Q-methodology was introduced more than 80 years ago to study subjective topics such as attitudes, perceptions, preferences, and feelings and there has not been much change in its statistical components since then. In ...Q-methodology was introduced more than 80 years ago to study subjective topics such as attitudes, perceptions, preferences, and feelings and there has not been much change in its statistical components since then. In Q-methodology, subjective topics are studied using a combination of qualitative and quantitative techniques. It involves development of a sample of statements and rank-ordering these statements by study participants using a grid known as Q-sort table. After completion of Q-sort tables by the participants, a by-person factor analysis (i.e., the factor analysis is performed on persons, not variables or traits) is used to analyze the data. Therefore, each factor represents a group of individuals with similar views, feelings, or preferences about the topic of the study. Then, each group (factor) is usually described by a set of statements, called distinguishing statements, or statements with high or low factor scores. In this article, we review one important statistical issue, i.e. the criteria for identifying distinguishing statements and provide a review of its mathematical calculation and statistical background. We show that the current approach for identifying distinguishing statements has no sound basis, which may result in erroneous findings and seems to be appropriate only when there are repeated evaluations of Q-sample from the same subjects. However, most Q-studies include independent subjects with no repeated evaluation. Finally, a new approach is suggested for identifying distinguishing statements based on Cohen’s effect size. We demonstrate the application of this new formula by applying the current and the suggested methods on a Q-dataset and explain the differences.展开更多
t Molecular dynamics （MD） simulations are carried out to characterize the mechanical and thermal responses of [011^-1]-oriented ZnO nanobelts with lateral dimensions of 21.22A × 18.95 A, 31.02A× 29.42 A, a...t Molecular dynamics （MD） simulations are carried out to characterize the mechanical and thermal responses of [011^-1]-oriented ZnO nanobelts with lateral dimensions of 21.22A × 18.95 A, 31.02A× 29.42 A, and40.81A ×39.89A over the temperature range of 300-1000 K. The Young＇s modulus and thermal conductivity of the nanobelts are evaluated. Significant surface effects on properties due to the highsurface-to-volume ratios of the nanobelts are observed. For the mechanical response, surface-stress-induced internal stress plays an important role. For the thermal response, surface scattering of phonons dominates. Calculations show that the Young＇s modulus is higher than the corresponding value for bulk ZnO and decreases by -33% as the lateral dimensions increase from 21.22 A × 18.95A to 40.81 A × 39.89A. The thermal conductivity is one order of magnitude lower than the corresponding value for bulk ZnO single crystal and decreases with wire size. Specifically, the conductivity of the 21.22 A × 18.95 A belt is approximately （31-18）% lower than that of the 40.81 A × 39.89 A belt over the temperature range analyzed. A significant dependence of properties on temperature is also observed, with the Young＇s modulus decreasing on average by 12% and the conductivity decreasing by 50% as temperature increases from 300 K to 1000 K.展开更多
The flat cylindrical indentation tests with different sizes of punch radius were investigated using finite element method （FEM） aimed to reveal the effect of punch size on the indentation behavior of the film/substr...The flat cylindrical indentation tests with different sizes of punch radius were investigated using finite element method （FEM） aimed to reveal the effect of punch size on the indentation behavior of the film/substrate system. Based on the FEM results analysis, two methods was proposed to separate film＇s reduced Young＇s modulus from a film/substrate system. The first method was based on a new weight function that quantifies film＇s and substrate＇s contributions to the overall mechanical properties of the film/substrate system in the flat cylindrical indentation test. The second method, a numerical approach, including fitting and extrapolation procedures was put forward. Both of the results from the two methods showed a reasonable agreement with the one input FE model. At last, the effect of maximum indentation depth and the surface micro-roughness of the thin film on the reduced Young＇s modulus of the film/substrate system were discussed. The methods proposed in the present study provide some new conceptions on evaluating other properties of thin films, e.g. creep, for which a flat-ended punch is also employed.展开更多
With the wide demands of cellular materials applications in aerospace and civil engineering,research effort sacrificed for this type of materials attains nowadays a higher level than ever before.This paper is focused ...With the wide demands of cellular materials applications in aerospace and civil engineering,research effort sacrificed for this type of materials attains nowadays a higher level than ever before.This paper is focused on the prediction methods of effective Young's modulus for periodical cellular materials.Based on comprehensive studies of the existing homogenization method(HM),the G-A meso-mechanics method(G-A MMM) and the stretching energy method(SEM) that are unable to reflect the size effect,we propose the bending energy method(BEM) for the first time,and a comparative study of these four methods is further made to show the generality and the capability of capturing the size effect of the BEM method.Meanwhile,the underlying characteristics of each method and their relations are clarified.To do this,the detailed finite element computing and existing experimental results of hexagonal honeycombs from the literature are adopted as the standard of comparison for the above four methods.Stretch and bending models of periodical cellular materials are taken into account,respectively for the comparison of stretch and flexural displacements resulting from the above methods.We conclude that the BEM has the strong ability of both predicting the effective Young's modulus and revealing the size effect.Such a method is also able to predict well the variations of structural displacements in terms of the cell size under stretching and bending loads including the non-monotonous variations for the hexagonal cell.On the contrary,other three methods can only predict the limited results whenever the cell size tends to be infinitely small.展开更多
文摘Q-methodology was introduced more than 80 years ago to study subjective topics such as attitudes, perceptions, preferences, and feelings and there has not been much change in its statistical components since then. In Q-methodology, subjective topics are studied using a combination of qualitative and quantitative techniques. It involves development of a sample of statements and rank-ordering these statements by study participants using a grid known as Q-sort table. After completion of Q-sort tables by the participants, a by-person factor analysis (i.e., the factor analysis is performed on persons, not variables or traits) is used to analyze the data. Therefore, each factor represents a group of individuals with similar views, feelings, or preferences about the topic of the study. Then, each group (factor) is usually described by a set of statements, called distinguishing statements, or statements with high or low factor scores. In this article, we review one important statistical issue, i.e. the criteria for identifying distinguishing statements and provide a review of its mathematical calculation and statistical background. We show that the current approach for identifying distinguishing statements has no sound basis, which may result in erroneous findings and seems to be appropriate only when there are repeated evaluations of Q-sample from the same subjects. However, most Q-studies include independent subjects with no repeated evaluation. Finally, a new approach is suggested for identifying distinguishing statements based on Cohen’s effect size. We demonstrate the application of this new formula by applying the current and the suggested methods on a Q-dataset and explain the differences.
