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Tribological behavior of lubricant-impregnated porous polyimide

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Friction 2024年第4期12卷 711-725页

作者： jinbang LI Ningning ZHOU janet s.s.wong school of Mechanical Engineering and Mechanics Ningbo UniversityNingbo 315211China Beijing Key Laboratory of Long-life Technology of precise Rotation and Transmission Mechanisms Beijing Institute of Control EngineeringBeijing 100029China Department of Mechanical Engineering Imperial College LondonLondon SW72AZUK

porous materials impregnated with lubricants can be used in conditions where limited lubricant is *** this work,three porous polyimides(ppI)with different densities were ***(pAO)impregnated ppI(ippI)discs were rubbed against steel and sapphire *** operando observations of the ippI-sapphire contacts show that oil is released under an applied load,forming a meniscus around *** at the outlet is created at high sliding *** amount of released oil increases with increasing ppI *** moduli,E*,estimated based on the actual contact size show that trapped oil in ippIs contributes to load *** higher speeds,tribological rehydration of the contact occurs in low density ippI,with that E*rises with *** high density ppIs,high speeds give a constantly high E*which is limited by the viscoelastic properties of the ppI network and possibly the rate of oil *** of ippI-steel contacts is governed by the mechanical properties of the ppI,the flow of the lubricant,and the roughness of the ppI *** low-and medium-density(highly porous,high roughness)ppIs,large amount of oil is released,and lubrication is mainly via lubricant restricted in the contact in the pores and possibly tribological *** high density(low porosity)ppI,with lower roughness,hydrodynamic lubrication is achieved which gives the lowest *** results show that polymeric porous materials for effective lubrication require the optimization of its surface roughness,stiffness,oil flow,and oil retentions.

关键词： polyimide porous material friction mechanism polymer limited lubrication

Enantioselective iridium-catalyzed allylic substitution with a Reformatsky reagent: direct construction of β-stereogenic homoallylic esters

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science China Chemistry 2024年第11期67卷 3791-3797页

作者： Debasis pal Kirana D.Veeranna Yuk Fai wong p.Andrew Evans Department of Chemistry Queen's University Xiangya school of pharmaceutical sciences Central South University

The Reformatsky reagent derived from ethyl bromoacetate circumvents the challenge associated with the direct regio-and enantioselective iridium-catalyzed allylic alkylation with an unstabilized aliphatic ester enolate. Notably, this work represents the first example of using a Reformatsky reagent in a metal-allyl reaction, which permits the direct construction of enantioenriched β-stereogenic homoallylic esters without preactivation of the pronucleophile or post-reaction modification of the product(e.g., thermal decarboxylation of a 1,3-dicarbonyl). Moreover, the process allows the coupling of a broad range of sterically and electronically diverse electrophiles bearing aryl, heteroaryl and alkenyl derivatives, including the significantly more challenging alkyl-substituted allylic carbonates. The versatility of the ester product is exemplified by a series of functional group manipulations and the development of a concise and efficient enantioselective total synthesis of the natural product,(+)-descurainolide A. Finally, mechanistic studies indicate that the zinc enolate behaves as a soft nucleophile that undergoes outer-sphere alkylation.

关键词： allylic substitution asymmetric catalysis mechanistic studies natural product synthesis Reformatsky reagent

Wettability,reactivity,and interface structure in Mg/Ni system

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journal of Magnesium and Alloys 2024年第2期12卷 659-672页

作者： s.Terlicka N.sobczak Ł.Maj p.Darłak j.j.sobczak Institute of Metallurgy and Materials science Polish Academy of Sciences25 Reymonta Str.KrakowPoland Faculty of Foundry Engineering AGH University23 Reymonta Str.KrakowPoland

The sessile drop method was applied to the experimental investigation of the wetting and spreading behaviors of liquid Mg drops on pure Ni *** comparison,the experiments were performed in two variants:(1)using the Capillary purification(Cp)procedure,which allows the non-contact heating and squeezing of a pure oxide-free Mg drop;(2)by classical Contact Heating(CH)*** high-temperature tests were performed under isothermal conditions(Cp:760℃for 30 s;CH:715℃for 300 s)using Ar+5 wt%H_(2) *** the sessile drop tests,images of the Mg/Ni couples were recorded by CCD cameras(57 fps),which were then applied to calculate the contact angles of metal/substrate *** and transmission electron microscopy analyses,both coupled with energy-dispersive X-ray spectroscopy,were used for detailed structural characterization of the solidified *** was found that an oxide-free Mg drop obtained by the Cp procedure showed a wetting phenomenon on the Ni substrate(an average contact angleθs),followed by fast spreading and good wetting over the Ni substrate(θ_((Cp))~20°in 5 s)to form a final contact angle ofθ_(f(Cp))~18°.In contrast,a different wetting behavior was observed for the CH procedure,where the unavoidable primary oxide film on the Mg surface blocked the spreading of liquid Mg showing apparently non-wetting behavior after 300 s contact at the test ***,in both cases,the deep craters formed in the Ni substrates under the Mg drops and significant change in the structure of initially pure Mg drops to Mg-Ni alloys suggest a strong dissolution of Ni in liquid Mg and apparent values of the final contact angles measured for the Mg/Ni system.

