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  1. Abstract The coupling between superconductors and oscillation cycles of light pulses, i.e., lightwave engineering, is an emerging control concept for superconducting quantum electronics. Although progress has been made towards terahertz-driven superconductivity and supercurrents, the interactions able to drive non-equilibrium pairing are still poorly understood, partially due to the lack of measurements of high-order correlation functions. In particular, the sensing of exotic collective modes that would uniquely characterize light-driven superconducting coherence, in a way analogous to the Meissner effect, is very challenging but much needed. Here we report the discovery of parametrically driven superconductivity by light-induced order-parameter collective oscillations in iron-based superconductors. The time-periodic relative phase dynamics between the coupled electron and hole bands drives the transition to a distinct parametric superconducting state out-of-equalibrium. This light-induced emergent coherence is characterized by a unique phase–amplitude collective mode with Floquet-like sidebands at twice the Higgs frequency. We measure non-perturbative, high-order correlations of this parametrically driven superconductivity by separating the terahertz-frequency multidimensional coherent spectra into pump–probe, Higgs mode and bi-Higgs frequency sideband peaks. We find that the higher-order bi-Higgs sidebands dominate above the critical field, which indicates the breakdown of susceptibility perturbative expansion in this parametric quantum matter.
    Free, publicly-accessible full text available December 5, 2023
  2. Free, publicly-accessible full text available January 19, 2024
  3. N/A (Ed.)
    For more than a century, Classical Nucleation Theory (CNT) has been used to explain the process of crystallization in supersaturated solutions. According to CNT, nucleation is a single-step process that occurs via monomer-by-monomer addition. However, recent findings from experiments and numerical simulations have shown that nucleation is a multi-step process that occurs via more complex pathways that involve intermediate species such as ion complexes, dense liquid precursors, or even nanocrystals. Such non-classical pathways observed in protein solutions, colloidal suspensions and electrolytes are reviewed in this paper. The formation of stable Pre-nucleation Clusters (PNCs) in the crystallization of biominerals is also discussed. In spite of the mounting evidence for non-classical nucleation behaviors, the knowledge about the structural evolution of the intermediate phases and their role in polymorph selection is still limited. It has also been observed that gravitational force interferes with the crystallization behavior of materials thereby posing limitation to ground-based experiments. Microgravity conditions, coupled with containerless processing techniques provide a suitable alternative to overcome these limitations.
    Free, publicly-accessible full text available July 31, 2023
  4. This paper presents a wireless and stand-alone subminiature propeller based on acoustic propulsion for the underwater robotic applications. The acoustic propulsion is generated by a MEMS-based self-focusing acoustic transducer (SFAT), fabricated on 1-mm-thick lead zirconate titanate (PZT) substrate, and operated at its thickness mode resonant frequency of 2.32 MHz. A 100F lithium-ion capacitor (LIC) is used as a power source due to its high energy and power densities. A drive electronic circuit is implemented on a flexible printed circuit board (PCB) and delivers 30Vpp sinusoidal signal to the acoustic propeller. The completed system is 18 x 18 x 38 mm3 in volume and weighs 12.56 grams, resulting in a mass density of 1.020 g/cm3. The acoustic propulsion generated by the acoustic propeller is measured to be 18.68μN with the electrical power of 358.7mW consumed by the propeller. Both vertical and horizontal propulsions are demonstrated successfully in sodium polytungstate (SPT) solution.
    Free, publicly-accessible full text available June 5, 2023
  5. Rotating machines, such as pumps and compressors, are critical components in refineries and chemical plants used to transport fluids between processing units. Bearings are often the critical parts of rotating machinery, and their failure could result in economic loss and/or safety issues. Therefore, estimation of the remaining useful life (RUL) of a bearing plays an important role in reducing production losses and avoiding machine damage. Because bearing failure mechanisms tend to be complex and stochastic, data-driven RUL estimation approaches have found more applications. This work proposes a novel RUL estimation method based on systematic feature engineering and extreme learning machine (ELM). The PRONOSTIA dataset is used to demonstrate the effectiveness of the proposed method.
