Evaluation of ambipolar potential barrier in the gas dynamic trap by Doppler spectroscopy

The recently developed Doppler spectroscopy diagnostic has been used to evaluate the height of the ambipolar potential barrier forming in the gas dynamic trap (GDT) plasma between the central cell and the region with a large magnetic expansion ratio beyond the mirror. The diagnostic technique based on the gas jet charge exchange target, allowed to measure the potential profile along the line of sight covering the radial range from the axis to the limiter. The on-axis potential drop was found to be 2.6÷3.1 in units of the central plane electron temperature, which supports the existing theoretical understanding of suppression of electron thermal conductivity in the GDT expander.

Using In Situ Measurements to Experimentally Characterize TiO2 Nanoparticle Synthesis in a Turbulent Isopropyl Alcohol Flame

The objective of the present work is to show the potential of in situ measurements for the investigation of nanoparticles production in turbulent spray flames. This is achieved by considering multiple diagnostics to characterize the liquid break-up, the reactive flow and the particles production in a spray burner for TiO2 nanoparticle synthesis. The considered liquid fuel is a solution of isopropyl alcohol and titanium tetraisopropoxide (TTIP) precursor. Measurements show that shadowgraphy can be used to simultaneously localize spray and nanoparticles, light scattering allows to characterize the TiO2 nanoparticles distribution in the flame central plane, and spontaneous CH* and OH* chemiluminescences, as well as global light emission results, can be used to visualize the reactive flow patterns that may differ with and without injection of TTIP. Concerning the liquid, it is observed that it is localized in a small region close to the injector nozzle where it is dispersed by the oxygen flow resulting in droplets. The liquid droplets rapidly evaporate and TTIP is quasi-immediately converted to TiO2 nanoparticles. Finally, results show high interactions between nanoparticles and the turbulent eddies.

Inertial and non-inertial focusing of a deformable capsule in a curved microchannel

A computational study is presented on cross-stream migration and focusing of deformable capsules in curved microchannels of square and rectangular sections under inertial and non-inertial regimes. The numerical methodology is based on immersed boundary methods for fluid–structure coupling, a finite-volume-based flow solver and finite-element method for capsule deformation. Different focusing behaviours in the two regimes are predicted that arise due to the interplay of inertia, deformation, altered shear gradient, streamline curvature effect and secondary flow. In the non-inertial regime, a single-point focusing occurs on the central plane, and at a radial location between the interior face (i.e. face with highest curvature) of the channel and the location of zero shear. The focusing position is nearly independent of capsule deformability (represented by the capillary number, $Ca$ ). A two-step migration is observed that is comprised of a faster radial migration, followed by a slower migration toward the centre plane. The focusing location progressively moves further toward the interior face with increasing curvature and width, but decreasing height. In the inertial regime, single-point focusing is observed near the interior face for channel Reynolds number $Re_{C}\sim {O}(1)$ , that is also highly sensitive to $Re_{C}$ and $Ca$ , and moves progressively toward the exterior face with increasing $Re_{C}$ but decreasing $Ca$ . As $Re_{C}$ increases by an order, secondary flow becomes stronger, and two focusing locations appear close to the centres of the Dean vortices. This location becomes practically independent of $Ca$ at even higher inertia. The inertial focusing positions move progressively toward the exterior face with increasing channel width and decreasing height. For wider channels, the equilibrium location is further toward the exterior face than the vortex centre.

Fabrication and Characterization of Line-by-Line Inscribed Tilted Fiber Bragg Gratings Using Femtosecond Laser

In this paper, we studied the basic characteristics of tilted fiber Bragg gratings (TFBGs), inscribed line-by-line. Experimental results showed that if the TFBGs were located within different planes parallel to the fiber axis, the spectra performed differently. For 2°TFBG, if it was located near the central plane, the Bragg resonance was stronger than ghost mode resonance, and the order reversed if it was located near the boundary between core and cladding. As the tilted angle increased, the range of cladding mode resonance increased. When the tilted angle was larger than 12°, the birefringence effect was observed. Based on the birefringence phenomenon, torsion characteristics were experimentally studied; the sensitivity was about 0.025 dB/degree in the linear variation range. The harmonic order of TFBGs also affected the transmission spectrum. Leaky mode resonance was observed in the 8th order TFBG, and torsion (or polarization) influenced the spectrum of the 8th order TFBG. Our research represented the theory of line-by-line inscribed TFBGs and provided an inscription guidance for TFBGs.

