Abstract
The characteristic excitation of a metal is its plasmon, which is a quantized collective oscillation of its electron density. In 1956, David Pines predicted that a distinct type of plasmon, ...dubbed a ‘demon’, could exist in three-dimensional (3D) metals containing more than one species of charge carrier
1
. Consisting of out-of-phase movement of electrons in different bands, demons are acoustic, electrically neutral and do not couple to light, so have never been detected in an equilibrium, 3D metal. Nevertheless, demons are believed to be critical for diverse phenomena including phase transitions in mixed-valence semimetals
2
, optical properties of metal nanoparticles
3
, soundarons in Weyl semimetals
4
and high-temperature superconductivity in, for example, metal hydrides
3,5–7
. Here, we present evidence for a demon in Sr
2
RuO
4
from momentum-resolved electron energy-loss spectroscopy. Formed of electrons in the
β
and
γ
bands, the demon is gapless with critical momentum
q
c
= 0.08 reciprocal lattice units and room-temperature velocity
v
= (1.065 ± 0.12) × 10
5
m s
−1
that undergoes a 31% renormalization upon cooling to 30 K because of coupling to the particle–hole continuum. The momentum dependence of the intensity of the demon confirms its neutral character. Our study confirms a 67-year old prediction and indicates that demons may be a pervasive feature of multiband metals.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
China finally underwent its modernizing (i.e., with increased labor productivity and incomes) agricultural revolution in 1980 to 2010, through dynamics unlike those of most other previous ...agricultural revolutions. It is "hidden" because the revolution has not come so much from the conventional and readily apparent increases of certain crops' output by weight due to new inputs, but rather mainly by the switch from grain production to more and more higher-value agricultural products like meat-poultry-fish, milk-eggs, and fruits and higher grade vegetables. That change has been driven by a revolution in the food consumption patterns of the Chinese people that came with rising incomes mainly from nonagricultural development. A comparison of China's agricultural history with others tells about the interactions of multiple factors, not just the role of markets and/or technology, or property systems, but rather their interactions with population-to-land resource endowments, differential rural-urban relations, state actions, and historical coincidences. China's is in fact most like India's, rather than "East Asia's," though even then with important differences stemming from its revolutionary legacies.
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The bulk-heterojunction blend of an electron donor and an electron acceptor material is the key component in a solution-processed organic photovoltaic device. In the past decades, a p-type conjugated ...polymer and an n-type fullerene derivative have been the most commonly used electron donor and electron acceptor, respectively. While most advances of the device performance come from the design of new polymer donors, fullerene derivatives have almost been exclusively used as electron acceptors in organic photovoltaics. Recently, nonfullerene acceptor materials, particularly small molecules and oligomers, have emerged as a promising alternative to replace fullerene derivatives. Compared to fullerenes, these new acceptors are generally synthesized from diversified, low-cost routes based on building block materials with extraordinary chemical, thermal, and photostability. The facile functionalization of these molecules affords excellent tunability to their optoelectronic and electrochemical properties. Within the past five years, there have been over 100 nonfullerene acceptor molecules synthesized, and the power conversion efficiency of nonfullerene organic solar cells has increased dramatically, from ∼2% in 2012 to >13% in 2017. This review summarizes this progress, aiming to describe the molecular design strategy, to provide insight into the structure–property relationship, and to highlight the challenges the field is facing, with emphasis placed on most recent nonfullerene acceptors that demonstrated top-of-the-line photovoltaic performances. We also provide perspectives from a device point of view, wherein topics including ternary blend device, multijunction device, device stability, active layer morphology, and device physics are discussed.
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IJS, KILJ, NUK, PNG, UL, UM
We report a novel small molecule acceptor (SMA) named FTTB-PDI4 obtained via ring-fusion between the thiophene and perylene diimide (PDI) units of a PDI-tetramer with a tetrathienylbezene (TTB) core. ...A small voltage loss of 0.53 V and a high power conversion efficiency of 10.58% were achieved, which is the highest value reported for PDI-based devices to date. By comparing the fused and nonfused SMAs, we show that the ring-fusion introduces several beneficial effects on the properties and performances of the acceptor material, including more favorable energy levels, enhanced light absorption and stronger intermolecular packing. Interestingly, morphology data reveal that the fused molecule yields higher domain purity and thus can better maintain its molecular packing and electron mobility in the blend. Theoretical calculations also demonstrate that FTTB-PDI4 exhibits a “double-decker” geometry with two pairs of mostly parallel PDI units, which is distinctively different from reported PDI-tetramers with highly twisted geometries and can explain the better performance of the material. This work highlights the promising design of PDI-based acceptors by the ring-fusion strategy.
