Flexible Counterparts Research Articles

Restricting Linker Rotation in Nanocages of ZIF-8 Membranes using Crown Ether "Molecular Locks" for Enhanced Propylene/Propane Separation.

ZIF-8 membranes have long been prized for their exceptional C3H6/C3H8 separation performance. On the other hand, ZIF-8 has structural flexibility, where the external pressure triggers channel expansion, potentially deteriorating the molecular sieving ability. Here, we demonstrate a reliable strategy to fine-tune the flexible pore structure of ZIF-8 by embedding crown ether within a ZIF-8 membrane. Benzo-15-crown-5 (15C5) was selected as the cavity occupant and perfectly confined in the sodalite (SOD) cage of ZIF-8. The 15C5 molecules, which have a size comparable to the nanocage, impose a spatial constraint on linker rotation, enabling the phase transition to a rigid structure in the flexible ZIF-8. The corresponding 15C5@ZIF-8 membranes achieve an ultrahigh C3H6/C3H8 selectivity of 220, outperforming that of most membranes. Unlike their flexible counterparts, the resulting membranes manifest a positive increase in the C3H6/C3H8 separation factor with elevated pressure, securing a record-high C3H6/C3H8 separation factor of 331 under 7 bar. More importantly, extraordinary separation stability was demonstrated with continuous measurement, which is highly desirable for practical applications.

Supercoiled ring polymers under shear flow.

We apply monomer-resolved computer simulations of supercoiled ring polymers under shear, taking full account of the hydrodynamic interactions, accompanied, in parallel, by simulations in which these are switched off. The combination of bending and torsional rigidities inherent in these polymers, in conjunction with hydrodynamics, has a profound impact on their flow properties. In contrast to their flexible counterparts, which dramatically deform and inflate under shear [Liebetreu et al., Commun. Mater. 2020, 1, 4], supercoiled rings undergo only weak changes in their overall shape and they display both a reduced propensity to tumbling (at fixed Weissenberg number) and a much stronger orientational resistance with respect to their flexible counterparts. In the presence of hydrodynamic interactions, the coupling of the polymer to solvent flow is capable of bringing about a topological transformation of writhe to twist at strong shear upon conservation of the overall linking number.

A paradigm shift in the room-temperature self-assembly of tunable metal–organic frameworks composed of flexible neutral linkers with six N-donor atoms and a curved dicarboxylate

A non-traditional strategy for making three-component Cd(ii) MOFs composed of flexible linkers with six N-donor atoms and a curved dicarboxylate.

Thorough Optimization for Intrinsically Stretchable Organic Photovoltaics.

The development of intrinsically stretchable organic photovoltaics (is-OPVs) with a high efficiency is of significance for practical application. However, their efficiencies lag far behind those of rigid or even flexible counterparts. To address this issue, an advanced top-illuminated OPV is designed and fabricated, which is intrinsically stretchable and has a high performance, through systematic optimizations from material to device. First, the stretchability of the active layer is largely increased by adding a low-elastic-modulus elastomer of styrene-ethylene-propylene-styrene tri-block copolymer (SEPS). Second, the stretchability and conductivity of the opaque electrode are enhanced by a conductive polymer/metal (denoted as M-PH1000@Ag) composite electrode strategy. Third, the optical and electrical properties of a sliver nanowire transparent electrode are improved by a solvent vapor annealing strategy. High-performance is-OPVs are successfully fabricated with a top-illuminated structure, which provides a record-high efficiency of 16.23%. Additionally, by incorporating 5-10% elastomer, a balance between the efficiency and stretchability of the is-OPVs is achieved. This study provides valuable insights into material and device optimizations for high-efficiency is-OPVs, with a low-cost production and excellent stretchability, which indicates a high potential for future applications of OPVs.

