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Laser additive manufacturing for infrastructure repair:A case study of a deteriorated steel bridge beam

Journal of Materials Science & Technology 2023年第23期154卷 149-158页

作者： Shengbiao Zhang Peijun Hou Jiyun Kang Tianyi Li Shahryar Mooraj Yang Ren Catherine H.Chen A.John Hart Simos Gerasimidis Wen Chen Department of Mechanical and Industrial Engineering University of Massachusetts Amherst MA 01003 USA Department of Civil and Environmental Engineering University of Massachusetts Amherst MA 01003 SA Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge MA 02139 USA X-ray Science Division Argonne National Laboratory Lemont IL 60439 USA massachusetts Department of Transportation Boston MA 02116 USA Department of Mechanical Engineering Massachusetts Institute of Technology Cambridge MA 02139 USA Department of Physics City University of Hong Kong Kowloon Hong Kong China

As our transportation infrastructure ages,its deterioration is becoming a growing *** and effective methods for repair can reduce the need for time-and cost-intensive replacement of structures such as roadway *** this work,laser-based additive manufacturing(AM)was developed for the repair of damaged beams in steel bridges.A corroded structural beam of low-carbon A36 steel was selected for this case study and 316L stainless steel was used for repair due to its excellent mechanical properties and corrosion *** repair experiments were performed on specimens extracted from the beam,and prepared with various groove shapes(Rectangular,Trapezoidal,and U-shaped).More in-depth parametric and microstructural studies were carried out with a series of U-shaped specimens repaired with the linear laser input energy varied from 19.5 to 30.0 J mm–*** tensile properties of the repaired specimens and interface structures were also investigated in *** was found that the repaired specimens had a slightly higher tensile strength despite a reduction in tensile elongation compared to the A36 steel base *** influence of interfacial microstructure and heterogeneity on the mechanical properties of the repaired specimens was *** work suggests the promising potential to employ AM for structural repair and provides fundamental insights into processing-structure-property relationships in laser AM-repaired materials.

关键词： Additive manufacturing Structural repair Mechanical properties Transportation infrastructure Dissimilar joint

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Dynamics in Deep Classifiers Trained with the Square Loss:Normalization,Low Rank,Neural Collapse,and Generalization Bounds

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Research 2023年第3期2023卷 69-89页

作者： Mengjia Xu Akshay Rangamani Qianli Liao Tomer Galantil Tomaso Poggio Center for Brains Minds and MachinesMassachusetts Institute of TechnologyCambridgeMAUSA Division of Applied Mathematics Brown UniversityProvidenceRIUSA

We overview several properties—old and new—of training overparameterized deep networks under the square *** first consider a model of the dynamics of gradient flow under the square loss in deep homogeneous rectified linear unit *** study the convergence to a solution with the absolute minimumρ,which is the product of the Frobenius norms of each layer weight matrix,when normalization by Lagrange multipliers is used together with weight decay under different forms of gradient descent.A main property of the minimizers that bound their expected error for a specific network architecture isρ.In particular,we derive novel norm-based bounds for convolutional layers that are orders of magnitude better than classical bounds for dense ***,we prove that quasi-interpolating solutions obtained by stochastic gradient descent in the presence of weight decay have a bias toward low-rank weight matrices,which should improve *** same analysis predicts the existence of an inherent stochastic gradient descent noise for deep *** both cases,we verify our predictions *** then predict neural collapse and its properties without any specific assumption—unlike other published *** analysis supports the idea that the advantage of deep networks relative to other classifiers is greater for problems that are appropriate for sparse deep architectures such as convolutional neural *** reason is that compositionally sparse target functions can be approximated well by“sparse”deep networks without incurring in the curse of dimensionality.

