Low A0 Research Articles

Individual Acceleration-Speed Profile Variables: Comparison and Reliability Between Linear and Curvilinear Sprints.

Miras-Moreno, S, García-Ramos, A, Sašek, M, Cvjetičanin, O, Šarabon, N, Kavčič, I, and Smajla, D. Individual acceleration-speed profile variables: comparison and reliability between linear and curvilinear sprints. J Strength Cond Res XX(X): 000-000, 2024-The aim of this study was to compare linear sprint (LS) and curvilinear sprint (CS) to provide (a) the goodness-of-fit of individual acceleration-speed profile (ASP) and (b) the magnitude and within- and between-session reliability of the ASP variables (A0 [theoretical maximal acceleration], S0 [theoretical maximal velocity], and ASslope [slope of the linear ASP]). Twenty-one sports science students performed 2 identical experimental sessions composed of 3 LS trials and 6 CS trials (3 for each testing side). The individual ASP was modeled considering only the fastest or combining the 3 trials of each sprint type. The individual ASP presented a very high goodness-of-fit for the 3 sprint types, but slightly higher for best (range r2 = 0.98 [0.75-1.00]) compared with combined trials (range r2 = 0.95 [0.84-0.99]). Linear sprints revealed higher S0 (effect size [ES] ≥ -1.88; p < 0.001) and ASslope (ES ≥ -2.80; p < 0.001) but lower A0 (ES ≥ 1.15; p < 0.001) compared with CS. The ASP variables generally showed an acceptable within-session absolute reliability (range coefficient of variation [CV] = 4.5% [2.4-6.9%]) but an overall poor relative reliability for ASslope (range intraclass correlation coefficient = 0.44 [0.24-0.69]). The between-session reliability was greater for the combined trials (range CV = 4.7% [1.9-8.6%]) compared with the best trial (range CV = 6.1% [2.9-8.7%]). This study opens the possibility of using the ASP to monitor CS, preferably by combining multiple trials to increase its between-session reliability.

Angular momentum transfer to charged particles by interaction with Laguerre–Gauss pulses

Orbital angular momentum of light and the associated Laguerre–Gauss modes have garnered increasing interest due to the many applications they promise in the fields of telecommunications and quantum information, as well as charged particle acceleration. Here, we use the numerical simulation of the dynamics of a large number of identical, charged, relativistic, but classical particles, forming a statistical ensemble and seen as test-particles in a time-dependent external electromagnetic field, to get insight into the process of a head-on collision with a pulsed Laguerre–Gauss mode. We have identified two steady-states regimes (low a0 and large a0), where the distribution of the final angular momentum gained by the particles as a function of their initial coordinates is well-behaved and does not change its structure with variations of the reduced amplitude. For small reduced amplitudes a0 of the incoming electromagnetic field, we have also found an analytic approximation of the expression for the angular momentum transferred to the particles after the pulse has left their region. Using both numerical integration and the analytic approximation, we have investigated the effects of the field’s gradient, initial phase of the field, polarization type, and azimuthal order m.

SSI effects on the inelastic displacement ratios of flag-shaped hysteretic SDOF systems

This paper presents a parametric study to evaluate the effects of soil-structure interaction (SSI) on the constant-strength inelastic displacement ratios (CR) of self-centering single-degree-of-freedom (SDOF) systems characterized by flag-shaped hysteretic behavior. The elastic homogeneous soil half-space below the foundation is simulated according to the concept of Cone model. Intensive nonlinear time-history analyses of soil-structure systems are conducted using three sets of 20 synthetic ground motions, which are matched to the design response spectra corresponding to very dense, stiff and soft soil classes. The effects of different parameters (i.e., fundamental period of the fixed-base superstructure, Tfix; strength reduction factor, R; structure-to-soil stiffness ratio, a0; aspect ratio of the superstructure, s; secondary stiffness ratio, α; and energy dissipation ratio of the flag-shaped model, β) on the inelastic displacement ratios are investigated and discussed. The analysis results indicate that similar trends are generally observed in inelastic displacement spectra with different soil class conditions, and ignoring SSI underestimates the peak inelastic displacement demands of the soil-structure systems. The inelastic displacement ratios increase when the value of R or a0 increases, while a rise in α or β leads to lower inelastic displacement ratios. It is found that aspect ratio has basically no influence on the inelastic displacement ratios for low a0 values, while has mitigating and amplifying influence on the inelastic displacement ratios below and above a threshold period for high a0 values.

