Evolution Of Shell Research Articles

Self-supporting thin Shells in Italy. Space and Structure of the Industrial Buildings (1930-1970)

In the Twentieth Century, the industrial buildings featured a broad experimentation on the load-bearing structures suited to the production spaces. Among the structural elements explicitly designed for factories were reinforced concrete thin shells. In Italy, where reinforced concrete was the predominant construction technique for the entire century, the evolution of the thin shells for industrial buildings traced a significant story: starting from the introduction of foreign systems and patents in the 1920s, the design and construction of the thin shells gradually stacked to national productive and technological specificities. This paper presents a historical investigation of the application of thin shells in Italy between 1930 and 1970, remarking, thus, the local contribution of Italian contractors and designers in the evolution of both the design solutions and production process. Furthermore, the study presents a systematic historical and technical framework related to thin shells to support the actions of knowledge and safeguard the industrial building heritage.

Evolution of bamboo derivative fiber-mollusk shell based calcite particulate hybrid reinforced epoxy bio-composites for sustainable applications

This study focused on the development of environmentally friendly epoxy-based biocomposites by incorporating bamboo fiber (BF) and calcite particles (CP) as reinforcements. A total of 125 specimens were fabricated with different weight percentages of BF and CP ranging from 0% to 15% to the epoxy. The biobased reinforcements were processed before incorporation, and the hand layup technique was used to fabricate the composites, which were then cured at ambient temperature. Evaluations of selected properties were carried out to ascertain the most probable areas of application, while the fracture surfaces were examined using SEM. The results indicated that the inclusion of these hybrid bio-reinforcements significantly enhanced the properties of the biocomposites compared to unreinforced samples. The optimal composition was identified as 12 wt% BF/CP, which demonstrated the highest ultimate tensile strength (32.84 MPa) and tensile modulus (1.9 GPa), attributed to the strong interfacial bonding between the epoxy matrix and the BF/CP reinforcements. Additionally, the flexural strength (55.38 MPa) and modulus (2.72 GPa) were improved due to the effective load transfer and stiffening effect of the calcite particles. The hardness (67 HS) and wear index (0.015 mg) were enhanced by the toughening mechanism provided by the bamboo fibers, while the density (1.195 g/cm³) remained within a desirable range for lightweight applications. Composites with 9 wt% BF/CP exhibited the highest impact strength (22.66 J/m2), likely due to the optimal balance of fiber-matrix interaction and energy absorption capacity. These findings indicate that the developed hybrid-reinforced biocomposite compositions hold great promise with the improved physical and mechanical properties as seen and can be utilized for various applications, including automotive, aerospace, and other engineering applications.

Influence of impact velocity on the semi-sealed cylindrical shell during water entry

To study the motion characteristics and cavity evolution of the cylindrical shell with different initial velocity, the numerical simulation based on the Star-CCM+ and ABAQUS collaborative simulation method is carried out in this paper. The results show that when the shell penetrates into the water at a lower speed, only a small amount of external fluid can enter into the shell, and the internal fluid shows a reciprocating motion trend. Moreover, the speed of the shell and the force at the bottom wall show a fluctuating trend. As the speed increases, the volume of fluid entering into the interior of the shell gradually increases. After the speed reaches 30 m/s, the fluid can impact the upper wall of the shell, which also causes sudden changes in velocity and displacement. When the initial velocity of the shell reaches 80 m/s, significant deformation occurs at the upper wall of the shell, and the deformation is not fully restored after the fluid leaves the upper wall. As the speed increases, the degree of deformation gradually increases, and the volume of the cavity gradually increases.

Accretion onto oscillating cosmic string loops

Cosmic string loops are non-linear density fluctuations which form in the early universe and could play an important role in explaining many phenomena which are in tension with the standard ΛCDM model. Hence, the accretion process onto cosmic string loops should be studied in detail. Most previous works view loops as point masses and ignore the impact of a finite loop size. In this work, we utilize the Zel'dovich approximation to calculate the non-linear mass sourced by a static extended loop with a time-averaged density profile derived from the trajectory of the loop oscillation, and compare the result with what is obtained for a point-mass source. We find that the finite size of a loop mainly affects the evolution of turnaround shells during the early stages of accretion, converging to the point mass result after a critical redshift, zc ( II)/( III). For zc ( II)/( III), the total accreted mass surrounding a loop is suppressed relative to the point mass case and has a growth rate proportional to (1+z)-3/2.As an immediate extension, we also qualitatively analyse the accretion onto moving point masses and onto moving extended loops. In addition to the reduction in the nonlinear mass, the loop finite size also changes the shape of the turnaround surface at early stages of accretion.

