Size Gradient Research Articles

Dual hetero-structured Ti composites by manipulating self-assembled powder embedded with nano-reinforcements

Traditional discontinuously micro-reinforced titanium matrix composites (DRTMCs) produced by casting or forging, are usually confronted with the strength-ductility trade-off dilemma. Their micro-scale reinforcements easily cause incompatible deformation and stress localization. Novel self-assembled composite powder embedding nano-reinforcements paired with additive manufacturing technology has great potential to address this dilemma. Here, we report a special dual-heterogeneous structure with micro-scale networks and grain size gradients. It bespoke exciting strength-ductility synergy and excellent uniform elongation surpassing the as-deposited Ti6Al4V alloy by 32 %, while manifesting a steadier strain hardening behavior. Primarily, alternating basal <a> and pyramidal <a> slips together with substantial pyramidal <c+a> slips induced by hetero-interfaces significantly improved the uniform deformation ability. Then geometrically necessary dislocation (GNDs) and long-range back stress induced by strain inhomogeneity remarkably enhanced the strain hardening ability. This work firstly determined the most preferred orientation relationship (OR) (58.91°/ [010]TiB) between TiBw and the adjoining α-Ti in as-deposited composites. These interfaces showed higher interface strength (16.42 GPa) than those with the most preferred OR of 0°/ [010]TiB in as-forged TMCs, making more contributions to promoting the load bearing capacity of TiBw. It provided scientific guidance for in-situ synthesizing heterogeneous structures with attractive mechanical properties in Ti composites.

Improved sound absorption by size gradient granular materials due to Brazil-nut effect

Granular material is attracting increasing research momentum due to its prevalence and rich unique properties. Nevertheless, compared with its numerous functions in other areas, the application of granular material in acoustic waves has received less attention. In this paper, we propose that by exploiting Brazil-nut effect induced particle size segregation in granular material, a significant improvement in the sound absorption can be achieved. Firstly, sound absorptions by particles with step-increasing sizes have been analyzed. It is found that size-dependent mechanisms of sound energy dissipation may occur. Secondly, sound absorptions by size-mixed particles with vibration treatment have been studied. As a result of the Brazil-nut effect induced size segregation, the size-mixed particles with initially limited sound absorptivity exhibited remarkably improved sound absorbing capability, with both broadened absorbing band and raised low-frequency absorption. This work demonstrates that simple processing of the granular material may become a promising way to create premium sound absorbers.

Effect of grain size gradient on the mechanical behavior of gradient nanograined pure iron: an atomic study

Abstract Using molecular dynamics (MD) simulation, the deformation mechanisms of gradient nanograined (GNG) pure iron (Fe) were investigated. Simulations of uniaxial tensile experiments were conducted on samples exhibiting different grain size gradients (GSGs). The simulation results reveal the presence of a critical GNG parameter (g), at which point the GNG-Fe attains its highest strength. The deformation mechanisms of three representative samples, namely GNG-2 with the g value at the threshold, GNG-1 with a g value smaller than the critical threshold and GNG-4 with a g value exceeding it, were thoroughly investigated. Within the coarse-grained (CG) region of GNG-1, the primary deformation mechanism is predominantly characterized by planar defects, rather than being dominated by dislocations. The mechanisms of both “strain hardening” and “softening” were observed and discussed in this region. The deformation of the coarse grains occurs in a coordinated manner, and the magnitude of the back-stress is insufficient to trigger grain boundary (GB) motion in the fine-grained (FG) region. In contrast, the deformation of the CG region in the GNG-4 primarily depends on dislocation. The “hardening” and “softening” effects of the dislocations were discussed. In the FG region of GNG-4, the grains undergo deformation primarily through GB motion, a phenomenon attributed to the significant back-stress generated by the uncoordinated deformation exhibited by the coarse grains. In the CG area of sample 2 with the g value at threshold, both dislocation- and planar defects-controlled mechanisms are observed. In the FG of this sample, neither GB migration and grain rotation are found. Only the GB width becomes larger, indicating that the back-stress transferred from the CG area makes the GB more active, but not large enough to induce the GB migration or grain rotation. The results of this work may provide some theoretical supports for the deformation mechanism of the GNG materials.

