Shells Of Variable Thickness Research Articles

Suitability of PSMA-PET Biology-Guided Radiotherapy for Low Volume Metastases in Newly Diagnosed Prostate Cancer

Biology-guided radiation therapy (BgRT) guides radiation therapy in real time based on positron emissions detected during treatment delivery. Protein specific membrane antigen (PSMA) is a positron emission tomography (PET) tracer with superior sensitivity and specificity for prostate cancer detection compared with conventional imaging. This study aims to quantify the ratio of standard uptake value (SUV) to background SUV for patients with low volume prostate cancer metastases, in the context of determining suitability of these lesions for BgRT. A single institutional patient subset from the ProPSMA prospective clinical trial underwent Ga-68-PSMA-11 at the time of prostate cancer diagnosis with suspected localized disease. From this cohort of 84 patients, 15 had at least one metastatic site disease diagnosed, 1 to 11 lesions per patient, with a total of 43 metastatic lesions (12 bones/31 viscerals). Metastatic gross tumor volume (GTV) were delineated on PSMA-PET images by using a patient-specific fixed SUV threshold method. In order to determine the suitability of various BgRT tracking zones, 3D shells of thickness 5 mm, 10 mm and 20 mm were constructed around the GTV to represent adjacent non-tumor background. Normalized SUV (nSUV) was calculated as the ratio of SUVmax in the GTV to SUVmean of adjacent shell. Sensitivity of nSUV to shell thickness variation was reported as the difference between nSUV values obtained for each thickness. GTV SUVmax ranged from 2.9 to 48.0 (median, 12.0; IQR, 5.1 to 19.5). nSUV ranged from 2.4 to 42.6 for 5 mm shell, 2.7 to 47.5 for 10 mm shell and 2.6 to 36.4 for 20 mm shell. Bone metastases had increased SUVmax compared with visceral metastases (SUVmax min/median/max 2.9/15.0/48.0 for bone compared with 2.9/11.0/40.0 for visceral). Furthermore, 90% of lesions had nSUV greater than 2.9 for a shell thickness of 5 mm, 3.1 for a shell thickness of 10 mm, and 3.2 for a shell thickness of 20 mm. Moreover, 100%/93%/84% of lesions would be suitable for BgRT by using nSUV cut-off of 2/3/4 and a shell thickness of 10 mm. nSUV decreased with increasing shell thickness for 17 lesions, indicating high signal in adjacent non-tumor tissue due to the proximity of bladder (5), bowel (4), other lesion (4), vessel (3) and liver (1). This study demonstrates that it is feasible to identify metabolically defined radiotherapy targets in the setting of BgRT. High lesion to background signal was observed for metastases visible on Ga-PSMA-EPT-11, however a subset of metastases had adjacent non-tumor uptake which may require exclusion from emission tracking during BgRT. Trial ID ACTRN12617000005358.

Surface-tension-induced double emulsion drops via phase separation of polymeric fluid confined in micromolds for capsule templates

We report a simple and rapid route to produce double emulsion drops by utilizing phase separation of the confined fluid in micromolds and surface-tension-induced drop formation. Specifically, we use cross-shaped micromolds containing prepolymer solution that phase-separates into two compartments upon addition of wetting fluid with separation agent (SA). Subsequently, Laplace pressure-driven flow allows it to form double emulsion drops without use of any surfactants and complex formulations of fluids. The size of each compartment in the emulsion drops can be controlled by tuning composition of the prepolymer solution and separation agent, making the double emulsion drops with varying shell thicknesses. The phase separation creates two compartments with different polarity (i.e. water-soluble and water-insoluble), enabling encapsulation of both hydrophilic and/-or hydrophobic cargoes in desired compartments depending on their solubility. In addition, we produce poly(N-isopropylacrylamide) (pNIPAm) hydrogel microcapsules by solidifying middle phase in the double emulsion drops; thus, hydrophilic large cargo loaded priorly in the core can be encapsulated within hydrogel shells. Finally, by taking advantage of hydrophilic-hydrophobic phase transition behavior of pNIPAm, we achieve encapsulation of small cargo via post-loading approach; the encapsulated cargo can be released by tuning temperature.

