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Search Results: 1 - 10 of 462365 matches for " Leszek A. Szmuchrowski "
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Electromyographic activity during maximal isometric contraction combined with local sinusoidal vibration
Jacielle C. Ferreira, Bruno M. L. Resende, Jo o B. Soldati, Jr., Jo o G. de Oliveira Claudino, Rafael S. Ribeiro, Bruno P. Couto, Leszek A. Szmuchrowski, Prof.
Biomedical Human Kinetics , 2011, DOI: 10.2478/v10101-011-0008-3
Abstract: Study aim: To compare the electromyographic activity during maximal isometric contraction alone or combined with local sinusoidal vibration. Material and methods: A group of 6 men aged 23 - 29 years performed 3 maximal voluntary contractions of the dominant elbow flexors lasting 10 s each and separated by 5-min intermissions. One repetition was without vibration, one was associated with 15-Hz and the other one with 20-Hz vibrations of 5-mm amplitude, the sequence of repetitions being random. A new system to generate local vibration was applied, the parameters of the vibratory stimulus being measured using an accelerometer. Force and EMG activity were also measured. The subjects performed the task in sitting position in a Scott Bench-type device. Results: Mean acceleration RMS significantly (p<0.01) differed between vibration frequencies for the X, Y, Z-axes. No significant differences were found, however, for EMG RMS. Vibration frequencies coincided with the machine-predicted ones; acceleration frequencies around 5 Hz were present in all situations, even without vibration, most likely brought about by tremor. Conclusion: The local vibration applied was not enough to generate different responses in EMG activity. The features of vibratory stimulus confirmed the expected frequency range and revealed frequencies around 5 Hz, that could be attributed to muscle tremor.
Efeito da aplica??o de vibra??o mecanica sobre a impuls?o vertical
Couto, Bruno Pena;Costa, Guilherme Augusto Silva da;Barbosa, Marcos Pinotti;Chagas, Mauro Heleno;Szmuchrowski, Leszek Antoni;
Motriz: Revista de Educa??o Física , 2012, DOI: 10.1590/S1980-65742012000300001
Abstract: several studies have indicated that vibratory training can contribute to the development of muscle strength and sports performance. the aim of this study was to investigate the effect of mechanical vibration application in the direction of the result of muscle forces vector addition on vertical jump. eighteen volunteers performed vertical jump test 20 s before and after the application of mechanical vibration of 20 hz and 6 mm amplitude in the direction of the result of muscle forces vector addition. the same volunteers were used as control group by performing the vertical jump test without pre- and post-test vibration application. the vibratory training caused an significantly increase of 8,5% at vertical jump height while jump height did not vary significantly in the control experiment. these data suggest that the application of mechanical vibration in the direction of muscle forces vector addition can increase the performance in vertical jumps.
Chaotic behavior of uniformly convergent nonautonomous systems with randomly perturbed trajectories
Leszek Sza?a
Mathematics , 2014,
Abstract: We study nonautonomous discrete dynamical systems with randomly perturbed trajectories. We suppose that such a system is generated by a sequence of continuous maps which converges uniformly to a map $f$. We give conditions, under which a recurrent point of a (standard) autonomous discrete dynamical system generated by the limit function $f$ is also recurrent for the nonautonomous system with randomly perturbed trajectories. We also provide a necessary condition for a nonautonomous discrete dynamical system to be nonchaotic in the sense of Li and Yorke with respect to small random perturbations.
