30 research outputs found
Birth places of extreme ultraviolet waves driven by impingement of solar jets upon coronal loops
Solar extreme ultraviolet (EUV) waves are large-scale propagating
disturbances in the corona. It is generally believed that the vital key for the
formation of EUV waves is the rapid expansion of the loops that overlie
erupting cores in solar eruptions, such as coronal mass ejections (CMEs) and
solar jets. However, the details of the interaction between the erupting cores
and overlying loops are not clear, because that the overlying loops are always
instantly opened after the energetic eruptions. Here, we present three typical
jet-driven EUV waves without CME to study the interaction between the jets and
the overlying loops that remained closed during the events. All three jets
emanated from magnetic flux cancelation sites in source regions. Interestingly,
after the interactions between jets and overlying loops, three EUV waves
respectively formed ahead of the top, the near end (close to the jet source),
and the far (another) end of the overlying loops. According to the magnetic
field distribution of the loops extrapolated from Potential Field Source
Surface method, it is confirmed that the birth places of three jet-driven EUV
waves were around the weakest magnetic field strength part of the overlying
loops. We suggest that the jet-driven EUV waves preferentially occur at the
weakest part of the overlying loops, and the location can be subject to the
magnetic field intensity around the ends of the loops
Twin extreme ultraviolet waves in the solar corona
Solar extreme ultraviolet (EUV) waves are spectacular propagating
disturbances with EUV enhancements in annular shapes in the solar corona. These
EUV waves carry critical information about the coronal magnetised plasma that
can shed light on the elusive physical parameters (e.g. the magnetic field
strength) by global solar coronal magneto-seismology. EUV waves are closely
associated with a wide range of solar atmospheric eruptions, from violent
flares and coronal mass ejections (CMEs) to less energetic plasma jets or
mini-filament eruptions. However, the physical nature and driving mechanism of
EUV waves is still controversial. Here, we report the unique discovery of twin
EUV waves (TEWs) that were formed in a single eruption with observations from
two different perspectives. In all earlier studies, a single eruption was
associated at most with a single EUV wave. The newly found TEWs urge to
re-visit our theoretical understanding about the underlying formation
mechanism(s) of coronal EUV waves. Two distinct scenarios of TEWs were found.
In the first scenario, the two waves were separately associated with a filament
eruption and a precursor jet, while in another scenario the two waves were
successively associated with a filament eruption. Hence, we label these
distinguished scenarios as "fraternal TEWs" and "identical TEWs", respectively.
Further, we also suggest that impulsive lateral expansions of two distinct
groups of coronal loops are critical to the formation of TEWs in a single
eruption
An integral gated mode single photon detector at telecom wavelengths
We demonstrate an integral gated mode single photon detector at telecom
wavelengths. The charge number of an avalanche pulse rather than the peak
current is monitored for single-photon detection. The transient spikes in
conventional gated mode operation are canceled completely by integrating, which
enables one to improve the performance of single photon detector greatly with
the same avalanche photodiode. This method has achieved a detection efficiency
of 29.9% at the dark count probability per gate equal to 5.57E-6/gate
(1.11E-6/ns) at 1550nm.Comment: word to PDF, 3 pages with 4 figure
On the validity of the local Fourier analysis
Local Fourier analysis (LFA) is a useful tool in predicting the convergence
factors of geometric multigrid methods (GMG). As is well known, on rectangular
domains with periodic boundary conditions this analysis gives the exact
convergence factors of such methods. In this work, using the Fourier method, we
extend these results by proving that such analysis yields the exact convergence
factors for a wider class of problems
Waiting Time Distributions of Transport through a Two-Channel Quantum System
In this work, the waiting time distribution (WTD) statistics of electron transport through a two-channel quantum system in a strong Coulomb blockade regime and non-interacting dots are investigated by employing a particle-number resolved master equation with the Born–Markov approximation. The results show that the phase difference between the two channels, the asymmetry of the dot-state couplings to the left and right electrodes, and Coulomb repulsion have obvious effects on the WTD statistics of the system. In a certain parameter range, the system manifests the coherent oscillatory behavior of WTDs in the strong Coulomb blockade regime, and the phase difference between the two channels is clearly reflected in the oscillation phase of the WTDs. The two-channel quantum dot (QD) system for non-interacting dots manifests nonrenewal characteristics, and the electron waiting time of the system is negatively correlated. The different phase differences between the two channels can clearly enhance the negative correlation. These results deepen our understanding of the WTD statistical properties of electron transport through a mesoscopic QD system and help pave a new path toward constructing nanostructured QD electronic devices
Full Counting Statistics of Electrons through Interaction of the Single Quantum Dot System with the Optical Field
In this paper, using the particle-number-resolved master equation, the properties of full counting statistics (FCS) are investigated for a single quantum dot (QD) system interacting with optical fields in the thermal state, Fock state, coherent state, and coherent state with random phase. In these diverse quantum states of optical fields, average tunneling currents have different step shoulder heights at a lower bias voltage with the same light intensity, and a staircase-shaped current can be induced unexpectedly in vacuum state optical field. The characteristics of the Fano factor and skewness in the coherent state differ from those in all of the other cases. For avalanche-like transport at a lower bias voltage, the mechanism is a dynamical channel blockade in a moderate electron–photon interaction regime. There is a pronounced negative differential conductance that results from tuning the phase of the coherent state optical field in a symmetric QD system
An extreme-ultraviolet wave associated with the possible expansion of sheared arcades
Context. Solar extreme-ultraviolet (EUV) waves are propagating disturbances in the corona, and they are usually accompanied with various solar eruptions, from large-scale coronal mass ejections to small-scale coronal jets.
Aims. Generally, it is believed that EUV waves are driven by the rapid expansion of coronal loops overlying the erupting cores. In this paper, we present an exception of an EUV wave that was not triggered by the expansion of coronal loops overlying the erupting core.
Methods. Combining the multiwavelength observations from multiple instruments, we studied the event in detail.
Results. The eruption was restricted in the active region (AR) and disturbed the nearby sheared arcades (SAs) connecting the source AR to a remote AR. Interestingly, following the disturbance, an EUV wave formed close to the SAs, but far away from the eruption source.
Conclusions. All the results show that the EUV wave had a closer temporal and spatial relationship with the disappearing part of SAs than the confined eruption. Hence, we suggest that the EUV wave was likely triggered by the expansion of some strands of SAs, rather than the expansion of erupting loops. It can be a possible complement for the driving mechanisms of EUV waves