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- Ge, R, et al.
(författare)
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Normative Modeling of Brain Morphometry Across the Lifespan Using CentileBrain: Algorithm Benchmarking and Model Optimization
- 2023
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Ingår i: bioRxiv : the preprint server for biology. - : Cold Spring Harbor Laboratory.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Background: Normative modeling is a statistical approach to quantify the degree to which a particular individual-level measure deviates from the pattern observed in a normative reference population. When applied to human brain morphometric measures it has the potential to inform about the significance of normative deviations for health and disease. Normative models can be implemented using a variety of algorithms that have not been systematically appraised. Methods: To address this gap, eight algorithms were compared in terms of performance and computational efficiency using brain regional morphometric data from 37,407 healthy individuals (53% female; aged 3-90 years) collated from 87 international MRI datasets. Performance was assessed with the mean absolute error (MAE) and computational efficiency was inferred from central processing unit (CPU) time. The algorithms evaluated were Ordinary Least Squares Regression (OLSR), Bayesian Linear Regression (BLR), Generalized Additive Models for Location, Scale, and Shape (GAMLSS), Parametric Lambda, Mu, Sigma (LMS), Gaussian Process Regression (GPR), Warped Bayesian Linear Regression (WBLG), Hierarchical Bayesian Regression (HBR), and Multivariable Fractional Polynomial Regression (MFPR). Model optimization involved testing nine covariate combinations pertaining to acquisition features, parcellation software versions, and global neuroimaging measures (i.e., total intracranial volume, mean cortical thickness, and mean cortical surface area). Findings: Statistical comparisons across models at PFDR<0.05 indicated that the MFPR-derived sex- and region-specific models with nonlinear polynomials for age and linear effects of global measures had superior predictive accuracy; the range of the MAE of the models of regional subcortical volumes was 70-520 mm3 and the corresponding ranges for regional cortical thickness and regional cortical surface area were 0.09-0.26 mm and 24-560 mm2, respectively. The MFPR-derived models were also computationally more efficient with a CPU time below one second compared to a range of 2 seconds to 60 minutes for the other algorithms. The performance of all sex- and region-specific MFPR models plateaued at sample sizes exceeding 3,000 and showed comparable MAEs across distinct 10-year age-bins covering the human lifespan. Interpretation: These results provide an empirically benchmarked framework for normative modeling of brain morphometry that is useful for interpreting prior literature and supporting future study designs. The model and tools described here are freely available through CentileBrain (https://centilebrain.org/), a user-friendly web platform.
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| 4. |
- Lim, H. D., et al.
(författare)
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Short-time proper orthogonal decomposition of time-resolved schlieren images for transient jet screech characterization
- 2020
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 107
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Tidskriftsartikel (refereegranskat)abstract
- Short-time Proper Orthogonal Decomposition (POD) is proposed as an image-based technique to study the transient jet screech characteristics of moderately under-expanded supersonic jets emanating from a circular baseline and two bevelled nozzles. Time-resolved schlieren imaging of turbulent flow structures were performed with an ultrahigh-speed schlieren setup. Short-time POD was performed by systematically sampling image-series with a short time delay, performing PODs and applying spectral analyses on the first POD mode coefficients, and plotting the peak frequencies from the resulting PSDs into a peak frequency-occurrence count histogram. The results are in good agreement with the near-field noise spectra and wavelet transform analysis of the microphone measurements, which revealed intermittent jet screech occurrences at St=0.25 for both baseline and 30 degrees bevelled jets, while none was detected for the 60 degrees bevelled jet. In particular, the occurrence counts of the frequency bins is proposed as a suitable parameter to characterize the intermittent nature of jet screech, with the frequency bin revealing the jet screech frequency if present. The present study demonstrates the advantage of short-time POD analysis on time-resolved schlieren images over traditional image-based POD methods, which includes computational gains from parallelization, the ability to handle much larger datasets and revealing insights into a transient flow and noise phenomenon.
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| 6. |
- Scrivens, A, et al.
