Fast Step Research Articles

POSSIBILITY ANALYSIS OF APPLICATION OF GROSS-EQUATIONS, PATHWAYS AND STATIONARY RATES FOR CHEMICAL SYSTEMS IN QUASI-EQUILIBRIUM AND QUASI-STATIONARY APPROACH

Conceptions of pathways, gross-equations and stationary rates were determined for chemical systems in quasi-stationary and quasi-equilibrium approach at different VPR and fast reversible steps.

O 077 - Walking across the street: Gait adaptations in stroke patients when approaching an elevated surface

A common technique to regain stability following an unexpected perturbation is reactive stepping, aimed to control the accelerated center of mass (COM). Many older adults (OA) struggle to execute the fast, coordinated stepping strategy required to arrest COM movement within the base of support (BOS) during these unexpected events, likely due to age-related physiological declines. Recent ecological data also suggests that many falls in OA occur due to errors in transferring or shifting body weight during activities of daily living. The present study utilized gait initiation, which requires a coordinated transition from quiet stance to dynamic gait, as an example of one of these difficult transitional movements.Our goal was to combine this inherently unstable task, gait initiation, with an unexpected mediolateral (ML) perturbation of the support surface to examine age-related changes in reactive stepping patterns during a novel transitional gait task.A total of 18 young adults (YA) and 16 OA (>65 years) performed 35 trials containing 10 unexpected ML perturbations of the support surface. To quantify age-related differences, we calculated step width, length, time and COM velocity in the first two steps following the perturbation.We observed that, in general, OA walked slower and took shorter, faster steps (reducing time in single support) compared to YA. Following the perturbation, OA altered their stepping patterns by reducing their BOS (more narrow step width compared to YA), and required more than the two steps used by YA to complete the goal-directed task.These age-related changes are concerning as a multi-step recovery strategy has been previously associated with an elevated risk of falls in OA.

Gait stability in response to platform, belt, and sensory perturbations in young and older adults

Perturbation-based gait assessment has been used to quantify gait stability in older adults. However, knowledge on which perturbation type is most suitable to identify poor gait stability is lacking. We evaluated the effects of ipsi- and contra-lateral sway, belt acceleration and deceleration, and visual and auditory perturbations on medio-lateral (ML) and anterior-posterior (AP) margins of stability (MoS) in young and older adults. We aimed to evaluate (1) which perturbation type disturbed the gait pattern substantially, (2) how participants recovered, and (3) whether recovery responses could discriminate between young and older adults. Nine young (25.1 ± 3.4 years) and nine older (70.1 ± 7.6 years) adults walked on the CAREN Extended (Motek BV, The Netherlands). The perturbation effect was quantified by deviation in MoS over six post-perturbation steps compared to baseline walking. Contra-lateral sway and deceleration perturbations resulted in the largest ML (1.9–4 times larger than other types) and AP (1.6–5.6 times larger than other types) perturbation effects, respectively. After both perturbation types, participants increased MoS by taking wider, shorter, and faster steps. No differences between young and older adults were found. We suggest to evaluate the potential of using contra-lateral sway and deceleration perturbations for fall risk identification by including both healthy and frail older adults.Graphical abstractMargins of stability during steady state (left) and perturbed (right) gait to quantify reactive gait stability in response to various perturbation types in young and older adults.

Biochemical characterization of Caulobacter crescentus xylose dehydrogenase

d-Xylose sugar is a common component of hemicellulose, the second largest fraction of biomass. Many groups have developed biological conversions of d-xylose to value-added products by recombinant expression of the xylose dehydrogenase enzyme from Caulobacter crescentus. This enzyme uses NAD+ as a cofactor to oxidize d-xylose to d-xylono-1,4-lactone. A detailed understanding of the mechanism of this enzyme could be useful in engineering more efficient versions. Therefore, we have conducted kinetic studies including both the forward and reverse physiological reactions of this enzyme. We demonstrate that the enzyme's substrate binding mode follows a sequential steady state ordered mechanism with NAD+ or NADH binding first. Furthermore, the kcat of the reaction in the direction of NAD+ reduction is 10-fold higher than that of the reverse reaction. From rapid reaction studies, we demonstrate the binding of NAD+ and NADH to the free enzyme and that hydride transfer occurs in a fast step followed by a much slower steady state. We calculate that the dissociations of the sugar products from the enzyme complexes are the major rate limiting steps in both directions.