关键词： Magnesium-based alloys sessile drop tests Capillary purification procedure Wettability Reactivity Contact angle

snapshotprune: A Novel Bitcoin-Based protocol Toward Efficient pruning and Fast Node Bootstrapping

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Tsinghua science and Technology 2024年第4期29卷 1037-1052页

作者： pengfei Huang Xiaojun Ren Teng Huang Arthur sandor Voundi Koe Duncan s wong Hai jiang Institute of Artificial Intelligence and Blockchain Guangzhou UniversityGuangzhou 510006China Institute of Artificial Intelligence and Blockchain Guangzhou UniversityGuangzhou 510006Chinaand also with Pazhou LabGuangzhou 510330China

Node synchronization is essential for the stability of the Bitcoin network. Critics have raised doubts about the ability of a new node to quickly and efficiently synchronize with the Bitcoin network and alleviate the storage pressure from existing full nodes to stockpile new data. Basic pruning and other techniques have been explored to address these concerns but have been insufficient to reduce node synchronization delay and effectively suppress the growth of synchronized data. In this study, we propose snapshotprune, a novel pruning and synchronization protocol that achieves fast node bootstrapping in the Bitcoin blockchain. Real Bitcoin historical data are leveraged to measure the synchronization time and monitor the network traffic during node bootstrapping. The protocol requires data downloads that are 99.70% less than Bitcoin Core, 81% less than Coinprune, and 60% less than snapshotsave, thereby saving 97.23% of download time. Findings show that the proposed design enhances the storage efficiency and reduces the node synchronization delay compared with existing techniques. We hypothesize that the efficiency of this protocol increases with the block height.

关键词： synchronization blockchain Unspent Transaction Output(UTXO)pruning snapshot fast bootstrapping

Background removal from global auroral images:Data-driven dayglow modeling

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Earth and planetary physics 2024年第1期8卷 247-257页

作者： A.Ohma M.Madelaire K.M.Laundal j.p.Reistad s.M.Hatch s.Gasparini s.j.Walker Birkeland Centre for space science Department of Physics and TechnologyUniversity of BergenBergenNorway

Global images of auroras obtained by cameras on spacecraft are a key tool for studying the near-Earth ***,the cameras are sensitive not only to auroral emissions produced by precipitating particles,but also to dayglow emissions produced by photoelectrons induced by *** emissions and scattered sunlight can contribute to the background *** fully utilize such images in space science,background contamination must be removed to isolate the auroral *** we outline a data-driven approach to modeling the background intensity in multiple images by formulating linear inverse problems based on B-splines and spherical *** approach is robust,flexible,and iteratively deselects outliers,such as auroral *** final model is smooth across the terminator and accounts for slow temporal variations and large-scale asymmetries in the *** demonstrate the model by using the three far ultraviolet cameras on the Imager for Magnetopause-to-Aurora Global Exploration(IMAGE)*** method can be applied to historical missions and is relevant for upcoming missions,such as the solar wind Magnetosphere Ionosphere Link Explorer(sMILE)mission.

关键词： aurora dayglow modeling global auroral images far ultraviolet images dayglow removal

Broadband nonreciprocal thermal emissivity and absorptivity

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Light(science & Applications) 2024年第9期13卷 1820-1827页

作者： Komron j.shayegan jae s.Hwang Bo Zhao Aaswath p.Raman Harry A.Atwater Thomas j.Watson Laboratory of Applied physics California Institute of TechnologyPasadenaCAUSA Department of Electrical Engineering California Institute of TechnologyPasadenaCAUSA Department of Materials science and Engineering University of CaliforniaLos AngelesLos AngelesCAUSA Department of Mechanical Engineering University of HoustonHoustonTXUSA

A body that violates Kirchhoff’s law of thermal radiation exhibits an inequality in its spectral directional absorptivity and *** such an inequality is of fundamental interest as well as a prerequisite for achieving thermodynamic limits in photonic energy conversion1 and radiative *** far,inequalities in the spectral directional emissivity and absorptivity have been limited to narrow spectral resonances3,or wavelengths well beyond the infrared *** the gap from basic demonstrations to practical applications requires control over a broad spectral range of the unequal spectral directional absorptivity and *** this work,we demonstrate broadband nonreciprocal thermal emissivity and absorptivity by measuring the thermal emissivity and absorptivity of gradient epsilon-near-zero InAs layers of subwavelength thicknesses(50 nm and 150 nm)with an external magnetic *** effect occurs in a spectral range(12.5–16μm)that overlaps with the infrared transparency window and is observed at moderate(1 T)magnetic fields.

