Amorphous Bimetallic Co₃Sn₂ Nanoalloys Are Better Than Crystalline Counterparts for Sodium Storage

Sodium-ion batteries are considered as a promising alternative to replace the existing lithium-ion batteries for energy storage due to the benefits of low cost and safety. However, it is still challenging to develop suitable electrode materials for reversible storage of sodium. Metal anodes have high capacity for sodium storage but suffer the issue of poor cyclability due to pulverization caused by large volume variation and electrode disintegration. To address this issue, amorphous bimetallic active–inactive nanoalloy Co–Sn with Sn acting as a high capacity active compound and Co acting as a conductive inactive matrix has been explored here. We demonstrated that amorphous nanoalloys exhibited superior electrochemical performances as compared to the low-crystalline and crystalline counterpart nanoalloys as negative electrode materials for sodium-ion batteries. The degree of crystallinity has negative effects on electrochemical performances. The improved performance of amorphous nanoalloys could be attributed to the easy accessibility for sodium ions, strain accommodation, and defect sites to host sodium ions

Convergence Properties of a Sequential Regression Multiple Imputation Algorithm

<div><p>A sequential regression or chained equations imputation approach uses a Gibbs sampling-type iterative algorithm that imputes the missing values using a sequence of conditional regression models. It is a flexible approach for handling different types of variables and complex data structures. Many simulation studies have shown that the multiple imputation inferences based on this procedure have desirable repeated sampling properties. However, a theoretical weakness of this approach is that the specification of a set of conditional regression models may not be compatible with a joint distribution of the variables being imputed. Hence, the convergence properties of the iterative algorithm are not well understood. This article develops conditions for convergence and assesses the properties of inferences from both compatible and incompatible sequence of regression models. The results are established for the missing data pattern where each subject may be missing a value on at most one variable. The sequence of regression models are assumed to be empirically good fit for the data chosen by the imputer based on appropriate model diagnostics. The results are used to develop criteria for the choice of regression models. Supplementary materials for this article are available online.</p></div

Mechanistic Insights into Synaptic Plasticity Behaviors of Electrolyte-Gated Flexible Transistor Devices

Biological synaptic function simulation using flexible electronic devices based on low-dimensional semiconductor materials is an emerging and rapidly evolving research field with promising applications in brain-like computers and artificial intelligence systems. In this work, we present the fabrication of solution compatible MoS2 thin-film transistors on the ultrathin polymethyl methacrylate substrates via layer-by-layer assembly followed by a one-step transfer printing method. The MoS2 transport channel is controlled by ionic liquid gating with 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, resulting in excellent synaptic performances for emulating memory and perception synapse functions. To investigate the synaptic behaviors, we conduct a series of synaptic spike-dependent experiments and propose an advanced model that delineates the long-term plasticity and short-term plasticity with separate characteristic factors. These findings provide insights into the fundamental mechanisms of synaptic plasticity in electric double-layer devices and contribute to a better understanding of their synaptic performances. In addition, we examine the effects of bending conditions on synaptic plasticity and synaptic weights, unveiling the synergistic interplay between mechanical deformation and synaptic behaviors. Our experimental results, combined with the developed model, are in good agreement and shed light on the influence of mechanical flexibility on the synaptic properties of the devices. In summary, this study establishes a solid foundation for further development of flexible synaptic devices from both practical and theoretical perspectives

An Optimal Hybrid Approach to Calculate Conditional Power

When used in clinical trial adaptive designs, conditional power (CP) is most commonly calculated assuming the current trend, but this approach has been criticized for substantially deviating from the actual CP due to “double-dipping” the interim data (i.e., using the interim data as part of the final analysis test statistic and as the assumption for the remainder of the trial). By contrast, CP assuming the design assumption preserves the shape of the CP curve by “single-dipping” the interim data (i.e., using the interim data once to construct the final test statistic) but is less robust against misspecification. To improve CP estimation, we propose a “1.w dipping” hybrid approach by using an assumption that optimally combines the current trend assumption with weight w and the design assumption with weight 1-w. The optimization of w accounts for the uncertainty of the true treatment effect size and can be linked with study priorities through customizable penalty functions. Through simulation using sample size re-estimation designs, we demonstrate that the proposed approach maximizes the precision of CP-based interim decision making on average and leads to other desirable operating characteristics. Given its flexibility and superior performance, we recommend this novel approach over the existing methods.</p

