Mobile-edge computation offloading (MECO) off-loads intensive mobile computation to clouds located at the edges of cellular networks. Thereby, MECO is envisioned as a promising technique for ...prolonging the battery lives and enhancing the computation capacities of mobiles. In this paper, we study resource allocation for a multiuser MECO system based on time-division multiple access (TDMA) and orthogonal frequency-division multiple access (OFDMA). First, for the TDMA MECO system with infinite or finite cloud computation capacity, the optimal resource allocation is formulated as a convex optimization problem for minimizing the weighted sum mobile energy consumption under the constraint on computation latency. The optimal policy is proved to have a threshold-based structure with respect to a derived offloading priority function, which yields priorities for users according to their channel gains and local computing energy consumption. As a result, users with priorities above and below a given threshold perform complete and minimum offloading, respectively. Moreover, for the cloud with finite capacity, a sub-optimal resource-allocation algorithm is proposed to reduce the computation complexity for computing the threshold. Next, we consider the OFDMA MECO system, for which the optimal resource allocation is formulated as a mixed-integer problem. To solve this challenging problem and characterize its policy structure, a low-complexity sub-optimal algorithm is proposed by transforming the OFDMA problem to its TDMA counterpart. The corresponding resource allocation is derived by defining an average offloading priority function and shown to have close-to-optimal performance in simulation.
The reversible and cooperative activation process, which includes electron transfer from surrounding redox mediators, the reversible valence change of cofactors and macroscopic functional/structural ...change, is one of the most important characteristics of biological enzymes, and has frequently been used in the design of homogeneous catalysts. However, there are virtually no reports on industrially important heterogeneous catalysts with these enzyme-like characteristics. Here, we report on the design and synthesis of highly active TiO2 photocatalysts incorporating site-specific single copper atoms (Cu/TiO2) that exhibit a reversible and cooperative photoactivation process. Our atomic-level design and synthetic strategy provide a platform that facilitates valence control of co-catalyst copper atoms, reversible modulation of the macroscopic optoelectronic properties of TiO2 and enhancement of photocatalytic hydrogen generation activity, extending the boundaries of conventional heterogeneous catalysts.Reversible and cooperative activation processes are important characteristics of biological enzymes and can be used in designing catalysts. Highly active TiO2 photocatalysts incorporated with site-specific single copper atoms are now shown to exhibit such a photoactivation process.
Despite the growing demand for hydrogen peroxide it is almost exclusively manufactured by the energy-intensive anthraquinone process. Alternatively, H2O2 can be produced electrochemically via the ...two-electron oxygen reduction reaction, although the performance of the state-of-the-art electrocatalysts is insufficient to meet the demands for industrialization. Interestingly, guided by first-principles calculations, we found that the catalytic properties of the Co–N4 moiety can be tailored by fine-tuning its surrounding atomic configuration to resemble the structure-dependent catalytic properties of metalloenzymes. Using this principle, we designed and synthesized a single-atom electrocatalyst that comprises an optimized Co–N4 moiety incorporated in nitrogen-doped graphene for H2O2 production and exhibits a kinetic current density of 2.8 mA cm−2 (at 0.65 V versus the reversible hydrogen electrode) and a mass activity of 155 A g−1 (at 0.65 V versus the reversible hydrogen electrode) with negligible activity loss over 110 hours.Producing H2O2 electrochemically currently use electrocatalysts that are insufficient to meet the demands for industrialization. A single-atom electrocatalyst with an optimized Co–N4 moiety incorporated in nitrogen-doped graphene is shown to exhibit enhanced performance for H2O2 production.
Single‐atom M‒N‒C catalysts have attracted tremendous attention for their application to electrocatalysis. Nitrogen‐coordinated mononuclear metal moieties (MNx moities) are bio‐inspired active sites ...that are analogous to various metal‐porphyrin cofactors. Given that the functions of metal‐porphyrin cofactors are highly dependent on the local coordination environments around the mononuclear active site, engineering MNx active sites in heterogeneous M‒N‒C catalysts would provide an additional degree of freedom for boosting their electrocatalytic activity. This work presents a local coordination structure modification of FeN4 moieties via morphological engineering of graphene support. Introducing highly wrinkled structure in graphene matrix induces nonplanar distortion of FeN4 moieties, resulting in the modification of electronic structure of mononuclear Fe. Electrochemical analysis combined with first‐principles calculations reveal that enhanced electrocatalytic lithium polysulfide conversion, especially the Li2S redox step, is attributed to the local structure modified FeN4 active sites, while increased specific surface area also contributes to improved performance at low C‐rates. Owing to the synergistic combination of atomic‐level modified FeN4 active sites and morphological advantage of graphene support, Fe‒N‒C catalysts with wrinkled graphene morphology show superior lithium–sulfur battery performance at both low and high C‐rates (particularly 915.9 mAh g−1 at 5 C) with promising cycling stability.
Atomic‐level engineering of MNx active sites is a desirable strategy to enhance and fine‐tune electrocatalytic performance of M‒N‒C catalysts. FeN4 active sites on wrinkled graphene support exhibits different structural and electronic properties compared to square‐planar FeN4 moieties. The synergistic combination of modified FeN4 active sites and morphological advantage of wrinkled graphene support improves the electrocatalytic performance for lithium–sulfur conversion chemistry.
