Search

Energy recovery ventilation plays a crucial role in providing fresh air and managing respiratory diseases, such as COVID-19. This study focuses on the computational fluid dynamics (CFD) analysis of a compact heat exchanger within a heat recovery ventilator and discusses the findings. However, conducting such an analysis is challenging due to the complex nature of the desired modules, which include intricate fin geometry and the combination of crossflow and counterflow regions in a compact heat exchanger, requiring extensive computational resources. To overcome these limitations, the entire model is treated as a computable unit cell, and the complex calculations involving crossflow and counterflow are simplified by summing individual simulations for each flow type. Furthermore, the detailed numerical modeling method is compared with experimental results, demonstrating the utility of the proposed CFD modeling approach for analyzing plate–fin compact heat exchangers. [ABSTRACT FROM AUTHOR]

In imaging systems, the mixed Poisson-Gaussian noise (MPGN) model can accurately describe the noise present. Total variation (TV) regularization-based methods have been widely utilized for Poisson-Gaussian removal with edge-preserving. However, TV regularization sometimes causes staircase artifacts with piecewise constants. To overcome this issue, we propose a new model in which the regularization term is represented by a combination of total variation and high-order total variation. We study the existence and uniqueness of the minimizer for the considered model. Numerically, the minimization problem can be efficiently solved by the alternating minimization method. Furthermore, we give rigorous convergence analyses of our algorithm. Experiments results are provided to demonstrate the superiority of our proposed hybrid model and algorithm for deblurring and denoising images simultaneously, in comparison with several state-of-the-art numerical algorithms. [ABSTRACT FROM AUTHOR]

This paper discusses the advantages of the multi active tuned mass dampers (MATMD) for vibration control of multi-degree-freedom structures and their distribution masses. The 11-story building having two ATMDs at different story and different ATMD mass under long and short period earthquakes is considered. A structural system with ATMDs using fuzzy logic control was simulated against the ground motion of the earthquakes. The time history of the story displacements and accelerations, and the frequency responses of both the uncontrolled and controlled structures are shown in this study to investigate the effectiveness of multiple ATMDs compared with single ATMD and distributed multiple tuned mass dampers (d-MTMDs). The gained results also present the effect of mass distribution of two ATMDs and their location on the building response that the distributed MATMD with same mass has better performance than the distributed MATMD with different mass and single ATMD in the most earthquake cases. [ABSTRACT FROM AUTHOR]

N‐(diethylthiocarbamoyl)benzimidoyl chloride reacts with methyl esters of glycine, L‐alanine, L‐valine under formation of pro‐ligands 1 which undergo de‐esterification in reactions with Cu(CH3COO)2 and finally form complexes 2 with the compositions of [{Cu(L‐gly)}4] (2 a), [{Cu(L‐ala)}∞] (2 b) and [{Cu(L‐val)}∞] (2 c). In all complexes, Cu(II) ion is coordinated by a dianion {L2−} via its (O,N,S) donor set and a bridging carboxylate O atom, and thus, adopts a distorted square‐planar coordination sphere. Treatment of complexes 2 with equimolar amounts of o‐phenanthroline results in the formation of square pyramidal ternary complexes with the compositions of [Cu(L)phen] (L=L‐gly, L‐ala, L‐val) (3). Antiproliferative effects of the compounds on MCF‐7 and Hep‐G2 cancer cells were studied. Generally, the ternary complexes 3 are more active than the complexes 2 and the pro‐ligands 1. In each series of compounds, the derivatives of L‐valine show higher cytotoxicity than those of L‐alanine and glycine. [ABSTRACT FROM AUTHOR]

A sol-gel method was employed to synthesize phase-pure (1-x)BiFeO3-xBi(Mn0.5Ti0.5)O3 (abbreviated as BFO-xBMT, x = 0–0.10) multiferroic ferrites. The investigation focused on the structure, optical, and magnetic properties, and their dependence on composition. X-ray diffraction analysis (XRD) revealed a single phase rhombohedral structure for BiFeO3 (BFO), with distinct double peaks (104)/(110) and (006)/(202) at diffraction angles 2θ ∼ 32.0° and 39.5°. As the content of Bi(Mn0.5Ti0.5)O3 (BMT) increased, a structural transition from rhombohedral (R3c) to pseudo-cubic (Pm3m) phase was observed. Doping with BMT led to a decrease in particle size. The band gap (Eg) of BFO-xBMT materials exhibited a slight increase from 1.99 eV in BFO to 2.18 eV in the BFO-0.10BMT composition. The introduction of BMT resulted in a significantly enhanced room temperature ferromagnetism in BiFeO3, with the maximum magnetic moment doubling to around 5.7 emu/g for the BFO-0.04BMT solid solution. This improvement is attributed to the addition of BMT inducing intrinsic strain in the crystal lattice, suppressing the intrinsic helical spin structure of BFO, and thus enhancing its latent magnetic potential. The research demonstrated the substantial influence of BMT perovskite on the structure, optical, and magnetic properties of BFO materials. Overall, the results suggest that the BFO-xBMT multiferroic ferrites with optimal composition hold promise for use in multifunctional devices. [ABSTRACT FROM AUTHOR]

