Gamma-ray bursts (GRBs) are the most intense transient gamma-ray events in the sky; this, together with the strong evidence (the isotropic and inhomogeneous distribution of GRBs detected by BASTE) that they are locat...Gamma-ray bursts (GRBs) are the most intense transient gamma-ray events in the sky; this, together with the strong evidence (the isotropic and inhomogeneous distribution of GRBs detected by BASTE) that they are located at cosmological distances, makes them the most energetic events ever known. For example, the observed radiation energies of some GRBs are equivalent to the total convertion into radiation of the mass energy of more than one solar mass. This is thousand times stronger than the energy of a supernova explosion. Some unconventional energy mechanism and extremely high conversion efficiency for these mysterious events are required. The discovery of host galaxies and association with supernovae at cosmological distances by the recently launched satellite of BeppoSAX and ground based radio and optical telescopes in GRB afterglow provides further support to the cosmological origin of GRBs and put strong constraints on their central engine. It is the aim of this article to review the possible central engines, energy mechanisms, dynamical and spectral evolution of GRBs, especially focusing on the afterglows in multi-wavebands.展开更多
We use a three-dimensional pulsar magnetosphere model to study the light curve and spectra of x-rays and gamma-rays from the Crab pulsar. In this model, the vertical size of the outer gap is first determined by a self...We use a three-dimensional pulsar magnetosphere model to study the light curve and spectra of x-rays and gamma-rays from the Crab pulsar. In this model, the vertical size of the outer gap is first determined by a self-consistent model in which the outer gap is limited by pair production from collisions of thermal photons produced by polar cap heating of backflow outer gap current and curvature photons emitted by gap accelerated charged particles. The transverse size of the outer gap is determined by local pair production conditions. In principle, there are two topologically disconnected outer gaps present in the magnetosphere of a pulsar, and both incoming and outgoing particle flows are allowed. However, double-peak light curves with strong bridges are most common, Making use of the three-dimensional structure of the outer gap and its local properties, we compare the results of our model with the light curve and phase-resolved spectra of the Crab pulsar.展开更多
We present a case study of the relevance of the radially pulsational instability of a two-temperature accretion disk around a neutron star to anomalous X-ray pulsars (AXPs). Our estimates are based on the approxima...We present a case study of the relevance of the radially pulsational instability of a two-temperature accretion disk around a neutron star to anomalous X-ray pulsars (AXPs). Our estimates are based on the approximation that such a neutron star disk with mass in the range of 10-6-10-5 M⊙ is formed by supernova fallback. We derive several peculiar properties of the accretion disk instability: a narrow interval of X-ray pulse periods; lower X-ray luminosities; a period derivative and an evolution time scale. All these results are in good agreement with the observations of the AXPs.展开更多
Microstructural stability of a nickel base single crystal alloy DD8 has been investigated.Standard heat treated specimen showed good microstructural stability at 950℃.While under the as-cast condition,a kind of rod-l...Microstructural stability of a nickel base single crystal alloy DD8 has been investigated.Standard heat treated specimen showed good microstructural stability at 950℃.While under the as-cast condition,a kind of rod-like phase precipitated in the interdendritic region of as-cast specimen during thermal exposure.The phase,which has bcc structure,was enriched with Cr.Thermo-calc also predicted precipitation of a bcc phase at around 950℃.The Cr-rich bcc phase was considered asα-Cr and formed due to the segregation of Cr under the as-cast condition.展开更多
In the frame of theγ-ray pulsar outer gap model,e^(±)pairs in the pulsar magnetosphere are produced by the cascade of e^(±)pairs through synchrotron radiation of the return current from the outer gap.These ...In the frame of theγ-ray pulsar outer gap model,e^(±)pairs in the pulsar magnetosphere are produced by the cascade of e^(±)pairs through synchrotron radiation of the return current from the outer gap.These pairs are accelerated mono-energetically to relativistic energies in the pulsar wind driven by low-frequency electromagnetic waves.Using Monte Carlo simulations,we generate a sample of the matureγ-ray pulsars in our Galaxy and calculate the positron production rate from these pulsars.With a simple leaky box model,we calculate the ratio of cosmic-ray positron to total electrons.Our result indicates that the pulsar contribution to the cosmic ray positron peaks at about 40 GeV and the observed e^(+)/(e^(-)+e^(+))ratio can be explained by this model.展开更多
