Faster Activation Rate Research Articles

Synergistic effect for improving the hydrogen storage capability and electrochemical performance of AB2 Laves phase alloys

The structure of a series AB2 Laves-type metal hydride alloys, in which Ce was doped into Ti0.24Zr0.76Ni1.15Mn0.7V0.15 and annealed the alloys, was studied and correlated to hydrogen storage properties and electrochemical performances. X-ray diffraction, scanning electron microscope, and energy-dispersive spectroscopy results revealed that Ce formed a CeNi3 secondary phase instead of entering the Laves phases. The synergistic effect of the CeNi3 and (Ti,Zr)Ni phase improved the hydrogen storage and electrochemical discharge properties of the Ce-doped (Ce0.02) alloy. Especially, the secondary phases could decrease the hydrogen absorption plateau, reduce the hysteresis phenomenon, and increase the hydrogen storage capacity (from 0.9 wt% to 1.4 wt% at 25 ℃). The formation of CeNi3Hx hydride on the surfaces of alloy electrodes led to a higher discharge capacity (∼500 mAh/g) and a faster activation rate. The Ce0.02 alloy also showed a good cyclic stability ∼82.08%, after 500 charge-discharge cycling, which could be ascribed to the good corrosion resistance of the CeNi3 phase on the surface of alloy. In addition, annealing treatment promoted the depletion of (Ti,Zr)Ni secondary phase and the transformation from the C14 to C15 phase. The Ce-doped AB2 alloy can be used as a hydrogen storage and hydride battery electrode material.

Influence of annealing temperature on the structure and electrochemical performance of the Fe3O4 anode material for alkaline secondary batteries

High-performance Fe3O4 polyhedrons as alkaline secondary battery anode materials have successfully been synthesized using a facile co-precipitation method with a subsequent annealing treatment at 700°C for 1h. The physical and electrochemical properties of the Fe3O4 samples annealed at different temperatures are investigated. It has been discovered that the annealing temperature plays a vital role in improving the physical and electrochemical performances of the Fe3O4 materials. The results also indicate that the Fe3O4 sample annealed at 700°C performs better (faster activation rate, higher specific discharge capacity, better high-rate ability and cycle stability) than the samples annealed at other temperatures. The specific discharge capacity of the 700°C-annealed Fe3O4 reaches 604.2mAh g-1 at a current density of 120mA g-1 with a charging efficiency of 83.9%. Moreover, discharge capacities of 587.6, 539.5 and 500.1 mAh g-1 are achieved at 240, 600 and 1200mA g-1, respectively, exhibiting remarkable high-rate discharge capability. This performance improvement may be attributable to better reaction reversibility, lower charge transfer impedance and better inhibiting effect on hydrogen evolution reaction of the material. We believe that this Fe3O4 polyhedron is a promising candidate as the anode material for high-performance alkaline secondary batteries.

Preparation and characterization of activated carbon for hydrogen storage from waste African oil-palm by microwave-induced LiOH basic activation

African palm shell-based activated carbon was prepared via a microwave-induced activation process using LiOH base as the activating agent. The effect on the activation process of various factors such as microwave intensity and duration of radiation at a LiOH/carbon ratio of 0.5 was studied. The optimal activation conditions were determined as: a microwave intensity of 800W, a radiation time 15min and a LiOH/carbon ratio of 0.5, under which a surface area of 1350m2/g with a hydrogen capacity of 6.5wt% could be achieved. The surface chemical properties were characterized using several methods including point of zero charge (pHpzc) measurement and FTIR spectra. Comparisons with the conventional thermal process demonstrated that the microwave-induced activation process had a faster activation rate and higher carbon yield. A textural analysis following the development of microporosity was also performed.

Preparation and characterization of activated carbon from bamboo by microwave-induced phosphoric acid activation

Bamboo-based activated carbon was prepared with a microwave-induced activation process using phosphoric acid as the activating agent. The effects of various factors such as microwave power, radiation time and phosphoric acid/carbon ratio on the activation have been studied. The optimal activation conditions were determined as: microwave power 350 W, radiation time 20 min and phosphoric acid/carbon ratio 1:1, under which a surface area of 1432 m 2/g and a carbon yield of 48% could be reached. The surface chemical properties were characterized with several methods including acid–base titration, point of zero charge (pH pzc) measurement, FTIR spectra and XPS spectra. The results demonstrated the existence of a large amount of acidic groups on the carbon surface, and the species and relative contents of these groups were analyzed in detail. Comparisons with the conventional thermal process demonstrated that the microwave-induced activation process had faster activation rate and higher carbon yield.

