Shells Of Different Thicknesses Research Articles

Practical calculations for uniform external pressure buckling in cylindrical shells with stepped walls

Metal cylindrical storage structures of significant size, such as silos and vertical-axis tanks, are almost always constructed from many short cylindrical shells of different thickness as the stress resultants on the wall progressively increase towards the base. The resulting increases in thickness are always made in step changes using metal sheets of uniform thickness because of the availability of such source materials. The result is a shell with a stepped wall with multiple discrete steps in thickness. Such shells are very susceptible to buckling under external pressure when empty or partially filled, but the buckling mode may involve only part of the shell height due to the changes in shell thickness. These changes must therefore be accounted for within the design process. A new method of determining the critical buckling resistance of such shells was recently developed, and although it has been shown to be valid, the methodology for its application in practical design has not been set out or shown. This paper therefore briefly describes the new method and demonstrates the manner in which it can be used to produce rapid, safe assessments of cylindrical shells with a wide range of patterns of wall thickness changes. The results are then suitable for direct introduction into such documents as the European standard on metal shells [1] and the ECCS Recommendations [2].

Ionothermal synthesis and lithium storage performance of core/shell structured amorphous@crystalline Ni–P nanoparticles

A new strategy for synthesizing Ni–P alloy nanoparticles with a core-shell structure is proposed, which involves a facile ionothermal process in a deep eutectic solvent (DES). The architecture of the core-shell structured Ni–P alloys is featured as amorphous spherical cores homogeneously wrapped by self-generated crystalline Ni3P shells of different thickness, which rely on the molar ratio of Ni2+/H2PO2− in the choline chloride (ChCl)/ethylene glycol (EG) based eutectic mixture. As an anode for lithium ion batteries, cyclic voltammetry curves, electrochemical impedance spectra, and cyclability of the novel structured Ni–P nanoparticles were evaluated. It was found that the sample with a thicker crystalline shell exhibited improved capability and reversibility over the sample with a thinner one, especially at a higher discharge–charge current density. It was suggested that the crystalline shell can enhance the conductivity of the amorphous cores, suppress the aggregation of active particles and increase the structural stability during cycling.

Single-Step Aerosol Synthesis and Deposition of Au Nanoparticles with Controlled Size and Separation Distributions

Immobilized noble metal nanoparticles are being explored for a variety of applications where control over the particle size and separation distance on the substrate is important for performance. A proof of concept is presented that Au nanoparticles can be deposited in a single step with control over the size and separation distributions using an aerosol process. Samples were deposited with mean particle diameters in the range from 15 to 43 nm, and mean separation distances from 11 to 39 nm. Depending on the separation distance, particles exhibited localized surface plasmon resonance dominated by either intra- or interparticle resonances, as determined by ultraviolet–visible extinction spectroscopy. Ultrathin TiO2 shells of different thicknesses, in the range from 0 to 24 nm, were deposited on the Au nanoparticles by atomic layer deposition to determine the sensing distance into the surrounding dielectric medium for these materials, which was estimated to be 10 nm.

A facile method for grafting of bisphenol A imprinted polymer shells onto poly(divinylbenzene) microspheres through precipitation polymerization

Core–shell structured polymers are usually prepared by “grafting to” or “grafting from” techniques, wherein polymer supports were first modified by vinyl bonds or initiators. Success can be immediate, but more often a learning curve needs to be traversed. In this paper, direct grafting bisphenol A imprinted polymer onto poly(divinylbenzene) microspheres through precipitation polymerization is introduced. The obtained microspheres were characterized by SEM, TEM, FTIR and BET. Firstly, mono-disperse poly(divinylbenzene) microspheres of 3 μm in size were prepared by precipitation polymerization. The solvent for grafting was then optimized and it was found that the mixtures of toluene and acetonitrile (30/70, v/v) were ideal choice from the image and structure analysis of the shells. Shells of different thickness (270–840 nm), depending on the concentrations of monomers in the precursor, were then directly grafted to the microspheres by a reactive, entropic capture mechanism. The recognition ability of the microspheres was evaluated by solid-phase extraction and clear selectivity showed toward bisphenol A. The leak of bisphenol A was not found after extraction and thus these core–shell structured imprinted polymers are believed to have potential applications in trace analysis area.

