5,955 research outputs found
Molecular Lines of 13 Galactic Infrared Bubble Regions
We investigated the physical properties of molecular clouds and star
formation processes around infrared bubbles which are essentially expanding HII
regions. We performed observations of 13 galactic infrared bubble fields
containing 18 bubbles. Five molecular lines, 12CO (J=1-0), 13CO (J=1-0),
C18O(J=1-0), HCN (J=1-0), and HCO+ (J=1-0), were observed, and several publicly
available surveys, GLIMPSE, MIPSGAL, ATLASGAL, BGPS, VGPS, MAGPIS, and NVSS,
were used for comparison. We find that these bubbles are generally connected
with molecular clouds, most of which are giant. Several bubble regions display
velocity gradients and broad shifted profiles, which could be due to the
expansion of bubbles. The masses of molecular clouds within bubbles range from
100 to 19,000 solar mass, and their dynamic ages are about 0.3-3.7 Myr, which
takes into account the internal turbulence pressure of surrounding molecular
clouds. Clumps are found in the vicinity of all 18 bubbles, and molecular
clouds near four of these bubbles with larger angular sizes show shell-like
morphologies, indicating that either collect-and-collapse or radiation-driven
implosion processes may have occurred. Due to the contamination of adjacent
molecular clouds, only six bubble regions are appropriate to search for
outflows, and we find that four of them have outflow activities. Three bubbles
display ultra-compact HII regions at their borders, and one of them is probably
responsible for its outflow. In total, only six bubbles show star formation
activities in the vicinity, and we suggest that star formation processes might
have been triggered.Comment: 55 Pages, 32 figures. Accepted for publication in A
Sub-quadratic scaling real-space random-phase approximation correlation energy calculations for periodic systems with numerical atomic orbitals
The random phase approximation (RPA) as formulated as an orbital-dependent,
fifth-rung functional within the density functional theory (DFT) framework
offers a promising approach for calculating the ground-state energies and the
derived properties of real materials. Its widespread use to large-size, complex
materials is however impeded by the significantly increased computational cost,
compared to lower-rung functionals. The standard implementation exhibits an
-scaling behavior with respect to system size . In this
work, we develop a low-scaling RPA algorithm for periodic systems, based on the
numerical atomic orbital (NAO) basis-set framework and a localized variant of
the resolution of identity (RI) approximation. The rate-determining step for
RPA calculations -- the evaluation of non-interacting response function matrix,
is reduced from to by just exploiting the
sparsity of the RI expansion coefficients, resultant from localized RI (LRI)
scheme and the strict locality of NAOs. The computational cost of this step can
be further reduced to linear scaling if the decay behavior of the Green's
function in real space can be further taken into account. Benchmark
calculations against existing -space based implementation confirms
the validity and high numerical precision of the present algorithm and
implementation. The new RPA algorithm allows us to readily handle
three-dimensional, closely-packed solid state materials with over 1000 atoms.
The algorithm and numerical techniques developed in this work also have
implications for developing low-scaling algorithms for other correlated methods
to be applicable to large-scale extended materials
Simulation and Analysis of Indoor Visible Light Propagation Characteristics Based on the Method of SBR/Image
The indoor visible light propagation characteristics are simulated and analyzed using the method of SBR/Image (shooting and bounding ray tracing/Image). A good agreement is achieved between the results simulated and the results given in published literature. So the correctness of the method has been validated. Some propagation parameters are obtained in the simulation, such as the indoor received power distribution, statistical distribution of phase angle of received power, RMS (root mean square) delay spread, direction of arrival, and Doppler shift. The foundation for the wireless network coverage of indoor visible light communication system is provided by the analysis of the above results
Chip-based photonic radar for high-resolution imaging
Radar is the only sensor that can realize target imaging at all time and all
weather, which would be a key technical enabler for future intelligent society.
Poor resolution and large size are two critical issues for radars to gain
ground in civil applications. Conventional electronic radars are difficult to
address both issues especially in the relatively low-frequency band. In this
work, we propose and experimentally demonstrate, for the first time to the best
of our knowledge, a chip-based photonic radar based on silicon photonic
platform, which can implement high resolution imaging with very small
footprint. Both the wideband signal generator and the de-chirp receiver are
integrated on the chip. A broadband photonic imaging radar occupying the full
Ku band is experimentally established. A high precision range measurement with
a resolution of 2.7 cm and an error of less than 2.75 mm is obtained. Inverse
synthetic aperture (ISAR) imaging of multiple targets with complex profiles are
also implemented.Comment: 4 pages, 6figure
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