Hasil untuk "cond-mat"

P. T. Ríos-Gallardo, L. E. Carranza-García, Martin S. Dietze-Hermosa et al.

Ríos-Gallardo, PT, Carranza-García, LE, Dietze-Hermosa, M, Gonzalez, MP, Balsalobre-Fernández, C, Dorgo, S, and Montalvo, S. Validity and reliability of an AI-based jump height app vs. infrared contact mat: minimal influence of skin pigmentation under standardized lighting. J Strength Cond Res XX(X): 000–000, 2026—This study examined the validity, reliability, and visual robustness of an artificial intelligence-based mobile application (My Jump Lab) for measuring countermovement jump (CMJ) and squat jump (SJ) height across a heterogeneous athletic population. A dual-session, test–retest design was implemented with 43 recreationally active adults (age: 21.2 ± 2.4 years), who performed 3 maximal-effort SJ and CMJ trials per session. Jump height was concurrently recorded using a force platform and the AI-based app. Validity was assessed through linear regression and Bland–Altman analyses, and reliability was evaluated using intraclass correlation coefficients (ICC) and coefficient of variation (CV). A linear mixed-effects model tested whether body dimensions, lighting conditions, or skin pigmentation influenced AI accuracy. The AI systematically overestimated jump height (bias = +2.81 cm, p 0.05). Although absolute error was higher in SJ, AI-based estimates remained stable across conditions. The level of significance was set at p ≤ 0.05. In conclusion, the AI-based app provides a valid and reliable alternative for field-based jump assessment. However, practitioners should interpret absolute values cautiously, especially for SJ. These findings support the utility of computer vision and AI to democratize biomechanical assessments without sacrificing measurement quality.

J. Moratelli, Clynton Lourenço Corrêa, A. Sonza et al.

ABSTRACT Moratelli, JA, Corrêa, CL, Sonza, A, and Guimarães, ACdA. Functional training and mat pilates are effective in improving cardiorespiratory capacity and strength in people with Parkinson's disease: a randomized clinical trial with follow-up. J Strength Cond Res XX(X): 000-000, 2025-The objective of this study was to analyze the effects of 2 12-week interventions with functional training and Mat Pilates on cardiorespiratory capacity, lower limb strength, and handgrip strength in people with Parkinson's disease, both in the short term and in the long term. Randomized clinical trial with people with Parkinson's randomized into 3 groups: functional training (n = 12), Mat Pilates (n = 11), and control group (n = 12), as well as 11 healthy individuals matched by sex and age, constituting the healthy reference group. The exercise groups received 2 60-minute sessions per week for 12 weeks. Assessments were conducted before and after the interventions with all participants and included submaximal functional capacity, handgrip strength, and lower limb muscle strength. Significance level p ≤ 0.05. In the intragroup comparison of functional training and Mat Pilates, the results indicated significant improvements in cardiorespiratory capacity and lower limb muscle strength in both the short and long terms (p < 0.001), as well as short-term improvement in right handgrip strength (p = 0.003). In the control group, a deterioration in right leg extension strength was observed in the short term and at the follow-up (p = 0.038). The study suggests that 12 weeks of functional training and Mat Pilates are effective in improving cardiorespiratory fitness, lower limb muscle strength, and right-hand handgrip strength in individuals with Parkinson's disease. These benefits are particularly relevant as they may contribute to maintaining autonomy, mobility, and quality of life in this population, reinforcing the importance of physical exercise as a complementary treatment for Parkinson's disease.

Mohammad Ghanem, P. Dollfus, J. Saint-Martin et al.

The progress in DFT-based description of the electron-phonon scattering allowed to describe the relaxation dynamics of hot or photoexcited electrons in several materials, in very good agreement with time-resolved spec- troscopy experiments [1-3]. As hot carriers also start to attract attention in the context of emerging concepts for energy conversion, here we present our first results related to the coupling of ab initio data with device-oriented Monte Carlo simulation methods [4]. We show that DFT-based description of the electron-phonon intervalley scattering in GaAs, coupled with stochastic Monte Carlo method, allows to describe the energy transfer from electrons to phonons in transient regime, in good agreement with previous time-resolved photoemission experiments. [1] J. Sjakste et al, J. Phys: Cond. Mat. 30, 353001 (2018). [2] Chen, Sjakste et al, PNAS 117, 21962-21967 (2020). [3] H. Tanimura et al, Phys. Rev. B 100, 035201 (2019). [4] R. Sen, N. Vast, J. Sjakste, Appl. Phys. Lett. 120, 082101 (2022).

