Charged Shell Research Articles

Thin shells surrounding black holes in F(R) gravity

In this article, we consider spherical thin shells of matter surrounding black holes in F(R) theories of gravity. We study the stability of the static configurations under perturbations that conserve the symmetry. In particular, we analyze the case of charged shells outside the horizon of non-charged black holes. We obtain that stable static thin shells are possible if the values of the parameters of the model are properly selected.

Poly(methyl methacrylate)‐functionalized reduced graphene oxide‐based core–shell structured beads for thermally conductive epoxy composites

ABSTRACTThermally conductive epoxy nanocomposite with core–shell structured filler beads has been prepared. The core represents plasma‐treated poly(methyl methacrylate) bead, and the shell, amine‐functionalized reduced graphene oxide (frGO) sheets. The negatively charged core and the positively charged shell form core–shell unified structure through electrostatic attraction and the conductive bridges are formed among neighboring filler particles in the composite mass. The epoxy composite prepared with these core–shell structured filler shows a thermal conductivity of 0.72 W m−1 K−1 for an overall frGO concentration of as low as 0.96 wt %. Pal model has been applied to evaluate the effective thermal conductivity of frGO sheets that have been realized in the epoxy composition. Assuming the maximum possible volume packing fraction of the spherical beads for random jamming to be equal to 0.63, the effective thermal conductivity has been estimated as 280 W m−1 K−1. Evaluation of the effective thermal conductivity is a step forward to in‐depth study of real contribution of the highly conductive fillers in the polymer composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47377.

Mechanism and Factors Influencing Formation and Stability of Chitosan/Lignosulfonate Nanoparticles

AbstractA set of new nanoparticles are synthesized in this work at room temperature by combining two oppositely charged non‐toxic biopolymer polyelectrolytes in the form of chitosan and lignosulfonate. The effects of intensity of mixing, solid content, and reactant ratio on nanoparticle size and composition are investigated using turbidity measurements, dynamic light scattering data, zeta potential values, surface tension data, and electron microscopy. The data support nanoparticle structures with a dense hydrophobic core surrounded by a positively charged hydrophilic shell. The chitosan and lignosulfonate domains are held in these nanoparticles primarily by the electrostatic force while hydrogen bonding plays a minor role. The particle size increases with an increase of the total solid content, while the ratio of the two reactants determines the number of particles.

Sedimentation Velocity and Potential in Dilute Suspensions of Charged Porous Shells

The sedimentation of a charged spherical porous shell with arbitrary inner and outer radii, which can model a permeable microcapsule or vesicle, in a general electrolyte solution is analytically examined. The relaxation effect in the electric double layers of arbitrary thickness around the porous shell is considered. The differential equations governing the electric potential profile, ionic electrochemical potential energy (or concentration) distributions, and fluid velocity field are linearized by taking the system to be only slightly distorted from equilibrium. These linearized equations are solved using a perturbation method with the density of the fixed charge of the porous shell as the small perturbation parameter. Closed-form formulas for the sedimentation velocity of a porous shell and sedimentation potential in a suspension of porous shells are obtained from a force balance and a zero current requirement, respectively. Both the charge-induced sedimentation velocity retardation and sedimentation potential are monotonic increasing functions of the relative shell thickness, and these increases are substantial if the shell is thin. The sedimentation velocity and potential are complex functions of the electrokinetic radius and normalized flow penetration length of the porous shell. In the limit of the porous shells with zero inner radius, our formulas for the sedimentation velocity and potential reduce to the results obtained for the intact porous spheres.

