Facilitative preparation of graphene/cellulose aerogels with tunable microwave absorption properties for ultra-lightweight applications.

Graphene aerogels, as a novel type of carbon-based composite material, have shown great potential in the field of wave absorption due to its characteristics of high conductivity, adjustable structure and good corrosion resistance. It is of great significance to precisely control the dielectric properties of graphene aerogel composites by effectively adjusting their microstructures through the preparing process design, ultimately leading to improve their wave-absorbing performances. In this study, two kinds of graphene/cellulose aerogel composites with three-dimensional porous structures, were successfully prepared using graphene and short staple cellulose as raw materials via the freeze-drying method based on the dissolution-regeneration strategy. A comparative analysis was conducted to examine the differences of microstructures, dielectric properties and corresponding electromagnetic wave absorption performances, which reveals that the graphene/cellulose aerogel composites with graphene nanosheets incorporated into the cellulose matrix realize superior absorbing performances. The graphene/cellulose aerogel composite with a 32 wt% graphene addition realizes effective electromagnetic wave absorbing (reflection loss less than -10 dB) in the whole X-band (8-12.4 GHz) in a relatively large thickness range (3.9-4.7 mm). The densities of the proposed aerogel are no more than 0.02 g/cm3, demonstrating great potential for excellent lightweight microwave absorbing materials. The multiscale electromagnetic wave absorption mechanism is summarized, which would provide an important reference for designing ultra-lightweight absorbing materials with perfect absorption in wideband.

Alkaline Modified Mesoporous Silica Supported Ruthenium Catalyst for Improved α-Amino Acid Synthesis.

Amino acids are a class of compounds with wide-ranging applications. The synthesis of amino acids from biomass-derived α-keto acids and ammonia is a sustainable way but the unstable primary imine intermediates (R-C=NH) easily form oligomers. Herein, targeting this problem, alkaline modified mesoporous silica was employed as a support for ruthenium (Ru/M-MCM-41), which could be used as a bifunctional catalyst in the reductive amination of α-keto acids to synthesize α-amino acids. The incorporation of Sr improved the dispersion of Ru nanoparticles and enhanced metal-support interactions via electron transfer from Sr to Ru, and the active Ru sites could efficiently hydrogenate primary imine intermediates to α-amino acids, thus prohibiting the formation of oligomers. Moreover, the Sr-dopant introduces base sites that could catalyze the hydrolysis of oligomers back to primary imine intermediates and finally hydrogenated to α-amino acids. As a result, >99 % yield of glycine was achieved from glyoxylic acid over Ru/Sr-MCM-41, which is nearly three times that achieved over Ru/MCM-41 (32.2 %).

LiveRetro: Visual Analytics for Strategic Retrospect in Livestream E-Commerce.

Livestream e-commerce integrates live streaming and online shopping, allowing viewers to make purchases while watching. However, effective marketing strategies remain a challenge due to limited empirical research and subjective biases from the absence of quantitative data. Current tools fail to capture the interdependence between live performances and feedback. This study identified computational features, formulated design requirements, and developed LiveRetro, an interactive visual analytics system. It enables comprehensive retrospective analysis of livestream e-commerce for streamers, viewers, and merchandise. LiveRetro employs enhanced visualization and time-series forecasting models to align performance features and feedback, identifying influences at channel, merchandise, feature, and segment levels. Through case studies and expert interviews, the system provides deep insights into the relationship between live performance and streaming statistics, enabling efficient strategic analysis from multiple perspectives.

Advancements in Microwave Absorption Motivated by Interdisciplinary Research.

Microwave absorption materials (MAMs) are originally developed for military purposes, but have since evolved into versatile materials with promising applications in modern technologies, including household use. Despite significant progress in bench-side research over the past decade, MAMs remain limited in their scope and have yet to be widely adopted. This review explores the history of MAMs from first-generation coatings to second-generation functional absorbers, identifies bottlenecks hindering their maturation. It also presents potential solutions such as exploring broader spatial scales, advanced characterization, introducing liquid media, utilizing novel toolbox (machine learning, ML), and proximity of lab to end-user. Additionally, it meticulously presents compelling applications of MAMs in medicine, mechanics, energy, optics, and sensing, which go beyond absorption efficiency, along with their current development status and prospects. This interdisciplinary research direction differs from previous research which primarily focused on meeting traditional requirements (i.e., thin, lightweight, wide, and strong), and can be defined as the next generation of smart absorbers. Ultimately, the effective utilization of ubiquitous electromagnetic (EM) waves, aided by third-generation MAMs, should be better aligned with future expectations.

