Sharif Digital Repository

Nanocars have been proposed to transport nanomaterials on the surface. Study of the mechanism of the motion of nanocars has attracted a lot of interests due to the potential ability of these nano-vehicles in the construction of nanostructures with bottom-up approach. Using molecular dynamics simulations, we study the motion of two nano-vehicles named “Nanocar” and “Nanotruck” on hexagonal boron-nitride monolayer. The obtained results reveals that, boron-nitride is an appropriate option to obtain higher mobility of nanocars compared with metal substrates. Considering different temperatures reveals that nanocars start to move on the BN at 200 K, while long range motions are observed at 400 K... 

Fundamental constraints imposing power-frequency trade-offs in conventional electronics have stimulated research on alternative technologies for millimeter-wave and sub-millimeter-wave applications. In this work, we use the picosecond threshold firing of nanoplasma switches to demonstrate on-chip millimeter-wave modulators that rely only on a single metal layer. We show amplitude shift keying (ASK) modulation with self-synthesized carrier frequencies up to 66 GHz (limited by the bandwidth of our experimental setup), with output powers up to 30 dBm. These all-metal nanoplasma modulators are low cost, and generally compatible with different platforms, from CMOS and III-V compounds to flexible... 

An analytical approach for design optimization of multi-stage LNAs with common source topology is developed. This paper reviews and analyses simultaneous noise and input impedance matching in three different topologies including common source amplifier with inductive degeneration, resistive feedback and dual feedback in order to achieve maximum available gain and minimum possible noise figure (NF). A study on multi-stage LNAs is performed to calculate optimum input impedance of each stage for minimum overall NF while considering the gain and NF of that stage in addition to the effect of noise of the following stages. MATLAB was used to calculate the starting point of design optimization in a... 

The CLLC resonant converter is a promising candidate for high efficient, bidirectional power transfer applications such as vehicle-to-grid (V2G) on-board charger and hybrid vehicle DC-DC converter. Nevertheless, the analysis of CLLC still remains challenging because of its complex multi-resonant nature and several storage elements. In this paper, a circuit analysis method based on change of variables is presented that maps the state space equations into two decoupled sets of equations. The analyses are carried out in two state-plane coordinate systems, then the results are mapped onto the original region. The proposed method is then used to thoroughly analyze the CLLC resonant converter... 

The CLLC resonant converter is a promising candidate for high efficient, bidirectional power transfer applications, such as vehicle-to-grid on-board charger and hybrid vehicle dc-dc converter. Nevertheless, the analysis of CLLC still remains challenging because of its complex multiresonant nature and several storage elements. In this article, a circuit analysis method based on change of variables is presented that maps the state-space equations into two decoupled sets of equations. The analyses are carried out in two state-plane coordinate systems, then the results are mapped onto the original region. The proposed method is then used to thoroughly analyze the CLLC resonant converter... 

Low-noise amplifiers (LNAs) with low-noise performance are critical components in communication systems. However, reaching a high level of performance is difficult. This study introduces a LNA for radio frequency front-end receivers with a frequency range of 6–12 GHz. The planned LNA contains a two-stage high-electron-mobility transistor cascade amplifier with a minimum measured noise figure of 0.8 dB and a peak gain of 25 dB at room temperature. The proposed LNA is based on a gallium arsenide field-effect transistor transistor (CE3512K2) because of its good low-noise performance at microwave frequency bands. The measured results demonstrate that the proposed LNA is perfectly matched over... 

In the present paper, phase and microstructural characterization of low carbon MgO-C refractories with addition of Fe-catalyzed phenolic resins as binder were investigated. Initially, phenolic resin was modified using various amounts of Fe particles as catalyst originated from iron nitrate ([Fe(NO3)3·9H2O]). The MgO-C matrix compositions were prepared by using 7% of modified phenolic resin, shaped and cured at 200 °C for 24 h. The cured samples were coked in the temperature range from 800 to 1400 °C and then characterized by XRD and FE-SEM techniques. Based on attained results, in-situ graphitic carbons, particularly in carbon nanotubes (CNTs) network were gradually formed from Fe-catalyzed... 

