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Natural river networks exhibit regular scaling laws in their topological organization. Here, we investigate whether these
scaling laws are unique characteristics of river networks or can be applicable to general binary tree networks. We generate
numerous binary trees, ranging from purely ordered trees to completely random trees. For each generated binary tree, we analyze
whether the tree exhibits any scaling property found in river networks, i.e., the power-laws in the size distribution, the
length distribution, the distance-load relationship, and the power spectrum of width function. We found that partially random
trees generated on the basis of two distinct types of deterministic trees, i.e., deterministic critical and supercritical
trees, show contrasting characteristics. Partially random trees generated on the basis of deterministic critical trees exhibit
all power-law characteristics investigated in this study with their fitted exponents close to the values observed in natural
river networks over a wide range of random-degree. On the other hand, partially random trees generated on the basis of deterministic
supercritical trees rarely follow scaling laws of river networks. 相似文献
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Jieun Lee Kyoungho Kim Hong Chan Lee Dongwoo Kim Myeonghee Kwon Hongil Joo Hong Y. Cho Heung Bae Jeon Hyun-jong Paik 《Journal of polymer science. Part A, Polymer chemistry》2022,60(2):258-265
A glasses-shaped triblock copolymer of poly(ε-caprolactone)-b-polystyrene-b-poly(ε-caprolactone) (PCL-b-PS-b-PCL) is prepared by combining atom transfer radical polymerization (ATRP) and ring opening polymerization (ROP). Polystyrene (PS) star polymers are prepared via ATRP using a tetra-functional initiator, followed by azidation to yield azide end-functionalized star polymers. An alkyne-functionalized coupling agent, 2,2-bis[(2-propyn-1-yloxy)methyl]-1-propanol is employed to produce hydroxy 8-shaped PS via copper(I)-catalyzed alkyne-azide cycloaddition. Herein, hydroxy 8-shaped PS with high purity is obtained through preparative size exclusion chromatography (Prep SEC) and high-performance liquid chromatography, followed by the characterizations using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), size exclusion chromatography (SEC), infrared, and proton nuclear magnetic resonance (1H NMR) spectroscopy. The hydroxy groups of the 8-shaped PS are utilized as initiators for the ROP of ε-caprolactone to obtain linear chains attached to the 8-shaped architecture. After SEC fractionation, the glasses-shaped triblock copolymer is characterized using 1H NMR and SEC. This unprecedented topology possesses two free chain-ends and two cycles; thus, both the properties of linear and cyclic polymers may be expected to be observed. 相似文献
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Ho Jung Paik 《General Relativity and Gravitation》2008,40(5):907-919
The angular momentum of the Earth produces gravitomagnetic components of the Riemann curvature tensor, which are of the order
of 10−10 of the Newtonian terms arising from the mass of the Earth. Due to the dragging of the local inertial frame by the spinning
Earth, there are also secular terms, which grow in time. These fields can be detected in principle by a set of orbiting superconducting
gravity gradiometers. The Riemann tensor components for various spacecraft orientations have been computed and the principle
of detecting the gravitomagnetic tidal force has been published. In this paper, we review the conclusions of the earlier analyses
and discuss the feasibility of the gravity gradiometer experiment. 相似文献
140.
A stereoscopic PIV (Particle Image Velocimetry) technique has been employed to measure the 3 dimensional flow structure of
turbulent wake behind a marine propeller with 5 blades. The out-of-plane velocity component was measured using particle images
captured simultaneously by two CCD cameras installed in the angular displacement configuration. 400 instantaneous velocity
fields were acquired for each of four different blade phases of 0°, 18°, 36° and 54°. They were ensemble averaged to investigate
the spatial evolution of propeller wake in the near wake region up to one propeller diameter (D) downstream. The phase-averaged
velocity fields show clearly the viscous wake formed by the boundary layers developed along both surfaces of the blade. Tip
vortices were generated periodically and the slipstream contraction occurs in the near-wake region. The out-of-plane velocity
component has large values at the locations of tip and trailing vortices. With going downstream, the axial turbulence intensity
and the strength of tip vortices were decreased due to the viscous dissipation, turbulence diffusion and blade-to-blade interaction.
The difference in the mean velocity fields measured by SPIV and 2-D PIV methods was about 5% ≈ 10%. However, the 2-D PIV results
also give sufficient information on propeller wake beyond the region of X/D=0.2. 相似文献