Fabrication of Oxidative and pH Dual-Responsive Photonic Crystals Based on Sulfide-Containing Block Copolymers

Photonic crystals (PCs) derived from responsive polymers exhibit adjustable photonic band gaps under external stimuli, and they have abundant applications in different fields. Herein, oxidative and pH dual-responsive copolymers were synthesized using reversible addition–fragmentation chain transfer (RAFT) polymerization with a functional monomer of combined phenyl vinyl sulfide (PVS) and N,N′-(dimethylamino) ethyl acrylate (DMAEA). The oxidatively responsive PVS segment generated copolymers with a refractive index (RI) change, and the pH-responsive DMAEA segment generated copolymers with a distance change in the aggregation state. Fabricating PCs with these copolymers resulted in unique dual-responsive behavior, e.g., the reflective peaks of PCs exhibited blue shifts to varying degrees under different oxidative and pH conditions. This report presents a high refractive index polymer derived from S-vinyl sulfide derivatives, in which the refractive index changed through selective oxidation and dual responsiveness was observed when the derivatives were combined with DMAEA units. Owing to changes in the RI and the period distance in PCs, a predictable change in the band gap of PCs for the aim of realizing a dual-responsive PC sensor was successfully obtained

Local Dielectric Environment Dependent Local Electric Field Enhancement in Double Concentric Silver Nanotubes

The local dielectric environment dependent local field enhancement properties in double concentric silver nanotubes have been obtained by using the plasmon hybridization method and quasi-static calculation. Because of the inserted silver nanotube, the geometrical parameter controlled intertube coupling greatly improves the tunability of the local dielectric dependent enhancement of local electric field. In the inner dielectric core, the most intense local field factor peak corresponds to the |ω_–⁺⟩ plasmon mode, and the major local field factor peak usually changes nonmonotonously as the inner core or spacer layer dielectric is increased. The maximum local field could be obtained by fine-tuning the local dielectric constant in the double tubes with thick inner and outer tube thickness. In the dielectric spacer layer, the most intense local field factor peak corresponds to the |ω_–^–⟩ plasmon mode. The intense local field could be obtained with small spacer layer dielectric constant and reaches the maximum value when the double tube has thick inner and outer tube thickness. This inner core and spacer layer dielectric dependent local field enhancement provides the potential application of the real time tubular nanosensor based on local field induced fluorescence enhancement and surface-enhanced Raman scattering (SERS)

Thermodynamic and Structural Insights into Nanocomposites Engineering by Comparing Two Materials Assembly Techniques for Graphene

Materials assembled by layer-by-layer (LBL) assembly and vacuum-assisted flocculation (VAF) have similarities, but a systematic study of their comparative advantages and disadvantages is missing. Such a study is needed from both practical and fundamental perspectives aiming at a better understanding of structure–property relationships of nanocomposites and purposeful engineering of materials with unique properties. Layered composites from polyvinyl alcohol (PVA) and reduced graphene (RG) are made by both techniques. We comparatively evaluate their structure, mechanical, and electrical properties. LBL and VAF composites demonstrate clear differences at atomic and nanoscale structural levels but reveal similarities in micrometer and submicrometer organization. Epitaxial crystallization and suppression of phase transition temperatures are more pronounced for PVA in LBL than for VAF composites. Mechanical properties are virtually identical for both assemblies at high RG contents. We conclude that mechanical properties in layered RG assemblies are largely determined by the thermodynamic state of PVA at the polymer/nanosheet interface rather than the nanometer scale differences in RG packing. High and nearly identical values of toughness for LBL and VAF composites reaching 6.1 MJ/m3 observed for thermodynamically optimal composition confirm this conclusion. Their toughness is the highest among all other layered assemblies from RG, cellulose, clay, etc. Electrical conductivity, however, is more than 10× higher for LBL than for VAF composites for the same RG contents. Electrical properties are largely determined by the tunneling barrier between RG sheets and therefore strongly dependent on atomic/nanoscale organization. These findings open the door for application-oriented methods of materials engineering using both types of layered assemblies

