1,414 research outputs found
Event Horizon Telescope observations of the jet launching and collimation in Centaurus A
No full textPublisher Copyright: © 2021, The Author(s).Very-long-baseline interferometry (VLBI) observations of active galactic nuclei at millimetre wavelengths have the power to reveal the launching and initial collimation region of extragalactic radio jets, down to 10-100 gravitational radii (r(g) equivalent to GM/c(2)) scales in nearby sources(1). Centaurus A is the closest radio-loud source to Earth(2). It bridges the gap in mass and accretion rate between the supermassive black holes (SMBHs) in Messier 87 and our Galactic Centre. A large southern declination of -43 degrees has, however, prevented VLBI imaging of Centaurus A below a wavelength of 1 cm thus far. Here we show the millimetre VLBI image of the source, which we obtained with the Event Horizon Telescope at 228 GHz. Compared with previous observations(3), we image the jet of Centaurus A at a tenfold higher frequency and sixteen times sharper resolution and thereby probe sub-lightday structures. We reveal a highly collimated, asymmetrically edge-brightened jet as well as the fainter counterjet. We find that the source structure of Centaurus A resembles the jet in Messier 87 on similar to 500 r(g) scales remarkably well. Furthermore, we identify the location of Centaurus A's SMBH with respect to its resolved jet core at a wavelength of 1.3 mm and conclude that the source's event horizon shadow(4) should be visible at terahertz frequencies. This location further supports the universal scale invariance of black holes over a wide range of masses(5,6).Peer reviewe
Samarium-Catalyzed Diastereoselective Double Addition of Phenylphosphine to Imines and Mechanistic Studies by DFT Calculations
No full textbibtex: ISI:000400097100003 bibtex\location:'POSTFACH 101161, 69451 WEINHEIM, GERMANY',publisher:'WILEY-V C H VERLAG GMBH',type:'Article',affiliation:'Cui, CM (Reprint Author), Nankai Univ, State Key Lab Elementoorgan Chem, Collaborat Innovat Ctr Chem Sci & Engn, Tianjin 300071, Peoples R China. Maron, L (Reprint Author), Univ Toulouse, LPCNO, CNRS, INSA,UPS,UMR 5215, 135 Ave Rangueil, F-31077 Toulouse, France. Li, Jianfeng; Song, Changhong; Liu, Jinxi; Fan, Guilan; Cui, Chunming, Nankai Univ, State Key Lab Elementoorgan Chem, Collaborat Innovat Ctr Chem Sci & Engn, Tianjin 300071, Peoples R China. Lamsfus, Carlos Alvarez; Maron, Laurent, Univ Toulouse, LPCNO, CNRS, INSA,UPS,UMR 5215, 135 Ave Rangueil, F-31077 Toulouse, France.','author-email':'[email protected] [email protected]',da:'2018-12-05','doc-delivery-number':'ET2JI',eissn:'1867-3899','funding-acknowledgement':'National Natural Science Foundation of China [21390401]; Humboldt Foundation; Chinese Academy of Sciences','funding-text':'We are grateful to the National Natural Science Foundation of China (21390401) for financial support. L.M. is a member of the Institut Universitaire de France. The Humboldt Foundation and the Chinese Academy of Sciences are acknowledged for financial support of this work. L.M. and C.A.L. are grateful to CalMip for the generous grant of computing time.','journal-iso':'ChemCatChem','keywords-plus':'H BOND ADDITION; AMINOPHOSPHINE LIGANDS; ASYMMETRIC ADDITION; CHIRAL 3,4-DIAZAPHOSPHOLANES; ALPHA-AMINOPHOSPHINES; EFFICIENT SYNTHESIS; METAL-COMPLEXES; HYDROPHOSPHINATION; ALKENES; CARBODIIMIDES','number-of-cited-references':'48','orcid-numbers':'Alvarez Lamsfus, Carlos/0000-0002-4442-7052','research-areas':'Chemistry','times-cited':'2','unique-id':'ISI:000400097100003','usage-count-last-180-days':'4','usage-count-since-2013':'13','web-of-science-categories':'Chemistry, Physical'\International audienceThe catalytic hydrophosphination of imines represents the most straightforward and atom-economical strategy for the preparation of alpha-aminophosphines, which are useful as biologically active molecules and ligands for catalysis. The first catalytic protocol for the rapid and high-yielding hydrophosphination of common imines enabled by an ene-diamido samarium methoxide catalyst was developed. The reaction allowed the efficient and diastereoselective synthesis of various bis(alpha-amino)phosphines through the double addition of PhPH2 to common imines. The catalytic reaction has a relatively wide substrate scope and offers high diastereoselectivities (up to 99: 1 dr for meso products) and high yields (up to 97%). DFT calculations disclosed an inner-sphere mechanism involving unprecedented activation of a Sm-O bond by a phosphine and stabilization of the addition intermediates by the metal center
