Sharif Digital Repository

Solid State Drives (SSDs) have recently emerged as a high speed random access alternative to classical magnetic disks. To date, SSD designs have been largely based on multi-channel bus architecture that confronts serious scalability problems in high-end enterprise SSDs with dozens of flash memory chips and a gigabyte host interface. This forces the community to rapidly change the bus-based inter-flash standards to respond to ever increasing application demands. In this paper, we first give a deep look at how different flash parameters and SSD internal designs affect the actual performance and scalability of the conventional architecture. Our experiments show that SSD performance improvement... 

The fresh groundwater lenses (FGLs) of small islands can be highly vulnerable to climate change impacts, including sea-level rise (SLR). Many real cases of atoll or sandy islands involve two-layer hydrogeological conceptualizations. In this paper, the influential factors that affect FGLs in two-layer small islands subject to SLR are investigated. An analytical solution describing FGLs in circular islands, composed of two geological layers, is developed for the simplified case of steady-state and sharp-interface conditions. An application of the developed model is demonstrated to estimate the FGL thickness of some real-world islands by comparison with existing FGL thickness data. Furthermore,... 

A high-order compact finite-difference lattice Boltzmann method (CFDLBM) is extended and applied to accurately simulate two-phase liquid-vapor flows with high density ratios. Herein, the He-Shan-Doolen-type lattice Boltzmann multiphase model is used and the spatial derivatives in the resulting equations are discretized by using the fourth-order compact finite-difference scheme and the temporal term is discretized with the fourth-order Runge-Kutta scheme to provide an accurate and efficient two-phase flow solver. A high-order spectral-type low-pass compact nonlinear filter is used to regularize the numerical solution and remove spurious waves generated by flow nonlinearities in smooth regions... 

Friction stir processing (FSP) is a solid state route with a capacity of preparing fine grained nanocomposites from metal sheets. In this work, we employed this process to finely distribute TiO2 nanoparticles throughout an Al-Mg alloy, aiming to enhance mechanical properties. Titanium dioxide particles (30 nm) were preplaced into grooves machined in the middle of the aluminium alloy sheet and multipass FSP was afforded. This process refined the grain structure of the aluminium alloy, distributed the hard nanoparticles in the matrix and promoted solid state chemical reactions at the interfaces of the metal/ceramic particles. Detailed optical and electron microscopic studies showed that the... 

In this investigation, the behavior of the interface between polymer concrete and sand was studied. For this purpose, two sets of interface direct shear tests (over 40 tests) were conducted on the polymer concrete and sand interface. Moreover, two sets of tests (over 30 tests) were performed on the cement concrete and sand interface for comparison. Based on the experiments, the shear stress versus tangential displacement curves at different normal stresses, the interface friction angles, and the adhesion were obtained for each interface. Then, three different constitutive models proposed for interfaces were used to predict the observed response. Finally, after a quantitative comparison of... 

In this paper, a new control strategy and power management for a stand-alone PV/battery hybrid power system has been suggested. The solar cell arrays provide energy in the steady-state and the battery provides energy in transient states. Here, a charge controller system based on the MPP tracking technology, suitable for using in the islanded micro grid that contains a solar panel and a battery is designed. The charge controller includes a unidirectional DC-DC converter as an interface circuit between the solar panel and the DC bus, a bidirectional DC-DC converter as an interface circuit between the battery and the DC bus with a control system and power management in different states of... 

Perovskite solar cells (PSCs) are one of the most promising emerging energy-conversion technologies because of their high power conversion efficiencies (PCEs) and potentially low fabrication cost. To improve PCE, it is necessary to develop PSCs with good interfacial engineering to reduce the trap states and carrier transport barriers present at the various interfaces of the PSCs' architecture. This work reports a facile method to improve the interface between the perovskite absorber layer and the hole transport layer (HTL) by adding a small amount of acetonitrile (ACN) in the Spiro-OMeTAD precursor solution. This small amount of ACN dissolves the surface of the perovskite layer, allowing the... 

Density functional theory (DFT) calculations have been performed to investigate the electronic structure and photocatalytic activity of a hybrid Ag3PO4(111)/g-C3N4 structure. Due to Ag(d) and O(p) states forming the upper part of the valence band and C(p), N(p), and Ag(s) the lower part of the conduction band, the band gap of the hybrid material is reduced from 2.75 eV for Ag3PO4(111) and 3.13 eV for monolayer of g-C3N4 to about 2.52 eV, enhancing the photocatalytic activity of the Ag3PO4(111) surface and g-C3N4 sheet in the visible region. We have also investigated possible reaction pathways for photocatalytic CO2 reduction on the Ag3PO4(111)/g-C3N4 nanocomposite to determine the most... 

