Sharif Digital Repository

In this research, rubber based nanocomposites with presence of nanoparticle has been studied. Styrene butadiene rubber (SBR)/nanocopper (NC) composites were prepared using two-roll mill method. Transmission electron microscope (TEM) and scanning electron microscope (SEM) images showed proper dispersion of NC in the SBR matrix without substantial agglomeration of nanoparticles. To evaluate the curing properties of nanocomposite samples, swelling and cure rheometric tests were conducted. Moreover, the rheological studies were carried out over a range of shear rates. The effect of NC particles was examined on the thermal behavior of the SBR using thermal gravimetric analysis (TGA). Furthermore,... 

This paper proposes a novel FPGA-based matrix-inversion technique that is specifically tailored and optimized for real-time electromagnetic transients simulation of power electronic converters with high switching frequency. This is the first reported solution that is capable of solving the real-time equations related to using ideal switch model and the associated circuitry in very small time-steps (e.g., an average of 36 ns in a three-phase back-to-back converter case study), without requiring large amount of memory, being limited to small number of switches, adding parasitic elements, or depending on a priori knowledge of the circuit operation or switching strategy. The accuracy of the... 

Actuator limitations hinder high-performance control of robotic manipulators. The problem is particularly challenging in case of underactuated robots where the issue has received less attention. In this brief, we investigate stabilization of manipulators under input constraints via total energy shaping. For this purpose, we use interconnection and damping assignment passivity-based control (IDA-PBC) together with an optimization technique to keep actuator torque close to allowable limits. Using a subsequent technique, the actuator torques are ensured to stay within the specified bounds for special classes of manipulators. The results are verified through simulations on a 2 degree-of-freedom... 

Previous experiments on the fouling/current and fouling/wave interactions were mostly limited to two dimensional (2D) net panels or isolated twines. The current paper deals with the wave-induced forces/moments in three dimensional (3D) physical models of a gravity net-cage. The colonial hydroid Ectopleura larynx, a common fouling organism in the aquaculture industry, was artificially modelled and considered in the current experiments. A clean cage and cages with different fouling lengths were tested under deep-water regular wave trains. The time series of the wave-induced forces/moments in the surge, sway, roll and pitch degrees of freedom were recorded and analysed. The experimental results... 

Employing a small Non-Volatile Memory (NVM) as the Persistent Journal Area (PJA) along with a DRAM-based buffer is an efficient approach to overcome DRAM vulnerability, named NVB-Buffer. Spin-Transfer Torque Magnetic Random Access Memory (STT-MRAM) is one of the most promising PJA candidates thanks to providing high endurance, non-volatility, and DRAM-like latency. Despite these advantages, STT-MRAM faces major reliability challenges, i.e. Retention Failure, Read Disturbance, and Write Failure, which have not been addressed in previously suggested NVB-Buffers. In this paper, we first demonstrate that the retention failure is the dominant source of errors in NVB-Buffers as it suffers from... 

Performance and reliability are two prominent factors in the design of data storage systems. To achieve higher performance, recently storage system designers use DynamicDynamic RAMRAM (DRAM)-based buffers. The volatility of DRAM brings up the possibility of data loss and data inconsistency. Thus, a part of the main storage is conventionally used as the journal area to be able of recovering unflushed data pages in the case of power failure. Moreover, periodically flushing buffered data pages to the main storage is a common mechanism to preserve a high level of reliability. This scheme, however, leads to a considerable increase in storage write traffic, which adversely affects the performance.... 

Study Design. A cross-sectional study to quantify trunk motor control during multidirectional isometric tracking tasks.Objective. To investigate the effect of chronic low back pain (LBP) on trunk neuromuscular performance while participants performed isometric exertions of trunk muscles to track targets in different angles with various magnitudes.Summary of Background Data. Tracking tasks especially in multidirectional activities are among the common research methods to quantify human motor control in different conditions. However, little information is available on trunk motor control during these tasks. There is no study investigating trunk accuracy during multidirectional isometric... 

Sensors are among essential building blocks of any Cyber-Physical Systems (CPSs). Acquisition and processing of their sensory data contribute to the power consumption and computation load of the overall CPSs. For data acquisition, the conventional fixed frequency sampling in many such systems is sub-optimal since a sizable number of samples do not contain important information. In this work, we propose a Signal-Dependent Sampling (SDS) method and present its associated circuit implementation. Using the proposed SDS method, the number of retained samples is significantly reduced with little or negligible compromise in the quality of the (reconstructed) signal. The associated error and added... 

Most deep learning models for computational imaging regress a single reconstructed image. In practice, however, ill-posedness, nonlinearity, model mismatch, and noise often conspire to make such point estimates misleading or insufficient. The Bayesian approach models images and (noisy) measurements as jointly distributed random vectors and aims to approximate the posterior distribution of unknowns. Recent variational inference methods based on conditional normalizing flows are a promising alternative to traditional MCMC methods, but they come with drawbacks: excessive memory and compute demands for moderate to high resolution images and underwhelming performance on hard nonlinear problems.... 

The Boolean satisfiability problem plays a central role in computational complexity and is often used as a starting point for showing NP lower bounds. Generalisations such as Succinct SAT, where a Boolean formula is succinctly represented as a Boolean circuit, have been studied in the literature in order to lift the Boolean satisfiability problem to higher complexity classes such as NEXP. While, in theory, iterating this approach yields complete problems for k-NEXP for all k > 0, using such iterations of Succinct SAT is at best tedious when it comes to proving lower bounds. The main contribution of this paper is to show that the Boolean satisfiability problem has another canonical... 

It has been suggested that the central nervous system simplifies muscle control through basic units, called synergies. In this study, we have developed a novel target-matching protocol and used non-negative matrix factorization (NMF) technique to extract trunk muscle synergies and corresponding torque synergies. Isometric torque data at the L5/S1 level and electromyographic patterns of twelve abdominal and back muscles from twelve healthy participants (five females) were simultaneously recorded. Each participant performed a total number of 24 isometric target-matching tasks using 12 different angular directions and 2 levels of uniaxial and biaxial exertions. Within- and between-subject... 

In this paper, a new fully analog technique is proposed by means of which the adverse effects of frequency dependent gain/phase errors in quadrature transmitters are suppressed. Two separate phase and gain mismatch cancellation loops are implemented which search for the minimum side-band component. A new sign detection method is also introduced which makes sure the direction of the loop is correct. Analytical models and mathematical derivations have been presented which corroborates the circuit implementation. A proof of concept prototype using off-the-shelf components have also been measured which suggests 38-dB side-band rejection (SBR). Furthermore, the measured TX EVM and BER are...