The Phased Array Feed(PAF)is considered as one of the next generation receivers for radio telescopes,which can significantly enlarge the instantaneous Field-of-View of large aperture single dish radio telescopes and e...The Phased Array Feed(PAF)is considered as one of the next generation receivers for radio telescopes,which can significantly enlarge the instantaneous Field-of-View of large aperture single dish radio telescopes and enable more flexible observing configurations.Study efforts on PAF development for radio telescopes have been made for more than two decades and have become more and more applicable.We report the development of an ambient-temperature 19 element L-band PAF system and the experimental results including its far field beam pattern and system temperature measurement,which achieve the expectations.Implementing the aperture array beam-forming method,we demonstrate a wide-field Galactic HI observations in the radio camera mode.The results indicate that this system might be applicable for strong Galactic transient detections.This system could be directly equipped to large telescopes like the Five-hundred-meter Aperture Spherical radio Telescope(FAST)and FAST array in the future.展开更多
In this paper,we report a real-time Fast Radio Burst(FRB)searching system that has been successfully implemented with the 19 beam receiver of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).The relativ...In this paper,we report a real-time Fast Radio Burst(FRB)searching system that has been successfully implemented with the 19 beam receiver of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).The relatively small field of view of FAST makes the search for new FRBs challenging,but its high sensitivity significantly improves the accuracy of FRB localization and enables the detection of high-precision neutral hydrogen absorption lines generated by FRBs.Our goal is to develop an FRB searching system capable of realtime detection of FRBs that allows high-time resolution spectro-temporal studies among the repeated bursts,as well as detailed investigations of these bursts and exploration of FRB progenitor models.The data from each beam of the 19-beam receiver are fed into a high-performance computing node server,which performs real-time searches for pulses with a wide dispersion measure(DM)range of 20–10,000 pc cm^(-3) with step efficiency of 25%in real time.Then,the head node server aggregates all the candidate signals from each beam within a given time,determining their authenticity based on various criteria,including arrival time,pulse width,signal-to-noise ratio and coincidence patterns among the 19 beams.Within the 1.05–1.45 GHz operating bandwidth of the FAST 19beam receiver,the system achieves a frequency resolution of 122.07 kHz and a time resolution of 270.336μs.Subsequently,our team detected a series of bursts with a DM of 566 on 2019 August 30 confirming them as FRB121102.The FRB searching system enables the 19-beam receiver of FAST to detect repeated/one-off pulses/bursts in real time.展开更多
The classification, characteristics and current situation of aluminum melt hydrogen-removal methods and technologies have been summarized. The latest studies and research results of aluminum melt degassing technology ...The classification, characteristics and current situation of aluminum melt hydrogen-removal methods and technologies have been summarized. The latest studies and research results of aluminum melt degassing technology have been summed up. The tendency and prospect of aluminum degassing technology was discussed.展开更多
Field portable X-ray fluorescence （PXRF） spectrometry has become an increasingly popular technique for in-situ elemental characterization of soils. The technique is fast, portable, and accurate, requiring minimal sa...Field portable X-ray fluorescence （PXRF） spectrometry has become an increasingly popular technique for in-situ elemental characterization of soils. The technique is fast, portable, and accurate, requiring minimal sample preparation and no consumables. However, soil moisture 〉 20% has been known to cause fluorescence denudation and error in elemental reporting and few studies have evaluated the presence of soil moisture in solid form as ice. Gelisols （USDA Soil Taxonomy）, permafrost-affected soils, cover a large amount of the land surface in the northern and southern hemispheres. Thus, the applicability of PXRF in those areas requires further investigation. PXRF was used to scan the elemental composition （Ba, Ca, Cr, Fe, K, Mn, Pb, Rb, Sr, Ti, Zn, and Zr） of 13 pedons in central and northern Alaska, USA. Four types of scans were completed： 1） in-situ frozen soil, 2） re-frozen soil in the laboratory, 3） melted soil/water mixture in the laboratory, and 4） moisture-corrected soil. All were then compared to oven dry soil scans. Results showed that the majority of PXRF readings from in-situ, re-frozen, and melted samples were significantly underestimated, compared to the readings on oven dry samples, owing to the interference expected by moisture. However, when the moisture contents were divided into 〉 40% and 〈 40〈 groups, the PXRF readings under different scanning conditions performed better in the group with 〈 40% moisture contents. Most elements of the scans on the melted samples with 〈 40% moisture contents acceptably compared to those of the dry samples, with R2 values ranging from 0.446 （Mn） to 0.930 （St）. However, underestimation of the melted samples was still quite apparent. Moisture-corrected sample PXRF readings provided the best correlation to those of the dry, ground samples as indicated by higher R2 values, lower root mean square errors （RMSEs）, and slopes closer to 1 in linear regression equations. However, the in-situ （frozen） sample scans did not differ appreciably from the melted sample scans in their correlations to dry sample scans in terms of R2 values （0.81 vs. 0.88）, RMSEs （1.06 vs. 0.85）, and slopes （0.88 vs. 0.92）. Notably, all of those relationships improved for the group with moisture contents 〈 40%.展开更多
