Single-atom catalysts,featuring some of the most unique activities,selectivity,and high metal utilization,have been extensively studied over the past decade.Given their high activity,selectivity,especially towards sma...Single-atom catalysts,featuring some of the most unique activities,selectivity,and high metal utilization,have been extensively studied over the past decade.Given their high activity,selectivity,especially towards small molecules or key intermediate conversions,they can be synergized together with other active species(typically other single atoms,atomic clusters,or nanoparticles)in either tandem or parallel or both,leading to much better performance in complex catalytic processes.Although there have been reports on effectively combining the multiple components into one single catalytic entity,the combination and synergy between single atoms and other active species have not been reviewed and examined in a systematic manner.Herein,in this overview,the key synergistic interactions,binary complementary effects,and the bifunctional functions of single atoms with other active species are defined and discussed in detail.The integration functions of their marriages are in-vestigated with particular emphasis on the homogeneous and heterogeneous combinations,spatial distribution,synthetic strategies,and the thus-derived outstanding catalytic performance,together with new light shined on the catalytic mechanisms by zooming in several case studies.The dynamic nature of each of the active species and in particular their interactions in such new catalytic entities in the heterogeneous electrocatalytic processes are visited,on the basis of the in situ/operando evidence.Last,we feature the current chal-lenges and future perspectives of these integrated catalytic entities that can offer guidance for advanced catalyst design by the rational combination and synergy of binary or multiple active species.展开更多
Motivated by the fact that calibrated light curves of Type Ia supernovae （SNe Ia） have become a major tool to determine the expansion history of the Universe, considerable attention has been given to, both, observat...Motivated by the fact that calibrated light curves of Type Ia supernovae （SNe Ia） have become a major tool to determine the expansion history of the Universe, considerable attention has been given to, both, observations and models of these events over the past 15 years. Here, we summarize new observational constraints, address recent progress in modeling Type Ia supernovae by means of three-dimensional hydrodynamic simulations, and discuss several of the still open questions. It will be be shown that the new models have considerable predictive power which allows us to study observable properties such as light curves and spectra without adjustable non-physical parameters. This is a necessary requisite to improve our understanding of the explosion mechanism and to settle the question of the applicability of SNe Ia as distance indicators for cosmology. We explore the capabilities of the models by comparing them be applied to study the origin of the diversity with observations and we show how such models can of SNe Ia.展开更多
I construct the class of supernovae and supernova progenitors that result from fatal common envelope evolution(CEE). The fatal CEE progenitors are stellar binary systems where a companion spirals-in inside the envelop...I construct the class of supernovae and supernova progenitors that result from fatal common envelope evolution(CEE). The fatal CEE progenitors are stellar binary systems where a companion spirals-in inside the envelope of a giant star and merges with the core. The companion can be a neutron star(NS;or a black hole) that destroys the core and by that forms a common envelope jets supernova(CEJSN), a white dwarf(WD) that merges with the core to form a massive WD that later might explode as a Type Ia supernova(the core degenerate scenario), or a main sequence companion. In the latter case the outcome might be a core collapse supernova(CCSN) of a blue giant, a CCSN of type IIb or of type Ib. In another member of this class two giant stars merge and the two cores spiral-in toward each other to form a massive core that later explodes as a CCSN with a massive circumstellar matter(CSM). I discuss the members of this class, their characteristics, and their common properties. I find that fatal CEE events account for ≈6%-10% of all CCSNe, and raise the possibility that a large fraction of peculiar and rare supernovae result from the fatal CEE. The study of these supernova progenitors as a class will bring insights on other types of supernova progenitors, as well as on the outcome of the CEE.展开更多
