Sharif Digital Repository

The performance of the tower based concentrated solar thermal (CST-tower) plant is very sensitive to the operation strategy of the plant and the incident heat flux on the receiver. To date, most studies have been examined only the design mode characteristics of the cavity receivers, but this paper significantly expands the literature by considering non-design operating conditions of this important sub-component of the CST-tower plants. A feasible non-design operating conditions of the cavity receivers that was considered in this study is the storage mode of operation. Two practical dynamic control strategies were examined then to find the most efficient approach: fixed solar field mass... 

The present study conducts a comprehensive comparative techno-economic analysis of some near-term sensible thermal energy storage (TES) alternatives to the ‘standard’ two-tank molten salt system for concentrated solar power (CSP) plants. As such, we conducted detailed, relative annual transient simulations for single-medium thermocline (SMT), dual-media thermocline (DMT), and shell-and-tube (ST) systems. To be consistent with recent literature, the DMT and ST systems use concrete with a porosity of 0.2 (e.g. where concrete occupies 80% of the system) as their low cost filler material. The systems were integrated into a validated 19.9 MWe Gemasolar CSP model, which has a solar multiple of... 

This paper presents an innovative hybrid approach for the estimation of the solar global radiation. New prediction equations were developed for the global radiation using an integrated search method of genetic programming (GP) and simulated annealing (SA), called GP/SA. The solar radiation was formulated in terms of several climatological and meteorological parameters. Comprehensive databases containing monthly data collected for 6 years in two cities of Iran were used to develop GP/SA-based models. Separate models were established for each city. The generalization of the models was verified using a separate testing database. A sensitivity analysis was conducted to investigate the... 

Internet-of-Things (IoT) devices have a strict necessity for power consumption to achieve the expected battery life. Therefore, measuring and optimizing the energy consumption of IoT nodes are essential. IoT nodes feature extreme current consumption range over 100 dB between their operating modes. The main focus of this article is to design and implement a low-power and low-cost current measurement circuit, which can be integrated into IoT nodes. A new pass element is introduced for measuring the current consumption. This element is placed in the current path to measure current over a high dynamic range with a constant voltage drop. The introduced pass element consists of a capacitor and... 

Bridgehead C-H bond dissociation enthalpies of 105.7 ± 2.0, 102.9 ± 1.7, and 102.4 ± 1.9 kcal mol -1 for bicyclo[2.2.1]heptane, bicyclo[2.2.2]octane, and adamantane, respectively, were determined in the gas phase by making use of a thermodynamic cycle (i.e., BDE(R-H) = ΔH° acid(H-X) - IE(H •) + EA(X •)). These results are in good accord with high-level G3 theory calculations, and the experimental values along with G3 predictions for bicyclo[1.1.1]pentane, bicyclo[2.1.1]hexane, bicyclo[3.1.1]heptane, and bicyclo[4.2.1]nonane were found to correlate with the flexibility of the ring system. Rare examples of alkyl anions in the gas phase are also provided  

Surface registration is a necessary step and widely used in medical image-aided surgery. It's relevance to medical imaging is that there is much useful anatomical information in the form of collected surface points which originate from complimentary modalities. In this study, the kinematic relations between two point clouds with different coordinate definitions have been generated. Using Influence Method of surface modeling for extracting point clouds functions, the transformation matrix would be resulted. The proposed method was applied for an experimental femur data points(651 points) using the MRI images. These data points were transformed in a 30 degrees flexion of knee. This... 

Internet of Things (IoT) devices have strict necessity for power consumption in order to achieve expected battery life. IoT nodes feature extreme power consumption range over 100 dB, between their operating modes. The main focus of this paper is to design and implement a high precision, high dynamic range, low power, and flexible power measurement system, which can be applied to different applications. The proposed system consists of a voltage regulating control loop, zero offset amplifiers, high precision analog to digital converters, and reference voltage. The proper operation of the proposed circuit are verified numerically with simulations and experimental measurements. The implemented... 

The power consumption of Internet-of-Things (IoT) devices is a major concern as it directly affects battery life. Therefore, measuring and monitoring the energy usage of IoT devices is vital. However, measuring the current consumption measurement of IoT devices is challenging as it must cover a wide range with low power consumption. In this paper, an improved design for the current measurement circuit is presented. The pass element which is placed in the current path to measure the current based on the charge and discharge of the capacitor is optimized to have reduced voltage drop, lower power consumption, decreased costs, and improved integration with IoT devices. The proposed circuit is... 

A new single-pixel Fourier photoacoustic microscopy (PAM), to the best of our knowledge, is proposed to improve the resolution and region of interest (ROI) of an acquired image. In the previous structure of single-pixel Fourier PAM, called spatially invariant resolution PAM (SIR-PAM), the lateral resolution and ROI are limited by the digital micromirror device (DMD) pixel size and the number of pixels. This limitation is overcome here through illuminating fixed angle interfering plane waves, changing the fringe frequency via varying the frequency of the laser source. Given that the fringe sinusoidal patterns here can be produced by two mirrors, the DMD usage can be omitted. In this way, the... 

Chitosan based polyseudorotaxane was designed as a pH-responsive supramolecular polymeric shell around the mesoporous silica-coated magnetic graphene oxide (Fe3O4@GO@mSiO2). It was used for doxorubicin delivery at cancerous tissue in a controlled manner. The core-shell nanocarrier was formed due to electrostatic interaction between chitosan and carboxylated surface of Fe3O4@GO@mSiO2. The maximum release occurred at pH 5.5 (pH of endosomes) because the shell collapsed at this pH. The drug nanocarrier has potential application in tumor therapy due to good pH-sensitive behavior, improved solubility and high colloidal stability in... 