Strength Evolution and Fracture Feature of Carbon Fiber-Reinforced Silica Sol Shell for Investment Casting

Strength Evolution and Fracture Feature of Carbon Fiber-Reinforced Silica Sol Shell for Investment Casting

A self-similar model of galaxy formation and dark halo relaxation

We develop a spherical self-similar model for the formation of a galaxy through gas collapsing in an isolated self-gravitating dark matter halo. As is well known, the self-similarity assumption makes the problem eminently tractable by reducing it to a system of ordinary differential equations. We improve upon the existing literature on self-similar collapse in two ways. First, we include the effects of radiative cooling and the formation of a pseudo-disk at the center of collapse, in a parametrised manner. More importantly, we solve for the evolution of gas and dark matter simultaneously and self-consistently using a novel iterative approach. As a result, our model produces shell trajectories of both gas and dark matter that qualitatively agree with the results of full hydrodynamical simulations of self-gravitating systems. We discuss the impact of various ingredients such as the accretion rate, gas equation of state, disk radius and cooling rate amplitude on the evolution of the gas shells, although we leave the inclusion of stellar and black hole activity to future work. The self-consistent evolution of gas and dark matter allows us to study the response (or `quasi-adiabatic relaxation') of the dark matter trajectories to the presence of collapsing gas, an effect that has gained increasing importance recently in the context of precision estimates of small-scale statistics like the matter power spectrum. Our default configuration produces a relaxation relation in qualitative agreement with that seen in cosmological hydrodynamical simulations, and further allows us to easily study the impact of the model ingredients mentioned above. As an initial application, we vary one ingredient at a time and find that the accretion rate and gas equation of state have the largest impact on the relaxation relation, while the cooling amplitude plays only a minor role. Our model thus provides a convenient framework to rapidly explore the coupled nonlinear impact of multiple astrophysical processes on the mass and velocity profiles of dark matter in galactic halos, and consequently on observables such as rotation curves and gravitational lensing signals.

Crack propagation and damage evolution of metallic cylindrical shells under internal explosive loading

This paper investigates the three-dimensional crack propagation and damage evolution process of metallic column shells under internal explosive loading. The calibration of four typical failure parameters for 40CrMnSiB steel was conducted through experiments and subsequently applied to simulations. The numerical simulation results employing the four failure criteria were compared with the differences and similarities observed in freeze-recovery tests and ultra-high-speed tests. This analysis addressed the critical issue of determining failure criteria for the fracture of a metal shell under internal explosive loads. Building upon this foundation, the damage parameter Dc, linked to the cumulative crack density, was defined based on the evolution characteristics of a substantial number of cracks. The relationship between the damage parameter and crack velocity over time was established, and the influence of the internal central pressure on the damage parameter and crack velocity was investigated. Variations in the fracture modes were found under different failure criteria, with the principal strain failure criterion proving to be the most effective for simulating 3D crack propagation in a pure shear fracture mode. Through statistical analysis of the shell penetration fracture radius data, it was determined that the fracture radius remained essentially constant during the crack evolution process and could be considered a constant. The propagation velocity of axial cracks ranged between 5300 m/s and 12600 m/s, surpassing the Rayleigh wave velocity of the shell material and decreasing linearly with time. The increase in shell damage exhibited an initial rapid phase, followed by deceleration, demonstrating accelerated damage during the propagation stage of the blast wave and decelerated damage after the arrival of the rarefaction wave. This study provides an effective approach for investigating crack propagation and damage evolution. The derived crack propagation and damage evolution law serves as a valuable reference for the development of crack velocity theory and the construction of shell damage evolution modes.

