CAS Center for Space Science and Applied Research

Beijing, China

CAS Center for Space Science and Applied Research

Beijing, China

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Cai R.-G.,CAS Institute of Theoretical Physics | Li L.,CAS Institute of Theoretical Physics | Li L.-F.,CAS Center for Space Science and Applied Research
Journal of High Energy Physics | Year: 2014

We study a holographic p-wave superconductor model in a four dimensional Einstein-Maxwell-complex vector field theory with a negative cosmological constant. The complex vector field is charged under the Maxwell field. We solve the full coupled equations of motion of the system and find black hole solutions with the vector hair. The vector hairy black hole solutions are dual to a thermal state with the U(1) symmetry as well as the spatial rotational symmetry broken spontaneously. Depending on two parameters, the mass and charge of the vector field, we find a rich phase structure: zeroth order, first order and second order phase transitions can happen in this model. We also find "retrograde condensation" in which the hairy black hole solution exists only for the temperatures above a critical value with the free energy much larger than the one of the black hole without the vector hair. We construct the phase diagram for this system in terms of the temperature and charge of the vector field. © 2014 SISSA.


Wang Y.,CAS Center for Space Science and Applied Research | Qin G.,CAS Center for Space Science and Applied Research
Astrophysical Journal | Year: 2015

This paper investigates the onset time of solar energetic particle (SEP) events with numerical simulations and analyzes the accuracy of the velocity dispersion analysis (VDA) method. Using a three-dimensional focused transport model, we calculate the fluxes of protons observed in the ecliptic at 1 AU in the energy range between 10 MeV and 80 MeV. In particular, three models are used to describe different SEP sources produced by flare or coronal shock, and the effects of particle perpendicular diffusion in the interplanetary space are also studied. We have the following findings. When the observer is disconnected from the source, the effects of perpendicular diffusion in the interplanetary space and particles propagating in the solar atmosphere have a significant influence on the VDA results. As a result, although the VDA method is valid with impulsive source duration, low background, and weak scattering in the interplanetary space or fast diffusion in the solar atmosphere, the method is not valid with gradual source duration, high background, or strong scattering. © 2015. The American Astronomical Society. All rights reserved..


Wang Y.,CAS Center for Space Science and Applied Research | Qin G.,CAS Center for Space Science and Applied Research
Astrophysical Journal | Year: 2015

The spatial and temporal invariance in the spectra of energetic particles in gradual solar events is reproduced in simulations. Based on a numerical solution of the focused transport equation, we obtain the intensity time profiles of solar energetic particles (SEPs) accelerated by an interplanetary shock in three-dimensional interplanetary space. The shock is treated as a moving source of energetic particles with a distribution function. The time profiles of particle fluxes with different energies are calculated in the ecliptic at 1 AU. According to our model, we find that shock acceleration strength, parallel diffusion, and adiabatic cooling are the main factors in forming the spatial invariance in SEP spectra, and perpendicular diffusion is a secondary factor. In addition, the temporal invariance in SEP spectra is mainly due to the effects of adiabatic cooling. Furthermore, a spectra invariant region, which agrees with observations but is different from the one suggested by Reames et al. is proposed based on our simulations. © 2015. The American Astronomical Society. All rights reserved.


Zhou Y.F.,CAS Center for Space Science and Applied Research | Feng X.S.,CAS Center for Space Science and Applied Research
Journal of Geophysical Research: Space Physics | Year: 2013