Magnetic field generated by neuronal activity could alter magnetic resonance imaging (MRI) signals but detection of such signal is under debate. Previous researches proposed that magnitude signal change is below current detectable level, but phase signal change (PSC) may be measurable with current MRI systems. Optimal imaging parameters like echo time, voxel size and external field direction, could increase the probability of detection of this small signal change. We simulate a voxel of cortical column to determine effect of such parameters on PSC signal. We extended a laminar network model for somatosensory cortex to find neuronal current in each segment of pyramidal neurons (PN). 60,000... 

Magnetic field generated by active neurons has recently been considered to determine location of neuronal activity directly with magnetic resonance imaging (MRI), but controversial results have been reported about detection of such small magnetic fields. In this study, multiple neuronal morphologies of rat tissue were modeled to investigate better estimation of MRI signal change produced by neuronal magnetic field (NMF). Ten pyramidal neurons from layer II to VI of rat somatosensory area with realistic morphology, biophysics, and neuronal density were modeled to simulate NMF of neuronal tissue, from which effects of NMF on MRI signals were obtained. Neuronal current MRI signals, which... 

Distribution systems management is becoming an increasingly complicated issue due to the introduction of new technologies, new energy trading strategies, and new deregulated environment. In the new deregulated energy market and considering the incentives coming from the technical and economical fields, it is reasonable to consider Distributed Generation (DG) as a viable option to solve the lacking electric power supply problem. This paper presents a mathematical distribution system planning model considering three planning options to system expansion and to meet the load growth requirements with a reasonable price as well as the system power quality problems. DG is introduced as an... 

By employing a few simple models of passive dynamic walking mechanism, we have shown the possibility of extending the boundaries of the maximum stable speed of these autonomous robots merely by changing their terrain. The replaced terrain consists of a series of parallel local slopes and is recognized as a general form of a ramp-stair surface. Although here, the mechanism of stabilization of the unstable locomotion patterns is not clearly known, the technique is quite simple and works effectively. The merit to the method over other strategies, could be described in two separate aspects: First, it is still completely passive; so we do not need any external energy to control the robot. Second,... 

This paper is concerned with global analysis of a delay SVEIR epidemiological model in a population of varying size. By using Lyapunov stability method and LaSalle's invariance principle for delay systems, we prove that when there is no endemic equilibrium, the disease free equilibrium is globally asymptotically stable, otherwise the endemic equilibrium is globally stable  

In the present study, we designed a pH-responsive drug nanocarrier based on polyamidoamine-modified Fe3O4 nanoparticles coated by PEGylated starch-co-poly(acrylic acid). This carrier was used for the controlled release of doxorubicin as an anticancer drug model. The purpose of using the polyethylene glycol moiety is to generate a biostable nanocarrier in blood stream as it has been reported widely in the pharmaceutical literature. The use of a poly(acrylic acid) segment also provided pH-sensitivity to the polymer. Besides, the magnetic nanoparticles facilitate the cancer cell targeting with an external magnetic field located near the tumor site. This carrier was... 

The World Health Organization (WHO) in 2013 reported that more than seven million unexpected losses every year are credited to air contamination. Because of incredible adaptability and expense viability of fibrous filters, they are broadly used for removing particulates from gasses. The influence of appropriate parameters, e.g., the fiber arrangement, solid volume fraction (SVF or α), fluid flow face velocity (mean inlet velocity), and filter thickness (Ix), on pressure drop and deposition efficiency are researched. Furthermore, to study the effects of variation of the laminar flow regime and fiber’s cross-sectional shape on the deposition of particles, only a single square fiber has been... 

Air pollutants are among the hazardous materials for human health. Therefore, many scientists are interested in removing particles from the carrier gas. In this study, flow of air and airborne particles through the virtual multi-fibrous filters that consist of different fiber cross-sectional shapes and arrangements is simulated where particle deposition and filtration performance are studied. Regular and irregular arrangements of fibers with the circular, elliptical, and equilateral triangular cross sections have been considered. Effects of important parameters such as solid volume fraction, internal structure, and filter thickness on particle collection efficiency and pressure drop are... 

A novel method is proposed in the scope of image segmentation that solves this problem by breaking it into two main blocks. The first block's functionality is a method to anticipate the color basis of each segment in segmented images. One of the challenges of image segmentation is the inappropriate distribution of colors in the RGB color space. To determine the color of each segment, after mapping the input image onto the HSI color space, the image colors are classified into some clusters by exploiting the K-Means. Then, the list of cluster centers is winnowed down to a short list of colors based on a set of criteria. The second block of the proposed method defines how each pixel of the... 

Inspired by the effects of a switching surface on the stability of passive dynamic walking (Safa and Naraghi in Robotica 33(01):195–207, 2015; Safa et al. in Nonlinear Dyn. 81(4):2127–2140, 2015), this paper suggests a new control strategy for stabilization of dynamic bipedal locomotion. It verifies that the stability improvement of a dynamic walking system is feasible while preserving the speed, step-length, period, natural dynamics, and the energy effectiveness of the gait. The proposed control policy goes behind the three primary principles: (i) The system’s switching surface has to be replaced by a new one if an external disturbance is induced. (ii) The new switching surface has to be...