Sharif Digital Repository

The growth of slant cracks by fretting fatigue of a half plane in contact with a flat rounded pad was studied. The mode I and mode II stress intensity factors for cracks of various lengths and directions were calculated using the semi-analytical method of the distribution of dislocations, and their cumulative effect on the crack growth was investigated using the strain energy density criterion. The results showed dominance of mode I fracture on crack growth, and based on the observation of strain energy density factor versus crack orientation, the results also suggest that depending on the crack length, the most critical orientations of cracks are at 0° to 20° outward the contact zone. Good... 

In this paper, the effect of geometrical parameters on the fretting fatigue of a half-plane in contact with a flat and rounded pad is studied. This is accomplished by calculating and comparing the stress states and stress intensity factors of fretting cracks for a number of pad geometries. The pad geometry is represented by the radius of its rounded corners and the width of its central flat part. The distribution of dislocation method is employed to calculate the stress intensity factors of fretting induced cracks of different lengths for different values of geometrical parameters. The results of this study can be insightful for improving the geometrical design of an aero-engine compressor... 

To improve our understanding of the chemistry of actinide complexes and to spur their development in the field of actinide markers, two new uranium complexes were synthesized using 8-hydroxyquinoline and 5,7-dichloro-8-hydroxyquinoline. The prepared complexes were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, ultraviolet− visible spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The impact of the electron-withdrawing group of the ligand on the photoluminescence spectra of the complexes in solution and in the solid state was scrutinized. The bandgap of the complexes was calculated using the density functional theory (DFT) method to... 

ZnO nanostructures in the shape of particle, rods, flower-like and micro-sphere were synthesized via facile hydrothermal methods and the effect of morphology on the decolorization of CI Acid Red 27 solution under direct irradiation of sunlight was investigated. XRD patterns showed that the synthesized nanostructures have Wurtzite-type hexagonal structure with high crystallinity and crystallite size in the range of 67-100 nm. UV-vis absorption spectra indicated that the ZnO nanorods have higher visible light harvesting as compared to the other morphologies. The decolorization obeys the first order kinetics rate with the kinetics constant of 4.5-19.5 × 10-3 min-1 dependent on the ZnO... 

Self-assembled dandelion-like hydroxyapatite (HAp) nanostructures were successfully synthesized via a mild template-free hydrothermal process, using ethylenediaminetetraacetic acid (EDTA) as the surfactant. The obtained dandelion-like HAp nanostructures were between 5 and 8 μm in diameter and were composed of radially oriented nanorods with an average diameter of about 200 nm. The X-ray diffraction analysis and Fourier transform infrared spectroscopy were used to characterize the crystalline phase and purity of the synthesized nanostructures. The Brunauer-Emmett-Teller surface area of the dandelion-like nanostructures was measured to be about 39 m2/g. The results of thermal analysis revealed... 

Spin lattice relaxation rate is investigated for 3D tilted cone Weyl semimetals (TCWSMs). The nuclear spin relaxation rate is presented as a function of temperature and tilt parameter. We find that the relaxation rate behaves as (1-ζ2)-α with α ≈ 9 where 0 ζ < 1 is the tilt parameter. We demonstrate that such a strong enhancement for ζ ≲ 1 that gives rise to very fast relaxation rates, is contributed by a new hyperfine interactions arising from the tilt itself. This can be attributed to the combination of anisotropy of the Fermi surface and an additional part related to the structure of the spacetime: extracting an effective density of states (DOS) ρ from the Korringa relation, we show that... 

Rosette-like boehmite nanostructures were prepared successfully via a simple hydrothermal process. The obtained material was characterized with X-ray powder diffractometry (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Using Scherrer formula, the average crystallite size of the obtained boehmite rosettes was measured to be about 8 nm. It was shown that boehmite nanopetals with average width of about 41 nm determined by TEM, were formed during the hydrothermal process and then self assembled due to weak hydrogen bonds to fabricate boehmite rosettes. The specific surface area of the obtained rosette-like nanostructures was calculated through BET... 

