arXiv subjects

C. Li

Publications and source records attributed to C. Li.

At least 163 records · Page 9Linked to original sources

arXiv2013

Major electron events and coronal magnetic configurations of the related solar active regions

A statistical survey of 26 major electron events during the period 2002 February through the end of solar cycle 23 is presented. We have obtained electron solar onset times and the peak flux spectra for each event by fitting to a powerlaw spectrum truncated by an exponential high-energy tail. We also derived the coronal magnetic configurations of the related solar active regions (ARs) from the potential-field source-surface model. It is found that (1) 10 of the 11 well-connected open field-line events are prompt events whose solar onset times coincide with the maxima of flare emission and 13 of the 14 closed field-line events are delayed events. (2) A not-wellconnected open field-line event and one of the closed field-line events are prompt events, they are both associated with large-scale coronal disturbances or dimming. (3)An averaged harder spectrum is found in open field-line events compared with the closed ones. Specifically, the averaged spectral index is of 1.6 +/- 0.3 in open field-line events and of 2.0 +/- 0.4 in closed ones. The spectra of three closed field-line events show infinite rollover energies E0. These correlations clearly establish a significant link between the coronal magnetic field-line topology and the escape of charged particles from the flaring ARs into interplanetary space during the major solar energetic particle events.

astro-ph.SR↗

arXiv2012

Suppression of the centrifugal barrier effects in the off-energy-shell neutron+$^{17}$O interaction

The reaction $^{17}$O($n,α$)$^{14}$C was studied at energies from $E_{cm}=0$ to $E_{cm}=350$ keV using the quasi-free deuteron break-up in the three body reaction $^{17}$O$+d \rightarrow α+ ^{14}$C$+p$, extending the Trojan Horse indirect method (THM) to neutron-induced reactions. It is found that the $^{18}$O excited state at $E^*=8.125 \pm 0.002$ MeV observed in THM experiments is absent in the direct measurement because of its high centrifugal barrier. The angular distributions of the populated resonances have been measured for the first time. The results unambiguously indicate the ability of the THM to overcome the centrifugal barrier suppression effect and to pick out the contribution of the bare nuclear interaction.

nucl-ex↗

arXiv2012

Asteroseismology of the ZZ Ceti star HS 0507+0434B

The pulsating DA white dwarfs (ZZ Ceti stars) are $g$-mode non-radial pulsators. Asteroseismology provides strong constraints on their global parameters and internal structure. Since all the DA white dwarfs falling in the ZZ Ceti instability strip do pulsate, the internal structure derived from asteroseismology brings knowledge for the DA white dwarfs as a whole group. HS 0507+0434B is one of the ZZ Ceti stars which lies approximately in the middle of the instability strip for which we have undertaken a detailed asteroseismological study. We carried out multisite observation campaigns in 2007 and from December 2009 to January 2010. In total, 206 hours of photometric time-series have been collected. They have been analysed by means of Fourier analysis and simultaneous multi-frequency sine-wave fitting. In total, 39 frequency values are resolved including 6 triplets and a number of linear combinations. We identify the triplets as $\ell$=1 $g$-modes split by rotation. We derived the period spacing, the rotational splitting and the rotation rate. From the comparison of the observed periods with the theoretical periods of a series of models we estimate the fundamental parameters of the star: its total mass M$_{*}$/M$_{\odot}$ = 0.675, its luminosity L/L$_{\odot}$=3.5$\times 10^{-3}$, and its hydrogen mass fraction M$_{H}$/M$_{*}$= 10$^{-8.5}$.

astro-ph.SR↗

arXiv2011

The BigBOSS Experiment

BigBOSS is a Stage IV ground-based dark energy experiment to study baryon acoustic oscillations (BAO) and the growth of structure with a wide-area galaxy and quasar redshift survey over 14,000 square degrees. It has been conditionally accepted by NOAO in response to a call for major new instrumentation and a high-impact science program for the 4-m Mayall telescope at Kitt Peak. The BigBOSS instrument is a robotically-actuated, fiber-fed spectrograph capable of taking 5000 simultaneous spectra over a wavelength range from 340 nm to 1060 nm, with a resolution R = 3000-4800. Using data from imaging surveys that are already underway, spectroscopic targets are selected that trace the underlying dark matter distribution. In particular, targets include luminous red galaxies (LRGs) up to z = 1.0, extending the BOSS LRG survey in both redshift and survey area. To probe the universe out to even higher redshift, BigBOSS will target bright [OII] emission line galaxies (ELGs) up to z = 1.7. In total, 20 million galaxy redshifts are obtained to measure the BAO feature, trace the matter power spectrum at smaller scales, and detect redshift space distortions. BigBOSS will provide additional constraints on early dark energy and on the curvature of the universe by measuring the Ly-alpha forest in the spectra of over 600,000 2.2 < z < 3.5 quasars. BigBOSS galaxy BAO measurements combined with an analysis of the broadband power, including the Ly-alpha forest in BigBOSS quasar spectra, achieves a FOM of 395 with Planck plus Stage III priors. This FOM is based on conservative assumptions for the analysis of broad band power (kmax = 0.15), and could grow to over 600 if current work allows us to push the analysis to higher wave numbers (kmax = 0.3). BigBOSS will also place constraints on theories of modified gravity and inflation, and will measure the sum of neutrino masses to 0.024 eV accuracy.