Study the effect of moulding sand properties for reducing shell wall thickness in zinc casting using three-dimensional printing

This paper aims to study the feasibility of reducing shell wall thickness of zinc (Zn) shell casting using three-dimensional printing. Experimentation started from the design of benchmark, printing of shells at different thicknesses, followed by supporting the shells with dry, green and molasses sands. Prototypes of Zn were produced at different shell thicknesses of moulds cavities. Cooling curves were drawn to explore the cooling rate/solidification rate of molten Zn metal in hybrid shells of different thicknesses. The dimensional accuracy of castings produced was measured with coordinate measuring machine and some mechanical properties of castings were also tested to observe the effects of sand properties over the prototypes produced, when casted with shells of different thicknesses from 12 to 1 mm. It has been observed that it is feasible to reduce shell wall thickness recommended from 12 to 1 mm. While comparing hardness of the specimens produced, it was observed that the hybrid casted component with green sand shows more hardness in comparison to components casted with dry and molasses sand. Results also indicate that hybrid casted prototype with green sand at 3 mm shell thickness shows better dimensional accuracy and mechanical properties.

Electrochemical preparation and magnetic properties of submicrometric core–shell CoPt–CoNi particles

Electrodeposition method has allowed the preparation of submicron CoPt particles covered with CoNi shells of different thicknesses. The magnetic properties of these particles have been analysed; a contribution of semi-hard magnetic behaviour and soft-magnetic behaviour, associated with the particles, and the CoNi shell, respectively, has been detected. Although a gradual decrease of the coercivity was observed by increasing the CoNi shell thickness, the CoPt core always dominates the magnetization–magnetic field curve shape.

On the optimization of the shell thickness of superficially porous particles

The thickness of the porous shells of superficially porous particles influences the separation power of columns packed with these packing materials. Models of the mass transfer kinetics across porous adsorbents permit the prediction of the HETP curves of columns packed with particles having shells of different thicknesses, for molecules of different sizes. Decreasing the thickness of the porous layer potentially results in lower values of the “C-term” of the HETP curve and of the minimum of these curves. The Poppe plots calculated under isocratic and gradient conditions show that the separation power of columns packed with superficially porous particles increases significantly with decreasing thickness of the porous layer but this increase is more important for larger than for smaller molecules. The resolution between pairs of compounds increases at constant values of their retention factors when the strength of the eluent must be reduced to compensate for the decrease of their retention that is caused by the reduction of the surface area of the stationary phase. Thus, the separation power of columns packed with superficially porous particles increases with decreasing shell thickness. In contrast, if analysts do not compensate for the retention decrease, the resolution between small molecular weight compounds becomes worse with thin than with thick superficially porous particles. Finally, the importance of using instruments providing low extra-column band broadening contributions is stressed.

Effect of Feed Liquid Temperature on the Structural Morphologies of d‐Limonene Microencapsulated Powder and Its Preservation

The influence of the feed liquid temperature of the spray drying was investigated on the particle morphology (vacuole size and shell thickness of hollow particle) and the stability of encapsulated d-limonene. The feed liquid was the mixture of d-limonene emulsified in a wall material of blending gum arabic (GA) and maltodextrin (MD) at the mass ratio of 1 : 2, and the liquid temperature was varied from 40 to 80 degrees C. The percentage of the hollow particle in the spray-dried powder was over 40% and slightly increased with the rising of the feed temperature. Hollow particles have shells of different thickness, which was estimated from the image with a confocal laser scanning microscope (CLSM). The shell thickness increased with the increase in the feed temperature. This finding was qualitatively supported by scanning electron microscopy (SEM) images of the fractured particles. In addition, release and oxidation stability of encapsulated d-limonene were measured at constant temperature and humidity. The powder at high temperature of feed has higher stability for release and oxidation of d-limonene than that at a lower feed temperature. The result may partly be attributed to the increase of the shell thickness of the particle at a higher feed temperature. The thicker shell wall possibly served as the barrier of the flavor release and the diffusion of oxygen and moisture from the surrounding environment.

