Sharif Digital Repository

We present a new high signal to noise ratio spectroscopic survey of the Northern hemisphere to probe the Local Bubble and its surroundings using the 5780Å and 5797Å Diffuse Interstellar Bands (DIBs). We have observed 432 sightlines to a distance of 200 pc over a duration of 3 years. In this study, for both inside and outside the Local Bubble, we establish the 5780and 5797correlations with Na i, Ca iiand E(B-V). The correlations show that among all neutral and ionized atoms, the Na ihas more similarity with 5780and Ca iihas strong correlation with 5797, which suggest that the ionization level of 5797is more than 5780. We study the 5780correlation with 5797, which shows a tight correlation... 

Molecular communication (MC), which utilizes molecules as its carriers of information, is one of the oldest mechanisms among micro-organisms on earth. In recent years, using MC for communication among nanomachines has attracted enormous interest because of its simplicity and bio-compatibility. Diffusion-based MC mechanism is one of the most important communication mechanisms, which has wide applications because of no needs for energy and prior infrastructure. The important challenges in MC systems include node complexity, inter-symbol interference (ISI), and co-channel interference (CCI). Due to the small sizes of the nodes in MC, complexity is a serious issue. Because nanomachines are... 

We used spectroscopic techniques to study self-assembled structures based on nucleobases like G-quadruplexes and macrocycles. Also we used DOSY NMR technique to study hydrogen bonding network in alcohol solutions. First part of our results indicate thermodynamic stability and slow kinetic of G-quadruplexes in apolar aromatic solvents like toluene. Also our results show easy monitoring of formation of each K+ or Na+ complex by NMR, due to the low solubility of alkaline metal salts in apolar media and possibility to stop at any given time in order to control G-quadruplex yield. When combined with suitable functional units, these valuable attributes may be used for the noncovalent synthesis of... 

In the present study, the axisymmetric liquid gas/air diffusion flame in the presence of fuel concentration oscillations and velocity perturbations has been investigated experimentally. Several industrial combustions take a place by diffusion mechanism which necessitate scientists to make far better understanding of diffusion flames. In order to study diffusion flames, the instrument with two separated lines of fuel and air has been developed. Nitrogen is used for fuel dilution oscillatory with pulse of 1, 2, and 4 Hz frequencies. The pulse duration effects on flame structure are also studied. The flame shape has been captured by high speed camera and the results are processed by image... 

The results of a theoretical and experimental study of a resonant interaction between a surface wave and two internal waves are presented. It is shown that the motion of a surface wave in a horizontally infinite two-layer fluid can lead to generation of two oblique internal waves. The internal waves have short wave length compared to the surface wave and have nearly opposite propagation directions. The frequencies of the internal waves are approximately half of the frequency of the surface wave.
In present thesis, Higher-order effects in sub-harmonic resonant interaction of a surface wave with a pair of interfacial waves in a two-layer fluid are studied theoretically and experimentally.... 

The instability and contamination leakage through tailings dams is one of the major problems of them. These dams are usually constructed through self-consolidation with minimum compaction effort, so special attention must be given to the stability of these structures. In addition, tailings dams contain considerable amounts of metals and chemically soluble contaminants resulting from mining processes in their reservoirs, making them more likely to leak contamination from the dam's foundation and body, causing pollution downstream. The infiltration of various chemical contaminants into the soil may alter its hydraulic and resistance properties. Laboratory studies have shown that pore solution... 

Type IV high pressure vessels are composite vessels with a polymeric liner, which are the best choice for storing hydrogen in hydrogen vehicles. The defect of these vessels is the penetration of light hydrogen molecules in the polymeric liner and the composite part. When depressurization the vessel, these molecules cannot release from the polymeric liner and the composite part according to the emptying rate of the vessel. Thus, concentration of the hydrogen molecules in the polymeric liner becomes more than inside the vessel which leads to a pressure difference between the two sides of the polymeric liner that causes the liner collapse. In this research, the partial differential equation for... 

Opinion formation is one of the major topics in social networks analysis and mining. A number of methods have been introduced for describing and simulating this phenomenon. In this thesis, we proposed a novel optimization framework based on an opinion formation model that used the Deffuant’s model with some changes in neighbors’ selection policy. Its efficiency was compared with a number of benchmark optimization methods including genetic algorithms, differential evolution and particle swarm optimization.The proposed model demonstrated better performance than the others.In the proposed, each person changes his opinion based on one of his neighbors who has the best performance in terms of the... 

Thermal penetration is one of the separation methods. In this process, due to the temperature difference, the concentration gradient in one of the gas or liquid phases in the resulting system and the relative separation of the components is possible. The column used for this work is the Classius-Dickel column. This column consists of two vertical plates, one warm and the other cold, spaced a short distance apart. Due to the temperature gradient, the gradient is deliberately created, which creates a concentration gradient in the column, so that the light component accumulates at the top of the column and the heavy component at the bottom of the column. The difference in concentration between... 

Various studies have confirmed that water salinity and its composition significantly affect the efficiency of the waterflooding process. Field-scale operation of low-salinity water injection has been proven to be a cost-effective enhanced oil recovery (EOR) method which is also compatible with the environmental regulations. Although this method has satisfactory results, it faces some challenges, such as in-situ mixing of the injection low-salinity water with the saline water in the host reservoir. The salinity of the injected water increases, as it contacts the high-salinity reservoir brine in the pores. This phenomenon significantly impairs the efficiency of this technique, and increases... 