СВОБОДНЫЕ И ВЫНУЖДЕННЫЕ КОЛЕБАНИЯ ОБОЛОЧЕК РАЗЛИЧНОЙ ФОРМЫ С УЧЕТОМ ПЕРЕМЕННОСТИ ТОЛЩИНЫ ИЗ НЕЛИНЕЙНО-УПРУГОГО МАТЕРИАЛА

the article considers issues of shell vibrations, which are widely used in various industries and construction. Shells serve as elements of building structures with large spans.
 The chapter “Introduction” discussed issues related to the use of shells in all areas of industry, in aviation, rocket and space technology, railway transport, in the oil and gas industry and provides examples of shells for use in ceilings of circuses, stations, hangars; in industry: shells of rotation used as tanks, containers, columns, reactors, etc. In the section “Materials and research methods” free and forced vibrations of shells of variable thickness made out of nonlinear elastic material reviewed. In shell calculations the Kirchhoff – Law hypothesis was used. It was found that, during vibrations, the shells experience relative deformation of elongation and shear of the surface with coordinates (x, y), as well as bending and torsion strains. It is established that vibrations in the shells lead to a rotation of the main directions of elasticity and regarding to the adopted coordinate axis to angle θ, and the elastic constants of the material depend on the elastic constant Biy – the main directions of the nonlinear elastic shells.
 When solving the system of equations of motion of the shell relative to the displacements arising in it during vibration, based on theory R and various methods. The values of the dimensionless frequency parameter for a spherical shell taking into account changes in its curvature, variability and thickness of elastic properties are obtained.

Dynamics of viscoelastic orthotropic shallow shells of variable thickness

Thin-walled structural elements such as plates, panels, and shells of variable thickness are widely used at present in engineering, machine-building, and construction. Modern technologies allow creating any structural elements of a given shape, material, and the law of thickness variation. Therefore, the solution to the problems of the statics and dynamics of plates, panels, and shells of variable thickness, considering the real properties of the material, is relevant. Nonlinear parametric oscillations of viscoelastic orthotropic shallow shells of variable thickness are considered in the paper. Using the Kirchhoff-Love hypothesis, a mathematical model of the problem is constructed in a geometrically nonlinear statement. To describe the viscoelastic properties of a shallow shell, the hereditary Boltzmann-Volterra theory with the Koltunov-Rzhanitsyn relaxation kernel is used. To obtain resolving equations of the problem, the Bubnov-Galerkin method was used in combination with the numerical method. The effects of various physico-mechanical and geometrical parameters of a shallow shell of variable thickness were investigated.

Effect of geometric imperfections on anchor loss and characterisation of a gyroscope resonator with high quality factor

A critical functional part of a hemispherical resonator gyroscope (HRG) is the mechanical resonator, and a few million quality factor (Q-factor) is needed for the lowest resolution. This paper focuses on anchor loss of a HRG of a few millimeters in size. A detailed parametric study of dimensions and shell imperfections due to fabrication is carried out. A sensitivity study of the effect of shell mean radius, shell thickness, stem radius, stem height on the Qanchor is carried out. The effect of geometric imperfections such as shell offset, shell tilt, shell thickness variation, and unbalance is studied in detail. From the study, it is inferred that the anchor loss becomes very significant and approaches other loss mechanisms even with minor geometric imperfections in the hardware realisation. Based on the sensitivity study, the dimensional and geometric tolerances are arrived for precision fabrication. Precision resonator is fabricated as per the requirement of minimum anchor loss. The significance of other damping mechanisms such as air damping, excitation-induced damping, thermoelastic dynamic damping and surface dissipation is also discussed. Surface characterisation before and after surface treatment has been carried out using nanoindentation technique with regard to surface loss. Functional parameters of operating frequency and Q-factor are evaluated using laser Doppler vibrometry (LDV).

Numerical method for analyzing the near-field enhancement of nonspherical dielectric-core metallic-shell particles accounting for the nonlocal dispersion.

Over the last few decades, dielectric core and metallic plasmonic shell (Die@Me) nanoparticles have found a wide variety of applications. The trend to reduce the thickness of the metallic coating requires to account for the influence of the nonlocal dispersion on the spectral response of such nanoparticles. In this paper, we use the discrete sources method and the generalized nonlocal optical response model to describe the nonlocality within the plasmonic metal shell. We found that the variation of the plasmonic shell thickness and the elongation of the nonspherical core-shell particle can enlarge the near-field enhancement and the absorption cross section by an order of magnitude. Besides, we show that the nonlocal dispersion can decrease the field enhancement in the wavelength domain up to 2.5 times with a small blue-shift of about 5 nm.