Magnetic nanoparticles with functional silanes: evolution of well-defined shells from anhydride containing silane.

Modification of iron oxide nanoparticles (NPs) synthesized by high temperature solvothermal routes is carried out using two silanes: (i) N-(6-aminohexyl)-aminopropyltrimethoxysilane (AHAPS) where only one end of the molecule reacts with the surface Fe-OH groups and (ii) 3-(triethoxysilyl)propylsuccinic anhydride (SSA) where both ends are reactive with Fe-OH. Depending on the NP synthesis protocol, the amount of surface OH groups on the NPs may differ, however, for all the cases presented here, the comparatively low OH group density prevents a high density of AHAPS coverage, yielding NP aggregates instead of single particles in aqueous solutions. Alternatively, use of SSA containing two terminal functionalities, anhydride and siloxy, which are both reactive towards the NP surface, results in the formation of discrete dense polymeric shells, providing stability of individual NPs in water. The mechanism of the SSA shell formation is discussed. The evolution of the chemical transformations leads to shells of different thickness and density, yet this evolution can be halted by hydrolysis, after which the NPs are water soluble, negatively charged and exhibit excellent stability in aqueous media.

Non-linear free periodic vibrations of open cylindrical shallow shells

This paper is concerned with the non-linear free periodic vibrations of thin, open, cylindrical and shallow shells vibrating in the geometrically non-linear regime. A multi-degree-of-freedom model with hierarchical basis functions is adopted and the principle of the virtual work is used to define the time domain equations of motion. These equations are transformed into the frequency domain by the harmonic balance method and are finally solved by an arc-length continuation method. Shells of different thicknesses and of different curvature radius are analysed, and the variation of the non-linear natural frequencies of these shells with the vibration amplitude are investigated in some detail. The variation of the mode shapes with the vibration amplitude is demonstrated. It is found that both softening and hardening spring effects occur and that the number of couplings between vibration modes is rather large in undamped shells.

Hybrid Diamond‐Graphite Nanowires Produced by Microwave Plasma Chemical Vapor Deposition

The hybrid diamond-graphite nanowires with lengths up to a few hundred nanometers have been identified as structural units in UNCD films synthesized by chemical vapor deposition with nitrogen gas added. This hybrid material consist of a single crystalline diamond core of 5–6 nm in diameter oriented along the [110] principal axis and graphitic shells of different thickness covering the core.

Study on the kinetics of hydrate formation in a bubble column

Gas hydrate formation experiments were performed using methane in the presence of tetrahydrofuran (THF) in aqueous solution in a transparent bubble column in which a single pipe or a sintered plate was used to produce bubbles. The mole fraction of THF in aqueous solution was fixed at 6%. The hydrate formation kinetic behaviors on the surface of the rising bubble, the mechanical stability of hydrate shell formed on the surface of the bubble, the interactions among the bubbles with hydrate shell were observed and investigated morphologically. The rise velocities of individual bubbles with hydrate shells of different thickness and the consumption rates of methane gas were measured. A kinetic model was developed to correlate the experimentally measured gas consumption rate data. It was found that the hydrate formation rate on the surface of the moving bubble was high, but the formed hydrate shell was not very easy to be broken up. The bubbles with hydrate shells tended to agglomerate rather than merge into bigger bubble. This kind of characteristic of hydrate shell hindered the further formation of hydrate and led to the lower consumption rate of methane. The consumption rate of methane was found to increase with the decrease of temperature or increase of pressure. The increase of gas flux led to a linear increase in consumption rate of methane. It was demonstrated that the developed kinetic model could be used to correlate the consumption rate satisfyingly.