Reconstructing urban vegetation evolution in China using multimodal deep learning and 30-years Landsat archive

To retrospect the impact of urbanization on vegetation, consistent and reliable maps that provide urban vegetation estimates are required. In this study, we make the first attempt to employ deep learning for urban vegetation mapping of 2120 cities in China using a 30-years Landsat archive (UV-30). We present a multimodal deep learning (MDL) model to combine features from 5 categories, namely reflective bands, remote sensing indices, texture variables, topographical variables, and time labels. We normalized elevation data locally to remove the inter-city differences, while retaining topographic details. We used time labels to account for spectral variability over time and Landsat sensors. The performance of the MDL models was compared with a vanilla deep neural network, random forest, and support vector regression. Results indicated that the fusion of different categories of features improved the prediction accuracy. The MDL performed best in most validation cities, and our results were superior to the fractional maps aggregated from high-resolution datasets in homogeneous urban landscapes. We further analyzed urban vegetation dynamics across the urban core-new town-outskirt gradients of different geographical regions and city sizes. We found a gradually diminishing de-greening trend in urban China, especially in urban cores and new towns. Nevertheless, we observed a more pronounced degradation of urban vegetation in the south regions of China compared to the north, and smaller cities show no evident urban vegetation increase. The suggested framework is valuable for urban vegetation assessments and facilitates a thorough understanding and management of urban ecosystems.

Effects of ultrasonic shot peening process on the microstructure and mechanical properties of nickel-based superalloys formed by selective laser melting

Selective laser melting (SLM) is an attractive additive manufacturing technique for fabricating high-performance superalloys engineering components. Unfortunately, these as-built parts generally exhibit unsatisfied mechanical properties because of their natural thermal residual stress and non-equilibrium microstructures. Ultrasonic shot peening (USP) can effectively inhibit defect expansion and even close pores, thereby improving the mechanical properties of alloys. In this study, the internal defects, residual stress and microhardness redistribution, tensile properties, as well as microstructural response of the GH3230 alloy treated by different ultrasonic peening time are systematically studied. USP treatment induces a significant carbides fragmentation and synthesizes surface gradient heterogeneous structure, which displays a microstructure gradient in grain size, carbides size and dislocation density from surface to core. Long-time USP treatment induces work softening of GH3230 alloys. The work softening mechanism of the GH3230 alloys after long-time USP treatment is ascribed to the increase of surface temperature and high stored strain energy. Both the microhardness and residual compressive stress in the softened region of GH3230 alloys are reduced. Work softening effect increases the surface plasticity of the GH3230 sample, which induces deeper gradient structure. The various strengthening mechanisms of gradient heterogeneous structures, as well as the multiple effects of hetero deformation induced (HDI) hardening, and densification strengthening are responsible for achieving strength-ductility synergy. The research findings provide new insights based on USP for improving the mechanical properties of heterogeneous superalloys engineering components.

Sex differences in paediatric onset hypertrophic cardiomyopathy

Abstract Background Hypertrophic Cardiomyopathy (HCM) is a heterogeneous disease characterised by age related incomplete penetrance and variable long term outcomes. Sex differences have been described in both the clinical phenotype and natural history of adults with the disease, which have been attributed to both biological (eg sex hormone effect) and non-biological (eg societal and cultural effects) factors. It is unknown if similar sex differences exist in childhood-onset HCM. Purpose This study aimed to investigate the influence of biological sex on the clinical characteristics and outcomes of children with HCM. Methods Retrospective cohort study from an international registry of patients diagnosed under the age of 18 years with HCM. Patients with syndromic disease (RASopathy syndromes, inborn errors of metabolism, neuromuscular disease) were excluded. Sex differences in baseline characteristics and clinical outcomes were described. Primary outcomes were all-cause mortality or cardiac transplantation, Major Arrhythmic Cardiac Event (MACE) and heart failure event (defined as heart failure death or cardiac transplantation) Results Of 1262 patients, 851 (67.4%) were male (median age 11 yrs (IQR 7.4, 14.4) vs 11.1 (IQR 6.9, 14.0) in females, p=0.0312). Female patients were more likely to have a sarcomeric variant identified (n=208, 85.6% vs 388 (79.4%), p=0.041) despite equivalent genetic testing utilisation between sexes. Female patients were more likely to have severe heart failure symptoms (NYHA 3 or 4) (n=19, 6.1% vs n=20, 2.5% p value 0.030) but there was no difference in the proportion on medical therapy (male n=328, 39.7%, female n=167, 41.8, p value 0.476). The clinical phenotype in terms of degree of hypertrophy, left atrial size and left ventricular outflow tract gradient did not differ by sex. Over a median follow up of 5.2 years (IQR 2.4, 9.9) all-cause mortality or cardiac transplantation did not vary by sex but females were more likely to experience a heart failure event (females 0.6/100,000 pt years (95% CI 0.39-0.92) vs males 0.32/100,000 pt years (95% CI 0.21 – 0.50), hazard ratio 1.89, p value 0.0467). The incidence of MACE did not differ by sex but there was a trend towards higher implantable cardioverter defibrillator implantation in females (n=123, 30.7% vs n=210, 25.4%, p value 0.051). Conclusions For the first time, this study has shown sex differences in paediatric-onset hypertrophic cardiomyopathy. Despite no difference in baseline clinical phenotype, young female patients are more likely to experience heart failure symptoms and heart failure events over follow up. Further studies are required to explore the underlying mechanisms for these observed differences.Table summarising outcomes by sexSurvival free from heart failure