Two novel benzoylthioureas derived from gallic acid, (tri‐O‐acetyl)galloyl‐N,N‐diethylthiourea HL1, and cinnamic acid, cinnamoyl‐N,N‐diethylthiourea HL2 have been successfully prepared and characterized by means of elemental analysis, IR, NMR, high‐resolution MS, and X‐ray crystallography. The organic ligands react with Ni(AcO)2 and Cu(AcO)2 in MeOH under formation of bis‐complexes with the compositions of [M(L)2] (M=Ni2+, Cu2+; L=L1, L2). Similar reactions with Co(AcO)2, however, result in Co(III) tris‐complexes [Co(L)3] (L=L1, L2) with the metal ions oxidized presumably by atmospheric dioxygen. X‐ray crystallography and spectroscopic characterization reveal a cis square‐planar coordination in the bis‐complexes and facial octahedral geometry in the tris‐complexes. In all of metal complexes, the deprotonated organic compounds ({L1}− and {L2}−) serve as (S,O)‐bidentate ligands. The ligand HL1 and its Ni(II) and Cu(II) complexes exhibit weak antiproliferative effects on the human MCF7 breast and HepG2 liver cancer cells with IC50 values in the range of 60–115 μM. Surprisingly, the tris‐complex [Co(L1)3] exhibits high cytotoxicity with IC50 values of 22.23±1.58 μM for MCF7 and 28.30±3.09 μM for HepG2 cancer cells. The activity against MCF7 cells is even more than that of cisplatin under the same conditions. [ABSTRACT FROM AUTHOR]

• A new method, namely, nonlocal strain gradient method is applied to the FG-CNTRC nanoplates. • Natural frequencies of the nanostructures are the intermediate step to find the responses or characteristics. • This study focuses on obtaining the mathematical formulas of natural frequencies. • The influence of material length scale and nonlocal parameter on vibrational responses is investigated. • The correlation between the geometry and material length scale is discussed. In this research paper, as initial endeavors, the vibrational responses of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) nanoplates taking into account the effect of nonlocal parameter and strain gradient coefficient are investigated. The study aims at developing mathematical modeling via an analytical solution to FG-CNTRC nanoplate structure with allowance for the nonlocal strain gradient effect. The four types of CNT distribution are used and compared in the context of the vibration of nanoplate in the presence of the small length scale effects, namely the (a) UD, (b) FG-V, (c) FG-O, and (d) FG-X. Some theoretical equations based on the first-order shear deformation plate theory (FSDT) are presented to provide a lucid understanding of how the small length-scale influences the FG-CNTRC nanoplate. For the vibrational analysis of a nanoplate, which is simply supported boundary condition, Navier solutions are obtained. Also, in contrast to earlier studies, an analytical approach is used to establish the governing equations of the FG-CNTRC nanoplate. Some specific numerical examples are given and compared with the results presented in the literature. In the section of numerical results, the influence of the nonlocal parameter, strain gradient coefficient, geometric parameters and vibrational modes on the non-dimensional natural frequency are investigated and discussed in detail. These could be useful to analysts and designers to estimate the fundamental natural frequencies in each of the four CNT distributions that the FG-CNTRC nanoplate possesses. [ABSTRACT FROM AUTHOR]

Modern engineering extensively employs complexly curved shell structures, presenting mathematical challenges in analyzing their mechanical behavior due to geometric intricacies. The recent trend of incorporating advanced lightweight materials into these structures drives the need to develop improved theories and methods. This study presents an investigation into the free vibration analysis of barrel-shaped sandwich (BSS) shells using a modified thick shell theory (MTST). These sandwich shells feature functionally graded (FG) ceramic-metal layers on both inner and outer surfaces, with a lightweight honeycomb core. Notably, the honeycomb layer's thickness surpasses that of the inner and outer layers, necessitating the application of thick shell theory for accurate analysis. However, previous studies have often used classical theories for thin shells, and those applying thick shell theory sometimes neglected the curvature effects in the fundamental equations and rotary inertia components. Thus, this research employs the MTST to overcome these limitations. The study includes comparative validations and explores the impact of material parameters and curvature radii on the natural frequencies of these barrel-shaped sandwich shells through numerical examples. [ABSTRACT FROM AUTHOR]

The study of the temperature dependence of Raman spectrum of graphene quantum dots is important for further understanding of the fine structure and properties of the material such as atomic bonds, thermal expansion, and thermal conductivity. In this work, we present new results on the temperature dependence of the frequency of G peak in the Raman spectra of bare GQDs and nitrogen-doped graphene quantum dots (N-GQDs), respectively. The nature of these GQDs is investigated using high-resolution transmission electron microscopy together with Raman, absorption, and photoluminescence spectra. We monitored a shift in G peak frequency toward lower frequencies with the temperature ranging from 81 to 663 K. In addition, a slight decrease in G peak intensity and an increase in D peak intensity have been observed, which is especially clear for Raman spectra of N-GQD sample. From the linear relationship of G peak frequency with temperature, we determine for the first time the value of the temperature coefficient χ of the G mode. Values of − 0.0222 ± 0.001 cm−1 K−1 for GQDs, and − 0.0243 ± 0.0013 cm−1 K−1 for N-GQDs were deduced. These results show a clear heat expansion in the graphene lattice, although small in size, when sample temperature is increased from 81 to 663 K. Our result is important to further understand physical effects induced by anharmonic phonons in QGDs and should be taken to account when designing efficient nanoelectronic devices employing GQDs. [ABSTRACT FROM AUTHOR]

The NiTiO3 ceramic was synthesized in nanostructured form by citrate gel method. The phase structure, microstructure and magnetic properties of synthesized compounds were investigated by X-ray diffraction (XRD), scanning electron microscope and vibrating sample magnetometer. Williamson–Hall plot was used to calculate the crystallite size and microstrain of sample. The XRD analysis showed the formation of rhombohedral crystal structure of synthesized powders. The crystallite size is about 35 nm and microstrain is 5. 9 × 1 0 − 4 . The optical band gap was estimated from UV-Visible spectrum with value of 2.43 eV. The NiTiO3 samples showed coexistence of ferroelectric and antiferromagnetic properties at room temperature. [ABSTRACT FROM AUTHOR]