The quantitative label-free detection of neurotransmitters provides critical clues in understanding neurological functions or disorders. However, the identification of neurotransmitters remains ...challenging for surface-enhanced Raman spectroscopy (SERS) due to the presence of noise. Here, we report spread spectrum SERS (ss-SERS) detection for the rapid quantification of neurotransmitters at the attomolar level by encoding excited light and decoding SERS signals with peak autocorrelation and near-zero cross-correlation. Compared to conventional SERS measurements, the experimental result of ss-SERS shows an exceptional improvement in the signal-to-noise ratio of more than three orders of magnitude, thus achieving a high temporal resolution of over one hundred times. The ss-SERS measurement further allows the attomolar SERS detection of dopamine, serotonin, acetylcholine, γ-aminobutyric acid, and glutamate without Raman reporters. This approach opens up opportunities not only for investigating the early diagnostics of neurological disorders or highly sensitive biomedical SERS applications but also for developing low-cost spectroscopic biosensing applications.
Compared to nanostructured platinum (Pt) catalysts, ordered Pt-based intermetallic nanoparticles supported on a carbon substrate exhibit much enhanced catalytic performance, especially in fuel cell ...electrocatalysis. However, direct synthesis of homogeneous intermetallic alloy nanocatalysts on carbonaceous supports with high loading is still challenging. Herein, we report a novel synthetic strategy to directly produce highly dispersed MPt alloy nanoparticles (M = Fe, Co, or Ni) on various carbon supports with high catalyst loading. Importantly, a unique bimetallic compound, composed of M(bpy)32+ cation (bpy = 2,2′-bipyridine) and PtCl62– anion, evenly decomposes on carbon surface and forms uniformly sized intermetallic nanoparticles with a nitrogen-doped carbon protection layer. The excellent oxygen reduction reaction (ORR) activity and stability of the representative reduced graphene oxide (rGO)-supported L10-FePt catalyst (37 wt %-FePt/rGO), exhibiting 18.8 times higher specific activity than commercial Pt/C catalyst without degradation over 20 000 cycles, well demonstrate the effectiveness of our synthetic approach toward uniformly alloyed nanoparticles with high homogeneity.
Biological wonders, found in insects such as antireflecting moth eyes, compound eyes in a honey bee, firefly lanterns, and iridescent butterfly wings, inspire human beings for advanced light imaging ...and illumination technologies. Dazzling advances of micro‐ and nanofabrication technologies allow insect‐inspired structures, for example, artificial compound eyes with a wide field of view and low aberration, bioinspired light‐emitting diode lenses, and structural coloration templates, featuring miniaturization. Besides, plasmonics and metamaterials offer an unprecedented approach that overcomes the diffraction limit and unveils unknown optical phenomena in ultrastructures inspired by insects. Here, insect‐inspired photonic structures for light imaging, light extraction, and structural coloration are reviewed, and photonic functions and structure fabrications inspired by insects that can be applied in advanced imaging and illumination applications are discussed.
Biological marvels, found in insects such as compound eyes and firefly lanterns, inspire human beings for advanced light imaging and illumination technologies. This article focuses on recent progress of photonic micro/nano structures inspired from insect smartness regarding with functions and fabrication methods. In addition, perspectives and prospects using plasmonics and metamaterials for insect inspired photonics are discussed.
Crystalline poly(3,4‐ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) nanofibrils with an electrical conductivity of 4380 S cm‐1 are formed via a solution process using H2SO4. The ...concentrated H2SO4 treatment induces a significant structural rearrangement of the PEDOT:PSS via a charge‐separated transition mechanism, resulting in highly ordered and densely packed PEDOT:PSS nanofibrils. The PEDOT:PSS electrode shows a sheet resistance of 46 Ω sq‐1 with 90% optical transmittance.
Visible-light-driven organic transformations are of great interest in synthesizing valuable fine chemicals under mild conditions. The merger of heterogeneous photocatalysts and transition metal ...catalysts has recently drawn much attention due to its versatility for organic transformations. However, these semi-heterogenous systems suffered several drawbacks, such as transition metal agglomeration on the heterogeneous surface, hindering further applications. Here, we introduce heterogeneous single Ni atoms supported on carbon nitride (NiSAC/CN) for visible-light-driven C-N functionalization with a broad substrate scope. Compared to a semi-heterogeneous system, high activity and stability were observed due to metal-support interactions. Furthermore, through systematic experimental mechanistic studies, we demonstrate that the stabilized single Ni atoms on CN effectively change their redox states, leading to a complete photoredox cycle for C-N coupling.
In this work, the first demonstration of heterogeneous photoredox C-N coupling is reported using Ni atoms on C
3
N
4
. Due to metal-support interactions, high activity and stability were observed during visible-light-driven C-N functionalization.
Storing solar energy in chemical bonds aided by heterogeneous photocatalysis is desirable for sustainable energy conversion. Despite recent progress in designing highly active photocatalysts, ...inefficient solar energy and mass transfer, the instability of catalysts and reverse reactions impede their practical large-scale applications. Here we tackle these challenges by designing a floatable photocatalytic platform constructed from porous elastomer-hydrogel nanocomposites. The nanocomposites at the air-water interface feature efficient light delivery, facile supply of water and instantaneous gas separation. Consequently, a high hydrogen evolution rate of 163 mmol h
m
can be achieved using Pt/TiO
cryoaerogel, even without forced convection. When fabricated in an area of 1 m
and incorporated with economically feasible single-atom Cu/TiO
photocatalysts, the nanocomposites produce 79.2 ml of hydrogen per day under natural sunlight. Furthermore, long-term stable hydrogen production in seawater and highly turbid water and photoreforming of polyethylene terephthalate demonstrate the potential of the nanocomposites as a commercially viable photocatalytic system.
PDF