Adult olfactory neurogenesis plays critical roles in maintaining olfactory functions.Newly-generated neurons in the subventricular zone migrate to the olfactory bulb(OB) and determine olfactory discrimination,but the ...Adult olfactory neurogenesis plays critical roles in maintaining olfactory functions.Newly-generated neurons in the subventricular zone migrate to the olfactory bulb(OB) and determine olfactory discrimination,but the mechanisms underlying the regulation of olfactory neurogenesis remain unclear.Our previous study indicated the potential of APPL2(adaptor protein,phosphotyrosine interacting with PH domain and leucine zipper 2) as a modulating factor for neurogenesis in the adult olfactory system.In the present study,we report how APPL2 affects neurogenesis in the OB and thereby mediates olfactory discrimination by using both in vitro neural stem cells(NSCs) and an in vivo animal model-APPL2 transgenic(Tg) mice.In the in vitro study,we found that APPL2 overexpression resulted in NSCs switching from neuronal differentiation to gliogenesis while APPL2 knockdown promoted neurogenesis.In the in vivo study,APPL2 Tg mice had a higher population of glial cells and dampened neuronal production in the olfactory system,including the corpus callosum,OB,and rostral migratory stream.Adult APPL2 Tg mice displayed impaired performance in olfactory discrimination tests compared with wild-type mice.Furthermore,we found that an interaction of APPL2 with Notch1 contributed to the roles of APPL2 in modulating the neurogenic lineage-switching and olfactory behaviors.In conclusion,APPL2 controls olfactory discrimination by switching the fate choice of NSCs via interaction with Notch1 signaling.展开更多
An ancient conflict between hosts and pathogens has driven the innate and adaptive arms of immunity.Knowledge about this interplay can not only help us identify biological mechanisms but also reveal pathogen vulnerabi...An ancient conflict between hosts and pathogens has driven the innate and adaptive arms of immunity.Knowledge about this interplay can not only help us identify biological mechanisms but also reveal pathogen vulnerabilities that can be leveraged therapeutically.The humoral response to SARS-CoV-2 infection has been the focus of intense research,and the role of the innate immune system has received significantly less attention.Here,we review current knowledge of the innate immune response to SARS-CoV-2 infection and the various means SARS-CoV-2 employs to evade innate defense systems.We also consider the role of innate immunity in SARS-CoV-2 vaccines and in the phenomenon of long COVID.展开更多
The establishment of a possible connection between neutrino emission and gravitational-wave(GW)bursts is important to our understanding of the physical processes that occur when black holes or neutron stars merge.In t...The establishment of a possible connection between neutrino emission and gravitational-wave(GW)bursts is important to our understanding of the physical processes that occur when black holes or neutron stars merge.In the Daya Bay experiment,using the data collected from December 2011 to August 2017,a search was per-formed for electron-antineutrino signals that coincided with detected GW events,including GW150914,GW151012,GW151226,GW170104,GW170608,GW 170814,and GW 170817.We used three time windows of±10,±500,and±1000 s relative to the occurrence of the GW events and a neutrino energy range of 1.8 to 100 MeV to search for correlated neutrino candidates.The detected electron-antineutrino candidates were consistent with the expected background rates for all the three time windows.Assuming monochromatic spectra,we found upper limits(90%confidence level)of the electron-antineutrino fluence of(1.13-2.44)×10^(11)cm^(-2)at 5 MeV to 8.0×10^(7)cm^(-2)at 100 MeV for the three time w indows.Under the assumption of a Fermi-Dirac spectrum,the upper limits were found to be(5.4-7.0)×10^(9)cm^(2)for the three time windows.展开更多
The prediction of reactor antineutrino spectra will play a crucial role as reactor experiments enter the precision era.The positron energy spectrum of 3.5 million antineutrino inverse beta decay reactions observed by ...The prediction of reactor antineutrino spectra will play a crucial role as reactor experiments enter the precision era.The positron energy spectrum of 3.5 million antineutrino inverse beta decay reactions observed by the Daya Bay experiment,in combination with the fission rates of fissile isotopes in the reactor,is used to extract the positron energy spectra resulting from the fission of specific isotopes.This information can be used to produce a precise,data-based prediction of the antineutrino energy spectrum in other reactor antineutrino experiments with different fission fractions than Daya Bay.The positron energy spectra are unfolded to obtain the antineutrino energy spectra by removing the contribution from detector response with the Wiener-SVD unfolding method.Consistent results are obtained with other unfolding methods.A technique to construct a data-based prediction of the reactor antineutrino energy spectrum is proposed and investigated.Given the reactor fission fractions,the technique can predict the energy spectrum to a 2%precision.In addition,we illustrate how to perform a rigorous comparison between the unfolded antineutrino spectrum and a theoretical model prediction that avoids the input model bias of the unfolding method.展开更多
基金a RGC grant of the Hong Kong Government and the National Natural Science Foundation of China.
