Hasil untuk "cond-mat"

S. Barroso-Solares, M. G. Zahedi, J. Pinto et al.

Herein we present the fabrication of hydrophobic and oleophilic poly(methyl methacrylate) based nanocomposite fibrous mats with magnetic properties, and their utilization for oil removal from stable water oil emulsions.

E. Silva, R. Marcon, S. Sarti et al.

Sani Y. Harouna-Mayer, Songsheng Tao, Z. Gong et al.

An approach is described for studying texture in nanostructured materials. The approach implements the real space texture PDF, txPDF, laid out in [Gong and Billinge (2018) arXiv:1805.10342 [cond-mat]]. It is demonstrated on a fiber textured polycrystalline Pt thin film. The approach uses 3D PDF methods to reconstruct the orientation distribution function (ODF) of the powder crystallites from a set of diffraction patterns taken at different tilt angles of the substrate with respect to the incident beam directly from the 3D PDF of the sample. A real space equivalent of the reciprocal space pole figure is defined in terms of interatomic vectors in the PDF and computed for various interatomic vectors in the Pt film. Further, it is shown how a valid isotropic PDF may be obtained from a weighted average over the tilt series, and the measurement conditions for the best approximant to the isotropic PDF from a single exposure, which for the case of the fiber textured film was in a nearly grazing incidence orientation of around 10 degrees. Finally, we describe an open source Python software package, Fourigui, that may be used to help in studies of texture from 3D reciprocal space data, and indeed for Fourier transforming and visualizing 3D PDF data in general.

Florian Hajek, M. Keller, W. Taube et al.

Abstract Hajek, F, Keller, M, Taube, W, von Duvillard, SP, Bell, JW, and Wagner, H. Testing-specific skating performance in ice hockey. J Strength Cond Res 35(12S): S70–S75, 2020—Skating performance generally determines overall performance in ice hockey but has not been measured adequately in the past. Consequently, the aim of the study was to develop and validate a specific overall skating performance test for ice hockey (SOSPT) that includes similar movements and intensities as in competition. Ten male elite under-14-year and under-18-year old ice hockey players performed the SOSPT (2 heats only) and a 40-m on-ice sprinting test twice within 8 days. Additionally, 14 under-15, 18 under-17, and 20 under-20 male elite ice hockey players performed only the SOSPT (4 heats). Time was measured from the first subject's movement during a V-start until crossing the line (40-m on-ice sprinting test), first touch of the shoulder on the mat (heat #1 in the SOSPT) or first touch of the puck with the stick (heat #2 in the SOSPT) using a hand stopwatch. We found a high test-retest reliability of the SOSPT and 40-m on-ice sprinting test (interclass correlation coefficient, >0.7; coefficient of variation, 0.70) between an expert rating and the SOSPT, and a low correlation between the 40-m on-ice sprinting test and the SOSPT in the under-14 and under-18 players. The results of the study reveal that the SOSPT is a reliable and valid test to determine the specific overall skating performance in ice hockey players and is more suitable compared with straight skating tests of the 40-m on-ice sprinting test.

P. Whitehead, Ryan T. Conners, T. S. Shimizu

Whitehead, PN, Conners, RT, and Shimizu, TS. The effect of in-season demands on lower-body power and fatigue in male collegiate hockey players. J Strength Cond Res 33(4): 1035-1042, 2019-The purpose of this study was to determine the effect of in-season demands, such as games, travel, and the subsequent fatigue related to these demands, on lower-body power (LBP) in collegiate hockey players. Two jump protocols (countermovement and squat jumps) were used to calculate LBP. Twenty-seven NCAA (National Collegiate Athletic Association) Division I male hockey players (age, 21.9 ± 1.4 years; height, 176.7 ± 6.5 cm; body mass, 81.4 ± 7.9 kg) participated in the study that spanned 18 weekly sessions. At each session, participants completed an 8-item fatigue questionnaire, which provided a cumulative numerical value for fatigue (total score of fatigue [TSF]), before performing maximal jumps on a contact mat. General linear modeling was conducted to compare dependent variables (jump height, relative LBP, TSF) across weekly sessions. Pearson product-moment correlation coefficients were calculated to examine the relationship between jump height and LBP across the jump protocols, as well as to examine the relationship of TSF with all measured variables. Jump height and LBP declined throughout the season with greater effect of travel observed following the longest travel sequence (p ≤ 0.05; η ≥ 0.60). Differences in TSF were observed from baseline (p ≤ 0.037), and a large effect was seen for away trips that included air travel (d ≥ 1.35). Total score of fatigue had a negative correlation with jump height and power during both jumps (r ≤ -0.742; p < 0.001). In conclusion, the in-season demands of ice hockey resulted in significant reductions in LBP throughout a hockey season, and the 8-item fatigue questionnaire is a sensitive tool reflective of athletic performance measures.

R. van den Tillaar

van den Tillaar, R. Comparison of step-by-step kinematics in repeated 30-m sprints in female soccer players. J Strength Cond Res 32(7): 1923-1928, 2018-The aim of this study was to compare kinematics in repeated 30-m sprints in female soccer players. Seventeen subjects performed seven 30-m sprints every 30 seconds in one session. Kinematics was measured with an infrared contact mat and laser gun, and running times with an electronic timing device. The main findings were that sprint times increased in the repeated-sprint ability test. The main changes in kinematics during the repeated-sprint ability test were increased contact time and decreased step frequency, whereas no change in step length was observed. The step velocity increased in almost each step until the 14th, which occurred around 22 m. After this, the velocity was stable until the last step, when it decreased. This increase in step velocity was mainly caused by the increased step length and decreased contact times. It was concluded that the fatigue induced in repeated 30-m sprints in female soccer players resulted in decreased step frequency and increased contact time. Using this approach in combination with a laser gun and infrared mat for 30 m makes it very easy to analyze running kinematics in repeated sprints in training. This extra information gives the athlete, coach, and sports scientist the opportunity to give more detailed feedback and helps to target these changes in kinematics better to enhance repeated-sprint performance.