Metabolic rate and foraging behaviour: a mechanistic link across body size and temperature gradients

The mechanistic link between metabolic rate and foraging behaviour is a crucial aspect of several energy‐based ecological theories. Despite its importance to ecology however, it remains unclear whether and how energy requirements and behavioural patterns are mechanistically connected. Here we aimed to assess how modes of behaviour, including cumulative space use, patch selection and time spent in an experimental resource‐patchy environment, are related to a forager's standard metabolic rate (SMR) and its main determinants, i.e. body mass and temperature. We tested the individual behavioural patterns and metabolic rates of a model organism, the amphipod Gammarus insensibilis, across a range of body masses and temperatures. We demonstrated quantitatively that body mass and temperature exert a major influence on foraging decisions and space use behaviour via their effects on metabolic rates and the marginal value of energy. Individual cumulative space use was found to scale allometrically with body mass and exponentially with temperature, with patch giving‐up time falling as body mass and temperature increased. In response to warmer temperatures, the specimens adaptively intensified their foraging effort and explored larger spaces to offset the elevated SMR. Our results showed that SMR explained more variation than body mass and temperature combined, and had greater predictive power for behavioural patterns. Furthermore, foraging decisions regarding patch choice and partitioning were strongly related to mass‐and‐temperature‐adjusted SMR (residual), which is a component of metabolic phenotype. Individuals with higher M–T adjusted SMR initially preferred the most profitable patch and, as time progressed, abandoned the patch earlier and explored more space than the others. These results demonstrate that foraging decisions are intimately associated with variations in standard metabolic rate, whether phenotypic or due to size and temperature combined. This, in turn, sheds light on higher‐order energy‐based ecological processes.

Sunflower pith inspired dual-gradient cellular polyurethane architecture with amplified mechanical functions

Artificial cellular materials with various mechanical functions are attracting increasing attentions from aerospace, transportation, and industrialization. However, many artificial cellular materials, despite of the hierarchically ordered structures and even unique performance to some, still lag behind many natural ones in amplification of mechanical functions owing to the limitations in intrinsic mechanical performance and sophisticated structural design. Herein, inspired with lightweight and high strength of sunflower piths, we proposed a dual-gradient structure consisting of pore size gradient and wall thickness gradient to engineer cellular architectures with desirable mechanical performance by harnessing vat photopolymerization 3D printing of double crosslinking networks polyurethane elastomer. The double-gradient cellular polyurethane architecture displays more exceptional capability in load-bearing and energy absorption compared with non– and single gradient structures. Besides, the specific compressive strength and energy absorption of the dual-gradient cellular architectures are 4 times higher than those of traditional mechanical metamaterial structures such as octet-truss lattice, gyroid lattice, and porous structure prepared with the same material. Potential mechanisms such as dual-gradient cellular structures to obtain selective flexural deformation behaviour increasing their energy absorption and dissipation capacity are fully elucidated. As the potential paradigms, we demonstrated the mechanical functions of biomimetic mechanical cellular architectures for efficient impact protection and noise isolation, which offered a promising perspective toward developing soft metamaterials with excellent mechanical functions for potential soft machines and engineering applications.