Parametric vibrations of viscoelastic orthotropic cylindrical panels of variable thickness

In modern engineering and construction, thin-walled plates and shells of variable thickness, subjected to various static and dynamic loads, are widely used as structural elements. Advances in the technology of manufacturing thin-walled structural elements of any shape made it possible to produce structures with predetermined patterns of thickness variation. Calculations of strength, vibration and stability of such structures play an important role in design of modern apparatuses, machines and structures. The paper considers nonlinear vibrations of viscoelastic orthotropic cylindrical panels of variable thickness under periodic loads. The equation of motion for cylindrical panels is based on the Kirchhoff-Love hypothesis in a geometrically nonlinear statement. Using the Bubnov-Galerkin method, based on a polynomial approximation of deflections, the problem is reduced to the study of a system of ordinary integro-differential partial differential equations, where time is an independent variable. The solution to the resulting system is found by a numerical method based on the feature elimination in the Koltunov-Rzhanitsyn kernel used in the calculations. The behavior of a cylindrical panel with a wide range of changes in physico-mechanical and geometrical parameters is investigated.

Enhancement of spectral shift of plasmon resonances in bimetallic noble metal nanoparticles in core–shell structure

Core-shell metal nanoparticles (NPs) exhibit unique optical, especially plasmonic, properties in the visible range of electromagnetic spectrum. Here we report the plasmonic properties of bimetallic core-shell spherical NPs consisting of noble metals in pair (such as Au-Ag, Ag-Cu, and Au-Cu, and their interchanging combinations) embedded in silica employing Mie theory. The core radius and shell thickness were considered in the range of 2–20 nm and 1–5 nm, respectively. In the case of varied core radius, shell thickness was kept fixed, and in the case of varied shell thickness, the core radius was kept fixed. The optical extinction spectra exhibited by these NPs have two surface plasmon resonance (SPR) absorption bands in the visible region of the electromagnetic spectrum, one corresponding to the core metal and the other corresponding to shell metal, respectively. The appearance of two absorption peaks is due to the fact that in the core-shell configuration there exists two SPR modes one at the interface between the core and shell, and other at the outer surface of the shell and embedding medium. These two SPR modes interact together and determine the shape of the extinction spectra. The position of the SPR band is found to shift as the radius or the thickness of the shell is increased. The shift of the SPR peak with high range of tunability has been observed in all the cases. Such tunability is beneficial to applications in surface-enhanced Raman scattering, fluorescence, optical sensing, bio-medicine, optoelectronic devices, and others.

Forced vibrations of beveled non-circular conical thin-walled structures of variable thickness

The stress distribution in shells of variable thickness must be taken into account when designing various elements of general and transport engineering, aviation, rocket and space technology, structures. The paper presents one of the possible approaches to the dynamic calculation of a thin-walled non-circular conical structure rigidly fixed along a beveled end section. The resolving system of ordinary differential equations was obtained in the framework of the technical theory of shells using the variational Lagrange principle. The boundary-value problem of determining dynamic stresses in the structure under consideration under the influence of a harmonic load is solved numerically by the method of orthogonal sweeping of a system of linear ordinary differential equations of the first order. In contrast to the known works, a variable thickness of the structure along the length is considered.

Magnetoelastic Deformation of Isotropic Variable-Stiffness Shells of Revolution: Allowing for Joule Heat and Geometrical Nonlinearity

The theory and derivation of the nonlinear thermomagnetoelastic equations of flexible variable-stiffness shells of revolution with allowance for Joule heat in a nonstationary magnetic field are considered. A technique for design of flexible variable-thickness shells of revolution in a magnetic field is proposed. The thermomagnetoelasticity of a truncated flexible conical axisymmetric shell with Joule heating taken into account is analyzed.

Free Vibration Analysis of Composite Conical Shells with Variable Thickness

Free vibration of conical shells of variable thickness is analysed under shear deformation theory with simply supported and clamped free boundary conditions by applying collocation with spline approximation. Sinusoidal thickness variation of layers is assumed in axial direction. Displacements and rotational functions are approximated by Bickley-type splines of order three and a generalized eigenvalue problem is obtained. This problem is solved numerically for an eigenfrequency parameter and an associated eigenvector of spline coefficients. The vibration of composite conical shells consisting of three layers and five layers where each layer is made up of different materials is analysed. Parametric studies are made for analysing the frequencies of the shell with respect to the coefficients of thickness variations, length ratio, cone angle, circumferential node number, and different ply angles with different combinations of the materials. The results are presented in terms of tables and graphs.

