2,486 research outputs found
Use of hydraulic rating to set environmental flows in the Zhangxi River, China
Ningbo city, China, is a rapidly growing residential and industrial centre, with a current population of 4 million. Its development has required a major water supply expansion programme providing 400,000 m3 of water per day from the upper reaches of the Zhangxi River by means of a cascade of reservoirs. Water resources management is achieved through operation of two major reservoirs, Jiaokou (75 million m3) and Zhougongzhai (93 million m3). Water is released from the reservoirs, via turbines (generating hydropower), for local industry, irrigated agriculture and public supply along the lower reaches of the River and to maintain the river ecosystem. Surveys of local residents along the Zhangxi River showed its important role in aspects of life, social activity, culture and leisure. Analysis of ecological monitoring data demonstrated the diverse nature of fish, plants and invertebrates within the river. Some elements of the ecosystem have a high local economic value to local people. This paper reports an assessment of the environmental flow needed to support key species in the river ecosystem. It employs hydraulic ratings to define sections of the river where flow velocity reaches 0.5 ms-1, required to stimulate spawning of the moonlight fish, an economically important and indicator species in the river. In two out of 6 cross-sections studied, flow releases from the reservoirs meet the needs of fish. The reservoirs reduce flood flows, which may lead to a loss of deep pools that are essential for the fish to survive during winter month
Sampling-based stochastic optimal control with metric interval temporal logic specifications
This paper describes a method to find optimal policies for stochastic dynamic systems that maximise the probability of satisfying real-time properties. The method consists of two phases. In the first phase, a coarse abstraction of the original system is created. In each region of the abstraction, a sampling-based algorithm is utilised to compute local policies that allow the system to move between regions. Then, in the second phase, the selection of a policy in each region is obtained by solving a reachability problem on the Cartesian product between the abstraction and a timed automaton representing a real-time specification given as a metric interval temporal logic formula. In contrast to current methods that require a fine abstraction, the proposed method achieves computational tractability by modelling the coarse abstraction of the system as a bounded-parameter Markov decision process (BMDP). Moreover, once the BMDP is created, this can be reused for new specifications assuming the same stochastic system and workspace. The method is demonstrated with an autonomous driving example
Challenges for foreign companies in China: Implications for research and practice
As a large country with great development potential, China has been one of the most popular foreign direct investment destinations. However, foreign companies increasingly face a variety of challenges especially during the “soft-landing” of the Chinese economy and amidst anti-globalization tendency. Based on a comprehensive review of the extant literature, we provide a critical overview of some of the key challenges for foreign companies in China, focusing on two challenges related to the business environment, namely regulatory and cultural challenges, and two management challenges, namely innovation and human resource management. We provide managerial implications and outline directions for future research
3D reconstruction of train accident scene based on monocular image
To help with making an emergency rescue plan for train accidents, a rapid 3D reconstruction
method of train accident scene based on a monocular image was proposed. Taking two
camera projection models for different application scenarios into consideration, the SIFT algorithm
was introduced to extract and match image feature with the CAD model of an accident train.
Geometric constraints between carriages were provided to transform the 3D reconstruction to
solving a nonlinear least square problem with constraints, by which the position and pose of accident
subjects were reduced at last. To quantitatively and qualitatively verify the calculation performance
of this method, the mimicked train accident scene and real train accident scene were
respectively used to carry out 3D reconstruction. The precise finite camera projection model was
applied in the mimicked train accident scene to carry out offline calibration, and the stable
pin-hole model was adopted in the real train accident scene to carry out auto calibration. Analysis
result shows that through quantitative analysis of mimicked scene the maximal and average relative
error of 8 nodes for measurement in reconstructing two carriages are 4.54% and 1.85% respectively.
Through qualitative analysis of the real scene, the 3D reduction of position and pose
for carriages can also be realized with combining the topographic information correction. The
whole accident environmental panorama can be reduced visually with the help of 3D visualization
engine. This method can also be used in developing emergency rescue electronic sand table for
train accident analysis and safety education
VSCAN: An Enhanced Video Summarization using Density-based Spatial Clustering
In this paper, we present VSCAN, a novel approach for generating static video
summaries. This approach is based on a modified DBSCAN clustering algorithm to
summarize the video content utilizing both color and texture features of the
video frames. The paper also introduces an enhanced evaluation method that
depends on color and texture features. Video Summaries generated by VSCAN are
compared with summaries generated by other approaches found in the literature
and those created by users. Experimental results indicate that the video
summaries generated by VSCAN have a higher quality than those generated by
other approaches.Comment: arXiv admin note: substantial text overlap with arXiv:1401.3590 by
other authors without attributio
Size-dependent decoherence of excitonic states in semiconductor microcrystallites
The size-dependent decoherence of the exciton states resulting from the
spontaneous emission is investigated in a semiconductor spherical
microcrystallite under condition . In general, the
larger size of the microcrystallite corresponds to the shorter coherence time.
