Flexible Shape Research Articles

Lignin Nanofiber Flexible Carbon Aerogels for Self-Standing Supercapacitors.

Renewable feedstocks are sought for clean technology applications, including energy storage applications. In this study, LignoForce™ lignin, a biobased aromatic polymer commercially isolated from wood, was fractioned into two parts using acetone, and the resulting lignin fractions had distinct thermo-rheological behavior. These two fractionated lignins were combined in various ratios and transformed into nanofibers by electrospinning. Subsequently, electrospun fiber materials were disrupted by agitating the mats in water, and the materials were transformed into ultralight 3D aerogels through lyophilization and post-process controlled heating. Using only this combination of two fractions, the morphology of lignin nanofibers was tailored by heat treatment, resulting in lignin aerogels with high flexibility and significant shape recovery properties. Various microscale structures of lignin fibers impacted the resulting physical properties of the elastic aerogel materials, such as resilience, compressive strength, and electrical conductivity for the corresponding carbonized samples. By exploiting lignin's sensitivity to heat and tailoring the thermal properties of the lignin through fractionation, the work provided an interesting path to form robust lignin-derived functional materials without any toxic chemical additives and significant ability to serve as free-standing electrodes with specific capacitance values better than some graphene-based supercapacitors.

Design of a low-power Digital-to-Pulse Converter (DPC) for in-memory-computing applications

Data converters such as analog-to-digital converters (ADCs), digital-to-analog converters (DACs), digital-to-time converters (DTCs), time-to-digital converters (TDCs), among others, are considered some of the most essential blocks in the field of integrated circuit design. In this work, we introduce a novel type of data converter known as the Digital-to-Pulse converter (DPC) and present its novel analog flow circuit implementation. The DPC system is a critical component in emerging artificial neural network accelerators and in-memory computing systems. The DPC system presented in this study offers two distinct operating modes. The first mode is the generation of a single pulse with a width that is modulated by the digital input. The second mode is an n-bit digital to discrete pulse converter, where the number of generated pulses is directly related to the value of the digital input. The proposed DPC system offers designers a high level of flexibility in shaping the characteristics of the output pulses, including the number of pulses, pulse width, and pulse amplitude. This empowers designers to accommodate different application requirements and scenarios effectively. The proposed circuit has been verified and tested using Virtuoso Cadence circuit tools in 180 nm CMOS technology with post-layout simulation and analysis. The results indicate a significant enhancement in average power consumption (∼12×), layout area (∼5×), and Latency (∼1.4×) with the proposed system compared to the digital Register Transfer Level (RTL) implementation under a power supply of 1.8V and a clock frequency of 1 GHz in the Application Specific Integrated Circuits (ASIC) flow. This demonstrates the suitability of the proposed system for low-power and high-speed applications.

Biogeography of Australian Camphorosmeae and Diversification in Climatic Space and Across Arid Habitat Types.

This study investigates the biogeography of the Australian Camphorosmeae (Amaranthaceae s.l.) lineage and how it relates to shifts in climatic niche and habitat types. Building on previous research and data resources, we integrate molecular phylogenetics, bioclimatic data and biogeographical models to deepen our understanding of the diversification and adaptation of this group across Australia's diverse landscapes in relation to palaeoclimatic changes. For 159 species representing 12 genera, georeferenced distribution points were used to define the most informative bioclimatic variables using principal component analysis. Evolutionary shifts in climatic niches and habitat types were analysed, revealing clade-specific shifts and adaptations to different habitats and climatic conditions. Biogeographical analyses allowed us to infer ancestral areas of Camphorosmeae in Australia and relate their expansion over evolutionary time to habitat shifts. Preadaptation of this group to warm and dry habitats coupled with key periods of aridification in Australia, particularly during the Late Miocene to Pliocene, were critical in driving its diversification through migration and local adaptation to varied habitats of arid Australia. Our analyses suggest that the 'Riverine Desert' habitat offered suitable conditions for ancestral Australian Camphorosmeae and facilitated their early widespread dispersal in the Western and Eastern Desert. We hypothesise that early diverging lineages such as Roycea adapted to the later emerging 'Desert Lake' habitat when it spread in Western Australia during the Early Pliocene. Further, habitat type shifts occurred from 'Riverine Desert' to 'Shield Plain', 'Karst Plain' and to 'Sand Desert' also during the Pliocene and Pleistocene once these habitat types emerged. This study illustrates the complex interplay between ecological flexibility and niche conservatism in shaping the biodiversity of Australian Camphorosmeae.

