Narrow Shell Research Articles

A new helcionelloid mollusc from the Cambrian of Green land and Idaho (Laurentia)

Ressericonella gen. nov., a new genus of helcionelloid mollusc, characterized by a narrow shell with a shallowly convex dorsal surface and flat to shallowly concave lateral areas, is described from the Cambrian of Greenland and Idaho. The type species is Helcionella aequa Resser, 1939 from the Langston Formation (Naomi Peak Limestone Member) of early middle Cambrian age (Miaolingian Series, Wuliuan Stage, Albertella Biozone). Ressericonella pipalukae gen. et sp. nov. occurs in the latest early Cambrian (Cambrian Series 2, Stage 4, Bonnia–Pagetides elegans Biozone) of southern Freuchen Land, North Greenland. Silicified specimens of Ressericonella pipalukae from North Greenland preserve two-layered shell structure in which an inner layer with a transverse fibrous pattern similar to lamello-fibrillar structure is overlain by an outer layer with fine threads radiating from the apex.

Continuous Casting Slab Mold: Key Role of Nozzle Immersion Depth.

Based on a physical water model with a scaling factor of 0.5 and a coupled flow-heat transfer-solidification numerical model, this study investigates the influence of the submerged entry nozzle (SEN) depth on the mold surface behavior, slag entrapment, internal flow field, temperature distribution, and initial solidification behavior in slab casting. The results indicate that when the SEN depth is too shallow (80 mm), the slag layer on the narrow face is thin, leading to slag entrapment. Within a certain range of SEN depths (less than 170 mm), increasing the SEN depth reduces the impact on the mold walls, shortening the "plateau period" of stagnated growth on the narrow face shell. This allows the upper recirculation flow to develop more fully, resulting in an increase in the surface flow velocity and an expansion in the high-temperature region near the meniscus, which promotes uniform slag melting but also heightens the risk of slag entrainment due to shear stress at the liquid surface (with 110 mm being the most stable condition). As the SEN depth continues to increase, the surface flow velocity gradually decreases, and the maximum fluctuation in the liquid surface diminishes, while the full development of the upper recirculation zone leads to a higher and more uniform meniscus temperature. This suggests that in practical production, it is advisable to avoid this critical SEN depth. Instead, the immersion depth should be controlled at a slightly shallower position (around 110 mm) or a deeper position (around 190 mm).

Observational Evidence for Magnetic Field Amplification in SN 1006

We report the first observational evidence for magnetic field amplification in the northeast/southwest (NE/SW) shells of supernova remnant SN 1006, one of the most promising sites of cosmic ray acceleration. In previous studies, the strength of magnetic fields in these shells was estimated to be B SED ≃ 25 μG from the spectral energy distribution, where the synchrotron emission from relativistic electrons accounted for radio to X-rays, along with the inverse Compton emission extending from the GeV to TeV energy bands. However, the analysis of broadband radio data, ranging from 1.37 to 100 GHz, indicated that the radio spectrum steepened from α 1 = 0.52 ± 0.02 to α 2 = 1.34 ± 0.21 by Δα = 0.85 ± 0.21. This is naturally interpreted as a cooling break under a strong magnetic field of B brk ≥ 2 mG. Moreover, the high-resolution MeerKAT image indicated that the width of the radio NE/SW shells was broader than that of the X-ray shell by a factor of only 3−20, as measured by Chandra. Such narrow radio shells can be naturally explained if the magnetic field responsible for the radio emissions is B R ≥ 2 mG. Assuming that the magnetic field is locally enhanced by a factor of approximately a = 100 along the NE/SW shells, we argue that the filling factor, which is the volume ratio of such a magnetically enhanced region to that of the entire shell, must be as low as approximately k = 2.5 × 10−5.