In this paper, we present an effective algorithm for solving the Poisson-Gaussian total variation model. The existence and uniqueness of solution for the mixed Poisson-Gaussian model are proved. Due to the strict convexity of the model, the split-Bregman method is employed to solve the minimization problem. Experimental results show the effectiveness of the proposed method for mixed Poisson-Gaussion noise removal. Comparison with other existing and well-known methods is provided as well. [ABSTRACT FROM AUTHOR]

The paper deals with the nonlinear buckling analysis of imperfect cylindrical shells made of porous metal foam subjected to axial compression. For the metal foam shells, porosities are dispersed by uniform, symmetric, and asymmetric distributions in the thickness direction. Using Donnell shell theory and von-Karman nonlinear kinematics, nonlinear equilibrium equations are derived. The critical buckling load and buckling equilibrium curves for both perfect and imperfect shells are solved by using the Galerkin's procedure. A comprehensive investigation into the influence of porosity coefficient, imperfections, porosity distribution, and geometry on the buckling behaviors of the cylindrical shell is performed. [ABSTRACT FROM AUTHOR]

Two thio­chromene com­pounds containing Br and F atoms, namely 2-(2-bromo-5-fluoro­phen­yl)-8-eth­oxy-3-nitro-2H-thio­chromene (C17H13BrFNO3S, A) and 2-(2-bromo-5-fluoro­phen­yl)-7-meth­oxy-3-nitro-2H-thio­chromene (C16H11BrFNO3S, B), were prepared via the condensation reaction between 2-mer­capto­benzaldehyde and nitro­styrene derivatives. In both com­pounds, the thio­chromene plane is almost perpendicular to the phenyl ring. In the structure of A, mol­ecules are assembled via π–π stacking and C—H∙∙∙O and C—F∙∙∙π inter­actions. In the crystal packing of B, mol­ecules are linked by C—H∙∙∙F, C—H∙∙∙O, C—H∙∙∙π and π–π inter­actions. [ABSTRACT FROM AUTHOR]

Highlights • Gaseous wet CH 3 I can become entrapped in interstitial positions in a silica-gel network. • Methylations of amine (in PEDA) and silanol (in surface) through the introduced gaseous wet CH 3 I are observed. • 270 kGy ionizing radiation of electron-beam causes propylethylenediamine in hybrid silica gels fragment. • Ag nanoparticles do not seem to directly react with CH 3 I to produce AgI in our experimental conditions. • Interactions between Ag nanoparticles and propylethylenediamine enhance the Raman signals significantly. Abstract Electron-beam (e-beam) irradiation (270 kGy), applied to Ag nanoparticle (Ag NP) production, causes a chain cleavage of propylethylenediamine in a Ag NP-embedded propylethylenediamine-anchored SiO 2 gel (Ag NP-PEDA gel) network, releasing some volatile organic compounds (VOCs) by thermalizing the gel at 150 °C. The introduced gaseous wet CH 3 I can become entrapped in interstitial positions and can surround the Ag NPs, the remaining organics, or the Ag NP-amine in a silica-gel network, and another CH 3 I was found to form a methoxy species, Si OCH 3 , on the silica surface with the iodine leaving group (I−) not being chemically detected. The interactions between Ag NPs and N donor (of amine) and between amine and the methyl group (of CH 3 I) were confirmed respectively. Ag NPs do not seem to directly produce AgI with CH 3 I under our experimental conditions. Significantly enhanced Raman signals, strong emissions, interesting but different results between Fourier transform infrared (FT-IR) and attenuated total reflectance (ATR) spectroscopy data, and newly released VOCs were all described to support the interaction properties between the very low concentration of gaseous wet CH 3 I and the prepared Ag NP-PEDA gel under the controlled experimental conditions. [ABSTRACT FROM AUTHOR]

In this note, we use methods from spectral graph theory to obtain bounds on the number of incidences between k-planes and h-planes in Fqd, which generalizes a recent result given by Bennett, Iosevich, and Pakianathan (2014). More precisely, we prove that the number of incidences between a set K of k-planes and a set H of h-planes with h ≥ 2k + 1, which is denoted by I(K,H), satisfies ... As an application of incidence bounds, we prove that almost all k-planes, 1 ≤ k ≤ d - 1, are spanned by a set of 3qd-1 points in Fqd. We also obtain results on the number of t-rich incident k-planes and h-planes in Fqd, with t ≥ 2. [ABSTRACT FROM AUTHOR]

Abstract The circular cylindrical shells have been widely used in modern engineering structures, especially in the aerospace industry such as the oil pipeline, the missile, spacecraft hull, storage tanks. In recent years, functionally graded carbon nanotube composites (FG-CNTRCs) have emerged, as a promising type of composites. Due to the increasing demands for high structures performance, this research paper proposes a closed-form solution to investigate the nonlinear buckling behavior of the FG-CNTRC cylindrical shells subjected to compressive load. The small initial imperfections of the FG-CNTRC cylindrical shells are also considered through analytical modeling. Effective properties of materials of the shells reinforced by single-walled carbon nanotubes (SWCNTs) are estimated through a micro-mechanical model based on the extended rule of mixtures. The Donnell shell theory and von-Karman nonlinear kinematics are used for nonlinear equilibrium equations. The novelty of this work is to exploit an exact solution via Galerkin procedure and term of the Airy stress function in order to reveal the impacts of the imperfection parameter, different types of CNTs distribution, the volume fraction of CNTs on nonlinear behavior and compressive equilibrium paths of FG-CNTRC cylindrical shells. Highlights • A closed form solution for nonlinear buckling analysis. • Carbon nanotubes (CNTs) distribution are dispersed by UD, FG-A, FG-V and FG-X distributions. • The Donnell shell theory and von-Karman nonlinear kinematics are used.. • The initial geometric imperfections of a cylindrical shell are considered. [ABSTRACT FROM AUTHOR]

