جستجوی مقالات مرتبط با کلیدواژه « Growth » در نشریات گروه « مکانیک »

The present study examined the pool boiling process in a specific geometry by designing, constructing a laboratory complex and Providing Empirical Relations. Investigation of pool boiling process, electrical resistance, critical heat flux, heat transfer coefficient, bubble growth and departure, bubble growth frequency, and nucleation site density by applying heat flux to critical heat flux was carried out on wire mesh element in deionized water at different temperatures. According to the results, increasing the size of mesh and fluid temperature decreased the critical heat flux. In the case of a wire mesh with a constant size of mesh, a fluid with a constant temperature, and the use of heat flux values less than the critical heat flux, the wire temperature increased, but it decreased in the case of increasing the size of mesh, a fluid with a constant temperature and applying critical heat flux values. In the case of a constant size of mesh, the heat transfer coefficient was constant by increasing fluid temperature at values of heat flux less than the critical heat flux, but the heat transfer coefficient was increased with increasing values of heat flux less than the critical heat flux and decreased at critical heat flux values. By increasing 4 times the mesh size in the fluid at 30, 70 and 100°C in the critical heat flux, the heat transfer coefficient decreases by 0.7%. The maximum bubble growth frequency is related to the 0.5 mm wire mesh in 100°C fluid with 0.0763 bubbles per millisecond.

Heart failure is one of the cardiovascular diseases that causes changes in the structure of the heart and reduces the output of the heart. This disease can be divided into two categories: diastolic and systolic heart failure. In diastolic heart failure, the thickness of the ventricular walls increased and is associated with concentric hypertrophy. In this study, concentric hypertrophy is considered to be caused by pressure overload, as a result of which, the number of sarcomeres increases in parallel, and as a result, causes a relative increase in the transverse area of the cardiomyocytes. Continuum equations of concentric hypertrophy by using an idealized biventricular geometry have been implemented in COMSOL Multiphysics software, the approach presented for implementing the equations is completely new and has fundamental advantages over the implementation of the previous approach, and does not require coding and can be easily implemented in a finite element software. The results of the simulation showed that the thickness of the ventricular walls increases and the volume of the ventricular chambers decreases. The mentioned results are consistent with the clinical observations of the disease and shows that computational modeling can be used as a powerful tool to increase specialist’s knowledge of diseases that have a high mortality rate.

The present study examined the pool boiling process in a specific geometry by designing and constructing a laboratory complex. Investigation of pool boiling process, electrical resistance, critical heat flux, heat transfer coefficient, bubble growth and departure, bubble growth frequency, and nucleation site density by applying heat flux to critical heat flux was carried out on a ring wire in deionized water at different temperatures. According to the results, increasing the number of rings and fluid temperature decreased the critical heat flux. In the case of a ring wire with a constant number of rings, a fluid with a constant temperature, and the use of heat flux values less than the critical heat flux, the wire temperature increased, but it decreased in the case of increasing the number of rings, a fluid with a constant temperature and applying critical heat flux values. In a ring wire with a constant number of rings, the heat transfer coefficient was constant by increasing fluid temperature at values of heat flux less than the critical heat flux, but the heat transfer coefficient decreased at critical heat flux values. The diameters of the produced bubbles were enhanced by increasing heat flux and they separated from the rings when combined. At the beginning of the reddening of the ring wire, a critical heat flux occurred, and considering 110% of the time required for the critical heat flux, the images of the state of the ring wire after the critical heat flux are presented.

In the present study, the dynamics associated with single bubble growth and its detachment has been studied using passive acoustic emission and high frame rate imaging methods. Synchronization of imaging with acoustic data acquisition demonstrated the functionality of the acoustic emission method in studying the dynamics of bubble growth and detachment. The investigations showed that the maximum amplitude of the oscillations in the time series of the acoustic emission signal occurs shortly before the bubble detaches. Instantly the rate of bubble volume rise is decelerating. in accordance with the dominant frequency of the acoustic emission wave that arises at the same time with the jump in acoustic time series, the bubble size based on the Minnaert equation with the corrected coefficients is estimated to be only 1.37% different from the results of image processing. According to the sequence of images recorded from the bubble growth frames, the ratio of the vertical and horizontal axis lengths of the bubble is continually changing during the bubble growth period and eventually, the bubble detaches from the orifice when the ratio approaches 1. Although by detachment, the bubble does not have a spherical shape due to the pressure forces.

Living organisms have evolved in the presence of constant gravity (1g) on Earth and their growth is related to rate of ribosome, protein biosynthesis, and regulation of cell cycle phases. Microgravity does not have the same effects on different phases of cell cycle such that activity of some phases is increased. It changes the number of cell cycles per time. In the cell growth process, rate of ribosome biosynthesis is decreased under simulated microgravity and a large variation is observed in abundance of nucleolar proteins (Nucleolin and Fibrillarin). Under normal conditions, growth and cell division are coupled, and microgravity uncouples these processes. The study of plant cellular response can help improvement of biological knowledge and preparation of life support systems in space.

LED light spectrums are the proper light source for plant research in the International Space Station and the life support system. In the present study, effects of different light spectrums on some growth parameters, and antioxidant activity were investigated in Anthemis gilanica. Seedlings irrigated with 1/2 Hougland solution under different light spectrums including white, red-blue and deep red. Seedlings were harvested for physiological and biochemical analyzes after 4 weeks. Results showed the fresh and dry weight, relative water content and root length increased under the red-blue light spectrum comparing to other spectrums. Hydrogen peroxide level didn't significantly change under different light spectrums. Seedlings treated with white spectrum showed the highest DPPH scavenging activity. Also, seedlings treated with deep red spectrum showed the maximum shoot length. It seems that decrease of growth under white spectrum is related to transfer carbon and energy sources for antioxidant compound biosynthesis.

The present study is devoted to experimental and numerical investigation of in-situ tensile tests to recognize the mechanisms of ductile fracture under different stress states. The GTN model, which is a micromechanical based damage model, has used for numerical simulations. The parameters related to this model for St12 steel were identified by response surface method (RSM) through minimizing the difference between numerical and experimental results of the tensile test on a standard specimen. The void related parameters of GTN model were determined 0.00107, 0.00716, 0.01, and 0.15 for ff, fc, fN, f0, respectively. After calibrating the damage model for the studied material, the tensile tests were carried out on the in-situ specimens with different geometries. The fractographic analysis was performed to identify the ductile fracture under a wide range of stress states and two failure mechanisms were observed. The calibrated damage model was applied to FE simulations of in-situ tensile specimens for numerical study of the experimentally observed fracture phenomenon. The extracted numerical results showed a good agreement with experimental observations comparing load-displacement plots with a margin of error within 5%. The location of fracture initiation, crack growth orientation, and the displacement at fracture zone in numerical studies also showed close correspondence with experiments.