Two-Stage Modulation Study for DAB Converter

The dual active bridge (DAB) is a dc/dc converter frequently employed in multiple applications due to its advantages of isolation, power flexibility, and input and output voltage defined by design. Different multi-phase modulations have been reported to increase DAB efficiency and reduce components stress but, certainly, the control and implementation complexity increases with every displacement angle added because of the multiple variable measurements. This paper presents two-stage modulations based on the single phase-shift (SPS), which allows maintaining simplicity while improving the efficiency of the DAB converter depending on the design conditions. The paper also gives a direction for selecting the proper modulation to achieve the best efficiency for each situation. The different two-stage modulations are described, analyzed, and experimentally tested.

Development of a Quantitative Method to Evaluate Pedicle Screw Loosening After Spinal Instrumentation Using Digital Tomosynthesis

BackgroundIn general, the diagnosis of pedicle screw (PS) loosening is evaluated qualitatively based on the presence of a radiolucent area around the implant wider than 1 mm on plain radiographs and computed tomography (CT). Digital tomosynthesis is a novel imaging technology that can acquire reconstructed tomographic images of patients in different postures with relatively low radiation. In this study, PS loosening is evaluated quantitatively by measuring the PS displacement angle in the vertebrae using digital tomosynthesis. MethodsWe evaluated 41 patients who underwent posterior spinal fusion surgery using PS. The 72 pedicle screws at the cranial end of the fused segments were evaluated. The patients were divided in two groups, one with PS loosening (7 patients, 12 screws) and the other without PS loosening (34 patients, 60 screws), based on conventional CT findings. All patients underwent tomosynthesis in two different postures during a single CT session. ResultsThe displacement angles of the PS in patients in a lying position and in a standing position were measured using selected slices of the same cross-sectional view from digital tomosynthesis. The displacement angle was significantly greater in the PS loosening group (5.7°) than in the group without PS loosening (0.6°) (p＜0.01). Based on the ROC analysis, the optimal cut-off value of the PS displacement angle for identification of loosened screws was 1.7° with a sensitivity of 100% and specificity of 93% (AUC=0.98). ConclusionsThis new method using digital tomosynthesis has the potential to aid diagnosis of PS loosening quantitatively and more accurately than conventional evaluations.

CT-derived 3D-diaphragm motion in emphysema and IPF compared to normal subjects

Image registration-based local displacement analysis enables evaluation of respiratory motion between two computed tomography-captured lung volumes. The objective of this study was to compare diaphragm movement among emphysema, idiopathic pulmonary fibrosis (IPF) and normal subjects. 29 normal, 50 emphysema, and 51 IPF subjects were included. A mass preserving image registration technique was used to compute displacement vectors of local lung regions at an acinar scale. Movement of the diaphragm was assumed to be equivalent to movement of the basal lung within 5 mm from the diaphragm. Magnitudes and directions of displacement vectors were compared between the groups. Three-dimensional (3D) and apico-basal displacements were smaller in emphysema than normal subjects (P = 0.003, P = 0.002). Low lung attenuation area on expiration scan showed significant correlations with decreased 3D and apico-basal displacements (r = − 0.546, P < 0.0001; r = − 0.521, P < 0.0001) in emphysema patients. Dorsal–ventral displacement was smaller in IPF than normal subjects (P < 0.0001). The standard deviation of the displacement angle was greater in both emphysema and IPF patients than normal subjects (P < 0.0001). In conclusion, apico-basal movement of the diaphragm is reduced in emphysema while dorsal–ventral movement is reduced in IPF. Image registration technique to multi-volume CT scans provides insight into the pathophysiology of limited diaphragmatic motion in emphysema and IPF.