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This article proposes a novel control strategy based on a broad fuzzy neural network (BFNN) which is subjected to contact with the unknown environment. Compared with the conventional fuzzy neural ...network (NN), a prominent feature can be achieved by taking the advantage of the broad learning system (BLS) to explicitly tackle the problem of how to choose a sufficient number of NN units to approximate the unknown dynamic model. Aiming at providing a soft compliant contact scheme without the requirement of the environment model, an adaptive impedance learning is developed to establish the optimal interaction between the robot and the environment. Meanwhile, the problems related to the state constraints are addressed by incorporating a barrier Lyapunov function (BLF) into the design of a trajectory tracking controller. The proposed method can achieve desired tracking and interaction performance while guaranteeing the stability of the closed-loop system. In addition, simulation and experimental studies are performed to verify the effectiveness of BFNN under optimal impedance control with a two degree-of-freedom (DOF) manipulator and a Baxter robot, respectively.
In socialist China today, neoliberal economics has actually come to wield institutionalized hegemonic power in academic evaluations of economic studies, while in neoliberal America, there is ...ironically considerably more pluralism in the practice of academic evaluations of economic studies. The origins of this state of affairs lie not in just a simple matter of ideology or policy choices, but rather in different tendencies in the operative practices of two different systems of governance. While China leans strongly toward centralized bureaucratism, along with scientism and numericism, the United States leans more toward multicentered pluralistic practices. Regardless, what scholarship needs is pluralistic contention for sustained long-term development.
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Chayanov, outside of his theoretical analysis of how peasant households are distinctive for being at once a production and a consumption unit and the multiple implications of that fact, has made two ...other major theoretical contributions, one making clear that peasant economies observe the logic of “differential optimums” rather than the simple logic of economies of scale and the other having to do with the need for co-operatives for “vertical integration” of small peasant economies in order to preserve for the peasants more of the value of their products in the BIG MARKET. The former can be readily observed in the “new agriculture revolution” of the Chinese economy in the past few decades; the latter can be readily seen in the striking modernization of the “East Asian” (i.e., Japan, South Korea, and the Taiwan area) economies since 1945. China’s annual “Number One Documents” about agriculture of the past two decades have shown how the country first mistakenly tried to imitate the simple scale-economy logic of the United States and then shifted since 2018 toward a new emphasis on the peasants as the principal agents of agricultural development and peasant villages as the basic unit for agricultural co-ops. Those have been the basis for new advances as well as for reinterpretations and modifications of Chayanov’s two major theoretical visions.
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In this paper, a strategy of asymmetric alkyl and alkoxy substitution is applied to state‐of‐the‐art Y‐series nonfullerene acceptors (NFAs), and it achieves great performance in organic solar cell ...(OSC) devices. Since alkoxy groups can have a significant influence on the material properties of NFAs, alkoxy substitution is applied to the Y6 molecule in a symmetric manner. The resulting molecule (named Y6‐2O), despite showing improved open‐circuit voltage (Voc), yields extremely poor performance due to low solubility and excessive aggregation properties, a change that is due to the conformational locking effect of alkoxy groups. In contrast, asymmetric alkyl and alkoxy substitution on Y6, yields a molecule named Y6‐1O that can maintain the positive effect of Voc improvement and obtain reasonably good solubility. The resulting molecule Y6‐1O enables highly efficient nonfullerene OSCs with 17.6% efficiency and the asymmetric side‐chain strategy has the potential to be applied to other NFA‐material systems to further improve their performance.
Novel asymmetric alkoxy and alkyl substitutions on the well‐known nonfullerene acceptor Y6 yield a molecule named Y6‐1O, and its photoelectric properties and photovoltaic performance are systematically compared with the two related symmetric molecules (Y6 and Y6‐2O), which suggests that this design strategy is promising and effective.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Kenneth Pomeranz and Li Bozhong have recently conceded that they had been wrong that “the great divergence” between China and the West occurred only after 1800, but they continue to insist that when ...it came to agriculture and its labor productivity, their earlier argument still holds. This article summarizes the broad differences between eighteenth-century England’s crops cum animal husbandry agriculture and China’s crops-only agriculture to demonstrate the fundamental differences between the two. It is time we recognize fully how very different the two were and are, and how and why each follows an entirely different pattern to modern development. It is simply wrong to continue to obscure those basic differences by insisting on equivalence between them.
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The “theory of practice” was developed mainly in order to rise above the common tendency to treat the subjective and the objective as an either/or binary. We might rely mainly on subjective ...presuppositions to arrive at our scholarly conclusions, or engage only in the compilation and accumulation of empirical evidence, but practice is unavoidably born of the interaction between the two dimensions. Precisely for this reason, we suggest that scholarly research proceed from actual practice, in order to rise above the either/or subjective/objective binary, and attend to both theoretical construction and empirical discovery, to focus deliberately on the inter-relating of the two. This article attempts to use actual scholarly practices as concrete examples to illustrate what is meant by the “social science of practice” approach to research.
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