Simultaneously Tailoring Zinc Deposition and Solvation Structure by Electrolyte Additive.

Aqueous zinc ion batteries (AZIBs) have attracted intense attention due to their high safety and low cost. Unfortunately, the serious dendrite growth and side reactions of the Zn metal anode in an aqueous electrolyte result in rapid battery failure, hindering the practical application of AZIBs. Herein, sodium gluconate as a dual-functional electrolyte additive has been employed to enhance the electrochemical performance of AZIBs. Gluconate anions preferentially adsorb on the surface of the Zn anode, which effectively prevents H2 evolution and induces uniform Zn deposition to suppress dendrite growth. Moreover, the gluconate anions can highly coordinate with Zn2+, promoting the dissolution of [Zn(H2O)6]2+ to inhibit side reactions and the water-induced corrosion reaction. As a result, the Zn||Zn symmetric battery exhibits a long-term cycling stability of over 3000 h at 1 mA cm-2/1 mA h cm-2 and 600 h at 10 mA cm-2/10 mA h cm-2. Furthermore, the NH4V4O10||Zn full battery also displays excellent cycling stability and a high reversible capacity of 193 mA h g-1 at 2 A g-1 after 1000 cycles. Given the low-cost advantage of SG, the proposed interface chemistry modulation strategy holds considerable potential for promoting the commercialization of AZIBs.

Robust Ti3C2Tx MXene foam modified with natural antioxidants for long-term effective electromagnetic interference shielding.

MXenes have been proven to be outstanding lossy phase of advanced electromagnetic interference (EMI) shielding materials. However, their poor tolerance to oxygen and water results in fast degradation of the pristine two-dimensional (2D) nanostructure and fading of the functional performance. Herein, in this research, natural antioxidants (e.g., melatonin, tea polyphenols, and phytic acid) were employed to protect the Ti3C2Tx MXene from its degradation in order to achieve a long-term stability of the EMI shielding performance. The results showed that the synthesized composites comprised of antioxidants and Ti3C2Tx exhibited a decelerating degradation rate resulting in an improved EMI shielding effective (SE) stability. The antioxidation mechanism of the applied antioxidants is discussed with respect to the nanostructure evolution of the Ti3C2Tx MXene. This work contributes to the basic foundations for the further development of advanced MXenes for stable applications in the EM field.

Construction of Hollow Carbon Nanofibers with Graphene Nanorods as Nano-Antennas for Lower-Frequency Microwave Absorption.

Electromagnetic (EM) wave absorbers at a lower-frequency region (2-8 GHz) require higher attenuation ability to achieve efficient absorption. However, the impedance match condition and attenuation ability are usually inversely related. Herein, one-dimensional hollow carbon nanofibers with graphene nanorods are prepared based on coaxial electrospinning technology. The morphology of graphene nanorods can be controlled by the annealing process. As the annealing time increased from 2 to 8 h, graphene nanospheres grew into graphene nanorods, which were catalyzed by Co catalysts derived from ZIF-67 nanoparticles. These nanorods can play the role of nano-antennas, which can guide EM waves into materials to enhance impedance match conditions. As a result, the carbon nanofibers with graphene nanorods possess a larger impedance match area with higher attenuation ability. The minimum reflection loss reaches -57.1 dB at a thickness of 4.6 mm, and the effective absorption bandwidth can cover almost both the S and C bands (2.4-8 GHz). This work contributes a meaningful perspective into the modulation of microwave absorption performance in the lower-frequency range.

Learning to Optimize on Riemannian Manifolds.