Influence of angle of attack on the semi-sealed cylindrical shell during high-speed water entry

The fluid–structure interaction based on STAR-CCM+ and ABAQUS collaborative simulation is adopted in this paper, which is combined with the overset mesh technology, and the cavity evolution and motion characteristics of the semi-sealed cylindrical shell with the angle of attack during high-speed water entry are studied. The results show that the shell with an angle of attack experiences significant deflection after penetrating into the water, which is due to the fluid hitting the upper wall of the shell and generating a large torque. The deformation of the horizontally placed shell is much more obvious than that of a vertically placed shell during water entry. Due to the deformation of the shell, the direction of the fluid's force can be changed, resulting in a horizontal component force, causing a horizontal movement of the horizontal shell during water entry. As the angle of attack decreases, the volume of fluid entering into the shell gradually decreases, resulting in a decrease in the volume of fluid flowing out of the shell. The shell with an angle of attack less than 75° causes the top wall to come into contact with the water surface during the deflection process, which also generates new cavities below.

Europa’s coupled ice–ocean system: Temporal evolution of a pure ice shell

Europa’s icy surface likely overlies an ocean, but the ice thickness is not known. Here we model the temporal growth of a Europan shell of pure ice subject to varying ice–ocean heat fluxes, ice rheologies, and internal heating rates. Both constant and viscosity-dependent internal heating rates are included, yielding similar results for particular viscosities. A growing shell starting from an ice-free initial state transitions from conduction to convection at O(105) to O(107) years, with thicknesses of O(1–10) km. For low ice–ocean heat fluxes and larger viscosities, and in the absence of internal heating of the shell, the time to reach a steady-state thickness exceeds the estimated age of Europa’s surface, whence the shell may still be growing. We conclude by presenting a method for inferring estimates of ice–ocean heat fluxes (modulo uncertainties introduced by internal heating) and vertical ocean velocities from the ice-thickness measurements expected from the upcoming Clipper mission, assuming the shell is in a conductive steady state.

Interfacial Polymerization Depth Mediated by the Shuttle Effect Regulating the Application Performance of Pesticide-Loaded Microcapsules.

The highly water-soluble nematicide fosthiazate is anticipated to undergo microencapsulation in order to enhance its retention around plant roots and mitigate leaching into groundwater. However, the underlying mechanism governing the influence of hydrophilicity of the microcapsule (MC) core on the evolution of the microcapsule shell remains unclear, posing challenges for encapsulating water-soluble core materials. This study elucidates the microlevel formation mechanism of microcapsules by investigating the impact of interfacial mass transfer on shell formation and proposes a method for regulating the structure of shells. The study reveals that enhancing the hydrophilicity of the core enhances the shuttle effect between the oil and aqueous phase, expands the region of polymerization reactions, and forms a loose and thick shell. The thickness of the microcapsule shell prepared using solvent oil 150# (MCs-SOL) measures only 264 nm, while that of the microcapsules prepared using propylene glycol diacetate and solvent oil 150# at a ratio of 2:1 (MCs-P2S1) is 5.2 times greater. The enhanced compactness of the shell reduced the release rate of microcapsules and the leaching distance of fosthiazate in soil, thereby mitigating the risk of leaching loss and facilitating the distribution of active ingredients within crop roots. The MCs-SOL had a limited leaching distance measurement of 8 cm and exhibited a satisfactory efficacy of 87.3% in controlling root galling nematodes. The thickness and compactness of the MCs shell can be regulated by manipulating the interfacial shuttle effect, providing a promising approach to enhancing utilization efficiency while mitigating potential environmental risks.

Core-shell gold-copper nanoparticles: Evolution of copper shells on gold cores at different gold/copper precursor ratios

Core-shell nanostructures usually exhibit tunable catalytic properties in comparison with their single core or shell counterpart due to electronic interaction and lattice strain between the core and shell regions. Herein, we report the intriguing evolution of copper (Cu) shells on the gold (Au) cores at different Au/Cu precursor ratios during the synthesis of core-shell Au–Cu nanoparticles at an organic medium via seed-mediated growth method. In brief, at relatively low Cu ratios, quasi-spherical Au–Cu nanoparticles with conventional core-shell structures are the majority products, in which the Cu shell thickness increases with the increase of Cu precursor ratios. The difference is that at high Cu ratios, the Cu shells no longer increase their thickness, but evolve into a dendritic structure. Interestingly, the core-shell Au–Cu nanoparticles with dendritic Cu shells could be transformed into interesting Au–Cu cage-bell structures after a ripening process at elevated temperature. Further, through galvanic replacement reaction with Pt precursors, the thin Cu shells could be converted into CuPt alloy shells on the Au cores, which exhibit enhanced activity towards methanol oxidation reaction with satisfactory durability, in comparison with that of commercial Pt/C catalysts.

