Sharif Digital Repository

The nonlinear capacitance in doped nanotube junctions is calculated self consistently. A negative differential capacitance is observed when the applied bias becomes larger than the pseudogap of the metallic armchair nanotube. For this device, one can deduce a relaxation time of approximately 0.1 fs. Because of its negative differential resistance (NDR), a switching time of less than a femtosecond, i.e., at least three orders smaller than present-day switching times, can also be estimated. This effect is important in designing ultrafast nano-electronic components. ©2005 The Physical Society of Japan  

The purpose of this paper is to study and review some major impacts of the disasters during the past 105 years and develop a new theoretical classification of disasters. Design/methodology/approach– A detailed study of disasters in the world during the period (1900‐2005) has been obtained from the recent published sources. In that period more than 40 lessons have been reported based on statistical data analysis of disasters. Furthermore, a two‐dimensional probability density function is developed to categorize the different types of disasters. This paper studies and reviews some major impacts of disasters during the past 105 years and summarizes some major lessons for the future.... 

Purpose - The purpose of this paper is to study and review some major impacts of the disasters during the past 105 years and develop a new theoretical classification of disasters. Design/methodology/approach - A detailed study of disasters in the world during the period (1900-2005) has been obtained from the recent published sources. In that period more than 40 lessons have been reported based on statistical data analysis of disasters. Furthermore, a two-dimensional probability density function is developed to categorize the different types of disasters. This paper studies and reviews some major impacts of disasters during the past 105 years and summarizes some major lessons for the future.... 

The current research attempted to apply a numerical investigation for external freestream-flow influence on thrust-vector control. The freestream-flow Mach numbers varying from 0.05 to 1.1 were studied at different flow conditions. Computational modeling and simulation of a converging diverging nozzle with shock-vector control structure was achieved with utilizing the Unsteady-RANS approach and Spalart-Allmaras turbulence model. The present investigation has shown that, freestream-flow is an essential parameter on performance of shock-vector nozzle. Numerical results demonstrate that, increasing freestream Mach number would reduce the thrust-vectoring effectiveness. Furthermore, optimizing... 

Periodic solutions and their existence are one of the most important subjects in dynamical systems. Fractional order systems like integer ones are no exception to this rule. Tavazoei and Haeri (2009) have shown that a time-invariant fractional order system does not have any periodic solution. In this article, this claim has been investigated and it is shown that although in any finite interval of time the solutions do not show any periodic behavior, when the steady state responses of fractional order systems are considered, periodic orbits can be detected  

In this work, the dynamic and vibrational behavior of a micro/nano-manipulator has been studied. The manipulator comprises three links attached serially. While the connection of the links is rigid, which makes the whole body a monolithic structure, the movement of the manipulator is derived from the links deflection. Piezoelectric layers were employed as an actuator to impose deflection on the links, thereby moving the manipulator. After defining the dynamic behavior of each link, manipulator equations of motion were developed. To evaluate the validity of the mathematical model, two FEM models were constructed. The observed results showed a good agreement between the models, and they... 

By using the planar laser induced florescence experiment (PLIF), a resorufin (RSRF) dye solution was tested as an oxygen probe. The photoreaction of RSRF dye was investigated and the oxidation process of this fluorescent probe molecule was demonstrated. The effect of the oxygen bubbles on tracing dissolved oxygen was also investigated in this study. Results obtained for this sensitive molecular probe dye are very interesting and verify that such an agent can be used effectively for investigating different interesting phenomena affecting the fluorescence. The temporal and spatial behaviors of the oxidation and fluorescence processes were described in this report. For a delay time of 4500 ms... 

In this work, the dynamic and vibrational behavior of a micro/nano-manipulator has been studied. The manipulator comprises three links attached serially. While the connection of the links is rigid, which makes the whole body a monolithic structure, the movement of the manipulator is derived from the links deflection. Piezoelectric layers were employed as an actuator to impose deflection on the links, thereby moving the manipulator. After defining the dynamic behavior of each link, manipulator equations of motion were developed. To evaluate the validity of the mathematical model, two FEM models were constructed. The observed results showed a good agreement between the models, and they... 