Many learning tasks are modeled as optimization problems with nonlinear constraints, such as principal component analysis and fitting a Gaussian mixture model. A popular way to solve such problems is resorting to Riemannian optimization algorithms, which yet heavily rely on both human involvement and expert knowledge about Riemannian manifolds. In this paper, we propose a Riemannian meta-optimization method to automatically learn a Riemannian optimizer. We parameterize the Riemannian optimizer by a novel recurrent network and utilize Riemannian operations to ensure that our method is faithful to the geometry of manifolds. The proposed method explores the distribution of the underlying data by minimizing the objective of updated parameters, and hence is capable of learning task-specific optimizations. We introduce a Riemannian implicit differentiation training scheme to achieve efficient training in terms of numerical stability and computational cost. Unlike conventional meta-optimization training schemes that need to differentiate through the whole optimization trajectory, our training scheme is only related to the final two optimization steps. In this way, our training scheme avoids the exploding gradient problem, and significantly reduces the computational load and memory footprint. We discuss experimental results across various constrained problems, including principal component analysis on Grassmann manifolds, face recognition, person re-identification, and texture image classification on Stiefel manifolds, clustering and similarity learning on symmetric positive definite manifolds, and few-shot learning on hyperbolic manifolds.

PromotionLens: Inspecting Promotion Strategies of Online E-commerce via Visual Analytics.

Promotions are commonly used by e-commerce merchants to boost sales. The efficacy of different promotion strategies can help sellers adapt their offering to customer demand in order to survive and thrive. Current approaches to designing promotion strategies are either based on econometrics, which may not scale to large amounts of sales data, or are spontaneous and provide little explanation of sales volume. Moreover, accurately measuring the effects of promotion designs and making bootstrappable adjustments accordingly remains a challenge due to the incompleteness and complexity of the information describing promotion strategies and their market environments. We present PromotionLens, a visual analytics system for exploring, comparing, and modeling the impact of various promotion strategies. Our approach combines representative multivariant time-series forecasting models and well-designed visualizations to demonstrate and explain the impact of sales and promotional factors, and to support "what-if" analysis of promotions. Two case studies, expert feedback, and a qualitative user study demonstrate the efficacy of PromotionLens.

Low Infrared Emissivity and Strong Stealth of Ti-Based MXenes.

Advanced scenario-adaptable infrared (IR) stealth materials are crucial for creating localized closed thermal environments. Low emissivity over the broadest possible band is expected, as is superior mechanical deformability. Herein, we report a series of Ti-based MXenes with naturally low emissivity as ideal IR shielding materials. Over a wavelength ranging from 2.5 to 25 µm, Ti3C2T X film delivers an average emissivity of 0.057 with the lowest point of 0.042. Such a low emissivity coupled with outstanding structural shaping capability is beyond the current grasp. The reflection-dominated mechanism is dissected. Also, some intriguing scenarios of IR stealth for wearable electronic devices and skin thermal control are demonstrated. This finding lights an encouraging path toward next-generation IR shielding by the expanding MXene family.

Ti3 C2 Tx /MoS2 Self-Rolling Rod-Based Foam Boosts Interfacial Polarization for Electromagnetic Wave Absorption.

Heterogeneous interface design to boost interfacial polarization has become a feasible way to realize high electromagnetic wave absorbing (EMA) performance of dielectric materials. However, interfacial polarization in simple structures such as particles, rods, and flakes is weak and usually plays a secondary role. In order to enhance the interfacial polarization and simultaneously reduce the electronic conductivity to avoid reflection of electromagnetic wave, a more rational geometric structure for dielectric materials is desired. Herein, a Ti3 C2 Tx /MoS2 self-rolling rod-based foam is proposed to realize excellent interfacial polarization and achieve high EMA performance at ultralow density. Different surface tensions of Ti3 C2 Tx and ammonium tetrathiomolybdate are utilized to induce the self-rolling of Ti3 C2 Tx sheets. The rods with a high aspect ratio not only remarkably improve the polarization loss but also are beneficial to the construction of Ti3 C2 Tx /MoS2 foam, leading to enhanced EMA capability. As a result, the effective absorption bandwidth of Ti3 C2 Tx /MoS2 foam covers the whole X band (8.2-12.4 GHz) with a density of only 0.009 g cm-3 , at a thickness of 3.3 mm. The advantages of rod structures are verified through simulations in the CST microwave studio. This work inspires the rational geometric design of micro/nanostructures for new-generation EMA materials.

The boomerang effect of zero pricing: when and why a zero price is less effective than a low price for enhancing consumer demand.