Observing the Structural Evolution of Quasi-Monolayer Pt Shell on Pd Core in the Electrocatalytic Oxygen-Reduction Reaction.

The use of a quasi-monolayer Pt shell (Ptqms) on a Pd core (Pdc) can reach cost and activity targets for the electrocatalytic oxygen-reduction reaction (ORR). The structure of PdcPtqms in the ORR will vary; however, direct observation of this issue is scarce. Here, during cyclic staircase voltammetry (ranging from 0.5 to 1.15 VRHE) in 0.1 M O2-saturated HClO4, the structure of PdcPtqms was monitored by in situ X-ray absorption spectroscopy. The qualitative and quantitative structural information clearly exhibits a complete picture that Ptqms will directly restructure to form Pt clusters and holes, while Pdc almost remains stable. These findings identify the initial structural evolution of PdcPtqms in the ORR, highlighting the importance of protecting Pdc in the development of high-performance PdcPtqms electrocatalysts.

Experimental study on high-speed vertical water entry of the semi-sealed cylindrical shell

The semi-sealed cylindrical shell is a hollow cylinder, of which one end is opened and the other end is sealed. In this paper, the hydrodynamic characteristics of a semi-sealed cylindrical shell at high-speed are studied experimentally. The influence of the slenderness and Froude number on the expansion characteristics of the cavity is preliminarily studied, with special attention paid to the cavity evolution, splash and kinetics of the cylindrical shell under the influence of the internal jet. The results show that, with the semi-sealed cylindrical shell penetrating into water, it forms supercavity on the outer shell surface similar to a solid cylinder. Subsequently, with the internal jet poured out the shell, a foggy cavity is formed below. As the internal jet continuously pours out of the shell, a new water surface is formed below the shell and the shell will impact on the new water surface, thus causing new cavities generated. This process will repeat continuously as the shell moves downward. Moreover, the slenderness of the shell and Froude number have remarkable influence on the motion characteristics and cavity evolution. The findings in this paper can be used as a reference for future designs of cylindrical shell projectile for water entry.

Convergent evolution of spherical shells in Miocene planktonic foraminifera documents the parallel emergence of a complex character in response to environmental forcing

AbstractThe spherical encompassing final chamber of the planktonic foraminifera Orbulina universa is a prime example of a complex character whose evolution has been documented by a sequence of intermediate forms. However, the mechanism that induced evolution of the spherical chamber remain unclear. Here we show that shortly after the emergence of Orbulina, documented throughout the oceans, a convergent evolutionary transition occurred in the semi-isolated Paratethys, leading to the emergence of the endemic Velapertina, which occupied a similar niche to Orbulina in the surface waters. Using X-ray computed tomography scanning, we show that the evolution of the encompassing final chamber involved the same sequence of steps in both lineages, combining a progressively spherical shell shape with changes in the position, number, and sizes of apertures. The similarity in the sequence of character acquisitions suggests structural determinism in the way foraminiferal shells are constructed and the presence of natural selection favoring a spherical morphology. Collectively, the emergence of spherical chambers in the two lineages at a similar time suggests that the evolution of this spectacular complex character occurred in response to a singular environmental driver.

Regional variations in observed fracture abundance and associated predictions for smaller fractures on Europa with implications for regional plume origins

