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Physical activity has several mental and psychological health benefits for students. Various studies in western countries have shown evidence of a relationship between physical activity and academic anxiety. Further, researchers have suggested testing the mechanism of this relationship. In this study, we aim to test the association between physical activity and academic anxiety of Canadian university students and to examine whether the mediation of self-enhancement and self-criticism explains this relationship. Four hundred and forty-two university students participated in the study. Structural equation modeling was applied to develop multiple mediation models. Results revealed that physical activity does not directly affect academic anxiety, but indirectly through self-enhancement and self-criticism. Based on the study findings, it is recommended that physical activity be promoted among students to promote self-enhancement, minimize negative thinking and self-criticism, and reduce their academic anxiety.

Background: The health of urban residents plays an important role in increasing the well-being of citizens, and therefore promoting the sustainable development of cities. Studies in Western countries have provided some evidence of the relationship between the urban residents&rsquo, perception of the recreational sports (RS), including perception of industry, space, experience, type, and support affecting recreational behaviors. Yet, evidence in China is not sufficient and, particularly, gender difference has not been discussed anywhere. Objectives: The present study aimed to see urban residents&rsquo, perception of RS and its effect on recreational sport participation by the residents. Method: The study was conducted in three big cities (Hangzhou, Chengdu, and Shanghai) of China to test the association between the urban residents&rsquo, perception of RS and their RS participation, in which gender differences were discussed. After taking their consent, a total of 764 participants (397 male and 367 female) aged from 15 to 65 were approached between April and October, 2018. The participants were given a survey to assess their perception and behavior of RS. T-test and the structural equation modeling were used to analyze gender differences in association between perception and behavior of RS. Results: For females, industry perception (&beta, = 0.17, p = 0.00), space perception (females: &beta, = 0.16, p = 0.00), and support perception (females: &beta, = 0.09, p = 0.03) had a significant positive effect on RS participation. For males, industry perception (males: &beta, = 0.13, p = 0.01) and type perception (males: &beta, = 0.23, p = 0.00) showed a significant positive impact on participation of RS. However, space perception of males (&beta, = &minus, 0.12, p = 0.01) and type perception of females (&beta, 0.11, p = 0.01) are negatively associated with their RS participation. The perception of experience was the most important factor influencing RS behaviors. Significant gender differences have appeared in all five different perception factors. The industry perception has significant and positive effects on both males and females&rsquo, RS participation. The type perception has significant positive effects on the male but negative on the female RS, while the space perception is just the opposite. The support perception has significant positive effects on the female RS practice but the influence is not obvious in the case of males. Conclusion: By adopting some measures, perception of RS may improve urban residents&rsquo, participation in RS.

The propagation properties of a pair of Lissajous singularities with opposite singularity indexes called the Lissajous singularity dipole (LSD) in free space are studied analytically and illustrated numerically. It is shown that the motion, creation, annihilation and change in the degree of polarization of the LSD, and change in the shape of Lissajous figures take place by suitably varying the waist width, off-axis distance or propagation distance. In particular, the creation and shift to infinity of a single Lissajous singularity may appear. A comparison with the free-space propagation of an optical vortex dipole and a C-dipole is also made.

The propagation was investigated of a pair of Lissajous singularities of opposite singularity index called the Lissajous singularity dipole (LSD) through an astigmatic lens. It is shown that after passing through the lens the positions of the singularities are inverted and more than two LSDs occur. Changes in the degree of polarization of the LSDs as well as in the shape of the Lissajous figures also occur. In addition, Lissajous singularities may take place at the focal plane, and a single Lissajous singularity may appear and vanish under certain conditions. The results are compared with those of previous work.

The interaction of the Lissajous singularity and singular Lissajous line in the presence of an astigmatic lens is studied. It is found that the singular Lissajous line is usually unstable, and disappears after passage through the lens. The creation and annihilation of one or two Lissajous singularities may take place by varying the astigmatic coefficient, off-axis parameter, and propagation distance. A comparison with the interaction of the Lissajous singularity and singular Lissajous line in the free-space propagation and in the presence of an ideal lens, and with the vortex–edge dislocation interaction is made. The results are illustrated numerically and interpreted analytically.

The interaction between a vortex and an edge dislocation nested in a cos‐Gaussian beam passing through a tilted lens was studied analytically and numerically. It is shown that in the presence of the tilted lens, by varying the cos‐part parameter of the beam, the slope of the edge dislocation, or the tilt coefficient of the lens, the topological charge is conserved for the case of the off‐axis edge dislocation, while charge conservation does not hold true for the case of an on‐axis edge dislocation, irrespective of the on‐axis or off‐axis vortex. The relation between the transverse positions (x, y) of vortices and the tilt coefficient is linear, and is interpreted.

A steady thermal model of photonic-bandgap fiber laser (PBFL) is presented. Temperature distribution in PBFL is analyzed by heat transfer equations and numerical finite-element method (FEM) separately. Thermal stress distribution caused by the temperature difference between the inner and outer claddings is calculated. The results show that the thermal stresses in this fiber structure are low less than the critical tensile stress in fused silica.

The temperature distribution and the thermal stress distribution of Bragg fiber laser are analyzed by solving thermal transfer equations. The changes of refractive index derived from the temperature and the thermal stress are discussed separately. Results indicate that the change of index refraction caused by temperature is larger than by thermal stress.

The propagation of Riemann-Silberstein (RS) vortices for Gaussian vortex beams with topological charges m=+1 through a lens is studied. It is shown that if there is an ideal lens, a RS vortex and a circular edge dislocation appear for Gaussian on-axis vortex beams, while only RS vortices take place for Gaussian off-axis vortex beams. In the presence of an astigmatic lens, there exist RS vortices but no edge dislocations for both Gaussian on-axis and off-axis beams. By varying the astigmatic coefficient, the off-axis parameter, and the propagation distance, the motion, creation, and annihilation of vortices may take place, and in the process, the total topological charge of RS vortices remains unchanged.