Each of us at some point in our life has been astonished by the observation of the collective motion of certain animals such as birds, fishes or insects. These coherent and synchronized structures are apparently produced without the active role of a leader in the grouping and it has been reported even for some microorganisms such as bacteria or red blood cells. In all the mentioned examples agents are surrounding with the moving fluid which can affect the collective behavior of the system. The collaborative flock of birds in windy conditions and the swimming of fishes in rivers or along oceanic currents are some examples. Moreover, micro-organisms produce different collective behavior in the... 

New materials as hybrid materials or laminate composites, due to combination of many properties, can be used in many industries. The aim of this research is bonding of three-layered St/AZ31/St composite by roll-bonding process. The roll-bonding process was performed at three preheating temperatures, 340, 400 and 450 ⁰C, with thickness reduction of 30 to 68% and different thicknesses of intermediate layer (AZ31). In order to improve the bonding strength, the as-rolled specimens were annealed at constant temperature of 375 ⁰C. For evaluation of bond strength and investigating the formation of a diffusion layer, the results of peel test and microscopic images were studied. Tensile specimens... 

The emergence of online social networks (OSN) has encouraged scientists to investigate them more deeply due to availability of excessive data and increased computational power. Diffusion is a fundamental process taking place in such networks. The spread of news, ideas, influence and diseases are examples of diffusion in social networks. The importance of information diffusion in different disciplines such as economics, politics and social behavior has motivated us to study diffusion networks in this thesis. Diffusion’s behavior is strongly influenced by the underlying network in social networks. Despite this fact most research done in this area ignores the dynamics of the underlying network.... 

In this essay, by putting in the framework of linear-quadratic optimal control (LQ),we study and solve the mean-variance portfolio selection problem. Two models will be studied in our work; in one we assume that the price process satisfies a diffusion stochastic differential equation, while in the second model, we assume it to satisfy a jump-diffusion stochastic differential equation. In both models, a formula for the efficient frontier is obtained. This essay is mainly obtained from the works of the following articles and books:
1)X.Y. Zhou and D. Li, Continuous-Time Mean-Variance Portfolio Selection:A Stochastic LQ Framework. Applied Mathematics and Optimization. 42(2000),... 

Bubble collapse is a two-phase problem whose numerical simulation has many important applications in science and technology. In hydrodynamics systems (pumps, ship propellers, …), bubbles form due to cavitation. These bubbles grow and collapse These bubbles grow and collapse farther downstream and their energy destroys the surrounding walls. In medical sciences, the shear force caused by collapse of a bubble can be used to destroy adipose tissues in arteries. The small scales time in this phenomenon, as well as the compressibility of the flow in bubble collapse, are interesting challenges researchers face. The present thesis targets are two-dimensional numerical simulation of bubble collapse... 

Flexible vegetation has a significant impact on the small-scale hydrodynamics of aquatic environments, which governs the dispersion of dissolved and particulate material. Flexible canopies bend and oscillate in both the in-line and cross-flow directions due to periodic forcing associated with vortex shedding. The resultant plant motion affects the vegetation wake structure and, hence, the rate of lateral dispersion in these environments. Despite a recently-developed understanding of dispersion in rigid canopies, a framework that can predict the effect of plant-induced vibrations on mixing in flexible canopy environments is still lacking. Here, we investigate the role of the flexibility of... 

Nowadays, a wind tunnel is a tool used in aerodynamic research to study the effects of air moving past solid objects. By employing a wind tunnel, we can compeletely control the conditions of aerodynamic testing on specific models. In this research, the design of a diffuser for the subsonic wind tunnel has been taken into account by CFD. The wind tunnel is of suction type and is powered by three axial fans which are manufactured by LTG Inc. The tunnel test section has a 140 cm height and 195cm width which can provide a necessary Mach number. Considering the setting of the three axial fans, located at the end of the diffuser and parallel to each other, it’s necessary to take into consideration... 

Nowadays, vegetations have an important role in protecting ecological systems. One of the impacts of vegetation in water system is pollution diffusion. The physical characteristics of plants, affect how vegetation influence the diffusion phenomenon. Plants’ flexibility may change the drag force and pollution diffusion. Also density variations of vegetation in depths have important affects on flow characteristics.
In this study we investigate experimentally the affects of flexible vegetations and their density changes in depths on vertical mass transport. Thus the current flume has modeled for crossing flow through the plants. To model the steep plants, inclined rigid cylinders have been... 

The elastic field is one of the challenges in optimizing the lifetime and capacity of the lithiumion batteries. Graphite nanoparticles have been widely used in Li-ion batteries, due to their mechanical, thermal and electrical properties. During the lithiation, chemical reactions occurred in the electrolyte, which forms a solid electrolyte interphase(SEI) in the surrounding of nanoparticles as well as stress fields inside the nanoparticles. Therefore, the purpose of this research is to examine the effects of the surface/interface on diffusion induced stresses(DIS) within core-shell nanosphere due to non-uniform distribution of eigenstrain fields. Due to the mechanical behavior of the phases,... 

The elastic field is one of the challenges in optimizing the lifetime and capacity of the lithium-ion batteries. Graphite nanoparticles have been widely used in Li-ion batteries, due to their mechanical, thermal and electrical properties. During the lithiation, chemical reactions occurred in the electrolyte, which forms a solid electrolyte interphase(SEI) in the surrounding of nanoparticles as well as stress fields inside the nanoparticles. Therefore, the purpose of this research is to examine the effects of the surface/interface on diffusion induced stresses(DIS) within core-shell nanosphere due to non-uniform distribution of eigenstrain fields. Due to the mechanical behavior of the phases,...