High-efficiency wide-angle anomalous refraction with acoustic metagrating

Abstract The emergent metagrating, with its unique and flexible beam shaping capabilities, offers new paths to efficient modulation of acoustic waves. In this work, an acoustic metagrating is demonstrated for high-efficiency and wide-angle anomalous refraction. It is shown that the normal reflection and transmission can be totally suppressed by properly modulating the amplitude and phase characteristics of the metagrating supercells for high-efficiency anomalous refraction. The anomalous refraction behavior is achieved in the wide range of incident angles from 28° to 78°, and the efficiency of -1st order diffraction is higher than 90% by finely designing the metagrating structure. The anomalous refraction behaviors are verified experimentally at incidence angle of 28°, 45° and 78°, respectively. The demonstrated metagrating is anticipated to possess efficient wide-angle composite wavefront engineering applications in such fields as communications.

Cellulose-based Conductive Materials for Bioelectronics.

The growing demand for electronic devices has led to excessive stress on Earth's resources, necessitating effective waste management and the search for renewable materials with minimal environmental impact. Bioelectronics, designed to interface with the human body, have traditionally been made from inorganic materials, such as metals, which, while having suitable electrical conductivity, differ significantly in chemical and mechanical properties from biological tissues. This can cause issues such as unreliable signal collection and inflammatory responses. Recently, natural biopolymers such as cellulose, chitosan, and silk have been explored for flexible devices, given their chemical uniqueness, shape flexibility, ease of processing, mechanical strength, and biodegradability. Cellulose is the most abundant natural biopolymer, has been widely used across industries, and can be transformed into electronically conductive carbon materials. This review focuses on the advancements in cellulose-based conductive materials for bioelectronics, detailing their chemical properties, methods to enhance conductivity, and forms used in bioelectronic applications. It highlights the compatibility of cellulose with biological tissues, emphasizing its potential in developing wearable sensors, supercapacitors, and other healthcare-related devices. The review also addresses current challenges in this field and suggests future research directions to overcome these obstacles and fully realize the potential of cellulose-based bioelectronics.

Comprehensive Geometric Parameterization and Computationally Eficient 3D Shape Matching Optimization of Realistic Stents

Abstract Flexible and compact shape representation schemes are essential for design optimization problems. Current shape representation schemes for coronary stent designs concern predominantly idealized or Independent Ring (IR) designs, which are outdated and only consider a small number of core design variables (such as strut width, height, and thickness) and ignore clinically critical characteristics such as the number of connectors. No reports exist on the geometry parameterization of the latest Helical Stents (HS) that have more complex designs than IR stents. Here, we present two new shape parameterization schemes to fully capture the 3D designs of contemporary IR and double-helix HS stents. We developed a 3D stent geometry builder based on 17 (IR) and 18 (HS) design variables, including strut width, thickness, height, number of connectors and rings, stent length, and strut centerline shape. The shape of the strut centerline was derived via a combination of NURBS, PARSEC, quarter circle, and straight line segments. Shape matching for complex 3D geometries, such as the contemporary stents within limited function evaluations, is not trivial and requires efficient parameterization and optimization algorithms. We used shape matching optimization with a limited function evaluation budget to test the proposed parameterization and two surrogate-assisted optimization algorithms relying on predictor believer and an expected improvement maximization formulation. The performance of these algorithms is objectively compared with a gradient-based optimization method to highlight their strengths. Our work paves the way for more realistic, full-fledged stent design optimization with structural and hemodynamic objectives in the future.

