In this paper, we discuss the two-stage and the Modified two-stage procedures for the estimation of the threshold autoregressive parameter in a first-order threshold autoregressive model (${\rm TAR(1)}$). This is motivated by the problem of finding a final sample size when the sample size is unknown in advance. For this purpose, a two-stage stopping variable and a class of Modified two-stage stopping variables are proposed. Afterward, we {prove} the significant properties of the procedures, including asymptotic efficiency and asymptotic risk efficiency for the point estimation based on least-squares estimators. To illustrate this theory, comprehensive Monte Carlo simulation studies is conducted to observe the significant properties of the procedures. Furthermore, the performance of procedures based on Yule-Walker estimators is investigated and the results are compared in practice that confirm our theoretical results. Finally, real-time-series data is studied to demonstrate the application of the procedures.

The main aim in the design of welded plate girders is to minimize the weight of the beam while satisfying design requirements which turns the design procedure into a nonlinear and complex optimization problem. In this paper, a two-stage optimization procedure is introduced to find the best design of welded plate girders in terms of both safety and economy. The total weight of the girder is considered as the objective function where some predefined constraints are applied using penalty functions to restrict the solution space. In the first stage, the theoretical optimum values of girder dimensions are obtained using the Artificial Bee Colony (ABC) algorithm based on the optimum use of steel material while satisfying restrictions on the flexural and shear strength, permissible deflection, and proportioning limits. Since the plate dimension values obtained by the first stage may not be available in the market, the second stage of optimization is carried out to reach a safe and economical design by considering available plate dimension values. The critical ratio of the designing procedure is obtained equal to one, which is the ideal design. To demonstrate the effectiveness of the proposed method, two examples are considered at the end of this article. The results show that the dimension of the plate girder calculated by the proposed approach is more economical and practical than that obtained by the traditional trial and error techniques.

Congenital kyphosis is a less common spinal malformation, which can progress and cause neurological deficits. The treatment of severe cases is complicated. There are several techniques of surgical intervention for the correction of kyphosis, but the selection of surgical methods is entirely dependent on the patient’ s condition. This article reports a 14-year-old girl with severe congenital kyphosis, who underwent hemiepiphysiodesis at age 2. Last year, her neurological deterioration began and led to paraplegia over a couple of months. To treat her, we performed 2-stage multi-level vertebral column resection (Schwab type 6). First, she underwent anterior T12-L1-L2 complete corpectomy and cord decompression. Then, the resection of posterior elements from T12 to L2 and posterior fusion with instrumentation from T8 to L5 were performed. However, concerning this kind of severe deformity, we suggest using 3D planning, which facilitates the operation.

Purpose: Open surgical reimplantation of ureters is a highly successful procedure, with reported correction rates of 95 to 99 percent regardless of the severity of vesicoureteral reflux (VUR). Leadbetter-Politano ureteroneocystostomy is one of the most preffered technique for open ureteroneocystostomy. The authors report the Modified Politano-Leadbetter technique with extravesical mobilization and transection of the ureter at the level of ureterovesical junction and intravesical reimplantation. Materials and Methods: Fifty-seven children with unilateral VUR, underwent Modified Leadbetter-Politano ureteral reimplantation with extravesical mobilization and transection of the ureter at the level of ureterovesical junction and intravesical reimplantation. Indications for open reimplantation were, persistence of VUR after endoscopic correction, breakthrough urinary infections, complications due to antibiotics, progressive renal scarring, and parental preference. Operations were done by two full-time pediatric surgeons. Operation time and hospital stay of the patients, reflux persistency, voiding dysfunction and complications were recorded. Results: No ipsilateral VUR was detected postoperatively. While mean operation time was 78. 42 min (± 7. 36 min; range, 70-86 min) Mean duration of the hospital stay is 82. 31 h (± 9. 48 h; range, 71-94 h) for classic Leadbetter-Politano procedure, mean operation time was 56. 54 min (± 8. 24 min; range, 52-67 min) and mean duration of the hospital stay is 62. 31 h (± 8. 35 h; range, 50-63 h) for Modified technique. Postoperative gross hematuria was not seen in any patients. No voiding dysfunction and no late complications was encountered. Conclusion: Modified Leadbetter-Politano technique is a good option to treat VUR with success rate up to 100% without any major complicatons such as viscus perforation and ureteral obstruction. It is a rather simple technique that require less operative time.

Performance of a two-stage multi-inter-cooling trans-critical CO2 refrigeration cycle containing internal heat exchanger, two intercoolers, ejector, and separator, has been analyzed after modification. In the present study, an internal heat exchanger has been included within this cycle for possible improvement in its cooling performance. The impacts of operational parameters such as gas cooler and evaporator temperatures and gas-cooler pressure, on cycle performance have been investigated. Results are validated against those available in the literature. Comparisons of the results show that there is excellent agreement between them. Obtained results showed that Modified cycle improved the maximum coefficient of performance (COP max), by 20.58% compared to the internal heat exchanger two-stage TRCC cycle and 23.2% compared to multi-inter-cooling two-stage TRCC cycle with ejector expansion device. Also, the total exergy destruction rate of the improved cycle is between its rates of two original cycles.