Deep deoxidization from liquid iron by hydrogen plasma arc melting

In the present study, removal of oxygen from liquid iron by Ar and (10%–40%) H2 plasma arc melting have been investigated experimentally. It is shown that the reduction of oxygen content is slight when the plasma gas was argon only. However, the oxygen content of the iron melt decreases sharply when adding hydrogen in plasma gas, and the rate of deoxidization increases with the hydrogen content. The final oxygen content can be as low as 1 ppm after hydrogen plasma arc melting (HPAM) with 40% H2 in plasma gas. The deoxidization from the iron melt by HPAM was a two-steps process: the fast 1st step and the slow 2nd step. From kinetic analysis, the oxygen removal by HPAM was found to obey a first-order rate law. In the 1st step, the reduction rate of oxygen increases proportionally to the approximately 0.44th power of the hydrogen volume proportion in plasma gas. The deoxidization process can be expressed as the following reaction: [O]+2H=H2O. The thermodynamic analysis indicates that deoxidization power of atomic H is higher than that of molecular H2.

Modeling the effect of adsorption on the degradation rate of propiconazole in profiles of Polish Luvisols

Laboratory adsorption and degradation studies were carried out to determine the effect of time-dependent adsorption on propiconazole degradation rates in samples from three Polish Luvisols. Strong propiconazole adsorption (organic carbon normalized adsorption coefficients Koc in the range of 1217–7777 mL/g) was observed in batch experiments, with a typical biphasic mechanism with a fast initial step followed by the time-dependent step, which finished within 48 h in the majority of soils. The time-dependent step observed in incubation experiments was longer (duration from 5 to 23 d), and its contribution to total adsorption was from 20% to 34%. The half-lives obtained at 25 °C and 40% maximum water holding capacity of soil, were in the range of 34.7–112.9 d in the Ap horizon and in the range of 42.3–448.8 d for subsoils. The very strong correlations, between degradation rates in pore water and soil organic carbon and soil microbial activity, indicated that microbial degradation of propiconazole was most likely the only significant process responsible for the decay of this compound under aerobic conditions for the whole of the examined soil profiles. Modeling of the processes showed that only models coupling adsorption and degradation were able to correctly describe the experimental data. The analysis of the bioavailability factor values showed that degradation was not limited by the rate of propiconazole desorption from soil, but sorption affected the degradation rate by decreasing its availability for microorganisms.

Ni-Catalyzed Dimerization and Hydroperfluoroarylation of 1,3-Dienes.

A nickel-catalyzed three-component coupling reaction between perfluoroarenes and two molecules of a 1,3-diene in the presence of an alkyl Grignard reagent, which acted as a hydride source, provided 3-perfluoroarylated-1,7-octadienes via 1,3-diene dimerization and subsequent perfluoroarylation upon C-F bond cleavage. The reaction proceeded smoothly in a regioselective manner by simply combining NiCl2 and PPh3 as a catalyst and tolerated various functional groups on the perfluoroarenes. When substituted perfluoroarenes were employed, the reaction selectively occurred at the para-position. Mechanistic studies revealed that an anionic Ni complex, generated upon the reaction of Ni(0) with two molecules of a 1,3-diene and an alkyl Grignard reagent, played an important role in the C-C bond forming step with perfluoroarenes. The C-F bond cleavage was found to be a relatively fast step in the catalytic cycle.

Age-related alterations in reactive stepping following unexpected mediolateral perturbations during gait initiation

BackgroundA common technique to regain stability following an unexpected perturbation is reactive stepping, aimed to control the accelerated center of mass (COM). Many older adults (OA) struggle to execute the fast, coordinated stepping strategy required to arrest COM movement within the base of support (BOS) during these unexpected events, likely due to age-related physiological declines. Recent ecological data also suggests that many falls in OA occur due to errors in transferring or shifting body weight during activities of daily living. The present study utilized gait initiation, which requires a coordinated transition from quiet stance to dynamic gait, as an example of one of these difficult transitional movements. Research QuestionOur goal was to combine this inherently unstable task, gait initiation, with an unexpected mediolateral (ML) perturbation of the support surface to examine age-related changes in reactive stepping patterns during a novel transitional gait task. MethodsA total of 18 young adults (YA) and 16 OA (>65 years) performed 35 trials containing 10 unexpected ML perturbations of the support surface. To quantify age-related differences, we calculated step width, length, time and COM velocity in the first two steps following the perturbation. ResultsWe observed that, in general, OA walked slower and took shorter, faster steps (reducing time in single support) compared to YA. Following the perturbation, OA altered their stepping patterns by reducing their BOS (more narrow step width compared to YA), and required more than the two steps used by YA to complete the goal-directed task. SignificanceThese age-related changes are concerning as a multi-step recovery strategy has been previously associated with an elevated risk of falls in OA.

