82,132 research outputs found
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A hybrid stabilization technique for simulating water wave - Structure interaction by incompressible Smoothed Particle Hydrodynamics (ISPH) method
The Smoothed Particle Hydrodynamics (SPH) method is emerging as a potential tool for studying water wave related problems, especially for violent free surface flow and large deformation problems. The incompressible SPH (ISPH) computations have been found not to be able to maintain the stability in certain situations and there exist some spurious oscillations in the pressure time history, which is similar to the weakly compressible SPH (WCSPH). One main cause of this problem is related to the non-uniform and clustered distribution of the moving particles. In order to improve the model performance, the paper proposed an efficient hybrid numerical technique aiming to correct the ill particle distributions. The correction approach is realized through the combination of particle shifting and pressure gradient improvement. The advantages of the proposed hybrid technique in improving ISPH calculations are demonstrated through several applications that include solitary wave impact on a slope or overtopping a seawall, and regular wave slamming on the subface of open-piled structure
Scatteract: Automated extraction of data from scatter plots
Charts are an excellent way to convey patterns and trends in data, but they
do not facilitate further modeling of the data or close inspection of
individual data points. We present a fully automated system for extracting the
numerical values of data points from images of scatter plots. We use deep
learning techniques to identify the key components of the chart, and optical
character recognition together with robust regression to map from pixels to the
coordinate system of the chart. We focus on scatter plots with linear scales,
which already have several interesting challenges. Previous work has done fully
automatic extraction for other types of charts, but to our knowledge this is
the first approach that is fully automatic for scatter plots. Our method
performs well, achieving successful data extraction on 89% of the plots in our
test set.Comment: Submitted to ECML PKDD 2017 proceedings, 16 page
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Study on wave-induced kinematic responses and flexures of ice floe by Smoothed Particle Hydrodynamics
In this paper, a Smoothed Particle Hydrodynamics (SPH) method is extended to simulate the wave–ice interactions. The main contribution of this work is that an improved fluid-ice interface treatment scheme is included into SPH code to deal with the contact between the fluid and ice particles. The proposed SPH approach is applied to model two typical patterns of the wave–ice interaction process: the kinematic response of a small ice floe and the flexural motion of a sea ice floe, induced by water waves. To verify the accuracy of SPH method for the wave–ice interactions, the numerical results of SPH are compared with corresponding experimental data. The good agreement between the two demonstrates that the SPH method can be a useful numerical tool for simulating the wave-induced motion and bending deformation of an ice floe
Causality in Non-Commutative Quantum Field Theories
We study causality in non-commutative quantum field theory with a space-space
non-commutativity. We employ the S-operator approach of Bogoliubov-Shirkov(BS).
We generalize the BS criterion of causality to the noncommutative theory. The
criterion to test causality leads to a nonzero difference between T*-product
and T-product as a condition of causality violation for a spacelike separation.
We discuss two examples; one in a scalar theory and one in the Yukawa theory.
In particular, in the context of a non-commutative Yukawa theory, with the
interaction Lagrangian , is observed to
be causality violating even in case of space-space noncommutativity for which
\theta^{0i}=0.
\Comment: 18 pages, LaTeX; A few changes in sections 3.2,3.3 and
Naturally Small Seesaw Neutrino Mass with No New Physics Beyond the TeV Scale
If there is no new physics beyond the TeV energy scale, such as in a theory
of large extra dimensions, the smallness of the seesaw neutrino mass, i.e.
, cannot be explained by a very large . In contrast to
previous attempts to find an alternative mechanism for a small , I show
how a solution may be obtained in a simple extension of the Standard Model,
without using any ingredient supplied by the large extra dimensions. It is also
experimentally testable at future accelerators.Comment: 9 pages, in final form for PR
Toeplitz operators on symplectic manifolds
We study the Berezin-Toeplitz quantization on symplectic manifolds making use
of the full off-diagonal asymptotic expansion of the Bergman kernel. We give
also a characterization of Toeplitz operators in terms of their asymptotic
expansion. The semi-classical limit properties of the Berezin-Toeplitz
quantization for non-compact manifolds and orbifolds are also established.Comment: 40 page
Water loss due to increasing planted vegetation over the Badain Jaran Desert, China
© 2018 by the authors. Water resources play a vital role in ecosystem stability, human survival, and social development in drylands. Human activities, such as afforestation and irrigation, have had a large impact on the water cycle and vegetation in drylands over recent years. The Badain Jaran Desert (BJD) is one of the driest regions in China with increasing human activities, yet the connection between human management and the ecohydrology of this area remains largely unclear. In this study, we firstly investigated the ecohydrological dynamics and their relationship across different spatial scales over the BJD, using multi-source observational data from 2001 to 2014, including: total water storage anomaly (TWSA) from Gravity Recovery and Climate Experiment (GRACE), normalized difference vegetation index (NDVI) from Moderate Resolution Imaging Spectroradiometer (MODIS), lake extent from Landsat, and precipitation from in situ meteorological stations. We further studied the response of the local hydrological conditions to large scale vegetation and climatic dynamics, also conducting a change analysis of water levels over four selected lakes within the BJD region from 2011. To normalize the effect of inter-annual variations of precipitation on vegetation, we also employed a relationship between annual average NDVI and annual precipitation, or modified rain-use efficiency, termed the RUEmo. A focus of this study is to understand the impact of the increasing planted vegetation on local ecohydrological systems over the BJD region. Results showed that vegetation increases were largely found to be confined to the areas intensely influenced by human activities, such as croplands and urban areas. With precipitation patterns remaining stable during the study period, there was a significant increasing trend in vegetation greenness per unit of rainfall, or RUEmo over the BJD, while at the same time, total water storage as measured by satellites has been continually decreasing since 2003. This suggested that the increased trend in vegetation and apparent increase in RUEmo can be attributed to the extraction of ground water for human-planted irrigated vegetation. In the hinterland of the BJD, we identified human-planted vegetation around the lakes using MODIS observations and field investigations. Four lake basins were chosen to validate the relationship between lake levels and planted vegetation. Our results indicated that increasing human-planted vegetation significantly increased the water loss over the BJD region. This study highlights the value of combining observational data from space-borne sensors and ground instruments to monitor the ecohydrological dynamics and the impact of human activities on water resources and ecosystems over the drylands
Structural results on convexity relative to cost functions
Mass transportation problems appear in various areas of mathematics, their
solutions involving cost convex potentials. Fenchel duality also represents an
important concept for a wide variety of optimization problems, both from the
theoretical and the computational viewpoints. We drew a parallel to the
classical theory of convex functions by investigating the cost convexity and
its connections with the usual convexity. We give a generalization of Jensen's
inequality for cost convex functions.Comment: 10 page
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