Three-step Transition Research Articles

Cationic Oxidative Leaching Engineering Modulated In Situ Self-Reconstruction of Nickel Sulfide for Superior Water Oxidation.

Tuning the electroactive surface species of electrocatalysts remains a significant challenge for achieving highly efficient oxygen evolution reactions. Herein, we propose an innovative in situ leaching strategy, modulated by cationic oxidation, to achieve active self-reconstruction of these catalysts. Vanadium is introduced as a cation into Ni3S2 and oxidized under low oxidative potential, leading to subsequent leaching into the electrolyte and triggering self-reconstruction. The structural evolution from V-Ni3S2 to Ni(OH)2 and subsequently to NiOOH is identified by operando Raman as a three-step transition. In contrast, V-free Ni3S2 is unable to bypass the thermodynamically predicted nickel oxysulfide products to transform into active NiOOH. As a result, the self-restructured V-Ni3S2 only needs an ultralow overpotential of 155 mV at 10 mA cm-2, outperforming V-free Ni3S2 and many other advanced catalysts. This work provides new guidelines for manipulating in situ leaching to modulate the self-reconstruction of catalysts.

Automated Path Searching Reveals the Mechanism of Hydrolysis Enhancement by T4 Lysozyme Mutants

Bacteriophage T4 lysozyme (T4L) is a glycosidase that is widely applied as a natural antimicrobial agent in the food industry. Due to its wide applications and small size, T4L has been regarded as a model system for understanding protein dynamics and for large-scale protein engineering. Through structural insights from the single conformation of T4L, a series of mutations (L99A,G113A,R119P) have been introduced, which have successfully raised the fractional population of its only hydrolysis-competent excited state to 96%. However, the actual impact of these substitutions on its dynamics remains unclear, largely due to the lack of highly efficient sampling algorithms. Here, using our recently developed travelling-salesman-based automated path searching (TAPS), we located the minimum-free-energy path (MFEP) for the transition of three T4L mutants from their ground states to their excited states. All three mutants share a three-step transition: the flipping of F114, the rearrangement of α0/α1 helices, and final refinement. Remarkably, the MFEP revealed that the effects of the mutations are drastically beyond the expectations of their original design: (a) the G113A substitution not only enhances helicity but also fills the hydrophobic Cavity I and reduces the free energy barrier for flipping F114; (b) R119P barely changes the stability of the ground state but stabilizes the excited state through rarely reported polar contacts S117OG:N132ND2, E11OE1:R145NH1, and E11OE2:Q105NE2; (c) the residue W138 flips into Cavity I and further stabilizes the excited state for the triple mutant L99A,G113A,R119P. These novel insights that were unexpected in the original mutant design indicated the necessity of incorporating path searching into the workflow of rational protein engineering.

Low-temperature magnetic order rearrangement in the layered van der Waals compound MnPS3

To stabilize the long-range magnetic ordering in two-dimensional (2D) materials is a challenge from both fundamental and application points of view. It is difficult to be realized due to the delicate competition between thermal energy, magnetic exchange energy, and spin frustration. Here we study the temperature and field effects on the spin structure of two-dimensional van der Waals system ${\mathrm{MnPS}}_{3}$ using dc magnetic susceptibility and electron spin resonance (ESR) techniques. Clear development of three-step transitions was observed in the in-plane susceptibility. A low-temperature plateau from 78 to 38 K can be related to the Heisenberg antiferromagnetic (HAFM) ordering with spins pointing to the $z$ direction. Following, a sharp rising after the plateau suggests a transition into the $XY$ system. The rising slope slows down at 30 K indicating a transition into another phase, possibly a vortex-antivortex state. By fitting the temperature-dependent ESR parameters with the Berezinskii-Kosterlitz-Thouless (BKT) model in the range 100--300 K, we propose a spin 2D system with the vortex-antivortex structure below the HAFM transition. Susceptibility and ESR data show that the application of a high field along the $z$ direction destroys both the $XY$ phase and the BKT transition, reconciling to the scenario of a topological phase transition at zero field.

