524 research outputs found
Exponential Qubit Reduction in Optimization for Financial Transaction Settlement
We extend the qubit-efficient encoding presented in [Tan et al., Quantum 5,
454 (2021)] and apply it to instances of the financial transaction settlement
problem constructed from data provided by a regulated financial exchange. Our
methods are directly applicable to any QUBO problem with linear inequality
constraints. Our extension of previously proposed methods consists of a
simplification in varying the number of qubits used to encode correlations as
well as a new class of variational circuits which incorporate symmetries,
thereby reducing sampling overhead, improving numerical stability and
recovering the expression of the cost objective as a Hermitian observable. We
also propose optimality-preserving methods to reduce variance in real-world
data and substitute continuous slack variables. We benchmark our methods
against standard QAOA for problems consisting of 16 transactions and obtain
competitive results. Our newly proposed variational ansatz performs best
overall. We demonstrate tackling problems with 128 transactions on real quantum
hardware, exceeding previous results bounded by NISQ hardware by almost two
orders of magnitude.Comment: 16 pages, 8 figure
ARtonomous: Introducing Middle School Students to Reinforcement Learning Through Virtual Robotics
Typical educational robotics approaches rely on imperative programming for
robot navigation. However, with the increasing presence of AI in everyday life,
these approaches miss an opportunity to introduce machine learning (ML)
techniques grounded in an authentic and engaging learning context. Furthermore,
the needs for costly specialized equipment and ample physical space are
barriers that limit access to robotics experiences for all learners. We propose
ARtonomous, a relatively low-cost, virtual alternative to physical,
programming-only robotics kits. With ARtonomous, students employ reinforcement
learning (RL) alongside code to train and customize virtual autonomous robotic
vehicles. Through a study evaluating ARtonomous, we found that middle-school
students developed an understanding of RL, reported high levels of engagement,
and demonstrated curiosity for learning more about ML. This research
demonstrates the feasibility of an approach like ARtonomous for 1) eliminating
barriers to robotics education and 2) promoting student learning and interest
in RL and ML.Comment: In Proceedings of Interaction Design and Children (IDC '22
Investigating the igneous petrogenesis of Martian volcanic rocks using augite quantitative textural analysis of the Yamato nakhlites
To better understand volcanism on planetary bodies other than the Earth, the quantification of physical processes is needed. Here, the petrogenesis of the achondrite Martian Yamato (Y) nakhlites (Y 000593, Y 000749, and Y 000802) is reinvestigated via quantitative analysis of augite (high-Ca clinopyroxene) phenocrysts: crystal size distribution (CSD), spatial distribution patterns (SDP), and electron backscatter diffraction (EBSD). Results from CSD and EBSD quantitative data sets show augite to have continuous uninterrupted growth resulting in calculated minimum magma chamber residence times of either 88–117 ± 6 yr or 9–12 yr. All samples exhibit low-intensity S-LS type crystallographic preferred orientation. Directional strain is observed across all samples with intracrystalline misorientation patterns indicative of (100)[001]:(001)[100] (Y 000593 and Y 000802) and {110}<001>or {110}1/2<110> (Y 000749) slip systems. SDP results indicate phenocryst-bearing crystal-clustered rock signatures. Combined findings from this work show that the Yamato nakhlites formed on Mars as individual low-viscosity lava flows or sills. This study shows that through combining these different quantitative techniques over multiple samples, one can more effectively compare and interpret resulting data to gain a more robust, geologically contextualized petrogenetic understanding of the rock suite being studied. The techniques used in this study should be equally applicable to igneous achondrites from other parent bodies
Diversity and abundance of phosphonate biosynthetic genes in nature