Large fractures on Europa's surface have been extensively studied for the insight they provide into the evolution of the satellite's ice shell. The presence of small fractures has not been characterized on a global or regional scale because of the resolution limits in the current image data. However, if smaller fractures are present they could significantly increase the overall fracture abundance and influence the mechanical properties of the ice shell. Regional variability in this abundance would also impact the spatial heterogeneity of ice shell characteristics. To investigate the possible contribution of smaller fractures to the influence of the fracture network on the behavior of the ice lithosphere, we measure the surface length of visible fractures in regions on Europa's surface and calculate their length distributions and fracture intensities. These outcomes are extrapolated, using best-fit functions, to consider the possible abundance and role of smaller fractures in these networks. The analysis of the visible fractures sampled different geologic terrains and geographic regions to consider the effect of terrain type and location. Fracture abundance in observable populations shows some variation with terrain type. However, observable abundance also changes with image resolution, indicating that current data limit the interpretation of visible fracture populations. Typical log-normal, exponential, and power-law fracture network distributions, based on analysis of terrestrial fracture networks, were considered as methods for extrapolating the observed fracture populations. Power-law was found to be the most appropriate extrapolation choice. It was also found to predict observed fracture abundance in one sample region with a smaller sub-region that had locally higher image resolution. Applying a power-law extrapolation for the fracture abundance as a function of length, we predict fracture abundance characteristics that are up to two orders of magnitude higher than abundance of observed fractures, and which vary by an order of magnitude between regions. Thus, the predicted fracture populations indicate that abundant small fractures would contribute significantly to the mechanical behavior of the ice lithosphere and create regional variations in fracture abundance. For example, where they are abundant, these smaller fractures could contribute to fracture networks providing localized migration pathways for plume activity on Europa. New image data from the Europa Clipper mission should enable fracture mapping at smaller scales to refine the roles of these networks and the smaller fractures on Europan lithospheric processes and rheology.

Comparative Single-Cell Transcriptomics Reveals Novel Genes Involved in Bivalve Embryonic Shell Formation and Questions Ontogenetic Homology of Molluscan Shell Types.

Mollusks are known for their highly diverse repertoire of body plans that often includes external armor in form of mineralized hardparts. Representatives of the Conchifera, one of the two major lineages that comprises taxa which originated from a uni-shelled ancestor (Monoplacophora, Gastropoda, Cephalopoda, Scaphopoda, Bivalvia), are particularly relevant regarding the evolution of mollusk shells. Previous studies have found that the shell matrix of the adult shell (teleoconch) is rapidly evolving and that the gene set involved in shell formation is highly taxon-specific. However, detailed annotation of genes expressed in tissues involved in the formation of the embryonic shell (protoconch I) or the larval shell (protoconch II) are currently lacking. Here, we analyzed the genetic toolbox involved in embryonic and larval shell formation in the quagga mussel Dreissena rostriformis using single cell RNA sequencing. We found significant differences in genes expressed during embryonic and larval shell secretion, calling into question ontogenetic homology of these transitory bivalve shell types. Further ortholog comparisons throughout Metazoa indicates that a common genetic biomineralization toolbox, that was secondarily co-opted into molluscan shell formation, was already present in the last common metazoan ancestor. Genes included are engrailed, carbonic anhydrase, and tyrosinase homologs. However, we found that 25% of the genes expressed in the embryonic shell field of D. rostriformis lack an ortholog match with any other metazoan. This indicates that not only adult but also embryonic mollusk shells may be fast-evolving structures. We raise the question as to what degree, and on which taxonomic level, the gene complement involved in conchiferan protoconch formation may be lineage-specific or conserved across taxa.

Evolution of Pluto's Impact‐Deformed Ice Shell Below Sputnik Planitia Basin

AbstractSputnik Planitia basin, the dominant surface feature of the dwarf planet Pluto, is located very close to the far point of Pluto‐Charon tidal axis. This position is currently believed to be a result of whole body reorientation driven by the combination of (a) the uplift of a subsurface ocean in response to a basin‐forming impact and (b) the nitrogen layer accumulated inside the basin. Since an ice shell made of pure water ice cannot maintain the uplift on timescales of billions of years, the presence of an insulating and highly viscous layer of methane clathrates at the base of the shell has recently been proposed. In this study, we solve the thermo‐mechanical evolution of the ice shell in a 2D spherical axisymmetric geometry and evaluate the gravity anomaly associated with the evolving ice shell shape. Taking into account the effect of impact heating and stress‐dependent rheology of both ice and clathrates, we show that a thick shell (≥200 km) loses the impact heat slowly which leads to fast uplift relaxation of the order of hundreds of million years. On the contrary, a thin shell (∼100 km) cools down quickly (∼10 Myr), becoming rigid and more likely to preserve the ocean/shell interface uplift till the present. These results suggest that a thick ocean may be present beneath Pluto's ice shell.