Z. Horváth, P. Horváthy, P. Stichel

J. Tallon, J. Loram

Abstract Underdoped high- T c superconductors are frequently characterised by a temperature, T * , below which the normal-state pseudogap opens. Two different “phase diagrams” based on the doping ( p ) dependence of T * are currently considered: one where T * falls to zero at a critical doping state and the other where T * merges with T c in the overdoped region. By examining the temperature dependence of the NMR Knight shift and relaxation rate, entropy, resistivity, infrared conductivity, Raman scattering, ARPES and tunnelling data, it is concluded that the second scenario is not at all supported. Neither can one distinguish a small and a large pseudogap as is often done. T * is an energy scale, which falls abruptly to zero at p =0.19. Colour figures are available at cond-mat/0005063.

Phạm Thành Tâm Hồ, Nguyễn Thái Nghe, N. C. Ngôn et al.

Sử dụng năng lượng mặt trời trong nuôi trồng thủy sản là giải pháp phát triển bền vững mà nhà nước đang khuyến khích. Bài báo này nhằm mục tiêu giới thiệu và cung cấp phương pháp triển khai giải thuật dò tìm và bám theo điểm công suất cực đại của tấm pin quang điện (tấm pin năng lượng mặt trời) dựa trên độ điện dẫn của tấm pin (giải thuật Incremental Conductance Maximum Power Point Tracking – Ind. Cond. MPPT). Đây là phần quan trọng để tạo cơ sở triển khai sử dụng năng lượng mặt trời trong các ao nuôi, đặc biệt là giải quyết nhu cầu về năng lượng cho các dàn quạt nước ao tôm (dùng cho cung cấp ôxy và đảo nước trong ao), vì nó giúp khai thác tối đa nguồn năng lượng từ tấm pin năng lượng mặt trời. Dựa trên cơ sở lý thuyết về mô hình của tấm pin quang điện, giải thuật Incremental Conductance được triển khai trong cấu hình mạch chuyển đổi điện áp DC-DC kiểu boost xen kẽ được điều khiển bởi bộ điều khiển kỹ thuật số khả trình (vi điều khiển STM32F1). Kết quả triển khai cho thấy điện áp tại điểm công suất cực đại của hệ pin được duy trì ổn định, công suất trích xuất được điều khiển bám theo công suất khả dụng tối đa của hệ các tấm pin, hệ thống với giải thuật Ind...

R. H. Sassi, W. Dardouri, M. H. Yahmed et al.

Tyler D Whitmer, A. Fry, Charles M Forsythe et al.

J. García-López, J. C. Morante, A. Ogueta-Alday et al.

Tom Reeve, C. Tyler

Ian C. Kenny, A. Ó. Cairealláin, T. Comyns

Didier Poilblanc

Coulomb repulsion between electrons moving on a frustrated lattice can give rise, at simple commensurate electronic densities, to exotic insulating phases of matter. Such a phenomenon is illustrated using an extended t--J model on a planar pyrochlore lattice for which the work on the quarter-filled case [cond-mat/0702367] is complemented and extended to 1/8- and 3/8-fillings. The location of the metal-insulator transition as a function of the Coulomb repulsion is shown to depend strongly on the sign of the hopping. Quite generally, the metal-insulator transition is characterized by lattice symmetry breaking but the nature of the insulating Mott state is more complex than a simple Charge Density Wave. Indeed, in the limit of large Coulomb repulsion, the physics can be described in the framework of (extended) quantum fully-packed loop or dimer models carrying extra spin degrees of freedom. Various diagonal and off-diagonal plaquette correlation functions are computed and the low-energy spectra are analyzed in details in order to characterize the nature of the insulating phases. We provide evidence that, as for an electronic density of n=1/2 (quarter-filling), the system at $n=1/4$ or $n=3/4$ exhibits also plaquette order by forming a (lattice rotationally-invariant) Resonating-Singlet-Pair Crystal, although with a quadrupling of the lattice unit cell (instead of a doubling for $n=1/2$) and a 4-fold degenerate ground state. Interestingly, qualitative differences with the bosonic analog (e.g. known to exhibit columnar order at n=1/4) emphasize the important role of the spin degrees of freedom in e.g. stabilizing plaquette phases w.r.t. rotational symmetry-breaking phases.