Ring symmetry in electric potential calculation extended to discs and cylinders

The electric potential—but not the electric field—of any charge distribution on a ring at a point on its axis is equivalent to that of an equal point charge placed anywhere on the ring; this is the well-known ring symmetry. We point out similar symmetries for finding the potential at points on the axis of a charged disc: disc symmetry, and the potential at points along the axes of a charged cylindrical shell and a solid cylinder; and cylinder symmetry. As such, a uniformly charged disc, or parts of it, map onto a line of equal charge parallel to its radius that gives the same potential at the same points on its axis. In the same manner, a uniformly charged thin cylindrical shell, or parts of it, maps onto a line of equal charge parallel to its axis that gives the same potential as the shell for points on its axis. Similarly, a cylinder, or parts of it, with a uniform volume charge density is seen to map onto a sheet carrying the same charge with the potential above one edge of the sheet equal to that at the corresponding points on the axis of the cylinder. The disc (cylinder) symmetry leads also to the fact the potential at points on the axis of a disc (cylinder) with charge distributions that vary with the azimuthal angle is the same as the potential of a uniformly charged disc (cylinder) at these points. These observations and their generalizations can supplement the methods for calculating the electric potential used in introductory electricity and magnetism classes as further useful symmetries that can be applied, whenever relevant, to find the electric potential.

Coulomb potential and energy of a uniformly charged cylindrical shell

Knowledge of electrical potential and energy is important to systems where electrostatic forces play a role. We calculate exactly the electrostatic potential of a uniformly charged cylindrical shell at an arbitrary point in space as well as its electrical energy. The expressions derived are applicable to cylindrical models containing charged particles and certain biological systems with cylindrical symmetry. An explicit analytical formula is provided for the total energy in terms of a class of special functions known as generalized Hypergeometric functions. The expressions when written in one-dimensional integral form are very suitable for numerical calculations.

Multilayer Hydrogel Capsules of Interpenetrated Network for Encapsulation of Small Molecules.

We report on a facile capsule-based platform for efficient encapsulation of a broad spectrum of hydrophilic compounds with molecular weight less than 1000 g mol-1. The encapsulated compounds extend from low-molecular-weight anionic Alexa Fluor 532 dye and cationic anticancer drug doxorubicin (DOX) to fluorescein isothiocyanate-dextrans with Mw ranging from 4000 to 40 000 g mol-1. The pH-sensitive hydrogel capsules with an interpenetrated network shell are synthesized by layer-by-layer assembly of poly(methacrylic acid) (PMAA, Mw = 150 000 g mol-1) and poly( N-vinylpyrrolidone) (PVPON, Mw = 1 300 000 g mol-1) on 5 μm silica microparticles followed by chemical cross-linking of the PMAA multilayers. Following core dissolution, the result is a hollow microcapsule with PVPON interpenetrated in the PMAA network. The capsules exhibit a reversible change in the diameter with a swelling ratio of 1.5 upon pH variation from 7.5 to 5.5. Capsules cross-linked for 4 h display high permeability toward molecules with molecular weight under 1000 g mol-1 at pH = 7.5 but exclude dextran molecules with Mw ≥ 40 000 g mol-1. Encapsulation of small molecules was achieved at pH = 7.5 followed by sealing the capsule wall with 40 000 g mol-1 dextran at pH = 5.5. This approach results in negatively charged molecules such as Alexa Fluor being entrapped within the capsule cavity, whereas positively charged molecules such as DOX are encapsulated within the negatively charged capsule shell. Considering the simple postloading approach, the ability to entrap both anionic and cationic small molecules, and the pH-responsiveness of the interpenetrated network in the physiologically relevant range, these capsules offer a versatile method for controlled delivery of multiple hydrophilic compounds.

Xanthan gum-functionalised span nanoparticles for gene targeting to endothelial cells.

Endothelial cells play a critical role in many physiological processes; therefore, there is increasing evidence that the future of many treatments for pathologies depends on the development of endothelium-targeting systems. Thus, we have incorporated the natural polysaccharide xanthan gum (XG) into sorbitan monooleate nanoparticles to provide them with a hydrophilic and negatively charged surface shell with stabilising properties and an inherent ability to target endothelial cells. Enhanced Green Fluorescent Protein plasmid (pEGFP) was incorporated into the nanosystem, and the protection ability and stability of this system was confirmed. Nanoparticle cytotoxicity and transfection capacity were successfully tested in Human Umbilical Vein Endothelial Cells (HUVECs) before confirming their biocompatibility in vivo. Finally, biodistribution studies after pEGFP-XG nanoparticle systemic administration to mice evidenced GFP expression in the vascular endothelium of lung, liver and kidney, thus confirming the potential of xanthan gum-functionalised span nanoparticles for gene targeting to endothelial cells.

