Portion Of Shell Research Articles

Constraining the Thickness of the Conductive Portion of Europa's Ice Shell Using Sparse Radar Echoes

AbstractIce penetrating radar sounding is the primary geophysical technique for imaging the subsurface of planetary ice shells and has the potential to directly detect the ice–ocean interface. However, many sounding measurements may lack laterally extensive features that would aid their physical interpretation. In this scenario, the detection of sparse echoes can also provide rich information on ice shell properties. To explore and demonstrate this possibility, we consider three cases of isolated radar signatures: pore‐curing, eutectic melt, and unattributed echoes. We show that through detection of unattributed sparse echoes, the thickness of the conductive portion of Europa's ice shell can be constrained. These constraints can be improved by attributing sparse echoes to thermally diagnostic signatures such as pore‐curing and eutectic melt. Notably, this approach to radar sounding echo analysis is particularly compatible with joint inversions with other planetary geophysical observations such as tidal deformation, magnetic induction, and rotation state.

Polymer–lipid hybrid nanoparticles as potential lipophilic anticancer drug carriers

Nanocarrier systems are widely used for drug delivery applications, but limitations such as the use of synthetic surfactants, leakage of toxic drugs, and a poor encapsulation capacity remain as challenges. We present a new hybrid nanocarrier system that utilizes natural materials to overcome these limitations and improve the safety and efficacy of drug delivery. The system comprises a biopolymeric shell and a lipid core, encapsulating the lipophilic anticancer drug paclitaxel. Bovine serum albumin and dextran, in various molecular weights, are covalently conjugated via Maillard reaction to form the shell which serves as a stabilizer to maintain nanoparticle integrity. The properties of the system, such as Maillard conjugate concentration, protein/polysaccharide molar ratio, and polysaccharide molecular weight, are optimized to enhance nanoparticle size and stability. The system shows high stability at different pH conditions, high drug loading capacity, and effective in vitro drug release through the trigger of enzymes and passive diffusion. Serine proteases are used to digest the protein portion of the nanoparticle shell to enhance the drug release. This nanocarrier system represents a significant advancement in the field of nanomedicine, offering a safe and effective alternative for the delivery of lipophilic drugs.Graphical abstract

Expression of Neural Crest Specifiers During the Two Waves of Trunk NCC Migration in Turtle Embryos

The bones of the plastron, the ventral portion of the turtle shell, develop through intramembranous ossification, in the same manner as facial bones, suggesting they are also produced by neural crest cells (NCCs). Previous work has demonstrated the existence of a unique second migration of NCCs away from the neural tube of turtle (Trachemys scripta) embryos; these migrate ventrally, appear to be skeletogenic and may contribute to the bones of the plastron. The goal of this project is to examine the expression of neural crest specifiers in the premigratory NCCs located in the neural tube and in migrating NCCs using immunofluorescence and whole mount in situ hybridization. During the switch‐over period, the neural crest specifiers Sox9 and Sox10 are both expressed in premigratory NCCs. However, their expression diverges in migrating NCCs; the cells that retain Sox10 are located within the major migratory stream in the rostral somite leading to the production of the dorsal root ganglion and other peripheral nerves, consistent with a neurogenic cell fate. By contrast, cells that retain Sox9 appear to take a novel migratory pathway through the caudal portion of the somite, and are excluded from the dorsal root ganglia, consistent with a non‐neurogenic and perhaps skeletogenic cell fate. We are currently examining the expression of transcription factors that have been found to be preferentially expressed in either trunk NCCs or cranial NCCs in the well‐characterized chicken (G. gallus) system. Elucidating the molecular control of NCC specification in the unique population of trunk NCCs would further our understanding of its role in the development of the turtle shell.

The Hantavirus Surface Glycoprotein Lattice and Its Fusion Control Mechanism

Hantaviruses are rodent-borne viruses causing serious zoonotic outbreaks worldwide for which no treatment is available. Hantavirus particles are pleomorphic and display a characteristic square surface lattice. The envelope glycoproteins Gn and Gc form heterodimers that further assemble into tetrameric spikes, the lattice building blocks. The glycoproteins, which are the sole targets of neutralizing antibodies, drive virus entry via receptor-mediated endocytosis and endosomal membrane fusion. Here we describe the high-resolution X-ray structures of the heterodimer of Gc and the Gn head and of the homotetrameric Gn base. Docking them into an 11.4-Å-resolution cryoelectron tomography map of the hantavirus surface accounted for the complete extramembrane portion of the viral glycoprotein shell and allowed a detailed description of the surface organization of these pleomorphic virions. Our results, which further revealed a built-in mechanism controlling Gcmembrane insertion for fusion, pave the way for immunogen design to protect against pathogenic hantaviruses.