Prior literature has demonstrated the power of zero pricing to boost consumer demand, but the current research shows a novel "boomerang effect": a zero (vs. low, nonzero) price can lower demand when the offer comes with high incidental costs (e.g., the time cost in commuting to an offline class; the physical risk of getting a new vaccine). Five studies show that zero pricing, relative to low pricing, has a boosting (boomerang) effect on demand when incidental costs are low (high). The diverging effects of zero pricing on demand are explained by a dual-process model with a positive affective pathway and negative scrutiny pathway. Zero pricing triggers both positive affect and cognitive scrutiny of incidental costs; when incidental costs are high, the scrutiny pathway overrides the affective pathway and decreases demand. The finding has managerial implications as incidental costs often vary widely between marketing channels and over a product's life cycle. Supplementary Information: The online version contains supplementary material available at 10.1007/s11747-022-00842-1.

Accelerating Selective Oxidation of Biomass-Based Hydroxyl Compounds with Hydrogen Bond Acceptors.

Hydrogen-bonding-initiated self-association makes the valorization of biomass-based hydroxyl compounds a formidable challenge at high concentration. Apart from enhancing the dehydration reaction of hydroxyl compounds with the noncovalent medium effects, insights into how these effects can be exploited to optimize the oxidative reactivity of concentrated hydroxyl compounds remain unclear. Herein, we elucidate that deaggregation of hydroxyl groups with a catalytic number of hydrogen bond acceptors is essential in improving the reactivity of the aerobic oxidation of biomass-based neat aromatic alcohols over the vanadium-based catalyst. The neat 5-hydroxymethylfurfural (HMF) deaggregated with 25 mol % N,N-dimethylformamide (DMF) shows a >7-fold increase in reactivity to produce corresponding aldehydes with excellent selectivity, in stark contrast to the contrary deactivation of reaction in excessive DMF.

Aprotic Amine-modified Manganese Dioxide Catalysts for Selectivity-tunable Oxidation of Amines.

Organic modifiers have shown promising potential for regulating the activity and selectivity of heterogeneous catalysts via tuning their surface properties. Despite the increasing application of organic modification technique in regulating the redox-acid catalysis of metal oxides, control of the acidity of metal oxide catalysts for enhanced reaction selectivity without sacrificing their redox activity remains a substantial challenge. Herein, we show the successful control of redox-acid catalysis of metal oxides with aprotic tertiary amine modifiers. Robust modification of manganese dioxide catalysts with N,N-dialkylcyclohexylamine selectively blocks the Lewis acid sites, with their redox activity mostly unaffected. This enables efficient synthesis of imines in high to excellent selectivity via aerobic oxidation of structurally diverse aryl amines.

Interfacial and defect polarization in MXene-like laminated spinel for electromagnetic wave absorption application.

Manufacturing advanced absorbers is an effective way to deal with the greater electromagnetic pollution challenges associated with the application of 5G technology. While reasonable morphology design is an efficacious method to improve the absorption performance of the absorber. Herein, a series of Co-based spinel Co3O4/ACo2O4 (A = Ni, Cu, Zn) were successfully synthesized via a facile PVP-assisted hydrothermal method. It is worth mentioning that the Co3O4/ZnCo2O4 with MXene-like laminated structure was synthesized successfully for the first time (to our knowledge) by changing the type of elements in A position. The EAB of MXene-like laminated Co3O4/ZnCo2O4 absorber can reach 6.24 GHz (from 11.6 to 17.84 GHz) with a matching thickness of 2.62 mm. This excellent performance can be attributed to the multiple scattering, interfacial polarization, and polarization induced by lattice defects and oxygen vacancies (the dominant). This work offers a novel pattern for improving the EMW absorption ability of pure spinel by manufacturing MXene-like laminated Co-based spinel and adjusting annealing temperature reasonably.

Synthesis and Electromagnetic Interference Shielding Performance of Ti3SiC2-Based Ceramics Fabricated by Liquid Silicon Infiltration.

In this work, Ti3SiC2-based ceramics were fabricated by the infiltration of liquid silicon into TiC preform by incorporating a small amount of Al. Al can play a catalytic role to promote the formation of TiC twins before liquid silicon infiltration (LSI), which leads to the increase of transformation efficiency from TiC to Ti3SiC2 in the LSI process. When the Al content in the TiC preform increases to 9 wt.%, the volume content of Ti3SiC2 reaches 85 vol.%, revealing the high electromagnetic interference shielding effectiveness of 39 dB in the frequency range of 8.2-12.4 GHz. The results indicate that it is an effective way to synthesize Ti3SiC2-based ceramics with excellent electromagnetic shielding performance.