Investigating Protostellar Accretion-driven Outflows across the Mass Spectrum: JWST NIRSpec Integral Field Unit 3–5 μm Spectral Mapping of Five Young Protostars

Investigating Protostellar Accretion is a Cycle 1 JWST program using the NIRSpec+MIRI integral field units to obtain 2.9–28 μm spectral cubes of five young protostars with luminosities of 0.2–10,000 L ⊙ in their primary accretion phase. This paper introduces the NIRSpec 2.9–5.3 μm data of the inner 840–9000 au with spatial resolutions from 28 to 300 au. The spectra show rising continuum emission; deep ice absorption; emission from H2, H i, and [Fe ii]; and the CO fundamental series in emission and absorption. Maps of the continuum emission show scattered light cavities for all five protostars. In the cavities, collimated jets are detected in [Fe ii] for the four <320 L ⊙ protostars, two of which are additionally traced in Brα. Knots of [Fe ii] emission are detected toward the most luminous protostar, and knots of [Fe ii] emission with dynamical times of <30 yr are found in the jets of the others. While only one jet is traced in H2, knots of H2 and CO are detected in the jets of four protostars. H2 is seen extending through the cavities, showing that they are filled by warm molecular gas. Bright H2 emission is seen along the walls of a single cavity, while in three cavities narrow shells of H2 emission are found, one of which has an [Fe ii] knot at its apex. These data show cavities containing collimated jets traced in atomic/ionic gas surrounded by warm molecular gas in a wide-angle wind and/or gas accelerated by bow shocks in the jets.

Modeling of ontogenetic changes in the shell cross section of the most ancient (Late Permian) representatives of &lt;i&gt;Otoceras&lt;/i&gt; (Ammonoidea)

For the first time, shell cross-sections were made for the most ancient (Late Permian) representatives of the genus Otoceras. From these cross-sections, ontogenetic changes in the shell shape of O. concavum Tozer were reconstructed at size stages ranging from tiny to very large. A moderately wide shell with a moderately narrow umbilicus narrows intensely to its tiny size, becoming a narrow shell. At the stage of very small size, the shell expands, again becoming moderately wide, and the umbilicus narrows slightly, remaining moderately narrow. However, at small sizes, the change in these characteristics occurs in the same direction, but with increased intensity. Moreover, important changes are observed at the medium-sized stage, when the expansion of the shell stops and the umbilicus becomes narrow. At the end of the studied ontogenesis, the morphological development of the mollusk was aimed at the formation of a moderately narrow shape with a very narrow umbilicus. Of the variety of shell shapes previously established among ammonoids, numbering 35 types, representatives of the species O. concavum throughout the studied ontogenesis had only three: subdiscocone, tumaricone, and pachycone. Finally, the constructed ontogenetic model clearly demonstrated the features of the development of the cross-sectional shape of O. concavum shells during their growth, emphasizing ontogenetic trends in changes in the most important parameters of the shell. We conclude that the identified transformations of the shell shape contribute to the diagnosis of small-sized Otoceras, and can serve as the basis for the subsequent reconstruction of the morphogenetic development of the family Otoceratidae.

Theoretical analysis for free vibration of submerged conical motor stator

The conical rim-driven motor stator is a structure with variable thickness and non-standard boundaries, which can be treated as an orthotropic conical shell. To prevent resonance and reduce electromagnetic noise, a modal analysis of the stator is necessary. This paper presents an analytical model for the free vibration of the conical stator in both onshore and underwater environments. Due to the relatively large thickness of the motor stator, the first-order shear deformation theory (FSDT) is employed. The fluid loading is calculated by discretizing the conical shell into a series of narrow cylindrical shells featuring diverse radii and thickness. The resulting equations are solved employing the transfer matrix method (TMM), which is capable of different types of boundary conditions (BCs). The convergence and accuracy of the proposed method are validated through a comparative analysis involving numerical simulations and outcomes derived from the thin shell theory. The importance of considering shear deformation and rotatory inertia in determining the natural frequency of motor stators is demonstrated. Finally, the impact of fluid loading on the vibration behavior of stators with various geometric parameters and boundary conditions are investigated and discussed. The proposed model presents a precise and convenient approach for analyzing the free vibration of submerged conical motor stators, and can be extended to conventional cylindrical motor stators through appropriate degradation procedures.