An investigation of fatigue response of well cement under cyclic loading and impact on zonal isolation performance

Cyclic bottomhole pressure fluctuation is very prevalent in modern well construction and enhanced petroleum recovery applications and poses a great challenge to annular seal integrity and successful zonal isolation, even in cases where the cement seal exhibits excellent initial quality. Thus, annular sealants must be designed to mitigate or minimize the deleterious effects of cyclic pressure fluctuations on the annular seal. Optimal cement designs for this purpose require a proper understanding of damage modes and mechanisms associated with a cyclic pressure regime, as well as the impact of the cement mechanical integrity evolution on the leakage of the cemented annulus. Using four cement formulations with distinct mechanical and microstructural properties, we investigated the mechanical integrity evolution and leakage characteristics of cemented pipe specimens subjected to confinement pressure fluctuations. Via microscopic inspection of the cement/pipe interface after pressure cycling and permeability measurements during pressure cycling, we attempted to correlate cement properties with leakage and suggest a recommendation for optimal cement design and successful zonal isolation in wellbores subjected to cyclic pressure. Test data indicate that under high enough pressure variation, interfacial cracking at the cement pipe interface is unavoidable and the cement seal's ability to maintain zonal isolation will be dependent on the microstructural morphology and microscale mechanical resilience of the cement formulation. Stiffer conventional cements also appear to have a higher chance of leakage through non-interfacial fractures than their more flexible counterparts. Latex cements show great promise for effective zonal isolation under cyclic bottomhole pressure conditions and should be studied in more detail.

Ada-LISTA: Learned Solvers Adaptive to Varying Models.

Neural networks that are based on the unfolding of iterative solvers as LISTA (Learned Iterative Soft Shrinkage), are widely used due to their accelerated performance. These networks, trained with a fixed dictionary, are inapplicable in varying model scenarios, as opposed to their flexible non-learned counterparts. We introduce, Ada-LISTA, an adaptive learned solver which receives as input both the signal and its corresponding dictionary, and learns a universal architecture to serve them all. This scheme allows solving sparse coding in linear rate, under varying models, including permutations and perturbations of the dictionary. We provide an extensive theoretical and numerical study, demonstrating the adaptation capabilities of our approach, and its application to the task of natural image inpainting.

An improved author-topic (AT) model with authorship credit allocation schemes

Authorship credit allocation schemes have attracted considerable research attention. However, no consensus about which one is the best has been attained until now, and limited evidence from practical tasks has been reported. Therefore, this study uses the author interest discovery task as a real-world task case to provide valuable insights into authorship credit allocation schemes and guidelines for further practical applications. For this purpose, a novel model, ATcredit, is proposed to strengthen the Author-Topic (AT) model with an authorship credit allocation scheme, and collapsed Gibbs sampling is used to approximate the posterior and estimate model parameters. Extensive experiments using the SynBio dataset reveal several interesting findings as follows. (a) Any scheme for allocating unequal authorship credits performs better than its equal-credit counterpart with our ATcredit model in terms of perplexity. (b) The fixed versions of four out of the six schemes work better than their flexible counterparts with our ATcredit model, regardless of the hyper-authorship strategy. (c) The variation coefficient of credit awards can serve as a criterion to decide whether the hyper-authorship strategy should be used. (d) When the number of authors in a scholarly article is less than three, the six authorship credit allocation schemes are similar to each other with our ATcredit model in terms of perplexity. (e) The harmonic counting scheme performs the best, followed by the arithmetic counting scheme, and the network-based counting scheme performs the worst with our ATcredit model in terms of perplexity. (f) The arithmetic counting scheme is similar to the harmonic counting scheme in terms of the normalised mutual information (NMI) of discovered interests, but the geometric counting scheme is different from the axiomatic and network-based counting schemes.

Tailoring the bending pattern of non-uniformly flexible pitching hydrofoils enhances propulsive efficiency

We present new measurements of non-uniformly flexible pitching foils fabricated with a rigid leading section joined to a flexible trailing section. This construction enables us to vary the bending pattern and resonance condition of the foils independently. A novel effective flexibility, defined as the ratio of added mass forces to elastic forces, is proposed and shown to provide a scaling for the natural frequencies of the fluid-structural system. Foils with very flexible trailing sections of EI < 1.81 × 10−5 N m2 do not show a detectable resonance and are classified as ‘non-resonating’ as opposed to ‘resonating’ foils. Moreover, the non-resonating foils exhibit a novel bending pattern where the foil has a discontinuous hinge-like deflection instead of the smooth beam-like deflection of the resonating foils. Performance measurements reveal that both resonating and non-resonating foils can achieve high propulsive efficiencies of around 50% or more. It is discovered that non-uniformly flexible foils outperform their rigid and uniformly flexible counterparts, and that there is an optimal flexion ratio from 0.4 ⩽ λ ⩽ 0.7 that maximizes the efficiency. Furthermore, this optimal range coincides with the flexion ratios observed in nature. Performance is also compared under the same dimensionless flexural rigidity, R*, which highlights that at the same flexion ratio more flexible foils achieve higher peak efficiencies. Overall, to achieve high propulsive efficiency non-uniformly flexible hydrofoils should (1) oscillate above their first natural frequency, (2) have a flexion ratio in the range of 0.4 ⩽ λ ⩽ 0.7 and (3) have a small dimensionless rigidity at their optimal flexion ratio. Scaling laws for rigid pitching foils are found to be valid for non-uniformly flexible foils as long as the measured amplitude response is used and the deflection angle of the trailing section β is < 45°. This work provides guidance for the development of high-performance underwater vehicles using simple purely pitching bio-inspired propulsive drives.

