Sharif Digital Repository

Large-scale simulation of spiking neural networks on hardware with a remarkable resemblance to their mathematical models is a key objective of the neuromorphic discipline. This issue is, however, considerably resource-intensive due to the presence of nonlinear terms in neuron models. This paper proposes a novel uniform piecewise linear segmentation approach for nonlinear function evaluations. Employing the proposed approach, we present a uniform-segmented adaptive exponential neuron model capable of accurately producing various responses exhibited by the original model and suitable for efficient large-scale implementation. In contrast to previous nonuniform-segmented neuron models, the... 

In this study a 2D cubic chamber model filled with paraffin is analyzed with and without the inclusion of magnetic Fe3O4 nanoparticles at concentrations of 0.5, 1, 1.5 and 2 wt%, and an external magnetic field of intensities 0.005, 0.01, 0.015 and 0.02 T. It is ascertained that adding magnetic nanoparticles leads the horizontal temperature gradient to be reduced owing to increments in thermal conductivity. Additionally, this feature is found to be accelerated by applying an external magnetic field, which shapes highly conductive cluster formations of nanoparticles. However, since the increase in nanoparticle concentration and magnetic intensity increases the composite viscosity, there is an... 

Various parameters affect thermal conductivity of nanofluid; however, some of them are more influential such as temperature, size and type of nano particles and volumetric concentration. In this study, artificial neural network as well as least square support vector machine (LSSVM) are applied in order to predict thermal conductivity ratio of alumina/water nanofluid as a function of particle size, temperature and volumetric concentration. LSSVM, Self-Organizing Map and Levenberg-Marquardt Back Propagation algorithms are applied to predict thermal conductivity ratio. Obtained results indicated that these algorithms are appropriate tool for thermal conductivity ratio prediction. The... 

Mixture of sandy soil and bentonite clay can be used to seal the sanitary landfills and prevent the spread of leachate. Over time, this mixture may be subjected to different landfill contaminants, including acidic pollutants and shear strength variations. The objective of this research was to study the effects of sulphuric acid pollutant with pH values of 7, 3 and 1 on the shear behaviour and strength of clean sand and sand mixed with bentonite clay using common consolidated undrained triaxial tests. The tests results showed that the presence of acid in the soil pore water changes the shear behaviour pattern of the soil. Acid pollutant decreases the clean sand shear strength. In... 

In this work, a new approach is described for the calculation of the relaxation time and magnetic anisotropy energy of magnetic nanoparticles. Ferrofluids containing monodispersed magnetite nanoparticles were synthesized via hydrothermal method and then heated using the 10 kA/m external AC magnetic fields in three different frequencies: 10, 50 and 100 kHz. By measuring the temperature variations during the application of the magnetic field, the total magnetic time constant including both Brownian and Neel relaxation times can be calculated. By measuring the magnetic core size and hydrodynamic size of particles, the magnetic anisotropy can be calculated too. Synthesized ferrofluids were... 

In this study, some stabilized magnetite based ferrofluids were synthesized using Dextran as a stabilizing agent. In order to achieve optimum experimental conditions for synthesizing ferrofluids as MRI contrast agents, the Taguchi method was used. This approach was employed to design and minimize the number of required experiments. By using the Taguchi orthogonal (L16) array, four parameters including solution temperature and alkalinity, reaction temperature and stirring rate were selected at four predetermined levels for 16 experiments. Synthesizing processes established based on this set of experimental conditions were carried out and the obtained ferrofluids were characterized using PCS,... 

In this paper, we evaluate the performance of both uncoded and coded multiple access TH-UWB systems introduced in [1-3], in multipath Rayleigh fading channels. The receiver is a selective diversity combining receiver, known as SRake. Based on Gaussian distribution assumption for the multiple access interference at the output of SRake receiver and by using virtual branch technique as introduced in [4-5], the hit error rates for uncoded and coded schemes are derived. Our analysis shows that the effective order of diversity achieved by the coded scheme is the product of the number of branches of SRake receiver and the Hamming distance of the code applied. Furthermore, it indicates that the... 

When the magnitude of the lateral elastic deformation of a pipe over its length is more prominent than in a linear situation, it is necessary to use nonlinear terms to reduce the gap between the mathematical model and the real system. Also, the importance of nonlinear terms is more considerable when a pipe conveying fluid is studied. Since the passive vibration control of pipes is of great significance, one may employ a nonlinear energy sink (NES) as the control configuration attached to the pipe. Hence, in this study, the dynamics of a harmonically excited nonlinear pipe conveying fluid attached to a local NES is investigated. The boundary conditions are assumed doubly clamped. The two... 

The ground surface settlement caused by underground excavation is an important matter in urban development. The settlement control of large span underground station in Tehran Metro is investigated using a full three-dimensional (3-D) finite element analysis. A method of underground construction by increasing the rigidity of the supporting system using Central Beam Column (CBC) structure is introduced. In construction of large underground space, effect of presence of CBC structure is compared to a case without CBC structure. The CBC structure increases the rigidity of supports and decrease the stress concentration and displacement in supporting system. It generally decreases the soil... 

This paper reports the results of SIMD implementation of a number of interpolation algorithms on common personal computers. These methods fit a curve on some given input points for which a mathematical function form is not known. We have implemented four widely used methods using vector processing capabilities embedded in Pentium processors. By using SSE (streaming SIMD extension) we could perform all operations on four packed single-precision (32-bit) floating point values simultaneously. Therefore, the running time decreases three times or even more depending on the number of points and the interpolation method. We have implemented four interpolation methods using SSE technology then... 