Orbital anatomy magnetic resonance imaging in diplopic versus non-diplopic patients after glaucoma drainage device placement

Purpose: New-onset persistent diplopia has become a common complication after glaucoma drainage device (GDD) placement. Understanding the orbital anatomy of such patients may provide information regarding risk of diplopia, GDD selection, and post-operative management. The purpose of this study was to examine the orbital anatomic differences in diplopic and non-diplopic patients after GDD implantation using high-resolution MRI. Methods: Seven eyes ( N = 4 with diplopia and N = 3 without diplopia after GDD placement) of seven patients that had undergone placement of Baerveldt 250 (B250), Baerveldt 350 (B350), or Ahmed FP7 (FP7) GDD were prospectively enrolled at a single institution. All patients underwent a 3.0T orbital MRI with 3D volumetric T1 and T2 weighted sequence. Images were analyzed for orbital volume, axial length, orbital distances, presence of superior rectus-lateral rectus (SR-LR) band, position of GDD, and SR-LR angles. Results: Patients with diplopia had smaller mean ± SD orbital axial (911.5 ± 111.8 mm3 vs 931.7 ± 79.7 mm3) and coronal volumes (1162.5 ± 145.5 mm3 vs 1180 ± 34.6 mm3) compared to non-diplopic patients. Average orbital rim distances were larger for the diplopic group. The SR-LR displacement angle for diplopic patients was larger (101.6° ± 8.1 vs 94.7° ± 17.6) while the SR-LR quadrantic angle (86.6° ± 4.2 vs 89.1° ± 4.3) was smaller. SR-LR band was present and intact in all patients. GDD malpositioning was not evident in any patient. Conclusion: The decreased orbital axial and coronal volumes as well as increased orbital rim distances in diplopic patients suggests the need for further studies to understand the role of orbital anatomy in occurrence of diplopia. Dynamic MRI imaging may be helpful in identifying differences in extraocular muscle function that reveal an etiology of diplopia in patients with GDD implantation.

Impact of cranks displacement angle on the motion non-uniformity of roller forming unit with energy-balanced drive

The impact of the cranks displacement angle on the motion non-uniformity is determined for three forming trolleys of a roller forming unit with an energy-balanced drive mechanism. At the same time, the specified unit is presented by a dynamic model with one freedom degree, where the extended coordinate is taken as the angular coordinate of the crank rotation. For such a model, a differential equation of motion is written, for solved which a numerical method was used. The inertia reduced moment of the whole unit, and the resistance forces moment, reduced to the crank rotation axis, to move of forming trolleys during the formation of products from building mixtures are determined, and also the nominal rated power of the electric motor was calculated, when solved a differential equation of motion. According to these data, asynchronous electric motor with a short-circuited rotor was chosen, for which a mechanical characteristic is constructed by the Kloss formula. Having solved the differential equation of motion with all defined characteristics, we obtain the change function of the crank angular velocity from start-up moment and during steady motion mode. After that, we calculated the time corresponding to the angular velocity value, and obtained the change function of the crank angular acceleration from start-up moment and during steady motion mode. The motion non-uniformity of the roller forming unit has been determined by the motion non-uniformity factor, the motion dynamism factor and the extended factor of motion assessment during steady motion mode. The impact of drive cranks displacement angle on the motion non-uniformity has been traced, as a result, the specified factors have the minimum values at cranks displacement on the angle Δφ=60°. The results may in the future are used to refine and improve the existing engineering methods for estimating the drive mechanisms of roller forming machines, both at design stages and in practical use.

Remodeling in Patients with in Situ Fixation for a Slipped Capital Femoral Epiphysis

Objective: This study has investigated the amount of bone remodeling in patients with a slipped capital femoral epiphysis (SCFE) treated with in situ fixation until closure of the epiphysis and the factors affecting remodeling. Method: Patients who underwent surgery for SCFE between January 2010 and January 2015 were retrospectively screened: Twenty-four male and 7 female patients (mean age 12.6 ± 1.9 years) were included in the study. Gender, age, history, and laterality of trauma, duration of hip pain (acute, chronic, acute on chronic background), and hip radiographs were evaluated. The Southwick and alpha angles were measured, and the factors affecting remodeling were assessed. The statistical analyses were conducted using SPSS 25.0 (IBM Corp., Armonk, NY); 95% confidence levels were calculated and p < 0.05 was considered to indicate statistical significance. Results: The preoperative displacement angles measured on the anteroposterior and lateral radiographs were 15.03° ± 9.1° and 25.93° ± 14.1° and at the last follow-up they were 11.63° ± 8.7° and 21.6° ± 12.1°, respectively. The alpha angles measured on the lateral radiographs preoperatively and at the end of follow-up were 52.33° ± 11.6° and 47.87° ± 11.8°, respectively. Significant remodeling was reflected in the angles measured on the anteroposterior and lateral X-ray images. Greater preoperative displacement angle was associated with less remodeling. Conclusion: Preoperative displacement affects the degree of postoperative remodeling. In patients with severe epiphyseal displacement, open reduction is an option but in situ pinning should be considered in that it is less invasive and more physiological.

