Number Of Periods Research Articles

Error field and correction coils in DTT: A preliminary analysis

The Divertor Tokamak Test (DTT) facility, construction starting at Frascati, Italy, is designed to test different solutions for divertor in view of DEMO. A preliminary analysis of the error fields (EFs) assumed a simplified model of rigid and independent displacements and rotations. A methodology based on the first order truncated Taylor expansion has been applied, linking the displacement parameters and the EFs within the required accuracies. A system of in-vessel copper coils has been designed to counteract EFs and the ampere-turns necessary to force them back within the request limits has been calculated. Here, the details of the analysis have been provided.

Computer vision-based measurement of wave force on the rectangular structure

Measurement of the wave force acting on the structure is normally achieved by the traditional load cells. In this study, a non-contact computer vision (CV)-based method is proposed, which can conveniently acquire the wave pressure and force without installing pressure sensors or load cell mounted on the structure. Based on the velocity field measured by the Optical Flow technique, the pressure field is successfully computed by solving the Poisson pressure equation, and the wave force is further determined by integrating the pressure over the surfaces of the structure. The proposed method is verified by conducting a series of laboratory experiments of wave interacting with the rectangular structure. The accuracy of the method is validated by comparing with the results measured by pressure sensors. It indicates that the CV obtained pressure and wave forces generally agree well with the sensor measured results, including the time history of wave force and the peak wave force, and the reasons for the deviation and error are also discussed. The effects of wave height and wave period on the pressure field and wave force are studied, and it is found that the Keulegan–Carpenter number is an important parameter determining the peak wave force. Finally, the limitations existed in this method are noted, including the two-dimensional simplification and air bubble effects, which need to be addressed in the future.

An Unusual Fullerene–Carbene Adduct: Thermal Motion, Disorder, or Both?**

AbstractA single‐crystal X‐ray study of a fullerene‐imidazole adduct at nine temperatures (80 K≤T≤480 K), accompanied by energy calculations, strongly suggested thermal motion of the C60 moiety with respect to the imidazolium heterocycle. Analysis of the anisotropic displacement parameters, calculations of frequencies, and the refinement of disorder models for the crystal at four temperatures (230 K≤T≤380 K) lead to the conclusion that the rotator is moving at all temperatures. The rotation barrier is low, with one preferred crystallographic site and several other energy minima.

Hydrodynamic loads of the bridge decks in wave-current combined flows

This work uses a Large Eddy Simulation (LES) model and the Volume of Fluid (VOF) scheme to investigate the hydrodynamic loads on submerged rectangular decks in wave-current combined flows. The influences of current velocity, wave height, deck length, and blockage ratio on the wave loads are examined, and a modified Morison equation is used to predict the hydrodynamic forces on the deck. The simulation results demonstrate that the wave loads are linearly proportional to wave height H when H ≤ 0.4h, h is the water depth. By setting the reference velocity as Ur = (gH)1/2 for wave-induced flow, the hydrodynamic loads can be separated into a steady term (current-induced load) and an acceleration term (wave-induced load). The crucial hydrodynamic load comes from the surface pressures on the upper side of the decks, owing to the deck length being much larger than the deck thickness. In addition, the drag coefficient is independent of the wave height H, aspect ratio L/D, and the Keulegan-Carpenter number KC; while the lift coefficient depends on the submergence ratio S/D. Bridge engineers could easily use the modified Morison equation and the maximum drag coefficient CD = 2.73, lift coefficient CL = −2.05, the inertia coefficients CMx = 0.95 and CMz = 2.53 to compute the maximum loads against wave-current combined flows.