We present here an effective scheme for image denoising based on total variation regularization. The proposed scheme allows to efficiently remove Poisson noise as well as Gaussian noise simultaneously with the help of a new kind of data fidelity term, suitable for the mixed Poisson-Gaussian noise model. The results show that the algorithm corresponding to our new scheme outperforms the existing methods for mixed Poisson-Gaussian noise removal. [ABSTRACT FROM AUTHOR]

The aim of this research paper is to present the elastic buckling and free vibration analyses of porous-cellular plates based on the first-order shear deformation theory (FSDT). In the porous-cellular plate model, porosities are dispersed by uniform and non-uniform (symmetric and asymmetric) distribution patterns. The material properties, such as Young's modulus and mass density of the porous-cellular plates are assumed to vary along the thickness direction in term of porosity coefficient. First, the dynamic version of Hamilton's principle is applied to derive the Euler–Lagrange equations. Then, in the case of simply supported boundary condition, the critical buckling load and natural frequency of the porous-cellular plates are obtained using the Navier procedure. Furthermore, the reliability of the current formulation is validated by several examples. Finally, a comprehensive examination into the influence of porosity coefficient, porosity distributions, and the geometric parameters on the buckling behavior and vibration response of the porous-cellular plates are performed. Numerical results indicate that the effect of porosity distributions on the structural performance and provide the useful insights into the porosity design to achieve appropriately natural frequency and buckling resistance. [ABSTRACT FROM AUTHOR]

The main objective of this research paper is to investigate the positive influence of the stiffeners on the vibration of functionally graded plates based on an exact approach via Navier solution. The plate is reinforced by stiffeners in both longitudinal and transversal directions. The material properties of functionally graded materials (FGMs) media are distributed across the thickness based on a sigmoid-law form and are assumed to be temperature-dependent. By using the Hamilton's principle and the classical plate theory (CPT), the governing equations of motion are obtained. Based on the Navier solution, an exact solution is proposed for natural frequencies of simply supported rectangular plates. In addition, the effects of related parameters on natural frequencies are also addressed in detail. Finally, numerical examples are presented and compared with existing results. [ABSTRACT FROM AUTHOR]

The article presents a semi-analytical solution for the free vibration problem in bi-directional functionally graded (FG) cylindrical shells with varying thickness, utilizing a modified shear deformation shell theory (MSDT). In this model, the mechanical properties of the cylindrical shells change along both the axial and thickness directions. Classical analytical methods for shell structures often face limitations in terms of boundary conditions, transverse shear deformation, and rotary inertia, making the use of MSDT and Galerkin procedure necessary for solving the problem of free vibration analysis in this study. The boundary conditions of the bi-directional FG cylindrical shells are chosen to be simply supported and clamped, and the presented method is compared to relevant results in the literature to validate its effectiveness. Moreover, a comprehensive parametric investigation is conducted to evaluate the influence of material and geometrical parameters on the natural frequencies. The results show that the natural frequency of the FG cylindrical shells is significantly affected by the material and geometrical parameters, including the power-law index, the thickness variation, the aspect ratio, and the boundary conditions. [ABSTRACT FROM AUTHOR]

In this research, the buckling behavior of hybrid-honeycomb sandwich (HHS) cylindrical shells under hydrostatic pressure is investigated. The HHS shells consist of two thin ceramic-metal functionally graded (FG) layers on the outer and inner surfaces, and a layer of lightweight, high-strength, low-density hybrid-honeycomb material in the center, with a thickness that is larger compared to the FG layers. The ceramic composition of the FG layers covers the entire outer surface of the cylindrical shells, which is intended to improve the performance of structures in highly corrosive and acidic environments, such as the ocean, and in other mining and metallurgical industries. The hybrid-honeycomb core has a negative Poisson's ratio, also called as auxetic materials, which have a unique microstructure that can affect the buckling behavior of cylindrical shells made from these materials, resulting in improved buckling resistance, stability, and enhanced energy absorption. Using classical shell theory, the governing equations for the buckling behavior problem are derived, and the critical buckling loads are then gained using the Galerkin solution. The results of the present study are validated through comparison with existing literature, and numerous numerical examples are conducted to showcase the interesting results of the study with various material and geometric parameters. • The HHS shells are a new type of sandwich cylindrical shell. • The hybrid-honeycomb core material with two wall angle parameters. • Study uses Galerkin method to determine HHS shell buckling loads. • Study aims to explore auxetic materials' impact on HHS shells' buckling. [ABSTRACT FROM AUTHOR]

This paper presents an analytical approach to analyze the nonlinear static buckling of imperfect functionally graded carbon nano-reinforced composite (FG-CNTRC) plates subjected to axial compression. The material properties of the FG-CNTRC are assumed to be graded through the thickness direction according to several linear distributions of the volume fraction of carbon nanotubes. The theoretical formulations are based on the classical plate theory (Kirchhoff plate) with von Karman-type of nonlinearity and the initial geometrical imperfection. The approximate solution is developed for simply supported and freely movable boundary conditions. By applying the traditional Galerkin method and the Airy stress function, the results for the critical load are obtained in closed-form solutions, which are convenient to be used in engineering design. Some illustrative examples are also presented in details to investigate the effects of the imperfection, carbon nanotubes, and geometrical parameters on the nonlinear static behavior the plates. [ABSTRACT FROM AUTHOR]