Effects of dietary nitrate on the O2 cost of submaximal exercise: Accounting for “noise” in pulmonary gas exchange measurements

ABSTRACT Dietary nitrate (NO3 –) supplementation can reduce the oxygen cost of submaximal exercise, but this has not been reported consistently. We hypothesised that the number of step transitions to moderate-intensity exercise, and corresponding effects on the signal-to-noise ratio for pulmonary O2, may be important in this regard. Twelve recreationally active participants were assigned in a randomised, double-blind, crossover design to supplement for 4 days in three conditions: 1) control (CON; water); 2); PL (NO3 –-depleted beetroot juice); and 3) BR (NO3 –-rich beetroot juice). On days 3 and 4, participants completed two 6-min step transitions to moderate-intensity cycle exercise. Breath-by-breath O2 data were collected and O2 kinetic responses were determined for a single transition and when the responses to 2, 3 and 4 transitions were ensemble-averaged. Steady-state O2 was not different between PL and BR when the O2 response to one-, two- or three-step transition was compared but was significantly lower in BR compared to PL when four-step transitions was considered (PL: 1.33 ± 0.34 vs. BR: 1.31 ± 0.34 L·min−1, P < 0.05). There were no differences in pulmonary O2 responses between CON and PL (P > 0.05). Multiple step transitions may be required to detect the influence of NO3 − supplementation on steady-state O2.

Measuring the Change by Using Markov Chain Approach in Time-Dependent Transitions and a Real Data Application

In this study, the use of the Markov chain to measure the change in time-dependent transitions is emphasized. Contingency tables were used to measure the time-dependent change of categorical data. Theoretically how to apply the Markov chain in the log-linear model with the help of one-step or higher-step transition matrices was demonstrated. In addition, the stationarity approach and the assessment of the order of the chain were given as the assumption of the model. In the real data application, 1217 undergraduate students, studying in Faculty of Political Science, Engineering, Science departments of Ankara University, were used. It was taken their cumulative average grades for 4 years, average grades for 8 semesters, beginning in the academic year 2013-2014.Whether the change in the success of the students is measurable in 8 semesters and 4 years, has been investigated. According to the results, before making any prediction: it concluded that one-step transition probabilities are not stationary and the three-step transition matrix is the second-order Markov Chain.

Experimental observation of dual magnetic states in topological insulators.

The recently discovered topological phase offers new possibilities for spintronics and condensed matter. Even insulating material exhibits conductivity at the edges of certain systems, giving rise to an anomalous quantum Hall effect and other coherent spin transport phenomena, in which heat dissipation is minimized, with potential uses for next-generation energy-efficient electronics. While the metallic surface states of topological insulators (TIs) have been extensively studied, direct comparison of the surface and bulk magnetic properties of TIs has been little explored. We report unambiguous evidence for distinctly enhanced surface magnetism in a prototype magnetic TI, Cr-doped Bi2Se3. Using synchrotron-based x-ray techniques, we demonstrate a "three-step transition" model, with a temperature window of ~15 K, where the TI surface is magnetically ordered while the bulk is not. Understanding the dual magnetization process has strong implications for defining a physical model of magnetic TIs and lays the foundation for applications to information technology.

Time-Weighted Multi-Touch Attribution and Channel Relevance in the Customer Journey to Online Purchase

We address statistical issues in attributing revenue to marketing channels and inferring the importance of individual channels in customer journeys toward an online purchase. We describe the relevant data structures and introduce an example. We suggest an asymmetric bathtub shape as appropriate for time-weighted revenue attribution to the customer journey, provide an algorithm, and illustrate the method. We suggest a modification to this method when there is independent information available on the relative values of the channels. To infer channel importance, we employ sequential data analysis ideas and restrict to data which ends in a purchase. We propose metrics for source, intermediary, and destination channels based on two- and three-step transitions in fragments of the customer journey. We comment on the practicalities of formal hypothesis testing. We illustrate the ideas and computations using data from a major UK online retailer. Finally, we compare the revenue attributions suggested by the methods...

