Sharif Digital Repository

Phase field theory for fracture is developed at large strains with an emphasis on a correct introduction of surface stresses at nanoscale. This is achieved by multiplying the cohesion and gradient energies by the local ratio of the crack surface areas in the deformed and undeformed configurations and with the gradient energy in terms of the gradient of the order parameter in the reference configuration. This results in an expression for the surface stresses which is consistent with the sharp surface approach. Namely, the structural part of the Cauchy surface stress represents an isotropic biaxial tension, with the magnitude of a force per unit length equal to the surface energy. The surface... 

A thermodynamically-consistent phase field approach for crack propagation which includes the following novel features is presented. (1) Scale dependency was included by relating the length scale to the number of cohesive interatomic planes at the crack tip. Because of this, the developed theory is applicable from the atomistic to the macroscopic scales. (2) The surface stresses (tension) are introduced by employing some geometrical nonlinearities even in small strain theory. They produce multiple contributions to the Ginzburg-Landau equation for crack propagation. (3) Crack propagation in the region with compressive closing stresses is eliminated by employing a stress-state-dependent kinetic... 

Laser Powder Bed Fusion (LPBF) technology is a new trend in manufacturing complex geometric structures from metals. This technology allows producing topologically optimized parts for aerospace, medical and industrial sectors where a high performance-to-weight ratio is required. Commonly the feature size for such applications is higher than 300–400 microns. However, for several possible applications of LPBF technology, for example, microfluidic devices, stents for coronary vessels, porous filters, dentistry, etc., a significant increase in the resolution is required. This work is aimed to study the resolution factors of LPBF technology for the manufacturing of superelastic instruments for... 

Deep learning has successfully solved a wide range of tasks in 2D vision as a dominant AI technique. Recently, deep learning on 3D point clouds has become increasingly popular for addressing various tasks in this field. Despite remarkable achievements, deep learning algorithms are vulnerable to adversarial attacks. These attacks are imperceptible to the human eye, but can easily fool deep neural networks in the testing and deployment stage. To encourage future research, this survey summarizes the current progress on adversarial attack and defense techniques on point-cloud classification. This paper first introduces the principles and characteristics of adversarial attacks and summarizes and... 

Rice bran is one of the most important co-products in the rice milling. In this research, antioxidant activity of two Iranian rice bran varieties, Fajr and Tarem, extracted by three different solvents (methanol, ethanol and ethyl acetate) was evaluated. The order of antioxidant activity was evaluated by measurement of total phenolic content, antioxidant activity in linoleic acid system, reducing power and scavenging capacity by DPPH radical. The methanolic extract of Fajr rice bran showed a total phenolic content of 3.31 mg Gallic acid/gr rice bran and a DPPH free radical-scavenging activity of 93.91%, achieved at 50 mg/ml concentration, and a percent inhibition of linoleic acid peroxidation... 

Assuming that Pauli channels simulate the effect of optical fibers on polarization entangled photons we theoretically find the threshold distance beyond which such pairs loose their entanglement. From the current experimental data and by taking into account all other loss factors, like absorption, we give estimates for these threshold distances. © 2006 Elsevier B.V. All rights reserved  

The combined action of ultraviolet irradiation and microwave heating onto acetonitrile solution of [Re((Formula presented.))(CO)3(NCMe)]OTf ((Formula presented.) =phenantroline and neocuproine) afforded cis,trans-Re((Formula presented.))(CO)2(NCMe)2]+ acetonitrile derivatives. Substitution of relatively labile NCMe with a series of aromatic N-donor ligands (pyridine, pyrazine, 4,4’-bipyridine, N-methyl-4,4’-bipyridine) gave a novel family of the diimine cis,trans-[Re((Formula presented.))(CO)2(L)2]+ complexes. Photophysical studies of the obtained compounds in solution revealed unusually high absorption across the visible region and NIR phosphorescence with emission band maxima ranging from... 

In this paper, designing of the LQR controller and observer with intelligent tools for the triple inverted pendulum is investigated. Intelligent tools are considered as GA and GA-PSO optimization algorithms and fuzzy logic to qualify achieving LQR gains. The pendulum is swung up from the vertical position to the unstable position. The rules for the controlled swing up are heuristically achieved such that each swing results are controlled. The inverted pendulum and cart system are modeled and constructed their equation based on energy method. Also, the performances of the proposed fuzzy logic controller, GA and GA-PSO tuning LQR gains are investigated and compared. Simulation results show... 

An investigation into the mixed mode fracture of steel fiber reinforced concrete (SFRC) beams with one percent volume fraction of steel fiber is presented. A series of notched beams with different notch depths and locations are tested under three-point bending. The test results for apparent fracture toughness, crack trajectories, and fracture energy are presented. The crack paths for SFRC and plain concrete beams are compared. The apparent fracture toughness values were more scattered for SFRC than for plain concrete. The load-deflection curves were used to obtain the fracture energy. To this end, two methods were utilized for center notched beams, and the results were comparable to each... 

This paper discusses the studies carried out for the optimal production of enzyme l-asparaginase (l-asparagine amidohydrolase, EC 3.5.1.1) from Escherichia coli (ATCC 11303). It was found that inoculum age of 18 h and inoculum size of 10% were the most favorable operating conditions for enzyme production. Lactose, yeast extract and KH 2PO 4 were found to be the best carbon, nitrogen and ion sources, respectively. Statistical method was used to survey how various medium conditions affect the enzyme production. By response surface methodology, the values of lactose, tryptone, yeast extract, KH 2PO 4 and l-asparagine concentration were investigated to obtain the maximum enzyme activity. The... 