Mechanical and Thermal Dehydrogenation of Lithium Alanate (LiAlH4) and Lithium Amide (LiNH2) Hydride Composites
Robert A. Varin,Leszek Zbroniec
Crystals , 2012, DOI: 10.3390/cryst2020159
Abstract: Hydrogen storage properties of the (nLiAlH 4 + LiNH 2) hydride composite where n = 1, 3, 11.5 and 30, synthesized by high energy ball milling have been investigated. The composite with the molar ratio n = 1 releases large quantities of H 2 (up to ~5 wt.%) during ball milling up to 100–150 min. The quantity of released H 2 rapidly decreases for the molar ratio n = 3 and is not observed for n = 11.5 and 30. The XRD studies indicate that the H 2 release is a result of a solid state decomposition of LiAlH 4 into (1/3)Li 3AlH 6 + (2/3)Al + H 2 and subsequently decomposition of (1/3)Li 3AlH 6 into LiH + (1/3)Al + 0.5H 2. Apparently, LiAlH 4 is profoundly destabilized during ball milling by the presence of a large quantity of LiNH 2 (37.7 wt.%) in the n = 1 composite. The rate of dehydrogenation at 100–170 °C (at 1 bar H 2) is adversely affected by insufficient microstructural refinement, as observed for the n = 1 composite, which was milled for only 2 min to avoid H 2 discharge during milling. XRD studies show that isothermal dehydrogenation of (nLiAlH 4 + LiNH 2) occurs by the same LiAlH 4 decomposition reactions as those found during ball milling. The ball milled n = 1 composite stored under Ar at 80 °C slowly discharges large quantities of H 2 approaching 3.5 wt.% after 8 days of storage.
Correlation between asymmetric profiles in slits and standard prewetting lines
Salvador A. Sartarelli,Leszek Szybisz
Papers in Physics , 2009, DOI: 10.4279/pip.010001
Abstract: The adsorption of Ar on substrates of Li is investigated within the framework of a density functional theory which includes an effective pair potential recently proposed. This approach yields good results for the surface tension of the liquid-vapor interface. The behavior of the adsorbate in the cases of a single planar wall and a slit geometry is analyzed as a function of temperature. Asymmetric density profiles are found for fluid confined in a slit built up of two identical planar walls leading to the spontaneous symmetry breaking (SSB) effect. We found that the asymmetric solutions occur even above the wetting temperature $T_w$ in a range of average densities $ho^*_{ssb1} le ho^*_{av} le ho^*_{ssb2}$, which diminishes with increasing temperatures until its disappearance at the critical prewetting point $T_{m cpw}$. In this way a correlation between the disappearance of the SSB effect and the end of prewetting lines observed in the adsorption on a one-wall planar substrate is established. In addition, it is shown that a value for $T_{m cpw}$ can be precisely determined by analyzing the asymmetry coefficients.
Full correspondence between asymmetric filling of slits and first-order phase transition lines
Leszek Szybisz,Salvador A. Sartarelli
AIP Advances , 2011, DOI: 10.1063/1.3664297
Abstract: Adsorption on single planar walls and filling of slits with identical planar walls are investigated in the frame of the density functional theory. In this sort of slits the external potential is symmetric with respect to its central plane. Calculations were carried out by applying both the canonical and grand canonical ensembles (CE and GCE, respectively). The behavior is analyzed by varying the strength of the adsorbate-substrate attraction, the temperature T, and the coverage Γ . Results obtained for physisorption of Xe on alkaline surfaces are reported in the present work. Prewetting (PW) lines and wetting temperatures, Tw, are determined from the analysis of adsorption on single walls. The filling of slits is analyzed for temperatures T > Tw. It is found that whenever for a given Xe-substrate combination the adsorption on a single wall exhibits a first-order wetting transition then asymmetric profiles that break the left-right symmetry of the external potential appear in the filling of an equivalent slit. These spontaneously symmetry breaking (SSB) solutions occur in a restricted range of Γ with a T-dependent width. In the case of closed slits analyzed in the CE scheme, the obtained asymmetric profiles exhibit lower Helmholtz free energies than the symmetric species and, therefore, could be stabilized in this geometry. For open slits, the GCE scheme yields all the symmetric and SSB states in the corresponding convex regimes of the free energy. It is shown that both the CE and the GCE frames yield three coexistent states, two symmetric and one asymmetric twofold degenerate. Both a PW line and the related SSB effect terminate at the same temperature. For rather strongly attractive surfaces reentrant SSB states are found at a fixed value of T.