The cylindrical shells reinforced by stringers have been widely used in modern engineering structures such as storage tanks, missile, submarine hull, oil-transmitting pipeline, etc. In this present article, the thermomechanical buckling and post-buckling behaviors of a cylindrical shell with functionally graded (FG) coatings are investigated by an analytical approach. The cylindrical shell is reinforced by outside stringers under torsional load in the thermal environment. The layers of FG coatings are assumed to be made by functionally graded materials (FGMS) combining of ceramic and metal phases and the core of the shell is made from homogeneous material. The classical shell theory based on the von-Karman assumptions is used to model the thin cylindrical shell. Using Galerkin's procedure and Airy stress function, the governing equations can be solved to obtain the closed-form solution for the critical buckling load and postbuckling load-deflection curves of simply supported shells. Moreover, many important parametric studies of stringers, temperature field, material volume fraction index, the thickness of metal layer, etc. are taken into investigation. According to numerical examples, it is revealed that the outside strings have considerably impact on thermomechanical buckling and postbuckling behaviors of the shells. [ABSTRACT FROM AUTHOR]

In this paper, we use methods from spectral graph theory to obtain some results on the sum–product problem over finite valuation rings R of order q r which generalize recent results given by Hegyvári and Hennecart (2013). More precisely, we prove that, for related pairs of two-variable functions f ( x , y ) and g ( x , y ) , if A and B are two sets in R ∗ with | A | = | B | = q α , then max { | f ( A , B ) | , | g ( A , B ) | } ≫ | A | 1 + Δ ( α ) , for some Δ ( α ) > 0 . [ABSTRACT FROM AUTHOR]

Lateral buckling of thin-walled functionally graded (FG) open-section beams is studied, regarding mono-symmetric I- and channel-sections. The approach based on assumption that the volume fraction of particles varies through the wall thickness according to a power law. Governing buckling equations and a finite element method have been developed to formulate the problem. By means of Vlasov’s assumption, the theory accounts for warping of cross-section and all the structural coupling coming from anisotropy of material. The lateral buckling parameter and mechanism are obtained for thin-walled FG beams under central point load, uniformly distributed load, and moment gradient with several types of material distributions. In order to show the validity of proposed theory, as a special case, a numerical comparison is carried out with available results in literature. Moreover, effects of load height, gradual law, end-moment ratio and ceramic skin-core-skin thickness on the buckling capacity of a thin-walled FG open-section beam are also included in the analysis. [ABSTRACT FROM AUTHOR]

This paper aims to present the flexural, torsional and flexural-torsional buckling of axially loaded thin-walled functionally graded (FG) open-section beams with various types of material distributions. Properties of metal-ceramic materials are described by a monotonic function of volume fraction of particles that varying across blade thickness according to a power law. The problem is formulated by using a two-noded 14-degree-of-freedom beam element. Governing buckling equations has been developed. Warping of cross-section and all the structural coupling coming from anisotropy of material are taken into account in this study. The critical load is obtained for thin-walled FG mono-symmetric I- and channel-sections with arbitrary distributions of material. As a special case, a numerical comparison is carried out to show the validity of the proposed theory with available results in the literature. In addition, effects of gradual law, ceramic core and skin, span-to-height on the buckling parameters of an axially loaded thin-walled FG open-section beam are also investigated. [ABSTRACT FROM AUTHOR]

The use of variable thickness can help the designers and researches reduce the weight of the functionally graded (FG) panel structures. For cases where reduction of weight is of high importance, such as space structures, ocean engineering, this type of panel is the best choice. Hence, this paper analyzes the effect of the variable thickness on nonlinear buckling of imperfect cylindrical panels made of sigmoid-functionally graded material (S-FGM) under combined axial compression and external pressure. The governing equations are in nonlinear form based on the classical shell theory with the von Karman assumption. By applying Galerkin procedure and the Airy stress function, the resulting equations are solved to obtain closed form expressions for critical buckling load and load–deflection curves. In numerical results, effect of variable thickness, the volume fraction index, imperfection size, loading as well as the geometric parameters on the load–dimensionless deflection curves are discussed in details. [ABSTRACT FROM AUTHOR]

The buckling behavior of thin curved panel with functionally graded (FG) coatings under combined axial compression and external pressure is investigated in the present work based on nonlinear analysis. The governing equations are developed using the classical (Kirchoff) shell theory (CST) with von Karman-type of nonlinearity and combining with initial geometrical imperfection. An Airy stress function and Galerkin's technique are applied to obtain closed-form expression of critical buckling loads and load-deflection relations. Besides, a detailed parametric study is conducted to verify and perform the effects of gradual law, thickness of the ceramic layer, imperfection parameter, aspect ratio of the panel including arc length-to-thickness and axial length-to-radius ratios as well as mechanical loading on the nonlinear buckling behavior of the imperfect thin curved panel with FG coatings. [ABSTRACT FROM AUTHOR]

Stiffened cylindrical shells are widely used in modern engineering structures, especially in aircraft, oil-transmitting pipeline, spacecraft industry and ocean engineering. Due to the increasing demands for high structures performances, this paper presents the effect of stiffeners on the nonlinear buckling of cylindrical shells with functionally graded (FG) coatings under torsional load. The cylindrical shell is reinforced with external axial stiffeners. The material properties are assumed to vary continuously through the thickness direction. Equilibrium and stability equations for cylindrical shells are derived by using the classical shell theory (CST) with von-Karman nonlinear kinematic relations. Using analytical approach, Galerkin procedure, and the Airy stress function, the resulting equations are employed to obtain the closed-form expression for the critical buckling loads and load–deflection relation. The influences of the number of stiffeners, volume fraction exponent, the thickness of the metal layer, and geometric parameters on the nonlinear buckling behavior of the cylindrical shell with FG coatings are examined in details. [ABSTRACT FROM AUTHOR]