A Locally Actuatable Soft Robotic Film for Actively Reconfiguring Shapes of Flexible Electronics.

Actively reconfigurable flexible electronics enabled by robotic technologies would provide opportunities to extensively broaden the application areas of flexible electronics compared with their passively flexible counterparts. Diverse reconfigurable shapes can be enabled by localized control of the film-type electronics while keeping a thin form factor for flexible electronics. The flexible electronics are usually designed to be thin to lower mechanical stress or strain when bending. In this article, we present a locally actuatable film designed to control actuating regions, bending directions, and curvatures by the electrical inputs. The film is in a thin form factor with multichannels realized by the proposed method of crimping electrical wires over shape memory alloy wires. The industry standard process should be convenient in terms of scaling up, increasing channels, or adding reconfigurable shapes for new applications. We demonstrate shape-changeable displays, self-rollable photovoltaics, and light art to prove the feasibility of the concept.

Self-assembly of cyclic grafted copolymers with rigid rings and their potential as drug nanocarriers

Enhancing the performance of polymer micelles by purposeful regulation of their structures is a challenging topic that receives widespread attention. In this study, we systematically conduct a comparative study between cyclic grafted copolymers with rigid and flexible rings in the self-assembly behavior via dissipative particle dynamics (DPD) simulation. With a focus on the possible stacking ways of rigid rings, we propose the energy-driven packing mechanism of cyclic grafted copolymers with rigid rings. For cyclic grafted copolymers with large ring size (14 and 21-membered rings), rigid rings present a novel channel-layer-combination layout, which is determined by the balance between the potential energy of micelles (Emicelle) and the interaction energy between water and micelles (Eint). Based on this mechanism, we further regulate a series of complex self-assembling structures, including curved rod-like, T-shape, annular and helical micelles. Compared with flexible copolymers, cyclic grafted copolymers with rigid rings provide a larger and loose hydrophobic core and higher structural stability with micelles due to the unique packing way of rigid rings. Therefore, their micelles have a great potential as drug nanocarriers. They possess a better drug loading capacity and disassemble more quickly than flexible counterparts under acidic tumor microenvironment. Furthermore, the endocytosis kinetics of rigid micelles is faster than the flexible counterparts for the adsorption and wrapping process. This study may provide a reasonable idea of structural design for polymer micelles to enhance their performance in biomedical applications.

Reinsurance, debt capacity and financial flexibility

Prior studies conclude that hedging has a positive effect on firms’ debt capacity; however, in the present study, we argue that this relationship is moderated by their financial flexibility. Using statutory data from 2001 to 2016 from the National Association of Insurance Commissioners database on U.S. property and casualty insurers and a simultaneous equations model, we examine how financial flexibility moderates the effect of reinsurance—a risk management tool commonly used by insurance firms—on debt capacity. We find that the relationship between reinsurance usage and debt capacity is positive for financially inflexible insurers, but negative for their financially flexible counterparts, thereby suggesting that the effects of reinsurance are actually dependent upon the financial flexibility of insurers. Several robustness checks are conducted and our main results remain qualitatively unchanged.