Multiphase Gas Interactions on Subarcsec Scales in the Shocked Intergalactic Medium of Stephan’s Quintet with JWST and ALMA

We combine James Webb Space Telescope (JWST) and Hubble Space Telescope imaging with Atacama Large Millimeter Array CO(2–1) spectroscopy to study the highly turbulent multiphase intergalactic medium (IGM) in Stephan’s Quintet on 25–150 pc scales. Previous Spitzer observations revealed luminous H2 line cooling across a 45 kpc-long filament, created by a giant shock wave, following the collision with an intruder galaxy, NGC 7318b. We demonstrate that the Mid-Infrared Instrument/F1000W/F770W filters are dominated by 0–0 S(3) H2 and a combination of polycyclic aromatic hydrocarbon and 0–0 S(5) H2 emission. These observations reveal the dissipation of kinetic energy as massive clouds experience collisions, interactions, and likely destruction/recycling within different phases of the IGM. In 1 kpc-scaled structure, warm H2 was seen to form a triangular-shaped head and tail of compressed and stripped gas behind a narrow shell of cold H2. In another region, two cold molecular clumps with very different velocities are connected by an arrow-shaped stream of warm, probably shocked, H2 suggesting a cloud–cloud collision is occurring. In both regions, a high warm-to-cold molecular gas fraction indicates that the cold clouds are being disrupted and converted into warm gas. We also map gas associated with an apparently forming dwarf galaxy. We suggest that the primary mechanism for exciting strong mid-IR H2 lines throughout Stephan’s Quintet is through a fog of warm gas created by the shattering of denser cold molecular clouds and mixing/recycling in the post-shocked gas. A full picture of the diverse kinematics and excitation of the warm H2 will require future JWST mid-IR spectroscopy. The current observations reveal the rich variety of ways that different gas phases can interact with one another.

Core-double-shell structure and heterojunction in CdS/SnS2 boosting fast carrier separation for ultrasensitive detection of carbohydrate antigen 125

Combining heterojunctions and advanced structures is an effective strategy for improving light capture capability and electron-hole pair separation of photoactive materials. In this work, we facilely constructed CdS/SnS2 with a unique core-double-shell structure (CS-CDSSs) using cobalt glycerate nanospheres as sacrificial templates. The one-step hydrothermal cation exchange method was used to construct energy-matched heterojunctions, simultaneously endowing CS-CDSSs with a distinctive morphology of coexisting core-shell and multi-shell structures. The enhanced photoconversion efficiency was attributed to (i) unique structural features and a narrow shell spacing; (ii) broadened optical response and shift toward the visible-light range; (iii) scattering/reflection effect of the incident light to increase light enrichment; and (iv) close contact at the interface between CdS and SnS2. Based on the excellent photoelectric conversion efficiency of CS-CDSSs, the fabricated photoelectrochemical (PEC) biosensors exhibit high performance with a wide linear range from 10−7 to 102 U·mL−1, and an ultralow detection limit of 5.48 × 10−8 U·mL−1 for carbohydrate antigen 125 (CA125). This novel strategy significantly improves the PEC performance of heterojunctions by preparing core-double-shell structures, which could provide more inspiration for constructing other functionalized photoactive materials.

Structural characterization of systems with competing interactions confined in narrow spherical shells.

Systems with short-range attraction and long-range repulsion can form ordered microphases in bulk and under confinement. In fact, confinement has been proven to be a good strategy to induce the formation of novel ordered microphases that might be appealing to the development of functional nanomaterials. Using Grand Canonical Monte Carlo (GCMC) simulations, we study a model colloidal system with competing interactions under confinement in narrow spherical shells at thermodynamic conditions under which the hexagonal phase is stable in bulk. We observe the formation of three parent ordered structures formed by toroidal clusters and two spherical clusters (Type I), toroidal clusters and one spherical cluster (Type II), and toroidal clusters alone (Type III), depending on the radius of the confining shell, that can often coexist with other related structures derived from these parent ones by a simple transformation, in which the system is divided into two hemispheres that are rotated with respect to each other by a given angle. We propose a general method to characterize and predict the structures obtained under confinement in spherical shells in systems able to self-assemble into a hexagonal phase in bulk. We also show that deforming the spherical shells into ellipsoidal ones affects the structure of the system in such a way that helical structures are favoured by prolate ellipsoids and toroidal structures by oblate ellipsoids.