Analysis of multi-step transitions in spin crossover nanochains

The temperature driven phase transition occurring in spin crossover nanochains has been studied by an Ising-like model considering both short-range and long-range interactions. Various types of spin crossover profiles have been described in this framework, including a novel three-step transition identified in a nanosystem with eight molecules, which is modeled for the first time. A special interest has been also given to stepwise transitions accompanied by two hysteresis loops. The edge and size effects on spin crossover behavior have been investigated in order to get a deeper insight of the underlying mechanisms involved in these unusual spin transitions.

Experimental Realization of a Spin-1/2Triangular-Lattice Heisenberg Antiferromagnet

We report the results of magnetization and specific heat measurements on Ba{3}CoSb{2}O{9}, in which the magnetic Co{2+} ion has a fictitious spin 1/2, and provide evidence that a spin-1/2 Heisenberg antiferromagnet on a regular triangular lattice is actually realized in Ba{3}CoSb{2}O{9}. We found that the entire magnetization curve including the one-third quantum magnetization plateau is in excellent quantitative agreement with the results of theoretical calculations. We also found that Ba{3}CoSb{2}O{9} undergoes a three-step transition within a narrow temperature range.

Influence of Notch Positions on Magnetization Reversal Processes in Permalloy Rings

Magnetoresistance measurements of permalloy rings with different arrangements of notches are performed to find out the conditions for repeatable and controllable magnetization reversal processes. It is observed experimentally that when the included angle between the notches and the field direction is 15°, the magnetization reversals are repeatable in the sweep-up and sweep-down processes, and the magnetization processes are controllable. In contrast, when the included angle between the notches and the field direction is 45° or 30°, the magnetization reversals are unrepeatable and random in the sweep-up and sweep-down processes. By appropriately arranging the positions of the notches, two-step and three-step transitions can be well controlled.

Two-photon decays of pseudotensor mesons π 2(1670), π 2(2250), and π 2(2510)

In terms of relativistic and gauge-invariant spectral-integral technique, we calculate amplitude for the π2 → γγ decay as a three-step transition π2 → q\( \bar q \)(2−+) → γ + q\( \bar q \)(1−−) → γγ. Using wave functions of the q\( \bar q \) components of photon (hep-ph/0406320) and those of pseudotensor mesons π2(1670), π2(2000), π2(2250), and π2(2510) (hep-ph/0511109), we obtain the following values for partial widths: Γπ2(1670)→γγ = 0.072 ± 0.007 keV, Γπ2(2000)→γγ = 0.037 ± 0.004 keV, Γπ2(2250)→γγ = 0.027 ± 0.003 keV, and Γπ2(2510)→γγ = 0.022 ± 0.002 keV. In the calculations, we use the momentum operator expansion, and, in this connection, discuss the problem of nilpotent operators inherent in the considered amplitude. It should be emphasized that measurement of two-photon decays of the π2 states can give valuable information about the long-range quark-antiquark forces which, as one may guess, are related to the quark confinement.

Stepwise transition from the Eocene greenhouse to the Oligocene icehouse

The Eocene–Oligocene transition is the largest global cooling in the Cenozoic period. A comparison of three independent proxies from the continental shelf and deep ocean reveals a three-step transition to cold glacial conditions, with ice sheets 25% larger than their present size.

China’s National Strategy and Policy-making towards Digital Broadcast Media

This paper analyses China’s strategy of developing digital broadcasting services, facing the challenge of digital transition from a policy-making perspective. It starts with an assessment of the goal of the transition from analogue to digital broadcasting within a 12-year time frame from 2003 to 2015. The three-step transition strategy to achieve the goal is discussed. The analysis focuses on China’s policy-making regarding digital broadcast media to narrow the urban-rural gap, supplement fixed broadcast networks with mobile multimedia broadcast networks, and develop a seamless national broadcast network involving terrestrial, cable, satellite and mobile services. The impact of these policies on the growth of various digital broadcast media such as digital broadcasting, cable, satellite, mobile broadcasting and high-definition TV is evaluated. The paper ends with a discussion of China’s digital experience and new issues in digital broadcasting policy-making.