Steady State Visual Evoked Potential (SSVEP) based Brain Computer Interfaces (BCI) can be great assistance for people suffering from physical disabilities due to their high accuracy, high speed, an acceptable number of possible targets, etc. Many researchers have managed to design such systems. Most of these BCIs utilize methods for frequency detection which cause the system to need a training phase for each new user, making the system a user-based one. That is why our goal was to design a BCI that not only has accuracy and speed comparable to similar systems, but also does not need any training phase and thus can be used by new users right away. Our final design got a mean accuracy of... 

Background and objective: Steady-state visual evoked potential (SSVEP) and rapid serial visual presentation (RSVP) are useful methods in the brain-computer interface (BCI) systems. Hybrid BCI systems that combine these two approaches can enhance the proficiency of the P300 spellers. Methods: In this study, a new hybrid RSVP/SSVEP BCI is proposed to increase the classification accuracy and information transfer rate (ITR) as compared with the other RSVP speller paradigms. In this paradigm, RSVP (eliciting a P300 response) and SSVEP stimulations are presented in such a way that the target group of characters is identified by RSVP stimuli, and the target character is recognized by SSVEP stimuli.... 

In this paper, the creep deformation mechanisms are investigated in nickel-based single crystal superalloys. Two-dimensional molecular dynamics (MD) simulations are conducted to model various temperatures, stress conditions, and phase interface crystal orientations. Ni-based single-crystal superalloys are of great importance in the aircraft industry due to their excellent high temperature creep resistance. This characteristic mainly originates from two features considered in their structure; firstly, their two-phase micro-structure comprising gamma γ and gamma prime γ′, and secondly the nature of this superalloy itself, which is a single-crystal. MD is a powerful tool to gain insight into... 

In this article, a time-domain non-linear model is proposed for quantum dynamics of interface traps. This model includes the effects of thermoionic emission, combined with the drift and tunneling currents. The model is simplified for the case of interface traps of the directly bonded Silicon wafers, and linearized. Therefore, an equivalent electrical circuit is obtained being composed of two resistive and capacitive branches. The theory predicts a close spacing between the corresponding zero and pole in the frequency response of the system, being justified by experiment on directly bonded n-type Silicon wafers. The low frequency response to a square-wave is quite in agreement with the... 

Although hematite (i.e., α-Fe2O3) has been widely investigated in photoelectrochemical water oxidation studies due to its high theoretical photocurrent density, it still suffers from serious surface charge recombination and low photoelectrochemical stability. Here we report an in situ electrochemical method to form a uniform and ultrathin (i.e., 3-5 nm) passivation layer all over the pores of an optimized ∼3.2% Ti-doped α-Fe2O3 photoanode. We unveil the amorphous and defective nature of the in situ derived layer assigned to a high concentration of oxygen vacancies and intercalated potassium atoms there, i.e., the formation of Ti/K co-doped defective α-Fe2O3−x. Owing to the efficient... 

The fabrication of Ni/Ti laminated composite via cross accumulative roll bonding (CARB) and subsequent annealing treatment has been studied. The relationships between annealing conditions and microstructure at interfaces of Ni/Ti have been investigated by SEM, XRD, and EDS analyses. The results show that the layers were well-bonded by the CARB process, and by increasing the temperature and time of annealing treatment, the interfacial layers grew as a result of the interdiffusion of Ni and Ti atoms. The main intermetallic phases were NiTi and NiTi2, both of which obeyed linear kinetics of growth. However, the calculated activation energy of NiTi was lower than that of NiTi2, indicating the... 

Spontaneous imbibition of water from fracture into the matrix is considered as one of the most important recovery mechanisms in the fractured porous media. However, water cannot spontaneously imbibe into the oil-wet rocks and as a result oil won't be produced, unless the capillary pressure barrier between fracture conduits and matrix is overcome. Wettability alteration is known as the main affecting mechanism for low salinity water flooding (LSWF), however, its effectiveness in fractured porous media has been less investigated, especially in the case of possible pore scale displacement mechanisms. In this study, the effectiveness of LSWF (diluted seawater) on oil recovery is compared to the... 

APS (3-Aminopropyl) trimethoxysilane) and APhS (p-Aminophenyl) trimethoxysilane) are the most commonly used linkers on a silicon surface. We investigate the surface properties of the structures, including APS or APhS on a silicon substrate. The studied structures consist of APS or APhS linkers with one, two, or three bonds with a substrate, which is a thin layer of Si with crystal orientation 〈1 0 0〉 or 〈1 1 1〉. Using a first-principles study based on density functional theory (DFT), we investigated the electronic and optical properties of the silicon-linker interface, such as interface states, orbital location, dielectric function, and photon absorption. The effects of linker type, number...