Bridging Systemic Immunity with Gastrointestinal Immune Responses via Oil-in-Polymer Capsules.

As peripheral lymphocytes are typically excluded from the gastrointestinal lymph tissues, current parenteral vaccinations fail to simultaneously induce systemic and mucosal responses. To break the natural barrier, "immunoticket" capsules are developed and heralded, which are designed with positive charged shells and oily core to spatiotemporally deliver antigens and all-trans retinoic acid (RA). After intramuscular vaccinations, these capsules function as an immunoticket to cultivate peripheral dendritic cells (DCs) with gut-homing receptors (CCR9). By hitchhiking on the concentration gradient of the CC-motif chemokine ligand 25 (CCL25), the primed DCs would home to the gut associated lymphoid tissues (GALTs) and induce antigen-specific IgA secretion and T cell engagements. Compared with the currently employed RA-involving formulations, the immunoticket capsules stimulate enhanced RA-mediated gut-tropism by mounting the inflammatory innate immunity. Through controlling the RA payload, the potential regulatory T cell engagement is circumvented. In ovalbumin (OVA) and EV71 vaccinations, the immunoticket capsules induce potent serum IgG titer and antigen-specific cytotoxic T cells in the peripheral lymph tissues, as well as robust IgA secretion and T cell engagements on gastrointestinal sites. The data suggest the potential of the immunotickets to serve as a facile, effective, and safe strategy to provide comprehensive immune responses against gastrointestinal infections and diseases.

A multifunctional nanoparticle constructed with a detachable albumin outer shell and a redox-sensitive inner core for efficient siRNA delivery to hepatocellular carcinoma cells

Successful delivery of small interfering RNA (siRNA) into the cytoplasm of target cells relies on biocompatible and efficient vectors. In this study, a novel multifunctional core/shell nanoparticle [CS-SS-9R/BSA-c(RGDyK)] was developed to effectively deliver siVEGF to hepatocellular carcinoma cells (Bel-7402 cells). To improve the gene payload and transfection efficiency, a positively charged inner core (CS-SS-9R) was constructed by grafting nona-arginine (9R) onto chitosan (CS) using disulphide bonds. The negatively charged outer shell [BSA-c(RGDyK)] assembled on the surface of the inner core by electrostatic forces that shielded high cationic charges and provided improved targeting. The protein outer shell gradually detached from the inner core in the acidic lysosomal environment, leaving the cationic inner core exposed in order to escape from lysosomes. The nanoparticles were capable of delivering siVEGF into Bel-7402 cells via integrin receptor-mediated endocytosis. Successful lysosomal escape of the inner core and the rapid release of siVEGF into the cytoplasm resulted in a 78.9% decrease in VEGF expression and 81.2% inhibition of tumour cell proliferation. In conclusion, this nanoparticle is responsive to the intracellular environment and accurately delivered siRNA into the cytoplasm, providing a safe and highly efficient gene delivery strategy for cancer therapy.

Self consistent field theory of virus assembly

The ground state dominance approximation (GSDA) has been extensively used to study the assembly of viral shells. In this work we employ the self-consistent field theory (SCFT) to investigate the adsorption of RNA onto positively charged spherical viral shells and examine the conditions when GSDA does not apply and SCFT has to be used to obtain a reliable solution. We find that there are two regimes in which GSDA does work. First, when the genomic RNA length is long enough compared to the capsid radius, and second, when the interaction between the genome and capsid is so strong that the genome is basically localized next to the wall. We find that for the case in which RNA is more or less distributed uniformly in the shell, regardless of the length of RNA, GSDA is not a good approximation. We observe that as the polymer–shell interaction becomes stronger, the energy gap between the ground state and first excited state increases and thus GSDA becomes a better approximation. We also present our results corresponding to the genome persistence length obtained through the tangent–tangent correlation length and show that it is zero in case of GSDA but is equal to the inverse of the energy gap when using SCFT.