Enhanced P-Type GaN Conductivity by Mg Delta Doped AlGaN/GaN Superlattice Structure.

A method of combining the AlGaN/GaN superlattices and Mg delta doping was proposed to achieve a high conductivity p-type GaN layer. The experimental results provided the evidence that the novel doping technique achieves superior p-conductivity. The Hall-effect measurement indicated that the hole concentration was increased by 2.06 times while the sheet resistivity was reduced by 48%. The fabricated green-yellow light-emitting diodes using the achieved high conductivity p-type GaN layer showed an 8- and 10-times enhancement of light output power and external quantum efficiency, respectively. The subsequent numerical calculation was conducted by using an Advanced Physical Model of Semiconductor Device to reveal the mechanism of enhanced device performance. This new doping technique offers an attractive solution to the p-type doping problems in wide-bandgap GaN or AlGaN materials.

Alkali counterions tune diruthenium(iii,iii)-based ferrimagnetic chain structured antiferromagnets exhibiting step-like hysteresis loops.

The synthesis of antiferromagnets (AFMs) has attracted extensive attention in the area of magnetic devices, such as spintronics and memory devices. Following our initial work on the employment of the homo-valent diruthenium(iii,iii) paddle wheel species with high spin states (S = 2) as building blocks and active components for the construction of molecule-based magnetic materials, the reaction of mixed-valent diruthenium(ii,iii) phosphates Ru2(H2PO4)2(H1.5PO4)2(H2O)2·2H2O (1) with H2O2, Cu2+ and ACl (A = K, Rb and Cs) in aqueous solution led to the formation of heterometallic copper diruthenium(iii,iii) phosphates A2[Cu(H2O)4Ru2(HPO4)2(PO4)2(H2O)2]·nH2O [A = K (2); A = Rb and n = 2 (3); A = Cs and n = 3 (4)]. The compounds consist of chain structures in which each octahedral environment of Cu(H2O)42+ bonds to two [Ru(HPO4)2(PO4)2]2- units in a trans manner, forming a ferrimagnetic negative chain {Cu(H2O)4Ru2(HPO4)2(PO4)2(H2O)2}n2n-, exhibiting anomalous magnetic properties. Long-range ordering temperatures, Tc, were observed around 10 K, and the control of the chain structured antiferromagnets exhibiting step-like hysteresis loops was successfully achieved through counterion tuning by replacing K with either Rb or Cs.

Oxidation Behavior of Tyranno ZMI-SiC Fiber/SiC-SiBC Matrix Composite from 800 to 1200 °C.

In this work, the self-healing Si-B-C matrix-modified ZMI-SiC fiber/SiC (SiC/SiC-SiBC) composite was prepared by a combined process of chemical vapor infiltration, slurry infiltration, and liquid silicon infiltration. The weight changes of the as-fabricate composite after oxidation at 800, 1000, and 1200 °C for 100 h were -0.41%, -0.06%, +0.05%, respectively. The corresponding strength retention ratios were 75%, 99%, 100%, respectively. With the increase of oxidation temperature, coating cracks would be closed. A dense oxidation film was formed with the oxidation of the SiBC matrix, preventing the oxidation of interphase and fiber and leading to excellent oxidation resistance at 1000 and 1200 °C.

A facile "air-molding" method for nanofabrication.

In this letter, we demonstrate a spherical nanocavities fabrication using an "air-molding" method, which is implemented by modulating the pressure difference across air-liquid interfaces in nanoholes on the mold. The cavities formation is theoretically considered and experimentally verified at macroscale first, and then a series of experiments are performed over a patterned surface with sub-300 nm holes by varying the pressure difference by sending a PDMS prepolymer coated mold into a vacuum chamber with changeable pressure. Results show that the air-molding method for spherical cavities fabrication is feasible not only at macroscale, but also at the nanoscale when introducing a pressure difference across the air-liquid interface. And the cavities shape is easily controlled by modulating the pressure in the vacuum chamber. The spherical cavities in this paper have application potential in the optical field and in micro- and nanofluidics.