High-Resolution Description of the Hantavirus Surface Glycoprotein Lattice and Its Membrane Fusion Control Mechanism

Hantaviruses are rodent-borne viruses causing serious zoonotic outbreaks worldwide for which no treatment is available. The hantavirus particles are pleomorphic and display a characteristic square surface lattice. The envelope glycoproteins Gn and Gc form heterodimeric protomers associated into tetrameric spikes, the lattice building blocks. The glycoproteins, which are the sole targets of neutralizing antibodies, drive virus entry via receptor-mediated endocytosis and endosomal membrane fusion. Here we describe the high-resolution X-ray structures of the Gn head / Gc heterodimer, and of the homotetrameric Gn base. Docking them into an 11.4 A resolution cryo- electron tomography map of the hantavirus surface accounted for the complete extracellular portion of the viral glycoprotein shell and provided unprecedented detail of the surface organization of a pleomorphic virus. These results, which further revealed an in-built mechanism controlling Gc membrane-insertion for fusion, pave the way for immunogen design to protect against pathogenic hantaviruses

In Situ Failure Investigation of Weld Cracking in a Linz–Donawitz Vessel

Linz–Donawitz (LD) vessel is an integral part of the blast furnace–basic oxygen furnace route of steelmaking. Failures of the LD vessel can result in safety issues as well as production loss. In the event of any such failure, the thrust should be to carry out the investigation at the minimum lead time and suggest for corrective actions to prevent any recurrence in the future. For this purpose, an on-site or in situ nondestructive method of investigation can be extremely useful. Present work is a case study of analysis of cracking of the shell of a vessel. Visual observation revealed that a large crack of around 6.5 m length developed at the bottom of the top cone connected to the vertical portion of the vessel shell by means of welding. Crack had propagated along the weld. The investigation consisted of chemical analysis using portable x-ray florescence spectroscopy, hardness testing across the weld and replica technique for microstructural analysis. These were aided by detailed analysis of refractory wall thickness measurements and thermography data for over a year. The study revealed that the failure occurred in thermo-mechanical fatigue mode from the weld joint due to use of inferior welding electrode. In contrast to the micro-alloyed base metal, no precipitation strengthening was present at the weld zone that resulted in the onset of softening mechanism therein. Recommendations are provided to prevent similar failures in the future.

The time-dependent generalized membrane shell model and its numerical computation

In this paper, we discuss the time-dependent generalized membrane shell model, which has not been addressed numerically in literature. We show that the solution of this model exists and is unique. We first provide a numerical method for the time-dependent generalized membrane shell. Concretely, we semi-discretize the space variable and fully discretize the problem using time discretization by the Newmark scheme. The corresponding numerical analyses of existence, uniqueness, stability and convergence with a priori error estimates are given. Finally, we present numerical experiments with a portion of the conical shell and a portion of the hyperbolic shell to verify theoretical convergence results and demonstrate the effectiveness of the numerical scheme.

Commentary: The Feasibility of Subduction and Implications for Plate Tectonics on Jupiter's Moon Europa

AbstractA new modeling‐based study by Johnson et al. (2017, https://doi.org/10.1002/2017JE005370) lends support to the hypothesis that portions of Europa's surface may have been removed by the process of subduction, as suggested by Kattenhorn and Prockter (2014, https://doi.org/10.1038/NGEO2245). Using a simple 1‐D model that tracks the thermal and density structure of a descending ice plate, Johnson et al. show that ice plates with 10% porosity and overall salt contents of ~5%, which differ in salt content by ~2.5% from the surrounding reference ice shell, are nonbuoyant and thus likely to sink through the underlying, convecting portion of the ice shell. The feasibility of subduction in an ice shell is critical to the existence of icy plate tectonics, which is hypothesized to exist at least locally on Europa, potentially making it the only other Solar System body other than Earth with a surface modified by plate tectonics.