(författare)
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Survey of transfusion practices in preterm infants in Europe
- 2023
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Ingår i: Archives of disease in childhood. Fetal and neonatal edition. - : BMJ. - 1468-2052 .- 1359-2998. ; 108:4, s. 360-366
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Tidskriftsartikel (refereegranskat)abstract
- Preterm infants commonly receive red blood cell (RBC), platelet and fresh frozen plasma (FFP) transfusions. The aim of this Neonatal Transfusion Network survey was to describe current transfusion practices in Europe and to compare our findings to three recent randomised controlled trials to understand how clinical practice relates to the trial data.MethodsFrom October to December 2020, we performed an online survey among 597 neonatal intensive care units (NICUs) caring for infants with a gestational age (GA) of <32 weeks in 18 European countries.ResultsResponses from 343 NICUs (response rate: 57%) are presented and showed substantial variation in clinical practice. For RBC transfusions, 70% of NICUs transfused at thresholds above the restrictive thresholds tested in the recent trials and 22% below the restrictive thresholds. For platelet transfusions, 57% of NICUs transfused at platelet count thresholds above 25×109/L in non-bleeding infants of GA of <28 weeks, while the 25×109/L threshold was associated with a lower risk of harm in a recent trial. FFP transfusions were administered for coagulopathy without active bleeding in 39% and for hypotension in 25% of NICUs. Transfusion volume, duration and rate varied by factors up to several folds between NICUs.ConclusionsTransfusion thresholds and aspects of administration vary widely across European NICUs. In general, transfusion thresholds used tend to be more liberal compared with data from recent trials supporting the use of more restrictive thresholds. Further research is needed to identify the barriers and enablers to incorporation of recent trial findings into neonatal transfusion practice.
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| 7. |
- Wei, X. F., et al.
(författare)
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Experimental Investigations of Screech Mitigation and Amplification by Beveled and Double-Beveled Nozzles
- 2022
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Ingår i: Journal of Aerospace Engineering. - : American Society of Civil Engineers (ASCE). - 0893-1321 .- 1943-5525. ; 35:4
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study was conducted to investigate and compare the effects of beveled and double-beveled circular nozzles on supersonic jet screech at a nozzle pressure ratio of 5. In particular, near- and far-field microphone measurements and schlieren visualizations were utilized to look into selected acoustic and flow features associated with jet screech radiation. Results show that beveled nozzles eliminate jet screech by producing asymmetric shock structures and instability waves that are mismatched in phase and amplitude. In contrast, double-beveled nozzles produce symmetric shock structures and amplify screech intensity, even when jet mixing effects have been significantly enhanced. It is further observed that amplified jet screeches produced by double-beveled nozzles are highly unsteady and undergo nonperiodic and stochastic temporal variations. Last but not least, double-beveled nozzles also significantly impact screech peak noise locations and confer different changes along different measurement planes. The present study demonstrates that not all beveled-type nozzles are able to mitigate jet screech, with nonoptimal designs amplifying it instead.
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| 8. |
- Wei, X. F., et al.
(författare)
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Near- and Far-Field Acoustic Measurements for Stepped Nozzles at Over- and Perfectly-Expanded Supersonic Jet Flow Conditions
- 2020
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Ingår i: Journal of Fluids Engineering. - : ASME International. - 0098-2202 .- 1528-901X. ; 142:11
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Tidskriftsartikel (refereegranskat)abstract
- Detailed near- and far-field acoustic measurements were conducted for two circularstepped nozzles with 30 deg and 60 deg design inclinations at over- and perfectlyexpandedsupersonic jet flow conditions and compared to those for a circular nonsteppednozzle. Far-field acoustic results show that stepped nozzles play an insignificant role inaltering noise emissions at perfectly expanded condition. At an over-expanded condition,however, the longer stepped nozzle produces significant noise reductions at the sidelineand upstream quadrants, while the shorter stepped nozzle does not. Noise spectra analysisand Schlieren visualizations show that noise reduction can be primarily attributed tomitigations in the broadband shock-associated noise (BSAN), due to the ability of the longerstepped nozzle in suppressing shock strengths at downstream region. Near-fieldacoustic measurements reveal that the source region, as well as the intensity of turbulentand shock noises, are highly sensitive to the stepped nozzle configuration. Furthermore,BSAN seems to be eliminated by the longer stepped nozzle in near-field region due to theshock structure modifications.
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