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.

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.

Background: Bilateral total knee arthroplasty (BTKA) under the same anesthesia (simultaneous) or staged are options for patients with end-stage arthritis of the knee that carries advantages and limitations. Not all patients are candidates for simultaneous BTKA, and therefore, surgeons prefer to stage the Two TKAs. The optimal safe interval between Two TKAs is not known. The present systematic review aimed to determine the optimal time interval between the Two stages of BTKA. Methods: Pubmed and Scopus databases were searched to identify publications from January 1979 to November 2017 in English that compared the outcomes of staged BTKA performed using various time intervals between the Two TKAs. Data on systemic and local complications following staged BTKA were extracted, and the pooled data were analyzed to adjust for age. Results: In total, 23 studies that enrolled 117, 090 patients undergoing staged BTKA were included in this systematic review. A significant increase was observed in the incidence of myocardial infarction (OR=8. 4 and 8. 32), other cardiac complications (OR=17. 71 and 18. 18), deep vein thrombosis (OR=4. 72 and 4. 89), pneumonia (OR=3. 37 and 3. 45), and knee revision (OR=3. 73 and 4. 14) in patients undergoing the second TKA within 30 days or 90 days of the first TKA. However, the replacement of the second knee within this time interval was associated with a significantly lower risk of pulmonary embolism (OR=0. 145 and 0. 128), superficial (OR=0. 14 and 0. 79) and deep knee infection (OR=0. 0 and 0. 0), as well as vascular complications (OR=0. 0 and 0. 42). Conclusion: Time interval of less than 30 or 90 days between Two TKAs performed in patients with BTKA was associated with a higher risk of systematic complications. However, the shorter time intervals between the Two TKA may reduce the risk of other complications. This information may help surgeons' council patients better when deciding on the optimal time interval between Two TKAs.

In this paper, the performance of EAM (Estimation After Modeling) and EBM (Estimation Before Modeling) techniques for aerodynamic parameter identification are compared. The results clea rly show that EAM has a superior performance over EBM. but both techniques fail when there is considerable modeling uncertainty. Given this shortcoming, a Two-step procedure is used that is a combination of EAM an EBM for estimating the aerodynamic parameters. Simulation results show that this new technique outperforms EAM when modeling uncertainties are considered. This technique will be applied to the problem of identifying the aerodynamic parameters of an anti-tank missile and its performance is compared with both EAM and EBM approaches.