Phosphonates, molecules containing direct carbon–phosphorus bonds, compose a structurally diverse class of natural products with interesting and useful biological properties. Although their synthesis in protozoa was discovered more than 50 y ago, the extent and diversity of phosphonate production in nature remains poorly characterized. The rearrangement of phosphoenolpyruvate (PEP) to phosphonopyruvate, catalyzed by the enzyme PEP mutase (PepM), is shared by the vast majority of known phosphonate biosynthetic pathways. Thus, the pepM gene can be used as a molecular marker to examine the occurrence and abundance of phosphonate-producing organisms. Based on the presence of this gene, phosphonate biosynthesis is common in microbes, with ∼5% of sequenced bacterial genomes and 7% of genome equivalents in metagenomic datasets carrying pepM homologs. Similarly, we detected the pepM gene in ∼5% of random actinomycete isolates. The pepM-containing gene neighborhoods from 25 of these isolates were cloned, sequenced, and compared with those found in sequenced genomes. PEP mutase sequence conservation is strongly correlated with conservation of other nearby genes, suggesting that the diversity of phosphonate biosynthetic pathways can be predicted by examining PEP mutase diversity. We used this approach to estimate the range of phosphonate biosynthetic pathways in nature, revealing dozens of discrete groups in pepM amplicons from local soils, whereas hundreds were observed in metagenomic datasets. Collectively, our analyses show that phosphonate biosynthesis is both diverse and relatively common in nature, suggesting that the role of phosphonate molecules in the biosphere may be more important than is often recognized
Individual differences in self-affirmation: distinguishing self-affirmation from positive self-regard
Research into self-affirmation has almost exclusively employed experimental manipulations. In this paper we address individual differences in the tendency to respond to threats with self-affirming cognitions and distinguish this from two overlapping constructs: habitual positive self-thought and trait self-esteem. Items we designed to measure self-affirmation were represented by three first-order factors and loaded on a higher-order factor, creating the Spontaneous Self-Affirmation Measure (SSAM). The SSAM correlated moderately with self-esteem and habitual positive self-thought. In competitive analyses, the SSAM was an independent predictor of a large number of outcomes. The studies provide evidence about the correlates of individual differences in reported spontaneous self-affirmation in response to threat and the contribution made to this response by habitual positive self-thought and trait self-esteem
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RNA exosome mutations in pontocerebellar hypoplasia alter ribosome biogenesis and p53 levels.
The RNA exosome is a ubiquitously expressed complex of nine core proteins (EXOSC1-9) and associated nucleases responsible for RNA processing and degradation. Mutations in EXOSC3, EXOSC8, EXOSC9, and the exosome cofactor RBM7 cause pontocerebellar hypoplasia and motor neuronopathy. We investigated the consequences of exosome mutations on RNA metabolism and cellular survival in zebrafish and human cell models. We observed that levels of mRNAs encoding p53 and ribosome biogenesis factors are increased in zebrafish lines with homozygous mutations of exosc8 or exosc9, respectively. Consistent with higher p53 levels, mutant zebrafish have a reduced head size, smaller brain, and cerebellum caused by an increased number of apoptotic cells during development. Down-regulation of EXOSC8 and EXOSC9 in human cells leads to p53 protein stabilisation and G2/M cell cycle arrest. Increased p53 transcript levels were also observed in muscle samples from patients with EXOSC9 mutations. Our work provides explanation for the pathogenesis of exosome-related disorders and highlights the link between exosome function, ribosome biogenesis, and p53-dependent signalling. We suggest that exosome-related disorders could be classified as ribosomopathies
A report of dangerously high carbon monoxide levels within the passenger compartment of a snow-obstructed vehicle
BACKGROUND: We sought to determine how quickly carbon monoxide would accumulate in the passenger compartment of a snow-obstructed vehicle. METHODS: A 1992 sedan was buried in snow to the level of the undercarriage, the ignition was then engaged and carbon monoxide levels recorded at 2.5-minute intervals. The primary outcome was the time at which a lethal carbon monoxide level was detected. Six trials were conducted: windows closed; windows open one inch; windows open 6 inches; windows closed and tailpipe swept clear of snow; windows closed and one cubic foot of snow removed around tailpipe; windows closed and tailpipe completely cleared of snow to ground level in a path 12 inches wide. RESULTS: Lethal levels of carbon monoxide occurred within 2.5 minutes in the vehicle when the windows were closed, within 5 minutes when the widows were opened one inch, and within 7.5 minutes when the widows were opened six inches. Dangerously high levels of carbon monoxide were detected within the vehicle when the tailpipe had been swept clear of snow and when a one cubic foot area had been cleared around the tailpipe. When the tailpipe was completely unobstructed the carbon monoxide level was zero. CONCLUSIONS: Lethal levels of carbon monoxide occurred within minutes in this snow-obstructed vehicle
