Ahmed Abdalla Mohamed

Surrogate-Based Circuit Design Centering

Circuit design centering is one of the most important problems concerning the optimal design of circuits. Circuit design centering seeks nominal values of designable circuit parameters that maximize the probability of satisfying the design specifications (yield function). Design centering can be performed geometrically by finding the center of the feasible region (region in the designable parameter space where the design specifications are satisfied), or by maximizing the yield function explicitly. For all cases, the high expense of circuit simulations required obstructs the design centering process, especially for microwave circuits. To overcome this, computationally cheap surrogate-based models (e.g., space mapping, response surfaces, kriging, and neural networks) can be used for approximating the response functions or the yield function itself. In this chapter the design centering problem is formulated as an optimization problem, and the estimation of the yield function through several sampling techniques is explained. The difficulties facing the design centering process, especially for microwave circuits, are discussed, and the role of surrogate-based models in overcoming these difficulties is demonstrated. Special interest is devoted to space mapping surrogates and microwave circuit design centering. Some of the important surrogate-based circuit design centering approaches are reviewed with an overview of their theoretical bases. Tutorial and practical circuit examples are given to show the effectiveness of these approaches.

A simple quantitative model for replacement of medical equipment proposed to developing countries

Along the medical equipment life cycle, hospitals need to take decisions on medical equipment acquisition, maintenance, use and replacement on the basis of complete and reliable information. In this paper, the authors focus on the replacement criteria in developing countries where there is a lack of scientific, realistic and comprehensive assessment. In the proposed model, we use Fault Tree analysis (FTA) to model the replacement process using a set of indicators that impact directly or indirectly the replacement decision. We include the vendor support as a fundamental technical indicator in the analysis. This model considers the replacement decision as a final and undesirable event. Using probability theory, the medical equipment status is classified into 4 groups. According to the final event score, the replacement decision is approved or not. Neonatal Intensive Care Unit (NICU) equipment of 8 different types, along three years, are utilized to investigate the proposed model. Our model proposes a priority list of equipment that should be replaced. The type and number of equipment to be purchased is determined according to the available budget. The results show that 15% of equipment should be replaced, 33% need to be tested, 33% are under surveillance and 19% could be maintained.

Statistical microwave circuit optimization via a non-derivative trust region approach and space mapping surrogates

A novel yield optimization technique for microwave circuits is presented. Yield optimization of microwave circuits is obstructed by the high expense of electromagnetic simulations required in yield evaluations in addition to the absence of any gradient information. In the proposed technique, surrogates using the generalized space mapping (GSM) algorithm is incorporated with a derivative-free trust region optimization method (NEWUOA: new unconstrained optimization algorithm). Moreover, a variance reduction technique is implemented in yield estimation process. Practical examples to demonstrate this new technique are included showing its efficiency.

A novel surrogate-based approach for optimal design of electromagnetic-based circuits

A new geometric design centring approach for optimal design of central processing unit-intensive electromagnetic (EM)-based circuits is introduced. The approach uses norms related to the probability distribution of the circuit parameters to find distances from a point to the feasible region boundaries by solving nonlinear optimization problems. Based on these normed distances, the design centring problem is formulated as a max–min optimization problem. A convergent iterative boundary search technique is exploited to find the normed distances. To alleviate the computation cost associated with the EM-based circuits design cycle, space-mapping (SM) surrogates are used to create a sequence of iteratively updated feasible region approximations. In each SM feasible region approximation, the centring process using normed distances is implemented, leading to a better centre point. The process is repeated until a final design centre is attained. Practical examples are given to show the effectiveness of the new design centring method for EM-based circuits.

RF cavity design exploiting a new derivative-free trust region optimization approach

In this article, a novel derivative-free (DF) surrogate-based trust region optimization approach is proposed. In the proposed approach, quadratic surrogate models are constructed and successively updated. The generated surrogate model is then optimized instead of the underlined objective function over trust regions. Truncated conjugate gradients are employed to find the optimal point within each trust region. The approach constructs the initial quadratic surrogate model using few data points of order O(n), where n is the number of design variables. The proposed approach adopts weighted least squares fitting for updating the surrogate model instead of interpolation which is commonly used in DF optimization. This makes the approach more suitable for stochastic optimization and for functions subject to numerical error. The weights are assigned to give more emphasis to points close to the current center point. The accuracy and efficiency of the proposed approach are demonstrated by applying it to a set of classical bench-mark test problems. It is also employed to find the optimal design of RF cavity linear accelerator with a comparison analysis with a recent optimization technique.

Optimal Design of Computationally Expensive EM-Based Systems: A Surrogate-Based Approach

It is quite a challenge to find the optimal design of computationally expensive engineering systems in different areas such as electrical engineering, structural mechanics, fluid dynamics, and electromagnetic-based (EM-based) systems. The optimal design of such systems requires solving huge optimization problems involving a lot of expensive function evaluations. For example, in microwave circuit design, a function evaluation requires running a full-wave electromagnetic simulator which may exhaust hours of CPU time. The total computational overhead makes the optimization of these engineering systems practically prohibitive. Computationally cheap surrogates (Response Surfaces, Space Mapping, Kriging models, Neural Networks, etc.) offer a good solution of such problems. Throughout the optimization process, iteratively updated surrogates are employed to replace the computationally expensive function evaluations.

