Comparison of Biomechanical Characteristics during the Second Landing Phase in Female Latin Dancers: Evaluation of the Bounce and Side Chasse Step

Research on dance lower extremity joint motion has been limited. Thus, the purpose of this study was to investigate the lower limb biomechanics differences between the side chasse step (SCS) and the bounce step (BS) of the second landing phase in Jive. Thirteen female recreational Latin dancers (Age: 22 ± 2.5 years; Height: 1.65 ± 0.05 m; Weight: 50 ± 4.5 kg; Dance experience: 4 ± 2 years) were involved in the experiment. The same music was used throughout the data collection period. We intended to determine whether these two steps generate different kinematic and kinetic data. The ankle, hip, and knee joint angle, moment, velocity, and ground reaction force were calculated for each step. Results demonstrated that the lower limb biomechanics of the two different steps showed significant differences. As a result, strengthening the lower limb muscles (gastrocnemius, Tibialis muscle, and quadriceps) is significantly important to balance the joint strength and prevent foot injury. According to the training time reasonably increasing the heel height should be recognized as important. The current study could provide new insights into reducing lower extremity injuries and improving dance performance.     

A kinetic comparison between E2P and the E2P-like state induced by a beryllium fluoride complex in the Na,K-ATPase. Interactions with Rb+

Metal-fluoride complexes have been used to induce E2P-like states with the aim of studying the events that occur during E2P hydrolysis in P-type ATPases. In the present work, we compared the E2P-like state induced by a beryllium fluoride complex (BeF_x) with the actual E2P state formed through backdoor phosphorylation of the Na,K-ATPase. Formation of E2P and E2P-like states were investigated employing the styryl dye RH421. We found that BeF_x is the only fluorinated phosphate analog that, like Pi, increases the RH421 fluorescence. The observed rate constant, k_obs, for the formation of E2P decreases with [Pi] whereas that of E2BeF_x increases with [BeF_x]. This might wrongly be taken as evidence of a mechanism where the binding of BeF_x induces a conformational transition. Here, we rather propose that, like for Pi, binding of BeF_x follows a conformational-selection mechanism, i.e. it binds to the E2 conformer forming a complex that is much more stable than E2P, as seen from its impaired capacity to return to E1 upon addition of Na⁺. Although E2P and E2BeF_x are able to form states with 2 occluded Rb⁺, both enzyme complexes differ in that the affinity for the binding and occlusion of the second Rb⁺ is much lower in E2BeF_x than in E2P. The higher rates of Rb⁺ occlusion and deocclusion observed for E2BeF_x, as compared to those observed for other E2P-like transition and product states suggest a more open access to the cation transport sites, supporting the idea that E2BeF_x mimics the E2P ground state.     

Growth kinetics and mathematical modeling of Synechocystis sp. PCC 6803 under flashing light

In photobioreactors and natural systems, microalgae are subjected to rapidly changing light intensities (LI) due to light attenuation and mixing. A controlled way to study the effect of rapidly changing LI is to subject cultures to flashing light. In this study, series of flashing-light experiments were conducted using Synechocystis sp. PCC6803 with constant overall average LI of approximately 84 μmol·m⁻²·s⁻¹ and relative times in the light and dark varied. The results were also compared with simulated results using a mathematical model including an absorbed pool of light energy, photoacclimation, and photoinhibition. With equal time in light and dark, the specific growth rate (μ) systematically decreased with increasing light duration, and µ decreased further when the ratio of light to dark was decreased. The model captured both trends with the mechanistic explanation that when the light duration was very short the changes in the pool of absorbed LI were smoothed out across the light and dark periods, whereas longer durations caused the biomass to experience discrete light and dark conditions that lead to reduced light absorption, more energy loss to nonphotochemical quenching, and more photodamage. These growth effects were accentuated as the ratio of light to dark decreased.     

Creation and validation of a reactor engineering model for multiphase red wine fermentations

Red wine fermentations are performed in the presence of grape skins and seeds to ensure the extraction of color and other phenolics. The presence of these solids results in two distinct phases in the fermentor, as the solids float to the top to form a “cap.” Modeling of red wine fermentation is, therefore, complex and must consider spatial heterogeneity to predict fermentation kinetics. We have developed a reactor-engineering model for red wine fermentations that includes the fundamentals of fermentation kinetics, heat transfer, diffusion, and compressible fluid flow. To develop the heat transfer component of the model, the heat transfer properties of grapes were experimentally determined as a function of fermentation progression. COMSOL was used to solve all components of the model simultaneously utilizing a finite element analysis approach. Predictions from this model were validated using prior experimental work. Model prediction and experimental data showed excellent agreement. The model was then used to predict spatial profiles of active yeast cell concentration and ethanol productivity, as well as liquid velocity profiles. Finally, the model was used to predict how these gradients would change with differences in initial bioavailable nitrogen concentration, a key parameter in predicting fermentation outcome in nitrogen-limited wine fermentations.     