Let q be a prime power, and Fq be the finite field of order q. In this short note, by using methods from spectral graph theory, we give sufficient conditions to guarantee that Fq \ {0} ⊆ {a1ux11 + · · · + aduxdd : 1 ⩽ xi ⩽ Mi, 1 ⩽ i ⩽ d} , where ai and ui are non-zero elements in Fq, and Mi are integers. This result generalizes a recent result given by CILLERUELO and ZUMALACÁRREGUI (2014). Using the same techniques, we extend this result in the setting of the finite cyclic ring. [ABSTRACT FROM AUTHOR]

In this paper, an analytical solution is developed to investigate the thermal buckling behavior of the imperfect rectangular plates with functionally graded (FG) coatings under uniform temperature rise. Material properties of the FG coatings are assumed to be temperature-dependent and to continuously vary in the thickness direction using the power law distribution of volume fraction of metal and ceramic. Theoretical formulations are based on the classical plate theory with von-Karman nonlinear kinematic relations. The initial geometrical imperfections of plates are also accounted. By using the Galerkin method and the Airy stress function, the resulting equations are solved to obtain the closed form expressions for nonlinear equilibrium paths. Effects of power law index, imperfection, geometric parameters, and temperature distributions on the response of rectangular plates with FG coatings are discussed in details. [ABSTRACT FROM AUTHOR]

This paper presents an analytical approach to study the nonlinear dynamic buckling of sigmoid functionally graded material (S-FGM) toroidal shell segments surrounded by elastic foundations subjected to axial compression. Shells are reinforced by closely spaced rings and stringers. The nonlinear dynamic buckling analysis is based on the classical shell theory with von Kármán–Donnell-type of geometrical nonlinearity. By using the Galerkin method, the closed-form expression of the deflection–time curves is obtained. Numerical solutions are presented in tabular and graphical forms to investigate the deflection–time curves of FGM shells surrounded by elastic foundations. Finally, the influences of geometrical parameters, volume fraction index, elastic foundations, and the effectiveness of stiffeners on the nonlinear dynamic buckling of the S-FGM toroidal shell segments are discussed. The present results are compared with the available data for a special case. [ABSTRACT FROM AUTHOR]

With the aim of reducing the weight of structures, functionally graded materials (FGM) plates with variable thickness have been widely used in various engineering applications such as aeronautical, mechanical and ocean structures. However so far, the analytical approaches for analyzing the instability behaviors of FGM plates with variable thickness are still somehow limited in the literature. The paper hence presents an analytical approach to investigate the influences of variable thickness on buckling and postbuckling behavior of imperfect sigmoid FGM (S-FGM) plates resting on elastic medium subjected to compressive loading. The material properties of S-FGM plates are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. Governing equations are based on the classical plate theory with von Karman-type geometric nonlinearity. The initial geometrical imperfections of plates are also accounted. By using the Galerkin procedure and the Airy stress function, the resulting equations are solved to obtain the closed form expressions for nonlinear equilibrium paths. The effects of power-law indices, coefficients of foundation, initial geometrical imperfections and geometrical parameters on nonlinear stability of plates are comprehensively investigated. The results reveal that the variable thickness of plate has a significant effect on the buckling behavior of S-FGM plates under compression loading. [ABSTRACT FROM AUTHOR]

We present a facile wet-chemistry method for efficient metal filling of the hollow inner cores of boron nitride nanotubes (BNNTs). The fillers conform to the cross-section of the tube cavity and extend in length from a few nm to hundreds of nm. The methodology is robust and is demonstrated for noble metals (Au, Pt, Pd, and Ag), transition metals (Co), and post-transition elements (In). Transmission electron microscopy and related electron spectroscopy confirm the composition and morphology of the filler nanoparticles. Up to 60% of BNNTs of a given preparation batch have some degree of metal encapsulation, and individual tubes can have up to 10% of their core volume filled during initial loading. The growth, movement, and fusing of metal nanoparticles within the BNNTs are also examined. [ABSTRACT FROM AUTHOR]

This article researches nonlinear response of imperfect eccentrically stiffened symmetric FGM thin circular cylindrical shells with ceramic-metal-ceramic layers, which are symmetric through the middle surface by Sigmoid-law distribution (S-FGM) and have stiffeners surrounded on elastic foundations under uniform radial load. The Donnell classical shell theory, stress function, and Galerkin method are used for investigation of the nonlinear stability of the S-FGM shell. The obtained results show the effects of the stiffeners, elastic foundations, mechanical load, and material parameters on the nonlinear buckling response of symmetric S-FGM circular cylindrical shells. [ABSTRACT FROM AUTHOR]

Thiocarbamoylbenzimidoyl chlorides, PhC(Cl)-N-(C-S)-NR¹R², react with 2-(iminodiacetic acid)benzylamine under formation of the potentially pentadentate ligands H3L (R¹, R² = Et) and H3L-COOEt (R¹ = Me, R² = C6H4-4-COOEt) in high yields. Hydrolysis of H3L-COOEt in NaOH/MeOH gives quantitatively another benzamidine ligand H3L-COOH. The novel ligands readily react with (NBu4)[MOCl4] (M = Re, Tc) under formation of stable complexes with the general composition [MO(L)], in which they are triply deprotonated and fully occupy the remaining five coordination positions of the {MO}3+ cores. In a "proof-of-principle" reaction for possible bioconjugations, the complex [ReO(L-COOH)] has been labeled with triglycine ethyl ester in high yields. [ABSTRACT FROM AUTHOR]