Samarium-Catalyzed Diastereoselective Double Addition of Phenylphosphine to Imines and Mechanistic Studies by DFT Calculations
No full textbibtex: ISI:000400097100003 bibtex\location:'POSTFACH 101161, 69451 WEINHEIM, GERMANY',publisher:'WILEY-V C H VERLAG GMBH',type:'Article',affiliation:'Cui, CM (Reprint Author), Nankai Univ, State Key Lab Elementoorgan Chem, Collaborat Innovat Ctr Chem Sci & Engn, Tianjin 300071, Peoples R China. Maron, L (Reprint Author), Univ Toulouse, LPCNO, CNRS, INSA,UPS,UMR 5215, 135 Ave Rangueil, F-31077 Toulouse, France. Li, Jianfeng; Song, Changhong; Liu, Jinxi; Fan, Guilan; Cui, Chunming, Nankai Univ, State Key Lab Elementoorgan Chem, Collaborat Innovat Ctr Chem Sci & Engn, Tianjin 300071, Peoples R China. Lamsfus, Carlos Alvarez; Maron, Laurent, Univ Toulouse, LPCNO, CNRS, INSA,UPS,UMR 5215, 135 Ave Rangueil, F-31077 Toulouse, France.','author-email':'[email protected] [email protected]',da:'2018-12-05','doc-delivery-number':'ET2JI',eissn:'1867-3899','funding-acknowledgement':'National Natural Science Foundation of China [21390401]; Humboldt Foundation; Chinese Academy of Sciences','funding-text':'We are grateful to the National Natural Science Foundation of China (21390401) for financial support. L.M. is a member of the Institut Universitaire de France. The Humboldt Foundation and the Chinese Academy of Sciences are acknowledged for financial support of this work. L.M. and C.A.L. are grateful to CalMip for the generous grant of computing time.','journal-iso':'ChemCatChem','keywords-plus':'H BOND ADDITION; AMINOPHOSPHINE LIGANDS; ASYMMETRIC ADDITION; CHIRAL 3,4-DIAZAPHOSPHOLANES; ALPHA-AMINOPHOSPHINES; EFFICIENT SYNTHESIS; METAL-COMPLEXES; HYDROPHOSPHINATION; ALKENES; CARBODIIMIDES','number-of-cited-references':'48','orcid-numbers':'Alvarez Lamsfus, Carlos/0000-0002-4442-7052','research-areas':'Chemistry','times-cited':'2','unique-id':'ISI:000400097100003','usage-count-last-180-days':'4','usage-count-since-2013':'13','web-of-science-categories':'Chemistry, Physical'\International audienceThe catalytic hydrophosphination of imines represents the most straightforward and atom-economical strategy for the preparation of alpha-aminophosphines, which are useful as biologically active molecules and ligands for catalysis. The first catalytic protocol for the rapid and high-yielding hydrophosphination of common imines enabled by an ene-diamido samarium methoxide catalyst was developed. The reaction allowed the efficient and diastereoselective synthesis of various bis(alpha-amino)phosphines through the double addition of PhPH2 to common imines. The catalytic reaction has a relatively wide substrate scope and offers high diastereoselectivities (up to 99: 1 dr for meso products) and high yields (up to 97%). DFT calculations disclosed an inner-sphere mechanism involving unprecedented activation of a Sm-O bond by a phosphine and stabilization of the addition intermediates by the metal center
Near-Field Raman Spectroscopy with Aperture Tips
No full textIn this paper, we review nano-Raman techniques based on aperture scanning near-field optical microscopy (SNOM). Fundamentals of SNOM and aperture tip -based near-field Raman spectroscopy and their applications in key technical issues, including Raman signal intensity and collection time, are introduced. Recent advances in the tip design are discussed, and applications of the aperture-SNOM-based nano-Raman technique are presented. We attempt to identify the most pressing open questions in this field. We believe that, by improving the power transmission efficiency and combining the local field enhancing technique with the tip-enhanced spectroscopy, the performance of aperture-SNOM can be significantly improved. Its nanometer-scale excitation volume and the consequent low background make the aperture-tip technique feasible for many important samples that cannot be measured by other optical nanospectroscopies.National Key Technologies R&D Program of China [2016YFA0201104]; National Basic Research Program of China (973 Program) [2015CB932403]; National Science Foundation of China [61422501, 11374023, 11374152, 11674012, 61176120, 61378059, 11574142, 61521004]; Beijing Natural Science Foundation [L140007]; Foundation for the Author of National Excellent Doctoral Dissertation of China [201420]; National Program for Support of Top-Notch Young Professionals; 1000 Young Talent Plan; Priority Academic Program Development (PAPD) of Jiangsu Higher Education InstitutionsSCI(E)REVIEW75095-510911