Experimental investigation of dynamic inflow effects with a scaled wind turbine in a controlled wind tunnel environment

Dynamic inflow is a phenomenon that leads to a load overshooting, for example by fast pitch angle changes. Established engineering models for this effect are known to still have deficits. Advanced control mechanisms for turbines like collective pitch control in order to alleviate tower loads or individual pitch control increase the need for accurate dynamic inflow models. We performed fast pitching step experiments with our MoWiTO 1.8 (Model Wind Turbine Oldenburg 1.8 m) in the WindLab wind tunnel of the University of Oldenburg and investigated the load overshooting of blade loads, torque and thrust as well as velocity transients in the near wake. Dynamic inflow phenomena were clearly visible and their non-dimensional time constants matched existing full scale and lab size experiments. The transient process of the different measured loads and flow in the near wake is disussed in the paper to gain a deeper understanding of the underlying physical phenomena.

Insight into nuclear body formation of phytochromes through stochastic modelling and experiment

Spatial relocalization of proteins is crucial for the correct functioning of living cells. An interesting example of spatial ordering is the light-induced clustering of plant photoreceptor proteins. Upon irradiation by white or red light, the red light-active phytochrome, phytochrome B, enters the nucleus and accumulates in large nuclear bodies (NBs). The underlying physical process of nuclear body formation remains unclear, but phytochrome B is thought to coagulate via a simple protein–protein binding process. We measure, for the first time, the distribution of the number of phytochrome B-containing NBs as well as their volume distribution. We show that the experimental data cannot be explained by a stochastic model of nuclear body formation via simple protein–protein binding processes using physically meaningful parameter values. Rather modelling suggests that the data is consistent with a two step process: a fast nucleation step leading to macroparticles followed by a subsequent slow step in which the macroparticles bind to form the nuclear body. An alternative explanation for the observed nuclear body distribution is that the phytochromes bind to a so far unknown molecular structure. We believe it is likely this result holds more generally for other nuclear body-forming plant photoreceptors and proteins.

Single-event kinetic modeling of ethene oligomerization on ZSM-5

The single-event kinetic modeling approach is extended to the ethene oligomerization process with products including paraffins and olefins, cyclic molecules and aromatics. The reaction network of olefin oligomerization on ZSM-5 with elementary steps of de/protonation, isomerization, alkylation, β-scission, cyclization and hydride transfer is computer-generated and consists of 10,456 elementary steps involving 2567 species within the up to C8 range. The fast elementary steps: de/protonation and isomerization are considered to reach quasi-equilibrium. The single-event kinetics approach allows the reduction of the number of independent kinetic parameters to 30. The kinetics of the model was then applied to 13 groups of isomers continuity equation with the kinetic data obtained from experimentation in a fixed bed isothermal reactor. Five space times and three temperatures were investigated. The model parameters were obtained using a combination of the genetic algorithm and the Levenberg-Marquardt approach. The single-events model is capable of correctly simulating the experimental data.

Effects of molar ratio and calcination temperature on the adsorption performance of Zn/Al layered double hydroxide nanoparticles in the removal of pharmaceutical pollutants

Abstract This work focuses on the development of zinc/aluminum layered double hydroxides (LDHs) phases intercalated by carbonates ions (Zn-Al-CO3) and their use in the removal of pharmaceutical pollutants. The materials were synthesized by the co-precipitation method at different Zn/Al molar ratios (r = 1, 3 and 5). Each synthesized material was calcined at 300, 400, 500 and 600 °C to increase their performance. Samples were characterized by various physicochemical techniques including XRD, FTIR, ICP-AES and TEM-EDX. The as-synthesized and calcined products were used for the removal of salicylic acid (SA) as a model of pharmaceutical pollutants. The results obtained show that the Zn/Al molar ratios and calcination temperatures have a great influence on the adsorption capacity. The optimum adsorption efficiency was found to be 94.59% for Zn/Al molar ratio of 3 and a calcination temperature of 300 °C. Kinetics of the adsorption takes place in two steps; the first fast rapid step can be interpreted by the adsorption on the external surface of the crystallites, while the second slow step could be due the reconstruction phenomenon of LDHs structure “memory effect”. After the adsorption processes, XRD patterns show that the calcined product (r = 3, T = 300 °C) was reconstructed by a salicylic acid. The adsorption performance was slightly decreased with regeneration cycles.

