simulation studies
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2022 ◽  
Valerie C Bradley ◽  
Thomas E Nichols

The UK Biobank is a national prospective study of half a million participants between the ages of 40 and 69 at the time of recruitment between 2006 and 2010, established to facilitate research on diseases of aging. The imaging cohort is a subset of UK Biobank participants who have agreed to undergo extensive additional imaging assessments. However, Fry et al (2017) find evidence of "healthy volunteer bias" in the UK Biobank -- participants are less likely to smoke, be obese, consume alcohol daily than the target population of UK adults. Here we examine selection bias in the UK Biobank imaging cohort. We address two common misconceptions: first, that study size can compensate for bias in data collection, and second that selection bias does not affect estimates of associations, which are the primary interest of the UK Biobank. We introduce inverse probability weighting (IPW) as an approach commonly used in survey research that can be used to address selection bias in volunteer health studies like the UK Biobank. We discuss 6 such methods -- five existing and one novel --, assess relative performance in simulation studies, and apply them to the UK Biobank imaging cohort. We find that our novel method, BART for predicting the probability of selection combined with raking, performs well relative to existing methods, and helps alleviate selection bias in the UK Biobank imaging cohort.

Energies ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 523
Ryszard Palka ◽  
Marcin Wardach

Design and Application of Electrical Machines is a Special Issue of Energies. In this Special Issue, authors from various research centers present the results of their scientific research on electrical machines. In eighteen papers, they presented simulation studies, design works, and experimental tests on built prototypes.

2022 ◽  
Zohreh Nazarian ◽  
Seyed Shahriar Arab

With the aim of gaining understanding of the molecular basis of Candida antarctica lipase B (CALB) catalyzed regioselective mono aza-Michael addition of Benzhydrazide to Diethyl maleat (DEM) we decided to carry out molecular dynamics (MD) simulation studies in parallel with our experimental study. We found a correlation between the activity of CALB and the choice of solvent. Our study showed that solvent affects the performance of the enzyme due to the binding of solvent molecules to the enzyme active site region, and the solvation energy of substrates in the different solvents. We found that CALB is only active in nonpolar solvent (i.e. Hexane), and therefore we investigated the influence of Hexane on the catalytic activity of CALB for the reaction. The results of this study and related experimental validation from our studies have been discussed here.

Mathematics ◽  
2022 ◽  
Vol 10 (2) ◽  
pp. 167
Niansheng Tang ◽  
Fan Liang

Various approaches including hypothesis test and confidence interval (CI) construction have been proposed to assess non-inferiority and assay sensitivity via a known fraction or pre-specified margin in three-arm trials with continuous or discrete endpoints. However, there is little work done on the construction of the non-inferiority margin from historical data and simultaneous generalized CIs (SGCIs) in a three-arm trial with the normally distributed endpoints. Based on the generalized fiducial method and the square-and-add method, we propose two simultaneous CIs for assessing non-inferiority and assay sensitivity in a three-arm trial. For comparison, we also consider the Wald-type Bonferroni simultaneous CI and parametric bootstrap simultaneous CI. An algorithm for evaluating the optimal sample size for attaining the pre-specified power is given. Simulation studies are conducted to investigate the performance of the proposed CIs in terms of their empirical coverage probabilities. An example taken from the mildly asthmatic study is illustrated using the proposed simultaneous CIs. Empirical results show that the proposed generalized fiducial method and the square-and-add method behave better than other two compared CIs.

2022 ◽  
pp. 109821402094330
Wendy Chan

Over the past ten years, propensity score methods have made an important contribution to improving generalizations from studies that do not select samples randomly from a population of inference. However, these methods require assumptions and recent work has considered the role of bounding approaches that provide a range of treatment impact estimates that are consistent with the observable data. An important limitation to bound estimates is that they can be uninformatively wide. This has motivated research on the use of propensity score stratification to narrow bounds. This article assesses the role of distributional overlap in propensity scores on the effectiveness of stratification to tighten bounds. Using the results of two simulation studies and two case studies, I evaluate the relationship between distributional overlap and precision gain and discuss the implications when propensity score stratification is used as a method to improve precision in the bounding framework.

Foods ◽  
2022 ◽  
Vol 11 (1) ◽  
pp. 119
Ebtihal Yaqoob Khojah ◽  
Ahmed Noah Badr ◽  
Dalia Amin Mohamed ◽  
Adel Gabr Abdel-Razek

Food is the source from where a person obtains the body’s daily requirements. People’s current daily habits force them to consume fast food, which is known for its poor nutritional and safety features. So, it is urgent to provide a suitable substitution product to solve this issue. The present investigation aimed to produce a bar with a dual function: nutritional and long shelf life. Two materials were chosen to support the bar manufacturing regarding their bioactive contents, barley malt grass (BMG) and pomegranate byproducts (PBD). Chemical composition, antioxidant, and antimicrobial potency were measured. Β-carotene, vitamin C, and tocopherol were determined using HPLC apparatus. Extracts’ bio-safety against cell lines was determined, besides their enhancement against cell-death factors. Simulation experiments were designed to evaluate extracts’ impact to extend bar shelf life. Data represented the richness of essential minerals and fibers. Results of the FTIR reflected the existence of various active groups in the contents. Phenolic fractions of PBD are distinctive for their content of ellagic (39.21 ± 5.42 mg/kg), ferulic acid fractions (31.28 ± 4.07 mg/kg) which is a known with antifungal activity. Extracts and their mix (1:1) represented inhibition zone diameters that reach 15.1 ± 1.66 mm for bacteria and 23.81 ± 1.41 mm for fungi. Extracts were shown to have better safety against the cell line strain of hepatic HL-7702, with an elevation of a harmful dose of aflatoxin (IC50 304.5 µg/mL for PBD, IC50 381 µg/mL for BMG). Sensory evaluation of fortified bars reflected a preferable application of mix (1:1) due to color attributes and panelist evaluations, the same result recorded for simulation studies. The experiment recommended applying a mix (1:1) of BMG: PBD in addition to their extracts (200 mg/kg dough) for functional bar manufacturing with antifungal properties.

2022 ◽  
Vol 26 (1) ◽  
pp. 43-54
Ahmed J. Abdulqader ◽  
Raad H. Thaher ◽  
Jafar R. Mohammed ◽  

In practice, random errors in the excitations (amplitude and phase) of array elements cause undesired variations in the array patterns. In this paper, the clustered array elements with tapered amplitude excitations technique are introduced to reduce the impact of random weight errors and recover the desired patterns. The most beneficial feature of the suggested method is that it can be used in the design stage to count for any amplitude errors instantly. The cost function of the optimizer used is restricted to avoid any unwanted rises in sidelobe levels caused by unexpected perturbation errors. Furthermore, errors on element amplitude excitations are assumed to occur either randomly or sectionally (i.e., an error affecting only a subset of the array elements) through the entire array aperture. The validity of the proposed approach is entirely supported by simulation studies.

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