Fast Hopping Research Articles

Exceptional Anhydrous Proton Conduction in Covalent Organic Frameworks.

Covalent organic frameworks (COFs) offer an irreplaceable platform for mass transport, as they provide aligned one-dimensional channels as pathways. Especially, proton conduction is of great scientific interest and technological importance. However, unlike proton conduction under humidity, anhydrous proton conduction remains a challenge, as it requires robust materials and proceeds under harsh conditions. Here, we report exceptional anhydrous proton conduction in stable crystalline porous COFs by integrating neat phosphoric acid into the channels to form extended hydrogen-bonding networks. The phosphoric acid networks in the pores are stabilized by hierarchical multipoint and multichain hydrogen-bonding interactions with the 3D channel walls. We synthesized five hexagonal COFs that possess different pore sizes, which are gradually tuned from micropores to mesopores. Remarkably, mesoporous COFs with a high pore volume exhibit an exceptional anhydrous proton conductivity of 0.31 S cm-1, which marks the highest conductivity among all examples reported for COFs. We observed that the proton conductivity is dependent on the pore volume, pore size, and content of phosphoric acid. Increasing the pore volume improves the proton conductivity in an exponential fashion. Remarkably, changing the pore volume from 0.41 to 1.60 cm3 g-1 increases the proton conductivity by 1150-fold. Interestingly, as the pore size increases, the activation energy barrier of proton conduction decreases in linear mode. The mesopores enable fast proton hopping across the channels, while the micropores follow sluggish vehicle conduction. Experiments on tuning phosphoric acid loading contents revealed that a well-developed hydrogen-bonding phosphoric acid network in the pores is critical for proton conduction.

All-natural 2D nanofluidics as highly-efficient osmotic energy generators

Two-dimensional nanofluidics based on naturally abundant clay are good candidates for harvesting osmotic energy between the sea and river from the perspective of commercialization and environmental sustainability. However, clay-based nanofluidics outputting long-term considerable osmotic power remains extremely challenging to achieve due to the lack of surface charge and mechanical strength. Here, a two-dimensional all-natural nanofluidic (2D-NNF) is developed as a robust and highly efficient osmotic energy generator based on an interlocking configuration of stacked montmorillonite nanosheets (from natural clay) and their intercalated cellulose nanofibers (from natural wood). The generated nano-confined interlamellar channels with abundant surface and space negative charges facilitate selective and fast hopping transport of cations in the 2D-NNF. This contributes to an osmotic power output of ~8.61 W m−2 by mixing artificial seawater and river water, higher than other reported state-of-the-art 2D nanofluidics. According to detailed life cycle assessments (LCA), the 2D-NNF demonstrates great advantages in resource consumption (1/14), greenhouse gas emissions (1/9), and production costs (1/13) compared with the mainstream 2D nanofluidics, promising good sustainability for large-scale and highly-efficient osmotic power generation.

Enhancing Arousal Level Detection in EEG Signals through Genetic Algorithm-based Feature Selection and Fast Bit Hopping.

This study explores a novel approach to detecting arousal levels through the analysis of electroencephalography (EEG) signals. Leveraging the Faller database with data from 18 healthy participants, we employ a 64-channel EEG system. The approach we employ entails the extraction of ten frequency characteristics from every channel, culminating in a feature vector of 640 dimensions for each signal instance. To enhance classification accuracy, we employ a genetic algorithm for feature selection, treating it as a multiobjective optimization task. The approach utilizes fast bit hopping for efficiency, overcoming traditional bit-string limitations. A hybrid operator expedites algorithm convergence, and a solution selection strategy identifies the most suitable feature subset. Experimental results demonstrate the method's effectiveness in detecting arousal levels across diverse states, with improvements in accuracy, sensitivity, and specificity. In scenario one, the proposed method achieves an average accuracy, sensitivity, and specificity of 93.11%, 98.37%, and 99.14%, respectively. In scenario two, the averages stand at 81.35%, 88.65%, and 84.64%. The obtained results indicate that the proposed method has a high capability of detecting arousal levels in different scenarios. In addition, the advantage of employing the proposed feature reduction method has been demonstrated.

