A simplified solution for piled-raft foundation analysis by using the two-phase approach

In common practice, the pile–soil–raft interaction still remains a challenging problem in the analysis of piled-raft foundations. In the present study, a simplified analytical approach is introduced to analyze a vertically-loaded piled-raft foundation by using a developed homogenization technique called the two-phase approach. In spite of classical and simplified methods in the literature, the proposed method considers the pile–soil interaction. The other major advantage is the ability to predict the axial pile load along the pile length. The problem is solved in the domain of elasticity and simple closed-form solutions are presented for the prediction of the settlement and the pile load sharing of a piled raft as well as the pile's axial force distribution along its length. The applicability of the proposed method is validated by considering case studies and field measurements. A comparison of the results indicates that the method can be utilized safely in a proper, quick, and effective manner with the least computational effort in comparison with sophisticated numerical approaches. The raft settlement can be accurately predicted while the pile load sharing might be over/under estimated. A parametric study is also carried out to investigate the response of piled-raft foundations including the influence of the parameters of the soil and the geometric characteristics of the piles.     

Synthesis of 7-hydroxy-6H-benzo[c]chromen-6-ones based on a ‘[3+3] cyclization/domino retro-Michael-aldol-lactonization’ strategy

The TiCl₄-mediated [3+3] cyclization of 2,4-bis(trimethylsilyloxy)penta-1,3-diene with 3-silyloxyalk-2-en-1-ones afforded 2-acetylphenols, which were transformed into functionalized chromones. The Me₃SiOTf-mediated condensation of the latter with 1,3-bis(silyl enol ethers) and subsequent domino ‘retro-Michael-aldol-lactonization’ reaction afforded 7-hydroxy-6H-benzo[c]chromen-6-ones.     

On the delamination and crack formation in a thin wall fabricated using laser solid freeform fabrication process: An experimental–numerical investigation

Parts fabricated using laser solid freeform fabrication (LSFF) are subject to thermal stresses due to the layer-by-layer material deposition and the temperature distribution characteristic throughout the process domain. The thermal stress patterns and intensity contribute significantly to potential delamination and crack formation. In this paper, the temperature distribution and stress field induced during the multilayer LSFF process, and their correlation with delamination and crack formation are studied. This is performed by a numerical and experimental investigation in the fabrication of a thin wall of 304L stainless steel. For time-dependent predictions on the locations of maximum temperatures and thermal stresses and their patterns, a three-dimensional (3D) transient finite element model is employed to simulate the process, including the geometry of the deposited materials as well as coupled temperature and stress distributions across the process domain. The experimental results are used to verify the numerical results as well as to investigate the correlation between the numerical results and micro-crack formations across the fabricated parts. The experiments are conducted with the same process parameters used in the numerical analyses using a 1 kW Nd:YAG pulsed laser. The trend of numerical and experimental results reveals that by preheating the substrate prior to the fabrication process, it is possible to substantially reduce the micro-cracks formed across the part. To demonstrate the feasibility of preheating on the reduction of micro-cracks, several simulations and experiments are performed in which a crack-free result is obtained when the substrate is preheated to 800 K. For this case, 22% reduction in thermal stresses is obtained throughout the process domain.     

Free-volume changes at nanoscale in doped polyacrylic acid studied by positron annihilation spectroscopy

Polyacrylic acid (PAA) doped with carbon black (CB), chromium oxide (Cr₂O₃) and cupferron with different wt% (0.25%, 0.50%, 0.75%, and 1%) was studied using positron annihilation lifetime (PAL) technique and Doppler broadening of annihilation radiation (DBAR). Ortho-positronium lifetime components (τ₃ and I₃) were used to estimate the nanoscale free-volume hole sizes (V_f) and its fractions (f). It was found that the hole size V_f and its fractions f as well as S-parameters decreased at high value of doping concentration due to dopants-polymer formation. These results are supported by a significant narrowing in the nanoscale free-volume hole size distributions.

The correlation between positron annihilation parameters and electric conductivity are discussed.     

