Sharif Digital Repository

Growing the need for long-life and high-available programs, dynamic reconfiguration is going to be an important research issue. Dynamic reconfiguration enables the software systems to change at runtime to decrease their down-time in case of any updating, upgrading or in any changes. Any invalid reconfiguration at runtime may lead programs into invalid states. In this paper, we investigate on validity of dynamic reconfiguration for component-based programs and propose validity conditions for it. We show that the problem of validity assurance in general is undecidable and there is no general-purpose algorithm to verify dynamic reconfiguration validity. To have a computable algorithm for... 

Simulation of x-ray generation from bombardment of various solid targets by quasimonoenergetic electrons is considered. The electron bunches are accelerated in a plasma produced by interaction of 500 mJ, 30 femtosecond laser pulses with a helium gas jet. These relativistic electrons propagate in the ion channel generated in the wake of the laser pulse. A beam of MeV electrons can interact with targets to generate x-ray radiation with keV energy. The MCNP-4C code based on Monte Carlo simulation is employed to compare the production of bremsstrahlung and characteristic x rays between 10 and 100 keV by using two quasi-Maxwellian and quasimonoenergetic energy distributions of electrons. For a... 

Pulsating heat pipes (PHPs) are heat transfer devices which are widely utilized in electronic devices and energy systems. Improvement in thermal performance of PHPs will lead to higher heat transfer capacity and enhancement in the efficiency of systems which PHPs are applied. In this study, an experimental investigation was performed on the thermal performance of a pulsating heat pipe by applying graphene oxide nanofluid as working fluid. Four concentrations of graphene oxide (0.25, 0.5, 1, and 1.5 g/lit) in water as base fluid were used in the PHP. Results indicate that adding graphene oxide sheets increased thermal conductivity and viscidity of the base fluid. Moreover, utilizing graphene... 

In this study, a mixture of nano-encapsulated phase change materials in water has been used as the working fluid in a pulsating heat pipe in order to investigate its thermal performance. The results of the experiments showed that using the nano-encapsulated paraffin dispersed in water as working fluid improves heat transfer and decreases the thermal resistance of the pulsating heat pipe. On the other hand, among the tested concentrations for nano-encapsulated paraffin, there is an optimal value in which increasing the concentration causes an increase in the thermal resistance of the pulsating heat pipe due to the increased dynamic viscosity of the fluid. Enhancement in the thermal... 

Heat pipes are useful devices in heat transfer and particularly, in cooling systems. Given the high demand for cooling systems in various applications, an improvement in the performance of heat pipes has gained much attraction in recent years. In this study, the effects of utilizing working fluids with different thermal properties on the performance of pulsating heat pipes (PHP) are experimentally studied. Hence, nano-encapsulated phase change material (NPCM), reduced graphene oxide nanosheets, and their mixture, as a novel hybrid nanofluid, are prepared and dispersed in water as a working fluid. NPCM at 3 concentrations of 5, 10, and 20 g/L, as well as nanosheets at three concentrations of... 

Tunability of the Fermi level of graphene is exploited to implement a plasmonic nano-color-sorter for scanning near-field optical microscope (SNOM) applications capable of handling large tip sample couplings. Nano-color-sorting has been used in SNOM through creating multiple spatially separated hot spots for different incident wavelengths. We show that in the presence of high-refractive-index samples an unwanted redshift in the spectral response of the dual-color probe occurs. This limitation can be compensated for using graphene and adjusting its chemical potential to obtain a blueshift in probe spectral response. The Method of Moments analysis technique is employed to engineer the probe... 

Near field scanning optical microscopy exploiting differential interference contrast enhancement is demonstrated. Beam splitting in the near field region is implemented using a dual color probe based on plasmonic color sorter idea. This provides the ability to illuminate two neighboring points on the sample simultaneously. It is shown that by modulating the two wavelengths employed in exciting such a probe, phase difference information can be retrieved through measuring the near field photoinduced force at the difference of the two modulation frequencies. This difference in frequency is engineered to correspond to the first resonant frequency of the cantilever, resulting in improved SNR, and... 

