Sharif Digital Repository

In this paper, we present a multi-user resource allocation framework using fragmented-spectrum synchronous OFDM-CDMA modulation over a frequency-selective fading channel. In particular, given pre-existing communications in the spectrum where the system is operating, a channel sensing and estimation method is used to obtain information of subcarrier availability. Given this information, some real-valued multi-level orthogonal codes, which are orthogonal codes with values of {±1, ±2, ±3, ±4,...}, are provided for emerging new users, i.e., cognitive radio users. Additionally, we have obtained a closed form expression for bit error rate of cognitive radio receivers in terms of detection... 

In Cognitive Radio (CR), in order to avoid interference in the Primary Users (PU), some subcarriers need to be deactivated. In systems based on Multicarrier Code Division Multiple Access (MC-CDMA), this causes losing orthogonality among different spreading codes, leading to poor Bit Error Rate (BER) performance. The performance of such system can be improved by using Generalized Hadamard Codes (GHC) instead of conventional Hadamard codes which avoids the loss of orthogonality. This is due to the fact that unlike conventional Hadamard codes, GHC are conjectured to exist for any arbitrary length. In this paper, we propose using a novel spreading code, namely, GHC for synchronous MC-CDMA in CR... 

This paper presents a fragmented-spectrum synchronous OFDM-CDMA modulation and utilize it as secondary users modulation in a cognitive radio-based network to provide high data rate by efficiently exploiting available spectrum bands in a target spectral range while simultaneously offering multiple-access capability. In particular, given preexisting communications in the spectrum where the system is operating, a channel sensing and estimation method is used to obtain information of subcarrier availability. Given this information, some three-level codes are provided for emerging new cognitive radio users. Furthermore, analytical results of the system performance in a typical cognitive radio... 

Considering the globalization concept, all companies around the world are able to communicate with each other, share their technologies, and eliminate their production incapability issues. To achieve this goal, Cloud manufacturing system has been proposed. One of the most important issues in Cloud manufacturing is service composition, in which composition of cloud services is determined to meet customer orders. This paper considers a single-product supply network over one period in Cloud manufacturing system with the goal of service composition optimization. The network is designed in a layered structure considering transportation and production services and customers can be classified in... 

The growth of a CoSi2 thin film has been studied for the Co/W/Si(100) system. The Co film with a thickness of about 30 nm was grown over 12 nm sputtered W interlayer using the evaporation technique. The deposited multilayer structure was annealed in an N2 (80%)+H2 (20%) environment in a temperature range from 400 to 1000 °C for 60 min. The samples were characterized by X-ray diffraction (XRD), four point probe sheet resistance (RS) measurement and scanning electron microscopy (SEM). Using the deposited Co/Si(100) system as a reference point, a CoSi2 layer was formed at 800 °C with undesirable crystalline structure and the RS value of about 1.6Ω/□. Instead, for the Co/W/Si(100) system, it has... 

Herein, a novel Pt-APA composite (APA = pyridinium bromide salt) based on magnetic graphene oxide was synthesized and used as an effective catalyst. In this way, Fe3O4 nanoparticles are grown on graphene oxide (GO) nanosheets by a simple and practical method which creates a unique nanostructure (Fe3O4/GO) through dispersing uniformly among graphene nanosheets. The resulted Pt-APA composite was obtained via adding PtCl2 to an ethanol solution of Fe3O4/GO and α-keto stabilized pyridinium ylide in related conditions. The synthesized nanocomposite structure was identified using field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive... 

A new impeller configuration with innovatively-designed shrouds is introduced, and its impact on the pressure head and efficiency of the semi-open centrifugal pump is explored using experimental and numerical approaches. The proposed design includes attaching specific plates called bladelets to a semi-open impeller to limit the secondary flows over the blades resulting in an increase in the pump head and efficiency. Hydraulic performance of a centrifugal pump with three different bladelets at angles of 30°, 60°, and 90° is investigated experimentally, and the results are compared to semi-open and closed impellers. The values of pressure head and efficiency of the proposed centrifugal pump... 

One of the main challenges for engineers in designing high-speed crafts is the evaluation of hydrodynamic loads during the impact of hull to wave’s surface. This paper presents an experimental investigation on the pressure distribution on three wedge-sections with 15°, 20° and 30° deadrise during water-entry. Assessment of pressure distribution on the effects of parameters such as drop heights, deadrise angles and the weights of the models had done. Time histories of impact pressure were recorded. It was showed that, the maximum pressure for 20° wedge had increased 2.4 times in comparison with 30° wedge while this number is 1.23 time for the 15° wedge. But the effects of weight and drop... 

Argon is often considered as an innocent probe that can be attached and detached to study the structure of a particular species without perturbing the species too much. We have investigated whether this assumption also holds for small copper cationic clusters and demonstrated that small but significant charge transfer from argon to metal changes the remaining binding positions, leading in general, to weaker binding of other argon atoms. The exception is binding to just one copper ion, where the binding of the first argon facilitates the binding of the second. © 2020 American Chemical Society  

Knee osteoarthritis (KOA) is a common musculoskeletal disorder resulting in altered gait patterns. Uncontrolled manifold (UCM) analysis has been demonstrated as a useful approach for quantitative analysis of motor variability and synergies. The present study aimed to investigate the changes in the kinematic synergy, controlling the center of mass (COM) position while walking on normal and narrow paths in people with KOA compared to asymptomatic participants. In this cross-sectional study, twenty people with mild to moderate KOA and twenty asymptomatic individuals walked at their comfortable preferred speed across normal and narrow paths on a treadmill. The UCM analysis was performed... 