A new thermography using inelastic scattering analysis of wavelength-resolved neutron transmission imaging

Thermography using energy-dependent neutron transmission imaging can non-invasively and non-destructively visualize a real-space distribution of interior temperatures of a material in a container. Previously, resonance absorption broadening analysis and Bragg-edge shift analysis using energy-resolved neutron transmission have been developed, however some issues remain, e.g., imaging efficiency, substance limitation and temperature sensitivity. For this reason, we propose a new neutron thermography using the temperature dependence of inelastic scattering of cold neutrons. This method has some advantages, for example, the imaging efficiency is high because cold neutrons are measured with moderate wavelength resolution, and light elements can be analysed in principle. We investigated the feasibility of this new neutron thermography at pulsed neutron time-of-flight imaging instruments at ISIS in the United Kingdom and HUNS in Japan. A Rietveld-type transmission spectrum analysis program (RITS) was employed to refine temperature and atomic displacement parameters from the inelastic scattering cross-section analysis. Finally, we demonstrated interior thermography of an α-Fe sample of 10 mm thickness inside a vacuum chamber by using a neutron time-of-flight imaging detector at the compact accelerator-driven pulsed neutron source HUNS.

Fully Atomistic Molecular Dynamics Simulation of a TIPS-Pentacene:Polystyrene Mixed Film Obtained via the Solution Process

Organic thin-film transistors using small-molecule semiconductor materials such as 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-P) have been recently studied for the production of flexible and printed electronic devices. Blending a semiconductor with an insulating polymer, such as polystyrene, is known to improve the device performance; however, its molecular-level structure remains unknown. In this study, we performed molecular dynamics (MD) simulations on a mixed system of TIPS-P and atactic polystyrene (aPS) with fully atomistic models to understand the structure of the mixed thin film at the molecular level and the influence on the device properties. To reproduce the deposition from the solution, we gradually reduced the number of toluene molecules in the simulation. The dynamic characteristics of the system, mean squared displacement, diffusion coefficient, density profile, and P2 order parameter were analyzed. Some of the simulated systems reached the equilibrium state. In these systems, the simulated structures suggested the presence of more TIPS-P molecules on the surface than inside the bulk, even at the low molecular weight of aPS, where phase separation was not observed experimentally. The results of the fully atomistic MD simulations are also a basis for the coarse-grained model to increase the speed of the MD simulation.

A laboratory study of wave-induced local scour at an emergent pile breakwater

A pile breakwater is a row of closely-spaced piles, placed in a side-by-side arrangement, to dissipate wave energy and prevent coastal erosion. It is important to understand the local scour at a pile breakwater for its foundation design. This paper reports a set of wave-flume tests on the local scour around the piles in regular waves. A laser scanner was used to measure the change in the three-dimensional bed elevation. Five values of Keulegan–Carpenter number were examined in this study. Scour holes near the pile breakwater were developed due to the oscillatory jet flow through the gaps between adjacent piles, and sand ripples were observed on both sides of the structure. The migration of the sand ripples was either onshore or offshore, depending on the wave conditions. The maximum scour-hole depth had an exponential growth with the duration of wave attack, and the equilibrium depth was found to be deeper than that for a standalone pile. Both the scour-hole depth and length were found to be scaled by the pile diameter. The ripple length and steepness were in general agreement with recent empirical formulas in the literature in spite of the presence of a pile breakwater.

Planar and spherical four-bar linkage [formula omitted] algebraic input–output equations

The algebraic polynomial input–output (IO) equations relating any two of the relative joint displacement parameters, called vi and vj, between any of the six distinct pairs of rigid links in arbitrary planar and spherical four-bar mechanisms are derived. First, the forward kinematics transformation matrices of the corresponding serial kinematic chains are computed in terms of their Denavit–Hartenberg parameters, but with all angles converted to tangent half-angle parameters. These matrices are mapped to their corresponding Study soma coordinates. The serial kinematic chain is closed by equating the soma coordinates to the identity array. Algebraic polynomial elimination methods are then used to obtain a single polynomial in terms of only the design and the selected IO joint displacement parameters. This yields six independent algebraic IO Equations for each of the planar and spherical 4R linkages; the same techniques are applied to derive six additional algebraic IO equations for each of the RRRP and PRRP planar linkages providing a catalogue of 24. The utility of these IO equation sets is demonstrated via discussion of the associated mobility and design parameter spaces.