Hollow Cocoon-Like Hematite Mesoparticles of Nanoparticle Aggregates: Structural Evolution and Superior Performances in Lithium Ion Batteries

We report the facile, fast, and template-free preparation of hollow α-Fe₂O₃ with unique cocoon-like structure by a one-pot hydrothermal method without any surfactants in a short reaction time of 3 h only. In contrast, typical hydrothermal methods to prepare inorganic hollow structures require 24 h or a few days. Templates and/or surfactants are typically used. The hollow α-Fe₂O₃ nanococoon was thoroughly characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Ex situ analysis of a series of samples prepared at different reaction times clearly revealed the structural evolution and possible formation mechanism. Superior electrochemical performance in terms of cyclability, specific capacity, and high rate was achieved, which could be attributed to its unique hollow cocoon-like structure. Structural stability was revealed by analyzing the samples after 120 charge–discharge cycles. The unusual structural stability of the hollow α-Fe₂O₃ nanococoons after 120 cycles, which is rarely observed for transition metal oxides of particle aggregates, will guarantee further research investigation. Experimental evidence further demonstrated that hollow nanococoons exceed solid nanococoons in reversible lithium-ion storage

Ultrastructural aspects of internal glands in leaves of <i>Pogostemon cablin</i>.

<p>An internal gland at secretory stage shows the unique characteristics (A–G). (A) A mature internal glands has a cytoplasmically dense head cell (HC), a narrow stalk cell (SC) with densely stained lateral cell wall (arrow) and a basal cell (BC). (B) The sub-cuticular space (SCS) contains fibrillar material (arrows) and lipid-like material (L). (C) There are numerous small vacuoles (V), mitochondria (M), abundant rough endoplasmic reticulum (RER) and many plastids (P) in the head cell. (D) The plastids (P) are observed to be in close to RER (arrow). (E) And the RER (arrow) is also close to the plasma membrane (PM). (F) The details of the stalk cell show the big nucleus (N), the plump chloroplast (C) and numerous mitochondria (M). (G) A part of transverse wall between stalk cell and head cell is penetrated by numerous plasmodesmata (arrows). (H–J) The ultrastructural aspects of internal glands at late-secretory stage are observed as follows. (H) The sub-cuticular space is filled with numerous lipid spherosomes (_*). (I) Plastids (P) contain numerous oil droplets (arrows). (J) Lipid droplets (L) in sub-cuticular space are surrounded by silk-like structure (arrows).</p

Micro Single Crystals of Hematite with Nearly 100% Exposed {104} Facets: Preferred Etching and Lithium Storage

The controlled synthesis of inorganic single crystals with a large percentage of exposed high-index facets has attracted much attention. However, high-index facets usually disappear during the early stage of crystal growth due to the minimization of surface energy and typically facet-controlling agents are employed. Here a facile fast hydrothermal method for the preparation of microsize α-Fe₂O₃ rhombohedra with nearly 100% exposed {104} facets was developed in a simple formulated solvent without any additives. The hydrothermal reaction time could be as short as 75 min, in contrast to typical hydrothermal reactions over days. The preferred etching edges along the diagonal axis of microsize rhombohedra by the self-generated ions was observed, which could be potentially extended to synthesize and tailor other transition metal oxides. The formation mechanism was revealed by ex situ FESEM observations of the samples prepared at different reaction times. Improved electrochemical performances in terms of cyclability, specific capacity, and high rate were achieved. The specific capacity was maintained at 550 mAh/g after 120 cycles at a rate of 200 mA/g. Experimental evidence clearly shows that the as-designed solid microsize α-Fe₂O₃ can effectively and reversibly store lithium ions with performance comparable to nanosize α-Fe₂O₃, suggesting electrode materials with particle size at the microscale will be worth further exploration