A social recommendation method based on an adaptive neighbor selection mechanism     

Sajad Ahmadian  Majid Meghdadi  Mohsen Afsharchi 《Information processing & management》2018,54(4):707-725

Recommender systems are techniques to make personalized recommendations of items to users. In e-commerce sites and online sharing communities, providing high quality recommendations is an important issue which can help the users to make effective decisions to select a set of items. Collaborative filtering is an important type of the recommender systems that produces user specific recommendations of the items based on the patterns of ratings or usage (e.g. purchases). However, the quality of predicted ratings and neighbor selection for the users are important problems in the recommender systems. Selecting suitable neighbors set for the users leads to improve the accuracy of ratings prediction in recommendation process. In this paper, a novel social recommendation method is proposed which is based on an adaptive neighbor selection mechanism. In the proposed method first of all, initial neighbors set of the users is calculated using clustering algorithm. In this step, the combination of historical ratings and social information between the users are used to form initial neighbors set for the users. Then, these neighbor sets are used to predict initial ratings of the unseen items. Moreover, the quality of the initial predicted ratings is evaluated using a reliability measure which is based on the historical ratings and social information between the users. Then, a confidence model is proposed to remove useless users from the initial neighbors of the users and form a new adapted neighbors set for the users. Finally, new ratings of the unseen items are predicted using the new adapted neighbors set of the users and the $top\_N$ interested items are recommended to the active user. Experimental results on three real-world datasets show that the proposed method significantly outperforms several state-of-the-art recommendation methods.  相似文献   

Diagnosing Competency Mastery in Science: An Application of GDM to TIMSS 2011 Data     

Masoud Kabiri  Mahmood Ghazi-Tabatabaei  Abbas Bazargan  Mohsen Shokoohi-Yekta  Kamal Kharrazi 《教育实用测度》2017,30(1):27-38

Numerous diagnostic studies have been conducted on large-scale assessments to illustrate the students’ mastery profile in the areas of math and reading; however, for science a limited number of investigations are reported. This study investigated Iranian eighth graders’ competency mastery of science and examined the utility of the General Diagnostic Model (GDM) to produce diagnostic information using TIMSS 2011 data. Eight diagnostic attributes were extracted, using documentary analysis of the major large-scale assessment frameworks, including basic science knowledge, using models, reasoning, using science, representing data, explaining of phenomena, predicting, and scientific inquiry. These attributes were then assigned to each item in order to construct the Q matrix, through focus group discussions, survey of head science teachers, think-aloud verbal protocol, and analysis of written answers. Results show the utility of GDM to generate rich diagnostic information for a national large-scale assessment. Moreover, the findings indicated that students performed relatively well in using science, but performed weakly in reasoning, explaining of phenomena, and scientific inquiry, which all required complex skills and higher-order thinking abilities.  相似文献   

Effect of environmental constraints on multi-segment coordination patterns during the tennis service in expert performers     

Mohsen Shafizadeh  Stuart Bonner  Jonathan Fraser  Andrew Barnes 《Journal of sports sciences》2019,37(9):1011-1020

The aims of this study were to examine the effect of different environmental constraints on kinematic multi-segment coordination patterns during the service and its coordination with service time variability. Ten expert tennis players (Age: 34.1 ± 5.3) volunteered to take part in this study. Participants served 30 times in 3 different conditions: control, target and opposition. The order of conditions was counterbalanced between participants. A wireless 3D motion capture system (STT Co, Spain) was used to measure 7 joint motions, with a 17 degrees of freedom biomechanical model created to capture the entire service action. Results of the principal component analysis showed that 4 synergies were created; however, their roles were changed relative to the perception of the environment. The results of repeated-measures analysis of variance did not show any significant difference on total variance and individual principal components between conditions; however, one synergy pattern significantly predicted the service time variability in both control and opposition conditions. In conclusion, the findings demonstrated that expert performers reduce the joint dimensionality by creating functional synergies in different phases of service and adapt the service action according to the perception of the environment.  相似文献   

Side-sloped surfaces substantially affect lower limb running kinematics     

Mohsen Damavandi  Mansour Eslami  David J. Pearsall 《Sports biomechanics / International Society of Biomechanics in Sports》2017,16(1):1-12

Running on side-sloped surfaces is a common obstacle in the environment; however, how and to what extent the lower extremity kinematics adapt is not well known. The purpose of this study was to determine the effects of side-sloped surfaces on three-dimensional kinematics of hip, knee, and ankle during stance phase of running. Ten healthy adult males ran barefoot along an inclinable runway in level (0°) and side-sloped (10° up-slope and down-slope inclinations, respectively) configurations. Right hip, knee, and ankle angles along with their time of occurrence were analysed using repeated measures MANOVA. Up-slope hip was more adducted (p = 0.015) and internally rotated (p = 0.030). Knee had greater external rotations during side-sloped running at heel-strike (p = 0.005), while at toe-off, it rotated externally and internally during up-slope and down-slope running, respectively (p = 0.001). Down-slope ankle had greatest plantar flexion (p = 0.001). Up-slope ankle had greatest eversion compared with down-slope (p = 0.043), while it was more externally rotated (p = 0.030). These motion patterns are necessary to adjust the lower extremity length during side-sloped running. Timing differences in the kinematic events of hip adduction and external rotation, and ankle eversion were observed (p = 0.006). Knowledge on these alterations is a valuable tool in adopting strategies to enhance performance while preventing injury.  相似文献