Conventional space-filling experimental design provides uniform coverage of a hypercube design space. When constraints are imposed, the results may contain many infeasible points. Simply omitting ...these points leads to fewer feasible points than desired and a design of experiments that is not optimally distributed. In this research, an adaptive method is developed to create space-filling points in arbitrarily constrained spaces. First, a design space reconstruction method is developed to reduce the invalid exploration space and enhance the efficiency of experimental designs. Then, a synthetic criterion of uniformity and feasibility is proposed and optimized by the enhanced stochastic evolutionary method to obtain the initial sampling combination. Finally, an adaptive adjustment strategy of design levels is constructed to obtain the required number of feasible points. Various test cases with convex and non-convex, connected and non-connected design spaces are implemented to verify the efficacy of the proposed method.
Support vector machine (SVM) is regarded as one of the most effective techniques for supervised learning, while the Gaussian kernel SVM is widely utilized due to its excellent performance ...capabilities. To ensure high performance of models, hyperparameters, i.e. kernel width and penalty factor must be determined appropriately. This paper studies the influence of hyperparameters on the Gaussian kernel SVM when such hyperparameters attain an extreme value (0 or ∞). In order to improve computing efficiency, a parameter optimization method based on the local density and accuracy of Leave-One-Out (LOO) method are proposed. Kernel width of each sample is determined based on the local density needed to ensure a higher separability in feature space while the penalty parameter is determined by an improved grid search using the LOO method. A comparison with grid method is conducted to verify validity of the proposed method. The classification accuracy of five real-life datasets from UCI database are 0.9733, 0.9933, 0.7270, 0.6101 and 0.8867, which is slightly superior to the grid method. The results also demonstrate that this proposed method is computationally cheaper by 1 order of magnitude when compared to the grid method.
Sensitivity analysis plays an important role in exploring the actual impact of adjustable parameters on response variables. Amongst the wide range of documented studies on sensitivity measures and ...analysis, Sobol' indices have received greater portion of attention due to the fact that they can provide accurate information for most models. In this paper, a novel analytical expression to compute the Sobol' indices is derived by introducing a method which uses the Gaussian Radial Basis Function to build metamodels of computationally expensive computer codes. Performance of the proposed method is validated against various analytical functions and also a structural simulation scenario. Results demonstrate that the proposed method is an efficient approach, requiring a computational cost of one to two orders of magnitude less when compared to the traditional Quasi Monte Carlo-based evaluation of Sobol' indices.
•RBF based sensitivity analysis method is proposed.•Sobol' decomposition of Gaussian RBF metamodel is obtained.•Sobol' indices of Gaussian RBF metamodel are derived based on the decomposition.•The efficiency of proposed method is validated by some numerical examples.
Background and aims
Endoscopic placement of enteral self-expandable metallic stents is an alternative to surgical gastrojejunostomy (GJ) for palliation of malignant gastric outlet obstruction (GOO). ...Factors associated with clinical outcomes are not known. The aims of this study are to compare the overall complication rate and effectiveness (duration of oral intake) between endoscopic stenting (ES) and GJ in patients with GOO and identify predictors of clinical outcomes.
Patients and methods
This was a retrospective cohort study at a single tertiary academic center. Patients who underwent ES or GJ for treatment of GOO between 1/2001 and 12/2010 were identified using an institutional claims database. The electronic medical records for each patient were reviewed. Univariate and multivariate logistic regression analyses were performed to study the association of treatment outcomes with patient factors and cancer therapy.
Results
120 patients had ES while 227 had GJ. Technical success was higher for GJ (99 vs. 96 %,
p
= 0.004). Complication rates were higher in the GJ group (22.10 vs. 11.66 %,
p
= 0.02). Reintervention was more common with ES adjusted odds ratio (OR) 9.18,
p
< 0.0001. Mean length of hospital stay (LOHS) was shorter (adjusted
p
= 0.005) in the ES compared with the GJ group. However, mean hospital charges, including reinterventions, were greater in the ES group (US $34,250 vs. US $27,599,
p
= 0.03). ES and GJ had comparable reintervention-free time in patients who had reintervention (88 vs. 106 days, respectively,
p
= 0.79). Chemotherapy adjusted hazard ratio (HR) 3 > 0.57,
p
= 0.04 and radiation therapy (adjusted HR 0.35,
p
= 0.03) were associated with significantly longer duration of oral intake after ES or GJ.
Conclusion
ES is associated with fewer complications, shorter LOHS, but higher reintervention rates and overall charges.
Background Although colonoscopy is currently the optimal method for detecting colorectal polyps, some are missed. The Third Eye Retroscope provides an additional retrograde view that may detect ...polyps behind folds. Objective To determine whether the addition of the Third Eye Retroscope to colonoscopy improves the adenoma detection rate. Design Prospective, multicenter, randomized, controlled trial. Setting Nine European and U.S. centers. Patients Of 448 enrolled subjects, 395 had data for 2 procedures. Interventions Subjects underwent same-day tandem examinations with standard colonoscopy (SC) and Third Eye colonoscopy (TEC). Subjects were randomized to SC followed by TEC or TEC followed by SC. Main Outcome Measurements Detection rates for all polyps and adenomas with each method. Results In the per-protocol population, 173 subjects underwent SC and then TEC, and TEC yielded 78 additional polyps (48.8%), including 49 adenomas (45.8%). In 176 subjects undergoing TEC and then SC, SC yielded 31 additional polyps (19.0%), including 26 adenomas (22.6%). Net additional detection rates with TEC were 29.8% for polyps and 23.2% for adenomas. The relative risk of missing with SC compared with TEC was 2.56 for polyps ( P < .001) and 1.92 for adenomas ( P = .029). Mean withdrawal times for SC and TEC were 7.58 and 9.52 minutes, respectively ( P < .001). The median difference in withdrawal times was 1 minute ( P < .001). The mean total procedure times for SC and TEC were 16.97 and 20.87 minutes, respectively ( P < .001). Limitations Despite randomization and a large cohort, there was disparity in polyp prevalence between the 2 groups of subjects. Conclusion The Third Eye Retroscope increases adenoma detection rate by visualizing areas behind folds. (Clinical trial registration number: NCT01044732 .)
In recent decades, surrogate-based optimization (SBO) has been developed to replace costly models with cheap surrogates to improve efficiency. In this article, an adaptive parallel infill strategy is ...proposed to balance exploration and exploitation over the design space during the optimization process of SBO. Within this method, an inaccurate search strategy is adopted to optimize the surrogate models, thereby helping to locate the exploitation point. An elite archive is exploited to store superior sampling points for batch sampling, while a customized batch size determination strategy is introduced. The proposed SBO method with its adaptive parallel sampling strategy is tested on six unconstrained and five constrained analytical cases with the optimization results compared to state-of-the-art optimization algorithms. The optimization of a 582-bar tower truss system is also performed and utilized to verify the proposed SBO method. The proposed SBO with the adaptive parallel sampling strategy shows excellent performance and better stability.
PDF