Recent advances in responsive liquid crystal elastomer‐contained fibrous composites

AbstractResponsive polymers can react to surrounding environments by changing their physical and/or chemical properties. Among them, liquid crystal elastomers (LCEs) have emerged as one of the important branches in the field of applied polymer science due to their significant advantages in flexible mechanics and shape memory. Manufacturing LCE fibers with a large specific surface area and functional fillers has become a research hotspot in recent years. This type of LCE‐contained fibrous composite (LCEF) exhibits not only extremely high response sensitivity but also excellent axial mechanical strength and a high degree of deformation freedom. In this paper, we provide a bird's eye view of recent developments in LCEF, including structural designs, synthesis and forming methods, mechanical response principles and modes. Furthermore, we discuss recent advances of LCEF in artificial muscles, smart textiles, biomimetic systems, intelligent soft machines, followed by challenges and possible routes in fabrications and applications of LCEF. At the end, we aim to provide a perspective for an emerging field of stimulus‐responsive polymeric fiber composites.

Impact of Iron Contamination on Liquid Properties and Microstructural Evolution in AlSi20

Additive manufacturing processes enable highly flexible and scalable shaping while maintaining rapid solidification processing conditions. This combination makes additive manufacturing particularly attractive for recycling contaminated alloys, as it allows critical brittle phases to be refined and utilized as alloying elements. However, little is known about the impact of contaminants on the fluid properties of liquid metals. Herein, thermodynamic modeling and experimental methods are combined to investigate the properties of AlSi20 and its contaminated variant, (AlSi20)95Fe5. The oscillating droplet method is used to experimentally determine surface tension and analyze solidified droplets to evaluate microstructure for different cooling rates. The findings indicate that while contaminants have a minor effect on fluid properties, they significantly influence microstructural properties.

Towards Photocrosslinkable Lyotropic Blends of Organosolv Lignin and Hydroxypropyl Cellulose for 3D Printing by Direct Ink Writing.

Polymer blends containing up to 70% organosolv lignin content and lyotropic cellulose derivatives have been established as "lignin inks" for direct ink writing of fully biobased 3D parts. However, a fast-crosslinking mechanism is needed to improve throughput and design space. In this paper, UV-photocrosslinkable organosolv lignin/hydroxypropyl cellulose inks are formulated through doping with common photocrosslinkers. The most potent photocrosslinkers for neat hydroxypropyl cellulose, lignin and their blends are determined through a series of DOEs. Hydroxypropyl cellulose is significantly more amenable to photocrosslinking than organosolv lignin. The optimal photocrosslinkable ink formulations are printable and exhibit up to 70% gel content, although thermal post-curing remains essential. Chemical, thermal, and mechanical investigations of the photocrosslinked 3D parts evidence efficient crosslinking of HPC through its hydroxyl groups, while lignin appears internally plasticized and/or degraded during inefficient photocrosslinking. Despite this, photocrosslinkable inks exhibit improved tensile properties, shape flexibility, and fidelity. The heterogeneous crosslinking and residual creep highlight the need to further activate lignin for homogeneous photocrosslinking in order to fully exploit the potential of lignin inks in DIW.

Propulsive efficiency of spatiotemporally asymmetric oscillating appendages at intermediate Reynolds numbers

Many organisms use flexible appendages for locomotion, feeding, and other functional behaviors. The efficacy of these behaviors is determined in large part by the fluid dynamics of the appendage interacting with its environment. For oscillating appendages at low Reynolds numbers, viscosity dominates over inertia, and appendage motion must be spatially asymmetric to generate net flow. At high Reynolds numbers, viscous forces are negligible and appendage motion is often also temporally asymmetric, with a fast power stroke and a slow recovery stroke; such temporal asymmetry does not affect the produced flow at low Reynolds numbers. At intermediate Reynolds numbers, both viscous and inertial forces play non-trivial roles---correspondingly, both spatial and temporal asymmetry can strongly affect overall propulsion. Here we perform experiments on three robotic paddles with different material flexibilities and geometries, allowing us to explore the effects of motion asymmetry (both spatial and temporal) on force production. We show how a flexible paddle's time-varying shape throughout the beat cycle can reorient the direction of the produced force, generating both thrust and lift. We also evaluate the propulsive performance of the paddle by introducing a new quantity, which we term "integrated efficiency". This new definition of propulsive efficiency can be used to directly evaluate an appendage's performance independently from full-body swimming dynamics. Use of the integrated efficiency allows for accurate performance assessment, generalization, and comparison of oscillating appendages in both robotic devices and behaving organisms. Finally, we show that a curved flexible paddle generates thrust more efficiently than a straight paddle, and produces spatially asymmetric motion---thereby improving performance---without the need for complex actuation and controls, opening new avenues for bioinspired technology development.