关键词： bounds stochastic decay

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High spectro-temporal compression on a nonlinear CMOS-chip

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Light(Science & Applications) 2021年第7期10卷 1347-1361页

作者： Ju Won Choi Ezgi Sahin Byoung-Uk Sohn George F.R.Chen Doris K.T.Ng Anuradha M.Agarwal Lionel C.Kimerling Dawn T.H.Tan Photonics Devices and System Group SUTD-MIT International Design CenterSingapore University of Technology and DesignSingapore 487372Singapore Institute of Microelectronics A*STAR(Agency for ScienceTechnology and Research)2 Fusionopolis Way#08-02Innovis TowerSingapore 138634Singapore Microphotonics Center Massachusetts Institute of Technology77 Massachusetts AvenueCambridgeMA 02139USA Materials Research Laboratory Massachusetts Institute of Technology77 Massachusetts AvenueCambridgeMA 02139USA Department of Materials Science and Engineering Massachusetts Institute of Technology77 Massachusetts AvenueCambridgeMA 02139USA

Optical pulses are fundamentally defined by their temporal and spectral *** ability to control pulse properties allows practitioners to efficiently leverage them for advanced metrology,high speed optical communications and attosecond ***,we report 11×temporal compression of 5.8 ps pulses to 0.55 ps using a low power of 13.3 *** result is accompanied by a significant increase in the pulse peak power by 9.4×.These results represent the strongest temporal compression demonstrated to date on a complementary metal–oxide–semiconductor(CMOS)*** addition,we report the first demonstration of on-chip spectral compression,3.0×spectral compression of 480 fs pulses,importantly while preserving the pulse *** strong compression achieved at low powers harnesses advanced on-chip device design,and the strong nonlinear properties of backend-CMOS compatible ultra-silicon-rich nitride,which possesses absence of two-photon absorption and 500×larger nonlinear parameter than in stoichiometric silicon nitride *** demonstrated work introduces an important new paradigm for spectro-temporal compression of optical pulses toward turn-key,on-chip integrated systems for all-optical pulse control.

关键词： pulse optical nonlinear

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Arginine: New and Exciting Developments for an“Old”Amino Acid

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Biomedical and Environmental Sciences 1996年第2期9卷 296-315页

作者： LOUIS BEAUMIER LETICIA CASTILLO YONG-MING YU ALFRED M. AJAMI AND VERNON R. YOUNG(Laboratory of Human Nutrition, School of Science, massachusetts Institute of Technology, cambridge, MA, 02139, USA Shriners Burns Institute,Boston, MA, 02114 USA mass Tra Laboratory of Human Nutrition School of Science Massachusetts Institute of Technology Cambridge 02139 USA

Arginine (2-amino-5-guanidino pentanoic acid) was shown in 1895 by Hedin to be present in the proteins of horn. Metabolic nitrogen balance studies, conducted in 1957 by Rose in human adults and in 1959 by Snyderman and coworkers in young infants, revealed that a dietary source of this amino acid was not an obligatory requirement for growth and maintenance of nitrogen homeostasis in healthy individuals. Hence, It was initially classified as a non-essential (dispensable) amino acid and, perhaps, for reasons of this classification arginine did not receivc the earlier atteniion it now deserves, in relation to an understanding of the nutritional biochemistry and physiology of its metabolism in humans subjects. However, there is currently a considerable interest in the cellular and tissue functions, as well as clinical, therapeutic significance, of arginine. In this paper we review the multiple functions of arginlne, including its role in the L-arginine-nitric oxide pathway,cellular regeneration, immune function, protein synthesis and protein breakdown. We then consider some in vivo aspects of the physiology of arginine metabolism, which varies greatly among eukaryotes, with particular reference to humans. Against this background, studies of arginine in the nutrition of humans under various pathophysiological conditions are reviewed briefly. Finally, a new, updated concept for the metabolic basis for the 'conditional essentiality' of arginine is proposed

关键词： Amino Acid USA Old Arginine New and Exciting Developments for an

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Magnetic and superconducting phase diagrams and transition temperatures predicted using text mining and machine learning

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npj Computational Materials 2020年第1期6卷 1521-1529页

作者： Callum J.Court Jacqueline M.Cole Cavendish Laboratory Department of PhysicsUniversity of CambridgeJ.J.Thomson AvenueCambridge CB30HEUK ISIS Neutron and Muon Source STFC Rutherford Appleton LaboratoryHarwell Science and Innovation CampusDidcotOxfordshire OX110QXUK Argonne National Laboratory 9700 South Cass AvenueArgonneIL 60439USA Department of Chemical Engineering and Biotechnology University of CambridgeWest Cambridge SitePhilippa Fawcett DriveCambridge CB30FSUK