Li-Ion Dynamics in Li2S:LiI Composites – on the Effect of Solid-Solution Formation on Overall Li+ Transport

The enormous interest in developing powerful all-solid-state Li-ion batteries led to a boost in electrolyte research. Some Li-ion conductors have Ag-bearing analogs; the fast Ag+ ion conductor, Ag3SI, could be one of such materials. So far, no clear evidence is available that the Li-counterpart, Li3SI, does exist. Here, we treated an equimolar mixture of Li2S and LiI in high-energy ball mills and followed structural changes via X-ray diffraction (XRD) and magic-angle spinning (MAS) 6,7Li nuclear magnetic resonance (NMR) measurements. Differences in local structures as sensed by MAS NMR will be discussed for annealed and non-annealed samples, that is, powder samples directly obtained after finishing the ball-milling procedure. For nanocrystalline, non-annealed Li2S:LiI, the MAS NMR response is characterized by a broad distribution of NMR lines showing chemical shifts between that of pure Li2S and LiI, hence pointing to the formation of solid-solution like regions.Ion dynamics on different length scales was probed with variable-temperature, potentiostatic conductivity spectroscopy as well as solid-state NMR spin-lattice relaxation (SLR) measurements. Defect-rich nanocrystalline Li2S:LiI has to be characterized by an overall conductivity that is 2 orders of magnitude higher as compared to that of the microcrystalline, annealed reference sample. SLR NMR experiments supports this result and reveal lower activation energies for both the fast local hopping ion dynamics and long-range ion diffusivity in the sample directly obtained after ball milling. Finally, mixing-time dependent 6Li 2D exchange NMR spectroscopy reveals even (very) slow Li+ exchange between the Li2S-rich and LiI-rich regions in the nanocrystalline sample. Off-diagonal intensities are especially seen for mixing times longer than 80 ms.

Covalently bridged bond assembly of MoS2 lamellae onto a graphene sheet: an outstanding electrode for high rate and long-life lithium/sodium-ion batteries

The practical application of Molybdenum sulphide (MoS2) electrodes has been hindered by its structural instability, and poor electrical conductivity. To enhance the cycle stability and rate performance of MoS2 in lithium/sodium-ion batteries (LIBs/SIBs), we synthesized a graphene-supported MoS2 composite (MoS2@rGO) with affluent covalent bridged bonds through a facile and scalable hydrothermal and annealing process. The covalent bridged bonds of Mo–S–C, Mo–O–C and C–O–S provide an effective charge transfer path between MoS2 and graphene, facilitating fast charge hopping and improving rate performance. As anode materials for LIBs, the MoS2@rGO exhibited exceptional long-term cycle life (906 mAh g−1 at 1.0 A g−1 after 400 cycles) and outstanding rate capability (1267.7/314.7 mAh g−1 at 0.1/6.5 A g−1). Additionally, the MoS2@rGO electrode demonstrated a stable reversible capacity of 521.7 mAh g−1 at 1.0 A g−1 after 700 cycles and excellent rate capabilities of 665.1 and 326.3 mAh g−1 at 0.1 and 10.0 A g−1 in SIBs. The edge Mo of MoS2 is directly coupled with the oxygen of the functional group on rGO, achieved by adjusting the pH value of the solution to tune the surface charge feature, can effectively enhance the structural stability of electrode even under higher current density.

Simultaneous High Ionic Conductivity and Lithium-Ion Transference Number in Single-Ion Conductor Network Polymer Enabling Fast-Charging Solid-State Lithium Battery.

Developing solid-state electrolyte with sufficient ionic conduction and flexible-intimate interface is vital to advance fast-charging solid-state lithium batteries. Solid polymer electrolyte yields the promise of interfacial compatibility, yet its critical bottleneck is how to simultaneously achieve high ionic conductivity and lithium-ion transference number. Herein, single-ion conducting network polymer electrolyte (SICNP) enabling fast charging is proposed to positively realize fast lithium-ion locomotion with both high ionic conductivity of 1.1 × 10-3 S cm-1 and lithium-ion transference number of 0.92 at room temperature. Experimental characterization and theoretical simulations demonstrate that the construction of polymer network structure for single-ion conductor not only facilitates fast hopping of lithium ions for boosting ionic kinetics, but also enables a high dissociation level of the negative charge for lithium-ion transference number close to unity. As a result, the solid-state lithium batteries constructed by coupling SICNP with lithium anodes and various cathodes (e.g., LiFePO4 , sulfur, and LiCoO2 ) display impressive high-rate cycling performance (e.g., 95% capacity retention at 5 C for 1000 cycles in LiFePO4 |SICNP|lithium cell) and fast-charging capability (e.g., being charged within 6min and discharged over than 180min in LiCoO2 |SICNP|lithium cell).Ourstudy provides a prospective direction for solid-state electrolyte that meets the lithium-ion dynamics for practical fast-charging solid-state lithium batteries.