This paper presents an analytical approach to investigate the nonlinear dynamic response and vibration of imperfect eccentrically stiffened functionally graded thick circular cylindrical shells surrounded on elastic foundations using both the first order shear deformation theory and stress function with full motion equations (not using Volmir's assumptions). Material properties are graded in the thickness direction according to a sigmoid power law distribution (S-FGM) in terms of the volume fractions of constituents with metal–ceramic–metal layers. The S-FGM shells are subjected to mechanical and damping loads. Numerical results for dynamic response of the shells are obtained by Runge–Kutta method. The results show the influences of geometrical parameters, the volume fractions of metal–ceramic–metal layers, imperfections, the elastic foundations, eccentrically stiffeners, pre-loaded axial compression and damping loads on the nonlinear dynamic response and nonlinear vibration of functionally graded cylindrical shells. The proposed results are validated by comparing with other results reported in the literature. [ABSTRACT FROM AUTHOR]

We study a variant of Erdős-Rényi graph over finite rings. We then use this graph to obtain a Szemerédi-Trotter type theorem a sum-product estimate in finite rings. [ABSTRACT FROM AUTHOR]

Thin cylindrical shells are widespread in structural engineering, such as civil engineering structures, oil rigs, oil pipes, rocket hull and aircraft fuselages. With the development of materials science, the behavior of the cylindrical shell structures made of advanced materials has attracted many scientists. This paper proposed an analytical approach through a closed-form solution for analyzing the free vibration characteristic of FG cylindrical thin and thick shells considering simultaneously the effect of porosities and the neutral surface. Both the classical shell theory (CST) and the shear deformation shell theory (SDST) are employed to establish governing equations for the free vibration problem. The natural frequencies of FG cylindrical shells with porosities are obtained by using the Navier solution. The results obtained from this study are confirmed by comparing with existing ones. In addition, the effects of the neutral surface, material parameter as well as mode vibration on the natural frequencies are examined. • A model of the FG cylindrical shell with porosities. • The effect of the physical neutral surface is considered. • An useful analytical solution is applied. • This study focuses on obtaining the formulas of natural frequencies. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, an analytical approach is presented to investigate the nonlinear static buckling and post-buckling for imperfect eccentrically stiffened functionally graded thin circular cylindrical shells surrounded on elastic foundation with ceramic–metal–ceramic layers (S-FGM) and subjected to axial compression. The Lekhnitsky smeared stiffeners technique with Pasternak type elastic foundation, stress function and Bubnov-Galerkin method are applied. Numerical results are given for evaluating effects of material and geometrical properties, elastic foundations and eccentrically outside stiffeners on the buckling and post-buckling of the S-FGM shells. The obtained results are validated by comparing with those in the literature. [Copyright &y& Elsevier]

Abstract: In this paper, an analytical approach is presented to investigate the nonlinear static buckling for imperfect eccentrically stiffened functionally graded thin circular cylindrical shells with temperature-dependent properties surrounded on elastic foundation in thermal environment. Both shells and stiffeners are deformed simultaneously due to temperature. Material properties are graded in the thickness direction according to a Sigmoid power law distribution in terms of the volume fractions of constituents (S-FGM) with metal–ceramic–metal layers. The Lekhnitsky smeared stiffeners technique with Pasternak type elastic foundation, stress function and the Bubnov–Galerkin method are applied. Numerical results are given for evaluating effects of temperature, material and geometrical properties, elastic foundations and eccentrically outside stiffeners on the buckling and post-buckling of the S-FGM shells. The obtained results are validated by comparing with those in the literature. [Copyright &y& Elsevier]

Abstract: The D1Q3 lattice Boltzmann (LB) shallow water equation is analyzed in detail and compared with other numerical schemes. Analytical results are derived and used to discuss the accuracy and stability of the model. We show how such D1Q3 LB models for canal reaches may be easily coupled with various hydraulic interconnection structures to build models of complex irrigation networks. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic fine particles of cobalt ferrite (CoFe2O4) have been synthesized using complexometric method in which ethylene diamine tetra acetic acid C10H16N2O8 (EDTA) acts as a complexing agent. The crystallographic structure, microstructure and magnetic properties of the synthesized powder were characterized by using X-ray diffraction (XRD), particle size analysis and vibrating sample magnetometry (VSM). The material crystallized in cubic spinel structure with lattice parameter of about 8.38Å. Depending on the calcining temperature, the particle size of the powders varies in the range of hundreds of nanometers to tens of micrometers. A desired relative density above 95% of the theoretical value is obtained for the bulk sample after sintering. The calcined powders and sintered sample exhibit saturation magnetizations around 80Am2/kg which is expected for inverse CoFe2O4. With increasing calcining temperature the coercivity of these samples decreases. This simple synthesis route leads to a reproducible and stoichiometric material. [Copyright &y& Elsevier]

We examined the feasibility, acceptability, and therapeutic efficacy of a culturally adapted cognitive-behavior therapy (CBT) for twelve Vietnamese refugees with treatment-resistant posttraumatic stress disorder (PTSD) and panic attacks. These patients were treated in two separate cohorts of six with staggered onset of treatment. Repeated measures Group x Time ANOVAs and between-group comparisons indicated significant improvements, with large effect sizes (Cohen's d) for all outcome measures: Harvard Trauma Questionnaire (HTQ; d = 2.5); Anxiety Sensitivity Index (ASI: d = 4.3); Hopkins Symptom Checklist-25 (HSCL-25), anxiety subscale (d = 2.2); and Hopkins Symptom Checklist-25, depression subscale (d = 2.0) scores. Likewise, the severity of (culturally related) headache-and orthostasis-cued panic attacks improved significantly across treatment [ABSTRACT FROM AUTHOR]