astro-ph.IM↗

arXiv2011

Strong terahertz radiation from relativistic laser interaction with solid density plasmas

We report a plasma-based strong THz source generated by using intense femtosecond laser pulses to irradiate solid targets at relativistic intensity >10^18W/cm2. Energies up to 50 microJ/sr per THz pulse is observed in the specular direction when the laser pulses are incident onto a copper foil at 67.5 degree. The source appears to be linearly polarized. The temporal, spectral properties of the THz are measured by a single shot, electro-optic sampling method with a chirped laser pulse. The THz radiation is attributed to the self-organized transient fast electron currents formed along the target surface. Such a strong THz source allows potential applications in THz nonlinear physics.

physics.optics↗

arXiv2011

Gamma-ray emission from the globular clusters Liller 1, M80, NGC 6139, NGC 6541, NGC 6624, and NGC 6752

Globular clusters (GCs) are emerging as a new class of gamma-ray emitters, thanks to the data obtained from the Fermi Gamma-ray Space Telescope. By now, eight GCs are known to emit gamma-rays at energies >100~MeV. Based on the stellar encounter rate of the GCs, we identify potential gamma-ray emitting GCs out of all known GCs that have not been studied in details before. In this paper, we report the discovery of a number of new gamma-ray GCs: Liller 1, NGC 6624, and NGC 6752, and evidence for gamma-ray emission from M80, NGC 6139, and NGC 6541, in which gamma-rays were found within the GC tidal radius. With one of the highest metallicity among all GCs in the Milky Way, the gamma-ray luminosity of Liller 1 is found to be the highest of all known gamma-ray GCs. In addition, we confirm a previous report of significant gamma-ray emitting region next to NGC 6441. We briefly discuss the observed offset of gamma-rays from some GC cores. The increasing number of known gamma-ray GCs at distances out to ~10 kpc is important for us to understand the gamma-ray emitting mechanism and provides an alternative probe to the underlying millisecond pulsar populations of the GCs.

astro-ph.HE↗

arXiv2010

Satellites in the field and lens galaxies: SDSS/COSMOS vs. SLACS/CLASS

The incidence of sub-galactic level substructures is an important quantity, as it is a generic prediction of high-resolution Cold Dark Matter (CDM) models which is susceptible to observational test. Confrontation of theory with observations is currently in an uncertain state. In particular, gravitational lens systems appear to show evidence for flux ratio anomalies, which are expected from CDM substructures although not necessarily in the same range of radius as observed. However, the current small samples of lenses suggest that the lens galaxies in these systems are unusually often accompanied by luminous galaxies. Here we investigate a large sample of unlensed elliptical galaxies from the COSMOS survey, and determine the fraction of objects with satellites, in excess of background counts, as a function of satellite brightness and separation from the primary object. We find that the incidence of luminous satellites within 20 kpc is typically a few tenths of one percent for satellites of a few tenths of the primary flux, comparable to what is observed for the wider but shallower SDSS survey. Although the environments of lenses in the SLACS survey are compatible with this observation, the CLASS radio survey lenses are significantly in excess of this.

astro-ph.CO↗

arXiv2009

Bayesian non-linear large scale structure inference of the Sloan Digital Sky Survey data release 7

In this work we present the first non-linear, non-Gaussian full Bayesian large scale structure analysis of the cosmic density field conducted so far. The density inference is based on the Sloan Digital Sky Survey data release 7, which covers the northern galactic cap. We employ a novel Bayesian sampling algorithm, which enables us to explore the extremely high dimensional non-Gaussian, non-linear log-normal Poissonian posterior of the three dimensional density field conditional on the data. These techniques are efficiently implemented in the HADES computer algorithm and permit the precise recovery of poorly sampled objects and non-linear density fields. The non-linear density inference is performed on a 750 Mpc cube with roughly 3 Mpc grid-resolution, while accounting for systematic effects, introduced by survey geometry and selection function of the SDSS, and the correct treatment of a Poissonian shot noise contribution. Our high resolution results represent remarkably well the cosmic web structure of the cosmic density field. Filaments, voids and clusters are clearly visible. Further, we also conduct a dynamical web classification, and estimated the web type posterior distribution conditional on the SDSS data.