Highly Ionic Conductive and Degradable Solid Electrolyte Enabled by a Three-Dimensional Cross-Linking Copolymeric Structure

High ionic conductivity is an essential prerequisite for the application of solid electrolyte (SE) oriented toward solid-state lithium battery (SSLB). Meanwhile, sustainability and environment friendliness of solid electrolytes are required from the green chemistry perspective. However, research on solid electrolytes with simultaneously high ionic conductivity and good degradability remains in its infancy. Herein, a degradable network copolymer solid electrolyte (DNCPSE) was designed and prepared for simultaneously realizing fast lithium-ion transport with a high ionic conductivity of 7.5 × 10–4 S cm–1 at room temperature and fast degradable properties (e.g., completely degraded within 1.5 h in alkaline condition). Experimental characterizations have demonstrated that the construction of a copolymeric network with sufficient polar groups not only boosts fast lithium-ion hopping but also facilitates the whole decomposition of DNCPSE. By virtue of the combined features, this DNCPSE presents remarkable degradable and electrochemical performances. As a result, the DNCPSE-based Li symmetrical cells display high stability (e.g., >1200 h at 0.1 mA cm–2). Moreover, the Li|DNCPSE|LiFePO4 full cells also display impressive cycling performance (e.g., >200 cycles at 1C). This work provides a promising designed rationale and strategy for sustainable solid electrolytes toward green and efficient solid-state lithium battery.

Development of ultrafast camera-based single fluorescent-molecule imaging for cell biology.

The spatial resolution of fluorescence microscopy has recently been greatly enhanced. However, improvements in temporal resolution have been limited, despite their importance for examining living cells. Here, we developed an ultrafast camera system that enables the highest time resolutions in single fluorescent-molecule imaging to date, which were photon-limited by fluorophore photophysics: 33 and 100 µs with single-molecule localization precisions of 34 and 20 nm, respectively, for Cy3, the optimal fluorophore we identified. Using theoretical frameworks developed for the analysis of single-molecule trajectories in the plasma membrane (PM), this camera successfully detected fast hop diffusion of membrane molecules in the PM, previously detectable only in the apical PM using less preferable 40-nm gold probes, thus helping to elucidate the principles governing the PM organization and molecular dynamics. Furthermore, as described in the companion paper, this camera allows simultaneous data acquisitions for PALM/dSTORM at as fast as 1 kHz, with 29/19 nm localization precisions in the 640 × 640 pixel view-field.

Reaction-Limited Quantum Reaction-Diffusion Dynamics.

We consider the quantum nonequilibrium dynamics of systems where fermionic particles coherently hop on a one-dimensional lattice and are subject to dissipative processes analogous to those of classical reaction-diffusion models. Particles can either annihilate in pairs, A+A→0, or coagulate upon contact, A+A→A, and possibly also branch, A→A+A. In classical settings, the interplay between these processes and particle diffusion leads to critical dynamics as well as to absorbing-state phase transitions. Here, we analyze the impact of coherent hopping and of quantum superposition, focusing on the so-called reaction-limited regime. Here, spatial density fluctuations are quickly smoothed out due to fast hopping, which for classical systems is described by a mean-field approach. By exploiting the time-dependent generalized Gibbs ensemble method, we demonstrate that quantum coherence and destructive interference play a crucial role in these systems and are responsible for the emergence of locally protected dark states and collective behavior beyond mean field. This can manifest both at stationarity and during the relaxation dynamics. Our analytical results highlight fundamental differences between classical nonequilibrium dynamics and their quantum counterpart and show that quantum effects indeed change collective universal behavior.