In the present paper, phase and microstructural characterization of low carbon MgO-C refractories with addition of Fe-catalyzed phenolic resins as binder were investigated. Initially, phenolic resin was modified using various amounts of Fe particles as catalyst originated from iron nitrate ([Fe(NO3)3·9H2O]). The MgO-C matrix compositions were prepared by using 7% of modified phenolic resin, shaped and cured at 200 °C for 24 h. The cured samples were coked in the temperature range from 800 to 1400 °C and then characterized by XRD and FE-SEM techniques. Based on attained results, in-situ graphitic carbons, particularly in carbon nanotubes (CNTs) network were gradually formed from Fe-catalyzed... 

Recent investigations on multifunctional piezoelectric semiconductors have shown their excellent potential as photovoltaic components in high-efficiency third-generation quantum nanostructure (QNS) solar cells. The current work is devoted to studying the electro-elastic behavior of high-density QNS photovoltaic semiconductors within which initial mismatch strains of arrays of quantum dots (QDs) or quantum wires (QWRs) induce coupled electro-mechanical fields. The inter-nanostructure couplings which are of great importance in high-density QNS arrays are incorporated in the presented analytical framework. In practice, QNSs with different geometries such as spherical, cuboidal, or pyramidal QDs... 

This article applies a systematic approach based on the normalized determinant function (NDF) theory to analyse stability in multi-loop circuits and to design the required stabilization network. Presenting several provisions, the return ratios are extracted by employing immittance or hybrid matrices (Z, Y, G or H) of active two ports. Using these matrices, instead of the S-parameters, facilitates the selection of an appropriate stabilizer network. As a practical case, a non-uniform distributed amplifier (NDA) is designed and inspected for potential instabilities. The presented procedure detects instability associated with one of the NDA circuit's loops, and an appropriate stabilization... 

Biogenic amines (BAs) are known as substantial indicators of the quality and safety of food. Developing rapid and visual detection methods capable of simultaneously monitoring BAs is highly desired due to their harmful effects on human health. In the present study, we have designed a multicolor sensor array consisting of two types of gold nanostructures (i.e., gold nanorods (AuNRs) and gold nanospheres (AuNSs)) for the discrimination and determination of critical BAs (i.e., spermine (SM), tryptamine (TT), ethylenediamine (EA), tyramine (TR), spermidine (SD), and histamine (HT)). The design principle of the probe was based on the metallization of silver ions on the surface of AuNRs and AuNSs... 

The development of polymer-based composites with thermal transport capability has now become essential in response to the efficient thermal management required in electronic and energy conversion devices. In this work, a novel hybrid filler consisting of graphene nanoplatelet (GNP) and boron nitride microparticles (micro-BN) is used to improve the thermal conductivity of epoxy composite. The GNPs with an average lateral size of 8 µm and an average thickness of 5 nm are in the same volume range with the 1 µm size micro-BN particles. According to the results, the thermal conductivity of the composites changes abruptly with increasing micro-BN loading at fixed GNP loading, which is attributed... 

This paper proposes a new variable frequency zero voltage switching (ZVS) control method for boost converter operating in boundary conduction mode (BCM). The intended method keeps the converter in BCM despide of the load and input voltage variations. This is done by changing switching frequency in a certain specified range. The proposed method can guarantee circuit performance in BCM via zero-crossing detection of the inductor current and changing the switching frequency. In addition, with a slight modification in control structure, it is possible to achieve a fully ZVS in all cases. This converter control is carried out in analog form without using microprocessors which, compared with the... 

Compton imaging is an imaging technique in which Compton scattering is used to produce images from a gamma-ray source. Compton imaging systems are also known as Compton camera. The basic design of Compton imaging systems consists of two-position detectors that are sensitive to the position and energy scattered from gamma rays. Compton camera efficiency is defined as the fraction of photons entering the scatterer (disperse) detector that undergoes only one Compton scattering and is then photoelectrically absorbed in the absorber detector. In the present study, the efficiency of a Compton camera was investigated based on semiconductor detectors using the GEANT4 simulation toolkit. In this... 