N. Read

We comment on the recent paper by Scarola, Park, and Jain [Nature v. 406, p. 863 (2000); cond-mat/0012030] on a trial wavefunction calculation of pairing in a fractional quantum Hall system at nu=5/2. We point out two errors that invalidate the claimed calculations of a binding energy for Cooper pairs and of an energy gap for charged excitations.

T. Masuda, A. Zheludev, A. Bush et al.

Exchanged interactions in recently observed helical structure in LiCu2O2 is probed by inelastic neutron scattering. The main conlusions of Refs. [1,2] are confirmed: nn interactions in single chains are ferromagnetic and frustrated by nnn antiferromagnetic ones. However, in apparent disagreement with Refs. [1,2] double-chain interactions are found to be of the same order of magnitude as the single-chain ones, and thus involved in the frustration mechanism. [1] Drechsler et al., cond-mat/0411418. [2] A. Gippius et al. Phys. Rev. B 70 (2004), R01426; cond-mat/0312576.

D. Foerster, H. Kachkachi

Warning: We have recently discovered a technical error in the paper cond-mat/9504032 and entitled here above, that invalidates part but not all of our conclusions. A corrected version will be soon put in.

A. Liebsch

A detailed comparison of QMC/DMFT results for the non-isotropic two-band Hubbard model by Liebsch [Phys. Rev. B 70, 165103 (2004)] and C. Knecht, N. Bluemer, and P. G. J. van Dongen [cond-mat/0505106 (submitted to Phys. Rev. Lett.)] is given. Both results are shown to be in excellent agreement. Thus, the claims by Knecht et al.: ``The second transition [was] not seen in earlier studies using QMC and IPT'' and ``Our high-precision data correct earlier QMC results by Liebsch'' are shown to be unfounded.

Dirk Helbing, Martin Treiber

This contribution presents a derivation of the steady-state distribution of velocities and distances of vehicles in freeway traffic which has been suggested for the evaluation of interaction potentials among vehicles (see preprint cond-mat/0301484). Despite the forwardly directed interactions and the additional driving terms in vehicle traffic, the steady-state velocity and distance distributions agree with the equilibrium distributions of classical many-particle systems with symmetrical interactions, if the system is large enough. Finally, this analytical result is confirmed by computer simulations.

Leon Balents, Lorenz Bartosch, Anton Burkov et al.

We study the phases of doped spin S=1/2 quantum antiferromagnets on the square lattice, as they evolve from paramagnetic Mott insulators with valence bond solid (VBS) order at zero doping, to superconductors at moderate doping. The interplay between density wave/VBS order and superconductivity is efficiently described by the quantum dimer model, which acts as an effective theory for the total spin S=0 sector. We extend the dimer model to include fermionic S=1/2 excitations, and show that its mean-field, static gauge field saddle points have projective symmetries (PSGs) similar to those of `slave' particle U(1) and SU(2) gauge theories. We account for the non-perturbative effects of gauge fluctuations by a duality mapping of the S=0 dimer model. The dual theory of vortices has a PSG identical to that found in a previous paper (L. Balents et al., cond-mat/0408329) by a duality analysis of bosons on the square lattice. The previous theory therefore also describes fluctuations across superconducting, supersolid and Mott insulating phases of the present electronic model. Finally, with the aim of describing neutron scattering experiments, we present a phenomenological model for collective S=1 excitations and their coupling to superflow and density wave fluctuations.

G. M. Minkov, S. A. Negashev, O. E. Rut et al.

It is shown that a new kind of information can be extracted from the Fourier transform of negative magnetoresistance (MR) in 2D semiconductor structures. The procedure proposed provides the information on the area distribution function of the closed paths and on the area dependence of the mean length of closed paths $\bar{L} (S)$ . Based on this line of attack the method of analysis of the negative MR is suggested. The method is used for data treatment of negative MR in 2D structures. In previous version (cond-mat/9902038) we suppoused that the difference in area dependence of $\bar{L} (S)$ for structures investigated came from the difference in scattering ansotropy. The more detailed analysis shows that main reason for such difference is different relations between momentum and phase relaxation times.

Steven H. Simon, Patrick A. Lee

Volovik and Kopnin make two seperate points regarding our recent paper (S. H. Simon and P. A. Lee, PRL 78, 1548 (1997); cond-mat/9611133). First they note that the scaling regime we address in our paper is limited by the curvature of the Fermi surface, and secondly they note that the crossover scale derived in our paper is incorrect. These points are valid and are discussed in this reply. With the exception of the incorrectly predicted crossover scale, the results of our paper remain unchanged.