Restricting the covariant gravitational phase spaces to the manifold of parametrized families of solutions, the mass, angular momenta, entropies, and electric charges can be calculated by a single ...and simple method. In this method, which has been called the “solution phase space method,” conserved charges are unambiguous and regular. Moreover, assuming the generators of the charges to be exact symmetries, entropies and other conserved charges can be calculated on almost arbitrary surfaces, not necessarily horizons or asymptotics. Hence, the first law of thermodynamics would be a local identity relating the exact symmetries to which the mass, angular momentum, electric charge, and entropy are attributed. In this paper, we apply this powerful method to the
f
(
R
) gravitational theories accompanied by the terms quadratic in the Riemann and Ricci tensors. Furthermore, conserved charges and the first law of thermodynamics for some of their black hole solutions are exemplified. The examples include warped AdS
3
, charged static BTZ, and 3-dimensional
z
=
3
Lifshitz black holes.
α-Graphyne nanotubes as quasi-one-dimensional structures could have interesting electronic and optical properties in comparison to graphene. In this work, we have calculated electronic band ...structure, density of states and optical absorption spectrum of some single-wall zigzag α-graphyne nanotubes by using a simple tight-binding method in a reduced lattice. The results show that two-thirds of nanotubes have semi-conductive behavior accompanied with an oscillatory decreasing band gap, while the rest presented metallic characteristics. The outcome reveals the optical gap fluctuates per different incremental nanotube diameters; in addition, the highest amount of optical absorption occurs when emission energies exceed 4 eV.
This paper presents the out-of-phase thermo-mechanical stress analysis of thermal barrier coating (TBC) system in real working conditions used as thermal barrier in diesel engine cylinder heads. The ...coating system in this research comprises 350μm zirconium oxide top coat (TC) and 150μm metallic bond coat (BC). These layers were deposited on the substrate, aluminum A356 alloy, by the aid of air plasma spray (APS) method. Afterwards, the specimen was subjected to thermo-mechanical fatigue (TMF) loadings. Based on the experimental conditions, FE simulations were performed by both time-independent and time-dependent substrate material properties in ABAQUS software. Simulation results related to heat transfer analysis demonstrate only about 10.5% comparative error compared to experimental results. Moreover, defining time-dependent properties, which were obtained from two-layer visco-plastic model, yields results with 15% less comparative error in comparison to the results based on time-independent material properties. In addition, the effects of roughness and porosity in coating layers and substrate were studied on three different models by the aid of a scanning electron microscopy image. Obtained results based on real geometry illustrate that consideration of porosity in TC layer has an effective role in the stress distribution of this layer. However, BC layer stress distribution is much more dependent on interface morphology.
•Study of out-of-phase thermo-mechanical stress analysis in TBC based on the experiment•Consideration of the real geometry (roughness and porosity) on stress distribution•Effect of using time-dependent material properties for substrate on stress results•Accumulation of axial stresses in all layers and its effect on total axial force•Comparison of both heat transfer and stress results (simulation and experiment)
In this research, a finite element model was developed in order to simulate the two-step residual stress distribution of a thermal barrier coating system, considered to be used in diesel engine ...cylinder head, with a real roughness and real porosity. Two steps including the bond coat and the top coat deposition processes were taken into account. The real geometry of coating layers, including the roughness and the porosity, was also considered based on a scanning electron microscopy image. Then, effects of the convective heat transfer coefficient and initial substrate and substrate/bond coat preheating temperatures on the residual stress were studied. Obtained results illustrate that the residual stress, regarding the two steps of coating processes, are different, particularly in the substrate. Numerical results indicate that while the convective heat transfer coefficient in BC deposition had no striking effect, it was an influential factor in the residual stress distribution when TC was deposited. Moreover, preheating temperature for depositions of the bond coat layer and the top coat layer has a pivotal role in stress distribution of all layers. In addition, consideration of the porosity in the top coat layer causes remarkable decrease in axial stress distribution in substrate and much more local stress concentrations in TC layer compared to those of BC layer due to larger and more irregular pores.
Malformations of the maxillofacial region has disturbing psychosocial effects and causes enormous socioeconomic concerns. The management of maxillofacial defects caused by congenital anomalies, ...trauma, osteoporotic fractures, periodontitis, or cancer treatment is challenging for oral and maxillofacial surgeons. Numerous approaches have been recommended for the managing of these deficiencies. The traditional treatment for maxillofacial defects or their repair is an intricate process by autologous bone grafts from the scapula, ribs, fibula, or iliac crest origins. Regenerative medicine is well thought-out as a perfect substitute approach for autologous bone grafts to renovate bone deficiencies. The use of stem cells has improved results and offered a technique to reconstruct craniofacial bone defects. The field of tissue engineering for the regeneration of maxillofacial needs integration of biochemical and biomaterial engineering aspects with cell transplantation to generate better-quality biomimetic scaffolds, prevascularize three-dimensional (3D) tissue structures, and engineer the composite interface of diverse facial tissues. In this review, we have discussed the application of different adult stem cells to repair oral and maxillofacial defects in animal models and clinical trials.
