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Motivated by an observation of Dehornoy, we study the roots of Alexander polynomials of knots and links that are closures of positive 3-strand braids. We give experimental data on random such braids and find that the roots exhibit marked patterns, which we refine into precise conjectures. We then prove several results along those lines, for example that generically at least 69% of the roots are on the unit circle, which appears to be sharp. We also show there is a large root-free region near the origin. We further study the equidistribution properties of such roots by introducing a Lyapunov exponent of the Burau representation of random positive braids, and a corresponding bifurcation measure. In the spirit of Deroin and Dujardin, we conjecture that the bifurcation measure gives the limiting measure for such roots, and prove this on a region with positive limiting mass. We use tools including work of Gambaudo and Ghys on the signature function of links, for which we prove a central limit theorem. 

Abstract It has been suggested that the visual system samples attended information rhythmically. Does rhythmic sampling also apply to distracting information? How do attended information and distracting information compete temporally for neural representations? We recorded electroencephalography from participants who detected instances of coherent motion in a random dot kinematogram (RDK; the target stimulus), overlayed on different categories (pleasant, neutral, and unpleasant) of affective images from the International Affective System (IAPS) (the distractor). The moving dots were flickered at 4.29 Hz whereas the IAPS pictures were flickered at 6 Hz. The time course of spectral power at 4.29 Hz (dot response) was taken to index the temporal dynamics of target processing. The spatial pattern of the power at 6 Hz was similarly extracted and subjected to a MVPA decoding analysis to index the temporal dynamics of processing pleasant, neutral, or unpleasant distractor pictures. We found that (1) both target processing and distractor processing exhibited rhythmicity at ∼1 Hz and (2) the phase difference between the two rhythmic time courses were related to task performance, i.e., relative phase closer to π predicted a higher rate of coherent motion detection whereas relative phase closer to 0 predicted a lower rate of coherent motion detection. These results suggest that (1) in a target-distractor scenario, both attended and distracting information were sampled rhythmically and (2) the more target sampling and distractor sampling were separated in time within a sampling cycle, the less distraction effects were observed, both at the neural and the behavioral level. 

ABSTRACT Rubisco, the most prevalent protein on Earth, catalyzes both a reaction that initiates C₃ carbon fixation, and a reaction that initiates photorespiration, which stimulates protein synthesis. Regulation of the balance between these reactions under atmospheric CO₂ fluctuations remains poorly understood. We have hypothesized that vascular plants maintain organic carbon‐to‐nitrogen homeostasis by adjusting the relative activities of magnesium and manganese in chloroplasts to balance carbon fixation and nitrate assimilation rates. The following examined the influence of magnesium and manganese on carboxylation and oxygenation for rubisco purified from two ecotypes of Plantago lanceolataL.: one adapted to the elevated CO₂ atmospheres that occur near a natural CO₂ spring and the other adapted to more typical CO₂ atmospheres that occur nearby. The plastid DNA coding for the large unit of rubisco was similar in both ecotypes. The kinetics of rubiscos from the two ecotypes differed more when associated with manganese than magnesium. Specificity for CO₂over O₂ (S_c/o) for rubisco from both ecotypes was higher when the enzymes were bound to magnesium than manganese. Differences in the responses of rubisco from P. lanceolata to the metals may account for the adaptation of this species to different CO₂ environments. 

Monitoring of pesticide concentration distribution across farm fields is crucial to ensure precise and efficient application while preventing overuse or untreated areas. 

Many bacteria secrete metallophores, low-molecular-weight organic compounds that bind ions with high selectivity and affinity, in order to access essential metals from the environment. Previous work has elucidated the structures and biosynthetic machinery of metallophores specific for iron, zinc, nickel, molybdenum, and copper. No physiologically relevant lanthanide-binding metallophore has been discovered despite the knowledge that lanthanide metals (Ln) have been revealed to be essential cofactors for certain alcohol dehydrogenases across a diverse range of phyla. Here, we report the biosynthetic machinery, the structure, and the physiological relevance of a lanthanophore, methylolanthanin. The structure of methylolanthanin exhibits a unique 4-hydroxybenzoate moiety which has not previously been described in other metallophores. We find that production of methylolanthanin is required for normal levels of Ln accumulation in the methylotrophic bacterium Methylobacterium extorquens AM1, while overexpression of the molecule greatly increases bioaccumulation and adsorption. Our results provide a clearer understanding of how Ln-utilizing bacteria sense, scavenge, and store Ln; essential processes in the environment where Ln are poorly bioavailable. More broadly, the identification of this lanthanophore opens doors for study of how biosynthetic gene clusters are repurposed for additional functions and the complex relationship between metal homeostasis and fitness. 

