RESUMEN

The present research investigated the association between a series of motivational factors and burnout syndrome among elite skiers at the contextual level within the Hierarchical Model of Intrinsic and Extrinsic Motivation (HMIEM). There are 352 subjects (258 males, 94 females, aged 18 to 25 years) across five skiing events from three sport universities in this study. Four psychological scales related to motivational factors and burnout syndrome were completed by subjects. Overall, the result showed that a task-involving climate had a positive relationship with basic psychological needs, eliciting a positive pathway to autonomous motivation, and thus negatively affecting burnout syndromes. On the other hand, an ego-involving climate had a negative relationship with basic psychological needs, eliciting a negative pathway to amotivation, and then positively affecting burnout syndromes. The results underscore the intricate associations between a variety of motivational factors and athletes' burnout syndrome, supporting the need to incorporate burnout syndrome elements into the outcomes of HMIEM sequence.

Asunto(s)

Atletas , Motivación , Esquí , Humanos , Femenino , Masculino , Adulto , Adulto Joven , Adolescente , Esquí/psicología , Atletas/psicología , Atletas/estadística & datos numéricos , Agotamiento Psicológico/psicología , Agotamiento Profesional/psicología

RESUMEN

First-principles calculations were employed to investigate the impact of quantum ionic fluctuations and lattice anharmonicity on the crystal structure and superconductivity of Pm3̄ AlM(M = Hf, Zr)H6 at pressures of 0.3-21.2 GPa (AlHfH6) and 4.7-39.5 GPa (AlZrH6) within the stochastic self-consistent harmonic approximation. A correction is predicted for the crystal lattice parameters, phonon spectra, and superconducting critical temperatures, previously estimated without considering ionic fluctuations on the crystal structure and assuming the harmonic approximation for lattice dynamics. The findings suggest that quantum ionic fluctuations have a significant impact on the crystal lattice parameters, phonon spectra, and superconducting critical temperatures. Based on our anharmonic phonon spectra, the structures will be dynamically stable at 0.3 GPa for AlHfH6 and 6.2 GPa for AlZrH6, ∼6 and 7 GPa lower than pressures given by the harmonic approximation, respectively. Due to the anharmonic correction of their frequencies, the electron-phonon coupling constants (λ) are suppressed by 28% at 11 GPa for AlHfH6 and 22% at 30 GPa for AlZrH6, respectively. The decrease in λ causes Tc to be overestimated by ∼12 K at 11 GPa for AlHfH6 and 30 GPa for AlZrH6. Even if the anharmonic and quantum effects are not as strong as those of Pm3̄n-AlH3, our results also indicate that metal hydrides with hydrogen atoms in interstitial sites are subject to anharmonic effects. Our results will inevitably stimulate future high-pressure experiments on synthesis, structural, and conductivity measurements.

RESUMEN

Two-dimensional metallic electrode materials with high energy density and excellent rate capability are crucial in rechargeable ion batteries. In this work, two-dimensional V2N MXene monolayer has been predicted to be an attractive candidate anode material for rechargeable lithium, sodium, and magnesium ion batteries by first-principles calculations. We observe that V2N monolayer is a metallic compound. The ion diffusion barriers on V2N monolayer are predicted to be 0.025, 0.014, 0.004, and 0.058 eV for Li, Na, K, and Mg ions, respectively, which are rather low on the state-of-the-art two-dimensional energy storage materials. In addition, the calculated theoretical capacities of V2N MXene monolayer are 925 mAh/g for Li ion, 463 mAh/g for Na ion, and 1850 mAh/g for Mg ion. The capacity of Li ions on V2N monolayer is much higher than that of Li ions on the conventional anode graphite, and the extralarge capacity for Mg ions on V2N monolayer is ascribed to the two-electron reaction and multilayer adsorption of Mg ions. Last, the average open circuit voltages of the V2N MXene monolayer are also calculated to be 0.32 V for Li ions, 0.24 V for Na ions, and 0.34 V for Mg ions. These results provide a fundamental insight into electrochemical energy storage applications of two-dimensional V2N MXene monolayer as a suitable candidate anode material for rechargeable Li, Na, and Mg ion batteries on the atomic scale.