A trust region approach with multivariate Padé model for optimal circuit design

ABSTRACT Since the optimization process requires a significant number of consecutive function evaluations, it is recommended to replace the function by an easily evaluated approximation model during the optimization process. The model suggested in this article is based on a multivariate Padé approximation. This model is constructed using data points of , where is the number of parameters. The model is updated over a sequence of trust regions. This model avoids the slow convergence of linear models of and has features of quadratic models that need interpolation data points of . The proposed approach is tested by applying it to several benchmark problems. Yield optimization using such a direct method is applied to some practical circuit examples. Minimax solution leads to a suitable initial point to carry out the yield optimization process. The yield is optimized by the proposed derivative-free method for active and passive filter examples.

The effect of useful life and vendor performance on replacement decision of medical equipment

Medical equipment management life cycle considers various stages ranging from planning to disposal or replacement. Replacement decision is critical and essential stage of medical equipment. A variety of criteria contributes to make an intelligent replacement decision. We enhance the Fault Tree Analysis (FTA) model for replacement of medical equipment, considering a combination of technical, financial, and safety criteria. The considered criteria are; hazard and alerts, cost, useful life, and vendor support. Throughout this model, we classify medical equipment life status into four groups; replacement, test, surveillance and keep. According to the final event score, the replacement decision is approved or not. Neonatal Intensive Care Unit (NICU) equipment of 12 different types for 3 hospitals, along three years, is utilized to investigate the proposed model. Our model proposes a priority list of equipment that should be replaced. According to the analysis to the proposed factors, the useful life factor is found to be the dominant factor. In addition, a high correlation between vendor performance and expended costs is realized.

Priming with different doses of metoclopramide preceded by tourniquet alleviates propofol induced pain: A comparative study with lidocaine

Abstract Objectives To evaluate the outcome of priming by varying-doses of metoclopramide on propofol injection pain in comparison to lidocaine as a standard control. Methods and materials 320 patients were randomly allocated into 4 equal groups: Group C received 50 mg lidocaine and Groups M1-3 received metoclopramide 2.5, 5 and 10 mg, respectively. An elastic tourniquet was applied to the mid of left arm, the priming solution was injected over 10 s and 1-min later, tourniquet was removed and one fourth of the total calculated dose of Propofol was injected over 30 s and pain assessment was made, during initial and at end of injection of Propofol trial dose, using the 4-point verbal rating scale: no, mild, moderate or severe pain. Then, the reminder of the full calculated induction dose of Propofol was completed. Results Lidocaine and metoclopramide mostly relieved pain of initiation of Propofol injection 174 patients (54.4%) had no pain 94 patients (29.4%) had mild pain and only 68 patients (21.25%) had moderate pain, while no patient had severe injection pain. At the end of injection of the total trial dose, 40% had no pain totally, 31.3% had mild pain, 19.3% had moderate pain and 9.4% had severe pain. Lidocaine provided significantly better analgesia compared to metoclopramide (2.5 mg), while the difference was non-significantly better compared to metoclopramide, 5 and 10 mg. Metoclopramide provided dose-dependent stepwise pain relieve peaking with 10 mg dose that showed significant superiority compared to 2.5 mg dose, but non-significantly compared to 5 mg dose. Moreover, the effect of 10 mg priming dose extended till completion of injection of the trial dose with significant difference Compared to the other two doses of metoclopramide. Conclusion venous priming with metoclopramide 10 mg with mid-arm tourniquet applied for one minute is effective modality for alleviation of Propofol injection pain else Patients received Lidocaine showed significantly better analgesia compared to those received 2.5 mg metoclopramide.

Management for failed back surgery syndrome: three-in-one procedure versus percutaneous spinal fixation alone

Objectives: To evaluate the short-term outcome of a 3-in-1 procedure including percutaneous facet radiofrequency, percutaneous spinal fixation and steroid with hyaluronidase enzyme injection versus percutaneous spinal fixation alone for cases with failed back surgery syndrome (FBSS). Patients and methods: The study included 50 patients who had had previous spinal surgery since a mean duration of 39.7 ± 8.5 months and developed recurrent back pain since a mean duration of 10 ± 2.1 months. Patients were randomly allocated into two groups; group A underwent percutaneous spinal fixation only and group B underwent the 3-in-1 procedure. Outcome was evaluated at the end of six months postoperatively (PO) using a pain numeric rating scale (NRS), the Oswestry Disability Index (ODI) and Odom’s criteria for evaluation of surgical outcome with evaluation of patients’ satisfaction by outcome. Results: All patients showed progressive decrease of NRS pain and ODI scores compared with preoperative scores. However, patients in group B showed significantly lower postoperative NRS pain scores and ODI with significantly higher frequency of patients having had > 50% reduction of both scores compared with patients in group A. PO analgesic consumption rate in both groups was significantly lower than the preoperative rate with a significant reduction of mean total scoring compared with preoperative scoring. The frequency of patients who found the provided therapeutic procedure satisfactory and its outcome good-to-excellent was significantly higher among patients in group B compared with group A. Conclusion: Short-term outcomes of the applied 3-in-1 procedure are promising for improvement of symptoms secondary to FBSS and may ultimately prove to be recommended as the therapeutic modality for such a challenging clinical problem.