Трансформации XXI века – человек, общество, ценности, ноономика: материальное VS идеальное, «физики» VS «лирики»

The article raises a conceptual problem that has both philosophical and socio-economic content: the nature of the interaction of material and spiritual principles in the context of the increasing role of knowledge and cultural values as factors of modern socio-economic development. The author shows that the process of searching for new knowledge has rapidly begun to play a predominant role in relation to the material foundations of production, since now it determines the very nature of these material foundations. But such a revolution in the relations of the material and the ideal in the production process itself rests on the transition to knowledge-intensive material production technologies and to the creation of a knowledge-intensive product. This change also leads to qualitative changes in property relations and in the nature of a human. Property relations are gradually eroding, which in the future may lead to their exhaustion, and a person, in order to ensure the development of society in the conditions of the modern technological revolution, must break through the narrow shell of an economic person, and become a truly reasonable person, a noohuman, who relies on the cultural imperatives of human development.

Flexible embryonic shell allies large offspring size and anti-predatory protection in viviparous snails

The evolutionary conflicts between viviparous reproductive mode and skeleton shape may occur whenever the space available for embryo development or delivery is limited by hard inflexible structures of a parent (bones, shell, etc.). In tetrapods, offspring size is at odds with female locomotion efficiency, which results in obstetric selection. We suggest a similar relationship for viviparous gastropods, where spacious canal needed for embryo delivery may interfere with anti-predatory role of narrow and toothed shell aperture. We explored this hypothesis in the group of viviparous land snails (Clausiliidae, subfamily Phaedusinae), known for complex apertural barriers protecting the shell interior. Most of the shell structure modifications we recorded facilitate the delivery of embryos but simultaneously reduce the safeguard of a narrow shell opening. However, we also observed highly flexible embryonic shells that may withstand squeezing between apertural barriers during birth. We investigated the microstructure of these flexible embryonic shells, compared to the typical hard shells of clausiliid embryos, which are rigid and unpliable already in the genital tract of the parent. Our results suggest that the unusual flexibility, which is related to a low number of organomineral layers in the shell, evolved in two phylogenetically distant lineages of Phaedusinae. This adaptation reduces mechanical constraints for birth of the neonates but allows to maintain the protective function of the apertural barriers.

An alloyed mid-shell strategy assisted realization of thick-shell violet-blue ZnSe/ZnSexS1-x/ZnS quantum dots with high color purity

Environmentally friendly zinc selenide (ZnSe) based core/shell quantum dots (QDs) are promising emitting materials for special light sources and displays. However, ZnSe-based core/shell QDs with violet-blue emission that simultaneously possess thick shells and narrow emission linewidths are still challenging thus far. We herein use a gradient ZnSexS1-x/ZnS shell strategy to target this goal. The ZnSexS1-x mid shell helps the lattice strain relaxation during the growth, whereas the wide bandgap ZnS outer shell benefits the optical properties by passivating the emitting cores and improving the quantum confinement effect. These ZnSe core QDs show a unity zinc blende structure and high crystallinity. The optimized ZnSe/ZnSexS1-x/ZnS QDs exhibit tunable emission wavelengths (415–445 nm), narrow photoluminescence linewidths (10.2–14.2 nm), thick shells (>3.9 nm), and high photoluminescence quantum yields (>50%). We postulate that these excellent features are due to the use of alloyed ZnSexS1-x layer at the core/shell interfaces. This study provides a feasible idea for the development of blue ZnSe-based QDs with perfect emitting properties.

Self-Assembly of Optimally Packed Cylindrical Clusters inside Spherical Shells.

Systems with short-range attraction and long-range repulsion can form ordered microphases in bulk and under confinement. Using grand canonical Monte Carlo simulations, we study a colloidal system with competing interactions under confinement in narrow spherical shells at thermodynamic conditions at which the hexagonal phase of cylindrical clusters is stable in bulk. We observe spontaneous formation of different ordered structures. The results of the simulations are in a very good agreement with the predictions of a simple mathematical model based on the geometry and optimal packing of colloidal clusters. The results of the simulations and the explanation provided by a relatively simple geometric model may be helpful in manufacturing copolymer nanocapsules and may indicate possible ways of coiling DNA strands on spherical objects.