The effect of vaginal delivery and Caesarean section on the anal Sphincter complex of Primipara based on optimized three-dimensional ultrasound image and nuclear regression Reconstruction Algorithm

Objective: The study used the optimized nuclear regression reconstruction algorithm to explore the value of three-dimensional perineal ultrasound evaluation of the effect of caesarean delivery and caesarean section on the anal sphincter complex of primipara. Methods: This study performed three-dimensional perineal ultrasound scanning of the anal sphincter complex of 157 primiparas 42 days after delivery. Among them, 77 were in caesarean delivery (spontaneous delivery group) and 80 were in caesarean section (caesarean delivery group) from September 2018 to December 2020 in our hospital. The thickness of the end plane, the middle plane, the distal plane and the distal plane of the external anal sphincter at 3, 6, 9, 12 o’clock direction, and measure the thickness of the central plane of the pubic rectum muscle at 4, 8 o’clock direction. At the same time, the study used tomography and volume contrast imaging to observe the morphology and integrity of the anal sphincter complex. Results: The thickness of the distal anal sphincter at the 12 o’clock direction, the proximal anal sphincter at 6, 12 o’clock, and the central plane at 9 and 12 o’clock in the obstetric group were smaller than those in the caesarean section group (all P < 0.05). There were no significant differences in the thickness of the remaining anal internal and external anal sphincter and puborectalis muscles between the two groups in different directions (all P>0.05). In the obstetric group, a perineal sphincter defect was found via three-dimensional perineal ultrasound. Conclusion: The delivery method has a certain influence on the shape of the anal sphincter complex. The thickness of the internal and external anal sphincter of the primiparous women in a certain direction is significantly smaller than that of caesarean section. Transperineally three-dimensional ultrasound can clearly show the morphological characteristics and integrity of the anal sphincter complex, and diagnose the defect of the anal sphincter complex. doi: https://doi.org/10.12669/pjms.37.6-WIT.4859 How to cite this:He N, Shi L. The effect of vaginal delivery and Caesarean section on the anal Sphincter complex of Primipara based on optimized three-dimensional ultrasound image and nuclear regression Reconstruction Algorithm. Pak J Med Sci. 2021;37(6):1641-1646. doi: https://doi.org/10.12669/pjms.37.6-WIT.4859 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Comparison Study on Stage Performance of Centrifugal Compressors With Shrouded and Unshrouded Impellers

The shrouded and unshrouded impellers are two typical kinds of impellers, which are widely utilized in centrifugal compressors of various applications. Centrifugal compressors with unshrouded impellers are generally recognized to display inferior performance to the shrouded impellers with the same geometry. In this paper, a comparative experiment shows some results inconsistent with conventional cognition. Measured performance indicates that the peak efficiency of the centrifugal compressor with an unshrouded impeller is higher than the shrouded one, where the two impellers have the same geometry of meridional profile and blade central plane, and matched the same vaneless diffuser and volute. In order to explore the causes of this divergence, the effects of factors such as blade thickness, surface roughness of components, tip clearance and sealing leakage characteristics on performance are analyzed by CFD code. Numerical results show that reasonable reduction in the blade thickness and improvement on the surface quality of the impeller could effectively increase the peak efficiency and the choke mass flow rate of the shrouded impeller. The unshrouded impeller with arbitrary blade surfaces would be deformed under the action of centrifugal force to achieve a small tip clearance during operation, and then obtains higher efficiency at design speed. The research results are helpful to evaluate the performance potential and sensitive design parameters of shrouded and unshrouded impellers.