Superstable copper nanowire network electrodes by single-crystal graphene covering and their applications in flexible nanogenerator and light-emitting diode

Copper nanowires (CuNWs), with excellent electronic properties and high cost-effectiveness, have tremendous potential in the field of transparent conductive electrodes for flexible electronics, large touch screen display and triboelectric energy harvesters, while their vulnerability to oxidation in air has impeded possible practical applications. Fortunately, it has been recognized that graphene encapsulation of CuNWs is capable of protecting CuNWs. However, neither self-assembled reduced graphene oxide nor chemical vapor deposition-grown polycrystalline graphene coatings can guarantee full protection to CuNWs, due to their ubiquitous voids, grain boundaries and wrinkles that allow water and oxygen molecules to pass through and result in the accelerated electrochemical corrosion at the graphene-copper interface, especially under folding conditions. Herein, we demonstrate a sandwich-structured single-crystal graphene/copper nanowire network/UV-curable resin (SCG/CuNW/UVR) composite film with ultrahigh electronic performance stability. The SCG/CuNW/UVR electrode exhibits a good optical and electrical performance (~19 Ω sq−1 under 84.3% transmittance), excellent mechanical robust and remarkably high oxidation resistance (ΔR/R0 < 0.2 within 180 days), in sharp contrast with the bare CuNWs (ΔR/R0 > 1 after 1 day) and polycrystalline graphene-covered CuNWs counterparts (ΔR/R0 > 1 after 7 days). Furthermore, the SCG/CuNW/UVR electrodes can replace indium tin oxide (ITO) electrodes to construct the triboelectric nanogenerators (TENG) and quantum dot light emitting diodes (QLED), comparable to the flexible commercial ITO counterparts. The fabrication of such high-performance SCG/CuNW/UVR electrode is facile to be scaled-up with low cost, providing the feasibility for industrial applications of flexible ITO-free electronic and optoelectronic devices.

Stretchable pumps for soft machines.

Machines made of soft materials bridge life sciences and engineering1. Advances in soft materials have led to skin-like sensors and muscle-like actuators for soft robots and wearable devices1-3. Flexible or stretchable counterparts of most key mechatronic components have been developed4,5, principally using fluidically driven systems6-8; other reported mechanisms include electrostatic9-12, stimuli-responsive gels13,14 and thermally responsive materials such as liquid metals15-17 and shape-memory polymers18. Despite the widespread use of fluidic actuation, there have been few soft counterparts of pumps or compressors, limiting the portability and autonomy of soft machines4,8. Here we describe a class of soft-matter bidirectional pumps based on charge-injection electrohydrodynamics19. These solid-state pumps are flexible, stretchable, modular, scalable, quiet and rapid. By integrating the pump into a glove, we demonstrate wearable active thermal management. Embedding the pump in an inflatable structure produces a self-contained fluidic 'muscle'. The stretchable pumps have potential uses in wearable laboratory-on-a-chip and microfluidic sensors, thermally active clothing and autonomous soft robots.

Tape-Imprinted Hierarchical Lotus Seedpod-Like Arrays for Extraordinary Surface-Enhanced Raman Spectroscopy.

A novel two-side-activatable high-performance surface-enhanced Raman spectroscopy (SERS) substrate is developed based on the tape-imprinting method. It features 3D full-space-distributed hot spots originating from the hierarchical lotus seedpod-like silver arrays, which offer ultrasensitive, uniform, reproducible, and reliable quantitative measurements with an inherent internal standard. This excellent SERS substrate also holds great promise in practical in situ molecule detection on curved surfaces, such as pesticides on fruit, which is not yet possible with the traditional rigid or flexible material-based SERS counterparts.

ЛІДЕРСТВО ЧЕРЕЗ ПРИЗМУ УПРАВЛІНСЬКИХ ЯКОСТЕЙ

The existence of such phenomena and processes as production, enterprise, management, as well as their creators, or those who perform them, personifies, namely: staff, managers, owners cannot exist in reality outside of individual and social production. In this case, the production of not only material goods, but also material goods is understood. Accordingly, the need as such can also be met differently and to varying degrees, depending on the quality, the level of development of those factors of production that are used in the enterprise through effective management. Currently, the main trends of effective leadership phenomenon associated with the transition from command to sole leadership, leadership from the vertical to the virtual and latent, tight localization of its leader to free movement. In this case, the article examines the vision of scientists on the composition and peculiarities of formation of leadership qualities of a manager in modern conditions in order to ensure effective management of the enterprise. Also, the analysis of effective leadership initiatives at the organizational environment level in turbulent economic conditions is conducted. However, given the pace of development of modern society in general, and economic relations in particular, we consider it necessary to express the view that an effective leader does not necessarily have stable qualities that differentiate him from other people. After all, what is required of a leader can very often depend on the circumstances. It's corny, but it's true. History knows many leaders who have found their time and place, whose qualities have lost their appeal as the situation has changed. Yes, some uncompromising managers who have been able to overcome managerial crises are not capable of being effective leaders in other circumstances. And their more flexible counterparts adapt to changing priorities and lead their people. Currently, the main trends in the development of the phenomenon of effective leadership are related to the transition from single to team leadership, from vertical leadership to virtual and latent, from rigid localization of the leader to his free movement

High Speed Epitaxial Perovskite Memory on Flexible Substrates.