Systematic enumeration and identification of unique 3D spatial topologies (STs) of complex engineering systems (such as automotive cooling systems, electric power trains, satellites, and aero-engines) are essential to navigation of these expansive design spaces with the goal of identifying new spatial configurations that can satisfy challenging system requirements. However, efficient navigation through discrete 3D ST options is a very challenging problem due to its combinatorial nature and can quickly exceed human cognitive abilities at even moderate complexity levels. This article presents a new, efficient, and scalable design framework that leverages mathematical spatial graph theory to represent, enumerate, and identify distinctive 3D topological classes for a generic 3D engineering system, given its system architecture (SA)—its components and their interconnections. First, spatial graph diagrams (SGDs) are generated for a given SA from zero to a specified maximum number of interconnect crossings. Then, corresponding Yamada polynomials for all the planar SGDs are generated. SGDs are categorized into topological classes, each of which shares a unique Yamada polynomial. Finally, within each topological class, 3D geometric models are generated using the SGDs having different numbers of interconnect crossings. Selected case studies are presented to illustrate the different features of our proposed framework, including an industrial engineering design application: ST enumeration of a 3D automotive fuel cell cooling system (AFCS). Design guidelines are also provided for practicing engineers to aid the application of this framework to different types of real-world problems such as configuration design and spatial packaging optimization. 

Abstract. We examine results from two transient modeling experiments that simulate the Last Interglacial period (LIG) using the state-of-the-art Community Earth System Model (CESM2), with a focus on climate and ocean changes relevant to the possible collapse of the Antarctic ice sheet. The experiments simulate the early millennia of the LIG warm period using orbital forcing, greenhouse gas concentrations, and vegetation appropriate for 127 ka. In the first case (127ka), no other changes are made; in the second case (127kaFW), we include a 0.2 Sv freshwater forcing in the North Atlantic. Both are compared with a pre-industrial control simulation (piControl). In the 127ka simulation, the global average temperature is only marginally warmer (0.004 °C) than in the piControl. When freshwater forcing is added (127kaFW), there is surface cooling in the Northern Hemisphere (NH) and warming in the Southern Hemisphere (SH), consistent with the bipolar seesaw effect. Near the Antarctic ice sheet, the 127ka simulation generates notable ocean warming (up to 0.4 °C) at depths below 200 m compared to the piControl. In contrast, the addition of freshwater in the North Atlantic in the 127kaFW run results in a multi-century subsurface ocean cooling that rebounds slowly over multiple millennia near the Antarctic ice sheet. These results have implications for the thermal forcing (and thereby mass balance) of the Antarctic ice sheet. We explore the physical processes that lead to this result and discuss implications for climate forcing of Antarctic ice sheet mass loss during the LIG. 

cis-Regulatory elements encode the genomic blueprints that ensure the proper spatiotemporal patterning of gene expression necessary for appropriate development and responses to the environment. Accumulating evidence implicates changes to gene expression as a major source of phenotypic novelty in eukaryotes, including acute phenotypes such as disease and cancer in mammals. Moreover, genetic and epigenetic variation affecting cis-regulatory sequences over longer evolutionary timescales has become a recurring theme in studies of morphological divergence and local adaptation. Here, we discuss the functions of and methods used to identify various classes of cis-regulatory elements, as well as their role in plant development and response to the environment. We highlight opportunities to exploit cis-regulatory variants underlying plant development and environmental responses for crop improvement efforts. Although a comprehensive understanding of cis-regulatory mechanisms in plants has lagged behind that in animals, we showcase several breakthrough findings that have profoundly influenced plant biology and shaped the overall understanding of transcriptional regulation in eukaryotes.