关键词： field. reciprocal thermal

Artificial intelligence analysis of videos to augment clinical assessment:an overview

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Neural Regeneration Research 2024年第4期19卷 717-718页

作者： David C.wong stefan Williams University of Leeds Leeds Teaching Hospitals Trust LeedsUK

Observation is a fundamental part of the practice of clinical *** of movement is particularly important for the *** such as parkinson’s disease,multiple sclerosis,stroke,epilepsy,and many others affect a person’s movement in characteristic *** some conditions,changes in the patient’s voice can be included in this-changes in sound caused by changes in the movements of *** clinician’s detection of a characteristic abnormality,and their judgment of its severity,plays a central role in both diagnosis and the assessment of prognosis or response to ***,that practice depends upon a limited resource of experienced *** addition,these experts are limited by human visual judgment,which cannot reliably or precisely detect and measure small or subtle changes in movement(Williams et al.,2023).

关键词： clinical epilepsy diagnosis

Free-electron crystals for enhanced X-ray radiation

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Light(science & Applications) 2024年第7期13卷 1299-1309页

作者： Lee Wei Wesley wong Xihang shi Aviv Karnieli jeremy Lim suraj Kumar sergio Carbajo Ido Kaminer Liang jie wong school of Electrical and Electronic Engineering Nanyang Technological University50 Nanyang AvenueSingapore 639798Singapore. solid state Institute and Faculty of Electrical and Computer Engineering Technion–Israel Institute of TechnologyHaifa 3200003Israel. school of Electrical Engineering Fleischman Faculty of EngineeringTel Aviv UniversityTel Aviv 69978Israel Department of Applied physics Stanford UniversityStanfordCA 94305USA. science Mathematics and TechnologySingapore University of Technology and Design8 Somapah RoadSingapore 487372Singapore. Electrical and Computer Engineering Department UCLA420 WestwoodLos AngelesCA 90095USA. physics and Astronomy Department UCLA475 Portola PlazaLos AngelesCA 90095USA. sLAC National Accelerator Laboratory Stanford University2575 Sand Hill RoadMenlo ParkCA 94025USA

Bremsstrahlung—the spontaneous emission of broadband radiation from free electrons that are deflected by atomic nuclei—contributes to the majority of X-rays emitted from X-ray tubes and used in applications ranging from medical imaging to semiconductor chip ***,we show that the bremsstrahlung intensity can be enhanced significantly—by more than three orders of magnitude—through shaping the electron wavefunction to periodically overlap with atoms in crystalline ***,we show how to shape the bremsstrahlung X-ray emission pattern into arbitrary angular emission profiles for purposes such as unidirectionality and ***,we find that these enhancements and shaped emission profiles cannot be attributed solely to the spatial overlap between the electron probability distribution and the atomic centers,as predicted by the paraxial and nonrecoil theory for free electron light *** work highlights an unprecedented regime of free electron light emission where electron waveshaping provides multi-dimensional control over practical radiation processes like *** results pave the way towards greater versatility in table-top X-ray sources and improved fundamental understanding of quantum electron-light interactions.

关键词： overlap attributed arbitrary

Construction of 2D/2D Ti_(3)C_(2)T_(x)MXene/Cds heterojunction with photothermal effect for efficient photocatalytic hydrogen production

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journal of Materials science & Technology 2024年第4期171卷 1-9页

作者： T.Y.Huang Z.Yang s.Y.Yang Z.H.Dai Y.j.Liu j.H.Liao G.Y.Zhong Z.j.Xie Y.p.Fang s.s.Zhang Key Laboratory for Biobased Materials and Energy of Ministry of Education Guangdong Laboratory for Lingnan Modern AgricultureCollege of Materials and EnergySouth China Agricultural UniversityGuangzhou 510643China school of physics and Optoelectronics South China University of TechnologyGuangzhou 510640China school of Chemical Engineering and Energy Technology Guangdong Provincial Key Laboratory of Distributed Energy SystemsDongguan University of TechnologyDongguan 523808China

The insensitivity of semiconductors to visible and infrared light is a key constraint on the utilization of light energy in photocatalytic *** photocatalysts with full-spectrum absorption through surface engineering is an effective approach to fully harnessing light energy in semiconductor ***,a novel stable Ti_(3)C_(2)T_(x)MXene/Cds heterojunction catalyst is obtained by in-situ epitaxial growth of two-dimensional(2D)Cds nanosheets on 2D MXene interface via a solvothermal *** exceptional light absorption properties of MXene confer outstanding full-spectrum driven photocat-alytic hydrogen evolution capability upon the heterogeneous *** unique 2D/2D structure effectively mitigated the recombination of photogenerated carriers,enhancing the photocatalytic performance of the ***,the composite catalyst exhibits a significantly higher surface temperature of 80.4℃under visible light irradiation at an intensity of 0.1 W/cm^(2),which is 1.84 times higher than that of *** irradiation of visible and near infrared light,the composite catalyst with photothermal ef-fect demonstrates a remarkable hydrogen evolution rate of 65.4 mmol g^(-1)h^(-1),which is 7.2 times higher than that of Cds *** study introduces a novel approach for constructing full-spectrum absorption catalysts and expands the application of the photothermal effect in photocatalytic hydrogen evolution research.

关键词： Two-dimensional structure Heterostructure photothermal effect photocatalyst Hydrogen evolution