The paper presents a computational model and the corresponding algorithm for estimating the arc energy distribution to conductive, convective and radiative heat transfer in an electric arc furnace (EAF). The proposed algorithm uses channel arc model (CAM) in order to compute the distribution of the arc energy through empirical equations (to approximate arc radius), ideal gas law (to approximate arc density) and results of magneto-hydro-dynamic (MHD) models (to approximate arc pressure, temperature and velocity). Results obtained using the proposed algorithm are comparable with other similar studies; however, in contrast to other arc-energy distribution models, this model requires only two... 

In this paper, a conceptual study and quantification of using a thermophotovoltaic system (TPV) to convert incident radiation on furnace panels to electrical energy is presented. In typical electric arc furnaces (EAF), a considerable amount of energy is wasted during the melting process, that is, steel enthalpy, off-gas extraction, vessel cooling, slag enthalpy, and others. Although a remarkable share of the energy is wasted in circulating water, the contained exergy is simply too low to be considered for heat recovery (under 0.5% of input exergy) in comparison to energy content of the extracted gasses and slag. In the performed study, a TPV power output is calculated as a function of arc... 

The paper presents a conceptual study on modification of the electric arc furnace (EAF) slag doors in order to allow removal of the excess slag from the EAF. The idea behind additional slag doors is to allow deslagging of the bath in certain unfavorable cases when the slag height is too great. Slags which exceed the optimal height cause unnecessary refractory corrosion and additional energy losses. The study proposes symmetric slag doors comprised of two hatches, i.e. upper and lower. The upper hatch is intended to decrease the slag height to the optimal level, while the lower hatch can be used to completely deslag the EAF at tapping. In this manner, tilting of the EAF is not necessary. A... 

The paper presents a comprehensive electric arc furnace (EAF) model, developed for simulation and model-based control of the EAF processes. The model consists of three sub models, i.e., (i) arc model; (ii) chemical and slag model; and (iii) heat-transfer model. Arc model predicts the amount of energy dissipated from the arcs using arc currents and arc lengths; chemical and slag model calculates chemical energy and changes of elements/compounds, slag height and slag quality; while the heat-transfer model uses calculations of the other two models in order to establish a reference energy system (RES) for each zone in the EAF due to the variations in arc length, slag height, and bath height. The... 

This paper presents an electric arc furnace (EAF) optimization framework intended to define optimal control profiles for the EAF, in order to increase its efficiency and thus reduce the energy consumption. The framework aims to minimize controllable losses and to maximize energy transfer to the bath and, consequently, minimize the operational costs. This is achieved through improved actuation of the EAF inputs, i.e., transformer power, oxygen lancing, and carbon addition. To achieve maximal energy transfer to the bath and to reduce the heat losses from the arcs, proper properties of the slag, such as foaminess and basicity, are a subject of considerable attention. The framework is designed... 

In this work, an expression for the free volume Gibbs energy model based on the local composition concept (LCC) has been proposed in correlating the solubility, the partitioning and the surface tension of β-lactam, tetracycline, fluoroquinolone and chloramphenicol antibiotic groups in water, alcohol, ketone, trihalomethane, ether and ester solvent groups. Similar to the LCC models the proposed model has two combinatorial and residual terms. The extended Guggenheim model is used as combinatorial term and a new local composition-based model, which is the extended local area fraction NRTL-NRF model, is proposed for the residual term. The results obtained from the proposed model have been... 

This paper presents synthesis and photophysical investigation of a very rare type of the ReI diimine complexes, [Re(diimine)(CO)3(OPR3)]+, R = Ph, Cy; diimine – phenanthroline and neocuproine, containing monodentate (unsupported) phosphine oxide ligands. The obtained compounds have been structurally characterized in solid phase by using XRD crystallography, which revealed unusual distortions in the pseudo octahedral rhenium environment, which may be ascribed to intramolecular interligand (phosphine oxide – diimine) interaction rather than to crystal packing effect. Optimization of the ground state structure of these molecules with the DFT method also confirmed intramolecular origin of the... 

Carbon nanotubes (CNTs) were dispersed without any solvent in poly(tetramethylene ether glycol), (PTMEG) well above its melting point by ultrasonication in the pulse mode and different times. The polyol/CNT suspensions were used to prepare in situ polymerized thermoplastic polyurethane TPU/CNT nanocomposites with the CNT concentration of ∼ 0.05 vol%, much below the CNT geometrical percolation threshold calculated at 0.43 vol%. Results of rotational rheological measurements and ultraviolet-visible (UV-Vis) spectroscopy analysis revealed improvement in the nanoscale CNT dispersion with sonication time. Moreover, the optical microscopic images and sedimentation behavior for these samples... 

The phase field approach (PFA) for the interaction of fracture and martensitic phase transformation (PT) is developed, which includes the change in surface energy during PT and the effect of unexplored scale parameters proportional to the ratio of the widths of the crack surface and the phase interface, both at the nanometer scale. The variation of these two parameters causes unexpected qualitative and quantitative effects: shift of PT away from the crack tip, "wetting" of the crack surface by martensite, change in the structure and geometry of the transformed region, crack trajectory, and process of interfacial damage evolution, as well as transformation toughening. The results suggest... 

Nitinol shape memory alloy is a biocompatible material that is suitable for biomedical applications due to its superelasticity, shape memory effect, good corrosion and fatigue resistance, and sound damping properties. With the selective laser melting (SLM) additive manufacturing process, it is possible to produce customized NiTi implants in the form of porous metamaterials with complex geometries. This paper presents a review of modeling, production, and application of NiTi implants. First, the fundamentals of shape memory alloys and the SLM process are summarized. Then, the effects of the SLM process on the transformation temperatures and the impacts of Heat treatments on these temperatures...