Recently, deep neural networks(DNNs) significantly outperform Gaussian mixture models in acoustic modeling for speech recognition. However, the substantial increase in computational load during the inference stage mak...Recently, deep neural networks(DNNs) significantly outperform Gaussian mixture models in acoustic modeling for speech recognition. However, the substantial increase in computational load during the inference stage makes deep models difficult to directly deploy on low-power embedded devices. To alleviate this issue,structure sparseness and low precision fixed-point quantization have been applied widely. In this work, binary neural networks for speech recognition are developed to reduce the computational cost during the inference stage.A fast implementation of binary matrix multiplication is introduced. On modern central processing unit(CPU)and graphics processing unit(GPU) architectures, a 5–7 times speedup compared with full precision floatingpoint matrix multiplication can be achieved in real applications. Several kinds of binary neural networks and related model optimization algorithms are developed for large vocabulary continuous speech recognition acoustic modeling. In addition, to improve the accuracy of binary models, knowledge distillation from the normal full precision floating-point model to the compressed binary model is explored. Experiments on the standard Switchboard speech recognition task show that the proposed binary neural networks can deliver 3–4 times speedup over the normal full precision deep models. With the knowledge distillation from the normal floating-point models, the binary DNNs or binary convolutional neural networks(CNNs) can restrict the word error rate(WER) degradation to within 15.0%,compared to the normal full precision floating-point DNNs or CNNs, respectively. Particularly for the binary CNN with binarization only on the convolutional layers, the WER degradation is very small and is almost negligible with the proposed approach.展开更多
BH Cen is a short-period early-type binary with a period of 0.792^d in the extremely young star-forming cluster IC 2944. New multi-color CCD photometric light curves in U, B, V, R and I bands are presented and are ana...BH Cen is a short-period early-type binary with a period of 0.792^d in the extremely young star-forming cluster IC 2944. New multi-color CCD photometric light curves in U, B, V, R and I bands are presented and are analyzed by using the Wilson-Devinney code. It is detected that BH Cen is a high-mass-ratio overcontact binary with a fill-out factor of 46.4% and a mass ratio of 0.89. The derived orbital inclination i is 88.9 degrees, indicating that it is a totally eclipsing binary and the photometric parameters can be determined reliably. By adding new eclipse times, the orbital period changes in the binary are analyzed. It is confirmed that the period of BH Cen shows a long-term increase while it undergoes a cyclic oscillation with an amplitude of A3 = 0.024 d and a period of P3 = 50.3 yr. The high mass ratio, overcontact configuration and long-term continuous increase in the orbital period all suggest that BH Cen is in the evolutionary state after the shortest-period stage of Case A mass transfer.The continuous increase in period can be explained by mass transfer from the secondary component to the primary one at a rate of˙M2 = 2.8×10^-6 M⊙per year. The cyclic change can be plausibly explained by the presence of a third body because both components in the BH Cen system are early-type stars. Its mass is determined to be no less than 2.2 M⊙ at an orbital separation of about 32.5 AU. Since no third light was found during the photometric solution, it is possible that the third body may be a candidate for a compact object.展开更多
The dynamics of compact binaries is very complicated because of spin-orbit cou- pling and spin-spin coupling. With Laskar＇s frequency map analysis （FMA） and frequency diffusion as an indicator, we found that misali...The dynamics of compact binaries is very complicated because of spin-orbit cou- pling and spin-spin coupling. With Laskar＇s frequency map analysis （FMA） and frequency diffusion as an indicator, we found that misalignment of the spins and orbital angular momentum has a great effect on the dynamics, and for systems with different mass ratios β = m2/ml chaos occurs at different spin-orbit configurations. For equal-mass binaries （β = 1）, chaos occurs when the spins nearly cancel each other out. For some other systems （for exampleβ - 1/2）, the binaries are irregular, even chaotic, when the spins are perpendicular to the orbital angular momentum. For the case where gravitational radiation is taken into account, we give an analytic estimation for the frequency diffusion based on the decay of the orbit, which is roughly consistent with our simulations. This means the FMA is not suitable as a chaos indicator for weak chaotic cases with dissipative terms.展开更多
