Sharif Digital Repository

Polyamide 66/SEBS-g-M alloys and their nanocomposites were prepared by melt compounding using a twin screw extruder. The mechanical properties, rheological behavior and morphology of these alloys and their nanocomposites were investigated. Morphological investigations with different methods show pseudo-one-phase type morphology for these prepared alloys at all percentage of rubber. Impact and tensile tests results showed that rubber toughened samples exhibit significantly more impact strength and elongation at break comparing to virgin Polyamide. Samples with 20% of rubber show impact strength about 15 times and elongation at yield several times more than those of virgin Polyamide. So, these... 

Stable and flexible super-hydrophilic nanotubular-based titanium oxide electrode has been utilized as the active electrode of self-powered humidity sensor. TiO2 nanotubular electrodes fabricated through anodization method and utilized in combination with Kapton electrode as the triboelectric nanogenerator (TENG). Vertical contact-separation mode TENG performance has been examined in various range of frequencies and the maximum output voltage and current more than 300 V and 40 μA respectively with maximum power of 1.25 ± 0.67 mW has been achieved at 4 Hz. The fabricated TENG has been employed as the active self-powered humidity sensor. Super-hydrophilic feature of TiO2 nanotubes resulted in... 

In this paper, general relations between two different stress tensors Tf and Tg, respectively conjugate to strain measure tensors f(U) and g(U) are found. The strain class f(U) is based on the right stretch tensor U which includes the Seth-Hill strain tensors. The method is based on the definition of energy conjugacy and Hill's principal axis method. The relations are derived for the cases of distinct as well as coalescent principal stretches. As a special case, conjugate stresses of the Seth-Hill strain measures are then more investigated in their general form. The relations are first obtained in the principal axes of the tensor U. Then they are used to obtain basis free tensorial equations... 

In this paper, conjugate stresses of the Seth-Hill strain measures are treated by means of the definition of energy conjugacy and Hill's principal axis method. This approach results in relations between components of two different conjugate stress tensors. The results are valid for distinct as well as coalescent principal stretches. Illustrative examples are solved to demonstrate the simplicity and usefulness of the derived relations between conjugate stress tensors. © 2000 Elsevier Science Ltd  

In this paper, for the first time, current distribution inside multiwall carbon nanotube (MWCNT) bundles is studied in the high frequency range in which resistance becomes saturated. It is shown that current distribution of MWCNT bundles in this range is not strictly decreasing vs. distance from surface as in Cu wires  

Multilevel interconnect network of a macrocell for 7.5 nm technology node is designed with carbon based interconnects (CBI) and Cu. Results are compared. Constrains of using CBI is discussed. It is shown that by using CBI power dissipation associated with wires could decrease by 32%. To use GNRs for more than one metal pair, reverse wire pitch idea is proposed that prevents undesirable increase in the number of metal layers  

Closed form model for skin and proximity effect is necessary for GSI interconnects. In this paper, exact formulation for current distribution inside multiwall carbon nanotube (MWCNT) bundles is derived using multiconductor transmission line model. The current distribution is different from copper wires and it is geometry dependent because of kinetic inductance and quantum capacitance. This current distribution is used to compute and formulate high frequency resistance of MWCNT bundles  

In this paper, n-tier methodology is developed to design multilevel interconnect architecture of macrocells using single-wall carbon nanotube (SWCNT) bundles. Upper limit of low-bias voltage of SWCNT bundle interconnects is derived and its dependence on temperature, SWCNTs' diameter, and interconnect length is studied. Possibility of using SWCNT bundles as local interconnects at 7.5-nm technology node is discussed, and it is shown that SWCNT bundles with 1 nm diameter cannot be used at the first interconnect metal level. Using Cu and SWCNT bundles, multilevel interconnect architecture of a 7.5-nm ASIC macrocell is designed which reduces the number of metal levels by 27% and power dissipation... 

Polypropylene (PP) is a semi-crystalline polymer with a very wide range of industrial applications. This is why its mechanical properties, including yielding, have been the subject of numerous studies. The current study has examined the influence of strain rate and thermal softening on yield stress and post yielding behavior of an isotactic PP. A two-process Ree and Eyring model and the heat equation in adiabatic deformation were coupled with a physical parameter described as the temperature sensitivity of the flow stress at yielding, to simulate the effect of gradual temperature rise in adiabatic heating on yielding behavior. Along with that, tensile bars were subjected to tests at... 

Polypropylene (PP) and its composites have an increasing use in automobile and domestic industries. Since the results published regarding effect of strain rate on yield behavior are not compatible, and there is a high attention paid to the effect of strain rate on deformation behavior, the understanding of structure–property relation in PP is crucial. In this research, the effect of strain rate on deformation mechanism of PP and its relation with stress whitening have been studied. Microscopic observations and tensile tests in different strain rates on neat PP samples have suggested that crazing is the prominent deformation mechanism in entire range of the examined strain rates... 