The Freedericksz Transition in a Spatially Varying Magnetic Field

Much is known about the Freedericksz transition induced by uniform electric and magnetic fields in nematic liquid crystals. In this work, we are interested in the effects of a spatially varying field on the transition. Specifically, we study the director configuration in a homeotropic nematic cell in a spatially varying magnetic field with cylindrical symmetry. The experiment is conducted with a ring magnet which provides a radial magnetic field with magnitude monotonically decreasing to zero at the center. The nematic cell is positioned in the central plane of the ring, with the cell normal parallel to the ring normal. Interference patterns of the nematic cell between crossed polarizers were observed. The director configuration in the nematic cell is modeled with Frank–Oseen theory, and the computed interference pattern from the simulated director field are compared with experiment. We conclude that if the magnetic field strength varies with position in the plane of the cell, there is no Freedericksz transition.

Influence of the Submerged Entry Nozzle’s Bottom Well on the Characteristics of Its Exit Jets

In vertical continuous casting machines the liquid steel from the tundish is poured into the mold through the Submerged Entry Nozzle (SEN). The shape and direction of the SEN exit jets affect the liquid steel dynamics inside the mold. This work quantifies the effect of the SEN pool on the principal characteristics of the jets emerging from it, precisely, the shape, the spread angles, and the mold impact point. Experimental and numerical simulations were carried out using a SEN simplified model, a square-shaped bore nozzle with square-shaped outlet ports whose length is minimal. These experiments showed two well-defined behaviors. When a single vortex dominates the hydrodynamics inside the simplified SEN, the exit jets spread out and are misaligned about the mold’s central plane. On the contrary, when the inner flow pattern shows two vortexes, the exit jets are compact and parallel to the mold wide walls. The measured difference on the jet’s falling angles is 5°, approximately, which implies that in an actual casting machine, the impingement point at the narrow mold wall would have a variation of 0.150 m. This hydrodynamic analysis would help design new SENs for continuous casting machines that improve steel quality.

Error modelling–based machining sequence optimization of a pocketed beam milling: part A, end supported beam

This paper, on the basis of error modelling, proved the optimal pocket machining sequences of a simply end supported pocketed beam using mathematic induction method. The optimal pocket machining sequence with the minimum pocket floor height error is the machining from both ends to the middle and the optimal sequence is not unique because of the symmetric supports about the central plane; meanwhile, the optimal pocket machining sequence with the minimum wall position error is the machining from the fixed end to the free end and the optimal machining sequence is unique. A beam of Al7075 (744 mm in length, 172 mm in width, and 100 in thickness ) with 9 pockets was used to demonstrate the optimal sequences. One of the optimal sequence with minimum floor height error was used in pocketing (roughing), and the maximum distortion was 0.693 mm in the middle and the maximum floor height error appeared on both sides rather than the middle, which were 0.477 mm and 0.388 mm, and part growth produced maximum wall position error was 0.719 mm. On the same part, further demonstrated the optimal sequence with minimum wall position error in finishing (with 1 mm dimension in stock for all surfaces) and the wall position errors were fully removed. The pocketed beam machining is a typical and representative case and the results and conclusion can be extended to pocketed plate/board machining and even surfacing.

Experimental Study of Twin Connected Pipe Jets

Two parallel pipe jets of 20 mm diameter were placed 1.2 mm diameter apart and were connected by a 4 mm wide channel all along the central plane of the jets. The mean velocity flow field of the jets was investigated for three Reynolds number 16300, 34400 and 49200. The Reynolds number was based on the exit velocity of the jets and jet diameter. The experiment was performed in an air jet facility and yaw meter was used for measurement of mean velocity and its direction. Their variations along the longitudinal, transverse, and lateral directions have been analyzed. A significant change of the jet flow field is observed near the exit of the jet. The combined effect of the jets diminishes the presence of recirculation region at the immediate exit rather enhances the energy and momentum transfer between their individual flow fields. Static pressure and kinetic energy distribution are also studied and a momentous variations have been noticed with varying Reynolds number.