Ultrafast electron dynamics and enhanced optical nonlinearities of CdS-capped Au∕BaTiO3 composite film

The third-order nonlinear optical responses of gold nanoparticles capped by CdS shells of different thicknesses embedded in BaTiO3 films were investigated by off-resonance femtosecond optical Kerr effect technology at 800nm. The nonlinearities of the Au–CdS core-shell composite nanoparticles exhibit a significant enhancement, compared with their single components, and the χ(3) value apparently increases with the increase in the CdS shell thickness. The electric-field distribution in the composite nanoparticles was calculated using Neeve’s theory [A. E. Neeves and M. H. Birnboim, J. Opt. Soc. Am. B 6, 787 (1989)] to explain the nonlinear enhancement mechanism, which was mainly attributed to the enhancement of the localized electric field in the CdS shell. The electron relaxation dynamics in the Au–CdS nanoparticles with a core-shell structure were found to be the same as that in pure gold nanoparticle systems using the time-resolved pump-probe technique measured at 800nm.

Enhancement of Third-Order Optical Nonlinearities in 3-Dimensional Films of Dielectric Shell Capped Au Composite Nanoparticles

The composite nanoparticles of Au-core capped by CdS shells of different thickness were prepared and assembled into densely packed 3-dimensional films by the layer-by-layer self-assembly (LBL) technique. These films exhibited the 3-dimensional structure of densely packed Au@CdS composite nanoparticles and the shell thickness was tunable by changing the concentration of Cd2+-thiourea complexes. These multilayer films exhibited enhanced third-order optical nonlinear responses and ultrafast response times (several picoseconds). The third-order nonlinear optical susceptibility of the film with the CdS shell thickness of 4.4 nm was estimated to be 1.48 x 10(-9) esu and the value decreases with the increase of the CdS shell thickness. The enhancement of the optical nonlinearity was explained based on the calculation according to the electrostatic approximation by the solution of Laplace's equation under the boundary conditions appropriate to the model of core-shell nanoparticles, and mainly attributed to localized electric field effects in the CdS shell region. Additionally, the nonlinearity was optimized by determination of the values of the dielectric constant and thickness of the different shell.

Effect of Temperature, pH and Shell Thickness on the Rate of Mg2+ and Ox2- Release from Multilayered Polyelectrolyte Shells Deposited onto Microcrystals of Magnesium Oxalate

The influence of temperature and pH on the rate of dissolving the naked magnesium oxalate microcrystals and the microcrystals coated with multilayered polyelectrolyte shells of different thickness and molecular composition(PAH−PSS)n and (PAH−PSS)nPAH, where n = 0, 5, 10, and 15 was studied by a conductometry technique. Only shells with n > 10 were found to noticeably slow the release rate of magnesium and oxalate (Ox2-) ions out of polyelectrolyte microcapsules, and the effect increases with n. The estimated lower value for the diffusion coefficient of Mg2+ and Ox2- transport across the walls of polyelectrolyte shells is approximately equal to 10-9 cm2/s, which is about four orders lower than that for free diffusion of Mg2+ and Ox2- in water solutions, but two orders higher than the diffusion coefficient for transport of low molecular weight organic substances (MW ∼ 400) through the polyelectrolyte shells. No effect of pH in the range from 4.5 to 9.0 was revealed on the permeability of multilayered polyel...

Coherent Excitation of Acoustic Breathing Modes in Bimetallic Core−Shell Nanoparticles

The low-frequency acoustic breathing modes in Au−Pb core−shell nanoparticles have been studied by time-resolved spectroscopy. The frequency of the breathing mode was determined for a series of samples with a 47 nm diameter Au core and Pb shells of different thickness. The measured frequencies decrease with increasing Pb content, but not to the extent expected from a classical model for a homogeneous sphere. These results show that the acoustic breathing modes of metallic core−shell particles are significantly perturbed when the two metals have different elastic properties.