High-altitude test facilities are usually used to evaluate the performance of space mission engines. The supersonic exhaust diffuser, a main part of high-altitude test facility, provides the required test cell vacuum conditions by self-pumping the nozzle exhaust gases to the atmosphere. However, the plume temperature is often much higher than the temperature the diffuser structure is able to withstand, usually above 2500 K. In this study, an efficient cooling system is designed and analyzed to resolve the thermal problem. A water spray cooling technique is preferred among various existing techniques. Here, a new algorithm is developed for a spray cooling system for a supersonic exhaust... 

Predicting the reaction and function of marine structures towards sea waves, is of significant importance in the design of them. There are some uncertain parameters which can be optimized to increase safety factors as well as to decrease the costs. Knowing the maximum oscillation of marine structures due to dynamic forces will play a great role on structures' safe design. The objective of this paper is to employ a reliable numerical technique to analyze the interaction between marine structures and sea waves. Simulink is an object oriented dynamic simulation package. It can develop new analysis tools aimed at a better understanding and prediction of the physics that governs the behavior of... 

Supersonic flow over a tapered body of revolution has been investigated both experimentally and numerically. The experimental study consisted of a series of wind tunnel tests on an ogive-cylinder body. Static pressure distributions on the body surfaces at several longitudinal cross sections, as well as the boundary layer profiles at various angles of attack have been measured. Further, the flow around the model was visualized using Schlieren technique. Tests with a natural development of the boundary layer and with tripping were also carried out. All tests were conducted in the trisonic wind tunnel of Qadr Research Center. Our results show that artificial boundary layer tripping has minor... 

Supersonic flow over tapered bodies of revolution is investigated using both experimental and numerical methods. The experimental study consisted of a series of wind tunnel tests on an ogive-cylinder body and included the surface static pressure and boundary layer profiles measurements, at various angles of attack. Further, the flow around the model was visualized using Schlieren technique. All tests were conducted in the trisonic wind tunnel of Qadr Research Center, Iran. Static surface pressure results show that the circumferential pressure at different nose sections vary significantly with angles of attack, in contrast to the circumferential pressure signatures along the cylindrical part... 

In this paper, an underwater wireless sensor network (UWSN) is modeled with the help of queueing theory in order to evaluate the maximum stable throughput of the network. To this end, a new scenario for multi-layer mobile UWSN is considered. Then, a new MAC algorithm comprised of random access scheme (like MACAW) and CDMA-based data transmission along with a simplified routing algorithm is proposed. In order to analyze the considered UWSN scenario, we propose two related queueing networks, one for modeling the wireless node mobility and the other for representing the process of multi-hop packet transmission according to considered MAC and routing algorithms. Finally, the maximum stable... 

A nonlinear inverse finite element method is developed for estimation of initial blank shape and strain distribution in final shape. This method often based on implicit static algorithms, causes sometimes convergence problems because of strong nonlinearities. In order to avoid the converging problems, especially in the quasi vertical walls, an appropriate initial guess is introduced. By using this initial guess, the number of iterations in the nonlinear numerical solution is decreased, solution speed is significantly increased and complicated geometries can be analyzed by this method with good accuracy. Application to a Srail part shows good agreement between commercially available finite... 

An experimental study was carried out on an axisymmetric supersonic inlet with external compression in order to investigate the buzz phenomenon at different angles of attack and mass flow rates. The model was equipped with accurate and high-frequency pressure sensors, and the tests were conducted at Mach numbers varying from 1.8 to 2.5, for various angles of attack. Shadowgraph visualization technique, together with a high-speed camera, was used to provide the visual description of the shock structure in front of the inlet and to study the characteristics of buzz. Furthermore, pressure distribution over the spike surface was measured using several pressure sensors. Frequency of the buzz and... 

An experimental study was carried out on an axisymmetric supersonic inlet with external compression in order to investigate the buzz phenomenon at different angles of attack and mass flow rates. The model was equipped with accurate and high-frequency pressure sensors, and the tests were conducted at Mach numbers varying from 1.8 to 2.5, for various angles of attack. Shadowgraph visualization technique, together with a high-speed camera, was used to provide the visual description of the shock structure in front of the inlet and to study the characteristics of buzz. Furthermore, pressure distribution over the spike surface was measured using several pressure sensors. Frequency of the buzz and... 

An experimental study was carried out on an axisymmetric supersonic inlet with external compression in order to investigate the buzz phenomenon at different angles of attack and mass flow rates. The model was equipped with accurate and high-frequency pressure sensors, and the tests were conducted at Mach numbers varying from 1.8 to 2.5, for various angles of attack. Shadowgraph visualization technique, together with a high-speed camera, was used to provide the visual description of the shock structure in front of the inlet and to study the characteristics of buzz. Furthermore, pressure distribution over the spike surface was measured using several pressure sensors. Frequency of the buzz and...