The growth of cobalt silicides layer has been studied in Co/Ta, Co/Ta0.5W0.5 and Co/W bilayers grown on Si(100) substrate. The Co and Ta-W films were deposited using thermal evaporation and sputtering techniques, respectively. All these samples were annealed at a temperature range from 400 to 1000 °C in an N2 (80%)+H2 (20%) environment for 60 min. The phase identification and electrical property of the annealed samples were determined by XRD and RS methods. In the Co/Ta/Si(100) system, we have obtained nearly a single crystalline CoSi2(200) layer with RS value of approximately 0.9 Ω/□ at 900 °C. However, reappearance of Co2Ta phase at 1000 °C exhibits unsatisfactory thermal stability for... 

We introduce dynamic plastic continuous neural network (DPCNN), which is comprised of neurons distributed in a nonlinear plastic medium where wire-like connections of neural networks are replaced with the continuous medium. We use finite element method to model the dynamic phenomenon of information processing within the DPCNNs. During the training, instead of weights, the properties of the continuous material at its different locations and some properties of neurons are modified. Input and output can be vectors and/or continuous functions over lines and/or areas. Delay and feedback from neurons to themselves and from outputs occur in the DPCNNs. We model a simple form of the DPCNN where the... 

A recently developed two-level undercut-profile substrate (2LUPS), containing two levels of plateaus connected by a curved wall with an undercut profile, enables self-forming filaments in a coated conductor during physical line-of-sight deposition of buffer and superconducting layers. In the present study, the 2LUPS concept is applied to a commercial cube-textured Ni-5at.%W tape, and the surface of the 2LUPS coated with two Gd2Zr2O7 buffer layers using chemical solution deposition is examined. Except for narrow regions near the edge of upper plateaus, the plateaus are found to be covered by strongly textured Gd2Zr2O7 buffer layers after dip coating and sintering  

The global demand for renewable energy sources has arisen significant research interests in marine hydrokinetic energy harvesting from flow induced vibrations. The current study deals with the hydrokinetic energy harvesting potentials of diamond and square oscillators at various inline configurations. Both the sharp edge sections and the wake induced vibrations in tandem arrangement can lead to galloping type of instability with high energy efficiency ratios. The present in-water towing tank experiments comprise 1DoF vibrating systems at Re ranging from 2 × 103 to 4.8 × 104. The results show that the upstream wake generally enhances the system efficiency and the mechanical work done by the... 

The hard corona, the protein shell that is strongly attached to the surface of nano-objects in biological fluids, is recognized as the first layer that interacts with biological objects (e.g., cells and tissues). The decoration of the hard corona (i.e., the type, amount, and conformation of the attached proteins) can define the biological fate of the nanomaterial. Recent developments have revealed that corona decoration strongly depends on the type of disease in human patients from which the plasma is obtained as a protein source for corona formation (referred to as the 'personalized protein corona'). In this study, we demonstrate that graphene oxide (GO) sheets can trigger different... 

Impellers play a critical role in hydrodynamic performance of centrifugal pumps. A new shroud geometric design was proposed in this study to integrate some advantages of both semi-open and close impeller configurations. Specific plates, which are called bladelets hereafter, were attached to semi-open impeller to reach to the proposed design. Five different impellers were designed and tested including a semi-open and a fully close impeller to compare with the proposed design. Experimental tests were performed to investigate pump head and efficiency using designed impellers. To better understanding of the phenomena, numerical techniques were applied using CFD tool, and pressure and velocity... 

In his book on compositions of quadratic forms, Shapiro asks whether a quadratic form decomposes as a tensor product of quadratic forms when its adjoint involution decomposes as a tensor product of involutions on central simple algebras. We give a positive answer for quadratic forms defined over local or global fields (or, more generally, over any linked field) and produce counterexamples over fields of rational fractions in two variables over any formally real field. © 2005 Elsevier Inc. All rights reserved  

Purpose: Triple-negative breast cancer (TNBC) is characterized by high mortality rate, and its clinical management is difficult and complex. Therefore, there is a need for extensive efforts aimed at accelerating the discovery of novel therapies for TNBC. CYP4Z1 has been implicated in the development of breast cancer. The current study aimed at characterizing the expression of CYP4Z1 on TNBC. Materials and Methods: Using immunohistochemistry, CYP4Z1 expression was evaluated on 122 TNBC samples, four samples of breast cancers expressing ER, PR, and HER-2, and four samples of normal breast tissues. The association between the enzyme and various histopathological features and survival of... 

The combined action of ultraviolet irradiation and microwave heating onto acetonitrile solution of [Re((Formula presented.))(CO)3(NCMe)]OTf ((Formula presented.) =phenantroline and neocuproine) afforded cis,trans-Re((Formula presented.))(CO)2(NCMe)2]+ acetonitrile derivatives. Substitution of relatively labile NCMe with a series of aromatic N-donor ligands (pyridine, pyrazine, 4,4’-bipyridine, N-methyl-4,4’-bipyridine) gave a novel family of the diimine cis,trans-[Re((Formula presented.))(CO)2(L)2]+ complexes. Photophysical studies of the obtained compounds in solution revealed unusually high absorption across the visible region and NIR phosphorescence with emission band maxima ranging from...