Energetic outflows from main sequence stars accreting mass at very high rates might account for the powering of some eruptive objects, such as merging main sequence stars, major eruptions of luminous blue variables, e...Energetic outflows from main sequence stars accreting mass at very high rates might account for the powering of some eruptive objects, such as merging main sequence stars, major eruptions of luminous blue variables, e.g., the Great Eruption of Eta Carinae, and other intermediate luminosity optical transients（ILOTs; red novae; red transients）. These powerful outflows could potentially also supply the extra energy required in the common envelope process and in the grazing envelope evolution of binary systems. We propose that a massive outflow/jets mediated by magnetic fields might remove energy and angular momentum from the accretion disk to allow such high accretion rate flows. By examining the possible activity of the magnetic fields of accretion disks, we conclude that indeed main sequence stars might accrete mass at very high rates, up to≈10^-2M⊙yr^-1for solar type stars, and up toion≈1 M⊙yr^-1for very massive stars. We speculate that magnetic fields amplified in such extreme condits might lead to the formation of massive bipolar outflows that can remove most of the disk＇s energy and angular momentum. It is this energy and angular momentum removal that allows the very high mass accretion rate onto main sequence stars.展开更多
Abstract We report the discovery of 45 high-velocity extreme horizontal branch （EHB） stars in the globular cluster Omega Centauri （NGC 5139）. The tangential ve- locities of these EHB stars are determined to be in ...Abstract We report the discovery of 45 high-velocity extreme horizontal branch （EHB） stars in the globular cluster Omega Centauri （NGC 5139）. The tangential ve- locities of these EHB stars are determined to be in the range 93-313 km s^-1, with an average uncertainty of -27 km s^-1. The central escape velocity of the cluster is determined to be in the range 60~105 km s^-1. These EHB stars are significantly more concentrated toward the cluster core compared with other cluster members. The formation mechanisms of these EHB stars are discussed. Our conclusions can be sum- marized as follows： （1） A comparison of the tangential velocities of these EHB stars to the central escape velocity of the cluster shows that most if not all of these EHB stars are unbound to the cluster; （2） These EHB stars obtained high velocities in the central cluster region no longer than - 1 Myr ago and may be subsequently ejected from the cluster in the next -1 Myr; （3） If the progenitors of these EHB stars were single stars, then they may have experienced a fast mass-loss process. If the progen- itors were in close binaries, then they may have formed through disruptions by the intermediate-mass black hole in the cluster center.展开更多
基金JW and team thank the support of MOE,Singapore(MOE2018-T2-2-095),for research conducted at the National University of Singapore.
文摘Single-atom catalysts,featuring some of the most unique activities,selectivity,and high metal utilization,have been extensively studied over the past decade.Given their high activity,selectivity,especially towards small molecules or key intermediate conversions,they can be synergized together with other active species(typically other single atoms,atomic clusters,or nanoparticles)in either tandem or parallel or both,leading to much better performance in complex catalytic processes.Although there have been reports on effectively combining the multiple components into one single catalytic entity,the combination and synergy between single atoms and other active species have not been reviewed and examined in a systematic manner.Herein,in this overview,the key synergistic interactions,binary complementary effects,and the bifunctional functions of single atoms with other active species are defined and discussed in detail.The integration functions of their marriages are in-vestigated with particular emphasis on the homogeneous and heterogeneous combinations,spatial distribution,synthetic strategies,and the thus-derived outstanding catalytic performance,together with new light shined on the catalytic mechanisms by zooming in several case studies.The dynamic nature of each of the active species and in particular their interactions in such new catalytic entities in the heterogeneous electrocatalytic processes are visited,on the basis of the in situ/operando evidence.Last,we feature the current chal-lenges and future perspectives of these integrated catalytic entities that can offer guidance for advanced catalyst design by the rational combination and synergy of binary or multiple active species.