Sub‐2‐nm Channels within Covalent Triazine Framework Enable Fast Proton‐Selective Transport in Flow Battery Membrane

AbstractIon conductive membranes (ICMs) with robust sub‐2‐nm channels show high proton transport rate in flow battery, but it remains a great challenge to precisely control the ion sieving of the membranes. Herein, as a promising proton‐selective carrier, sulfonated piperazine covalent triazine framework (s‐pCTF) with the channel size of ≈1.5 nm and abundant fast proton hopping sites is introduced into sulfonated poly(ether ether ketone) (SPEEK) to fabricate advanced ICM for vanadium flow battery (VFB) application. The interior protoplasmic channels of s‐pCTF demonstrate significant Donnan exclusion effect, resulting in a high proton/vanadium ion selectivity in theory (6.22 × 105). Meanwhile, the nitrogen‐rich sub‐2‐nm channels yield fast proton highway, and exterior‐grafted sulfonic acid groups further facilitate the proton transfer. By regulating the ion sieving and proton conductivity, the optimal hybrid membrane exhibits synchronously improved battery performance with an enhanced energy efficiency (92.41% to 78.53% at 40–200 mA cm−2) and long‐term stability for 900 cycles over 400 h (EE: 87.2–85% at 120 mA cm−2), outperforming pure SPEEK and Nafion212 membranes. This study validates the applicability of organic porous CTF with sub‐2‐nm channels and desired functionality in ICMs for high‐performance VFB application.

Effect of Proton Transfer on Electrocatalytic Water Oxidation by Manganese Phosphates

AbstractThe effect of proton transfer on water oxidation has hardly been measurably established in heterogeneous electrocatalysts. Herein, two isomorphous manganese phosphates (NH4MnPO4 ⋅ H2O and KMnPO4 ⋅ H2O) were designed to form an ideal platform to study the effect of proton transfer on water oxidation. The hydrogen‐bonding network in NH4MnPO4 ⋅ H2O has been proven to be solely responsible for its better activity. The differences of the proton transfer kinetics in the two materials indicate a fast proton hopping transfer process with a low activation energy in NH4MnPO4 ⋅ H2O. In addition, the hydrogen‐bonding network can effectively promote the proton transfer between adjacent Mn sites and further stabilize the MnIII−OH intermediates. The faster proton transfer results in a higher proportion of zeroth‐order in [H+] for OER. Thus, proton transfer‐affected electrocatalytic water oxidation has been measurably observed to bring detailed insights into the mechanism of water oxidation.

Effect of Proton Transfer on Electrocatalytic Water Oxidation by Manganese Phosphates.

The effect of proton transfer on water oxidation has hardly been measurably established in heterogeneous electrocatalysts. Herein, two isomorphous manganese phosphates (NH4 MnPO4 ⋅ H2 O and KMnPO4 ⋅ H2 O) were designed to form an ideal platform to study the effect of proton transfer on water oxidation. The hydrogen-bonding network in NH4 MnPO4 ⋅ H2 O has been proven to be solely responsible for its better activity. The differences of the proton transfer kinetics in the two materials indicate a fast proton hopping transfer process with a low activation energy in NH4 MnPO4 ⋅ H2 O. In addition, the hydrogen-bonding network can effectively promote the proton transfer between adjacent Mn sites and further stabilize the MnIII -OH intermediates. The faster proton transfer results in a higher proportion of zeroth-order in [H+ ] for OER. Thus, proton transfer-affected electrocatalytic water oxidation has been measurably observed to bring detailed insights into the mechanism of water oxidation.

The Effectiveness of Lateral Hop and Leg Press Training on Limb Strength and Explosive Power for Athletes

The aim of the study was to examine the effectiveness of fast lateral hop (LHC), slow lateral hop (LHL) and leg press (LLP) training on increasing the strength and explosive power of the leg muscles simultaneously. The approach method is in the form of an experiment using a Randomized Pretest-Posttest Control Group Design. The sample is 51 people divided into three groups using the ordinal pairing matched technique. Data were obtained using test and non-test instruments and collected using experimental techniques, observation and physical condition tests. Data analysis using one-way Manova technique Hotelings Trace method. The results of the analysis found that the F test = 25,413 and the significance of F = 0.000 < 0.05, meaning that LHC, LHL and LLP training were effective in increasing the strength and explosive power of the leg muscles simultaneously. The results of the Between-Subjects Effects analysis in the form of partial eta squared variation KOT 15.6% and variation DEOT = 63.4%. The conclusion of the study was that there was a significant effect of LHC, LHL and LLP training on increasing the strength and explosive power of the leg muscles simultaneously. LLP training is more effective in increasing leg muscle strength, and LHC training is more effective in increasing the power of leg muscles.

