Observations and modelling support a scenario in which a dust clump formed recently in the vicinity of the star, owing to a local temperature decrease in a cool patch that appeared on the photosphere. The directly imaged brightness variations of Betelgeuse evolved on a timescale of weeks. Our findings suggest that a component of mass loss from red supergiants8 is inhomogeneous, linked to a very contrasted and rapidly changing photosphere.
    • The dynamics of explore–exploit decisions reveal a signal-to-noise mechanism for random exploration

      Feng, Samuel F.; Wang, Siyu; Zarnescu, Sylvia; Wilson, Robert C.; Department of Psychology, University of Arizona; Cognitive Science Program, University of Arizona (Nature Research, 2021-02-04)
      Growing evidence suggests that behavioral variability plays a critical role in how humans manage the tradeoff between exploration and exploitation. In these decisions a little variability can help us to overcome the desire to exploit known rewards by encouraging us to randomly explore something else. Here we investigate how such ‘random exploration’ could be controlled using a drift-diffusion model of the explore–exploit choice. In this model, variability is controlled by either the signal-to-noise ratio with which reward is encoded (the ‘drift rate’), or the amount of information required before a decision is made (the ‘threshold’). By fitting this model to behavior, we find that while, statistically, both drift and threshold change when people randomly explore, numerically, the change in drift rate has by far the largest effect. This suggests that random exploration is primarily driven by changes in the signal-to-noise ratio with which reward information is represented in the brain.