An analytical approach of finding out the equilibrium scour depth at a cylindrical pier when the current is making an angle with the wave

The present work describes the development of a mathematical model for the evaluation of the equilibrium scour depth around a single cylindrical pier under the influence of co-existing waves and current. The presented equation includes the effect of the Keulegan–Carpenter number and Froude number on the formation of scour hole. The principle of energy balance is used to form a nonlinear equation of scour, where the energy of incoming flow when collided with the pier is equated with the weight of the sediments moving away from the vicinity of the pier to establish an equilibrium scour depth. An effort has been made to capture the nature of the flow along x-, y-, and z-directions when the current is inclined at an angle θ with the direction of progress of the wave. Further, the scour profile chosen can incorporate any shape and size of the scour hole. The model has been tested against published experimental data pertaining to two cases, namely when the waves are following the current and when the waves are traveling normal to the current. Here, only linear wave is considered while deriving the equation.

Local heterogeneity analysis of crystallographic and cryo-EM maps using shell-approximation

In X-ray crystallography and cryo-EM, experimental maps can be heterogeneous, showing different level of details in different regions. In this work we interpret heterogeneity in terms of two parameters, assigned individually for each atom, combining the conventional atomic displacement parameter with the resolution of the atomic image in the map. We propose a local real-space procedure to estimate the values of these heterogeneity parameters, assuming that a fragment of the density map and atomic positions are given. The procedure is based on an analytic representation of the atomic image, as a function of the inhomogeneity parameters and atomic coordinates. In this article, we report the results of the tests both with maps simulated and those derived from experimental data. For simulated maps containing regions with different resolutions, the method determines the local map resolution around the atomic centers and the values of the displacement parameter with reasonable accuracy. For experimental maps, obtained as a Fourier synthesis of a given global resolution, estimated values of the local resolution are close to the global one, and the values of the estimated displacement parameters are close to the respective values of the closest atoms in the refined model. Shown successful applications of the proposed method to experimental crystallographic and cryo-EM maps can be seen as a practical proof of method.

A THREE-DIMENSIONAL VISUALIZATION STUDY OF THE OSCILLATORY FLOW AROUND A WALL-MOUNTED CYLINDER AT KEULEGAN-CARPENTER NUMBER, KC = 20

Several flow visualization techniques are applied on the computed hydrodynamic fields for the oscillatory flow around wall-mounted cylinder with a Keulegan−Carpenter KC = 20. To solve the three-dimensional Navier−Stokes equations, the direct numerical simulation is conducted using Open-source Field Operation and Manipulation (OpenFOAM®). Details obtained from such flow visualizations increase in dimensionality and complexity. Streamlines, contours of dynamic pressure over the cylinder surface and wall shear stress in the vicinity of the cylinder-wall junction surface contours, and coherent structures using Q-criterion represent lineal-, areal-, and volume-based flow features, respectively. Line integral convolution as well as particle trajectories are shown at different phases of the background oscillatory flows to illustrate and describe the underlying flow mechanisms.

Experimental Study of Local Scour Around Circularcrossing and Square-crossing Piles in Waves and Current

Experimental tests of local scour around a circular-crossing pile (CCP) and a square-crossing pile (SCP) were carried out to study the effects of superimposed waves upon current in the local scour process and the differences in characteristics in the two shaped piles. Non-uniform sediment with a gradation of 1.6 was used in the tests. Stokes waves of 0.11 m in height and 1.6 s in period were generated in a 50 cm water depth flume. The ratios of Shields number to critical Shields number in the current-only tests, the waves-only test, and the waves-current tests were individually 0.90, 1.48, and 1.83, respectively. The Keulegan-Carpenter number (KC) was kept at a constant value of 2.9, which was expected not to generate a horseshoe vortex or a wake vortex in the waves-only condition. The topography at various scour durations, temporal bed elevation profiles, and temporal scour depths were measured and discussed. The results showed that sediment backfilling into the scour hole was caused by moving sand ripples. The limit value under which the horseshoe vortex or wake vortex was absent in the waves-only condition was reduced in the waves-current condition. The temporal bed elevation profiles and scour depth development were very similar between the SCP and CCP, although the scour hole and sand dunes in the former were individually deeper and larger than the latter. The maximum scour depth in the SCP was nearly equal to that of the CCP in the waves-current condition, but it was much larger in the current-only condition.

