The Boltzmann-Bhatnagar-Gross-Krook（BGK）model is investigated for its validity regarding the collision term approximation through relaxation evaluation. The evaluation is based on theoretical analysis and numerical ...The Boltzmann-Bhatnagar-Gross-Krook（BGK）model is investigated for its validity regarding the collision term approximation through relaxation evaluation. The evaluation is based on theoretical analysis and numerical comparison between the BGK and direct simulation Monte Carlo（DSMC） results for three specifically designed relaxation problems. In these problems, one or half component of the velocity distribution is characterized by another Maxwellian distribution with a different temperature. It is analyzed that the relaxation time in the BGK model is unequal to the molecular mean collision time. Relaxation of component distribution fails to involve enough contribution from other component distributions, which makes the BGK model unable to capture details of velocity distribution, especially when discontinuity exists in distribution. The BGK model,however, predicts satisfactory results including fluxes during relaxation when the temperature difference is small. Particularly, the model-induced error in the BGK model increases with the temperature difference, thus the model is more reliable for low-speed rarefied flows than for hypersonic flows.展开更多
Background Early autism screening is of great value,but there is lack of a screening tool of early age (2-5 years) in China.The Autism Spectrum Rating Scale (ASRS,2-5 years) is a newly developed autism screening tool ...Background Early autism screening is of great value,but there is lack of a screening tool of early age (2-5 years) in China.The Autism Spectrum Rating Scale (ASRS,2-5 years) is a newly developed autism screening tool in the USA.This study aimed to evaluate the reliability and validity of the translated Chinese version of ASRS (C_ASRS) in Chinese children population before its application in China for early autism screening.Methods Caregivers of general children aged 2-5 years from 17 kindergartens and autism spectrum disorder (ASD) cases from five special education schools in five cities were recruited to complete the C_ASRS.1910 valid questionnaires from kindergarteners and 192 from ASD cases were included for analyses.Results The item reliability (Cronbach's alpha) was more than 0.80 in the screening scale and DSM-5 scale,and 0.51-0.81 in the treatment scale.ASD cases scored higher on total score and most subscales compared to the kindergarteners (Cohen's d ranging from 1.34 to 3.37).C_ASRS showed good discriminatory validity with an area under the receiver operating characteristic curve of 0.850 (95% confidence interval:0.819-0.881).The cutoff ≥ 60 achieved sensitivity of 65.63% and specificity of 85.63% in discriminating autism children from the general population.Conclusion The results indicate that C_ASRS (2-5 years) could be used as an early level-2 screening tool for autism screening in China and should be further revised for level-1 screening.展开更多
基金supported by the National Natural Science Foundation of China(91116013,11372325,and 11111120080)
文摘The Boltzmann-Bhatnagar-Gross-Krook（BGK）model is investigated for its validity regarding the collision term approximation through relaxation evaluation. The evaluation is based on theoretical analysis and numerical comparison between the BGK and direct simulation Monte Carlo（DSMC） results for three specifically designed relaxation problems. In these problems, one or half component of the velocity distribution is characterized by another Maxwellian distribution with a different temperature. It is analyzed that the relaxation time in the BGK model is unequal to the molecular mean collision time. Relaxation of component distribution fails to involve enough contribution from other component distributions, which makes the BGK model unable to capture details of velocity distribution, especially when discontinuity exists in distribution. The BGK model,however, predicts satisfactory results including fluxes during relaxation when the temperature difference is small. Particularly, the model-induced error in the BGK model increases with the temperature difference, thus the model is more reliable for low-speed rarefied flows than for hypersonic flows.
文摘Background Early autism screening is of great value,but there is lack of a screening tool of early age (2-5 years) in China.The Autism Spectrum Rating Scale (ASRS,2-5 years) is a newly developed autism screening tool in the USA.This study aimed to evaluate the reliability and validity of the translated Chinese version of ASRS (C_ASRS) in Chinese children population before its application in China for early autism screening.Methods Caregivers of general children aged 2-5 years from 17 kindergartens and autism spectrum disorder (ASD) cases from five special education schools in five cities were recruited to complete the C_ASRS.1910 valid questionnaires from kindergarteners and 192 from ASD cases were included for analyses.Results The item reliability (Cronbach's alpha) was more than 0.80 in the screening scale and DSM-5 scale,and 0.51-0.81 in the treatment scale.ASD cases scored higher on total score and most subscales compared to the kindergarteners (Cohen's d ranging from 1.34 to 3.37).C_ASRS showed good discriminatory validity with an area under the receiver operating characteristic curve of 0.850 (95% confidence interval:0.819-0.881).The cutoff ≥ 60 achieved sensitivity of 65.63% and specificity of 85.63% in discriminating autism children from the general population.Conclusion The results indicate that C_ASRS (2-5 years) could be used as an early level-2 screening tool for autism screening in China and should be further revised for level-1 screening.
