80,102 research outputs found
Discovery of a new supernova remnant G150.3+4.5
Large-scale radio continuum surveys have good potential for discovering new
Galactic supernova remnants (SNRs). Surveys of the Galactic plane are often
limited in the Galactic latitude of |b| ~ 5 degree. SNRs at high latitudes,
such as the Cygnus Loop or CTA~1, cannot be detected by surveys in such limited
latitudes. Using the available Urumqi 6 cm Galactic plane survey data, together
with the maps from the extended ongoing 6 cm medium latitude survey, we wish to
discover new SNRs in a large sky area. We searched for shell-like structures
and calculated radio spectra using the Urumqi 6 cm, Effelsberg 11 cm, and 21 cm
survey data. Radio polarized emission and evidence in other wavelengths are
also examined for the characteristics of SNRs. We discover an enclosed
oval-shaped object G150.3+4.5 in the 6 cm survey map. It is about 2.5 degree
wide and 3 degree high. Parts of the shell structures can be identified well in
the 11 cm, 21 cm, and 73.5 cm observations. The Effelsberg 21 cm total
intensity image resembles most of the structures of G150.3+4.5 seen at 6 cm,
but the loop is not closed in the northwest. High resolution images at 21 cm
and 73.5 cm from the Canadian Galactic Plane Survey confirm the extended
emission from the eastern and western shells of G150.3+4.5. We calculated the
radio continuum spectral indices of the eastern and western shells, which are
and between 6 cm and 21 cm, respectively.
The shell-like structures and their non-thermal nature strongly suggest that
G150.3+4.5 is a shell-type SNR. For other objects in the field of view,
G151.4+3.0 and G151.2+2.6, we confirm that the shell-like structure G151.4+3.0
very likely has a SNR origin, while the circular-shaped G151.2+2.6 is an HII
region with a flat radio spectrum, associated with optical filamentary
structure, H, and infrared emission.Comment: 5 pages, 3 figures, accepted for publication of Astronomy and
Astrophysic
Supersolid and charge density-wave states from anisotropic interaction in an optical lattice
We show anisotropy of the dipole interaction between magnetic atoms or polar
molecules can stabilize new quantum phases in an optical lattice. Using a well
controlled numerical method based on the tensor network algorithm, we calculate
phase diagram of the resultant effective Hamiltonian in a two-dimensional
square lattice - an anisotropic Hubbard model of hard-core bosons with
attractive interaction in one direction and repulsive interaction in the other
direction. Besides the conventional superfluid and the Mott insulator states,
we find the striped and the checkerboard charge density wave states and the
supersolid phase that interconnect the superfluid and the striped solid states.
The transition to the supersolid phase has a mechanism different from the case
of the soft-core Bose Hubbard model.Comment: 5 pages, 5 figures
Numerical simulation of the world ocean circulation
A multi-level model, based on the primitive equations, is developed for simulating the temperature and velocity fields produced in the world ocean by differential heating and surface wind stress. The model ocean has constant depth, free slip at the lower boundary, and neglects momentum advection; so that there is no energy exchange between the barotropic and baroclinic components of the motion, although the former influences the latter through temperature advection. The ocean model was designed to be coupled to the UCLA atmospheric general circulation model, for the study of the dynamics of climate and climate changes. But here, the model is tested by prescribing the observed seasonally varying surface wind stress and the incident solar radiation, the surface air temperature and humidity, cloudiness and the surface wind speed, which, together with the predicted ocean surface temperature, determine the surface flux of radiant energy, sensible heat and latent heat
Collision-free trajectory planning algorthm for manipulators
Collision-free trajectory planning for robotic manipulators is investigated. The task of the manipulator is to move its end-effector from one point to another point in an environment with polyhedral obstacles. An on-line algorithm is developed based on finding the required joint angles of the manipulator, according to goals with different priorities. The highest priority is to avoid collisions, the second priority is to plan the shortest path for the end effector, and the lowest priority is to minimize the joint velocity for smooth motion. The pseudo-inverse of the Jacobian matrix is applied for inverse kinematics. When a possible collision is detected, a constrained inverse kinematic problem is solved such that the collision is avoided. This algorithm can also be applied to a time-variant environment
Criticality and Continuity of Explosive Site Percolation in Random Networks
This Letter studies the critical point as well as the discontinuity of a
class of explosive site percolation in Erd\"{o}s and R\'{e}nyi (ER) random
network. The class of the percolation is implemented by introducing a best-of-m
rule. Two major results are found: i). For any specific , the critical
percolation point scales with the average degree of the network while its
exponent associated with is bounded by -1 and . ii).
Discontinuous percolation could occur on sparse networks if and only if
approaches infinite. These results not only generalize some conclusions of
ordinary percolation but also provide new insights to the network robustness.Comment: 5 pages, 5 figure
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