A method is described for the simultaneous generation of two or more wavelengths from a dye laser pumped by a copper vapor laser (CVL). The dye laser cavity consists of one dye cell, two pairs of gratings and tuning mirrors, and one beam-splitting Thompson prism and an output mirror. This configuration allows decomposition of the dye laser beams into two grazing incidence cavities. These two emissions can have the same or different linewidth. The two collinear output beams are independently tunable over the entire gain profile of the dye, with mutually orthogonal polarizations. The gain competition effect is observed to be low  

Efficient sunlight harvesting is of great significance for environmental remediation through photocatalysis. Herein, very small (20 nm) upconverter SrF2:Yb,Tm@CaF2:Yb@Fluorine-doped TiO2heteronanoparticles (denoted as UCNPs@TiO2) with strong UV-blue emission and broadband photocatalytic performance were prepared via a facile three-step hydrothermal method for the first time. The SrF2:Yb,Tm upconverter nanoparticles (NPs) were produced as the light-emitting core, epitaxially grown CaF2:Yb as the middle shell to enhance the upconversion luminescence output and TiO2as the photocatalyst outermost layer. Superior photocatalytic functioning of UCNPs@TiO2was affirmed through methylene blue (MB)... 

Three-dimensional (3D) bundles of self-assembled lanthanum hydroxide nanorods with average crystallite size of about 20 nm were fabricated via a facile and rapid microwave-assisted chemical route. The obtained material was characterized with X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations. The obtained nanorods have average diameter of about 115 nm and average length of about 730 nm. Self-assembly of primary La(OH)3 nanoparticles and their subsequent anisotropic growth along 〈2 0 0〉 direction, was proposed to be the mechanism for the formation of 3D bundles of nanorods, using TEM images. The thermal behavior of the... 

Using multiple antennas at the transmit and receive sides of a passive radar brings both the benefits of MIMO radar and passive radar. However one of the obstacles arisen in such configuration is the receive antennas placement in proper positions so that the radar performance is improved. Here we just consider the case of positioning one receiver among multiple illuminators of opportunity. Indeed it is a start for the solution of optimizing the geometry of the multiple receivers in a passive radar  

SbCl3 supported on montmorillonite K-10 is an efficient catalyst for the ring opening of epoxides with aromatic amines under solvent-free conditions and microwave irradiation to give the corresponding b-amino alcohols in high yields with high regioselectivity  

In this paper, we consider an integrated sensing and communication (ISAC) system with wireless power transfer (WPT) where an unmanned aerial vehicle (UAV)-based radar serves a group of energy-limited communication users in addition to its sensing functionality. In this architecture, the radar senses the environment in phase 1 (namely sensing phase) and mean-while, the communications users (nodes) harvest and store the energy from the radar transmit signal. The stored energy is then used for information transmission from the nodes to UAV in phase 2, i.e., uplink phase. Performance of the radar system depends on the transmit signal as well as the receive filter; the energy of the transmit... 

One of the important obstacles in MIMO (Multiple Input Multiple Output) radars is the issue of designing proper transmit signals. Indeed, the capability of signal design is a significant advantage in MIMO radars, through which, the system can achieve much better performance. Many different aspects of this performance improvement have been considered yet, and the transmit signals have been designed to attain such goal, e.g., getting higher SNR or better detector's performance at the receiver. However, an important tool for evaluating the radar's performance is its ambiguity function. In this paper, we consider the problem of transmit signal design, in order to optimize the ambiguity function... 

Two gains play key roles in recently developed MIMO wireless communication systems: "spatial diversity" gain and "spatial multiplexing" gain. The diversity gain refers to the capability to decrease the error rate of the MIMO channel, while the multiplexing gain implicitly refers to the amount of increase in the capacity of the MIMO channel. It has been shown that there is a fundamental tradeoff between these two types of gains, meaning interplay between increasing reliability (via an increase in the diversity gain) and increasing data rate (via an increase in the multiplexing gain). On the other hand, recently, MIMO radars have attracted much attention for their superior ability to enhance... 

It is a well known fact that using multiple antennas at transmit and receive sides improves the detection performance. However, in such multiple-input multiple-output (MIMO) configuration, proper positioning of transmitters and receivers is a big challenge that can have significant influence on the performance of the overall system. In addition, determining the power of each transmitter under a total power constraint is a problem that should be solved in order to enhance the performance and coverage of such a system. In this paper, we design the Neyman-Pearson detector under the Rayleigh scatter model and use it to introduce a criterion for the antenna placement at both transmit and receive...