Light-matter interaction of 2D materials: Physics and device applications
No full textIn the last decade, the rise of two-dimensional (2D) materials has attracted a tremendous amount of interest for the entire field of photonics and opto-electronics. The mechanism of light-matter interaction in 2D materials challenges the knowledge of materials physics, which drives the rapid development of materials synthesis and device applications. 2D materials coupled with plasmonic effects show impressive optical characteristics, involving efficient charge transfer, plasmonic hot electrons doping, enhanced light-emitting, and ultrasensitive photodetection. Here, we briefly review the recent remarkable progress of 2D materials, mainly on graphene and transition metal dichalcogenides, focusing on their tunable optical properties and improved opto-electronic devices with plasmonic effects. The mechanism of plasmon enhanced light-matter interaction in 2D materials is elaborated in detail, and the state-of-the-art of device applications is comprehensively described. In the future, the field of 2D materials holds great promise as an important platform for materials science and opto-electronic engineering, enabling an emerging interdisciplinary research field spanning from clean energy to information technology.National Basic Research Program of China [2015CB932403]; National Natural Science Foundation of China [61422501, 11674012, 11374023, 61521004]; Beijing Natural Science Foundation, China [L140007]; Foundation for the Author of National Excellent Doctoral Dissertation of China [201420]; National Program for Support of Top-notch Young Professionals, ChinaSCI(E)REVIEW32
The global burden of childhood and adolescent cancer in 2017: an analysis of the Global Burden of Disease Study 2017
No full textAbstract: Background Accurate childhood cancer burden data are crucial for resource planning and health policy prioritisation. Model-based estimates are necessary because cancer surveillance data are scarce or non-existent in many countries. Although global incidence and mortality estimates are available, there are no previous analyses of the global burden of childhood cancer represented in disability-adjusted life-years (DALYs). Methods Using the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017 methodology, childhood (ages 0-19 years) cancer mortality was estimated by use of vital registration system data, verbal autopsy data, and population-based cancer registry incidence data, which were transformed to mortality estimates through modelled mortality-to-incidence ratios (MIRs). Childhood cancer incidence was estimated using the mortality estimates and corresponding MIRs. Prevalence estimates were calculated by using MIR to model survival and multiplied by disability weights to obtain years lived with disability (YLDs). Years of life lost (YLLs) were calculated by multiplying age-specific cancer deaths by the difference between the age of death and a reference life expectancy. DALYs were calculated as the sum of YLLs and YLDs. Final point estimates are reported with 95% uncertainty intervals. Findings Globally, in 2017, there were 11.5 million (95% uncertainty interval 10.6-12.3) DALYs due to childhood cancer, 97.3% (97.3-97.3) of which were attributable to YLLs and 2.7% (2.7-2.7) of which were attributable to YLDs. Childhood cancer was the sixth leading cause of total cancer burden globally and the ninth leading cause of childhood disease burden globally. 82.2% (82.1-82.2) of global childhood cancer DALYs occurred in low, low-middle, or middle Socio-demographic Index locations, whereas 50.3% (50.3-50.3) of adult cancer DALYs occurred in these same locations. Cancers that are uncategorised in the current GBD framework comprised 26.5% (26.5-26.5) of global childhood cancer DALYs. Interpretation The GBD 2017 results call attention to the substantial burden of childhood cancer globally, which disproportionately affects populations in resource-limited settings. The use of DALY-based estimates is crucial in demonstrating that childhood cancer burden represents an important global cancer and child health concern. (C) 2019 The Author(s). Published by Elsevier Ltd