基金The project supported by the US National Science Foundation through CAREER grant no. CMS9984298the National Natural Science Foundation of China (10528205)
文摘t Molecular dynamics （MD） simulations are carried out to characterize the mechanical and thermal responses of [011^-1]-oriented ZnO nanobelts with lateral dimensions of 21.22A × 18.95 A, 31.02A× 29.42 A, and40.81A ×39.89A over the temperature range of 300-1000 K. The Young＇s modulus and thermal conductivity of the nanobelts are evaluated. Significant surface effects on properties due to the highsurface-to-volume ratios of the nanobelts are observed. For the mechanical response, surface-stress-induced internal stress plays an important role. For the thermal response, surface scattering of phonons dominates. Calculations show that the Young＇s modulus is higher than the corresponding value for bulk ZnO and decreases by -33% as the lateral dimensions increase from 21.22 A × 18.95A to 40.81 A × 39.89A. The thermal conductivity is one order of magnitude lower than the corresponding value for bulk ZnO single crystal and decreases with wire size. Specifically, the conductivity of the 21.22 A × 18.95 A belt is approximately （31-18）% lower than that of the 40.81 A × 39.89 A belt over the temperature range analyzed. A significant dependence of properties on temperature is also observed, with the Young＇s modulus decreasing on average by 12% and the conductivity decreasing by 50% as temperature increases from 300 K to 1000 K.
基金supports from National Natural Science Foundation of China (Nos.50775183 and 50805118)Research Fund for Doctoral Programof higher Education (N6CJ0001)National High Technical Research and Development Programme of China (No.2009AA04Z418)
文摘The flat cylindrical indentation tests with different sizes of punch radius were investigated using finite element method （FEM） aimed to reveal the effect of punch size on the indentation behavior of the film/substrate system. Based on the FEM results analysis, two methods was proposed to separate film＇s reduced Young＇s modulus from a film/substrate system. The first method was based on a new weight function that quantifies film＇s and substrate＇s contributions to the overall mechanical properties of the film/substrate system in the flat cylindrical indentation test. The second method, a numerical approach, including fitting and extrapolation procedures was put forward. Both of the results from the two methods showed a reasonable agreement with the one input FE model. At last, the effect of maximum indentation depth and the surface micro-roughness of the thin film on the reduced Young＇s modulus of the film/substrate system were discussed. The methods proposed in the present study provide some new conceptions on evaluating other properties of thin films, e.g. creep, for which a flat-ended punch is also employed.
基金Supported by the National Natural Science Foundation of China (Grant No. 50775184)the National Basic Research Program of China (Grant No. 2006CB601-205)+2 种基金the Aeronautical Science Foundation (Grant No. 2008ZA53007)the Doctorate Foundation of Northwestern Polytechnical University (Grant No. CX200610)the State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University (Grant No. 30715003)
文摘With the wide demands of cellular materials applications in aerospace and civil engineering,research effort sacrificed for this type of materials attains nowadays a higher level than ever before.This paper is focused on the prediction methods of effective Young's modulus for periodical cellular materials.Based on comprehensive studies of the existing homogenization method(HM),the G-A meso-mechanics method(G-A MMM) and the stretching energy method(SEM) that are unable to reflect the size effect,we propose the bending energy method(BEM) for the first time,and a comparative study of these four methods is further made to show the generality and the capability of capturing the size effect of the BEM method.Meanwhile,the underlying characteristics of each method and their relations are clarified.To do this,the detailed finite element computing and existing experimental results of hexagonal honeycombs from the literature are adopted as the standard of comparison for the above four methods.Stretch and bending models of periodical cellular materials are taken into account,respectively for the comparison of stretch and flexural displacements resulting from the above methods.We conclude that the BEM has the strong ability of both predicting the effective Young's modulus and revealing the size effect.Such a method is also able to predict well the variations of structural displacements in terms of the cell size under stretching and bending loads including the non-monotonous variations for the hexagonal cell.On the contrary,other three methods can only predict the limited results whenever the cell size tends to be infinitely small.