Multimodal Image Fusion Framework for End-to-End Remote Sensing Image Registration

We formulate the registration as a function that maps the input reference and sensed images to eight displacement parameters between prescribed matching points, as opposed to the usual techniques (feature extraction - description - matching - geometric restrictions). The projection transformation matrix (PTM) is then computed in the neural network and used to warp the sensed image, uniting all matching tasks under one framework. In this paper, we offer a multimodal image fusion network with self-attention to merge the feature representation of the reference and sensed images. The integration information is then utilized to regress the prescribed points’ displacement parameters to get PTM between the reference and sensed images. Finally, PTM is supplied into the spatial transformation network (STN), which warps the sensed image to the same coordinates as the reference image, achieving end-to-end matching. Additionally, a dual-supervised loss function is proposed to optimize the network from both the prescribed point displacement and the overall pixel matching perspectives. The effectiveness of our method is validated by qualitative and quantitative experimental results on multimodal remote sensing image matching tasks. The code is available at: https://github.com/liliangzhi110/E2EIR.

Application of Mobile Vibration Online Comparison Sensor in Wind Power Field

MEMS sensor is a new type of sensor manufactured by micro electronics and micro machining technology. Compared with traditional sensors, it has the characteristics of small size, light weight, low cost, low power consumption, high reliability, suitable for batch production, easy integration and intelligent realization. This project adopts a multi in one sensor based on MEMS principle. The sensor is a wireless passive three-axis sensor that integrates acceleration, speed, displacement, temperature, inclination and other parameters. It is very convenient to install and disassemble, and can realize the cycle monitoring of the whole wind field.

Electron density and thermal motion of diamond at elevated temperatures.

The electron density and thermal motion of diamond are determined at nine temperatures between 100 K and 1000 K via synchrotron powder X-ray diffraction (PXRD) data collected on a high-accuracy detector system. Decoupling of the thermal motion from the thermally smeared electron density is performed via an iterative Wilson-Hansen-Coppens-Rietveld procedure using theoretical static structure factors from density functional theory (DFT) calculations. The thermal motion is found to be harmonic and isotropic in the explored temperature range, and excellent agreement is observed between experimental atomic displacement parameters (ADPs) and those obtained via theoretical harmonic phonon calculations (HPC), even at 1000 K. The Debye temperature of diamond is determined experimentally to be ΘD = 1883 (35) K. A topological analysis of the electron density explores the temperature dependency of the electron density at the bond critical point. The properties are found to be constant throughout the temperature range. The robustness of the electron density confirms the validity of the crystallographic convolution approximation for diamond in the explored temperature range.

Investigation of Structural with Electronic Properties of Methylammonium Lead Iodide Perovskite Using Density Functional Theory

Employing first-principles calculations based on density functional theory (DFT), we have investigated bulk properties as well as the functions of lattice parameter, unit cell volume calculations, displacement parameter, the interatomic distance, internal bond angle of relevant atoms on the optimized structures where the dependences of k-point summation and cut-off energies with corresponding lattice parameter variations are not dominant. The optimized structure’s property of orthorhombic CH3NH3PbI3 has great similarities with the prevalent experimental and/or theoretical data and shows a direct band gap crystal with a minimum band gap 1.80 eV at the gamma symmetry point.

