288 research outputs found
Experimental study on flow-induced motion and energy conversion for two triangular prisms in tandem arrangement
Experimental tests on two tandem triangular prisms were accomplished in synergistic flow-induced motion (FIM) to collect ocean current energy (OCE) with varied spacing ratios and Reynolds number ranges. Typical FIM responses and energy conversion are discussed and presented. The effects of parameters (system stiffness, spacing ratio, and load resistance) were considered to improve the energy harvesting of the system. The main findings can be summarized as follows: 1) with varied spacing ratios between the two tandem prisms, the active power (Pharn) was up to 1.95 times that of the single triangular prism (STP); 2) In general, the harnessed OCE capacity of the upstream triangular prism (UTP) was improved, while the energy harvesting of the downstream triangular prism (DTP) was suppressed by the interaction of the two prisms, 3) In the tests, electricity was generated at U = 0.516 m/s, and the active power, which consistently increased as flow velocity increased, reached Pharn = 32.24 W, with a corresponding efficiency of ηharn = 10.31%; and 4) The best energy conservation performance for harvesting the OCE occurred at L/D = 5, and the optimal load resistance was found at RL = 11 Ω
The Mollow triplets under few-photon excitation
Resonant excitation is an essential tool in the development of semiconductor
quantum dots (QDs) for quantum information processing. One central challenge is
to enable a transparent access to the QD signal without post-selection
information loss. A viable path is through cavity enhancement, which has
successfully lifted the resonantly scattered field strength over the laser
background under \emph{weak} excitation. Here, we extend this success to the
\emph{saturation} regime using a QD-micropillar device with a Purcell factor of
10.9 and an ultra-low background cavity reflectivity of just 0.0089. We achieve
a signal to background ratio of 50 and an overall system responsivity of 3~\%,
i.e., we detect on average 0.03 resonantly scattered single photons for every
incident laser photon. Raising the excitation to the few-photon level, the QD
response is brought into saturation where we observe the Mollow triplets as
well as the associated cascade single photon emissions, without resort to any
laser background rejection technique. Our work offers a new perspective toward
QD cavity interface that is not restricted by the laser background.Comment: 8 Figures and 9 Pages. Comments are welcom
Redox Processes of Manganese Oxide in Catalyzing Oxygen Evolution and Reduction: An
Manganese oxides with rich redox chemistry have been widely used in (electro)catalysis in applications of energy and environmental consequence. While they are ubiquitous in catalyzing the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), redox processes occurring on the surface of manganese oxides are poorly understood. We report valence changes at OER- and ORR-relevant voltages of a layered manganese oxide film prepared by electrodeposition. X-ray absorption spectra were collected in situ in O[subscript 2]-saturated 0.1 M KOH using inverse partial fluorescence yield (IPFY) at the Mn L[subscript 3,2]-edges and partial fluorescence yield (PFY) at the O K-edge. Overall, we found reversible yet hysteretic Mn redox and qualitatively reproducible spectral changes by Mn L[subscript 3,2]IPFY XAS. Oxidation to a mixed Mn[superscript 3+/4+] valence preceded the oxygen evolution at 1.65 V vs RHE, while manganese reduced below Mn[superscript 3+] and contained tetrahedral Mn[superscript 2+] during oxygen reduction at 0.5 V vs RHE. Analysis of the pre-edge in O K-edge XAS provided the Mn-O hybridization, which was highest for Mn[superscript 3+](e[subscript g][superscript 1]). Our study demonstrates that combined in situ experiments at the metal L- and oxygen K-edges are indispensable to identify both the active valence during catalysis and the hybridization with oxygen adsorbates, critical to the rational design of active catalysts for oxygen electrocatalysis.National Science Foundation (U.S.) (Grant DGE-1122374
Mastering Surface Reconstruction of Metastable Spinel Oxides for Better Water Oxidation
International audienceDeveloping highly active electrocatalysts for oxygen evolution reaction (OER) is critical for the commercial effectiveness of water splitting to produce hydrogen fuels. Low-cost spinel oxides have attracted increasing interest as alternatives to noble-metal-based OER catalysts. A rational design of spinel catalysts can be guided by studying the structural/elemental properties which determine the reaction mechanism and activity. Here, using densit
Dysfunctional gut microbiota and relative co-abundance network in infantile eczema
Additional file 1. The representative sequences of OTUs in 33 infants
Observation of Rydberg moir\'e excitons
Rydberg excitons, the solid-state counterparts of Rydberg atoms, have sparked
considerable interest in harnessing their quantum application potentials,
whereas a major challenge is realizing their spatial confinement and
manipulation. Lately, the rise of two-dimensional moir\'e superlattices with
highly tunable periodic potentials provides a possible pathway. Here, we
experimentally demonstrate this capability through the observation of Rydberg
moir\'e excitons (XRM), which are moir\'e trapped Rydberg excitons in monolayer
semiconductor WSe2 adjacent to twisted bilayer graphene. In the strong coupling
regime, the XRM manifest as multiple energy splittings, pronounced redshift,
and narrowed linewidth in the reflectance spectra, highlighting their
charge-transfer character where electron-hole separation is enforced by the
strongly asymmetric interlayer Coulomb interactions. Our findings pave the way
for pursuing novel physics and quantum technology exploitation based on the
excitonic Rydberg states.Comment: 24 pages, including 4 figures and 6 supplementary figure
In Situ X-ray Absorption Spectroscopy of Metal/Nitrogen-doped Carbons in Oxygen Electrocatalysis
Metal/nitrogen-doped carbons (M−N−C) are promising candidates as oxygen electrocatalysts due to their low cost, tunable catalytic activity and selectivity, and well-dispersed morphologies. To improve the electrocatalytic performance of such systems, it is critical to gain a detailed understanding of their structure and properties through advanced characterization. In situ X-ray absorption spectroscopy (XAS) serves as a powerful tool to probe both the active sites and structural evolution of catalytic materials under reaction conditions. In this review, we firstly provide an overview of the fundamental concepts of XAS and then comprehensively review the setup and application of in situ XAS, introducing electrochemical XAS cells, experimental methods, as well as primary functions on catalytic applications. The active sites and the structural evolution of M−N−C catalysts caused by the interplay with electric fields, electrolytes and reactants/intermediates during the oxygen evolution reaction and the oxygen reduction reaction are subsequently discussed in detail. Finally, major challenges and future opportunities in this exciting field are highlighted.</p
Asymmetric Chiral Coupling in a Topological Resonator
Chiral light-matter interactions supported by topological edge modes at the
interface of valley photonic crystals provide a robust method to implement the
unidirectional spin transfer. The valley topological photonic crystals possess
a pair of counterpropagating edge modes. The edge modes are robust against the
sharp bend of and , which can form a resonator with
whispering gallery modes. Here, we demonstrate the asymmetric emission of
chiral coupling from single quantum dots in a topological resonator by tuning
the coupling between a quantum emitter and a resonator mode. Under a magnetic
field in Faraday configuration, the exciton state from a single quantum dot
splits into two exciton spin states with opposite circularly polarized
emissions due to Zeeman effect. Two branches of the quantum dot emissions
couple to a resonator mode in different degrees, resulting in an asymmetric
chiral emission. Without the demanding of site-control of quantum emitters for
chiral quantum optics, an extra degree of freedom to tune the chiral contrast
with a topological resonator could be useful for the development of on-chip
integrated photonic circuits.Comment: 13 pages, 4 figure
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