文摘Motivated by the fact that calibrated light curves of Type Ia supernovae （SNe Ia） have become a major tool to determine the expansion history of the Universe, considerable attention has been given to, both, observations and models of these events over the past 15 years. Here, we summarize new observational constraints, address recent progress in modeling Type Ia supernovae by means of three-dimensional hydrodynamic simulations, and discuss several of the still open questions. It will be be shown that the new models have considerable predictive power which allows us to study observable properties such as light curves and spectra without adjustable non-physical parameters. This is a necessary requisite to improve our understanding of the explosion mechanism and to settle the question of the applicability of SNe Ia as distance indicators for cosmology. We explore the capabilities of the models by comparing them be applied to study the origin of the diversity with observations and we show how such models can of SNe Ia.
基金supported by the E. and J. Bishop Research Fund at the Technionby a grant from the Israel Science Foundation
文摘I construct the class of supernovae and supernova progenitors that result from fatal common envelope evolution(CEE). The fatal CEE progenitors are stellar binary systems where a companion spirals-in inside the envelope of a giant star and merges with the core. The companion can be a neutron star(NS;or a black hole) that destroys the core and by that forms a common envelope jets supernova(CEJSN), a white dwarf(WD) that merges with the core to form a massive WD that later might explode as a Type Ia supernova(the core degenerate scenario), or a main sequence companion. In the latter case the outcome might be a core collapse supernova(CCSN) of a blue giant, a CCSN of type IIb or of type Ib. In another member of this class two giant stars merge and the two cores spiral-in toward each other to form a massive core that later explodes as a CCSN with a massive circumstellar matter(CSM). I discuss the members of this class, their characteristics, and their common properties. I find that fatal CEE events account for ≈6%-10% of all CCSNe, and raise the possibility that a large fraction of peculiar and rare supernovae result from the fatal CEE. The study of these supernova progenitors as a class will bring insights on other types of supernova progenitors, as well as on the outcome of the CEE.
基金the National Natural Science Foundation of China (Nos. 61603252 and U1736202)experiments have been carried out on the Pi supercomputer at Shanghai Jiao Tong University.
文摘Recently, deep neural networks(DNNs) significantly outperform Gaussian mixture models in acoustic modeling for speech recognition. However, the substantial increase in computational load during the inference stage makes deep models difficult to directly deploy on low-power embedded devices. To alleviate this issue,structure sparseness and low precision fixed-point quantization have been applied widely. In this work, binary neural networks for speech recognition are developed to reduce the computational cost during the inference stage.A fast implementation of binary matrix multiplication is introduced. On modern central processing unit(CPU)and graphics processing unit(GPU) architectures, a 5–7 times speedup compared with full precision floatingpoint matrix multiplication can be achieved in real applications. Several kinds of binary neural networks and related model optimization algorithms are developed for large vocabulary continuous speech recognition acoustic modeling. In addition, to improve the accuracy of binary models, knowledge distillation from the normal full precision floating-point model to the compressed binary model is explored. Experiments on the standard Switchboard speech recognition task show that the proposed binary neural networks can deliver 3–4 times speedup over the normal full precision deep models. With the knowledge distillation from the normal floating-point models, the binary DNNs or binary convolutional neural networks(CNNs) can restrict the word error rate(WER) degradation to within 15.0%,compared to the normal full precision floating-point DNNs or CNNs, respectively. Particularly for the binary CNN with binarization only on the convolutional layers, the WER degradation is very small and is almost negligible with the proposed approach.
基金supported by the National Natural Science Foundation of China(Grant No.11325315)
文摘BH Cen is a short-period early-type binary with a period of 0.792^d in the extremely young star-forming cluster IC 2944. New multi-color CCD photometric light curves in U, B, V, R and I bands are presented and are analyzed by using the Wilson-Devinney code. It is detected that BH Cen is a high-mass-ratio overcontact binary with a fill-out factor of 46.4% and a mass ratio of 0.89. The derived orbital inclination i is 88.9 degrees, indicating that it is a totally eclipsing binary and the photometric parameters can be determined reliably. By adding new eclipse times, the orbital period changes in the binary are analyzed. It is confirmed that the period of BH Cen shows a long-term increase while it undergoes a cyclic oscillation with an amplitude of A3 = 0.024 d and a period of P3 = 50.3 yr. The high mass ratio, overcontact configuration and long-term continuous increase in the orbital period all suggest that BH Cen is in the evolutionary state after the shortest-period stage of Case A mass transfer.The continuous increase in period can be explained by mass transfer from the secondary component to the primary one at a rate of˙M2 = 2.8×10^-6 M⊙per year. The cyclic change can be plausibly explained by the presence of a third body because both components in the BH Cen system are early-type stars. Its mass is determined to be no less than 2.2 M⊙ at an orbital separation of about 32.5 AU. Since no third light was found during the photometric solution, it is possible that the third body may be a candidate for a compact object.
