Sharif Digital Repository

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. ©... 

Gas permeation through nanoscale pores is ubiquitous in nature and has an important role in many technologies 1,2 . Because the pore size is typically smaller than the mean free path of gas molecules, the flow of the gas molecules is conventionally described by Knudsen theory, which assumes diffuse reflection (random-angle scattering) at confining walls 3-7 . This assumption holds surprisingly well in experiments, with only a few cases of partially specular (mirror-like) reflection known 5,8-11 . Here we report gas transport through ångström-scale channels with atomically flat walls 12,13 and show that surface scattering can be either diffuse or specular, depending on the fine details of the... 

Despite the considerable effort has been put on the application of Non-Volatile Memories (NVMs) in Field-Programmable Gate Arrays FPGAs, previously suggested designs are not mature enough to substitute the state of-the-art SRAM-based counterparts mainly due to the inefficient building blocks and/or the overhead of programming structure which can impair their potential benefits. In this paper, we present a Resistive Random Access Memory RRAM-based FPGA architecture employing efficient Switch Box (SB) and Look-Up Table (LUT) designs with programming circuitry integrated in both SB and LUT designs that creates area and power efficient programmable components while precluding performance... 

Over the last few decades, polymer concrete (PC) has been finding use in quick repairing of concrete structures. However, there have been only few studies on the mechanical behavior of PC. The aim of this study is to evaluate the mechanical behavior of PC using destructive and non-destructive tests (NDT). The mixtures were prepared with three different polymer ratios (10%, 12%, and 14%) and two different coarse aggregate sizes (4.75–9.5 mm and 9.5–19 mm). The samples were subsequently tested under three different temperatures (−15 °C, +25 °C, and +65 °C). The Taguchi method and analysis of variance (ANOVA) were used to optimize PC mixes based on the compressive, splitting-tensile, and... 

Drift step recovery diodes (DSRDs) have a special place in high-power short-pulse generation. In this paper, a cascaded configuration of two DSRD-based high-power short-pulse generators with gas discharge switches was used. The high-power pulses generated in the first stage feed the second stage in order to generate shorter pulses with higher peak powers. A prototype was implemented based on this idea. In the first stage, 1.2-kV pulses were generated from a 50-V power supply. At the output of the second stage, 2.1-kV pulses with a repetition rate of more than 50 Hz were obtained. The output peak voltage was limited by the breakdown voltage of the used DSRD. Repetitive pulses with 4-ns rise... 

In search of finding the dominant mechanism in high temperature superconductivity phenomena, the Y3Ba5Cu8O18 compound was synthesized through the standard solid-state reaction technique. Characteristic XRD experiment was performed on the samples and was analyzed by the MAUD software refinement program. The analysis results indicate a 358 phase structure with the initial nominal stoichiometry. The electrical resistivity and its behavior under different magnetic field were measured. The electrical resistivity indicates the transition temperature Tc onset = 102 K with transition width ΔTc = 2.4 K. This is the first observation of such a high transition temperature in the Y-based compound.... 

So-called negative capacitance seems to remain an obscure feature in the analysis of the frequency-dependent impedance of perovskite solar cells. It belongs to one of the puzzling peculiarities arising from the mixed ionic-electronic conductivity of this class of semiconductor. Here we show that apparently high capacitances in general (positive and negative) are not related to any capacitive feature in the sense of a corresponding charge accumulation. Instead, they are a natural consequence of slow transients mainly in forward current of the diode upon ion displacement when changing voltage. The transient current leads to a positive or negative ‘capacitance’ dependent on the sign of its... 

