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  1. Abstract Because of the extreme purity, lack of disorder, and complex order parameter, the first-order superfluid 3 He A–B transition is the leading model system for first order transitions in the early universe. Here we report on the path dependence of the supercooling of the A phase over a wide range of pressures below 29.3 bar at nearly zero magnetic field. The A phase can be cooled significantly below the thermodynamic A–B transition temperature. While the extent of supercooling is highly reproducible, it depends strongly upon the cooling trajectory: The metastability of the A phase is enhanced by transiting through regions where the A phase is more stable. We provide evidence that some of the additional supercooling is due to the elimination of B phase nucleation precursors formed upon passage through the superfluid transition. A greater understanding of the physics is essential before 3 He can be exploited to model transitions in the early universe. 
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    Free, publicly-accessible full text available December 1, 2024
  2. Ants have remarkably diverse diets and extraordinary species richness, making them an excellent model system to study the evolution of taste. In this entirely eusocial clade, food choice and the mechanisms that regulate feeding have both individual and social dimensions. How taste receptors and sensory processing drive food preferences to generate dietary breadth in ants is poorly understood. It is additionally unclear how elements of colony organization such as division of labor and social food flow impact the mechanistic basis and evolution of taste. Previous work on dipteran, lepidopteran, and hymenopteran gustatory systems, while foundational, provide limited insights into ant dietary specialization. Here we synthesize and analyze research on ant gustation to identify mechanisms, sociobiological correlates, and phylogenetic patterns. We discuss the current state of genomic analyses of taste and future research. We propose that strikingly polymorphic species of Pheidole , Cephalotes , Camponotus , and leafcutter ants ( Atta and Acromyrmex ) offer compelling social systems to explore adaptive variation in gustation because of their pronounced division of labor in which morphologically, behaviorally, and neurally differentiated workers vary in feeding behavior. Research on ant gustation within and among species will advance our understanding of sensory systems and provide insight into the impact of taste on the evolution of species diversity and how social organization influences gustation. 
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    Free, publicly-accessible full text available May 2, 2024
  3. Single-molecule fluorescence approaches have revolutionized biological and materials microscopy. However, many questions can only be addressed by multicolor imaging of multiple targets, a capability that is limited by the small subset of available, well-performing, and spectrally-distinct fluorescent probes. We recently introduced an alternative single-molecule multiplexing approach termed blinking-based multiplexing (BBM), wherein individual molecules are classified on the basis of their intrinsic blinking dynamics. We demonstrate accurate (>93.5%) binary classification of spectrally-overlapped rhodamine and quantum dot emitters using BBM, even when substantial blinking heterogeneity is observed. Classification can be accomplished using change point detection (CPD) analysis of blinking dynamics or a deep learning (DL) algorithm, the latter of which provides up to 96.6% accuracy. Here, we use CPD and DL algorithms to probe the excitation power, environmental, and molecular dependence of BBM. In addition to providing new opportunities in single-molecule spectroscopy and imaging, BBM represents a new take on single-molecule research, where blinking dynamics can be harnessed for more than just traditional localization or nanoreporting. 
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    Free, publicly-accessible full text available April 1, 2024
  4. We explore the statistical radio frequency interference (RFI) mitigation technique spectral kurtosis (SK) in the context of simulated realistic RFI signals. SK is a per-channel RFI detection metric that estimates the kurtosis of a collection of M power values in a single channel to discern between human-made RFI and incoherent astronomical signals of interest. We briefly test the ability of SK to flag signals with various representative modulation types, data rates, and duty cycles, as well as accumulation lengths M and multi-scale SK bin shapes. Multi-scale SK uses a rolling window to combine information from adjacent time-frequency pixels to mitigate weaknesses in single-scale SK. High data rate RFI signals with significant sidelobe emission are harder to flag, as well as signals with a 50% effective duty cycle. Multi-scale SK using at least one extra channel can detect both the center channel and side-band interference, flagging most of the signal at the expense of larger false positive rates. 
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  5. A cyclostationary process is one whose autocorrelation function is periodic or nearly periodic. The modulation schemes used to encode information give rise to cyclostationarity in many human-generated sources of interference. In contrast, nearly all astrophysical signals are expected to be wide-sense stationary on timescales of interest, making cyclostationarity a potentially robust way of discriminating between interference and astronomical sources. We are developing an algorithm that employs a well-known method of detecting cyclostationary signals and testing its efficacy against a suite of simulated interference covering a wide range of modulation schemes. We present receiver operating characteristic curves and binary classification scores for different types of interfering signals. Our algorithm performs well for many modulation schemes, with F1 and φ coefficient scores in excess of 0.9 in some cases, though it shows weaknesses in the case of frequency modulation. We also apply our algorithm to archived Robert C. Byrd Green Bank Telescope observations of a bright millisecond pulsar. We use standard pipelines for blindly detecting and timing pulsars and preliminarily find improvement in data quality according to several metrics, though some undesirable effects are still present. We also show that our algorithm has no negative impact when detecting Galactic HI emission. We thus believe that cyclostationary signal processing shows promise as a means of interference mitigation and discuss opportunities and challenges for employing it more widely. 
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  6. Abstract

    We investigate the effectiveness of the statistical radio frequency interference (RFI) mitigation technique spectral kurtosis (SK^) in the face of simulated realistic RFI signals.SK^estimates the kurtosis of a collection ofMpower values in a single channel and provides a detection metric that is able to discern between human-made RFI and incoherent astronomical signals of interest. We test the ability ofSK^to flag signals with various representative modulation types, data rates, duty cycles, and carrier frequencies. We flag with various accumulation lengthsMand implement multiscaleSK^, which combines information from adjacent time-frequency bins to mitigate weaknesses in single-scaleSK^. We find that signals with significant sidelobe emission from high data rates are harder to flag, as well as signals with a 50% effective duty cycle and weak signal-to-noise ratios. MultiscaleSK^with at least one extra channel can detect both the center channel and sideband interference, flagging greater than 90% as long as the bin channel width is wider in frequency than the RFI.