Porosity and Salt Content Determine if Subduction Can Occur in Europa's Ice Shell

AbstractMotivated by recent evidence for subduction in Europa's ice shell, we explore the geophysical feasibility of this process. Here we construct a simple model to track the evolution of porosity and temperature within a slab that is forced to subduct. We also vary the initial salt content in Europa's ice shell and determine the buoyancy of our simulated subducting slab. We find that porosity and salt content play a dominant role in determining whether the slab is nonbuoyant and subduction in Europa's ice shell is actually possible. Generally, we find that initially low porosities and high salt contents within the conductive lid are more conducive to subduction. If salt contents are laterally homogenous, and Europa has a reasonable surface porosity of ϕ0 = 0.1, the conductive portion of Europa's shell must have salt contents exceeding ~22% for subduction to occur. However, if salt contents are laterally heterogeneous, with salt contents varying by a few percent, subduction may occur for a surface porosity of ϕ0 = 0.1 and overall salt contents of ~5%. Thus, we argue that under plausible conditions, subduction in Europa's ice shell is possible. Moreover, assuming that subduction is actively occurring or has occurred in Europa's recent past provides important constraints on the structure and composition of the ice shell.

The time-dependent Koiter model and its numerical computation

• Existence and uniqueness of the time-dependent Koiter model. • Newmark scheme for the time-dependent Koiter model. • Analyses of existence, uniqueness, stability, convergence and priori error estimate for elastodynamic problems. The theory of elastic shells is one of the most important branches of the theory of elasticity. Among all the shell models, a classical and widely recognized model is the Koiter model. In this paper, we discuss the time-dependent Koiter model, which has not been addressed numerically. We show that the solution of this model exists and is unique. We semi-discretize the space variable and fully discretize the problem using the time discretization by the Newmark scheme. The corresponding analyses of existence, uniqueness, stability, convergence and a priori error estimate are given. Finally, we provide numerical experiments with a portion of spherical shell and a portion of cylindrical shell to demonstrate the efficiency of the model.

The effect of inflating pressure on the finite pure bending of hyperelastic tubes

The problem of nonlinear bending of a curved tube made of incompressible rubber-like material is considered. The tube shaped like a portion of a thin-walled toroidal shell between two radial planes is inflated by pressure and then subjected to in-plane bending moments. To investigate nonlinear response and stability of the tube under these loading conditions, a finite-element approach is proposed. A special shell finite element is formulated under the assumption of uniform deformation along the tube length. The effect of wrinkling on nonlinear response of the tube is described using the tension-field theory. A change in the inflating pressure resulting from deformation of the tube due to bending is taken into account in the formulation of the governing equations. The effect of pressure on the bending stiffness, stability, and deformations of a curved tube is examined and discussed.

Effects of a single bilateral infusion of R-ketamine in the rat brain regions of a learned helplessness model of depression

Effects of a single bilateral infusion of R-enantiomer of ketamine in rat brain regions of learned helplessness model of depression were examined. A single bilateral infusion of R-ketamine into infralimbic (IL) portion of medial prefrontal cortex (mPFC), CA3 and dentate gyrus (DG) of the hippocampus showed antidepressant effects. By contrast, a single bilateral infusion of R-ketamine into prelimbic (PL) portion of mPFC, shell and core of nucleus accumbens, basolateral amygdala and central nucleus of the amygdala had no effect. This study suggests that IL of mPFC, CA3 and DG of hippocampus might be involved in the antidepressant actions of R-ketamine.

A Study in Three-Dimensional Chaotic Dynamics: Granular Flow and Transport in a Bi-Axial Spherical Tumbler

We study 3D chaotic dynamics through an analysis of transport in a granular flow in a half-full spherical tumbler rotated sequentially about two orthogonal axes (a bi-axial "blinking" tumbler). The flow is essentially quasi-2D in any vertical slice of the sphere during rotation about a single axis, and we provide an explicit exact solution to the model in this case. Hence, the cross-sectional flow can be represented by a twist map, allowing us to express the 3D flow as a linked twist map (LTM). We prove that if the rates of rotation about each axis are equal, then (in the absence of stochasticity) particle trajectories are restricted to 2D surfaces consisting of a portion of a hemispherical shell closed by a "cap"; if the rotation rates are unequal, then particles can leave the surface they start on and traverse a volume of the tumbler. The period-one structures of the governing LTM are examined in detail: analytical expressions are provided for the location of period-one curves, their extent into the bulk of the granular material, and their dependence on the protocol parameters (rates and durations of rotations). Exploiting the restriction of trajectories to 2D surfaces in the case of equal rotation rates about the axes, a method is proposed for identifying and constructing 3D Kolmogorov-Arnold-Moser (KAM) tubes around the normally elliptic period-one curves. The invariant manifold structure arising from the normally hyperbolic period-one curves is also examined. When the motion is restricted to 2D surfaces, the structure of manifolds of the hyperbolic points in the bulk differs from that corresponding to hyperbolic points in the flowing layer. Each is reminiscent of a template provided by a non-integrable perturbation to a Hamiltonian system, though the governing LTM is not. This highlights the novel 3D chaotic behaviors observed in this model dynamical system.