Phytotoxicity of Sodium Fluoride and Uptake of Fluoride in Willow Trees

The willow tree (Salix viminalis) toxicity test and a cress seed germination test (Lepidium sativum) were used to determine uptake of F and phytotoxicity of NaF. Concentrations in hydroponic solutions were 0–1000 mg F/L and 0–400 mg F/L in the preliminary and definitive test. A third test was done with soils collected from a fluoride-contaminated site at Fredericia, Denmark. The EC₁₀, EC₂₀ and EC₅₀-values for inhibition of transpiration were determined to 38.0, 59.6 and 128.7 mg F/L, respectively. The toxicity test with soil showed strong inhibition for the sample with the highest fluoride concentration (405 mg free F per kg soil, 75 mg F per L soil solution). The seed germination and root elongation test with cress gave EC₁₀, EC₂₀ and EC₅₀-values of 61.4, 105.0 and 262.8 mg F/L, respectively. At low external concentrations, fluoride was taken up more slowly than water and at high external concentrations at the same velocity. This indicates that an efflux pump becomes overloaded at concentrations above 210 mg F/L. Uptake kinetics were simulated with a non-linear mathematical model, and the Michaelis-Menten parameters were determined to half-saturation constant K_M near 2 g F/L and maximum enzymatic removal rate v_max at 9 g/(kg d).     

Asymmetric Rate Behavior of Si Anodes for Lithium‐Ion Batteries: Ultrafast De‐Lithiation versus Sluggish Lithiation at High Current Densities

The combined effect of lithium‐ion diffusion, potential‐concentration gradient, and stress plays a critical role in the rate capability and cycle life of Si‐based anodes of lithium‐ion batteries. In this work, Si nanofilm anodes are shown to exhibit an asymmetric rate performance: around 72% of the total available capacity can be delivered during de‐lithiation under a high current density of 420 A g^‐1 (100C where C is the charge‐rate) in 22 s; in striking contrast, only 1% capacity can be delivered during lithiation. A mathematical model of single‐ion diffusion is established to elucidate the asymmetric rate performance, which can be mainly attributed to the potential‐concentration profile associated with the active material and the ohmic voltage shift under high currents; the difference in chemical diffusion coefficients during lithiation and de‐lithiation also plays a role. This clarifies that the charge and discharge rates of lithium‐ion‐battery electrodes should be evaluated separately due to the asymmetric effect in the electrochemical system.     

Probing kinetic drug binding mechanism in voltage-gated sodium ion channel: open state versus inactive state blockers

The kinetics and nonequilibrium thermodynamics of open state and inactive state drug binding mechanisms have been studied here using different voltage protocols in sodium ion channel. We have found that for constant voltage protocol, open state block is more efficient in blocking ionic current than inactive state block. Kinetic effect comes through peak current for mexiletine as an open state blocker and in the tail part for lidocaine as an inactive state blocker. Although the inactivation of sodium channel is a free energy driven process, however, the two different kinds of drug affect the inactivation process in a different way as seen from thermodynamic analysis. In presence of open state drug block, the process initially for a long time remains entropy driven and then becomes free energy driven. However in presence of inactive state block, the process remains entirely entropy driven until the equilibrium is attained. For oscillating voltage protocol, the inactive state blocking is more efficient in damping the oscillation of ionic current. From the pulse train analysis it is found that inactive state blocking is less effective in restoring normal repolarisation and blocks peak ionic current. Pulse train protocol also shows that all the inactive states behave differently as one inactive state responds instantly to the test pulse in an opposite manner from the other two states.     

Temperature manifold for a stopped-flow machine to allow measurements from −10 to +40 °C

Conducting enzymatic stopped-flow experiments at temperatures far removed from ambient can be very problematic because extremes in temperature (<10 °C or >30 °C) can damage the machine or the enzyme. We have devised a simple manifold that can be attached to most commercial stopped-flow systems that is independently heated or cooled separate from the main stopped-flow system. Careful calibration of the flow circuit allows the sample to be heated or cooled to the measurement temperature (−8 to +40 °C) 1 to 2 s before mixing in the reaction chamber. This approach allows measurements at temperatures where the stopped flow or the protein is normally unstable. To validate the manifold, we investigated the well-defined ATP-induced dissociation of rabbit muscle myosin subfragment 1 (S1) from its complex with pyrene-labeled actin. This process has both temperature-dependent and -independent components. Use of ethylene glycol allowed us to measure the reaction below 0 °C and up to 42 °C, and as expected the second-order rate constant (K₁k₊₂) and the maximum rate of dissociation (k₊₂) both increased with temperature, whereas 1/K₁ is unaffected by the change in temperature.     

Isothermal titration calorimetry determination of individual rate constants of trypsin catalytic activity

Determination of individual rate constants for enzyme-catalyzed reactions is central to the understanding of their mechanism of action and is commonly obtained by stopped-flow kinetic experiments. However, most natural substrates either do not fluoresce/absorb or lack a significant change in their spectra while reacting and, therefore, are frequently chemically modified to render adequate molecules for their spectroscopic detection. Here, isothermal titration calorimetry (ITC) was used to obtain Michaelis–Menten plots for the trypsin-catalyzed hydrolysis of several substrates at different temperatures (278–318 K): four spectrophotometrically blind lysine and arginine N-free esters, one N-substituted arginine ester, and one amide. A global fitting of these data provided the individual rate constants and activation energies for the acylation and deacylation reactions, and the ratio of the formation and dissociation rates of the enzyme–substrate complex, leading also to the corresponding free energies of activation. The results indicate that for lysine and arginine N-free esters deacylation is the rate-limiting step, but for the N-substituted ester and the amide acylation is the slowest step. It is shown that ITC is able to produce quality kinetic data and is particularly well suited for those enzymatic reactions that cannot be measured by absorption or fluorescence spectroscopy.