基金Supported by the National Natural Science Foundation of China.
文摘The dynamics of compact binaries is very complicated because of spin-orbit cou- pling and spin-spin coupling. With Laskar＇s frequency map analysis （FMA） and frequency diffusion as an indicator, we found that misalignment of the spins and orbital angular momentum has a great effect on the dynamics, and for systems with different mass ratios β = m2/ml chaos occurs at different spin-orbit configurations. For equal-mass binaries （β = 1）, chaos occurs when the spins nearly cancel each other out. For some other systems （for exampleβ - 1/2）, the binaries are irregular, even chaotic, when the spins are perpendicular to the orbital angular momentum. For the case where gravitational radiation is taken into account, we give an analytic estimation for the frequency diffusion based on the decay of the orbit, which is roughly consistent with our simulations. This means the FMA is not suitable as a chaos indicator for weak chaotic cases with dissipative terms.
文摘Energetic outflows from main sequence stars accreting mass at very high rates might account for the powering of some eruptive objects, such as merging main sequence stars, major eruptions of luminous blue variables, e.g., the Great Eruption of Eta Carinae, and other intermediate luminosity optical transients（ILOTs; red novae; red transients）. These powerful outflows could potentially also supply the extra energy required in the common envelope process and in the grazing envelope evolution of binary systems. We propose that a massive outflow/jets mediated by magnetic fields might remove energy and angular momentum from the accretion disk to allow such high accretion rate flows. By examining the possible activity of the magnetic fields of accretion disks, we conclude that indeed main sequence stars might accrete mass at very high rates, up to≈10^-2M⊙yr^-1for solar type stars, and up toion≈1 M⊙yr^-1for very massive stars. We speculate that magnetic fields amplified in such extreme condits might lead to the formation of massive bipolar outflows that can remove most of the disk＇s energy and angular momentum. It is this energy and angular momentum removal that allows the very high mass accretion rate onto main sequence stars.
基金supported by the National Natural Science Foundation of China(NSFC,Grant No.11403004)the School Foundation of Changzhou University(ZMF1002121)+3 种基金support by the 973 Program(2014CB845702)the Strategic Priority Research Program The Emergence of Cosmological Structures of the Chinese Academy of Sciences(CASgrant XDB09010100)by the NSFC(No.11373054)
文摘Abstract We report the discovery of 45 high-velocity extreme horizontal branch （EHB） stars in the globular cluster Omega Centauri （NGC 5139）. The tangential ve- locities of these EHB stars are determined to be in the range 93-313 km s^-1, with an average uncertainty of -27 km s^-1. The central escape velocity of the cluster is determined to be in the range 60~105 km s^-1. These EHB stars are significantly more concentrated toward the cluster core compared with other cluster members. The formation mechanisms of these EHB stars are discussed. Our conclusions can be sum- marized as follows： （1） A comparison of the tangential velocities of these EHB stars to the central escape velocity of the cluster shows that most if not all of these EHB stars are unbound to the cluster; （2） These EHB stars obtained high velocities in the central cluster region no longer than - 1 Myr ago and may be subsequently ejected from the cluster in the next -1 Myr; （3） If the progenitors of these EHB stars were single stars, then they may have experienced a fast mass-loss process. If the progen- itors were in close binaries, then they may have formed through disruptions by the intermediate-mass black hole in the cluster center.