A new approximate model of nonlinearly elastic flexural shell and its numerical computation

In this article, we construct a two‐dimensional model for the nonlinearly elastic flexural shell using differential geometry and tensor analysis under the assumption that flexural energy is dominant, that is, the metric of middle surface remains invariant. We conduct a numerical experiment for special shell—a portion of cylinder shell, which is applied to the forces along the opposite direction of the normal vector. The displacements distribution of all points in the middle surface when the shell deforms is obtained. Numerical experiment results are consistent with the theory, which proves the validity of the proposed model. We then compare the proposed model and Ciarlet's model with 3D model, which proves that the proposed model is more approximate to 3D model than Ciarlet's. © 2013 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 30: 1727–1739, 2014

굴패각 배합 석고재료의 열전도 특성 연구

We investigated one-dimensional thermal conduction for gypsum objects incorporating oyster shell powder. We presumed that according to the portion of oyster shell in the hybrid structure conductive characteristics of that would also change as some physicochemical properties such as volatile organic compound (VOC) adsorption were found to be changed cons- iderably. Based on Fourier's 2nd law of heat conduction an analytical analysis in a flat slab (one axis perpendicular to an infinite plane) was performed. We found that composition of oyster shell and conduction-related coefficients and parameters could greatly influence on the thermal profile of that conduction, and some model experiments also served for it in the affirmative.

Photoinduced perturbations of the magnetic superexchange in core@shell Prussian blue analogues

Cubic heterostructured core@shell particles of Prussian blue analogues, composed of a shell (∼80nm thick) of ferromagnetic K0.3Ni[Cr(CN)6]0.8·1.3H2O (A), Tc∼70K, surrounding a bulk (∼350 nm) core of photoactive ferrimagnetic Rb0.4Co[Fe(CN)6]0.8·1.2H2O (B), Tc∼20K, have been studied. Below nominally 70K, these CoFe@NiCr samples exhibit a persistent photoinduced decrease in low-field magnetization, and these results resemble data from other BA core@shell particles and analogous ABA heterostructured films. This net decrease suggests that the photoinduced lattice expansion in the B layer generates a strain-induced decrease in the magnetization of the NiCr layer, similar to a pressure-induced decrease observed by others in a similar, pure NiCr material and by us in our CoFe@NiCr cubes. Upon further examination, the data also reveal a significant portion of the NiCr shell whose magnetic superexchange, J, is perturbed by the photoinduced strain from the CoFe constituent.

X-RAY PROPER MOTIONS AND SHOCK SPEEDS ALONG THE NORTHWEST RIM OF SN 1006

We report the results of an X-ray proper motion measurement for the NW rim of SN1006, carried out by comparing Chandra observations from 2001 and 2012. The NW limb has predominantly thermal X-ray emission, and it is the only location in SN1006 with significant optical emission: a thin, Balmer-dominated filament. For most of the NW rim, the proper motion is about 0.30 arcsec/yr, essentially the same as has been measured from the H-alpha filament. Isolated regions of the NW limb are dominated by nonthermal emission, and here the proper motion is much higher, 0.49 arcsec/yr, close to the value measured in X-rays along the much brighter NE limb, where the X-rays are overwhelmingly nonthermal. At the 2.2 kpc distance to SN1006, the proper motions imply shock velocities of about 3000 km/s and 5000 km/s in the thermal and nonthermal regions, respectively. A lower velocity behind the H-alpha filament is consistent with the picture that SN1006 is encountering denser gas in the NW, as is also suggested by its overall morphology. In the thermally-dominated portion of the X-ray shell, we also see an offset in the radial profiles at different energies; the 0.5-0.6 keV peak dominated by O VII is closer to the shock front than that of the 0.8-3 keV emission--due to the longer times for heavier elements to reach ionization states where they produce strong X-ray emission.