Analysis on Displacement Angle of Phase-Shifted Carrier PWM for Modular Multilevel Converter

This paper provides theoretical and experimental discussions on the characteristics of the modular multilevel converter (MMC) when phase-shifted carrier sinusoidal pulse-width modulation (PSC-SPWM) is applied. Harmonic-cancellation characteristics of output voltage and circulating current are analyzed on the basis of a general implementation of PSC-SPWM with two freedom displacement angles. Five available PSC-SPWM schemes with different carrier displacement angles were obtained, and a detailed performance comparison about output voltage and circulating current harmonic characteristics is presented. On the basis of the equivalent circuit with ideal transformer representation of the SMs, capacitor voltages affected by PSC-SPWM schemes are also briefly analyzed. The proposed PSC-SPWM schemes can unify two different cases of odd and even SM situations for output voltage and circulating current harmonic minimization, respectively. Lastly, the optimal schemes for practical MMC application were verified by simulation and experiments on an MMC prototype.

Collapse-Pounding Dynamic Responses of Adjacent Frame Structures under Earthquake Action

There are a large number of adjacent buildings in practical engineering application. The structure will collapse and impact the adjacent structures once the weak column is destroyed under seismic action, and, finally, the earthquake damage is aggravated. Material nonlinearity, initial imperfections, and contact problems in the process of collapse-pounding are considered, and the three-dimensional calculation model with unequal 8-story and 6-story height adjacent frames is established. The dynamic response of adjacent structures caused by collapse-pounding is investigated when there is a weak column at different positions in the 8-story frame, and the influence of gap size on the dynamic responses of adjacent structures is discussed. The results show that the impact force is larger when the weak column of the 8-story frame is close to the top of the 6-story frame; pounding increases the interlayer displacement angle of the 8-story frame and decreases the interlayer displacement angle of the 6-story frame in general; the impact force decreases first, then increases, and after that decreases with the increase of gap size; and the interlayer displacement angle distribution of the 6-story frame is significantly affected after the collapse-pounding of the 8-story frame with a weak column. The collapse-pounding problem of adjacent buildings under seismic action is very complex, which should be paid enough attention in engineering design and application.

Physical and engineering properties of BARI released three groundnut varieties

The knowledge of the physical characteristics of particles is essential for the designer of agricultural machines. The study was aimed to determine physical and engineering properties of three selected varieties of groundnuts cultivated in Bangladesh such as Dhaka-1, BARI Badam-8 and BARI Badam-9 at safe storage moisture content of 7.5%. One hundred groundnut pods and kernels were randomly selected and the length, width and thickness were measured using a vernier caliper. The geometric mean diameter, sphericity, aspect ratio was calculated using standard formula and measured values. Bulk density, true density, mass and porosity were found through direct weighing and water displacement. Angle of repose of pods and kernels was also measured on wood, glass and mild steel sheet surfaces. BARI Badam-9 had the highest pod geometric mean diameter and BARI Badam-8 had the highest kernel geometric mean diameter. Sphericity of groundnut pod was the highest for Dhaka-1. Surface area of pod and aspect ratio of both pod and kernel were the highest in BARI Badam-9. Porosity of the pod was the least for BARI Badam-8. Angle of repose of kernel varied on wood and glass. But it was similar for kernel on MS sheet for the varieties. This result will be useful to design and develop groundnut processing equipment for different varietal variability Bangladesh J. Agril. Res. 44(4): 609-620, December 2019