Evidence for Carbonate System Mediated Shape Shift in an Intertidal Predatory Gastropod

Phenotypic plasticity represents an important first-line organism response to newly introduced or changing environmental constraints. Knowledge about structural responses to environmental stressors could thus be an essential measure to predict species and ecosystem responses to a world in change. In this study, we combined morphometric analyses with environmental modelling to identify direct shape responses of the predatory gastropod Nucella lapillus to large-scale variability in sea surface temperature and the carbonate system. Our models suggest that the state of the carbonate system and, more specifically, the substrate inhibitor ratio ([HCO3−][H+]−1) (SIR) has a dominant effect on the shell shape of this intertidal muricid. Populations in regions with a lower SIR tend to form narrower shells with a higher spire to body whorl ratio, whereas populations in areas with a higher SIR form wider shells with a much lower spire to body whorl ratio. These results indicate that a widespread phenotypic response of N. lapillus to continuing ocean acidification can be expected, potentially altering the phenotypic response pattern to predator or wave exposure regimes with profound implications for North Atlantic rocky shore communities.

A semi-analytical method for free vibration of semi-closed shells of revolution with variable curvature

This study is concerned with the free vibration analysis of semi-closed shells of revolution with variable curvature, with a focus on the analytical solution to the natural frequency of such shells. A semi-closed shell of revolution with variable curvature is firstly divided into some narrow small shell segments, then the first small shell segment with a closed shell apex is approximated with a semi-closed conical shell, while the remaining small shell segments are approximated with a series of progressively larger truncated conical shells. Since each small conical shell is part of the large semi-closed shell of revolution with variable curvature and has to vibrate in sync with the large shell, the analytical solution to the axisymmetric free vibration of the large shell can be transformed into the analytical solutions to the synchronous free vibration of these small conical shells. The general solutions for the natural frequencies of all small conical shells are analytically derived under the condition that conical shells have zero meridional curvature. The undetermined constants in the general solutions are determined by letting all natural frequencies of these small conical shells be equal. Finally, the analytical solution for the axisymmetric free vibration of semi-closed shells of revolution with variable curvature is presented and is proved to be basically reliable by conducting a confirmatory experiment based on polymer 3D-printing technique.

Patterns of shell utilization and preference in two sipunculan genera, Phascolion and Aspidosiphon

AbstractSipunculans are non-segmented marine worms with an anterior retractable introvert, which are commonly included in Annelida based on molecular phylogenetic and phylogenomic analyses. They generally burrow in the soft sediments or live inside the crevices of hard substrata (e.g. calcareous/coralline rocks). However, members of some sipunculan genera (mainly Phascolion and Aspidosiphon) are known to have a peculiar habit of dwelling in vacant shells of gastropods or scaphopods. In this study, we investigated the shell utilization and preference pattern of the species of Phascolion and Aspidosiphon in Japan. We collected 302 sipunculans, comprising 273 and 29 individuals in Phascolion and Aspidosiphon, respectively, from 57–800 m depth of three study sites in the Pacific coast of Honshu Island, Japan. The species of Phascolion were found in vacant shells of 38 genera of 27 families of gastropods and six genera of four families of scaphopods, whereas the species of Aspidosiphon were found in 11 genera of 11 families of gastropods and one genus of scaphopod. These results suggest that members of each genus use a wide range of gastropod and scaphopod shells. The body size of the sipunculans was positively correlated with the shell size, suggesting that they change the shells as they grow. Furthermore, we investigated the shell preference of Phascolion species by comparing morphological characteristics of shells occupied and unoccupied by sipunculans. Generalized linear mixed model (GLMM) analyses suggest that the species of Phascolion tend to use long and narrow shells. Such shells likely fit well the elongated trunk of sipunculans.

Vibro-acoustic analysis of double-walled cylindrical shells through a novel semi-analytic method

A novel semi-analytic model is developed for vibro-acoustic analysis of immersed double-walled cylindrical shells coupled by annular plates and annular fluid between two shells. For structural model, it is firstly divided to inner shell, outer shell and annular plates, and the inner and outer shells are further divided to narrow shell segments. By utilizing Flügge shell theory and power series method, all shell segments and annular plates are uniformly analyzed as conical shells, and they are rapidly assembled to the overall structural model via boundary conditions and continuity conditions between segments. For acoustic model, interior annular fluid region and exterior infinite fluid region are separately analyzed via the Helmholtz surface integral equation. Two surface integrals are simplified to two line integrals after expanding surface sound pressure and velocity as Fourier series, so the pressure is further expressed as displacements of all segments. Through adding the pressure to the continuity conditions, the structural model is coupled with acoustic model. High efficiency and accuracy are demonstrated via comparing vibro-acoustic results of present method with ones in the literature or calculated by coupled finite element-boundary element method. Furthermore, effects of annular plates, annular fluid and excitation on vibro-acoustics of double-walled shells are discussed.