The propeptide in the precursor form of carboxypeptidase Y ensures cooperative unfolding and the carbohydrate moiety exerts a protective effect against heat and pressure.

The heat- and pressure-induced unfolding of the glycosylated and unglycosylated forms of mature carboxypeptidase Y and the precursor procarboxypeptidase Y were analysed by differential scanning calorimetry and/or by their intrinsic fluorescence in the temperature range of 20-75 degrees C or the pressure range of 0.1-700 MPa. Under all conditions, the precursor form showed a clear two-state transition from a folded to an unfolded state, regardless of the presence of the carbohydrate moiety. In contrast, the mature form, which lacks the propeptide composed of 91 amino acid residues, showed more complex behaviour: differential scanning calorimetry and pressure-induced changes in fluorescence were consistent with a three-step transition. These results show that carboxypeptidase Y is composed of two structural domains, which unfold independently but that procarboxypeptidase Y behaves as a single domain, thus ensuring cooperative unfolding. The carbohydrate moiety has a slightly protective role in heat-induced unfolding and a highly protective role in pressure-induced unfolding.

Ca(II)- and Tb(III)-induced stabilization and refolding of anticoagulation factor I from the venom of Agkistrodon acutus.

Anticoagulation factor I (ACF I) isolated from the venom of Agkistrodon acutus is an activated coagulation factor X-binding protein in a Ca(2+)-dependent fashion with marked anticoagulant activity. The equilibrium unfolding/refolding of apo-ACF I, holo-ACF I, and Tb(3+)-reconstituted ACF I in guanidine hydrochloride (GdnHCl) solutions was studied by following the fluorescence and circular dichroism. Metal ions were found to increase the structural stability of ACF I against GdnHCl and thermal denaturation and, furthermore, influence its unfolding/refolding behavior. The GdnHCl-induced unfolding/refolding of both apo-ACF I and Tb(3+)-ACF I is a two-state process with no detectable intermediate state(s), whereas the GdnHCl-induced unfolding/refolding of holo-ACF I in the presence of 1 mM Ca(2+) follows a three-step transition, with intermediate state a (Ia) and intermediate state b (Ib). Ca(2+) ions play an important role in the stabilization of the Ia and Ib states. The decalcification of holo-ACF I shifts the ending zone of unfolding/refolding curve toward lower GdnHCl concentration, whereas the reconstitution of apo-ACF I with Tb(3+) ions shifts the initial zone of denaturation curve toward higher GdnHCl concentration. Therefore, it is possible to find a denaturant concentration (2.0 M GdnHCl) at which refolding from the fully denatured state of apo-ACF I to the Ib state of holo-ACF I or to the native state of Tb(3+)-ACF I can be initiated merely by adding the 1 mM Ca(2+) ions or 10 microM Tb(3+) ions to the unfolded state of apo-ACF I, respectively, without changing the concentration of the denaturant. Using Tb(3+) as a fluorescence probe of Ca(2+), the kinetic results of metal ions-induced refolding provide evidence that the compact Tb(3+)-binding region forms first, and subsequently, the protein undergoes further conformational rearrangements to form the native structure.

Electrochemical identification of intermediate forms of urea denaturation of horse heart cytochrome c

The electrochemical identification of the urea denaturation of horse heart cytochrome c in bulk solution at the 4,4′-dithiodipyridine-modified gold electrode is reported. The results are similar to the three-step transitions of equilibrium studies (Myer et al., Biochemistry, 19 (1980) 199) of urea denaturation of cytochrome c in bulk solution. This method permits a clear resolution of which of the three steps of urea denaturation is electrochemically related. In addition, by analysing the effects of urea on the structural forms of cytochrome c and on the solution properties, as well as the cyclic voltammetric responses of the protein, the individual forms of the urea denaturation of cytochrome c can be understood. The results reflect the superposition of protein denaturation on the electrode surface and in solution.

Multistep transitions between Rydberg states of Na induced by blackbody radiation.