Accurately Localizing Multiple Nanoparticles in a Multishelled Matrix Through Shell-to-Core Evolution for Maximizing Energy-Storage Capability.

Robust and fast lithium energy storage with a high energy density is highly desired to accelerate the market adoption of electric vehicles. To realize such a goal requires the development of electrode materials with a high capacity, however, such electrode materials suffer from huge volume expansion and induced short cycling life. Here, using tin (Sn) as an example, an ideal structure is designed to effectively solve these problems by separately localizing multiple Sn nanoparticles in a nitrogen-doped carbon hollow multishelled structure with duplicated layers for carbon shell (Sn NPs@Nx C HoMS-DL). The fabricated composite can promote ion and electron diffusion owing to the conductive network formed by connected multiple shells and cores, effectively buffer the volume expansion, and maintain a stable electrode-electrolyte interface. Despite the challenging fabrication, such a structure is realized through an innovative and facile synthesis strategy of "in situ evolution of shell to core", which is applicable for diverse low-melting-point materials. As expected, such a structure enables the high-capacity electrode material to realize nearly its theoretical lithium-storage capability: the developed Sn NPs@Nx C HoMS-DL electrode maintains 96% of its theoretical capacity after 2000 cycles at 2C.

Nonsingular quantum gravitational dynamics of an Lemaître-Tolman-Bondi dust shell model: The role of quantization prescriptions

We study some consequences of the loop quantization of the outermost dust shell in the Lema\^{\i}tre-Tolman-Bondi spacetime with a homogeneous dust density using different quantization strategies motivated by loop quantum gravity. Prior work has dealt with loop quantizing this model by employing holonomies and the triads, following the procedure in standard loop quantum cosmology. In this work we compare this quantization with the one in which holonomies and gauge-covariant fluxes are used. While both of the quantization schemes resolve the central singularity, they lead to different mass gaps at which a trapped surface forms. This trapped surface which is matched to an exterior generalized Vaidya spacetime disappears when the density of the dust cloud is in the Planck regime. We find that the quantization based on holonomies and gauge-covariant fluxes generically results in an asymmetric evolution of the dust shell in which the Vaidya mass associated with the white hole as seen by an external observer is $2/\ensuremath{\pi}$ of the one for the black hole. This effective difference in masses results from difference in the classical limits in pre- and postbounce regimes in the two quantizations. This distinctive feature rules out formation of any black-hole-white-hole twins in presence of gauge-covariant flux modifications, which is in contrast to the quantization using holonomies and triads where the gravitational collapse always leads to black hole--white hole twins. Another striking difference lies in the fact that for the quantization based on holonomies and gauge-covariant fluxes there can be situations in which during a nonsingular collapse only a black hole forms without a white hole.

Hydrophilic Shell Matrix Proteins of Nautilus pompilius and the Identification of a Core Set of Conchiferan Domains.

Despite being a member of the shelled mollusks (Conchiferans), most members of extant cephalopods have lost their external biomineralized shells, except for the basally diverging Nautilids. Here, we report the result of our study to identify major Shell Matrix Proteins and their domains in the Nautilid Nautilus pompilius, in order to gain a general insight into the evolution of Conchiferan Shell Matrix Proteins. In order to do so, we performed a multiomics study on the shell of N. pompilius, by conducting transcriptomics of its mantle tissue and proteomics of its shell matrix. Analyses of obtained data identified 61 distinct shell-specific sequences. Of the successfully annotated 27 sequences, protein domains were predicted in 19. Comparative analysis of Nautilus sequences with four Conchiferans for which Shell Matrix Protein data were available (the pacific oyster, the pearl oyster, the limpet and the Euhadra snail) revealed that three proteins and six protein domains were conserved in all Conchiferans. Interestingly, when the terrestrial Euhadra snail was excluded, another five proteins and six protein domains were found to be shared among the four marine Conchiferans. Phylogenetic analyses indicated that most of these proteins and domains were probably present in the ancestral Conchiferan, but employed in shell formation later and independently in most clades. Even though further studies utilizing deeper sequencing techniques to obtain genome and full-length sequences, and functional analyses, must be carried out in the future, our results here provide important pieces of information for the elucidation of the evolution of Conchiferan shells at the molecular level.