In this paper, the optimum alkali activator solution properties in alkali-activated pastes based on ground granulated blast furnace slag (GGBFS) and micro-silica (MS) were investigated. For this purpose, sodium hydroxide (NH) solutions with molarities of 8 M, 12 M, and 16 M were prepared and mixed with sodium silicate (NS) solutions at NS:NH ratios of 1.0, 2.5, and 4.0 to produce the final activator solution. Two sets of pastes were manufactured: (1) pastes based on GGBFS, and (2) pastes in which 10% by weight of GGBFS was replaced with MS. The fresh density increased with increasing NH molarity and NS:NH ratio; whereas, the final setting time reduced with an increase in the aforementioned... 

In a nutshell, this study outlines the efficacy of mixed dimensional (2D/3D) hybrid perovskites by developing a new class of triple-cation quasi-2D perovskites having (S0.97S′0.03)2[Cs0.05(FA0.97MA0.03)0.95]n-1Pbn(I0.07Br0.03)3n+1 general composition, in which a mixture of ý5-ammonium valeric acid ýiodideý (S) and tetra-n-octylammonium ýbromide (S′) was employed ýas a spacer.ý The effect of the 2D and 3D structures molar ratios (i.e., C=2D/2D+3D) in the range of 0-100 % on photovoltaic performance of the deposited photoanodes was systemically studied. Drawing a comparison between such compounds and an analogous triple-cation 3D counterpart (i.e., Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3) as... 

A high performance asymmetric supercapacitor (ASC)has been fabricated by using nickel oxide-cobalt oxide nanosheets (NiO–CoO NSs), which were directly grown on carbon nanotubes (CNTs)and hydrothermal carbon spheres (HTCs)as positive and negative electrodes, respectively. Both electrode materials are binder-free prepared by using a catalytic chemical vapour deposition (CVD)approach followed by a facile hydrothermal method for cathode and a one-step environmental-friendly route called hydrothermal carbonization for anode. Using NiO–CoO NSs@CNTs and HTCs, which were directly grown on Ni foam, not only leads to a very small equivalent series resistance, but also provides an impressive capacitive... 

It has long been an aspirational goal to create artificial structures that allow fast permeation of water but reject even the smallest hydrated ions, replicating the feat achieved by nature in protein channels (e.g., aquaporins). Despite recent progress in creating nanoscale pores and capillaries, these structures still remain distinctly larger than protein channels. We report capillaries made by effectively extracting one atomic plane from bulk crystals, which leaves a two-dimensional slit of a few angstroms in height. Water moves through these capillaries with little resistance, whereas no permeation could be detected even for such small ions as Na + and Cl − . Only protons (H + ) can... 

Development of simple yet precise sensing platforms for rapid determination of biological species and drugs is of paramount importance, not only for analysis of pharmaceutical formulations during the production stage, but also in clinical practices and medical diagnosis. In the present research, we report on the electrochemical determination of atorvastatin (ATOR) by using silver nanowires/gold-modified glassy carbon electrode (Ag NWs/Au/GCE). The modified electrode was constructed through a two-step procedure in which narrow silver nanowires synthesized via a polyol method are drop casted on a pre-modified GCE with electrodeposited gold particles. The results of XRD analysis indicated the... 

The present research sheds new light on the development of a triple-cation quasi-two-dimensional (2D) perovskite family with the general formula of (S1−xS′x)2[Cs0.05(FA1−xMAx)0.95]3Pb4(I1−xBrx)13, in which two spacers, namely 5-ammonium valeric acid iodide (S) and tetra-n-octylammonium bromide (S′) were simultaneously incorporated. Morphology, crystal structure, optical properties, photovoltaic performance, and internal resistances of such compound were systemically studied in comparison with an analogous single-cation 2D counterpart (i.e. (S)2(FA)3Pb4I13) as a reference. X-ray diffraction set forth that the films deposited based upon these compounds had a 2D perovskite crystal structure... 

We prepared copper-carbon nanocomposite films by co-deposition of RF-Sputtering and RF-PECVD methods at room temperature. These films contain different copper concentration and different size of copper nanoparticles. The copper content of these films was obtained from Rutherford Back Scattering (RBS) analyze. We studied electrical resistivity of samples versus copper content. A metal-nonmetal transition was observed by decreasing of copper content in these films. The electrical conductivity of dielectric and metallic samples was explained by tunneling and percolation models respectively. In the percolation threshold conduction results from two mechanisms: percolation and tunneling. In the... 