Nature of the possible magnetic phases in a frustrated hyperkagome iridate
No full textBased on the Kitaev-Heisenberg model with Dzyaloshinskii-Moriya (DM) interactions, we studied the nature of possible magnetic phases in the frustrated hyperkagome iridate, Na4Ir3O8 (Na-438). Using Monte Carlo simulation, we showed that the phase diagram is mostly covered by two competing magnetic ordered phases, the Z(2) symmetry breaking (SB) phase and the Z(6) SB phase, latter of which is stabilized by the classical order by disorder. These two phases are intervened by a first-order phase-transition line with Z(8)-like symmetry. The critical nature at the Z(6) SB ordering temperature is characterized by the three-dimensional XY universality class, below which U(1) to Z(6) crossover phenomenon appears: the Z(6) spin anisotropy becomes irrelevant in a length scale shorter than a crossover length A,, while it becomes relevant otherwise. A possible phenomenology of polycrystalline Na-438 is discussed based on this crossover phenomenon.SCI(E)[email protected]
Topological Phonon Modes in a Two-Dimensional Wigner Crystal
No full textWe investigate the spin-orbit coupling effect in a two-dimensional (2D) Wigner crystal. It is shown that sufficiently strong spin-orbit coupling and an appropriate sign of g-factor could transform the Wigner crystal to a topological phonon system. We demonstrate the existence of chiral phonon edge modes in finite size samples, as well as the robustness of the modes in the topological phase. We explore the possibility of realizing the topological phonon system in 2D Wigner crystals confined in semiconductor quantum wells/heterostructure. It is found that the spin-orbit coupling is too weak for driving a topological phase transition in these systems. It is argued that one may look for topological phonon systems in correlated Wigner crystals with emergent effective spin-orbit coupling.National Basic Research Program of China [2015CB921101]; National Natural Science Foundation of China [11325416]SCI(E)ARTICLE33
Topological Phase Transition in Single Crystals of (Cd1-xZnx)(3)As-2
No full textSingle crystals of (Cd1-xZnx)(3)As-2 were synthesized from high-temperature solutions and characterized in terms of their structural and electrical properties. Based on the measurements of resistivity and Hall signals, we revealed a chemical-doping-controlled transition from a three-dimensional Dirac semimetal to a semiconductor with a critical point x(c) similar to 0.38. We observed structural transitions from a body-center tetragonal phase to a primitive tetragonal phase then back to a body-center tetragonal phase in the solid solutions as well, which are irrelevant to the topological phase transition. This continuously tunable system controlled by chemical doping provides a platform for investigating the topological quantum phase transition of three-dimensional Dirac electrons.National Basic Research Program of China [2013CB921901, 2014CB239302]SCI(E)ARTICLE
Single-photon transport through a waveguide coupling to a quadratic optomechanical system
No full textWe study the coherent transport of a single photon, which propagates in a one-dimensional waveguide and is scattered by a quadratic optomechanical system. Our approach, which is based on the Lippmann-Schwinger equation, gives an analytical solution to describe the single-photon transmission and reflection properties. We analyze the transport spectra and find they are not only related to the optomechanical system's energy-level structure, but also dependent on the optomechanical system's inherent parameters. For the existence of atomic degrees of freedom, we get a Rabi-splitting-like or an electromagnetically induced transparency (EIT)-like spectrum, depending on the atom-cavity coupling strength. Here, we focus on the single-photon strong-coupling regime so that single-quantum effects could be seen.SCI(E)ARTICLE19
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