The effect of an axial electric field on the stability of cylindrical flows in the presence of mass and heat transfer and absence of gravity

The effect of an axial electric field on the Kelvin-Helmholtz instability of a cylindrical interface, which admits mass and heat transfer, between two fluids is studied. The fluids are in the form of coaxial cylindrical shells of different thicknesses. The gravitational effects are neglected. A dispersion relation that accounts for the growth of asymmetric waves is derived. It is found that the uniform axial electric field has a strong stabilizing influence on the cylindrical interface for all short and long wavelengths in all symmetric and asymmetric modes of perturbation. In contrast, the streaming shows a strong destabilizing influence. It is also found that the surface tension may be stabilized or destabilized according to certain conditions. The present analysis indicates that the instability criterion of the system is independent of the mass and heat transfer coefficient, but it is different from that in the same problem without mass and heat transfer: A comparison of the results, in the two cases, shows the destabilizing effect of the mass and heat transfer. In the absence of mass and heat transfer, it is demonstrated that there is a critical Weber number, below which the nonaxisymmetric disturbance becomes unstable. The Weber number, herein, is defined as the ratio of surface tension force to the inertial force. The critical Weber number depends on the wavelength of the disturbances, the density ratio between the two fluids and the Alfvén wave velocity.

Simplified Methods for Calculation of Redundant Moments and Forces at the Discontinuities in Pressure Vessels—Part II: Hemisphere—Shell and Shells of Different Thicknesses

Following a similar idea as described in Part I of this paper, the redundant bending moment and the redundant shearing force at the junctures of hemispherical/cylindrical shells and of cylindrical shells of different thicknesses are shown to be unique functions of λ (ratio of the thickness of the joint members) and η (ratio of the thickness of the cylindrical shell to its mean diameter). Thereby, simplification of the calculation for the redundant moment and the redundant force is proposed and demonstrated to possess a good accuracy.

Explosive-driven cylindrical imploding shocks

Cylindrical imploding shocks are analyzed numerically. The shocks are supposed to be generated by detonating cylindrical explosive shells. Detonations are assumed to be initiated either from the inner or the outer surface of the shells. Explosive shells of different thicknesses are compared. The conversion mechanism of the chemical energy of explosives into gas energy is investigated. In the implosion stage general features of the flow near the shock front are much the same between two different initiations. The same is also true among different explosive thicknesses. However, in the reflection stage after the shock is reflected from the axis, thicker explosives produce higher pressure and temperature near the axis. The difference in the initiation method does not make a very noticeable difference, even in the reflection stage. Shock trajectories, temperatures at the shock front, and evolutions of the pressure at a fixed point are compared between numerical and experimental results. Agreements between the two results are close.

Morphology of suspension polymerized polyacrylamide

In the course of studies on the characterization of commercial polyacrylamides used in tertiary oil recovery, samples of BASF Sepaflood suspension polymerized polyacrylamide with varying degrees of hydrolysis were observed using a Hitachi S-450 scanning electron microscope. Figs ! and 2 show an overall view of a nonhydrolysed (CE 5093) and highly hydrolysed (CE 5095) Sepaflood sample, respectively. Although in both cases the expected bead morphology of a suspension polymer is observed, the photographs reveal the presence of certain individual beads with differing morphologies. Hollow shells (Fig. 1) and nested spheres within the beads (Fig. 2) can be seen in the samples. After having observed many samples, the following conclusions were drawn: 1. The majority of the beads are either solid (Fig. 3) or hollow with shells of different thicknesses (Fig. 4). Figure 2 Overall view of sample CE 5095. Scale bar is 620/tm. (Arrows point to nested spheres in beads).