Gradient structured Al alloy with a synergistic improvement of strength-ductility obtained by friction stir processing

One Al 6061 with gradient microstructure is prepared by friction stir processing (FSP). Microscopic characterization indicates that the regulation of grain size gradient could be achieved by adjusting the process parameters of FSP. The mechanical property test indicates that one gradient Al 6061 combines an ultimate tensile strength of 266 MPa with a uniform elongation of 27 %, and the other comes 258 MPa with 29 %, which provides an excellent combination of strength and ductility. Moreover, the molecular dynamics (MD) method is employed to reconstruct and simulate the mechanical behavior of the gradient region and the dynamic evolution of the microstructure. When the stacking faults (SFs) with antisymbolic Burgers vector meet and detwinning occurs, grain refinement will induce localized strengthening. When the Shockley partials occur cross-slip, numerous sessile dislocations obstruct the dislocation motion more facilitate strain hardening. Meanwhile, a unique interaction mechanism between shear bands (SBs) and intergranular cracks in Al 6061 is discovered in plastic deformation. The coarse net-like SBs in the small-grain region are highly susceptible to catastrophic fracture of the material, and the large cracks formed within the severely band-like SBs in the large-grain region weaken the strength substantially. However, the formation of sessile dislocations in the gradient region effectively mitigates strain localization and inhibits the nucleation of large cracks. The results interpret the dynamic evolution process of gradient microstructure prepared by FSP and the mechanism of strengthening and toughening and provide process and theoretical references for the research and development of new engineering materials.

Bioinspired polylactic acid/polyethylene glycol @ silicon dioxide microfibrous tarpaulin with dual-layer heterogeneous structure for enhanced daytime radiative cooling

Fibrous tarpaulin serves as the core barrier that protects goods, people, or areas from the adverse impacts of the external environment, such as rain, dust, and sunlight. However, conventional tarpaulins exhibit inadequate mechanical properties, a low solar reflectance, and are susceptible to pollution. To address these issues, a bioinspired polylactic acid/polyethylene glycol @silicon dioxide (PLA/PEG@SiO₂) microfibrous tarpaulin with a dual-layer heterogeneous structure was fabricated via in-situ drafting melt-blowing combined with thermal bonding, inspired by the layered structure of shells. This bioinspired dual-layer heterogeneous structure, with an adjustable heterodyne angle and SiO₂ size gradient, significantly improved the mechanical performance of the PLA/PEG@SiO2 microfibrous tarpaulin, and specifically manifested as an increase in the bursting strength of the sample to 25.5 N. Moreover, PLA/PEG@SiO2 microfibrous tarpaulin demonstrated excellent anti-pollution properties, effectively repelling liquids and dust. Additionally, its radiative cooling efficiency was notably enhanced, achieving a temperature reduction of ~9.8 °C compared with conventional fabrics, with reflectance of ~88.6 % and emissivity of ~98.3 %. These findings suggest that dual-layered PLA/PEG@SiO₂ microfibrous tarpaulin with multifunctional capabilities is a promising candidate for radiative cooling in outdoor shelters, wearable cooling devices, and energy-efficient building insulation materials.

Prediction of wellbore gas hydrate generation based on temperature-pressure coupling model in deepwater testing

With the advancement of oil and gas exploration and development technology, the development of the world's oil and gas resources is gradually advancing from land and shallow waters to deep waters. During the development of gas wells in deepwater regions, the temperature of the wellbore decreases from the bottom of the well to the wellhead, and therefore, common well conditions of high pressure, low temperature, and the presence of free water are encountered, which can lead to gas hydrate plugging of the pipeline and affect the transportation of natural gas. Simulation of temperature and pressure along the wellbore and identification of gas hydrate-generating zones in the wellbore can be used to take timely preventive measures and minimize losses. In this study, a wellbore gas hydrate generation and prediction model is developed by combining the mass, momentum, and energy conservation equations, and the model is solved by the fourth-order Runge-Kutta method, taking into account the temperature-pressure coupling in the wellbore. The effects of gas production, specific heat capacity, thermal conductivity, tubing size, test duration, and ground temperature gradient on the location of gas hydrate generation and the amount of inhibitor used were analyzed in a case study well in the South China Sea. Some suggestions for practical engineering operations, such as increasing the gas production in moderation and choosing smaller tubing sizes within the acceptable range, were given. The study's results can provide a theoretical basis for flow assurance for hydrocarbon production in the wellbore of deepwater gas wells.

Correlation between shot peening coverage and surface microstructural evolution in AISI 9310 steel: An EBSD and surface morphology analysis

In this study, martensitic high-strength steel serves as the subject of investigation, with both conventional and severe shot peening experiments being conducted. The coverage levels for conventional shot peening (CSP) are set at 100 % and 200 %, while severe shot peening (SSP) sees levels of 800 % and 1200 %. For the first time, the use of kernel average misorientation (KAM) enables the calculation of geometrically necessary dislocation (GND) density after peening, facilitating the study of GND density distribution across different coverage and offering a method for the visual assessment of peening degree. Results reveal that, under CSP, the gradient distribution of grain size is relatively uniform, whereas SSP leads to a pronounced gradient in grain size distribution. Taking into account the heterogeneous distribution of the initial material microstructure, a gradient in grain size from the surface to the interior of the material will appear after the coverage reaches a certain value, which is 400 % for AISI 9310 steel. Compared with CSP, SSP will further reduce the surface roughness Sa and improve the surface quality. The research presented further understands the relationship between shot peening process parameters and martensitic steel microstructure, providing an important reference for revealing the strengthening mechanism and selecting reasonable process parameters.