This study presents a comprehensive investigation on hydrodynamic and thermal transport properties of mixed electroosmotically and pressure driven flow in microtubes. Particular emphasis is given to investigating the combined consequences of viscous dissipation, non-uniform Joule heating, and variable thermophysical properties. Analytical solutions are obtained using the Debye-Hückel linearization and constant fluid properties assumption, while a numerical solution is presented for variable fluid properties and non-uniform distribution of Joule heating. The results indicate that, viscous heating effect is pronounced significantly when a favorable pressure gradient exists and cannot be... 

We present a study of the structural and electrical behavior of nano-polycrystalline mixed barium and alkali substituted lanthanum-based manganite, (La1-yKy)0.7Ba0.3MnO 3 with y=0.00.3. The samples were synthesized by the polymerization complex solgel method. The powder X-ray diffraction (XRD) data of the samples show a single-phase character with R3c space group. The magnetic and electrical transport properties of the nano-polycrystalline samples have been investigated in the temperature range 50300 K and a magnetic field up to 10 kOe. The metalinsulator transition temperature Tp of all the samples decreased with potassium doping, and also, it increased slightly with the application of... 

We prepared Cu nanoparticles in a-C:H thin films by co-deposition of RF-sputtering and RF-PECVD methods at room temperature. By increasing Cu content in these films a nonmetalmetal (NM) transition is observed. This transition is explainable by the power law of percolation theory. The critical metal content is obtained 56% and the critical exponent is obtained 1.6, which is larger than the exponent for 2 dimension systems and smaller than the one for 3 dimension systems. The electrical conductivity of dielectric samples was explained by tunneling. Activation tunneling energy that was obtained from temperature dependence of electrical resistivity correlates with near infrared absorption peak... 

The nanocrystallization process of amorphous Fe73.5Si13.5B9Nb3Cu 1 was investigated by active screen plasma nitriding (ASPN) treatment at temperatures ranging from 410 °C to 560 °C for 3 h in two gas mixtures of 75% N2-25% H2 and 25% N2-75% H2 at 5 mbar atmosphere. The amorphous ribbons were then annealed under vacuum at the same time and temperatures mentioned above. The structure of the samples was analyzed using various techniques such as X-ray diffraction (XRD), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). Microhardness measurements, electrical resistivity and Vibrating Sample Magnetometer (VSM) were used to study mechanical, electrical and magnetic... 

We have studied the effect of negative chemical pressure in the RuGd 1.5(Ce 0.5-xPr x)Sr 2Cu 2O 10-δ with Pr content of 0.0 ≤ x ≤ 0.2. This is also investigated using the bond length results obtained from the Rietveld refinement analysis. The c parameter and cell volume increase with x for 0.0 ≤ x ≤ 0.15. The width of the resistivity transition also increases with Pr concentration, indicating higher inhomogeneity and oxygen deficiency. The difference in the ionic valences of Pr 3+,4+ and Ce 4+ causing different hole doping, the difference in the ionic radii, and oxygen stoichiometry affect the superconducting transition. The magnetoresistance shows a cusp around 135 K which lies between the... 

Background: Glucose sensors have been extensively researched in patent studies and manufactured a tool for clinical diabetes diagnosis. Although some kinds of electrochemical enzymatic glucose sensors have been commercially successful, there is still room for improvement, in selectivity and reliability of these sensors. Because of the intrinsic disadvantages of enzymes, such as high fabrication cost and poor stability, non-enzymatic glucose sensors have recently been promoted as next generation diagnostic tool due to their relatively low cost, high stability, prompt response, and accuracy. Objective: In this research, a novel free standing and binder free non-enzymatic electrochemical sensor...