Predicting the properties of materials prior to their synthesis is of great importance in materials *** and superconducting materials exhibit a number of unique properties that make them useful in a wide variety of applications,including solid oxide fuel cells,solid-state refrigerants,photon detectors and metrology *** all these applications,phase transitions play an important role in determining the feasibility of the materials in ***,we present a pipeline for fully integrating data extracted from the scientific literature into machine-learning tools for property prediction and materials *** advanced natural language processing(NLP)and machine-learning techniques,we successfully reconstruct the phase diagrams of well-known magnetic and superconducting compounds,and demonstrate that it is possible to predict the phase-transition temperatures of compounds not present in the *** provide the tool as an online open-source platform,forming the basis for further research into magnetic and superconducting materials discovery for potential device applications.

关键词： phase transition superconducting

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Towards Disaggregate Dynamic Travel Forecasting Models

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Tsinghua Science and Technology 2007年第2期12卷 115-130页

作者： Moshe Ben-Akiva Jon Bottom Song Gao Haris N. Koutsopoulos Yang Wen massachusetts Institute of Technology 77 Massachusetts Avenue Room 1-181 Cambridge MA 02139 USA CRA International 200 Clarendon Street T-33 Boston MA 02116 USA Caliper Corporation 1172 Beacon Street Newton MA 02461 USA Northeastern University 437 Snell Engineering Center Boston MA 02115 USA

The authors argue that travel forecasting models should be dynamic and disaggregate in their representation of demand, supply, and supply-demand interactions, and propose a framework for such models. The proposed framework consists of disaggregate activity-based representation of travel choices of individual motorists on the demand side integrated with disaggregate dynamic modeling of network performance, through vehicle-based traffic simulation models on the supply side. The demand model generates individual members of the population and assigns to them socioeconomic characteristics. The generated motorists maintain these characteristics when they are loaded on the network by the supply model. In an equilibrium setting, the framework lends itself to a fixed-point formulation to represent and resolve demand-supply interactions. The paper discusses some of the remaining development challenges and presents an example of an existing travel forecasting model system that incorporates many of the proposed elements.

关键词： disaggregate dynamic travel forecasting

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Raman lasing and soliton mode-locking in lithium niobate microresonators

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Light(Science & Applications) 2020年第1期9卷 1925-1931页

作者： Mengjie Yu Yoshitomo Okawachi Rebecca Cheng Cheng Wang Mian Zhang Alexander L.Gaeta Marko Loncar Department John A.Paulson School of Engineering and Applied Sciences Harvard UniversityCambridgeMA 02138USA Department of Applied Physics and Applied Mathematics Columbia UniversityNew YorkNY 10027USA Department of Electronic Engineering&State Key Laboratory of Terahertz and Millimeter Waves City University of Hong KongKowloonHong KongChina HyperLight Corporation 501 Massachusetts AvenueCambridgeMA 02139USA

The recent advancement in lithium-niobite-on-insulator(LNOI)technology is opening up new opportunities in optoelectronics,as devices with better performance,lower power consumption and a smaller footprint can be realised due to the high optical confinement in the *** LNOI platform offers both largeχ(2)andχ(3)nonlinearities along with the power of dispersion engineering,enabling brand new nonlinear photonic devices and applications for the next generation of integrated photonic ***,Raman scattering and its interaction with other nonlinear processes have not been extensively studied in dispersion-engineered LNOI *** this work,we characterise the Raman radiation spectra in a monolithic lithium niobate(LN)microresonator via selective excitation of Raman-active phonon *** dominant mode for the Raman oscillation is observed in the backward direction for a continuous-wave pump threshold power of 20mW with a high differential quantum efficiency of 46%.We explore the effects of Raman scattering on Kerr optical frequency comb *** achieve mode-locked states in an X-cut LNOI chip through sufficient suppression of the Raman effect via cavity geometry *** analysis of the Raman effect provides guidance for the development of future chip-based photonic devices on the LNOI platform.

