224,333 research outputs found
Coronal rain in magnetic bipolar weak fields
We intend to investigate the underlying physics for the coronal rain
phenomenon in a representative bipolar magnetic field, including the formation
and the dynamics of coronal rain blobs. With the MPI-AMRVAC code, we performed
three dimensional radiative magnetohydrodynamic (MHD) simulation with strong
heating localized on footpoints of magnetic loops after a relaxation to quiet
solar atmosphere. Progressive cooling and in-situ condensation starts at the
loop top due to radiative thermal instability. The first large-scale
condensation on the loop top suffers Rayleigh-Taylor instability and becomes
fragmented into smaller blobs. The blobs fall vertically dragging magnetic
loops until they reach low beta regions and start to fall along the loops from
loop top to loop footpoints. A statistic study of the coronal rain blobs finds
that small blobs with masses of less than 10^10 g dominate the population. When
blobs fall to lower regions along the magnetic loops, they are stretched and
develop a non-uniform velocity pattern with an anti-parallel shearing pattern
seen to develop along the central axis of the blobs. Synthetic images of
simulated coronal rain with Solar Dynamics Observatory Atmospheric Imaging
Assembly well resemble real observations presenting dark falling clumps in hot
channels and bright rain blobs in a cool channel. We also find density
inhomogeneities during a coronal rain "shower", which reflects the observed
multi-stranded nature of coronal rain.Comment: 8 figure
Integrated Design and Implementation of Embedded Control Systems with Scilab
Embedded systems are playing an increasingly important role in control
engineering. Despite their popularity, embedded systems are generally subject
to resource constraints and it is therefore difficult to build complex control
systems on embedded platforms. Traditionally, the design and implementation of
control systems are often separated, which causes the development of embedded
control systems to be highly time-consuming and costly. To address these
problems, this paper presents a low-cost, reusable, reconfigurable platform
that enables integrated design and implementation of embedded control systems.
To minimize the cost, free and open source software packages such as Linux and
Scilab are used. Scilab is ported to the embedded ARM-Linux system. The drivers
for interfacing Scilab with several communication protocols including serial,
Ethernet, and Modbus are developed. Experiments are conducted to test the
developed embedded platform. The use of Scilab enables implementation of
complex control algorithms on embedded platforms. With the developed platform,
it is possible to perform all phases of the development cycle of embedded
control systems in a unified environment, thus facilitating the reduction of
development time and cost.Comment: 15 pages, 14 figures; Open Access at
http://www.mdpi.org/sensors/papers/s8095501.pd
Cross-Layer Adaptive Feedback Scheduling of Wireless Control Systems
There is a trend towards using wireless technologies in networked control
systems. However, the adverse properties of the radio channels make it
difficult to design and implement control systems in wireless environments. To
attack the uncertainty in available communication resources in wireless control
systems closed over WLAN, a cross-layer adaptive feedback scheduling (CLAFS)
scheme is developed, which takes advantage of the co-design of control and
wireless communications. By exploiting cross-layer design, CLAFS adjusts the
sampling periods of control systems at the application layer based on
information about deadline miss ratio and transmission rate from the physical
layer. Within the framework of feedback scheduling, the control performance is
maximized through controlling the deadline miss ratio. Key design parameters of
the feedback scheduler are adapted to dynamic changes in the channel condition.
An event-driven invocation mechanism for the feedback scheduler is also
developed. Simulation results show that the proposed approach is efficient in
dealing with channel capacity variations and noise interference, thus providing
an enabling technology for control over WLAN.Comment: 17 pages, 12 figures; Open Access at
http://www.mdpi.org/sensors/papers/s8074265.pd
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