Supercapacitor electrodes based on Ru/RuO2 decorated on N,S-doped few-layer graphene

Innovatively designed flexible and high-performance shape memory polymer supercapacitors are promising next-generation energy storage devices for portable and wearable electronics. Therefore, thermally induced smart shape memory polymer polyurethane was synthesized using polycaprolactone/poly(ethylene glycol)/hexamethylene diisocyanate (PCL/PEG/HDI) in which the incorporation of PEG successfully assisted in lowering the transition temperature. The resulting polymer exhibits a remarkable transition temperature of 50 °C and a shape recovery ratio of 100 % at a strain of 300 %. The smart polymer was coated with a silver paste to ease the electron flow followed by coating with the electrode. Hybrid electrode materials are prepared in two stages. Initially, a few layers of holey-graphene were synthesized, where BET surface area reveals the presence of pores that are tuned by isothermal treatments in O2-atmosphere. Subsequently, active hybrid electrode materials nanostructured Ru/RuO2 decorated N, S-doped few layers of holey graphene were synthesized using hydrothermal methods. Here, nitrogen and sulfur doping in the basal or edge plane served as catalysts and metal coordination sites, facilitating the uniform distribution of ruthenium nanoparticles on the graphene. It is further confirmed by the density function theory (DFT) calculation using the adsorption energy. The optimized hybrid electrode material demonstrates a specific capacitance of 1297 mFcm−2 at a current density of 2 mAcm−2. A flexible-shape memory polymer supercapacitor exhibits a notable device-specific capacitance of 189 mFcm−2 at a current density of 1 mAcm−2, a high energy density of 45 µWhcm−2 at a power density of 0.25 mWcm−2, with 81 % of specific capacitance retention after eight shape programming and recovery cycle. Excellent shape recoverability and robust electrochemical performance make the as-fabricated symmetric supercapacitors a promising candidate for integration in flexible electronic applications.

Study on the influence of geometric characteristics of micro-periodic structures with slits on sound absorption properties

In recent years, there has been considerable interest in acoustic metamaterial technology that leverages sub-wavelength scale microperiodic structures to control the behavior of sound waves for sound absorption material development. This technology offers high design flexibility in unit shapes and holds promise for the development of sound absorption materials with diverse characteristics. However, the field remains in its foundational exploration phase, with the detailed relationship between geometric shapes and sound absorption properties yet to be fully elucidated. To address this gap, we conducted a thorough investigation focusing on their relationship by examining the transport parameters of the Johnson-Champoux-Allard-Lafarge-Pride (JCALP) model, which are closely associated with sound absorption properties. We designed a cubic lattice with slits on the incident surface of the unit shape as a microperiodic structure and examined the normal incident sound absorption characteristics using the finite element method. Our results indicate that manipulation of slit partition numbers and slit widths allows for control of transport parameters, suggesting the potential to achieve various sound absorption properties.