In this paper, we analyze and quantitatively study the deflection of coronal mass ejection (CME) in the latitudinal direction during its propagation from the Corona to interplanetary (IP) space using a three-dimensional (3-D) numerical magnetohydrodynamics (MHD) simulation. To this end, 12 May 1997 CME event during the Carrington rotation 1922 is selected. First, we try to reproduce the physical properties for this halo CME event observed by the WIND spacecraft. Then, we study the deflection of CME, and quantify the effect of the background magnetic field and the initiation parameters (such as the initial magnetic polarity and the parameters of the CME model) on the latitudinal deflection of CMEs. The simulations show that the initial magnetic polarity substantially affects the evolution of CMEs. The "parallel" CMEs (with the CME's initial magnetic field parallel to that of the ambient field) originating from high latitude show a clear Equatorward deflection at the beginning and then propagate almost parallel to heliospheric current sheet and the "antiparallel" CMEs (with the CME's initial magnetic field opposite to that of the ambient field) deflect toward the pole. Our results demonstrate that the latitudinal deflection extent of the "parallel" CMEs is mainly controlled not only by the background magnetic field strength but also by the initial magnetic field strength of the CMEs. There is an anticorrelation between the latitudinal deflection extent and the CME average transit speed and the energy ratio Ecme/Esw. Key Points The time-dependent propagation of CME using a 3D MHD model The quantitative study of the deflection of CME in the latitudinal direction The analysis of the factors influencing the CME's deflection ©2013. American Geophysical Union. All Rights Reserved.


Zhang Y.Z.,CAS Center for Space Science and Applied Research
Astrophysical Journal | Year: 2013

Following the two-stage catastrophic flux rope model presented by Zhang et al., we investigate how magnetic flux emergence affects the formation and evolution of solar quiescent prominences. The magnetic properties of the flux rope are described with its toroidal magnetic flux per radian Φp and poloidal flux Φφ, and Φp is defined as the emerging strength (ES) of the magnetic flux. After the first catastrophe, the quiescent prominences are supported by the vertical current sheet and located in cavities below the curved transverse current sheet in the inner corona, for which both ES and Φφ are in the certain ranges. We calculate the strength range as 0.25 < ES < 0.50 for the quadrupolar field, and obtain the equation Φp Φφ = const., that is, the relationship between Φp and Φφ of the emerging flux for which the quiescent prominences are formed in the inner corona. After the second catastrophe, the quiescent prominences would either fall down onto the solar surface or erupt as an important part of coronal mass ejections. During the eruption of the quiescent prominences, most of the magnetic energy in the flux rope is lost, and less than half of the energy loss of the rope is released in the form of Alfvèn waves. We argue that there would be two important conditions required for the formation and eruption of solar quiescent prominences, a complicated source region and emerging toroidal magnetic flux that exceeds a critical strength. © 2013. The American Astronomical Society. All rights reserved.


Jiang C.,CAS Center for Space Science and Applied Research | Feng X.,CAS Center for Space Science and Applied Research
Astrophysical Journal | Year: 2013

Due to the absence of direct measurement, the magnetic field in the solar corona is usually extrapolated from the photosphere in a numerical way. At the moment, the nonlinear force-free field (NLFFF) model dominates the physical models for field extrapolation in the low corona. Recently, we have developed a new NLFFF model with MHD relaxation to reconstruct the coronal magnetic field. This method is based on CESE-MHD model with the conservation-element/solution- element (CESE) spacetime scheme. In this paper, we report the application of the CESE-MHD-NLFFF code to Solar Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI) data with magnetograms sampled for two active regions (ARs), NOAA AR 11158 and 11283, both of which were very non-potential, producing X-class flares and eruptions. The raw magnetograms are preprocessed to remove the force and then inputted into the extrapolation code. Qualitative comparison of the results with the SDO/AIA images shows that our code can reconstruct magnetic field lines resembling the EUV-observed coronal loops. Most important structures of the ARs are reproduced excellently, like the highly sheared field lines that suspend filaments in AR 11158 and twisted flux rope which corresponds to a sigmoid in AR 11283. Quantitative assessment of the results shows that the force-free constraint is fulfilled very well in the strong-field regions but apparently not that well in the weak-field regions because of data noise and numerical errors in the small currents. © 2013. The American Astronomical Society. All rights reserved.