Effect of Geometric Imperfections on Anchor Loss and Characterisation of a Gyroscope Resonator with High Quality Factor

A critical functional part of a hemispherical resonator gyroscope (HRG) is the mechanical resonator, and a few million quality factor (Q-factor) is needed for the lowest resolution. This paper focuses on anchor loss of a HRG of a few millimeters in size. A detailed parametric study of dimensions and shell imperfections due to fabrication is carried out. A sensitivity study of the effect of shell mean radius, shell thickness, stem radius, stem height on the Qanchor is carried out. The effect of geometric imperfections such as shell offset, shell tilt, shell thickness variation, and unbalance is studied in detail. From the study, it is inferred that the anchor loss becomes very significant and approaches other loss mechanisms even with minor geometric imperfections in the hardware realisation. Based on the sensitivity study, the dimensional and geometric tolerances are arrived for precision fabrication. Precision resonator is fabricated as per the requirement of minimum anchor loss. The significance of other damping mechanisms such as air damping, excitationinduced damping, thermoelastic dynamic damping and surface dissipation is also discussed. Surface characterisation before and after surface treatment has been carried out using nanoindentation technique with regard to surface loss. Functional parameters of operating frequency and Q-factor are evaluated using laser Doppler vibrometry (LDV).

Natural vibrations of truncated conical shells of variable thickness

The paper presents the results of studying the natural frequencies of circular truncated conical shells, the thickness of which varies along the length according to different laws. The behavior of elastic structure is described in the framework of the classical theory of shells based on the Kirchhoff-Love hypotheses. The corresponding geometric and physical relations together with the equations of motion are reduced to a system of ordinary differential equations for new unknowns. The solution to the formulated boundary value problem is found using Godunov's orthogonal sweep method involving the numerical integration of differential equations by the fourth order Runge-Kutta method. The natural frequencies of vibrations are evaluated using a combination of a step-wise procedure and subsequent refinement by the interval bisection method. The reliability of the obtained results is verified by making a comparison with the known numerical-analytical solutions. The dependences of the minimum vibration frequencies obtained at shell thicknesses subject to a power-law variation (linear and quadratic, having symmetric and asymmetric shapes) and harmonic variation (with positive and negative curvature) are investigated for shells with different combinations of boundary conditions (free support, rigid and cantilever fastening), cone angles and linear dimensions. The results of the study confirm the existence of configurations, which provide a significant increase in the frequency spectrum in comparison with shells of constant thickness under the same limitations on the weight of the structure.

НАПРЯЖЕННО-ДЕФОРМИРОВАННОЕ СОСТОЯНИЕ КОНИЧЕСКОЙ ОБОЛОЧКИ ПЕРЕМЕННОЙ ТОЛЩИНЫ НА ОСНОВЕ ТРЕХМЕРНЫХ УРАВНЕНИЙ ТЕОРИИ УПРУГОСТИ

The results of a study of the stress-strain state of a conical shell of variable thickness based on a non-classical theory are presented. The sought-for displacements of the shell are approximated by polynomials in the normal coordinate to the median surface two degrees higher in relation to the classical theory of the Kirchhoff-Love type. When developing the theory, the three-dimensional equations of the theory of elasticity, as well as Lagrange variational principle are used as the equation of the shell state. As the result of minimizing the specified value of the total energy of the shell, a mathematical model is constructed, which is a system of differential equations of equilibrium in the displacements with variable coefficients and the corresponding boundary conditions. Two cases are considered: the shell is under the action of symmetric and asymmetric loads. Two-dimensional equations are transformed to the system of ordinary differential equations by means of trigonometric sequences as per circumferential coordinate. To solve the formulated boundary value problem, finite difference and matrix sweep methods are applied. The calculations have been made by means of a computer program. After having determined the displacements, shell deformations and tangential stresses are found from geometric and physical equations, transverse stresses - from the equilibrium equations of the three-dimensional theory of elasticity. As an example, a conical shell rigidly restrained at the two edges, with asymmetrically varying thickness is considered. Compared are the results of the VAT calculations obtained as per the improved and classical theories. The significant contribution of additional stresses in the boundary zone to the total stress state of the shell is shown. The received results can be used in the strength and durability calculations and tests of machine-building facilities of various purposes.

Manipulating Charge Transfer from Core to Shell in CdSe/CdS/Au Heterojunction Quantum Dots.

The photophysics of charge-transfer and recombination mechanisms in a heterojunction structure of CdSe/CdS/Au quantum dots (QDs) are studied by temperature-dependent steady-state photoluminescence (PL) and time-resolved PL (TRPL). We manipulate the charge transfer from core to shell surface by varying the tunneling barrier height resulting from temperature variation and the barrier width resulting from shell thickness variation. The charge-transfer process, which can be described by a tunneling transmission model, is manifested by two competitive recombination processes, an intrinsic exciton emission and a trap emission in the near-infrared (NIR) range. Our study establishes the photophysics foundation for the core/shell/metal application in photocatalyst and optoelectronics.