Computational Multiscattering of Spherical Multilayered Gold Nanoshells

A generalized computational methodology is developed and applied to study multiscattering phenomena associated with an aggregate of multilayered nanoshells under excitation of a plane wave. The development is based on a combination of the vector addition theorem for spherical wave functions and the efficient recursive procedure for multilayered nanoshells. Calculated results are compared well with spectral measurements for a Au@SiO2 nanodimer. They are also in qualitative agreement with laboratory observations. Resonance behavior of a Au@SiO2 nanoshell chain depends on the number of particles in the chain, the orientation of the chain, and the interparticle spacing. Strong localized field enhancement is observed in the gap between two adjacent particles, and intense Joule heating occurs in the portion of the metal shell where the field enhancement is weak. The coupled plasmonic resonance of a multilayered nanodimer is analyzed, and its application as a plasmon ruler is discussed.

Tracking of transplanted mesenchymal stem cells labeled with fluorescent magnetic nanoparticle in liver cirrhosis rat model with 3-T MRI

In vivo visualization of transplanted stem cells with noninvasive technique is essential for the monitoring of cell implantation, homing and differentiation. At present, superparamagnetic iron oxide (SPIO) is most commonly used for cell labeling. However, stem cells lack phagocytic capacity and transfection agent is required for sufficient internalization of SPIO for cellular imaging. However, the potential hazards of transfection agents are not fully investigated. Instead of SPIO, we used commercially available new tagging material, fluorescent magnetic nanoparticle (MNP) containing rhodamine B isothiocyanate within a silica shell (Biterials, Seoul, Korea). This tagging material does not require transfection agents for the cell labeling. In addition to that, the core of this MNP is composed of ferrite and the inner portion of silica shell contains fluorescent materials, therefore, it has both magnetic and optical features. This study was designed to track intrasplenically injected bone marrow mesenchymal stem cells (MSCs) labeled with fluorescent MNP in liver cirrhosis rat model with 3-T magnetic resonance equipment. We compared magnetic resonance imaging (MRI) of livers in rats which were injected with non-labeled stem cells or labeled stem cells with MNP or SPIO. We found that the respective liver-to-muscle contrast-to-noise ratios at 3 and 5 h after MNP or SPIO-labeled stem cell injection was significantly lower than that of pre-injection and non-labeled group. There was no significant difference between MNP-labeled group and SPIO-labeled group. We can effectively detect intrasplenically injected MNP-labeled MSCs in an experimental rat model of liver cirrhosis with 3-T MRI.

In vivo voltammetric monitoring of catecholamine release in subterritories of the nucleus accumbens shell

Fast-scan cyclic voltammetry (FSCV) at carbon-fiber microelectrodes has been used to demonstrate that sub-second changes in catecholamine concentration occur within the nucleus accumbens (NAc) shell during motivated behaviors, and these fluctuations have been attributed to rapid dopamine signaling. However, FSCV cannot distinguish between dopamine and norepinephrine, and caudal regions of the NAc shell receive noradrenergic projections. Therefore, in the present study, we examined the degree to which norepinephrine contributes to catecholamine release within rostral and caudal portion of NAc shell. Analysis of tissue content revealed that dopamine was the major catecholamine detectable in the rostral NAc shell, whereas both dopamine and norepinephrine were found in the caudal subregion. To examine releasable catecholamines, electrical stimulation was used to evoke release in anesthetized rats with either stimulation of the medial forebrain bundle, a pathway containing both dopaminergic and noradrenergic projections to the NAc, or the ventral tegmental area/substantia nigra, the origin of dopaminergic projections. The catecholamines were distinguished by their responses to different pharmacological agents. The dopamine autoreceptor blocker, raclopride, as well as the monoamine and dopamine transporter blockers, cocaine and GBR 12909, increased evoked catecholamine overflow in both the rostral and caudal NAc shell. The norepinephrine autoreceptor blocker, yohimbine, and the norepinephrine transporter blocker, desipramine, increased catecholamine overflow in the caudal NAc shell without significant alteration of evoked responses in the rostral NAc shell. Thus, the neurochemical and pharmacological results show that norepinephrine signaling is restricted to caudal portions of the NAc shell. Following raclopride and cocaine or raclopride and GBR 12909, robust catecholamine transients were observed within the rostral shell but these were far less apparent in the caudal NAc shell, and they did not occur following yohimbine and desipramine. Taken together, the data demonstrate that catecholamine signals in the rostral NAc shell detected by FSCV are due to change in dopamine transmission.