We report on measurements of the time dependence of the populations of Rydberg states of Na with n=25--33 produced by stepwise excitation or deexcitation from the initially populated state 28s, stimulated by room-temperature blackbody radiation. We also present a theoretical modeling of the experiments, which mainly consists of solving the set of coupled rate equations for all the states involved. The results of the calculations show that for times of the order of the lifetime of 28s the populations of ns and nd states produced via two-step transitions can be up to 30% of the populations of np states. We also find that np states get repopulated via three-step transitions at the 2--12 % level. A comparison between the data and calculations shows good agreement.

Markov chain analysis finds a significant influence of neighboring bases on the occurrence of a base in eucaryotic nuclear DNA sequences both protein-coding and noncoding.

Sixty-four eucaryotic nuclear DNA sequences, half of them coding and half noncoding, have been examined as expressions of first-, second-, or third-order Markov chains. Standard statistical tests found that most of the sequences required at least second-order Markov chains for their representation, and some required chains of third order. For all 64 sequences the observed one-step second-order transition count matrices were effective in predicting the two-step transition count matrices, and 56 of 64 were effective in predicting the three-step transition count matrices. The departure from random expectation of the observed first- and second-order transition count matrices meant that a considerable sample of eucaryotic nuclear DNA sequences, both protein coding and noncoding, have significant local structure over subsequences of three to five contiguous bases, and that this structure occurs throughout the total length of the sequence. These results suggested that present DNA sequences may have arisen from the duplication, concatenation, and gradual modification of very early short sequences.

Study of the formation, crystallization and electrical properties of Pd(0.83?x)XxSi0.17 (X=Fe, Co, Ni;x=0.05, 0.10, 0.15) metallic glasses

The substitution of Fe, Co, and Ni (upto 15 at. %) for Pd in Pd-Si metallic glasses raises the crystallization temperature and stability in the order of Fe, Co, and Ni as checked by resistivity and DTA techniques. The 2KF (diameter of the Fermi sphere) is calculated using the nearly free electron model, and the values ofKP (wave number) are determined from the x-ray diffractograms. The criteria of Nagel and Taue (KP=2KF) is found to be valid for all the glasses. The room temperature electrical resistivityϱ293K also increases in the order of Fe, Co, and Ni, and the values are three times higher as compared to the crystalline state. All these glasses show a linear temperature dependence of resistivity between 77K andTcr and some of them are also checked down to 10 K.ϱ−1dϱ/dI values are ∼ 10−4 between 77 K andTcr and increase by a factor of 10 upon crystallization. For some glasses a threestep transition from the amorphous to the crystalline state is observed. In general, ϱ drops upon crystallization but in the case of Pd0.83Fe0.05Si0.17 it increases upon crystallization.Tcr increases with the heating rate.Tcr also increases with the increase in ϱ293K and decrease ofϱ−1dϱ/T.

Gamma Rays from the Proton Bombardment of Sodium

The yield of the (p, $\ensuremath{\gamma}$) capture process in ${\mathrm{Na}}^{23}$ has been studied for proton energies ranging between 0.85 and 1.70 Mev. Resonances were observed corresponding to excited levels of ${\mathrm{Mg}}^{24}$ at 12.71, 12.72, 12.79, 12.86, 12.90, 12.94, 12.97, 13.01, 13.02, 13.08, 13.10, 13.14, and 13.32 Mev. The energies of the $\ensuremath{\gamma}$ rays emitted from the most pronounced resonances were measured by photographing the pulse-height spectrum obtained with a single crystal scintillation spectrometer. These experiments indicate two competing modes of decay: the radiative cascade decay leading to the ground state of ${\mathrm{Mg}}^{24}$ and the emission of a low-energy $\ensuremath{\gamma}$ ray of energy 1.6 Mev which is attributed to the ${\mathrm{Na}}^{23}(\mathrm{p}, \ensuremath{\alpha}\ensuremath{\gamma}){\mathrm{Ne}}^{20}$ reaction. No single-step transitions to the ground state were found in the capture process. Both two - and three-step transitions are observed, but all except one of the $\ensuremath{\gamma}$-ray cascades lead to the well-known 1.37-Mev state in ${\mathrm{Mg}}^{24}$.