Density profiles of Ar adsorbed in slits of CO_2: spontaneous symmetry breaking
Leszek Szybisz,Salvador A. Sartarelli
Physics , 2007, DOI: 10.1063/1.2895747
Abstract: A recently reported symmetry breaking of density profiles of fluid argon confined by two parallel solid walls of carbon dioxide is studied. The calculations are performed in the framework of a nonlocal density functional theory. It is shown that the existence of such asymmetrical solutions is restricted to a special choice for the adsorption potential, where the attraction of the solid-fluid interaction is reduced by the introduction of a hard-wall repulsion. The behavior as a function of the slit's width is also discussed. All the results are placed in the context of the current knowledge on this matter.
On Some Integrated Approaches to Inference
Mark A. Kon,Leszek Plaskota
Computer Science , 2012,
Abstract: We present arguments for the formulation of unified approach to different standard continuous inference methods from partial information. It is claimed that an explicit partition of information into a priori (prior knowledge) and a posteriori information (data) is an important way of standardizing inference approaches so that they can be compared on a normative scale, and so that notions of optimal algorithms become farther-reaching. The inference methods considered include neural network approaches, information-based complexity, and Monte Carlo, spline, and regularization methods. The model is an extension of currently used continuous complexity models, with a class of algorithms in the form of optimization methods, in which an optimization functional (involving the data) is minimized. This extends the family of current approaches in continuous complexity theory, which include the use of interpolatory algorithms in worst and average case settings.
Finite-time singularity in the evolution of hyperinflation episodes
Martin A. Szybisz,Leszek Szybisz
Quantitative Finance , 2008,
Abstract: A model proposed by Sornette, Takayasu, and Zhou for describing hyperinflation regimes based on adaptive expectations expressed in terms of a power law which leads to a finite-time singularity is revisited. It is suggested to express the price index evolution explicitly in terms of the parameters introduced along the theoretical formulation avoiding any combination of them used in the original work. This procedure allows to study unambiguously the uncertainties of such parameters when an error is assigned to the measurement of the price index. In this way, it is possible to determine an uncertainty in the critical time at which the singularity occurs. For this purpose, Monte Carlo simulation techniques are applied. The hyperinflation episodes of Peru (1969-90) and Weimar Germany (1920-3) are reexamined. The first analyses performed within this framework of the very extreme hyper-inflations occurred in Greece (1941-4) and Yugoslavia (1991-4) are reported. The study of the hyperinflation spiral experienced just nowadays in Zimbabwe predicts a singularity, i.e., a complete economic crash within two years.
Structure and properties of selected cemented carbides and cermets covered with TiN/(Ti,Al,Si)N/TiN coatings obtained by the cathodic arc evaporation process
Dobrza?ski, Leszek A.;Golombek, Klaudiusz;
Materials Research , 2005, DOI: 10.1590/S1516-14392005000200002
Abstract: this study presents the results of microstructural examinations, mechanical tests and service performance tests carried out on thin tin/(ti,al,si)n/tin wear resistance coatings obtained by the cae process on cermet and cemented carbide substrates. microstructural examinations of the applied coatings and the substrate were made with an opton dsm 940 sem and a leica mef4a light microscope. adhesion of the coatings on cemented carbides and cermets was measured using the scratch test. the cutting properties of the materials were determined from service tests in which continuous machining of c45e steel was carried out. the hardness of the substrate and the microhardness of the coatings were determined with a duh 202 shimadzu ultra microhardness tester with a load of 70 mn. roughness tests were also carried out before applying the coatings and after the pvd process. cutting tests confirmed the advantages of the tin/(ti,al,si)n/tin type coatings obtained using the pvd method in the cae mode on cemented carbides and cermets, as a material that undergoes very low abrasive, thermal and adhesion wear. these coatings extend tool life compared to commercially available uncoated tools with single and multi-layer coatings deposited using pvd/cvd methods.
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