Extremal tunneling and Anti-de Sitter instantons

We rederive and extend the amplitude for charged spherical shells tunneling through the outer horizon of charged black holes. In particular, we explicitly confirm that an effective action approach with natural initial conditions for a spherical shell, including backreaction, reduces to the tunneling integral. Consequently, we establish a universal expression for the probability of emission in terms of the change in the horizon entropy. Notably, the result for the charged black hole also captures the superradiant regime of charged particle decay at low energies. We then explore an appropriately regulated extremal and near-horizon limit, relating the tunneling amplitude to a family of gravitational instantons in the near-horizon Anti-de Sitter geometry, reducing to the known result for AdS2 domain walls to leading order in the probe limit. We comment on the relation to the Weak Gravity Conjecture and the conjectured instability of (non-supersymmetric) Anti-de Sitter vacua.

The Amount of Impurity Elements in Diamond-Containing Soot and Detonation Nanodiamonds upon Nitric Acid Treatment

The influence of the explosive charge shell composition and the explosive charge modification by various compounds on the yield of DND and DS, content of impurities and their elemental composition has been studied. With proper choice compounds, one can increase the DS yield to 18.6 wt % and the DND yield to 7.6 wt %, reduce the amount of impurities down to 0.23 wt % in DS and to 0.3 wt % in DND. The phosphorus concentration was brought to 0.665 wt % in DS and to 0.244 wt % in DND; the boron content was brought to 0.96 wt % in DS and to 0.472 wt % in DND.

Formation and evaporation of an electrically charged black hole in conformal gravity

Extending previous work on the formation and the evaporation of black holes in conformal gravity, in the present paper we study the gravitational collapse of a spherically symmetric and electrically charged thin shell of radiation. The process creates a singularity-free black hole. Assuming that in the evaporation process the charge Q is constant, the final product of the evaporation is an extremal remnant with M=Q, which is reached in an infinite amount of time. We also discuss the issue of singularity and thermodynamics of black holes in Weyl’s conformal gravity.

Entropy-Driven Reversible Agglomeration of Crown Ether Capped Gold Nanoparticles.

It is shown that plasmonic gold nanoparticles functionalised with a thiolated 18-crown-6 ligand shell agglomerate spontaneously from aqueous dispersion at elevated temperatures. This process takes place over a narrow temperature range, is accompanied by a colour change from red to purple-blue and is fully reversible. Moreover, the temperature at which it occurs can be adjusted by the degree of complexation of the crown ether moiety with appropriate cations. More complexation leads to higher transition temperatures. The process has been studied by UV/Vis spectroscopy, electron microscopy, dynamic light scattering and zeta potential measurements. A thermodynamic rationale is provided to suggest an entropy-driven endothermic agglomeration process based on attractive hydrophobic interactions of the complexed crowns that are competing against electrostatic repulsion of the charged ligand shells.

Diffusiophoresis of a charged porous shell in electrolyte gradients

The diffusiophoresis of a charged spherical porous shell or permeable microcapsule with arbitrary inner and outer radii, fluid permeability, and electric double layer thickness in an ionic solution is analyzed. With the assumption that the imposed electrolyte concentration gradient is relatively weak and the transport system is only perturbed slightly from equilibrium, the electrostatic potential, ionic concentration (electrochemical potential energy), and fluid velocity fields are determined as power-series expansions of the small fixed charge density of the porous shell by solving the relevant linearized electrokinetic equations. An explicit expression for the diffusiophoretic velocity of the porous shell correct to the second order of the fixed charge density results from balancing the exerted electrostatic and hydrodynamic forces. Both the electrophoretic (first-order) and chemiphoretic (second-order) mobilities increase with an increase in the normalized thickness of the porous shell, and these increases are significant when the porous shell is thin. However, the diffusiophoretic velocity of the porous shell, which is the sum of the electrophoretic and chemiphoretic velocities, may not be a monotonic function of its normalized thickness. The variation in the normalized fixed charge density of the porous shell from negative to positive values can lead to more than one reversals in the direction of the diffusiophoretic velocity.

Evaluation of the Active Targeting of Melanin Granules after Intravenous Injection of Dendronized Nanoparticles.