In this brief, a design technique for tapered distributed low-noise amplifiers (LNAs) is presented. A circuit model is developed for gain and noise analysis of a nonuniform distributed amplifier (DA). It is shown that by optimal tapering of gate and drain transmission lines and transistors, the tapered distributed LNA can provide lower broadband average noise figure (NF) compared to a uniform DA. A proof-of-concept integrated circuit is implemented using a 0.1-μm GaAs pHEMT process. The amplifier provides average gain of 15.2 dB and 3-dB bandwidth of 43.3 GHz. The average NF of 2.3 dB and minimum NF of 2.0 dB are achieved over 2-40 GHz. The chip consumes 55 mA current from a 2-V supply. ©... 

We investigate the underlying physics of degradation/recovery of a metal/n-CdTe Schottcky junction under reverse or forward bias stressing conditions. We used Sah-Noyce-Shockley (SNS) theory to investigate if the swept of Fermi level pinning at different levels (under forward/reverse bias) is the origin of change in current-voltage characteristics of the device. This theory is based on Shockley-Read-Hall recombination within the depletion width and takes into account the interface defect levels. Fermi Level Pinning theory was primarily introduced by Ponpon and developed to thin film solar cells by Dharmadasa's group in Sheffield University-UK. The theory suggests that Fermi level pinning at... 

In this paper, we analyze the tradeoff between the profits gained by mobile virtual network operators (MVNOs) in an orthogonal frequency division multiple access (OFDMA)-based virtualized wireless network (VWN). In this respect, MVNOs rent the network resources from a mobile network operator (MNO) to create virtual resources based on allocated rates and the cost due to allocated transmit powers in two different strategies: resource-based isolation strategy and rate-based isolation strategy. In resource-based isolation strategy, it is assumed that the whole bandwidth in each base station is divided equally between MVNOs whereas in rate-based isolation strategy, the whole bandwidth in each... 

This paper, for the first time, presents a lateral tunneling transistor based on a two-dimensional boron nitride (BN) and hexagonal boron-carbon-nitrogen (hBCN) heterostructure. The device operation is analyzed based on a non-equilibrium Greens Function (NEGF) method and an atomistic tight-binding (TB) model. The TB hopping parameters are achieved by fitting the bandstructure to density functional theory (DFT) results. This model has been used to calculate the electrical characteristics of the device, such as ION/IOFFratio, subthreshold swing, and intrinsic gate-delay time. The results indicate a switching ratio of over eight orders of magnitude, much higher than the previous two-dimensional... 

Herein, a series of superhydrophobic thin polyacrylic resin-coated carbon black (CB)/hexagonal boron nitride (h-BN)@Fe3O4/cellulose composite papers with good flexibility, low density (~0.67 g/cm3), high electrical conductivity (~0.065 S/cm), good thermal conductivity (0.462 W.m−1. K−1), and with water contact angle (WCA) of 153° were successfully fabricated by a facile dip-coating/spraying method. The CB-BN@Fe3O4 distribution in cellulose matrix provided high electrical conductivity in the in-plane and thickness directions. The electrical conductivity in both in-plane and thickness directions increased by increasing the number of vacuum-assisted dip-coating cycles. Moreover, these... 

Herein, we demonstrated a facile method for the fabrication of magnetic and superhydrophobic polyurethane sponge with water contact angle of 159° as an adsorbent for cleanup the marine oil spill pollution. For this aim, a polyurethane sponge was coated with carbon black (CB), hexagonal boron nitride (h-BN)@Fe3O4, and acrylic resin and then characterized by different techniques. Owing to the chemical and thermal stability of h-BN and CB, the modified sponge was stable under corrosive conditions (pH = 1–14 and salt solutions) and at different temperatures (−12 °C–105 °C). In addition to common oils and organic solvents, we also used the real spilled oils containing monoaromatics and...