Heterostructured materials,defined as materials that contain multiple zones with dramatically different flow stresses,have the potential to push the envelope of the strength-ductility of metals and alloys beyond what ...Heterostructured materials,defined as materials that contain multiple zones with dramatically different flow stresses,have the potential to push the envelope of the strength-ductility of metals and alloys beyond what can be obtained conventionally[1–3].A prominent example is the heterogeneous lamella Ti that is as strong as its ultrafine-grained Ti,while as ductile as the coarsegrained Ti[4].展开更多
We consider the design of an effective and reliable adaptive finite element method(AFEM)for the nonlinear Poisson-Boltzmann equation(PBE).We first examine the two-term regularization technique for the continuous probl...We consider the design of an effective and reliable adaptive finite element method(AFEM)for the nonlinear Poisson-Boltzmann equation(PBE).We first examine the two-term regularization technique for the continuous problem recently proposed by Chen,Holst and Xu based on the removal of the singular electrostatic potential inside biomolecules;this technique made possible the development of the first complete solution and approximation theory for the Poisson-Boltzmann equation,the first provably convergent discretization and also allowed for the development of a provably convergent AFEM.However,in practical implementation,this two-term regularization exhibits numerical instability.Therefore,we examine a variation of this regularization technique which can be shown to be less susceptible to such instability.We establish a priori estimates and other basic results for the continuous regularized problem,as well as for Galerkin finite element approximations.We show that the new approach produces regularized continuous and discrete problemswith the samemathematical advantages of the original regularization.We then design an AFEM scheme for the new regularized problem and show that the resulting AFEM scheme is accurate and reliable,by proving a contraction result for the error.This result,which is one of the first results of this type for nonlinear elliptic problems,is based on using continuous and discrete a priori L¥estimates.To provide a high-quality geometric model as input to the AFEM algorithm,we also describe a class of feature-preserving adaptive mesh generation algorithms designed specifically for constructing meshes of biomolecular structures,based on the intrinsic local structure tensor of the molecular surface.All of the algorithms described in the article are implemented in the Finite Element Toolkit(FETK),developed and maintained at UCSD.The stability advantages of the new regularization scheme are demonstrated with FETK through comparisons with the original regularization approach for a model problem.The convergence and accuracy of the overall AFEMalgorithmis also illustrated by numerical approximation of electrostatic solvation energy for an insulin protein.展开更多
基金supported by the National Key R&D Program of China under grant No.2018YFA0404703the Open Project Program of the Key Laboratory of FAST,NAOC,Chinese Academy of Sciences。
文摘The Phased Array Feed(PAF)is considered as one of the next generation receivers for radio telescopes,which can significantly enlarge the instantaneous Field-of-View of large aperture single dish radio telescopes and enable more flexible observing configurations.Study efforts on PAF development for radio telescopes have been made for more than two decades and have become more and more applicable.We report the development of an ambient-temperature 19 element L-band PAF system and the experimental results including its far field beam pattern and system temperature measurement,which achieve the expectations.Implementing the aperture array beam-forming method,we demonstrate a wide-field Galactic HI observations in the radio camera mode.The results indicate that this system might be applicable for strong Galactic transient detections.This system could be directly equipped to large telescopes like the Five-hundred-meter Aperture Spherical radio Telescope(FAST)and FAST array in the future.
基金the International Partnership Program of the Chinese Academy of Sciences No.114A11-KYSB20200029the National Natural Science Foundation of China(NSFC,Grant No.12041301)the National Key R&D Program of China No.2020YC2201700。
文摘In this paper,we report a real-time Fast Radio Burst(FRB)searching system that has been successfully implemented with the 19 beam receiver of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).The relatively small field of view of FAST makes the search for new FRBs challenging,but its high sensitivity significantly improves the accuracy of FRB localization and enables the detection of high-precision neutral hydrogen absorption lines generated by FRBs.Our goal is to develop an FRB searching system capable of realtime detection of FRBs that allows high-time resolution spectro-temporal studies among the repeated bursts,as well as detailed investigations of these bursts and exploration of FRB progenitor models.The data from each beam of the 19-beam receiver are fed into a high-performance computing node server,which performs real-time searches for pulses with a wide dispersion measure(DM)range of 20–10,000 pc cm^(-3) with step efficiency of 25%in real time.Then,the head node server aggregates all the candidate signals from each beam within a given time,determining their authenticity based on various criteria,including arrival time,pulse width,signal-to-noise ratio and coincidence patterns among the 19 beams.Within the 1.05–1.45 GHz operating bandwidth of the FAST 19beam receiver,the system achieves a frequency resolution of 122.07 kHz and a time resolution of 270.336μs.Subsequently,our team detected a series of bursts with a DM of 566 on 2019 August 30 confirming them as FRB121102.The FRB searching system enables the 19-beam receiver of FAST to detect repeated/one-off pulses/bursts in real time.