The biodistribution of dendronized iron oxides, NPs10@D1_DOTAGA and melanin-targeting NPs10@D1_ICF_DOTAGA, was studied in vivo using magnetic resonance imaging (MRI) and planar scintigraphy through [177Lu]Lu-radiolabeling. MRI experiments showed high contrast power of both dendronized nanoparticles (DPs) and hepatobiliary and urinary excretions. Little tumor uptake could be highlighted after intravenous injection probably as a consequence of the negatively charged DOTAGA-derivatized shell, which reduces the diffusion across the cells' membrane. Planar scintigraphy images demonstrated a moderate specific tumor uptake of melanoma-targeted [177Lu]Lu-NPs10@D1_ICF_DOTAGA at 2 h post-intravenous injection (pi), and the highest tumor uptake of the control probe [177Lu]Lu-NPs10@D1_DOTAGA at 30 min pi, probably due to the enhanced permeability and retention effect. In addition, ex vivo confocal microscopy studies showed a high specific targeting of human melanoma samples impregnated with NPs10@D1_ICF_Alexa647_ DOTAGA.

The electric field of a uniformly charged cubic shell

As an integrative and insightful example for undergraduates learning about electrostatics, we discuss how to use symmetry, Coulomb's law, superposition, Gauss's law, and visualization to understand the electric field E(x,y,z) produced by a uniformly charged cubic shell. We first discuss how to deduce qualitatively, using freshman-level physics, the perhaps surprising fact that the interior electric field is nonzero and has a complex structure, pointing inwards from the middle of each face of the shell and pointing outwards towards each edge and corner. We then discuss how to understand the quantitative features of the electric field by plotting an analytical expression for E along symmetry lines and on symmetry surfaces of the shell.

Amphiphilic xylan–cholic acid conjugates: synthesis and self-assembly behaviors in aqueous solution

A novel amphiphilic biopolymer was synthesized by incorporating hydrophobic segment cholic acid (CA) into hydrophilic segment carboxymethyl xylan (CX) through coupling agent. Structural characteristics and self-assembly behaviors of the amphiphilic conjugates in aqueous solution were investigated in detail. Results showed that the conjugates provided monodispersed self-assembled micelles in distilled water, with average diameters in the range of 90–135 nm, depending on the DS of CA. TEM and AFM images proved that the self-assembly micelles were spherical. The micelles were covered with negatively charged carboxymethyl xylan shells, exhibiting zeta potential about − 38 mV. The aggregation concentration of the conjugate (0.0079–1.25 × 10−2 g/L) was closely related to the DS of CA and solution pH. Moreover, CX–CA nanoparticles were sensitive to the pH of release media. The cellular uptake of DOX-loaded CX–CA nanoparticles was better than that of free DOX, and thus CX–CA nanoparticles can be used as a new carrier for antitumor drug delivery.

Time-Resolved Fluorescence Spectroscopy Reveals Fine Structure and Dynamics of Poly(l-lysine) and Polyethylenimine Based DNA Polyplexes.

Structural dynamics of the polyethylenimine-DNA and poly(l-lysine)-DNA complexes (polyplexes) was studied by steady-state and time-resolved fluorescence spectroscopy using the fluorescence resonance energy transfer (FRET) technique. During the formation of the DNA polyplexes, the negative phosphate groups (P) of DNA are bound by the positive amine groups (N) of the polymer. At N/P ratio 2, nearly all of the DNA's P groups are bound by the polymer N groups: these complexes form the core of the polyplexes. The excess polymer, added to this system to increase the N/P ratio to the values giving efficient gene delivery, forms a positively charged shell around the core polyplex. We investigated whether the exchange between the core and shell regions of PEI and PLL polyplexes takes place. Our results demonstrated a clear difference between the two studied polymers. Shell PEI can replace PEIs previously attached to DNA in the polyplex core, while PLL cannot. Such a dynamic structure of PEI polyplexes compared to a more static one found for PLL polyplexes partially explains the observed difference in the DNA transfection efficiency of these polyplexes. Moreover, the time-resolved fluorescence spectroscopy revealed additional details on the structure of PLL polyplexes: in between the core and shell, there is an intermediate layer where both core and shell PLLs or their parts overlap.