Gradient nonlinearity correction in liver DWI using motion-compensated diffusion encoding waveforms

Objective To experimentally characterize the effectiveness of a gradient nonlinearity correction method in removing ADC bias for different motion-compensated diffusion encoding waveforms. Methods The diffusion encoding waveforms used were the standard monopolar Stejskal–Tanner pulsed gradient spin echo (pgse) waveform, the symmetric bipolar velocity-compensated waveform (sym-vc), the asymmetric bipolar velocity-compensated waveform (asym-vc) and the asymmetric bipolar partial velocity-compensated waveform (asym-pvc). The effectiveness of the gradient nonlinearity correction method using the spherical harmonic expansion of the gradient coil field was tested with the aforementioned waveforms in a phantom and in four healthy subjects. Results The gradient nonlinearity correction method reduced the ADC bias in the phantom experiments for all used waveforms. The range of the ADC values over a distance of ± 67.2 mm from isocenter reduced from 1.29 × 10–4 to 0.32 × 10–4 mm2/s for pgse, 1.04 × 10–4 to 0.22 × 10–4 mm2/s for sym-vc, 1.22 × 10–4 to 0.24 × 10–4 mm2/s for asym-vc and 1.07 × 10–4 to 0.11 × 10–4 mm2/s for asym-pvc. The in vivo results showed that ADC overestimation due to motion or bright vessels can be increased even further by the gradient nonlinearity correction. Conclusion The investigated gradient nonlinearity correction method can be used effectively with various motion-compensated diffusion encoding waveforms. In coronal liver DWI, ADC errors caused by motion and residual vessel signal can be increased even further by the gradient nonlinearity correction.

Investigation on Vortex Characteristics of a Multi-Blade Centrifugal Fan near Volute Outlet Region

The origins and effects of the complex vortex structure near the volute outlet of a multi-blade centrifugal fan are investigated in this paper. Due to the wide blade and short blade channel, the airflow maintains a large radial velocity during the blade channel. This continuous radial partial velocity causes vortices to be generated at the region of volute outlet. Then, the secondary flow close to the impeller generate from the center to the sides in volute. It is obtained that the streamlines are divided into two parts (backflow and outflow) at volute outlet. Although the vortices near volute outlet region are complex, the main features of flow behavior caused by the vortex are understandable.

Note on Analyzing Perturbation Growth in a Tropical Cyclone–Like Vortex Radiating Inertia–Gravity Waves

A method is outlined for quantitatively assessing the impact of inertia–gravity wave radiation on the multimechanistic instability modes of a columnar stratified vortex that resembles an intense tropical cyclone. The method begins by decomposing the velocity field into one part that is formally associated with sources inside the vortex and another part that is attributed to radiation. The relative importance of radiation is assessed by comparing the rates at which the two partial velocity fields act to amplify the perturbation of an arbitrary tracer field—such as potential vorticity—inside the vortex. Further insight is gained by decomposing the formal vortex contribution to the amplification rate into subparts that are primarily associated with distinct vortex Rossby waves and critical-layer perturbations.

Recursive Dynamic Algorithm of Open-Chain Multibody System

Open-chain multibody systems have been extensively studied because of their widespread application. Based on the structural characteristics of such a system, the relationship between its hinged bodies was transformed into recursive constraint relationships among the position, velocity, and acceleration of the bodies. The recursive relationships were used along with the Huston-Kane method to select the appropriate generalized coordinates and determine the partial velocity of each body and to develop an algorithm of the entire system. The algorithm was experimentally validated; it has concise steps and low susceptibility to error. Further, the algorithm can readily solve and analyze open-chain multibody systems.

Fluid Dynamics Analysis and Research of Electrostatic Oiler Knife Beam

The research object of this paper is about the oil equipments’ fluid properties during spraying of the electrostatic spraying technology. Establishing the mathematical model of fluid inside the oiling machine in the process of computer simulation and using fluid dynamics analysis software ( CFD ) FLUENT to analyse numerical simulation within spraying fluid effectively. According to the actual situation, reach knife beam’s pressure distribution, velocity distribution, flow trajectories, partial velocity diagram. Finally, verify the correctness and feasibility of the simulation by the contrast of the experimental and simulation data in the course of experiments. In view of the analysis and study of the electrostatic oiler internal fluid, it can be extended to the electrostatic spraying technology. The paper is supplement for further research of electrostatic spraying technology and data support for next step simulation analysis of loading of high-voltage electric field.