Stacked microporous layers with a rational gradient in pore size enhance the performance of proton exchange membrane fuel cells

Stacked microporous layers with a rational gradient in pore size enhance the performance of proton exchange membrane fuel cells

Control of photothermal liquid jets through microbubble Regulation: Fundamental mechanisms and Developing Strategies

Plasmon-induced photoacoustic streaming, considered as a potential application for micro-pumps in microfluidics, currently encounters ongoing debates concerning its fundamental mechanisms. In this study, we investigate the crucial role played by microbubbles in generation of jets in an ethanol aqueous solution. The power density threshold for bubble generation and its dependency on jet initiation are confirmed and the microbubble behavior is well regulated by manipulating the laser and liquid properties. Through simulations coupling fluidic and thermal fields, the significant role of Marangoni effect is validated in jet formation. Specifically, the temperature gradient of microbubbles is determined to be a pivotal factor in the generation of collimated jets. Additionally, factors influencing jetting, such as microbubble size and temperature gradients are studied, and noticeably, a stabilized jet lasting over 4 h is achieved based upon.

Seeds go up and down: The role of dung beetles in soil seed movement in the Southern Atlantic Forest of Argentina

Abstract The vertical movement of seeds performed by dung beetles from the soil bank and in animal faeces influences seed germination and the temporal dynamic of forest regeneration. While this process has been explored at the community level, the individual role of species is less understood. Here, we investigated the role of dung beetle size and seed size in this vertical movement under experimental conditions. We performed experiments using a gradient of dung beetle sizes and three sizes of artificial seeds (plastic beads) in two situations: inside faeces (secondary dispersal) and buried in the ground (soil bank). Through regression analysis, we related dung beetle size, seed size, and the initial position of seeds on the soil bank to the final position of seeds and their potential germination. For seeds in the soil bank, upward movement and exhumation were mainly of medium and large seeds, initially located at shallower depths, with larger beetles being primarily responsible for this movement. The downward movement was similar for all seed sizes. In dung seeds, the percentage of small seeds buried gradually increased with beetle size, while larger beetles made the main contribution for medium and large seeds. Besides, all seed sizes were buried at an average maximum bury depth of nearly 4 cm (the limit of the germination zone). The relative contribution of species depended on the interaction between dung beetles and seed sizes. Moreover, large dung beetles were essential for burying large seeds in the Southern Atlantic Forest.

Synthesis of bioinspired gradient MoS2/TiO2 coatings for enhancing tribological performance of titanium alloys

To enhance the tribological performance of titanium alloys under high frictional load, a MoS2/TiO2 composite coating with grain size gradient (GSG) distribution was presented. Inspired by the design principles of dental structures, the coating was fabricated through precise control of step-up voltage during plasma electrolytic oxidation (PEO). The variation in the frequency distribution of MoS2 grain sizes along the coating growth direction, ranging from approximately 43.23 ∼ 48.46 nm and 5.32 ∼ 8.16 nm, is attributed to increased energy supply and a higher degree of subcooling as the PEO voltage was elevated. The GSG coating significantly reduces the average coefficient of friction and abrasion loss by 65.44 % and 30.62 % with loads increasing to 10 N, compared with the MoS2/TiO2 coating. This improvement is attributed to the cooperative deformation of grains with varying sizes within the GSG structure under high frictional loads, which promotes strain delocalization and facilitates the formation of strain transition zones. These mechanisms effectively mitigate strain localization and ultimately achieve superior anti-friction performance. This study is essential for enhancing the broad application of titanium alloys in high-frictional environments.