Heterobimetallic Catalysis: Platinum‐Gold‐Catalyzed Tandem Cyclization/C−X Coupling Reaction of (Hetero)Arylallenes with Nucleophiles

AbstractHeterobimetallic catalysis offers new opportunities for reactivity and selectivity but still presents challenges, and only a few metal combinations have been explored so far. Reported here is a Pt‐Au heterobimetallic catalyst system for the synthesis of a family of multi‐heteroaromatic structures through tandem cyclization/C−X coupling reaction. Au‐catalyzed 6‐endo‐cyclization takes place as the first fast step. Pt‐Au clusters are proposed to be responsible for the increased reactivity in the second step, that is, the intermolecular nucleophilic addition which occurs through an outer‐sphere mechanism by hybrid homogeneous‐heterogeneous catalysis.

Heterobimetallic Catalysis: Platinum-Gold-Catalyzed Tandem Cyclization/C-X Coupling Reaction of (Hetero)Arylallenes with Nucleophiles.

Heterobimetallic catalysis offers new opportunities for reactivity and selectivity but still presents challenges, and only a few metal combinations have been explored so far. Reported here is a Pt-Au heterobimetallic catalyst system for the synthesis of a family of multi-heteroaromatic structures through tandem cyclization/C-X coupling reaction. Au-catalyzed 6-endo-cyclization takes place as the first fast step. Pt-Au clusters are proposed to be responsible for the increased reactivity in the second step, that is, the intermolecular nucleophilic addition which occurs through an outer-sphere mechanism by hybrid homogeneous-heterogeneous catalysis.

Computational design of a light-driven imine-based motor with bulky chiral stator

A light-driven imine-based motor with bulky chiral stator has been computationally designed by investigation of the topographical features of the potential energy surfaces. The electronically excited model imine with a P-helical trans form directly goes to the conical intersection (CIX) in S1 on the downhill surface with respect to the CN torsion. After electronic relaxation into S0 around CIX with a double cone topography, the model imine goes to another P-helical cis-imine without any trap in the M-helical region through the CN torsion. Thereby, the full rotary process of the imine-based motor consists of two fast photochemical steps of (P)-trans → (P)-cis and (P)-cis → (P)-trans, which is possible to realize smooth rotation by repetitive photoexcitation, unlike the previous imine-based motors with four chemical steps. In addition, the other full rotary cycle with two steps is also open, of which latter-half process of (P)-cis → (P)-trans is the slow thermal N-inversion.

Direct Electronic Load Control for Demand Response in a DC Microgrid Using a Virtual Internal Impedance Screening Model and PID Controller

To reduce peak loads, direct and indirect load control are common strategies used to change demand during peak hours. Voltage dependent demand response (DR) is a direct load control for changing loads in a DC mircogrid. The characteristics of electronic loads can be controlled with a switch-mode DC boost or buck converter. They have faster response to maintain stable output voltage under the fluctuating load condition and heavy load condition. Applying a fast load step to voltage regulator can maintain a well regulated voltages and load currents. The increased load resistance will cause voltage drop when load current is increased during heavy loads. Thus, their adjustable internal load impedances can change the absorbed currents by regulating the duty ratio. In this study, a screening model is employed to estimate the virtual internal impedances of power electronic loads. Then, the desired duty ratio can be determined to perform the DR program, while the boost converter acts to step-up or step-down the load voltages using the PID (proportional-integral-derivative) controller. For a DC microgrid, simulation results show the feasibility of the proposed methods: (1) exact control of load voltage at both the power source side and load sides and (2) regulation of absorbed currents to modify load voltages and reduce line voltage drops and line losses during heavy loads.