文摘Gamma-ray bursts (GRBs) are the most intense transient gamma-ray events in the sky; this, together with the strong evidence (the isotropic and inhomogeneous distribution of GRBs detected by BASTE) that they are located at cosmological distances, makes them the most energetic events ever known. For example, the observed radiation energies of some GRBs are equivalent to the total convertion into radiation of the mass energy of more than one solar mass. This is thousand times stronger than the energy of a supernova explosion. Some unconventional energy mechanism and extremely high conversion efficiency for these mysterious events are required. The discovery of host galaxies and association with supernovae at cosmological distances by the recently launched satellite of BeppoSAX and ground based radio and optical telescopes in GRB afterglow provides further support to the cosmological origin of GRBs and put strong constraints on their central engine. It is the aim of this article to review the possible central engines, energy mechanisms, dynamical and spectral evolution of GRBs, especially focusing on the afterglows in multi-wavebands.
基金Supported by the National Science Foundation of Yunnan Province under Grant No.98A140R and RGC grant of the Hong Kong Government.
文摘We use a three-dimensional pulsar magnetosphere model to study the light curve and spectra of x-rays and gamma-rays from the Crab pulsar. In this model, the vertical size of the outer gap is first determined by a self-consistent model in which the outer gap is limited by pair production from collisions of thermal photons produced by polar cap heating of backflow outer gap current and curvature photons emitted by gap accelerated charged particles. The transverse size of the outer gap is determined by local pair production conditions. In principle, there are two topologically disconnected outer gaps present in the magnetosphere of a pulsar, and both incoming and outgoing particle flows are allowed. However, double-peak light curves with strong bridges are most common, Making use of the three-dimensional structure of the outer gap and its local properties, we compare the results of our model with the light curve and phase-resolved spectra of the Crab pulsar.
文摘We present a case study of the relevance of the radially pulsational instability of a two-temperature accretion disk around a neutron star to anomalous X-ray pulsars (AXPs). Our estimates are based on the approximation that such a neutron star disk with mass in the range of 10-6-10-5 M⊙ is formed by supernova fallback. We derive several peculiar properties of the accretion disk instability: a narrow interval of X-ray pulse periods; lower X-ray luminosities; a period derivative and an evolution time scale. All these results are in good agreement with the observations of the AXPs.
文摘Microstructural stability of a nickel base single crystal alloy DD8 has been investigated.Standard heat treated specimen showed good microstructural stability at 950℃.While under the as-cast condition,a kind of rod-like phase precipitated in the interdendritic region of as-cast specimen during thermal exposure.The phase,which has bcc structure,was enriched with Cr.Thermo-calc also predicted precipitation of a bcc phase at around 950℃.The Cr-rich bcc phase was considered asα-Cr and formed due to the segregation of Cr under the as-cast condition.
基金Supported by the Natural Science Foundation of Yunnan Province under Grant No.98A140Ran RGC grant of the Hong Kong GovernmentSubsidized by the Special Funds for Major State Basic Research Projects.
文摘In the frame of theγ-ray pulsar outer gap model,e^(±)pairs in the pulsar magnetosphere are produced by the cascade of e^(±)pairs through synchrotron radiation of the return current from the outer gap.These pairs are accelerated mono-energetically to relativistic energies in the pulsar wind driven by low-frequency electromagnetic waves.Using Monte Carlo simulations,we generate a sample of the matureγ-ray pulsars in our Galaxy and calculate the positron production rate from these pulsars.With a simple leaky box model,we calculate the ratio of cosmic-ray positron to total electrons.Our result indicates that the pulsar contribution to the cosmic ray positron peaks at about 40 GeV and the observed e^(+)/(e^(-)+e^(+))ratio can be explained by this model.
基金supported by Areas of Excellence (AoE/P-705/16)the General Research Fund,Hong Kong SAR (GRF No.777313 M)。
文摘Adult olfactory neurogenesis plays critical roles in maintaining olfactory functions.Newly-generated neurons in the subventricular zone migrate to the olfactory bulb(OB) and determine olfactory discrimination,but the mechanisms underlying the regulation of olfactory neurogenesis remain unclear.Our previous study indicated the potential of APPL2(adaptor protein,phosphotyrosine interacting with PH domain and leucine zipper 2) as a modulating factor for neurogenesis in the adult olfactory system.In the present study,we report how APPL2 affects neurogenesis in the OB and thereby mediates olfactory discrimination by using both in vitro neural stem cells(NSCs) and an in vivo animal model-APPL2 transgenic(Tg) mice.In the in vitro study,we found that APPL2 overexpression resulted in NSCs switching from neuronal differentiation to gliogenesis while APPL2 knockdown promoted neurogenesis.In the in vivo study,APPL2 Tg mice had a higher population of glial cells and dampened neuronal production in the olfactory system,including the corpus callosum,OB,and rostral migratory stream.Adult APPL2 Tg mice displayed impaired performance in olfactory discrimination tests compared with wild-type mice.Furthermore,we found that an interaction of APPL2 with Notch1 contributed to the roles of APPL2 in modulating the neurogenic lineage-switching and olfactory behaviors.In conclusion,APPL2 controls olfactory discrimination by switching the fate choice of NSCs via interaction with Notch1 signaling.