State-restricted adaptive control of a multilevel rotating electromagnetic mechanical flexible device using electromagnetic actuators

This work presents the development of a multilevel electromagnetic actuation system that controls the shape of a flexible rotatory robotic structure. An array of electromagnets is used as the set of actuators that regulate the position of permanent magnets within the flexible device. The primary outcome of this study is the design and experimental validation of the multilevel rotating device. In addition, the theoretical description of the system motion under electromagnetic actuation is formulated using Euler–Lagrange and electromagnetic theories. Given the developed model, a theoretical study leads to designing an adaptive control that considers motion restrictions in the flexible device. The controller aims to modify the current applied to the electromagnets, which changes the interaction forces between the electromagnet and the permanent magnets in the robotic flexible structure. A set of numerical simulations confirms the proposed controller’s effectiveness compared to the traditional state feedback approach that does not consider the state restrictions, which is implemented in devices that also operate under an electromagnetic approach. Furthermore, an experimental version of the flexible device allows for testing of the developed controller. The experimental results show the suitability of the proposed control to generate non-oscillatory controlled motion during the regulation of the flexible mechanic device shape.

Constraining the Initial Mass Function via Stellar Transients

The stellar initial mass function (IMF) represents a fundamental quantity in astrophysics and cosmology describing the mass distribution of stars from low mass all the way up to massive and very massive stars. It is intimately linked to a wide variety of topics, including stellar and binary evolution, galaxy evolution, chemical enrichment, and cosmological reionization. Nonetheless, the IMF still remains highly uncertain. In this work, we aim to determine the IMF with a novel approach based on the observed rates of transients of stellar origin. We parametrize the IMF with a simple but flexible Larson shape, and insert it into a parametric model for the cosmic UV luminosity density, local stellar mass density, type Ia supernova (SN Ia), core-collapse supernova (CCSN), and long gamma-ray burst (LGRB) rates as a function of redshift. We constrain our free parameters by matching the model predictions to a set of empirical determinations for the corresponding quantities via a Bayesian Markov Chain Monte Carlo method. Remarkably, we are able to provide an independent IMF determination with a characteristic mass mc=0.10−0.08+0.24M⊙ and high-mass slope ξ=−2.53−0.27+0.24 that are in accordance with the widely used IMF parameterizations (e.g., Salpeter, Kroupa, Chabrier). Moreover, the adoption of an up-to-date recipe for the cosmic metallicity evolution allows us to constrain the maximum metallicity of LGRB progenitors to Zmax=0.12−0.05+0.29Z⊙. We also find which progenitor fraction actually leads to SN Ia or LGRB emission (e.g., due to binary interaction or jet-launching conditions), put constraints on the CCSN and LGRB progenitor mass ranges, and test the IMF universality. These results show the potential of this kind of approach for studying the IMF, its putative evolution with the galactic environment and cosmic history, and the properties of SN Ia, CCSN, and LGRB progenitors, especially considering the wealth of data incoming in the future.

The Immersed Boundary Conformal Method for Kirchhoff–Love and Reissner–Mindlin shells

This work utilizes the Immersed Boundary Conformal Method (IBCM) to analyze linear elastic Kirchhoff–Love and Reissner–Mindlin shell structures within an immersed domain framework. Immersed boundary methods involve embedding complex geometries within a background grid, which allows for great flexibility in modeling intricate shapes and features despite the simplicity of the approach. The IBCM method introduces additional layers conformal to the boundaries, allowing for the strong imposition of Dirichlet boundary conditions and facilitating local refinement. In this study, the construction of boundary layers is combined with high-degree spline-based approximation spaces to further increase efficiency. The Nitsche method, employing non-symmetric average operators, is used to couple the boundary layers with the inner patch, while stabilizing the formulation with minimal penalty parameters. High-order quadrature rules are applied for integration over cut elements and patch interfaces. Numerical experiments demonstrate the efficiency and accuracy of the proposed formulation, highlighting its potential for complex shell structures modeled through Kirchhoff–Love and Reissner–Mindlin theories. These tests include the generation of conformal interfaces, the coupling of Kirchhoff–Love and Reissner–Mindlin theories, and the simulation of a cylindrical shell with a through-the-thickness crack.