The kinetics of reentrant glass transition in metallic liquids

Reentrant glass transition is a new glass-transition phenomenon in which a devitrified liquid reenters a second glassy state and is well-known in some colloidal systems. Reentrant glass transition has been recently discovered in metallic-liquid systems but its ongoing mechanisms remain mostly unknown. Here, the reentrant glass transition of a series of Pd-Ni-P metallic liquids are investigated using fast-calorimetric analyses and ab-initio molecular dynamics simulation. While the amount of heat release of reentrant glass transition in different Pd-Ni-P liquids are similar, the change of liquid kinetics itself results in different reentrant-glass-transition behaviors: the transition kinetics is governed by the fast hopping of P atoms rather than the cooperative liquid motions related with vitrification. The reentrant glass transition is found to be related to medium-range structural ordering process through vertex-sharing of the P-centered polyhedral clusters. The kinetics map of liquid freezing for Pd-Ni-P glass-forming liquids over broad ranges of heating-rate and composition is presented.

Interlayer Hopping Kinetics of Vacancies in CrI3 Layers Leading to Monolayer/Bilayer Heterostructures

Abstract2D magnets, especially their multilayer structures exhibit promising applications in magnetic sensing and data storage due to magnetoresistance effect. Defects have significant influence on the performance of devices and are widely investigated for typical 2D magnets. However, the defects in multilayer structures are rarely studied. Here, based on density functional theory, an interesting synergy of the interlayer migration of I and Cr vacancies in bilayer CrI3 is found. Cr vacancies attract I vacancies in adjacent layers and greatly reduce the intermigration barrier of I. On the other hand, I vacancies also facilitate the interlayer migration of Cr vacancies. A monolayer/bilayer heterostructure is expected to form after annealing at about 500 K due to the fast hopping of vacancies between layers and the strong driving force for vacancies clustering. The interlayer hopping and merge of vacancies help eliminate defect states in bilayer CrI3. These results provide an atomic‐scale understanding of vacancy migration between CrI3 layers, which is important for defect engineering and applications of bilayer and multilayer CrI3.

Nonadiabatic Dynamics of Polaron Hopping and Coupling with Water on Reduced TiO2.

By interplay between first-principles molecular dynamics and nonadiabatic molecular dynamics simulations based on the decoherence-induced surface-hopping approach, we investigate and quantify the mechanisms through which different electron polaron hopping regimes in the reduced anatase TiO2(101) surface influence recombination of photogenerated charge carriers, also in the presence of adsorbed water (H2O) molecules. The simulations reveal that fast hopping regimes promote ultrafast recombination of photogenerated charge-carriers. Conversely, charge recombination is delayed in the presence of slower polaron hopping and even more so if the polaron is pinned at one Ti-site, as typical following adsorption of H2O on the anatase(101) surface. These trends are related to the observed enhancement of the space and energy overlap between conduction band minimum and polaron band gap states, and the ensuing nonadiabatic couplings (NAC) strengths, during a polaronic hop. We expect these insights on the beneficial role of polaron diffusion pinning for the extended lifetime of photoexcitations in TiO2 to sustain ongoing developments of photocatalytic strategies based on this substrate.