Structural Evolution from Neutron Powder Diffraction of Nanostructured SnTe Obtained by Arc Melting

Among chalcogenide thermoelectric materials, SnTe is an excellent candidate for intermediate temperature applications, in replacement of toxic PbTe. We have prepared pure polycrystalline SnTe by arc melting, and investigated the structural evolution by temperature-dependent neutron powder diffraction (NPD) from room temperature up to 973 K. In this temperature range, the sample is cubic (space group Fm-3m) and shows considerably larger displacement parameters for Te than for Sn. The structural analysis allowed the determination of the Debye model parameters and provided information on the Sn–Te chemical bonds. SEM images show a conspicuous nanostructuration in layers below 30 nm thick, which contributes to the reduction of the thermal conductivity down to 2.5 W/m·K at 800 K. The SPS treatment seems to reduce the number of Sn vacancies, thus diminishing the carrier density and increasing the Seebeck coefficient, which reaches 60 μV K−1 at 700 K, as well as the weighted mobility, almost doubled compared with that of the as-grown sample.

On the polymorphism of La2SiMoO8: New metastable high temperature forms and NTE (negative thermal expansion) phase transitions

Following a previous study on scheelite LT-La2SiMoO8, a new high temperature polymorph was discovered after metastabilization down to room temperature (HT). An attempt at structural determination by neutron diffraction led to large atomic displacement parameters of the Mo cation and/or of some of its oxygen neighbors, suggesting structural instability. It was confirmed by thermal analysis and X-ray thermodiffraction, showing the existence of a phase transition at 440 ​°C between two very close polymorphs, probably mixed in the HT sample. The structural derivation of the two HT forms from the baryte-type BaSO4 structure was identified, with alternating [LaMoO4]+ and [LaSiO4]- layers. The differentiation between these two forms most likely comes from a slightly different arrangement of their respective [LaMoO4] layers. The anisotropic thermal expansion is accompanied by a volume contraction of −0.56% between the two HT forms, and a much larger one (−5.3%) at higher temperatures when the LT form stabilizes.

Pair distribution function analysis driven by atomistic simulations: Application to microwave radiation synthesized TiO[formula omitted] and ZrO[formula omitted

A workflow is presented for performing pair distribution function (PDF) analysis of defected materials using structures generated from atomistic simulations. A large collection of structures, which differ in the types and concentrations of defects present, are obtained through energy minimization with an empirical interatomic potential. Each of the structures is refined against an experimental PDF. The structures with the lowest goodness of fit Rw values are taken as being representative of the experimental structure. The workflow is applied to anatase titanium dioxide (a-TiO2) and tetragonal zirconium dioxide (t-ZrO2) synthesized in the presence of microwave radiation, a low temperature process that generates disorder. The results suggest that titanium vacancies and interstitials are the dominant defects in a-TiO2, while oxygen vacancies dominate in t-ZrO2. Analysis of the atomic displacement parameters extracted from the PDF refinement and mean squared displacements calculated from molecular dynamics simulations indicate that while these two quantities are closely related, it is challenging to make quantitative comparisons between them. The workflow can be applied to other materials systems, including nanoparticles.

Effect of Openings in Shear wall on Seismic Behaviour of RC Buildings

Shear walls along the exterior perimeter of buildings increase the efficiency of buildings to resist seismic forces. In some conditions, the locations of shear walls are very critical because of the demand of architectural openings like doors and windows in the exterior face of the buildings. The literature has revealed that stiffness and seismic response of the structure is affected by the size of openings and location of openings in shear walls. This paper demonstrates effect of static and dynamic actions on 15 storey RC building having shear walls with openings. 32 building models have been prepared in commercial software STAAD for various inline and staggered openings in shear walls. Seismic coefficient method and Response spectrum method are used for seismic analysis. The analysis is carried out for the seismic zones III and IV for hard and medium soil conditions. The paper compares the response of these building models having shear wall with and without openings on parameters of time period, base shear, storey displacement, storey drifts and surface stress distribution. Uniform stress distribution was observed in shear wall with staggered opening as compared to inline openings.