Design and modeling of a class of scanning near-field optical microscope (SNOM) probe for improving performance are reported. The basic idea is to generate more than one hot spot with well-known spatial distribution. This not only enables one to calibrate out many sorts of errors in conventional SNOM but also results in the increase in the speed of imaging. We utilize plasmonic nanocolor sorter structures to design aperture probes that create two spatially distinct hot spots. The method of moment analysis technique is employed to tune the probe for operation at standard Ar-ion laser wavelengths (457.9 and 514.5 nm). © 2018 Optical Society of America  

In this paper we achieve non-reciprocity in a silicon optical ring resonator, by introducing two small time-modulated perturbations into the ring. Isolators are designed using this time-perturbed ring, side-coupled to waveguides. The underlying operation of the time-modulated ring and isolator is analyzed using Temporal Coupled Mode Theory (TCMT). The TCMT is used to find the angular distance, phase difference and thickness of the two time-modulated points on the ring resonator and also to find and justify the optimum values for the modulation frequency and amplitude, which yields maximum isolation in the isolator arrangements. Insight into the major players that determine isolation are also... 

This paper proposes a robust investment and operation model to attend the power and heat needs of a microgrid (MG) connected to the distribution system. The optimization algorithm decides on the best investment and operation of combined heat and power (CHP), boilers, PV power generation and battery energy storage systems (BESS). For the BESS, the algorithm estimates the optimal energy storage capacity (MWh) as well as the maximum hourly delivery capacity (MW). The non-linear and non-concave heat rate chart is recast by a mix-integer linear model to have a tractable and precise model. The model considers the uncertain in some parameters using probability density function (pdf) to portrait its... 

In this study magnetite nanoparticles (Fe3 O4) were synthesized and embedded in activated carbon (AC) derived from waste tire rubber to produce magnetic activated carbon. The atrazine (C8 H14 ClN5) adsorption was performed over (AC/Fe3 O4) nanocomposite in an aqueous solution and adsorp-tion isotherms and kinetics were determined. The effects of some parameters such as (pH, contact time, adsorbent dosage and initial pesticide concentration) were investigated. Characterization of nanocomposite was carried out by high-resolution scanning electron microscopy and transmission electron microscopy, X-ray powder diffraction, vibrating sample magnetometer, Brunauer–Emmett– Teller, Fourier-transform... 

Modeling and analysis of information system vulnerabilities helps us to predict possible attacks to networks using the network configuration and vulnerabilities information. As a fact, exploiting most of vulnerabilities result in access rights alteration. In this paper, we propose a new vulnerability analysis method based on the Take-Grant protection model. We extend the initial Take-Grant model to address the notion of vulnerabilities and introduce the vulnerabilities rewriting rules to specify how the protection state of the system can be changed by exploiting vulnerabilities. Our analysis is based on a bounded polynomial algorithm, which generates the closure of the Take-Grant graph... 

We study the translocation of stiff polymers through a nanopore, driven by the chemical-potential gradient exerted by binding proteins (chaperones) on the trans side of the pore. Bound chaperones prevent backsliding through the pore and, therefore, partially rectify the polymer passage. We show that the sequence of chain monomers with different binding affinity for the chaperones significantly affects the translocation dynamics. In particular, we investigate the effect of the nearest-neighbor adjacency probability of the two monomer types. Depending on the magnitude of the involved binding energies, the translocation speed may either increase or decrease with the adjacency probability. We... 

Combining the advection-diffusion equation approach with Monte Carlo simulations we study chaperone driven polymer translocation of a stiff polymer through a nanopore. We demonstrate that the probability density function of first passage times across the pore depends solely on the Péclet number, a dimensionless parameter comparing drift strength and diffusivity. Moreover it is shown that the characteristic exponent in the power-law dependence of the translocation time on the chain length, a function of the chaperone-polymer binding energy, the chaperone concentration, and the chain length, is also effectively determined by the Péclet number. We investigate the effect of the chaperone size on...