文摘An ancient conflict between hosts and pathogens has driven the innate and adaptive arms of immunity.Knowledge about this interplay can not only help us identify biological mechanisms but also reveal pathogen vulnerabilities that can be leveraged therapeutically.The humoral response to SARS-CoV-2 infection has been the focus of intense research,and the role of the innate immune system has received significantly less attention.Here,we review current knowledge of the innate immune response to SARS-CoV-2 infection and the various means SARS-CoV-2 employs to evade innate defense systems.We also consider the role of innate immunity in SARS-CoV-2 vaccines and in the phenomenon of long COVID.
基金Daya Bay is supported in part by the Ministry of Science and Technology o f China, the U.S. Department o f Energy, the Chinese Academy of Sciences, the CASCenter for Excellence in Particle Physics, the National Natural Science Foundation of China, the Guangdong provincial government, the Shenzhen municipal government,the China General Nuclear Power Group, Key Laboratory of Particle and Radiation Imaging (Tsinghua University), the Ministry of Education, Key Laboratory ofParticle Physics and Particle Irradiation (Shandong University), the Ministry o f Education, Shanghai Laboratory for Particle Physics and Cosmology, the ResearchGrants Council o f the Hong Kong Special Administrative Region of China, the University Development Fund of the University of Hong Kong, the MOE program forResearch of Excellence at National Taiwan University, National Chiao-Tung University, NSC fund support from Taiwan, the U.S. National Science Foundation, the AlfredP. Sloan Foundation, the Ministry o f Education, Youth, and Sports of the Czech Republic, the Charles University GAUK (284317), the Joint Institute o f NuclearResearch in Dubna, Russia, the National Commission of Scientific and Technological Research of Chile, and the Tsinghua University Initiative Scientific Research Program.
文摘The establishment of a possible connection between neutrino emission and gravitational-wave(GW)bursts is important to our understanding of the physical processes that occur when black holes or neutron stars merge.In the Daya Bay experiment,using the data collected from December 2011 to August 2017,a search was per-formed for electron-antineutrino signals that coincided with detected GW events,including GW150914,GW151012,GW151226,GW170104,GW170608,GW 170814,and GW 170817.We used three time windows of±10,±500,and±1000 s relative to the occurrence of the GW events and a neutrino energy range of 1.8 to 100 MeV to search for correlated neutrino candidates.The detected electron-antineutrino candidates were consistent with the expected background rates for all the three time windows.Assuming monochromatic spectra,we found upper limits(90%confidence level)of the electron-antineutrino fluence of(1.13-2.44)×10^(11)cm^(-2)at 5 MeV to 8.0×10^(7)cm^(-2)at 100 MeV for the three time w indows.Under the assumption of a Fermi-Dirac spectrum,the upper limits were found to be(5.4-7.0)×10^(9)cm^(2)for the three time windows.
基金Supported in part by the Ministry of Science and Technology of Chinathe U.S.Department of Energy,the Chinese Academy of Sciences,the CAS Center for Excellence in Particle Physics,the National Natural Science Foundation of China+3 种基金the Guangdong provincial governmentthe Shenzhen municipal government,the China General Nuclear Power Group,the Research Grants Council of the Hong Kong Special Administrative Region of China,the Ministry of Education in TWthe U.S.National Science Foundation,the Ministry of Education,Youth,and Sports of the Czech Republic,the Charles University Research Centre UNCE,the Joint Institute of Nuclear Research in Dubna,Russiathe National Commission of Scientific and Technological Research of Chile。
文摘The prediction of reactor antineutrino spectra will play a crucial role as reactor experiments enter the precision era.The positron energy spectrum of 3.5 million antineutrino inverse beta decay reactions observed by the Daya Bay experiment,in combination with the fission rates of fissile isotopes in the reactor,is used to extract the positron energy spectra resulting from the fission of specific isotopes.This information can be used to produce a precise,data-based prediction of the antineutrino energy spectrum in other reactor antineutrino experiments with different fission fractions than Daya Bay.The positron energy spectra are unfolded to obtain the antineutrino energy spectra by removing the contribution from detector response with the Wiener-SVD unfolding method.Consistent results are obtained with other unfolding methods.A technique to construct a data-based prediction of the reactor antineutrino energy spectrum is proposed and investigated.Given the reactor fission fractions,the technique can predict the energy spectrum to a 2%precision.In addition,we illustrate how to perform a rigorous comparison between the unfolded antineutrino spectrum and a theoretical model prediction that avoids the input model bias of the unfolding method.