If the initial state is a superposition of two different excitonic coherent
states, the coherence time depends on both the overlap of two excitonic
coherent states and the size of the microcrystallite. When the system with
fixed size is initially in the even or odd coherent states, the larger average
number of the excitons corresponds to the faster decoherence. When the average
number of the excitons is given, the bigger size of the microcrystallite
corresponds to the faster decoherence. The decoherence of the exciton states
for the materials GaAs and CdS is numerically studied by our theoretical
analysis.Comment: 4 pages, two figure
Domain Growth, Wetting and Scaling in Porous Media
The lattice Boltzmann (LB) method is used to study the kinetics of domain
growth of a binary fluid in a number of geometries modeling porous media.
Unlike the traditional methods which solve the Cahn-Hilliard equation, the LB
method correctly simulates fluid properties, phase segregation, interface
dynamics and wetting. Our results, based on lattice sizes of up to , do not show evidence to indicate the breakdown of late stage dynamical
scaling, and suggest that confinement of the fluid is the key to the slow
kinetics observed. Randomness of the pore structure appears unnecessary.Comment: 13 pages, latex, submitted to PR
On geometric problems related to Brown-York and Liu-Yau quasilocal mass
We discuss some geometric problems related to the definitions of quasilocal
mass proposed by Brown-York \cite{BYmass1} \cite{BYmass2} and Liu-Yau
\cite{LY1} \cite{LY2}. Our discussion consists of three parts. In the first
part, we propose a new variational problem on compact manifolds with boundary,
which is motivated by the study of Brown-York mass. We prove that critical
points of this variation problem are exactly static metrics. In the second
part, we derive a derivative formula for the Brown-York mass of a smooth family
of closed 2 dimensional surfaces evolving in an ambient three dimensional
manifold. As an interesting by-product, we are able to write the ADM mass
\cite{ADM61} of an asymptotically flat 3-manifold as the sum of the Brown-York
mass of a coordinate sphere and an integral of the scalar curvature plus
a geometrically constructed function in the asymptotic region outside
. In the third part, we prove that for any closed, spacelike, 2-surface
in the Minkowski space for which the Liu-Yau mass is
defined, if bounds a compact spacelike hypersurface in ,
then the Liu-Yau mass of is strictly positive unless lies on
a hyperplane. We also show that the examples given by \'{O} Murchadha, Szabados
and Tod \cite{MST} are special cases of this result.Comment: 28 page
Statistical Properties of Cross-Correlation in the Korean Stock Market
We investigate the statistical properties of the correlation matrix between
individual stocks traded in the Korean stock market using the random matrix
theory (RMT) and observe how these affect the portfolio weights in the
Markowitz portfolio theory. We find that the distribution of the correlation
matrix is positively skewed and changes over time. We find that the eigenvalue
distribution of original correlation matrix deviates from the eigenvalues
predicted by the RMT, and the largest eigenvalue is 52 times larger than the
maximum value among the eigenvalues predicted by the RMT. The
coefficient, which reflect the largest eigenvalue property, is 0.8, while one
of the eigenvalues in the RMT is approximately zero. Notably, we show that the
entropy function with the portfolio risk for the original
and filtered correlation matrices are consistent with a power-law function,
, with the exponent and
those for Asian currency crisis decreases significantly
Plane waves with weak singularities
We study a class of time dependent solutions of the vacuum Einstein equations
which are plane waves with weak null singularities. This singularity is weak in
the sense that though the tidal forces diverge at the singularity, the rate of
divergence is such that the distortion suffered by a freely falling observer
remains finite. Among such weak singular plane waves there is a sub-class which
do not exhibit large back reaction in the presence of test scalar probes.
String propagation in these backgrounds is smooth and there is a natural way to
continue the metric beyond the singularity. This continued metric admits string
propagation without the string becoming infinitely excited. We construct a one
parameter family of smooth metrics which are at a finite distance in the space
of metrics from the extended metric and a well defined operator in the string
sigma model which resolves the singularity.Comment: 22 pages, Added references and clarifying comment
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