50,822 research outputs found
The role of nonthermal electrons in the optical continuum of stellar flares
We explore the possibility that the continuum emission in stellar flares is
powered by nonthermal electrons accelerated during the flares. We compute the
continuum spectra from an atmospheric model for a dMe star, AD Leo, at its
quiescent state, when considering the nonthermal excitation and ionisation
effects by precipitating electron beams. The results show that if the electron
beam has an energy flux large enough, the U band brightening and, in
particular, the U-B colour are roughly comparable with observed values for a
typical large flare. Moreover, for electron beams with a moderate energy flux,
a decrease of the emission at the Paschen continuum appears. This can explain
at least partly the continuum dimming observed in some stellar flares. Adopting
an atmospheric model for the flaring state can further raise the continuum flux
but it yields a spectral colour incomparable with observations. This implies
that the nonthermal effects may play the chief role in powering the continuum
emission in some stellar flares.Comment: 6 pages, 4 figures, LaTeX (psfigs.sty), to appear in MNRA
Quantum logic for control and manipulation of molecular ions using a frequency comb
Due to their rich level structure, molecules are well-suited for probing time
variation of fundamental constants, precisely measuring parity violation and
time-reversal non-invariance effects, studying quantum mechanical aspects of
chemical reactions, and implementing scalable quantum information processing
architectures. Molecular ions are particularly attractive for these
applications due to their long storage times and the near-perfect isolation
from environment that result in long coherence times required to achieve high
measurement precision and reduce systematic errors. However, the control of
molecular quantum states remains a challenge. Based on quantum logic
techniques, we propose a scheme for preparation, manipulation, and detection of
quantum states of single molecular ions. The scheme relies on coherent coupling
between internal and motional degrees of freedom of the molecular ion via a
frequency comb laser field, while detection and cooling of the motion of ions
is done via a co-trapped atomic ion.Comment: 5 pages, 3 figure
On general systems with network-enhanced complexities
In recent years, the study of networked control systems (NCSs) has gradually become an active research area due to the advantages of using networked media in many aspects such as the ease of maintenance and installation, the large flexibility and the low cost. It is well known that the devices in networks are mutually connected via communication cables that are of limited capacity. Therefore, some network-induced phenomena have inevitably emerged in the areas of signal processing and control engineering. These phenomena include, but are not limited to, network-induced communication delays, missing data, signal quantization, saturations, and channel fading. It is of great importance to understand how these phenomena influence the closed-loop stability and performance properties
- …