Determining the Thickness and Completeness of the Shell of Polymer Core–Shell Nanoparticles by X-ray Photoelectron Spectroscopy, Secondary Ion Mass Spectrometry, and Transmission Scanning Electron Microscopy

Core–shell nanoparticles (CSNPs) have become indispensable in various industrial applications. However, their real internal structure usually deviates from an ideal core–shell structure. To control how the particles perform with regard to their specific applications, characterization techniques are required that can distinguish an ideal from a nonideal morphology. In this work, we investigated poly(tetrafluoroethylene)–poly(methyl methacrylate) (PTFE–PMMA) and poly(tetrafluoroethylene)–polystyrene (PTFE–PS) polymer CSNPs with a constant core diameter (45 nm) but varying shell thicknesses (4–50 nm). As confirmed by transmission scanning electron microscopy (T-SEM), the shell completely covers the core for the PTFE–PMMA nanoparticles, while the encapsulation of the core by the shell material is incomplete for the PTFE–PS nanoparticles. X-ray photoelectron spectroscopy (XPS) was applied to determine the shell thickness of the nanoparticles. The software SESSA v2.0 was used to analyze the intensities of the e...

Controlled Growth Factor Release in 3D-Printed Hydrogels.

Growth factors (GFs) are critical components in governing cell fate during tissue regeneration. Their controlled delivery is challenging due to rapid turnover rates in vivo. Functionalized hydrogels, such as heparin-based hydrogels, have demonstrated great potential in regulating GF release. While the retention effects of various concentrations and molecular weights of heparin have been investigated, the role of geometry is unknown. In this work, 3D printing is used to fabricate GF-embedded heparin-based hydrogels with arbitrarily complex geometry (i.e., teabag, flower shapes). Simplified cylindrical core-shell structures with varied shell thickness are printed, and the rates of GF release are measured over the course of 28 days. Increasing the shell layers' thickness decreases the rate of GF release. Additionally, a mathematical model is developed, which is found capable of accurately predicting GF release kinetics in hydrogels with shell layers greater than 0.5 mm thick (R2 > 0.96). Finally, the sequential release is demonstrated by printing two GFs in alternating radial layers. By switching the spatial order, the delivery sequence of the GFs can be modulated. This study demonstrates how 3D printing can be utilized to fabricate user-defined structures with unique geometry in order to control the rate of GF release in hydrogels.

Highly Tunable Growth and Etching of Silica Shells on Surfactant‐Free Gold Nanostars

AbstractHerein, we report an efficient method to coat gold nanostars with a silica shell of variable thickness and then tunably etch it by using a mild silica etching reagent, NaBH4. This method generates a novel type of nanostar coating in which silica only covers the core, leaving the tips variably exposed.

Variation of shell thickness in ZnO-SnO2 core-shell nanowires for optimizing sensing behaviors to CO, C6H6, and C7H8 gases

ZnO-SnO2 core-shell nanowires (C-S NWs) with different shell thicknesses (0–120 nm) were prepared and their sensing behavior was systematically studied. ZnO-SnO2 C-S NWs were prepared using a two-step synthesis procedure, where core ZnO NWs were synthesized by a vapor-liquid-solid growth technique, and subsequently these cores were coated with SnO2 shell layers by using an advanced atomic layer deposition technique. The sensors were exposed to 10-ppm CO, C6H6, and C7H8 gases at an optimal working temperature. The shell thickness was optimized to be 40 nm, for which the sensor revealed the highest sensitivity and fastest dynamics to the above-mentioned gases. The sensing mechanism was discussed in detail and the dominant mechanism was related to the radial modulation effect as well as the volume fraction of the shell to the total volume of C-S NWs.

Hollow Covalent Triazine Frameworks with Variable Shell Thickness and Morphology

AbstractCovalent triazine frameworks (CTFs) are a class of semiconductive porous materials, showing enormous potential in many applications, such as gas adsorption and storage, and heterogeneous catalysis. At present, most of the studies on CTFs are focused on the structural design, synthesis, and applications, whereas very little attention is paid to morphological study, probably due to the difficulty in the control of the morphology via the conventional synthetic methods. In this work, a general approach is reported to fabricate morphological controllable CTFs by virtue of a mild polycondensation reaction via template method. As a proof of concept, a new type of hollow‐structured CTFs is developed for the first time. The shell thickness of the hollow CTFs can be conveniently tuned by varying the amount of the template. Notably, the morphologies can be transformed from sphere to bowl with the decrease of the shell thicknesses. The hollow morphology of CTFs can efficiently improve the photocatalytic hydrogen evolution performance, in which the hydrogen evolution rate can be boosted by about 4 times as compared to the bulk state. The present study not only shows an effective strategy to construct morphology controllable CTFs, but also demonstrates an effective way to enhance photocatalytic performance for CTFs.