astro-ph.CO↗

arXiv2009

Structural-configurated magnetic plasmon bands in connected ring chains

Magnetic resonance coupling between connected split ring resonators (SRRs) and magnetic plasmon (MP) excitations in the connected SRR chains were theoretically studied. By changing the connection configuration, two different coupling behaviors were observed, and therefore two kinds of MP bands were formed in the connected ring chains, accordingly. These MPs were revealed with positive and negative dispersion for the homo- and anti-connected chain, respectively. Notably, these two MP modes both have wide bandwidth due to the conductive coupling. Moreover, the anti-connected chain is found supporting a novel negative propagating wave with a wide band starting from zero frequency, which is a fancy phenomenon in one-dimensional system.

physics.optics↗

arXiv2009

Perspectives of a Midrapidity Dimuon Program at RHIC: A Novel and Compact Muon Telescope Detector

We propose a large-area, cost-effective Muon Telescope Detector (MTD) for the Solenoidal Tracker at RHIC (STAR) at mid-rapidity and for the next generation of detectors at a possible electron-ion collider. We utilize Multi-gap Resistive Plate Chambers with large modules and long readout strips (Long-MRPC) in the detector design. The results from cosmic ray and beam tests show the intrinsic timing and spatial resolution for a Long-MRPC are 60-70 ps and $\sim1$ cm, respectively. The prototype performance of such a novel muon telescope detector at STAR indicates that muon identification at the transverse momentum of a few GeV/$c$ can be achieved through the combined information of track matching with the MTD, ionization energy loss in the Time Projection Chamber, and time-of-flight measurements. A primary muon over secondary muon ratio of better than 1/3 can be achieved. This provides a promising device for future quarkonium programs and primordial dilepton measurements at RHIC. Simulations of the muon efficiency, the signal-to-background ratio of $J/ψ$, the separation of $Υ$ 1S from 2S+3S states, and the electron-muon correlation from charm pair production in the RHIC environment are presented.

nucl-ex↗

arXiv2008

Feedback control on geometric phase in dissipative two-level systems

The effect of feedback on a two-level dissipative system is studied in this paper. The results show that it is possible to control the phase in the open system even if its state can not be manipulated from an arbitrary initial one to an arbitrary final one. The dependence of the geometric phase on the control parameters is calculated and discussed.

quant-ph↗

arXiv2008

Electronic theory of ultrafast spin dynamics

NiO is a good candidate for ultrafast magnetic switching because of its large spin density, antiferromagnetic order, and clearly separated intragap states. In order to detect and monitor the switching dynamics, we develop a systematic approach to study optical second harmonic generation (SHG) in NiO, both at the (001) surface and in the bulk. In our calculations NiO is modeled as a doubly embedded cluster. All intragap \emph{d}-states of the bulk and the (001) surface are obtained with highly-correlational quantum chemistry and propagated in time under the influence of a static magnetic field and a laser pulse. We find that demagnetization and switching can be best achieved in a subpicosecond regime with linearly rather than circularly polarized light. We also show the importance of including an external magnetic field in order to distinguish spin-up and spin-down states and the necessity of including magnetic-dipole transitions in order to realize the $Λ$-process in the centrosymmetric bulk. Having already shown the effects of phonons in the SHG for the bulk NiO within the frozen-phonon approximation, and following the same trail of thoughts, we discuss the role of phonons in a fully quantized picture as a symmetry-lowering mechanism in the switching scenario and investigate the electronic and lattice temperature effects.

cond-mat.other↗

arXiv2008

New Prototype Multi-gap Resistive Plate Chambers with Long Strips

A new kind of Multi-gap Resistive Plate Chamber (MRPC) has been built for the large-area Muon Telescope Detector (MTD) for the STAR experiment at RHIC. These long read-out strip MRPCs (LMRPCs) have an active area of 87.0 x 17.0 cm2 and ten 250 um-thick gas gaps arranged as a double stack. Each read-out strip is 2.5 cm wide and 90 cm long. The signals are read-out at both ends of each strip. Cosmic ray tests indicate a time resolution of ~70 ps and a detection efficiency of greater than 95%. Beam tests performed at T963 at Fermilab indicate a time resolution of 60-70 ps and a spatial resolution of ~1 cm along the strip direction.

physics.ins-det↗

arXiv2008

Measurable Concurrence of Mixed States

We show that bipartite concurrence for rank-2 mixed states of qubits is written by an observable which can be exactly and directly measurable in experiment by local projective measurements, provided that four copies of the composite quantum system are available. In addition, for a tripartite quantum pure state of qubits, the 3-tangle is also shown to be measurable only by projective measurements on the reduced density matrices of a pair of qubits conditioned on four copies of the state.