Simulation study of flexible wavefront shaping in Smith-Purcell radiation with aperiodic metagratings

Smith-Purcell radiation (SPR) is a versatile platform for finely tuning nanoscale light across a broad spectral range. This study introduces a theoretical approach for shaping SPR wavefronts using aperiodic metagratings (AMGs). The AMGs consist of arrays of identical metal nano-rods (MNRs), with each MNR's spatial position precisely adjustable. This precise adjustment allows for effective modulation of the spatial phase distribution of SPR. To demonstrate the efficacy of this method, we conduct simulations to achieve diverse wavefront profiles of focusing, deflection, Bessel beams, and Airy beams. Additionally, our approach allows for integrating multiple SPR wavefront functionalities within a combo AMG. By employing the asymmetric L-shaped meta-atom design, we achieve simultaneous SPR polarization conversion and wavefront shaping. This method is promising for developing highly adaptable and multifunctional nanoscale light sources.

The impact of market power and financial flexibility on corporate investment policy

ABSTRACT This study explores how market power and financial flexibility shape corporate investment policies among U.S. large and mature corporations, by estimating firm-specific, time-varying investment-to-added-value sensitivities. We find that firms with market power exhibit lower investment sensitivities, and this effect is more pronounced for the most financially flexible firms. We show that the firm’s debt capacity is an important moderator in the relationship between market power and investment sensitivities. Our findings support theoretical predictions that market power and financial flexibility jointly influence investment decisions. The implication is that a lack of competition impedes corporate investments. For investors, these findings highlight the need to monitor both the competitive landscape and financial flexibility of firms in their portfolios.

Virtual Model Predictive Control for Inverters to Achieve Flexible Output Impedance Shaping in Harmonic Interactions With Weak Grids

Virtual Model Predictive Control for Inverters to Achieve Flexible Output Impedance Shaping in Harmonic Interactions With Weak Grids

Jet mixing optimization using a flexible nozzle, distributed actuators, and machine learning

In this paper, we introduce the first jet nozzle allowing simultaneous shape variation and distributed active control, termed “Smart Nozzle” in the sequel. Our Smart Nozzle manipulates the jet with an adjustable flexible shape via 12 equidistant stepper motors and 12 equidistantly placed inward-pointing minijets. The mixing performance is evaluated with a 7 × 7 array of Pitot tubes at the end of the potential core. The experimental investigation is carried out in three steps. First, we perform an aerodynamic characterization of the unforced round jet flow. Second, we investigate the mixing performance under five representative nozzle geometries, including round, elliptical, triangular, squared, and hexagonal shapes. The greatest mixing area is achieved with the square shape. Third, the symmetric forcing parameters are optimized for each specified nozzle shape with a machine learning algorithm. The best mixing enhancement for a symmetric active control is obtained by the squared shape, which results in a 1.93-fold mixing area increase as compared to the unforced case. Symmetrically unconstrained forcing achieves a nearly 4.5-fold mixing area increase. The Smart Nozzle demonstrates the feasibility of novel flow control techniques that combine shape variation and active control, leveraging the capabilities of machine learning optimization algorithms.

Flexibility Stigma Across Europe: How National Contexts can Shift the Extent to which Flexible Workers are Stigmatised

Although flexible working has expanded rapidly, especially during the pandemic, biased views against flexible workers – namely, flexibility stigma - are still prevalent and returning. Flexibility stigma hinders worker’s take up of flexible working arrangements and can make flexible working arrangements result in negative outcomes for worker’s well-being and productivity. This study examines how national cultural and policy contexts shape flexibility stigma levels within a country. We use a multilevel approach using the Eurobarometer dataset of 2018, covering 28 European countries, matched with national level aggregate data on policy and culture. Results show that in countries with a more work-life balance work culture and egalitarian gender norms, we see less prevalence of flexibility stigma. Similarly, in countries with generous family-friendly policies, workers are less likely to have negative perception towards flexible working. Finally, stronger bargaining positions of workers, may it be through stronger union power or through better labour market conditions, helps remove stigmatised views around workers who use flexible working arrangements. This study evidences the importance of contexts that shape views around flexible working, to help us better understand policy changes needed to ensure better flexible working practices.