A fast and robust trajectory surface hopping method: Application to the intermolecular photodissociation of a carbon dioxide dimer cation (CO2)2+

Our recently developed trajectory surface hopping method uses numerical time derivatives of adiabatic potential gradients to estimate the nonadiabatic transition probability and the hopping direction. To demonstrate the practicality of the novel method, we applied it to the intermolecular photodissociation of a carbon dioxide dimer cation (CO2)2 +. Our simulations reproduced the measured velocity distribution of CO2 + fragments consisting of two (fast and slow) components and revealed that nonadiabatic transitions occur promptly toward the electronic ground state regardless of the fragment velocity. The structure of (CO2)2 + at optical excitation governs the fate of subsequent nonadiabatic dynamics leading to a fast or slow dissociation. Our method gave similar results to the fewest switches algorithm at lower computational expense. Our fast and robust surface hopping method is promising for the investigation of nonadiabatic dynamics in large and complex systems.

Effects of locomotion task constraints on running in boys with overweight/obesity: The mediating role of developmental delays.

Childhood obesity adversely affects the musculoskeletal system and is accompanied with motor development delays. Movement interventions that change the body composition and movement patterns is suggested as an effective way to minimise the childhood obesity adverse effects. Whether a locomotion task constraints intervention is effective to change body composition, motor performance and running efficiency in overweight/obese boys with different levels of motor development. Forty young boys (age: 8.21 ± 1.01 years) whose body mass index (BMI) was above the 85th normative ranked score were divided into 4 independent groups according to their development and BMI: intervention-typical, intervention-delay, control-typical and control-delay. A 6-week task constraints intervention with an emphasis on improving locomotion skills such as fast walking, running, jumping, hopping, skipping and leaping were carried out in the intervention group. The pre and post-intervention difference score on the sample dependent variables showed decreases in body mass and BMI and improvements in agility, joint kinematics and running economy in the intervention-typical group relative to other groups. The findings highlight that the boys with overweight/obesity and typical development can benefit more from a short-term developmentally-appropriate intervention to refine the running pattern and agility skill that was accompanied by positive changes in body composition.

A novel fast and fair asynchronous channel hopping rendezvous scheme in cognitive radio networks for internet of things

Recent years have witnessed significant growth in the area of Internet of things (IoT) and is further expected to increase manifolds in the foreseeable future. Such a massive usage of IoT comes with spectrum scarcity issues. In the last few years, Cognitive Radio Network (CRN) has been widely researched because of its potential to be an effective solution to the problem of spectrum scarcity. The unlicensed users in CRN need to rendezvous on a commonly available channel for the purpose of necessary information exchange. Channel hopping (CH) is one of the representative technique to achieve rendezvous in CRNs in which users hop among available channels according to a pre-defined sequence. Providing guaranteed rendezvous which is fair and having full rendezvous diversity in minimum possible time is a challenging issue in CRN. In this paper, we propose an asymmetric asynchronous CH algorithm that provides guaranteed, fair and full rendezvous diversity among the users. The idea is to construct sender and receiver matrices to generate CH sequences based on the number of available channels of sender and receiver. Analytical and simulation results verify that the proposed algorithm outperform some existing state of the art rendezvous algorithms in terms of maximum time to rendezvous (MTTR), provide full rendezvous diversity and rendezvous fairness among the users.

Role of Molecular Architecture on Ion Transport in Ethylene oxide-Based Polymer Electrolytes

This work aims to develop a detailed mechanistic understanding of the role of a graft polymer architecture on lithium ion (Li+) transport in poly(ethylene oxide)-based polymer electrolytes. Specifically, we compare Li+ transport in poly(ethylene oxide) (PEO) versus poly(oligo oxyethylene methacrylate) (POEM) polymers doped with lithium bis(trifluoromethanesulfonyl) (LiTFSI) salts, using both experimental electrochemical characterization and molecular dynamics (MD) simulations. Our results indicate that POEM exhibits a range of relaxation processes that cannot be interpreted solely in terms of glass-transition temperature (Tg) effects. Due to its side-chain architecture, the segmental relaxation of POEM is nonuniform across ether oxygens (EOs) and shows a more pronounced sensitivity to temperature above Tg compared to PEO. Moreover, POEM also exhibits a nonuniform Li+ coordination behavior, in which Li+ is primarily solvated by two different chains in POEM, compared to a single chain in PEO. Li+ transport in POEM occurs via two events with distinct characteristic times: a fast intrachain hopping along side chains and a slow interchain hopping between side chains. Taken together, the relaxation processes and ion transport mechanisms identified in POEM provide useful insights into design of more effective solid polymer electrolytes.