The effect of temperature and thermal acclimation on the sustainable performance of swimming scup

There is a significant reduction in overall maximum power output of muscle at low temperatures due to reduced steady-state (i.e. maximum activation) power-generating capabilities of muscle. However, during cyclical locomotion, a further reduction in power is due to the interplay between non-steady-state contractile properties of muscle (i.e. rates of activation and relaxation) and the stimulation and the length-change pattern muscle undergoes in vivo. In particular, even though the relaxation rate of scup red muscle is slowed greatly at cold temperatures (10 degrees C), warm-acclimated scup swim with the same stimulus duty cycles at cold as they do at warm temperature, not affording slow-relaxing muscle any additional time to relax. Hence, at 10 degrees C, red muscle generates extremely low or negative work in most parts of the body, at all but the slowest swimming speeds. Do scup shorten their stimulation duration and increase muscle relaxation rate during cold acclimation? At 10 degrees C, electromyography (EMG) duty cycles were 18% shorter in cold-acclimated scup than in warm-acclimated scup. But contrary to the expectations, the red muscle did not have a faster relaxation rate, rather, cold-acclimated muscle had an approximately 50% faster activation rate. By driving cold- and warm-acclimated muscle through cold- and warm-acclimated conditions, we found a very large increase in red muscle power during swimming at 10 degrees C. As expected, reducing stimulation duration markedly increased power output. However, the increased rate of activation alone produced an even greater effect. Hence, to fully understand thermal acclimation, it is necessary to examine the whole system under realistic physiological conditions.

Molecular tuning of fast gating in pentameric ligand-gated ion channels

Neurotransmitters such as acetylcholine (ACh) and glycine mediate fast synaptic neurotransmission by activating pentameric ligand-gated ion channels (LGICs). These receptors are allosteric transmembrane proteins that rapidly convert chemical messages into electrical signals. Neurotransmitters activate LGICs by interacting with an extracellular agonist-binding domain (ECD), triggering a tertiary/quaternary conformational change in the protein that results in the fast opening of an ion pore domain (IPD). However, the molecular mechanism that determines the fast opening of LGICs remains elusive. Here, we show by combining whole-cell and single-channel recordings of recombinant chimeras between the ECD of alpha7 nicotinic receptor (nAChR) and the IPD of the glycine receptor (GlyR) that only two GlyR amino acid residues of loop 7 (Cys-loop) from the ECD and at most five alpha7 nAChR amino acid residues of the M2-M3 loop (2-3L) from the IPD control the fast activation rates of the alpha7/Gly chimera and WT GlyR. Mutual interactions of these residues at a critical pivot point between the agonist-binding site and the ion channel fine-tune the intrinsic opening and closing rates of the receptor through stabilization of the transition state of activation. These data provide a structural basis for the fast opening of pentameric LGICs.

Chronic ethanol exposure induces an N-type calcium channel splice variant with altered channel kinetics

Chronic ethanol exposure increases the density of N-type calcium channels in brain. We report that ethanol increases levels of mRNA for a splice variant of the N channel specific subunit α 12.2 that lacks exon 31a. Whole cell recordings demonstrated an increase in N-type current with a faster activation rate and a shift in activation to more negative potentials after chronic alcohol exposure, consistent with increased abundance of channels containing this variant. These results identify a novel mechanism whereby chronic ethanol exposure can increase neuronal excitability by altering levels of channel splice variants.

Rapid desensitization of G protein-gated inwardly rectifying K+ currents is determined by G protein cycle

Activation of G protein-gated inwardly rectifying K(+) (GIRK) channels, found in the brain, heart, and endocrine tissue, leads to membrane hyperpolarization that generates neuronal inhibitory postsynaptic potentials, slows the heart rate, and inhibits hormone release. During stimulation of G(i/o)-coupled receptors and subsequent channel activation, it has been observed that the current desensitizes. In this study we examined mechanisms underlying fast desensitization of cloned heteromeric neuronal Kir3.1+3.2A and atrial Kir3.1+3.4 channels and also homomeric Kir3.0 currents in response to stimulation of several G(i/o) G protein-coupled receptors (GPCRs) expressed in HEK-293 cells (adenosine A(1), adrenergic alpha(2A), dopamine D(2S), M(4) muscarinic, and GABA(B1b/2) receptors). We found that all agonist-induced currents displayed a similar degree of desensitization except the adenosine A(1) receptor, which exhibits an additional desensitizing component. Using the nonhydrolyzable GTP analog guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS), we found that this is due to a receptor-dependent, G protein-independent process. Using Ca(2+) imaging we showed that desensitization is unlikely to be accounted for solely by phospholipase C activation and phosphatidylinositol 4,5-bisphosphate (PIP(2)) hydrolysis. We examined the contribution of the G protein cycle and found the following. First, agonist concentration is strongly correlated with degree of desensitization. Second, competitive inhibition of GDP/GTP exchange by using nonhydrolyzable guanosine 5'-O-(2-thiodiphosphate) (GDPbetaS) has two effects, a slowing of channel activation and an attenuation of the fast desensitization phenomenon. Finally, using specific Galpha subunits we showed that ternary complexes with fast activation rates display more prominent desensitization than those with slower activation kinetics. Together our data suggest that fast desensitization of GIRK currents is accounted for by the fundamental properties of the G protein cycle.

The influence of thermal acclimation on power production during swimming. II. Mechanics of scup red muscle under in vivo conditions.