•Gas phase velocity is the key parameter in controlling the mass transfer rate.•A very long-term study of 35 days on the membranes was performed.•Liquid phase velocity has a marginal effect on the ...mass transfer rate.
In this study, diethylene glycol (DEG) as an absorbent was used for gas dehydration. For this purpose, hollow fiber membrane contactor was fabricated from polyvinyl chloride. The effect of surface modification with polydimethylsiloxane in the presence of calcium carbonate nanoparticles, relative humidity percentage of inlet air, variation in the gas and liquid flow rates in a dehydration process were investigated. The surface modification of the membranes increased the contact angle from 64° to 101° and a liquid entry pressure of as high as 7bar was achieved. Moreover, increasing the gas flow rate led to a significant enhancement in absorption performance. Conversely, it was observed that the liquid flow rate had marginal effect on the mass transfer efficiency and flux i.e. RM+L/RM+G=0.001–0.01. This revealed that the mass transfer resistance was not controlled by the liquid phase. Although higher fluxes were observed for the unmodified membrane contactor, the membrane modified with polydimethylsiloxane and calcium carbonate nanoparticles (i.e. M0.5-1) was more effective compared to the neat membrane (M0) in a 35-day long-term performance test i.e. ηM0.5-1≈0.12 versus ηM0=1.0. The results show that the applied technique for fabricating the hollow fiber membrane contactor can be a promising technique in gas conditioning.
Band structure of the carbon doped zigzag boron nitride nanotubes (BNNTs) is calculated by a simple tight-binding model. It was found that the doping effect of B-substituted and N-substituted BNNT is ...different and carbon substitution for either boron or nitrogen in BNNTs reduces the band gap. Investigations show the dependence of band gap to the axial magnetic and transverse electric fields for C-doped BNNTs. The applied high electric field causes transition from semiconductor to conductor in C-doped BNNTs. The band gap of C-doped BNNTs oscillates as a function of magnetic flux with period ∅°in the magnetic fields. Influence of C-doping on the absorption spectrum is also discussed in this paper.
In this study, the stress relaxation has been measured experimentally and has been also calculated numerically by the finite element method in the A356·0 aluminium-silicon-magnesium alloy, under ...out-of-phase thermomechanical cyclic loadings. To get this objective, strain based thermomechanical fatigue tests were performed on cylindrical specimens, at an out-of-phase condition. In this loading condition, when the temperature was maximum, the mechanical strain was compressive and vice versa. These fatigue experiments were repeated at various dwell times, in which the temperature was held at the maximum temperature. This hold time was considered as 5, 30, 60 and 180 s and then the stress relaxation was measured during the mid-life cycle of each test. Besides, the finite element analysis was also conducted on the material to simulate the stress relaxation numerically. A two-layer visco-plastic model was applied to simulate the high temperature cyclic behavior of the material. Finite element results showed a good agreement with experimental results, which were obtained from thermomechanical fatigue tests on the A356·0 aluminium alloy. The two-layer visco-plastic model could properly predict the stress relaxation at elevated temperatures, during various dwell times.
The study investigated the stomach content of Sillago sihama in Hormuzgan Province waters located in the northern Persian Gulf from October 2009 to March 2010. The stomach analysis was carried out ...using frequency of occurrence and numeric methods. Diatoms, blue- green algae and dinoflagellates constituted main food of plant origin. Diatoms were found to be the most preferable food of plant origin where it occurred in more than 60.8% of food item by number and 59.5% by occurrence. Crustacean including crabs and their larvae, shrimps, copepods, eggs and larval forms comprised the maximum part of the food of animal origin. It was concluded that Sillago sihama in the Coastal waters of Hormuzgan Province is planktonivorous and feeding on a wide range of food of planktonic and benthic organisms.
Characterization of preferential flow in soils through normal water tracer studies are, in most cases, inconclusive because of the inability of most solute sampling devices to detect the spatial ...pattern of preferential flow pathways. In this study, a number of field-plot experiments were performed to provide direct observation of the preferential flow of water and solutes by adding soluble dye to stain the flow pathways. In addition to characterizing the spatial structure of preferential flow pathways, the dye trace patterns were used to investigate the interactive role of soil structure and irrigation methods on the preferential flow patterns of water and solutes. A narrow pulse of an anionic water-soluble dye, Acid-Red 1, was applied to the surface of a number of 1.5 by 1.5 m field plots, some of which had the top layer completely disturbed to the depth of 30 to 40 cm. The distribution patterns of the dye in these plots were examined after the plots received 100 mm of irrigation water, under either ponding or daily sprinkler irrigation. The observed vertical and horizontal distribution patterns of the water-soluble dye clearly indicated the preferential flow patterns for each experimental condition. These include vertical fingering of dye traces 5 to 20 cm wide, which extended more than twice as deep as the mean displacement of the dye, as well as isolated patches of dye indicating lateral flow
PDF