     
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  7. In an effort to design deep-blue light emitting materials for use in OLEDs, the optical and electronic properties of a series of tetraarylbenzobis[1,2- d :4,5- d ′]oxazole (BBO) cruciforms were evaluated using density functional theory (DFT) and time-dependent DFT (TD-DFT). Of the nine possible combinations of phenyl-, furan-2-yl-, and thiophen-2-yl-substituted BBO cruciforms, five were predicted to have ideal optical and electronic properties for use in blue-light emitting diodes. These five cruciforms were synthesized and then characterized electrochemically and spectroscopically. Additionally, they were solution-processed into functional organic light-emitting diodes (OLED). Several of the OLEDs exhibited deep-blue EL ( λ EL < 452 nm; CIE y ≤ 0.12) with maximum luminance efficacies reaching 0.39 lm W −1 and maximum current efficiencies of 0.59 cd A −1 . A comparison of identical device architectures showed that heterocycles such as furan and thiophene helped improve device efficiencies with only a minor red-shift of the electroluminescence (EL). Although these BBO cruciforms produced the desired deep-blue emission their modest performance in host–guest OLEDs demonstrates the incorporation of heterocycles onto the BBO cruciform motif is detrimental to the fluroescence quantum yield. These results add to the knowledge base on structure–property relationships that will inform the design of better blue emitting materials. 
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  8. null (Ed.)
    The 74 ka Youngest Toba Tuff (YTT) was discovered as cryptotephra in South African archaeological sites at Pinnacle Point (PP) 5-6N, Vleesbaai [1] and Klasies River on the Indian Ocean, and the Diepkloof Rock Shelter on the Atlantic coast nearly 750 km west of PP. The YTT eruption distributed tephra across eastern and southern Africa and provides a widespread isochron useful for dating archaeological deposits, testing age models, and precisely determining the timing of changes in human behavior. At PP, we demonstrated that the MIS 4-5 transition began just before the YTT eruption. Humans thrived both through the YTT event and the changing climate, and important changes in technology occurred just after the Toba eruption [1]. Controversy related to trapped charge age models at the Diepkloof rock shelter [2,3] were resolved by identifying YTT at a location in the stratigraphic section that confirmed the Jacobs et al. [2] model for the site, confirming that technological changes similar to those observed at PP occurred synchronously to those at Diepkloof, not substantially before as suggested by a prior published age model [3]. Processing samples with very low abundance cryptotephra, such as that found in South Africa, is a challenge and requires revision of standard laboratory techniques. Samples with high organic or clay content benefit by being treated with 10% HCl and 3% hydrogen peroxide (H2O2). This step does not degrade shard integrity or affect chemistry and is useful in separating shards from clay and organic particles allowing better recovery in heavy liquids. We also modified the heavy liquid density range from 1.95 - 2.55 to 2.2 - 2.5 g/cm3 to more effectively remove quartz and feldspar as well as biogenic silica. This density range captures shards ranging from rhyolite to dacite in composition. [1] Smith, E. I. et al. Nature 555, 511, 2018 [2] Jacobs, Z. & Roberts, R. G. Journal of Archaeological Science 63, 175-192, 2015. [3] Tribolo, C. et al. Journal of Archaeological Science 40, 3401-3411 2013. 
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  9. Winemiller, KO. (Ed.)
    The widespread importance of variable types of primary production, or energy channels, to consumer communities has become increasingly apparent. However, the mechanisms underlying this “multichannel” feeding remain poorly understood, especially for aquatic ecosystems that pose unique logistical constraints given the diversity of potential energy channels. Here, we use bulk tissue isotopic analysis along with carbon isotope (δ13C) analysis of individual amino acids to characterize the relative contribution of pelagic and benthic energy sources to a kelp forest consumer community in northern Chile. We measured bulk tissue δ13C and δ15N for >120 samples; of these we analyzed δ13C values of six essential amino acids (EAA) from nine primary producer groups (n = 41) and 11 representative nearshore consumer taxa (n = 56). Using EAA δ13C data, we employed linear discriminant analysis (LDA) to assess how distinct EAA δ13C values were between local pelagic (phytoplankton/particulate organic matter), and benthic (kelps, red algae, and green algae) endmembers. With this model, we were able to correctly classify nearly 90% of producer samples to their original groupings, a significant improvement on traditional bulk isotopic analysis. With this EAA isotopic library, we then generated probability distributions for the most important sources of production for each individual consumer and species using a bootstrap‐resampling LDA approach. We found evidence for multichannel feeding within the community at the species level. Invertebrates tended to focus on either pelagic or benthic energy, deriving 13–67% of their EAA from pelagic sources. In contrast, mobile (fish) taxa at higher trophic levels used more equal proportions of each channel, ranging from 19% to 47% pelagically derived energy. Within a taxon, multichannel feeding was a result of specialization among individuals in energy channel usage, with 37 of 56 individual consumers estimated to derive >80% of their EAA from a single channel. Our study reveals how a cutting‐edge isotopic technique can characterize the dynamics of energy flow in coastal food webs, a topic that has historically been difficult to address. More broadly, our work provides a mechanism as to how multichannel feeding may occur in nearshore communities, and we suggest this pattern be investigated in additional ecosystems. 
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