Oil leakage of transportation pipelines causes a change in its environmental temperature. This effect is employed to detect the leakage and its positions. The Raman Optical Time Domain Reflectometer (ROTDR) and Brillouin Optical Time Domain Amplifier (BOTDA) sensors are two of the most precise oil pipeline leak detector systems operate based on this effect. The position of leakage is determined by the time difference between the sending and backscattered laser pulses. In this paper, the transient response of BOTDA and ROTDR sensors are obtained through solution of the mass, energy and heat transfer in soil and fiber cable. It is shown that the mechanical rise time is of the order of a few... 

In this work, ultraviolet photodetectors based on electrodeposited ZnO sheet thin films were fabricated on a glass substrate. Before electrodeposition, a thin buffer layer of ZnO was deposited on the glass by pulsed laser deposition method. This layer not only acted as a nucleation site for ZnO sheet growth, but also made it possible to use cheap glass substrate instead of conventional fluorine-doped tin oxide (FTO) substrate. Our results showed that photoresponse properties of the photodetectors strongly depend on the sheet sizes. The smaller sheets exhibited enhanced photosensitivity, shortened fall times and decreased gain compared to larger ones. We showed that photodetectors based on... 

Traditionally, DVFS has been the main mechanism to trade-off performance and power. We observe that Deep Neural Network (DNN) applications offer the possibility to trade-off performance, power, and accuracy using both DVFS and numerical precision levels. Our proposed approach, Power-Inference accuracy Trading (PIT), monitors the server's load, and accordingly adjusts the precision of the DNN model and the DVFS setting of GPU to trade-off the accuracy and power consumption with response time. At high loads and tight request arrivals, PIT leverages INT8-precision instructions of GPU to dynamically change the precision of deployed DNN models and boosts GPU frequency to execute the requests... 

The ceramic fracture in output RF window is one of the most important failure factors in high power microwave sources. Fast protection systems are used to protect the source. The methods for determining the required protection response time are conservative and rough. In this paper, an investigation is presented about the twin growth in the ceramic of RF window in faulty condition. It is shown that the twin growth in ceramic can be a reliable figure of merit for the response time calculation of the microwave source protection system  

The energy efficiency of emerging nonvolatile processors equipped with FRAM-SRAM memory makes them a promising solution for energy harvesting systems. To enable correct functionality and forward progress with an unreliable power supply, the system must accumulate sufficient energy in the capacitor to execute tasks atomically, even in the worst case scenario. Due to the large gap between the average and worst case energy consumption of tasks, state of the art approaches like eM-map require a large capacitor to execute tasks on the SRAM. However, the size, cost, and charging time of the capacitor are major concerns in the energy harvesting systems. In this paper, we proposed CHANCE, a... 

Microbial fuel cells (MFCs) have been a potential green energy source for a long time but one of the problems is that either the technology must be used on a large scale or special equipment have been necessary to keep the fuel cells running such as syringe pumps. Paper-based microbial fuel cells do not need to have a syringe pump to run and can run entirely by themselves when placed in contact with the fluids that are necessary for it to run. Paper-based microbial fuel cells are also more compact than traditional MFCs since the device doesn't need any external equipment to run. The goal of this paper is to develop a microbial fuel cell that does not require a syringe pump to function. This... 

In this paper, performance of grid computing environment is studied in the presence of failure-repair of the resources. To achieve this, in the first step, each of the grid resource is individually modeled using Stochastic Reward Nets (SRNs), and mean response time of the resource for grid tasks is computed as a performance measure. In individual models, three different scheduling schemes called random selection, non-preemptive priority, and preemptive priority are considered to simultaneously schedule local and grid tasks to the processors of a single resource. In the next step, single resource models are combined to shape an entire grid environment. Since the number of the resources in a... 

An easily synthesized fluorescent probe for detecting copper in aqueous samples, with a short response time and at neutral pH, has been investigated. Through the chelation of Cu2+ ions or by binding to CuO nanoparticles, the fluorescence emission of the 2-(aminomethyl)aniline derivative H2L is quenched by over 50%. Spectroscopic determination of the association constants of H2L with some metal ions showed that the ligand has a higher affinity toward Cu2+ than toward other d-block metal ions. The comparative bonding ability of the aniline-based fluorescent probe in d-block metal complexes was studied in solution by a combination of UV-Vis, 1H NMR and mass spectrometry analyses. Besides these,...