The PHASES Differential Astrometry Data Archive. III. Limits to Tertiary Companions
The Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES)
monitored 51 subarcsecond binary systems to evaluate whether tertiary
companions as small as Jovian planets orbited either the primary or secondary
stars, perturbing their otherwise smooth Keplerian motions. Twenty-one of those
systems were observed 10 or more times and show no evidence of additional
companions. A new algorithm is presented for identifying astrometric companions
and establishing the (companion mass)-(orbital period) combinations that can be
excluded from existence with high confidence based on the PHASES observations,
and the regions of mass-period phase space being excluded are presented for 21
PHASES binaries.Comment: 16 pages, Accepted to A
European and Mediterranean hydroclimate responses to tropical volcanic forcing over the last millennium
Volcanic eruptions have global climate impacts, but their effect on the hydrologic cycle is poorly understood. We use a modified version of superposed epoch analysis, an eruption year list collated from multiple data sets, and seasonal paleoclimate reconstructions (soil moisture, precipitation, geopotential heights, and temperature) to investigate volcanic forcing of spring and summer hydroclimate over Europe and the Mediterranean over the last millennium. In the western Mediterranean, wet conditions occur in the eruption year and the following 3 years. Conversely, northwestern Europe and the British Isles experience dry conditions in response to volcanic eruptions, with the largest moisture deficits in posteruption years 2 and 3. The precipitation response occurs primarily in late spring and early summer (April–July), a pattern that strongly resembles the negative phase of the East Atlantic Pattern. Modulated by this mode of climate variability, eruptions force significant, widespread, and heterogeneous hydroclimate responses across Europe and the Mediterranean
Plant responses to fertilization experiments in lowland, species-rich, tropical forests.
We present a meta-analysis of plant responses to fertilization experiments conducted in lowland, species-rich, tropical forests. We also update a key result and present the first species-level analyses of tree growth rates for a 15-yr factorial nitrogen (N), phosphorus (P), and potassium (K) experiment conducted in central Panama. The update concerns community-level tree growth rates, which responded significantly to the addition of N and K together after 10 yr of fertilization but not after 15 yr. Our experimental soils are infertile for the region, and species whose regional distributions are strongly associated with low soil P availability dominate the local tree flora. Under these circumstances, we expect muted responses to fertilization, and we predicted species associated with low-P soils would respond most slowly. The data did not support this prediction, species-level tree growth responses to P addition were unrelated to species-level soil P associations. The meta-analysis demonstrated that nutrient limitation is widespread in lowland tropical forests and evaluated two directional hypotheses concerning plant responses to N addition and to P addition. The meta-analysis supported the hypothesis that tree (or biomass) growth rate responses to fertilization are weaker in old growth forests and stronger in secondary forests, where rapid biomass accumulation provides a nutrient sink. The meta-analysis found no support for the long-standing hypothesis that plant responses are stronger for P addition and weaker for N addition. We do not advocate discarding the latter hypothesis. There are only 14 fertilization experiments from lowland, species-rich, tropical forests, 13 of the 14 experiments added nutrients for five or fewer years, and responses vary widely among experiments. Potential fertilization responses should be muted when the species present are well adapted to nutrient-poor soils, as is the case in our experiment, and when pest pressure increases with fertilization, as it does in our experiment. The statistical power and especially the duration of fertilization experiments conducted in old growth, tropical forests might be insufficient to detect the slow, modest growth responses that are to be expected
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