Simple determination of some antidementia drugs in wastewater and human plasma samples by tandem dispersive liquid–liquid microextraction followed by high‐performance liquid chromatography

In this work, a simple method, namely, tandem dispersive liquid-liquid microextraction, with a high sample clean-up is applied for the rapid determination of the antidementia drugs rivastigmine and donepezil in wastewater and human plasma samples. This method, which is based on two consecutive dispersive microextractions, is performed in 7min. In the method, using a fast back-extraction step, the applicability of the dispersive microextraction methods in complicated matrixes is conveniently improved. This step can be performed in less than 2min, and very simple tools are required for this purpose. To achieve the best extraction efficiency, optimization of the variables affecting the method was carried out. Under the optimized experimental conditions, the relative standard deviations for the method were in the range of 6.9-8.7%. The calibration curves were obtained in the range of 2-1100ng/mL with good correlation coefficients, higher than 0.995, and the limits of detection ranged between 0.5 and 1.0ng/mL.

Magnetoresistor with Planar Magnetic Concentrator as Wideband Contactless Current Sensor for Power Electronics Applications

High-frequency power electronic converters require lossless, accurate, and isolated current measurement. High-frequency currents through a printed circuit board (PCB) trace generate nonuniform magnetic field around the trace. The nonuniform magnetic fields can be normalized by means of magnetic field concentrators (MCONs) using conductive materials. In this study, a novel technique for high-frequency contactless current sensing using magnetoresistor (MR) sensors with planar magnetic concentrators (MCON) utilizing conductive materials has been proposed. The effect of different MCONs on the performance of anisotropic MR (AMR) sensors for high-frequency contactless current detection has been investigated. The performance of the AMR sensor equipped with different MCONs is demonstrated experimentally with respect to a fast rise step current. A detailed frequency analysis is performed on the sensor response with different MCONs to determine the effect on the detection bandwidth of the current sensors.

Radioiodination and Biological Evaluation of Tizanidine as a Potential Brain Imaging Agent

LABELING was carried out by direct iodination of tizanidine (100 µg) with radioiodine (125I) in a fast single step at room temperature, to produce 125I-tizanidine (125I-TZN). 50 µg chloramine-T (CAT) was used as an oxidizing agent to oxidize the iodide ion to the iodonium ion, at neutral pH = 7 within 15 min. A high radiochemical yield of 92.8 % ± 0.1 was obtained. 125I-TZN was stable for 2 h without detection of any by-products in the reaction mixture. The partition coefficient value of 125I-TZN was 2.21 ± 0.02, showing that it is very lipophilic and can easily cross the blood brain barrier. Biodistribution studies and in vivo imaging showed that the initial brain uptake correlated fairly well with the brain-binding affinity of the compound. The brain uptake of 125I-TZN was as high as 5.2 % and 8.0 % in biodistribution studies and in vivo imaging at 120 min post injection, respectively. Thus, 125I-TZN is promising in radioreceptor assays for brain imaging.

Number of raised steps: A tool to assess brief and intense effort involving anaerobic metabolism

BackgroundAlthough the initial anaerobic component of exercise adaptation is unavoidable, no specific functional test is available for use in routine non-sporting practice to evaluate it. ObjectiveTo assess the bioenergetic and biomechanical properties of the Short and Fast Step Test (SFST), which consists of walking up and down a step as many times as possible in 1minute and to analyse its ability to explore the initial anaerobic component of effort in comparison to a reference self-paced step test. MethodsOverall, 31 healthy subjects (19 women; mean [SD] age, 32.4 [10.2] years) completed a test–retest of a self-paced step test and the SFST, with pre- and post-test measurement of blood lactate concentration and continuous recording of VO2 and modelling of excess post-exercise oxygen consumption (EPOC), near-infrared spectroscopy (NIRS) of the quadriceps and mechanical power (estimated by the number of steps climbed and 3-D motion analysis). ResultsBoth step tests were well tolerated. The reliability of the bioenergetics parameters, number of raised steps, mechanical power and NIRS tissue saturation index was good. Indirect mechanical power (estimated from number of steps) was correlated with direct power (computed from the centre of mass). Lactate accumulation was significantly increased during exercise with only the SFST (mean [SD] increase, 3.86 [3.26]mmolL−1 from resting values, P<0.05). EPOC was higher with the SFST than the self-paced step test (P<0.05). Only the SFST showed significant correlations between number of steps climbed and EPOC (r=0.84; P<0.001) and decreased tissue saturation index (NIRS) and EPOC area (r=−0.39; P<0.05). ConclusionsSFST is feasible, well tolerated, reliable and responsive to explore a brief exercise involving anaerobic metabolism at submaximal intensity. The number of steps taken in 1minute seems a suitable parameter for practical application.