A modification of the Newtonian dynamics as a possible alternative to the hidden mass hypothesis

view Abstract Citations (2400) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A modification of the Newtonian dynamics as a possible alternative to the hidden mass hypothesis. Milgrom, M. Abstract The author considers the possibility that there is not, in fact, much hidden mass in galaxies and galaxy systems. If a certain modified version of the Newtonian dynamics is used to describe the motion of bodies in a gravitational field (of a galaxy, say), the observational results are reproduced with no need to assume hidden mass in appreciable quantities. Various characteristics of galaxies result with no further assumptions. The basis of the modification is the assumption that in the limit of small acceleration a very low a0, the acceleration of a particle at distance r from a mass M satisfies approximately a2/a0 ≈ MGr-2, where a0 is a constant of the dimensions of an acceleration. Publication: The Astrophysical Journal Pub Date: July 1983 DOI: 10.1086/161130 Bibcode: 1983ApJ...270..365M Keywords: Cosmology; Galactic Structure; Nonrelativistic Mechanics; Stellar Motions; Particle Acceleration; Solar System; Astrophysics full text sources ADS |

Regulation of Glycogen Synthase Activity in Choriocarcinoma Cells Effect of Glucose Starvation on the Conversion of Synthase D to Synthase I and the Kinetic Properties of the Enzyme

Choriocarcinoma cell glycogen synthase exists predominantly in the form dependent on glucose‐6‐phosphate during growth. This enzyme can not be converted to the form independent of glucose 6‐phosphate by endogenous phosphoprotein phosphatase, rabbit liver phosphoprotein phosphatase, or human placental alkaline phosphatase. However, the glycogen synthase present in the extract of cells which have been subjected to glucose starvation for 24 h can be converted to the form independent of glucose 6‐phosphate by these phosphatases. The activity which converts the form dependent on glucose 6‐phosphate to the form independent of glucose 6‐phosphate by the endogenous phosphatase is progressively increased during starvation. This increase in activity is blocked by the presence of 20 μM cycloheximide in the medium. Analysis of the kinetic properties of glycogen synthase isolated from cells during starvation shows that the A0.5 value (the activator concentration giving 50% maximal activity) for glucose 6‐phosphate and the S0.5 value (the substrate concentration giving 50% maximum activity) for UDP‐glucose are reduced. This reduction in the kinetic constants of the enzyme is also prevented by the presence of cycloheximide. The starvation‐induced change in the kinetic properties of the enzyme can be reversed by the incubation of the starved‐cell extract with ATP, Mg2+, and cyclic AMP or by refeeding the starved cells with medium containing high glucose. Also, the glycogen synthase which has similar kinetic properties to the enzyme found in the starved cells can be derived from the enzyme present in normal cultures. This involves mixing a small portion of the starved‐cell extract with a large portion of normal cellular extract and incubating under conditions favoring dephosphorylation. It appears that during glucose starvation glycogen synthase is partially dephosphorylated, and the resulting enzyme, still in a form dependent on glucose 6‐phosphate, has a lower A0.5 value for glucose 6‐phosphate and a lower S0.5 value for UDP‐glucose than the enzyme from cells without starvation. The starvation‐induced modification of the form of the enzyme dependent on glucose 6‐phosphate transforms it into a better substrate for phosphoprotein phosphatase.

Crystallographic Study of Chromium Spinels

Several chromium spinels have been prepared and regular x-ray diffraction intensities were measured on the powders. A Fortran program was developed in order to process the data. It appeared that the results, so obtained, were comparable to those from neutron diffraction techniques. A plot of the U parameter versus a0 for the thiochromites shows that metallic CuCr2S4 is exceptional. For its value of U, it has a much lower a0 than would be expected from a comparison of Mn, Fe, Co, and Zn thiochromites.