RESUMEN

Although it is well known that hydrogen bonds commonly exist in ammonia clusters and play an important role, there are still many challenges in understanding the electronic structure properties of hydrogen bonds. In this paper, the geometric and electronic structure properties of cyclic ammonia clusters are investigated by using first-principles density functional theory (DFT) and the Møller-Plesset perturbation theory (MP2). The calculation results show that the pentamer and hexamer have deviated from the perfect plane, while the trimer and tetramer present planarization that has been confirmed by infrared (IR) spectra. The electronic structure analysis further shows that the covalent properties play a non-negligible role in hydrogen bonding. The results also indicate that the electronic structure facilitates structure planarization. Our work not only provides insight into the role and nature of hydrogen bonds in ammonia clusters but also provides a theoretical basis for frontier science in fields such as atmospheric haze and biomolecular functions.

RESUMEN

Systematic first-principles calculations are designed to investigate the interaction between isolated S8, lithium polysulfide (PS) Li2S n (n = 1-8, at different lithiated stages) clusters and two-dimensional (2D) graphdiyne (GDY) materials. By the calculations of their detailed interaction, we investigate the 2D GDY ability of trapping lithium PS clusters in order to evaluate the anchoring effect of 2D GDY materials for lithium-sulfur batteries. The theoretical results show that lithium PS intermediates/B-GDY systems have a moderate binding energy, indicating that the 2D B-GDY material is a suitable candidate for the anchoring materials of Li-S batteries. From the analysis of their charge density differences, the B-S σ bond and Li bond play an important role in the anchoring effect of 2D B-GDY substrates.

RESUMEN

We have extensively explored the stable crystal structures of early-transition metal pernitrides (TMN2, TM = Ti, V, Cr, Mn, Zr, Nb, Mo, Hf, and Ta) at ambient and high pressures using effective CALYPSO global structure search algorithm in combination with first-principles calculations. We identified for the first time the ground-state structures of MnN2, TaN2, NbN2, VN2, ZrN2, and HfN2 pernitrides, and proposed their synthesis pressures. All predicted crystal structures contain encapsulated N2 dumbbells in which the two N atoms are singly bonded to a [N2]4- pernitride unit utilizing the electrons transferred from the transition metals. The strong nature of the single dinitrogen bond and transition metal-nitrogen charge transfer induce extraordinary mechanic properties in the predicted transition metal pernitrides including large bulk modulus and high Vickers hardness. Among the predictions the hardness of MnN2 is 36.6 GPa, suggesting that it is potentially a hard material. The results obtained in the present study are important to the understanding of structure-property relationships in transition metal pernitrides and will hopefully encourage future synthesis of these technologically important materials.

RESUMEN

A carbon-coated Mg0.5Ti2(PO4)3 polyanion material was prepared by the sol-gel method and then studied as the negative electrode materials for lithium-ion and sodium-ion batteries. The material showed a specific capacity of 268.6 mAh g-1 in the voltage window of 0.01-3.0 V vs Na+/Na0. Due to the fast diffusion of Na+ in the NASICON framework, the material exhibited superior rate capability with a specific capacity of 94.4 mAh g-1 at a current density of 5A g-1. Additionally, 99.1% capacity retention was achieved after 300 cycles, demonstrating excellent cycle stability. By comparison, Mg0.5Ti2(PO4)3 delivered 629.2 mAh g-1 in 0.01-3.0 V vs Li+/Li0, much higher than that of the sodium-ion cells. During the first discharge, the material decomposed to Ti/Mg nanoparticles, which were encapsulated in an amorphous SEI and Li3PO4 matrix. Li+ ions were stored in the Li3PO4 matrix and the SEI film formed/decomposed in subsequent cycles, contributing to the large Li+ capacity of Mg0.5Ti2(PO4)3. However, the lithium-ion cells exhibited inferior rate capability and cycle stability compared to the sodium-ion cells due to the sluggish electrochemical kinetics of the electrode.