We have previously shown that the power output of red muscle from warm-acclimated scup is greatly reduced when the fish swim at low temperatures. This reduction occurs primarily because, despite the slowing of muscle relaxation rate at cold temperatures, warm-acclimated scup swim with the same tail-beat frequency and the same stimulation durations, thereby not affording the slower-relaxing muscle any extra time to relax. We hypothesize that power output during swimming could be increased if the stimulus duration were reduced or if the relaxation rate of the red muscle were increased during cold acclimation. Scup were acclimated to 10 degrees C (cold-acclimated) and 20 degrees C (warm-acclimated) for at least 6 weeks. Cold acclimation dramatically increased the ability of scup red muscle to produce power at 10 degrees C. Power output measured from cold-acclimated muscle bundles driven through in vivo conditions measured from cold-acclimated scup swimming at 10 degrees C (i.e. work loops) was generally much greater than that from warm-acclimated muscle driven through its respective in vivo conditions at 10 degrees C. The magnitude of the increase depended both on the anatomical location of the muscle and on swimming speed. Integrated over the length of the fish, the red musculature from cold-acclimated fish generated 2.7, 8.9 and 5.8 times more power than the red musculature from warm-acclimated fish while swimming at 30 cm s(-)(1), 40 cm s(-)(1) and 50 cm s(-)(1), respectively. Our analysis suggests that the cold-acclimated fish should be able to swim in excess of 40 cm s(-)(1) with just their red muscle whereas the warm-acclimated fish must recruit their pink muscle well below this speed. Because the red muscle is more aerobic than the pink muscle, cold acclimation may increase the sustained swimming speed at which scup perform their long seasonal migrations at cool temperatures. We then explored the underlying mechanisms for the increase in muscle power output in cold-acclimated fish. Contrary to our expectations, cold-acclimated muscle did not have a faster relaxation rate; instead, it had an approximately 50 % faster activation rate. Our work-loop studies showed that this faster activation rate, alone, can increase the mechanical power production during cyclical contractions to a surprising extent. By driving cold-acclimated muscle through warm- and cold-acclimated in vivo conditions, we were able to partition the improvement in power production associated with increased activation rate and the approximately 20 % reduction in the duration of electromyographic activity found in the accompanying study. Depending on the position and swimming speed, approximately 60 % of the increase in power output was due to the change in the red muscle's contractile properties (i.e. faster activation); the remainder was due to the shorter stimulus duty cycle of cold-acclimated scup. Thus, by both shortening the in vivo stimulation duration and speeding up the rate of muscle activation as part of cold-acclimation, scup achieve a very large increase in the power output of their red muscle during swimming at low temperature. This increase in power output probably results in an increase in muscle efficiency and, hence, a reduction in the energetic cost of swimming. This increase in power output also reduces reliance on the less aerobic and less fatigue-resistant pink muscle. Both these abilities may increase the swimming speed at which prolonged aerobic muscle activity can occur and thus reduce the travel time for the long seasonal migrations in which scup engage.

Rapid activation by photolysis of nitr-5 in skinned fibres of the striated adductor muscle from the scallop

Photolysis of nitr-5, a caged calcium molecule, has been used for rapid activation of skinned fibre bundles of a myosin-regulated muscle, the striated adductor of the scallop, Pecten maximus. Chemically skinned fibre bundles (diameter 70–200 μm) were equilibrated in solutions containing 1–3 mM nitr-5 (p Ca 6.1) and then activated by ultraviolet laser pulse (25 ns). Pulse energies of 60–95 mJ gave contractions of over 90% maximum tension and a mean half-time for tension rise of 43 ms ( n = 4) at 12°C. Electrically stimulated bundles of intact fibres develop a tetanus with a rise half-time of 60.2 ms at 10°C ( n = 5) (Rall, J.A. (1981) J. Physiol. 321, 287–295, and personal communication). At lower pulse energies the skinned fibres gave smaller amplitude contractions with slower rates of rise (up to 260 ms half-time). In addition, a slower component of tension development (mean rise half-time 13.3 s) was often observed. In ATP-free solutions containing hexokinase and glucose, rigour tension developed with a delayed onset. Rapid release of ATP (0.47–0.59 mM) from photolysis of caged ATP (2 mM) at p Ca 4.5 then caused a rapid contraction with a mean half-time for tension development of 17 ms ( n = 4). The fast activation rates obtained by the photorelease of Ca 2+ from nitr-5 are similar to those obtained with skinned skeletal fibres of actin-regulated muscle. The results imply that the rate-limiting step in excitation-contraction coupling of the scallop muscle is not the increase in sarcoplasmic Ca 2+, but rather the activation of the muscle in response to this increase. The half-times of ATP-induced contractions at p Ca 4.5 suggest that in a contraction activated by a rapid Ca 2+ jump the process comprising ATP hydrolysis and cross-bridge cycling occurs at a somewhat faster rate than the Ca 2+-dependent activation process which preceds it.