Garrett M Hester, Z. Pope, John H. Sellers et al.

Shinya Ogaya, T. Ikezoe, N. Soda et al.

Xantal Borràs, Xavier Balius, F. Drobnic et al.

J. Mayhew, Jeremy Houser, B. B. Briney et al.

G. Moir, P. Shastri, Chris Connaboy

D. Stauffer, D. Sornette, D. Sornette

In the Cont–Bouchaud model [cond-mat/9712318] of stock markets, percolation clusters act as buying or selling investors and their statistics controls that of the price variations. Rather than fixing the concentration controlling each cluster connectivity artificially at or close to the critical value, we propose that clusters shatter and aggregate continuously as the concentration evolves randomly, reflecting the incessant time evolution of groups of opinions and market moods. By the mechanism of “sweeping of an instability” [Sornette, J. Phys. I 4, 209(1994)], this market model spontaneously exhibits reasonable power-law statistics for the distribution of price changes and accounts for the other important stylized facts of stock market price fluctuations.

C. Castagna, A. Chaouachi, E. Rampinini et al.

D. Klimov, D. Thirumalai

We point out that the correlation between folding times and $\sigma = (T_{\theta } - T_{f})/T_{\theta }$ in protein-like heteropolymer models where $T_{\theta }$ and $T_{f}$ are the collapse and folding transition temperatures was already established in 1993 before the other presumed equivalent criterion (folding times correlating with $T_{f}$ alone) was suggested. We argue that the folding times for these models show no useful correlation with the energy gap even if restricted to the ensemble of compact structures as suggested by Karplus and Shakhnovich (cond-mat/9606037).

P. Talkner, P. Hänggi

Starting out from the recently established quantum correlation function expression of the characteristic function for the work performed by a force protocol on the system in Talkner et al (2007 Phys. Rev. E 75 050102 (Preprint cond-mat/0703213)) the quantum version of the Crooks fluctuation theorem is shown to emerge almost immediately by the mere application of an inverse Fourier transformation.

Q. Zhang, S. Thota, F. Guillou et al.

Magnetic properties of a series of (La0.7Sr0.3MnO3/SrRuO3) superlattices, where the SrRuO3 layer thickness is varying, are examined. A room-temperature magnetocaloric effect is obtained owing to the finite size effect which reduces the TC of La0.7Sr0.3MnO3 layers. While the working temperature ranges are enlarged,, -DeltaSmax values remains similar to the values in polycrystalline La0.7Sr0.3MnO3. Consequently, the relative cooling powers are significantly improved, the microscopic mechanism of which is related to the effect of the interfaces at La0.7Sr0.3MnO3/SrRuO3 and higher nanostructural disorder. This study indicates that artificial oxide superlattices/multilayers might provide an alternative pathway in searching for efficient room-temperature magnetic refrigerators for (nano)microscale systems.

M. Saad, P. Baxter, R. Bowman et al.

E. Emberly, G. Kirczenow

M. Simkin, V. Roychowdhury

Recently we proposed a model in which when a scientist writes a manuscript, he picks up several random papers, cites them and also copies a fraction of their references (cond-mat/0305150). The model was stimulated by our discovery that a majority of scientific citations are copied from the lists of references used in other papers (cond-mat/0212043). It accounted quantitatively for several properties of empirically observed distribution of citations. However, important features, such as power-law distribution of citations to papers published during the same year and the fact that the average rate of citing decreases with aging of a paper, were not accounted for by that model. Here we propose a modified model: when a scientist writes a manuscript, he picks up several random recent papers, cites them and also copies some of their references. The difference with the original model is the word recent. We solve the model using methods of the theory of branching processes, and find that it can explain the aforementioned features of citation distribution, which our original model couldn't account for. The model can also explain "sleeping beauties in science", i.e., papers that are little cited for a decade or so, and later "awake" and get a lot of citations. Although much can be understood from purely random models, we find that to obtain a good quantitative agreement with empirical citation data one must introduce Darwinian fitness parameter for the papers.

Luciano da Fontoura Costa, F. N. Silva

While the majority of approaches to the characterization of complex networks has relied on measurements considering only the immediate neighborhood of each network node, valuable information about the network topological properties can be obtained by considering further neighborhoods. The current work considers the concept of virtual hierarchies established around each node and the respectively defined hierarchical node degree and clustering coefficient (introduced in cond-mat/0408076), complemented by new hierarchical measurements, in order to obtain a powerful set of topological features of complex networks. The interpretation of such measurements is discussed, including an analytical study of the hierarchical node degree for random networks, and the potential of the suggested measurements for the characterization of complex networks is illustrated with respect to simulations of random, scale-free and regular network models as well as real data (airports, proteins and word associations). The enhanced characterization of the connectivity provided by the set of hierarchical measurements also allows the use of agglomerative clustering methods in order to obtain taxonomies of relationships between nodes in a network, a possibility which is also illustrated in the current article.