文摘The classification, characteristics and current situation of aluminum melt hydrogen-removal methods and technologies have been summarized. The latest studies and research results of aluminum melt degassing technology have been summed up. The tendency and prospect of aluminum degassing technology was discussed.
文摘Field portable X-ray fluorescence （PXRF） spectrometry has become an increasingly popular technique for in-situ elemental characterization of soils. The technique is fast, portable, and accurate, requiring minimal sample preparation and no consumables. However, soil moisture 〉 20% has been known to cause fluorescence denudation and error in elemental reporting and few studies have evaluated the presence of soil moisture in solid form as ice. Gelisols （USDA Soil Taxonomy）, permafrost-affected soils, cover a large amount of the land surface in the northern and southern hemispheres. Thus, the applicability of PXRF in those areas requires further investigation. PXRF was used to scan the elemental composition （Ba, Ca, Cr, Fe, K, Mn, Pb, Rb, Sr, Ti, Zn, and Zr） of 13 pedons in central and northern Alaska, USA. Four types of scans were completed： 1） in-situ frozen soil, 2） re-frozen soil in the laboratory, 3） melted soil/water mixture in the laboratory, and 4） moisture-corrected soil. All were then compared to oven dry soil scans. Results showed that the majority of PXRF readings from in-situ, re-frozen, and melted samples were significantly underestimated, compared to the readings on oven dry samples, owing to the interference expected by moisture. However, when the moisture contents were divided into 〉 40% and 〈 40〈 groups, the PXRF readings under different scanning conditions performed better in the group with 〈 40% moisture contents. Most elements of the scans on the melted samples with 〈 40% moisture contents acceptably compared to those of the dry samples, with R2 values ranging from 0.446 （Mn） to 0.930 （St）. However, underestimation of the melted samples was still quite apparent. Moisture-corrected sample PXRF readings provided the best correlation to those of the dry, ground samples as indicated by higher R2 values, lower root mean square errors （RMSEs）, and slopes closer to 1 in linear regression equations. However, the in-situ （frozen） sample scans did not differ appreciably from the melted sample scans in their correlations to dry sample scans in terms of R2 values （0.81 vs. 0.88）, RMSEs （1.06 vs. 0.85）, and slopes （0.88 vs. 0.92）. Notably, all of those relationships improved for the group with moisture contents 〈 40%.
基金supported by the US Army Research Office[W911 NF-12-1-0009]financial support from the National Science Foundation(NSF)under award no.1929646performed in part at the AIF facility,which is supported by the State of North Carolina and the National Science Foundation[ECCS-1542015]
文摘Heterostructured materials,defined as materials that contain multiple zones with dramatically different flow stresses,have the potential to push the envelope of the strength-ductility of metals and alloys beyond what can be obtained conventionally[1–3].A prominent example is the heterogeneous lamella Ti that is as strong as its ultrafine-grained Ti,while as ductile as the coarsegrained Ti[4].
基金supported in part by NSF Awards 0715146,0821816,0915220 and 0822283(CTBP)NIHAward P41RR08605-16(NBCR),DOD/DTRA Award HDTRA-09-1-0036+1 种基金CTBP,NBCR,NSF and NIHsupported in part by NIH,NSF,HHMI,CTBP and NBCR.The third,fourth and fifth authors were supported in part by NSF Award 0715146,CTBP,NBCR and HHMI.
文摘We consider the design of an effective and reliable adaptive finite element method(AFEM)for the nonlinear Poisson-Boltzmann equation(PBE).We first examine the two-term regularization technique for the continuous problem recently proposed by Chen,Holst and Xu based on the removal of the singular electrostatic potential inside biomolecules;this technique made possible the development of the first complete solution and approximation theory for the Poisson-Boltzmann equation,the first provably convergent discretization and also allowed for the development of a provably convergent AFEM.However,in practical implementation,this two-term regularization exhibits numerical instability.Therefore,we examine a variation of this regularization technique which can be shown to be less susceptible to such instability.We establish a priori estimates and other basic results for the continuous regularized problem,as well as for Galerkin finite element approximations.We show that the new approach produces regularized continuous and discrete problemswith the samemathematical advantages of the original regularization.We then design an AFEM scheme for the new regularized problem and show that the resulting AFEM scheme is accurate and reliable,by proving a contraction result for the error.This result,which is one of the first results of this type for nonlinear elliptic problems,is based on using continuous and discrete a priori L¥estimates.To provide a high-quality geometric model as input to the AFEM algorithm,we also describe a class of feature-preserving adaptive mesh generation algorithms designed specifically for constructing meshes of biomolecular structures,based on the intrinsic local structure tensor of the molecular surface.All of the algorithms described in the article are implemented in the Finite Element Toolkit(FETK),developed and maintained at UCSD.The stability advantages of the new regularization scheme are demonstrated with FETK through comparisons with the original regularization approach for a model problem.The convergence and accuracy of the overall AFEMalgorithmis also illustrated by numerical approximation of electrostatic solvation energy for an insulin protein.