Understanding error rejection of differential impedance spectroscopy for the in situ characterization of highly conductive fluids

Abstract Differential impedance spectroscopy (DIS) can offer distinct advantages over conventional impedance spectroscopy (IS), particularly for the in situ characterization of highly conductive, corrosive fluids. To enhance the understanding of DIS and determine the conditions under which this method is preferable over conventional IS with fixed electrode positions, error calculations were performed. Two scenarios were analyzed, one accounting solely for random instrument errors and the other including random errors as well as systematic errors from a serial offset impedance. Our analyses reveal that while permittivity measurements of highly conductive media remain challenging regardless of whether a conventional or differential impedance approach is used, DIS enables highly accurate conductivity measurements across a wide frequency and conductivity range. Studying different cell dimensions with equal cell constants revealed that despite the increased influence of systematic errors at small scales, conductivity can still be accurately measured, underscoring the applicability of DIS for microfluidic applications. Other potential parasitic effects, such as those arising from the electromagnetic skin effect, stray capacitances, electrode size, and temperature gradients, are discussed, providing a comprehensive framework for sample characterization with DIS.

Phenological Shifts in Lake Ice Cover Across the Northern Hemisphere: A Glimpse Into the Past, Present, and the Future of Lake Ice Phenology

AbstractLong‐term ice phenology records quantify the effects of climate change on Northern Hemisphere lakes. This study uses lake ice phenological records across a gradient of lake sizes (0.1–31,967.8 km2 in lake surface area) obtained from community science networks. We compiled in situ ice phenological records for 2,499 lakes across 15 countries for an average of 30 years. These data revealed that for the last 50 years (1971–2020), the annual mean duration of lake ice cover decreased at a rate of 9 days per decade, with a regime shift in lake ice phenology in the late 1980s. We projected that at the end of the century (2070–2099), ice duration will decrease by an average of 10 days when compared to the historical time period (1971–2000) for the shared socioeconomic pathway (SSP) 1–2.6 climate scenario (SSP126), 23 days for SSP370, and 28 days for the SSP585. Impending human development can enhance or attenuate lake ice loss, as adaptation strategies can accelerate fossil fuel use, result in conflict, or seek strategies apart from fossil fuel development. These future pathways have critical implications for the future preservation of lake ice cover.

The influence of sample size and sampling design on estimating population-level intra specific trait variation (ITV) along environmental gradients.

Understanding the relationship between intraspecific trait variability (ITV) and its biotic and abiotic drivers is crucial for advancing population and community ecology. Despite its importance, there is a lack of guidance on how to effectively sample ITV and reduce bias in the resulting inferences. In this study, we explored how sample size affects the estimation of population-level ITV, and how the distribution of sample sizes along an environmental gradient (i.e., sampling design) impacts the probabilities of committing Type I and II errors. We investigated Type I and II error probabilities using four simulated scenarios which varied sampling design and the strength of the ITV-environment relationships. We also applied simulation scenarios to empirical data on populations of the small mammal, Peromyscus maniculatus across gradients of latitude and temperature at sites in the National Ecological Observatory Network (NEON) in the continental United States. We found that larger sample sizes reduce error rates in the estimation of population-level ITV for both in silico and Peromyscus maniculatus populations. Furthermore, the influence of sample size on detecting ITV-environment relationships depends on how sample sizes and population-level ITV are distributed along environmental gradients. High correlations between sample size and the environment result in greater Type I error, while weak ITV-environmental gradient relationships showed high Type II error probabilities. Therefore, having large sample sizes that are even across populations is the most robust sampling design for studying ITV-environment relationships. These findings shed light on the complex interplay among sample size, sampling design, ITV, and environmental gradients.

Elucidating nanostructural organization and photonic properties of butterfly wing scales using hyperspectral microscopy.

Biophotonic nanostructures in butterfly wing scales remain fascinating examples of biological functional materials, with intriguing open questions with regard to formation and evolutionary function. One particularly interesting butterfly species, Erora opisena (Lycaenidae: Theclinae), develops wing scales that contain three-dimensional photonic crystals that closely resemble a single gyroid geometry. Unlike most other gyroid-forming butterflies, E. opisena develops discrete gyroid crystallites with a pronounced size gradient hinting at a developmental sequence frozen in time. Here, we present a novel application of a hyperspectral (wavelength-resolved) microscopy technique to investigate the ultrastructural organization of these gyroid crystallites in dry, adult wing scales. We show that reflectance corresponds to crystallite size, where larger crystallites reflect green wavelengths more intensely; this relationship could be used to infer size from the optical signal. We further successfully resolve the red-shifted reflectance signal from wing scales immersed in refractive index liquids with varying refractive index, including values similar to water or cytosol. Such photonic crystals with lower refractive index contrast may be similar to the hypothesized nanostructural forms in the developing butterfly scales. The ability to resolve these fainter signals hints at the potential of this facile light microscopy method for in vivo analysis of nanostructure formation in developing butterflies.