[en] A time-resolved radiographic technique has been developed for probing the fuel distribution close to the nozzle of a high-pressure single-hole diesel injector. The measurement was made using X-ray absorption of monochromatic synchrotron-generated radiation, allowing quantitative determination of the fuel distribution in this optically impenetrable region with a time resolution of better than 1 μs. These quantitative measurements constitute the most detailed near-nozzle study of a fuel spray to date

[en] A quantitative and time-resolved radiographic technique has been used to characterize hollow-cone gasoline sprays in the near-nozzle region. The highly penetrative nature of x-rays promises the direct measurements of dense sprays that are difficult to study by visible-light based techniques. Time-resolved x-radiography measurement enables us to map the mass distribution near the spray nozzle, even immediately adjacent to the orifice. The quantitative nature of the measurement also permits the re-construction of spray structure and the progress of the spray development. It is observed that the speed of fuel injected in the later part of the injection is higher than injected earlier and that the initial fuel speed variation caused the spray plume to be compressed in space

[en] In this paper, three classes of laboratory plasma experiments are investigated in terms of global energy balance relations. The three types of experiment considered are rotating plasmas with radial geometry, typically plasma centrifuges, rotating plasmas with axial geometry, or vacuum arc centrifuges, and linear plasma-neutral gas collision experiments. All three experiments yield plasma velocities close to the Alfven critical velocity for a range of experimental conditions. To explain the experimental observations, it has been postulated that a special interaction occurs whenever the relative velocity between neutral gas and plasma reaches the critical velocity ν_a = (2ε₁/m)^1/2, where ε₁ is the first ionization potential of the neutral particles and m is their mass. Here, we look at the experiments from the energy balance point of view and conclude that it is not necessary to postulate any special interaction occurring at the critical velocity to explain the experimental data

[en] Highlights: • Structural and dielectric properties of (Ba_1−xLa_x)(Ti_1−x/2Ca_x/2)O₃ were studied. • A pseudo-cubic ceramic with x = 0.03 is a novel dielectric for X7R applications. • A symmetric (2 0 0) XRD peak and sharp Raman band are characteristics of pseudo-cubic. • The unit cell volume (V₀) of BLTC increases linearly with x, satisfying Vegard’s law. • Formation of defect complexes with much larger Ti-site Ca²⁺ is responsible for X7R. -- Abstract: (Ba_1−xLa_x)(Ti_1−x/2Ca_x/2)O₃ (0.03 ⩽ x ⩽ 0.06) (BLTC) ceramics were prepared using a mixed oxides method. The structure, microstructure, and dielectric properties of BLTC were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, atomic force microscope, and dielectric measurements. Both symmetric (2 0 0) XRD peak indicative of cubicity and sharp 308 cm⁻¹ Raman band indicative of tetragonality are characteristics of pseudo-cubic symmetry of BLTC. The unit cell volume of BLTC increased linearly with x, satisfying Vegard’s law. A strong “Raman charge effect” appeared at 836 cm⁻¹ because of the aliovalent double substitution in BLTC. The x = 0.03 sample because of its higher permittivity (ε′ = ∼2000) and lower loss (tan δ < 0.04) is a novel dielectric for X7R applications. The formation of La_Ba^·-Ca_Ti^″-La_Ba^· defect complexes was responsible for the dielectric-temperature stability of BLTC

[en] Short communication

[en] The development of a model of high-pressure rotating plasmas and its experimental validation are reported. The model has been compared with experiment for argon plasmas at a pressure of about 600 Pa, radial currents of 60 A and axial magnetic fields up to 0.21 T. Under these conditions the plasma has a low level of ionization and the boundary layers are fully developed (the centrifuge width is 30 mm) Experimental data collected includes plasma voltage and velocities determined by cross-correlation of photodiode signals. (author). 8 refs, 5 figs

[en] Short communication

[en] This work describes a one-dimensional (1-D) steady-state model of the Hartmann boundary layers appropriate to a high-density rotating plasma which is in local thermodynamic equilibrium. The purpose of the model is to predict the performance of high-pressure plasma centrifuges, and approximations appropriate to magnetohydrodynamic plasmas are made. Transport properties are calculated using a chemical equilibrium approximation which should apply at high densities in a plasma centrifuge. As well as rotation in the azimuthal direction, the model shows that there is plasma circulation in the radial direction, arising both from convection of the neutral particles with the ions (''ion wind'') and the nonuniform distribution of the centrifugal force in the axial direction (conventional secondary flow). Calculated results have been compared with experimental data from a rotating argon plasma. The agreement is reasonable

[en] Modelling of three common entrainment mechanisms in fluid flow, namely plunging jet, return wave and rising jet, that generating defects during casting were conducted and validated by A356 alloy. Previous research highlighted surface turbulence in liquid metals could result in the fold-in of surface films into bulk liquid and leave cracks or porosity in the solidified component. An algorithm applied face normals of free surface and their interaction to capture the entrainment of surface films was used in study. The model integrated the algorithm into CFD package FLOW-3D and was used to track the entrainment defects formation and distribution involved in different entrainment behaviours in casting process. The defects density in local volume plotted by the model was then employed as quantitative criteria to predict the reliability of castings. Directly observation of transient flows in moulds by real-time X-ray radiography showed good correlation between real filling scenario and simulation results. Fracture strength achieved by four-point bend tests on the samples from corresponding locations with models in castings showed some extent relationship between defects density and reliability of castings quantitatively. Studies also indicated the plunging jet mechanism usually leaded to high variation of mechanical properties due to intense turbulence and entrainment.

[en] Purpose: To develop a retrospective 4D-MRI technique (respiratory phase-resolved 3D-MRI) for providing an accurate assessment of tumor motion secondary to respiration. Methods: A 3D projection reconstruction (PR) sequence with self-gating (SG) was developed for 4D-MRI on a 3.0T MRI scanner. The respiration-induced shift of the imaging target was recorded by SG signals acquired in the superior-inferior direction every 15 radial projections (i.e. temporal resolution 98 ms). A total of 73000 radial projections obtained in 8-min were retrospectively sorted into 10 time-domain evenly distributed respiratory phases based on the SG information. Ten 3D image sets were then reconstructed offline. The technique was validated on a motion phantom (gadolinium-doped water-filled box, frequency of 10 and 18 cycles/min) and humans (4 healthy and 2 patients with liver tumors). Imaging protocol included 8-min 4D-MRI followed by 1-min 2D-realtime (498 ms/frame) MRI as a reference. Results: The multiphase 3D image sets with isotropic high spatial resolution (1.56 mm) permits flexible image reformatting and visualization. No intra-phase motion-induced blurring was observed. Comparing to 2D-realtime, 4D-MRI yielded similar motion range (phantom: 10.46 vs. 11.27 mm; healthy subject: 25.20 vs. 17.9 mm; patient: 11.38 vs. 9.30 mm), reasonable displacement difference averaged over the 10 phases (0.74mm; 3.63mm; 1.65mm), and excellent cross-correlation (0.98; 0.96; 0.94) between the two displacement series. Conclusion: Our preliminary study has demonstrated that the 4D-MRI technique can provide high-quality respiratory phase-resolved 3D images that feature: a) isotropic high spatial resolution, b) a fixed scan time of 8 minutes, c) an accurate estimate of average motion pattern, and d) minimal intra-phase motion artifact. This approach has the potential to become a viable alternative solution to assess the impact of breathing on tumor motion and determine appropriate treatment margins. Comparison with 4D-CT in a clinical setting is warranted to assess the value of 4D-MRI in radiotherapy planning. This work supported in part by grant 1R03CA173273-01