quant-ph↗

arXiv2007

The acceleration characteristics of solar energetic particles in the 2000 July 14 event

In large gradual solar energetic particle (SEP) events, especially the ground-level enhancement (GLE) events, where and how energetic particles are accelerated is still a problem. By using imaging data from TRACE, Yohkoh/HXT, SOHO/MDI and SOHO/EIT, along with the data from the GOES, Apatity NM, and SOHO/LASCO CME catalog, the evolution of the X5.7 two-ribbon flare and the associated SEP event on 14 July 2000 are studied. It is found that the magnetic reconnection in this event consists of two parts, and the induced electric field Erec is temporally correlated with the evolution of hard X-ray and gamma-ray emission. In particular, the first hard X-ray and gamma-ray emission peak occurred at 10:22 UT, corresponding to the magnetic reconnection in the western part of the flare ribbons and the maximum Erec of 9.5 V/cm; the second emission peak at 10:27 UT, corresponding to the eastern part and the maximum Erec of 13.0 V/cm. We also analyze the SEP injection profiles as functions of time and CME-height, and find two-component injection which may result from different acceleration mechanisms. A reasonable conclusion is that reconnection electric field makes a crucial contribution to the acceleration of relativistic particles and to the impulsive component of the large gradual SEP event, while CME-driven shocks play a dominant role in the gradual component.

astro-ph↗

arXiv2007

Flare magnetic reconnection and relativistic particles in the 2003 October 28 event

An X17.2 solar flare occurred on 2003 October 28, accompanied by multi-wavelength emissions and a high flux of relativistic particles observed at 1AU. We present the analytic results of the TRACE, SOHO, RHESSI, ACE, GOES, hard X-ray (INTEGRAL satellite), radio (Onderejov radio telescope), and neutron monitor data. It is found that the inferred magnetic reconnection electric field correlates well with the hard X-ray, gamma-ray, and neutron emission at the Sun. Thus the flare's magnetic reconnection probably makes a crucial contribution to the prompt relativistic particles, which could be detected at 1 AU. Since the neutrons were emitted a few minutes before the injection of protons and electrons, we propose a magnetic-field evolution configuration to explain this delay. We do not exclude the effect of CME-driven shock, which probably plays an important role in the delayed gradual phase of solar energetic particles.

astro-ph↗

arXiv2005

Spectroscopic study of blue compact galaxies V. oxygen abundance and the metallicity-luminosity relation

This is the fifth paper in a series studying the stellar components, star formation histories, star formation rates and metallicities of a blue compact galaxy (BCG) sample. Based on our high-quality ground-based spectroscopic observations, we have determined the electron temperatures, electron densities, nitrogen abundances and oxygen abundances for 72 star-forming BCGs in our sample, using different oxygen abundance indicators. The oxygen abundance covers the range 7.15 < 12 + log (O/H)< 9.0, and nitrogen is found to be mostly a product of secondary nucleosynthesis for 12 + log (O/H)>8.2 and apparently a product of primary nucleosynthesis for 12 + log (O/H)< 8.2. To assess the possible systematic differences among different oxygen abundance indicators, we have compared oxygen abundances of BCGs obtained with the Te method, R23 method, P method, N2 method and O3N2 method. The oxygen abundances derived from the Te method are systematically lower by 0.1-0.25 dex than those derived from the strong line empirical abundance indicators, consistent with previous studies based on region samples. We confirm the existence of the metallicity-luminosity relation in BCGs over a large range of abundances and luminosities. Our sample of galaxies shows that the slope of the metallicity-luminosity relation for the luminous galaxies (~-0.05) is slightly shallower than that for the dwarf galaxies (~-0.17). An offset was found in the metallicity-luminosity relation of the local galaxies and that of the intermediate redshift galaxies. It shows that the metallicity-luminosity relation for the emission line galaxies at high redshift is displaced to lower abundances, higher luminosities, or both.

astro-ph↗

arXiv2005

Charge Qubit Storage and Its Engineered Decoherence via Microwave Cavity

We study the entanglement of the superconducting charge qubit with the quantized electromagnetic field in a microwave cavity. It can be controlled dynamically by a classical external field threading the SQUID within the charge qubit. Utilizing the controllable quantum entanglement, we can demonstrate the dynamic process of the quantum storage of information carried by charge qubit. On the other hand, based on this engineered quantum entanglement, we can also demonstrate a progressive decoherence of charge qubit with quantum jump due to the coupling with the cavity field in quasi-classical state.

quant-ph↗