The evolution of turbulence characteristics in the wake of a horizontal axis tidal stream turbine

The evolution of turbulence characteristics downstream of a laboratory-scale three-bladed horizontal axis turbine is investigated in this study. Large eddy simulation (LES) coupled with the Actuator Line Modelling (ALM) is used to simulate the flow. The numerical results compare well against experimental data, which shows that the LES/ALM technique is a powerful tool for simulating tidal stream turbines. The present study aims to obtain a better understanding of the turbulence characteristics of flow in the turbine wake by removing deterministic velocity fluctuations stemmed from the turbine rotation. Large eddy simulation is able to provide high-resolution spatial and temporal information needed for this work. The filtering process helps to have a clearer view of the flow structures downstream by tracking the streamwise variations of turbulence intensity and turbulent kinetic energy and, reveals a transition zone started shortly behind the turbine with a peak in the turbulence intensity. This study introduces turbulence intensity and turbulent kinetic energy as quantitative criteria to split the turbine wake into distinct regions. This research shows that to investigate and explain the influence of different upstream and operation conditions on the flow characteristics in the turbine wake, a well understanding of flow characteristic changes in the transition zone is necessary.This work was funded by the Supergen Marine Challenge Programme of the EPSRC (EP/J010359/1)

Thermodynamic and Tunneling Density of States of the Integer Quantum Hall Critical State

We examine the long wave length limit of the self-consistent Hartree-Fock approximation irreducible static density-density response function by evaluating the charge induced by an external charge. Our results are consistent with the compressibility sum rule and inconsistent with earlier work that did not account for consistency between the exchange-local-field and the disorder potential. We conclude that the thermodynamic density of states is finite, in spite of the vanishing tunneling density of states at the critical energy of the integer quantum Hall transition.Comment: 5 pages, 4 figures, minor revisions, published versio

Spaceborne SAR attitude steering method for smart imaging mode

The current spaceborne synthetic aperture radar systems are operated to illuminate the scene along the satellite flying direction. However, in many cases, the interested areas are not parallel to the flying direction, so an innovative smart imaging mode is acquired, which can be employed for illuminating scene along a given direction. A novel three-axis attitude steering method is proposed for smart imaging mode. First, mathematical model of the attitude steering is built by considering the restrictive conditions of zero-Doppler centroid requirement and the position of interested area. Then, an iterative optimisation algorithm is designed to calculate the three-axis steering angles. Finally, experiment results using the satellite tool kit tool validate the proposed methods well, especially in the case of coastline imaging

Scaling of Aharonov-Bohm couplings and the dynamical vacuum in gauge theories

Recent results on the vacuum polarization induced by a thin string of magnetic flux lead us to suggest an analogue of the Copenhagen `flux spaghetti' QCD vacuum as a possible mechanism for avoiding the divergence of perturbative QED, thus permitting consistent completion of the full, nonperturbative theory. The mechanism appears to operate for spinor, but not scalar, QED.Comment: 11 pages, ITP-SB-92-40, (major conceptual evolution from original

The new chiral ligand 3-ethoxy-4-E(1R,2SS)-(2-hydroxy-1,2-diphenylethyl)amino -3-cyclobutene-1 ,2-dione

The asymmetric unit of C20H19NO4 contains two molecules with slightly different conformations, In the crystal,the molecules are linked by O-H ... O and N-H ... O hydrogen bonds [O ... O 2.764 (3) and 2.811 (3) Angstrom; N ... O 2.907 (3) and 3.968 (3) Angstrom] to form a two-dimensional network

Form factors of the XXZ Heisenberg spin-1/2 finite chain

Form factors for local spin operators of the XXZ Heisenberg spin-1/2 finite chain are computed. Representation theory of Drinfel'd twists for the sl2 quantum affine algebra in finite dimensional modules is used to calculate scalar products of Bethe states (leading to Gaudin formula) and to solve the quantum inverse problem for local spin operators in the finite XXZ chain. Hence, we obtain the representation of the n-spin correlation functions in terms of expectation values(in ferromagnetic reference state) of the operator entries of the quantum monodromy matrix satisfying Yang-Baxter algebra. This leads to the direct calculation of the form factors of the XXZ Heisenberg spin-1/2 finite chain as determinants of usual functions of the parameters of the model. A two-point correlation function for adjacent sites is also derived using similar techniques.Comment: 30 pages, LaTeX2

Modeling and Optimization of the Dilute Sulfuric Acid Treatment on Corn Stover at Low Temperature

Corn stover was hydrolyzed using dilute sulfuric acid at concentrations of 2, 4, and 6% over reaction times up to 300 minutes at 80oC. The concentrations of sugars (xylose and glucose) and degradation product (furfural) were determined and the kinetic parameters of mathematical models for predicting them in the hydrolysates were obtained. According to the models, an optimal condition for hydrolysis was achieved which was 5% H2SO4 at 80°C for 240min and the liquor contained up to 13.21g/l xylose, 5.07g /l glucose and 0.80g/l furfural. The hydrolysates obtained from corn stover can be used to produce hydrogen and methane by anaerobic fermentation process. The models could be used successfully to predict the concentrations of xylose, glucose and furfural within 0-300min under experimental acid concentration

Long-term trends in tropical cyclone tracks around Korea and Japan in late summer and early fall

This study investigates long-term trends in tropical cyclones (TCs) over the extratropical western North Pacific (WNP) over a period of 35 years (1982-2016). The area analyzed extended across 30-45 degrees N and 120-150 degrees E, including the regions of Korea and Japan that were seriously affected by TCs. The northward migration of TCs over the WNP to the mid-latitudes showed a sharp increase in early fall. In addition, the duration of TCs over the WNP that migrated northwards showed an increase, specifically in early to mid-September. Therefore, more recently, TC tracks have been observed to significantly extend into the mid-latitudes. The recent northward extension of TC tracks over the WNP in early fall was observed to be associated with changes in environmental conditions that were favorable for TC activities, including an increase in sea surface temperature (SST), decrease in vertical wind shear, expansion of subtropical highs, strong easterly steering winds, and an increase in relative vorticity. In contrast, northward migrations of TCs to Korea and Japan showed a decline in late August, because of the presence of unfavorable environmental conditions for TC activities. These changes in environmental conditions, such as SST and vertical wind shear, can be partially associated with the Pacific decadal oscillation

Onset of entanglement

We have developed a theory of polymer entanglement using an extended Cahn-Hilliard functional, with two extra terms. One is a nonlocal attractive term, operating over mesoscales, which is interpreted as giving rise to entanglement, and the other a local repulsive term indicative of excluded volume interactions. We show how such a functional can be derived using notions from gauge theory. We go beyond the Gaussian approximation, to the one-loop level, to show that the system exhibits a crossover to a state of entanglement as the average chain length between points of entanglement decreases. This crossover is marked by critical slowing down, as the effective diffusion constant goes to zero. We have also computed the tensile modulus of the system, and we find a corresponding crossover to a regime of high modulus.Comment: 18 pages, with 4 figure