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In this paper, we
analyze the default risk of Chinese real estate companies with KMV model and
time-varying copula. We collected the data of the listed real estate companies
in Shanghai and Shenzhen Exchanges from 2007 to 2012 to calculate the default
distance and correlations. Experiments results show that the default risk increases
during the financial crisis. Moreover, results also indicate the default risk aggregation.
The difference of default risk between the large size and small size companies
is also examined in this research. Due to the high asset liability ratio, the large
size companies face higher default risk than the small size companies. Finally,
time-varying copula shows that the correlation between different-sized
companies fluctuates severely during the financial crisis and then goes
smoothly after the crisis.
Manufacturing accuracy, especially position
accuracy of fastener holes, directly affects service life and security of aircraft.
The traditional modification has poor robustness, while the modification based on
laser tracker costs too much. To improve the relative position accuracy of aircraft
assembly drilling, and ensure the hole-edge distance requirement, a method was presented
to modify the coordinates of drilling holes. Based on online inspecting two positions
of pre-assembly holes and their theoretical coordinates, the spatial coordinate
transformation matrix of modification could be calculated. Thus the straight drilling
holes could be modified. The method improves relative position accuracy of drilling
on simple structure effectively. And it reduces the requirement of absolute position
accuracy and the cost of position modification. And the process technician also
can use this method to decide the position accuracy of different pre-assembly holes
based on the accuracy requirement of assembly holes.
Gait planning based on linear inverted pendulum
(LIPM) on structured road surface can be quickly generated because of the
simple model and definite physical meaning. However, over-simplifi- cation of
the model and discontents of zero velocity and acceleration boundary
conditions when robot starts and stops walking lead to obvious
difference between the model and the real robot. In this paper, parameterized
gait is planned and trajectories’ smoothness of each joint angle and centroid
are ensured using the 3-D LIPM theory. Static walking method is used to satisfy
zero velocity and acceleration boundary conditions. Besides, a multi-link model
is built to validate the stability. Simulation experiments show that: despite
of some deviation from the theoretical solution, the actual zero-moment point
(ZMP) is still within the support polygon, and the robot walks steadily. In
consequence, the rationality and validity of model simplification of
LIPM is demonstrated.