• Material properties are simultaneously distributed in two directions. • A more in-depth study is presented to clearly understand the effect of material parameter and nonlocal parameter. • The nonlocal strain gradient theory is used to investigate the bending and buckling behaviors of the BDFG nanobeam structure. The main goal of this research paper is to present the modeling and analysis of bi-directional functionally graded (BDFG) nanobeams within the framework of the Timoshenko beam theory and nonlocal strain gradient theory. According to the DBFG material model, the material properties of the nanobeams are simultaneously distributed in two different directions (thickness and length directions). Besides, the volume fraction of component material is described by a function that combines the power and exponential distribution rules. The study focuses strongly on understanding the mechanical behavior of the BDFG nanobeams and in calculating important parameters of materials and nonlocal strain gradient coefficients. In addition, equilibrium and stability equations for DBFG nanobeams are systematically formulated to static bending and buckling problems with the corresponding boundary condition. The highlight is the combination of two different technical solutions as Navier solution and the Galerkin technique. In the numerical results section, some specific examples are presented to verify the proposed solution, and thereby, a good agreement is observed. Finally, a detailed investigation is performed, with a particular focus on the influences of material properties, nonlocal parameter on the critical buckling load and transverse deflection of the BDFG nanobeams. [ABSTRACT FROM AUTHOR]

Exploring magnetic order in nonferromagnetic substances, such as CuO:ZnO, becomes especially attractive when introducing defect states through nonmagnetic ion doping. In this study, we delved into the impact of Yb doping on the structural, morphological, optical, and magnetic properties of CuO:ZnO. The Yb doped CuO:ZnO was prepared with different Yb concentrations (x = 0.00–20 %) via the temperature-assisted co-precipitation method. X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), UV–Vis spectroscopy, and vibrating sample magnetometer (VSM) were used to investigate the structural, morphological, optical, and magnetic properties of Yb doped CuO:ZnO nanocomposites. The incorporation of Yb in CuO:ZnO nanocomposites leads to a notable shift of the characteristic XRD peaks of CuO and ZnO to lower angles, accompanied by an increase in the lattice parameters. UV–visible absorption spectroscopy shows an overall decrease in the optical band gap energy of ZnO as the Yb defect level increases. FE-SEM studies revealed the transformation of spherical structures into agglomerated non-spherical structures upon the introduction of Yb ions into CuO:ZnO nanocomposites. According to XPS data, the predominant valences of Yb-doped CuO:ZnO nanocomposites are Zn2+, Cu2+, and Yb3+. One noteworthy observation from the XPS results is that, in comparison to the intensity of O L or O ad peaks, the intensity of O V (Oxygen vacancy) defect peak increases when the Yb impurity concentration increases. Magnetic measurements demonstrated a diamagnetic order in pure ZnO, which converts to a ferromagnetic order with the incorporation of Yb defect states. The ferromagnetic properties of the Yb-doped CuO:ZnO nanocomposite can be ascribed to the exchange interaction of Yb3+ ions with defect states (Oxygen Vacancy) in ZnO and CuO. [ABSTRACT FROM AUTHOR]

For the first time, an investigation on the shape and material optimization for buckling behavior of functionally graded (FG) toroidal shells using differential evolution (DE) algorithm is presented in this paper. For buckling analysis, an analytical approach is used to derive governing equations, then combining with the Galerkin procedure to obtain the critical buckling load. In the optimization problem, the material distribution of functionally graded material is described by interpolated points whose coordinates of these interpolated points are located along the thickness direction of the toroidal shell using Hermite cubic functions. The design variables are volume fraction at the interpolated points. The DE algorithm is employed to find maximum critical buckling loads with ceramic volume fraction constraints. In the section of numerical results, the reliability of the current formulation is validated by several examples. Furthermore, a comprehensive examination of the influences of geometric and material parameters, etc., on the buckling behavior of the FG toroidal shells are performed. Besides, the study sets out to explore current optimal results to its effectiveness and robustness, in particular distributions, in order to examine its impact on critical buckling loads. • Material distribution optimization for functionally graded toroidal shells. • An analytical solution is used for buckling behavior of toroidal shells. • The toroidal shells are subjected to combined loadings. [ABSTRACT FROM AUTHOR]

The article discusses study on the analog of α-tocopherol from Livistona halongensis. It says that species Livistona halongensis was discovered in Ha Long Bay, Quang Ninh Province in Vietnam in June 2009. It states that during the phytochemical Investigation of the species, an α-tocopherol analog, 6-O-acetyl-2R,8-dimethyl-2-(4R,8R,11-trimethyltridecene- 12)chroman were isolated from the n-hexane extract of its roots and barks.

• Formulation of TMD-PSEH system attached to an undamped primary structure. • Extension of the fixed point theory to the TMD-PSEH system. • Close-form expression of optimal tuning, damping, and resistance ratios. • Insight into the power flow analysis. • Performance of the system along with attendant numerical simulations. A tuned mass damper with a piezoelectric stack energy harvester (TMD-PSEH) is a passive vibration control device for the dual purpose of absorbing vibration and harvesting energy. This paper develops the fixed point theory for the optimal design of a TMD-PSEH attached to an undamped primary structure under harmonic external excitation. It has been proven that the existence of two fixed points of the amplitude-frequency curve doest not depend on the damping of the primary structure. Based on the requirements for suppressing the vibration of the primary structure and enlarging the harvested power, the analytical expressions for the optimal tuning, damping, and resistance ratios are determined. It is found that the minimum damping ratio occurs in the vicinity of the electrical resistance ratio α = 1 for various values of the electromechanical coupling coefficient. Power flow analysis is carried out resulting in closed-form expressions of instantaneous and average powers. Numerical examinations of the system with the obtained optimal parameters are performed demonstrating a very good compatibility between theory and computation. In addition, the effect of damping in the primary structure is also investigated. It is shown that not only the vibration of the primary structure effectively reduces, but also a large amount of the harvested energy can be captured in the main resonance region. [ABSTRACT FROM AUTHOR]