关键词： scattering pump lithium

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Organic Iono-Electronics,a New Front for Semiconducting Polymers to Shine

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Accounts of Materials Research 2022年第7期3卷 669-671页

作者： Aristide Gumyusenge Department of Materials Science&Engineering Massachusetts Institute of TechnologyCambridgeMassachusetts 02139United States

Structural tunability,low-cost solution processability,mechanical deformability,and biocompatibility were among several keywords that made organic semiconductors a popular class of materials.1 Here we are over three decades later with very few practical devices using organic semiconductors,and many wondering what is next for the field of organic electronics and whether organics were destined for nothing more than low-grade electronics and displays.

关键词： materials nothing electronics

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Photoluminescence evolution in self-ion-implanted and annealed silicon

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Chinese Physics B 2009年第11期18卷 4906-4911页

作者：杨宇王茺杨瑞东李亮熊飞 Bao Ji-Ming Institute of Optoelectronic Information Materials Yunnan University Kunming 650091 China School of Engineering and Applied Sciences Harvard University Cambridge Massachusetts 02138 USA

Si^＋ ion-implanted silicon wafers are annealed at different temperatures from room temperature to 950℃ and then characterized by using the photoluminescence （PL） technique at different recorded temperatures （RETs）. Plentiful optical features are observed and identified clearly in these PL curves. The PL spectra of these samples annealed in different temperature ranges are correspondingly dominated by different emission peaks. Several characteristic features, such as an R line, S bands, a W line, the phonon-assistant WTA and SiTO peaks, can be detected in the PL spectra of samples annealed at different temperatures. For the samples annealed at 800℃, emission peaks from the dislocations bounded at the deep energy levels of the forbidden band, such as D1 and D2 bands, can be observed at a temperature as high as 280 K. These data strongly indicate that a severe transformation of defect structures could be manipulated by the annealing and recorded temperatures. The deactivation energies of the main optical features are extracted from the PL data at different temperatures.

关键词： photoluminescence silicon self-ion-implanted defects

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Mitochondrial H_(2)S_(n)-Mediated Anti-Inflammatory Theranostics

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Nano-Micro Letters 2021年第12期13卷 1-13页

作者： Won Young Kim Miae Won Seyoung Koo Xingcai Zhang Jong Seung Kim Department of Chemistry Korea UniversitySeoul 02841Korea John A.Paulson School of Engineering and Applied Sciences Harvard UniversityCambridgeMA 02138USA School of Engineering Massachusetts Institute of TechnologyCambridgeMA 02139USA

The insistent demand for space-controllable delivery,which reduces the side effects of non-steroidal antiinflammatory drugs(NSAIDs),has led to the development of a new theranostics-based approach for anti-inflammatory *** current anti-inflammatory treatments can be improved by designing a drug delivery system responsive to the inflammatory site biomarker,hydrogen polysulfide(H_(2)S_(n)).Here,we report a noveltheranostic agent 1(TA1),consisting of three parts:H_(2)S_(n)-mediated triggering part,a two-photon fluorophore bearing mitochondria targeting unit(Rhodol-TPP),and anti-inflammatory COX inhibitor(indomethacin).In vitro experiments showed that TA1 selectively reacts with H_(2)S_(n)to concomitantly release both Rhodol-TPP and ***-microscopy imaging of inflammation-inducedlive cells suggested that TA1 is localized in the mitochondria where the H_(2)S_(n)is *** TA1 reacted with H_(2)S_(n)in the endogenous and exogenous H_(2)S_(n)environments and in lipopolysaccharide treated inflammatory ***,TA1 suppressed COX-2 level in the inflammatory-induced cells and prostaglandin E 2(PGE2)level in blood serum from inflammation-induced mouse *** vivo experiments with inflammation-induced mouse models suggested that TA1 exhibits inflammation-site-elective drug release followed by significant therapeutic e ects,showing its function as a theranostic agent,capable of both anti-inflammatory therapy and precise *** behavior of TA1 is highly applicable in vivo model therapeutics for the inflammatory disease.

关键词： Theranostics Anti-inflammation Mitochondria Hydrogen polysulfides

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