Numerical investigation of corner angle and wing number effects on fluid flow characteristics of a turbulent stellar jet

In this research the fluid dynamics characteristics of a stellar turbulent jet flow is studied numerically and the results of three dimensional jet issued from a stellar nozzle are presented. A numerical method based on control volume approach with collocated grid arrangement is employed. The turbulent stresses are approximated using k–ε and k–ω models with four different inlet conditions. The velocity field is presented and the rate of decay at jet centerline is noted. Special attention is drawn on the influence of corner angle and number of wings on mixing in stellar cross section jets. Stellar jets with three; four and five wings and 15–65° corner angles are studied. Also the effect of Reynolds number (based on hydraulic diameter) as well as the inflow conditions on the evolution of the stellar jet is studied. The Numerical results show that the jet entrains more with corner angle 65° and five wings number. The jet is close to a converged state for high Reynolds numbers. Also the influence of the inflow conditions on the jet characteristics is so strong.     

How Does Tempering Affect the Local and Global Properties of Fractional Brownian Motion?

Journal of Theoretical Probability - The present paper investigates the effects of tempering the power law kernel of the moving average representation of a fractional Brownian motion (fBm) on some...     

二氧化钛纳米粒子催化合成Hantzsch酯和多氢喹啉衍生物(英文)

1,4-Dihydropyridine and polyhydroquinoline derivatives have been prepared efficiently in a one-pot synthesis via Hantzsch condensation using nanosized titanium dioxide as a heterogeneous catalyst.The present methodology offers several advantages such as excellent yields,short reaction times (30-120 min),environmentally benign,and mild reaction conditions.The catalyst can be readily separated from the reaction products and recovered in excellent purity for direct reuse.     

Tris(tetraceno)triquinacenes: Synthesis and Photophysical Properties of Threefold Linearly Extended Tribenzotriquinacenes

The linear extension of the rigid, C_3v‐symmetrical carbon framework of tribenzotriquinacene (TBTQ) along its three wings is reported. The key step of the extension procedure consists of a Diels–Alder reaction of three ortho‐quinodimethane units generated in situ at the triquinacene core. The use of 1,4‐naphthoquinone provides a facile and particularly efficient access to tris(tetraceno)‐annellated triquinacenes. The steady‐state photophysical properties of these new oligotetracenes bearing three mutually orthogonal chomophores are determined and analyzed by DFT calculations.     

Investigation of keto–enol tautomerism in tetraketonate ligands

Molecular structure, vibration analysis, and natural bond orbital study of four derivatives of tetraketonate ligand were investigated in three different solvents using density functional theory B3LYP/6-31++G** method. The solution phase studies were carried out using an Onsager model. According to the obtained results the enol form of the ligands is more stable than keto form, even in solvents with high dielectric constant such as DMSO. This result is also confirmed experimentally using NMR studies for tetraacetylethane. Their stabilities are due to the presence of hydrogen bonding in the enol tautomers. A comparison among different possible enol forms of the substituted tetraketonate ligands demonstrated that three factors control the stability of the compounds as hydrogen bonding, steric hindrance, and charge distribution. The effectiveness of each of these factors on the stability of ligands depends on the nature of the substituent attached to the ligand.     

Exact three-dimensional interface stress and electrode-effect analysis of multilayer piezoelectric transducers under torsion

In this paper, exact three-dimensional analysis for torsion of multilayer piezoelectric transducers is presented to highlight the remarkable effects of electrode and size effects on interface stresses and deformation. A generalized formulation is introduced for torsion of an arbitrarily layered cross section. In order to reach an advanced and better device, multilayer piezoelectric materials with different properties are formulated while axis of torsion and the polarization axes of each layer make different orientations with respect to each other. An exact formulation for n-layer piezoelectric device with rectangular cross section is presented to compensate considerable deviation of previous studies’ results from exact solution due to the assumption of linear distribution for the electric potential. In order to improve the performance of the transducers, being utilized in industry, several case studies are presented in order to investigate the influence of different parameters, e.g. thickness and material properties of electrodes over shear and peel stresses. Besides, a correction factor is introduced to completely compensate the effect of ignoring electrodes.