Jiang C.,CAS Center for Space Science and Applied Research | Feng X.,CAS Center for Space Science and Applied Research
Astrophysical Journal | Year: 2012

The magnetic field in the solar corona is usually extrapolated from a photospheric vector magnetogram using a nonlinear force-free field (NLFFF) model. NLFFF extrapolation needs considerable effort to be devoted to its numerical realization. In this paper, we present a new implementation of the magnetohydrodynamics (MHD) relaxation method for NLFFF extrapolation. The magnetofrictional approach, which is introduced for speeding the relaxation of the MHD system, is realized for the first time by the spacetime conservation-element and solution-element scheme. A magnetic field splitting method is used to further improve the computational accuracy. The bottom boundary condition is prescribed by incrementally changing the transverse field to match the magnetogram, and all other artificial boundaries of the computational box are simply fixed. We examine the code using two types of NLFFF benchmark tests, the Low & Lou semi-analytic force-free solutions and a more realistic solar-like case constructed by van Ballegooijen et al. The results show that our implementation is successful and versatile for extrapolations of either the relatively simple cases or the rather complex cases that need significant rebuilding of the magnetic topology, e.g., a flux rope. We also compute a suite of metrics to quantitatively analyze the results and demonstrate that the performance of our code in extrapolation accuracy basically reaches the same level of the present best-performing code, i.e., that developed by Wiegelmann. © 2012. The American Astronomical Society. All rights reserved.


Patent
CAS Center for Space Science and Applied Research | Date: 2014-05-07

The invention relates to an ultra-weak light multispectral imaging method and an ultra-weak light multispectral imaging system, which can realize multispectral two-dimensional imaging of an ultra-weak light object by constituting a linear array from single-photon detectors of all response wavelengths and combining it with light-splitting technology. The ultra-weak light multispectral two-dimensional imaging system realizes high-resolution optical modulation by adopting the compressive sensing (CS) theory and the digital light processing (DLP) technology and using a linear array single-photon detector as a detection element; the ultra-weak light multispectral two-dimensional imaging system comprises a light filter (6), a first lens (1), a DMD control system (7), a second lens (2), a spectrophotometer (3), a linear array single-photon detector(4) consisting of a plurality of single-photon detectors with different response wavelengths, and a central processing unit (5); and the sensitivity of the system can reach the single-photon level. The invention can be widely applied in the fields of biological self-illumination, medical diagnosis, nondestructive material analysis, astronomical observation, national defense and military, spectral measurement, quantum electronics and the like.


Patent
CAS Center for Space Science and Applied Research | Date: 2014-07-16

The invention provides a time-resolved single-photon or ultra-weak light multi-D imaging spectral system and a time-resolved single-photon or ultra-weak light multi-D imaging spectral method. On the one hand, in order to realize rough time resolution, the invention provides a time-resolved single-photon counting 2D imaging system for forming color or grey imaging. Moreover, in order to realize high-precision time resolution, the multi-D imaging system provided in the invention mainly comprises a light source, an imaging spectral measurement unit, an electric detection unit, a system control unit and an algorithm unit, wherein the light carrying the information of an object is imaged on a spatial light modulator and randomly modulated according to the compressed sensing theory, the emergent light of a grating is collected by using a point or array single-photon detector, meanwhile, the number of photons and the photon arrival time are recorded, and reconstruction is carried out by using the compressed sensing algorithm and the related algorithm of the spectral imaging. The system has the advantages of single-photon detection sensitivity, high time resolution and wide spectral range, and can be widely applied in the areas of numerous new high-tech industries such as unicellular biophysics and material defect detection.


Patent
CAS Center for Space Science and Applied Research | Date: 2014-01-15

The invention relates to a single-photon counting imaging system and a single-photon counting imaging method. The system comprises a light filter, a first lens (1), a digital micro-mirror device (DMD) control system, a second lens (2), a single-photon counter and a data processing unit, wherein the DMD together with the first lens (1) and the second lens (2), is used for converting two-dimensional image data into a one-dimensional sequence to complete compressive sampling of signals to be measured; the stray light in the ultra-weak light is filtered through the light filter, after which the ultra-weak light forms an image at the DMD control system through the first lens (1), the DMD control system controls the probability that photons are reflected to the second lens (2) and the second lens (2) controls the focusing of the photons; and the data processing unit together with the single-photon counter to complete sparse reconstruction, the data processing unit converts the number of photons counted by the single-photon counter within a certain period of time into the probability of detected photon counts, as the measured value, and a photon density image is reconstructed by adopting an optimization algorithm applied to a measurement matrix on the DMD control system and the measured value, thereby solving out the two-dimensional image.

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