    Free, publicly-accessible full text available June 1, 2023
  6. Free, publicly-accessible full text available June 29, 2023
  7. Abstract We use a high-precision radial velocity survey of FGKM stars to study the conditional occurrence of two classes of planets: close-in small planets (0.023–1 au, 2–30 M ⊕ ) and distant giant planets (0.23–10 au, 30–6000 M ⊕ ). We find that 41 − 13 + 15 % of systems with a close-in, small planet also host an outer giant, compared to 17.6 − 1.9 + 2.4 % for stars irrespective of small planet presence. This implies that small planet hosts may be enhanced in outer giant occurrences compared to all stars with 1.7 σ significance. Conversely, we estimate that 42 − 13 + 17 % of cold giant hosts also host an inner small planet, compared to 27.6 − 4.8 + 5.8 % of stars irrespective of cold giant presence. We also find that more massive and close-in giant planets are not associated with small inner planets. Specifically, our sample indicates that small planets are less likely to have outer giant companions more massive than approximately 120 M ⊕ and within 0.3–3 au, than to have less massive or more distant giant companions, with ∼2.2 σ confidence. This implies that massive gas giants within 0.3–3 au may suppressmore »inner small planet formation. Additionally, we compare the host-star metallicity distributions for systems with only small planets and those with both small planets and cold giants. In agreement with previous studies, we find that stars in our survey that only host small planets have a metallicity distribution that is consistent with the broader solar-metallicity-median sample, while stars that host both small planets and gas giants are distinctly metal rich with ∼2.3 σ confidence.« less
    Free, publicly-accessible full text available August 17, 2023
  8. The electrochemical doping/dedoping kinetics, and the organic electrochemical transistor (OECT) performance of a series of polythiophene homopolymers with ethylene glycol units in their side chains using both kosmotropic and chaotropic anion solutions were studied. We compare their performance to a reference polymer, the polythiophene derivative with diethylene glycol side chains, poly(3-{[2-(2-methoxyethoxy)ethoxy]methyl}thiophene-2,5-diyl) (P3MEEMT). We find larger OECT material figure of merit, μC *, where μ is the carrier mobility and C * is the volumetric capacitance, and faster doping kinetics with more oxygen atoms on the side chains, and if the oxygen atom is farther from the polythiophene backbone. Replacing the oxygen atom close to the polythiophene backbone with an alkyl unit increases the film π-stacking crystallinity (higher electronic conductivity in the undoped film) but sacrifices the available doping sites (lower volumetric capacitance C * in OECT). We show that this variation in C * is the dominant factor in changing the μC * product for this family of polymers. With more oxygen atoms on the side chain, or with the oxygen atom farther from the polymer backbone, we observe both more passive swelling and higher C *. In addition, we show that, compared to the doping speed, the dedoping speed,more »as measured via spectroelectrochemistry, is both generally faster and less dependent on ion species or side chain oxygen content. Last, through OECT, electrochemical impedance spectroscopy (EIS) and spectroelectrochemistry measurements, we show that the chaotropic anion PF 6 − facilitates higher doping levels, faster doping kinetics, and lower doping thresholds compared to the kosmotropic anion Cl − , although the exact differences depend on the polymer side chains. Our results highlight the importance of balancing μ and C * when designing molecular structures for OECT active layers.« less
    Free, publicly-accessible full text available May 17, 2023
  9. When a group member commits wrongdoing, people sometimes assign responsibility and blame not only to the wrongdoer but also to other members of the same group. We examined such assignment of collective responsibility in the context of exploitation of one family by another. Participants were recruited from the United States and South Korea, which are known to vary in cultural norms and endorsement of collectivistic values. Participants in both countries rated the degree to which an agent (grandson) should be held responsible for his grandfather’s exploitation of a victimized family, while varying the closeness of familial connection. Participants’ responsibility judgments showed sensitivity to whether the grandson received financial benefit from the wrongdoer and to the perceived closeness between the grandson and the wrongdoer. Korean participants imposed greater responsibility on the agent than did American participants. Implications for understanding the influence of social norms on moral judgments are discussed.
  10. In offline reinforcement learning (RL), a learner leverages prior logged data to learn a good policy without interacting with the environment. A major challenge in applying such methods in practice is the lack of both theoretically principled and practical tools for model selection and evaluation. To address this, we study the problem of model selection in offline RL with value function approximation. The learner is given a nested sequence of model classes to minimize squared Bellman error and must select among these to achieve a balance between approximation and estimation error of the classes. We propose the first model selection algorithm for offline RL that achieves minimax rate-optimal oracle inequalities up to logarithmic factors. The algorithm, MODBE, takes as input a collection of candidate model classes and a generic base offline RL algorithm. By successively eliminating model classes using a novel one-sided generalization test, MODBE returns a policy with regret scaling with the complexity of the minimally complete model class. In addition to its theoretical guarantees, it is conceptually simple and computationally efficient, amounting to solving a series of square loss regression problems and then comparing relative square loss between classes. We conclude with several numerical simulations showing it ismore »capable of reliably selecting a good model class.« less