The shell phenotypic variability of the keyhole limpet Fissurella latimarginata: insights from an experimental approach using a water flow flume

ABSTRACT Hydrodynamics are a major environmental factor on intertidal rocky shores. Morphological responses to this factor are expected to strongly influence spatial distribution of species across environmental gradients. We here analysed the shell phenotypic variability of the limpet Fissurella latimarginata using geometric morphometric analysis. The limpets were obtained from a sheltered intertidal coastal area and a wave-exposed environment. To determine whether the shell shape variation of the intertidal molluscs is linked to their resistance to differential intertidal wave exposure, mesocosm studies were developed in a hydraulic flume to explore the effects of hydrodynamic forces on this limpet species. A unidirectional current was used to test the impacts of step-by-step increased current flow velocities for each limpet. The phenotypic variability observed in the populations of F. latimarginata was associated with habitats characterized by contrasting wave exposure. Limpets from exposed environments showed a flattened, round to laterally wider and posteriorly narrower shell shape, larger foot and higher full limpet height, and were dislodged at higher velocities. A more laterally compressed and peaked shape was found in limpets from sheltered areas and these showed a lower resistance to wave action by dislodging at lower velocities.

Toward Precisely Controllable Acoustic Response of Shell-Stabilized Nanobubbles: High Yield and Narrow Dispersity.

Understanding the pressure dependence of the nonlinear behavior of ultrasonically excited phospholipid-stabilized nanobubbles (NBs) is important for optimizing ultrasound exposure parameters for implementations of contrast enhanced ultrasound, critical to molecular imaging. The viscoelastic properties of the shell can be controlled by the introduction of membrane additives, such as propylene glycol as a membrane softener or glycerol as a membrane stiffener. We report on the production of high-yield NBs with narrow dispersity and different shell properties. Through precise control over size and shell structure, we show how these shell components interact with the phospholipid membrane, change their structure, affect their viscoelastic properties, and consequently change their acoustic response. A two-photon microscopy technique through a polarity-sensitive fluorescent dye, C-laurdan, was utilized to gain insights on the effect of membrane additives to the membrane structure. We report how the shell stiffness of NBs affects the pressure threshold (Pt) for the sudden amplification in the scattered acoustic signal from NBs. For narrow size NBs with 200 nm mean size, we find Pt to be between 123 and 245 kPa for the NBs with the most flexible membrane as assessed using C-Laurdan, 465–588 kPa for the NBs with intermediate stiffness, and 588–710 kPa for the NBs with stiff membranes. Numerical simulations of the NB dynamics are in good agreement with the experimental observations, confirming the dependence of acoustic response to shell properties, thereby substantiating further the development in engineering the shell of ultrasound contrast agents. The viscoelastic-dependent threshold behavior can be utilized for significantly and selectively enhancing the diagnostic and therapeutic ultrasound applications of potent narrow size NBs.

Thermodynamic properties of SnO2/GaAs core/shell nanofiber

We provide a comprehensive computational investigation concerning the effects of confinement and temperature on the thermodynamic properties of cylindrical core/shell quantum dots with a large band offset. This model can also be applied to hollow cylindrical quantum dots or nanofibers. Within the framework of the effective mass approximation, we solve the Schrödinger equation analytically in two bands model, determining the energies of all excited states. Following Boltzmann–Gibbs distribution and introducing the canonical partition function, energy states are used to evaluate the thermodynamic properties: the mean energy, heat capacity, entropy, and Helmholtz free energy. Our numerical calculation shows that all thermodynamic properties depend on the temperature, the size of the dot, and the shell thickness. According to our numerical results, it is found that in the narrow shell case, the heat capacity shows a Schottky-like anomaly at low temperatures, but this effect disappears for small values of core radius. Another important conclusion, is that the determination of the Helmholtz free energy makes it possible to predict the thermodynamic stability of quantum dots. We also show that the competition between the temperature, the core dimension, and the shell thickness influences the thermodynamic stability. Despite the simplicity of our approach, our study can be considered as a useful information source and as an excellent qualitative indicator for understanding the thermodynamic properties of quantum dots.