Single-crystal perovskite ferroelectric material is integrated at room temperature on a flexible substrate by the layer transfer technique. Two terminal memory devices fabricated with these materials exhibit faster switching speed, lower operating voltage, and superior endurance than other existing flexible counterparts. The research provides an avenue toward combining the rich functionality of charge and spin states, offered by the general class of complex oxides, onto a flexible platform.

Vagal flexibility: A physiological predictor of social sensitivity.

This research explores vagal flexibility--dynamic modulation of cardiac vagal control--as an individual-level physiological index of social sensitivity. In 4 studies, we test the hypothesis that individuals with greater cardiac vagal flexibility, operationalized as higher cardiac vagal tone at rest and greater cardiac vagal withdrawal (indexed by a decrease in respiratory sinus arrhythmia) during cognitive or attentional demand, perceive social-emotional information more accurately and show greater sensitivity to their social context. Study 1 sets the foundation for this investigation by establishing that vagal flexibility can be elicited consistently in the laboratory and reliably over time. Study 2 demonstrates that vagal flexibility has different associations with psychological characteristics than does vagal tone, and that these characteristics are primarily social in nature. Study 3 links individual differences in vagal flexibility with accurate detection of social and emotional cues depicted in still facial images. Study 4 demonstrates that individuals with greater vagal flexibility respond to dynamic social feedback in a more context-sensitive manner than do individuals with less vagal flexibility. Specifically, compared with their less flexible counterparts, individuals with greater vagal flexibility, when assigned to receive negative social feedback, report more shame, show more pronounced blood pressure responses, and display less sociable behavior, but when receiving positive social feedback display more sociable behavior. Taken together, these findings suggest that vagal flexibility is a useful individual difference physiological predictor of social sensitivity, which may have implications for clinical, developmental, and health psychologists.

Cluster Glasses of Semiflexible Ring Polymers.

We present computer simulations of concentrated solutions of unknotted nonconcatenated semiflexible ring polymers. Unlike in their flexible counterparts, shrinking involves a strong energetic penalty, favoring interpenetration and clustering of the rings. We investigate the slow dynamics of the centers-of-mass of the rings in the amorphous cluster phase, consisting of disordered columns of oblate rings penetrated by bundles of prolate ones. Scattering functions reveal a striking decoupling of self- and collective motions. Correlations between centers-of-mass exhibit slow relaxation, as expected for an incipient glass transition, indicating the dynamic arrest of the cluster positions. However, self-correlations decay at much shorter time scales. This feature is a manifestation of the fast, continuous exchange and diffusion of the individual rings over the matrix of clusters. Our results reveal a novel scenario of glass formation in a simple monodisperse system, characterized by self-collective decoupling, soft caging, and mild dynamic heterogeneity.

Conformational restriction: an effective tactic in 'follow-on'-based drug discovery.

The conformational restriction (rigidification) of a flexible ligand has often been a commonly used strategy in drug design, as it can minimize the entropic loss associated with the ligand adopting a preferred conformation for binding, which leads to enhanced potency for a given physiological target, improved selectivity for isoforms and reduced the possibility of drug metabolism. Therefore, the application of conformational restriction strategy is a core aspect of drug discovery and development that is widely practiced by medicinal chemists either deliberately or subliminally. The present review will highlight current representative examples and a brief overview on the rational design of conformationally restricted agents as well as discuss its advantages over the flexible counterparts.

Magnetic Microstructure of Rolled‐Up Single‐Layer Ferromagnetic Nanomembranes

The magnetic microstructure of rolled-up magnetic nanomembranes is revealed both theoretically and experimentally. Two types of nanomembranes are considered, one with a non-magnetic spacer layer and the other without. Experimentally, by using different materials and tuning the dimensions of the rolled-up nanomembranes, domain patterns consisting of spiral-like and azimuthally magnetized domains are observed, which are in qualitative agreement with the theoretical predictions.