In the present study, exergoeconomic optimization of a trigeneration system for cooling, heating and power purposes has been carried out. The system is made up of air compressor, combustion chamber, gas turbine, dual pressure heat recovery steam generator and absorption chiller in order to produce cooling, heating and power. The design parameters of this study are selected as: air compressor pressure ratio, gas turbine inlet temperature, pinch point temperatures in dual pressure heat recovery steam generator, pressure of steam that enters the generator of absorption chiller, process steam pressure and evaporator of the absorption chiller chilled water outlet temperature. The economic model... 

The primary source of surgical site infection is the deposition of flakes released from the exposed skin of surgical staff or the patient on the exposed surgical wound. In this study, a computational model for simulating air ow and thermal conditions in an operating room is developed, and transport and deposition of particulate contaminants near the wound are analyzed. The results show the formation of a thermal plume over the wound tissue, which is typically at a higher temperature than the surrounding. The thermal plume protects the wound from the deposition of contaminants. In addition, the computational model predicts an optimum value for the inlet air velocity that is mainly maintaining... 

In this paper, the performances of both uncoded and coded multiple access TH-UWB systems, introduced in [1-3] in multipath Rayleigh fading channels, are evaluated. The receiver is a selective diversity combining receiver, known as SRake. Based on a Gaussian distribution assumption for the multiple access interference at the output of the SRake receiver and by using a virtual branch technique, as introduced in [4,5], the bit error rates for uncoded and coded schemes are derived. The performance analysis shows that the effective order of diversity achieved by the coded scheme is the product of the number of branches of the SRake receiver and the Hamming distance of the code applied.... 

The study design is a prospective, case-control. The aim of this study was to develop a reliable measurement technique for the assessment of lumbar spine kinematics using digital video fluoroscopy in a group of patients with low back pain (LBP) and a control group. Lumbar segmental instability (LSI) is one subgroup of nonspecific LBP the diagnosis of which has not been clarified. The diagnosis of LSI has traditionally relied on the use of lateral functional (flexion-extension) radiographs but use of this method has proven unsatisfactory. Fifteen patients with chronic low back pain suspected to have LSI and 15 matched healthy subjects were recruited. Pulsed digital videofluoroscopy was used... 

Pulsating heat pipes are cooling devices that are partially filled with working fluid. Working fluid thermophysical properties affect the thermal performance of pulsating heat pipes. In this research, the effect of adding a Triton X-100 surfactant to pure water and using the mixture as a working fluid is investigated experimentally. The results indicate that adding surfactant leads to improvement in the thermal performance of the pulsating heat pipe. In particular, the maximum of the thermal resistance improvement is about 61%, which is attributed to 0.01% surfactant concentration. Higher heat transfer ability is attributed to lower surface tension and the contact angle of the mixture... 

Process variation has an increasingly dramatic effect on delay and power as process geometries shrink. Even if the amount of variation remains the same as in previous generations, it accounts for a greater percentage of process geometries as they get smaller. So an accurate prediction of path delay and power variability for real digital circuits in the current technologies is very important; however, its main drawback is the high runtime cost. In this paper, we present a new fast EDA tool which accelerates Monte Carlo based statistical static timing analysis (SSTA) for complex digital circuit. Parallel platforms like Message Passing Interface and POSIX® Threads and also the GPU-based CUDA... 

Composites of unsaturated polyester containing 5 wt% nanoclay and different amounts of lead monoxide particles (0, 10, 20, and 30 wt%) were prepared. XRD patterns showed the exfoliation of nanoclay layers in the polymer. Morphological properties of the composites were studied using SEM micrographs. The prepared composites were investigated for their thermal resistance and mechanical properties using thermogravimetric analysis and tensile testing method, respectively. Addition of lead monoxide to the polymer worsened its thermal resistance and tensile properties, whereas the observed negative effects could be moderated by the clay nanoparticle. Gamma attenuation performance of the composites... 

The sand–bentonite mixture is used as the buffer layer in nuclear waste disposals. The buffer layer, as a non-permeable protective layer, is generally exposed to temperature gradients and the long-term subjection to temperature results in creep and more intact structure for the layer. In the present study, thermally induced structure and its effects on the isotropic compression behavior and volume change behavior of buffer layer are evaluated. Thermal consolidation tests were conducted using a modified triaxial cell capable of handling temperatures up to 90 °C. In order to investigate the effects of thermal gradients on the behavior of the mixture, saturated specimens were cured at constant... 

Dispersive soils, as one of the main categories of problematic soils, can be found in some parts of the earth, such as the eastern-south of Iran, nearby the Gulf of Oman. One of the most important factors enhancing the dispersive potential is the existence of dissolved salts in the soil water. The main objective of this study is to explore the influence of water salinity on the instability of a railway embankment due to rainfall infiltration. In order to achieve this goal, the embankment resting on a dispersive stratum is numerically modeled and subjected to transient infiltration flow. The effect of dispersion is simplified through variations in the soil-water retention curve with salinity.... 

In this work, magnetite nanoparticles (mean particle size about 20 nm) were synthesized via coprecipitation method. In order to investigate the kinetics of nanoparticle formation, variation in the amount of reactants within the process was measured using pH-meter and atomic absorption spectroscopy (AAS) instruments. Results show that nanoparticle formation behavior can be described by Avrami equations. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were performed to study the chemical and morphological characterization of nanoparticles. Some simplifying assumptions were employed for estimating the nucleation and growth rate of magnetite nanoparticles